Alternative Splicing of the NMDA Receptor Subunit GluN1 Mediated by Polypyrimidine Tract-Binding Protein Dimerization in the Trigeminal Ganglion Contributes to Orofacial Allodynia.

Orofacial neuropathic pain, a debilitating condition associated with trigeminal nerve injury, is often characterized by allodynia. N-methyl-d-aspartate receptors (NMDARs), particularly the GluN1 subunit, play a central role in mediating this pain. The GluN1 subunit undergoes alternative splicing at exon 5, generating isoforms GluN1a (lacking the exon 5-encoded N1 cassette) and GluN1b (retaining the N1 cassette), which have distinct functional roles. However, the contribution of GluN1 exon 5 splicing and the mechanisms governing this process in orofacial neuropathic pain are not fully understood. This study investigates the role of GluN1 exon 5 splicing in the development of orofacial allodynia utilizing a mouse model of chronic constriction injury of the infraorbital nerve (CCI-ION). We found that CCI-ION induces enhanced exon 5 splicing in the trigeminal ganglion (TG), promoting the expression of GluN1a and contributing to orofacial allodynia. A key regulator of this splicing event is the polypyrimidine tract-binding protein (PTB), which binds to GluN1 pre-mRNA in a manner dependent on PTB dimerization. We also identified protein disulfide isomerase 3 (PDIA3) as a modulator of PTB dimerization. PDIA3 regulates the formation of PTB dimers in the nucleus, which drives GluN1 exon 5 splicing and the development of orofacial allodynia. These findings reveal a PDIA3-PTB-GluN1 axis that regulates alternative splicing of GluN1 exon 5 in response to trigeminal nerve injury, providing new insights into the molecular mechanisms underlying orofacial neuropathic pain and potential therapeutic targets for its treatment.