Endothelin-1 (ET-1) is a multifunctional hormone which regulates the physiology of the cardiovascular and renal systems. ET-1 modulates cardiac contractility, systemic and renal vascular resistance, salt and water renal reabsorption, and glomerular function. ET-1 is responsible for a variety of cellular events: contraction, proliferation, apoptosis, etc. These effects take place after the activation of the two endothelin receptors ET(A) and ET(B), which are present - among others - on cardiomyocytes, fibroblasts, smooth muscle and endothelial cells, glomerular and tubular cells of the kidney. The complex and numerous intracellular pathways, which can be contradictory in term of functional response depending on the receptor type, cell type and physiological situation, are described in this review. Many diseases share an enhanced ET-1 expression as part of the pathophysiology. However, the use of endothelin blockers is currently restricted to pulmonary arterial hypertension, and more recently to digital ulcer. The complexity of the endothelin system does not facilitate the translation of the molecular knowledge to clinical applications. Endothelin antagonists can prevent disease development but secondary undesirable effects limit their usage. Nevertheless, the increasing understanding of the effects of ET-1 on the cardiac and renal physiology maintains the endothelin system as a promising therapeutic target.

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This study underscores the significance of ET-1 from the vasculature in the process of AngII-induced cardiac hypertrophy and fibrosis, independently from blood pressure. Endothelial ET-1 represents therefore a possible pharmacological target.

Endothelin-1 (ET-1) is one of the most potent biologic vasoconstrictors. Nevertheless, transgenic mice that overexpress ET-1 exhibit normal BP. It was hypothesized that vascular effects of ET-1 may be antagonized by an increase of the endothelial counterpart of ET-1, nitric oxide (NO), which is produced by the endothelial NO synthase (eNOS). Therefore, cross-bred animals of ET transgenic mice (ET؉/؉) and eNOS knockout (eNOS؊/؊) mice and were generated, and BP and endothelial function were evaluated in these animals. Endothelium-dependent and -independent vascular function was assessed as relaxation/contraction of isolated preconstricted aortic rings. The tissue ET and NO system was determined in aortic rings by quantitative real-time PCR and Western blotting. Systolic BP was similar in ET؉/؉ and wild-type (WT) mice but was significantly elevated in eNOS؊/؊ mice (117 ؎ 4 mmHg versus 94 ؎ 6 mmHg in WT mice; P < 0.001) and even more elevated in ET؉/؉ eNOS؊/؊ cross-bred mice (130 ؎ 4 mmHg; P < 0.05 versus eNOS؊/؊). Maximum endothelium-dependent relaxation was enhanced in ET؉/؉ mice (103 ؎ 6 versus 87 ؎ 4% of preconstriction in WT littermates; P < 0.05) and was completely blunted in eNOS؊/؊ (؊3 ؎ 4%) and ET؉/؉ eNOS؊/؊ mice (؊4 ؎ 4%), respectively. Endothelium-independent relaxation was comparable among all groups. T he intact endothelium produces a variety of vasoactive substances, such as nitric oxide (NO), thromboxane, and the 21-amino acid peptide endothelin-1 (ET-1). ET-1 is a potent vasoconstrictor (1) and mitogen in vivo and in vitro and exerts its biologic effects via activation of specific receptors: Whereas on vascular smooth muscle cells the predominant ET receptor is the ET A receptor (ET A R) subtype (2,3), contributing to long-lasting vasoconstriction, endothelial cells express the ET B receptor (ET B R), mediating the formation of NO (4) and prostacyclin (5) and featuring the pulmonary clearance of circulating ET-1 (6) as well as the reuptake of ET-1 by endothelial cells (7).Correspondingly, intravenous administration of ET-1 causes a rapid and transient vasodilation followed by a sustained increase in BP (8). In addition to the negative feedback loop via ET B R, ET-1 production in the vascular wall is inhibited by NO (9) and prostacyclin (10) via cGMP-dependent mechanisms. Therefore, the NO system may be considered as the functional counterpart of the ET system (11-16), thus warranting the sub-

eNOS(-/-) mice developed diastolic dysfunction; this was rescued by ET-1 transgenic overexpression. This study furthermore suggests that cardiac ET-1 overexpression in case of eNOS deficiency causes specifically the regulation of proteins playing a role in oxidative stress, myocytes contractility, and energy metabolism.

Elevated cardiovascular risk in postmenopausal women and beneficial actions of estrogen replacement in animal models have been related to protective effects of estrogens. However, randomized trials of hormone replacement therapy with synthetic estrogens in humans failed confirmation and phytoestrogens, natural plant hormones with agonistic properties for estrogen receptors, could represent potential alternatives. The aim of the present study is to characterize an animal model for alternative hormone replacement with genistein as a natural estrogenic compound. We performed a 2-DE/ESI-LC-MS approach in order to identify protein species varying with genistein receipt and sex in their relative abundance in the healthy murine heart (http://www.mpiib-berlin.mpg.de/2D-PAGE). Oral genistein treatment revealed a substantial effect on the relative abundance of both estrogen receptors. Several enzymes of the fatty acid metabolism and their transcriptional regulators varied differentially in male and in female animals, at the transcript and/or the protein species level. Increased levels of enzyme species involved in the oxidative phosphorylation and generation of ROS were accompanied by decreased amounts of antioxidants in male mice receiving genistein compared with control males, which have been previously associated with various pathological conditions. Exposure of female animals to genistein provoked an increased abundance of two species of LIM domain-binding protein and one species of desmin. These proteins have been associated with cardiac hypertrophy and our data warrant caution for the use of them as molecular markers, since the animals did not exhibit any histological signs of cardiac hypertrophy.

Endothelin-1 (ET-1) has been shown to be involved in human pulmonary fibrosis. However, recent clinical trials targeting the ET-1 pathway with ET-1 receptor antagonists failed to achieve beneficial outcomes. Another strategy opposing the actions of ET-1 involves the inhibition of endothelin-converting enzyme-1 (ECE-1). We hypothesize that ECE-1 inhibition exerts beneficial effects on pulmonary fibrosis. Pulmonary fibrosis was induced by instilling bleomycin intratracheally into ECE-1 heterozygous knockout mice (ECE-1(+/-)) and their wild-type control mice (ECE-1(+/+)). Lung inflammation and fibrosis were assessed on Days 7, 14, and 28 after bleomycin instillation. The activity of ECE-1 and the concentrations of its related peptides, ET-1, bradykinin, atrial natriuretic peptide (ANP), and calcitonin gene-related peptide (CGRP), were determined. ECE-1(+/-) mice demonstrated less lung inflammation and limited fibrosis compared with control mice. ECE-1 activity was half-reduced in ECE-1(+/-) mice, and this activity also altered ET-1 and CGRP concentrations, but not concentrations of bradykinin and ANP. ET-1 concentrations were found to be lower in ECE-1(+/-) mice after the development of fibrosis, in contrast to the unaltered concentrations during inflammation. Reduced ECE-1 activity resulted in higher CGRP concentrations, which altered the pathological functionality of the lung, indicating the activation of the CGRP pathway involving cyclic adenosine monophosphate (cAMP)/exchange protein directly activated by cAMP and cAMP/protein kinase A in ECE-1(+/-) mice. Bleomycin instillation on Day 14 induced the accumulation of M2 macrophages expressing CGRP receptors in ECE-1(+/-) mice. Our results emphasize that the in vivo ECE-1-mediated degradation of CGRP promotes the transition from lung inflammation to fibrosis. Further, our study identified M2 macrophages as the target cells of CGRP action during this transition.

BackgroundEndothelin-1 participates in the pathophysiology of heart failure. The reasons for the lack of beneficial effect of endothelin antagonists in heart failure patients remain however speculative. The anti-apoptotic properties of ET-1 on cardiomyocytes could be a reasonable explanation. We therefore hypothesized that blocking the pro-apoptotic TNF-α pathway using pentoxifylline could prevent the deleterious effect of the lack of ET-1 in a model for heart failure.MethodsWe performed transaortic constriction (TAC) in vascular endothelial cells specific ET-1 deficient (VEETKO) and wild type (WT) mice (n = 5–9) and treated them with pentoxifylline for twelve weeks.ResultsTAC induced a cardiac hypertrophy in VEETKO and WT mice but a reduction of fractional shortening could be detected by echocardiography in VEETKO mice only. Cardiomyocyte diameter was significantly increased by TAC in VEETKO mice only. Pentoxifylline treatment prevented cardiac hypertrophy and reduction of fractional shortening in VEETKO mice but decreased fractional shortening in WT mice. Collagen deposition and number of apoptotic cells remained stable between the groups as did TNF-α, caspase-3 and caspase-8 messenger RNA expression levels. TAC surgery enhanced ANP, BNP and bcl2 expression. Pentoxifylline treatment reduced expression levels of BNP, bcl2 and bax.ConclusionsLack of endothelial ET-1 worsened the impact of TAC-induced pressure overload on cardiac function, indicating the crucial role of ET-1 for normal cardiac function under stress. Moreover, we put in light a TNF-α-independent beneficial effect of pentoxifylline in the VEETKO mice suggesting a therapeutic potential for pentoxifylline in a subpopulation of heart failure patients at higher risk.