Abstract 17304: Brief Exposures to Air Pollutants Dysregulates PCK1 Expression, Carbohydrate and Lipid Metabolism in ApoE Knockout Mice

Introduction: Previous animal studies have shown that long exposures to particulate matter (PM) and diesel exhaust particles (DEP) promote atherosclerosis. Air pollutants are also reported to cause nonalcoholic steatohepatitis (NASH), liver fibrosis and insulin resistance in animals exposed to PM<2.5 μm. We hypothesized that even brief exposures to air pollutants may alter metabolic pathways that could be responsible for vascular and liver diseases. Methods: ApoE null mice were briefly exposed to diesel exhaust (DE) or filtered air (FA) to assess liver content of lipids, lipid and carbohydrate metabolism. Illumina microarrays and metabolomic analysis were performed in liver tissue. Transcriptomic data was analyzed using the Illumina Beadstudio software. Gluconeogenesis and glycogenolysis were evaluated in HepG2 cells after treatment with diesel exhaust particles (DEP). Gene expression was determined by qPCR. Results: DE exposures led to a significant increase in both liver triglyceride (Mean ± SEM, FA: 0.16 ± 0.01 vs DE: 0.22 ± 0.02 mg/mg protein, n=7, p=0.02) and cholesterol (FA: 15.53 ± 1.53 vs DE: 23.26 ± 2.16 μg/mg protein, n=5, p=0.02) content in ApoE null mice. Microarray analysis depicted a dysregulation of 477 genes, and metabolomic analysis identified 70 metabolites significantly upregulated in the DE group while 48 metabolites were downregulated. Interestingly, metabolites in the citric acid cycle demonstrated significant changes after DE exposure likely due to mitochondrial dysfunction. Key driver analysis revealed Pck1 as a key driver gene. In-vitro experiments in HepG2 cells treated with DEP exhibited a significant upregulation in PCK1 mRNA expression (DEP: 7.31 ± 0.2 vs control: 1.07 ± 0.07, n=3, p<0.01). Although treatment with DEP substantially depleted glycogen content as seen by periodic acid-schiff stain in cells, it significantly enhanced gluconeogenesis (DEP: 23.3 ± 1.2 vs control: 5.5 ± 0.6 μg/ml/mg protein, n=5, p<0.001), effects that were inhibited in the presence of a metabolic inhibitor of PCK1: 3-Mercaptopicolinic acid (3-MPA) (DEP: 23.28 ± 1.18 vs DEP + 3-MPA: 16.04 ± 1.16 μg/ml/mg protein, n=5, p=0.002) indicating that DEP-induced glucose production was due to increased gluconeogenesis. Conclusion: Exposure to diesel exhaust leads to multiple alterations in carbohydrate and lipid metabolism including increased glycogenolysis, gluconeogenesis and PCK1 upregulation.