Background and Objective: High-mobility-group box 1 functions as a late-phase inflammatory mediator. It can be released extracellularly by macrophages and necrotic cells through lipopolysaccharide and tumor necrosis factor-alpha. The objective of this study was to clarify the source of high-mobility-group box 1 in chronic periodontitis tissues and tumor necrosis factor-alpha-stimulated gingival epithelial cells, and subsequently elucidate its inducible inflammatory pathway.
Material and Methods: Chronic periodontitis and healthy gingival sections were stained for high-mobility-group box 1 by immunohistochemistry and immunofluorescence. The amounts of high-mobility-group box 1 released into the gingival crevicular fluid and supernatants from gingival epithelial cells stimulated by tumor necrosis factor-alpha were examined by western blot. The phosphorylation of mitogen-activated protein kinases (MAPKs) in gingival epithelial cells was also examined.
Results: High-mobility-group box 1 was detected in the cytoplasm and nucleus of gingival epithelial cells with periodontitis. Western blotting revealed a significant increase in high-mobility-group box 1 expression in the gingival crevicular fluid from periodontitis patients. High-mobility-group box 1 production in gingival epithelial cells was increased following stimulation with tumor necrosis factor-alpha. The molecular dialogue between tumor necrosis factor-alpha and gingival epithelial cells involved modulation of the activities of p38MAPK, Jun N-terminal kinase and p44/42. Interestingly, only phosphorylation of p38MAPK contributed to more than half of the signaling initiated by tumor necrosis factor-alpha-elicited high-mobility-group box 1 release.
Conclusion: High-mobility-group box 1 is continuously released from the gingival epithelial cells modulated by tumor necrosis factor-alpha. These findings imply that high-mobility-group box 1 expression and possibly p38MAPK constitute important features in periodontitis.