Interaction Between Enterococcus faecalis and Fusobacterium nucleatum Regulated Macrophage Transcriptional Profiling and Reprogrammed Cellular Immune and Metabolic Response.

Refractory apical periodontitis (RAP), a persistent infection after root canal treatment, still has no effective treatment. Enterococcus faecalis (E. faecalis) and Fusobacterium nucleatum (F. nucleatum) are frequently detected in the lesion. We previously found that coaggregation altered gene expression of E. faecalis and F. nucleatum and promoted immune evasion by suppressing pro-inflammatory cytokine secretion of macrophages (Mφs) while sustaining low-grade inflammation. In this study, we further investigated the synergistic effect of coaggregated E. faecalis and F. nucleatum on modulating Mφ immune and metabolic responses. Using transmission electron microscope, flow cytometry, RNA-seq and functional assays, we demonstrated that coaggregated E. faecalis and F. nucleatum caused nuclear shrinkage and increased mitochondria in Mφ while inducing M1 polarization, ROS production, and lipid accumulation of Mφ. The key driver genes causing the difference between single species-infected and coaggregated bacteria-infected Mφ mainly included IFN-stimulated genes and genes related to the chemokine signaling pathway. These findings indicate that the synergism of E. faecalis and F. nucleatum can regulate the immune and metabolic response of Mφ, offering novel insights into therapeutic targets for refractory apical periodontitis.