This project is designed to investigate the effects of ethanol on the activities of peroxisome proliferator activated receptor (PPARs) and sterol regulatory element (SRE)-binding protein (SREBPs). We have determined that ethanol treatment of hepatoma cells or hepatocytes decreases the ability of PPARalpha to activate a PPAR responsive reporter plasmid. This effect of ethanol depends on ethanol metabolism and is mediated by acetaldehyde. Further, in nuclear extracts from ethanol-treated cells, we have noted decreased binding of the PPARalpha/RXRalpha heterodimer to an oligonucleotide containing the PPAR response element. We have also found that ethanol treatment increases SREBP-regulated transcription of a SRE reporter in a dose-dependent manner in two hepatoma cell lines but not in CV-1 cells, suggesting that ethanol metabolism is also required for this effect. This effect is mediated via the SREBP proteolytic maturation cascade and is blocked by increasing concentration of sterols. We hypothesize that ethanol causes the development and maintenance of fatty liver by effects on these transcription factors, in addition to its well known effects on redox state and oxidative stress. This will be tested in both animals and cell culture models. We will examine the effect of alcohol feeding on levels of PPARs, their DNA-binding activity, levels of PPAR-regulated mRNAs, and responsiveness to WY14643. We will examine the effects of alcohol feeding on levels of SREBP-regulated mRNAs, and responsiveness of the system to cholesterol and metformin. The activities of these transcription factors and the genes they regulate will be correlated with hepatic histology, lipid content, and measures of total body lipid metabolism. Mechanisms for these activities of alcohol will be tested in hepatoma cells to better understand the molecular basis for the effects. Since these pathways can be manipulated by pharmacological agents, this hypothesis suggests possible new therapies for alcoholic fatty liver and possibly steatohepatitis.
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