A disease mutation reveals a role for NaV1.9 in acute itch
Juan Salvatierra, … , Xinzhong Dong, Frank Bosmans
Juan Salvatierra, … , Xinzhong Dong, Frank Bosmans
Published November 5, 2018
Citation Information: J Clin Invest. 2018;128(12):5434-5447. https://doi.org/10.1172/JCI122481.
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Research Article Neuroscience

A disease mutation reveals a role for NaV1.9 in acute itch

Abstract

Itch (pruritis) and pain represent two distinct sensory modalities; yet both have evolved to alert us to potentially harmful external stimuli. Compared with pain, our understanding of itch is still nascent. Here, we report a new clinical case of debilitating itch and altered pain perception resulting from the heterozygous de novo p.L811P gain-of-function mutation in NaV1.9, a voltage-gated sodium (NaV) channel subtype that relays sensory information from the periphery to the spine. To investigate the role of NaV1.9 in itch, we developed a mouse line in which the channel is N-terminally tagged with a fluorescent protein, thereby enabling the reliable identification and biophysical characterization of NaV1.9-expressing neurons. We also assessed NaV1.9 involvement in itch by using a newly created NaV1.9–/– and NaV1.9L799P/WT mouse model. We found that NaV1.9 is expressed in a subset of nonmyelinated, nonpeptidergic small-diameter dorsal root ganglia (DRGs). In WT DRGs, but not those of NaV1.9–/– mice, pruritogens altered action potential parameters and NaV channel gating properties. Additionally, NaV1.9–/– mice exhibited a strong reduction in acute scratching behavior in response to pruritogens, whereas NaV1.9L799P/WT mice displayed increased spontaneous scratching. Altogether, our data suggest an important contribution of NaV1.9 to itch signaling.

Authors

Juan Salvatierra, Marcelo Diaz-Bustamante, James Meixiong, Elaine Tierney, Xinzhong Dong, Frank Bosmans

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Figure 7

sfGFP-NaV1.9L799P/WT mice show higher basal scratching and more CQ-responsive neurons.

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sfGFP-NaV1.9L799P/WT mice show higher basal scratching and more CQ-respo...
(A) Schematic diagram showing the initial cassette inserted to generate sfGFP-NaV1.9L799P/WT mice and subsequent breeding to generate mice for experimentation. (B) sfGFP-NaV1.9L799P/WT mice showed a higher level of scratching compared with their littermate controls (WT n = 8, sfGFP-NaV1.9L799P/+ n = 9, P = 0.043). (C–H) Fura-2 ratiometric Ca2+ imaging studies were performed in sfGFP-NaV1.9L799P/+ mice and littermate controls. No differences were seen after histamine application in either the total percentage of responsive neurons (C; WT and sfGFP-NaV1.9L799P/WT n ≥ 700 cells, P = 0.15) or the magnitude of the response (D; WT and NaV1.9–/– n ≥ 700 cells, P = 0.36). For BAM8-22, no differences were observed for either the percentage of responsive cells (E; WT and sfGFP-NaV1.9L799P/WT n ≥ 700 cells, P = 0.19) or the magnitude of the response (F; WT and sfGFP-NaV1.9L799P/WT n ≥ 700 cells, P = 0.83). For CQ, the percentage of responsive cells was significantly higher (G; WT and sfGFP-NaV1.9L799P/WT n ≥ 700 cells, n = 0.042), but no difference was seen in the magnitude of the response (H; WT and sfGFP-NaV1.9L799P/WT n ≥ 700 cells, P = 0.59). (I) RMPs in MrgprA3+ DRGs from WT (–40.0 ± 1.3 mV, n = 13) and NaV1.9L799P/WT (–23.9 ± 1.8 mV, n = 21) mice differ significantly (P = 0.0007). (J–L) WT MrgprA3+ neurons require ≥50 pA current injection to spike (J), whereas MrgprA3+;NaV1.9L799P/WT DRGs consist of a subset (17/21) that does not fire AP at large current injections (≥500 pA; RMP = –42 mV) and a smaller group (4/21) that fires in response to current injections as low as 10 pA and repetitive APs at 50 pA (RMP = –26 mV) (K and L). *P < 0.05 and ***P < 0.001, by 2-tailed, unpaired Student’s t test for Ca2+ imaging/current-clamp experiments and Mann-Whitney test for behavioral comparisons. Data are represented as mean ± SEM.