Abstract

Dental implant placement stimulates a response in the supporting tissue; the response involves bone remodeling and release of wound-healing factors, including cytokines. Important factors such as transforming growth factor–β (TGF-β), which promotes matrix synthesis, and prostaglandin E2 (PGE2), a mediator of inflammation, have the potential to alter the communication between bone cells and interfere with implant site healing. Cells responsible for the formation of bone are interconnected to form a multicellular network. Cell-to-cell communication in this network occurs in part via gap junctions. In bone cells, the predominant gap junction protein is connexin-43. TGF-β is a growth modulator produced by osteoblasts and released from the matrix in response to resorption and may influence the progression of periodontal disease. TGF-β also promotes the synthesis of extracellular matrix proteins such as collagen, fibronectin, and adhesion molecules. PGE2 is a mediator of inflammation produced in response to periodontal pathogens. PGE2 levels in the gingival sulcular fluid have been correlated with attachment loss and bone resorption. The relationship between these factors and connexin-43 is unclear. Oral-derived (alveolar) bone was used because the phenotype of bone can differ between species and between different sites in the body. For our studies, explants of human osteoblasts were cultured on eight well plates and characterized by their expression of osteocalcin, osteonectin, alkaline phosphatase, type 1 collagen, and connexin-43. Cells were grown to near confluence on 12 well plates in 20% fetal bovine serum (FBS) Dulbecco modified Eagle medium (DMEM) and then cultured for 24 hours in 0.5% FBS DMEM before exposure to either 1, 5, or 10 ng/mL of TGF-β in serum-free DMEM for 12 or 24 hours or to 20, 80, or 300 ng/mL of PGE2 in serum-free DMEM for 12 or 24 hours. After incubation, cells were removed from plates by scraping and assayed for connexin-43 protein, first by Western blot to confirm the specificity of the anti–connexin-43 antibody and then by slot blot analysis for quantitative comparison of connexin-43 expression. Our studies showed no significant changes in connexin-43 expression in response to either factor. These studies suggest that exogenous TGF-β and PGE2 do not alter connexin-43 expression.

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