Nix Is Critical to Two Distinct Phases of Mitophagy, Reactive Oxygen Species-mediated Autophagy Induction and Parkin-Ubiquitin-p62-mediated Mitochondrial Priming

Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 09/2010; 285(36):27879-90. DOI: 10.1074/jbc.M110.119537
Source: PubMed


Damaged mitochondria can be eliminated by autophagy, i.e. mitophagy, which is important for cellular homeostasis and cell survival. Despite the fact that a number of factors have been found to be important for mitophagy in mammalian cells, their individual roles in the process had not been clearly defined. Parkin is a ubiquitin-protein isopeptide ligase able to translocate to the mitochondria that are to be removed. We showed here in a chemical hypoxia model of mitophagy induced by an uncoupler, carbonyl cyanide m-chlorophenylhydrazone (CCCP) that Parkin translocation resulted in mitochondrial ubiquitination and p62 recruitment to the mitochondria. Small inhibitory RNA-mediated knockdown of p62 significantly diminished mitochondrial recognition by the autophagy machinery and the subsequent elimination. Thus Parkin, ubiquitin, and p62 function in preparing mitochondria for mitophagy, here referred to as mitochondrial priming. However, these molecules were not required for the induction of autophagy machinery. Neither Parkin nor p62 seemed to affect autophagy induction by CCCP. Instead, we found that Nix was required for the autophagy induction. Nix promoted CCCP-induced mitochondrial depolarization and reactive oxygen species generation, which inhibited mTOR signaling and activated autophagy. Nix also contributed to mitochondrial priming by controlling the mitochondrial translocation of Parkin, although reactive oxygen species generation was not involved in this step. Deletion of the C-terminal membrane targeting sequence but not mutations in the BH3 domain disabled Nix for these functions. Our work thus distinguished the molecular events responsible for the different phases of mitophagy and placed Nix upstream of the events.

    • "NIX or BNIP3 may serve as a mitophagy receptor that bridges mitochondria and LC3 to selectively induce mitochondrial degradation141516. NIX/Bnip3 is inserted into the outer mitochondrial membrane through its C-terminal transmembrane domains, and recruits autophagy machinery by directly binding to LC3/GABARAP proteins on the autophagosome via the N-terminal LC3-interacting motifs [109,110]. "
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    ABSTRACT: Diabetes is a well-known risk factor for heart failure. Diabetic heart damage is closely related to mitochondrial dysfunction and increased ROS generation. However, clinical trials have shown no effects of antioxidant therapies on heart failure in diabetic patients, suggesting that simply antagonizing existing ROS by antioxidants is not sufficient to reduce diabetic cardiac injury. A potentially more effective treatment strategy may be to enhance the overall capacity of mitochondrial quality control to maintain a pool of healthy mitochondria that are needed for supporting cardiac contractile function in diabetic patients. Mitochondrial quality is controlled by a number of coordinated mechanisms including mitochondrial fission and fusion, mitophagy and biogenesis. The mitochondrial damage consistently observed in the diabetic hearts indicates a failure of the mitochondrial quality control mechanisms. Recent studies have demonstrated a crucial role for each of these mechanisms in cardiac homeostasis and have begun to interrogate the relative contribution of insufficient mitochondrial quality control to diabetic cardiac injury. In this review, we will present currently available literature that links diabetic heart disease to the dysregulation of major mitochondrial quality control mechanisms. We will discuss the functional roles of these mechanisms in the pathogenesis of diabetic heart disease and their potentials for targeted therapeutical manipulation.
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    • "in the recruitment of mitochondria to APs and localisation to perinuclear clusters (Narendra et al. 2010a;Okatsu et al. 2010). Similar to previous reports, we found that p62 was necessary for mitophagy to occur (Ding et al. 2010;Geisler et al. 2010). An increase in p62 protein levels has also been found in HeLa cells (Sarraf et al. 2013) and MEFs (Ichimura et al. 2013) following treatment with depolarising agents CCCP and valinomycin respectively . "
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    • "(Ding et al. 2010, Lee et al. 2010, Cali et al. 2013 "
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