Misplaced Pages

SCN9A
Available structures PDB Ortholog search: PDBe RCSB List of PDB id codes 5EK0
Identifiers
Aliases	SCN9A, ETHA, FEB3B, GEFSP7, HSAN2D, NE-NA, NENA, Nav1.7, PN1, SFNP, sodium voltage-gated channel alpha subunit 9
External IDs	OMIM: 603415; MGI: 107636; HomoloGene: 2237; GeneCards: SCN9A; OMA:SCN9A - orthologs
Gene location (Human) Chr. Chromosome 2 (human) Band 2q24.3 Start 166,195,185 bp End 166,376,001 bp
Gene location (Mouse) Chr. Chromosome 2 (mouse) Band 2 C1.3|2 39.13 cM Start 66,310,424 bp End 66,465,306 bp
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in sural nerve spinal ganglia stromal cell of endometrium trigeminal ganglion testicle Achilles tendon epithelium of colon right lobe of liver right testis left testis Top expressed in lumbar spinal ganglion olfactory epithelium trigeminal ganglion superior cervical ganglion median eminence arcuate nucleus supraoptic nucleus paraventricular nucleus of hypothalamus dorsomedial hypothalamic nucleus ventromedial nucleus More reference expression data BioGPS n/a
Gene ontology Molecular function sodium ion binding sodium channel activity voltage-gated ion channel activity ion channel activity voltage-gated sodium channel activity Cellular component voltage-gated sodium channel complex integral component of membrane membrane integral component of plasma membrane cell projection plasma membrane axon Biological process membrane depolarization during action potential sodium ion transport regulation of ion transmembrane transport post-embryonic development ion transport behavioral response to pain transmembrane transport sensory perception of pain inflammatory response response to toxic substance neuronal action potential sodium ion transmembrane transport Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 6335 20274 Ensembl ENSG00000169432 ENSMUSG00000075316 UniProt Q15858 Q62205 RefSeq (mRNA) NM_002977 NM_001365536 NM_001290674 NM_001290675 NM_018852 RefSeq (protein) NP_002968 NP_001352465 NP_001277603 NP_001277604 Location (UCSC) Chr 2: 166.2 – 166.38 Mb Chr 2: 66.31 – 66.47 Mb PubMed search
Wikidata
View/Edit Human View/Edit Mouse

Sodium voltage-gated channel alpha subunit 9 (also Na_v1.7) is a sodium ion channel that, in humans, is encoded by the SCN9A gene. It is usually expressed at high levels in two types of neurons: the nociceptive (pain) neurons at the dorsal root ganglion (DRG) and trigeminal ganglion; and sympathetic ganglion neurons, which are part of the autonomic (involuntary) nervous system.

Function

Sodium voltage-gated channel alpha subunit 9 plays a critical role in the generation and conduction of action potentials and is thus important for electrical signaling by most excitable cells. Na_v1.7 is present at the endings of pain-sensing nerves, the nociceptors, close to the region where the impulse is initiated. Stimulation of the nociceptor nerve endings produces "generator potentials", which are small changes in the voltage across the neuronal membranes. The Na_v1.7 channel amplifies these membrane depolarizations, and when the membrane potential difference reaches a specific threshold, the neuron fires. In sensory neurons, multiple voltage-dependent sodium currents can be differentiated by their voltage dependence and by sensitivity to the voltage-gated sodium-channel blocker tetrodotoxin. The Na_v1.7 channel produces a rapidly activating and inactivating current which is sensitive to the level of tetrodotoxin. Na_v1.7 is important in the early phases of neuronal electrogenesis. Na_v1.7 activity consists of a slow transition of the channel into an inactive state when it is depolarized, even to a minor degree. This property allows these channels to remain available for activation with even small or slowly developing depolarizations. Stimulation of the nociceptor nerve endings produces "generator potentials", small changes in the voltage across the neuronal membranes. This brings neurons to a voltage that stimulate Na_v1.8, which has a more depolarized activation threshold that produces most of the transmembrane current responsible for the depolarizing phase of action potentials.

Cell-Based Assays

Heteromultimeric ion channels such as Na_v1.7 comprise multiple subunits including a pore forming subunits and accessory subunits. Creation of laboratory cells that comprise multiple subunits is challenging. Fluorogenic signaling probes and flow cytometry have been used to create laboratory cells that comprise heteromultimetic Na_v1.7 including at least two of its accessory subunits.

Clinical significance

Animal studies

The critical role of Na_v1.7 in nociception and pain was originally shown using Cre-Lox recombination tissue specific knockout mice. These transgenic mice specifically lack Na_v1.7 in Na_v1.8 positive nociceptors and showed reduced behavioural responses, specifically to acute mechanical and inflammatory pain assays. At the same time, behavioural responses to acute thermal and neuropathic pain assays remained intact. However, the expression of Na_v1.7 is not restricted to Na_v1.8 positive DRG neurons. Further work examining the behavioural response of two other transgenic mouse strains; one lacking Na_v1.7 in all DRG neurons and the other lacking Na_v1.7 in all DRG neurons as well as all sympathetic neurons, has revealed distinct sets of modality specific peripheral neurons. Therefore, Na_v1.7 expressed in Na_v1.8 positive DRG neurons is critical for normal responses to acute mechanical and inflammatory pain assays. Whilst Na_v1.7 expressed in Na_v1.8 negative DRG neurons is critical for normal responses to acute thermal pain assays. Finally, Nav1.7 expressed in sympathetic neurons is critical for normal behavioural responses to neuropathic pain assays.

Primary erythromelalgia

Mutation in Na_v1.7 may result in primary erythromelalgia (PE), an autosomal dominant, inherited disorder which is characterized by attacks or episodes of symmetrical burning pain of the feet, lower legs, and sometimes hands, elevated skin temperature of affected areas, and reddened extremities. The mutation causes excessive channel activity which suggests that Na_v1.7 sets the gain on pain signaling in humans. It was observed that a missense mutation in the SCN9A gene affected conserved residues in the pore-forming α subunit of the Na_v1.7 channel. Multiple studies have found a dozen SCN9A mutations in multiple families as causing erythromelagia. All of the observed erythromelalgia mutations that are observed are missense mutations that change important and highly conserved amino acid residues of the Na_v1.7 protein. The majority of mutations that cause PE are located in cytoplasmic linkers of the Na_v1.7 channel, however some mutations are present in transmembrane domains of the channel. The PE mutations cause a hyperpolarizing shift in the voltage dependence of channel activation, which allows the channel to be activated by smaller than normal depolarizations, thus enhancing the activity of Na_v1.7. Moreover, the majority of the PE mutations also slow deactivation, thus keeping the channel open longer once it is activated. In addition, in response to a slow, depolarizing stimulus, most mutant channels will generate a larger than normal sodium current. Each of these alterations in activation and deactivation can contribute to the hyperexcitability of pain-signaling DRG neurons expressing these mutant channels, thus causing extreme sensitivity to pain (hyperalgesia). While the expression of PE Na_v1.7 mutations produces hyperexcitability in DRG neurons, studies on cultured rat in sympathetic ganglion neurons indicate that expression of these same PE mutations results in reduction of excitability of these cells. This occurs because Na_v1.8 channels, which are selectively expressed in addition to Na_v1.7 in DRG neurons, are not present within sympathetic ganglion neurons. Thus lack of Na_v1.7 results in inactivation of the sodium channels results in reduced excitability. Thus physiological interaction of Na_v1.7 and Na_v1.8 can explain the reason that PE presents with pain due to hyperexcitability of nociceptors and with sympathetic dysfunction that is most likely due to hypoexcitability of sympathetic ganglion neurons. Recent studies have associated a defect in SCN9A with congenital insensitivity to pain.

Paroxysmal extreme pain disorder

Paroxysmal extreme pain disorder (PEPD) is another rare, extreme pain disorder. Like primary erythromelalgia, PEPD is similarly the result of a gain-of-function mutation in the gene encoding the Na_v1.7 channel. The decreased inactivation caused by the mutation is cause of prolonged action potentials and repetitive firing. Such altered firing will cause increased pain sensation and increased sympathetic nervous system activity, producing the phenotype observed in patients with PEPD.

Congenital insensitivity to pain

Individuals with congenital insensitivity to pain have painless injuries beginning in infancy but otherwise normal sensory responses upon examination. Patients frequently have bruises and cuts, and are often only diagnosed because of limping or lack of use of a limb. Individuals have been reported to be able to walk over burning coals and to insert knives and drive spikes through their arms. It has been observed that the insensitivity to pain does not appear to be due to axonal degeneration.

A mutation that causes loss of Na_v1.7 function has been detected in three consanguineous families from northern Pakistan. All mutations observed were nonsense mutation, with the majority of affected patients having a homozygous mutation in the SCN9A gene. This discovery linked loss of Na_v1.7 function with the inability to experience pain. This is in contrast with the genetic basis of primary erythromelalgia in which the disorder results from gain-of-function mutations.

Clinical analgesics

Local anesthetics such as lidocaine, but also the anticonvulsant phenytoin, mediate their analgesic effects by non-selectively blocking voltage-gated sodium channels. Na_v1.7, as well as Na_v1.3, Na_v1.8, and Na_v1.9, are the specific channels that have been implicated in pain signaling. Thus, the blockade of these specific channels is likely to underlie the analgesia of local anesthetics and anticonvulsants such as phenytoin. In addition, inhibition of these channels is also likely responsible for the analgesic efficacy of certain tricyclic antidepressants, and of mexiletine.

Itch

Mutations of Na_v1.7 have been linked to itching (pruritus), and genetic knockouts of Na_v1.7 and an antibody that inhibits Na_v1.7 also appear to inhibit itching.

Future prospects

As the Na_v1.7 channel appears to be a highly important component in nociception, with null activity conferring total analgesia, there has been immense interest in developing selective Na_v1.7 channel blockers as potential novel analgesics. Since Na_v1.7 is not present in heart tissue or the central nervous system, selective blockers of Na_v1.7, unlike non-selective blockers such as local anesthetics, could be safely used systemically for pain relief. Moreover, selective Na_v1.7 blockers may prove to be far more effective analgesics, and with fewer undesirable effects, relative to current pharmacotherapies.

A number of selective Na_v1.7 (and/or Na_v1.8) blockers are in clinical development, including funapide (TV-45070, XEN402), PF-05089771, DSP-2230, NKTR-171, GDC-0276, and RG7893 (GDC-0287). Ralfinamide (formerly NW-1029, FCE-26742A, PNU-0154339E) is a multimodal, non-selective Na_v channel blocker which is under development for the treatment of pain.

Surprisingly, many potent Na_v1.7 blockers have been found to be clinically effective but only relatively weak analgesics. Recently, it has been elucidated that congenital loss of Nav_v1.7 results in a dramatic increase in the levels of endogenous enkephalins, and it was found that blocking these opioids with the opioid antagonist naloxone allowed for pain sensitivity both in Nav_v1.7 null mice and in a woman with a defective Nav_v1.7 gene and associated congenital insensitivity to pain. Development of the venom-derived peptide, JNJ63955 allowed for selective inhibition of Na_v1.7 only while it was in the closed state, which produced results, in mice, much more similar to knock-out models. It is possible that channel blockade is maximal only when the channel is inhibited in its closed state. It appears that complete inactivation of Na_v1.7-mediated sodium efflux is necessary to upregulate enkephalin expression enough to achieve complete analgesia. Prior to the development of JNJ63955, the most potent antagonists had failed in regards to achieving the same degree of analgesia as congenital Na_v1.7 inactivity. The proposed mechanism also suggests that the analgesic effects of Na_v1.7 blockers may be greatly potentiated by the co-administration of exogenous opioids or enkephalinase inhibitors. Supporting this idea, a strong analgesic synergy between local anesthetics and topical opioids has already been observed in clinical research.

An additional implication of the aforementioned findings is that congenital insensitivity to pain may be clinically treatable with opioid antagonists.

In 2021, researchers described a novel approach, developing a CRISPR-dCas9 epigenome editing method for a potential treatment of chronic pain by repressing Na_v1.7 gene expression which showed therapeutic potential in three mouse models of chronic pain.

References

1. ^ GRCh38: Ensembl release 89: ENSG00000169432 – Ensembl, May 2017
2. ^ GRCm38: Ensembl release 89: ENSMUSG00000075316 – Ensembl, May 2017
3. "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
4. "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
5. Klugbauer N, Lacinova L, Flockerzi V, Hofmann F (March 1995). "Structure and functional expression of a new member of the tetrodotoxin-sensitive voltage-activated sodium channel family from human neuroendocrine cells". The EMBO Journal. 14 (6): 1084–1090. doi:10.1002/j.1460-2075.1995.tb07091.x. PMC 398185. PMID 7720699.
6. Plummer NW, Meisler MH (April 1999). "Evolution and diversity of mammalian sodium channel genes". Genomics. 57 (2): 323–331. doi:10.1006/geno.1998.5735. PMID 10198179.
7. Catterall WA, Goldin AL, Waxman SG (December 2005). "International Union of Pharmacology. XLVII. Nomenclature and structure-function relationships of voltage-gated sodium channels". Pharmacological Reviews. 57 (4): 397–409. doi:10.1124/pr.57.4.4. PMID 16382098. S2CID 7332624.
8. Raymond CK, Castle J, Garrett-Engele P, Armour CD, Kan Z, Tsinoremas N, et al. (October 2004). "Expression of alternatively spliced sodium channel alpha-subunit genes. Unique splicing patterns are observed in dorsal root ganglia". The Journal of Biological Chemistry. 279 (44): 46234–46241. doi:10.1074/jbc.M406387200. PMID 15302875. S2CID 17753425.
9. ^ Rush AM, Dib-Hajj SD, Liu S, Cummins TR, Black JA, Waxman SG (May 2006). "A single sodium channel mutation produces hyper- or hypoexcitability in different types of neurons". Proceedings of the National Academy of Sciences of the United States of America. 103 (21): 8245–8250. Bibcode:2006PNAS..103.8245R. doi:10.1073/pnas.0602813103. PMC 1472458. PMID 16702558.
10. Catterall WA (2000). "Structure and regulation of voltage-gated Ca2+ channels". Annual Review of Cell and Developmental Biology. 16: 521–555. doi:10.1146/annurev.cellbio.16.1.521. PMID 11031246.
11. ^ Cummins TR, Howe JR, Waxman SG (December 1998). "Slow closed-state inactivation: a novel mechanism underlying ramp currents in cells expressing the hNE/PN1 sodium channel". The Journal of Neuroscience. 18 (23): 9607–9619. doi:10.1523/JNEUROSCI.18-23-09607.1998. PMC 6793269. PMID 9822722.
12. Renganathan M, Cummins TR, Waxman SG (August 2001). "Contribution of Na(v)1.8 sodium channels to action potential electrogenesis in DRG neurons". Journal of Neurophysiology. 86 (2): 629–640. doi:10.1152/jn.2001.86.2.629. PMID 11495938. S2CID 11579149.
13. Shekdar K, Langer J, Venkatachalan S, Schmid L, Anobile J, Shah P, et al. (May 2021). "Cell engineering method using fluorogenic oligonucleotide signaling probes and flow cytometry". Biotechnology Letters. 43 (5): 949–958. doi:10.1007/s10529-021-03101-5. PMC 7937778. PMID 33683511.
14. Nassar MA, Stirling LC, Forlani G, Baker MD, Matthews EA, Dickenson AH, et al. (August 2004). "Nociceptor-specific gene deletion reveals a major role for Nav1.7 (PN1) in acute and inflammatory pain". Proceedings of the National Academy of Sciences of the United States of America. 101 (34): 12706–12711. Bibcode:2004PNAS..10112706N. doi:10.1073/pnas.0404915101. PMC 515119. PMID 15314237.
15. Minett MS, Nassar MA, Clark AK, Passmore G, Dickenson AH, Wang F, et al. (April 2012). "Distinct Nav1.7-dependent pain sensations require different sets of sensory and sympathetic neurons". Nature Communications. 3 (4): 791. Bibcode:2012NatCo...3..791M. doi:10.1038/ncomms1795. PMC 3337979. PMID 22531176.
16. Dib-Hajj SD, Yang Y, Black JA, Waxman SG (January 2013). "The Na(V)1.7 sodium channel: from molecule to man". Nature Reviews. Neuroscience. 14 (1): 49–62. doi:10.1038/nrn3404. PMID 23232607. S2CID 5489010.
17. Tang Z, Chen Z, Tang B, Jiang H (September 2015). "Primary erythromelalgia: a review". Orphanet Journal of Rare Diseases. 10: 127. doi:10.1186/s13023-015-0347-1. PMC 4589109. PMID 26419464.
18. Drenth JP, Michiels JJ (June 1994). "Erythromelalgia and erythermalgia: diagnostic differentiation". International Journal of Dermatology. 33 (6): 393–397. doi:10.1111/j.1365-4362.1994.tb04037.x. PMID 8056469. S2CID 3033396.
19. ^ Golshani AE, Kamdar AA, Spence SC, Beckmann NM (August 2014). "Congenital indifference to pain: an illustrated case report and literature review". Journal of Radiology Case Reports. 8 (8): 16–23. doi:10.3941/jrcr.v8i8.2194. PMC 4242143. PMID 25426241.
20. ^ Allerton C, Fox D (2013). Pain Therapeutics: Current and Future Treatment Paradigms. Royal Society of Chemistry. pp. 146–148. ISBN 978-1-84973-645-9.
21. ^ Kew JN, Davies CH (2010). Ion Channels: From Structure to Function. Oxford University Press. pp. 153–154. ISBN 978-0-19-929675-0.
22. Fertleman CR, Baker MD, Parker KA, Moffatt S, Elmslie FV, Abrahamsen B, et al. (December 2006). "SCN9A mutations in paroxysmal extreme pain disorder: allelic variants underlie distinct channel defects and phenotypes". Neuron. 52 (5): 767–774. doi:10.1016/j.neuron.2006.10.006. PMID 17145499. S2CID 11715780.
23. Peddareddygari LR, Oberoi K, Grewal RP (2014-09-18). "Congenital insensitivity to pain: a case report and review of the literature". Case Reports in Neurological Medicine. 2014: 141953. doi:10.1155/2014/141953. PMC 4182687. PMID 25309764.
24. ^ Mashour GA, Lydic R (7 September 2011). Neuroscientific Foundations of Anesthesiology. Oxford University Press. p. 154. ISBN 978-0-19-987546-7.
25. Chahine M. Recent advances in voltage-gated sodium channels, their pharmacology and related diseases. Frontiers E-books. p. 90. ISBN 978-2-88919-128-4.
26. Lamberth C, Dinges J (9 August 2012). Bioactive Heterocyclic Compound Classes: Pharmaceuticals. John Wiley & Sons. p. 127. ISBN 978-3-527-66448-1.
27. Cairns BE (1 September 2009). Peripheral Receptor Targets for Analgesia: Novel Approaches to Pain Management. John Wiley & Sons. pp. 66–68. ISBN 978-0-470-52221-9.
28. James WD, Berger T, Elston D (12 April 2015). "Cutaneous Vascular Diseases". Andrews' Diseases of the Skin: Clinical Dermatology. Elsevier Health Sciences. pp. 810–. ISBN 978-0-323-31969-0.
29. Devigili G, Eleopra R, Pierro T, Lombardi R, Rinaldo S, Lettieri C, et al. (September 2014). "Paroxysmal itch caused by gain-of-function Nav1.7 mutation". Pain. 155 (9): 1702–1707. doi:10.1016/j.pain.2014.05.006. PMID 24820863. S2CID 24462006.
30. "An SCN9A variant, known to cause pain, is now found to cause itch" (PDF). Pain.
31. Gingras J, Smith S, Matson DJ, Johnson D, Nye K, Couture L, et al. (2014). "Global Nav1.7 knockout mice recapitulate the phenotype of human congenital indifference to pain". PLOS ONE. 9 (9): e105895. Bibcode:2014PLoSO...9j5895G. doi:10.1371/journal.pone.0105895. PMC 4154897. PMID 25188265.
32. Martz L. "Nav-i-gating antibodies for pain". SciBX.
33. Yong S (May 22, 2014). "One Molecule To Block Both Pain And Itch".
34. ^ Altman RB, Flockhart D, Goldstein DB (23 January 2012). Principles of Pharmacogenetics and Pharmacogenomics. Cambridge University Press. p. 224. ISBN 978-1-107-37747-9.
35. Waxman SG (December 2006). "Neurobiology: a channel sets the gain on pain". Nature. 444 (7121): 831–832. Bibcode:2006Natur.444..831W. doi:10.1038/444831a. PMID 17167466. S2CID 4300362.
36. Dib-Hajj SD, Cummins TR, Black JA, Waxman SG (November 2007). "From genes to pain: Na v 1.7 and human pain disorders". Trends in Neurosciences. 30 (11): 555–563. doi:10.1016/j.tins.2007.08.004. PMID 17950472. S2CID 15131517.
37. Bagal SK, Chapman ML, Marron BE, Prime R, Storer RI, Swain NA (August 2014). "Recent progress in sodium channel modulators for pain". Bioorganic & Medicinal Chemistry Letters. 24 (16): 3690–3699. doi:10.1016/j.bmcl.2014.06.038. PMID 25060923.
38. Martz L (2014). "Nav-i-gating antibodies for pain". Science-Business EXchange. 7 (23): 662. doi:10.1038/scibx.2014.662. ISSN 1945-3477.
39. McMahon S, Koltzenburg M, Tracey I, Turk DC (2013). Wall & Melzack's Textbook of Pain (6 ed.). Elsevier Health Sciences. p. 508. ISBN 978-0-7020-4059-7. OCLC 1008841684.
40. Simpson DM, McArthur JC, Dworkin RH (21 June 2012). Neuropathic Pain: Mechanisms, Diagnosis and Treatment. Oxford University Press. pp. 40–. ISBN 978-0-19-539470-2.
41. ^ Minett MS, Pereira V, Sikandar S, Matsuyama A, Lolignier S, Kanellopoulos AH, et al. (December 2015). "Endogenous opioids contribute to insensitivity to pain in humans and mice lacking sodium channel Nav1.7". Nature Communications. 6: 8967. Bibcode:2015NatCo...6.8967M. doi:10.1038/ncomms9967. PMC 4686868. PMID 26634308.
42. Flinspach M, Xu Q, Piekarz AD, Fellows R, Hagan R, Gibbs A, et al. (January 2017). "Insensitivity to pain induced by a potent selective closed-state Nav1.7 inhibitor". Scientific Reports. 7: 39662. Bibcode:2017NatSR...739662F. doi:10.1038/srep39662. PMC 5206724. PMID 28045073.
43. "Unique CRISPR gene therapy offers opioid-free chronic pain treatment". New Atlas. 11 March 2021. Retrieved 18 April 2021.
44. Moreno AM, Alemán F, Catroli GF, Hunt M, Hu M, Dailamy A, et al. (March 2021). "Long-lasting analgesia via targeted in situ repression of Na_V1.7 in mice". Science Translational Medicine. 13 (584): eaay9056. doi:10.1126/scitranslmed.aay9056. PMC 8830379. PMID 33692134. S2CID 232170826.

Further reading

• Emery EC, Luiz AP, Wood JN (August 2016). "Nav1.7 and other voltage-gated sodium channels as drug targets for pain relief". Expert Opinion on Therapeutic Targets. 20 (8): 975–983. doi:10.1517/14728222.2016.1162295. PMC 4950419. PMID 26941184.

External links

• SCN9A+protein,+human at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
• GeneReviews/NCBI/NIH/UW entry on SCN9A-Related Inherited Erythromelalgia
• Overview of all the structural information available in the PDB for UniProt: Q15858 (Sodium channel protein type 9 subunit alpha) at the PDBe-KB.

• Genes on human chromosome 2
• Sodium channels