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UBC Theses and Dissertations

The structural and functional importance of the CD34 family in lung function and vascular cell biology Debruin, Erin Jacquelyn Frohwerk


Despite the widespread use of CD34-family sialomucins (CD34, podocalyxin (Podxl) and endoglycan) as vascular endothelial cell (EC) markers, there is remarkably little known of their role in vascular development and functions with the exception of vessel lumen formation in the developing mouse embryo (Podxl) and vessel patency during tumor angiogenesis and inflammation (CD34). Because germ-line deletion of Podxl in mice causes perinatal death, we generated mice that conditionally delete Podxl in vascular endothelial cells (PodxlΔEC mice) to study the role of podocalyxin in adult mouse vessels. Although PodxlΔEC adult mice are viable and thrive, we discovered increased basal and inflammationinduced pulmonary vascular permeability. Furthermore, PodxlΔEC mouse adult lungs display airspace enlargement with increased collagen deposition and exhibit a gene expression profile similar to regenerating lung. To study whether endothelial cell morphology influences the defective lung architecture and the vascular permeability phenotype in PodxlΔEC mice, we isolated primary vascular ECs from lung tissue. PodxlΔEC ECs display enhanced adhesion to fibronectin (FN) in a static adhesion assay. When plated on matrix-coated transwells, PodxlΔEC EC spread normally on FN but display defective spreading on laminin and collagen I. Thus, expression of Podxl in EC is required for normal lung architecture and function in adult mice and adhesion of EC to extracellular matrix components. Although its expression has not been well characterized, in humans, endoglycan expression has been reported in vascularized tissues. In mouse blood vessels, we showed that vascular smooth muscle cells (vSMC), but not EC, express the highest levels of endoglycan. Using a mouse aortic smooth muscle line (MOVAS-1) we found that forced expression of endoglycan enhances basal but not platelet derived growth factor (PDGF)ββ-dependent vSMC migration in vitro. Further studies to understand the role of endoglycan in primary vSMC showed that endoglycan is upregulated with differentiation to a contractile phenotype, but is not influenced by inflammatory stimuli or mitogenic factors. The findings of this thesis suggest that the CD34 family regulates vascular development and function with a role for podocalyxin in EC-matrix adhesion relevant to normal lung function and a role for endoglycan in SMC differentiation and migration.

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