Diarrhée | EPFL Graph Search

vignette|Espérance de vie corrigée de l'incapacité causée par la diarrhée (2004) La diarrhée est une quantité de selles émises dans un volume plus important que la normale (plus de par jour) et avec une plus grande fréquence (plus de trois selles par jour). Les selles sont généralement liquides, mais parfois simplement molles, accompagnées de glaires ou de sang et d'un cortège de symptômes variables dépendant de la cause de la diarrhée. Il est même possible dans certains cas que ce ne soit que de l'eau ou un liquide transparent. Dans les cas extrêmes, comme le choléra, plus de 20 litres de fluide peuvent être perdus par jour. Les diarrhées sont généralement accompagnées de crampes et de douleurs aux intestins qui peuvent rendre le sujet mal à l'aise, ainsi que de frissons et de sueurs froides dans certains cas. Les diarrhées sont la seconde cause de mortalité infantile dans les pays du tiers monde (après les pneumonies), et sont responsables de 18 % des morts d'enfants de moins de 5

Unraveling the Physiological Role of Capillary Morphogenesis Gene 2 in Health and Disease

Jérôme Bürgi

Capillary Morphogenesis Gene 2 (CMG2) is a 55kDa single-pass transmembrane protein best described as the main Anthrax Toxin Receptor. However, CMG2 physiological role remains elusive and understanding better its in vivo function was the main objective of my thesis. My first aim was to investigate the prevalence of intrinsically disordered domains in the human transmembrane proteome. Using prediction tools, I found that 50% of transmembrane proteins had at least one domain of minimum 30 amino-acids predicted as intrinsically disordered (IDD), these proteins being mainly involved in cell signaling and adhesion. The majority of the IDDs were localized in the cytoplasm, and the intrinsic disorder containing proteins were significantly more phosphorylated and interacted on average with more proteins than fully ordered proteins, corroborating their role in signaling. CMG2 loss-of-function mutations is the known cause of a rare inherited genetic disorder called Hyaline Fibromatosis Syndrome (HFS). HFS patients develop subcutaneous nodules, gingival hypertrophy, contracture of the large joints, and in the most severe cases diarrhea and premature death. In a second part of my thesis, I was involved in understanding the molecular defects underlying missense mutations localized in the ectodomain and a highly conserved cytoplasmic domain of CMG2. We found that CMG2 was able to bind the actin cytoskeleton through Talin and Vinculin when free of its extracellular ligand. Interestingly, the HFS mutation p.C218R, altered the cytoskeleton release and led to a CMG2 protein able to bind both the extracellular ligand and the actin cytoskeleton. Strikingly, we observed that all but one cytoplasmic missense mutation hindered actin binding, a defect potentially relevant to HFS pathogenesis. Furthermore, we showed that the Src-like kinase family are involved in the release of Talin upon ligand binding and that CMG2 binding to its extracellular ligand is critical for the correct orientation of the mitotic spindle of zebrafish epiblast cells, which allows cell division along the Animal/Vegetal axis. Through the analysis of cmg2 knock-out mice, along with the study of HFS patient samples, we aimed at better defining CMG2 function. We showed that type VI Collagen was strongly accumulating in the cmg2 KO mice uterus tissue leading to failure of parturition, an accumulation that was also observed in HFS patient nodules. In addition, we observed that CMG2 was able to interact and potentiate MT1-MMP, and that type VI Collagen is a bona fide ligand for CMG2, its binding leading to the phosphorylation of the receptor. With the scope to understand the HFS patient subcutaneous nodules pathogenesis, we investigated the gene expression profile of fibroblasts derived from non-affected and affected tissues by RNA sequencing. Fibroblasts derived from affected tissues appeared to differentially express genes involved in the TGFBeta pathway and cytoskeleton, such as alpha smooth muscle actin, a marker of myofibroblast activation. We observed the presence of myofibroblasts in the patient nodules, and showed that CMG2 was limiting their activation process, loss-of-function mutations in CMG2 leading to an exacerbated differentiation. As we observed CMG2 interaction with the TGFBeta receptor 2, we postulated that CMG2 influence the TGFBeta pathway, a process that is altered in HFS patient and potentially lead to the formation of nodules.

EPFL2015

How Vibrio cholerae adapts to the environment: from cell shape transitions to antagonistic behavior

Leonardo Filipe Lemos Rocha

The bacterium Vibrio cholerae is the causative agent of the diarrheal disease cholera, which affects millions of people every year. Apart from being a human pathogen, V. cholerae is also a common member of aquatic habitats. Whilst the mechanism that allow it to transit from an environmental to a pathogenic lifestyle is still understudied, it is well established that virulence induction is linked to the bacterium's ability to sense its surroundings. Therefore, this thesis aimed to shed new light on the general sensing capacity of V. cholerae and its adaptation to the surrounding environment. Specifically, we explored the functions of the virulence-associated regulatory two-component system VarS/VarA, which was shown to regulate the major virulence factors of V. cholerae. In this thesis, we identified a new function of this regulatory system in modulating the pathogen's cellular shape. Precisely, we demonstrated that a strain lacking the response regulator VarA loses its normal curve-shaped morphology and transits to spherical shape during stationary phase of growth. This rounding phenotype was not observed on cells lacking the sensor histidine kinase VarS, which suggests the existence of additional VarA activators. Through analysis of the cells's peptidoglycan (PG), we found that the cause of the atypical shape was due to high abundance of dipeptides and reduced peptide cross-links. This abnormal PG composition and consequent cell rounding could be abrogated through cell wall recycling of wild type-derived PG subunits. Through a transposon mutagenesis screen, we identified the carbon storage regulator A (CsrA) as a key player in this phenotype. We showed that varA-deficient cells have an increased activity of CsrA, which led to an overproduction of the aspartate ammonia lyase enzyme (AspA). Our results indicate that AspA overproduction likely reduced the pool of aspartate in varA-deficient cells, which subsequently impaired the biosynthesis of the cell wall precursor meso-diaminopimelic acid. Ultimately, this compromised production of PG precursors resulted in the altered PG composition and consequent cell rounding. Furthermore, and consistent with findings in Enterobacteriaceae, our results also suggest that the VarA-CsrA regulatory circuit modulates chemotaxis and motility in V. cholerae. Finally, in two different collaborative studies, we also addressed how V. cholerae might interact with other bacteria in the environment taking bacterial antagonism strategies into consideration. Firstly, we showed that a subset of human gut microbiota isolates is able to withstand type VI secretion system (T6SS)-mediated attacks by V. cholerae in an immunity protein-independent manner. Moreover, our preliminary data indicates a superior T6SS-mediated killing potential from a specific environmental strain of V. cholerae compared to a particular toxigenic strain. Secondly, we demonstrated that the environmental V. cholerae strain SA7G harbors a specific plasmid, pSA7G1, that confers a competitive advantage over neighboring bacteria likely through type IV secretion system-mediated killing. Collectively, the findings of this thesis contribute to better understanding how V. cholerae adapts to the environment, namely with specific sensing-response mechanisms such as the VarA-CsrA signaling pathway.

EPFL2022

Molecular insights into Vibrio cholerae’s intra-amoebal host-pathogen interactions

Melanie Blokesch, Natalia Carolina Drebes Dörr, Graham Knott, Catherine Maclachlan, Tiziana Scrignari, Candice Stoudmann, Sandrine Stutzmann, Charles Ulric V Van der Henst, Audrey Sophie Vanhove

Vibrio cholerae, which causes the diarrheal disease cholera, is a species of bacteria commonlyfound in aquatic habitats. Within such environments, the bacterium must defend itselfagainst predatory protozoan grazers. Amoebae are prominent grazers, withAcanthamoebacastellaniibeing one of the best-studied aquatic amoebae. We previously showed thatV.choleraeresists digestion byA. castellaniiand establishes a replication niche within the host’sosmoregulatory organelle. In this study, we decipher the molecular mechanisms involved inthe maintenance ofV. cholerae’s intra-amoebal replication niche and its ultimate escape fromthe succumbed host. We demonstrate that minor virulence features important for disease inmammals, such as extracellular enzymes andflagellum-based motility, have a key role in thereplication and transmission ofV. choleraein its aqueous environment. This work, therefore,describes new mechanisms that provide the pathogen with afitness advantage in its primaryhabitat, which may have contributed to the emergence of these minor virulence factors in thespeciesV. cholerae.