Pain sensation in neuropathic pain is complex consisting of weakness, sensory deficits and numbness, reflex changes, abnormal sensations that occur either spontaneously or in reaction to external stimuli, hyperalgesia and allodynia. Perturbations in dorsal root ganglion (DRG) neuron excitability are key in precipitating neuropathic pain, especially during diabetes, the most common cause of neuropathic pain. During diabetes, the p38 mitogen-activated protein kinase (p38MAPK) signaling system is activated and when this pathway is inhibited, diabetes-induced neuropathic pain is attenuated. However, the major ion conductances involved in the neuropathic process of DRG neurons are unclear. DRG neurons possess high levels of a novel, understudied family of potassium channels called sodium-activated potassium channels (KNa). Our previous work has shown that KNa is a considerable component of the outward potassium current and is responsible for firing accommodation in DRG neurons. When we experimentally reduce the expression of these channels in DRG neurons, it produces hyperexcitability that resembles neuropathic neurons. There are two genes encoding these channels, Slack and Slick. In heterologous expression systems, the Slick and Slack subunits can co-assemble to form heteromeric channels systems with very slow activation kinetics ideal for controlling firing accommodation. Moreover, homomeric Slick channels appear to be subject to Nedd4l-dependent ubiquitination, suggesting that Slack/Slick heteromeric channels are the preferred configuration of native KNa channels. Slack and Slick also have p38MAPK consensus phosphorylation sites proximal to the sodium binding/gating region of the channels. A decrease in KNa channel activity likely ensues after diabetes-activated p38MAPK signaling. Since diabetes also affects transcriptional activities, we expect to find long-term changes in KNa channel expression in neurons. Using electrophysiological, biochemical, molecular, pain behavioral assays and a previously uncharacterized Slick knockout mouse, we will test the hypotheses: heteromeric KNa channels constrain sensory neuron hyperexcitability and neuropathic pain is associated with decreased KNa channel activity in DRG neurons.
The specific aims are (1) To study the regulation of DRG KNa channels by p38MAPK (2) To investigate the subunit properties of KNa channels in DRG neurons (3) To study neuronal KNa channel activity during diabetes and compare pain behavior to Slick knockout mice. This research project will assess the involvement of KNa channels in the diabetic neuropathy.

Public Health Relevance

Elucidating the mechanisms underlying persistent pain in peripheral neuropathy is of vital importance for future treatment strategies. This proposal is designed to determine how sodium-activated potassium channels regulate sensory neuron excitability and if they are down regulated during neuropathic pain. The conclusions of these studies may identify these channels as analgesic targets for neuropathic pain.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS078184-02
Application #
8535232
Study Section
Somatosensory and Chemosensory Systems Study Section (SCS)
Program Officer
Babcock, Debra J
Project Start
2012-09-01
Project End
2017-05-31
Budget Start
2013-06-01
Budget End
2014-05-31
Support Year
2
Fiscal Year
2013
Total Cost
$325,497
Indirect Cost
$114,403
Name
State University of New York at Buffalo
Department
Pharmacology
Type
Schools of Medicine
DUNS #
038633251
City
Buffalo
State
NY
Country
United States
Zip Code
14260
Evely, Katherine M; Pryce, Kerri D; Bausch, Anne E et al. (2017) Slack KNa Channels Influence Dorsal Horn Synapses and Nociceptive Behavior. Mol Pain 13:1744806917714342
Gururaj, Sushmitha; Evely, Katherine M; Pryce, Kerri D et al. (2017) Protein kinase A-induced internalization of Slack channels from the neuronal membrane occurs by adaptor protein-2/clathrin-mediated endocytosis. J Biol Chem 292:19304-19314
Tomasello, Danielle L; Hurley, Edward; Wrabetz, Lawrence et al. (2017) Slick (Kcnt2) Sodium-Activated Potassium Channels Limit Peptidergic Nociceptor Excitability and Hyperalgesia. J Exp Neurosci 11:1179069517726996
Evely, Katherine M; Pryce, Kerri D; Bhattacharjee, Arin (2017) The Phe932Ile mutation in KCNT1 channels associated with severe epilepsy, delayed myelination and leukoencephalopathy produces a loss-of-function channel phenotype. Neuroscience 351:65-70
Gururaj, Sushmitha; Palmer, Elizabeth Emma; Sheehan, Garrett D et al. (2017) A De Novo Mutation in the Sodium-Activated Potassium Channel KCNT2 Alters Ion Selectivity and Causes Epileptic Encephalopathy. Cell Rep 21:926-933
Gururaj, Sushmitha; Fleites, John; Bhattacharjee, Arin (2016) Slack sodium-activated potassium channel membrane expression requires p38 mitogen-activated protein kinase phosphorylation. Neuropharmacology 103:279-89
Tomasello, Danielle L; Gancarz-Kausch, Amy M; Dietz, David M et al. (2015) Transcriptional Regulation of the Sodium-activated Potassium Channel SLICK (KCNT2) Promoter by Nuclear Factor-?B. J Biol Chem 290:18575-83