BDNF regulates the expression and distribution of vesicular glutamate transporters in cultured hippocampal neurons

PLoS One. 2013;8(1):e53793. doi: 10.1371/journal.pone.0053793. Epub 2013 Jan 11.

Abstract

BDNF is a pro-survival protein involved in neuronal development and synaptic plasticity. BDNF strengthens excitatory synapses and contributes to LTP, presynaptically, through enhancement of glutamate release, and postsynaptically, via phosphorylation of neurotransmitter receptors, modulation of receptor traffic and activation of the translation machinery. We examined whether BDNF upregulated vesicular glutamate receptor (VGLUT) 1 and 2 expression, which would partly account for the increased glutamate release in LTP. Cultured rat hippocampal neurons were incubated with 100 ng/ml BDNF, for different periods of time, and VGLUT gene and protein expression were assessed by real-time PCR and immunoblotting, respectively. At DIV7, exogenous application of BDNF rapidly increased VGLUT2 mRNA and protein levels, in a dose-dependent manner. VGLUT1 expression also increased but only transiently. However, at DIV14, BDNF stably increased VGLUT1 expression, whilst VGLUT2 levels remained low. Transcription inhibition with actinomycin-D or α-amanitine, and translation inhibition with emetine or anisomycin, fully blocked BDNF-induced VGLUT upregulation. Fluorescence microscopy imaging showed that BDNF stimulation upregulates the number, integrated density and intensity of VGLUT1 and VGLUT2 puncta in neurites of cultured hippocampal neurons (DIV7), indicating that the neurotrophin also affects the subcellular distribution of the transporter in developing neurons. Increased VGLUT1 somatic signals were also found 3 h after stimulation with BDNF, further suggesting an increased de novo transcription and translation. BDNF regulation of VGLUT expression was specifically mediated by BDNF, as no effect was found upon application of IGF-1 or bFGF, which activate other receptor tyrosine kinases. Moreover, inhibition of TrkB receptors with K252a and PLCγ signaling with U-73122 precluded BDNF-induced VGLUT upregulation. Hippocampal neurons express both isoforms during embryonic and neonatal development in contrast to adult tissue expressing only VGLUT1. These results suggest that BDNF regulates VGLUT expression during development and its effect on VGLUT1 may contribute to enhance glutamate release in LTP.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anisomycin / pharmacology
  • Brain-Derived Neurotrophic Factor* / genetics
  • Brain-Derived Neurotrophic Factor* / metabolism
  • Cells, Cultured
  • Dactinomycin / pharmacology
  • Gene Expression Regulation, Developmental
  • Glutamic Acid / genetics
  • Glutamic Acid / metabolism
  • Hippocampus / cytology
  • Hippocampus / metabolism*
  • Long-Term Potentiation / genetics*
  • Long-Term Potentiation / physiology
  • Neurites / metabolism
  • Neuronal Plasticity / genetics
  • Neurons / cytology
  • Neurons / metabolism*
  • Rats
  • Synapses / genetics
  • Synapses / metabolism
  • Up-Regulation / drug effects
  • Vesicular Glutamate Transport Protein 1 / genetics*
  • Vesicular Glutamate Transport Protein 1 / metabolism
  • Vesicular Glutamate Transport Protein 2 / genetics*
  • Vesicular Glutamate Transport Protein 2 / metabolism

Substances

  • Brain-Derived Neurotrophic Factor
  • Slc17a6 protein, rat
  • Slc17a7 protein, rat
  • Vesicular Glutamate Transport Protein 1
  • Vesicular Glutamate Transport Protein 2
  • Dactinomycin
  • Glutamic Acid
  • Anisomycin

Grants and funding

FCT (Fundação para a Ciência e a Tecnologia) and FEDER (Fundo Europeu de Desenvolvimento Regional, Portugal) (grants PTDC/SAU-NMC/120144/2010 and PTDC/SAU-NEU/104297/2008) funded this study. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.