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 es sential for vascular development and remodeling in the embryo but little is known regarding the regulation of their expression and their role in the m aintenance and repair of the adult vascular system. We examined the express ion of Tie1 and Tie2 in normal vessels and during reendothelialization foll owing balloon injury of the adult rat carotid artery. Tie proteins were det ected in quiescent endothelial cells of the adult rat carotid artery. Tiel and Tie2 proteins were also detected in human and rat platelets, A weak exp ression of Tiel and Tie2 proteins was detected in young endothelial cells w hich sparsely repopulated the denuded surface by day 14. Protein levels inc reased in the confluent layer of endothelial cells by day 28. Based on thes e observations, we tested whether Tiel and Tie2 mRNA and protein levels are regulated by cell density. Tie1 and Tie2 expression significantly increase d with higher density in cultured human endothelial cells, and this upregul ation 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.