PGC-1α modulates denervation-induced mitophagy in skeletal muscle

Background: Alterations in skeletal muscle contractile activity necessitate an efficient remodeling mechanism. In particular, mitochondrial turnover is essential for tissue homeostasis during muscle adaptations to chronic use and disuse. While mitochondrial biogenesis appears to be largely governed by the transcriptional co-activator peroxisome proliferator co-activator 1 alpha (PGC-1 alpha), selective mitochondrial autophagy (mitophagy) is thought to mediate organelle degradation. However, whether PGC-1 alpha plays a direct role in autophagy is currently unclear. Methods: To investigate the role of the co-activator in autophagy and mitophagy during skeletal muscle remodeling, PGC-1 alpha knockout (KO) and overexpressing (Tg) animals were unilaterally denervated, a common model of chronic muscle disuse. Results: Animals lacking PGC-1 alpha exhibited diminished mitochondrial density alongside myopathic characteristics reminiscent of autophagy-deficient muscle. Denervation promoted an induction in autophagy and lysosomal protein expression in wild-type (WT) animals, which was partially attenuated in KO animals, resulting in reduced autophagy and mitophagy flux. PGC-1 alpha overexpression led to an increase in lysosomal capacity as well as indicators of autophagy flux but exhibited reduced localization of LC3II and p62 to mitochondria, compared to WT animals. A correlation was observed between the levels of the autophagy-lysosome master regulator transcription factor EB (TFEB) and PGC-1 alpha in muscle, supporting their coordinated regulation. Conclusions: Our investigation has uncovered a regulatory role for PGC-1 alpha in mitochondrial turnover, not only through biogenesis but also via degradation using the autophagy-lysosome machinery. This implies a PGC-1 alpha-mediated cross-talk between these two opposing processes, working to ensure mitochondrial homeostasis during muscle adaptation to chronic disuse.