Involvement of cyclooxygenase-2 in interleukin-1α-induced prostaglandin production by human periodontal ligament cells

Background: Human periodontal ligament (PDL) cells produce prostaglandin (PG) E-2 in response to proinflammatory cytokines. However, the mechanism of PGE(2) production is not well understood. The purpose of the present study was to investigate the involvement of cyclooxygenase (COX)-1 and COX-2 in PGE(2) production by PDL cells stimulated with a proinflammatory cytokine, interleukin-1 alpha (IL-1 alpha), and to examine the regulation of PGE(2) production by cell-cell interaction of human gingival keratinocytes and PDL cells. Methods: The levels of PGE(2) in the culture media of PDL cells stimulated with IL-1 alpha or culture media of human gingival keratinocytes were determined by an enzyme-linked immunosorbent assay. Expression of COX-1 and -2 mRNA and protein was studied by Northern blot analysis and Western blot analysis, respectively. Results: IL-1 alpha-stimulated PDL cells produced PGE(2) in a time-dependent manner. Indomethacin, a non-selective COX-1/COX-2 inhibitor, and NS-398, a selective COX-2 inhibitor, completely inhibited PGE(2) production by the IL-1 alpha-stimulated cells. COX-2 mRNA was detected after IL-1 alpha stimulation, although it was not detected in unstimulated cells. There was no difference in expression of COX-1 mRNA between unstimulated cells and IL-1 alpha-stimulated cells. Expression of COX-2 protein in IL-1 alpha-stimulated cells was increased, compared with that in unstimulated cells, whereas COX-1 protein expression was almost the same in both the cells. Treatment of IL-1 alpha-stimulated PDL cells with dexamethasone, known to inhibit COX-2 expression, prevented PGE(2) production and COX-2 mRNA expression. Addition of the culture media of human gingival keratinocytes to PDL cells increased PGE(2) production. The PGE(2) production was depressed by treatment of the cells with IL-1 receptor antagonist and anti- IL-1 alpha antibody, not with anti-IL-1 beta antibody. The PGE(2) production was also inhibited by treatment with NS-398 and dexamethasone. Conclusions: We suggest that PDL cells stimulated with IL-1 alpha produce PGE(2) through de novo synthesis of COX-2 and that the cell interaction of gingival keratinocytes and PDL cells controls COX-2 expression and PGE(2) production via IL-1 alpha or a IL-1 alpha-like factor(s). Selective COX-2 inhibitors, which have the advantage of reduced gastric toxicity, may provide a useful approach to treatment of periodontal disease.