Low-Dose Rapamycin Facilitates Recovery from Exercise-Induced Muscle Injury

Abstract

Rapamycin has been shown to have a dose-dependent effect on multiple signaling proteins in skeletal muscle cells that influence protein synthesis and calcium handling. However, it has yet to be determined if a low-dose of rapamycin impacts skeletal muscle during recovery from an exercise-induced injury. PURPOSE: To determine if low-dose rapamycin affects the rate of isometric strength recovery, muscle ubiquitination levels and markers of autophagy compared to saline control 14 days after exercise induced injury. METHODS: Mice were injected with either saline (SAL; 0.9%) or low-dose rapamycin (RAP; 10 μg/kg body weight) every other day for 2 weeks before and after a single bout of 150 eccentric contractions of the left anterior crural muscles. The recovery of strength of the anterior crural muscles was measured in vivo immediately, 7 days, and 14 days after injury induction. The magnitude of expression of beclin-1, ubiquitin, and ubiquitinated protein in injured and contralateral control TA muscles (i.e., primary anterior crural muscle) were analyzed via Western blot at 14 days after injury. RESULTS: Isometric twitch torque values did not differ between groups at any time point. No group differences in peak isometric tetanic torque were observed pre-injury, post-injury or 7 days following injury. However at 14 days, RAP mice recovered to pre-injury peak isometric torque values (Pre= 2.30 ± .07 Nmm; 14d= 2.25 ± 0.08 Nmm) while SAL group was significantly lower than pre-injury. At 14 days, RAP mice generated 15.4% higher maximal torque than SAL group (p = 0.04). Beclin-1 and free ubiquitin expression in TA muscles were significantly increased in both SAL (1.4-fold and 2.3-fold, respectively) and RAP (2.2-fold and 8.0-fold, respectively) mice at 14 days after injury compared to the uninjured muscle. The increase in the free ubiquitin in the injured muscle was 3.3-fold greater in the RAP treatment compared to SAL (p = 0.001). There were no significant changes in the ubiquitination of proteins among the groups at 14 days post-injury. CONCLUSION: Chronic low-dose rapamycin treatment in mice enhances recovery of skeletal muscle from eccentric contraction-induced injury at the 14th day and accentuates the upregulation of free ubiquitin.