TLR4Signaling Inhibits Phagocytic Ability Of Sertoli Cells

Background and objectives:Microbial infections, either localized or systemic, can lead to male infertility that may be transitive or persistent. About75%of spermatogenic cells are estimated to undergo apoptosis during mammalian spermatogenesis, and the cytoplasmic portions of the rest germ cells are shed and form residual bodies before they mature into spermatozoa. The apoptotic spermatogenic cells and residual bodies are phagocytosed and degraded by Sertoli cells. Privious studies focus on the phagocytosis by Sertoli cells in the normal physiological condition. However, the effect of inflammatory condition on the phagocytic ability of Sertoli cells remain to be clarified. Here, we investigate the effect of TLR4activation on phagocytosis of apoptotic spermatogenic cells by mouse Sertoli cells.Materials and methods:Mouse Sertoli cells were isolated and identified by immune staining with WT1. Expression of TLRs in mouse Sertoli cells were detected by RT-PCR. Tyro3subfamily receptors in mouse Sertoli cells were analysed by immunohistochemical staining and Western blotting. Mouse germ cells were isolated and cultured at35℃in serum-free medium for48h to induce spontaneous apoptosis. The apoptotic rate of germ cells was assessed by AO/EB staining. Phagocytosis was assessed by oil red O staining. The mechanism of TLR4signal pathway in regulating phagocytosis in Sertoli cells was studied using qRT-PCR and ELISA.Results:Tyro3subfamily receptors express in mouse Sertoli cells, and Mer is necessary to activate phagocytosis in Sertoli cells. Gas6can stimulate phagocytic ability of Sertoli cells. TLR4activated by LPS and specifically inhibits phagocytosis of apoptotic germ cells by Sertoli cells through NF-κB pathway. LPS-induced TNF-a production inhibits phagocytosis in an autocrine manner. TLR4activated by LPS can inhibit phagocytosis through supressing expression of Gas6and Mer in Sertoli cells.Conclusions:The activation of TLR4inhibits the engulfing of apoptotic germ cells by mouse Sertoli cells through induction of TNF-a and suppression of Gas6and Mer. Data provide novel insights into the regulation of phagocytic clearance of apoptotic germ cells by TLR4signaling.