Expression and regulation of MMP-1 and MMP-3 in human gingival fibroblasts

Abstract: Matrix metalloproteinases (MMPs) are a group of proteolytic enzymes collectively responsible for the metabolism of extra cellular matrix components. Disturbance of the physiological balance between MMPs and their endogenous inhibitors, tissue inhibitors of metalloproteinases (TIMPs), is implicated in several inflammatory diseases characterized by tissue degradation. Enhanced expression of MMPs including MMP-1 and MMP-3 is demonstrated in gingival connective tissue of individuals with periodontal diseases, but the underlying mechanisms are not well understood. The general aim of this thesis was to investigate the expression and regulation of MMP-1 and MMP-3 as well as their inhibitor TIMP- 1 in human gingival fibroblasts in response to cell interactions with monocytes or to inflammatory mediators. The effect of cell interactions between gingival fibroblasts and monocytes on the expression of MMP-1 and TIMP-1 was studied using a co-culture model, where the cells were cultured either in direct cell-to-cell contact or separated by a membrane to prevent cell contact. Cell interactions of fibroblasts and monocytes stimulated the expression of MMP-1 and TIMP-1 in the fibroblasts as well as in the co-culture medium. The stimulatory effect of cell interactions of fibroblasts and monocytes on the expression of MMP-1 was partly dependent on cell-to-cell contact as well as on the number of fibroblasts and monocytes in the co-cultures. The increased expression of MMP-1 in the fibroblasts was mediated partly by the adhesion molecule inter-cellular adhesion molecule-1 (ICAM-1) and the signal pathway p38 mitogen activated protein kinase (p38 MAPK). Furthermore, the expression of MMP-1 was reduced in the presence of dexamethasone and doxycycline. The effect of cytokines on the expression of MMP-1 and MMP-3 was investigated by culturing the gingival fibroblasts in the absence or presence of interleukin-1beta (IL-1beta), tumor necrosis factor a (TNFalpha) or epidermal growth factor (EGF). These cytokines stimulated the expression of MMP-1 as well as MMP-3 in a time-dependent manner. Furthermore, the stimulatory effect of IL-1beta OBS 1 P and TNFalpha on MMP-1 and MMP-3 expression was mediated partly by the signal transduction pathways tyrosine kinase and p38 MAPK. The expression of MMP-1 and TIMP-1 in gingival fibroblasts was also stimulated by the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA). The PMA stimulated MMP-1 expression was synergistically upregulated by IL-10 as well as by the Ca2+-ionophore A23187. However, the expression of TIMP-1 was not upregulated by the cytokine IL-1beta and reduced by the Ca2+-ionophore. In summary, this thesis demonstrates that cell interactions between gingival fibroblasts and monocytes result in enhanced expression of MMP-1 and TIMP-1 in human gingival fibroblasts and that ICAM-1 and p38 MAPK are involved in the stimulated MMP-1 expression. Expression of MMP-1 and MMP-3 in gingival fibroblasts is also stimulated by the cytokines IL-1beta, TNFalpha and EGF and partly regulated by p38 MAPK, tyrosine kinase and PKC. The stimulatory effect of monocytes and inflammatory mediators on the expression of MMP-1 and MMP-3 in gingival fibroblasts may contribute to tissue degradation in periodontal diseases.