Disruption of canonical AHR-mediated induction of hepatocyte PKM2 expression compromises antioxidant defenses and increases TCDD-induced hepatotoxicity

Abstract

Metabolic reprogramming by the pyruvate kinase M2 isoform is associated with cell proliferation and reactive oxygen species (ROS) defenses. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), an environmental contaminant that induces ROS and hepatotoxicity, dose-dependently induces pyruvate kinase muscle isoform M2 (PKM2) in the liver. To further investigate its role in combating TCDD hepatotoxicity, a Pkm^ΔDRE mouse was constructed lacking the dioxin response element mediating aryl hydrocarbon receptor (AHR) induction. TCDD failed to induce hepatic PKM2 in Pkm^ΔDRE mice and in primary hepatocytes isolated from an AHR knockout model (AHR^V375Afl/flAlb-Cre^ERT2), demonstrating induction is AHR dependent. Both wild-type (WT) and Pkm^ΔDRE mice exhibited dose-dependent increases in liver weight after treatment with TCDD every 4 days for 28 days. Glutathione (GSH) levels increased in WT mice while oxidized glutathione (GSSG) levels increased in both models with a 24-fold decrease in the GSH/GSSG ratio in Pkm^ΔDRE mice suggesting lower antioxidant and recycling capacity. Moreover, TCDD-induced fibrosis was more severe in Pkm^ΔDRE mice while Pkm^ΔDRE hepatocytes exhibited greater cytotoxicity following co-treatment with TCDD and hydrogen peroxide. TCDD also induced PKM2 in human HepaRG™ cells with AHR enrichment at a conserved DRE core within the locus. These results suggest AHR-mediated PKM2 induction is a novel antioxidant response to TCDD.