Ablation of Akt2 prevents paraquat-induced myocardial mitochondrial injury and contractile dysfunction: Role of Nrf2

Abstract

Paraquat is a quaternary nitrogen herbicide triggering oxidative stress, mitochondrial damage and multi-organ injuries including hearts. To date, effective measure to combat paraquat toxicity is still lacking. Recent evidence has revealed a role for Akt in cardiac homeostasis. To this end, this study was designed to examine the role of Akt2 in acute paraquat exposure-induced cardiac contractile and mitochondrial injury using a unique murine model of Akt2 knockout. Cardiac contractile and intracellular Ca2+ properties were evaluated. Mitochondrial integrity, ROS production, lipid peroxidation, ER stress and apoptosis were evaluated using aconitase assay, citrate synthase activity, DHE staining, mitochondrial permeation pore opening, 4-hydroxy-nonenal (4-HNE) and Western blot. Our results revealed compromised echocardiographic, contractile and intracellular Ca2+ handling properties along with overt mitochondrial damage (reduced levels of PGC-1α, aconitase, citrate synthase activity and NAD+) in mice challenged with paraquat (45mg/kg, single injection, i.p.), the effects of which were attenuated by Akt ablation. Paraquat triggered O2− production, lipid peroxidation and apoptosis as evidenced by increased DHE staining, 4-HNE, caspase-3 activity, Bax and reduced Bcl-2 levels in association with unchanged ER stress. The redox signaling molecule nuclear factor erythroid related factor 2 (Nrf2) was upregulated in response to paraquat challenge. Findings from in vitro study revealed that stimulation of Nrf2 using sulforaphane (10μM) negated Akt2 ablation-offered beneficial effect against paraquat whereas inhibition of Nrf2 using luteolin (20μM) mimicked Akt2 ablation-induced beneficial effect against paraquat challenge. Taken together, our data indicate that Akt2 ablation may protect against paraquat toxicity-induced cardiac contractile defect and apoptosis possibly via regulation of Nrf2 activation and mitochondrial homeostasis.