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标题：Hepatic deletion of X-box binding protein 1 impairs bile acid metabolism in mice
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作者：Xiaoying Liu ; Anne S. Henkel ; Brian E. LeCuyer 等
期刊名称：JLR Papers In Press
印刷版ISSN：0022-2275
电子版ISSN：1539-7262
出版年度：2017
卷号：58
期号：3
页码：504-511
DOI：10.1194/jlr.M071266
语种：English
出版社：American Society for Biochemistry and Molecular Biology
摘要：The unfolded protein response (UPR) is an adaptive response to endoplasmic reticulum stress and the inositol-requiring enzyme 1α/X-box binding protein 1 (IRE1α/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 7α-hydroxy-4-cholesten-3-one (C4) levels compared with Xbp1 ^fl/fl mice, indicating reduced cholesterol 7α-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 Xbp1 ^fl/fl mice, respectively. However, serum C4 levels remained unchanged and were lower than both groups of Xbp1 ^fl/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 Xbp1 ^fl/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 IRE1α/XBP1 regulating bile acid metabolism.
关键词：cholesterol ; cholesterol 7-alpha hydroxylase ; liver ; gene expression ; endoplasmic reticulum ; unfolded protein response ; serum 7α-hydroxy-4-cholesten-3-one