The mTOR inhibitor rapamycin ameliorates the clinical and biochemical phenotype of mouse, worm, and cellular models of mitochondrial disease, via an unclear mechanism. Here, the authors show that prolonged rapamycin treatment improved motor endurance, corrected morphological abnormalities of muscle, and increased cytochrome c oxidase (COX) activity of a muscle-specific Cox15 knockout mouse (Cox15 sm/sm ). Rapamycin treatment restored autophagic flux, which was impaired in naïve Cox15 sm/sm muscle, and reduced the number of damaged mitochondria, which accumulated in untreated Cox15 sm/sm mice. Conversely, rilmenidine, an mTORC1-independent autophagy inducer, was ineffective on the myopathic features of Cox15 sm/sm animals. This stark difference supports the idea that inhibition of mTORC1 by rapamycin has a key role in the improvement of the mitochondrial function in Cox15 sm/sm muscle. In contrast to rilmenidine, rapamycin treatment also activated lysosomal biogenesis in muscle. This effect was associated with increased nuclear localization of TFEB, a master regulator of lysosomal biogenesis, which is inhibited by mTORC1-dependent phosphorylation.
