| First Author | Liu X | Year | 2017 |
| Journal | J Lipid Res | Volume | 58 |
| Issue | 3 | Pages | 504-511 |
| PubMed ID | 28039331 | Mgi Jnum | J:239685 |
| Mgi Id | MGI:5829501 | Doi | 10.1194/jlr.M071266 |
| Citation | Liu X, et al. (2017) Hepatic deletion of X-box binding protein 1 impairs bile acid metabolism in mice. J Lipid Res 58(3):504-511 |
| abstractText | The unfolded protein response (UPR) is an adaptive response to endoplasmic reticulum stress and the inositol-requiring enzyme 1alpha/X-box binding protein 1 (IRE1alpha/XBP1) pathway of the UPR is important in lipid metabolism. However, its role in bile acid metabolism remains unknown. We demonstrate that liver-specific Xbp1 knockout (LS-Xbp1-/-) mice had a 45% reduction in total bile acid pool. LS-Xbp1-/- mice had lower serum 7alpha-hydroxy-4-cholesten-3-one (C4) levels compared with Xbp1fl/fl mice, indicating reduced cholesterol 7alpha-hydroxylase (CYP7A1) synthetic activity. This occurred without reductions of hepatic CYP7A1 protein expression. Feeding LS-Xbp1-/- mice cholestyramine increased hepatic CYP7A1 protein expression to levels 2-fold and 8-fold greater than cholestyramine-fed and chow-fed Xbp1fl/fl mice, respectively. However, serum C4 levels remained unchanged and were lower than both groups of Xbp1fl/fl mice. In contrast, although feeding LS-Xbp1-/- mice cholesterol did not increase CYP7A1 expression, serum C4 levels increased significantly up to levels similar to chow-fed Xbp1fl/fl mice and the total bile acid pool normalized. In conclusion, loss of hepatic XBP1 decreased the bile acid pool and CYP7A1 synthetic activity. Cholesterol feeding, but not induction of CYP7A1 with cholestyramine, increased CYP7A1 synthetic activity and corrected the genotype-specific total bile acid pools. These data demonstrate a novel role of IRE1alpha/XBP1 regulating bile acid metabolism. |
