Effects of neuromyelitis optica–IgG at the blood–brain barrier in vitro

Abstract

Objective:To address the hypothesis that physiologic interactions between astrocytes and endothelial cells (EC) at the blood–brain barrier (BBB) are afflicted by pathogenic inflammatory signaling when astrocytes are exposed to aquaporin-4 (AQP4) antibodies present in the immunoglobulin G (IgG) fraction of serum from patients with neuromyelitis optica (NMO), referred to as NMO-IgG.Methods:We established static and flow-based in vitro BBB models incorporating co-cultures of conditionally immortalized human brain microvascular endothelial cells and human astrocyte cell lines with or without AQP4 expression.Results:In astrocyte–EC co-cultures, exposure of astrocytes to NMO-IgG decreased barrier function, induced CCL2 and CXCL8 expression by EC, and promoted leukocyte migration under flow, contingent on astrocyte expression of AQP4. NMO-IgG selectively induced interleukin (IL)-6 production by AQP4-positive astrocytes. When EC were exposed to IL-6, we observed decreased barrier function, increased CCL2 and CXCL8 expression, and enhanced leukocyte transmigration under flow. These effects were reversed after application of IL–6 neutralizing antibody.Conclusions:Our results indicate that NMO-IgG induces IL-6 production by AQP4-positive astrocytes and that IL-6 signaling to EC decreases barrier function, increases chemokine production, and enhances leukocyte transmigration under flow.

Autoantibody-induced internalization of CNS AQP4 water channel and EAAT2 glutamate transporter requires astrocytic Fc receptor

“…IL-6 is a critical mediator of CNS inflammation in NMO (23,24), as evidenced by the therapeutic benefit of monoclonal IgG blockade of IL-6 (25). Ex vivo, IL-6 released by astrocytes exposed to NMO-IgG reduced CNS capillary endothelial barrier function, increased CCL2 and CXCL8 production, and promoted leukocyte transmigration under flow conditions; these effects were neutralized by IL-6-specific IgG (12). Transient removal of the CD32B inhibitory receptor from astrocyte surfaces in the course of NMO-IgG-induced FcγR signaling might enhance IL-6 release.…”

“…Outcomes documented in vitro after NMO-IgG binds to the AQP4 extracellular domain on astrocytes include AQP4 endocytosis and lysosomal degradation, loss of its physically linked major excitatory amino acid transporter 2 (EAAT2), reduced glutamate uptake, impaired water fluxes, granulocyte chemotaxis, and complement factor transcription, secretion, and activation (1,(6)(7)(8)(9)(10)(11). Ensuing endothelial permeation of circulating immunoglobulins, complement components, and leukocytes magnifies the initial inflammatory response (6)(7)(8)(9)(10)(11)(12). Immunopathological analyses of NMO patients' CNS tissues attest to these events occurring in vivo and inform lesional evolution at the target astrocyte level (1).…”

“…A neglected potential initiator of NMO pathophysiology is the AQP4-IgG-activated astrocyte's response: synthesis and secretion of complement, cytokines, chemokines (12)(13)(14), and inflammatory mediators attracting NMO-characteristic granulocytes. Focally enhanced BBB permeability (7,12) plausibly accounts for initially reversible early NMO symptoms and MRI abnormalities. Early lesions contain viable, phenotypically activated astrocytes lacking AQP4 and EAAT2 (6,15), with myelin intact but focally edematous (9).…”

Diffusion tensor imaging for multilevel assessment of the visual pathway: possibilities for personalized outcome prediction in autoimmune disorders of the central nervous system

“…The discovery and investigation of aquaporin-4 (AQP4)-antibodies [21,[31][32][33][34][35] have revolutionized NMOSD diagnostics by setting the disease apart from MS [36,37] and substantially changing NMOSD treatment [38] which considerably differs from classic diseasemodifying treatment in MS [39][40][41][42][43][44][45][46][47][48]. However, especially against the background of emerging evidence on myelin oligodendrocyte glycoprotein (MOG) -antibody-positive cases related to NMOSD, the heterogeneous pathophysiology of NMOSD still needs to be fully elucidated [49][50][51][52][53][54][55][56][57][58].…”

Finding NMO

“…In this issue of Neurology® Neuroimmunology & Neuroinflammation , Takeshita et al 7 aim to identify complement-independent pathways by which NMO-IgG cause lesion formation. They generated both static and flow-based in vitro brain–blood barrier co-culture models utilizing human brain microvascular endothelial cells and a human astrocyte cell line, either expressing AQ4 or not expressing AQ4.…”