Human Autoantibodies Against N-Methyl-D-Aspartate Receptor Modestly Alter Dopamine D1 Receptor Surface Dynamics

Abstract

Circulating autoantibodies directed against extracellular domains of the glutamatergic N-methyl-D-aspartate receptors (NMDAR-Ab) elicit psychotic symptoms in humans and behavioral deficits in animal models. Recent advances suggest that NMDAR-Ab exert their pathogenic action by altering the trafficking of NMDAR, which results in a synaptic NMDAR hypofunction consistent with the consensual glutamatergic hypothesis of psychotic disorders. Yet, dysfunction in the dopaminergic signaling is also proposed to be at the core of psychotic disorders. Since NMDAR and dopamine D1 receptors (D1R) form membrane signaling complexes, we investigated whether NMDAR-Ab purified from patients with NMDAR-encephalitis or schizophrenia impaired D1R surface dynamics. As previous data demonstrated that NMDAR-Ab, at least from NMDAR-encephalitis patients, mainly bind to hippocampal NMDAR, we used single nanoparticle imaging to track D1R specifically at the surface of hippocampal neurons that were exposed to either purified G type immunoglobulins (IgGs) from NMDAR-Ab seropositive patients suffering from NMDAR-encephalitis or schizophrenia, or control IgGs from healthy NMDAR-Ab seropositive or seronegative subjects. We report that overnight incubation with NMDAR-Ab from patients, but not from healthy carriers, decreased the surface dynamics of D1R compared with NMDAR-Ab seronegative IgGs. This decrease was abolished, and even reversed, in D1R mutant that cannot physically interact with NMDAR. Overall, our data indicate that NMDAR-Ab from patients with psychotic symptoms alter the trafficking of D1R, likely through the surface crosstalk between NMDAR and D1R.

Keywords: autoimmune psychosis; autoimmunity; dopamine; encephalitis; hippocampal neurons; schizophrenia; single molecule imaging.

Figure 1

NMDAR-Ab from patients with NMDAR-encephalitis (Enceph) or schizophrenia (SCZ+), but not from healthy carriers (Healthy+), alter the surface dynamics of D1R compared with healthy seronegative subjects (Healthy-). (A) Schematic representation of the experimental design. Before tracking, D1R-CFP-antiGFPAb-QD complexes, hippocampal cultures (12 to 15 days in vitro) were incubated overnight with different purified type G immunoglobulins (IgGs, 5 µm/ml) samples from either patients with NMDAR-encephalitis (Enceph), schizophrenia (SCZ+), healthy carriers (Healthy+), or healthy seronegative subjects (Healthy-) (top panel). Representative trajectory of a single D1R-CFP-antiGFPAb-QD complex (500 frames, 50 ms acquisition) on the dendritic shaft (dashed lines). Scale bar: 500 nm (bottom panel). (B) Comparison of D1R-CFP-antiGFPAb-QD complexes mean square displacements (MSD, mean ± SEM) in the absence (Healthy-) or presence of NMDAR-Ab from healthy carriers (Healthy+), or from patients with NMDAR-encephalitis (Enceph) or schizophrenia (SCZ+). ****SCZ+ vs Healthy- p < 0.0001, ^####Enceph vs Healthy- p < 0.0001, ^##Enceph vs Healthy- p = 0.0048. (C) Comparison of D1R-CFP-antiGFPAb-QD complexes instantaneous diffusion coefficients (median ± interquartile range 25–75%) in the absence (Healthy-) or the presence of NMDAR-Ab from healthy carriers (Healthy+) or patients with NMDAR-encephalitis (Enceph) or schizophrenia (SCZ+). ****p < 0.0001, ***p = 0.0006, *p = 0.0119. (D) Representation of full D1R containing t2 segment enabling the physical interaction with NMDAR (top) and the mutated D1R (D1RΔt2-CFP) preventing its binding to NMDAR (bottom) (left). Comparison of D1R-CFP-antiGFPAb-QD/D1RΔt2-CFP-antiGFPAb-QD complexes surface dynamics (MSD, mean ± SEM) in the absence (Healthy-) or presence (SCZ+) of NMDAR-Ab from patient #2 with schizophrenia (right).