Regulation of MAP kinase pathway activity in vivo in human skeletal muscle

Insulin and exercise potently stimulate glucose metabolism and gene transcription in vivo in skeletal muscle. A single bout of exercise increases the rate of insulin-stimulated glucose uptake and metabolism in skeletal muscle in the postexercise period. The nature of the intracellular signaling mechanisms that control responses to exercise is not known. In mammalian tissues, numerous reports have established the existence of the mitogen- activated protein (MAP) kinase signaling pathway that is activated by a variety of growth factors and hormones. This study was undertaken to determine how a single bout of exercise and physiological hyper-insulinemia activate the MAP kinase pathway. The euglycemic-hyper-insulinemic clamp and cycle ergometer exercise techniques combined with percutaneous muscle biopsies were used to answer this question. In healthy subjects, within 30 min, insulin significantly increased MAP kinase [isoforms p4(MAPK) and p44(MAPK) (ERK1 and ERK2)] phosphorylation (141 ± 2%, P < 0.05) and activity (177 ± 5%, P < 0.05), and the activity of its upstream activator MEK1 (161 ± 16%, P < 0.05). Insulin also increased the activity of the MAP kinase downstream substrate, the p90 ribosomal S6 kinase 2 (RSK2) almost twofold (198 ± 45%, P < 0.05). In contrast, a single 30-min bout of moderate- intensity exercise had no effect on the MAP kinase pathway activation from MEK to RSK2 in muscle of healthy subjects. However, 60 min of exercise did increase extracellular signal-related kinase activity. Therefore, despite similar effects on glucose metabolism after 30 min, insulin and exercise regulate the MAP kinase pathway differently. Insulin more rapidly activates the MAP kinase pathway.