Altered mTOR signaling and enhanced CYFIP2 expression levels in subjects with Fragile X syndrome

Center for Neural Science, New York University, New York, NY, USA.
Genes Brain and Behavior (Impact Factor: 3.66). 01/2012; 11(3):332-41. DOI: 10.1111/j.1601-183X.2012.00768.x
Source: PubMed


Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and autism. The protein (FMRP) encoded by the fragile X mental retardation gene (FMR1), is an RNA-binding protein linked to translational control. Recently, in the Fmr1 knockout mouse model of FXS, dysregulated translation initiation signaling was observed. To investigate whether an altered signaling was also a feature of subjects with FXS compared to typical developing controls, we isolated total RNA and translational control proteins from lymphocytes of subjects from both groups (38 FXS and 14 TD). Although we did not observe any difference in the expression level of messenger RNAs (mRNAs) for translational initiation control proteins isolated from participant with FXS, we found increased phosphorylation of the mammalian target of rapamycin (mTOR) substrate, p70 ribosomal subunit 6 kinase1 (S6K1) and of the mTOR regulator, the serine/threonine protein kinase (Akt), in their protein lysates. In addition, we observed increased phosphorylation of the cap binding protein eukaryotic initiation factor 4E (eIF4E) suggesting that protein synthesis is upregulated in FXS. Similar to the findings in lymphocytes, we observed increased phosphorylation of S6K1 in brain tissue from patients with FXS (n = 4) compared to normal age-matched controls (n = 4). Finally, we detected increased expression of the cytoplasmic FMR1-interacting protein 2 (CYFIP2), a known FMRP interactor. This data verify and extend previous findings using lymphocytes for studies of neuropsychiatric disorders and provide evidence that misregulation of mTOR signaling observed in the FXS mouse model also occurs in human FXS and may provide useful biomarkers for designing targeted treatments in FXS.

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Available from: Flora Tassone, Aug 27, 2014
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    • "ls of other candidate molecules up - and downstream of mTORC1 - S6K1 and ERK in our search for reliable markers . We did not find any candidates that were reliably dysregulated in our cohort of FXS patients . In particular , we had expected to find enhanced p - Akt levels as previously ob - served in peripheral blood leukocytes from FXS patients [ Hoeffer et al . , 2012 ] ; the lack of a robust effect highlights cell type specific differences in regulation of the signaling that controls translation . Although group differences are important to ascertain disease phenotypes , interindividual variability determines the differential response to therapy in all diseases . This aspect has become critical to t"
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    ABSTRACT: Fragile X Syndrome (FXS) is the most frequent cause of inherited intellectual disability and autism. It is caused by the absence of the fragile X mental retardation 1 (FMR1) gene product, FMRP, an RNA-binding protein involved in the regulation of translation of a subset of brain mRNAs. In Fmr1 knockout (KO) mice, the absence of FMRP results in elevated protein synthesis in the brain as well as increased signaling of many translational regulators. Whether protein synthesis is also dysregulated in FXS patients is not firmly established. Here, we demonstrate that fibroblasts from FXS patients have significantly elevated rates of basal protein synthesis along with increased levels of phosphorylated mechanistic target of rapamycin (p-mTOR), phosphorylated extracellular signal regulated kinase 1/2 (p-ERK 1/2) and phosphorylated p70 ribosomal S6 kinase 1 (p-S6K1). Treatment with small molecules that inhibit S6K1, and a known FMRP target, phosphoinositide 3-kinase (P13K) catalytic subunit p110β, lowered the rates of protein synthesis in both control and patient fibroblasts. Our data thus demonstrate that fibroblasts from FXS patients may be a useful in vitro model to test the efficacy and toxicity of potential therapeutics prior to clinical trials, as well as for drug screening and designing personalized treatment approaches.This article is protected by copyright. All rights reserved
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    • "In the future, there may be biomarkers that can pinpoint for high risk for ASD diagnosis. For example, a mother who may be high risk for immune dysfunction leading to ASD in a second child once the first child has ASD (29) or the increase in the Akt-mTOR pathway, which can be seen in fragile X syndrome and in other ASD subtypes (30). "
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    ABSTRACT: Autism spectrum disorders (ASDs) are complex, heterogeneous disorders caused by an interaction between genetic vulnerability and environmental factors. In an effort to better target the underlying roots of ASD for diagnosis and treatment, efforts to identify reliable biomarkers in genetics, neuroimaging, gene expression, and measures of the body's metabolism are growing. For this article, we review the published studies of potential biomarkers in autism and conclude that while there is increasing promise of finding biomarkers that can help us target treatment, there are none with enough evidence to support routine clinical use unless medical illness is suspected. Promising biomarkers include those for mitochondrial function, oxidative stress, and immune function. Genetic clusters are also suggesting the potential for useful biomarkers.
    Full-text · Article · Aug 2014 · Frontiers in Psychiatry
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    • "Given the En2-IGF1 interaction we describe, one might speculate whether altered EN2 expression may coincide with abnormal IGF1 to contribute to ASD pathogenesis, a question that remains to be investigated. From a therapeutic perspective, the Akt-mTOR-S6K pathway is dysregulated in multiple animal models of monogenic causes of ASD including fragile X mental retardation [108], Rett syndrome [109] and tuberous sclerosis [110], whereas IGF1 ligands may improve neurodevelopmental symptoms in Rett [111] and the SHANK3 autism-related mouse model of Phelan-McDermid syndrome [112]. It is intriguing that yet another autism-associated gene, in this case EN2, implicates disordered Akt-mTOR-S6K signaling in the disease phenotype [113]. "
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    ABSTRACT: The homeobox transcription factor Engrailed2 (En2) has been studied extensively in neurodevelopment, particularly in the midbrain/hindbrain region and cerebellum, where it exhibits dynamic patterns of expression and regulates cell patterning and morphogenesis. Because of its roles in regulating cerebellar development and evidence of cerebellar pathology in autism spectrum disorder (ASD), we previously examined an ENGRAILED2 association and found evidence to support EN2 as a susceptibility gene, a finding replicated by several other investigators. However, its functions at the cell biological level remain undefined. In the mouse, En2 gene is expressed in granule neuron precursors (GNPs) just as they exit the cell cycle and begin to differentiate, raising the possibility that En2 may modulate these developmental processes. To define En2 functions, we examined proliferation, differentiation and signaling pathway activation in En2 knockout (KO) and wild-type (WT) GNPs in response to a variety of extracellular growth factors and following En2 cDNA overexpression in cell culture. In vivo analyses of cerebellar GNP proliferation as well as responses to insulin-like growth factor-1 (IGF1) treatment were also conducted. Proliferation markers were increased in KO GNPs in vivo and in 24-h cultures, suggesting En2 normally serves to promote cell cycle exit. Significantly, IGF1 stimulated greater DNA synthesis in KO than WT cells in culture, a finding associated with markedly increased phospho-S6 kinase activation. Similarly, there was three-fold greater DNA synthesis in the KO cerebellum in response to IGF1 in vivo. On the other hand, KO GNPs exhibited reduced neurite outgrowth and differentiation. Conversely, En2 overexpression increased cell cycle exit and promoted neuronal differentiation. In aggregate, our observations suggest that the ASD-associated gene En2 promotes GNP cell cycle exit and differentiation, and modulates IGF1 activity during postnatal cerebellar development. Thus, genetic/epigenetic alterations of EN2 expression may impact proliferation, differentiation and IGF1 signaling as possible mechanisms that may contribute to ASD pathogenesis.
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