Neuromyelitis optica: aquaporin-4 based pathogenesis mechanisms and new therapies

Aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders: progress of experimental models based on disease pathogenesis

Neuromyelitis optica spectrum disorders are neuroinflammatory demyelinating disorders that lead to permanent visual loss and motor dysfunction. To date, no effective treatment exists as the exact causative mechanism remains unknown. Therefore, experimental models of neuromyelitis optica spectrum disorders are essential for exploring its pathogenesis and in screening for therapeutic targets. Since most patients with neuromyelitis optica spectrum disorders are seropositive for IgG autoantibodies against aquaporin-4, which is highly expressed on the membrane of astrocyte endfeet, most current experimental models are based on aquaporin-4-IgG that initially targets astrocytes. These experimental models have successfully simulated many pathological features of neuromyelitis optica spectrum disorders, such as aquaporin-4 loss, astrocytopathy, granulocyte and macrophage infiltration, complement activation, demyelination, and neuronal loss; however, they do not fully capture the pathological process of human neuromyelitis optica spectrum disorders. In this review, we summarize the currently known pathogenic mechanisms and the development of associated experimental models in vitro, ex vivo, and in vivo for neuromyelitis optica spectrum disorders, suggest potential pathogenic mechanisms for further investigation, and provide guidance on experimental model choices. In addition, this review summarizes the latest information on pathologies and therapies for neuromyelitis optica spectrum disorders based on experimental models of aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders, offering further therapeutic targets and a theoretical basis for clinical trials.

Lycium barbarum glycopeptide ameliorates motor and visual deficits in autoimmune inflammatory diseases

BACKGROUND

Lycium barbarum glycopeptide (LbGp), extracted from the traditional Chinese medicine (TCM) of Lycium barbarum (LB), provides a neuroprotective effect against neurodegenerative and neuroimmune disorders contributing to its immunomodulatory and anti-inflammatory roles. Neuromyelitis optica spectrum disorders (NMOSD) is an autoimmune-mediated central nervous system (CNS) demyelinating disease, clinically manifested as transverse myelitis (TM) and optic neuritis. However, no drug has been demonstrated to be effective in relieving limb weakness and visual impairment of NMOSD patients.

PURPOSE

This study investigates the potential role of LbGp in ameliorating pathologic lesions and improving neurological dysfunction during NMOSD progression, and to elucidate the underlying mechanisms for the first time.

STUDY DESIGN

We administrate LbGp in experimental NMOSD models in ex vivo and in vivo to explore its effect on NMOSD.

METHODS

To evaluate motor function, both rotarod and gait tasks were performed in systemic NMOSD mice models. Furthermore, we assessed the severity of NMO-like lesions of astrocytes, organotypic cerebellar slices, as well as brain, spinal cord and optic nerve sections from NMOSD mouse models with LbGp treatment by immunofluorescent staining. In addition, demyelination levels in optic nerve were measured by G-ratio through Electro-microscopy (EM). And inflammation response was explored through detecting the protein levels of proinflammatory cytokines and NF-κB signaling in astrocytic culture medium and spinal cord homogenates respectively by Elisa and by Western blotting.

RESULTS

LbGp could significantly reduce astrocytes injury, demyelination, and microglial activation in NMOSD models. In addition, LbGp also improved locomotor and visual dysfunction through preventing neuron and retinal ganglion cells (RGCs) from inflammatory attack in a systemic mouse model. Mechanistically, LbGp inhibits proinflammatory factors release via inhibition of NF-κB signaling in NMOSD models.

CONCLUSION

This study provides evidence to develop LbGp as a functional TCM for the clinical treatment of NMOSD.

Retinal structural and microvascular deterioration independent of optic neuritis in aquaporin-4 antibody-positive neuromyelitis optica spectrum disorders: An optical coherence tomography angiography study

PURPOSE

To assess the retinal structural and microvascular change in aquaporin-4 antibody (AQP4) positive neuromyelitis optica spectrum disorder (NMOSD) patients and the correlation with clinical features.

METHODS

A cross-sectional study was performed with optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) to measure retinal structure and microvascular parameters in AQP4 positive NMOSD patients.

RESULTS

Sixty-two NMOSD patients (44 eyes with ON, NMOSD+ON; 77 eyes without ON, NMOSD-ON) and 62 healthy controls (HC, 124 eyes) were included. BCVA was worse in NMOSD patients compared to HC (p<0.001). Peripapillary retinal nerve fiber layer (pRNFL, p<0.001) and ganglion cell complex (GCC, p<0.001) was thinner in NMOSD+ON eyes compared to NMOSD-ON eyes and HC. Compared to HC, pRNFL (p = 0.002) and GCC (p = 0.001) was thinner in NMOSD-ON eyes. The vessel density (VD) in superficial capillary plexus (SCP, NMOSD+ON vs HC p<0.001, NMOSD-ON vs HC p = 0.002) and radial peripapillary capillary (RPC, NMOSD+ON vs HC p<0.001, NMOSD-ON vs HC p = 0.001) were also lower in NMOSD patients than HC independent of the history of ON. ON frequency and BCVA were correlated with the thickness of pRNFL and GCC, and VD in SCP and RPC (all p<0.001). EDSS was correlated with thickness of GCC (p = 0.008), and VD in SCP (p = 0.013), DCP (p<0.001) and RPC (p = 0.009).

CONCLUSIONS

Subclinical degradation of retinal structure and microvasculature was found in NMOSD patients before the occurrence of ON, and was correlated with clinical disability. Retinal parameter might be a tool to estimate the disease progression and investigate the pathogenesis of NMOSD.

Methyl-CpG-Binding Protein 2 Emerges as a Central Player in Multiple Sclerosis and Neuromyelitis Optica Spectrum Disorders

MECP2 and its product methyl-CpG binding protein 2 (MeCP2) are associated with multiple sclerosis (MS) and neuromyelitis optica spectrum disorders (NMOSD), which are inflammatory, autoimmune, and demyelinating disorders of the central nervous system (CNS). However, the mechanisms and pathways regulated by MeCP2 in immune activation in favor of MS and NMOSD are not fully understood. We summarize findings that use the binding properties of MeCP2 to identify its targets, particularly the genes recognized by MeCP2 and associated with several neurological disorders. MeCP2 regulates gene expression in neurons, immune cells and during development by modulating various mechanisms and pathways. Dysregulation of the MeCP2 signaling pathway has been associated with several disorders, including neurological and autoimmune diseases. A thorough understanding of the molecular mechanisms underlying MeCP2 function can provide new therapeutic strategies for these conditions. The nervous system is the primary system affected in MeCP2-associated disorders, and other systems may also contribute to MeCP2 action through its target genes. MeCP2 signaling pathways provide promise as potential therapeutic targets in progressive MS and NMOSD. MeCP2 not only increases susceptibility and induces anti-inflammatory responses in immune sites but also leads to a chronic increase in pro-inflammatory cytokines gene expression (IFN-γ, TNF-α, and IL-1β) and downregulates the genes involved in immune regulation (IL-10, FoxP3, and CX3CR1). MeCP2 may modulate similar mechanisms in different pathologies and suggest that treatments for MS and NMOSD disorders may be effective in treating related disorders. MeCP2 regulates gene expression in MS and NMOSD. However, dysregulation of the MeCP2 signaling pathway is implicated in these disorders. MeCP2 plays a role as a therapeutic target for MS and NMOSD and provides pathways and mechanisms that are modulated by MeCP2 in the regulation of gene expression.

The aquaporin-4 water channel and updates on its potential as a drug target for Alzheimer's disease

INTRODUCTION

Although there are several FDA-approved treatments for Alzheimer's disease (AD), only recently have disease-modifying therapies received approval for use in patients. In this narrative review, we examine the history of aquaporin-4 (AQP4) as a therapeutic target for NMOSD (neuromyelitis optica spectrum disorder) and as a potential therapeutic target for AD.

AREAS COVERED

We review the basic science and discovery of AQP4, a transmembrane water-channel essential to regulating water balance in the central nervous system (CNS). We also review the pathogenesis of NMOSD, an autoimmune disease characterized by the destruction of cells that express AQP4. Then, we review how AQP4 is likely involved in the pathogenesis of Alzheimer's disease (AD). Finally, we discuss future challenges with drug design that would modulate AQP4 to potentially slow AD development. The literature search for this article consisted of searching Google Scholar and PubMed for permutations of the keywords 'Alzheimer's disease,' 'aquaporin-4,' 'neuromyelitis optica,' and their abbreviations.

EXPERT OPINION

We place research into AQP4 into context with other recent developments in AD research. A major difficulty with drug development for Alzheimer's is the lack of strategies to cleanly target the early pathogenesis of the disease. Targeting AQP4 may provide such a strategy.

Neuromyelitis Optica Spectrum Disorder: A Rare Case of Transverse Myelitis and Autonomic Dysfunction

Neuromyelitis optica spectrum disorder (NMOSD) is a demyelinating central nervous system disease commonly presenting with optic neuritis and transverse myelitis. Its pathology is mediated by serum aquaporin 4 immunoglobulin G (AQP4-IgG) and myelin oligodendrocyte glycoprotein (MOG) antibodies. It can present in a relapsing and monophasic pattern and is diagnosed using the diagnostic criteria published in 2015 by the international panel on neuromyelitis optica (NMO) diagnosis. We describe the case of a 25-year-old man who had a history of painful eye movement and complete loss of vision affecting his left eye for which he was diagnosed with optic neuritis two months prior to presentation. The patient presented with transverse myelitis followed by a picture of autonomic dysfunction in the form of labile blood pressure and heart rate readings associated with profuse sweating as well as significant MRI findings. Neuromyelitis optica was diagnosed with positive AQP4-IgG and longitudinally extensive transverse myelitis. Treatment was initiated with pulse steroid and plasmapheresis followed by oral prednisolone and azathioprine following which the patient's condition stabilized.

Clinical and imagenologic significance of the neutrophil-to-lymphocyte ratio in neuromyelitis optica spectrum disorder: A systematic review with meta-analysis

BACKGROUND

Recently, the neutrophil-lymphocyte ratio (NLR) has become a biomarker for assessing inflammatory stress and prognosis in different diseases.

OBJECTIVE

We aimed to conduct a systematic review and meta-analysis to summarize the current evidence on the capacity of the NLR to serve as a biomarker in neuromyelitis optica spectrum disorder (NMOSD).

METHODS

Through a comprehensive systematic search up to December 2021 and using the search terms "neutrophil-to-lymphocyte ratio" and "neuromyelitis optica spectrum disorder" we selected studies evaluating NLR values in NMOSD patients. A meta-analysis was planned, and a narrative synthesis was performed when this was not possible. Subgroup and sensitivity analyses were planned. The Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach was used to assess certainty of the evidence.

RESULTS

Six studies were included (1036 patients). A significant increase in the NLR was observed between NMOSD patients and healthy controls with high heterogeneity (MD: 1.04; 95% CI: 0.76; 1.32; I2 = 59%). Regarding NMOSD prognosis, relapse (OR: 1.33 -OR: 2.14) was evaluated as being related to NLR with low certainty. An association with Expanded Disability Status Scale (EDSS) score ≥4 (OR: 1.23 -OR: 1.43) was reported with moderate certainty. An association with the occurrence of lesions on MRI was reported with an OR of 1.52.

CONCLUSION

We found the NLR to be useful as a biomarker of NMOSD as it was significantly increased in the patient group compared to the healthy control group with high certainty. Additionally, the NLR was applicable as an indicator of poor prognosis with low to moderate certainty.

The circadian rhythms regulated by Cx43-signaling in the pathogenesis of Neuromyelitis Optica

Introduction

Neuromyelitis Optica (NMO) is an inflammatory demyelinating disease of the central nervous system (CNS). NMO manifests as selective and severe attacks on axons and myelin of the optic nerve and spinal cord, resulting in necrotic cavities. The circadian rhythms are well demonstrated to profoundly impact cellular function, behavior, and disease. This study is aimed to explore the role and molecular basis of circadian rhythms in NMO.

Methods

We used an Aquaporin 4(AQP4) IgG-induced NMO cell model in isolated astrocytes. The expression of Cx43 and Bmal1 were detected by real-time PCR and Western Blot. TAT-Gap19 and DQP-1105 were used to inhibit Cx43 and glutamate receptor respectively. The knockdown of Bmal1 were performed with the shRNA containing adenovirus. The levels of glutamate, anterior visual pathway (AVP), and vasoactive intestinal peptide (VIP) were quantified by ELISA kits.

Results

We found that Bmal1 and Clock, two essential components of the circadian clock, were significantly decreased in NMO astrocytes, which were reversed by Cx43 activation (linoleic acid) or glutamate. Moreover, the expression levels of Bmal1 and Clock were also decreased by Cx43 blockade (TAT-Gap19) or glutamate receptor inhibition (DQP-1105). Furthermore, adenovirus-mediated Bmal1 knockdown by shRNA (Ad-sh-Bmal1) dramatically decreased the levels of glutamate, AVP, and VIP from neurons, and significantly down-regulated the protein level of Cx43 in NMO astrocytes with Cx43 activation (linoleic acid) or glutamate treatment. However, Bmal1 knockdown did not alter these levels in normal astrocytes with Cx43 blockade (TAT-Gap19) or glutamate receptor inhibition (DQP-1105).

Discussion

Collectively, these results suggest that Cx43-glutamate signaling would be a critical upstream regulator that contributes to the NMO-induced rhythmic damage in SCN astrocytes.

A novel association of osmotic demyelination in Sjögren's syndrome prompts revisiting role of aquaporins in CNS demyelinating diseases: A literature review

BACKGROUND

Primary Sjögren's syndrome (SS) is a chronic systemic autoimmune disease with varied neurological manifestations. SS is associated with anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD), a demyelinating autoimmune disorder of the central nervous system (CNS). Intriguingly, there are reports of osmotic demyelinating syndrome (ODS), a supposedly non-inflammatory disorder, in the context of SS and renal tubular acidosis (RTA), both of which are not yet established risk factors for ODS.

METHODS

A literature search was undertaken to identify case reports of ODS in patients with SS. Details of the clinical and laboratory features of these patients were compiled. Additionally, we searched for NMOSD in patients with SS. We looked for co-existing RTA in patients with SS-ODS as well as SS-NMOSD. We also screened for reports of ODS in RTA without underlying SS.

RESULTS & DISCUSSION

We identified 15 patients (all women, median age 40 years) with ODS in SS, and all of these patients had comorbid RTA. There were only three reported cases of ODS in RTA without underlying SS. We identified a total of 67 patients with SS-NMOSD, of whom only 3 (4.5%) had RTA. Hence, unlike NMOSD, the development of ODS in SS requires a prolonged osmotic or electrolyte abnormality caused by the comorbid RTA. The 15 patients with ODS and SS -RTA, showed heterogeneous clinical manifestations and outcomes. The most common symptom was quadriparesis, seen in 14 of the 15 patients. Eleven of the 15 patients had one of the following features, either alone or in combination: worsening of the sensorium, extensor plantar response, dysphagia/dysarthria, and facial palsy. The latter four manifestations were present at the onset in 7 patients and later in the course of the illness in the remaining 4 patients. Ocular palsy was seen in only four of the 15 patients and was a late manifestation. One patient who had extensive long-segment myelitis and subsequent ODS died, but most patients recovered without significant sequelae. None had hyponatremia, while all patients had hypokalemia and/or hypernatremia. Hypokalemia causing nephrogenic diabetes insipidus (NDI) followed by rapid rise in sodium and the resultant osmotic stress could potentially explain the occurrence of ODS in SS-RTA. Aquaporin (AQP) in astrocytes is implicated in ODS, and renal AQP is downregulated in NDI. Antibodies against AQPs are present in some patients with SS. Defective AQP is therefore a common link underlying all the connected diseases, namely SS, NDI, and ODS, raising the possibility of immune-mediated AQP dysfunction in the pathogenesis.

CONCLUSION

The hitherto unreported association between SS-RTA and ODS may implicate SS and/or RTA in the development of ODS. In the setting of SS-RTA, ODS must be suspected when a patient with flaccid quadriparesis does not respond to the correction of potassium or develops additional neurological features along with a rise in sodium. Defective functions of AQPs may be a possible mechanism linking demyelinating CNS lesions, SS, and RTA. Studies evaluating AQP functions and serum antibodies against AQPs in these conditions are warranted.

Classification of Extracellular Vesicles Based on Surface Glycan Structures by Spongy-like Separation Media

Extracellular vesicles (EVs) are lipid bilayer vesicles that enclose various biomolecules. EVs hold promise as sensitive biomarkers to detect and monitor various diseases. However, they have heterogeneous molecular compositions. The compositions of EVs from identical donor cells obtained using the same purification methods may differ, which is a significant obstacle for elucidating objective biological functions. Herein, the potential of a novel lectin-based affinity chromatography (LAC) method to classify EVs based on their glycan structures is demonstrated. The proposed method utilizes a spongy-like monolithic polymer (spongy monolith, SPM), which consists of poly(ethylene-co-glycidyl methacrylate) with continuous micropores and allows an efficient in situ protein reaction with epoxy groups. Two distinct lectins with different specificities, Sambucus sieboldiana agglutinin and concanavalin A, are effectively immobilized on SPM without impacting the binding activity. Moreover, high recovery rates of liposomal nanoparticles as a model of EVs are achieved due to the large flow-through pores (>10 μm) of SPM compared to a typical agarose gel. Finally, lectin-immobilized SPMs are employed to classify EVs based on the surface glycan structures and demonstrate different subpopulations by proteome profiling. This is the first approach to clarify the variation of protein contents in EVs by the difference of surface glycans via lectin immobilized media.

Genetics behind Cerebral Disease with Ocular Comorbidity: Finding Parallels between the Brain and Eye Molecular Pathology

Cerebral visual impairments (CVIs) is an umbrella term that categorizes miscellaneous visual defects with parallel genetic brain disorders. While the manifestations of CVIs are diverse and ambiguous, molecular diagnostics stand out as a powerful approach for understanding pathomechanisms in CVIs. Nevertheless, the characterization of CVI disease cohorts has been fragmented and lacks integration. By revisiting the genome-wide and phenome-wide association studies (GWAS and PheWAS), we clustered a handful of renowned CVIs into five ontology groups, namely ciliopathies (Joubert syndrome, Bardet-Biedl syndrome, Alstrom syndrome), demyelination diseases (multiple sclerosis, Alexander disease, Pelizaeus-Merzbacher disease), transcriptional deregulation diseases (Mowat-Wilson disease, Pitt-Hopkins disease, Rett syndrome, Cockayne syndrome, X-linked alpha-thalassaemia mental retardation), compromised peroxisome disorders (Zellweger spectrum disorder, Refsum disease), and channelopathies (neuromyelitis optica spectrum disorder), and reviewed several mutation hotspots currently found to be associated with the CVIs. Moreover, we discussed the common manifestations in the brain and the eye, and collated animal study findings to discuss plausible gene editing strategies for future CVI correction.

Relationship between the Clinical Characteristics in Patients with Neuromyelitis Optica Spectrum Disorders and Clinical Immune Indicators: A Retrospective Study

Objective: T lymphocytes, complement, and immunoglobulin play an important role in neuromyelitis optica spectrum disorders (NMOSD). As common clinical examination indicators, they have been used as routine indicators in many hospitals, which is convenient for being carried out in clinical work, but there are few articles of guiding significance for clinical practice. The purpose of this study was to study the relationship between commonly used immune indicators and clinical characteristics in patients with NMOSD. Methods: We compared clinical characteristics and clinical immune indicators in 258 patients with NMOSD and 200 healthy controls (HCs). We used multiple linear regression to study the relationship between immunotherapy, disease phase, sex, age, AQP4-IgG, and immune indicators. In addition, lymphocyte subsets were compared before and after immunotherapy in 24 of the 258 patients. We explored the influencing factors and predictors of severe motor disability. Results: The percentages of CD3 ratio (71.4% vs. 73.8%, p = 0.013), CD4 ratio (38.8% vs. 42.2%, p < 0.001), and CD4/CD8 ratio (1.43 vs. 1.66, p < 0.001) in NMOSD patients were significantly lower than those in the HC group. In addition, complement C4 (0.177 g/L vs. 0.221 g/L, p < 0.001) and peripheral blood IgG (10.95 g/L vs. 11.80 g/L, p = 0.026) in NMOSD patients were significantly lower than those in the HC group. CD3 percentage was correlated with blood collection age and disease stage; CD8 percentage was correlated with blood collection age, disease stage, and treatment; CD4/CD8 percentage was correlated with blood collection age and treatment; complement C4 was correlated with blood collection age and sex; and IgG was correlated with disease stage and treatment. Twenty-four patients before and after treatment showed that the percentages of CD3 ratio (74.8% vs. 66.7%, p = 0.001) and CD8 ratio (32.4% vs. 26.2%, p < 0.001) after treatment in NMOSD patients were significantly increased, and the percentage of CD3 before treatment was moderately negatively correlated with ARR (r = −0.507, p = 0.011). Binary logistic regression analysis showed that peripheral blood complement C3 is a serious influencing factor for severe motor disability (EDSS score ≥ 6 points). Peripheral blood complement C3 and C4 are predictors of severe motor disability (p < 0.05). Conclusion: Our results suggest that peripheral blood T lymphocytes, C3, C4 and immunoglobulin are convenient and routine clinical indicators that are convenient for implementation in clinical work. They have certain reference values for disease staging, recurrence, drug efficacy, and motor disability. They have improved our understanding of clinical immune indicators for NMOSD patients, but whether they can be used as biomarkers for clinical prognosis remains to be further studied.

Lost or fragmented bony septum of the optic canal facing the sphenoid sinus: a histological study using elderly donated cadavers

PURPOSE

To histologically describe a direct contact (the so-called dehiscence) of the optic nerve (ON) and/or internal carotid artery (ICA) to the mucosa of posterior paranasal sinuses represented by the sphenoid sinus (SS).

METHODS

Observations of histological sections of unilateral or bilateral skull bases (parasellar area and orbital apex) from 22 elderly cadavers were made.

RESULTS

A bony septum was less than 300 µm between the SS and ICA and 200 µm between the SS and optic nerve. Parts of the septa were sometimes absent due to fragmentation and holes of the bony lamella (2/22 facing the ICA; 4 facing the ICA in combination with an absent bony septum facing the nerve). In these dehiscence sites, the SS submucosal tissue attached to a thick sheath (50-100 µm in thickness) enclosing the optic nerve and ophthalmic artery and/or the ICA adventitia (50-200 µm in thickness). The ICA sometimes contained a sclerotic plaque that attached to or even protruded into the SS. With or without dehiscence, the SS mucosa was always thin (50-100 µm in thickness) and accompanied no mononuclear cellular infiltration or tumor.

CONCLUSIONS

A thin bony septum of the optic nerve or ICA had been notable as a danger point during surgery, but even a 0.05-mm-thick bone lamella might be an effective barrier against cellular infiltration or bacterial invasion from the SS. Fragmentation and holes of the bony lamella in 4 cadavers might allow cellular invasion to the optic nerve. Accordingly, unknown immunological cross talks might occur to cause demyelination.

A prospective study on tryptophan immunoadsorption in AQP4 antibody-positive neuromyelitis optica spectrum disorders

INTRODUCTION

Neuromyelitis optica spectrum disorders (NMOSD) is a rare inflammatory demyelinating disease of the central nervous system. NMOSD pathogenesis is mainly mediated by antibodies directed against aquaporin4 (AQP4 antibody). Immunoadsorption (IA) could specifically remove pathogenic antibody to alleviate the disease. Until now, prospective studies concerning the efficacy of IA on NMOSD are scarce. This study aims to prospectively evaluate the efficacy and safety of IA in the treatment of NMOSD.

PATIENTS AND METHODS

We included patients with AQP4 antibody-positive NMOSD who were hospitalized from September 2019 to September 2020, with no significant improvement in symptoms after 1 week of high-dose intravenous steroid therapy. Tryptophan IA therapy was initiated with five sessions on alternate days. Expanded Disability Status Scale (EDSS), visual acuity, and laboratory values were measured before and after IA, with a follow-up of 6 months. Spinal magnetic resonance imaging (MRI) characteristics were collected. Related side effects were recorded.

RESULTS

Seven patients were enrolled in the present study. After five IA, the patients' EDSS decreased from 5.71 ± 2.04 to 4.64 ± 2.29, P = .006. The visual acuity of the three visually impaired patients was improved. AQP4-IgG decreased significantly from 80.00 (interquartile range [IQR], 21.00-80.00) (U/mL) to 9.72 (IQR, 5.21-55.57) (U/mL) (P = .018). MRI of the spinal cord showed the scope of the myelopathy was narrowed and no significant enhancement was observed on postcontrast T1-weighted image at 90 days after treatment. Only one patient had transient hypotension.

CONCLUSIONS

Tryptophan IA therapy effectively and safely improved neurological function and visual acuity, and reduced the AQP4 antibody concentration in patients with NMOSD.

Neuromyelitis optica (NMO)-IgG-driven organelle reorganization in human iPSC-derived astrocytes

Neuromyelitis optica (NMO) is an autoimmune disease that primarily targets astrocytes. Autoantibodies (NMO-IgG) against the water channel protein, aquaporin 4 (AQP4), are a serologic marker in NMO patients, and they are known to be responsible for the pathophysiology of the disease. In the brain, AQP4 is mainly expressed in astrocytes, especially at the end-feet, where they form the blood-brain barrier. Following the interaction between NMO-IgG and AQP4 in astrocytes, rapid AQP4 endocytosis initiates pathogenesis. However, the cellular and molecular mechanisms of astrocyte destruction by autoantibodies remain largely elusive. We established an in vitro human astrocyte model system using induced pluripotent stem cells (iPSCs) technology in combination with NMO patient-derived serum and IgG to elucidate the cellular and functional changes caused by NMO-IgG. Herein, we observed that NMO-IgG induces structural alterations in mitochondria and their association with the endoplasmic reticulum (ER) and lysosomes at the ultrastructural level, which potentially leads to impaired mitochondrial functions and dynamics. Indeed, human astrocytes display impaired mitochondrial bioenergetics and autophagy activity in the presence of NMO-IgG. We further demonstrated NMO-IgG-driven ER membrane deformation into a multilamellar structure in human astrocytes. Together, we show that NMO-IgG rearranges cellular organelles and alter their functions and that our in vitro system using human iPSCs offers previously unavailable experimental opportunities to study the pathophysiological mechanisms of NMO in human astrocytes or conduct large-scale screening for potential therapeutic compounds targeting astrocytic abnormalities in patients with NMO.

Application of deep-learning to the seronegative side of the NMO spectrum

OBJECTIVES

To apply a deep-learning algorithm to brain MRIs of seronegative patients with neuromyelitis optica spectrum disorders (NMOSD) and NMOSD-like manifestations and assess whether their structural features are similar to aquaporin-4-seropositive NMOSD or multiple sclerosis (MS) patients.

PATIENTS AND METHODS

We analyzed 228 T2- and T1-weighted brain MRIs acquired from aquaporin-4-seropositive NMOSD (n = 85), MS (n = 95), aquaporin-4-seronegative NMOSD [n = 11, three with anti-myelin oligodendrocyte glycoprotein antibodies (MOG)], and aquaporin-4-seronegative patients with NMOSD-like manifestations (idiopathic recurrent optic neuritis and myelitis, n = 37), who were recruited from February 2010 to December 2019. Seventy-three percent of aquaporin-4-seronegative patients with NMOSD-like manifestations also had a clinical follow-up (median duration of 4 years). The deep-learning neural network architecture was based on four 3D convolutional layers. It was trained and validated on MRI scans of aquaporin-4-seropositive NMOSD and MS patients and was then applied to aquaporin-4-seronegative NMOSD and NMOSD-like manifestations. Assignment of unclassified aquaporin-4-seronegative patients was compared with their clinical follow-up.

RESULTS

The final algorithm differentiated aquaporin-4-seropositive NMOSD and MS patients with an accuracy of 0.95. All aquaporin-4-seronegative NMOSD and 36/37 aquaporin-4-seronegative patients with NMOSD-like manifestations were classified as NMOSD. Anti-MOG patients had a similar probability of being NMOSD or MS. At clinical follow-up, one unclassified aquaporin-4-seronegative patient evolved to MS, three developed NMOSD, and the others did not change phenotype.

CONCLUSIONS

Our findings support the inclusion of aquaporin4-seronegative patients into NMOSD and suggest a possible expansion to aquaporin-4-seronegative unclassified patients with NMOSD-like manifestations. Anti-MOG patients are likely to have intermediate brain features between NMOSD and MS.

Aquaporin-4 Removal from the Plasma Membrane of Human Müller Cells by AQP4-IgG from Patients with Neuromyelitis Optica Induces Changes in Cell Volume Homeostasis: the First Step of Retinal Injury?

Aquaporin-4 (AQP4) is the target of the specific immunoglobulin G autoantibody (AQP4-IgG) produced in patients with neuromyelitis optica spectrum disorders (NMOSD). Previous studies demonstrated that AQP4-IgG binding to astrocytic AQP4 leads to cell-destructive lesions. However, the early physiopathological events in Müller cells in the retina are poorly understood. Here, we investigated the consequences of AQP4-IgG binding to AQP4 of Müller cells, previous to the inflammatory response, on two of AQP4's key functions, cell volume regulation response (RVD) and cell proliferation, a process closely associated with changes in cell volume. Experiments were performed in a human retinal Müller cell line (MIO-M1) exposed to complement-inactivated sera from healthy volunteers or AQP4-IgG positive NMOSD patients. We evaluated AQP4 expression (immunofluorescence and western blot), water permeability coefficient, RVD, intracellular calcium levels and membrane potential changes during hypotonic shock (fluorescence videomicroscopy) and cell proliferation (cell count and BrdU incorporation). Our results showed that AQP4-IgG binding to AQP4 induces its partial internalization, leading to the decrease of the plasma membrane water permeability, a reduction of swelling-induced increase of intracellular calcium levels and the impairment of RVD in Müller cells. The loss of AQP4 from the plasma membrane induced by AQP4-IgG positive sera delayed Müller cells' proliferation rate. We propose that Müller cell dysfunction after AQP4 removal from the plasma membrane by AQP4-IgG binding could be a non-inflammatory mechanism of retinal injury in vivo, altering cell volume homeostasis and cell proliferation and consequently, contributing to the physiopathology of NMOSD.

Connexins in neuromyelitis optica: a link between astrocytopathy and demyelination

Neuromyelitis optica, a rare neuroinflammatory demyelinating disease of the CNS, is characterized by the presence of specific pathogenic autoantibodies directed against the astrocytic water channel aquaporin 4 (AQP4) and is now considered as an astrocytopathy associated either with complement-dependent astrocyte death or with astrocyte dysfunction. However, the link between astrocyte dysfunction and demyelination remains unclear. We propose glial intercellular communication, supported by connexin hemichannels and gap junctions, to be involved in demyelination process in neuromyelitis optica. Using mature myelinated cultures, we demonstrate that a treatment of 1 h to 48 h with immunoglobulins purified from patients with neuromyelitis optica (NMO-IgG) is responsible for a complement independent demyelination, compared to healthy donors' immunoglobulins (P < 0.001). In parallel, patients' immunoglobulins induce an alteration of connexin expression characterized by a rapid loss of astrocytic connexins at the membrane followed by an increased size of gap junction plaques (+60%; P < 0.01). This was co-observed with connexin dysfunction with gap junction disruption (-57%; P < 0.001) and increased hemichannel opening (+17%; P < 0.001), associated with glutamate release. Blocking connexin 43 hemichannels with a specific peptide was able to prevent demyelination in co-treatment with patients compared to healthy donors' immunoglobulins. By contrast, the blockade of connexin 43 gap junctions with another peptide was detrimental for myelin (myelin density -48%; P < 0.001). Overall, our results suggest that dysregulation of connexins would play a pathogenetic role in neuromyelitis optica. The further identification of mechanisms leading to connexin dysfunction and soluble factors implicated, would provide interesting therapeutic strategies for demyelinating disorders.

Eculizumab: A Review in Neuromyelitis Optica Spectrum Disorder

The terminal complement protein (C5) inhibitor eculizumab (Soliris^®) is the first agent to be specifically approved in the EU, USA, Canada and Japan for the treatment of neuromyelitis optica spectrum disorder (NMOSD) in adults who are aquaporin-4 water channel autoantibody (AQP4-IgG) seropositive and (in the EU only) for those with a relapsing course of disease. In the phase III PREVENT trial, eculizumab significantly reduced the risk of adjudicated relapse relative to placebo in patients with AQP4-IgG-seropositive NMOSD, approximately a quarter of whom did not receive concomitant immunosuppressive therapies. The beneficial effect of eculizumab was seen across all patient subgroups analysed and was accompanied by improvements in neurological and functional disability assessments, as well as generic health-related quality of life measures; it was sustained through 4 years of treatment, according to combined data from the PREVENT trial and an interim analysis of its ongoing open-label extension study. The safety profile of eculizumab in AQP4-IgG-seropositive NMOSD was consistent with that seen for the drug in other approved indications. Thus, eculizumab provides an effective, generally well tolerated and approved treatment option for this rare, disabling and potentially life-threatening condition.

Evidence of subclinical quantitative retinal layer abnormalities in AQP4-IgG seropositive NMOSD

BACKGROUND

Prior studies have suggested that subclinical retinal abnormalities may be present in aquaporin-4 immunoglobulin G (AQP4-IgG) seropositive neuromyelitis optica spectrum disorder (NMOSD), in the absence of a clinical history of optic neuritis (ON).

OBJECTIVE

Our aim was to compare retinal layer thicknesses at the fovea and surrounding macula between AQP4-IgG+ NMOSD eyes without a history of ON (AQP4-nonON) and healthy controls (HC).

METHODS

In this single-center cross-sectional study, 83 AQP4-nonON and 154 HC eyes were studied with spectral-domain optical coherence tomography (OCT).

RESULTS

Total foveal thickness did not differ between AQP4-nonON and HC eyes. AQP4-nonON eyes exhibited lower outer nuclear layer (ONL) and inner photoreceptor segment (IS) thickness at the fovea (ONL: -4.01 ± 2.03 μm, p = 0.049; IS: -0.32 ± 0.14 μm, p = 0.029) and surrounding macula (ONL: -1.98 ± 0.95 μm, p = 0.037; IS: -0.16 ± 0.07 μm, p = 0.023), compared to HC. Macular retinal nerve fiber layer (RNFL: -1.34 ± 0.51 μm, p = 0.009) and ganglion cell + inner plexiform layer (GCIPL: -2.44 ± 0.93 μm, p = 0.009) thicknesses were also lower in AQP4-nonON compared to HC eyes. Results were similar in sensitivity analyses restricted to AQP4-IgG+ patients who had never experienced ON in either eye.

CONCLUSIONS

AQP4-nonON eyes exhibit evidence of subclinical retinal ganglion cell neuronal and axonal loss, as well as structural evidence of photoreceptor layer involvement. These findings support that subclinical anterior visual pathway involvement may occur in AQP4-IgG+ NMOSD.

Could Galectin-3 be a key player in the etiology of neuromyelitis optica spectrum disorder?

Neuromyelitis Optica Spectrum Disorder (NMOSD) is a chronic, inflammatory, demyelinating disorder of the central nervous system (CNS) characterized primarily by transverse myelitis (TM) and optic neuritis (ON). Serum antibodies of the IgG class to the water channel protein aquaporin-4 (AQP4) are associated with NMOSD in most cases. These antibodies are thought to cause functional abnormality or changed expressional pattern of AQP4 channel proteins in the CNS lesions. Activation of microglia is one of the chief antibody-mediated effects in NMOSD and it has opposing detrimental and protective effects in NMOSD. On the one hand, it promotes neuroinflammation, demyelination and BBB breakdown. On the other, it aids in remyelination. What controls the switch between these effects is unknown. Recently, Galectin- 3, a lectin, has been identified as a key player in several neurodegenerative diseases. In transient focal brain ischemia, alzheimer's disease (AD), huntington disease (HD), and experimental autoimmune encephalitis (EAE), Galectin-3 promotes microglia-mediated inflammation. Conversely, in amyotrophic lateral sclerosis (ALS), Galectin-3 reduces inflammation. It also suppresses Th17 cytokines, which play a crucial role in NMOSD pathogenesis. Being devoid of a leader signal, Gal-3 localizes in different cellular compartments and is subject to various post-translational modifications. These reasons explain why Galectin-3 expression has opposing effects under different physiological conditions. Microglia-mediated inflammation in NMOSD has not been extensively studied. The factors that regulate microglia-mediated inflammation in NMOSD are unknown. Here, I hypothesize that Galectin-3 might be an etiological factor in NMOSD that regulates microglia-mediated inflammation. Analysing the role of Gal-3 in NMOSD could help in the development of novel therapies to treat NMOSD.

Rodent Models of Optic Neuritis

Optic neuritis (ON) is an inflammatory attack of the optic nerve that leads to visual disability. It is the most common optic neuropathy affecting healthy young adults, most commonly women aged 20-45 years. It can be idiopathic and monophasic or as part of a neurologic disease such as multiple sclerosis with recurrence and cumulative damage. Currently, there is no therapy to repair the damage from optic neuritis. Animal models are an essential tool for the understanding of the pathogenesis of optic neuritis and for the development of potential treatment strategies. Experimental autoimmune encephalomyelitis (EAE) is the most commonly used experimental rodent model for human autoimmune inflammatory demyelinating diseases of the central nervous system (CNS). In this review, we discuss the latest rodent models regarding optic neuritis, focusing on EAE model, and on its recent achievements and developments.

Can Gut Microbiota Affect Dry Eye Syndrome?

Using metagenomics, continuing evidence has elicited how intestinal microbiota trigger distant autoimmunity. Sjögren's syndrome (SS) is an autoimmune disease that affects the ocular surface, with frequently unmet therapeutic needs requiring new interventions for dry eye management. Current studies also suggest the possible relation of autoimmune dry eye with gut microbiota. Herein, we review the current knowledge of how the gut microbiota interact with the immune system in homeostasis as well as its influence on rheumatic and ocular autoimmune diseases, and compare their characteristics with SS. Both rodent and human studies regarding gut microbiota in SS and environmental dry eye are explored, and the effects of prebiotics and probiotics on dry eye are discussed. Recent clinical studies have commonly observed a correlation between gut dysbiosis and clinical manifestations of SS, while environmental dry eye portrays characteristics in between normal and autoimmune. Moreover, a decrease in both the Firmicutes/Bacteroidetes ratio and genus Faecalibacterium have most commonly been observed in SS subjects. The presumable pathways forming the "gut dysbiosis-ocular surface-lacrimal gland axis" are introduced. This review may provide perspectives into the link between the gut microbiome and dry eye, enhance our understanding of the pathogenesis in autoimmune dry eye, and be useful in the development of future interventions.

Use of therapeutic plasma exchange for pediatric neurological diseases

Therapeutic plasma exchange is used to treat neurological diseases in the pediatric population. Since its first use in pediatric patients with hepatic coma in the form of manual whole blood exchange, therapeutic plasma exchange has been increasingly used to treat these disorders of the nervous system. This expansion is a result of improved techniques and apheresis instruments suitable for small children, as well as the recognition of its applicability to many diseases in the pediatric population. This review provides a historical overview of the use of therapeutic apheresis in children and highlights the most common applications for therapeutic plasma exchange to treat neurological disorders in children.

Review of approved NMO therapies based on mechanism of action, efficacy and long-term effects

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Neuromyelitis optica (NMO - including NMO spectrum disorders [NMOSD]) is a devastating disease.

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Up until recently, there was no proven agent to treat to prevent relapses.

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We now have three agents indicated for the treatment of NMO.

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We might suggest the following sequence – 1st line using eculizumab for rapid efficacy and stabilization without effect on the acquired immune system followed by satrilizumab (long term immunomodulation).

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Reserve inebilizumab (immunosuppressant) for breakthrough disease and salvage the severe with AHSCBMT.

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In NMO, control the complement, transition to modulation, and reserve suppression – and salvage the severe with AHSCBMT.

Importance

Neuromyelitis optica (NMO - including NMO spectrum disorders [NMOSD]) is a devastating disease. Eighty-three percent of patients with transverse myelitic (TM) attacks and 67% of patients with optic neuritis (ON) attacks have no or a partial recovery.

Observations

Up until recently, there was no proven agent to treat to prevent relapses. The neuro-immunological community had a dearth of indicated agents for NMOSD. We now have three agents indicated for the treatment of NMO including (eculizumab [Soliris®]), an anti-C5 complement inhibitor, satralizumab (ENSRYNG®), a monoclonal antibody against the IL-6 receptor (IL-6R) that blocks B cell antibody production and inebilizumab (Uplinza®), a monoclonal antibody that binds to the B-cell surface antigen CD19 with subsequent B and plasmablast cell lymphocytolysis with decreasing antibody production. Autologous hematopoietic stem cell bone marrow transplantation (AHSCBMT) has also been used. How do we sequence NMO therapies with the understanding of the acuteness and severity of the disease, the individual mechanism of action (MOA) and rapidity of onset of action, onset of efficacy and long-term safety of each agent?

Conclusions and Relevance

We might suggest the following sequence – 1st line using eculizumab for rapid efficacy and stabilization without effect on the acquired immune system followed by satrilizumab (long term immunomodulation). Reserve inebilizumab (immunosuppressant) for breakthrough disease and salvage the severe with AHSCBMT. In NMO, control the complement, transition to modulation, and reserve suppression – and salvage the severe with AHSCBMT.

Intestinal Barrier Breakdown and Mucosal Microbiota Disturbance in Neuromyelitis Optical Spectrum Disorders

Background and Purpose

The mechanism underlying the pathology of neuromyelitis optica spectrum disorders (NMOSD) remains unclear even though antibodies to the water channel protein aquaporin-4 (AQP4) on astrocytes play important roles. Our previous study showed that dysbiosis occurred in the fecal microbiota of NMOSD patients. In this study, we further investigated whether the intestinal barrier and mucosal flora balance are also interrupted in NMOSD patients.

Methods

Sigmoid mucosal biopsies were collected by endoscopy from six patients with NMOSD and compared with samples from five healthy control (HC) individuals. These samples were processed for electron microscopy and immunohistochemistry to investigate changes in ultrastructure and in the number and size of intestinal inflammatory cells. Changes in mucosal flora were also analyzed by high-throughput 16S ribosomal RNA gene amplicon sequencing.

Results

The results from bacterial rRNA gene sequencing showed that bacterial diversity was decreased, but Streptococcus and Granulicatella were abundant in the colonic mucosa specimens of NMOSD patients compared to the HC individuals. The intercellular space between epithelia of the colonic mucosa was wider in NMOSD patients compared to the HC subjects (p < 0.01), and the expression of tight junction proteins [occludin, claudin-1 and zonula occludens-1 (ZO-1)] in NMOSD patients significantly decreased compared to that in the HC subjects. We also found numerous activated macrophages with many inclusions within the cytoplasm, mast cells with many particles in their cytoplasm, and enlarged plasma cells with rich developed rough endoplasmic reticulum in the lamina propria of the mucosa of the patients with NMOSD. Quantitative analysis showed that the percentages of small CD38+ and CD138+ cells (plasma cells) were lower, but the percentage of larger plasma cells was higher in NMOSD patients.

Conclusion

The present study demonstrated that the intestinal barrier was disrupted in the patients with NMOSD, accompanied by dysbiosis and inflammatory activation of the gut. The mucosal microbiota imbalance and inflammatory responses might allow pathogens to cross the damaged intestinal barrier and participate in pathological process in NMOSD. However, further study on the pathological mechanism of NMOSD underlying gut dysbiosis is warranted in the future.

Aquaporin-4 Surface Trafficking Regulates Astrocytic Process Motility and Synaptic Activity in Health and Autoimmune Disease

Astrocytes constantly adapt their ramified morphology in order to support brain cell assemblies. Such plasticity is partly mediated by ion and water fluxes, which rely on the water channel aquaporin-4 (AQP4). The mechanism by which this channel locally contributes to process dynamics has remained elusive. Using a combination of single-molecule and calcium imaging approaches, we here investigated in hippocampal astrocytes the dynamic distribution of the AQP4 isoforms M1 and M23. Surface AQP4-M1 formed small aggregates that contrast with the large AQP4-M23 clusters that are enriched near glutamatergic synapses. Strikingly, stabilizing surface AQP4-M23 tuned the motility of astrocyte processes and favors glutamate synapse activity. Furthermore, human autoantibodies directed against AQP4 from neuromyelitis optica (NMO) patients impaired AQP4-M23 dynamic distribution and, consequently, astrocyte process and synaptic activity. Collectively, it emerges that the membrane dynamics of AQP4 isoform regulate brain cell assemblies in health and autoimmune brain disease targeting AQP4.

Statins in Neuro-ophthalmology

Statins are effective and well-tolerated hypolipidaemic agents which have been increasingly studied for their pleiotropic immunomodulatory and anti-inflammatory effects. Statins have potential therapeutic benefit in a range of neuro-ophthalmological conditions but may also induce or exacerbate certain neurological disorders. This literature review examines evidence from clinical and in vitro studies assessing the effects of statins in myasthenia gravis, myopathy, multiple sclerosis, neuromyelitis optica, idiopathic intracranial hypertension (pseudotumour cerebri), migraine, giant cell arteritis, Bell's palsy, ocular ischaemia, stroke, Alzheimer's disease and Parkinson's disease.

Decreased mRNA Expressions of CD40L in Patients with Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune disease that preferentially affects central nerve system. Herein, we evaluated changes of CD40L and CD40 mRNA expressions in NMOSD and controls to explore their potential roles in development of NMOSD. The expressions of CD40L and CD40 mRNA in peripheral blood mononuclear cells (PBMCs) from patients with NMOSD and healthy controls were detected by quantitative real-time PCR (qPCR). Kruskal-Wallis tests were used to compare expression levels of CD40L and CD40 mRNA between groups, and Spearman correlation analysis was performed to evaluate correlation between mRNA expression levels and annual relapse rate (ARR) of NMOSD. A total of 71 patients with NMOSD and 42 gender- and age-matched healthy volunteers were recruited in our study. Compared with healthy controls, expression of CD40L mRNA was significantly decreased in untreated patients with NMOSD, and similar trends were observed also in CD40 mRNA expression although the difference was not significant. Other than that, immunosuppressants not only successfully increased CD40L and CD40 mRNA levels during remission of NMOSD, but also corrected the negative correlation between CD40L mRNA expression and annual relapse rate (ARR) of patients NMOSD. These results favored the long-term prognosis of NMOSD patients. Our results suggest that decreased expressions of CD40L mRNA may be involved in developing of NMOSD and the proper CD40L mRNA levels benefit to prevent attacks of NMOSD. Nevertheless, the relationship between protein and mRNA expressions of CD40L and their underlying roles in the pathogenesis of NMOSD remains to be further studied.

Experimental animal models of aquaporin-4-IgG-seropositive neuromyelitis optica spectrum disorders: progress and shortcomings

Neuromyelitis optica spectrum disorders (NMOSD) is a heterogeneous group of neuroinflammatory conditions associated with demyelination primarily in spinal cord and optic nerve, and to a lesser extent in brain. Most NMOSD patients are seropositive for IgG autoantibodies against aquaporin-4 (AQP4-IgG), the principal water channel in astrocytes. There has been interest in establishing experimental animal models of seropositive NMOSD (herein referred to as NMO) in order to elucidate NMO pathogenesis mechanisms and to evaluate drug candidates. An important outcome of early NMO animal models was evidence for a pathogenic role of AQP4-IgG. However, available animal models of NMO, based largely on passive transfer to rodents of AQP4-IgG or transfer of AQP4-sensitized T cells, often together with pro-inflammatory maneuvers, only partially recapitulate the clinical and pathological features of human NMO, and are inherently biased toward humoral or cellular immune mechanisms. This review summarizes current progress and shortcomings in experimental animal models of seropositive NMOSD, and opines on the import of advancing animal models.

Review: Recent advances in the understanding of the pathophysiology of neuromyelitis optica spectrum disorder

Neuromyelitis optica is an autoimmune inflammatory disorder of the central nervous system that preferentially targets the spinal cord and optic nerve. Following the discovery of circulating antibodies against the astrocytic aquaporin 4 (AQP4) water channel protein, recent studies have expanded our knowledge of the unique complexities of the pathogenesis of neuromyelitis optica and its relationship with the immune response. This review describes and summarizes the recent advances in our understanding of the molecular mechanisms underlying neuromyelitis optica disease pathology and examines their potential as therapeutic targets. Additionally, we update the most recent research by proposing major unanswered questions regarding how peripheral AQP4 antibodies are produced and their entry into the central nervous system, the causes of AQP4-IgG-seronegative disease, why peripheral AQP4-expressing organs are spared from damage, and the impact of this disease on pregnancy.

Astrocyte dysfunction and neurovascular impairment in neurological disorders: Correlation or causation?

The neurovascular unit, consisting of neurons, astrocytes, and vascular cells, has become the focus of much discussion in the last two decades and emerging literature now suggests an association between neurovascular dysfunction and neurological disorders. In this review, we synthesize the known and suspected contributions of astrocytes to neurovascular dysfunction in disease. Throughout the brain, astrocytes are centrally positioned to dynamically mediate interactions between neurons and the cerebral vasculature, and play key roles in blood-brain barrier maintenance and neurovascular coupling. It is increasingly apparent that the changes in astrocytes in response to a variety of insults to brain tissue -collectively referred to as "reactive astrogliosis" - are not just an epiphenomenon restricted to morphological alterations, but comprise functional changes in astrocytes that contribute to the phenotype of neurological diseases with both beneficial and detrimental effects. In the context of the neurovascular unit, astrocyte dysfunction accompanies, and may contribute to, blood-brain barrier impairment and neurovascular dysregulation, highlighting the need to determine the exact nature of the relationship between astrocyte dysfunction and neurovascular impairments. Targeting astrocytes may represent a new strategy in combinatorial therapeutics for preventing the mismatch of energy supply and demand that often accompanies neurological disorders.

Membrane assembly of aquaporin-4 autoantibodies regulates classical complement activation in neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune CNS disorder mediated by pathogenic aquaporin-4 (AQP4) water channel autoantibodies (AQP4-IgG). Although AQP4-IgG-driven complement-dependent cytotoxicity (CDC) is critical for the formation of NMO lesions, the molecular mechanisms governing optimal classical pathway activation are unknown. We investigated the molecular determinants driving CDC in NMO using recombinant AQP4-specific autoantibodies (AQP4 rAbs) derived from affected patients. We identified a group of AQP4 rAbs targeting a distinct extracellular loop C epitope that demonstrated enhanced CDC on target cells. Targeted mutations of AQP4 rAb Fc domains that enhance or diminish C1q binding or antibody Fc-Fc interactions showed that optimal CDC was driven by the assembly of multimeric rAb platforms that increase multivalent C1q binding and facilitate C1q activation. A peptide that blocks antibody Fc-Fc interaction inhibited CDC induced by AQP4 rAbs and polyclonal NMO patient sera. Super-resolution microscopy revealed that AQP4 rAbs with enhanced CDC preferentially formed organized clusters on supramolecular AQP4 orthogonal arrays, linking epitope-dependent multimeric assembly with enhanced C1q binding and activation. The resulting model of AQP4-IgG CDC provides a framework for understanding classical complement activation in human autoantibody-mediated disorders and identifies a potential new therapeutic avenue for treating NMO.

Paraneoplastic neuromyelitis optica associated with fever of unknown origin as an early manifestation: A case report

Tumors have been frequently reported to be associated with neuromyelitis optica (NMO). Here we review a case of a 34-year-old woman who presented with complaint of one-sided visual loss. All Lab tests exhibited negative results which decreased the possibility of Auto-immune or neuro-inflammatory disorders. Magnetic resonance imaging (MRI) of the brain and spinal cord was done as a part of work up, which showed Meningioma in anterior fossa without any other findings supporting neuro-demyelinating disorders. After complete surgical removal of the meningioma, patient's visual loss was completely resolved. 4 weeks later, she was admitted to the hospital for the second time with fever fulfilling the Fever of Unknown Origin (FUO) criteria. One week after she was discharged, she came back with paraplegia. MRI with Gadolinium showed an enhancing lesion involving T6-T9 segments of the thoracic spine. In order to rule in NMO, we checked for antibody to aquaporin-4 (AQP4-Ab) and the result was positive. This is the first report showing a probable association between FUO and NMO. Our case also demonstrates how variable the clinical presentations of NMO can be. We suggest that the diagnosis of NMO should be considered in the appropriate clinical setting despite of the presence of unconventional manifestations.

Blood Brain Barrier Permeability Could Be a Biomarker to Predict Severity of Neuromyelitis Optica Spectrum Disorders: A Retrospective Analysis

Background: Blood-brain barrier (BBB) pathology exists in neuromyelitis optica spectrum disorders (NMOSD). However, the clinical use of BBB permeability, such as predicting disease severity of NMOSD, has rarely been studied in a large cohort of patients. Objectives: The current study explored the association between BBB permeability and clinical parameters in order to assess if BBB permeability could be a biomarker to predict disease severity and clinical characteristics of NMOSD. Methods: Among 69 enrolled NMOSD patients, 47 with albumin index over 5 × 10-3 were assigned to the increased BBB permeability group, and the remaining 22 were to the normal BBB permeability group. Disease severity was assessed using the Expanded Disability Status Scale (EDSS). Results: Patients in the increased BBB permeability group had significantly higher EDSS scores, anti-aquporin-4 immunoglobulin G titers, more dense cerebrospinal fluid protein concentrations, white blood cell counts, myelin basic protein levels and more dense complement 3 concentrations than found in the comparative normal BBB permeability group. The albumin index was positively correlated to the length of lesions in spinal cord. Conclusions: BBB permeability was associated with clinical features, laboratory results and radiological data of NMOSD patients, and may be a potential biomarker to predict disease severity and clinical characteristics of NMOSD.

Open-label, add-on trial of cetirizine for neuromyelitis optica

Objective

This pilot study preliminarily examined the efficacy and tolerability of cetirizine as an add-on to standard therapy for neuromyelitis optica (NMO).

Methods

Eligible participants met the Wingerchuk 2006 diagnostic criteria or had a single typical episode along with positive NMO immunoglobulin G. After baseline clinical and laboratory assessments, participants began treatment with cetirizine 10 mg orally daily, in addition to their usual disease-modifying therapy for NMO, and continued for 1 year. The primary end point was the annualized relapse rate (ARR) while on the same disease-modifying therapy before starting cetirizine compared with after taking cetirizine. Additional end points included disability (Expanded Disability Status Scale [EDSS]), relapse severity, tolerability, especially with respect to drowsiness measured by the Epworth Sleepiness Scale (ESS), and laboratory parameters.

Results

The ARR before cetirizine was 0.4 ± 0.80 and after cetirizine was 0.1 ± 0.24 (p = 0.047). There was no statistically significant difference in the EDSS (mean 3.9 ± 2.18 before the start of the study and 3.2 ± 2.31 at the conclusion of the study, p = 0.500). The ESS remained fairly consistent throughout the study (mean 6.5 ± 5.33 at baseline and 6.9 ± 4.50 at month 12, p = 0.740). Laboratory studies were unrevealing.

Conclusions

In this pilot study, cetirizine was well tolerated, and the prespecified primary efficacy end point was satisfied. However, the open-label design and the small sample size of this pilot study preclude definitive conclusions. Further research is needed.

Classification of evidence

This study provides Class IV evidence that in patients with NMO, the addition of cetirizine to standard therapy is safe, well tolerated, and reduces relapses.

Mutation of the cellular adhesion molecule NECL2 is associated with neuromyelitis optica spectrum disorder

AIMS

To investigate the association of the Nectin/Necl family genes with the risk of developing NMOSD.

METHODS

Whole-exome sequencing was performed on two familial NMOSD cases and two unaffected family members. Additionally, 106 patients with sporadic NMOSD and 212 healthy controls (HCs) underwent screening for mutant Necl2. Finally, the molecular weight and cellular localization of mutant NECL2 was examined in transfected HeLa cells.

RESULTS

We identified a novel deletion mutation in Necl2 (c.1052_1060delCCACCACCA; p. Thr351_Thr353del), which was associated with disease manifestation in the NMOSD familial cases. The frequency at which the mutation occurred in patients with sporadic NMOSD was significantly higher than for HCs (5.7% and 0, respectively; p<0.01). The mutation was located in the extracellular domain close to the transmembrane region, at a point in the protein sequence characterized by threonine enrichment. The mutant NECL2 had a lower molecular weight and exhibited defective trafficking to the cell surface.

CONCLUSIONS

Our results suggest that the Necl2 mutation identified herein may be associated with the risk of developing NMOSD. Furthermore, mutated NECL2 may play a role in the pathogenesis of the disease, potentially through its roles in axonal regeneration and/or via neuron-glia interactions that are relevant to myelination.

Stratification of astrocytes in healthy and diseased brain

Astrocytes, a subtype of glial cells, come in variety of forms and functions. However, overarching role of these cell is in the homeostasis of the brain, be that regulation of ions, neurotransmitters, metabolism or neuronal synaptic networks. Loss of homeostasis represents the underlying cause of all brain disorders. Thus, astrocytes are likely involved in most if not all of the brain pathologies. We tabulate astroglial homeostatic functions along with pathological condition that arise from dysfunction of these glial cells. Classification of astrocytes is presented with the emphasis on evolutionary trails, morphological appearance and numerical preponderance. We note that, even though astrocytes from a variety of mammalian species share some common features, human astrocytes appear to be the largest and most complex of all astrocytes studied thus far. It is then an imperative to develop humanized models to study the role of astrocytes in brain pathologies, which is perhaps most abundantly clear in the case of glioblastoma multiforme.

Aquaporin-4 positive neuromyelitis optica spectrum disorders secondary to thrombopenic purpura: A case report

RATIONALE

Neuromyelitis optica spectrum disorders (NMOSD) is considered as an immune-mediated disorder in the central nervous system (CNS). Numerous autoimmune diseases are frequently complicated with NMOSD and distinct clinical characteristics are noted in NMOSD patients with other autoimmune diseases. However, to our best knowledge, co-occurrence of NMOSD and thrombopenic purpura is rarely identified.

PATIENT CONCERNS

We presented a rare case of a 72-year-old female with 6-year history of thrombopenic purpura, and 1-month history of blurred vision as well as chest zonethesia. Anti-aquaporin-4 (AQP4) antibodies was positive in the serum of the patient.

DIAGNOSES

With the addition of laboratory findings, iconography findings and physical examination results, the diagnosis of NMOSD was established according to the most recent diagnostic criteria.

INTERVENTIONS AND OUTCOMES

With the treatment of intravenous immunoglobulin (IVIg), the patient felt better at discharge without changing of expanded disability status scale (EDSS) score.

LESSONS

The case indicates that NMOSD could co-occur with thrombopenic purpura. The disturbance of immune system balance may explain this overlap. Further studies are warranted to reveal the mechanism and to explore whether patients with NMOSD with and without thrombopenic purpura have distinct clinical feature, drug responsiveness or prognosis.

Toward Clinical use of the IgG Specific Enzymes IdeS and EndoS against Antibody-Mediated Diseases

The endoglycosidase EndoS and the protease IdeS from the human pathogen Streptococcus pyogenes are immunomodulating enzymes hydrolyzing human IgG. IdeS cleaves IgG in the lower hinge region, while EndoS hydrolyzes the conserved N-linked glycan in the Fc region. Both enzymes are remarkably specific for human IgG that after hydrolysis loses most of its effector functions, such as binding to leukocytes and complement activation, all contributing to bacterial evasion of adaptive immunity. However, taken out of their infectious context, we and others have shown that IdeS and EndoS can alleviate autoimmune disease in a number of animal models of antibody-mediated disorders. In this chapter, we will briefly describe the discovery and characterization of these unique enzymes, present the findings from a number of animal models of autoimmunity where the enzymes have been tested, and outline the ongoing clinical testing of IdeS. Furthermore, we will discuss the rationale for further development of IdeS and EndoS into novel pharmaceuticals against diseases where IgG antibodies contribute to the pathology, including, but not restricted to, chronic and acute autoimmunity, transplant rejection, and antidrug antibody reactions.

Role of the H-bond between L53 and T56 for Aquaporin-4 epitope in Neuromyelitis Optica

Aquaporin-4 (AQP4) is the CNS water channel organized into well-ordered protein aggregates called Orthogonal Arrays of Particles (OAPs). Neuromyelitis Optica (NMO) is an autoimmune disease caused by anti-OAP autoantibodies (AQP4-IgG). Molecular Dynamics (MD) simulations have identified an H-bond between L53 and T56 as the key for AQP4 epitope and therefore of potential interest for drug design in NMO field. In the present study, we have experimentally tested this MD-prediction using the classic mutagenesis approach. We substituted T56 with V56 and tested this mutant for AQP4 aggregates and AQP4-IgG binding. gSTED super-resolution microscopy showed that the mutation does not affect AQP4 aggregate dimension; immunofluorescence and cytofluorimetric analysis demonstrated its unaltered AQP4-IgG binding, therefore invalidating the MD-prediction. We later investigated whether AQP4, expressed in Sf9 insect and HEK-293F cells, is able to correctly aggregate before and after the purification steps usually applied to obtain AQP4 crystal. The results demonstrated that AQP4-IgG recognizes AQP4 expressed in Sf9 and HEK-293F cells by immunofluorescence even though BN-PAGE analysis showed that AQP4 forms smaller aggregates when expressed in insect cells compared to mammalian cell lines. Notably, after AQP4 purification, from both insect and HEK-293F cells, no aggregates are detectable by BN-PAGE and AQP4-IgG binding is impaired in sandwich ELISA assays. All together these results indicate that 1) the MD prediction under analysis is not supported by experimental data and 2) the procedure to obtain AQP4 crystals might affect its native architecture and, as a consequence, MD simulations. In conclusion, given the complex nature of the AQP4 epitope, MD might not be the suitable for molecular medicine advances in NMO.

Aquaporin-4 antibody titration in NMO patients treated with rituximab: A retrospective study

Objective:

We undertook an observational retrospective study to investigate the usefulness of aquaporin-4 (AQP4) antibodies (Ab) titration in the management of patients with neuromyelitis optica (NMO) treated with rituximab (RTX) by studying (1) the correlation between AQP4-Ab titer and disease activity, (2) the influence of RTX on antibody levels, and (3) the association between AQP4-Ab levels and responsiveness to RTX.

Methods:

A cell-based assay was used for AQP4-Ab titration in 322 serum samples from 7 patients with NMO treated with RTX (median follow-up 65 months), according to a treatment-to-target approach. Serum samples were collected every month following standardized procedures.

Results:

(1) In group analysis, AQP4-Ab titers correlated with the disease activity, showing higher titers during and preceding relapses than during remission. However, in individual analysis, an increase in AQP4-Ab titers and CD19+ B cells did not always precede a relapse. (2) A reduction of AQP4-Ab titers in the short-term and long-term period was observed during RTX treatment. (3) Reduction of AQP4-Ab titers was observed in responder patients both 3 months after RTX infusion and in the long-term follow-up. In one nonresponder patient, AQP4-Ab levels never decreased during the treatment period.

Conclusions:

Titration of AQP4-Abs could be useful in the clinical management of patients with NMO treated with RTX: titration before each reinfusion and 3 months after each reinfusion may provide information about responsiveness to RTX. Although a relationship among AQP4-Ab levels, disease activity, and response to RTX was observed, the usefulness of AQP4-Ab titration to predict relapses is limited.

Hydrocephalus: the role of cerebral aquaporin-4 channels and computational modeling considerations of cerebrospinal fluid

Aquaporin-4 (AQP4) channels play an important role in brain water homeostasis. Water transport across plasma membranes has a critical role in brain water exchange of the normal and the diseased brain. AQP4 channels are implicated in the pathophysiology of hydrocephalus, a disease of water imbalance that leads to CSF accumulation in the ventricular system. Many molecular aspects of fluid exchange during hydrocephalus have yet to be firmly elucidated, but review of the literature suggests that modulation of AQP4 channel activity is a potentially attractive future pharmaceutical therapy. Drug therapy targeting AQP channels may enable control over water exchange to remove excess CSF through a molecular intervention instead of by mechanical shunting. This article is a review of a vast body of literature on the current understanding of AQP4 channels in relation to hydrocephalus, details regarding molecular aspects of AQP4 channels, possible drug development strategies, and limitations. Advances in medical imaging and computational modeling of CSF dynamics in the setting of hydrocephalus are summarized. Algorithmic developments in computational modeling continue to deepen the understanding of the hydrocephalus disease process and display promising potential benefit as a tool for physicians to evaluate patients with hydrocephalus.

Association of CD40 Gene Polymorphisms with Susceptibility to Neuromyelitis Optica Spectrum Disorders

The CD40 gene is associated with many autoimmune diseases; however, there are few studies in literatures that investigate the association between CD40 and neuromyelitis optica spectrum disorders (NMOSD). This study aimed to estimate the potential association of CD40 gene polymorphisms with susceptibility to NMOSD. Four SNPs (rs1883832, rs3765459, rs4810485, and rs6074022) were selected and genotyped in a Chinese cohort comprising 162 patients with NMOSD and 237 healthy controls. P values, odds ratios (ORs), and 95 % confidential intervals (CI) for four test models (allelic, additive, dominant, and recessive) were used to assess relationships between CD40 and NMOSD. Results showed that the rs3765459 variant was significantly associated with increased risk of NMOSD in allelic model (OR = 1.48, 95 % CI 1.10-1.98, P = 0.009, P ^corr = 0.037), and similar results were detected in the additive and recessive models (OR = 1.47, 95 % CI 1.09-1.97, P = 0.010, P ^corr = 0.042; OR = 2.12, 95 % CI 1.18-3.8, P = 0.012, P ^corr = 0.048, respectively). Other three SNPs showed protections on NMOSD in dominant models (rs6074022, OR = 0.64, 95 % CI 0.42-0.95, P = 0.031; rs1883832, OR = 0.65, 95 % CI 0.43-0.97, P = 0.036; and rs4810485, OR = 0.63, 95 % CI 0.42-0.95, P = 0.029, respectively), but not significantly after Bonferroni corrections for multiple tests. In addition, haplotype analysis of these SNPs in tight linkage did not reveal significant association with NMOSD. This study indicates that the rs3765459 variant in CD40 gene is associated with susceptibility to NMOSD. Larger sample size studies in other ethnicities are needed to verify this association.

Characterization of the binding pattern of human aquaporin-4 autoantibodies in patients with neuromyelitis optica spectrum disorders

BACKGROUND

The discovery of a highly specific antibody against the aquaporin-4 (AQP4) water channel (AQP4-IgG) unified the spectrum of neuromyelitis optica spectrum disorders (NMOSD), which are considered to be antibody-mediated autoimmune diseases. The AQP4 water channel is located on astrocytic end-feet processes and consists of six transmembrane helical domains forming three extracellular loops A, C, and E in which defined amino acids were already proven to be critical for AQP4-IgG binding. However, the clinical relevance of these findings is unclear. Therefore, we have characterized the epitope specificity of AQP4-IgG-positive NMOSD patients.

METHODS

We established a cell-based flow cytometry assay for the quantitative detection of AQP4-IgG-positive serum samples. Human embryonic kidney (HEK) cells were transiently transfected with an EmGFP-tagged AQP4-M23, AQP4-M1, or six AQP4-M23 extracellular loop mutants including two mutations in loop A (serial AA substitution, insertion of a myc-tag), two in loop C (N153Q, insertion of a myc-tag), and two in loop E (H230G, insertion of a myc-tag). Fourty-seven baseline and 49 follow-up serum samples and six paired cerebrospinal fluid (CSF) baseline samples of 47 AQP4-IgG-positive Austrian NMOSD patients were then tested for their binding capability to AQP4-M1 and AQP4-M23 isoforms and these six extracellular loop mutants.

RESULTS

Overall, we could identify two broad patterns of antibody recognition based on differential sensitivity to mutations in extracellular loop A. Pattern A was characterized by reduced binding to the two mutations in loop A, whereas pattern B had only partial or no reduced binding to these mutations. These two patterns were not associated with significant differences in demographic and clinical parameters or serum titers in this retrospective study. Interestingly, we found a change of AQP4-IgG epitope recognition pattern in seven of 20 NMOSD patients with available follow-up samples. Moreover, we found different binding patterns in five of six paired CSF versus serum samples, with a predominance of pattern A in CSF.

CONCLUSIONS

Our study demonstrates that AQP4-IgG in sera of NMOSD patients show distinct patterns of antibody recognition. The clinical and diagnostic relevance of these findings have to be addressed in prospective studies.

Neuromyelitis optica study model based on chronic infusion of autoantibodies in rat cerebrospinal fluid

Background

Devic’s neuromyelitis optica (NMO) is an autoimmune astrocytopathy, associated with central nervous system inflammation, demyelination, and neuronal injury. Several studies confirmed that autoantibodies directed against aquaporin-4 (AQP4-IgG) are relevant in the pathogenesis of NMO, mainly through complement-dependent toxicity leading to astrocyte death. However, the effect of the autoantibody per se and the exact role of intrathecal AQP4-IgG are still controversial.

Methods

To explore the intrinsic effect of intrathecal AQP4-IgG, independent from additional inflammatory effector mechanisms, and to evaluate its clinical impact, we developed a new animal model, based on a prolonged infusion of purified immunoglobulins from NMO patient (IgG^AQP4+, NMO-rat) and healthy individual as control (Control-rat) in the cerebrospinal fluid (CSF) of live rats.

Results

We showed that CSF infusion of purified immunoglobulins led to diffusion in the brain, spinal cord, and optic nerves, the targeted structures in NMO. This was associated with astrocyte alteration in NMO-rats characterized by loss of aquaporin-4 expression in the spinal cord and the optic nerves compared to the Control-rats (p = 0.001 and p = 0.02, respectively).

In addition, glutamate uptake tested on vigil rats was dramatically reduced in NMO-rats (p = 0.001) suggesting that astrocytopathy occurred in response to AQP4-IgG diffusion. In parallel, myelin was altered, as shown by the decrease of myelin basic protein staining by up to 46 and 22 % in the gray and white matter of the NMO-rats spinal cord, respectively (p = 0.03). Loss of neurofilament positive axons in NMO-rats (p = 0.003) revealed alteration of axonal integrity. Then, we investigated the clinical consequences of such alterations on the motor behavior of the NMO-rats. In a rotarod test, NMO-rats performance was lower compared to the controls (p = 0.0182). AQP4 expression, and myelin and axonal integrity were preserved in AQP4-IgG-depleted condition. We did not find a major immune cell infiltration and microglial activation nor complement deposition in the central nervous system, in our model.

Conclusions

We establish a link between motor-deficit, NMO-like lesions and astrocytopathy mediated by intrathecal AQP4-IgG. Our study validates the concept of the intrinsic effect of autoantibody against surface antigens and offers a model for testing antibody and astrocyte-targeted therapies in NMO.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0577-8) contains supplementary material, which is available to authorized users.