Growth hormone (GH) is a powerful stimulator of the Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) pathway. Acute exercise is a known stimulus for GH secretion.
Purpose: The purpose of this study was to determine the phosphorylation of the JAK2-STAT5 pathway in human skeletal muscle in response to acute aerobic exercise.
Methods: Eleven young (22.5 ± 0.6, mean ± SE), healthy, aerobically trained males performed 30 min of cycling at 70% V˙O2max. Blood samples were collected at 10- to 15-min intervals and analyzed for human GH, immunofunctional (IF) GH, GH binding protein, and insulin-like growth factor I (IGF-I). Muscle biopsies were taken from the vastus lateralis before exercise, immediately after exercise, as well as, 30 and 60 min postexercise. Muscle samples were analyzed for changes in JAK2 and STAT5 tyrosine phosphorylation, as well as changes in JAK2 and STAT5 protein content.
Results: Multivariate ANOVA with post hoc comparisons demonstrated that GH and IF GH were significantly elevated immediately after exercise compared with preexercise (P < 0.001). Exercise significantly increased the phosphorylation of JAK2 immediately after exercise (P = 0.004). A trend toward increasing levels of STAT5 phosphorylation was observed immediately after exercise (P = 0.08) and was significantly elevated 30 min after exercise (P = 0.002), compared with preexercise levels. Muscle JAK2 and STAT5 protein content did not change.
Conclusion: The results demonstrate that the JAK2-STAT5 pathway is activated in response to acute aerobic exercise in human skeletal muscle and suggests that the exercise-induced release of GH may play a role in the activation of this pathway.