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Abstract
Many of the interactions between the human intestine and microbes are mediated by changes in the host cytoskeleton. By inducing these changes, microbes promote their own attachment to host cells, enhance invasion, and facilitate trafficking within the eukaryotic host, resulting in a disruption of intestinal epithelial barrier integrity.
In this thesis project, I demonstrated how bacteria manipulate the host cytoskeleton for their own benefit, and highlighted the role of host cell factors in mediating these effects. For example, infection of polarized epithelial cells with Campylobacter jejuni leads to cell-type-dependent disruption of monolayers. Human colon T84 cells are more susceptible than canine kidney MDCK-I cells to these effects, as well as to invasion by C. jejuni, which is mediated by cell microtubules. Inhibition of invasion protects T84 monolayers from C. jejuni-induced increased permeability, suggesting that barrier disruption by this bacterium is mediated by invasion.
Subsequent in vivo experiments, using Citrobacter rodentium, showed that the tyrosine phosphatase PTPσ is involved in maintaining adherens junctions. In the absence of functional PTPσ, mice are more susceptible to bacterial infection with C. rodentium , which leads to inflammation, epithelial cell hyperplasia, and bacterial translocation, likely through effects on apical junctions. Finally, osteopontin, a multifunctional phosphoglycoprotein, mediates epithelial cell hyperplasia in response to C. rodentium infection. This effect develops due to intimate attachment of bacteria to epithelial cells and associated rearrangements of the cytoskeleton, which are absent in cells lacking osteopontin and are restored when this protein is reintroduced to cells.
I show herein that host factors determine responses to bacteria through changes in the cytoskeleton. Since each of these complementary infection models is related to inflammatory bowel diseases, they provide insight into mechanisms leading to human disease, and provide candidate approaches for novel interventions that could modify inflammation through altering host cytoskeleton responses to bacterial infections.
