Porphyromonas gingivalis is an important gram-negative periopathogen strongly associated with adult type periodontitis. P. gingivalis lipopolysaccharide (LPS) displays an unusual amount of lipid A structural heterogeneity which we hypothesized may be a potential modulator of the innate host defense response. During the previous funding period we discovered a novel molecular mechanism used by P. gingivalis to evade and subvert the TLR4 component of human innate immune system. Signal transduction following binding of lipopolysaccharide (LPS) to Toll-like receptor 4 (TLR4) is an essential aspect of host innate immune responses to infection by Gram negative pathogens. We found that P. gingivalis, uses endogenous lipid A 1- and 4'-phosphatase activities to modify its LPS, creating immunologically silent, nonphosphorylated lipid A. This unique lipid A provides a highly effective mechanism employed by this bacterium to evade TLR4 sensing and to resist killing by cationic anti- microbial peptides. Therefore our overall hypothesis for this renewal application is: """"""""P. gingivalis modulates its interactions with the host innate defense system through regulation of lipid A phosphatase activity"""""""". Specifically we have found that hemin regulates the lipid A structural composition of P. gingivalis such that a low hemin concentration a TLR4 silent LPS is made whereas at high hemin concentrations a TLR4 antagonist lipid A is found. Our results indicate that the hemin concentration regulation of lipid A phosphatase activity shifts P. gingivalis lipid A activity from TLR4 evasive to TLR4 suppressive, potentially altering critical interactions between this bacterium, the local microbial community, and the host innate immune system. Our hypothesis will be examined by directly determining lipid A 1 and 4'phosphatase enzymatic activity (Aim 1), characterizing lipid A 1 and 4'phosphatase protein expression (Aim 2), and genetic regulation (Aim 3). Furthermore, Aim 4 will examine the ability of the TLR4 evasive and suppressive lipid A structures to alter the local microbial community associated with disease and the host innate immune system in a rabbit model of periodontitis. These studies will elucidate the mechanisms by which P. gingivalis regulates its lipopolysaccharide interactions with the innate host defense system and test the contribution of lipid A structural regulation in an animal model of disease.

Public Health Relevance

Porphyromonas gingivalis is an oral bacterium that is believed to contribute to the form of gum disease that affects a large percentage of adults. The mechanism's that this bacterium employs to induce disease are not well understood. This proposal will examine a unique characteristic of this bacterium that allows the bacterium to either activate or suppress a form of inflammation. We suspect the modulation of the host immune response contributes to its ability to cause disease.

National Institute of Health (NIH)
National Institute of Dental & Craniofacial Research (NIDCR)
Research Project (R01)
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Special Emphasis Panel (ZRG1-MOSS-B (03))
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Lunsford, Dwayne
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University of Washington
Schools of Dentistry
United States
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To, Thao T; Gümü?, Pinar; Nizam, Nejat et al. (2016) Subgingival Plaque in Periodontal Health Antagonizes at Toll-Like Receptor 4 and Inhibits E-Selectin Expression on Endothelial Cells. Infect Immun 84:120-6
Coats, Stephen R; Hashim, Ahmed; Paramonov, Nikolay A et al. (2016) Cardiolipins Act as a Selective Barrier to Toll-Like Receptor 4 Activation in the Intestine. Appl Environ Microbiol 82:4264-78
Herath, Thanuja D K; Darveau, Richard P; Seneviratne, Chaminda J et al. (2016) Heterogeneous Porphyromonas gingivalis LPS modulates immuno-inflammatory response, antioxidant defense and cytoskeletal dynamics in human gingival fibroblasts. Sci Rep 6:29829
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Ding, P-H; Wang, C-Y; Darveau, R P et al. (2013) Nuclear factor-?B and p38 mitogen-activated protein kinase signaling pathways are critically involved in Porphyromonas gingivalis lipopolysaccharide induction of lipopolysaccharide-binding protein expression in human oral keratinocytes. Mol Oral Microbiol 28:129-41

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