bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2020‒09‒20
39 papers selected by
Kelsey Fisher-Wellman, East Carolina University

  1. Sci Rep. 2020 Sep 14. 10(1): 15021
      Ubiquinol-cytochrome c reductase hinge protein (UQCRH) is the hinge protein for the multi-subunit complex III of the mitochondrial electron transport chain and is involved in the electron transfer reaction between cytochrome c1 and c. Recent genome-wide transcriptomic and epigenomic profiling of clear cell renal cell carcinoma (ccRCC) by The Cancer Genome Atlas (TCGA) identified UQCRH as the top-ranked gene showing inverse correlation between DNA hypermethylation and mRNA downregulation. The function and underlying mechanism of UQCRH in the Warburg effect metabolism of ccRCC have not been characterized. Here, we verified the clinical association of low UQCRH expression and shorter survival of ccRCC patients through in silico analysis and identified KMRC2 as a highly relevant ccRCC cell line that displays hypermethylation-induced UQCRH extinction. Ectopic overexpression of UQCRH in KMRC2 restored mitochondrial membrane potential, increased oxygen consumption, and attenuated the Warburg effect at the cellular level. UQCRH overexpression in KMRC2 induced higher apoptosis and slowed down in vitro and in vivo tumor growth. UQCRH knockout by CRISPR/Cas9 had little impact on the metabolism and proliferation of 786O ccRCC cell line, suggesting the dispensable role of UQCRH in cells that have entered a Warburg-like state through other mechanisms. Together, our study suggests that loss of UQCRH expression by hypermethylation may promote kidney carcinogenesis through exacerbating the functional decline of mitochondria thus reinforcing the Warburg effect.
  2. Pharmacol Res. 2020 Sep 09. pii: S1043-6618(20)31504-8. [Epub ahead of print] 105196
      SAM50, a 7-8 nm diameter β-barrel channel of the mitochondrial outer membrane, is the central channel of the sorting and assembly machinery (SAM) complex involved in the biogenesis of β-barrel proteins. Interestingly, SAM50 is not known to have channel translocase activity; however, we have recently found that this channel is necessary and sufficient for mitochondrial entry of cytotoxic proteases. Cytotoxic lymphocytes eliminate cells that pose potential hazards, such as virus- and bacteria-infected cells as well as cancer cells. They induce cell death following the delivery of granzyme cytotoxic proteases into the cytosol of the target cell. Although granzyme A and granzyme B (GA and GB), the best characterized of the five human granzymes, trigger very distinct apoptotic cascades, they share the ability to directly target the mitochondria. GA and GB do not have a mitochondrial targeting signal, yet they enter the target cell mitochondria to disrupt respiratory chain complex I and induce mitochondrial reactive oxygen species (ROS)-dependent cell death. We found that granzyme mitochondrial entry requires SAM50 and the translocase of the inner membrane 22 (TIM22). Preventing granzymes' mitochondrial entry compromises their cytotoxicity, indicating that this event is unexpectedly an important step for cell death. Although mitochondria are best known for their roles in cell metabolism and energy conversion, these double-membrane organelles are also involved in Ca2+ homeostasis, metabolite transport, cell cycle regulation, cell signaling, differentiation, stress response, redox homeostasis, aging, and cell death. This multiplicity of functions is matched with the complexity and plasticity of the mitochondrial proteome as well as the organelle's morphological and structural versatility. Indeed, mitochondria are extremely dynamic and undergo fusion and fission events in response to diverse cellular cues. In humans, there are 1,500 different mitochondrial proteins, the vast majority of which are encoded in the nuclear genome and translated by cytosolic ribosomes, after which they must be imported and properly addressed to the right mitochondrial compartment. To this end, mitochondria are equipped with a very sophisticated and highly specific protein import machinery. The latter is centered on translocase complexes embedded in the outer and inner mitochondrial membranes working along five different import pathways. We will briefly describe these import pathways to put into perspective our finding regarding the ability of granzymes to enter the mitochondria.
    Keywords:  SAM50; cytotoxic lymphocytes; granzyme; mitochondria; mitochondrial protein import
  3. Biochim Biophys Acta Mol Cell Res. 2020 Sep 11. pii: S0167-4889(20)30212-3. [Epub ahead of print] 118854
      Mitochondria are highly dynamic organelles. Alterations in mitochondrial dynamics are causal or are linked to numerous neurodegenerative, neuromuscular, and metabolic diseases. It is generally thought that cells with altered mitochondrial structure are prone to mitochondrial dysfunction, increased reactive oxygen species generation and widespread oxidative damage. The objective of the current study was to investigate the relationship between mitochondrial dynamics and the master cellular antioxidant, glutathione (GSH). We reveal that mouse embryonic fibroblasts (MEFs) lacking the mitochondrial fusion machinery display elevated levels of GSH, which limits oxidative damage. Moreover, targeted metabolomics and 13C isotopic labeling experiments demonstrate that cells lacking the inner membrane fusion GTPase OPA1 undergo widespread metabolic remodeling altering the balance of citric acid cycle intermediates and ultimately favoring GSH synthesis. Interestingly, the GSH precursor and antioxidant n-acetylcysteine did not increase GSH levels in OPA1 KO cells, suggesting that cysteine is not limiting for GSH production in this context. Post-mitotic neurons were unable to increase GSH production in the absence of OPA1. Finally, the ability to use glycolysis for ATP production was a requirement for GSH accumulation following OPA1 deletion. Thus, our results demonstrate a novel role for mitochondrial fusion in the regulation of GSH synthesis, and suggest that cysteine availability is not limiting for GSH synthesis in conditions of mitochondrial fragmentation. These findings provide a possible explanation for the heightened sensitivity of certain cell types to alterations in mitochondrial dynamics.
    Keywords:  Mitofusin 1 & 2; Optic Atrophy 1; glutathione; metabolism; mitochondrial dynamics; mitochondrial fusion
  4. Nat Commun. 2020 Sep 17. 11(1): 4684
      Cancer cells have a characteristic metabolism, mostly caused by alterations in signal transduction networks rather than mutations in metabolic enzymes. For metabolic drugs to be cancer-selective, signaling alterations need to be identified that confer a druggable vulnerability. Here, we demonstrate that many tumor cells with an acquired cancer drug resistance exhibit increased sensitivity to mechanistically distinct inhibitors of cancer metabolism. We demonstrate that this metabolic vulnerability is driven by mTORC1, which promotes resistance to chemotherapy and targeted cancer drugs, but simultaneously suppresses autophagy. We show that autophagy is essential for tumor cells to cope with therapeutic perturbation of metabolism and that mTORC1-mediated suppression of autophagy is required and sufficient for generating a metabolic vulnerability leading to energy crisis and apoptosis. Our study links mTOR-induced cancer drug resistance to autophagy defects as a cause of a metabolic liability and opens a therapeutic window for the treatment of otherwise therapy-refractory tumor patients.
  5. Sci Adv. 2020 Jul;pii: eaba5345. [Epub ahead of print]6(31):
      Heteroplasmy, multiple variants of mitochondrial DNA (mtDNA) in the same cytoplasm, may be naturally generated by mutations but is counteracted by a genetic mtDNA bottleneck during oocyte development. Engineered heteroplasmic mice with nonpathological mtDNA variants reveal a nonrandom tissue-specific mtDNA segregation pattern, with few tissues that do not show segregation. The driving force for this dynamic complex pattern has remained unexplained for decades, challenging our understanding of this fundamental biological problem and hindering clinical planning for inherited diseases. Here, we demonstrate that the nonrandom mtDNA segregation is an intracellular process based on organelle selection. This cell type-specific decision arises jointly from the impact of mtDNA haplotypes on the oxidative phosphorylation (OXPHOS) system and the cell metabolic requirements and is strongly sensitive to the nuclear context and to environmental cues.
  6. EMBO J. 2020 Sep 16. e103420
      Short telomeres are a principal defining feature of telomere biology disorders, such as dyskeratosis congenita (DC), for which there are no effective treatments. Here, we report that primary fibroblasts from DC patients and late generation telomerase knockout mice display lower nicotinamide adenine dinucleotide (NAD) levels, and an imbalance in the NAD metabolome that includes elevated CD38 NADase and reduced poly(ADP-ribose) polymerase and SIRT1 activities, respectively, affecting many associated biological pathways. Supplementation with the NAD precursor, nicotinamide riboside, and CD38 inhibition improved NAD homeostasis, thereby alleviating telomere damage, defective mitochondrial biosynthesis and clearance, cell growth retardation, and cellular senescence of DC fibroblasts. These findings reveal a direct, underlying role of NAD dysregulation when telomeres are short and underscore its relevance to the pathophysiology and interventions of human telomere-driven diseases.
    Keywords:  CD38 NADase; NAD metabolism; mitochondrial impairment; replicative senescence; telomere biology disorders
  7. Sci Rep. 2020 Sep 18. 10(1): 15336
      The study of skeletal muscle continues to support the accurate diagnosis of mitochondrial disease and remains important in delineating molecular disease mechanisms. The heterogeneous expression of oxidative phosphorylation proteins and resulting respiratory deficiency are both characteristic findings in mitochondrial disease, hence the rigorous assessment of these at a single cell level is incredibly powerful. Currently, the number of proteins that can be assessed in individual fibres from a single section by immunohistochemistry is limited but imaging mass cytometry (IMC) enables the quantification of further, discrete proteins in individual cells. We have developed a novel workflow and bespoke analysis for applying IMC in skeletal muscle biopsies from patients with genetically-characterised mitochondrial disease, investigating the distribution of nine mitochondrial proteins in thousands of single muscle fibres. Using a semi-automated analysis pipeline, we demonstrate the accurate quantification of protein levels using IMC, providing an accurate measure of oxidative phosphorylation deficiency for complexes I-V at the single cell level. We demonstrate signatures of oxidative phosphorylation deficiency for common mtDNA variants and nuclear-encoded complex I variants and a compensatory upregulation of unaffected oxidative phosphorylation components. This technique can now be universally applied to evaluate a wide range of skeletal muscle disorders and protein targets.
  8. Cancer Manag Res. 2020 ;12 8023-8035
      Objective: Monoamine oxidase A (MAO-A) is a mitochondrial protein involved in tumourigenesis in different types of cancer. However, the biological function of MAO-A in gastric cancer development remains unknown.Methods: We examined MAO-A expression in gastric cancer tissues and in gastric cancer cell lines by immunohistochemistry and Western blot analyses. CCK8, FACS and bromodeoxyuridine incorporation assays were performed to assess the effects of MAO-A on gastric cancer cell proliferation. The role of MAO-A in mitochondrial function was determined through MitoSOX Red staining, ATP generation and glycolysis assays.
    Results: In the present study, we observed that MAO-A was significantly upregulated in gastric cancer tissues and in AGS and MGC803 cells. The observed MAO-A inhibition indicated decreased cell cycle progression and proliferation. Silencing MAO-A expression was associated with suppressed migration and invasion of gastric cancer cells in vitro. Moreover, alleviated mitochondrial damage in these cells was demonstrated by decreased levels of mitochondrial reactive oxygen species and increased ATP generation. MAO-A knockdown also regulated the expression of the glycolysis rate-limiting enzymes hexokinase 2 and pyruvate dehydrogenase. Finally, we observed that the glycolysis-mediated effect was weakened in AGS and MGC803 cells when MAO-A was blocked.
    Conclusion: The findings of the present study indicate that MAO-A is responsible for mitochondrial dysfunction and aerobic glycolysis, which in turn leads to the proliferation and metastasis of human gastric tumour cells.
    Keywords:  gastric cancer; glycolysis; mitochondrial dysfunction; monoamine oxidase A
  9. Theranostics. 2020 ;10(22): 10290-10308
      Background: Oxidative stress from elevated reactive oxygen species (ROS) has been reported to induce cell apoptosis and may provide a means to target cancer cells. Celastrol is a natural bioactive compound that was recently shown to increase ROS levels and cause apoptosis in cancer cells. However, the underlying mechanism for this cytotoxic action remains unclear and direct molecular targets of Celastrol have not been identified. Methods: Proteome microarray, surface plasmon resonance, isothermal titration calorimetry and molecular simulation were used to identify the molecular target of Celastrol. Binding and activity assays were used to validate the interaction of Celastrol with target protein in cell-free and gastric cancer cell lysates. We then assessed target transcript levels in in biopsy specimens obtained from patients with gastric cancer. Gastric cancer growth-limiting and cytotoxic activity of Celastrol was evaluated in BALB/c nu/nu mice. Results: Our data show that Celastrol directly binds to an antioxidant enzyme, peroxiredoxin-2 (Prdx2), which then inhibits its enzyme activity at both molecular and cellular level. Inhibition of Prdx2 by Celastrol increased cellular ROS levels and led to ROS-dependent endoplasmic reticulum stress, mitochondrial dysfunction, and apoptosis in gastric cancer cells. Functional tests demonstrated that Celastrol limits gastric cancer cells, at least in part, through targeting Prdx2. Celastrol treatment of mice implanted with gastric cancer cells also inhibited tumor growth, associated with Prdx2 inhibition and increased ROS. Analysis of human gastric cancer also showed increased Prdx2 levels and correlation with survival. Conclusion: Our studies have uncovered a potential Celastrol-interacting protein Prdx2 and a ROS-dependent mechanism of its action. The findings also highlight Prdx2 as a potential target for the treatment of gastric cancer.
    Keywords:  Celastrol; Peroxiredoxin 2; gastric cancer; oxidative stress; reactive oxygen species
  10. Methods Mol Biol. 2021 ;2179 327-340
      The critical role of metabolism in facilitating cancer cell growth and survival has been demonstrated by a combination of methods including, but not limited to, genomic sequencing, transcriptomic and proteomic analyses, measurements of radio-labelled substrate flux and the high throughput measurement of oxidative metabolism in unlabelled live cells using the Seahorse Extracellular Flux (XF) technology. These studies have revealed that tumour cells exhibit a dynamic metabolic plasticity, using numerous pathways including both glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to support cell proliferation, energy production and the synthesis of biomass. These advanced technologies have also demonstrated metabolic differences between cancer cell types, between molecular subtypes within cancers and between cell states. This has been exemplified by examining the transitions of cancer cells between epithelial and mesenchymal phenotypes, referred to as epithelial-mesenchymal plasticity (EMP). A growing number of studies are demonstrating significant metabolic alterations associated with these transitions, such as increased use of glycolysis by triple negative breast cancers (TNBC) or glutamine addiction in lung cancer. Models of EMP, including invasive cell lines and xenografts, isolated circulating tumour cells and metastatic tissue have been used to examine EMP metabolism. Understanding the metabolism supporting molecular and cellular plasticity and increased metastatic capacity may reveal metabolic vulnerabilities that can be therapeutically exploited. This chapter describes protocols for using the Seahorse Extracellular Flux Analyzer (XFe96), which simultaneously performs real-time monitoring of oxidative phosphorylation and glycolysis in living cells. As an example, we compare the metabolic profiles generated from two breast cancer sublines that reflect epithelial and mesenchymal phenotypes, respectively. We use this example to show how the methodology described can generate bioenergetic results that in turn can be correlated to EMP phenotypes. Normalisation of bioenergetic studies should be considered with respect to cell number, and to potential differences in mitochondrial mass, itself being an important bioenergetics endpoint.
    Keywords:  Cellular bioenergetics; Epithelial-to-mesenchymal plasticity; Extracellular acidification; Glycolysis; Metabolic phenotype; Metabolism; Mitochondrial CMxRos; Mitochondrial RedFM; Oxidative phosphorylation; Oxygen consumption; Respiration; Seahorse Extracellular Flux Analyzer
  11. Cell Calcium. 2020 Aug 28. pii: S0143-4160(20)30122-6. [Epub ahead of print]92 102280
      Mitochondrial Ca2+ signaling is a well-appreciated regulator of cell metabolism and energy production. A major function of mitochondria in brown adipose tissue (BAT) is thermogenesis. Assali et al. offer new insights into how the mitochondrial Ca2+ extrusion mediator NCLX is crucial for BAT survival and thermogenesis.
    Keywords:  Brown adipose tissue; Mitochondrial Ca(2+) signaling; Mitochondrial Na(+)/Ca(2+) exchanger NCLX; Non-shivering thermogenesis
  12. BMC Cancer. 2020 Sep 18. 20(1): 896
      BACKGROUND: Anticancer compound 3-bromopyruvate (3-BrPA) suppresses cancer cell growth via targeting glycolytic and mitochondrial metabolism. The malignant peripheral nerve sheath tumor (MPNST), a very aggressive, therapy resistant, and Neurofibromatosis type 1 associated neoplasia, shows a high metabolic activity and affected patients may therefore benefit from 3-BrPA treatment. To elucidate the specific mode of action, we used a controlled cell model overexpressing proteasome activator (PA) 28, subsequently leading to p53 inactivation and oncogenic transformation and therefore reproducing an important pathway in MPNST and overall tumor pathogenesis.METHODS: Viability of MPNST cell lines S462, NSF1, and T265 in response to increasing doses (0-120 μM) of 3-BrPA was analyzed by CellTiter-Blue® assay. Additionally, we investigated viability, reactive oxygen species (ROS) production (dihydroethidium assay), nicotinamide adenine dinucleotide dehydrogenase activity (NADH-TR assay) and lactate production (lactate assay) in mouse B8 fibroblasts overexpressing PA28 in response to 3-BrPA application. For all experiments normal and nutrient deficient conditions were tested. MPNST cell lines were furthermore characterized immunohistochemically for Ki67, p53, bcl2, bcl6, cyclin D1, and p21.
    RESULTS: MPNST significantly responded dose dependent to 3-BrPA application, whereby S462 cells were most responsive. Human control cells showed a reduced sensitivity. In PA28 overexpressing cancer cell model 3-BrPA application harmed mitochondrial NADH dehydrogenase activity mildly and significantly failed to inhibit lactate production. PA28 overexpression was associated with a functional glycolysis as well as a partial resistance to stress provoked by nutrient deprivation. 3-BrPA treatment was not associated with an increase of ROS. Starvation sensitized MPNST to treatment.
    CONCLUSIONS: Aggressive MPNST cells are sensitive to 3-BrPA therapy in-vitro with and without starvation. In a PA28 overexpression cancer cell model leading to p53 inactivation, thereby reflecting a key molecular feature in human NF1 associated MPNST, known functions of 3-BrPA to block mitochondrial activity and glycolysis were reproduced, however oncogenic cells displayed a partial resistance. To conclude, 3-BrPA was sufficient to reduce NF1 associated MPNST viability potentially due inhibition of glycolysis which should lead to the initiation of further studies and promises a potential benefit for NF1 patients.
    Keywords:  3-BrPA; B8 fibroblasts; Cell cycle; Glycolysis; MPNST; Mitochondrial respiration; NF1; PA28; Starvation; p53
  13. Aging Cell. 2020 Sep 15. e13229
      Epigenetic clocks, developed using DNA methylation data, have been widely used to quantify biological aging in multiple tissues/cells. However, many existing epigenetic clocks are weakly correlated with each other, suggesting they may capture different biological processes. We utilize multi-omics data from diverse human tissue/cells to identify shared features across eleven existing epigenetic clocks. Despite the striking lack of overlap in CpGs, multi-omics analysis suggested five clocks (Horvath1, Horvath2, Levine, Hannum, and Lin) share transcriptional associations conserved across purified CD14+ monocytes and dorsolateral prefrontal cortex. The pathways enriched in the shared transcriptional association suggested links between epigenetic aging and metabolism, immunity, and autophagy. Results from in vitro experiments showed that two clocks (Levine and Lin) were accelerated in accordance with two hallmarks of aging-cellular senescence and mitochondrial dysfunction. Finally, using multi-tissue data to deconstruct the epigenetic clock signals, we developed a meta-clock that demonstrated improved prediction for mortality and robustly related to hallmarks of aging in vitro than single clocks.
    Keywords:  DNA methylation; biological aging; cellular senescence; epigenetic clock; mitochondria
  14. Biochim Biophys Acta Biomembr. 2020 Sep 12. pii: S0005-2736(20)30314-X. [Epub ahead of print] 183471
      Mitochondria have emerged as important determinants in cancer progression and malignancy. However, the role of mitochondrial membranes in cancer onset and progression has not been thoroughly investigated. This study compares the structural and functional properties of mitochondrial membranes in prostate and colon cancer cells in comparison to normal mitochondria, and possible therapeutic implications of these membrane changes. Specifically, isolation of cell mitochondria and preparation of inverted sub-mitochondrial particles (SMPs) illuminated significant cancer-induced modulations of membrane lipid compositions, fluidity, and activity of cytochrome c oxidase, one of the key mitochondrial enzymes. The experimental data further show that cancer-associated membrane transformations may account for mitochondria targeting by betulinic acid and resveratrol, known anti-cancer molecules. Overall, this study probes the relationship between cancer and mitochondrial membrane transformations, underlying a potential therapeutic significance for mitochondrial membrane targeting in cancer.
    Keywords:  Betulinic acid; Cardiolipin; Colon cancer; Mitochondrial membrane; Prostate cancer; Resveratrol; Submitochondrial particles (SMPs)
  15. Sci Adv. 2020 Aug;6(35): eaaz5752
      Hydrogen sulfide (H2S) is a gasotransmitter and a potential therapeutic agent. However, molecular targets relevant to its therapeutic actions remain enigmatic. Sulfide-quinone oxidoreductase (SQR) irreversibly oxidizes H2S. Therefore, SQR is assumed to inhibit H2S signaling. We now report that SQR-mediated oxidation of H2S drives reverse electron transport (RET) at mitochondrial complex I, which, in turn, repurposes mitochondrial function to superoxide production. Unexpectedly, complex I RET, a process dependent on high mitochondrial membrane potential, induces superoxide-dependent mitochondrial uncoupling and downstream activation of adenosine monophosphate-activated protein kinase (AMPK). SQR-induced mitochondrial uncoupling is separated from the inhibition of mitochondrial complex IV by H2S. Moreover, deletion of SQR, complex I, or AMPK abolishes therapeutic effects of H2S following intracerebral hemorrhage. To conclude, SQR mediates H2S signaling and therapeutic effects by targeting mitochondrial electron transport to induce mitochondrial uncoupling. Moreover, SQR is a previously unrecognized target for developing non-protonophore uncouplers with broad clinical implications.
  16. Cancer Sci. 2020 Sep 17.
      Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of hepatocellular carcinoma (HCC), but the underlying mechanisms behind the correlation of non-alcoholic fatty liver disease (NAFLD) with hepatocellular carcinoma (HCC) are unclear. We aim to uncover the genes and potential mechanisms that drive the progression. This study uncovered the genes and potential mechanisms through a multiple-omics integration approach. The quantitative proteomics combined with phenotype-association analysis was performed. To investigate the potential mechanisms, a comprehensive transcriptome/lipidome/phenome-wide association analysis was performed in Genetic reference panel BXD mice strains. The quantitative proteomics combined with phenotype-association results showed that VDAC1 was significantly increased in tumor tissues and correlated with NAFLD related traits. The gene co-expression network analysis indicated that VDAC1 is involved in mitochondria dysfunction in the tumorigenic/tumor progression. The association between VDAC1 and mitochondria dysfunction can be explained by VDAC1 is associated with mitochondria membrane lipids cardiolipin (CL) composition shift. VDAC1 is correlated with the suppression of mature specie CL(LLLL) and elevation level of nascent CL species. Such profiling shift was supported by the significant positive correlation between VDAC1 and PTPMT1, as well as negative correlation with CL remodeling enzyme Tafazzin (TAZ). This study confirmed that the expression of VADC1 is dysregulated in NAFLD-driven HCC and associated with NAFLD progression. The VDAC1-driven mitochondria dysfunction is associated with cardiolipin composition shift, which caused mitochondria membrane property alteration.
    Keywords:  Hepatocellular carcinoma (HCC); Mitochondria dysfunction; Non-alcoholic fatty liver disease (NAFLD); System biology; Voltage dependent anion channel (VDAC1)
  17. Front Oncol. 2020 ;10 1426
      Cancer cells adjust their metabolic profiles to evade treatment. Metabolic adaptation is complex and hence better understood by an integrated theoretical-experimental approach. Using a minimal kinetic model, we predicted a previously undescribed Low/Low (L/L) phenotype, characterized by low oxidative phosphorylation (OXPHOS) and low glycolysis. Here, we report that L/L metabolism is observed in BRAF-mutated melanoma cells that enter a drug-tolerant "idling state" upon long-term MAPK inhibition (MAPKi). Consistently, using publicly available RNA-sequencing data of both cell lines and patient samples, we show that melanoma cells decrease their glycolysis and/or OXPHOS activity upon MAPKi and converge toward the L/L phenotype. L/L metabolism is unfavorable for tumor growth, yet supports successful cell division at ~50% rate. Thus, L/L drug-tolerant idling cells are a reservoir for accumulating mutations responsible for relapse, and it should be considered as a target subpopulation for improving MAPKi outcomes in melanoma treatment.
    Keywords:  drug tolerance; idling; low-low; melanoma; metabolism
  18. Sci Adv. 2020 Aug;6(35): eabb0780
      The phospholipid cardiolipin has pleiotropic structural and functional roles that are collectively essential for mitochondrial biology. Yet, the molecular details of how this lipid supports the structure and function of proteins and protein complexes are poorly understood. To address this property of cardiolipin, we use the mitochondrial adenosine 5'-diphosphate/adenosine 5'-triphosphate carrier (Aac) as a model. Here, we have determined that cardiolipin is critical for both the tertiary and quaternary assembly of the major yeast Aac isoform Aac2 as well as its conformation. Notably, these cardiolipin-provided structural roles are separable. In addition, we show that multiple copies of Aac2 engage in shared complexes that are largely dependent on the presence of assembled respiratory complexes III and IV or respiratory supercomplexes. Intriguingly, the assembly state of Aac2 is sensitive to its transport-related conformation. Together, these results expand our understanding of the numerous structural roles provided by cardiolipin for mitochondrial membrane proteins.
  19. Cancers (Basel). 2020 Sep 15. pii: E2632. [Epub ahead of print]12(9):
      Mitochondrial respiratory defects have been implicated in cancer progression and metastasis, but how they control tumor cell aggressiveness remains unclear. Here, we demonstrate that a mitochondrial respiratory defect induces nuclear factor-erythroid 2 like 1 (NFE2L1) expression at the transcriptional level via reactive oxygen species (ROS)-mediated STAT3 activation. We identified syntaxin 12 (STX12) as an effective downstream target of NFE2L1 by performing cDNA microarray analysis after the overexpression and depletion of NFE2L1 in hepatoma cells. Bioinformatics analysis of The Cancer Genome Atlas Liver Hepatocellular carcinoma (TCGA-LIHC) open database (n = 371) also revealed a significant positive association (r = 0.3, p = 2.49 × 10-9) between NFE2L1 and STX12 expression. We further demonstrated that STX12 is upregulated through the ROS/STAT3/NFE2L1 axis and is a key downstream effector of NFE2L1 in modulating hepatoma cell invasiveness. In addition, gene enrichment analysis of TCGA-LIHC also showed that epithelial-mesenchymal transition (EMT)-related core genes are significantly upregulated in tumors co-expressing NFE2L1 and STX12. The positive association between NFE2L1 and STX12 expression was validated by immunohistochemistry of the hepatocellular carcinoma tissue array. Finally, higher EMT gene enrichment and worse overall survival (p = 0.043) were observed in the NFE2L1 and STX12 co-expression group with mitochondrial defect, as indicated by low NDUFA9 expression. Collectively, our results indicate that NFE2L1 is a key mitochondrial retrograde signaling-mediated primary gene product enhancing hepatoma cell invasiveness via STX12 expression and promoting liver cancer progression.
    Keywords:  NFE2L1; STAT3; STX12; hepatocellular carcinoma; mitochondrial defect; retrograde signaling
  20. Cancers (Basel). 2020 Sep 10. pii: E2574. [Epub ahead of print]12(9):
      Mitochondria are organelles that are mainly involved in the generation of ATP by cellular respiration. In addition, they modulate several intracellular functions, ranging from cell proliferation and differentiation to cell death. Importantly, mitochondria are social and can interact with other organelles, such as the Endoplasmic Reticulum, lysosomes and peroxisomes. This symbiotic relationship gives advantages to both partners in regulating some of their functions related to several aspects of cell survival, metabolism, sensitivity to cell death and metastasis, which can all finally contribute to tumorigenesis. Moreover, growing evidence indicates that modulation of the length and/or numbers of these contacts, as well as of the distance between the two engaged organelles, impacts both on their function as well as on cellular signaling. In this review, we discuss recent advances in the field of contacts and communication between mitochondria and other intracellular organelles, focusing on how the tuning of mitochondrial function might impact on both the interaction with other organelles as well as on intracellular signaling in cancer development and progression, with a special focus on calcium signaling.
    Keywords:  contact sites; mitochondria; signaling
  21. Cell. 2020 Sep 09. pii: S0092-8674(20)31073-4. [Epub ahead of print]
      Cardiomyocytes are subjected to the intense mechanical stress and metabolic demands of the beating heart. It is unclear whether these cells, which are long-lived and rarely renew, manage to preserve homeostasis on their own. While analyzing macrophages lodged within the healthy myocardium, we discovered that they actively took up material, including mitochondria, derived from cardiomyocytes. Cardiomyocytes ejected dysfunctional mitochondria and other cargo in dedicated membranous particles reminiscent of neural exophers, through a process driven by the cardiomyocyte's autophagy machinery that was enhanced during cardiac stress. Depletion of cardiac macrophages or deficiency in the phagocytic receptor Mertk resulted in defective elimination of mitochondria from the myocardial tissue, activation of the inflammasome, impaired autophagy, accumulation of anomalous mitochondria in cardiomyocytes, metabolic alterations, and ventricular dysfunction. Thus, we identify an immune-parenchymal pair in the murine heart that enables transfer of unfit material to preserve metabolic stability and organ function.
    Keywords:  autophagy; heart; macrophage; mitochondria; phagocytosis; proteostasis
  22. Nat Metab. 2020 Sep;2(9): 974-988
      Proinflammatory macrophages are key in the development of obesity. In addition, reactive oxygen species (ROS), which activate the Fgr tyrosine kinase, also contribute to obesity. Here we show that ablation of Fgr impairs proinflammatory macrophage polarization while preventing high-fat diet (HFD)-induced obesity in mice. Systemic ablation of Fgr increases lipolysis and liver fatty acid oxidation, thereby avoiding steatosis. Knockout of Fgr in bone marrow (BM)-derived cells is sufficient to protect against insulin resistance and liver steatosis following HFD feeding, while the transfer of Fgr-expressing BM-derived cells reverts protection from HFD feeding in Fgr-deficient hosts. Scavenging of mitochondrial peroxides is sufficient to prevent Fgr activation in BM-derived cells and HFD-induced obesity. Moreover, Fgr expression is higher in proinflammatory macrophages and correlates with obesity traits in both mice and humans. Thus, our findings reveal the mitochondrial ROS-Fgr kinase as a key regulatory axis in proinflammatory adipose tissue macrophage activation, diet-induced obesity, insulin resistance and liver steatosis.
  23. Aging Cell. 2020 Sep 16. e13238
      Non-alcoholic fatty liver disease (NAFLD), characterized by an increase in hepatic triglyceride (TG) content, is the most common liver disease worldwide. Aging has been shown to increase susceptibility to NAFLD; however, the underlying molecular mechanism remains poorly understood. In the present study, we examined hepatic TG content and gene expression profiles in body weight-matched young (3 months old), middle-aged (10 months old), and old (20 months old) C57BL/6 mice and found that TGs were markedly accumulated while mitochondrial β-oxidation-related genes, including PPARα, were downregulated in the liver of old mice. In addition, advanced glycation end product receptor (RAGE), a key regulator of glucose metabolism, was upregulated in the old mice. Mechanistically, suppression of RAGE upregulated PPARα and its downstream target genes, which in turn led to reduced TG retention. Finally, we found that hepatic RAGE expression was increased in aging patients, a finding that correlated with decreased PPARα levels. Taken together, our findings demonstrate that the upregulation of RAGE may play a critical role in aging-associated liver steatosis.
    Keywords:  PPARα; RAGE; aging; hepatic steatosis; mitochondria
  24. J Cell Physiol. 2020 Sep 15.
      The previous research has shown that mitochondrial flash (mitoflash) genesis are functionally and mechanistically integrated with mitochondrial electron transport chain (ETC) energy metabolism. However, the response of mitoflash to superoxide is not entirely consistent with the response of MitoSOX Red. The generation mechanism of mitoflash is still unclear. Here, we investigated mitoflash activities, using the different combinations of ETC substrates and inhibitors, in permeabilized cardiomyocytes or hearts. We found that blocking the complete electron flow, from Complex I to IV, with any one of ETC inhibitors including rotenone (Rot), antimycin A (AntA), myxothiazol (Myxo), stigmatellin, and sodium cyanide, will lead to the abolishment of mitoflashes triggered by substrates in adult permeabilized cardiomyocytes. However, Myxo boosted mitoflashes triggered by the reverse electron of N,N,N',N'-tetramethyl-p-phenylenediamine/ascorbate. Moreover, Rot and AntA furtherly enhanced mitoflash activity rather than depressed it, suggesting that mitoflashes generated at the Complex III Qo site. Meanwhile, the inhibition of Complex III protein expression resulted in the activity of Complex III decrease, which decreased mitoflash frequency. The function defect (no change of protein level) of the Qo site of Complex III in aging hearts augmented mitoflash generation confirmed the Qo site function was critical to mitoflash genesis. Thus, our results indicate that mitoflash detected by circularly permuted yellow fluorescent protein is generated at the Qo site of Complex III.
    Keywords:  Qo site; deficiency; mitochondrial function; mitoflash; oxidative stress
  25. Biochem Biophys Res Commun. 2020 Sep 14. pii: S0006-291X(20)31699-5. [Epub ahead of print]
      The tumor microenvironment (TME) controls many aspects of cancer development but little is known about its effect in Glioblastoma (GBM), the main brain tumor in adults. Tumor-activated stromal cell (TASC) population, a component of TME in GBM, was induced in vitro by incubation of MSCs with culture media conditioned by primary cultures of GBM under 3D/organoid conditions. We observed mitochondrial transfer by Tunneling Nanotubes (TNT), extracellular vesicles (EV) and cannibalism from the TASC to GBM and analyzed its effect on both proliferation and survival. We created primary cultures of GBM or TASC in which we have eliminated mitochondrial DNA [Rho 0 (ρ0) cells]. We found that TASC, as described in other cancers, increased GBM proliferation and resistance to standard treatments (radiotherapy and chemotherapy). We analyzed the incorporation of purified mitochondria by ρ0 and ρ+ cells and a derived mathematical model taught us that ρ+ cells incorporate more rapidly pure mitochondria than ρ0 cells.
    Keywords:  Mesenchymal stromal cells; Mitochondria; Primary GBM cultures; Tunneling nanotubes
  26. Pharmacol Res. 2020 Sep 15. pii: S1043-6618(20)31512-7. [Epub ahead of print] 105204
      Lactate is highly produced under conditions of respiratory dysfunction such as anaerobic respiration and various types of mitochondrial diseases, and it was also known as an active molecule that plays various roles both within and between cells. High levels of extracellular lactate may lead to lactic acidosis, which has been related to pathology of the mitochondrial diseases with mutated mitochondrial DNA (mtDNA). In this study, to elucidate the poorly understood molecular roles of extracellular lactate in mitochondrial regulation, we analyzed mouse B82 cells and their cybrid cells carrying mutated mtDNA with a large-scale deletion (ΔmtDNA). Inhibition of lactate production by sodium dichloroacetate (DCA) treatment improved mitochondrial respiration in cells carrying ΔmtDNA through the activation of mitochondrial biogenesis. Chronic exposure to extracellular lactate (more than 3 days) repressed mitochondrial respiration in healthy cells via calcium and CaMK signaling, leading to a decrease in PGC1α-mediated mitochondrial biogenesis. These mitochondrial dysfunctions induced by the lactate treatment were repressed by pH buffering of the medium. These results suggest that lactate, produced in respiration-deficient cells, acts not only as an intracellular source of energy through the TCA cycle, but also as an extracellular messenger molecule regulating the respiratory activity of both cells carrying ΔmtDNA and the surrounding cells, which could cause whole-body repression of respiratory activity. (211 words).
    Keywords:  acidosis; lactate; mitochondrial DNA; mitochondrial diseases; respiration
  27. PLoS Comput Biol. 2020 Sep 14. 16(9): e1008202
      Hydrogen peroxide (H2O2) promotes a range of phenotypes depending on its intracellular concentration and dosing kinetics, including cell death. While this qualitative relationship has been well established, the quantitative and mechanistic aspects of H2O2 signaling are still being elucidated. Mitochondria, a putative source of intracellular H2O2, have recently been demonstrated to be particularly vulnerable to localized H2O2 perturbations, eliciting a dramatic cell death response in comparison to similar cytosolic perturbations. We sought to improve our dynamic and mechanistic understanding of the mitochondrial H2O2 reaction network in HeLa cells by creating a kinetic model of this system and using it to explore basal and perturbed conditions. The model uses the most current quantitative proteomic and kinetic data available to predict reaction rates and steady-state concentrations of H2O2 and its reaction partners within individual mitochondria. Time scales ranging from milliseconds to one hour were simulated. We predict that basal, steady-state mitochondrial H2O2 will be in the low nM range (2-4 nM) and will be inversely dependent on the total pool of peroxiredoxin-3 (Prx3). Neglecting efflux of H2O2 to the cytosol, the mitochondrial reaction network is expected to control perturbations well up to H2O2 generation rates ~50 μM/s (0.25 nmol/mg-protein/s), above which point the Prx3 system would be expected to collapse. Comparison of these results with redox Western blots of Prx3 and Prx2 oxidation states demonstrated reasonable trend agreement at short times (≤ 15 min) for a range of experimentally perturbed H2O2 generation rates. At longer times, substantial efflux of H2O2 from the mitochondria to the cytosol was evidenced by peroxiredoxin-2 (Prx2) oxidation, and Prx3 collapse was not observed. A refined model using Monte Carlo parameter sampling was used to explore rates of H2O2 efflux that could reconcile model predictions of Prx3 oxidation states with the experimental observations.
  28. FASEB J. 2020 Sep 18.
      The physiological role played by uncoupling protein 3 (UCP3) in brown adipose tissue (BAT) has not been fully elucidated so far. In the present study, we evaluated the impact of the absence of UCP3 on BAT mitochondrial functionality and morphology. To this purpose, wild type (WT) and UCP3 Knockout (KO) female mice were housed at thermoneutrality (30°C), a condition in which BAT contributes to energy homeostasis independently of its cold-induced thermogenic function. BAT mitochondria from UCP3 KO mice presented a lower ability to oxidize the fatty acids and glycerol-3-phosphate, and an enhanced oxidative stress as revealed by enhanced mitochondrial electron leak, lipid hydroperoxide levels, and induction of antioxidant mitochondrial enzymatic capacity. The absence of UCP3 also influenced the mitochondrial super-molecular protein aggregation, an important feature for fatty acid oxidation rate as well as for adequate cristae organization and mitochondrial shape. Indeed, electron microscopy revealed alterations in mitochondrial morphology in brown adipocytes from KO mice. In the whole, data here reported show that the absence of UCP3 results in a significant alteration of BAT mitochondrial physiology and morphology. These observations could also help to clarify some aspects of the association between metabolic disorders associated with low UCP3 levels, as previously reported in human studies.
    Keywords:  metabolism; oxidative stress; respiratory chain
  29. Mol Cell Oncol. 2020 ;7(5): 1771959
      While genomic instability and mitochondrial homeostasis are integral for cancer progression, how these two hallmarks interact remains poorly understood. Here, we reflect on the dialogue between chromatin-based genomic instability and impairment of mitochondrial function and depict the importance of this interaction in cancer progression to metastasis.
    Keywords:  Genomic instability; cancer; chromatin; metabolism; mitochondrial homeostasis
  30. Onco Targets Ther. 2020 ;13 8735-8747
      Purpose: Malic enzyme 1 (ME1) catalyzes malate to pyruvate and thus promotes glycolysis. Its function in breast cancer remains to be fully clarified. The aim of this work was to investigate the prognostic value of ME1 and its possible mechanism in breast cancer.Methods: We evaluated ME1 expression in 220 early breast cancer patients with tissue microarray-based immunohistochemistry and explored the relationships between ME1 expression and clinicopathological features. Survival analyses were further performed to determine its prognostic value. The public database was used to confirm tissue microarray results. Further, cell proliferation, migration, invasion ability and reactive oxygen species (ROS) were examined in breast cancer cells.
    Results: In breast cancer tissues, high ME1 expression was significantly associated with larger tumor size, higher incidence of lymph node metastasis and higher incidence of lymph-vascular invasion. High ME1 expression significantly correlated with worse recurrence-free survival (RFS), and was an independent prognostic factor for RFS, which was confirmed by mRNA results in the public database. In vitro, upregulation of ME1 by transfecting MCF-7 cells with virus vector remarkably enhanced viability, motility and epithelial-mesenchymal transition (EMT) and decreased ROS levels, whereas knockdown in MDA-MB-468 cells produced totally opposite effects as expected. When pretreated with oxidizing agent, MCF-7 cells overexpressing ME1 lost its motility, whereas MDA-MB-468 cells with knockdown of ME1 restored its motility when pretreated with antioxidant.
    Conclusion: To our knowledge, these clinical and experiment works first suggested that ME1 may be a novel biomarker and potential therapeutic target for breast cancer metastasis, and its biological effect is mainly controlled by manipulating ROS.
    Keywords:  breast cancer; malic enzyme 1; metastasis; prognosis; reactive oxygen species
  31. Mol Cell. 2020 Sep 04. pii: S1097-2765(20)30578-5. [Epub ahead of print]
      Immune cell function depends on specific metabolic programs dictated by mitochondria, including nutrient oxidation, macromolecule synthesis, and post-translational modifications. Mitochondrial adaptations have been linked to acute and chronic inflammation, but the metabolic cues and precise mechanisms remain unclear. Here we reveal that histone deacetylase 3 (HDAC3) is essential for shaping mitochondrial adaptations for IL-1β production in macrophages through non-histone deacetylation. In vivo, HDAC3 promoted lipopolysaccharide-induced acute inflammation and high-fat diet-induced chronic inflammation by enhancing NLRP3-dependent caspase-1 activation. HDAC3 configured the lipid profile in stimulated macrophages and restricted fatty acid oxidation (FAO) supported by exogenous fatty acids for mitochondria to acquire their adaptations and depolarization. Rather than affecting nuclear gene expression, HDAC3 translocated to mitochondria to deacetylate and inactivate an FAO enzyme, mitochondrial trifunctional enzyme subunit α. HDAC3 may serve as a controlling node that balances between acquiring mitochondrial adaptations and sustaining their fitness for IL-1β-dependent inflammation.
  32. Phys Rev E. 2020 Aug;102(2-1): 022401
      As the places where most of the fuel of the cell, namely, ATP, is synthesized, mitochondria are crucial organelles in eukaryotic cells. The shape of the invaginations of the mitochondria inner membrane, known as a crista, has been identified as a signature of the energetic state of the organelle. However, the interplay between the rate of ATP synthesis and the crista shape remains unclear. In this work, we investigate the crista membrane deformations using a pH-dependent Helfrich model, maintained out of equilibrium by a diffusive flux of protons. This model gives rise to shape changes of a cylindrical invagination, in particular to the formation of necks between wider zones under variable, and especially oscillating, proton flux.
  33. Br J Cancer. 2020 Sep 16.
      BACKGROUND: Microcalcification is one of the most reliable clinical features of the malignancy risk of breast cancer, and it is associated with enhanced tumour aggressiveness and poor prognosis. However, its underlying molecular mechanism remains unclear.METHODS: Clinical data were retrieved to analyse the association between calcification and bone metastasis in patients with breast cancer. Using multiple human breast cancer cell lines, the osteogenic cocktail model was established in vitro to demonstrate calcification-exacerbated metastasis. Migration and invasion characteristics were determined by wound healing and transwell migration. mRNA and protein expression were identified by quantitative PCR and western blotting. Metabolic alterations in breast cancer cells were evaluated using Seahorse Analyser.
    RESULTS: The osteogenic differentiation of human breast cancer cells activated the classical TGF-β/Smad signalling pathway and the non-canonical MAPK pathway, which, in turn, exacerbated the progression of epithelial-mesenchymal transition (EMT). The metabolic programme switched to enhancing mitochondrial oxidative phosphorylation (OXPHOS) upon osteogenic differentiation. Rotenone was used to inhibit the OXPHOS complex during osteogenesis to block mitochondrial function, consequently reversing the EMT phenotype.
    CONCLUSIONS: This study provides important insights into the mechanisms involved in breast cancer bone metastasis, and outlines a possible strategy to intervene in OXPHOS for the treatment of breast tumours.
  34. J Cell Biol. 2020 Oct 05. pii: e202001071. [Epub ahead of print]219(10):
      An ability to comprehensively track the assembly intermediates (AIs) of complex I (CI) biogenesis in Drosophila will enable the characterization of the precise mechanism(s) by which various CI regulators modulate CI assembly. Accordingly, we generated 21 novel antibodies to various mitochondrial proteins and used this resource to characterize the mechanism by which apoptosis-inducing factor (AIF) regulates CI biogenesis by tracking the AI profile observed when AIF expression is impaired. We find that when the AIF-Mia40 translocation complex is disrupted, the part of CI that transfers electrons to ubiquinone is synthesized but fails to progress in the CI biosynthetic pathway. This is associated with a reduction in intramitochondrial accumulation of the Mia40 substrate, MIC19. Importantly, knockdown of either MIC19 or MIC60, components of the mitochondrial contact site and cristae organizing system (MICOS), fully recapitulates the AI profile observed when AIF is inhibited. Thus, AIF's effect on CI assembly is principally due to compromised intramitochondrial transport of the MICOS complex.
  35. Cell. 2020 Sep 15. pii: S0092-8674(20)31081-3. [Epub ahead of print]
      In response to skeletal muscle contraction during exercise, paracrine factors coordinate tissue remodeling, which underlies this healthy adaptation. Here we describe a pH-sensing metabolite signal that initiates muscle remodeling upon exercise. In mice and humans, exercising skeletal muscle releases the mitochondrial metabolite succinate into the local interstitium and circulation. Selective secretion of succinate is facilitated by its transient protonation, which occurs upon muscle cell acidification. In the protonated monocarboxylic form, succinate is rendered a transport substrate for monocarboxylate transporter 1, which facilitates pH-gated release. Upon secretion, succinate signals via its cognate receptor SUCNR1 in non-myofibrillar cells in muscle tissue to control muscle-remodeling transcriptional programs. This succinate-SUCNR1 signaling is required for paracrine regulation of muscle innervation, muscle matrix remodeling, and muscle strength in response to exercise training. In sum, we define a bioenergetic sensor in muscle that utilizes intracellular pH and succinate to coordinate tissue adaptation to exercise.
    Keywords:  SUCNR1; exercise; innervation; muscle; succinate
  36. Biochim Biophys Acta Mol Basis Dis. 2020 Sep 10. pii: S0925-4439(20)30310-0. [Epub ahead of print] 165962
      Chondrosarcoma is the second most common primary bone malignancy, representing one fourth of all primary bone sarcomas. It is typically resistant to radiation and chemotherapy treatments. However, the molecular mechanisms that contribute to cancer aggressiveness in chondrosarcomas remain poorly characterized. Here, we studied the role of mitochondrial transporters in chondrosarcoma aggressiveness including chemotherapy resistance. Histological grade along with stage are the most important prognostic biomarkers in chondrosarcoma. We found that high-grade human chondrosarcoma tumors have higher expression of the mitochondrial protein, translocase of the outer mitochondrial membrane complex subunit 20 (TOMM20), compared to low-grade tumors. TOMM20 overexpression in human chondrosarcoma cells induces chondrosarcoma tumor growth in vivo. TOMM20 drives proliferation, resistance to apoptosis and chemotherapy resistance. Also, TOMM20 induces markers of epithelial to mesenchymal transition (EMT) and metabolic reprogramming in these mesenchymal tumors. In conclusion, TOMM20 drives chondrosarcoma aggressiveness and resistance to chemotherapy.
    Keywords:  apoptosis; chemotherapy resistance; chondrosarcoma; mitochondria; proliferation
  37. Cell. 2020 Sep 10. pii: S0092-8674(20)31076-X. [Epub ahead of print]
      Metazoan organisms rely on conserved stress response pathways to alleviate adverse conditions and preserve cellular integrity. Stress responses are particularly important in stem cells that provide lifetime support for tissue formation and repair, but how these protective systems are integrated into developmental programs is poorly understood. Here we used myoblast differentiation to identify the E3 ligase CUL2FEM1B and its substrate FNIP1 as core components of the reductive stress response. Reductive stress, as caused by prolonged antioxidant signaling or mitochondrial inactivity, reverts the oxidation of invariant Cys residues in FNIP1 and allows CUL2FEM1B to recognize its target. The ensuing proteasomal degradation of FNIP1 restores mitochondrial activity to preserve redox homeostasis and stem cell integrity. The reductive stress response is therefore built around a ubiquitin-dependent rheostat that tunes mitochondrial activity to redox needs and implicates metabolic control in coordination of stress and developmental signaling.
    Keywords:  FEM1B; FNIP1; KEAP1; mitochondria; oxidative stress; proteasome; reactive oxygen; reductive stress; ubiquitin
  38. Nat Commun. 2020 09 14. 11(1): 4611
      Pancreatic ductal adenocarcinoma (PDAC) and cancer-associated cachexia (CAC) are multifactorial and characterized by dysregulated inflammatory networks. Whether the proinflammatory cytokine IL-20 is involved in the complex networks of PDAC and CAC remains unclear. Here, we report that elevated IL-20 levels in tumor tissue correlate with poor overall survival in 72 patients with PDAC. In vivo, we establish a transgenic mouse model (KPC) and an orthotopic PDAC model and examine the therapeutic efficacy of an anti-IL-20 monoclonal antibody (7E). Targeting IL-20 not only prolongs survival and attenuates PD-L1 expression in both murine models but also inhibits tumor growth and mitigates M2-like polarization in the orthotopic PDAC model. Combination treatment with 7E and an anti-PD-1 antibody shows better efficacy in inhibiting tumor growth than either treatment alone in the orthotopic PDAC model. Finally, 7E mitigates cachexic symptoms in CAC models. Together, we conclude IL-20 is a critical mediator in PDAC progression.
  39. Cell. 2020 Sep 05. pii: S0092-8674(20)31000-X. [Epub ahead of print]
      Mitochondria, which play central roles in immunometabolic diseases, have their own genome. However, the functions of mitochondria-located noncoding RNAs are largely unknown due to the absence of a specific delivery system. By circular RNA (circRNA) expression profile analysis of liver fibroblasts from patients with nonalcoholic steatohepatitis (NASH), we observe that mitochondrial circRNAs account for a considerable fraction of downregulated circRNAs in NASH fibroblasts. By constructing mitochondria-targeting nanoparticles, we observe that Steatohepatitis-associated circRNA ATP5B Regulator (SCAR), which is located in mitochondria, inhibits mitochondrial ROS (mROS) output and fibroblast activation. circRNA SCAR, mediated by PGC-1α, binds to ATP5B and shuts down mPTP by blocking CypD-mPTP interaction. Lipid overload inhibits PGC-1α by endoplasmic reticulum (ER) stress-induced CHOP. In vivo, targeting circRNA SCAR alleviates high fat diet-induced cirrhosis and insulin resistance. Clinically, circRNA SCAR is associated with steatosis-to-NASH progression. Collectively, we identify a mitochondrial circRNA that drives metaflammation and serves as a therapeutic target for NASH.