Abstract
Purpose :
Prior research has implicated microglia and recruited myeloid cells in glaucoma pathogenesis, but their role remains poorly understood. The goal of this study was to investigate the microglial molecular signature in two experimental models of glaucoma in order to test the hypothesis that in glaucoma, retinal microglia acquire a neurodegeneration-associated phenotype similar to that seen in neurodegenerative diseases of the brain.
Methods :
We investigated the microglial molecular signature in two murine glaucoma models: the microbead injection model, which leads to a surgically induced eye pressure elevation, and DBA/2J, a genetic model of pigmentary glaucoma. Retinal microglia were isolated one month after microbead injection in C57BL/6 animals from the injected, contralateral, sham-injected, and naïve eyes as CD11b+, Ly6C-, FCRLS+ cells and underwent Smart-Seq2 RNA sequencing. The same approach was used for isolation and RNA sequencing of microglia from 12-month-old DBA/2J mice and genetically matched controls. The role of one significantly upregulated gene, APOE, was investigated by injecting microbeads in Cx3cr1Cre/+ APOEfl/fl animals and controls and quantifying Brn3a+ retinal ganglion cell number 1 month following IOP induction.
Results :
We have found that in both the microbead glaucoma model and DBA/2J model, microglia suppress homeostatic genes and induce a disease-associated molecular signature, which is shared with brain neurodegenerative diseases. In addition to the induction of proinflammatory cytokines and neurotoxic substances liked endothelin-1, neurodegeneration-associated microglia also significantly upregulate production of APOE, the major lipoprotein in the brain that is genetically linked to Alzheimer’s disease, age-related macular degeneration, and glaucoma. Furthermore, we have found that mice in which APOE is targeted in microglia and recruited myeloid cells (Cx3cr1Cre/+ APOEfl/fl) are protected from microbead-induced glaucoma (p < 0.05).
Conclusions :
In this study we have identified the microglial molecular signature in two mouse models of glaucoma and found that targeting APOE in myeloid cells is neuroprotective in glaucoma. We propose that, similar to its role in brain microglia, APOE signaling controls microglial activation in the context of retinal ganglion cell death, and that this process may be targeted to develop novel neuroprotective therapies for glaucoma.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.