Srivastava Sanjay, Chandrasekar Bysani, Gu Yan, Luo Jianzhu, Hamid Tariq, Hill Bradford G, Prabhu Sumanth D
Louisville VAMC and Institute of Molecular Cardiology, Department of Medicine, University of Louisville, Louisville, KY 40202, United States.
Cardiovasc Res. 2007 Jun 1;74(3):445-55. doi: 10.1016/j.cardiores.2007.02.016. Epub 2007 Feb 20.
Sustained beta-adrenergic receptor (beta-AR) activation augments oxidative stress in the heart; whether alterations in antioxidant enzymes contribute to this effect is unknown.
Adult male Wistar rats were implanted with osmotic minipumps to infuse either l-isoproterenol (ISO, 25 microg/kg/h) or saline (SAL). After 7-days, ISO-treated hearts exhibited significant (p<0.005): 1) concentric hypertrophy and augmentation of systolic function, 2) reductions of end-systolic wall stress, and 3) augmentation of oxidative stress, with a approximately 3-fold increase in 4-hydroxy-2-nonenal-and malondialdehyde-protein adducts. ISO-treated hearts also exhibited significant (p<0.01) reductions of CuZn-superoxide dismutase (SOD) enzyme activity (30%), protein (40%), and mRNA (60%), without changes in Mn-SOD, catalase, or glutathione peroxidase. Elk-1 and YinYang1 (YY1) are transcription factors that positively and negatively regulate CuZn-SOD expression, respectively. ISO-treated hearts exhibited a 3-fold increase in YY1 and a 2-fold reduction in Elk-1 DNA binding activity, strongly favoring CuZn-SOD gene repression. In isolated cardiomyocytes, sustained (24 h) ISO stimulation significantly (p<0.01) increased reactive oxygen species (ROS), an effect blocked by CGP20712A, a beta1-AR antagonist, but not by ICI118,551, a beta2-AR antagonist. CuZn-SOD downregulation paralleled the increase in ROS, and were similarly blocked by beta1- but not beta2-AR blockade. There were no changes in CuZn-SOD mRNA stability or myocyte size with ISO treatment. However, nuclear run-on revealed a 40% reduction in CuZn-SOD mRNA expression (p<0.01), consistent with transcriptional repression. ISO also depressed total cellular antioxidant capacity, reduced glutathione (GSH) levels, and the GSH:GSSG ratio. Moreover, CuZn-SOD siRNA transfection of H9c2 cardiomyocytes to suppress CuZn-SOD protein by approximately 40-50% (analogous to the in vivo changes) induced cellular apoptosis.
Sustained beta-AR stimulation transcriptionally downregulates CuZn-SOD in myocardium via the beta1-AR, thereby contributing to beta-AR-mediated oxidative stress.
β-肾上腺素能受体（β-AR）的持续激活会增强心脏中的氧化应激；抗氧化酶的改变是否促成这种效应尚不清楚。
成年雄性Wistar大鼠植入渗透微型泵，以输注左旋异丙肾上腺素（ISO，25微克/千克/小时）或生理盐水（SAL）。7天后，ISO处理的心脏表现出显著（p<0.005）：1）向心性肥厚和收缩功能增强，2）收缩末期壁应力降低，3）氧化应激增强，4-羟基-2-壬烯醛和丙二醛-蛋白质加合物增加约3倍。ISO处理的心脏还表现出铜锌超氧化物歧化酶（SOD）酶活性（30%）、蛋白质（40%）和mRNA（60%）显著（p<0.01）降低，而锰超氧化物歧化酶、过氧化氢酶或谷胱甘肽过氧化物酶无变化。Elk-1和阴阳1（YY1）是分别正向和负向调节铜锌超氧化物歧化酶表达的转录因子。ISO处理的心脏YY1增加3倍，Elk-1 DNA结合活性降低2倍，强烈有利于铜锌超氧化物歧化酶基因的抑制。在分离的心肌细胞中，持续（24小时）ISO刺激显著（p<0.01）增加活性氧（ROS），β1-AR拮抗剂CGP20712A可阻断此效应，但β2-AR拮抗剂ICI118,551不能阻断。铜锌超氧化物歧化酶的下调与活性氧的增加平行，且同样被β1-AR阻断而非β2-AR阻断。ISO处理后铜锌超氧化物歧化酶mRNA稳定性或心肌细胞大小无变化。然而，核转录分析显示铜锌超氧化物歧化酶mRNA表达降低40%（p<0.01），与转录抑制一致。ISO还降低了总细胞抗氧化能力、谷胱甘肽（GSH）水平以及GSH:GSSG比值。此外，对H9c2心肌细胞进行铜锌超氧化物歧化酶小干扰RNA转染以抑制铜锌超氧化物歧化酶蛋白约40%-50%（类似于体内变化）可诱导细胞凋亡。
持续的β-AR刺激通过β1-AR在转录水平上下调心肌中的铜锌超氧化物歧化酶，从而促成β-AR介导的氧化应激。
