Impaired expression of the mPer2 circadian clock gene in the suprachiasmatic nuclei of aging mice

The expression of circadian clock genes was investigated in the suprachiasmatic nuclei (SCN) of young adult and old laboratory mice. Samples were taken at two time points, which corresponded to the expected maximum (circadian time 7 [CT7]) or minimum (CT21) of mPer mRNA expression. Whereas the young mice had a stable and well-synchronized circadian activity/rest cycle, the rhythms of old animals were less stable and were phase advanced. The expression of mPer1 mRNA and mPer2 mRNA was rhythmic in both groups, with peak values at CT7. The levels of mClock and mCry1 mRNA were not different depending on the time of day and did not vary with age. In contrast, an age-dependent difference was found in the case of mPer2 (but not mPer1) mRNA expression, with the maximum at CT7 significantly lower in old mice. The decreased expression of mPer2 may be relevant for the observed differences in the overt activity rhythm of aged mice. (Chronobiology International, 18(3), 559-565, 2001)     

Human intestinal circadian clock: expression of clock genes in colonocytes lining the crypt

Biological clock components have been detected in many epithelial tissues of the digestive tract of mammals (oral mucosa, pancreas, and liver), suggesting the existence of peripheral circadian clocks that may be entrainable by food. Our aim was to investigate the expression of main peripheral clock genes in colonocytes of healthy humans and in human colon carcinoma cell lines. The presence of clock components was investigated in single intact colonic crypts isolated by chelation from the biopsies of 25 patients (free of any sign of colonic lesions) undergoing routine colonoscopy and in cell lines of human colon carcinoma (Caco2 and HT29 clone 19A). Per-1, per-2, and clock mRNA were detected by real-time RT-PCR. The three-dimensional distributions of PER-1, PER-2, CLOCK, and BMAL1 proteins were recorded along colonic crypts by immunofluorescent confocal imaging. We demonstrate the presence of per-1, per-2, and clock mRNA in samples prepared from colonic crypts of 5 patients and in all cell lines. We also demonstrate the presence of two circadian clock proteins, PER-1 and CLOCK, in human colonocytes on crypts isolated from 20 patients (15 patients for PER-1 and 6 for CLOCK) and in colon carcinoma cells. Establishing the presence of clock proteins in human colonic crypts is the first step toward the study of the regulation of the intestinal circadian clock by nutrients and feeding rhythms.