We have analysed the interactions of three proteoglycans of the decorin family, decorin, biglycan and fibromodulin, with transforming growth factor beta (TGF-beta). The proteoglycan core proteins, expressed from human cDNAs as fusion proteins with Escherichia coli maltose-binding protein, each bound TGF-beta 1. They showed only negligible binding to several other growth factors. Intact decorin, biglycan and fibromodulin isolated from bovine tissues competed with the fusion proteins for the TGF-beta binding. Affinity measurements suggest a two-site binding model with Kd values ranging from 1 to 20 nM for a high-affinity binding site and 50 to 200 nM for the lower-affinity binding site. The stoichiometry indicated that the high-affinity binding site was present in one of ten proteoglycan core molecules and that each molecule contained a low-affinity binding site. Tissue-derived biglycan and decorin were less effective competitors for TGF-beta binding than fibromodulin or the non-glycosylated fusion proteins; removal of the chondroitin/dermatan sulphate chains of decorin and biglycan (fibromodulin is a keratan sulphate proteoglycan) increased the activities of decorin and biglycan, suggesting that the glycosaminoglycan chains may hinder the interaction of the core proteins with TGF-beta. The fusion proteins competed for the binding of radiolabelled TGF-beta to Mv 1 Lu cells and endothelial cells. Affinity labelling showed that the binding of TGF-beta to betaglycan and the type-I receptors in Mv 1 Lu cells and to endoglin in endothelial cells was reduced, but the binding to the type-II receptors was unaffected. TGF-beta 2 and 3 also bound to all three fusion proteins. Latent recombinant TGF-beta 1 precursor bound slightly to fibromodulin and not at all to decorin and biglycan. The results show that the three decorin-type proteoglycans each bind TGF-beta isoforms and that slight differences exist in their binding properties. They may regulate TGF-beta activities by sequestering TGF-beta into extracellular matrix.

Angiotensin II (Ang II) has been implicated in the development of progressive glomerulosclerosis, but the precise mechanism of this effect remains unclear. In an experimental model, we have shown previously that TGF-,6 plays a key role in glomerulosclerosis by stimulating extracellular matrix protein synthesis, increasing matrix protein receptors, and altering protease /protease-inhibitor balance, thereby inhibiting matrix degradation. We hypothesized that Ang II contributes to glomerulosclerosis through induction of TGF-fl. Ang 6 blocked the Ang II-induced increases in matrix protein expression. Continuous in vivo administration of Ang II to normal rats for 7 d resulted in 70% increases in glomerular mRNA for both TGF-ft and collagen type I. These results indicate that Ang II induces mesangial cell synthesis of matrix proteins and show that these effects are mediated by Ang II induction of 6 expression. This mechanism may well contribute to glomerulosclerosis in vivo. (J. Clin. Invest. 1994. 93:2431-2437

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The central pathological feature of human kidney disease that leads to kidney failure is the accumulation of extracellular matrix in glomeruli. Overexpression of transforming growth factor-beta (TGF-beta) underlies the accumulation of pathological matrix in experimental glomerulonephritis. Administration of an antibody raised against TGF-beta to glomerulonephritic rats suppresses glomerular matrix production and prevents matrix accumulation in the injured glomeruli. One of the matrix components induced by TGF-beta, the proteoglycan decorin, can bind TGF-beta and neutralize its biological activity, so decorin may be a natural regulator of TGF-beta (refs 3, 4). We tested whether decorin could antagonize the action of TGF-beta in vivo using the experimental glomerulonephritis model. We report here that administration of decorin inhibits the increased production of extracellular matrix and attenuates manifestations of disease, confirming our hypothesis. On the basis of our results, decorin may eventually prove to be clinically useful in diseases associated with overproduction of TGF-beta.

Diabetes is now the most common cause of progressive kidney failure leading to dialysis or transplantation. The central pathological feature of diabetic nephropathy is accumulation of extracellular matrix within the glomeruli. The factors in the diabetic milieu responsible for extracellular matrix accumulation are not understood. Here we report that in glomeruli of rats made diabetic there is a slow, progressive increase in the expression of transforming growth factor 1B (TGF-3) mRNA and TGF-,3 protein. A key action of TGF-,B is induction of extraceliular matrix production, and specific matrix proteins known to be induced by TGF-(3 were increased in diabetic rat glomeruli. These proteins include an alternatively spliced form of fibronectin, tenascin, and the proteoglycan biglycan. TGF-f8 has not previously been implicated in the matrix accumulation that occurs in the diabetic kidney. Glomeruli from humans with diabetic nephropathy also showed a striking increase in immunoreactive TGF-,B protein and deposition of the special form of fibronectin, whereas glomeruli from normal subjects or from individuals with other glomerular diseases (where extracellular matrix accumulation is not a feature) were negative or barely positive. These results implicate TGF-13 in the pathogenesis of diabetic nephropathy.Development of kidney disease is one of the most frequent and serious complications of diabetes and eventually occurs in patients despite treatment with insulin (1, 2). The dominant histological feature of diabetic nephropathy is the expansion of extracellular matrix in the mesangial areas of the glomeruli with resulting glomerulosclerosis and obliteration of the capillary surface area for filtration (3,4). Expansion of the mesangial matrix correlates strongly with the clinical onset of proteinuria, hypertension, and kidney failure (3, 4). Diabetes is considered a hormonal disorder, and organ complications such as kidney disease are usually attributed to metabolic consequences of abnormal glucose regulation such as elevated blood and tissue levels of glycosylated proteins (5) and/or hemodynamic changes within the kidney (6). However, whether this hypothesis is correct is unclear, and little is known about the molecular events underlying the matrix accumulation. This report presents evidence for the idea that diabetes can lead to elevated transforming growth factor ,B (TGF-f) expression and that this cytokine may be one cause of matrix deposition in the diabetic kidney.Three isoforms of B,81,82, are expressed in mammals and to date show similar properties in vitro (7). The role of TGF-,3 in regulating repair and regeneration following tissue injury is well documented (8). Platelets contain high concentrations of TGF-/3 and upon degranulation at a site of injury release TGF-P into the surrounding tissue (9). TGF-P then initiates a sequence of events that promotes healing including (i) chemoattraction of monocytes, neutrophils, and fibroblasts (10, 11); (ii) autoinduction ofTGF-f3 production and stimulation of ...