The mitophagy receptor BNIP3L/Nix coordinates nuclear calcium signaling to modulate the muscle phenotype.

Mitochondrial quality control is critical in muscle to ensure contractile and metabolic function. BNIP3L/Nix is a BCL2 member, a mitophagy receptor, and has been implicated in muscle atrophy. Human genome-wide association studies (GWAS) suggest altered BNIP3L expression could predispose to mitochondrial disease. To investigate BNIP3L function, we generated a muscle-specific knockout model. bnip3l knockout mice displayed a ragged-red fiber phenotype, along with accumulation of mitochondria and endo/sarcoplasmic reticulum with altered morphology. Intriguingly, bnip3l knockout mice were more insulin sensitive with a corresponding increase in glycogen-rich muscle fibers. Kinome and gene expression analyses revealed that bnip3l knockout impairs NFAT and MSTN (myostatin) signaling, with alterations in muscle fiber-type and evidence of regeneration. Mechanistic experiments demonstrated that BNIP3L modulates mitophagy, along with reticulophagy leading to altered nuclear calcium signaling. Collectively, these observations identify novel roles for BNIP3L coordinating selective autophagy, oxidative gene expression, and signaling pathways that maintain the muscle phenotype.