Calorie restriction (CR) has been known to produce many beneficial health effects, and lowered cell proliferation from CR has been shown to produce anti-cancer effects in some tissues. In this study the rate of epidermal cell proliferation in aging Fischer 344 rats from ad libitum fed (AL) and CR colonies was assessed in relation to changes in epidermal thickness with age. Proliferating cell nuclear antigen (PCNA) was detected using immunohistochemical method on paraffin sections in the epidermis of dorsal skin and footpad in these animals obtained from the National Institute on Aging. The proliferating cell index was compared with morphometric measurement of epidermis in young, young adult and old animals (six per group). Data were analyzed by Excel and SPSS 14.0 softwares for statistical evaluation. Two-way analysis of variance (ANOVA) was applied to data to test the effects of age, diet, and age-diet interaction.
The following significant effects were noted: (I) age and age-diet effects in dorsal skin epidermal width, and PCNA; (II) age, and diet effect on footpad epidermal thickness, and PCNA index. There was a trend of increasing epidermal thickness in the dorsal skin in normally feeding aging rats which was depressed with CR in the two younger groups. PCNA index showed a trend of attrition from young to old. The thickness of epidermis in foot pad showed a curvilinear trend in both AL and CR groups with lowest mean values in the old group, and more predominant effect in CR-exposed animals. The proliferation index in the foot pad demonstrated a trend of reduction in old specimens with lower mean values in each corresponding CR age group. This report agrees with CR-inhibited cell proliferation reported in many organs by other investigators, and the observed results might have been caused by physiological or endocrine mechanisms affecting the epithelium in these calorie-restricted animals.