Presynaptic α2δ subunits are key organizers of glutamatergic synapses

In nerve cells the genes encoding for α2δ subunits of voltage-gated calcium channels (VGCCs) 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 loss-of-function model, we demonstrate a failure in presynaptic differentiation 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. Mutating the MIDAS site in α2δ-2 dissociates rescuing presynaptic synapsin expression from 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. Firstly, our study suggests that postsynaptic differentiation is secondary to presynaptic differentiation. Secondly, 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 trans-synaptic organizers of glutamatergic synapses, thereby aligning the synaptic active zone with the postsynaptic density.