Comparative analysis between cyclic GMP and cyclic AMP signalling in human sperm

Abstract

The principal involvement of cyclic nucleotides in regulating sperm functions is well established, but the factors controlling their generation and actions have not yet been entirely resolved. In particular, specific roles for cyclic (c)GMP in mammalian sperm are poorly understood. In this study, we have characterized comparatively the cAMP and cGMP signalling systems in ejaculated human sperm. Mean concentrations of cGMP (0.1 micromol/l) were found to be 100-fold lower than those of cAMP in non-stimulated cells, and adenylyl cyclase (AC) activities predominate by far guanylyl cyclase (GC) activities in both particulate and soluble protein fractions. By different experimental approaches (photoaffinity labelling, cyclase assays, immunoblotting), we provide evidence for the presence (guanylyl cyclase-A, soluble guanylyl cyclase, regulatory and catalytic subunits of cAMP-dependent protein kinase) or absence (guanylyl cyclase-B, natriuretic peptide clearance receptor, neuronal nitric oxide synthase, cGMP-dependent protein kinase I) of different factors involved in either cAMP or cGMP pathways. Functional studies showed that cGMP, at high concentrations, can enhance sperm protein tyrosine phosphorylation but not serine phosphorylation of glycogen synthase kinase. This study reveals that human sperm are characterized by an exceptional predominance of cAMP signalling and indicates potential roles for cGMP.

The expression of atrial natriuretic peptide in the oviduct and its functions in pig spermatozoa

“…The absence or presence of PKG I in pig sperm needs further study. It is also possible that other signal transduction pathways (such as cGMP-gated ion channels) might be involved in this process (Willipinski-Stapelfeldt et al 2004). The optimal concentration of ANP for induction of the acrosome reaction in pig spermatozoa in the present study was consistent with dissociation constants obtained for ANP binding to human spermatozoa (Silvestroni et al 1992) and also with concentrations in follicular fluids (Anderson et al 1994), suggesting a physiological role for ANP in the regulation of the acrosome reaction.…”

“…that PKG I is absent in human sperm, and the effect of high concentration cGMP may be explained by a crossactivation of PKA (Willipinski-Stapelfeldt et al 2004). However, H89, a PKA inhibitor, could not block cGMPinduced acrosome reaction in our study.…”

Stimulation of the nitric oxide/cyclic guanosine monophosphate signaling pathway elicits human sperm chemotaxis in vitro

“…The PKGs are a family of serine/threonine kinases that are expressed in mammals under two different isoforms, PKG I and PKG II (20). In a recent study, no PKG I was detectable by immunoblotting in human sperm (8); this does not rule out the possibility that the PKG II isoform might be involved in human sperm chemotaxis. Indeed, Rp-8-BrcGMPS is a nonspecific PKG inhibitor, and is able to block both isoforms (21).…”

“…One of its main activators is nitric oxide (NO), a highly reactive free radical gas which participates as a mediator in several biologic processes, such as vasodilatation, neurotransmission, immune response, and apoptosis, and is synthesized from L-arginine by NADPH-dependent NO synthases (NOS) (7). The sGC isoform has been recently identified in human sperm by immunoblotting (8), and NO has been shown to increase the intracellular levels of cGMP in spermatozoa: the NO donors sodium nitroprusside and spermine-NONOate have been reported to increase the intracellular cGMP levels in human and murine spermatozoa, respectively (9,10). It has been reported that low concentrations of NO enhance the motility of mouse, hamster, and human spermatozoa, the acrosomal reactivity of mouse, bull, and human spermatozoa, and the zona pellucida-binding ability of human spermatozoa (9,10).…”

Nitric oxide stimulates human sperm motility via activation of the cyclic GMP/protein kinase G signaling pathway

“…The NO donors sodium nitroprusside and SPNO have been shown to increase the intracellular levels of cGMP in human (Zhang & Zheng 1996, Revelli et al 2001 and murine (Herrero et al 1998) spermatozoa respectively, and recently the sGC has been identified in human sperm by immunoblotting (Willipinski-Stapelfeldt et al 2004). Although its levels in human sperm are about 100-fold lower than the cAMP content (Willipinski-Stapelfeldt et al 2004), cGMP has been implicated in several sperm signaling pathways functions, such as capacitation, acrosome reaction, chemotaxis, and sperm-egg interaction (Revelli et al 2001, 2002, Herrero et al 2003, Miraglia et al 2007. cGMP is thought to modulate also sperm motility.…”