bims-mitdyn Biomed News
on Mitochondrial dynamics: mechanisms
Issue of 2020‒10‒04
twenty-one papers selected by
Edmond Chan
Queen’s University, School of Medicine

  1. Nat Cell Biol. 2020 Oct;22(10): 1180-1186
    Rey T, Zaganelli S, Cuillery E, Vartholomaiou E, Croisier M, Martinou JC, Manley S.
      Mitochondria contain the genetic information and expression machinery to produce essential respiratory chain proteins. Within the mitochondrial matrix, newly synthesized RNA, RNA processing proteins and mitoribosome assembly factors form punctate sub-compartments referred to as mitochondrial RNA granules (MRGs)1-3. Despite their proposed importance in regulating gene expression, the structural and dynamic properties of MRGs remain largely unknown. We investigated the internal architecture of MRGs using fluorescence super-resolution localization microscopy and correlative electron microscopy, and found that the MRG ultrastructure consists of compacted RNA embedded within a protein cloud. Using live-cell super-resolution structured illumination microscopy and fluorescence recovery after photobleaching, we reveal that MRGs rapidly exchange components and can undergo fusion, characteristic properties of fluid condensates4. Furthermore, MRGs associate with the inner mitochondrial membrane and their fusion coincides with mitochondrial remodelling. Inhibition of mitochondrial fission or fusion leads to an aberrant accumulation of MRGs into concentrated pockets, where they remain as distinct individual units despite their close apposition. Together, our findings reveal that MRGs are nanoscale fluid compartments, which are dispersed along mitochondria via membrane dynamics.
  2. Nat Commun. 2020 10 01. 11(1): 4913
    Guo L, Cui C, Wang J, Yuan J, Yang Q, Zhang P, Su W, Bao R, Ran J, Wu C.
      Reprograming of proline metabolism is critical for tumor growth. Here we show that PINCH-1 is highly expressed in lung adenocarcinoma and promotes proline synthesis through regulation of mitochondrial dynamics. Knockout (KO) of PINCH-1 increases dynamin-related protein 1 (DRP1) expression and mitochondrial fragmentation, which suppresses kindlin-2 mitochondrial translocation and interaction with pyrroline-5-carboxylate reductase 1 (PYCR1), resulting in inhibition of proline synthesis and cell proliferation. Depletion of DRP1 reverses PINCH-1 deficiency-induced defects on mitochondrial dynamics, proline synthesis and cell proliferation. Furthermore, overexpression of PYCR1 in PINCH-1 KO cells restores proline synthesis and cell proliferation, and suppresses DRP1 expression and mitochondrial fragmentation. Finally, ablation of PINCH-1 from lung adenocarcinoma in mouse increases DRP1 expression and inhibits PYCR1 expression, proline synthesis, fibrosis and tumor growth. Our results identify a signaling axis consisting of PINCH-1, DRP1 and PYCR1 that regulates mitochondrial dynamics and proline synthesis, and suggest an attractive strategy for alleviation of tumor growth.
  3. EMBO J. 2020 Oct 01. 39(19): e103530
    Beretta M, Santos CX, Molenaar C, Hafstad AD, Miller CC, Revazian A, Betteridge K, Schröder K, Streckfuß-Bömeke K, Doroshow JH, Fleck RA, Su TP, Belousov VV, Parsons M, Shah AM.
      Cells subjected to environmental stresses undergo regulated cell death (RCD) when homeostatic programs fail to maintain viability. A major mechanism of RCD is the excessive calcium loading of mitochondria and consequent triggering of the mitochondrial permeability transition (mPT), which is especially important in post-mitotic cells such as cardiomyocytes and neurons. Here, we show that stress-induced upregulation of the ROS-generating protein Nox4 at the ER-mitochondria contact sites (MAMs) is a pro-survival mechanism that inhibits calcium transfer through InsP3 receptors (InsP3 R). Nox4 mediates redox signaling at the MAM of stressed cells to augment Akt-dependent phosphorylation of InsP3 R, thereby inhibiting calcium flux and mPT-dependent necrosis. In hearts subjected to ischemia-reperfusion, Nox4 limits infarct size through this mechanism. These results uncover a hitherto unrecognized stress pathway, whereby a ROS-generating protein mediates pro-survival effects through spatially confined signaling at the MAM to regulate ER to mitochondria calcium flux and triggering of the mPT.
    Keywords:  InsP3 receptor; NADPH oxidase-4; calcium signaling; cell death; mitochondria-associated membrane
  4. Sci Rep. 2020 Sep 29. 10(1): 16041
    Bisbach CM, Hutto RA, Poria D, Cleghorn WM, Abbas F, Vinberg F, Kefalov VJ, Hurley JB, Brockerhoff SE.
      Rods and cones use intracellular Ca2+ to regulate many functions, including phototransduction and neurotransmission. The Mitochondrial Calcium Uniporter (MCU) complex is thought to be the primary pathway for Ca2+ entry into mitochondria in eukaryotes. We investigate the hypothesis that mitochondrial Ca2+ uptake via MCU influences phototransduction and energy metabolism in photoreceptors using a mcu-/- zebrafish and a rod photoreceptor-specific Mcu-/- mouse. Using genetically encoded Ca2+ sensors to directly examine Ca2+ uptake in zebrafish cone mitochondria, we found that loss of MCU reduces but does not eliminate mitochondrial Ca2+ uptake. Loss of MCU does not lead to photoreceptor degeneration, mildly affects mitochondrial metabolism, and does not alter physiological responses to light, even in the absence of the Na+/Ca2+, K+ exchanger. Our results reveal that MCU is dispensable for vertebrate photoreceptor function, consistent with its low expression and the presence of an alternative pathway for Ca2+ uptake into photoreceptor mitochondria.
  5. PLoS Pathog. 2020 Sep 30. 16(9): e1008918
    Mahmud SA, Qureshi MA, Sapkota M, Pellegrino MW.
      The mitochondrial unfolded protein response (UPRmt) is a stress-activated pathway promoting mitochondrial recovery and defense against infection. In C. elegans, the UPRmt is activated during infection with the pathogen Pseudomonas aeruginosa-but only transiently. As this may reflect a pathogenic strategy to target a pathway required for host survival, we conducted a P. aeruginosa genetic screen to uncover mechanisms associated with this temporary activation. Here, we find that loss of the P. aeruginosa acyl-CoA dehydrogenase FadE2 prolongs UPRmt activity and extends host survival. FadE2 shows substrate preferences for the coenzyme A intermediates produced during the breakdown of the branched-chain amino acids valine and leucine. Our data suggests that during infection, FadE2 restricts the supply of these catabolites to the host hindering host energy metabolism in addition to the UPRmt. Thus, a metabolic pathway in P. aeruginosa contributes to pathogenesis during infection through manipulation of host energy status and mitochondrial stress signaling potential.
  6. Trends Cancer. 2020 Sep 23. pii: S2405-8033(20)30236-3. [Epub ahead of print]
    Tasdogan A, McFadden DG, Mishra P.
      Mitochondria play an essential role in cellular metabolism, generation of reactive oxygen species (ROS), and the initiation of apoptosis. These properties enable mitochondria to be crucial integrators in the pathways of tumorigenesis. An open question is to what extent variation in the mitochondrial genome (mtDNA) contributes to the biological heterogeneity observed in human tumors. In this review, we summarize our current understanding of the role of mtDNA genetics in relation to human cancers.
    Keywords:  cancer; haplotypes; mitochondria; mtDNA; oncocytoma
  7. Am J Physiol Endocrinol Metab. 2020 Sep 28.
    Townsend LK, Brunetta BS, Mori MA.
      Obesity and insulin resistance (IR) are associated with endoplasmic reticulum (ER) stress and mitochondrial dysfunction in several tissues. Although for many years mitochondrial and ER function were studied separately, these organelles also connect to produce interdependent functions. Communication occurs at mitochondria-associated ER membranes (MAM) and regulates lipid and calcium homeostasis, apoptosis, and the exchange of adenine nucleotides, among other things. Recent evidence suggests that MAMs contribute to organelle, cellular, and systemic metabolism. In obesity and IR models, metabolic tissues such as the liver, skeletal muscle, pancreas, and adipose tissue present alterations in MAM structure or function. The purpose of this mini-review is to highlight the MAM disruptions that occur in each tissue during obesity and IR and its relationship with glucose homeostasis and IR. We also discuss the current controversy that surrounds MAMs' role in the development of insulin resistance.
    Keywords:  MAMs; endoplasmic reticulum; glucose metabolism; insulin resistance; mitochondria
  8. Cell Mol Gastroenterol Hepatol. 2020 Sep 26. pii: S2352-345X(20)30156-9. [Epub ahead of print]
    Mancini NL, Rajeev S, Jayme TS, Wang A, Keita ÅV, Workentine ML, Hamed S, Söderholm JD, Lopes F, Shutt TE, Shearer J, McKay DM.
      BACKGROUND & AIMS: Adherent-invasive E. coli (AIEC) are implicated in inflammatory bowel disease (IBD), and mitochondrial dysfunction has been observed in IBD-patient biopsies. As a novel aspect of AIEC-epithelial interaction we hypothesized that E. coli (strain LF82) would elicit substantial disruption of epithelial mitochondrial form and function.METHODS: Monolayers of human colon-derived epithelial cell lines were exposed to E. coli-LF82 or commensal E. coli and RNA-sequence analysis, mitochondrial function (ATP synthesis) and dynamics (mitochondrial network imaging, immunoblotting for fission and fusion proteins), and epithelial permeability (transepithelial resistance, flux of FITC-dextran and bacteria) were assessed.
    RESULTS: E. coli-LF82 significantly affected epithelial expression of ∼8600 genes, many relating to mitochondrial function. E. coli-LF82-infected epithelia displayed swollen mitochondria, reduced mitochondrial membrane potential and ATP, and fragmentation of the mitochondrial network: events not observed with dead E. coli-LF82, medium from bacterial cultures, or control E. coli. Treatment with Mdivi1 (inhibits dynamin-related peptide 1 (Drp1), GTPase principally responsible for mitochondrial fission) or P110 (prevents Drp1 binding to mitochondrial fission 1 protein) partially reduced E. coli-LF82-induced mitochondrial fragmentation in the short-term. E. coli-LF82-infected epithelia showed loss of the long isoform of optic atrophy factor 1 (OPA1-L), which mediates mitochondrial fusion. Mdivi1 reduced the magnitude of E. coli-LF82 induced increased transepithelial flux of FITC-dextran. By 8h post-infection, increased cytosolic cytochrome C and DNA fragmentation were apparent without evidence of caspase-3 or apoptosis inducing factor (AIF) activation.
    CONCLUSIONS: Epithelial mitochondrial fragmentation caused by E. coli-LF82 could be targeted to maintain cellular homeostasis and mitigate infection-induced loss of epithelial barrier function.
    Keywords:  Drp1; bacteria; caspase-3; epithelial permeability; human epithelial cell lines; mitochondrial fission and fusion
  9. Front Immunol. 2020 ;11 1834
    Li W, Zhang L.
      Memory T cells persist for long term to mediate robust recall response upon rechallenging with previous encountered pathogens. The memory T cell pool is highly heterogeneous based on distinct phenotypic, functional, and locational properties, and contains discrete subsets, which contribute to diverse immune responses. In this mini-review, we will briefly discuss the distinct subsets of memory T cells and then focus on mitochondria-related metabolic and epigenetic regulations of CD8+ T cell memory formation. In particular, we discuss many aspects of mitochondrial quality control systems (biogenesis, dynamics, etc.) in regulating CD8+ T cell fate decision and antitumor immunity. Importantly, targeting mitochondrial metabolism to boost T cell memory formation and metabolic fitness might represent an attractive strategy to improve cancer immunotherapy including CAR-T therapy.
    Keywords:  CD8 T cell; cancer; immunotherapy; memory; mitochondria
  10. Biochem Soc Trans. 2020 Sep 28. pii: BST20200120. [Epub ahead of print]
    Horn A, Jaiswal JK.
      Mitochondria are central to the health of eukaryotic cells. While commonly known for their bioenergetic role, mitochondria also function as signaling organelles that regulate cell stress responses capable of restoring homeostasis or leading the stressed cell to eventual death. Damage to the plasma membrane is a potentially fatal stressor incurred by all cells. Repairing plasma membrane damage requires cells to mount a rapid and localized response to injury. Accumulating evidence has identified a role for mitochondria as an important facilitator of this acute and localized repair response. However, as mitochondria are organized in a cell-wide, interconnected network, it is unclear how they collectively sense and respond to a focal injury. Here we will discuss how mitochondrial shape change is an integral part of this localized repair response. Mitochondrial fragmentation spatially restricts beneficial repair signaling, enabling a localized response to focal injury. Conservation of mitochondrial fragmentation in response to cell and tissue damage across species demonstrates that this is a universal pro-survival adaptation to injury and suggests that mitochondrial fragmentation may provide cells a mechanism to facilitate localized signaling in contexts beyond repairing plasma membrane injury.
    Keywords:  calcium homoeostasis; fragmentation; redox signaling
  11. Mol Biol Cell. 2020 Sep 30. mbcE20080524
    Friedl J, Knopp MR, Groh C, Paz E, Gould SB, Herrmann JM, Boos F.
      Most mitochondrial proteins are synthesized as precursors that carry N-terminal presequences. After import into mitochondria, these targeting signals are cleaved off by the mitochondrial processing peptidase MPP. Using the mitochondrial tandem protein Arg5,6 as model substrate, we demonstrate that MPP has an additional role in preprotein maturation, beyond the removal of presequences. Arg5,6 is synthesized as a polyprotein precursor that is imported into mitochondria and subsequently separated into two distinct enzymes. This internal processing is performed by MPP, which cleaves the Arg5,6 precursor at its N-terminus and at an internal site. The peculiar organization of Arg5,6 is conserved across fungi and reflects the polycistronic arginine operon in prokaryotes. MPP cleavage sites are also present in other mitochondrial fusion proteins from fungi, plants and animals. Hence, besides its role as "ticket canceller" for removal of presequences, MPP exhibits a second, conserved activity as internal processing peptidase for complex mitochondrial precursor proteins.
  12. Sci Signal. 2020 Sep 29. pii: eaba3300. [Epub ahead of print]13(651):
    Ledderose C, Bromberger S, Slubowski CJ, Sueyoshi K, Aytan D, Shen Y, Junger WG.
      T cells must migrate to encounter antigen-presenting cells and perform their roles in host defense. Here, we found that autocrine stimulation of the purinergic receptor P2Y11 regulates the migration of human CD4 T cells. P2Y11 receptors redistributed from the front to the back of polarized cells where they triggered intracellular cAMP/PKA signals that attenuated mitochondrial metabolism at the back. The absence of P2Y11 receptors at the front of cells resulted in hotspots of mitochondrial metabolism and localized ATP production that stimulated P2X4 receptors, Ca2+ influx, and pseudopod protrusion at the front. This regulatory function of P2Y11 receptors depended on their subcellular redistribution and autocrine stimulation by cellular ATP release and was perturbed by indiscriminate global stimulation. We conclude that excessive extracellular ATP-such as in response to inflammation, sepsis, and cancer-disrupts this autocrine feedback mechanism, which results in defective T cell migration, impaired T cell function, and loss of host immune defense.
  13. Cell Death Dis. 2020 Sep 29. 11(9): 814
    Deng Q, Wen R, Liu S, Chen X, Song S, Li X, Su Z, Wang C.
      Excessive mitochondrial fission plays a key role in podocyte injury in diabetic kidney disease (DKD), and long noncoding RNAs (lncRNAs) are important in the development and progression of DKD. However, lncRNA regulation of mitochondrial fission in podocytes is poorly understood. Here, we studied lncRNA maternally expressed gene 3 (Meg3) in mitochondrial fission in vivo and in vitro using human podocytes and Meg3 podocyte-specific knockdown mice. Expression of lncRNA Meg3 in STZ-induced diabetic mice was higher, and correlated with the number of podocytes. Excessive mitochondrial fission of podocytes and renal histopathological and physiological parameters were improved in podocyte-specific Meg3 knockdown diabetic mice. Elongated mitochondria with attenuated podocyte damage, as well as mitochondrial translocation of dynamin-related protein 1 (Drp1), were decreased in Meg3 knockout podocytes. By contrast, increased fragmented mitochondria, podocyte injury, and Drp1 expression and phosphorylation were observed in lncRNA Meg3-overexpressing podocytes. Treatment with Mdivi1 significantly blunted more fragmented mitochondria and reduced podocyte injury in lncRNA Meg3-overexpressing podocytes. Finally, fragmented mitochondria and Drp1 mitochondrial translocation induced by high glucose were reduced following treatment with Mdivi1. Our data show that expression of Meg3 in podocytes in both human cells and diabetic mice was higher, which regulates mitochondrial fission and contributes to podocyte injury through increased Drp1 and its translocation to mitochondria.
  14. J Genet Genomics. 2020 Aug 01. pii: S1673-8527(20)30114-4. [Epub ahead of print]
    Nguyen H, LaFramboise T.
      Mutations in the human mitochondrial genome have been observed in all types of human cancer, indicating that mutations might contribute to tumorigenesis, metastasis, recurrence, or drug response. This possibility is appealing because of the known shift from oxidative metabolism to glycolysis, known as the Warburg effect, that occurs in malignancy. Mitochondrial DNA (mtDNA) mutations could either be maternally inherited and predispose to cancer (germ line mutations) or occur sporadically in the mtDNA of specific tissues (tissue- or tumor-specific somatic mutations) and contribute to the tumor initiation and progression process. High-throughput sequencing technologies now enable comprehensive detection of mtDNA variation in tissues and bodily fluids, with the potential to be used as an early detection tool that may impact the treatment of cancer. Here, we discuss insights into the roles of mtDNA mutations in carcinogenesis, highlighting the complexities involved in the analysis and interpretation of mitochondrial genomic content, technical challenges in studying their contribution to pathogenesis, and the value of mtDNA mutations in developing early detection, diagnosis, prognosis, and therapeutic strategies for cancer.
    Keywords:  Cancer; Genetic variation; Mitochondrial DNA
  15. Bioeng Transl Med. 2020 Sep;5(3): e10184
    Moon SJ, Dong W, Stephanopoulos GN, Sikes HD.
      Mitochondrial NADPH protects cells against mitochondrial oxidative stress by serving as an electron donor to antioxidant defense systems. However, due to technical challenges, it still remains unknown as to the pool size of mitochondrial NADPH, its dynamics, and NADPH/NADP+ ratio. Here, we have systemically modulated production rates of H2O2 in mitochondria and assessed mitochondrial NADPH metabolism using iNap sensors, 13C glucose isotopic tracers, and a mathematical model. Using sensors, we observed decreases in mitochondrial NADPH caused by excessive generation of mitochondrial H2O2, whereas the cytosolic NADPH was maintained upon perturbation. We further quantified the extent of mitochondrial NADPH/NADP+ based on the mathematical analysis. Utilizing 13C glucose isotopic tracers, we found increased activity in the pentose phosphate pathway (PPP) accompanied small decreases in the mitochondrial NADPH pool, whereas larger decreases induced both PPP activity and glucose anaplerosis. Thus, our integrative and quantitative approach provides insight into mitochondrial NADPH metabolism during mitochondrial oxidative stress.
    Keywords:  NADPH; NADPH metabolism; NADPH sensor; hydrogen peroxide; mitochondria; oxidative stress; redox kinetic model
  16. Front Physiol. 2020 ;11 1054
    Alam S, Abdullah CS, Aishwarya R, Morshed M, Bhuiyan MS.
      Mitochondria are the key to properly functioning energy generation in the metabolically demanding cardiomyocytes and thus essential to healthy heart contractility on a beat-to-beat basis. Mitochondria being the central organelle for cellular metabolism and signaling in the heart, its dysfunction leads to cardiovascular disease. The healthy mitochondrial functioning critical to maintaining cardiomyocyte viability and contractility is accomplished by adaptive changes in the dynamics, biogenesis, and degradation of the mitochondria to ensure cellular proteostasis. Recent compelling evidence suggests that the classical protein quality control system in cardiomyocytes is also under constant mitochondrial control, either directly or indirectly. Impairment of cytosolic protein quality control may affect the position of the mitochondria in relation to other organelles, as well as mitochondrial morphology and function, and could also activate mitochondrial proteostasis. Despite a growing interest in the mitochondrial quality control system, very little information is available about the molecular function of mitochondria in cardiac proteostasis. In this review, we bring together current understanding of the adaptations and role of the mitochondria in cardiac proteostasis and describe the adaptive/maladaptive changes observed in the mitochondrial network required to maintain proteomic integrity. We also highlight the key mitochondrial signaling pathways activated in response to proteotoxic stress as a cellular mechanism to protect the heart from proteotoxicity. A deeper understanding of the molecular mechanisms of mitochondrial adaptations and their role in cardiac proteostasis will help to develop future therapeutics to protect the heart from cardiovascular diseases.
    Keywords:  cardiac proteostasis; mitochondria; mitochondrial dysfunction; mitochondrial proteostasis; mitochondrial unfolded protein response; proteotoxicity
  17. Mol Cell Biochem. 2020 Sep 29.
    Sarkar A, Gandhi V.
      Ataxia telangiectasia mutated (ATM), a critical DNA damage sensor, also possesses non-nuclear functions owing to its presence in extra-nuclear compartments, including peroxisomes, lysosomes, and mitochondria. ATM is frequently altered in several human cancers. Recently, we and others have shown that loss of ATM is associated with defective mitochondrial autophagy (mitophagy) in ataxia-telangiectasia (A-T) fibroblasts and B-cell lymphomas. Further, we reported that ATM protein but not ATM kinase activity is required for mitophagy. However, the mechanism of ATM kinase activation during ionophore-induced mitophagy is unknown. In the work reported here, using several ionophores in A-T and multiple T-cell and B-cell lymphoma cell lines, we show that ionophore-induced mitophagy triggers oxidative stress-induced ATMSer1981 phosphorylation through ROS activation, which is different from neocarzinostatin-induced activation of ATMSer1981, Smc1Ser966, and Kap1Ser824. We used A-T cells overexpressed with WT or S1981A (auto-phosphorylation dead) ATM plasmids and show that ATM is activated by ROS-induced oxidative stress emanating from ionophore-induced mitochondrial damage and mitophagy. The antioxidants N-acetylcysteine and glutathione significantly inhibited ROS production and ATMSer1981 phosphorylation but failed to inhibit mitophagy as determined by retroviral infection with mt-mKeima construct followed by lysosomal dual-excitation ratiometric pH measurements. Our data suggest that while ATM kinase does not participate in mitophagy, it is activated via elevated ROS.
    Keywords:  ATM kinase; Leukemia; Lymphoma; Mitophagy; ROS
  18. Cell Death Dis. 2020 Oct 01. 11(9): 819
    Zhou Y, Wang Y, Wu S, Yan Y, Hu Y, Zheng Z, Li J, Wu W.
      Here we uncovered the involved subcellular mechanisms that sulforaphane-cysteine (SFN-Cys) inhibited invasion in human glioblastoma (GBM). SFN-Cys significantly upregulated 45 and downregulated 14 microtubule-, mitophagy-, and invasion-associated proteins in GBM cells via HPLC-MS/MS and GEO ontology analysis; SFN-Cys disrupted microtubule by ERK1/2 phosphorylation-mediated downregulation of α-tubulin and Stathmin-1 leading to the inhibition of cell migration and invasion; SFN-Cys downregulated invasion-associated Claudin-5 and S100A4, and decreased the interaction of α-tubulin to Claudin-5. Knockdown of Claudin-5 and S100A4 significantly reduced the migration and invasion. Besides, SFN-Cys lowered the expressions of α-tubulin-mediated mitophagy-associated proteins Bnip3 and Nix. Transmission electron microscopy showed more membrane-deficient mitochondria and accumulated mitophagosomes in GBM cells, and mitochondria fusion might be downregulated because that SFN-Cys downregulated mitochondrial fusion protein OPA1. SFN-Cys increased the colocalization and interplay of LC3 to lysosomal membrane-associated protein LAMP1, aggravating the fusion of mitophagosome to lysosome. Nevertheless, SFN-Cys inhibited the lysosomal proteolytic capacity causing LC3II/LC3I elevation but autophagy substrate SQSTM1/p62 was not changed, mitophagosome accumulation, and the inhibition of migration and invasion in GBM cells. These results will help us develop high-efficiency and low-toxicity anticancer drugs to inhibit migration and invasion in GBM.
  19. Front Pharmacol. 2020 ;11 578599
    Gatti P, Ilamathi HS, Todkar K, Germain M.
      SARS-CoV-2 is a positive sense RNA coronavirus that constitutes a new threat for the global community and economy. While vaccines against SARS-CoV-2 are being developed, the mechanisms through which this virus takes control of an infected cell to replicate remains poorly understood. Upon infection, viruses completely rely on host cell molecular machinery to survive and replicate. To escape from the immune response and proliferate, viruses strategically modulate cellular metabolism and alter subcellular organelle architecture and functions. One way they do this is by modulating the structure and function of mitochondria, a critical cellular metabolic hub but also a key platform for the regulation of cellular immunity. This versatile nature of mitochondria defends host cells from viruses through several mechanisms including cellular apoptosis, ROS signaling, MAVS activation and mitochondrial DNA-dependent immune activation. These events are regulated by mitochondrial dynamics, a process by which mitochondria alter their structure (including their length and connectivity) in response to stress or other cues. It is therefore not surprising that viruses, including coronaviruses hijack these processes for their survival. In this review, we highlight how positive sense RNA viruses modulate mitochondrial dynamics and metabolism to evade mitochondrial mediated immune response in order to proliferate.
    Keywords:  RNA viruses; SARS-CoV-2; immune response; metabolism; mitochondria; mitochondrial dynamics
  20. Front Cell Dev Biol. 2020 ;8 853
    Xin T, Lv W, Liu D, Jing Y, Hu F.
      Mitochondrial dysfunction contributes to cardiovascular disorders, especially post-infarction cardiac injury, through incompletely characterized mechanisms. Among the latter, increasing evidence points to alterations in mitochondrial quality control, a range of adaptive responses regulating mitochondrial morphology and function. Optic atrophy 1 (Opa1) is a mitochondrial inner membrane GTPase known to promote mitochondrial fusion. In this study, hypoxia-mediated cardiomyocyte damage was induced to mimic post-infarction cardiac injury in vitro. Loss- and gain-of-function assays were then performed to evaluate the impact of Opa1 expression on mitochondrial quality control and cardiomyocyte survival and function. Hypoxic stress reduced cardiomyocyte viability, impaired contractile/relaxation functions, and augmented the synthesis of pro-inflammatory mediators. These effects were exacerbated by Opa1 knockdown, and significantly attenuated by Opa1 overexpression. Mitochondrial quality control was disturbed by hypoxia, as reflected by multiple mitochondrial deficits; i.e., increased fission, defective fusion, impaired mitophagy, decreased biogenesis, increased oxidative stress, and blunted respiration. By contrast, overexpression of Opa1 normalized mitochondrial quality control and sustained cardiomyocyte function. We also found that ERK, AMPK, and YAP signaling can regulate Opa1 expression. These results identify Opa1 as a novel regulator of mitochondrial quality control and highlight a key role for Opa1 in protecting cardiomyocytes against post-infarction cardiac injury.
    Keywords:  Opa1; hypoxia; mitochondria; mitochondrial quality control; post-infarction cardiac injury
  21. Biomolecules. 2020 Sep 30. pii: E1395. [Epub ahead of print]10(10):
    Aminzadeh-Gohari S, Weber DD, Catalano L, Feichtinger RG, Kofler B, Lang R.
      Drastically elevated glycolytic activity is a prominent metabolic feature of cancer cells. Until recently it was thought that tumor cells shift their entire energy production from oxidative phosphorylation (OXPHOS) to glycolysis. However, new evidence indicates that many cancer cells still have functional OXPHOS, despite their increased reliance on glycolysis. Growing pre-clinical and clinical evidence suggests that targeting mitochondrial metabolism has anti-cancer effects. Here, we analyzed mitochondrial respiration and the amount and activity of OXPHOS complexes in four melanoma cell lines and normal human dermal fibroblasts (HDFs) by Seahorse real-time cell metabolic analysis, immunoblotting, and spectrophotometry. We also tested three clinically approved antibiotics, one anti-parasitic drug (pyrvinium pamoate), and a novel anti-cancer agent (ONC212) for effects on mitochondrial respiration and proliferation of melanoma cells and HDFs. We found that three of the four melanoma cell lines have elevated glycolysis as well as OXPHOS, but contain dysfunctional mitochondria. The antibiotics produced different effects on the melanoma cells and HDFs. The anti-parasitic drug strongly inhibited respiration and proliferation of both the melanoma cells and HDFs. ONC212 reduced respiration in melanoma cells and HDFs, and inhibited the proliferation of melanoma cells. Our findings highlight ONC212 as a promising drug for targeting mitochondrial respiration in cancer.
    Keywords:  BRAF; NRAS; ONC212; Warburg effect; anti-parasitic drug; antibiotic; melanoma; mitochondrial respiration