Yi-Chun Zhu

Cellular Distribution of Angiotensin-Converting Enzyme After Myocardial Infarction

We studied the cellular distribution of angiotensin-converting enzyme (ACE) in the heart related to the cell types involved in left ventricular repair and remodeling before and after myocardial infarction by immunohistochemical techniques using monoclonal and polyclonal antibodies. In noninfarcted myocardium of both human and rat, ACE expression was confined to endothelial cells and subendocardial cell layers of the aortic valve. ACE was prominent in endothelia of small arteries and arterioles, whereas only half the coronary capillaries were immunoreactive and venous vessels were almost completely devoid of the enzyme. In a rat model of myocardial infarction, ACE distribution was determined 1, 3, and 7 days and 2, 3, and 6 weeks after coronary occlusion. Three and 7 days after infarction, endothelial cells of sprouting capillaries and macrophages in the marginal zone of necrosis revealed ACE expression. In both human and rat with the onset of fibrosis, intense staining of the enzyme was found in the marginal zone of the repair tissue. In situ hybridization for collagen type I in the rat revealed that zones with high collagen content had almost no ACE immunoreactivity. Vascular smooth muscle cells and cardiomyocytes revealed no ACE expression throughout the study. We conclude that endothelial cells are the principal source for the expression of ACE after myocardial infarction. The observed induction of ACE with the onset of fibrosis suggests a role of this enzyme that is related to tissue repair and remodeling.

Hydrogen sulphide is an inhibitor of L-type calcium channels and mechanical contraction in rat cardiomyocytes

AIMS Hydrogen sulphide (H(2)S) is an endogenously generated gaseous transmitter that has recently been suggested to regulate cardiovascular functions. To date, there is no direct evidence for a potential role of H(2)S in regulating calcium channels in the heart. The present study aims to examine the hypothesis that H(2)S is a novel inhibitor of the L-type calcium channel current (I(Ca,L)). METHODS AND RESULTS Electrophysiological measurements were performed in cardiomyocytes isolated from Wistar-Kyoto and spontaneously hypertensive rats. Bath application of 100 microM NaHS (a H(2)S donor) significantly reduced the time required for the repolarization of the action potential. Inhibition of the peak I(Ca,L) by NaHS was determined to be concentration-dependent (25, 50, 100, 200, and 400 microM). NaHS inhibited the recovery from depolarization-induced inactivation. Electric field-induced [Ca(2+)]i transients and contraction of single cardiomyocytes and isolated papillary muscles were reduced by NaHS treatment. In contrast, caffeine induced an increase in [Ca(2+)]i that was not altered by NaHS. NaHS had no effect on the K(ATP) current or on the levels of cAMP and cGMP in the current study. CONCLUSION H(2)S is a novel inhibitor of L-type calcium channels in cardiomyocytes. Moreover, H(2)S-induced inhibition of [Ca(2+)]i appears to be a secondary effect owing to its initial action towards I(Ca,L). The inhibitory effect of H(2)S on I(Ca,L) requires further investigation, particularly in the exploration of new pathways involved in cardiac calcium homeostasis and disease pathology.

Hydrogen sulfide protects cardiomyocytes from hypoxia/reoxygenation-induced apoptosis by preventing GSK-3β-dependent opening of mPTP

Hydrogen sulfide (H(2)S) is an endogenously generated gaseous transmitter, which has recently been suggested to regulate cardiovascular functions. The present study aims to clarify the mechanisms underlying the cardioprotective effects of H(2)S. Signaling elements were examined in cardiomyocytes cultured under hypoxia/reoxygenation conditions and in a rat model of ischemia-reperfusion. In cultured cardiomyocytes, sodium hydrosulfide (NaHS; 10, 30, and 50 mumol/l) showed concentration-dependent inhibitory effects on cardiomyocyte apoptosis induced by hypoxia/reoxygenation. These effects were associated with an increase in phosphorylation of glycogen synthase kinase-3beta (GSK-3beta) (Ser9) and a decrease in Bax translocation, caspase-3 activation, and mitochondrial permeability transition pore (mPTP) opening. Transfection of a phosphorylation-resistant mutant of GSK-3beta at Ser9 attenuated the effects of NaHS in reducing cardiomyocyte apoptosis, Bax translocation, caspase-3 activation, and mPTP opening. In a rat model of ischemia-reperfusion, NaHS administration reduced myocardial infarct size and increased the phosphorylation of GSK-3beta (Ser9) at a dose of 30 mumol/kg. In conclusion, the H(2)S donor prevents cardiomyocyte apoptosis by inducing phosphorylation of GSK-3beta (Ser9) and subsequent inhibition of mPTP opening.

The role of urotensin II in cardiovascular and renal physiology and diseases

1 Urotensin II (U‐II) is a cyclic neuropeptide that was first isolated from teleost fish some 35 years ago. Mammalian U‐II is a powerful vasoconstrictor with a potency greater than that of endothelin‐1. 2 Nevertheless, unlike endothelin‐1, which constricts all or nearly all vascular beds, the vasoactive effects of U‐II are reported to be dependent both on the species and on the regional vascular bed examined. Typical regional variability occurs in the rat in which vasoconstriction to U‐II is most robust in thoracic aorta proximal to the aortic arch and decreases gradually towards the distal peripheral arteries. As small peripheral arteries but not larger arteries such as the aorta play a major role in regulating peripheral resistance and consequent blood pressure as well as workload on the heart, doubts have been raised concerning the importance of this peptide in cardiovascular physiology. Moreover, an interaction between U‐II and other endogenous vasoactive molecules may add a level of complexity to the vascular actions of U‐II. 3 On the other hand, recent experimental and clinical studies have revealed increased expression of U‐II and urotensin receptor (UT receptor) in animals with experimentally induced myocardial infarction, heart failure, and in patients with hypertension, atherosclerosis, and diabetic nephropathy, which suggests a potential role for U‐II in both cardiovascular and renal diseases. A series of peptidic and nonpeptidic UT receptor ligands have been shown to be effective in antagonizing the effects of U‐II in the cardiorenal system. 4 This article aims to review recent advances in our understanding of the physiology and pathophysiology of U‐II with particular references to its role in cardiovascular health and disease.

Role of angiotensin AT1 and AT2 receptors in cardiac hypertrophy and cardiac remodelling

1. Left ventricular hypertrophy (LVH) is an independent cardiovascular risk factor. Angiotensin AT1 receptor antagonism has been considered as a specific approach to block the renin–angiotensin system and been demonstrated to be able to prevent or regress LVH by interfering with the remodelling process of the heart.

Effects of losartan on haemodynamic parameters and angiotensin receptor mRNA levels in rat heart after myocardial infarction

We investigated the haemodynamic parameters and the regulation of cardiac mRNA levels of the angiotensin receptor subtypes, AT1 and AT2, by the AT1-receptor antagonist losartan in rat heart during the acute phase of myocardial infarction. AT1- and AT2-receptor mRNA levels markedly increased at 30 minutes and peaked at 24 hours post myocardial infarction (12.6-fold increase for AT1- and 17.2-fold increase for AT2 compared with controls). Losartan significantly reduced mean blood pressure in sham-operated rats and decreased mean blood pressure and left ventricular end-diastolic pressure in myocardial infarction rats. However, the AT1- and AT2-receptor mRNA levels of losartan-treated rats showed a pattern similar to that of water-treated rats. The time-dependent increase of AT 1- and AT2receptor mRNA levels is associated with the early remodelling process of non-infarcted myocardium post MI and is independent of AT1-receptor blockade.

Mechanisms of angiogenesis: Role of hydrogen sulphide

1. Hydrogen sulphide (H2S) has recently been recognized as a gasotransmitter that regulates angiogenesis in vitro and in vivo under physiological and ischaemic conditions.

PI3K p110α isoform-dependent Rho GTPase Rac1 activation mediates H2S-promoted endothelial cell migration via actin cytoskeleton reorganization.

Hydrogen sulfide (H2S) is now considered as the third gaseotransmitter, however, the signaling pathways that modulate the biomedical effect of H2S on endothelial cells are poorly defined. In the present study, we found in human endothelial cells that H2S increased cell migration rates and induced a marked reorganization of the actin cytoskeleton, which was prevented by depletion of Rac1. Pharmacologic inhibiting vascular endothelial growth factor receptor (VEGFR) and phosphoinositide 3-kinase (PI3K) both blunted the activation of Rac1 and the promotion of cell migration induced by H2S. Moreover, H2S-induced Rac1 activation was selectively dependent on the presence of the PI3K p110α isoform. Activated Rac1 by H2S thus in turn resulted in the phosphorylation of the F-actin polymerization modulator, cofilin. Additionally, inhibiting of extracellular signal-regulated kinase (ERK) decreased the augmented cell migration rate by H2S, but had no effect on Rac1 activation. These results indicate that Rac1 conveys the H2S signal to microfilaments inducing rearrangements of actin cytoskeleton that regulates cell migration. VEGFR-PI3K was found to be upstream pathway of Rac1, while cofilin acted as a downstream effector of Rac1. ERK was also shown to be involved in the action of H2S on endothelial cell migration, but independently of Rac1.

Survivin mediates the anti-apoptotic effect of δ-opioid receptor stimulation in cardiomyocytes

Survivin is known to be essential for cell division and to inhibit apoptosis during embryonic development and in adult cancerous tissues. However, the cardiovascular role of survivin is unknown. We observed that in cardiomyocytes cultured under conditions of serum and glucose deprivation (DEPV), the levels of survivin, Bcl-2 and extracellular signal-regulated kinase (ERK) were positively correlated with the anti-apoptotic action of a δ-opioid receptor agonist, [D-Ala2, D-Leu5]-enkephalin acetate (DADLE). By contrast, Bax translocation, mitochondrial membrane damage and reactive oxygen species (ROS) production were inversely correlated with the changes of survivin and Bcl-2. The use of RNA interference (RNAi) targeting survivin increased DEPV-induced cardiomyocyte apoptosis, whereas the anti-apoptotic effect of DADLE was blunted by survivin RNAi. Moreover, survivin transfection and overexpression provided protection against DEPV-induced cardiomyocyte apoptosis. Inhibition of ERK prevented the DADLE-induced decrease in apoptosis and Bax translocation, and increase in survivin and Bcl-2. DADLE-induced increase in survivin was also blunted by phosphoinositol 3-kinase (PI 3-kinase) inhibition. In conclusion, the present study provides the first direct evidence of an anti-apoptotic role of survivin mediating the anti-apoptotic effect of δ-opioid receptor activation in cardiomyocytes. ERK and PI 3-kinase were found to be upstream regulators of survivin. Mitochondrial membranes as well as ROS, Bcl-2 and Bax were also involved in this anti-apoptotic action.

Substrate Metabolism, Hormone Interaction, and Angiotensin-Converting Enzyme Inhibitors in Left Ventricular Hypertrophy

Left ventricular hypertrophy is considered to be an independent risk factor giving rise to ischemia, arrhythmias, and left ventricular dysfunction. Slow movement of intracellular calcium contributes to the impaired contraction and relaxation function of hypertrophied myocardium. Myofibril content may also be shifted to fetal-type isoforms with decreased contraction and relaxation properties in left ventricular hypertrophy. Myocyte hypertrophy and interstitial fibrosis are regulated independently by mechanical and neurohumoral mechanisms. In severely hypertrophied myocardium, capillary density is reduced, the diffusion distance for oxygen, nutrients, and metabolites is increased, and the ratio of energy-production sites to energy-consumption sites is decreased. The metabolic state of severely hypertrophied myocardium is anaerobic, as indicated by the shift of lactate dehydrogenase marker enzymes. Therefore, the hypertrophied myocardium is more vulnerable to ischemie events. As a compensatory response to severe cardiac hypertrophy and congestive heart failure, the ADP/ATP carrier is activated and atrial natriuretic peptide is released to increase high-energy phosphate production and reduce cardiac energy consumption by vasodilation and sodium and fluid elimination. However, in severely hypertrophied and failing myocardium, vasoconstrictor and sodium- and fluid-retaining factors, such as the renin-angiotensin system, aldosterone, and sympathetic nerve activity, play an overwhelming role. Angiotensin-converting enzyme inhibitors (ACEIs) are able to prevent cardiac hypertrophy and improve cardiac function and metabolism. Under experimental conditions, these beneficial effects can be ascribed mainly to bradykinin potentiation, although a contribution of the ACEI-induced angiotensin II reduction cannot be excluded.