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 1

Generation and characterization of NaV1.9 mouse lines.

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Generation and characterization of NaV1.9 mouse lines. (A) After healing...
(A) After healing, wounds from scratching left marks that resembled bruising (black arrows) in the p.L811P patient. (B) Schematic diagram of the flexible accelerated Neo-STOP tetracycline-inducible (FAST) cassette illustrating the generation of global-knockout NaV1.9 mice (red box) and Cre-mediated expression of sfGFP-tagged NaV1.9 mice (green box). (C) A DRG section from an sfGFP-tagged NaV1.9 (top) and a WT mouse (bottom) showing the overlap between endogenous fluorescent signal (green) and autofluorescence, followed by staining with an antibody against GFP (red). (D) Western blot of DRG tissue from a WT, an sfGFP-NaV1.9, and an NaV1.9–/– mouse stained for GFP. An HSP90 antibody was used as a loading control. (E) Western blot of tissues taken from an sfGFP-NaV1.9 mouse and stained for GFP, stripped, and reprobed for NaV1.9 using a commercial antibody. An HSP90 antibody was used as a loading control. TG, trigeminal ganglia. (F and G) Representative current traces from ND7/23 cell lines expressing WT (black) or sfGFP-NaV1.9 (green) channels. (H–J) Current-voltage (I-V) (H) and deduced conductance-voltage (G-V) (I) and steady-state inactivation (SSI) (J) relationships of WT (black) and sfGFP-NaV1.9 (green). (G-V: WT-NaV1.9 V1/2 = –25.5 ± 0.5 mV, n = 16; GFP-NaV1.9 V1/2 = –24.0 ± 0.2 mV, n = 11, P = 0.52; SSI: WT-NaV1.9 V1/2 = –29.3 ± 3.5 mV, n = 7; GFP-NaV1.9 V1/2 = –26.6 ± 1.7 mV, n = 7, P = 0.49.). Data are represented as mean ± SEM. Scale bar: 50 μm.