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Jelena Marie Kezic, Xiangting Chen, Elizabeth P. Rakoczy, Paul G. McMenamin; The Effects of Age and Cx3cr1 Deficiency on Retinal Microglia in the Ins2Akita Diabetic Mouse. Invest. Ophthalmol. Vis. Sci. 2013;54(1):854-863. doi: 10.1167/iovs.12-10876.
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Diabetic retinopathy (DR) is a major cause of visual impairment in developed countries. While DR has been described classically as a microvascular disease, recent evidence suggests that changes to retinal microglia are an early feature of retinopathy. In our study, we assessed changes in microglial distribution and morphology in vivo and ex vivo in a mouse model of non-proliferative DR, and further examined effects of age and the absence of the functional chemokine receptor Cx3cr1 on the progression of these changes.
To isolate the effects of the three variables: diabetic status, age, and role of Cx3cr1, the Ins2Akita mouse was crossed with Cx3cr1-eGFP reporter mice. Eyes were assessed clinically in vivo at 10, 20, 30, and 46 weeks of age, and the retinal structure and arrangement of GFP+ microglia was examined ex vivo using whole mount immunofluorescence staining and confocal microscopy.
Clinical examination of the fundus, vasculature, or GFP+ microglial distribution did not reveal any macroscopic changes related to diabetic status: however, ex vivo microscopic analysis revealed alterations in microglial network organization, and evidence of cell shape changes regarded classically as signs of activation, in Ins2Akita mice from 10 weeks of age. These changes were exacerbated in older diabetic mice whose microglia lacked Cx3cr1 (Ins2Akita Cx3cr1gfp/gfp mice). Diabetic status and Cx3cr1 deficiency led to accumulations of Iba-1+ hyalocytes (vitreal macrophages) and subretinal macrophages.
These data showed that changes to murine retinal microglia occur in response to systemic diabetic status in the absence of overt retinopathy and inflammation. These changes are exaggerated in mice lacking Cx3cr1, suggesting fractalkine- Cx3cr1 interactions may have a role in early neuronal changes in preproliferative DR.
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