Role of TEM7 in Neovascular Endothelial Cells of Fibrovascular Membranes From Patients With Proliferative Diabetic Retinopathy

Abstract

Purpose: : Proliferative diabetic retinopathy (PDR) results from the formation of fibrovascular membranes (FVMs) in the posterior fundus that can lead to a severe decrease of vision. Tumor endothelial marker 7 (TEM7) is a protein that is highly expressed in the endothelial cells of tumors, but whether it plays a role in FVMs is not known. The purpose of this study was to determine whether TEM7 is associated with the formation of FVMs.

Methods: : FVMs were obtained during vitrectomy from patients with PDR. RT-PCR was performed to determine the level of expression of the mRNA of TEM7. The splice variants of TEM7 were identified by direct sequencing. Immunohistochemical analyses and in situ hybridization was performed to determine the sites of TEM7 in the FVMs.

Results: : The level of the mRNA of TEM7 was high in 10 of 10 FVMs, but barely detectable in the 5 idiopathic epiretinal membranes (ERMs). Direct sequencing of subcloned TEM7 PCR products revealed several splice variants (intracellular, secreted, and membrane-bound forms of TEM7) in the FVMs. Immunohistochemical analysis showed co-localization of TEM7 and CD34, an endothelial cell marker, in most of the neovascular endothelial cells in the FVMs. Immunoelectron microscopy revealed that membrane-bound TEM7 was expressed on the luminal surface of the vascular endothelial cells of FVMs.

Conclusions: : Our study indicates that TEM7 may play a significant role in the proliferation and maintenance of neovascular endothelial cells in the FVMs. If correct, then TEM7 may be a molecular target for new diagnostic and therapeutic strategies for PDR.

Keywords: diabetic retinopathy • neovascularization • gene/expression