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Atherosclerosis is recognized as an inflammatory disease. Recent data suggest that NLRP3 inflammasome mediates caspase-1 activation and IL-1β production and may lead to vascular inflammation. In this study, we investigated the role of a naturally occurring negatively charged LDL in the induction of inflammasome activation and characterized the signaling pathway in subsequent IL-1β secretion in human macrophages.
Native and negatively charged LDL (nLDL and LDL-) were isolated from plasma of patients with acute myocardial infarction by ultracentrifugation followed by ion-exchange chromatography. Human macrophages, differentiated from THP-1 monocytes with phorbol ester, were treated with nLDL, LDL- or copper-induced oxidized LDL (oxLDL) for 6 to 24 h. Levels of IL-1β and caspase-1 mRNA were determined by RT-PCR. IL-1β and caspase-1 protein in the medium were quantitated by ELISA. Lentivirus carrying a LOX-1 shRNA was used to knockdown LOX-1 in THP-1 cells.
LDL- remarkably induced expression of IL-1β mRNA and secretion of IL-1β in THP-1 macrophages in a time- and dose-dependent manner; while nLDL and oxLDL did not exert such effects. Treatment with zYVAD-fmk, a specific caspase-1 inhibitor, abolished LDL-induced production of IL-1β, suggesting that the process is capase-1 dependent. We also demonstrated that the cleaved form of caspase-1, which represented the major component of inflammasome, was significantly induced by LDL- but not nLDL or oxLDL. When LOX-1 expression was knocked down by a LOX-1 shRNA, the LDL-induced production of IL-1β and cleaved caspase-1 was significantly attenuated.
This study has demonstrated, for the first time, that the naturally occurring LDL- activates NLRP3 inflammasome through a LOX-1 dependent pathway and upregulates the expression of the inflammatory cytokine IL-1β. We therefore propose a novel role of LDL- in the inflammatory cascade of atherosclerosis.
Moderated Poster Contributions
Poster Sessions, Expo North
Saturday, March 09, 2013, 3:45 p.m.-4:30 p.m.
Session Title: Acute Coronary Syndromes: Basic II
Abstract Category: 2. Acute Coronary Syndromes: Basic
Presentation Number: 1169M-175
- 2013 American College of Cardiology Foundation