心肌细胞依靠适当的线粒体稳态来维持收缩性并达到最佳的心脏性能。线粒体稳态受线粒体裂变控制,聚变,和线粒体自噬(线粒体自噬)。线粒体自噬在促进终末分化细胞中功能失调的线粒体降解中起着特别重要的作用。然而,在心肌细胞中实现这一点的确切机制仍然不透明。我们的研究将GRAF1确定为PINK1-Parkin通路依赖性线粒体自噬的重要介质。心肌细胞中GRAF1(Arhgap26)的耗竭导致肌动蛋白重塑缺陷,次优的线粒体聚类,和间隙。机械上,GRAF1促进Parkin-LC3复合物的形成并将自噬体引导至受损的线粒体。在这里,我们发现这些功能是被调节的,至少在某种程度上,通过GRAF1与磷酸肌醇的直接结合(PI(3)P,PI(4)P,和PI(5)P)对自噬体的作用。此外,Parkin的PINK1依赖性磷酸化促进Parkin-GRAF1-LC3复合物的形成,GRAF1的PINK1依赖性磷酸化(在S668和S671上)促进线粒体的聚集和清除。在这里,我们开发了针对这些位点的新的磷特异性抗体,并表明这些翻译后修饰在人类肥厚型心肌病和扩张型心肌病中具有差异修饰.此外,我们使用异丙肾上腺素治疗的WT和GRAF1CKO小鼠血清进行的代谢研究显示,线粒体自噬依赖性心肌细胞燃料灵活性存在缺陷,对全身代谢有广泛影响.总之,我们的研究表明,GRAF1共同调节肌动蛋白和膜动力学以促进心肌细胞有丝分裂,GRAF1翻译后修饰的失调可能是心脏疾病发病机制的基础.
Cardiomyocytes rely on proper mitochondrial homeostasis to maintain contractility and achieve optimal cardiac performance. Mitochondrial homeostasis is controlled by mitochondrial fission, fusion, and mitochondrial autophagy (mitophagy). Mitophagy plays a particularly important role in promoting the degradation of dysfunctional mitochondria in terminally differentiated cells. However, the precise mechanisms by which this is achieved in cardiomyocytes remain opaque. Our study identifies
GRAF1 as an important mediator in PINK1-Parkin pathway-dependent mitophagy. Depletion of
GRAF1 (Arhgap26) in cardiomyocytes results in actin remodeling defects, suboptimal mitochondria clustering, and clearance. Mechanistically, GRAF1 promotes Parkin-LC3 complex formation and directs autophagosomes to damaged mitochondria. Herein, we found that these functions are regulated, at least in part, by the direct binding of
GRAF1 to phosphoinositides (PI(3)P, PI(4)P, and PI(5)P) on autophagosomes. In addition, PINK1-dependent phosphorylation of Parkin promotes Parkin-
GRAF1-LC3 complex formation, and PINK1-dependent phosphorylation of
GRAF1 (on S668 and S671) facilitates the clustering and clearance of mitochondria. Herein, we developed new phosphor-specific antibodies to these sites and showed that these post-translational modifications are differentially modified in human hypertrophic cardiomyopathy and dilated cardiomyopathy. Furthermore, our metabolic studies using serum collected from isoproterenol-treated WT and GRAF1CKO mice revealed defects in mitophagy-dependent cardiomyocyte fuel flexibility that have widespread impacts on systemic metabolism. In summary, our study reveals that GRAF1 co-regulates actin and membrane dynamics to promote cardiomyocyte mitophagy and that dysregulation of GRAF1 post-translational modifications may underlie cardiac disease pathogenesis.