AQP4-transfected Cells Research Articles

In vitrogeneration of disease-specific autoantibodies produced by B cells from patients with NMOSD and MOGAD.

Abstract The main pathogenic feature of neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein associated disease (MOGAD) is the presence of autoantibodies against water channel, aquaporin-4 (AQP4) and myelin oligodendrocyte glycoprotein (MOG), respectively. However, the underlying mechanisms in which the B cells from these patients produce autoantibodies is largely unknown. Our study aims to establish a human culture system that could characterize the contribution of B cells in the production of these autoantibodies. PBMCs were obtained from NMOSD (n=30) and MOG (n=10) patients. B cells were differentiated into plasmablasts in vitrowith different stimuli resembling the mechanism related with NMOSD and MOGAD development. After 6d culture, cell proliferation and plasmablast frequency were assessed. Quantification of total IgG levels and detection of AQP4-IgG or MOG-IgG were determined on D13. Our data showed that the presence of R848 (TLR7/8), regardless of sCD40L or cytokines, resulted in B cell proliferation in NMOSD (ave: 78.2% ± 18.5 SEM) and MOGAD patients (ave: 90.4% ± 5.2 SEM). Moreover, in vitrogeneration of plasmablasts require sCD40L and R848 in NMOSD (ave: 45.6 ± 21.1 SEM) and MOGAD (ave: 54.4% ± 11.5 SEM). Further culture until D13 resulted in IgG secretion by the plasmablasts generated from NMOSD (ave: 18,150.07 ng/mL) and MOGAD (ave: 17,959.25 ng/mL). For all the conditions that generated plasmablasts, autoantibodies were detected to be reactive with either AQP4-transfected cells in NMOSD (10/30 patients) or MOG-transfected cells in MOGAD (6/10 patients). This in vitromodel have important implications for therapy selection and understanding the mechanisms of NMOSD and MOGAD development. This study was supported by the International Cooperation Education Program of National Cancer Center Korea (NCCRI·NCCI 52210-52211).

Human C5-specific single-chain variable fragment ameliorates brain injury in a model of NMOSD.

ObjectiveUsing phage display, we sought to screen single-chain variable fragments (scFvs) against complement C5 to treat neuromyelitis optica spectrum disorder (NMOSD).MethodsAfter 5 rounds of phage display, we isolated individual clones and identified phage clones specifically binding to C5 using ELISA. Using aquaporin-4 (AQP4)-transfected cells in vitro, we confirmed whether these scFvs prevented complement-dependent cytotoxicity (CDC) caused by the serum of patients with NMOSD and human complement (hC). We selected an NMOSD mouse model, in which intracerebral NMOSD immunoglobulin G (IgG) and hC injections induce NMOSD-like lesions in vivo.ResultsWe obtained scFvs to test specificity and blocking efficiency. The scFv C5B3 neutralized C5 in the complement activation pathway, which prevented AQP4-IgG–mediated CDC in AQP4-transfected cells. In an NMOSD mouse model, C5B3 prevented AQP4 and astrocyte loss, decreased demyelination, and reduced inflammatory infiltration and membrane attack complex formation in lesions.ConclusionsWe used phage display to screen C5B3 against C5, which was effective in inhibiting cytotoxicity in vitro and preventing CNS pathology in vivo.

Prognostic factors and disease course in aquaporin-4 antibody-positive Chinese patients with acute optic neuritis.

The objective is to assess the frequency of AQP4-Ab in Chinese patients with optic neuritis (ON) and to investigate the prognostic implications of AQP4-Ab seropositivity in such patients. The presence of aquaporin-4 (AQP4) antibodies in human AQP4-transfected cells was determined by indirect immunofluorescence, and the diagnostic and prognostic relevance of AQP4 antibodies in 215 Chinese patients with optic neuritis was evaluated. The patients were enrolled from the Chinese People's Liberation Army General Hospital (PLAGH) and followed up to 1-228months. Kaplan-Meier survival analysis was used to investigate the visual outcomes and prognostic characteristics of 70 patients who were aquaporin-4 antibody seropositive, and altogether 115 eyes were involved. AQP4-Ab was detectable in 70/215 (32.6%) patients with acute monosymptomatic optic neuritis. These AQP4-Ab seropositive patients were diagnosed as sufferers of neuromyelitis optica (NMO) (n=10), NMO spectrum disease (NMOSD) (n=41), multiple sclerosis (MS) (n=1), and acute optic neuritis (AON) (n=18). Moreover, AQP4-Ab levels did not vary between seropositive AON and NMO-ON and did not correlate with disease severity. Finally, the male gender, older age at onset, number of relapses, concomitant autoimmune antibodies, and optic lesions in magnetic resonance imaging (MRI) were associated with the AQP4-Ab seropositive status and the risk of developing permanent visual disability. Acute optic neuritis has a higher incidence of anti-aquaporin-4 antibody in China than in Western countries, and AQP4 antibody is a sensitive and specific biomarker for discriminating NMO-ON from other types of optic neuritis during the early stage of the disease course.

Complement-dependent and -independent aquaporin 4-antibody-mediated cytotoxicity in human astrocytes: Pathogenetic implications in neuromyelitis optica

BackgroundNeuromyelitis optica (NMO) is an inflammatory disease caused by the aquaporin (AQP)-4-antibody. Pathological studies on NMO have revealed extensive astrocytic damage, as evidenced by the loss of AQP4 and glial fibrillary acidic protein (GFAP), specifically in perivascular regions with immunoglobulin and complement depositions, although other pathological patterns, such as a loss of AQP4 without astrocyte destruction and clasmatodendrosis, have also been observed. Previous studies have shown that complement-dependent antibody-mediated astrocyte lysis is likely a major pathomechanism in NMO. However, there are also data to suggest antibody-mediated astrocyte dysfunction in the absence of complement. Thus, the importance of complement inhibitory proteins in complement-dependent AQP4-antibody-mediated astrocyte lysis in NMO is unclear. In most of the previous studies, the complement and target cells (astrocytes or AQP4-transfected cells) were derived from different species; however, the complement inhibitory proteins that are expressed on the cell surface cannot protect themselves against complement-dependent cytolysis unless the complements and complement inhibitory proteins are from the same species. To resolve these issues, we studied human astrocytes in primary culture treated with AQP4-antibody in the presence or absence of human complement and examined the effect of complement inhibitory proteins using small interfering RNA (siRNA). MethodsPurified IgG (10mg/mL) was obtained from 5 patients with AQP4-antibody-positive NMO, 3 patients with multiple sclerosis (MS), and 3 healthy controls. Confluent human astrocytes transfected with Venus-M1-AQP4-cDNA were incubated with IgG (5% volume). After washing, we cultured the cells with human complements with or without heat inactivation. We observed time-lapse morphological and immunohistochemical changes using a fluorescence microscope. We also evaluated cytotoxicity using a propidium iodide (PI) kit and the lactate dehydrogenase (LDH) assay. ResultAQP4-antibody alone caused clustering and degradation followed by endocytosis of membraneous AQP4, thereby resulting in decreased cellular adherence and the shrinkage of astrocytic processes. However, these changes were partially reversed by the removal of IgG in culture. In contrast, following the application of AQP4-antibody and non-heated human complements, the cell bodies and nuclei started to swell. At 3h, most of the astrocytes had lost mobility and adherence and were eventually destroyed or had swollen and were then destroyed. In addition, the remaining adherent cells were mostly PI-positive, indicating necrosis. Astrocyte lysis caused by rabbit complement occurred much faster than did cell lysis with human complement. However, the cell lysis was significantly enhanced by the transfection of astrocytes with siRNA against human CD55 and CD59, which are major complement inhibitory proteins on the astrocyte membrane. AQP4-antibody-negative IgG in MS or control did not induce such changes. ConclusionTaken together, these findings suggest that both complement-dependent and complement-independent AQP4-antibody-mediated astrocytopathies may operate in NMO, potentially contributing to diverse pathological patterns. Our results also suggest that the effect of complement inhibitory proteins should be considered when evaluating AQP4-antibody-mediated cytotoxicity in AQP4-expressing cells.

C1q-targeted monoclonal antibody prevents complement-dependent cytotoxicity and neuropathology in in vitro and mouse models of neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune disorder with inflammatory demyelinating lesions in the central nervous system, particularly in the spinal cord and optic nerve. NMO pathogenesis is thought to involve binding of anti-aquaporin-4 (AQP4) autoantibodies to astrocytes, which causes complement-dependent cytotoxicity (CDC) and downstream inflammation leading to oligodendrocyte and neuronal injury. Vasculocentric deposition of activated complement is a prominent feature of NMO pathology. Here, we show that a neutralizing monoclonal antibody against the C1q protein in the classical complement pathway prevents AQP4 autoantibody-dependent CDC in cell cultures and NMO lesions in ex vivo spinal cord slice cultures and in mice. A monoclonal antibody against human C1q with 11nM binding affinity prevented CDC caused by NMO patient serum in AQP4-transfected cells and primary astrocyte cultures, and prevented complement-dependent cell-mediated cytotoxicity (CDCC) produced by natural killer cells. The anti-C1q antibody prevented astrocyte damage and demyelination in mouse spinal cord slice cultures exposed to AQP4 autoantibody and human complement. In a mouse model of NMO produced by intracerebral injection of AQP4 autoantibody and human complement, the inflammatory demyelinating lesions were greatly reduced by intracerebral administration of the anti-C1q antibody. These results provide proof-of-concept for C1q-targeted monoclonal antibody therapy in NMO. Targeting of C1q inhibits the classical complement pathway directly and causes secondary inhibition of CDCC and the alternative complement pathway. As C1q-targeted therapy leaves the lectin complement activation pathway largely intact, its side-effect profile is predicted to differ from that of therapies targeting downstream complement proteins.

Aquaporin-4 antibody–positive cases beyond current diagnostic criteria for NMO spectrum disorders

To analyze aquaporin-4 (AQP4) antibody-positive patients who do not fulfill the current diagnostic criteria of neuromyelitis optica (NMO) and NMO spectrum disorders (NMOSD). We used a cell-based assay (CBA) with AQP4-transfected cells to detect AQP4 antibody in 298 consecutive patients with inflammatory CNS disorders seen at Tohoku University Hospital from 2007 to 2012. The patients were diagnosed as NMO, NMOSD, multiple sclerosis, or others using the respective current diagnostic criteria. The seropositive samples by CBA were also tested using a commercial ELISA. Seventy-two patients were AQP4 antibody positive. Among them, 18.1% (13/72) did not meet the NMO or NMOSD criteria (7 with monophasic optic neuritis, 2 with attacks restricted to the brainstem, and 4 with myelitis with less than 3 vertebral segments) and 84.6% (11/13) of these had only a single attack. The ELISA results were negative in 38.4% (5/13) of those patients, and they had lower antibody titers by CBA than patients with NMO/NMOSD. Although these patients had a shorter follow-up and few attacks, they shared some clinical features with NMO/NMOSD patients such as onset age, female predominance, presence of other autoantibodies, severe optic neuritis attacks, centrally located spinal cord lesions, persisting hiccups, and nausea or vomiting episodes. AQP4 antibody-positive patients with single or recurrent attacks of optic neuritis, myelitis, or brain/brainstem disease not fulfilling the current criteria of NMO or NMOSD may not be uncommon, and they should also be included in the NMO spectrum.

The role of aquaporin-4 antibodies in Chinese patients with neuromyelitis optica

We determined the presence of aquaporin-4 (AQP4) antibodies by indirect immunofluorescence in human AQP4-transfected cells, and evaluated the diagnostic and prognostic relevance of AQP4 antibodies in 210 Chinese patients with neuromyelitis optica (NMO), high-risk NMO (HR-NMO), classic multiple sclerosis (MS), and other neurologic diseases. Patients were enrolled from The General Hospital of the Chinese People’s Liberation Army and followed-up for a median of 2years. The patients with HR-NMO had optico-spinal MS (OSMS; n=3), longitudinally extensive transverse myelitis (TM) (n=35), recurrent optic neuritis (ON) (n=2), ON with Sjögren’s syndrome (n=1) and TM positive for Sjögren-A(SSA) antibody (n=1). The sensitivity and specificity of AQP4 antibodies in NMO were 70.9% and 91%, respectively. The median AQP4 antibody titer was significantly higher in patients with NMO (1:320) than in those with HR-NMO (1:100) and MS (1:50). Relapse of ON or TM was more likely in patients with AQP4 seropositive, than AQP4 seronegative, HR-NMO. Among AQP4 seropositive patients, 66.7% (36/55) had severe ON, 75.9% (41/55) had TM, and 55.6% (30/55) had spinal cord lesions longer than three segments, and there were relapses in eight of 55 patients with ON (14.8%) and 19 of 55 patients with TM (35.2%) during the 2-year follow-up. In conclusion, our study reveals that AQP4 antibody is a sensitive and specific biomarker for discrimination of NMO, classic MS, and other neurological diseases, and is particularly useful for the diagnosis of HR-NMO. AQP4 antibody-positive patients showed higher frequencies of relapse of ON or TM compared with AQP4 antibody-negative patients.

Post‐Golgi Supramolecular Assembly of Aquaporin‐4 in Orthogonal Arrays

The supramolecular assembly of aquaporin-4 (AQP4) in orthogonal arrays of particles (OAPs) involves N-terminus interactions of the M23-AQP4 isoform. We found AQP4 OAPs in cell plasma membranes but not in endoplasmic reticulum (ER) or Golgi, as shown by: (i) native gel electrophoresis of brain and AQP4-transfected cells, (ii) photobleaching recovery of green fluorescent protein-AQP4 chimeras in live cells and (iii) freeze-fracture electron microscopy (FFEM). We found that AQP4 OAP formation in plasma membranes, but not in the Golgi, was not related to AQP4 density, pH, membrane lipid composition, C-terminal PDZ domain interactions or α-syntrophin expression. Remarkably, however, fusion of AQP4-containing Golgi vesicles with (AQP4-free) plasma membrane vesicles produced OAPs, suggesting the involvement of plasma membrane factor(s) in AQP4 OAP formation. In investigating additional possible determinants of OAP assembly we discovered membrane curvature-dependent OAP assembly, in which OAPs were disrupted by extrusion of plasma membrane vesicles to ∼110 nm diameter, but not to ∼220 nm diameter. We conclude that AQP4 supramolecular assembly in OAPs is a post-Golgi phenomenon involving plasma membrane-specific factor(s). Post-Golgi and membrane curvature-dependent OAP assembly may be important for vesicle transport of AQP4 in the secretory pathway and AQP4-facilitated astrocyte migration, and suggests a novel therapeutic approach for neuromyelitis optica.

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

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. To compare the prognostic utility of NMO-IgG titer and quantitative measures of complement-mediated injury to AQP4-expressing cells in NMO attacks. A retrospective clinical-serological correlative study at Mayo Clinic's Neuroimmunology Laboratory was undertaken. Over an 18-month 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. Attack severity (mild or severe), percentage of AQP4-transfected cells lesioned, and NMO-IgG titer. 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). A laboratory measure of complement-mediated cell injury may serve as a prognostic biomarker in NMO. Larger prospective studies are required to validate this observation.

Automated Cell-Based Assay for Screening of Aquaporin Inhibitors

Aquaporins form water channels that play major roles in a variety of physiological processes so that altered expression or function may underlie pathological conditions. In order to identify compounds that modulate aquaporin function, we have implemented a functional assay based on rapid measurement of osmotically induced cell volume changes to screen several libraries of diverse drugs. The time course of fluorescence changes in calcein-loaded cells was analyzed during an osmotic challenge using a 96-multiwell fluorescence plate reader. This system was validated using astrocyte primary cultures and fibroblasts that strongly express endogenous AQP4 and AQP1 proteins, respectively, as well as AQP4-transfected cells. We screened 3575 compounds, including 418 FDA-approved and commercially available drugs, for their effect on AQP-mediated water transport. Primary screening yielded 10 compounds that affected water transport activity in both astrocytes and AQP4-transfected cells and 42 compounds that altered cell volume regulation in astrocytes. Selected drugs were then analyzed on AQP1-expressing erythrocytes and AQP4-expressing membrane vesicles by stopped-flow light scattering. Four molecules of the National Cancer Institute's chemical library (NSC164914, NSC670229, NSC168597, NSC301460) were identified that differentially affected both AQP4 and AQP1 mediated water transport, with EC50 values between 20 and 50 microM. This fluorescence microplate reader-based assay may, thus, provide a platform for high-throughput screening which, when coupled to a secondary evaluation to confirm target specificity, should allow discovery of AQP-specific compounds for novel therapeutic strategies in the treatment of water balance disorders.

Anti-aquaporin-4 antibody is involved in the pathogenesis of NMO: a study on antibody titre

NMO-IgG is a disease-specific autoantibody for neuromyelitis optica (NMO) and its target antigen is aquaporin-4 (AQP4) water channel. Recently, we established a sensitive anti-AQP4 antibody assay using human AQP4-transfected cells, which appeared more sensitive than the original NMO-IgG assay. So far, there has been no large-scale study on anti-AQP4 antibody titre in NMO and related disorders. We tested 148 sera of patients with NMO, high-risk syndrome of NMO, multiple sclerosis (MS), clinically isolated syndrome suggestive of MS and miscellaneous diseases. We analysed the relation of anti-AQP4 antibody titres and clinical and laboratory parameters. The sensitivity of anti-AQP4 antibody assay was 91% (95% CI 79-100) for NMO and 85% (65-100) for high-risk syndrome, and the specificity was 100% (91-100) for NMO and high-risk syndrome, that is, none with the other disorders was positive. Among 21 anti-AQP4 antibody-positive cases whose NMO-IgG were tested, 15 were NMO-IgG-positive and 6 were NMO-IgG-negative. Higher anti-AQP4 antibody titres were associated with complete blindness and extensive or large cerebral lesions on MRI. The lengths of spinal cord lesions on MRI were positively correlated with the titres of anti-AQP4 antibody at the nadir of exacerbations. A few patients who had short (approx. one to two vertebral segments) spinal cord lesions on MRI were also seropositive with low anti-AQP4 antibody titres, but did have other clinical and MRI features of NMO. Anti-AQP4 antibody titres became lower after high-dose methylprednisolone, and a follow-up showed anti-AQP4 antibody titres remained low in relapse-free periods under immunosuppression. Cerebrospinal fluid (CSF)-anti-AQP4 antibody was detected when the serum-antibody titres exceeded 512x, at the ratio of 1 (CSF) to 500 (serum). Using a sensitive assay, the results of the present study suggest that NMO and high-risk syndrome may be essentially anti-AQP4 antibody-associated disorders, and that the anti-AQP4 antibody titres have significant clinical and immunological implications in NMO.