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Nivetha Murugesan, Allen C Clermont, LeiLei Sun, Edward P Feener; Proteomic characterization of retinal edema in rats. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):4693.
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© ARVO (1962-2015); The Authors (2016-present)
Diabetic macular edema (DME) is a leading cause of vision loss in diabetic patients. Recent findings have implicated the role of plasma kallikrein kinin system in DME. We have previously shown that up-regulation of this system induces retinal edema in rodents. The goal of this work is to characterize the proteome and ultrastructure of retinal edema in bradykinin-induced retinal edema in rats.
Sprague-Dawley rats received intravitreal (IVT) injections of 2 μM bradykinin (BK), 10ng VEGF, or saline (PBS). The time course of changes in retinal thickness and ultrastructural were quantified over a time course of 5 days using spectral domain optical coherence tomography (OCT). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis was performed on retinal samples harvested 24hrs after IVT injection.
BK and VEGF similarly increased retinal thickening by 46 μm (24.6%) vs. 39 μm (20.3%), respectively (p<0.01 vs. baseline) at 24 hours post IVT injection, and retinal thicknesses normalized at day 4. 1424 proteins were identified from LC-MS/MS analysis of BK vs. PBS treated retina. Retina with BK-induced thickening contained 2 to 10-fold (p<0.05) increases in plasma proteins, including haptoglobin, complement C3, C-reactive protein, albumin, hemopexin, antitrypsin, α2macroglobulin, and kininogen1, and striking decreases in vimentin, lamin, spectrin, and glial fibrillary acidic protein, while most intracellular retinal proteins remained unchanged. Peptide counts for a subset of plasma proteins correlated (R2>0.72) with BK-induced retinal thickening OCT data for each animal, suggesting plasma protein extravasation and intermediate filament remodeling contributed to retinal edema. BK also decreased neuroretinal proteins associated with neuroprotection, including astrocytic phosphoprotein PEA-15 (0.541 fold, p= 0.017) and glutathione S-transferase (0.545, p=0.049) and increased levels of synaptogyrin1 (2.86 fold, p=0.041).
Bradykinin and VEGF similarly increased retinal thickness, which was maximal at 24hrs post IVT. Retinal thickening is associated with increased levels of a subset of proinflammatory plasma proteins. Moreover, retinal thickening was characterized with reduced levels of proteins involved in neuroprotection and intermediate filaments. Characterization of the retinal proteome in rats with BK and VEGF-induced retinal thickening identifies changes that may contribute to neuronal dysfunction and edema.
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