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.

Summary Sentence

Dimethyl-α-cyclodextrin induces capacitation by changing the membrane environment, including membrane fluidity, lipid raft relocalization and the acrosome reaction.

Graphical Abstract

Figure Abstract Overview of experimental design. Sperm were treated with BSA, MBCD (cholesterol acceptors), and DMACD (phospholipid acceptor). After incubation with BSA, MBCD, or DMACD, sperm functions were evaluated (lipids efflux, capacitation markers, fertilization ability, and developmental ability). In the analysis of lipids efflux, cholesterol and phospholipids released from sperm membrane were quantified. In the analysis of capacitation markers, membrane fluidity, localization of lipid raft, and acrosome reaction were evaluated. In the analysis of fertilization ability, fertilization rate was evaluated by in vitro fertilization. In the analysis of developmental ability, developmental rates of two-cell embryos to blastocysts or pups were examined by in vitro culture and embryo transfer.