bims-mecmid Biomed News
on Membrane communication in mitochondrial dynamics
Issue of 2021–10–03
eleven papers selected by
Mauricio Cardenas Rodriguez, University of Padova
  1. Mapping protein interactions in the active TOM-TIM23 supercomplex.
  2. Mitochondrial F1 FO ATP synthase determines the local proton motive force at cristae rims.
  3. The modified mitochondrial outer membrane carrier MTCH2 links mitochondrial fusion to lipogenesis.
  4. The Alterations in Mitochondrial Dynamics Following Cerebral Ischemia/Reperfusion Injury.
  5. Comparative Untargeted Metabolomic Profiling of Induced Mitochondrial Fusion in Pancreatic Cancer.
  6. CRISPR-Cas9 correction of OPA1 c.1334G>A: p.R445H restores mitochondrial homeostasis in dominant optic atrophy patient-derived iPSCs.
  7. Dose- and Time-Dependent Effects of Oleate on Mitochondrial Fusion/Fission Proteins and Cell Viability in HepG2 Cells: Comparison with Palmitate Effects.
  8. Drp1-dependent mitochondrial fission mediates corneal injury induced by alkali burn.
  9. Protective Effects of Inhibition of Mitochondrial Fission on Organ Function After Sepsis.
  10. MFN2 Stabilization: A Bridge for Endoplasmic Reticulum Stress Sensitivity in Melanoma.
  11. Atomic structure of human TOM core complex.
  1. Nat Commun. 2021 Sep 29. 12(1): 5715
    Mapping protein interactions in the active TOM-TIM23 supercomplex.
    Ridhima Gomkale, Andreas Linden, Piotr Neumann, Alexander Benjamin Schendzielorz, Stefan Stoldt, Olexandr Dybkov, Markus Kilisch, Christian Schulz, Luis Daniel Cruz-Zaragoza, Blanche Schwappach, Ralf Ficner, Stefan Jakobs, Henning Urlaub, Peter Rehling.
      Nuclear-encoded mitochondrial proteins destined for the matrix have to be transported across two membranes. The TOM and TIM23 complexes facilitate the transport of precursor proteins with N-terminal targeting signals into the matrix. During transport, precursors are recognized by the TIM23 complex in the inner membrane for handover from the TOM complex. However, we have little knowledge on the organization of the TOM-TIM23 transition zone and on how precursor transfer between the translocases occurs. Here, we have designed a precursor protein that is stalled during matrix transport in a TOM-TIM23-spanning manner and enables purification of the translocation intermediate. Combining chemical cross-linking with mass spectrometric analyses and structural modeling allows us to map the molecular environment of the intermembrane space interface of TOM and TIM23 as well as the import motor interactions with amino acid resolution. Our analyses provide a framework for understanding presequence handover and translocation during matrix protein transport.
    DOI:  https://doi.org/10.1038/s41467-021-26016-1
  2. EMBO Rep. 2021 Sep 30. e52727
    Mitochondrial F1 FO ATP synthase determines the local proton motive force at cristae rims.
    Bettina Rieger, Tasnim Arroum, Marie-Theres Borowski, Jimmy Villalta, Karin B Busch.
      The classical view of oxidative phosphorylation is that a proton motive force (PMF) generated by the respiratory chain complexes fuels ATP synthesis via ATP synthase. Yet, under glycolytic conditions, ATP synthase in its reverse mode also can contribute to the PMF. Here, we dissected these two functions of ATP synthase and the role of its inhibitory factor 1 (IF1) under different metabolic conditions. pH profiles of mitochondrial sub-compartments were recorded with high spatial resolution in live mammalian cells by positioning a pH sensor directly at ATP synthase's F1 and FO subunits, complex IV and in the matrix. Our results clearly show that ATP synthase activity substantially controls the PMF and that IF1 is essential under OXPHOS conditions to prevent reverse ATP synthase activity due to an almost negligible ΔpH. In addition, we show how this changes lateral, transmembrane, and radial pH gradients in glycolytic and respiratory cells.
    Keywords:  IF1; Mitochondrial F1FO ATP synthase; local pH measurements; proton motive force; ΔpH
    DOI:  https://doi.org/10.15252/embr.202152727
  3. J Cell Biol. 2021 Nov 01. pii: e202103122. [Epub ahead of print]220(11):
    The modified mitochondrial outer membrane carrier MTCH2 links mitochondrial fusion to lipogenesis.
    Katherine Labbé, Shona Mookerjee, Maxence Le Vasseur, Eddy Gibbs, Chad Lerner, Jodi Nunnari.
      Mitochondrial function is integrated with cellular status through the regulation of opposing mitochondrial fusion and division events. Here we uncover a link between mitochondrial dynamics and lipid metabolism by examining the cellular role of mitochondrial carrier homologue 2 (MTCH2). MTCH2 is a modified outer mitochondrial membrane carrier protein implicated in intrinsic cell death and in the in vivo regulation of fatty acid metabolism. Our data indicate that MTCH2 is a selective effector of starvation-induced mitochondrial hyperfusion, a cytoprotective response to nutrient deprivation. We find that MTCH2 stimulates mitochondrial fusion in a manner dependent on the bioactive lipogenesis intermediate lysophosphatidic acid. We propose that MTCH2 monitors flux through the lipogenesis pathway and transmits this information to the mitochondrial fusion machinery to promote mitochondrial elongation, enhanced energy production, and cellular survival under homeostatic and starvation conditions. These findings will help resolve the roles of MTCH2 and mitochondria in tissue-specific lipid metabolism in animals.
    DOI:  https://doi.org/10.1083/jcb.202103122
  4. Antioxidants (Basel). 2021 Aug 30. pii: 1384. [Epub ahead of print]10(9):
    The Alterations in Mitochondrial Dynamics Following Cerebral Ischemia/Reperfusion Injury.
    Jirapong Vongsfak, Wasana Pratchayasakul, Nattayaporn Apaijai, Tanat Vaniyapong, Nipon Chattipakorn, Siriporn C Chattipakorn.
      Cerebral ischemia results in a poor oxygen supply and cerebral infarction. Reperfusion to the ischemic area is the best therapeutic approach. Although reperfusion after ischemia has beneficial effects, it also causes ischemia/reperfusion (I/R) injury. Increases in oxidative stress, mitochondrial dysfunction, and cell death in the brain, resulting in brain infarction, have also been observed following cerebral I/R injury. Mitochondria are dynamic organelles, including mitochondrial fusion and fission. Both processes are essential for mitochondrial homeostasis and cell survival. Several studies demonstrated that an imbalance in mitochondrial dynamics after cerebral ischemia, with or without reperfusion injury, plays an important role in the regulation of cell survival and infarct area size. Mitochondrial dysmorphology/dysfunction and inflammatory processes also occur after cerebral ischemia. Knowledge surrounding the mechanisms involved in the imbalance in mitochondrial dynamics following cerebral ischemia with or without reperfusion injury would help in the prevention or treatment of the adverse effects of cerebral injury. Therefore, this review aims to summarize and discuss the roles of mitochondrial dynamics, mitochondrial function, and inflammatory processes in cerebral ischemia with or without reperfusion injury from in vitro and in vivo studies. Any contradictory findings are incorporated and discussed.
    Keywords:  fission; fusion; ischemia; mitochondria; reperfusion
    DOI:  https://doi.org/10.3390/antiox10091384
  5. Metabolites. 2021 Sep 15. pii: 627. [Epub ahead of print]11(9):
    Comparative Untargeted Metabolomic Profiling of Induced Mitochondrial Fusion in Pancreatic Cancer.
    Nicholas D Nguyen, Meifang Yu, Vinit Y Reddy, Ariana C Acevedo-Diaz, Enzo C Mesarick, Joseph Abi Jaoude, Min Yuan, John M Asara, Cullen M Taniguchi.
      Mitochondria are dynamic organelles that constantly alter their shape through the recruitment of specialized proteins, like mitofusin-2 (Mfn2) and dynamin-related protein 1 (Drp1). Mfn2 induces the fusion of nearby mitochondria, while Drp1 mediates mitochondrial fission. We previously found that the genetic or pharmacological activation of mitochondrial fusion was tumor suppressive against pancreatic ductal adenocarcinoma (PDAC) in several model systems. The mechanisms of how these different inducers of mitochondrial fusion reduce pancreatic cancer growth are still unknown. Here, we characterized and compared the metabolic reprogramming of these three independent methods of inducing mitochondrial fusion in KPC cells: overexpression of Mfn2, genetic editing of Drp1, or treatment with leflunomide. We identified significantly altered metabolites via robust, orthogonal statistical analyses and found that mitochondrial fusion consistently produces alterations in the metabolism of amino acids. Our unbiased methodology revealed that metabolic perturbations were similar across all these methods of inducing mitochondrial fusion, proposing a common pathway for metabolic targeting with other drugs.
    Keywords:  fission; fusion; leflunomide; metabolomic reprogramming; metabolomics; mitochondrial morphology; mitofusin-2; pancreatic cancer
    DOI:  https://doi.org/10.3390/metabo11090627
  6. Mol Ther Nucleic Acids. 2021 Dec 03. 26 432-443
    CRISPR-Cas9 correction of OPA1 c.1334G>A: p.R445H restores mitochondrial homeostasis in dominant optic atrophy patient-derived iPSCs.
    Paul E Sladen, Pedro R L Perdigão, Grace Salsbury, Tatiana Novoselova, Jacqueline van der Spuy, J Paul Chapple, Patrick Yu-Wai-Man, Michael E Cheetham.
      Autosomal dominant optic atrophy (DOA) is the most common inherited optic neuropathy in the United Kingdom. DOA has an insidious onset in early childhood, typically presenting with bilateral, central visual loss caused by the preferential loss of retinal ganglion cells. 60%-70% of genetically confirmed DOA cases are associated with variants in OPA1, a ubiquitously expressed GTPase that regulates mitochondrial homeostasis through coordination of inner membrane fusion, maintenance of cristae structure, and regulation of bioenergetic output. Whether genetic correction of OPA1 pathogenic variants can alleviate disease-associated phenotypes remains unknown. Here, we demonstrate generation of patient-derived OPA1 c.1334G>A: p.R445H mutant induced pluripotent stem cells (iPSCs), followed by correction of OPA1 through CRISPR-Cas9-guided homology-directed repair (HDR) and evaluate the effect of OPA1 correction on mitochondrial homeostasis. CRISPR-Cas9 gene editing demonstrated an efficient method of OPA1 correction, with successful gene correction in 57% of isolated iPSCs. Correction of OPA1 restored mitochondrial homeostasis, re-establishing the mitochondrial network and basal respiration and ATP production levels. In addition, correction of OPA1 re-established the levels of wild-type (WT) mitochondrial DNA (mtDNA) and reduced susceptibility to apoptotic stimuli. These data demonstrate that nuclear gene correction can restore mitochondrial homeostasis and improve mtDNA integrity in DOA patient-derived cells carrying an OPA1 variant.
    Keywords:  CRISPR; OPA1; apoptosis; bioenergetics; gene correction; gene editing; iPSC; mitochondria; optic atrophy; retinal ganglion cell
    DOI:  https://doi.org/10.1016/j.omtn.2021.08.015
  7. Int J Mol Sci. 2021 Sep 10. pii: 9812. [Epub ahead of print]22(18):
    Dose- and Time-Dependent Effects of Oleate on Mitochondrial Fusion/Fission Proteins and Cell Viability in HepG2 Cells: Comparison with Palmitate Effects.
    Isy F de Sousa, Vincenzo Migliaccio, Marilena Lepretti, Gaetana Paolella, Ilaria Di Gregorio, Ivana Caputo, Eliane Beraldi Ribeiro, Lillà Lionetti.
      Mitochondrial impairments in dynamic behavior (fusion/fission balance) associated with mitochondrial dysfunction play a key role in cell lipotoxicity and lipid-induced metabolic diseases. The present work aimed to evaluate dose- and time-dependent effects of the monounsaturated fatty acid oleate on mitochondrial fusion/fission proteins in comparison with the saturated fatty acid palmitate in hepatic cells. To this end, HepG-2 cells were treated with 0, 10 μM, 50 μM, 100 μM, 250 μM or 500 μM of either oleate or palmitate for 8 or 24 h. Cell viability and lipid accumulation were evaluated to assess lipotoxicity. Mitochondrial markers of fusion (mitofusin 2, MFN2) and fission (dynamin-related protein 1, DRP1) processes were evaluated by Western blot analysis. After 8 h, the highest dose of oleate induced a decrease in DRP1 content without changes in MFN2 content in association with cell viability maintenance, whereas palmitate induced a decrease in cell viability associated with a decrease mainly in MFN2 content. After 24 h, oleate induced MFN2 increase, whereas palmitate induced DRP1 increase associated with a higher decrease in cell viability with high doses compared to oleate. This finding could be useful to understand the role of mitochondria in the protective effects of oleate as a bioactive compound.
    Keywords:  DRP1; MFN2; cellular adaptation; hepatocytes; lipotoxicity; mitochondrial dynamics; monounsaturated fatty acids; saturated fatty acids
    DOI:  https://doi.org/10.3390/ijms22189812
  8. Free Radic Biol Med. 2021 Sep 22. pii: S0891-5849(21)00739-5. [Epub ahead of print]176 149-161
    Drp1-dependent mitochondrial fission mediates corneal injury induced by alkali burn.
    Kun Zhang, Miao-Yu Guo, Qiu-Gen Li, Xiao-Hua Wang, Yu-Ying Wan, Zhang-Jian Yang, Min He, Yun-Min Yi, Li-Ping Jiang, Xin-Hui Qu, Xiao-Jian Han.
      Corneal alkali burn, one of the most serious ophthalmic emergencies, is difficult to be cured by conservative treatments. It is well known that oxidative stress, inflammation and neovascularization are the main causes of corneal damage after alkali burn, but its underlying mechanism remains to be elucidated. Here, we reported that the expression and phosphorylation (Ser616) of mitochondrial fission protein Drp1 were up-regulated at day 3 after alkali burn, while mitochondrial fusion protein Mfn2 was down-regulated. The phosphorylation of ERK1/2 in corneas was increased at day 1, 3, 7 and peaked at day 3 after alkali burn. In human corneal epithelial cells (HCE-2), NaOH treatment induced mitochondrial fission, intracellular ROS production and mitochondrial membrane potential disruption, which was prevented by Drp1 inhibitor Mdivi-1. In corneas, Mdivi-1 or knockdown of Drp1 by Lenti-Drp1 shRNA attenuated alkali burn-induced ROS production and phosphorylation of IκBα and p65. In immunofluorescence staining, it was detected that Mdivi-1 also prevented NaOH-induced nuclear translocation of p65 in HCE-2 cells. Moreover, the expression of NADPH oxidase NOX2 and NOX4 in corneas peaked at day 7 after alkali burn. Mdivi-1, Lenti-Drp1 shRNA or the mitochondria-targeted antioxidant mito-TEMPO efficiently alleviated activation of NF-κB, expression of NOX2/4 and inflammatory cytokines including IL-6, IL-1β and TNF-α in corneas after alkali burn. In pharmacological experiments, both Mdivi-1 and NADPH oxidases inhibitor Apocynin protected the corneas against alkali burn-induced neovascularization. Intriguingly, the combined administration of Mdivi-1 and Apocynin had a synergistic inhibitory effect on corneal neovascularization after alkali burn. Taken together, these results indicate that Drp1-dependent mitochondrial fission is involved in alkali burn-induced corneal injury through regulating oxidative stress, inflammatory responses and corneal neovascularization. This might provide a novel therapeutic target for corneal injury after alkali burn in the future.
    Keywords:  Corneal alkali burn; Corneal neovascularization; Inflammation; Mitochondrial fission; NADPH oxidase; Oxidative stress
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2021.09.019
  9. Front Pharmacol. 2021 ;12 712489
    Protective Effects of Inhibition of Mitochondrial Fission on Organ Function After Sepsis.
    Yu Zhu, Lei Kuang, Yue Wu, Haoyue Deng, Han She, Yuanqun Zhou, Jie Zhang, Liangming Liu, Tao Li.
      Sepsis-associated organ dysfunction plays a critical role in its high mortality, mainly in connection with mitochondrial dysfunction. Whether the inhibition of mitochondrial fission is beneficial to sepsis-related organ dysfunction and underlying mechanisms are unknown. Cecal ligation and puncture induced sepsis in rats and dynamic related protein 1 knockout mice, lipopolysaccharide-treated vascular smooth muscle cells and cardiomyocytes, were used to explore the effects of inhibition of mitochondrial fission and specific mechanisms. Our study showed that mitochondrial fission inhibitor Mdivi-1 could antagonize sepsis-induced organ dysfunction including heart, vascular smooth muscle, liver, kidney, and intestinal functions, and prolonged animal survival. The further study showed that mitochondrial functions such as mitochondrial membrane potential, adenosine-triphosphate contents, reactive oxygen species, superoxide dismutase and malonaldehyde were recovered after Mdivi-1 administration via improving mitochondrial morphology. And sepsis-induced inflammation and apoptosis in heart and vascular smooth muscle were alleviated through inhibition of mitochondrial fission and mitochondrial function improvement. The parameter trends in lipopolysaccharide-stimulated cardiomyocytes and vascular smooth muscle cells were similar in vivo. Dynamic related protein 1 knockout preserved sepsis-induced organ dysfunction, and the animal survival was prolonged. Taken together, this finding provides a novel effective candidate therapy for severe sepsis/septic shock and other critical clinical diseases.
    Keywords:  Drp1; Mdivi-1; mitochondrial fission; organ function; sepsis
    DOI:  https://doi.org/10.3389/fphar.2021.712489
  10. J Invest Dermatol. 2021 Sep 23. pii: S0022-202X(21)01224-0. [Epub ahead of print]
    MFN2 Stabilization: A Bridge for Endoplasmic Reticulum Stress Sensitivity in Melanoma.
    Charles H Adelmann, Inbal Rachmin, David E Fisher.
      In a new article in the Journal of Investigative Dermatology, Wang et al. (2021) report that mitochondrial quality control modulates responses to endoplasmic reticulum (ER) stress in melanoma. They implicate a linear pathway of XBP1, MARCH5, and MFN2 that act together to regulate mitochondrial fission and mitophagy and ultimately mediate melanoma cell sensitivity to ER stress. This work informs therapeutic combinations and biomarker strategies for targeting melanoma organellar homeostasis as well as for life‒death decisions.
    DOI:  https://doi.org/10.1016/j.jid.2021.05.003
  11. Cell Discov. 2020 Sep 29. 6(1): 67
    Atomic structure of human TOM core complex.
    Wenhe Wang, Xudong Chen, Laixing Zhang, Jingbo Yi, Qingxi Ma, Jian Yin, Wei Zhuo, Jinke Gu, Maojun Yang.
      The translocase of the outer mitochondrial membrane (TOM) complex is the main entry gate for mitochondrial precursor proteins synthesized on cytosolic ribosomes. Here we report the single-particle cryo-electron microscopy (cryo-EM) structure of the dimeric human TOM core complex (TOM-CC). Two Tom40 β-barrel proteins, connected by two Tom22 receptor subunits and one phospholipid, form the protein-conducting channels. The small Tom proteins Tom5, Tom6, and Tom7 surround the channel and have notable configurations. The distinct electrostatic features of the complex, including the pronounced negative interior and the positive regions at the periphery and center of the dimer on the intermembrane space (IMS) side, provide insight into the preprotein translocation mechanism. Further, two dimeric TOM complexes may associate to form tetramer in the shape of a parallelogram, offering a potential explanation into the unusual structural features of Tom subunits and a new perspective of viewing the import of mitochondrial proteins.
    DOI:  https://doi.org/10.1038/s41421-020-00198-2
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