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. Diabetes 51: 168 -173, 2002

Hypertension affects nearly 20% of the population in Western countries and strongly increases the risk for cardiovascular diseases. In the pathogenesis of hypertension, the vasoactive peptide of the renin-angiotensin system, angiotensin II and its G protein–coupled receptors (GPCRs), play a crucial role by eliciting reactive oxygen species (ROS) and mediating vessel contractility. Here we show that mice lacking the GPCR-activated phosphoinositide 3-kinase (PI3K)γ are protected from hypertension that is induced by administration of angiotensin II in vivo. PI3Kγ was found to play a role in angiotensin II–evoked smooth muscle contraction in two crucial, distinct signaling pathways. In response to angiotensin II, PI3Kγ was required for the activation of Rac and the subsequent triggering of ROS production. Conversely, PI3Kγ was necessary to activate protein kinase B/Akt, which, in turn, enhanced L-type Ca2+ channel–mediated extracellular Ca2+ entry. These data indicate that PI3Kγ is a key transducer of the intracellular signals that are evoked by angiotensin II and suggest that blocking PI3Kγ function might be exploited to improve therapeutic intervention on hypertension.

Alzheimer's disease (AD) has been recently associated with vascular risk factors. ␤-amyloid peptides (A␤P), the main component of senile plaques typical of AD, circulate in soluble globular form in bloodstream. Interestingly, A␤P is able to induce endothelial dysfunction, and this effect may represent the link between vascular and neuronal pathophysiological factors involved in AD. We aimed to clarify the molecular mechanisms underlying globular A␤P-induced vascular toxicity. Using several methodological approaches, we have observed that in vascular tissues globular A␤P is unable to induce oxidative stress, one of the mechanisms hypothesized involved in ␤-amyloid toxicity. More important, we have demonstrated that globular A␤P is able to localize on vascular endothelium, where it inhibits eNOS enzymatic activity. In particular, A␤P enhances eNOS phosphorylation on threonine 495 and serine 116 and reduces acetylcholine-induced phosphorylation on serine 1177. Such an effect depends on a PKC signaling pathway, as suggested by its phosphorylation on serine 660. In fact, selective inhibition of the calcium-dependent group of PKC is able to rescue ␤-amyloid-induced alteration of eNOS phosphorylation, NO production, and endothelial vasorelaxation. The activation of these Ca 2؉ -dependent pathways is probably due to the ability of A␤P to evoke Ca 2؉ leakage from inositol 1,4,5-triphosphate receptors on endoplasmic reticulum. Our data demonstrate that globular A␤P-induced endothelial NO dysfunction can be attributed to an alteration of intracellular Ca 2؉ homeostasis, which could lead to the activation of calcium-dependent group of PKC with a consequent change of the eNOS phosphorylation pattern. These mechanisms could contribute to shed further light on the toxic effect of ␤-amyloid in vascular tissues. Alzheimer's disease (AD)1 is a progressive neurodegenerative disorder characterized by irreversible cognitive and physical deterioration. It is a major cause of death and a growing public health problem as life expectancy in the general population increases (1).Typical features of AD are the senile plaques present in the brain, cerebral blood vessels, and other tissues (2). The plaques are composed mainly of fibrillar amyloid ␤ peptides (A␤P) generated from the amyloid precursor protein, a ubiquitously expressed transmembrane glycoprotein. The amyloid peptides, constituted primarily of 39 -42 residues (A␤P 1-39, 1-40, and 1-42), are released continuously during cellular metabolism. These peptides circulate in soluble globular form in the bloodstream (3, 4) and accumulate on the vascular wall of AD patients (5). In the brain, soluble ␤-amyloid monomers are able to deposit and transform into insoluble and fibrillar aggregates, forming amyloid plaques (6, 7).Although AD has been considered for long to be of nonvascular origin, a growing body of recent studies has indicated the possibility that vascular risk factors could be involved in the pathophysiology of AD (8). In particular, patients with AD have morphological alterat...

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