Platelets as a surrogate disease model of neurodevelopmental disorders: Insights from Fragile X Syndrome.

Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability and the leading monogenic cause of autism spectrum disorders (ASD). Despite a large number of therapeutics developed in past years, there is currently no targeted treatment approved for FXS. In fact, translation of the positive and very promising preclinical findings from animal models to human subjects has so far fallen short owing in part to the low predictive validity of the Fmr1 ko mouse, an overly simplistic model of the complex human disease. This issue stresses the critical need to identify new surrogate human peripheral cell models of FXS, which may in fact allow for the identification of novel and more efficient therapies. Of all described models, blood platelets appear to be one of the most promising and appropriate disease models of FXS, in part owing to their close biochemical similarities with neurons. Noteworthy, they also recapitulate some of FXS neuron's core molecular dysregulations, such as hyperactivity of the MAPK/ERK and PI3K/Akt/mTOR pathways, elevated enzymatic activity of MMP9 and decreased production of cAMP. Platelets might therefore help furthering our understanding of FXS pathophysiology and might also lead to the identification of disease-specific biomarkers, as was shown in several psychiatric disorders such as schizophrenia and Alzheimer's disease. Moreover, there is additional evidence suggesting that platelet signaling may assist with prediction of cognitive phenotype and could represent a potent readout of drug efficacy in clinical trials. Globally, given the neurobiological overlap between different forms of intellectual disability, platelets may be a valuable window to access the molecular underpinnings of ASD and other neurodevelopmental disorders (NDD) sharing similar synaptic plasticity defects with FXS. Platelets are indeed an attractive model for unraveling pathophysiological mechanisms involved in NDD as well as to search for diagnostic and therapeutic biomarkers.

Effect of manufacturing and experimental conditions on the mechanical and surface properties of silicone elastomer scaffolds used in endothelial mechanobiological studies.

BACKGROUND: Mechanobiological studies allow the characterization of cell response to mechanical stresses. Cells need to be supported by a material with properties similar to the physiological environment. Silicone elastomers have been used to produce various in vitro scaffolds of different geometries for endothelial cell studies given its relevant mechanical, optical and surface properties. However, obtaining defined and repeatable properties is a challenge as depending on the different manufacturing and processing steps, mechanical and surface properties may vary significantly between research groups. METHODS: The impact of different manufacturing and processing methods on the mechanical and surface properties was assessed by measuring the Young's modulus and the contact angle. Silicone samples were produced using different curing temperatures and processed with different sterilization techniques and hydrophilization conditions. RESULTS: Different curing temperatures were used to obtain materials of different stiffness with a chosen silicone elastomer, i.e. Sylgard 184®. Sterilization by boiling had a tendency to stiffen samples cured at lower temperatures whereas UV and ethanol did not alter the material properties. Hydrophilization using sulphuric acid allowed to decrease surface hydrophobicity, however this effect was lost over time as hydrophobic recovery occurred. Extended contact with water maintained decreased hydrophobicity up to 7 days. Mechanobiological studies require complete cell coverage of the scaffolds used prior to mechanical stresses exposure. Different concentrations of fibronectin and collagen were used to coat the scaffolds and cell seeding density was varied to optimize cell coverage. CONCLUSION: This study highlights the potential bias introduced by manufacturing and processing conditions needed in the preparation of scaffolds used in mechanobiological studies involving endothelial cells. As manufacturing, processing and cell culture conditions are known to influence cell adhesion and function, they should be more thoroughly assessed by research groups that perform such mechanobiological studies using silicone.

SARS-CoV-2 mRNA vaccine-induced immune responses in rheumatoid arthritis.

Our objective was to characterize T and B cell responses to vaccination with SARS-CoV-2 antigens in immunocompromised rheumatoid arthritis (RA) patients. In 22 RA patients, clinical and biological variables were analyzed before and 4 weeks after each of 3 messenger RNA (mRNA) vaccine doses and compared with unmatched healthy individuals. Sequentially sampled peripheral blood mononuclear cells and sera were collected to determine immune profiles and to analyze the T cell response to a spike peptide pool and B cell specificity to the receptor-binding domain (RBD). Anti-spike antibodies were detectable in 6 of 22 RA patients after 1 dose of vaccine with increasing titers after each booster dose, although the overall response was lower compared with that in healthy control individuals. Responding patients after the first dose were more likely to have RA antibodies and a higher baseline proportion of circulating follicular B cells. In RA patients, the mRNA vaccine elicited a robust CD4+ T response to a spike peptide pool following the first and second doses. Consistent with the serologies, RBD-specific B cells exhibited a modest increase after the first dose and the second dose resulted in marked increases only in a fraction of the RA patients to both ancestral and omicron RBD. Our results highlight the importance of multidose COVID-19 vaccination in RA patients to develop a protective humoral response. However, these patients rapidly develop specific T CD4+ responses, despite delayed B cell responses.

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.

New insights of altered lipid profile in Fragile X Syndrome.

BACKGROUND: Fragile X Syndrome (FXS) is the main genetic cause of autism and intellectual deficiency resulting the absence of the Fragile X Mental Retardation Protein (FMRP). Clinical picture is characterized by cognitive impairment associated with a broad spectrum of psychiatric comorbidities including autism spectrum disorders and attention-deficit/hyperactivity disorders. Some of these disorders have been associated with lipid abnormalities and lower cholesterol levels. Since lipids are important for neuronal development, we aim to investigate the lipid profile of French Canadian-FXS individuals and to identify the altered components of cholesterol metabolism as well as their association with clinical profile. METHODS: Anthropometric data were collected from 25 FXS individuals and 26 controls. Lipid assessment included: total cholesterol (TC), triglycerides, LDL, HDL, ApoB, ApoA1, PCSK9, Lp(a) and lipoprotein electrophoresis. Aberrant and adaptive behaviour of affected individuals was respectively assessed by the ABC-C and ABAS questionnaires. RESULTS: FXS participants had a higher body mass index as compared to controls while 38% of them had TC<10th percentile. Lower levels of LDL, HDL and apoA1 were observed in FXS group as compared to controls. However, PCSK9 levels did not differ between the two groups. As expected, PCSK9 levels correlated with total cholesterol (rs = 0.61, p = 0.001) and LDL (rs = 0.46, p = 0.014) in the control group, while no association was present in the FXS group. An inverse relationship was observed between total cholesterol and aberrant behaviour as determined by ABC-C total score. CONCLUSION: Our results showed the presence of hypocholesterolemia in French Canadian-FXS population, a condition that seems to influence their clinical phenotype. We identified for the first time a potential underlying alteration of PCSK9 function in FXS that could result from the absence of FMRP. Further investigations are warranted to better understand the association between cholesterol metabolism, PCSK9, FMRP and clinical profile.