Fibrin aggravates periodontitis through inducing NETs formation from mitochondrial DNA

Objectives: This study investigated the role of fibrin on neutrophil extracellular traps (NETs) formation from neutrophils and to elucidate the involvement of mitochondria in NETs formation during periodontitis.

Materials and methods: Plasminogen-deficient (Plg^-/-) mice were employed to evaluate the effects of fibrin deposition on inflammation, bone resorption, and neutrophil infiltration in periodontal tissues. In addition, in vitro tests evaluated fibrin's impact on neutrophil-driven inflammation. Mitochondrial reactive oxygen species (mtROS) levels within neutrophils were quantified utilizing flow cytometry and immunofluorescence in vitro. Furthermore, the anti-inflammatory properties of the mtROS scavenger, Mito-TEMPO, were confirmed to regulate the NET formation in vitro and in vivo.

Results: Plasminogen deficiency resulted in increased fibrin deposition, neutrophil infiltration, inflammatory factors concentration, and alveolar bone resorption in periodontal tissues. After neutrophils were treated by fibrin in vitro, the expression of inflammatory factors, the formation of mtROS, and NETs enriched in mitochondrial DNA (mtDNA) were upregulated, which were reversed by Mito-TEMPO in vitro. Moreover, Mito-TEMPO alleviated inflammation in Plg^-/- mice.

Conclusions: This study showed that fibrin deposition in gingiva induced the NET formation in Plg^-/- mice, in which the DNA in NETs was from mitochondria depending on increasing mtROS.