bims-midtic Biomed News
on Mitochondrial dynamics and trafficking in cells
Issue of 2023–08–20
seventeen papers selected by
Omkar Joshi, Turku Bioscience
  1. Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis.
  2. Discovery of Potent Allosteric DRP1 Inhibitors by Disrupting Protein-Protein Interaction with MiD49.
  3. Temporal control of contact site formation reveals a relationship between mitochondrial division and Num1-mediated mitochondrial tethering.
  4. NME3 binds to phosphatidic acid and mediates PLD6-induced mitochondrial tethering.
  5. When mitophagy dictates the outcome of cellular infection: the case of Brucella abortus.
  6. E4 ubiquitin ligase promotes mitofusin turnover and mitochondrial stress response.
  7. Endoplasmic reticulum stress induced by turbulence of mitochondrial fusion and fission was involved in stressed cardiomyocyte injury.
  8. Propionic acid induces alterations in mitochondrial morphology and dynamics in SH-SY5Y cells.
  9. Mitochondria-related signaling pathways involved in breast cancer regulate ferroptosis.
  10. Milton assembles large mitochondrial clusters, mitoballs, to sustain spermatogenesis.
  11. The mitophagy pathway and its implications in human diseases.
  12. Exploring the therapeutic potential of the mitochondrial transfer-associated enzymatic machinery in brain degeneration.
  13. IL-12/15/18-induced cell death and mitochondrial dynamics of human NK cells.
  14. Optogenetic cleavage of the Miro GTPase reveals the direct consequences of real-time loss of function in Drosophila.
  15. The AAA-ATPase Yta4/ATAD1 interacts with the mitochondrial divisome to inhibit mitochondrial fission.
  16. Mitochondria are secreted in extracellular vesicles when lysosomal function is impaired.
  17. Inhibition of ERK downregulates autophagy via mitigating mitochondrial fragmentation to protect SH-SY5Y cells from OGD/R injury.
  1. Am J Physiol Cell Physiol. 2023 Aug 14.
    Muscle mitochondrial transplantation can rescue and maintain cellular homeostasis.
    Debasmita Bhattacharya, Mikhaela B Slavin, David A Hood.
      Mitochondria control cellular functions through their metabolic role. Recent research that has gained considerable attention is their ability to transfer between cells. This has the potential of improving cellular functions in pathological or energy deficit conditions, but little is known about the role of mitochondrial transfer in sustaining cellular homeostasis. Few studies have investigated the potential of skeletal muscle as a source of healthy mitochondria that can be transferred to other cell types. Thus, we isolated intermyofibrillar mitochondria from murine skeletal muscle and incubated them with host cells. We observed dose- and time-dependent increases in mitochondrial incorporation into myoblasts. This resulted in elongated mitochondrial networks and an enhancement of bioenergetic profile of the host cells. Mitochondrial donation also rejuvenated the functional capacities of the myoblasts when respiration efficiency and lysosomal function were inhibited by complex I inhibitor rotenone and bafilomycin A, respectively. Mitochondrial transfer was accomplished via tunneling nanotubes, extracellular vesicles, gap junctions and by macropinocytosis internalization. Murine muscle mitochondria were also effectively transferred to human fibroblast cells having mitochondrial DNA mutations, resulting in augmented mitochondrial dynamics and metabolic functions. This improved cell function by diminishing ROS emission in the diseased cells. Our findings suggest that mitochondria from donor skeletal muscle can be integrated in both healthy and functionally compromised host cells leading to mitochondrial structural refinement and respiratory boost. This mitochondrial trafficking and bioenergetic reprogramming to maintain and revitalise tissue homeostasis could be a useful therapeutic strategy in treating diseases.
    Keywords:  Lysosome; Mitochondrial DNA Defects; Mitochondrial Dynamics; Mitochondrial Transplantation; Oxygen Consumption
    DOI:  https://doi.org/10.1152/ajpcell.00212.2023
  2. ACS Med Chem Lett. 2023 Aug 10. 14(8): 1095-1099
    Discovery of Potent Allosteric DRP1 Inhibitors by Disrupting Protein-Protein Interaction with MiD49.
    Takeru Furuya, Jean Lin, Arina Afanaseva, Lisa Molz, Bharat Lagu, Bin Ma.
      Mitochondrial dysfunction has been attributed to many disease indications, including metabolic, cardiovascular, neoplastic, and neurodegenerative diseases. Dynamin related protein 1 (DRP1) is crucial in regulating mitochondrial fission and maintaining mitochondrial homeostasis. MiD49 is a dynamic peripheral protein receptor on the surface of the mitochondrial membrane that recruits DRP1 protein to induce mitochondrial binary fission. By targeting the protein-protein interaction of DRP1/MiD49, we have discovered a novel and potent allosteric DRP1 inhibitor that inhibits mitochondria fragmentation in vitro. X-ray cocrystal structure revealed that it locked the closed DRP1 conformation by induced dimerization.
    DOI:  https://doi.org/10.1021/acsmedchemlett.3c00223
  3. Mol Biol Cell. 2023 Aug 16. mbcE23050168
    Temporal control of contact site formation reveals a relationship between mitochondrial division and Num1-mediated mitochondrial tethering.
    Clare S Harper, Jason C Casler, Laura L Lackner.
      Mitochondrial division is critical for maintenance of mitochondrial morphology and cellular homeostasis. Previous work has suggested that the mitochondria-ER-cortex anchor (MECA), a tripartite membrane contact site between mitochondria, the ER, and the plasma membrane, is involved in mitochondrial division. However, its role is poorly understood. We developed a system to control MECA formation and depletion, which allowed us to investigate the relationship between MECA-mediated contact sites and mitochondrial division. Num1 is the protein that mediates mitochondria-ER-plasma membrane tethering at MECA sites. Using both rapamycin-inducible dimerization and auxin-inducible degradation components coupled with Num1, we developed systems to temporally control the formation and depletion of the native contact site. Additionally, we designed a regulatable Num1-independant mitochondria-PM tether. We found that mitochondria-PM tethering alone is not sufficient to rescue mitochondrial division and that a specific feature of Num1-mediated tethering is required. This study demonstrates the utility of systems that regulate contact site formation and depletion in studying the biological functions of membrane contact sites. [Media: see text] [Media: see text].
    DOI:  https://doi.org/10.1091/mbc.E23-05-0168
  4. J Cell Biol. 2023 10 02. pii: e202301091. [Epub ahead of print]222(10):
    NME3 binds to phosphatidic acid and mediates PLD6-induced mitochondrial tethering.
    You-An Su, Hsin-Yi Chiu, Yu-Chen Chang, Chieh-Ju Sung, Chih-Wei Chen, Reika Tei, Xuang-Rong Huang, Shao-Chun Hsu, Shan-Shan Lin, Hsien-Chu Wang, Yu-Chun Lin, Jui-Cheng Hsu, Hermann Bauer, Yuxi Feng, Jeremy M Baskin, Zee-Fen Chang, Ya-Wen Liu.
      Mitochondria are dynamic organelles regulated by fission and fusion processes. The fusion of membranes requires elaborative coordination of proteins and lipids and is particularly crucial for the function and quality control of mitochondria. Phosphatidic acid (PA) on the mitochondrial outer membrane generated by PLD6 facilitates the fusion of mitochondria. However, how PA promotes mitochondrial fusion remains unclear. Here, we show that a mitochondrial outer membrane protein, NME3, is required for PLD6-induced mitochondrial tethering or clustering. NME3 is enriched at the contact interface of two closely positioned mitochondria depending on PLD6, and NME3 binds directly to PA-exposed lipid packing defects via its N-terminal amphipathic helix. The PA binding function and hexamerization confer NME3 mitochondrial tethering activity. Importantly, nutrient starvation enhances the enrichment efficiency of NME3 at the mitochondrial contact interface, and the tethering ability of NME3 contributes to fusion efficiency. Together, our findings demonstrate NME3 as a tethering protein promoting selective fusion between PLD6-remodeled mitochondria for quality control.
    DOI:  https://doi.org/10.1083/jcb.202301091
  5. Autophagy. 2023 Aug 17. 1-2
    When mitophagy dictates the outcome of cellular infection: the case of Brucella abortus.
    Jérémy Verbeke, Xavier De Bolle, Thierry Arnould.
      Mitochondria are at the basis of various cellular functions ranging from metabolism and redox homeostasis to inflammation and cell death regulation. Mitochondria therefore constitute an attractive target for invading pathogens to fulfil their infectious cycle. This involves the modulation to their advantage of mitochondrial metabolism and dynamics, including the controlled degradation of mitochondria through mitophagy. Mitophagy might for instance be beneficial for bacterial survival as it can clear bactericidal mitochondrial ROS produced by damaged organelle fragments from the intracellular niche. In the case of the bacterial pathogen Brucella abortus, mitophagy induction has another role in the intracellular lifecycle of the bacteria. Indeed, in our study, we showed that B. abortus triggers an iron-dependent BNIP3L-mediated mitophagy response required for proper bacterial egress and infection of neighboring cells. These results highlight the diversity of mitophagy processes that might be crucial for several stages of cellular infection.
    Keywords:  BNIP3L; Brucella; HIF1A; intracellular trafficking; iron; mitophagy
    DOI:  https://doi.org/10.1080/15548627.2023.2246354
  6. Mol Cell. 2023 Aug 17. pii: S1097-2765(23)00563-4. [Epub ahead of print]83(16): 2976-2990.e9
    E4 ubiquitin ligase promotes mitofusin turnover and mitochondrial stress response.
    Vincent Anton, Ira Buntenbroich, Tânia Simões, Mariana Joaquim, Leonie Müller, Reinhard Buettner, Margarete Odenthal, Thorsten Hoppe, Mafalda Escobar-Henriques.
      Ubiquitin-dependent control of mitochondrial dynamics is important for protein quality and neuronal integrity. Mitofusins, mitochondrial fusion factors, can integrate cellular stress through their ubiquitylation, which is carried out by multiple E3 enzymes in response to many different stimuli. However, the molecular mechanisms that enable coordinated responses are largely unknown. Here we show that yeast Ufd2, a conserved ubiquitin chain-elongating E4 enzyme, is required for mitochondrial shape adjustments. Under various stresses, Ufd2 translocates to mitochondria and triggers mitofusin ubiquitylation. This elongates ubiquitin chains on mitofusin and promotes its proteasomal degradation, leading to mitochondrial fragmentation. Ufd2 and its human homologue UBE4B also target mitofusin mutants associated with Charcot-Marie-Tooth disease, a hereditary sensory and motor neuropathy characterized by progressive loss of the peripheral nerves. This underscores the pathophysiological importance of E4-mediated ubiquitylation in neurodegeneration. In summary, we identify E4-dependent mitochondrial stress adaptation by linking various metabolic processes to mitochondrial fusion and fission dynamics.
    Keywords:  CMT2A; Cdc48/p97; E4; Fzo1; MFN2; UBE4B; Ufd2; fusion; mitochondria; mitofusin; stress; ubiquitin
    DOI:  https://doi.org/10.1016/j.molcel.2023.07.021
  7. J Cell Mol Med. 2023 Aug 18.
    Endoplasmic reticulum stress induced by turbulence of mitochondrial fusion and fission was involved in stressed cardiomyocyte injury.
    Shengnan Zhang, Yingmin Li, Weihao Zhu, Lihua Zhang, Lei Lei, Xiaofei Tian, Ke Chen, Weibo Shi, Bin Cong.
      Mitochondria are sensitive organelles that sense intrinsic and extrinsic stressors and maintain cellular physiological functions through the dynamic homeostasis of mitochondrial fusion and fission. Numerous pathological processes are associated with mitochondrial fusion and fission disorders. However, the molecular mechanism by which stress induces cardiac pathophysiological changes through destabilising mitochondrial fusion and fission is unclear. Therefore, this study aimed to investigate whether the endoplasmic reticulum stress signalling pathway initiated by the turbulence of mitochondrial fusion and fission under stressful circumstances is involved in cardiomyocyte damage. Based on the successful establishment of the classical stress rat model of restraint plus ice water swimming, we measured the content of serum lactate dehydrogenase. We used haematoxylin-eosin staining, special histochemical staining, RT-qPCR and western blotting to clarify the cardiac pathology, ultrastructural changes and expression patterns of mitochondrial fusion and fission marker proteins and endoplasmic reticulum stress signalling pathway proteins. The results indicated that mitochondrial fusion and fission markers and proteins of the endoplasmic reticulum stress JNK signalling pathway showed significant abnormal dynamic changes with the prolongation of stress, and stabilisation of mitochondrial fusion and fission using Mdivi-1 could effectively improve these abnormal expressions and ameliorate cardiomyocyte injury. These findings suggest that stress could contribute to pathological cardiac injury, closely linked to the endoplasmic reticulum stress JNK signalling pathway induced by mitochondrial fusion and fission turbulence.
    Keywords:  endoplasmic reticulum stress; mitochondrial fission; mitochondrial fusion; myocardial injury; stress
    DOI:  https://doi.org/10.1111/jcmm.17901
  8. Sci Rep. 2023 08 15. 13(1): 13248
    Propionic acid induces alterations in mitochondrial morphology and dynamics in SH-SY5Y cells.
    Erin Buchanan, Caitlyn Mahony, Sophia Bam, Mohamed Jaffer, Sarah Macleod, Asandile Mangali, Mignon van der Watt, Sholto de Wet, Rensu Theart, Caron Jacobs, Ben Loos, Colleen O'Ryan.
      Propionic acid (PPA) is used to study the role of mitochondrial dysfunction in neurodevelopmental conditions like autism spectrum disorders. PPA is known to disrupt mitochondrial biogenesis, metabolism, and turnover. However, the effect of PPA on mitochondrial dynamics, fission, and fusion remains challenging to study due to the complex temporal nature of these mechanisms. Here, we use complementary quantitative visualization techniques to examine how PPA influences mitochondrial ultrastructure, morphology, and dynamics in neuronal-like SH-SY5Y cells. PPA (5 mM) induced a significant decrease in mitochondrial area (p < 0.01), Feret's diameter and perimeter (p < 0.05), and in area2 (p < 0.01). Mitochondrial event localiser analysis demonstrated a significant increase in fission and fusion events (p < 0.05) that preserved mitochondrial network integrity under stress. Moreover, mRNA expression of cMYC (p < 0.0001), NRF1 (p < 0.01), TFAM (p < 0.05), STOML2 (p < 0.0001), and OPA1 (p < 0.01) was significantly decreased. This illustrates a remodeling of mitochondrial morphology, biogenesis, and dynamics to preserve function under stress. Our data provide new insights into the influence of PPA on mitochondrial dynamics and highlight the utility of visualization techniques to study the complex regulatory mechanisms involved in the mitochondrial stress response.
    DOI:  https://doi.org/10.1038/s41598-023-40130-8
  9. Genes Dis. 2024 Jan;11(1): 358-366
    Mitochondria-related signaling pathways involved in breast cancer regulate ferroptosis.
    Xinrui Dong, Ye Li, Xiaonan Sheng, Weihang Zhou, Aijun Sun, Huijuan Dai.
      Ferroptosis is a novel form of regulated cell death characterized by iron-dependent excessive lipid peroxidation. The core organelle involved in ferroptosis is mitochondria. Mitochondria undergoing ferroptosis are distinct from normal mitochondria in terms of morphology, biochemistry, gene expression, and energy metabolism. An increasing number of studies have shown that mitochondria and their associated metabolic pathways mediate ferroptosis in the development and progression of breast cancer. In this review, we discuss the relevant research about ferroptosis in breast cancer and provide a comprehensive summary of mitochondrial regulation in ferroptosis from the perspective of lipid metabolism, oxidative phosphorylation, ion metabolism, glycometabolism, and nucleotide metabolism. We also summarize the application of mitochondrial metabolism-related pathways as ferroptosis treatment targets. Here we provide new insights into the relationship between mitochondria, ferroptosis, and breast cancer treatment.
    Keywords:  Breast cancer; Cancer treatment; Ferroptosis; Lipid metabolism; Mitochondria; Oxidative phosphorylation
    DOI:  https://doi.org/10.1016/j.gendis.2023.03.019
  10. Proc Natl Acad Sci U S A. 2023 08 22. 120(34): e2306073120
    Milton assembles large mitochondrial clusters, mitoballs, to sustain spermatogenesis.
    Andy Y Z Li, Ying Di, Sumaera Rathore, Ason C-Y Chiang, Jan Jezek, Hansong Ma.
      Mitochondria are dynamic organelles that undergo frequent remodeling to accommodate developmental needs. Here, we describe a striking organization of mitochondria into a large ball-like structure adjacent to the nucleus in premeiotic Drosophila melanogaster spermatocytes, which we term "mitoball". Mitoballs are transient structures that colocalize with the endoplasmic reticulum, Golgi bodies, and the fusome. We observed similar premeiotic mitochondrial clusters in a wide range of insect species, including mosquitos and cockroaches. Through a genetic screen, we identified that Milton, an adaptor protein that links mitochondria to microtubule-based motors, mediates mitoball formation. Flies lacking a 54 amino acid region in the C terminus of Milton completely lacked mitoballs, had swollen mitochondria in their spermatocytes, and showed reduced male fertility. We suggest that the premeiotic mitochondrial clustering is a conserved feature of insect spermatogenesis that supports sperm development.
    Keywords:  Milton-mediated mitochondrial trafficking; insect spermatogenesis; male fertility; mitoballs; mitochondrial clustering
    DOI:  https://doi.org/10.1073/pnas.2306073120
  11. Signal Transduct Target Ther. 2023 08 16. 8(1): 304
    The mitophagy pathway and its implications in human diseases.
    Shouliang Wang, Haijiao Long, Lianjie Hou, Baorong Feng, Zihong Ma, Ying Wu, Yu Zeng, Jiahao Cai, Da-Wei Zhang, Guojun Zhao.
      Mitochondria are dynamic organelles with multiple functions. They participate in necrotic cell death and programmed apoptotic, and are crucial for cell metabolism and survival. Mitophagy serves as a cytoprotective mechanism to remove superfluous or dysfunctional mitochondria and maintain mitochondrial fine-tuning numbers to balance intracellular homeostasis. Growing evidences show that mitophagy, as an acute tissue stress response, plays an important role in maintaining the health of the mitochondrial network. Since the timely removal of abnormal mitochondria is essential for cell survival, cells have evolved a variety of mitophagy pathways to ensure that mitophagy can be activated in time under various environments. A better understanding of the mechanism of mitophagy in various diseases is crucial for the treatment of diseases and therapeutic target design. In this review, we summarize the molecular mechanisms of mitophagy-mediated mitochondrial elimination, how mitophagy maintains mitochondrial homeostasis at the system levels and organ, and what alterations in mitophagy are related to the development of diseases, including neurological, cardiovascular, pulmonary, hepatic, renal disease, etc., in recent advances. Finally, we summarize the potential clinical applications and outline the conditions for mitophagy regulators to enter clinical trials. Research advances in signaling transduction of mitophagy will have an important role in developing new therapeutic strategies for precision medicine.
    DOI:  https://doi.org/10.1038/s41392-023-01503-7
  12. Front Physiol. 2023 ;14 1217815
    Exploring the therapeutic potential of the mitochondrial transfer-associated enzymatic machinery in brain degeneration.
    Noymar Luque-Campos, Ricardo Riquelme, Luis Molina, Gisela Canedo-Marroquín, Ana María Vega-Letter, Patricia Luz-Crawford, Felipe A Bustamante-Barrientos.
      Mitochondrial dysfunction is a central event in the pathogenesis of several degenerative brain disorders. It entails fission and fusion dynamics disruption, progressive decline in mitochondrial clearance, and uncontrolled oxidative stress. Many therapeutic strategies have been formulated to reverse these alterations, including replacing damaged mitochondria with healthy ones. Spontaneous mitochondrial transfer is a naturally occurring process with different biological functions. It comprises mitochondrial donation from one cell to another, carried out through different pathways, such as the formation and stabilization of tunneling nanotubules and Gap junctions and the release of extracellular vesicles with mitochondrial cargoes. Even though many aspects of regulating these mechanisms still need to be discovered, some key enzymatic regulators have been identified. This review summarizes the current knowledge on mitochondrial dysfunction in different neurodegenerative disorders. Besides, we analyzed the usage of mitochondrial transfer as an endogenous revitalization tool, emphasizing the enzyme regulators that govern this mechanism. Going deeper into this matter would be helpful to take advantage of the therapeutic potential of mitochondrial transfer.
    Keywords:  cellular therapy; degenerative brain disorders; enzymes; fission and fusion; mitochondrial dysfunction; mitochondrial transfer; mitophagy; oxidative damage
    DOI:  https://doi.org/10.3389/fphys.2023.1217815
  13. Front Immunol. 2023 ;14 1211839
    IL-12/15/18-induced cell death and mitochondrial dynamics of human NK cells.
    Iñigo Terrén, Víctor Sandá, Ainhoa Amarilla-Irusta, Ainara Lopez-Pardo, Arrate Sevilla, Gabirel Astarloa-Pando, Laura Amo, Olatz Zenarruzabeitia, Luca Scorrano, Francisco Borrego.
      Natural killer (NK) cells are lymphocytes with potent antitumor functions and, consequently, several NK cell-based strategies have been developed for cancer immunotherapy. A remarkable therapeutic approach is the adoptive transfer of NK cells stimulated with IL-12, IL-15 and IL-18. This cytokine stimulation endows NK cells with properties that resemble immunological memory and, for this reason, they are known as cytokine-induced memory-like (CIML) NK cells. Very promising results have been reported in clinical trials and yet, there are still unknown aspects of CIML NK cells. Here, we have conducted a preliminary study of their mitochondrial dynamics. Our results show that upon IL-12/15/18 stimulation the viability of NK cells decreased and an increment in mitochondrial superoxide levels was observed. In addition, we found that mitochondria appeared slightly elongated and their cristae density decreased following IL-12/15/18 stimulation, possibly in a process mediated by the low levels of optic atrophy type 1 (OPA1) protein. Interestingly, although mitophagy was slightly impaired, an increase in autophagic flux was observed, which might explain the reduced viability and the accumulation of unfit mitochondria. Our findings could be of relevance in order to design new strategies intended to improve the mitochondrial fitness of IL-12/15/18-stimulated NK cells with the aim of improving their therapeutic efficacy.
    Keywords:  IL-12; IL-15; IL-18; NK cells; cancer immunotherapy; cytokine-preactivated NK cells; memory-like; mitochondria
    DOI:  https://doi.org/10.3389/fimmu.2023.1211839
  14. PLoS Biol. 2023 Aug 17. 21(8): e3002273
    Optogenetic cleavage of the Miro GTPase reveals the direct consequences of real-time loss of function in Drosophila.
    Francesca Mattedi, Ethlyn Lloyd-Morris, Frank Hirth, Alessio Vagnoni.
      Miro GTPases control mitochondrial morphology, calcium homeostasis, and regulate mitochondrial distribution by mediating their attachment to the kinesin and dynein motor complex. It is not clear, however, how Miro proteins spatially and temporally integrate their function as acute disruption of protein function has not been performed. To address this issue, we have developed an optogenetic loss of function "Split-Miro" allele for precise control of Miro-dependent mitochondrial functions in Drosophila. Rapid optogenetic cleavage of Split-Miro leads to a striking rearrangement of the mitochondrial network, which is mediated by mitochondrial interaction with the microtubules. Unexpectedly, this treatment did not impact the ability of mitochondria to buffer calcium or their association with the endoplasmic reticulum. While Split-Miro overexpression is sufficient to augment mitochondrial motility, sustained photocleavage shows that Split-Miro is surprisingly dispensable to maintain elevated mitochondrial processivity. In adult fly neurons in vivo, Split-Miro photocleavage affects both mitochondrial trafficking and neuronal activity. Furthermore, functional replacement of endogenous Miro with Split-Miro identifies its essential role in the regulation of locomotor activity in adult flies, demonstrating the feasibility of tuning animal behaviour by real-time loss of protein function.
    DOI:  https://doi.org/10.1371/journal.pbio.3002273
  15. PLoS Biol. 2023 Aug 17. 21(8): e3002247
    The AAA-ATPase Yta4/ATAD1 interacts with the mitochondrial divisome to inhibit mitochondrial fission.
    Jiajia He, Ke Liu, Yifan Wu, Chenhui Zhao, Shuaijie Yan, Jia-Hui Chen, Lizhu Hu, Dongmei Wang, Fan Zheng, Wenfan Wei, Chao Xu, Chengdong Huang, Xing Liu, Xuebiao Yao, Lijun Ding, Zhiyou Fang, Ai-Hui Tang, Chuanhai Fu.
      Mitochondria are in a constant balance of fusion and fission. Excessive fission or deficient fusion leads to mitochondrial fragmentation, causing mitochondrial dysfunction and physiological disorders. How the cell prevents excessive fission of mitochondria is not well understood. Here, we report that the fission yeast AAA-ATPase Yta4, which is the homolog of budding yeast Msp1 responsible for clearing mistargeted tail-anchored (TA) proteins on mitochondria, plays a critical role in preventing excessive mitochondrial fission. The absence of Yta4 leads to mild mitochondrial fragmentation in a Dnm1-dependent manner but severe mitochondrial fragmentation upon induction of mitochondrial depolarization. Overexpression of Yta4 delocalizes the receptor proteins of Dnm1, i.e., Fis1 (a TA protein) and Mdv1 (the bridging protein between Fis1 and Dnm1), from mitochondria and reduces the localization of Dnm1 to mitochondria. The effect of Yta4 overexpression on Fis1 and Mdv1, but not Dnm1, depends on the ATPase and translocase activities of Yta4. Moreover, Yta4 interacts with Dnm1, Mdv1, and Fis1. In addition, Yta4 competes with Dnm1 for binding Mdv1 and decreases the affinity of Dnm1 for GTP and inhibits Dnm1 assembly in vitro. These findings suggest a model, in which Yta4 inhibits mitochondrial fission by inhibiting the function of the mitochondrial divisome composed of Fis1, Mdv1, and Dnm1. Therefore, the present work reveals an uncharacterized molecular mechanism underlying the inhibition of mitochondrial fission.
    DOI:  https://doi.org/10.1371/journal.pbio.3002247
  16. Nat Commun. 2023 Aug 18. 14(1): 5031
    Mitochondria are secreted in extracellular vesicles when lysosomal function is impaired.
    Wenjing Liang, Shakti Sagar, Rishith Ravindran, Rita H Najor, Justin M Quiles, Liguo Chi, Rachel Y Diao, Benjamin P Woodall, Leonardo J Leon, Erika Zumaya, Jason Duran, David M Cauvi, Antonio De Maio, Eric D Adler, Åsa B Gustafsson.
      Mitochondrial quality control is critical for cardiac homeostasis as these organelles are responsible for generating most of the energy needed to sustain contraction. Dysfunctional mitochondria are normally degraded via intracellular degradation pathways that converge on the lysosome. Here, we identified an alternative mechanism to eliminate mitochondria when lysosomal function is compromised. We show that lysosomal inhibition leads to increased secretion of mitochondria in large extracellular vesicles (EVs). The EVs are produced in multivesicular bodies, and their release is independent of autophagy. Deletion of the small GTPase Rab7 in cells or adult mouse heart leads to increased secretion of EVs containing ubiquitinated cargos, including intact mitochondria. The secreted EVs are captured by macrophages without activating inflammation. Hearts from aged mice or Danon disease patients have increased levels of secreted EVs containing mitochondria indicating activation of vesicular release during cardiac pathophysiology. Overall, these findings establish that mitochondria are eliminated in large EVs through the endosomal pathway when lysosomal degradation is inhibited.
    DOI:  https://doi.org/10.1038/s41467-023-40680-5
  17. Cell Commun Signal. 2023 Aug 14. 21(1): 204
    Inhibition of ERK downregulates autophagy via mitigating mitochondrial fragmentation to protect SH-SY5Y cells from OGD/R injury.
    Zhang-Li Yuan, Yan-Zi Mo, De-Li Li, Lu Xie, Meng-Hua Chen.
       BACKGROUND: Cerebral ischemia-reperfusion injury (CIRI) is the main cause leading to high mortality and neurological disability in patients with cardiac arrest/cardiopulmonary resuscitation (CA/CPR). Our previous study found that extracellular signal-regulated kinase (ERK) activation, dynamin-related protein1 (Drp1)/Mitofusin2 (Mfn2)-dependent mitochondrial dynamics imbalance, and excessive autophagy were involved in the mechanism of nerve injury after CA/CPR. However, the specific pathological signaling pathway is still unknown. This study aimed to explore the molecular function changes of ERK-Drp1/Mfn2-autophagy signaling pathway in SH-SY5Y cell oxygen-glucose deprivation/reoxygenation (OGD/R) model, to further clarify the pathophysiological mechanism of CIRI, and to provide a new strategy for cerebral protection after CIRI.
    METHODS: SH-SY5Y cells were pretreated with drugs 24 h before OGD/R. The Drp1 and Mfn2 knockdown were adopted small interfering RNAs. The overexpression of p-Drp1S616 and Mfn2 were used recombinant plasmids. The expression levels of mitochondrial dynamics proteins (p-Drp1, Drp1, Mfn2, Mfn1 and Opa1) and autophagy markers (LC3, Beclin1 and p62) were measured with the Western blotting. The mRNA levels after transfection were determined by PCR. Cell injury and viability were evaluated with released LDH activity and CCK8 assay kits. Mitochondria morphology and autophagosome were observed under transmission electron microscopy. Mitochondrial function was detected by the mitochondrial permeability transition pore assay kit. The co-expression of p-ERK, p-Drp1 and LC3 was assessed with multiple immunofluorescences. One-way analysis of variance followed by least significance difference post hoc analysis (for equal homogeneity) or Dunnett's T3 test (for unequal homogeneity) were used for statistical tests.
    RESULTS: ERK inhibitor-PD98059 (PD) protects SH-SY5Y cells from OGD/R-induced injury; while ERK activator-TPA had the opposite effect. Similar to autophagy inhibitor 3-MA, PD downregulated autophagy to improve cell viability; while autophagy activator-rapamycin further aggravated cell death. PD and Drp1-knockdown synergistically attenuated OGD/R-induced Drp1 activation, mPTP opening and cell injury; overexpression of Drp1S616E or ablating Mfn2 partly abolished the protective effects of PD. Multiple immunofluorescences showed that p-ERK, p-Drp1 and LC3 were co-expressed.
    CONCLUSION: Inhibition of ERK downregulates autophagy via reducing Drp1/Mfn2-dependent mitochondrial fragmentation to antagonize mitochondrial dysfunction and promotes cell survival in the SH-SY5Y cells OGD/R model. Video Abstract.
    Keywords:  Autophagy; CIRI; Drp1; ERK; Mfn2; Mitochondrial dynamics; OGD/R
    DOI:  https://doi.org/10.1186/s12964-023-01211-3
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