Regulation of Collagenase Expression during Replicative Senescence in Human Fibroblasts by Akt-Forkhead Signaling

Abstract

The expression of collagenase (matrix metalloproteinase 1) in human fibroblasts increases during aging both in vivo and in vitro. This age-associated increase in collagenase expression has been postulated to contribute to the age related decline in tissue function by increasing proteolysis of matrix components, but little is known regarding the regulation of collagenase expression. We examined the role that the serine/threonine kinase Akt plays in collagenase expression during in vitro senescence of WI-38 normal human lung fibroblast cells. Our results indicate that Akt-mediated signals, acting through the forkhead transcription factor FKHRL1, can regulate collagenase expression in WI-38 fibroblasts. Dominant negative forms of Akt increase collagenase promoter activity in early passage WI-38 fibroblasts, whereas an active form of Akt suppresses steady state levels of collagenase mRNA in senescent WI-38 fibroblasts. In addition, the activity of a synthetic promoter containing forkhead-specific binding sites, as measured by luciferase activity, is much higher in senescent cells compared with early passage WI-38 fibroblasts. These results indicate that members of the forkhead family of transcription factors play a role in the regulation of the collagenase promoter and that increased activity of forkhead transcription factors may underlie the increase in collagenase expression observed during replicative senescence.