Shiga toxin-producing E. coli (STEC) comprise a group of pathogenic organisms that elaborate a family of protein exotoxins known as Shiga toxins (Stxs). Intestinal infection with these organisms may lead to hemorrhagic colitis and hemolytic uremic syndrome, a life-threatening condition characterized by thrombocytopenia, non-immune hemolytic anemia, and acute renal failure. Vascular endothelial damage is believed to be a key initiating event in Stx-mediated diseases. At the molecular level, these toxins depurinate human 28S rRNA and inhibit translation. In addition, at concentrations that only minimally affect global protein synthesis, they have been found to alter expression of specific target genes. To better understand the endothelial damage induced by Stx, we investigated the global effects of Stx on endothelial gene expression, and defined a specific group of genes whose expression was altered by the toxin. Of interest, the CXCR4/CXCR7/SDF-1 chemokine pathway, a pathway central to vascular biology, was activated by Stx. In vitro studies demonstrated that Stx enhanced both transcript levels of these molecules, as well as their association with ribosomes. To define the relevance of these findings in vivo, a mouse model was established and key changes were noted in plasma and tissue content of CXCR4/CXCR7/SDF-1 following Stx exposure. Inhibition of CXCR4/SDF-1 interaction decreased indices of endothelial activation and organ injury and improved animal survival. Importantly, in children infected with E. coli O157:H7, plasma SDF-1 levels were significantly elevated in individuals who progressed to hemolytic uremic syndrome.
A second pathway critical to endothelial health and function is VEGF signaling. Of interest, our endothelial gene expression analyses revealed changes in this pathway in vitro. VEGF mRNA association with cellular polyribosomes increased following Stx treatment. Further studies in vivo demonstrated decreased cardiac function and blood pressure, and increased vascular permeability in specific tissues. VEGF, an important inducer of vascular permeability, increased in mouse plasma. Additionally, altered mRNA expression was observed in key organs, such as the kidney and heart, following Stx challenge. Inhibition of VEGF significantly improved survival of animals treated with Stx, indicating that VEGF plays a role in Stx-mediated pathogenesis. Moreover, in vitro studies demonstrated that Stx-mediated endothelial permeability was attenuated in the presence of a VEGF inhibitor. Taken together, these data indicate that E. coli-derived Stxs induce pathological changes in two pathways key to vascular biology. These pathways represent novel targets for the development of preventative and therapeutic strategies for complications associated with Shiga toxin-producing E. coli infection.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/32863 |
| Date | 31 August 2012 |
| Creators | Petruzziello, Tania Nadia |
| Contributors | Marsden, Philip A. |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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