Expression of the angiotensinogen gene and localization of its protein in the human heart

Canagliflozin improves coronary microvascular vasodilation and increases absolute blood flow to the myocardium independent of angiogenesis

OBJECTIVES

Sodium-glucose cotransporter-2 inhibitor, canagliflozin, improves myocardial perfusion to ischemic territory without accompanying changes in vascular density. We aimed to (1) characterize effects on angiogenic pathways, (2) use multiomics to identify gene expression and metabolite profiles relevant to regulation of myocardial blood flow, and (3) investigate drug effect on coronary microvascular reactivity.

METHODS

A nondiabetic swine model of chronic myocardial ischemia and nondiabetic rat model were used to study functional and molecular effects of canagliflozin on myocardium and in vitro microvascular reactivity.

RESULTS

Canagliflozin resulted in increased coronary microvascular vasodilation and decreased vasoconstriction (P < .05) without changes in microvascular density (P > .3). Expression of the angiogenic modulator, endostatin, increased (P = .008), along with its precursor, collagen 18 (P < .001), and factors that increase its production, including cathepsin L (P = .004). Endostatin and collagen 18 levels trended toward an inverse correlation with blood flow to ischemic territory at rest. Proangiogenic fibroblast growth factor receptor was increased (P = .03) and matrix metalloproteinase-9 was decreased (P < .001) with canagliflozin treatment. Proangiogenic vascular endothelial growth factor A (P = .13), Tie-2 (P = .10), and Ras (P = .18) were not significantly altered. Gene expression related to the cardiac renin-angiotensin system was significantly decreased.

CONCLUSIONS

In chronic myocardial ischemia, canagliflozin increased absolute blood flow to the myocardium without robustly increasing vascular density or proangiogenic signaling. Canagliflozin resulted in altered coronary microvascular reactivity to favor vasodilation, likely through direct effect on vascular smooth muscle. Downregulation of cardiac renin-angiotensin system demonstrated local regulation of perfusion. VIDEO ABSTRACT.

The Role of Renin-Angiotensin System in Diabetic Cardiomyopathy: A Narrative Review

Diabetic cardiomyopathy refers to myocardial dysfunction in type 2 diabetes, but without the traditional cardiovascular risk factors or overt clinical atherosclerosis and valvular disease. The activation of the renin-angiotensin system (RAS), oxidative stress, lipotoxicity, maladaptive immune responses, imbalanced mitochondrial dynamics, impaired myocyte autophagy, increased myocyte apoptosis, and fibrosis contribute to diabetic cardiomyopathy. This review summarizes the studies that address the link between cardiomyopathy and the RAS in humans and presents proposed pathophysiological mechanisms underlying this association. The RAS plays an important role in the development and progression of diabetic cardiomyopathy. The over-activation of the classical RAS axis in diabetes leads to the increased production of angiotensin (Ang) II, angiotensin type 1 receptor activation, and aldosterone release, contributing to increased oxidative stress, fibrosis, and cardiac remodeling. In contrast, Ang-(1-7) suppresses oxidative stress, inhibits tissue fibrosis, and prevents extensive cardiac remodeling. Angiotensin-converting-enzyme (ACE) inhibitors and angiotensin receptor blockers improve heart functioning and reduce the occurrence of diabetic cardiomyopathy. Experimental studies also show beneficial effects for Ang-(1-7) and angiotensin-converting enzyme 2 infusion in improving heart functioning and tissue injury. Further research is necessary to fully understand the pathophysiology of diabetic cardiomyopathy and to translate experimental findings into clinical practice.

Spatially resolved multiomics of human cardiac niches

The function of a cell is defined by its intrinsic characteristics and its niche: the tissue microenvironment in which it dwells. Here we combine single-cell and spatial transcriptomics data to discover cellular niches within eight regions of the human heart. We map cells to microanatomical locations and integrate knowledge-based and unsupervised structural annotations. We also profile the cells of the human cardiac conduction system1. The results revealed their distinctive repertoire of ion channels, G-protein-coupled receptors (GPCRs) and regulatory networks, and implicated FOXP2 in the pacemaker phenotype. We show that the sinoatrial node is compartmentalized, with a core of pacemaker cells, fibroblasts and glial cells supporting glutamatergic signalling. Using a custom CellPhoneDB.org module, we identify trans-synaptic pacemaker cell interactions with glia. We introduce a druggable target prediction tool, drug2cell, which leverages single-cell profiles and drug-target interactions to provide mechanistic insights into the chronotropic effects of drugs, including GLP-1 analogues. In the epicardium, we show enrichment of both IgG+ and IgA+ plasma cells forming immune niches that may contribute to infection defence. Overall, we provide new clarity to cardiac electro-anatomy and immunology, and our suite of computational approaches can be applied to other tissues and organs.

The Tissue Renin-Angiotensin System and Its Role in the Pathogenesis of Major Human Diseases: Quo Vadis?

Evidence has arisen in recent years suggesting that a tissue renin-angiotensin system (tRAS) is involved in the progression of various human diseases. This system contains two regulatory pathways: a pathological pro-inflammatory pathway containing the Angiotensin Converting Enzyme (ACE)/Angiotensin II (AngII)/Angiotensin II receptor type 1 (AGTR1) axis and a protective anti-inflammatory pathway involving the Angiotensin II receptor type 2 (AGTR2)/ACE2/Ang1–7/MasReceptor axis. Numerous studies reported the positive effects of pathologic tRAS pathway inhibition and protective tRAS pathway stimulation on the treatment of cardiovascular, inflammatory, and autoimmune disease and the progression of neuropathic pain. Cell senescence and aging are known to be related to RAS pathways. Further, this system directly interacts with SARS-CoV 2 and seems to be an important target of interest in the COVID-19 pandemic. This review focuses on the involvement of tRAS in the progression of the mentioned diseases from an interdisciplinary clinical perspective and highlights therapeutic strategies that might be of major clinical importance in the future.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Renin Activity in Heart Failure with Reduced Systolic Function-New Insights

Regardless of the cause, symptomatic heart failure (HF) with reduced ejection fraction (rEF) is characterized by pathological activation of the renin–angiotensin–aldosterone system (RAAS) with sodium retention and extracellular fluid expansion (edema). Here, we review the role of active renin, a crucial, upstream enzymatic regulator of the RAAS, as a prognostic and diagnostic plasma biomarker of heart failure with reduced ejection fraction (HFrEF) progression; we also discuss its potential as a pharmacological bio-target in HF therapy. Clinical and experimental studies indicate that plasma renin activity is elevated with symptomatic HFrEF with edema in patients, as well as in companion animals and experimental models of HF. Plasma renin activity levels are also reported to be elevated in patients and animals with rEF before the development of symptomatic HF. Modulation of renin activity in experimental HF significantly reduces edema formation and the progression of systolic dysfunction and improves survival. Thus, specific assessment and targeting of elevated renin activity may enhance diagnostic and therapeutic precision to improve outcomes in appropriate patients with HFrEF.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Evidence for a role of an intracardiac renin-angiotensin system in normal and failing hearts

Although substantial evidence of a cardiac RAS has been obtained in the past decade, a number of important questions remain unanswered. These include identification and localization of the cell types responsible for production of the system's components as well as the regulation of synthesis, storage, and secretion pathways for each component. Future studies, which will utilize tools of molecular biology that have become recently available (for example, transgenic animal models), renin inhibitors, angiotensin receptor antagonists, and bradykinin antagonists, will help to elucidate specific roles of the cardiac RAS in normal and failing hearts.

Promoter polymorphism G-6A, which modulates angiotensinogen gene expression, is associated with non-familial sick sinus syndrome

BACKGROUND

It is well known that familial sick sinus syndrome (SSS) is caused by functional alterations of ion channels and gap junction. Limited information is available on the mechanism of age-related non-familial SSS. Although evidence shows a close link between arrhythmia and the renin-angiotensin system (RAS), it remains to be determined whether the RAS is involved in the pathogenesis of non-familial SSS.

METHODS

In this study, 113 patients with documented non-familial SSS and 125 controls were screened for angiotensinogen (AGT) and gap junction protein-connexin 40 (Cx40) promoter polymorphisms by gene sequencing, followed by an association study. A luciferase assay was used to determine the transcriptional activity of the promoter polymorphism. The interaction between nuclear factors and the promoter polymorphism was characterized by an electrophoretic mobility shift assay (EMSA).

RESULTS

Association study showed the Cx40 -44/+71 polymorphisms are not associated with non-familial SSS; however, it indicated that four polymorphic sites at positions -6, -20, -152, and -217 in the AGT promoter are linked to non-familial SSS. Compared to controls, SSS patients had a lower frequency of the G-6A AA genotype (OR 2.88, 95% CI 1.58-5.22, P = 0.001) and a higher frequency of the G allele at -6 position (OR 2.65, 95% CI 1.54-4.57, P = 0.0003). EMSA and luciferase assays confirmed that nucleotide G at position -6 modulates the binding affinity with nuclear factors and yields a lower transcriptional activity than nucleotide A (P<0.01).

CONCLUSION

G-6A polymorphism, which modulates the transcriptional activity of the AGT promoter, may contribute to non-familial SSS susceptibility.

Molecular determinants of cardiac transient outward potassium current (I(to)) expression and regulation

Rapidly activating and inactivating cardiac transient outward K(+) currents, I(to), are expressed in most mammalian cardiomyocytes, and contribute importantly to the early phase of action potential repolarization and to plateau potentials. The rapidly recovering (I(t)(o,f)) and slowly recovering (I(t)(o,s)) components are differentially expressed in the myocardium, contributing to regional heterogeneities in action potential waveforms. Consistent with the marked differences in biophysical properties, distinct pore-forming (alpha) subunits underlie the two I(t)(o) components: Kv4.3/Kv4.2 subunits encode I(t)(o,f), whereas Kv1.4 encodes I(t)(o,s), channels. It has also become increasingly clear that cardiac I(t)(o) channels function as components of macromolecular protein complexes, comprising (four) Kvalpha subunits and a variety of accessory subunits and regulatory proteins that influence channel expression, biophysical properties and interactions with the actin cytoskeleton, and contribute to the generation of normal cardiac rhythms. Derangements in the expression or the regulation of I(t)(o) channels in inherited or acquired cardiac diseases would be expected to increase the risk of potentially life-threatening cardiac arrhythmias. Indeed, a recently identified Brugada syndrome mutation in KCNE3 (MiRP2) has been suggested to result in increased I(t)(o,f) densities. Continued focus in this area seems certain to provide new and fundamentally important insights into the molecular determinants of functional I(t)(o) channels and into the molecular mechanisms involved in the dynamic regulation of I(t)(o) channel functioning in the normal and diseased myocardium.

Intracardiac and intrarenal renin-angiotensin systems: mechanisms of cardiovascular and renal effects

The renin-angiotensin system (RAS) is a hormonal system that controls body fluid volume, blood pressure, and cardiovascular function in both health and disease. Various tissues, including the heart and kidneys, possess individual locally regulated RASs. In each RAS, the substrate protein angiotensinogen is cleaved by the peptidases renin and angiotensin-converting enzyme to form the biologically active product angiotensin II, which acts as an intracrine cardiac and renal hormone. The components of each RAS, including aldosterone (ALDO), may be produced locally and/or may be delivered by or sequestered from the circulation. Overactivity of the cardiac RAS has been associated with cardiac diseases, including cardiac hypertrophy due to volume and/or pressure overload, heart failure, coronary artery disease with myocardial infarction, and hypertension. Overactivity of the renal RAS has been associated with various kidney diseases, including nephropathies and renal artery stenosis. The principal effects of an overactive RAS include the generation of reactive oxygen species, which leads to "oxidative stress," activation of the nuclear transcription factor kappaB, and stimulation of pathways and genes that promote vasoconstriction, endothelial dysfunction, cell hypertrophy, fibroblast proliferation, inflammation, excess extracellular matrix deposition, atherosclerosis, and thrombosis. It has been suggested that oxidative stress is the central mechanism underlying the pathogenesis of RAS-related and ALDO-related chronic cardiovascular and renal tissue injury and of cardiac arrhythmias and conduction disturbances.

Angiotensin Receptor Type 1 Forms a Complex with the Transient Outward Potassium Channel Kv4.3 and Regulates Its Gating Properties and Intracellular Localization

We report a novel signal transduction complex of the angiotensin receptor type 1. In this complex the angiotensin receptor type 1 associates with the potassium channel alpha-subunit Kv4.3 and regulates its intracellular distribution and gating properties. Co-localization of Kv4.3 with angiotensin receptor type 1 and fluorescent resonance energy transfer between those two proteins labeled with cyan and yellow-green variants of green fluorescent protein revealed that Kv4.3 and angiotensin receptor type I are located in close proximity to each other in the cell. The angiotensin receptor type 1 also co-immunoprecipitates with Kv4.3 from canine ventricle or when co-expressed with Kv4.3 and its beta-subunit KChIP2 in human embryonic kidney 293 cells. Treatment of the cells with angiotensin II results in the internalization of Kv4.3 in a complex with the angiotensin receptor type 1. When stimulated with angiotensin II, angiotensin receptors type 1 modulate gating properties of the remaining Kv4.3 channels on the cell surface by shifting their activation voltage threshold to more positive values. We hypothesize that the angiotensin receptor type 1 provides its internalization molecular scaffold to Kv4.3 and in this way regulates the cell surface representation of the ion channel.

Newly recognized components of the renin-angiotensin system: potential roles in cardiovascular and renal regulation

The renin-angiotensin system (RAS) is a coordinated hormonal cascade in the control of cardiovascular, renal, and adrenal function that governs body fluid and electrolyte balance, as well as arterial pressure. The classical RAS consists of a circulating endocrine system in which the principal effector hormone is angiotensin (ANG) II. ANG is produced by the action of renin on angiotensinogen to form ANG I and its subsequent conversion to the biologically active octapeptide by ANG-converting enzyme. ANG II actions are mediated via the ANG type 1 receptor. Here, we discuss recent advances in our understanding of the components and actions of the RAS, including local tissue RASs, a renin receptor, ANG-converting enzyme-2, ANG (1-7), the function of the ANG type 2 receptor, and ANG receptor heterodimerization. The role of the RAS in the regulation of cardiovascular and renal function is reviewed and discussed in light of these newly recognized components.

Local cardiac renin-angiotensin system: hypertension and cardiac failure

In addition to the effect on arterial pressure, angiotensin II, the effector peptide of the renin-angiotensin system (RAS), exerts mitogenic and growth promoting effects on cardiac myocytes and non-myocytic elements; and both of these effects significantly contribute to the development and progression of hypertensive heart disease (HHD). The traditional concept of the RAS as a systemic, endocrine system has been expanded and the identification of its components in many organs and tissue has been amassed. This paper reviews evidence that supports the concept that the cardiac RAS participate importantly in the development and risk of HHD.

JC virus large T protein transforms rodent cells but is not involved in human medulloblastoma

JC virus (JCV) together with Simian virus 40 (SV40) and BK virus (BKV), belong to the polyomavirus group and these viruses are neuro-oncogenic to rodents by expression of large T antigen (LT), which binds to cellular p53 and pRB thus reducing the anticancer potential of the cell. The function of LT has not been clarified because small t antigen (st) is transcribed from the same start codon as the overlapping reading frame of LT, and is translated as a different protein with the same N-terminal residues (1-81 amino acids) by a splice-site variant of mRNA. To elucidate the function of LT without st, we constructed plasmids that express LT only by deleting the splicing region including the C-terminus of st, and consequently stable cell lines were established that express only JCLT, SV40LT and BKLT. The growth rates of these cells were examined in colonies on soft agar and it was found that LT alone has a transforming capacity; the order of efficiency being SV40LT, BKLT and JCLT. In addition, to verify the involvement of JCV in human medulloblastoma, eight cases of medulloblastoma, six cases of frozen material and five cases of paraffin-embedded tissues which included three cases of frozen tissues, were examined. PCR assay, genomic Southern blotting, and in situ hybridization were applied to detect the JCV genome, and LT and st were examined by immunohistochemistry; the results were compared with JCV-infected tissues as a positive control. All methods failed to detect not only JCV genome but also LT protein in medulloblastoma and it was concluded that JCV LT has transforming activities in rodent cells, but is not related to human medulloblastoma.

Effects of acute and chronic angiotensin receptor blockade on myocardial vascular blood volume and perfusion in a pig model of coronary microembolization

Based on the reduction of ischemic cardiac events in clinical trials and experimental observations, inhibition of the effects of angiotensin II on coronary microcirculatory function may afford myocardial protection after injury. The immediate effects of intracoronary AT1 receptor blockade with irbesartan were examined in a pig model in the healthy myocardium and in acute ischemia induced by injection of 30-microm microspheres into the left anterior descending coronary artery (LAD). Electron-beam computed tomography was performed for in-vivo quantitative measurements of regional intramyocardial vascular blood volume (V(B)) and perfusion (F(M)), as well as left ventricular ejection fraction (LVEF) and muscle mass. Ratios of V(B) and F(M) in the anterior (LAD-supplied)/ inferior (control) myocardium were generated. At baseline, 0.2 mg/kg irbesartan injected into the LAD increased V(B) and F(M) ratios significantly by 27 +/- 8% and 51 +/- 13%, respectively. After anterior coronary microembolization, V(B) and F(M) ratios were 0.60 +/- 0.05 and 0.51 +/- 0.05, respectively, and were significantly increased by irbesartan (by 24 +/- 10% and by 36 +/- 11%, respectively). After 4 weeks of treatment with oral irbesartan (n = 7) or placebo (n = 7), an improved LVEF (56 +/- 4% v 44 +/- 4%, P = .046) was observed in irbesartan-treated animals, but no difference in LV end-diastolic volumes or muscle mass. Resting V(B) (0.95 +/- 0.06 v 0.76 +/- 0.06; P = .047) and F(M) (0.84 +/- 0.05 v 0.64 +/- 0.04; P = .016) ratios were significantly greater in irbesartan-treated animals. Using adenosine, there was a trend for higher V(B) and F(M) ratios in irbesartan- v placebo-treated animals. Therefore, in a pig model of acute myocardial ischemia, AT1 receptor blockade by irbesartan induced microvascular vasodilation and, ostensibly, conveyed myocardial protection. Long-term treatment with irbesartan resulted in moderate enhancements of resting V(B) and F(M) compared with placebo, suggesting a role for coronary microcirculatory effects of chronic AT1 receptor blockade in preserving LVEF.

[The renin-angiotensin system in cardiovascular diseases]

BACKGROUND

The renin-angiotensin system is mainly involved in several cardiovascular diseases and in the pathophysiology of heart failure. It exists as a circulating and a local system which can be differently regulated. Interventions in this system by angiotensin-converting enzyme (ACE) antagonists or angiotensin-receptor antagonists slow the progression of heart failure and result in prolongation of life expectancy and improvement of hemodynamics.

MECHANISMS OF ACTION

The main underlying mechanisms are: 1. Heart failure results in activation of the renin-angiotensin system as a compensatory mechanism with elevation of circulating angiotensin II, norepinephrine and vasopressin. Antagonists of this compensatory mechanisms acutely result in improvement of the hemodynamic situation. 2. Elevated circulating and local renin-angiotensin systems cause chronic structural myocardial and vascular effects. Angiotensin-converting enzyme antagonists and angiotensin-receptor blockers modulate and partly antagonize these structural changes such as myocardial hypertrophy, myocardial fibrosis and vascular proliferative responses. Gene and receptor regulation of the system are currently not fully understood and are subject of intensive research. 3. The renin-angiotensin system is closely related to the bradykinin system and thus indirectly to nitric oxide and endothelial function. Bradykinin has multiple other effects on the hemostatic system as a well as on the myocardium and vascular system.

CONCLUSION

These complex interactions require further evaluation. Research with specific bradykinin antagonists will give new insights into this system.

Synthesis of kininogen and degradation of bradykinin by PC12 cells

1. In this study, the abilities of PC12 cells to synthesize and degrade kinins were investigated. Kinin formation was assessed as kinin and kininogen content of cells and supernatants in serum-free incubations by use of a bradykinin-specific radioimmunoassay. Expression of kininogen mRNA was demonstrated by reverse-transcriptase PCR. Kinin degradation pathways of intact PC12 cells were characterized by identification of the kinin fragments generated from tritiated bradykinin either in the absence or presence of the angiotensin I-converting enzyme inhibitor ramiprilat. 2. Kinin immunoreactivity in the supernatant of PC12 cell cultures accumulated in a time-dependent fashion during incubations in serum-free media. This effect was solely due to de novo synthesis and release of kininogen (35 pg bradykinin h-1 mg-1 protein) since it could be suppressed by cycloheximide. Continuous synthesis of kininogen was a specific property of PC12 cells, as it was not observed in cultured macro- or microvascular endothelial cells. PC12 cells contained only minor amounts of stored kininogen. The rate of kininogen synthesis was not affected by ramiprilat, bacterial lipopolysaccharide, nerve growth factor or dexamethasone, but was stimulated 1.4 fold when cells were pretreated for 1 day with 1 microM desoxycorticosterone. 3. By use of cDNA probes specific for kininogen subtype mRNAs, expression of low-molecular-weight kininogen and T-kininogen in PC12 cells was confirmed. Expression of high molecular weight kininogen mRNA was also shown, though only at the lowest limit of detection of the assay. 4. Degradation of tritiated bradykinin by PC12 cells occurred with a half-life of 48 min resulting in the main fragments [1-7]- and [1-5]-bradykinin. The degradation rate of bradykinin decreased to 15% in the presence of ramiprilat (250 nM). Apart from angiotensin I-converting enzyme direct cleavage of bradykinin to [1-7]- and [1-5]-bradykinin still occurred under this condition as a result of additional kininase activities. 5. Along with previous findings of B2-receptor-mediated catecholamine release, these results now confirm the hypothesis that a cellular kinin system is expressed in PC12 cells. The presence of such a system may reflect a role of kinins as local neuromodulatory mediators in the peripheral sympathetic system.

Prorenin, renin, angiotensinogen, and angiotensin-converting enzyme in normal and failing human hearts. Evidence for renin binding

BACKGROUND

A local renin-angiotensin system in the heart is often invoked to explain the beneficial effects of ACE inhibitors in heart failure. The heart, however, produces little or no renin under normal conditions.

METHODS AND RESULTS

We compared the cardiac tissue levels of renin-angiotensin system components in 10 potential heart donors who died of noncardiac disorders and 10 subjects with dilated cardiomyopathy (DCM) who underwent cardiac transplantation. Cardiac levels of renin and prorenin in DCM patients were higher than in the donors. The cardiac and plasma levels of renin in DCM were positively correlated, and extrapolation of the regression line to normal plasma levels yielded a tissue level close to that measured in the donor hearts. The cardiac tissue-to-plasma concentration (T/P) ratios for renin and prorenin were threefold the ratio for albumin, which indicates that the tissue levels were too high to be accounted for by admixture with blood and diffusion into the interstitial fluid. Cell membranes from porcine cardiac tissue bound porcine renin with high affinity. The T/P ratio for ACE, which is membrane bound, was fivefold the ratio for albumin. Cardiac angiotensinogen was lower in DCM patients than in the donors, and its T/P ratio was half that for albumin, which is compatible with substrate consumption by cardiac renin.

CONCLUSIONS

These data in patients with heart failure support the concept of local angiotensin production in the heart by renin that is taken up from the circulation. Membrane binding may be part of the uptake process.

Myofibroblasts and local angiotensin II in rat cardiac tissue repair

Tissue repair is a fundamental property of vascularized tissue. At sites of injury, phenotypically transformed fibroblast-like cells are responsible for fibrous tissue formation, expressed principally as type I and III fibrillar collagens. These cells are termed myofibroblasts because they contain alpha-smooth muscle actin microfilaments and are contractile. In vivo studies of injured rat cardiac tissues and in vitro cell culture studies have shown that such fibroblast-like cells contain requisite components for angiotensin peptide generation and angiotensin II receptors. Such locally generated angiotensin II acts in an autocrine paracrine manner to regulate collagen turnover and thereby tissue homeostasis in injured tissue.

Altered signal transduction system in hypertrophied myocardium: angiotensin II stimulates collagen synthesis in hypertrophied hearts

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 of 10-week-old spontaneously hypertensive rats and age-matched WKY rats. Basal collagen synthesis in cardiac fibroblasts from spontaneously hypertensive rats was 1.6-fold greater than that in the cell of WKY 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 vs 128 +/- 19% in WKY rats, P < .01). This effect was receptor-specific, because it was blocked by the competitive inhibitors saralasin and MK 954. These results indicate that collagen production is enhanced in cardiac fibroblasts from spontaneously hypertensive rats, that angiotensin II has a stimulatory effect on collagen synthesis in cardiac fibroblasts, and that cardiac fibroblasts from spontaneously hypertensive rats are hyper-responsive to stimulation by angiotensin II. In the hearts of spontaneously hypertensive rats, mRNA of the renin-angiotensin system (renin, angiotensinogen, angiotensin converting enzyme) was expressed. Levels of angiotensinogen and renin mRNA expressed in ventricles, and angiotensinogen mRNA expressed in fibroblasts from SHR were higher than those from WKY. ACE mRNA was also more strongly expressed in the ventricles and fibroblasts from SHR compared with those of WKY. These findings suggest that the cardiac reninangiotensin system may play an important role in collagen accumulation in hypertensive cardiac hypertrophy (fig.4).

Endogenous cardiac vasoactive factors modulate endothelin production by cardiac fibroblasts in culture

Endothelin, a potent vasoconstrictor, is produced by cardiac fibroblasts in culture and induces hypertrophy in cardiac myoctes. The purpose of this study was to determine whether vasoactive factors endogenous to the heart affect the production of endothelin by cultured cardiac fibroblasts. Vasoactive factors have been shown to play multiple roles in the adaptation of the heart to chronic overload, affecting both vascular tone and cell growth. Both atrial (ANP) and brain (BNP) natriuretic peptides are endogenous cardiac vasodilators and are produced by cultured myocytes in response to stimulation with endothelin. Treatment of cardiac fibroblasts with these peptides decreased endothelin production. Nitroprusside, an activator of guanylyl cyclase, decreased endothelin production indicating the involvement of cGMP in the response. Carbaprostacyclin, a stable derivative of prostacyclin, another endogenous cardiac vasodilator, also decreased endothelin production by fibroblasts. The combination of BNP and carbaprostacyclin was additive in decreasing endothelin production. In contrast, PGF2α and angiotensin II, both endogenous cardiac vasoconstrictors, increased endothelin production and overcame the inhibition induced by BNP and carba-prostacyclin. In summary, endothelin production by cardiac fibroblasts was decreased by the endogenous cardiac vasodilators ANP, BNP, and prostacyclin and increased by the endogenous vasoconstrictors PGF2α and angiotensin II.

Expression of renin and angiotensin-converting enzyme in human hearts

To understand the significance of the tissue renin-angiotensin system in the heart, we examined the expression of renin and angiotensin-converting enzyme (ACE) in autopsied human hearts. Samples were taken from organs obtained at autopsy from 15 patients without heart disease and 3 patients with heart disease (old myocardial infarctions, acute myocardial infarctions, and hypertrophic cardiomyopathy). We examined the expression of renin and ACE mRNA by using the reverse transcription-polymerase chain reaction (RT-PCR). RT-PCR showed the expression of renin in the right atria in all patients. However, expression of renin mRNA in the left ventricles was not found in any of the 15 hearts without heart disease. In contrast, renin mRNA was detected in the left ventricles in hearts with heart disease. ACE mRNA was detected in both the atria and the ventricles in normal hearts, and its expression did not alter in diseased hearts. These findings suggest that renin mRNA is expressed mainly in the right atria in normal hearts, but that its expression in the left ventricle can be activated in some pathological conditions.

The distribution of angiotensin II type 1 receptors, and the tissue renin-angiotensin systems

Since its discovery, the functions of the renin-angiotensin system (RAS) have attracted a great deal of attention, and the roles it plays under normal conditions, and in disease, acquire a deepening significance with every year. In general, the RAS has been considered largely in terms of its roles in sodium and potassium homeostasis and the regulation of blood pressure. The continued acquisition of information on the distribution of angiotensin receptors, however, emphasizes that our interpretation needs to be widened, and it is now clear that angiotensin II has an array of functions in the tissues, which are unrelated to its systemic roles. This paracrine function is brought about by the existence of complete, localized tissue RASs, which respond to physiological demand independently from the systemic system.

Renin-angiotensin system in failing heart

Extrahepatic synthesis and localization of angiotensinogen have been described in animals, thus establishing the tissue renin-angiotensin system. We examined angiotensinogen messenger RNA synthesis by northern blotting. It was detected not only in the liver, but also in both the atrial and ventricular heart tissues, suggesting that angiotensinogen is synthesized in the human heart. Immunohistochemical studies using a specific antibody to angiotensinogen revealed a stronger reaction in the endocardial layer of the human left ventricle, than in the epicardial layer, and intense immunoreactivity in the conduction system and right atrium. Furthermore, our experiments revealed a widespread immunopositive reaction for angiotensinogen in the left ventricle of diseased hearts. We examined the participation of the collagen in the occurrence and progression of cardiomyopathy. The acetic acid solubility of collagen and reducible crosslink decreased in cardiomyopathic hamsters as the fibrosis progressed, but was unchanged in controls. These findings indicate that in the early phase of cardiomyopathy the extracellular matrix of the myocardium is similar to immature tissues. In the later phase, the matrix resembles that of hard tissues, and is insoluble. Furthermore, we examined the relationship between angiotensin II and collagen synthesis. Basal collagen synthesis in cardiac fibroblasts from spontaneously hypertensive rats was 1.6-fold greater than that in Wistar-Kyoto rats. The responsiveness of collagen production to Ang II was significantly enhanced in SHR. This effect was angiotensin receptor-specific, because it was blocked by the competitive inhibitor. These results indicate angiotensin II may play an important role in collagen accumulation in hypertensive cardiac hypertrophy.

Intracardiac angiotensin-converting enzyme inhibition improves diastolic function in patients with left ventricular hypertrophy due to aortic stenosis

BACKGROUND

Cardiac hypertrophy is associated with elevated intracardiac angiotensin-converting enzyme activity, which may contribute to diastolic dysfunction.

METHODS AND RESULTS

We infused enalaprilat (0.05 mg/min) for 15 minutes into the left coronary arteries of 20 adult patients with left ventricular (LV) hypertrophy due to aortic stenosis (mean aortic valve area, 0.7 +/- 0.2 cm2) and 10 patients with dilated cardiomyopathy (mean ejection fraction, 35 +/- 4%) and assessed (1) simultaneous changes in LV micromanometer pressure and dimensions, (2) LV regional wall motion analyzed by the area method, and (3) Doppler flow-velocity profiles. Systemic neurohormonal activation did not occur with the selective left coronary artery infusion; there were no changes in plasma renin activity, angiotensin-converting enzyme activity, or atrial natriuretic peptide. In patients with aortic stenosis, LV end-diastolic pressure declined from 25 +/- 2 to 20 +/- 2 mm Hg (P < .05). LV pressure-volume and LV pressure-dimension relations showed downward shifts by ventriculography and echocardiography, respectively, indicating improved diastolic distensibility. Regional area change during isovolumic relaxation increased in the anterior segments perfused with enalaprilat but decreased in the inferior segments, indicating acceleration of isovolumic relaxation in the anterior segments and reciprocal shortening in the inferior segments. Regional peak filling rate increased in the anterior segments but not in the inferior segments, and the regional area stiffness constant decreased in the anterior segments but not in the inferior segments. There were no changes in heart rate, cardiac output, or right atrial pressure, excluding alterations in right ventricular/pericardial constraint. In contrast, in the patients with dilated cardiomyopathy the decrease in LV end-diastolic pressure from 22 +/- 2 to 18 +/- 2 mm Hg (P < .05) was accompanied by a significant fall in right atrial pressure (9 +/- 1 to 6 +/- 1 mm Hg), implicating alterations in pericardial constraint. The patients with dilated cardiomyopathy showed no improvement in regional diastolic relaxation, filling, or distensibility.

CONCLUSIONS

Intracoronary enalaprilat at a dosage that did not cause systemic neurohormonal activation improved LV diastolic chamber distensibility and regional relaxation and filling in patients with LV hypertrophy due to aortic stenosis. In contrast, these effects of intracoronary enalaprilat on diastolic function were not observed in patients with dilated cardiomyopathy who did not have concentric hypertrophy. These observations support the hypothesis that the cardiac renin-angiotensin system is activated in patients with concentric pressure-overload hypertrophy and that this activation may contribute to impaired diastolic function.

Modulation of expression of monocyte/macrophage plasminogen activator activity and its implications for attenuation of vasculopathy

BACKGROUND

The binding of urokinase-type plasminogen activator (uPA) to its receptor (uPAR) on cell surfaces has the potential to influence degradation of extracellular matrix (ECM). Thus, uPA bound to monocyte/macrophages and its interactions with plasminogen activator inhibitors types 1 and 2 (PAI-1 and PAI-2) may modify atherogenesis by altering cell-associated proteolytic activity, degradation of ECM, and neointimal formation at sites of vascular injury.

METHODS AND RESULTS

To determine whether the expression of proteins on the surface of cells involved in fibrinolysis changes in human cells in response to mediators implicated in atherogenesis, we exposed U937 cells (an immortal human monocyte-like cell line) to transforming growth factor-beta (TGF-beta) and to thrombin. Induction of uPAR mRNA occurred with TGF-beta (5 ng/mL) in a time-dependent fashion (P = .05; n = 4). Thrombin (5 National Institutes of Health [NIH] U/mL) increased uPAR mRNA by 2.8-fold above control (n = 4) without altering PAI-1 mRNA or protein synthesis (n = 4). The increase in uPAR gene expression in cells exposed to either TGF-beta or thrombin translated into a functional increase in cell-surface proteolytic activity. Under control conditions, U937 cells expressed PAI-2 but not PAI-1 mRNA. PAI-2 mRNA expression increased (P < .05; n = 4) with thrombin (5 NIH U/mL) but was suppressed by TGF-beta (5 ng/mL). TGF-beta induced PAI-1 mRNA within 6 hours accompanied by a 9-fold increase in PAI-1 protein from 6 hours (2.9 +/- 1.9 ng/mL) to 24 hours (20.0 +/- 9.6 ng/mL, P = .005; n = 3) paralleled by increased synthesis as shown in metabolic labeling experiments with 35S-methionine and immunoprecipitation of labeled PAI-1. PAI-1 mRNA and protein expression were seen in human coronary artery atherectomy specimens as well and were localized to analogous monocyte/macrophages and to smooth muscle cells as judged from results of in situ hybridization and immunocytochemistry studies.

CONCLUSIONS

The results indicate that there is induction of PAI-1 and uPAR in U937 cells exposed to TGF-beta and thrombin. In atheroma, analogous processes may modulate early migration of luminal monocytes into the subintimal space and proteolysis of ECM. Thus, cell surface, monocyte-directed fibrinolysis may influence atherosclerosis, restenosis, or both.

Increased angiotensin-I converting enzyme gene expression in the failing human heart. Quantification by competitive RNA polymerase chain reaction

Local activation of the components of the renin angiotensin system in the heart is regarded as an important modulator of cardiac phenotype and function; however, little is known about their presence, regulation, and potential activation in the human heart. To investigate the gene expression of major angiotensin-II-forming enzymes in left ventricles of normal (n = 9) and failing human hearts (n = 20), we established a competitive RNA-polymerase chain reaction (PCR) for mRNA quantification of angiotensin-I converting enzyme (ACE) and human heart chymase. For each gene, competitor RNA targets with small internal deletions were used as internal standards to quantify the original number of transcripts and to control reverse transcription and PCR. In PCR, each target and the corresponding competitor were amplified by competing for the same primer oligonucleotides. The variability of ACE RNA-PCR was 11% indicating a high reproducibility of this method. In addition, ACE mRNA levels obtained by competitive RNA-PCR correlated favorably with traditional slot blot hybridization (r = 0.69, n = 10; P < 0.05). Compared with nonfailing hearts, the number of ACE transcripts referred to 100 ng of total RNA was increased threefold in patients with chronic heart failure (4.2 +/- 2.5 vs. 12.8 +/- 6 x 10(5); P < 0.0005). In contrast, no significant difference was found in chymase gene expression between normal and failing hearts. Thus, the expression of the cardiac ACE but not of human heart chymase is upregulated in failing human heart indicating an activation of the cardiac renin-angiotensin system in patients with advanced heart failure.

Distribution of angiotensinogen in diseased human hearts

Extrahepatic synthesis and localization of angiotensinogen (ATN) have been described in animals, thus establishing the tissue renin-angiotensin (RA) system. However, there had been no reports of tissue RA systems in human organs, including the heart. In earlier, we have reported the possibility of ATN synthesis in the human heart using ribonuclease protection assay system. ATN mRNA was detected not only in the liver, but also in both the atrial and ventricular heart tissues, suggesting that ATN is synthesized in the human heart. In this report, we looked for the distribution of ATN in diseased human heart. Northern blot hybridization of cDNA with total RNA extracted from human liver, brain, kidney, atrial and ventricular tissues revealed that ATN mRNA exists in cardiac ventricule. Immunohistochemical studies using a specific antibody to ATN revealed a stronger reaction in the endocardial layer of the human left ventricle, than in the epicardial layer, and intense immunoreactivity in the conduction system and right atrium. This distribution pattern was similar to that of human atrial natriuretic peptide (hANP), which functions a smooth muscle relaxant. Double immunostaining of ATN and hANP demonstrated that all myocytes in the right atrium had immunopositive reactions to ATN, hANP or both of ATN and hANP. Double immunoelectron staining enabled us to show more detailed localization of ATN and hANP; hANP only existed in the specific granules and ATN existed in the myofibril, but not in the granule. Furthermore, our experiments provide evidence of ATN in healthy human hearts and also reveal a widespread immunopositive reaction for ATN in the left ventricle of diseased hearts.

Potentiation by hypercholesterolemia of the induction of aortic intramural synthesis of plasminogen activator inhibitor type 1 by endothelial injury

Accumulation of plasminogen activator inhibitor type 1 (PAI-1) in the arterial wall may accelerate atherogenesis by inhibiting fibrinolysis, diminishing proteolysis of extracellular matrix proteins, or modifying migration of vascular smooth muscle cells. Increased intramural expression of the PAI-1 gene is induced by thrombosis. To determine whether it occurs also in response to a sustained mechanical insult to endothelium, hypercholesterolemia, or both, rabbits were subjected to sustained aortic injury induced by implantation of indwelling polyethylene tubing, to hyperlipidemia induced by cholesterol and peanut oil feeding over a period of 8 weeks, or both. Sustained vascular injury alone did not increase plasma PAI-1. However, hypercholesterolemia with or without mechanically induced vascular injury increased plasma PAI-1 twofold. The expression of PAI-1 mRNA in aorta (Northern blots) was significantly increased when vascular injury was combined with hyperlipidemia. In situ hybridization showed that the increase with mechanical injury alone occurred in endothelial cells covering the neointima (positive for factor VIII and thrombomodulin), in abnormally differentiated vascular smooth muscle cells (positive for embryonic myosin heavy chain), and in macrophages (positive for the RAM-11 anti-macrophage antibody). Qualitatively similar but much more marked increases in PAI-1 gene expression were seen when arterial injury was accompanied by hypercholesterolemia. Neither vitronectin, known to stabilize PAI-1, nor vitronectin mRNA increased in liver. However, immunocytochemistry and Western blots demonstrated marked aortic accumulation of vitronectin protein with hyperlipidemia, particularly in subendothelial fibrotic regions, accompanied by increased neointimal vitronectin mRNA as shown by in situ hybridization. These results suggest that increased synthesis and stabilization of vascular PAI-1 may potentiate accumulation of extracellular matrix, thereby accelerating atherosclerosis.

Reduction of myocardial infarct size by ramiprilat is independent of angiotensin II synthesis inhibition

The angiotensin-converting enzyme inhibitor ramiprilat, the angiotensin II receptor antagonist losartan, angiotensin II, ramiprilat plus angiotensin II, or saline (N = 6 each group), were administered i.v. in anesthetized, open-chest rabbit preparations of acute myocardial ischemia. Animals were instrumented for measurement of systemic hemodynamics and left ventricular +dP/dtmax, then subjected to 30 min of left anterior descending coronary artery occlusion (marginal branch) followed by 2 h of reperfusion. Ramiprilat (50 micrograms/kg), losartan (10 mg/kg), or saline were administered prior to reperfusion, and angiotensin II (2.5 ng/kg per min) was infused 15 min prior to occlusion and throughout the remainder of the experiment. Losartan was supplemented (10 mg/kg) after 1 h of reperfusion. These non-hypotensive doses of ramiprilat and losartan were demonstrated to significantly antagonize the systemic pressor effects of i.v. challenge with angiotensin I (15% of control, maximum) and II (5% of control, maximum), respectively, for the duration of the experiment. Systemic hemodynamic and +dP/dtmax changes due to occlusion/reperfusion or drug administration were similar between treatment groups. Infarct size was measured post-experimentally using tetrazolium staining and is reported as a percent of area at risk. Infarct size/area at risk (%) was significantly lower in rabbits administered ramiprilat only (20 +/- 6%*) or ramiprilat plus angiotensin II (26 +/- 5%*), compared to those receiving saline (41 +/- 6%), angiotensin II (51 +/- 4%), or losartan (52 +/- 4%, mean +/- S.E.M., * P < 0.05). These data indicate that direct angiotensin II receptor stimulation or receptor antagonism does not alter the degree of myocardial necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Augmented arterial wall expression of type-1 plasminogen activator inhibitor induced by thrombosis

Type-1 plasminogen activator inhibitor (PAI-1), the primary physiological inhibitor of endogenous plasminogen activators, modulates fibrinolysis, cell migration, and tissue repair. To determine whether genetic expression of PAI-1 is augmented in the walls of vessels exposed to thrombi but not to a direct physical insult such as electrical injury, we induced arterial thrombosis in rabbit carotid arteries with intraluminal surgical silk sutures and performed in situ hybridization for PAI-1 messenger RNA (mRNA) and immunohistochemistry for PAI-1 antigen at selected intervals. PAI-1 activity in plasma remained virtually constant. In contrast, PAI-1 mRNA increased in endothelial cells juxtaposed to thrombi, in smooth muscle cells adjacent to the neointima, and in macrophages surrounding the suture material. PAI-1 protein was detected in regions in which PAI-1 mRNA was expressed. The increased expression of PAI-1 mRNA colocalized with PAI-1 protein in the endothelium juxtaposed to thrombi may potentiate thrombosis by shifting the local balance between fibrinolysis and thrombosis toward thrombosis. Furthermore, it may alter vascular remodeling and predispose to stenosis after interventions such as angioplasty, in which local thrombosis cannot be avoided.