Role of Notch-1/PLA2-IIA in oral dysbiosis, inflammation, and periodontal disease

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The mechanisms by which mucosal responses to the microbiota in the presence of specific pathogenic bacterial species (e.g. P. gingivalis-Pg), could abrogate the host-microbe symbiotic relationship leading to dysbiosis and inflammatory disease remain not fully understood. Our pioneering R21 studies demonstrated that Pg-induced phospholipase A2 group IIA (PLA2-IIA), in a mechanism that involves activation of Notch-1 receptor (N1R) by Pg gingipains, modulates the antimicrobial properties of oral epithelial cells (OECs). This is consistent with in vivo and clinical evidence supporting the potent (ng/mL) antimicrobial effects of PLA2-IIA. Noteworthy, oral bacterial species exhibited differential antimicrobial susceptibility to PLA2-IIA. Moreover, gingival PLA2-IIA expression and N1R activation were elevated during initiation and progression of periodontal disease, which was concurrent with oral dysbiosis in non-human primates. In agreement with these observations, new preliminary studies using mice models demonstrated increased gingival PLA2-IIA expression and N1R activation early after Pg infection. Remarkably, the oral microbiome of transgenic mice overexpressing PLA2-IIA (PLA2-IIA-Tg) exhibited significant differences in the abundance of bacterial species (decreased Firmicutes and increased Proteobacteria) compared to their wild type co-caged littermates. Oral dysbiosis in PLA2-IIA-Tg mice was associated with changes in the gingival expression of genes involved in intracellular sensing (NOD2), classical antimicrobial factors (S100a8/S100a9, hBD1), and M1/M2 macrophage chemokines. N1R is a critical modulator of mucosal immunity; therefore, the ability of Pg to activate N1R in OECs is an exciting and innovative observation. Preliminary data suggested that other OEC functions/responses (bacterial sensing, apoptosis, and autophagy) could involve Pg-induced N1R activation. Based on this evidence, we hypothesize that activation of Notch-1/PLA2-IIA pathway in gingival epithelial surfaces would be an innovative and plausible mechanism by which pathogens such as Pg could specifically enhance oral dysbiosis, inflammation and periodontal disease. To test this hypothesis, we propose three specific aims: (i) To determine the role of PLA2-IIA in Pg-induced oral dysbiosis, inflammation and periodontal disease, (ii) To determine the role of epithelial Notch-1 in Pg-induced PLA2-IIA and periodontitis, and (iii) To identify and validate oral epithelial innate responses modulated by Pg through Notch-1 activation. To address these knowledge gaps, we will use the Pg-induced periodontitis oral gavage model in mouse strains with or without a natural PLA2-IIA mutation, PLA2-IIA-Tg mice with their WT littermates, epithelial-specific N1R deficient mice, as well as OEC cultures to validate the role of this pathway in Pg-induced oral dysbiosis and periodontal disease. These findings will enable a better understanding of the cellular and molecular mechanisms that are specifically modulated by pathogens to alter microbial communities at mucosal surfaces as well as contribute to the evidence for future research designed to determine the role of N1R in oral health and other diseases (e.g., oral cancer).