Authors :
Yvan Hanscom-Trofy, BS – University of Nebraska Medical Center
Raymond Dingledine, PhD – Emory University School of Medicine
Howard Fox, MD, PhD – University of Nebraska Medical Center
Fetweh Al-Saleem, PhD – Lankenau Institute for Medical Research
Scott Dessain, MD – Lankenau Institute for Medical Research
Kelly Stauch, PhD – University of Nebraska Medical Center
Nashanthea Roland, PhD – University of Nebraska Medical Center
Bailey Bockelmann, BS candidate – University of Nebraska, College of Arts and Sciences
Farzaneh Tavakkoli Ghazazn, BS – University of Nebraska, College of Arts and Sciences
Presenting Author: Olga Taraschenko, MD – Department of Neurological Sciences, University of Nebraska Medical Center, Omaha, NE
Rationale:
Anti-NMDA receptor encephalitis (anti-NMDARE) presents with encephalopathy, seizures, and sleep disruption that respond poorly to conventional therapies, prompting the need for novel effective treatments. Previously, we developed a mouse model of NMDARE in which intracerebroventricular (i.c.v.) infusion of monoclonal IgG derived from affected patients precipitates seizures and memory loss in mice. Previous studies in anti-NMDARE showed that autoantibodies induce internalization of NMDARs. Further, GluN2B-containing NMDARs play a prominent role in seizure generation and cognition; however, their role in the expression of encephalitis phenotype remains unclear. Using our model, we investigated how pathogenic IgG affects the expression of GluN1 and GluN2B-containing NMDARs. Further, we evaluated whether the administration of a selective GluN2B antagonist modulates seizures and sleep function.
Methods:
Male C57BL/6 mice (8–12 weeks) were implanted with an i.c.v. guide cannula, an EEG head mount, and two subdural EEG electrodes. Mice were continuously infused for 14 days with monoclonal anti-NMDAR IgG derived from a patient with encephalitis and seizures, or control monoclonal IgG, which does not bind GluN. Seizures and sleep were monitored with continuous EEG. Traxoprodil (CP-101,606; 10 mg/kg), a selective NR2B antagonist, was administered intraperitoneally daily throughout the 14-day infusion period. At the end of the treatment, synaptosomes were isolated from brain tissue, and expression of GluN11 and GluN2B proteins was assessed using Western blot.
Results:
Consistent with our previous studies, 75% of mice exposed to anti-NMDAR IgG developed seizures. The median number of seizures over two weeks was 4.5 (interquartile range: 0.8–11.5; n = 8). Administration of traxoprodil significantly reduced seizure counts in anti-NMDAR IgG-treated mice (p = 0.04, t-test). The protein levels of GluN1 (mean ± SEM) were markedly reduced in the synaptosomal fractions of vehicle-treated, anti-NMDAR IgG-infused mice (0.2 ± 0.04; n = 8) compared to mice infused with control IgG (1.3 ± 0.2; n = 6), representing a 6.8-fold difference. Similarly, GluN2B protein levels were lower in anti-NMDAR IgG-treated mice (0.23 ± 0.04) compared to control antibody-treated mice (1.1 ± 0.2). Traxoprodil treatment restored the expression of GluN1 and GluN2 in anti-NMDAR IgG-infused mice (p = 0.001 and p = 0.0008, respectively; t-tests vs. vehicle). In contrast, traxoprodil did not affect the levels of GluN1 and GluN2 in control IgG-infused mice. Assessment of sleep function during exposure to anti-NMDAR IgG and traxoprodil is currently ongoing.
Conclusions:
Our findings demonstrate that prolonged exposure to human-derived anti-NMDAR IgG induces seizures and reduces synaptic levels of GluN1 and GluN2. The decline in GluN1 levels was more pronounced than that of GluN2 suggesting a complex influence of antibodies on NMDAR dynamics at the synapse. Treatment with traxoprodil prevented seizure development and restored synaptic GluN1 and GluN2 expression. These findings suggest that GluN2B antagonists may represent a promising therapeutic strategy for seizure control in anti-NMDARE.
Funding:
NIH P20GM130447 Award