title: Ablation of Akt2 protects against lipopolysaccharide-induced cardiac dysfunction: role of Akt ubiquitination E3 ligase TRAF6.
abstract: Lipopolysaccharide (LPS), an essential component of the outer membrane of Gram-negative bacteria, plays a pivotal role in myocardial anomalies in sepsis. Recent evidence has depicted a role of Akt in LPS-induced cardiac sequelae although little information is available with regard to the contribution of Akt isoforms in the endotoxin-induced cardiac dysfunction. This study examined the effect of Akt2 knockout on LPS-induced myocardial contractile dysfunction and the underlying mechanism(s) with a focus on TNF receptor-associated factor 6 (TRAF6). Echocardiographic properties and cardiomyocyte contractile function [peak shortening (PS), maximal velocity of shortening/relengthening, time-to-PS, time-to-90% relengthening] were examined in wild-type and Akt2 knockout mice following LPS challenge (4mg/kg, 4h). LPS challenge enlarged LV end systolic diameter, reduced fractional shortening and cardiomyocyte contractile capacity, prolonged TR90, promoted apoptosis, upregulated caspase-3/-12, ubiquitin, and the ubiquitination E3 ligase TRAF6 as well as decreased mitochondrial membrane potential without affecting the levels of TNF-α, toll-like receptor 4 and the mitochondrial protein ALDH2. Although Akt2 knockout failed to affect myocardial function, apoptosis, and ubiquitination, it significantly attenuated or mitigated LPS-induced changes in cardiac contractile and mitochondrial function, apoptosis and ubiquitination but not TRAF6. LPS facilitated ubiquitination, phosphorylation of Akt, GSK3β and p38, the effect of which with the exception of p38 was ablated by Akt2 knockout. TRAF6 inhibitory peptide or RNA silencing significantly attenuated LPS-induced Akt2 ubiquitination, cardiac contractile anomalies and apoptosis. These data collectively suggested that TRAF6 may play a pivotal role in mediating LPS-induced cardiac injury via Akt2 ubiquitination.
authors.affiliation: Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, PR China; Shanghai Institute of Cardiovascular Diseases, Zhongshan Hospital, Fudan University, Shanghai 200032, PR China; Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071, USA.
authors.forename: Yingmei
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071, USA.
authors.forename: Xihui
authors.initials: X
authors.lastname: Xu
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071, USA.
authors.forename: Asli F
authors.initials: AF
authors.lastname: Ceylan-Isik
authors.affiliation: Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071, USA; Department of Burn and Cutaneous Surgery, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, PR China.
authors.forename: Maolong
authors.initials: M
authors.lastname: Dong
authors.affiliation: Department of Cardiology, The Third Hospital of Nanchang, Nanchang, Jiangxi 330009, PR China. Electronic address: 15179192775@126.com.
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Pei
authors.affiliation: Department of Cardiology, Xijing Hospital, Fourth Military Medical University, Xi'an 710032, PR China. Electronic address: liyanfmmu@hotmail.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Shanghai Institute of Cardiovascular Diseases, Zhongshan Hospital, Fudan University, Shanghai 200032, PR China; Center for Cardiovascular Research and Alternative Medicine, University of Wyoming College of Health Sciences, Laramie, WY 82071, USA. Electronic address: jren@uwyo.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
mesh_terms: D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000071396:Aldehyde Dehydrogenase, Mitochondrial; D000818:Animals; D017209:Apoptosis; D009202:Cardiomyopathies / Q000139:chemically induced / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D008070:Lipopolysaccharides; D053078:Membrane Potential, Mitochondrial; D051379:Mice; D018345:Mice, Knockout; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000172:deficiency / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D048029:TNF Receptor-Associated Factor 6 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics* / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D008070:Lipopolysaccharides; D034741:RNA, Small Interfering; D048029:TNF Receptor-Associated Factor 6; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D014409:Tumor Necrosis Factor-alpha; D025801:Ubiquitin; C515029:ALDH2 protein, mouse; D000444:Aldehyde Dehydrogenase; D000071396:Aldehyde Dehydrogenase, Mitochondrial; C494922:Akt2 protein, mouse; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D048051:p38 Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; D020169:Caspases
keywords: Apoptosis; Cardiac function; Lipopolysaccharide; TRAF6; Ubiquitination