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Background and Objective: Periodontitis is a highly prevalent chronic inflammatory disease that causes tooth loss, morbidity and confers an increased risk for systemic disease. Tissue destruction during periodontitis is due in large part to collagen-degrading matrix metalloproteinases (MMPs) released by resident cells of the periodontium in response to pro-inflammatory cytokines. Platelets are immune-competent blood cells with a newly recognized role in chronic inflammation, however their role in the pathogenesis of periodontitis is undefined. Consequently, the objective of this study was to assess the effect of platelet factor 4 (PF4), a major platelet-derived cytokine, on MMP-1 (collagenase) expression in human gingival fibroblasts (HGFs).Methods: HGFs were cultured in the presence or absence of recombinant PF4. Pro-MMP-1 secretion was quantified by enzyme-linked immunosorbent assay (ELISA) analysis of the cell culture supernatants. MMP-1 transcription was quantified by real-time polymerase chain reaction (qPCR). Regulation of MMP-1 production by the p44/42 MAP kinase (MAPK) signaling pathway was examined in the presence or absence of PF4.Results: Exposure to PF4 caused a ~2-3-fold increase in MMP-1 transcription and secretion from cultured human gingival fibroblasts (HGFs). PF4 treatment also enhanced phosphorylation of p44/42 MAP kinase (MAPK), which has been previously shown to induce MMP-1 expression in fibroblasts. Blockade of p44/42 MAPK signaling with the cell-permeant inhibitors PD98059 and PD184352 abrogated PF4-induced pro-MMP-1 transcription upregulation and release from cultured HGFs. Conclusion: We conclude that platelet factor 4 upregulates MMP-1 expression in human gingival fibroblasts in a p44/42 MAPK-dependent manner. These findings point to a previously unidentified role for platelets in the pathogenesis of periodontal diseases.
Aim: Platelets contribute to chronic inflammation but their role in periodontitis is not well understood. The aim of this study was to compare platelet recruitment and activation in healthy and inflamed periodontium. Materials and Methods: Gingival crevicular fluid (GCF) samples were obtained from sites of healthy periodontium, gingivitis and periodontitis. Platelets were quantified in the GCF by staining and microscopy. GCF concentrations of platelet factor 4 (PF4) [PF4]GCF and glycoprotein IIbIIIa ([GPIIbIIIa]GCF) were determined by ELISA. Blood samples were obtained from the 3 patient groups. Platelets were isolated from whole blood and stimulated with lipopolysaccharide (LPS) from P. gingivalis to evaluate and compare the LPS-induced PF4 release. Results: Compared to controls, platelet recruitment was increased at gingivitis and periodontitis sites, based on platelet counts and [GPIIbIIIa]GCF. [PF4]GCF was elevated in periodontal pockets but not at gingivitis or healthy sites. Circulating plasma levels of PF4 were higher in patients with generalized severe periodontitis (SP), compared to patients with gingivitis or healthy periodontium. Platelets isolated from SP patients contained and released more PF4 in response to P. gingivalis LPS than platelets from gingivitis or periodontally healthy patients. Conclusions: Periodontitis is associated with increased platelet activation and PF4 release, both locally and systemically.