Inactivated Bacillus subtilis R0179 Inhibits Porphyromonas Gingivalis-Induced Gingival Inflammation Via TLR2/NF-κB Signaling in a Murine Model of Periodontitis

This study aims to explore the mechanism by which heat-inactivated Bacillus subtilis (B. subtilis) R0179 modulates the TLR2/NF-κB signaling pathway to inhibit Porphyromonas gingivalis (P. gingivalis) induced gingival inflammation. In vitro experiments showed that P. gingivalis could invade gingival epithelial cells within 2 h of infection, as observed by transmission electron microscopy, and infection with P. gingivalis upregulated the expression of TLR1, TLR2, TLR4, TLR6, and p-NF-κB in gingival epithelial cells while promoting the release of IL-1β, IL-6, and TNF-α. The addition of heat-inactivated B. subtilis R0179 during P. gingivalis infection inhibited the expression of TLR2, TLR4, and p-NF-κB and suppressed the release of IL-1β, IL-6, and TNF-α. In vivo experiments using a mouse model of P. gingivalis-induced experimental periodontitis confirmed these findings, with heat-inactivated B. subtilis R0179 application reducing gingival inflammation, as observed by Hematoxylin and Eosin staining, and downregulating TLR2, TLR4, p-NF-κB, IL-1β, IL-6, and TNF-α signals, as detected by immunohistochemistry. Further investigation using TLR2 and TLR4 agonists revealed that TLR2 receptor agonists antagonized the B. subtilis R0179-induced downregulation of p-NF-κB, IL-6, IL-1β, and TNF-α. These results suggest that B. subtilis R0179 may inhibit P. gingivalis-induced gingival inflammation by suppressing the TLR2/NF-κB signaling pathway, consequently decreasing the production of pro-inflammatory cytokines.