Effect of caloric dietary restriction on the structure of aged skin and liver in male mice: a histological and immunohistochemical study

ABSTRACT

Caloric restriction [CR] exerts beneficial effects on most age-related degenerative changes throughout the body. However, its effect on aged skin and liver has not been thoroughly explored. To document the histological alterations of aged mouse skin and liver and to investigate the effect of CR on these changes. Thirty male mice, aged 1 month, were used in this study. They were equally divided into three groups. Group I [adult-ad libitium group] mice, fed an ad-libitum diet and sacrificed at 6 months of age, served as the control group. Group II [aged-ad libitum group] mice were fed an ad-libitum diet and were sacrificed when they reached the age of 1 8 months. Group III [aged-ad libitum group] mice were fed a calorie-restricted diet and were sacrificed at 18 months of age. Specimens from dorsal mouse skin and liver were dissected out and processed for light and immunohistochemical study. Epidermal thickness, area percentage of collagen, elastic fibers of the skin, and proliferating cell nuclear antigen [PCNA]-positive cells of the liver were all morphometrically measured and statistically analyzed. Thin skin of aged animals [group II] showed a significant reduction in the mean thickness of nucleated epidermal keratinocytes as compared with the control group [group I]. Most epidermal cells appeared with small, deeply stained nuclei and vacuolated cytoplasm. The dermis showed a few disorganized collagen bundles and thin, short elastic fibers. Immunohistochemical analysis revealed a reduction of bcl2 expression in the basal keratinocytes of aged animals. Group III showed signs of improvement of aged skin manifested by a significant increase in the thickness of nucleated keratinocytes and area percentage of collagen fibers. Most keratinocytes regained their characteristic histological appearance with increased bcl2 expression in basal keratinocytes. Regarding liver results, the aged animals [group II] showed many hepatocytes with pyknotic nuclei and vacuolated cytoplasm. A highly significant decrease in the percentage of PCNA-positive nuclei was estimated. CR animals [group III] showed preservation of the histological structure of many hepatocytes and more reduction in the percentage of PCNA-positive nuclei. Various histological alterations were observed in the skin and liver of aged animals. Beneficial effects of CR on these changes were recorded. In addition, CR protects basal keratinocytes from early apoptosis, permitting the renewal potency of skin epidermis. CR also induced suppression of hepatocyte proliferation, and is thus considered as an effective tool to suppress tumor genesis in the liver