Rapamycin Does Not Compromise Exercise-Induced Muscular Adaptations in Female Mice

An increasing number of physically active adults are taking the mTOR inhibitor rapamycin off label with the goal of extending healthspan. However, frequent rapamycin dosing disrupts metabolic health during sedentary conditions and abates the anabolic response to exercise. Intermittent once-weekly rapamycin dosing minimizes many negative metabolic side effects of frequent rapamycin in sedentary mice. However, it remains unknown how different rapamycin dosing schedules impact metabolic, physical, and skeletal muscle adaptations to voluntary exercise training. Therefore, we tested the hypothesis that intermittent rapamycin (2 mg/kg; 1×/week) would avoid detrimental effects on adaptations to 8 weeks of progressive weighted wheel running (PoWeR) in adult female mice (5-month-old) by evading the sustained inhibitory effects on mTOR signaling by more frequent dosing schedules (2 mg/kg; 3×/week). PoWeR improved maximal exercise capacity, absolute grip strength, and myofiber hypertrophy with no differences between vehicle or rapamycin-treated mice despite greater voluntary running volume with intermittent rapamycin treatment. Conversely, frequent and intermittent rapamycin-treated mice had impaired glucose tolerance and insulin sensitivity compared to vehicle-treated mice after PoWeR; however, intermittent rapamycin reduced the impact on glucose intolerance versus frequent rapamycin. Collectively, these data in adult female mice suggest that (1) rapamycin is largely compatible with the physical and skeletal muscle benefits of PoWeR and (2) the detrimental effects of rapamycin on glucose metabolism in the context of voluntary exercise may be reduced by intermittent dosing.