Effects of specific prostanoid EP receptor agonists on cell proliferation and intracellular Ca²⁺ concentrations in human airway smooth muscle cells

Increased airway smooth muscle mass due to cell proliferation contributes to airway hyper-responsiveness and remodeling in patients with asthma. Prostaglandin E₂ (PGE₂) inhibits proliferation of airway smooth muscle cells, but the role of prostanoid EP receptor subtypes in mechanisms involved has not been fully elucidated yet. We investigated the effects of specific prostanoid EP receptor agonists on cell proliferation and intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in human airway smooth muscle cells. Cell numbers were assessed by mitochondria-dependent reduction of 4-[3-(4-lodophenyl)-2-(4-nitrophenyl)-2H-5- tetrazolio]-1, 3-benzene disulfonate to formazan (WST-1 assay). RT-PCR data showed that human airway smooth muscle cells express EP2, EP3, and EP4 but not EP1 receptor mRNA. PGE₂ (1 nM-1 μM) inhibited cell proliferation induced by 5% fetal bovine serum (FBS) in a concentration-dependent manner. (16S)-9-deoxy-9β-chloro-15-deoxy-16-hydroxy-17, 17-trimethylene-19, 20-didehydro PGE₂ sodium salt (ONO-AE1-259-01; EP2 receptor agonist) and 16-(3-methoxymethyl)phenyl-ω-tetranor-3,7-dithia PGE₂ (ONO-AE1-329; EP4 receptor agonist) inhibited the 5% FBS-induced cell proliferation. ONO-AE1-259-01 and ONO-AE1-329 also significantly increased the cytosolic cAMP levels. In contrast, 11,15-O-dimethyl PGE₂ (ONO-AE-248; EP3 receptor agonist) elicited an oscillatory increase in [Ca ²⁺]_i but did not affect the cell growth or cAMP levels. [(17S)-2,5-ethano-6-oxo-17,20-dimethyl PGE₁] (ONO-DI-004; EP1 receptor agonist) did not affect cell growth, cAMP levels, or [Ca ²⁺]_i. In conclusion, PGE₂ inhibits FBS-induced cell proliferation mostly via EP2 and EP4 receptor activation and subsequent cAMP elevation. The EP3 receptor agonist causes an increase in [Ca ²⁺]_i without affecting cell growth. There is no functional expression of the EP1 receptor. Research on prostanoid EP receptors may lead to novel therapeutic strategies for treatment of asthma.