Intracellular angiotensin II disrupts chemical communication and impairs metabolic cooperation between cardiac myocytes

The influence of intracellular angiotensin II (Ang II) on the process of chemical communication and metabolic cooperation between cardiac cells is discussed. Emphasis is given to the influence of pathological conditions like heart failure, myocardial ischemia or hyperglycemia on the activation of the intracrine renin angiotensin aldosterone system (RAAS) and its consequence for the metabolic cooperation between heart cells. Furthermore, the influence of high glucose on the process of chemical communication was described as well as its implication for the failing and diabetic heart. The major conclusion is that the activation of the intracrine renin angiotensin induced by heart failure, hyperglycemia, aldosterone or myocardial ischemia generates metabolic imbalance in the heart with serious consequences for the cardiac function.     

Novel aspects of angiotensin II action in the heart. Implications to myocardial ischemia and heart failure

The influence of angiotensin II (Ang II) on cardiac structural and electrophysiological remodeling was discussed including the novel concept that the renin angiotensin aldosterone is involved in the regulation heart cell volume. Particular attention was given to the role of Ang II AT1 receptors as mechanosensors which are activated by mechanic stretch independently of Ang II. These findings highly suggest that RAS inhibitors or AT1 receptor blockers have additional beneficial therapeutics effects by changing mechanical transduction. The influence of cell swelling on cell communication as well as the effect of Ang II on cell volume and the consequent activation of ionic channels and the generation of cardiac arrhythmias was reviewed. The discovery of ACE2 and its relevance to heart pathology was also discussed.     

Local renin-angiotensin systems

The existence of a local cardiovascular renin-angiotensin system (RAS) is often invoked to explain the long-term beneficial effects of RAS inhibitors in heart failure and hypertension. The implicit assumption is that all components of the RAS are synthesized in situ, so that local angiotensin II formation may occur independently of the circulating RAS. Evidence for this assumption however is lacking. The angiotensin release from isolated perfused rat hearts or hindlimbs depends on the presence of renal renin. When calculating the in vivo angiotensin production at tissue sites in humans and pigs, taking into account the extensive regional angiotensin clearance by infusing radiolabeled angiotensin I or II, it was found that angiotensin production correlated closely with plasma renin activity. Moreover, in pigs the cardiac tissue levels of renin and angiotensin were directly correlated with their respective plasma levels, and both in tissue and plasma the levels were undetectably low after nephrectomy. Similarly, rat vascular renin and angiotensin decrease to low or undetectable levels within 48 h after nephrectomy. Aortic renin has a longer half life than plasma renin, suggesting that renin may be bound by the vessel wall. In support of this assumption, both renin receptors and renin-binding proteins have been described. Like ACE, renin was enriched in a purified membrane fraction prepared from cardiac tissue. Binding of renin to cardiac or vascular membranes may therefore be part of a mechanism by which renin is taken up from plasma. It appears that the concept of a local RAS needs to be reassessed. Local angiotensin formation in heart and vessel wall does occur, but depends, at least under normal circumstances, on the uptake of renal renin from the circulation. Tissues may regulate their local angiotensin concentrations by varying the number of renin receptors and/or renin-binding proteins, the ACE level, the amount of metabolizing enzymes and the angiotensin receptor density.Abbreviations RAS renin-angiotensin system - ANG angiotensin - ACE angiotensin-converting enzyme - PRA plasma renin activity     

The role of local and systemic renin angiotensin system activation in a genetic model of sympathetic hyperactivity-induced heart failure in mice

Sympathetic hyperactivity (SH) and renin angiotensin system (RAS) activation are commonly associated with heart failure (HF), even though the relative contribution of these factors to the cardiac derangement is less understood. The role of SH on RAS components and its consequences for the HF were investigated in mice lacking alpha(2A) and alpha(2C) adrenoceptor knockout (alpha(2A)/alpha(2C)ARKO) that present SH with evidence of HF by 7 mo of age. Cardiac and systemic RAS components and plasma norepinephrine (PN) levels were evaluated in male adult mice at 3 and 7 mo of age. In addition, cardiac morphometric analysis, collagen content, exercise tolerance, and hemodynamic assessments were made. At 3 mo, alpha(2A)/alpha(2C)ARKO mice showed no signs of HF, while displaying elevated PN, activation of local and systemic RAS components, and increased cardiomyocyte width (16%) compared with wild-type mice (WT). In contrast, at 7 mo, alpha(2A)/alpha(2C)ARKO mice presented clear signs of HF accompanied only by cardiac activation of angiotensinogen and ANG II levels and increased collagen content (twofold). Consistent with this local activation of RAS, 8 wk of ANG II AT(1) receptor blocker treatment restored cardiac structure and function comparable to the WT. Collectively, these data provide direct evidence that cardiac RAS activation plays a major role underlying the structural and functional abnormalities associated with a genetic SH-induced HF in mice.     

Proteases and antiproteases in the progression of chronic renal insufficiency lesions. The role of the tissue renin-angiotensin system and the renin receptor

The role of proteases and of antiproteases in the progression of renal disease is well established. Most studies have focused on the serine-proteases of the plasmin/plasminogen activator system and on matrix metalloproteases. Recently, renin, an aspartyl-protease, has attracted much attention because of the role of angiotensin II in the progression of renal lesions and because of the discovery of a functional renin receptor. This receptor is a 45 kDa membrane-protein that binds specifically renin and prorenin. The binding of renin induces an increase of the catalytic efficiency of angiotensinogen conversion into angiotensin I by receptor-bound renin compared to renin in soluble phase, and a rapid phosphorylation of the receptor on serine and tyrosine residues associated with an activation of MAP kinases ERK1/2. Immunofluorescence and confocal analyses on normal human kidney and cardiac biopsies show that the receptor is localized within the mesangial area of glomeruli and in the sub-endothelium of kidney and coronary arteries, associated to smooth-muscle cells. In summary, this receptor exerts dual effects, mediating renin cellular response and increasing the efficiency of angiotensinogen cleavage by membrane-bound renin. These observations emphasizes the importance of angiotensin II generation at the cell surface and the cellular effects of renin add new dimensions (and complexity) to the classical dogma that angiotensin II is the only effector of the RAS.     

High Salt Intake Damages the Heart through Activation of Cardiac (Pro) Renin Receptors Even at an Early Stage of Hypertension

Objective

It has not yet been fully elucidated whether cardiac tissue levels of prorenin, renin and (P)RR are activated in hypertension with a high salt intake. We hypothesized that a high salt intake activates the cardiac tissue renin angiotensin system and prorenin-(pro)renin receptor system, and damages the heart at an early stage of hypertension.

Methods

Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) received regular (normal-salt diet, 0.9%) and high-salt (8.9%) chow for 6 weeks from 6 to 12 weeks of age. The systolic blood pressure, plasma renin activity (PRA) and plasma angiotensin II concentration were measured, and the protein expressions of prorenin, (pro)renin receptor, angiotensinogen, angiotensin II AT1 receptor, ERK1/2, TGF-β, p38MAPK and HSP27 in the myocardium were investigated. The cardiac function was assessed by echocardiography, and histological analysis of the myocardium was performed.

Results

The high-salt diet significantly increased the systolic blood pressure, and significantly reduced the PRA and plasma angiotensin II concentration both in the WKYs and SHRs. Cardiac expressions of prorenin, renin, (P)RR, angiotensinogen, angiotensin II AT1 receptor, phosphorylated (p)-ERK1/2, p-p38MAPK, TGF-β and p-HSP27 were significantly increased by the high salt diet both in the WKYs and SHRs. The high-salt diet significantly increased the interventricular septum thickness and cardiomyocyte size, and accelerated cardiac interstitial and perivascular fibrosis both in the WKYs and SHRs. On the other hand, dilatation of left ventricular end-diastolic dimension and impairment of left ventricular fractional shortening was shown only in salt loaded SHRs.

Conclusion

The high-salt diet markedly accelerated cardiac damage through the stimulation of cardiac (P)RR and angiotensin II AT1 receptor by increasing tissue prorenin, renin and angiotensinogen and the activation of ERK1/2, TGF-β, p38MAPK and HSP27 under higher blood pressure.     

Presence of renin, angiotensinogen, angiotensin II in the lamb anterior pituitary gland: immunocytochemical study after cryoultramicrotomy.

The presence of renin, angiotensin I-converting enzyme and angiotensin II detected by immunocytochemistry in the adult male rat anterior pituitary has suggested the existence of a pituitary renin-angiotensin system. To establish another mammalian experimental model we have investigated the presence of renin, angiotensinogen, angiotensin I-converting enzyme, and angiotensin II II in five normal lamb anterior pituitaries by immunocytochemistry after cryoultramicrotomy. Renin, angiotensinogen and angiotensin II immunoreactivities were observed only in cytoplasmic granules of lactotrophs, and the three proteins were found co-localized with prolactin in the same granules by double immunolabelling. No immunoreactive angiotensin I-converting enzyme was observed. These results suggest an activation of renin in the cytoplasmic granules of lactotrophs leading to a local synthesis of angiotensin II. Thus, the lamb anterior pituitary may provide a good experimental model for investigating the possible autocrine action of a local renin-angiotensin system on prolactin release in the human pituitary.     

RAS inhibition in resident fibroblast biology

Angiotensin II (Ang II) is a primary mediator of profibrotic signaling in the heart and more specifically, the cardiac fibroblast. Ang II-mediated cardiomyocyte hypertrophy in combination with cardiac fibroblast proliferation, activation, and extracellular matrix production compromise cardiac function and increase mortality in humans. Profibrotic actions of Ang II are mediated by increasing production of fibrogenic mediators (e.g. transforming growth factor beta, scleraxis, osteopontin, and periostin), recruitment of immune cells, and via increased reactive oxygen species generation. Drugs that inhibit Ang II production or action, collectively referred to as renin angiotensin system (RAS) inhibitors, are first line therapeutics for heart failure. Moreover, transient RAS inhibition has been found to persistently alter hypertensive cardiac fibroblast responses to injury providing a useful tool to identify novel therapeutic targets. This review summarizes the profibrotic actions of Ang II and the known impact of RAS inhibition on cardiac fibroblast phenotype and cardiac remodeling.     

The role of Jak/STAT signaling in heart tissue renin-angiotensin system

The involvement of the Renin Angiotensin System (RAS) and the role of its primary effector, angiotensin II (Ang II), in etiology of myocardial hypertrophy and ischemia is well documented. In several animal models, the RAS is activated in cardiac cell types that express the receptor AT₁, and/or AT₂, through which the Ang II mediated effects are promoted. In this article, we briefly review recent experimental evidence on the critical role of a prominent signaling pathway, the Jak/Stat pathway in activation and maintenance of the local RAS in cardiac hypertrophy and ischemia. Recent studies in our laboratory document that the promoter of the prohormone angiotensinogen (Ang) gene serves as the target site for STAT proteins, thereby linking the Jak/Stat pathway to activation of heart tissue autocrine Ang II loop. Stat5A and Stat6, are selectively activated when the heart is subjected to ischemic injury, whereas activation of Stat3 and Stat5A is involved in myocardial hypertrophy. Blockage of RAS activation by treatment with specific inhibitor promotes a remarkable recovery in functional hemodynamics of the myocardium. Thus, activation of selective sets of Stat proteins constitutes the primary signaling event in the pathogenesis of myocardial hypertrophy and ischemia.     

Presence of renin,angiotensinogen, angiotensin II in the lamb anterior pituitary gland: immunocytochemical study after cryoultramicrotomy

Summary The presence of renin, angiotensin I-converting enzyme and angiotensin II detected by immunocytochemistry in the adult male rat anterior pituitary has suggested the existence of a pituitary renin-angiotensin system. To establish another mammalian experimental model we have investigated the presence of renin, angiotensinogen, angiotensin I-converting enzyme, and angiotensin II in five normal lamb anterior pituitaries by immunocytochemistry after cryoultramicrotomy. Renin, angiotensinogen and angiotensin II immunoreactivities were observed only in cytoplasmic granules of lactotrophs, and the three proteins were found co-localized with prolactin in the same granules by double immunolabelling. No immunoreactive angiotensin I-converting enzyme was observed. These results suggest an activation of renin in the cytoplasmic granules of lactotrophs leading to a local synthesis of angiotensin II. Thus, the lamb anterior pituitary may provide a good experimental model for investigating the possible autocrine action of a local renin-angiotensin system on prolactin release in the human pituitary.     

Renin substrate and the renin-angiotensin system in hog tissues

The individual components of the renin-angiotensin system has been identified in numerous tissues. In this study we have examined whether a functional renin-angiotensin system is operative in several hog tissues including brain, aorta, and liver. The contribution of tissue renin substrate to the rate of local angiotensin generation was also assessed. Electrophoretic differences in plasma and tissue renin substrates, indicating structural differences, were employed as an index of independence of the tissue system from that of the peripheral circulation. Our results indicate that all tissues studied had the potential to locally generate angiotensin and that renin substrate limited to rate of the renin reaction in these tissues. Electrophoretic parameters, polyacrylamide gel electrophoresis, and isoelectric focusing suggest that the tissue renin systems are of local origin. The potential magnitude of local angiotensin production is such that tissue renin-angiotensin systems may significantly contribute to the control and regulation of blood pressure and other regulatory mechanisms influenced by angiotensin.     

Increased mRNA expression of cardiac renin-angiotensin system and collagen synthesis in spontaneously hypertensive rats

Hypertensive cardiac hypertrophy is associated with the accumulation of collagen in the myocardial interstitium. Previous studies have demonstrated that this myocardial fibrosis accounts for impaired myocardial stiffness and ventricular dysfunction. Although cardiac fibroblasts are responsible for the synthesis of fibrillar collagen, the factors that regulate collagen synthesis in cardiac fibroblasts are not fully understood. We investigated the effects of angiotensin II on cardiac collagen synthesis in cardiac fibroblasts. Cardiac fibroblasts of 10 week old spontaneously hypertensive rats and age-matched Wistar-Kyoto rats were prepared and maintained in culture medium supplemented with 10% fetal calf serum. The expression of mRNA of the renin-angiotensin system (renin, angiotensinogen, angiotensin converting enzyme) was determined by using a ribonuclease protection assay. Basal collagen synthesis in cardiac fibroblasts from spontaneously hypertensive rats was 1.6 fold greater than that in the cell of Wistar-Kyoto rats. Angiotensin II stimulated collagen synthesis in cardiac fibroblasts in a dose-dependent manner. The responsiveness of collagen production to angiotensin II was significantly enhanced in cardiac fibroblasts from spontaneously hypertensive rats (100 nM angiotensin II resulted in 185 ± 18% increase above basal levels, 185 ± 18 versus 128 ± 19% in Wistar-Kyoto rats p < 0.01). This effect was receptor-specific, because it was blocked by the competitive inhibitor saralasin and MK 954. These results indicate that collagen production was enhanced in cardiac fibroblasts from spontaneously hypertensive rats, that angiotensin II had a stimulatory effect on collagen synthesis in cardiac fibroblasts, and that cardiac fibroblasts from spontaneously hypertensive rats were hyper-responsive to stimulation by angiotensin II.Level of angiotensin and renin mRNA expressed in ventricles, and angiotensinogen mRNA expressed in fibroblasts from SHR were higher than those from WKY.These findings suggest that the cardiac renin-angiotensin system may play an important role in collagen accumulation in hypertensive cardiac hypertrophy.     

Angiotensin II stimulates α-skeletal actin expression in cadiomyocytes in vitro and in vivo in the absence of hypertension

Using a specific alpha-skeletal actin antibody, we have previously shown, that during hypertension-associated cardiac hypertrophy in the rat, the expression of alpha-skeletal actin in the myocardium is increased, but maintains focal distribution, compared to normotensive animals. In the present study, we have investigated whether alpha-skeletal actin expression can be induced in the absence of hypertension. For this purpose, we have examined transgenic mice overexpressing angiotensinogen exclusively in the heart. These animals are characterized by high cardiac angiotensin II levels and cardiac hypertrophy accompanied or not by high blood pressure depending on their genetic background, i.e. presence of one or two renin genes. Alpha-skeletal actin levels were highly increased in transgenic compared to wild-type myocardium independently of the number of renin genes, indicating that angiotensin II can stimulate alpha-skeletal actin expression in normotensive animals. Additional in vitro experiments using cultured mouse and rat cardiomyocytes showed that angiotension II not only increases alpha-skeletal actin expression but also induces an increase of its incorporation within II-bands compared to control cardiomyocytes. Angiotensin II increases also the expression of alpha-smooth muscle actin in sarcomeres of cardiomyocytes as well as in fibroblastic cells present within the culture.     

Effects of Direct Renin Inhibition on Myocardial Fibrosis and Cardiac Fibroblast Function

Myocardial fibrosis, a major pathophysiologic substrate of heart failure with preserved ejection fraction (HFPEF), is modulated by multiple pathways including the renin-angiotensin system. Direct renin inhibition is a promising anti-fibrotic therapy since it attenuates the pro-fibrotic effects of renin in addition to that of other effectors of the renin-angiotensin cascade. Here we show that the oral renin inhibitor aliskiren has direct effects on collagen metabolism in cardiac fibroblasts and prevented myocardial collagen deposition in a non-hypertrophic mouse model of myocardial fibrosis. Adult mice were fed hyperhomocysteinemia-inducing diet to induce myocardial fibrosis and treated concomitantly with either vehicle or aliskiren for 12 weeks. Blood pressure and plasma angiotensin II levels were normal in control and hyperhomocysteinemic mice and reduced to levels lower than observed in the control group in the groups treated with aliskiren. Homocysteine-induced myocardial matrix gene expression and fibrosis were also prevented by aliskiren. In vitro studies using adult rat cardiac fibroblasts also showed that aliskiren attenuated the pro-fibrotic pattern of matrix gene and protein expression induced by D,L, homocysteine. Both in vivo and in vitro studies demonstrated that the Akt pathway was activated by homocysteine, and that treatment with aliskiren attenuated Akt activation. In conclusion, aliskiren as mono-therapy has potent and direct effects on myocardial matrix turnover and beneficial effects on diastolic function.     

Poly(ADP-ribose) polymerase-1-deficient mice are protected from angiotensin II-induced cardiac hypertrophy

Poly(ADP-ribose) polymerase-1 (PARP), a chromatin-bound enzyme, is activated by cell oxidative stress. Because oxidative stress is also considered a main component of angiotensin II-mediated cell signaling, it was postulated that PARP could be a downstream target of angiotensin II-induced signaling leading to cardiac hypertrophy. To determine a role of PARP in angiotensin II-induced hypertrophy, we infused angiotensin II into wild-type (PARP(+/+)) and PARP-deficient mice. Angiotensin II infusion significantly increased heart weight-to-tibia length ratio, myocyte cross-sectional area, and interstitial fibrosis in PARP(+/+) but not in PARP(-/-) mice. To confirm these results, we analyzed the effect of angiotensin II in primary cultures of cardiomyocytes. When compared with PARP(-/-) cardiomyocytes, angiotensin II (1 microM) treatment significantly increased protein synthesis in PARP(+/+) myocytes, as measured by (3)H-leucine incorporation into total cell protein. Angiotensin II-mediated hypertrophy of myocytes was accompanied with increased poly-ADP-ribosylation of nuclear proteins and depletion of cellular NAD content. When cells were treated with cell death-inducing doses of angiotensin II (10-20 microM), robust myocyte cell death was observed in PARP(+/+) but not in PARP(-/-) myocytes. This type of cell death was blocked by repletion of cellular NAD levels as well as by activation of the longevity factor Sir2alpha deacetylase, indicating that PARP induction and subsequent depletion of NAD levels are the sequence of events causing angiotensin II-mediated cardiomyocyte cell death. In conclusion, these results demonstrate that PARP is a nuclear integrator of angiotensin II-mediated cell signaling contributing to cardiac hypertrophy and suggest that this could be a novel therapeutic target for the management of heart failure.     

ICS II protects against cardiac hypertrophy by regulating metabolic remodelling,not by inhibiting autophagy

Cardiac hypertrophy is characterized by a shift in metabolic substrate utilization. Therefore, the regulation of ketone body uptake and metabolism may have beneficial effects on heart injuries that induce cardiac remodelling. In this study, we investigated whether icariside II (ICS II) protects against cardiac hypertrophy in mice and cardiomyocytes. To create cardiac hypertrophy animal and cell models, mice were subjected to transverse aortic constriction (TAC), and embryonic rat cardiomyocytes (H9C2) were stimulated with angiotensin II, a neurohumoral stressor. Both the in vivo and in vitro results suggest that ICS II treatment ameliorated pressure overload–induced cardiac hypertrophy and preserved heart function. In addition, apoptosis and oxidative stress were reduced in the presence of ICS II. Moreover, ICS II inhibited excess autophagy in TAC-induced hearts and angiotensin II–stimulated cardiomyocytes. Mechanistically, we found that ICS II administration regulated SIRT3 expression in cardiac remodelling. SIRT3 activation increased ketone body transportation and utilization. Collectively, our data show that ICS II attenuated cardiac hypertrophy by modulating ketone body and fatty acid metabolism, and that this was likely due to the activation of the SIRT3-AMPK pathway. ICS II treatment may provide a new therapeutic strategy for improving myocardial metabolism in cardiac hypertrophy and heart failure.