bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2021‒05‒16
forty-eight papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Nature. 2021 May 12.
      Ferroptosis, a form of regulated cell death that is induced by excessive lipid peroxidation, is a key tumour suppression mechanism1-4. Glutathione peroxidase 4 (GPX4)5,6 and ferroptosis suppressor protein 1 (FSP1)7,8 constitute two major ferroptosis defence systems. Here we show that treatment of cancer cells with GPX4 inhibitors results in acute depletion of N-carbamoyl-L-aspartate, a pyrimidine biosynthesis intermediate, with concomitant accumulation of uridine. Supplementation with dihydroorotate or orotate-the substrate and product of dihydroorotate dehydrogenase (DHODH)-attenuates or potentiates ferroptosis induced by inhibition of GPX4, respectively, and these effects are particularly pronounced in cancer cells with low expression of GPX4 (GPX4low). Inactivation of DHODH induces extensive mitochondrial lipid peroxidation and ferroptosis in GPX4low cancer cells, and synergizes with ferroptosis inducers to induce these effects in GPX4high cancer cells. Mechanistically, DHODH operates in parallel to mitochondrial GPX4 (but independently of cytosolic GPX4 or FSP1) to inhibit ferroptosis in the mitochondrial inner membrane by reducing ubiquinone to ubiquinol (a radical-trapping antioxidant with anti-ferroptosis activity). The DHODH inhibitor brequinar selectively suppresses GPX4low tumour growth by inducing ferroptosis, whereas combined treatment with brequinar and sulfasalazine, an FDA-approved drug with ferroptosis-inducing activity, synergistically induces ferroptosis and suppresses GPX4high tumour growth. Our results identify a DHODH-mediated ferroptosis defence mechanism in mitochondria and suggest a therapeutic strategy of targeting ferroptosis in cancer treatment.
  2. Dev Cell. 2021 May 11. pii: S1534-5807(21)00357-9. [Epub ahead of print]
      PI5P4Ks are a class of phosphoinositide kinases that phosphorylate PI-5-P to PI-4,5-P2. Distinct localization of phosphoinositides is fundamental for a multitude of cellular functions. Here, we identify a role for peroxisomal PI-4,5-P2 generated by the PI5P4Ks in maintaining energy balance. We demonstrate that PI-4,5-P2 regulates peroxisomal fatty acid oxidation by mediating trafficking of lipid droplets to peroxisomes, which is essential for sustaining mitochondrial metabolism. Using fluorescent-tagged lipids and metabolite tracing, we show that loss of the PI5P4Ks significantly impairs lipid uptake and β-oxidation in the mitochondria. Further, loss of PI5P4Ks results in dramatic alterations in mitochondrial structural and functional integrity, which under nutrient deprivation is further exacerbated, causing cell death. Notably, inhibition of the PI5P4Ks in cancer cells and mouse tumor models leads to decreased cell viability and tumor growth, respectively. Together, these studies reveal an unexplored role for PI5P4Ks in preserving metabolic homeostasis, which is necessary for tumorigenesis.
    Keywords:  PI-4,5-P(2); PI-5-P; PI5P4Ks; cancer; fatty acid; lipid; lipid droplet; metabolism; mitochondria; peroxisome; phosphoinositide; phosphoinositide kinase; sarcoma; β-oxidation
  3. Science. 2021 May 14. 372(6543): 716-721
      Transcription and metabolism both influence cell function, but dedicated transcriptional control of metabolic pathways that regulate cell fate has rarely been defined. We discovered, using a chemical suppressor screen, that inhibition of the pyrimidine biosynthesis enzyme dihydroorotate dehydrogenase (DHODH) rescues erythroid differentiation in bloodless zebrafish moonshine (mon) mutant embryos defective for transcriptional intermediary factor 1 gamma (tif1γ). This rescue depends on the functional link of DHODH to mitochondrial respiration. The transcription elongation factor TIF1γ directly controls coenzyme Q (CoQ) synthesis gene expression. Upon tif1γ loss, CoQ levels are reduced, and a high succinate/α-ketoglutarate ratio leads to increased histone methylation. A CoQ analog rescues mon's bloodless phenotype. These results demonstrate that mitochondrial metabolism is a key output of a lineage transcription factor that drives cell fate decisions in the early blood lineage.
  4. Biochim Biophys Acta Rev Cancer. 2021 May 06. pii: S0304-419X(21)00056-1. [Epub ahead of print]1876(1): 188559
      Recent studies have established that tumors can reprogram the pathways involved in nutrient uptake and metabolism to withstand the altered biosynthetic, bioenergetics and redox requirements of cancer cells. This phenomenon is called metabolic reprogramming, which is promoted by the loss of tumor suppressor genes and activation of oncogenes. Because of alterations and perturbations in multiple metabolic pathways, renal cell carcinoma (RCC) is sometimes termed as a "metabolic disease". The majority of metabolic reprogramming in renal cancer is caused by the inactivation of von Hippel-Lindau (VHL) gene and activation of the Ras-PI3K-AKT-mTOR pathway. Hypoxia-inducible factor (HIF) and Myc are other important players in the metabolic reprogramming of RCC. All types of RCCs are associated with reprogramming of glucose and fatty acid metabolism and the tricarboxylic acid (TCA) cycle. Metabolism of glutamine, tryptophan and arginine is also reprogrammed in renal cancer to favor tumor growth and oncogenesis. Together, understanding these modifications or reprogramming of the metabolic pathways in detail offer ample opportunities for the development of new therapeutic targets and strategies, discovery of biomarkers and identification of effective tumor detection methods.
    Keywords:  Cancer; Metabolic reprogramming; Metabolism; Renal cell carcinoma
  5. Cancer Metab. 2021 May 10. 9(1): 22
      Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.
    Keywords:  Cancer metabolism; DHODH inhibitors; De novo pyrimidine biosynthesis; Dihydroorotate dehydrogenase; Mitochondria
  6. J Inherit Metab Dis. 2021 May 15.
      Over the last few years, various inborn disorders have been reported in the malate aspartate shuttle (MAS). The MAS consists of 4 metabolic enzymes and 2 transporters, one of them having two isoforms that are expressed in different tissues. Together they form a biochemical pathway that shuttles electrons from the cytosol into mitochondria, as the inner mitochondrial membrane is impermeable to the electron carrier NADH. By shuttling NADH across the mitochondrial membrane in the form of a reduced metabolite (malate), the MAS plays an important role in mitochondrial respiration. In addition, the MAS maintains the cytosolic NAD+ /NADH redox balance, by using redox reactions for the transfer of electrons. This explains why the MAS is also important in sustaining cytosolic redox-dependent metabolic pathways, such as glycolysis and serine biosynthesis. The current review provides insights into the clinical and biochemical characteristics of MAS deficiencies. To date, 5 out of 7 potential MAS deficiencies have been reported. Most of them present with a clinical phenotype of infantile epileptic encephalopathy. Although not specific, biochemical characteristics include high lactate, high glycerol 3-phosphate, a disturbed redox balance, TCA abnormalities, high ammonia and low serine, which may be helpful in reaching a diagnosis in patients with an infantile epileptic encephalopathy. Current implications for treatment include a ketogenic diet, as well as serine and vitamin B6 supplementation. This article is protected by copyright. All rights reserved.
    Keywords:  AGC1; AGC2; GOT2; Inborn metabolic disorder; MDH1; MDH2; Malate Aspartate Shuttle; NAD(H); Redox
  7. Cell Rep. 2021 May 11. pii: S2211-1247(21)00445-9. [Epub ahead of print]35(6): 109111
      The f subunit is localized at the base of the ATP synthase peripheral stalk. Its function in the human enzyme is poorly characterized. Because full disruption of its ATP5J2 gene with the CRISPR-Cas9 strategy in the HAP1 human model has been shown to cause alterations in the amounts of other ATP synthase subunits, here we investigated the role of the f subunit in HeLa cells by regulating its levels through RNA interference. We confirm the role of the f subunit in ATP synthase dimer stability and observe that its downregulation per se does not alter the amounts of the other enzyme subunits or ATP synthase synthetic/hydrolytic activity. We show that downregulation of the f subunit causes abnormal crista organization and decreases permeability transition pore (PTP) size, whereas its re-expression in f subunit knockdown cells rescues mitochondrial morphology and PTP-dependent swelling.
    Keywords:  ATP synthase; f subunit; mitochondrial morphology; permeability transition pore, PTP
  8. Cell Rep. 2021 May 11. pii: S2211-1247(21)00435-6. [Epub ahead of print]35(6): 109101
      Depleting the microenvironment of important nutrients such as arginine is a key strategy for immune evasion by cancer cells. Many tumors overexpress arginase, but it is unclear how these cancers, but not T cells, tolerate arginine depletion. In this study, we show that tumor cells synthesize arginine from citrulline by upregulating argininosuccinate synthetase 1 (ASS1). Under arginine starvation, ASS1 transcription is induced by ATF4 and CEBPβ binding to an enhancer within ASS1. T cells cannot induce ASS1, despite the presence of active ATF4 and CEBPβ, as the gene is repressed. Arginine starvation drives global chromatin compaction and repressive histone methylation, which disrupts ATF4/CEBPβ binding and target gene transcription. We find that T cell activation is impaired in arginine-depleted conditions, with significant metabolic perturbation linked to incomplete chromatin remodeling and misregulation of key genes. Our results highlight a T cell behavior mediated by nutritional stress, exploited by cancer cells to enable pathological immune evasion.
    Keywords:  ASS1; ATF4; H3K27me3; T cell chromatin; arginine; cancer metabolism; immunometabolism; immunosuppression; metabolic regulation; nutritional stress
  9. Nat Commun. 2021 May 11. 12(1): 2665
      With age, hematopoietic stem cells (HSC) undergo changes in function, including reduced regenerative potential and loss of quiescence, which is accompanied by a significant expansion of the stem cell pool that can lead to haematological disorders. Elevated metabolic activity has been implicated in driving the HSC ageing phenotype. Here we show that nicotinamide riboside (NR), a form of vitamin B3, restores youthful metabolic capacity by modifying mitochondrial function in multiple ways including reduced expression of nuclear encoded metabolic pathway genes, damping of mitochondrial stress and a decrease in mitochondrial mass and network-size. Metabolic restoration is dependent on continuous NR supplementation and accompanied by a shift of the aged transcriptome towards the young HSC state, more youthful bone marrow cellular composition and an improved regenerative capacity in a transplant setting. Consequently, NR administration could support healthy ageing by re-establishing a more youthful hematopoietic system.
  10. Autophagy. 2020 Dec 01. 1-16
      As a highly dynamic organelle, mitochondria undergo constant fission and fusion to change their morphology and function, coping with various stress conditions. Loss of the balance between fission and fusion leads to impaired mitochondria function, which plays a critical role in the pathogenesis of Parkinson disease (PD). Yet the mechanisms behind mitochondria dynamics regulation remain to be fully illustrated. Chaperone-mediated autophagy (CMA) is a lysosome-dependent process that selectively degrades proteins to maintain cellular proteostasis. In this study, we demonstrated that MARCHF5, an E3 ubiquitin ligase required for mitochondria fission, is a CMA substrate. MARCHF5 interacted with key CMA regulators and was degraded by lysosomes. Severe oxidative stress compromised CMA activity and stabilized MARCHF5, which facilitated DNM1L translocation and led to excessive fission. Increase of CMA activity promoted MARCHF5 turnover, attenuated DNM1L translocation, and reduced mitochondria fragmentation, which alleviated mitochondrial dysfunction under oxidative stress. Furthermore, we showed that conditional expression of LAMP2A, the key CMA regulator, in dopaminergic (DA) neurons helped maintain mitochondria morphology and protected DA neuronal viability in a rodent PD model. Our work uncovers a critical role of CMA in maintaining proper mitochondria dynamics, and loss of this regulatory control may occur in PD and underlie its pathogenic process.Abbreviations: CMA: chaperone-mediated autophagy; DA: dopaminergic; DNM1L: dynamin 1 like; FCCP: carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone; HSPA8: heat shock protein family A (Hsp70) member 8; LAMP2A: lysosomal associated membrane protein 2A; MARCHF5: membrane-associated ring-CH-type finger 5; MMP: mitochondria membrane potential; OCR: oxygen consumption rate; 6-OHDA: 6-hydroxydopamine; PD: Parkinson disease; SNc: substantia nigra pars compacta; TEM: transmission electron microscopy; TH: tyrosine hydroxylase; TMRE: tetramethylrhodamine ethyl ester perchlorate; WT: wild type.
    Keywords:  Autophagy/mitochondria/oxidative stress/Parkinson disease/proteostasis
  11. Sci Adv. 2021 May;pii: eabg4000. [Epub ahead of print]7(20):
      Mitochondrial complex I (NADH:ubiquinone oxidoreductase), a major contributor of free energy for oxidative phosphorylation, is increasingly recognized as a promising drug target for ischemia-reperfusion injury, metabolic disorders, and various cancers. Several pharmacologically relevant but structurally unrelated small molecules have been identified as specific complex I inhibitors, but their modes of action remain unclear. Here, we present a 3.0-Å resolution cryo-electron microscopy structure of mammalian complex I inhibited by a derivative of IACS-010759, which is currently in clinical development against cancers reliant on oxidative phosphorylation, revealing its unique cork-in-bottle mechanism of inhibition. We combine structural and kinetic analyses to deconvolute cross-species differences in inhibition and identify the structural motif of a "chain" of aromatic rings as a characteristic that promotes inhibition. Our findings provide insights into the importance of π-stacking residues for inhibitor binding in the long substrate-binding channel in complex I and a guide for future biorational drug design.
  12. Commun Biol. 2021 May 14. 4(1): 584
      Most humans carry a mixed population of mitochondrial DNA (mtDNA heteroplasmy) affecting ~1-2% of molecules, but rapid percentage shifts occur over one generation leading to severe mitochondrial diseases. A decrease in the amount of mtDNA within the developing female germ line appears to play a role, but other sub-cellular mechanisms have been implicated. Establishing an in vitro model of early mammalian germ cell development from embryonic stem cells, here we show that the reduction of mtDNA content is modulated by oxygen and reaches a nadir immediately before germ cell specification. The observed genetic bottleneck was accompanied by a decrease in mtDNA replicating foci and the segregation of heteroplasmy, which were both abolished at higher oxygen levels. Thus, differences in oxygen tension occurring during early development likely modulate the amount of mtDNA, facilitating mtDNA segregation and contributing to tissue-specific mutation loads.
  13. FEBS J. 2021 May 10.
      To ensure correct function, mitochondria have developed several mechanisms of protein quality control (QC). Protein homeostasis highly relies on chaperones and proteases to maintain proper folding and remove damaged proteins that might otherwise form cell-toxic aggregates. Besides quality control, mitochondrial proteases modulate and regulate many essential functions, such as trafficking, processing, and activation of mitochondrial proteins, mitochondrial dynamics, mitophagy, and apoptosis. Therefore, the impaired function of mitochondrial proteases is associated with various pathological conditions, including cancer, metabolic syndromes, and neurodegenerative disorders. This review recapitulates and discusses the emerging roles of two major proteases of the mitochondrial matrix, LON and ClpXP. Although commonly acknowledge for their protein quality control role, recent advances have uncovered several highly regulated processes controlled by the LON and ClpXP connected to mitochondrial gene expression and respiratory chain function maintenance. Furthermore, both proteases have been lately recognized as potent targets for anti-cancer therapies, and we summarize those findings.
    Keywords:  ClpXP; LONP1; cancer; degradation; metabolism; mitochondria; mitochondrial matrix; mtDNA; proteases; protein quality control; proteolysis; respiratory complexes
  14. Front Nutr. 2021 ;8 663560
      After almost a century of misunderstanding, it is time to appreciate that lactate shuttling is an important feature of energy flux and metabolic regulation that involves a complex series of metabolic, neuroendocrine, cardiovascular, and cardiac events in vivo. Cell-cell and intracellular lactate shuttles in the heart and between the heart and other tissues fulfill essential purposes of energy substrate production and distribution as well as cell signaling under fully aerobic conditions. Recognition of lactate shuttling came first in studies of physical exercise where the roles of driver (producer) and recipient (consumer) cells and tissues were obvious. One powerful example of cell-cell lactate shuttling was the exchange of carbohydrate energy in the form of lactate between working limb skeletal muscle and the heart. The exchange of mass represented a conservation of mass that required the integration of neuroendocrine, autoregulatory, and cardiovascular systems. Now, with greater scrutiny and recognition of the effect of the cardiac cycle on myocardial blood flow, there brings an appreciation that metabolic fluxes must accommodate to pressure-flow realities within an organ in which they occur. Therefore, the presence of an intra-cardiac lactate shuttle is posited to explain how cardiac mechanics and metabolism are synchronized. Specifically, interruption of blood flow during the isotonic phase of systole is supported by glycolysis and subsequent return of blood flow during diastole allows for recovery sustained by oxidative metabolism.
    Keywords:  exercise; fatty acids; glucose; heart; ketones; lactate; metabolism; muscle
  15. Cell Metab. 2021 May 11. pii: S1550-4131(21)00180-7. [Epub ahead of print]
      The cell-intrinsic nature of tumor metabolism has become increasingly well characterized. The impact that tumors have on systemic metabolism, however, has received less attention. Here, we used adult zebrafish harboring BRAFV600E-driven melanoma to study the effect of cancer on distant tissues. By applying metabolomics and isotope tracing, we found that melanoma consume ~15 times more glucose than other tissues measured. Despite this burden, circulating glucose levels were maintained in disease animals by a tumor-liver alanine cycle. Excretion of glucose-derived alanine from tumors provided a source of carbon for hepatic gluconeogenesis and allowed tumors to remove excess nitrogen from branched-chain amino acid catabolism, which we found to be activated in zebrafish and human melanoma. Pharmacological inhibition of the tumor-liver alanine cycle in zebrafish reduced tumor burden. Our findings underscore the significance of metabolic crosstalk between tumors and distant tissues and establish the adult zebrafish as an attractive model to study such processes.
    Keywords:  alanine cycle; cancer; cancer metabolism; isotope tracing; melanoma; metabolite exchange; metabolomics; zebrafish
  16. Autophagy. 2021 May 14. 1-2
      Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest forms of cancer. The elevated macroautophagy/autophagy in these tumors supports growth, promotes immune evasion, and increases therapeutic resistance. Therefore, targeting autophagy is a therapeutic strategy that is being pursued to treat PDAC patients. Whereas autophagy inhibition impairs mitochondrial metabolism in PDAC, the specific metabolite(s) that becomes limiting when autophagy is inhibited has not been identified. We report that loss of autophagy specifically results in intracellular cysteine depletion under nutrient-replete conditions. Mechanistically, we show that PDAC cells utilize the autophagy machinery to regulate the activity and localization of the cystine transporter SLC7A11 at the plasma membrane. Upon inhibition of autophagy, SLC7A11 is localized to lysosomes in an MTORC2-dependent manner. Our findings reveal a novel connection between autophagy and cysteine metabolism in pancreatic cancer.
    Keywords:  Autophagy; SLC7A11; cysteine; lysosome; metabolism; pancreatic ductal adenocarcinoma
  17. Adv Exp Med Biol. 2021 ;1269 169-177
      Contrary to Warburg's original thesis, accelerated aerobic glycolysis is not a primary and permanent consequence of dysfunctional mitochondria compensating for a poor ATP yield per mole glucose. Instead, the Warburg effect is an essential part of a "selfish" metabolic reprogramming, which results from the interplay between (normoxic or hypoxic) HIF-1 overexpression, oncogene activation (cMyc, Ras), loss of function of tumor suppressors (mutant p53, mutant PTEN, microRNAs and sirtuins with suppressor functions), activated (PI3K/Akt/mTORC1, Ras/Raf/Mek/Erk/c-Myc) or deactivated (AMPK) signaling pathways, components of the tumor microenvironment, and HIF-1 cooperations with epigenetic mechanisms. Molecular and functional processes of the Warburg effect include (a) considerably accelerated glycolytic fluxes; (b) adequate ATP generation per unit time to maintain energy homeostasis; (c) backup and diversion of glycolytic intermediates facilitating the biosynthesis of nucleotides, nonessential amino acids, lipids, and hexosamines; (d) inhibition of pyruvate entry into mitochondria; (e) excessive formation and accumulation of lactate which stimulates tumor growth and suppression of antitumor immunity (in addition, lactate can serve as an energy source for normoxic cancer cells, contributes to extracellular acidosis, and thus drives malignant progression and resistances to conventional therapies); (f) maintenance of the cellular redox homeostasis and low ROS formation; and (g) HIF-1 overexpression, mutant p53, and mutant PTEN which inhibit mitochondrial biogenesis and functions, thus negatively impacting cellular respiration rate. The glycolytic switch is an early event in oncogenesis and primarily supports cell survival. All in all, the Warburg effect, i.e., aerobic glycolysis in the presence of oxygen and - in principle - functioning mitochondria, constitutes a major driver of the cancer progression machinery, resistance to conventional therapies, and - finally - poor patient outcome.
    Keywords:  ATP generation; Aerobic glycolysis; Biosynthesis of macromolecules; Energy homeostasis; Glycolytic phenotype; Glycolytic switch; Lactate accumulation; Metabolic reprogramming; Oncogenesis; Redox homeostasis; Tumor acidosis; Tumor glucose metabolism; Tumor mitochondria; Warburg effect
  18. Nature. 2021 May 12.
      Adaptive thermogenesis has attracted much attention because of its ability to increase systemic energy expenditure and to counter obesity and diabetes1-3. Recent data have indicated that thermogenic fat cells use creatine to stimulate futile substrate cycling, dissipating chemical energy as heat4,5. This model was based on the super-stoichiometric relationship between the amount of creatine added to mitochondria and the quantity of oxygen consumed. Here we provide direct evidence for the molecular basis of this futile creatine cycling activity in mice. Thermogenic fat cells have robust phosphocreatine phosphatase activity, which is attributed to tissue-nonspecific alkaline phosphatase (TNAP). TNAP hydrolyses phosphocreatine to initiate a futile cycle of creatine dephosphorylation and phosphorylation. Unlike in other cells, TNAP in thermogenic fat cells is localized to the mitochondria, where futile creatine cycling occurs. TNAP expression is powerfully induced when mice are exposed to cold conditions, and its inhibition in isolated mitochondria leads to a loss of futile creatine cycling. In addition, genetic ablation of TNAP in adipocytes reduces whole-body energy expenditure and leads to rapid-onset obesity in mice, with no change in movement or feeding behaviour. These data illustrate the critical role of TNAP as a phosphocreatine phosphatase in the futile creatine cycle.
  19. Nat Commun. 2021 May 11. 12(1): 2620
      Tumor associated macrophage responses are regulated by distinct metabolic states that affect their function. However, the ability of specific signals in the local tumor microenvironment to program macrophage metabolism remains under investigation. Here, we identify NAMPT, the rate limiting enzyme in NAD salvage synthesis, as a target of STAT1 during cellular activation by interferon gamma, an important driver of macrophage polarization and antitumor responses. We demonstrate that STAT1 occupies a conserved element within the first intron of Nampt, termed Nampt-Regulatory Element-1 (NRE1). Through disruption of NRE1 or pharmacological inhibition, a subset of M1 genes is sensitive to NAMPT activity through its impact on glycolytic processes. scRNAseq is used to profile in vivo responses by NRE1-deficient, tumor-associated leukocytes in melanoma tumors through the creation of a unique mouse strain. Reduced Nampt and inflammatory gene expression are present in specific myeloid and APC populations; moreover, targeted ablation of NRE1 in macrophage lineages results in greater tumor burden. Finally, elevated NAMPT expression correlates with IFNγ responses and melanoma patient survival. This study identifies IFN and STAT1-inducible Nampt as an important factor that shapes the metabolic program and function of tumor associated macrophages.
  20. Front Aging Neurosci. 2021 ;13 660843
      Rare mutations in the mitochondrial protein coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) are associated with Parkinson's disease (PD) and other Lewy body disorders. CHCHD2 is a bi-organellar mediator of oxidative phosphorylation, playing crucial roles in regulating electron flow in the mitochondrial electron transport chain and acting as a nuclear transcription factor for a cytochrome c oxidase subunit (COX4I2) and itself in response to hypoxic stress. CHCHD2 also regulates cell migration and differentiation, mitochondrial cristae structure, and apoptosis. In this review, we summarize the known disease-associated mutations of CHCHD2 in Asian and Caucasian populations, the physiological functions of CHCHD2, how CHCHD2 mutations contribute to α-synuclein pathology, and current animal models of CHCHD2. Further, we discuss the necessity of continued investigation into the divergent functions of CHCHD2 and CHCHD10 to determine how mutations in these similar mitochondrial proteins contribute to different neurodegenerative diseases.
    Keywords:  CHCHD10; CHCHD2; Lewy body disorders; Parkinson’s disease; mitochondria
  21. Comp Biochem Physiol B Biochem Mol Biol. 2021 May 06. pii: S1096-4959(21)00053-1. [Epub ahead of print] 110614
      Mitochondria are recognized as centrally important to cellular reactive oxygen species (ROS), both as a potential source and due to their substantial antioxidant capacity. While much of the initial ROS formed by mitochondria is superoxide, this is rapidly converted to hydrogen peroxide (H2O2) which more readily crosses membranes making H2O2 important in both redox signalling mechanisms and conditions of oxidative stress. Here I outline our studies on mitochondrial H2O2 metabolism with a focus on some of the challenges and strategies involved with developing an integrated model of mitochondria being intrinsic regulators of H2O2. This view of mitochondria as regulators of H2O2 goes beyond the simpler contention of them being net producers or consumers. Moreover, the integration of both consumption and production can then be tied to a putative mechanism linking energy sensing at the level of the mitochondrial protonmotive force. This mechanism would provide a means of mitochondria communicating their energetic status the extramitochondrial compartment via local H2O2 concentrations. I conclude by explaining how these concepts developed using rodent muscle as a model have high relevance and applicability to comparative studies.
    Keywords:  Auranofin; CDNB; Peroxidase; Reactive oxygen species (ROS)
  22. J Cell Biol. 2021 Jul 05. pii: e202010006. [Epub ahead of print]220(7):
      The ER tethers tightly to mitochondria and the mitochondrial protein FUNDC1 recruits Drp1 to ER-mitochondria contact sites, subsequently facilitating mitochondrial fission and preventing mitochondria from undergoing hypoxic stress. However, the mechanisms by which the ER modulates hypoxia-induced mitochondrial fission are poorly understood. Here, we show that USP19, an ER-resident deubiquitinase, accumulates at ER-mitochondria contact sites under hypoxia and promotes hypoxia-induced mitochondrial division. In response to hypoxia, USP19 binds to and deubiquitinates FUNDC1 at ER-mitochondria contact sites, which facilitates Drp1 oligomerization and Drp1 GTP-binding and hydrolysis activities, thereby promoting mitochondrial division. Our findings reveal a unique hypoxia response pathway mediated by an ER protein that regulates mitochondrial dynamics.
  23. Nat Commun. 2021 May 12. 12(1): 2745
      In mice, time of day strongly influences lethality in response to LPS, with survival greatest at the beginning compared to the end of the light cycle. Here we show that feeding, rather than light, controls time-of-day dependent LPS sensitivity. Mortality following LPS administration is independent of cytokine production and the clock regulator BMAL1 expressed in myeloid cells. In contrast, deletion of BMAL1 in hepatocytes globally disrupts the transcriptional response to the feeding cycle in the liver and results in constitutively high LPS sensitivity. Using RNAseq and functional validation studies we identify hepatic farnesoid X receptor (FXR) signalling as a BMAL1 and feeding-dependent regulator of LPS susceptibility. These results show that hepatocyte-intrinsic BMAL1 and FXR signalling integrate nutritional cues to regulate survival in response to innate immune stimuli. Understanding hepatic molecular programmes operational in response to these cues could identify novel pathways for targeting to enhance endotoxemia resistance.
  24. Nat Metab. 2021 May 10.
      Metabolism negotiates cell-endogenous requirements of energy, nutrients and building blocks with the immediate environment to enable various processes, including growth and differentiation. While there is an increasing number of examples of crosstalk between metabolism and chromatin, few involve uptake of exogenous metabolites. Solute carriers (SLCs) represent the largest group of transporters in the human genome and are responsible for the transport of a wide variety of substrates, including nutrients and metabolites. We aimed to investigate the possible involvement of SLC-mediated solutes uptake and cellular metabolism in regulating cellular epigenetic states. Here, we perform a CRISPR-Cas9 transporter-focused genetic screen and a metabolic compound library screen for the regulation of BRD4-dependent chromatin states in human myeloid leukaemia cells. Intersection of the two orthogonal approaches reveal that loss of transporters involved with purine transport or inhibition of de novo purine synthesis lead to dysfunction of BRD4-dependent transcriptional regulation. Through mechanistic characterization of the metabolic circuitry, we elucidate the convergence of SLC-mediated purine uptake and de novo purine synthesis on BRD4-chromatin occupancy. Moreover, adenine-related metabolite supplementation effectively restores BRD4 functionality on purine impairment. Our study highlights the specific role of purine/adenine metabolism in modulating BRD4-dependent epigenetic states.
  25. Nature. 2021 May 12.
      Ageing of the immune system, or immunosenescence, contributes to the morbidity and mortality of the elderly1,2. To define the contribution of immune system ageing to organism ageing, here we selectively deleted Ercc1, which encodes a crucial DNA repair protein3,4, in mouse haematopoietic cells to increase the burden of endogenous DNA damage and thereby senescence5-7 in the immune system only. We show that Vav-iCre+/-;Ercc1-/fl mice were healthy into adulthood, then displayed premature onset of immunosenescence characterized by attrition and senescence of specific immune cell populations and impaired immune function, similar to changes that occur during ageing in wild-type mice8-10. Notably, non-lymphoid organs also showed increased senescence and damage, which suggests that senescent, aged immune cells can promote systemic ageing. The transplantation of splenocytes from Vav-iCre+/-;Ercc1-/fl or aged wild-type mice into young mice induced senescence in trans, whereas the transplantation of young immune cells attenuated senescence. The treatment of Vav-iCre+/-;Ercc1-/fl mice with rapamycin reduced markers of senescence in immune cells and improved immune function11,12. These data demonstrate that an aged, senescent immune system has a causal role in driving systemic ageing and therefore represents a key therapeutic target to extend healthy ageing.
  26. Front Oncol. 2021 ;11 644857
      Isocitrate dehydrogenase (IDH) is a key metabolic enzyme catalyzing the interconversion of isocitrate to α-ketoglutarate (α-KG). Mutations in IDH lead to loss of normal enzymatic activity and gain of neomorphic activity that irreversibly converts α-KG to 2-hydroxyglutarate (2-HG), which can competitively inhibit a-KG-dependent enzymes, subsequently induces cell metabolic reprograming, inhibits cell differentiation, and initiates cell tumorigenesis. Encouragingly, this phenomenon can be reversed by specific small molecule inhibitors of IDH mutation. At present, small molecular inhibitors of IDH1 and IDH2 mutant have been developed, and promising progress has been made in preclinical and clinical development, showing encouraging results in patients with IDH2 mutant cancers. This review will focus on the biological roles of IDH2 mutation in tumorigenesis, and provide a proof-of-principle for the development and application of IDH2 mutant inhibitors for human cancer treatment.
    Keywords:  2-HG; IDH2 inhibitors; IDH2 mutation; cancer metabolism; cancers
  27. Curr Diab Rep. 2021 May 11. 21(7): 21
      PURPOSE OF REVIEW: Diabetic kidney disease (DKD), a leading cause of end-stage kidney disease, is the result of metabolic network alterations in the kidney. Therefore, metabolomics is an effective tool for understanding its pathophysiology, finding key biomarkers, and developing a new treatment strategy. In this review, we summarize the application of metabolomics to DKD research.RECENT FINDINGS: Alterations in renal energy metabolism including the accumulation of tricarboxylic acid cycle and glucose metabolites are observed in the early stage of DKD, and they finally lead to mitochondrial dysfunction in advanced DKD. Mitochondrial fission-fusion imbalance and dysregulated organelle crosstalk might contribute to this process. Moreover, metabolomics has identified several uremic toxins including phenyl sulfate and tryptophan derivatives as promising biomarkers that mediate DKD progression. Recent advances in metabolomics have clarified the role of dysregulated energy metabolism and uremic toxins in DKD pathophysiology. Integration of multi-omics data will provide additional information for identifying critical drivers of DKD.
    Keywords:  Biomarker; Diabetic kidney disease; Metabolomics; Mitochondria; Organelle crosstalk; Uremic toxin
  28. Cell Death Dis. 2021 May 12. 12(5): 475
      Mitochondrial dynamics and mitophagy are constitutive and complex systems that ensure a healthy mitochondrial network through the segregation and subsequent degradation of damaged mitochondria. Disruption of these systems can lead to mitochondrial dysfunction and has been established as a central mechanism of ischemia/reperfusion (I/R) injury. Emerging evidence suggests that mitochondrial dynamics and mitophagy are integrated systems; however, the role of this relationship in the context of I/R injury remains unclear. To investigate this concept, we utilized primary cortical neurons isolated from the novel dual-reporter mitochondrial quality control knockin mice (C57BL/6-Gt(ROSA)26Sortm1(CAG-mCherry/GFP)Ganl/J) with conditional knockout (KO) of Drp1 to investigate changes in mitochondrial dynamics and mitophagic flux during in vitro I/R injury. Mitochondrial dynamics was quantitatively measured in an unbiased manner using a machine learning mitochondrial morphology classification system, which consisted of four different classifications: network, unbranched, swollen, and punctate. Evaluation of mitochondrial morphology and mitophagic flux in primary neurons exposed to oxygen-glucose deprivation (OGD) and reoxygenation (OGD/R) revealed extensive mitochondrial fragmentation and swelling, together with a significant upregulation in mitophagic flux. Furthermore, the primary morphology of mitochondria undergoing mitophagy was classified as punctate. Colocalization using immunofluorescence as well as western blot analysis revealed that the PINK1/Parkin pathway of mitophagy was activated following OGD/R. Conditional KO of Drp1 prevented mitochondrial fragmentation and swelling following OGD/R but did not alter mitophagic flux. These data provide novel evidence that Drp1 plays a causal role in the progression of I/R injury, but mitophagy does not require Drp1-mediated mitochondrial fission.
  29. Nat Rev Immunol. 2021 May 12.
      Cytotoxic CD8+ T cells play a key role in the elimination of intracellular infections and malignant cells and can provide long-term protective immunity. In the response to infection, CD8+ T cell metabolism is coupled to transcriptional, translational and epigenetic changes that are driven by extracellular metabolites and immunological signals. These programmes facilitate the adaptation of CD8+ T cells to the diverse and dynamic metabolic environments encountered in the circulation and in the tissues. In the setting of disease, both cell-intrinsic and cell-extrinsic metabolic cues contribute to CD8+ T cell dysfunction. In addition, changes in whole-body metabolism, whether through voluntary or disease-induced dietary alterations, can influence CD8+ T cell-mediated immunity. Defining the metabolic adaptations of CD8+ T cells in specific tissue environments informs our understanding of how these cells protect against pathogens and tumours and maintain tissue health at barrier sites. Here, we highlight recent findings revealing how metabolic networks enforce specific CD8+ T cell programmes and discuss how metabolism is integrated with CD8+ T cell differentiation and function and determined by environmental cues.
  30. Nat Cell Biol. 2021 May;23(5): 497-510
      The Drosophila trachea, as the functional equivalent of mammalian blood vessels, senses hypoxia and oxygenates the body. Here, we show that the adult intestinal tracheae are dynamic and respond to enteric infection, oxidative agents and tumours with increased terminal branching. Increased tracheation is necessary for efficient damage-induced intestinal stem cell (ISC)-mediated regeneration and is sufficient to drive ISC proliferation in undamaged intestines. Gut damage or tumours induce HIF-1α (Sima in Drosophila), which stimulates tracheole branching via the FGF (Branchless (Bnl))-FGFR (Breathless (Btl)) signalling cascade. Bnl-Btl signalling is required in the intestinal epithelium and the trachea for efficient damage-induced tracheal remodelling and ISC proliferation. Chemical or Pseudomonas-generated reactive oxygen species directly affect the trachea and are necessary for branching and intestinal regeneration. Similarly, tracheole branching and the resulting increase in oxygenation are essential for intestinal tumour growth. We have identified a mechanism of tracheal-intestinal tissue communication, whereby damage and tumours induce neo-tracheogenesis in Drosophila, a process reminiscent of cancer-induced neoangiogenesis in mammals.
  31. Elife. 2021 May 11. pii: e66921. [Epub ahead of print]10
      Myocardial infarction (MI) promotes a range of systemic effects, many of which are unknown. Here, we investigated the alterations associated with MI progression in heart and other metabolically active tissues (liver, skeletal muscle, and adipose) in a mouse model of MI (induced by ligating the left ascending coronary artery) and sham-operated mice. We performed a genome-wide transcriptomic analysis on tissue samples obtained 6- and 24-hours post MI or sham operation. By generating tissue-specific biological networks, we observed: (1) dysregulation in multiple biological processes (including immune system, mitochondrial dysfunction, fatty-acid beta-oxidation, and RNA and protein processing) across multiple tissues post MI; and (2) tissue-specific dysregulation in biological processes in liver and heart post MI. Finally, we validated our findings in two independent MI cohorts. Overall, our integrative analysis highlighted both common and specific biological responses to MI across a range of metabolically active tissues.
    Keywords:  computational biology; medicine; mouse; systems biology
  32. Nat Rev Nephrol. 2021 May 10.
      Chronic kidney disease (CKD) induces modifications in lipid and lipoprotein metabolism and homeostasis. These modifications can promote, modulate and/or accelerate CKD and secondary cardiovascular disease (CVD). Lipid and lipoprotein abnormalities - involving triglyceride-rich lipoproteins, LDL and/or HDL - not only involve changes in concentration but also changes in molecular structure, including protein composition, incorporation of small molecules and post-translational modifications. These alterations modify the function of lipoproteins and can trigger pro-inflammatory and pro-atherogenic processes, as well as oxidative stress. Serum fatty acid levels are also often altered in patients with CKD and lead to changes in fatty acid metabolism - a key process in intracellular energy production - that induce mitochondrial dysfunction and cellular damage. These fatty acid changes might not only have a negative impact on the heart, but also contribute to the progression of kidney damage. The presence of these lipoprotein alterations within a biological environment characterized by increased inflammation and oxidative stress, as well as the competing risk of non-atherosclerotic cardiovascular death as kidney function declines, has important therapeutic implications. Additional research is needed to clarify the pathophysiological link between lipid and lipoprotein modifications, and kidney dysfunction, as well as the genesis and/or progression of CVD in patients with kidney disease.
  33. Am J Physiol Endocrinol Metab. 2021 May 10.
      Retinopathy is a leading cause of blindness, and there is currently no cure. Earlier identification of the progression of retinopathy could provide a better chance for intervention. Diet has profound effects on retinal function. A maternal high fructose diet (HFD) triggers diseases in multiple organs. However, whether maternal HFD impairs retinal function in adult offspring is currently unknown. By using the rodent model of maternal HFD during pregnancy and lactation, our data indicated a reduced b-wave of electroretinography (ERG) in HFD female offspring at 3 months of age compared with age-matched offspring of dams fed regular chow (ND). Immunofluorescence and Western blot analyses indicated that the distributions and expressions of synaptophysin, postsynaptic density protein 95 (PSD95), and phospho(p)-Ca2+/calmodulin-stimulated protein kinase IIa (CaMKIIa) were significantly suppressed in the HFD group. Furthermore, the ATP content and the mitochondrial respiratory protein, Mt CPX 4-2, were decreased. Moreover, the expressions of peroxisome proliferator-activated receptor g coactivator 1-α (PGC-1α) and mitochondrial transcription factor A (TFAM) in the retina of the HFD group were downregulated. Treatment with coenzyme Q10 (Q10), a key mediator of the electron transport chain, effectively reversed these abovementioned dysfunctions. Together, these results suggested that maternal HFD impaired retinal function in adult female offspring. The mechanism underlying early-onset retinopathy may involve the reduction in the capacity of mitochondrial energy production and the suppression of synaptic plasticity. Most importantly, mitochondria could be a feasible target to reprogram maternal HFD-damaged retinal function.
    Keywords:  maternal high fructose diet; mitochondrial bioenergetics; mitochondrial biogenesis; retina; synaptic plasticity
  34. Crit Rev Biochem Mol Biol. 2021 May 10. 1-29
      The evolution of organisms has been a subject of paramount debate for hundreds of years and though major advances in the field have been made, the precise mechanisms underlying evolutionary processes remain fragmentary. Strikingly, the majority of the core principles accepted across the many fields of biology only consider genetic information as the major - if not exclusive - biological information carrier and thus consider it as the main evolutionary avatar. However, the real picture appears far more complex than originally anticipated, as compelling data suggest that nongenetic information steps up when highly dynamic evolutionary frameworks are explored. In light of recent evidence, we discuss herein the dynamic nature and complexity of nongenetic information carriers, and their emerging relevance in the evolutionary process. We argue that it is possible to overcome the historical arguments which dismissed these carriers, and instead consider that they are indeed core to life itself as they support a sustainable, continuous source of rapid adaptation in ever-changing environments. Ultimately, we will address the intricacies of genetic and non-genetic networks underlying evolutionary models to build a framework where both core biological information concepts are considered non-negligible and equally fundamental.
    Keywords:  Nongenetic; evolution; heterogeneity; information; plasticity
  35. Front Physiol. 2021 ;12 660068
      Mitochondrial dysfunction is a crucial contributor to heart diseases. Alterations in energetic metabolism affect crucial homeostatic processes, such asATP production, the generation of reactive oxygen species, and the release of pro-apoptotic factors, associated with metabolic abnormalities. In response to energetic deficiency, the cardiomyocytes activate the Mitochondrial Quality Control (MQC), a critical process in maintaining mitochondrial health. This process is compromised in cardiovascular diseases depending on the pathology's severity and represents, therefore, a potential therapeutic target. Several potential targeting molecules within this process have been identified in the last years, and therapeutic strategies have been proposed to ameliorate mitochondria monitoring and function. In this context, physical exercise is considered a non-pharmacological strategy to protect mitochondrial health. Physical exercise regulates MQC allowing the repair/elimination of damaged mitochondria and synthesizing new ones, thus recovering the metabolic state. In this review, we will deal with the effect of physical exercise on cardiac mitochondrial function tracing its ability to modulate specific steps in MQC both in physiologic and pathologic conditions.
    Keywords:  cardiovascular disease; energetic metabolism; heart; mitochondrial dysfunction; physical activity
  36. Cancer Cell. 2021 May 10. pii: S1535-6108(21)00169-0. [Epub ahead of print]39(5): 596-598
      Su et al. demonstrate that upon inhibiting autophagy, an intracellular nutrient recycling pathway, pancreatic ductal adenocarcinoma cells upregulate NRF2-mediated transcription of macropinocytosis pathway components, thereby triggering an alternate route for tumors to scavenge nutrients from extracellular sources. Accordingly, the combined inhibition of autophagy and macropinocytosis may improve cancer treatment.
  37. CA Cancer J Clin. 2021 May 13.
      Cancer has myriad effects on metabolism that include both rewiring of intracellular metabolism to enable cancer cells to proliferate inappropriately and adapt to the tumor microenvironment, and changes in normal tissue metabolism. With the recognition that fluorodeoxyglucose-positron emission tomography imaging is an important tool for the management of many cancers, other metabolites in biological samples have been in the spotlight for cancer diagnosis, monitoring, and therapy. Metabolomics is the global analysis of small molecule metabolites that like other -omics technologies can provide critical information about the cancer state that are otherwise not apparent. Here, the authors review how cancer and cancer therapies interact with metabolism at the cellular and systemic levels. An overview of metabolomics is provided with a focus on currently available technologies and how they have been applied in the clinical and translational research setting. The authors also discuss how metabolomics could be further leveraged in the future to improve the management of patients with cancer.
    Keywords:  cancer; intracellular; metabolism; metabolomics
  38. Front Cell Dev Biol. 2021 ;9 654337
      Cancer cells reprogram glucose metabolism to meet their malignant proliferation needs and survival under a variety of stress conditions. The prominent metabolic reprogram is aerobic glycolysis, which can help cells accumulate precursors for biosynthesis of macromolecules. In addition to glycolysis, recent studies show that gluconeogenesis and TCA cycle play important roles in tumorigenesis. Here, we provide a comprehensive review about the role of glycolysis, gluconeogenesis, and TCA cycle in tumorigenesis with an emphasis on revealing the novel functions of the relevant enzymes and metabolites. These functions include regulation of cell metabolism, gene expression, cell apoptosis and autophagy. We also summarize the effect of glucose metabolism on chromatin modifications and how this relationship leads to cancer development. Understanding the link between cancer cell metabolism and chromatin modifications will help develop more effective cancer treatments.
    Keywords:  epigenetic modifications; gene transcription; histone modifications; metabolism; tumorigenesis
  39. PLoS Pathog. 2021 May 14. 17(5): e1009597
      Macrophages metabolic reprogramming in response to microbial insults is a major determinant of pathogen growth or containment. Here, we reveal a distinct mechanism by which stimulator of interferon genes (STING), a cytosolic sensor that regulates innate immune responses, contributes to an inflammatory M1-like macrophage profile upon Brucella abortus infection. This metabolic reprogramming is induced by STING-dependent stabilization of hypoxia-inducible factor-1 alpha (HIF-1α), a global regulator of cellular metabolism and innate immune cell functions. HIF-1α stabilization reduces oxidative phosphorylation and increases glycolysis during infection with B. abortus and, likewise, enhances nitric oxide production, inflammasome activation and IL-1β release in infected macrophages. Furthermore, the induction of this inflammatory profile participates in the control of bacterial replication since absence of HIF-1α renders mice more susceptible to B. abortus infection. Mechanistically, activation of STING by B. abortus infection drives the production of mitochondrial reactive oxygen species (mROS) that ultimately influences HIF-1α stabilization. Moreover, STING increases the intracellular succinate concentration in infected macrophages, and succinate pretreatment induces HIF-1α stabilization and IL-1β release independently of its cognate receptor GPR91. Collectively, these data demonstrate a pivotal mechanism in the immunometabolic regulation of macrophages during B. abortus infection that is orchestrated by STING via HIF-1α pathway and highlight the metabolic reprogramming of macrophages as a potential treatment strategy for bacterial infections.
  40. Nat Commun. 2021 May 11. 12(1): 2656
      Activating mutants of RAS are commonly found in human cancers, but to date selective targeting of RAS in the clinic has been limited to KRAS(G12C) through covalent inhibitors. Here, we report a monobody, termed 12VC1, that recognizes the active state of both KRAS(G12V) and KRAS(G12C) up to 400-times more tightly than wild-type KRAS. The crystal structures reveal that 12VC1 recognizes the mutations through a shallow pocket, and 12VC1 competes against RAS-effector interaction. When expressed intracellularly, 12VC1 potently inhibits ERK activation and the proliferation of RAS-driven cancer cell lines in vitro and in mouse xenograft models. 12VC1 fused to VHL selectively degrades the KRAS mutants and provides more extended suppression of mutant RAS activity than inhibition by 12VC1 alone. These results demonstrate the feasibility of selective targeting and degradation of KRAS mutants in the active state with noncovalent reagents and provide a starting point for designing noncovalent therapeutics against oncogenic RAS mutants.
  41. PLoS Biol. 2021 May 13. 19(5): e3001252
      The mitochondrial ATP synthase emerges as key hub of cellular functions controlling the production of ATP, cellular signaling, and fate. It is regulated by the ATPase inhibitory factor 1 (IF1), which is highly abundant in neurons. Herein, we ablated or overexpressed IF1 in mouse neurons to show that IF1 dose defines the fraction of active/inactive enzyme in vivo, thereby controlling mitochondrial function and the production of mitochondrial reactive oxygen species (mtROS). Transcriptomic, proteomic, and metabolomic analyses indicate that IF1 dose regulates mitochondrial metabolism, synaptic function, and cognition. Ablation of IF1 impairs memory, whereas synaptic transmission and learning are enhanced by IF1 overexpression. Mechanistically, quenching the IF1-mediated increase in mtROS production in mice overexpressing IF1 reduces the increased synaptic transmission and obliterates the learning advantage afforded by the higher IF1 content. Overall, IF1 plays a key role in neuronal function by regulating the fraction of ATP synthase responsible for mitohormetic mtROS signaling.
  42. Cancer Sci. 2021 May 02.
      The BRAF V600E mutation occurs in approximately 10% of patients with metastatic colorectal cancer (CRC) and constitutes a distinct subtype of the disease with extremely poor prognosis. To address this refractory disease, we investigated the unique metabolic gene profile of BRAF V600E-mutated tumors via in silico analysis using a large-scale clinical database. We found that BRAF V600E-mutated tumors exhibited a specific metabolic gene expression signature, including some genes that are associated with poor prognosis in CRC. We discovered that BRAF V600E-mutated tumors expressed high levels of glycolytic enzyme enolase 2 (ENO2), which is mainly expressed in neuronal tissues under physiological conditions. In vitro experiments using CRC cells demonstrated that BRAF V600E-mutated cells exhibited enhanced dependency on ENO2 compared to BRAF wild-type cancer cells and that knockdown of ENO2 led to the inhibition of proliferation and migration of BRAF V600E-mutated cancer cells. Moreover, inhibition of ENO2 resulted in enhanced sensitivity to vemurafenib, a selective inhibitor of BRAF V600E. We identified AP-1 transcription factor subunit (FOSL1) as being involved in the transcription of ENO2 in CRC cells. In addition, both MAPK and PI3K/Akt signaling were suppressed upon inhibition of ENO2, implying an additional oncogenic role of ENO2. These results suggest the crucial role of ENO2 in the progression of BRAF V600E-mutated CRC and indicate the therapeutic implications of targeting this gene.
    Keywords:  BRAF V600E-mutated colorectal cancer; ENO2; FOSL1; glycolysis; metabolic genes
  43. BMC Biol. 2021 May 10. 19(1): 85
      BACKGROUND: Radioactive or stable isotopic labeling of metabolites is a strategy that is routinely used to map the cellular fate of a selected labeled metabolite after it is added to cell culture or to the circulation of an animal. However, a labeled metabolite can be enzymatically changed in cellular metabolism, complicating the use of this experimental strategy to understand how a labeled metabolite moves between organs. These methods are also technically demanding, expensive and potentially toxic. To allow quantification of the bulk movement of metabolites between organs, we have developed a novel application of stable isotope ratio mass spectrometry (IRMS).RESULTS: We exploit natural differences in 13C/12C ratios of plant nutrients for a low-cost and non-toxic carbon labeling, allowing a measurement of bulk carbon transfer between organs in vivo. IRMS measurements were found to be sufficiently sensitive to measure organs from individual Drosophila melanogaster larvae, giving robust measurements down to 2.5 μg per sample. We apply the method to determine if carbon incorporated into a growing solid tumor is ultimately derived from food or host tissues.
    CONCLUSION: Measuring tumor growth in a D. melanogaster larvae tumor model reveals that these tumors derive a majority of carbon from host sources. We believe the low cost and non-toxic nature of this methodology gives it broad applicability to study carbon flows between organs also in other animals and for a range of other biological questions.
    Keywords:  CATSIR; Carbon; Flux; Food; Host; IRMS; Metabolite; Transfer; Tumor
  44. Front Cell Dev Biol. 2021 ;9 684049
    Keywords:  autophagy; cancer; cell metabolism; inflammation; nutrients and energy
  45. Nat Commun. 2021 May 10. 12(1): 2616
      FUN14 domain-containing protein 1 (FUNDC1) is an integral mitochondrial outer-membrane protein, and mediates the formation of mitochondria-associated endoplasmic reticulum membranes (MAMs). This study aims to determine the contributions of FUNDC1-mediated MAMs to angiogenesis in vitro and in vivo. In cultured endothelial cells, VEGF significantly increases the formation of MAMs and MAM-related proteins, including FUNDC1. Endothelial cell-specific deletion of FUNDC1, which disrupts MAM formation in endothelial cells, lowers VEGFR2 expression and reduces tube formation, spheroid-sprouting, and functional blood vessel formation in vitro and in vivo. Conversely, increased MAM formation using MAM linkers mimics the effects of VEGF and promotes endothelial angiogenesis. Mechanistically, increased MAMs formation led to increased levels of Ca2+ in cytosol, promoted the phosphorylation of serum response factor (SRF) and enhanced the binding of SRF to VEGFR2 promoter, resulting in increased VEGFR2 production, with consequent angiogenesis. Moreover, blocking FUNDC1-related MAM formation with a cell-penetrating inhibitory peptide significantly suppresses the expressions of downstream angiogenic genes and inhibits tumor angiogenesis. We conclude that decreased MAMs formation by silencing FUNDC1 can inhibit angiogenesis by decreasing VEGFR2 expression, and targeting FUNDC1-dependent MAMs might be a promising approach for treating human disorders characterized by defective angiogenesis.
  46. Cancer Res. 2021 May 14. pii: canres.CAN-20-2562-A.2020. [Epub ahead of print]
      In pancreatic cancer, the robust fibroinflammatory stroma contributes to immune suppression and renders tumors hypoxic, altering intra-tumoral metabolic pathways and leading to poor survival. One metabolic enzyme activated during hypoxia is lactate dehydrogenase A (LDHA). As a result of its promiscuous activity under hypoxia, LDHA produces L-2 hydroxyglutarate, an epigenetic modifier, that regulates the tumor transcriptome. However, the role of L-2HG in remodeling the pancreatic tumor microenvironment is not known. Here we used mass spectrometry to detect L-2HG in serum samples from pancreatic cancer patients, comprising tumor cells as well as stromal cells. Both hypoxic pancreatic tumors as well as serum from pancreatic cancer patients accumulated L-2HG as a result of promiscuous activity of LDHA. This abnormally accumulated L-2HG led to H3 hypermethylation and altered gene expression, which regulated a critical balance between stemness and differentiation in pancreatic tumors. Secreted L-2HG inhibited T cell proliferation and migration, suppressing anti-tumor immunity. In a syngeneic orthotopic model of pancreatic cancer, inhibition of LDHA with GSK2837808A decreased L-2HG, induced tumor regression, and sensitized tumors to anti-PD1 therapy. In conclusion, hypoxia-mediated promiscuous activity of LDHA produces L-2HG in pancreatic tumor cells, regulating the stemness-differentiation balance and contributing to immune evasion. Targeting LDHA can be developed as a potential therapy to sensitize pancreatic tumors to checkpoint inhibitor therapy.
  47. Immunity. 2021 May 11. pii: S1074-7613(21)00170-9. [Epub ahead of print]54(5): 976-987.e7
      Aerobic glycolysis-the Warburg effect-converts glucose to lactate via the enzyme lactate dehydrogenase A (LDHA) and is a metabolic feature of effector T cells. Cells generate ATP through various mechanisms and Warburg metabolism is comparatively an energy-inefficient glucose catabolism pathway. Here, we examined the effect of ATP generated via aerobic glycolysis in antigen-driven T cell responses. Cd4CreLdhafl/fl mice were resistant to Th17-cell-mediated experimental autoimmune encephalomyelitis and exhibited defective T cell activation, migration, proliferation, and differentiation. LDHA deficiency crippled cellular redox balance and inhibited ATP production, diminishing PI3K-dependent activation of Akt kinase and thereby phosphorylation-mediated inhibition of Foxo1, a transcriptional repressor of T cell activation programs. Th17-cell-specific expression of an Akt-insensitive Foxo1 recapitulated the defects seen in Cd4CreLdhafl/fl mice. Induction of LDHA required PI3K signaling and LDHA deficiency impaired PI3K-catalyzed PIP3 generation. Thus, Warburg metabolism augments glycolytic ATP production, fueling a PI3K-centered positive feedback regulatory circuit that drives effector T cell responses.
    Keywords:  ATP; LDHA; PI3K; Th17 cell; autoimmunity; glycolysis; redox balance