NMO spectrum of disorders: A paradigm for astrocyte-targeting autoimmunity and its implications for MS and other CNS inflammatory diseases

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.

Inhibition of complement C3 signaling ameliorates locomotor and visual dysfunction in autoimmune inflammatory diseases

Neuromyelitis optica (NMO) is an autoimmune inflammatory disease of the central nervous system (CNS) characterized by transverse myelitis and optic neuritis. The pathogenic serum IgG antibody against the aquaporin-4 (AQP4) on astrocytes triggers the activation of the complement cascade, causing astrocyte injury, followed by oligodendrocyte injury, demyelination, and neuronal loss. Complement C3 is positioned as a central player that relays upstream initiation signals to activate downstream effectors, potentially stimulating and amplifying host immune and inflammatory responses. However, whether targeting the inhibition of C3 signaling could ameliorate tissue injury, locomotor defects, and visual impairments in NMO remains to be investigated. In this study, using the targeted C3 inhibitor CR2-Crry led to a significant decrease in complement deposition and demyelination in both slice cultures and focal intracerebral injection models. Moreover, the treatment downregulated the expression of inflammatory cytokines and improved motor dysfunction in a systemic NMO mouse model. Similarly, employing serotype 2/9 adeno-associated virus (AAV2/9) to induce permanent expression of CR2-Crry resulted in a reduction in visual dysfunction by attenuating NMO-like lesions. Our findings reveal the therapeutic value of inhibiting the complement C3 signaling pathway in NMO.

Association of retinal microvascular abnormalities and neuromyelitis optica spectrum disorders with optical coherence tomography angiography

Introduction

Neuromyelitis optica spectrum disorders (NMOSD) are autoimmune central nervous system diseases characterized by the immune system's abnormal attack on glial cells and neurons. Optic neuritis (ON) is one of the indicators of NMOSD, often starting unilaterally and potentially affecting both eyes later in the disease progression, leading to visual impairment. Optical coherence tomography angiography (OCTA) has the potential to aid in the early diagnosis of NMOSD by examining ophthalmic imaging and may offer a window for disease prevention.

Methods

In this study, we collected OCTA images from 22 NMOSD patients (44 images) and 25 healthy individuals (50 images) to investigate retinal microvascular changes in NMOSD. We employed effective retinal microvascular segmentation and foveal avascular zone (FAZ) segmentation techniques to extract key OCTA structures for biomarker analysis. A total of 12 microvascular features were extracted using specifically designed methods based on the segmentation results. The OCTA images of NMOSD patients were classified into two groups: optic neuritis (ON) and non-optic neuritis (non-ON). Each group was compared separately with a healthy control (HC) group.

Results

Statistical analysis revealed that the non-ON group displayed shape changes in the deep layer of the retina, specifically in the FAZ. However, there were no significant microvascular differences between the non-ON group and the HC group. In contrast, the ON group exhibited microvascular degeneration in both superficial and deep retinal layers. Sub-regional analysis revealed that pathological variations predominantly occurred on the side affected by ON, particularly within the internal ring near the FAZ.

Discussion

The findings of this study highlight the potential of OCTA in evaluating retinal microvascular changes associated with NMOSD. The shape alterations observed in the FAZ of the non-ON group suggest localized vascular abnormalities. In the ON group, microvascular degeneration in both superficial and deep retinal layers indicates more extensive vascular damage. Sub-regional analysis further emphasizes the impact of optic neuritis on pathological variations, particularly near the FAZ's internal ring.

Conclusion

This study provides insights into the retinal microvascular changes associated with NMOSD using OCTA imaging. The identified biomarkers and observed alterations may contribute to the early diagnosis and monitoring of NMOSD, potentially offering a time window for intervention and prevention of disease progression.

Serial analyses of clinical spectra and outcomes in Chinese women with pregnancy-induced optic neuritis

Objective

This study aimed to investigate the clinical spectra and outcomes in pregnancy-related optic neuritis (ON).

Methods

We analyzed the clinical subtype and prognosis of women with pregnancy-related ON in the neuro-ophthalmology department of the First Medical Center at the Chinese PLA General Hospital from January 2014 to December 2019.

Results

A total of 54 patients, including 21 (38.9%) with idiopathic ON (ION), 27 (50.0%) with aquaporin-4 (AQP4)-ON, and 6 (11.6%) with myelin oligodendrocyte glycoprotein (MOG)-ON, who experienced 58 informative pregnancies and 67 episodes of pregnancy-related ON were assessed. Among the ON attacks, there were 11 (16.4%) during pregnancy and 56 (83.6%) within 1 year postpartum (PP1) or after abortion, including 33 (49.3%) in the first trimester. In total, 14 (25.9%) patients with ON onset before pregnancy had a higher relapse rate during PP1 than within 1 year before pregnancy (p = 0.021), and 24 (85.7%) eyes with ION and nine (100%) with MOG-ON had significantly better visual outcomes (p ≥ 0.5) than those with AQP4-ON (14, 35%) (p < 0.001 and p < 0.001, respectively). Two AQP4-ON patients had premature birth and low baby weight, respectively. There were no birth defects or stillbirths.

Conclusion

The significantly increased relapse rate and numerous cases of ON after pregnancy suggest that delivery adversely affects the course of ON.

Study on the Anti-demyelination Mechanism of Bu-Shen-Yi-Sui Capsule in the Central Nervous System Based on Network Pharmacology and Experimental Verification

Methods

The potential active ingredients and corresponding potential targets of BSYS Capsule were obtained from the TCMSP, BATMAN-TCM, Swiss Target Prediction platform, and literature research. Disease targets of CNSD were explored through the GeneCards and the DisGeNET databases. The matching targets of BSYS in CNSD were identified from a Venn diagram. The protein-protein interaction (PPI) network was constructed using bioinformatics methods. Gene Ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to predict the mechanisms of BSYS. Furthermore, the neuroprotective effects of BSYS were evaluated using a cell model of hydrogen peroxide- (H₂O₂-) induced cell death in OLN-93 cells.

Results

A total of 59 potential bioactive components of BSYS Capsule and 227 intersection targets were obtained. Topological analysis showed that AKT had the highest connectivity degrees in the PPI network. Enrichment analysis revealed that the targets of BSYS in the treatment of CNSD were the PI3K-Akt and MAPK signaling pathway, among other pathways. GO analysis results showed that the targets were associated with various biological processes, including apoptosis, reactive oxygen species metabolic process, and response to oxidative stress, among others. The experimental results demonstrated that BSYS drug-containing serum alleviated the H₂O₂-induced increase in LDH, MDA, and ROS levels and reversed the decrease in SOD and mitochondrial membrane potential induced by H₂O₂. BSYS treatment also decreased the number of TUNEL (+) cells, downregulated Bcl-2 expression, and upregulated Bax and c-caspase-3 expression by promoting Akt phosphorylation.

Conclusion

BSYS Capsule alleviated H₂O₂-induced OLN-93 cell injury by increasing Akt phosphorylation to suppress oxidative stress and cell apoptosis. Therefore, BSYS can be potentially used for CNSD treatment. However, the results of this study are only derived from in vitro experiments, lacking the validation of in vivo animal models, which is a limitation of our study. We will further verify the underlying mechanisms of BSYS in animal experiments in the future.

Aquaporin-4 prevents exaggerated astrocytosis and structural damage in retinal inflammation

Abstract

Aquaporin-4 (AQP4) is the molecular target of the immune response in neuromyelitis optica (NMO) that leads to severe structural damage in the central nervous system (CNS) and in the retina. Conversely, AQP4 might be upregulated in astrocytes as a compensatory event in multiple sclerosis. Thus, the functional relevance of AQP4 in neuroinflammation needs to be defined. Here, we tested the role of AQP4 in the retina in MOG(35–55)-induced experimental autoimmune encephalomyelitis (EAE) using optical coherence tomography (OCT), OCT angiography, immunohistology, flow cytometry, and gene expression analysis in wild-type and Aqp4^–/– mice. No direct infiltrates of inflammatory cells were detected in the retina. Yet, early retinal expression of TNF and Iba1 suggested that the retina participated in the inflammatory response during EAE in a similar way in wild-type and Aqp4^–/– mice. While wild-type mice rapidly cleared retinal swelling, Aqp4^–/– animals exhibited a sustainedly increased retinal thickness associated with retinal hyperperfusion, albumin extravasation, and upregulation of GFAP as a hallmark of retinal scarring at later stages of EAE. Eventually, the loss of retinal ganglion cells was higher in Aqp4^–/– mice than in wild-type mice. Therefore, AQP4 expression might be critical for retinal Müller cells to clear the interstitial space from excess vasogenic edema and prevent maladaptive scarring in the retina during remote inflammatory processes of the CNS.

Key messages

Genetic ablation of AQP4 leads to a functional derangement of the retinal gliovascular unit with retinal hyperperfusion during autoimmune CNS inflammation.

Genetic ablation of AQP4 results in a structural impairment of the blood retina barrier with extravasation of albumin during autoimmune CNS inflammation.

Eventually, the lack of AQP4 in the retina during an inflammatory event prompts the exaggerated upregulation of GFAP as a hallmark of scarring as well as loss of retinal ganglion cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-022-02202-6.

Type I interferon detection in autoimmune diseases: challenges and clinical applications

INTRODUCTION

Accumulating data highlights that the dysregulation of type I interferon (IFN) pathways plays a central role in the pathogenesis of several systemic and organ-specific autoimmune diseases. Advances in understanding the role of type I IFNs in these disorders can lead to targeted drug development as well as establishing potential disease biomarkers.

AREAS COVERED

Here, we summarize current knowledge regarding the role of type I IFNs in the major systemic, as well as organ-specific, autoimmune disorders, including prominent inflammatory CNS disorders like multiple sclerosis.

EXPERT OPINION

Type I IFN involvement and its clinical associations in a wide spectrum of autoimmune diseases represents a promising area for research aiming to unveil common pathogenetic pathways in systemic and organ-specific autoimmunity.

Experience of Using Adrenocorticotropic Hormone in the Treatment of Patients With Acute Neuromyelitis Optica Who Failed Systemic Steroids: A Case Series

OBJECTIVES

Neuromyelitis optica (NMO) has a complex pathology. Clinical symptoms, derived from damage to optic nerves and spinal cord, cause optic neuritis and/or longitudinally extensive myelitis. Treatment options are limited. We assessed adrenocorticotropic hormone (ACTH) use in patients developing exacerbations on systemic steroid treatment and declining other treatments.

METHODS

Patients with NMO who initiated intravenous methylprednisolone (IVMP) for exacerbations and experienced a subsequent exacerbation on monthly IVMP or had inadequate response to IVMP received ACTH 80 U/d intramuscularly for 7 days (for acute relapse), followed by 80 U every 2 weeks (for long taper down/maintenance). Every 1 to 3 months, relapse, Expanded Disability Status Scale, laboratory, and adverse event assessments were performed.

RESULTS

Six patients (mean age: 48.6 years; NMO-suggestive clinical/imaging presentations; cerebral spinal fluid revealing no oligoclonal bands; aquaporin-4 positive [n = 5]) were identified: 5 experiencing subsequent exacerbations with monthly IVMP and 1 with inadequate response to IVMP. No relapses occurred during ACTH treatment or taper-down period, laboratory values indicated no safety concerns, and annual follow-up magnetic resonance imagings were stable. Adverse events were generally characterized as improved or unchanged versus with IVMP, although 1 patient reported transient edema (lower extremities) only during ACTH treatment. Potential treatment-related AEs included edema, acne, urinary tract infection, and insomnia and were reportedly less severe with ACTH treatment than IVMP.

CONCLUSIONS

Adrenocorticotropic hormone treatment for acute NMO was associated with clinical improvement, suggesting that ACTH could have a role in treating acute NMO patients failing IVMP and declining other treatments. Fewer/less severe AEs were observed with ACTH versus IVMP. Larger, controlled clinical studies are needed.

Research and progress on biomarkers of neuromyelitis optica spectrum disorders

Neuromyelitis optica spectrum disorders (NMOSD) are a demyelinating disorder of the central nervous system based on the involvement of the optic nerve and/or spinal cord. The disease is characterized by high recurrence and disability. NMOSD is mainly diagnosed by AQP4-IgG and MOG-IgG. However, there are still some patients with negative or undetermined double-antibody, and AQP4-IgG and MOG-IgG cannot indicate the clinical disease activity. Therefore, it is urgent to explore interesting biomarkers in serum and cerebrospinal fluid to promote early clinical diagnosis and/or as a target for diagnosis and treatment. This article summarized the research progress in serum and cerebrospinal fluid biomarkers of astrocytes, neurons, myelin sheath, and other damage after the onset of NMOSD. Besides the value of microglial activation-related proteins in the diagnosis and treatment of NMOSD was prospected, so as to promote the research progress of NMOSD.

Lack of association between unipolar or bipolar depression and serum aquaporin-4 autoantibodies

Aquaporin-4 (AQP4), an astrocyte water channel protein, is the target antigen of serum immunoglobulin G (IgG) autoantibody in neuromyelitis optica spectrum disorders (NMOsd), a group of inflammatory, demyelinating diseases of the central nervous system. Recently, a reduction in blood vessels coverage by AQP4-immunoreactive astrocytes was demonstrated in depressed patients, indicating a role for AQP4 in mood disorders. Moreover, a possible association between depression and serum AQP4-IgG was suggested in a case report of a treatment resistant depression (TRD) patient diagnosed with NMOsd with positive serum AQP4 autoantibodies. We investigated, for the first time, the presence of serum AQP4-IgG in patients with unipolar and bipolar depression and healthy controls (HCs). In this multicenter study, 25 major depressive disorder (MDD) and 25 bipolar disorder (BD) patients, during an acute major depressive episode (MDE), and 30 matched HCs were screened for the presence of serum AQP4-IgG, using a cell-based assay. The MDE patients underwent a repeated AQP4-IgG assessment at a 3-month follow-up visit. The MDE group (N = 50) had illness duration of 12.7 years (SD = 10.5), 12% of them were psychotropic medication-free and 26% were defined as TRD. All MDE patients and HCs, including three BD patients who experienced a manic switch, were seronegative for AQP4-IgG at baseline and follow-up assessments. In conclusion, contrary to our hypothesis, AQP4 autoantibodies were not detected in serum of unipolar and bipolar depressed patients. However, AQP4 may still play a role in the pathogenesis of mood disorders through different mechanisms of action such as altered brain AQP4 expression.

Inflammation in CNS neurodegenerative diseases

Neurodegenerative diseases, the leading cause of morbidity and disability, are gaining increased attention as they impose a considerable socioeconomic impact, due in part to the ageing community. Neuronal damage is a pathological hallmark of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, Huntington's disease, spinocerebellar ataxia and multiple sclerosis, although such damage is also observed following neurotropic viral infections, stroke, genetic white matter diseases and paraneoplastic disorders. Despite the different aetiologies, for example, infections, genetic mutations, trauma and protein aggregations, neuronal damage is frequently associated with chronic activation of an innate immune response in the CNS. The growing awareness that the immune system is inextricably involved in shaping the brain during development as well as mediating damage, but also regeneration and repair, has stimulated therapeutic approaches to modulate the immune system in neurodegenerative diseases. Here, we review the current understanding of how astrocytes and microglia, as well as neurons and oligodendrocytes, shape the neuroimmune response during development, and how aberrant responses that arise due to genetic or environmental triggers may predispose the CNS to neurodegenerative diseases. We discuss the known interactions between the peripheral immune system and the brain, and review the current concepts on how immune cells enter and leave the CNS. A better understanding of neuroimmune interactions during development and disease will be key to further manipulating these responses and the development of effective therapies to improve quality of life, and reduce the impact of neuroinflammatory and degenerative diseases.

Astrocytic Interleukin-15 Reduces Pathology of Neuromyelitis Optica in Mice

Astrocyte loss induced by neuromyelitis optica (NMO)-IgG and complement-dependent cytotoxicity (CDC) is the hallmark of NMO pathology. The survival of astrocytes is thought to reflect astrocyte exposure to environmental factors in the CNS and the response of astrocytes to these factors. However, still unclear are how astrocytes respond to NMO-IgG and CDC, and what CNS environmental factors may impact the survival of astrocytes. In a murine model of NMO induced by intracerebral injection of NMO-IgG and human complement, we found dramatic upregulation of IL-15 in astrocytes. To study the role of astrocytic IL-15 in NMO, we generated a transgenic mouse line with targeted expression of IL-15 in astrocytes (IL-15^tg), in which the expression of IL-15 is controlled by a glial fibrillary acidic protein promoter. We showed that astrocyte-targeted expression of IL-15 attenuates astrocyte injury and the loss of aquaporin-4 in the brain. Reduced blood–brain barrier leakage and immune cell infiltration are also found in the lesion of IL-15^tg mice subjected to NMO induction. IL-15^tg astrocytes are less susceptible to NMO-IgG-mediated CDC than their wild-type counterparts. The enhanced resistance of IL-15^tg astrocytes to cytotoxicity and cell death involves NF-κB signaling pathway. Our findings suggest that IL-15 reduces astrocyte loss and NMO pathology.

Importance of Regular and Maintenance Therapy Adherence in Neuromyelitis Optica (NMO): Lessons from a Repeating Relapse Case

Patient: Female, 58

Final Diagnosis: NMO

Symptoms: New-onset right leg weakness and pain

Medication: —

Clinical Procedure: Progressive and recurring

Specialty: Neurology

Complement regulator CD59 prevents peripheral organ injury in rats made seropositive for neuromyelitis optica immunoglobulin G

Pathogenesis in aquaporin-4 immunoglobulin G (AQP4-IgG) seropositive neuromyelitis optica spectrum disorders (herein called NMO) involves complement-dependent cytotoxicity initiated by AQP4-IgG binding to astrocyte AQP4. We recently reported that rats lacking complement inhibitor protein CD59 were highly susceptible to development of NMO pathology in brain and spinal cord following direct AQP4-IgG administration (Yao and Verkman, Acta Neuropath Commun 2017, 5:15). Here, we report evidence that CD59 is responsible for protection of peripheral, AQP4-expressing tissues in seropositive NMO. Rats made seropositive by intraperitoneal injection of AQP4-IgG developed marked weakness by 24 h and died soon thereafter. Serum creatine phosphokinase at 24 h was >900-fold greater in seropositive CD59^-/- rats than in seropositive CD59^+/+ (or control) rats. AQP4-expressing cells in skeletal muscle and kidney, but not in stomach, of seropositive CD59^-/- rats showed injury with deposition of AQP4-IgG and activated complement C5b-9, and inflammation. Organ injury in seropositive CD59^-/- rats was prevented by a complement inhibitor. Significant pathological changes in seropositive CD59^-/- rats were not seen in optic nerve, spinal cord or brain, including circumventricular tissue. These results implicate a major protective role of CD59 outside of the central nervous system in seropositive NMO, and hence offer an explanation as to why peripheral, AQP4-expressing cells are largely unaffected in NMO.

The poor recovery of neuromyelitis optica spectrum disorder is associated with a lower level of CXCL12 in the human brain

Neuromyelitis optica spectrum disorders (NMOSDs) are blindness-causing neuritis. In NMOSD patients, NMO-IgG evokes astrocytopathy that in turn causes demyelination. While measurement of NMO-IgG titer will help neurologists make the diagnosis of NMOSDs, it is not sufficient to evaluate the severity of astrocytopathy. In this study, we compared the different levels of an astrocyte biomarker in cerebrospinal fluid of NMOSD patients with good or poor recovery, and then linked their differences to the changes in remyelinating promoter (CXCL12) levels. Our results indicate that NMO-IgG down-regulated CXCL12 and impaired the remyelinating process, this may be a mechanism contributing to the poor recovery of NMOSDs.

MLC1 protein: a likely link between leukodystrophies and brain channelopathies

Megalencephalic leukoencephalopathy with subcortical cysts (MLCs) disease is a rare inherited, autosomal recessive form of childhood-onset spongiform leukodystrophy characterized by macrocephaly, deterioration of motor functions, epileptic seizures and mental decline. Brain edema, subcortical fluid cysts, myelin and astrocyte vacuolation are the histopathological hallmarks of MLC. Mutations in either the MLC1 gene (>75% of patients) or the GlialCAM gene (<20% of patients) are responsible for the disease. Recently, the GlialCAM adhesion protein was found essential for the membrane expression and function of the chloride channel ClC-2 indicating MLC disease caused by mutation in GlialCAM as the first channelopathy among leukodystrophies. On the contrary, the function of MLC1 protein, which binds GlialCAM, its functional relationship with ClC-2 and the molecular mechanisms underlying MLC1 mutation-induced functional defects are not fully understood yet. The human MLC1 gene encodes a 377-amino acid membrane protein with eight predicted transmembrane domains which shows very low homology with voltage-dependent potassium (K⁺) channel subunits. The high expression of MLC1 in brain astrocytes contacting blood vessels and meninges and brain alterations observed in MLC patients have led to hypothesize a role for MLC1 in the regulation of ion and water homeostasis. Recent studies have shown that MLC1 establishes structural and/or functional interactions with several ion/water channels and transporters and ion channel accessory proteins, and that these interactions are affected by MLC1 mutations causing MLC. Here, we review data on MLC1 functional properties obtained in in vitro and in vivo models and discuss evidence linking the effects of MLC1 mutations to brain channelopathies.

GAD65 epitope mapping and search for novel autoantibodies in GAD-associated neurological disorders

Antibodies against Glutamic-acid-decarboxylase (GAD65) are seen in various CNS excitability disorders including stiff-person syndrome, cerebellar ataxia, encephalitis and epilepsy. To explore pathogenicity, we examined whether distinct epitope specificities or other co-existing antibodies may account for each disorder. The epitope recognized by all 27 tested patients, irrespective of clinical phenotype, corresponded to the catalytic core of GAD. No autoantibodies against known GABAergic antigens were found. In a screen for novel specificities using live hippocampal neurons, three epilepsy patients, but no other, were positive. We conclude that no GAD-specific epitope defines any neurological syndrome but other antibody specificities may account for certain phenotypes.

Changes of CXCL12, CXCL14 and PDGF levels in the brain of patients with idiopathic demyelinating optic neuritis and neuromyelitis optica

The CXC chemokines (CXC-motif ligand 12 and CXC-motif ligand 14) and platelet-derived growth factor are suggested to modulate remyelination in the course of many demyelinating diseases. The present study compared the difference in the brain levels of these chemokines between patients with idiopathic demyelinating optic neuritis (IDON) and neuromyelitis optica (NMO) by measuring their concentrations in the cerebrospinal fluid using an enzyme linked immunosorbent assay. Our data indicate that the prognosis of neuritis depends on the remyelinating process that is impaired due to decreased chemokines. The much lower levels of chemokines would specifically indicate the severe neuritis, such as NMO.