Early-onset epileptic encephalopathy caused by gain-of-function mutations in the voltage sensor of Kv7.2 and Kv7.3 potassium channel subunits.
Mutations in Kv7.2 (KCNQ2) and Kv7.3 (KCNQ3) genes, encoding for voltage-gated K(+) channel subunits underlying the neuronal M-current, have been associated with a wide spectrum of early-onset epileptic disorders ranging from benign familial neonatal seizures to severe epileptic encephalopathies. The aim of the present work has been to investigate the molecular mechanisms of channel dysfunction caused by voltage-sensing domain mutations in Kv7.2 (R144Q, R201C, and R201H) or Kv7.3 (R230C) recently found in patients with epileptic encephalopathies and/or intellectual disability. Electrophysiological studies in mammalian cells transfected with human Kv7.2 and/or Kv7.3 cDNAs revealed that each of these four mutations stabilized the activated state of the channel, thereby producing gain-of-function effects, which are opposite to the loss-of-function effects produced by previously found mutations. Multistate structural modeling revealed that the R201 residue in Kv7.2, corresponding to R230 in Kv7.3, stabilized the resting and nearby voltage-sensing domain states by forming an intricate network of electrostatic interactions with neighboring negatively charged residues, a result also confirmed by disulfide trapping experiments. Using a realistic model of a feedforward inhibitory microcircuit in the hippocampal CA1 region, an increased excitability of pyramidal neurons was found upon incorporation of the experimentally defined parameters for mutant M-current, suggesting that changes in network interactions rather than in intrinsic cell properties may be responsible for the neuronal hyperexcitability by these gain-of-function mutations. Together, the present results suggest that gain-of-function mutations in Kv7.2/3 currents may cause human epilepsy with a severe clinical course, thus revealing a previously unexplored level of complexity in disease pathogenetic mechanisms.
Department of Neuroscience, University of Naples Federico II, 80131 Naples, Italy.
Francesco
F
Miceli
Department of Medicine and Health Science, University of Molise, 86100 Campobasso, Italy, and.
Maria Virginia
MV
Soldovieri
Department of Medicine and Health Science, University of Molise, 86100 Campobasso, Italy, and.
Paolo
P
Ambrosino
Department of Medicine and Health Science, University of Molise, 86100 Campobasso, Italy, and.
Michela
M
De Maria
Institute of Biophysics, National Research Council, 90146 Palermo, Italy.
Michele
M
Migliore
Institute of Biophysics, National Research Council, 90146 Palermo, Italy.
Rosanna
http://orcid.org/0000-0001-9034-7849
R
Migliore
Department of Neuroscience, University of Naples Federico II, 80131 Naples, Italy, Department of Medicine and Health Science, University of Molise, 86100 Campobasso, Italy, and m.taglialatela@unimol.it.
Maurizio
http://orcid.org/0000-0002-8202-0560
M
Taglialatela
D000595:Amino Acid Sequence; D000818:Animals; D019921:Biotinylation / Q000235:genetics; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D020936:Epilepsy, Benign Neonatal / Q000235:genetics* / Q000503:physiopathology*; D006801:Humans; D051658:KCNQ2 Potassium Channel / Q000235:genetics*; D051659:KCNQ3 Potassium Channel / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D017434:Protein Structure, Tertiary
D018076:DNA, Complementary; D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel
Kv7 potassium channels; epileptic encephalopathies; gating; mutations; voltage-sensing domain