bims-mitdyn Biomed News
on Mitochondrial dynamics
Issue of 2020‒08‒02
eleven papers selected by
Edmond Chan
Queen’s University, School of Medicine

  1. Sci Signal. 2020 Jul 28. pii: eaaz8240. [Epub ahead of print]13(642):
    Li J, Agarwal E, Bertolini I, Seo JH, Caino MC, Ghosh JC, Kossenkov AV, Liu Q, Tang HY, Goldman AR, Languino LR, Speicher DW, Altieri DC.
      Mitochondria are signaling hubs in eukaryotic cells. Here, we showed that the mitochondrial FUN14 domain-containing protein-1 (FUNDC1), an effector of Parkin-independent mitophagy, also participates in cellular plasticity by sustaining oxidative bioenergetics, buffering ROS production, and supporting cell proliferation. Targeting this pathway in cancer cells suppressed tumor growth but rendered transformed cells more motile and invasive in a manner dependent on ROS-mediated mitochondrial dynamics and mitochondrial repositioning to the cortical cytoskeleton. Global metabolomics and proteomics profiling identified a FUNDC1 interactome at the mitochondrial inner membrane, comprising the AAA+ protease, LonP1, and subunits of oxidative phosphorylation, complex V (ATP synthase). Independently of its previously identified role in mitophagy, FUNDC1 enabled LonP1 proteostasis, which in turn preserved complex V function and decreased ROS generation. Therefore, mitochondrial reprogramming by a FUNDC1-LonP1 axis controls tumor cell plasticity by switching between proliferative and invasive states in cancer.
  2. Nature. 2020 Jul 29.
    Hernansanz-Agustín P, Choya-Foces C, Carregal-Romero S, Ramos E, Oliva T, Villa-Piña T, Moreno L, Izquierdo-Álvarez A, Cabrera-García JD, Cortés A, Lechuga-Vieco AV, Jadiya P, Navarro E, Parada E, Palomino-Antolín A, Tello D, Acín-Pérez R, Rodríguez-Aguilera JC, Navas P, Cogolludo Á, López-Montero I, Martínez-Del-Pozo Á, Egea J, López MG, Elrod JW, Ruíz-Cabello J, Bogdanova A, Enríquez JA, Martínez-Ruiz A.
      All metazoans depend on the consumption of O2 by the mitochondrial oxidative phosphorylation system (OXPHOS) to produce energy. In addition, the OXPHOS uses O2 to produce reactive oxygen species that can drive cell adaptations1-4, a phenomenon that occurs in hypoxia4-8 and whose precise mechanism remains unknown. Ca2+ is the best known ion that acts as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential10. Here we show that Na+ acts as a second messenger that regulates OXPHOS function and the production of reactive oxygen species by modulating the fluidity of the inner mitochondrial membrane. A conformational shift in mitochondrial complex I during acute hypoxia11 drives acidification of the matrix and the release of free Ca2+ from calcium phosphate (CaP) precipitates. The concomitant activation of the mitochondrial Na+/Ca2+ exchanger promotes the import of Na+ into the matrix. Na+ interacts with phospholipids, reducing inner mitochondrial membrane fluidity and the mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III. The inhibition of Na+ import through the Na+/Ca2+ exchanger is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences for cellular metabolism.
  3. J Mol Cell Cardiol. 2020 Jul 24. pii: S0022-2828(20)30231-5. [Epub ahead of print]
    Moyzis AG, Lally NS, Liang W, Leon LJ, Najor RH, Orogo AM, Gustafsson ÅB.
      Myeloid cell leukemia-1 (Mcl-1) is a structurally and functionally unique anti-apoptotic Bcl-2 protein. While elevated levels of Mcl-1 contribute to tumor cell survival and drug resistance, loss of Mcl-1 in cardiac myocytes leads to rapid mitochondrial dysfunction and heart failure development. Although Mcl-1 is an anti-apoptotic protein, previous studies indicate that its functions extend beyond regulating apoptosis. Mcl-1 is localized to both the mitochondrial outer membrane and matrix. Here, we have identified that Mcl-1 in the outer mitochondrial membrane mediates mitochondrial fission, which is independent of its anti-apoptotic function. We demonstrate that Mcl-1 interacts with Drp1 to promote mitochondrial fission in response to various challenges known to perturb mitochondria morphology. Induction of fission by Mcl-1 reduces nutrient deprivation-induced cell death and the protection is independent of its BH3 domain. Finally, cardiac-specific overexpression of Mcl-1OM, but not Mcl-1Matrix, contributes to a shift in the balance towards fission and leads to reduced exercise capacity, suggesting that a pre-existing fragmented mitochondrial network leads to decreased ability to adapt to an acute increase in workload and energy demand. Overall, these findings highlight the importance of Mcl-1 in maintaining mitochondrial health in cells.
    Keywords:  Drp1; Fission; Heart; Mcl-1; Mitochondria
  4. Nat Metab. 2020 Jul 27.
    Pinkosky SL, Scott JW, Desjardins EM, Smith BK, Day EA, Ford RJ, Langendorf CG, Ling NXY, Nero TL, Loh K, Galic S, Hoque A, Smiles WJ, Ngoei KRW, Parker MW, Yan Y, Melcher K, Kemp BE, Oakhill JS, Steinberg GR.
      Long-chain fatty acids (LCFAs) play important roles in cellular energy metabolism, acting as both an important energy source and signalling molecules1. LCFA-CoA esters promote their own oxidation by acting as allosteric inhibitors of acetyl-CoA carboxylase, which reduces the production of malonyl-CoA and relieves inhibition of carnitine palmitoyl-transferase 1, thereby promoting LCFA-CoA transport into the mitochondria for β-oxidation2-6. Here we report a new level of regulation wherein LCFA-CoA esters per se allosterically activate AMP-activated protein kinase (AMPK) β1-containing isoforms to increase fatty acid oxidation through phosphorylation of acetyl-CoA carboxylase. Activation of AMPK by LCFA-CoA esters requires the allosteric drug and metabolite site formed between the α-subunit kinase domain and the β-subunit. β1 subunit mutations that inhibit AMPK activation by the small-molecule activator A769662, which binds to the allosteric drug and metabolite site, also inhibit activation by LCFA-CoAs. Thus, LCFA-CoA metabolites act as direct endogenous AMPK β1-selective activators and promote LCFA oxidation.
  5. J Biol Chem. 2020 Jul 30. pii: jbc.RA120.012680. [Epub ahead of print]
    Huang LS, Kotha SR, Avasarala S, VanScoyk M, Winn RA, Pennathur A, Yashaswini PS, Bandela M, Salgia R, Tyurina YY, Kagan VE, Zhu X, Reddy SP, Sudhadevi T, Punathil-Kannan PK, Harijith A, Ramchandran R, Bikkavilli RK, Natarajan V.
      Lysocardiolipin acyltransferase (LYCAT), a cardiolipin (CL)-remodeling enzyme, is crucial for maintaining normal mitochondrial function and vascular development. Despite the well-characterized role for LYCAT in the regulation of mitochondrial dynamics, it's involvement in lung cancer, if any, remains incompletely understood. In this study, in silico analysis of TCGA lung cancer datasets revealed a significant increase in LYCAT expression, which was later corroborated in human lung cancer tissues and immortalized lung cancer cell lines via indirect immunofluorescence and immunoblotting, respectively. Stable knockdown of LYCAT in NSCLC cell lines not only reduced CL and increased monolyso CL levels but also reduced in vivo tumor growth, as determined by xenograft studies in athymic nude mice. Furthermore, blocking LYCAT activity using a LYCAT mimetic peptide, attenuated cell migration, suggesting a novel role for LYCAT activity in promoting NSCLC. Mechanistically, the pro-proliferative effects of LYCAT were mediated by an increase in mitochondrial fusion, and a G1/S cell cycle transition, both of which are linked to increased cell proliferation. Taken together, these results demonstrate a novel role for LYCAT in promoting NSCLC and suggests that targeting LYCAT expression or activity in NSCLC may provide new avenues for the therapeutic treatment of lung cancer.
    Keywords:  Cardiolipin; Cell migration; Cell proliferation; LYCAT; NSCLC; cardiolipin; cell cycle; cell migration; cell proliferation; lung cancer
  6. Dev Cell. 2020 Jul 15. pii: S1534-5807(20)30546-3. [Epub ahead of print]
    Williams R, Laskovs M, Williams RI, Mahadevan A, Labbadia J.
      The loss of protein homeostasis (proteostasis) is a primary driver of age-related tissue dysfunction. Recent studies have revealed that the failure of proteostasis with age is triggered by developmental and reproductive cues that repress the activity of proteostasis-related pathways in early adulthood. In Caenorhabditis elegans, reduced mitochondrial electron transport chain (ETC) function during development can override signals that promote proteostasis collapse in aged tissues. However, it is unclear precisely how these beneficial effects are mediated. Here, we reveal that in response to ETC impairment, the PP2A complex generates a dephosphorylated, mitochondrial stress-specific variant of the transcription factor HSF-1. This results in the selective induction of small heat shock proteins in adulthood, thereby protecting against age-related proteostasis collapse. We propose that mitochondrial signals early in life can protect the aging cytosolic proteome by tailoring HSF-1 activity to preferentially drive the expression of non-ATP-dependent chaperones.
    Keywords:  HSF1; PP2A; aging; mitochondria; molecular chaperones; protein aggregation; proteostasis; stress responses
  7. Front Physiol. 2020 ;11 782
    Dorn GW.
      A causal relationship between Mitofusin (MFN) 2 gene mutations and the hereditary axonal neuropathy Charcot-Marie-Tooth disease type 2A (CMT2A) was described over 15 years ago. During the intervening period much has been learned about MFN2 functioning in mitochondrial fusion, calcium signaling, and quality control, and the consequences of these MFN2 activities on cell metabolism, fitness, and development. Nevertheless, the challenge of defining the central underlying mechanism(s) linking mitochondrial abnormalities to progressive dying-back of peripheral arm and leg nerves in CMT2A is largely unmet. Here, a different perspective of why, in humans, MFN2 dysfunction preferentially impacts peripheral nerves is provided based on recent insights into its role in determining whether individual mitochondria will be fusion-competent and retained within the cell, or are fusion-impaired, sequestered, and eliminated by mitophagy. Evidence for and against a regulatory role of mitofusins in mitochondrial transport is reviewed, nagging questions defined, and implications on mitochondrial fusion, quality control, and neuronal degeneration discussed. Finally, in the context of recently described mitofusin activating peptides and small molecules, an overview is provided of potential therapeutic applications for pharmacological enhancement of mitochondrial fusion and motility in CMT2A and other neurodegenerative conditions.
    Keywords:  Charcot-Marie-Tooth disease; mitochondrial fusion; mitochondrial transport; mitophagy; neurodegeneration
  8. Proc Natl Acad Sci U S A. 2020 Jul 31. pii: 202008021. [Epub ahead of print]
    Wei W, Ruvkun G.
      Mitochondrial fission and fusion are highly regulated by energy demand and physiological conditions to control the production, activity, and movement of these organelles. Mitochondria are arrayed in a periodic pattern in Caenorhabditis elegans muscle, but this pattern is disrupted by mutations in the mitochondrial fission component dynamin DRP-1. Here we show that the dramatically disorganized mitochondria caused by a mitochondrial fission-defective dynamin mutation is strongly suppressed to a more periodic pattern by a second mutation in lysosomal biogenesis or acidification. Vitamin B12 is normally imported from the bacterial diet via lysosomal degradation of B12-binding proteins and transport of vitamin B12 to the mitochondrion and cytoplasm. We show that the lysosomal dysfunction induced by gene inactivations of lysosomal biogenesis or acidification factors causes vitamin B12 deficiency. Growth of the C. elegans dynamin mutant on an Escherichia coli strain with low vitamin B12 also strongly suppressed the mitochondrial fission defect. Of the two C. elegans enzymes that require B12, gene inactivation of methionine synthase suppressed the mitochondrial fission defect of a dynamin mutation. We show that lysosomal dysfunction induced mitochondrial biogenesis, which is mediated by vitamin B12 deficiency and methionine restriction. S-adenosylmethionine, the methyl donor of many methylation reactions, including histones, is synthesized from methionine by S-adenosylmethionine synthase; inactivation of the sams-1 S-adenosylmethionine synthase also suppresses the drp-1 fission defect, suggesting that vitamin B12 regulates mitochondrial biogenesis and then affects mitochondrial fission via chromatin pathways.
    Keywords:  interorganelle communication; methionine restriction; mitochondrial dynamics; vacuolar V-ATPase; vitamin B12
  9. Cell Rep. 2020 Jul 28. pii: S2211-1247(20)30924-4. [Epub ahead of print]32(4): 107943
    Federspiel JD, Cook KC, Kennedy MA, Venkatesh SS, Otter CJ, Hofstadter WA, Jean Beltran PM, Cristea IM.
      Nearly all biological processes rely on the finely tuned coordination of protein interactions across cellular space and time. Accordingly, generating protein interactomes has become routine in biological studies, yet interpreting these datasets remains computationally challenging. Here, we introduce Inter-ViSTA (Interaction Visualization in Space and Time Analysis), a web-based platform that quickly builds animated protein interaction networks and automatically synthesizes information on protein abundances, functions, complexes, and subcellular localizations. Using Inter-ViSTA with proteomics and molecular virology, we define virus-host interactions for the human cytomegalovirus (HCMV) anti-apoptotic protein, pUL37x1. We find that spatiotemporal controlled interactions underlie pUL37x1 functions, facilitating the pro-viral remodeling of mitochondria and peroxisomes during infection. Reciprocal isolations, microscopy, and genetic manipulations further characterize these associations, revealing the interplay between pUL37x1 and the MIB complex, which is critical for mitochondrial integrity. At the peroxisome, we show that pUL37x1 activates PEX11β to regulate fission, a key aspect of virus assembly and spread.
    Keywords:  HCMV; IP-MS; Inter-ViSTA; MICOS; mitochondria; pUL37; peroxisome; protein interactions; vMIA; virus-host interactions
  10. Nat Metab. 2020 Jul 27.
    Orozco JM, Krawczyk PA, Scaria SM, Cangelosi AL, Chan SH, Kunchok T, Lewis CA, Sabatini DM.
      The mechanistic target of rapamycin complex 1 (mTORC1) kinase regulates cell growth by setting the balance between anabolic and catabolic processes. To be active, mTORC1 requires the environmental presence of amino acids and glucose. While a mechanistic understanding of amino acid sensing by mTORC1 is emerging, how glucose activates mTORC1 remains mysterious. Here, we used metabolically engineered human cells lacking the canonical energy sensor AMP-activated protein kinase to identify glucose-derived metabolites required to activate mTORC1 independent of energetic stress. We show that mTORC1 senses a metabolite downstream of the aldolase and upstream of the GAPDH-catalysed steps of glycolysis and pinpoint dihydroxyacetone phosphate (DHAP) as the key molecule. In cells expressing a triose kinase, the synthesis of DHAP from DHA is sufficient to activate mTORC1 even in the absence of glucose. DHAP is a precursor for lipid synthesis, a process under the control of mTORC1, which provides a potential rationale for the sensing of DHAP by mTORC1.