In

agreement with previous findings,33 colesevelam treatment resulted in increased relative and absolute contents of fecal DCA (Supporting Fig. 4A,B). Under sequestrant-fed conditions, the loss of bile salts is mainly compensated by an increased hepatic synthesis of CA that results in an increased relative abundance of CA-derived bile salts in bile (Fig. 4D and Supporting Fig. 4C,D). However, LRH-1-KD animals cannot compensate for the sequestrant-induced loss of bile salts by up-regulating CA and DCA synthesis (Supporting Fig. 4B) and this results in a decrease in the relative abundance of CA-derived bile salts and an LY2109761 mw increase in the relative abundance of CDCA-derived bile salts in bile (Fig. 4D, Supporting Fig. 4C,D). LRH-1 is a nuclear receptor that regulates the expression of a variety of genes involved in cholesterol Imatinib nmr and bile salt metabolism. Cultured cell studies have shown that both CYP7A1 and CYP8B1, two key enzymes in bile salt synthesis, are regulated by LRH-1. Cyp7a1 was initially identified as an LRH-1 target gene in an unbiased screen.8 Subsequent cell studies showed that LRH-1 acts as a positive transcription factor as well as a docking site for the transcriptional repressor SHP.22, 23 Comprehensive analysis of the physiological importance of LRH-1 in vivo has been hampered by the embryonic lethality

of Lrh-1 knockout mice. Two laboratories independently generated conditional liver-specific Lrh-1 knockout models.30, 31 Surprisingly, hepatocyte-specific deficiency of Lrh-1 had no significant effect on Cyp7a1 expression,30, 31 and heterozygous Lrh-1 knockout mice exhibited 5 to 7-fold higher Cyp7a1 expression levels.32 Proposed explanations for these surprising findings were that LRH-1 either does not regulate Cyp7a1in vivo, or that compensatory responses or redundant factors maintain Cyp7a1 expression in the absence of LRH-1.31 In this study we used conditional whole-body LRH-1 knockdown mice to establish the involvement of LRH-1 on Cyp7a1 transcription in vivo. Our data unequivocally

demonstrate that LRH-1 is a critical transcription factor that is required for adequate up-regulation medchemexpress of Cyp7a1 expression under conditions associated with high fecal bile salt loss, as caused by sequestrant treatment. Hence, the inability to up-regulate Cyp7a1 expression translated into relatively low bile salt synthesis rates in LRH-1 knockdown animals compared to wildtypes during sequestrant treatment. Together, our data resolve the apparent discrepancy between the outcomes of in vitro cell studies8, 22, 23 and in vivo mouse studies.30, 31 This proves the previously predicted role of LRH-1 in CYP7A1 expression and complements the proposed mechanism of bile acid inhibition of CYP7A1 expression by way of the FXR-SHP-LRH-1 cascade. In this pathway bile acid activation of FXR leads to induction of SHP, which in turn inhibits CYP7A1 activation by LRH-1.