Systemic hypertension induced by hepatic overexpression of human preproendothelin-1 in rats

Endothelin-1 impairs nitric oxide signaling in endothelial cells through a protein kinase Cdelta-dependent activation of STAT3 and decreased endothelial nitric oxide synthase expression

In an ovine model of persistent pulmonary hypertension of the newborn (PPHN), endothelin-1 (ET-1) expression is increased, while endothelial nitric oxide synthase (eNOS) expression is decreased. However, the molecular mechanisms by which ET-1 attenuates eNOS expression in endothelial cells are not completely understood. Thus, the goal of this study was to determine if the overexpression of ET-1 decreases eNOS expression in pulmonary arterial endothelial cells isolated from fetal lambs. To increase the ET-1 expression, cells were transfected with a plasmid coding for Prepro-ET-1, a precursor of ET-1. After overexpression of Prepro-ET-1, ET-1 levels in the culture medium were significantly increased (control = 805.3 +/- 69.8; Prepro-ET-1 overexpression = 1351 +/- 127.9). eNOS promoter activity, protein levels, and NO generation were all significantly decreased by the overexpression of Prepro-ET-1. The decrease in transcription correlated with increased activity of protein kinase Cdelta (PKCdelta) and STAT3. Further, DNA binding activity of STAT3 was also increased by Prepro-ET-1 overexpression. The increase in STAT3 activity and decrease in eNOS promoter activity were inhibited by the overexpression of dominant negative mutants of PKCdelta or STAT3. Further, a 2 bp mutation in the STAT3 binding site in the eNOS promoter inhibited STAT3 binding and led to enhanced promoter activity in the presence of Prepro-ET-1 overexpression. In conclusion, ET-1 secretion is increased by Prepro-ET-1 overexpression. This results in activation of PKCdelta, which phosphorylates STAT3, increasing its binding to the eNOS promoter. This in turn decreases eNOS promoter activity, protein levels, and NO production. Thus, ET-1 can reduce eNOS expression and NO generation in fetal pulmonary artery endothelial cells through PKCdelta-mediated activation of STAT3.

Design of mutant beta2 subunits as decoy molecules to reduce the expression of functional Ca2+ channels in cardiac cells

Calcium influx through long-lasting ("L-type") Ca(2+) channels (Ca(V)) drives excitation-contraction in the normal heart. Dysregulation of this process contributes to Ca(2+) overload, and interventions that reduce expression of the pore-forming alpha(1) subunit may alleviate cytosolic Ca(2+) excess. As a molecular approach to disrupt the assembly of Ca(V)1.2 (alpha(1C)) channels at the cell membrane, we targeted the Ca(2+) channel beta(2) subunit, an intracellular chaperone that interacts with alpha(1C) via its beta interaction domain (BID) to promote Ca(V)1.2 channel expression. Recombinant adenovirus expressing either the full beta(2) subunit (Full-beta(2)) or truncated beta(2) subunit constructs lacking either the C terminus, N terminus, or both (N-BID, C-BID, and BID, respectively) fused to green fluorescent protein were developed as potential decoys and overexpressed in HL-1 cells. Fluorescence microscopy revealed that the localization of Full-beta(2) at the surface membrane was associated with increased Ca(2+) current mainly attributed to Ca(V)1.2 channels. In contrast, truncated N-BID and C-BID constructs showed punctate intracellular expression, and BID showed a diffuse cytosolic distribution. Total expression of the alpha(1C) protein of Ca(V)1.2 channels was similar between groups, but HL-1 cells overexpressing C-BID and BID exhibited reduced Ca(2+) current. C-BID and BID also attenuated Ca(2+) current associated with another L-type Ca(2+) channel, Ca(V)1.3, but they did not reduce transient Ca(2+) currents attributed to Ca(V)3 channels. These results suggest that beta(2) subunit mutants lacking the N terminus may preferentially disrupt the proper localization of L-type Ca(2+) channels in the cell membrane. Cardiac-specific delivery of these decoy molecules in vivo may represent a gene-based treatment for pathologies involving Ca(2+) overload.

Delivery of ion channel genes to treat cardiovascular diseases

Modifying ion channel expression and function in the heart and vasculature are potentially useful, novel approaches to managing cardiac hypertrophy, atrial fibrillation and hypertension. Calcium channels play a pivotal role in the heart and vasculature in controlling muscle contraction as well as other aspects of calcium-dependent signaling. The present investigation reports development of mutated L-type calcium channel beta subunits that are delivered by an adenoviral vector to vascular smooth muscle tissue. Wild type subunits serve a chaperone function for the pore-forming alpha(1C) subunit of the calcium channel, localize to the cell membrane and enhance calcium current. Conversely, mutated subunits function as dominant negative, defective chaperone molecules that disrupt targeting to the cell membrane and decrease calcium current. The dominant negative genes can be delivered in vitro and ex vivo, and have the potential to decrease arterial tone and lower blood pressure in vivo.

Circulating levels of endothelin-1 in a homogenous Gulf Arab population with untreated essential hypertension

BACKGROUND

Racial variations are reported in the natural history of hypertension. For example, hypertension is significantly more prevalent in blacks than whites. Endothelial cells are important regulators of vascular tone and homeostasis, in part through secretions of vasoactive substances including endothelin-1 (ET-1), a small peptide with potent vasopressor actions. In black hypertensives, ET-1 levels are higher than in normotensive blacks and in both hypertensive and normotensive whites. Since ET-1 might play a significant role in the development and severity of hypertension in the indigenous Arab population of the United Arab Emirates, we investigated the circulating levels of ET-1 in this homogenous population.

PATIENTS AND METHODS

ET-1 levels were measured in plasma samples from 60 untreated hypertensive Arabs and compared with 60 age- and sex-matched normotensive controls.

RESULTS

ET-1 levels were significantly higher in hypertensives (mean 10.1 +/- 1 pmol/L) than normotensives (mean 2.2 +/- 0.5 pmol/L). Body mass index (BMI) was slightly higher among the hypertensives. For all subjects these levels significantly (P < 0.001) correlated with systolic blood pressure and less significantly (P < 0.05) with diastolic blood pressure and body weight. The correlation between ET-1 and both systolic and diastolic blood pressure was persistently significant after adjusting for BMI.

CONCLUSION

Plasma concentrations of ET-1 are significantly higher in hypertensive Gulf Arabs as compared with reported levels in white hypertensives and ET-1 could be a risk factor for cardiovascular diseases in this population. The endothelial system might be particularly important with respect to hypertension in this racial group and merits further study.

Genetic variations of regulator of G-protein signaling 2 in hypertensive patients and in the general population

OBJECTIVES

Mice deficient in the regulator of G-protein signaling 2 (RGS2) exhibit a strong hypertensive phenotype. We studied whether genetic variations in RGS2 are implicated in hypertension or other phenotypes in Japanese hypertensive individuals and the general population.

METHODS

We sequenced all exons of RGS2 and the promoter region in 953 and 48 hypertensive individuals, respectively. Genotyping by the TaqMan polymerase chain reaction method was performed for six missense or frameshift mutations and common single nucleotide polymorphisms in the general population, with a sample size of 1872 individuals (862 men and 1011 women).

RESULTS

We identified five novel missense mutations (Q2L; n = 2, Q2R; n = 1, M5V; n = 1, R44H; n = 2, Q78H; n = 1) and one novel frameshift mutation (1925-1926insT; n = 2) in a heterozygous state, in addition to 33 variations including five common single nucleotide polymorphisms. Six missense/frameshift mutations and three common single nucleotide polymorphisms (-638A > G, 1026T > A, 1891-1892delTC) were successfully genotyped in the general population. Mutations Q2L (n = 2), M5V (n = 1), and 1925-1926insT (n = 2) were only identified in hypertensive subjects. Six out of seven individuals with the R44H mutation, which occurs in the amphipathic alpha-helical domain of RGS2, had hypertension. The results showed a significant association of two common single nucleotide polymorphisms, 1026T > A [TT versus TA + AA: odds ratio (OR) 1.33; 95% confidence interval (CI) 1.02-1.74; P = 0.035] and 1891-1892delTC (I: insertion allele, D: deletion allele, II versus ID + DD: OR 1.47; 95% CI 1.09-1.97; P = 0.012), with hypertension in women by multivariate logistic regression analysis.

CONCLUSION

Our results suggest that genetic variations in RGS2 contribute partly to the hypertensive phenotype.

Endothelin-1 plasma levels and hypertension in cyclosporine-treated renal transplant patients

Experimental models suggest that endothelin-1 (ET-1) has a significant role in the pathogenesis of cyclosporin A (CyA)-induced hypertension. However, its serum levels evaluated in different studies, including patients who received solid organ transplants, exhibited controversial results. Our study population consisted of 43 renal transplant patients: 33 were taking CyA as a component of their immunosuppressive regimen (CyA group) and 10 that were not taking CyA (control group). Baseline laboratory data, blood pressure and ET-1 levels were taken at baseline and 3 and 4 h after the ingestion of CyA. In the control group samples were collected in the corresponding periods of time. Blood pressure was significantly higher in the CyA group (mean blood pressure: 101.2 +/- 9.5 vs. 91.1 +/- 10.7 mmHg; p < 0.001), who also presented higher serum creatinine (1.2 +/- 0.28 vs. 0.97 +/- 0.13 mg/dL; p < 0.001) and ET-1 levels. In the CyA group an ET-1 peak was evident by the third hour after CyA ingestion that showed its maximum concentration after 1-2 h; the control group exhibited significantly lower levels of ET-1 (p = 0.044). ET-1 levels compared between patients with and without hypertension showed a non-statistically significant difference (1.54 +/- 0.76 vs. 1.27 +/- 0.62 ng/mL; p = 0.27, respectively). In conclusion, in the present study chronic CyA ingestion was associated with higher blood pressure and plasma ET-1 levels.

Hypertension and prolonged vasoconstrictor signaling in RGS2-deficient mice

Signaling by hormones and neurotransmitters that activate G protein-coupled receptors (GPCRs) maintains blood pressure within the normal range despite large changes in cardiac output that can occur within seconds. This implies that blood pressure regulation requires precise kinetic control of GPCR signaling. To test this hypothesis, we analyzed mice deficient in RGS2, a GTPase-activating protein that greatly accelerates the deactivation rate of heterotrimeric G proteins in vitro. Both rgs2+/- and rgs2-/- mice exhibited a strong hypertensive phenotype, renovascular abnormalities, persistent constriction of the resistance vasculature, and prolonged response of the vasculature to vasoconstrictors in vivo. Analysis of P2Y receptor-mediated Ca2+ signaling in vascular smooth muscle cells in vitro indicated that loss of RGS2 increased agonist potency and efficacy and slowed the kinetics of signal termination. These results establish that abnormally prolonged signaling by G protein-coupled vasoconstrictor receptors can contribute to the onset of hypertension, and they suggest that genetic defects affecting the function or expression of RGS2 may be novel risk factors for development of hypertension in humans.

Human endothelin converting enzyme-2 (ECE2): characterization of mRNA species and chromosomal localization

Generation of the functionally pleiotropic members of the endothelin vasoactive peptide family is critically catalyzed by unique type II metalloproteases, termed endothelin converting enzymes (ECE). Isolation of human ECE-2 (EC 3.4.24.71) cDNAs revealed deduced open reading frames of 787 and 765 amino acids with approximately 60% identity with human ECE-1. Characterization of mRNA variants revealed mRNA structural diversity at the 5'-terminus. Two mRNA species exist containing distinct first and second exons. Furthermore, in one of these species, an in-frame deletion of the intracytoplasmic domain removed 29 amino acids. Because of the previously reported human genetic diseases ascribed to germline mutations of member genes of the endothelin family, ECE2 was localized in human chromosomes with fluorescence in situ hybridization and radiation hybrid mapping to 3q28-q29 and SHGC-20171/D3S1571, respectively.

Mechanisms Mediating the Renal Profibrotic Actions of Vasoactive Peptides in Transgenic Mice

Abstract. Transgenic mice are useful tools to investigate the mechanisms of the renal profibrotic actions of endothelin and angiotensin II. The overexpression of angiotensinogen and renin genes induces renal sclerosis independently of changes in systemic hemodynamics. The same results are observed when the endothelin-1 gene is overexpressed. Transgenic mice harboring the luciferase gene, under the control of the collagen I α2 chain promoter, and made hypertensive by induction of a nitric oxide (NO) deficiency have been studied. In this strain of mice, luciferase activity is an early index of renal and vascular fibrosis. Luciferase activity was increased in preglomerular arterioles and glomeruli when mice were treated with Nω-nitro-L-arginine methyl ester, an inhibitor of NO synthases. Bosentan (an endothelin receptor antagonist) was as efficient as losartan (an AT1 receptor antagonist) in preventing renal fibrosis, although it did not decrease BP. In short-term experiments, angiotensin II produced an increase in luciferase activity that was entirely prevented by losartan but also by bosentan. It can be concluded that, during chronic inhibition of NO, the collagen I gene is activated, which contributes to the development of nephroangiosclerosis and glomerulosclerosis. Angiotensin II plays a major role in this fibrogenic process, and its effect is at least partly independent of systemic hemodynamics and mediated by the profibrotic action of endothelin-1.

Tissue endothelin-converting enzyme activity correlates with cardiovascular risk factors in coronary artery disease

BACKGROUND

Endothelin-converting enzymes (ECEs) are the key enzymes in endothelin-1 (ET-1) generation. However, their pathophysiological role in patients with cardiovascular disease remains elusive.

METHODS AND RESULTS

Vascular reactivity to big endothelin-1 (bigET-1; 10(-9) to 10(-7) mol/L) and ET-1 (10(-9) to 10(-7) mol/L) were examined in the internal mammary artery (IMA, n=33) and saphenous vein (SV, n=27) of patients with coronary artery disease with identified cardiovascular risk factors. Vascular ECE activity was determined by conversion of exogenously added bigET-1 to ET-1. Tissue contents of bigET-1 and ET-1 were measured by radioimmunoassay. In addition, the effects of LDL and oxidized LDL on ECE-1 protein levels were determined by Western blot analysis in human IMA endothelial cells. In the IMA, vascular ECE activity showed an inverse correlation with serum LDL levels (r=-0.76; P<0.01) and systolic and diastolic blood pressure and a positive correlation with fibrinogen (r=0.58; P<0.05). In the SV, fibrinogen was the only parameter to be correlated with vascular ECE activity. Vascular tissue content of bigET-1 was attenuated in the IMA of patients with hyperfibrinogenemia but increased in patients with elevated systolic blood pressure and increased serum LDL levels (P<0.05). Most interestingly, LDL and oxidized LDL downregulated ECE-1 protein levels in human IMA endothelial cells (P<0.05).

CONCLUSIONS

These data demonstrate, for the first time, that vascular ECE activity is (1) inversely correlated with serum LDL levels and blood pressure and (2) positively associated with fibrinogen in human vascular tissue. Hence, ECE-1 activity may modulate cardiovascular risk in patients with coronary artery disease.

Effects of chronic neutral endopeptidase inhibition in rats with cyclosporine-induced hypertension

OBJECTIVE

Cyclosporine (CysA), a potent immunosuppressant, is associated with hypertension and nephrotoxicity. Neutral endopeptidase (NEP) degrades vasoactive peptides, including the natriuretic peptides and endothelin-1 (ET-1). We conducted the present study to determine whether or not the NEP inhibitor, ecadotril, prevents cyclosporine-induced hypertension and to clarify the mechanisms responsible for the hypotensive effects of ecadotril.

DESIGN AND METHODS

We studied the chronic effects of ecadotril (30 mg/kg per day) on blood pressure; the production of ET-1 and C-type natriuretic peptide (CNP); endothelial nitric oxide synthase (eNOS) activity; and the expression of messenger RNA (mRNA), for each substance in blood vessels of CysA-induced hypertensive rats.

RESULTS

CysA (25 mg/kg per day) given for 4 weeks increased the blood pressure from 116 +/- 14 mmHg to 159 +/- 15 mmHg, in rats. This increase was blunted by the co-administration of ecadotril (blood pressure: 134 +/- 14 mmHg). CysA increased plasma NEP activity. CysA increased the production of ET-1 and the expression of ET-1 mRNA without affecting CNP synthesis and endothelin converting enzyme (ECE)-1 mRNA expression. CysA decreased the eNOS activity and eNOS mRNA levels. Addition of the NEP inhibitor decreased the synthesis of ET-1 and ET-1 mRNA levels and increased the eNOS activity and the eNOS mRNA levels. Vascular CNP synthesis and ECE-1 mRNA expression in rats treated with ecadotril did not differ from those in rats treated with CysA and ecadotril.

CONCLUSION

These results indicate that chronic NEP inhibition may prevent the CysA-induced hypertension by decreasing local ET-1 synthesis and partly increasing vascular nitric oxide production.

Angiotensin converting enzyme inhibitors and vascular protection in hypertension

Strategically located between the circulating blood and the vascular smooth muscle, endothelial cells release numerous vasoactive substances regulating the function of vascular smooth muscle and circulating blood cells. Endothelium-derived vasodilators include prostacyclin, nitric oxide and endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin, nitric oxide exerts potent antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by vasoconstrictors, such as angiotensin II and endothelin (ET)-1, both of which exert prothrombotic and growth-promoting properties. In hypertension, elevated blood pressure causes vascular disease by inducing endothelial dysfunction. Hence, modern therapeutic strategies in human hypertension focus on preserving or restoring endothelial integrity. Beyond inhibiting the renin-angiotensin system, angiotensin-converting enzyme (ACE) inhibitors diminish the inactivation of bradykinin, thus leading to an augmentation of nitric oxide release. In addition, the compounds stabilize the B2-receptor, and reduce oxidative stress and tissue ET-1 levels. In patients with coronary artery disease, chronic ACE inhibition improves endothelial function. Further clinical studies are already under way which will prove whether these beneficial vascular effects of ACE inhibitors on endothelial dysfunction result in a clinical benefit for patients with hypertension.

Elevation of blood pressure by genetic and pharmacological disruption of the ETB receptor in mice

Exogenously administered endothelin (ET) elicits both pressor and depressor responses through the ETA and/or the ETB receptor on vascular smooth muscle cells and ETB on endothelial cells. To test whether ETB has pressor or depressor effects under basal physiological conditions, we determined arterial blood pressure (BP) in ETB-deficient mice obtained by crossing inbred mice heterozygous for targeted disruption of the ETB gene with mice homozygous for the piebald (s) mutation of the ETB gene (ETBs/s). F1 ETB-/s and ETB+/s progeny share an identical genetic background but have ETB levels that are approximately (1)/(8) and (5)/(8), respectively, of wild-type mice (ETB+/+). BP in ETB-/s mice was significantly higher, by approximately 20 mmHg, than that in ETB+/s or ETB+/+ mice. Immunoreactive ET-1 concentration in plasma as well as respiratory parameters was not different between ETB-/s and ETB+/s mice. A selective ETB antagonist, BQ-788, increased BP in ETB+/s and ETB+/+ but not in ETB-/s mice. Pretreatment with indomethacin, but not with NG-monomethyl-L-arginine, can attenuate the observed pressor response to BQ-788. The selective ETA antagonist BQ-123 did not ameliorate the increased BP in ETB-/s mice. Moreover, BP in mice heterozygous for targeted disruption of the ETA gene was not different from that in wild-type controls. These results suggest that endogenous ET elicits a depressor effect through ETB under basal conditions, in part through tonic production of prostaglandins, and not through secondary mechanisms involving respiratory control or clearance of circulating ET.

Endothelin antagonists

The very potent endogenous vasoconstrictor endothelin was discovered in 1988. We know now that there are three isoforms (1, 2, and 3) and two receptor subtypes (A and B). A whole range of peptide and non-peptide antagonists has been developed, some selective for A or B receptors and others with non-selective A/B antagonistic activity. So far the main application of these agents has been experimental--ie, endothelin blockers are used to throw light on disease mechanisms, most notably cardiovascular and renal. However, the non-selective antagonist bosentan and a few other agents have been studied clinically. Evidence so far from preclinical studies and healthy volunteers and from the limited number of investigations in patients permits a listing of the potential areas of clinical interest. These are mainly cardiovascular (eg, hypertension, cerebrovascular damage, and possibly heart failure) and renal. Clouds on the horizon are the need to show that these new agents are better than existing drugs; the possibility of conflicting actions if mixed A/B antagonists are used; and animal evidence hinting that endothelin blockade during development could be dangerous.

Mechanisms of FK 506-induced hypertension in the rat

-Tacrolimus (FK 506) is a powerful, widely used immunosuppressant. The clinical utility of FK 506 is complicated by substantial hypertension and nephrotoxicity. To clarify the mechanisms of FK 506-induced hypertension, we studied the chronic effects of FK 506 on the synthesis of endothelin-1 (ET-1), the expression of mRNA of ET-1 and endothelin-converting enzyme-1 (ECE-1), the endothelial nitric oxide synthase (eNOS) activity, and the expression of mRNA of eNOS and C-type natriuretic peptide (CNP) in rat blood vessels. In addition, the effect of the specific endothelin type A receptor antagonist FR 139317 on FK 506-induced hypertension in rats was studied. FK 506, 5 mg. kg-1. d-1 given for 4 weeks, elevated blood pressure from 102+/-13 to 152+/-15 mm Hg and increased the synthesis of ET-1 and the levels of ET-1 mRNA in the mesenteric artery (240% and 230%, respectively). Little change was observed in the expression of ECE-1 mRNA and CNP mRNA. FK 506 decreased eNOS activity and the levels of eNOS mRNA in the aorta (48% and 55%, respectively). The administration of FR 139317 (10 mg. kg-1. d-1) prevented FK 506-induced hypertension in rats. These results indicate that FK 506 may increase blood pressure not only by increasing ET-1 production but also by decreasing NO synthesis in the vasculature.

A role for endothelin in the pathogenesis of hypertension: fact or fiction?

Endothelin-1 (ET-1) was discovered 10 years ago. Because it is one of the most potent vasoconstrictors in vivo, a pathophysiological role for the peptide as a mediator of hypertension has been postulated. Several clinical studies, however, have been unable to identify elevated ET levels in the plasma of hypertensive patients, suggesting that it does not play a prominent role in this disease. More recently, evidence has been presented that ETs act predominantly at the autocrine/paracrine level and that measurements of plasma levels can give only an indirect view of the activity of the system. In addition, transgenic technology has uncovered new actions of the peptide systems in recent years, which point to a key function of the system in prenatal development. Moreover, investigation of conditions associated with hypertensive end-organ damage, such as chronic renal failure, has led to a re-evaluation of the role of the ET system in hypertension. This article discusses this recent evidence and defines the exact role of the ET system in hypertension and hypertensive end-organ damage.

In vivo role of endothelin-converting enzyme-1 as examined by adenovirus-mediated overexpression in rats

We previously reported that adenovirus-mediated overexpression of endothelin-1 (ET-1) elevates systemic blood pressure in rats. In this model, plasma big ET-1: ET-1 ratios were almost 30, whereas they were only 5 in the control group, suggesting that endothelin-converting enzyme (ECE) may be a rate-limiting step in the production of ET-1 under these conditions. To further investigate the role of ECE in vivo, we prepared recombinant adenovirus strains carrying a soluble, secretory form of bovine ECE-1 cDNA (Ad.CMV. secECE), human ET-1 cDNA (Ad.CMV.ET-1), and, as a control, E. coli lacZ (Ad.CMV.beta-gal). Ad.CMV.secECE (1-10 x 10(9) pfu/ml) was injected into the caudal vein of male Wistar rats and the animals were studied 96 h later. Immunoblot analysis of circulating plasma confirmed the expression of the soluble ECE-1. The plasma levels of big ET-1 and mature ET-1 were similar in Ad.CMV.secECE and Ad.CMV.beta-gal groups (0.3-0.5 pM). When Ad.CMV.secECE was co-injected with Ad.CMV.ET-1 (2.5 x 10(9) pfu/ml each), plasma ET-1 levels were significantly elevated compared to the control group co-injected with Ad.CMV.secECE and Ad.CMV.beta-gal (10.2 +/- 2.4 vs. 1.1 +/- 0.2 pM). Big ET-1 levels were threefold higher (3.7 +/- 1.1 vs. 1.2 +/- 0.4 pM), and systemic blood pressure was significantly elevated (132 +/- 3 vs. 90 +/- 3 mm Hg) in the Ad.CMV.secECE + Ad.CMV.ET-1 group. Administration of an ECE inhibitor (CGS 26303, 30 mg/kg) significantly reduced the blood pressure in the Ad.CMV.secECE + Ad.CMV.ET-1 group (from 125 +/- 5 to 74 +/- 6 mm Hg) but not in the control group (from 85 +/- 2 to 75 +/- 3 mm Hg). Infusion of an ETA antagonist (FR 139317; 0.2 mg/kg/min for 30 min) also significantly reduced the blood pressure only in the Ad.CMV.secECE + Ad.CMV.ET-1 group, without any significant effect in the control group. This study demonstrates that even though overexpression of ECE-1 in itself does not lead to systemic hypertension, the enzyme can be a crucial rate-limiting factor in the production of mature ET-1 in vivo. Furthermore, this model may prove to be useful for in vivo screening of ECE inhibitors.

Endothelin-1 inhibits endothelin-converting enzyme-1 expression in cultured rat pulmonary endothelial cells

BACKGROUND

The lung expresses large amounts of endothelin-converting enzyme-1 (ECE-1), which catalyzes a step in the biosynthesis of potent vasoactive endothelin-1 (ET-1) from the inactive intermediate big ET-1. Because there has been no report concerning a possible relationship between ET-1 and ECE-1, we investigated the effects of ET-1 on ECE-1 expression in cultured rat pulmonary endothelial cells.

METHODS AND RESULTS

ECE-1 messenger RNA (mRNA) and protein expression in cultured endothelial cells were assayed by Northern and Western blotting, respectively. Incubation with ET-1 for 6 hours caused a significant decrease in ECE-1 mRNA expression. The action of ET-1 on ECE-1 mRNA expression was antagonized by pretreatment with BQ788, a specific ETB receptor antagonist, but not by pretreatment with BQ123, a specific ETA receptor antagonist. The expression of ECE-1 protein was also inhibited at 6 hours after incubation with ET-1. The effects of ET-1 on ECE-1 mRNA and protein expression were shown to be mimicked by ionomycin, a calcium ionophore, but not by 12-O-tetradecanoylphorbol 13-acetate, a protein kinase C activator.

CONCLUSIONS

The present results demonstrate that ET-1 suppressed ECE-1 protein levels by inhibiting ECE-1 mRNA expression through the ETB receptor, suggesting the existence of a feedback action of ET-1 on ECE-1 in pulmonary endothelial cells.

Endothelin converting enzyme-1 gene expression in the kidney of spontaneously hypertensive rats

Abnormal renal handling of water and sodium is implicated in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). Alteration of renal endothelin-1 synthesis is also reported in SHR. Endothelin-1, a potent vasoconstrictor and regulator of sodium reabsorption in the nephron, has a pathophysiological potential in the development of hypertension. Because synthesis of bioactive endothelin-1 requires endothelin converting enzyme-1 (ECE-1), we investigated whether renal ECE-1 gene expression is altered in the kidney of SHR. Kidneys from both 4- and 12-week-old SHR and age-matched Wistar-Kyoto rats (WKY) were studied. ECE-1 mRNA in microdissected nephron segments was assessed by reverse transcription-competitive polymerase chain reaction, and ECE-1 protein level by Western blot. In 4-week-old SHR, ECE-1 mRNA was significantly increased in the proximal straight tubule, medullary thick ascending limb, cortical thick ascending limb, and inner medullary collecting duct. ECE-1 protein level was increased in both the outer and inner medulla. In 12-week-old SHR, ECE-1 gene expression was significantly increased in the proximal straight tubule, medullary thick ascending limb, and also in the glomeruli. Glomerular preproendothelin-1 mRNA expression was not different between the two strains at both 4 and 12 weeks. We conclude that high ECE-1 gene expression in the nephron, via increase of endothelin-1 synthesis, may promote sodium retention that contributes to the development and/or maintenance of hypertension in SHR.