No abstract

Angiotensin II (Ang II) is considered the major final mediator of the renin-angiotensin system. The actions of Ang II have been implicated in many cardiovascular conditions, such as hypertension, atherosclerosis, coronary heart disease, restenosis, and heart failure. Ang II can act through two different receptors: Ang II type 1 (AT(1)) receptor and Ang II type 2 (AT(2)) receptor. The AT(1) receptor is ubiquitously expressed in the cardiovascular system and mediates most of the physiological and pathophysiological actions of Ang II. The AT(2) receptor is highly expressed in the developing foetus, but its expression is very low in the cardiovascular system of the normal adult. Expression of the AT(2) receptor can be modulated by pathological states associated with tissue remodelling or inflammation such as hypertension, atherosclerosis, and myocardial infarction. The precise role of the AT(2) receptor remains under debate. However, it appears that the AT(2) receptor plays a vasodilatory role, and may be enhanced as a countervailing mechanism in cardiac hypertrophy, and in presence of vascular injury in hypertension and atherosclerosis. Signalling pathways induced by the stimulation of the AT(2) receptor are poorly understood, but three main mechanisms have been described: (a) activation of protein phosphatases causing protein dephosphorylation; (b) activation of bradykinin/nitric oxide/cyclic guanosine 3',5'-monophosphate pathway; and (c) stimulation of phospholipase A(2) and release of arachidonic acid. Vasodilatory effects of the AT(2) receptor, probably the only well-established role of the AT(2) receptor, have been attributed to the second of these mechanisms. The participation of the AT(2) receptor in cardiovascular remodelling and inflammation is more controversial. In vitro, AT(2) receptor stimulation clearly inhibits cardiac and vascular smooth muscle growth and proliferation, and stimulates apoptosis. In vivo, the situation is less clear, and depending on the studies, the AT(2) receptor appears to be required for cardiac hypertrophic growth or contrariwise, the AT(2) receptor has demonstrated no effects on cardiac hypertrophy. Similar controversial findings have been reported in atherosclerosis. Here we discuss the role of the AT(2) receptor on cardiovascular structure and disease, and the signalling pathways induced by its activation.

Background-High blood pressure causes a change in vascular wall structure involving altered extracellular matrix composition, but how this process occurs is not fully understood. Methods and Results-Using mouse carotid arteries maintained in organ culture for 3 days, we detected increased gelatin zymographic activity of matrix metalloproteinase (MMP)-2 (168Ϯ13%, PϽ0.05) in vessels kept at low intraluminal pressure (10 mm Hg) compared with vessels at 80 mm Hg (100%), whereas in vessels maintained at high pressure (150 mm Hg), both MMP-2 and MMP-9 activity was induced (182Ϯ32%, PϽ0.05, and 194Ϯ21%, PϽ0.01, respectively). MMPs were detected in endothelial and smooth muscle cells by immunohistochemistry and in situ gelatin zymography. In vessels at 150 mm Hg, MMP activation was associated with a shift in the pressure-diameter curve toward greater distensibility (PϽ0.01) compared with vessels at 80 mm Hg. However, distensibility was not altered in vessels at 10 mm Hg, in which only activated MMP-2 was detected. The role of MMPs in high pressure-induced vessel distensibility was confirmed by use of the MMP inhibitor FN-439, which prevented the shift in the pressure-diameter relationship. Furthermore, in carotid arteries from MMP-9 -deficient mice, the pressure-dependent increase in MMP-2 and in situ gelatinolytic activity were maintained, but the upward shift in the pressure-diameter curve was abolished. Conclusions-MMP-9 seems to play a key role in the early stages of hypertensive vascular remodeling. (Circulation.

Immune cells have been implicated in the pathogenesis of hypertension. We hypothesized that under the influence of chromosome (chr)2, T lymphocytes contribute to vascular inflammation in genetic salt-sensitive hypertension. Normotensive (Brown Norway), hypertensive (Dahl salt-sensitive), and consomic rats (SSBN2; in which chr2 has been transferred from Brown Norway to Dahl rats) were studied. Systolic blood pressure, measured by tail cuff, and aortic preproendothelin mRNA, measured by quantitative RT-PCR, were elevated in Dahl rats compared with Brown Norway rats and were reduced in SSBN2 rats compared with Dahl rats (P < 0.01). Compared with Brown Norway rats, Dahl rats exhibited increased inflammatory markers and mediators such as nuclear translocation of the aortic p65 subunit of NF-kappaB as well as VCAM-1, ICAM-1, chemokine (C-C motif) receptor 5, and CD4 mRNA, all of which were reduced in SSBN2 rats. Aortic CD8 mRNA was equally increased in Dahl and SSBN2 rats relative to Brown Norway rats. CD4(+) T cell infiltration in the aorta of SSBN2 rats was reduced compared with Dahl rats, whereas the aortic protein expression of Foxp3b and immunosuppressors transforming growth factor (TGF)-beta(1) and IL-10, the three markers associated with the regulatory T cell lineage, were enhanced in SSBN2 rats. Activation in vitro of T cells demonstrated that CD4(+)CD25(+) and CD8(+)CD25(+) cells (Tregs) produce IL-10 in SSBN2 rats. Thus, increased vascular inflammatory responses and hypertension in a genetic salt-sensitive hypertensive rodent model are reduced by transfer of chr2 from a normotensive strain, and this is associated with enhanced levels of immunosuppressive mediators.

Arsenic is a widespread environmental contaminant to which millions of people are exposed worldwide. Exposure to arsenic is epidemiologically linked to increased cardiovascular disease, such as atherosclerosis. However, the effects of moderate concentrations of arsenic on atherosclerosis formation are unknown. Therefore, we utilized an in vivo ApoE(-/-) mouse model to assess the effects of chronic moderate exposure to arsenic on plaque formation and composition in order to facilitate mechanistic investigations. Mice exposed to 200 ppb arsenic developed atherosclerotic lesions, a lower exposure than previously reported. In addition, arsenic modified the plaque content, rendering them potentially less stable and consequently, potentially more dangerous. Moreover, we observed that the lower exposure concentration was more atherogenic than the higher concentration. Arsenic-enhanced lesions correlated with several proatherogenic molecular changes, including decreased liver X receptor (LXR) target gene expression and increased proinflammatory cytokines. Significantly, our observations suggest that chronic moderate arsenic exposure may be a greater cardiovascular health risk than previously anticipated.

Gas6 (growth arrest-specific 6) belongs structurally to the family of plasma vitamin K-dependent proteins. Gas6 has a high structural homology with the natural anticoagulant protein S, sharing the same modular composition. Interestingly, despite the presence of a g-carboxyglutamic acid domain in its structure, no role in the coagulation cascade has been identified for gas6. Gas6 has been shown to be involved in vascular homeostasis and more precisely is involved in proliferation, apoptosis, efferocytosis, leukocyte migration, and sequestration and platelet aggregation. It is also involved in the activation of different cell types, from platelets to endothelial and vascular smooth muscle cells. Thus, it has been shown to play a role in several pathophysiological processes such as atherosclerosis, cancer, and thrombosis. Interestingly, studies using gas6 null mice highlighted that gas6 may represent a novel potential target for anticoagulant therapy, because these animals are protected from lethal venous thromboembolism without excessive bleeding. However, the mechanism in thrombus occurrence remains to be further explored. In the present review, we will focus on the role of gas6 in innate immunity, atherosclerosis, thrombosis, and cancer-related events.

Key Words: aldosterone Ⅲ AT 1 R Ⅲ AT 1a R Ⅲ AT 1b R Ⅲ intracellular signaling P athophysiological synergistic effects between angiotensin II (Ang II) and aldosterone have been described on vascular cells and support the concept that combination of aldosterone and Ang II receptor blockade may be therapeutically beneficial. [1][2][3][4] In the past few years, investigators have demonstrated that blockade of mineralocorticoid receptor (MR) reduced mortality caused by progressive heart failure and sudden death from cardiac causes, as well as rate of hospitalization for heart failure. These results were observed in patients with severe heart failure who were also being treated with an angiotensin-converting enzyme inhibitor and included subjects developing heart failure after myocardial infarction. 5,6 Growing evidence has shown that aldosterone could influence the signaling or trafficking of the Ang II type 1 receptor (AT 1 R). Indeed, mineralocorticoids such as deoxycorticosterone and aldosterone caused upregulation of Ang II binding to blood vessels and cultured VSMCs. 4,7,8 Spironolactone, a specific antagonist of MR, has been shown to inhibit Ang II-stimulated proliferation of VSMCs. 9 Recent studies have unraveled further evidence of a crosstalk between AT 1 R and MR. Ang II could directly stimulated nuclear localization of MR in human coronary and aortic VSMCs, supporting a role of MR in gene expression after Ang II stimulation. 10 Spironolactone also inhibits Ang II-induced senescence of VSMCs. These studies suggest that vascular responses to Ang II could be mediated via direct signaling crosstalk between MR and AT 1 R. 11 Among rodents, mice have 2 subtypes of AT 1 R, AT 1a R and Ang II type 1b receptor (AT 1b R). In the present study, we hypothesized that AT 1a R and AT 1b R interact differentially with MR to signal intracellularly. We sought to understand more precisely the molecular mechanisms underlying crosstalk between the 2 subtypes of AT 1 R present in the mouse, AT 1a R and AT 1b R, and MR. We focused on the effects that potential crosstalk had on activation of extracel- Original received February 27, 2009; revision received September 8, 2009; accepted September 9, 2009 Methods Cell Culture and TransfectionVSMCs derived from mesenteric arteries of 8 weeks male C57Bl/6 and AT 1a R knockout mice were isolated and characterized as described previously. 12,13 AT 1a R knockout mice were produced at Duke University 14 and later bred in the animal facility at the Lady Davis Institute. Briefly, mesenteric arteries were cleaned of adipose and connective tissue and VSMCs were dissociated by the enzymatic digestion of vascular arcades. Quantitative RT-PCREfficiency of siRNA targeting AT 1a R, AT 1b R, and MR was verified by quantitative real-time polymerase chain reaction (QRT-PCR). VSMC RNA was isolated by homogenization in TRIzol reagent (Invitrogen) followed by chloroform extraction and isopropanol precipitation. One microgram of total RNA was reversed-transcribed with random hexamers and Superscript II (...

Angiotensin II (Ang II) is considered the main final mediator of the renin-angiotensin-aldosterone system (RAAS). The actions of Ang II have been implicated in many cardiovascular conditions, such as hypertension, atherosclerosis, coronary heart disease, restenosis after injury, and heart failure. The Ang II type 1 receptor (AT(1)R), a G-protein-coupled receptor, mediates most of the physiological and pathophysiological actions of Ang II. This receptor is predominantly expressed in cardiovascular cells, such as vascular smooth muscle cells where it activates various signaling cascades leading to vascular remodeling and inflammation. Besides Ang II, aldosterone has emerged as an important component and mediator of the effects of the RAAS. Aldosterone-induced genomic effects mediated through binding to the mineralocorticoid receptor (MR), a member of the steroid hormone receptor superfamily, which functions as a ligand-dependent transcription factor, are characterized by a delay of minutes to hours corresponding to a long series of subcellular events that include gene activation and protein synthesis. Besides its well-known genomic actions, there is evidence of aldosterone-mediated rapid effects which lead to the activation of ion channels and other signaling pathways. Some of the effects of aldosterone occur through similar pathways as Ang II-induced signaling events. Indeed, recent studies suggest complex interactions between Ang II and aldosterone: it has become evident that aldosterone may influence the signaling or trafficking of the AT(1)R. Thus, growing evidence demonstrates the existence of cross-talk between Ang II and aldosterone which could potentially modulate Ang II signal transduction. These interactions between Ang II and aldosterone activate specific signaling pathways, sometimes in ways distinct from those that they induce on their own, one which may lead to pathogenic effects on target organs. Here we focus on recent findings and concepts that suggest the existence of novel signaling mechanisms whereby the cross-talk between Ang II and aldosterone plays a role in cardiovascular disease. We also discuss the importance of investigating Ang II/aldosterone cross-talk as a mean of developing new therapeutic strategies to combat cardiovascular disease.