ABSTRACT
Capillary tube or lumen formation subsequently results in the completion of capillary sprouts and loops and the envelopment of capillaries with new basement membrane structures along with recruitment of perivascular support cells, such as pericytes. Tip cells are crucial to completing this process as they fuse with other tip cells to create a fused (linked) network of capillaries. Pericytes (a single layer of periendothelial smooth muscle cells) modulate endothelial cell function, and are therefore crucial for the development of a mature vascular network. Pericytes regulate vascular function, including vessel diameter (and thus blood flow) and vascular permeability (Gerhardt and Betsholtz 2003). They also provide mechanical support and stability to the vascular wall and maintain endothelial cell survival through direct cell-cell contact and paracrine circuits (Reinmuth et al. 2001; Gerhardt and Betsholtz 2003). While the role of COX and LOX signaling in this angiogenic process has not been well investigated, COX-2 has been shown to regulate a number of molecules involved in the participation of pericytes and vascular mural cells (VMC) in developing vessels. These include platelet-derived growth factor (a key mediator of endothelial-VMC interaction) and CXCR4, which functions in homing of vascular progenitor cells to sites of active angiogenesis (Nagatsuka et al. 2002; Salcedo et al. 2003).
