Presynaptic α2δ-2 Calcium Channel Subunits Regulate Postsynaptic GABAA Receptor Abundance and Axonal Wiring

Presynaptic α 2 δ subunits of voltage-gated calcium channels regulate channel abundance and are involved in glutamatergic synapse formation. Yet little is known about the specific functions of the individual α 2 δ isoforms and their role in GABAergic synapses. Using primary neuronal cultures of embryonic mice of both sexes we here report that presynaptic overexpression of α 2 δ-2 in GABAergic synapses strongly increases clustering of postsynaptic GABA A -receptors. Strikingly, presynaptic α 2 δ-2 exerts the same effect in glutamatergic synapses, leading to a mismatched localization of GABA A Rs. This mismatching is caused by an aberrant wiring of glutamatergic presynaptic boutons with GABAergic postsynaptic positions. The trans-synaptic effect of α 2 δ-2 is independent of the prototypical cell-adhesion molecules α-neurexins; however, α-neurexins together with α 2 δ-2 can modulate postsynaptic GABA A R abundance. Finally, exclusion of the alternatively spliced exon 23 of α 2 δ-2 is essential for the trans-synaptic mechanism. The novel function of α 2 δ-2 identified here may explain how abnormal α 2 δ subunit expression can cause excitatory-inhibitory imbalance often associated with neuropsychiatric disorders. SIGNIFICANCE STATEMENT Voltage-gated calcium channels regulate important neuronal functions such as synaptic transmission. α 2 δ subunits modulate calcium channels and are emerging as regulators of brain connectivity. Still, little is known about how individual α 2 δ subunits contribute to synapse specificity. Here we show that presynaptic expression of a single α 2 δ variant can modulate synaptic connectivity and the localization of inhibitory postsynaptic receptors. Our findings provide basic insights into the development of specific synaptic connections between nerve cells and contribute to our understanding of normal nerve cell functions. Furthermore, the identified mechanism may explain how an altered expression of calcium channel subunits can result in aberrant neuronal wiring often associated with neuropsychiatric disorders such as autism or schizophrenia.