Loss of aquaporin 4 in lesions of neuromyelitis optica: distinction from multiple sclerosis

Biomarkers for neuromyelitis optica: a visual analysis of emerging research trends

Neuromyelitis optica is an inflammatory demyelinating disease of the central nervous system that differs from multiple sclerosis. Over the past 20 years, the search for biomarkers for neuromyelitis optica has been ongoing. Here, we used a bibliometric approach to analyze the main research focus in the field of biomarkers for neuromyelitis optica. Research in this area is consistently increasing, with China and the United States leading the way on the number of studies conducted. The Mayo Clinic is a highly reputable institution in the United States, and was identified as the most authoritative institution in this field. Furthermore, Professor Wingerchuk from the Mayo Clinic was the most authoritative expert in this field. Keyword analysis revealed that the terms "neuromyelitis optica" (261 times), "multiple sclerosis" (220 times), "neuromyelitis optica spectrum disorder" (132 times), "aquaporin 4" (99 times), and "optical neuritis" (87 times) were the most frequently used keywords in literature related to this field. Comprehensive analysis of the classical literature showed that the majority of publications provide conclusive research evidence supporting the use of aquaporin-4-IgG and neuromyelitis optica-IgG to effectively diagnose and differentiate neuromyelitis optica from multiple sclerosis. Furthermore, aquaporin-4-IgG has emerged as a highly specific diagnostic biomarker for neuromyelitis optica spectrum disorder. Myelin oligodendrocyte glycoprotein-IgG is a diagnostic biomarker for myelin oligodendrocyte glycoprotein antibody-associated disease. Recent biomarkers for neuromyelitis optica include cerebrospinal fluid immunological biomarkers such as glial fibrillary acidic protein, serum astrocyte damage biomarkers like FAM19A5, serum albumin, and gamma-aminobutyric acid. The latest prospective clinical trials are exploring the potential of these biomarkers. Preliminary results indicate that glial fibrillary acidic protein is emerging as a promising candidate biomarker for neuromyelitis optica spectrum disorder. The ultimate goal of future research is to identify non-invasive biomarkers with high sensitivity, specificity, and safety for the accurate diagnosis of neuromyelitis optica.

IL-33 relieves nerve injury by mediating microglial polarization in neuromyelitis optica spectrum disorders via the IL-33/ST2 pathway

Interleukin-33 (IL-33) is a member of the interleukin-1 cytokine family. Its function in regulating microglial M1/M2 polarization in neuromyelitis optica spectrum disorder (NMOSD) is still unelucidated. To evaluate the role of IL-33 in NMOSD, we constructed NMOSD mice model by injecting purified serum IgG from AQP4-IgG seropositive NMOSD patients into experimental autoimmune encephalomyelitis (EAE) mice, and IL-33 was intraperitoneally injected into NMOSD mice 3 d before the model induction. We found that pretreatment of the NMOSD mice with IL-33 relieved brain neuron loss, and demyelination and improved the structure of axons, astrocytes, and mitochondria. In the neuronal and microglial coculture system, pretreatment with IL-33 in microglia alleviated NMOSD serum-induced inflammation and damaged morphology in cultured neurons. IL-33 transformed microglia to the M2 phenotype, and NMOSD serum promoted microglia to the M1 phenotype in cultured BV2 cells. Moreover, IL-33 influenced microglial polarity via the IL-33/ST2 pathway. IL-33 may be a novel insight useful for further developing NMOSD-targeted therapy and drug development.

Photobiomodulation reduces spinal cord edema by decreasing the expression of AQP4 in the astrocytes of male spinal cord injury rats via the JAK2/STAT3 signaling pathway

BACKGROUND

Spinal cord swelling commonly occurs following SCI. Previous studies suggest that PBM may reduce inflammation and scar formation after SCI. However, whether PBM can alleviate post-spinal cord injury edema and its underlying mechanisms have not yet been reported. This study aims to investigate the effects of PBM on spinal cord swelling in rats following SCI and explore the underlying mechanisms.

METHODS

A rat model of SCI was established, and the rats received continuous PBM therapy for two weeks. Tissue hydration, motor function, AQP4 expression, and pathological changes in the spinal cord were evaluated at different time points. In vitro, astrocytes were subjected to PBM and treated with either cucurbitacin I or TGN020 following OGD.

RESULTS

The results indicate that PBM reduces tissue swelling in rats with SCI, improves motor function recovery, and inhibits the upregulation of AQP4 and GFAP associated with SCI. In vitro, PBM reduces abnormal activation of the JAK2/STAT3 signaling pathway in astrocytes, leading to decreased AQP4 synthesis and astrocyte activation.

CONCLUSIONS

These findings suggest that PBM reduces spinal cord swelling in rats after injury. This effect is associated with the inhibition of JAK2/STAT3 signaling pathway activation in astrocytes and the reduction in AQP4 expression.

The Efficacy of Eculizumab in the Acute Phase of Neuromyelitis Optica Spectrum Disorder: A Case Series Study

Eculizumab, a monoclonal antibody against complement C5, has been approved to prevent neuromyelitis optica spectrum disorder (NMOSD) relapse. Although complement activation leads to neuroinflammation and tissue necrosis in NMOSD attacks, clinical reports on the efficacy of eculizumab in the acute phase of NMOSD are limited. To clarify its effectiveness against clinical symptoms in NMOSD attacks, we described five patients with NMOSD who were administered eculizumab soon after treatment for an attack. The patients included four female patients and one male patient aged 50-93 years. The index attacks were optic neuritis in three cases, myelitis in one case, and brainstem encephalitis and myelitis in one case. Three patients had not received any maintenance therapy. Although all patients had received intravenous methylprednisolone (IVMP) and plasma exchange (PE) several times, these treatments were not sufficient to improve their symptoms. Thereafter, eculizumab was initiated between 35 and 61 days after the attack onset and partially ameliorated the symptoms in all cases. These cases suggest eculizumab as a treatment option to lessen the symptoms of severe NMOSD attacks, although the efficacy of IVMP and PE before eculizumab administration cannot be excluded.

NMOSD and MOGAD: an evolving disease spectrum

Neuromyelitis optica (NMO) spectrum disorder (NMOSD) is a relapsing inflammatory disease of the CNS, characterized by the presence of serum aquaporin 4 (AQP4) autoantibodies (AQP4-IgGs) and core clinical manifestations such as optic neuritis, myelitis, and brain or brainstem syndromes. Some people exhibit clinical characteristics of NMOSD but test negative for AQP4-IgG, and a subset of these individuals are now recognized to have serum autoantibodies against myelin oligodendrocyte glycoprotein (MOG) - a condition termed MOG antibody-associated disease (MOGAD). Therefore, the concept of NMOSD is changing, with a disease spectrum emerging that includes AQP4-IgG-seropositive NMOSD, MOGAD and double-seronegative NMOSD. MOGAD shares features with NMOSD, including optic neuritis and myelitis, but has distinct pathophysiology, clinical profiles, neuroimaging findings (including acute disseminated encephalomyelitis and/or cortical encephalitis) and biomarkers. AQP4-IgG-seronegative NMOSD seems to be a heterogeneous condition and requires further study. MOGAD can manifest as either a monophasic or a relapsing disease, whereas NMOSD is usually relapsing. This Review summarizes the history and current concepts of NMOSD and MOGAD, comparing epidemiology, clinical features, neuroimaging, pathology and immunology. In addition, we discuss new monoclonal antibody therapies for AQP4-IgG-seropositive NMOSD that target complement, B cells or IL-6 receptors, which might be applied to MOGAD in the near future.

CNS B cell infiltration in tumefactive anti-myelin oligodendrocyte glycoprotein antibody-associated disease

Background

Few studies have examined B cells among patients with anti-myelin oligodendrocyte glycoprotein (MOG) antibody-associated disease (MOGAD), including brain pathology.

Objective

To describe cases of tumefactive MOGAD with B-cell dominant central nervous system (CNS) infiltration.

Methods

In this study, we reviewed three cases with clinical and brain histopathological features with tumefactive MOGAD.

Results

Forty-nine cases of tumefactive brain lesions (TBL) between January 2003 and December 2023 were included; of these, seven had MOGAD. Three underwent a brain biopsy. B-cell dominant CNS infiltration was observed in two cases. In two cases with B-cell dominant CNS infiltration, symptoms included fever, headache, nausea, somnolence, and focal neurological deficits. Cerebrospinal fluid examination revealed both mild pleocytosis and negative oligoclonal IgG bands. Magnetic resonance imaging of the brain revealed large abnormal lesions extending from the basal ganglia to the parietotemporal lobe in both cases. These cases showed a good response to steroids; however, one case relapsed. Brain pathology showed demyelination and perivascular lymphocytic infiltration. One showed small vessel vasculitis. Deposition of the activated complement component was absent or rarely observed. Loss of MOG was observed in two cases.

Conclusion

MOGAD could exhibit B-cell dominant CNS infiltration and small vessel vasculitis. MOGAD should be considered in differential diagnosis of TBL.

The efficacy and safety of eculizumab in patients and the role of C5 polymorphisms

Eculizumab is an orphan drug with indications for extremely rare autoimmune disorders. It is primarily prescribed for use in patients with paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome; but is also highly effective in the treatment of myasthenia gravis, among others. By binding to the C5 protein in the complement system, eculizumab effectively inhibits cellular hemolysis and autoimmune reactions. Despite this effective treatment, some patients reported no improvement in symptoms. Genetic sequencing revealed three distinct C5 mutations in the non-responders and these polymorphisms appeared to be most prevalent among Japanese, Korean and African populations. Here, we present an overview of the current and potential future applications of eculizumab, as well as the disadvantages of eculizumab treatment in patients with C5 polymorphisms.

Spinal Cord Imaging in Multiple Sclerosis and Related Disorders

Spinal cord MRI plays an important role in the diagnosis and prognosis of multiple sclerosis (MS) and related disorders. The ANATOMICAL, pathologic, imaging and prognostic consideriations for the spinal cord for MS and the most important other demyelinating disorders, neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein-associated disease, are reviewed. Finally, differential diagnostic considerations of spinal cord MRI in MS and related disorders are discussed.

Correlation between severe attacks and serum aquaporin-4 antibody titer in neuromyelitis optica spectrum disorder

Aquaporin 4-immunoglobulin G (AQP4-IgG) specifically targets aquaporin 4 in approximately 80% of Neuromyelitis Optica Spectrum Disorder (NMOSD) cases. NMOSD is presently categorized as anti-AQP4-antibody (Ab) positive or negative based on AQP4-Ab presence. The association between antibody titers and patient prognosis remains unclear. Therefore, the present study explores the correlation between severe attacks and serum AQP4 Ab titers in patients with neuromyelitis optica spectrum disorder. Data were gathered retrospectively from 546 patients with NMOSD between September 1, 2009, and December 1, 2021. Patients were categorized based on their AQP4-Ab titers: AQP4 titer ≥ 1:320 were classified as the high-titer group, AQP4 (+ +), and AQP4 titer of ≤ 1:100 were classified as the low-titer group, AQP4 ( +). Clinical characteristics and prognoses between the two groups were compared. Patients with AQP4 ( +) exhibited few severe optic neuritis (SON) attacks (false discovery rate [FDR] corrected p < 0.001), a reduced percentage experiencing SON attacks, and a lower incidence of visual disability than patients with AQP4 (+ +). Patients with AQP4 (+ +) and AQP4 ( +) NMOSD exhibited significant difference in annual recurrence rate (ARR) (FDR-corrected p < 0.001). The lower AQP4 Ab titer group demonstrated reduced susceptibility to severe relapse with conventional immunosuppressive agents and rituximab (RTX) than the higher titer group. No significant differences in sex, age at onset, coexisting connective tissue diseases, motor disability, or mortality rates were observed between the two groups. Higher AQP4 Ab titers correlated with increased disease severity and visual disability in patients with NMOSD.

Water channels in the brain and spinal cord-overview of the role of aquaporins in traumatic brain injury and traumatic spinal cord injury

Knowledge about the mechanisms underlying the fluid flow in the brain and spinal cord is essential for discovering the mechanisms implicated in the pathophysiology of central nervous system diseases. During recent years, research has highlighted the complexity of the fluid flow movement in the brain through a glymphatic system and a lymphatic network. Less is known about these pathways in the spinal cord. An important aspect of fluid flow movement through the glymphatic pathway is the role of water channels, especially aquaporin 1 and 4. This review provides an overview of the role of these aquaporins in brain and spinal cord, and give a short introduction to the fluid flow in brain and spinal cord during in the healthy brain and spinal cord as well as during traumatic brain and spinal cord injury. Finally, this review gives an overview of the current knowledge about the role of aquaporins in traumatic brain and spinal cord injury, highlighting some of the complexities and knowledge gaps in the field.

Inhibition of repulsive guidance molecule-a ameliorates compromised blood-spinal cord barrier integrity associated with neuromyelitis optica in rats

The influx of pathogenic aquaporin-4 antibodies (AQP4-Abs) across the blood-spinal cord barrier (BSCB) is crucial for the development and exacerbation of neuromyelitis optica (NMO). We examined whether prophylactic intravenous administration of anti-repulsive guidance molecule-a antibodies (RGMa-Abs) has disease-modifying effects on BSCB dysfunction using an NMO model elicited by peripheral administration of AQP4-Abs to rats. RGMa-Ab treatment attenuated the acute exacerbation of perivascular astrocytopathy in the spinal cord and clinical symptoms, which were highly correlated with neurofilament light chain levels in both the cerebrospinal fluid (CSF) and serum. Additionally, RGMa-Ab treatment suppressed the expression of proinflammatory cytokines/chemokines and the infiltration of inflammatory cells into the spinal cord. CSF analysis of NMO rats revealed that RGMa-Ab treatment improved the CSF/serum albumin ratio and suppressed AQP4-Abs influx. RGMa inhibition using RGMa-Abs is suggested as a potential therapeutic option for BSCB dysfunction associated with NMO.

Risk factors and prognosis of orotracheal intubation in aquaporin-4-IgG neuromyelitis optica spectrum disorder attacks

BACKGROUND

Aquaporin-4 immunoglobulin G Neuro Myelitis Optica spectrum disorders attacks (NMOSD-AQP4-IgG+ attacks) can cause respiratory failure requiring orotracheal intubation (OTI), but the risk factors and outcomes of OTI during attacks remain unclear. Our primary objective was to identify the clinical and radiological risk factors for OTI in NMOSD-AQP4-IgG+ attacks. As a secondary objective, we aimed to evaluate the prognosis of OTI-attacks.

METHODS

We retrospectively analyzed NMOSD-AQP4-IgG+ attacks at the Pitié-Salpêtrière Hospital (Jan 2010-Jan 2021), excluding isolated optic neuritis. The primary outcome was the need for OTI due to neurological dysfunction an attack (OTI-attack). The secondary outcome was attack's poor recovery after 12 months, defined as a modified Rankin score (mRS) > 2 in patients with an initial mRS ≤ 2, or an increase ≥ 1 point in mRS in other patients. Analyses were performed using a binomial generalized linear mixed model, with a random intercept for the patient ID to account for within-patient correlations.

RESULTS

Seventy-three attacks in 44 patients NMOSD-AQP4-IgG+ were analyzed. Of 73 attacks, 8 (11%) required OTI during the attack, related to acute restrictive respiratory failure (n = 7) and/or severe swallowing disorder (n = 2). None of the OTI-attacks occurred in patients previously treated with active disease-modifying treatment (DMT), while 36 (55.4%) of the non-OTI-attacks occurred in patients who were already on active DMT. On admission, OTI-attacks were more likely to have upper limbs motor paresis of (75.0% versus 29.2%, p = 0.366) and dyspnea (3 [50.0%] versus 4 [6.6%], p = 0.002) compared to non-OTI-attacks. MRI analysis showed that OTI-attacks had edematous lesions in the cervical spinal cord, mainly at levels C1 (75% versus 0% in non-OTI-attacks), C2 (75% versus 1.9%), C3 (62.5% versus 1.9%), and C4 and C5 levels (50% versus to 3.9%). One OTI-attack resulted in the death of one patient. Five patients with OTI-attack had mRS ≤ 2 one year after OTI-attack. Two (25%) OTI-attacks had poor recovery compared to 15 (24.2%) non-OTI-attacks (p = 0.468).

CONCLUSION

OTI-attacks occurred in untreated NMOSD-AQP4-IgG+ patients and were associated with edematous upper cervical lesions. The prognosis of these attacks may be favorable, and warrant maximal medical and supportive treatment. Trial registration This was a retrospective observational monocentric cohort study nested in the NOMADMUS cohort (ClinicalTrials.gov Identifier: NCT02850705).

Tocilizumab treatment in neuromyelitis optica spectrum disorders: Updated meta-analysis of efficacy and safety

This systematic review and meta-analysis summarize the efficacy and safety of Tocilizumab (TCZ) in treating NMOSD and investigates the factors that affect its efficacy. TCZ is the first monoclonal antibody against the IL-6 receptor for treating NMOSD, and its efficacy and safety vary in different studies. We collected English-language research literature until January 1, 2023, by searching databases such as PubMed, MEDLINE, Embase, Cochrane Library, and clinicaltrials.gov, and identified 9 studies involving 153 patients (139 female and 14 male) that met our inclusion criteria. In these studies, the average ARR ratio and EDSS score reduction values in the TCZ treatment group were -1.34 (95 % CI, -1.60 to -1.09) and -0.81 (95 % CI, -1.04 to -0.58), respectively. Based on the data we have collected, compared to the AQP4-IgG negative NMOSD patients, TCZ demonstrates a more pronounced effectiveness in AQP4-IgG positive NMOSD patients. The study also found that the effectiveness of TCZ in reducing NMOSD patients' ARR ratio was related to gender, race, and TCZ dosage, while the effectiveness of reducing EDSS score was not related to these factors. Among the 153 patients receiving TCZ treatment, 101 (66 %) experienced mild adverse reactions, and one patient experienced a severe adverse reaction (facial cellulitis). The comprehensive data indicate that TCZ treatment can reduce the frequency of NMOSD relapses, improve patients' neurological function, and have good safety. The effectiveness of TCZ in reducing NMOSD patients' ARR ratio is related to multiple factors.

Structural disconnection is associated with disability in the neuromyelitis optica spectrum disorder

OBJECTIVES

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory disease of the central nervous system. Accumulating evidence suggests there is a distinct pattern of brain lesions characteristic of NMOSD, and brain MRI has potential prognostic implications. However, the question of how the brain lesions in NMOSD are associated with its distinct clinical course remains incompletely understood. Here, we aimed to investigate the association between neurological impairment and brain lesions via brain structural disconnection.

METHODS

Twenty patients were diagnosed with NMOSD according to the 2015 International Panel for NMO Diagnosis criteria. The white matter lesions were manually drawn section by section. Whole-brain structural disconnection was estimated, and connectome-based predictive modeling (CPM) was used to estimate the patient's Expanded Disability Status Scale score (EDSS) from their disconnection severity matrix. Furthermore, correlational tractography was performed to assess the fractional anisotropy (FA) and axial diffusivity (AD) of white matter fibers, which negatively correlated with the EDSS score.

RESULTS

CPM successfully predicted the EDSS using the disconnection severity matrix (r = 0.506, p = 0.028; q2 = 0.274). Among the important edges in the prediction process, the majority of edges connected the motor to the frontoparietal network. Correlational tractography identified a decreased FA and AD value according to EDSS scores in periependymal white matter tracts.

DISCUSSION

Structural disconnection-based predictive modeling and local connectome analysis showed that frontoparietal and periependymal white matter disconnection is predictive and associated with the EDSS score of NMOSD patients.

Microfibrillar-associated protein 4 as a potential marker of acute relapse in inflammatory demyelinating diseases of the central nervous system: Pathological and clinical aspects

BACKGROUND

Microfibrillar-associated protein 4 (MFAP4) is an extracellular matrix protein not previously described in the human central nervous system (CNS).

OBJECTIVES

We determined MFAP4 CNS expression and measured cerebrospinal fluid (CSF) and serum levels.

METHODS

Tissue was sampled at autopsy from patients with acute multiple sclerosis (MS) (n = 3), progressive MS (n = 3), neuromyelitis optica spectrum disorder (NMOSD) (n = 2), and controls (n = 9), including 6 healthy controls (HC). MFAP4 levels were measured in 152 patients: 49 MS, 62 NMOSD, 22 myelin oligodendrocyte glycoprotein-associated disease (MOGAD), and 19 isolated optic neuritis (ION).

RESULTS

MFAP4 localized to meninges and vascular/perivascular spaces, intense in the optic nerve. At sites of active inflammation, MFAP4 reactivity was reduced in NMOSD and acute MS and less in progressive MS. CSF MFAP4 levels were reduced during relapse and at the onset of diseases (mean U/mL: MS 14.3, MOGAD 9.7, and ION 14.6 relative to HC 17.9. (p = 0.013, p = 0.000, and p = 0.019, respectively). Patients with acute ON (n = 68) had reduced CSF MFAP4 (mean U/mL: 14.5, p = 0.006). CSF MFAP4 levels correlated negatively with relapse severity (rho = -0.41, p = 0.017).

CONCLUSION

MFAP4 immunoreactivity was reduced at sites of active inflammation. CSF levels of MFAP4 were reduced following relapse and may reflect disease activity.

Recurrent Regional Autonomic Dysfunction as a Presentation of Relapsing Neuromyelitis Optica Spectrum Disorder, Responsive to Ketamine Infusion

Diagnostic criteria of neuromyelitis optica spectrum disorders (NMOSD) have expanded to include many new symptoms since the original description of Devic's disease in 1894, and the formulation of diagnostic criteria in 2006. Herein, we describe a patient with serum aquaporin positive NMOSD with the unusual presentation of recurrent regional autonomic dysfunction, with concordant MRI findings. The symptomatic treatment of the patient's causalgia required IV ketamine infusion. Besides, as the long segment myelitis occurred in the setting of extensively drug-resistant tuberculosis (XDR TB), there was the added challenge of ruling out TB myelitis and choosing an immunosuppressant that would have the least risk of reactivation of TB.

Pathology of myelin oligodendrocyte glycoprotein antibody-associated disease: a comparison with multiple sclerosis and aquaporin 4 antibody-positive neuromyelitis optica spectrum disorders

Myelin oligodendrocyte glycoprotein (MOG) is expressed on the outermost layer of the myelin sheath in the central nervous system. Recently, the clinical concept of MOG antibody-associated disease (MOGAD) was established based on the results of human MOG-transfected cell-based assays which can detect conformation-sensitive antibodies against MOG. In this review, we summarized the pathological findings of MOGAD and discussed the issues that remain unresolved. MOGAD pathology is principally inflammatory demyelination without astrocyte destruction, characterized by perivenous demyelination previously reported in acute disseminated encephalomyelitis and by its fusion pattern localized in both the white and gray matter, but not by radially expanding confluent demyelination typically seen in multiple sclerosis (MS). Some of demyelinating lesions in MOGAD show severe loss of MOG staining compared with those of other myelin proteins, suggesting a MOG-targeted pathology in the disease. Perivascular cuffings mainly consist of macrophages and T cells with CD4-dominancy, which is also different from CD8+ T-cell-dominant inflammation in MS. Compared to aquaporin 4 (AQP4) antibody-positive neuromyelitis optica spectrum disorders (NMOSD), perivenous complement deposition is less common, but can be seen on myelinated fibers and on myelin degradation products within macrophages, resembling MS Pattern II pathology. Thus, the pathogenetic contribution of complements in MOGAD is still debatable. Together, these pathological features in MOGAD are clearly different from those of MS and AQP4 antibody-positive NMOSD, suggesting that MOGAD is an independent autoimmune demyelinating disease entity. Further research is needed to clarify the exact pathomechanisms of demyelination and how the pathophysiology relates to the clinical phenotype and symptoms leading to disability in MOGAD patients.

Autoimmune-mediated astrocytopathy

Recently accumulating evidence identified the disease entity where astrocytes residing within the central nervous system (CNS) are the target of autoantibody-mediated autoimmunity. Aquaporin4 (AQP4) is the most common antigen to serve as astrocyte-targeted autoimmune responses. Here, in this review, the clinical and pathological aspects of AQP4-mediated astrocyte disease are discussed together with the pathogenic role of anti-AQP4 antibody. More recently, the mechanism of immune dysregulation resulting in the production of astrocyte-targeted autoantibody is also revealed, and the postulated hypothesis is discussed.

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 disorders with a benign course. Analysis of 544 patients

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) most commonly cause severe disability which is related to disease attacks. However, some patients retain good neurological function for a long time after disease onset.

OBJECTIVES

To determine the frequency, demographic and the clinical features of good outcome NMOSD, and analyze their predictive factors.

METHODS

We selected patients who met the 2015 International Panel for NMOSD diagnostic criteria from seven MS Centers. Assessed data included age at disease onset, sex, race, number of attacks within the first and three years from onset, annualized relapsing rate (ARR), total number of attacks, aquaporin-IgG serum status, presence of cerebrospinal fluid (CSF)-specific oligoclonal bands (OCB) and the Expanded Disability Status Scale (EDSS) score at the last follow-up visit. NMOSD was classified as non-benign if patients developed sustained EDSS score >3.0 during the disease course, or benign if patients had EDSS score ≤3.0 after ≥15 years from disease onset. Patients with EDSS <3.0 and disease duration shorter than 15 years were not qualified for classification. We compared the demographic and clinical characteristics of benign and non-benign NMOSD. Logistic regression analysis identified predictive factors of outcome.

RESULTS

There were 16 patients with benign NMOSD (3% of the entire cohort; 4.2% of those qualified for classification; and 4.1% of those who tested positive for aquaporin 4-IgG), and 362 (67.7%) with non-benign NMOSD, whereas 157 (29.3%) did not qualify for classification. All patients with benign NMOSD were female, 75% were Caucasian, 75% tested positive for AQP4-IgG, and 28.6% had CSF-specific OCB. Regression analysis showed that female sex, pediatric onset, and optic neuritis, area postrema syndrome, and brainstem symptoms at disease onset, as well as fewer relapses in the first year and three years from onset, and CSF-specific OCB were more commonly found in benign NMOSD, but the difference did not reach statistical significance. Conversely, non-Caucasian race (OR: 0.29, 95% CI: 0.07-0.99; p = 0.038), myelitis at disease presentation (OR: 0.07, 95% CI: 0.01-0.52; p <0.001), and high ARR (OR: 0.07, 95% CI: 0.01-0.67; p = 0.011) were negative risk factors for benign NMOSD.

CONCLUSION

Benign NMOSD is very rare and occurs more frequently in Caucasians, patients with low ARR, and those who do not have myelitis at disease onset.

How does neurovascular unit dysfunction contribute to multiple sclerosis?

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system (CNS) and the most common non-traumatic cause of neurological disability in young adults. Multiple sclerosis clinical care has improved considerably due to the development of disease-modifying therapies that effectively modulate the peripheral immune response and reduce relapse frequency. However, current treatments do not prevent neurodegeneration and disease progression, and efforts to prevent multiple sclerosis will be hampered so long as the cause of this disease remains unknown. Risk factors for multiple sclerosis development or severity include vitamin D deficiency, cigarette smoking and youth obesity, which also impact vascular health. People with multiple sclerosis frequently experience blood-brain barrier breakdown, microbleeds, reduced cerebral blood flow and diminished neurovascular reactivity, and it is possible that these vascular pathologies are tied to multiple sclerosis development. The neurovascular unit is a cellular network that controls neuroinflammation, maintains blood-brain barrier integrity, and tightly regulates cerebral blood flow, matching energy supply to neuronal demand. The neurovascular unit is composed of vessel-associated cells such as endothelial cells, pericytes and astrocytes, however neuronal and other glial cell types also comprise the neurovascular niche. Recent single-cell transcriptomics data, indicate that neurovascular cells, particular cells of the microvasculature, are compromised within multiple sclerosis lesions. Large-scale genetic and small-scale cell biology studies also suggest that neurovascular dysfunction could be a primary pathology contributing to multiple sclerosis development. Herein we revisit multiple sclerosis risk factors and multiple sclerosis pathophysiology and highlight the known and potential roles of neurovascular unit dysfunction in multiple sclerosis development and disease progression. We also evaluate the suitability of the neurovascular unit as a potential target for future disease modifying therapies for multiple sclerosis.

Utility of the tibial nerve somatosensory evoked potentials in differentiating between neuromyelitis optica spectrum disorders and multiple sclerosis

BACKGROUND

Somatosensory evoked potentials (SEPs) are widely used for the diagnosis and evaluation of neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS). However, whether the parameters of tibial nerve SEPs can help to distinguish NMOSD from MS remains unclear. Thus, the aim of this study was to investigate the utility of tibial nerve SEP parameters in differentiating patients with NMOSD and MS.

METHODS

The clinical data of patients with NMOSD or MS treated in our institution between 2005 and 2021 were retrospectively extracted from our electronic database. Additional inclusion criteria were presentation with sensory symptoms in the lower extremities with corresponding lesions in the magnetic resonance images as well as available data on anti-aquaporin-4 antibodies and tibial nerve SEPs. The Z-scores of the N21-P38 interval (central sensory conduction time), P38 latency, and P38 amplitude were compared between the patients with NMOSD and MS. The relationship of disease severity with the parameters of the tibial nerve SEPs was also evaluated.

RESULTS

Twenty patients with NMOSD and 13 patients with MS were enrolled. The Z-scores of the N21-P38 interval and P38 latency were significantly higher in the MS group than in the NMOSD group (p < 0.05 and p < 0.01, respectively), whereas there was no difference in the Z-scores of the P38 amplitude between the two groups. In the MS group, only the N21-P38 interval and P38 latency were significantly correlated with disease severity (p < 0.05 and p < 0.01, respectively). In contrast, none of the tibial nerve SEP parameters were significantly correlated with disease severity in the NMOSD group.

CONCLUSION

Evaluation of the N21-P38 interval and P38 latency in tibial nerve SEPs potentially helps in differentiating between NMOSD and MS.

Assessment of intelligence quotient in patients with neuromyelitis optica spectrum disease and multiple sclerosis

BACKGROUND

Cognitive impairment is common in people living with neuromyelitis optica spectrum disease (NMOSD) and multiple sclerosis (MS). However, there is little published data on intelligence quotient (IQ) in NMOSD patients. Therefore, we performed the present study to compare IQ scores across NMOSD, MS, and control groups.

METHOD

In this cross-sectional study, 49 NMOSD (30 with positive aquaporin4 antibody), 41 MS, and 20 control individuals were recruited. The IQ score for each person was measured using Wechsler Adult Intelligence Scale-Revised (WAIS-R). Participants were reported on eleven scores of subsets, verbal IQ (VIQ), performance IQ (PIQ), and full score IQ (FSIQ).

RESULT

The scores of FSIQ, VIQ, PIQ, vocabulary, similarities, and digit-symbol in NMOSD and MS individuals were lower than the control group. Relative to control, NMOSD patients reported a lower score of information. We found no difference between NMOSD and MS groups, except in vocabulary and similarities. No significant difference between seropositive and seronegative NMOSD groups was observed except for the information and block design. In NMOSD group, a greater EDSS score was associated with decreased scores of FSIQ, VIQ, and PIQ. Being employed and being married were associated with greater scores of VIQ and PIQ, respectively. In both NMOSD and MS groups, advanced education was associated with increased scores of FSIQ and VIQ.

CONCLUSION

Our study showed decreased IQ scores in NMOSD and MS. Further studies are required to examine intellectual quotient in people with NMOSD and MS.

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.

Advances in Antibody-Based Therapeutics for Cerebral Ischemia

Cerebral ischemia is an acute disorder characterized by an abrupt reduction in blood flow that results in immediate deprivation of both glucose and oxygen. The main types of cerebral ischemia are ischemic and hemorrhagic stroke. When a stroke occurs, several signaling pathways are activated, comprising necrosis, apoptosis, and autophagy as well as glial activation and white matter injury, which leads to neuronal cell death. Current treatments for strokes include challenging mechanical thrombectomy or tissue plasminogen activator, which increase the danger of cerebral bleeding, brain edema, and cerebral damage, limiting their usage in clinical settings. Monoclonal antibody therapy has proven to be effective and safe in the treatment of a variety of neurological disorders. In contrast, the evidence for stroke therapy is minimal. Recently, Clone MTS510 antibody targeting toll-like receptor-4 (TLR4) protein, ASC06-IgG1 antibody targeting acid sensing ion channel-1a (ASIC1a) protein, Anti-GluN1 antibodies targeting N-methyl-D-aspartate (NMDA) receptor associated calcium influx, GSK249320 antibody targeting myelin-associated glycoprotein (MAG), anti-High Mobility Group Box-1 antibody targeting high mobility group box-1 (HMGB1) are currently under clinical trials for cerebral ischemia treatment. In this article, we review the current antibody-based pharmaceuticals for neurological diseases, the use of antibody drugs in stroke, strategies to improve the efficacy of antibody therapeutics in cerebral ischemia, and the recent advancement of antibody drugs in clinical practice. Overall, we highlight the need of enhancing blood-brain barrier (BBB) penetration for the improvement of antibody-based therapeutics in the brain, which could greatly enhance the antibody medications for cerebral ischemia in clinical practice.

Diagnostik der Neuromyelitis-optica-Spektrum-Erkrankung (NMOSD) und der MOG-Antikörper-assoziierten Erkrankung (MOGAD)

Die Aquaporin-4-Antikörper-positive Neuromyelitis-optica-Spektrum-Erkrankung (engl. NMOSD) und die Myelin-Oligodendrozyten-Glykoprotein-Antikörper-assoziierte Erkrankung (engl. MOGAD) sind Autoimmunerkrankungen des zentralen Nervensystems. Typische Erstmanifestationen sind bei Erwachsenen Optikusneuritis und Myelitis. Eine Beteiligung auch von Hirn und Hirnstamm, spätestens im weiteren Verlauf, ist häufig. Während die NMOSD nahezu immer schubförmig verläuft, nimmt die MOGAD gelegentlich einen monophasischen Verlauf. Die Differenzialdiagnostik ist anspruchsvoll und stützt sich auf u. a. auf radiologische und serologische Befunde. Die Abgrenzung von der häufigeren neuroinflammatorischen Erkrankung, Multiple Sklerose (MS), ist von erheblicher Bedeutung, da sich Behandlung und langfristige Prognose von NMOSD, MOGAD und MS wesentlich unterscheiden. Die vielfältigen Symptome und die umfangreiche Diagnostik machen eine enge Zusammenarbeit zwischen Ophthalmologie, Neurologie und Radiologie erforderlich. Dieser Artikel gibt einen Überblick über typische MRT-Befunde und die serologische Antikörperdiagnostik bei NMOSD und MOGAD. Zwei illustrative Fallberichte aus der ärztlichen Praxis ergänzen die Darstellung.

A novel aquaporin-4-associated optic neuritis rat model with severe pathological and functional manifestations

Background

Optic neuritis (ON) is a common manifestation of aquaporin-4 (AQP4) antibody seropositive neuromyelitis optica (NMO). The extent of tissue damage is frequently severe, often leading to loss of visual function, and there is no curative treatment for this condition. To develop a novel therapeutic strategy, elucidating the underlying pathological mechanism using a clinically relevant experimental ON model is necessary. However, previous ON animal models have only resulted in mild lesions with limited functional impairment. In the present study, we attempted to establish a feasible ON model with severe pathological and functional manifestations using a high-affinity anti-AQP4 antibody. Subsequently, we aimed to address whether our model is suitable for potential drug evaluation by testing the effect of minocycline, a well-known microglia/macrophage inhibitor.

Methods

AQP4-immunoglobulin G (IgG)-related ON in rats was induced by direct injection of a high-affinity anti-AQP4 monoclonal antibody, E5415A. Thereafter, the pathological and functional characterizations were performed, and the therapeutic potential of minocycline was investigated.

Results

We established an experimental ON model that reproduces the histological characteristics of ON in seropositive NMO, such as loss of AQP4/glial fibrillary acidic protein immunoreactivity, immune cell infiltration, and extensive axonal damage. We also observed that our rat model exhibited severe visual dysfunction. The histological analysis showed prominent accumulation of macrophages/activated microglia in the lesion site in the acute phase. Thus, we investigated the possible effect of the pharmacological inhibition of macrophages/microglia activation by minocycline and revealed that it effectively ameliorated axonal damage and functional outcome.

Conclusions

We established an AQP4-IgG-induced ON rat model with severe functional impairments that reproduce the histological characteristics of patients with NMO. Using this model, we revealed that minocycline treatment ameliorates functional and pathological outcomes, highlighting the usefulness of our model for evaluating potential therapeutic drugs for ON in NMO.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02623-7.

Cellular changes at the glia-neuro-vascular interface in definite idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a subtype of dementia with overlap toward Alzheimer's disease. Both diseases show deposition of the toxic metabolites amyloid-β and tau in brain. A unique feature with iNPH is that a subset of patients may improve clinically following cerebrospinal fluid (CSF) diversion (shunt) surgery. The patients responding clinically to shunting are denoted Definite iNPH, otherwise iNPH is diagnosed as Possible iNPH or Probable iNPH, high-lightening that the clinical phenotype and underlying pathophysiology remain debated. Given the role of CSF disturbance in iNPH, the water channel aquaporin-4 (AQP4) has been suggested a crucial role in iNPH. Altered expression of AQP4 at the astrocytic endfeet facing the capillaries could affect glymphatic function, i.e., the perivascular transport of fluids and solutes, including soluble amyloid-β and tau. This present study asked how altered perivascular expression of AQP4 in subjects with definite iNPH is accompanied with cellular changes at the glia-neuro-vascular interface. For this purpose, information was retrieved from a database established by the author, including prospectively collected management data, physiological data and information from brain biopsy specimens examined with light and electron microscopy. Individuals with definite iNPH were included together with control subjects who matched the definite iNPH cohort closest in gender and age. Patients with definite iNPH presented with abnormally elevated pulsatile intracranial pressure measured overnight. Cortical brain biopsies showed reduced expression of AQP4 at astrocytic endfeet both perivascular and toward neuropil. This was accompanied with reduced expression of the anchor molecule dystrophin (Dp71) at astrocytic perivascular endfeet, evidence of altered cellular metabolic activity in astrocytic endfoot processes (reduced number of normal and increased number of pathological mitochondria), and evidence of reactive changes in astrocytes (astrogliosis). Moreover, the definite iNPH subjects demonstrated in cerebral cortex changes in capillaries (reduced thickness of the basement membrane between astrocytic endfeet and endothelial cells and pericytes, and evidence of impaired blood-brain-barrier integrity). Abnormal changes in neurons were indicated by reduced post-synaptic density length, and reduced number of normal mitochondria in pre-synaptic terminals. In summary, definite iNPH is characterized by profound cellular changes at the glia-neurovascular interface, which probably reflect the underlying pathophysiology.

P2R Inhibitors Prevent Antibody-Mediated Complement Activation in an Animal Model of Neuromyelitis Optica : P2R Inhibitors Prevent Autoantibody Injury

Purinergic 2 receptors (P2Rs) contribute to disease-related immune cell signaling and are upregulated in various pathological settings, including neuroinflammation. P2R inhibitors have been used to treat inflammatory diseases and can protect against complement-mediated cell injury. However, the mechanisms behind these anti-inflammatory properties of P2R inhibitors are not well understood, and their potential in CNS autoimmunity is underexplored. Here, we tested the effects of P2R inhibitors on glial toxicity in a mouse model of neuromyelitis optica spectrum disorder (NMOSD). NMOSD is a destructive CNS autoimmune disorder, in which autoantibodies against astrocytic surface antigen Aquaporin 4 (AQP4) mediate complement-dependent loss of astrocytes. Using two-photon microscopy in vivo, we found that various classes of P2R inhibitors prevented AQP4-IgG/complement-dependent astrocyte death. In vitro, these drugs inhibited the binding of AQP4-IgG or MOG-IgG to their antigen in a dose-dependent manner. Size-exclusion chromatography and circular dichroism spectroscopy revealed a partial unfolding of antibodies in the presence of various P2R inhibitors, suggesting a shared interference with IgG antibodies leading to their conformational change. Our study demonstrates that P2R inhibitors can disrupt complement activation by direct interaction with IgG. This mechanism is likely to influence the role of P2R inhibitors in autoimmune disease models and their therapeutic impact in human disease.

Treatment and Relapse Prevention of Typical and Atypical Optic Neuritis

Optic neuritis (ON) is an inflammatory condition involving the optic nerve. Several important typical and atypical ON variants are now recognized. Typical ON has a more favorable prognosis; it can be idiopathic or represent an early manifestation of demyelinating diseases, mostly multiple sclerosis (MS). The atypical spectrum includes entities such as antibody-driven ON associated with neuromyelitis optica spectrum disorder (NMOSD) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD), chronic/relapsing inflammatory optic neuropathy (CRION), and sarcoidosis-associated ON. Appropriate and timely diagnosis is essential to rapidly decide on the appropriate treatment, maximize visual recovery, and minimize recurrences. This review paper aims at presenting the currently available state-of-the-art treatment strategies for typical and atypical ON, both in the acute phase and in the long-term. Moreover, emerging therapeutic approaches and novel steps in the direction of achieving remyelination are discussed.

Risk of Parkinson's disease in multiple sclerosis and neuromyelitis optica spectrum disorder: a nationwide cohort study in South Korea

BACKGROUND

Neurodegeneration is associated with pathogenesis of both multiple sclerosis (MS) and neuromyelitis optica (NMOSD). Parkinson's disease (PD) is a representative neurodegenerative disease, however, whether MS or NMOSD is associated with risk of PD is not known.

METHODS

MS and NMOSD cohorts were collected from the Korean National Health Insurance Service between 1 January 2010 and 31 December 2017, using International Classification of Diseases 10th revision diagnosis codes and information in the Rare Intractable Disease management programme. The PD incidence rate that occurred after a 1-year lag period was calculated and compared with that of a control cohort matched for age, sex, hypertension, diabetes and dyslipidaemia in a 1:5 ratio.

RESULTS

The incidence rates of PD in patients with MS and NMOSD were 3.38 and 1.27 per 1000 person-years, respectively, and were higher than that of their matched control groups. The adjusted HR of PD was 7.73 (95% CI, 3.87 to 15.47) in patients with MS and 2.61 (95% CI, 1.13 to 6.02) in patients with NMOSD compared with matched controls. In both patients with MS and NMOSD, there were no significant differences in relative risk when stratified by sex, age, diabetes, hypertension and dyslipidaemia.

CONCLUSION

The PD risk was higher in patients with MS and NMOSD compared with healthy controls and was particularly high in patients with MS. Further investigations should be performed to determine the pathophysiology and occurrence of PD in patients with MS and NMOSD.

Clinical features of organizing pneumonia in anti-aquaporin-4 antibody-positive neuromyelitis optica spectrum disorders

BACKGROUND

Anti-aquaporin-4 (AQP4) antibody is an autoantibody marker often observed in patients with neuromyelitis optica spectrum disorder (NMOSD). The pathological relevance of complicated pulmonary disorders in anti-AQP4 antibody-positive NMOSD remains unclear. We aimed to assess the clinical and histological relevance of complicated pulmonary disorders in anti-AQP4 antibody-positive NMOSD.

METHODS

We retrospectively reviewed the medical records of 52 patients with anti-AQP4 antibody-positive NMOSD and conducted immunohistochemical evaluations of the lung biopsy specimens.

RESULTS

Among 52 patients with anti-AQP4 antibody-positive NMOSD, 4 patients showed pulmonary involvement with a diagnosis of organizing pneumonia (OP). The proportion of males was larger (75% vs. 12.5%; p = 0.013) and creatine kinase levels were higher (458.3 U/L vs. 83.9 U/L; p = 0.003) in patients with OP than in those without OP. OP development preceded or coincided with the NMOSD symptoms. Chest computed tomography findings were consistent with OP in all four patients. Bronchoalveolar lavage fluid predominantly contained lymphocytes. Transbronchial lung biopsy revealed intraluminal plugs of inflammatory debris within the alveoli. Alveolar epithelial cells covering the OP lesions exhibited AQP4 loss, immunoglobulin G deposition, and complement activation. Corticosteroid treatment resulted in clinical improvement of OP.

CONCLUSION

OP may be considered a pulmonary manifestation of anti-AQP4 antibody-positive NMOSD beyond the central nervous system. Complement-dependent cytotoxicity of the lung epithelial cells caused by anti-AQP4 antibody is at least partly involved in OP development. When diagnosing NMOSD, the possibility of OP should be carefully evaluated based on the detailed history and chest imaging findings.

Progress in treatment of neuromyelitis optica spectrum disorders (NMOSD): Novel insights into therapeutic possibilities in NMOSD

Neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune inflammatory demyelinating disorder of the central nervous system (CNS), which is a severely disabling disorder leading to devastating sequelae or even death. Repeated acute attacks and the presence of aquaporin-4 immunoglobulin G (AQP4-IgG) antibody are the typical characteristics of NMOSD. Recently, the phase III trials of the newly developed biologicals therapies have shown their effectiveness and good tolerance to a certain extent when compared with the traditional therapy with the first- and second-line drugs. However, there is still a lack of large sample, double-blind, randomized, clinical studies to confirm their efficacy, safety, and tolerability. Especially, these drugs have no clear effect on NMOSD patients without AQP4-IgG and refractory patients. Therefore, it is of strong demand to further conduct large sample, double-blind, randomized, clinical trials, and novel therapeutic possibilities in NMOSD are discussed briefly here.

NMO-IgG induce interleukin-6 release via activation of the NF-κB signaling pathway in astrocytes

Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory demyelinating disorder of the central nervous system (CNS) that frequently affects the optic nerve and spinal cord. Interleukin-6 (IL-6) is considered a key cytokine in the pathogenesis of NMOSD, and the level of IL-6 is significantly increased in the sera and cerebrospinal fluid (CSF) of patients with NMOSD. We have reported that the production of IL-6 depends on the JAK/STAT3 signaling pathway. However, it is not clear whether the NF-κB-dependent inflammatory response stimulated by neuromyelitis optica IgG (NMO-IgG) could also drive the production of IL-6 in astrocytes. In this study, we used an in vitro model of primary rat astrocytes stimulated by NMO-IgG to study the role of the NF-κB signaling pathway in mediating the release of IL-6. First, we confirmed that the level of IL-6 was significantly higher in the sera of NMOSD patients than that of healthy people by humoral fluid analysis and that NMO-IgG can significantly induce the release of IL-6 from astrocytes by enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Then, Western blotting and immunocytochemistry showed that NMO-IgG can activate the intracellular NF-κB signaling pathway. Finally, it was found that S3633, an inhibitor of the NF-κB signaling pathway, can effectively inhibit the increase in IL-6 levels. These results prove that the production of IL-6 is partly mediated by the NF-κB signaling pathway, providing a potential effective strategy for targeted treatment of NMOSD.

Astrocytes and Microglia in Stress-Induced Neuroinflammation: The African Perspective

Background: Africa is laden with a youthful population, vast mineral resources and rich fauna. However, decades of unfortunate historical, sociocultural and leadership challenges make the continent a hotspot for poverty, indoor and outdoor pollutants with attendant stress factors such as violence, malnutrition, infectious outbreaks and psychological perturbations. The burden of these stressors initiate neuroinflammatory responses but the pattern and mechanisms of glial activation in these scenarios are yet to be properly elucidated. Africa is therefore most vulnerable to neurological stressors when placed against a backdrop of demographics that favor explosive childbearing, a vast population of unemployed youths making up a projected 42% of global youth population by 2030, repressive sociocultural policies towards women, poor access to healthcare, malnutrition, rapid urbanization, climate change and pollution. Early life stress, whether physical or psychological, induces neuroinflammatory response in developing nervous system and consequently leads to the emergence of mental health problems during adulthood. Brain inflammatory response is driven largely by inflammatory mediators released by glial cells; namely astrocytes and microglia. These inflammatory mediators alter the developmental trajectory of fetal and neonatal brain and results in long-lasting maladaptive behaviors and cognitive deficits. This review seeks to highlight the patterns and mechanisms of stressors such as poverty, developmental stress, environmental pollutions as well as malnutrition stress on astrocytes and microglia in neuroinflammation within the African context.

An Autopsy Confirmed Neuromyelitis Optica Spectrum Disorder with Extensive Brain White Matter Lesion and Optic Neuritis but Intact Spinal Cord, Clinically Mimicking a Secondary Progressive Multiple Sclerosis-like Course

A 57-year-old woman presented with optic neuritis with repeated clinical symptoms of focal demyelination of the cerebral white matter and brain stem for 14 years. At the end of the patient's course, the clinical signs mimicked secondary progressive multiple sclerosis, but whether it was caused by interferon administration or neuromyelitis optica spectrum disorders (NMOSD) - or a combination of both or others - was unclear. Histopathological findings indicated the etiology to be NMOSD, with no apparent plaque in spinal cord specimens. This case suggests that an accurate clinical diagnosis requires serum anti-aquaporin 4 antibody measurements as well as an autopsy examination.

Aquaporin-4 in Neuromyelitis Optica Spectrum Disorders: A Target of Autoimmunity in the Central Nervous System

Since the discovery of a specific autoantibody in patients with neuromyelitis optica spectrum disorder (NMOSD) in 2004, the water channel aquaporin-4 (AQP4) has attracted attention as a target of autoimmune diseases of the central nervous system. In NMOSD, the autoantibody (NMO-IgG) binds to the extracellular loops of AQP4 as expressed in perivascular astrocytic end-feet and disrupts astrocytes in a complement-dependent manner. NMO-IgG is an excellent marker for distinguishing the disease from other inflammatory demyelinating diseases, such as multiple sclerosis. The unique higher-order structure of AQP4—called orthogonal arrays of particles (OAPs)—as well as its subcellular localization may play a crucial role in the pathogenesis of the disease. Recent studies have also demonstrated complement-independent cytotoxic effects of NMO-IgG. Antibody-induced endocytosis of AQP4 has been suggested to be involved in this mechanism. This review focuses on the binding properties of antibodies that recognize the extracellular region of AQP4 and the characteristics of AQP4 that are implicated in the pathogenesis of NMOSD.

Immunopathology of Tumefactive Demyelinating Lesions-From Idiopathic to Drug-Related Cases

Tumefactive demyelinating lesions (TDL) represent a diagnostic dilemma for clinicians, and in rare atypical cases a collaboration of a neuroradiologist, a neurologist, and a neuropathologist is warranted for accurate diagnosis. Recent advances in neuropathology have shown that TDL represent an umbrella under which many different diagnostic entities can be responsible. TDL can emerge not only as part of the spectrum of classic multiple sclerosis (MS) but also can represent an idiopathic monophasic disease, a relapsing disease with recurrent TDL, or could be part of the myelin oligodendrocyte glycoprotein (MOG)- and aquaporin-4 (AQP4)-associated disease. TDL can appear during the MS disease course, and increasingly cases arise showing an association with specific drug interventions. Although TDL share common features with classic MS lesions, they display some unique features, such as extensive and widespread demyelination, massive and intense parenchymal infiltration by macrophages along with lymphocytes (mainly T but also B cells), dystrophic changes in astrocytes, and the presence of Creutzfeldt cells. This article reviews the existent literature regarding the neuropathological findings of tumefactive demyelination in various disease processes to better facilitate the identification of disease signatures. Recent developments in immunopathology of central nervous system disease suggest that specific pathological immune features (type of demyelination, infiltrating cell type distribution, specific astrocyte pathology and complement deposition) can differentiate tumefactive lesions arising as part of MS, MOG-associated disease, and AQP4 antibody-positive neuromyelitis optica spectrum disorder. Lessons from immunopathology will help us not only stratify these lesions in disease entities but also to better organize treatment strategies. Improved advances in tissue biomarkers should pave the way for prompt and accurate diagnosis of TDL leading to better outcomes for patients.

RGMa signal in Macrophages Induces Neutrophil-related Astrocytopathy in NMO

OBJECTIVE

Repulsive guidance molecule-a (RGMa) is a glycosylphosphatidylinositol-linked glycoprotein which has multiple functions including axon growth inhibition and immune regulation. However, its role in the pathophysiology of neuromyelitis optica (NMO) is poorly understood. Perivascular astrocytopathy, which is induced by the leakage of aquaporin-4 (AQP4)-specific IgG into the central nervous system parenchyma, is a key feature of NMO pathology. We investigated the RGMa involvement in the pathology of NMO astrocytopathy, and tested a therapeutic potential of humanized anti-RGMa monoclonal antibody (RGMa-mAb).

METHODS

Using a clinically relevant NMO rat model, we evaluated the therapeutic effect of a RGMa-mAb by behavioral testing, immunohistochemistry, and gene expression assay. We further performed in vitro experiments to address the RGMa-signaling in macrophages.

RESULTS

In both NMO rats and an NMO-autopsied sample, RGMa was expressed by the spared neurons and astrocytes, whereas its receptor neogenin was expressed by infiltrating macrophages. AQP4-IgG-induced astrocytopathy and clinical exacerbation in NMO rats were ameliorated by RGMa-mAb treatment. RGMa-mAb treatment significantly suppressed neutrophil infiltration, and decreased the expression of neutrophil chemoattractants. Interestingly, neogenin-expressing macrophages accumulated in the lesion expressed CXCL2, a strong neutrophil chemoattractant, and further analysis revealed that RGMa directly regulated CXCL2 expression in macrophages. Finally, we found that our NMO rats developed neuropathic pain, and RGMa-mAb treatment effectively ameliorated the severity of neuropathic pain.

INTERPRETATION

RGMa signaling in infiltrated macrophages is a critical driver of neutrophil-related astrocytopathy in NMO lesions, and RGMa-mAb may provide an efficient therapeutic strategy for NMO-associated neuropathic pain and motor deficits in patients with NMO. This article is protected by copyright. All rights reserved.

1,2-Dichloroethane induces cortex demyelination by depressing myelin basic protein via inhibiting aquaporin 4 in mice

1,2-Dichloroethane (1,2-DCE) is a pervasive environmental pollutant, and overexposure to this hazardous material causes brain edema and demyelination in humans. We found that 1,2-DCE inhibits aquaporin 4 (AQP4) and is a primary pathogenic effector of 1,2-DCE-induced brain edema in animals. However, AQP4 down-regulation's link with cortex demyelination after 1,2-DCE exposure remains unclear. Thus, we exposed wild-type (WT) CD-1 mice and AQP4 knockout (AQP4-KO) mice to 0, 100, 350 and 700 mg/m³ 1,2-DCE by inhalation for 28 days. We applied label-free proteomics and a cell co-culture system to elucidate the role of AQP4 inhibition in 1,2-DCE-induced demyelination. The results showed that 1,2-DCE down-regulated AQP4 in the WT mouse cortexes. Both 1,2-DCE exposure and AQP4 deletion induced neurotoxicity in mice, including increased brain water content, abnormal pathological vacuolations, and neurobehavioral damage. Tests for interaction of multiple regression analysis highlighted different effects of 1,2-DCE exposure level depending on the genotype, indicating the core role of AQP4 in regulation on 1,2-DCE-caused neurotoxicity. We used label-free quantitative proteomics to detect differentially expressed proteins associated with 1,2-DCE exposure and AQP4 inhibition, and identified down-regulation in myelin basic protein (MBP) and tyrosine-protein kinase Fyn (FYN) in a dose-dependent manner in WT mice but not in AQP4-KO mice. 1,2-DCE and AQP4 deletion separately resulted in demyelination, as detected by Luxol fast blue staining, and manifested as disordered nerve fibers and cavitation in the cortexes. Western blot and immunofluorescence confirmed the decreased AQP4 in the astrocytes and the down-regulated MBP in the oligodendrocytes by 1,2-DCE exposure and AQP4 inhibition, respectively. Finally, the co-culture results of SVG p12 and MO3.13 cells showed that 1,2-DCE-induced AQP4 down-regulation in the astrocytes was responsible for demyelination, by decreasing MBP in the oligodendrocytes. In conclusion, 1,2-DCE induced cortex demyelination by depressing MBP via AQP4 inhibition in the mice.

A comparison between subjective and objective measurements of spasticity in neuromyelitis optica spectrum disorder patients

BACKGROUND

Spasticity is a common and disabling problem in multiple sclerosis (MS), but its effect in other CNS inflammatory demyelinating diseases (CNSIDDs), such as neuromyelitis optica spectrum disorder (NMOSD) is not widely studied. This study aims to compare subjective and objective measurements of spasticity in NMOSD patients and determine associated factors.

METHODS

A prospective cross-sectional study was performed on CNSIDD patients attending the Multiple Sclerosis and Related Disorders Clinic at Siriraj Hospital, a tertiary hospital in Thailand, from June to November 2020 was performed. MS, NMOSD, and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) patients were included. Patients' self-rated Numeric Rating Scale (NRS) for spasticity and clinician-evaluated Modified Ashworth Scale (MAS) scores on the same visit were compared and assessed for correlations. Data on characteristics of patients including demographics, number of transverse myelitis (TM) attacks, disease duration, and Expanded Disability Status Scale (EDSS) score were collected.

RESULTS

Seventy-nine CNSIDD patients were included with 25 MS, 53 NMOSD, and 1 MOGAD. There was a statistically significant correlation between NRS and MAS scores (r = 0.934, p < 0.001). Spasticity was more commonly observed in NMOSD patients compared to MS (34% vs 8%, p = 0.016). Clinical characteristics strongly associated with spasticity were higher number of TM attacks (p < 0.001), severe TM attacks (p < 0.001), longitudinally extensive transverse myelitis attacks (p < 0.001), longer disease duration (p = 0.025), higher EDSS (p < 0.001), and pyramidal Functional System Scale scores (p = 0.001).

CONCLUSIONS

Patients' self-reported NRS score had a good correlation with clinician-evaluated MAS score for spasticity assessment in NMOSD and CNSIDD patients overall. Number and severity of TM attacks were associated with spasticity. Spastic patients had more disability measured by EDSS.

Can Immune Tolerance Be Re-established in Neuromyelitis Optica?

Neuromyelitis optica (NMO) is a chronic inflammatory disease of the central nervous system that primarily affects the optic nerves and spinal cord of patients, and in some instances their brainstem, diencephalon or cerebrum as spectrum disorders (NMOSD). Clinical and basic science knowledge of NMO has dramatically increased over the last two decades and it has changed the perception of the disease as being inevitably disabling or fatal. Nonetheless, there is still no cure for NMO and all the disease-modifying therapies (DMTs) are only partially effective. Furthermore, DMTs are not disease- or antigen-specific and alter all immune responses including those protective against infections and cancer and are often associated with significant adverse reactions. In this review, we discuss the pathogenic mechanisms of NMO as they pertain to its DMTs and immune tolerance. We also examine novel research therapeutic strategies focused on induction of antigen-specific immune tolerance by administrating tolerogenic immune-modifying nanoparticles (TIMP). Development and implementation of immune tolerance-based therapies in NMO is likely to be an important step toward improving the treatment outcomes of the disease. The antigen-specificity of these therapies will likely ameliorate the disease safely and effectively, and will also eliminate the clinical challenges associated with chronic immunosuppressive therapies.

Pathobiology, Diagnosis, and Current Biomarkers in Neuromyelitis Optica Spectrum Disorders

Background

Neuromyelitis optica spectrum disorder (NMOSD) is characterized by chronic inflammation of the central nervous system (CNS), particularly the optic nerves and spinal cord. Although it displays some clinical features similar to multiple sclerosis (MS), the etiology and treatment are distinct, and therefore accurate diagnosis is essential. Autoantibodies targeting the water channel protein aquaporin-4 (AQP4) and the myelin sheath protein myelin oligodendrocyte glycoprotein are the major antigen-specific serological biomarkers known to date, with destruction of astrocytes as the primary mode of CNS damage in AQP4-positive disease.

Content

This mini-review summarizes the pathobiology, clinical features, and current methods of serological testing used to assess NMOSD and differentiate this disorder from MS. A brief summary of emerging therapies is also presented.

Summary

NMOSD can be distinguished from MS through a combination of clinical findings, imaging investigations, and serological analysis. Seronegative cases are particularly difficult to diagnose and can pose a challenge to clinicians. As knowledge deepens, new therapies and biomarkers are expected to improve treatment of this rare debilitating disease.

A Comparison of IgG Index and Oligoclonal Band in the Cerebrospinal Fluid for Differentiating between RRMS and NMOSD

As the oligoclonal band in the cerebrospinal fluid (CSF-OCB) in predicting relapsing-remitting multiple sclerosis (RRMS) is less sensitive in Asian populations than that in westerners, it remains elusive whether the IgG index could serve as an alternative. The purpose of this study was to compare these two methods of differentiating between RRMS and neuromyelitis optica spectrum disorder (NMOSD) in Chinese patients. A total of 171 patients (81 RRMS and 90 NMOSD) were retrospectively recruited, of whom 82 (56 RRMS and 26 NMOSD) received the CSF-OCB testing additionally. When the onset age was ≤38.5 years, IgG index with the threshold of 0.67 had a significant agreement (k = 0.4, p < 0.001) with the diagnosis while CSF-OCB failed to discriminate (k = 0.1, p = 0.578). However, when the onset age was >38.5 years, both IgG index with the threshold of 0.8 and CSF-OCB were moderately consistent with the diagnosis (both k > 0.4, p < 0.05). In total, our optimized algorithm had the sensitivity, specificity, and predictive accuracy of 0.778, slightly outperforming the CSF-OCB model. Accordingly, a combination of the onset age and IgG index could serve as an alternative to CSF-OCB for differentiating between RRMS and NMOSD in Chinese patients.

The role of aquaporin 4 (AQP4) in spinal cord injury

Aquaporin-4 (AQP-4) is an aquaporin composed of six helical transmembrane domains and two highly conserved ASN-pro-ALA (NPA) motifs. It is strongly expressed in rodent and human spinal cord tissues and plays a key role in the pathological process after SCI. After SCI, edema, glial scarring, and inflammation can accelerate the progression of injury and lead to deterioration of function. Many studies have reported that AQP-4 plays an important role in SCI. In particular, it plays an important role in secondary pathological processes (spinal cord edema, glial scar formation, and inflammatory response) after SCI. Loss of AQP-4 has been associated with reduced spinal edema and improved prognosis after SCI in mice. In addition, downregulation of AQP-4 reduces glial scar formation and the inflammatory response after SCI. There is a consensus from numerous studies that AQP-4 may be a potential target for SCI therapy, which guides the ongoing investigation for molecular therapy of SCI. Here, we review the structure of AQP-4, its expression in normal and damaged spinal cord, and its role in SCI, as well as discuss the theoretical basis for the treatment of SCI.

Dynamics of AQP4 upon exposure to seropositive patient serum before and after Rituximab therapy in Neuromyelitis Optica: A cell-based study

Neuromyelitis Optica (NMO) is an autoimmune inflammatory disease that affects the optic nerves and spinal cord. The autoantibody is generated against the abundant water channel protein of the brain, Aquaporin 4 (AQP4). Of the two isoforms of AQP4, the shorter one (M23) often exists as a supramolecular assembly known as an orthogonal array of particles (OAPs). There have been debates about the fate of these AQP4 clusters upon binding to the antibody, the exact mechanism of its turnover, and the proteins associated with the process. Recently several clinical cases of NMO were reported delineating the effect of Rituximab (RTX) therapy. Extending these reports at the cell signaling level, we developed a glioma based cellular model that mimicked antibody binding and helped us track the subsequent events including a variation of AQP4 levels, alterations in cellular morphology, and the changes in downstream signaling cascades. Our results revealed the extent of perturbations in the signaling pathways related to stress involving ERK, JNK, and AKT1 together with markers for cell death. We could also decipher the possible routes of degradation of AQP4, post-exposure to antibody. We further investigated the effect of autoantibody on AQP4 transcriptional level and involvement of FOXO3a and miRNA-145 in the regulation of transcription. This study highlights the differential outcome at the cellular level when treated with the serum of the same patient pre and post RTX therapy and for the first time mechanistically describes the effect of RTX.