Protective effect of butanol extracts of skin of Anguilla japonica against endoplasmic reticulum stress-induced insulin resistance via the AMPK pathway in L6 myotubes

The effect of butanol extracts of the skin of Anguilla japonica (BESA) on endoplasmic reticulum (ER) stress-induced insulin resistance in L6 myotubes was investigated. Western blotting revealed that BESA increased phosphorylation of AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase, and stimulated glucose uptake in L6 myotubes. Stimulation of AMPK and glucose uptake by BESA were significantly (p<0.05) reduced by siRNA LKB1 or siRNA AMPK, compared with controls, suggesting that enhanced glucose uptake by BESA was predominantly accomplished via an LKB1-mediated AMPK activation pathway. In addition, BESA effectively reduced phosphorylation of ER stress markers, RNA-activated protein kinase-like ER resident kinase, JNK, and significantly (p<0.01) increased glucose uptake via AMPK activation in tunicamycin-treated L6 myotubes, compared with controls. Improvement of insulin sensitivity under ER stress conditions by BESA is predominantly accomplished via an LKB1-AMPK-dependent pathway.