Acute hypertension induces oxidative stress in brain tissues.

Arterial hypertension is not only a major risk factor for cerebrovascular accidents, such as stroke and cerebral hemorrhage, but is also associated to milder forms of brain injury. One of the main causes of neurodegeneration is the increase in reactive oxygen species (ROS) that is also a common trait of hypertensive conditions, thus suggesting that such a mechanism could play a role even in the onset of hypertension-evoked brain injury. To investigate this issue, we have explored the effect of acute-induced hypertensive conditions on cerebral oxidative stress. To this aim, we have developed a mouse model of transverse aortic coarctation (TAC) between the two carotid arteries, which imposes acutely on the right brain hemisphere a dramatic increase in blood pressure. Our results show that hypertension acutely induced by aortic coarctation induces a breaking of the blood-brain barrier (BBB) and reactive astrocytosis through hyperperfusion, and evokes trigger factors of neurodegeneration such as oxidative stress and inflammation, similar to that observed in cerebral hypoperfusion. Moreover, the derived brain injury is mainly localized in selected brain areas controlling cognitive functions, such as the cortex and hippocampus, and could be a consequence of a defect in the BBB permeability. It is noteworthy to emphasize that, even if these latter events are not enough to produce ischemic/hemorrhagic injury, they are able to alter mechanisms fundamental for maintaining normal brain function, such as protein synthesis, which has a prominent role for memory formation and cortical plasticity.

Melusin, a muscle-specific integrin beta1-interacting protein, is required to prevent cardiac failure in response to chronic pressure overload.

Cardiac hypertrophy is an adaptive response to a variety of mechanical and hormonal stimuli, and represents an early event in the clinical course leading to heart failure. By gene inactivation, we demonstrate here a crucial role of melusin, a muscle-specific protein that interacts with the integrin beta1 cytoplasmic domain, in the hypertrophic response to mechanical overload. Melusin-null mice showed normal cardiac structure and function in physiological conditions, but when subjected to pressure overload--a condition that induces a hypertrophic response in wild-type controls--they developed an abnormal cardiac remodeling that evolved into dilated cardiomyopathy and contractile dysfunction. In contrast, the hypertrophic response was identical in wild-type and melusin-null mice after chronic administration of angiotensin II or phenylephrine at doses that do not increase blood pressure--that is, in the absence of cardiac biomechanical stress. Analysis of intracellular signaling events induced by pressure overload indicated that phosphorylation of glycogen synthase kinase-3beta (GSK-3beta) was specifically blunted in melusin-null hearts. Thus, melusin prevents cardiac dilation during chronic pressure overload by specifically sensing mechanical stress.

Regulation of myocardial contractility and cell size by distinct PI3K-PTEN signaling pathways.

The PTEN/PI3K signaling pathway regulates a vast array of fundamental cellular responses. We show that cardiomyocyte-specific inactivation of tumor suppressor PTEN results in hypertrophy, and unexpectedly, a dramatic decrease in cardiac contractility. Analysis of double-mutant mice revealed that the cardiac hypertrophy and the contractility defects could be genetically uncoupled. PI3Kalpha mediates the alteration in cell size while PI3Kgamma acts as a negative regulator of cardiac contractility. Mechanistically, PI3Kgamma inhibits cAMP production and hypercontractility can be reverted by blocking cAMP function. These data show that PTEN has an important in vivo role in cardiomyocyte hypertrophy and GPCR signaling and identify a function for the PTEN-PI3Kgamma pathway in the modulation of heart muscle contractility.

Increased basal nitric oxide release despite enhanced free radical production in hypertension.

INTRODUCTION: Although in hypertension a defect in stimulated nitric oxide (NO) is well established, little is known about basal NO levels. Thus, we measured directly in vessels from normotensive [Wistar-Kyoto (WKY)] rats and spontaneously hypertensive rats (SHR) both basal and stimulated NO production using a novel technique [4,5-diaminofluorescein (DAF-2) fluorescence]. METHODS: Isolated vessels were exposed to the fluorescent probe DAF-2. After the technique was validated with increasing doses of acetylcholine in the presence and absence of NG-nitro-L-arginine methyl ester (l-NAME), we measured NO production in vessels from WKY rats and SHR in the same experimental setting. Finally, to explore the impact of reactive oxygen species (ROS) on NO release, we analysed the effect of an antioxidant, such as ascorbic acid, on basal and stimulated NO in aortic rings of WKY rats and SHR. RESULTS: Aortic rings from SHR exhibited a higher basal NO production and a lower responsiveness to agonist-induced NO release as compared with those observed in WKY rats. Also in resistance vessels such as mesenteric arteries, basal NO production was higher in hypertension. In hypertensive rats, ascorbic acid was able to further increase basal NO release and recovered the impaired stimulated NO production, whereas no effect was detected in normotensive rats. CONCLUSIONS: Our data reveal an increased basal NO availability in hypertension despite the increased production of ROS, suggesting a greater complexity in hypertensive endothelial dysfunction when the analysis is focused on direct NO measurement.

Cardiovascular influences of alpha1b-adrenergic receptor defect in mice.

BACKGROUND: The alpha1-adrenergic receptors (alpha1-ARs) play a key role in cardiovascular homeostasis. However, the functional role of alpha1-AR subtypes in vivo is still unclear. The aim of this study was to evaluate the cardiovascular influences of alpha1b-AR. METHODS AND RESULTS: In transgenic mice lacking alpha1-AR (KO) and their wild-type controls (WT), we evaluated blood pressure profile and cardiovascular remodeling induced by the chronic administration (18 days via osmotic pumps) of norepinephrine, angiotensin II, and subpressor doses of phenylephrine. Our results indicate that norepinephrine induced an increase in blood pressure levels only in WT mice. In contrast, the hypertensive state induced by angiotensin II was comparable between WT and KO mice. Phenylephrine did not modify blood pressure levels in either WT or KO mice. The cardiac hypertrophy and eutrophic vascular remodeling evoked by norepinephrine was observed only in WT mice, and this effect was independent of the hypertensive state because it was similar to that observed during subpressor phenylephrine infusion. Finally, the cardiac hypertrophy induced by thoracic aortic constriction was comparable between WT and KO mice. CONCLUSIONS: Our data demonstrate that the lack of alpha1b-AR protects from the chronic increase of arterial blood pressure induced by norepinephrine and concomitantly prevents cardiovascular remodeling evoked by adrenergic activation independently of blood pressure levels.

Leptin effect on endothelial nitric oxide is mediated through Akt-endothelial nitric oxide synthase phosphorylation pathway.

Recent evidence suggests that besides its action on the central nervous system, leptin can modulate vascular tone through local mechanisms involving nitric oxide (NO) release. In this study, using a fluorescent probe for direct determination of NO, we demonstrated both in endothelial cells and in vessels that leptin is able to stimulate NO release. The effect of leptin on NO is abolished by erbstatin A, a Ca(2+)-independent tyrosine kinase inhibitor, whereas it is not influenced by calcium removal or by other protein phosphorylation inhibitors, such as genistein (an ATP-dependent tyrosine-kinase inhibitor) or wortmannin and LY294002 (two different phosphatidylinositol [PI] 3-kinase inhibitors). Accordingly, leptin-induced vasorelaxation in aortic rings was abolished only by erbstatin A. Furthermore, immunoblotting studies revealed that leptin evokes Akt phosphorylation, with a comparable time course in both endothelial cells and vessels. Also in this experimental system, the effect of leptin was abolished by erbstatin A and not by other inhibitors. Finally, a considerable increase in endothelial NO synthase (eNOS) phosphorylation in Ser(1177) was found when vessels were treated with leptin. In conclusion, leptin induces NO production by activating a PI 3-kinase-independent Akt-eNOS phosphorylation pathway.