PDE-4 Inhibition Rescues Aberrant Synaptic Plasticity inDrosophilaand Mouse Models of Fragile X Syndrome
Catherine H. ChoiBrian P. SchoenfeldEliana D WeiszAaron BellDaniel B. ChambersJoseph HincheyRichard J. ChoiPaul HincheyMaria KollarosMichael GertnerNeal FerrickAllison M. TerlizziNicole L. YohnEric KoenigsbergDavid A. LiebeltR. Suzanne ZukinNewton H. WooMichael R. TranfagliaNatalia LounevaSteven E. ArnoldSteven J. SiegelFrançois V. BolducThomas V. McDonaldThomas A. JongensSean McBride
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Fragile X syndrome (FXS) is the leading cause of both intellectual disability and autism resulting from a single gene mutation. Previously, we characterized cognitive impairments and brain structural defects in a Drosophila model of FXS and demonstrated that these impairments were rescued by treatment with metabotropic glutamate receptor (mGluR) antagonists or lithium. A well-documented biochemical defect observed in fly and mouse FXS models and FXS patients is low cAMP levels. cAMP levels can be regulated by mGluR signaling. Herein, we demonstrate PDE-4 inhibition as a therapeutic strategy to ameliorate memory impairments and brain structural defects in the Drosophila model of fragile X. Furthermore, we examine the effects of PDE-4 inhibition by pharmacologic treatment in the fragile X mouse model. We demonstrate that acute inhibition of PDE-4 by pharmacologic treatment in hippocampal slices rescues the enhanced mGluR-dependent LTD phenotype observed in FXS mice. Additionally, we find that chronic treatment of FXS model mice, in adulthood, also restores the level of mGluR-dependent LTD to that observed in wild-type animals. Translating the findings of successful pharmacologic intervention from the Drosophila model into the mouse model of FXS is an important advance, in that this identifies and validates PDE-4 inhibition as potential therapeutic intervention for the treatment of individuals afflicted with FXS.Keywords:
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A mouse model for the fragile X syndrome, the most common form of inherited mental retardation, was generated a number of years ago. It shows characteristics compatible with the clinical symptoms of human patients. These include pathological changes such as macroorchidism, behavioral problems, and diminished visuo-spatial abilities. To investigate whether the fragile X syndrome is a potentially correctable disorder, several groups attempted to rescue the knockout mutation by introduction of an intact copy of the FMR1 gene in the knockout mouse. Two different types of rescue mice have been created by injection of constructs based on FMR1 cDNA or on FMR1 genomic DNA. Several pathological, behavioral and cognitive function tests were performed on these two different rescue mouse lines to compare their characteristics with those of the knockout and control littermates. Each rescue line resembled the control in some aspects though neither of the 2 lines was a full rescue, e.g. resemble the control in all aspects investigated. Thus, rescue of some aspects of the phenotype has been achieved by introduction of FMR1 constructs in the fragile X knockout mice. The results implicate that, even if FMR1 production is cell type specific, the quantity of the FMRP expression is highly critical as overproduction may have a harmful effect. Keywords: X Syndrome, FMR1 gene, FMR1 cDNA, reading frame (ORF), KNOCKOUT MUTATION, Transgenesis, YAC VECTOR
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Transgenic fragile X knockout mice have been constructed to provide an animal model to study the physiologic function of the fragile X gene (FMR1) and to gain more insight into the clinical phenotype caused by the absence of the fragile X protein. Initial experiments suggested that the knockout mice show macroorchidism and cognitive and behavioral deficits, abnormalities comparable to those of human fragile X patients. In the present study, we have extended our experiments, and conclude that the Fmr1 knockout mouse is a reliable transgenic model to study the fragile X syndrome. © 1996 Wiley-Liss, Inc.
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Fragile X Syndrome (FXS) is a trinucleotide repeat disorder that results in the silencing of the Fragile X Mental Retardation 1 gene (FMR1), leading to a lack of the FMR1 protein (FMRP). FMRP is an mRNA-binding protein that regulates the translation of hundreds of mRNAs important for synaptic plasticity. Several of these pathways have been identified and have guided the development of targeted treatments for FXS. Here we present evidence that serotonin is dysregulated in FXS and treatment with the selective serotonin reuptake inhibitor (SSRI) sertraline may be beneficial for individuals with FXS, particularly in early childhood.
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Fragile X syndrome, diagnosed by Fragile X Mental Retardation 1 (FMR1) DNA testing, is the most common single-gene cause of inherited intellectual disability. The expanded CGG mutation in the FMR1 gene, once thought to have clinical significance limited to fragile X syndrome, is now well established as the cause for other fragile X-associated disorders including fragile X-associated primary ovarian insufficiency and fragile X-associated tremor ataxia syndrome in individuals with the premutation (carriers). The importance of early diagnostic and management issues, in conjunction with the identification of family members at risk for or affected by FMR1 mutations, has led to intense discussion about the appropriate timing for early identification of FMR1 mutations. This review includes an overview of the fragile X-associated disorders and screening efforts to date, and discussion of the advantages and barriers to FMR1 screening in newborns, during childhood, and in women of reproductive age. Comparison with screening programs for other common genetic conditions is discussed to arrive at action steps to increase the identification of families affected by FMR1 mutations.
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The 5′ untranslated CGG repeat in the fragile X mental retardation-1 (FMR1) gene is expanded in families with fragile X syndrome, with more than 200 CGGs resulting in mental retardation due to the absence of the encoded fragile X mental retardation protein (FMRP). Intermediate and premutation alleles, containing between approximately 40 and 200 repeats, express grossly normal FMRP levels and such carriers are widely believed to be non-penetrant, despite continued reports of subtle cognitive/psychosocial impairment and other phenotypes. Using a highly sensitive quantification assay, we demonstrate significantly diminished FMRP levels in carriers, negatively correlated with repeat number. Despite reduced FMRP, these carrier alleles overexpress FMR1, resulting in a positive correlation between repeat number and FMR1 message level. These biochemical deviations associated with intermediate and premutation FMR1 alleles, found in ∼4% of the population, suggest that the phenotypic spectrum of fragile X syndrome may need to be revisited.
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