Excessive astrocyte-derived neurotrophin-3 contributes to the abnormal neuronal dendritic development in a mouse model of fragile X syndrome

PLoS Genet. 2012;8(12):e1003172. doi: 10.1371/journal.pgen.1003172. Epub 2012 Dec 27.

Abstract

Fragile X syndrome (FXS) is a form of inherited mental retardation in humans that results from expansion of a CGG repeat in the Fmr1 gene. Recent studies suggest a role of astrocytes in neuronal development. However, the mechanisms involved in the regulation process of astrocytes from FXS remain unclear. In this study, we found that astrocytes derived from a Fragile X model, the Fmr1 knockout (KO) mouse which lacks FMRP expression, inhibited the proper elaboration of dendritic processes of neurons in vitro. Furthermore, astrocytic conditioned medium (ACM) from KO astrocytes inhibited proper dendritic growth of both wild-type (WT) and KO neurons. Inducing expression of FMRP by transfection of FMRP vectors in KO astrocytes restored dendritic morphology and levels of synaptic proteins. Further experiments revealed elevated levels of the neurotrophin-3 (NT-3) in KO ACM and the prefrontal cortex of Fmr1 KO mice. However, the levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), and ciliary neurotrophic factor (CNTF) were normal. FMRP has multiple RNA-binding motifs and is involved in translational regulation. RNA-binding protein immunoprecipitation (RIP) showed the NT-3 mRNA interacted with FMRP in WT astrocytes. Addition of high concentrations of exogenous NT-3 to culture medium reduced the dendrites of neurons and synaptic protein levels, whereas these measures were ameliorated by neutralizing antibody to NT-3 or knockdown of NT-3 expression in KO astrocytes through short hairpin RNAs (shRNAs). Prefrontal cortex microinjection of WT astrocytes or NT-3 shRNA infected KO astrocytes rescued the deficit of trace fear memory in KO mice, concomitantly decreased the NT-3 levels in the prefrontal cortex. This study indicates that excessive NT-3 from astrocytes contributes to the abnormal neuronal dendritic development and that astrocytes could be a potential therapeutic target for FXS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Astrocytes* / cytology
  • Astrocytes* / metabolism
  • Cells, Cultured
  • Culture Media, Conditioned
  • Dendrites / physiology
  • Disease Models, Animal
  • Fragile X Mental Retardation Protein* / genetics
  • Fragile X Mental Retardation Protein* / metabolism
  • Fragile X Syndrome* / genetics
  • Fragile X Syndrome* / metabolism
  • Mice
  • Mice, Knockout
  • Nerve Growth Factors* / genetics
  • Nerve Growth Factors* / metabolism
  • Neurons / cytology
  • Neurons / physiology
  • Protein Binding
  • RNA-Binding Proteins / genetics
  • RNA-Binding Proteins / metabolism

Substances

  • Culture Media, Conditioned
  • Fmr1 protein, mouse
  • Nerve Growth Factors
  • RNA-Binding Proteins
  • neurotropin 3, mouse
  • Fragile X Mental Retardation Protein

Grants and funding

This work was supported by National Natural Science Foundation of China (31070923, 31271144, 2011ZXJ09106-01C, and Program for New Century Excellent Talents in University). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.