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Digestion of Whole Mouse Eyes for Multi-Parameter Flow Cytometric Analysis of Mononuclear Phagocytes
Published on: June 17, 2020
Infiltrating Monocyte Fate Switch in Retinal Degeneration: From Early Pathology to Late Homeostasis
Wenxin Ma1, Quyan Zhang1, Lijin Dong1
1National Eye Institute.
Abstract:
The contribution of infiltrating monocyte-derived macrophages (MDMs) to neurodegeneration remains poorly understood. Using a CCR2-CreER-based lineage-tracing and ablation strategy in mouse models of retinal degeneration, we precisely tracked infiltrating monocytes and defined their functional evolution. We found that monocytes entering the degenerating retina rapidly downregulate CCR2 and progressively acquire microglial markers (e.g., TMEM119, P2RY12), adopt a ramified morphology, and acquire a transcriptional signature highly analogous to that of resident microglia-derived macrophages (MiDMs). While a subset of monocytes is cleared by activated microglia during the acute phase, others persist and integrate into the retinal macrophage niche, restoring myeloid homeostasis in later stages. Functionally, early monocyte infiltration is pathogenic; it amplifies neuroinflammation by inducing Müller cells to produce complement C3 and shifts microglial complement regulation toward the alternative pathway. Critically, selective ablation of monocytes during this acute phase attenuated C3 deposition, suppressed microglial activation, and preserved photoreceptors. Together, these findings reveal a temporally bifurcated role for infiltrating monocytes-as early drivers of complement-mediated pathology and later contributors to immune homeostasis-and identify monocyte infiltration as a stage-specific therapeutic target in neurodegenerative disease.
Insights
Infiltrating monocytes initially worsen neuroinflammation and retinal damage but later help restore immune balance. Targeting these monocytes early may protect against neurodegeneration.
Area of Science:
- Neuroscience
- Immunology
- Ophthalmology
Background:
- The role of infiltrating monocyte-derived macrophages (MDMs) in neurodegeneration is unclear.
- Understanding their precise function and evolution in the degenerating retina is crucial.
Purpose of the Study:
- To track and define the functional evolution of infiltrating monocytes in retinal degeneration models.
- To investigate the pathogenic and homeostatic roles of these cells.
- To identify stage-specific therapeutic targets.
Main Methods:
- Utilized a CCR2-CreER-based lineage-tracing and ablation strategy in mouse models of retinal degeneration.
- Monitored monocyte infiltration, marker acquisition (TMEM119, P2RY12), morphology, and transcriptional changes.
- Assessed the impact of monocyte ablation on neuroinflammation, complement deposition, and photoreceptor survival.
Main Results:
- Infiltrating monocytes downregulate CCR2, acquire microglial markers, and adopt a microglial-like phenotype.
- Early monocyte infiltration exacerbates neuroinflammation by inducing Müller cell C3 production and promoting microglial alternative pathway complement regulation.
- Selective ablation of acute-phase monocytes reduced C3 deposition, suppressed microglial activation, and preserved photoreceptors.
Conclusions:
- Infiltrating monocytes have a dual role: early pathogenic drivers and later contributors to immune homeostasis.
- Monocyte infiltration is a critical, stage-specific therapeutic target for neurodegenerative diseases.
- These findings elucidate the complex interplay between monocytes, microglia, and Müller cells in retinal degeneration.
