Testosterone supplementation upregulates androgen receptor expression and translational capacity during severe energy deficit

Abstract

Testosterone supplementation during energy deficit promotes whole-body lean mass accretion, but the mechanisms underlying that effect remain unclear. To elucidate those mechanisms, skeletal muscle molecular adaptations were assessed from muscle biopsies collected before (Resting), 1 h (Post) and 6 h (Recovery) after exercise and a mixed meal (40 g protein, 1 h post-exercise) following 14 days of weight maintenance (WM) and 28 days of an exercise- and diet-induced 55% energy deficit (ED) in 50 physically active, non-obese men treated with 200 mg testosterone enanthate/week (TEST) or placebo (PLA) during the ED. Participants (n=10/group) exhibiting substantial increases (TEST) in leg lean mass and total testosterone were compared to those exhibiting decreases in both of these measures (PLA). Resting androgen receptor (AR) protein content was higher and fibroblast growth factor-inducible 14 (Fn14), IL-6 receptor (IL-6R), and muscle ring-finger protein-1 (MuRF1) gene expression were lower in TEST versus PLA during ED relative to WM (P < 0.05). Changes in inflammatory, myogenic, and proteolytic gene expression did not differ between groups after exercise and recovery feeding. Mechanistic target of rapamycin (mTOR) signaling (i.e., translational efficiency) was also similar between groups at rest and after exercise and the mixed meal. Muscle total RNA content (i.e., translational capacity) increased more during ED in TEST than PLA (P < 0.05). These findings indicate that attenuated proteolysis at rest, possibly downstream of AR, Fn14, and IL-6R signaling, and increased translational capacity, not efficiency, may drive lean mass accretion with testosterone administration during energy deficit.