Nox2-containing NADPH oxidase and Akt activation play a key role in angiotensin II-induced cardiomyocyte hypertrophy

Abstract

. Nox2-containing NADPH oxidase and Akt activation play a key role in angiotensin II-induced cardiomyocyte hypertrophy. Physiol Genomics 26: 180 -191, 2006. First published May 2, 2006 doi:10.1152/physiolgenomics.00029.2005.-Angiotensin II (ANG II) has profound effects on the development and progression of pathological cardiac hypertrophy; however, the intracellular signaling mechanisms are not fully understood. In this study, we used genetic tools to test the hypothesis that increased formation of superoxide (O 2 Ϫ ⅐) radicals from a Rac1-regulated Nox2-containing NADPH oxidase is a key upstream mediator of ANG II-induced activation of serine-threonine kinase Akt, and that this signaling cascade plays a crucial role in ANG II-dependent cardiomyocyte hypertrophy. ANG II caused a significant time-dependent increase in Rac1 activation and O 2 Ϫ ⅐ production in primary neonatal rat cardiomyocytes, and these responses were abolished by adenoviral (Ad)-mediated expression of a dominant-negative Rac1 (AdN17Rac1) or cytoplasmic Cu/ZnSOD (AdCu/ZnSOD). Moreover, both AdN17Rac1 and AdCu/ZnSOD significantly attenuated ANG II-stimulated increases in cardiomyocyte size. Quantitative real-time PCR analysis demonstrated that Nox2 is the homolog expressed at highest levels in primary neonatal cardiomyocytes, and small interference RNA (siRNA) directed against it selectively decreased Nox2 expression by Ͼ95% and abolished both ANG II-induced O 2 Ϫ ⅐ generation and cardiomyocyte hypertrophy. Finally, ANG II caused a time-dependent increase in Akt activity via activation of AT 1 receptors, and this response was abolished by Ad-mediated expression of cytosolic human O 2 Ϫ ⅐ dismutase (AdCu/ ZnSOD). Furthermore, pretreatment of cardiomyocytes with dominant-negative Akt (AdDNAkt) abolished ANG II-induced cellular hypertrophy. These findings suggest that O 2 Ϫ ⅐ generated by a Nox2-containing NADPH oxidase is a central mediator of ANG II-induced Akt activation and cardiomyocyte hypertrophy, and that dysregulation of this signaling cascade may play an important role in cardiac hypertrophy. superoxide radicals; renin-angiotensin system; dominant-negative Rac1; small interference RNA; oxidative stress CARDIAC HYPERTROPHY is one of the most significant sequelae of ischemic heart disease, hypertension, and valvular disease (14). Initially an adaptive response that preserves cardiac output and minimizes wall tension, cardiac hypertrophy predisposes to ischemia, arrhythmia, and heart failure. Signal transduction pathways important in the pathogenesis of hypertrophy have been the target of many recent investigations, with angiotensin II (ANG II) emerging as a key molecule both in compensatory cardiac hypertrophy and in the pathogenesis of progressive myocardial dysfunction leading to heart failure (48, 54). Despite the importance of ANG II in cardiac hypertrophy, the signaling cascades downstream of ANG II receptor activation remain to be fully elucidated.The small GTP-binding protein Rac1, a member of the Rho family of GTPases (51), has eme...

NADPH oxidase signaling and cardiac myocyte function

“…We found that the in vivo cardiac hypertrophic response to short-term subpressor angiotensin II infusion was markedly inhibited in Nox2−/− mice compared to wild-type, and that this was associated with a blunting of the increase in molecular markers of hypertrophy such as ANF mRNA [10]. In line with this finding, angiotensin II-induced hypertrophy of isolated cardiomyocytes was subsequently also definitively shown to involve the activation of Nox2 oxidase [11]. Further strong evidence for an involvement of Nox2 in the in vivo hypertrophic response to angiotensin II came from a study in mice with conditional cardiac-specific knockout of Rac1, which had blunted hypertrophy as well as reduced myocardial Nox2 oxidase activity [59].…”

“…Nox2 is expressed in endothelial cells [8] and [9], cardiomyocytes [10], [11] and [12], fibroblasts [13] and some VSMCs [14]. Nox4 is expressed in endothelial cells [15], VSMCs [16], cardiomyocytes [17] and [18] and fibroblasts [19].…”

“…The details of the specific isoform(s) activated by these stimuli remain to be fully established and may vary according to cell type. The majority of information to date is derived from analyses of Nox1 activation in VSMCs [23] and [25] and Nox2 activation in endothelial cells [26], [27], [28] and [29], with only a handful of studies examining Nox isoform-specific activation in cardiomyocytes [11] and [30].…”

Transactivation of the epidermal growth factor receptor in responses to myocardial stress and cardioprotection

“…Ang II) induces NADPH oxidase subunit expression and complex assembly at the cell membrane, increasing cardiomyocyte ROS production (Nakagami et al, 2003;Hingtgen et al, 2006). Activation of the small GTPase Rac also promotes membrane recruitment of NADPH oxidase complex components (Gregg et al, 2003), while the p47phox subunit (necessary for oxidase activation) is phospho-regulated by both PKC (Fontayne et al, 2002) and the PI3K/Akt pathways (Hoyal et al, 2003).…”

Serotonin 5-HT 2B Receptor Blockade Prevents Reactive Oxygen Species–Induced Cardiac Hypertrophy in Mice

“…9 We tested whether the blockade of 5-HT 2B Rs could reduce Ang II-induced hypertrophy and cardiac ROS generation in mice. Ang II induced a left ventricular hypertrophy associated with an increase in O 2 ⅐Ϫ production but no increase of SODmediated protection.…”