BACKGROUND AND PURPOSE Cerebral aneurysm is a frequent cerebrovascular event and a major cause of fatal subarachnoid haemorrhage, but there is no medical treatment for this condition. Haemodynamic stress and, recently, chronic inflammation have been proposed as major causes of cerebral aneurysm. Nevertheless, links between haemodynamic stress and chronic inflammation remain ill‐defined, and to clarify such links, we evaluated the effects of prostaglandin E₂ (PGE₂), a mediator of inflammation, on the formation of cerebral aneurysms.EXPERIMENTAL APPROACH Expression of COX and prostaglandin E synthase (PGES) and PGE receptors were examined in human and rodent cerebral aneurysm. The incidence, size and inflammation of cerebral aneurysms were evaluated in rats treated with COX‐2 inhibitors and mice lacking each prostaglandin receptor. Effects of shear stress and PGE receptor signalling on expression of pro‐inflammatory molecules were studied in primary cultures of human endothelial cells (ECs).KEY RESULTS COX‐2, microsomal PGES‐1 and prostaglandin E receptor 2 (EP₂) were induced in ECs in the walls of cerebral aneurysms. Shear stress applied to primary ECs induced COX‐2 and EP₂. Inhibition or loss of COX‐2 or EP₂in vivo attenuated each other's expression, suppressed nuclear factor κB (NF‐κB)‐mediated chronic inflammation and reduced incidence of cerebral aneurysm. EP₂ stimulation in primary ECs induced NF‐κB activation and expression of the chemokine (C‐C motif) ligand 2, essential for cerebral aneurysm.CONCLUSIONS AND IMPLICATIONS These results suggest that shear stress activated PGE₂‐EP₂ pathway in ECs and amplified chronic inflammation via NF‐κB. We propose EP₂ as a therapeutic target in cerebral aneurysm.

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