Protective Role of Autophagy in Nlrp3 Inflammasome Activation and Medial Thickening of Mouse Coronary Arteries

We hypothesized that autophagy and associated lysosome function serve as a critical modulator during Nod-like receptor family pyrin domain containing 3 (Nlrp3) inflammasome activation on proatherogenic stimuli. We first demonstrated that 7-ketocholesterol stimulated Nlrp3 inflammasome formation and activation as shown by increased colocalization of inflammasome components [Nlrp3 versus apoptosis associated speck-like protein (Asc) or caspase-1] and enhanced cleavage of caspase-1 into active caspase-1 to generate IL-1β in coronary artery smooth muscle cells. Deletion of the CD38 gene (CD38(−/−)) that regulates lysosome function and autophagic flux also led to Nlrp3 inflammasome formation and activation. In the presence of rapamycin, the effects of either 7-ketocholesterol treatment or CD38 gene deletion were abolished. The autophagy inhibitor spautin-1 and the lysosome function blocker bafilomycin A1 also enhanced Nlrp3 inflammasome formation and activation. In animal experiments, we found that increased colocalization of Nlrp3 versus Asc or caspase-1 enhanced IL-1β accumulation and caspase-1 activity in the coronary arterial wall of CD38(−/−) mice on the Western diet compared with CD38(+/+) mice. This increased colocalization was blocked by treatment with rapamycin but enhanced by chloroquine, a water-soluble blocker of autophagic flux. Morphologic examinations confirmed that the media of coronary arteries was significantly thicker in CD38(−/−) mice on the Western diet than CD38(+/+) mice. In conclusion, the deficiency of autophagic flux promotes Nlrp3 inflammasome formation and activation in coronary artery smooth muscle cells on proatherogenic stimulation, leading to medial thickening of the coronary arterial wall.