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Andrew S Mendiola, Sandra M Cardona, Andrew T C Tsin, Astrid E Cardona; Role of fractalkine receptor (CX3CR1) in microglial mediated inflammation in the Diabetic Retina. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2251.
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© ARVO (1962-2015); The Authors (2016-present)
Diabetic retinopathy (DR) is the leading cause of blindness in working Americans and a common complication of diabetes mellitus. Resident microglia can play detrimental and protective roles during CNS inflammation. Previous data from our laboratory showed that in the normal CNS the fractalkine receptor (CX3CR1) inhibits microglia activation and neurotoxicity. Although it is reported that microglia increase in number and release TNF-α and VEGF in the diabetic retina, the contribution of CX3CR1 in microglial activation and neuronal cell loss during DR is unclear. We hypothesize that CX3CR1 deficiency in resident microglia cells exacerbates activation signaling and promotes an inflammatory milieu that leads to neuronal and vascular damage associated with early stage DR.
Ins2Akita mice have a point mutation in the insulin2 gene causing protein misfolding and loss of pancreatic β-cells, which results in hyperglycemia by 4 weeks of age. These mice were crossed with CX3CR1-deficient mice on a C57BL/6 background to generate diabetic wildtype (Ins2Akita-WT) and CX3CR1 deficient-mice (Ins2Akita-KO). Whole retinas isolated from 10-week old diabetic and non-diabetic mice were assayed for: fractalkine production, immunohistochemical analysis to evaluate microglia phenotype and retina pathology using confocal microscopy, and in vitro production of nitric oxide levels upon different stimuli utilizing the Griess assay.
Our data showed a significant increase in the number of retinal microglia cells in diabetic and non-diabetic CX3CR1 deficient mice (CX3CR1-KO) in comparison to age-matched CX3CR1 wild type mice. Conversely, fractalkine levels were decreased in the diabetic mouse retina. Our in vitro studies revealed that retinal microglia are responsive to LPS, IFN-γ and PolyIC stimulation. In addition, CX3CR1-deficient mice showed significantly increased microglia cell roundness, suggesting an activated state. Whereas nitric oxide levels in the culture media were decreased in the retina of CX3CR1 heterozygotes.
These data suggest that the absence of CX3CR1 in hyperglycemia promotes an environment that leads to the proliferation and activation of resident microglia, which may contribute to the pathology of early DR.
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