A study of the intracellular signalling events involved in the zona pellucida-induced acrosome reaction in human spermatozoa

[摘要] ENGLISH ABSTRACT:In this study the author presents new data that will shed light on the fairly nebulousknowledge of intracellular pathways involved in the physiologically induced acrosomereaction and the subsequent events leading to fertilization. The zona pellucidainducedacrosome reaction, sperm-zona interaction as well as various sperm motioncharacteristics were investigated.The first part of the study focussed on the role of extracellular signal regulated kinase(ERK), a member of the family of mitogen activated protein kinases, during the zonapellucida-induced acrosome reaction and sperm-oocyte interaction. It was shown thatthe inhibition of ERK significantly reduced the zona pellucida-induced acrosomereaction as measured by fluorescent microscopy. This suggests that ERKs aredirectly or indirectly involved in the signal transduction pathway through which thehuman sperm acrosome reaction is induced by the zona pellucida. In an attempt toprovide further proof that ERK was involved in human acrosome signalling hemizonaassays were employed to test sperm-oocyte binding. From these sperm-oocytebindingexperiments it was clear that the inhibition of ERK leads to increased binding.These results support the idea that the zona pellucida-induced acrosome reaction,and therefore the physiologically relevant exocytotic event, is regulated by an ERKmediatedsignal transduction process.In the second part of the study the significance of phosphatidylinositol 3-kinase(PI3K) in the process of human sperm motility, acrosome reaction and sperm-oocytebinding, was investigated by employing the specific PI3K, LY294002. PI3K inhibitionincreased the percentage motility and percentage progressive motility in asthenozoospermia patients. Under the present laboratory conditions PI3K inhibitionfurthermore did not influence the acrosome reaction, whilst it enhanced sperm-oocytebinding. These results therefore imply that PI3K negatively affect sperm motility andzona-binding.In the last part of the study the possible effects of intracellular cGMP accumulationvia acute in vivo sildenafil citrate (ViagraTM) administration was investigated onseminal parameters, induction of the acrosome reaction, sperm-oocyte binding andsperm motility. As was expected no changes in the macro- and microscopicallyseminal parameters were caused by sildenafil citrate when compared to placebo.Furthermore the acrosome reaction was also not initiated or potentiated by sildenafilcitrate at concentrations of 50mg orally. Sperm-oocyte binding, smooth path velocity,straight line velocity and the percentage rapid cells all increased after sildenafil citratetreatment.From these results it appear that there are various role players in the zona pellucidainducedacrosome reaction intracellular signalling system. A thorough understandingof such signal transduction systems and the crosstalk in-between will ultimately yieldinformation regarding the nature of receptors to which these signal transductionpathways are coupled in human spermatozoa as well as the intracellular effectorsthat ultimately regulate sperm function. Moreover, an understanding of theseregulatory pathways will be essential for the future development of clinicalapproaches designed to enhance or preclude fertilization.

[发布机构] Stellenbosch University