Autistic spectrum disorder (ASD) has been associated to genetic alterations of proteins involved in synaptic function such as the point mutation R451C in neuroligin 3 (NLGN3), a postsynaptic adhesion molecule which binds its presynaptic partner neurexin at both excitatory and inhibitory synapses. In the present study, by exploiting the transgenic NLGN3-R451C knock-in (KI) mice as an ASD animal model, we aimed at investigating the role of this mutation in the coordination of both excitatory and inhibitory synaptic plasticity. We found that, in basal conditions, the NLGN3R451C protein was less expressed at the neuronal surface and showed increased lateral diffusion at GABAergic synapses with respect to WT condition. However, in spite of these differences, we observed comparable basal synaptic excitatory and inhibitory transmission in both KI and WT mice. Next, we tested WT and KI neurons for the expression of synaptic plasticity. In WT animals, we found that, in response to a chemical protocol for the induction of plasticity (NMDA treatment), excitatory synaptic currents were depressed (LTD) whereas the inhibitory ones were potentiated (iLTP). Interestingly, such opposed synaptic plasticity was abolished in KI neurons. These effects were paralleled by increased immunoreactivity for GABAAR and the scaffold protein gephyrin at synapses. Along the same line, NMDA treatment induced the decrease of the GluA1 and GluA2 subunits of AMPA receptors in WT mice, whereas the same protocol left AMPARs unchanged in KI mice. In contrast, no significant changes in molecular composition were observed in KI mice at both excitatory and inhibitory synapses. In addition, the quantification of NLGN3 clusters fluorescence intensity revealed that, after the NMDA treatment, surface NLGN3 decreased in WT neurons while it was unaffected in KI neurons. Moreover, in KI conditions, we found changes in the expression of the GluN2B subunit of NMDA receptor that may determine the altered coordination of excitatory and inhibitory plasticity through the perturbation of intracellular spatio-temporal calcium dynamics. Collectively, our results reveal that the perturbed synaptic molecular composition of both glutamatergic and GABAergic synapses induced by the NLGN3-R451C mutation disrupts the coordination of excitatory and inhibitory synaptic plasticity thus potentially contributing to the pathophysiology of ASD.

Impaired excitatory and inhibitory synaptic plasticity in the NLGN3 R451C mouse model of autism spectrum disorder

BRUNO, MARTINA
2023-04-26

Abstract

Autistic spectrum disorder (ASD) has been associated to genetic alterations of proteins involved in synaptic function such as the point mutation R451C in neuroligin 3 (NLGN3), a postsynaptic adhesion molecule which binds its presynaptic partner neurexin at both excitatory and inhibitory synapses. In the present study, by exploiting the transgenic NLGN3-R451C knock-in (KI) mice as an ASD animal model, we aimed at investigating the role of this mutation in the coordination of both excitatory and inhibitory synaptic plasticity. We found that, in basal conditions, the NLGN3R451C protein was less expressed at the neuronal surface and showed increased lateral diffusion at GABAergic synapses with respect to WT condition. However, in spite of these differences, we observed comparable basal synaptic excitatory and inhibitory transmission in both KI and WT mice. Next, we tested WT and KI neurons for the expression of synaptic plasticity. In WT animals, we found that, in response to a chemical protocol for the induction of plasticity (NMDA treatment), excitatory synaptic currents were depressed (LTD) whereas the inhibitory ones were potentiated (iLTP). Interestingly, such opposed synaptic plasticity was abolished in KI neurons. These effects were paralleled by increased immunoreactivity for GABAAR and the scaffold protein gephyrin at synapses. Along the same line, NMDA treatment induced the decrease of the GluA1 and GluA2 subunits of AMPA receptors in WT mice, whereas the same protocol left AMPARs unchanged in KI mice. In contrast, no significant changes in molecular composition were observed in KI mice at both excitatory and inhibitory synapses. In addition, the quantification of NLGN3 clusters fluorescence intensity revealed that, after the NMDA treatment, surface NLGN3 decreased in WT neurons while it was unaffected in KI neurons. Moreover, in KI conditions, we found changes in the expression of the GluN2B subunit of NMDA receptor that may determine the altered coordination of excitatory and inhibitory plasticity through the perturbation of intracellular spatio-temporal calcium dynamics. Collectively, our results reveal that the perturbed synaptic molecular composition of both glutamatergic and GABAergic synapses induced by the NLGN3-R451C mutation disrupts the coordination of excitatory and inhibitory synaptic plasticity thus potentially contributing to the pathophysiology of ASD.
26-apr-2023
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11567/1111795
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