Involvement of p38 Mitogen-Activated Protein Kinase and Inducible Nitric Oxide Synthase in Apoptotic Signaling of Murine and Human Male Germ Cells after Hormone Deprivation

Abstract

This study investigates the role of p38 MAPK, inducible nitric oxide synthase (iNOS), and the intrinsic pathway signaling in male germ cell death in rats after hormonal deprivation by a potent GnRH antagonist treatment. Germ cell apoptosis, involving exclusively middle (VII-VIII) stages, was activated by d 5 after GnRH antagonist treatment. Initiation of germ cell apoptosis was preceded by p38 MAPK activation and induction of iNOS. p38 MAPK activation and iNOS induction were further accompanied by a marked perturbation of the BAX/BCL-2 rheostat, cytochrome c, and DIABLO release from mitochondria, caspase activation, and poly(ADP-ribose) polymerase cleavage. Concomitant administration of aminoguanidine, a selective iNOS inhibitor, significantly prevented hormone deprivation-induced germ cell apoptosis. Inhibitors of iNOS or p38 MAPK were also effective in preventing human male germ cell apoptosis induced by hormone-free culture conditions. Together, these results establish a new signal transduction pathway involving p38 MAPK and iNOS that, through activation of the intrinsic pathway signaling, promotes male germ cell death in response to a lack of hormonal stimulation across species.

Regucalcin is broadly expressed in male reproductive tissues and is a new androgen-target gene in mammalian testis

“…On the other hand, androgens are known to inhibit apoptosis of male germ cells (Erkkila et al 1997, Pentikainen et al 2000 and testosterone withdrawal stimulates their apoptosis (Nandi et al 1999, Tesarik et al 2002. Germ cell apoptosis induced by androgen deprivation seems to be associated with caspases activation (Vera et al 2006, Johnson et al 2008. The role of RGN controlling apoptotic cell death has been established.…”

Hormonal regulation of male germ cell development

“…Conversely, concomitant administration of human chorionic gonadotropin (hCG) with male hormonal contraception demonstrated normal spermiation (Matthiesson et al 2006), suggesting the importance of testosterone for spermiation. In humans, testosterone alone or together with FSH acts as a survival factor for spermatocytes and spermatids by regulating both the intrinsic and the extrinsic apoptotic pathways (Tesarik et al 1998, 2002, Vera et al 2006. This was also observed in the non-human primate model, where increases in spermatocyte and spermatid apoptosis were observed in rhesus monkeys following gonadotrophin suppression (Zhou et al 2001, Zhang et al 2003.…”

“…Similar to rodents, FSH, together with testosterone, acts as a survival factor for spermatocytes and spermatids by regulating both the intrinsic and the extrinsic apoptotic pathways in men. Human seminiferous tubules cultured in a medium without FSH or testosterone showed significantly increased DNA fragmentation in primary spermatocytes and elongating/ elongated spermatids via the intrinsic and extrinsic apoptotic pathways (Tesarik et al 1998, 2002, Vera et al 2006.…”

Downregulation of cold-inducible RNA-binding protein activates mitogen-activated protein kinases and impairs spermatogenic function in mouse testes

“…35,36 Furthermore, p38 mediates germ cell apoptosis after hormone deprivation. 37 The possible roles of activated p44/p42 in germ cell apoptosis are currently unclear and are controversial, but it is clear that activation of p38 and SAPK/JNK promotes apoptosis in the testes. p38 activates the iNOS gene, 38,39 resulting in increased NO production and subsequent activation of the cytochrome c-mediated death pathway.…”