Abstract
Elevated levels of prostaglandins such as PGE~2~ in inflamed gingiva play a significant role in the tissue destruction caused by periodontitis, partly by targeting local fibroblasts. Only very few studies have shown that PGE~2~ inhibits the proliferation of a gingival fibroblast (GF) cell line, and we expanded this research by using primary human GFs (hGFs) and looking into the mechanisms of the PGE~2~ effect. GFs derived from healthy human gingiva were treated with PGE~2~ and proliferation was assessed by measuring cell number and DNA synthesis and potential signaling pathways were investigated using selective activators or inhibitors. PGE~2~ inhibited the proliferation of hGFs dose‐dependently. The effect was mimicked by forskolin (adenylate cyclase stimulator) and augmented by IBMX (a cAMP‐breakdown inhibitor), pointing to involvement of cAMP. Indeed, PGE~2~ and forskolin induced cAMP generation in these cells. Using selective EP receptor agonists we found that the anti‐proliferative effect of PGE~2~ is mediated via the EP~2~ receptor (which is coupled to adenylate cyclase activation). We also found that the effect of PGE~2~ involved activation of Epac (exchange protein directly activated by cAMP), an intracellular cAMP sensor, and not PKA. While serum increased the amount of phospho‐ERK in hGFs by ∼300%, PGE~2~ decreased it by ∼50%. Finally, the PGE~2~ effect does not require endogenous production of prostaglandins since it was not abrogated by two COX‐inhibitors. In conclusion, in human gingival fibroblasts PGE~2~ activates the EP~2~—cAMP—Epac pathway, reducing ERK phosphorylation and inhibiting proliferation. This effect could hamper periodontal healing and provide further insights into the pathogenesis of inflammatory periodontal disease. J. Cell. Biochem. 108: 207–215, 2009. © 2009 Wiley‐Liss, Inc.