Chronic presence of blood circulating anti-NMDAR1 autoantibodies impairs cognitive function in mice

Partial rescue of schizophrenia-related phenotypes in young adult Sp4 hypomorphic mice

The Schizophrenia Exome Sequencing Meta-Analysis (SCHEMA) Consortium found that truncation of one copy of the SP4 gene has an odds ratio of 9.37 (3.38-29.7) for schizophrenia (SCZ). Human SP4 gene is also one of the 69 schizophrenia-risk genes prioritized by parallel genome-wide association studies (GWAS) and one of the two schizophrenia-risk genes shared between the SCHEMA and the GWAS, suggesting that more subtle common variants of the SP4 gene with a partial loss-of-function are likely involved in the pathogenesis of schizophrenia in the general population of patients. SP4 may also act as a hub of network in the regulation of many other schizophrenia-risk genes. Sp4 hypomorphic mice that have reduced Sp4 expression recapitulate several behavioral phenotypes related to schizophrenia such as deficient prepulse inhibition (PPI), hypersensitivity to ketamine in locomotion, and deficient context memory. We previously demonstrated cell-specific rescue of ketamine hypersensitivity by restoring Sp4 expression in forebrain GABAergic inhibitory neurons during embryogenesis. However, it is unknown whether restoration of Sp4 expression in young adult Sp4 hypomorphic mice may rescue these schizophrenia-related phenotypes when these phenotypes are still emerging. Such studies are critical for evaluation of SP4 as a potential target gene for schizophrenia drug development. Here, we use AAV.PHP.eB virus carrying Cre recombinase to restore Sp4 expression in the whole brains of young adult Sp4 hypomorphic mice. Our preliminary studies suggested that Sp4 partial restoration attenuated PPI deficits and ketamine locomotor hypersensitivity in adult male Sp4 hypomorphic mice but did not improve deficient context memory in Sp4 hypomorphic mice transduced with AAV/PHP.eB virus carrying the Cre gene. A large cohort of Sp4 hypomorphic mice is needed for the rescue experiments to validate our findings.

A novel simple immunoassay for quantification of blood anti-NMDAR1 autoantibodies

Low titers of blood circulating anti-NMDAR1 autoantibodies have been reported in a significant subset of the general human population. Currently, immunohistochemical staining and cell-based assays are the standard methods for their detection and semi-quantification. However, detection and quantification of these low titers of blood circulating anti-NMDAR1 autoantibodies are problematic because of high non-specific background. Development of a new method to more accurately quantify these low titers of blood anti-NMDAR1 autoantibodies will facilitate studies on their potential impacts on psychiatric symptoms and cognition. We previously reported a robust production of anti-NMDAR1 autoantibodies against the ligand binding domain of NMDAR1. As a proof of principle, we report the development of a novel simple immunoassay for quantification of cross-species blood anti-NMDAR1 autoantibodies and its validation with immunohistochemistry and cell-based assays in both humans and mice. Specificity of our quantification was also investigated.

Natural Anti-NMDAR1 Autoantibodies Associate with Slowed Decline of Cognitive Functions in Alzheimer's Diseases

Anti-NMDAR1 autoantibodies can bind NMDA receptors to suppress glutamate excitotoxicity in the brain. Low titers of blood circulating natural anti-NMDAR1 autoantibodies were reported in ~10% of the general human population. We developed a new method to more accurately quantify these low titers of natural anti-NMDAR1 autoantibodies. After quantifying natural anti-NMDAR1 autoantibodies in the plasma of 324 age- and sex-matched subjects (163 healthy controls; 161 Alzheimer's disease (AD) patients), I found that AD patients carrying higher levels of natural anti-NMDAR1 autoantibodies have significantly (p value: 0.003) higher scores of Mini-Mental State Examination (MMSE score: 23.5) than AD patients carrying lower levels of natural anti-NMDAR1 autoantibodies (MMSE score: 21.4). No significant differences in MMSE scores were however found between healthy controls with either higher or lower levels of natural anti-NMDAR1 autoantibodies, indicating little harmful effect of the autoantibodies. Consistently, superior cognitive performances were found in AD patients carrying higher levels of natural anti-NMDAR1 autoantibodies in comparison with AD patients carrying lower levels of the autoantibodies. These data suggest that natural anti-NMDAR1 autoantibodies may have neuroprotective effects against cognitive decline in AD patients.

A Novel Simple ImmunoAssay for Quantification of Blood Anti-NMDAR1 Autoantibodies

High titers of anti-NMDAR1 autoantibodies in human brain cause anti-NMDAR1 encephalitis, a rare disease that displays a variety of psychiatric symptoms and neurological symptoms. Currently, immunohistochemical staining and cell-based assays are the standard methods for detection and semi-quantification of the anti-NMDAR1 autoantibodies. Low titers of blood circulating anti-NMDAR1 autoantibodies have been reported in a significant subset of the general human population. However, detection and quantification of these low titers of blood circulating anti-NMDAR1 autoantibodies are problematic because of high non-specific background from less diluted serum/plasma. Development of a new method to quantify these low titers of blood anti-NMDAR1 autoantibodies is necessary to understand their potential impacts on psychiatric symptoms and cognition. Based on our previous One-Step assay, we report the development of a novel simple immunoassay to quantify cross-species blood anti-NMDAR1 autoantibodies, and its validation with immunohistochemistry and cell-based assays in both humans and mice.

A peptide from the Japanese encephalitis virus failed to induce the production of anti-N-methyl-d-aspartate receptor antibodies via molecular mimicry in mice

Background

The development of anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis following viral encephalitis, such as Japanese encephalitis, has received increasing attention in recent years. However, the mechanism of anti-NMDAR antibody production following Japanese encephalitis has not been explored.

Methods

A peptide from the Japanese encephalitis virus (JEV), which shares a similar amino acid sequence with GluN1, was identified by sequence comparison. We then explored whether active subcutaneous immunization with the JEV peptide could induce the production of anti-NMDAR antibodies and related pathophysiological and behavioral changes in mice. In addition, a published active immune model of anti-NMDAR encephalitis using a GluN1 peptide was used as the positive control.

Results

A 6-amino-acid sequence with 83 % similarity between the envelope protein of the JEV (HGTVVI) and GluN1 (NGTHVI) was identified, and the sequence included the N368/G369 region. Active immunization with the JEV peptide induced a substantial and specific immune response in mice. However, anti-NMDAR antibodies were not detected in the serum of mice immunized with the JEV peptide by ELISA, CBA, and TBA. Moreover, mice immunized with the JEV peptide presented no abnormities related to anti-NMDAR antibodies according to western blotting, patch clamp, and a series of behavioral tests. In addition, active immunization with a recently reported GluN1 peptide failed to induce anti-NMDAR antibody production in mice.

Conclusions

In this study, the attempt of active immunization with the JEV peptide to induce the production of anti-NMDAR antibodies via molecular mimicry failed. The pathogenesis of anti-NMDAR encephalitis following Japanese encephalitis remains to be elucidated.

Preventive and Therapeutic Autoantibodies Protect against Neuronal Excitotoxicity

High titers of anti-NMDAR1 IgG autoantibodies were found in the brains of patients with anti-NMDAR1 encephalitis that exhibits psychosis, impaired memory, and many other psychiatric symptoms in addition to neurological symptoms. Low titers of blood circulating anti-NMDAR1 IgG autoantibodies are sufficient to robustly impair spatial working memory in mice with intact blood-brain barriers (BBB). On the other hand, anti-NMDAR1 autoantibodies were reported to protect against neuronal excitotoxicity caused by excessive glutamate in neurological diseases. Activation of extrasynaptic NMDARs is responsible for neuronal excitotoxicity, whereas activation of synaptic NMDARs within the synaptic cleft is pro-survival and essential for NMDAR-mediated neurotransmission. Unlike small IgG, IgM antibodies are large and pentameric (diameter of ~30 nm). It is plausible that IgM anti-NMDAR1 autoantibodies may be restricted to bind extrasynaptic NMDARs and thereby specifically inhibit neuronal excitotoxicity, but physically too large to enter the synaptic cleft (width: 20-30 nm) to suppress synaptic NMDAR-mediated neurotransmission in modulation of cognitive function and neuronal pro-survival signaling. Hence, blood circulating anti-NMDAR1 IgM autoantibodies are both neuroprotective and pro-cognitive, whereas blood circulating anti-NMDAR1 IgG and IgA autoantibodies are detrimental to cognitive function. Investigation of anti-NMDAR1 IgM autoantibodies may open up a new avenue for the development of long-lasting preventive and therapeutic IgM anti-NMDAR1 autoantibodies that protect from neuronal excitotoxicity in many neurological diseases and psychiatric disorders.

NMDA Receptor Antibodies and Neuropsychiatric Symptoms in Parkinson's Disease

OBJECTIVE

N-methyl-d-aspartate receptor (NMDAR) encephalitis is an autoantibody-mediated neurological syndrome with prominent cognitive and neuropsychiatric symptoms. The clinical relevance of NMDAR antibodies outside the context of encephalitis was assessed in this study.

METHODS

Plasma from patients with Parkinson's disease (PD) (N=108) and healthy control subjects (N=89) was screened at baseline for immunoglobulin A (IgA), IgM, and IgG NMDAR antibodies, phosphorylated tau 181 (p-tau181), and the neuroaxonal injury marker neurofilament light (NfL). Clinical assessment of the patients included measures of cognition (Mini-Mental State Examination [MMSE]) and neuropsychiatric symptoms (Hospital Anxiety and Depression Scale; Non-Motor Symptoms Scale for Parkinson's Disease). A subgroup of patients (N=61) was followed annually for up to 6 years.

RESULTS

Ten (9%) patients with PD tested positive for NMDAR antibodies (IgA, N=5; IgM, N=6; IgG, N=0), and three (3%) healthy control subjects had IgM NMDAR antibodies; IgA NMDAR antibodies were detected significantly more commonly among patients with PD than healthy control subjects (χ²=4.23, df=1, p=0.04). Age, gender, and disease duration were not associated with NMDAR antibody positivity. Longitudinally, antibody-positive patients had significantly greater decline in annual MMSE scores when the analyses were adjusted for education, age, disease duration, p-tau181, NfL, and follow-up duration (adjusted R²=0.26, p=0.01). Neuropsychiatric symptoms were not associated with antibody status, and no associations were seen between NMDAR antibodies and p-tau181 or NfL levels.

CONCLUSIONS

NMDAR antibodies were associated with greater cognitive impairment over time in patients with PD, independent of other pathological biomarkers, suggesting a potential contribution of these antibodies to cognitive decline in PD.

Immunopsychiatry – Innovative Technology to Characterize Disease Activity in Autoantibody-Associated Psychiatric Diseases

Background

Anti-neural autoantibody-associated psychiatric disease is a novel field in immunopsychiatry that has been attracting attention thanks to its potentially positive therapeutic outcome and distinct prognosis compared with non-organic psychiatric disease. This review aims to describe recent novel technological developments for improving diagnostics in the field of autoantibody-related psychiatric disease.

Methods

We screened for relevant articles in PubMed for this narrative article. We focused on research methods such as neuroimaging, immune cells and inflammation markers, and molecular biomarkers in human biofluids like serum and cerebrospinal fluid and plasma proteomics.

Results

We introduce several novel methods for investigating autoinflammation with the aim of optimizing therapies for autoantibody-associated psychiatric disease. We describe measuring the translocator protein 18kDa in activated microglia via positron emission tomography imaging, brain volumetric assessment, flow cell cytometry of cerebrospinal fluid and blood, and blood biological probes as well as psychopathological cues to help us gain insights into diagnosing inflammation and brain damage better in psychiatric patients presenting a suspected autoimmune etiology.

Conclusion

Our short methodological review provides an overview of recent developments in the field of autoantibody-related immunopsychiatry. More research is needed to prove their usefulness in diagnosing and treating autoantibody-associated psychiatric disease and its subtypes.

NMDAR1 autoantibodies amplify behavioral phenotypes of genetic white matter inflammation: a mild encephalitis model with neuropsychiatric relevance

Encephalitis has an estimated prevalence of ≤0.01%. Even with extensive diagnostic work-up, an infectious etiology is identified or suspected in <50% of cases, suggesting a role for etiologically unclear, noninfectious processes. Mild encephalitis runs frequently unnoticed, despite slight neuroinflammation detectable postmortem in many neuropsychiatric illnesses. A widely unexplored field in humans, though clearly documented in rodents, is genetic brain inflammation, particularly that associated with myelin abnormalities, inducing primary white matter encephalitis. We hypothesized that "autoimmune encephalitides" may result from any brain inflammation concurring with the presence of brain antigen-directed autoantibodies, e.g., against N-methyl-D-aspartate-receptor NR1 (NMDAR1-AB), which are not causal of, but may considerably shape the encephalitis phenotype. We therefore immunized young female Cnp^-/- mice lacking the structural myelin protein 2'-3'-cyclic nucleotide 3'-phosphodiesterase (Cnp) with a "cocktail" of NMDAR1 peptides. Cnp^-/- mice exhibit early low-grade inflammation of white matter tracts and blood-brain barrier disruption. Our novel mental-time-travel test disclosed that Cnp^-/- mice are compromised in what-where-when orientation, but this episodic memory readout was not further deteriorated by NMDAR1-AB. In contrast, comparing wild-type and Cnp^-/- mice without/with NMDAR1-AB regarding hippocampal learning/memory and motor balance/coordination revealed distinct stair patterns of behavioral pathology. To elucidate a potential contribution of oligodendroglial NMDAR downregulation to NMDAR1-AB effects, we generated conditional NR1 knockout mice. These mice displayed normal Morris water maze and mental-time-travel, but beam balance performance was similar to immunized Cnp^-/-. Immunohistochemistry confirmed neuroinflammation/neurodegeneration in Cnp^-/- mice, yet without add-on effect of NMDAR1-AB. To conclude, genetic brain inflammation may explain an encephalitic component underlying autoimmune conditions.