Berberine-stimulated glucose uptake in L6 myotubes involves both AMPK and p38 MAPK
Zhe Cheng, Tao Pang, Min Gu, An-Hui Gao, Chuan-Ming Xie, Jing-Ya Li, Fa-Jun Nan and Jia Li
National Center for Drug Screening, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 201203, P. R. China
Received 17 May 2006; revised 13 September 2006; accepted 13 September 2006. Available online 20 September 2006.
Berberine is a plant alkaloid used in traditional Chinese medicine and has been reported to have antihyperglycemic activity in NIDDM patients. However, the molecular basis for this action is yet to be elucidated. Here we investigate the effects and signaling pathways of berberine on L6 rat skeletal muscles. Our study demonstrates that berberine stimulates glucose uptake in a time- and dose-dependent manner. Intriguingly, berberine-stimulated glucose uptake does not vary as insulin concentration increases, and could not be blocked by the PI 3-kinase inhibitor wortmannin. Berberine only weakly stimulates the phosphorylation of Akt/PKB, a key molecule in the insulin signaling pathway, but strongly promotes the phosphorylation of AMPK and p38 MAPK. The effects of berberine are not a result of pro-oxidant action, but a consequence of an increased cellular AMP:ATP ratio. Moreover, berberine-stimulated glucose uptake is inhibited by the AMPK inhibitor Compound C and the p38 MAPK inhibitor SB202190. Inhibition of AMPK reduces p38 MAPK phosphorylation, suggesting that AMPK lies upstream of p38 MAPK. These results suggest that berberine circumvents insulin signaling pathways and stimulates glucose uptake through the AMP-AMPK-p38 MAPK pathway, which may account for the antihyperglycemic effects of this drug.