title: 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.
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071 USA.
authors.forename: Shuyi
authors.initials: S
authors.lastname: Wang
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071 USA; Department of Anesthesiology, Xijing Hospital, the Fourth Military Medical University, Xi'an, China.
authors.forename: Xiaoling
authors.initials: X
authors.lastname: Zhu
authors.affiliation: Department of Anesthesiology, Xijing Hospital, the Fourth Military Medical University, Xi'an, China.
authors.forename: Lize
authors.initials: L
authors.lastname: Xiong
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071 USA; Shanghai Institute of Cardiovascular Diseases, Zhongshan Hospital, Fudan University, Shanghai 200032, China. Electronic address: jren@uwyo.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000235:genetics / Q000378:metabolism; D004452:Echocardiography; D005786:Gene Expression Regulation; D006540:Herbicides / Q000633:toxicity*; D017879:Isothiocyanates / Q000737:chemistry; D015227:Lipid Peroxidation / Q000187:drug effects; D047311:Luteolin / Q000737:chemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000378:metabolism; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D010269:Paraquat / Q000633:toxicity*; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D013454:Sulfoxides; D051028:bcl-2-Associated X Protein / Q000235:genetics / Q000378:metabolism
chemical_list: C494827:Bax protein, mouse; D006540:Herbicides; D017879:Isothiocyanates; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D019253:Proto-Oncogene Proteins c-bcl-2; D017382:Reactive Oxygen Species; D013454:Sulfoxides; D051028:bcl-2-Associated X Protein; C052617:Bcl2 protein, mouse; D002950:Citrate (si)-Synthase; C494922:Akt2 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; C505409:Casp3 protein, mouse; D053148:Caspase 3; C016766:sulforaphane; D047311:Luteolin; D010269:Paraquat; D002118:Calcium
keywords: Akt2; Cardiac; Contraction; Mitochondrial homeostasis; Nrf2; Paraquat