The epilepsy and intellectual disability-associated protein TBC1D24 regulates the maintenance of excitatory synapses and animal behaviors

PLoS Genet. 2020 Jan 31;16(1):e1008587. doi: 10.1371/journal.pgen.1008587. eCollection 2020 Jan.

Abstract

Perturbation of synapse development underlies many inherited neurodevelopmental disorders including intellectual disability (ID). Diverse mutations on the human TBC1D24 gene are strongly associated with epilepsy and ID. However, the physiological function of TBC1D24 in the brain is not well understood, and there is a lack of genetic mouse model that mimics TBC1D24 loss-of-function for the study of animal behaviors. Here we report that TBC1D24 is present at the postsynaptic sites of excitatory synapses, where it is required for the maintenance of dendritic spines through inhibition of the small GTPase ARF6. Mice subjected to viral-mediated knockdown of TBC1D24 in the adult hippocampus display dendritic spine loss, deficits in contextual fear memory, as well as abnormal behaviors including hyperactivity and increased anxiety. Interestingly, we show that the protein stability of TBC1D24 is diminished by the disease-associated missense mutation that leads to F251L amino acid substitution. We further generate the F251L knock-in mice, and the homozygous mutants show increased neuronal excitability, spontaneous seizure and pre-mature death. Moreover, the heterozygous F251L knock-in mice survive into adulthood but display dendritic spine defects and impaired memory. Our findings therefore uncover a previously uncharacterized postsynaptic function of TBC1D24, and suggest that impaired dendritic spine maintenance contributes to the pathophysiology of individuals harboring TBC1D24 gene mutations. The F251L knock-in mice represent a useful animal model for investigation of the mechanistic link between TBC1D24 loss-of-function and neurodevelopmental disorders.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Epilepsy / genetics*
  • Excitatory Postsynaptic Potentials*
  • GTPase-Activating Proteins / genetics*
  • Hippocampus / metabolism
  • Hippocampus / pathology
  • Hippocampus / physiology
  • Intellectual Disability / genetics*
  • Memory
  • Mice
  • Mice, Inbred C57BL
  • Mutation, Missense
  • Neurons / metabolism
  • Neurons / pathology
  • Neurons / physiology

Substances

  • GTPase-Activating Proteins
  • Tbc1d24 protein, mouse

Grant support

This study was supported in part by the Research Grant Council of Hong Kong [General Research Fund (GRF) 16100814, 17135816, 17106018 and Early Career Scheme (ECS) 27119715]; the Area of Excellence Scheme (Grant AoE/M-604/16) and the Theme-based Research Scheme (T13-605/18-W) of the University Grants Committee of Hong Kong; the Liu Po Shan/Dr. Vincent Liu Endowment Fund for Motor Neurone Disease, and University of Hong Kong Seed Funding for Basic Research (201407159004 and 201511159170). These grants are awarded to K.O.L. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.