Prostaglandin E2inhibits NLRP3 inflammasome activation through EP4 receptor and intracellular cAMP in human macrophages

Abstract

Prostaglandin E 2 is a potent lipid mediator involved in maintaining homeostasis but also promotion of acute inflammation or immune suppression. NLRP3 inflammasome plays an important role in host defense. Uncontrolled activation of NLRP3 inflammasome, due to mutations in the NLRP3 gene causes cryopyrin-associated periodic syndromes (CAPS). Here, we showed that NLRP3 inflammasome activation is inhibited by PGE 2 in human macrophages. This effect was mediated through prostaglandin E receptor 4 (EP4) and an increase in intracellular cAMP, independently of protein kinase A (PKA) or exchange protein directly activated by cAMP (Epac). A specific agonist of EP4 mimicked, while its antagonist or EP4 knockdown reversed PGE 2 -mediated NLRP3 inhibition. PGE 2 caused an increase in intracellular cAMP. Blockade of adenylate cyclase by its inhibitor reversed PGE 2 -mediated NLRP3 inhibition. Increase of intracellular cAMP by an activator of adenylate cyclase or an analog of cAMP, or a blockade of cAMP degradation by phosphodiesterase inhibitor decreased NLRP3 activation. PKA or Epac agonists did not mimic and their antagonists did not reverse PGE 2 -mediated NLRP3 inhibition. Constitutive IL-1β secretion from LPS-primed PBMCs of CAPS patients was substantially reduced by high doses of PGE 2 . Moreover, blocking cytosolic phospholipase A 2 α by its inhibitor or siRNA or inhibiting cyclooxygenase 2, resulting in inhibition of endogenous PGE 2 production, caused an increase in NLRP3 inflammasome activation. Our results suggest that PGE 2 might play a role in maintaining homeostasis during the resolution phase of inflammation and might serve as a autocrine and paracrine regulator.