Motamed Khorasani A, Cheung A P, Lee C Y
Department of Obstetrics and Gynecology, University of British Columbia, Vancouver, Canada.
J Androl. 2000 Jul-Aug;21(4):586-94.
Progesterone (P4) is known to induce an acrosome reaction in mammalian sperm in vitro, whereas cholesterol is a major inhibitor of acrosome reaction. This study had three objectives: to study the in vitro effects of exogenous cholesterol on acrosome reactions in human sperm, to study the mechanism by which cholesterol affects P4-induced acrosome reaction and those induced by dibutyryl cyclic adenosine monophosphate (db-cAMP), and to study the status of the P4 surface receptor during capacitation and acrosome reaction and its relationship with cholesterol and different acrosome reaction inducers. Acrosome reaction was induced with exposure to 10 microg/mL of P4 for 30 minutes and 1 mM of db-cAMP for 30 minutes in motile sperm either in the presence or absence of 0.1-1 microg/mL of cholesterol for 30 minutes. The effects of a 30-minute exposure to 1 microg/mL of beta-sitosterol, a cholesterol plant analogue, as well as the effects of cholesterol on P4-induced acrosome reactions were compared. Fluorescein isothiocyanate-labeled albumin-progesterone conjugate (P4-FITC-BSA) was used as the probe in order to quantify the percentage of sperm in which the P, surface receptor was exposed. The results of this study indicate that cholesterol inhibited P4-induced acrosome reactions when added to the sperm during capacitation (long incubation) and when it was added with P4 during the induction of acrosome reactions (short incubation). Similarly, acrosome reaction that was induced by db-cAMP was also inhibited by cholesterol. Fifty percent of P4-induced acrosome reaction was inhibited by a cholesterol concentration of 0.2 microg/mL. Cholesterol's inhibition of induced acrosome reaction was independent of P4 concentration. Beta-sitosterol inhibited P4-induced acrosome reaction in a dose-dependent manner that was identical to that of cholesterol. We observed that increases in the P4 surface receptor exposure were time-dependent and receptors migrated toward the equatorial segment during the first 2 hours of capacitation. We also found that db-cAMP induced the appearance of the P4 surface receptor in the sperm plasma membrane and that cholesterol inhibited it. The results of this study suggest that cholesterol inhibits acrosome reaction in a noncompetitive manner by modifying the structure of the sperm plasma membrane, which prevents exposure of the P4 surface receptor for P4 binding.
已知孕酮（P4）可在体外诱导哺乳动物精子发生顶体反应，而胆固醇是顶体反应的主要抑制剂。本研究有三个目的：研究外源性胆固醇对人精子顶体反应的体外影响，研究胆固醇影响P4诱导的顶体反应以及二丁酰环磷酸腺苷（db - cAMP）诱导的顶体反应的机制，研究顶体反应获能过程中P4表面受体的状态及其与胆固醇和不同顶体反应诱导剂的关系。在有或没有0.1 - 1微克/毫升胆固醇存在的情况下，将活动精子暴露于10微克/毫升的P4中30分钟和1毫摩尔的db - cAMP中30分钟，以诱导顶体反应。比较了暴露于1微克/毫升β - 谷甾醇（一种胆固醇植物类似物）30分钟的效果以及胆固醇对P4诱导的顶体反应的影响。使用异硫氰酸荧光素标记的白蛋白 - 孕酮共轭物（P4 - FITC - BSA）作为探针，以量化暴露P4表面受体的精子百分比。本研究结果表明，在获能（长时间孵育）期间向精子中添加胆固醇以及在诱导顶体反应（短时间孵育）期间与P4一起添加胆固醇时，胆固醇会抑制P4诱导的顶体反应。同样，db - cAMP诱导的顶体反应也受到胆固醇的抑制。胆固醇浓度为0.2微克/毫升时可抑制50%的P4诱导的顶体反应。胆固醇对诱导的顶体反应的抑制作用与P4浓度无关。β - 谷甾醇以与胆固醇相同的剂量依赖性方式抑制P4诱导的顶体反应。我们观察到P4表面受体暴露的增加是时间依赖性的，并且在获能的前2小时内受体向赤道段迁移。我们还发现db - cAMP诱导精子质膜中P4表面受体的出现，而胆固醇会抑制这一过程。本研究结果表明，胆固醇通过改变精子质膜的结构以非竞争性方式抑制顶体反应，这会阻止P4表面受体暴露以进行P4结合。
