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The Journal of Neuroscience, March 25, 2009, 29(12):3956-3968; doi:10.1523/JNEUROSCI.3992-08.2009

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Cellular/Molecular
Macrophages Promote Axon Regeneration with Concurrent Neurotoxicity

John C. Gensel,¹ Satoshi Nakamura,² Zhen Guan,¹ Nico van Rooijen,³ Daniel P. Ankeny,¹ and Phillip G. Popovich¹

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, ²Department of Neurosurgery, Tokyo Women's Medical University Medical Center East, Tokyo 116-8567, Japan, and ³Department of Molecular Cell Biology, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands

Correspondence should be addressed to Phillip G. Popovich, 786 Biomedical Research Tower, 460 West 12th Avenue, Columbus, OH 43210. Email: Phillip.Popovich{at}osumc.edu

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.

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Received Aug. 21, 2008; revised Feb. 18, 2009; accepted Feb. 22, 2009.

Correspondence should be addressed to Phillip G. Popovich, 786 Biomedical Research Tower, 460 West 12th Avenue, Columbus, OH 43210. Email: Phillip.Popovich{at}osumc.edu

This article has been cited by other articles:

				Y. Yin, Q. Cui, H.-y. Gilbert, Y. Yang, Z. Yang, C. Berlinicke, Z. Li, C. Zaverucha-do-Valle, H. He, V. Petkova, et al. Oncomodulin links inflammation to optic nerve regeneration PNAS, November 17, 2009; 106(46): 19587 - 19592. [Abstract] [Full Text] [PDF]

				K. A. Kigerl, J. C. Gensel, D. P. Ankeny, J. K. Alexander, D. J. Donnelly, and P. G. Popovich Identification of Two Distinct Macrophage Subsets with Divergent Effects Causing either Neurotoxicity or Regeneration in the Injured Mouse Spinal Cord J. Neurosci., October 28, 2009; 29(43): 13435 - 13444. [Abstract] [Full Text] [PDF]

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