Molecular Regulation of Angiogenesis

Abstract: Angiogenesis, de novo formation of blood vessels from the pre-existing vasculature, is crucial in embryo development, and in processes in the adult such as wound healing and ovulation. Angiogenesis is also involved in pathological conditions such as cancer and chronic inflammatory diseases, which are propagated by dysregulated, excess angiogenesis. On the other hand, lack of functional vessels and poor blood flow is a major problem in myocardial and peripheral ischemia. A detailed understanding of the molecular mechanisms underlying angiogenesis is of vital importance for the development of drugs to regulate angiogenesis. The aim of this thesis has been to identify genes involved in regulation of angiogenesis.We have investigated gene expression over time in endothelial cells (ECs), using different in vitro models. We show that the proteoglycan endocan is upregulated in ECs invading a fibrin matrix in response to vascular endothelial growth factor (VEGF)-A. There was increased expression of endocan in renal tumour cells and tumour vessels compared to normal renal tissues, indicating that endocan might have a role in tumour growth and tumour angiogenesis.We also show that vascular endothelial protein tyrosine phosphatase (VE-PTP) is induced in ECs during differentiation into vessel structures in a three dimensional collagen matrix. Silencing of VE-PTP disrupts vessel formation and increases the activity of VEGF receptor-2 (VEGFR-2) and downstream signalling, leading to increased EC proliferation. This presents a possible mechanism for the failure of vessel formation, as EC morphogenesis requires growth arrest of the cells. We also show that VE-PTP and VEGFR-2 are closely associated in resting ECs. VEGF-A stimulation leads to rapid loss of association, coinciding with increased phosphorylation of VEGFR-2.The function of VE-PTP in vivo was investigated using the zebrafish model. We demonstrate specific expression of a zebrafish VE-PTP orthologue (zVE-PTP) in the developing vasculature. Silencing of zVE-PTP leads to defective vessel sprouting and branching, indicating a critical role for zVE-PTP in development of the zebrafish vasculature.In conclusion, this thesis presents gene regulation during endothelial cell morphogenesis and details the expression pattern of endocan and the function of VE-PTP in regulation of VEGFR-2-driven angiogenesis.