Research On The Mechanisms Of Berberine-stimulated Glucose Uptake In L6 Myotubes

Berberine is an isoquinoline alkaloid with a long history of medicinal application. It has been used as an antipyretic, antidotal and antibacterial drug for many years. Recently, clinical investigation has revealed an antihyperglycemic activity of this drug on Type 2 Diabetes Mellitus patients. This effect has been confirmed on diabetic rat models. However, the mechanism of this action, especially on the cell level, is still unclear.Here with the L6 myotube as the target cell, we show that berberine significantly stimulates glucose uptake. The aim of this research is to find out the molecular targets and the signaling pathways beneath this phenomenon.In the insulin signaling pathway, berberine weakly enhances the phosphorylation of Akt/PKB, and the specific PI 3-kinase inhibitor wortmannin cannot inhibit berberine-stimulated glucose uptake. In contrast, berberine significantly stimulates AMPK and p38 MAPK phosphorylation. Moreover, the specific AMPK inhibitor Compound C and the specific p38 MAPK inhibitor SB202190 reduce berberine-stimulated glucose uptake by 80% and 55%, respectively. Compound C reduces p38 MAPK phosphorylation, while SB202190 has no effect on the phosphorylation of either AMPK itself or its downstream target ACC, suggesting that p38 MAPK locates downstream of AMPK in berberine-triggered signaling cascade.While searching for the targets of berberine upstream of AMPK, we find that the cellular AMP:ATP ratio was increased. The specific inhibitor of CaMKKβ, STO-609, does not affect berberine-stimulated glucose uptake or AMPK activation. Furthermore, berberine does not enhance AMPK or ACC phosphorylation in HeLa cells which lack the expression of LKB1. These results suggest that berberine activates AMPK through AMP:ATP ratio change, and this effect is possibly dependent on LKB1.Our work reveals the mechanism underlying berberine-stimulated glucose uptake in L6 myotubes, and proves berberine to be an AMPK activator on the cell level. The perspective of berberine as a possible drug candidate for diabetes is supported by our work.