PINK1-PRKN Mediated Mitophagy

This is the process of selective removal of damaged mitochondria by autophagosomes and subsequent catabolism by lysosomes. In healthy mitochondria, PTEN-induced putative kinase 1 (PINK1) is imported to the inner mitochondrial membrane, presumably through the TOM/TIM complex. The TIM complex associated protease, mitochondrial MPP, cleaves PINK1 mitochondrial targeting sequence (MTS). PINK1 may be cleaved by the inner membrane presenilin-associated rhomboid-like protease (PARL) and ultimately proteolytically degraded. Loss of membrane potential in damaged mitochondria prevents the import of PINK1 which accumulates on the mitochondrial outer membrane (MOM) of the defective mitochondria. Activation of PINK1 at MOM is achieved via dimerization-mediated trans-autophosphorylation of PINK1 at multiple sites including S228 and S402 (Okatsu K et al., 2012, 2013; Aerts L et al., 2015; Rasool S et al., 2018, 2022; Gan ZY et al., 2022). Activated PINK1 phosphorylates S65 of ubiquitin (Ub) on MOM proteins which leads to increased recruitment of the E3 ubiquitin ligase Parkin (PRKN) to damaged mitochondria (Koyano F et al., 2014; Shiba-Fukushima K et al., 2014; Ordureau A et al., 2015). Activated PINK1 also phosphorylates PRKN at S65 in the N-terminal Ub-like domain inducing the E3 ligase activity of PRKN (Kondapalli et al., 2012; Kazlauskaite A et al., 2015; Ordureau A et al., 2015). Activated PRKN promotes the ubiquitination of mitochondrial substrates including mitofusin 1 and 2 (MFN1, 2) and the voltage-dependent anion channel 1 and 3 (VDAC1, 3). The E3 ligase activity of PRKN generates Ub moieties for PINK1-mediated phosphorylation of Ub thus leading to a feedforward loop in the PINK1:PRKN pathway (Ordureau A et al., 2015; Sauve V et al., 2022). Ubiquitin chains on PRKN-ubiquitinated substrates recruit cargo receptors such as SQSTM1 (p62) and OPTN linking the ubiquitinated substrates to the microtubule-associated proteins 1A/1B light chain 3 (LC3, MAP1LC3) (Heo LM et al., 2015; Lazarou M et al., 2015). The recruitment of both MAP1LC3 (LC3) complexes and the autophagy proteins 5 and 12 (Atg5: Atg12) complex to the autophagosome membrane promotes autophagosome formation. The mitochondrion is engulfed after the isolation membrane grows to a sufficient size to engulf the mitochondrion. Once autophagic vesicle formation is complete, vesicle fusion with lysosomes occurs to form autophagolysosomes in which the lysosomal hydrolases (cathepsins and lipases) degrade the intra autophagosomal content. Cathepsin also degrades LC3 on the intra autophagosomal surface of the autophagic vesicle.

此过程涉及自噬体对受损线粒体的选择性清除及其后续由溶酶体介导的分解代谢。在健康线粒体中，PTEN诱导的假激酶1（PINK1）通过TOM/TIM复合体被导入线粒体内膜。TIM复合体相关蛋白酶，线粒体MPP，切割PINK1的线粒体靶向序列（MTS）。PINK1可能被内膜与早老素相关菱形蛋白酶（PARL）切割，并最终通过蛋白水解降解。受损线粒体的膜电位丧失阻止了PINK1的导入，导致PINK1在缺陷线粒体的线粒体外膜（MOM）上积累。PINK1在MOM的激活通过在多个位点（包括S228和S402）介导的PINK1的转自磷酸化实现，这一过程由Okatsu K等（2012，2013）、Aerts L等（2015）、Rasool S等（2018，2022）以及Gan ZY等（2022）的研究证实。激活的PINK1在MOM上磷酸化泛素（Ub）的S65位点，从而增加了E3泛素连接酶Parkin（PRKN）对受损线粒体的招募（Koyano F等，2014；Shiba-Fukushima K等，2014；Ordureau A等，2015）。激活的PINK1还磷酸化PRKN的N端泛素样结构域中的S65位点，诱导PRKN的E3连接酶活性（Kondapalli等，2012；Kazlauskaite A等，2015；Ordureau A等，2015）。激活的PRKN促进线粒体底物，包括线粒体融合蛋白1和2（MFN1，2）以及电压依赖性阴离子通道1和3（VDAC1，3）的泛素化。PRKN的E3连接酶活性生成泛素基团，以促进PINK1介导的泛素磷酸化，从而在PINK1:PRKN通路中形成正反馈环（Ordureau A等，2015；Sauve V等，2022）。PRKN泛素化底物上的泛素链招募货物受体，如SQSTM1（p62）和OPTN，将泛素化底物与微管相关蛋白1A/1B轻链3（LC3，MAP1LC3）相连接（Heo LM等，2015；Lazarou M等，2015）。MAP1LC3（LC3）复合物和自噬蛋白5和12（Atg5: Atg12）复合物招募到自噬体膜上，促进自噬体形成。隔离膜生长至足够大以吞噬线粒体后，线粒体被吞噬。一旦自噬泡形成完成，自噬泡与溶酶体的融合发生，形成自噬溶酶体，其中溶酶体水解酶（组织蛋白酶和脂肪酶）降解自噬泡内的内容物。组织蛋白酶还降解自噬泡内表面的LC3。