Porphyromonas gingivalis‐Lipopolysaccharide Induced Gingival Fibroblasts Trained Immunity Sustains Inflammation in Periodontitis

ABSTRACT Aim To investigate whether trained immunity occurs in gingival fibroblasts (GFs) and its relationship to the persistence of inflammation in periodontitis. Methods Periodontally healthy and inflammatory gingival fibroblasts (HGFs and IGFs) were cultured through continuous adherence subculture of tissue blocks. Trained immunity in HGFs was evaluated via a classic in vitro model, with relevant markers assessed via enzyme‐linked immunosorbent assay, lactate content assay, glycolytic rate assay, and chromatin immunoprecipitation. A histone methyltransferase blocker and a PI3K inhibitor were added to investigate the mechanisms underlying trained immunity. The relationship between trained immunity and periodontitis was further examined via immunofluorescence staining and chromatin immunoprecipitation on IGFs. Results Compared with untrained cells, GFs trained with Porphyromonas gingivalis ‐lipopolysaccharide ( P. gingivalis ‐LPS) exhibited a significant increase in IL‐6 and TNF‐α secretion, enhanced glycolytic metabolism, and enriched mono‐methylation of lysine 4 on histone H3 (H3K4me1) at the enhancer regions of TNF‐α and IL‐6. The addition of a histone methyltransferase blocker and a PI3K inhibitor greatly reduced trained immunity. Additionally, the response of IGFs to P. gingivalis ‐LPS stimulation and their epigenetic modifications were similar to those observed in trained HGFs. Conclusion This study novelly discovered that both P. gingivalis ‐LPS‐stimulated HGFs and IGFs in periodontitis acquired trained immunity. Following P. gingivalis ‐LPS stimulation, HGFs underwent metabolic and epigenetic changes via the PI3K/AKT pathway, with these epigenetic changes also observed in IGFs. This finding suggests that trained immunity in GFs may be a key mechanism underlying the recurrence and persistence of periodontitis.