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Expression of Tie1 and Tie2 Proteins during Reendothelialization in Balloon-Injured Rat Carotid Artery

The novel endothelial cell tyrosine kinase receptors, Tie1 and Tie2, are essential for vascular development and remodeling in the embryo but little is known regarding the regulation of their expression and their role in the maintenance and repair of the adult vascular system. We examined the expression of Tie1 and Tie2 in normal vessels and during reendothelialization following balloon injury of the adult rat carotid artery. Tie proteins were detected in quiescent endothelial cells of the adult rat carotid artery. Tie1 and Tie2 proteins were also detected in human and rat platelets. A weak expression of Tie1 and Tie2 proteins was detected in young endothelial cells which sparsely repopulated the denuded surface by day 14. Protein levels increased in the confluent layer of endothelial cells by day 28. Based on these observations, we tested whether Tie1 and Tie2 mRNA and protein levels are regulated by cell density. Tie1 and Tie2 expression significantly increased with higher density in cultured human endothelial cells, and this upregulation required cell-cell interaction. These data suggest that Tie1 and Tie2 may play a role in the maintenance and repair of the adult vascular system and that the expression of these proteins is regulated by cell density.