Implication of the endocannabidiome and metabolic pathways in fragile X syndrome pathophysiology.

Fragile X Syndrome (FXS) results from the silencing of the FMR1 gene and is the most prevalent inherited cause of intellectual disability and the most frequent monogenic cause of autism spectrum disorder. It is well established that Fragile X individuals are subjected to a wide array of comorbidities, ranging from cognitive, behavioural, and medical origin. Furthermore, recent studies have also described metabolic impairments in FXS individuals. However, the molecular mechanisms linking FMRP deficiency to improper metabolism are still misunderstood. The endocannabinoidome (eCBome) is a lipid-based signalling system that regulates several functions across the body, ranging from cognition, behaviour and metabolism. Alterations in the eCBome have been described in FXS animal models and linked to neuronal hyperexcitability, a core deficit of the disease. However, the potential link between dysregulation of the eCBome and altered metabolism observed in FXS remains unexplored. As such, this review aims to overcome this issue by describing the most recent finding related to eCBome and metabolic dysfunctions in the context of FXS. A better comprehension of this association will help deepen our understanding of FXS pathophysiology and pave the way for future therapeutic interventions.

Cholesterol alterations in fragile X syndrome, autism spectrum disorders and other neurodevelopmental disorders.

Neurodevelopmental disorders (NDDs) are a group of etiologically diverse diseases primarily associated with abnormal brain development, impaired cognition, and various behavioral problems. The majority of NDDs present a wide range of clinical phenotypes while sharing distinct cellular and biochemical alterations. Low plasma cholesterol levels have been reported in a subset of NNDs including, autism spectrum disorder (ASD) and fragile X syndrome (FXS). The present review focuses on cholesterol metabolism and discusses the current evidence of lipid disruption in ASD, FXS, and other genetically related NDDs. The characterization of these common deficits might provide valuable insights into their underlying physiopathology and help identify potential therapeutic targets.

A neuron-specific microexon ablates the novel DNA-binding function of a histone H3K4me0 reader PHF21A.

How cell-type-specific chromatin landscapes emerge and progress during metazoan ontogenesis remains an important question. Transcription factors are expressed in a cell-type-specific manner and recruit chromatin-regulatory machinery to specific genomic loci. In contrast, chromatin-regulatory proteins are expressed broadly and are assumed to exert the same intrinsic function across cell types. However, human genetics studies have revealed an unexpected vulnerability of neurodevelopment to chromatin factor mutations with unknown mechanisms. Here, we report that 14 chromatin regulators undergo evolutionary-conserved neuron-specific splicing events involving microexons. Of the 14 chromatin regulators, two are integral components of a histone H3K4 demethylase complex; the catalytic subunit LSD1 and an H3K4me0-reader protein PHF21A adopt neuron-specific forms. We found that canonical PHF21A (PHF21A-c) binds to DNA by AT-hook motif, and the neuronal counterpart PHF21A-n lacks this DNA-binding function yet maintains H3K4me0 recognition intact. In-vitro reconstitution of the canonical and neuronal PHF21A-LSD1 complexes identified the neuronal complex as a hypomorphic H3K4 demethylating machinery with reduced nucleosome engagement. Furthermore, an autism-associated PHF21A missense mutation, 1285 G>A, at the last nucleotide of the common exon immediately upstream of the neuronal microexon led to impaired splicing of PHF21A -n. Thus, ubiquitous chromatin regulatory complexes exert unique intrinsic functions in neurons via alternative splicing of their subunits and potentially contribute to faithful human brain development.

A new strategy to uncover fragile X proteomic biomarkers using the nascent proteome of peripheral blood mononuclear cells (PBMCs).

Fragile X syndrome (FXS) is the most prevalent inherited cause of intellectual disabilities and autism spectrum disorders. FXS result from the loss of expression of the FMRP protein, an RNA-binding protein that regulates the expression of key synaptic effectors. FXS is also characterized by a wide array of behavioural, cognitive and metabolic impairments. The severity and penetrance of those comorbidities are extremely variable, meaning that a considerable phenotypic heterogeneity is found among fragile X individuals. Unfortunately, clinicians currently have no tools at their disposal to assay a patient prognosis upon diagnosis. Since the absence of FMRP was repeatedly associated with an aberrant protein synthesis, we decided to study the nascent proteome in order to screen for potential proteomic biomarkers of FXS. We used a BONCAT (Biorthogonal Non-canonical Amino Acids Tagging) method coupled to label-free mass spectrometry to purify and quantify nascent proteins of peripheral blood mononuclear cells (PBMCs) from 7 fragile X male patients and 7 age-matched controls. The proteomic analysis identified several proteins which were either up or downregulated in PBMCs from FXS individuals. Eleven of those proteins were considered as potential biomarkers, of which 5 were further validated by Western blot. The gene ontology enrichment analysis highlighted molecular pathways that may contribute to FXS physiopathology. Our results suggest that the nascent proteome of PBMCs is well suited for the discovery of FXS biomarkers.

An "Omic" Overview of Fragile X Syndrome.

Fragile X syndrome (FXS) is a neurodevelopmental disorder associated with a wide range of cognitive, behavioral and medical problems. It arises from the silencing of the fragile X mental retardation 1 (FMR1) gene and, consequently, in the absence of its encoded protein, FMRP (fragile X mental retardation protein). FMRP is a ubiquitously expressed and multifunctional RNA-binding protein, primarily considered as a translational regulator. Pre-clinical studies of the past two decades have therefore focused on this function to relate FMRP's absence to the molecular mechanisms underlying FXS physiopathology. Based on these data, successful pharmacological strategies were developed to rescue fragile X phenotype in animal models. Unfortunately, these results did not translate into humans as clinical trials using same therapeutic approaches did not reach the expected outcomes. These failures highlight the need to put into perspective the different functions of FMRP in order to get a more comprehensive understanding of FXS pathophysiology. This work presents a review of FMRP's involvement on noteworthy molecular mechanisms that may ultimately contribute to various biochemical alterations composing the fragile X phenotype.

Rates of protein synthesis are reduced in peripheral blood mononuclear cells (PBMCs) from fragile X individuals.

BACKGROUND: Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability and is caused by the loss of expression of the Fragile X mental retardation protein (FMRP). In animal model of FXS, the absence of FMRP leads to an aberrant rate of neuronal protein synthesis, which in turn is believed to be at the origin of defects regarding spine morphology and synaptic plasticity. Normalisation of protein synthesis in these models has been associated with a rescue of FXS behavioral and biochemicals phenotype, thus establishing the rate of protein synthesis as one of the most promising monitoring biomarker for FXS. However, rate of protein synthesis alteration in fragile X individuals is not well characterized. METHOD: We applied a robust radiolabeled assay to measure rate of protein synthesis in freshly extracted peripheral blood mononuclear cells (PBMCs) and blood platelets. We ultimately settle on PBMCs to measure and compare rate of protein synthesis in 13 males with fragile X and 14 matched controls individuals. RESULTS: Using this method, we measured a 26.9% decrease (p = 0,0193) in the rate of protein synthesis in fragile X individuals PBMCs. Furthermore, the rate of protein synthesis measurements obtained were highly reproducible, highlighting the robustness of the method. CONCLUSION: Our work presents the first evidence of a diminution of the rate of protein synthesis in a human peripheral model of fragile X. Our results also support the finding of previous studies using brain PET imaging in Fragile X individuals. Since our assay only requires a simple venous puncture, it could be used in other cases of intellectual disability in order to determine if an aberrant rate of protein synthesis is a common general mechanism leading to impairment in synaptic plasticity and to intellectual disability.

Geodesic Binding for Degenerate Character Geometry Using Sparse Voxelization.

We propose a fully automatic method for specifying influence weights for closed-form skinning methods, such as linear blend or dual quaternion skinning. Our method is designed to work with production meshes that may contain non-manifold geometry, be non-watertight, have intersecting triangles, or be comprised of multiple connected components. Starting from a character rest pose mesh and skeleton hierarchy, we first voxelize the input geometry. The resulting sparse voxelization is then used to calculate binding weights, based on the geodesic distance between each voxel lying on a skeleton "bone" and all non-exterior voxels. This yields smooth weights at interactive rates, without time-constants, iteration parameters, or costly optimization at bind or pose time. By decoupling weight assignment from distance computation we make it possible to modify weights interactively, at pose time, without additional pre-processing or computation. This allows artists to assess impact of weight selection in the context in which they are used.