NFκB signaling drives pro-granulocytic astroglial responses to neuromyelitis optica patient IgG.

Margaret E Walker-Caulfield,Patrick D Fitz-Gibbon,Renee K Johnson,Claudia F Lucchinetti,Christina B Mccarthy,Charles L Howe,Yong Guo

doi:10.1186/s12974-015-0403-8

Margaret E Walker-Caulfield, Patrick D Fitz-Gibbon + Show 5 more

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https://doi.org/10.1186/s12974-015-0403-8

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Abstract

BackgroundAstrocytes expressing the aquaporin-4 water channel are a primary target of pathogenic, disease-specific immunoglobulins (IgG) found in patients with neuromyelitis optica (NMO). Immunopathological analyses of active NMO lesions highlight a unique inflammatory phenotype marked by infiltration of granulocytes. Previous studies characterized this granulocytic infiltrate as a response to vasculocentric complement activation and localized tissue destruction. In contrast, we observe that granulocytic infiltration in NMO lesions occurs independently of complement-mediated tissue destruction or active demyelination. These immunopathological findings led to the hypothesis that NMO IgG stimulates astrocyte signaling that is responsible for granulocytic recruitment in NMO.MethodsHistopathology was performed on archival formalin-fixed paraffin-embedded autopsy-derived CNS tissue from 23 patients clinically and pathologically diagnosed with NMO or NMO spectrum disorder. Primary murine astroglial cultures were stimulated with IgG isolated from NMO patients or control IgG from healthy donors. Transcriptional responses were assessed by microarray, and translational responses were measured by ELISA. Signaling through the NFκB pathway was measured by western blotting and immunostaining.ResultsStimulation of primary murine astroglial cultures with NMO IgG elicited a reactive and inflammatory transcriptional response that involved signaling through the canonical NFκB pathway. This signaling resulted in the release of pro-granulocytic chemokines and was inhibited by the clinically relevant proteasome inhibitors bortezomib and PR-957.ConclusionsWe propose that the astrocytic NFκB-dependent inflammatory response to stimulation by NMO IgG represents one of the earliest events in NMO pathogenesis, providing a target for therapeutic intervention upstream of irreversible cell death and tissue damage.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-015-0403-8) contains supplementary material, which is available to authorized users.

Highlights

Astrocytes expressing the aquaporin-4 water channel are a primary target of pathogenic, diseasespecific immunoglobulins (IgG) found in patients with neuromyelitis optica (NMO)
Granulocytic infiltration in NMO pathology is not dependent on terminal complement complex formation, active demyelination, or tissue destruction To determine whether granulocytic infiltration in NMO is dependent on formation of the terminal complement complex, demyelination, or tissue destruction, as the conventional model of NMO pathogenesis suggests, we semi-quantitatively assessed the extent of eosinophil and neutrophil infiltration in 1048 regions in 337 blocks from 23 NMO patients
(See figure on previous page.) Fig. 1 Granulocytic infiltrate occurs in the absence of demyelination, terminal complement complex formation, and overt tissue destruction in NMO white matter. a hematoxylin and eosin (H&E) staining reveals robust perivascular inflammation in the white matter of autopsy tissue collected from an NMO patient. b An enlarged view of (a) and the magnified inset confirm the presence of eosinophils as a component of this perivascular infiltration. c Staining for the astrocyte marker glial fibrillary acidic protein (GFAP) demonstrates the presence of reactive astrocytes with abnormal morphology in close association with granulocytic perivascular infiltration in a section consecutive to a

Summary

Introduction

Astrocytes expressing the aquaporin-4 water channel are a primary target of pathogenic, diseasespecific immunoglobulins (IgG) found in patients with neuromyelitis optica (NMO). Walker-Caulfield et al Journal of Neuroinflammation (2015) 12:185 interpreted in support of a model for NMO pathogenesis wherein NMO IgG gains entry into the CNS, binds to AQP4 on astrocytic foot processes, and induces complement activation and deposition of the terminal membrane attack complex, resulting in astrocyte injury and death that leads to recruitment of eosinophils and neutrophils into the lesions [4, 10] In this model, complementmediated astrocyte death is the key driver of chemokine, cytokine, and toxic effector production in lesions that results in the recruitment of macrophages that induce demyelination and the death of oligodendrocytes and neurons [11]. This suggests that alternative mechanisms may be responsible for granulocytic recruitment in early NMO lesions

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