Although classical and non-classical signaling of testosterone (T) has been observed in the testis, the enigma of the non-classical pathway is not fully resolved. While some researchers favor the androgen receptor (AR), others propose a membrane-bound receptor for non-classical T signaling. Although silencing of the AR in Sertoli cells (SC) resulted in infertility and suggested no involvement of the non-classical pathway, recent experiments using an inhibitor of the non-classical signaling blocked meiosis in prepubertal mice. In this study, we will present data showing that the non-classical T signaling is mediated by the membrane-bound receptor ZIP9, a Zn(2+) transporter from the family of the ZRT, IRT-like proteins (ZRT=zinc-regulated transporter; IRT=iron-regulated transporter), which directly interact with the G-protein Gnα11. The close contacts of both proteins could be demonstrated by an in situ proximity assay. Silencing of the expression of either of these two proteins completely blocked all non-classical T signaling effects addressed. Furthermore, we observed that non-classical T signaling activated Erk1/2, and the transcription factors CREB and ATF-1, an effect which was not mediated by the classical AR. We also found that T increased the expression of the tight junction (TJ) proteins claudin-1 and claudin-5 in rat SCs. Furthermore, increased expression of both TJ proteins resulted in TJ formation between neighboring cells. Taken together, we suggest that non-classical T signaling in testis is mediated by ZIP9 and Gn α11 through Erk1/2, CREB and ATF-1 resulting in increased claudin expression. This will contribute to the blood-testis barrier which is essential for male fertility.
Funding This work was supported in part through the German Research Foundation (DFG), grant number SCHE 307/7-1 and partially the DFG within the framework of the International Research Training Group (IRTG) between Justus Liebig University of Giessen and Monash University Melbourne (GRK 1871/1) on Molecular pathogenesis of male reproductive disorders.
Presenting Author: Lutz Konrad, Center of Gynecology and Obstetrics, Faculty of Medicine, Justus-Liebig-University Giessen, Feulgenstr. 10-12, 35392 Giessen, Germany. Email: firstname.lastname@example.org