Growing evidence suggests that the cytokine IL-6 plays a protective role in alcoholic (and other) liver disease, and that alcohol use interferes with IL-6 signaling in hepatocytes. IL-6 appears to protect against steatosis, but the mechanisms underlying this effect are unknown. IL-6 can activate AMP-dependent protein kinase (AMPK) and induce PPARa; since ethanol treatment inhibits AMPK and PPARa, and these factors are critical to lipid metabolism in the liver, we suggest that ethanol may also inhibit the ability of IL-6 to activate AMPK and PPARa. Effects of IL-6 on SREBP-1, the master regulator of lipid synthesis in the liver, are largely unexplored. In addition, the mechanisms for ethanol inhibition of IL-6 signaling after acute or chronic exposure are incompletely understood. We will therefore test the following hypotheses: 1. Determine if IL-6 activates AMPK and PPARa, and inhibits SREBP-1 in isolated hepatocytes, and the effect of acute exposure of the cells to ethanol; 2. Determine if the ability of IL-6 to activate AMPK and PPARa, and inhibit SREBP-1 is blunted by chronic alcohol feeding, and determine the effect of IL-6 on fatty acid synthesis and oxidation; 3. Determine the mechanism for the acute effects of ethanol on IL- 6 signaling. We will examine the role of activation of PKC or protein phosphatase 2 (PP2A), and inhibition of STATS acetylation. These studies will be carried out with isolated hepatocytes prepared from naive or chronically alcohol-fed rats. The effects of IL-6 will be tested by assaying activation of individual steps in the signaling cascade, the induction of mRNAs regulated by the transcription factors, the rate of fatty acid oxidation and synthesis by the cells, and the ability of activators and inhibitors of PKC and PP2A to affect IL-6 signaling and ethanol effects. The biomedical ramifications of this project are several. IL-6 could be developed as a therapy for alcoholic and other forms of fatty liver. IL-6 gene variants might be associated with susceptibility to alcoholic liver disease, and the role of IL-6 signaling via STAT3 might explain interactions between heavy alcohol use and progression of hepatitis C. ? ? ?
| Liangpunsakul, Suthat; Sozio, Margaret S; Shin, Eric et al. (2010) Inhibitory effect of ethanol on AMPK phosphorylation is mediated in part through elevated ceramide levels. Am J Physiol Gastrointest Liver Physiol 298:G1004-12 |
| Sozio, Margaret S; Liangpunsakul, Suthat; Crabb, David (2010) The role of lipid metabolism in the pathogenesis of alcoholic and nonalcoholic hepatic steatosis. Semin Liver Dis 30:378-90 |
| Sozio, Margaret S; Chalasani, Naga; Liangpunsakul, Suthat (2009) What advice should be given to patients with NAFLD about the consumption of alcohol? Nat Clin Pract Gastroenterol Hepatol 6:18-9 |
