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RasV12 Expression in Microglia Initiates Retinal Inflammation and Induces Photoreceptor Degeneration
Yuta Moriuchi1, Toshiro Iwagawa1, Asano Tsuhako1
1Division of Molecular and Developmental Biology, Institute of Medical Science, University of Tokyo, Tokyo, Japan.
Purpose:
The role of activated retinal microglia in driving retinal degeneration has been implicated in a number of in vivo disease models. Here, we investigated the primary consequences of microglial activation by the specific expression of constitutively active Ras in microglia in a transgenic mouse model before the onset of any degenerative changes in the retina.
Methods:
The double transgenic lines CAG-LSL-RasV12-IRES-EGFP; Cx3cr1CreER/+ (Cx3cr1-RasV12 mice) and CAG-LSL-EGFP; Cx3cr1CreER_+ (control mice) were generated. The expression of RasV12 was induced in microglia by tamoxifen administration, and the retinas were examined by immunohistochemistry of frozen sections, RT-qPCR, and live imaging.
Results:
RasV12 expression in retinal microglial cells promoted cell proliferation, cytokine expression, and phagocytosis. RasV12-expressing microglia migrated toward the inner and outer layers of the retina. Examination of glial fibrillary acidic protein (GFAP) expression revealed activation of Müller glia in the retina. We also observed loss of the photoreceptors in the outer nuclear layer in close proximity to microglial cells. However, no significant neurodegeneration was detected in the inner nuclear layer (INL) or ganglion cell layer (GCL). The morphology of RasV12-expressing microglia in the GCL and INL retained more ramified features compared with the predominantly-ameboid morphology found in outer retinal microglia.
Conclusions:
The expression of RasV12 is sufficient to activate microglia and lead to photoreceptor degeneration. Neurons in the inner side of the retina were not damaged by the RasV12-activated microglia, suggesting that microenvironment cues may modulate the microglial phenotypic features and effects of microglial activation.
Insights
Constitutively active Ras in retinal microglia triggers photoreceptor degeneration. Activated microglia exhibit altered morphology and migration, but inner retinal neurons remain protected, suggesting microenvironmental influences.
Area of Science:
- Ophthalmology
- Neuroscience
- Immunology
Background:
- Retinal microglia play a critical role in retinal health and disease.
- Microglial activation is implicated in various retinal degeneration models.
- Understanding the early events of microglial activation is crucial for developing therapeutic strategies.
Purpose of the Study:
- To investigate the consequences of specific microglial activation using a transgenic mouse model.
- To examine the effects of constitutively active Ras expression in microglia before retinal degeneration onset.
- To elucidate the role of activated microglia in photoreceptor integrity and retinal structure.
Main Methods:
- Generation of transgenic mice with inducible RasV12 expression in microglia (Cx3cr1-RasV12).
- Tamoxifen-induced expression of RasV12 in microglia.
- Retinal analysis using immunohistochemistry, RT-qPCR, and live imaging.
Main Results:
- RasV12 expression activated microglia, promoting proliferation, cytokine release, and phagocytosis.
- Activated microglia migrated towards retinal layers and induced Müller glia activation (GFAP expression).
- Photoreceptor loss was observed near activated microglia, while inner retinal neurons remained unaffected.
Conclusions:
- Inducible RasV12 expression is sufficient to activate microglia and cause photoreceptor degeneration.
- Inner retinal neurons are protected from RasV12-activated microglia, indicating microenvironmental modulation of microglial effects.
- Microglial activation can lead to specific retinal cell degeneration, highlighting the importance of localized responses.
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