Presynaptic α ₂ δ subunits are key organizers of glutamatergic synapses

Abstract

In nerve cells the genes encoding for α2δ subunits of voltage-gated calcium channels have been linked to synaptic functions and neurological disease. Here we show that α2δ subunits are essential for the formation and organization of glutamatergic synapses. Using a cellular α2δ subunit triple-knockout/knockdown model, we demonstrate a failure in presynaptic differentiation evidenced by defective presynaptic calcium channel clustering and calcium influx, smaller presynaptic active zones, and a strongly reduced accumulation of presynaptic vesicle-associated proteins (synapsin and vGLUT). The presynaptic defect is associated with the downscaling of postsynaptic AMPA receptors and the postsynaptic density. The role of α2δ isoforms as synaptic organizers is highly redundant, as each individual α2δ isoform can rescue presynaptic calcium channel trafficking and expression of synaptic proteins. Moreover, α2δ-2 and α2δ-3 with mutated metal ion-dependent adhesion sites can fully rescue presynaptic synapsin expression but only partially calcium channel trafficking, suggesting that the regulatory role of α2δ subunits is independent from its role as a calcium channel subunit. Our findings influence the current view on excitatory synapse formation. First, our study suggests that postsynaptic differentiation is secondary to presynaptic differentiation. Second, the dependence of presynaptic differentiation on α2δ implicates α2δ subunits as potential nucleation points for the organization of synapses. Finally, our results suggest that α2δ subunits act as transsynaptic organizers of glutamatergic synapses, thereby aligning the synaptic active zone with the postsynaptic density.

Impaired Subcortical Processing of Amplitude-Modulated Tones in Mice Deficient for Cacna2d3, a Risk Gene for Autism Spectrum Disorders in Humans

“…The neuronal information flow along the ascending auditory pathway employs fast and reliable glutamatergic synapses with presynaptic Ca v 2.1 Ca 2+ channels ( Lin et al, 2011 ) and postsynaptic AMPA receptors containing predominantly GluA3 and GluA4 subunits ( Yang et al, 2011 ; García-Hernández et al, 2017 ). All three neuronal isoforms of auxiliary α 2 δ subunits of voltage-gated Ca 2+ channel are key organizers of glutamatergic synapses and can co-assemble with any high voltage-activated Ca 2+ channel, either presynaptic or postsynaptic or somatic ( Ablinger et al, 2020 ; Geisler et al, 2021 ; Schöpf et al, 2021 ). Because α 2 δ3 is strongly expressed in principal neurons in the auditory pathway such as spiral ganglion neurons, neurons of the dorsal and ventral cochlear nucleus, the medial nucleus of the trapezoid body (MNTB), the ventral nucleus of the lateral lemniscus (VNLL), and in some neurons of the IC itself ( Cole et al, 2005 ; Pirone et al, 2014 ; Stephani et al, 2019 ), it appears to play a specific role at the ultrafast Ca v 2.1-containing synapses along the auditory pathway.…”

The voltage-gated Ca2+ channel subunit α2δ-4 regulates locomotor behavior and sensorimotor gating in mice

“…For example, α 2 δ-1 binding to thromobospondins promotes synapse formation in a manner that is inhibited by the analgesic and anti-convulsant drug, gabapentin [ 11 ]. In cultures of hippocampal neurons, α 2 δ-1, α 2 δ-2, and α 2 δ-3 play essential and redundant roles in regulating the formation and organization of glutamatergic synapses [ 12 ]. At the Drosophila neuromuscular junction, α 2 δ-3 is required for proper synapse morphogenesis—a process that does not involve its association with the Ca v 2.1 channel [ 13 ].…”

Cacna2d2 inhibits axonal regeneration following surgical decompression in a rat model of cervical spondylotic myelopathy

“…Recently, α2δ informs (α2δ2 and α2δ3) have been recognized as important regulators of synapse formation and plasticity [10,17,18]. Importantly, α2δ2 has showed a suppression of axonal regeneration in adult mice after spinal cord injury [10].…”