Loss of androgen signaling in mesenchymal sonic hedgehog responsive cells diminishes prostate development, growth, and regeneration

Prostate embryonic development, pubertal and adult growth, maintenance, and regeneration are regulated through androgen signaling-mediated mesenchymal-epithelial interactions. Specifically, the essential role of mesenchymal androgen signaling in the development of prostate epithelium has been observed for over 30 years. However, the identity of the mesenchymal cells responsible for this paracrine regulation and related mechanisms are still unknown. Here, we provide the first demonstration of an indispensable role of the androgen receptor (AR) in sonic hedgehog (SHH) responsive Gli1-expressing cells, in regulating prostate development, growth, and regeneration. Selective deletion of AR expression in Gli1-expressing cells during embryogenesis disrupts prostatic budding and impairs prostate development and formation. Tissue recombination assays showed that urogenital mesenchyme (UGM) containing AR-deficient mesenchymal Gli1-expressing cells combined with wildtype urogenital epithelium (UGE) failed to develop normal prostate tissue in the presence of androgens, revealing the decisive role of AR in mesenchymal SHH responsive cells in prostate development. Prepubescent deletion of AR expression in Gli1-expressing cells resulted in severe impairment of androgen-induced prostate growth and regeneration. RNA-sequencing analysis showed significant alterations in signaling pathways related to prostate development, stem cells, and organ morphogenesis in AR-deficient Gli1-expressing cells. Among these altered pathways, the transforming growth factor β1 (TGFβ1) pathway was up-regulated in AR-deficient Gli1-expressing cells. We further demonstrated the activation of TGFβ1 signaling in AR-deleted prostatic Gli1-expressing cells, which inhibits prostate epithelium growth through paracrine regulation. These data demonstrate a novel role of the AR in the Gli1-expressing cellular niche for regulating prostatic cell fate, morphogenesis, and renewal, and elucidate the mechanism by which mesenchymal androgen-signaling through SHH-responsive cells elicits the growth and regeneration of prostate epithelium.
Author summary Prostate formation, growth, and regeneration, as well as tumorigenesis, depend on androgens and androgen receptor (AR)-mediated signaling pathways. Tissue recombination assays done more than 30 years ago demonstrated a decisive role for stromal androgen signaling in prostatic epithelium development. However, in the intervening time, the identity of the mesenchymal cells in the urogenital sinus mesenchyme that convey androgen signaling and control prostate epithelium development, morphogenesis, and regeneration has not been determined. In this study, using mouse genetic tools, we demonstrate for the first time that selective deletion of AR in mesenchymal Gli1-expressing cells abolishes early development of prostate tissue and normal prostate formation, and diminishes prostate pubertal growth and regeneration. In addition, using tissue recombination assays, we directly determined an essential requirement for AR expression in mesenchymal Gli1-expressing cells during prostate epithelium development. Our results not only resolve a 30-year-old scientific puzzle by identifying the mesenchymal cell properties of androgen-responsive cells that elicit development of the embryonic prostate epithelium, but also explore a new regulatory mechanism for androgen and Shh signaling-mediated cellular niches in regulating prostatic cell fate, growth, and renewal through paracrine regulation. Given the importance of sex hormone and hedgehog signaling pathways in human development and tumorigenesis, this study extends beyond the field of prostate biology, raising new questions underlying sex hormone and SHH signaling in development and tumorigenesis.