タイトル；Cyclodextrins elucidate novel mechanisms of sperm capacitation by changing membrane environment.
（熊本大学 生命資源研究・支援センター 資源開発分野）
In order to accomplish fertilization, mammalian sperm must undergo physical, physiological and biochemical change to acquire fertilization ability, which is called as “capacitation.” Cholesterol efflux from sperm membrane is known as a trigger of capacitation. Previously, we reported methyl--cyclodextrin (MBCD) facilitated cholesterol efflux from mouse sperm membrane and increased fertilization rate in vitro. However, the detailed mechanism of MBCD on sperm capacitation is still unclear. Therefore, we evaluated effect of two different types of cyclodextrin (MBCD and dimethyl-a-cyclodextrin: DMACD) on sperm fertility and membrane environment to comprehend the mechanism of sperm capacitation and evaluate the efficacy of cyclodextrins as sperm activator. As a result, both MBCD and DMACD increased fertilization rate of mouse sperm in vitro. MBCD indicated high ability of cholesterol efflux, while DMACD had no ability of removing cholesterol. Both MBCD and DMACD induced phospholipid efflux, and DMACD had higher ability of removing phospholipids from sperm. MBCD shortened the time to increase membrane fluidity. Both MBCD and DMACD changed lipid raft localization of sperm membrane. In addition, both MBCD and DMACD facilitated acrosome reaction. In conclusion, MBCD and DMACD increases fertilization rate by changing sperm membrane environment. In addition, DMACD facilitates sperm capacitation without removing cholesterol. These results are contributed to understand the mechanism of sperm capacitation and applicable to improve the technique of in vitro fertilization.