Aging and circadian clock gene expression in peripheral tissues in rats

Aging is associated with alterations of the circadian rhythms (shortened amplitude and phase-advance). We studied by quantitative RT-PCR the influence of aging on the expression of circadian clock genes (Clock, Bmal1, Cry1,2, Per1-3) in peripheral tissues (liver and heart) of middle-aged (13 months) and old (27 months) rats of the Wag/Rij strain exposed to a 12 hours light/12 hours dark cycle. Rats were killed at the light-dark transition (8 am and 8 pm). In the liver, Per, Cry et Bmal1 genes showed a morning/evening difference of expression; in addition, old rats exhibited a significant decrease of Per gene expression in the evening vs middle-aged rats. The heart showed similar profiles with only a tendency toward a decrease of Per expression and an increased Bmal1 expression in the evening in old rats. These results show that aging is associated with circadian gene expression changes.