Assessing the impact of pain-linked Nav1.7 variants: An example of two variants with no biophysical effect

ABSTRACT

Mutations in the voltage-gated sodium channel Nav1.7 are linked to human pain. The Nav1.7/N1245S variant was described before in several patients suffering from primary erythromelalgia and/or olfactory hypersensitivity. We have identified this variant in a pain patient and a patient suffering from severe and life-threatening orthostatic hypotension. In addition, we report a female patient suffering from muscle pain and carrying the Nav1.7/E1139K variant. We tested both Nav1.7 variants by whole-cell voltage-clamp recordings in HEK293 cells, revealing a slightly enhanced current density for the N1245S variant when co-expressed with the β1 subunit. This effect was counteracted by an enhanced slow inactivation. Both variants showed similar voltage dependence of activation and steady-state fast inactivation, as well as kinetics of fast inactivation, deactivation, and use-dependency compared to WT Nav1.7. Finally, homology modeling revealed that the N1245S substitution results in different intramolecular interaction partners. Taken together, these experiments do not point to a clear pathogenic effect of either the N1245S or E1139K variant and suggest they may not be solely responsible for the patients’ pain symptoms. As discussed previously for other variants, investigations in heterologous expression systems may not sufficiently mimic the pathophysiological situation in pain patients, and single nucleotide variants in other genes or modulatory proteins are necessary for these specific variants to show their effect. Our findings stress that biophysical investigations of ion channel mutations need to be evaluated with care and should preferably be supplemented with studies investigating the mutations in their context, ideally in human sensory neurons.

KEYWORDS:

• Erythromelalgia
• pain
• orthostatic hypotension
• nav1.7 mutation
• hek293t cells
• patch-clamp recordings
• inherited pain
• sodium channel
• homology modeling

Acknowledgments

This work was funded by the Deutsche Forschungsgemeinschaft (German Research Foundation LA 2740/3–1, 363055819/GRK2415 Mechanobiology of 3D epithelial tissues (ME3T); 368482240/GRK2416, MultiSenses-MultiScales, MR RO4046/2–1 and/2–2, Emmy Noether Program), by a grant from the Interdisciplinary Centre for Clinical Research within the faculty of Medicine at the RWTH Aachen University (IZKF TN1–1/IA 532001, TN1–9, 532009, TN1–7, 532007), and by the BMBF consortium “Bio²Treat” (German Federal Ministry of Education and Research/Bundesministerium für Bildung und Forschung, BMBF, “Chronische Schmerzen – Innovative medizintechnische Lösungen zur Verbesserung von Prävention, Diagnostik und Therapie,” contract number 13GW0334B).

Disclosure statement

In accordance with Taylor & Francis policy and our ethical obligation as a researcher, AL is reporting to have a research contract with Hoffmann-La Roche on a project unrelated to the one presented here.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft (DFG); German Federal Ministry of Education and Research (BMBF); Interdisciplinary Centre for Clinical Research RWTH Aachen University (IZKF).