The Transcriptional and DNA Binding Activity of Peroxisome Proliferator-activated Receptor α Is Inhibited by Ethanol Metabolism

Abstract

Fatty acids are ligands for the peroxisome proliferator-activated receptor ␣ (PPAR␣). Fatty acid levels are increased in liver during the metabolism of ethanol and might be expected to activate PPAR␣. However, ethanol inhibited PPAR␣ activation of a reporter gene in H4IIEC3 hepatoma cells expressing alcohol-metabolizing enzymes but not in CV-1 cells, which lack these enzymes. Ethanol also reduced the ability of the PPAR␣ ligand WY14,643 to activate reporter constructs in the hepatoma cells or cultured rat hepatocytes. This effect of ethanol was abolished by the alcohol dehydrogenase inhibitor 4-methylpyrazole and augmented by the aldehyde dehydrogenase inhibitor cyanamide, indicating that acetaldehyde was responsible for the action of ethanol. PPAR␣/retinoid X receptor extracted from hepatoma cells exposed to ethanol or acetaldehyde bound poorly to an oligonucleotide containing peroxisome proliferator response elements. This effect was also blocked by 4-methylpyrazole and augmented by cyanamide. Furthermore, in vitro translated PPAR␣ exposed to acetaldehyde failed to bind DNA. Thus, ethanol metabolism blocks transcriptional activation by PPAR␣, in part due to impairment of its ability to bind DNA. This effect of ethanol may promote the development of alcoholic fatty liver and other hepatic consequences of alcohol abuse.

Role of Adiponectin in the Protective Action of Dietary Saturated Fat Against Alcoholic Fatty Liver in Mice * #

“…4B, adiponectin, at 1 g/mL, increased the reporter activity more than threefold. Ethanol inhibited activity of PPRE3-tk-luciferase as reported, 13 and coincubation of adiponectin (1 g/mL) partially restored the ethanol-inhibited reporter activity. More interestingly, the activation of the PPAR-␣-responsive promoter by adiponectin requires coexpression of Fig.…”

“…29 Cell transfection assays were performed as previously described. 13 Primary rat hepatocytes were isolated from fed male Sprague-Dawley rats via collagenase digestion. 12 The rate of oxidation of [1-14 C]-palmitic acid to carbon dioxide was performed as previously described.…”

“…Ethanol treatment impairs hepatic fatty acid oxidation by inhibiting the transcriptional activities of PPAR-␣. 13 PGC-1␣ is a coactivator of PPAR-␣ 33,34 ; therefore, we examined the mRNA and protein levels of PGC-1␣. As shown in Fig.…”

“…The effect of adiponectin on PPAR-␣ activity was examined using a PPAR-␣-responsive reporter plasmid transfected into H4IIEC3 cells. Because the levels of endogenous PPAR-␣ and PGC-1␣ were low in H4IIEC3 cells, 13 PPAR-␣ and PGC-1␣ expression plasmids were cotransfected into cells. As shown in Fig.…”

“…Chronic ethanol administration in mice is associated with inhibition of AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor (PPAR) ␣, two critical signaling molecules controlling the pathways of hepatic fatty acid oxidation. [12][13][14][15] These molecules are the major mediators of the metabolic effect of adiponectin. 16,17 Adiponectin is exclusively expressed and secreted from adipose tissue.…”