Expression of endoglin in choroidal neovascularization.

Endoglin (CD105) is a membrane protein involved in the TGF-beta receptor signalling pathway with predominant expression by proliferating endothelial cells. The aim of this study is to analyze the expression of Endoglin in choroidal neovascularization membranes (CNVM) and to compare it to the overall proliferative status of CNVM. Thirty surgically excised CNVM, secondary to age-related macular degeneration, were investigated using light microscopic immunohistochemistry and confocal immunofluorescence microscopy using verified antibodies directed against the endothelial cell markers Endoglin, von Willebrand factor (vWF) and CD34 and the proliferation marker Ki-67. Donor eyes were used as controls. A selective expression of CD34 and vWF as well as Endoglin was found in endothelial cells. Endoglin expression was elevated in vascular endothelial cells contained within CNVM, but a moderate Endoglin expression could also be visualized in quiescent CD34 and vWF positive ocular vasculature. Ki-67 positive cells were detected in CNVM, but these were rarely endothelial cells. Endoglin expression in endothelial cells of CNVM is increased, but rarely associated with a concomitant expression of the proliferation marker Ki-67. The elevated expression of Endoglin in surgically excised CNVM suggests a persisting post-mitotic activation in an advanced stage of this neovascular tissue.