Effect of growth factors on collagen metabolism in cultured human heart fibroblasts

Using human heart fibroblasts (HHF), we studied the effect of basic fibroblast growth factor (bFGF) and transforming growth factor-beta (TGF-beta) on the gene expression of type I collagen, collagenase and tissue inhibitor of metalloproteinases (TIMP). Initially, treatment of HHF with bFGF alone (10 ng/ml) resulted in elevated secretion of collagenase into the culture medium. Subsequent treatment of HHF with TGF-beta in combination with bFGF suppressed collagenase secretion. Northern blot analysis reinforced this observation by revealing an enhancement of the steady-state mRNA level of collagenase in response to bFGF. In order to examine if the collagenase gene was affected by bFGF at the transcriptional level, transfection experiments were carried out with a plasmid containing collagenase promoter linked to chloramphenicol acetyltransferase gene (CAT). Basic FGF stimulated CAT activity by four-fold, indicating increased promoter activity whereas the combination of TGF-beta and bFGF resulted in decreased CAT activity. TGF-beta was shown to increase type I collagen and TIMP mRNA levels by 2.5- and 2.1-fold, respectively. These results suggest that TGF-beta and bFGF may play a pivotal role in regulating collagen metabolism in HHF.