Elsa Bonnafé

Biochemical and biophysical combined study of bicarinalin, an ant venom antimicrobial peptide.

We have recently characterized bicarinalin as the most abundant peptide from the venom of the ant Tetramorium bicarinatum. This antimicrobial peptide is active against Staphylococcus and Enterobacteriaceae. To further investigate the antimicrobial properties of this cationic and cysteine-free peptide, we have studied its antibacterial, antifungal and antiparasitic activities on a large array of microorganisms. Bicarinalin was active against fifteen microorganisms with minimal inhibitory concentrations ranging from 2 and 25μmolL(-1). Cronobacter sakazakii, Salmonella enterica, Candida albicans, Aspergilus niger and Saccharomyces cerevisiae were particularly susceptible to this novel antimicrobial peptide. Resistant strains of Staphylococcus aureus, Pseudomonas aeruginosa and C. albicans were as susceptible as the canonical strains. Interestingly, bicarinalin was also active against the parasite Leishmania infantum with a minimal inhibitory concentrations of 2μmolL(-1). The bicarinalin pre-propeptide cDNA sequence has been determined using a combination of degenerated primers with RACE PCR strategy. Interestingly, the N-terminal domain of bicarinalin pre-propeptide exhibited sequence similarity with the pilosulin antimicrobial peptide family previously described in the Myrmecia venoms. Moreover, using SYTOX green uptake assay, we showed that, for all the tested microorganisms, bicarinalin acted through a membrane permeabilization mechanism. Two dimensional-NMR experiments showed that bicarinalin displayed a 10 residue-long α-helical structure flanked by two N- and C-terminal disordered regions. This partially amphipathic helix may explain the membrane permeabilization mechanism of bicarinalin observed in this study. Finally, therapeutic value of bicarinalin was highlighted by its low cytotoxicity against human lymphocytes at bactericidal concentrations and its long half-life in human serum which was around 15h.

De novo transcriptome sequencing and analysis of freshwater snail (Radix balthica) to discover genes and pathways affected by exposure to oxazepam

Pharmaceuticals are increasingly found in aquatic ecosystems due to the non-efficiency of waste water treatment plants. Therefore, aquatic organisms are frequently exposed to a broad diversity of pharmaceuticals. Freshwater snail Radix balthica has been chosen as model to study the effects of oxazepam (psychotropic drug) on developmental stages ranging from trochophore to hatching. In order to provide a global insight of these effects, a transcriptome deep sequencing has been performed on exposed embryos. Eighteen libraries were sequenced, six libraries for three conditions: control, exposed to the lowest oxazepam concentration with a phenotypic effect (delayed hatching) (TA) and exposed to oxazepam concentration found in freshwater (TB). A total of 39,759,772 filtered raw reads were assembled into 56,435 contigs having a mean length of 1579.68 bp and mean depth of 378.96 reads. 44.91% of the contigs have at least one annotation. The differential expression analysis between the control condition and the two exposure conditions revealed 146 contigs differentially expressed of which 144 for TA and two for TB. 34.0% were annotated with biological function. There were four mainly impacted processes: two cellular signalling systems (Notch and JNK) and two biosynthesis pathways (Polyamine and Catecholamine pathways). This work reports a large-scale analysis of differentially transcribed genes of R. balthica exposed to oxazepam during egg development until hatching. In addition, these results enriched the de novo database of potential ecotoxicological models.

P17, an Original Host Defense Peptide from Ant Venom, Promotes Antifungal Activities of Macrophages through the Induction of C-Type Lectin Receptors Dependent on LTB4-Mediated PPARγ Activation

Despite the growing knowledge with regard to the immunomodulatory properties of host defense peptides, their impact on macrophage differentiation and on its associated microbicidal functions is still poorly understood. Here, we demonstrated that the P17, a new cationic antimicrobial peptide from ant venom, induces an alternative phenotype of human monocyte-derived macrophages (h-MDMs). This phenotype is characterized by a C-type lectin receptors (CLRs) signature composed of mannose receptor (MR) and Dectin-1 expression. Concomitantly, this activation is associated to an inflammatory profile characterized by reactive oxygen species (ROS), interleukin (IL)-1β, and TNF-α release. P17-activated h-MDMs exhibit an improved capacity to recognize and to engulf Candida albicans through the overexpression both of MR and Dectin-1. This upregulation requires arachidonic acid (AA) mobilization and the activation of peroxisome proliferator-activated receptor gamma (PPARγ) nuclear receptor through the leukotriene B4 (LTB4) production. AA/LTB4/PPARγ/Dectin-1-MR signaling pathway is crucial for P17-mediated anti-fungal activity of h-MDMs, as indicated by the fact that the activation of this axis by P17 triggered ROS production and inflammasome-dependent IL-1β release. Moreover, we showed that the increased anti-fungal immune response of h-MDMs by P17 was dependent on intracellular calcium mobilization triggered by the interaction of P17 with pertussis toxin-sensitive G-protein-coupled receptors on h-MDMs. Finally, we also demonstrated that P17-treated mice infected with C. albicans develop less severe gastrointestinal infection related to a higher efficiency of their macrophages to engulf Candida, to produce ROS and IL-1β and to kill the yeasts. Altogether, these results identify P17 as an original activator of the fungicidal response of macrophages that acts upstream PPARγ/CLRs axis and offer new immunomodulatory therapeutic perspectives in the field of infectious diseases.

Pharmacokinetic and antimicrobial activity of a new carvacrol-based product against a human pathogen, Campylobacter jejuni

In vitro and in vivo studies were conducted to test a new carvacrol‐based product designed to delay the carvacrol release so that it could reach the caeca of broiler chickens in order to control Campylobacter jejuni.

Monoterpenoid‐based preparations in beehives affect learning, memory, and gene expression in the bee brain

Bees are exposed in their environment to contaminants that can weaken the colony and contribute to bee declines. Monoterpenoid-based preparations can be introduced into hives to control the parasitic mite Varroa destructor. The long-term effects of monoterpenoids are poorly investigated. Olfactory conditioning of the proboscis extension reflex (PER) has been used to evaluate the impact of stressors on cognitive functions of the honeybee such as learning and memory. The authors tested the PER to odorants on bees after exposure to monoterpenoids in hives. Octopamine receptors, transient receptor potential-like (TRPL), and γ-aminobutyric acid channels are thought to play a critical role in the memory of food experience. Gene expression levels of Amoa1, Rdl, and trpl were evaluated in parallel in the bee brain because these genes code for the cellular targets of monoterpenoids and some pesticides and neural circuits of memory require their expression. The miticide impaired the PER to odors in the 3 wk following treatment. Short-term and long-term olfactory memories were improved months after introduction of the monoterpenoids into the beehives. Chronic exposure to the miticide had significant effects on Amoa1, Rdl, and trpl gene expressions and modified seasonal changes in the expression of these genes in the brain. The decrease of expression of these genes in winter could partly explain the improvement of memory. The present study has led to new insights into alternative treatments, especially on their effects on memory and expression of selected genes involved in this cognitive function. Environ Toxicol Chem 2017;36:337-345.

Learning the cell cycle with a game: Virtual experiments in cell biology

Cell Cycle Learn (CCL) is a learning game designed for undergraduate students in Biology to learn common knowledge about the cell-division cycle along with practical skills related with setting up an experiment and the scientific method in general. In CCL, learners are guided through the process of formulating hypotheses, conducting virtual experiments and analysing the results in order to validate or invalidate the hypotheses. The game has been designed in the University of Toulouse and introduced last year as part of the curriculum of a cellular biology class. This paper presents early results of an evaluation of the game enabled by questionnaires filled by the participants and game data collected during the training sessions. The results demonstrate with examples that both types of data can be used to assess the games utility.