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Interaction of complement system and microglia activation in retina and optic nerve in a NMDA damage model
Sandra Kuehn1, Sabrina Reinehr1, Gesa Stute1
1Experimental Eye Research Institute, University Eye Hospital, Ruhr-University Bochum, In der Schornau 23-25, 44892 Bochum, Germany.
Abstract:
It is known that intravitreally injected N-methyl-d-aspartate (NMDA) leads to fast retina and optic nerve degeneration and can directly activate microglia. Here, we analyzed the relevance for microglia related degenerating factors, the proteins of the complement system, at a late stage in the NMDA damage model. Therefore, different doses of NMDA (0 (PBS), 20, 40, 80 nmol) were intravitreally injected in rat eyes. Proliferative and activated microglia/macrophages (MG/Mϕ) were found in retina and optic nerve 2 weeks after NMDA injection. All three complement pathway proteins were activated in retinas after 40 and 80 nmol NMDA treatment. 80 nmol NMDA injection also lead to more numerous depositions of complement factors C3 and membrane attack complex (MAC) in retina and MAC in optic nerve. Additionally, more MAC+ depositions were detected in optic nerves of the 40 nmol NMDA group. In this NMDA model, the retina is first affected followed by optic nerve damage. However, we found initiating complement processes in the retina, while more deposits of the terminal complex were present 2 weeks after NMDA injection in the optic nerve. The complement system can be activated in waves and possibly a second wave is still on-going in the retina, while the first activation wave is in the final phase in the optic nerve. Only the damaged tissues showed microglia activation as well as proliferation and an increase of complement proteins. Interestingly, the microglia/macrophages (MG/Mϕ) in this model were closely connected with the inductors of the classical and lectin pathway, but not with the alternative pathway. However, all three initiating complement pathways were upregulated in the retina. The alternative pathway seems to be triggered by other mechanisms in this NMDA model. Our study showed an ongoing interaction of microglia and complement proteins in a late stage of a degenerative process.
Insights
N-methyl-d-aspartate (NMDA) eye injections activate microglia and complement proteins in damaged retina and optic nerve tissues. This study reveals ongoing interactions between microglia and complement system components during late-stage degeneration.
Area of Science:
- Neuroscience
- Immunology
- Ophthalmology
Background:
- Intravitreal N-methyl-d-aspartate (NMDA) injection causes rapid retina and optic nerve degeneration.
- Microglia (MG/Mϕ) are activated by NMDA and play a role in neuroinflammation.
- The complement system's role in late-stage NMDA-induced degeneration is not fully understood.
Purpose of the Study:
- To investigate the involvement of complement system proteins in late-stage NMDA-induced retinal and optic nerve degeneration.
- To analyze the interaction between activated microglia/macrophages (MG/Mϕ) and complement factors.
- To understand the temporal and spatial activation patterns of the complement system in this model.
Main Methods:
- Intravitreal injection of varying NMDA doses (0, 20, 40, 80 nmol) into rat eyes.
- Analysis of retina and optic nerve tissues 2 weeks post-injection.
- Assessment of microglia/macrophage (MG/Mϕ) activation and proliferation.
- Detection and quantification of complement pathway proteins (C3, MAC) and pathway activators.
Main Results:
- NMDA injection led to proliferative and activated microglia/macrophages (MG/Mϕ) in retina and optic nerve.
- All three complement pathways were activated in retinas at higher NMDA doses (40 and 80 nmol).
- Increased deposition of C3 and MAC in retina, and MAC in optic nerve, observed with 80 nmol NMDA; MAC also increased in optic nerve with 40 nmol NMDA.
- Microglia/macrophages (MG/Mϕ) were associated with classical and lectin pathway components, but not the alternative pathway, despite its upregulation in the retina.
- Complement activation appeared to occur in waves, with retina showing initiating processes and optic nerve showing later-stage terminal complex deposits.
Conclusions:
- Microglia and complement proteins interact dynamically during late-stage NMDA-induced neurodegeneration.
- Complement system activation is a significant component of the inflammatory response in this model.
- The findings suggest a complex, potentially wave-like activation of the complement system in response to retinal and optic nerve injury.
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