Deborde, Sylvie; (2001) Human placental inositolphosphoglycans may be released by glycosylphosphatidylinositol-phospholipase D, both present in the syncytial brush border membrane investigation in normal and pre-eclamptic placentae. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Pre-eclampsia is a disorder affecting 5 to 10% of all pregnancies. In the pre-eclamptic placenta, increased levels of an inositolphosphoglycan (IPG) second messengers have been reported. The objective of this thesis has been the study of IPGs in the placenta and their possible release by the glycosylphosphatidylinositol-phospholipase D (GPI-PLD) enzyme. The presence of IPGs was investigated in the placenta. Immunostaining on sections of chorionic villi revealed the presence of IPGs and confirmed the higher levels of IPGs in pre-eclampsia. IPGs of both sub-types A and P were extracted from microvilli preparations of both normal and pre-eclamptic placentae. After showing the presence of biologically active IPGs in microvilli preparation, the next step was to investigate the presence of glycosylphosphatidylinositol (GPI), the putative precursor molecule of IPGs. GPI was extracted from microvilli of normal placenta but unexpectedly not detected in pre-eclamptic samples. An elevated GPI-PLD activity could cause increased catabolism of GPI, and thus be responsible for both the absence of detectable GPI and the increased IPG levels found in pre-eclamptic samples. GPI-PLD hydrolysis activity was measured in microvilli preparations from both normal and pre-eclamptic placenta. Whereas GPI-PLD is described as a 100 kDa protein, a protein of 50 kDa was mainly detected. GPI-PLD mRNA was not detected in the placenta. We therefore propose a model in which placental GPI-PLD is taken up by the syncytiotrophoblast from the maternal blood and transferred to a lysosomal compartment where it is cleaved into an active 50 kDa protein before returning to the plasma membrane. Finally, the susceptibility of extracted placental GPI to hydrolysis by recombinant GPI-PLD has been studied. GPI-PLD was able to cleave GPI in vitro. To conclude, this work confirms the presence of IPGs in placenta and more specifically in microvilli and supports previous reports of increased IPG-P type in preeclampsia. The study of placental GPI and GPI-PLD throws light on the possible mechanism underlying the generation of IPGs in both normal and pre-eclamptic microvilli.

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