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Steven F. Abcouwer, Sumathi Shanmugam, Cheng-mao Lin; Microgliosis and Macrophage Infiltration Coincides with Retinal Apoptosis in Ischemic and Diabetic Retinas. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1860.
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© ARVO (1962-2015); The Authors (2016-present)
Microglia comprise the innate immune system of the retina. In response to neurodegeneration microglia adopt an altered phenotype that affords phagocytic clearance of apoptotic neurons. A morphological alteration of microglia from a highly ramified to a more amoeboid shape is observed during diabetic retinopathy (DR). We utilized flow cytometric analysis of dissociated retinal cells to examine microgliosis and infiltration of monocytic cells into retinas of streptozotocin (STZ)-induced diabetic rats and rat retinas subjected to ischemia-reperfusion (IR) injury, as an acute model of retinal neurodegeneration.
Retinas were enzymatically dissociated and cells analyzed for expression of the monocytic markers CD11b and CD45, MHC class II antigen, and granularity by flow cytometry. Retinal cell apoptosis was assayed using the Roche Cell Death Detection ELISA to measure internucleosomal DNA cleavage.
IR injury caused retinal cell death as indicated by DNA fragmentation. IR produced a marked increase in CD45 expression of CD11b+/CD45low microglia, indicative of their activation. IR also caused an increase in the number of CD11b+/CD45high macrophage cells in the retina. MHC class II expression and granularity increased in microglia following IR, suggesting increased phagocytic activity. Retinal microglia in rats experiencing 6 weeks of diabetes exhibited qualitatively similar, but lesser, increases in CD45 expression, MHC class II expression and granularity. Pretreatment with the α2 adrenergic receptor (α2AR) agonist, brimonidine, effectively inhibited cell death, coinciding with a pronounced inhibition of the increase in CD45 expression, MHC class II expression and granularity of retinal microglia. Guanfacine, an α2AR agonist highly selective for the α2A receptor subtype, also significantly inhibited cell death, microglial CD45 expression, MHC class II expression and granularity following retinal IR.
Flow cytometric analysis allowed the direct quantitative measurement of retinal microgliosis and macrophage infiltration. DR caused less microgliosis and macrophage infiltration than did IR, in keeping with the diminished rate of neurodegeneration in the chronic diabetic condition compared to the pronounced acute neurodegeneration caused by ischemia. Activation of the α2A subtype of the α2AR effectively prevented retinal neurodegeneration and microgliosis following IR.
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