Ascorbic acid and transforming growth factor-beta 1 increase collagen biosynthesis via different mechanisms: coordinate regulation of pro alpha 1(I) and Pro alpha 1(III) collagens.

The specific mechanisms of collagen induction in human dermal fibroblasts by ascorbic acid and transforming growth factor-beta 1 (TGF-beta 1) and their effect in combination are uncertain. Collagen synthesis and steady-state levels of pro alpha 1(I) and pro alpha 1(III) collagen RNA were examined in human dermal fibroblasts treated with 100 microM ascorbic acid, 2.5 ng/ml TGF-beta 1, or both. Within 72 h ascorbic acid and TGF-beta 1 had increased collagen synthesis by 2.55 +/- 0.32- and 1.98 +/- 0.13-fold, respectively; in the presence of both, collagen synthesis increased 4.51 +/- 0.74-fold, appearing additive. Ascorbic acid acts specifically by increasing relative collagen synthesis whereas TGF-beta 1 increases overall protein synthesis. Steady-state levels of the pro alpha 1(I) collagen (5.8 and 4.8 kb) and pro alpha 1(III) collagen (5.4 and 4.8 kb) mRNAs were examined independently. Under each condition the steady-state levels of the longer transcripts for pro alpha 1(I) and pro alpha 1(III) collagens appeared coordinately and preferentially elevated. In the presence of both ascorbic acid and TGF-beta 1 the steady-state RNA levels did not increase in an additive manner, suggesting that the additive increase in collagen synthesis results from additional post-transcriptional mechanisms.