Na _V 1.7-dependent peripheral sensitization drives chronic pain in Parkinson's disease

Pain is among the most prevalent and disabling nonmotor symptoms of Parkinson's disease (PD), yet its mechanisms remain poorly defined and effective treatments are limited. Safinamide is one of the few drugs reported to improve pain in PD, but the mechanism underlying this effect is unknown. Here, we show that nigrostriatal neurodegeneration produces persistent hyperexcitability of primary sensory neurons associated with dysregulation of the voltage-gated sodium channel Na _V 1.7. In a brain-restricted 6-hydroxydopamine (6-OHDA) model, small-diameter dorsal root ganglion (DRG) neurons exhibited increased sodium current density and altered voltage-dependent inactivation, with the excess current eliminated by selective Na _V 1.7 blockade. Safinamide directly inhibited a Na _V 1.7-dependent component of sensory neuron sodium current and reversed established pain-like behaviors. Pharmacological disruption of Na _V 1.7 regulation by collapsin response mediator protein 2 (CRMP2) normalized DRG hyperexcitability and reversed mechanical and thermal hypersensitivity, whereas genetic disruption of the Na _V 1.7 CRMP2 regulatory sequence prevented the development of 6-OHDA-induced pain-like behaviors for up to 30 weeks despite preservation of the Parkinsonian motor phenotype. Transcriptomic profiling of human PD DRGs revealed limited global transcriptional remodeling with selective alterations in genes associated with sensory neuron excitability. Together, these findings demonstrate that dopaminergic neurodegeneration initiated within the brain is sufficient to drive persistent peripheral sensory neuron dysfunction and identify CRMP2-dependent regulation of Na _V 1.7 as a therapeutic target for Parkinsonian pain.