The steady-state levels of type I collagen mRNA are reduced in senescent fibroblasts.

The decreased collagen content in aging skin could be a consequence of decreased synthesis or increased degradation. The possibility that decreased synthesis of collagen results from decreased synthesis of mRNAs for Type I collagen, the major collagen in skin, was investigated by assessing the steady-state levels of alpha 1(I) and alpha 2(I) collagen mRNAs in actively proliferating and senescent WI-38 fibroblasts. The levels of both alpha 1(I) mRNA and alpha 2(I) mRNA were significantly lower in senescent fibroblasts, suggesting that one factor contributing to the decreased collagen content of aging skin may be decreased synthesis of these collagen mRNAs by senescent fibroblasts. Both mRNAs were reduced to the same extent, suggesting that coordinate regulation of the two Type I collagen genes is maintained in senescent fibroblasts.