Angiotensin blockade inhibits SIF DNA binding activities via STAT3 after myocardial infarction

Angiotensin II Type-2 receptors modulate inflammation through signal transducer and activator of transcription proteins 3 phosphorylation and TNFα production

Angiotensin subtype-1 receptor (AT(1)R) influences inflammatory processes through enhancing signal transducer and activator of transcription proteins 3 (STAT3) signal transduction, resulting in increased tumor necrosis factor-α (TNF-α) production. Although angiotensin subtype-2 receptor (AT(2)R), in general, antagonizes AT(1)R-stimulated activity, it is not known if AT(2)R has any anti-inflammatory effects. In this study, we tested the hypothesis that AT(2)R activation plays an anti-inflammatory role by reducing STAT3 phosphorylation and TNF-α production. Changes in AT(2)R expression, TNF-α production, and STAT3 phosphorylation were quantified by Western blotting, Bio-Plex cytokine, and phosphoprotein cellular signaling assays in PC12W cells that express AT(2)R but not AT(1)R, in response to the AT(2)R agonist, CGP-42112 (CGP, 100 nm), or AT(2)R antagonist PD-123319 (PD, 1 μm). A 100% increase in AT(2)R expression in response to stimulation with its agonist CGP was observed. Further, AT(2)R activation reduced TNF-α production by 39% and STAT3 phosphorylation by 83%. In contrast, PD decreased AT(2)R expression by 76%, increased TNF-α production by 84%, and increased STAT3 phosphorylation by 67%. These findings suggest that increased AT(2)R expression may play a role in the observed decrease in inflammatory pathway activation through decreased TNF-α production and STAT3 signaling. Restoration of AT(2)R expression and/or its activation constitute a potentially novel therapeutic target for the management of inflammatory processes.

The frail renin-angiotensin system

Over the last few decades, the understanding of the renin-angiotensin system (RAS) has advanced dramatically. RAS is now thought to play a crucial role in physiologic and pathophysiologic mechanisms in almost every organ system and is a key regulator of hypertension, cardiovascular disease, and renal function. Angiotensin II (Ang II) promotes inflammation and the generation of reactive oxygen species and governs onset and progression of vascular senescence, which are all associated with functional and structural changes, contributing to age-related diseases. Although the vast majority of the actions of Ang II, including vascular senescence, are mediated by the Ang II type 1 receptor (AT1R), the identification, characterization, and cloning of the angiotensin type 2 receptor has focused attention on this receptor and to its antagonistic effect on the detrimental effects of AT1R. This review provides an overview of the changes in RAS with aging and age-disease interactions culminating in the development of frailty.

Ginsenoside-Rb1 attenuates dilated cardiomyopathy in cTnT(R141W) transgenic mouse

Familial dilated cardiomyopathy (FDCM) is caused by defective genes and specific medicines are not currently available to treat this. Ginsenoside-Rb1 provides cardioprotection in the experimental models of myocardial ischemia-reperfusion injury. Here we investigate Rb1's effect on DCM in cTnT(R141W) transgenic mouse. The transgene-positive mice aged 2 months were randomized into the model group and Rb1 [70 mg/(kg.day)] group; transgene-negative mice were used as a control. After 4-month treatment, cardiac function was assessed by echocardiography; cardiac tissues were prepared for histology and electron microscopy. Expression levels of molecular markers of cardiac hypertrophy, fibrosis, and intercalated disc proteins were detected by RT-PCR. Rb1 significantly decreased mortality, chamber dilation, and contractile dysfunction in cTnT(R141W) mice. Rb1 attenuated cardiac hypertrophy, interstitial fibrosis, ultrastructural degeneration, and intercalated disc remodeling in DCM hearts. Western blotting showed that Rb1 significantly decreased heparin-binding epidermal growth factor-like growth factor (HB-EGF) expression and signal transduction and activators of transcription 3 (STAT3) activation, which were gradually increased in DCM hearts. Our results showed that Rb1 clearly alleviated cardiac dysfunction and remodeling in the cTnT(R141W) transgenic mouse, indicating its potential utility in the treatment of FDCM.

Role of c-Jun NH2-terminal kinase in G-protein-coupled receptor agonist-induced cardiac plasminogen activator inhibitor-1 expression

Plasminogen activator inhibitor-1 (PAI-1) has been implicated as a contributing risk factor for cardiovascular disease. However, little is known about molecular mechanisms of cardiac PAI-1 gene expression. To elucidate these mechanisms, dominant negative mutants of c-Jun NH(2)-terminal kinase (JNK), p38MAPK, apoptosis signal-regulating kinase-1 (ASK-1) and c-Jun were overexpressed in rat neonatal ventricular cardiac myocytes and fibroblasts by adenovirus vector to abrogate the activation of the corresponding endogenous proteins. One hundred nmol/l of angiotensin II significantly enhanced the JNK and p38MAPK activities of cardiomyocytes (2.3-fold and 1.9-fold, P < 0.05) and fibroblasts (3.2-fold and 2.5-fold, P < 0.05). At 3 h after stimulation, angiotensin II was found to have significantly increased PAI-1 mRNA, by 5.2-fold in cardiomyocytes and by 9.7-fold in fibroblasts. Dominant negative mutants of JNK, ASK-1 and c-Jun significantly inhibited PAI-1 mRNA expression and protein synthesis in both cardiomyocytes and fibroblasts, whereas a dominant negative mutant of p38MAPK did not change this expression. Moreover, a dominant negative mutant of JNK also significantly prevented the induction of PAI-1 mRNA expression by 100 nmol/l endothelin-1 and 10 micromol/l phenylephrine. In conclusion, G-protein-coupled receptor agonist-induced PAI-1 expression is partially mediated through JNK activation.

Involvement of Apoptosis Signal-Regulating Kinase-1 on Angiotensin II-Induced Monocyte Chemoattractant Protein-1 Expression

OBJECTIVE

Monocyte chemoattractant protein 1 (MCP-1) could contribute to enhanced leukocyte recruitment and activation resulting in chronic tissue damage. However, little is known about the molecular mechanisms of cardiac MCP-1 expression. To elucidate these molecular mechanisms, angiotensin II-induced expression of MCP-1 was examined in cultured rat neonatal ventricular cardiomyocytes and fibroblasts by adenovirus gene transfer.

METHODS AND RESULTS

MCP-1 mRNA increased 3.6-fold in cardiac fibroblasts at 3 hours after 100 nmol/L angiotensin-II stimulation (P<0.01), whereas MCP-1 mRNA in cardiomyocytes was unchanged. Angiotensin II significantly enhanced JNK, p38MAPK, and nuclear factor-kappaB (NF-kappaB) activities of cardiac fibroblasts. Wild-type ASK-1 increased MCP-1 expression of cardiac fibroblasts, whereas dominant negative mutant of ASK-1 (DN-ASK), dominant negative mutant of p38MAPK (DN-p38MAPK), and pyrrolidine dithiocarbamate significantly inhibited such expression. The increased MCP-1 mRNA expression in wild-type ASK-1 transfected fibroblasts was inhibited by cotransfection with adenovirus expressing DN-p38MAPK. On the contrary, the decreased MCP-1 mRNA expression in DN-ASK transfected cells was increased by cotransfection with adenovirus expressing constitutively active MKK6.

CONCLUSIONS

Angiotensin II induced MCP-1 gene expression in cardiac fibroblasts. The angiotensin II-induced activation of ASK-1 followed by p38MAPK and NF-kappaB signaling in cardiac fibroblasts is partially involved in myocardial MCP-1 expression.

Interplay between the cardiac renin angiotensin system and JAK-STAT signaling: role in cardiac hypertrophy, ischemia/reperfusion dysfunction, and heart failure

Recent studies have shown that the JAK-STAT signaling pathway plays a central role in cardiac pathophysiology. JAK-STAT signaling has been implicated in pressure overload-induced cardiac hypertrophy and remodeling, ischemic preconditioning, and ischemia/reperfusion-induced cardiac dysfunction. The different STAT family members expressed in cardiac myocytes appear to be linked to different, and at times, opposite responses, such as cell growth/survival and apoptosis. Thus, differential activation and/or selective inhibition of the STAT proteins by agonists for G-protein coupled receptors, such as angiotensin II, may contribute to cardiac dysfunction during ischemia and heart failure. In addition, JAK-STAT signaling may represent one limb of an autocrine loop for angiotensin II generation, that serves to amplify the actions of angiotensin II on cardiac muscle. The purpose of this article is to provide an overview of recent findings that have been made for JAK-STAT signaling in cardiac myocytes and to highlight some unresolved issues for future investigation. The central focus of this review is on recent studies suggesting that modulation or activation of JAK-STAT signaling by ANG II has pathological consequences for heart function.

Dominant negative mutant of c-Jun inhibits cardiomyocyte hypertrophy induced by endothelin 1 and phenylephrine

The activator protein 1 (AP-1) transcriptional complex, containing Jun and Fos proteins, is involved in regulating many cellular processes such as proliferation and differentiation. However, little is known about a direct relationship between AP-1 activities and cardiomyocyte hypertrophy. To elucidate the roles of myocardial AP-1 activities, dominant negative mutant of c-Jun (DNJun) was overexpressed in cultured rat neonatal ventricular myocytes by adenovirus vector to abrogate endogenous AP-1 activation. Cardiomyocytes were treated with 100 nmol/L endothelin 1 (ET) and 10 micromol/L phenylephrine (PE) to induce myocardial cell hypertrophy. Both ET and PE significantly enhanced AP-1 DNA binding activities (3.4-fold by ET and 4.8-fold by PE at 3 hours, P<0.01). At 48 hours after stimulation, ET and PE significantly increased incorporation of (3)H-phenylalanine (1.4-fold by ET and 1.5-fold by PE, P<0.01), cell size (2.3-fold and 2.5-fold, P<0.01), and mRNA expression of atrial natriuretic peptide (ANP; 1.9-fold and 1.8-fold, P<0.01) and brain natriuretic peptide (BNP; 1.6-fold and 1.6-fold, P<0.01). Adenovirus carrying DNJun prevented the transcriptional activation of the AP-1 by ET and PE, using AP-1 reporter enzyme firefly luciferase assay. Moreover, DNJun prevented the increase in incorporation of (3)H-phenylalanine, cell size, and the mRNA expression of ANP and BNP by ET and PE. In conclusion, we provide the first evidence that DNJun inhibits cardiomyocyte hypertrophy through inhibition of AP-1 transcriptional activity.

Role of STAT3 in ischemic preconditioning

We recently demonstrated that ischemic preconditioning (IPC) induced by cyclic episodes of short durations of ischemia and reperfusion potentiates a signal transduction cascade involving protein tyrosine kinases and MAP kinases. A rapid activation of janus kinase (JAK) and several signal transducers and activators of the transcription (STATs) including STAT3, STAT5A and STAT6 has been shown to occur during myocardial ischemia and reperfusion. This study sought to examine if JAK/STAT signaling pathway play any role in classical early phase of IPC. Isolated working rat hearts were perfused for 15 min with KHB buffer in the absence or presence of a JAK kinase inhibitor tyrphostin AG490 (5 microm) followed by IPC, 30 min global ischemia and 2 h of reperfusion. The results demonstrated extensive phosphorylation of JAK2 and STAT3 in the IPC hearts which was almost completely abolished by an inhibitor of JAK2, AG490. IPC displayed cardioprotection as evidenced by improved post-ischemic contractile recovery, decreased myocardial infarct size and reduced number of apoptotic cardiomyocytes. AG490 blocked IPC-mediated cardioprotection by altering the IPC-mediated survival signal into death signal. Thus, IPC-induced upregulation of antiapoptotic gene bcl-2 and downregulation of pro-apoptotic gene bax are decreased and increased, respectively, in the AG490 treated hearts. The results suggest that early phase of IPC potentiates JAK/STAT signaling by activating STAT3 which transmits a survival signal to the myocardium.

Myocardial ischemia activates the JAK-STAT pathway through angiotensin II signaling in in vivo myocardium of rats

There have been many studies concerning the hemodynamics and physiological mechanisms in ischemic heart disease, little is known about molecular mechanisms during myocardial ischemia in in vivo study. As the signal transduction pathway responsible for myocardial hypertrophy and apoptosis, janus kinase (JAK) and signal transducers and activators of transcription (STAT) are suggested to play an important role. However, whether in vivo activation of JAK-STAT pathway occurs during myocardial ischemia is still unknown. The purpose of this study was to determine whether myocardial JAK or STAT is activated in ischemic heart, and to evaluate the angiotensin blockade on the pathway. Myocardial infarction was produced by ligation of the coronary artery in Wistar rats. After myocardial ischemia, we analysed both activated levels and total amounts of JAK1, JAK2, STAT1 and STAT3 by Western blot analyses at 0, 5, 15, 30, 60, 120 and 240 min. Compared with JAK activities at 0 min, JAK1 activities were significantly increased at 60 and 120 min (3.0- and 3.7-fold, respectively, P<0.01). JAK2 and STAT1 activities of ischemic myocardium were unchanged through the time course. STAT3 activities were increased at 5 min (3.3-fold, P<0.01) and markedly enhanced at 30, 60 and 120 min (4.6-, 7.7- and 8.7-fold, respectively, P<0.01). Pretreatment with imidapril (ACE inhibitor) and candesartan cilexitil (AT1 receptor antagonist) significantly prevented the increase in the phosphorylation of JAK1 at 120 min and STAT3 at 30 and 120 min. Sis-inducing factor (SIF) DNA complex was supershifted by specific anti-STAT3 antibody, indicating that increased SIF complex at least contained activated STAT3 proteins in ischemic myocardium. Imidapril and candesartan cilexitil inhibited the activation of SIF DNA binding at 1 day after coronary ligation. In conclusion, we showed that JAK1 and STAT3 were activated by ischemia from the basal activities in in vivo rat myocardial ischemia model. Imidapril and candesartan cilexitil prevented the increase in phosphorylated JAK1 and STAT3, thereby suggesting that angiotensin II, especially angiotensin II type I receptor, partially mediates activation of myocardial JAK-STAT pathway in acute myocardial ischemia.

The late phase of preconditioning

Unlike the early phase of preconditioning (PC), which lasts 2 to 3 hours and protects against infarction but not against stunning, the late phase of PC lasts 3 to 4 days and protects against both infarction and stunning, suggesting that it may have greater clinical relevance. It is now clear that late PC is a polygenic phenomenon that requires the simultaneous activation of multiple stress-responsive genes. Chemical signals released by a sublethal ischemic stress (such as NO, reactive oxygen species, and adenosine) trigger a complex cascade of signaling events that includes the activation of protein kinase C, Src protein tyrosine kinases, and nuclear factor kappaB and culminates in increased synthesis of inducible NO synthase, cyclooxygenase-2, aldose reductase, Mn superoxide dismutase, and probably other cardioprotective proteins. An analogous sequence of events can be triggered by a variety of stimuli, such as heat stress, exercise, and cytokines. Thus, late PC appears to be a universal response of the heart to stress in general. Importantly, the cardioprotective effects of late PC can be reproduced pharmacologically with clinically relevant agents (eg, NO donors, adenosine receptor agonists, endotoxin derivatives, or opioid receptor agonists), suggesting that this phenomenon might be exploited for therapeutic purposes. The purpose of this review is to summarize current information regarding the pathophysiology and mechanism of late PC.