Abstract
Purpose :
The retinal microglia become activated in numerous pathological conditions, but the molecular signatures of this change are poorly understood. Here, we evaluated activated retinal microglia after optic nerve injury to clarify their characteristics.
Methods :
The retinal microglia of Iba1-EGFP mice that underwent optic nerve crush were isolated with FACS, and changes in gene expression in the microglia were identified with RNA sequencing. A network pathway analysis was performed (Ingenuity Pathway Analysis; Qiagen). To clarify the pathological mechanisms that initiated the activation of disease-associated microglia, the mice underwent optic nerve crush and daily intraperitoneal treatment with ripasudil, a rho kinase inhibitor. GPR84-knockout mice were used to evaluate whether disease-associated microglia contributed to retinal ganglion cell death after optic nerve crush.
Results :
A disease-associated microglial cluster was identified and characterized as expressing IL-1ahigh/TNFhigh 4 days after optic nerve injury in mice. GPR84 was identified as an upstream molecule of IL-1a and TNF in the pathway analysis, and it was also marked in the IL-1ahigh/TNFhigh-expressing microglial cluster. The retinal microglial cells classified as being part of this disease-associated cluster decreased with ripasudil treatment in mice that underwent optic nerve crush. The loss of retinal ganglion cells in the GPR84-knockout mice was attenuated compared to wild-type mice 7 days after optic nerve crush.
Conclusions :
Excessive activation of rho kinase is one of the causes of disease-associated microglia activation. GPR84 is a neurotoxic microglial marker that promotes RGC death; GPR84 has potential as a therapeutic target for conditions such as glaucoma and optic neuropathy.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.