title: β₁-adrenoceptor stimulation promotes LPS-induced cardiomyocyte apoptosis through activating PKA and enhancing CaMKII and IκBα phosphorylation.
abstract: BACKGROUND
  Caspase activation and cardiomyocyte apoptosis have been implicated in lipopolysaccharide (LPS)-induced cardiac contractile dysfunction. We have recently demonstrated that β1-adrenoceptor (AR) activation by endogenous norepinephrine contributes to cardiomyocyte apoptosis in endotoxemic mice. Here, we further investigated the molecular mechanisms for the enhancing effect of β₁-AR activation on LPS-induced cardiomyocyte apoptosis.
  
  
  METHODS
  The adult mouse ventricular myocytes were exposed to LPS, dobutamine, protein kinase A (PKA) inhibitor or/and nifedipine, an L-type Ca(2+) channel blocker. Male BALB/c mice were treated with LPS or/ and β₁-AR antagonist, atenolol. Cardiomyocyte apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling (TUNEL) assay and apoptosis-associated molecules were detected.
  
  
  RESULTS
  LPS induced apoptosis in adult mouse ventricular myocytes, dobutamine (DOB), a β₁-AR agonist, promoted apoptosis, caspase-8, 9 and 3 activation and increased cytosolic Ca(2+) concentration in LPS-challenged cardiomyocytes. DOB also up-regulated TNF-α expression, decreased Bcl-2 levels, promoted Bax translocation to mitochondria, mitochondrial membrane potential loss and cytochrome c release as well as IκBα, p38 MAPK, JNK and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation in LPS-treated cardiomyocytes. PKA inhibitor abolished the effects of DOB on caspase-9 activation, Bcl-2 levels as well as JNK and p38 MAPK phosphorylation, but not on IκBα phosphorylation, TNF-α expression and caspase-8 activation in LPS-stimulated cardiomyocytes. Pretreatment with nifedipine not only significantly blocked the enhancing effects of DOB on LPS-induced elevation in cytosolic Ca(2+) concentration and CaMKII phosphorylation in cardiomyocytes, but also partly reversed the effects of DOB on caspase-9 and caspase-3/7 activities in LPS-treated cardiomyocytes. Furthermore, atenolol suppressed TNF-α expression, JNK, p38 MAPK and CaMKII phosphorylation, increased Bcl-2 expression, and inhibited cytochrome c release and cardiomyocyte apoptosis in the myocardium of endotoxemic mice.
  
  
  CONCLUSIONS
  β1-AR activation promotes LPS-induced apoptosis through activating PKA, increasing CaMKII phosphorylation as well as enhancing IκBα phosphorylation and TNF-α expression in cardiomyocytes.
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. ywang98@gsu.edu.
authors.forename: Yiyang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. wangyuan602@126.com.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. 1319069233@qq.com.
authors.forename: Duomeng
authors.initials: D
authors.lastname: Yang
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. yuxiaohui0319@foxmail.com.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Yu
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. lihongmei083@qq.com.|Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. lihongmei083@qq.com.
authors.forename: Hongmei
authors.initials: H
authors.lastname: Li
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. 2541519018@qq.com.|Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. 2541519018@qq.com.
authors.forename: Xiuxiu
authors.initials: X
authors.lastname: Lv
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. ldx@jnu.edu.cn.|Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. ldx@jnu.edu.cn.
authors.forename: Daxiang
authors.initials: D
authors.lastname: Lu
authors.affiliation: Department of Pathophysiology, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. owanghd@jnu.edu.cn.|Key Laboratory of State Administration of Traditional Chinese Medicine of the People's Republic of China, School of Medicine, Jinan University, Guangzhou, 510632, Guangdong, China. owanghd@jnu.edu.cn.
authors.forename: Huadong
authors.initials: H
authors.lastname: Wang
mesh_terms: D058665:Adrenergic beta-1 Receptor Agonists / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004280:Dobutamine / Q000627:therapeutic use; D019446:Endotoxemia / Q000139:chemically induced / Q000188:drug therapy / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D009543:Nifedipine / Q000819:agonists; D009638:Norepinephrine / Q000494:pharmacology / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D058665:Adrenergic beta-1 Receptor Agonists; D002121:Calcium Channel Blockers; D008070:Lipopolysaccharides; D018342:Receptors, Adrenergic, beta-1; D004280:Dobutamine; D017868:Cyclic AMP-Dependent Protein Kinases; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D048051:p38 Mitogen-Activated Protein Kinases; D020169:Caspases; D009543:Nifedipine; D009638:Norepinephrine