Toll-like receptor 2-mediated alternative activation of microglia is protective after spinal cord injury.

Abstract

Improving neurological outcome after spinal cord injury is a major clinical challenge because axons, once severed, do not regenerate but 'dieback' from the lesion site. Although microglia, the immunocompetent cells of the brain and spinal cord respond rapidly to spinal cord injury, their role in subsequent injury or repair remains unclear. To assess the role of microglia in spinal cord white matter injury we used time-lapse two-photon and spectral confocal imaging of green fluorescent protein-labelled microglia, yellow fluorescent protein-labelled axons, and Nile Red-labelled myelin of living murine spinal cord and revealed dynamic changes in white matter elements after laser-induced spinal cord injury in real time. Importantly, our model of acute axonal injury closely mimics the axonopathy described in well-characterized clinically relevant models of spinal cord injury including contusive-, compressive- and transection-based models. Time-lapse recordings revealed that microglia were associated with some acute pathophysiological changes in axons and myelin acutely after laser-induced spinal cord injury. These pathophysiological changes included myelin and axonal spheroid formation, spectral shifts in Nile Red emission spectra in axonal endbulbs detected with spectral microscopy, and 'bystander' degeneration of axons that survived the initial injury, but then succumbed to secondary degeneration. Surprisingly, modulation of microglial-mediated release of neurotoxic molecules failed to protect axons and myelin. In contrast, sterile stimulation of microglia with the specific toll-like receptor 2 agonist Pam2CSK4 robustly increased the microglial response to ablation, reduced secondary degeneration of central myelinated fibres, and induced an alternative (mixed M1:M2) microglial activation profile. Conversely, Tlr2 knock out: Thy1 yellow fluorescent protein double transgenic mice experienced greater axonal dieback than littermate controls. Thus, promoting an alternative microglial response through Pam2CSK4 treatment is neuroprotective acutely following laser-induced spinal cord injury. Therefore, anti-inflammatory treatments that target microglial activation may be counterintuitive after spinal cord injury.

• Authors: David P Stirling, Karen Cummins, Manoj Mishra, Wulin Teo, V Wee Yong, Peter Stys
• Journal: Brain : a journal of neurology (Brain) Vol. 137 Issue Pt 3 Pg. 707-23 (Mar 2014) ISSN: 1460-2156 [Electronic] England
• PMID: 24369381 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• Bacterial Proteins
• Lipopeptides
• Luminescent Proteins
• Neuroprotective Agents
• Pam2CSK4 lipopeptide
• Toll-Like Receptor 2
• yellow fluorescent protein, Bacteria
• Green Fluorescent Proteins

Topics

• Animals
• Axons (drug effects, pathology, ultrastructure)
• Bacterial Proteins
• Disease Models, Animal
• Green Fluorescent Proteins
• Lasers (statistics & numerical data)
• Lipopeptides (pharmacology)
• Luminescent Proteins
• Mice
• Mice, Inbred C57BL
• Mice, Knockout
• Microglia (drug effects, pathology, ultrastructure)
• Microscopy, Confocal
• Myelin Sheath (drug effects, pathology, ultrastructure)
• Neuroprotective Agents (pharmacology)
• Spinal Cord Injuries (etiology, metabolism, pathology)
• Toll-Like Receptor 2 (agonists, metabolism)