The Physiological Function Of Mitophagy Receptor FUNDC1 In Skeletal Muscle

Skeletal muscle is the largest metabolic demanding tissue that depends critically on mitochondrial function.The decline of skeletal muscle mitochondrial function with age can lead to a series of degenerative changes in skeletal muscle structure and metabolic function,and eventually can cause insulin resistance,obesity and diabetes.Mitochondria autophagy(mitophagy)serves as a critical quality-control mechanism for selective targeting and removal of damaged or dysfunctional mitochondria.Emerging evidence demonstrates that mitophagy receptors such as PINK1,Parkin,NIX/BNIP3,BCL2L13,and PBH2 play important roles in controlling mitochondrial quality.Mitochondrial dynamic regulators MFN1,MFN2,OPA1,DRP1,FIS1 and mitochondrial matrix protease LONP1 and CLPP,mitochondrial inner membrane protein YME1L1,AFG3L2 and SPG7 are also essential for mitochondrial quality control.FUNDC1,a new identified mitophagy receptor,regulates mitophagy upon stress conditions.When knocked down FUNDC1 in mammalian cells,mitophagy was significantly blocked under hypoxia stimulation.However,the in vivo physiological relevance and molecular working mechanisms of FUNDC1-dependent mitophagy in skeletal muscle remain unc ear.In this study,we generated two independent skeletal muscle-specific FU-NDC1 knockout mice lines by breeding Fundclf/f mice with HSA-Cre or MCK-Cre mice,to study the role of mitophagy receptor FUNDC1-mediated mitochondrial quality control in skeletal muscle.The expression of FUNDC1 reduced markedly in multiple muscle types.By isolating mitochondria of skeletal muscle or primary myocyte,we found that the LC3-? and P62 protein levels reduced significantly in FUNDC 1 deficiency isolated mitochondria samples.Primary myocytes infected with GFP-LC3 adenovirus or mt-Keima lentivirus revealed a markly defect mitophagy in FUNDC1 KO cells upon a mitophagy inducer FCCP treatment,which was also verified by transmission electron microscopy.Based on in vivo and in vitro studies,we further demonstrated that mitophagy deficiency caused by FUNDC1 knockout impairs mitochondrial energetics with decreased ATP level,decreased MMP level and increased ROS level.Moreover,mice with skeletal muscle deletion of FUNDC1 exhibited a higher RER,consumed less oxygen(VO2),reduced VO2max and decreased muscle fat utilization and endurance exercise capacity during exercise.Surprisingly,mice with skeletal muscle FUNDC1 ablation showed decreased fat mass during HFD feeding and were resistant to HFD-induced obesity and insulin resistance.We demonstrated that muscle FUNDC1 deficiency promotes thermogenic remodeling of WAT(both eWAT and iWAT)with significantly increased the expression of UCP1,Cidea and Dio2.Mechanistically,the browning of WAT was due to the induction of muscle mitokine FGF21.FUNDC1-deficiency regulated FGF21 gene expression through ROS-dependent retrograde response mediated by P-eIF-2a/ATF4 pathway.FGF21 disruption abolished the FUNDC1 deficiency-mediated benefit metabolic effect during HFD feeding.Taken together,muscle FUNDC1 deletion mediated mitophagy defect causes mitochondrial dysfunction,increases ROS level and triggers a retrograde response to induce the expression of Fgf21,which acts in an endocrine manner to decrease fat mass by driving the thermogenic gene program in WAT,thus protect mice from HFD-induced obesity and insulin resistance.We have revealed a pivotal role of skeletal muscle FUNDC1-dependent mitophagy in controlling muscle-adipose dialogue to alleviate dietary obesity,which suggest a potential therapeutic strategy for treatment of metabolic disorders by targeting mitophagy in skeletal muscle.