Fig. 5: Microbial extracellular DNA (eDNA) is a potent activator of gingival Ctsk.

a OFS-1 was IV injected 3 days after the 1 h topical application of eDNA or iDNA to the mouse palatal gingiva and the fluorescent signal was recorded 4 days after the eDNA or iDNA topical application. b Quantification of OFS-1 fluorescent signal (n = 3–6). c Relative abundance of microbial genera in the mouse periodontitis model. The palatal gingival swabs were collected before (D0), 1 day (D1), and 7 days (D7) after ligature placement (n = 3 per time point). The ligatures were recovered from the mouse maxillary second molar D1 and D7 (n = 4 per time point). eDNA and iDNA samples were prepared (n = 4 per sample that were combined) and subjected to 16 S rRNA sequencing. d SYTOX green-fluorescent images of subgingival plaque collected from human subjects with clinically diagnosed periodontitis (scale bar: 20 μm) and a pair of incident-light and SYTOX orange-fluorescent images of a recovered ligature from the mouse periodontitis model. Arrowheads indicate eDNA. e The proposed mechanism of periodontitis initiation (red letters and arrows). The present study indicated that eDNA component of the dental plaque biofilm might be readily recognized by gingival fibroblasts through TLR9. Upon the activation, gingival fibroblasts may release Ctsk, resulting in gingival degradation leading to the periodontal pocket formation (dotted line). ANOVA with Tukey’s multiple-comparison test (b). Data are presented as mean values ± SD; p < 0.05 was considered significant. The source data are provided in Supplementary Data 1, Fig. 5b.