Update on local cardiac renin-angiotensin system:

Fibroblasts activation by embryonic signal switching: A novel mechanism of placental growth factor-induced cardiac remodeling

INTRODUCTION

Cardiac remodeling is defined as cellular interstitial changes that lead dysfunction of the heart after injury. Placental growth factor (PlGF), a member of the VEGF family, has been reported to regulate cardiac hypertrophy in hemodynamic state. We therefore analyze the function of PlGF during cardiac remodeling using cardiac cells and fibroblasts, under Angiotensin II (AngII) stimulation.

METHODS

PlGF overexpressed mouse embryonic fibroblasts derived from C57BL/6 mice, were made by deficient retrovirus vector, designated as C57/PlGF. Only retrovirus vector introduced C57 cells (C57/EV) were used as control. After AngII stimulation, wound scratching assay and MTT proliferation assay with or without p38 MAPK inhibitor, SB205580 were performed in retrovirally-introduced C57 cells. Reactive oxygen species (ROS) production, NF-kB activation, IL-6 and TNF-α production were also measured. Then we assessed AngII-induced cell proliferation of mouse cardiac fibroblasts (CFs) and rat primary cardiomyocytes incubating with C57/PlGF conditioned-medium.

RESULTS

The PlGF production in C57/PlGF were confirmed by ELISA (1093.48 ± 3.5 pg/ml, ±SE). AngII-induced cell migration, proliferation and H2O2 production were increased in C57/PlGF compared with C57/EV. SB205580 inhibited the AngII-induced cell proliferation in C57/PlGF. In C57/PlGF cells, NF-kB activation was higher, followed by up-regulation of IL-6 and TNF-α production. CFs and cardiomyocytes proliferation increased when stimulated with C57/PlGF conditioned-medium.

DISCUSSION

The activation of fibroblast is stimulated by PlGF signaling via p38 MAPK/NF-kB pathway accompanied by elevation of ROS and inflammatory response. Furthermore, these signals stimulate the activation of CFs and cardiomyocytes, indicating that high circulating level of PlGF have a potential to regulate cardiac remodeling.

Peptides Are Cardioprotective Drugs of the Future: The Receptor and Signaling Mechanisms of the Cardioprotective Effect of Glucagon-like Peptide-1 Receptor Agonists

The high mortality rate among patients with acute myocardial infarction (AMI) is one of the main problems of modern cardiology. It is quite obvious that there is an urgent need to create more effective drugs for the treatment of AMI than those currently used in the clinic. Such drugs could be enzyme-resistant peptide analogs of glucagon-like peptide-1 (GLP-1). GLP-1 receptor (GLP1R) agonists can prevent ischemia/reperfusion (I/R) cardiac injury. In addition, chronic administration of GLP1R agonists can alleviate the development of adverse cardiac remodeling in myocardial infarction, hypertension, and diabetes mellitus. GLP1R agonists can protect the heart against oxidative stress and reduce proinflammatory cytokine (IL-1β, TNF-α, IL-6, and MCP-1) expression in the myocardium. GLP1R stimulation inhibits apoptosis, necroptosis, pyroptosis, and ferroptosis of cardiomyocytes. The activation of the GLP1R augments autophagy and mitophagy in the myocardium. GLP1R agonists downregulate reactive species generation through the activation of Epac and the GLP1R/PI3K/Akt/survivin pathway. The GLP1R, kinases (PKCε, PKA, Akt, AMPK, PI3K, ERK1/2, mTOR, GSK-3β, PKG, MEK1/2, and MKK3), enzymes (HO-1 and eNOS), transcription factors (STAT3, CREB, Nrf2, and FoxO3), KATP channel opening, and MPT pore closing are involved in the cardioprotective effect of GLP1R agonists.

Differential regulation of angiotensin-(1-12) in plasma and cardiac tissue in response to bilateral nephrectomy

We examined the effects of 48 h bilateral nephrectomy on plasma and cardiac tissue expression of angiotensin-(1-12) [ANG-(1-12)], ANG I, and ANG II in adult Wistar-Kyoto rats to evaluate functional changes induced by removing renal renin. The goal was to expand the evidence of ANG-(1-12) being an alternate renin-independent, angiotensin-forming substrate. Nephrectomy yielded divergent effects on circulating and cardiac angiotensins. Significant decreases in plasma ANG-(1-12), ANG I, and ANG II levels postnephrectomy accompanied increases in cardiac ANG-(1-12), ANG I, and ANG II concentrations compared with controls. Plasma ANG-(1-12) decreased 34% following nephrectomy, which accompanied 78 and 66% decreases in plasma ANG I and ANG II, respectively (P < 0.05 vs. controls). Contrastingly, cardiac ANG-(1-12) in anephric rats averaged 276 +/- 24 fmol/mg compared with 144 +/- 20 fmol/mg in controls (P < 0.005). Cardiac ANG I and ANG II values were 300 +/- 15 and 62 +/- 7 fmol/mg, respectively, in anephric rats compared with 172 +/- 8 fmol/mg for ANG I and 42 +/- 4 fmol/mg for ANG II in controls (P < 0.001). Quantitative immunofluorescence revealed significant increases in average grayscale density for cardiac tissue angiotensinogen, ANG I, ANG II, and AT(1) receptors of WKY rats postnephrectomy. Faint staining of cardiac renin, unchanged by nephrectomy, was associated with an 80% decrease in cardiac renin mRNA. These changes were accompanied by significant increases in p47(phox), Rac1, and Nox4 isoform expression. In conclusion, ANG-(1-12) may be a functional precursor for angiotensin peptide formation in the absence of circulating renin.

How hematopoietic stem cells know and act in cardiac microenvironment for stem cell plasticity? Impact of local renin-angiotensin systems

Bone marrow-derived hematopoietic stem cells (HSC) can exhibit tremendous differentiation activity in numerous non-hematopoietic organs. This enigmatic process is called as 'stem cell plasticity' (SCP). HSC may promote structural and functional repair in several organs such as heart, liver, brain, and skeletal muscle via the SCP. The differentiation capacity of HSC is dependent on the specific signals present in the local tissue microenvironment. Those specific molecular signals required for the interactions of HSC and host tissues are currently unknown. The aim of this report is to propose a hypothesis on how HSC reach, recognize, and function in cardiac tissues in the context of SCP. Locally signaling cardiac microenvironment is essential for the seeding, expansion, and 'cardiomyocyte differentiation' of the HSC in the heart. Our hypothesis is that the receptors, ligands, and signaling pathways of the tissue renin-angiotensin system (RAS) serve as the link between HSC and local cardiac microenvironment in SCP. The RAS is considered as a 'tissue-based system' exhibiting paracrine functions within many organs. The presence of local hematopoietic bone marrow RAS and local cardiac RAS have been suggested. Both local tissue RASs share similar angiotensin peptide-signaling pathways such as JAK-STAT and mitogen-activated protein kinases. HSC have angiotensin type I (AT1a) receptors for the binding of angiotensin II, the active component of the RAS. Binding of angiotensin II to AT1a can increase hematopoietic progenitor cell proliferation. Local cardiac RAS has critical (patho)biological functions in the cardiomyocyte survival, renewal, and growth, as well as in cardiac remodeling. Therefore, the components of the local cardiac RAS and hematopoietic RAS could interact with each other during the SCP through myocardial tissue repair. Activation of the local myocardial RAS after injury may be related to homing and engraftment of the HSC to the cardiac tissue. Regenerating myocardial tissue may exert regulatory functions on circulating or resident HSC via the locally active RAS. Understanding the exact molecular basis of SCP in relation to local tissue RAS could offer new frontiers in the better management of ischemic cardiac diseases.

Tonin in rat heart with experimental hypertrophy

The present study was undertaken to determine tonin expression and activity in rat heart presenting isoproterenol-induced hypertrophy. Renin, angiotensin-converting enzyme (ACE), and angiotensinogen (AG) expression were also determined. Wistar rats were treated with isoproterenol for 7 days (5 mg x kg(-1) x day(-1) sc). For untreated animals, the levels of tonin-specific activity in the atrium were 2.6- and 5.5-fold higher than those of the left and right ventricle, respectively. After treatment, the levels of tonin-specific activity increased twofold in the atrium but did not change in the ventricles. Renin expression was not detectable in these structures, and ACE expression levels did not change with treatment. AG expression was detected in the left ventricle at very low levels compared with the atrium and increased significantly only in the hypertrophied atrium (1.8-fold). Tonin mRNA was not detected in the ventricle but was found at low levels in the atrium, which increased after isoproterenol treatment. Our results permit us to conclude that tonin may play a role in the process of heart hypertrophy in the rat.

Towards the understanding of the local hematopoietic bone marrow renin-angiotensin system

The classical view of the renin-angiotensin system (RAS) as a circulating endocrine system has evolved to organ- and tissue-based systems that perform paracrine/autocrine functions. Angiotensin II (Ang II), the dominant effector peptide of the RAS, regulates cellular growth in a wide variety of tissues in (patho)biological states. In 1996, we hypothesized that there exists a locally active RAS in the bone marrow affecting the growth, production, proliferation and differentiation of hematopoietic cells. Evidences supporting this hypothesis are growing. Ang II, through interacting with Ang II type 1 (AT1) receptor stimulates erythroid differentiation. This stimulatory effect of Ang II on erythropoiesis was completely abolished by a specific AT1 receptor antagonist, losartan. AT1a receptors are present on human CD34(+) hematopoietic stem cells. Ang II increases hematopoietic progenitor cell proliferation and this effect was also blocked by losartan. Angiotensin-converting enzyme (ACE) is involved in enhancing the recruitment of primitive stem cells into S-phase in hematopoietic bone marrow by degrading tetrapeptide AcSDKP. ACE inhibitors modified the circulating hematopoietic progenitors in healthy subjects. RAS may also affect pathological/neoplastic hematopoiesis. Renin has been isolated from leukemic blast cells. Higher bone marrow ACE levels in acute leukemic patients suggested that ACE is produced at higher quantities in the leukemic bone marrow. In this review, the 'State of the Art' of the local bone marrow RAS is summarized. A local RAS in the bone marrow can mediate, in an autocrine/paracrine fashion, some of the principal steps of hematopoietic cell production. To show a causal link between the components of RAS and the other regulatory hematopoietic growth factors is not only an academic curiosity. Elucidation of such a local bone marrow system may offer novel therapeutic approaches in pathologic/neoplastic conditions.

Regulation of insulin-like growth factor-1 by the renin-angiotensin system during regression of cardiac eccentric hypertrophy through angiotensin-converting enzyme inhibitor and AT1 antagonist

Angiotensin II (Ang II) mediates its effects through its non-tyrosine-kinase G protein coupled Ang-II type 1 receptor (AT1). Growing evidence indicates that a functional insulin-like growth factor-1 (IGF-1) tyrosine kinase receptor is required for Ang-II-induced mitogenesis. Along with Ang II, we have previously shown that changes in IGF-1 receptor binding at myofibers are causative agents for cardiac eccentric hypertrophy. This study investigated the interaction of the renin-angiotensin system with the IGF-1 receptor during the development and regression of cardiac hypertrophy. Alterations in IGF-1 binding were evaluated in the CHAPS-pretreated perfused heart. Four weeks of aortocaval shunt increased relative heart mass by 76% without a major change in body mass or systolic blood pressure. Binding studies showed that IGF-1 has a higher affinity for the cardiac myofibers of shunt than sham rats. Two weeks of treatment with the angiotensin-converting enzyme (ACE) inhibitor captopril (0.5 g/L in drinking water) or the AT1-antagonist losartan (10 mg/(kg x day)) reduced cardiac hypertrophy by 54 and 42%, respectively. However, while both ACE inhibition and AT1-antagonist treatments produced equivalent regression in ventricular hypertrophy, captopril was more efficacious than losartan in the regression of atrial hypertrophy. Regression of cardiac hypertrophy in the shunt by either captopril or losartan was accompanied with a reduction or normalization of the elevated IGF-1 affinity. Thus, the induction and regression of cardiac eccentric hypertrophy seems to be largely dependent on cross talk between the renin-angiotensin system and the IGF-1 axis at the receptor level.

Two-dimensional and M-mode echocardiographic predictors of disease severity in dogs with congenital subaortic stenosis

Echocardiographic studies from 50 dogs with congenital subaortic stenosis were examined. The degree of concentric, left-ventricular hypertrophy as assessed by M-mode measurement demonstrated a positive relationship (P<0.05) to disease severity. However, the clinical utility of these measures is hindered by a large amount of individual variation (r2=0.243 to 0.473). Two-dimensional ultrasound was used to compare the cross-sectional area of the left-ventricular outflow tract to the cross-sectional area of the aortic root. The ratio of these two areas demonstrated a strong inverse relationship (P=0.001; r2=0.778) with disease severity. This ratio provides a method of estimating severity of disease by two-dimensional echocardiography.

Permanent cardiovascular protection from hypertension by the AT(1) receptor antisense gene therapy in hypertensive rat offspring

Our previous studies have demonstrated that the introduction of angiotensin II type I receptor antisense (AT(1)R-AS) cDNA by a retrovirally mediated delivery system prevents the development of hypertension in the spontaneously hypertensive rat (SHR), an animal model for primary hypertension in humans. These results have led us to propose the hypothesis that an interruption of the renin-angiotensin system (RAS) activity at a genetic level would prevent hypertension on a permanent basis. F(1) and F(2) generations of offspring from a retroviral vector, LNSV- and LNSV-AT(1)R-AS-treated SHR, were generated, and various physiological parameters indicative of hypertension were studied and compared with those of their parents to investigate this hypothesis. Both F(1) and F(2) generations of LNSV-AT(1)R-AS-treated SHR expressed a persistently lower blood pressure, decreased cardiac hypertrophy and fibrosis, decreased medial thickness, and normalization of renal artery excitation-contraction coupling, Ca(2+) current, and [Ca(2+)](i) when compared with offspring derived from the LNSV-treated SHR. In fact, the magnitude of the prevention of these pathophysiological alterations was similar to that observed in the LNSV-AT(1)R-AS-treated SHR parent. The prevention of cardiovascular pathophysiology and expression of normotensive phenotypes are, at least in part, a result of integration and subsequent transmission of AT(1)R-AS from the SHR parents to offspring. These data demonstrate that a single intracardiac injection of LNSV-AT(1)R-AS causes a permanent cardiovascular protection against hypertension as a result of a genomic integration and germ line transmission of the AT(1)R-AS in the SHR offspring.

Protective action of angiotensin converting enzyme inhibitors on cardiac hypertrophy in the aortic-banded rat

Imidapril, enalapril and quinapril were subcutaneously administered to aortic-banded rats by osmotic minipumps to compare the suppressive actions of these angiotensin converting enzyme (ACE) inhibitors on pressure-induced cardiac hypertrophy. Among the three drugs tested, imidapril was most potent for the prevention of cardiac hypertrophy, although equipotent hypotensive doses were used. Imidapril reduced both serum and cardiac ACE activities, while enalapril reduced only the former. Quinapril also reduced both, however, it was less potent at reducing the former compared to imidapril. Moreover, only imidapril significantly decreased left ventricular end diastolic pressure, which tended to be increased by aortic-banding. The lipophilicity of ACE inhibitors could not explain the more potent suppressive action of imidapril on cardiac hypertrophy because the lipophilicity of imidaprilat, an active metabolite of imidapril, was as low as an active metabolite of enalapril; i.e., much lower than an active metabolite of quinapril. The efficacy of ACE inhibitors on pressure-induced cardiac hypertrophy depends not only on an inhibitory effect on cardiac ACE activity, but also on other actions such as their effect on left ventricular end diastolic pressure.

Blockade of AT(1) receptors and Na(+)/H(+) exchanger and LV dysfunction after myocardial infarction in rats

Mechanical stretch, ANG II, and alpha(1)-receptor stimulation may contribute to cardiac remodeling after myocardial infarction (MI). Each of these mechanisms involves different signaling pathways for the cellular hypertrophic response. All three also activate the Na(+)/H(+) exchanger. In the present study we evaluated the hypothesis that activation of the Na(+)/H(+) exchanger is involved in parallel with other signaling mechanisms for ANG II. Three days before coronary artery ligation, rats were randomly allocated to no treatment or treatment with amiloride, losartan, or amiloride and losartan in combination. Four weeks after coronary artery ligation, left ventricular (LV) function was assessed from in vivo resting cardiac pressures, hemodynamic responses to cardiac volume and pressure load, and cardiac remodeling by in vitro pressure-volume curves and LV and right ventricle (RV) weight. Amiloride and losartan given alone to a similar extent attenuated the shift of the pressure-volume curve to the right. This effect was significantly more pronounced with amiloride and losartan in combination. Each drug alone to a minor extent improved LV responses to pressure and volume load. However, with amiloride and losartan in combination, close-to-normal responses to pressure and volume load were observed. Losartan and amiloride alone had only a small effect on development of RV hypertrophy after MI but in combination completely prevented the RV hypertrophy. Amiloride and losartan appear to be complementary in prevention of cardiac remodeling and LV dysfunction after MI. This finding suggests that, besides ANG II, other mechanisms activating the Na(+)/H(+) exchanger contribute to cardiac remodeling after MI.

Dietary-sodium-induced cardiac remodeling in spontaneously hypertensive rat versus Wistar-Kyoto rat

OBJECTIVE

To study the effects of short-term and long-term high sodium intake on cardiac mass and design in sodium-sensitive spontaneously hypertensive rats versus sodium-resistant Wistar-Kyoto rats.

METHODS

Young spontaneously hypertensive rats and Wistar-Kyoto rats were randomly allocated to control diet, 2 or 8% dietary sodium for 2-12 weeks and changes in resting hemodynamics, cardiac angiotensin II level, sympathetic activity and cardiac structure evaluated. Sympathetic activity was assessed by measuring levels of plasma catecholamines, responses of blood pressure to ganglionic blockade, and rates of cardiac turnover of norepinephrine.

RESULTS

High sodium intake for 4 weeks increased left ventricle weight of Wistar-Kyoto rats aged 4 weeks (by 11 and 25% for 2 and 8% NaCl diets, respectively). This hypertrophic response was temporary, however, had already diminished after 6 weeks, and was absent after 12 weeks of a high sodium intake. However, after prolonged exposure concentric remodeling occurred (i.e. left ventricle wall thickness : radius ratio increased with no change in left ventricle mass). High sodium intake did not affect resting blood pressure, cardiac index, cardiac angiotensin II level, and general sympathetic activity of Wistar-Kyoto rats. Short-term high sodium intake did not increase left ventricle mass of young spontaneously hypertensive rats, unless sodium intake was so high (8% NaCl) that blood pressure and general sympathetic activity increased, too. However, a prolonged moderate (2%) increase in sodium intake also caused concentric remodeling in spontaneously hypertensive rats without increasing left ventricle mass, blood pressure, cardiac index, and general and cardiac sympathetic activities.

CONCLUSIONS

The blood pressure in young Wistar-Kyoto rats is sodium-insensitive but the heart structure is sodium-sensitive and high dietary sodium intake causes an early hypertrophic response, and then concentric remodeling. In contrast, hypertrophic response appears to occur after the response of blood pressure in spontaneously hypertensive rats, whereas the remodeling is similar to that in Wistar-Kyoto rats.