Glomerular activin A overexpression is linked to fibrosis in anti-Thy1 glomerulonephritis

Abstract

Activin A, a member of the transforming growth factor-beta (TGF-beta) superfamily of proteins, shares many biological features with the pro-fibrotic cytokine TGF-beta1, which is primarily responsible for the accumulation of extracellular matrix proteins in renal disease. This study was designed to identify regulators of activin A production in glomerular mesangial cells and test if activin A acts as a pro-fibrotic cytokine in mesangial cells. The effect of inflammatory cytokines on activin A production and the effect of exogenous activin A on mediators of fibrosis were analysed in cultured rat mesangial cells. Expression of activin A and of established mediators of fibrosis was analysed in a rat model of glomerular fibrosis (anti-Thy1 glomerulonephritis). In cultured mesangial cells, interleukin-1 and basic fibroblast growth factor, both mediators of glomerular inflammatory injury, dose-dependently increased activin A expression. Incubation with activin A significantly stimulated TGF-beta1, PAI-1 and connective tissue growth factor RNA expression and increased production of extracellular matrix proteins in mesangial cells. In rats with anti-Thy1 glomerulonephritis, expression of glomerular activin A mRNA and protein paralled the expression of TGF-beta and other indices of fibrosis, showing little change from normal on day 1, a marked, 70-fold increase of activin protein production on day 6, and a subsequent decrease at day 12. Antifibrotic therapy with the angiotensin-converting enzyme inhibitor enalapril significantly reduced glomerular activin A production. Taken together, the results of this study link overexpression of activin A to glomerular matrix protein expansion in vivo and in vitro, suggesting that activin A acts as pro-fibrotic cytokine in renal disease.