title: Early-onset epileptic encephalopathy caused by a reduced sensitivity of Kv7.2 potassium channels to phosphatidylinositol 4,5-bisphosphate.
abstract: Kv7.2 and Kv7.3 subunits underlie the M-current, a neuronal K+current characterized by an absolute functional requirement for phosphatidylinositol 4,5-bisphosphate (PIP2). Kv7.2 gene mutations cause early-onset neonatal seizures with heterogeneous clinical outcomes, ranging from self-limiting benign familial neonatal seizures to severe early-onset epileptic encephalopathy (Kv7.2-EE). In this study, the biochemical and functional consequences prompted by a recurrent variant (R325G) found independently in four individuals with severe forms of neonatal-onset EE have been investigated. Upon heterologous expression, homomeric Kv7.2 R325G channels were non-functional, despite biotin-capture in Western blots revealed normal plasma membrane subunit expression. Mutant subunits exerted dominant-negative effects when incorporated into heteromeric channels with Kv7.2 and/or Kv7.3 subunits. Increasing cellular PIP2levels by co-expression of type 1γ PI(4)P5-kinase (PIP5K) partially recovered homomeric Kv7.2 R325G channel function. Currents carried by heteromeric channels incorporating Kv7.2 R325G subunits were more readily inhibited than wild-type channels upon activation of a voltage-sensitive phosphatase (VSP), and recovered more slowly upon VSP switch-off. These results reveal for the first time that a mutation-induced decrease in current sensitivity to PIP2is the primary molecular defect responsible for Kv7.2-EE in individuals carrying the R325G variant, further expanding the range of pathogenetic mechanisms exploitable for personalized treatment of Kv7.2-related epilepsies.
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Maria Virginia
authors.initials: MV
authors.lastname: Soldovieri
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Ambrosino
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Mosca
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: De Maria
authors.affiliation: CNR Institute of Neuroscience, Department of Medical Biotechnology and Translational Medicine (BIOMETRA), University of Milan, Milan, Italy.
authors.forename: Edoardo
authors.initials: E
authors.lastname: Moretto
authors.affiliation: Department of Neuroscience, University of Naples Federico II, Naples, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Miceli
authors.affiliation: Centre for Integrative Biology (CIBIO), University of Trento, Trento, Italy.|Instituto Biofisika (UPV/EHU, CSIC), Leioa, Spain.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Alaimo
authors.affiliation: Department of Pharmacy, University of Salerno, Fisciano, Salerno, Italy.
authors.forename: Nunzio
authors.initials: N
authors.lastname: Iraci
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Manocchio
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Medoro
authors.affiliation: CNR Institute of Neuroscience, Department of Medical Biotechnology and Translational Medicine (BIOMETRA), University of Milan, Milan, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Passafaro
authors.affiliation: Department of Medicine and Health Sciences, University of Molise, Campobasso, Italy.|Department of Neuroscience, University of Naples Federico II, Naples, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Taglialatela
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001927:Brain Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016466:CHO Cells; D003412:Cricetulus; D004829:Epilepsy, Generalized / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D051658:KCNQ2 Potassium Channel / Q000235:genetics / Q000378:metabolism*; D051659:KCNQ3 Potassium Channel / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials; D020125:Mutation, Missense; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000235:genetics / Q000378:metabolism*; D051381:Rats
chemical_list: D051658:KCNQ2 Potassium Channel; D051659:KCNQ3 Potassium Channel; D019269:Phosphatidylinositol 4,5-Diphosphate