Recombinant human OVGP1 increases intracellular calcium and further potentiates the effects of progesterone on human sperm.

PURPOSE: To investigate the effects of recombinant human oviduct-specific glycoprotein (rHuOVGP1) alone and in combination with progesterone (P4) on intracellular Ca(2+) concentration [Ca(2+)](i) and to investigate if rHuOVGP1 in combination with P4 can further enhance tyrosine phosphorylation (pY) of sperm proteins during human sperm capacitation. METHODS: Fluorometric flow cytometry was performed to examine the effects of rHuOVGP1 on [Ca(2+)](i) in human sperm during capacitation. Confocal microscopy was used in conjunction with live cell imaging to analyze the influence of rHuOVGP1 and P4 on [Ca(2+)](i) in the sperm tail and to examine the involvement of CatSper channels in their effect on [Ca(2+)](i). Western blot analysis was performed to assess the protein levels of p105, a major tyrosine-phosphorylated sperm protein. RESULTS: rHuOVGP1 increases [Ca(2+)](i) in human sperm at the beginning of capacitation and further increases and sustains the level of [Ca(2+)](i) in the sperm tail following the addition of P4. Inhibition of CatSper channels impedes the effects of rHuOVGP1 on [Ca(2+)](i) in the sperm tail. P4 alone can increase pY of a major human sperm protein, p105, yet yields a further increase when used in combination with rHuOVGP1. CONCLUSION: The present study revealed that rHuOVGP1 may work with P4 to upregulate [Ca(2+)](i) at the beginning of capacitation in part through CatSper channels which, in turn, leads to the downstream event of pY of sperm proteins and enhancement of sperm capacitation.