Neurotrophins and Neurotrophin Receptors in Proliferative Diabetic Retinopathy

Ahmed M Abu El-Asrar,Kathleen Van Den Eynde,Ghislain Opdenakker,Mohammad Mairaj Siddiquei,Gert De Hertogh,Ghulam Mohammad,Mohd Imtiaz Nawaz,Karel Geboes,Sofie Struyf,Michael E Boulton

doi:10.1371/journal.pone.0065472

Ahmed M Abu El-Asrar, Kathleen Van Den Eynde + Show 8 more

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https://doi.org/10.1371/journal.pone.0065472

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Abstract

Neurotrophins (NTs) are emerging as important mediators of angiogenesis and fibrosis. We investigated the expression of the NTs nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4) and their receptors TrkA, TrkB, and TrkC in proliferative diabetic retinopathy (PDR). As a comparison, we examined the expression of NTs and their receptors in the retinas of diabetic rats. Vitreous samples from 16 PDR and 15 nondiabetic patients were studied by Western blot analysis and enzyme-linked immunosorbent assay (ELISA). Epiretinal membranes from 17 patients with PDR were studied by immunohistochemistry. Rats were made diabetic with a single high dose of streptozotocin and retinas of rats were examined by Western blot analysis. Western blot analysis revealed a significant increase in the expression of NT-3 and NT-4 and the shedding of receptors TrkA and TrkB in vitreous samples from PDR patients compared to nondiabetic controls, whereas NGF and BDNF and the receptor TrkC were not detected with the use of Western blot analysis and ELISA. In epiretinal membranes, vascular endothelial cells and myofibroblasts expressed NT-3 and the receptors TrkA, TrkB and TrkC in situ, whereas NT-4 was not detected. The expression levels of NT-3 and NT-4 and the receptors TrkA and TrkB, both in intact and solubilized forms, were upregulated in the retinas of diabetic rats, whereas the receptor TrkC was not detected. Co-immunoprecipitation studies revealed binding between NT-3 and the receptors TrkA and TrkB in the retinas of diabetic rats. Our findings in diabetic eyes from humans and rats suggest that the increased expression levels within the NT-3 and NT-4/Trk axis are associated with the progression of PDR.

Highlights

Ischemia-induced retinal angiogenesis in association with the outgrowth of fibrovascular epiretinal membranes at the vitreoretinal interface is the pathological hallmark in proliferative diabetic retinopathy (PDR) and often leads to catastrophic loss of vision due to vitreous hemorrhage and/or traction retinal detachment
With the use of the Western blot analysis we demonstrated that NT-3, NT-4, TrkA, and TrkB were detected in all vitreous samples from patients with PDR and at lower levels in control patients without diabetes
With the use of enzyme-linked immunosorbent assay (ELISA), we confirmed that nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) were not detected in vitreous samples from patients with PDR and nondiabetic control patients

Summary

Introduction

Ischemia-induced retinal angiogenesis in association with the outgrowth of fibrovascular epiretinal membranes at the vitreoretinal interface is the pathological hallmark in proliferative diabetic retinopathy (PDR) and often leads to catastrophic loss of vision due to vitreous hemorrhage and/or traction retinal detachment. The key cellular mediator of fibrosis is the myofibroblast, a cell type differentiated form quiescent fibroblasts. Myofibroblasts are contractile cells, characterized by the expression of a-smooth muscle actin (a-SMA), and their presence is a marker of progressive disease. They have the capacity to produce several extracellular matrix components including collagens, and to induce fibrosis [2]. Previous studies have shown that a-SMAexpressing myofibroblasts are the principal cellular components of PDR epiretinal membranes [3]

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