Duchenne muscular dystrophy (DMD) is caused by the absence of functional dystrophin protein and results in progressive muscle wasting. Dystrophin deficiency leads to a host of dysfunctional cellular processes including impaired autophagy. Autophagic dysfunction appears to be due, at least in part, to decreased lysosomal abundance mediated by decreased nuclear localization of transcription factor EB (TFEB), a transcription factor responsible for lysosomal biogenesis. PGC‐1α overexpression decreased disease severity in dystrophin‐deficient skeletal muscle and increased PGC‐1α has been linked to TFEB activation in healthy muscle. The purpose of this study was to determine the extent to which PGC‐1α overexpression increased nuclear TFEB localization, increased lysosome abundance, and increased autophagosome degradation. We hypothesized that overexpression of PGC‐1α would drive TFEB nuclear translocation, increase lysosome biogenesis, and improve autophagosome degradation. To address this hypothesis, we delivered PGC‐1α via adeno‐associated virus (AAV) vector injected into the right limb of 3‐week‐old mdx mice and the contralateral limbs received a sham injection. At 6 weeks of age, this approach increased PGC‐1α transcript by 60‐fold and increased TFEB nuclear localization in gastrocnemii from PGC‐1α treated limbs by twofold compared to contralateral controls. Furthermore, lamp2, a marker of lysosome abundance, was significantly elevated in muscles from limbs overexpressing PGC‐1α. Lastly, increased LC3II and similar p62 in PGC‐1α overexpressing‐limbs compared to contralateral limbs are supportive of increased degradation of autophagosomes. These data provide mechanistic insight into PGC‐1α‐mediated benefits to dystrophin‐deficient muscle, such that increased TFEB nuclear localization in dystrophin‐deficient muscle leads to increased lysosome biogenesis and autophagy.

Duchenne muscular dystrophy is a severe muscle wasting disease caused by the absence of functional dystrophin protein. We have previously established that increased peroxisome proliferator‐activated receptor gamma coactivator 1‐alpha (PGC‐1α) pathway activity is therapeutic in dystrophic muscle. The purpose of this study was to determine the extent to which increased PGC‐1α pathway activity increased nuclear localization and activity of transcription factor EB (TFEB), a transcription factor that leads to lysosomal biogenesis. We hypothesized that increased PGC‐1α pathway activity would increase TFEB nuclear migration, lysosome abundance, and the restoration of impaired autophagosome degradation. To address this hypothesis, 3‐week‐old mdx mice were injected in one limb with an adeno‐associated virus that drives PGC‐1α gene expression and the other limb was injected with an empty capsid. Animals were sacrificed at 6 weeks of age and the gastrocnemii were harvested. PGC‐1α overexpression was confirmed by qPCR. Total TFEB protein abundance was similar between groups, however, nuclear TFEB was significantly increased in PGC‐1α treated limbs consistent with our hypothesis. We also discovered that Lamp2, a lysosomal marker, was significantly elevated in PGC‐1α treated muscle. Finally, abundance of autophagy‐related proteins were compared between treated and control gastrocnemii of mdx mice as well as to gastrocnemii from adult C57 mice. LC3 II, an indicator of autophagosome formation, was significantly elevated in PGC‐1α‐treated limbs compared to both the C57 and mdx‐control muscles. However, p62, an inverse correlate of autophagosome degradation, was similar between groups suggesting elevated degradation of autophagosomes in PGC‐1α treated limbs. These data suggest increased PGC‐1α pathway activity increased lysosomal degradation of autophagosomes in dystrophic muscle, likely through a TFEB‐mediated mechanism.Support or Funding InformationSupported by the American Physiological Society.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.