The endothelin system and endothelin-converting enzyme in the brain: molecular and cellular studies

Sovateltide (ILR-1620) Improves Motor Function and Reduces Hyperalgesia in a Rat Model of Spinal Cord Injury

BACKGROUND

Spinal cord injury (SCI) presents a major global health challenge, with rising incidence rates and substantial disability. Although progress has been made in understanding SCI's pathophysiology and early management, there is still a lack of effective treatments to mitigate long-term consequences. This study investigates the potential of sovateltide, a selective endothelin B receptor agonist, in improving clinical outcomes in an acute SCI rat model.

METHODS

Thirty male Sprague-Dawley rats underwent sham surgery (group A) or SCI and treated with vehicle (group B) or sovateltide (group C). Clinical tests, including Basso, Beattie, and Bresnahan scoring, inclined plane, and allodynia testing with von Frey hair, were performed at various time points. Statistical analyses assessed treatment effects.

RESULTS

Sovateltide administration significantly improved motor function, reducing neurological deficits and enhancing locomotor recovery compared with vehicle-treated rats, starting from day 7 post injury. Additionally, the allodynic threshold improved, suggesting antinociceptive properties. Notably, the sovateltide group demonstrated sustained recovery, and even reached preinjury performance levels, whereas the vehicle group plateaued.

CONCLUSIONS

This study suggests that sovateltide may offer neuroprotective effects, enhancing neurogenesis and angiogenesis. Furthermore, it may possess anti-inflammatory and antinociceptive properties. Future clinical trials are needed to validate these findings, but sovateltide shows promise as a potential therapeutic strategy to improve functional outcomes in SCI. Sovateltide, an endothelin B receptor agonist, exhibits neuroprotective properties, enhancing motor recovery and ameliorating hyperalgesia in a rat SCI model. These findings could pave the way for innovative pharmacological interventions for SCI in clinical settings.

An organism-wide atlas of hormonal signaling based on the mouse lemur single-cell transcriptome

Hormones mediate long-range cell communication and play vital roles in physiology, metabolism, and health. Traditionally, endocrinologists have focused on one hormone or organ system at a time. Yet, hormone signaling by its very nature connects cells of different organs and involves crosstalk of different hormones. Here, we leverage the organism-wide single cell transcriptional atlas of a non-human primate, the mouse lemur (Microcebus murinus), to systematically map source and target cells for 84 classes of hormones. This work uncovers previously-uncharacterized sites of hormone regulation, and shows that the hormonal signaling network is densely connected, decentralized, and rich in feedback loops. Evolutionary comparisons of hormonal genes and their expression patterns show that mouse lemur better models human hormonal signaling than mouse, at both the genomic and transcriptomic levels, and reveal primate-specific rewiring of hormone-producing/target cells. This work complements the scale and resolution of classical endocrine studies and sheds light on primate hormone regulation.

Emerging trends in the blood spinal-cord barrier: A bibliometric analysis

BACKGROUND

The blood-spinal cord barrier (BSCB) is a unique protective barrier located between the circulatory system and the central nervous system. BSCB plays a vital role in various diseases. However, there is little systematic research and recording in this field by bibliometrics analysis. We aim to visualize this field through bibliometrics to analyze the hotspots and trends of BSCB and in order to facilitate an understanding of future developments in basic and clinical research.

METHODS

To conduct a bibliometric study of original publications and their references, the keywords Blood Spinal-Cord Barrier and BSCB are searched and filtered from the Web of Science database (2000-2022), focusing on citations, authors, journals, and countries/regions. Additionally, clustering of the references and co-citation analysis was completed, including a total of 1926 articles and comments.

RESULTS

From the results, 193 authors were identified, among which Sharma Hs played a key role. As far as the analysis result of the clustering of the references is concerned, the most common type in cluster analysis is spinal cord injury (SCI) which is a current and developing research field. The keywords are also the specific content under these clusters. The most influential organization is Univ Calif San Francisco, and "Proceedings of The National Academy of Sciences of The United States of America" magazine is the most cited magazine.

CONCLUSION SUBSECTIONS

The research on BSCB is booming focusing mainly on "BSCB in SCI" including "activation," "pathway," and "drug delivery" which is also the trend of future research.

SNHG15 enhances cisplatin resistance in lung adenocarcinoma by affecting the DNA repair capacity of cancer cells

BACKGROUND

Lung adenocarcinoma (LUAD) is a prevalent malignancy. SNHG15 has been demonstrated to be oncogenic in many kinds of cancers, however the mechanism of SNHG15 in LUAD cisplatin (DDP) resistance remains unclear. In this study, we demonstrated the effect of SNHG15 on DDP resistance in LUAD and its related mechanism.

METHODS

Bioinformatics analysis was adopted to assess SNHG15 expression in LUAD tissues and predict the downstream genes of SNHG15. The binding relationship between SNHG15 and downstream regulatory genes was proved through RNA immunoprecipitation, chromatin immunoprecipitation and dual-luciferase reporter assays. Cell counting kit-8 assay was adopted to evaluate LUAD cell viability, and gene expression was determined by Western blot and quantitative real-time polymerase chain reaction. We then performed comet assay to assess DNA damage. Cell apoptosis was detected by Tunnel assay. Xenograft animal models were created to test the function of SNHG15 in vivo.

RESULTS

SNHG15 was up-regulated in LUAD cells. Moreover, SNHG15 was also highly expressed in drug-resistant LUAD cells. Down-regulated SNHG15 strengthened the sensitivity of LUAD cells to DDP and induced DNA damage. SNHG15 could elevate ECE2 expression through binding with E2F1, and it could induce DDP resistance by modulating the E2F1/ECE2 axis. In vivo experiments verified that the SNHG15 could enhance DDP resistance in LUAD tissue.

CONCLUSION

The results suggested that SNHG15 could up-regulate ECE2 expression by recruiting E2F1, thereby enhancing the DDP resistance of LUAD.

Engineered Human Antibody with Improved Endothelin Receptor Type A Binding Affinity, Developability, and Serum Persistence Exhibits Excellent Antitumor Potency

Endothelin receptor A (ET_A), a class A G protein-coupled receptor (GPCR), is a promising tumor-associated antigen due to its close association with the progression and metastasis of many types of cancer, such as colorectal, breast, lung, ovarian, and prostate cancer. However, only small-molecule drugs have been developed as ET_A antagonists with anticancer effects. In a previous study, we identified an antibody (AG8) with highly selective binding to human ET_A through screening of a human naïve immune antibody library. Although both in vitro and in vivo experiments indicated that the identified AG8 had anticancer effects, there is a need for improvement in biochemical and physicochemical properties such as the ET_A binding affinity, thermostability, and productivity. In this study, we engineered the framework regions of AG8 and isolated an anti-ET_A antibody (MJF1) exhibiting significantly improved thermostability and ET_A binding affinity. Subsequently, our previously isolated PFc29, an Fc variant with an enhanced pH-dependent human FcRn binding profile, was introduced to MJF1, and the resulting Fc-engineered anti-ET_A antibody (MJF1-PFc29) inhibited the proliferation of tumor cells comparably to MJF1 and showed a 4.2-fold increased serum half-life in human FcRn transgenic mice. Moreover, MJF1-PFc29 elicited higher tumor growth inhibition in colorectal cancer xenograft mice compared to MJF1. Our results demonstrate that the engineered human anti-ET_A antibody MJF1-PFc29 has great therapeutic potential and high antitumor potency against various types of cancers including colorectal cancer.

Investigation of the Molecular Mechanisms by Which Endothelin-3 Stimulates Preadipocyte Growth

Endothelins induce many biological responses, and they are composed of three peptides: ET-1, ET-2, and ET-3. Reports have indicated that ET-1 regulates cell proliferation, adipogenesis, and other cell responses and that ET-3 stimulates the growth of gastrointestinal epithelial cells and melanocytes. However, the signalling pathways of ET3 that mediate the growth of fat cells are still unclear. Using 3T3-L1 white preadipocytes, we found that ET-3 induced increases in both cell number and BrdU incorporation. Pretreatment with an ETAR antagonist (but not an ETBR antagonist) blocked the ET-3-induced increases in both cell number and BrdU incorporation. Additionally, BQ610 suppressed the ET-3-induced increases in phosphorylation of AMPK, c-JUN, and STAT3 proteins, and pretreatment with specific inhibitors of AMPK, JNK/c-JUN, or JAK/STAT3 prevented the ET-3-induced increases in phosphorylation of AMPK, c-JUN, and STAT3, respectively. Neither p38 MAPK inhibitor nor PKC inhibitor altered the effects of ET-3 on cell growth. These data suggest that ET-3 stimulates preadipocyte growth through the ETAR, AMPK, JNK/c-JUN, and STAT3 pathways. Moreover, ET-3 did not alter HIB1B brown preadipocyte and D12 beige preadipocyte growth, suggesting a preadipocyte type-dependent effect. The results of this study may help explain how endothelin mediates fat cell activity and fat cell-associated diseases.

Modulation of the Endothelin System in Colorectal Cancer Liver Metastasis: Influence of Epigenetic Mechanisms?

Targeting of endothelin system genes is a promising strategy in cancer therapy. The modulation of these genes was explored in a model of colorectal cancer (CRC) liver metastasis and in a panel of CRC tumor cell lines that were exposed to the demethylating agent decitabine. The CC531 rat model mimicking CRC liver metastasis was used for tumor cell re-isolation and analysis of the endothelin system genes and DNA methyltransferases (DNMTs) by microarray. To mimic the effects caused by methylation changes, a panel of seven CRC cell lines was treated with the demethylating agent decitabine. Three genes of the endothelin system were potently modulated at messenger RNA (mRNA) level in rat CC531 cells during liver colonization. The concomitant decrease of two DNMTs suggested an influence from altered methylation. Changes in gene expression were also accomplished by exposure of CRC cells to the demethylating agent decitabine, when using daily low concentrations for 3 days, with minimal cytotoxic effects. Sensitive human SW480 cells showed an almost 100fold upregulation of endothelin-1 mRNA compared to untreated cells. This, however, was different in LS174T cells, which showed no significant increase in gene expression although the methylation levels were significantly decreased at a variety of corresponding loci. We suggest that the mechanism induced by methylation on gene expression in metastatic CRC cells can be compromised. The results question the overall success of treating metastatic CRC by methylation inhibitors.

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.

Lysosomal Cathepsin A Plays a Significant Role in the Processing of Endogenous Bioactive Peptides

Lysosomal serine carboxypeptidase Cathepsin A (CTSA) is a multifunctional enzyme with distinct protective and catalytic function. CTSA present in the lysosomal multienzyme complex to facilitate the correct lysosomal routing, stability and activation of with beta-galactosidase and alpha-neuraminidase. Beside CTSA has role in inactivation of bioactive peptides including bradykinin, substances P, oxytocin, angiotensin I and endothelin-I by cleavage of 1 or 2 amino acid(s) from C-terminal ends. In this study, we aimed to elucidate the regulatory role of CTSA on bioactive peptides in knock-in mice model of CTSA^S190A . We investigated the level of bradykinin, substances P, oxytocin, angiotensin I and endothelin-I in the kidney, liver, lung, brain and serum from CTSA^S190A mouse model at 3- and 6-months of age. Our results suggest CTSA selectively contributes to processing of bioactive peptides in different tissues from CTSA^S190A mice compared to age matched WT mice.

Propitious Therapeutic Modulators to Prevent Blood-Spinal Cord Barrier Disruption in Spinal Cord Injury

The blood-spinal cord barrier (BSCB) is a specialized protective barrier that regulates the movement of molecules between blood vessels and the spinal cord parenchyma. Analogous to the blood-brain barrier (BBB), the BSCB plays a crucial role in maintaining the homeostasis and internal environmental stability of the central nervous system (CNS). After spinal cord injury (SCI), BSCB disruption leads to inflammatory cell invasion such as neutrophils and macrophages, contributing to permanent neurological disability. In this review, we focus on the major proteins mediating the BSCB disruption or BSCB repair after SCI. This review is composed of three parts. Section 1. SCI and the BSCB of the review describes critical events involved in the pathophysiology of SCI and their correlation with BSCB integrity/disruption. Section 2. Major proteins involved in BSCB disruption in SCI focuses on the actions of matrix metalloproteinases (MMPs), tumor necrosis factor alpha (TNF-α), heme oxygenase-1 (HO-1), angiopoietins (Angs), bradykinin, nitric oxide (NO), and endothelins (ETs) in BSCB disruption and repair. Section 3. Therapeutic approaches discusses the major therapeutic compounds utilized to date for the prevention of BSCB disruption in animal model of SCI through modulation of several proteins.

Amyloid-clearing proteins and their epigenetic regulation as a therapeutic target in Alzheimer's disease

Abnormal elevation of amyloid β-peptide (Aβ) levels in the brain is the primary trigger for neuronal cell death specific to Alzheimer’s disease (AD). It is now evident that Aβ levels in the brain are manipulable due to a dynamic equilibrium between its production from the amyloid precursor protein (APP) and removal by amyloid clearance proteins. Clearance can be either enzymic or non-enzymic (binding/transport proteins). Intriguingly several of the main amyloid-degrading enzymes (ADEs) are members of the M13 peptidase family (neprilysin (NEP), NEP2 and the endothelin converting enzymes (ECE-1 and -2)). A distinct metallopeptidase, insulin-degrading enzyme (IDE), also contributes to Aβ degradation in the brain. The ADE family currently embraces more than 20 members, both membrane-bound and soluble, and of differing cellular locations. NEP plays an important role in brain function terminating neuropeptide signals. Its decrease in specific brain areas with age or after hypoxia, ischaemia or stroke contribute significantly to the development of AD pathology. The recently discovered mechanism of epigenetic regulation of NEP (and other genes) by the APP intracellular domain (AICD) and its dependence on the cell type and APP isoform expression suggest possibilities for selective manipulation of NEP gene expression in neuronal cells. We have also observed that another amyloid-clearing protein, namely transthyretin (TTR), is also regulated in the neuronal cell by a mechanism similar to NEP. Dependence of amyloid clearance proteins on histone deacetylases and the ability of HDAC inhibitors to up-regulate their expression in the brain opens new avenues for developing preventive strategies in AD.

Targeting endothelin receptors A and B attenuates the inflammatory response and improves locomotor function following spinal cord injury in mice

After spinal cord injury (SCI), the disruption of blood-spinal cord barrier by activation of the endothelin (ET) system is a critical event leading to leukocyte infiltration, inflammatory response and oxidative stress, contributing to neurological disability. In the present study, we showed that blockade of ET receptor A (ETAR) and/or ET receptor B (ETBR) prevented early inflammatory responses directly via the inhibition of neutrophil and monocyte diapedesis and inflammatory mediator production following traumatic SCI in mice. Long-term neurological improvement, based on a series of tests of locomotor performance, occurred only in the spinal cord‑injured mice following blockade of ETAR and ETBR. We also examined the post‑traumatic changes of the micro-environment within the injured spinal cord of mice following blockade of ET receptors. Oxidative stress reflects an imbalance between malondialdehyde and superoxide dismutase in spinal cord‑injured mice treated with vehicle, whereas blockade of ETAR and ETBR reversed the oxidation state imbalance. In addition, hemeoxygenase-1, a protective protease involved in early SCI, was increased in spinal cord‑injured mice following the blockade of ETAR and ETBR, or only ETBR. Matrix metalloproteinase-9, a tissue-destructive protease involved in early damage, was decreased in the injured spinal cord of mice following blockade of ETAR, ETBR or a combination thereof. The findings of the present study therefore suggested an association between ETAR and ETBR in regulating early pathogenesis of SCI and determining the outcomes of long‑term neurological recovery.

Are amyloid-degrading enzymes viable therapeutic targets in Alzheimer's disease?

: The amyloid cascade hypothesis of Alzheimer's disease envisages that the initial elevation of amyloid β-peptide (Aβ) levels, especially of Aβ(1-42) , is the primary trigger for the neuronal cell death specific to onset of Alzheimer's disease. There is now substantial evidence that brain amyloid levels are manipulable because of a dynamic equilibrium between their synthesis from the amyloid precursor protein and their removal by amyloid-degrading enzymes (ADEs) providing a potential therapeutic strategy. Since the initial reports over a decade ago that two zinc metallopeptidases, insulin-degrading enzyme and neprilysin (NEP), contributed to amyloid degradation in the brain, there is now an embarras de richesses in relation to this category of enzymes, which currently number almost 20. These now include serine and cysteine proteinases, as well as numerous zinc peptidases. The experimental validation for each of these enzymes, and which to target, varies enormously but up-regulation of several of them individually in mouse models of Alzheimer's disease has proved effective in amyloid and plaque clearance, as well as cognitive enhancement. The relative status of each of these enzymes will be critically evaluated. NEP and its homologues, as well as insulin-degrading enzyme, remain as principal ADEs and recently discovered mechanisms of epigenetic regulation of NEP expression potentially open new avenues in manipulation of AD-related genes, including ADEs.

Expression and functional profiling of neprilysin, insulin-degrading enzyme, and endothelin-converting enzyme in prospectively studied elderly and Alzheimer's brain

The brain steady state level of β-amyloid (Aβ) is determined by the balance between its production and removal, the latter through egress across blood and CSF barriers as well as Aβ degradation. The major Aβ-degrading enzymes are neprilysin (NEP), insulin-degrading enzyme (IDE), and endothelin-converting enzyme (ECE-1). Although evidence suggests that NEP is down-regulated in Alzheimer's disease (AD), the role of IDE and ECE in the Aβ accumulation in aging and dementia remains less certain. In this study, we examined mRNA and protein expression, as well as biological activity of NEP, IDE, and ECE-1 in human frontal cortex by real-time RT-PCR for mRNA, immunoblotting for protein, and highly sensitive and specific fluorescence assays for activity. The relationships between Aβ-degrading enzymes and pathologic measures and clinical features were also assessed. The results showed that NEP mRNA, protein level, and activity were decreased in AD compared with normal controls with no cognitive impairment (NCI). In contrast, IDE activity was unchanged, but there was higher expression of IDE mRNA, indicating a possible compensatory reaction because of deficits in activity. ECE-1 expression in AD brain showed no significant difference compared with age-matched controls. Correlation analyses suggested that NEP expression was correlated with Aβ accumulation and clinical diagnosis, being lower in AD than in no cognitive impairment. In contrast, neither IDE nor ECE-1 correlated with Aβ or clinical diagnosis. These findings provide additional support for NEP as the major protease involved in Aβ degradation and suggest its possible therapeutic targeting in AD.

Endothelin receptor antagonism and cancer

The endothelin peptides have an important role in the cancer-stromal interactions that promote tumour growth. Endothelin-1 (ET-1), clinically the most investigated endothelin, is a vital agent in the growth and progression of several tumours including prostate, ovarian, colorectal, bladder, breast and lung carcinomas. ET-1 exerts its effects through the activation of two distinct receptors, ET(A) and ET(B). Once activated, these receptors transmit signals via numerous intracellular signalling pathways. The effects of ET receptor stimulation in cancer cells or cancer-associated cells include proliferation, resistance to apoptosis, angiogenesis, migration and subsequent invasion. At present, the manipulation of the endothelin axis within the pre-clinical setting is the subject of intense investigation. Recent studies into ET receptor antagonism have produced interesting results highlighting the fact that these receptors may provide novel targets for a new generation of chemotherapeutic agents in a variety of cancers.

Effects of 4-hydroxy-nonenal and Amyloid-beta on expression and activity of endothelin converting enzyme and insulin degrading enzyme in SH-SY5Y cells

The cerebral accumulation of amyloid-beta (Abeta) is a consistent feature of and likely contributor to the development of Alzheimer's disease (AD). In addition to dysregulated production, increasing experimental evidence suggests reduced catabolism plays an important role in Abeta accumulation. Although endothelin converting enzyme (ECE) and insulin degrading enzyme (IDE) degrade and thus contribute to regulating the steady-state levels of Abeta, how these enzymes are regulated remain poorly understood. In this study, we investigated the effects of 4-hydroxy-nonenal (HNE) and Abeta on the expression and activity of ECE-1 and IDE in human neuroblastoma SH-SY5Y cells. Treatment with HNE or Abeta upregulated ECE-1 mRNA and protein, while IDE was unchanged. Although both ECE-1 and IDE were oxidized within 24 h of HNE or Abeta treatment, ECE-1 catalytic activity was elevated while IDE specific activity was unchanged. The results demonstrated for the first time that both ECE-1 and IDE are substrates of HNE modification induced by Abeta. In addition, the results suggest complex mechanisms underlying the regulation of their enzymatic activity.

Regulation of glial inflammatory mediators synthesis: possible role of endothelins

Endothelins are well known as modulators of inflammation in the periphery, but little is known about their possible role in brain inflammation. Stimulation of astrocyte prostaglandin, an inflammatory mediator, synthesis was shown so far only by endothelin 3 (ET-3). By contrast, several studies showed no change or slight decrease of basal nitric oxide synthesis after treatment of astrocytes with endothelin 1 (ET-1) and ET-3. However, a significant increase in astrocytic and microglial nitric oxide synthase (NOS) was observed after exposure to ET-1 and ET-3 in a model of forebrain ischaemia. Here we demonstrate that all three endothelins (ET-1, ET-2, ET-3) significantly enhanced the synthesis of prostaglandin E(2) and nitric oxide in glial cells. Each of the selective antagonists for ETA and ETB receptors (BQ123 and BQ788 respectively), significantly inhibited endothelins-induced production of both nitric oxide and prostaglandin E(2). These results suggest a regulatory mechanism of endothelins, interacting with both endothelin receptors, on glial inflammation. Therefore, inhibition of endothelin receptors may have a therapeutic potential in pathological conditions of the brain, when an uncontrolled inflammatory response is involved.

Long-term modulation of tyrosine hydroxylase activity and expression by endothelin-1 and -3 in the rat anterior and posterior hypothalamus

Brain catecholamines are involved in the regulation of biological functions, including cardiovascular activity. The hypothalamus presents areas with high density of catecholaminergic neurons and the endothelin system. Two hypothalamic regions intimately related with the cardiovascular control are distinguished: the anterior (AHR) and posterior (PHR) hypothalamus, considered to be sympathoinhibitory and sympathoexcitatory regions, respectively. We previously reported that endothelins (ETs) are involved in the short-term tyrosine hydroxylase (TH) regulation in both the AHR and PHR. TH is crucial for catecholaminergic transmission and is tightly regulated by well-characterized mechanisms. In the present study, we sought to establish the effects and underlying mechanisms of ET-1 and ET-3 on TH long-term modulation. Results showed that in the AHR, ETs decreased TH activity through ETBreceptor activation coupled to the nitric oxide, phosphoinositide, and CaMK-II pathways. They also reduced total TH level and TH phosphorylated forms (Ser 19 and 40). Conversely, in the PHR, ETs increased TH activity through a G protein-coupled receptor, likely an atypical ET receptor or the ETCreceptor, which stimulated the phosphoinositide and adenylyl cyclase pathways, as well as CaMK-II. ETs also increased total TH level and the Ser 19, 31, and 40 phosphorylated sites of the enzyme. These findings support that ETs are involved in the long-term regulation of TH activity, leading to reduced sympathoinhibition in the AHR and increased sympathoexcitation in the PHR. Present and previous studies may partially explain the cardiovascular effects produced by ETs when applied to the brain.

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.

Short-term regulation of tyrosine hydroxylase activity and expression by endothelin-1 and endothelin-3 in the rat posterior hypothalamus

Brain catecholamines are involved in several biological functions regulated by the hypothalamus. We have previously reported that endothelin-1 and -3 (ET-1 and ET-3) modulate norepinephrine release in the anterior and posterior hypothalamus. As tyrosine hydroxylase (TH) is the rate-limiting enzyme in catecholamine biosynthesis, the aim of the present work was to investigate the effects of ET-1 and ET-3 on TH activity, total enzyme level and the phosphorylated forms of TH in the rat posterior hypothalamus. Results showed that ET-1 and ET-3 diminished TH activity but the response was abolished by both selective ET(A) and ET(B) antagonists (BQ-610 and BQ-788, respectively). In addition ET(A) and ET(B) selective agonists (sarafotoxin S6b and IRL-1620, respectively) failed to affect TH activity. In order to investigate the intracellular signaling coupled to endothelins (ETs) response, nitric oxide (NO), phosphoinositide, cAMP/PKA and CaMK-II pathways were studied. Results showed that N(omega)-nitro-l-arginine methyl ester and 7-nitroindazole (NO synthase and neuronal NO synthase inhibitors, respectively), 1H-[1,2,4]-oxadiazolo[4,3-alpha]quinozalin-1-one and KT-5823 (soluble guanylyl cyclase, and PKG inhibitors, respectively) inhibited ETs effect on TH activity. Further, sodium nitroprusside and 8-bromoguanosine-3',5'-cyclic monophosphate (NO donor and cGMP analog, respectively) mimicked ETs response. ETs-induced reduction of TH activity was not affected by a PKA inhibitor but it was abolished by PLC, PKC and CaMK-II inhibitors as well as by an IP(3) receptor antagonist. On the other hand, both ETs did not modify TH total level but reduced the phosphorylation of serine residues of the enzyme at positions 19, 31 and 40. Present results suggest that ET-1 and ET-3 diminished TH activity through an atypical ET or ET(C) receptor coupled to the NO/cGMP/PKG, phosphoinositide and CaMK-II pathways. Furthermore, TH diminished activity may result from the reduction of the phosphorylated sites of the enzyme without changes in its total level. Taken jointly present and previous results support that ET-1 and ET-3 may play a relevant role in the modulation of catecholaminergic neurotransmission in the posterior hypothalamus of the rat.

Monitoring neuropeptide-specific proteases: processing of the proopiomelanocortin peptides adrenocorticotropin and alpha-melanocyte-stimulating hormone in the skin

The neuroendocrine precursor protein proopiomelanocortin (POMC) and its derived neuropeptides are involved in a number of important regulatory processes in the central nervous system as well as in peripheral tissues. Despite its important role in controlling the local activation of melanocortin (MC) receptors, the extracellular proteolytic processing of POMC peptides has received little attention. The mechanisms relevant for controlling the bioavailability of adrenocorticotropin and melanocyte-stimulating hormones for the corresponding MC receptors in the skin by specific peptidases such as neprilysin (neutral endopeptidase; NEP) or angiotensin-converting enzyme (ACE) have been addressed in a number of recent investigations. This review summarizes the current body of knowledge concerning the qualitative and quantitative POMC peptide processing with respect to the action and specificity of NEP and ACE and discusses relevant recent analytical methodologies.

Involvement of nitric oxide pathways in short term modulation of tyrosine hydroxylase activity by endothelins 1 and 3 in the rat anterior hypothalamus

The ability of endothelins 1 and 3 (ET-1 and ET-3) to reduce neuronal norepinephrine release through ETB receptor activation involving nitric oxide (NO) pathways in the rat anterior hypothalamus region (AHR) was previously reported. In the present work, we studied the effects of ET-1 and -3 on tyrosine hydroxylase (TH) activity and the possible involvement of NO pathways. Results showed that ET-1 and -3 (10 nM) diminished TH activity in AHR and this effect was blocked by a selective ETB receptor antagonist (100 nM BQ-788), but not by a ET(A) receptor antagonist (BQ-610). To confirm these results, 1 microM IRL-1620 (ET(B) agonist) reduced TH activity whereas 300 nM sarafotoxin S6b falled to modify it. N(omega)-Nitro-L-arginine methyl ester (10 microM), 7-nitroindazole (10 microM), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-ona (10 microM), KT5823 (2 microM), inhibitors of nitric oxide synthase, neuronal nitric oxide synthase, NO-sensitive-guanylyl cyclase, and protein kinase G, respectively, did not modify the reduction of TH activity produced by ETs. In addition, both 100 microM sodium nitroprusside and 50 microM 8-bromoguanosine-3',5'-cyclic monophosphate (NO donor and guanosine-3',5'-cyclic monophosphate analog, respectively) diminished TH activity. Present results showed that ET-1 and ET-3 diminished TH activity through the activation of ET(B) receptors involving the NO/guanosine-3',5'-cyclic monophosphate/protein kinase G pathway. Taken jointly present and previous results it can be concluded that both ETs play an important role as modulators of norepinephrine neurotransmission in the rat AHR.

Endothelin B Receptor Antagonist Increases Preproendothelin-1 Transcription in Bovine Aortic Endothelial Cells and In Vivo

Endothelin-1 (ET-1) receptor antagonists increase plasma immunoreactive ET-1 levels. However, their effect on preproendothelin-1 (PPE-1) mRNA levels is still controversial. Few studies have found a decrease in PPE-1 mRNA levels in endothelial cells treated with the nonselective ETA/B receptor antagonist, and others demonstrated that an ETB blockade by the selective antagonist BQ788 increases PPE-1 mRNA levels. We studied the effect of ETA and ETB selective receptor antagonists on PPE-1 transcription, both in vitro and in vivo. Endothelial cells, transiently transfected with PPE-1 luciferase plasmid, were treated with ET-1 receptor antagonists. Bosentan, a dual ETA/B receptor antagonist, and BQ788 (ETB receptor antagonist) treatment resulted in a 1.6-fold and 1.3-fold increase, respectively in luciferase activity as compared with the untreated control. In contrast, the ETA receptor antagonist, BQ123, had no effect on luciferase activity. Transgenic mice that express the luciferase gene under the control of PPE-1 promoter were treated with Bosentan. Luciferase activity, PPE-1 mRNA levels, and plasma immunoreactive ET-1 levels were increased by 1.6-fold to 2.0-fold in the Bosentan-treated group compared with the untreated, control group. ET-1 receptor blockade increased PPE-1 transcription both in vitro and in vivo. The increased transcription can be attributed to ETB receptor blockade, because BQ-788, but not BQ-123, increased PPE-1 transcription.

Intraspinal application of endothelin results in focal ischemic injury of spinal gray matter and restricts the differentiation of engrafted neural stem cells

Previous data have shown that pluripotent stem cells engrafted into the contused spinal cord differentiate only along an astrocytic lineage. The unknown restrictive cues appear to be quite rigid as even neuronal-restricted precursors fail to differentiate to the mature potential they exhibit in vitro after similar grafting into the contused spinal cord. It has been hypothesized that this potent lineage restriction is, in part, the result of the significant loss of both gray and white matter observed following spinal contusion, which elicits a massive acute inflammatory response and is manifested chronically by dramatic cystic cavitation. To evaluate the gray matter component, we developed a clinically relevant model of focal gray matter ischemic injury using the potent vasoconstrictor endothelin (ET-1) and characterized the differentiation of pluripotent stem cells transplanted into this atraumatic vascular SCI. Results demonstrate that low dose ET-1 microinjection into cervical spinal gray matter results in an inflammatory response that is temporally comparable to that observed following traumatic SCI, as well as chronic gray matter loss, but without significant cystic cavitation or white matter degeneration. However, despite the preservation of host spinal parenchyma, no elaboration of neuronal phenotypes was observed from engrafted stem or precursor cells. These results suggest that a common pathologic component responsible for this lineage restriction exists between contusive SCI and ET-1 mediated focal ischemic SCI.

Endothelin-Converting Enzyme-1 Inhibition and Growth of Human Glioblastoma Cells

Endothelin-1 (ET-1) is mitogenic and/or antiapoptotic in human cancers, and antagonists to ET-1 receptors are under evaluation for cancer treatment. Inhibition of ET-1 activation by the endothelin-converting enzymes 1(a)(-)(d) (ECE-1(a)(-)(d); EC 3.4.24.71) represents another approach to block the ET-1 effect in cancer. To evaluate this potential, we synthesized and characterized a series of low nanomolar nonpeptidic thiol-containing ECE-1 inhibitors, and evaluated their effect, as well as the effect of inhibitors for the related metalloproteases neprilysin (NEP; EC 3.4.24.11) and angiotensin-converting enzyme (ACE; EC 3.4.15.1), on human glioblastoma cell growth. Only ECE-1 inhibitors inhibited DNA synthesis by human glioblastoma cells. Exogenous addition of ET-1 or bigET-1 to glioblastoma cells did not counterbalance the growth inhibition elicited by ECE-1 inhibitors, suggesting that ECE-1 inhibitors block the proliferation of human glioblastoma cells most likely via a mechanism not involving extracellular production of ET-1. This class of molecules may thus represent novel therapeutic agents for the potential treatment of human cancer.

Effect of Dietary Sodium Intake on the Expression of Endothelin-Converting Enzyme in the Renal Medulla

BACKGROUND/AIM

Endothelin-converting enzyme (ECE) catalyzes the generation of endothelin-1 (ET-1) from its inactive precursor big-ET-1. Previous studies suggested that the ET-1 system is involved in the regulation of sodium excretion by the kidney. In particular, ET-1 via the ET(B) receptor-mediated signaling has been shown to increase renal medullary blood flow and decrease sodium transport in the collecting duct, both acting to promote renal sodium excretion. The present study was designed to evaluate the possibility that alterations in dietary salt intake may regulate the ECE-1.

METHODS

Wistar rats were fed for 3 days either with a diet containing low salt (0.01% NaCl), normal salt (0.5% NaCl), or high salt intake, either by high salt diet (4% NaCl) or normal salt diet plus 0.9% saline drinking. The expression of and immunoreactive protein levels of ECE-1 in the renal medulla was studied by RT-PCR, Northern blotting and Western blotting techniques.

RESULTS

The expression of ECE-1 mRNA (by RT-PCR and Northern blotting), as well as the immunoreactive levels of ECE-1, were significantly higher in the renal medulla of rats exposed to high salt intake than in rats on normal salt diet.

CONCLUSION

The findings suggest that upregulation of ECE-1, leading to increased generation of ET-1 in the renal medulla, may be a compensatory mechanism promoting enhanced sodium excretion by the kidney in response to high salt intake.

Nuclear Localization of Endothelin-Converting Enzyme-1

Objective— The biosynthesis of endothelin-1 (ET-1), the most potent vasoconstrictor with mitogenic properties, involves the processing of intermediate protein big ET-1 by a unique metalloprotease, endothelin-converting enzyme-1 (ECE-1). ECE-1 has 4 subisoforms that possess the same catalytic properties but different localization patterns on the plasma membrane and cytosol. We investigated the trafficking of ECE-1 subisoforms using green fluorescent protein–tagged recombinant enzymes in target and nontarget cells.

Methods and Results— ECE-1 localization was studied using confocal microscopy, which provides evidence for the first time that both ET-1 and ECE-1a are also found in the nuclear compartment in transiently transfected cells as well as in native endothelial cells that endogenously possess the ET system. In cells maintained in high-glucose medium, ECE-1a–specific staining shifted from plasma membrane to intracellular compartments. ECE-1b subisoform, however, is mainly in the cytosolic compartment, indicating a subisoform specificity for nuclear localization.

Conclusions— Our findings define a novel localization pattern for the ET system, which may be differentially regulated under pathophysiological conditions.

Endothelin receptor expression in the normal and injured spinal cord: potential involvement in injury-induced ischemia and gliosis

The endothelins (ETs) are a family of peptides that exert their biological effects via two distinct receptors, the endothelin A receptor (ET(A)R) and the endothelin B receptor (ET(B)R). To more clearly define the potential actions of ETs following spinal cord injury, we used immunohistochemistry and confocal microscopy to examine the protein expression of ET(A)R and ET(B)R in the normal and injured rat spinal cord. In the normal spinal cord, ET(A)R immunoreactivity (IR) is expressed by vascular smooth muscle cells and a subpopulation of primary afferent nerve fibers. ET(B)R-IR is expressed primarily by radial glia, a small population of gray and white matter astrocytes, ependymal cells, vascular endothelial cells, and to a lesser extent in smooth muscle cells. Fourteen days following compression injury to the spinal cord, there was a significant upregulation in both the immunoexpression and number of astrocytes expressing the ET(B)R in both gray and white matter and a near disappearance of ET(B)R-IR in ependymal cells and ET(A)R-IR in primary afferent fibers. Conversely, the vascular expression of ET(A)R and ET(B)R did not appear to change. As spinal cord injury has been shown to induce an immediate increase in plasma ET levels and a sustained increase in tissue ET levels, ETs would be expected to induce an initial marked vasoconstriction via activation of vascular ET(A)R/ET(B)R and then days later a glial hypertrophy via activation of the ET(B)R expressed by astrocytes. Strategies aimed at blocking vascular ET(A)R/ET(B)R and astrocyte ET(B)Rs following spinal cord injury may reduce the resulting ischemia and astrogliosis and in doing so increase neuronal survival, regeneration, and function.

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.

Molecular isolation and characterization of novel four subisoforms of ECE-2

Endothelin-converting enzymes (ECEs) are the key enzymes in the endothelin (ET) biosynthesis that catalyze the conversion of big ET, the biologically inactive precursor of mature ET. Two enzymes, termed ECE-1 and ECE-2, have been molecularly identified. Here, we report novel four subisoforms of ECE-2 that differ in their N-terminal cytoplasmic tails, termed ECE-2a-1, ECE-2a-2, ECE-2b-1, and ECE-2b-2. RT-PCR analysis of these subisoforms in bovine tissues demonstrated that their tissue distribution was strikingly different. ECE-2a-1 and ECE-2a-2 are expressed in a variety of tissues including liver, kidney, adrenal gland, testis, and endothelial cells, while ECE-2b-1 and ECE-2b-2 are expressed abundantly in brain and adrenal gland. Furthermore, ECE-2a-1 and ECE-2b-2 were revealed to be predominant forms as compared to ECE-2a-2 and ECE-2b-1, respectively. Immunohistochemical analyses of CHO cells, stably expressing ECE-2a-1 or ECE-2b-2, revealed that both ECE-2a-1 and ECE-2b-2 were localized in intracellular compartments but not on the cell surface. Detailed analysis of ECE-2 subisoforms will provide crucial information to clarify the physiological function of ECE-2.

The chorea of McLeod syndrome

Among the movement disorders associated with acanthocytosis, McLeod syndrome (McKusick 314850) is the one that is best characterized on the molecular level. Its defining feature is low reactivity of Kell erythrocyte antigens. This is due to absence of membrane protein KX that forms a complex with the Kell protein. KX is coded for by the XK gene on the X-chromosome. We present six males (aged 29 to 60 years), with proven XK mutations, to discuss the chorea associated with McLeod syndrome. The movement disorder commonly develops in the fifth decade and is progressive. It affects the limbs, the trunk and the face. In addition to facial grimacing, involuntary vocalization can be present. In early stages there may only be some restlessness or slight involuntary distal movements of ankles and fingers. Lip-biting and facial tics seem more common in autosomal recessive choreoacanthocytosis linked to chromosome 9. This, together with the absence of dysphagia in McLeod syndrome, may help in differential diagnosis. Recent findings suggest a role for the endothelin system of the striatum in the pathogenesis of McLeod syndrome.

Role of the astrocytic ET(B) receptor in the regulation of extracellular endothelin-1 during hypoxia

Astrocytes are known to possess an effective endothelin (ET) eliminatory system which involves astrocytic ET(A) and ET(B) receptors and may become particularly relevant under pathophysiological conditions. The present study has therefore been designed to explore the effect of standardized hypoxia on extracellular concentrations of endothelin-1 (ET-1) and on endothelin-converting enzyme (ECE) activity in primary rat astrocytes genetically (sl/sl) or experimentally (dexamethasone) deficient in ET(B) receptors. The results revealed (1) a hypoxia-mediated decrease of extracellular ET-1 in wildtype astrocytes (+/+) that was not observed in ET(B)-deficient (sl/sl) cultures; (2) an ET receptor antagonist-induced increase in ET-1 in the media of both genotypes with further elevation upon hypoxia in +/+ cultures only; (3) augmentation of the dexamethasone-induced increase in extracellular ET-1 by hypoxia in +/+, but not in sl/sl cultures; (4) synergistic reduction of ET(B) gene transcription by hypoxia and dexamethasone; and (5) significant increases in endothelin-converting enzyme activity in the presence of hypoxia. To conclude, hypoxia stimulates astrocytic release of mature ET-1. This stimulation is (over)compensated for by increased ET-1 binding to functional ET(B) receptors. ET(B) deficiency, whether genetic or experimentally induced, impairs elimination of extracellular ET-1.

The neprilysin family in health and disease

The mammalian neprilysin (NEP) family comprises at least seven members: NEP itself, Kell blood group antigen (KELL), the endothelin-converting enzymes (ECE-1 and ECE-2), the enzyme PEX, associated with X-linked hypophosphataemia, "X-converting enzyme" (XCE) a CNS-expressed orphan peptidase and a soluble, secreted endopeptidase (SEP). These zinc metallopeptidases are all type II integral membrane proteins. Where identified, these enzymes have roles in the processing or metabolism of regulatory peptides and therefore represent potential therapeutic targets. A distinct feature of ECE-1 species is their existence as distinct isoforms differing in their N-terminal cytoplasmic tails. These tails play a role in enzyme targeting and turnover with di-leucine and tyrosine-based motifs affecting localization. Additional anchorage of these enzymes can also occur through palmitoylation. Bacterial homologues of the neprilysin family exist, for example the products of the pepO genes from L. lactis and S. parasanguis, and a recently described gene product of P. gingivalis which is an ECE-1 homologue that can catalyse the conversion of big endothelin to endothelin. A genomics based approach to understanding the functions of this proteinase family is aided by the completion of the C. elegans and Drosophila genomes, both of which encode multiple copies of NEP-like enzymes.

Endothelin-converting enzymes and endothelin receptor B messenger RNAs are expressed in different neural cell species and these messenger RNAs are coordinately induced in neurons and astrocytes respectively following nerve injury

There is some evidence that endothelins may be a signal mediator between neuronal and glial cells, at least in some regions of the brain. To evaluate this possibility, the localization of messenger RNAs for endothelin-converting enzymes and endothelin receptor B in the rat brain were examined using in situ hybridization histochemistry. The messenger RNAs for endothelin-converting enzyme-1 and endothelin-converting enzyme-2 were expressed mainly in neurons located in various brain regions, whereas the messenger RNA for endothelin receptor B was mainly localized in the astrocytes located throughout the brainstem, Bergmann glia, choroid plexus and ependymal cells. The localization patterns of endothelin-converting enzyme and endothelin receptor B messenger RNAs were strikingly different. For instance, in the cerebellum, endothelin-converting enzyme-1 messenger RNA was localized in Purkinje cells, and endothelin-converting enzyme-2 mRNA was expressed in Purkinje cells and granule cells. On the other hand, endothelin receptor B messenger RNA was expressed in Bergmann glia and the astrocytes located in the granule cell layer. This suggests that final cleavages of big endothelins are performed on neuronal cells, and the major target of the processed endothelins could be astrocytes, which express endothelin receptor B most abundantly in the brain. Since evidence that endothelin is implicated in brain injury has also accumulated, we examined whether the expressions of endothelin-converting enzymes and endothelin receptor B are regulated by nerve injury. Following hypoglossal nerve injury, expression of messenger RNA for endothelin-converting enzymes-1 and -2 and endothelin receptor B was enhanced in the injured motor neurons and astrocytes respectively. The up-regulation of these messenger RNAs was also confirmed by a reverse transcription-polymerase chain reaction based strategyThese results lead us to suggest that endothelin can be an inducible intercellular mediator between injured neurons and astrocytes in response to nerve injury.

N-arginine dibasic convertase (nardilysin) isoforms are soluble dibasic-specific metalloendopeptidases that localize in the cytoplasm and at the cell surface

N-arginine (R) dibasic (NRD) convertase (nardilysin; EC 3.4.24.61), a metalloendopeptidase of the M16 family, specifically cleaves peptide substrates at the N-terminus of arginines in dibasic motifs in vitro. In rat testis, the enzyme localizes within the cytoplasm of spermatids and associates with microtubules of the manchette and axoneme. NRD1 and NRD2 convertases, two NRD convertase isoforms, differ by the absence (isoform 1) or presence (isoform 2) of a 68-amino acid insertion close to the active site. In this study, we overexpressed both isoforms, either by vaccinia virus infection of BSC40 cells or transfection of COS-7 cells. The partially purified enzymes exhibit very similar biochemical and enzymic properties. Microsequencing revealed that NRD convertase is N-terminally processed. Results of immunocytofluorescence, immunoelectron microscopy and subcellular fractionation studies argue in favour of a primary cytosolic localization of both peptidases. Although the putative signal peptide did not direct NRD convertase into microsomes in an in vitro translation assay, biotinylation experiments clearly showed the presence of both isoforms at the cell surface. In conclusion, although most known processing events at pairs of basic residues are achieved by proprotein convertases within the secretory pathway, NRD convertase may fulfil a similar function in the cytoplasm and/or at the cell surface.

Differential glial and vascular expression of endothelins and their receptors in rat brain after neurotrauma

We characterized the time-course, intensity of expression and cellular origin of components of the endothelin (ET) system in the rat brain after a standardized neurotrauma (cryogenic lesion of the parietal cortex). ET mRNAs were expressed at sham level after neurotrauma, whereas immunoreactivity for ET-1 was enhanced in glia and endothelium of the lesioned hemisphere and both hippocampi. The number of ET-3 positive mononuclear cells in the lesion perimeter increased starting at 24h after injury. At 48h after neurotrauma, ET-receptor immunoreactivity was increased in astrocytes. In basilar artery endothelium, ETB-immunoreactivity was reduced at 48h to 72h recovering at 7 days whereas ETA-receptor and ET-peptide immunoreactivities were not altered. In summary, neurotrauma leads to a multicellular stimulation of endothelins in the brain along with a delayed selective loss of vascular ETB-receptors. These changes seem to be posttranscriptional and cell type specific. They favor vasoconstriction increasing the risk of late vasospasm and ischemia.

Endothelin and dopamine release

Endothelins and endothelin receptors are widespread in the brain. There is increasing evidence that endothelins play a role in brain mechanisms associated with behaviour and neuroendocrine regulation as well as cardiovascular control. We review the evidence for an interaction of endothelin with brain dopaminergic mechanisms. Our work has shown that particularly endothelin-1 and ET(B) receptors are present at significant levels in typical brain dopaminergic regions such as the striatum. Moreover, lesion studies showed that ET(B) receptors are present on dopaminergic neuronal terminals in striatum and studies with local administration of endothelins into the ventral striatum showed that activation of these receptors causes dopamine release, as measured both with in vivo voltammetry and behavioural methods. While several previous studies have focussed on the possible role of very high levels of endothelins in ischemic and pathological mechanisms in the brain, possibly mediated by ET(A) receptors, we propose that physiological levels of these peptides play an important role in normal brain function, at least partly by interacting with dopamine release through ET(B) receptors.

Endothelin converting enzyme activity in primary rat astrocytes is modulated by endothelin B receptors

Astrocytes express endothelin-1 (ET-1), ET-3, and their receptors, ET(A) and ET(B). We report here that activated astrocytes in vivo also express endothelin converting enzyme-1 (ECE-1). Higher basal ET-1 concentrations in astrocyte media from ET(B)-deficient (sl/sl) versus wildtype (+/+) rats suggested that altered ECE activity may be related to the absence of ET(B) receptors. Quantification of ECE activity in membranes from sl/sl astrocytes yielded a 50% higher conversion compared to +/+ astrocytes, with indistinguishable ECE-1 mRNA and protein levels. Kinetic analysis of ECE activity revealed similar V(max) values in sl/sl and +/+ astrocytes. Enzyme activity was competitively inhibited by phosphoramidon with K(i) values of 0. 6 and 0.3 microM, respectively. The K(m) value of ECE was 0.5 microM in +/+ and 0.2 microM in sl/sl astrocytes. Two-dimensional focussing of astrocytic ECE-1 uncovered heterogeneity of charge and molecular weight. ECE-1 from sl/sl revealed a glycosylation pattern different from +/+ astrocytes. In conclusion, the ET(B) receptor may, via ECE-1 glycosylation, exert a negative feedback on ECE activity in the astrocytic endothelin system.

Endothelin B receptor-deficient rats as a subtraction model to study the cerebral endothelin system

Endothelins, due to their potent vasoactivity and mitogenicity, appear to play an important role in the brain, where all components of the endothelin system, peptides, receptors and converting enzyme, are expressed. To further elucidate the role of the cerebral endothelin system, astrocytes and cerebral vessels from sl/sl rats, devoid of functional endothelin B receptors, have been employed. Astrocytes from sl/sl rats display the following abnormalities as compared to wild-type (+/+) cells: (i) elevated basal extracellular endothelin-1 levels; (ii) exclusive presence of functional endothelin A receptors; (iii) increased extracellular endothelin-1 levels upon endothelin A receptor blockade; (iv) augmented basal endothelin-converting enzyme activity; (v) altered calcium response to endothelin-1. The basilar artery of sl/sl rats shows an enhanced constricting response to endothelin-1 and fails to dilate in response to endothelin-3, shifting the endothelin vasomotor balance to constriction. In conclusion, endothelin B receptors may be essential for restricting extracellular endothelin-1 levels in the brain, as well as for a balanced cerebral vasomotor action of endothelins.

cDNA cloning and molecular characterization of human brain metalloprotease MP100: a beta-secretase candidate?

Metalloprotease MP100 was originally isolated as a beta-secretase candidate from human brain using a beta-amyloid precursor protein (beta-APP)-derived p-nitroanilide (pNA) peptide substrate. Peptide sequences from purified MP100 were now found to resemble sequences reported for a puromycin-sensitive aminopeptidase (PSA) highly enriched in brain, and cDNA cloning revealed nearly complete homology of MP100 to PSA, with only a single bp difference resulting in an amino acid change at position 184. Another MP100 cDNA encoded a protein with a 36-amino acid deletion (positions 180-217) and a two-amino acid insertion after Val533. Purified recombinant human MP100 cleaved the original pNA substrate as well as a free beta-site-spanning amyloid beta (A beta) peptide (A beta(-10/+10)), generating A beta(1-10). The latter substrate, however, remained uncleaved, if N- and C-terminally blocked, and also purified beta-APP was not cleaved. Double immunoimaging revealed partial, patchy, colocalization of beta-APP and MP100 in doubly transfected human embryonic kidney cells (HEK cells) and in normal neuroblastoma cells, and both proteins could be coimmunoprecipitated from rat brain extracts, suggesting their close vicinity in vivo. Coexpression of MP100 and beta-APP695, however, did not boost A beta levels in HEK cells, although active enzyme was produced. Thus, MP100 does not exert true beta-secretase-like function in cells, although it may well act as a secondary exoprotease in a complex beta-APP/A beta metabolism.