Methods: Gingival fibroblasts derived from healthy human gingiva were cultured with or without exogenous PGE2. Cell number and DNA synthesis were measured and potential signaling pathways, which could be involved in the growth inhibitory effect, were investigated using selective activators or antagonists or by measuring the endogenous production of signal transduction molecules in response to PGE2.
Results: PGE2 inhibited the proliferation of human gingival fibroblasts in a dose-dependent manner. The effect was mimicked by forskolin and augmented by IBMX, pointing to cAMP involvement. Indeed, direct measurements indicated significant cAMP production in response to PGE2. In agreement, this effect was mediated via the EP2 receptor (which operates via cAMP generation) but none of the other EP receptors. cAMP generation resulted in activation of Epac, a recently discovered cAMP sensor, and not PKA. Finally, the anti-mitogenic effect of PGE2 in human gingival fibroblasts does not require endogenous, COX-mediated, production of prostanoids.
Conclusions: We have shown that PGE2 inhibits the proliferation of human gingival fibroblasts via the EP2 – cAMP – Epac pathway. Additional studies are ongoing to define the PGE2-induced pathways downstream of Epac leading to cell cycle arrest in these cells.