Abstract

SPINKL, a serine protease inhibitor kazal-type-like protein initially found in mouse seminal vesicle secretions, possesses structurally conserved six-cysteine residues of the kazal-type serine protease inhibitor family. However, it has no inhibitory activity against serine proteases. Previously, it was found to have the ability to suppress murine sperm capacitation in vitro. Herein, we investigated the mechanisms underlying the suppressive effect of SPINKL on sperm capacitation. Three in vitro capacitation-enhancing agents, including bovine serum albumin (BSA), methyl-beta-cyclodextrin (MBCD), and dibutyryl cyclic AMP (dbcAMP), coupled with 3-isobutyl-1-methylxanthine (IBMX), were used to evaluate the influence of SPINKL on capacitation signaling. Preincubation of sperm with SPINKL suppressed BSA- and MBCD-induced sperm capacitation by blocking three upstream signals of capacitation that is the cholesterol efflux from sperm plasma membranes, extracellular calcium ion influx into sperm, and increases in intracellular cAMP. Moreover, SPINKL also inhibited downstream signal transduction of capacitation since it suppressed dbcAMP/IBMX and N(6) -phenyl cAMP (6-Phe-cAMP)-activated cAMP-dependent protein kinase-associated protein tyrosine phosphorylation. Such inhibition is probably mediated by attenuation of SRC tyrosine kinase activity. Furthermore, SPINKL could not reverse capacitation once sperm had been capacitated by capacitation-enhancing agents or capacitated in vivo in the oviduct. SPINKL bound to sperm existed in the uterus but had disappeared from sperm in the oviduct during the sperm's transit through the female reproductive tract. Therefore, SPINKL may serve as an uncapacitation factor in the uterus to prevent sperm from precocious capacitation and the subsequent acrosome reaction and thus preserve the fertilization ability of sperm.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.