Metabolic phenotypes of Fragile X Syndrome – METABOXFRA

We will first investigate a selection of metabolic pathways identified by iMIM, based on their potential importance at the pathophysiological level and yet poorly explored in FXS. Furthermore, we will identify novel pathways involved in the metabotype of FXS by performing the integration of metabolomic data to large-scale “-omics” data derived from analysis of the transcriptome and proteome of FXS mouse model. The pathways predicted in silico in the previous step will be futher validated in vivo. Finally, we will use metabonomics as an analytical and predictive tool to derive transversal metabolic biomarkers of FXS in biofluids (urine, plasma) of mouse and human. This will highlight the systemic dysfunctions in metabolism involved in FXS. The metabolic biomarkers will be used in mouse to establish a metabolomic drug treatment efficacy index in the mouse model of FXS to test therapeutical molecules targeting the pathways identified in the previous steps.

Exploration of the altered metabolic pathways in FXS. To dissect dysfunctions of metabolic pathways in Fmr1-KO mice, we have analysed by quantitative RT-PCR the levels of enzymes and transporters involved in the glutamate/glutamine/GABA and cholinergic pathways. We have confirmed significant deregulations of the enzymes Gad2, Got1, Glud1 and transporter Slc17a8 mRNAs in the cerebellum, which is in line with the described altered levels of glutamate, GABA and glutamine (Davidovic et al., 2011).
Integration of global metabolic deficits to other ì-omicsî alterations in various brain regions of the FXS mouse model. We have now obtained several omics datasets:
-Transcriptomics. We have performed the RNAseq analysis of Fmr1-KO and WT cerebellum and cortices at the IPMC Genomic Platform.
-Metabolomics. LC/GC-MS analysis were performed by Metabolon Inc. (USA) on Fmr1-KO and WT cerebellum and cortices (n=8 per genotype). This analysis complement the initial 1H-NMR metabolic profiling previously performed (Davidovic et al., 2011).
Development of FXS metabolic biomarkers. We have completed the NMR-based metabolic profiling of urinary and plasmatic samples from Fmr1-KO and WT adult mice. This analysis has lead to the identification of several perturbed metabolites). Notably, abnormal urinary excretion of several metabolites and anomalies in plasmatic glucose and amino acids levels were detected in Fmr1-KO mice.

This multidisciplinary project combines molecular approaches to integrative biology to generate novel biological hypotheses to understand the metabolic phenotypes of FXS. Finally, the MetaboXFra project has great translational potential and will lead to the identification of biomarkers and therapeutic targets for FXS.

Dumas, M.-E. & Davidovic, L.* (2013) Metabolic phenotyping and systems biology approaches to understand neurological disorders. F1000Prime Rep. 2013 Jun 3;5:18. doi: 10.12703. (*) corresponding author. PMC3672944

Intellectual Disability (ID) is the main cause of children heavy handicap and is a major social and medical problem. Worldwide, 20-30 millions of individuals are affected by moderate to severe ID. The Fragile X syndrome (FXS) is the first cause of inherited ID, affecting 1/4,000 males and 1/7,000 females and the leading identified genetic cause for autism spectrum disorders (ASD). FXS is caused by mutation and subsequent inactivation of a single X-linked gene, the Fragile X Mental Retardation 1 (FMR1) gene encoding the FMRP protein. Most of the research performed in the Fragile X field reduce this pathology to a synaptopathy, affecting synaptic development and causing ID, owing to the acknowledged role of FMRP in synaptic plasticity. However, we still do not know how this mutation influences and targets molecular pathways at the systemic level leading to the full expression of the disease phenotypes. I have recently published a study using a metabonomics and a systems biology approach to identify a metabolic signature and biomarkers associated with FXS and better understand FXS pathophysiology in its mouse model (Davidovic et al. (2011) A metabolomic and systems biology perspective on the brain of the Fragile X Syndrome mouse model. Genome Research). This landmark study has demonstrated for the first time the existence of a metabolic component in FXS phenotypes (metabotype), which remains yet virtually unexplored. Concomitantly, I have developed an integrative approach, integrated metabolome and interactome mapping (iMIM), which enabled to identify the altered metabolic pathways that directly contribute to FXS metabotype. This study grounds my current working hypothesis which is that certain phenotypes of FXS are underpinned by systemic dysfunctions in metabolism. The purpose of this MetaboXFra basic research proposal is to explore this hypothesis and its biological correlates.
We will first investigate a selection of metabolic pathways identified by iMIM, based on their potential importance at the pathophysiological level and yet poorly explored in FXS. Furthermore, we will identify novel pathways involved in the metabotype of FXS by performing the integration of metabolomic data to large-scale “-omics” data derived from analysis of the transcriptome and proteome of FXS mouse model. The pathways predicted in silico in the previous step will be futher validated in vivo. Finally, we will use metabonomics as an analytical and predictive tool to derive transversal metabolic biomarkers of FXS in biofluids (urine, plasma) of mouse and human. This will highlight the systemic dysfunctions in metabolism involved in FXS. The metabolic biomarkers will be used in mouse to establish a metabolomic drug treatment efficacy index in the mouse model of FXS to test therapeutical molecules targeting the pathways identified in the previous steps.
This multidisciplinary ANR JCJC proposal combines molecular approaches to integrative biology to generate novel biological hypotheses to understand the metabolic phenotypes of FXS. Finally, the MetaboXFra project has great translational potential and will lead to the identification of biomarkers and therapeutic targets for FXS.