Aryl Hydrocarbon Receptor Deficiency Enhances Insulin Sensitivity and Reduces PPAR-α Pathway Activity in Mice

BACKGROUND: Numerous man-made pollutants activate the aryl hydrocarbon receptor (AhR) and are risk factors for type 2 diabetes. AhR signaling also affects molecular clock genes to influence glucose metabolism. OBJECTIVE: We investigated mechanisms by which AhR activation affects glucose metabolism. METHODS: Glucose tolerance, insulin resistance, and expression of peroxisome proliferator activated receptor-alpha (PPAR-alpha) and genes affecting glucose metabolism or fatty acid oxidation and clock gene rhythms were investigated in wild-type (WT) and AhR-deficient [knockout (KO)] mice. AhR agonists and small interfering RNA (siRNA) were used to examine the effect of AhR on PPAR-alpha expression and glycolysis in the liver cell line Hepa-1c1c7 (c7) and its c12 and c4 derivatives. Brain, muscle ARNT-like protein 1 (Bmal1) siRNA and Ahr or Bmal1 expression plasmids were used to analyze the effect of BMAL1 on PPAR-alpha expression in c7 cells. RESULTS: KO mice displayed enhanced insulin sensitivity and improved glucose tolerance, accompanied by decreased PPAR-alpha and key gluconeogenic and fatty acid oxidation enzymes. AhR agonists increased PPAR-alpha expression in c7 cells. Both Ahr and Bmal1 siRNA reduced PPAR-alpha and metabolism genes. Moreover, rhythms of BMAL1 and blood glucose were altered in KO mice. CONCLUSIONS: These results indicate a link between AhR signaling, circadian rhythms, and glucose metabolism. Furthermore, hepatic activation of the PPAR-alpha pathway provides a mechanism underlying AhR-mediated insulin resistance.