The epithelial layer of host mucosal surfaces presents an initial interface for colonizing microorganisms. In addition to constituting a physical barrier to the ingress of organisms, epithelial cells can sense and respond to the presence of bacteria through an elaborate signaling network that can also communicate information to the underlying immune effector cells in the mucosa. Bacteria that colonize the epithelial surface often engage epithelial cells in a complex molecular dialog which results in significant changes to the host cell transcriptional program and can fundamentally alter epithelial properties. Moreover, in vivo, bacteria on epithelial surfaces tend to accumulate into polymicrobial communities, and communities of organisms can exhibit properties distinct from individual constituent species in isolation. Ultimately, it is the collective action of the community organisms that determines the impact of the microbial challenge on the host. Our ongoing studies of gingival epithelial cells (GECs) show that the periodontal pathogen Porphyromonas gingivalis can regulate the activity of a number of transcription factors and co-factors which control inflammation, cell viability and proliferation. These include ?-catenin which is proteolytically activated by P. gingivalis, and FOXO1 which is activated by site specific dephosphorylation. Activation of ?-catenin and FOXO1 by P. gingivalis leads to the regulation of ZEB2, a transcription factor pivotal for governing essential epithelial properties and tissue integrity. Moreover ZEB2 can control the maturation of immune cells and the production of inflammatory mediators such as IL-6. We also found that manipulation of the ?-catenin-FOXO1 axis by P. gingivalis can be antagonized by Streptococcus gordonii and S. oralis, but remains unaffected by other common oral streptococci. Hence our hypotheses are that i) the interplay between ?-catenin and FOXO1 controls ZEB2 expression in response to P. gingivalis, and impacts epithelial cell characteristics with relevance to the maintenance of tissue homeostasis; and ii) specific oral community profiles can modulate the influence of P. gingivalis on epithelial signaling pathways that regulate ?-catenin and FOXO1 function.
The Aims of the project are thus: 1. To characterize the functional integration of ?-catenin and FOXO1 in the control of ZEB2 by P. gingivalis. 2. To determine the functional relevance of site-specific dephosphorylation of FOXO1 by P. gingivalis for the FOXO1 transcriptional program and ZEB2 regulation. 3. To characterize the mechanisms by which S. gordonii can subvert P. gingivalis-induced activation of the ?-catenin-FOXO1-ZEB2 axis. Successful completion of this project will define novel mechanisms for the integration and control of epithelial cell transcription factors, and characterize modulation of these pathways by P. gingivalis both as a single species infection and in the context of a community. These studies will increase our understanding of oral diseases that arise from dysbiotic host responses, such as periodontitis and potentially oral squamous cell carcinoma.
Severe periodontal (gum) diseases occur when there is an imbalance in the interaction between colonizing bacteria and the host response. We will characterize the interface between oral bacteria and human epithelial cells which leads to a disruption in the integrity of periodontal tissue. An understanding of this process could ultimately form the basis of treatments designed to maintain host tissue in a healthy state even in the presence of disease-causing bacteria.
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