Differential activation of cardiac c-jun amino-terminal kinase and extracellular signal-regulated kinase in angiotensin II-mediated hypertension

α-Melanocyte-stimulating hormone alleviates pathological cardiac remodeling via melanocortin 5 receptor

α-Melanocyte-stimulating hormone (α-MSH) regulates diverse physiological functions by activating melanocortin receptors (MC-R). However, the role of α-MSH and its possible target receptors in the heart remain completely unknown. Here we investigate whether α-MSH could be involved in pathological cardiac remodeling. We found that α-MSH was highly expressed in the mouse heart with reduced ventricular levels after transverse aortic constriction (TAC). Administration of a stable α-MSH analog protected mice against TAC-induced cardiac hypertrophy and systolic dysfunction. In vitro experiments revealed that MC5-R in cardiomyocytes mediates the anti-hypertrophic signaling of α-MSH. Silencing of MC5-R in cardiomyocytes induced hypertrophy and fibrosis markers in vitro and aggravated TAC-induced cardiac hypertrophy and fibrosis in vivo. Conversely, pharmacological activation of MC5-R improved systolic function and reduced cardiac fibrosis in TAC-operated mice. In conclusion, α-MSH is expressed in the heart and protects against pathological cardiac remodeling by activating MC5-R in cardiomyocytes. These results suggest that analogs of naturally occurring α-MSH, that have been recently approved for clinical use and have agonistic activity at MC5-R, may be of benefit in treating heart failure.

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.

Novel therapeutic targets in the management of atrial fibrillation

Atrial fibrillation (AF) is the most common cardiac arrhythmia, contributing to increased morbidity and reduced survival through its associations with stroke and heart failure. AF contributes to a four- to fivefold increase in the risk of stroke in the general population and is responsible for 10-15 % of all ischemic strokes. Diagnosis and treatment of AF require considerable health care resources. Current therapies to restore sinus rhythm in AF are suboptimal and are limited either by their pro-arrhythmic effects or by their procedure-related complications. These limitations have necessitated identification of newer therapeutic targets to expand the treatment options. There has been a considerable amount of research interest in investigating the mechanisms of initiation and propagation of AF. Despite extensive research focused on the pathogenesis of AF, a thorough understanding of various pathways mediating initiation and propagation of AF still remains limited. Research efforts focused on the identification of these pathways and molecular mediators have generated a great degree of interest for developing more targeted therapies. This review discusses the potential therapeutic targets and the results from experimental and clinical research investigating these targets.

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.

Pravastatin slows the progression of heart failure by inhibiting the c-Jun N-terminal kinase-mediated intrinsic apoptotic signaling pathway

Tumor necrosis factor‑α (TNF-α) and c‑Jun N‑terminal kinases (JNKs) are known to be associated with apoptosis and are important in cardiac remodeling. It remains to be determined whether statins inhibit cardiac remodeling through interfering with TNF‑α‑JNK‑related signaling pathways. This study was designed to investigate the effect of pravastatin on the progression of hypertrophy to heart failure in transverse aortic constriction (TAC) and the associations with TNF‑α‑JNK signaling. Either pravastatin (5 or 20 mg/kg/day) or vehicle was orally administered to male C57BL/6J mice with TAC. Cardiac remodeling and left ventricular hemodynamics, as well as JNK-dependent apoptotic signals were analyzed 4 weeks following TAC. Neonatal rat cardiomyocytes were cultured to investigate the effect of pravastatin on TNF‑α‑induced JNK‑related apoptotic signals. Notably, pravastatin reduced the heart/body weight and lung/body weight ratios. In addition, a decrease of left ventricular (LV) echocardiographic dimensions, an increase of LV fractional shortening and diastolic index, a reduction of JNK activity, caspase‑12 and Bax were observed in the pravastatin‑treated groups. The TNF‑α‑induced phosphorylation of JNK and upregulation of caspase‑12 and Bax in cultured cardiomyocytes was inhibited by pravastatin. These results indicated that pravastatin attenuates cardiac remodeling by inhibiting JNK‑dependent pro‑apoptotic signaling.

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.

Garlic Oil Alleviates MAPKs- and IL-6-mediated Diabetes-related Cardiac Hypertrophy in STZ-induced DM Rats

Garlic oil has been reported to protect the cardiovascular system; however, the effects and mechanisms behind the cardioprotection of garlic oil on diabetes-induced cardiaomyopathy are unclear. In this study, we used streptozotocin (STZ)-induced diabetic rats to investigate whether garlic oil could protect the heart from diabetes-induced cardiomyopathy. Wistar STZ-induced diabetic rats received garlic oil (0, 10, 50 or 100 mg kg^_1 body weight) by gastric gavage every 2 days for 16 days. Normal rats without diabetes were used as control. Cardiac contractile dysfunction and cardiac pathologic hypertrophy responses were observed in diabetic rat hearts. Cardiac function was examined using echocardiography. In addition to cardiac hypertrophy-related mitogen-activated protein kinases (MAPK) pathways (e.g., p38, c-Jun N-terminal kinases (JNK) and extracellularly responsive kinase (ERK1/2)), the IL-6/MEK5/ERK5 signaling pathway was greatly activated in the diabetic rat hearts, which contributes to the up-regulation of cardiac pathologic hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP), and leads to cardiac contractile dysfunction. Garlic oil treatment significantly inhibited the up-regulation in MAPK (e.g., p38, JNK and ERK1/2) and IL-6/MEK5/ERK5 signaling pathways in the diabetic rat hearts, reducing the levels of cardiac pathologic hypertrophy markers such as ANP and BNP, and improving the cardiac contractile function. Collectively, data from these studies demonstrate that garlic oil shows the potential cardioprotective effects for protecting heart from diabetic cardiomyopathy.

Alterations of cardiac ERK1/2 expression and activity due to volume overload were attenuated by the blockade of RAS

The activities and protein content of extracellular signal-regulated kinase (ERK)1/2 in the heart were measured in rats at 4 and 16 weeks after volume overload due to aortocaval shunt. Protein content of phosphorylated ERK1/2 was increased at both 4 and 16 weeks, whereas protein content of total ERK1/2 was increased only at 16 weeks of inducing volume overload. The ERK1/2 activities, estimated as phospho-Elk-1 content, were also increased at 4 and 16 weeks of inducing volume overload. The increased phosphorylated ERK1/2 and E-26-like (Elk)-1 protein content in 16 weeks failing hearts was much greater than that in 4 weeks hypertrophied hearts. These changes in phosphorylated ERK1/2 and Elk-1 protein content in both 4 and 16 weeks volume overloaded animals were attenuated by treatment with enalapril and/or losartan. The results indicate that activation of ERK1/2 may be involved in the development of cardiac hypertrophy and heart failure due to volume overload, and these changes are partially prevented by blockade of the renin-angiotensin system (RAS).

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.

Lipopolysaccharide induces cellular hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 myocardiac cells

Evidences suggest that lipopolysaccharide (LPS) participates in the inflammatory response in the cardiovascular system; however, it is unknown if LPS is sufficient to cause the cardiac hypertrophy. In the present study, we treated H9c2 myocardiac cells with LPS to explore whether LPS causes cardiac hypertrophy, and to identify the precise molecular and cellular mechanisms behind hypertrophic responses. Here we show that LPS challenge induces pathological hypertrophic responses such as the increase in cell size, the reorganization of actin filaments, and the upregulation of hypertrophy markers including atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) in H9c2 cells. LPS treatment significantly promotes the activation of GATA-4 and the nuclear translocation of NFAT-3, which act as transcription factors mediating the development of cardiac hypertrophy. After administration of inhibitors including U0126 (ERK1/2 inhibitor), SB203580 (p38 MAPK inhibitor), SP600125 (JNK1/2 inhibitor), CsA (calcineurin inhibitor), FK506 (calcineurin inhibitor), and QNZ (NFkappaB inhibitor), LPS-induced hypertrophic characteristic features, such as increases in cell size, actin fibers, and levels of ANP and BNP, and the nuclear localization of NFAT-3 are markedly inhibited only by calcineurin inhibitors, CsA and FK506. Collectively, these results suggest that LPS leads to myocardiac hypertrophy through calcineurin/NFAT-3 signaling pathway in H9c2 cells. Our findings further provide a link between the LPS-induced inflammatory response and the calcineurin/NFAT-3 signaling pathway that mediates the development of cardiac hypertrophy.

Atrial fibrosis: mechanisms and clinical relevance in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the clinical setting, and traditional pharmacological approaches have proved to have important weaknesses. Structural remodeling has been observed in both clinical and experimental AF paradigms, and is an important feature of the AF substrate, producing fibrosis that alters atrial tissue composition and function. The precise mechanisms underlying atrial fibrosis are not fully elucidated, but recent experimental studies and clinical investigations have provided valuable insights. A variety of signaling systems, particularly involving angiotensin II and related mediators, seem to be centrally involved in the promotion of fibrosis. This paper reviews the current understanding of how atrial fibrosis creates a substrate for AF, summarizes what is known about the mechanisms underlying fibrosis and its progression, and highlights emerging therapeutic approaches aimed at attenuating structural remodeling to prevent AF.

Evolution of Left Atrial Systolic and Diastolic Functions in Different Stages of Hypertension: Distinct Effects of Blood Pressure Control

BACKGROUND

To evaluate the left atrial (LA) volume, and LA systolic (contractile) and diastolic (expansion) functions in different stages of hypertension with or without atrial fibrillation (AF), as well as the effects of good blood pressure control.

METHODS

A prospective observational study. Individuals including 22 normotensive controls, 23 patients with mild hypertension, 20 with severe hypertension, and 17 with hypertension and paroxysmal AF were recruited for paired echocardiography studies at baseline and 6 months after control of hypertension.

RESULTS

With increasing severity of hypertension, left ventricular (LV) diastolic function deteriorated with decreasing LV septal E'/A' and increasing E/E' ratios. LA expansion index was reduced in parallel. LA expansion index was correlated positively with LV E'/A' (r = 0.43, p = 0.022) and inversely with LV E/E' (r = 0.49, p = 0.009). Significant improvement of LV diastolic function and LA expansion index preceded the reduction of LA volume after blood pressure control. In patients with paroxysmal AF, LA volume reduction was more evident in patients receiving angiotensin-converting enzyme inhibitors or angiotensin II type 1 receptor blockers.

CONCLUSIONS

With progressive LV diastolic dysfunction in hypertension, there was a corresponding deterioration in LA diastolic function. Effective blood pressure control for 6 months improved LA diastolic function.

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.

Stretch-induced MAP kinase activation in cardiac myocytes: differential regulation through beta1-integrin and focal adhesion kinase

Mitogen-activated protein (MAP) kinases have been implicated in hemodynamic load induced heart failure. Both angiotensin II (Ang II) and mechanical stretch activate MAP kinases in cardiac myocytes. In this study, we used a neonatal rat ventricular myocyte (NRVM) model to determine the role of focal-adhesion kinase (FAK) in beta1 integrin mediated MAP kinase activation in response to mechanical stretch in presence and absence of Ang II receptor blockade (ATB). NRVM plated on deformable membranes coated with collagen IV were exposed to 20% equiaxial static-stretch. beta1 integrin signaling was blocked by adenovirus-mediated expression of a dominant-negative form of beta1D integrin (tac-beta1D). FAK signaling was disrupted by infecting NRVM with adenovirus expressing FAK-related non-kinase (FRNK). Western blot analysis was used to assess the phosphorylation of MAP kinases. In the presence and absence of ATB, mechanical stretch caused maximal phosphorylation of ERK, p38 and JNK at 5 min, which was significantly attenuated in NRVM expressing tac-beta1D. In the presence of ATB, FRNK overexpression significantly increased basal phosphorylation of ERK (40.2+/-8.6% P<0.05), p38 (39.5+/-11.7%, P<0.05), JNK (86+/-29.4%, P<0.05) and stretch-induced p38 (48.1+/-8.7%, P<0.05) and JNK (85.0+/-19.4%, P<0.05) phosphorylation. However, in the absence of ATB, FRNK overexpression significantly reduced basal and stretch-induced phosphorylation of only ERK. Examination of FAK activation revealed that beta1 integrin was required for stretch-induced phosphorylation of FAK at Y397 and Y925, but not Y861. In summary, mechanical stretch-activated ERK1/2, p38 and JNK through FAK independent and dependent mechanisms. Beta1 integrin was required for FAK independent activation of all three MAP kinases, whereas cross-talk between beta1 integrin and Ang II receptors mediated FAK dependent regulation of ERK1/2.

AGT and ACE genes influence classic mitral valve prolapse predisposition in Marfan patients

BACKGROUND

In Marfan syndrome, the mitral valve prolapse, ranging from nonclassic to classic form on the basis of the leaflet thickness, is a common condition characterized by a highly variable structural abnormality. We investigated the role of angiotensinogen (AGT) M235T, angiotensin converting enzyme (ACE) I/D and angiotensin II type 1 receptor (AT1R) A1166C polymorphisms in influencing the susceptibility to classic or non-classic mitral valve prolapse in Marfan patients.

METHODS

We studied 135 Marfan patients with mitral valve prolapse, diagnosed by echocardiography. AGT, ACE, and AT1R polymorphisms were identified by polymerase chain reaction-based restriction analysis.

RESULTS

The frequency of the ACE D, but not AGT 235T and AT1R 1166C allele, was significantly higher in patients with classic mitral valve prolapse in comparison to that observed in the non-classic one (p=0.03). The percentage of subjects with the contemporaneous presence of ACE D and AGT 235T alleles was significantly higher in the classic mitral valve prolapse group in comparison to the non-classic one (79% vs. 55%, respectively; p=0.008). The concomitant presence of these two alleles was associated with increased susceptibility to the classic mitral valve prolapse (OR 3.02, p=0.016).

CONCLUSIONS

Our findings show a possible role of ACE and AGT genes as predisposing factors to classic mitral valve prolapse in Marfan patients, thus suggesting a role of renin angiotensin system genes in modulating mitral valve abnormality, and the need for an interventional study with angiotensin II type 1 receptor antagonists, which considers the leaflet thickness progression in Marfan patients with MVP.

Pirfenidone prevents the development of a vulnerable substrate for atrial fibrillation in a canine model of heart failure

BACKGROUND

Atrial fibrosis is an important substrate in atrial fibrillation (AF), particularly in the setting of structural heart disease. In a canine model, congestive heart failure (CHF) produces significant atrial fibrosis and the substrate for sustained AF. This atrial remodeling is a potential therapeutic target. The objective of the present study is to evaluate the effects of the antifibrotic drug pirfenidone (PFD) on arrhythmogenic atrial remodeling in a canine CHF model.

METHODS AND RESULTS

We studied 15 canines, divided equally into 3 groups: control, CHF canines not treated with PFD, and CHF canines treated with PFD. CHF was induced by ventricular tachypacing (220 bpm for 3 weeks), and oral PFD was administered for the 3-week pacing period. We performed electrophysiology and AF vulnerability studies, atrial fibrosis measurements, and atrial cytokine expression studies. Only canines in the untreated CHF group developed sustained AF (>30 minutes, 4 of 5 canines; P<0.05). Treatment of CHF canines with PFD resulted in an attenuation of arrhythmogenic left atrial remodeling, with a significant reduction in left atrial conduction heterogeneity index (median [25% to 75% interquartile range] 4.96 [3.53 to 5.64] versus 2.52 [2.11 to 2.82], P<0.01; pacing cycle length 300 ms), left atrial fibrosis (16.0% [13.0% to 17.5%] versus 8.7% [5.7% to 10.6%], P<0.01), and AF duration (1800 [1020 to 1800] seconds versus 6 [5 to 22] seconds, P<0.01). Immunoblotting studies demonstrated the drug's effects on multiple cytokines, including a reduction in transforming growth factor-beta1 expression.

CONCLUSIONS

Treatment of CHF canines with PFD results in significantly reduced arrhythmogenic atrial remodeling and AF vulnerability. Pharmacological therapy targeted at the fibrotic substrate itself may play an important role in the management of AF.

Distinct modulation of angiotensin II-induced early left ventricular hypertrophic gene programming by dietary fat type

Long-term dietary fatty acid intake alters the development of left ventricular hypertrophy, but the linking signaling pathways are unclear. We studied the role and underlying signaling mechanisms of dietary fat intake in the early phase of the hypertrophic process. Rats assigned for 4 weeks of high-oil, high-fat, or standard diet were subjected to angiotensin II (Ang II; 33 microg/kg/h, subcutaneous) or vehicle infusion for 24 h. The Ang II-induced increase in left ventricular mRNA levels of hypertrophy-associated genes was higher in rats fed the high-oil diet compared with the standard diet. Western blotting revealed that, in parallel with changes in gene expression, the high-oil diet increased c-Jun N-terminal kinase phosphorylation (P < 0.001). Ang II increased p38 mitogen-activated protein kinase (MAPK) phosphorylation in rats fed the high-fat diet (3-fold; P < 0.01). The increase in transcription factor activator protein-1 (AP-1) DNA binding activity in response to Ang II was higher in rats fed the high-oil diet compared with those fed the standard diet (P < 0.001). Ang II downregulated inducible nitric oxide synthase mRNA levels in fatty acid-supplemented groups compared with the standard diet group. These results show that dietary fat type modulates the early activation of hypertrophic genes in pressure-overloaded myocardium involving the distinct activation of AP-1 and MAPK signal transduction pathways.

Oxidative stress contributes to the enhanced expression of Gialpha proteins and adenylyl cyclase signaling in vascular smooth muscle cells from spontaneously hypertensive rats

OBJECTIVE

We have previously shown an enhanced expression of Gialpha proteins in spontaneously hypertensive rats (SHR) that precedes the development of hypertension. Since oxidative stress has been shown to be increased in SHR, the present studies were undertaken to examine the role of oxidative stress in enhanced expression of Gialpha proteins in SHR.

METHODS

Aortic vascular smooth muscle cells (VSMC) from 12-week-old SHR and Wistar-Kyoto (WKY) rats were used for the present studies. The levels of inhibitory guanine nucleotide regulatory proteins (Gialpha-2 and Gialpha-3) and stimulatory proteins (Gsalpha) were determined by western blotting techniques. Adenylyl cyclase activity was determined by measuring [32P]cAMP formation from [alpha-32P]ATP.

RESULTS

VSMC from SHR exhibited enhanced expression of Gialpha-2 and Gialpha-3 proteins as compared with age-matched WKY rats; however, the levels of Gsalpha proteins were not different between the two groups. The levels of superoxide anion (O2-) were also increased in SHR as compared with WKY rats, and losartan, an AT1 receptor antagonist, restored the enhanced levels to control WKY rat levels. Treatment of VSMC with antioxidants such as N-acetyl-L-cysteine (NAC) or diphenyleneiodonium (DPI) for 24 h decreased the enhanced expression of Gialpha-2 and Gialpha-3 proteins in a concentration-dependent manner in VSMC from SHR. In addition, the inhibition of forskolin-stimulated enzyme activity by low concentrations of GTPgammaS (receptor-independent Gi functions) and C-ANP4-23-mediated inhibition of adenylyl cyclase (receptor-dependent Gi functions) that were significantly enhanced in SHR were restored to WKY rat levels by NAC and DPI treatments. Similarly, diminished stimulation of adenylyl cyclase by GTPgammaS, isoproterenol and sodium fluoride in SHR was also restored towards control WKY rat levels by NAC and DPI treatments. Furthermore, PD98059, a selective inhibitor of mitogen-activated protein kinase, was able to restore the enhanced expression of Gialpha proteins in VSMC from SHR towards WKY rat levels. In addition, the enhanced activity of extracellular signal-regulated kinase 1/2 in SHR as compared with WKY rats, as demonstrated by enhanced phosphorylation of extracellular signal-regulated kinase 1/2, was also restored to WKY rat levels by NAC or DPI.

CONCLUSIONS

These results suggest that enhanced levels of Gialpha proteins and associated functions in SHR may be attributed to the enhanced oxidative stress present in SHR, which exerts its effects through the mitogen-activated protein kinase signaling pathway.

The role of bradykinin B1 receptor on cardiac remodeling in stroke-prone spontaneously hypertensive rats (SHR-SP)

An angiotensin-converting enzyme inhibitor (ACE-I) reduces cardiac remodeling and a bradykinin B2 receptor (B2R) antagonist partially abolishes this ACE-I effect. However, bradykinin has two different types of receptor, the B1 receptor (B1R) and B2R. Although B1R is induced under several pathological conditions, including hypertension, the role of cardiac B1R in hypertension is not clear. We therefore investigated the role of cardiac B1R in stroke-prone spontaneously hypertensive rats (SHR-SP) and Wistar-Kyoto (WKY) rats. The B1R mRNA expression level in the heart was significantly higher in SHR-SP than in WKY rats. Chronic infusion of a B1R antagonist for 4 weeks significantly elevated blood pressure and left-ventricular weight of SHR-SP. Morphological analysis indicated that cardiomyocyte size and cardiac fibrosis significantly increased after administration of the B1R antagonist. The phosphorylation of mitogen-activated protein (MAP) kinases, including ERK, p38, and JNK, was significantly increased in the hearts of SHR-SP rats receiving the B1R antagonist. The TGF-β1 expression level was significantly increased in SHR-SP rats treated with the B1R antagonist compared to that in WKY rats. The B1R antagonist significantly increased phosphorylation of Thr495 in endothelial nitric oxide synthase (eNOS), which is an inhibitory site of eNOS. These results suggest that the role of B1R in the heart may be attenuation of cardiac remodeling via inhibition of the expression of MAP kinases and TGF-β1 through an increase in eNOS activity in a hypertensive condition.

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.

Androgen receptor gene knockout male mice exhibit impaired cardiac growth and exacerbation of angiotensin II-induced cardiac fibrosis

Androgen has anabolic effects on cardiac myocytes and has been shown to enhance left ventricular enlargement and function. However, the physiological and patho-physiological roles of androgen in cardiac growth and cardiac stress-induced remodeling remains unclear. We aimed to clarify whether the androgen-nuclear androgen receptor (AR) system contributes to the cardiac growth and angiotensin II (Ang II)-stimulated cardiac remodeling by using systemic AR-null male mice. AR knock-out (ARKO) male mice, at 25 weeks of age, and age-matched wild-type (WT) male mice were treated with or without Ang II stimulation (2.0 mg/kg/day) for 2 weeks. ARKO mice with or without Ang II stimulation showed a significant reduction in the heart-to-body weight ratio compared with those of WT mice. In addition, echocardiographic analysis demonstrated impairments of both the concentric hypertrophic response and left ventricular function in Ang II-stimulated ARKO mice. Western blot analysis of the myocardium revealed that activation of extracellular signal-regulated kinases (ERK) 1/2 and ERK5 by Ang II stimulation were lower in ARKO mice than those of WT mice. Ang II stimulation caused more prominent cardiac fibrosis in ARKO mice than in WT mice with enhanced expression of types I and III collagen and transforming growth factor-beta1 genes and with increased Smad2 activation. These results suggest that, in male mice, the androgen-AR system participates in normal cardiac growth and modulates cardiac adaptive hypertrophy and fibrosis during the process of cardiac remodeling under hypertrophic stress.

Time-dependent transition of tempol-sensitive reduction of blood pressure in angiotensin II-induced hypertension

OBJECTIVE

Reactive oxygen species (ROS) participate in the intracellular signalling of angiotensin II. However, the mechanisms of the interaction of ROS with hypertension and mitogen-activated protein kinase (MAPK) in vivo have remained unclear. Angiotensin II infusion provokes sustained hypertension accompanied with enhancement of ROS production; initially hypertension is non-sensitive to ROS, but thereafter becomes sensitive. We examined the time-dependent transition of ROS-sensitive vasoconstriction during angiotensin II infusion and also ROS sensitivity to cardiovascular MAPK activation in acutely and chronically angiotensin II-infused rats.

METHODS AND RESULTS

During infusion of a pressor dose of angiotensin II to conscious Sprague-Dawley rats, tempol, a superoxide dismutase mimetic, was administered at 10 min, some 1, 3, 6, 12 and 24 h after the start of infusion. The magnitude of the reduction in blood pressure by tempol was initially negligible, but gradually enlarged, and reached a maximum of 96% of delta increase by angiotensin II at 12 h. However, even after sensitization to tempol, superimposed angiotensin II enabled an increase of blood pressure under tempol treatment. In chronically angiotensin II-infused rats, superimposed angiotensin II exhibited tempol quenchable MAPK activation.

CONCLUSIONS

These results indicate that the mechanisms of angiotensin II-induced vasoconstriction may shift from being non-sensitive to ROS to sensitive within 12 h; nevertheless, both ROS non-sensitive vasoconstriction and ROS-sensitive MAPK activation by angiotensin II, which are both seen in the acute phase of infusion, are restored in the late maintaining phase of prolonged angiotensin II infusion.

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.

Mesenteric artery remodeling and effects of imidapril and irbesartan on it in spontaneously hypertensive rats

AIM: To investigate the remodeling of mesenteric artery and the expression of TGF-β₁, c-Jun in mesenteric artery and effects of imidapril and irbesartan on the remodeling in spontaneously hypertensive rats (SHR).

METHODS: Thirty SHR (male/female, 21/9), aged 13 wk, were randomly divided into 3 groups (7 male rats and 3 female rats each group): SHR group, imidapril group (imidapril 3 mg/kg·d was given in drinking water for 14 wk), and irbesartan group (irbesartan 50 mg/kg·d was given in drinking water foe 14 wk). Ten homogenous Wistar Kyoto rats, 5 males and 5 females, weighing 206 ± 49 g, were selected as normal control group (WKY group). Systolic pressure was measured on day 1, 2, 4, 6, 8, 10, 12 and 14 during the experiment and the rats were killed at the end of the experiment. Angiotensin II (Ang II) level in plasma and mesenteric arteries was measured by radioimmunoassay. The morphology of the secondary branches of mesenteric artery were examined by light microscopy and electron microscopy. Reverse transcription polymerase chain reaction (RT-PCR) was used to detect the expression of transforming growth factor TGF-β₁ and c-Jun mRNA.

RESULTS: Compared with imidapril group and irbesartan group, the blood pressure was remarkably increased in SHR group. Ang II level in plasma and mesenteric arteries in SHR group was the same or lower than that in WKY group, and was higher in irbesartan group and lower in imidapril group. The remodeling of mesenteric arteries in SHR group was mostly obvious among the 4 groups. The ratio of TGF-β₁ absorbed light value to GAPDH absorbed light value in the SHR group was 0.887 ± 0.019, which was significantly higher than that in WKY group, imidapril group, and irbesartan group with the ratios of 0.780 ± 0.018, 0.803 ± 0.005, and 0.847 ± 0.017, respectively (P < 0.01). Ang II level in plasma and mesenteric arteries in imidapril group was significantly lower than that in irbesartan group (P < 0.05). The c-Jun absorbed light value/GAPDH absorbed light value of mesenteric arteries in the SHR group was 0.850 ± 0.015, which was significantly higher than that in the WKY, imidapril, and irbesartan groups (0.582 ± 0.013, 0.743 ± 0.012, and 0.789 ± 0.013, respectively, P < 0.01), and was significantly lower in imidapril group than in irbesartan group (P < 0.05).

CONCLUSION: Imidapril and irbesartan can not only control blood pressure but also inhibit mesenteric arteries remodeling and mRNA expression of TGF-β₁, c-Jun in SHR. Imidapril is more effective than irbesartan.

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.

Dominant-negative mutant of c-Jun gene transfer: a novel therapeutic strategy for colorectal cancer

Activator protein-1 (AP-1), a transcription factor, is activated through many oncogenic signals. However, its biological role in colorectal cancer has not been fully elucidated. To investigate the role of AP-1 in colorectal cancer, we constructed an adenovirus-expressing TAM67, a dominant-negative mutant of c-Jun lacking the transactivation domain of wild c-Jun (DN-c-Jun), to inhibit endogenous AP-1. AP-1 DNA-binding activity was increased in colon cancer cells (HT-29 cells) by serum stimulation, followed by an increase in both [(3)H]thymidine incorporation and cell number. Transfection of Ad-DN-c-Jun to HT-29 cells significantly inhibited serum-induced cell proliferation in vitro. As shown by flow cytometric analysis, DN-c-Jun significantly inhibited entrance into S phase after serum stimulation, thereby leading to G(1) arrest. In vivo transfection of Ad-DN-c-Jun into xenografted HT-29 cell tumors in nude mice significantly decreased tumor volume on day 21 after treatment. A change was associated with decrease in Ki-67 labeling index. These observations together showed that AP-1 is a critical modulator for proliferation and cell cycle of HT-29 cells. We obtained the first evidence that DN-c-Jun gene transfer exerted a significant antitumor effect on colon cancer both in vitro and in vivo. DN-c-Jun gene transfer may be a new candidate for treatment of colorectal cancer.

Activation of JNK in rat heart by exercise: effect of training

The purpose of the study was to determine whether exercise would activate JNK in the heart and whether chronic exercise training would alter the response. Untrained rats were familiarized with the treadmill and assigned to one of four groups: low intensity (LI), 10 min, 0%, 15 m/min; medium intensity (MI), 10 min, 0%, 33 m/min; high intensity (HI), 10 min, 25%, 33 m/min; long duration (LD), 30 min, 0%, 15 m/min. Another cohort of rats was subjected to a progressive 6 wk high-intensity training protocol that produced a 12% increase in heart mass. In untrained rats, JNK activity was LI: 1.5 (fold nonrun control), MI: 2.0, HI: 2.5, LD: 1.25 immediately after a single bout of exercise. In trained rats, no activation of JNK above baseline was detected after either a 10-min or 1-h bout of exercise. We concluded that treadmill exercise activates JNK in the rat heart in an intensity-dependent manner and that chronic training abrogates the myocardial JNK response to a bout of exercise.

Cardiac hypertrophy: the good, the bad, and the ugly

Cardiac hypertrophy is the heart's response to a variety of extrinsic and intrinsic stimuli that impose increased biomechanical stress. While hypertrophy can eventually normalize wall tension, it is associated with an unfavorable outcome and threatens affected patients with sudden death or progression to overt heart failure. Accumulating evidence from studies in human patients and animal models suggests that in most instances hypertrophy is not a compensatory response to the change in mechanical load, but rather is a maladaptive process. Accordingly, modulation of myocardial growth without adversely affecting contractile function is increasingly recognized as a potentially auspicious approach in the prevention and treatment of heart failure. In this review, we summarize recent insights into hypertrophic signaling and consider several novel antihypertrophic strategies.

Stress and vascular responses: mitogen-activated protein kinases and activator protein-1 as promising therapeutic targets of vascular remodeling

Mitogen-activated protein kinases (MAP kinases), including extracellular signal-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and p38, play a central role in cellular responses by various stress stimuli such as cell proliferation, apoptosis, migration, or gene expression. Furthermore, activator protein-1 (AP-1), a transcription factor which can be activated by MAP kinases, also is involved in a variety of celllar responses, as well as MAP kinases. MAP kinases and AP-1 are significantly activated in vascular tissues by hypertension, angiotensin II, or balloon injury. We have made dominant negative mutants of MAP kinases or c-Jun, to specifically inhibit in vivo activation of MAP kinases or AP-1. Vascular gene transfer of each dominant negative mutant of MAP kinases or c-Jun prevents intimal hyperplasia after balloon injury, which is associated with the inhibition of smooth muscle cell proliferation in the intima and the media and probably also associated with inhibition of smooth muscle cell migration. However, in vitro findings on cultured vascular smooth muscle cells suggest that the molecular mechanism underlying inhibition of intimal hyperplasia may be different among each dominant negative mutant of MAP kinases and c-Jun. MAP kinases and c-Jun seem to be the promising therapeutic target for vascular remodeling.

Aging-induced decrease in the PPAR-alpha level in hearts is improved by exercise training

Peroxisome proliferator-activated receptor (PPAR)-alpha, a transcriptional activator, regulates genes of fatty acid (FA) metabolic enzymes. To study the contribution of PPAR-alpha to exercise training-induced improvement of FA metabolic capacity in the aged heart, we investigated whether PPAR-alpha signaling and expression of its target genes in the aged heart are affected by exercise training. We used hearts of sedentary young rat (4 mo old), sedentary aged rat (23 mo old), and swim-trained aged rat (23 mo old, training for 8 wk). The mRNA and protein expression of PPAR-alpha in the heart was significantly lower in the sedentary aged rats compared with the sedentary young rats and was significantly higher in the swim-trained aged rats compared with the sedentary aged rats. The activity of PPAR-alpha DNA binding to the transcriptional regulating region on the FA metabolic enzyme genes, the mRNA expression of 3-hydroxyacyl CoA dehydrogenase (HAD) and carnitine palmitoyl transferase-I, which are PPAR-alpha target genes, and the enzyme activity of HAD in the heart altered in association with changes of the myocardial PPAR-alpha mRNA and protein levels. These findings suggest that exercise training improves aging-induced downregulation in myocardial PPAR-alpha-mediated molecular system, thereby contributing to the improvement of the FA metabolic enzyme activity in the trained-aged hearts.

Dominant negative c-jun gene transfer inhibits vascular smooth muscle cell proliferation and neointimal hyperplasia in rats

We previously reported that activator protein-1 (AP-1), containing c-Jun, is rapidly activated in balloon-injured artery. Therefore, we examined the role of c-Jun in vascular smooth muscle cell (SMC) proliferation, by using in vitro and in vivo gene transfer techniques. (1) Serum (2%) stimulation significantly increased AP-1 DNA binding activity in aortic SMCs, followed by the increase in both 3H-thymidine incorporation and cell number. Aortic SMCs were infected with recombinant adenovirus containing TAM67, a dominant negative c-Jun lacking transactivation domain of wild c-Jun (Ad-DN-c-Jun), to specifically inhibit AP-1. Ad-DN-c-Jun significantly inhibited serum-induced SMC proliferation, by inhibiting the entrance of SMC into S phase. (2) The effect of DN-c-Jun was examined on balloon injury-induced intimal hyperplasia in rats. Before balloon injury, DN-c-Jun was transfected into rat carotid artery using the hemagglutinating virus of Japan-liposome method. In vivo transfection of DN-c-Jun significantly inhibited vascular SMC proliferation in the intima and the media and subsequently prevented intimal thickening at 14 days after balloon injury. We obtained the first evidence that DN-c-Jun gene transfer prevented vascular SMC proliferation in vitro and in vivo, and c-Jun was involved in balloon injury-induced intimal hyperplasia. Thus, AP-1 seems to be the new therapeutic target for treatment of vascular diseases.

Activation of mitogen-activated protein kinases in the non-ischemic myocardium of an acute myocardial infarction in rats

As one of the signal transduction pathways related to myocardial remodeling, mitogen-activated protein kinases (MAPKs) possibly play an important role in ischemic heart disease, but it is still unknown whether myocardial MAPKs are activated in the non-ischemic region of an acute myocardial infarction (AMI). Therefore, the present study investigated the myocardial activity of extracellular signal-regulated kinases (ERKs), c-Jun NH2 terminal kinases (JNKs) and p38MAPK during the acute phase of an infarction of the rat heart, and measured the geometrical ventricular changes by echocardiography. All MAPKs were significantly activated in the ischemic myocardium (IM), non-ischemic septal wall (SW), and right ventricular wall (RV). Furthermore, the activation patterns of MAPKs differed in each region. The activation of p44ERK, JNKs and p38MAPK in the IM occurred rapidly after myocardial ischemia, followed by those in the SW and RV. The activator protein-1 DNA binding activities of the IM, SW and RV increased significantly at I day after coronary ligation. Echocardiography showed increased SW motion and RV dilatation. In conclusion, this is the first in vivo evidence that myocardial MAPKs are activated in the non-ischemic region of an AMI. Echocardiographic results suggest that acceleration of workload and/or stretch may partially induce the activation of MAPKs.

Differential ANG II-induced growth activation pathways in mesenteric artery smooth muscle cells from SHR

Angiotensin II-induced growth signaling mechanisms were investigated in vascular smooth muscle cells (VSMCs) from mesenteric arteries of spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). In WKY, angiotensin II significantly increased protein synthesis ([(3)H]leucine incorporation) but not DNA synthesis ([(3)H]thymidine incorporation). In SHR, angiotensin II increased protein and DNA synthesis. VSMCs from both strains expressed angiotensin type 1 (AT(1)) and type 2 (AT(2)) receptors. Losartan (an AT(1) receptor antagonist) but not PD-123319 (an AT(2) receptor antagonist) attenuated angiotensin II-stimulated protein synthesis in WKY VSMCs. In SHR, losartan and PD-123319 partially inhibited angiotensin II-induced VSMC proliferation. The mitogen-activated protein kinase or extracellular signal-regulated protein kinase (ERK) kinase inhibitor PD-98059 blocked VSMC growth responses to angiotensin II in both strains. Angiotensin II increased ERK1/2 activation more in SHR than WKY, an effect inhibited by losartan but not PD-123319. LY-294002 [a phosphatidylinositol-3 (PI3) kinase inhibitor] blocked angiotensin II-stimulated ERK1/2 activation in SHR but not in WKY, whereas bisindolylmaleimide [a protein kinase C (PKC) inhibitor] was ineffective. In conclusion, angiotensin II stimulates VSMC proliferation via AT(1) and AT(2) receptors in SHR. In WKY, angiotensin II induces VSMC hypertrophy via AT(1) receptors. ERK1/2-dependent pathways regulated by intracellular Ca(2+) but not PKC mediate these effects. In SHR VSMCs, PI3 kinase plays a role in augmented angiotensin II-induced ERK1/2 phosphorylation. These angiotensin II-mediated signaling events could contribute to vascular remodeling in SHR.

Cytoplasmic signaling pathways that regulate cardiac hypertrophy

This review discusses the rapidly progressing field of cardiomyocyte signal transduction and the regulation of the hypertrophic response. When stimulated by a wide array of neurohumoral factors or when faced with an increase in ventricular-wall tension, individual cardiomyocytes undergo hypertrophic growth as an adaptive response. However, sustained cardiac hypertrophy is a leading predictor of future heart failure. A growing number of intracellular signaling pathways have been characterized as important transducers of the hypertrophic response, including specific G protein isoforms, low-molecular-weight GTPases (Ras, RhoA, and Rac), mitogen-activated protein kinase cascades, protein kinase C, calcineurin, gp130-signal transducer and activator of transcription, insulin-like growth factor I receptor pathway, fibroblast growth factor and transforming growth factor beta receptor pathways, and many others. Each of these signaling pathways has been implicated as a hypertrophic transducer, which collectively suggests an emerging paradigm whereby multiple pathways operate in concert to orchestrate a hypertrophic response

Angiotensin II-induced stimulation of p21-activated kinase and c-Jun NH2-terminal kinase is mediated by Rac1 and Nck

p21-activated kinase (PAK) has been shown to be an upstream mediator of JNK in angiotensin II (AngII) signaling. Little is known regarding other signaling molecules involved in activation of PAK and JNK by AngII. Rho family GTPases Rac and Cdc42 have been shown to enhance PAK activity by binding to p21-binding domain of PAK (PAK-PBD). In vascular smooth muscle cells (VSMC) AngII stimulated Rac1 binding to GST-PAK-PBD fusion protein. Pretreatment of VSMC by genistein inhibited AngII-induced Rac1 activation, whereas Src inhibitor PP1 had no effect. Inhibition of protein kinase C by phorbol 12,13-dibutyrate pretreatment also decreased AngII-mediated activation of Rac1. The adaptor molecule Nck has been shown previously to mediate PAK activation by facilitating translocation of PAK to the plasma membrane. In VSMC AngII stimulated translocation of Nck and PAK to the membrane fraction. Overexpression of dominant-negative Nck in Chinese hamster ovary (CHO) cells, stably expressing the AngII type I receptor (CHO-AT1), inhibited both PAK and JNK activation by AngII, whereas it did not affect ERK1/2. Finally, dominant-negative Nck inhibited AngII-induced DNA synthesis in CHO-AT1 cells. Our data provide evidence for Rac1 and Nck as upstream mediators of PAK and JNK in AngII signaling and implicate JNK in AngII-induced growth responses.

Angiotensin blockade inhibits increased JNKs, AP-1 and NF- kappa B DNA-binding activities in myocardial infarcted rats

Inhibition of the renin-angiotensin system has been shown to prevent left ventricular remodeling after myocardial infarction. However, the effect of angiotensin on the signal transduction pathway of left ventricular remodeling after myocardial infarction is as yet unknown. The purpose of this study was to measure myocardial MAPKs and AP-1, NF- kappa B, and Sp-1 DNA-binding activities after myocardial infarction. Moreover, we evaluated the effects of angiotensin converting enzyme (ACE) inhibitor and angiotensin receptor blocker (ARB) on signal transduction pathway. Myocardial infarction was produced by ligation of the coronary artery in Wistar rats. Temocapril (ACE inhibitor) (3 and 30 mg/kg/day) and candesartan cilexitil (ARB) (1 and 10 mg/kg/day) were orally administered once a day. After ligation of the left descending coronary artery, JNKs (p46JNK and p55JNK) increased to 2.0- (P<0.01) and 2.8-fold (P<0.01) at 7 days, respectively. ERKs (p44ERK and p42ERK) and p38 activities did not increase significantly. AP-1 and NF- kappa B binding activities increased at 5 days, reached their peak 2.2- and 2.0-fold at 7 days. Sp-1 did not change. ACE inhibitor and ARB inhibited JNKs, NF- kappa B and AP-1 activities. Increased JNKs, AP-1, NF- kappa B, and Sp-1 DNA-binding activities were suppressed by both drugs in the infarcted region. Doppler-echocardiography showed that ACE inhibitor and ARB prevented the dilatation of left ventricular cavity at 14 days and improved diastolic filling pattern. JNKs, AP-1 and NF- kappa B activation in myocardial infarcted rats could be responsible for left ventricular remodeling after myocardial infarction and angiotensin may be related to the activation of these signals.

Differential activation of extracellular signal-regulated protein kinase 1/2 and p38 mitogen activated-protein kinase by AT1 receptors in vascular smooth muscle cells from Wistar-Kyoto rats and spontaneously hypertensive rats

OBJECTIVES

The present study investigates effects of angiotensin II on activation of extracellular signal-regulated protein kinase (ERK) 1/2, p38 mitogen activated-protein kinase (p38MAPK) and c-Jun amino terminal kinase (JNK) in vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

Vascular smooth muscle cells (VSMC) from mesenteric arteries of Wistar-Kyoto (WKY) rats and SHR were studied. Angiotensin II-induced phosphorylation of ERK1/2, JNK and p38MAPK were assessed by Western blot analysis. c-fos mRNA expression by angiotensin II was determined by reverse transcriptase-polymerase chain reaction in the absence and presence of PD98059, selective inhibitor of ERK1/2-dependent pathways and SB202190, selective p38MAPK inhibitor.

RESULTS

Angiotensin II increased phosphorylation of ERK1/2 and p38MAPK, but not JNK. Responses were significantly increased in SHR compared with WKY. Irbesartan, AT1 receptor antagonist, but not PD123319, AT2 receptor blocker, abolished angiotensin II-induced effects. PP2, selective Src inhibitor, decreased angiotensin II-mediated activation of MAP kinases. Angiotensin II increased c-fos mRNA expression in SHR and had a small stimulatory effect in WKY. These actions were inhibited by PD98059, whereas SB202190 had no effect.

CONCLUSIONS

Angiotensin II-induced activation of vascular ERK1/2 and p38MAPK is increased in SHR. These effects are mediated via AT1 receptors, which activate Src-dependent pathways. Overexpression of c-fos mRNA in SHR is due to ERK1/2-dependent, p38MAPK-independent pathways. Our results suggest that angiotensin II activates numerous MAP kinases in VSMCs and that differential activation of these kinases may be important in altered growth signaling in VSMCs from SHR.

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-induced cardiac hypertrophy is associated with different mitogen-activated protein kinase activation in normotensive and hypertensive mice

OBJECTIVE

In addition to its haemodynamic effects, angiotensin II (AngII) is thought to contribute to the development of cardiac hypertrophy via its growth factor properties. The activation of mitogen-activated protein kinases (MAPK) is crucial for stimulating cardiac growth. Therefore, the present study aimed to determine whether the trophic effects of AngII and the AngII-induced haemodynamic load were associated with specific cardiac MAPK pathways during the development of hypertrophy. Methods The activation of the extracellular-signal-regulated kinase (ERK), the c-jun N-terminal kinase (JNK) and the p38 kinase was followed in the heart of normotensive and hypertensive transgenic mice with AngII-mediated cardiac hypertrophy. Secondly, we used physiological models of AngII-dependent and AngII-independent renovascular hypertension to study the activation of cardiac MAPK pathways during the development of hypertrophy.

RESULTS

In normotensive transgenic animals with AngII-induced cardiac hypertrophy, p38 activation is associated with the development of hypertrophy while ERK and JNK are modestly stimulated. In hypertensive transgenic mice, further activation of ERK and JNK is observed. Moreover, in the AngII-independent model of renovascular hypertension and cardiac hypertrophy, p38 is not activated while ERK and JNK are strongly stimulated. In contrast, in the AngII-dependent model, all three kinases are stimulated.

CONCLUSIONS

These data suggest that p38 activation is preferentially associated with the direct effects of AngII on cardiac cells, whereas stimulation of ERK and JNK occurs in association with AngII-induced mechanical stress.

Increased JNK, AP-1 and NF-kappa B DNA binding activities in isoproterenol-induced cardiac remodeling

The in vivo signal transduction pathway, responsible for isoproterenol-induced cardiac hypertrophy or remodeling, remains to be clarified. The purpose of this study was to examine c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), activator protein-1 (AP-1) and nuclear factor-kappa B (NK-kappa B) DNA binding activity, which seem to be important in a signal transduction cascade upstream of the increased level of mRNA expression observed in isoproterenol-induced cardiac remodeling. Rats were continuously infused with saline and isoproterenol by intravenous injection (a short period; 0.5 microgram/kg/min) and an osmotic minipump (a long period; 0.5 or 3 mg/kg/day). Cardiac morphology was measured by echocardiography. JNK and ERK were measured by in gel kinase assay. AP-1 and NF-kappa B DNA binding activity was determined using an electrophoretic mobility shift assay. Echocardiogram showed that the thickness of the left ventricular anterior wall (AW) and left ventricular posterior wall (PW) increased at day 1 in low doses, and at day 1 in high doses. Isoproterenol significantly increased ERK and JNK activity at 15 min after intravenous infusion of 0.5 microgram/kg/min isoproterenol. At late phase about JNK and ERK activity, only a high dose of isoproterenol increased JNK. AP-1 DNA binding activities spurred by low or high doses of isoproterenol administration increased at 12 h, reached their peak of 24.1- and 37.1-fold (P < 0.01), respectively, at 24 h, and thereafter decreased. Although low doses of isoproterenol did not change the level of NF-kappa B DNA binding activities, high doses increased it to 10.9-fold (P < 0.01) at day 2. This study showed increased JNK, ERK, AP-1 and NF-kappa B DNA binding activities in isoproterenol-induced cardiac remodeling. AP-1 may contribute to the isoproterenol-induced cardiac remodeling, and JNK or NF-kappa B may also play some roles in it.