P. gingivalis interactions with gingival epithelial cells

University Of Louisville, Louisville KY

Investigators

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Abstract

Porphyromonas gingivalis is considered a major pathogen in periodontal disease. Virulence, however, is only expressed in the context of a polymicrobial community which contains both pathobionts and homeostatic commensals, and P. gingivalis is non-pathogenic in germ-free animal models of periodontal disease. Through selective re-inoculations of germ-free mice, we have established that a polymicrobial consortium (PMC) comprising Fusobacterium nucleatum, Filifactor alocis, Selenomoas sputigena and Streptococcus gordonii, is synergistically pathogenic with P. gingivalis. Characterization of the virulence factors of P. gingivalis that are operational in the community context, along with the molecular and cellular basis of synergistic pathogenicity is the goal of this proposal. We have found that a tyrosine phosphatase, Ltp1, secreted by P. gingivalis is active within gingival epithelial cells (GECs) and is unaffected by the PMC. Ltp1 suppressed GEC production of IP-10, a T-cell chemokine that at basal levels contributes to immune surveillance at the gingival barrier. Elevated levels of IP-10, however, increase mobilization of tissue-damaging Th1 and Th17 cells. A reduction in Th1 and Th17 activity mediated by Ltp1 is consistent with the lack of pathogenicity of P. gingivalis as a monoinfection. However, disruption of immune surveillance can be predicted to facilitate pathobiont outgrowth. In a model of pathobiont overgrowth, we found that prolonged action of the PMC on GECs incites IFN-β synthesis which reverses P. gingivalis-induced inhibition of IP-10. Our overall hypothesis, therefore, is that P. gingivalis Ltp1 induces a transient immune suppression by reducing basal levels of IP-10 at the gingival interface. While recruitment of tissue damaging T-cells is thus diminished, the ensuing impaired immune surveillance facilitates expansion of pathobionts in the microbial community. The pathobionts overwhelm immune suppression, and the resulting increased IP-10 levels recruit tissue damaging Th1 and Th17 cells leading to alveolar bone loss. The mechanism of action of Ltp1 is the focus of the first Aim. We shall examine Ltp1-dependent modulation of GEC signaling pathways, focusing on the Ltp1-target STAT1, which control the transcriptional activity of IP-10. In the second Aim we shall molecularly dissect the IFN-β dependent GEC pathway by which the PMC overcomes suppression of IP-10. The third Aim will define the biological consequences of Ltp1-induced polymicrobial synergy through the characterization of pathobiont expansion together with T-cell and cytokine responses in the gingival tissue of germ-free mice. Collectively, this proposal will define a novel tyrosine dephosphorylation-based mechanism by which P. gingivalis can re-program host cell signaling pathways to compromise immune surveillance at the gingival epithelial interface. We will further establish the basis of synergistic polymicrobial pathogenicity with regard to the dysbiotic host responses which are associated with tissue destruction in vivo. This work will achieve a new level of integration of molecular virulence with polymicrobial community pathogenicity and the consequent destructive inflammatory responses in periodontal tissues.