OBJECTIVEOxidative stress is implicated in cardiac insulin resistance, a critical risk factor for cardiac failure, but the direct evidence remains missing. This study explored a causal link between oxidative stress and insulin resistance with a focus on a regulatory role of redox sensitive transcription factor NF-E2–related factor 2 (Nrf2) in the cardiac cells in vitro and in vivo.RESEARCH DESIGN AND METHODSChronic treatment of HL-1 adult cardiomyocyte with hydrogen peroxide led to insulin resistance, reflected by a significant suppression of the insulin-induced glucose uptake. This was associated with an exaggerated phosphorylation of extracellular signal–related kinase (ERK). Although U0126, an ERK inhibitor, enhanced insulin sensitivity and attenuated oxidative stress–induced insulin resistance, LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), worsened the insulin resistance. Moreover, insulin increased Nrf2 transcriptional activity, which was blocked by LY294002 but enhanced by U0126. Forced activation of Nrf2 by adenoviral over-expression of Nrf2 inhibited the increased ERK activity and recovered the blunted insulin sensitivity on glucose uptake in cardiomyocytes that were chronically treated with H2O2. In the hearts of streptozotocin-induced diabetic mice and diabetic patients Nrf2 expression significantly decreased along with significant increases in 3-nitrotyrosine accumulation and ERK phosphorylation, whereas these pathogenic changes were not observed in the heart of diabetic mice with cardiac-specific overexpression of a potent antioxidant metallothionein. Upregulation of Nrf2 by its activator, Dh404, in cardiomyocytes in vitro and in vivo prevented hydrogen peroxide– and diabetes-induced ERK activation and insulin-signaling downregulation.CONCLUSIONSERK-mediated suppression of Nrf2 activity leads to the oxidative stress–induced insulin resistance in adult cardiomyocytes and downregulated glucose utilization in the diabetic heart.

Background-Reactive oxygen species (ROS) play an important role in the maintenance of cardiovascular homeostasis. The present study sought to determine whether nuclear factor erythroid-2 related factor 2 (Nrf2), a master gene of the endogenous antioxidant defense system, is a critical regulator of the cardiac hypertrophic response to pathological stress. Methods and Results-Cardiac hypertrophy and dysfunction were established in mice by transverse aortic constriction (TAC). Nrf2 expression was transiently increased and then declined to the basal level while impairment of cardiac function proceeded. The knockout of Nrf2 (Nrf2 Ϫ/Ϫ ) did not cause any apparent structural and functional abnormalities in the unstressed heart. However, Nrf2Ϫ/Ϫ mice after TAC developed pathological cardiac hypertrophy, significant myocardial fibrosis and apoptosis, overt heart failure, and increased mortality, which were associated with elevated myocardial levels of 4-hydroxy-2-nonenal and 8-hydroxydeoxyguanosine and a complete blockade of the myocardial expression of several antioxidant genes. Overexpression of Nrf2 dramatically inhibited hypertrophic factor-induced ROS production and growth in both cardiomyocytes and cardiac fibroblasts, whereas knockdown of Nrf2 exerted opposite effects in both cells.Conclusions-These findings demonstrate that activation of Nrf2 provides a novel mechanism to protect the murine heart against pathological cardiac hypertrophy and heart failure via suppressing oxidative stress. Key Words: antioxidants Ⅲ apoptosis Ⅲ cardiomyopathies Ⅲ hypertrophy Ⅲ Nrf2 I n response to stress from neurohumoral activation, hypertension, or other myocardial injury, the heart initially compensates with an adaptive enlargement of the myocardium (ie, cardiac hypertrophy that is characterized by an increase in the size of individual cardiac myocytes and whole-organ mass). However, sustained cardiac hypertrophy is detrimental and leads to stroke, heart failure, and sudden death. [1][2][3] The latest epidemiological data has revealed that cardiac hypertrophy is a major predictor of heart failure, with a mortality as high as 80% for men and 70% for women within 8 years. 4 Despite the prominent contribution of cardiac hypertrophy to heart failure, the molecular mechanisms responsible for the transition from compensated hypertrophy to failure are poorly understood.It is firmly established that oxidative stress plays a causative role in the pathogenesis of cardiovascular disease including pathological cardiac hypertrophy and heart failure. 5-10 Surprisingly, larger clinical trials have shown that ROS scavengers of antioxidant vitamins for treatment of cardiovascular disease are ineffective or even harmful. [5][6][7][8] Because these studies have not examined hypertrophic heart disease or heart failure per se, additional studies with specific targeting of the source of oxidative stress or enhancing intrinsic antioxidant pathways are needed. Such studies will not only further extend our understanding of the role of oxidative stress b...

The epithelial Na ؉ Channel (ENaC) mediates Na ؉ reabsorption in a variety of epithelial tissues. ENaC is composed of three homologous subunits, termed ␣, ␤, and ␥. All three subunits participate in channel formation as the absence of any one subunit results in a significant reduction or complete abrogation of Na ؉ current expression in Xenopus oocytes. To determine the subunit stoichiometry, a biophysical assay was employed utilizing mutant subunits that display significant differences in sensitivity to channel blockers from the wild type channel. Our results indicate that ENaC is a tetrameric channel with an ␣ 2 ␤␥ stoichiometry, similar to that reported for other cation selective channels, such as K v , K ir , as well as voltage-gated Na ؉ and Ca 2؉channels that have 4-fold internal symmetry.Epithelial Na ϩ channels are expressed in apical plasma membranes of principal cells in the distal nephron, airway and alveolar epithelia in the lung, surface cells in the distal colon, urinary bladder epithelia, and other tissues including ducts of salivary and sweat glands (1-3). These channels mediate reabsorptive Na ϩ transport across epithelial cell layers (2-5) and are selectively inhibited by submicromolar concentrations of the diuretic amiloride (6). Epithelial Na ϩ channels have a key role in the regulation of urinary Na ϩ reabsorption, extracellular fluid volume homeostasis, and control of blood pressure, and are a major site of action of volume regulatory hormones, including aldosterone (2,7,8). The role of Na ϩ channels in blood pressure regulation has been illustrated in recent studies that have identified mutations in ENaC as the basis of the pathogenesis of Liddle's disease, a disorder characterized by volume expansion and hypertension (9, 10); as well as type I pseudohypoaldosteronism, a disorder characterized by volume depletion and hypotension (11).The epithelial Na ϩ channel consists of at least three structurally related subunits, termed ␣-ENaC, 1 ␤-ENaC, and ␥-ENaC (epithelial Na ϩ channel) (12). The primary and predicted secondary structures of these ENaCs have been described (12-15). Each subunit has two predicted ␣-helical membrane spanning regions separated by a large extracellular domain. Significant amino acid sequence similarities across species have been observed for individual subunits (on the order of ϳ60% to greater than 90% amino acid homology), although regions are present that are more highly conserved. A family of genes identified in Caenorhabditis elegans based on mutations that result in mechanosensation defects (mecs) and degeneration of selected neuronal cells (degs) are structurally related to . Several of these genes, including mec-4, mec-6, and mec-10, are thought to form an ion channel in a manner analogous to the three ENaC subunits (16,19). These observations suggest that ENaCs and mecs (and degs) are members of a new gene superfamily. Members of this family include ENaCs, mecs and degs, FaNaCh (a peptide-gated channel cloned from the marine snail Helix aspers), ␦-ENaC, and BN...

Nuclear factor E2-related factor 2 (Nrf2) is a transcription factor that controls the basal and inducible expression of a battery of antioxidant genes and other cytoprotective Phase II detoxifying enzymes. Nrf2 is ubiquitously expressed in the cardiovascular system. While several Nrf2 downstream genes have been implicated in protection against the pathogenesis of cardiovascular diseases, the precise role of Nrf2 in the cardiovascular system remains to be elucidated. Nevertheless, mounting evidence has revealed that Nrf2 is a critical regulator of cardiovascular homeostasis via the suppression of oxidative stress, a major causative factor for the development and progression of cardiovascular diseases. Therefore, Nrf2 promises to be an attractive therapeutic target for the treatment of cardiovascular disease. Herein, we review the current literature that suggests that Nrf2 is a valuable therapeutic target for cardiovascular disease, as well as experiments that illustrate the mechanisms of Nrf2 cardioprotection.