Proliferation and differentiation of prostatic stromal cells

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Abstract
Objectives To investigate the effects of androgen, transforming growth factor β1 (TGF‐β) and basic fibroblast growth factor (bFGF) on the proliferation and differentiation of prostatic stromal cells of the dog in vivo and human stromal cells in vitro. Materials and methods Twenty‐two dogs had their serum concentration of testosterone and oestradiol determined by radioimmunoassay before and after castration. Light microscopy, transmission electron microscopy and an in situ cell‐death assay were carried out successively before and after castration to evaluate prostatic histomorphology. A semi‐quantitative reverse transcriptase‐polymerase chain reaction (RT‐PCR) was used to evaluate the expression of TGF‐β, bFGF and myosin in the canine prostate tissue after castration. In vitro serum‐free cell cultures from human prostatic stroma were established and exposed to dihydrotestosterone (DHT), TGF‐β and bFGF in various concentrations. The proliferation of the cell cultures was detected by the tetrazolium assay. The differentiation from fibroblasts to smooth muscle cells (SMCs) was deduced by measuring the expression of SMC‐specific proteins (myosin and smoothelin) using immunohistochemistry and RT‐PCR. Results Castration resulted in a significant decrease in circulating testosterone levels (P < 0.01), but did not affect the circulating oestradiol levels (P > 0.05). The prostatic stromal cells, including SMCs and fibroblasts, diminished and underwent a serial pathological change of atrophy and apoptosis after castration. The atrophic cells were filled with intracellular lipofuscin. The expression of SMC myosin declined after castration, coincident with the increase in TGF‐β mRNA level and decline in bFGF mRNA. In vitro, TGF‐β inhibited the growth of human prostatic stromal cells during exponential growth, while enhancing myosin staining and stimulating the expression of smoothelin in confluent cultured stromal cells. bFGF stimulated the growth of the culture and inhibited the expression of smoothelin. DHT caused a weak increase in the proliferation and expression of SMC‐specific proteins (P < 0.05). However, DHT and bFGF together stimulated the proliferation of stromal cells significantly more than either agent alone (P < 0.01). The combination of DHT and TGF‐β greatly enhanced the expression of SMC‐specific proteins (P < 0.01), more strongly than either alone (P < 0.01). Conclusions The whole prostate gland is an androgen‐sensitive organ, with both the epithelium and stroma under the control of androgen. Androgen may direct the proliferation and differentiation of prostatic stromal cells by regulating the expression of TGF‐β and bFGF. Thus DHT, TGF‐β and bFGF may have important roles in regulating stromal cell homeostasis.