Inhibition of sperm production in mice by annexin V microinjected into seminiferous tubules: possible etiology of phagocytic clearance of apoptotic spermatogenic cells and male infertility

Abstract

Many differentiating spermatogenic cells die by apoptosis during the process of mammalian spermatogenesis. However, very few apoptotic spermatogenic cells are detected by histological examination of the testis, probably due to the rapid elimination of dying cells by phagocytosis. Previous in vitro studies showed that Sertoli cells selectively phagocytose dying spermatogenic cells by recognizing the membrane phospholipid phosphatidylserine (PS), which is exposed to the surface of spermatogenic cells during apoptosis. We examined here whether PS-mediated phagocytosis of apoptotic spermatogenic cells occurs in vivo. For this purpose, the PS-binding protein annexin V was microinjected into the seminiferous tubules of normal live mice, and their testes were examined. The injection of annexin V caused no histological changes in the testis, but significantly increased the number of apoptotic spermatogenic cells as assessed by the terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assay. The number of Sertoli cells did not change in the annexin V-injected testes, and annexin V itself did not induce apoptosis in primary cultured spermatogenic cells. These results indicate that annexin V inhibited the phagocytic clearance of apoptotic spermatogenic cells and suggest that PS-mediated phagocytosis of those cells occurs in vivo. Furthermore, the injection of annexin V into the seminiferous tubules brought about a significant reduction in the number of spermatogenic cells and epididymal sperm in anticancer drug-treated mice. This suggests that the elimination of apoptotic spermatogenic cells is required for the production of sperm.

Unexpected requirement for a binding partner of the syntaxin family in phagocytosis by murine testicular Sertoli cells

“…Previously, blockage of SC phagocytosis by annexin V delays spermatogenic recovery in drug-treated mice and leads to the number of epididymal sperm to decrease. 33 In our study, however, asthenozoospermia, not oligozoospermia, appeared to be responsible for the fertility impairment following HS (Figure 4b). Two reasons may help to explain this discrepancy.…”

Aquaporin AQP11 in the testis: molecular identity and association with the processing of residual cytoplasm of elongated spermatids

“…AQP11 may be important in facilitating the elimination of these surplus intracellular organelles and their contents without causing damage to the Sertoli cells after their phagocytosis and degradation. This would allow not only recycling of surplus proteins and organelles of spermatid origin, but also homeostasis of the Sertoli cells in the support of spermatogenesis, as suggested for the clearance of apoptotic spermatogenic cells, the failure of which may result in decreased sperm production (Maeda et al 2002). Malfunction of the clearance mechanism may even cause a breakdown of selftolerance leading to autoimmune orchitis (Pelletier et al 2009).…”

Aquaporins in spermatozoa and testicular germ cells: identification and potential role

“…In the testis, AQP11 may have a role in the degradation of surplus cytoplasmic components of spermatid origin, which may even be used to produce ATP by Sertoli cells after phagocytosis [84]. Furthermore, failure in such clearance would upset the homeostasis of the germinal epithelium and disrupt normal spermatogenesis [85], or may even result in a breakdown of self-tolerance leading to autoimmune orchitis [86].…”