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No description available.

Atherosclerosis is a major cause of mortality in industrialized nations. Atherosclerosis is characterized by plaque deposition which decreases the lumen diameter into a stenosis. The creation of a restriction increases shear rates pathologic levels exceeding 3,500/s. Following plaque cap rupture, thrombus may form from the accumulation of millions of platelets, occluding the vessel, leading to heart attack and stroke. Studies of high shear thrombosis show that platelet activation, GPIIb/IIIa and vWF are involved. However, some recent studies also suggest that high shear aggregation is not dependent on activation or GPIIb/IIIa. Several antiplatelet pharmaceuticals against activation and GPIIb/IIIa have been proposed, but their efficacy in patients remains mixed. The overall objective of this project is to determine the factors necessary for thrombosis to occlusion in very high shear regions seen in diseased arteries. Our central hypotheses are that platelet activation and the subsequent conformational change in GPIIb/IIIa are necessary for thrombosis, and that higher concentrations of vWF in the plasma will increase thrombosis. To this end, we developed a new high shear hemodynamic model utilizing 30mLs of whole blood and quantified thrombus thickness, volume accumulation and accumulation rates. We demonstrate that thrombosis to occlusion stems from a second phase of Rapid Platelet Accumulation (RPA). Thrombus accumulation is completely prevented by PGE1 inhibition of platelet activation. Similarly, GPIIb/IIIa blockade via abciximab prevented significant thrombus deposition and RPA. We also found that increasing plasma vWF levels in high shear regions increased thrombus thickness and suggestively increased RPA rates. The results clarify the need for activation of mural platelets for long term thrombus accumulation without the activation of circulating platelets.

Megakaryocytes (Mks) are unique bone marrow cells, which produce platelets. Dysregulated Mk development can lead to abnormal platelet number and the production of functionally defective platelets, causing bleeding, thrombotic events, and leukaemia. Understanding the molecular mechanisms driving megakaryopoiesis may yield insights into the molecular genetics and cellular pathophysiology of a diversity of disorders. The primary aim of this thesis was to gain insight into the molecular events required for normal Mk development. As transcription factors and cytokines play a central role in driving Mk development, both of these processes were investigated. Fli-1 and GATA-1 are key transcription factors regulating Mk-gene expression, alone and co-operatively. To understand the mechanism of transcriptional synergy exerted by Fli-1 and GATA-1, in vitro assays were carried out investigating the interactions between Fli-1, GATA-1 and DNA that mediate synergy. A novel mechanism of synergy was identified, where Fli-1 DNA binding is not required, although an interaction between Fli-1 and GATA-1, and GATA-1 DNA binding is required. Importantly, the results demonstrate that Fli-1 DNA binding is not essential for promoting Mk-gene expression in primary murine bone marrow cells. Thrombopoietin (TPO) is the primary cytokine responsible for Mk and platelet development. Identifying novel TPO gene-targets may provide invaluable information to aid the understanding of the complex and unique processes required for Mk development. Using microarray technology, IFI16 was identified as a TPO-responsive gene that has not previously been studied in the Mk lineage. This work demonstrated that IFI16 is expressed in CD34+ HSC-derived Mks, and that the Jak/STAT pathway is essential for the activation of IFI16 by both TPO and IFN-??. Of biological significance, IFI16 was found to regulate both the proliferation and differentiation of primary Mks, suggesting that IFI16 may control the balance between these two essential processes. In conclusion, the data in this thesis presents a novel mechanism through which Fli-1 and GATA-1 regulate the synergistic activation of Mk genes. The identification and functional characterisation of a novel TPO-inducible gene, IFI16, involved in regulating the proliferation and differentiation of Mks is also described. These findings have implications for several congenital and malignant conditions affecting Mk and platelet development, and possibly a mechanism for IFN-induced thrombocytopaenia.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: John L. Brash. Includes bibliographical references. Also available online.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2007. / Härtill 4 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2002. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 6 uppsatser.

Diss. (sammanfattning) Stockholm : Karol inst., 2003. / Härtill 5 uppsatser.