Prostaglandin E₂ inhibits the proliferation of human gingival fibroblasts via the EP₂ receptor and Epac

Elevated levels of prostaglandins such as PGE₂ 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 PGE₂ 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 PGE₂ effect. GFs derived from healthy human gingiva were treated with PGE₂ 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 PGE₂ is mediated via the EP₂ receptor (which is coupled to adenylate cyclase activation). We also found that the effect of PGE₂ 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%, PGE₂ decreased it by ∼50%. Finally, the PGE₂ effect does not require endogenous production of prostaglandins since it was not abrogated by two COX-inhibitors. In conclusion, in human gingival fibroblasts PGE₂ 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.