Biology subjects

Robert, J.

Publications and source records attributed to Robert, J..

15 recordsLinked to original sources

bioRxiv2026

The protein and lipid compositions of brain apolipoprotein E particles are cell type-specific

Genetic variation in APOE, which encodes a lipid transporter apolipoprotein E (apoE), is the strongest risk factor for late-onset Alzheimer's disease (AD). Although central nervous system (CNS) apoE is produced by various cell types, including astrocytes, microglia, and pericytes, it is unclear whether apoE lipoproteins are a homogeneous population or if their molecular composition varies depending on their cellular origin. Emerging evidence suggests that CNS apoE lipoproteins contribute to AD-related processes, including amyloid deposition, neuroinflammation, synaptic maintenance, and blood-brain barrier function in a cell type-specific manner. We hypothesized that the compositions of CNS apoE lipoproteins depend on their cellular origin and investigated the lipid and protein profiles of apoE particles secreted by induced pluripotent stem cell (iPSC)-derived brain cells and derived from human cerebrospinal fluid (CSF) using liquid chromatography-mass spectrometry (LC-MS/MS). Our results demonstrate that astrocytes, pericytes, and microglia secrete apoE lipoproteins with distinct, cell type-specific lipid and protein profiles. Astrocyte-secreted particles were enriched in sphingomyelins and proteins linked to lipid metabolism, whereas pericyte-secreted particles contained ether-linked phospholipids and proteins associated with antioxidant activity. The lipidation of microglial apoE was markedly lower, but these particles had higher levels of transferrin, apoC-II, and cathepsin D. Notably, one-third of identified features were cell type-specific, highlighting the substantial molecular specialization across cell types. Most lipids and proteins identified in cell-secreted apoE were also detected in CSF-derived particles. Our findings advance the understanding of apoE biology by shifting the focus from apoE as a single, homogeneous entity to a diverse population of complex particles, the composition of which might be linked to functions in health and neurodegenerative diseases.

neuroscience↗

bioRxiv2026

MHC-II acts as a fusion-triggering receptor for bat influenza virus

Influenza A virus hemagglutinin is a prototypical class I viral fusion protein that binds sialylated glycans and is activated by low pH in endosomes. In contrast, bat-derived IAV subtypes H17N10 and H18N11 use major histocompatibility complex class II (MHC-II) as an entry receptor, but how this receptor contributes to membrane fusion remains unknown. We find that MHC-II-dependent hemagglutinin subtypes H17, H18, and H19 possess an increased negative net charge relative to canonical HAs. Using cryo-electron tomography, we demonstrate that H18N11 morphology remains stable and H18 is in prefusion conformation at strongly acidic pH. Remarkably, H18 undergoes fusion-relevant conformational changes only when both MHC-II binding and low pH are present. By reconstitution of H18N11 fusion with liposomes and purified MHC-II, we show that receptor engagement is required to trigger the fusion activity of H18. These findings identify MHC-II as a receptor that directly triggers membrane fusion and reveal a previously unrecognized receptor-dependent mechanism of influenza virus entry. SignificanceBat-derived influenza A viruses (IAV) challenged established paradigms because they use major histocompatibility complex class II (MHC-II) molecules instead of sialylated glycans for cell entry. Recent studies suggest that MHC-II usage extends beyond bats, with avian, swine, and human strains showing dual receptor specificity. However, how MHC-II contributes to membrane fusion has remained unclear. We show that, unlike conventional HAs that are activated by acidity alone, the H18 fusion protein requires receptor engagement and low pH to undergo fusion-relevant conformational changes leading to membrane fusion. Hence, we reveal a novel receptor-dependent mechanism of membrane fusion for the MHC-II dependent entry of H18N11.

microbiology↗

bioRxiv2026

The COPI coatomer influences LDL receptor activity, hepatic lipid storage, and apoB secretion

BackgroundDecreased hepatic removal of low density lipoproteins (LDL) and increased apolipoprotein B (apoB) production cause hypercholesterolemia, a major causal risk factor of atherosclerotic cardiovascular disease (ASCVD). By a genome-wide siRNA screen, we previously identified subunits of the Coat protein I (COPI) complex to limit LDL uptake into Huh-7 hepatocarcinoma cells. MethodsThese findings were validated by targeted in vitro experiments as well as genetic association studies in humans and three mouse models with mutated or disrupted COPI genes. ResultsSilencing of COPA, COPB1, COPB2, ARCN1, COPG1, and COPZ1 in Huh-7 cells resulted in decreased uptake of LDL and aberrant glycosylation and altered cell surface abundance of the LDL receptor (LDLR) as well as increased apoB secretion and cellular lipid storage. Single nucleotide polymorphisms of ARCN1 were associated with lower ARCN1 expression and higher levels of LDL-cholesterol (LDL-C). Rare variants of COPA and COPG1 were enriched among patients with LDL-C > 5 mmol/L. Patients and mice carrying other rare immunopathogenic missense variants of COPA and COPG1 did not present with elevated plasma levels of LDL-C, while hepatic knockdown of murine Copg1 increased the concentrations of non-HDL-cholesterol in plasma and triglycerides in the liver. ConclusionsThe COPI coatomer regulates LDLR activity and apoB secretion as well as lipid content of liver cells. Loss of function of some variants of COPI genes are associated with higher LDL-C levels.

cell biology↗

bioRxiv2026

Glutathione impacts both Batrachochytrium dendrobatidis virulence and amphibian cellular defence in a chytridiomycosis model

Glutathione has important roles in diverse infections, yet its involvement in the interaction between the deadly fungal pathogen Batrachochytrium dendrobatidis (Bd) and its amphibian hosts is still unclear. Using in vitro assays and a cell infection model, we examined how glutathione influences Bd virulence traits and cellular host disease resistance. For Bd, inhibition of glutathione reductase rapidly killed zoospores, indicating that glutathione is essential for this pathogen. In addition, exposure to exogenous glutathione promoted the potential for virulence through accelerated and increased zoospore release. In host amphibian cells, Bd infection decreased intracellular glutathione content and increased reactive oxygen species, suggesting that chytridiomycosis pathogenesis may involve oxidative stress. Depletion of host glutathione before exposure to Bd increased infection severity and Bd growth, whereas amphibian cells with slightly elevated glutathione levels were partially protected against Bd. However, manipulation of host glutathione levels after the establishment of Bd infection did not impact its intracellular growth, implying that the host glutathione-mediated resistance only occurs during the initial Bd invasion process. Importantly, this effect of glutathione on host resistance is not a general response to pathogens, as it was not observed in cells exposed to viral pathogen FV3. As glutathione increased both infectious zoospore production and host resistance to zoospore infection, our study suggests that this antioxidant may play an important role in the host/pathogen interaction during chytridiomycosis. Thus, environmental conditions and therapeutic approaches that affect glutathione systems in the host and/or pathogen have the potential to alter chytridiomycosis dynamics and should be further explored.

pathology↗

bioRxiv2025

Angiopoietin like protein 3 regulates low-density lipoprotein transport through aortic endothelial cells via endothelial lipase.

Angiopoietin-like protein 3 (ANGPTL3) inhibits endothelial lipase (EL, encoded by LIPG) and lipoprotein lipase (LPL) and has emerged as a promising target for lipid-lowering therapies. While ANGPTL3 inhibition lowers circulating triglycerides and low-density lipoprotein cholesterol (LDL-C), its impact on atherosclerotic cardiovascular disease (ASCVD) remains uncertain. This study investigates the roles of ANGPTL3 and EL in the trans-endothelial transport of LDL and high-density lipoprotein (HDL), an early step in atherogenesis. Using primary human aortic endothelial cells (HAEC), we demonstrate that EL promotes binding, uptake, and transcytosis of LDL and HDL, with its catalytic activity being essential for transport but not for surface association. ANGPTL3 selectively reduced the transport of LDL but not HDL through HAEC. Mechanistically, EL and scavenger receptor BI (SR-BI) act sequentially to mediate LDL uptake, but independently of each other towards HDL uptake. Ex vivo, ANGPTL3 reduced LDL accumulation within bovine aorta. Interestingly, ANGPTL4 had no measurable effect on lipoprotein transport, while ANGPTL8 modestly inhibited both LDL and HDL association with endothelial cells. Our findings provide evidence that ANGPTL3 inhibits EL-mediated transendothelial LDL transport. Opposing effects of ANGPTL3 inhibition on LDL-C concentration and LDL entry into the arterial wall may explain why recent population studies did not reveal any genetically causal association of ANGPTL3 and LIPG with ASCVD risk.

molecular biology↗

bioRxiv2025

Both the low-density lipoprotein receptor and apolipoprotein E define blood-borne high-density lipoprotein entry into the brain.

Data from epidemiological and genetic studies as well as animal experiments indicate that high-density lipoproteins (HDL) play a role in the pathogenesis of central nervous system (CNS) diseases. Apolipoprotein A-I, the major protein of HDL, has been immunolocalized in the brain although it is produced exclusively by the liver and intestine. We therefore investigated how HDL cross the blood-brain barrier (BBB), using both in vitro and in vivo approaches. In vitro, we found that HDL bind to, are internalized by, and are transported through human brain endothelial cells via mechanisms involving the scavenger receptor BI (SR-BI) and the low-density lipoprotein receptor (LDLR). Notably, we discovered that LDLR facilitates only the transport of HDL particles containing apolipoprotein E (apoE). In vivo, HDL injected into the bloodstream enter into the brain through brain endothelial cells, and accumulated in medulla, cerebellum, olfactory bulb, hippocampus and cortex. Further investigation in Ldlr-/- mice revealed region-specific changes in HDL accumulation with reduced levels in the medulla and mixture of midbrain/cortex/hippocampus, no change in the olfactory bulb, and increased levels in the cerebellum. Together, these findings provide new insight on the interaction of the lipoprotein metabolism between the periphery and CNS. For the first time, we show that brain endothelial receptors and HDL composition jointly dictate HDLs crossing through the BBB and their localization within the brain.

neuroscience↗

bioRxiv2025

Metabolic Origins of Neurotoxic 1-deoxySphingolipids in Type 2 Diabetes

Type 2 diabetes (T2D) and diabetic peripheral neuropathy (DPN) are associated with disruptions in sphingolipid (SL) metabolism, including an increased formation of neurotoxic 1-deoxysphingolipids (1-deoxySL). Here we report data from an untargeted proteomics, lipidomics and metabolomics profiling in plasma and skin samples of a carefully characterized T2D cohort and age-matched healthy controls. We investigated the association between plasma and skin amino acids and the sphingolipidome in blood and skin of T2D patients and several diabetic rodent models. We developed a hypothesis on how changes in the metabolism of the two amino acids relates to SL formation and DPN. To test this hypothesis and identify key enzymes responsible for the 1-deoxySL formation we developed stable isotope based SL flux assays, using UC13Glucose, 15NGlutamine, D4-Palmitic acid, D4-Alanine and D3N15-Serine as tracers. In combination with genetic interference approaches, we identified pathways that are responsible for shifting between the formation of 1-deoxySL and canonical SL in T2D. Furthermore, we verified these findings in vivo in several rodent models. This study links disturbances in amino acids, lipids, and protein homeostasis to DPN in T2D.

neuroscience↗

bioRxiv2024

The bat Influenza A virus subtype H18N11 induces nanoscale MHCII clustering upon host cell attachment

Prior to the discovery of the bat influenza A virus (IAV) subtypes H17N10 and H18N11, it was believed that all IAVs bind via the viral hemagglutinin (HA) to sialic acid residues to mediate attachment and subsequent viral entry. Both HA subtypes, H17 and H18, however, do not bind to sialic acids but instead engage a proteinaceous receptor: major histocompatibility complex class II (MHCII). The mechanistic details of this hitherto unknown protein-mediated entry are not understood. Since conventional IAVs require attachment to clusters of sialylated glycans to overcome the low affinity of the HA-sialic acid interaction, we hypothesized that bat HA would likewise interact with multiple MHCII molecules. Here, we used photoactivated localization microscopy (PALM) on fixed and live cells expressing MHCII fused to appropriate fluorescent reporters. We show that bat IAV particles attach to pre-existing MHCII clusters present on susceptible cells and that the local HA-MHCII interaction results in an increased cluster size. To measure the impact of viral attachment on the dynamics of MHCII, we utilized an experimental setup designated "inverse infection" where intact viral particles were immobilized on coverslips before live MHCII-expressing cells were seeded on top. Recording the trajectories of single MHCII molecules, this approach revealed that the mobility of MHCII was indeed slowed down in viral proximity leading to a local enrichment of MHCII molecules beneath the viral particle. Taken together, these data suggest that attachment of viral particles leads to clustering of MHCII, a process similar to the MHCII dynamics observed during the formation of an immunological synapse.

microbiology↗

bioRxiv2022

Integrative analysis of genomic and transcriptomic alterations of AGR2 and AGR3 in cancer

The AGR2 and AGR3 genes have been shown by numerous groups to be functionally associated to adenocarcinoma progression and metastasis. We explore in this paper the data available in databases concerning genomic and transcriptomic features concerning these two genes: the NCBI dbSNP database was used to explore the presence and roles of constitutional SNPs, and the NCI, CCLE and TCGA databases were used to explore somatic mutations and copy number variations (CNVs), as well as mRNA expression of these genes in human cancer cell lines and tumours. Relationships of AGR2/3 expression with whole genome mRNA expression and cancer features (i.e. mutations and CNVs of oncogenes and tumour suppressor genes [TSG]) were established using CCLE and TCGA databases. In addition, the CCLE data concerning CRISPR gene extinction screens (Achilles project) were explored concerning these two genes and a panel of oncogenes and TSG. We observed that no functional polymorphism or recurrent mutation could be detected in AGR2 or AGR3. The expression of these genes was positively correlated with the expression of epithelial genes and inversely correlated with that of mesenchymal genes. It was also significantly associated with several cancer features, such as TP53 or SMAD4 mutations, depending on the gene and the cancer type. The CRISPR screens revealed in addition the absence of cell fitness modification upon gene extinction, in contrast to oncogenes (cell fitness decrease) and TSG (cell fitness increase). Overall, these explorations revealed that AGR2 and AGR3 proteins appear as common non-genetic evolutionary factors in the process of human tumorigenesis.

cancer biology↗

bioRxiv2021

Anterior Gradient-2 (AGR2) overexpression in colon cancer: a potential prognostic biomarker

BackgroundColon cancer is one of the most common leading causes of death worldwide. Prognostic at an early stage is an efficient way to decrease mortality. The Endoplasmic Reticulum (ER)-resident protein anterior gradient-2 (AGR2), a Protein Disulfide Isomerase (PDI) is highly expressed in various tumours and is involved in tumour-associated processes. This study aims at examining the expression of AGR2 protein in colon cancer. MethodsAGR2 protein expression was determined using immunohistochemistry on tissue samples issued from a cohort of 82 colorectal carcinomas. ResultsAGR2 protein expression was significantly higher in tumours than in adjacent nontumour controls. AGR2 expression subgroup analyses indicated that AGR2 low expression in colon cancer patients was significantly associated with worse overall survival. Mucinous colon cancers exhibited higher AGR2 expression levels than non-mucinous cancers. Additionally, tumours with microsatellite instability (MSI) were characterised by a strong upregulation of AGR2 mRNA and protein expression despite an absence of MLH1/MSH2 mutations. ConclusionsOur findings indicate that high AGR2 protein expression is correlated with longer patient survival and that AGR2 overexpression is associated with MSI tumours and could represent an MSI biomarker. Overall, AGR2 might serve as a biomarker to stratify colon tumours and to contribute to the prognosis of colon cancer patients.

cancer biology↗

bioRxiv2021

Virus-Targeted Transcriptomic Analyses Implicate Ranaviral Interaction with Host Interferon Response in Frog Virus 3-infected Frog Tissues

Frog Virus 3 (FV3) is a large dsDNA virus that cause global infections in amphibians, fish and reptiles, and contribute to amphibian declines. FV3s genome contains near 100 putative open reading frames (ORFs). Previous studies have classified these coding genes into temporal classes as immediate early, delayed early and late viral transcripts based on their sequential expression during FV3 infection. To genome-wide characterize ranaviral gene expression, we performed a whole transcriptomic analysis (RNA-Seq) using total RNA samples containing both viral and cellular transcripts from FV3-infected Xenopus laevis adult tissues using two FV3 strains, a wild type (FV3-WT) and an ORF64R-deleted recombinant (FV3-{Delta}64R). In samples from the infected intestine, liver, spleen, lung and especially kidney, a FV3-targeted transcriptomic analysis mapped reads spanning the full-genome coverage at [~]10x depth on both positive and negative strands. By contrast, reads were only mapped to partial genomic regions in samples from the infected thymus, skin and muscle. Extensive analyses validated the expression of almost all annotated 98 ORFs and profiled their differential expression in a tissue-, virus-, and temporal class-dependent manners. Further studies identified several putative ORFs that encode hypothetical proteins containing viral mimicking conserved domains found in host interferon (IFN) regulatory factors (IRFs) and IFN receptors. This study provides the first comprehensive genome-wide viral transcriptome profiling during infection and across multiple amphibian host tissues that will serve as instrumental reference. It also presents evidence implying that ranaviruses like FV3 have acquired previously unknown molecular mimics interfering with host IFN signaling during evolution. ImportanceFrog Virus 3 (FV3), are large dsDNA viruses that cause devastating infections globally in amphibians, fish and reptiles, and contribute to catastrophic amphibian declines. FV3s large genome encodes near 100 coding genes, of which most have been functionally uncharacterized in the viral pathogenesis. Using a whole transcriptomic analysis (RNA-Seq) in FV3-infected amphibian samples, we determined a genome-wide virus transcriptome and profiled their differential expression in a tissue-, virus-, and temporal class-dependent manners. Further studies identified several putative ORFs that encode hypothetical proteins containing viral mimicking conserved domains found in host interferon (IFN) regulatory factors (IRFs) and IFN receptors. This study provides the first comprehensive genome-wide viral transcriptome profiling during infection and across multiple amphibian host tissues that will serve as instrumental reference. It also presents evidence implying that ranaviruses like FV3 have acquired previously unknown molecular mimics interfering with host IFN signaling during evolution.

microbiology↗

bioRxiv2020

Activation of cGAS/STING pathway upon paramyxovirus infection

During inflammatory diseases, cancer and infection, the cGAS/STING pathway is known to recognize foreign or self-DNA in the cytosol and activate an innate immune response. Here, we report that negative-strand RNA paramyxoviruses, Nipah virus (NiV) and Measles virus (MeV), can also trigger the cGAS/STING axis. While mice deficient for MyD88, TRIF and MAVS still moderately control NiV infection when compared to WT mice, additional STING deficiency resulted in 100% lethality, suggesting synergistic roles of these pathways in host protection. Moreover, deletion of cGAS or STING resulted in decreased type-I interferon production with enhanced paramyxoviral infection in both human and murine cells. Finally, the phosphorylation and ubiquitination of STING, observed during viral infections, confirmed the activation of cGAS/STING pathway by NiV and MeV. Our data suggest that cGAS/STING activation is critical in controlling paramyxovirus infection, and possibly represent attractive targets to develop countermeasures against severe disease induced by these pathogens.

immunology↗

bioRxiv2019

Q203 containing fully intermittent oral regimens exhibited high sterilizing activity against Mycobacterium ulcerans in mice

Buruli ulcer (BU), caused by Mycobacterium ulcerans is currently treated by a daily combination of rifampin and either injectable streptomycin or oral clarithromycin. An intermittent oral regimen would facilitate the treatment supervision. We first evaluated the bactericidal activity of newer antimicrobials against M. ulcerans using a BU animal model. The imidazopyridine amine Q203 exhibited high bactericidal activity whereas tedizolid (oxazolidinone close to linezolid), selamectine and ivermectine (avermectine compound) and the benzothiazinone PBTZ169 were not active. Consequently, Q203 was evaluated for its bactericidal and sterilizing activities in combined intermittent regimens. Q203 given twice a week in combination with one of the other long half-life compounds, rifapentine or bedaquiline, sterilized the mice footpads in 8 weeks, i.e. after a total of only 16 doses, and prevented relapse during a period of 20 weeks after stopping the treatment. These results are very promising for future intermittent oral regimens which would greatly simplify BU treatments in the field.\n\nAuthor summaryThe current treatment of Buruli ulcer (BU), infection caused by Mycobacterium ulcerans is based on a daily antibiotic combination of rifampin associated with streptomycin or clarithromycin. A shorter or intermittent treatment without an injectable drug would clearly simplify the management on the field. We evaluated the bactericidal activity of several new antimicrobials drugs in a mice model of BU and found that the Q203 exhibited the highest bactericidal effect. We subsequently identified new antibiotic combinations containing Q203 with high sterilizing activity when administrated twice a week for 8 weeks.

microbiology↗

bioRxiv2019

Thinking small: next-generation sensor networks close the size gap in vertebrate biologging

Recent advances in animal tracking technology have ushered in a new era in biologging. However, the considerable size of many sophisticated biologging devices restricts their application to larger animals, while old-fashioned techniques often still represent the state-of-the-art for studying small vertebrates. In industrial applications, low-power wireless sensor networks fulfill requirements similar to those needed to monitor animal behavior at high resolution and at low tag weight. We developed a wireless biologging network (WBN), which enables simultaneous direct proximity sensing, high-resolution tracking, and long-range remote data download at tag weights of one to two grams. Deployments to study wild bats created social networks and flight trajectories of unprecedented quality. Our developments highlight the vast capabilities of WBNs and their potential to close an important gap in biologging: fully automated tracking and proximity sensing of small animals, even in closed habitats, at high spatial and temporal resolution.

animal behavior and cognition↗

bioRxiv2018

Quantitative characterization of translational riboregulators using an in vitro transcription-translation system

Riboregulators are short RNA sequences that, upon binding to a ligand, change their secondary structure and influence the expression rate of a downstream gene. They constitute an attractive alternative to transcription factors for building synthetic gene regulatory networks because they can be engineered de novo and they have a fast turnover and a low metabolic burden. However, riboregulators are generally designed in silico and tested in vivo, which only provides a yes/no evaluation of their performances, thus hindering the improvement of design algorithms. Here we show that a cell-free transcription-translation (TX-TL) system provides valuable quantitative information about the performances of in silico designed riboregulators. In particular, we use the ribosome as an exquisite molecular machine that detects functional riboregulators, precisely measures their concentration and linearly amplifies the signal by generating a fluorescent protein. We apply this method to characterize two types of translational riboregulators composed of a cis-repressed (cr) and a trans-activating (ta) strand. At the DNA level we demonstrate that high concentrations of taDNA poisoned the activator until total shut off. At the RNA level, we show that this approach provides a fast and simple way to measure dissociation constants of functional riboregulators, in contrast to standard mobility-shift assays. Our method opens the route for using cell-free TX-TL systems for the quantitative characterization of functional riboregulators in order to improve their design in silico.

synthetic biology↗