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Neonatal estrogen exposure alters the transforming growth factor-beta signaling system in the developing rat prostate
W Y Chang1, L Birch, C Woodham
1Department of Urology, University of Illinois College of Medicine, Chicago 60612, USA.
Abstract:
Exposure of male rats to estrogens during the neonatal period retards prostate branching morphogenesis, blocks epithelial differentiation, and predisposes the adult prostate to hyperplasia and dysplasia. The mechanism of neonatal estrogenization is not well understood. The present study evaluated transforming growth factor-beta (TGFbeta) in the neonatally estrogenized ventral prostate to determine whether this paracrine/autocrine factor may in part mediate the effects ofestrogen on the developing prostate gland. Immunocytochemistry using antibodies against active TGFbeta1 and its latency-associated peptide localized this molecule to the periductal smooth muscle cells in the developing prostate. Although neonatal estrogenization increased the accumulation of total and active TGFbeta1 in the smooth muscle layer as early as day 6 of life, it was physically separated from the epithelial ducts by a proliferating layer of fibroblasts surrounding the basement membrane. RT-PCR demonstrated that alterations in TGFbeta1 levels were not due to alterations in TGFbeta1 transcription. TGFbeta2 and TGFbeta3 were primarily immunolocalized to differentiating epithelial cells in developing prostates, and this was markedly dampened between days 10-30 after neonatal estrogen exposure. Immunocytochemistry for TGFbeta signaling components revealed that neonatal estrogenization transiently reduced TGFbeta type I receptor levels in the prostate epithelium, but not in stroma, between days 6-15, whereas there was no effect on TGFbeta type II receptor. Levels of the intracellular signal Smad2 (52 kDa) were detected in epithelial cells but were not altered after estrogenization. To analyze the functional status of the TGFbeta signaling pathway, immunocytochemistry was performed for p21(cip-1/waf-1), a cyclin-dependent kinase inhibitor that is inducible by TGFbeta1 in the prostate. Transient nuclear localization of p21(cip-1/waf-1) was normally observed in epithelial cells between days 6-15 and was associated with entry of cells into a terminal differentiation pathway. Neonatal estrogenization prevented this transient expression of p21(cip-1/waf-1). The present findings demonstrate that the TGFbeta signaling system is perturbed at several levels in the estrogenized prostate, which may in part account for the epithelial cell differentiation blockade as well as the proliferation of periductal fibroblasts in this model.
Insights
Neonatal estrogen exposure disrupts transforming growth factor-beta (TGFbeta) signaling in developing rat prostates, impairing epithelial differentiation and promoting abnormal cell growth. This study reveals TGFbeta pathway perturbations contributing to prostate abnormalities after early-life estrogenization.
Area of Science:
- Developmental biology
- Endocrinology
- Prostate cancer research
Background:
- Neonatal exposure to estrogens in male rats causes prostate developmental abnormalities, including impaired morphogenesis and differentiation.
- The underlying mechanisms by which neonatal estrogenization affects prostate development remain incompletely understood.
- Transforming growth factor-beta (TGFbeta) is a critical signaling pathway involved in prostate development and homeostasis.
Purpose of the Study:
- To investigate the role of TGFbeta signaling in the ventral prostate of rats neonatally exposed to estrogens.
- To determine if TGFbeta pathway alterations mediate the effects of neonatal estrogenization on prostate development.
Main Methods:
- Immunocytochemistry was used to localize active TGFbeta1, its latency-associated peptide, and TGFbeta signaling components (receptors, Smad2, p21(cip-1/waf-1)) in rat prostates.
- Reverse transcription-polymerase chain reaction (RT-PCR) assessed TGFbeta1 transcription levels.
- Neonatal estrogenization was induced in male rats, and prostates were analyzed at various time points post-exposure.
Main Results:
- Neonatal estrogenization increased TGFbeta1 accumulation in smooth muscle but not its transcription; TGFbeta2 and TGFbeta3 levels in epithelial cells were reduced.
- Estrogen exposure transiently decreased TGFbeta type I receptor in prostate epithelium and prevented the normal induction of p21(cip-1/waf-1), a TGFbeta-inducible marker of differentiation.
- These perturbations in the TGFbeta signaling system occurred alongside epithelial differentiation blockade and periductal fibroblast proliferation.
Conclusions:
- The TGFbeta signaling system is significantly perturbed at multiple levels in the neonatally estrogenized rat prostate.
- These disruptions in TGFbeta signaling likely contribute to the observed blockade of epithelial cell differentiation.
- Altered TGFbeta signaling may also play a role in the proliferation of periductal fibroblasts, leading to prostate abnormalities.