Chronic air pollution exposure exaggerates obesity-induced tissue inflammation and insulin resistance by activating inflammasome

Abstract

Abstract Background: Air pollution has been associated with cardiometabolic diseases such as obesity and insulin resistance. However, the underlying mechanisms were not fully understood. In this study, we examined the role of NLRP3 inflammasome in chronic air pollution-induced tissue inflammation and insulin resistance. Methods: 8 weeks old male WT and NLRP3−/− mice were exposed to filtered air (FA) or concentrated ambient particles (CAPS) in a small animal whole-body exposure system with or without high fat diet for 6 hours/day, 5 days/week, for a total of 12 weeks (n= 5–8 per group). Results: CAPS exposure enhanced insulin resistance in the WT mice but not in the NLRP3−/− mice. Cytokine array and ELISA assays indicated that IL-1β secretion was increased in the culture supernatant of macrophages isolated from CAPS-exposed WT mice, compared to that of FA-exposed mice. Electronic microscopy showed particulate deposites in the peritoneal macrophages isolated from the peritoneal cavity of CAPS-exposed animals. The gene expression of Nlrp3 and Il-1β, the rate-limiting factor of NLRP3 inflammasome activation, were also increased in CAPS-exposed WT mice. Deficiency of NLRP3 blocked CAPS exposure-induced lung inflammation, inflammatory gene expression, and IL-1β secretion in mice. Subsequent ex vivo experiments by culturing macrophages with particulate matters indicate that air pollution particles not only initiate the transcription of Nlrp3 and Il-1β, the first signal for inflammasome activation, but also induce the activation of caspase-1, the second signal for inflammasome activation. Conclusions: Our data suggest that NLRP3 inflammasome activation mediates air pollution-induced tissue inflammation and insulin resistance.