Cardiac Redd1 expression increases with advancing age. (A, B) Representative photomicrographs and quantitative analysis of myocardial p16INK4a immunofluorescent staining in young group mice (3~4 months old) and old group mice (24 months old) (n = 6 per group). (C, D) Representative photomicrographs of myocardial p21 immunofluorescent staining and quantitative expression analysis in young group mice and old group mice (n = 6 per group). (E, F) Western blotting detection and quantification of Redd1, p16INK4a, and p21 protein expression in the heart of young group mice and old group mice (n = 6–8 per group). Data are mean ± SEM. *p < 0.05 vs. young group.