Exploring the Complex Interplay Between Oral Fusobacterium nucleatum Infection, Periodontitis, and Robust microRNA Induction Including Multiple Known Oncogenic miRNAs

Fusobacterium nucleatum (F. nucleatum, Fn), an oral commensal that can become pathogenic, is associated with periodontitis (PD), adverse pregnancy outcomes, and colorectal cancer (CRC). MicroRNAs (miRNAs) are conserved, non-coding RNAs that play a regulatory role in gene expression and are detected in microbial infections. The aim of this study was to characterize the global microRNA expression kinetics in the mandibles of C57BL/6J mice infected with F. nucleatum for 8 and 16 weeks, and to identify miRNAs as biomarkers of the PD process using high-throughput NanoString nCounter® miRNA panels. Mice were divided into four groups: 8 weeks of Fn infection, 16 weeks of Fn infection, and their respective sham infection. Fn-infected mice at both 8- and 16 weeks showed 100% bacterial colonization on the gingival surface, along with a significant increase in alveolar bone resorption (p<0.0001) and intravascular dissemination to heart, indicating its invasive potential. Out of 577 miRNAs analyzed, seven miRNAs (miR-361-5p, miR-99b-5p) were upregulated, and two miRNAs (miR-362-3p and miR-720) were downregulated in the 8-week Fn infection group. In the 16-week Fn infection group, seven miRNAs (miR-361-5p, miR-99b-5p) were upregulated miRNAs and 13 miRNAs (miR-323-3p, miR-488) were downregulated. Notably, miRNAs such as miR-205, miR-210, miR-199a-3p which were differentially expressed (DE) in the Fn-infected mice at 8 weeks and miR-28 at 16 weeks, have been previously reported in human periodontitis. The 13 miRNAs induced by F. nucleatum (miR-361-5p) are linked to multiple malignancies, including esophageal, gastric, pancreatic, and colorectal cancers. Additionally, the DE miR-126-5p in the 8-week infection group has been identified as a potential biomarker for patients with PD and cardiovascular disease. The results indicate that F. nucleatum acts as a potent oncomicrobe, inducing several miRNAs associated with PD and linking it to systemic comorbidities. Furthermore, the study revealed similar expressions between PD-associated miRNAs and nine CRC tumor-expressed miRNAs.