Gastroenterology

Gastroenterology

Volume 133, Issue 4, October 2007, Pages 1240-1249
Gastroenterology

Basic–alimentary tract
Insight Into the Circadian Clock Within Rat Colonic Epithelial Cells

https://doi.org/10.1053/j.gastro.2007.05.053Get rights and content

Background & Aims: The gastrointestinal tract exhibits diurnal rhythms in many physiologic functions. These rhythms are driven by food intake but are also preserved during food deprivation, suggesting the presence of endogenous circadian rhythmicity. The aim of the study was to provide insight into the circadian core clock mechanism within the rat colon. Moreover, the potency of a restricted feeding regime to shift the circadian clock in the colon was tested. The question of whether the colonic clock drives circadian expression in NHE3, an electroneutral Na+/H+ exchanger, was also addressed. Methods: Daily profiles in expression of clock genes Per1, Per2, Cry1, Bmal1, Clock, and Rev-erbα, and the NHE3 transporter were examined by reverse transcriptase–polymerase chain reaction and their mRNA levels, as well as PER1 and BMAL1 protein levels, were localized in the colonic epithelium by in situ hybridization and immunocytochemistry, respectively. Results: Expression of Per1, Per2, Cry1, Bmal1, Clock, Rev-erbα, and NHE3, as well as PER1 and BMAL1 protein levels, exhibited circadian rhythmicity in the colon. The rhythms were in phase with those in the liver but phase-delayed relative to the master clock in the suprachiasmatic nucleus. Restricted feeding entrained the clock in the colon, because rhythms in clock genes as well as in NHE3 expression were phase-advanced similarly to the clock in the liver. Conclusions: The rat colon harbors a circadian clock. The colonic clock is likely to drive rhythmic NHE3 expression. Restricted feeding resets the colonic clock similarly to the clock in the liver.

Section snippets

Experimental Animals

Two-month-old male Wistar rats (Bio Test, Konarovice, Czech Republic) were maintained for at least 4 weeks in a temperature of 23°C ± 2°C under light–dark cycle with 12 hours of light and 12 hours of darkness per day. Light was provided by overhead 40-W fluorescent tubes, and illumination was between 50 and 300 lux, depending on cage position in the animal room. Animals had free access to food and water. On the day of the experiment, animals were divided into 2 groups. The control group was fed

Profiles in clock gene expression

In the rat colon (Figure 1, colon), the one-way ANOVA revealed a significant effect of time on expression of Per1, Per2, Cry1 (P < .05), Rev-erbα, and Bmal1 (P < .01) but not on expression of Clock. Per1 mRNA level at CT12 was significantly higher than those at CT8, CT20, and CT24 (P < .05); the levels thus rose between CT8 and CT12 and declined between CT12 and CT20. Per2 mRNA level at CT12 and CT16 was higher than that at CT8 (P < .05); the levels rose between CT8 and CT12 and then declined

Discussion

In this study, we show daily rhythms of expression of canonical clock genes Per1, Per2, Rev-erbα, Cry1, Bmal1, but not of Clock within the rat colonic epithelial cells. Moreover, PER1 and BMAL1 proteins are expressed within these cells. These findings provide evidence of the presence of a functional circadian clock in the intestinal compartment. This colonic clock is in phase with the clock in the liver and phase-delayed relative to the master clock in the SCN. In the colon, the clock is

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    Supported by the Academy of Sciences of the Czech Republic grant No. A500110605.

    All authors declare that they have no conflict of interest to disclose.

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