Autophagic Adaptation Is Associated With Exercise-induced Fiber-type Shifting In Skeletal Muscle

Abstract

Acute exercise is known to activate autophagy in skeletal muscle. However, little is known about how basal autophagy in skeletal muscle adapts to chronic exercise. Moreover, the association between autophagy and fiber type shifting remains largely unknown. PURPOSE: To examine whether long-term habitual exercise alters the basal autophagic signalling in skeletal muscle and the association between autophagicy signaling and fiber type shifting. METHODS: Adult female Sprague-Dawley rats aged 2 months were randomly assigned to control and exercise groups. Animals in exercise group were kept in cages equipped with free access running wheels to perform habitual exercise for 5 months. Animals in the control group were caged in the absence of running wheels. Animals were sacrificed after the 5-month experimental period. Plantaris muscle tissues were harvested for analysis. RESULTS: we showed that lLong-term habitual exercise enhanced cellular autophagic capacity by increasing LC3-II reserve, but without altering the basal autophagic flux. Furthermore, we suspected that different types of muscle fiber adapted to chronic exercise in different ways. Llong-term habitual exercise resulted in fiber type shifting from type IIX to IIA, and intriguingly, . Intriguingly, our analysis demonstrated that LC3-II protein abundance iwas positively correlated to the proportion of type IIA fiber. In contrast, LC3-II abundance whereas it was negatively correlated to the proportion of type IIX fiber. PGC-1α protein abundance was positively associated with the proportion of type IIA fiber and LC3-II. CONCLUSION: These results suggest that autophagic signalling is not altered in skeletal muscle after long-term habitual exercise and, however, but the LC3-II-related autophagic adaptation might be associated with fiber type shifting. Supported by The Hong Kong Polytechnic University Research Funds (RTAS, G-U469 and A-PA7N) and General Research Fund (PolyU 5632/10M).