Difference in proangiogenic potential of systemic and pulmonary endothelium: Role of CXCR₂

The systemic vasculature in and surrounding the lung is proangiogenic, whereas the pulmonary vasculature rarely participates in neovascularization. We studied the effects of the proangiogenic ELR+ CXC chemokine MIP-2 (macrophage inflammatory protein-2) on endothelial cell proliferation and chemotaxis. Mouse aortic, pulmonary arterial, and lung microvascular endothelial cells were isolated and subcultured. Proliferation ([³H]thymidine uptake) and migration (Transwell chemotaxis) were evaluated in each cell type at baseline and upon exposure to MIP-2 (1-100 ng/ml) without and with exposure to hypoxia (24 h)-reoxygenation. Baseline proliferation did not vary among cell types, and all cells showed increased proliferation after MIP-2. Aortic cell chemotaxis increased markedly upon exposure to MIP-2; however, neither pulmonary artery nor lung microvascular endothelial cells responded to this chemokine. Assessment of CXCR₂, the G protein-coupled receptor through which MIP-2 signals, displayed no baseline difference in mRNA, protein, or cell surface expression among cell types. Exposure to hypoxia increased expression of CXCR₂ of aortic endothelial cells only. Additionally, aortic cells, compared with pulmonary cells, showed significantly greater protein and activity of cathepsin S, a proteolytic enzyme important for cell motility. Thus the combined effects of increased cathepsin S activity, providing increased motility and enhanced CXCR₂ expression after hypoxia, both contribute to the proangiogenic phenotype of systemic arterial endothelial cells.