Lipid metabolic adaption to long-term ambient PM_2.5 exposure in mice

Emerging evidence has demonstrated that exposure to fine particulate matter (PM_2.5) is a risk factor for lipid metabolic disorders in the liver. However, the effects of PM_2.5 exposure time duration on hepatic lipid metabolism remain unknown. In this study, C57BL/6 mice were randomly divided into ambient PM_2.5 (PM) or filtered air (FA) exposure chamber for short-term (4 weeks) or long-term (24 weeks) exposure via a whole body exposure system. We measured hepatic triglyceride and free fatty acid levels and analyzed the alteration of lipometabolism-related molecules in the liver. We found that triglyceride levels were significantly elevated in both short-term and long-term PM_2.5-exposed mice and free fatty acid levels were increased after long-term PM_2.5 exposure. Besides, enzymes for lipolysis and fatty acid oxidation in the liver were inhibited after short-term PM_2.5 exposure but adaptively enhanced after long-term PM_2.5 exposure. Furthermore, molecules for fatty acid uptake were down-regulated in the short-term PM_2.5-exposed mice whereas molecules for lipid export were induced after long-term PM_2.5 exposure. Therefore, ambient PM_2.5 exposure disturbed hepatic lipid metabolism and the effects varied in different exposure duration. These findings in mice provide new insight into the biological basis of PM_2.5-induced human metabolic dysfunction and specific strategies may be applied based on different exposure time periods.