Prolonged exposure to low-dose traffic-derived PM_2.5 causes fatty liver disorder in mice

There is no safe level of exposure to air pollution, including particulate matter smaller than 2.5 µm (PM_2.5), to human health. Whilst it is well known that exposure to heavily polluted air is associated with several liver disorders, it is unclear how long-term exposure to low-level traffic-derived PM_2.5 affects liver health. BALB/c mice (5 weeks, male) were exposed to traffic-derived PM_2.5 (10 µg/mouse/day, intranasally) daily for 4, 8 and 12 weeks. Markers of inflammation and fibrosis were measured at each time point. Changes in liver proteome and lipid profiles were measured using proteomics and lipidomics at 12 weeks. Low-dose PM_2.5 exposure increased macrophage infiltration, pro-inflammatory cytokine production, and increased collagen deposition at 12 weeks. Despite liver lipid metabolism being increased, the abundance of triglycerides, precursor diacylglycerols, and ceramide was also significantly increased by PM_2.5 exposure, whereas glycogen content was reduced. Proteomics analysis revealed 64 proteins to be significantly changed in PM_2.5-exposed mice, and KEGG pathway enrichment analysis indicated their involvement in lipid metabolism, alcohol-related liver disease, neutrophil extracellular trap formation, and transcriptional dysregulation related to cancer. In conclusion, prolonged exposure to low-dose traffic-derived PM_2.5 promotes pathological changes in the liver, suggestive of an increased risk of metabolic dysfunction-associated fatty liver disease. Future studies can enable the identification of the signalling pathways underlying low-dose PM_2.5-induced lipid accumulation in the liver.