ECE-1: a membrane-bound metalloprotease that catalyzes the proteolytic activation of big endothelin-1

Respiratory dysfunction in old mice could be related to inflammation and lung fibrosis induced by hyperphosphatemia

BACKGROUND

With age, lungs undergo typical changes that lead to a deterioration of respiratory function. Our aim was to assess the role of age-associated hyperphosphatemia in these changes.

METHODS

We used C57BL6 mice to study an ageing model in vivo and human lung fibroblasts were treated with a phosphate donor, beta-glycerophosphate (BGP), to explore mechanisms involved. Respiratory function was registered with a double chamber plethysmograph. Lung structure was analysed by different staining, phosphate and cytokines levels by colorimeric kits, expression of fibrosis, inflammation and ET-1 system by western blot or RT-PCR.

RESULTS

Old mice showed hyperphosphatemia, along with lung fibrosis, loss of elastin, increased expression of pro-inflammatory cytokines and impaired respiratory function. BGP induced inflammation and fibrosis in fibroblasts through the activation and binding of NFkB to the MCP-1 or FN promoters. BGP increased ECE-1 expression by inducing NFkB binding to the ECE-1 promoter. QNZ, an NFkB inhibitor, blocked these effects. When ECE-1 was inhibited with phosphoramidon, BGP-induced inflammation and fibrosis were significantly reduced, suggesting a role for ET-1 in BGP-mediated effects.ET-1 produced effects similar to those of BGP, which were also dependent on NFkB. To study the pathophysiological relevance of hyperphosphatemia in vivo, a low-P diet was administered to a group of old animals, showing an improvement in fibrosis, inflammation and respiratory function compared to old mice on a standard diet.

CONCLUSION

These results suggest that age-related hyperphosphatemia induces inflammation, fibrosis, and impaired respiratory function in old mice; these effects appear to be mediated by ET-1 and NFkB activation.

Long-term prognostic value of big endothelin-1 and its combination with late gadolinium enhancement in patients with idiopathic restrictive cardiomyopathy

BACKGROUND AND AIMS

Idiopathic restrictive cardiomyopathy (RCM) has a low incidence. This study aimed to determine the prognostic value of big endothelin-1 (ET-1) in idiopathic RCM.

MATERIALS AND METHODS

We prospectively enrolled patients with idiopathic RCM from 2009 to 2017 and followed them up. The primary outcome was a composite of all-cause mortality and cardiac transplantation, and the secondary outcome was a composite of cardiac death and cardiac transplantation.

RESULTS

Ninety-one patients were divided into the high big ET-1 (>0.85 pmol/L, n = 56) and low big ET-1 (≤0.85 pmol/L, n = 35) groups, and 87 of them completed the follow-up. Big ET-1 concentrations (hazard ratio: 1.756, 95 % confidence interval [CI]: 1.117-2.760) and late gadolinium enhancement (LGE) (hazard ratio: 3.851, 95 % CI: 1.238-11.981) were independent risk factors for the primary outcome. Big ET-1 concentrations (C-statistic estimation: 0.764, 95 % CI: 0.657-0.871) and the combination of LGE and big ET-1 concentrations (C-statistic estimation: 0.870, 95 % CI: 0.769-0.970) could accurately predict the 5-year transplant-free survival rate, and 0.85 pmol/L was a suitable cutoff for big ET-1.

CONCLUSION

Big ET-1 and its combination with LGE may be useful to predict an adverse prognosis in patients with idiopathic RCM.

Unveiling the peptidases of parasites from the office chair - The endothelin-converting enzyme case study

The emergence of high-throughput methodologies such as next-generation sequencing and proteomics has necessitated significant advancements in biological databases and bioinformatic tools, therefore reshaping the landscape of research into parasitic peptidases. In this review we outline the development of these resources along the -omics technologies and their transformative impact on the field. Apart from extensive summary of general and specific databases and tools, we provide a general pipeline on how to use these resources effectively to identify candidate peptidases from these large datasets and how to gain as much information about them as possible without leaving the office chair. This pipeline is then applied in an illustrative case study on the endothelin-converting enzyme 1 homologue from Schistosoma mansoni and attempts to highlight the contemporary capabilities of bioinformatics. The case study demonstrate how such approach can aid to hypothesize enzyme functions and interactions through computational analysis alone effectively and emphasizes how such virtual investigations can guide and optimize subsequent wet lab experiments therefore potentially saving precious time and resources. Finally, by showing what can be achieved without traditional wet laboratory methods, this review provides a compelling narrative on the use of bioinformatics to bridge the gap between big data and practical research applications, highlighting the key role of these technologies in furthering our understanding of parasitic diseases.

Molecular basis of selective amyloid-β degrading enzymes in Alzheimer's disease

The accumulation of the small 42-residue long peptide amyloid-β (Aβ) has been proposed as a major trigger for the development of Alzheimer's disease (AD). Within the brain, the concentration of Aβ peptide is tightly controlled through production and clearance mechanisms. Substantial experimental evidence now shows that reduced levels of Aβ clearance are present in individuals living with AD. This accumulation of Aβ can lead to the formation of large aggregated amyloid plaques-one of two detectable hallmarks of the disease. Aβ-degrading enzymes (ADEs) are major players in the clearance of Aβ. Stimulating ADE activity or expression, in order to compensate for the decreased clearance in the AD phenotype, provides a promising therapeutic target. It has been reported in mice that upregulation of ADEs can reduce the levels of Aβ peptide and amyloid plaques-in some cases, this led to improved cognitive function. Among several known ADEs, neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1), insulin degrading enzyme (IDE) and angiotensin-1 converting enzyme (ACE) from the zinc metalloprotease family have been identified as important. These ADEs have the capacity to digest soluble Aβ which, in turn, cannot form the toxic oligomeric species. While they are known for their amyloid degradation, they exhibit complexity through promiscuous nature and a broad range of substrates that they can degrade. This review highlights current structural and functional understanding of these key ADEs, giving some insight into the molecular interactions that leads to the hydrolysis of peptide substrates, the crucial tasks performed by them and the potential for therapeutic use in the future.

Endothelin signaling in development

Since the discovery of endothelin 1 (EDN1) in 1988, the role of endothelin ligands and their receptors in the regulation of blood pressure in normal and disease states has been extensively studied. However, endothelin signaling also plays crucial roles in the development of neural crest cell-derived tissues. Mechanisms of endothelin action during neural crest cell maturation have been deciphered using a variety of in vivo and in vitro approaches, with these studies elucidating the basis of human syndromes involving developmental differences resulting from altered endothelin signaling. In this Review, we describe the endothelin pathway and its functions during the development of neural crest-derived tissues. We also summarize how dysregulated endothelin signaling causes developmental differences and how this knowledge may lead to potential treatments for individuals with gene variants in the endothelin pathway.

Nascent Aβ42 Fibrillization in Synaptic Endosomes Precedes Plaque Formation in a Mouse Model of Alzheimer's-like β-Amyloidosis

Accumulation of amyloid-β peptide (Aβ) aggregates in synapses may contribute to the profound synaptic loss characteristic of Alzheimer's disease (AD). The origin of synaptic Aβ aggregates remains elusive, but loss of endosomal proteostasis may trigger their formation. In this study, we identified the synaptic compartments where Aβ accumulates, and performed a longitudinal analysis of synaptosomes isolated from brains of TgCRND8 APP transgenic mice of either sex. To evaluate the specific contribution of Aβ-degrading protease endothelin-converting enzyme (ECE-1) to synaptic/endosomal Aβ homeostasis, we analyzed the effect of partial Ece1 KO in brain and complete ECE1 KO in SH-SY5Y cells. Global inhibition of ECE family members was used to further assess their role in preventing synaptic Aβ accumulation. Results showed that, before extracellular amyloid deposition, synapses were burdened with detergent-soluble Aβ monomers, oligomers, and fibrils. Levels of all soluble Aβ species declined thereafter, as Aβ42 turned progressively insoluble and accumulated in Aβ-producing synaptic endosomal vesicles with characteristics of multivesicular bodies. Accordingly, fibrillar Aβ was detected in brain exosomes. ECE-1-deficient mice had significantly increased endogenous synaptosomal Aβ42 levels, and protease inhibitor experiments showed that, in TgCRND8 mice, synaptic Aβ42 became nearly resistant to degradation by ECE-related proteases. Our study supports that Aβ accumulating in synapses is produced locally, within endosomes, and does not require the presence of amyloid plaques. ECE-1 is a determinant factor controlling the accumulation and fibrillization of nascent Aβ in endosomes and, in TgCRND8 mice, Aβ overproduction causes rapid loss of Aβ42 solubility that curtails ECE-mediated degradation.SIGNIFICANCE STATEMENT Deposition of aggregated Aβ in extracellular plaques is a defining feature of AD. Aβ aggregates also accumulate in synapses and may contribute to the profound synaptic loss and cognitive dysfunction typical of the disease. However, it is not clear whether synaptotoxic Aβ is mainly derived from plaques or if it is produced and aggregated locally, within affected synaptic compartments. Filling this knowledge gap is important for the development of an effective treatment for AD, as extracellular and intrasynaptic pools of Aβ may not be equally modulated by immunotherapies or other therapeutic approaches. In this manuscript, we provide evidence that Aβ aggregates building up in synapses are formed locally, within synaptic endosomes, because of disruptions in nascent Aβ proteostasis.

The Tetraspanin Tspan8 Associates with Endothelin Converting Enzyme ECE1 and Regulates Its Activity

Tspan8 is a member of the tetraspanins family of cell surface molecules. The ability of tetraspanins to organize membrane microdomains with other membrane molecules and interfere with their function suggests that they could act as surface integrators of external or internal signals. Among the first identified tetraspanins, Tspan8 promotes tumor progression and metastasis, presumably by stimulating angiogenesis and cell motility. In patients, its expression on digestive tract tumors seems to be associated with a bad prognosis. We showed previously that Tspan8 associates with E-cadherin and EGFR and modulates their effects on cell motility. Using Mass spectrometry and western blot, we found a new partner, the endothelin converting enzyme ECE1, and showed that Tspan8 amplifies its activity of conversion of the endothelin-1 precursor bigET1 to endothelin. This was observed by transduction of the colon carcinoma cell line Isreco1, which does not express Tspan8, and on ileum tissue fragments of tspan8ko mice versus wild type mice. Given these results, Tspan8 appears to be a modulator of the endothelin axis, which could possibly be targeted in case of over-activity of endothelins in biological processes of tissues expressing Tspan8.

Monocyte-derived macrophages orchestrate multiple cell-type interactions to repair necrotic liver lesions in disease models

The liver can fully regenerate after partial resection, and its underlying mechanisms have been extensively studied. The liver can also rapidly regenerate after injury, with most studies focusing on hepatocyte proliferation; however, how hepatic necrotic lesions during acute or chronic liver diseases are eliminated and repaired remains obscure. Here, we demonstrate that monocyte-derived macrophages (MoMFs) were rapidly recruited to and encapsulated necrotic areas during immune-mediated liver injury and that this feature was essential in repairing necrotic lesions. At the early stage of injury, infiltrating MoMFs activated the Jagged1/notch homolog protein 2 (JAG1/NOTCH2) axis to induce cell death-resistant SRY-box transcription factor 9+ (SOX9+) hepatocytes near the necrotic lesions, which acted as a barrier from further injury. Subsequently, necrotic environment (hypoxia and dead cells) induced a cluster of complement 1q-positive (C1q+) MoMFs that promoted necrotic removal and liver repair, while Pdgfb+ MoMFs activated hepatic stellate cells (HSCs) to express α-smooth muscle actin and induce a strong contraction signal (YAP, pMLC) to squeeze and finally eliminate the necrotic lesions. In conclusion, MoMFs play a key role in repairing the necrotic lesions, not only by removing necrotic tissues, but also by inducing cell death-resistant hepatocytes to form a perinecrotic capsule and by activating α-smooth muscle actin-expressing HSCs to facilitate necrotic lesion resolution.

Analysis of the relationship between the expression of EBV-related antibodies and ET-1 axis in gastric cancer

BACKGROUND AND OBJECTIVE: EBV-associated gastric cancer (EBVaGC) is a distinct subtype of GC, and EBV plays an important role in tumor progress. The standard method to identify EBV-positive tumor is determined by in situ hybridization for EBV-encoded EBERs in tumor tissues. The present study aims to detect the serological expression of EBV-related antibodies and ET-1 axis to provide a noninvasive method for diagnosis of EBVaGC. METHODS: The content of EBV-related antibodies and ET-1 axis in preoperative peripheral blood of GC was performed by Chemiluminescence and ELISA assay. The EBV DNA copy number was measured by qRT-PCR. RESULTS: The results showed that the levels of anti-EBV early antigen (EA) IgG, viral capsid antigen (VCA) IgA, nuclear antigen (NA) IgG, and EBV DNA copy number were significantly higher in EBVaGC. The ET-1 axis level was much lower in EBVaGC than EBVnGC. CONCLUSIONS: The combined detection of specific anti-EBV antibodies and ET-1 axis might provide new molecular markers for the identification of EBVaGC.

ET-1 as a Sex-Specific Mechanism Impacting Age-Related Changes in Vascular Function

Aging is a primary risk factor for cardiovascular disease (CVD), which is the leading cause of death in developed countries. Globally, the population of adults over the age of 60 is expected to double by the year 2050. CVD prevalence and mortality rates differ between men and women as they age in part due to sex-specific mechanisms impacting the biological processes of aging. Measures of vascular function offer key insights into cardiovascular health. Changes in vascular function precede changes in CVD prevalence rates in men and women and with aging. A key mechanism underlying these changes in vascular function is the endothelin (ET) system. Studies have demonstrated sex and sex hormone effects on endothelin-1 (ET-1), and its receptors ETA and ETB. However, with aging there is a dysregulation of this system resulting in an imbalance between vasodilation and vasoconstriction. Thus, ET-1 may play a role in the sex differences observed with vascular aging. While most research has been conducted in pre-clinical animal models, we describe more recent translational data in humans showing that the ET system is an important regulator of vascular dysfunction with aging and acts through sex-specific ET receptor mechanisms. In this review, we present translational evidence (cell, tissue, animal, and human) that the ET system is a key mechanism regulating sex-specific changes in vascular function with aging, along with therapeutic interventions to reduce ET-mediated vascular dysfunction associated with aging. More knowledge on the factors responsible for the sex differences with vascular aging allow for optimized therapeutic strategies to attenuate CVD risk in the expanding aging population.

Endothelin and the Cardiovascular System: The Long Journey and Where We Are Going

Simple Summary

In this review, we describe the basic functions of endothelin and related molecules, including their receptors and enzymes. Furthermore, we discuss the important role of endothelin in several cardiovascular diseases, the relevant clinical evidence for targeting the endothelin pathway, and the scope of endothelin-targeting treatments in the future. We highlight the present uses of endothelin receptor antagonists and the advancements in the development of future treatment options, thereby providing an overview of endothelin research over the years and its future scope.

Abstract

Endothelin was first discovered more than 30 years ago as a potent vasoconstrictor. In subsequent years, three isoforms, two canonical receptors, and two converting enzymes were identified, and their basic functions were elucidated by numerous preclinical and clinical studies. Over the years, the endothelin system has been found to be critical in the pathogenesis of several cardiovascular diseases, including hypertension, pulmonary arterial hypertension, heart failure, and coronary artery disease. In this review, we summarize the current knowledge on endothelin and its role in cardiovascular diseases. Furthermore, we discuss how endothelin-targeting therapies, such as endothelin receptor antagonists, have been employed to treat cardiovascular diseases with varying degrees of success. Lastly, we provide a glimpse of what could be in store for endothelin-targeting treatment options for cardiovascular diseases in the future.

Role of Chrononutrition in the Antihypertensive Effects of Natural Bioactive Compounds

Hypertension (HTN) is one of the main cardiovascular risk factors and is considered a major public health problem. Numerous approaches have been developed to lower blood pressure (BP) in hypertensive patients, most of them involving pharmacological treatments. Within this context, natural bioactive compounds have emerged as a promising alternative to drugs in HTN prevention. This work reviews not only the mechanisms of BP regulation by these antihypertensive compounds, but also their efficacy depending on consumption time. Although a plethora of studies has investigated food-derived compounds, such as phenolic compounds or peptides and their impact on BP, only a few addressed the relevance of time consumption. However, it is known that BP and its main regulatory mechanisms show a 24-h oscillation. Moreover, evidence shows that phenolic compounds can interact with clock genes, which regulate the biological rhythm followed by many physiological processes. Therefore, further research might be carried out to completely elucidate the interactions along the time–nutrition–hypertension axis within the framework of chrononutrition.

proANP Metabolism Provides New Insights Into Sacubitril/Valsartan Mode of Action

BACKGROUND

Sacubitril/valsartan (S/V) treatment is associated with clinical benefits in patients with heart failure with reduced ejection fraction (HFrEF), but its mode of action remains elusive, although it involves the increase of ANP (atrial natriuretic peptide).

METHODS AND RESULTS

Using a cohort of 73 HFrEF patients treated with S/V and controls, we deciphered the proteolytic cascade that converts proANP into 4 vasoactive peptides, including ANP, which exert vasodilatory actions. We found that proANP processing is sequential and involved meprin B, ECE (endothelin-converting enzyme) 1, and ANPEP (aminopeptidase N). This processing is limited in HFrEF patients when compared with controls via the downregulation of proANP production, corin, and meprin B activities by miR-425 and miR1-3p, resulting in limited production of proANP-derived bioactive peptides. S/V restored or compensated proANP processing by downregulating miR-425 and miR1-3p beyond levels observed in controls, hence increasing levels of proANP-derived bioactive peptides and vasodilation. In contrast, S/V directly and indirectly partially inhibited ECE1 and ANPEP. Consequently, ECE1 partial inhibition resulted in a lower-than-expected increase in ET1 (endothelin 1), tilting the vasoactive balance toward vasodilation, possibly explaining the hypotensive action of S/V. Finally, we show that proANP glycosylation interferes with the midregional proANP assay-a clinical surrogate for proANP production, preventing any pathophysiological interpretation of the results. Finally, the analysis of S/V dose escalation with respect to baseline treatments suggests S/V-specific effects.

CONCLUSIONS

These findings offer mechanistic evidence to the natriuretic peptide-defective state in HFrEF, which is improved by S/V. These data also strongly suggest that S/V increases plasma ANP by multiple mechanisms that involve the indirect regulation of 2 microRNAs, besides its protection from NEP (neprilysin) cleavage. Altogether, these data provide new insights on HFrEF pathophysiology and the mode of action of S/V.

Dominant role of CACNA1D exon mutations for blood pressure regulation

BACKGROUND

CACNA1D gene, which encodes the α1 subunit of the Cav1.3 L-type calcium channel effectively regulates intracellular Ca2+ stability. In recent years, clinical studies have shown that the CACNA1D polymorphisms were associated with hypertension.

OBJECTIVE

The purpose of this study was to evaluate the effects of CACNA1D exon mutation on blood pressure (BP) in Sprague-Dawley rats.

METHODS

The rats with CACNA1D p.D307G, CACNA1D p.V936I or CACNA1D p.R1516Q were constructed using CRISPR-Cas9 technology. SBP measurements of rats were taken for 32 weeks. Tissue morphology of rats and vasoactive substances in serum was tested. Furthermore, the effects of L-type calcium channel blocker isradipine and endothelin-1 (ET-1) inhibitor BQ-123 on BP of double mutation rats (CACNA1D p.D307G/p.R1516Q) were tested. Then we examined the effects of CACNA1D gene mutation on gene expression in human umbilical vein endothelial cells (HUVECs) and vascular smooth muscle cells (VSMCs).

RESULTS

Elevated SBP and increased circulating ET-1 was observed in CACNA1D p.D307G mutant rats. Morphological assessments showed that the vascular, cardiac and renal remodeling could also be observed in rats with p.D307G mutant. Cav1.3 protein expression and calcineurin phosphatase activity in VSMCs of rats with CACNA1D p.D307G were increased in vitro, and the vascular ring tension test of mesenteric grade 3 arteries in CACNA1D p.D307G rats were increased in vivo. Furthermore, ET-1 expression were increased in isolated primary aortic endothelial cells in p.D307G mutant rats and transfected p.D307G mutant HUVECs. Finally, double heterozygosity rats with CACNA1D p.D307G/p.R1516Q or CACNA1D p.D307G/p.V936I further accelerated the rise of SBP compared with p.D307G mutation rats, and isradipine and BQ-123 reduced BP to the same extent in CACNA1D p.D307G/p.R1516Q rats.

CONCLUSION

CACNA1D gene is key players in the regulation of blood pressure. CACNA1D mutation rat may be a new hypertension animal model.

Endothelin B receptor dysfunction mediates elevated myogenic tone in cerebral arteries from aged male Fischer 344 rats

The human brain requires adequate cerebral blood flow to meet the high demand for nutrients and to clear waste products. With age, there is a chronic reduction in cerebral blood flow in small resistance arteries that can eventually limit proper brain function. The endothelin system is a key mediator in the regulation of cerebral blood flow, but the contributions of its constituent receptors in the endothelial and vascular smooth muscle layers of cerebral arteries have not been well defined in the context of aging. We isolated posterior cerebral arteries from young and aged Fischer 344 rats, as well as ET_B receptor knock-out rats and mounted the vessels in plexiglass pressure myograph chambers to measure myogenic tone in response to increasing pressure and targeted pharmacological treatments. We used an ET_A receptor antagonist (BQ-123), an ET_B receptor antagonist (BQ-788), endothelin-1, an endothelin-1 synthesis inhibitor (phosphoramidon), and vessel denudation to dissect the roles of each receptor in aging vasculature. Aged rats exhibited a higher myogenic tone than young rats, and the tone was sensitive to the ET_A antagonist, BQ-123, but insensitive to the ET_B antagonist, BQ-788. By contrast, the tone in the vessels from young rats was raised by BQ-788 but unaffected by BQ-123. When the endothelial layer that is normally enriched with ET_B1 receptors was removed from young vessels, myogenic tone increased. However, denudation of the endothelial layer did not influence vessels from aged animals. This indicated that endothelial ET_B1 receptors were not functional in the vessels from aged rats. There was also an increase in ET_A receptor expression with age, whereas ET_B receptor expression remained constant between young and aged animals. These results demonstrate that in young vessels, ET_B1 receptors maintain a lower myogenic tone, but in aged vessels, a loss of ET_B receptor activity allows ET_A receptors in vascular smooth muscle cells to raise myogenic tone. Our findings have potentially important clinical implications for treatments to improve cerebral perfusion in older adults with diseases characterized by reduced cerebral blood flow.

Mast Cell Degranulation Increases Mouse Mast Cell Protease 4-Dependent Vasopressor Responses to Big Endothelin-1 But Not Angiotensin I

Mouse mast cell protease 4 (mMCP-4), the murine functional analog to the human chymase, is a serine protease synthesized and stored in mast cell secretory granules. Our previous studies reported physiologic and pathologic roles for mMCP-4 in the maturation and synthesis of the vasoactive peptide endothelin-1 (ET-1) from its precursor, big ET-1. The aim of this study was to investigate the impact of mast cell degranulation or stabilization on mMCP-4-dependent pressor responses after the administration of big ET-1 or angiotensin I (Ang I). In anesthetized mice, mast cell degranulation induced by compound 48/80 (C48/80) or stabilization by cromolyn enhanced or repressed, respectively, the dose-dependent vasopressor responses to big ET-1 in wild-type (WT) mice but not in mMCP-4 knockout mice in a chymase inhibitor (TY-51469)-sensitive fashion. In addition, mMCP-4-dependent hydrolysis of the fluorogenic substrate Suc-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin was depleted or enhanced in peritoneal mast cells isolated from mice pretreated with C48/80 or cromolyn, respectively. Furthermore, C48/80 or cromolyn markedly increased or abolished, respectively, ET-1 (1-31) conversion from exogenous big ET-1 in WT mice peritoneal fluid-isolated mast cells, in vitro. Finally, the vasopressor responses to Ang I were unaffected by mast cell activation or stabilization, whereas those induced by the angiotensin-converting enzyme-resistant Ang I analog, [Pro¹¹, D-Ala¹²] Ang I, were potentiated by C48/80. Altogether, the present study shows that mast cell activation enhances the mMCP-4-dependent vasoactive properties of big ET-1 but not Ang I in the mouse model. SIGNIFICANCE STATEMENT: The current work demonstrates a significant role for mast cell stability in the cardiovascular pharmacology of big endothelin-1 but not angiotensin I in the murine systemic circulation.

Dysregulation of Endothelin-1: Implications for Health Disparities in Alzheimer's Disease

Alzheimer's disease (AD) and related dementias disproportionately impact racial and ethnic minorities. The racial and ethnic disparities in AD could be explained by differences in cerebral vascular disease pathology. Endothelin-1 (ET-1) is a potent vasoconstrictive peptide that regulates smooth muscle, endothelial cell, and pericyte contractions that may result in cerebral vascular constriction, leading to cerebral hypoperfusion; over time, ET-1 may result in neuronal injury contributing to the pathology of AD. Upregulation of the ET-1 system has been observed in African Americans when compared with non-Hispanic Whites. The role of the ET-1 system as a driver of ethnic disparities in AD requires further investigation. Targeting of the ET-1 system as a therapeutic intervention that could impact AD progression also needs further study. Dysregulation of ET-1 in Hispanic/Latino populations largely have been unexplored. Genetics linking ET-1 dysregulation and racial disparities in AD also needs further investigation. In this review, I examine how AD effects underserved minority populations and how dysregulation of the ET-1 system specifically predisposes ethnic minorities to AD. In addition, I examine the molecular interactions of the ET-1 system and amyloid beta, the role the ET-1 system in neurodegeneration, potential therapeutics for ET-1 dysregulation, and the impact on AD progression.

Endothelin converting enzyme-1 (ECE-1) deletion in association with Endothelin-1 downregulation ameliorates kidney fibrosis in mice

Kidney fibrosis is a common final pathway of chronic kidney diseases, which are characterized by renal architecture damage, inflammation, fibroblast expansion and myofibroblast formation. Endothelin converting enzyme-1 (ECE-1) contributes to activation of Endothelin-1 (ET-1), a potent vasoconstrictor and pro-fibrotic substance. This study elucidated the effect of ECE-1 knockout in kidney fibrosis model in mice in association of ET-1 downregulation. Kidney fibrosis was performed in ECE-1 knockout (ECE-1 KO) and vascular endothelial derived ET-1 KO (VEETKO) mice (2 months, 20-30 g, n = 30) and their wild type (WT) littermates using unilateral ureteral obstruction (UUO) procedure. Mice were euthanized on day-7 and day-14 after UUO. Histopathological analysis was conducted for fibrosis and tubular injury. Immunostainings were done to quantify macrophages (F4/80), fibroblasts (FSP-1) and myofibroblasts (α-SMA). Monocyte Chemoattractant Protein-1 (MCP-1), ECE-1 and preproET-1 (ppET-1) mRNA expression were quantified with qRT-PCR, while Transforming Growth Factor-β1 (TGF-β1) and α-SMA protein level were quantified with Western blot. ECE-1 KO mice demonstrated reduction of ECE-1 and ppET-1 mRNA expression, attenuation of kidney fibrosis, tubular injury, MCP-1 mRNA expression and macrophage number compared to WT. Double immunostaining revealed fibroblast to myofibroblast formation after UUO, while ECE-1 KO mice had significantly lower fibroblast number and myofibroblast formation compared to WT, which were associated with significantly lower TGF-β1 and α-SMA protein levels in day-14 of UUO. VEETKO mice also demonstrated attenuation of ET-1 protein level, fibrosis and myofibroblast formation. In conclusion, ECE-1 knockout and ET-1 downregulation attenuated kidney fibrosis.

Placental endothelin-converting enzyme-1 is decreased in preeclampsia

Endothelin-converting enzyme-1(ECE-1) is a key regulatory enzyme in the processing of endothelin-1 (ET-1). We quantified and localized ECE-1 in normal and preeclamptic placentas. Normal (n=6) and preeclamptic (n=6) placentas were serially sectioned for immunofluorescence (IF). Cell type specific markers identified endothelial, trophoblast, macrophage, smooth muscle, and fibroblast cells. Quantitative analyses were performed by western blot and ELISA. IF identified ECE-1 expression within the stroma and villous space. Cellular localization of ECE-1 was limited to endothelial membranes. There was significantly less ECE-1 in preeclamptic placentas, suggesting ECE-1 is important for proper regulation of ET-1 within the placenta.

Identification of Alzheimer's disease-associated rare coding variants in the ECE2 gene

Accumulation of amyloid β protein (Aβ) due to increased generation and/or impaired degradation plays an important role in Alzheimer's disease (AD) pathogenesis. In this report, we describe the identification of rare coding mutations in the endothelin-converting enzyme 2 (ECE2) gene in 1 late-onset AD family, and additional case-control cohort analysis indicates ECE2 variants associated with the risk of developing AD. The 2 mutations (R186C and F751S) located in the peptidase domain in the ECE2 protein were found to severely impair the enzymatic activity of ECE2 in Aβ degradation. We further evaluated the effect of the R186C mutation in mutant APP-knockin mice. Overexpression of wild-type ECE2 in the hippocampus reduced amyloid load and plaque formation, and improved learning and memory deficits in the AD model mice. However, the effect was abolished by the R186C mutation in ECE2. Taken together, the results demonstrated that ECE2 peptidase mutations contribute to AD pathogenesis by impairing Aβ degradation, and overexpression of ECE2 alleviates AD phenotypes. This study indicates that ECE2 is a risk gene for AD development and pharmacological activation of ECE2 could be a promising strategy for AD treatment.

Renal Autocrine and Paracrine Signaling: A Story of Self-protection

Autocrine and paracrine signaling in the kidney adds an extra level of diversity and complexity to renal physiology. The extensive scientific production on the topic precludes easy understanding of the fundamental purpose of the vast number of molecules and systems that influence the renal function. This systematic review provides the broader pen strokes for a collected image of renal paracrine signaling. First, we recapitulate the essence of each paracrine system one by one. Thereafter the single components are merged into an overarching physiological concept. The presented survey shows that despite the diversity in the web of paracrine factors, the collected effect on renal function may not be complicated after all. In essence, paracrine activation provides an intelligent system that perceives minor perturbations and reacts with a coordinated and integrated tissue response that relieves the work load from the renal epithelia and favors diuresis and natriuresis. We suggest that the overall function of paracrine signaling is reno-protection and argue that renal paracrine signaling and self-regulation are two sides of the same coin. Thus local paracrine signaling is an intrinsic function of the kidney, and the overall renal effect of changes in blood pressure, volume load, and systemic hormones will always be tinted by its paracrine status.

The Role of Endothelin and Endothelin Antagonists in Chronic Kidney Disease

Background

Endothelins (ET) are a family of peptides that act as potent vasoconstrictors and pro-fibrotic growth factors. ET-1 is integral to renal and cardiovascular pathophysiology and exerts effects via autocrine, paracrine and endocrine signaling pathways tied to regulation of aldosterone, catecholamines, and angiotensin. In the kidney, ET-1 is critical to maintaining renal perfusion and controls glomerular arteriole tone and hemodynamics. It is hypothesized that ET-1 influences the progression of chronic kidney disease (CKD), and the objective of this review is to discuss the pathophysiology, and role of ET and endothelin receptor antagonists (ERAs) in CKD.

Summary

The use of ERAs in hypertensive nephropathy has the potential to decrease proteinuria, and in diabetic nephropathy has the potential to restore glycocalyx thickness, also decreasing proteinuria. Focal segmental glomerular sclerosis has no specific Food and Drug Administration-approved therapy currently, however, ERAs show promise in decreasing proteinuria and slowing tissue damage. ET-1 is a potential biomarker for autosomal dominant polycystic kidney disease progression and so it is thought that ERAs may be of some therapeutic benefit.

Key Messages

Multiple studies have shown the utility of ERAs in CKD. These agents have shown to reduce blood pressure, proteinuria, and arterial stiffness. However, more clinical trials are needed, and the results of active or recently concluded studies are eagerly awaited.

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.

Diffuse osteosclerosis as a presentation of recurrent breast cancer: role of endothelin 1

We report a 46-yr-old woman with a history of breast cancer who presented with diffuse myalgias, bone pain, and osteosclerosis. She was found to have recurrent breast cancer producing endothelin-1.

INTRODUCTION

Acquired osteosclerosis can be caused by various disorders. Endothelin -1 is believed to contribute to osteosclerosis caused by breast cancer.

METHODS

Although the bone marrow biopsy did not reveal breast cancer, she developed skin lesions consistent with metastatic breast cancer. She ultimately died from progressive disease. At autopsy immunohistochemistry for endothelin-1 was performed on a section from the L5 vertebral body.

RESULTS

The section from the L5 vertebral body showed small foci of cells consistent with metastatic carcinoma and a prominent sclerotic response. Immunohistochemistry for endothelin-1 was strongly positive.

CONCLUSIONS

Recurrent breast cancer may present with diffuse osteosclerosis. Endothelin-1 may be a paracrine factor responsible for increased bone formation and osteosclerosis.

Endothelin and the heart in health and diseases

Endothelin-1 (ET-1), a 21-amino acid peptide, was initially identified in 1988 as a potent vasoconstrictor and pressor substance isolated from the culture supernatant of porcine aortic endothelial cells. From human genomic DNA analysis, two other family peptides, ET-2 and ET-3, were found. They showed different effects and distribution, suggesting that each peptide may play separate roles in different organs. In the heart, ET-1 also causes positive inotropic and chronotropic responses and hypertrophic activity of the cardiomyocytes. ETs act via activation of two receptor subtypes, ET_A and ET_B receptors, both of which are coupled to various GTP-binding proteins depending on cell types. Endogenous ET-1 may be involved in progression of various cardiovascular diseases. ET antagonists are currently used clinically in the treatment for patients with pulmonary hypertension, and are considered to have further target diseases as heart failure, cardiac hypertrophy and other cardiac diseases, renal diseases, systemic hypertension, and cerebral vasospasm.

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.

Ecel1 Knockdown With an AAV2-Mediated CRISPR/Cas9 System Promotes Optic Nerve Damage-Induced RGC Death in the Mouse Retina

Purpose

To assess the therapeutic potential of endothelin-converting enzyme-like 1 (Ecel1) in a mouse model of optic nerve crush.

Methods

Ecel1 expression was evaluated with real time quantitative (qRT)-PCR, Western blotting, and immunohistochemistry in mouse retinas after optic nerve crush. Vinblastine administration to the optic nerve and the intravitreal injection of N-methyl-d-aspartate (NMDA) were used to assess Ecel1 gene expression. Ecel1 was deleted with an adeno-associated viral (AAV) clustered regulatory interspaced short palindromic repeat (CRISPR)/Cas9 system, and retinal ganglion cell (RGC) survival was investigated with retrograde labeling, qRT-PCR, and visual evoked potential.

Results

Optic nerve crush induced Ecel1 expression specifically in the RGCs, peaking on day 4 after optic nerve crush. Ecel1 gene expression was induced by the vinblastine-induced inhibition of axonal flow, but not by NMDA-induced excitotoxicity, even though both are triggers of RGC death. Knockdown of Ecel1 promoted the loss of RGCs after optic nerve crush.

Conclusions

Our data suggest that Ecel1 induction is part of the retinal neuroprotective response to axonal injury in mice. These findings might provide insight into novel therapeutic targets for the attenuation of RGC damage, such as occurs in traumatic optic neuropathy.

Clearance of Amyloid Beta and Tau in Alzheimer's Disease: from Mechanisms to Therapy

Alzheimer's disease (AD) is the most common neurodegenerative disease. Pathological proteins of AD mainly contain amyloid-beta (Aβ) and tau. Their deposition will lead to neuron damage by a series of pathways, and then induce memory and cognitive impairment. Thus, it is pivotal to understand the clearance pathways of Aβ and tau in order to delay or even halt AD. Aβ clearance mechanisms include ubiquitin-proteasome system, autophagy-lysosome, proteases, microglial phagocytosis, and transport from the brain to the blood via the blood-brain barrier (BBB), arachnoid villi and blood-CSF barrier, which can be named blood circulatory clearance. Recently, lymphatic clearance has been demonstrated to play a key role in transport of Aβ into cervical lymph nodes. The discovery of meningeal lymphatic vessels is another direct evidence for lymphatic clearance in the brain. Furthermore, periphery clearance also contributes to Aβ clearance. Tau clearance is almost the same as Aβ clearance. In this review, we will mainly introduce the clearance mechanisms of Aβ and tau proteins, and summarize corresponding targeted drug therapies for AD.

Regulation, signalling and functions of hormonal peptides in pulmonary vascular remodelling during hypoxia

Hypoxic state affects organism primarily by decreasing the amount of oxygen reaching the cells and tissues. To adjust with changing environment organism undergoes mechanisms which are necessary for acclimatization to hypoxic stress. Pulmonary vascular remodelling is one such mechanism controlled by hormonal peptides present in blood circulation for acclimatization. Activation of peptides regulates constriction and relaxation of blood vessels of pulmonary and systemic circulation. Thus, understanding of vascular tone maintenance and hypoxic pulmonary vasoconstriction like pathophysiological condition during hypoxia is of prime importance. Endothelin-1 (ET-1), atrial natriuretic peptide (ANP), and renin angiotensin system (RAS) function, their receptor functioning and signalling during hypoxia in different body parts point them as disease markers. In vivo and in vitro studies have helped understanding the mechanism of hormonal peptides for better acclimatization to hypoxic stress and interventions for better management of vascular remodelling in different models like cell, rat, and human is discussed in this review.

The Role of Big Endothelin-1 in Colorectal Cancer

Introduction

Changes in liver blood flow caused by an unknown splanchnic vasoconstrictor have been noted in colorectal cancer patients with liver metastases. This prospective study was performed to assess whether plasma levels of big endothelin-1 (big ET-1) were raised in patients with colorectal cancer.

Methods

Plasma samples from peripheral vein of patients who underwent surgery for primary colorectal cancer (n=60) and those with known colorectal liver metastases (n=45) for a period of 15 months were taken prior to treatment and compared to age- and sex-matched controls (n=20). Plasma samples were analysed by using a single-step sandwich enzyme immunoassay. Immunohistochemistry and in situ hybridisation were also performed on tumour sections to investigate the expression of ET-1 by cancer cells.

Results

The median (range) plasma concentration of big ET-1 in controls was 2.1 pg/mL (1.2–13.4 pg/mL). The median (range) plasma concentration of big ET-1 in colorectal cancer patients with no overt hepatic metastases was 3.8 pg/mL (1.2–15.8 pg/mL), p=0.002, and the median (range) plasma concentration of big ET-1 in colorectal cancer patients with hepatic metastases was 5.2 pg/mL (1.7–30 pg/mL), p=0.0001; both were significantly elevated compared to the control group. A significant difference in immunostaining for big ET-1 was noted between paired normal colonic mucosa (median score-1) and tumour sections (median score-3), p=0.01.

Conclusion

This study has demonstrated elevated concentrations of big ET-1 in colorectal cancer patients, especially in those with hepatic metastases. Upregulation of ET activity in colorectal cancer could be inferred by the increased immunostaining of big ET-1 in cancer cells. Therefore, plasma big ET-1 levels should be evaluated as a potential tumour marker for the identification of hepatic metastases at an earlier stage.

High endothelin-converting enzyme-1 expression independently predicts poor survival of patients with esophageal squamous cell carcinoma

Patients with esophageal squamous cell carcinoma have poor survival and high recurrence rate, thus an effective prognostic biomarker is needed. Endothelin-converting enzyme-1 is responsible for biosynthesis of endothelin-1, which promotes growth and invasion of human cancers. The role of endothelin-converting enzyme-1 in esophageal squamous cell carcinoma is still unknown. Therefore, this study investigated the significance of endothelin-converting enzyme-1 expression in esophageal squamous cell carcinoma clinically. We enrolled patients with esophageal squamous cell carcinoma who provided pretreated tumor tissues. Tumor endothelin-converting enzyme-1 expression was evaluated by immunohistochemistry and was defined as either low or high expression. Then we evaluated whether tumor endothelin-converting enzyme-1 expression had any association with clinicopathological findings or predicted survival of patients with esophageal squamous cell carcinoma. Overall, 54 of 99 patients with esophageal squamous cell carcinoma had high tumor endothelin-converting enzyme-1 expression, which was significantly associated with lymph node metastasis ( p = 0.04). In addition, tumor endothelin-converting enzyme-1 expression independently predicted survival of patients with esophageal squamous cell carcinoma, and the 5-year survival was poorer in patients with high tumor endothelin-converting enzyme-1 expression ( p = 0.016). Among patients with locally advanced and potentially resectable esophageal squamous cell carcinoma (stage II and III), 5-year survival was poorer with high tumor endothelin-converting enzyme-1 expression ( p = 0.003). High tumor endothelin-converting enzyme-1 expression also significantly predicted poorer survival of patients in this population. In patients with esophageal squamous cell carcinoma, high tumor endothelin-converting enzyme-1 expression might indicate high tumor invasive property. Therefore, tumor endothelin-converting enzyme-1 expression could be a good biomarker to identify patients with worse survival and higher risks of recurrence, who might benefit from the treatment by endothelin-converting enzyme-1 inhibitor.

Drug Treatment of Hypertension: Focus on Vascular Health

Hypertension, the most common preventable risk factor for cardiovascular disease and death, is a growing health burden. Serious cardiovascular complications result from target organ damage including cerebrovascular disease, heart failure, ischaemic heart disease and renal failure. While many systems contribute to blood pressure (BP) elevation, the vascular system is particularly important because vascular dysfunction is a cause and consequence of hypertension. Hypertension is characterised by a vascular phenotype of endothelial dysfunction, arterial remodelling, vascular inflammation and increased stiffness. Antihypertensive drugs that influence vascular changes associated with high BP have greater efficacy for reducing cardiovascular risk than drugs that reduce BP, but have little or no effect on the adverse vascular phenotype. Angiotensin converting enzyme ACE inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) improve endothelial function and prevent vascular remodelling. Calcium channel blockers also improve endothelial function, although to a lesser extent than ACEIs and ARBs. Mineralocorticoid receptor blockers improve endothelial function and reduce arterial stiffness, and have recently become more established as antihypertensive drugs. Lifestyle factors are essential in preventing the adverse vascular changes associated with high BP and reducing associated cardiovascular risk. Clinicians and scientists should incorporate these factors into treatment decisions for patients with high BP, as well as in the development of new antihypertensive drugs that promote vascular health.

Endothelin Signaling in Bone

The endothelin (ET) system includes 3 small peptide hormones and a pair of G-protein-coupled receptors. This review first outlines the ET signaling pathway and ET metabolism. Next, it summarizes the role of ET1 signaling in craniofacial development. Then, it discusses observations relating ET signaling to osteoblastic and other osteosclerotic processes in cancer. Finally, it describes recent work in our laboratory that points to endothelin signaling as an upstream mediator of WNT signaling, promoting bone matrix synthesis and mineralization. It concludes with a statement of some remaining gaps in knowledge and proposals for future research.

Nkx2.5 regulates endothelin converting enzyme-1 during pharyngeal arch patterning

In gnathostomes, dorsoventral (D-V) patterning of neural crest cells (NCC) within the pharyngeal arches is crucial for the development of hinged jaws. One of the key signals that mediate this process is Endothelin-1 (EDN1). Loss of EDN1 binding to the Endothelin-A receptor (EDNRA) results in loss of EDNRA signaling and subsequent facial birth defects in humans, mice and zebrafish. A rate-limiting step in this crucial signaling pathway is the conversion of immature EDN1 into a mature active form by Endothelin converting enzyme-1 (ECE1). However, surprisingly little is known about how Ece1 transcription is induced or regulated. We show here that Nkx2.5 is required for proper craniofacial development in zebrafish and acts in part by upregulating ece1 expression. Disruption of nkx2.5 in zebrafish embryos results in defects in both ventral and dorsal pharyngeal arch-derived elements, with changes in ventral arch gene expression consistent with a disruption in Ednra signaling. ece1 mRNA rescues the nkx2.5 morphant phenotype, indicating that Nkx2.5 functions through modulating Ece1 expression or function. These studies illustrate a new function for Nkx2.5 in embryonic development and provide new avenues with which to pursue potential mechanisms underlying human facial disorders.

Major amyloid-β-degrading enzymes, endothelin-converting enzyme-2 and neprilysin, are expressed by distinct populations of GABAergic interneurons in hippocampus and neocortex

Impaired clearance of amyloid-β peptide (Aβ) has been postulated to significantly contribute to the amyloid accumulation typical of Alzheimer's disease. Among the enzymes known to degrade Aβ in vivo are endothelin-converting enzyme (ECE)-1, ECE-2, and neprilysin (NEP), and evidence suggests that they regulate independent pools of Aβ that may be functionally significant. To better understand the differential regulation of Aβ concentration by its physiological degrading enzymes, we characterized the cell and region-specific expression pattern of ECE-1, ECE-2, and NEP by in situ hybridization and immunohistochemistry in brain areas relevant to Alzheimer's disease. In contrast to the broader distribution of ECE-1, ECE-2 and NEP were found enriched in GABAergic neurons. ECE-2 was majorly expressed by somatostatin-expressing interneurons and was active in isolated synaptosomes. NEP messenger RNA was found mainly in parvalbumin-expressing interneurons, with NEP protein localized to perisomatic parvalbuminergic synapses. The identification of somatostatinergic and parvalbuminergic synapses as hubs for Aβ degradation is consistent with the possibility that Aβ may have a physiological function related to the regulation of inhibitory signaling.

Endothelin-1: Biosynthesis, Signaling and Vasoreactivity

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide originally isolated from endothelial cells. Its synthesis, mainly regulated at the gene transcription level, involves processing of a precursor by a furin-type proprotein convertase to an inactive intermediate, big ET-1. The latter peptide can then be cleaved directly by an endothelin-converting enzyme (ECE) into ET-1 or reach the active metabolite through a two-step process involving chymase hydrolyzing big ET-1 to ET-1 (1-31), itself needing conversion to ET-1 by neprilysin (NEP) to exert physiological activity. ET-1 signals through two G protein-coupled receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB). Both receptors induce an increase in intracellular Ca(2+), mainly from the extracellular space through voltage-independent mechanisms, the receptor-operated channels and store-operated channels. ET-1 also induces signaling through epidermal growth factor receptor transactivation, oxidative stress induction, rho-kinase, and the activation (ETA) or inhibition (ETB) of the adenylate cyclase/cyclic adenosine monophosphate pathway. Arterial vasoconstriction is mediated mainly by the ETA receptor. ET-1, via endothelium-located ETB, relaxes arteries or constricts vessels following activation of the same receptor type on the smooth muscle, where it can interact with ETA. In addition, ETB-dependent vasoconstriction seems more prominent in the venous vasculature. A better understanding of how ET-1 is synthesized and how ETA and ETB receptors interact could help design better pharmacological agents in the treatment of cardiovascular diseases where targeting the ET-1 system is indicated.

Endothelin-Receptor Antagonists beyond Pulmonary Arterial Hypertension: Cancer and Fibrosis

The endothelin axis and in particular the two endothelin receptors, ETA and ETB, are targets for therapeutic intervention in human diseases. Endothelin-receptor antagonists are in clinical use to treat pulmonary arterial hypertension and have been under clinical investigation for the treatment of several other diseases, such as systemic hypertension, cancer, vasospasm, and fibrogenic diseases. In this Perspective, we review the molecules that have been evaluated in human clinical trials for the treatment of pulmonary arterial hypertension, as well as other cardiovascular diseases, cancer, and fibrosis. We will also discuss the therapeutic consequences of receptor selectivity with regard to ETA-selective, ETB-selective, or dual ETA/ETB antagonists. We will also consider which chemical characteristics are relevant to clinical use and the properties of molecules necessary for efficacy in treating diseases against which known molecules displayed suboptimal efficacy.

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.

Combined exposure to big endothelin-1 and mechanical loading in bovine sternal cores promotes osteogenesis

Increased bone formation resulting from mechanical loading is well documented; however, the interactions of the mechanotransduction pathways are less well understood. Endothelin-1, a ubiquitous autocrine/paracrine signaling molecule promotes osteogenesis in metastatic disease. In the present study, it was hypothesized that exposure to big endothelin-1 (big ET1) and/or mechanical loading would promote osteogenesis in ex vivo trabecular bone cores. In a 2×2 factorial trial of daily mechanical loading (-2000με, 120cycles daily, "jump" waveform) and big ET1 (25ng/mL), 48 bovine sternal trabecular bone cores were maintained in bioreactor chambers for 23days. The bone cores' response to the treatment stimuli was assessed with percent change in core apparent elastic modulus (ΔEapp), static and dynamic histomorphometry, and prostaglandin E2 (PGE2) secretion. Two-way ANOVA with a post hoc Fisher's LSD test found no significant treatment effects on ΔEapp (p=0.25 and 0.51 for load and big ET1, respectively). The ΔEapp in the "no load + big ET1" (CE, 13±12.2%, p=0.56), "load + no big ET1" (LC, 17±3.9%, p=0.14) and "load + big ET1" (LE, 19±4.2%, p=0.13) treatment groups were not statistically different than the control group (CC, 3.3%±8.6%). Mineralizing surface (MS/BS), mineral apposition (MAR) and bone formation rates (BFR/BS) were significantly greater in LE than CC (p=0.037, 0.0040 and 0.019, respectively). While the histological bone formation markers in LC trended to be greater than CC (p=0.055, 0.11 and 0.074, respectively) there was no difference between CE and CC (p=0.61, 0.50 and 0.72, respectively). Cores in LE and LC had more than 50% greater MS/BS (p=0.037, p=0.055 respectively) and MAR (p=0.0040, p=0.11 respectively) than CC. The BFR/BS was more than two times greater in LE (p=0.019) and LC (p=0.074) than CC. The PGE2 levels were elevated at 8days post-osteotomy in all groups and the treatment groups remained elevated compared to the CC group on days 15, 19 and 23. The data suggest that combined exposure to big ET1 and mechanical loading results in increased osteogenesis as measured in biomechanical, histomorphometric and biochemical responses.

Endothelin

The endothelins comprise three structurally similar 21-amino acid peptides. Endothelin-1 and -2 activate two G-protein coupled receptors, ETA and ETB, with equal affinity, whereas endothelin-3 has a lower affinity for the ETA subtype. Genes encoding the peptides are present only among vertebrates. The ligand-receptor signaling pathway is a vertebrate innovation and may reflect the evolution of endothelin-1 as the most potent vasoconstrictor in the human cardiovascular system with remarkably long lasting action. Highly selective peptide ETA and ETB antagonists and ETB agonists together with radiolabeled analogs have accurately delineated endothelin pharmacology in humans and animal models, although surprisingly no ETA agonist has been discovered. ET antagonists (bosentan, ambrisentan) have revolutionized the treatment of pulmonary arterial hypertension, with the next generation of antagonists exhibiting improved efficacy (macitentan). Clinical trials continue to explore new applications, particularly in renal failure and for reducing proteinuria in diabetic nephropathy. Translational studies suggest a potential benefit of ETB agonists in chemotherapy and neuroprotection. However, demonstrating clinical efficacy of combined inhibitors of the endothelin converting enzyme and neutral endopeptidase has proved elusive. Over 28 genetic modifications have been made to the ET system in mice through global or cell-specific knockouts, knock ins, or alterations in gene expression of endothelin ligands or their target receptors. These studies have identified key roles for the endothelin isoforms and new therapeutic targets in development, fluid-electrolyte homeostasis, and cardiovascular and neuronal function. For the future, novel pharmacological strategies are emerging via small molecule epigenetic modulators, biologicals such as ETB monoclonal antibodies and the potential of signaling pathway biased agonists and antagonists.

In silico based investigation of dynamic variations in neprilysin (NEP and NEP2) proteins for extracting the point of specificity

Neprilysin-2 (NEP2) in the central nervous system controls Alzheimer's protein (amyloid-β) deposition, and prevents its occurrence. However, in the peripheral system, its closest homolog, neutral endopeptidase (NEP), regulates hypertension and heart related diseases. Inhibitors of NEP with a lesser degree of specificity can treat hypertension with an increased risk of cerebral deposition of amyloid-β. In order to rationalize the point of selectivity, the dynamic behavior of human NEP and NEP2 proteins was monitored by conducting molecular dynamics (MD) simulations. A computationally reliable model of NEP2 was achieved with 79.9%, 19.1% and 0.2% residues in the allowed, additionally allowed and disallowed regions respectively, using as a reference protein. Additionally, molecular docking studies were carried out for a set of five already known inhibitors of NEP and modeled NEP2 to obtain the comparative behaviors of the complexes. MD results highlighted their different responses along with important residues having a part in ligand-protein binding. For substrate and inhibitor binding, Arg664/661 and Zn697/694 were identified as the most conserved residues. High degree flexible transitions during the MD simulations were also observed in loop areas along with active site residues. Energy calculations, hydrogen bonds and their occupancy rates helped to conclude each ligand's potency towards a particular target. In most complexes of hNEP2, the ligands showed weak interactions which might be due to its larger pocket size or huge conformational variations in active site residues upon complexation. In the case of inhibitors of a small size like thiorphan, Arg49 and Arg664 are found to be acting to support the ligand binding in NEP while only Arg661 is acting in NEP2.