Growth factors and receptors in bladder development and obstruction.

During fetal and neonatal development and experimental obstruction, the bladder wall undergoes changes in both the amount and composition of the urothelium, extracellular matrix, and smooth muscle. We hypothesize that cell-cell signaling among the different layers of the bladder wall mediates these changes. Growth factors likely to be involved in this process are keratinocyte growth factor (KGF) and transforming growth factor (TGF)-alpha, -beta 2, and -beta 3. Whole rodent bladders were analyzed by RNase protection assays for KGF, KGF receptor, TGF alpha, epidermal growth factor receptor, and TGF beta 2 and -beta 3 transcripts at Fetal Day 14 (before smooth muscle differentiation) and Fetal Day 18 (after smooth muscle differentiation), at birth, and 60 days postnatal. Growth factor transcripts were also analyzed in partially obstructed rodent bladders and in sham-operated animals. TGF beta 2 and -beta 3 mRNA expression decreased as a function of gestational age, whereas TGF alpha mRNA increased. KGF mRNA was low before smooth muscle differentiation at 14 days' gestation, then increased. The mRNA of receptors for KGF and EGF remained essentially unchanged throughout bladder development. In bladders subjected to partial urethral outlet obstruction, there was a 2-fold increase in mRNA for TGF beta 2, a 5-fold increase in TGF beta 3, and a 10-fold increase TGF alpha mRNA. In contrast, there was no change in transcripts for either KGF or receptors for KGF and epidermal growth factor. Immunohistochemical localization of the protein for these growth factors showed selective localization to the epithelium and/or smooth muscle for TGF beta 2 and -beta 3, whereas TGF alpha and the epidermal growth factor receptor localized throughout the bladder wall. In conclusion, growth factor mRNA expression is modulated in bladder development and obstruction, which implies a possible mechanistic role of growth factors for the observed changes in the bladder wall and extracellular matrix.