Dynamic expression patterns of transforming growth factor-β2 and transforming growth factor-β receptors in experimental glomerulonephritis

Numerous studies have demonstrated the involvement of the transforming growth factor (TGF) isoform β1 in the pathogenesis of renal fibroproliferative diseases. Although in vitro studies suggest that TGF-β2 is equally potent to TGF-β1 in terms of its antimitogenic and fibrogenic effects, much less is known about the regulation of TGF-β2 in renal diseases associated with glomerular cell hyperplasia and matrix expansion. Here we investigated the glomerular expression patterns of TGF-β2 and of the TGF-β receptors I, II, and III during the course of rat anti-Thy1.1 nephritis (days 2, 6, 12, and 56), a model characterized by transient mesangial hypercellularity and extracellular matrix accumulation. TGF-β2 exhibited dynamic changes in expression. Immunohistochemical double-staining of renal sections revealed that most TGF-β2-positive cells in control glomeruli were podocytes with few TGF-β2-positive mesangial cells. This staining pattern could also be observed in human kidney. On day 6 of anti-Thy1.1 nephritis both TGF-β2 positive podocytes and mesangial cells were more abundant. By western blot analysis of isolated glomeruli from nephritic rats, protein expression of TGF-β2 was upregulated tenfold over control glomeruli, peaking on day 6 of the disease. In cultured rat mesangial cells we found that the TGF-β2 and TGF-β1 isoforms were equally potent in terms of nuclear accumulation of phosphorylated Smad 2/3, inhibition of DNA synthesis, and induction of β1-integrin and type I collagen protein synthesis. Protein expression of the TGF-β receptor I was not detected by immunohistochemistry in control glomeruli but was markedly induced in the mesangium on day 6 of nephritis. Mesangial staining for TGF-β receptors II and III was detected in normal kidneys. Expression of TGF-β receptor II was strongly enhanced on days 6 and 12 of disease, while TGF-β receptor III was upregulated only on day 6. In summary, we report marked yet transient upregulation of TGF-β2 protein and of TGF-β receptors I, II, and III in glomerular cells during anti-Thy1.1 nephritis. These results are in keeping with the notion that TGF-β2 and its receptors participate in the pathogenesis and/or resolution of this transient form of glomerulonephritis.