The nicotinic α6 subunit gene determines variability in chronic pain sensitivity via cross-inhibition of P2X2/3 receptors

Chronic pain is a highly prevalent and poorly managed human health problem. We used microarray-based expression genomics in 25 inbred mouse strains to identify dorsal root ganglion (DRG)–expressed genetic contributors to mechanical allodynia, a prominent symptom of chronic pain. We identified expression levels of Chrna6, which encodes the α6 subunit of the nicotinic acetylcholine receptor (nAChR), as highly associated with allodynia. We confirmed the importance of α6* (α6-containing) nAChRs by analyzing both gain- and loss-of-function mutants. We find that mechanical allodynia associated with neuropathic and inflammatory injuries is significantly altered in α6* mutants, and that α6* but not α4* nicotinic receptors are absolutely required for peripheral and/or spinal nicotine analgesia. Furthermore, we show that Chrna6's role in analgesia is at least partially due to direct interaction and cross-inhibition of α6* nAChRs with P2X2/3 receptors in DRG nociceptors. Finally, we establish the relevance of our results to humans by the observation of genetic association in patients suffering from chronic postsurgical and temporomandibular pain. ; © 2015 American Association for the Advancement of Science. Submitted 7 July 2014; accepted 11 March 2015; published 13 May 2015. We thank T. Earley, T. Miyamoto, and M. Petrus for assistance with DRG dissection. We thank S. Ranade and V. Uzzell for data analysis. Funding: Supported by the Canadian Institutes for Health Research and the Louise and Alan Edwards Foundation (J.S.M.) and the NIH (D.A.D., H.A.L., and A.P.). Author contributions: The study was conceived by A.P. and J.S.M. and designed by J.S.W., L.D., I.B., M.I.D., H.A.L., A.P., and J.S.M. J.S.W., J. Mathur, W.L., M.R.P., M.A.-Q., R.E.S., L.J.M., K.F., J.-S.A., J.Z., J. Marcovitz, A.H.T., P.M.S., S.C., J.J., S.A.S., E.K.A., R.B., C.I.R., H.K., and J.W. collected data. D.V.Z., S.B.S., F.D., R.M.D., S.K.S., W.L., G.D.S., and A.I.S. analyzed data. U.M., J.-P.C., and M.D. provided reagents or data. W.M., L.D., ...