Aquaporin-4–binding autoantibodies in patients with neuromyelitis optica impair glutamate transport by down-regulating EAAT2

Hinson, Shannon R.; Roemer, Shanu F.; Lucchinetti, Claudia F.; Fryer, James P.; Kryzer, Thomas J.; Chamberlain, Jayne L.; Howe, Charles L.; Pittock, Sean J.; Lennon, Vanda A.

doi:10.1084/jem.20081241

Cited by 308 publications

(322 citation statements)

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“…EAAT2 loss is a striking feature of early, nondestructive spinal gray matter lesions in autopsied NMO patients (6). Furthermore, live astrocytes exposed in vitro to NMO-IgG transport less glutamate (6,11,21) because, being noncovalently linked to AQP4, EAAT2 is coendocytosed (6). We therefore evaluated NMO-F(ab′) 2 effect on EAAT2.…”

Section: Astrocytic Eaat2 Glutamate Transporter Degradation Requires mentioning

confidence: 99%

“…We previously demonstrated that NMO-IgG binding to AQP4 in live cells causes membrane AQP4 to relocate to the endolysosomal path (6,9,10). To separate early events from downstream Fc-dependent events, we investigated F(ab′) 2 prepared from NMO patients and healthy subjects.…”

Section: Aqp4mentioning

confidence: 99%

“…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).…”

mentioning

confidence: 99%

“…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).…”

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confidence: 99%

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

Hinson

Clift

Luo

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Aquaporin-4 (AQP4) water channel-specific IgG distinguishes neuromyelitis optica (NMO) from multiple sclerosis and causes characteristic immunopathology in which central nervous system (CNS) demyelination is secondary. Early events initiating the pathophysiological outcomes of IgG binding to astrocytic AQP4 are poorly understood. CNS lesions reflect events documented in vitro following IgG interaction with AQP4: AQP4 internalization, attenuated glutamate uptake, intramyelinic edema, interleukin-6 release, complement activation, inflammatory cell recruitment, and demyelination. Here, we demonstrate that AQP4 internalization requires AQP4-bound IgG to engage an astrocytic Fcγ receptor (FcγR). IgG-lacking Fc redistributes AQP4 within the plasma membrane and induces interleukin-6 release. However, AQP4 endocytosis requires an activating FcγR's gamma subunit and involves astrocytic membrane loss of an inhibitory FcγR, CD32B. Interaction of the IgG-AQP4 complex with FcγRs triggers coendocytosis of the excitatory amino acid transporter 2 (EAAT2). Requirement of FcγR engagement for internalization of two astrocytic membrane proteins critical to CNS homeostasis identifies a complement-independent, upstream target for potential early therapeutic intervention in NMO.N euromyelitis optica (NMO) is a relapsing inflammatory autoimmune demyelinating disease of the central nervous system (CNS), long considered a severe form of multiple sclerosis (MS). Attacks are generally more severe, onset of paralysis and blindness more rapid (1), and standard MS therapies can worsen NMO (2, 3). A specific serum IgG allows early distinction from MS, thus ensuring timely appropriate therapy (4, 5).The aquaporin-4 (AQP4) water channel is the CNS target (4). 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, 6-11). Ensuing endothelial permeation of circulating immunoglobulins, complement components, and leukocytes magnifies the initial inflammatory response (6-12). Immunopathological analyses of NMO patients' CNS tissues attest to these events occurring in vivo and inform lesional evolution at the target astrocyte level (1). The blood-brain barrier (BBB) does not absolutely restrict IgG entry into the CNS, but it does exclude macromolecular C1q, essential for activating the classical complement cascade.Experimental studies of lesional events in vitro and in animal models of NMO have emphasized complement-mediated inflammation and astrocyte cytolysis, late events associated with extensive BBB disruption. A neglected potential initiator of NMO pathophysiology is the AQP4-IgG-activated astrocyte's response: synthesis and secretion of complement, cytokines, chemokines (12-14), and inflammatory mediators attracting NMO-characteristic gra...

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Section: Astrocytic Eaat2 Glutamate Transporter Degradation Requires mentioning

confidence: 99%

Section: Aqp4mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

Hinson

Clift

Luo

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Lesions characteristically affect the spinal cord and optic nerve, but do not spare the brain. Independent laboratories have demonstrated that NMO-IgG binding initiates AQP4 down-regulation with accompanying endocytosis of its physically associated glutamate transporter, EAAT2, complement activation, impairment of blood-brain barrier integrity, inflammation, and astrocyte injury (4)(5)(6)(7)(8). Demyelination is a proposed consequence of both paranodal targeting of AQP4 near oligodendroglial loops (4) and glutamate toxicity to oligodendrocytes (5).…”

mentioning

confidence: 99%

Molecular outcomes of neuromyelitis optica (NMO)-IgG binding to aquaporin-4 in astrocytes

Hinson¹,

Romero²,

Popescu³

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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The astrocytic aquaporin-4 (AQP4) water channel is the target of pathogenic antibodies in a spectrum of relapsing autoimmune inflammatory central nervous system disorders of varying severity that is unified by detection of the serum biomarker neuromyelitis optica (NMO)-IgG. Neuromyelitis optica is the most severe of these disorders. The two major AQP4 isoforms, M1 and M23, have identical extracellular residues. This report identifies two novel properties of NMO-IgG as determinants of pathogenicity. First, the binding of NMO-IgG to the ectodomain of astrocytic AQP4 has isoform-specific outcomes. M1 is completely internalized, but M23 resists internalization and is aggregated into larger-order orthogonal arrays of particles that activate complement more effectively than M1 when bound by NMO-IgG. Second, NMO-IgG binding to either isoform impairs water flux directly, independently of antigen down-regulation. We identified, in nondestructive central nervous system lesions of two NMO patients, two previously unappreciated histopathological correlates supporting the clinical relevance of our in vitro findings: (i) reactive astrocytes with persistent foci of surface AQP4 and (ii) vacuolation in adjacent myelin consistent with edema. The multiple molecular outcomes identified as a consequence of NMO-IgG interaction with AQP4 plausibly account for the diverse pathological features of NMO: edema, inflammation, demyelination, and necrosis. Differences in the nature and anatomical distribution of NMO lesions, and in the clinical and imaging manifestations of disease documented in pediatric and adult patients, may be influenced by regional and maturational differences in the ratio of M1 to M23 proteins in astrocytic membranes.T he most abundant water channel in the central nervous system (CNS) is aquaporin-4 (AQP4), which is confined to astrocytes and ependyma; is enriched at glial-pial and glialendothelial interfaces; and surrounds nodes of Ranvier and paranodes, adjacent oligodendroglial loops, and synapses (1). In 2005, we identified AQP4 as the target of pathogenic autoantibodies in a spectrum of inflammatory CNS disorders of varying severity that is unified by detection of the serum biomarker neuromyelitis optica (NMO)-IgG (2, 3). These disorders are now recognized collectively as IgG-mediated autoimmune astrocytopathies. Before discovery of this antibody, NMO spectrum disorders were misclassified as multiple sclerosis variants. NMOIgG is centrally involved in the pathogenesis of NMO spectrum disorders. Its detection predicts frequent relapses that cause cumulative neurological impairment. Lesions characteristically affect the spinal cord and optic nerve, but do not spare the brain. Independent laboratories have demonstrated that NMO-IgG binding initiates AQP4 down-regulation with accompanying endocytosis of its physically associated glutamate transporter, EAAT2, complement activation, impairment of blood-brain barrier integrity, inflammation, and astrocyte injury (4-8). Demyelination is a proposed consequence of both pa...

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Prediction of Neuromyelitis Optica Attack Severity by Quantitation of Complement-Mediated Injury to Aquaporin-4–Expressing Cells

Hinson¹,

McKeon²,

Fryer³

et al. 2009

Arch Neurol

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Background: Recent reports support a pathogenic role in neuromyelitis optica (NMO) for the aquaporin-4 (AQP4)-specific autoantibody (NMO-IgG). Neuromyelitis optica is an inflammatory demyelinating central nervous system disease, usually relapsing, that causes variable degrees of attack-related disability. The NMO-IgG binds in vitro to the extracellular domain of AQP4, activates complement, and causes astrocyte lesioning. Objective: To compare the prognostic utility of NMO-IgG titer and quantitative measures of complementmediated injury to AQP4-expressing cells in NMO attacks. Design, Setting, and Participants: A retrospective clinical-serological correlative study at Mayo Clinic's Neuroimmunology Laboratory was undertaken. Over an 18month period, we identified NMO-IgG-seropositive patients in whom sufficient serum and adequate clinical information pertaining to NMO attacks (6 severe, 6 mild) were available to analyze clinical-serological correlations. Sera from 9 patients with multiple sclerosis and 9 healthy subjects (all NMO-IgG seronegative) served as controls. Complement activation was measured by quantifying the number of green fluorescent protein-AQP4-transfected HEK 293 cells permeable to the viability dye propidium iodide after exposure to patient serum and active complement. Main Outcome Measures: Attack severity (mild or severe), percentage of AQP4-transfected cells lesioned, and NMO-IgG titer. Results: The median percentage of AQP4-transfected cells lesioned by complement in the presence of serum from patients with NMO was 14% for patients with mild attacks and 54% for patients with severe attacks (P=.005). Median complement activation values for sera from healthy subjects and patients with multiple sclerosis were 8% and 12%, respectively. Patients with mild NMO attacks and patients with severe NMO attacks did not differ significantly with respect to NMO-IgG titer (P=.089). Conclusions: A laboratory measure of complementmediated cell injury may serve as a prognostic biomarker in NMO. Larger prospective studies are required to validate this observation.

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Aquaporin-4–binding autoantibodies in patients with neuromyelitis optica impair glutamate transport by down-regulating EAAT2

Cited by 308 publications

References 29 publications

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

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

Molecular outcomes of neuromyelitis optica (NMO)-IgG binding to aquaporin-4 in astrocytes

Prediction of Neuromyelitis Optica Attack Severity by Quantitation of Complement-Mediated Injury to Aquaporin-4–Expressing Cells

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