Abstract 566: High-density Lipoprotein Inhibits Serum Amyloid a -Mediated Inflammasome Activation

Abstract

Objectives: Interleukin-1beta (IL-1β) has been implicated in inflammatory diseases, including atherosclerosis and abdominal aortic aneurysm (AAA). Production of bioactive IL-1β is controlled by the inflammasome, a multi-protein complex that regulates caspase-1 activity. Serum Amyloid A (SAA) is an acute-phase protein whose levels in circulation is elevated in individuals with chronic inflammation. We previously reported that deficiency of SAA protects mice from angiotensin II (AngII)-induced AAA. Here we report that reduced AngII-induced AAA in SAA-deficient mice is accompanied by significant reductions in plasma IL-1β, indicating that SAA is required for inflammasome activation in AngII-infused mice. The objective of this study is to investigate mechanisms involved in SAA-mediated inflammasome activation. Methods/Results: SAA dose-dependently induced both caspase-1 activation and IL-1β secretion in J774 macrophage-like cells incubated with 0-25 μg/ml purified mouse SAA. The ability of SAA to induce IL-1β secretion was significantly reduced in bone marrow-derived macrophages deficient in NLRP3. A caspase-1inhibitor, Z-YVAD-FMK, significantly suppressed IL-1β secretion induced by SAA, whereas the P2X7-receptor antagonist, AA38079, had no effect. Inhibition of reactive oxygen species (ROS), cathepsin-B activation, and cellular potassium efflux by N-acetyl-L-cysteine, CA-074, and glyburide, respectively, blocked NLRP3 inflammasome activation by SAA. Pre-incubating SAA with HDL prior to cell treatments completely abrogated SAA-mediated inflammasome activation. In contrast, HDL did not alter inflammasome activation triggered by ATP. Conclusions: SAA-mediated NLRP3 inflammasome activation in macrophages is dependent on ROS generation, release of cathepsin-B, and potassium efflux, and is independent of the P2X7 receptor. Moreover, our data identify a novel mechanism by which HDL may exert cardioprotective effects.