Peroxynitrite Mediates Retinal Neurodegeneration by Inhibiting Nerve Growth Factor Survival Signaling in Experimental and Human Diabetes

Abstract

OBJECTIVE-Recently we have shown that diabetes-induced retinal neurodegeneration positively correlates with oxidative stress and peroxynitrite. Studies also show that peroxynitrite impairs nerve growth factor (NGF) survival signaling in sensory neurons. However, the causal role of peroxynitrite and the impact of tyrosine nitration on diabetes-induced retinal neurodegeneration and NGF survival signaling have not been elucidated. RESEARCH DESIGN AND METHODS-Expression of NGFand its receptors was examined in retinas from human and streptozotocin-induced diabetic rats and retinal ganglion cells (RGCs). Diabetic animals were treated with FeTPPS (15 mg ⅐ kg Ϫ1 ⅐ day Ϫ1 ip), which catalytically decomposes peroxynitrite to nitrate. After 4 weeks of diabetes, retinal cell death was determined by TUNEL assay. Lipid peroxidation and nitrotyrosine were determined using MDA assay, immunofluorescence, and Slot-Blot analysis. Expression of NGF and its receptors was determined by enzyme-linked immunosorbent assay (ELISA), real-time PCR, immunoprecipitation, and Western blot analyses.RESULTS-Analyses of retinal neuronal death and NGF showed ninefold and twofold increases, respectively, in diabetic retinas compared with controls. Diabetes also induced increases in lipid peroxidation, nitrotyrosine, and the pro-apoptotic p75 NTR receptor in human and rat retinas. These effects were associated with tyrosine nitration of the pro-survival TrkA receptor, resulting in diminished phosphorylation of TrkA and its downstream target, Akt. Furthermore, peroxynitrite induced neuronal death, TrkA nitration, and activation of p38 mitogen-activated protein kinase (MAPK) in RGCs, even in the presence of exogenous NGF. FeTPPS prevented tyrosine nitration, restored NGF survival signal, and prevented neuronal death in vitro and in vivo. CONCLUSIONS-Together

Diabetes-induced peroxynitrite impairs the balance of pro-nerve growth factor and nerve growth factor, and causes neurovascular injury

“…Treatment with atorvastatin had no effect on body weight or blood glucose levels in diabetic rats (27.3 mmol/l) or in treated controls (9.1 mmol/l). As shown before, treatment with FeTPPs had no effect on body weight or blood glucose levels in diabetic rats [1].…”

“…However, we and others have reported paradoxical increases in levels of NGF despite neuronal death in clinical and experimental diabetic retinopathy [1,6,7]. Our recent study described a mechanism of peroxynitrite-induced impairment of NGF signal via tyrosine nitration of tyrosine receptor kinase A (TrkA), the NGF survival receptor, and upregulation of p75 NTR (NTR is also known as NGFR), the neurotrophin receptor, causing retinal neurodegeneration in clinical and experimental diabetes [1].…”

“…Human vitreous samples were kept refrigerated and retinas were snap-frozen for further analyses. Demographics and retinal pathology of post mortem samples were recently published by our group [1].…”

“…These changes lead to accelerated cell death within the inner retinal and ganglion cells [1][2][3] and blood-retinal barrier (BRB) breakdown resulting in macular oedema and neovascularisation [4]. Clinically, the disease manifests as diabetic retinopathy and eventually leads to impaired vision.…”

“…The molecular link between two well-documented early hallmarks of diabetic retinopathy, i.e. accelerated neuronal death and vascular permeability, remains obscure [1][2][3][10][11][12][13]. While proinflammatory cytokines are known to activate Rho family kinases leading to actin cytoskeleton rearrangement and cell permeability in vasculature, Rho family members are also essential regulators of neuronal survival in the nervous system, as reviewed by Linseman and Loucks [14].…”