Feedback regulation of bile acid synthesis in human liver:: Importance of HNF-4α for regulation of CYP7A1

A great number of nuclear factors are involved in the negative feedback mechanism regulating bile acid synthesis. There are two major ways for the negative feedback to effect the synthesis; the SHP-dependent, involving FXR, and the SHP-independent way, affecting HNF-4 alpha. We studied 23 patients with gallstone disease. Eight patients were treated with chenodeoxycholic acid, 7 with cholestyramine prior to operation, and 8 served as controls. Liver biopsies were analyzed with Real-time-PCR. In the cholestyramine-treated group mRNA levels of CYP7Al were increased about 10-fold. Treatment with CDCA decreased the mRNA levels of CYP7Al by about 70%. The mRNA levels of CYP8Bl, CYP27Al, and CYP7Bl were not significantly altered in the treated groups. The analysis of mRNA levels for HNF-4a showed 64% higher levels in the cholestyramine-treated group compared to the controls. These levels showed positive and highly significant correlation to the levels of mRNA of CYP7Al when studied in all three groups together. FXR, SHP, and LRH-1/FTF were not significantly affected by the different treatments. Our results indicate that when bile acid synthesis is upregulated by cholestyramine treatment the SHP-independent pathway for controlling CYP7Al transcription dominates over the SHP-dependent pathway. (c) 2005 Elsevier Inc. All rights reserved.