Biology subjects

Schmitt, F.

Publications and source records attributed to Schmitt, F..

8 recordsLinked to original sources

bioRxiv2025

Resting calcium ion fluxes protect cells from fast mitochondrial fragmentation, cell stress responses, and immediate transcriptional reprogramming

Homeostatic calcium ion (Ca2+) fluxes between the endoplasmic reticulum, cytosol, and extracellular space occur not only in response to cell stimulation but also in unstimulated cells. Using murine astrocytes as a model, we asked whether there is a signaling function of these resting Ca2+-fluxes. The data showed that endoplasmic reticulum (ER) Ca{superscript 2} depletion, induced by sarcoplasmic/endoplasmic reticulum Ca{superscript 2}-ATPase (SERCA) inhibition, resulted to prolonged Ca{superscript 2} influx and mitochondrial fragmentation within 10 to 30 minutes. This mitochondrial fragmentation could be prevented in Ca2+- free medium or by inhibiting store-operated Ca2+ entry (SOCE). Similarly, attenuation of STIM proteins, which are vital ER Ca2+ sensors, protected mitochondrial morphology. On the molecular level, ER Ca2+ depletion, achieved either by removing extracellular Ca2+ or through acute SERCA inhibition, led to changes in gene expression of about 13% and 41% of the transcriptome within an hour, respectively. Transcriptome changes were associated with universal biological processes such as transcription, differentiation, or cell stress. Strong increase in expression was observed for the transcription factor ATF4, which is under control of the kinase PERK (EIF2AK3), a key protein involved in ER stress. Corroborating these findings, PERK was rapidly phosphorylated in Ca2+-free medium or after acute pharmacological inhibition of SOCE. In summary, resting, homeostatic Ca2+ fluxes prevent immediate- early cell stress and transcriptional reprogramming.

physiology↗

bioRxiv2024

Vertical sleeve gastrectomy in rodents: impact on metabolic, cardiovascular and hepatic functions of mothers and perinatal consequences

BackgroundMaternal obesity is a well-known risk factor for obstetrical complications during pregnancy, and cardiovascular and metabolic pathologies in the offspring. In the last two decades, bariatric surgery has emerged as the most effective treatment for severe obesity, and is known to improve fertility, leading to a rise in procedures among women of childbearing age. ObjectivesThis study investigates the impact of pre-conceptional sleeve gastrectomy (SG) on metabolic, cardiovascular and hepatic functions of mothers at short and middle terms after surgery, and its perinatal consequences. MethodsSprague-Dawley female control rats (CM) received a standard diet, while others were fed a high-fat, high-sugar diet (HFHS). HFHS rats were divided into obese mothers (OM) and sleeve gastrectomy mothers (SM). One month after surgery, all groups underwent gestation and subsequent lactation Metabolic function was assessed at 1 and 4 months after surgery; cardiovascular and hepatic functions were evaluated only 4 months after SG. ResultsFrom 1 month post-surgery, SM showed normalized leptin and insulin levels compared to OM. Moreover, SG normalized body weight associated with a decreased white adipose tissue weight and adipocyte size at 4 months post-surgery. Interestingly, although steatosis has been detected in HFHS rats, SM exhibited only hepatic fibrosis at 4 months post-surgery. Moreover, SM showed a hypertrophic remodeling of thoracic aorta without effect on its vasoreactivity but along with endothelial dysfunction of mesenteric artery, associated with a stronger involvement of COX/PGI2 pathway. In the offspring, obesity in mothers was associated to a decreased liter size, reversed by sleeve gastrectomy without any effect on the birth weight of pups. ConclusionWhile this study reports an improvement of metabolic function at short- and medium-terms after bariatric surgery, our results highlight an alteration of hepatic and vascular functions by sleeve gastrectomy, with minimal effect on the offspring in the perinatal period.

physiology↗

bioRxiv2024

Effects of vertical sleeve gastrectomy prior to pregnancy on bone mass, microarchitecture and material properties in the female rat

Obesity is a major public health issue worldwide. Despite various approaches to weight loss, the most effective technique for reducing obesity, as well as diabetes and associated diseases, is bariatric surgery. Increasingly, young women without children are undergoing bariatric surgery, vertical sleeve gastrectomy (VSG) being the most common procedure nowadays. However, despite several reports suggesting bone loss after VSG, little is known about the potential additive effects of gestation and lactation after VSG to bone health. This study investigated the combined effects of pre-gestational VSG and subsequent gestation/lactation on bone metabolism in a rat model fed a high fat high sugar (HFHS) diet, with a focus on bone biomechanics, mass, microarchitecture and material properties. Furthermore, bone mass and remodelling was followed longitudinally by microCT prior to surgery, 4 weeks post-surgery, after weaning and at sacrifice. Significant alterations in bone mass and microarchitecture, characterized by changes in trabecular thickness and number, as well as changes in bone formation and resorption were influenced by both surgery and reproductive demands. Mechanical testing at sacrifice demonstrated compromised long bone fragility, in rat with HFHS regardless of the surgical procedure (Sham or VSG). Furthermore, analysis of bone material properties highlighted potential disruptions in the pattern of bone mineralization in sham and VSG animals fed a HFHS diet. These findings underscore the complex interplay between pre-gestational VSG and subsequent gestation/lactation in modulating bone metabolism. Understanding these combined effects is essential for optimizing surgical strategies and developing targeted interventions to mitigate potential bone-related complications associated with VSG in reproductive-aged individuals.

physiology↗

bioRxiv2024

Deciphering the impact of cancer cells secretome and its derived-peptide VGF on breast cancer brain metastasis

Brain metastases (BM) are one of the most serious clinical problems in breast cancer (BC) progression, associated with lower survival rates and a lack of effective therapies. Thus, to dissect the early stages of the brain metastatic process, we have searched for a brain-tropic metastatic signature on BC cells secretome, as a promising source for the discovery of new biomarkers involved in brain metastatic progression. Therefore, six specifically deregulated peptides were found to be enriched in the secretome of brain organotropic BC cells. Importantly, these secretomes caused significant blood-brain barrier (BBB) disruption, as well as microglial activation, in vitro and in vivo. We identified the VGF nerve growth factor inducible as a brain-specific peptide, promoting BBB dysfunction similar to the secretome of brain organotropic BC cells. Concerning microglial activation, a slight increase was also observed upon VGF treatment. In a series of human breast tumors, VGF was found to be expressed in both cancer cells and in the adjacent stroma. VGF-positive tumors showed a significant worse prognosis and were associated with HER2 overexpression and triple-negative molecular signatures. Finally, in a cohort including primary breast tumors and their corresponding metastatic locations to the lung, bone, and brain, we found that VGF significantly correlates with the brain metastatic site. In conclusion, we found a specific BC brain metastatic signature, where VGF was identified as a key mediator in this process. Importantly, its expression was associated with poor prognosis for BC patients, probably due to its associated increased risk of developing BM.

cancer biology↗

bioRxiv2022

Intermediate Gray Matter Interneurons in the Lumbar Spinal Cord Play a Critical and Necessary Role in Coordinated Locomotion

Locomotion is a complex task involving excitatory and inhibitory circuitry in spinal gray matter. While genetic knockouts examine the function of unique spinal interneuron (SpIN) subtypes, the phenotype of combined premotor interneuron loss remains to be explored. We modified a kainic acid lesion to damage intermediate gray matter (laminae V-VII) in the lumbar spinal enlargement (spinal L2-L4) in female rats. A thorough, tailored behavioral evaluation revealed deficits in gross hindlimb function, skilled walking, coordination, balance and gait two-weeks post-injury. Using a Random Forest algorithm, we combined these behavioral assessments into a highly predictive binary classification system which strongly correlated with structural deficits in the rostro-caudal axis. Machine-learning quantification confirmed interneuronal damage to laminae V-VII in spinal L2-L4 correlates with hindlimb dysfunction. White matter damage and lower motoneuron loss did not correlate with behavioral deficits. Animals do not regain lost sensorimotor function three months after injury, indicating that natural recovery of the spinal cord cannot compensate for loss of laminae V-VII neurons. As spinal cord injuries are often located at spinal enlargements, this research lays the groundwork for new neuroregenerative therapies to replace these lost neuronal pools vital to sensorimotor function. HighlightsO_LIFunctional deficits in coordination, balance, rhythmic walking and gait follow two weeks after a lumbar (L2-L4) intermediate (V-VII) gray matter spinal cord injury in rats C_LIO_LIDeficits correlate with neuronal loss in laminae V-VII in spinal levels L2-L4 but do not correlate with lower motoneuron loss or white matter damage nor do animals show signs of sensory dysfunction due to spinal cord injury C_LIO_LICoordination deficits remain after three months, indicating that natural recovery cannot compensate for this interneuronal loss C_LIO_LINewly developed machine-learning models non-invasively fully classify injured animals by functional readouts equivalent to time-intensive endpoint histological analysis C_LI

neuroscience↗

bioRxiv2022

Rhythmic interactions between the mediodorsal thalamus and prefrontal cortex precede human visual perception

The thalamus is much more than a simple sensory relay. High-order thalamic nuclei, such as the mediodorsal thalamus, exert a profound influence over animal cognition. However, given the difficulty of directly recording from the thalamus in humans, next-to-nothing is known about thalamic and thalamocortical contributions to human cognition. To address this, we analysed simultaneously-recorded thalamic iEEG and whole-head MEG in six patients (four female, two male; plus MEG recordings from twelve healthy controls) as they completed a visual detection task. We observed that the phase of both ongoing mediodorsal thalamic and prefrontal low-frequency activity was predictive of perceptual performance. Critically however, mediodorsal thalamic activity mediated prefrontal contributions to perceptual performance. These results suggest that it is thalamocortical interactions, rather than cortical activity alone, that is predictive of upcoming perceptual performance and, more generally, highlights the importance of accounting for the thalamus when theorising about cortical contributions to human cognition.

neuroscience↗

bioRxiv2021

Neonicotinoid and pyrethroid combination: A tool to manage insecticide resistance in malaria vectors? Insights from experimental evolution

BackgroundThe introduction of neonicotinoids for managing insecticide resistance in mosquitoes is of high interest as they interact with a biochemical target not previously used in public health. In this concern, Bayer developed a combination of the neonicotinoid clothianidin and the pyrethroid deltamethrin (brand name Fludora(R) Fusion) as a new vector control tool. Although this combination proved to be efficient against pyrethroid-resistant mosquitoes, its ability to prevent the selection of pyrethroid and neonicotinoid resistance alleles was not investigated. In this context, the objective of this work was to study the dynamics and the molecular mechanisms of resistance of An. gambiae to the separated or combined components of this combination. A field-derived An. gambiae line carrying resistance alleles to multiple insecticides at low frequencies was used as a starting for 33 successive generations of controlled selection. Resistance levels to each insecticide and target site mutation frequencies were monitored throughout the selection process. Cross resistance to other public health insecticides were also investigated. RNA-seq was used to compare gene transcription variations and polymorphisms across all lines. ResultsThis study confirmed the potential of this insecticide combination to impair the selection of resistance as compared to its two separated components. Deltamethrin selection led to the rapid enrichment of the kdr L1014F target-site mutation while clothianidin selection led to the over-transcription of multiple cytochrome P450s including some showing high homology with the ones conferring neonicotinoid resistance in other insects. A strong selection signature associated with clothianidin selection was observed on a cytochrome P450 gene cluster previously associated with resistance. Within this cluster, the gene CYP6M1 showed the highest selection signature together with a transcription profile supporting a role in clothianidin resistance. Modelling the impact of point mutations selected by clothianidin on CYP6M1 protein structure suggested that the selection of variants affecting its active site can enhance clothianidin metabolism. ConclusionsIn the context of the recent deployment of neonicotinoids for mosquito control and their frequent usage in agriculture, the present study highlights the benefit of combining them with other insecticides for preventing the selection of resistance and sustaining vector control activities.

evolutionary biology↗

bioRxiv2020

HPM Live μ for full CLEM workflow

With the development of advanced imaging methods that took place in the last decade, the spatial correlation of microscopic and spectroscopic information - known as multimodal imaging or correlative microscopy (CM) - has become a broadly applied technique to explore biological and biomedical materials at different length scales. Among the many different combinations of techniques, Correlative Light and Electron Microscopy (CLEM) has become the flagship of this revolution. Where light (mainly fluorescence) microscopy can be used directly for the live imaging of cells and tissues, for almost all applications, electron microscopy (EM) requires fixation of the biological materials. Although sample preparation for EM is traditionally done by chemical fixation and embedding in a resin, rapid cryogenic fixation (vitrification) has become a popular way to avoid the formation of artefacts related to the chemical fixation/embedding procedures. During vitrification, the water in the sample transforms into an amorphous ice, keeping the ultrastructure of the biological sample as close as possible to the native state. One immediate benefit of this cryo-arrest is the preservation of protein fluorescence, allowing multi-step multi-modal imaging techniques for CLEM. To further explore the potential of cryo-fixation, we developed a high-pressure freezing (HPF) system that allows vitrification under different environmental parameters and applied it in different CLEM workflows. In this chapter, we introduce our novel HPF live instrument with a focus on its coupling to a light microscope. We elaborate on the optimization of sample preservation and the time needed to capture a biological event, going from live imaging to cryo-arrest using HPF. We will address the adaptation of HPF to novel correlation workflows related to the forthcoming transition from imaging 2D (cell monolayers) to imaging 3D samples (tissue) and the associated importance of homogeneous deep vitrification. Lastly, we will discuss the potential of our HPM within CLEM protocols especially for correlating live imaging using the Zeiss LSM900 with electron microscopy.

biophysics↗