bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒08‒25
fifty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Cell Rep. 2019 Aug 20. pii: S2211-1247(19)31000-9. [Epub ahead of print]28(8): 1971-1980.e8
    Buj R, Chen CW, Dahl ES, Leon KE, Kuskovsky R, Maglakelidze N, Navaratnarajah M, Zhang G, Doan MT, Jiang H, Zaleski M, Kutzler L, Lacko H, Lu Y, Mills GB, Gowda R, Robertson GP, Warrick JI, Herlyn M, Imamura Y, Kimball SR, DeGraff DJ, Snyder NW, Aird KM.
      Reprogrammed metabolism and cell cycle dysregulation are two cancer hallmarks. p16 is a cell cycle inhibitor and tumor suppressor that is upregulated during oncogene-induced senescence (OIS). Loss of p16 allows for uninhibited cell cycle progression, bypass of OIS, and tumorigenesis. Whether p16 loss affects pro-tumorigenic metabolism is unclear. We report that suppression of p16 plays a central role in reprogramming metabolism by increasing nucleotide synthesis. This occurs by activation of mTORC1 signaling, which directly mediates increased translation of the mRNA encoding ribose-5-phosphate isomerase A (RPIA), a pentose phosphate pathway enzyme. p16 loss correlates with activation of the mTORC1-RPIA axis in multiple cancer types. Suppression of RPIA inhibits proliferation only in p16-low cells by inducing senescence both in vitro and in vivo. These data reveal the molecular basis whereby p16 loss modulates pro-tumorigenic metabolism through mTORC1-mediated upregulation of nucleotide synthesis and reveals a metabolic vulnerability of p16-null cancer cells.
    Keywords:  BRAF; cancer metabolism; cell cycle; melanoma; nevi; pancreatic cancer; pentose phosphate pathway; ribonucleotide reductase M2; ribose-5-phosphate isomerase A; senescence
  2. Annu Rev Nutr. 2019 Aug 21. 39 201-226
    Yang X, Zhang R, Nakahira K, Gu Z.
      A wide spectrum of human diseases, including cancer, neurodegenerative diseases, and metabolic disorders, have been shown to be associated with mitochondrial dysfunction through multiple molecular mechanisms. Mitochondria are particularly susceptible to nutrient deficiencies, and nutritional intervention is an essential way to maintain mitochondrial homeostasis. Recent advances in genetic manipulation and next-generation sequencing reveal the crucial roles of mitochondrial DNA (mtDNA) in various pathophysiological conditions. Mitophagy, a term coined to describe autophagy that targets dysfunctional mitochondria, has emerged as an important cellular process to maintain mitochondrial homeostasis and has been shown to be regulated by various nutrients and nutritional stresses. Given the high prevalence of mtDNA mutations in humans and their impact on mitochondrial function, it is important to investigate the mechanisms that regulate mtDNA mutation. Here, we discuss mitochondrial genetics and mtDNA mutations and their implications for human diseases. We also examine the role of mitophagy as a therapeutic target, highlighting how nutrients may eliminate mtDNA mutations through mitophagy.
    Keywords:  heteroplasmy; mitochondria; mitophagy; mtDNA; nutrients
  3. Cell Rep. 2019 Aug 20. pii: S2211-1247(19)30954-4. [Epub ahead of print]28(8): 1949-1960.e6
    Costa R, Peruzzo R, Bachmann M, Montà GD, Vicario M, Santinon G, Mattarei A, Moro E, Quintana-Cabrera R, Scorrano L, Zeviani M, Vallese F, Zoratti M, Paradisi C, Argenton F, Brini M, Calì T, Dupont S, Szabò I, Leanza L.
      Wnt signaling affects fundamental development pathways and, if aberrantly activated, promotes the development of cancers. Wnt signaling is modulated by different factors, but whether the mitochondrial energetic state affects Wnt signaling is unknown. Here, we show that sublethal concentrations of different compounds that decrease mitochondrial ATP production specifically downregulate Wnt/β-catenin signaling in vitro in colon cancer cells and in vivo in zebrafish reporter lines. Accordingly, fibroblasts from a GRACILE syndrome patient and a generated zebrafish model lead to reduced Wnt signaling. We identify a mitochondria-Wnt signaling axis whereby a decrease in mitochondrial ATP reduces calcium uptake into the endoplasmic reticulum (ER), leading to endoplasmic reticulum stress and to impaired Wnt signaling. In turn, the recovery of the ATP level or the inhibition of endoplasmic reticulum stress restores Wnt activity. These findings reveal a mechanism that links mitochondrial energetic metabolism to the control of the Wnt pathway that may be beneficial against several pathologies.
    Keywords:  ER stress; SERCA; canonical Wnt signaling; colon cancer; mitochondrial ATP; mitochondrial fitness; β-catenin
  4. Nat Commun. 2019 Aug 19. 10(1): 3726
    Bartok A, Weaver D, Golenár T, Nichtova Z, Katona M, Bánsághi S, Alzayady KJ, Thomas VK, Ando H, Mikoshiba K, Joseph SK, Yule DI, Csordás G, Hajnóczky G.
      Contact sites of endoplasmic reticulum (ER) and mitochondria locally convey calcium signals between the IP3 receptors (IP3R) and the mitochondrial calcium uniporter, and are central to cell survival. It remains unclear whether IP3Rs also have a structural role in contact formation and whether the different IP3R isoforms have redundant functions. Using an IP3R-deficient cell model rescued with each of the three IP3R isoforms and an array of super-resolution and ultrastructural approaches we demonstrate that IP3Rs are required for maintaining ER-mitochondrial contacts. This role is independent of calcium fluxes. We also show that, while each isoform can support contacts, type 2 IP3R is the most effective in delivering calcium to the mitochondria. Thus, these studies reveal a non-canonical, structural role for the IP3Rs and direct attention towards the type 2 IP3R that was previously neglected in the context of ER-mitochondrial calcium signaling.
  5. ChemMedChem. 2019 Aug 18.
    Sileikyte J, Devereaux J, de Jong J, Schiavone M, Jones K, Nilsen A, Bernardi P, Forte M, Cohen M.
      Excessive mitochondrial matrix Ca2+ and oxidative stress leads to the opening of a high-conductance channel of the inner mitochondrial membrane referred to as the mitochondrial permeability transition pore (mtPTP). Because mtPTP opening can lead to cell death under diverse pathophysiological conditions (e.g. ischemia-reperfusion injury and muscular dystrophy), inhibitors of mtPTP are potential therapeutics for various human diseases. High throughput screening efforts led to the identification of a 3-carboxamide-5-phenol-isoxazole compounds as mtPTP inhibitors. While they showed nM potency against mtPTP, they exhibited poor plasma stability, precluding their use in in vivo studies. Herein, we describe a series of structurally related analogs in which the core isoxazole was replaced with a triazole, and this replacement resulted in a substantial improvement in plasma stability. These analogs could be readily generated using the copper-catalyzed "click chemistry". One analog, TR001, was efficacious in a zebrafish model of muscular dystrophy that results from mtPTP dysfunction whereas the isoxazole isostere had minimal effect.
    Keywords:  Inhibitors; calcium; click chemistry; mitochondria; permeability transition pore
  6. Nat Commun. 2019 Aug 21. 10(1): 3763
    Xiao Z, Dai Z, Locasale JW.
      The tumor milieu consists of numerous cell types each existing in a different environment. However, a characterization of metabolic heterogeneity at single-cell resolution is not established. Here, we develop a computational pipeline to study metabolic programs in single cells. In two representative human cancers, melanoma and head and neck, we apply this algorithm to define the intratumor metabolic landscape. We report an overall discordance between analyses of single cells and those of bulk tumors with higher metabolic activity in malignant cells than previously appreciated. Variation in mitochondrial programs is found to be the major contributor to metabolic heterogeneity. Surprisingly, the expression of both glycolytic and mitochondrial programs strongly correlates with hypoxia in all cell types. Immune and stromal cells could also be distinguished by their metabolic features. Taken together this analysis establishes a computational framework for characterizing metabolism using single cell expression data and defines principles of the tumor microenvironment.
  7. Front Immunol. 2019 ;10 1878
    Raychaudhuri D, Bhattacharya R, Sinha BP, Liu CSC, Ghosh AR, Rahaman O, Bandopadhyay P, Sarif J, D'Rozario R, Paul S, Das A, Sarkar DK, Chattopadhyay S, Ganguly D.
      Plasmacytoid dendritic cells are the most efficient producers of type I interferons, viz. IFNα, in the body and thus have the ability to influence anti-tumor immune responses. But repression of effective intra-tumoral pDC activation is a key immuno-evasion strategy exhibited in tumors-tumor-recruited pDCs are rendered "tolerogenic," characterized by deficiency in IFNα induction and ability to expand regulatory T cells in situ. But the tumor-derived factors that drive this functional reprogramming of intra-tumoral pDCs are not established. In this study we aimed at exploring if intra-tumoral abundance of the oncometabolite lactate influences intra-tumoral pDC function. We found that lactate attenuates IFNα induction by pDCs mediated by intracellular Ca2+ mobilization triggered by cell surface GPR81 receptor as well as directly by cytosolic import of lactate in pDCs through the cell surface monocarboxylate transporters, affecting cellular metabolism needed for effective pDC activation. We also found that lactate enhances tryptophan metabolism and kynurenine production by pDCs which contribute to induction of FoxP3+ CD4+ regulatory T cells, the major immunosuppressive immune cell subset in tumor microenvironment. We validated these mechanisms of lactate-driven pDC reprogramming by looking into tumor recruited pDCs isolated from patients with breast cancers as well as in a preclinical model of breast cancer in mice. Thus, we discovered a hitherto unknown link between intra-tumoral abundance of an oncometabolite resulting from metabolic adaptation in cancer cells and the pro-tumor tolerogenic function of tumor-recruited pDCs, revealing new therapeutic targets for potentiating anti-cancer immune responses.
    Keywords:  FoxP3+ T cells; breast cancer; lactate; plasmacytoid dendritic cells; type I IFN
  8. J Surg Res. 2019 Aug 14. pii: S0022-4804(19)30551-7. [Epub ahead of print]245 273-280
    Tan YB, Pastukh VM, Gorodnya OM, Mulekar MS, Simmons JD, Machuca TN, Beaver TM, Wilson GL, Gillespie MN.
      BACKGROUND: Transplantation of lungs procured after donation after circulatory death (DCD) is challenging because postmortem metabolic degradation may engender susceptibility to ischemia-reperfusion (IR) injury. Because oxidative mitochondrial DNA (mtDNA) damage has been linked to endothelial barrier disruption in other models of IR injury, here we used a fusion protein construct targeting the DNA repair 8-oxoguanine DNA glycosylase-1 (OGG1) to mitochondria (mtOGG1) to determine if enhanced repair of mtDNA damage attenuates endothelial barrier dysfunction after IR injury in a rat model of lung procurement after DCD.MATERIALS AND METHODS: Lungs excised from donor rats 1 h after cardiac death were cold stored for 2 h after which they were perfused ex vivo in the absence and presence of mt-OGG1 or an inactive mt-OGG1 mutant. Lung endothelial barrier function and mtDNA integrity were determined during and at the end of perfusion, respectively.
    RESULTS AND CONCLUSIONS: Mitochondria-targeted OGG1 attenuated indices of lung endothelial dysfunction incurred after a 1h post-mortem period. Oxidative lung tissue mtDNA damage as well as accumulation of proinflammatory mtDNA fragments in lung perfusate, but not nuclear DNA fragments, also were reduced by mitochondria-targeted OGG1. A repair-deficient mt-OGG1 mutant failed to protect lungs from the adverse effects of DCD procurement.
    CONCLUSIONS: These findings suggest that endothelial barrier dysfunction in lungs procured after DCD is driven by mtDNA damage and point to strategies to enhance mtDNA repair in concert with EVLP as a means of alleviating DCD-related lung IR injury.
    Keywords:  Lung IR injury; Lung transplant; mtDNA DAMPs; mtDNA damage
  9. Science. 2019 Aug 22. pii: eaax4468. [Epub ahead of print]
    Liu Y, You Y, Lu Z, Yang J, Li P, Liu L, Xu H, Niu Y, Cao X.
      Host cell metabolism can be modulated by viral infection, affecting viral survival or clearance. The cellular metabolism rewiring mediated by N 6-methyladenosine (m6A) modification in virus-host interaction remains largely unknown. Here we report that in response to viral infection, host cells impair the enzymatic activity of RNA m6A demethylase ALKBH5. This increases the m6A methylation on α-ketoglutarate dehydrogenase (OGDH) mRNA to reduce its mRNA stability and protein expression. Reduced OGDH decreases the production of metabolite itaconate that is required for viral replication. With reduced OGDH and itaconate production in vivo, ALKBH5-deficient mice display an innate immune response-independent resistance to viral challenge. Our findings reveal that m6A RNA modification-mediated down-regulation of OGDH-Itaconate pathway reprograms cellular metabolism to inhibit viral replication, proposing potential targets for controlling viral infection.
  10. Cell Mol Life Sci. 2019 Aug 20.
    Yang J, Ren B, Yang G, Wang H, Chen G, You L, Zhang T, Zhao Y.
      Pancreatic ductal adenocarcinoma is prone to distant metastasis and is expected to become the second leading cause of cancer-related death. In an extremely nutrient-deficient and hypoxic environment resulting from uncontrolled growth, vascular disturbances and desmoplastic reactions, pancreatic cancer cells utilize "metabolic reprogramming" to satisfy their energy demand and support malignant behaviors such as metastasis. Notably, pancreatic cancer cells show extensive enhancement of glycolysis, including glycolytic enzyme overexpression and increased lactate production, and this is caused by mitochondrial dysfunction, cancer driver genes, specific transcription factors, a hypoxic tumor microenvironment and stromal cells, such as cancer-associated fibroblasts and tumor-associated macrophages. The metabolic switch from oxidative phosphorylation to glycolysis in pancreatic cancer cells regulates the invasion-metastasis cascade by promoting epithelial-mesenchymal transition, tumor angiogenesis and the metastatic colonization of distant organs. In addition to aerobic glycolysis, oxidative phosphorylation also plays a critical role in pancreatic cancer metastasis in ways that remain unclear. In this review, we expound on the intracellular and extracellular causes of the enhancement of glycolysis in pancreatic cancer and the strong association between glycolysis and cancer metastasis, which we expect will yield new therapeutic approaches targeting cancer metabolism.
    Keywords:  Epithelial–mesenchymal transition; Hybrid metabolic phenotype; Metastatic niche; Mitochondrial respiration; Tumor microenvironment; Warburg effect
  11. PLoS Biol. 2019 Aug 21. 17(8): e3000420
    Shi L, Chen X, Zang A, Li T, Hu Y, Ma S, Lü M, Yin H, Wang H, Zhang X, Zhang B, Leng Q, Yang J, Xiao H.
      Dendritic cells (DCs) play pivotal roles in T-cell homeostasis and activation, and metabolic programing has been recently linked to DC development and function. However, the metabolic underpinnings corresponding to distinct DC functions remain largely unresolved. Here, we demonstrate a special metabolic-epigenetic coupling mechanism orchestrated by tuberous sclerosis complex subunit 1 (TSC1)-mechanistic target of rapamycin (mTOR) for homeostatic DC function. Specific ablation of Tsc1 in the DC compartment (Tsc1DC-KO) largely preserved DC development but led to pronounced reduction in naïve and memory-phenotype cluster of differentiation (CD)8+ T cells, a defect fully rescued by concomitant ablation of mTor or regulatory associated protein of MTOR, complex 1 (Rptor) in DCs. Moreover, Tsc1DC-KO mice were unable to launch efficient antigen-specific CD8+ T effector responses required for containing Listeria monocytogenes and B16 melanomas. Mechanistically, our data suggest that the steady-state DCs tend to tune down de novo fatty acid synthesis and divert acetyl-coenzyme A (acetyl-CoA) for histone acetylation, a process critically controlled by TSC1-mTOR. Correspondingly, TSC1 deficiency elevated acetyl-CoA carboxylase 1 (ACC1) expression and fatty acid synthesis, leading to impaired epigenetic imprinting on selective genes such as major histocompatibility complex (MHC)-I and interleukin (IL)-7. Remarkably, tempering ACC1 activity was able to divert cytosolic acetyl-CoA for histone acetylation and restore the gene expression program compromised by TSC1 deficiency. Taken together, our results uncover a crucial role for TSC1-mTOR in metabolic programing of the homeostatic DCs for T-cell homeostasis and implicate metabolic-coupled epigenetic imprinting as a paradigm for DC specification.
  12. Nature. 2019 Aug 21.
    Paggio A, Checchetto V, Campo A, Menabò R, Di Marco G, Di Lisa F, Szabo I, Rizzuto R, De Stefani D.
      Mitochondria provide chemical energy for endoergonic reactions in the form of ATP, and their activity must meet cellular energy requirements, but the mechanisms that link organelle performance to ATP levels are poorly understood. Here we confirm the existence of a protein complex localized in mitochondria that mediates ATP-dependent potassium currents (that is, mitoKATP). We show that-similar to their plasma membrane counterparts-mitoKATP channels are composed of pore-forming and ATP-binding subunits, which we term MITOK and MITOSUR, respectively. In vitro reconstitution of MITOK together with MITOSUR recapitulates the main properties of mitoKATP. Overexpression of MITOK triggers marked organelle swelling, whereas the genetic ablation of this subunit causes instability in the mitochondrial membrane potential, widening of the intracristal space and decreased oxidative phosphorylation. In a mouse model, the loss of MITOK suppresses the cardioprotection that is elicited by pharmacological preconditioning induced by diazoxide. Our results indicate that mitoKATP channels respond to the cellular energetic status by regulating organelle volume and function, and thereby have a key role in mitochondrial physiology and potential effects on several pathological processes.
  13. Cancers (Basel). 2019 Aug 16. pii: E1199. [Epub ahead of print]11(8):
    Mayr-Buro C, Schlereth E, Beuerlein K, Tenekeci U, Meier-Soelch J, Schmitz ML, Kracht M.
      The frequently occurring heterogeneity of cancer cells and their functional interaction with immune cells in the tumor microenvironment raises the need to study signaling pathways at the single cell level with high precision, sensitivity, and spatial resolution. As aberrant NF-κB activity has been implicated in almost all steps of cancer development, we analyzed the dynamic regulation and activation status of the canonical NF-κB pathway in control and IL-1α-stimulated individual cells using proximity ligation assays (PLAs). These systematic experiments allowed the visualization of the dynamic dissociation and re-formation of endogenous p65/IκBα complexes and the nuclear translocation of NF-κB p50/p65 dimers. PLA combined with immunostaining for p65 or with NFKBIA single molecule mRNA-FISH facilitated the analysis of (i) further levels of the NF-κB pathway, (i) its functionality for downstream gene expression, and (iii) the heterogeneity of the NF-κB response in individual cells. PLA also revealed the interaction between NF-κB p65 and the P-body component DCP1a, a new p65 interactor that contributes to efficient p65 NF-κB nuclear translocation. In summary, these data show that PLA technology faithfully mirrored all aspects of dynamic NF-κB regulation, thus allowing molecular diagnostics of this key pathway at the single cell level which will be required for future precision medicine.
    Keywords:  DCP1a; NF-κB; P-bodies; interleukin-1 signaling; posttranscriptional gene regulation; proximity ligation assays; single cell analysis; transcription; tumor heterogeneity
  14. Dev Cell. 2019 Jul 30. pii: S1534-5807(19)30581-7. [Epub ahead of print]
    Barbosa AD, Lim K, Mari M, Edgar JR, Gal L, Sterk P, Jenkins BJ, Koulman A, Savage DB, Schuldiner M, Reggiori F, Wigge PA, Siniossoglou S.
      Cells dynamically adjust organelle organization in response to growth and environmental cues. This requires regulation of synthesis of phospholipids, the building blocks of organelle membranes, or remodeling of their fatty-acyl (FA) composition. FAs are also the main components of triacyglycerols (TGs), which enable energy storage in lipid droplets. How cells coordinate FA metabolism with organelle biogenesis during cell growth remains unclear. Here, we show that Lro1, an acyltransferase that generates TGs from phospholipid-derived FAs in yeast, relocates from the endoplasmic reticulum to a subdomain of the inner nuclear membrane. Lro1 nuclear targeting is regulated by cell cycle and nutrient starvation signals and is inhibited when the nucleus expands. Lro1 is active at this nuclear subdomain, and its compartmentalization is critical for nuclear integrity. These data suggest that Lro1 nuclear targeting provides a site of TG synthesis, which is coupled with nuclear membrane remodeling.
    Keywords:  lipid droplet; nuclear membrane; nucleus; phospholipid; triglyceride
  15. Autophagy. 2019 Aug 21.
    Niu K, Fang H, Chen Z, Zhu Y, Tan Q, Wei D, Li Y, Balajee AS, Zhao Y.
      PRKN/parkin activation through phosphorylation of its ubiquitin and ubiquitin-like domain by PINK1 is critical in mitophagy induction for eliminating the damaged mitochondria. Deubiquitinating enzymes (DUBs) functionally reversing PRKN ubiquitination are critical in controlling the magnitude of PRKN-mediated mitophagy process. However, potential DUBs that directly target PRKN and antagonize its pro-mitophagy effect remains to be identified and characterized. Here, we demonstrated that USP33/VDU1 is localized at the outer membrane of mitochondria and serves as a PRKN DUB through their interaction. Cellular and in vitro assays illustrated that USP33 deubiquitinates PRKN in a DUB activity-dependent manner. USP33 prefers to remove K6, K11, K48 and K63-linked ubiquitin conjugates from PRKN, and deubiquitinates PRKN mainly at Lys435. Mutation of this site leads to a significantly decreased level of K63-, but not K48-linked PRKN ubiquitination. USP33 deficiency enhanced both K48- and K63-linked PRKN ubiquitination, but only K63-linked PRKN ubiquitination was significantly increased under mitochondrial depolarization. Further, USP33 knockdown increased both PRKN protein stabilization and its translocation to depolarized mitochondria leading to the enhancement of mitophagy. Moreover, USP33 silencing protects SH-SY5Y human neuroblastoma cells from the neurotoxin MPTP-induced apoptotic cell death. Our findings convincingly demonstrate that USP33 is a novel PRKN deubiquitinase antagonizing its regulatory roles in mitophagy and SH-SY5Y neuron-like cell survival. Thus, USP33 inhibition may represents an attractive new therapeutic strategy for PD patients.
    Keywords:  PRKN/parkin; USP33 deubiquitinase; apoptosis; mitophagy; ubiquitination
  16. J Biol Chem. 2019 Aug 21. pii: jbc.RA119.009477. [Epub ahead of print]
    Harisseh R, Abrial M, Chiari P, Al-Mawla R, Villedieu C, Tessier N, Bidaux G, Ovize M, Gharib A.
      Calcium (Ca2+) homeostasis is essential for cell survival and is precisely controlled by several cellular actors such as the sarco/endoplasmic reticulum and mitochondria. Upon stress induction, Ca2+ released from sarco/endoplasmic reticulum stores and from extracellular Ca2+ pools accumulates in the cytosol and in the mitochondria. This induces Ca2+ overload and ultimately the opening of the mitochondrial permeability transition pore (mPTP), promoting cell death. Currently, it is unclear whether intracellular Ca2+ stores are sufficient to promote the mPTP opening. Ca2+ retention capacity (CRC) corresponds to the maximal Ca2+ uptake by the mitochondria before mPTP opening. In this study, using permeabilized cardiomyocytes isolated from adult mice, we modified the standard CRC assay by specifically inducing reticular Ca2+ release to investigate the respective contributions of reticular Ca2+ and extracellular Ca2+ to mPTP opening in normoxic conditions or after anoxia-reoxygenation. Our experiments revealed that Ca2+ released from the sarco/endoplasmic reticulum is not sufficient to trigger mPTP opening and corresponds to approximately 50% of the total Ca2+ levels required to open the mPTP. We also studied mPTP opening after anoxia-reoxygenation in the presence or absence of extracellular Ca2+. In both conditions, Ca2+ leakage from internal stores could not trigger mPTP opening by itself, but significantly decreased the CRC. Our findings highlight how a modified CRC assay enables the investigation of the role of reticular and extracellular Ca2+ pools in the regulation of the mPTP. We propose that this method may be useful for screening molecules of interest implicated in mPTP regulation.
    Keywords:  anoxia-reoxygenation; caffeine; calcium; cardiac infarction; cardiomyocyte; mitochondria; mitochondrial permeability transition (MPT); ryanodine; ryanodine receptor; sarcoplasmic reticulum (SR)
  17. Int J Mol Sci. 2019 Aug 19. pii: E4048. [Epub ahead of print]20(16):
    Garten A, Grohmann T, Kluckova K, Lavery GG, Kiess W, Penke M.
      Sorafenib is a multi-kinase inhibitor and one of the few systemic treatment options for patients with advanced hepatocellular carcinomas (HCCs). Resistance to sorafenib develops frequently and could be mediated by the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin (SIRT)1. We aimed to test whether sorafenib efficacy is influenced by cellular NAD levels and NAD-dependent SIRT1 function. We analyzed sorafenib effects on apoptosis induction, NAD salvage, mitochondrial function, and related signaling pathways in HCC cell lines (HepG2, Hep3B, und HUH7) overexpressing SIRT1 or supplemented with the NAD metabolite nicotinamide mononucleotide (NMN) compared to controls. Treatment of HCC cell lines with sorafenib dose-dependently induced apoptosis and a significant decrease in cellular NAD concentrations. The SIRT1 protein was downregulated in HUH7 cells but not in Hep3B cells. After sorafenib treatment, mitochondrial respiration in permeabilized cells was lower, citrate synthase activity was attenuated, and cellular adenosine triphosphate (ATP) levels were decreased. Concomitant to increased phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), sorafenib treatment led to decreased activity of the mechanistic target of rapamycin (mTOR), indicative of energy deprivation. Transient overexpression of SIRT1, as well as NAD repletion by NMN, decreased sorafenib-induced apoptosis. We can, therefore, conclude that sorafenib influences the NAD/SIRT1/AMPK axis. Overexpression of SIRT1 could be an underlying mechanism of resistance to sorafenib treatment in HCC.
    Keywords:  AMP-activated protein kinase; NAMPT; SIRT1; mTOR; mitochondria; sorafenib
  18. Nature. 2019 Aug 21.
    Yoneshiro T, Wang Q, Tajima K, Matsushita M, Maki H, Igarashi K, Dai Z, White PJ, McGarrah RW, Ilkayeva OR, Deleye Y, Oguri Y, Kuroda M, Ikeda K, Li H, Ueno A, Ohishi M, Ishikawa T, Kim K, Chen Y, Sponton CH, Pradhan RN, Majd H, Greiner VJ, Yoneshiro M, Brown Z, Chondronikola M, Takahashi H, Goto T, Kawada T, Sidossis L, Szoka FC, McManus MT, Saito M, Soga T, Kajimura S.
      Branched-chain amino acid (BCAA; valine, leucine and isoleucine) supplementation is often beneficial to energy expenditure; however, increased circulating levels of BCAA are linked to obesity and diabetes. The mechanisms of this paradox remain unclear. Here we report that, on cold exposure, brown adipose tissue (BAT) actively utilizes BCAA in the mitochondria for thermogenesis and promotes systemic BCAA clearance in mice and humans. In turn, a BAT-specific defect in BCAA catabolism attenuates systemic BCAA clearance, BAT fuel oxidation and thermogenesis, leading to diet-induced obesity and glucose intolerance. Mechanistically, active BCAA catabolism in BAT is mediated by SLC25A44, which transports BCAAs into mitochondria. Our results suggest that BAT serves as a key metabolic filter that controls BCAA clearance via SLC25A44, thereby contributing to the improvement of metabolic health.
  19. Biochem J. 2019 Aug 20. pii: BCJ20190405. [Epub ahead of print]
    Martínez J, Tarallo D, Martínez-Palma L, Victoria S, Bresque M, Rodríguez-Bottero S, Marmisolle I, Escande C, Cassina P, Casanova G, Bollati-Fogolín M, Agorio C, Moreno M, Quijano C.
      Cellular senescence is an endpoint of chemotherapy, and targeted therapies in melanoma and the senescence-associated secretory phenotype (SASP) can affect tumor growth and microenvironment, influencing treatment outcomes. Metabolic interventions can modulate the SASP, and an enhanced mitochondrial energy metabolism supports resistance to therapy in melanoma cells.Herein we assessed mitochondrial function of therapy-induced senescent melanoma cells obtained after exposing the cells to temozolomide (TMZ), a methylating chemotherapeutic agent. Senescence induction in melanoma was accompanied by a substantial increase in mitochondrial basal, ATP-linked, and maximum respiration rates and in coupling efficiency, spare respiratory capacity, and respiratory control ratio. Further examinations revealed an increase in mitochondrial mass and length. Alterations in mitochondrial function and morphology were confirmed in isolated senescent cells, obtained by cell-size sorting.An increase in mitofusin 1 and 2 (MFN1 and 2) expression and levels was observed in senescent cells, pointing to alterations in mitochondrial fusion. Silencing mitofusins expression with short hairpin RNA (shRNA) prevented the increase in mitochondrial length, oxygen consumption rate and secretion of interleukin 6 (IL-6), a component of the SASP, in melanoma senescent cells.Our results represent the first in-depth study of mitochondrial function in therapy-induced senescence in melanoma. They indicate that senescence increases mitochondrial mass, length and energy metabolism; and highlight mitochondria as potential pharmacological targets to modulate senescence and the SASP.
    Keywords:  bioenergetics; cell senescence; chemotherapy; melanoma; mitochondria; mitofusin
  20. Mol Cell Proteomics. 2019 Aug 21. pii: mcp.RA119.001621. [Epub ahead of print]
    Yang L, Cao Y, Zhao J, Fang Y, Liu N, Zhang Y.
      Aging is characterized by a gradual deterioration in proteome. However, how protein dynamics that changes with normal aging and in disease is less well understood. Here, we profiled the snapshots of aging proteome in Drosophila, from head and muscle tissues of post-mitotic somatic cells, and the testis of mitotically-active cells. Our data demonstrated that dysregulation of proteome homeostasis, or proteostasis, might be a common feature associated with age. We further used pulsed metabolic stable isotope labeling analysis to characterize protein synthesis. Interestingly, this study determined an age-modulated decline in protein synthesis with age, particularly in the pathways related to mitochondria, neurotransmission, and proteostasis. Importantly, this decline became dramatically accelerated in Pink1 mutants, a Drosophila model of human age-related Parkinson's disease. Taken together, our multidimensional proteomic study revealed tissue-specific protein dynamics with age, highlighting mitochondrial and proteostasis-related proteins. We suggest that declines in proteostasis and mitochondria early in life are critical signals prior to the onset of aging and aging-associated diseases.
    Keywords:  Aging; Drosophila melanogaster*; Mitochondria function or biology; Protein Synthesis*; Quantification; proteome homeostasis
  21. Nutrients. 2019 Aug 16. pii: E1926. [Epub ahead of print]11(8):
    Desideri E, Ciccarone F, Ciriolo MR.
      Glutathione (GSH) is the predominant low-molecular-weight antioxidant with a ubiquitous distribution inside the cell. The steady-state level of cellular GSH is dependent on the balance between synthesis, hydrolysis, recycling of glutathione disulphide (GSSG) as well as cellular extrusion of reduced, oxidized, or conjugated-forms. The augmented oxidative stress typical of cancer cells is accompanied by an increase of glutathione levels that confers them growth advantage and resistance to a number of chemotherapeutic agents. Targeting glutathione metabolism has been widely investigated for cancer treatment although GSH depletion as single therapeutic strategy has resulted largely ineffective if compared with combinatorial approaches. In this review, we circumstantiate the role of glutathione in tumour development and progression focusing on how interfering with different steps of glutathione metabolism can be exploited for therapeutic purposes. A dedicated section on synthetic lethal interactions with GSH modulators will highlight the promising option of harnessing glutathione metabolism for patient-directed therapy in cancer.
    Keywords:  GSH; cancer therapy; ferroptosis; synthetic lethality
  22. Cancer Res. 2019 Aug 21. pii: canres.1789.2019. [Epub ahead of print]
    Xu S, Herschman HR.
      Since Warburg's observation that most cancers exhibit elevated glycolysis, decades of research have attempted to reduce tumor glucose utilization as a therapeutic approach. Hexokinase (HK) activity is the first glycolytic enzymatic step; despite many attempts to inhibit HK activity, none has reached clinical application. Identification of HK isoforms, and recognition that most tissues express only HK1 while most tumors express HK1 and HK2, stimulated reducing HK2 activity as a therapeutic option. However, studies using HK2 shRNA and isogenic HK1+HK2- and HK1+HK2+ tumor cell pairs demonstrated that tumors expressing only HK1, while exhibiting reduced glucose consumption, progressed in vivo as well as tumors expressing both HK1 and HK2. However, there exist HK1-HK2+ tumor subpopulations among many cancers. shRNA HK2 suppression in HK1-HK2+ liver cancer cells reduced xenograft tumor progression, in contrast to HK1+HK2+ cells. HK2 Inhibition, and partial inhibition of both oxidative phosphorylation and fatty acid oxidation using HK2 shRNA and small molecule drugs, prevented human liver HK1-HK2+ cancer xenograft progression. Using human multiple myeloma xenografts and mouse allogeneic models to identify potential clinical translational agents, triple therapies that include antisense HK2 oligonucleotides, metformin and perhexiline prevent progression. These results suggest an agnostic approach for HK1-HK2+ cancers, regardless of tissue origin.
  23. EMBO Rep. 2019 Aug 21. e48014
    Koerver L, Papadopoulos C, Liu B, Kravic B, Rota G, Brecht L, Veenendaal T, Polajnar M, Bluemke A, Ehrmann M, Klumperman J, Jäättelä M, Behrends C, Meyer H.
      The autophagic clearance of damaged lysosomes by lysophagy involves extensive modification of the organelle with ubiquitin, but the underlying ubiquitination machinery is still poorly characterized. Here, we use an siRNA screening approach and identify human UBE2QL1 as a major regulator of lysosomal ubiquitination, lysophagy, and cell survival after lysosomal damage. UBE2QL1 translocates to permeabilized lysosomes where it associates with damage sensors, ubiquitination targets, and lysophagy effectors. UBE2QL1 knockdown reduces ubiquitination and accumulation of the critical autophagy receptor p62 and abrogates recruitment of the AAA-ATPase VCP/p97, which is essential for efficient lysophagy. Crucially, it affects association of LC3B with damaged lysosomes indicating that autophagosome formation was impaired. Already in unchallenged cells, depletion of UBE2QL1 leads to increased lysosomal damage, mTOR dissociation from lysosomes, and TFEB activation pointing to a role in lysosomal homeostasis. In line with this, mutation of the homologue ubc-25 in Caenorhabditis elegans exacerbates lysosome permeability in worms lacking the lysosome stabilizing protein SCAV-3/LIMP2. Thus, UBE2QL1 coordinates critical steps in the acute endolysosomal damage response and is essential for maintenance of lysosomal integrity.
    Keywords:   mTOR ; TAX1BP1; autophagy; p97; ubiquitin-conjugating enzyme
  24. Cell Stress. 2019 Jul 16. 3(8): 280-283
    Dadsena S, Hassan DG, Holthuis JCM.
      Ceramides are central intermediates of sphingolipid metabolism that can activate a variety of tumor suppressive cellular programs, including cell cycle arrest, senescence and apoptosis. Indeed, perturbations in ceramide generation and turnover are frequently linked to cancer cell survival and resistance to chemotherapy. Consequently, the potential of ceramide-based therapeutics in the treatment of cancer has become a major focus of interest. A growing body of evidence indicates that ceramides can act directly on mitochondria to trigger apoptotic cell death. However, molecular details of the underlying mechanism are scarce. In our recent study (Dadsena S et al., 2019, Nat Commun 10:1832), we used a photoactivatable ceramide probe combined with computer simulations and functional studies to identify the voltage-dependent anion channel VDAC2 as a critical effector of ceramide-induced mitochondrial apoptosis. Collectively, our findings provide a novel molecular framework for how ceramides execute their widely acclaimed anti-neoplastic activities.
    Keywords:  ceramide transfer protein; hexokinase; mitochondrial apoptosis; photo-activatable lipids; tumor suppressor lipid; voltage-dependent anion channel
  25. Dev Cell. 2019 Aug 13. pii: S1534-5807(19)30622-7. [Epub ahead of print]
    Swartz SZ, McKay LS, Su KC, Bury L, Padeganeh A, Maddox PS, Knouse KA, Cheeseman IM.
      Centromeres provide a robust model for epigenetic inheritance as they are specified by sequence-independent mechanisms involving the histone H3-variant centromere protein A (CENP-A). Prevailing models indicate that the high intrinsic stability of CENP-A nucleosomes maintains centromere identity indefinitely. Here, we demonstrate that CENP-A is not stable at centromeres but is instead gradually and continuously incorporated in quiescent cells including G0-arrested tissue culture cells and prophase I-arrested oocytes. Quiescent CENP-A incorporation involves the canonical CENP-A deposition machinery but displays distinct requirements from cell cycle-dependent deposition. We demonstrate that Plk1 is required specifically for G1 CENP-A deposition, whereas transcription promotes CENP-A incorporation in quiescent oocytes. Preventing CENP-A deposition during quiescence results in significantly reduced CENP-A levels and perturbs chromosome segregation following the resumption of cell division. In contrast to quiescent cells, terminally differentiated cells fail to maintain CENP-A levels. Our work reveals that quiescent cells actively maintain centromere identity providing an indicator of proliferative potential.
    Keywords:  cell division; centromere; epigenetics; kinetochore; meiosis; mitosis; oocyte; quiescence; terminal differentiation
  26. Cancer Res. 2019 Aug 22. pii: canres.1059.2019. [Epub ahead of print]
    Shang S, Ji X, Zhang L, Chen J, Li C, Shi R, Xiang W, Kang X, Zhang D, Yang F, Dai R, Chen P, Chen S, Chen Y, Li Y, Miao H.
      Metabolic reprogramming in tumor-associated macrophages (TAMs) is associated with cancer development, however, the role of macrophage triglyceride metabolism in cancer metastasis is unclear. Here, we showed that TAMs exhibit heterogeneous expression of abhydrolase domain containing 5 (ABHD5), an activator of triglyceride hydrolysis, with migratory TAMs expressing lower levels of ABHD5 compared to the non-migratory TAMs. ABHD5 expression in macrophages inhibited cancer cell migration in vitro, in xenograft models and in genetic cancer models. The effects of macrophage ABHD5 on cancer cell migration were dissociated from its metabolic function as neither triglycerides nor ABHD5-regulated metabolites from macrophages affected cancer cell migration. Instead, ABHD5 deficiency in migrating macrophages promoted NF-κB p65-dependent production of matrix metalloproteinases (MMPs). ABHD5 expression negatively correlated with MMP expression in TAMs and was associated with better survival in colorectal cancer patients. Taken together, our findings show that macrophage ABHD5 suppresses NF-κB-dependent MMP production and cancer metastasis and may serve as a prognostic marker in colorectal cancer.
  27. Cell Death Differ. 2019 Aug 21.
    Strappazzon F, Di Rita A, Peschiaroli A, Leoncini PP, Locatelli F, Melino G, Cecconi F.
      Receptor-mediated mitophagy is a crucial process involved in mitochondria quality control. AMBRA1 is a mitophagy receptor for the selective removal of damaged mitochondria in mammalian cells. A critical unresolved issue is how AMBRA1-mediated mitophagy is controlled in response to cellular stress. Here, we investigated the role of BCL2-family proteins on AMBRA1-dependent mitophagy and showed that MCL1 delays AMBRA1-dependent mitophagy. Indeed, MCL1 overexpression is sufficient to inhibit recruitment to mitochondria of the E3 Ubiquitin ligase HUWE1, a crucial dynamic partner of AMBRA1, upon AMBRA1-mediated mitophagy induction. In addition, we found that during mitophagy induced by AMBRA1, MCL1 levels decreased but were sustained by inhibition of the GSK-3β kinase, which delayed AMBRA1-mediated mitophagy. Also, we showed that MCL1 was phosphorylated by GSK-3β at a conserved GSK-3 phosphorylation site (S159) during AMBRA1-mediated mitophagy and that this event was accompanied by HUWE1-dependent MCL1 degradation. Altogether, our results demonstrate that MCL1 stability is regulated by the kinase GSK-3β and the E3 ubiquitin ligase HUWE1 in regulating AMBRA1-mediated mitophagy. Our work thus defines MCL1 as an upstream stress-sensitive protein, functional in AMBRA1-mediated mitophagy.
  28. Cancer Discov. 2019 Aug 21.
    Amaravadi RK, Kimmelman AC, Debnath J.
      Autophagy, a multistep lysosomal degradation pathway that supports nutrient recycling and metabolic adaptation, has been implicated as a process that regulates cancer. Although autophagy induction may limit the development of tumors, evidence in mouse models demonstrates that autophagy inhibition can limit the growth of established tumors and improve response to cancer therapeutics. Certain cancer genotypes may be especially prone to autophagy inhibition. Different strategies for autophagy modulation may be needed depending on the cancer context. Here, we review new advances in the molecular control of autophagy, the role of selective autophagy in cancer, and the role of autophagy within the tumor microenvironment and tumor immunity. We also highlight clinical efforts to repurpose lysosomal inhibitors, such as hydroxychloroquine, as anticancer agents that block autophagy, as well as the development of more potent and specific autophagy inhibitors for cancer treatment, and review future directions for autophagy research.Significance: Autophagy plays a complex role in cancer, but autophagy inhibition may be an effective therapeutic strategy in advanced cancer. A deeper understanding of autophagy within the tumor microenvironment has enabled the development of novel inhibitors and clinical trial strategies. Challenges and opportunities remain to identify patients most likely to benefit from this approach.
  29. Nat Rev Endocrinol. 2019 Aug 22.
    Foretz M, Guigas B, Viollet B.
      Despite its position as the first-line drug for treatment of type 2 diabetes mellitus, the mechanisms underlying the plasma glucose level-lowering effects of metformin (1,1-dimethylbiguanide) still remain incompletely understood. Metformin is thought to exert its primary antidiabetic action through the suppression of hepatic glucose production. In addition, the discovery that metformin inhibits the mitochondrial respiratory chain complex 1 has placed energy metabolism and activation of AMP-activated protein kinase (AMPK) at the centre of its proposed mechanism of action. However, the role of AMPK has been challenged and might only account for indirect changes in hepatic insulin sensitivity. Various mechanisms involving alterations in cellular energy charge, AMP-mediated inhibition of adenylate cyclase or fructose-1,6-bisphosphatase 1 and modulation of the cellular redox state through direct inhibition of mitochondrial glycerol-3-phosphate dehydrogenase have been proposed for the acute inhibition of gluconeogenesis by metformin. Emerging evidence suggests that metformin could improve obesity-induced meta-inflammation via direct and indirect effects on tissue-resident immune cells in metabolic organs (that is, adipose tissue, the gastrointestinal tract and the liver). Furthermore, the gastrointestinal tract also has a major role in metformin action through modulation of glucose-lowering hormone glucagon-like peptide 1 and the intestinal bile acid pool and alterations in gut microbiota composition.
  30. Trends Cancer. 2019 Aug;pii: S2405-8033(19)30118-9. [Epub ahead of print]5(8): 457-459
    Sayin VI, LeBoeuf SE, Papagiannakopoulos T.
      Lung cancer remains one of the most genetically complex, aggressive, and lethal solid malignancies. Understanding how distinct lung cancer mutations give rise to altered nutrient requirements and promote immune evasion in the context of a heterogeneous lung tumor microenvironment is vital for the development of novel personalized therapeutic strategies.
    Keywords:  KEAP1; STK11/LKB1; immune evasion; lung cancer; metabolism; microenvironment
  31. Cancer Res. 2019 Aug 20. pii: canres.0217.2019. [Epub ahead of print]
    Yeung C, Gibson AE, Issaq SH, Oshima N, Baumgart JT, Edessa LD, Rai G, Urban DJ, Johnson MS, Benavides GA, Squadrito GL, Yohe ME, Lei H, Eldridge S, Hamre J, Dowdy T, Ruiz-Rodado V, Lita A, Mendoza A, Shern JF, Larion M, Helman LJ, Stott G, Krishna MC, Hall MD, Darley-Usmar V, Neckers LM, Heske CM.
      Altered cellular metabolism, including an increased dependence on aerobic glycolysis, is a hallmark of cancer. Despite the fact that this observation was first made nearly a century ago, effective therapeutic targeting of glycolysis in cancer has remained elusive. One potentially promising approach involves targeting the glycolytic enzyme lactate dehydrogenase (LDH), which is overexpressed and plays a critical role in several cancers. Here, we used a novel class of LDH inhibitors to demonstrate, for the first time, that Ewing sarcoma (EWS) cells are exquisitely sensitive to inhibition of LDH. EWS-FLI1, the oncogenic driver of EWS, regulated LDHA expression. Genetic depletion of LDHA inhibited proliferation of EWS cells and induced apoptosis, phenocopying pharmacological inhibition of LDH. LDH inhibitors impacted EWS cell viability both in vitro and in vivo by reducing glycolysis. Intravenous administration of LDH inhibitors resulted in the greatest intratumoral drug accumulation, inducing tumor cell death and reducing tumor growth. The major dose-limiting toxicity observed was hemolysis, indicating that a narrow therapeutic window exists for these compounds. Taken together, these data suggest that targeting glycolysis through inhibition of LDH should be further investigated as a potential therapeutic approach for cancers such as EWS that exhibit oncogene-dependent expression of LDH and increased glycolysis.
  32. Oncogene. 2019 Aug 23.
    Pölönen P, Jawahar Deen A, Leinonen HM, Jyrkkänen HK, Kuosmanen S, Mononen M, Jain A, Tuomainen T, Pasonen-Seppänen S, Hartikainen JM, Mannermaa A, Nykter M, Tavi P, Johansen T, Heinäniemi M, Levonen AL.
      Accumulating evidence suggests that constitutively active Nrf2 has a pivotal role in cancer as it induces pro-survival genes that promote cancer cell proliferation and chemoresistance. The mechanisms of Nrf2 dysregulation and functions in cancer have not been fully characterized. Here, we jointly analyzed the Broad-Novartis Cancer Cell Line Encyclopedia (CCLE) and the Cancer Genome Atlas (TCGA) multi-omics data in order to identify cancer types where Nrf2 activation is present. We found that Nrf2 is hyperactivated in a subset of glioblastoma (GBM) patients, whose tumors display a mesenchymal subtype, and uncover several different mechanisms contributing to increased Nrf2 activity. Importantly, we identified a positive feedback loop between SQSTM1/p62 and Nrf2 as a mechanism for activation of the Nrf2 pathway. We also show that autophagy and serine/threonine signaling regulates p62 mediated Keap1 degradation. Our results in glioma cell lines indicate that both Nrf2 and p62 promote proliferation, invasion and mesenchymal transition. Finally, Nrf2 activity was associated with decreased progression free survival in TCGA GBM patient samples, suggesting that treatments have limited efficacy if this transcription factor is overactivated. Overall, our findings place Nrf2 and p62 as the key components of the mesenchymal subtype network, with implications to tumorigenesis and treatment resistance. Thus, Nrf2 activation could be used as a surrogate prognostic marker in mesenchymal subtype GBMs. Furthermore, strategies aiming at either inhibiting Nrf2 or exploiting Nrf2 hyperactivity for targeted gene therapy may provide novel treatment options for this subset of GBM.
  33. Cells. 2019 Aug 21. pii: E950. [Epub ahead of print]8(9):
    Kim EJ, Lee M, Kim DY, Kim KI, Yi JY.
      An understanding of cellular processes that determine the response to ionizing radiation exposure is essential for improving radiotherapy and assessing risks to human health after accidental radiation exposure. Radiation exposure leads to many biological effects, but the mechanisms underlying the metabolic effects of radiation are not well known. Here, we investigated the effects of radiation exposure on the metabolic rate and mitochondrial bioenergetics in skeletal muscle. We show that ionizing radiation increased mitochondrial protein and mass and enhanced proton leak and mitochondrial maximal respiratory capacity, causing an increase in the fraction of mitochondrial respiration devoted to uncoupling reactions. Thus, mice and cells treated with radiation became energetically efficient and displayed increased fatty acid and amino acid oxidation metabolism through the citric acid cycle. Finally, we demonstrate that radiation-induced alterations in mitochondrial energy metabolism involved adenosine monophosphate-activated kinase signaling in skeletal muscle. Together, these results demonstrate that alterations in mitochondrial mass and function are important adaptive responses of skeletal muscle to radiation.
    Keywords:  AMPK; CPT1; PGC1; ionizing radiation; mitochondrial bioenergetics
  34. BJR Case Rep. 2019 May 02. pii: 20190003. [Epub ahead of print]5(3):
    Tran M, Latifoltojar A, Neves JB, Papoutsaki MV, Gong F, Comment A, Costa ASH, Glaser M, Tran-Dang MA, El Sheikh S, Piga W, Bainbridge A, Barnes A, Young T, Jeraj H, Awais R, Adeleke S, Holt C, O'Callaghan J, Twyman F, Atkinson D, Frezza C, Årstad E, Gadian D, Emberton M, Punwani S.
      Intratumoral genetic heterogeneity and the role of metabolic reprogramming in renal cell carcinoma (RCC) have been extensively documented. However, the distribution of these metabolic changes within the tissue has not been explored. We report on the first-in-human in vivo non-invasive metabolic interrogation of RCC using hyperpolarized carbon-13 (13C) magnetic resonance imaging (HP-MRI) and describe the validation of in vivo lactate metabolic heterogeneity against multi-regional ex vivo mass spectrometry. HP-MRI provides an in vivo assessment of metabolism and provides a novel opportunity to safely and non-invasively assess cancer heterogeneity.
    Keywords:  Renal cell carcinoma; magnetic resonance imaging; metabolism
  35. Cell Biol Int. 2019 Aug 23.
    Huddleston ME, Xiao N, Both AP, Gordon DM.
      Key to mitochondrial activities is the maintenance of mitochondrial morphology, specifically cristae structures formed by the invagination of the inner membrane that are enriched in proteins of the electron transport chain. In S. cerevisiae, these cristae folds are a result of the membrane fusion activities of Mgm1p and the membrane bending properties of ATP synthase oligomerization. An additional protein linked to mitochondrial morphology is Pcp1p, a serine protease responsible for the proteolytic processing of Mgm1p. Here we have used hydroxylamine-based random mutagenesis to identify amino acids important for Pcp1p peptidase activity. Using this approach we have isolated five single amino acid mutants that exhibit respiratory growth defects that correlate with loss of mitochondrial genome stability. Reduced Pcp1p protease activity was confirmed by immunoblotting with the accumulation of improperly processed Mgm1p. Ultra-structural analysis of mitochondrial morphology in these mutants found a varying degree of defects in cristae organization. However, not all of the mutants presented with decreased ATP synthase complex assembly as determined by BN-PAGE. Together, these data suggest that there is a threshold level of processed Mgm1p required to maintain ATP synthase super complex assembly and mitochondrial cristae organization. This article is protected by copyright. All rights reserved.
    Keywords:  ATP synthase; Blue Native-PAGE; Cristae structure; Mitochondrial morphology; Pcp1p; Peptidase activity
  36. Life Sci Alliance. 2019 Aug;pii: e201900348. [Epub ahead of print]2(4):
    Kimura T, Kimura AK, Ren M, Monteiro V, Xu Y, Berno B, Schlame M, Epand RM.
      Lipid homeostasis is crucial in human health. Barth syndrome (BTHS), a life-threatening disease typically diagnosed with cardiomyopathy and neutropenia, is caused by mutations in the mitochondrial transacylase tafazzin. By high-resolution 31P nuclear magnetic resonance (NMR) with cryoprobe technology, recently we found a dramatic loss of choline plasmalogen in the tafazzin-knockdown (TAZ-KD) mouse heart, besides observing characteristic cardiolipin (CL) alterations in BTHS. In inner mitochondrial membrane where tafazzin locates, CL and diacyl phosphatidylethanolamine are known to be essential via lipid-protein interactions reflecting their cone shape for integrity of respiratory chain supercomplexes and cristae ultrastructure. Here, we investigate the TAZ-KD brain, liver, kidney, and lymphoblast from patients compared with controls. We identified common yet markedly cell type-dependent losses of ethanolamine plasmalogen as the dominant plasmalogen class therein. Tafazzin function thus critically relates to homeostasis of plasmalogen, which in the ethanolamine class has conceivably analogous and more potent molecular functions in mitochondria than diacyl phosphatidylethanolamine. The present discussion of a loss of plasmalogen-protein interaction applies to other diseases with mitochondrial plasmalogen loss and aberrant forms of this organelle, including Alzheimer's disease.
  37. Cancer Sci. 2019 Aug 20.
    Mori T, Ohmori H, Luo Y, Mori S, Miyagawa Y, Nukaga S, Goto K, Fujiwara-Tani R, Kishi S, Sasaki T, Fujii K, Kawahara I, Kuniyasu H.
      Skeletal muscle volume is associated with prognosis of cancer patients. Maintenance of skeletal muscle is an essential issue in cancer treatment. In nutritional intervention, it is important to focus on differences in metabolism between tumor and skeletal muscle. We examined the influence of oral intake of glucose (0%, 10%, 50%) and 2% medium-chain fatty acid (lauric acid, LAA, C12:0) on tumor growth and skeletal muscle atrophy in mouse peritoneal metastasis models using CT26 mouse colon cancer cells and HT29 human colon cancer cells. After 2 weeks of experimental breeding, skeletal muscle and tumor were removed and analyzed. Glucose intake contributed to prevention of skeletal muscle atrophy in a sugar concentration-dependent manner and also promoted tumor growth. LAA ingestion elevated the level of skeletal muscle protein and suppressed tumor growth by inducing tumor-selective oxidative stress production. When a combination of glucose and LAA was ingested, skeletal muscle mass increased and tumor growth was suppressed. Our results confirmed that, although glucose is an important nutrient for the prevention of skeletal muscle atrophy, it may also foster tumor growth. However, the ingestion of LAA inhibited tumor growth, and its combination with glucose promoted skeletal muscle integrity and function, without stimulating tumor growth. These findings suggest novel strategies for the prevention of skeletal muscle atrophy. This article is protected by copyright. All rights reserved.
    Keywords:  Glucose; Medium-chain fatty acid; Warburg effect; cachexia; sarcopenia
  38. FEBS Lett. 2019 Aug 21.
    Audano M, Pedretti S, Crestani M, Caruso D, De Fabiani E, Mitro N.
      The metabolic transition from anaerobic glycolysis and fatty acid β-oxidation to glycolysis coupled to oxidative phosphorylation is a key process for the transition of quiescent neural stem cells to proliferative neural progenitor cells. However, a full characterization of the metabolic shift and the involvement of mitochondria during the last step of neurogenesis, from neuroblasts to neuron maturation, is still elusive. Here, we describe a model of neuroblasts, Neuro2a cells, with impaired differentiation capacity due to mitochondrial dysfunction. Using a detailed biochemical characterization consisting of steady state metabolomics and metabolic flux analysis, we find increased fatty acid β-oxidation as a peculiar feature of neuroblasts with altered mitochondria. The consequent metabolic switch favors neuroblast proliferation at the expense of neuron maturation. This article is protected by copyright. All rights reserved.
    Keywords:  Energy metabolism; Mitochondria; Neuro2a cells; Neuron maturation
  39. Semin Cancer Biol. 2019 Aug 17. pii: S1044-579X(19)30020-3. [Epub ahead of print]
    Das CK, Banerjee I, Mandal M.
      Autophagy is an evolutionary conserved catabolic process that regulates the cellular homeostasis by targeting damaged cellular contents and organelles for lysosomal degradation and sustains genomic integrity, cellular metabolism, and cell survival during diverse stress and adverse conditions. Recently, the role of autophagy is extremely debated in the regulation of cancer initiation and progression. Although autophagy has a dichotomous role in the regulation of cancer, growing numbers of studies largely indicate the pro-survival role of autophagy in cancer progression and metastasis. In this review, we discuss the detailed mechanisms of autophagy, the role of pro-survival autophagy that positively drives several classical as well as emerging hallmarks of cancer for tumorigenic progression, and also we address various autophagy inhibitors that could be harnessed against pro-survival autophagy for effective cancer therapeutics. Finally, we highlight some outstanding problems that need to be deciphered extensively in the future to unravel the role of autophagy in tumor progression.
    Keywords:  Pro-survival autophagy; cancer; hallmarks; inhibitors
  40. Oncogene. 2019 Aug 23.
    Alptekin A, Ye B, Yu Y, Poole CJ, van Riggelen J, Zha Y, Ding HF.
      Genomic amplification of the oncogene MYCN is a major driver in the development of high-risk neuroblastoma, a pediatric cancer with poor prognosis. Given the challenge in targeting MYCN directly for therapy, we sought to identify MYCN-dependent metabolic vulnerabilities that can be targeted therapeutically. Here, we report that the gene encoding glycine decarboxylase (GLDC), which catalyzes the first and rate-limiting step in glycine breakdown with the production of the one-carbon unit 5,10-methylene-tetrahydrofolate, is a direct transcriptional target of MYCN. As a result, GLDC expression is markedly elevated in MYCN-amplified neuroblastoma tumors and cell lines. This transcriptional upregulation of GLDC expression is of functional significance, as GLDC depletion by RNA interference inhibits the proliferation and tumorigenicity of MYCN-amplified neuroblastoma cell lines by inducing G1 arrest. Metabolomic profiling reveals that GLDC knockdown disrupts purine and central carbon metabolism and reduces citrate production, leading to a decrease in the steady-state levels of cholesterol and fatty acids. Moreover, blocking purine or cholesterol synthesis recapitulates the growth-inhibitory effect of GLDC knockdown. These findings reveal a critical role of GLDC in sustaining the proliferation of neuroblastoma cells with high-level GLDC expression and suggest that MYCN amplification is a biomarker for GLDC-based therapeutic strategies against high-risk neuroblastoma.
  41. Commun Biol. 2019 ;2 313
    Kim BG, Sung JS, Jang Y, Cha YJ, Kang S, Han HH, Lee JH, Cho NH.
      Tumor growth increases compressive stress within a tissue, which is associated with solid tumor progression. However, very little is known about how compressive stress contributes to tumor progression. Here, we show that compressive stress induces glycolysis in human breast cancer associated fibroblast (CAF) cells and thereby contributes to the expression of epithelial to mesenchymal (EMT)- and angiogenesis-related genes in breast cancer cells. Lactate production was increased in compressed CAF cells, in a manner dependent on the expression of metabolic genes ENO2, HK2, and PFKFB3. Conditioned medium from compressed CAFs promoted the proliferation of breast cancer cells and the expression of EMT and/or angiogenesis-related genes. In patient tissues with high compressive stress, the expression of compression-induced metabolic genes was significantly and positively correlated with EMT and/or angiogenesis-related gene expression and metastasis size. These findings illustrate a mechanotransduction pathway involving stromal glycolysis that may be relevant also for other solid tumours.
    Keywords:  Breast cancer; Cancer metabolism; Cancer microenvironment
  42. Oncogene. 2019 Aug 21.
    Rajabi H, Hata T, Li W, Long MD, Hu Q, Liu S, Raina D, Kui L, Yazumizu Y, Hong D, Samur M, Kufe D.
      RASSF1A encodes a tumor suppressor that inhibits the RAS→RAF→MEK→ERK pathway and is one of the most frequently inactivated genes in human cancers. MUC1-C is an oncogenic effector of the cancer cell epigenome that is overexpressed in diverse carcinomas. We show here that MUC1-C represses RASSF1A expression in KRAS wild-type and mutant cancer cells. Mechanistically, MUC1-C occupies the RASSF1A promoter in a complex with the ZEB1 transcriptional repressor. In turn, MUC1-C/ZEB1 complexes recruit DNA methyltransferase 3b (DNMT3b) to the CpG island in the RASSF1A promoter. Targeting MUC1-C, ZEB1, and DNMT3b thereby decreases methylation of the CpG island and derepresses RASSF1A transcription. We also show that targeting MUC1-C regulates KRAS signaling, as evidenced by RNA-seq analysis, and decreases MEK/ERK activation, which is of importance for RAS-mediated tumorigenicity. These findings define a previously unrecognized role for MUC1-C in suppression of RASSF1A and support targeting MUC1-C as an approach for inhibiting MEK→ERK signaling.
  43. Physiol Rev. 2019 Aug 22.
    Chang AR, Ferrer CM, Mostoslavsky R.
      Mammalian Sirtuins have emerged in recent years as critical modulators of multiple biological processes, regulating cellular metabolism, DNA repair, gene expression, and mitochondrial biology. As such, they evolved to play key roles in organismal homeostasis, and defects in these proteins have been linked to a plethora of diseases, including cancer, neurodegeneration and aging. In this Review, we will describe the multiple roles of SIRT6, a chromatin deacylase with unique and important functions in maintaining cellular homeostasis. We will attempt to provide a framework for such different functions, for the ability of SIRT6 to interconnect chromatin dynamics with metabolism and DNA repair, and the open questions the field will face in the future, particularly in the context of putative therapeutic opportunities.
    Keywords:  SIRT6; Sirtuins; cancer; chromatin; epigenetics
  44. Front Oncol. 2019 ;9 686
    Demas DM, Demo S, Fallah Y, Clarke R, Nephew KP, Althouse S, Sandusky G, He W, Shajahan-Haq AN.
      Dependence on the glutamine pathway is increased in advanced breast cancer cell models and tumors regardless of hormone receptor status or function. While 70% of breast cancers are estrogen receptor positive (ER+) and depend on estrogen signaling for growth, advanced ER+ breast cancers grow independent of estrogen. Cellular changes in amino acids such as glutamine are sensed by the mammalian target of rapamycin (mTOR) complex, mTORC1, which is often deregulated in ER+ advanced breast cancer. Inhibitor of mTOR, such as everolimus, has shown modest clinical activity in ER+ breast cancers when given with an antiestrogen. Here we show that breast cancer cell models that are estrogen independent and antiestrogen resistant are more dependent on glutamine for growth compared with their sensitive parental cell lines. Co-treatment of CB-839, an inhibitor of GLS, an enzyme that converts glutamine to glutamate, and everolimus interrupts the growth of these endocrine resistant xenografts. Using human tumor microarrays, we show that GLS is significantly higher in human breast cancer tumors with increased tumor grade, stage, ER-negative and progesterone receptor (PR) negative status. Moreover, GLS levels were significantly higher in breast tumors from African-American women compared with Caucasian women regardless of ER or PR status. Among patients treated with endocrine therapy, high GLS expression was associated with decreased disease free survival (DFS) from a multivariable model with GLS expression treated as dichotomous. Collectively, these findings suggest a complex biology for glutamine metabolism in driving breast cancer growth. Moreover, targeting GLS and mTOR in advanced breast cancer may be a novel therapeutic approach in advanced ER+ breast cancer.
    Keywords:  CB-839; breast cancer; endocrine resistance; everolimus; glutamine metabolism; mTOR
  45. Autophagy. 2019 Aug 23.
    Liu J, Yang M, Kang R, Klionsky DJ, Tang D.
      Macroautophagy (hereafter referred to as autophagy) involves a lysosomal degradation pathway and plays a context-dependent role in promoting either cell survival or cell death during stress; excessive or impaired autophagy is implicated in various types of cell death. In particular, lipid peroxidation-associated ferroptosis has recently been recognized as a type of autophagy-dependent cell death, but the mechanisms involved remain largely obscure. Our recent findings demonstrate that clockophagy, namely the selective autophagic degradation of the circadian clock regulator ARNTL/BMAL1, promotes ferroptotic cancer cell death in vitro and in vivo. Mechanically, the cargo receptor SQSTM1/p62 is responsible for the autophagic degradation of ARNTL in response to type 2 ferroptosis inducers (e.g., RSL3 and FIN56), but not type 1 ferroptosis inducers (e.g., erastin, sulfasalazine, and sorafenib). Consequently, clockophagy-mediated ARNTL degradation promotes lipid peroxidation and subsequent ferroptosis through blocking HIF1A-dependent fatty acid uptake and lipid storage. These findings highlight a novel type of selective autophagy in regulated cell death.
    Keywords:  autophagy; cargo receptor; cell death; circadian rhythm; fatty acid uptake; ferroptosis; hypoxia; lipid droplets; lipid peroxidation; lipid storage
  46. Cell Metab. 2019 Aug 09. pii: S1550-4131(19)30383-3. [Epub ahead of print]
    Bravo-San Pedro JM, Sica V, Martins I, Pol J, Loos F, Maiuri MC, Durand S, Bossut N, Aprahamian F, Anagnostopoulos G, Niso-Santano M, Aranda F, Ramírez-Pardo I, Lallement J, Denom J, Boedec E, Gorwood P, Ramoz N, Clément K, Pelloux V, Rohia A, Pattou F, Raverdy V, Caiazzo R, Denis RGP, Boya P, Galluzzi L, Madeo F, Migrenne-Li S, Cruciani-Guglielmacci C, Tavernarakis N, López-Otín C, Magnan C, Kroemer G.
      Autophagy facilitates the adaptation to nutritional stress. Here, we show that short-term starvation of cultured cells or mice caused the autophagy-dependent cellular release of acyl-CoA-binding protein (ACBP, also known as diazepam-binding inhibitor, DBI) and consequent ACBP-mediated feedback inhibition of autophagy. Importantly, ACBP levels were elevated in obese patients and reduced in anorexia nervosa. In mice, systemic injection of ACBP protein inhibited autophagy, induced lipogenesis, reduced glycemia, and stimulated appetite as well as weight gain. We designed three approaches to neutralize ACBP, namely, inducible whole-body knockout, systemic administration of neutralizing antibodies, and induction of antiACBP autoantibodies in mice. ACBP neutralization enhanced autophagy, stimulated fatty acid oxidation, inhibited appetite, reduced weight gain in the context of a high-fat diet or leptin deficiency, and accelerated weight loss in response to dietary changes. In conclusion, neutralization of ACBP might constitute a strategy for treating obesity and its co-morbidities.
    Keywords:  anorexia; autophagy; lipid metabolism; obesity
  47. Nat Biotechnol. 2019 Aug 19.
    Deuse T, Hu X, Agbor-Enoh S, Koch M, Spitzer MH, Gravina A, Alawi M, Marishta A, Peters B, Kosaloglu-Yalcin Z, Yang Y, Rajalingam R, Wang D, Nashan B, Kiefmann R, Reichenspurner H, Valantine H, Weissman IL, Schrepfer S.
      The utility of autologous induced pluripotent stem cell (iPSC) therapies for tissue regeneration depends on reliable production of immunologically silent functional iPSC derivatives. However, rejection of autologous iPSC-derived cells has been reported, although the mechanism underlying rejection is largely unknown. We hypothesized that de novo mutations in mitochondrial DNA (mtDNA), which has far less reliable repair mechanisms than chromosomal DNA, might produce neoantigens capable of eliciting immune recognition and rejection. Here we present evidence in mice and humans that nonsynonymous mtDNA mutations can arise and become enriched during reprogramming to the iPSC stage, long-term culture and differentiation into target cells. These mtDNA mutations encode neoantigens that provoke an immune response that is highly specific and dependent on the host major histocompatibility complex genotype. Our results reveal that autologous iPSCs and their derivatives are not inherently immunologically inert for autologous transplantation and suggest that iPSC-derived products should be screened for mtDNA mutations.
  48. Ann N Y Acad Sci. 2019 Aug 23.
    Algieri C, Trombetti F, Pagliarani A, Ventrella V, Bernardini C, Fabbri M, Forni M, Nesci S.
      The properties of the mitochondrial F1 FO -ATPase catalytic site, which can bind Mg2+ , Mn2+ , or Ca2+ and hydrolyze ATP, were explored by inhibition kinetic analyses to cast light on the Ca2+ -activated F1 FO -ATPase connection with the permeability transition pore (PTP) that initiates cascade events leading to cell death. While the natural cofactor Mg2+ activates the F1 FO -ATPase in competition with Mn2+ , Ca2+ is a noncompetitive inhibitor in the presence of Mg2+ . Selective F1 inhibitors (Is-F1 ), namely NBD-Cl, piceatannol, resveratrol, and quercetin, exerted different mechanisms (mixed and uncompetitive inhibition) on either Ca2+ - or Mg2+ -activated F1 FO -ATPase, consistent with the conclusion that the catalytic mechanism changes when Mg2+ is replaced by Ca2+ . In a partially purified F1 domain preparation, Ca2+ -activated F1 -ATPase maintained Is-F1 sensitivity, and enzyme inhibition was accompanied by the maintenance of the mitochondrial calcium retention capacity and membrane potential. The data strengthen the structural relationship between Ca2+ -activated F1 FO -ATPase and the PTP, and, in turn, on consequences, such as physiopathological cellular changes.
    Keywords:  ATP hydrolysis; F1FO-ATPase; divalent cofactors; inhibition kinetics; mitochondrial permeability transition pore; partially purified F1 fraction
  49. Nat Commun. 2019 Aug 20. 10(1): 3739
    Bleu M, Gaulis S, Lopes R, Sprouffske K, Apfel V, Holwerda S, Pregnolato M, Yildiz U, Cordoʹ V, Dost AFM, Knehr J, Carbone W, Lohmann F, Lin CY, Bradner JE, Kauffmann A, Tordella L, Roma G, Galli GG.
      Transcription factor networks shape the gene expression programs responsible for normal cell identity and pathogenic state. Using Core Regulatory Circuitry analysis (CRC), we identify PAX8 as a candidate oncogene in Renal Cell Carcinoma (RCC) cells. Validation of large-scale functional genomic screens confirms that PAX8 silencing leads to decreased proliferation of RCC cell lines. Epigenomic analyses of PAX8-dependent cistrome demonstrate that PAX8 largely occupies active enhancer elements controlling genes involved in various metabolic pathways. We selected the ferroxidase Ceruloplasmin (CP) as an exemplary gene to dissect PAX8 molecular functions. PAX8 recruits histone acetylation activity at bound enhancers looping onto the CP promoter. Importantly, CP expression correlates with sensitivity to PAX8 silencing and identifies a subset of RCC cases with poor survival. Our data identifies PAX8 as a candidate oncogene in RCC and provides a potential biomarker to monitor its activity.
  50. Mol Med. 2019 Aug 22. 25(1): 40
    Tani T, Okamoto K, Fujiwara M, Katayama A, Tsuruoka S.
      BACKGROUND: Clinically applied as anti-gout drugs, xanthine oxidoreductase (XOR) inhibitors, especially the potent, selective, non-purine-analog XOR inhibitors febuxostat and topiroxostat, exert organ-protective effects. We tested the hypothesis that preservation of tissue concentrations of high-energy phosphates, such as ATP and ADP, contributes to organ-protective effects through CE-TOFMS metabolomics.METHODS: Rats were subjected to 30 min of renal ischemia-reperfusion (I/R) injury 60 min after oral administration of 10 mg/kg febuxostat, 10 mg/kg topiroxostat, 50 mg/kg allopurinol, or vehicle.
    RESULTS: In non-purine-analog XOR inhibitor-treated groups, renal concentrations of high-energy phosphates were greater before and after I/R injury, and renal adenine compounds were less depleted by I/R injury than in the vehicle and allopurinol groups. These findings were well in accordance with the proposed hypothesis that the recomposition of high-energy phosphates is promoted by non-purine-analog XOR inhibitors via the salvage pathway through blockade of hypoxanthine catabolism, whereas non-specific inhibitory effects of allopurinol on purine/pyrimidine enzymes impede this re-synthesis process.
    CONCLUSIONS: This metabolic approach shed light on the physiology of the organ-protective effects of XOR inhibitors.
    Keywords:  Ischemia-reperfusion injury; Metabolome; Xanthine oxidoreductase inhibitor
  51. Philos Trans R Soc Lond B Biol Sci. 2019 Aug 19. 374(1779): 20180224
    Disanza A, Bisi S, Frittoli E, Malinverno C, Marchesi S, Palamidessi A, Rizvi A, Scita G.
      Selective evolutionary pressure shapes the processes and genes that enable cancer survival and expansion in a tumour-suppressive environment. A distinguishing lethal feature of malignant cancer is its dissemination and seeding of metastatic foci. A key requirement for this process is the acquisition of a migratory/invasive ability. However, how the migratory phenotype is selected for during the natural evolution of cancer and what advantage, if any, it might provide to the growing malignant cells remain open issues. In this opinion piece, we discuss three possible answers to these issues. We will examine lines of evidence from mathematical modelling of cancer evolution that indicate that migration is an intrinsic selectable property of malignant cells that directly impacts on growth dynamics and cancer geometry. Second, we will argue that migratory phenotypes can emerge as an adaptive response to unfavourable growth conditions and endow cells not only with the ability to move/invade, but also with specific metastatic traits, including drug resistance, self-renewal and survival. Finally, we will discuss the possibility that migratory phenotypes are coincidental events that emerge by happenstance in the natural evolution of cancer. This article is part of a discussion meeting issue 'Forces in cancer: interdisciplinary approaches in tumour mechanobiology'.
    Keywords:  cancer evolution; cell migration; collective motility; endocytosis
  52. Cell. 2019 Aug 22. pii: S0092-8674(19)30848-7. [Epub ahead of print]178(5): 1115-1131.e15
    Cheng CW, Biton M, Haber AL, Gunduz N, Eng G, Gaynor LT, Tripathi S, Calibasi-Kocal G, Rickelt S, Butty VL, Moreno-Serrano M, Iqbal AM, Bauer-Rowe KE, Imada S, Ulutas MS, Mylonas C, Whary MT, Levine SS, Basbinar Y, Hynes RO, Mino-Kenudson M, Deshpande V, Boyer LA, Fox JG, Terranova C, Rai K, Piwnica-Worms H, Mihaylova MM, Regev A, Yilmaz ÖH.
      Little is known about how metabolites couple tissue-specific stem cell function with physiology. Here we show that, in the mammalian small intestine, the expression of Hmgcs2 (3-hydroxy-3-methylglutaryl-CoA synthetase 2), the gene encoding the rate-limiting enzyme in the production of ketone bodies, including beta-hydroxybutyrate (βOHB), distinguishes self-renewing Lgr5+ stem cells (ISCs) from differentiated cell types. Hmgcs2 loss depletes βOHB levels in Lgr5+ ISCs and skews their differentiation toward secretory cell fates, which can be rescued by exogenous βOHB and class I histone deacetylase (HDAC) inhibitor treatment. Mechanistically, βOHB acts by inhibiting HDACs to reinforce Notch signaling, instructing ISC self-renewal and lineage decisions. Notably, although a high-fat ketogenic diet elevates ISC function and post-injury regeneration through βOHB-mediated Notch signaling, a glucose-supplemented diet has the opposite effects. These findings reveal how control of βOHB-activated signaling in ISCs by diet helps to fine-tune stem cell adaptation in homeostasis and injury.
    Keywords:  HDAC; Hmgcs2; Intestinal stem cell; Notch; beta-hydroxybutyrate; ketogenic diet; ketone bodies
  53. Nat Commun. 2019 Aug 19. 10(1): 3732
    Gottschalk B, Klec C, Leitinger G, Bernhart E, Rost R, Bischof H, Madreiter-Sokolowski CT, Radulović S, Eroglu E, Sattler W, Waldeck-Weiermair M, Malli R, Graier WF.
      Recently identified core proteins (MICU1, MCU, EMRE) forming the mitochondrial Ca2+ uniporter complex propelled investigations into its physiological workings. Here, we apply structured illumination microscopy to visualize and localize these proteins in living cells. Our data show that MICU1 localizes at the inner boundary membrane (IBM) due to electrostatic interaction of its polybasic domain. Moreover, this exclusive localization of MICU1 is important for the stability of cristae junctions (CJ), cytochrome c release and mitochondrial membrane potential. In contrast to MICU1, MCU and EMRE are homogeneously distributed at the inner mitochondrial membrane under resting conditions. However, upon Ca2+ elevation MCU and EMRE dynamically accumulate at the IBM in a MICU1-dependent manner. Eventually, our findings unveil an essential function of MICU1 in CJ stabilization and provide mechanistic insights of how sophistically MICU1 controls the MCU-Complex while maintaining the structural mitochondrial membrane framework.