Epithelial Membrane Protein-2 in Human Proliferative Vitreoretinopathy and Epiretinal Membranes

Abstract

Purpose: To determine the level of epithelial membrane protein-2 (EMP2) expression in preretinal membranes from surgical patients with proliferative vitreoretinopathy (PVR) or epiretinal membranes (ERMs). EMP2, an integrin regulator, is expressed in the retinal pigment epithelium and understanding EMP2 expression in human retinal disease may help determine whether EMP2 is a potential therapeutic target.

Methods: Preretinal membranes were collected during surgical vitrectomies after obtaining consents. The membranes were fixed, processed, sectioned, and protein expression of EMP2 was evaluated by immunohistochemistry. The staining intensity (SI) and percentage of positive cells (PP) in membranes were compared by masked observers. Membranes were categorized by their cause and type including inflammatory and traumatic.

Results: All of the membranes stained positive for EMP2. Proliferative vitreoretinopathy-induced membranes (all causes) showed greater expression of EMP2 than ERMs with higher SI (1.81 vs. 1.38; P = 0.07) and PP (2.08 vs. 1.54; P = 0.09). However all the PVR subgroups had similar levels of EMP2 expression without statistically significant differences by Kruskal-Wallis test. Inflammatory PVR had higher expression of EMP2 than ERMs (SI of 2.58 vs. 1.38); however, this was not statistically significant. No correlation was found between duration of PVR membrane and EMP2 expression. EMP2 was detected by RT-PCR in all samples (n = 6) tested.

Conclusions: All studied ERMs and PVR membranes express EMP2. Levels of EMP2 trended higher in all PVR subgroups than in ERMs, especially in inflammatory and traumatic PVR. Future studies are needed to determine the role of EMP2 in the pathogenesis and treatment of various retinal conditions including PVR.

Figure 1

Immunohistochemistry showing EMP2 staining at ×40 (violet) in two examples of PVR (A, B) with nuclear counterstaining (blue). Bottom row shows positive and negative controls for comparison.

Figure 2

Examples of EMP2 staining (violet) in PVR and ERM surgical specimens. Top row demonstrates increasing EMP2 staining with increased PVR membrane formation. Middle row shows increased EMP2 staining in traumatic PVR. Bottom row shows moderate EMP2 staining in spontaneous ERMs.

Figure 3

Scoring of PVR and epiretinal membranes graded by four masked observers for EMP2 SI and PP as described in the Materials and Methods. EMP2 staining was found to be higher in PVR samples than in ERM patients.

Figure 4

Scoring of PVR membranes for EMP2 SI and PP as described in the Materials and Methods. EMP2 was found to be higher in PVR associated with retinal detachments with inflammation (e.g., endophthalmitis, uveitis). The difference between groups was not found to be statistically significant by Kruskal-Wallis test.

Figure 5

Increased EMP2 staining was not found to be associated with age or duration of PVR or ERM. Here EMP2 staining (SI and PP) is plotted versus the age of the patient with ERM or PVR. No significant trend for duration of PVR and EMP2 expression was found by regression analysis with an R² coefficient of 0.008 (SI) and 0.013 (PP). Regression analysis of age and EMP2 expression also showed no significant correlation with an R² coefficient of 0.021 (SI) and 0.0006 (PP).

Figure 6

Tissue samples from PVR surgery were used to isolate mRNA and test for EMP2 mRNA by RT-PCR. All samples tested were found to have significantly high copy number of mRNA for EMP2. The cell line ARPE-19, which is known to express EMP2, was used as a positive control.