Myelin Activates FAK/Akt/NF-kB Pathways and Provokes CR3-Dependent Inflammatory Response in Murine System Xin Sun1,2, Xi Wang1, Tianxiang Chen1, Tianyi Li1, Kai Cao1, Andrew Lu1, Yongxiong Chen 1 , Dongming Sun1, Jianhong Luo2, Jianqing Fan3, Wise Young 1 , Yi Ren 1 * 1 W. M. Keck Center for Collaborative Neuroscience, Department of Cell Biology and Neuroscience, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States of America, 2 Department of Neurobiology, Institute for Neuroscience, Zhejiang University School of Medicine, Hangzhou, People’s Republic of China, 3 Statistics Laboratory, Princeton University, Princeton, New Jersey, United States of America Abstract Inflammatory response following central nervous system (CNS) injury contributes to progressive neuropathology and reduction in functional recovery. Axons are sensitive to mechanical injury and toxic inflammatory mediators, which may lead to demyelination. Although it is well documented that degenerated myelin triggers undesirable inflammatory responses in autoimmune diseases such as multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE), there has been very little study of the direct inflammatory consequences of damaged myelin in spinal cord injury (SCI), i.e., there is no direct evidence to show that myelin debris from injured spinal cord can trigger undesirable inflammation in vitro and in vivo. Our data showed that myelin can initiate inflammatory responses in vivo, which is complement receptor 3 (CR3)-dependent via stimulating macrophages to express pro-inflammatory molecules and down- regulates expression of anti-inflammatory cytokines. Mechanism study revealed that myelin-increased cytokine expression is through activation of FAK/PI3K/Akt/NF-kB signaling pathways and CR3 contributes to myelin-induced PI3K/Akt/NF-kB activation and cytokine production. The myelin induced inflammatory response is myelin specific as sphingomyelin (the major lipid of myelin) and myelin basic protein (MBP, one of the major proteins of myelin) are not able to activate NF-kB signaling pathway. In conclusion, our results demonstrate a crucial role of myelin as an endogenous inflammatory stimulus that induces pro-inflammatory responses and suggest that blocking myelin-CR3 interaction and enhancing myelin debris clearance may be effective interventions for treating SCI. Citation: Sun X, Wang X, Chen T, Li T, Cao K, et al. (2010) Myelin Activates FAK/Akt/NF-kB Pathways and Provokes CR3-Dependent Inflammatory Response in Murine System. PLoS ONE 5(2): e9380. doi:10.1371/journal.pone.0009380 Editor: Fabrizio Gelain, University of Milan-Bicocca, Italy Received October 29, 2009; Accepted February 4, 2010; Published February 23, 2010 Copyright: 2010 Sun et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by National Science Foundation (DMS-0714589), National Institutes of Health (NIH) (R01-GM072611) and Joyce and Les Goodman scholarship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: ren@dls.rutgers.edu Introduction Inflammatory response induced by trauma in the central nervous system (CNS), including traumatic brain injury (TBI) and spinal cord injury (SCI), contributes progressive neuropathol- ogy and reduction in functional recovery. The inflammatory response includes invasion of inflammatory cells, activation of CNS-resident glial cells and release of cytokines and chemokines [1,2,3]. Pro-inflammatory cytokines such as tumor necrosis factor- a (TNF-a), interleukin-1b (IL-1b), IL-6 and chemokines such as macrophage chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1a (MIP-1a), and chemokine (C-X-C motif) ligand 10 (CXCL 10), are produced by both infiltrating cells and CNS-resident glial cells, orchestrating a pathogenic cascade leading to inflammation and axonal damage [4]. TNF-a and IL- 1 activate the nuclear factor kappa B (NF-kB) pathway and then further stimulate production of inflammatory mediators such as inducible nitric oxide synthase (iNOS) and prostaglandin E2 [5]. IL-6 not only mediates spinal cord neural injury via JAK/STAT activation [6] but may also be a potential inhibitor of neurogenesis [7]. In addition, these inflammatory processes enhance recruit- ment and activation of leukocytes, leading to amplification of inflammation and further tissue damage. However, there is no direct evidence to show where these pro-inflammatory cytokines come from and whether myelin is major stimulus responsible for inflammatory mediator production in SCI. Myelin degeneration occurs after injury and in multiple sclerosis (MS) and its animal model, experimental autoimmune encepha- lomyelitis (EAE). Demyelinated areas in the CNS of patients with MS are characterized by inflammatory infiltrates that contain blood-derived myelin-specific T cells, B cells and macrophages. Degenerated myelin containing inhibitory molecules such as NogoA, Oligodendrocyte-myelin glycoprotein (OMgp) and mye- lin-associated glycoprotein (MAG) inhibits axon regeneration [8,9] and further activates complement system to destroy intact myelin. Although it is well documented that degenerated myelin triggers undesirable inflammatory responses in MS and EAE, there has been very little study of the direct inflammatory consequences of damaged myelin in spinal cord injury (SCI), i.e. there is no direct evidence to show that myelin debris from injured spinal cord can PLoS ONE | www.plosone.org 1 February 2010 | Volume 5 | Issue 2 | e9380