Redox regulation of angiotensin II signaling in the heart

Genetic Deletion of the p66 Shc Adaptor Protein Protects From Angiotensin II–Induced Myocardial Damage

Angiotensin II (Ang II), acting through its G protein-coupled AT1 receptor (AT1), contributes to the precocious heart senescence typical of patients with hypertension, atherosclerosis, and diabetes. AT1 was suggested to transactivate an intracellular signaling controlled by growth factors and their tyrosin-kinase receptors. In cultured vascular smooth muscle cells, this downstream mechanism comprises the p66Shc adaptor protein, previously recognized to play a role in vascular cell senescence and death. The aim of the present study was 2-fold: (1) to characterize the cardiovascular phenotype of p66Shc knockout mice (p66Shc(-/-)), and (2) to test the novel hypothesis that disrupting the p66Shc might protect the heart from the damaging action of elevated Ang II levels. Compared with wild-type littermates (p66Shc(+/+)), p66Shc(-/-) showed similar blood pressure, heart rate, and left ventricular wall thickness. However, cardiomyocyte number was increased in mutant animals, indicating a condition of myocardial hyperplasia. In p66Shc(+/+), infusion of a sub-pressor dose of Ang II (300 nmol/kg body weight [BW] daily for 28 days) caused left ventricular hypertrophy and apoptotic death of cardiomyocytes and endothelial cells. In contrast, p66Shc(-/-) were resistant to the proapoptotic/hypertrophic action of Ang II. Consistently, in vitro experiments showed that Ang II causes apoptotic death of cardiomyocytes isolated from p66Shc(+/+) hearts to a greater extent as compared with p66Shc(-/-) cardiomyocytes. Our results indicate a fundamental role of p66Shc in Ang II-mediated myocardial remodeling. In perspective, p66Shc inhibition may be envisioned as a novel way to prevent the deleterious effects of Ang II on the heart.

Angiotensin II-induced over-activation of p47phox in fibroblasts from hypertensives: which role in the enhanced ERK1/2 responsiveness to angiotensin II?

BACKGROUND

Fibroblasts are involved in the remodeling of the heart and of the vasculature associated to arterial hypertension, and an abnormal extracellular signal-regulated kinase 1/2 (ERK1/2) activation by angiotensin II (Ang II) plays a pivotal role in this process. However, the intracellular pathways leading to cell hypertrophy and hyperplasia, as well as to collagen production, are still incompletely known.

OBJECTIVE

To investigate the role of superoxide anion (O2) and of nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase in Ang II-stimulated ERK1/2 over-activation in fibroblasts from hypertensive patients.

METHODS

O2 production was measured in skin fibroblasts from hypertensives (HT, n = 11) and from normotensive controls (NT, n = 10) by electron spin resonance technique. ERK1/2 phosphorylation and p47phox NAD(P)H oxidase subunit translocation were measured by western blot.

RESULTS

Ang II (1 micromol/l) induced a larger p47phox subunit translocation and increased intracellular O2 production to a larger extent in HT in comparison to NT and this effect was blocked by apocynin, an inhibitor of the NAD(P)H oxidase. Ang II increased ERK1/2 phosphorylation more in HT than in NT. The Ang II-induced ERK1/2 phosphorylation was inhibited by apocynin in a dose-dependent manner in NT, but not in HT.

CONCLUSIONS

The chain of cellular events leading to increased ERK1/2 responsiveness to Ang II in hypertension include an exaggerated response of p47phox, NAD(P)H oxidase and O2, but it is partially resistant to apocynin. Therefore, NAD(P)H-dependent reactive oxygen species (ROS) production is not the only determinant of the exaggerated ERK1/2 responsiveness in fibroblasts of hypertensives (HT).

Altered mechanical and electrical activities of the diabetic heart: Possible use of new therapeutics?

Diabetes mellitus produces functional, biochemical and morphological myocardial abnormalities independent of coronary atherosclerosis and hypertension. Although tight glycemic control decreases the risk of heart failure in patients with diabetes, the effects of different diabetic treatment regimens on heart failure have yet to be determined and remain subject to further investigation.Evidence suggests that reactive oxygen species play an important role in the development of diabetic cardiomyopathy, and antioxidants have been used to reduce cardiomyopathy in patients with diabetes. Therefore, the present study examines the treatment of streptozotocin-induced diabetic rats with sodium selenite (5 mumol/kg/day, intraperitoneally). The results showed that sodium selenite treatment could restore the altered mechanical and electrical activities of diabetic rat hearts. The results also demonstrate that the beneficial effects of this treatment on diabetic rat heart dysfunction appear to be due to the restoration of diminished K(+) currents; the restoration of increased intracellular Ca(2+) concentrations in diabetes; and all these beneficial effects are partially related to the restoration of the cell glutathione redox cycle.It has been hypothesized that the angiotensin II (Ang II) signalling pathway may also play a role in the development of diabetic cardiomyopathy. It is the ability of Ang II to produce reactive oxygen species and the involvement of these molecules in signal transduction that are the hallmark of Ang II activation. Although action potential prolongation and diminished K(+) currents were reversed by angiotensin receptor type I (AT(1)) blockers in diabetic rat heart, their effects on Ca(2+) homeostasis in diabetic cardiomyocytes are not yet clear. Thus, the effects of AT(1) blocker treatment (candesartan cilexetil) on cardiac Ca(2+) metabolism, and on the contractile state and electrical activity of papillary muscle in diabetic rats were examined. It was shown that treatment with an AT(1) blocker restored the altered kinetics of Ca2+ transients in cardiomyocytes and the contractile activity in papillary muscle strips from diabetic rats. Thus, Ang II receptor blockade protects the heart from the development of cellular alterations that are typically related to diabetes.

Redox regulation of cardiac protein kinase C

The two extremes of redox stress imposed on cardiac tissue under ischemia and reperfusion change the redox potential of the cells and affect numerous redox-sensitive molecules, including the ones involved in intracellular communication. Protein kinase C (PKC), a key signalling kinase, is one of those subject to redox control. Activation of PKC by oxidation represents a new paradigm of the alternate signalling principle. Reactive oxygen species act directly on PKC, releasing chelated Zn(2+) ions from the zinc finger of the regulatory domain. Zn(2+) release from PKC by oxidative stress has been shown at the level of isolated protein fragments, PKC immune complexes and single cells. Zn(2+) movements have been further characterized in cryosections prepared from adult rat hearts subjected to in vivo stress by global ischemia followed by reperfusion. The morphology of labile zinc in cardiac tissue and zinc release following PKC stimulation with lipid activator are described. The studies lead to an unexpected and intriguing result, suggesting that in addition to serving a structural function, Zn(2+) ions are likely to play a dynamic regulatory role in PKC. The cysteine-rich domains of the serine/threonine kinases are identified as redox sensors. Thus, being an integrated composite of redox signalling systems, free Zn(2+) reflects the protein redox status and serves as a valid biomarker of stressed tissue and its capacity to respond to stimuli.