Biology subjects

Ramond, E.

Publications and source records attributed to Ramond, E..

6 recordsLinked to original sources

bioRxiv2020

ROS-dependent innate immune mechanisms control Staphylococcus aureus MRSA virulence in the Drosophila larval model

Antibiotics multi-resistant Staphylococcus aureus strains constitute a major public health concern worldwide and are responsible of both healthcare- and community-associated infections. Here we have established a robust and simple S. aureus oral infection model, using Drosophila melanogaster larva, which allowed to follow S. aureus fate at the whole organism level as well as the host immune responses. Fluorescence microscopy and Light sheet 3D imaging revealed bacterial clustering at the posterior midgut that displays neutral pH. Our study demonstrates that S. aureus infection triggers host H2O2 production through Duox enzyme, consequently empowering antimicrobial peptides production through Toll pathway activation. We also show that catalase-mediated quenching of H2O2 not only enhances S. aureus survival but also minimizes host antimicrobial response, hence reducing bacterial clearance in vivo. Finally, we confirm the versatility of this model by demonstrating the colonization and host stimulation capacities of two other bacterial pathogens: Salmonella Typhimurium and Shigella flexneri. Overall, the drosophila larva may constitute a general model to follow in vivo host innate immune responses triggered upon infection with human pathogens.

microbiology↗

bioRxiv2020

Comparative RNA-Seq Analyses of Drosophila Plasmatocytes Reveal Gene Specific Signatures In Response To Clean Injury And Septic Injury

Drosophila melanogasters blood cells (hemocytes) play essential roles in wound healing and are involved in clearing microbial infections. Here, we report the transcriptional changes of larval plasmatocytes after clean injury or infection with the Gram-negative bacterium Escherichia coli or the Gram-positive bacterium Staphylococcus aureus compared to hemocytes recovered from unchallenged larvae via RNA-Sequencing. This study reveals 676 differentially expressed genes (DEGs) in hemocytes from clean injury samples compared to unchallenged samples, and 235 and 184 DEGs in E. coli and S. aureus samples respectively compared to clean injury samples. The clean injury samples showed enriched DEGs for immunity, clotting, cytoskeleton, cell migration, hemocyte differentiation, and indicated a metabolic reprogramming to aerobic glycolysis, a well-defined metabolic adaptation observed in mammalian macrophages. Microbial infections trigger significant transcription of immune genes, with significant differences between the E. coli and S. aureus samples suggesting that hemocytes have the ability to engage various programs upon infection. Collectively, our data bring new insights on Drosophila hemocyte function and open the route to post-genomic functional analysis of the cellular immune response.

immunology↗

bioRxiv2019

Metabolic adjustment of Drosophila hemocyte number and sessility by an adipokine

In animals, growth is regulated by the complex interplay between paracrine and endocrine signals. When food is scarce, tissues compete for nutrients, leading to critical resource allocation and prioritization. Little is known about how the immune system maturation is coordinated with the growth of other tissues. Here, we describe a signaling mechanism that regulates the number of hemocytes (blood cells) according to the nutritional state of the Drosophila larva. Specifically, we found that the adipokine NimB5 is produced in the fat body upon nutrient scarcity downstream of metabolic sensors. NimB5 is then secreted and bind to hemocytes to down-regulate their proliferation and adhesion. Blocking this signaling loop results in conditional lethality when larvae are raised on a poor diet, due to excessive hemocyte numbers and insufficient energy storage. Similar regulatory mechanisms shaping the immune system in response to nutrient availability are likely to be widespread in animals.\n\nAuthor summaryDrosophila larval hemocytes (blood cells) are found in two compartments: the lymph gland considered as a reservoir, and the peripheral compartment. Peripheral hemocytes form sessile patches attached to the internal surface of the larval body wall or are found freely circulating in the hemolymph. Little is known about the signals that regulate hemocytes proliferation and localization in the peripheral compartment. In this study, we have identified a new gene, NimrodB5, coding for the NimB5 protein, which is secreted by the fat body and binds to hemocytes. NimB5 inhibits hemocyte proliferation while promoting sessility, leading to an increased number of circulating hemocytes and adhesion defects in NimB5 mutant. We show that nimrodB5 expression by the fat body is controlled by metabolic cues to adjust hemocyte number to the physiological state of the larvae.\n\nInterestingly, deregulation of NimB5 causes lethality when larvae are raised on a poor diet due to a defect in regulating hemocytes proliferation. In conclusion, we have identified a new adipokine that optimizes hemocytes number to the physiological state of larvae. Our study also reveals a major role of the fat body in peripheral hematopoiesis regulation and outline how it can be costly to maintain a basal immune defense.

immunology↗

bioRxiv2019

Transketolase is involved in the control of Sigma B during chronic infection by Staphylococcus aureus

Staphylococcus aureus is a leading cause of both acute and chronic infections in humans. The importance of the pentose phosphate pathway (PPP) during S. aureus infection is currently largely unexplored. Here, we focused on one key PPP enzyme, transketolase. We showed that inactivation of the unique gene encoding transketolase activity in S. aureus USA300 ({triangleup}tkt) led to drastic metabolomic changes. Using time-lapse video imaging and mice infection, we observed a major defect of the {triangleup}tkt strain compared to wild-type strain in early intracellular proliferation and in the ability to colonise kidneys. Transcriptional activity of the two master regulators Sigma B and RpiRc was drastically reduced in the {triangleup}tkt mutant during host cells invasion. The concomitant increased RNAIII transcription, suggests that TKT-or a functional PPP-strongly influences the ability of S. aureus to proliferate within host cells by modulating key transcriptional regulators.

microbiology↗

bioRxiv2018

Two Nimrod receptors, NimC1 and Eater, synergistically contribute to bacterial phagocytosis in Drosophila melanogaster

Eater and NimC1 are transmembrane receptors of the Drosophila Nimrod family, specifically expressed in hemocytes, the insect blood cells. Previous ex vivo and in vivo RNAi studies have pointed to their role in the phagocytosis of bacteria. Here, we have created a novel null mutant in NimC1 to re-evaluate the role of NimC1, alone or in combination with Eater, in the cellular immune response. We show that NimC1 functions as an adhesion molecule ex vivo, but in contrast to Eater is not required for hemocyte sessility in vivo. Ex vivo phagocytosis assays and electron microscopy experiments confirmed that Eater is the main phagocytic receptor for Gram-positive, but not Gram-negative bacteria, and contributes to microbe tethering to hemocytes. Surprisingly, the NimC1 deletion did not impair phagocytosis of bacteria, nor their adhesion to the hemocytes. However, phagocytosis of both types of bacteria was almost abolished in NimC11;eater1 hemocytes. This indicates that both receptors contribute synergistically to the phagocytosis of bacteria, but that Eater can bypass the requirement for NimC1. Finally, we uncovered that NimC1, but not Eater, is essential for uptake of latex beads and zymosan particles. We conclude that Eater and NimC1 are the two main receptors for phagocytosis of bacteria in Drosophila, and that each receptor likely plays distinct roles in microbial uptake.

immunology↗

bioRxiv2018

Persistent Staphylococcus aureus infections in children with chronic lung disease: a multi-omics analysis of bacterial adaptation to define novel therapeutic approaches

BackgroundChronic lung infection of cystic fibrosis (CF) patients by Staphylococcus aureus is a well-established epidemiological fact. Indeed, S. aureus is the most commonly identified pathogen in the lungs of CF patients. Strikingly the molecular mechanisms underlying S. aureus persistency are not understood.\n\nMethodsWe selected pairs of sequential S. aureus isolates from 3 patients with CF and from one patient with non-CF chronic lung disease. We used a combination of genomic, proteomic and metabolomic approaches with functional assays for in-depth characterization of S. aureus long-term persistence.\n\nResultsFor the first time, we show that late S. aureus isolates from CF patients have an increased ability for intracellular survival in CFBE-F508del cells compared to ancestral early isolates. Importantly, the increased ability to persist intracellularly was confirmed for S. aureus isolates within the own patient F508del epithelial cells. An increased ability to form biofilm was also demonstrated.\n\nFurthermore, we identified the underlying genetic modifications inducing altered protein expression profiles and notable metabolic changes. These modifications affect several metabolic pathways and virulence regulators that could constitute therapeutic targets.\n\nConclusionsOur results strongly suggest that the intracellular environment might constitute an important niche of persistence and relapse necessitating adapted antibiotic treatments.\n\nSummaryS. aureus persists for years in the lungs of patients with cystic fibrosis despite antibiotic therapies. We demonstrate that S. aureus adaptation leads to increased intracellular persistence suggesting a key role for intracellular niche during S. aureus chronic lung infection.

microbiology↗