Direct and acute effects of human monoclonal anti-GluN1 autoantibodies on NMDA receptor channel function

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Specific antibodies to the NMDA receptor (NMDAR) GluN1 subunit aminoterminal domain (ATD) induce symptoms of NMDAR encephalitis. Long-term effects of NMDAR antibodies on receptor internalization have been described but direct and acute effects of antibodies to the GluN1 ATD on NMDAR channel kinetics and modulation are unexplored. In the past funding period, we found that some patient-derived monoclonal human IgG autoantibodies against the GluN1 subunit downregulate ion channel activity and synaptic NMDAR currents whereas human Fab fragments do not affect ion channel activity. Furthermore, structural analyses revealed that different monoclonal antibodies may cover distinct non-overlapping epitopes on the GluN1 ATD. Here, we continue on investigating direct effects of specific human NMDAR antibodies possibly contributing to disease-relevant receptor and neuronal dysfunction. We will unravel effects channel open probabilities and fine structure of NMDAR channel kinetics by cell-attached single channel recordings. We will test different patient-derived and genetically modified recombinant monoclonal IgG antibodies and Fabs in transfected HEK cells and neurons to differentiate between crosslinking and intrinsic effects on NMDAR channel function. Furthermore, we will test GluN1 IgG-mediated effects on NMDAR ligand, pH, and Zn2+ dependent modulation and on NMDAR nanodomain coupling with large-conductance calcium- and voltage-activated K+ (BK) channels. Non-functional GluN1 IgG antibodies and Fab fragments will be evaluated as possible therapeutic options.