bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒06‒23
seventy papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Nature. 2019 Jun 19.
    Bailis W, Shyer JA, Zhao J, Canaveras JCG, Al Khazal FJ, Qu R, Steach HR, Bielecki P, Khan O, Jackson R, Kluger Y, Maher LJ, Rabinowitz J, Craft J, Flavell RA.
      Activated CD4 T cells proliferate rapidly and remodel epigenetically before exiting the cell cycle and engaging acquired effector functions. Metabolic reprogramming from the naive state is required throughout these phases of activation1. In CD4 T cells, T-cell-receptor ligation-along with co-stimulatory and cytokine signals-induces a glycolytic anabolic program that is required for biomass generation, rapid proliferation and effector function2. CD4 T cell differentiation (proliferation and epigenetic remodelling) and function are orchestrated coordinately by signal transduction and transcriptional remodelling. However, it remains unclear whether these processes are regulated independently of one another by cellular biochemical composition. Here we demonstrate that distinct modes of mitochondrial metabolism support differentiation and effector functions of mouse T helper 1 (TH1) cells by biochemically uncoupling these two processes. We find that the tricarboxylic acid cycle is required for the terminal effector function of TH1 cells through succinate dehydrogenase (complex II), but that the activity of succinate dehydrogenase suppresses TH1 cell proliferation and histone acetylation. By contrast, we show that complex I of the electron transport chain, the malate-aspartate shuttle and mitochondrial citrate export are required to maintain synthesis of aspartate, which is necessary for the proliferation of T helper cells. Furthermore, we find that mitochondrial citrate export and the malate-aspartate shuttle promote histone acetylation, and specifically regulate the expression of genes involved in T cell activation. Combining genetic, pharmacological and metabolomics approaches, we demonstrate that the differentiation and terminal effector functions of T helper cells are biochemically uncoupled. These findings support a model in which the malate-aspartate shuttle, mitochondrial citrate export and complex I supply the substrates needed for proliferation and epigenetic remodelling early during T cell activation, whereas complex II consumes the substrates of these pathways, which antagonizes differentiation and enforces terminal effector function. Our data suggest that transcriptional programming acts together with a parallel biochemical network to enforce cell state.
    DOI:  https://doi.org/10.1038/s41586-019-1311-3
  2. Cell Rep. 2019 Jun 18. pii: S2211-1247(19)30695-3. [Epub ahead of print]27(12): 3587-3601.e4
    Park S, Safi R, Liu X, Baldi R, Liu W, Liu J, Locasale JW, Chang CY, McDonnell DP.
      Most cancer cells exhibit metabolic flexibility, enabling them to withstand fluctuations in intratumoral concentrations of glucose (and other nutrients) and changes in oxygen availability. While these adaptive responses make it difficult to achieve clinically useful anti-tumor responses when targeting a single metabolic pathway, they can also serve as targetable metabolic vulnerabilities that can be therapeutically exploited. Previously, we demonstrated that inhibition of estrogen-related receptor alpha (ERRα) significantly disrupts mitochondrial metabolism and that this results in substantial antitumor activity in animal models of breast cancer. Here we show that ERRα inhibition interferes with pyruvate entry into mitochondria by inhibiting the expression of mitochondrial pyruvate carrier 1 (MPC1). This results in a dramatic increase in the reliance of cells on glutamine oxidation and the pentose phosphate pathway to maintain nicotinamide adenine dinucleotide phosphate (NADPH) homeostasis. In this manner, ERRα inhibition increases the efficacy of glutaminase and glucose-6-phosphate dehydrogenase inhibitors, a finding that has clinical significance.
    Keywords:  ERR⍺; MPC1; NADPH; breast cancer; glutaminase; mitochondrial metabolism; nuclear receptor; oxidative stress; pentose phosphate pathway; pyruvate carrier
    DOI:  https://doi.org/10.1016/j.celrep.2019.05.066
  3. J Biol Chem. 2019 Jun 18. pii: jbc.RA119.009442. [Epub ahead of print]
    Libiad M, Vitvitsky V, Bostelaar T, Bak DW, Lee HJ, Sakamoto N, Fearon ER, Lyssiotis CA, Weerapana E, Banerjee R.
      Unlike most other tissues, the colon epithelium is exposed to high levels of H2S derived from gut microbial metabolism. H2S is a signaling molecule that modulates various physiological effects. It is also a respiratory toxin that inhibits complex IV in the electron transfer chain (ETC). Colon epithelial cells are adapted to high environmental H2S exposure as they harbor an efficient mitochondrial H2S oxidation pathway, which is dedicated to its disposal. Herein, we report that the sulfide oxidation pathway enzymes are apically localized in human colonic crypts at the host-microbiome interface, but that the normal apical-to-crypt gradient is lost in colorectal cancer epithelium. We found that sulfide quinone oxidoreductase (SQR), which catalyzes the committing step in the mitochondrial sulfide oxidation pathway and couples to complex III, is a critical respiratory shield against H2S poisoning. H2S at concentrations ≤20 µM stimulated the oxygen consumption rate in colon epithelial cells but, when SQR expression was ablated, H2S concentrations as low as 5 µM, poisoned cells. Mitochondrial H2S oxidation altered cellular bioenergetics, inducing a reductive shift in the NAD+/NADH redox couple. The consequent electron acceptor insufficiency caused uridine and aspartate deficiency and enhanced glutamine-dependent reductive carboxylation. The metabolomic signature of this H2S-induced stress response mapped in part, to redox-sensitive nodes in central carbon metabolism. Colorectal cancer tissues and cell lines appeared to counter the growth restricting effects of H2S by overexpressing sulfide oxidation pathway enzymes. Our findings reveal an alternative mechanism for H2S signaling, arising from alterations in mitochondrial bioenergetics that drives metabolic reprogramming.
    Keywords:  bioenergetics; cell metabolism; cell signaling; colonocytes; colorectal cancer; gut epithelium; hydrogen sulfide; metabolic reprogramming; microbiome; redox signaling
    DOI:  https://doi.org/10.1074/jbc.RA119.009442
  4. Pharmacol Res. 2019 Jun 17. pii: S1043-6618(19)30869-2. [Epub ahead of print] 104317
    Simula L, Campanella M, Campello S.
      Mitochondria are dynamic organelles whose processes of fusion and fission are tightly regulated by specialized proteins, known as mitochondria-shaping proteins. Among them, Drp1 is the main pro-fission protein and its activity is tightly regulated to ensure a strict control over mitochondria shape according to the cell needs. In the recent years, mitochondrial dynamics emerged as a new player in the regulation of fundamental processes during T cell life. Indeed, the morphology of mitochondria directly regulates T cell differentiation, this by affecting the engagment of alternative metabolic routes upon activation. Further, Drp1-dependent mitochondrial fission sustains both T cell clonal expansion and T cell migration and invasivness. By this review, we aim at discussing the most recent findings about the roles played by the Drp1-dependent mitochondrial fission in T cells, and at highlighting how its pharmacological modulation could open the way to future therapeutic approaches to modulate T cell response.
    Keywords:  Drp1; T cells; mitochondrial dynamics; pharmacological approaches; tumor immune-surveillance
    DOI:  https://doi.org/10.1016/j.phrs.2019.104317
  5. Sci Adv. 2019 Jun;5(6): eaaw1386
    Namba T.
      The endoplasmic reticulum (ER) is composed of large membrane-bound compartments, and its membrane subdomain appears to be in close contact with mitochondria via ER-mitochondria contact sites. Here, I demonstrate that the ER membrane protein, BAP31, acts as a key factor in mitochondrial homeostasis to stimulate the constitution of the mitochondrial complex I by forming an ER-mitochondria bridging protein complex. Within this complex, BAP31 interacts with mitochondria-localized proteins, including Tom40, to stimulate the translocation of NDUFS4, the component of complex I from the cytosol to the mitochondria. Disruption of the BAP31-Tom40 complex inhibits mitochondrial complex I activity and oxygen consumption by the decreased NDUFS4 localization to the mitochondria. Thus, the BAP31-Tom40 ER-mitochondria bridging complex mediates the regulation of mitochondrial function and plays a role as a previously unidentified stress sensor, representing a mechanism for the establishment of ER-mitochondria communication via contact sites between these organelles.
    DOI:  https://doi.org/10.1126/sciadv.aaw1386
  6. Am J Physiol Endocrinol Metab. 2019 Jun 18.
    Rose S, Carvalho E, Diaz EC, Cotter M, Bennuri SC, Azhar G, Frye RE, Adams SH, Børsheim E.
      Skeletal muscle mitochondrial respiration is thought to be altered in obesity, insulin resistance and type 2 diabetes; however, the invasive nature of tissue biopsies is an important limiting factor for studying mitochondrial function. Recent findings suggest that bioenergetics profiling of circulating cells may inform on mitochondrial function in other tissues in lieu of biopsies. Thus, we sought to determine whether mitochondrial respiration in circulating cells (peripheral blood mononuclear cells [PBMCs] and platelets) reflects that of skeletal muscle fibers derived from the same subjects. PBMCs, platelets and skeletal muscle (vastus lateralis) samples were obtained from 32 young (25-35 years) women of varying BMIs. Using extracellular flux analysis and high-resolution respirometry, mitochondrial respiration was measured in intact blood cells as well as in permeabilized cells and permeabilized muscle fibers. Respiratory parameters were not correlated between permeabilized muscle fibers and intact PBMCs or platelets. In a sub-set of samples with permeabilized blood cells available, raw measures of substrate (pyruvate, malate, glutamate, and succinate)-driven respiration did not correlate between permeabilized muscle (per mg tissue) and permeabilized PBMCs (per 106 cells); however, complex I leak and OXPHOS coupling efficiency correlated between permeabilized platelets and muscle (Spearman's ρ = 0.64; p = 0.030, Spearman's ρ = 0.72; p = 0.010; respectively). Our data indicate that bioenergetics phenotypes in circulating cells cannot recapitulate muscle mitochondrial function. Select circulating cell bioenergetics phenotypes may possibly inform on overall metabolic health, but this postulate awaits validation in cohorts spanning a larger range of insulin resistance and type 2 diabetes status.
    Keywords:  PBMC; Platelets; bioenergetics; mitochondrial respiration; skeletal muscle
    DOI:  https://doi.org/10.1152/ajpendo.00084.2019
  7. Am J Physiol Endocrinol Metab. 2019 06 18.
    Kappler L, Hoene M, Hu C, von Toerne C, Li J, Bleher D, Hoffmann C, Böhm A, Kollipara L, Zischka H, Königsrainer A, Häring HU, Peter A, Xu G, Sickmann A, Hauck SM, Weigert C, Lehmann R.
      Mitochondria are dynamic organelles with diverse functions in tissues such as liver and skeletal muscle. To unravel the mitochondrial contribution to tissue-specific physiology, we performed a systematic comparison of the mitochondrial proteome and lipidome of mice and assessed the consequences hereof for respiration. Liver and skeletal muscle mitochondrial protein composition was studied by data-independent UHPLC-MS/MS-proteomics, lipid profiles were compared by UHPLC-MS/MS lipidomics. Mitochondrial function was investigated by high-resolution respirometry in samples from mice and humans. Enzymes of pyruvate oxidation as well as several subunits of complex I, III, and ATP synthase were more abundant in muscle mitochondria. Muscle mitochondria were enriched in cardiolipins associated with higher oxidative phosphorylation capacity and flexibility, in particular CL(18:2)4 and 22:6-containing cardiolipins. In contrast, protein equipment of liver mitochondria indicated a shuttling of complex I substrates towards gluconeogenesis and ketogenesis and a higher preference for electron transfer via the flavoprotein quinone oxidoreductase pathway. Concordantly, muscle and liver mitochondria showed distinct respiratory substrate preferences. Muscle respired significantly more on the complex I substrates pyruvate and glutamate, while in liver maximal respiration was supported by complex II substrate succinate. This was a consistent finding in mouse liver and skeletal muscle mitochondria and human samples. Muscle mitochondria are tailored to produce ATP with a high capacity for complex I‑linked substrates. Liver mitochondria are more connected to biosynthetic pathways, preferring fatty acids and succinate for oxidation. The physiologic diversity of mitochondria may help to understand tissue-specific disease pathologies and to develop therapies targeting mitochondrial function.
    Keywords:  cardiolipins; liver; mitochondria; skeletal muscle; substrate preference
    DOI:  https://doi.org/10.1152/ajpendo.00088.2019
  8. Proc Natl Acad Sci U S A. 2019 Jun 18. pii: 201904005. [Epub ahead of print]
    Carroll J, He J, Ding S, Fearnley IM, Walker JE.
      The opening of the permeability transition pore, a nonspecific channel in inner mitochondrial membranes, is triggered by an elevated total concentration of calcium ions in the mitochondrial matrix, leading to disruption of the inner membrane and necrotic cell death. Cyclosporin A inhibits pore opening by binding to cyclophilin D, which interacts with the pore. It has been proposed that the pore is associated with the ATP synthase complex. Previously, we confirmed an earlier observation that the pore survives in cells lacking membrane subunits ATP6 and ATP8 of ATP synthase, and in other cells lacking the enzyme's c8 rotor ring or, separately, its peripheral stalk subunits b and oligomycin sensitive conferral protein. Here, we investigated whether the pore is associated with the remaining membrane subunits of the enzyme. Individual deletion of subunits e, f, g, and 6.8-kDa proteolipid disrupts dimerization of the complex, and deletion of DAPIT (diabetes-associated protein in insulin sensitive tissue) possibly influences oligomerization of dimers, but removal of each subunit had no effect on the pore. Also, we removed together the enzyme's membrane bound c8 ring and the δ-subunit from the catalytic domain. The resulting cells assemble only a subcomplex derived from the peripheral stalk and membrane-associated proteins. Despite diminished levels of respiratory complexes, these cells generate a membrane potential to support uptake of calcium into the mitochondria, leading to pore opening, and retention of its characteristic properties. It is most unlikely that the ATP synthase, dimer or monomer, or any component, provides the permeability transition pore.
    Keywords:  ATP synthase; human mitochondria; permeability transition
    DOI:  https://doi.org/10.1073/pnas.1904005116
  9. Cell Stress. 2017 Dec 23. 2(1): 1-3
    Lang A, Piekorz RP.
      Mammalian sirtuins are fundamental regulators of a plethora of cellular functions, including gene expression, proliferation, metabolism, and ultimatively cellular aging and organismal life-span. The mitochondrial sirtuin SIRT4 acts as metabolic tumor suppressor and is down-regulated in many cancer types. We showed that SIRT4 expression was up-regulated during replicative senescence and by different anti-proliferative and senescence inducing stressors, including UVB and ionizing radiation, due to inhibition of its negative regulator, microRNA miR-15b. In our recent studies we addressed the molecular consequences of increased SIRT4 expression for mitochondrial function and quality control. We demonstrated that SIRT4 reduces O2 consumption and decreases mitochondrial membrane potential in line with an increased generation of mitochondrial reactive oxygen species (mtROS). This led to the accumulation of dysfunctional mitochondria and a more fused mitochondrial network associated with a decreased mitophagic clearance. Mechanistically, our data indicate that SIRT4 promotes mitochondrial fusion in an enzymatically dependent manner through interaction with and stabilization of the dynamin-related GTPase L-OPA1, thereby opposing fission and mitophagy. Our findings provide novel insight in the role of SIRT4 as stress triggered factor that causes mitochondrial dysfunction and impaired mitochondrial quality control through decreased mitophagy, a major hallmark of aging.
    Keywords:  OPA1; SIRT4; aging; mitochondrial quality control; mitophagy; senescence
    DOI:  https://doi.org/10.15698/cst2018.01.118
  10. Cell Stress. 2018 Nov 15. 2(12): 332-339
    Derle A, De Santis MC, Gozzelino L, Ratto E, Martini M.
      Pancreatic cancer is the fourth most common cause of cancer-related mortality, with a dismal prognosis that has changed little over the past few decades. Despite extensive efforts in understanding the oncogenetics of this pathology, pancreatic cancer remained largely elusive. One of the main characteristics of pancreatic cancer is the reduced level of oxygen and nutrient perfusion, caused by the new matrix formation, through the activation of stromal cells (desmoplasia). This stromal reaction leads to metabolic adaptations in surviving tumor cells in order to cope with these challenging conditions. The oncogenic signaling driven by KRAS mutation is necessary to fuel pancreatic tumors by activating key metabolic processes, including enhanced glycolysis and glutamine consumption. Here we review our current understanding of the pancreatic cancer metabolism as well as discuss recent work pointing to the importance of various metabolic strategies as well as autophagy and macropinocytosis as critical nutrient supply pathways. The elucidation of these metabolic networks may highlight new opportunities to further develop novel therapeutic strategies.
    Keywords:  autophagy; macropinocytosis; metabolic rewiring; nutrient stress; pancreatic cancer
    DOI:  https://doi.org/10.15698/cst2018.12.166
  11. Mitochondrion. 2019 Jun 14. pii: S1567-7249(19)30024-8. [Epub ahead of print]
    Baker N, Patel J, Khacho M.
      The dynamic and fluid nature of mitochondria allows for modifications in mitochondrial shape, connectivity and cristae architecture. The precise balance of mitochondrial dynamics is among the most critical features in the control of mitochondrial function. In the past few years, mitochondrial shape has emerged as a key regulatory factor in the determination of the bioenergetic capacity of cells. This is mostly due to the recent discoveries linking changes in cristae organization with supercomplex assembly of the electron transport chain (ETC), also defined as the formation of respirosomes. Here we will review the most current advances demonstrating the impact of mitochondrial dynamics and cristae shape on oxidative metabolism, respiratory efficiency, and redox state. Furthermore, we will discuss the implications of mitochondrial dynamics and supercomplex assembly under physiological and pathological conditions.
    DOI:  https://doi.org/10.1016/j.mito.2019.06.003
  12. J Steroid Biochem Mol Biol. 2019 Jun 13. pii: S0960-0760(18)30612-5. [Epub ahead of print]192 105413
    Helfenberger KE, Castillo AF, Mele PG, Fiore A, Herrera L, Finocchietto P, Podestá EJ, Poderoso C.
      In steroid-producing cells, cholesterol transport from the outer to the inner mitochondrial membrane is the first and rate-limiting step for the synthesis of all steroid hormones. Cholesterol can be transported into mitochondria by specific mitochondrial protein carriers like the steroidogenic acute regulatory protein (StAR). StAR is phosphorylated by mitochondrial ERK in a cAMP-dependent transduction pathway to achieve maximal steroid production. Mitochondria are highly dynamic organelles that undergo replication, mitophagy and morphology changes, all processes allowed by mitochondrial fusion and fission, known as mitochondrial dynamics. Mitofusin (Mfn) 1 and 2 are GTPases involved in the regulation of fusion, while dynamin-related protein 1 (Drp1) is the major regulator of mitochondrial fission. Despite the role of mitochondrial dynamics in neurological and endocrine disorders, little is known about fusion/fission in steroidogenic tissues. In this context, the present work aimed to study the role of angiotensin II (Ang II) in protein subcellular compartmentalization, mitochondrial dynamics and the involvement of this process in the regulation of aldosterone synthesis. We demonstrate here that Ang II stimulation promoted the recruitment and activation of PKCε, ERK and its upstream kinase MEK to the mitochondria, all of them essential for steroid synthesis. Moreover, Ang II prompted a shift from punctate to tubular/elongated (fusion) mitochondrial shape, in line with the observation of hormone-dependent upregulation of Mfn2 levels. Concomitantly, mitochondrial Drp1 was diminished, driving mitochondria toward fusion. Moreover, Mfn2 expression is required for StAR, ERK and MEK mitochondrial localization and ultimately for aldosterone synthesis. Collectively, this study provides fresh insights into the importance of hormonal regulation in mitochondrial dynamics as a novel mechanism involved in aldosterone production.
    Keywords:  Adrenocortical human cells; Angiotensin II; Mitochondrial fusion; Mitofusin 2; Protein kinases; StAR
    DOI:  https://doi.org/10.1016/j.jsbmb.2019.105413
  13. Exp Mol Med. 2019 Jun 20. 51(6): 66
    Chang S, Yim S, Park H.
      Recent studies on mutations in cancer genomes have distinguished driver mutations from passenger mutations, which occur as byproducts of cancer development. The cancer genome atlas (TCGA) project identified 299 genes and 24 pathways/biological processes that drive tumor progression (Cell 173: 371-385 e318, 2018). Of the 299 driver genes, 12 genes are involved in histones, histone methylation, and demethylation (Table 1). Among these 12 genes, those encoding the histone demethylases JARID1C/KDM5C and UTX/KDM6A were identified as cancer driver genes. Furthermore, gain-of-function mutations in genes encoding metabolic enzymes, such as isocitrate dehydrogenases (IDH)1/2, drive tumor progression by producing an oncometabolite, D-2-hydroxyglutarate (D-2HG), which is a competitive inhibitor of α-ketoglutarate, O2-dependent dioxygenases such as Jumonji domain-containing histone demethylases, and DNA demethylases. Studies on oncometabolites suggest that histone demethylases mediate metabolic changes in chromatin structure. We have reviewed the most recent findings regarding cancer-specific metabolic reprogramming and the tumor-suppressive roles of JARID1C/KDM5C and UTX/KDM6A. We have also discussed mutations in other isoforms such as the JARID1A, 1B, 1D of KDM5 subfamilies and the JMJD3/KDM6B of KDM6 subfamilies, which play opposing roles in tumor progression as oncogenes or tumor suppressors depending on the cancer cell type. Table 1 Cancer driver genes involved in epigenetics Pathways involved in epigenetics Driver genes Tumor suppressor/oncogene prediction (by 20/20+a) Approved name Activity Cancer typeb Other driver genes in this pathways Histone modification KDM6A tsg Lysine demethylase 6A, UTX H3K27me2/3 demethylase BLCA, HNSC, KIRP, LUSC, PAAD, PANCAN, PRAD PPP6C SETD2 tsg SET domain-containing 2 H3K36 methyl transferase KIRC, KIRP, LGG, LUAD, MESO, PANCAN Chromatin histone modifiers KDM5C tsg Lysine demethylase 5C, JARID1C H3K4me2/3 demethylase KIRC, PANCAN ARID5B, CREBBP, EP300, KANSL1, MEN1, NCOR1, NSD1, SIN3A, WHSC1, ZMYM3 KMT2A tsg Lysine methyltransferase 2A H3K4 methyl transferase PANCAN KMT2B tsg Lysine methyltransferase 2B H3K4 methyl transferase PANCAN, UCEC KMT2C tsg Lysine methyltransferase 2C H3K4 methyl transferase BLCA, BRCA, CESC, PANCAN, UCEC KMT2D tsg Lysine methyltransferase 2D H3K4 methyl transferase BLCA, CESC, DLBC, ESCA, HNSC, LUSC, PANCAN, PRAD Chromatin (other) H3F3A Possible oncogene H3 histone family member 3A, H3.3A PANCAN AJUBA, ASXL1, ASXL2, ATF7IP, BCOR, CHD3, CHD4, CHD8, CTCF, NIPBL, NPM1 H3F3C - H3 histone family member 3C, H3.5 PANCAN HIST1H1E Possible oncogene HIST1H1E, H1.4 DLBC Possible tsg HIST1H1E, H1.4 LIHC Metabolism IDH1 Oncogene Isocitrate dehydrogenase (NADP(+)) 1 NADP-dependent IDH, Cytosolic CHOL, GBM, LAML, LGG, LIHC, PANCAN, PRAD, SKCM - IDH2 Oncogene Isocitrate dehydrogenase (NADP(+)) 2 NADP-dependent IDH, Mitochondrial LAML, LGG, PANCAN Among the 299 driver genes mentioned by Bailey et al.47, only the epigenetics-related pathways have been sorted out a20/20+: Classifies genes as an oncogene, tumor suppressor gene, or as a nondriver gene using Random Forests, http://2020plus.readthedocs.org bBLCA (bladder urothelial carcinoma), BRCA (breast invasive carcinoma), CESC (cervical squamous cell carcinoma and endocervical adenocarcinoma), CHOL (cholangiocarcinoma), DLBC (lymphoid neoplasm diffuse large B-cell lymphoma), ESCA (esophageal carcinoma), GBM (glioblastoma multiforme), HNSC (head and neck squamous cell carcinoma), KIRC (kidney renal clear cell carcinoma), KIRP (kidney renal papillary cell carcinoma), LAML (acute myeloid leukemia), LGG (brain lower grade glioma), LIHC (liver hepatocellular carcinoma), LUAD (lung adenocarcinoma), LUSC (lung squamous cell carcinoma), MESO (mesothelioma), PAAD (pancreatic adenocarcinoma), PANCAN (Pan-cancer), PRAD (prostate adenocarcinoma), SKCM (skin cutaneous melanoma), THCA (thyroid carcinoma), UCEC (uterine corpus endometrial carcinoma).
    DOI:  https://doi.org/10.1038/s12276-019-0230-6
  14. Arch Physiol Biochem. 2019 Jun 19. 1-7
    Brandão SR, Ferreira R, Rocha H.
      Mitochondrial fatty acid β-oxidation disorders (FAOD) are among the diseases detected by newborn screening in most developed countries. Alterations of mitochondrial functionality are characteristic of these metabolic disorders. However, many questions remain to be clarified, namely how the interplay between the signaling pathways harbored in mitochondria contributes to the disease-related phenotype. Herein, we overview the role of mitochondria on the regulation of cell homeostasis through the production of ROS, mitophagy, apoptosis, and mitochondrial biogenesis. Emphasis is given to the signaling pathways involving MnSOD, sirtuins and PGC-1α, which seem to contribute to FAOD phenotype, namely to multiple acyl-CoA dehydrogenase deficiency (MADD). The association between phenotype and genotype is not straightforward, suggesting that specific molecular mechanisms may contribute to MADD pathogenesis, making MADD an interesting model to better understand this interplay. However, more work needs to be done envisioning the development of novel therapeutic strategies.
    Keywords:  fatty acid β-oxidation; mitochondrial dynamics; multiple acyl-CoA dehydrogenase deficiency; newborn screening
    DOI:  https://doi.org/10.1080/13813455.2019.1628065
  15. Cells. 2019 Jun 15. pii: E597. [Epub ahead of print]8(6):
    Romanello V, Scalabrin M, Albiero M, Blaauw B, Scorrano L, Sandri M.
      The maintenance of muscle mass and its ability to function relies on a bioenergetic efficient mitochondrial network. This network is highly impacted by fusion and fission events. We have recently shown that the acute deletion of the fusion protein Opa1 induces muscle atrophy, systemic inflammatory response, precocious epithelial senescence, and premature death that are caused by muscle-dependent secretion of FGF21. However, both fusion and fission machinery are suppressed in aging sarcopenia, cancer cachexia, and chemotherapy-induced muscle wasting. We generated inducible muscle-specific Opa1 and Drp1 double-knockout mice to address the physiological relevance of the concomitant impairment of fusion and fission machinery in skeletal muscle. Here we show that acute ablation of Opa1 and Drp1 in adult muscle causes the accumulation of abnormal and dysfunctional mitochondria, as well as the inhibition of autophagy and mitophagy pathways. This ultimately results in ER stress, muscle loss, and the reduction of force generation. However, the simultaneous inhibition of the fission protein Drp1 when Opa1 is absent alleviates FGF21 induction, oxidative stress, denervation, and inflammation rescuing the lethal phenotype of Opa1 knockout mice, despite the presence of any muscle weakness. Thus, the simultaneous inhibition of fusion and fission processes mitigates the detrimental effects of unbalanced mitochondrial fusion and prevents the secretion of pro-senescence factors.
    Keywords:  FGF21; fission; mitochondrial fusion; mitophagy; muscle dystrophy; muscle wasting
    DOI:  https://doi.org/10.3390/cells8060597
  16. Mol Cell Neurosci. 2019 Jun 16. pii: S1044-7431(19)30094-6. [Epub ahead of print]
    Flannery PJ, Trushina E.
      Mitochondrial dysfunction is now recognized as a contributing factor to the early pathology of multiple human conditions including neurodegenerative diseases. Mitochondria are signaling organelles with a multitude of functions ranging from energy production to a regulation of cellular metabolism, energy homeostasis, stress response, and cell fate. The success of these complex processes critically depends on the fidelity of mitochondrial dynamics that include the ability of mitochondria to change shape and location in the cell, which is essential for the maintenance of proper function and quality control, particularly in polarized cells such as neurons. This review highlights several aspects of alterations in mitochondrial dynamics in Alzheimer's disease, which may contribute to the etiology of this debilitating condition. We also discuss therapeutic strategies to improve mitochondrial dynamics and function that may provide an alternative approach to failed amyloid-directed interventions.
    Keywords:  Alzheimer's disease; Axonal trafficking; Fission; Fusion; Mitochondria; Mitochondria-targeted therapeutics; Mitophagy
    DOI:  https://doi.org/10.1016/j.mcn.2019.06.009
  17. Mol Plant Pathol. 2019 Jun 20.
    Kou Y, He Y, Qiu J, Shu Y, Yang F, Deng Y, Naqvi NI.
      Magnaporthe oryzae causes blast disease, which is one of the most devastating infections in rice and several important cereal crops. Magnaporthe oryzae needs to coordinate gene regulation, morphological changes, nutrient acquisition and host evasion in order to invade and proliferate within the plant tissues. Thus far, the molecular mechanisms underlying the regulation of invasive growth in planta have remained largely unknown. We identified a precise filamentous-punctate-filamentous cycle in mitochondrial morphology during Magnaporthe-rice interaction. Interestingly, disruption of such mitochondrial dynamics by deletion of genes regulating either the mitochondrial fusion (MoFzo1) or fission (MoDnm1) machinery, or inhibition of mitochondrial fission using Mdivi-1 caused significant reduction in M. oryzae pathogenicity. Furthermore, exogenous carbon source(s) but not antioxidant treatment delayed such mitochondrial dynamics/transition during invasive growth. In contrast, carbon starvation induced the breakdown of the mitochondrial network and led to more punctate mitochondria in vitro. Such nutrient-based regulation of organellar dynamics preceded MoAtg24-mediated mitophagy, which was found to be essential for proper biotrophic development and invasive growth in planta. We propose that precise mitochondrial dynamics and mitophagy occur during the transition from biotrophy to necrotrophy and are required for proper induction and establishment of the blast disease in rice.
    Keywords:  Atg24; Dnm1; Fzo1; Magnaporthe oryzae-rice interaction; mitochondrial fusion and fission; mitophagy; rice blast
    DOI:  https://doi.org/10.1111/mpp.12822
  18. Mol Neurobiol. 2019 Jun 16.
    Martín-Maestro P, Sproul A, Martinez H, Paquet D, Gerges M, Noggle S, Starkov AA.
      Adult neurogenesis defects have been demonstrated in the brains of Alzheimer's disease (AD) patients. The neurogenesis impairment is an early critical event in the course of familiar AD (FAD) associated with neuronal loss. It was suggested that neurologic dysfunction in AD may be caused by impaired functioning of hippocampal neural stem cells (NSCs). Multiple metabolic and structural abnormalities in neural mitochondria have long been suspected to play a critical role in AD pathophysiology. We hypothesize that the cause of such abnormalities could be defective elimination of damaged mitochondria. In the present study, we evaluated mitophagy efficacy in a cellular AD model, hiPSC-derived NSCs harboring the FAD-associated PS1 M146L mutation. We found several mitochondrial respiratory chain defects such as lower expression levels of cytochrome c oxidase (complex IV), cytochrome c reductase (complex III), succinate dehydrogenase (complex II), NADH:CoQ reductase (complex I), and also ATP synthase (complex V), most of which had been previously associated with AD. The mitochondrial network morphology and abundance in these cells was aberrant. This was associated with a marked mitophagy failure stemming from autophagy induction blockage, and deregulation of the expression of proteins involved in mitochondrial dynamics. We show that treating these cells with autophagy-stimulating drug bexarotene restored autophagy and compensated mitochondrial anomalies in PS1 M146L NSCs, by enhancing the clearance of mitochondria. Our data support the hypothesis that pharmacologically induced mitophagy enhancement is a relevant and novel therapeutic strategy for the treatment of AD.
    Keywords:  Alzheimer’s disease; Bexarotene; Mitophagy; Presenilin 1; hiPSC-derived neural stem cells
    DOI:  https://doi.org/10.1007/s12035-019-01665-y
  19. J Immunol. 2019 Jun 17. pii: ji1900288. [Epub ahead of print]
    Remedios KA, Meyer L, Zirak B, Pauli ML, Truong HA, Boda D, Rosenblum MD.
      Signaling through CD27 plays a role in T cell activation and memory. However, it is currently unknown how this costimulatory receptor influences CD4+ effector T (Teff) cells in inflamed tissues. In the current study, we used a murine model of inducible self-antigen expression in the epidermis to elucidate the functional role of CD27 on autoreactive Teff cells. Expression of CD27 on Ag-specific Teff cells resulted in enhanced skin inflammation when compared with CD27-deficient Teff cells. CD27 signaling promoted the accumulation of IFN-γ and IL-2-producing T cells in skin draining lymph nodes in a cell-intrinsic fashion. Surprisingly, this costimulatory pathway had minimal effect on early T cell activation and proliferation. Instead, signaling through CD27 resulted in the progressive survival of Teff cells during the autoimmune response. Using BH3 profiling to assess mitochondrial cell priming, we found that CD27-deficient cells were equally as sensitive as CD27-sufficient cells to mitochondrial outer membrane polarization upon exposure to either BH3 activator or sensitizer peptides. In contrast, CD27-deficient Teff cells expressed higher levels of active caspase 8. Taken together, these results suggest that CD27 does not promote Teff cell survival by increasing expression of antiapoptotic BCL2 family members but instead acts by preferentially suppressing the cell-extrinsic apoptosis pathway, highlighting a previously unidentified role for CD27 in augmenting autoreactive Teff cell responses.
    DOI:  https://doi.org/10.4049/jimmunol.1900288
  20. Cell Death Differ. 2019 Jun 17.
    Fan F, Duan Y, Yang F, Trexler C, Wang H, Huang L, Li Y, Tang H, Wang G, Fang X, Liu J, Jia N, Chen J, Ouyang K.
      To maintain healthy mitochondrial enzyme content and function, mitochondria possess a complex protein quality control system, which is composed of different endogenous sets of chaperones and proteases. Heat shock protein 60 (HSP60) is one of these mitochondrial molecular chaperones and has been proposed to play a pivotal role in the regulation of protein folding and the prevention of protein aggregation. However, the physiological function of HSP60 in mammalian tissues is not fully understood. Here we generated an inducible cardiac-specific HSP60 knockout mouse model, and demonstrated that HSP60 deletion in adult mouse hearts altered mitochondrial complex activity, mitochondrial membrane potential, and ROS production, and eventually led to dilated cardiomyopathy, heart failure, and lethality. Proteomic analysis was performed in purified control and mutant mitochondria before mutant hearts developed obvious cardiac abnormalities, and revealed a list of mitochondrial-localized proteins that rely on HSP60 (HSP60-dependent) for correctly folding in mitochondria. We also utilized an in vitro system to assess the effects of HSP60 deletion on mitochondrial protein import and protein stability after import, and found that both HSP60-dependent and HSP60-independent mitochondrial proteins could be normally imported in mutant mitochondria. However, the former underwent degradation in mutant mitochondria after import, suggesting that the protein exhibited low stability in mutant mitochondria. Interestingly, the degradation could be almost fully rescued by a non-specific LONP1 and proteasome inhibitor, MG132, in mutant mitochondria. Therefore, our results demonstrated that HSP60 plays an essential role in maintaining normal cardiac morphology and function by regulating mitochondrial protein homeostasis and mitochondrial function.
    DOI:  https://doi.org/10.1038/s41418-019-0374-x
  21. Nat Commun. 2019 Jun 20. 10(1): 2701
    Jin N, Bi A, Lan X, Xu J, Wang X, Liu Y, Wang T, Tang S, Zeng H, Chen Z, Tan M, Ai J, Xie H, Zhang T, Liu D, Huang R, Song Y, Leung EL, Yao X, Ding J, Geng M, Lin SH, Huang M.
      One of the biggest hurdles for the development of metabolism-targeted therapies is to identify the responsive tumor subsets. However, the metabolic vulnerabilities for most human cancers remain unclear. Establishing the link between metabolic signatures and the oncogenic alterations of receptor tyrosine kinases (RTK), the most well-defined cancer genotypes, may precisely direct metabolic intervention to a broad patient population. By integrating metabolomics and transcriptomics, we herein show that oncogenic RTK activation causes distinct metabolic preference. Specifically, EGFR activation branches glycolysis to the serine synthesis for nucleotide biosynthesis and redox homeostasis, whereas FGFR activation recycles lactate to fuel oxidative phosphorylation for energy generation. Genetic alterations of EGFR and FGFR stratify the responsive tumors to pharmacological inhibitors that target serine synthesis and lactate fluxes, respectively. Together, this study provides the molecular link between cancer genotypes and metabolic dependency, providing basis for patient stratification in metabolism-targeted therapies.
    DOI:  https://doi.org/10.1038/s41467-019-10427-2
  22. FEBS Lett. 2019 Jun 18.
    Bala Bhaskara Rao K, Katragunta K, Sarma UM, Jain N.
      Isocitrate dehydrogenases (IDHs) are metabolic enzymes that are mutated in several cancers, resulting in overproduction of D-2-hydroxyglutarate. However, the signalling pathways and factors that regulate mutant IDHs or their metabolites remain elusive. Here, we report that in synchronized cells and cells treated with anti-mitotic agents, wild-type and mutant IDH proteins are induced maximally in G2/M. Moreover, mutant IDH1-expressing cells arrested in G2/M harbour high D-2-hydroxyglutarate levels. Genetic or pharmacological perturbation of Forkhead box protein M1 (FOXM1) abrogates the levels of IDH1 mRNA, protein and D-2-hydroxyglutarate in G2/M. Conversely, overexpression of FOXM1 or hyperactive FOXM1 activates the IDH1 promoter and increases the abundance of its protein levels. In summary, our results show that in G2/M, higher D-2-hydroxyglutarate levels are dependent on FOXM1-mediated transcription of IDH1. This article is protected by copyright. All rights reserved.
    Keywords:  Cell cycle; D-2HG; FOXM1; G2/M; Gene regulation; IDH1 and IDH2; Metabolism; Transcription factor
    DOI:  https://doi.org/10.1002/1873-3468.13500
  23. Int Rev Neurobiol. 2019 ;pii: S0074-7742(19)30018-2. [Epub ahead of print]145 127-176
    Rumora AE, Savelieff MG, Sakowski SA, Feldman EL.
      Peripheral neuropathy is a common and debilitating complication of diabetes and prediabetes. Recent clinical studies have identified an association between the development of neuropathy and dyslipidemia in prediabetic and diabetic patients. Despite the prevalence of this complication, studies identifying molecular mechanisms that underlie neuropathy progression in prediabetes or diabetes are limited. However, dysfunctional mitochondrial pathways in hereditary neuropathy provide feasible molecular targets for assessing mitochondrial dysfunction in neuropathy associated with prediabetes or diabetes. Recent studies suggest that elevated levels of dietary saturated fatty acids (SFAs) associated with dyslipidemia impair mitochondrial dynamics in sensory neurons by inducing mitochondrial depolarization, compromising mitochondrial bioenergetics, and impairing axonal mitochondrial transport. This causes lower neuronal ATP and apoptosis. Conversely, monounsaturated fatty acids (MUFAs) restore nerve and sensory mitochondrial function. Understanding the mitochondrial pathways that contribute to neuropathy progression in prediabetes and diabetes may provide therapeutic targets for the treatment of this debilitating complication.
    Keywords:  Bioenergetics; Charcot-Marie-Tooth disease; Diabetes; Fission; Fusion; Hereditary neuropathy; Mitochondria; Mitochondrial associated membranes; Mitochondrial trafficking; Prediabetes
    DOI:  https://doi.org/10.1016/bs.irn.2019.05.002
  24. Cell Stress. 2018 Oct 10. 2(11): 311-324
    Liu Z, Sin KWT, Ding H, Doan HA, Gao S, Miao H, Wei Y, Wang Y, Zhang G, Li YP.
      Muscle wasting is the key manifestation of cancer-associated cachexia, a lethal metabolic disorder seen in over 50% of cancer patients. Autophagy is activated in cachectic muscle of cancer hosts along with the ubiquitin-proteasome pathway (UPP), contributing to accelerated protein degradation and muscle wasting. However, established signaling mechanism that activates autophagy in response to fasting or denervation does not seem to mediate cancer-provoked autophagy in skeletal myocytes. Here, we show that p38β MAPK mediates autophagy activation in cachectic muscle of tumor-bearing mice via novel mechanisms. Complementary genetic and pharmacological manipulations reveal that activation of p38β MAPK, but not p38α MAPK, is necessary and sufficient for Lewis lung carcinoma (LLC)-induced autophagy activation in skeletal muscle cells. Particularly, muscle-specific knockout of p38β MAPK abrogates LLC tumor-induced activation of autophagy and UPP, sparing tumor-bearing mice from muscle wasting. Mechanistically, p38β MAPK-mediated activation of transcription factor C/EBPβ is required for LLC-induced autophagy activation, and upregulation of autophagy-related genes LC3b and Gabarapl1. Surprisingly, ULK1 activation (phosphorylation at S555) by cancer requires p38β MAPK, rather than AMPK. Activated ULK1 forms a complex with p38β MAPK in myocytes, which is markedly increased by a tumor burden. Overexpression of a constitutively active p38Tbeta; MAPK in HEK293 cells increases phosphorylation at S555 and other amino acid residues of ULK1, but not several of AMPK-mediated sites. Finally, ULK1 activation is abrogated in tumor-bearing mice with muscle-specific knockout of p38β MAPK. Thus, p38β MAPK appears a key mediator of cancer-provoked autophagy activation, and a therapeutic target of cancer-induced muscle wasting.
    Keywords:  C/EBPβ; Gabarapl1; LC3b; ULK1; cachexia; muscle wasting
    DOI:  https://doi.org/10.15698/cst2018.11.163
  25. iScience. 2019 May 27. pii: S2589-0042(19)30168-3. [Epub ahead of print]16 340-355
    Greotti E, Fortunati I, Pendin D, Ferrante C, Galla L, Zentilin L, Giacca M, Kaludercic N, Di Sante M, Mariotti L, Lia A, Gómez-Gonzalo M, Sessolo M, Carmignoto G, Bozio R, Pozzan T.
      Genetically Encoded Ca2+ Indicators (GECIs) are extensively used to study organelle Ca2+ homeostasis, although some available probes are still plagued by a number of problems, e.g., low fluorescence intensity, partial mistargeting, and pH sensitivity. Furthermore, in the most commonly used mitochondrial Förster Resonance Energy Transfer based-GECIs, the donor protein ECFP is characterized by a double exponential lifetime that complicates the fluorescence lifetime analysis. We have modified the cytosolic and mitochondria-targeted Cameleon GECIs by (1) substituting the donor ECFP with mCerulean3, a brighter and more stable fluorescent protein with a single exponential lifetime; (2) extensively modifying the constructs to improve targeting efficiency and fluorescence changes caused by Ca2+ binding; and (3) inserting the cDNAs into adeno-associated viral vectors for in vivo expression. The probes have been thoroughly characterized in situ by fluorescence microscopy and Fluorescence Lifetime Imaging Microscopy, and examples of their ex vivo and in vivo applications are described.
    Keywords:  Biological Sciences Tools; Cell Biology; Optical Imaging
    DOI:  https://doi.org/10.1016/j.isci.2019.05.031
  26. J Biol Chem. 2019 Jun 17. pii: jbc.RA118.007020. [Epub ahead of print]
    Gross AS, Zimmermann A, Pendl T, Schroeder S, Schoenlechner H, Knittelfelder O, Lamplmayr L, Santiso A, Aufschnaiter A, Waltenstorfer D, Ortonobes Lara S, Stryeck S, Kast C, Ruckenstuhl C, Hofer SJ, Michelitsch B, Woelflingseder M, Müller R, Carmona-Gutierrez D, Madl T, Büttner S, Fröhlich KU, Shevchenko A, Eisenberg T.
      Autophagy, a membrane-dependent catabolic process, ensures survival of aging cells and depends on the cellular energetic status. Acetyl-coenzyme A carboxylase 1 (Acc1) connects central energy- to lipid metabolism and is rate limiting for the de novo synthesis of lipids. However, it is unclear how de novo lipogenesis and its metabolic consequences affect autophagic activity. Here we show that in aging yeast, autophagy levels highly depend on the activity of Acc1. Constitutively active Acc1 or a deletion of the Acc1 negative regulator, Snf1 (yeast AMPK), show elevated autophagy levels, which can be reversed by the Acc1 inhibitor soraphen A. Vice versa, pharmacological inhibition of Acc1 drastically reduces cell survival and results in the accumulation of Atg8-positive structures at the vacuolar membrane, suggesting late defects in the autophagic cascade. As expected, acc1S/A cells exhibit a reduction in acetate/acetyl-CoA availability along with elevated cellular lipid content. However, concomitant administration of acetate fails to fully revert the increase in autophagy exerted by acc1S/A. Instead, administration of oleate - while mimicking constitutively active Acc1 in wild-type cells - alleviates the vacuolar fusion defects induced by Acc1 inhibition. Our results argue for a largely lipid-dependent process of autophagy regulation downstream of Acc1. We present a versatile genetic model to investigate the complex relationship between acetate metabolism, lipid homeostasis and autophagy, and propose Acc1-dependent lipogenesis as a fundamental metabolic path downstream of Snf1 to maintain autophagy and survival during cellular aging.
    Keywords:  AMPK; Acc1; Acetyl-CoA carboxylase 1; Snf1; acetyl coenzyme A (acetyl-CoA); aging; autophagy; lipid metabolism; oleate; yeast
    DOI:  https://doi.org/10.1074/jbc.RA118.007020
  27. J Biol Chem. 2019 Jun 18. pii: jbc.RA119.009045. [Epub ahead of print]
    Małecki J, Willemen HLDM, Pinto R, Ho AYY, Moen A, Eijkelkamp N, Falnes PØ.
      Lysine methylation is a common post-translational modification of nuclear and cytoplasmic proteins, but is also present in mitochondria. The human protein denoted "family with sequence similarity 173 member B" (FAM173B) was recently uncovered as a mitochondrial lysine (K)-specific methyltransferase (KMT) targeting the c-subunit of mitochondrial ATP synthase (ATPSc), and was therefore renamed ATPSc-KMT. We here set out to investigate the biochemical function of its yet uncharacterized paralogue FAM173A. We demonstrate that FAM173A localizes to mitochondria, mediated by a non-canonical targeting sequence that is partially retained in the mature protein. Immunoblotting analysis using methyllysine-specific antibodies revealed that FAM173A knock-out (KO) abrogates lysine methylation of a single mitochondrial protein in human cells. Mass spectrometry analysis identified this protein as adenine nucleotide translocase (ANT), represented by two highly similar isoforms ANT2 and ANT3. We found that methylation occurs at Lys-52 of ANT, which was previously reported to be trimethylated. Complementation of KO cells with WT or enzyme-dead FAM173A indicated that the enzymatic activity of FAM173A is required for ANT methylation at Lys-52 to occur. Both in human cells and in rat organs, Lys-52 was exclusively trimethylated, indicating that this modification is constitutive, rather than regulatory and dynamic. Moreover, FAM173A-deficient cells displayed increased mitochondrial respiration compared with FAM173A-proficient cells. In summary, we demonstrate that FAM173A is the long-sought KMT responsible for ANT methylation at Lys-52, and point out the functional significance of Lys-52 methylation in ANT. Based on the established naming nomenclature for KMTs, we propose to rename FAM173A to ANT-KMT (gene name ANTKMT).
    Keywords:  ADP/ATP carrier; ADP/ATP translocase; ANT-KMT; FAM173A; adenine nucleotide translocase; bioenergetics; cardiolipin; membrane enzyme; mitochondria; mitochondrial transport; nucleoside/nucleotide transport; post-translational modification (PTM); protein methylation; proteomics; transmembrane domain
    DOI:  https://doi.org/10.1074/jbc.RA119.009045
  28. Am J Cancer Res. 2019 ;9(5): 1079-1090
    Miao B, Wei C, Qiao Z, Han W, Chai X, Lu J, Gao C, Dong R, Gao D, Huang C, Ke A, Zhou J, Fan J, Shi G, Lan F, Cai J.
      eIF3a is the largest subunit of eIF3 complex and is a key player in translational control. Recently eIF3a is recognized as a proto-oncogene, which is overexpressed and connected to tumorigenesis of many cancers. However, the mechanistic roles of eIF3a during the tumorigenesis remain largely elusive. Here, we report that depletion of eIF3a significantly reduced HIF1α protein level and cellular glycolysis ability. Mechanistically, we found that eIF3a regulates HIF1α protein synthesis through internal ribosomal entry site (IRES)-dependent translation. Importantly, through analyses of our own sample collection, we found that eIF3a is overexpressed in hepatocellular carcinoma (HCC) tissues, and a high level of eIF3a predicts poor prognosis of HCC patients. TCGA analyses further confirmed that eIF3a is coincident with an elevated activity of HIF1α pathway genes. Collectively, we identify eIF3a as a regulator for glycolysis through HIF1α IRES-dependent translational regulation, which may be a potential therapeutic target for HCC.
    Keywords:  HCC; HIF1α; eIF3a; glycolysis
  29. Cell Stress. 2019 Mar 15. 3(4): 110-114
    Li Y, Liu L, Zhu Y, Chen Q.
      Mitochondria have relatively independent protein quality control systems, including their own chaperones for protein folding and AAA proteases for protein degradation. Accumulating evidence has shown that cytosolic proteins and disease-causing misfolded proteins can be translocated into mitochondria and then impinge upon their function. It is important to understand the interplay between cellular proteostasis and mitochondria, as impaired proteostasis and mitochondrial dysfunction are causally linked with aging and age-related disorders. This review highlights our recent finding showing that the outer mitochondrial membrane protein FUNDC1, a previously reported mitophagy receptor, interacts with the chaperone protein HSC70 to mediate the mitochondrial translocation of cytosolic proteasomal substrates via the TOM/TIM complex into the mitochondrial matrix where they can be degraded by LONP1 protease. Excessive accumulation of unfolded proteins within mitochondria triggers the formation of Mitochondrion-Associated Protein Aggregates (MAPAs), which are subsequently autophagically degraded in a FUNDC1-dependent manner. We suggest that mitochondria actively organize the cellular proteostatic response and that the interaction between FUNDC1 and HSC70 may represent a new link between impaired proteostasis, mitochondrial dysfunction and cellular aging.
    Keywords:  cellular senescence; mitochondrial quality control; proteostasis
    DOI:  https://doi.org/10.15698/cst2019.04.181
  30. Cell Chem Biol. 2019 Jun 04. pii: S2451-9456(19)30175-8. [Epub ahead of print]
    Li H, Ericsson M, Rabasha B, Budnik B, Chan SH, Freinkman E, Lewis CA, Doench JG, Wagner BK, Garraway LA, Schreiber SL.
      The proteinaceous extracellular matrix (ECM) is vital for the survival, proliferation, migration, and differentiation of many types of cancer. However, little is known regarding metabolic pathways required for ECM secretion. By using an unbiased computational approach, we searched for enzymes whose suppression may lead to disruptions in protein secretion. Here, we show that 6-phosphogluconate dehydrogenase (PGD), a cytosolic enzyme involved in carbohydrate metabolism, is required for ER structural integrity and protein secretion. Chemical inhibition or genetic suppression of PGD activity led to cell stress accompanied by significantly expanded ER volume and was rescued by compensating endogenous glutathione supplies. Our results also suggest that this characteristic ER-dilation phenotype may be a general marker indicating increased ECM protein congestion inside cells and decreased secretion. Thus, PGD serves as a link between cytosolic carbohydrate metabolism and protein secretion.
    Keywords:  6-phosphogluconate dehydrogenase; ECM; ER dilation; PGD; cancer; endoplasmic reticulum; extracellular matrix; glutathione; protein misfolding; protein secretion
    DOI:  https://doi.org/10.1016/j.chembiol.2019.05.006
  31. Cell Metab. 2019 Jun 10. pii: S1550-4131(19)30258-X. [Epub ahead of print]
    Li M, Zhang CS, Zong Y, Feng JW, Ma T, Hu M, Lin Z, Li X, Xie C, Wu Y, Jiang D, Li Y, Zhang C, Tian X, Wang W, Yang Y, Chen J, Cui J, Wu YQ, Chen X, Liu QF, Wu J, Lin SY, Ye Z, Liu Y, Piao HL, Yu L, Zhou Z, Xie XS, Hardie DG, Lin SC.
      Fructose-1,6-bisphosphate (FBP) aldolase links sensing of declining glucose availability to AMPK activation via the lysosomal pathway. However, how aldolase transmits lack of occupancy by FBP to AMPK activation remains unclear. Here, we show that FBP-unoccupied aldolase interacts with and inhibits endoplasmic reticulum (ER)-localized transient receptor potential channel subfamily V, inhibiting calcium release in low glucose. The decrease of calcium at contact sites between ER and lysosome renders the inhibited TRPV accessible to bind the lysosomal v-ATPase that then recruits AXIN:LKB1 to activate AMPK independently of AMP. Genetic depletion of TRPVs blocks glucose starvation-induced AMPK activation in cells and liver of mice, and in nematodes, indicative of physical requirement of TRPVs. Pharmacological inhibition of TRPVs activates AMPK and elevates NAD+ levels in aged muscles, rejuvenating the animals' running capacity. Our study elucidates that TRPVs relay the FBP-free status of aldolase to the reconfiguration of v-ATPase, leading to AMPK activation in low glucose.
    Keywords:  AMP-activated protein kinase; AMPK; TRPV; aldolase; glucose sensing; transient receptor potential channels; v-ATPase
    DOI:  https://doi.org/10.1016/j.cmet.2019.05.018
  32. EMBO J. 2019 Jun 17. pii: e100978. [Epub ahead of print]
    He X, Zhu Y, Zhang Y, Geng Y, Gong J, Geng J, Zhang P, Zhang X, Liu N, Peng Y, Wang C, Wang Y, Liu X, Wan L, Gong F, Wei C, Zhong H.
      Viral infection triggers the formation of mitochondrial antiviral signaling protein (MAVS) aggregates, which potently promote immune signaling. Autophagy plays an important role in controlling MAVS-mediated antiviral signaling; however, the exact molecular mechanism underlying the targeted autophagic degradation of MAVS remains unclear. Here, we investigated the mechanism by which RNF34 regulates immunity and mitophagy by targeting MAVS RNF34 binds to MAVS in the mitochondrial compartment after viral infection and negatively regulates RIG-I-like receptor (RLR)-mediated antiviral immunity. Moreover, RNF34 catalyzes the K27-/K29-linked ubiquitination of MAVS at Lys 297, 311, 348, and 362 Arg, which serves as a recognition signal for NDP52-dependent autophagic degradation. Specifically, RNF34 initiates the K63- to K27-linked ubiquitination transition on MAVS primarily at Lys 311, which facilitates the autophagic degradation of MAVS upon RIG-I stimulation. Notably, RNF34 is required for the clearance of damaged mitochondria upon viral infection. Thus, we elucidated the mechanism by which RNF34-mediated autophagic degradation of MAVS regulates the innate immune response, mitochondrial homeostasis, and infection.
    Keywords:   MAVS ; RNF34; innate immune response; selective mitophagy; ubiquitination
    DOI:  https://doi.org/10.15252/embj.2018100978
  33. Biochemistry (Mosc). 2019 Jan;84(Suppl 1): S225-S232
    Mamaev DV, Zvyagilskaya RA.
      Mitochondria play a crucial role in energy production, general cell metabolism, cell signaling, and apoptosis. Mitochondria are also the main source of reactive oxygen species, especially in the case of their dysfunction. Therefore, damaged or even superfluous mitochondria not required for normal cell functioning represent risk factors and should be removed in order to maintain cell homeostasis. Mitochondria removal occurs via mitophagy, a type of selective autophagy (from Greek autos, self and phagein, to eat) that takes place in parallel with mitochondrial biogenesis and other processes. This review outlines general views on autophagy and mitophagy and summarizes information on the autophagy-related (Atg) proteins and their complexes involved in these processes. Yeast, especially Saccharomyces cerevisiae, is a convenient model system for studying molecular mechanisms of mitophagy because yeast genome, transcriptome, and proteome have been well characterized and because genetic manipulations with yeast are relatively simple and fast. Furthermore, yeast contain a number of orthologs of human proteins. Mitophagy in yeast is promoted by various factors, such as starvation, aging, oxidative stress, mitochondrial dysfunction, signaling proteins, and modification of mitochondrial proteins. In this review, we discuss molecular mechanisms underlying mitophagy and its regulation in yeast and present examples of relationships between mitophagy and ubiquitination-deubiquitination processes, as well as between mitophagy and other types of autophagy.
    DOI:  https://doi.org/10.1134/S000629791914013X
  34. Nat Commun. 2019 Jun 20. 10(1): 2698
    van Weverwijk A, Koundouros N, Iravani M, Ashenden M, Gao Q, Poulogiannis G, Jungwirth U, Isacke CM.
      The different stages of the metastatic cascade present distinct metabolic challenges to tumour cells and an altered tumour metabolism associated with successful metastatic colonisation provides a therapeutic vulnerability in disseminated disease. We identify the aldo-keto reductase AKR1B10 as a metastasis enhancer that has little impact on primary tumour growth or dissemination but promotes effective tumour growth in secondary sites and, in human disease, is associated with an increased risk of distant metastatic relapse. AKR1B10High tumour cells have reduced glycolytic capacity and dependency on glucose as fuel source but increased utilisation of fatty acid oxidation. Conversely, in both 3D tumour spheroid assays and in vivo metastasis assays, inhibition of fatty acid oxidation blocks AKR1B10High-enhanced metastatic colonisation with no impact on AKR1B10Low cells. Finally, mechanistic analysis supports a model in which AKR1B10 serves to limit the toxic side effects of oxidative stress thereby sustaining fatty acid oxidation in metabolically challenging metastatic environments.
    DOI:  https://doi.org/10.1038/s41467-019-10592-4
  35. Cell Stress. 2018 Nov 27. 3(1): 9-18
    Chalmin F, Bruchard M, Vegran F, Ghiringhelli F.
      Adaptive T cell immune response is essential for tumor growth control. The efficacy of immune checkpoint inhibitors is regulated by intratumoral immune response. The tumor microenvironment has a major role in adaptive immune response tuning. Tumor cells generate a particular metabolic environment in comparison to other tissues. Tumors are characterized by glycolysis, hypoxia, acidosis, amino acid depletion and fatty acid metabolism modification. Such metabolic changes promote tumor growth, impair immune response and lead to resistance to therapies. This review will detail how these modifications strongly affect CD8 and CD4 T cell functions and impact immunotherapy efficacy.
    Keywords:  T cells; acidosis; amino acids; antitumor immmunity; fatty acid; hypoxia; metabolic stress
    DOI:  https://doi.org/10.15698/cst2019.01.171
  36. Biochem J. 2019 Jun 19. 476(12): 1695-1712
    Karwi QG, Jörg AR, Lopaschuk GD.
      The heart is the organ with highest energy turnover rate (per unit weight) in our body. The heart relies on its flexible and powerful catabolic capacity to continuously generate large amounts of ATP utilizing many energy substrates including fatty acids, carbohydrates (glucose and lactate), ketones and amino acids. The normal health mainly utilizes fatty acids (40-60%) and glucose (20-40%) for ATP production while ketones and amino acids have a minor contribution (10-15% and 1-2%, respectively). Mitochondrial oxidative phosphorylation is the major contributor to cardiac energy production (95%) while cytosolic glycolysis has a marginal contribution (5%). The heart can dramatically and swiftly switch between energy-producing pathways and/or alter the share from each of the energy substrates based on cardiac workload, availability of each energy substrate and neuronal and hormonal activity. The heart is equipped with a highly sophisticated and powerful mitochondrial machinery which synchronizes cardiac energy production from different substrates and orchestrates the rate of ATP production to accommodate its contractility demands. This review discusses mitochondrial cardiac energy metabolism and how it is regulated. This includes a discussion on the allosteric control of cardiac energy metabolism by short-chain coenzyme A esters, including malonyl CoA and its effect on cardiac metabolic preference. We also discuss the transcriptional level of energy regulation and its role in the maturation of cardiac metabolism after birth and cardiac adaptability for different metabolic conditions and energy demands. The role post-translational modifications, namely phosphorylation, acetylation, malonylation, succinylation and glutarylation, play in regulating mitochondrial energy metabolism is also discussed.
    Keywords:  acetylation; fatty acid oxidation; glucose oxidation; malonyl CoA; malonylation; succinylation
    DOI:  https://doi.org/10.1042/BCJ20180617
  37. Biochim Biophys Acta Bioenerg. 2019 Jun 18. pii: S0005-2728(19)30058-1. [Epub ahead of print]
    Yoga EG, Haapanen O, Wittig I, Siegmund K, Sharma V, Zickermann V.
      Respiratory complex I catalyses the reduction of ubiquinone (Q) from NADH coupled to proton pumping across the inner membrane of mitochondria. The electrical charging of the inner mitochondrial membrane drives the synthesis of ATP, which is used to power biochemical reactions of the cell. The recent surge in structural data on complex I from bacteria and mitochondria have contributed to significant understanding of its molecular architecture. However, despite these accomplishments, the role of various subdomains in redox-coupled proton pumping remains entirely unclear. In this work, we have mutated conserved residues in the loop of the PSST subunit that faces the ~30 Å long unique Q-binding tunnel of respiratory complex I. The data show a drastic decrease in Q reductase activity upon mutating several residues despite full assembly of the complex. In-silico modeling and multiple microsecond long molecular dynamics simulations of wild-type and enzyme variants with exchanges of conserved arginine residues revealed remarkable ejection of the bound Q from the site near terminal electron donor N2. Based on experiments and long-time scale molecular simulations, we identify microscopic elements that dynamically control the diffusion of Q and are central to redox-coupled proton pumping in respiratory complex I.
    Keywords:  Cell respiration; Electron transfer; Proton pumping; Quinone dynamics; Redox-coupled proton pumping
    DOI:  https://doi.org/10.1016/j.bbabio.2019.06.006
  38. Oxid Med Cell Longev. 2019 ;2019 2105607
    Cenini G, Lloret A, Cascella R.
      Age is the main risk factor for a number of human diseases, including neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, which increasing numbers of elderly individuals suffer. These pathological conditions are characterized by progressive loss of neuron cells, compromised motor or cognitive functions, and accumulation of abnormally aggregated proteins. Mitochondrial dysfunction is one of the main features of the aging process, particularly in organs requiring a high-energy source such as the heart, muscles, brain, or liver. Neurons rely almost exclusively on the mitochondria, which produce the energy required for most of the cellular processes, including synaptic plasticity and neurotransmitter synthesis. The brain is particularly vulnerable to oxidative stress and damage, because of its high oxygen consumption, low antioxidant defenses, and high content of polyunsaturated fats very prone to be oxidized. Thus, it is not surprising the importance of protecting systems, including antioxidant defenses, to maintain neuronal integrity and survival. Here, we review the role of mitochondrial oxidative stress in the aging process, with a specific focus on neurodegenerative diseases. Understanding the molecular mechanisms involving mitochondria and oxidative stress in the aging and neurodegeneration may help to identify new strategies for improving the health and extending lifespan.
    DOI:  https://doi.org/10.1155/2019/2105607
  39. Trends Endocrinol Metab. 2019 Jul;pii: S1043-2760(19)30073-6. [Epub ahead of print]30(7): 419-431
    Rabbani N, Thornalley PJ.
      Hexokinase-2 (HK2) was recently found to produce increased metabolic flux through glycolysis in hyperglycemia without concurrent transcriptional or other functional regulation. Rather, stabilization to proteolysis by increased glucose substrate binding produced unscheduled increased glucose metabolism in response to high cytosolic glucose concentration. This produces abnormal increases in glycolytic intermediates or glycolytic overload, driving cell dysfunction and vulnerability to the damaging effects of hyperglycemia in diabetes, explaining tissue-specific pathogenesis. Glycolytic overload is also activated in ischemia-reperfusion injury and cell senescence. A further key feature is HK2 displacement from mitochondria by increased glucose-6-phosphate concentration, inducing mitochondrial dysfunction and oxidative stress. This pathogenic mechanism suggested new targets for therapeutics development that gave promising outcomes in initial clinical evaluation.
    DOI:  https://doi.org/10.1016/j.tem.2019.04.011
  40. Cell Death Differ. 2019 Jun 19.
    Charmpilas N, Tavernarakis N.
      The C. elegans germline recapitulates mammalian stem cell niches and provides an effective platform for investigating key aspects of stem cell biology. However, the molecular and physiological requirements for germline stem cell homeostasis remain largely elusive. Here, we report that mitochondrial biogenesis and function are crucial for germline stem cell identity. We show that general transcription activity in germline mitochondria is highly compartmentalized, and determines mitochondrial maturation. RPOM-1, the mitochondrial RNA polymerase, is differentially expressed as germ nuclei progress from the distal to the proximal gonad arm to form oocytes. Mitochondria undergo changes from globular to tubular morphology and become polarized, as they approach the proximal gonad arm. Notably, this mitochondrial maturation trajectory is evolutionarily conserved. We find that a similar transition and temporal mitochondrial RNA polymerase expression profile characterizes differentiation of mammalian stem cells. In C. elegans, ATP, and ROS production increases sharply during maturation. Impaired mitochondrial bioenergetics causes gonad syncytium tumor formation by disrupting the balance between mitosis and differentiation to oocytes, which results in a marked reduction of fecundity. Consequently, compensatory apoptosis is induced in the germline. Sperm-derived signals promote mitochondrial maturation and proper germ cell differentiation via the MEK/ERK kinase pathway. Germ cell fate decisions are determined by a crosstalk between Insulin/IGF-1 and TGF-β signaling, mitochondria and protein synthesis. Our findings demonstrate that mitochondrial transcription activity determines a shift in mitochondrial bioenergetics, which in turn regulates germline stem cell survival and differentiation. Perturbation of mitochondrial transcription hinders proper germ cell differentiation and causes germline tumor development.
    DOI:  https://doi.org/10.1038/s41418-019-0375-9
  41. J Exp Clin Cancer Res. 2019 Jun 20. 38(1): 271
    Babbar M, Huang Y, Curtiss CM, Sheikh MS.
      BACKGROUND: Recently, we have reported the characterization of a novel protein named Coiled-coil Helix Tumor and Metabolism 1 (CHTM1). CHTM1 localizes to both cytosol and mitochondria. Sequence corresponding to CHTM1 is also annotated in the database as CHCHD5. CHTM1 is deregulated in human breast and colon cancers and its deficiency in human cancer cells leads to defective lipid metabolism and poor growth under glucose/glutamine starvation.METHODS: Human cancer cell lines and tissue specimens were used. CHTM1 knockdown was done via lentiviral approach. CHTM1-expresssion constructs were developed and mutants were generated via site-directed mutagenesis approach. Western blotting, immunostaining, immunohistochemistry, cell fractionation and luciferase assays were performed. Reactive oxygen species and reactive nitrogen species were also measured.
    RESULTS: Here we report that CHTM1 deficiency sensitizes human lung cancer cells to metabolic stress-induced cell death mediated by glucose/glutamine deprivation and metformin treatment. CHTM1 interacts with Apoptosis Inducing Factor 1 (AIF1) that is one of the important death inducing molecules. CHTM1 appears to negatively regulate AIF1 by preventing AIF1 translocation to cytosol/nucleus and thereby inhibit AIF1-mediated caspase-independent cell death. Our results also indicate that p38, a stress kinase, plays a critical role in metabolic stress-induced cell death in CHTM1-deficient cells. Furthermore, p38 appears to enhance AIF1 translocation from mitochondria to cytosol particularly in metabolically stressed CHTM1-deficient cells and CHTM1 negatively regulates p38 kinase activity. The expression status of CHTM1 in lung cancer patient samples is also investigated and our results indicate that CHTM1 levels are increased in the majority of lung tumors when compared to their matching normal tissues.
    CONCLUSION: Thus, CHTM1 appears to be an important metabolic marker that regulates cancer cell survival under metabolic stress conditions, and has the potential to be developed as a predictive tumor marker.
    Keywords:  AIF; CHCHD5; Cancer metabolism; Cell death; Lung cancer; Metabolic stress; p38
    DOI:  https://doi.org/10.1186/s13046-019-1253-5
  42. Proc Natl Acad Sci U S A. 2019 Jun 17. pii: 201903847. [Epub ahead of print]
    Lee JS, Mo Y, Gan H, Burgess RJ, Baker DJ, van Deursen JM, Zhang Z.
      Cellular senescence defines an irreversible cell growth arrest state linked to loss of tissue function and aging in mammals. This transition from proliferation to senescence is typically characterized by increased expression of the cell-cycle inhibitor p16INK4a and formation of senescence-associated heterochromatin foci (SAHF). SAHF formation depends on HIRA-mediated nucleosome assembly of histone H3.3, which is regulated by the serine/threonine protein kinase Pak2. However, it is unknown if Pak2 contributes to cellular senescence. Here, we show that depletion of Pak2 delayed oncogene-induced senescence in IMR90 human fibroblasts and oxidative stress-induced senescence of mouse embryonic fibroblasts (MEFs), whereas overexpression of Pak2 accelerated senescence of IMR90 cells. Importantly, depletion of Pak2 in BubR1 progeroid mice attenuated the onset of aging-associated phenotypes and extended life span. Pak2 is required for expression of genes involved in cellular senescence and regulated the deposition of newly synthesized H3.3 onto chromatin in senescent cells. Together, our results demonstrate that Pak2 is an important regulator of cellular senescence and organismal aging, in part through the regulation of gene expression and H3.3 nucleosome assembly.
    Keywords:  Pak2; aging; histone H3.3; nucleosome assembly; senescence
    DOI:  https://doi.org/10.1073/pnas.1903847116
  43. Tumour Biol. 2019 Jun;41(6): 1010428319846231
    Odin E, Sondén A, Carlsson G, Gustavsson B, Wettergren Y.
      5-fluorouracil in combination with the folate leucovorin is the cornerstone in treatment of colorectal cancer. Transport of leucovorin into cells, and subsequent metabolic action, require expression of several genes. The aim was to analyze if tumoral expression of genes putatively involved in leucovorin transport, polyglutamation, or metabolism was associated with outcome of patients with stage III colorectal cancer treated with adjuvant chemotherapy. A total of 363 stage III colorectal cancer patients who received adjuvant bolus 5-fluorouracil + leucovorin alone, or in combination with oxaliplatin according to Nordic bolus regimes were included. Expression of 11 folate pathway genes was determined in tumors using quantitative real-time polymerase chain reaction and related to disease-free survival. The median follow-up time was 5 years. During follow-up, 114 (31%) patients suffered from recurrent disease. A high tumoral expression of the genes SLC46A1/PCFT, SLC19A1/RFC-1, ABCC3/MRP3, GGH, and MTHFD1L, which are involved in folate transport, polyglutamation, or metabolism, was associated with longer disease-free survival of the patients. Each of these genes either encodes mitochondrial enzymes or is being regulated by mitochondrial transcription factors. Expression of the SLC46A1/PCFT gene was most strongly associated with disease-free survival, regardless of treatment regimen. In conclusion, the results show that expression of folate pathway genes are associated with outcome of colorectal cancer patients treated with adjuvant 5-fluorouracil in combination with leucovorin. A prospective study needs to be conducted to determine if expression of these genes can be used to predict response to leucovorin and other folates that are now being tested in clinical studies. Moreover, there seems to be a link between folate metabolism and mitochondrial biogenesis and respiration that deserves further exploration.
    Keywords:  5-fluorouracil; SLC19A1/RFC-1; SLC46A1/PCFT; colorectal cancer; folate; gene expression; leucovorin
    DOI:  https://doi.org/10.1177/1010428319846231
  44. Biochem Biophys Res Commun. 2019 Jun 12. pii: S0006-291X(19)31151-9. [Epub ahead of print]
    Zhang S.
      Mitochondria, the centers of energy production, are highly organized with inner membranes, cristae and outer membranes. The mitochondrial architecture determines their functions in all cellular processes. Changes in the mitochondrial ultrastructure are tightly related to a wide variety of diseases. MGARP, a mitochondria-localized protein, was predicted by bioinformatics and confirmed by cellular and biochemical methods to be located in mitochondria, but there is no direct and clear evidence for its precise location. This report demonstrates the precise ultrastructural location of MGARP within mitochondria by the ascorbate peroxidase 2 (APEX2) system in combination with electron microscopy (EM). EM revealed that more MGARP is located in the inner/cristae membranes, with its C-terminus at the inner faces of the intramembrane spaces, than in the outer membranes. MGARP overexpression caused both mitochondrial remodeling and cristae shaping, leading to the collapse of the mitochondrial network. The mitochondrial morphologies in MGARP-overexpressing cells were diverse; the cells became round or short, and their cristae were deformed and became discontinuous or circular. An engineered MGARP mutant deficient in its transmembrane domain no longer localized to the mitochondria and lost its effects on mitochondrial structure, confirming that the localization of MGARP in the mitochondria depends on its structural integrity. Collectively, our findings define the location of MGARP within the mitochondria, which is associated with its functional implications for the architecture and organization of mitochondria.
    Keywords:  Cristae shaping; MGARP; Mitochondria remodeling; Mitochondrial network; Ultrastructural localization
    DOI:  https://doi.org/10.1016/j.bbrc.2019.06.028
  45. Cell Stress. 2019 May 23. 3(6): 195-207
    Rodríguez-Nuevo A, Zorzano A.
      Mitochondria are the source of damage-associated molecular patterns (DAMPs), which are molecules that play a key modulatory role in immune cells. These molecules include proteins and peptides, such as N-formyl peptides and TFAM, as well as lipids, and metabolites such as cardiolipin, succinate and ATP, and also mitochondrial DNA (mtDNA). Recent data indicate that somatic cells sense mitochondrial DAMPs and trigger protective mechanisms in response to these signals. In this review we focus on the well-described effects of mitochondrial DAMPs on immune cells and also how these molecules induce immunogenic responses in non-immune cells. Special attention will be paid to the response to mtDNA.
    Keywords:  DAMP; TLR9; cGAS; immunity; mitochondria; mitochondrial DNA
    DOI:  https://doi.org/10.15698/cst2019.06.190
  46. Sci Rep. 2019 Jun 19. 9(1): 8785
    Torregrosa-Muñumer R, Hangas A, Goffart S, Blei D, Zsurka G, Griffith J, Kunz WS, Pohjoismäki JLO.
      Replication stalling has been associated with the formation of pathological mitochondrial DNA (mtDNA) rearrangements. Yet, almost nothing is known about the fate of stalled replication intermediates in mitochondria. We show here that replication stalling in mitochondria leads to replication fork regression and mtDNA double-strand breaks. The resulting mtDNA fragments are normally degraded by a mechanism involving the mitochondrial exonuclease MGME1, and the loss of this enzyme results in accumulation of linear and recombining mtDNA species. Additionally, replication stress promotes the initiation of alternative replication origins as an apparent means of rescue by fork convergence. Besides demonstrating an interplay between two major mechanisms rescuing stalled replication forks - mtDNA degradation and homology-dependent repair - our data provide evidence that mitochondria employ similar mechanisms to cope with replication stress as known from other genetic systems.
    DOI:  https://doi.org/10.1038/s41598-019-45244-6
  47. Trends Cancer. 2019 Jun;pii: S2405-8033(19)30073-1. [Epub ahead of print]5(6): 327-329
    Zhao H, Zheng B.
      In two recent articles, Kinsey et al. (Nature Medicine 2019;25:620-627) and Bryant et al. (Nature Medicine 2019;25:628-640) reported that inhibition of MEK-ERK signaling in KRAS-mutated cancers induced autophagic flux, presumably as a metabolic adaptation mechanism. Importantly, they demonstrated that autophagy blockade via chloroquine (CQ) or hydroxychloroquine (HCQ) enhanced the efficacy of MEK-ERK inhibition in various preclinical models of KRAS-driven cancers, providing a rational basis for future clinical evaluation of this combination therapy.
    Keywords:  AMPK; KRAS; MEK inhibitor; autophagy; metabolism
    DOI:  https://doi.org/10.1016/j.trecan.2019.04.003
  48. Front Physiol. 2019 ;10 639
    Sowton AP, Griffin JL, Murray AJ.
      The increasing global prevalence of diabetes has been accompanied by a rise in diabetes-related conditions. This includes diabetic cardiomyopathy (DbCM), a progressive form of heart disease that occurs with both insulin-dependent (type-1) and insulin-independent (type-2) diabetes and arises in the absence of hypertension or coronary artery disease. Over time, DbCM can develop into overt heart failure. Like other forms of cardiomyopathy, DbCM is accompanied by alterations in metabolism which could lead to further progression of the pathology, with metabolic derangement postulated to precede functional changes in the diabetic heart. Moreover in the case of type-2 diabetes, underlying insulin resistance is likely to prevent the canonical substrate switch of the failing heart away from fatty acid oxidation toward increased use of glycolysis. Analytical chemistry techniques, collectively known as metabolomics, are useful tools for investigating the condition. In this article, we provide a comprehensive review of those studies that have employed metabolomic techniques, namely chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy, to profile metabolic remodeling in the diabetic heart of human patients and animal models. These studies collectively demonstrate that glycolysis and glucose oxidation are suppressed in the diabetic myocardium and highlight a complex picture regarding lipid metabolism. The diabetic heart typically shows an increased reliance on fatty acid oxidation, yet triacylglycerols and other lipids accumulate in the diabetic myocardium indicating probable lipotoxicity. The application of lipidomic techniques to the diabetic heart has identified specific lipid species that become enriched and which may in turn act as plasma-borne biomarkers for the condition. Metabolomics is proving to be a powerful approach, allowing a much richer analysis of the metabolic alterations that occur in the diabetic heart. Careful physiological interpretation of metabolomic results will now be key in order to establish which aspects of the metabolic derangement are causal to the progression of DbCM and might form the basis for novel therapeutic intervention.
    Keywords:  animal models; diabetic cardiomyopathy; heart failure; lipidomics; metabolomics; mitochondria
    DOI:  https://doi.org/10.3389/fphys.2019.00639
  49. Transl Neurodegener. 2019 ;8 17
    Chang CY, Liang MZ, Chen L.
      Background: Mitochondria are the major source of intracellular adenosine triphosphate (ATP) and play an essential role in a plethora of physiological functions, including the regulation of metabolism and the maintenance of cellular homeostasis. Mutations of mitochondrial DNA, proteins and impaired mitochondrial function have been implicated in the neurodegenerative diseases, stroke and injury of the central nervous system (CNS). The dynamic feature of mitochondrial fusion, fission, trafficking and turnover have also been documented in these diseases.Perspectives: A major bottleneck of traditional approach to correct mitochondria-related disorders is the difficulty of drugs or gene targeting agents to arrive at specific sub-compartments of mitochondria. Moreover, the diverse nature of mitochondrial mutations among patients makes it impossible to develop one drug for one disease. To this end, mitochondrial transplantation presents a new paradigm of therapeutic intervention that benefits neuronal survival and regeneration for neurodegenerative diseases, stroke, and CNS injury. Supplement of healthy mitochondria to damaged neurons has been reported to promote neuronal viability, activity and neurite re-growth. In this review, we provide an overview of the recent advance and development on mitochondrial therapy.
    Conclusion: Key parameters for the success of mitochondrial transplantation depend on the source and quality of isolated mitochondria, delivery protocol, and cellular uptake of supplemented mitochondria. To expedite clinical application of the mitochondrial transplantation, current isolation protocol needs optimization to obtain high percentage of functional mitochondria, isolated mitochondria may be packaged by biomaterials for successful delivery to brain allowing for efficient neuronal uptake.
    Keywords:  Mitochondrial dynamics; Mitochondrial therapy; Neurodegenerative diseases; Neuronal regeneration; Stroke
    DOI:  https://doi.org/10.1186/s40035-019-0158-8
  50. Trends Cancer. 2019 Jun;pii: S2405-8033(19)30080-9. [Epub ahead of print]5(6): 329-332
    Ackermann T, Tardito S.
      Historic cell culture media were designed to ensure continuous cancer cell proliferation in vitro. However, their composition does not recapitulate the nutritional environment of the tumor. Recent studies show that novel media formulations alleviate the nonphysiological constraints imposed by historic media, and lead to cell culture results that are more relevant to tumor metabolism.
    Keywords:  cancer metabolism; cancer models; physiological medium
    DOI:  https://doi.org/10.1016/j.trecan.2019.05.004
  51. J Physiol. 2019 Jun 22.
    Lima TI, Guimarães D, Sponton CH, Bajgelman MC, Palameta S, Toscaro JM, Reis O, Silveira LR.
      KEY POINTS: Here we report that the PGC-1α/PPARβ axis is a crucial mediator of Ucp3 expression in skeletal muscle cells through the transactivativation of a distal PPAR response element (PPRE) at the Ucp3 gene promoter. This mechanism is activated during the myogenic process and by high concentrations of fatty acids independently of PGC-1α protein levels. Ucp3 is essential for PGC-1α-induced oxidative capacity and adaptive mitochondrial response to fatty acid exposure. These findings provide further evidence for the broad spectrum of the coactivator action in mitochondrial homeostasis placing the PGC-1ɑ/PPARβ axis as an essential component of the molecular regulation of Ucp3 gene in skeletal muscle cells.ABSTRACT: Uncoupling protein 3 (UCP3) have an essential role in fatty acid metabolism and mitochondrial redox regulation in skeletal muscle. However, the molecular mechanisms involved in the expression of Ucp3 are poorly known. Here, we show that the PGC-1α/PPARβ axis is a crucial mediator of Ucp3 expression in skeletal muscle cells. In silico analysis of the UCP3 promoter and qChIP experiments revealed that the induction of the UCP3 transcript is mediated by the transactivation of a distal PPAR response element (PPRE) at the Ucp3 gene promoter by the coactivator PGC-1α. This mechanism is activated during myogenesis and during metabolic stress induced by fatty acids independently of PGC-1α protein levels. We also provide evidence that Ucp3 is essential for PGC-1α-induced oxidative capacity. Taken together our results highlight PGC-1ɑ/PPARβ as an essential component of the molecular regulation of Ucp3 gene in skeletal muscle cells. This article is protected by copyright. All rights reserved.
    DOI:  https://doi.org/10.1113/JP278006
  52. Cell Stress. 2017 Oct 01. 1(1): 68-69
    Zhao Q, Jiang Y.
      Limited supply of nutrient normally causes cell growth arrest. Our recent study (Nat Cell Biol. (7):833-843) shows that fumarase (FH), a key enzyme responsible for the conversion between fumarate and malate in tricarboxylic acid cycle, is importantly involved in the cellular response to nutrient condition.
    Keywords:  cellular response; fumarase; nutrient condition
    DOI:  https://doi.org/10.15698/cst2017.10.107
  53. PLoS Pathog. 2019 Jun 21. 15(6): e1007835
    Morgan EL, Macdonald A.
      Persistent human papillomavirus (HPV) infection is the leading cause of cervical cancer. Although the fundamental link between HPV infection and oncogenesis is established, the specific mechanisms of virus-mediated transformation are not fully understood. We previously demonstrated that the HPV encoded E6 protein increases the activity of the proto-oncogenic transcription factor STAT3 in primary human keratinocytes; however, the molecular basis for STAT3 activation in cervical cancer remains unclear. Here, we show that STAT3 phosphorylation in HPV positive cervical cancer cells is mediated primarily via autocrine activation by the pro-inflammatory cytokine Interleukin 6 (IL-6). Antibody-mediated blockade of IL-6 signalling in HPV positive cells inhibits STAT3 phosphorylation, whereas both recombinant IL-6 and conditioned media from HPV positive cells leads to increased STAT3 phosphorylation within HPV negative cervical cancer cells. Interestingly, we demonstrate that activation of the transcription factor NFκB, involving the small GTPase Rac1, is required for IL-6 production and subsequent STAT3 activation. Our data provides new insights into the molecular re-wiring of cancer cells by HPV E6. We reveal that activation of an IL-6 signalling axis drives the autocrine and paracrine phosphorylation of STAT3 within HPV positive cervical cancers cells and that activation of this pathway is essential for cervical cancer cell proliferation and survival. Greater understanding of this pathway provides a potential opportunity for the use of existing clinically approved drugs for the treatment of HPV-mediated cervical cancer.
    DOI:  https://doi.org/10.1371/journal.ppat.1007835
  54. Trends Cancer. 2019 Jun;pii: S2405-8033(19)30072-X. [Epub ahead of print]5(6): 332-334
    Zhang Y, Commisso C.
      Macropinocytosis is an important nutrient-scavenging pathway in numerous cancer types, including pancreatic, lung, prostate, and bladder. This Forum highlights recent work identifying the key regulators of macropinocytosis that support tumor cell fitness in different contexts, providing a unique framework for strategies to target macropinocytosis in the treatment of cancer.
    Keywords:  AMPK; PTEN; Ras; Wnt; integrin αvβ3; macropinocytosis; metabolism
    DOI:  https://doi.org/10.1016/j.trecan.2019.04.002
  55. Cell Stress. 2019 Apr 29. 3(5): 141-161
    Meng T, Lin S, Zhuang H, Huang H, He Z, Hu Y, Gong Q, Feng D.
      Autophagy (here refers to macroautophagy) is a catabolic pathway by which large protein aggregates and damaged organelles are first sequestered into a double-membraned structure called autophago-some and then delivered to lysosome for destruction. Recently, tremen-dous progress has been made to elucidate the molecular mechanism and functions of this essential cellular metabolic process. In addition to being either a rubbish clearing system or a cellular surviving program in response to different stresses, autophagy plays important roles in a large number of pathophysiological conditions, such as cancer, diabetes, and especially neurodegenerative disorders. Here we review recent progress in the role of autophagy in neurological diseases and discuss how dysregulation of autophagy initiation, autophagosome formation, maturation, and/or au-tophagosome-lysosomal fusion step contributes to the pathogenesis of these disorders in the nervous system.
    Keywords:  Alzheimer's disease; Amyotrophic lateral sclerosis; Huntington's disease; Parkinson's disease; autophagy; mTOR; neuro-degenerative diseases
    DOI:  https://doi.org/10.15698/cst2019.05.186
  56. Curr Dev Nutr. 2019 Jun;pii: nzz030.OR04-04-19. [Epub ahead of print]3(Suppl 1):
    Donohoe D, Park B, Kim JY, Simon E, Porter H, Whelan J, Bettaieb A.
      Objectives: Dietary fiber has been proposed to protect against colorectal cancer. Butyrate, a fiber metabolite that is produced by bacteria in the colon, is known to inhibit cell proliferation and promote cell differentiation, while also inducing apoptotic cell death in colorectal cancer cells at physiologically relevant concentrations. Unlike the majority of cells in the human body that prefer utilizing glucose, non-cancerous colonocytes use butyrate as their primary energy source. However, colorectal cancer cells shift away from utilizing butyrate towards glucose (the Warburg effect). A decrease in butyrate utilization by the colonocyte has been reported in ulcerative colitis (UC) and colorectal cancer (CRC). In both of these diseases, the protein called Pyruvate Kinase Isoform M2 (PKM2) is a factor that has been found to be elevated in colonocytes and is known to catalyze a key step in glycolysis. We hypothesize that upregulation of PKM2 in ulcerative colitis and colorectal cancer results in diminished butyrate oxidation, and increased glucose utilization in colonocytes.Methods: Mitochondrial function, substrate utilization will be analyzed in several colorectal cell lines, isolated colonocytes, or colonocytes grown in 3-D culture where PKM2 is knocked down, knocked-out, or overexpressed. An in vivo mouse model of colitis will be used to study the impact of PKM2 in the injury and repair process.
    Results: Knockdown of PKM2 in cancerous colonocytes was associated with reduced proliferation and increased apoptosis. Butyrate oxidation was also increased in PKM2 knockdown cells. PKM2 regulated mitochondrial function and impacted the expression of uncoupling proteins (UCPs). Elevated PKM2 in primary colonocytes was associated with diminished butyrate utilization. Finally, conditional knockout of PKM2 in the colon resulted inhibited DSS-induced colitis.
    Conclusions: These results show an important role for PKM2 in promoting ulcerative colitis and colorectal cancer through shifting colonocyte metabolism away from butyrate utilization.
    Funding Sources: University of Tennessee - Start-up Funds.
    DOI:  https://doi.org/10.1093/cdn/nzz030.OR04-04-19
  57. Vet Microbiol. 2019 Jul;pii: S0378-1135(19)30371-2. [Epub ahead of print]234 51-60
    Roperto S, Russo V, De Falco F, Rosati A, Catoi C, Roperto F.
      E5 protein, the major oncoprotein of the bovine Deltapapillomavirus genus, has been detected in 17 of the 19 urothelial cancers by molecular and morphological procedures. In 10 urothelial cancers, the oxygen sensitive subunit HIF-1α, which is upregulated by hypoxia, was overexpressed. Mitophagy, the selective autophagic removal of dysfunctional mitochondria, was upregulated in hypoxic neoplastic cells infected by BPVs which was mediated by FUNDC1, a mitochondrial outer-membrane protein. The FUNDC1 receptor was amplified by PCR, and amplicon sequencing showed a 100% homology with bovine FUNDC1 sequences deposited in GenBank (accession number: NM_001104982). Both transcripts and protein levels of FUNDC1 were significantly decreased in hypoxic neoplastic cells relative to healthy, non-neoplastic cells. FUNDC1 interacted with the LC3 protein, a marker of autophagosome (mitophagosome) membrane, the Hsc70/Hsp70 chaperone, and Bag3 co-chaperone. Bag3 may play a role in mitophagosome formation together with the Synpo2 protein, and may be involved in the degradation of Hsc70/Hsp70-bound CHIP-ubiquitinated cargoes, in association with its chaperone. Ultrastructural findings revealed the presence of mitochondria exhibiting severe fragmentation and loss of cristae, as well as numerous mitochondria-containing autophagosomes. Total and phosphorylated GTPase dynamin-related protein 1 (DRP1), which plays a crucial role in mitochondrial fission, a pre-requisite for mitophagy, was overexpressed at the mitochondrial level. Total and phosphorylated mitochondrial fission factor (Mff), mitochondrial fission protein 1 (Fis1), mitochondrial dynamics 51 (MiD51), and MiD49, which are DRP1 receptors responsible and/or co-responsible for its mitochondrial recruitment were overexpressed.
    Keywords:  BPV E5 oncoprotein; Bag3; DRP1; DRP1 receptors; FUNDC1; Receptor mitophagy
    DOI:  https://doi.org/10.1016/j.vetmic.2019.05.017
  58. Int Rev Neurobiol. 2019 ;pii: S0074-7742(19)30019-4. [Epub ahead of print]145 211-238
    Stacpoole PW, Martyniuk CJ, James MO, Calcutt NA.
      Dichloroacetate (DCA) has been the focus of research by both environmental toxicologists and biomedical scientists for over 50 years. As a product of water chlorination and a metabolite of certain industrial chemicals, DCA is ubiquitous in our biosphere at low μg/kg body weight daily exposure levels without obvious adverse effects in humans. As an investigational drug for numerous congenital and acquired diseases, DCA is administered orally or parenterally, usually at doses of 10-50mg/kg per day. As a therapeutic, its principal mechanism of action is to inhibit pyruvate dehydrogenase kinase (PDK). In turn, PDK inhibits the key mitochondrial energy homeostat, pyruvate dehydrogenase complex (PDC), by reversible phosphorylation. By blocking PDK, DCA activates PDC and, consequently, the mitochondrial respiratory chain and ATP synthesis. A reversible sensory/motor peripheral neuropathy is the clinically limiting adverse effect of chronic DCA exposure and experimental data implicate the Schwann cell as a toxicological target. It has been postulated that stimulation of PDC and respiratory chain activity by DCA in normally glycolytic Schwann cells causes uncompensated oxidative stress from increased reactive oxygen species production. Additionally, the metabolism of DCA interferes with the catabolism of the amino acids phenylalanine and tyrosine and with heme synthesis, resulting in accumulation of reactive molecules capable of forming adducts with DNA and proteins and also resulting in oxidative stress. Preliminary evidence in rodent models of peripheral neuropathy suggest that DCA-induced neurotoxicity may be mitigated by naturally occurring antioxidants and by a specific class of muscarinic receptor antagonists. These findings generate a number of testable hypotheses regarding the etiology and treatment of DCA peripheral neuropathy.
    Keywords:  Anti-oxidants; Clinical trial; Dichloroacetate; Glutathione-S-transferase zeta 1; Metabolic disease; Mitochondria; Oxidative damage; Peripheral neuropathy; Tyrosine
    DOI:  https://doi.org/10.1016/bs.irn.2019.05.003
  59. Cell Stress. 2017 Oct 02. 1(2): 79-89
    Aki T, Unuma K, Uemura K.
      Recent research indicates crucial roles of autophagy during sepsis. In animal models of sepsis induced by cecal ligation and puncture (CLP) or the systemic administration of lipopolysaccharides (LPS), autophagy is implicated in the activation and/or damage of various cells/organs, such as immune cells, heart, lung, kidney, and liver. Since sepsis is associated with an increased production of pro- as well as anti-inflammatory cytokines, it has long been considered that hypercytokinemia is a fetal immune response leading to multiple organ failure (MOF) and mortality of humans during sepsis. However, a recent paradigm illuminates the crucial roles of mitochondrial dysfunction as well as the perturbation of autophagy in the pathogenesis of sepsis. In the livers of animal models of sepsis, autophagy is involved in the elimination of damaged mitochondria to prevent the generation of mitochondrial ROS and the initiation of the mitochondrial apoptotic pathway. In addition, many reports now indicate that the role of autophagy is not restricted to the elimination of hazardous malfunctioning mitochondria within the cells; autophagy has been shown to be involved in the regulation of inflammasome activation and the release of cytokines as well as other inflammatory substances. In this review, we summarize recent literature describing the versatile role of autophagy and its possible implications in the pathogenesis of sepsis in the liver.
    Keywords:  autophagy; immune response; liver; mitochondrial dysfunction; mitophagy; non-canonical autophagy; secretion; sepsis
    DOI:  https://doi.org/10.15698/cst2017.11.110
  60. Front Physiol. 2019 ;10 657
    Sonnay S, Chakrabarti A, Thevenet J, Wiederkehr A, Christinat N, Masoodi M.
      Medium-chain triglyceride (MCT) ketogenic diets increase ketone bodies, which are believed to act as alternative energy substrates in the injured brain. Octanoic (C8:0) and decanoic (C10:0) acids, which produce ketone bodies through β-oxidation, are used as part of MCT ketogenic diets. Although the ketogenic role of MCT is well-established, it remains unclear how the network metabolism underlying β-oxidation of these medium-chain fatty acids (MCFA) differ. We aim to elucidate basal β-oxidation of these commonly used MCFA at the cellular level. Human-induced pluripotent stem cell-derived (iPSC) astrocytes were incubated with [U-13C]-C8:0 or [U-13C]-C10:0, and the fractional enrichments (FE) of the derivatives were used for metabolic flux analysis. Data indicate higher extracellular concentrations and faster secretion rates of β-hydroxybutyrate (βHB) and acetoacetate (AcAc) with C8:0 than C10:0, and an important contribution from unlabeled substrates. Flux analysis indicates opposite direction of metabolic flux between the MCFA intermediates C6:0 and C8:0, with an important contribution of unlabeled sources to the elongation in the C10:0 condition, suggesting different β-oxidation pathways. Finally, larger intracellular glutathione concentrations and secretions of 3-OH-C10:0 and C6:0 were measured in C10:0-treated astrocytes. These findings reveal MCFA-specific ketogenic properties. Our results provide insights into designing different MCT-based ketogenic diets to target specific health benefits.
    Keywords:  13C-metabolic flux analysis; decanoic acid; induced pluripotent stem cell-derived astrocytes; octanoic acid; β-oxidation
    DOI:  https://doi.org/10.3389/fphys.2019.00657
  61. J Mol Cell Cardiol. 2019 Jun 12. pii: S0022-2828(18)31292-6. [Epub ahead of print]
    Koentges C, Cimolai MC, Pfeil K, Wolf D, Marchini TO, Tarkhnishvili A, Hoffmann MM, Odening KE, Diehl P, von Zur Mühlen C, Alvarez S, Bode C, Zirlik A, Bugger H.
      BACKGROUND: Sepsis-induced cardiomyopathy contributes to the high mortality of septic shock in critically ill patients. Since the underlying mechanisms are incompletely understood, we hypothesized that sepsis-induced impairment of sirtuin 3 (SIRT3) activity contributes to the development of septic cardiomyopathy.METHODS AND RESULTS: Treatment of mice with lipopolysaccharide (LPS) for 6 h resulted in myocardial NAD+ depletion and increased mitochondrial protein acetylation, indicating impaired myocardial SIRT3 activity due to NAD+ depletion. LPS treatment also resulted in impaired cardiac output in isolated working hearts, indicating endotoxemia-induced cardiomyopathy. Maintaining normal myocardial NAD+ levels in LPS-treated mice by Poly(ADP-ribose)polymerase 1 (PARP1) deletion prevented cardiac dysfunction, whereas additional SIRT3 deficiency blunted this beneficial effect, indicating that impaired SIRT3 activity contributes to cardiac dysfunction in endotoxemia. Measurements of mitochondrial ATP synthesis suggest that LPS-induced contractile dysfunction may result from cardiac energy depletion due to impaired SIRT3 activity. Pharmacological inhibition of mitochondrial calpains using MDL28170 normalized LPS-induced cleavage of the ATP5A1 subunit of ATP synthase and normalized contractile dysfunction, suggesting that cardiac energy depletion may result from calpain-mediated cleavage of ATP5A1. These beneficial effects were completely blunted by SIRT3 deficiency. Finally, a gene set enrichment analysis of hearts of patients with septic, ischemic or dilated cardiomyopathy revealed a sepsis-specific suppression of SIRT3 deacetylation targets, including ATP5A1, indicating a functional relevance of SIRT3-dependent pathways in human sepsis.
    CONCLUSIONS: Impaired SIRT3 activity may mediate cardiac dysfunction in endotoxemia by facilitating calpain-mediated disruption of ATP synthesis, suggesting SIRT3 activation as a potential therapeutic strategy to treat septic cardiomyopathy.
    Keywords:  Cardiomyopathy; Metabolism; Pathophysiology
    DOI:  https://doi.org/10.1016/j.yjmcc.2019.06.008
  62. Neoplasia. 2019 Jun 14. pii: S1476-5586(19)30148-4. [Epub ahead of print]21(8): 731-739
    Jones AT, Yang J, Narov K, Henske EP, Sampson JR, Shen MH.
      In tuberous sclerosis (TSC)-associated tumors, mutations in the TSC genes lead to aberrant activation of the mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway. mTORC1 signaling impacts many biological processes including the epithelial-mesenchymal transition (EMT), which is suggested to promote tumor progression and metastasis in various types of cancer. In this study, we report hybrid cells with epithelial and mesenchymal features in angiomyolipomas and partial EMT in carcinomas from TSC patients and describe a new model of EMT activation during tumor progression from cyst to papillary adenoma to solid carcinoma in the kidneys of Tsc2+/- mice. Features of EMT occurred infrequently in TSC-associated cysts but increased as the lesions progressed through papillary adenoma to solid carcinoma where epithelial-mesenchymal hybrid cells were abundant, indicating partial EMT. We also compared the effects of the novel ATP-competitive mTOR inhibitor AZD2014 with the allosteric mTOR inhibitor rapamycin on EMT and tumor burden. Both AZD2014 and rapamycin potently suppressed EMT of renal tumors and effectively blocked tumor progression in Tsc2+/- mice. These results suggest that partial EMT is a shared feature of TSC-associated renal tumors in humans and mice and occurs during TSC-associated tumor progression. EMT-related signaling pathways may represent therapeutic targets for tumors associated with mutations in the TSC genes.
    DOI:  https://doi.org/10.1016/j.neo.2019.05.003
  63. Life Sci. 2019 Jun 17. pii: S0024-3205(19)30513-2. [Epub ahead of print] 116587
    Lan B, He Y, Sun H, Zheng X, Gao Y, Li N.
      The endoplasmic reticulum (ER) and mitochondria are two important organelles in cells. Mitochondria-associated membranes (MAMs) are lipid raft-like domains formed in the ER membranes that are in close apposition to mitochondria. They play an important role in signal transmission between these two essential organelles. When cells are exposed to internal or external stressful stimuli, the ER will activate an adaptive response called the ER stress response, which has a significant effect on mitochondrial function. Mitochondrial quality control is an important mechanism to ensure the functional integrity of mitochondria and the effect of ER stress on mitochondrial quality control through MAMs is of great significance. Therefore, in this review, we introduce ER stress and mitochondrial quality control, and discuss how ER stress signals are transmitted to mitochondria through MAMs. We then review the important roles of MAMs in mitochondrial quality control under ER stress.
    Keywords:  Ca(2+); Endoplasmic reticulum stress; Mitochondria associated membranes; Mitochondrial quality control
    DOI:  https://doi.org/10.1016/j.lfs.2019.116587
  64. EMBO J. 2019 Jun 17. pii: e100990. [Epub ahead of print]
    Oka OB, van Lith M, Rudolf J, Tungkum W, Pringle MA, Bulleid NJ.
      Activation of the ATF6α signaling pathway is initiated by trafficking of ATF6α from the ER to the Golgi apparatus. Its subsequent proteolysis releases a transcription factor that translocates to the nucleus causing downstream gene activation. How ER retention, Golgi trafficking, and proteolysis of ATF6α are regulated and whether additional protein partners are required for its localization and processing remain unresolved. Here, we show that ER-resident oxidoreductase ERp18 associates with ATF6α following ER stress and plays a key role in both trafficking and activation of ATF6α. We find that ERp18 depletion attenuates the ATF6α stress response. Paradoxically, ER stress accelerates trafficking of ATF6α to the Golgi in ERp18-depleted cells. However, the translocated ATF6α becomes aberrantly processed preventing release of the soluble transcription factor. Hence, we demonstrate that ERp18 monitors ATF6α ER quality control to ensure optimal processing following trafficking to the Golgi.
    Keywords:  ATF6α; ER stress; ERp18; protein trafficking; unfolded protein response
    DOI:  https://doi.org/10.15252/embj.2018100990
  65. FEBS Lett. 2019 Jun 18.
    Chapman J, Fielder E, Passos JF.
      Cellular senescence and mitochondrial dysfunction have both been defined as classical hallmarks of the ageing process. Here, we review the intricate relationship between the two. In the context of ageing, it is now well regarded that cellular senescence is a key driver in both ageing and the onset of a number of age-related pathologies. Emerging evidence has pinpointed mitochondria as one of the key modulators in the development of the senescence phenotype, particularly the pro-inflammatory senescence associated secretory phenotype (SASP). This review focuses on the contribution of homeostatic mechanisms, as well as of reactive oxygen species (ROS) and mitochondrial metabolites in the senescence programme. Furthermore, we discuss emerging pathways and mitochondrial-mediated mechanisms that may be influencing the SASP and, subsequently, explore how these may be exploited to open up new therapeutic avenues. This article is protected by copyright. All rights reserved.
    Keywords:  Ageing; Mitochondria; Senescence; Senolytics; Senostatics
    DOI:  https://doi.org/10.1002/1873-3468.13498
  66. Proc Natl Acad Sci U S A. 2019 Jun 18. pii: 201902658. [Epub ahead of print]
    Boned Del Río I, Young LC, Sari S, Jones GG, Ringham-Terry B, Hartig N, Rejnowicz E, Lei W, Bhamra A, Surinova S, Rodriguez-Viciana P.
      Despite the crucial role of RAF kinases in cell signaling and disease, we still lack a complete understanding of their regulation. Heterodimerization of RAF kinases as well as dephosphorylation of a conserved "S259" inhibitory site are important steps for RAF activation but the precise mechanisms and dynamics remain unclear. A ternary complex comprised of SHOC2, MRAS, and PP1 (SHOC2 complex) functions as a RAF S259 holophosphatase and gain-of-function mutations in SHOC2, MRAS, and PP1 that promote complex formation are found in Noonan syndrome. Here we show that SHOC2 complex-mediated S259 RAF dephosphorylation is critically required for growth factor-induced RAF heterodimerization as well as for MEK dissociation from BRAF. We also uncover SHOC2-independent mechanisms of RAF and ERK pathway activation that rely on N-region phosphorylation of CRAF. In DLD-1 cells stimulated with EGF, SHOC2 function is essential for a rapid transient phase of ERK activation, but is not required for a slow, sustained phase that is instead driven by palmitoylated H/N-RAS proteins and CRAF. Whereas redundant SHOC2-dependent and -independent mechanisms of RAF and ERK activation make SHOC2 dispensable for proliferation in 2D, KRAS mutant cells preferentially rely on SHOC2 for ERK signaling under anchorage-independent conditions. Our study highlights a context-dependent contribution of SHOC2 to ERK pathway dynamics that is preferentially engaged by KRAS oncogenic signaling and provides a biochemical framework for selective ERK pathway inhibition by targeting the SHOC2 holophosphatase.
    Keywords:  ERK; MRAS; RAF; RAS; SHOC2
    DOI:  https://doi.org/10.1073/pnas.1902658116
  67. Antioxid Redox Signal. 2019 Jun 20.
    Xiao W, Loscalzo J.
      SIGNIFICANCE: Reducing equivalents (NAD(P)H and GSH) are essential for maintaining cellular redox homeostasis and for modulating cellular metabolism. Reductive stress induced by excessive levels of NADH, NADPH, and GSH is as harmful as oxidative stress and is implicated in many pathological processes. Recent Advances: Reductive stress broadens our view of the importance of cellular redox homeostasis and the influences of an imbalanced redox niche on biological functions, including cell metabolism.CRITICAL ISSUES: The distribution of cellular NAD(H), NADP(H), and GSH/GSSG is highly compartmentalized. Understanding how cells coordinate different pools of redox couples under unstressed and stressed conditions is critical for a comprehensive view of redox homeostasis and stress. It is also critical to explore the underlying mechanisms of reductive stress and its biological consequences, including effects on energy metabolism.
    FUTURE DIRECTIONS: Future studies are needed to investigate how reductive stress affects cell metabolism and how cells adapt their metabolism to reductive stress. Whether or not NADH shuttles and mitochondrial nicotinamide nucleotide transhydrogenase (NNT) enzyme can regulate hypoxia-induced reductive stress is also a worthy pursuit. Developing strategies (e.g., anti-reductant approaches) to counteract reductive stress and its related adverse biological consequences also requires extensive future efforts.
    DOI:  https://doi.org/10.1089/ars.2019.7803
  68. Cell Stress. 2018 Jul 13. 2(8): 184-199
    Pacheu-Grau D, Rucktäschel R, Deckers M.
      Mitochondrial bioenergetics require the coordination of two different and independent genomes. Mutations in either genome will affect mitochondrial functionality and produce different sources of cellular stress. Depending on the kind of defect and stress, different tissues and organs will be affected, leading to diverse pathological conditions. There is no curative therapy for mitochondrial diseases, nevertheless, there are strategies described that fight the various stress forms caused by the malfunctioning organelles. Here, we will revise the main kinds of stress generated by mutations in mitochondrial genes and outline several ways of fighting this stress.
    Keywords:  cellular stress; mitochondrial dysfunction; mitochondrial pathology; therapy
    DOI:  https://doi.org/10.15698/cst2018.07.147
  69. BMC Cancer. 2019 Jun 17. 19(1): 600
    Li J, Halfter K, Zhang M, Saad C, Xu K, Bauer B, Huang Y, Shi L, Mansmann UR.
      BACKGROUND: Receptor tyrosine kinase (RTK) inhibitors are frequently used to treat cancers and the results have been mixed, some of these small molecule drugs are highly successful while others show a more modest response. A high number of studies have been conducted to investigate the signaling mechanisms and corresponding therapeutic influence of RTK inhibitors in order to explore the therapeutic potential of RTK inhibitors. However, most of these studies neglected the potential metabolic impact of RTK inhibitors, which could be highly associated with drug efficacy and adverse effects during treatment.METHODS: In order to fill these knowledge gaps and improve the therapeutic utilization of RTK inhibitors a large-scale computational simulation/analysis over multiple types of cancers with the treatment responses of RTK inhibitors was performed. The pharmacological data of all eight RTK inhibitor and gene expression profiles of 479 cell lines from The Cancer Cell Line Encyclopedia were used.
    RESULTS: The potential metabolic impact of RTK inhibitors on different types of cancers were analyzed resulting in cancer-specific (breast, liver, pancreas, central nervous system) metabolic signatures. Many of these are in line with results from different independent studies, thereby providing indirect verification of the obtained results.
    CONCLUSIONS: Our study demonstrates the potential of using a computational approach on signature-based-analysis over multiple cancer types. The results reveal the strength of multiple-cancer analysis over conventional signature-based analysis on a single cancer type.
    Keywords:  Cancer metabolism; Computational modeling; Systems biology; Treatment prediction
    DOI:  https://doi.org/10.1186/s12885-019-5804-0
  70. Am J Physiol Cell Physiol. 2019 Jun 19.
    Sussman W, Stevenson M, Mowdawalla C, Mota S, Ragolia L, Pan X.
      The transcription factor BMAL1 (aryl hydrocarbon receptor nuclear translocator-like protein 1) is an essential regulator of the circadian clock, which controls the 24-hr cycle of physiological processes such as nutrient absorption. To examine the role of BMAL1 in small intestinal glucose absorption, we used differentiated human colon adenocarcinoma cells (Caco-2 cells). Here, we show that BMAL1 regulates glucose uptake in differentiated Caco-2 cells and that this process is dependent on the glucose transporter SGLT1. Mechanistic studies show that BMAL1 regulates glucose uptake by controlling the transcription of SGLT1 involving the paired-homeodomain transcription factor 4 (PAX4), a transcriptional repressor. This is supported by the observation that CRISPR-Cas9-knock down of PAX4 increases SGLT1 and glucose uptake. ChIP and ChIP-qPCR assays show that the knock down or overexpression of BMAL1 decreases or increases the binding of PAX4 to the HNF1α binding site of the SGLT1 promoter, respectively. These findings identify BMAL1 as a critical mediator of small intestine carbohydrate absorption and SGLT1.
    Keywords:  BMAL1; Caco-2; PAX4; SGLT1; transporter
    DOI:  https://doi.org/10.1152/ajpcell.00058.2019