In vitro studies on the roles of transforming growth factor-γ1 in rat metanephric development

Background. The development of the permanent kidney (metanephros) involves the interplay between both positive and negative regulatory molecules. Transforming growth factor-β1 (TGF-β1) has previously been shown to negatively regulate ureteric duct growth. However, its potential role in nephron development and glomerulogenesis has been largely ignored. Methods. In situ hybridization and reverse transcription-polymerase chain reaction were employed to examine the temporal and spatial localization of TGF-β1 mRNA and a TGF-β type I receptor (activin-like receptor kinase-5; ALK-5) mRNA in developing rat metanephroi. The addition of exogenous TGF-β1 to rat metanephric organ culture at different time points was used to examine the role of TGF-β1 in ureteric duct growth and nephron development. Results. TGF-β1 mRNA did not colocalize with ALK-5 mRNA. Instead, TGF-β1 mRNA colocalized with the TGF-β type II receptor mRNA. The addition of recombinant human TGF-β1 to rat metanephric organ culture at the beginning of the culture period inhibited total metanephric growth and the growth of the ureteric tree, resulting in a decrease in nephron number. Similarly, the addition of TGF-β1 to metanephroi after 48 hours of culture inhibited ureteric duct growth, decreasing nephron number. The addition of TGF-β1 at days 0 or 2 of culture promoted hypertrophy of the renal capsule. Conclusions. These findings confirm that TGF-β1 inhibits ureteric duct growth and thereby nephron endowment in developing rat metanephroi in vitro. However, TGF-β1 does not appear to play a significant role in nephron development per se once the epithelial vesicle has formed.