OR15 - Role of Neutrophil Extracellular Traps in Apical Periodontitis Development

Apical periodontitis (AP) is characterized by the pathological destruction of tooth-surrounding tissues induced by the host inflammatory response to root canal infection. Neutrophil Extracellular Traps (NET) comprise networks of extracellular fibers that bind to pathogens allowing neutrophils to mobilize and kill them. Peptidyl arginine deiminase 4 (PAD4) is essential for NET-mediated antibacterial function. PAD4 mice are more susceptible to bacterial infection due to lack of NET. The role of neutrophils and NETs in AP development is poorly understood. Here, we investigated the role of NET in AP development using an in vivo experimental model of AP. Dental pulps of first mandibular molars of 26-week-old C57BL/6NJ and PAD4 mice (n=4/each strain) were exposed to the oral environment for establishment of AP. Animals without pulp exposure served as controls. Mice were euthanized at 7 and 21 days after pulp exposure, and one hemimandible was used for histological and micro–computed tomography analyses, and the other for RNA sequencing. PAD4 mice showed significantly increased apical bone resorption in comparison with wild-type mice at both time periods (P < 0.05, T-test). RNA sequencing identified 626 genes as differentially expressed. Genes with functions related to leukocyte migration and chemotaxis, response to interferon-beta, regulation of defense response and cytokine-mediated signaling pathways were upregulated while genes related to myofibril assembly, muscle contraction, cell morphology and differentiation were downregulated in PAD4 (P < 3x10^-14), suggesting dysregulated inflammatory response. Later stages of AP development may also represent a shift in cytokine networks in favor of an anti-inflammatory effect.