α2δ-2 regulates synaptic GluK1 kainate receptors in Purkinje cells and motor coordination

Gabapentin and pregabalin are inhibitory ligands of both alpha 2 delta-1 and alpha 2 delta-2 proteins (also known as subunits of voltage-activated Ca2+ channels) and are commonly prescribed for the treatment of neuropathic pain and epilepsy. However, these drugs can cause gait disorders and ataxia through unknown mechanisms. alpha 2 delta-2 and GluK1, a glutamate-gated kainate receptor subtype, are coexpressed in cerebellar Purkinje cells. In this study, we used a heterologous expression system and Purkinje cells to investigate the potential role of alpha 2 delta-2 in regulating GluK1-containing kainate receptor activity.Whole-cell patch-clamp recordings showed that alpha 2 delta-2 coexpression augmented GluK1, but not GluK2, currents in HEK293 cells, and pregabalin abolished this augmentation. Pregabalin lost its inhibitory effect on GluK1 currents in HEK293 cells expressing both GluK1 and the alpha 2 delta-2(R282A) mutant. Blocking GluK1-containing receptors with UBP310 substantially reduced the amplitude of excitatory post-synaptic currents at parallel fibre-Purkinje cell synapses in mice. Also, pregabalin markedly attenuated the amplitude of excitatory post-synaptic currents and currents elicited by ATPA, a selective GluK1 receptor agonist, in Purkinje cells in Cacna2d1 knockout mice. Co-immunoprecipitation assays indicated that alpha 2 delta-2, but not alpha 2 delta-1, formed a protein complex with GluK1 in cerebellar tissues and HEK293 cells through its C-terminus. Furthermore, alpha 2 delta-2 coexpression potentiated surface expression of GluK1 proteins in HEK293 cells, whereas pregabalin reduced GluK1 proteins in cerebellar synaptosomes.Disrupting alpha 2 delta-2-GluK1 interactions using alpha 2 delta-2 C-terminus peptide abrogated the potentiating effect of alpha 2 delta-2 on GluK1 currents and attenuated the amplitude of GluK1-mediated excitatory post-synaptic currents in Purkinje cells. However, neither pregabalin nor alpha 2 delta-2 C-terminus peptide had significant effect on P/Q-type currents in HEK293 cells. Additionally, CRISPR/Cas9-induced conditional knockdown of Cacna2d2 or Grik1 in Purkinje cells, in addition to microinjection of alpha 2 delta-2 C-terminus peptide or UBP310 into the cerebellum, substantially impaired beam-walking and rotarod performance in mice.Our study reveals that alpha 2 delta-2 directly interacts with GluK1 independently of its conventional role as a voltage-activated Ca2+ channel subunit. alpha 2 delta-2 regulates motor coordination by promoting synaptic expression and activity in GluK1-containing kainate receptors in Purkinje cells. Using cell lines and Purkinje cells, Zhou et al. show that the alpha 2 delta-2 protein physically interacts with and promotes synaptic trafficking of GluK1 kainate receptors. Disrupting alpha 2 delta-2-GluK1 complexes in the cerebellum impairs motor coordination, providing an explanation for why gabapentinoids can cause gait abnormalities and ataxia.