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

Du Plessis, S. S.(Simon Stephanus) (2002-12)

Thesis (PhD)--Stellenbosch University, 2002.

Thesis

ENGLISH ABSTRACT: In this study the author presents new data that will shed light on the fairly nebulous knowledge of intracellular pathways involved in the physiologically induced acrosome reaction and the subsequent events leading to fertilization. The zona pellucidainduced acrosome reaction, sperm-zona interaction as well as various sperm motion characteristics 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 zona pellucida-induced acrosome reaction and sperm-oocyte interaction. It was shown that the inhibition of ERK significantly reduced the zona pellucida-induced acrosome reaction as measured by fluorescent microscopy. This suggests that ERKs are directly or indirectly involved in the signal transduction pathway through which the human sperm acrosome reaction is induced by the zona pellucida. In an attempt to provide further proof that ERK was involved in human acrosome signalling hemizona assays were employed to test sperm-oocyte binding. From these sperm-oocytebinding experiments 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 ERKmediated signal 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-oocyte binding, was investigated by employing the specific PI3K, LY294002. PI3K inhibition increased the percentage motility and percentage progressive motility in asthenozoospermia patients. Under the present laboratory conditions PI3K inhibition furthermore did not influence the acrosome reaction, whilst it enhanced sperm-oocyte binding. These results therefore imply that PI3K negatively affect sperm motility and zona-binding. In the last part of the study the possible effects of intracellular cGMP accumulation via acute in vivo sildenafil citrate (ViagraTM) administration was investigated on seminal parameters, induction of the acrosome reaction, sperm-oocyte binding and sperm motility. As was expected no changes in the macro- and microscopically seminal parameters were caused by sildenafil citrate when compared to placebo. Furthermore the acrosome reaction was also not initiated or potentiated by sildenafil citrate at concentrations of 50mg orally. Sperm-oocyte binding, smooth path velocity, straight line velocity and the percentage rapid cells all increased after sildenafil citrate treatment. From these results it appear that there are various role players in the zona pellucidainduced acrosome reaction intracellular signalling system. A thorough understanding of such signal transduction systems and the crosstalk in-between will ultimately yield information regarding the nature of receptors to which these signal transduction pathways are coupled in human spermatozoa as well as the intracellular effectors that ultimately regulate sperm function. Moreover, an understanding of these regulatory pathways will be essential for the future development of clinical approaches designed to enhance or preclude fertilization.

AFRIKAANSE OPSOMMING: Die outeur lê in hierdie studie nuwe data voor ten einde meer lig te werp op die relatief vae veld van intrasellulêre seintransduksie paaie betrokke by die fisiologiesgeïnduseerde akrosoomreaksie en die daaropvolgende gebeure wat aanleiding gee tot bevrugting. Die zona pellucida-geïnduseerde akrosoomreaksie, sperm-zona interaksie sowel as spermmotiliteitseienskappe is ondersoek. Die eerste gedeelte van die studie fokus op die rol van ekstrasellulêreseingereguleerde- kinase (ERK), 'n lid van die familie van mitogeen-geaktiveerde proteïenkinases, tydens die zona pellucida-geïnduseerde akrosoomreaksie en sperm-oosiet interaksie. Daar word aangetoon dat die inhibisie van ERK die zona pellucida geïnduseerde akrosoomreaksie, soos gemeet met behulp van fluorosensie mikroskopie, betekenisvol verminder. Dit suggereer dat ERK direk of indirek betrokke is by die seintransduksie paaie waardeur die akrosoomreaksie van die menslike sperm deur die zona pellucida geïnduseer word. In 'n poging om onomwonde te bewys dat ERK betrokke is by menslike akrosoom-seintransduksie, is hemizona essais gebruik om sperm-oesiet binding te bepaal. Van hierdie sperm-oosiet bindingeksperimente is dit duidelik dat die inhibisie van ERK aanleiding gee tot verhoogde binding. Hierdie resultate ondersteun dus die idee dat die zona pellucidageïnduseerde akrosoomreaksie en dus die fisiologies relevante eksositotiese gebeurtenis gereguleer word deur 'n ERK-gemediëerde seintransduksie proses. In die tweede gedeelte van die studie is die belang van fosfatidielinositol 3-kinase (PI3K) in die proses van menslike spermmotiliteit, akrosoomreaksie en sperm-oesiet binding ondersoek deur van die spesifieke PI3K inhibitor LY294002, gebruik te maak. Pl3K-inhibisie het die persentasie motiliteit en progressiewe motiliteit by astenozoospermiese pasiënte verhoog. Onder hierdie laboratoriumtoestande het Pl3K-inhibisie nie die akrosoomreaksie beïnvloed nie, terwyl sperm-oosiet binding verhoog is. Hierdie resultate beteken dus dat PI3K spermmotiliteit en zona-binding negatief beïnvloed. In die laaste gedeelte van die studie is die effekte van intrasllulêre cGMP akkumulasie deur akute in vivo sildenafil sitraat (ViagraTM) toediening op seminale parameters, induksie van die akrosoomreaksie, sperm-oesiet binding en spermmotiliteit ondersoek. Soos verwag is geen veranderinge in die makro- en mikroskopiese seminale parameters deur sildenafil sitraat in vergelyking met plasebo veroorsaak nie. Verder is die akrosoomreaksies ook nie deur 50mg orale sildenafil sitraat geïnisieer of potensieer nie. Sperm-oosiet binding, geplaneerde snelheid, reguitlyn snelheid en persentasie vinnigbewegende selle was almal vehoog na sildenafil sitraat behandeling. Uit hierdie resultate blyk dit dat daar verskeie rolspelers in die zona pellucidageïnduseerde akrosoomreaksie is. 'n Deeglike insig van al hierdie seintransduksiepaaie en die onderlinge kruiskontak tussen mekaar sal uiteindelik die nodige inligting rakende die reseptore waaraan hierdie seintransduksie paaie gekoppel is, verskaf sowel as die intrasellulêre effektore wat uiteindelik spermfunksie beheer. Nog te meer sal die begrip van hierdie regulatoriese paaie verder noodsaaklik wees vir die toekomstige ontwikkeling van kliniese benaderings om bevrugting te bevorder of te voorkom.

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