Potential Role for Epithelial Membrane Protein 2 (EMP2) in Proliferative Vitreoretinopathy

Abstract

Abstract: : Purpose:Proliferative vitreoretinopathy (PVR) is believed to result in part from de–differentiation of retinal pigment epithelium (RPE) with cellular migration into the vitreous cavity, membrane formation, and contraction in an aberrant wound–healing strategy. Specific a and b integrin subunits are implicated in both cell adhesion and migration of RPE and are believed to play a critical role in PVR. Epithelial membrane protein 2 (EMP2), a four transmembrane protein, controls recruitment and cell surface delivery of specific integrin isoforms in the RPE cell line ARPE–19. The purpose of this study was to investigate the role of EMP–2 expression in PVR. Methods:ARPE–19 cell line was obtained from the ATCC, and the levels of EMP2 modulated through stable transfections of an EMP–2 overexpressing construct, EMP2 ribozyme, or vector alone. Expression of EMP2 was quantified and validated using Western blot. An in vitro gel contraction assay was used in which RPE cells were seeded on a collagen gel and the percent of gel contraction was measured after 48 hours in culture. Measurement of the gel size was obtained using image capture (Gel Doc) and quantified using NIH Image software. These stable transfectant cell lines were also used in a rabbit model of PVR. Results: In the gel contraction studies, reduction of EMP2 expression by use of the ribozyme was associated with a significant increase in contraction (P = 0.01). No significant change was noted using the cell line which overexpressed EMP2, although there was a trend towards decreased contraction. Pilot experiments indicate that EMP2 overexpression allows PVR development at similar rates to vector–controls, similar to the in vitro contraction result. Conclusions:Reduction of EMP2 expression induces an increase in gel contraction by cultured ARPE–19 cells. In contrast, overexpression of EMP2 in this cell line was associated with decreased contraction, implying a potential role for EMP2 in controlling physiologically–relevant RPE behavior. These results validate the potential for controlling RPE biology through a change in EMP2 expression. Additional studies are designed to further elucidate the role of EMP2 in PVR.

Keywords: proliferative vitreoretinopathy • retinal pigment epithelium • protein structure/function