Cellular distribution of endothelin-converting enzyme-1 in human tissues

Early transcriptomic changes in peripheral blood 7 days after embryo transfer in dairy cattle

A common goal of the dairy industry is to shorten the calving interval to reap several benefits associated with improved fertility. Early pregnancy detection is crucial to shorten this interval, allowing for prompt re-insemination of cows that failed to conceive after the first service. Currently, the industry lacks a method to accurately predict pregnancy within the first 3 wk. The polypeptide cytokine IFN-tau (IFNT) is the primary signal for maternal recognition of pregnancy in ruminants. As IFNT is released from the early conceptus, it initiates a cascade of effects, including upregulation of IFN-stimulated genes (ISG). Expression of ISG can be detected in the peripheral blood. The present study aimed to characterize peripheral transcriptomic changes, including the ISG, as early as d 7 after embryo transfer. A total of 170 Holstein heifers received in vitro-produced embryos. Whole blood was collected from these heifers within 24 h of the embryo transfer (d 0), d 7, and d 14 after embryo transfer. The heifers were divided into 2 groups, pregnant and nonpregnant, based on pregnancy diagnosis on d 28 via ultrasound. Total RNA was extracted from the peripheral blood of pregnant and nonpregnant heifers, pooled and sequenced. Expression analysis on d 7 heifers resulted in 13 significantly differentially expressed genes mostly related to innate immunity. Differential expression analysis comparing pregnant heifers on d 0 to the same heifers on d 14 showed 51 significantly differentially expressed genes. Eight genes were further quantified through reverse-transcription quantitative real-time PCR for biological validation. On d 7 after embryo transfer, mRNA transcriptions of EDN1, CXCL3, CCL4, and IL1A were significantly upregulated in pregnant heifers (n = 14) compared with nonpregnant heifers (n = 14), with respective fold changes of 8.10, 18.12, 29.60, and 29.97. Although on d 14 after embryo transfer, mRNA transcriptions of ISG15, MX2, OASY1, and IFI6 were significantly upregulated in the blood of pregnant heifers (n = 14) compared with the same heifers on d 0, with respective fold changes of 5.09, 2.59, 3.89, and 3.08. These findings demonstrate that several immune-related genes and ISG are activated during the first 2 wk after embryo transfer, which may explain how the maternal immune system accommodates the allogenic conceptus. To further investigate the diagnostic potentials of these genes, future studies are warranted to analyze the specificity and sensitivity of these biomarkers to predict early pregnancy.

Susceptibility of ECE1 polymorphisms to Hirschsprung's disease in southern Chinese children

BACKGROUND

Hirschsprung's disease (HSCR) is currently considered to be a congenital gastrointestinal malformation caused mainly by genetic factors. Endothelin Converting Enzyme-1 (ECE1) has been reported to be associated with HSCR. However, the relationship between ECE1 single nucleotide polymorphism (SNP) rs169884 and HSCR in the southern Chinese population remains unknown.

METHODS

1,470 HSCR patients and 1,473 controls from a southern Chinese population were recruited. The intronic SNP rs169884 in ECE1 was genotyped in all samples. We tested the association between rs169884 and HSCR under various genetic models. We also evaluated the effect of rs169884 on HSCR subtypes, including short-segment HSCR (S-HSCR), long-segment HSCR (L-HSCR) and total colonic aganglionosis (TCA). External epigenetic data were integrated to investigate the potential biological function of rs169884.

RESULTS

Chromatin states data from derived neuron cells or fetal colon tissue revealed that rs169884 might control ECE1 expression through regulating its enhancer function. We did not find a significant association between rs169884 and HSCR. For HSCR subtypes, although no significant associations were detected between rs169884 and S-HSCR (OR = 1.00, 95% CI: 0.89∼1.12, P_adj = 0.77) or TCA (OR = 1.00, 95% CI: 0.72∼1.38, P_adj = 0.94), we found that rs169884 could increase the risk of L-HSCR (OR = 1.23, 95% CI 1.02∼1.45, P_adj = 0.024).

CONCLUSION

These results suggested that rs169884 might play a regulatory role for ECE1 expression and increase susceptibility of L-HSCR in southern Chinese children.

Novel Therapeutic Approaches Targeting the Renin-Angiotensin System and Associated Peptides in Hypertension and Heart Failure

Despite the success of renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers, current therapies for hypertension and related cardiovascular diseases are still inadequate. Identification of additional components of the RAS and associated vasoactive pathways, as well as new structural and functional insights into established targets, have led to novel therapeutic approaches with the potential to provide improved cardiovascular protection and better blood pressure control and/or reduced adverse side effects. The simultaneous modulation of several neurohumoral mediators in key interconnected blood pressure-regulating pathways has been an attractive approach to improve treatment efficacy, and several novel approaches involve combination therapy or dual-acting agents. In addition, increased understanding of the complexity of the RAS has led to novel approaches aimed at upregulating the ACE2/angiotensin-(1-7)/Mas axis to counter-regulate the harmful effects of the ACE/angiotensin II/angiotensin III/AT1R axis. These advances have opened new avenues for the development of novel drugs targeting the RAS to better treat hypertension and heart failure. Here we focus on new therapies in preclinical and early clinical stages of development, including novel small molecule inhibitors and receptor agonists/antagonists, less conventional strategies such as gene therapy to suppress angiotensinogen at the RNA level, recombinant ACE2 protein, and novel bispecific designer peptides.

Symbiotic microbes affect the expression of male reproductive genes in Glossina m. morsitans

Background

Tsetse flies (Diptera, Glossinidae) display unique reproductive biology traits. Females reproduce through adenotrophic viviparity, nourishing the growing larva into their modified uterus until parturition. Males transfer their sperm and seminal fluid, produced by both testes and male accessory glands, in a spermatophore capsule transiently formed within the female reproductive tract upon mating. Both sexes are obligate blood feeders and have evolved tight relationships with endosymbionts, already shown to provide essential nutrients lacking in their diet. However, the partnership between tsetse and its symbionts has so far been investigated, at the molecular, genomic and metabolomics level, only in females, whereas the roles of microbiota in male reproduction are still unexplored.

Results

Here we begin unravelling the impact of microbiota on Glossina m. morsitans (G. morsitans) male reproductive biology by generating transcriptomes from the reproductive tissues of males deprived of their endosymbionts (aposymbiotic) via maternal antibiotic treatment and dietary supplementation. We then compared the transcriptional profiles of genes expressed in the male reproductive tract of normal and these aposymbiotic flies. We showed that microbiota removal impacts several male reproductive genes by depressing the activity of genes in the male accessory glands (MAGs), including sequences encoding seminal fluid proteins, and increasing expression of genes in the testes. In the MAGs, in particular, the expression of genes related to mating, immunity and seminal fluid components’ synthesis is reduced. In the testes, the absence of symbionts activates genes involved in the metabolic apparatus at the basis of male reproduction, including sperm production, motility and function.

Conclusions

Our findings mirrored the complementary roles male accessory glands and testes play in supporting male reproduction and open new avenues for disentangling the interplay between male insects and endosymbionts. From an applied perspective, unravelling the metabolic and functional relationships between tsetse symbionts and male reproductive physiology will provide fundamental information useful to understanding the biology underlying improved male reproductive success in tsetse. This information is of particular importance in the context of tsetse population control via Sterile Insect Technique (SIT) and its impact on trypanosomiasis transmission.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1289-2) contains supplementary material, which is available to authorized users.

ECE-1 overexpression in head and neck cancer is associated with poor tumor differentiation and patient outcome

BACKGROUND

Endothelin-converting enzyme-1 (ECE-1) primarily converts big endothelins (ETs) into active endothelin-1 (ET-1). However, the expression pattern and prognostication status of ECE-1 in head and neck cancer (HNC) are enigmatic. In this study, we investigated ECE-1 expression and assessed the roles of ECE-1 as a predictor for HNC differentiation and prognosis.

MATERIALS AND METHODS

ECE-1 expressions were evaluated by immunohistochemical analysis using a tissue microarray (TMA) composed of 100 cases of head and neck squamous cell carcinoma. The correlation of ECE-1 expression with clinicopathologic variables and patient outcomes was analyzed.

RESULTS

ECE-1 may be overexpressed in HNC carcinoma cells. Higher ECE-1 level was detected more frequently in moderately to poorly differentiated tumors and showed a lower differentiation category compared to the G1 cases (p = 0.015); this finding was further confirmed by an adjusted odds ratio (OR) of 4.071 (p = 0.042). Moreover, Kaplan-Meier survival analyses showed that a higher ECE-1 expression was associated with a poorer survival in patients with HNC (p < 0.0001). On multivariate Cox proportional hazards models analysis, ECE-1 of high expression proved to be an independent prognostic factor with a hazard ratio (HR) of 3.985 (p < 0.001).

CONCLUSION

Our data provide the first evidence that overexpression of ECE-1 in HNC is a predictor of poor tumor differentiation and prognosis.

Endothelins in inflammatory neurological diseases

Endothelins were discovered more than thirty years ago as potent vasoactive compounds. Beyond their well-documented cardiovascular properties, however, the contributions of the endothelin pathway have been demonstrated in several neuroinflammatory processes and the peptides have been reported as clinically relevant biomarkers in neurodegenerative diseases. Several studies report that endothelin-1 significantly contributes to the progression of neuroinflammatory processes, particularly during infections in the central nervous system (CNS), and is associated with a loss of endothelial integrity at the blood brain barrier level. Because of the paucity of clinical trials with endothelin-1 antagonists in several infectious and non-infectious neuroinflammatory diseases, it remains an open question whether the 21 amino acid peptide is a mediator/modulator rather than a biomarker of the progression of neurodegeneration. This review focuses on the potential roles of endothelins in the pathology of neuroinflammatory processes, including infectious diseases of viral, bacterial or parasitic origin in which the synthesis of endothelins or its pharmacology have been investigated from the cell to the bedside in several cases, as well as in non-infectious inflammatory processes such as neurodegenerative disorders like Alzheimers Disease or central nervous system vasculitis.

Association between ECE1 gene polymorphisms and risk of intracerebral haemorrhage

OBJECTIVE

To determine whether endothelin converting enzyme-1 (ECE1) gene polymorphisms contribute to susceptibility to intracerebral haemorrhage (ICH) by influencing blood pressure.

METHODS

This case-control study enrolled patients with ICH and healthy control subjects from a Southern Han Chinese population. The ECE1 gene polymorphisms rs212528 and rs213045 were genotyped. The association between the genotypes and the risk of ICH was assessed. The effects of these two ECE1 gene polymorphisms on blood pressure were also analysed.

RESULTS

A total of 389 patients with ICH and 404 healthy control subjects participated in the study. There was no significant association between the ECE1 rs212528 and rs213045 polymorphisms and ICH even after adjusting for different confounding variables. In patients with ICH, the systolic blood pressure of patients with the rs212528 AA genotype was significantly lower than that of patients with the AG/GG genotypes.

CONCLUSIONS

These results indicated that the ECE1 rs212528 and rs213045 polymorphisms had no major role to play in the genetic susceptibility to ICH, although rs212528 might influence blood pressure in patients with ICH.

An arterial-specific enhancer of the human endothelin converting enzyme 1 (ECE1) gene is synergistically activated by Sox17, FoxC2, and Etv2

Endothelin-converting enzyme-1 (Ece-1), a crucial component of the Endothelin signaling pathway, is required for embryonic development and is an important regulator of vascular tone, yet the transcriptional regulation of the ECE1 gene has remained largely unknown. Here, we define the activity and regulation of an enhancer from the human ECE1 locus in vivo. The enhancer identified here becomes active in endothelial progenitor cells shortly after their initial specification and is dependent on a conserved FOX:ETS motif, a composite binding site for Forkhead transcription factors and the Ets transcription factor Etv2, for activity in vivo. The ECE1 FOX:ETS motif is bound and cooperatively activated by FoxC2 and Etv2, but unlike other described FOX:ETS-dependent enhancers, ECE1 enhancer activity becomes restricted to arterial endothelium and endocardium by embryonic day 9.5 in transgenic mouse embryos. The ECE1 endothelial enhancer also contains an evolutionarily-conserved, consensus SOX binding site, which is required for activity in transgenic mouse embryos. Importantly, the ECE1 SOX site is bound and activated by Sox17, a transcription factor involved in endothelial cell differentiation and an important regulator of arterial identity. Moreover, the ECE1 enhancer is cooperatively activated by the combinatorial action of FoxC2, Etv2, and Sox17. Although Sox17 is required for arterial identity, few direct transcriptional targets have been identified in endothelial cells. Thus, this work has important implications for our understanding of endothelial specification and arterial subspecification.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Endothelin-converting enzymes and related metalloproteases in Alzheimer's disease

The efficient clearance of amyloid-β (Aβ) is essential to modulate levels of the peptide in the brain and to prevent it from accumulating in senile plaques, a hallmark of Alzheimer's disease (AD) pathology.We and others have shown that failure in Aβ catabolism can produce elevations in Aβ concentration similar to those observed in familial forms of AD. Based on the available evidence, it remains plausible that in late-onset AD, disturbances in the activity of Aβ degrading enzymes could induce Aβ accumulation, and that this increase could result in AD pathology. The following review presents a historical perspective of the parallel discovery of three vasopeptidases (neprilysin and endothelin-converting enzymes-1 and -2) as important Aβ degrading enzymes. The recognition of the role of these vasopeptidases in Aβ degradation, beyond bringing to light a possible explanation of how cardiovascular risk factors may influence AD risk, highlights a possible risk of the use of inhibitors of these enzymes for other clinical indications such as hypertension. We will discuss in detail the experiments conducted to assess the impact of vasopeptidase deficiency (through pharmacological inhibition or genetic mutation) on Aβ accumulation, as well as the cooperative effect of multiple Aβ degrading enzymes to regulate the concentration of the peptide at multiple sites, both intracellular and extracellular, throughout the brain.

Altered endothelin expression in granulosa-lutein cells of women with polycystic ovary syndrome

AIMS

To examine the levels of endothelin system components in granulosa lutein cells (GLCs) of women with PCOS and compare them to normally ovulating women undergoing In Vitro Fertilization (IVF). Polycystic ovary syndrome (PCOS) is one of the most common endocrine-metabolic disorders in women of reproductive age. Endothelins are locally produced by endothelial and granulosa cells of the preovulatory follicle. Abnormal expression or production of endothelins may be a contributing factor in PCOS pathogenesis.

MAIN METHODS

Follicular aspirates containing GLCs were obtained from PCOS and normally ovulating patients undergoing oocyte retrieval during the IVF cycle. RNA was extracted and endothelin system components were quantified using real-time PCR. GLCs were cultured in basal media for 7 days, and then challenged with various luteinizing agents (luteinizing hormone, hCG, or forskolin) for 24 h.

KEY FINDINGS

In GLCs from women with PCOS, Endothelin-1 mRNA expression was elevated (2.2-fold) as compared with normally ovulating women, whereas endothelin-2 mRNA was reduced (1.8-fold). ET receptors and endothelin-converting enzyme showed the same expression levels in the two groups. In vitro modeling showed that although the steroidogenic response was preserved in GLC, endothelin expression levels were not exhibited in vitro in their original pattern.

SIGNIFICANCE

Dysregulation of ovarian endothelin expression may induce a pathologic ovulation pattern characteristic of PCOS.

Endothelin-converting enzyme-1 actions determine differential trafficking and signaling of corticotropin-releasing factor receptor 1 at high agonist concentrations

CRF receptor 1 (CRF(1)), a key neuroendocrine mediator of the stress response, has two known agonists corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1). Here we report that endothelin-converting enzyme-1 (ECE-1) differentially degrades CRF and Ucn1; ECE-1 cleaves Ucn1, but not CRF, at critical residue Arginine-34/35', which is essential for ligand-receptor binding. At near K(D) agonist concentration (30 nm), both Ucn1- and CRF-mediated Ca(2+) mobilization are ECE-1 dependent. Interestingly, at high agonist concentration (100 nm), Ucn1-mediated Ca(2+) mobilization remains ECE-1 dependent, whereas CRF-mediated mobilization becomes independent of ECE-1 activity. At high agonist concentration, ECE-1 inhibition disrupted Ucn1-, but not CRF-induced CRF(1) recycling and resensitization, but did not prolong the association of CRF(1) with β-arrestins. RNA interference-mediated knockdown of Rab suggests that both Ucn1- and CRF-induced CRF(1) resensitization is dependent on activity of Rab11, but not of Rab4. CRF(1) behaves like a class A G protein-coupled receptor with respect to transient β-arrestins interaction. We propose that differential degradation by ECE-1 is a novel mechanism by which CRF(1) receptor is protected from overactivation by physiologically relevant high concentrations of higher affinity ligand to mediate distinct resensitization and downstream signaling.

Expression pattern of endothelin system components and localization of smooth muscle cells in the human pre-ovulatory follicle

BACKGROUND

Whether ovarian follicular rupture involves contractile activity or not has been debated for decades. Recently, study in the rodents has indicated that an endogenously produced potent vasoconstrictive peptide, endothelin-2 (EDN2), may induce follicular constriction immediately prior to ovulation. This study was aimed to systematically characterize the human ovarian endothelin system and localize smooth muscle cells to assess the possible involvement of contractile activity in human ovulation.

METHODS

This is a prospective experimental study. Study subjects were 20 women aged 20-38 years who underwent IVF owing to tubal or male factors. Expression patterns of messenger RNAs (mRNAs) for EDN1, EDN2, EDN3, endothelin-converting enzyme-1 (ECE1 and ECE2), endothelin receptor A (ET(A)) and ET(B) in the granulosa cells (GCs) and cumulus cells and endothelin peptide concentration in the pre-ovulatory follicles were measured at 36 h after hCG injection. In addition, localization of ovarian smooth muscle cells and endothelin receptor expression were determined in normal (non-IVF patient) ovaries.

RESULTS

Pre-ovulatory follicles express mRNA for EDN1 and EDN2, ECE1, ECE2, ET(A) and ET(B), but not EDN3, contain highly concentrated endothelin peptides (105.9 pg/ml) and are surrounded by theca externa that are made mostly of multicell layer non-vascular smooth muscle cells. ET(A) expression is localized in the smooth muscle cells of theca externa, theca interna and GC, whereas ET(B) expression is confined to theca interna.

CONCLUSIONS

Pre-ovulatory follicles contain highly concentrated endothelins and are surrounded by non-vascular smooth muscle cells that express endothelin receptor, suggesting involvement of endothelin-induced contractile action in ovulation in the human ovary.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Protein kinase C-regulated aβ production and clearance

Alzheimer's disease (AD) is the most common form of dementia among the elderly population. AD, which is characterized as a disease of cognitive deficits, is mainly associated with an increase of amyloid β-peptide (Aβ) in the brain. A growing body of recent studies suggests that protein kinase C (PKC) promotes the production of the secretory form of amyloid precursor protein (sAPPα) via the activation of α-secretase activity, which reduces the accumulation of pathogenic Aβ levels in the brain. Moreover, activation of PKCα and mitogen-activated protein kinase (MAPK) is known to increase sAPPα. A novel type of PKC, PKCε, activates the Aβ degrading activity of endothelin converting enzyme type 1 (ECE-1), which might be mediated via the MAPK pathway as well. Furthermore, dysregulation of PKC-MAPK signaling is known to increase Aβ levels in the brain, which results in AD phenotypes. Here, we discuss roles of PKC in Aβ production and clearance and its implication in AD.

At the heart of tissue: endothelin system and end-organ damage

ET (endothelin)-1 was first described as a potent vasoconstrictor. Since then, many other deleterious properties mediated via its two receptors, ETA and ETB, have been described, such as inflammation, fibrosis and hyperplasia. These effects, combined with a wide tissue distribution of the ET system, its up-regulation in pathological situations and a local autocrine/paracrine activity due to a high tissue receptor binding, make the tissue ET system a key local player in end-organ damage. Furthermore, ET-1 interacts in tissues with other systems such as the RAAS (renin-angiotensin-aldosterone system) to exert its effects. In numerous genetically modified animal models, non-specific or organ-targeted ET-1 overexpression causes intense organ damage, especially hypertrophy and fibrosis, in the absence of haemodynamic changes, confirming a local activity of the ET system. ET receptor antagonists have been shown to prevent and sometimes reverse these tissue alterations in an organ-specific manner, leading to long-term benefits and an improvement in survival in different animal models. Potential for such benefits going beyond a pure haemodynamic effect have also been suggested by clinical trial results in which ET receptor antagonism decreased the occurrence of new digital ulcers in patients with systemic sclerosis and delayed the time to clinical worsening in patients with PAH (pulmonary arterial hypertension). The tissue ET system allows therapeutic interventions to provide organ selectivity and beneficial effects in diseases associated with tissue inflammation, hypertrophy or fibrosis.

beta-Amyloid degradation and Alzheimer's disease

Extensive β-amyloid (Aβ) deposits in brain parenchyma in the form of senile plaques and in blood vessels in the form of amyloid angiopathy are pathological hallmarks of Alzheimer's disease (AD). The mechanisms underlying Aβ deposition remain unclear. Major efforts have focused on Aβ production, but there is little to suggest that increased production of Aβ plays a role in Aβ deposition, except for rare familial forms of AD. Thus, other mechanisms must be involved in the accumulation of Aβ in AD. Recent data shows that impaired clearance may play an important role in Aβ accumulation in the pathogenesis of AD. This review focuses on our current knowledge of Aβ-degrading enzymes, including neprilysin (NEP), endothelin-converting enzyme (ECE), insulin-degrading enzyme (IDE), angiotensin-converting enzyme (ACE), and the plasmin/uPA/tPA system as they relate to amyloid deposition in AD.

Induction of endothelin-2 expression by luteinizing hormone and hypoxia: possible role in bovine corpus luteum formation

The pattern and regulation of endothlin-2 (EDN2) expression and its putative roles in bovine ovaries were investigated. EDN2 mRNA was determined in corpus luteum (CL) and during folliculoluteal transition induced by GnRH in vivo. EDN2 was elevated only in the early CL and was not present in older CL. In the young CL, EDN2 mRNA was identified mainly in luteal cells but not endothelial cells that expressed the EDN1 gene. Similarly, in preovulatory follicles, EDN2 was expressed in the granulosa cells (GCs) and not in the vascular theca interna. LH and hypoxia are two major stimulants of CL formation. Therefore, GCs were cultured with bovine LH, under hypoxic conditions. GCs incubated with bovine LH resulted in increased EDN2 mRNA 42 h later. CoCl2, a hypoxia-mimicking agent, elevated EDN2 in GCs in a dose-dependent manner. Incubation of the human GC line (Simian virus 40 large T antigen) under low oxygen tension (1%) augmented EDN2 6 and 24 h later. In these two cell types, along with EDN2, hypoxia augmented VEGF. EDN2 induced in GCs changes that characterize the developing CL: cell proliferation as well as up-regulation of vascular endothelial growth factor and cyclooxygenase-2 (mRNA and protein levels). Human chorionic gonadotropin also up-regulated these two genes. Small interfering RNA targeting EDN-converting enzyme-1 effectively reduced its mRNA levels. This treatment, expected to lower the mature EDN2 peptide production, inhibited VEGF mRNA levels and GC numbers. Together these data suggest that elevated EDN2 in the early bovine CL, triggered by LH surge and hypoxia, may facilitate CL formation by promoting angiogenesis, cell proliferation, and differentiation.

Endothelin-converting enzyme 1 promotes re-sensitization of neurokinin 1 receptor-dependent neurogenic inflammation

BACKGROUND AND PURPOSE

The metalloendopeptidase endothelin-converting enzyme 1 (ECE-1) is prominently expressed in the endothelium where it converts big endothelin to endothelin-1, a vasoconstrictor peptide. Although ECE-1 is found in endosomes in endothelial cells, the role of endosomal ECE-1 is unclear. ECE-1 degrades the pro-inflammatory neuropeptide substance P (SP) in endosomes to promote recycling and re-sensitization of its neurokinin 1 (NK(1)) receptor. We investigated whether ECE-1 regulates NK(1) receptor re-sensitization and the pro-inflammatory effects of SP in the endothelium.

EXPERIMENTAL APPROACH

We examined ECE-1 expression, SP trafficking and NK(1) receptor re-sensitization in human microvascular endothelial cells (HMEC-1), and investigated re-sensitization of SP-induced plasma extravasation in rats.

KEY RESULTS

HMEC-1 expressed all four ECE-1 isoforms (a-d), and fluorescent SP trafficked to early endosomes containing ECE-1b/d. The ECE-1 inhibitor SM-19712 prevented re-sensitization of SP-induced Ca2+ signals in HMEC-1 cells. Immunoreactive ECE-1 and NK(1) receptors co-localized in microvascular endothelial cells in the rat. SP-induced extravasation of Evans blue in the urinary bladder, skin and ears of the rat desensitized when the interval between two SP injections was 10 min, and re-sensitized after 480 min. SM-19712 inhibited this re-sensitization.

CONCLUSIONS AND IMPLICATIONS

By degrading endocytosed SP, ECE-1 promotes the recycling and re-sensitization of NK(1) receptors in endothelial cells, and thereby induces re-sensitization of the pro-inflammatory effects of SP. Thus, ECE-1 inhibitors may ameliorate the pro-inflammatory actions of SP.

The ovarian endothelin network: an evolving story

The endothelin (ET) system consists of three ET isopeptides, several converting enzyme isoforms and two G-protein-coupled receptors, ETA and ETB, which are linked to multiple signaling pathways. Less than 20 years after the initial detection of ET-1 in granulosa cells, the ovarian ET network continues to expand with the discovery of new members and functions. ETs influence a broad range of essential reproductive processes, such as ovulation, steroidogenesis and luteolysis. Therefore, a more comprehensive understanding of the ovarian ET network might provide new strategies for controlling reproduction. This review presents up-to-date findings on the ET network in the ovary.

Endothelin-converting enzyme-1 regulates endosomal sorting of calcitonin receptor-like receptor and beta-arrestins

Although cell surface metalloendopeptidases degrade neuropeptides in the extracellular fluid to terminate signaling, the function of peptidases in endosomes is unclear. We report that isoforms of endothelin-converting enzyme-1 (ECE-1a–d) are present in early endosomes, where they degrade neuropeptides and regulate post-endocytic sorting of receptors. Calcitonin gene-related peptide (CGRP) co-internalizes with calcitonin receptor-like receptor (CLR), receptor activity-modifying protein 1 (RAMP1), β-arrestin2, and ECE-1 to early endosomes, where ECE-1 degrades CGRP. CGRP degradation promotes CLR/RAMP1 recycling and β-arrestin2 redistribution to the cytosol. ECE-1 inhibition or knockdown traps CLR/RAMP1 and β-arrestin2 in endosomes and inhibits CLR/RAMP1 recycling and resensitization, whereas ECE-1 overexpression has the opposite effect. ECE-1 does not regulate either the resensitization of receptors for peptides that are not ECE-1 substrates (e.g., angiotensin II), or the recycling of the bradykinin B₂ receptor, which transiently interacts with β-arrestins. We propose a mechanism by which endosomal ECE-1 degrades neuropeptides in endosomes to disrupt the peptide/receptor/β-arrestin complex, freeing internalized receptors from β-arrestins and promoting recycling and resensitization.

Endothelin signaling pathways in rat adrenal medulla

1. We further characterized the effect of endothelins (ETs) on receptor-mediated phosphoinositide (PI) turnover, nitric oxide synthase (NOS) activation, and cGMP formation in whole rat adrenal medulla. 2. The PI hydrolysis was assessed as accumulation of inositol monophosphates (InsP(1)) in the presence of 10 mM LiCl in whole tissue and the analysis of inositol-1-phosphate by Dowex anion exchange chromatography. NOS activity was assayed by monitoring the conversion of radiolabeled L-arginine to L-citrulline. Cyclic GMP formation was assessed as accumulation of cGMP in whole tissue in the presence of phosphodiesterase inhibition, and the amount of cGMP formed was determined by radioimmuno-antibody procedure. 3. ET-1 and ET-3 increased PI turnover by 30% in whole adrenal medulla prelabeled with [(3)H] myoinositol. Both ETs isoforms, at equimolar doses, increased NOS activity and cGMP levels in similar degree. The selective ET(B) receptor agonist, IRL-1620, also increased cGMP formation, mimicking the effects of ETs, while IRL-1620 did not alter the PI metabolism. ETs-induced InsP(1) accumulation and cGMP was dependent on extracellular calcium. The effect of ETs on PI turnover was inhibited by neomycin. The L-arginine analogue, N-nitro-L-arginine (L-NAME), and two inhibitors of soluble guanylyl cyclase, methylene blue and ODQ, significantly inhibited the increase in cGMP production induced by ETs or IRL-1620. The selective ET(A) receptor antagonist, BQ 123, inhibited the ETs-induced increase in PI turnover, while the selective ET(B) receptor antagonist, BQ 788, was ineffective. Likewise, BQ 788, significantly inhibited ET-1- or ET-3-induced NOS activation and cGMP generation but not ETs-induced InsP(1) accumulation. 4. Our data indicate that stimulation of PI turnover and NO-induced cGMP generation constitutes ETs signaling pathways in rat adrenal medulla. The former action is mediated through activation of ET(A) receptor, while the latter through the activation of ET(B) receptor. These results support the role of endothelins in the regulation of adrenal medulla function.

PKCepsilon increases endothelin converting enzyme activity and reduces amyloid plaque pathology in transgenic mice

Deposition of plaques containing amyloid beta (Abeta) peptides is a neuropathological hallmark of Alzheimer's disease (AD). Here we demonstrate that neuronal overexpression of the epsilon isozyme of PKC decreases Abeta levels, plaque burden, and plaque-associated neuritic dystrophy and reactive astrocytosis in transgenic mice expressing familial AD-mutant forms of the human amyloid precursor protein (APP). Compared with APP singly transgenic mice, APP/PKCepsilon doubly transgenic mice had decreased Abeta levels but showed no evidence for altered cleavage of APP. Instead, PKCepsilon overexpression selectively increased the activity of endothelin-converting enzyme, which degrades Abeta. The activities of other Abeta-degrading enzymes, insulin degrading enzyme and neprilysin, were unchanged. These results indicate that increased neuronal PKCepsilon activity can promote Abeta clearance and reduce AD neuropathology through increased endothelin-converting enzyme activity.

Genomic organisation of the mouse gene encoding endothelin-converting enzyme-1 (ECE-1) and mRNA expression of ECE-1 isoforms in murine tissues

Mouse knockout-models have previously revealed important biological functions of endothelin-converting enzyme-1 (ECE-1) in normal cardiac and craniofacial development. Since human ECE-1 is expressed in various isoforms, termed a, b, c, and d, expression of which is controlled by alternative promoters, we postulated that corresponding isoforms may also be transcribed from the murine Ece1 gene. By comparative sequence analysis using exon-specific sequences of human and rat ECE-1 we have resolved the complete exon-intron structure of the murine Ece1 locus on chromosome 4. The murine Ece1 gene comprises 23 exons distributed over 100 kb of genomic DNA and was found to be structurally highly conserved when compared to the human ECE1 gene. As with the human gene, the exons containing isoform-specific sequences were localised in the 5' terminal region of the murine Ece1 gene. Using specific sense primers, isoform-specific expression of murine ECE-1 mRNA in various mouse tissues was confirmed by RT-PCR. Using real-time PCR we demonstrated that ECE-1c was the most abundantly expressed isoform in most tissues, except for heart and aorta displaying a more even isoform distribution. We detected an additional isoform-specific exon, designated c2, which was apparently constitutively spliced and expressed only as minor fraction of ECE-1c transcripts. Our results provide evidence of structural conservation of mammalian genes encoding ECE-1 and will facilitate a more refined analysis of ECE-1 mRNA expression in the mouse model organism.

Adventitia contribution in vascular tone: insights from adventitia‐derived cells in a tissue‐engineered human blood vessel

Whether the adventitia component of blood vessels directly participates in the regulation of vascular tone remains to be demonstrated. We have recently developed a human tissue-engineered blood vessel comprising the three tunicae of a native blood vessel using the self-assembly approach. To investigate the role of the adventitia in the modulation of vascular tone, this tissue-engineering method was used to produce three vascular constructs from cells explanted and proliferated from donor vessel tunicae 1) an adventitia + a media, or only 2) an adventitia, or 3) a media. The vasoconstriction responses of these 3 constructs to endothelin, the most potent vasopressor known up-to-date, as well as to nonselective and selective agonists and antagonists, were compared. The adventitia contracted to endothelin-1, -2, whereas the media and the media+adventitia contracted to all three endothelins. Endothelin-induced contraction of the adventitia was dependent on ET(A) receptors, whereas that of the media and the adventitia+media was ET(A) and ET(B) receptor-dependent. RT-PCR studies corroborated these results. SNP induced a dose-dependent relaxation of the three tissue constructs. We also demonstrated that the endothelin-converting enzyme, responsible for the formation of the active endothelin peptides, was present and functional in the adventitia. In conclusion, this is the first direct demonstration that the adventitia has the capacity to contract and relax in response to vasoactive factors. The present study suggests that the adventitia of a blood vessel could play a greater role than expected in the modulation of blood vessel tone.

Endothelin-converting Enzyme-1, Abundance of Isoforms a-d and Identification of a Novel Alternatively Spliced Variant Lacking a Transmembrane Domain

Endothelin-converting enzyme-1 (ECE-1) cleaves big endothelins, as well as bradykinin and beta-amyloid peptide. Several isoforms of ECE-1 (a-d) have been identified to date; they differ only in their NH(2) terminus but share the catalytic domain located in the COOH-terminal end. Using quantitative PCR, we found ECE-1d to be the most abundant type in several endothelial cells (EC) types. In addition to full-length ECE-1 forms we have identified novel, alternatively spliced mRNAs of ECE-1 b-d. These splice variants (SVs) lack exon 3', which codes for the transmembrane region and is present in full-length forms. SVs mRNA were highly expressed in EC derived from macro and microvascular beds but much less so in other, non-endothelial cells expressing ECE-1, which suggests that the splicing mechanism is cell-specific. Analyses of ECE-1d and its SV form in stably transfected HEK-293 cells revealed that both proteins were recognized by anti COOH-terminal ECE-1 antibodies, but anti NH(2)-terminal antibodies only bound ECE-1d. The novel protein, designated ECE-1 sv, has an apparent molecular mass of 75 kDa; by using site-directed mutagenesis its start site was identified in a region common to all ECE-1 forms suggesting that ECE-1 b-d SV mRNAs are translated into the same protein. In agreement with the findings demonstrating common COOH terminus for ECE-1sv and ECE-1d, both exhibited a similar catalytic activity. However, immunofluorescence staining and differential centrifugation revealed a distinct intracellular localization for these two proteins. The presence of ECE-1sv in different cellular compartments than full-length forms of the enzyme may suggest a distinct physiological role for these proteins.

Histochemical distribution of endothelin-converting enzyme subtypes in Podarcis sicula (Squamata, Lacertidae) tissues

The distribution of endothelin-converting enzyme (ECE) in the lizard Podarcis sicula was investigated immunohistochemically using antibodies against endothelin-converting enzyme ECE-1 and endothelin-converting enzyme ECE-2 homologues. In all the tissues examined, immunoreactivity for both antibodies was found, although the distribution and degree of expression varied. Strong immunoreactivity was found in the endothelial cells and chromaffin tissue for both enzymes, whereas other tissues such as nervous tissue, renal tissue and hepatocytes display distinct patterns. Current knowledge does not allow correlation of these distribution patterns to specific functions but the data suggest that, in reptiles as in mammals, ECE is probably involved in physiological functions such as paracrine activity through endothelins and/or other substrates.

Tissue-engineered human vascular media with a functional endothelin system

BACKGROUND

Cardiovascular diseases remain a major cause of death and disability in the Western world. Among the various approaches adopted to counteract the morbidity associated with these diseases, surgical procedures and cardiac and vascular xenotransplantations or allotransplantations are routinely performed. The suitable vascular graft would be as close as possible to the native and healthy vessel composed exclusively of human components provided by the patient and would adapt to the donor's hemodynamics. We have developed such a tissue-engineered human blood vessel reconstructed with human cells. Because endothelin is the most potent vasopressor known to date, we were interested in investigating the functionality of the endothelinergic system in our reconstructed human blood vessel.

METHODS AND RESULTS

Vasoconstriction studies were performed with nonselective and selective agonists and antagonists to demonstrate that ET(A) receptors were present and functional in tissue-engineered human vascular media constructed with the self-assembly method. Reverse-transcriptase polymerase chain reaction studies demonstrated that mRNA of the ET(A) but not the ET(B) receptor was present in these human tissue-engineered blood vessels. Furthermore, we demonstrated that the endothelin-converting enzyme, the main enzyme responsible for the formation of the biologically active endothelin peptides, was present and functional in these same bioengineered vascular media.

CONCLUSIONS

Our results suggest that the media component of our tissue-engineered blood vessel has the potential of controlling vascular resistance via the presence of functional endothelin ET(A) receptors and endothelin-converting enzyme.

Localization of the endothelin system in human diffuse astrocytomas

BACKGROUND

Endothelin-1 (ET-1), a vasoconstrictor and mitogen, has recently been implicated in the pathogenesis of human glioblastoma, neuroblastoma, and meningioma. ET-1, formed by proteolysis of the propeptide big ET-1 by endothelin-converting enzyme-1 (ECE-1), mediates its cellular actions through ETA and ETB receptors. Because only immunoreactive ET-1 has been observed within human astrocytic tumor cells, the authors investigated the localization of the entire ET-1 system (ET-1 mRNA, ET-1, ECE-1, ETA and ETB receptors) in surgical samples of human diffuse astrocytomas WHO Grade II (n = 6).

METHODS

ET-1 mRNA expression was elucidated by in situ reverse transcriptase polymerase chain reaction (RT-PCR) using synthetic primers. Polyclonal antibodies were used to localize ET-1, ECE-1, ETA and ETB receptors by immunocytochemistry.

RESULTS

All ET components were detected in the six tumor samples. Intense (3+) cytoplasmic ET-1 mRNA labeling was observed in more than 75% of cells in all 6 astrocytomas. Up to 75% of tumor cells displayed intense ET-1 and ECE-1 immunolabeling distributed throughout their cytoplasm. Immunoreactive ETA and ETB receptors, observed in 25% to 75% of astrocytic tumor cells, were of moderate intensity. In addition, all components of the ET system were seen within endothelial cells of tumor blood vessels.

CONCLUSIONS

The presence of ET-1 mRNA, ECE-1, and ET-1 within tumor astrocytes suggests local ET synthesis and processing. The mitogenic and antiapoptotic properties of ET-1, as well as the vasodilatory signaling of ETB receptors, may promote tumorigenesis.

Reduced fertility in male mice deficient in the zinc metallopeptidase NL1

Members of the M13 family of zinc metalloendopeptidases have been shown to play critical roles in the metabolism of various neuropeptides and peptide hormones, and they have been identified as important therapeutic targets. Recently, a mouse NL1 protein, a novel member of the family, was identified and shown to be expressed mainly in the testis as a secreted protein. To define its physiological role(s), we used a gene targeting strategy to disrupt the endogenous murine Nl1 gene by homologous recombination and generate Nl1 mutant mice. The Nl1(-/-) mice were viable and developed normally, suggesting that zygotic expression of Nl1 is not required for development. However, Nl1(-/-) males produced smaller litters than their wild-type siblings, indicating specific male fertility problems. Reduced fertility may be explained by two impaired processes, decreased egg fertilization and perturbed early development of fertilized eggs. These two phenotypes did not result from gross anatomical modifications of the testis or from impaired spermatogenesis. Basic sperm parameters were also normal. Thus, our findings suggest that one of the roles of NL1 in mice is related to sperm function and that NL1 modulates the processes of fertilization and early embryonic development in vivo.

Cellular distribution of the endothelin system in the human brain

The vasoconstrictor endothelin-1 (ET-1) may also act as a neuropeptide. ET-1 is formed by the catalytic action of endothelin-converting enzyme-1 (ECE-1) on big ET-1 and its cellular actions are mediated via ET(A) and ET(B) receptors. Although localisation of these components in rodent brain has been extensively investigated, no single study has mapped their distribution in human brain. Here we describe the localisation of ET-1 mRNA, ET-1, ECE-1, ET(A) and ET(B) receptors within 24 human brain regions. In situ RT-PCR has previously detected ET-1 mRNA in 22 areas (excluding the post-central gyrus and pineal gland), and ET-1 immunoreactivity was visualised in cells of all regions. Using specific antibodies we have immunolocalised ECE-1 and ET(B) receptors in cells of 24 areas, and ET(A) receptors in nine regions (choroidal epithelial cells, neurones in the diencephalon, hippocampus, amygdaloid, dentate nucleus, Purkinje cells of the cerebellum, flocculo-nodular lobe and vermis). ET-1 mRNA, ET-1, ECE-1 and ET(B) receptors were observed in cortical pyramidal cells, neurones (brainstem, basal nuclei, thalamus, insula and claustrum, limbic region), cells in the anterior pituitary gland; nerve cell processes in the pars nervosa; pinealocytes and choroidal epithelial cells. Only ET-1 mRNA, ET-1, ECE-1, and ET(B) receptors were visualised in cerebral capillary endothelial cells. The presence of ET-1 mRNA, ECE-1 and ET-1 in 22 brain regions confirms ET expression and processing in human brain. The localisation of ET-1 and ET(B) receptors suggests receptor-mediated action akin to a neurotransmitter role for ET-1.

À quoi sert le système endothéline ?

Endothelins are a family of three peptides of 21 amino acids with strong vasoconstrictor effects. The three peptides are encoded by three different genes and derived from precursors (" big endothelins") which are cleaved by metalloproteases, named endothelin-converting enzyme. Two receptors have been cloned, ET-A and ET-B which bind the three endothelins with various affinities. The diverse expression pattern of the endothelin system (ET) components is associated with a complex pharmacology and its counteracting physiological actions. New modulators of the ET system have been described : retinoic acid, leptin, prostaglandins, hypoxia. Endothelins can be considered as regulators working in paracrine and autocrine fashion in a variety of organs in different cellular types. The ET system has beneficial and detrimental roles in mammals. The different components have been shown to be essential for a normal embryonic and neonatal development, for renal homeostasis and maintenance of basal vascular tone. They are involved in physiological and tumoral angiogenesis. They affect the physiology and pathophysiology of the liver, muscle, skin, adipose tissue and reproductive tract. The endothelin system participates in the development of atherosclerosis as well as pulmonary hypertension, and mediates cardiac remodeling in heart failure. Elaboration of new animal models (knock-out, pathophysiological models em leader ) will allow the clear genetic dissection of physiological and pathophysiological roles of the endothelin system.

Immunohistochemical Localization of Endothelin-Converting Enzyme-1 in Neuroendocrine Tumors and Normal Human Tissue

Endothelin-converting enzyme-1 (ECE-1) is the key enzyme of endothelin biosynthesis, catalyzing the final step in the process. In this study, we investigated the cellular distribution of ECE-1 in 19 normal human tissues and 16 neuroendocrine tumors using immunohistochemical staining with antigen retrieval. ECE-1 was expressed in vessel endothelial cells as well as nearly all epithelial cells, glands and duct cells in normal human tissues including the esophagus, stomach, small intestine, appendix, colon, liver, gallbladder, pancreas, endometrium, cervix, breast, skin, prostate, urinary bladder, lung, kidney, sympathetic ganglion, thyroid gland, and adrenal gland. The most interesting finding was that ECE-1 was expressed in normal neuroendocrine cells. ECE-1 was also expressed in all 16 neuroendocrine tumors, including three paragangliomas, five pheochromocytomas, three carcinoid tumors, four medullary carcinomas of the thyroid, and one islet cell tumor of the pancreas. In conclusion, ECE-1 is enriched in neuroendocrine cells and neuroendocrine tumors, suggesting an important biologic role for the enzyme in the neuroendocrine system.

Regulation of the major isoform of human endothelin-converting enzyme-1 by a strong housekeeping promoter modulated by polymorphic microsatellites

BACKGROUND

Human endothelin-converting enzyme (ECE)-1, the key enzyme in endothelin biosynthesis, shows broad cell and tissue expression within the cardiovascular system. Expression of ECE-1c, which represents the major ECE-1 isoform, is directed by an alternative promoter, but the mechanisms of ECE-1c promoter regulation are largely unknown. As ECE-1c transcription is initiated from several start sites, we hypothesized that the ECE-1c promoter functions as a housekeeping promoter.

OBJECTIVE

To investigate the putative housekeeping function of the ECE-1c promoter in vascular endothelial cells, which represent a main site of its expression.

RESULTS

Using promoter reporter assays, gel shift and supershift assays, we have demonstrated, in human endothelial EA.hy926 cells, functionality of cis-acting elements for binding of the CAAT-box binding protein NF-YB, GATA-2) E2F-2, and a GC-box binding factor, which are spatially associated with transcriptional start sites of ECE-1c. In the more upstream promoter region we have identified three highly polymorphic dinucleotide repeats, 5'-(CA)n, (CG)n and 3'-(CA)n, which strongly affected promoter function in endothelial EA.hy926 cells (2.7-fold activation comparing the most active to the least active allele) and, in a similar manner, in human neuronal KELLY cells. Finally, by in-vitro methylation, we were able to achieve strong suppression of the ECE-1c promoter activity in endothelial cells.

CONCLUSION

Our results provide a molecular explanation for constitutive expression of ECE-1c mRNA. Modulation by genetic and epigenetic mechanisms as revealed in our study may account for interindividual variation of the constitutive endothelin system activity in humans and thus influence individual predisposition to cardiovascular disease.

Endothelin-converting enzyme-1 (ECE-1) is a downstream target of the homeobox transcription factor Nkx2-5

The homeobox transcription factor Nkx2-5 and the zinc metalloprotease endothelin-converting enzyme-1 (ECE-1) are essential for cardiac development. Here, we demonstrate for the first time a functional link between Nkx2-5 and ECE-1. In transiently transfected rat H9c2 cardiomyoblasts, the alternative promoters specific for ECE-1a, ECE-1b, and ECE-1c are activated by Nkx2-5 coexpression. Lack of a consensus sequence for Nkx2-5 binding within the ECE-1c promoter and mutational analyses of Nkx2-5 consensus sequences identified in the ECE-1a and ECE-1b promoters, respectively, reveal an indirect mechanism of activation that is supported by gel shift assays. Furthermore, we have evidence of an additional direct activation mechanism of the ECE-1b promoter by Nkx2-5. With the use of RNase protection assay, Northern blot, and real-time PCR, the activating effect of Nkx2-5 on mRNA expression of ECE-1 isoforms was confirmed in the chromatin context of H9c2 and endothelial EA.hy926 cells, respectively, by stable Nkx2-5 overexpression. The interaction presented in this work provides a possible explanation for distinct phenotypic aspects of patients carrying mutations in the Nkx2-5 gene and may also be of significance for the pathophysiology of heart failure.

Synthesis and degradation of endothelin-1

The endothelin-converting enzyme (ECE) is the main enzyme responsible for the genesis of the potent pressor peptide endothelin-1 (ET-1). It is suggested that the ECE is pivotal in the genesis of ET-1, considering that the knockout of both genes generates the same lethal developments during the embryonic stage. Several isoforms of the ECE have been disclosed, namely ECE-1, ECE-2, and ECE-3. Within each of the first two groups, several sub-isoforms derived through splicing of single genes have also been identified. In this review, the characteristics of each sub-isoform for ECE-1 and 2 will be discussed. It is important to mention that the ECE is, however, not the sole enzyme involved in the genesis of endothelins. Indeed, other moieties, such as chymase and matrix metalloproteinase II, have been suggested to be involved in the production of ET intermediates, such as ET-1 (1-31) and ET-1 (1-32), respectively. Other enzymes, such as the neutral endopeptidase 24-11, is curiously not only involved in the degradation and inactivation of ET-1, but is also responsible for the final production of the peptide via the hydrolysis of ET-1 (1-31). In this review, we will attempt to summarize, through the above-mentioned characteristics, the current wisdom on the role of these different enzymes in the genesis and termination of effect of the most potent pressor peptide reported to date.

Alzheimer's disease beta-amyloid peptide is increased in mice deficient in endothelin-converting enzyme

The abnormal accumulation of beta-amyloid (Abeta) in the brain is an early and invariant feature in Alzheimer's disease (AD) and is believed to play a pivotal role in the etiology and pathogenesis of the disease. As such, a major focus of AD research has been the elucidation of the mechanisms responsible for the generation of Abeta. As with any peptide, however, the degree of Abeta accumulation is dependent not only on its production but also on its removal. In cell-based and in vitro models we have previously characterized endothelin-converting enzyme-1 (ECE-1) as an Abeta-degrading enzyme that appears to act intracellularly, thus limiting the amount of Abeta available for secretion. To determine the physiological significance of this activity, we analyzed Abeta levels in the brains of mice deficient for ECE-1 and a closely related enzyme, ECE-2. Significant increases in the levels of both Abeta40 and Abeta42 were found in the brains of these animals when compared with age-matched littermate controls. The increase in Abeta levels in the ECE-deficient mice provides the first direct evidence for a physiological role for both ECE-1 and ECE-2 in limiting Abeta accumulation in the brain and also provides further insight into the factors involved in Abeta clearance in vivo.

Heterodimerization of endothelin-converting enzyme-1 isoforms regulates the subcellular distribution of this metalloprotease

Endothelin-converting enzyme (ECE) is a membrane metalloprotease that generates endothelin from its direct precursor big endothelin. Four isoforms of ECE-1 are produced from a single gene through the use of alternate promoters. These isoforms share the same extracellular catalytic domain and contain unique cytosolic tails, which results in their specific subcellular targeting. We investigated the distribution of ECE-1 isoforms in transfected AtT-20 neuroendocrine cells. Whereas ECE-1a and 1c were present at the plasma membrane, ECE-1b and ECE-1d were retained inside the cells. We found that both intracellular isoforms were concentrated in the endosomal system: ECE-1d in recycling endosomes, and ECE-1b in late endosomes/multivesicular bodies. Leucine-based motifs were involved in the intracellular retention of these isoforms, and the targeting of ECE-1b to the degradation pathway required an additional signal in the N terminus. The concentration of ECE-1 isoforms in the endosomal system suggested new functions for these enzymes. Potential novel functions include redistribution of other isoforms through direct interaction. We have showed that ECE-1 isoforms could heterodimerize, and that in such heterodimers the ECE-1b targeting signal was dominant. Interaction of a plasma membrane isoform with ECE-1b resulted in its intracellular localization and decreased its extracellular activity. These data demonstrated that the targeting signals specific for ECE-1b constitute a regulatory domain per se that could modulate the localization and the activity of other isoforms.

The nitric oxide-endothelin-1 connection

Nitric oxide (NO) and endothelin-1 (ET-1) are endothelium-derived mediators that play important roles in vascular homeostasis. This review is focused on the role and reciprocal interactions between NO and ET-1 in health and diseases associated with endothelium dysfunction. We will also discuss the clinical significance of NO donors and drugs that antagonize ET receptors.

Enhancement of neurokinin A-induced smooth muscle contraction in human urinary bladder by mucosal removal and phosphoramidon: relationship to peptidase inhibition

Neurokinin A (NKA) is potent in contracting the human detrusor muscle. Here, we have investigated whether these contractile responses are influenced by the presence of the mucosa, by the peptidase inhibitor phosphoramidon or by possible modulators, prostaglandins and nitric oxide. Contractile responses to neurokinin A were unaffected by indomethacin or N-omega-nitro-L-arginine, but were significantly reduced in strips containing mucosa. Phosphoramidon, an inhibitor of neutral endopeptidase 24.11 (neprilysin, CD10), was ineffective at 10 microM, but at 100 microM, significant increase in the maximum response was achieved by neurokinin A in detrusor strips with and without mucosa. In immunohistochemical studies, neutral endopeptidase immunoreactivity occurred in peripheral nerve trunks in the detrusor and in a fibrous meshwork in the subepithelial lamina propria. Our data indicate that neutral endopeptidase is present in bladder mucosa and detrusor, and support the concept that this metalloprotease and/or related enzymes are important in regulating the actions of tachykinins.

Mapping the active site of endothelin-converting enzyme-1 through subsite specificity and mutagenesis studies: a comparison with neprilysin

Endothelin-converting enzyme-1 (ECE-1) is a membrane-bound zinc metallopeptidase that is homologous to neprilysin in amino acid sequence. A major in vivo function of ECE-1 is the generation of endothelin-1, a potent vasoconstrictor, from big endothelin-1. ECE-1 is also potentially involved in the processing or degradation of other peptide hormones. In this study we have used substrates based on the sequence of the COOH-terminal half of big endothelin-1 to examine the subsite specificity of recombinant ECE-1. The big endothelin-1 [16-38] peptides were systematically varied at either position 21 (P(1)) or position 22 (P'(1)) and used in steady-state kinetic analyses of ECE-1. The results indicate that the S(1) pocket of ECE-1 is relatively nonselective, but that the S'(1) subsite of ECE-1 has a preference for large hydrophobic side chains. The peptidyl carboxydipeptidase activity of ECE-1 was also characterized, revealing that substrates with COOH-terminal carboxylates are highly preferred over the cognate amides and esters. A site-directed mutagenesis study was carried out to identify the active-site amino acid residues specifically involved in binding to the COOH-terminal carboxylate of substrates. The data indicate that Arg(133) of ECE-1, which corresponds to Arg(102) of neprilysin that has been identified as an active-site residue of neprilysin involved in binding to the free carboxylate of some substrate peptides, may not play the same role. However, the low activity observed for an ECE-1 Arg(726) mutant is consistent with a role for this arginine residue in the binding of substrates, a role which has been ascribed to arginine residues in both thermolysin (Arg(203)) and neprilysin (Arg(717)).

Transcriptional mechanism of protein kinase C-induced isoform-specific expression of the gene for endothelin-converting enzyme-1 in human endothelial cells

Isoform-specific expression of endothelin-converting enzyme (ECE)-1, the major big endothelin-processing enzyme, is controlled by alternative promoters. Signaling pathways and transcriptional mechanisms of ECE-1 mRNA expression are largely unknown. To investigate ECE-1 isoform expression after protein kinase C (PKC) activation, we used phorbol 12-myristate 13-acetate (PMA) to stimulate primary cultured human umbilical vein endothelial cells and the related EA.hy926 cell line. ECE-1a mRNA was up-regulated (approximately 3-fold), whereas mRNA of alternative isoforms (b, c, and d) was unchanged, which was confirmed on the protein level. PMA effects on mRNA expression were suppressed by the PKC inhibitors H-7 and Calphostin C. Because increased ECE-1a expression was preceded by induction of the transcription factor Ets-1, we performed gel shift assays and demonstrated specific DNA/protein interactions involving the ETS binding motif GGAA. Luciferase reporter assays showed that PMA induced ECE-1a promoter activity about 2.5-fold in EA.hy926 cells. Similarly, coexpression of Ets-1 protein resulted in a dose-dependent increase in ECE-1a promoter activity (more than 8-fold). Using gel shift assays and mutation analysis, we identified two tandemly arranged Ets-1 binding sites (EBS) at -638 and -658, respectively, that are involved in transcriptional activation of the ECE-1a promoter by PMA or Ets-1. Moreover, we also found evidence for binding of a transcriptional repressor to EBS -638. The inhibitor of mitogen-activated protein kinase kinase, PD98059, inhibited PMA effects on ECE-1a mRNA expression and promoter activity, respectively. Our results provide the first detailed analysis of signaling pathways and transcriptional mechanisms involved in isoform-specific ECE-1 gene expression.

Localization of the endothelin system in aldosterone-producing adenomas

Endothelin-1 (ET-1) could play a role in the regulation of aldosterone secretion of the human adrenal gland. The presence of the endothelin-converting enzyme 1 (ECE-1) and ET-1 suggests that there is a local ET system in the adrenal cortex, but the in situ synthesis of ET-1 remains to be confirmed. The cellular distribution of the whole ET system was evaluated in 20 cases of aldosterone-producing adenomas. Polymerase chain reaction studies gave strong signals for ECE-1 mRNA and the mRNAs for endothelin type A (ET(A)) and B (ET(B)) receptors and faint signals for prepro-ET-1 mRNA. In situ hybridization showed ET(A) receptors scattered throughout the adenoma, in both secretory cells and vascular structures (score, +). There were more ET(B) receptors (score, ++), but they were restricted mainly to the endothelium. ECE-1 mRNA and protein were ubiquitous and abundant in secretory cells (score, +++) and vascular structures (score, ++); the enzyme was active on big ET-1. There was no prepro-ET-1 mRNA in the cortex, except in the thickened precapillary arterioles present in only 30% of the aldosterone-producing adenomas studied. ET-1 immunoreactivity was detected in vascular structures (score, +), probably bound to receptors, suggesting that ET-1 has an endocrine action. The low concentrations of ET-1 could also indicate that it acts in a paracrine-autocrine fashion to control adrenal blood flow. The discrepancy between the concentrations of ECE-1 and its substrate suggests that ECE-1 has another role in the adrenal secretory cells. Our data indicate that ET probably is not a primary cause of the development or maintenance of the adenoma.

Degradation of the Alzheimer's amyloid beta peptide by endothelin-converting enzyme

Deposition of beta-amyloid (Abeta) peptides in the brain is an early and invariant feature of all forms of Alzheimer's disease. As with any secreted protein, the extracellular concentration of Abeta is determined not only by its production but also by its catabolism. A major focus of Alzheimer's research has been the elucidation of the mechanisms responsible for the generation of Abeta. Much less, however, is known about the mechanisms responsible for Abeta removal in the brain. In this report, we describe the identification of endothelin-converting enzyme-1 (ECE-1) as a novel Abeta-degrading enzyme. We show that treatment of endogenous ECE-expressing cell lines with the metalloprotease inhibitor phosphoramidon causes a 2-3-fold elevation in extracellular Abeta concentration that appears to be due to inhibition of intracellular Abeta degradation. Furthermore, we show that overexpression of ECE-1 in Chinese hamster ovary cells, which lack endogenous ECE activity, reduces extracellular Abeta concentration by up to 90% and that this effect is completely reversed by treatment of the cells with phosphoramidon. Finally, we show that recombinant soluble ECE-1 is capable of hydrolyzing synthetic Abeta40 and Abeta42 in vitro at multiple sites.

Neutral endopeptidase is expressed on the follicular granulosa cells of rabbit ovaries

Neutral endopeptidase (NEP) is a zinc metallopeptidase ubiquitously distributed in various tissues in mammals. This peptidase is involved in the post-secretory metabolism of various neuropeptides and peptide hormones in vivo, such as enkephalins, bradykinin, atrial natriuretic peptide, substance P and endothelins. In this paper we show that NEP is expressed in ovaries as a 110-kDa glycosylated integral membrane protein with enzymatic properties similar to those of the kidney protein. Using immunohistochemistry, we localize the peptidase in the granulosa cells of follicles at all stages of maturation, with the exception of atretic follicles. We also observe immunoreactive staining in the epithelia that lines the blood vessels in the medulla and the surface of the ovary. The co-localization of NEP and bioactive peptides known to be physiological substrates of NEP in other tissues suggests an important role for this protein in processes such as follicle maturation, ovulation, and/or regulation of ovarian blood flow, by modulating the physiological function of these peptides.

The role of endothelin in the pathogenesis of Chagas' disease

Infection with Trypanosoma cruzi causes a generalised vasculitis of several vascular beds. This vasculopathy is manifested by vasospasm, reduced blood flow, focal ischaemia, platelet thrombi, increased platelet aggregation and elevated plasma levels of thromboxane A(2) and endothelin-1. In the myocardium of infected mice, myonecrosis and a vasculitis of the aorta, coronary artery, smaller myocardial vessels and the endocardial endothelium are observed. Immunohistochemistry studies employing anti-endothelin-1 antibody revealed increased expression of endothelin-1, most intense in the endocardial and vascular endothelium. Elevated levels of mRNA for prepro endothelin-1, endothelin converting enzyme and endothelin-1 were observed in the infected myocardium. When T. cruzi-infected mice were treated with phosphoramidon, an inhibitor of endothelin converting enzyme, there was a decrease in heart size and severity of pathology. Mitogen-activated protein kinases and the transcription factor activator-protein-1 regulate the expression of endothelin-1. Therefore, we examined the activation of mitogen-activated protein kinases in the myocardium by T. cruzi. Western blot demonstrated an extracellular signal regulated kinase. In addition, the activator-protein-1 DNA binding activity, as determined by electrophoretic mobility shift assay, was increased. Increased expression of cyclins A and cyclin D1 was observed in the myocardium, and immunohistochemistry studies revealed that interstitial cells and vascular and endocardial endothelial cells stained intensely with antibodies to these cyclins. These data demonstrate that T. cruzi infection of the myocardium activates extracellular signal regulated kinase, activator-protein-1, endothelin-1, and cyclins. The activation of these pathways is likely to contribute to the pathogenesis of chagasic heart disease. These experimental observations suggest that the vasculature plays a role in the pathogenesis of chagasic cardiomyopathy. Additionally, the identification of these pathways provides possible targets for therapeutic interventions to ameliorate or prevent the development of cardiomyopathy during T. cruzi infection.