Angiotensin II-forming heart chymase is a mast-cell-specific enzyme

Early life adversity drives sex-specific anhedonia and meningeal immune gene expression through mast cell activation

Exposure to early life adversity (ELA) in the form of physical and/or psychological abuse or neglect increases the risk of developing psychiatric and inflammatory disorders later in life. It has been hypothesized that exposure to ELA results in persistent, low grade inflammation that leads to increased disease susceptibility by amplifying the crosstalk between stress-processing brain networks and the immune system, but the mechanisms remain largely unexplored. The meninges, a layer of three overlapping membranes that surround the central nervous system (CNS)- dura mater, arachnoid, and piamater - possess unique features that allow them to play a key role in coordinating immune trafficking between the brain and the peripheral immune system. These include a network of lymphatic vessels that carry cerebrospinal fluid from the brain to the deep cervical lymph nodes, fenestrated blood vessels that allow the passage of molecules from blood to the CNS, and a rich population of resident mast cells, master regulators of the immune system. Using a mouse model of ELA consisting of neonatal maternal separation plus early weaning (NMSEW), we sought to explore the effects of ELA on sucrose preference behavior, dura mater expression of inflammatory markers and mast cell histology in adult male and female C57Bl/6 mice. We found that NMSEW alone does not affect sucrose preference behavior in males or females, but it increases the dura mater expression of the genes coding for mast cell protease CMA1 (cma1) and the inflammatory cytokine TNF alpha (tnf alpha) in females. When NMSEW is combined with an adult mild stress (that does not affect behavior or gene expression in NH animals) females show reduced sucrose preference and even greater increases in meningeal cma1 levels. Interestingly, systemic administration of the mast cell stabilizer Ketotifen before exposure to adult stress prevents both, reduction in sucrose preference an increases in cma1 expression in NMSEW females, but facilitates stress-induced sucrose anhedonia in NMSEW males and NH females. Finally, histological analyses showed that, compared to males, females have increased baseline activation levels of mast cells located in the transverse sinus of the dura mater, where the meningeal lymphatics run along, and that, in males and females exposed to adult stress, NMSEW increases the number of mast cells in the interparietal region of the dura mater and the levels of mast cell activation in the sagittal sinus regions of the dura mater. Together, our results indicate that ELA induces long-term meningeal immune gene changes and heightened sensitivity to adult stress-induced behavioral and meningeal immune responses and that these effects could mediated via mast cells.

Histamine receptors in heart failure

The biogenic amine, histamine, is found predominantly in mast cells, as well as specific histaminergic neurons. Histamine exerts its many and varied actions via four G-protein-coupled receptors numbered one through four. Histamine has multiple effects on cardiac physiology, mainly via the histamine 1 and 2 receptors, which on a simplified level have opposing effects on heart rate, force of contraction, and coronary vasculature function. In heart failure, the actions of the histamine receptors are complex, the histamine 1 receptor appears to have detrimental actions predominantly in the coronary vasculature, while the histamine 2 receptor mediates adverse effects on cardiac remodeling via actions on cardiomyocytes, fibroblasts, and even endothelial cells. Conversely, there is growing evidence that the histamine 3 receptor exerts protective actions when activated. Little is known about the histamine 4 receptor in heart failure. Targeting histamine receptors as a therapeutic approach for heart failure is an important area of investigation given the over-the-counter access to many compounds targeting these receptors, and thus the relatively straight forward possibility of drug repurposing. In this review, we briefly describe histamine receptor signaling and the actions of each histamine receptor in normal cardiac physiology, before describing in more detail the known role of each histamine receptor in adverse cardiac remodeling and heart failure. This includes information from both clinical studies and experimental animal models. It is the goal of this review article to bring more focus to the possibility of targeting histamine receptors as therapy for heart failure.

Manipulating angiotensin metabolism with angiotensin converting enzyme 2 (ACE2) in heart failure

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Heart failure is increasing in prevalence associated with a huge economic burden.

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ACE2 is a negative regulator of the renin–angiotensin system.

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Elevated ACE2 activity is a biomarker in heart failure.

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Enhancing ACE2 action may have unique therapeutic effects in patients with heart failure.

Angiotensin converting enzyme 2 (ACE2), is a monocarboxypeptidase which metabolizes several peptides including the degradation of Ang II, a peptide with vasoconstrictive/proliferative/effects, to generate Ang 1–7, which acting through its receptor Mas exerts vasodilatory/anti-proliferative actions. The classical pathway of the RAS involving the ACE-Ang II-AT₁ receptor axis is antagonized by the second arm constituted by the ACE2-Ang 1–7/Mas receptor axis. Loss of ACE2 enhances the adverse pathological remodeling susceptibility to pressure-overload and myocardial infarction. Human recombinant ACE2 is also a negative regulator of Ang II-induced myocardial hypertrophy, fibrosis and diastolic dysfunction and suppresses pressure-overload induced heart failure. Due to its characteristics, the ACE2-Ang 1–7/Mas axis may represent new possibilities for developing novel therapeutic strategies for the treatment of heart failure. Human recombinant ACE2 has been safely administered to healthy human volunteers intravenously resulting in sustained lowering of plasma Ang II levels. In this review, we will summarize the beneficial effects of ACE2 in heart disease and the potential use of human recombinant ACE2 as a novel therapy for heart failure.

Role of angiotensin-converting enzyme 2 (ACE2) in diabetic cardiovascular complications

Diabetes mellitus results in severe cardiovascular complications, and heart disease and failure remain the major causes of death in patients with diabetes. Given the increasing global tide of obesity and diabetes, the clinical burden of diabetes-induced cardiovascular disease is reaching epidemic proportions. Therefore urgent actions are needed to stem the tide of diabetes which entails new prevention and treatment tools. Clinical and pharmacological studies have demonstrated that AngII (angiotensin II), the major effector peptide of the RAS (renin–angiotensin system), is a critical promoter of insulin resistance and diabetes mellitus. The role of RAS and AngII has been implicated in the progression of diabetic cardiovascular complications and AT1R (AngII type 1 receptor) blockers and ACE (angiotensin-converting enzyme) inhibitors have shown clinical benefits. ACE2, the recently discovered homologue of ACE, is a monocarboxypeptidase which converts AngII into Ang-(1–7) [angiotensin-(1–7)] which, by virtue of its actions on the MasR (Mas receptor), opposes the effects of AngII. In animal models of diabetes, an early increase in ACE2 expression and activity occurs, whereas ACE2 mRNA and protein levels have been found to decrease in older STZ (streptozotocin)-induced diabetic rats. Using the Akita mouse model of Type 1 diabetes, we have recently shown that loss of ACE2 disrupts the balance of the RAS in a diabetic state and leads to AngII/AT1R-dependent systolic dysfunction and impaired vascular function. In the present review, we will discuss the role of the RAS in the pathophysiology and treatment of diabetes and its complications with particular emphasis on potential benefits of the ACE2/Ang-(1–7)/MasR axis activation.

Mast cells activate the renin angiotensin system and contribute to migraine: a hypothesis

Migraine is a chronic disease with episodic attacks, which, when frequent or severe, can be associated with poor quality of life, increased health resource utilization, lost productivity, and significant disability. Preventive therapy can therefore have a significant beneficial clinical and economic impact. However, many migraineurs are treated suboptimally. There is increasing evidence that activation and degranulation of meningeal mast cells result in meningeal irritation, vascular dilation, and stimulation of nearby nociceptive nerve endings of the trigeminal nerve, thus potentially contributing to the pathogenesis of migraine headache. The renin angiotensin system and its peptides are well represented in the mammalian central nervous system and can also promote neurogenic inflammation. Interestingly, mast cells are capable of releasing renin and increasing local production of Angiotensin II. We therefore hypothesize that mast cells contribute to migraine headache through activation of the renin angiotensin system. This hypothesis may help explain the association between migraine and cardiovascular disease as well as observations that medications that modulate the renin angiotensin system can reduce migraine-related morbidity in patients with frequently recurring migraine attacks.

Human umbilical cord blood-derived mast cells: a unique model for the study of neuro-immuno-endocrine interactions

Findings obtained using animal models have often failed to reflect the processes involved in human disease. Moreover, human cultured cells do not necessarily function as their actual tissue counterparts. Therefore, there is great demand for sources of human progenitor cells that may be directed to acquire specific tissue characteristics and be available in sufficient quantities to carry out functional and pharmacological studies. Acase in point is the mast cell, well known for its involvement in allergic reactions, but also implicated in inflammatory diseases. Mast cells can be activated by allergens, anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines, leading to selective release of mediators. These could be involved in many inflammatory diseases, such as asthma and atopic dermatitis, which worsen by stress, through activation by local release of corticotropin-releasing hormone or related peptides. Umbilical cord blood and cord matrix-derived mast cell progenitors can be separated magnetically and grown in the presence of stem cell factor, interleukin-6, interleukin-4, and other cytokines to yield distinct mast cell populations. The recent use of live cell array, with its ability to study such interactions rapidly at the single-cell level, provides unique new opportunities for fast output screening of mast cell triggers and inhibitors.

The critical role of mast cells in allergy and inflammation

Mast cells are well known for their involvement in allergic and anaphylactic reactions, but recent findings implicate them in a variety of inflammatory diseases affecting different organs, including the heart, joints, lungs, and skin. In these cases, mast cells appear to be activated by triggers other than aggregation of their IgE receptors (FcepsilonRI), such as anaphylatoxins, immunoglobulin-free light chains, superantigens, neuropeptides, and cytokines leading to selective release of mediators without degranulation. These findings could explain inflammatory diseases, such as asthma, atopic dermatitis, coronary inflammation, and inflammatory arthritis, all of which worsen by stress. It is proposed that the pathogenesis of these diseases involve mast cell activation by local release of corticotropin-releasing hormone (CRH) or related peptides. Combination of CRH receptor antagonists and mast cell inhibitors may present novel therapeutic interventions.

A new cardiac MASTer switch for the renin-angiotensin system

The aspartyl protease renin was first isolated from the kidney by Tigerstedt more than a century ago. In the kidney, renin secretion is tightly linked to sodium intake and renal perfusion pressure, reflecting the important role of the renin-angiotensin system (RAS) in controlling body fluid volume and blood pressure. The study by Mackins et al. in this issue of the JCI describes a novel source of renin: the mast cell (see the related article beginning on page 1063). This discovery suggests a distinct pathway for activation of the RAS that may have a particular impact on the pathogenesis of chronic tissue injury as well as more acute pathology such as arrhythmias in the heart.

Critical role of mast cells in inflammatory diseases and the effect of acute stress

Mast cells are not only necessary for allergic reactions, but recent findings indicate that they are also involved in a variety of neuroinflammatory diseases, especially those worsened by stress. In these cases, mast cells appear to be activated through their Fc receptors by immunoglobulins other than IgE, as well as by anaphylatoxins, neuropeptides and cytokines to secrete mediators selectively without overt degranulation. These facts can help us better understand a variety of sterile inflammatory conditions, such as multiple sclerosis (MS), migraines, inflammatory arthritis, atopic dermatitis, coronary inflammation, interstitial cystitis and irritable bowel syndrome, in which mast cells are activated without allergic degranulation.

Sheep mast cell proteinase-1: characterization as a member of a new class of dual-specific ruminant chymases

Sheep mast cell proteinase 1 (SMCP-1), which is abundantly expressed in gastrointestinal but not skin mast cells, was isolated and its substrate specificity was investigated. Peptide substrates, including angiotensin I, substance P, bradykinin and oxidized insulin B chain were hydrolysed at P1 Phe, Leu or Tyr residues, conforming to the known chymotrypsin-like properties of the enzyme. However, SMCP-1 was found to hydrolyse some chromogenic substrates with P1 Lys and Arg residues. The enzyme also demonstrated trypsin-like activity against protein substrates, cleaving BSA at Lys114-Leu115, Lys238-Val239, Lys260-Tyr261 and Lys376-His377. Bovine fibrinogen beta-chain was cleaved at Lys28-Lys29. To ensure homogeneity of the enzyme, the ratio of chymotrypsin-like to trypsin-like activity was observed; it was found to be constant during purification and between different preparations of SMCP-1. Treatment of SMCP-1 with a range of inhibitors decreased chymotrypsin-like and trypsin-like activities by similar extents, supporting the assertion that both activities are the property of a single enzyme. In terms of activity, and by N-terminal amino acid sequencing, SMCP-1 strongly resembles the similarly dual-specific bovine duodenal proteinase, duodenase. It is proposed that SMCP-1 and duodenase represent a new class of ruminant chymases with unusual dual specificities.

Cloning of cDNA for human granzyme 3

A serine protease gene was cloned from cDNA prepared from tissue isolated from human ascites. The gene codes for a protein of 264 amino acids, identified as human granzyme 3 by the N-terminal amino acid sequence. Granzyme 3 has the expected features of the chymotrypsin family of serine proteases, and is closely related to other human granzymes (40-45% identity). However, the closest granzyme 3 homologue is the recently characterized rat tryptase, RNK-Tryp-2 (75% identity). From Northern blots, granzyme 3 appears to be highly expressed in peripheral blood leukocytes, spleen, thymus, and lung tissues.

Cellular localization and regional distribution of an angiotensin II-forming chymase in the heart

The human heart is a target organ for the octapeptide hormone, angiotensin II (Ang II). Recent studies suggest that the human heart contains a dual pathway of Ang II formation in which the major Ang II-forming enzymes are angiotensin I-converting enzyme (ACE) and chymase. Human heart chymase has recently been purified and its cDNA and gene cloned. This cardiac serine proteinase is the most efficient and specific Ang II-forming enzyme described. To obtain insights into the cardiac sites of chymase-dependent Ang II formation, we examined the cellular localization and regional distribution of chymase in the human heart. Electron microscope immunocytochemistry using an anti-human chymase antibody showed the presence of chymase-like immunoreactivity in the cardiac interstitium and in cytosolic granules of mast cells, endothelial cells, and some mesenchymal interstitial cells. In the cardiac interstitium, chymase-like immunoreactivity is associated with the extracellular matrix. In situ hybridization studies further indicated that chymase mRNA is expressed in endothelial cells and in interstitial cells, including mast cells. Tissue chymase levels were determined by activity assays and by Western blot analyses. Chymase levels were approximately twofold higher in ventricles than in atria. There were no significant differences in chymase levels in ventricular tissues obtained from non-failing donor hearts, failing ischemic hearts, or hearts from patients with ischemic cardiomyopathy. These findings suggest that a major site of chymase-dependent Ang II formation in the heart is the interstitium and that cardiac mast cells, mesenchymal interstitial cells, and endothelial cells are the cellular sites of synthesis and storage of chymase. In the human heart, because ACE levels are highest in the atria and chymase levels are highest in ventricles, it is likely that the relative contribution of ACE and chymase to cardiac Ang II formation varies with the cardiac chamber. Such differences may lead to differential suppression of cardiac Ang II levels during chronic ACE inhibitor therapy in patients with congestive heart failure.

Peptidases and smooth muscle cell angiotensin II receptor pharmacology

Angiotensin (A) II receptors on rat aortic smooth muscle (RASM) cell membranes were characterized using the radioligand [125I][Sar1Ile8]AII ([125I]SI-AII). Angiotensin I, AII, and AIII inhibited specific [125I]SI-AII binding, and their rank order of potencies, and Ki values (nM) were: AII (3.7) > AI (32.5) > or = AIII (54.0), which differed from that observed for rat adrenal cortex: AII (0.85) > AIII (3.3) >> AI (100). Similar results were observed for RASM membranes in the presence of guanine nucleotides, and for intact cells in the absence or presence of an internalization inhibitor. Lowering the incubation temperature from 37 degrees C to 4 degrees C, or inclusion of PMSF (1 mM), and preparing membranes in the presence of EGTA (1 mM) altered the rank order of potencies and Ki values (nM) of the angiotensin peptides to: AII (1.1) > AIII (7.0) >> AI (144). [125I]Angiotensin I was metabolized completely over the course of 90 min to small (<tetrapeptide) fragments as measured by HPLC. There was no evidence for formation of AII or AIII from AI, which would have explained the unusually high potency of AI. [125I]Angiotensin I metabolism could be attenuated by inhibitors of serine proteases PMSF, aprotinin, and chymostatin. The beneficial effects of PMSF and EGTA suggested that serine protease(s) and metalloproteases contribute to the observed anomalous pharmacological characteristics of AI and AIII, respectively. The RASM cell membranes contained a homogeneous population of binding sites for losartan, and its Ki value differed in the absence (50 nM) or presence (16 nM) of protease inhibitors, which suggests that the receptor may also be a target for these peptidases.(ABSTRACT TRUNCATED AT 250 WORDS)

The cardiac renin-angiotensin system: physiological relevance and pharmacological modulation

Many cell types in myocardial tissue, including cardiocytes, contain receptors for angiotensin-II, but the activation of these receptors requires angiotensin concentrations in the micromolar range, which do not occur in plasma in vivo. However, angiotensins formed locally in the heart can activate these receptors in a paracrine and autocrine mode. In cardiac hypertrophy due to hemodynamic overload, the myocardial angiotensin formation is enhanced due to an augmented expression of angiotensinogen and ACE. Though the mRNA for prorenin is expressed in myocardium, the formation of active renin within the heart has not yet been demonstrated and myocardial renin activity is mainly due to contamination from circulating active renin. Intracoronary application of ACE inhibitors in hypertrophied hearts in vivo and in vitro indicates that the locally formed angiotensin-II contributes to coronary constriction, impairment of diastolic relaxation and marginally to the maintenance of systolic tension development. Angiotensin-II can exert trophic effects on cardiocytes and cardiac fibroblasts, and chronic inhibition of the cardiac RAS by ACE-inhibitors or AT receptor antagonists can induce partial regression of overload hypertrophy, even without normalizing the overload. This anti-trophic action may be partially due to the impairment of the angiotensin axis, but also due to enhancement of bradykinin availability, which results in an augmented release of endothelial anti-trophic signals such as EDRF/NO and prostacyclin. Preliminary evidence is compatible with the hypothesis that an activated local RAS in elastic arteries contributes to the localization and progression of atherosclerosis by suppressing EDRF releasability. However, the anti-atherosclerotic potential of ACE inhibitors and AT receptor antagonists in humans is still unknown.

Pathophysiology of heart failure and the renin-angiotensin-system

For more than a decade, the inhibition of the renin-angiotensin system in heart failure has been regarded as pure vasodilator therapy. Consequently, the role of the renin-angiotension system has been seen as contributing to hemodynamic overload by vasoconstriction and volume retention. Meanwhile, clinical experience was indicated that important additional aspects of ACE-inhibition in heart failure are attenuation of the enhanced neuroendocrine activity and reversal or prevention of inappropriate trophic reactions of the overloaded myocardium. In overloaded hearts there is enhanced intracardiac formation of angiotensin due to enhanced expression of angiotensinogen and ACE, and due to accumulation of circulating, nephrogenic active renin. In human hearts, a mast-cell-derived chymase, which is not blocked by ACE-inhibition, contributes to intracardiac angiotensin formation. The enhanced intracardiac angiotensin-II formation in overloaded hearts is involved in coronary constriction, impairment of diastolic relaxation, myocyte enlargement and interstitial fibrosis, which aggravate the diastolic impairment. The major problem in overloaded, hypertrophied cardiocytes is the dedifferentiation with instabilization of Ca(++)-homeostasis due to an altered program of gene expression. Dedifferentiated cardiocytes have a reduced expression of sarcoplasmic reticulum Ca(++)-ATPase and an enhanced expression of the sarcolemmal Na+/Ca(++)-exchanger, resulting in an attenuation of active diastole (Ca(++)-reaccumulation into the sarcoplasmic reticulum), a depressed force-frequency relation, and an enhanced susceptibility for fatal arrhythmias. Furthermore, an enhanced local renin-angiotensin system in distensible coronary and systemic arteries seems to contribute to a reduced releasability of endothelium-derived relaxing factor, probably by reducing bradykinin availability. This modulation of endothelial function appears to contribute to the localization and progression of atheroma development in presence of risks factors for atherosclerosis.

Modulation of myocardial sarcoplasmic reticulum Ca(++)-ATPase in cardiac hypertrophy by angiotensin converting enzyme?

Myocardial hypertrophy in response to hemodynamic overload is an established risk factor for cardiovascular morbidity and mortality. Partially, this may be due to alterations in cardiac gene expression, resulting in a more fetal-like myocyte phenotype with a fragile Ca(++)-homeostasis. Depressed expression of the sarcoplasmic reticulum Ca(++)-ATPase is the hallmark of this overload phenotype, contributing to prolonged cytosolic Ca(++)-transients, disturbed diastolic relaxation, altered force-frequency relation, and probably, electrophysiologic instability with susceptibility to malignant arrhythmias. Since angiotensin II is a growth-promoting factor in several cellular systems, the local formation of angiotensin II within the myocardium might contribute to the trophic response and the phenotype shift of overloaded myocardium. Several observations are consistent with this hypothesis: the cardiac expression of ACE and angiotensinogen is enhanced in experimental myocardial overload and in human endstage congestive heart failure; prolonged observations of experimental cardiac overload with hypertrophy-induced putative normalisation of myocardial systolic wall stress demonstrated a renormalization of ventricular tissue ACE activity and of ventricular sarcoplasmic Ca(++)-ATPase expression and activity; normalizing ventricular tissue ACE activity in experimental cardiac overload by chronic nonhypotensive ACE inhibitor therapy caused a parallel partial normalization of hypertrophy and underexpression of sarcoplasmic CA(++)-ATPase. This partial normalization of myocyte Ca(++)-homeostasis in overload hypertrophy by non-hypotensive chronic ACE-inhibition is attenuated by concomitant chronic application of bradykinin-2 receptor blockade, indicating an involvement of altered bradykinin metabolism in the phenotype modulation due to chronic ACE inhibition. While these observations are consistent with a direct influence of local ACE activity on the sarcoplasmic reticulum, the cell type contributing to the enhanced ACE expression in overload and the specific mechanism of this influence are unknown.