Figure 2.

A less robust circadian clock in mouse cartilage during aging. A, Representative traces of PER2::luc bioluminescence from xiphoid cartilage of young adult mice (ages 3–4 months; n = 7) and aged mice (ages 20–24 months; n = 9). Arrow indicates time of treatment with 100 nM dexamethasone (Dex) (n = 4 young mice, n = 3 aged mice). B, Oscillation amplitude (left) and circadian period (right) in cartilage tissue from aged mice compared to young mice. ∗ = P = 0.015 by t-test. NS = not significant. C, Circadian phase at the time between 12-hour cull and the first peak of bioluminescence in culture. Vertical lines represent the mean for each group (P = 0.46). D, Similar extent of induction of oscillation amplitude by dexamethasone treatment in young and aged mouse cartilage tissue; amplitude is expressed as a percentage of the amplitude of the young tissue before treatment. Results are the mean ± SEM. Data were analyzed by two-way analysis of variance. There were no significant effects of age group (P = 0.77), and interactions were not significantly different (P = 0.9992). ∗∗ = P = 0.003.