ObjectiveThis study aims to explore the potential relationships of cell-free DNA (cfDNA) in gingival crevicular fluid (GCF) with periodontal clinical indicators and the expression of DNA receptor pathway cyclic guanosine phosphate-adenosine phosphate synthase (cGAS)-stimulator of interferon genes (STING) in gingival tissues and human gingival fibroblasts (HGFs).MethodsGCF and gingival tissue samples were collected from periodontally healthy individuals and patients diagnosed with periodontitis. Periodontal clinical indicators were recorded, including plaque index (PLT), bleeding index (BI), probing depth (PD), and clinical attachment level (CAL). The concentration of cfDNA in GCF was quantified, and the correlation between GCF and periodontal clinical indicators was analyzed. Immunofluorescence and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were used to assess the distribution of cGAS, STING, and p-STING in gingival tissues. Additionally, the mRNA expression levels of the key components of the cGAS-STING signaling pathway, namely, cGAS, STING, inhibitory of kappa-B kinase (IKK), nuclear factor kappa-B p65 (NF-κB p65), interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α), were measured. Furthermore, cfDNA extracted from GCF was employed to stimulate HGFs in the healthy control and periodontitis groups, and the mRNA expression levels of the key molecules of cGAS-STING signaling pathway were detected through Western blot and RT-qPCR.ResultsThe concentration of cfDNA in GCF was found to be significantly elevated in the periodontitis group compared with the control group. Moreover, cfDNA concentration demonstrated a strong positive correlation with the periodontal clinical indicators. Immunofluorescence analysis revealed considerably increased percentage of fluorescence co-localization of cGAS, STING, and p-STING with the gingival fibroblast FSP-1 marker in the gingival tissues of the periodontitis group. The mRNA expression levels of cGAS, STING, IKK, NF-κB p65, IL-1β, IL-6,and TNF-α were significantly higher in the periodontitis group.In vitrostimulation of HGFs with GCF-derived cfDNA resulted in increased protein expression of cGAS and p-STING and considerably upregulated the mRNA expression levels of cGAS, STING, IKK, NF-κB p65, IL-1β, IL-6, and TNF-α in the healthy and periodontitis groups compared with the blank group. Correlation analysis showed that the concentration of cfDNA at the sampling site was positively correlated with the mRNA expression levels of cGAS, STING, NF-κB p65, and IL-6 in gingival tissues.ConclusioncfDNA concentrations in the GCF of patients with periodontitis are considerably elevated, and are associated with the activation of the cGAS-STING signaling pathway in HGFs. These findings suggest that cfDNA contributes to the progression of periodontitis.
