Platelet Factor 4 Signaling in Human Gingival Fibroblasts

Objectives: Inflammatory periodontal disease (periodontitis) is a common global health problem. During periodontal infection, microbial pathogens signal the resident cells of the gingival connective tissues (gingival fibroblasts) to release matrix metalloproteinases (MMPs) such as collagenase (MMP-1) that degrade the extracellular matrix, leading to tissue destruction and tooth loss. However, the signals that cause fibroblasts to release tissue-destructive MMPs are not defined. Platelets are cells that regulate hemostasis but are now known to influence the activity of many other cells through their release of growth factors and cytokines. A major cytokine housed within platelet alpha (a)-granules is platelet factor 4 (PF4), which has documented effects on the behaviour of neutrophils, monocytes and T-cells.
Importantly, the effect of PF4 on fibroblasts is unknown. The objective of this project is to study the role of platelet factor 4 in modulating MMP-1 (collagenase) release from gingival fibroblasts.
Methods: Human gingival fibroblasts were serum-starved and cultured in the presence or absence of recombinant PF4 (200-2000 ng/mL). To test the hypothesis that PF4 regulates MMP-1 production and/or secretion by gingival fibroblasts, the staining intensity of MMP-1 was determined via confocal microscopy and quantified with ImageJ software. The amount of secreted pro-MMP-1 was quantified by enzyme-linked immunosorbent assay (ELISA) analysis of the cell culture supernatants.
Results: Cells stimulated with recombinant PF4 displayed increased MMP-1 staining intensity compared to unstimulated controls. This increase was also observed at various time points ranging from 1 h to 24 hrs. Compared to unstimulated controls, cells incubated with PF4 released ~80% more pro-MMP-1 over a 24-hr period, as determined by ELISA.
Conclusions: Based on these preliminary data, platelets may promote the degradation of periodontal connective tissues by stimulating the production and/or release of MMP-1 by human gingival fibroblasts.