177. ANTIBODIES AGAINST BMPR-IB UNCOVERS A PARACRINE FUNCTION FOR THE RECEPTOR IN MALE MOUSE LEYDIG CELL TESTOSTERONE PRODUCTION IN VITRO

Abstract

The male reproductive system is regulated by pituitary gonadotrophins and local testicular factors including the transforming growth factor-β superfamily members which up-regulate and modulate testosterone production respectively. Type I and type II bone morphogenetic protein (BMP) receptors have been identified in both steroidogenic and non-steroidogenic cells in the testis and have been reported to impact steroid production via their effect on steroidogenic enzymes. In this study we investigated if BMPR-IB had an autocrine or paracine role in testosterone production using BMPR-IB antibodies in testis tissue and Leydig cell culture in vitro. Immature (21d) and mature (60d) mice were sacrificed by CO2 asphyxiation and the testis removed, decapsulated and cultured in basal and equine chorionic gonadotrophin (eCG)-conditioned media for three hours at 32 °C in 5 % CO2, in the presence and absence of anti-BMPR-IB. Additionally, Leydig cells were Percoll purified from adult mouse testicular interstitial cells and cultured for three hours with and without anti-BMPR-IB under human chorionic gonadotrophin (hCG) stimulated or unstimulated conditions. After three hours of incubation the culture media was aspirated into labeled vials and assayed for testosterone using a radioimmunoassay. In adult testicular slice culture, treatment with anti-BMPR-IB resulted in a significant decrease in basal and eCG-stimulated testosterone production by 37 % and 41 % respectively, while having no significant effect on basal or eCG-stimulated testosterone production by the immature testis. In purified Leydig cell culture from adult male mice BMPR-IB immunization had no effect on testosterone production in basal or hCG-stimulated conditions. In conclusion, anti-BMPR-IB significantly reduced testosterone production in adult testicular slice culture but not in cell culture, demonstrating that BMP paracrine signalling from the seminiferous tubules is likely to be important in modulating testosterone production by Leydig cells. Additionally, the paracrine signalling appears to be developmentally regulated only occurring in the adult testis.