Transcriptomic Regulation of Apical Periodontitis by Nociceptors

Apical periodontitis (AP) is a painful inflammatory disease resulting from tooth infection that affects millions worldwide with a marked impact on quality of life and is accompanied by bone loss surrounding the affected tooth. There is growing evidence that the nociceptive fibers densely innervating teeth regulate the disease progression, in addition to their sensorial function. We hypothesized that nociceptors regulate the transcriptomic profile of the periapical osteolytic lesion in a mouse model of AP. Male control (Nav1.8 cre+/-) and nociceptor-ablated (Nav1.8cre+/- DTAlox+/-) mice were generated and underwent pulp exposure procedures on all 4 first molars and at 8 weeks of age. At either 0, 7, or 14 days after pulp exposure, periapical tissues were dissected from mice (n=3-4/strain/time point). Total RNA was extracted from the pooled periapical lesions from each animal and submitted for total RNA sequencing and bioinformatic analysis. We found that pulp exposure triggers the differential expression of hundreds of genes within the periapical lesion over the course of infection with marked differences between in both control and mice with nociception ablation. Importantly, at 14 days post pulp-exposure, 422 genes were differentially expressed between nociceptor-ablated and control mice with greater enrichment of biological processes related to inflammation, specifically immune cell chemotaxis and migration, compared to control mice. Among these inflammatory markers, TNFα, IL-1α, and IL-1β, that are known to play a crucial role in AP were significantly upregulated in nociceptor-ablated mice. In conclusion, nociceptor-ablation regulates the transcriptomic profile of periapical lesions in a mouse model of AP, shifting the gene expression profile to a greater enrichment of inflammatory genes, suggesting nociceptors play a role in the kinetics of the immune response. This newly uncovered neuro-immune axis and its mechanisms in AP can potentially be an important therapeutic target for the treatment of this prevalent disease. 3-4 male mice (~8 weeks old) were used from each strain (Nav1.8cre+ [control] and Nav1.8cre+/DTA+ [nociceptor-ablated]) at each time point (Day 0, Day 7, and Day 14), 20 samples total.