ENDOGENOUS TGF-BETA ACTIVITY IS MODIFIED DURING CELLULAR AGING - EFFECTS ON METALLOPROTEINASE AND TIMP-1 EXPRESSION

In culture, nontransformed human diploid fibroblasts divide a limited number of times, resulting in a nonproliferating senescent cell cultur e which exhibits an altered pattern of gene expression. Previously we reported that an early event in the process of replicative senescence was an increase in the synthesis of two connective tissue degrading me talloproteinases, collagenase and stromelysin, and a decrease in the s ynthesis of the physiological inhibitor of those enzymes, tissue inhib itor of metalloproteinases-1 (TIMP-1). The cytokine TGF-beta 1 is know n to regulate the expression of each of these three genes and to be sy nthesized and secreted by cultured human fibroblasts. This suggested t he hypothesis that the age-specific modulation of collagenase, stromel ysin, and TIMP-1 expression is the result of a change in TGF-beta 1 ac tivity during replicative senescence. To test this hypothesis, the res ponses of early, mid, and late passage (presenescent) fibroblast cell cultures to a TGF-beta neutralizing antibody were evaluated. In early passage cell cultures, exposure to TGF-beta neutralizing antibody resu lted in a significant increase in the expression of collagenase and st romelysin and decreased TIMP-1 expression. The antibody did not affect expression of either of those genes by late passage cell cultures, al though late passage cultures did respond to added TGF-beta 1. Quantifi cation of the levels of active TGF-beta, using a growth inhibition ass ay, indicates that the level of active TGF-beta 1 is decreased during replicative senescence, supporting the conclusion that the modulation of collagenase, stromelysin, and TIMP-1 expression results from dimini shed TGF-beta activity. (C) 1996 Academic Press, Inc.