Lxr alpha deficiency hampers the hepatic adaptive response to fasting in mice

Besides its well established role in control of cellular cholesterol homeostasis, the liver X receptor (LXR) has been implicated in the regulation of hepatic gluconeogenesis. We investigated the role of the major hepatic LXR isoform in hepatic glucose metabolism during the feeding-to-fasting transition in vivo. In addition, we explored hepatic glucose sensing by LXR during carbohydrate refeeding. Lxr alpha(-/-) mice and their wild-type littermates were subjected to a fasting-refeeding protocol and hepatic carbohydrate fluxes as well as whole body insulin sensitivity were determined in vivo by stable isotope procedures. Lxr alpha(-/-) mice showed an impaired response to fasting in terms of hepatic glycogen depletion and triglyceride accumulation. Hepatic glucose 6-phosphate turnover was reduced in 9-h fasted Lxr alpha(-/-) mice as compared with controls. Although hepatic gluconeogenic gene expression was increased in 9-h fasted Lxr alpha(-/-) mice compared with wild-type controls, the actual gluconeogenic flux was not affected by Lxr alpha deficiency. Hepatic and peripheral insulin sensitivity were similar in Lxr alpha(-/-) and wildtype mice. Compared with wild-type controls, the induction of hepatic lipogenic gene expression was blunted in carbohydrate-refed Lxr alpha(-/-) mice, which was associated with lower plasma triglyceride concentrations. Yet, expression of "classic" LXR target genes Abca1, Abcg5, and Abcg8 was not affected by Lxr alpha deficiency in carbohydrate-refed mice. In summary, these studies identify LXR alpha as a physiologically relevant mediator of the hepatic response to fasting. However, the data do not support a role for LXR in hepatic glucose sensing.