Complement C5a receptor knockout has diminished light-induced microglia/macrophage retinal migration

Area of Science:

• Ophthalmology
• Neuroscience
• Immunology

Background:

• The complement system plays a role in age-related macular degeneration (AMD) pathogenesis.
• Activated microglia are implicated in AMD.
• The relationship between complement anaphylatoxin receptors and microglial recruitment in retinal degeneration is not fully understood.

Purpose of the Study:

• To investigate the role of complement anaphylatoxin receptors, specifically C3a receptor (C3aR) and C5a receptor (C5aR), in microglial recruitment during light-induced retinal damage.
• To determine if C5aR or C3aR is primarily responsible for recruiting microglia/macrophages to the outer retina.

Main Methods:

• Utilized knockout (KO) mouse models lacking C3aR or C5aR.
• Induced retinal damage using light exposure.
• Assessed microglial/macrophage migration via immunofluorescence and real-time quantitative PCR (RT-qPCR).
• Quantified mRNA levels of complement components (C3, C5, Cfb, Cfd) and microglial markers (Iba1).

Main Results:

• mRNA levels of C3, C5, C3aR, C5aR, Cfb, and Cfd were upregulated post-light exposure.
• Retinal microglia/macrophages express both C3aR and C5aR.
• Light damage increased Iba1-positive cell numbers and Iba1 mRNA levels.
• This increase was significantly attenuated in C5aR KO mice, but not in C3aR KO mice.

Conclusions:

• C5aR, but not C3aR, promotes the recruitment of microglia/macrophages in a light-induced retinal damage model.
• These distinct roles of complement anaphylatoxin receptors suggest potential therapeutic targets for retinal neurodegenerative diseases.