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Alfred K Yu, Luca Della Santina, Kelly Mai, Yvonne Ou; Microglial activation in experimental glaucoma is mediated by complement signaling. Invest. Ophthalmol. Vis. Sci. 2020;61(7):270.
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© ARVO (1962-2015); The Authors (2016-present)
While the mechanisms of retinal ganglion cell (RGC) degeneration in glaucoma are complex and incompletely understood, evidence suggests complement signaling may be playing a role in synaptic pruning during development and disease. We previously demonstrated microglial activation following intraocular pressure (IOP) elevation (increased number, volume, complexity, and process speed retraction and extraction). We characterized C1q deposits throughout the inner retina and tested the hypothesis that C1q accumulation is correlated with microglial activation and thus playing a role in synapse disassembly.
Laser-induced ocular hypertension (LIOH) was performed unilaterally on adult CD-1 mice expressing Cx3cr1-GFP, in which microglia are fluorescently labeled. Mice were sacrificed 7 days-post LIOH and individual RGCs were labeled by ballistic delivery of dextran dye. Immunolabeling was used to detect expression of C1q, an initial response element of the innate immune system. Z-stacks were acquired using confocal microscopy (0.1x0.1x0.3 μm/voxel), and binary masks were created of individual RGCs, microglia, and C1q deposits. Volume and distribution of C1q deposits colocalized with RGCs and microglia was evaluated throughout the inner plexiform layer (IPL) using VolumeCut (https://lucadellasantina.github.io/VolumeCut/). Statistics were performed using the two-tailed Student’s t-test.
After IOP elevation, the volume of C1q expression increased (247%; p=0.009) along with colocalization with microglia (305%; p=0.004); however, the percentage of C1q colocalized with microglia is similar in control (66%) vs LIOH (74%), suggesting that the increase in C1q is primarily due to microglial proliferation and activation. C1q colocalization with individual RGCs decreased (13%; p=0.02) following IOP elevation; this colocalization was highly correlated with triple colocalization with microglia (R2=0.9945). When analyzing colocalization of C1q, RGC, and microglia based on RGC types, we found that there are RGC type-specific alternations.
Microglial activation in the IPL of the retina following IOP elevation is accompanied by an increase in C1q deposits, and these C1q deposits are colocalized with microglia. In contrast, overall C1q colocalization with individual RGCs varied by type, suggesting a mechanism of differential susceptibility of RGCs to glaucomatous injury.
This is a 2020 ARVO Annual Meeting abstract.
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