Characterization of microglial and retinal ganglion cell changes following optic nerve crush in CD11c.YFP.Venus mice

Abstract

Purpose : Neuroinflammation has emerged as a critical driver in neurodegenerative diseases including glaucoma; understanding this process facilitates novel neuroprotective drug discovery. A prominent feature of neuroinflammation - microgliosis - is observed in postmortem glaucomatous retinas and across preclinical glaucoma models. However, accounts of microglia assuming neuroprotective, neurotoxic or bystander roles in the retinal ganglion cell (RGC) fate have all been reported. Here, we used CD11c.YFP.Venus mice to characterize activated microglia and axonal changes in the retinas following optic nerve crush (ONC), aiming to assess whether microglial inhibition exacerbates or ameliorates neurodegeneration.

Methods : CD11c.YFP.Venus mice were subjected to unilateral ONC injury and longitudinally imaged by the Phoenix MICRON imaging system. At Day (D) 0, D1, D2, D4, D7 and D14 post ONC, retinas are collected for wholemount labeling and imaging. High dimension morphometric data of activated microglia and RGC/axons were quantified. To determine the involvement of microglial reactivity in glaucomatous injury, ONC injury was induced in CD11c.YFP.Venus mice after small molecule-mediated microglia depletion or suppression (e.g., PLX5622, TD139). RGCs were then counted and axons were graded.

Results : Compared to naïve and uncrushed (contralateral) retinas, significant CD11c-YFP cells are detected in the ONC retinas beginning at day (D) 4 post injury, reaching peak number at D7 and persisting until D14 (D0-2 vs. D4 ONC p<0.0001; D4 vs. D7 ONC p<0.0001). In addition to density change, activated microglia show qualitatively reduced branching and increased soma size. Consistent with the ongoing axonal degeneration, the axon bundle diameter is visibly reduced. Axon beading, a feature of Wallerian degeneration, is frequently observed in the ONC retinas.

Conclusions : ONC induces microglial activation in the retina within the first week of injury and acutely causes RGC death and degeneration in the two-week study. Pairing non-invasive fundus imaging with CD11c.YFP.Venus mice (or other fluorescent reporter lines) enables a direct and rapid assessment of retinal microglial activation and can serve as a malleable platform for neuroinflammation drug screening/optimization.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.