The Influence of Androgen Receptors on Muscle Repair and Hypertrophy
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abstract
The mechanisms underlying inter‐individual variation in adaptation to exercise have yet to be fully elucidated. Recently, high responders to resistance training (RT) have demonstrated greater levels of androgen receptor (AR) content, and therefore AR may be a factor underlying the variation in the adaptive response to resistance exercise. Moreover, there has been inconclusive findings surrounding the impact of AR content in females as well as following damage. In the current study, twenty‐six healthy young men (n=13) and women (n=13) underwent an acute bout of damaging exercise consisting of 300 eccentric kicks, followed by 10 weeks of full‐body RT to investigate changes in AR content following acute muscle damage and following chronic resistance exercise. This was assessed in the context of the satellite cell response and during muscle repair and hypertrophy. Skeletal muscle biopsies from the vastus lateralis were taken at baseline, 48 hours post damage and 48 hours following the last bout of RT. RT‐qPCR and western blots were performed to quantify AR gene expression and protein content, respectively. An immunofluorescence staining protocol was optimized for the visualization of AR protein abundance. Results were considered in the context of the SC response and muscle hypertrophy data from the same cohort. AR content increased from baseline (30457 +/‐ 4399 a.u.) to post‐damage (66448 +/‐ 8083 a.u.) by 218% (p=0.005) and post RT (60889 +/‐ 6636 a.u.) by 199% (p=0.003). Those with the greatest increase in SC content post‐damage also had the greatest increase in AR content (p=0.01). Individuals with the greatest increase in leg‐lean mass following RT also had the greatest increase in AR content (p=0.05). Preliminary data from western blot analysis revealed that AR protein content post‐damage in males was correlated with activated SC number (MyoD+ cells) (p=0.01). We then aimed to investigate sex differences in the context of AR content since there is a paucity of work in females. Males (61550 +/‐ 10961 a.u.) had a 198% greater change in AR content than females (31104 +/‐ 7499 a.u) from baseline to post‐damage (p=0.03). Males also had a greater change in AR content (3.186 +/‐ 0.5443) than females (2.003 +/‐ 0.2625) post‐RT, relative to baseline. In males, those with greater relative gains in muscle fibre CSA (high responders), post‐RT, had a 373% greater change in AR content (64936 +/‐ 11783 a.u.) from baseline to post‐RT than low responders (17388 +/‐ 15438) (p = 0.03). Interestingly in females, those with greater relative gain in CSA post‐RT (1.681 +/‐ 0.4120) had a trend towards lower AR content post‐RT compared to low responders (2.502 +/‐ 0.1946) (p = 0.06). This study is the first to immunofluorescently stain AR content for visualization and quantification in skeletal muscle. Collectively, these findings suggest that AR content influences SC activity and exhibits sex differences following damage and chronic resistance exercise.
