The endothelial protein C receptor (EPCR) binds to protein C (PC) and increases the rate of activated protein C (APC) generation by the thrombin-thrombomodulin (TM) complex. APC exerts anticoagulant, anti-inflammatory, and cytoprotective effects, which are EPCR-dependent. The thrombin-TM complex is also a potent activator of thrombin activable fibrinolysis inhibitor (TAFI), leading to impaired clot lysis. Mutations and polymorphisms identified in the EPCR gene, which can affect the efficiency of PC activation, have been associated with an increased risk of thrombosis. In this thesis we investigate the impact of impaired PC binding to EPCR on coagulation, inflammation, and fibrinolysis using novel in vitro and in vivo models. Using a murine model that harbours a variant of EPCR that does not bind PC (R84A), we demonstrate that upon thrombotic challenge, there is an increase in thrombin generation and fibrin deposition in the lungs. Upon inflammatory challenge, impaired PC/EPCR interactions also result in increased thrombin generation and increased neutrophil infiltration into the lungs. Using cells that express TM and a human variant of EPCR that does not bind PC (R96C), we demonstrate that clot lysis is delayed in normal plasma independent of TAFI activation, suggesting PC and TAFI do not compete for activation by the thrombin-TM complex. In contrast, delayed clot lysis in plasma deficient of PC is a result of greater TAFI activation by the thrombin-TM complex. Taken together, impairment of the PC pathway contributes to thrombosis through pro-coagulant, pro-inflammatory and anti-fibrinolytic mechanisms. Interestingly, mice with EPCR variant R84A, develop bone marrow failure and splenomegaly, revealing a novel role for EPCR in the bone marrow. Taken together, PC/EPCR interactions regulate the coagulation, inflammation, and fibrinolytic pathways, which may have a significant impact on maintaining hematopoietic homeostasis. / Thesis / Doctor of Philosophy (PhD) / Under normal conditions, blood is maintained in a fluid state. Upon injury or infection, the blood begins to form a clot to prevent bleeding. Once bleeding has stopped the clot is dissolved and blood regains its fluid state. The formation of a blood clot is a serious and potentially life threatening disease. A blood clot formed inside a blood vessel can block the flow of blood through the circulation, leading to organ damage. Approximately 50% of blood clots are caused by known genetic or environmental factors, leaving 50% of blood clots caused by unknown factors. In this thesis we investigate the unknown factors that contribute to blood clotting. In patients who have experienced blood clots with no known cause, we have identified genetic mutations in a blood vessel wall protein, known as the endothelial protein C receptor (EPCR) that renders it non-functional. We demonstrate both in vitro and in vivo that non-functional EPCR not only leads to the formation of a blood clot but also delays the removal of the blood clot. Our in vivo studies have also revealed a previously unknown role for EPCR in the bone marrow, likely through its effects on blood coagulation. Taken together, loss of EPCR function contributes to the development of clot formation and likely impacts other organ systems.

<p>The aim of this study was to examine the expression of Thrombomodulin, Tissue Factor, Tissue Factor Pathway Inhibitor and Endothelial Protein C Receptor in placenta throughout the three phases of the third trimester in the normal placenta and in IUGR placenta from full term.</p><p>Twenty-five normal placenta samples and twenty-five IUGR placenta samples were obtained and each sample was stained by immunohistochemistry using monoclonal antibodies. Each antibody was optimised for antigen retrieval method and for optimal dilution, before been applied to the test tissue.</p><p>The results showed that each of the antibodies mentioned was expressed in normal placenta and in IUGR placenta.</p><p>No significant difference could be established concerning the expression of each antibody mentioned between normal and IUGR placenta.</p>

The aim of this study was to examine the expression of Thrombomodulin, Tissue Factor, Tissue Factor Pathway Inhibitor and Endothelial Protein C Receptor in placenta throughout the three phases of the third trimester in the normal placenta and in IUGR placenta from full term. Twenty-five normal placenta samples and twenty-five IUGR placenta samples were obtained and each sample was stained by immunohistochemistry using monoclonal antibodies. Each antibody was optimised for antigen retrieval method and for optimal dilution, before been applied to the test tissue. The results showed that each of the antibodies mentioned was expressed in normal placenta and in IUGR placenta. No significant difference could be established concerning the expression of each antibody mentioned between normal and IUGR placenta.

Il est désormais admis que le caractère invasif d'une tumeur est lié, non seulement, au génotype des cellules cancéreuses, mais aussi à leurs interactions avec le microenvironnement tumoral (MT). Au sein du MT, une déstabilisation de la matrice stromale favorise la progression tumorale et la dissémination métastatique. Le remaniement de la matrice extracellulaire est souvent piloté par des enzymes protéolytiques. En revanche, les effets de l'inhibition de la formation de cette matrice sont peu étudiés. C’est dans cette optique que nous nous sommes intéressés à la protéine C (PC) et son récepteur endothélial (EPCR) et à leur rôle dans la tumorigenèse des leucémies et des cancers solides.L’EPCR est exprimé par un grand nombre de lignées cellulaires cancéreuses. Il est aussi détecté dans le compartiment tumoral chez des patients atteints de pathologie tumorale. Son gène est hautement conservé. Il possède cependant plusieurs polymorphismes. Un de ces SNPs (single nucleotide polymorphism) - 6936A/G - se traduit par la libération d'une forme soluble circulante de l'EPCR (EPCRs) résultant de la protéolyse de la forme membranaire. Chez des patients leucémiques, une fréquence élevée du SNP 6936A/G est observée et associée à la survenue de thrombose. D'autre part, l’EPCR est détecté in situ dans la majorité des biopsies tumorales testées et sécrété en grande quantité dans les ascites. La fixation de la PC sur l’EPCR et son activation augmentent la survie et le potentiel migratoire des cellules cancéreuses. Aussi, la PCA est capable de moduler, par communication paracrine, la sécrétion de plusieurs interleukines et cytokines. Ainsi, la stimulation de cellules du cancer de l'ovaire par la PCA induit la synthèse d'une thrombopoéïtine ovarienne fonctionnelle. Cette cytokine étant régulatrice de la production de plaquettes, la PCA semble être de nouveau à l'interface entre troubles de l'hémostase et pathologie cancéreuse. L’élucidation du rôle complexe de la PCA et de son récepteur endothélial dans la carcinogenèse permettrait non seulement de dégager de nouvelles approches thérapeutiques, mais aussi de prévenir le risque de thrombose associée au cancer et d’en réduire la morbidité. / It is now recognized that the invasiveness of tumor cells is not only related to the genotype of these cells but also to their interaction with tumor microenvironment (TM). Within the TM, stromal matrix destabilization promotes tumor progression and metastatic dissemination. The extracellular matrix remodeling is often driven by proteolytic enzymes. However, few studies have investigated the effects of an impairment of the matrix formation. Given these facts and circumstances, we were interested in protein C (PC) and its endothelial receptor (EPCR), as well as in their role in tumorigenesis in leukemia and solid cancers. EPCR is expressed by a wide range of cancer cell lines. It is also detected within the tumor compartment in patients with malignant diseases. EPCR gene is highly conserved but nevertheless contains polymorphisms. One of these SNPs (single nucleotide polymorphism) - 6936A/G – reflects – in the release of a soluble circulating form (EPCRs) resulting from the proteolysis of membrane-associated form. In leukemic patients a high incidence of 6936A/G SNP is observed and associated with thrombosis events. Moreover, EPCR is detected in the majority of tumor biopsies and is abundantly secreted in ascitic fluid. The PC attachment to EPCR and its activation promotes cell survival and migratory potential of tumor cells. Also, APC is able to modulate, by a paracrine manner, interleukins and cytokines secretion. Thus, ovarian cancer cells stimulation by APC induces the synthesis of a functional ovarian thrombopoietin. As this cytokine has a regulatory effect on platelet production, APC may be once again at the interface between hemostasis disorders and coagulation. The elucidation of the intricate role of APC and its endothelial receptor could permit not only to identify new therapeutic approaches but also to prevent cancer-associated thrombosis risk and to decrease morbidity in cancer patients.

This thesis aims to investigate if the endothelial protein C receptor is expressed in the murine kidney. This was done by performing flow cytometry and Western blot analysis on cultivated murine kidney endothelial cells (mKECs) as well as SDS-PAGE and Western blot analysis on murine kidney tissue. Flow cytometry was also performed on cultivated ARPE19 and 4T1 cells for comparison. It was discovered that ≥95,5% of the mKECs, ≥93,6% of the ARPE19 cells and ≥60,9% of the 4T1 cells express the receptor according to the flow cytometry data. A dot blot was performed to validate the primary antibody used for detection of EPCR in Western blot and SDS-PAGE. According to the dot blot, the primary antibody can be visualised in the dilution range from 1:2000 to 1:10. The dot blot also showed that the secondary antibody binds specifically to the primary antibody. Yet, Western blot analysis did not detect the receptor neither in mKECs nor tissue lysate. This was likely due to the fact that the primary antibody used did not bind specifically to the receptor, and may not be applicable for this method. SDS-PAGE did not show any indication that the receptor was present in the kidney tissue. In conclusion, it was discovered that the EPCR was expressed in the murine kidneys endothelial cells through flow cytometry, but the presented methods for Western blot and SDS-PAGE could not confirm the expression of the receptor.