Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice - PubMed (original) (raw)

Rescue of behavioral phenotype and neuronal protrusion morphology in Fmr1 KO mice

Femke M S de Vrij et al. Neurobiol Dis. 2008 Jul.

Abstract

Lack of fragile X mental retardation protein (FMRP) causes Fragile X Syndrome, the most common form of inherited mental retardation. FMRP is an RNA-binding protein and is a component of messenger ribonucleoprotein complexes, associated with brain polyribosomes, including dendritic polysomes. FMRP is therefore thought to be involved in translational control of specific mRNAs at synaptic sites. In mice lacking FMRP, protein synthesis-dependent synaptic plasticity is altered and structural malformations of dendritic protrusions occur. One hypothesized cause of the disease mechanism is based on exaggerated group I mGluR receptor activation. In this study, we examined the effect of the mGluR5 antagonist MPEP on Fragile X related behavior in Fmr1 KO mice. Our results demonstrate a clear defect in prepulse inhibition of startle in Fmr1 KO mice, that could be rescued by MPEP. Moreover, we show for the first time a structural rescue of Fragile X related protrusion morphology with two independent mGluR5 antagonists.

PubMed Disclaimer

Figures

Fig.1

Fig.1. Rescue of prepulse inhibition of startle in Fmr1 KO mice

Both wild type and Fmr1 KO mice were subjected to prepulse inhibition of startle procedures. Fmr1 KO mice displayed a dramatic impairment of PPI on day 1 (baseline levels). This reduction was rescued to wild type levels on day 2 by injection of 20 mg/kg MPEP 30 minutes prior to training. Interestingly, the wild types showed an equal improvement of PPI performance after injection of MPEP.

Fig.2

Fig.2

Representative image of a wild type E18 hippocampal mouse neuron (DIV21), transfected with a β-actin-mCherry construct.

Fig.3

Fig.3. Dendrite branching is normal in Fmr1 KO primary hippocampal neurons

Sholl analysis of wild type and Fmr1 KO primary hippocampal neurons cultured in parallel was performed with Metamorph software. Average of three independent experiments.

Fig.4

Fig.4. Fmr1 KO primary hippocampal neurons have an immature protrusion phenotype

Protrusion densities of wild type and Fmr1 KO primary hippocampal neurons cultured in parallel were counted with Metamorph software. Fmr1 KO neurons had significantly more filopodia than wild type neurons (p<0,001), corresponding to an immature phenotype. Averages of 3 independent experiments, compared with Student's T tests. The distinction between spines and filopodia was made objectively by using a threshold ratio of 0,5 for the width/length ratio of protrusions.

Fig.5

Fig.5. Rescue of protrusion morphology in Fmr1 KO primary hippocampal neurons

Fmr1 KO and wild type neurons were treated for four hours with 200 μm MPEP or 300 μm fenobam. The total amount of protrusions (A) and the amount of mature spines (B) were unaffected by mGluR5 antagonist treatment. The Fmr1 KO phenotype showing an increased number of filopodia was completely rescued by both mGluR5 antagonists (C). Averages of 3 independent experiments, compared with Student's T tests (*=p<0,05, **=p<0,01).

Fig.6

Fig.6. mGluR5 antagonist treatment changes the distribution of spines and filopodia in Fmr1 KO neurons

The average spine/filopodia ratio changes significantly in Fmr1 KO primary hippocampal neurons after treatment with two independent mGluR5 antagonists. As total protrusion density is not different between wild type and Fmr1 KO neurons, we can conclude that the excess of filopodia in Fmr1 KO neurons can successfully be changed into or replaced by spines.

Similar articles

Cited by

References

    1. Antar LN, et al. Localization of FMRP-associated mRNA granules and requirement of microtubules for activity-dependent trafficking in hippocampal neurons. Genes Brain Behav. 2005;4:350–9. - PubMed
    1. Antar LN, et al. Local functions for FMRP in axon growth cone motility and activity-dependent regulation of filopodia and spine synapses. Mol Cell Neurosci. 2006;32:37–48. - PubMed
    1. Bagni C, Greenough WT. From mRNP trafficking to spine dysmorphogenesis: the roots of fragile X syndrome. Nat Rev Neurosci. 2005;6:376–87. - PubMed
    1. Bakker CE, et al. Fmr1 knockout mice: A model to study fragile X mental retardation. Cell. 1994;78:23–33. - PubMed
    1. Bardoni B, et al. The fragile X syndrome: exploring its molecular basis and seeking a treatment. Expert Rev Mol Med. 2006;8:1–16. - PubMed

Publication types

MeSH terms

Substances

Grants and funding

LinkOut - more resources