Neuregulin-2 ablation results in dopamine dysregulation and severe behavioral phenotypes relevant to psychiatric disorders

OPEN Molecular Psychiatry (2018) 23, 1233–1243 www.nature.com/mp ORIGINAL ARTICLE Neuregulin-2 ablation results in dopamine dysregulation and severe behavioral phenotypes relevant to psychiatric disorders L Yan1,4,5, A Shamir1,4,6, M Skirzewski1,4, E Leiva-Salcedo1,7, OB Kwon1,8, I Karavanova1, D Paredes1,9, O Malkesman2,10, KR Bailey3,11, D Vullhorst1, JN Crawley3,12 and A Buonanno1 Numerous genetic and functional studies implicate variants of Neuregulin-1 (NRG1) and its neuronal receptor ErbB4 in schizophrenia and many of its endophenotypes. Although the neurophysiological and behavioral phenotypes of NRG1 mutant mice have been investigated extensively, practically nothing is known about the function of NRG2, the closest NRG1 homolog. We found that NRG2 expression in the adult rodent brain does not overlap with NRG1 and is more extensive than originally reported, including expression in the striatum and medial prefrontal cortex (mPFC), and therefore generated NRG2 knockout mice (KO) to study its function. NRG2 KOs have higher extracellular dopamine levels in the dorsal striatum but lower levels in the mPFC; a pattern with similarities to dopamine dysbalance in schizophrenia. Like ErbB4 KO mice, NRG2 KOs performed abnormally in a battery of behavioral tasks relevant to psychiatric disorders. NRG2 KOs exhibit hyperactivity in a novelty-induced open field, deficits in prepulse inhibition, hypersensitivity to amphetamine, antisocial behaviors, reduced anxiety-like behavior in the elevated plus maze and deficits in the T-maze alteration reward test—a task dependent on hippocampal and mPFC function. Acute administration of clozapine rapidly increased extracellular dopamine levels in the mPFC and improved alternation T-maze performance. Similar to mice treated chronically with N-methyl-D-aspartate receptor (NMDAR) antagonists, we demonstrate that NMDAR synaptic currents in NRG2 KOs are augmented at hippocampal glutamatergic synapses and are more sensitive to ifenprodil, indicating an increased contribution of GluN2B-containing NMDARs. Our findings reveal a novel role for NRG2 in the modulation of behaviors with relevance to psychiatric disorders. Molecular Psychiatry (2018) 23, 1233–1243; doi:10.1038/mp.2017.22; published online 21 March 2017 INTRODUCTION The Neuregulins (NRG 1–4) and their cognate neuronal receptor ErbB4 are among the numerous genetic variants associated with a risk for schizophrenia1–4 and many of its endophenotypes.5 Moreover, studies using human induced pluripotent stem cells from affected subjects,6 as well as work in mice with targeted mutations in NRG17–9 and ErbB4,10 provide strong experimental evidence for 'biological plausibility' of this pathway in psychiatric disorders.11 Most psychiatric diseases, such as attention-deficit hyperactivity disorder (ADHD) and schizophrenia, manifest during development and exhibit a high degree of heritability. Although current pharmacological interventions for ADHD and schizophrenia target the dopamine system, multiple neurotransmitter systems including dopamine, glutamate, GABA and acetylcholine have been implicated in their pathophysiology. The different regional, temporal and cellular expression patterns of NRG isoforms in the brain suggest distinct and non- overlapping functions. NRG1 transcripts are abundantly expressed in the embryonic and fetal brain but become restricted during postnatal development,12 whereas NRG2 transcript levels markedly increase shortly after birth, suggesting important functions in the postnatal and adult brain.13 In the hippocampus and neocortex, ErbB4 is confined to GABAergic interneurons,14 and in the ventral tegmental area and substantia nigra compacta, ErbB4 is expressed in dopaminergic neurons15,16 where it regulates activity from glutamatergic inputs.17 NRG1 treatment acutely and markedly increases extracellular dopamine levels in behaving rats,18 and regulates glutamatergic synaptic plasticity in acute hippocampal slices19 and the power of gamma oscillations20,21—a type of local neuronal network activity associated with cognitive deficits in persons with psychiatric disorders.22 Most, if not all, NRG effects are abolished in ErbB4 knockout mice (KO).10 Consistent with these findings, ErbB4 KOs exhibit altered excitation/inhibition balance and numerous deficits 1 Section on Molecular Neurobiology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, MD, USA; 2Laboratory of Molecular Pathophysiology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA and 3Laboratory of Behavioral Neuroscience, National Institute of Mental Health, National Institutes of Health, Bethesda, MD, USA. Correspondence: Professor A Buonanno, Section on Molecular Neurobiology, Eunice Kennedy Shriver National Institute of Child Health, National Institutes of Health Porter Neuroscience Research Center, Bldg. 35, Room 2C-1000, Bethesda, MD 20892, USA. E-mail: 4 These authors contributed equally to this work. 5 Current address: University Medical Center Brackenridge, Austin, TX, USA. 6 Current address: Mazor Mental Health Center & Faculty of Medicine, Technion D.N. Oshrat, Akko, Israel. 7 Current address: Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, Santiago, Chile. 8 Current address: Daegu-Gyeongbuk Medical Innovation Foundation, New Drug Development Center, Daegu, Korea. 9 Current address: Knoebel Institute for Healthy Aging, University of Denver, CO, USA. 10 Current address: Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA. 11 Current address: Susquehanna University, Selinsgrove, PA, USA. 12 Current address: MIND Institute, Department of Psychiatry and Behavioral Sciences, University of California Davis School of Medicine, Sacramento, CA, USA. Received 13 August 2015; revised 16 November 2016; accepted 21 December 2016; published online 21 March 2017 NRG2 and its relevance to psychiatric disorders L Yan et al 1234 in behavioral tasks modeling schizophrenia and its endophenotypes, including prepulse inhibition (PPI; somatosensory gating), rewarded T-maze alternation (requires working memory) and social interactions.7–10 Molecular Psychiatry (2018), 1233 – 1243 Despite its prominent expression in the postnatal and adult brain, little is known about NRG2 function and its potential involvement in neurodegenerative and neuropsychiatric disorders. Children with de novo overlapping 5q31 microdeletions, NRG2 and its relevance to psychiatric disorders L Yan et al 1235 encompassing three genes that include NRG2, share clinical features that include white matter abnormalities and severe developmental and intellectual delays.23,24 Although the region encompassing the NRG2 locus (5q23–33) has been associated with risk for schizophrenia25–28 and genetically linked with ADHD in genome-wide scans of multigenerational extended families,29 at the present time, genetic stud (...truncated)