Beneficial effects of beta-sitosterol on glucose and lipid metabolism in L6 myotube cells are mediated by AMP-activated protein kinase.

AMP-activated protein kinase (AMPK) is an energy-sensing enzyme that has been implicated as a key factor for controlling intracellular lipids and glucose metabolism. Beta-sitosterol, a plant sterol known to prevent cardiovascular disease was identified from Schizonepeta tenuifolia to an AMPK activator. In L6 myotube cells, beta-sitosterol significantly increased phosphorylation of the AMPKalpha subunit and acetyl-CoA carboxylase (ACC) with stimulating glucose uptake. In contrast, beta-sitosterol treatment reduced intracellular levels of triglycerides and cholesterol in L6 cells. These effects were all reversed by pretreatment with AMPK inhibitor Compound C or LKB1 destabilizer radicicol. Similarly, beta-sitosterol-induced phosphorylation of AMPK and ACC was not increased in HeLa cells lacking LKB1. These results together suggest that beta-sitosterol-mediated enhancement of glucose uptake and reduction of triglycerides and cholesterol in L6 cells is predominantly accomplished by LKB1-mediated AMPK activation. Our findings further reveal a molecular mechanism underlying the beneficial effects of beta-sitosterol on glucose and lipid metabolism.