The role of AMP-activated protein kinase in the action of ethanol in the liver

BACKGROUND & AIMS: Our previous work has shown that ethanol induces the fatty acid synthesis pathway by activation of sterol regulatory element-binding protein 1 (SREBP-1). In the present study, we studied the mechanisms of this activation by identifying a new target of ethanol, AMP-activated protein kinase (AMPK). METHODS: The effects of ethanol on AMPK, acetyl-CoA carboxylase (ACC), and SREBP-1 were assessed in rat hepatic cells and in the livers of ethanol-fed mice. RESULTS: In rat hepatoma H4IIEC3 or McA-RH 7777 cell lines, ethanol-induced transcription of an SREBP-regulated promoter was suppressed by the presence of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) or metformin, 2 known AMPK activators. Consistent with this, over expression of a constitutively active form of AMPK blocked the effect of ethanol, whereas coexpression of a dominant-negative form of AMPK augmented the effect. Moreover, activation of AMPK by metformin or AICAR largely blocked the ability of ethanol to increase levels of mature SREBP-1 protein. These findings suggest that the effect of ethanol on SREBP-regulated promoter activation was partially mediated through AMPK inhibition. We further demonstrated that AMPK was inhibited by ethanol in hepatic cells. In parallel, ethanol increased the activity of ACC and suppressed the rate of palmitic acid oxidation. Finally, feeding mice a low-fat diet with ethanol resulted in significantly reduced hepatic AMPK activity, increased ACC activity, and enhanced malonyl CoA content. CONCLUSIONS: Taken together, our findings suggest that AMPK may play a key role in regulating the effects of ethanol on SREBP-1 activation, fatty acid metabolism, and development of alcoholic fatty liver.