In vivo imaging reveals an essential role of vasoconstriction in rupture of the ovarian follicle at ovulation.

Rupture of the ovarian follicle releases the oocyte at ovulation, a timed event that is critical for fertilization. It is not understood how the protease activity required for rupture is directed with precise timing and localization to the outer surface, or apex, of the follicle. We hypothesized that vasoconstriction at the apex is essential for rupture. The diameter and blood flow of individual vessels and the thickness of the apical follicle wall were examined over time to expected ovulation using intravital multiphoton microscopy. Vasoconstriction of apical vessels occurred within hours preceding follicle rupture in wild-type mice, but vasoconstriction and rupture were absent in Amhr2(cre/+)SmoM2 mice in which follicle vessels lack the normal association with vascular smooth muscle. Vasoconstriction is not simply a response to reduced thickness of the follicle wall; vasoconstriction persisted in wild-type mice when thinning of the follicle wall was prevented by infusion of protease inhibitors into the ovarian bursa. Ovulation was inhibited by preventing the periovulatory rise in the expression of the vasoconstrictor endothelin 2 by follicle cells of wild-type mice. In these mice, infusion of vasoconstrictors (either endothelin 2 or angiotensin 2) into the bursa restored the vasoconstriction of apical vessels and ovulation. Additionally, infusion of endothelin receptor antagonists into the bursa of wild-type mice prevented vasoconstriction and follicle rupture. Processing tissue to allow imaging at increased depth through the follicle and transabdominal ultrasonography in vivo showed that decreased blood flow is restricted to the apex. These results demonstrate that vasoconstriction at the apex of the follicle is essential for ovulation.

Identification of endothelin 2 as an inflammatory factor that promotes central nervous system remyelination.

The development of new regenerative therapies for multiple sclerosis is hindered by the lack of potential targets for enhancing remyelination. The study of naturally regenerative processes such as the innate immune response represents a powerful approach for target discovery to solve this problem. By 'mining' these processes using transcriptional profiling we can identify candidate factors that can then be tested individually in clinically-relevant models of demyelination and remyelination. Here, therefore, we have examined a previously described in vivo model of the innate immune response in which zymosan-induced macrophage activation in the retina promotes myelin sheath formation by oligodendrocytes generated from transplanted precursor cells. While this model is not itself clinically relevant, it does provide a logical starting point for this study as factors that promote myelination must be present. Microarray analysis of zymosan-treated retinae identified several cytokines (CXCL13, endothelin 2, CCL20 and CXCL2) to be significantly upregulated. When tested in a cerebellar slice culture model, CXCL13 and endothelin 2 promoted myelination and endothelin 2 also promoted remyelination. In studies to identify the receptor responsible for this regenerative effect of endothelin 2, analysis of both remyelination following experimental demyelination and of different stages of multiple sclerosis lesions in human post-mortem tissue revealed high levels of endothelin receptor type B in oligodendrocyte lineage cells. Confirming a role for this receptor in remyelination, small molecule agonists and antagonists of endothelin receptor type B administered in slice cultures promoted and inhibited remyelination, respectively. Antagonists of endothelin receptor type B also inhibited remyelination of experimentally-generated demyelination in vivo. Our work therefore identifies endothelin 2 and the endothelin receptor type B as a regenerative pathway and suggests that endothelin receptor type B agonists represent a promising therapeutic approach to promote myelin regeneration.

Endothelin receptor signaling: new insight into its regulatory mechanisms.

The endothelin (ET) system consists of two G protein coupled-receptors (GPCRs), ET type A receptor (ETAR) and ET type B receptor (ETBR), and three endogenous ligands, ET-1, ET-2, and ET-3. Stimulation of ETRs with ET-1 induces an increase in intracellular Ca(2+) concentration that is involved in a diverse array of physiological and pathophysiological processes, including vasoconstriction, and cell proliferation. Store-operated Ca(2+) entry and receptor-operated Ca(2+) entry triggered by activation of ETRs are regulated or modulated by endoplasmic reticulum Ca(2+) sensor (stromal interaction molecule 1) and voltage-independent cation channels (transient receptor potential canonical channels and Orai1). The ET-1-induced Ca(2+) mobilization results from activation of heterotrimeric G proteins by ETRs. In contrast, GPCR biology including modulation of receptor function and trafficking is regulated by a variety of GPCR interacting proteins (GIPs) that generally interact with the C-terminal domain of GPCRs. The ETR signaling is also regulated by GIPs such as Jun activation domain-binding protein 1. This review focuses on the regulatory mechanisms of the ETR signaling with special attention to the components involved in Ca(2+) signaling and to GIPs in the signal transduction, modification, and degradation of ETRs.

Growth and regression in bovine corpora lutea: regulation by local survival and death pathways.

The bovine corpus luteum (CL) is a transient gland with a life span of only 18 days in the cyclic cow. Mechanisms controlling CL development and secretory function may involve factors produced both within and outside this gland. Although luteinizing hormone (LH) surge is the main trigger of ovulation and granulosa cells luteinization, many locally produced agents such as arachidonic acid (AA) metabolites, growth factors and cytokines were shown to complement gonadotropins action in the process of CL development. Bovine CL is a highly vascular gland, where the very rapid angiogenesis rate (until Day 5 of the cycle) results in the development of a capillary network, endowing this gland with one of the highest blood flow rate per unit mass in the body. Angiogenesis in the developing CL is later followed by either controlled regression of the microvascular tree in the non-fertile cycle or maintenance and stabilization of the blood vessels, as seen during pregnancy. Different luteal cell types (both steroidogenic and accessory luteal cells: immune cells, endothelial cells, pericytes and fibroblasts) are involved in the pro- and/or anti-angiogenic responses. The balance between pro- and anti-angiogenic responses to the main luteolysin - prostaglandin F2α (PGF2α) could be decisive in whether or not PGF2α induces CL regression. Fibroblast growth factor-2 (FGF2) may be one of the factors that modulate the angiogenic response to PGF2α. Manipulation of local production and action of FGF2 will provide new tools for reproductive management of dairy cattle. Luteolysis is characterized by a rapid decrease in progesterone production, followed by structural regression. Factors like endothelin-1, cytokines (tumour necrosis factorα, interferons) and nitric oxide were all shown to play critical roles in functional and structural regression of the CL by inhibiting steroidogenesis and inducting apoptosis.

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.

The ovarian endothelin network: an evolving story.

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

A novel pathway involving progesterone receptor, endothelin-2, and endothelin receptor B controls ovulation in mice.

The steroid hormone progesterone (P) plays a pivotal role during ovulation. Mice lacking P receptor (Pgr) gene fail to ovulate due to a defect in follicular rupture. The P receptor (PGR)-regulated pathways that modulate ovulation, however, remain poorly understood. To identify these pathways, we performed gene expression profiling using ovaries from mice subjected to gonadotropin-induced superovulation in the presence and in the absence of CDB-2914, a synthetic PGR antagonist. Prominent among the genes that were down-regulated in response to CDB-2914 was endothelin (ET)-2, a potent vasoactive molecule. ET-2 mRNA was transiently induced in mural granulosa cells of the preovulatory follicles immediately preceding ovulation. This induction was absent in the ovaries of PGR null mice, indicating a critical role of this receptor in ET-2 expression. To investigate the functional role of ET-2 during ovulation, we employed selective antagonists of endothelin receptors, ETR-A and ETR-B. Mice treated with an ETR-B antagonist exhibited a dramatic (>85%) decline in the number of released oocytes. Strong expression of ETR-B was observed in the mural and cumulus granulosa cells of the preovulatory follicles as well as in the capillaries lining the inner border of the theca interna. We also identified cGMP-dependent protein kinase II, a previously reported PGR-regulated gene, as a downstream target of ET-2 during ovulation. Collectively, our studies uncovered a unique pathway in which ET-2, produced by PGR in mural granulosa cells, acts in a paracrine or autocrine manner on multiple cell types within the preovulatory follicle to control the final events leading to its rupture.

Endothelin-2 in ovarian follicle rupture.

The ovulatory process is activated by a surge of LH, a pituitary gonadotropin, which initiates a cohort of dramatic changes in biochemical, physical, and gene expression in the ovary, leading to follicle rupture and oocyte release. Here we report the identification of endothelin-2 (EDN2) as a last moment-trigger of follicle rupture. In the ovary, EDN2 is exclusively and transiently expressed in the granulosa cells immediately before ovulation. Administration of EDN2 to the ovarian tissue induced rapid contraction, whereas addition of tezosentan, an endothelin receptor antagonist, diminishes the EDN2 effect. In vivo, treatment of tezosentan before ovulation substantially decreases gonadotropin-induced superovulation. As a target tissue of EDN2 action, we identified a layer of smooth muscle cells in the follicular wall of each follicle. Taken together, our data indicate that EDN2 induces follicular rupture by constricting periovulatory follicles.

A role for endothelin-2 and its receptors in breast tumor cell invasion.

We have studied the role of endothelins (ET-1, ET-2 and ET-3) and ET receptors (ET-RA and ET-RB) in the invasive capacity of breast tumor cells, which express ET-1 and ET-2 as well as ET-RA and ET-RB. Of five human breast tumor cell lines tested, all expressed mRNAs for ET-1, ET-2, and ET-RB. ET-RA mRNA was expressed by four of five tumor cell lines. Breast tumor cells migrated toward ET-1 and ET-2 but not toward ET-3. Chemotaxis involved signaling via both receptors, and a pertussis toxin-sensitive p42/p44 mitogen-activated protein kinase (MAPK)-mediated pathway that could be inhibited by MAPK kinase (MEK)1/2 antagonists. Chemotaxis toward ETs did not involve p38 or stress-activated protein kinase (SAPK)/Jun N-terminal kinase (JNK) and was not inhibited by hypoxia. Incubation of tumor cells with ET-2 also increased chemotaxis toward the chemokines CXCL12 and CCL21. As well as inducing chemotaxis of tumor cells, ET-1 and ET-2 increased tumor cell invasion through Matrigel. Furthermore, stimulation of macrophage/tumor cell cocultures with ETs led to increased matrix metalloproteinase (MMP)-2 and -9 production by macrophages and a marked increase in invasion of tumor cells. Antagonism of either ET-RA or ET-RB decreased the invasion seen in ET-stimulated cocultures, as did a broad-spectrum MMP inhibitor. Immunohistochemical staining of human breast tumor sections showed increased ET and ET receptor protein expression by tumor cells in invasive ductal carcinoma compared with normal breast tissue or ductal carcinoma in situ. Furthermore, tumor cell ET and receptor expression was stronger at the invasive margin of invasive ductal carcinomas, in the lymphovascular space, and in lymph node metastases. ET expression often colocalized with ET-RB expression in all neoplastic tissue indicating a possible autocrine action of ETs. We suggest that expression of ETs and their receptors by human breast tumors, particularly in conjunction with a high macrophage infiltrate, may have a role in the progression of breast cancer and the invasion of tumor cells.

Role of endothelin in the increased vascular tone of patients with essential hypertension.

We investigated the possible role of endothelin in the increased vasoconstrictor tone of hypertensive patients using antagonists of endothelin receptors. Forearm blood flow (FBF) responses (strain-gauge plethysmography) to intraarterial infusion of blockers of endothelin-A (ETA) (BQ-123) and endothelin-B (ETB) (BQ-788) receptors, separately and in combination, were measured in hypertensive patients and normotensive control subjects. In healthy subjects, BQ-123 alone or in combination with BQ-788 did not significantly modify FBF (P=0.78 and P=0.63, respectively). In hypertensive patients, in contrast, BQ-123 increased FBF by 33+/-7% (P<0.001 versus baseline), and the combination of BQ-123 and BQ-788 resulted in a greater vasodilator response (63+/-12%; P=0.006 versus BQ-123 alone in the same subjects). BQ-788 produced a divergent vasoactive effect in the two groups, with a decrease of FBF (17+/-5%; P=0.004 versus baseline) in control subjects and transient vasodilation (15+/-7% after 20 minutes) in hypertensive patients (P<0.001, hypertensives versus controls). The vasoconstrictor response to endothelin-1 was slightly higher (P=0.04) in hypertensive patients (46+/-4%) than in control subjects (32+/-4%). Our data indicate that patients with essential hypertension have increased vascular endothelin activity, which may be of pathophysiological relevance to their increased vascular tone. In these patients, nonselective ETA and ETB blockade seems to produce a greater vasodilator effect than selective ETA blockade.

Paracrine regulation of ovarian cancer by endothelin.

Previous studies have demonstrated that endothelin (ET) isoforms (ET-1, ET-2 and ET-3) can act in an autocrine manner in ovarian cancer while in breast cancer their role has been proposed to be that of a paracrine mitogen. To explore the possibility that endothelin isoforms might function not only as autocrine regulators but also as paracrine mitogens in ovarian cancers, we investigated their effects on the growth of ovarian fibroblasts derived from ovarian carcinomas, the interaction between ovarian carcinoma and fibroblast cells and the location of the isoform expression in primary ovarian tumours. ET-1, ET-2 and ET-3 stimulated the growth of three ovarian fibroblast cell lines at concentrations ranging from 10(-12) M to 10(-7) M. Inhibition of 125I-ET binding by the ETA receptor antagonist BQ123 and the ETB receptor antagonist BQ788 suggested the presence of both types of ET receptors in fibroblast cells. In the absence of ET-1, neither BQ 123 nor BQ 788 inhibited growth. However, both antagonists inhibited ET-1 stimulated growth suggesting the involvement of both receptor types in ET-1 growth regulation. In contrast to carcinoma cells which secrete measurable levels of ET-1, fibroblast cell lines did not secrete detectable protein. Co-culture experiments (using porous membrane insert wells) of fibroblasts with carcinoma cells demonstrated that growth of both populations of cells was increased compared with either grown in isolation. In this system, growth of the fibroblast cell line was partially inhibited by both BQ123 and BQ788, whilst growth of the PE014 carcinoma cell line was inhibited by only BQ123. RT-PCR measurements detected the presence of the ETA receptor subtype in 10/10 primary ovarian cancers but the presence of ETB receptor in only 6/10 cancers. Using specific antibodies, ET-1 was found in 11/15, ET-2 in 5 of 7 and ET-3 in 5/7 primary ovarian cancers predominantly in the epithelial cells but with some stromal expression. These data indicate that the ET isoforms may stimulate growth of the fibroblast population within an ovarian cancer in addition to stimulating the epithelial cells and since the ETs are expressed in the majority of ovarian cancers, this paracrine effect may contribute to the overall growth of the tumour.

Endothelin causes contraction of human esophageal muscularis mucosae through interaction with both ETA and ETB receptors.

Endothelin (ET) causes contraction of the muscularis mucosae in the guinea pig esophagus, but its role in the human esophagus remains unknown. To investigate effects of ET in the human esophagus, we measured contraction of isolated human esophageal muscularis mucosae strips caused by ET related peptides and binding of 125I-ET-1 to cell membranes prepared from the human esophageal muscularis mucosae. Autoradiography demonstrated specific binding of 125I-ET-1 to the muscularis mucosae and muscularis propria (muscularis externa) of the human esophagus. ET-1 caused tetrodotoxin and atropine-insensitive contraction of muscularis mucosae strips. In terms of the maximal tension of contraction, ET-1 and ET-2 were equal in efficacy. The relative potencies for ET related peptides to cause contraction were ET-1=ET-2>ET-3>sarafotoxin S6c (SX6c), an ETB receptor agonist. ET-1 caused contraction was mildly inhibited by BQ-123, an ETA receptor antagonist, and not by BQ-788, an ETB receptor antagonist. It was moderately inhibited by the combination of both antagonists, indicating synergistic inhibition. Furthermore, desensitization to SX6c with SX6c pretreatment failed to abolish the contractile response to ET-1, which was completely inhibited by BQ-123. These indicate the involvement of both ETA and ETB receptors in the contraction. Binding of 125I-ET-1 to cell membranes of the muscularis mucosae was saturable and specific. Analysis of dose-inhibition curves demonstrated the presence of ETA and ETB receptors. This study demonstrates that, the muscularis mucosae of the human esophagus, similar to that of the guinea pig esophagus, possesses both ETA and ETB receptors mediating muscle contraction.

Endothelin in human inflammatory bowel disease: comparison to rat trinitrobenzenesulphonic acid-induced colitis.

There have been suggestions that endothelins (ET-1, ET-2, ET-3) are involved in the pathogenesis of human inflammatory bowel disease (IBD). Furthermore, the non-selective endothelin receptor antagonist, bosentan, ameliorates colonic inflammation in TNBS colitis in rats. However, no studies have measured the tissue expression and release of endothelins in human IBD in direct comparison to experimental TNBS colitis. Mucosal biopsies were obtained from 114 patients (42 Crohn's colitis, 35 ulcerative colitis and 37 normal) and compared to whole colonic segments from rats with TNBS colitis. ET-1/2 levels were reduced in human IBD but greatly increased in experimental TNBS colitis. RT-PCR indicated ET-2 was the predominant endothelin isoform in human IBD whereas ET-1 prevailed in the TNBS model. No associations were found between human IBD and tissue expression, content or release of ET-1/2. Our study shows, therefore, that unlike TNBS colitis in rats, in which ET-1/2 levels are greatly elevated and ET receptor antagonists are efficacious, there is no significant link between endothelins and human IBD.

[Participation of endothelium-derived vasoconstrictor factors in arterial hypertension]. / Participación de los factores constrictores derivados del endotelio en la hipertensión arterial.

Vascular endothelial cells synthesize and release vasodilator (nitric oxide, prostacyclin, endothelium-derived hyperpolarizing factor) and vasoconstrictor factors (thromboxane A2, prostaglandin H2, endothelin 1), which play a key role in the local regulation of vascular tone and participate in a crucial manner in the regulation of blood pressure. Hypertension has been shown to be associated with functional changes in the endothelium. In fact, decreased endothelium-dependent relaxations and increased endothelium-dependent contractions have been reported in both conduit arteries and resistance arteries obtained from various animal models of hypertension. During hypertension, the vessel wall experiences changes in the balance of the oxidative and the antioxidative enzyme system, resulting in increases in O2- release. This contributes to endothelial dysfunction by nitric oxide oxidation and the subsequent formation of peroxynitrite (ONOO-), a potent oxidant and potential mediator of vascular tissue injury. Finally, hypertension also allows the action or the production of vasoconstrictor factors such as endothelin 1 and thromboxane A2. As a consequence of these mechanisms, basal and/or stimulated nitric oxide availability is reduced, allowing vasoconstrictor systems, such as angiotensin II, sympathetic nervous system and others to over-express their actions. The mechanisms responsible for the alterations leading to endothelial dysfunction not only affect vasomotor tone, but also platelet aggregation and coagulation mechanisms.

Endothelin-1 and endothelin-2 initiate and maintain contractile responses by different mechanisms in rat mesenteric and cerebral arteries.

BACKGROUND AND PURPOSE: Endothelin (ET)-1 and ET-2 cause potent long-lasting vasoconstrictions by tight binding to smooth muscle ETA receptors. We tested the hypotheses that different mechanisms mediate initiation and maintenance of arterial contractile responses to ET-1 and ET-2 and that this differs among vascular beds. EXPERIMENTAL APPROACH: Segments of rat mesenteric resistance artery (MRA) and basilar artery (BA) were studied in wire myographs with and without functional antagonists. KEY RESULTS: Sensitivity and maximum of MRA contractile responses to ET-1 were not, or only moderately, reduced by stimulation of soluble GC, AC or K(+) -channels and by an inhibitor of receptor-operated ion channels. However, each of these reduced maintenance of ET-1 effects and relaxed ET-1-induced contractions in MRA. A calcium channel antagonist did not alter sensitivity, maximum and maintenance of ET-1 effects, but relaxed ET-1-induced contractions in MRA. A PLC inhibitor prevented contractile responses to ET-1 and ET-2 in MRA and BA, and relaxed ET-1- and ET-2-induced responses in MRA and ET-1 effects in BA. A Rho-kinase inhibitor did not modify sensitivity, maximum and maintenance of responses to both peptides in both arteries but relaxed ET-2, but not ET-1, effects in MRA and ET-1 effects in BA. CONCLUSIONS AND IMPLICATIONS: PLC played a key role in arterial contractile responses to ETs, but ET-1 and ET-2 initiated and maintained vasoconstriction through different mechanisms, and these differed between MRA and BA. Selective functional antagonism may be considered for agonist- and vascular bed selective pharmacotherapy of ET-related diseases.

Why two endothelins and two receptors for ovulation and luteal regulation?

The ovary is a dynamic organ that undergoes cyclic structural and functional changes. Structurally, the internal architecture of the ovary constantly changes as follicles grow, rupture and transform into corpora lutea in a cyclical manner. Functionally, a variety of regulatory ovarian hormones are sequentially produced, and eggs are periodically released. As a highly vascularized organ, the ovarian structures and functions change in response to external stimuli that include but are not limited to pituitary gonadotropins. Following stimulation, the ovary synthesizes and releases autocrine and paracrine signals that play unique roles in regulating its function. Recent studies have identified endothelins as local regulators in the ovary that modulate multiple cyclic events, such as follicle growth, steroidogenesis, oocyte maturation, ovulation, corpus luteum formation and luteolysis. Interestingly, in all mammalian species examined to date, a common observation has been made: the ovary produces two pharmacologically similar endothelins (ET-1 and ET-2) but expresses two functionally different endothelin receptors (ET(A) and ET(B)) that often give rise to opposite physiological outcomes following activation by an endothelin. In this review, the physiological significance of the presence of the two ligand-two receptor endothelin system in the ovary will be discussed.

Radiation treatment inhibits monocyte entry into the optic nerve head and prevents neuronal damage in a mouse model of glaucoma.

Glaucoma is a common ocular disorder that is a leading cause of blindness worldwide. It is characterized by the dysfunction and loss of retinal ganglion cells (RGCs). Although many studies have implicated various molecules in glaucoma, no mechanism has been shown to be responsible for the earliest detectable damage to RGCs and their axons in the optic nerve. Here, we show that the leukocyte transendothelial migration pathway is activated in the optic nerve head at the earliest stages of disease in an inherited mouse model of glaucoma. This resulted in proinflammatory monocytes entering the optic nerve prior to detectable neuronal damage. A 1-time x-ray treatment prevented monocyte entry and subsequent glaucomatous damage. A single x-ray treatment of an individual eye in young mice provided that eye with long-term protection from glaucoma but had no effect on the contralateral eye. Localized radiation treatment prevented detectable neuronal damage and dysfunction in treated eyes, despite the continued presence of other glaucomatous stresses and signaling pathways. Injection of endothelin-2, a damaging mediator produced by the monocytes, into irradiated eyes, combined with the other glaucomatous stresses, restored neural damage with a topography characteristic of glaucoma. Together, these data support a model of glaucomatous damage involving monocyte entry into the optic nerve.

Role of the endothelin axis and its antagonists in the treatment of cancer.

The endothelins (ET) are a group of proteins that act through G-protein coupled receptors. Endothelin-1 (ET-1) was initially identified as a potent vasoconstrictor and dysregulation of the ET axis contributes to pathological processes responsible for cardiovascular disease states. More recently, the ET axis, in particular ET-1 acting through the endothelin A receptor (ET(A) ), has been implicated in the development of several cancers through activation of pathways involved in cell proliferation, migration, invasion, epithelial-mesenchymal transition, osteogenesis and angiogenesis. The endothelin B receptor (ET(B) ) may counter tumour progression by promoting apoptosis and clearing ET-1; however, it has recently been implicated in the development of some tumour types including melanomas and oligodendrogliomas. Here, we review emerging preclinical and clinical data outlining the role of the ET axis in cancer, and its antagonism as an attractive and challenging approach to improve clinical cancer management. Clinical data of ET(A) antagonists in patients with prostate cancer are encouraging and provide promise for new ET(A) antagonist-based treatment strategies. Given the unexpected opportunities to affect pleiotrophic tumorigenic signals by targeting ET(A)-mediated pathways in a number of cancers, the evaluation of ET-targeted therapy in cancer warrants further investigation.

Molecular clustering identifies complement and endothelin induction as early events in a mouse model of glaucoma.

Glaucoma is one of the most common neurodegenerative diseases. Despite this, the earliest stages of this complex disease are still unclear. This study was specifically designed to identify early stages of glaucoma in DBA/2J mice. To do this, we used genome-wide expression profiling of optic nerve head and retina and a series of computational methods. Eyes with no detectable glaucoma by conventional assays were grouped into molecularly defined stages of disease using unbiased hierarchical clustering. These stages represent a temporally ordered sequence of glaucoma states. We then determined networks and biological processes that were altered at these early stages. Early-stage expression changes included upregulation of both the complement cascade and the endothelin system, and so we tested the therapeutic value of separately inhibiting them. Mice with a mutation in complement component 1a (C1qa) were protected from glaucoma. Similarly, inhibition of the endothelin system with bosentan, an endothelin receptor antagonist, was strongly protective against glaucomatous damage. Since endothelin 2 is potently vasoconstrictive and was produced by microglia/macrophages, our data provide what we believe to be a novel link between these cell types and vascular dysfunction in glaucoma. Targeting early molecular events, such as complement and endothelin induction, may provide effective new treatments for human glaucoma.

Contractile effects of endothelins on isolated human ureter.

The aim of our study was to investigate mechanism of action of endothelins 1, 2 and 3 on spontaneous activity, tone and intraluminal pressure of human ureter. Both longitudinal tension and intraluminal pressure were recorded from the isolated segments of proximal human ureter. Endothelins 1, 2 and 3 (5.35x10(-11) M - 5.05x10(-8) M) produced concentration-dependent tonic contraction and sustained increase in intraluminal pressure of isolated preparations of human ureter. Endothelins 1 and 3 produced also concentration-dependent inhibition of spontaneous, phasic contractions of the isolated preparations. Selective antagonist of ET(A) receptors BQ123 and selective antagonist of ET(B) receptors BQ788 produced significant inhibition of endothelin-1-induced tonic contraction (pA(2)=8.80 and 6.55, respectively) and increase in intraluminal pressure (pA(2)=8.68 and 7.02, respectively), while they did not affect endothelin-1-induced inhibition of spontaneous activity. Endothelin 1 produces increase in tone and intraluminal pressure of isolated human ureter acting on both ET(A) and ET(B) receptors, the first one being functionally more important. Only endothelins 1 and 3 inhibit spontaneous, phasic activity of human ureter, but this effect was not blocked by selective antagonists of ET(A) and ET(B) receptors.