CALORIC RESTRICTION - CONSERVATION OF CELLULAR REPLICATIVE CAPACITY IN-VITRO ACCOMPANIES LIFE-SPAN EXTENSION IN MICE

We have tested whether life-long caloric restriction (CR) slows or del ays the age-related loss of cellular replicative potential that occurs during normal aging in ad libitum (AL) fed mice. Both mean and maximu m life spans of the restricted animals (60% of AL intake) were signifi cantly extended 30-40% by CR treatment. Proliferative potential, measu red by determining the fraction of cells capable of forming large clon es in vitro, was compared in five cell types from six tissue sites fro m two strains of mice (Male (C57BL/6 X DBA/2)F1(''B6D2F1'') and female (C57B1/6 X C3H)F1 (''B6C3F1'')). This included four nonhematopoietic organ sites: fibroblast cells from ear skin, tail skin, and subdermal connective tissue and epithelial cells from the medullary part of the kidney and two cell types, myofibroblasts and endothelial-like cells, from spleen and bone marrow. The proliferative potential of cells from AL mice decreased progressively with age in all tissues sites of both mouse strains. CR delayed or decreased the loss of proliferative pote ntial in all situations, but the timing of this was tissue specific. F or cells from the four nonhematopoietic tissue sites from female B6C3F 1 female mice, CR delayed the onset of proliferative loss, such that t he fraction of large clones was significantly greater for the CR 18- t o a 24-month-old mice than in AL controls at three of four sites (as d etermined by the fraction of large clones after 1 week of clonal growt h). The proliferative loss in CR tissues then accelerated from 24 to 3 0 months, so that both CR and AL mice had similar fractions of large c lones after 30 months of age. CR was also seen to delay loss of prolif erative potential in cells from skin and kidney of B6D2F1 male mice at 23-24 months of age when cloned for 2 weeks. For fibroblast and endot helial-like cells from bone marrow and spleen stromal sites from both strains of mice, CR also significantly decreased loss of proliferative potential; furthermore, in these tissues the proliferative advantages remained or increased from 24 to over 30 months of age. In companion studies (N.S. Wolf et al., 1995. Exp. Cell. Res. 217, 000-000), CR was seen to decrease age-related losses in the maximal rates of cell repl ication in vivo in a panel of tissues from B6D2F1 male mice. The prese rvation of replicative potential by CR mice in all tissues tested, bot h in vitro and in vivo, indicates that CR preserves proliferative capa cities in the cells and tissues of chronically restricted mice and may permit CR mice to better respond to proliferative stresses in old age . (C) 1995 Academic Press, Inc.