title: FHF2 isoforms differentially regulate Nav1.6-mediated resurgent sodium currents in dorsal root ganglion neurons.
abstract: Nav1.6 and Nav1.6-mediated resurgent currents have been implicated in several pain pathologies. However, our knowledge of how fast resurgent currents are modulated in neurons is limited. Our study explored the potential regulation of Nav1.6-mediated resurgent currents by isoforms of fibroblast growth factor homologous factor 2 (FHF2) in an effort to address the gap in our knowledge. FHF2 isoforms colocalize with Nav1.6 in peripheral sensory neurons. Cell line studies suggest that these proteins differentially regulate inactivation. In particular, FHF2A mediates long-term inactivation, a mechanism proposed to compete with the open-channel blocker mechanism that mediates resurgent currents. On the other hand, FHF2B lacks the ability to mediate long-term inactivation and may delay inactivation favoring open-channel block. Based on these observations, we hypothesized that FHF2A limits resurgent currents, whereas FHF2B enhances resurgent currents. Overall, our results suggest that FHF2A negatively regulates fast resurgent current by enhancing long-term inactivation and delaying recovery. In contrast, FHF2B positively regulated resurgent current and did not alter long-term inactivation. Chimeric constructs of FHF2A and Navβ4 (likely the endogenous open channel blocker in sensory neurons) exhibited differential effects on resurgent currents, suggesting that specific regions within FHF2A and Navβ4 have important regulatory functions. Our data also indicate that FHFAs and FHF2B isoform expression are differentially regulated in a radicular pain model and that associated neuronal hyperexcitability is substantially attenuated by a FHFA peptide. As such, these findings suggest that FHF2A and FHF2B regulate resurgent current in sensory neurons and may contribute to hyperexcitability associated with some pain pathologies.
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University, Indianapolis, IN, USA.|Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Cindy
authors.initials: C
authors.lastname: Barbosa
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University, Indianapolis, IN, USA.|Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Yucheng
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University, Indianapolis, IN, USA.|Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Johnson
authors.affiliation: Department of Anesthesiology, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Wenrui
authors.initials: W
authors.lastname: Xie
authors.affiliation: Department of Anesthesiology, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Judith A
authors.initials: JA
authors.lastname: Strong
authors.affiliation: Department of Anesthesiology, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: Jun-Ming
authors.initials: JM
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University, Indianapolis, IN, USA. trcummin@iupui.edu.|Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN, USA. trcummin@iupui.edu.|Department of Biology, Indiana University - Purdue University Indianapolis, Indianapolis, IN, USA. trcummin@iupui.edu.
authors.forename: Theodore R
authors.initials: TR
authors.lastname: Cummins
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D005727:Ganglia, Spinal / Q000378:metabolism*; D015640:Ion Channel Gating / Q000502:physiology; D008297:Male; D062557:NAV1.6 Voltage-Gated Sodium Channel / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
chemical_list: C496249:Fgf13 protein, rat; D062557:NAV1.6 Voltage-Gated Sodium Channel; D020033:Protein Isoforms; D005346:Fibroblast Growth Factors; D012964:Sodium
keywords: Dorsal root ganglia neurons; FHF; Fibroblast growth factor homologous factor; Resurgent Na+ current; Resurgent current