Brunner syndrome associated MAOA mutations result in NMDAR hyperfunction and increased network activity in human dopaminergic neurons

Neurobiol Dis. 2022 Feb:163:105587. doi: 10.1016/j.nbd.2021.105587. Epub 2021 Dec 16.

Abstract

Monoamine neurotransmitter abundance affects motor control, emotion, and cognitive function and is regulated by monoamine oxidases. Among these, Monoamine oxidase A (MAOA) catalyzes the degradation of dopamine, norepinephrine, and serotonin into their inactive metabolites. Loss-of-function mutations in the X-linked MAOA gene have been associated with Brunner syndrome, which is characterized by various forms of impulsivity, maladaptive externalizing behavior, and mild intellectual disability. Impaired MAOA activity in individuals with Brunner syndrome results in bioamine aberration, but it is currently unknown how this affects neuronal function, specifically in dopaminergic (DA) neurons. Here we generated human induced pluripotent stem cell (hiPSC)-derived DA neurons from three individuals with Brunner syndrome carrying different mutations and characterized neuronal properties at the single cell and neuronal network level in vitro. DA neurons of Brunner syndrome patients showed reduced synaptic density but exhibited hyperactive network activity. Intrinsic functional properties and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated synaptic transmission were not affected in DA neurons of individuals with Brunner syndrome. Instead, we show that the neuronal network hyperactivity is mediated by upregulation of the GRIN2A and GRIN2B subunits of the N-methyl-d-aspartate receptor (NMDAR), resulting in increased NMDAR-mediated currents. By correcting a MAOA missense mutation with CRISPR/Cas9 genome editing we normalized GRIN2A and GRIN2B expression, NMDAR function and neuronal population activity to control levels. Our data suggest that MAOA mutations in Brunner syndrome increase the activity of dopaminergic neurons through upregulation of NMDAR function, which may contribute to the etiology of Brunner syndrome associated phenotypes.

Keywords: Brunner syndrome; Dopaminergic neuron; Human iPSC; MAOA; Microelectrode array; NMDA receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aggression
  • Disruptive, Impulse Control, and Conduct Disorders / genetics*
  • Disruptive, Impulse Control, and Conduct Disorders / metabolism
  • Disruptive, Impulse Control, and Conduct Disorders / physiopathology
  • Dopaminergic Neurons / metabolism*
  • Genetic Diseases, X-Linked / genetics*
  • Genetic Diseases, X-Linked / metabolism
  • Genetic Diseases, X-Linked / physiopathology
  • Humans
  • Induced Pluripotent Stem Cells
  • Intellectual Disability / genetics*
  • Intellectual Disability / metabolism
  • Intellectual Disability / physiopathology
  • Male
  • Monoamine Oxidase / deficiency*
  • Monoamine Oxidase / genetics*
  • Monoamine Oxidase / metabolism
  • Mutation*
  • Nerve Net / metabolism
  • Nerve Net / physiopathology
  • Polymorphism, Single Nucleotide*
  • Receptors, N-Methyl-D-Aspartate / metabolism*
  • Synapses / metabolism
  • Synaptic Transmission / genetics

Substances

  • Receptors, N-Methyl-D-Aspartate
  • Monoamine Oxidase

Supplementary concepts

  • Brunner Syndrome