Dibenzoylmethane (DBM) has been shown to exert a variety of beneficial effects on human health. However, the mechanism of action is poorly understood. In this study, DBM increased phosphorylation of AMP-activated protein kinase (AMPK) and stimulated glucose uptake in a skeletal muscle cell line. Both knockdown of AMPK with siRNA and inhibition with AMPK inhibitor blocked DBM-induced glucose uptake. DBM increased the concentration of intracellular calcium and glucose uptake due to DBM was abolished by STO-609 (a calcium/calmodulin-dependent protein kinase inhibitor). DBM stimulated phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK), which was blocked by pretreatment with compound C, an AMPK inhibitor. The expression of glucose transporter type 4 (GLUT4) was increased by DBM. The translocation of GLUT4 to the plasma membrane was also increased by DBM in AMPK dependently. In addition, DBM suppressed weight gain and prevented fat accumulation in the liver and abdomen in mice fed a high-fat diet. In pre-adipocyte cells, DBM decreased the activity of acetyl-CoA carboxylase (ACC), the rate-limiting enzyme of fatty acid synthesis. Expression of the adipogenic gene, fatty acid synthase (FAS), was suppressed by DBM in an AMPK-dependent manner. These results showed that the beneficial metabolic effects of DBM might be due to regulation of glucose uptake via AMPK in skeletal muscle and inhibition of adipogenesis in pre-adipocytes.

Follistatin-like 1 (FSTL-1) is a novel myokine; however, little is known about its metabolic role. Here, FSTL-1 stimulated glucose uptake in an AMP-activated protein kinase (AMPK)-dependent manner in L6 rat skeletal muscle cells. FSTL-1 increased intracellular calcium concentration. Calcium/calmodulin-dependent protein kinase kinase (CaMKK) inhibition blocked FSTL-1-induced AMPK phosphorylation and glucose uptake. In addition, FSTL-1 stimulated the phosphorylation of p21-activated kinase 1 (PAK1), a small GTPase Rac1 downstream protein. PAK1 knockdown or inhibition of Rac1 blocked FSTL-1-induced glucose uptake; moreover, kalirin, a Rac1 guanine nucleotide exchange factor (GEF), was induced by FSTL-1. Kalirin knockdown with siRNA blocked FSTL-1-induced PAK1 phosphorylation and glucose uptake. Consistent with the induction of Rac1 GEF kalirin, the GTP-bound form of Rac1 was increased by FSTL-1. FSTL-1 increased the production of glucose transporter type 4 (GLUT4) protein and also stimulated the translocation of GLUT4 to the plasma membrane. Translocation of GLUT4 was not observed in cells pre-treated with AMPK inhibitor, Rac1 inhibitor, or kalirin siRNA. In primary myoblast cell culture, FSTL-1 increased glucose uptake in an AMPK-dependent manner. A CaMKK inhibitor or kalirin knockdown blocked FSTL-1-induced glucose uptake. These results suggest that kalirin and Rac1 GEF play important roles in FSTL-1-mediated glucose regulation in skeletal muscle cells.

Isoeugenol exerts various beneficial effects on human health. However, the mechanisms underlying these effects are poorly understood. In this study, we observed that isoeugenol activated AMP-activated protein kinase (AMPK) and increased glucose uptake in rat L6 myotubes. Isoeugenol-induced increase in intracellular calcium concentration and glucose uptake was inhibited by STO-609, an inhibitor of calcium/calmodulin-dependent protein kinase kinase (CaMKK). Isoeugenol also increased the phosphorylation of protein kinase C-α (PKCα). Chelation of calcium with BAPTA-AM blocked isoeugenol-induced AMPK phosphorylation and glucose uptake. Isoeugenol stimulated p38MAPK phosphorylation that was inhibited after pretreatment with compound C, an AMPK inhibitor. Isoeugenol also increased glucose transporter type 4 (GLUT4) expression and its translocation to the plasma membrane. GLUT4 translocation was not observed after the inhibition of AMPK and CaMKK. In addition, isoeugenol activated the Akt substrate 160 (AS160) pathway, which is downstream of the p38MAPK pathway. Knockdown of the gene encoding AS160 inhibited isoeugenol-induced glucose uptake. Together, these results indicate that isoeugenol exerts beneficial health effects by activating the AMPK/p38MAPK/AS160 pathways in skeletal muscle.