Acid stress modulates metabolo-inflammatory pathways in oral epithelial cells

Acidification of the oral environment has been implicated in the initiation and progression of oral pathologies including oral cancer, but how acidic environments modulate normal oral epithelial cell (OEC) responses to microbial ligands is not understood. This study examined the impact of acidic stress on OEC morphological, molecular, and functional responses to toll-like-receptor ligand engagement in vitro. OEC cultures were exposed to either normal (pH≈8.0) or acidified growth media (pH≈3.0) for 24 hours prior to machine-learning-guided morphological analysis and exposure to either toll-like receptor (TLR)5 (flagellin) or TLR2/TLR1 (Pam3CSK4) agonists. Multiplex gene expression technology was used to quantify the transcriptional responses of metabolic- and immune-related genes at 6 hours post-TLR agonist exposure. OEC-mediated production of transforming growth factor-beta (TGF-β) was assessed by enzyme-linked immunosorbent assay at 2-, 6-, and 24-hours post-agonist exposure. Results showed that acid exposure induced significant changes to OEC morphology resembling epithelial-mesenchymal transition, the differential expression of n=197 metabolic- and n=43 immune-related genes and significantly increased OEC TGF-β1 production. The results demonstrate that acid stress skews normal OECs towards pro-inflammatory and pro-oncogenic phenotypes when faced with concomitant microbial ligand challenge and provide key molecular clues to OEC survival strategies with potential implications for elucidating the early molecular events in the development of epithelial dysplasia.