Muscle Damage Increases Autophagy Activation In Untrained Young Men

Abstract

INTRODUCTION: The autophagic process is a key regulator of muscle repair and steroid hormones have been shown to alter this autophagic response. To date, no study has determined the effects of the acute resistance exercise (RE)-induced hormonal response on the autophagic process during muscle regeneration. PURPOSE: To examine the effect of the acute RE-induced hormone response on the autophagic process in untrained young men. METHODS: Untrained young men (n=8, 22 ± 3y; height: 180 ± 5.7cm; weight: 80 ± 15kg) completed two sessions of 80 unilateral maximal eccentric knee extensions. Immediately after knee extensions, participants completed either 20-min of rest (CON) or upper body resistance exercise (EX). Muscle samples were collected from the vastus lateralis before exercise (BL), and 12-hr and 24-hr after exercise sessions. Real-time PCR was used to determine the gene expression for autophagic initiation signaling markers (i.e. FOXO3, MTOR, and AKT) and autophagic markers (i.e., ATG5, ATG7, LC3A, LC3B, ULK1, and p62). RESULTS: A significant (p<0.05) time effect was found for AKT, FOXO3A, ATG5, and p62 expression. AKT expression increased from BL to 12-hr (1.97 ± 0.34-fold) and 24-hr (1.33 ± 0.12-fold) and FOXO3A expression decreased from BL at 12-hr (3.15 x 10-4 ± 2.94 x 10-4 -fold) and 24-hr (1.43 x 10-5 ± 3.02 x 10-6 -fold). Additionally, p62 increased from BL at 12-hr (4.11 ± 1.26-fold) and ATG-5 expressions increased from BL at 12-hr (1.62 ± 0.30-fold). A trend was found for MTOR towards an increase from BL at 12-hr. CONCLUSION: In response to muscle damage, the autophagic response increased from baseline in untrained young men; however, our data suggest that exercise-induced circulatory factors did not affect the autophagic process in untrained men.