Neuronal degeneration and associated alterations in cytokine and protein in an experimental branch retinal venous occlusion model

Abstract

The mechanisms of neuronal degeneration and associated acute alterations in intraretinal cytokine and protein levels remain poorly understood in variable ischaemic retinopathies such as in branch retinal vein occlusion (BRVO). Herein we investigate neuronal damage and alterations in retinal cytokines and proteins in a pig model of acute BRVO. Twelve pigs had a BRVO induced photothrombotically in both eyes. Three pigs (6 eyes) each at 2, 6, 10 and 20 days were sacrificed together with an additional 3 control (6 eyes), enucleated, retinas dissected and processed. Apoptosis in the inner retina was determined by terminal deoxyynuclotidyl transferase mediated dUTP nick end labelling (TUNEL) and histology. Expression of glial acidic fibrillary protein (GFAP), aquaporin-4 (AQP4), inward rectifier potassium channel 10 protein (Kir 4.1) encoded by KCNJ10 gene, vascular endothelial growth factor (VEGF), stromal derived growth factor-1α (SDF-1) encoded by CXCL12 gene and interleukin (IL) −6 and 8 were analysed by quantitative reverse transcription polymerase chain reaction (RT-qPCR) and immunohistochemistry. TUNEL labelling showed positive nuclei in the ganglion cell layer (GCL) and the inner nuclear layer (INL) which was significantly higher at 2 days after BRVO compared to other time points (p < 0.05). Analysis by RT-qPCR revealed that compared with controls, BRVO significantly increased mRNA expression of GFAP at 6, 10 and 20, AQP4 at 20, VEGF at 6, SDF-1 at 20 and IL-8 at 2 and 10 days respectively (p < 0.05): Kir 4.1 at 6, VEGF at 2 and 10, and IL-6 at 2 days were significantly decreased (p < 0.05). This study indicates that neural cell death occurs early in this acute model and the responses include inflammation and breakdown of osmohomeostasis as evidenced by the upregulation of GFAP and IL-8 and down regulation of Kir 4.1 associated with glyotic changes. Early short term VEGF upregulation seen may be related to involvement of Muller glial cells. These findings support the development of acute therapeutic strategies aimed at preservation of retinal neural cells as part of an overall management plan for BRVO.