Overexpression of myofibrillogenesis regulator-1 aggravates cardiac hypertrophy induced by angiotensin II in mice

Myofibrillogenesis regulator-1 (MR-1) augments cardiomyocytes hypertrophy induced by angiotensin II (Ang II) in vitro. However, its roles in cardiac hypertrophy in vivo remain unknown. Here, we investigate whether MR-1 can promote cardiac hypertrophy induced by Ang II in vivo and elucidate the molecular mechanisms of MR-1 on cardiac hypertrophy. We used a model of Ang II-induced cardiac hypertrophy by infusion of Ang II in female mice. In wild-type mice subjected to the Ang II infusion, cardiac hypertrophy developed after 2 weeks. In mice overexpressing human MR-1 (transgenic), however, cardiac hypertrophy was significantly greater than in wild-type mice as estimated by heart weight:body weight ratio, cardiomyocyte area, and echocardiographic measurements, as well as cardiac atrial natriuretic peptide and B-type natriuretic peptide mRNA and protein levels. Our further results showed that cardiac inflammation and fibrosis observed in wild-type Ang II mice were augmented in transgenic Ang II mice. Importantly, increased nuclear factor kappaB activation was significantly increased higher in transgenic mice compared with wild-type mice after 2 weeks of Ang II infusion. In vitro experiments also revealed that overexpression of MR-1 enhanced Ang II-induced nuclear factor kappaB activation, whereas downregulation of MR-1 blocked it in cardiac myocytes. In conclusion, our results suggest that MR-1 plays an aggravative role in the development of cardiac hypertrophy via activation of the nuclear factor kappaB signaling pathway.     

Essential role of vascular endothelial growth factor in angiotensin II-induced vascular inflammation and remodeling

Angiotensin II (Ang II) upregulates vascular endothelial growth factor (VEGF) and activates vascular inflammation. However, the decisive role of VEGF in Ang II-induced vascular inflammation and remodeling has not been addressed. Ang II infusion to wild-type mice increased local expression of VEGF and its receptors in cells of aortic wall and plasma VEGF, and caused aortic inflammation (monocyte infiltration) and remodeling (wall thickening and fibrosis). Hypoxia-inducible factor-1alpha colocalized with VEGF-positive cell types. Blockade of VEGF by the soluble VEGF receptor 1 (sFlt-1) gene transfer attenuated the Ang II-induced inflammation and remodeling. The sFlt-1 gene transfer also inhibited the increased expression of VEGF and inflammatory factors such as monocyte chemoattractant protein-1. In contrast, sFlt-1 gene transfer did not affect Ang II-induced arterial hypertension and cardiac hypertrophy. VEGF is an essential mediator in Ang II-induced vascular inflammation and structural changes through its proinflammatory actions.     

Apoptosis signal-regulating kinase 1 plays a pivotal role in angiotensin II-induced cardiac hypertrophy and remodeling

Multiple lines of evidence establish that angiotensin II (Ang II) induces not only hypertension but also directly contributes to cardiac diseases. Apoptosis signal-regulating kinase 1 (ASK1), one of mitogen-activated protein kinase kinase kinases, plays a key role in stress-induced cellular responses. However, nothing is known about the role of ASK1 in cardiac hypertrophy and remodeling in vivo. In this study, by using mice deficient in ASK1 (ASK1-/- mice), we investigated the role of ASK1 in cardiac hypertrophy and remodeling induced by Ang II. Left ventricular (LV) ASK1 was activated by Ang II infusion in wild-type mice, which was mediated by angiotensin II type 1 receptor and superoxide. Although Ang II-induced hypertensive effect was comparable to wild-type and ASK1-/- mice, LV ASK1 activation by Ang II was not detectable in ASK1-/- mice, and p38 and c-Jun N-terminal kinase (JNK) activation was lesser in ASK-/- mice than in wild-type mice. Elevation of blood pressure by continuous Ang II infusion was comparable between ASK1-/- and wild-type mice. However, Ang II-induced cardiac hypertrophy and remodeling, including cardiomyocyte hypertrophy, cardiac hypertrophy-related mRNA upregulation, cardiomyocyte apoptosis, interstitial fibrosis, coronary arterial remodeling, and collagen gene upregulation, was significantly attenuated in ASK1-/- mice compared with wild-type mice. These results provided the first in vivo evidence that ASK1 is the critical signaling molecule for Ang II-induced cardiac hypertrophy and remodeling. Thus, ASK1 is proposed to be a potential therapeutic target for cardiac diseases.     

A critical role of cardiac fibroblast-derived exosomes in activating renin angiotensin system in cardiomyocytes

Chronic activation of the myocardial renin angiotensin system (RAS) elevates the local level of angiotensin II (Ang II) thereby inducing pathological cardiac hypertrophy, which contributes to heart failure. However, the precise underlying mechanisms have not been fully delineated. Herein we report a novel paracrine mechanism between cardiac fibroblasts (CF)s and cardiomyocytes whereby Ang II induces pathological cardiac hypertrophy. In cultured CFs, Ang II treatment enhanced exosome release via the activation of Ang II receptor types 1 (AT₁R) and 2 (AT₂R), whereas lipopolysaccharide, insulin, endothelin (ET)-1, transforming growth factor beta (TGFβ)1 or hydrogen peroxide did not. The CF-derived exosomes upregulated the expression of renin, angiotensinogen, AT₁R, and AT₂R, downregulated angiotensin-converting enzyme 2, and enhanced Ang II production in cultured cardiomyocytes. In addition, the CF exosome-induced cardiomyocyte hypertrophy was blocked by both AT₁R and AT₂R antagonists. Exosome inhibitors, GW4869 and dimethyl amiloride (DMA), inhibited CF-induced cardiomyocyte hypertrophy with little effect on Ang II-induced cardiomyocyte hypertrophy. Mechanistically, CF exosomes upregulated RAS in cardiomyocytes via the activation of mitogen-activated protein kinases (MAPKs) and Akt. Finally, Ang II-induced exosome release from cardiac fibroblasts and pathological cardiac hypertrophy were dramatically inhibited by GW4869 and DMA in mice. These findings demonstrate that Ang II stimulates CFs to release exosomes, which in turn increase Ang II production and its receptor expression in cardiomyocytes, thereby intensifying Ang II-induced pathological cardiac hypertrophy. Accordingly, specific targeting of Ang II-induced exosome release from CFs may serve as a novel therapeutic approach to treat cardiac pathological hypertrophy and heart failure.     

Involvement of reactive oxygen species in angiotensin II-induced endothelin-1 gene expression in rat cardiac fibroblasts

OBJECTIVES: The aim of this study was to investigate the effects of angiotensin II (Ang II) on fibroblast proliferation and endothelin-1 (ET-1) gene induction, focusing especially on reactive oxygen species (ROS)-mediated signaling in cardiac fibroblasts. BACKGROUND: Angiotensin II increases ET-1 expression, which plays an important role in Ang II-induced fibroblast proliferation. Angiotensin II also stimulates ROS generation in cardiac fibroblasts. However, whether ROS are involved in Ang II-induced proliferation and ET-1 expression remains unknown. METHODS: Cultured neonatal rat cardiac fibroblasts were stimulated with Ang II, and then [(3)H]thymidine incorporation and the ET-1 gene expression were examined. We also examined the effects of antioxidants on Ang II-induced proliferation and mitogen-activated protein kinase (MAPK) phosphorylation to elucidate the redox-sensitive pathway in fibroblast proliferation and ET-1 gene expression. RESULTS: Both AT(1) receptor antagonist (losartan) and ET(A) receptor antagonist (BQ485) inhibited Ang II-increased DNA synthesis. Endothelin-1 gene was induced with Ang II as revealed by Northern blotting and promoter activity assay. Angiotensin II increased intracellular ROS levels, which were inhibited with losartan and antioxidants. Antioxidants further suppressed Ang II-induced ET-1 gene expression, DNA synthesis, and MAPK phosphorylation. PD98059, but not SB203580, fully inhibited Ang II-induced ET-1 expression. Truncation and mutational analysis of the ET-1 gene promoter showed that AP-1 binding site was an important cis-element in Ang II-induced ET-1 gene expression. CONCLUSIONS: Our data suggest that ROS are involved in Ang II-induced proliferation and ET-1 gene expression. Our findings imply that the combination of AT(I) and ET(A) receptor antagonists plus antioxidants may be beneficial in preventing the formation of excessive cardiac fibrosis.     

Role of osteopontin in cardiac fibrosis and remodeling in angiotensin II-induced cardiac hypertrophy

Osteopontin (OPN) is upregulated in several experimental models of cardiac fibrosis and remodeling. However, its direct effects remain unclear. We examined the hypothesis that OPN is important for the development of cardiac fibrosis and remodeling. Moreover, we examined whether the inhibitory effect of eplerenone (Ep), a novel aldosterone receptor antagonist, was mediated through the inhibition of OPN expression against cardiac fibrosis and remodeling. Wild-type (WT) and OPN-deficient mice were treated with angiotensin II (Ang II) for 4 weeks. WT mice receiving Ang II were divided into 2 groups: a control group and an Ep treatment group. Ang II treatment significantly elevated blood pressure and caused cardiac hypertrophy and fibrosis in WT mice. Ep treatment and OPN deficiency could reduce the Ang II-induced elevation of blood pressure and ameliorate the development of cardiac fibrosis, whereas Ep-only treatment abolished the development of cardiac hypertrophy. Most compelling, the reduction of cardiac fibrosis led to an impairment of cardiac systolic function and subsequent left ventricular dilatation in Ang II-treated OPN-deficient mice. These results suggest that OPN has a pivotal role in the development of Ang II-induced cardiac fibrosis and remodeling. Moreover, the effect of Ep on the prevention of cardiac fibrosis, but not cardiac hypertrophy, might be partially mediated through the inhibition of OPN expression.     

Pitavastatin, an HMG-CoA reductase inhibitor, exerts eNOS-independent protective actions against angiotensin II induced cardiovascular remodeling and renal insufficiency

Angiotensin II (Ang II) plays a pivotal role in cardiovascular remodeling leading to hypertension, myocardial infarction, and stroke. Pitavastatin, an HMG-CoA reductase inihibitor, is known to have pleiotropic actions against the development of cardiovascular remodeling. The objectives of this study were to clarify the beneficial effects as well as the mechanism of action of pitavastatin against Ang II-induced organ damage. C57BL6/J mice at 10 weeks of age were infused with Ang II for 2 weeks and were simultaneously administered pitavastatin or a vehicle. Pitavastatin treatment improved Ang II-induced left ventricular hypertrophy and diastolic dysfunction and attenuated enhancement of cardiac fibrosis, cardiomyocyte hypertrophy, coronary perivascular fibrosis, and medial thickening. Ang II-induced oxidative stress, cardiac TGFbeta-1 expression, and Smad 2/3 phosphorylation were all attenuated by pitavastatin treatment. Pitavastatin also reduced Ang II-induced cardiac remodeling and diastolic dysfunction in eNOS-/- mice as in wild-type mice. In eNOS-/- mice, the Ang II-induced cardiac oxidative stress and TGF-beta-Smad 2/3 signaling pathway were enhanced, and pitavastatin treatment attenuated the enhanced oxidative stress and the signaling pathway. Moreover, pitavastatin treatment reduced the high mortality rate and improved renal insufficiency in Ang II-treated eNOS-/- mice, with suppression of glomerular oxidative stress and TGF-beta-Smad 2/3 signaling pathway. In conclusion, pitavastatin exerts eNOS-independent protective actions against Ang II-induced cardiovascular remodeling and renal insufficiency through inhibition of the TGF-beta-Smad 2/3 signaling pathway by suppression of oxidative stress.     

Cardiac angiotensin II type 2 receptor activates the kinin/NO system and inhibits fibrosis

We have previously demonstrated that stimulation of the angiotensin (Ang) II type 2 receptor in vascular smooth muscle cells caused bradykinin production by activating kininogenase in transgenic mice. The aim of this study was to determine whether overexpression of AT2 receptors in cardiomyocytes attenuates Ang II-induced cardiomyocyte hypertrophy or interstitial fibrosis through a kinin/nitric oxide (NO)-dependent mechanism in mice. Ang II (1.4 mg/kg per day) or vehicle was subcutaneously infused into transgenic mice and wild-type mice for 14 days. The amount of cardiac AT2 receptor relative to AT1 receptor in transgenic mice was 22% to 37%. Ang II caused similar elevations in systolic blood pressure (by approximately 45 mm Hg) in transgenic mice and wild-type mice. Myocyte hypertrophy assessed by an increase in myocyte cross-sectional area, left ventricular mass, and atrial natriuretic peptide mRNA levels were similar in transgenic and wild-type mice. Ang II induced prominent perivascular fibrosis of the intramuscular coronary arteries, the extent of which was significantly less in transgenic mice than in wild-type mice. Inhibition of perivascular fibrosis in transgenic mice was abolished by cotreatment with HOE140, a bradykinin B2 receptor antagonist, or L-NAME, an inhibitor of NO synthase. Cardiac kininogenase activity was markedly increased (approximately 2.6-fold, P<0.001) after Ang II infusion in transgenic mice but not in wild-type mice. Immunohistochemistry indicated that both bradykinin B2 receptors and endothelial NO synthase were expressed in the vascular endothelium, whereas only B2 receptors were present in fibroblasts. These results suggest that stimulation of AT2 receptors present in cardiomyocytes attenuates perivascular fibrosis by a kinin/NO-dependent mechanism. However, the effect on the development of cardiomyocyte hypertrophy was not detected in this experimental setting.     

Angiotensin II-induced ventricular hypertrophy and extracellular signal-regulated kinase activation are suppressed in mice overexpressing brain natriuretic peptide in circulation.

Atrial and brain (B-type) natriuretic peptides (ANP and BNP, respectively) are known to exert various cardioprotective effects. For instance, knocking out the expression of ANP, BNP, or their receptor, guanylyl cyclase-A, induces cardiac hypertrophy and/or fibrosis. The cardiac effects of elevated circulating natriuretic peptides are less well understood, however. We therefore compared angiotensin (Ang) II-induced cardiac hypertrophy and fibrosis in BNP-transgenic (Tg) mice, in which circulating BNP levels were elevated by increased secretion from the liver, and their non-Tg littermates. Left ventricular expression of Ang II type 1a receptor was similar in BNP-Tg and non-Tg mice, and there was no significant difference in the elevation of blood pressure elicited by chronic infusion or acute injection of Ang II. Nevertheless, cardiac hypertrophy and fibrosis were significantly diminished in BNP-Tg mice chronically infused with Ang II. In addition, ventricular activation of extracellular signal-regulated kinase (ERK) induced by acute injection of Ang II was also diminished in BNP-Tg mice, as was activation of ERK kinase (MEK). Conversely, expression of mitogen-activated protein kinase phosphatase (MKP) was significantly increased in the ventricles of BNP-Tg mice. Based on these findings, we conclude that elevated circulating BNP exerts cardioprotective effects via inhibition of a ventricular ERK pathway. The mechanism responsible for this inhibition likely involves 1) increased ventricular MKP expression and 2) inhibition of transduction mediators situated upstream of ERK.     

Activation of the cardiac proteasome promotes angiotension II-induced hypertrophy by down-regulation of ATRAP

Proteasomal degradation is critical to maintaining cardiac function and is altered in various diseases. Angiotensin II (Ang II) acts as a growth factor to induce cardiac growth. Here we aimed to test whether proteasome is involved in the development of Ang II-induced cardiac hypertrophy and dissect its molecular mechanisms. Cardiac hypertrophy was induced by Ang II infusion (1000 ng/kg/min) using mini-osmotic pumps. Starting 1 day before implantation, the mice were injected with the proteasome inhibitor bortezomib (BTZ, 50 μg/kg, 3 times per week) or with vehicle. After 14 days, the pool of ubiquitinated proteins was reduced but the protein expression of proteasome subunits (including β1i, β2i and β5/β5i) was markedly up-regulated in left ventricular hypertrophy versus control, which was accompanied by a significant increase in proteasome activities. Furthermore, Ang II-treated mice showed a significant increase in blood pressure but decrease in cardiac contractile function, and significant left ventricular hypertrophy, fibrosis and inflammation, which were all attenuated in BTZ-treated mice. Mechanistically, these beneficial effects were associated with the inhibition of degradation of angiotensin II type 1 receptor-associated protein (ATRAP) and inactivation of AT1R-mediated p38 MAPK and STAT3 signaling pathways. In conclusion, our data indicate that the activation of proteasome is required for the Ang II-induced cardiac hypertrophy, and suggest that the inhibition of proteasome activity by BTZ could be a potential therapeutic strategy for the treatment of cardiac hypertrophy and other heart diseases.     

Soluble epoxide hydrolase plays an essential role in angiotensin II-induced cardiac hypertrophy

Pathophysiological cardiac hypertrophy is one of the most common causes of heart failure. Epoxyeicosatrienoic acids, hydrolyzed and degraded by soluble epoxide hydrolase (sEH), can function as endothelium-derived hyperpolarizing factors to induce dilation of coronary arteries and thus are cardioprotective. In this study, we investigated the role of sEH in two rodent models of angiotensin II (Ang II)-induced cardiac hypertrophy. The protein level of sEH was elevated in the heart of both spontaneously hypertensive rats and Ang II-infused Wistar rats. Blocking the Ang II type 1 receptor with losartan could abolish this induction. Administration of a potent sEH inhibitor (sEHI) prevented the pathogenesis of the Ang II-induced hypertrophy, as demonstrated by decreased left-ventricular hypertrophy assessed by echocardiography, reduced cardiomyocyte size, and attenuated expression of hypertrophy markers, including atrial natriuretic factor and β-myosin heavy chain. Because sEH elevation was not observed in exercise- or norepinephrine-induced hypertrophy, the sEH induction was closely associated with Ang II-induced hypertrophy. In vitro, Ang II upregulated sEH and hypertrophy markers in neonatal cardiomyocytes isolated from rat and mouse. Expression of these marker genes was elevated with adenovirus-mediated sEH overexpression but decreased with sEHI treatment. These results were supported by studies in neonatal cardiomyocytes from sEH^−/− mice. Our results suggest that sEH is specifically upregulated by Ang II, which directly mediates Ang II-induced cardiac hypertrophy. Thus, pharmacological inhibition of sEH would be a useful approach to prevent and treat Ang II-induced cardiac hypertrophy.     

Angiotensin II induces endothelin-1 gene expression via extracellular signal-regulated kinase pathway in rat aortic smooth muscle cells

OBJECTIVE: Angiotensin II (Ang II) increases vascular endothelin-1 (ET-1) tissue levels, which in turn mediate a major part of Ang II-stimulated vascular growth and hypertension in vivo. Ang II also stimulates reactive oxygen species (ROS) generation in vascular smooth muscle cells (SMCs). However, whether ROS are involved in Ang II-induced ET-1 gene expression and the related intracellular mechanisms in vascular SMCs remains to be determined. METHODS: Cultured rat aortic SMCs were stimulated with Ang II, [3H]thymidine incorporation and the ET-1 gene expression was examined. Antioxidants pretreatment on Ang II-induced extracellular signal-regulated kinase (ERK) phosphorylation were performed to elucidate the redox-sensitive pathway in proliferation and ET-1 gene expression. RESULTS: Ang II-increased DNA synthesis was inhibited by AT(1) receptor antagonist (olmesartan) and ET(A) receptor antagonist (BQ485). ET-1 gene was induced with Ang II as revealed by Northern blotting and promoter activity assay. Ang II-increased intracellular ROS levels were inhibited by olmesartan and antioxidants. Antioxidants suppressed Ang II-induced ET-1 gene expression and ERK phosphorylation. An ERK inhibitor U0126 fully inhibited Ang II-induced ET-1 expression. Co-transfection of dominant negative mutant of Ras, Raf and MEK1 attenuated the Ang II-increased ET-1 promoter activity, suggesting that the Ras-Raf-ERK pathway is required for Ang II-induced ET-1 gene. Truncation and mutational analysis of the ET-1 gene promoter showed that activator protein-1 (AP-1) binding site was an important cis-element in Ang II-induced ET-1 gene expression. Moreover, Ang II- or H(2)O(2)-induced AP-1 reporter activities were also inhibited by antioxidants. CONCLUSIONS: Our data suggest that ROS are involved in Ang II-induced proliferation and the redox-sensitive ERK pathway plays a role in ET-1 gene expression in rat aortic SMCs.     

Targeting the calpain/calpastatin system as a new strategy to prevent cardiovascular remodeling in angiotensin II-induced hypertension

In hypertension, angiotensin (Ang) II is a critical mediator of cardiovascular remodeling, whose prominent features include myocardial and vascular media hypertrophy, perivascular inflammation, and fibrosis. The signaling pathways responsible for these alterations are not completely understood. Here, we investigated the importance of calpains, calcium-dependent cysteine proteases. We generated transgenic mice constitutively expressing high levels of calpastatin, a calpain-specific inhibitor. Chronic infusion of Ang II led to similar increases in systolic blood pressure in wild-type and transgenic mice. In contrast, compared with wild-type mice, transgenic mice displayed a marked blunting of Ang II-induced hypertrophy of left ventricle. Ang II-dependent vascular remodeling, ie, media hypertrophy and perivascular inflammation and fibrosis, was also limited in both large arteries (aorta) and small kidney arteries from transgenic mice as compared with wild type. In vitro experiments using vascular smooth muscle cells showed that calpastatin transgene expression blunted calpain activation by Ang II through epidermal growth factor receptor transactivation. In vivo and in vitro models of inflammation showed that impaired recruitment of mononuclear cells in transgenic mice was attributable to a decrease in both the release of and the chemotactic response to monocyte chemoattractant protein-1. Finally, results from collagen synthesis assay and zymography suggested that limited fibrogenesis was attributable to a decrease in collagen deposition rather than an increase in collagen degradation. These results indicate a critical role for calpains as downstream mediators in Ang II-induced cardiovascular remodeling and, thus, highlight an attractive therapeutic target.     

Interleukin-10 inhibits chronic angiotensin II-induced pathological autophagy

BackgroundAlthough autophagy is an essential cellular salvage process to maintain cellular homeostasis, pathological autophagy can lead to cardiac abnormalities and ultimately heart failure. Therefore, a tight regulation of autophagic process would be important to treat chronic heart failure. Previously, we have shown that IL-10 strongly inhibited pressure overload-induced hypertrophy and heart failure, but role of IL-10 in regulation of pathological autophagy is unknown. Here we tested the hypothesis that IL-10 inhibits angiotensin II-induced pathological autophagy and this process, in part, leads to improve cardiac function.Methods and resultsChronic Ang II strongly induced mortality, cardiac dysfunction in IL-10 Knockout mice. IL-10 deletion exaggerated pathological autophagy in response to Ang II treatment. In isolated cardiac myocytes, IL-10 attenuated Ang II-induced pathological autophagy and activated Akt/mTORC1 signaling. Pharmacological or molecular inhibition of Akt and mTORC1 signaling attenuated IL-10 effects on Ang II-induced pathological autophagy. Furthermore, lysosomal inhibition in autophagic flux experiments further confirmed that IL-10 inhibits pathological autophagy via mTORC1 signaling.ConclusionOur data demonstrate a novel role of IL-10 in regulation of pathological autophagy; thus can act as a potential therapeutic molecule for treatment of chronic heart disease.     

G1 cyclins are involved in the mechanism of cardiac myocyte hypertrophy induced by angiotensin II

The importance of the cell cycle in proliferating cells is well known, but little is known about the role of cell cycle regulatory proteins in cardiac myocytes, which are fully differentiated cells. The present study determined, in vitro, the effect of angiotensin II (Ang II) treatment of neonatal rat cardiac myocytes on protein levels of cyclins and retinoblastoma gene product (pRb) phosphorylation. The role of G1 cyclin/cdk in Ang II-induced cardiac myocyte hypertrophy by overexpressing cdk inhibitor p21Cip1/Waf1 or p16INK4a was also examined using recombinant adenoviral vectors encoding these genes. Western blot analysis revealed that Ang II stimulated cyclin D1, D2, D3 and A protein levels in cardiac myocytes. Moreover, Ang II phosphorylated pRb on serine 780, which is known to occur in mitotic cells during cell cycle progression. Cultured cardiac myocytes treated with Ang II and infected with either control or recombinant adenovirus indicated that expression of p21 and p16 inhibited Ang II-induced cardiac myocyte hypertrophy, [3H]leucine incorporation into total cellular proteins, and skeletal alpha-actin (SK-A) and atrial natriuretic peptide (ANP) mRNA accumulation. Control virus had no effects on these parameters. These results suggest that G1 cyclins play an important role in cardiac myocyte hypertrophy stimulated by Ang II.     

Effects of TCV-116 on endothelin-1 and PDGF A-chain expression in angiotensin II-induced hypertensive rats.

Angiotensin II (Ang II) has been shown to stimulate cardiac growth and collagen synthesis in cultured vascular smooth muscle cells and to increase fibroblast proliferation. Chronic infusion with Ang II increases blood pressure and activates growth mechanisms to produce hypertrophy of the heart. This study investigated the effects of an Ang II type 1 receptor antagonist, TCV-116, on preproendothelin-1 (preproET-1), ETA receptor and platelet-derived growth factor (PDGF) A-chain expression in the left ventricle of Wistar-Kyoto rats treated for 2 weeks with Ang II (200 ng x kg(-1) x min(-1)), and the relation of these effects to myocardial remodeling. Rats given Ang II alone (ANGII-V) were compared with rats also receiving TCV-116 (ANGII-TCV). In both groups, blood pressure was similar and significantly higher than in control rats. The preproET-1, ET(A) receptor and PDGF A-chain expressions in the left ventricle were significantly increased in ANGII-V compared with control rats, and were significantly suppressed in ANGII-TCV compared with ANGII-V rats. ANGII-V rats showed a significant increase of the type I collagen expression, wall-to-lumen ratio, perivascular fibrosis, and myocardial fibrosis, with all these parameters being significantly improved by TCV-116. Myocardial remodeling in Ang II-induced hypertensive rats was significantly ameliorated by a subdepressor dose of TCV-116, which may have been due to a decrease in ET-1 and PDGF A-chain expression in the left ventricle.     

Angiotensin II induces vascular dysfunction without exacerbating blood pressure elevation in a mouse model of menopause-associated hypertension

BACKGROUND: Follitropin-receptor knockout (FORKO) mice are estrogen-deficient, hyperandrogenic and exhibit features of menopause and elevated blood pressure (BP). Because the renin-angiotensin system has been implicated in menopause-associated hypertension, we questioned whether angiotensin II (Ang II) challenge would further increase BP in FORKO mice and whether this is associated with cardiovascular remodeling and inflammation. RESULTS: Ang II (400 ng/kg per min) increased BP, assessed by radiotelemetry, similarly in female FORKO and wild-type (WT) mice. Acetylcholine-induced vasodilation was attenuated and Ang II-induced contraction was enhanced in FORKO mice (P < 0.05). This was associated with increased expression of vascular Ang type 1 receptors (AT1R) and estrogen receptor alpha (ERalpha). Vascular structure (media/lumen ratio) was similar in both groups. Abundance of gp91, nitrotyrosine formation and superoxide production, indices of inflammation and cardiac collagen content were increased in Ang II-treated FORKO compared to Ang II-treated WT mice (P < 0.05). CONCLUSIONS: Thus, in FORKO mice Ang II exacerbates endothelial dysfunction, augments contractility, increases oxidative stress, and promotes cardiac fibrosis without worsening vascular remodeling or BP elevation compared to Ang II-treated WT controls. Our findings suggest that in FORKO mice Ang II may be more important in influencing vascular tone and endothelial function, possibly through oxidative stress and altered ERalpha signaling, than in arterial remodeling and BP elevation.     

Activation of AMP-activated protein kinase enhances angiotensin ii-induced proliferation in cardiac fibroblasts

AMP-activated kinase (AMPK) is a highly conserved heterotrimeric kinase that functions as a metabolic regulator of cellular enzymes involved in carbohydrate and fat metabolism, which regulate ATP conservation and synthesis. Here, we investigated whether AMPK signaling has a role in the regulation of angiotensin II (Ang II)-induced proliferation in rat cardiac fibroblasts. Aminoimidazole-4-carboxamide-1-beta-ribofuranoside (AICAR) activated AMPK in rat cardiac fibroblasts and increased Ang II-induced extracellular signal-regulated kinase 1/2 phosphorylation and activity. AICAR also increased Ang II-induced c-fos mRNA expression in the cells. [3H]-thymidine and [3H]-proline incorporation by cardiac fibroblasts treated with Ang II was enhanced when the cells were pretreated with AICAR. Inhibition of AMPK by small interfering RNA for AMPKalpha1 suppressed Ang II-induced extracellular signal-regulated kinase activity, c-fos mRNA expression, and cell proliferation. Treatment of rats with AICAR (1 mg/g body weight per day) for 1 week significantly enhanced Ang II-induced hypertrophy of the myocardium. Our findings indicate that AMPK works as a stimulator of the Ang II-induced proliferative pathway in cardiac fibroblasts. Inhibition of AMPK signaling might serve as a new therapeutic target of remodeling of the hypertrophic myocardium.