Pan-neurexin perturbation results in compromised synapse stability and a reduction in readily releasable synaptic vesicle pool size

Abstract

Neurexins are a diverse family of cell adhesion molecules that localize to presynaptic specializations of CNS neurons. Heterologous expression of neurexins in non-neuronal cells leads to the recruitment of postsynaptic proteins in contacting dendrites of co-cultured neurons, implicating neurexins in synapse formation. However, isoform-specific knockouts of either all α- or all β-neurexins show defects in synaptic transmission but an unaltered density of glutamatergic synapses, a finding that argues against an essential function of neurexins in synaptogenesis. To address the role of neurexin in synapse formation and function, we disrupted the function of all α- and β-neurexins in cultured hippocampal neurons by shRNA knockdown or by overexpressing a neurexin mutant that is unable to bind to postsynaptic neurexin ligands. We show that neurexin perturbation results in an attenuation of neurotransmitter release that is in large part due to a reduction in the number of readily releasable synaptic vesicles. We also find that neurexin perturbation fails to alter the ability of neurons to form synapses, but rather leads to more frequent synapse elimination. These experiments suggest that neurexins are dispensable for the formation of initial synaptic contacts, but play an essential role in the stabilization and functional maturation of synapses.

Neurexin 3 transmembrane and soluble isoform expression and splicing haplotype are associated with neuron inflammasome and Alzheimer’s disease

“…Substantial microscopic Aβ plaques are observed in old adult brains with intact cognition function [ 6 ]; however, nano-synaptic-space distribution of AβO is less known and neurexin complexes are known partners of Aβ [ 8 ]. Complex neurexin alternative splicing codes define synaptic specificity, strength, plasticity [ 15 , 31 ], and vulnerability toward AβO [ 64 ]. The trans-synaptic anterograde and retrograde signaling of the neurexin-neuroligin-endocannabinoid system [ 13 , 31 , 65 , 66 ] provides an attractive pathway for AD therapeutic development.…”

Neuronal impact of patient-specific aberrant NRXN1α splicing

“…The consensus roles for neurexins are as organizers of neurotransmitter release by coupling calcium channels to the presynaptic machinery 8 and trans-synaptic organizers of post-synaptic proteins resulting in stabilization of AMPARs 39 , 40 . Although neurexins and their ligands have also been linked to synapse formation 41 – 45 , deletion of all three α-Nrxns 8 or all three β-Nrxns 46 impaired neurotransmitter release without altering glutamatergic synapse density in mice, and pan-Nrxn disruption of all α - and β-Nrxns dramatically reduced synapse stabilization and functional maturation 47 . Our scRNA-seq, morphological, and population-wide neuronal activity analyses fit a model whereby NRXN1 +/− hiPSC-neurons do not mature along the same trajectory as control hiPSC-neurons.…”

Dendritic structural plasticity and neuropsychiatric disease

“…The presynaptic neurexins (neurexin 1 (NRXN1)–NRXN3) participate in heterophilic trans-synaptic interactions with the postsynaptic neuroligins, which triggers the recruitment of the scaffolding molecules and receptors necessary for synapse formation in co-culture models 78 . In vitro, disruption of all neurexins in hippocampal neurons reduces synaptic stability and increases synapse elimination, implicating neurexins in the stabilization of nascent synapses 79 . In cultured rat hippocampal neurons, neuroligin 1 (NLGN1) overexpression increases spine density, whereas knockdown of NLGN1, NLGN2 or NLGN3 reduces spine number 80 .…”