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.     

Angiotensinogen and angiotensin-converting enzyme mRNA decrease and AT1 receptor mRNA and protein increase in epididymal fat tissue accompany age-induced elevation of adiposity and reductions in expression of GLUT4 and peroxisome proliferator-activated receptor (PPARγ)

Elevated adiposity is one of the accompanying features of increased age in humans and animals. Angiotensin II (Ang II) is considered as growth promoting peptide to be involved in hypertrophic enlargement of adipose tissue. However, systemic renin-angiotensin system (RAS) seems to decrease with increased age of rats. Local adipose tissue RAS might be independent of the systemic one. Therefore we performed a comprehensive study using rats with increased age from 9 to 26 weeks and evaluated angiotensinogen, angiotensin-converting enzyme (ACE) and AT(1) receptor mRNA in epididymal adipose tissue by RT-PCR. In addition, we determined AT(1) receptor protein by Western blotting and Ang II binding. These RAS parameters were correlated with expression of selected adiposity-dependent proteins such as leptin, adiponectin, insulin-dependent glucose transporter (GLUT4) and PPARgamma. Angiotensinogen and ACE expression decreased with increased age and adiposity. On the contrary, AT(1) receptor mRNA and protein was significantly elevated in 26-week-old rats though the Ang II binding was not different between 9 and 26-week-old animals. These results suggest dynamic adaptation of local adipose tissue RAS components to increased age and adiposity most likely by decreasing local Ang II formation which is thereafter compensated by increased expression of AT(1) receptor. However, this increase in AT(1) receptor mRNA and protein is not reflected in increased receptor binding. We believe that this complex regulation of adipose tissue RAS slows down the negative age and adiposity related changes in adipose tissue leptin, adiponectin, GLUT4 and PPARgamma.     

Distribution of angiotensin-converting enzyme and angiotensin II-receptor binding sites in the rat ovary

Recent reports of the presence of components of the renin-angiotensin system (RAS) in the mammalian ovary suggest that angiotensin II (Ang II) may be elaborated by this structure. In this study, angiotensin-converting enzyme (ACE), a key enzyme in the synthesis of Ang II, was identified enzymatically and localized to the germinal epithelium surrounding corpora lutea, granulosa cells of some--but not all--follicles, and blood vessels of the rat ovary using a potent and specific radiolabeled ACE inhibitor, 125I-351A. Follicles that bound 125I-351A also contained Ang II-receptor binding sites. Co-localization of RAS components to the follicular granulosa cells and the ability of Ang II to promote estrogen formation suggest that the ovarian RAS may promote follicular development and assertion of dominance.     

Counteraction between angiotensin II and angiotensin-(1-7) via activating angiotensin type I and Mas receptor on rat renal mesangial cells

In the updated concept of renin-angiotensin system (RAS), it contains the angiotensin converting enzyme (ACE)-angiotensin (Ang) II-angtiogensin type 1 receptor (AT1) axis and the angiotensin-converting enzyme-related carboxypeptidase (ACE2)-Ang-(1-7)-Mas axis. The former axis has been well demonstrated performing the vasoconstrictive, proliferative and pro-inflammatory functions by activation of AT1 receptors, while the later new identified axis is considered counterbalancing the effects of the former. The present study is aimed at observing the interaction between Ang-(1-7) and Ang II on cultured rat renal mesangial cells (MCs). RT-PCR, Western blot and immunofluorescent staining and confocal microscopy results showed that both AT1 and Mas receptor were co-distributed in rat renal MCs. Ang-(1-7) showed similar effects on Ang II in cultured MCs that stimulated phosphorylated extracellular signal-regulated kinase (ERK)1/2 phosphorylation and transforms growth factor-β1 synthesis, and cell proliferation and extracellular matrix synthesis. Co-treatment of the cell with Ang-(1-7) and Ang II, Ang-(1-7) counteracted AngII-induced effects in a concentration dependent manner, but failed to alter the changes induced by endothelin-1. The stimulating effect of Ang II was mediated by AT1 receptor while all the effects of Ang-(1-7) were blocked by Mas receptor antagonist A-779, but not by AT1 receptor antagonist losartan or AT2 receptor antagonist PD123319. These results suggest that Ang-(1-7) and Ang II specifically interact with each other on rat renal MCs via activation of their specific receptors, Mas and AT1 receptor respectively.     

Localization of the renin-angiotensin system in the bovine ovary: cyclic variation of the angiotensin II receptor expression.

Angiotensin (Ang) II may modulate reproductive function in the bovine ovary. Therefore, expression and localization of a local ovarian renin-angiotensin system (RAS) were investigated by elucidating the influence of the estrus cycle, pregnancy, and the presence of follicular cysts. Receptor analysis and autoradiography were used to characterize and localize Ang II receptors. Cyclic variations in the density of ovarian Ang II receptors were found with a higher value in estrus than in diestrus. The density in ovaries with follicular cysts was in the same order of magnitude as in estrus. The Ang II receptor type 2 (AT(2)) dominated in all three groups. Autoradiography showed that the majority of antral follicles and follicular cysts had intense AT(2) receptor binding in the theca externa. Binding was less intense in the theca interna, whereas there was no binding in the granulosa layer. In the corpora lutea, the AT(2) receptor was dominant in the capsule and in connective tissue infoldings, whereas no binding was observed in the luteal tissue. The type 1 Ang II receptor (AT(1)) was dominant in the stroma and showed no cyclic changes. Angiotensin-converting enzyme (ACE) activity was detected in all aspirated follicular fluids and homogenates of ovarian tissue. Autoradiography showed that most of the ACE was localized on endothelial cells. Renin immunoreactivity was found in granulosa and thecal cells of antral follicles and in luteal cells. Furthermore, solitary cells in the stroma, presumably macrophages, displayed intense staining. Our finding of cyclic changes support the concept of an active and regulated RAS in the bovine ovary.     

The levels of renin-angiotensin related components are modified in the hippocampus of rats submitted to pilocarpine model of epilepsy

We previously showed that patients with temporal lobe epilepsy (TLE) present an increased expression of angiotensin II (AngII) AT1 and AT2 receptors in the hippocampus, supporting the idea of an upregulation of renin-angiotensin system (RAS) in this disease. This study aimed to verify the relationship between the RAS and TLE during epileptogenesis. Levels of the peptides angiotensin I (AngI), angiotensin II (AngII) and angiotensin 1-7 (Ang 1-7), were detected by HPLC assay. Angiotensin AT1 and AT2 receptors, Mas mRNA receptors and angiotensin converting enzyme (ACE), tonin and neutral endopeptidase (NEP) mRNA were also quantified at the hippocampus of Wistar rats by real time PCR, during acute (n=10), silent (n=10) and chronic (n=10) phases of pilocarpine-induced epilepsy. We observed an increased peptide level of Ang1-7 into acute and silent phases, decreasing importantly (p≤0.05) in the chronic phase, suggesting that AngI may be converted into Ang 1-7 by NEP, which is present in high levels in these periods. Our results also showed increased peptide level of AngII in the chronic phase of this model. In contraposition, the ACE expression is reduced in all periods. These data suggest that angiotensinogen or AngI may be cleaved to AngII by tonin, which showed increased expression in all phases. We found changes in AT1, AT2 and Mas mRNA receptors levels suggesting that Ang1-7 could act at Mas receptor during the silent period. Herein, we demonstrated for the first time, changes in angiotensin-related peptides, their receptors as well as the releasing enzymes in the hippocampus of rats during pilocarpine-induced epilepsy.     

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.     

Angiotensin II bi-directionally regulates cyclooxygenase-2 expression in intestinal epithelial cells

We previously demonstrated that angiotensin II (Ang II) receptor signaling is involved in azoxymethane-induced mouse colon tumorigenesis. In order to clarify the role of Ang II in COX-2 expression in the intestinal epithelium, the receptor subtype-specific effect on COX-2 expression in a rat intestinal epithelial cell line (RIE-1) has been investigated. Ang II dose- and time-dependently increased the expression of COX-2, but not COX-1 mRNA and protein. This stimulation was completely blocked by the AT(1) receptor antagonist but not the AT(2) receptor antagonist. Ang II and lipopolysaccharide (LPS) additively induced COX-2 protein in RIE-1 cells, whereas the LPS-induced COX-2 expression was significantly attenuated by low concentrations of Ang II or the AT(2) agonistic peptide CGP-42112A only in AT(2) over-expressed cells. These data indicate that Ang II bi-directionally regulates COX-2 expression via both AT(1) and AT(2) receptors. Control of COX-2 expression through Ang II signaling may have significance in cytokine-induced COX-2 induction and colon tumorigenesis.     

The CNS renin-angiotensin system

The renin-angiotensin system (RAS) is one of the best-studied enzyme-neuropeptide systems in the brain and can serve as a model for the action of peptides on neuronal function in general. It is now well established that the brain has its own intrinsic RAS with all its components present in the central nervous system. The RAS generates a family of bioactive angiotensin peptides with variable biological and neurobiological activities. These include angiotensin-(1–8) [Ang II], angiotensin-(3–8) [Ang IV], and angiotensin-(1–7) [Ang-(1–7)]. These neuroactive forms of angiotensin act through specific receptors. Only Ang II acts through two different high-specific receptors, termed AT1 and AT2. Neuronal AT1 receptors mediate the stimulatory actions of Ang II on blood pressure, water and salt intake, and the secretion of vasopressin. In contrast, neuronal AT2 receptors have been implicated in the stimulation of apoptosis and as being antagonistic to AT1 receptors. Among the many potential effects mediated by stimulation of AT2 are neuronal regeneration after injury and the inhibition of pathological growth. Ang-(1–7) mediates its antihypertensive effects by stimulating the synthesis and release of vasodilator prostaglandins and nitric oxide and by potentiating the hypotensive effects of bradykinin. New data concerning the roles of Ang IV and Ang-(1–7) in cognition also support the existence of complex site-specific interactions between multiple angiotensins and multiple receptors in the mediation of important central functions of the RAS. Thus, the RAS of the brain is involved not only in the regulation of blood pressure, but also in the modulation of multiple additional functions in the brain, including processes of sensory information, learning, and memory, and the regulation of emotional responses.     

The Interplay between the Renin Angiotensin System and Pacing Postconditioning Induced Cardiac Protection

BackgroundAccumulating evidence suggests a cardioprotective role of pacing postconditioning (PPC) maneuvers in animal models and more recently in humans. The procedure however remains to be optimized and its interaction with physiological systems remains to be further explored. The renin angiotensin system (RAS) plays a dual role in ischemia/reperfusion (I/R) injury. The interaction between RAS and PPC induced cardiac protection is however not clearly understood. We have recently demonstrated that angiotensin (1–7) via Mas receptor played a significant role in PPC mediated cardiac protection against I/R injury.ObjectiveThe objective of this study was to investigate the role of angiotensin converting enzyme (ACE)—chymase—angiotensin II (Ang II)—angiotensin receptor 1 (AT1) axes of RAS in PPC mediated cardiac protection.MethodsIsolated rat hearts were subjected to I/R (control) or PPC in the presence or absence of Ang II, chymostatin (inhibitor of locally produced Ang II), ACE blocker (captopril) or AT1 antagonist (irbesartan). Hemodynamics data was computed digitally and infarct size was determined histologically using TTC staining and biochemically by measuring creatine kinase (CK) and lactate dehydrogenase levels.ResultsCardiac hemodynamics were significantly (P<0.001) improved and infarct size and cardiac enzymes were significantly (P<0.001) reduced in hearts subjected to PPC relative to hearts subjected to I/R injury. Exogenous administration of Ang II did not affect I/R injury or PPC mediated protection. Nonetheless inhibition of endogenously synthesized Ang II protected against I/R induced cardiac damage yet did not block or augment the protective effects of PPC. The administration of AT1 antagonist did not alleviate I/R induced damage. Interestingly it abrogated PPC induced cardiac protection in isolated rat hearts. Finally, PPC induced protection and blockade of locally produced Ang II involved enhanced activation of ERK1/2 and Akt components of the reperfusion injury salvage kinase (RISK) pathway.ConclusionsThis study demonstrate a novel role of endogenously produced Ang II in mediating I/R injury and highlights the significance of AT1 signaling in PPC mediated cardiac protection in isolated rodents hearts ex vivo. The interaction between Ang II-AT1 and PPC appears to involve alterations in the activation state of ERK1/2 and Akt components of the RISK pathway.     

Role of brain renin angiotensin system in neurodegeneration: An update

Renin angiotensin system (RAS) is an endocrine system widely known for its physiological roles in electrolyte homeostasis, body fluid volume regulation and cardiovascular control in peripheral circulation. However, brain RAS is an independent form of RAS expressed locally in the brain, which is known to be involved in brain functions and disorders. There is strong evidence for a major involvement of excessive brain angiotensin converting enzyme (ACE)/Angiotensin II (Ang II)/Angiotensin type-1 receptor (AT-1R) axis in increased activation of oxidative stress, apoptosis and neuroinflammation causing neurodegeneration in several brain disorders. Numerous studies have demonstrated strong neuroprotective effects by blocking AT1R in these brain disorders. Additionally, the angiotensin converting enzyme 2 (ACE2)/Angiotensin (1–7)/Mas receptor (MASR), is another axis of brain RAS which counteracts the damaging effects of ACE/Ang II/AT1R axis on neurons in the brain. Thus, angiotensin II receptor blockers (ARBs) and activation of ACE2/Angiotensin (1–7)/MASR axis may serve as an exciting and novel method for neuroprotection in several neurodegenerative diseases. Here in this review article, we discuss the expression of RAS in the brain and highlight how altered RAS level may cause neurodegeneration. Understanding the pathophysiology of RAS and their links to neurodegeneration has enormous potential to identify potentially effective pharmacological tools to treat neurodegenerative diseases in the brain.     

ACE2 – From the renin–angiotensin system to gut microbiota and malnutrition

The renin–angiotensin system (RAS) is a complex network that regulates blood pressure, electrolyte and fluid homeostasis, as well as the function of several organs. Angiotensin-converting enzyme 2 (ACE2) was identified as an enzyme that negatively regulates the RAS by converting Ang II, the main bioactive molecule of the RAS, to Ang 1–7. Thus, ACE2 counteracts the role of angiotensin-converting enzyme (ACE) which generates Ang II from Ang I. ACE and ACE2 have been implicated in several pathologies such as cardiovascular and renal disease or acute lung injury. In addition, ACE2 has functions independent of the RAS: ACE2 is the receptor for the SARS coronavirus and ACE2 is essential for expression of neutral amino acid transporters in the gut. In this context, ACE2 modulates innate immunity and influences the composition of the gut microbiota, which can explain diarrhea and intestinal inflammation observed in Hartnup disorder, Pellagra, or under conditions of severe malnutrition. Here we review and discuss the diverse functions of ACE2 and its relevance to human pathologies.     

The physiological significance of the alternative pathways of angiotensin II production.

Although the use of angiotensin converting enzyme inhibitors (ACE-Is) in clinical practice brought the great chance to recognize the RAS role in the physiology and pathology, there are still many questions which we cannot answer. This article reviews actually known pathways of angiotensin II (Ang II) and other peptides of renin-angiotensin system (RAS) production and their physiological significance. The various carboxy- and aminopeptidases generate a range of peptides, like Ang II, Ang III, Ang IV, Ang-(1-7) and Ang-(1-9) possessing their own and known biological activity. In this issue especially the alternative pathways of Ang II synthesis involving enzymes other than angiotensin-converting enzyme (ACE) are discussed. We present many evidences for the significance of a new pathway of Ang II production. It has been clearly shown that Ang I may be converted to Ang-(1-9) by angiotensin-converting enzyme-related carboxypeptidase (ACE-2) and then into Ang II in some tissues, but the enzymes responsible for this process are unknown till now. Although there are many data proving the existence of alternative pathways of Ang II production, we can still block only ACE and angiotensin receptor 1 (AT(1)) in clinical practice. It seems that a lot needs to be done before we can wildly complexively control RAS and treat more effectively cardiovascular disorders such as hypertension or heart failure.     

High Na intake increases renal angiotensin II levels and reduces expression of the ACE2-AT(2)R-MasR axis in obese Zucker rats

High sodium intake is known to regulate the renal renin-angiotensin system (RAS) and is a risk factor for the pathogenesis of obesity-related hypertension. The complex nature of the RAS reveals that its various components may have opposing effects on natriuresis and blood pressure regulation. We hypothesized that high sodium intake differentially regulates and shifts a balance between opposing components of the renal RAS, namely, angiotensin-converting enzyme (ACE)-ANG II-type 1 ANG II receptor (AT(1)R) vs. AT(2)-ACE2-angiotensinogen (Ang) (1-7)-Mas receptor (MasR), in obesity. In the present study, we evaluated protein and/or mRNA expression of angiotensinogen, renin, AT(1A/B)R, ACE, AT(2)R, ACE2, and MasR in the kidney cortex following 2 wk of a 8% high-sodium (HS) diet in lean and obese Zucker rats. The expression data showed that the relative expression pattern of ACE and AT(1B)R increased, renin decreased, and ACE2, AT(2)R, and MasR remained unaltered in HS-fed lean rats. On the other hand, HS intake in obese rats caused an increase in the cortical expression of ACE, a decrease in ACE2, AT(2)R, and MasR, and no changes in renin and AT(1)R. The cortical levels of ANG II increased by threefold in obese rats on HS compared with obese rats on normal salt (NS), which was not different than in lean rats. The HS intake elevated mean arterial pressure in obese rats (27 mmHg) more than in lean rats (16 mmHg). This study suggests that HS intake causes a pronounced increase in ANG II levels and a reduction in the expression of the ACE2-AT(2)R-MasR axis in the kidney cortex of obese rats. We conclude that such changes may lead to the potentially unopposed function of AT(1)R, with its various cellular and physiological roles, including the contribution to the pathogenesis of obesity-related hypertension.     

Reduced plasma angiotensin II levels are reversed by hydroxyurea treatment in mice with sickle cell disease

Aims

Sickle cell disease (SCD) pathogenesis leads to recurrent vaso-occlusive and hemolytic processes, causing numerous clinical complications including renal damage. As vasoconstrictive mechanisms may be enhanced in SCD, due to endothelial dysfunction and vasoactive protein production, we aimed to determine whether the expression of proteins of the renin–angiotensin system (RAS) may be altered in an animal model of SCD.

Main methods

Plasma angiotensin II (Ang II) was measured in C57BL/6 (WT) mice and mice with SCD by ELISA, while quantitative PCR was used to compare the expressions of the genes encoding the angiotensin-II-receptors 1 and 2 (AT1R and AT2R) and the angiotensin-converting enzymes (ACE1 and ACE2) in the kidneys, hearts, livers and brains of mice. The effects of hydroxyurea (HU; 50–75 mg/kg/day, 4 weeks) treatment on these parameters were also determined.

Key findings

Plasma Ang II was significantly diminished in SCD mice, compared with WT mice, in association with decreased AT1R and ACE1 expressions in SCD mice kidneys. Treatment of SCD mice with HU reduced leukocyte and platelet counts and increased plasma Ang II to levels similar to those of WT mice. HU also increased AT1R and ACE2 gene expression in the kidney and heart.

Significance

Results indicate an imbalanced RAS in an SCD mouse model; HU therapy may be able to restore some RAS parameters in these mice. Further investigations regarding Ang II production and the RAS in human SCD may be warranted, as such changes may reflect or contribute to renal damage and alterations in blood pressure.     

Real-time changes of the local vasoactive peptide systems (angiotensin,endothelin) in the bovine corpus luteum after induced luteal regression

There is evidence that angiotensin II (Ang II) and endothelin-1 (ET-1) may interact in an additive or synergistic way during luteal regression. The aim of the study was to investigate real time changes in luteal tissue of angiotensin and endothelin system members in mRNA expression, tissue concentrations, tissue localization, and ACE (angiotensin converting enzyme) antagonist application after prostaglandin F(2alpha) (PG) induced (days 8-12) luteal regression in cow. Corpora lutea (CL) were collected by transvaginal ovaryectomy before and 2, 4, 12, 24, 48, and 64 hr (n = 5/time point) after PG injection. ACE mRNA expression (RT-PCR) increased continuously and peaked at 12, 24 hr; ECE-1 (endothelin converting enzyme) peaked at 12 hr, and both peptides in tissue (Ang II and ET-1) increased significantly and peaked at 24 hr. The expression of receptors for Ang II (AT1R and AT2R) did not change in contrast to ET receptors (ETR-A and ETR-B), which were up-regulated. Localization in tissue revealed very weak staining for Ang II and ET-1 before PG application followed by a clear increase of staining predominantly in large luteal cells, but also in endothelial cells. In two experiments, the attempt was made to block ACE by the antagonist captopril with two different doses. In both experiments with captopril, progesterone levels were not significantly different from controls. Ang II alone seems to be not essential for functional luteolysis in bovine system. In conclusion, the results suggest that both Ang II and ET-1 are in parallel up-regulated during luteal regression and may act as vasoconstrictors during functional luteolysis, but also as apoptosis inducer during functional/structural luteolysis.     

Skeletal muscle RAS and exercise performance

A local renin-angiotensin system (RAS) may be suggested by evidence of gene expression of RAS components within the tissue as well as physiological responsiveness of this gene expression. This review will focus on the evidence supporting the existence of the constituent elements of a physiologically functional paracrine muscle RAS. The effect of local skeletal muscle RAS on human exercise performance will be explored via its relation with pharmacological intervention and genetic studies.The most likely configuration of the muscle RAS is a combination of in situ synthesis and uptake from the circulation of RAS components. A reduction in angiotensin-converting enzyme (ACE) activity reverses the decline in physical performance due to peripheral muscle factors in those with congestive heart failure and may halt or slow decline in muscle strength in elderly women. Genetic studies suggest that increased ACE and angiotensin II (Ang II) mediate greater strength gains perhaps via muscle hypertrophy whereas lower ACE levels and reduced bradykinin (BK) degradation mediate enhanced endurance performance perhaps via changes in substrate availability, muscle fibre type and efficiency.