Epigenetic suppression of mouse Per2 expression in the suprachiasmatic nucleus by the inhalational anesthetic, sevoflurane

Abstract

Background: We previously reported that sevoflurane anesthesia reversibly suppresses the expression of the clock gene, Period2 (Per2), in the mouse suprachiasmatic nucleus (SCN). However, the molecular mechanisms underlying this suppression remain unclear. In this study, we examined the possibility that sevoflurane suppresses Per2 expression via epigenetic modification of the Per2 promoter.

Methods: Mice were anesthetized with a gas mixture of 2.5% sevoflurane/40% oxygen at a 6 L/min flow for 1 or 4 h. After termination, brains were removed and samples of SCN tissue were derived from frozen brain sections. Chromatin immunoprecipitation (ChIP) assays using anti-acetylated-histone antibodies were performed to investigate the effects of sevoflurane on histone acetylation of the Per2 promoter. Interaction between the E'-box (a cis-element in the Per2 promoter) and CLOCK (the Clock gene product) was also assessed by a ChIP assay using an anti-CLOCK antibody. The SCN concentration of nicotinamide adenine dinucleotide (NAD(+)), a CLOCK regulator, was assessed by liquid chromatography-mass spectrometry.

Results: Acetylation of histone H4 in the proximal region of the Per2 promoter was significantly reduced by sevoflurane. This change in the epigenetic profile of the Per2 gene was observed prior to suppression of Per2 expression. Simultaneously, a reduction in the CLOCK-E'-box interaction in the Per2 promoter was observed. Sevoflurane treatment did not affect the concentration of NAD(+) in the SCN.

Conclusions: Independent of NAD(+) concentration in the SCN, sevoflurane decreases CLOCK binding to the Per2 promoter E'-box motif, reducing histone acetylation and leading to suppression of Per2 expression.

Figure 1. Inhibition of Per2 expression in the SCN under sevoflurane anesthesia.

(A) The light/dark conditions and sampling periods are illustrated in the upper scheme. White and black bars indicate light and dark periods, respectively. Arrowheads indicate the time of sampling. Lower graph shows the quantitative diurnal change in Per2 expression. (B) The light/dark condition, sampling periods, and time of anesthetic treatment (gray bar) are illustrated in the upper scheme. Changes in Per2 expression under anesthetic treatment are shown in the lower graph. Data are mean ± SEM. * denotes a statistically significant difference between anesthetic treatment and control (two-way ANOVA; p<0.05).

Figure 2. DNA methylation profile of the Per2 promoter region following sevoflurane anesthesia.

(A) Diagram of CpG island around the Per2 locus. CpG sites are numbered and indicated by upward arrowheads. Arrows indicate pairs of methylation-specific primers used to amplify the region of the CpG island containing the E’-box. (B) Methylation rate of 10 individual sites in the Per2 promoter and four CpG sites in exon 1.

Figure 3. Changes in histone acetylation at CRE and E’-box in the Per2 promoter under sevoflurane anesthesia.

(A) Schematic representation of the light/dark condition, sampling periods, and time of anesthetic treatment (gray bar). Arrowheads indicate the time of sampling. (B) Schematic representation of Per2 promoter. The positions of primer pairs used for PCR are indicated by arrows. (C, D) Representative PCR results and acetylation levels of histone H3 or H4 at the proximal (C) or distal (D) regions of the Per2 promoter. Data are mean ± SEM. * denotes a statistically significant difference between control and anesthetic treatment. † denotes a statistically significant difference between the different time periods of anesthetic exposure (two-way ANOVA followed by Bonferroni test; p<0.05).

Figure 4. Suppression of CLOCK binding to the E’-box in the Per2 promoter region under sevoflurane anesthesia.

The light/dark condition, sampling periods, and time of anesthetic treatment (gray bar) are illustrated in the upper scheme. Arrowheads indicate the time of sampling. Representative PCR results are shown in the middle panel. CLOCK-E’-box binding in each sample is shown in the lower graph. Data are mean ± SEM. * denotes a statistically significant difference between control and anesthetic treatment (Student’s t-test; p<0.05).

Figure 5. Effects of sevoflurane treatment on NAD+, NMN, and NAM levels in the SCN.

Data were normalized using estimations of the total protein in each sample, and are shown as mean ± SEM (Student’s t-test; p<0.05).