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

Background. The development of the permanent kidney (metanephros) involves the interplay between both positive and negative regulatory molecules. Tran sforming growth factor-beta1 (TGF-beta1) has previously been shown to negat ively 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 r eaction were employed to examine the temporal and spatial localization of T GF-beta1 mRNA and a TGF-beta type I receptor (activin-like receptor kinase- 5: ALK-5) mRNA in developing rat metanephroi. The addition of exogenous TGF -beta1 to rat metanephric organ culture at different time points was used t o examine the role of TGF-beta1 in ureteric duct growth and nephron develop ment. Results. TGF-beta1 mRNA did not colocalize with ALK-5 mRNA. Instead, TGF-be ta1 mRNA colocalized with the TGF-beta1 type II receptor mRNA. The addition of recombinant human TGF-beta1 to rat metanephric organ culture at the beg inning of the culture period inhibited total metanephric growth and the gro wth of the ureteric tree, resulting in a decrease in nephron number. Simila rly, the addition of TGF-beta1 to metanephroi after 48 hours of culture inh ibited ureteric duct growth, decreasing nephron number. The addition of TGF -beta1 at days 0 or 2 of culture promoted hypertrophy of the renal capsule. Conclusions. These findings confirm that TGF-beta1 inhibits ureteric duct g rowth and thereby nephron endowment in developing rat metanephroi in vitro. However, TGF-beta1 does not appear to play a significant role in nephron d evelopment per se once the epithelial vesicle has formed.