Adhesion to oviduct glycans regulates porcine sperm Ca2+ influx and viability.

Before fertilization, sperm bind to epithelial cells of the oviduct isthmus to form a reservoir that regulates sperm viability and capacitation. The sperm reservoir maintains optimum fertility in species, like swine, in which semen deposition and ovulation may not be well synchronized. We demonstrated previously that porcine sperm bind to two oviductal glycan motifs, a biantennary 6-sialylated N-acetyllactosamine (bi-SiaLN) oligosaccharide and 3-O-sulfated Lewis X trisaccharide (suLeX). Here, we assessed the ability of these glycans to regulate sperm Ca2+ influx, capacitation and affect sperm lifespan. After 24 h, the viability of sperm bound to immobilized bi-SiaLN and suLeX was higher (46% and 41% respectively) compared to viability of free-swimming sperm (10-12%). Ca2+ is a central regulator of sperm function so we assessed whether oviduct glycans could affect the Ca2+ influx that occurs during capacitation. Using a fluorescent intracellular Ca2+ probe, we observed that both oviduct glycans suppressed the Ca2+ increase that occurs during capacitation. Thus, specific oviduct glycans can regulate intracellular Ca2+. Because the increase in intracellular Ca2+ was suppressed by oviduct glycans, we examined whether glycans affected capacitation, as determined by protein tyrosine phosphorylation and the ability to undergo a Ca2+ ionophore-induced acrosome reaction. We found no discernable suppression of capacitation in sperm bound to oviduct glycans. We also detected no effect of oviduct glycans on sperm motility during capacitation. In summary, LeX and bi-SiaLN glycan motifs found on oviduct oligosaccharides suppress the Ca2+ influx that occurs during capacitation and extend sperm lifespan but do not affect sperm capacitation or motility.