Genetic model for cell-fate tracking and ablation of CCR2-expressing infiltrating monocytes in retinal degeneration: Implications for inhibition of monocyte infiltration as a therapeutic strategy

Abstract

Purpose : Microglia/macrophages are present in disease lesions in retinal degenerations and are implicated in disease progression. However, the complexity of contributing macrophage populations complicates the elucidation of specific underlying mechanisms. Specifically, the presence, number, persistence, and contribution of infiltrating monocyte-derived macrophages are incompletely understood. To address this, we developed a CCR2-CreER mouse line for cell-fate tracking and manipulation of this cellular subset in the context of retinal injury.

Methods : We generated CCR2-CreER knock-in mice by replacing endogenous sequences coding for CCR2 with those coding for CreER. These mice were crossed into “floxed” transgenic lines coding for the marker tdTomato (tdT), and diphtheria toxin (DTA), and into the rd10 background to generate the following lines: (1) CCR2^CreER/+;tdT^F/+ (CCR2-tdT); (2) rd10;CCR2^CreER/+;tdT^F/+ (rd10-CCR2-tdTand (3) rd10;CCR2^CreER/+;tdT^F/+;DTA^F/+ (rd10-CCR2-DTA). Tamoxifen administration was used to induce tdT and DTA expression. Electroretinography (ERG) was used to assess photoreceptor function.

Results : 7 days following tamoxifen administration, the percentages of tdT+ monocytes/macrophages (labeled with Ly6C) in blood and bone marrow of CCR2-tdT mice were 43.89% and 54.35%, respectively. In the NaIO₃-induced RPE injury model, tdT+ monocyte-derived macrophages were found in the retina soon after injury (3 days) and persisted over the long term (40 days and 6 months). In the retinas of postnatal day- P16 rd10-CCR2-tdT mice, infiltrating tdT+ monocytes were detected; these were absent in rd10-CCR2-DTA mice in which tdT+ monocytes were ablated. Comparison of ERG responses in these two groups showed greater preservation of a- and b-wave amplitudes in animals in which monocytic ablation was induced, particularly in female animals.

Conclusions : The CCR2-CreER mouse model enabled long- and short-term cell-fate tracking of CCR2+ peripheral monocytes that infiltrate the retina following retinal injury. Genetic ablation of these infiltrating cells correlated with improved retinal function, suggesting their deleterious contribution to retinal degeneration and related therapeutic opportunities to preserve function in retinal degenerations.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.