CREM modulates the circadian expression of CYP51, HMGCR and cholesterogenesis in the liver

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Abstract

We show for the first time that isoforms of the cAMP response element modulator Crem, regulate the circadian expression of Cyp51 and other cholesterogenic genes in the mouse liver. In the wild type mice the expression of Cyp51, Hmgs, Fpps, and Sqs is minimal between CT12 and CT16 and peaks between CT20 and CT24. Cyp51, Fpps, and Sqs lost the circadian behavior in Crem−/− livers while Hmgcr is phase advanced from CT20 to CT12. This coincides with a phase advance of lathosterol/cholesterol ratio, as detected by GC–MS. Overexpression of CREMτ and ICER has little effect on the Hmgcr proximal promoter while they influence expression from the CYP51 promoter. Our data indicate that Crem-dependent regulation of Cyp51 in the liver results in circadian expression of this gene. We propose that cAMP signaling might generally be involved in the circadian regulation of cholesterol synthesis on the periphery.

Section snippets

Materials and methods

Animals. The Crem−/− animals originate from the laboratory of Dr. P. Sassone-Corsi, IGBMC, Strasbourg, France. The protocols for animal care followed the EU regulations. Male mice (13–24 weeks old) were for 7 days under 12 h light and 12 h dark condition, followed by a 24 h dark cycle before being sacrificed. Sacrification took place in the dark, under red light. Blood was collected into EDTA-coated tubes, centrifuged (plasma), livers cut into pieces and immediately frozen in liquid N2. Samples

CREM/ICER influence the expression of cholesterogenic genes

RT-PCR analyses of cholerestogenic Hmgs, Fpps, Sqs, Cyp51, Srebp-2, and Hmgcr from w.t. and Crem−/− mouse liver tissue are shown in Fig 1. In wild type animals (grey lines), the one-way ANOVA (p < 0.05) of Hmgcr expression (Fig. 1B) showed maximal expression in the dark phase at CT20 which is in accordance by previous works [17] and is consistent with the HMGCR activity [18]. The expression of other genes of cholesterol synthesis (Hmgs, Fpps, Sqs, Cyp51) is minimal between CT12 and CT16 (start of

Discussion

Liver is a central organ of the bodies homeostasis and has a unique ability to regenerate. Liver is also a circadian organ where many metabolic processes exhibit a rhythmic regulation. Increased cAMP levels and the cAMP regulatory element modulator isoforms CREM and ICER were so far shown to be involved in the hepatic regeneration and proliferation [22], ICER was overexpressed in the hepatocellular carcinoma, [23] and was induced after the forskolin treatment in immortal cell lines, including

Acknowledgments

The work was supported by the Slovenian Research Agency, Grants J1-6713, J1-9428 and P1-0104. Thanks also to FEBS (Federation of European Biochemical Societies) for fellowship grant to Jure Acimovic and to EMBO (European Molecular Biology Organization) for the fellowship to D. Rozman. Part of the work has been generated in the context of the STEROLTALK project, funded by the European Community as contract No. LSHG-CT-2005-512096 under 6th Framework Programme for Research and Technological

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