Authors :
Presenting Author: Olga Taraschenko, MD, PhD – University of Nebraska Medical Center
Howard Fox, MD. PhD – University of Nebraska Medical Center; Ember Eldridge, BS – University of Nebraska Medical Center; Priscilla Heliso, BS – University of Nebraska Medical Center; Fetweh Al-Saleem, PhD – Lankenau Institute for Medical Research; Scott Dessain, MD – Lankenau Institute for Medical Research; George Casale, PhD – University of Nebraska Medical Center; Kayley Anderson, BS – University of Nebraska Medical Center; Raymond DIngledilne, PhD – Emory University School of Medicine
Rationale:
Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis manifests with acute memory loss and severe seizures that can result in death or permanent cognitive disability. Using the passive transfer of monoclonal antibodies derived from affected patients to mice, we previously showed that antibodies are pathogenic for seizures and memory loss. We also demonstrated that central inflammation mediated by interleukin-1 (IL-1) pathway contributes to the severity of these presentations. In the present study we assessed the contribution of the myeloid differentiation primary response gene 88 (MyD88), a critical adapter protein in the Toll-like receptor (TLR) signaling which is activated along with IL-1 signaling during seizures. Specifically, using the MyD88
-/- mice in our seizure model, we defined the role of MyD88 protein in generation of seizures, memory loss, and the expression of hippocampal inflammation.
Methods:
Male and female MyD88
-/- mice and control C56BL/6J mice (WT) were stereotactically implanted with the intracerebroventricular infusion cannula, an EEG head mount and two subdural cortical screw EEG electrodes. One week later they were implanted with subcutaneous osmotic minipump that delivered solution of monoclonal anti-NMDAR antibodies or control inactive antibodies for two weeks; the corresponding video EEG was recorded continuously. Upon completion of the infusion, the memory phenotype was assessed using the novel object tests (NO). The immune activation in the hippocampus was assessed using the immunohistochemistry for astrocytic (GFAP) and microglial (Iba-1) markers and qRT-PCR for the key inflammatory mediators relevant for seizures.
Results:
Consistent with our previous reports, 80% of WT mice infused with anti-NMDAR antibodies (n=10) developed seizures (p=0.004, t-test, vs. control antibodies). The median number of seizures in two weeks was 12 (1-23, IQR). In contrast, only three (21%) MyD88
-/- mice exposed to anti-NMDAR antibodies (n= 14) developed seizures (0; 0-0.25). At the conclusion of the infusion, WT mice with anti-NMDAR antibody-induced seizures developed memory loss as assessed by comparing time exploring the familiar and novel objects (p= 0.37, paired t test) in the NO paradigm. Such memory deficits were not apparent in MyD88
-/- mice treated with anti-NMDAR antibodies (p= 0.03) or control antibodies (p=0.04). In contrast to the WT mice exposed to anti-NMDAR antibodies, the MyD88
-/ mice that completed the same treatment had a significantly lower activation of the chemokine (C-C motif) ligand 2 (CCL2) and cyclooxygenase 2 (Cox-2) in the hippocampus (p < 0.0001 and p=0.048, Sidak tests). There were no significant changes in the expression of GFAP and Iba-1 in the MyD88
-/ mice treated with anti-NMDAR and control antibodies.
Conclusions:
These findings suggest that MyD88-mediated signaling is a key contributor to the seizure and memory phenotype in anti-NMDAR encephalitis and that CCL2 activation could participate in the expression of these features. The removal of MyD88 inflammation may be protective and therapeutically relevant in encephalitis.
Funding:
O.T. received salary support from the NIH P20GM130447 (Cognitive Neuroscience and Development of Aging [CoNDA] Award).