PPARα transcriptionally induces AhR expression in Caco-2, but represses AhR pro-inflammatory effects

In this work we demonstrate that Caco-2 cell treatment with WY-14643 (a potent PPARα agonist) causes an increase in AhR expression. Luciferase assays and directed mutagenesis experiments showed that induction mainly occurred at transcriptional level and involved a PPRE site located within the AhR promoter. These results were further confirmed by the use of PPARα knockout mice in which AhR induction by WY14643 was abrogated. In addition to CYP1 regulation, AhR has been described as being involved in inflammation, so we also studied the effect of AhR regulation by PPARα on the expression of some inflammation target genes. 3-Methylcholanthrene (a potent AhR agonist) increased the expression (mRNA) of the major inflammatory targets IL-1β and MMP9. WY-14643 co-treatment abrogated the 3-methylcholanthrene pro-inflammatory effect. Hence the anti-inflammatory effect of PPARα overrides the pro-inflammatory effect of AhR.