Cell proliferation as a biomarker of aging and effect of caloric restriction in mouse lens

The replication of cells is important in growth, development, regeneration and senescence. Caloric restriction is the only known experimental modulator that retards aging and increases the life span of rodents. My first hypothesis is that the measurement of cellular proliferation in vitro and in vivo reflects the biological age of mammals and that caloric restriction is associated with a relative preservation of cellular proliferation potential. My second hypothesis is that the protective role of caloric restriction is associated with enhanced resistance of cells to oxidative stress. I focused on the lens epithelial cells and asked the following questions. (1) Is decreased cellular proliferation capacity associated with aging in the lens and is this decline modulated by long-term caloric restriction? (2) What cellular damage is induced by hydrogen peroxide in lens epithelial cells in vitro? (3) Does long-term caloric restriction enhance resistance of the cells to this oxidative stress?;To answer the first question, I examined a variety of cells from mice of several ages on either ad libitum-fed or calorically restricted diets, and from transgenic mice overexpressing a bovine growth hormone gene. Skin fibroblasts from dogs of selected size and age groups, and monkeys on either ad libitum or calorically restricted diets were studied as well. Cell proliferation potentials in vitro were measured by using clone size distribution analysis. Cell replication rates in vivo were determined by using BrdU labeling. I then focused on the effects of aging and caloric restriction on cell proliferation potential and replication rate of lens epithelial cells. The second question was approached by using an in vitro system in which bovine lens epithelial cells were exposed to hydrogen peroxide and then assayed for DNA breaks and repair kinetics, DNA synthesis and cell proliferation potential. The system of H;Conclusions: (1) Clone size distribution and BrdU labeling are simple and useful methods to measure cellular proliferation potentials or rates in vitro and in vivo, respectively. (2) Cellular proliferation potential or rate correlates with extension or shortened life spans of animals. (3) Cellular proliferation potential and mouse life spans are enhanced by caloric restriction. (4) Caloric restriction protects cells from age-related loss of cellular proliferation and protective roles for caloric restriction may be associated with enhanced resistance of cells to free radical damages. Future studies will focus on the mechanism by which CR induces more efficient biological systems to resist or repair oxidative damage in the ocular lens.