Abstract 15349: The Electronegative L5 From Patients With ST-Elevation Myocardial Infarction Induces NLRP3 Inflammasome Activation and Interleukin-1β Secretion in Human Macrophages
Background: A naturally occurring oxidized LDL, named L5, is significantly elevated in patients with ST-segment elevation myocardial infarction (STEMI). The NLRP3 inflammasome which mediates caspase-1 activation and IL-1β production may lead to vascular inflammation in STEMI. However, the interaction between electronegative L5 and IL-1β is not known. This study was aimed at defining the mechanism and signaling pathways how L5 activates inflammasome and IL-1β expression.
Methods and Results: Native and most negatively charged LDL (nLDL and L5, respectively) were isolated from the plasma of patients with acute STEMI by ultracentrifugation followed by ion-exchange chromatography. Human macrophages were differentiated from THP-1 monocytes with phorbol ester, and were treated with nLDL, L5 or copper-induced oxidized LDL (oxLDL). The levels of IL-1β mRNA were determined by real-time PCR. Protein levels of IL-1β and caspase-1 in the medium were quantitated by ELISA. We showed that the most electronegative LDL L5 from STEMI patients remarkably induced the expression of IL-1β mRNA and secretion of IL-1β in THP-1 macrophages in a time- and dose-dependent manner. In contrast, nLDL and oxLDL did not exert such effects. We further demonstrated that the cleaved form of caspase-1, which represented the major component of inflammasome NLRP3, was significantly induced by L5 but not nLDL or oxLDL. Treatment with zYVAD-fmk, a specific caspase-1 inhibitor, abolished L5-induced production of IL-1β, suggesting that the process is capase-1 dependent. When the lectin-type oxidized LDL receptor 1 (LOX-1) expression was knocked down by a lentivirus carrying LOX-1 shRNA, the L5-induced production of IL-1β and cleaved caspase-1 was significantly attenuated. In addition, knockdown of NLRP3 and its adaptor protein ASC using a lentivirus system abolished the L5-induced IL-1β secretion.
Conclusions: This study has demonstrated, for the first time, that the naturally occurring electronegative L5 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 L5 in the inflammatory cascade of atherothrombosis in acute myocardial infarction.
- © 2013 by American Heart Association, Inc.