Differential expression of metalloproteinase and tissue inhibitor of metalloproteinase genes in aged human fibroblasts

Abstract

The basal levels of mRNAs encoding two metalloproteinases, collagenase and stromelysin, were increased as a function of in vitro serial subcultivation (cellular aging) of human fibroblasts. Procollagenase and prostromelysin synthesis and secretion were also greater in the old cultures (late passage). In contrast, the steady-state expression of mRNA for an inhibitor of metalloproteinases, tissue inhibitor of metalloproteinase-1 (TIMP-1), in late-passage cultures was lower than that in young cell cultures (early passage). Each mRNA was analyzed using total RNA preparations isolated from normal fibroblast cultures at different phases of the in vitro life span and from cultures derived from donors with the premature senescence syndromes characterized as Werner syndrome, progeria (Hutchinson-Gilford) syndrome, or Cockayne syndrome. In normal cell cultures expression of metalloproteinase mRNAs was increased after the culture had completed greater than 90% of the in vitro life span, and the reduction in TIMP-1 mRNA expression occurred after the culture had completed greater than 74% of the in vitro lifespan. In Werner syndrome cultures expression of metalloproteinase and TIMP-1 mRNAs was similar to the level of expression observed in late-passage cell cultures. Levels of metalloproteinase and TIMP-1 mRNA expression in progeria and Cockayne syndromes were similar to those of early-passage cell cultures. To determine if young and old cells were each responsive to mediators of metalloproteinase synthesis, cultures were treated with phorbol ester or cytokines. 12-O-tetradecanoylphorbol-13-acetate treatment increased the steady-state levels of all three mRNAs in young, old, and Werner syndrome cultures and increased procollagenase levels in all cultures. Early- and late-passage cell cultures also responded to cytokines. Interleukin-1 alpha treatment increased collagenase and stromelysin mRNA levels while transforming growth factor-beta reduced the steady-state levels of both transcripts. Neither cytokine affected the steady-state level of TIMP-1 mRNA. The results indicate that in vitro cellular aging is associated with changes in expression of mRNAs encoding proteins that mediate inflammatory responses and connective tissue remodeling.