Hepatic scavenger receptor class B, type I is stimulated by peroxisome proliferator-activated receptor gamma and hepatocyte nuclear factor 4alpha.

Excessive cellular cholesterol is transported to the liver by a pathway called 'reverse cholesterol transport.' Scavenger receptor class B, type I (SR-BI) mediates cholesterol uptake in the liver. Polyunsaturated fatty acids, known to activate peroxisome proliferator-activated receptor (PPAR), have been reported to increase hepatic cholesterol uptake. We found in the present study that PPARgamma induces expression of SR-BI in rat hepatocytes, liver endothelial cells, and Kupffer cells. In contrast, PPARalpha increased SR-BI levels only in hepatocytes and liver endothelial cells. PPARgamma/RXR binds to a response element between -459 and -472 bp in the human SR-BI promoter. Furthermore, hepatocyte nuclear factor 4alpha (HNF4alpha) was found to enhance PPARgamma-mediated SR-BI transcription. Thiazolidinedione (TZD)-activated PPARgamma/RXR increased hepatic SR-BI levels, which may lead to increased hepatic cholesterol uptake and less accumulation of lipids in peripheral tissues. The present results are in agreement with previous reports, indicating that specific PPARgamma-agonists (such as TZDs) protect against atherosclerosis.