Ankyrin-G isoform imbalance and interneuronopathy link epilepsy and bipolar disorder

• Published in: Molecular psychiatry Vol. 22; no. 10; pp. 1464 - 1472
• Main Authors: Lopez, A Y, Wang, X, Xu, M, Maheshwari, A, Curry, D, Lam, S, Adesina, A M, Noebels, J L, Sun, Q-Q, Cooper, E C
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.10.2017; Nature Publishing Group
• Subjects: 631/378; 692/699/476/1333; 692/699/476/1414; Action potential; Adolescent; Alternative Splicing; Animals; Ankyrins; Ankyrins - genetics; Ankyrins - metabolism; Behavioral Sciences; Biological Psychology; Bipolar disorder; Bipolar Disorder - genetics; Bipolar Disorder - metabolism; Bipolar Disorder - pathology; Child; Epilepsy; Epilepsy - genetics; Epilepsy - metabolism; Epilepsy - pathology; Exons; Gene dosage; Genetic aspects; Genetic Predisposition to Disease; Genome-wide association studies; Genome-Wide Association Study; Genomes; Health aspects; Humans; Interneurons; Interneurons - metabolism; Interneurons - pathology; Isoforms; Medicine; Medicine & Public Health; Membrane proteins; Mice; Mice, Transgenic; Neurosciences; original-article; Parvalbumin; Parvalbumins - metabolism; Pharmacotherapy; Phenotypes; Polymorphism, Single Nucleotide; Protein Isoforms; Psychiatry; Risk factors; Rodents; Sodium; Sodium channels (voltage-gated); Therapeutic targets; Transgenic mice; United States
• ISSN: 1359-4184; 1476-5578
• DOI: 10.1038/mp.2016.233

ANK3 , encoding the adaptor protein Ankyrin-G (AnkG), has been implicated in bipolar disorder by genome-wide association studies. ANK3 has multiple alternative first exons, and a bipolar disorder-associated ANK3 variant has been shown to reduce the expression of exon 1b. Here we identify mechanisms through which reduced ANK3 exon 1b isoform expression disrupts neuronal excitation–inhibition balance. We find that parvalbumin (PV) interneurons and principal cells differentially express ANK3 first exon subtypes. PV interneurons express only isoforms containing exon 1b, whereas excitatory principal cells express exon 1e alone or both 1e and 1b. In transgenic mice deficient for exon 1b, PV interneurons lack voltage-gated sodium channels at their axonal initial segments and have increased firing thresholds and diminished action potential dynamic range. These mice exhibit an Ank3 gene dosage-dependent phenotype including behavior changes modeling bipolar disorder, epilepsy and sudden death. Thus ANK3 ’s important association with human bipolar susceptibility may arise from imbalance between AnkG function in interneurons and principal cells and resultant excessive circuit sensitivity and output. AnkG isoform imbalance is a novel molecular endophenotype and potential therapeutic target.