Antimicrobial and Inflammatory Epithelial Responses Modulated by P. Gingivalis-Induced PLA2-IIA

Although specific oral pathogenic bacterial species [i.e., P. gingivalis (Pg)] have been related to established periodontal lesions and can recapitulate disease in animal models, the early events associated with epithelial-oral pathogen interactions in a complex microbial ecology that creates a microenvironment enabling the initiation of periodontitis (i.e., periodontal dysbiosis) remain unclear. Current studies in our laboratory identifying global gene expression profiles of immunoinflammatory genes in OECs exposed to oral bacteria species, indicated that Pg is able to induce a remarkable increase in the transcription of secreted phospholipase A2-group IIA (PLA2G2A), whose expression levels clearly exceeded 20-30 times those of classical immunoinflammatory mediators (e.g., cytokines/chemokines and antimicrobial peptides). Protein levels determination indicated that PLA2-IIA expression appears to be Pg-specific response since other oral G+ and G- bacterial species failed to induce similar PLA2-IIA responses. PLA2-IIA belongs to a subgroup of 11 mammalian secreted phospholipases A2 members with antimicrobial and immunomodulatory activities. Moreover, evidence indicates that Notch-1 is a central regulator of mucosal immune responses and is involved in PLA2-IIA expression by intestinal epithelial cells. Consistently, we observed that Pg induced the expression of the NOTCH1 gene and its activation in OECs. PLA2-IIA is a highly cationic lipolytic enzyme produced by multiple cells and plays a critical role in infection and inflammation through its potent antimicrobial properties (especially against Gram-positive bacteria), as well as its effects on activating inflammatory cells and lipid mediator production. Thus, modulation of epithelial PLA2-IIA levels particularly at mucosal surfaces could be a plausible strategy for pathogenic bacterial species to break the host-microbiota symbiotic interactions leading to inflammatory disease. Therefore, we hypothesize that antimicrobial and immunoinflammatory responses of OECs are modulated by P. gingivalis through differential activation of PLA2-IIA in a mechanism that involves the Notch-1 receptor. To test this hypothesis we propose the following two specific aims: (i) to identify the OEC signaling pathways involved in P. gingivalis-induced PLA2-IIA, and (ii) to determine the cellular location and function of OEC-produced PLA2-IIA in response to P. gingivalis. To address these knowledge gaps, we will use oral epithelial cell culture models, as well as different Pg strains, combined with neutralization experiments using monoclonal antibodies, chemical inhibitors or siRNA approaches to: (i) identify OEC receptors/pathways involved in Pg-induced PLA2-IIA, and (ii) determine the cellular location and function of OEC-produced PLA2-IIA after Pg challenge to more fully understand the potential role of this interesting molecule in the initial states of infection and inflammation of the oral mucosa. This contribution's significance will enable a better understanding of the cellular and molecular mechanisms involved in Pg-induced PLA2-IIA as a potential mechanism involved in Pg-induced dysbiosis. The results are expected to contribute to a strong evidence-based foundation for future studies designed to identify molecular target(s) associated with Pg-induced epithelial PLA2-IIA production in vitro (using primary OECs and organotypic cultures) and in vivo (using a nonhuman primate model) that could increase the risk for oral mucosa dysbiosis. More focused control of this dysbiosis process should ultimately provide new opportunities for the development of innovative approaches to prevent/treat periodontitis.