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Macrophages: their myelinotrophic or neurotoxic actions depend upon tissue oxidative stress
B L Bartnik1, B H Juurlink, R M Devon
1Department of Anatomy and Cell Biology and The Cameco Multiple Sclerosis and Neuroscience Research Centre, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK S7N 5E5 Canada.
Abstract:
There are still questions regarding whether macrophages found in MS lesions are agents of recovery or of destruction. To address this, we examined in aggregate cultures prepared from dissociated embryonic spinal cord tissue, with or without addition of exogenous macrophages, the effect of menadione-induced oxidative stress. Similar to findings of other laboratories, we observed that in the absence of oxidative stress macrophage enrichment promoted myelinogenesis. In macrophage-poor cultures, menadione at 5 microM had very little effect upon the status of the aggregate cultures; however, increasing this to 10 and 20 microM did result in some damage to axons and myelin. By contrast, in macrophage enriched cultures, menadione at a concentration as little as 5 microM caused the complete destruction of the aggregates. We suggest that in neural tissues that have sufficiently high macrophage numbers, oxidative stress results in a positive inflammatory feedback loop that results in massive tissue destruction. We further suggest that what we see in macrophage-enriched aggregates subjected to oxidative stress may represent what happens in the Marburg-type of MS lesion.
Insights
Macrophages in neural tissue can cause destruction during oxidative stress, particularly in high-density environments. This finding offers insights into inflammatory processes in conditions like multiple sclerosis (MS) lesions.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Macrophages play a complex role in the central nervous system, with their function in diseases like multiple sclerosis (MS) debated.
- Oxidative stress is implicated in neurodegenerative processes, but its interaction with macrophages in neural tissue requires further elucidation.
Purpose of the Study:
- To investigate the dual role of macrophages (recovery vs. destruction) in neural tissue under oxidative stress conditions.
- To determine the effect of varying macrophage concentrations on neural aggregate cultures exposed to menadione-induced oxidative stress.
Main Methods:
- Utilized aggregate cultures of embryonic spinal cord tissue.
- Introduced exogenous macrophages to create macrophage-rich and macrophage-poor conditions.
- Applied menadione to induce oxidative stress at different concentrations (5, 10, 20 microM).
- Assessed the impact on myelinogenesis, axon integrity, and overall tissue structure.
Main Results:
- Macrophage enrichment promoted myelinogenesis in the absence of oxidative stress.
- In macrophage-poor cultures, moderate menadione concentrations caused minimal damage.
- In macrophage-rich cultures, even low menadione concentrations led to complete aggregate destruction.
- Oxidative stress in high-macrophage environments triggered a destructive inflammatory feedback loop.
Conclusions:
- High concentrations of macrophages in neural tissue can exacerbate damage during oxidative stress.
- The findings suggest a mechanism for massive tissue destruction in inflammatory conditions like Marburg-type MS lesions.
- Macrophage-mediated inflammatory responses under oxidative stress are critical factors in neuroinflammation.