Copyright © 2007, European Society of Cardiology
Downregulation of CuZn-superoxide dismutase contributes to β-adrenergic receptor-mediated oxidative stress in the heart
aLouisville VAMC and Institute of Molecular Cardiology, Department of Medicine, University of Louisville, Louisville, KY, United States
bMedicine/Cardiology, University of Texas Health Science Center, San Antonio, TX, United States
* Corresponding author. Medicine/Cardiology, University of Louisville, ACB, 3rd Floor, 550 South Jackson Street, Louisville, KY 40202, United States. Tel.: +1 502 852 7959; fax: +1 502 852 7147. Email address: sprabhu{at}louisville.edu
Objective: Sustained β-adrenergic receptor (β-AR) activation augments oxidative stress in the heart; whether alterations in antioxidant enzymes contribute to this effect is unknown.
Methods and results: Adult male Wistar rats were implanted with osmotic minipumps to infuse either L-isoproterenol (ISO, 25 µg/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 
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 β1-AR antagonist, but not by ICI118,551, a β2-AR antagonist. CuZn–SOD downregulation paralleled the increase in ROS, and were similarly blocked by β1- but not β2-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 40–50% (analogous to the in vivo changes) induced cellular apoptosis.
Conclusions: Sustained β-AR stimulation transcriptionally downregulates CuZn–SOD in myocardium via the β1-AR, thereby contributing to β-AR-mediated oxidative stress.
KEYWORDS β-adrenergic receptor; Oxidative stress; Copper-zinc superoxide dismutase
Time for primary review 29 days
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