Biology subjects

Gautier, H.

Publications and source records attributed to Gautier, H..

3 recordsLinked to original sources

bioRxiv2024

Neurons as biosensors for discriminating neurological disorders in a brain-on-chip platform: Application to Alzheimer s Disease using patient CSF

Alzheimers disease (AD) is characterized by the accumulation of aggregated amyloid beta peptide (A{beta}) leading to progressive neuronal loss and dysfunction. Current ADs diagnosis involves biomarkers assays in cerebrospinal fluid (CSF) as A{beta} to validate the diagnosis. However, these methods are time-consuming, expensive, and can result in inaccurate diagnoses by not accounting for differential diagnose. To overcome these challenges, researchers are exploring new technologies for detecting AD biomarkers in biological fluids, though progress is hindered by an incomplete understanding of AD mechanisms and CSF composition. In this study, we used a standardized microfluidic platform to investigate the effects of synthetic A{beta} peptides and cerebrospinal fluid (CSF) from AD and healthy patients on neuronal functional activity. First, human neurons derived from induced pluripotent stem cells (iPSCs) were characterized. Then, to modulate the functional activity of neurons, tetrodotoxin (TTX), a specific sodium channel blocker, was used as a control for inhibiting neuronal activity. Subsequently, glutamatergic neurons were chronically exposed to A{beta}O and patients CSF. MEA recordings were performed before and after the treatments to assess changes in network activity. Our results demonstrated that extracting key electrophysiological metrics allows for discrimination between healthy and AD CSF samples. This system could offer the potential for differential diagnosis and development of personalized therapeutic strategies.

neuroscience↗

bioRxiv2024

Substrate stiffness regulates neuronal maturation via Piezo1-mediated TTR activity

During brain development, neurons extend axons to connect to their target cells while initiating a maturation process during which neurons start expressing voltage-gated ion channels, form synapses, express synaptic transmitters and receptors, and start communicating via action potentials. Little is known about external factors regulating this process. Here, we identified environmental mechanics as an important regulator of neuronal maturation, and a molecular pathway linking tissue stiffness to this process. Using patch clamp electrophysiology, calcium imaging and immunofluorescence, we found that neurons cultured on stiffer substrates showed a delay in voltage-gated ion channel activity, spontaneous and evoked action potentials, and synapse formation. RNA sequencing and CRISPR/Cas9 knockdown revealed that the mechanosensitive ion channel Piezo1 supresses transthyretin (TTR) expression on stiffer substrates, slowing down synapse formation and consequently electrical maturation. In agreement, the stiffness of developing Xenopus laevis brain negatively correlated with local synapse densities, and stiffening of brain tissue resulted in a significant delay of synaptic activity in vivo. Our data indicate that environmental stiffness represents a fundamental regulator of neuronal maturation, which is important for the development of normal circuitry in the brain, and potentially for neurodevelopmental disorders. Furthermore, the mechanical regulation of TTR downstream of Piezo1 may be found in many other biological systems.

developmental biology↗

bioRxiv2021

The biosynthetic pathway of ubiquinone contributes to pathogenicity of Francisella

Francisella tularensis is the causative agent of tularemia. Because of its extreme infectivity and high mortality rate, this pathogen was classified as a biothreat agent. Francisella spp are strict aerobe and ubiquinone (UQ) has been previously identified in these bacteria. While the UQ biosynthetic pathways were extensively studied in Escherichia coli allowing the identification of fifteen Ubi-proteins to date, little is known about Francisella spp. In this study, and using Francisella novicida as a surrogate organism, we first identified UQ8 as the major quinone found in the membranes of this bacterium. Then, we characterized the UQ biosynthetic pathway in F. novicida using a combination of bioinformatics, genetics and biochemical approaches. Our analysis disclosed the presence in Francisella of ten putative Ubi-proteins and we confirmed eight of them by heterologous complementation in E. coli. The UQ biosynthetic pathways from F. novicida and E. coli share a similar pattern. However, differences were highlighted: the decarboxylase remains unidentified in Francisella spp and homologs of the Ubi-proteins involved in the O2-independent UQ pathway are not present. This is in agreement with the strictly aerobic niche of this bacterium. Then, via two approaches, i.e. the use of an inhibitor (3-amino-4-hydroxybenzoic acid) and a transposon mutant, which both strongly impair the synthesis of UQ, we demonstrated that UQ is essential for the growth of F. novicida in a respiratory medium and contributes to its pathogenicity in Galleria mellonella used as an alternative animal model. ImportanceFrancisella tularensis is the causative bacterium of tularemia and is classified as a biothreat agent. Using multidisciplinary approaches, we investigated the ubiquinone (UQ) biosynthetic pathway that operates in F. novicida used as a surrogate. We showed that UQ8 is the major quinone identified in the membranes of Francisella novicida. We identified a new competitive inhibitor, which strongly decreased the biosynthesis of UQ. Our demonstration of the crucial role of UQ for the respiratory metabolism of F. novicida and for the involving in its pathogenicity in the Galleria mellonella model should stimulate the search for selective inhibitors of bacterial UQ biosynthesis.

microbiology↗