Short Communication: Taurine Long-Term Treatment Prevents the Development of Cardiac Hypertrophy, and Premature Death in Hereditary Cardiomyopathy of the Hamster Is Sex-Independent

Recently, we reported that during the hypertrophic phase (230 days old) of hereditary cardiomyopathy of the hamster (HCMH), short-term treatment (20 days) with 250 mg/kg/day of taurine prevents the development of hypertrophy in males but not in females. However, the mortality rate in non-treated animals was higher in females than in males. To verify whether the sex-dependency effect of taurine is due to the difference in the disease's progression, we treated the 230-day-old animals for a longer time period of 122 days. Our results showed that long-term treatment with low and high concentrations of taurine significantly prevents cardiac hypertrophy and early death in HCMH males (p < 0.0001 and p < 0.05, respectively) and females (p < 0.01 and p < 0.0001, respectively). Our results demonstrate that the reported sex dependency of short-term treatments with taurine is due to a higher degree of heart remodeling in females when compared to males and not to sex dependency. In addition, sex-dependency studies should consider the differences between the male and female progression of the disease. Thus, long-term taurine therapies are recommended to prevent remodeling and early death in hereditary cardiomyopathy.

Taurine Prevents Angiotensin II-Induced Human Endocardial Endothelium Morphological Remodeling and the Increase in Cytosolic and Nuclear Calcium and ROS

Endocardial endothelium (EE) is a layer of cells covering the cardiac cavities and modulates cardiomyocyte function. This cell type releases several cardioactive factors, including Angiotensin II (Ang II). This octopeptide is known to induce cardiac hypertrophy. However, whether this circulating factor also induces EE hypertrophy is not known. Taurine is known to prevent cardiac hypertrophy. Whether this endogenous antioxidant prevents the effect of Ang II on human EE (hEE) will be verified. Using quantitative fluorescent probe imaging for calcium and reactive oxygen species (ROS), our results show that Ang II induces (10-7 M, 48 h treatment) an increase in hEE cell (hEEC) volume and its nucleus. Pretreatment with 20 mM of taurine prevents morphological remodeling and increases intracellular calcium and ROS. These results suggest that the reported Ang II induces cardiac hypertrophy is associated with hEEC hypertrophy. This later effect is prevented by taurine by reducing intracellular calcium and ROS overloads. Thus, taurine could be an excellent tool for preventing Ang II-induced remodeling of hEECs.

High salt-induced morphological and glycocalyx remodeling of human vascular smooth muscle cells is reversible but induces a high sodium salt-like sensitive memory

Our recent work showed that short-term treatment (1-2 days) with high sodium salt had no effect on the morphology of human vascular smooth muscle cells (hVSMCs). However, chronic (long-term treatment, 6-16 days) high sodium salt (CHSS) induced hypertrophy and decreased the relative density of the glycocalyx in hVSMCs. Whether this CHSS effect is reversible at both the morphological and the intracellular calcium and sodium levels is unknown. In the present study, we tested the hypothesis that the effect of CHSS on the morphological and functional levels of hVSMCs is reversible. However, it induced an irreversible increase in the sensitivity of the cells following short-term treatment with high extracellular Na+. We tested the effects of the removal of CHSS treatment on the morphology and intracellular sodium and calcium of hVSMCs. Our results showed that restoring average sodium concentration (145 mM) modeled back the relative density of the glycocalyx, the intracellular resting calcium and sodium levels, and the whole cell and nuclear volumes of hVSMCs. In addition, it induced a permanent remodeling of hVSMCs' response to a short-term increase in the extracellular level of sodium salt by developing spontaneous cytosolic and nuclear calcium waves. Our results showed that CHSS is reversible at both the morphological and basal intracellular ionic levels. However, it maintained a high sensitivity to short-term elevation of extracellular sodium. These results suggest that even if chronic high salt is corrected, it induces a high sodium salt-like sensitive memory.

Calcium Homeostasis, Transporters, and Blockers in Health and Diseases of the Cardiovascular System

Calcium is a highly positively charged ionic species. It regulates all cell types' functions and is an important second messenger that controls and triggers several mechanisms, including membrane stabilization, permeability, contraction, secretion, mitosis, intercellular communications, and in the activation of kinases and gene expression. Therefore, controlling calcium transport and its intracellular homeostasis in physiology leads to the healthy functioning of the biological system. However, abnormal extracellular and intracellular calcium homeostasis leads to cardiovascular, skeletal, immune, secretory diseases, and cancer. Therefore, the pharmacological control of calcium influx directly via calcium channels and exchangers and its outflow via calcium pumps and uptake by the ER/SR are crucial in treating calcium transport remodeling in pathology. Here, we mainly focused on selective calcium transporters and blockers in the cardiovascular system.

Morphological and Functional Remodeling of Vascular Endothelium in Cardiovascular Diseases

The vascular endothelium plays a vital role during embryogenesis and aging and is a cell monolayer that lines the blood vessels. The immune system recognizes the endothelium as its own. Therefore, an abnormality of the endothelium exposes the tissues to the immune system and provokes inflammation and vascular diseases such as atherosclerosis. Its secretory role allows it to release vasoconstrictors and vasorelaxants as well as cardio-modulatory factors that maintain the proper functioning of the circulatory system. The sealing of the monolayer provided by adhesion molecules plays an important role in cardiovascular physiology and pathology.

Age-depend effect of insulin in the regulation of intracellular calcium in ventricular cardiomyocytes

In this study, we wanted to verify if the effect of insulin on calcium homeostasis depends on the heart's development stage. Using a quantitative 3D confocal microscopy, we tested the effect of a high insulin concentration (100 µU) in freshly cultured ventricular cardiomyocytes from newborn and adult rats. Our results showed that the cytosolic basal level of calcium was higher in newborn cardiomyocytes with no change in the nuclear basal calcium level compared to the adult cardiomyocytes; in addition, insulin-induced a slow increase of cytosolic and nuclear calcium in newborn ventricular cardiomyocytes, followed by two phases. However, the first phase of slow cytosolic and nuclear calcium increase was absent in adult rat ventricular cardiomyocytes. Furthermore, the time to the onset of increase of cytosolic and nuclear calcium was longer in newborn cardiomyocytes compared to adults. Moreover, the time to peak of the calcium transient was shorter in newborns than in adult cardiomyocytes. These results demonstrate that insulin differently regulates calcium homeostasis in newborns than in adult cardiomyocytes. Thus, newborn rat cardiomyocytes, commonly used in research as a model for adult cardiomyocytes, should be used with caution when dealing with insulin in normal and disease conditions.

Short-Communication: Short-Term Treatment with Taurine Prevents the Development of Cardiac Hypertrophy and Early Death in Hereditary Cardiomyopathy of the Hamster and Is Sex-Dependent

Premature death due to heart failure is a major health problem. Taurine is a non-essential amino acid that has received much attention. However, although many studies have been carried out on the beneficial effects of taurine in cardiac pathophysiology, no studies have investigated the effect of taurine treatment on the development of hereditary cardiomyopathy (HCM) associated with hypertrophy, heart failure, and early death. This study aims to verify whether short-term treatment (20 days) with taurine in tap water prevents the development of hypertrophy and premature death in hereditary cardiomyopathy of the hamster (HCMH) of the line UM-X7.1 and if its effect is sex-dependent. Our results show that treatment for 20 days with taurine (250 mg/kg/day or 25 mg/animal/day) during the development of the hypertrophic phase (220 days old) significantly decreased (p < 0.01) the heart weight to body weight ratio in male HCMHs without affecting the female. During the 20 days (220−240 days old), there were nearly 40% premature deaths in non-treated males HCMHs and 50% in female HCMHs. Treatment for 20 days wholly and significantly prevented early death in both males and females HCMHs. Our results demonstrate that short-term treatment with taurine prevents the development of cardiac hypertrophy associated with HCM in a sex-dependent manner; however, it prevents early death in a sex-independent fashion. Our results suggest that taurine supplementation could be used to treat HCM.

Potentiation of B2 receptor signaling by AltB2R, a newly identified alternative protein encoded in the human bradykinin B2 receptor gene

Recent functional and proteomic studies in eukaryotes (www.openprot.org) predict the translation of alternative open reading frames (AltORFs) in mature G-protein-coupled receptor (GPCR) mRNAs, including that of bradykinin B2 receptor (B2R). Our main objective was to determine the implication of a newly discovered AltORF resulting protein, termed AltB2R, in the known signaling properties of B2R using complementary methodological approaches. When ectopically expressed in HeLa cells, AltB2R presented predominant punctate cytoplasmic/perinuclear distribution and apparent cointeraction with B2R at plasma and endosomal/vesicular membranes. The presence of AltB2R increases intracellular [Ca²⁺] and ERK1/2-MAPK activation (via phosphorylation) following B2R stimulation. Moreover, HEK293A cells expressing mutant B2R lacking concomitant expression of AltB2R displayed significantly decreased maximal responses in agonist-stimulated Gα_q-Gα_i2/3-protein coupling, IP₃ generation, and ERK1/2-MAPK activation as compared with wild-type controls. Conversely, there was no difference in cell-surface density as well as ligand-binding properties of B2R and in efficiencies of cognate agonists at promoting B2R internalization and β-arrestin 2 recruitment. Importantly, both AltB2R and B2R proteins were overexpressed in prostate and breast cancers, compared with their normal counterparts suggesting new associative roles of AltB2R in these diseases. Our study shows that BDKRB2 is a dual-coding gene and identifies AltB2R as a novel positive modulator of some B2R signaling pathways. More broadly, it also supports a new, unexpected alternative proteome for GPCRs, which opens new frontiers in fields of GPCR biology, diseases, and drug discovery.

Vascular smooth muscle remodeling in health and disease

In blood vessels, vascular smooth muscle cells (VSMCs) generally exist in two major phenotypes: contractile and non-contractile (synthetic). The contractile phenotype is predominant and includes quiescent or differentiated VSMCs, which function as the regulators of blood vessel diameter and blood flow. According to some literature in the field, contractile VSMCs do not switch to the non-contractile phenotype due to the activation of specific transcription factors that are considered as guardians of the contractile phenotype. However, a vast amount of the literature uses the terms remodeling and phenotype switching of contractile VSMCs interchangeably based mainly on studies dealing with atherosclerosis. The use of the terms remodeling and switching to describe changes in phenotype based on morphological criteria can be confusing. The term remodeling was first used to describe morphological changes in the heart and was soon used to describe phenotype changes of contractile VSMCs based on morphological criteria. The latter were introduced in early studies, and new molecular criteria were later added, including changes in gene expression, which could be irreversible. In this review, we will discuss the different views concerning remodeling and possible switching of contractile VSMCs to a non-contractile phenotype. We conclude that only remodeling of contractile VSMCs may take place upon vascular injury and disease.

Taurine and cardiac disease: state of the art and perspectives

Taurine is a nonessential amino acid that has received much attention. Two organs, the heart and the brain, are known to produce their own taurine, but in very limited quantities. It is for this reason that supplementation with this amino acid is necessary. Today, taurine is present in almost all energy drinks. A very vast literature reported beneficial effects of taurine in hepatic dysfunction, gastrointestinal injury, kidney diseases, diabetes, and cardiovascular diseases. Most of its effects were attributed to its modulation of Ca2+homeostasis as well as to its antioxidant properties. In this review, we will focus on the current status of taurine modulation of the cardiovascular system and discuss future avenues for its use as a supplement therapy in a specific cardiovascular disease, namely hypertrophy, and heart failure.

Increase of NADPH oxidase 3 in heart failure of hereditary cardiomyopathy

During the development of heart failure in humans and animal models, an increase in reactive oxygen species (ROS) levels was observed. However, there is no information whether this increase of ROS is associated with an increase in the density of specific isoforms of NADPH oxidases (NOXs) 1–5. The objective of this study was to verify whether the densities of NOXs 1–5 change during the development of heart failure. Using the well-known model of cardiomyopathic hamsters, the UM-X 7.1 line, a model that strongly resembles the pathology observed in humans from a morphological and functional point of view, our studies showed that, as in humans, NOXs 1–5 are present in both normal and UM-X7.1 hamster hearts. Even though the densities of NOXs 2 and 5 were unchanged, the levels of both NOXs 1 and 4 significantly decreased in UM-X7.1 hamster hearts during heart failure. These changes were accompanied with a significant increase in NOX3 level. These results suggest that, during heart failure, NOX3 plays a vital role in compensating the decrease of NOXs 1 and 4. This increase in NOX3 may also be responsible, at least in part, for the reported increase in ROS levels in heart failure.

Extracellular and intracellular tumor necrosis factor alpha modulates cytosolic and nuclear calcium in human cardiovascular cells 1

Tumor necrosis factor alpha (TNFα) and its type 1 receptor (TNFR1) are implicated in several autoimmune diseases, including rheumatoid arthritis, and are associated with complications at the cardiovascular level. Using human cardiomyocytes, vascular smooth muscle, vascular endothelial, and endocardial endothelial cells coupled to indirect immunofluorescence, our results showed the presence of TNFR1 at the levels of the plasma membrane (including the cytosol) and mostly at the level of the nuclear membranes (including the nucleoplasm). The distribution of the receptor is different between cell types; however, the density is significantly higher at the nuclear level in all 4 cell types. The density of the receptor was the highest in contractile cells including the cardiomyocytes and vascular smooth muscle cells, compared with endothelial cells including endocardial endothelial and vascular endothelial cells. Using the Ca²⁺ probe Fluo-3 coupled to quantitative confocal microscopy, our results showed that the cytokine induced a sustained Ca²⁺ increase in both the cytosol and nucleoplasm of all 4 cell types. This increase was more significant at the nuclear level, mainly in endothelial cells. Our results demonstrated the presence of TNFR1 at both the cell and nuclear membranes of cardiovascular cells, and that its activation modulated both cytosolic and nuclear Ca²⁺.

Angiotensin II induces apoptosis of human right and left ventricular endocardial endothelial cells by activating the AT2 receptor 1

Endocardial endothelial cells (EECs) form a monolayer lining the ventricular cavities. Studies from our laboratory and the literature have shown differences between EECs isolated from the right and left ventricles (EECRs and EECLs, respectively). Angiotensin II (Ang II) was shown to induce apoptosis of different cell types mainly via AT₁ receptor activation. In this study, we verified whether Ang II induces apoptosis of human EECRs and EECLs (hEECRs and hEECLs, respectively) and via which type of receptor. Using the annexin V labeling and in situ TUNEL assays, our results showed that Ang II induced apoptosis of both hEECRs and hEECLs in a concentration-dependent manner. Our results using specific AT₁ and AT₂ receptor antagonists showed that the Ang-II-induced apoptosis in both hEECRs and hEECLs is mediated mainly via the AT₂ receptor. However, AT₁ receptor blockade partially prevented Ang-II-induced apoptosis, particularly in hEECRs. Hence, our results suggest that mainly AT₂ receptors mediate Ang-II-induced apoptosis of hEECRs and hEECLs. The damage of EECs would affect their function as a physical barrier between the blood and cardiomyocytes, thus affecting cardiomyocyte functions.

High salt-induced hypertrophy of human vascular smooth muscle cells associated with a decrease in glycocalyx

All health organizations agree that, presently, the average daily salt (sodium chloride) consumption per person has attained almost double the recommended amount. A chronic high salt diet contributes to the increase in blood pressure and to the development of cardiovascular disease. Although our knowledge of hypertension, in general, is abundant, little is known about salt-sensitive hypertension. Here we tested the hypothesis that acute and/or chronic high salt mimicking that present in high-salt sensitive hypertensive patients may induce hypertrophy of human vascular smooth muscle cells (hVSMCs) and their nuclei that are associated with damage to the plasma membrane glycocalyx. Using quantitative 3D confocal microscopy coupled to immunofluorescence techniques, we tested the effects of acute (2-4 days) and chronic (6-16 days) treatments of hVSMCs without (145 mM) or with high (149 mM) extracellular sodium chloride. Our results showed that acute treatment with high salt significantly decreased the relative density of membrane glycocalyx without affecting the whole cell and nuclear volumes of hVSMCs. However, chronic treatments with high salts induced significant decreases in the relative density of glycocalyx accompanied by significant increases in the whole cell and nuclear volumes as well as in the protein/DNA ratio. The high salt-induced hVSMC hypertrophy was associated with a sustained increase in intracellular sodium and calcium. Our results clearly showed that, increasing salt concentration by as little as 4 mM immediately induced damage to the cell membrane glycocalyx leading to chronic Na⁺ and Ca²⁺ overloads and hVSMC hypertrophy. The latter may reduce the lumen of arteries leading to an increase in blood pressure. Future identification of the mechanisms that are implicated in a high salt-induced remodeling of hVSMCs may permit the development of new therapeutic interventions for the treatment of high salt-sensitive hypertension and the prevention of the associated cardiovascular diseases.

Physical contact between human vascular endothelial and smooth muscle cells modulates cytosolic and nuclear calcium homeostasis

The interaction between vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) plays an important role in the modulation of vascular tone. There is, however, no information on whether direct physical communication regulates the intracellular calcium levels of human VECs (hVECs) and (or) human VSMCs (hVSMCs). Thus, the objective of the study is to verify whether co-culture of hVECs and hVSMCs modulates cytosolic ([Ca²⁺]_c) and nuclear calcium ([Ca²⁺]_n) levels via physical contact and (or) factors released by both cell types. Quantitative 3D confocal microscopy for [Ca²⁺]_c and [Ca²⁺]_n measurement was performed in cultured hVECs or hVSMCs or in co-culture of hVECs-hVSMCs. Our results show that: (1) physical contact between hVECs-hVECs or hVSMCs-hVSMCs does not affect [Ca²⁺]_c and [Ca²⁺]_n in these 2 cell types; (2) physical contact between hVECs and hVSMCs induces a significant increase only of [Ca²⁺]_n of hVECs without affecting the level of [Ca²⁺]_c and [Ca²⁺]_n of hVSMCs; and (3) preconditioned culture medium of hVECs or hVSMCs does not affect [Ca²⁺]_c and [Ca²⁺]_n of both types of cells. We concluded that physical contact between hVECs and hVSMCs only modulates [Ca²⁺]_n in hVECs. The increase of [Ca²⁺]_n in hVECs may modulate nuclear functions that are calcium dependent.

Angiotensin II receptors’ modulation of calcium homeostasis in human vascular endothelial cells

Angiotensin II (AngII) plays an important role in the regulation of vascular smooth muscle function. However, little is known about AngII and its receptors AT1 (AT1R) and AT2 (AT2R) and their modulation of intracellular calcium in vascular endothelial cells (VECs) in general and more particularly of human origin. Using western blots, our results showed that AT1Rs and AT2Rs are present in human VECs (hVECs). Using quantitative 3D confocal imaging, our results showed that AngII is present at the cytoplasmic and nucleoplasmic levels and its relative density is lower in the nucleoplasm. However, both AngII receptors AT1 and AT2 are present at both the plasma and the nuclear envelope membranes (NEMs). AngII (10−10 mol/L) induces a transient decrease of the relative density of cytosolic and nuclear AT1Rs. Blockade of AT1Rs with losartan or blocking protein synthesis with cycloheximide does not prevent internalization and nuclear translocation of AT1Rs but prevents de novo AT1R synthesis. In addition, AngII induces cytosolic and nuclear increases (EC50 near 5 × 10−14 mol/L) of calcium via the activation of AT1Rs. These results demonstrate that both AT1 and AT2 receptors are present in hVECs, and that only AT1Rs seem to undergo transcellular trafficking and modulate cytosolic and nuclear calcium homeostasis.

Neuropeptide Y and its receptors in ventricular endocardial endothelial cells

Endocardial endothelial cells (EECs) constitute an important component of the heart. These cells form a monolayer that covers the cavities of the right (EECRs) and left (EECLs) ventricles. They play an important role in cardiac excitation-contraction coupling via their secretion of cardioactive factors such as neuropeptide Y (NPY). They also contribute to cardiac pathology such as arrhythmia, hypertrophy, and heart failure. Differences between EECRs and EECLs contribute to tuning of circulating factors at the entry and exit of the ventricles. NPY, via activation of its receptors, modulates the excitation-secretion coupling of EECs, thus, indirectly modulating cardiac function and remodeling.

Role of endothelin-1 and its receptors, ETA and ETB, in the survival of human vascular endothelial cells

Our previous work showed the presence of endothelin-1 (ET-1) receptors, ET_A and ET_B, in human vascular endothelial cells (hVECs). In this study, we wanted to verify whether ET-1 plays a role in the survival of hVECs via the activation of its receptors ET_A and (or) ET_B (ET_AR and ET_BR, respectively). Our results showed that treatment of hVECs with ET-1 prevented apoptosis induced by genistein, an effect that was mimicked by treatment with ET_BR-specific agonist IRL1620. Furthermore, blockade of ET_BR with the selective ET_BR antagonist A-192621 prevented the anti-apoptotic effect of ET-1 in hVECs. However, activation of ET_A receptor alone did not seem to contribute to the anti-apoptotic effect of ET-1. In addition, the anti-apoptotic effect of ET_BR was found to be associated with caspase 3 inhibition and does not depend on the density of this type of receptor. In conclusion, our results showed that ET-1 possesses an anti-apoptotic effect in hVECs and that this effect is mediated, to a great extent, via the activation of ET_BR. This study revealed a new role for ET_BR in the survival of hVECs.

Difference in the response to angiotensin II between left and right ventricular endocardial endothelial cells

Previous studies focused on the right ventricular endocardial endothelial cells (EECRs) and showed that angiotensin II (Ang II) induced increase in cytosolic and nuclear calcium via AT₁ receptor activation. In the present study, we verified whether the response of left EECs (EECLs) to Ang II is different than that of EECRs. Our results showed that the EC₅₀ of the Ang II-induced increase of cytosolic and nuclear calcium in EECLs was 10× higher (around 2 × 10^-13 mol/L) than in EECRs (around 8 × 10^-12 mol/L). The densities of both AT₁ and AT₂ receptors were also higher in EECLs than those previously reported in EECRs. The effect of Ang II was mediated in both cell types via the activation of AT₁ receptors. Treatment with Ang II induced a significant increase of cytosolic and nuclear AT₁ receptors in EECRs, whereas the opposite was found in EECLs. In both cell types, there was a transient increase of cytosolic and nuclear AT₂ receptors following the Ang II treatment. In conclusion, our results showed that both AT₁ and AT₂ receptors densities are higher in both EECLs compared to what was reported in EECRs. The higher density of AT₁ receptors in EECLs compared to REECs may explain, in part, the higher sensitivity of EECLs to Ang II.

Na+-H+ exchanger and proton channel in heart failure associated with Becker and Duchenne muscular dystrophies

Cardiomyopathy is found in patients with Duchenne (DMD) and Becker (BMD) muscular dystrophies, which are linked muscle diseases caused by mutations in the dystrophin gene. Dystrophin defects are not limited to DMD but are also present in mild BMD. The hereditary cardiomyopathic hamster of the UM-X7.1 strain is a particular experimental model of heart failure (HF) leading to early death in muscular dystrophy (dystrophin deficiency and sarcoglycan mutation) and heart disease (δ-sarcoglycan deficiency and dystrophin mutation) in human DMD. Using this model, our previous work showed a defect in intracellular sodium homeostasis before the appearance of any apparent biochemical and histological defects. This was attributed to the continual presence of the fetal slow sodium channel, which was also found to be active in human DMD. Due to muscular intracellular acidosis, the intracellular sodium overload in DMD and BMD was also due to sodium influx through the sodium-hydrogen exchanger NHE-1. Lifetime treatment with an NHE-1 inhibitor prevented intracellular Na⁺ overload and early death due to HF. Our previous work also showed that another proton transporter, the voltage-gated proton channel (Hv1), exists in many cell types including heart cells and skeletal muscle fibers. The Hv1 could be indirectly implicated in the beneficial effect of blocking NHE-1.

Inhibition of platelet aggregation ex vivo is repressed in apolipoprotein E deficient mice

In the present study, we assessed whether the endogenous platelet inhibitory mechanisms are altered in the early to moderate stages of the atherosclerotic process. Apolipoprotein E deficient mice (ApoE-/-), a mouse model of atherosclerosis, and their wild-type (WT) counterparts were used to assess agonist-stimulated synthesis of prostacyclin (PGI₂), inhibition of platelet aggregation ex vivo, and intra-platelet cAMP levels. Basal U46619 and ADP -induced platelet aggregation in vitro were increased in ApoE-/- mice at 18-20 weeks in comparison with 8-10 weeks of age. Systemically administered endothelin-1 (ET-1) or bradykinin (BK) inhibited platelet aggregation in a similar fashion in 8- to 10-week-old ApoE-/- and WT mice, but not in the ApoE-/- mice at 18-20 weeks of age, although both peptides maintained their capacity to increase plasma levels of the PGI₂. Intravenous infusion of PGI₂ also failed to inhibit platelet aggregation ex vivo in 18- to 20-week-old ApoE-/- mice. Interestingly, both BK and PGI₂ retained their ability to increase intraplatelet cAMP in WT and ApoE-/- mice. Our results suggest that a loss of activity of endogenous inhibitorymechanisms could contribute to the increased platelet reactivity in ApoE-/- mice, and that this phenomenon occurs early in the intermediate stage of the atherosclerotic process.

ETA and ETB receptors contribute to neuropeptide Y-induced secretion of endothelin-1 in right but not left human ventricular endocardial endothelial cells

Our recent work showed that neuropeptide Y-induced secretion of endothelin-1 (ET-1) in left and right human ventricular endocardial endothelial cells (hLEECs or hREECs respectively) via the activation of neuropeptide Y2 or Y5 receptors depending on the cell type. The aim of this study was to verify whether hLEECs or hREECs secretion of ET-1 induced by NPY is due, in part, to the activation of ETA and/or ETB receptors by the secreted ET-1. Using the technique of indirect immunofluorescence coupled to real 3-D confocal microscopy, as well as ELISA, our results show that in hREECs, the NPY-induced release of ET-1 seems to be due, in part, to the activation of both ETA and ETB receptors. On the other hand, in hLEECs, ETA and ETB receptors do not contribute to the ET-1 released by NPY. Therefore, our results suggest that the NPY-induced release of ET-1 in EECRs is due to NPY receptor activation and the subsequent activation of the ETA and ETB receptors by the released ET-1. However, the release of ET-1 by NPY in hLEECs is mainly due to NPY receptor activation. Furthermore, this secretory process of ET-1 is different between the right and left ventricular cells and highlights the important tuning roles that right and left ventricular EECs possess as well as their contribution to the physiological and pathophysiological states of the underlying heart muscle.

Na+–H+ exchanger inhibitor prevents early death in hereditary cardiomyopathy

Using the UM-X7.1 hereditary cardiomyopathic and muscular dystrophy hamsters (HCMH), we tested the effects of lifelong preventive or curative treatments during the heart failure phase with the NHE-1 inhibitor EMD 87580 (EMD) or with the angiotensin-converting enzyme inhibitor cilazapril on the intracellular Na+ and Ca2+ overloads, elevated level of NHE-1, necrosis, hypertrophy, heart failure, and early death. Our results showed that 310-day pretreatment of 30-day-old HCMHs with EMD significantly prevented cardiac necrosis, cardiomyocyte hypertrophy, and reduced the heart to body mass ratio. This treatment significantly prevented Na+ and Ca2+ overloads and the increase in NHE-1 protein level observed in HCMHs. Importantly, this lifelong preventive treatment significantly decreased the levels of creatine kinase and prevented early death of HCMHs. Curative treatment of hypertrophic 275-day-old HCMHs for 85 days with EMD significantly prevented hypertrophy and early death of HCMHs. However, treatments with cilazapril did not have any significant effects on the cardiac parameters studied or on early death of HCMHs. Our results suggest that the increase in the NHE-1 level and the consequent Na+ and Ca2+ overloads are implicated in the pathological process leading to heart failure and early death in HCMHs, and treatment with the NHE-1 inhibitor is promising for preventing early death in hereditary cardiomyopathy.

Nuclear membrane R-type calcium channels mediate cytosolic ET-1-induced increase of nuclear calcium in human vascular smooth muscle cells

The objective of this work was to verify whether, as in the case of the plasma membrane of human vascular smooth muscle cells (hVSMCs), cytosolic ET-1-induced increase of nuclear calcium is mediated via the activation of calcium influx through the steady-state R-type calcium channel. Pharmacological tools to identify the R-type calcium channels, as well as real 3-D confocal microscopy imaging techniques coupled to calcium fluorescent probes, were used to study the effect of cytosolic ET-1 on nuclear calcium in isolated nuclei of human hepatocytes and plasma membrane perforated hVSMCs. Our results showed that pre-treatment with pertussis toxin (PTX) or cholera toxin (CTX) prevented cytosolic ET-1 (10−9 mol/L) from inducing a sustained increase in nuclear calcium. Furthermore, the L-type calcium channel blocker nifedipine did not prevent cytosolic ET-1 from inducing an increase in nuclear calcium, as opposed to the dual L- and R-type calcium channel blocker isradipine (PN200-110) (in the presence of nifedipine). In conclusion, the preventative effect with PTX and CTX, and the absence of an effect with nifedipine, as well as the blockade by isradipine on cytosolic ET-1-induced increase in nuclear calcium, suggest that this nuclear calcium influx in hVSMCs is due to activation of the steady-state R-type calcium channel. The sarcolemmal and nuclear membrane R-type calcium channels in hVSMCs are involved in ET-1 modulation of vascular tone in physiology and pathology.

Nuclear membranes GPCRs: implication in cardiovascular health and diseases

G-protein coupled receptors (GPCRs) are commonly present at the plasma membrane and their signaling modulates excitation-contraction coupling and excitation-secretion coupling of excitable and non-excitable cells of the cardiovascular system. Their effect on excitation-gene expression coupling was attributed, in part, to the nuclear translocation of their signaling and/or to the entry into the nuclear membrane of the internalized GPCRs. However, the recently established paradigm showed that, in addition to plasma membrane G-proteins, GPCRs exist as native nuclear membranes receptors and they modulate nuclear ionic homeostasis and function. These nuclear membrane GPCRs could function independently of plasma membrane GPCRs. Growing evidence also shows that these nuclear membrane GPCRs contribute to protein synthesis and also undergo changes in pathological conditions. The presence of a GPCR at both the plasma and nuclear membranes and/or only at the nuclear membranes represents a new challenge to better understand their contribution to cell physiology and pathology and, consequently, to the development of new therapeutic drugs targeting this category of receptors.

High salt-induced hypertension in B2 knockout mice is corrected by the ETA antagonist, A127722

BACKGROUND AND PURPOSE

The contribution of endothelin-1 (ET-1) in a B2KO mouse model of a high salt-induced arterial hypertension was investigated.

EXPERIMENTAL APPROACH

Wild-type (WT) or B2KO mice receiving a normal diet (ND) or a high-salt diet (HSD) were monitored by radiotelemetry up to a maximum of 18 weeks. At the 12th week of diet, subgroups under ND or HSD received by gavage the ETA antagonist A127722 during 5 days. In addition, blood samples were collected and, following euthanasia, the lungs, heart and kidneys were extracted, homogenized and assayed for ET-1 by RIA. In a separate series of experiments, the ETA antagonist, BQ123 was tested against the pressor responses to a NOS inhibitor L-N(G)-nitroarginine methyl ester (L-NAME) in anaesthetized WT and B2KO mice.

KEY RESULTS

In B2KO, but not WT mice, 12 weeks of HSD triggered a maximal increase of the mean arterial pressure (MAP) of 19.1 ± 2.8 mmHg, which was corrected by A127722 to MAP levels found in B2KO mice under ND. Significant increases in immunoreactive ET-1 were detected only in the lungs of B2KO mice under HSD. On the other hand, metabolic studies showed that sodium urinary excretion was markedly reduced in B2KO compared with WT mice under ND. Finally, BQ123 (2 mg·kg(-1)) reduced by 50% the pressor response to L-NAME (2 mg·kg(-1)) in B2KO, but not WT mice under anaesthesia.

CONCLUSIONS AND IMPLICATIONS

Our results support the concept that functional B2 receptors oppose high salt-induced increments in MAP, which are corrected by an ETA receptor antagonist in this mouse model of experimental hypertension.

Whole-cell and nuclear NADPH oxidases levels and distribution in human endocardial endothelial, vascular smooth muscle, and vascular endothelial cells

The results of our study show that whole-cell and nuclear levels of NADPH oxidase-1 (NOX1) are similar in human vascular endothelial cells (hVECs) and smooth muscle cells (hVSMCs), but lower in human endocardial endothelial cells (hEECs). NOX2 levels were higher in hVECs and lower in hVSMCs. NOX3 levels were the same in hVECs and hVSMCs, but lower in hEECs. NOX4 levels were similar in all of the cell types. NOX4 levels were higher in hVECs than in hVSMCs. NOX5 was also present throughout the 3 cell types, including their nuclei, in the following order: hEECs > hVSMCs > hVECs. The level of basal reactive oxygen species (ROS) was highest in hVECs and lowest in hVSMCs. However, the Ca2+ level was highest in hVSMCs and lowest in hVECs. These findings suggest that all types of NOXs exist in hEECs, hVECs, and hVSMCs, although their density and distribution are cell-type dependent. The density of the different NOXs correlated with the ROS level, but not with the Ca2+ level. In conclusion, NOXs, including NOX3, exist in cardiovascular cells and their nuclei. The nucleus is a major source of ROS generation. The nuclear NOXs may contribute to ROS and Ca2+ homeostasis, which may affect cell remodeling, including the formation of nuclear T-tubules in vascular diseases and aging.

Differences in neuropeptide Y-induced secretion of endothelin-1 in left and right human endocardial endothelial cells

The aim of the study was to test the hypothesis that neuropeptide Y (NPY) may induce endothelin-1 (ET-1) secretion in left (hLEECs) and right (hREECs) human endocardial endothelial cells. Furthermore, the type of NPY receptor implicated could be different in NPY-induced secretion in hLEECs and hREECs. Using immunofluorescence coupled to real 3D confocal microscopy and ELISA, our results showed that stimulation of secretion by NPY induced the release of ET-1 from both right and left human ventricular endocardial endothelial cells (hEECs) in a time-dependent manner. Furthermore, the secretory capacity of hREECs was higher than that of hLEECs. In addition, our results showed that the effect of NPY on ET-1 secretion in hLEECs was only due to activation of Y(5) receptors. However, the effect of NPY on ET-1 secretion in hREECs was due to mainly Y(2) and partially Y(5) receptors activation. In conclusion, our results suggest that differences in excitation-secretion coupling exist between hREECS and hLEECs which may contribute to the functional differences between right and left ventricular muscle. Furthermore, high NPY level contributes to ET-1 release by hEECs and Y(2) and Y(5) receptors antagonists may be used for regulation of ET-1 secretion in the heart.

Endothelin and bradykinin: 'brothers-in-arms' in Chagas vasculopathies?

Reports of Chagas disease are increasing in non-endemic populations across the globe. Apart from vector eradication and prevention efforts by public health organizations, current pharmacological interventions are sparse and show important side effects. In this issue of the BJP, Andrade et al. elegantly demonstrate a new pharmacological paradigm whereby Trypanosoma cruzi host cell invasion requires significant cross-talk between receptors for kinins and endothelins. It is shown, for example, that acting via both ET(A) and ET(B) receptors, endothelin-1 (ET-1) cooperates with the (TLR2/CXCR2/B(2) kinin receptor) complex to activate inflammatory processes in response to invading trypomastigotes. This study by Andrade et al. prompts, however, several important questions, summarized in this Commentary, such as the putative role of chymase-dependent production of ET-1, the contentious protective role of ACE inhibitors in Chagasic patients, the unexplored role of de novo formed B(1) receptors for kinins triggered by cytokines and the putative role of compartmentalized calcium pools in host cell invasion by trypomastigotes.

Receptors and ionic transporters in nuclear membranes: new targets for therapeutical pharmacological interventions

Work from our group and other laboratories showed that the nucleus could be considered as a cell within a cell. This is based on growing evidence of the presence and role of nuclear membrane G-protein coupled receptors and ionic transporters in the nuclear membranes of many cell types, including vascular endothelial cells, endocardial endothelial cells, vascular smooth muscle cells, cardiomyocytes, and hepatocytes. The nuclear membrane receptors were found to modulate the functioning of ionic transporters at the nuclear level, and thus contribute to regulation of nuclear ionic homeostasis. Nuclear membranes of the mentioned types of cells possess the same ionic transporters; however, the type of receptors is cell-type dependent. Regulation of cytosolic and nuclear ionic homeostasis was found to be dependent upon a tight crosstalk between receptors and ionic transporters of the plasma membranes and those of the nuclear membrane. This crosstalk seems to be the basis for excitation–contraction coupling, excitation–secretion coupling, and excitation – gene expression coupling. Further advancement in this field will certainly shed light on the role of nuclear membrane receptors and transporters in health and disease. This will in turn enable the successful design of a new class of drugs that specifically target such highly vital nuclear receptors and ionic transporters.

Nuclear membrane receptors for ET-1 in cardiovascular function

Plasma membrane endothelin type A (ETA) receptors are internalized and recycled to the plasma membrane, whereas endothelin type B (ETB) receptors undergo degradation and subsequent nuclear translocation. Recent studies show that G protein-coupled receptors (GPCRs) and ion transporters are also present and functional at the nuclear membranes of many cell types. Similarly to other GPCRs, ETA and ETB are present at both the plasma and nuclear membranes of several cardiovascular cell types, including human cardiac, vascular smooth muscle, endocardial endothelial, and vascular endothelial cells. The distribution and density of ETARs in the cytosol (including the cell membrane) and the nucleus (including the nuclear membranes) differ between these cell types. However, the localization and density of ET-1 and ETB receptors are similar in these cell types. The extracellular ET-1-induced increase in cytosolic ([Ca]c) and nuclear ([Ca]n) free Ca2+ is associated with an increase of cytosolic and nuclear reactive oxygen species. The extracellular ET-1-induced increase of [Ca]c and [Ca]n as well as intracellular ET-1-induced increase of [Ca]n are cell-type dependent. The type of ET-1 receptor mediating the extracellular ET-1-induced increase of [Ca]c and [Ca]n depends on the cell type. However, the cytosolic ET-1-induced increase of [Ca]n does not depend on cell type. In conclusion, nuclear membranes' ET-1 receptors may play an important role in overall ET-1 action. These nuclear membrane ET-1 receptors could be targets for a new generation of antagonists.

ETA receptors are present in human aortic vascular endothelial cells and modulate intracellular calcium

Using immunofluorescence and real 3-D confocal microscopy, our results showed the presence of ET-1, ETA, and ETB receptors in isolated human aortic vascular endothelial cells (hVECs). The level of the peptide and its receptors was significantly higher in the nucleus (including the nuclear envelope membranes) than in the cytosol (including the cell membrane). Furthermore, using the Western blot technique we demonstrated the presence of both ETA and ETB receptors. Using intact and isolated human hVECs and the Fura-2 calcium (Ca2+) measurement technique, we showed that ET-1 induced a dose-dependent increase of total intracellular free Ca2+, with an EC50 of 1.3 x 10-10 mol/L. The specific ETA receptor antagonist ABT-627 (10-7 mol/L), but not the ETB receptor antagonist A-192621 (10-7 mol/L), prevented the ET-1 (10-9 mol/L) induced increase of total intracellular Ca2+. In conclusion, these results clearly show that similar to ETB receptors, ETA receptors are also present in human aortic vascular endothelial cells and their levels are higher than ETB in the nucleus when compared with the cytosol. Furthermore, we suggest that ETA, but not ETB, receptors mediate the effect of ET-1 on total intracellular Ca2+ of human aortic vascular endothelial cells.

Presence of tubular and reticular structures in the nucleus of human vascular smooth muscle cells

In recent decades, studies addressing nuclear calcium (Ca(2+)) homeostasis and signaling contributed to redefining the role of the nucleus. Yet many aspects of nuclear Ca(2+) signaling and homeostasis are only modestly understood. The present study aimed at investigating the presence of nuclear structures which could contribute to the regulation of nuclear Ca(2+) homeostasis. Using real 3D confocal microscopy, coupled to utilization of appropriate organelle probes and specific antibodies, we identified two entities in the nuclei of intact human vascular smooth muscle cells (hVSMCs) as well as in isolated hVSMCs nuclei. Our results demonstrate the presence of an ER-like nuclear reticular structure in nuclei of intact hVSMCs and in isolated nuclei. Similar to the ER/SR, this structure possesses thapsigargin binding sites, IP(3)Rs and RyRs, thus it was named nucleoplasmic reticulum (NR). Furthermore, nuclear tubular structures were also detected. The latter, similar to the nuclear envelope membranes, possess nuclear pores, thapsigargin binding sites, Angiotensin II receptor AT(2), and are associated with Lamin A/C. However, unlike the NR and the nuclear envelope membranes, these tubular structures disappeared when the nuclei were isolated from the cells. The nuclear tubular structures were called Nuclear T-Tubules (NTTs). Our calcium studies in isolated nuclei utilizing IP(3) and Ryanodine suggest that the NR may participate in nuclear Ca(2+) signaling. On the other hand, presence of nuclear pores on the NTTs suggests that these structures can play a role in cytosol-nucleus exchange. In conclusion, two distinct structures are present in the nucleus of hVSMCs and might play an important role in nuclear Ca(2+) homeostasis.

Nitric oxide and reactive oxygen species in the nucleus revisitedThis review is one of a selection of papers published in a Special Issue on Oxidative Stress in Health and Disease

Recent work from our group showed that the nuclear envelope membranes contain several G protein-coupled receptors, including prostaglandin E2 (EP3R) and endothelin-1 (ET-1) receptors. Activation of EP3R increased endothelial nitric oxide synthase (eNOS) RNA expression in nuclei. eNOS and inducible NOS (iNOS) are reported to also be present at the nuclear level. Furthermore, reactive oxygen species (ROS) were also localized at the nuclear level. In this review, we show that stimulation with NO donor sodium nitroprusside results in an increase of intranuclear calcium that was dependent on guanylate cyclase activation, but independent of MAPK. This increase in nuclear calcium correlated with an increase in nuclear transcription of iNOS. H2O2 and ET-1 increase both cytosolic and nuclear ROS in human endocardial endothelial cells and in human aortic vascular smooth muscle cells. This increase in ROS levels by H2O2 and ET-1 was reversed by the antioxidant glutathione. In addition, our results strongly suggest that cytosolic signalization is not only transmitted to the nucleus but is also generated by the nucleus. Furthermore, we demonstrate that oxidative stress can be sensed by the nucleus. These results highly suggest that ROS formation is also generated directly by the nucleus and that free radicals may contribute to ET-1 regulation of nuclear Ca2+ homeostasis.

Nuclear membrane receptors and channels as targets for drug development in cardiovascular diseases

The use of confocal microscopy has shown that the nucleus plays an important role in excitation-contraction and excitation-secretion coupling of several excitable and nonexcitable cardiovascular cells. It has shown that the nuclear membranes, like the sarcolemmal membrane, possess ionic transporters as well as G protein-coupled receptors (GPCRs), which play a major role in modulating both cytosolic and nuclear ionic homeostasis and nuclear signalling. During spontaneous contraction of heart cells, the increase in cytosolic Ca2+ was immediately followed by a transient increase in nuclear Ca2+. The nuclear Ca2+ rise during excitation-contraction and excitation-secretion coupling was both dependent and independent of changes in cytosolic Ca2+. Nuclear membrane GPCRs, such as those of angiotensin II, neuropeptide Y, and ET-1, were functional and contributed to modulation of nuclear ionic homeostasis via direct and (or) indirect modulation of nuclear membrane ionic transporters such as channels, pumps, and exchangers. The signalling of nuclear membrane GPCRs may also contribute to modulation of gene expression, which may regulate proliferation and remodelling of cells and, indeed, life and death. Direct or indirect targeting of nuclear membrane ionic transporters and GPCRs may constitute a new target for drug action.

Nonpeptidic antagonists of ETA and ETB receptors reverse the ET-1-induced sustained increase of cytosolic and nuclear calcium in human aortic vascular smooth muscle cells

Our previous work showed that ET-1 induced a concentration-dependent increase of cytosolic Ca2+ ([Ca]c) and nuclear Ca2+ ([Ca]n) in human aortic vascular smooth muscle cells (hVSMCs). In the present study, using hVSMCs and 3-dimensional confocal microscopy coupled to the Ca2+ fluorescent probe Fluo-3, we showed that peptidic antagonists of ETA and ETB receptors (BQ-123 (10(-6) mol/L) and BQ-788 (10(-7) mol/L), respectively) prevented, but did not reverse, ET-1-induced sustained increase of [Ca]c and [Ca]n. In contrast, nonpeptidic antagonists of ETA and ETB (respectively, BMS-182874 (10(-8)-10(-6) mol/L) and A-192621 (10(-7) mol/L)) both prevented and reversed ET-1-induced sustained increase of [Ca]c and [Ca]n. Furthermore, activation of the ETB receptor alone using the specific agonist IRL-1620 (10(-9) mol/L) induced sustained increases of [Ca]c and [Ca]n, and subsequent administration of ET-1 (10(-7) mol/L) further increased nuclear Ca2+. ET-1-induced increase of [Ca]c and [Ca]n was completely blocked by extracellular application of the Ca2+ chelator EGTA. Pretreatment with the G protein inhibitors pertussis toxin (PTX) and cholera toxin (CTX) also prevented the ET-1 response; however, strong membrane depolarization with KCl (30 mmol/L) subsequently induced sustained increase of [Ca]c and [Ca]n. Pretreatment of hVSMCs with either the PKC activator phorbol-12,13-dibutyrate or the PKC inhibitor bisindolylmaleimide did not affect ET-1-induced sustained increase of intracellular Ca2+. These results suggest that both ETA- and ETB-receptor activation contribute to ET-1-induced sustained increase of [Ca]c and [Ca]n in hVSMCs. Moreover, in contrast to the peptidic antagonists of ET-1 receptors, the nonpeptidic ETA-receptor antagonist BMS-182874 and the nonpeptidic ETB-receptor antagonist A-192621 were able to reverse the effect of ET-1. Nonpeptidic ETA- and ETB-receptor antagonists may therefore be better pharmacological tools for blocking ET-1-induced sustained increase of intracellular Ca2+ in hVSMCs. Our results also suggest that the ET-1-induced sustained increase of [Ca]c and [Ca]n is not mediated via activation of PKC, but via a PTX- and CTX-sensitive G protein calcium influx through the R-type Ca2+ channel.

Expression of endogenous nuclear bradykinin B2 receptors mediating signaling in immediate early gene activation

Bradykinin (BK) represents a pro-inflammatory mediator that partakes in many inflammatory diseases. The mechanism of action of BK is thought to be primarily mediated by specific cell surface membrane B2 receptors (B2Rs). Some evidence has suggested, however, the existence of an intracellular/nuclear B2R population. Whether these receptors are functional and contribute to BK signaling remains to be determined. In this study, by mean of Western blotting, 3D-confocal microscopy, receptor autoradiography and radioligand binding analysis, we showed that plasma membrane and highly purified nuclei from isolated rat hepatocytes contain specific B2R that bind BK. The results depicting B2R nuclear expression in isolated nuclear organelles were reproduced in situ on hepatic sections by immunogold labeling and transmission electron microscopy. Functional tests on single nuclei, by means of confocal microscopy and the calcium-sensitive probe fluo-4AM, showed that BK induces concentration-dependent transitory mobilization of nucleoplasmic calcium; these responses were blocked by B2R antagonist HOE 140, not by the B1R antagonist R954 and, were also found in wild-type C57/Bl6 mice, but not in B2R-KO mice. In isolated nuclei, BK elicited activation/phosphorylation of Akt, acetylation of histone H3 and ensuing pro-inflammatory iNOS gene induction as determined by Western blot and RT-PCR. ChIP assay confirmed binding of acetylated-histone H3 complexes, but not B2R, to promoter region of iNOS gene suggesting that B2R-mediated gene expression is bridged with accessory downstream effectors. This study discloses a previously undescribed mechanism in BK-induced transcriptional events, via intracrine B2R-mediated signaling, occurring in rat autologous hepatic cells.