Intracellular FGF14 (iFGF14) Is Required for Spontaneous and Evoked Firing in Cerebellar Purkinje Neurons and for Motor Coordination and Balance

J Neurosci. 2015 Apr 29;35(17):6752-69. doi: 10.1523/JNEUROSCI.2663-14.2015.

Abstract

Mutations in FGF14, which encodes intracellular fibroblast growth factor 14 (iFGF14), have been linked to spinocerebellar ataxia (SCA27). In addition, mice lacking Fgf14 (Fgf14(-/-)) exhibit an ataxia phenotype resembling SCA27, accompanied by marked changes in the excitability of cerebellar granule and Purkinje neurons. It is not known, however, whether these phenotypes result from defects in neuronal development or if they reflect a physiological requirement for iFGF14 in the adult cerebellum. Here, we demonstrate that the acute and selective Fgf14-targeted short hairpin RNA (shRNA)-mediated in vivo "knock-down" of iFGF14 in adult Purkinje neurons attenuates spontaneous and evoked action potential firing without measurably affecting the expression or localization of voltage-gated Na(+) (Nav) channels at Purkinje neuron axon initial segments. The selective shRNA-mediated in vivo "knock-down" of iFGF14 in adult Purkinje neurons also impairs motor coordination and balance. Repetitive firing can be restored in Fgf14-targeted shRNA-expressing Purkinje neurons, as well as in Fgf14(-/-) Purkinje neurons, by prior membrane hyperpolarization, suggesting that the iFGF14-mediated regulation of the excitability of mature Purkinje neurons depends on membrane potential. Further experiments revealed that the loss of iFGF14 results in a marked hyperpolarizing shift in the voltage dependence of steady-state inactivation of the Nav currents in adult Purkinje neurons. We also show here that expressing iFGF14 selectively in adult Fgf14(-/-) Purkinje neurons rescues spontaneous firing and improves motor performance. Together, these results demonstrate that iFGF14 is required for spontaneous and evoked action potential firing in adult Purkinje neurons, thereby controlling the output of these cells and the regulation of motor coordination and balance.

Keywords: FGF14; channel inactivation; fibroblast growth factor homologous factor 4 (FHF4); intrinsic excitability; spinocerebellar ataxia 27; voltage-gated sodium (Nav) channels.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Action Potentials / genetics*
  • Action Potentials / physiology
  • Animals
  • Ankyrins / metabolism
  • Axons / metabolism
  • Cell Line, Transformed
  • Cerebellum / cytology*
  • Cricetulus
  • Female
  • Fibroblast Growth Factors / genetics
  • Fibroblast Growth Factors / metabolism*
  • Gene Expression Regulation / genetics
  • In Vitro Techniques
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • MicroRNAs / genetics
  • MicroRNAs / metabolism
  • NAV1.1 Voltage-Gated Sodium Channel / metabolism
  • Postural Balance / genetics*
  • Psychomotor Performance / physiology*
  • Purkinje Cells / cytology
  • Purkinje Cells / physiology*

Substances

  • Ank3 protein, mouse
  • Ankyrins
  • MicroRNAs
  • Mirn30d microRNA, mouse
  • NAV1.1 Voltage-Gated Sodium Channel
  • Scn1a protein, mouse
  • fibroblast growth factor 14
  • Fibroblast Growth Factors