Peroxynitrite Mediates Retinal Neurodegeneration by Inhibiting Nerve Growth Factor Survival Signaling: An Approach for Experimental and Human Diabetes

Objective: We have discovered that oxidative stress and peroxynitrite are positively correlated with diabetes-induced retinal neurodegeneration. Peroxynitrite also inhibits nerve growth factor (NGF) survival signalling in sensory neurons, according to studies. However, the relevance of peroxynitrite in diabetes-induced retinal neurodegeneration and NGF survival signalling, as well as the influence of tyrosine nitration, remain unknown. Research Design and Methods: The expression of NGF and its receptors was studied in human and streptozotocin-induced diabetic rats retinas, as well as retinal ganglion cells (RGCs). FeTPPS (15 mg • kg1 • day1 ip) was given to diabetic animals, which catalytically decomposes peroxynitrite to nitrate.TUNEL assay was used to determine retinal cell death after 4 weeks of diabetes. MDA assay, immunofluorescence, and Slot-Blot analysis were used to determine lipid peroxidation and nitrotyrosine.The enzyme-linked immunosorbent assay (ELISA), real-time PCR, immunoprecipitation, and Western blot analyses were used to determine the expression of NGF and its receptors. Results: In diabetic retinas, analyses of retinal neuronal mortality and NGF revealed ninefold and twofold increases, respectively, when compared to controls. In human and rat retinas, diabetes increased lipid peroxidation, nitrotyrosine, and the pro-apoptotic p75NTR receptor. These effects were linked to tyrosine nitration of the pro-survival TrkA receptor, which resulted in TrkA and its downstream target, Akt, being phosphorylated less. Furthermore, even in the presence of exogenous NGF, peroxynitrite caused neuronal death, TrkA nitration, and p38 mitogen-activated protein kinase (MAPK) activation in RGCs. In vitro and in vivo, FeTPPS reduced tyrosine nitration, restored NGF survival signal, and prevented neuronal death. Conclusions: These findings imply that diabetes-induced peroxynitrite impairs NGF neuronal survival via nitrating the TrkA receptor and increasing the expression of the p75NTR.