Long-lasting analgesia via targeted in situ repression of Na_V1.7 in mice

The authors have presented a novel method for treating pain in a variety of pain models using an impressive genetic repression approach. However, there are some concerning oversights that obscure the conclusion drawn due to a lack of exhaustive experimental design which we believe limits the potential translatability of this method and required comment. First, it appears only male animals are used in this manuscript. Biological relevance and clinical translatability can only be truly considered if male and female animals are included. In fact, in an effort to increase rigor and reproducibility, the NIH has made it a requirement to consider potential sex differences(1). There is an ever-growing body of literature that supports the idea that male and female nociception differs from both neurobiological and pathophysiological standpoints (2,3,4). Secondly, while the authors show that lumbar injection of the AAV9-mCherry results in transduction of DRG neurons distal from the site of injection with increasing viral titer, they do not indicate what effect their intrathecal delivery method has on NaV1.7 transcript levels in the spinal cord despite NaV1.7 having been shown to be expressed in deep lamina within the dorsal horn (5). We believe that this obscures the role of the DRGs in this context. Further, the authors solely utilize qPCR and RNAscope as methods to validate knockdown of NaV1.7. Although these approaches are exhaustive in scope, demonstrating protein expression changes (in the form of fluorescent images or western blots) and/or electrophysiological confirmation of Nav1.7 repression would serve to strengthen the therapeutic arguments presented in the article given that the extent of blockade of NaV1.7 is considered a potential cause of the continued failure of myriad NaV1.7 channel blockers in clinical trials (6). The authors present the argument that there is a lack of good NaV1.7 antibodies however others have performed successful immunofluorescent staining and western blotting of NaV1.7 in DRGs (7). Taken together, we believe that these shortcomings obscure the reported conclusions and limit the potential for translatability of this approach.
References:
1. Collins, F. S., & Tabak, L. A. (2014). Policy: NIH plans to enhance reproducibility. Nature, 505(7485), 612–613. https://doi.org/10.1038/505612a
2. Sorge, R. E., & Totsch, S. K. (2017). Sex Differences in Pain. Journal of Neuroscience Research, 95(6), 1271–1281. https://doi.org/10.1002/jnr.23841
3. Jensen, M. T., & Petersen, K. L. (2006). Gender differences in pain and secondary hyperalgesia after heat/capsaicin sensitization in healthy volunteers. The Journal of Pain, 7(3), 211–217. https://doi.org/10.1016/j.jpain.2005.10.013
4. Nasir, H., Mahboubi, H., Gyawali, S., Ding, S., Mickeviciute, A., Ragavendran, J. V., Laferrière, A., Stochaj, U., & Coderre, T. J. (2016). Consistent sex-dependent effects of PKMζ gene ablation and pharmacological inhibition on the maintenance of referred pain. Molecular Pain, 12, 1744806916675347. https://doi.org/10.1177/1744806916675347
5. Li, Y., North, R. Y., Rhines, L. D., Tatsui, C. E., Rao, G., Edwards, D. D., Cassidy, R. M., Harrison, D. S., Johansson, C. A., Zhang, H., & Dougherty, P. M. (2018). DRG Voltage-Gated Sodium Channel 1.7 Is Upregulated in Paclitaxel-Induced Neuropathy in Rats and in Humans with Neuropathic Pain. The Journal of Neuroscience: The Official Journal of The Society for Neuroscience, 38(5), 1124–1136. https://doi.org/10.1523/JNEUROSCI.0899-17.2017
6. Kingwell K. (2019). Nav1.7 withholds its pain potential. Nature Reviews. Drug Discovery, 10.1038/d41573-019-00065-0. Advance online publication. https://doi.org/10.1038/d41573-019-00065-0
7. Liu, C., Cao, J., Ren, X., & Zang, W. (2012). Nav1.7 protein and mRNA expression in the dorsal root ganglia of rats with chronic neuropathic pain. Neural Regeneration Research, 7(20), 1540–1544. https://doi.org/10.3969/j.issn.1673-5374.2012.20.003