Insight Into the Circadian Clock Within Rat Colonic Epithelial Cells

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.