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Updated: Jun 24, 2026
Neuron-Macrophage Co-cultures to Activate Macrophages Secreting Molecular Factors with Neurite Outgrowth Activity
Published on: March 30, 2018
Macrophages promote axon regeneration with concurrent neurotoxicity
John C Gensel1, Satoshi Nakamura, Zhen Guan
1Center for Brain and Spinal Cord Repair, Department of Molecular Virology, Immunology, and Medical Genetics, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
Abstract:
Activated macrophages can promote regeneration of CNS axons. However, macrophages also release factors that kill neurons. These opposing functions are likely induced simultaneously but are rarely considered together in the same experimental preparation. A goal of this study was to unequivocally document the concurrent neurotoxic and neuroregenerative potential of activated macrophages. To do so, we quantified the length and magnitude of axon growth from enhanced green fluorescent protein-expressing dorsal root ganglion (DRG) neurons transplanted into the spinal cord in relationship to discrete foci of activated macrophages. Macrophages were activated via intraspinal injections of zymosan, a potent inflammatory stimulus known to increase axon growth and cause neurotoxicity. Using this approach, a significant increase in axon growth up to macrophage foci was evident. Within and adjacent to macrophages, DRG and spinal cord axons were destroyed. Macrophage toxicity became more evident when zymosan was injected closer to DRG soma. Under these conditions, DRG neurons were killed or their ability to extend axons was dramatically impaired. The concurrent induction of pro-regenerative and neurotoxic functions in zymosan-activated macrophages (ZAMs) was confirmed in vitro using DRG and cortical neurons. Importantly, the ability of ZAMs to stimulate axon growth was transient; prolonged exposure to factors produced by ZAMs enhanced cell death and impaired axon growth in surviving neurons. Lipopolysaccharide, another potent macrophage activator, elicited a florid macrophage response, but without enhancing axon growth or notable toxicity. Together, these data show that a single mode of activation endows macrophages with the ability to simultaneously promote axon regeneration and cell killing.
Insights
Activated macrophages exhibit dual roles in central nervous system (CNS) axon regeneration, promoting growth near their location while simultaneously causing neurotoxicity. This study documents these opposing functions, revealing transient pro-regenerative effects and lasting neurotoxicity.
Area of Science:
- Neuroscience
- Immunology
- Regenerative Medicine
Background:
- Activated macrophages play a complex role in the central nervous system (CNS), with potential for both promoting axon regeneration and causing neuronal death.
- These opposing functions are often induced simultaneously but rarely studied together in a single experimental setup.
Purpose of the Study:
- To unequivocally document the concurrent neurotoxic and neuroregenerative potential of activated macrophages in the CNS.
- To investigate the impact of macrophage activation on dorsal root ganglion (DRG) and spinal cord axon growth and survival.
Main Methods:
- Quantified axon growth from enhanced green fluorescent protein-expressing DRG neurons transplanted into the spinal cord in relation to activated macrophage foci.
- Activated macrophages using intraspinal injections of zymosan, a known inflammatory stimulus.
- In vitro experiments using DRG and cortical neurons exposed to zymosan-activated macrophages (ZAMs).
Main Results:
- A significant increase in axon growth was observed up to macrophage foci.
- DRG and spinal cord axons were destroyed within and adjacent to macrophages.
- Macrophage toxicity was more pronounced when zymosan was injected closer to DRG cell bodies, leading to neuron death or impaired axon extension.
- In vitro studies confirmed the concurrent pro-regenerative and neurotoxic functions of ZAMs.
- Pro-regenerative effects of ZAMs were transient; prolonged exposure led to enhanced cell death and impaired axon growth.
Conclusions:
- A single activation method (zymosan) endows macrophages with the ability to simultaneously promote axon regeneration and cause cell killing.
- The neuroregenerative potential of activated macrophages is transient and can be overshadowed by potent neurotoxicity with prolonged exposure.
- Lipopolysaccharide activation of macrophages did not enhance axon growth or cause significant toxicity, highlighting stimulus-dependent effects.
