Spinal α2δ-1 induces GluA3 degradation to regulate assembly of calcium-permeable AMPA receptors and pain hypersensitivity.

Abstract

The increased prevalence of GluA2-lacking, Ca2+-permeable AMPA receptors (CP-AMPARs) at spinal cord sensory synapses amplifies nociceptive transmission and maintains chronic neuropathic pain. Nerve injury-induced upregulation of α2δ-1 disrupts the assembly of GluA1/GluA2 heteromers, favoring the synaptic incorporation of GluA1 homotetramers in the spinal dorsal horn. Although GluA1-GluA3 subunits are broadly expressed, whether α2δ-1 regulates GluA3-containing AMPARs remains unknown. Here, we unexpectedly found that coexpression with α2δ-1 - but not α2δ-2 or α2δ-3 - diminished GluA3 AMPAR currents and protein levels, an effect blocked by pregabalin, an α2δ-1 C-terminus peptide, or proteasome inhibition. Both nerve injury and α2δ-1 overexpression reduced protein levels of GluA3 and GluA2/GluA3 heteromers in the spinal cord. Furthermore, α2δ-1 coexpression or nerve injury increased GluA3 ubiquitination, with K861 at the C-terminus of GluA3 identified as a key ubiquitination site mediating α2δ-1-induced GluA3 degradation. Additionally, intrathecal delivery of the Gria3 gene reversed nerve injury-induced nociceptive hypersensitivity and synaptic CP-AMPARs by restoring protein levels of GluA3 and GluA2/GluA3 heteromers in the spinal cord. These findings reveal that α2δ-1 promotes GluA1 homotetramer assembly and synaptic CP-AMPAR expression by driving ubiquitin-proteasome-mediated degradation of GluA3, providing insights into the molecular mechanisms of neuropathic pain and the therapeutic actions of gabapentinoids.