REV-ERBalpha participates in circadian SREBP signaling and bile acid homeostasis - PubMed (original) (raw)

REV-ERBalpha participates in circadian SREBP signaling and bile acid homeostasis

Gwendal Le Martelot et al. PLoS Biol. 2009 Sep.

Abstract

In mammals, many aspects of behavior and physiology, and in particular cellular metabolism, are coordinated by the circadian timing system. Molecular clocks are thought to rely on negative feedback loops in clock gene expression that engender oscillations in the accumulation of transcriptional regulatory proteins, such as the orphan receptor REV-ERBalpha. Circadian transcription factors then drive daily rhythms in the expression of clock-controlled output genes, for example genes encoding enzymes and regulators of cellular metabolism. To gain insight into clock output functions of REV-ERBalpha, we carried out genome-wide transcriptome profiling experiments with liver RNA from wild-type mice, Rev-erbalpha knock-out mice, or REV-ERBalpha overexpressing mice. On the basis of these genetic loss- and gain-of-function experiments, we concluded that REV-ERBalpha participates in the circadian modulation of sterol regulatory element-binding protein (SREBP) activity, and thereby in the daily expression of SREBP target genes involved in cholesterol and lipid metabolism. This control is exerted via the cyclic transcription of Insig2, encoding a trans-membrane protein that sequesters SREBP proteins to the endoplasmic reticulum membranes and thereby interferes with the proteolytic activation of SREBPs in Golgi membranes. REV-ERBalpha also participates in the cyclic expression of cholesterol-7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in converting cholesterol to bile acids. Our findings suggest that this control acts via the stimulation of LXR nuclear receptors by cyclically produced oxysterols. In conclusion, our study suggests that rhythmic cholesterol and bile acid metabolism is not just driven by alternating feeding-fasting cycles, but also by REV-ERBalpha, a component of the circadian clockwork circuitry.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. REV-ERBα controls the temporal nuclear accumulation of SREBP and the transcription of SREBP target genes.

(A) Affymetrix-microarray analysis of liver RNA from mice of various genotypes. The heat map displays transcripts with differential accumulation in WT, Rev-KO, and TgRev mice. Differentially expressed transcripts of mice with different genotypes are clustered into four classes: class I: Rev-KO>WT≥TgRev; class II: Rev-KO>WT

<tgrev; iii:="" rev-ko<wt≤tgrev;="" iv:="" rev-ko<wt="">TgRev (see also Figure S2). (B) Temporal accumulation of SREBP1c in liver nuclear extract. (C) Temporal expression of transcripts from selected SREBP1c genes. (D) Temporal expression of transcripts from selected SREBP2 target genes. (E) Temporal expression of Insig2 transcripts. The data displayed in (C–E) were obtained by quantitative (Q) RT-PCR experiments on whole-cell liver RNA from WT, Rev-KO, and TgRev animals. The data represent the mean±SEM (n = 4–6).</tgrev;>

Figure 2

Figure 2. Fasting–feeding regulation of SREBP targeted genes in Rev-KO mice.

(A) Feeding activity of three Rev-KO and WT mice as measured by an infrared detection system. (B) Mice that were either fasted for 24 h or (C) fed a high carbohydrate–no fat diet for 18 d were humanely killed at ZT12, and the accumulation of selected mRNAs was measured in WT and Rev-KO (n = 4 per each data point) using Q-RT PCR. (D) Insulin measurement from blood samples collected at ZT4, ZT12, and ZT16 (n = 5 per each data point). (B–D) data represent the mean±SEM.

Figure 3

Figure 3. Accumulation of cholesterol and triglycerides in liver and plasma of WT and Rev-KO mice.

(A) Total hepatic triglycerides and (B) cholesterol in WT mice (ZT12 n = 8, ZT20 n = 6) and Rev-KO mice (ZT12 n = 10, ZT20 n = 4). (C) Plasma LDL-cholesterol and (D) HDL-cholesterol in WT and Rev-KO (n = 6 per each data point). (E) Plasma samples from animals humanely killed at ZT12 and ZT20 were pooled (n = 6) and lipoproteins separated by fast protein liquid chromatography (FPLC). (A–D) data represent the mean±SEM. _p_-Values: *, <0.05; **, <0.005.

Figure 4

Figure 4. REV-ERBα controls Cyp7a1 transcription and bile acid accumulation.

(A) Temporal Cyp7a1 mRNA accumulation in the livers of WT, Rev-KO, and (B) TgRev mice. The data represent the mean±SEM (n = 4–6). (C) Primary and secondary bile acid levels in gallbladders from WT and Rev-KO mice. Data represent the mean±SEM (n = 6). _p_-Values: *, <0.05; **, <0.005.

Figure 5

Figure 5. LXR participates in the circadian transcription of Cyp7a1.

Temporal Cyp7a1 mRNA accumulation was measured in the livers of (A) Dbp/Tef/Hlf triple knock-out mice (B) E4bp4/Nfil3 knock-out mice and (C) _LXR_α/β double knock-out animals. Data represent the mean±SEM (n = 4).

Figure 6

Figure 6. The role of REV-ERBα in circadian lipid and bile acid homeostasis.

The cartoon illustrates how REV-ERBα may modulate circadian lipid, cholesterol, and bile acid synthesis by controlling the accumulation of SREBP in the nucleus. In liver hepatocytes, REV-ERBα accumulates to maximal levels at ZT8–ZT12 and represses Insig2 transcription. Thereby, it promotes the proteolytic activation and nuclear accumulation of SREBP proteins. In turn, the circadian activation of SREBP transcription factors drives the cyclic transcription of Hmgcr, encoding the rate-limiting enzyme of cholesterol biosynthesis. As a consequence the levels of oxysterols, which serve as ligands for LXR, also oscillate during the day, and cyclically activated LXR then controls rhythmic Cyp7a1 transcription.

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References

    1. Gachon F, Nagoshi E, Brown S. A, Ripperger J, Schibler U. The mammalian circadian timing system: from gene expression to physiology. Chromosoma. 2004;113:103–112. - PubMed
    1. Reppert S. M, Weaver D. R. Coordination of circadian timing in mammals. Nature. 2002;418:935–941. - PubMed
    1. Balsalobre A, Brown S. A, Marcacci L, Tronche F, Kellendonk C, et al. Resetting of circadian time in peripheral tissues by glucocorticoid signaling. Science. 2000;289:2344–2347. - PubMed
    1. Brown S. A, Zumbrunn G, Fleury-Olela F, Preitner N, Schibler U. Rhythms of mammalian body temperature can sustain peripheral circadian clocks. Curr Biol. 2002;12:1574–1583. - PubMed
    1. Le Minh N, Damiola F, Tronche F, Schutz G, Schibler U. Glucocorticoid hormones inhibit food-induced phase-shifting of peripheral circadian oscillators. Embo J. 2001;20:7128–7136. - PMC - PubMed

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