NLRP3 inflammasome: a novel link between lipoproteins and atherosclerosis

INTRODUCTION Pattern recognition receptor-mediated signaling pathways have recently been elucidated to bridge the innate immune system and atherosclerosis. NLRP3 is a member of the NLR family. Upon activation, it initiates IL-1β and IL-18 processing, a key step in the inflammatory process of atherosclerosis. MATERIAL AND METHODS We used three different types of lipoproteins, ox-LDL, ox-HDL, and HDL, in Thp-1 at the concentration of 50 mg/l, 100 mg/l, and 150 mg/l respectively. Using real-time polymerase chain reaction and western blot, ELISA detected the expression of NLRP3 and downstream cytokines. NLRP3 siRNA was constructed to down-regulate expression of the NLRP3 gene via the RNA interference technique. 150 mg/l of ox-LDL, ox-HDL and HDL was added to the Thp-1 cell line respectively. We observed the changes in the expression of caspase-1, IL-1β and IL-18 when the NLRP3 gene was down-regulated. RESULTS Ox-LDL and ox-HDL addition not only increases the expression of NLRP3, but also activates the NLRP3 downstream cytokines and caspase-1 and induces IL-1β and IL-18 secretion. Moreover, the effects of activation and induction are shown to have a dose-dependent manner. Expression of NLRP3 and its downstream inflammatory cytokines is reduced in the presence of HDL (p < 0.05). Furthermore, our data demonstrated that NLRP3 siRNA downregulates NLRP3 expression in mononuclear cells, thus leading to a dramatic reduction in the expression of caspase-1, IL-1β and IL-18 (p < 0.05). CONCLUSIONS The data suggest that activation of the NLRP3 inflammasome is a critical step in caspase-1 activation and IL-1β and IL-18 secretion. Interference with the NLRP3 inflammasome can significantly inhibit the generation of cytokines, thus impeding the pathogenesis of inflammation.