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K. T. Breen, A. Bosco, C. T. Fu, D. W. Sretavan, M. L. Vetter; Retinal Microglia Activate in a Mouse Model of Acute Ocular Hypertension. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2097. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize the timecourse, location, and extent of retinal microglial cell activation in a mouse model of glaucoma. To correlate phases of microglia activation to stages of retinal ganglion cells (RGCs) decline.
Intraocular pressure (IOP) was acutely elevated (> 21 mm Hg) for 1, 4, and 7 days in the right eyes by vein laser photocoagulation (LAS retinas) of 3 and 4 month-old albino CD-1 mice (Fu and Sretavan, IOVS 2009). The contralateral retinas (CTR) were used as normotensive internal controls. Retinal wholemounts were immunostained for Iba1 and the central 0.41 mm2 was imaged using confocal microscopy (Nikon A1). Microglia localized to the inner retina were counted and classified by cell morphology in 3 LAS and CTR retinas from the 4 and 7 day time points. To distinguish resting from activated microglia we quantified several parameters of cell complexity, such as number of branch points, using 3D image analysis (Imaris x64). As a reference we characterized the shape of resting, ramified microglia in retinas from age-matched naïve CD1 mice. Retinal vertical cryosections (16 µm) were immunostained for cleaved-caspase 3 and Brn3 to quantify apoptotic RGCs by fluorescent microscopy (Olympus IX70).
In LAS retinas, the number of microglial cells increased 4 and 7 days post-treatment, both in the GCL (680±217 and 643±22 cells/mm2, respectively) and the IPL (339±105 and 322±95). CTR retinas maintained 5-fold less microglia (144±10). The percentage of activated microglia increased in the GCL after 4 and 7 days (24% and 19% over CTR, respectively), but in the IPL this elevation was modest (12% and 8%). Preliminary analysis 1-day post-treatment, shows intense microglial activation within the GCL (39% over CTR). Increased number of apoptotic RGCs was apparent after 7 days (LAS: 25±4 vs. CTR: 2±1 cells per section; n=8).
Acute IOP elevation induces microglia activation prior to RGC death, making this a useful model to study the role of microglia in glaucoma pathogenesis. The regulation of retinal microglia activation could affect the outcome of RGC degeneration during hypertension or glaucoma.
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