Male secretory protein SPINK3 acts as a decapacitation factor by blocking calcium influx in mouse sperm

STIVAL, CINTIA; ZALAZAR, LUCIA; NICOLLI, ANABELLA R.; DE BLAS, GERARDO A.; KRAPF, DARIO; CESARI, ANDREINA

Conferencia; American Society of Andrology 45th Annual Conference (ASA2020); 2020

American Society of Andrology

In vivo, sperm capacitation occurs in the female reproductive tract and is regulated by both female and semen molecules present at the time of ejaculation (and thereafter) by still unclear mechanisms. Semen factors prevent either premature or off-site capacitation. One such factor is SPINK3, a decapacitating protein from the seminal vesicle suggested to affect intracellular calcium levels in mammalian sperm. In this manuscript, we show that SPINK3 prevents plasma membrane potential hyperpolarization leading to inability of sperm to acrosome react. Lack of hyperpolarization relies on inactivity of Src kinase, evidenced by lack of phosphorylated tyr416-Src. However, SPINK3 did not block the acrosome reaction when exposed to capacitated sperm. Calcium entry induced by BSA or alkalization was prevented by SPINK3, suggesting reduced CatSper activity. The presence of SPINK3 during capacitation abolished the onset of hyperactivation. However, SPINK3 did not affect PKA activity or tyrosine-phosphorylation. SPINK3 binds to the principal piece of non-capacitated sperm, but no binding was observed on capacitated sperm. We propose SPINK3 as a decapacitation factor by preventing hyperpolarization, and thus related events as intracellular Ca2+ increase and hyperactivation.