Human BDNF/TrkB variants impair hippocampal synaptogenesis and associate with neurobehavioural abnormalities

Takuhiro Sonoyama,David C Dewitt,Magdalena Jura,Fuki Hisama,Bas Brouwers,I Sadaf Farooqi,Peter Kirwan,Mingyan Zhu,Inês Barroso,Lukas K J Stadler,Elana Henning,Suzanne M Appleyard,Julia M Keogh,Florian T Merkle,Marko Hyvönen,Beata K Blaszczyk,Gary A Wayman

doi:10.1038/s41598-020-65531-x

Abstract

Brain-derived neurotrophic factor (BDNF) signals through its high affinity receptor Tropomyosin receptor kinase-B (TrkB) to regulate neuronal development, synapse formation and plasticity. In rodents, genetic disruption of Bdnf and TrkB leads to weight gain and a spectrum of neurobehavioural phenotypes. Here, we functionally characterised a de novo missense variant in BDNF and seven rare variants in TrkB identified in a large cohort of people with severe, childhood-onset obesity. In cells, the E183K BDNF variant resulted in impaired processing and secretion of the mature peptide. Multiple variants in the kinase domain and one variant in the extracellular domain of TrkB led to a loss of function through multiple signalling pathways, impaired neurite outgrowth and dominantly inhibited glutamatergic synaptogenesis in hippocampal neurons. BDNF/TrkB variant carriers exhibited learning difficulties, impaired memory, hyperactivity, stereotyped and sometimes, maladaptive behaviours. In conclusion, human loss of function BDNF/TrkB variants that impair hippocampal synaptogenesis may contribute to a spectrum of neurobehavioural disorders.

Highlights

Brain-derived neurotrophic factor (BDNF) signals through its high affinity receptor Tropomyosin receptor kinase-B (TrkB) to regulate neuronal development, synapse formation and plasticity
We first tested whether the E183K BDNF variant had any functional impact on BDNF globally, by transfecting wild-type (WT) and mutant BDNF into PC12 cells, which stably express human TrkB (PC12TrkB), followed by measurement of neurite outgrowth 48 hours later
We found that mutant BDNF was significantly impaired in its ability to stimulate neurite outgrowth compared to WT (Fig. 1B, n = 4, p < 0.05), demonstrating that the E183K substitution causes a loss-of-function

Summary

Introduction

Brain-derived neurotrophic factor (BDNF) signals through its high affinity receptor Tropomyosin receptor kinase-B (TrkB) to regulate neuronal development, synapse formation and plasticity. We use these human variants as tools with which to explore the consequences of impaired BDNF-TrkB signalling on dendritic spine structure and function, which forms the neural substrate for learning and memory in hippocampal neurons.

Results

Conclusion