Differential Autophagy Response in Men and Women After Muscle Damage.

Hui-Ying Luk,Casey Appell,Jakob L Vingren,Danielle E Levitt,Nigel C Jiwan

doi:10.3389/fphys.2021.752347

Abstract

Following muscle damage, autophagy is crucial for muscle regeneration. Hormones (e.g., testosterone, cortisol) regulate this process and sex differences in autophagic flux exist in the basal state. However, to date, no study has examined the effect of a transient hormonal response following eccentric exercise-induced muscle damage (EE) between untrained young men and women. Untrained men (n = 8, 22 ± 3 years) and women (n = 8, 19 ± 1 year) completed two sessions of 80 unilateral maximal eccentric knee extensions followed by either upper body resistance exercise (RE; designed to induce a hormonal response; EE + RE) or a time-matched rest period (20 min; EE + REST). Vastus lateralis biopsy samples were collected before (BL), and 12 h, and 24 h after RE/REST. Gene and protein expression levels of selective markers for autophagic initiation signaling, phagophore initiation, and elongation/sequestration were determined. Basal markers of autophagy were not different between sexes. For EE + RE, although initiation signaling (FOXO3) and autophagy-promoting (BECN1) genes were greater (p < 0.0001; 12.4-fold, p = 0.0010; 10.5-fold, respectively) for women than men, autophagic flux (LC3-II/LC3-I protein ratio) did not change for women and was lower (p < 0.0001 3.0-fold) than men. Furthermore, regardless of hormonal changes, LC3-I and LC3-II protein content decreased (p = 0.0090; 0.547-fold, p = 0.0410; 0.307-fold, respectively) for men suggesting increased LC3-I lipidation and autophagosome degradation whereas LC3-I protein content increased (p = 0.0360; 1.485-fold) for women suggesting decreased LC3-I lipidation. Collectively, our findings demonstrated basal autophagy was not different between men and women, did not change after EE alone, and was promoted with the acute hormonal increase after RE only in men but not in women. Thus, the autophagy response to moderate muscle damage is promoted by RE-induced hormonal changes in men only.

Highlights

Autophagy is a highly regulated evolutionarily conserved catabolic process responsible for sequestering and recycling dysfunctional and damaged proteins (Yang and Klionsky, 2010)
Gene expression for selected markers of autophagy initiation signaling (FOXO3, protein kinase B (AKT), mammalian target of rapamycin (mTOR)), phagophore initiation (ULK1, ATG5, BECN1), and elongation and sequestration (ATG7, LC3A, LC3B, p62), as well as protein expression for microtubule-associated protein 1A/1B-light chain 3 (LC3)-I, LC3-II, and p62 were analyzed in skeletal muscle samples collected at BL, and 12 h and 24 h after the upper body resistance exercise (RE) or time-matched rest
With mounting evidence on the regulating role of hormones on autophagy and the wellestablished endogenously increases in these hormones from a bout of heavy RE, it is important to evaluate if the sexspecific hormonal acute changes from RE can alter the autophagy response to exerciseinduced muscle damage (EE)

Summary

Introduction

Autophagy is a highly regulated evolutionarily conserved catabolic process responsible for sequestering and recycling dysfunctional and damaged proteins (Yang and Klionsky, 2010). The activation of autophagic signaling [i.e., forkhead box O3 (FOXO3)] promotes downstream targeted autophagy-related proteins (ATG) (i.e., ATG7, ATG5), microtubule-associated protein light chain 3 LC3) (Mammucari et al, 2007), and the activation of the unc-51-like kinase (ULK1)/ATG complex followed by beclin-1 (BECN1)/vacuolar protein sorting 34 (VPS34) to regulate phagophore initiation (Russell et al, 2013) This results in the elongation of the phagophore indicated by the increase in lipidation of LC3A to LC3B controlled by ATG5 and ATG7 (Mizushima et al, 2003). Jamart et al (2012) reported increased ATG4B, ATG12, and LC3B gene expression after an ultra-endurance exercise in middle-aged men Together, these results suggest that autophagy in skeletal muscle increases after damage, and this response might be delayed or impaired with age in men. Autophagy signaling is critical to skeletal muscle regeneration and functional recovery after muscle damage

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