RAT MESANGIAL CELL HYPERTROPHY IN RESPONSE TO TRANSFORMING GROWTH-FACTOR-BETA-1

Central features of progressive glomerular sclerosis are initial glomerular hypertrophy and subsequent accumulation of extracellular matrix proteins. Since TGF-beta1 may play a key role in this glomerular response to injury, the present study sought to explore further TGF-beta1 actions and regulated expression of its receptor in rat mesangial cells. The rat TGF-beta type II receptor (TGF-betaRII) homolog was cloned by screening a rat kidney cDNA library with a human TGF-betaRII cDNA probe, and sequenced. Expression of this receptor subtype in rat mesangial cells was then demonstrated by RNase protection assay, and by Northern blot analysis of poly (A)+ RNA, TGF-betaRII expression was down-regulated in cells treated with exogenous TGF-beta1. Affinity cross linking studies demonstrated presence of this receptor on cell surface. Rat mesangial cells also expressed TGF-beta1 and autoinduction by TGF-beta1 was observed in the same cells, suggesting that this polypeptide may act in an autocrine fashion on mesangial cells, and that it may stimulate a positive autoamplification loop. TGF-beta1 inhibited mesangial cell proliferation and stimulated significant overall protein and collagen production. Furthermore, mesangial cell size increased in response to chronic TGF-beta1 treatment. These findings demonstrate that rat mesangial cells express key components of the TGF-beta system and raise the intriguing possibility that in the glomerular mesangium, TGF-beta1 may not only induce extracellular matrix synthesis, but may also participate in the process of glomerular hypertrophy in response to injury.