Astrocytes initiate inflammation in the injured mouse spinal cord by promoting the entry of neutrophils and inflammatory monocytes in an IL-1 receptor/MyD88-dependent fashion
Brain Behav Immun. 2010 May;24(4):540-53. doi: 10.1016/j.bbi.2009.11.007. Epub 2009 Nov 22.
Isabelle Pineau 1 , Libo Sun, Dominic Bastien, Steve Lacroix
1 Department of Molecular Medicine, Laval University, Québec, Québec, Canada G1V 4G2.
DOI: 10.1016/j.bbi.2009.11.007
CNS injury stimulates the expression of several proinflammatory cytokines and chemokines, some of which including MCP-1 (also known as CCL2), KC (CXCL1), and MIP-2 (CXCL2) act to recruit Gr-1(+) leukocytes at lesion sites. While earlier studies have reported that neutrophils and monocytes/macrophages contribute to secondary tissue loss after spinal cord injury (SCI), recent work has shown that depletion of Gr-1(+) leukocytes compromised tissue healing and worsened functional recovery. Here, we demonstrate that astrocytes distributed throughout the spinal cord initially contribute to early neuroinflammation by rapidly synthesizing MCP-1, KC, and MIP-2, from 3 up to 12h post-SCI. Chemokine expression by astrocytes was followed by the infiltration of blood-derived immune cells, such as type I "inflammatory" monocytes and neutrophils, into the lesion site and nearby damaged areas. Interestingly, astrocytes from mice deficient in MyD88 signaling produced significantly less MCP-1 and MIP-2 and were unable to synthesize KC. Analysis of the contribution of MyD88-dependent receptors revealed that the astrocytic expression of MCP-1, KC, and MIP-2 was mediated by the IL-1 receptor (IL-1R1), and not by TLR2 or TLR4. Flow cytometry analysis of cells recovered from the spinal cord of MyD88- and IL-1R1-knockout mice confirmed the presence of significantly fewer type I "inflammatory" monocytes and the almost complete absence of neutrophils at 12h and 4days post-SCI. Together, these results indicate that MyD88/IL-1R1 signals regulate the entry of neutrophils and, to a lesser extent, type I "inflammatory" monocytes at sites of SCI.
Copyright 2009 Elsevier Inc. All rights reserved.
Astrocytes / immunology*
Astrocytes / metabolism
Chemokine CCL2 / genetics
Chemokine CCL2 / metabolism*
Chemokine CXCL1 / genetics
Chemokine CXCL1 / metabolism*
Fluorescent Antibody Technique
Mice, Inbred C3H
Mice, Knockout
Monocytes / immunology
Myeloid Differentiation Factor 88 / deficiency*
Neutrophils / immunology
Receptors, Interleukin-1 Type I / deficiency*
Spinal Cord / cytology
Spinal Cord Injuries / immunology*
Spinal Cord Injuries / metabolism
Toll-Like Receptor 2 / deficiency
Ccl2 protein, mouse
Chemokine CCL2
Chemokine CXCL1
Cxcl1 protein, mouse
Myd88 protein, mouse
Myeloid Differentiation Factor 88
Receptors, Interleukin-1 Type I
Tlr2 protein, mouse
Toll-Like Receptor 2
Canadian Institutes of Health Research/Canada