Differential Expression of Epithelial Membrane Protein 2 in Human Epiretinal Membranes

Abstract

Purpose: : Epithelial Membrane Protein 2 (EMP2) is found in variety of different cell types and controls cell surface expression and function of specific integrin isoforms. We have previously shown that EMP2 expression correlates with proliferative vitreoretinopathy (PVR) formation. In animal models of PVR, blocked EMP2 expression leads to a reduction of PVR pre-retinal membranes. Our purpose in this study was to examine and compare EMP2 expression in pre-retinal membranes that are unassociated with other ocular problems (idiopathic) and those that are secondary to such causes as rhegmatogenous retinal detachment or trauma.

Methods: : Idiopathic and secondary epiretinal membranes were collected from patients during surgical pars plana vitrectomy with consent. The membranes were then fixed and processed for paraffin embedding. The membranes were then sectioned and protein expression of EMP2 was evaluated by immunohistochemical analysis. Two masked observers rated the intensity of staining and percentage of positive cells based on a previously described protocol.

Results: : EMP2 expression was found to vary in pre-retinal membranes of different etiologies. Two different types of pre-retinal membranes were compared: secondary epiretinal membranes (i.e. PVR) and idiopathic membranes. EMP2 protein expression was rated according to staining intensity and percentage of cells that stained. 100% of both secondary and idiopathic membranes expressed EMP2. The average staining intensity by masked observer was found to be significantly less in the idiopathic membranes scored at 1.03 than in the secondary membranes scored at 2.11. (p = 0.008). These secondary membranes were also found to have a significant higher percentage of positive cells with a score of 2.31 vs 1.55 for the idiopathic membranes (p = 0.04).

Conclusions: : EMP2 is highly expressed in pre-retinal membranes. EMP2 has increased expression in cases of secondary epiretinal membrane from PVR compared to idiopathic membranes. This increase can be seen both in staining intensity and the number of cells expressing EMP2, which is statistically significant. High expression of EMP2 in secondary membranes support future studies to determine if blockade of EMP2 could be of therapeutic benefit.

Keywords: proliferative vitreoretinopathy • immunohistochemistry • retinal pigment epithelium