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Mitochondrial fission facilitates the selective mitophagy of protein aggregates.

ABSTRACT: Within the mitochondrial matrix, protein aggregation activates the mitochondrial unfolded protein response and PINK1-Parkin-mediated mitophagy to mitigate proteotoxicity. We explore how autophagy eliminates protein aggregates from within mitochondria and the role of mitochondrial fission in mitophagy. We show that PINK1 recruits Parkin onto mitochondrial subdomains after actinonin-induced mitochondrial proteotoxicity and that PINK1 recruits Parkin proximal to focal misfolded aggregates of the mitochondrial-localized mutant ornithine transcarbamylase (?OTC). Parkin colocalizes on polarized mitochondria harboring misfolded proteins in foci with ubiquitin, optineurin, and LC3. Although inhibiting Drp1-mediated mitochondrial fission suppresses the segregation of mitochondrial subdomains containing ?OTC, it does not decrease the rate of ?OTC clearance. Instead, loss of Drp1 enhances the recruitment of Parkin to fused mitochondrial networks and the rate of mitophagy as well as decreases the selectivity for ?OTC during mitophagy. These results are consistent with a new model that, instead of promoting mitophagy, fission protects healthy mitochondrial domains from elimination by unchecked PINK1-Parkin activity.

SUBMITTER: Burman JL

PROVIDER: S-EPMC5626535 | biostudies-literature | 2017 Oct

REPOSITORIES: biostudies-literature

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Mitochondrial fission facilitates the selective mitophagy of protein aggregates.

Burman Jonathon L JL Pickles Sarah S Wang Chunxin C Sekine Shiori S Vargas Jose Norberto S JNS Zhang Zhe Z Youle Alice M AM Nezich Catherine L CL Wu Xufeng X Hammer John A JA Youle Richard J RJ

The Journal of cell biology 20170911 10

Within the mitochondrial matrix, protein aggregation activates the mitochondrial unfolded protein response and PINK1-Parkin-mediated mitophagy to mitigate proteotoxicity. We explore how autophagy eliminates protein aggregates from within mitochondria and the role of mitochondrial fission in mitophagy. We show that PINK1 recruits Parkin onto mitochondrial subdomains after actinonin-induced mitochondrial proteotoxicity and that PINK1 recruits Parkin proximal to focal misfolded aggregates of the mi ...[more]

PMID: 28893839

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Project description:Although mitochondrial fission has been reported to increase proliferative capacity and collagen production, it can also contribute to mitochondrial impairment, which is detrimental to cell survival. The aim of the present study was to investigate the role of mitochondrial fission in cardiac fibroblasts (CF) activation and explore the mechanisms involved in the maintenance of mitochondrial health under this condition. For this, changes in the levels of mitochondrial fission/fusion-related proteins were assessed in transforming growth factor beta 1 (TGF-β1)-activated CF, whereas the role of mitochondrial fission during this process was also elucidated, as were the underlying mechanisms. The interaction between mitochondrial fission and mitophagy, the main defense mechanism against mitochondrial impairment, was also explored. The results showed that the mitochondria in TGF-β1-treated CF were noticeably more fragmented than those of controls. The expression of several mitochondrial fission-related proteins was markedly upregulated, and the levels of fusion-related proteins were also altered, but to a lesser extent. Inhibiting mitochondrial fission resulted in a marked attenuation of TGF-β1-induced CF activation. The TGF-β1-induced increase in glycolysis was greatly suppressed in the presence of a mitochondrial inhibitor, whereas a glycolysis-specific antagonist exerted little additional antifibrotic effects. TGF-β1 treatment increased cellular levels of reactive oxygen species (ROS) and triggered mitophagy, but this effect was reversed following the application of ROS scavengers. For the signals mediating mitophagy, the expression of Pink1, but not Bnip3l/Nix or Fundc1, exhibited the most significant changes, which could be counteracted by treatment with a mitochondrial fission inhibitor. Pink1 knockdown suppressed CF activation and mitochondrial fission, which was accompanied by increased CF apoptosis. In conclusion, mitochondrial fission resulted in increased glycolysis and played a crucial role in CF activation. Moreover, mitochondrial fission promoted reactive oxygen species (ROS) production, leading to mitophagy and the consequent degradation of the impaired mitochondria, thus promoting CF survival and maintaining their activation.

Project description:Hyperglycemia-induced mitochondrial dysfunction plays a key role in the pathogenesis of diabetic cardiomyopathy. Injured mitochondrial segments are separated by mitochondrial fission and eliminated by autophagic sequestration and subsequent degradation in the lysosome, a process termed mitophagy. However, it remains poorly understood how high glucose affects the activities of, and the relationship between, mitochondrial fission and mitophagy in cardiomyocytes. In this study, we determined the functional roles of mitochondrial fission and mitophagy in hyperglycemia-induced cardiomyocyte injury. High glucose (30 mM, HG) reduced mitochondrial connectivity and particle size and increased mitochondrial number in neonatal rat ventricular cardiomyocytes, suggesting an enhanced mitochondrial fragmentation. SiRNA knockdown of the pro-fission factor dynamin-related protein 1 (DRP1) restored mitochondrial size but did not affect HG toxicity, and Mdivi-1, a DRP1 inhibitor, even increased HG-induced cardiomyocyte injury, as shown by superoxide production, mitochondrial membrane potential and cell death. However, DRP1 overexpression triggered mitochondrial fragmentation and mitigated HG-induced cardiomyocyte injury, suggesting that the increased mitochondrial fission is beneficial, rather than detrimental, to cardiomyocytes cultured under HG conditions. This is in contrast to the prevailing hypothesis that mitochondrial fragmentation mediates or contributes to HG cardiotoxicity. Meanwhile, HG reduced mitophagy flux as determined by the difference in the levels of mitochondria-associated LC3-II or the numbers of mitophagy foci indicated by the novel dual fluorescent reporter mt-Rosella in the absence and presence of the lysosomal inhibitors. The ability of HG to induce mitochondrial fragmentation and inhibit mitophagy was reproduced in adult mouse cardiomyocytes. Overexpression of Parkin, a positive regulator of mitophagy, or treatment with CCCP, a mitochondrial uncoupler, induced mitophagy and attenuated HG-induced cardiomyocyte death, while Parkin knockdown had opposite effects, suggesting an essential role of mitophagy in cardiomyocyte survival under HG conditions. Strikingly, Parkin overexpression increased mitochondrial fragmentation, while DRP1 overexpression accelerated mitophagy flux, demonstrating a reciprocal activation loop that controls mitochondrial fission and mitophagy. Thus, strategies that promote the mutual positive interaction between mitochondrial fission and mitophagy while simultaneously maintain their levels within the physiological range would be expected to improve mitochondrial health, alleviating hyperglycemic cardiotoxicity.

Project description:RationaleThe role of Parkin in hearts is unclear. Germ-line Parkin knockout mice have normal hearts, but Parkin is protective in cardiac ischemia. Parkin-mediated mitophagy is reportedly either irrelevant, or a major factor, in the lethal cardiomyopathy evoked by cardiac myocyte-specific interruption of dynamin-related protein 1 (Drp1)-mediated mitochondrial fission.ObjectiveTo understand the role of Parkin-mediated mitophagy in normal and mitochondrial fission-defective adult mouse hearts.Methods and resultsParkin mRNA and protein were present at low levels in normal mouse hearts, but were upregulated after cardiac myocyte-directed Drp1 gene deletion in adult mice. Alone, forced cardiac myocyte Parkin overexpression activated mitophagy without adverse effects. Likewise, cardiac myocyte-specific Parkin deletion evoked no adult cardiac phenotype, revealing no essential function for, and tolerance of, Parkin-mediated mitophagy in normal hearts. Concomitant conditional Parkin deletion with Drp1 ablation in adult mouse hearts prevented Parkin upregulation in mitochondria of fission-defective hearts, also increasing 6-week survival, improving ventricular ejection performance, mitigating adverse cardiac remodeling, and decreasing cardiac myocyte necrosis and replacement fibrosis. Underlying the Parkin knockout rescue was suppression of Drp1-induced hyper-mitophagy, assessed as ubiquitination of mitochondrial proteins and mitochondrial association of autophagosomal p62/sequestosome 1 (SQSTM1) and processed microtubule-associated protein 1 light chain 3 (LC3-II). Consequently, mitochondrial content of Drp1-deficient hearts was preserved. Parkin deletion did not alter characteristic mitochondrial enlargement of Drp1-deficient cardiac myocytes.ConclusionsParkin is rare in normal hearts and dispensable for constitutive mitophagic quality control. Ablating Drp1 in adult mouse cardiac myocytes not only interrupts mitochondrial fission, but also markedly upregulates Parkin, thus provoking mitophagic mitochondrial depletion that contributes to the lethal cardiomyopathy.

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Mitochondrial fission facilitates the selective mitophagy of protein aggregates.

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Mitochondrial fission facilitates the selective mitophagy of protein aggregates.

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