bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2022‒07‒10
37 papers selected by
Christian Frezza
University Hospital Cologne


  1. Nat Rev Mol Cell Biol. 2022 Jul 08.
      Mitochondrial energetic adaptations encompass a plethora of conserved processes that maintain cell and organismal fitness and survival in the changing environment by adjusting the respiratory capacity of mitochondria. These mitochondrial responses are governed by general principles of regulatory biology exemplified by changes in gene expression, protein translation, protein complex formation, transmembrane transport, enzymatic activities and metabolite levels. These changes can promote mitochondrial biogenesis and membrane dynamics that in turn support mitochondrial respiration. The main regulatory components of mitochondrial energetic adaptation include: the transcription coactivator peroxisome proliferator-activated receptor-γ (PPARγ) coactivator 1α (PGC1α) and associated transcription factors; mTOR and endoplasmic reticulum stress signalling; TOM70-dependent mitochondrial protein import; the cristae remodelling factors, including mitochondrial contact site and cristae organizing system (MICOS) and OPA1; lipid remodelling; and the assembly and metabolite-dependent regulation of respiratory complexes. These adaptive molecular and structural mechanisms increase respiration to maintain basic processes specific to cell types and tissues. Failure to execute these regulatory responses causes cell damage and inflammation or senescence, compromising cell survival and the ability to adapt to energetically demanding conditions. Thus, mitochondrial adaptive cellular processes are important for physiological responses, including to nutrient availability, temperature and physical activity, and their failure leads to diseases associated with mitochondrial dysfunction such as metabolic and age-associated diseases and cancer.
    DOI:  https://doi.org/10.1038/s41580-022-00506-6
  2. Nat Commun. 2022 Jul 07. 13(1): 3775
      Mitofusins reside on the outer mitochondrial membrane and regulate mitochondrial fusion, a physiological process that impacts diverse cellular processes. Mitofusins are activated by conformational changes and subsequently oligomerize to enable mitochondrial fusion. Here, we identify small molecules that directly increase or inhibit mitofusins activity by modulating mitofusin conformations and oligomerization. We use these small molecules to better understand the role of mitofusins activity in mitochondrial fusion, function, and signaling. We find that mitofusin activation increases, whereas mitofusin inhibition decreases mitochondrial fusion and functionality. Remarkably, mitofusin inhibition also induces minority mitochondrial outer membrane permeabilization followed by sub-lethal caspase-3/7 activation, which in turn induces DNA damage and upregulates DNA damage response genes. In this context, apoptotic death induced by a second mitochondria-derived activator of caspases (SMAC) mimetic is potentiated by mitofusin inhibition. These data provide mechanistic insights into the function and regulation of mitofusins as well as small molecules to pharmacologically target mitofusins.
    DOI:  https://doi.org/10.1038/s41467-022-31324-1
  3. Biochim Biophys Acta Mol Basis Dis. 2022 Jul 02. pii: S0925-4439(22)00152-1. [Epub ahead of print] 166481
      Mitochondrial-derived reactive oxygen species are important as antimicrobial agents and redox signals in pro-inflammatory macrophages. Macrophages produce superoxide in response to the TLR4 ligand LPS. However, the mechanism of LPS-induced superoxide generation is not fully understood. Superoxide is produced at complex I and complex III of the electron transport chain. Production of superoxide at either of these sites is highly dependent on the metabolic state of the cell which is dramatically altered by TLR4-induced metabolic reprogramming. This review will outline how metabolism impacts superoxide production in LPS-activated macrophages downstream of TLR4 signalling and address outstanding questions in this field.
    Keywords:  Complex I; Macrophages; Metabolism; Mitochondria; Reverse electron transport; Superoxide
    DOI:  https://doi.org/10.1016/j.bbadis.2022.166481
  4. Annu Rev Cell Dev Biol. 2022 Jul 08.
      Mitochondria are traditionally known as the powerhouse of the cell, but their functions extend far beyond energy production. They are vital in cellular and organismal pathways that direct metabolism, stress responses, immunity, and cellular fate. To accomplish these tasks, mitochondria have established networks of both intra- and extracellular communication. Intracellularly, these communication routes comprise direct contacts between mitochondria and other subcellular components as well as indirect vesicle transport of ions, metabolites, and other intracellular messengers. Extracellularly, mitochondria can induce stress responses or other cellular changes that secrete mitochondrial cytokine (mitokine) factors that can travel between tissues as well as respond to immune challenges from extracellular sources. Here we provide a current perspective on the major routes of communication for mitochondrial signaling, including their mechanisms and physiological impact. We also review the major diseases and age-related disorders associated with defects in these signaling pathways. An understanding of how mitochondrial signaling controls cellular homeostasis will bring greater insight into how dysfunctional mitochondria affect health in disease and aging. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 38 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
    DOI:  https://doi.org/10.1146/annurev-cellbio-120420-015303
  5. Cancer Res. 2022 Jul 05. 82(13): 2354-2356
      Understanding how carcinogenesis can expose cancers to synthetically lethal vulnerabilities has been an essential underpinning of development of modern anticancer therapeutics. Isocitrate dehydrogenase wild-type (IDHWT) glioblastoma multiforme (GBM), which is known to have upregulated branched-chain amino acid transaminase 1 (BCAT1) expression, has not had treatments developed to the same extent as the IDH mutant counterpart, despite making up the majority of cases. In this issue, Zhang and colleagues utilize a metabolic screen to identify α-ketoglutarate (AKG) as a synthetically lethal treatment in conjunction with BCAT1 inhibition in IDHWT GBM. These treatments synergize in a multipronged approach that limits substrate catabolism and disrupts mitochondrial homeostasis through perturbing the balance of NAD+/NADH, leading to mTORC1 inhibition and a reduction of nucleotide biosynthesis. Based on these results, the authors propose combination treatment targeting branched chain amino acid catabolism as a potential option for patients with IDHWT GBM. See related article by Zhang et al., p. 2388.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-22-1619
  6. Cancer Metab. 2022 Jul 04. 10(1): 10
      BACKGROUND: Metabolic adaptations can allow cancer cells to survive DNA-damaging chemotherapy. This unmet clinical challenge is a potential vulnerability of cancer. Accordingly, there is an intense search for mechanisms that modulate cell metabolism during anti-tumor therapy. We set out to define how colorectal cancer CRC cells alter their metabolism upon DNA replication stress and whether this provides opportunities to eliminate such cells more efficiently.METHODS: We incubated p53-positive and p53-negative permanent CRC cells and short-term cultured primary CRC cells with the topoisomerase-1 inhibitor irinotecan and other drugs that cause DNA replication stress and consequently DNA damage. We analyzed pro-apoptotic mitochondrial membrane depolarization and cell death with flow cytometry. We evaluated cellular metabolism with immunoblotting of electron transport chain (ETC) complex subunits, analysis of mitochondrial mRNA expression by qPCR, MTT assay, measurements of oxygen consumption and reactive oxygen species (ROS), and metabolic flux analysis with the Seahorse platform. Global metabolic alterations were assessed using targeted mass spectrometric analysis of extra- and intracellular metabolites.
    RESULTS: Chemotherapeutics that cause DNA replication stress induce metabolic changes in p53-positive and p53-negative CRC cells. Irinotecan enhances glycolysis, oxygen consumption, mitochondrial ETC activation, and ROS production in CRC cells. This is connected to increased levels of electron transport chain complexes involving mitochondrial translation. Mass spectrometric analysis reveals global metabolic adaptations of CRC cells to irinotecan, including the glycolysis, tricarboxylic acid cycle, and pentose phosphate pathways. P53-proficient CRC cells, however, have a more active metabolism upon DNA replication stress than their p53-deficient counterparts. This metabolic switch is a vulnerability of p53-positive cells to irinotecan-induced apoptosis under glucose-restricted conditions.
    CONCLUSION: Drugs that cause DNA replication stress increase the metabolism of CRC cells. Glucose restriction might improve the effectiveness of classical chemotherapy against p53-positive CRC cells. The topoisomerase-1 inhibitor irinotecan and other chemotherapeutics that cause DNA damage induce metabolic adaptations in colorectal cancer (CRC) cells irrespective of their p53 status. Irinotecan enhances the glycolysis and oxygen consumption in CRC cells to deliver energy and biomolecules necessary for DNA repair and their survival. Compared to p53-deficient cells, p53-proficient CRC cells have a more active metabolism and use their intracellular metabolites more extensively. This metabolic switch creates a vulnerability to chemotherapy under glucose-restricted conditions for p53-positive cells.
    Keywords:  Adaptation; Colorectal cancer; Glucose; Irinotecan; Metabolism; Warburg effect; p53
    DOI:  https://doi.org/10.1186/s40170-022-00286-9
  7. Nat Commun. 2022 Jul 05. 13(1): 3856
      AMP-activated protein kinase (AMPK) is a master regulator of cellular energetics which coordinates metabolism by phosphorylating a plethora of substrates throughout the cell. But how AMPK activity is regulated at different subcellular locations for precise spatiotemporal control over metabolism is unclear. Here we present a sensitive, single-fluorophore AMPK activity reporter (ExRai AMPKAR), which reveals distinct kinetic profiles of AMPK activity at the mitochondria, lysosome, and cytoplasm. Genetic deletion of the canonical upstream kinase liver kinase B1 (LKB1) results in slower AMPK activity at lysosomes but does not affect the response amplitude at lysosomes or mitochondria, in sharp contrast to the necessity of LKB1 for maximal cytoplasmic AMPK activity. We further identify a mechanism for AMPK activity in the nucleus, which results from cytoplasmic to nuclear shuttling of AMPK. Thus, ExRai AMPKAR enables illumination of the complex subcellular regulation of AMPK signaling.
    DOI:  https://doi.org/10.1038/s41467-022-31190-x
  8. Nat Commun. 2022 Jul 08. 13(1): 3947
      Succinate dehydrogenase, which is known as mitochondrial complex II, has proven to be a fascinating machinery, attracting renewed and increased interest in its involvement in human diseases. Herein, we find that succinate dehydrogenase assembly factor 4 (SDHAF4) is downregulated in cardiac muscle in response to pathological stresses and in diseased hearts from human patients. Cardiac loss of Sdhaf4 suppresses complex II assembly and results in subunit degradation and complex II deficiency in fetal mice. These defects are exacerbated in young adults with globally impaired metabolic capacity and activation of dynamin-related protein 1, which induces excess mitochondrial fission and mitophagy, thereby causing progressive dilated cardiomyopathy and lethal heart failure in animals. Targeting mitochondria via supplementation with fumarate or inhibiting mitochondrial fission improves mitochondrial dynamics, partially restores cardiac function and prolongs the lifespan of mutant mice. Moreover, the addition of fumarate is found to dramatically improve cardiac function in myocardial infarction mice. These findings reveal a vital role for complex II assembly in the development of dilated cardiomyopathy and provide additional insights into therapeutic interventions for heart diseases.
    DOI:  https://doi.org/10.1038/s41467-022-31548-1
  9. Hemasphere. 2022 Jul;6(7): e740
      Cellular metabolism is a key regulator of hematopoietic stem cell (HSC) maintenance. HSCs rely on anaerobic glycolysis for energy production to minimize the production of reactive oxygen species and shift toward mitochondrial oxidative phosphorylation upon differentiation. However, increasing evidence has shown that HSCs still maintain a certain level of mitochondrial activity in quiescence, and exhibit high mitochondrial membrane potential, which both support proper HSC function. Since glycolysis and the tricarboxylic acid (TCA) cycle are not directly connected in HSCs, other nutrient pathways, such as amino acid and fatty acid metabolism, generate acetyl-CoA and provide it to the TCA cycle. In this review, we discuss recent insights into the regulatory roles of cellular metabolism in HSCs. Understanding the metabolic requirements of healthy HSCs is of critical importance to the development of new therapies for hematological disorders.
    DOI:  https://doi.org/10.1097/HS9.0000000000000740
  10. Cancer Metab. 2022 Jul 07. 10(1): 11
      BACKGROUND: 13C tracer analysis is increasingly used to monitor cellular metabolism in vivo and in intact cells, but data interpretation is still the key element to unveil the complexity of metabolic activities. The distinct 13C labeling patterns (e.g., M + 1 species in vivo but not in vitro) of metabolites from [U-13C]-glucose or [U-13C]-glutamine tracing in vivo and in vitro have been previously reported by multiple groups. However, the reason for the difference in the M + 1 species between in vivo and in vitro experiments remains poorly understood.METHODS: We have performed [U-13C]-glucose and [U-13C]-glutamine tracing in sarcoma-bearing mice (in vivo) and in cancer cell lines (in vitro). 13C enrichment of metabolites in cultured cells and tissues was determined by LC coupled with high-resolution mass spectrometry (LC-HRMS). All p-values are obtained from the Student's t-test two-tailed using GraphPad Prism 8 unless otherwise noted.
    RESULTS: We observed distinct enrichment patterns of tricarboxylic acid cycle intermediates in vivo and in vitro. As expected, citrate M + 2 or M + 4 was the dominant mass isotopologue in vitro. However, citrate M + 1 was unexpectedly the dominant isotopologue in mice receiving [U-13C]-glucose or [U-13C]-glutamine infusion, but not in cultured cells. Our results are consistent with a model where the difference in M + 1 species is due to the different sources of CO2 in vivo and in vitro, which was largely overlooked in the past. In addition, a time course study shows the generation of high abundance citrate M + 1 in plasma of mice as early as few minutes after [U-13C]-glucose infusion.
    CONCLUSIONS: Altogether, our results show that recycling of endogenous CO2 is substantial in vivo. The production and recycling of 13CO2 from the decarboxylation of [U-13C]-glucose or [U-13C]-glutamine is negligible in vitro partially due to dilution by the exogenous HCO3-/CO2 source, but in vivo incorporation of endogenous 13CO2 into M + 1 metabolites is substantial and should be considered. These findings provide a new paradigm to understand carbon atom transformations in vivo and should be taken into account when developing mathematical models to better reflect carbon flux.
    Keywords:  13C tracing; Anaplerotic metabolism; CO2 recycling; High-resolution mass spectrometry
    DOI:  https://doi.org/10.1186/s40170-022-00287-8
  11. Cell Stem Cell. 2022 Jul 07. pii: S1934-5909(22)00253-3. [Epub ahead of print]29(7): 1119-1134.e7
      Hematopoietic stem cells (HSCs) adapt their metabolism to maintenance and proliferation; however, the mechanism remains incompletely understood. Here, we demonstrated that homeostatic HSCs exhibited high amino acid (AA) catabolism to reduce cellular AA levels, which activated the GCN2-eIF2α axis, a protein synthesis inhibitory checkpoint to restrain protein synthesis for maintenance. Furthermore, upon proliferation conditions, HSCs enhanced mitochondrial oxidative phosphorylation (OXPHOS) for higher energy production but decreased AA catabolism to accumulate cellular AAs, which inactivated the GCN2-eIF2α axis to increase protein synthesis and coupled with proteotoxic stress. Importantly, GCN2 deletion impaired HSC function in repopulation and regeneration. Mechanistically, GCN2 maintained proteostasis and inhibited Src-mediated AKT activation to repress mitochondrial OXPHOS in HSCs. Moreover, the glycolytic metabolite, NAD+ precursor nicotinamide riboside (NR), accelerated AA catabolism to activate GCN2 and sustain the long-term function of HSCs. Overall, our study uncovered direct links between metabolic alterations and translation control in HSCs during homeostasis and proliferation.
    Keywords:  GCN2; amino acid; hematopoietic stem cells; metabolism; nicotinamide riboside; oxidative phosphorylation; protein translation; proteostasis
    DOI:  https://doi.org/10.1016/j.stem.2022.06.004
  12. Front Neurosci. 2022 ;16 900338
      Neurodegenerative diseases (NDs) are generally considered proteinopathies but whereas this may initiate disease in familial cases, onset in sporadic diseases may originate from a gradually disrupted organellar homeostasis. Herein, endolysosomal abnormalities, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and altered lipid metabolism are commonly observed in early preclinical stages of major NDs, including Parkinson's disease (PD) and Alzheimer's disease (AD). Among the multitude of underlying defective molecular mechanisms that have been suggested in the past decades, dysregulation of inter-organellar communication through the so-called membrane contact sites (MCSs) is becoming increasingly apparent. Although MCSs exist between almost every other type of subcellular organelle, to date, most focus has been put on defective communication between the ER and mitochondria in NDs, given these compartments are critical in neuronal survival. Contributions of other MCSs, notably those with endolysosomes and lipid droplets are emerging, supported as well by genetic studies, identifying genes functionally involved in lysosomal homeostasis. In this review, we summarize the molecular identity of the organelle interactome in yeast and mammalian cells, and critically evaluate the evidence supporting the contribution of disturbed MCSs to the general disrupted inter-organellar homeostasis in NDs, taking PD and AD as major examples.
    Keywords:  endolysosome; inter-organellar communication; lipid metabolism; membrane contact site; mitochondria; neurodegenerative disease
    DOI:  https://doi.org/10.3389/fnins.2022.900338
  13. Biochem Biophys Res Commun. 2022 Jun 28. pii: S0006-291X(22)00952-4. [Epub ahead of print]621 1-7
      Hepatic gluconeogenesis is crucial for maintaining blood glucose during starvation, and a major contributor for hyperglycemia. Cellular redox state is related to mitochondrial biology and regulates conversion of specific metabolites to glucose. General control of amino acid synthesis 5 (GCN5) like-1 (GCN5L1) is a mitochondria-enriched protein which modulates glucose and amino acid metabolism. Here we show a new regulatory mode of GCN5L1 on gluconeogenesis using lactate and glycerol. We observed GCN5L1 deletion dramatically inhibited glucose production derived from glycerol and lactate, due to increased cytosolic redox state. The underlying mechanism is that GCN5L1 directly binds to the key component of mitochondrial shuttle glycerol phosphate dehydrogenase 2 (GPD2) and modulates its activity. These results have significant implications for understanding the physiological role and regulatory mechanism of mitochondrial shuttle in diabetes development and provide a novel therapeutic potential for diabetes.
    Keywords:  Cytosolic redox state; GCN5L1; Gluconeogenesis; Glycerol-3-phosphate dehydrogenase 2; Mitochondrial redox state
    DOI:  https://doi.org/10.1016/j.bbrc.2022.06.092
  14. Cell Metab. 2022 Jul 05. pii: S1550-4131(22)00229-7. [Epub ahead of print]34(7): 944-946
      Tumor-supporting roles of ammonia have gained greater appreciation in recent years and normally focus on ammonia's role as a nitrogen source. Recently in Nature Metabolism,Cheng et al. (2022) demonstrate a novel, non-nitrogen, metabolism-related role of ammonia as a key activator for lipogenesis by facilitating SREBP-1 activation.
    DOI:  https://doi.org/10.1016/j.cmet.2022.06.009
  15. Cell Rep. 2022 Jul 05. pii: S2211-1247(22)00826-9. [Epub ahead of print]40(1): 111032
      How mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of cellular metabolism, affects dendritic cell (DC) metabolism and T cell-priming capacity has primarily been investigated in vitro, but how mTORC1 regulates this in vivo remains poorly defined. Here, using mice deficient for mTORC1 component raptor in DCs, we find that loss of mTORC1 negatively affects glycolytic and fatty acid metabolism and maturation of conventional DCs, particularly cDC1s. Nonetheless, antigen-specific CD8+ T cell responses to infection are not compromised and are even enhanced following skin immunization. This is associated with increased activation of Langerhans cells and a subpopulation of EpCAM-expressing cDC1s, of which the latter show an increased physical interaction with CD8+ T cells in situ. Together, this work reveals that mTORC1 limits CD8+ T cell priming in vivo by differentially orchestrating the metabolism and immunogenicity of distinct antigen-presenting cell subsets, which may have implications for clinical use of mTOR inhibitors.
    Keywords:  CD8(+) T cells; CP: Immunology; IL-12; Langerhans cells; MHCI; immunization; mTORC1; metabolism; type 1 conventional dendritic cells
    DOI:  https://doi.org/10.1016/j.celrep.2022.111032
  16. Nat Cell Biol. 2022 Jul 07.
      Anchored cells of the basal epidermis constantly undergo proliferation in an overcrowded environment. An important regulator of epidermal proliferation is YAP, which can be controlled by both cell-matrix and cell-cell interactions. Here, we report that THY1, a GPI-anchored protein, inhibits epidermal YAP activity through converging molecular mechanisms. THY1 deficiency leads to increased adhesion by activating the integrin-β1-SRC module. Notably, regardless of high cellular densities, the absence of THY1 leads to the dissociation of an adherens junction complex that enables the release and translocation of YAP. Due to increased YAP-dependent proliferation, Thy1-/- mice display enhanced wound repair and hair follicle regeneration. Taken together, our work reveals THY1 as a crucial regulator of cell-matrix and cell-cell interactions that controls YAP activity in skin homeostasis and regeneration.
    DOI:  https://doi.org/10.1038/s41556-022-00944-6
  17. Hepatology. 2022 Jul 05.
      BACKGROUND&AIM: Injury to hepatocyte mitochondria is common in metabolic dysfunction-associated fatty liver disease. Here, we investigated whether changes in the content of essential fatty acid-derived lipid autacoids affect hepatocyte mitochondrial bioenergetics and metabolic efficiency.APPROACH&RESULTS: The study was performed in transgenic mice for the fat-1 gene, which allows the endogenous replacement of the membrane omega-6-polyunsaturated fatty acid (PUFA) composition by omega-3-PUFA. Transmission electron microscopy revealed that hepatocyte mitochondria of fat-1 mice had more abundant intact cristae and higher mitochondrial aspect ratio. Fat-1 mice had increased expression of oxidative phosphorylation complexes I and II and translocases of both inner (TIM44) and outer (TOM20) mitochondrial membranes. Fat-1 mice also showed increased mitofusin-2 and reduced DRP1 phosphorylation, which mediate mitochondrial fusion and fission, respectively. Mitochondria of fat-1 mice exhibited enhanced oxygen consumption rate, fatty acid β-oxidation and energy substrate utilization as determined by high-resolution respirometry, [1-14 C]-oleate oxidation and NADH/FADH2 production, respectively. Untargeted lipidomics identified a rich hepatic omega-3-PUFA composition and a specific docosahexaenoic acid (DHA)-enriched lipid fingerprint in fat-1 mice. Targeted lipidomics uncovered a higher content of DHA-derived lipid autacoids, namely resolvin D1 and maresin 1, which rescued hepatocytes from TNFα-induced mitochondrial dysfunction, unblocked the tricarboxylic acid cycle flux and metabolic utilization of long-chain acyl-carnitines, amino acids and carbohydrates. Importantly, fat-1 mice were protected against mitochondrial injury induced by obesogenic and fibrogenic insults.
    CONCLUSION: Our data uncover the importance of a lipid membrane composition rich in DHA and its lipid autacoid derivatives to have optimal hepatic mitochondrial and metabolic efficiency.
    DOI:  https://doi.org/10.1002/hep.32647
  18. Cell. 2022 Jul 07. pii: S0092-8674(22)00708-5. [Epub ahead of print]185(14): 2401-2421
      Ferroptosis, a form of cell death driven by iron-dependent lipid peroxidation, was identified as a distinct phenomenon and named a decade ago. Ferroptosis has been implicated in a broad set of biological contexts, from development to aging, immunity, and cancer. This review describes key regulators of this form of cell death within a framework of metabolism, ROS biology, and iron biology. Key concepts and major unanswered questions in the ferroptosis field are highlighted. The next decade promises to yield further breakthroughs in the mechanisms governing ferroptosis and additional ways of harnessing ferroptosis for therapeutic benefit.
    DOI:  https://doi.org/10.1016/j.cell.2022.06.003
  19. Nature. 2022 Jul 05.
      Brown adipose tissue (BAT) dissipates energy1,2 and promotes cardio-metabolic health3. Loss of BAT during obesity and aging is a principal hurdle for BAT-centered obesity therapies, but not much is known about BAT apoptosis. Here, untargeted metabolomics demonstrated that apoptotic brown adipocytes release a specific pattern of metabolites with purine metabolites being highly enriched. Interestingly, this apoptotic secretome enhances expression of the thermogenic program in healthy adipocytes. This effect is mediated by the purine inosine which stimulates energy expenditure (EE) in brown adipocytes via the cAMP/protein kinase A signaling pathway. Treatment of mice with inosine increased BAT-dependent EE and induced "browning" of white adipose tissue. Mechanistically, the equilibrative nucleoside transporter 1 (ENT1, SLC29A1) regulates inosine levels in BAT: ENT1-deficiency increases extracellular inosine levels and consequently enhances thermogenic adipocyte differentiation. In mice, pharmacological inhibition of ENT1 as well as global and adipose-specific ablation enhanced BAT activity and counteracted diet-induced obesity, respectively. In human brown adipocytes, knockdown or blockade of ENT1 increased extracellular inosine, which enhanced thermogenic capacity. Conversely, high ENT1 levels correlated with lower expression of the thermogenic marker UCP1 in human adipose tissues. Finally, the Ile216Thr loss of function mutation in human ENT1 was associated with significantly lower BMI and 59% lower odds of obesity for individuals carrying the Thr variant. Our data identify inosine as a metabolite released during apoptosis with "replace me" signaling function that regulates thermogenic fat and counteracts obesity.
    DOI:  https://doi.org/10.1038/s41586-022-05041-0
  20. Nutrients. 2022 Jul 01. pii: 2752. [Epub ahead of print]14(13):
      Through evolution, eukaryote organisms have developed the ability to use different molecules as independent precursors to generate nicotinamide adenine dinucleotide (NAD+), an essential molecule for life. However, whether these different precursors act in an additive or complementary manner is not truly well understood. Here, we have evaluated how combinations of different NAD+ precursors influence intracellular NAD+ levels. We identified dihydronicotinic acid riboside (NARH) as a new NAD+ precursor in hepatic cells. Second, we demonstrate how NARH, but not any other NAD+ precursor, can act synergistically with nicotinamide riboside (NR) to increase NAD+ levels in cultured cells and in mice. Finally, we demonstrate that the large increase in NAD+ prompted by the combination of these two precursors is due to their chemical interaction and conversion to dihydronicotinamide riboside (NRH). Altogether, this work demonstrates for the first time that NARH can act as a NAD+ precursor in mammalian cells and how different NAD+ precursors can interact and influence each other when co-administered.
    Keywords:  NAD+; dihydronicotinamide riboside; dihydronicotinic acid riboside; nicotinamide; nicotinamide riboside; nicotinic acid; nicotinic acid riboside; vitamin B3
    DOI:  https://doi.org/10.3390/nu14132752
  21. Nat Commun. 2022 Jul 04. 13(1): 3835
      Global obesity epidemics impacts human health and causes obesity-related illnesses, including the obesity-related kidney and liver diseases. UTX, a histone H3K27 demethylase, plays important roles in development and differentiation. Here we show that kidney-specific knockout Utx inhibits high-fat diet induced lipid accumulation in the kidney and liver via upregulating circulating serine levels. Mechanistically, UTX recruits E3 ligase RNF114 to ubiquitinate phosphoglycerate dehydrogenase, the rate limiting enzyme for de novo serine synthesis, at Lys310 and Lys330, which leads to its degradation, and thus suppresses renal and circulating serine levels. Consistently, phosphoglycerate dehydrogenase and serine levels are markedly downregulated in human subjects with diabetic kidney disease or obesity-related renal dysfunction. Notably, oral administration of serine ameliorates high-fat diet induced fatty liver and renal dysfunction, suggesting a potential approach against obesity related metabolic disorders. Together, our results reveal a metabolic homeostasis regulation mediated by a renal UTX-PHGDH-serine axis.
    DOI:  https://doi.org/10.1038/s41467-022-31476-0
  22. Front Microbiol. 2022 ;13 908304
      The accumulation of the compatible solute L-proline by Bacillus subtilis via synthesis is a cornerstone in the cell's defense against high salinity as the genetic disruption of this biosynthetic process causes osmotic sensitivity. To understand how B. subtilis could potentially cope with high osmolarity surroundings without the functioning of its natural osmostress adaptive L-proline biosynthetic route (ProJ-ProA-ProH), we isolated suppressor strains of proA mutants under high-salinity growth conditions. These osmostress-tolerant strains carried mutations affecting either the AhrC transcriptional regulator or its operator positioned in front of the argCJBD-carAB-argF L-ornithine/L-citrulline/L-arginine biosynthetic operon. Osmostress protection assays, molecular analysis and targeted metabolomics showed that these mutations, in conjunction with regulatory mutations affecting rocR-rocDEF expression, connect and re-purpose three different physiological processes: (i) the biosynthetic pathway for L-arginine, (ii) the RocD-dependent degradation route for L-ornithine, and (iii) the last step in L-proline biosynthesis. Hence, osmostress adaptation without a functional ProJ-ProA-ProH route is made possible through a naturally existing, but inefficient, metabolic shunt that allows to substitute the enzyme activity of ProA by feeding the RocD-formed metabolite γ-glutamate-semialdehyde/Δ1-pyrroline-5-carboxylate into the biosynthetic route for the compatible solute L-proline. Notably, in one class of mutants, not only substantial L-proline pools but also large pools of L-citrulline were accumulated, a rather uncommon compatible solute in microorganisms. Collectively, our data provide an example of the considerable genetic plasticity and metabolic resourcefulness of B. subtilis to cope with everchanging environmental conditions.
    Keywords:  L-proline; compatible solutes; gene regulation; metabolomics; osmotic stress; suppressor mutations
    DOI:  https://doi.org/10.3389/fmicb.2022.908304
  23. Neurobiol Dis. 2022 Jun 30. pii: S0969-9961(22)00200-5. [Epub ahead of print]171 105808
      Wallerian degeneration (WD) is a conserved axonal self-destruction program implicated in several neurological diseases. WD is driven by the degradation of the NAD+ synthesizing enzyme NMNAT2, the buildup of its substrate NMN, and the activation of the NAD+ degrading SARM1, eventually leading to axonal fragmentation. The regulation and amenability of these events to therapeutic interventions remain unclear. Here we explored pharmacological strategies that modulate NMN and NAD+ metabolism, namely the inhibition of the NMN-synthesizing enzyme NAMPT, activation of the nicotinic acid riboside (NaR) salvage pathway and inhibition of the NMNAT2-degrading DLK MAPK pathway in an axotomy model in vitro. Results show that NAMPT and DLK inhibition cause a significant but time-dependent delay of WD. These time-dependent effects are related to NMNAT2 degradation and changes in NMN and NAD+ levels. Supplementation of NAMPT inhibition with NaR has an enhanced effect that does not depend on timing of intervention and leads to robust protection up to 4 days. Additional DLK inhibition extends this even further to 6 days. Metabolite analyses reveal complex effects indicating that NAMPT and MAPK inhibition act by reducing NMN levels, ameliorating NAD+ loss and suppressing SARM1 activity. Finally, the axonal NAD+/NMN ratio is highly predictive of cADPR levels, extending previous cell-free evidence on the allosteric regulation of SARM1. Our findings establish a window of axon protection extending several hours following injury. Moreover, we show prolonged protection by mixed treatments combining MAPK and NAMPT inhibition that proceed via complex effects on NAD+ metabolism and inhibition of SARM1.
    Keywords:  NAD(+); NMNAT2; Neurodegeneration; Neuropathy; Niacin; SARM1
    DOI:  https://doi.org/10.1016/j.nbd.2022.105808
  24. Nat Commun. 2022 Jul 08. 13(1): 3956
      β-Adrenergic signaling is a core regulator of brown adipocyte function stimulating both lipolysis and transcription of thermogenic genes, thereby expanding the capacity for oxidative metabolism. We have used pharmacological inhibitors and a direct activator of lipolysis to acutely modulate the activity of lipases, thereby enabling us to uncover lipolysis-dependent signaling pathways downstream of β-adrenergic signaling in cultured brown adipocytes. Here we show that induction of lipolysis leads to acute induction of several gene programs and is required for transcriptional regulation by β-adrenergic signals. Using machine-learning algorithms to infer causal transcription factors, we show that PPARs are key mediators of lipolysis-induced activation of genes involved in lipid metabolism and thermogenesis. Importantly, however, lipolysis also activates the unfolded protein response and regulates the core circadian transcriptional machinery independently of PPARs. Our results demonstrate that lipolysis generates important metabolic signals that exert profound pleiotropic effects on transcription and function of cultured brown adipocytes.
    DOI:  https://doi.org/10.1038/s41467-022-31525-8
  25. Cell Metab. 2022 Jul 05. pii: S1550-4131(22)00224-8. [Epub ahead of print]34(7): 937-939
      
    DOI:  https://doi.org/10.1016/j.cmet.2022.06.004
  26. Annu Rev Cell Dev Biol. 2022 Jul 08.
      Cellular senescence is implicated in a wide range of physiological and pathological conditions throughout an organism's entire lifetime. In particular, it has become evident that senescence plays a causative role in aging and age-associated disorders. This is not due simply to the loss of function of senescent cells. Instead, the substantial alterations of the cellular activities of senescent cells, especially the array of secretory factors, impacts the surrounding tissues or even entire organisms. Such non-cell-autonomous functionality is largely coordinated by tissue-specific genes, constituting a cell fate-determining state. Senescence can be viewed as a gain-of-function phenotype or a process of cell identity shift. Cellular functionality or lineage-specific gene expression is tightly linked to the cell type-specific epigenetic landscape, reinforcing the heterogeneity of senescence across cell types. Here, we aim to define the senescence cellular functionality and epigenetic features that may contribute to the gain-of-function phenotype. Expected final online publication date for the Annual Review of Cell and Developmental Biology Volume 38 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
    DOI:  https://doi.org/10.1146/annurev-cellbio-120420-013537
  27. Int J Mol Sci. 2022 Jul 05. pii: 7467. [Epub ahead of print]23(13):
      During erythropoiesis, there is an enormous demand for the synthesis of the essential cofactor of hemoglobin, heme. Heme is synthesized de novo via an eight enzyme-catalyzed pathway within each developing erythroid cell. A large body of data exists to explain the transcriptional regulation of the heme biosynthesis enzymes, but until recently much less was known about alternate forms of regulation that would allow the massive production of heme without depleting cellular metabolites. Herein, we review new studies focused on the regulation of heme synthesis via carbon flux for porphyrin synthesis to post-translations modifications (PTMs) that regulate individual enzymes. These PTMs include cofactor regulation, phosphorylation, succinylation, and glutathionylation. Additionally discussed is the role of the immunometabolite itaconate and its connection to heme synthesis and the anemia of chronic disease. These recent studies provide new avenues to regulate heme synthesis for the treatment of diseases including anemias and porphyrias.
    Keywords:  aminolevulinic acid synthase; ferrochelatase; heme; iron; itaconate; porphyrin; posttranslational modification
    DOI:  https://doi.org/10.3390/ijms23137467
  28. JCI Insight. 2022 Jul 05. pii: e159430. [Epub ahead of print]
      NLRP3 inflammasome and interferon stimulated gene (ISG) induction are key biological drivers of ineffective hematopoiesis and inflammation in Myelodysplastic Syndromes (MDS). Gene mutations involving messenger RNA splicing and epigenetic regulatory pathways induce inflammasome activation and myeloid lineage skewing in MDS through yet undefined mechanisms. Using immortalized murine hematopoietic stem and progenitor cells harboring these somatic gene mutations and primary MDS bone marrow specimens, we show accumulation of unresolved R-loops and micronuclei with concurrent activation of the cytosolic sensor, cGAS. cGAS-STING signaling caused interferon stimulated gene (ISG) induction, NLRP3 inflammasome activation, and maturation of the effector protease, caspase-1. Deregulation of RNA polymerase III drives cytosolic R-loop generation, which upon inhibition, extinguishes ISG and inflammasome response. Mechanistically, caspase-1 degrades the master erythroid transcription factor, GATA1, provoking anemia and myeloid lineage bias that is reversed by cGAS inhibition in vitro and in Tet2-/- hematopoietic stem and progenitor cell transplanted mice. Together, these data identity a novel mechanism by which functionally distinct mutations converge upon the cGAS-STING-NLRP3 axis in MDS directing ISG induction, pyroptosis and myeloid lineage skewing.
    Keywords:  Hematology; Leukemias; Oncology
    DOI:  https://doi.org/10.1172/jci.insight.159430
  29. Gut. 2022 Jul 08. pii: gutjnl-2022-326928. [Epub ahead of print]
      OBJECTIVE: Methionine metabolism is involved in a myriad of cellular functions, including methylation reactions and redox maintenance. Nevertheless, it remains unclear whether methionine metabolism, RNA methylation and antitumour immunity are molecularly intertwined.DESIGN: The antitumour immunity effect of methionine-restricted diet (MRD) feeding was assessed in murine models. The mechanisms of methionine and YTH domain-containing family protein 1 (YTHDF1) in tumour immune escape were determined in vitro and in vivo. The synergistic effects of MRD or YTHDF1 depletion with PD-1 blockade were also investigated.
    RESULTS: We found that dietary methionine restriction reduced tumour growth and enhanced antitumour immunity by increasing the number and cytotoxicity of tumour-infiltrating CD8+ T cells in different mouse models. Mechanistically, the S-adenosylmethionine derived from methionine metabolism promoted the N6-methyladenosine (m6A) methylation and translation of immune checkpoints, including PD-L1 and V-domain Ig suppressor of T cell activation (VISTA), in tumour cells. Furthermore, MRD or m6A-specific binding protein YTHDF1 depletion inhibited tumour growth by restoring the infiltration of CD8+ T cells, and synergised with PD-1 blockade for better tumour control. Clinically, YTHDF1 expression correlated with poor prognosis and immunotherapy outcomes for cancer patients.
    CONCLUSIONS: Methionine and YTHDF1 play a critical role in anticancer immunity through regulating the functions of T cells. Targeting methionine metabolism or YTHDF1 could be a potential new strategy for cancer immunotherapy.
    Keywords:  colorectal cancer; immunotherapy; methylation
    DOI:  https://doi.org/10.1136/gutjnl-2022-326928
  30. Nature. 2022 Jul 06.
      Individuals can exhibit differences in metabolism that are caused by the interplay of genetic background, nutritional input, microbiota and other environmental factors1-4. It is difficult to connect differences in metabolism to genomic variation and derive underlying molecular mechanisms in humans, owing to differences in diet and lifestyle, among others. Here we use the nematode Caenorhabditis elegans as a model to study inter-individual variation in metabolism. By comparing three wild strains and the commonly used N2 laboratory strain, we find differences in the abundances of both known metabolites and those that have not to our knowledge been previously described. The latter metabolites include conjugates between 3-hydroxypropionate (3HP) and several amino acids (3HP-AAs), which are much higher in abundance in one of the wild strains. 3HP is an intermediate in the propionate shunt pathway, which is activated when flux through the canonical, vitamin-B12-dependent propionate breakdown pathway is perturbed5. We show that increased accumulation of 3HP-AAs is caused by genetic variation in HPHD-1, for which 3HP is a substrate. Our results suggest that the production of 3HP-AAs represents a 'shunt-within-a-shunt' pathway to accommodate a reduction-of-function allele in hphd-1. This study provides a step towards the development of metabolic network models that capture individual-specific differences of metabolism and more closely represent the diversity that is found in entire species.
    DOI:  https://doi.org/10.1038/s41586-022-04951-3
  31. JCI Insight. 2022 Jul 07. pii: e159204. [Epub ahead of print]
      Hepatic de novo lipogenesis is influenced by the branched-chain α-keto acid dehydrogenase (BCKDH) kinase (BCKDK). We aimed to determine whether circulating levels of the immediate substrates of BCKDH, the branched-chain α-ketoacids (BCKAs) and hepatic BCKDK expression are associated with the presence and severity of non-alcoholic fatty liver disease (NAFLD). Eighty metabolites (3 BCKA, 14 amino acids, 43 acylcarnitines, 20 ceramides) were quantified in plasma from 288 bariatric surgery patients with severe obesity (BMI > 35 kg/m2) with scored liver biopsy samples. Metabolite principal component analysis (PCA) factors, BCKA, branched-chain amino acids (BCAA), and the BCKA:BCAA ratio were tested for associations with steatosis grade and presence of non-alcoholic steatohepatitis (NASH). Of all analytes tested, only the valine-derived BCKA, α-ketoisovalerate, and the BCKA:BCAA ratio were associated with both steatosis grade and NASH. Gene expression analysis in liver samples from two independent bariatric surgery cohorts showed that hepatic BCKDK mRNA expression correlates with steatosis, ballooning, and levels of the lipogenic transcription factor SREBP1. Experiments in AML12 hepatocytes showed that SREBP1 inhibition lowers BCKDK mRNA expression. These findings demonstrate that higher plasma levels of BCKA and hepatic expression of BCKDK are features of human NAFLD/NASH and identify SREBP1 as a transcriptional regulator of BCKDK.
    Keywords:  Amino acid metabolism; Hepatology; Metabolism; Obesity
    DOI:  https://doi.org/10.1172/jci.insight.159204
  32. Int J Biochem Cell Biol. 2022 Jul 04. pii: S1357-2725(22)00108-X. [Epub ahead of print] 106263
      Cancers are genetically divergent but intriguingly display similar patterns of epigenetic deregulation, including global DNA hypomethylation and hypermethylation of promoter CpG islands. Early developmental programmes mirror this cancer epigenome suggesting that reactivation of embryonic programmes is essential to the initiation of cancer. We propose a scenario where two waves of dedifferentiation underlie key cell transitions: the first from normal to cancer, and the second driving malignancy. The possibility that early developmental programmes underpin both normal development and the switch to cancer has huge therapeutic implications. The reignition of embryonic programmes and pluripotency networks in seemingly healthy tissues could provide unique cellular targets, to eliminate pre-cancerous or cancer promoting cells before they have the opportunity to form tumours. We conclude that focusing on epigenetic gatekeepers, and peri-implantation cellular identities, could transform the diagnosis and prevention of cancer, especially if these programmes crosscut many cancer types, solid and haematological.
    Keywords:  Dedifferentiation; embryogenesis; epigenetics; transformation
    DOI:  https://doi.org/10.1016/j.biocel.2022.106263
  33. Trends Cell Biol. 2022 Jul 01. pii: S0962-8924(22)00140-4. [Epub ahead of print]
      Peroxisomes are essential metabolic organelles, well known for their roles in the metabolism of complex lipids and reactive ionic species. In the past 10 years, peroxisomes have also been cast as central regulators of immunity. Lipid metabolites of peroxisomes, such as polyunsaturated fatty acids (PUFAs), are precursors for important immune mediators, including leukotrienes (LTs) and resolvins. Peroxisomal redox metabolism modulates cellular immune signaling such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. Additionally, peroxisomal β-oxidation and ether lipid synthesis control the development and aspects of the activation of both innate and adaptive immune cells. Finally, peroxisome number and metabolic activity have been linked to inflammatory diseases. These discoveries have opened avenues of investigation aimed at targeting peroxisomes for therapeutic intervention in immune disorders, inflammation, and cancer.
    Keywords:  host–pathogen interaction; immune signaling; immunometabolism; peroxisome; phagocytosis
    DOI:  https://doi.org/10.1016/j.tcb.2022.06.001
  34. Oncogene. 2022 Jul 06.
      The transcription factor, forkhead box M1 (FOXM1), has been implicated in the natural history and outcome of newly diagnosed high-risk myeloma (HRMM) and relapsed/refractory myeloma (RRMM), but the mechanism with which FOXM1 promotes the growth of neoplastic plasma cells is poorly understood. Here we show that FOXM1 is a positive regulator of myeloma metabolism that greatly impacts the bioenergetic pathways of glycolysis and oxidative phosphorylation (OxPhos). Using FOXM1-deficient myeloma cells as principal experimental model system, we find that FOXM1 increases glucose uptake, lactate output, and oxygen consumption in myeloma. We demonstrate that the novel 1,1-diarylethylene small-compound FOXM1 inhibitor, NB73, suppresses myeloma in cell culture and human-in-mouse xenografts using a mechanism that includes enhanced proteasomal FOXM1 degradation. Consistent with the FOXM1-stabilizing chaperone function of heat shock protein 90 (HSP90), the HSP90 inhibitor, geldanamycin, collaborates with NB73 in slowing down myeloma. These findings define FOXM1 as a key driver of myeloma metabolism and underscore the feasibility of targeting FOXM1 for new approaches to myeloma therapy and prevention.
    DOI:  https://doi.org/10.1038/s41388-022-02398-4
  35. Nat Commun. 2022 Jul 04. 13(1): 3837
      Single-cell analysis methods are valuable tools; however, current approaches do not easily enable live cell retrieval. That is a particular issue when further study of cells that were eliminated during experimentation could provide critical information. We report a clonal molecular barcoding method, called SunCatcher, that enables longitudinal tracking and live cell functional analysis. From complex cell populations, we generate single cell-derived clonal populations, infect each with a unique molecular barcode, and retain stocks of individual barcoded clones (BCs). We develop quantitative PCR-based and next-generation sequencing methods that we employ to identify and quantify BCs in vitro and in vivo. We apply SunCatcher to various breast cancer cell lines and combine respective BCs to create versions of the original cell lines. While the heterogeneous BC pools reproduce their original parental cell line proliferation and tumor progression rates, individual BCs are phenotypically and functionally diverse. Early spontaneous metastases can also be identified and quantified. SunCatcher thus provides a rapid and sensitive approach for studying live single-cell clones and clonal evolution, and performing functional analyses.
    DOI:  https://doi.org/10.1038/s41467-022-31536-5