Peroxisome proliferator-activated receptor gamma (PPARgamma) transcriptional activity is inhibited by acetaldehyde in human hepatic stellate cells (HSC)

Acetaldehyde may influence collagen synthesis by enhancing trancription of the pro-alphal(1) collagen gene in HSC. Recently, we pointed out that PPARg, member of a nuclear receptor superfamily of ligand-dependent trascription factors, has an important role to mantain the “resting” phenotype of HSC, and that activation of PPAR/RXR trancriptional control inhibits proliferation and collagen synthesis in activated HSC. AIM of our study was to evaluate the effect of acetaldehyde on PPARg trancriptional control in activated HSC. PPAR trancriptional activity was evaluated by transient transfection of a reporter gene PPRE3-tk-LUC containing three copies of PPARg response element. Activated HSC were also cotransfected with pSVZCAT as internal control for transfection efficiency and with humanPPARg expression plasmid. Twenty four hours after transfection cells were treated with ethanol or acetaldehyde with/without specific inhibitors of the enzymes involved in ethanol metabolism. DNA binding of PPAR was evaluated by EMSA using nuclear extracts from control and treated cells. Acetaldehyde significantly inhibits ligand (15d-PGJ2 or ciglitizone)- induced PPARg trancriptional activity in a dose dependent manner and impairs DNA binding. This effect is enhanced by the ALDH inhibitor cyanamide. Ethanol treatment has a slight effect in trasfection experiment but combination with cyanamide significantly reduces PPARg trancriptional modulation. This inhibitory effect is blocked by the ADH inhibitor 4-methyl-pyrazole. In conclusion, this study demonstrates that acetaldehyde inhibits PPARg trancriptional control in activated HSC suggesting a putative mechanism by which ethanol metabolism contributes to the activation of HSC and induces collagen synthesis in such cells.