G-protein-coupled receptor MAS deletion produces a preeclampsia-like phenotype in FVB/N mice.

BACKGROUND: An unbalance in the renin-angiotensin (Ang) system (RAS) between the Ang II/AT1 and Ang-(1-7)/Mas axis appears to be involved in preeclampsia (PE), in which a reduction in Ang-(1-7) was observed. Here, we tested whether the reduction in the activity of the Ang-(1-7)/Mas axis could be a contributing factor for the development of PE, using Mas-deficient (Mas-/-) mice. METHODS AND RESULTS: Cardiovascular parameters were evaluated by telemetry before, during pregnancy and 4 days postpartum in 20-week-old Mas-/- and wild-type (WT) female mice. Mas-/- mice presented reduced arterial blood pressure (BP) at baseline (91.3 ± 0.8 in Mas-/- vs. 94.0 ± 0.9 mmHg in WT, Diastolic, P<0.05). However, after the 13th day of gestation, BP in Mas-/- mice started to increase, time-dependently, and at day 19 of pregnancy, these animals presented a higher BP in comparison with WT group (90.5 ± 0.7 in Mas-/- vs. 80.3 ± 3.5 mmHg in WT, Diastolic D19, P<0.0001). Moreover, pregnant Mas-/- mice presented fetal growth restriction, increase in urinary protein excretion as compared with nonpregnant Mas-/-, oliguria, increase in cytokines, endothelial dysfunction and reduced ACE, AT1R, ACE2, ET-1A, and eNOS placental mRNA, similar to some of the clinical manifestations found in the development of PE. CONCLUSIONS: These results show that Mas-deletion produces a PE-like state in FVB/N mice.

Hemodynamic phenotyping of transgenic rats with ubiquitous expression of an angiotensin-(1-7)-producing fusion protein.

Activation of the angiotensin (Ang)-converting enzyme (ACE) 2/Ang-(1-7)/MAS receptor pathway of the renin-angiotensin system (RAS) induces protective mechanisms in different diseases. Herein, we describe the cardiovascular phenotype of a new transgenic rat line (TG7371) that expresses an Ang-(1-7)-producing fusion protein. The transgene-specific mRNA and the corresponding protein were shown to be present in all evaluated tissues of TG7371 with the highest expression in aorta and brain. Plasma Ang-(1-7) levels, measured by radioimmunoassay (RIA) were similar to control Sprague-Dawley (SD) rats, however high Ang-(1-7) levels were found in the hypothalamus. TG7371 showed lower baseline mean arterial pressure (MAP), assessed in conscious or anesthetized rats by telemetry or short-term recordings, associated with increased plasma atrial natriuretic peptide (ANP) and higher urinary sodium concentration. Moreover, evaluation of regional blood flow and hemodynamic parameters with fluorescent microspheres showed a significant increase in blood flow in different tissues (kidneys, mesentery, muscle, spleen, brown fat, heart and skin), with a resulting decrease in total peripheral resistance (TPR). TG7371 rats, on the other hand, also presented increased cardiac and global sympathetic tone, increased plasma vasopressin (AVP) levels and decreased free water clearance. Altogether, our data show that expression of an Ang-(1-7)-producing fusion protein induced a hypotensive phenotype due to widespread vasodilation and consequent fall in peripheral resistance. This phenotype was associated with an increase in ANP together with an increase in AVP and sympathetic drive, which did not fully compensate the lower blood pressure (BP). Here we present the hemodynamic impact of long-term increase in tissue expression of an Ang-(1-7)-fusion protein and provide a new tool to investigate this peptide in different pathophysiological conditions.

Chronic Overexpression of Bradykinin in Kidney Causes Polyuria and Cardiac Hypertrophy.

Acute intra-renal infusion of bradykinin increases diuresis and natriuresis via inhibition of vasopressin activity. However, the consequences of chronically increased bradykinin in the kidneys have not yet been studied. A new transgenic animal model producing an excess of bradykinin by proximal tubular cells (KapBK rats) was generated and submitted to different salt containing diets to analyze changes in blood pressure and other cardiovascular parameters, urine excretion, and composition, as well as levels and expression of renin-angiotensin system components. Despite that KapBK rats excrete more urine and sodium, they have similar blood pressure as controls with the exception of a small increase in systolic blood pressure (SBP). However, they present decreased renal artery blood flow, increased intrarenal expression of angiotensinogen, and decreased mRNA expression of vasopressin V1A receptor (AVPR1A), suggesting a mechanism for the previously described reduction of renal vasopressin sensitivity by bradykinin. Additionally, reduced heart rate variability (HRV), increased cardiac output and frequency, and the development of cardiac hypertrophy are the main chronic effects observed in the cardiovascular system. In conclusion: (1) the transgenic KapBK rat is a useful model for studying chronic effects of bradykinin in kidney; (2) increased renal bradykinin causes changes in renin angiotensin system regulation; (3) decreased renal vasopressin sensitivity in KapBK rats is related to decreased V1A receptor expression; (4) although increased renal levels of bradykinin causes no changes in mean arterial pressure (MAP), it causes reduction in HRV, augmentation in cardiac frequency and output and consequently cardiac hypertrophy in rats after 6 months of age.

High aminopeptidase A activity contributes to blood pressure control in ob/ob mice by AT2 receptor-dependent mechanism.

Obesity is assumed to be a major cause of human essential hypertension; however, the mechanisms responsible for weight-related increase in blood pressure (BP) are not fully understood. The prevalence of hypertension induced by obesity has grown over the years, and the role of the renin-angiotensin-aldosterone system (RAAS) in this process continues to be elucidated. In this scenario, the ob/ob mice are a genetic obesity model generally used for metabolic disorder studies. These mice are normotensive even though they present several metabolic conditions that predispose them to hypertension. Although the normotensive trait in these mice is associated with the poor activation of sympathetic nervous system by the lack of leptin, we demonstrated that ob/ob mice present massively increased aminopeptidase A (APA) activity in the circulation. APA enzyme metabolizes angiotensin (ANG) II into ANG III, a peptide associated with intrarenal angiotensin type 2 (AT2) receptor activation and induction of natriuresis. In these mice, we found increased ANG-III levels in the circulation, high AT2 receptor expression in the kidney, and enhanced natriuresis. AT2 receptor blocking and APA inhibition increased BP, suggesting the ANG III-AT2 receptor axis as a complementary BP control mechanism. Circulating APA activity was significantly reduced by weight loss independently of leptin, indicating the role of fat tissue in APA production. Therefore, in this study we provide new data supporting the role of APA in BP control in ob/ob mouse strain. These findings improve our comprehension about obesity-related hypertension and suggest new tools for its treatment.NEW & NOTEWORTHY In this study, we reported an increased angiotensin III generation in the circulation of ob/ob mice caused by a high aminopeptidase A activity. These findings are associated with an increased natriuresis found in these mice and support the role of renin-angiotensin-aldosterone system as additional mechanism regulating blood pressure in this genetic obese strain.

Receptor MAS protects mice against hypothermia and mortality induced by endotoxemia.

The renin-angiotensin (Ang) system is involved in maintaining cardiovascular function by regulating blood pressure and electrolyte homeostasis. More recently, alternative pathways within the renin-angiotensin system have been described, such as the ACE-2/Ang-(1-7)/Mas axis, with opposite effects to the ones of the ACE/Ang-II/AT1 axis. Correspondingly, our previous work reported that Ang-(1-7) via its receptor Mas inhibits the mRNA expression of the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor-α increased by lipopolysaccharide (LPS) in mouse peritoneal macrophages. These data led us to investigate the functional role of the Ang-(1-7)/Mas axis in an in vivo LPS model. In this work, we present evidence that Ang-(1-7) via Mas significantly reduced the LPS-increased production of circulating cytokines, such as IL-6, IL-12, and CXCL-1. This inhibitory effect was mediated by Mas because it was not detectable in Mas-deficient (Mas) mice. Accordingly, IL-6, CXCL-1, and CXCL-2 levels were higher after LPS treatment in the absence of Mas. Mas mice were less resistant to LPS-induced endotoxemia, their survival rate being 50% compared with 95% in wild-type mice. Telemetric analyses showed that Mas mice presented more pronounced LPS-induced hypothermia with a 3°C lower body temperature compared with wild-type mice. Altogether, our findings suggest that Ang-(1-7) and Mas inhibit LPS-induced cytokine production and hypothermia and thereby protect mice from the fatal consequences of endotoxemia.

Oral administration of angiotensin-(1-7) ameliorates type 2 diabetes in rats.

UNLABELLED: Diabetes mellitus type 2 (DM2) is a disease with increasing importance in modern societies and insufficient treatment options. Pharmacological stimulation of insulin signaling, which is blunted in DM2, is a promising approach to treat this disease. It has been shown that activation of the angiotensin (Ang)-(1-7)/Mas axis of the renin-angiotensin system leads to an improved glucose uptake. In this study, we intended to evaluate, whether this effect could be exploited therapeutically. We first confirmed that Ang-(1-7) improves insulin signaling and glucose uptake in vitro in cultured cardiomyocytes. We then evaluated the therapeutic effect of a newly developed hydro-xypropyl-ß-cyclodextrin-based Ang-(1-7) nano-formulation in a novel transgenic rat model of inducible insulin resistance and DM2. The chronic administration of this compound prevented the marked elevation in blood glucose levels in these rats at a dose of 30 µg/kg, reversed the established hyperglycemic state at a dose of 100 µg/kg, and resulted in improved insulin sensitivity, reduced plasma insulin and decreased diabetic nephropathy. In conclusion, an oral Ang-(1-7) formulation reverses hyperglycemia and its consequences in an animal model of DM2 and represents a novel therapeutic option for the treatment of DM2 and other cardio-metabolic diseases. KEY MESSAGE: A novel rat model with inducible diabetes can be used to evaluate new therapies. Angiotensin-(1-7) is effective in an oral formulation packaged in cyclodextrine. Angiotensin-(1-7) is a promising antidiabetic drug.

Leptin regulates ACE activity in mice.

Leptin is a hormone related to metabolism. It also influences blood pressure, but the mechanisms triggered in this process are not yet elucidated. Angiotensin-I converting enzyme (ACE) regulates cardiovascular functions and recently has been associated with metabolism control and obesity. Here, we used ob/ob mice, a model lacking leptin, to answer the question whether ACE and leptin could interact to influence blood pressure, thereby linking the renin-angiotensin system and obesity. These mice are obese and diabetic but have normal 24 h mean arterial pressure. Our results show that plasma and lung ACE activities as well as ACE mRNA expression were significantly decreased in ob/ob mice. In agreement with these findings, the hypotensive effect produced by enalapril administration was attenuated in the obese mice. Plasma renin, angiotensinogen, angiotensin I, bradykinin, and angiotensin 1-7 were increased, whereas plasma angiotensin II concentration was unchanged in obese mice. Chronic infusion of leptin increased renin activity and angiotensin II concentration in both groups and increased ACE activity in ob/ob mice. Acute leptin infusion restored ACE activity in leptin-deficient mice. Moreover, the effect of an ACE inhibitor on blood pressure was not changed in ob/+ mice during leptin treatment but increased four times in obese mice. In summary, our findings show that the renin-angiotensin system is altered in ob/ob mice, with markedly reduced ACE activity, which suggests a possible connection between the renin-angiotensin system and leptin. These results point to an important interplay between the angiotensinergic and the leptinergic systems, which may play a role in the pathogenesis of obesity, hypertension, and metabolic syndrome.

Altered cardiovascular reflexes responses in conscious Angiotensin-(1-7) receptor Mas-knockout mice.

This study evaluated the physiological importance of Angiotensin-(1-7) receptor Mas on reflex control of circulation. Experiments were performed in male Mas-knockout (Mas-KO) and Wild Type (WT) conscious mice (12-20 wk of age). Baroreceptor reflex was evaluated by the bradycardic response induced by phenylephrine (0.25 µg/5 µl, i.v.). Bezold-Jarisch reflex was evaluated by phenylbiguanide (0.5 µg/5 µl, i.v.) and chemoreflex by potassium cyanide (2.5 µg/5 µl, i.v.). Baseline mean arterial pressure was higher in Mas-KO (n=14) as compared with WT mice (n=18) (118±1 mmHg vs. 109±2 mmHg); however, heart rate was similar in both strains (615±30 bpm vs. 648±13 bpm). Baroreflex bradycardia was lower (0.78±0.44 ms/mmHg vs. 1.30±0.14 ms/mmHg) in Mas-KO compared with WT mice. The depressor (-17±5 mmHg vs. -45±6 mmHg) and bradycardic (-212±36 bpm vs. -391±29 bpm) components of the Bezold-Jarisch reflex were also lower in Mas-KO mice. In addition, chemoreflex pressor response (+20±3 mmHg vs. +12±0.8 mmHg) and bradycardic response (-250±74 bpm vs. -52±26 bpm) were significantly higher in Mas-KO. These results further advances previous studies by showing that the lack of Mas receptor induced important imbalance in the neural control of blood pressure, altering not only the baroreflex but also the chemo- and Bezold-Jarisch reflexes.

Predisposition to atherosclerosis and aortic aneurysms in mice deficient in kinin B1 receptor and apolipoprotein E.

Kinin B1 receptor is involved in chronic inflammation and expressed in human atherosclerotic lesions. However, its significance for lesion development is unknown. Therefore, we investigated the effect of kinin B1 receptor deletion on the development of atherosclerosis and aortic aneurysms in apolipoprotein E-deficient (ApoE(-/-)) mice. Mice deficient both in ApoE and in kinin B1 receptor (ApoE(-/-)-B(1)(-/-)) were generated and analyzed for their susceptibility to atherosclerosis and aneurysm development under cholesterol rich-diet (western diet) and angiotensin II infusion. Kinin B1 receptor messenger RNA (mRNA) expression was significantly increased in ApoE(-/-) mice after Western-type diet. Although no difference in serum cholesterol was found between ApoE(-/-)-B(1)(-/-) and ApoE(-/-) mice under Western-type diet, aortic lesion incidence was significantly higher in ApoE(-/-)-B(1)(-/-) after this treatment. In accordance, we observed increased endothelial dysfunction in these mice. The mRNA expression of cyclic guanosine monophosphate-dependent protein kinase I, CD-11, F4/80, macrophage colony-stimulating factor, and tumor necrosis factor-alpha were increased in the aorta of double-deficient mice following Western-type diet, whereas the levels of peroxisome proliferator-activated receptor gamma protein and the activity of matrix metalloproteinase-9 activity were decreased. In addition to the increased atherosclerotic lesions, the lack of kinin B(1) receptor also increased the incidence of abdominal aortic aneurysms after angiotensin II infusion. In conclusion, our results show that kinin B(1) receptor deficiency aggravates atherosclerosis and aortic aneurysms under cholesterolemic conditions, supporting an antiatherogenic role for the kinin B(1) receptor.

Ablation of angiotensin (1-7) receptor Mas in C57Bl/6 mice causes endothelial dysfunction.

The Mas gene codes for an angiotensin (1-7) receptor. There is accumulating evidence that Mas is involved in vascular homeostasis. We have recently backcrossed Mas-knockout mice to two different genetic backgrounds, C57Bl/6 and FVB/N. FVB/NMas-deficient mice exhibited elevation in blood pressure (BP) and impaired endothelial function. In the present study, we aimed to address the question whether this phenotype is strain-specific. Therefore, we evaluated endothelial function in C57Bl/6Mas-deficient mice. Similar to FVB/NMas-knockout animals, Mas-deficiency in C57Bl/6 mice leads to endothelial dysfunction evaluated by the acute BP effect of acetylcholine administration. Measurements of nitric oxide (NO) and reactive oxygen species (ROS) and the systems involved in their metabolism revealed an imbalance between these vasoactive factors in C57Bl/6Mas-knockout mice, which may explain the impairment of endothelial function in these animals. However, endothelial dysfunction was less prominent in Mas-deficient mice on a C57Bl/6 background compared to FVB/N. Moreover, C57Bl/6Mas-deficient mice remained normotensive while FVB/N-based animals exhibited elevated BP. The impairment of endothelium-dependent vasodilatory response to acetylcholine in two different mouse strains with Mas deficiency indicates a key role of Mas in endothelial function by its effects on the generation and metabolism of NO and ROS.