Astrocyte response to IFN-γ limits IL-6-mediated microglia activation and progressive autoimmune encephalomyelitis

• Authors: Carine Savarin, Cleveland Clinic Foundation; David R. Hinton, University of Southern California, Los Angeles; Alice Valentin-Torres, Cleveland Clinic Foundation; Zhihong Chen, Emory University; Bruce D. Trapp, Cleveland Clinic Foundation; Cornelia C. Bergmann, Cleveland Clinic Foundation; Stephen A. Stohlman, Cleveland Clinic Foundation
• Journal Title: Journal of Neuroinflammation
• Volume: Volume 12, Number 1
• Publisher: BMC (part of Springer Nature) | 2015-12-12, Pages 79-79
• Type of Work: Article | Final Publisher PDF
• Publisher DOI: http://doi.org/10.1186/s12974-015-0293-9
• Subjects: Health Sciences, Pathology; Health Sciences, Immunology
• Keywords: Animals; Antibodies, Neutralizing; Astrocytes; Demyelinating Diseases; Encephalomyelitis, Autoimmune, Experimental; Glial Fibrillary Acidic Protein; Gliosis; Humans; Interferon-gamma; Interleukin-6; Macrophage Activation; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microglia; Multiple Sclerosis; Promoter Regions, Genetic

Abstract

Background: Therapeutic modalities effective in patients with progressive forms of multiple sclerosis (MS) are limited. In a murine model of progressive MS, the sustained disability during the chronic phase of experimental autoimmune encephalomyelitis (EAE) correlated with elevated expression of interleukin (IL)-6, a cytokine with pleiotropic functions and therapeutic target for non-central nervous system (CNS) autoimmune disease. Sustained IL-6 expression in astrocytes restricted to areas of demyelination suggested that IL-6 plays a major role in disease progression during chronic EAE. Methods: A progressive form of EAE was induced using transgenic mice expressing a dominant negative interferon-γ (IFN-γ) receptor alpha chain under control of human glial fibrillary acidic protein (GFAP) promoter (GFAPγR1Δ mice). The role of IL-6 in regulating progressive CNS autoimmunity was assessed by treating GFAPγR1Δ mice with anti-IL-6 neutralizing antibody during chronic EAE. Results: IL-6 neutralization restricted disease progression and decreased disability, myelin loss, and axonal damage without affecting astrogliosis. IL-6 blockade reduced CNS inflammation by limiting inflammatory cell proliferation; however, the relative frequencies of CNS leukocyte infiltrates, including the Th1, Th17, and Treg CD4 T cell subsets, were not altered. IL-6 blockade rather limited the activation and proliferation of microglia, which correlated with higher expression of Galectin-1, a regulator of microglia activation expressed by astrocytes. Conclusions: These data demonstrate that astrocyte-derived IL-6 is a key mediator of progressive disease and support IL-6 blockade as a viable intervention strategy to combat progressive MS.