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.