Deficient CX3CR1 Signaling Promotes Recovery after Mouse Spinal Cord Injury by Limiting the Recruitment and Activation of Ly6C(lo)/iNOS(+) Macrophages

Center for Brain and Spinal Cord Repair, The Ohio State University, Columbus, Ohio 43210, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 07/2011; 31(27):9910-22. DOI: 10.1523/JNEUROSCI.2114-11.2011
Source: PubMed


Macrophages exert divergent effects in the injured CNS, causing either neurotoxicity or regeneration. The mechanisms regulating these divergent functions are not understood but can be attributed to the recruitment of distinct macrophage subsets and the activation of specific intracellular signaling pathways. Here, we show that impaired signaling via the chemokine receptor CX3CR1 promotes recovery after traumatic spinal cord injury (SCI) in mice. Deficient CX3CR1 signaling in intraspinal microglia and monocyte-derived macrophages (MDMs) attenuates their ability to synthesize and release inflammatory cytokines and oxidative metabolites. Also, impaired CX3CR1 signaling abrogates the recruitment or maturation of MDMs with presumed neurotoxic effects after SCI. Indeed, in wild-type mice, Ly6C(lo)/iNOS(+)/MHCII(+)/CD11c(-) MDMs dominate the lesion site, whereas CCR2(+)/Ly6C(hi)/MHCII(-)/CD11c(+) monocytes predominate in the injured spinal cord of CX3CR1-deficient mice. Replacement of wild-type MDMs with those unable to signal via CX3CR1 resulted in anatomical and functional improvements after SCI. Thus, blockade of CX3CR1 signaling represents a selective anti-inflammatory therapy that is able to promote neuroprotection, in part by reducing inflammatory signaling in microglia and MDMs and recruitment of a novel monocyte subset.

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Available from: Kristina A Kigerl, Feb 03, 2014
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    • "Monocyte trafficking to the brain is usually observed in association with substantial CNS-related tissue pathology and inflammation, e.g., multiple sclerosis, traumatic injury, stroke, Alzheimer's disease, or infection (Hafler et al., 2005; Gate et al., 2010; Donnelly et al., 2011; Hawthorne and Popovich, 2011; McGavern and Kang, 2011; de Vries et al., 2012). Therefore, the possibility that RSD could induce monocyte trafficking to the brain was intriguing because it would occur in the absence of CNS tissue pathology (Wohleb et al., 2013). "
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    ABSTRACT: The development and exacerbation of depression and anxiety are associated with exposure to repeated psychosocial stress. Stress is known to affect the bidirectional communication between the nervous and immune systems leading to elevated levels of stress mediators including glucocorticoids (GCs) and catecholamines and increased trafficking of proinflammatory immune cells. Animal models, like the repeated social defeat (RSD) paradigm, were developed to explore this connection between stress and affective disorders. RSD induces activation of the sympathetic nervous system (SNS) and hypothalamic-pituitary (HPA) axis activation, increases bone marrow production and egress of primed, GC-insensitive monocytes, and stimulates the trafficking of these cells to tissues including the spleen, lung, and brain. Recently, the observation that these monocytes have the ability to traffic to the brain perivascular spaces and parenchyma have provided mechanisms by which these peripheral cells may contribute to the prolonged anxiety-like behavior associated with RSD. The data that have been amassed from the RSD paradigm and others recapitulate many of the behavioral and immunological phenotypes associated with human anxiety disorders and may serve to elucidate potential avenues of treatment for these disorders. Here, we will discuss novel and key data that will present an overview of the neuroendocrine, immunological and behavioral responses to social stressors. Copyright © 2015 IBRO. Published by Elsevier Ltd. All rights reserved.
    Neuroscience 01/2015; 289. DOI:10.1016/j.neuroscience.2015.01.001 · 3.36 Impact Factor
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    • "Furthermore, stress-induced myeloid cell recruitment coincides with neuroinflammatory mediators that promote trafficking of myeloid cells to the brain (Prinz and Priller, 2010). For example, CCR2 is critical for directing monocytes from the blood to the brain, while CX 3 CR1 is essential for their integration in the brain perivascular space and parenchyma (Mahad et al., 2006; Donnelly et al., 2011). This is pertinent because there was no prolonged anxiety-like behavior associated with RSD in models where myeloid cells could not traffic to the brain (i.e., IL-1R1, CCR2, and CX3CR1 deficiency) (Wohleb et al., 2011, 2013). "
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    ABSTRACT: Repeated social defeat (RSD) in mice causes myeloid cell trafficking to the brain that contributes to the development of prolonged anxiety-like behavior. Myeloid cell recruitment following RSD occurs in regions where neuronal and microglia activation is observed. Thus, we hypothesized that crosstalk between neurons, microglia, and endothelial cells contributes to brain myeloid cell trafficking via chemokine signaling and vascular adhesion molecules. Here we show that social defeat caused an exposure- and brain region-dependent increase in several key adhesion molecules and chemokines involved in the recruitment of myeloid cells. For example, RSD induced distinct patterns of adhesion molecule expression that may explain brain region-dependent myeloid cell trafficking. VCAM-1 and ICAM-1 mRNA expression were increased in an exposure-dependent manner. Furthermore, RSD-induced VCAM-1 and ICAM-1 protein expression were localized to the vasculature of brain regions implicated in fear and anxiety responses, which spatially corresponded to previously reported patterns of myeloid cell trafficking. Next, mRNA expression of additional adhesion molecules (E- and P-selectin, PECAM-1) and chemokines (CXCL1, CXCL2, CXCL12, CCL2) were determined in the brain. Social defeat induced an exposure-dependent increase in mRNA levels of E-selectin, CXCL1, and CXCL2 that increased with additional days of social defeat. While CXCL12 was unaffected by RSD, CCL2 expression was increased by six days of social defeat. Last, comparison between enriched CD11b(+) cells (microglia/macrophages) and enriched GLAST-1(+)/CD11b(-) cells (astrocytes) revealed RSD increased mRNA expression of IL-1β, CCL2, and CXCL2 in microglia/macrophages but not in astrocytes. Collectively, these data indicate that key mediators of leukocyte recruitment were increased in the brain vasculature following RSD in an exposure- and brain region-dependent manner. Copyright © 2014. Published by Elsevier Ltd.
    Neuroscience 10/2014; 302. DOI:10.1016/j.neuroscience.2014.10.004 · 3.36 Impact Factor
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    • "Following induction of focal cerebral ischemia within CX3CR1-/- mice, no difference was observed in the number of IL-1β-expressing microglia; rather, decreased leukocyte infiltration is involved in the development of smaller infarcts [15]. Conversely, in an animal model of spinal cord injury, modest but significantly more recruited monocytes (CD45hi) accumulate in the spinal cord of CX3CR1-/- mice by 3 days post-injury [16]; however, a decrease in the number of CD11b+/Ly6Clo/iNOS+ macrophages after 7 days post-injury was associated with reduced neuropathology and enhanced functional recovery in these CX3CR1-deficient mice [16]. To date, little is known about the CX3CL1/CX3CR1 pathway in the context of microglia activation following brain ischemia. "
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    ABSTRACT: Chemokine (C-X3-C motif) ligand 1 (CX3CL1)/ CX3C chemokine receptor 1 (CX3CR1) signaling is important in modulating the communication between neurons and resident microglia/migrated macrophages in the central nervous system (CNS). Although CX3CR1 deficiency is associated with an improved outcome following ischemic brain injury, the mechanism of this observation is largely unknown. The aim of this study was to investigate how CX3CR1 deficiency influences microglia/macrophage functions in the context of its protection following brain ischemia. Wild-type (WT) and CX3CR1-deficient (CX3CR1-/-) mice were subjected to transient middle cerebral artery occlusion (MCAO) and reperfusion. The ischemic brain damage was monitored by rodent high-field magnetic resonance imaging. Neurological deficit was assessed daily. Neuronal apoptotic death and reactive oxygen species (ROS) production were analyzed by immunostaining and live imaging. Activation/inflammatory response of microglia/macrophage were assessed using immunohistochemistry, flow cytometry, 5-bromo-2-deoxyuridine labeling, cytokine ELISA, and real-time PCR. CX3CR1-/- mice displayed significantly smaller infarcts and less severe neurological deficits compared to WT controls, following MCAO. In addition, CX3CR1-/- MCAO mice displayed fewer apoptotic neurons and reduced ROS levels. Impaired CX3CR1 signaling abrogated the recruitment of monocyte-derived macrophages from the periphery, suppressed the proliferation of CNS microglia and infiltrated macrophage, facilitated the alternative activation (M2 state) of microglia/macrophages, and attenuated their ability to synthesize and release inflammatory cytokines. Our results suggest that inhibition of CX3CR1 signaling could function as a therapeutic modality in ischemic brain injury, by reducing recruitment of peripheral macrophages and expansion/activation of CNS microglia and macrophages, resulting in protection of neurological function.
    Journal of Neuroinflammation 02/2014; 11(1):26. DOI:10.1186/1742-2094-11-26 · 5.41 Impact Factor
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