Regulation of human mesangial cell collagen expression by transforming growth factor-beta1.

Transforming growth factor (TGF)-beta1 has been implicated in glomerular extracellular matrix accumulation. Since the spectrum and mechanism of changes in collagen turnover have not been fully characterized, we evaluated effects of TGF-beta1 on collagen expression by human mesangial cells. TGF-beta1 induced increased alpha1(I), alpha1(III), and alpha1(IV) collagen mRNA expression. Greater mRNA expression of matrix metalloproteinase (MMP)-2 was compensated by increased tissue inhibitor of metalloproteinases (TIMP)-2 mRNA. There was no change in TIMP-1 or membrane-type MMP mRNA expression, whereas MMP-1 mRNA decreased. Types I and IV collagen protein accumulated in both the cell layer and medium. Changes in collagen mRNA and protein occurred within 4 and 8 h, respectively. MMP-2 and TIMP-1 and -2 activities showed little change. Cycloheximide markedly decreased collagen detection within 4 h and reversed late, but not early, changes in alpha1(I) collagen mRNA. In this system, increased synthesis may be more significant than degradation for collagen accumulation, but collagen is short-lived in culture. Diverse TGF-beta1 actions on collagen turnover may be either immediate or mediated through synthesis of regulatory molecules.