Nav1.7-A1632G Mutation from a Family with Inherited Erythromelalgia: Enhanced Firing of Dorsal Root Ganglia Neurons Evoked by Thermal Stimuli

Abstract

Voltage-gated sodium channel Nav1.7 is a central player in human pain. Mutations in Nav1.7 produce several pain syndromes, including inherited erythromelalgia (IEM), a disorder in which gain-of-function mutations render dorsal root ganglia (DRG) neurons hyperexcitable. Although patients with IEM suffer from episodes of intense burning pain triggered by warmth, the effects of increased temperature on DRG neurons expressing mutant Nav1.7 channels have not been well documented. Here, using structural modeling, voltage-clamp, current-clamp, and multielectrode array recordings, we have studied a newly identified Nav1.7 mutation, Ala1632Gly, from a multigeneration family with IEM. Structural modeling suggests that Ala1632 is a molecular hinge and that the Ala1632Gly mutation may affect channel gating. Voltage-clamp recordings revealed that the Nav1.7-A1632G mutation hyperpolarizes activation and depolarizes fastinactivation, both gain-of-function attributes at the channel level. Whole-cell current-clamp recordings demonstrated increased spontaneous firing, lower current threshold, and enhanced evoked firing in rat DRG neurons expressing Nav1.7-A1632G mutant channels. Multielectrode array recordings further revealed that intact rat DRG neurons expressing Nav1.7-A1632G mutant channels are more active than those expressing Nav1.7 WT channels. We also showed that physiologically relevant thermal stimuli markedly increase the mean firing frequencies and the number of active rat DRG neurons expressing Nav1.7-A1632G mutant channels, whereas the same thermal stimuli only increase these parameters slightly in rat DRG neurons expressing Nav1.7 WT channels. The response of DRG neurons expressing Nav1.7-A1632G mutant channels upon increase in temperature suggests a cellular basis for warmth-triggered pain in IEM.

Small‐fiber neuropathy: Expanding the clinical pain universe

“…170,171,173 Gain-of-function variants that shift activation of Na v 1.7 in a hyperpolarizing direction, slow deactivation, and enhance ramp currents cause IEM. Over 20 different IEM variants have been discovered in Na v 1.7, and almost all variants investigated so far result in a hyperpolarizing shift of activation, allowing Na v 1.7 to open at lower potentials compared with the wild type, [174][175][176][177][178][179][180][181][182][183][184][185][186][187] in familial cases, 175,[188][189][190] and children. 178,191 This left shift of activation enhances excitability, intuitively explaining the pain phenotype.…”

A mathematical investigation of chemotherapy-induced peripheral neuropathy

“…DRG neuron firing has been correlated with neuropathic pain in vitro [36,37], thus analyzing changes in firing patterns allows for a surrogate to study "pain in a dish". Recent advances in neuroelectrophysiology technology have allowed for more temporal and spatial dynamic data collection on live cells.…”

Reverse pharmacogenomics: carbamazepine normalizes activation and attenuates thermal hyperexcitability of sensory neurons due to Nav1.7 mutation I234T

“…A channel construct encoding eGFP with a ‘StopGo’ 2A linker (Atkins et al ., ) in‐frame with the N‐terminus of human Na v 1.7‐WT channel that has been rendered resistant to tetrodotoxin (TTX‐R) by the Tyr362Ser substitution has been previously described (Huang et al ., ) (Yang et al ., ). The I234T mutation was created using a site‐directed mutagenesis kit (Agilent).…”

“…MEA experiments were carried out according to our recently developed protocol (Yang et al ., ). Briefly, dissociated neurons were maintained at 37°C in a 5% CO 2 incubator for 3 days before MEA recordings.…”

“…A spike detection criterion of >6 standard deviations above background signals was used to separate action potential spikes from noise. We defined active electrodes as registering >1 recorded spike over a 200 s period (Yang et al ., ). MEA data were analysed using Axion Integrated Studio AxIS2.1 (Axion Biosystems) and NeuroExplorer (Nex Technologies, Madison, AL, USA).…”