Sodium channel protein type 9 subunit alpha
axon terminus
Defining the Functional Role of Na&lt;sub&gt;V&lt;/sub&gt;1.7 in Human Nociception.
Loss-of-function mutations in Na<sub>V</sub>1.7 cause congenital insensitivity to pain (CIP); this voltage-gated sodium channel is therefore a key target for analgesic drug development. Utilizing a multi-modal approach, we investigated how Na<sub>V</sub>1.7 mutations lead to human pain insensitivity. Skin biopsy and microneurography revealed an absence of C-fiber nociceptors in CIP patients, reflected in a reduced cortical response to capsaicin on fMRI. Epitope tagging of endogenous Na<sub>V</sub>1.7 revealed the channel to be localized at the soma membrane, axon, axon terminals, and the nodes of Ranvier of induced pluripotent stem cell (iPSC) nociceptors. CIP patient-derived iPSC nociceptors exhibited an inability to properly respond to depolarizing stimuli, demonstrating that Na<sub>V</sub>1.7 is a key regulator of excitability. Using this iPSC nociceptor platform, we found that some Na<sub>V</sub>1.7 blockers undergoing clinical trials lack specificity. CIP, therefore, arises due to a profound loss of functional nociceptors, which is more pronounced than that reported in rodent models, or likely achievable following acute pharmacological blockade. VIDEO ABSTRACT.