Neuropathic pain and inflammatory pain occur frequently after traumatic nerve injury, spinal cord injury (SCI), and limb amputation, and represent unmet medical needs for VA and, more generally, the U.S. population. Currently available treatments are often ineffective or only partially effective, in part because of off-target cardiac and CNS side effects. Inappropriate spontaneous firing and hyper-responsiveness of dorsal root ganglion (DRG) neurons, due to activity of voltage-gated Na channels (Nav), are major contributors to neuropathic and inflammatory pain.
Our aim i s to identify and characterize Na channel isoforms and functionally-related molecules that drive DRG neuron hyperexcitability, so that we can target them for more effective pain relief. Preferential expression of several Na channel isoforms in DGR neurons including nociceptors, and the up-regulation after nerve injury of another isoform, which is not present at high levels within the CNS or cardiac tissue, makes these Na channel subtypes potentially attractive as therapeutic targets for pain. Highly specific interactions with binding partners may regulate activity of these channels, suggesting that targeting of Na channel partners may expand therapeutic strategies for pain. Our recent progress has included identification of Na channel Nav1.7 as a key player in human pain, and demonstration of accumulation of three Na channel isoforms, Nav1.7, Nav1.8 and Nav1.3 within painful human neuromas. We have also demonstrated the presence of several MAP kinases (activated p38 and ERK1/2) within neuromas. We now plan to build upon our progress, via the following specific aims: 1. Examine the contribution of specific Na channel isoforms, their accessory molecules, and other related channel proteins to mechanosensitivity in experimental neuromas. 2. Analyze the expression of specific Na channel isoforms, their accessory molecules, and other related channel proteins in human painful neuromas. 3. Study FHF2-mediated regulation of Nav1.7 and Nav1.8 Na channels that drive chronic pain. 4. Study MAPK-mediated modulation of Nav1.7 and Nav1.8 Na Channels that drive chronic pain. 5. Investigate whether contusive SCI triggers sensitization of DRG neurons via regulation of Na channel expression or modulation of their functional properties, thereby producing enhanced nociceptor hyperexcitability and pain.

Public Health Relevance

Among the major health challenges for the Department of Veterans Affairs are spinal cord Injury (SCI; approximately 40,000 veterans);multiple sclerosis (MS;affects at least 23,000 veterans);nerve injury and traumatic limb amputation. These medical conditions are commonly associated with neuropathic pain and inflammatory pain. Clinically significant pain affects over 50 % of patients with SCI, and 50% to 80% of patients with MS. Currently available treatments are often not effective or only partially effective. Neuropathic pain and inflammatory pain, therefore, represent an unmet medical need for the VA. Studies have shown that, following nerve injury, pain arises due to inappropriate firing of dorsal root ganglion (DRG) neurons. Our aim is to discover molecules that affect DRG neuron behavior, so that we can identify more effective treatments for neuropathic and inflammatory pain.

Agency
National Institute of Health (NIH)
Institute
Veterans Affairs (VA)
Type
Non-HHS Research Projects (I01)
Project #
5I01BX000605-03
Application #
8258650
Study Section
Neurobiology C (NURC)
Project Start
2009-10-01
Project End
2013-09-30
Budget Start
2011-10-01
Budget End
2012-09-30
Support Year
3
Fiscal Year
2012
Total Cost
Indirect Cost
Name
VA Connecticut Healthcare System
Department
Type
DUNS #
039624291
City
West Haven
State
CT
Country
United States
Zip Code
06516
Dib-Hajj, Sulayman D; Geha, Paul; Waxman, Stephen G (2017) Sodium channels in pain disorders: pathophysiology and prospects for treatment. Pain 158 Suppl 1:S97-S107
Akin, Elizabeth J; Solé, Laura; Dib-Hajj, Sulayman D et al. (2015) Preferential targeting of Nav1.6 voltage-gated Na+ Channels to the axon initial segment during development. PLoS One 10:e0124397
Tan, Andrew M; Waxman, Stephen G (2015) Dendritic spine dysgenesis in neuropathic pain. Neurosci Lett 601:54-60
Han, Chongyang; Yang, Yang; de Greef, Bianca T A et al. (2015) The Domain II S4-S5 Linker in Nav1.9: A Missense Mutation Enhances Activation, Impairs Fast Inactivation, and Produces Human Painful Neuropathy. Neuromolecular Med 17:158-69
Estacion, M; Vohra, B P S; Liu, S et al. (2015) Ca2+ toxicity due to reverse Na+/Ca2+ exchange contributes to degeneration of neurites of DRG neurons induced by a neuropathy-associated Nav1.7 mutation. J Neurophysiol 114:1554-64
Bandaru, Samira P; Liu, Shujun; Waxman, Stephen G et al. (2015) Dendritic spine dysgenesis contributes to hyperreflexia after spinal cord injury. J Neurophysiol 113:1598-615
Han, Chongyang; Estacion, Mark; Huang, Jianying et al. (2015) Human Na(v)1.8: enhanced persistent and ramp currents contribute to distinct firing properties of human DRG neurons. J Neurophysiol 113:3172-85
Huang, Jianying; Han, Chongyang; Estacion, Mark et al. (2014) Gain-of-function mutations in sodium channel Na(v)1.9 in painful neuropathy. Brain 137:1627-42
Dib-Hajj, Sulayman D; Waxman, Stephen G (2014) Translational pain research: Lessons from genetics and genomics. Sci Transl Med 6:249sr4
Waxman, Stephen G; Merkies, Ingemar S J; Gerrits, Monique M et al. (2014) Sodium channel genes in pain-related disorders: phenotype-genotype associations and recommendations for clinical use. Lancet Neurol 13:1152-1160