Reduced nitro-oxidative stress and neural cell death suggests a protective role for microglial cells in TNFalpha-/- mice in ischemic retinopathy.
OBJECTIVE
Neovascularization occurs in response to tissue ischemia and growth factor stimulation. In ischemic retinopathies, however, new vessels fail to restore the hypoxic tissue; instead, they infiltrate the transparent vitreous. In a model of oxygen-induced retinopathy (OIR), TNFalpha and iNOS, upregulated in response to tissue ischemia, are cytotoxic and inhibit vascular repair. The aim of this study was to investigate the mechanism for this effect.


METHODS
Wild-type C57/BL6 (WT) and TNFalpha(-/-) mice were subjected to OIR by exposure to 75% oxygen (postnatal days 7-12). The retinas were removed during the hypoxic phase of the model. Retinal cell death was determined by TUNEL staining, and the microglial cells were quantified after Z-series capture with a confocal microscope. In situ peroxynitrite and superoxide were measured by using the fluorescent dyes DCF and DHE. iNOS, nitrotyrosine, and arginase were analyzed by real-time PCR, Western blot analysis, and activity determined by radiolabeled arginine conversion. Astrocyte coverage was examined after GFAP immunostaining.


RESULTS
The TNFalpha(-/-) animals displayed a significant reduction in TUNEL-positive apoptotic cells in the inner nuclear layer of the avascular retina compared with that in the WT control mice. The reduction coincided with enhanced astrocytic survival and an increase in microglial cells actively engaged in phagocytosing apoptotic debris that displayed low ROS, RNS, and NO production and high arginase activity.


CONCLUSIONS
Collectively, the results suggest that improved vascular recovery in the absence of TNFalpha is associated with enhanced astrocyte survival and that both phenomena are dependent on preservation of microglial cells that display an anti-inflammatory phenotype during the early ischemic phase of OIR.
Stevenson
Laura
L
Centre for Vision and Vascular Sciences, Queen's University Belfast, Belfast, Northern Ireland, United Kingdom.
Matesanz
Nuria
N
Colhoun
Liza
L
Edgar
Kevin
K
Devine
Adrian
A
Gardiner
Tom A
TA
McDonald
Denise M
DM
D000818:Animals; D017209:Apoptosis; D001119:Arginase / Q000378:metabolism; D015153:Blotting, Western; D002452:Cell Count; D016923:Cell Death; D002470:Cell Survival; D020287:In Situ Nick-End Labeling; D007511:Ischemia / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D017628:Microglia / Q000166:cytology*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D015538:Nitrosation; D018384:Oxidative Stress; D010100:Oxygen / Q000633:toxicity; D026361:Reactive Nitrogen Species / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D012164:Retinal Diseases / Q000378:metabolism* / Q000473:pathology; D055351:Retinal Neurons / Q000473:pathology*; D012171:Retinal Vessels / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
D026361:Reactive Nitrogen Species; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; C002744:3-nitrotyrosine; D014443:Tyrosine; D052247:Nitric Oxide Synthase Type II; C496317:Nos2 protein, mouse; D001119:Arginase; D010100:Oxygen