Visfatin is a novel adipocytokine produced by visceral fat. In the present study, visfatin increased AMP-activated protein kinase (AMPK) phosphorylation in mouse C2C12 skeletal muscle cells. It also increased phosphorylation of the insulin receptor, whose knockdown blocked visfatin-induced AMPK phosphorylation and glucose uptake. Visfatin stimulated glucose uptake in differentiated skeletal muscle cells. However, inhibition of AMPKα2 with an inhibitor or with knockdown of AMPKα2 using siRNA blocked visfatin-induced glucose uptake, which indicates that visfatin stimulates glucose uptake through the AMPKα2 pathway. Visfatin increased the intracellular Ca2+concentration. STO-609, a calmodulin-dependent protein kinase kinase inhibitor, blocked visfatin-induced AMPK phosphorylation and glucose uptake. Visfatin-mediated activation of p38 MAPK was AMPKα2-dependent. Furthermore, both inhibition and knockdown of p38 MAPK blocked visfatin-induced glucose uptake. Visfatin increased glucose transporter type 4 (GLUT4) mRNA and protein levels. In addition, visfatin stimulated the translocation of GLUT4 to the plasma membrane, and this effect was suppressed by AMPKα2 inhibition. The present results indicate that visfatin plays an important role in glucose metabolism via the Ca2+-mediated AMPK–p38 MAPK pathway.
Hypoglycemic Effect of Opuntia ficus-indica var. saboten Is Due to Enhanced Peripheral Glucose Uptake through Activation of AMPK/p38 MAPK Pathway