Oxidized phosphatidylcholine induces the activation of NLRP3 inflammasome in macrophages

TLDR

The NLRP3 inflammasome, a multiprotein complex that activates caspase‑1 and IL‑1β, is triggered by endogenous danger signals such as oxidized phospholipids that accumulate during cellular stress and are linked to chronic inflammation. This study examined whether oxidized phosphatidylcholine, specifically POVPC, activates the NLRP3 inflammasome in macrophages to induce IL‑1β secretion. POVPC activates the inflammasome through mitochondrial reactive oxygen species generated by intracellular Ca²⁺ signaling and mitochondrial destabilization. POVPC induced caspase‑1 activation, ASC oligomerization, and IL‑1β production in macrophages, effects that were absent in NLRP3‑ or caspase‑1‑deficient cells and replicated in mouse models, confirming that oxidized phosphatidylcholines drive NLRP3‑mediated inflammation.

Abstract

Abstract The NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome is a multiprotein complex consisting of a receptor, an adaptor protein, and procaspase-1 that induces the secretion of the mature form of IL-1β in response to microbial infection and danger signals. Activation of the NLRP3 inflammasome induced by endogenous danger signal molecules is closely linked to the development and progress of chronic inflammatory diseases. The oxidation of phospholipids occurs upon cellular stress and damage, resulting in the accumulation of oxidized phosphatidylcholines (oxPAPC) such as 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-phosphocholine (POVPC) at inflammatory sites. In this study, we investigated whether oxidized phosphatidylcholine induces the activation of NLRP3 inflammasome in macrophages, leading to the secretion of IL-1β. POVPC induced the degradation of procaspase-1 to caspase-1(p10), the cleavage of pro-IL-1β to IL-1β, and oligomerization of ASC in primary mouse bone marrow-derived macrophages. POVPC-induced production of caspase-1, and IL-1β was abolished in macrophages derived from NLRP3- or caspase-1-deficient mice. In an air pouch model and a peritonitis model in mice, POVPC injection resulted in the production of caspase-1(p10), IL-1β, and IL-18 in wild-type, but not in NLRP3-deficient, mice. POVPC-induced inflammasome activation was mediated by mitochondrial reactive oxygen species resulting from intracellular Ca2+ signaling and mitochondrial destabilization. Our results demonstrate that endogenously produced oxidized phosphatidylcholines such as POVPC induce the activation of NLRP3 inflammasome, leading to the production of IL-1β in macrophages. The results provide an insight to understand how the oxidized lipids endogenously produced upon cellular stress and tissue damage contribute to the inflammatory reaction at pathologic sites.