Signal transduction mechanisms of the type i interferons in the human endometrium

Unlike humans, the primary signal for maternal recognition ofpregnancy in ruminants is the Type I interferon (IFN) IFN-t. IFN1: is produced by the conceptus and acts upon the endometrium where it inhibits the production ofprostaglandin F2a and subsequent luteolysis ofthe corpus luteum. It is difficult to establish what precise role interferonlike signalling might play in human reproduction due to ethical barriers. However, indirect investigations are possible by in vitro investigation . of human endometrial . response to Type I IFN stimulation. Type I IFNs (a, P and 1:) activate a common tyrosine kinase signalling pathway' involving the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) proteins. However, the Type I IFNs elicit different cellular responses. The aim of this thesis is to establish that, whilst it is known that the Type I IFNs trigger~e JAKISTAT activation pathway, there is a simultaneous activation of different phospholipase pathways which determines the specificity of the response. This hypothesis was investigated using human endometrial tissue which is known to respond to Type I IFNs. Long-term primary human endometrial cell cultures were established from tissue taken from the proliferative and secretory phases of the menstrual cycle. Cell function and viability were determined by measuring placental proteins and cytokines. 33p labelled endometrial cells exposed to IFNs a and 1: showed hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2) with corresponding production of diacylglycerol (DAG). IFNa and IFN1: also stimulated hydrolysis of phosphatidylinositol-4- phosphate (pIP). These IFNs did not demonstrate activation of any other phospholipase. There was no phospholipid turnover via any phospholipase in response to IFN~. Using imrnunoprecipitation, SDS-PAGE and Western blotting it was possible to show the presence of phosphorylated STATl a in unstimulated endometrial cells. In response to stimulation by IFN a and ~ there was an increase in phosphorylated STATla, STATI and Tyk2 (a member ofthe Janus kinase family). In contrast, IFN1: activated the phosphorylation of Tyk2 but not STATla or STATI. There was no stimulation of JAKl phosphorylation by any of the IFNs. In summary, Type I IFNs u, ~ and 1: each elicit a different pattern of signal transduction response in cultured human endometrial cells, not only via the JAKISTAT pathway but also via phospholipase activation. The ability of IFN't to stimulate a signalling pathway, distinct from that of IFNu and ~ is sufficient circumstantial evidence to suggest that at least a residual signalling pathway for IFN't exists in the human endometrium and further investigation is warranted.EThOS - Electronic Theses Online ServiceGBUnited Kingdo