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Jeroen Bastiaans, Jan C van Meurs, Verena C Mulder, Petrus M Van Hagen, Herbert Hooijkaas, Willem A Dik; The role of thrombin in proliferative vitreoretinopathy. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1114.
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Proliferative vitreoretinopathy (PVR) is a difficult to treat inflammatory fibrotic disorder complicating retinal detachment. Understanding of the activating processes involved in PVR is still incomplete. Because breakdown of the outer blood-retinal barrier is one of the first events in PVR development we believe that coagulation proteins may be involved. In recently published studies we demonstrated that factor Xa and, more potently, thrombin induces the production of a broad panel of pro-inflammatory cytokines and growth factors by RPE. This resulted in the differentiation of RPE into a mesenchymal cell type via autocrine PDGF-R signaling. In our current study we demonstrate that thrombin activity is significantly higher in the vitreous of patients with established PVR compared to control groups. We also show that this vitreous contributes to PVR-associated changes in RPE cell behavior.
Thrombin activity in vitreous (macular pucker n=8, retinal detachment (no PVR development after 3 months) n=15, retinal detachment (PVR development after 3months) n=11 and established PVR n=14) was determined with a thrombin-specific substrate (Tos-Gly-Pro-Arg-pNA) in the absence/presence of hirudin, a direct thrombin-inhibitor. RPE cells were cultured with vitreous or thrombin (5 U/ml) in the absence/presence of hirudin. Changes in cytokine and growth factor expression levels were determined by RQ-PCR. Proliferation of RPE was determined with the MTT assay.
Thrombin activity was significantly (P < 0.05) higher in vitreous of patients with established PVR compared to all other groups. RPE cells cultured with vitreous of PVR patients showed significantly (P < 0.05) higher mRNA expression levels of cytokines and growth factors like IL6, IL8, PDGFA and PDGFB, compared to control groups. All increased expression levels of cytokines and growth factors were significantly (P < 0.05) inhibited by hirudin. Vitreous from all groups did not affect RPE proliferation.
Our data clearly imply involvement of thrombin in PVR pathology via activation of pro-inflammatory and pro-fibrotic pathways in RPE. The effects of the vitreous on RPE can be inhibited with a direct thrombin-inhibitor. These data demonstrate that thrombin may therefore be an interesting therapeutic target in the prevention of PVR development.
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