α2δ-4 and Cachd1 Proteins Are Regulators of Presynaptic Functions

• Published in: International journal of molecular sciences 2022-08, Vol.23 (17), p.9885
• Main Authors: Ablinger, Cornelia, Eibl, Clarissa, Geisler, Stefanie M., Campiglio, Marta, Stephens, Gary J., Missler, Markus, Obermair, Gerald J.
• Format: Article
• Language: English
• Subjects: Calcium; Calcium channels; Calcium channels (voltage-gated); Central nervous system; Channels; Differentiation; Genotype & phenotype; Glutamatergic transmission; Hippocampus; Homology; Isoforms; Localization; Neuromodulation; Neurons; Peptides; Photoreceptors; Protein interaction; Proteins; Retina; Synapses; Synaptogenesis
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms23179885

The α2δ auxiliary subunits of voltage-gated calcium channels (VGCC) were traditionally regarded as modulators of biophysical channel properties. In recent years, channel-independent functions of these subunits, such as involvement in synapse formation, have been identified. In the central nervous system, α2δ isoforms 1, 2, and 3 are strongly expressed, regulating glutamatergic synapse formation by a presynaptic mechanism. Although the α2δ-4 isoform is predominantly found in the retina with very little expression in the brain, it was recently linked to brain functions. In contrast, Cachd1, a novel α2δ-like protein, shows strong expression in brain, but its function in neurons is not yet known. Therefore, we aimed to investigate the presynaptic functions of α2δ-4 and Cachd1 by expressing individual proteins in cultured hippocampal neurons. Both α2δ-4 and Cachd1 are expressed in the presynaptic membrane and could rescue a severe synaptic defect present in triple knockout/knockdown neurons that lacked the α2δ-1-3 isoforms (α2δ TKO/KD). This observation suggests that presynaptic localization and the regulation of synapse formation in glutamatergic neurons is a general feature of α2δ proteins. In contrast to this redundant presynaptic function, α2δ-4 and Cachd1 differentially regulate the abundance of presynaptic calcium channels and the amplitude of presynaptic calcium transients. These functional differences may be caused by subtle isoform-specific differences in α1-α2δ protein–protein interactions, as revealed by structural homology modelling. Taken together, our study identifies both α2δ-4 and Cachd1 as presynaptic regulators of synapse formation, differentiation, and calcium channel functions that can at least partially compensate for the loss of α2δ-1-3. Moreover, we show that regulating glutamatergic synapse formation and differentiation is a critical and surprisingly redundant function of α2δ and Cachd1.