Epithelial membrane protein-2 in human proliferative vitreoretinopathy and epiretinal membranes

Retina Epithelial Membrane Protein-2 in Human Proliferative Vitreoretinopathy and Epiretinal Membranes David G. Telander, 1 Alfred K. Yu, 1 Krisztina I. Forward, 1 Shawn A. Morales, 2 Lawrence S. Morse, 1 Susanna S. Park, 1 and Lynn K. Gordon 2 Department of Ophthalmology, University of California, Davis, Sacramento, California, United States Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, Los Angeles, California, United States Correspondence: David G. Telander, 3939 J Street, Suite 106, Sacramento, CA 95819, USA; dgtelander@ucdavis.edu. Submitted: July 26, 2015 Accepted: February 29, 2016 Citation: Telander DG, Yu AK, For- ward KI, et al. Epithelial membrane protein-2 in human proliferative vitre- oretinopathy and epiretinal mem- branes. Invest Ophthalmol Vis Sci. 2016;57:3112–3117. DOI:10.1167/ iovs.15-17791 P URPOSE . 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. M ETHODS . 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. R ESULTS . 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 ¼ 0.07) and PP (2.08 vs. 1.54; P ¼ 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 ¼ 6) tested. C ONCLUSIONS . 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. Keywords: proliferative vitreoretinopathy, epithelial membrane protein-2, EMP2, retinal pigment epithelium, fibrosis, retinal detachment, therapy, epiretinal membrane P roliferative vitreoretinopathy (PVR) is the most frequent cause of recurrent retinal detachment following surgical repair, which has been reported to occur in up to 10% of cases. 1,2 Ocular trauma increases the risk of developing PVR, with rates of up to 43% following ocular perforation. 3 Many risk factors for PVR have been identified including vitreous hemorrhage, severe trauma, longstanding retinal detachments, extensive retinal detachments, the use of intraocular tamponade such as gas during surgery, extensive use of cryotherapy or photocoagulation, and surgical failures. 1,2 The extent of ocular/retinal damage most likely causes increased inflammation and cytokine production, inducing an increase in PVR. Many cytokines such as IL-1, IL-6, IL-8, TNF-a, IFN-c, and monocyte chemoattractant protein-1 (MCP-1) are increased in eyes with PVR; however, the level of cytokine production has not been found to directly correlate with PVR severity. 4 The pathogenesis of PVR is complex, and the retinal pigment epithelium (RPE) cells have been implicated as one of the several cell types that play a key role in disease pathogenesis. 5 Following trauma or retinal detachment, RPE cells are released into the vitreous, or these cells can be stimulated to migrate to the vitreous from their subretinal location. These RPE cells can then proliferate, de-differentiate, and undergo an epithelial to mesenchymal transformation (EMT), to help create the preretinal membranes of PVR. 4 The RPE cells also likely cause membrane contraction and tractional forces that can result in recurrent retinal detachments and vision loss. 2,6 Prevention of membrane growth and contraction is a principal goal in inhibiting the PVR response. In an in vitro experimental PVR model, we have demonstrated that the activation of focal adhesion kinase (FAK) through ligation of integrins (a1, a2, and a3) is a crucial control point for collagen gel contraction. 7 The tetraspan (4-TM) superfamily is a class of proteins that controls the types of intracellular trafficking and signaling molecules assembled with integrins and other receptor complexes. 8 Our laboratory has found that epithelial membrane protein-2 (EMP2), a member of this 4-TM family, regulates specific integrin distribution and signaling though FAK. 9 Epithelial membrane protein is highly expressed in RPE 10 and is a member of the growth arrest–specific gene 3/ peripheral myelin protein 22 (GAS3/PMP22) 4-TM protein family. 10–16 Therefore, as EMP2 is a regulator of integrins, and iovs.arvojournals.org j ISSN: 1552-5783 This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License. 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