Important role of angiotensin II-mediated c-Jun NH(2)-terminal kinase activation in cardiac hypertrophy in hypertensive rats

Parkia speciosa Hassk. Empty Pod Extract Alleviates Angiotensin II-Induced Cardiomyocyte Hypertrophy in H9c2 Cells by Modulating the Ang II/ROS/NO Axis and MAPK Pathway

Cardiac hypertrophy is characteristic of heart failure in patients who have experienced cardiac remodeling. Many medicinal plants, including Parkia speciosa Hassk., have documented cardioprotective effects against such pathologies. This study investigated the activity of P. speciosa empty pod extract against cardiomyocyte hypertrophy in H9c2 cardiomyocytes exposed to angiotensin II (Ang II). In particular, its role in modulating the Ang II/reactive oxygen species/nitric oxide (Ang II/ROS/NO) axis and mitogen-activated protein kinase (MAPK) pathway was examined. Treatment with the extract (12.5, 25, and 50 μg/ml) prevented Ang II-induced increases in cell size, NADPH oxidase activity, B-type natriuretic peptide levels, and reactive oxygen species and reductions in superoxide dismutase activity. These were comparable to the effects of the valsartan positive control. However, the extract did not significantly ameliorate the effects of Ang II on inducible nitric oxide synthase activity and nitric oxide levels, while valsartan did confer such protection. Although the extract decreased the levels of phosphorylated extracellular signal-related kinase, p38, and c-Jun N-terminal kinase, valsartan only decreased phosphorylated c-Jun N-terminal kinase expression. Phytochemical screening identified the flavonoids rutin (1) and quercetin (2) in the extract. These findings suggest that P. speciosa empty pod extract protects against Ang II-induced cardiomyocyte hypertrophy, possibly by modulating the Ang II/ROS/NO axis and MAPK signaling pathway via a mechanism distinct from valsartan.

Antihypertensive activity of a new c-Jun N-terminal kinase inhibitor in spontaneously hypertensive rats

c-Jun N-terminal kinases (JNKs) are involved in the myocardial and aortic remodeling, increased arterial tone, and arterial blood pressure elevation associated with hypertension. The aim of the present study was to investigate the antihypertensive effect of a new JNK inhibitor, 1H-indeno[1,2-b]quinoxalin-11-one oxime sodium salt (IQ-1S), on spontaneously hypertensive rats (SHRs). Experiments were performed using normotensive Wistar-Kyoto (WKY) rats and SHRs. Experimental groups of SHRs received IQ-1S intragastrically for 6 weeks in daily doses of 5 and 50 mg/kg; experimental groups of WKY rats received 50 mg/kg IQ-1S according to the same regimen. The IQ-1S administration regimen induced decreases in systolic blood pressure, mean arterial blood pressure, total peripheral resistance, blood viscosity, hematocrit, myocardial cell cross-sectional area, and aortic wall thickness in SHRs vs untreated SHRs. There were no significant differences in systolic blood pressure values between the control and experimental groups of WKY rats during the treatment period. A concentration-dependent decrease in the tone of carotid arterial rings isolated from SHRs was observed after JNK inhibitor application in vitro. Application of the JNK inhibitor diminished endothelin-1 secretion by human umbilical vein endothelial cells in vitro. The main mechanisms of the antihypertensive effect of IQ-1S included the attenuation of blood viscosity due to decreased hematocrit, a vasodilatory effect on arterial smooth muscle cells, and a decrease in endothelin-1 production by endothelial cells.

Candesartan abrogates G protein-coupled receptors agonist-induced MAPK activation and cardiac myocyte hypertrophy

The renin-angiotensin-aldosterone system (RAAS) has been identified as a major contributor to the development of cardiac hypertrophy and the subsequent transition to heart failure. G protein-coupled receptors agonists such as angiotensin II (Ang II), endothelin-1 (ET-1) and phenylephrine (PE) have been implicated in hypertrophic responses in ventricular myocytes through the activation of several families of MAP kinases. In this study we examined the effect of candesartan, an Ang II type 1-(AT1)-receptor antagonist, on cardiac hypertrophy by using cultured neonatal rat cardiomyocytes. Stimulation with Ang II (100 nM), ET-1 (100 nM) or PE (1 µM) induced marked increases in [3H]Leucine incorporation (≥ 50%), compatible with enhanced protein synthesis. The addition of candesartan abrogated the increase in [3H]Leucine incorporation in response not only to Ang II but also to ET-1 and PE. To elucidate the mechanisms involved in this antihypertrophic effect of candesartan, we studied the activation of p38-MAPK, extracellular signal-regulated kinases (ERK1/2) and stress-activated protein kinases (SAPKs). Ang II, ET-1 and PE increased the phosphorylation levels of ERK1/2, p54 SAPK and p46SAPK and p38 in a time-dependent manner. This activation was completely blocked in the case of Ang II by pretreatment with candesartan. ET-1-induced activation of ERKs, SAPKs and p38 was also partially, but significantly, reduced by candesartan. PE-induced activation of SAPKs, but not ERKs and p38, was also reduced by candesartan. These results suggest that the hypertrophic response to ET-1 and PE, along with Ang II, is dependent upon a functioning AT1-receptor and may be mediated by AT 1 activation of the MAP kinases.

miR-155 functions downstream of angiotensin II receptor subtype 1 and calcineurin to regulate cardiac hypertrophy

Cardiac hypertrophy is characterized by maladaptive tissue remodeling that may lead to heart failure or sudden death. MicroRNAs (miRs) are negative regulators of angiotensin II and the angiotensin II receptor subtype 1 (AGTR₁), which are two components involved in cardiac hypertrophy. In the present study, the interaction between angiotensin II receptor subtype 1 (AGTR₁) signaling and miR-155 was investigated. Rat H9C2 (2-1) cardiomyocytes were transfected with miR-155 analogues or inhibitors, then stimulated with angiotensin II to induce cardiac hypertrophy. miR-155 expression was revealed to be altered following transfection with chemically-modified miR-155 analogues and inhibitors in rat cardiomyocytes. In cell cardiac hypertrophy models, the cell surface area, AGTR₁, atrial natriuretic peptide and myosin heavy chain-β mRNA expression levels were revealed to be lower in cells stimulated with miR-155 analogue-transfected cells treated with angiotensin II compared with cells stimulated with angiotensin alone (P<0.05), as determined using reverse transcription-polymerase chain reaction (PCR), quantitative PCR and western blot analyses. Furthermore, calcineurin mRNA and protein, intracellular free calcium and nuclear factor of activated T-cells-4 proteins were downregulated in miR-155 analogue-transfected cells treated with angiotensin II, as compared with cells stimulated with angiotensin II alone (P<0.05). In conclusion, the current study indicates that miR-155 may improve cardiac hypertrophy by downregulating AGTR₁ and suppressing the calcium signaling pathways activated by AGTR₁.

Regulation of Nox enzymes expression in vascular pathophysiology: Focusing on transcription factors and epigenetic mechanisms

NADPH oxidases (Nox) represent a family of hetero-oligomeric enzymes whose exclusive biological function is the generation of reactive oxygen species (ROS). Nox-derived ROS are essential modulators of signal transduction pathways that control key physiological activities such as cell growth, proliferation, migration, differentiation, and apoptosis, immune responses, and biochemical pathways. Enhanced formation of Nox-derived ROS, which is generally associated with the up-regulation of different Nox subtypes, has been established in various pathologies, namely cardiovascular diseases, diabetes, obesity, cancer, and neurodegeneration. The detrimental effects of Nox-derived ROS are related to alterations in cell signalling and/or direct irreversible oxidative damage of nucleic acids, proteins, carbohydrates, and lipids. Thus, understanding of transcriptional regulation mechanisms of Nox enzymes have been extensively investigated in an attempt to find ways to counteract the excessive formation of Nox-derived ROS in various pathological states. Despite the numerous existing data, the molecular pathways responsible for Nox up-regulation are not completely understood. This review article summarizes some of the recent advances and concepts related to the regulation of Nox expression in the vascular pathophysiology. It highlights the role of transcription factors and epigenetic mechanisms in this process. Identification of the signalling molecules involved in Nox up-regulation, which is associated with the onset and development of cardiovascular dysfunction may contribute to the development of novel strategies for the treatment of cardiovascular diseases.

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Nox is a unique class of enzymes whose sole function is the generation of ROS.

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Nox-derived ROS play a major role in cell physiology.

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Enhanced expression and activation of Nox has been reported in numerous pathologies.

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Nox expression is regulated via complex transcription factor-epigenetic mechanisms.

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Understanding of Nox regulation is essential to counteract ROS-induced cell damage.

Quercetin inhibits left ventricular hypertrophy in spontaneously hypertensive rats and inhibits angiotensin II-induced H9C2 cells hypertrophy by enhancing PPAR-γ expression and suppressing AP-1 activity

BACKGROUND

Quercetin is the most abundant flavonoid in fruit and vegetables and is believed to attenuate cardiovascular disease. We hypothesized that quercetin inhibits cardiac hypertrophy by blocking AP-1 (c-fos, c-jun) and activating PPAR-γ signaling pathways.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of this study was to identify the mechanism underlying quercetin-mediated attenuation of cardiac hypertrophy. Quercetin therapy reduced blood pressure and markedly reduced the ratio of left ventricular to body weight (LVW/BW) (P<0.05, vs. spontaneously hypertensive rats (SHRs)). In vitro, quercetin also significantly attenuated Ang II-induced H9C2 cells hypertrophy, as indicated by its concentration dependent inhibitory effects on [³H]leucine incorporation into H9C2 cells (64% reduction) and by the reduced hypertrophic surface area in H9C2 cells compared with the Ang II group (P<0.01, vs. Ang II group). Concurrently, we found that PPAR-γ activity was significantly increased in the quercetin-treated group both in vivo and in vitro when analyzed using immunofluorescent or immunohistochemical assays (P<0.05, vs. SHRs or P<0.01, vs. the Ang II group). Conversely, in vivo, AP-1 (c-fos, s-jun) activation was suppressed in the quercetin-treated group, as was the downstream hypertrophy gene, including mRNA levels of ANP and BNP (P<0.05, vs. SHRs). Additionally, both western blotting and real time-PCR demonstrated that PPAR-γ protein and mRNA were increased in the myocardium and AP-1 protein and mRNA were significantly decreased in the quercetin-treated group (P<0.05, vs. SHRs). Furthermore, western blotting and real time-PCR analyses also showed that transfection with PPAR-γ siRNA significantly increased AP-1 signaling and reversed the effects of quercetin inhibition on mRNA expression levels of genes such as ANP and BNP in hypertrophic H9C2 cells.

CONCLUSIONS

Our data indicate that quercetin may inhibit cardiac hypertrophy by enhancing PPAR-γ expression and by suppressing the AP-1 signaling pathway.

Loss of oxidative stress tolerance in hypertension is linked to reduced catalase activity and increased c-Jun NH2-terminal kinase activation

Hypertension is accompanied by increased levels of reactive oxygen species, which may contribute to progressive renal injury and dysfunction. Here we tested the hypothesis that sensitivity to exogenous hydrogen peroxide (H(2)O(2)) is enhanced in immortalized renal proximal tubular epithelial cells from spontaneously hypertensive rats (SHR) compared to normotensive control Wistar Kyoto rats (WKY). We found that SHR cells were more sensitive to H(2)O(2)-induced cell death than WKY cells. Lower survival in SHR cells correlated with increased DNA fragmentation, chromatin condensation, and caspase-3 activity, indicating apoptosis. H(2)O(2) degradation was slower in SHR than in WKY cells, suggesting that reduced antioxidant enzyme activity might be the basis for their increased sensitivity. In fact, catalase activity was downregulated in SHR cells, whereas glutathione peroxidase activity was similar in both cell types. We next examined whether MAPK signaling pathways contributed to H(2)O(2)-mediated apoptosis. Inhibition of c-Jun NH(2)-terminal kinase (JNK) with SP600125 partially rescued H(2)O(2)-induced apoptosis in WKY but not in SHR cells. In addition, p54 JNK2 isoform was robustly phosphorylated by H(2)O(2), this effect being more pronounced in SHR cells. Together, these results suggest that the survival disadvantage of SHR cells upon exposure to H(2)O(2) stems from impaired antioxidant mechanisms and activated JNK proapoptotic signaling pathways.

Angiotensins inhibit cell growth in GH3 lactosomatotroph pituitary tumor cell culture: a possible involvement of the p44/42 and p38 MAPK pathways

The local renin-angiotensin system is present in the pituitary. We investigated the effects of angiotensins on GH3 lactosomatotroph cells proliferation in vitro and the involvement of p44/42 and p38 MAPK inhibitors in the growth-regulatory effects of angiotensins. Materials and Methods. Cell viability using the Mosmann method and proliferation by the measurement of BrdU incorporation during DNA synthesis were estimated. Results. Ang II and ang IV decreased the viability and proliferation of GH3 cells. Inhibitor of p44/42 MAPK attenuated the effects of ang II on cell viability and proliferation but did not affect the ang 5-8-dependent actions. Inhibitor of p38 MAPK prevented the decrease in the number of GH3 cells in ang-II- and ang-IV-treated groups. Conclusions. The growth-inhibitory effect of ang II is possibly mediated by the p44/42 MAPK. The p38 MAPK appears to mediate the inhibitory effects of both ang II and ang 5-8 upon cell survival.

Plasma concentration of pigment epithelium-derived factor is closely associated with blood pressure and predicts incident hypertension in Chinese: a 10-year prospective study

OBJECTIVES

Pigment epithelium-derived factor (PEDF) is secreted from the adipose tissue. It circulates at high concentrations, and was reported to play a causal role in obesity-induced insulin resistance and metabolic dysfunctions in mice. Previous cross-sectional studies also demonstrated plasma PEDF concentration correlated positively with systolic blood pressure (BP) and pulse pressure, and inversely with small artery elasticity. Here we investigated the relationship of plasma PEDF concentration with BP and incident hypertension in a 10-year prospective study.

METHODS

Baseline plasma PEDF concentrations were measured by ELISA in 520 Chinese subjects, aged 51 ± 12 years, followed up long-term from the population-based Hong Kong Cardiovascular Risk Factor Prevalence Study. The association between plasma PEDF concentration and BP was investigated in both cross-sectional and prospective studies, using multiple linear regression and path analyses. Cox proportional hazards analysis was used to determine whether baseline PEDF concentration was independently related to the subsequent development of hypertension over 10 years.

RESULTS

Baseline plasma concentrations of PEDF were higher in men (P < 0·001), and were directly related to systolic BP at 2 and 5 years, and to diastolic BP at 2 years, after adjustment for covariates. Of the 386 normotensive subjects at baseline, high baseline PEDF concentration was predictive of incident hypertension, independent of the effects of age, sex, baseline BP and obesity parameters (hazard ratio: 1·135; 95% CI: 1·039-1·241; P = 0·005).

CONCLUSION

Our data suggest that plasma PEDF concentration is significantly associated with BP, and incident hypertension. PEDF may be involved in the pathogenesis of hypertension in humans.

Role of c-Jun N-terminal kinase in the regulation of vascular tone

The c-Jun N-terminal kinases (JNKs) belong to the mitogen-activated protein kinases superfamily, which play an important role in the pathogenesis of cardiovascular and metabolic diseases. However, it is still unclear whether JNK participates in the regulation of vascular tone. We investigated the effect of JNK inhibitors on vascular reactivity in aortic rings in organ bath and on angiotensin (Ang) II-induced pressor responses in vivo in Sprague-Dawley (SD) rats. In aortic rings from SD rats, KCl, norepinephrine (NE), Ang II, or endothelin 1 (ET)-1 induced a dose-dependent vasoconstriction. Preincubation with the JNK inhibitor SP600125 (20 micromol/L) slightly inhibited KCl-induced vasoconstriction (Emax: -19%) and markedly inhibited vasoconstriction to NE (-42%), Ang II (-54%), and ET-1 (-42%). SP600125 induced a dose-dependent relaxation in the NE-preconstricted aortic rings (-54%) but exerted minimal relaxation in the KCI-preconstriction rings. To exclude the nonspecific effect of SP600125, we performed additional experiments using JNK peptide inhibitor 1, L-stereoisomer (L-JNKI1), a cell-permeable peptide inhibitor specific for JNK. Compared to SP600125, L-JNKI1 (20 micromol/L) had a smaller but still significant inhibitory effect on NE-induced vasoconstriction (-18%) and did not inhibit KCI-induced vasoconstriction. Next, we investigated the effect of L-JNKI1 (5 mg/kg intravenously [IV]) in vivo on Ang II-induced pressor responses in SD rats. Ang II induces a dose-dependent increase in systolic blood pressure and L-JNKI1 slightly attenuated the Ang II-induced pressor response. These results suggest that JNK signaling plays a role in the regulation of vascular tone.

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 beta-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.

Endothelin-1 induces connective tissue growth factor expression in cardiomyocytes

Endothelin (ET)-1 is a vasoconstrictor involved in cardiovascular diseases. Connective tissue growth factor/CCN2 (CTGF) is a fibrotic mediator overexpressed in human atherosclerotic lesions, myocardial infarction, and hypertension. In different cell types CTGF regulates cell proliferation/apoptosis, migration, and extracellular matrix (ECM) accumulation and plays important roles in angiogenesis, chondrogenesis, osteogenesis, tissue repair, cancer and fibrosis. In the present study, we investigated the ET-1 signaling which triggers CTGF expression in cultured adult mouse atrial-muscle HL-1 cells used as a model system. ET-1 activated the CTGF promoter and induced CTGF expression at both mRNA and protein levels. Real-time PCR analysis revealed CTGF induction also in isolated rat heart preparations perfused with ET-1. Several intracellular signals elicited by ET-1 via ET receptors and even Epidermal Growth Factor Receptor (EGFR) contributed to the up-regulation of CTGF, including ERK activation and induction of the AP-1 components c-fos and c-jun, as also evaluated by ChIP analysis. Moreover, in cells treated with ET-1 the expression of ECM component decorin was abolished by CTGF silencing, indicating that CTGF is involved in ET-1 induced ECM accumulation not only in a direct manner but also through downstream effectors. Collectively, our data indicate that CTGF could be a mediator of the profibrotic effects of ET-1 in cardiomyocytes. CTGF inhibitors should be considered in setting a comprehensive pharmacological approach towards ET-1 induced cardiovascular diseases.

Early responses of the left ventricle to pressure overload in Wistar rats

The early events leading to the establishment of left ventricular hypertrophy associated to pressure overload (PO) are not well characterized. To explore these early events, aortic banding (AB) was performed in rats to induce left ventricle (LV) PO. Animals were sacrificed after 24, 48 h or 14 days. An echocardiogram was performed before the procedure and at sacrifice. LVs were preserved for the evaluation of fibrosis, angiotensin II (AT) receptors expression and stress-related MAP kinases (ERK 1/2, JNK and p38) pathways. We observed that concentric LV hypertrophy was established after only 14 days. Collagen I and fibronectin gene expressions were decreased the first 2 days after AB induction whereas AT receptors mRNA levels were sharply increased. ERK 1/2 and JNK activities in LV homogenates were decreased 24 h after AB but came back to normal after 14 days. p38 activity however was stable during the period studied. We also evaluated the presence of two phosphorylated transcription factors related to JNK signaling pathway (ATF-2 and c-Jun) in cardiomyocyte nuclei. The proportion of LV cell nuclei positive for these two activated transcription factors was significantly reduced in AB rats compared to sham. These results suggest that the early response of the LV to acute PO is to attenuate the expression of some pro-fibrotic and pro-hypertrophic signaling pathways and possibly AT signaling by decreasing ERK 1/2 and JNK relative activities.

Cardiac BNP gene activation by angiotensin II in vivo

The transcription factors involved in the activation of cardiac gene expression by angiotensin II (Ang II) in vivo are not well understood. Here we studied the contribution of transcriptional elements to the activation of the cardiac B-type natriuretic peptide (BNP) gene promoter by Ang II in conscious rats and in angiotensin II type 1 receptor (AT1R) transgenic mice. Rat BNP luciferase reporter gene constructs were injected into the left ventricular wall. The mean luciferase activity was 1.8-fold higher (P<0.05) in the ventricles of animals subjected to 2-week Ang II infusion as compared with vehicle infusion. Our results indicate that GATA binding sites at -90 and -81 in the rat BNP promoter are essential for the in vivo response to Ang II. The GATA factor binding to these sites is GATA-4. BNP mRNA levels and GATA-4 binding activity are also increased in the hypertrophied hearts of aged AT1R transgenic mice.

Fibroblast apoptosis precedes cardiomyocyte mass reduction during left ventricular remodeling in hypertensive rats treated with amlodipine

BACKGROUND

A transient induction of apoptosis accompanies the normalization of left ventricular mass index in spontaneously hypertensive rats (SHR) treated with dihydropyridine calcium-channel blockers. However, the cell type undergoing apoptosis in this model and the temporal correlation with onset cardiac remodeling remain undefined.

METHODS AND RESULTS

SHR were treated either with vehicle or amlodipine (20 mg/kg per day) for 4, 7, 10, 14 or 28 days. Amlodipine stably reduced systolic blood pressure by day 2 (-26 +/- 2%) and stably reduced the left ventricular concentration of atrial natriuretic peptide (ANP) mRNA by approximately 50% as early as day 4, suggesting the early reduction of cardiomyocyte stress. Left ventricular mass index was significantly reduced by day 7 (-4.6 +/- 1.5%), in coordination with reduced DNA content (-23 +/- 2%) and non-cardiomyocyte number (-17 +/- 4%). However, the cardiomyocyte cross-sectional area was reduced only starting from day 14. Caspase-3 cleavage was significantly increased at day 7 only. Ultimately, amlodipine for 28 days induced a slight increase in capillary density without affecting total cardiomyocyte number, while reducing the total number of non-cardiomyocytes down to levels seen in untreated normotensive Wistar-Kyoto rats. Bax to Bcl-2 protein ratios were increased from day 7 to day 28. In situ double labeling by the terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) method (apoptosis) combined with rhodamine-labeled lectin binding (endothelial cell marker) revealed a significant increase (> 3-fold) in TUNEL-positive, lectin-negative non-cardiomyocytes in the interstitium between days 7 and 14.

CONCLUSIONS

Left ventricular remodeling induced by amlodipine in SHR involves selective deletion of excess fibroblasts via apoptosis prior to cardiomyocyte mass reduction, but after attenuation of ANP gene expression.

Dominant-negative c-Jun inhibits rat cardiac hypertrophy induced by angiotensin II and hypertension

Cardiac activator protein-1 (AP-1), composed of c-Jun, is significantly activated by hypertension or angiotensin II (AngII). This study was undertaken to elucidate whether c-Jun could be the potential target for treatment of cardiac hypertrophy. We constructed recombinant adenovirus carrying dominant-negative mutant of c-Jun (Ad.DN-c-Jun). Using catheter-based technique of adenoviral gene transfer, we achieved global myocardial transduction of DN-c-Jun in rats, to specifically inhibit cardiac AP-1. (1) AngII (200 ng/kg/min) infusion in rats caused cardiac hypertrophy, increased cardiac p70S6 kinase activity by 1.3-fold (P<0.05) and enhanced the gene expression of cardiac hypertrophic markers. Ad.DN-c-Jun, which was transferred to the heart 2 days before AngII infusion, prevented cardiac hypertrophy (P<0.01), decreased p70S6 kinase phosphorylation (P<0.05), and suppressed cardiac gene expression of brain natriuretic peptide, collagen I, III, and IV, monocyte chemoattractant protein-1 (MCP-1) and plasminogen activator inhibitor-1 (PAI-1) (P<0.01). (2) In genetically hypertensive rats with cardiac hypertrophy, cardiac gene transfer of Ad.DN-c-Jun, without affecting hypertension, regressed cardiac hypertrophy (P<0.05), and suppressed p70S6 kinase phosphorylation by 20% (P<0.05) and suppressed the enhanced expression of collagen I, III, and IV, MCP-1 and PAI-1. These results provided the first evidence that in vivo blockade of cardiac c-Jun inhibits pathologic cardiac hypertrophy.

Inhibition of NF-κB induces regression of cardiac hypertrophy, independent of blood pressure control, in spontaneously hypertensive rats

The transcription factor nuclear factor (NF)-κB plays a leading role in cardiac hypertrophy associated with heart failure, but whether it is involved in cardiac mass reduction is not known. We evaluated whether inhibiting the NF-κB cascade with pyrrolidine dithiocarbamate (PDTC) in spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto rats (WKYs) affected hypertrophy. We measured NF-κB signaling components [NF-κB translocation, IκBα, p65, mRNA and protein levels, and IκB kinase-β (IKKβ) activity] at 12 and 36 wk in WKYs and SHRs and at 10 wk in PDTC-treated rats ( n = 9). NF-κB activation was also evaluated in rats treated for 10 wk with captopril or hydralazine alone or with either drug plus PDTC. All components were increased in SHRs compared with WKYs. After PDTC treatment, NF-κB activity was inhibited, and heart weight-to-body weight ratio in SHRs was significantly attenuated (3.52 ± 0.04 to 3.32 ± 0.05 mg/kg). Captopril treatment significantly reduced cardiac mass (3.5 vs. 3.05 mg/kg; n = 9) and inhibited NF-κB activity (169.71 ± 5.70 to 106.7 ± 12.44). Hydralazine had no effect on cardiac mass (3.5 vs. 3.42 mg/kg) or NF-κB activity (169.71 ± 5.70 to 155.52 ± 6.11). Hydralazine plus PDTC reduced blood pressure (191.16 ± 1.7 to 158.5 ± 2.36 mmHg) and inhibited NF-κB activity (169.71 ± 5.70 to 97.29 ± 3.65). Our data suggest that 1) cardiac hypertrophy in SHRs is partly due to NF-κB activation, 2) inhibition of NF-κB activity by PDTC parallels regression of hypertrophy, and 3) regression of hypertrophy is partly due to inhibition of NF-κB activity, independent of hypertension. The relationship between NF-κB activity and cardiac remodeling is causal, not coincidental.

Angiotensin II stimulates protein synthesis and inhibits proliferation in primary cultures of rat adrenal glomerulosa cells

Angiotensin II (Ang II) is one of the most important stimuli of rat adrenal glomerulosa cells. The aim of the present study was to investigate whether Ang II can stimulate cell proliferation and/or hypertrophy and investigate pathways and intracellular targets. A 3-d treatment with Ang II (5-100 nm), through the Ang II type 1 receptor subtype, abolished cell proliferation observed in control cells but increased protein synthesis. Preincubation with PD98059 (a MAPK kinase inhibitor) abolished basal proliferation and had no effect on basal protein synthesis but did reverse the effect of Ang II on protein synthesis. The p38 MAPK inhibitor SB203580 reversed the inhibitory effect on cell proliferation and abolished the increase in protein synthesis, whereas the c-Jun N-terminal kinase inhibitor SP600125 had no effect. Time-course studies revealed that Ang II stimulated phosphorylation of both p42/p44mapk and p38 MAPK but did not activate c-Jun N-terminal kinase. Ang II had no effect on the level of cyclin E expression but increased the expression of the cyclin-dependent kinase, p27Kip1, an effect abolished in cells preincubated with SB203580 and PD98059. In conclusion, in cultured rat glomerulosa cells, a 3-d treatment with Ang II increases protein synthesis, with a concomitant decrease in proliferation. These effects are mediated by both the p42/p44mapk and p38 MAPK pathways, which increase expression of the steroidogenic enzymes, steroidogenic acute regulatory protein and 3beta-hydroxysteroid dehydrogenase and p27Kip1, a protein known to block the cell cycle in G1 phase. Together these results support the key role of Ang II as a stimulus of steroid synthesis rather than a proliferating factor.

Salutary effects of attenuation of angiotensin II on coronary perivascular fibrosis associated with insulin resistance and obesity

Obesity and insulin resistance confer increased risk for accelerated coronary disease and cardiomyopathic phenomena. We have previously shown that inhibition of angiotensin-converting enzyme (ACE) prevents coronary perimicrovascular fibrosis in genetically obese mice that develop insulin resistance. This study was performed to elucidate mechanism(s) implicated and to determine the effects of attenuation of angiotensin II (Ang) II. Genetically obese ob/ob mice were given ACE inhibitor (temocapril) or Ang II type 1 (AT(1)) receptor blocker (olmesartan) from 10 to 20 weeks. Cardiac expressions of plasminogen activator inhibitor (PAI)-1, the major physiologic inhibitor of fibrinolysis, and transforming growth factor (TGF)-beta(1), a prototypic profibrotic molecule, were determined and extent of perivascular coronary fibrosis was measured. Twenty-week-old obese mice exhibited increased plasma levels of PAI-1 and TGF-beta(1) compared with the values in lean counterpart. Perivascular coronary fibrosis in arterioles and small arteries was evident in obese mice that also showed increased left ventricular collagen as measured by hydroxyproline assay. Immunohistochemistry confirmed the deposition of perivascular type 1 collagen. Markedly increased PAI-1 and TGF-beta were seen immunohistochemically in coronary vascular wall and confirmed by western blotting. When obese mice were treated with temocapril or olmesartan from 10 to 20 weeks, both were equally effective and prevented increases in perivascular fibrosis, plasma PAI-1 and TGF-beta(1), left ventricular collagen and mural immunoreactivity for PAI-1, TGF-beta and collagen type 1. The c-Jun NH(2)-terminal kinase (JNK) activity was elevated in the left ventricle of obese mice (western) and blocked by temocapril and olmesartan. Ang II-mediated upregulation of PAI-1 and TGF-beta(1) with collagen deposition may explain the mechanism of perivascular fibrosis in obese mice. ACE inhibition and blockade of AT(1) receptor may prevent coronary perivascular fibrosis and collagen deposition even before development of overt diabetes. JNK activation may be a mediator of obesity-related cardiac dysfunction and a potential therapeutic target.

Excess Aldosterone under Normal Salt Diet Induces Cardiac Hypertrophy and Infiltration via Oxidative Stress

Aldosterone is known to play a role in the pathophysiology of some cardiovascular diseases. However, previous studies on aldosterone infusion have been mostly performed in animals receiving sodium loading and uninephrectomy, and thus the cardiac action of aldosterone alone remains to be fully clarified. The present study was undertaken to investigate the direct cardiac action of aldosterone infusion alone in rats not subjected to salt loading and uninephrectomy. Aldosterone (0.75 microg/h) was subcutaneously infused into rats via an osmotic minipump for 14 days. Aldosterone infusion, under a normal salt diet, induced only a slight increase in the blood pressure of normal rats throughout the infusion. However, aldosterone significantly induced cardiac hypertrophy, as shown by echocardiography and measurement of cardiomyocyte cross-sectional area. Furthermore, aldosterone caused not only cardiac interstitial macrophage infiltration but also cardiac focal inflammatory lesions, which were associated with an increase in cardiac monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNA. The slight elevation of blood pressure by aldosterone infusion was completely prevented by tempol, the superoxide dismutase mimetic. However, tempol failed to suppress cardiac hypertrophy, the formation of inflammatory lesions, and upregulation of cardiac MCP-1 and osteopontin by aldosterone, while N-acetylcysteine could inhibit all of them. Our data provide evidence that aldosterone alone can induce cardiac hypertrophy and severe inflammatory response in the heart, independently of blood pressure, even in the absence of salt loading or nephrectomy. Aldosterone seems to induce cardiac inflammation and gene expression via oxidative stress that is inhibited by N-acetylcysteine but not by tempol.

Effect of angiotensin II type 2 receptor blockade on mitogen activated protein kinases during myocardial ischemia-reperfusion

Mitogen-activated protein kinases (MAPKs) have been implicated during ischemia-reperfusion (IR) and angiotensin II (AngII) type 2 receptor (AT2R) blockade has been shown to induce cardioprotection involving protein kinase Cepsilon (PKCepsilon) signaling after IR. We examined whether the 3 major MAPKs, p38, c-Jun NH2-terminal kinase (JNK-1 and JNK-2), and extracellular signal regulated kinases (ERK-1 and ERK-2) are activated after IR and whether treatment with the AT2R antagonist PD123,319 (PD) alters their expression. Isolated rat hearts were randomized to control (aerobic perfusion, 80 min), IR (no drug; 50 min of perfusion, 30 min global ischemia and 30 min reperfusion; working mode), and IR + PD (0.3 micromol/l) and left ventricular (LV) work was measured. We measured LV tissue content of p38, p-p38, p-JNK-1 (54 kDa), p-JNK-2 (46 kDa), p-ERK-1 (44 kDa), p-ERK-2 (42 kDa) and PKCepsilon proteins by immunoblotting and cGMP by enzyme immunoassay. IR resulted in significant LV dysfunction, increase in p-p38 and p-JNK-1/-2, no change in p-ERK-1/-2 or PKCepsilon, and decrease in cGMP. PD improved LV recovery after IR, induced a slight increase in p-p38 (p < 0.01 vs. control), normalized p-JNK-1, did not change p-ERK-1/-2, and increased PKCepsilon and cGMP. The overall results suggest that p38 and JNK might play a significant role in acute IR injury and the cardioprotective effect of AT2R blockade independent of ERK. The activation of p38 and JNKs during IR may be linked, in part, to AT2R stimulation.

Myocardial hypertrophy is not a prerequisite for changes in early gene expression in left ventricular volume overload

Currently it is not certain whether hypertrophy or the underlying disease is the primary trigger of the alterations in early gene expression in the progression of cardiac disease to end-stage heart failure. In this study, we tested the notion that in left ventricular overload disorders, the changes in early gene expression in the progression to heart failure is independent of the manifestation of cardiac hypertrophy. We compared the expression of the early genes c-fos, c-myc, and c-jun in six dilated cardiomyopathic hearts (DCM) and 15 patients with left ventricular volume overload (VOL) resulting from mitral/aortic regurgitation and no significant stenosis or hypertrophic manifestations, using eight healthy donor hearts as controls. In VOL, c-myc was elevated by 88% (P < 0.01) in the left ventricle, 46% in the right ventricle, onefold (P < 0.01) in the left atrium, and 54% (P < 0.05) in the right atrium, while in DCM, it was increased by 71% (P < 0.02), 55%, 48% (P < 0.05) and 91% (P < 0.05), respectively. Similarly, c-jun was elevated by 41% (P < 0.01) in the left ventricle, 39% (P < 0.05) in the right ventricle, 83% (P < 0.02) in the left atrium and 21% in the right atrium in VOL, while in DCM it was elevated by 13% in the left ventricle, 29% in the left atrium, and 41% in the right atrium, but decreased by 13% in the right ventricle. In contrast, c-fos was slightly decreased in the left ventricle and atrium of both DCM and VOL, and in left atrium of the VOL group, but remained unchanged in the other myocardial chambers. These results show that, in the human myocardium, the three early genes are regulated differently, possibly in disease- and chamber-specific fashions, and manifestation of left ventricular hypertrophy is not a prerequisite for the elevation in their expression in left ventricular overload disorders.

Molecular mechanisms in endothelial regulation of cardiac function

Endothelium is now recognized as a massive, regionally specific, multifunctional organ. Given its strategic anatomic location between the circulating blood components and the vascular smooth muscle or the cardiac muscle, it is a biologically significant interface whose dysfunction can be a critical factor in various pathological conditions. Two types of endothelial cells are recognized in the heart, the endocardial endothelial (EE) cells and the microvascular endothelial cells (MVE). Both produce common autacoids and share similar roles in signal transduction induced by neurotransmitters, hormones or mechanical stimuli. They are however two distinct cell populations with dissimilar embryological origin, cytoskeletal organization, receptor mediated functions and electrophysiological properties. Both the MVE and EE are modulators of cardiac performance. Myocardial contraction may be modulated by cardioactive agents such as nitric oxide, prostanoids, endothelin, natriuretic peptides, angiotensin II, kinins, reactive oxygen species and adenyl purines released from the cardiac endothelium. Two mechanisms have been proposed for the signal transduction from EE to the underlying myocytes: stimulus-secretion-contraction coupling and blood-heart barrier. Nitric oxide, bradykinin and myofilament desensitizing agent are probably important in short-term regulation of myocardial functions. Endothelin and Angiotensin II are probably involved in long-term regulation. Besides its sensory function and paracrine modulation of myocardial performance, EE as a blood-heart barrier could be of significance for the ionic homeostasis of the cardiac interstitium. In cardiac diseases, the damage to EE or MVE leading to failure of the endothelial cells to perform its regulatory and modulator functions may have serious consequences. A better understanding of the endothelial signaling pathways in cardiac physiology and pathophysiology may lead to the development of novel therapeutic strategies.

Transcription activator protein 1 mediates alpha- but not beta-adrenergic hypertrophic growth responses in adult cardiomyocytes

In some models of cardiac hypertrophy, activation of activator protein 1 (AP-1) correlates with growth. However, AP-1 is also activated by stimuli not involved in cardiac growth. This raises the following questions: does AP-1 plays a causal role for cardiomyocyte growth, and is this role model or stimulus dependent? We used a single model to address these questions, i.e., ventricular cardiomyocytes of adult rats, and two growth stimuli, i.e., alpha- and beta-adrenoceptor agonists [10 microM phenylephrine (PE) and 1 microM isoprenaline (Iso), respectively]. After 1 h of stimulation with PE, mRNA expression of c-Fos and c-Jun was upregulated to 185 +/- 32 and 132 +/- 13% of control. Fos and Jun proteins formed the AP-1 complex. PE stimulated DNA binding activity of AP-1 to 165 +/- 22% of control within 2 h and increased protein synthesis to 161 +/- 27% of control and cross-sectional area to 126 +/- 4% of control. Inhibition of AP-1 binding activity by cAMP response element (CRE) decoy oligonucleotides abolished both of these growth responses. Iso stimulated AP-1 binding activity to 203 +/- 19% of control within 2 h and stimulated protein synthesis to 145 +/- 17% of control. However, the growth effect of Iso was not abolished by CRE decoys: Iso increased protein synthesis to 158 +/- 17% of control in the presence of CRE. In conclusion, AP-1 is a causal mediator of the alpha-adrenergic, but not the beta-adrenergic, growth response of cardiomyocytes.

Angiotensin II induces thrombospondin-1 production in human mesangial cells via p38 MAPK and JNK: a mechanism for activation of latent TGF-beta1

ANG II induces secretion and activation of transforming growth factor-beta (TGF-beta) by glomerular mesangial cells. However, the mechanisms that operate this are unclear. Thrombospondin-1 (TSP-1), which is produced by mesangial cells in damaged glomeruli, is one of several molecules known to activate the latent TGF-beta1 complex. Therefore, we examined whether the ANG II-induced activation of latent TGF-beta1 in human mesangial cells (HMC) operates via TSP-1. The addition of ANG II (1-100 nM) to HMC significantly increased TSP-1 mRNA within 6 h, followed by an increase in TSP-1 protein production as shown by Western blot analysis of cells and immunoassay of the culture supernatant. Production of ANG II-induced TSP-1 mRNA and protein was completely inhibited by an ANG II type 1 (AT1)-receptor antagonist but was unaffected by an AT2-receptor antagonist. Use of a TSP-1-specific blocking peptide demonstrated that the ANG II-induced activation of latent TGF-beta1 operates via TSP-1. Next, we investigated the role of ERK1/2, p38 MAPK, and JNK in ANG II-induced TSP-1 production in HMC. The addition of the upstream ERK1/2 inhibitor PD-98059 did not affect ANG II-induced TSP-1 production, whereas addition of either the p38 MAPK inhibitor SB-203580 or the JNK inhibitor SP-600125 significantly reduced TSP-1 production. In conclusion, this study has demonstrated that ANG II-induced activation of latent TGF-beta1 in HMC operates via TSP-1. Furthermore, ANG II-induced TSP-1 production is dependent on p38 MAPK and JNK signaling.

Kallikrein gene delivery attenuates cardiac remodeling and promotes neovascularization in spontaneously hypertensive rats

Hypertension that results in left ventricular (LV) hypertrophy and/or fibrosis can lead to cardiac dysfunction. Spontaneously hypertensive rats (SHR) develop high blood pressure and LV hypertrophy at an early age and are a popular model of human essential hypertension. To investigate the role of the tissue kallikrein-kinin system in cardiac remodeling, an adenovirus containing the human tissue kallikrein gene was injected intravenously into adult SHR and normotensive Wistar-Kyoto (WKY) rats. The blood pressure of WKY rats remained unchanged throughout the experiment. Alternatively, kallikrein gene transfer reduced blood pressure in SHR for the first 2 wk, but had no effect from 3 to 5 wk. Five weeks after kallikrein gene delivery, SHR showed significant reductions in LV-to-heart weight ratio, LV long axis, and cardiomyocyte size; however, these parameters were unaffected in WKY rats. Interestingly, cardiac collagen density was decreased in both SHR and WKY rats receiving the kallikrein gene. Kallikrein gene transfer also increased cardiac capillary density in SHR, but not in WKY rats. The morphological changes after kallikrein gene transfer were associated with decreases in JNK activation as well as transforming growth factor (TGF)-beta 1 and plasminogen activator inhibitor-1 levels in the heart. In addition, kallikrein gene delivery elevated LV nitric oxide and cGMP levels in both rat strains. These results indicate that kallikrein-kinin attenuates cardiac hypertrophy and fibrosis and enhances capillary growth in SHR through the suppression of JNK, TGF-beta 1, and plasminogen activator inhibitor-1 via the nitric oxide-cGMP pathway.

Angiotensin II stimulates hyperplasia but not hypertrophy in immature ovine cardiomyocytes

Rat and sheep cardiac myocytes become binucleate as they complete the 'terminal differentiation' process soon after birth and are not able to divide thereafter. Angiotensin II (Ang II) is known to stimulate hypertrophic changes in rodent cardiomyocytes under both in vivo and in vitro conditions via the AT1 receptor and intracellular extracellular regulated kinase (ERK) signalling cascade. We sought to develop culture methods for immature sheep cardiomyocytes in order to test the hypothesis that Ang II is a hypertrophic agent in the immature myocardium of the sheep. We isolated fetal sheep cardiomyocytes and cultured them for 96 h, added Ang II and phenylephrine (PE) for 48 h, and measured footprint area and proliferation (5-bromo-2'-deoxyuridine (BrdU) uptake) separately in mono- vs. binucleate myocytes. We found that neither Ang II nor PE changed the footprint area of mononucleated cells. PE stimulated an increase in footprint area of binucleate cells but Ang II did not. Ang II increased myocyte BrdU uptake compared to serum free conditions, but PE did not affect BrdU uptake. The MAP kinase kinase (MEK) inhibitor UO126 prevented BrdU uptake in Ang II-stimulated cells and prevented cell hypertrophy in PE-stimulated cells. This paper establishes culture methods for immature sheep cardiomyocytes and reports that: (1) Ang II is not a hypertrophic agent; (2) Ang II stimulates hyperplastic growth among mononucleate myocytes; (3) PE is a hypertrophic agent in binucleate myocytes; and (4) the ERK cascade is required for the proliferation effect of Ang II and the hypertrophic effect of PE.

Testosterone, cytochrome P450, and cardiac hypertrophy

Cytochrome P450 mono-oxygenases (CYP) play an essential role in steroid metabolism, and there is speculation that sex hormones might influence cardiac mass and physiology. As CYP mono-oxygenases activity is frequently altered during disease, we tested our hypothesis that CYP mono-oxygenase expression and testosterone metabolism are altered in cardiac hypertrophy. We investigate major CYP mono-oxygenase isoforms and other steroid-metabolizing enzymes and the androgen receptor in normal, hypertrophic, and assist device-supported human hearts and in spontaneously hypertensive rats (SHR). We show increased and idiosyncratic metabolism of testosterone in hypertrophic heart and link these changes to altered CYP mono-oxygenase expression. We show significant induction of 5-alpha steroid reductase and P450 aromatase gene expression and enhanced production of dihydrotestosterone, which can be inhibited by the 5-alpha reductase inhibitor finasteride. We show increased gene expression of the androgen receptor and increased levels of lipid peroxidation in diseased hearts, the latter being markedly inhibited by CYP mono-oxygenase inactivation. We show alpha-MHC to be significantly repressed in cardiac hypertrophy and restored to normal on testosterone supplementation. We conclude that heart-specific steroid metabolism is of critical importance in cardiac hypertrophy

Molecular and cellular mechanisms of mechanical stress-induced cardiac hypertrophy

Congestive heart failure is one of the major issues for cardiologists. Since cardiac hypertrophy deteriorates into heart failure, it is important to elucidate the mechanisms of cardiac hypertrophy. Hemodynamic overload, namely mechanical stress, is a major cause for cardiac hypertrophy. Mechanical stress induces various hypertrophic responses such as activation of phosphorylation cascades of many protein kinases, expression of specific genes and an increase in protein synthesis. During this process, secretion and production of vasoactive peptides such as angiotensin II and endothelin-1, are increased and play critical roles in the induction of these hypertrophic responses. Recently, a Ca2+ dependent protein kinase, CaMK, and a Ca2+ dependent protein phosphatase, calcineurin, have attracted great attention as critical molecules that induce cardiac hypertrophy. In this review, we described the mechanisms by which mechanical stress induces cardiac hypertrophy, especially focusing on the role of calcineurin in the development of cardiac hypertrophy.