Abstract
Capacitation is an important event in the completion of fertilization by mammalian sperm. Cholesterol efflux is a trigger of capacitation. In general, cholesterol acceptors of albumin and β-cyclodextrins are used to induce capacitation during in vitro fertilization. Previously, we reported that methyl-β-cyclodextrin (MBCD), which is composed of seven glucoses, had a higher ability to induce capacitation than bovine serum albumin (BSA) in frozen–thawed mouse sperm. Comparison of albumin and cyclodextrins is helpful for understanding the mechanism of capacitation. In this study, we examined the effects of albumin, MBCD, and a different type of cyclodextrin, dimethyl-α-cyclodextrin (DMACD), which is composed of six glucoses, on several events of sperm capacitation. We showed that DMACD induced sperm capacitation and promoted fertilization ability. The time required to increase the fertilization rate differed among BSA, MBCD, and DMACD. BSA and MBCD enhanced cholesterol and phospholipid efflux, whereas DMACD enhanced only phospholipid efflux. BSA, MBCD, and DMACD increased sperm membrane fluidity, rearrangement of the lipid raft, and the acrosome reaction. These findings suggest that phospholipid efflux is a novel trigger of capacitation. Increasing the choice of sperm capacitation inducers may be useful for improving in vitro fertilization (IVF) techniques not only in mice, but also in various species in which it has been difficult to produce embryos by IVF.
