Transforming growth factor-beta production in anti-glomerular basement membrane disease in the rabbit

The purpose of this study was to assay for the presence of collagen synthesis stimulatory activity in the kidney during immune-induced renal injury that results in severe fibrosis in both glomerular and interstitial compartments. A model of antiglomerular basement (anti-GBM) disease in the rabbit was induced on day 0 by the injection of anti-GBM antibody and renal cortex tissues were then sampled at various time points. Only conditioned media prepared from diseased renal cortical samples showed collagen synthesis stimulatory activity when tested on rabbit mesangial cells. The activity had an estimated molecular weight range of 16 to 25 kd and was neutralized by antibody to transforming growth factor-beta (TGF-beta). A standard assay for TGF-beta using a mink lung epithelial cell line confirmed the increase in TGF-beta activity in conditioned media of diseased cortex from day 7 and day 14 animals, which was not significantly activated by previous acidification. This suggests that most of the TGF-beta present in renal conditioned media was in the active form. The increase in renal cortical secretion of active TGF-beta was accompanied by increases in renal cortical TGF-beta mRNA content on days 4 and 7 after induction, with subsequent return to control levels. A similar increase in TGF-beta activity was present in nonacidified conditioned media of purified glomeruli from diseased days 7 and 14 animals, which was also accompanied by significant increases in TGF-beta mRNA. However with acidification no significant differences were noted between control and diseased samples, suggesting the presence of substantial latent TGF-beta activity in control glomerular conditioned media. These same control-conditioned media contained inhibitor activity for added exogenous TGF-beta. These results support the conclusion that the association between increased TGF-beta secretion and increased renal cortical collagen synthesis in this model is consistent with a role for this cytokine in directing fibrogenesis in the kidney.