| Abstract: | In vitro and in vivo studies described the myokine IL ‐15 and its receptor IL ‐15Rα as anabolic/anti‐atrophy agents, however, the protein expression of IL ‐15Rα has not been measured in human skeletal muscle and data regarding IL ‐15 expression remain inconclusive. The purpose of the study was to determine serum and skeletal muscle IL ‐15 and IL ‐15Rα responses to resistance exercise session and to analyze their association with myofibrillar protein synthesis (MPS ). Fourteen participants performed a bilateral leg resistance exercise composed of four sets of leg press and four sets of knee extension at 75% 1RM to task failure. Muscle biopsies were obtained at rest, 0, 4 and 24 hours post‐exercise and blood samples at rest, mid‐exercise, 0, 0.3, 1, 2, 4 and 24 hours post‐exercise. Serum IL ‐15 was increased by ~5.3‐fold immediately post‐exercise, while serum IL ‐15Rα decreased ~75% over 1 hour post‐exercise (P <.001). Skeletal muscle IL ‐15Rα mRNA and protein expression were increased at 4 hours post‐exercise by ~2‐fold (P <.001) and ~1.3‐fold above rest (P =.020), respectively. At 24 hours post‐exercise, IL ‐15 (P =.003) and IL ‐15Rα mRNA s increased by ~2‐fold (P =.002). Myofibrillar fractional synthetic rate between 0‐4 hours was associated with IL ‐15Rα mRNA at rest (r =.662, P =.019), 4 hours (r =.612, P =.029), and 24 hours post‐exercise (r =.627, P =.029). Finally, the muscle IL ‐15Rα protein up‐regulation was related to Leg press 1RM (r =.688, P =.003) and total weight lifted (r =.628, P =.009). In conclusion, IL ‐15/IL ‐15Rα signaling pathway is activated in skeletal muscle in response to a session of resistance exercise. |
