Regulation of endothelin 1 gene by fluid shear stress is transcriptionally mediated and independent of protein kinase C and cAMP

Endothelin signaling in development

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

The role of endothelial cell in cardiac hypertrophy: Focusing on angiogenesis and intercellular crosstalk

Cardiac hypertrophy is characterized by cardiac structural remodeling, fibrosis, microvascular rarefaction, and chronic inflammation. The heart is structurally organized by different cell types, including cardiomyocytes, fibroblasts, endothelial cells, and immune cells. These cells highly interact with each other by a number of paracrine or autocrine factors. Cell-cell communication is indispensable for cardiac development, but also plays a vital role in regulating cardiac response to damage. Although cardiomyocytes and fibroblasts are deemed as key regulators of hypertrophic stimulation, other cells, including endothelial cells, also exert important effects on cardiac hypertrophy. More particularly, endothelial cells are the most abundant cells in the heart, which make up the basic structure of blood vessels and are widespread around other cells in the heart, implicating the great and inbuilt advantage of intercellular crosstalk. Cardiac microvascular plexuses are essential for transport of liquids, nutrients, molecules and cells within the heart. Meanwhile, endothelial cell-mediated paracrine signals have multiple positive or negative influences on cardiac hypertrophy. However, a comprehensive discussion of these influences and consequences is required. This review aims to summarize the basic function of endothelial cells in angiogenesis, with an emphasis on angiogenic molecules under hypertrophic conditions. The secondary objective of the research is to fully discuss the key molecules involved in the intercellular crosstalk and the endothelial cell-mediated protective or detrimental effects on other cardiac cells. This review provides a more comprehensive understanding of the overall role of endothelial cells in cardiac hypertrophy and guides the therapeutic approaches and drug development of cardiac hypertrophy.

The Molecular Mechanism of Aerobic Exercise Improving Vascular Remodeling in Hypertension

The treatment and prevention of hypertension has been a worldwide medical challenge. The key pathological hallmark of hypertension is altered arterial vascular structure and function, i.e., increased peripheral vascular resistance due to vascular remodeling. The aim of this review is to elucidate the molecular mechanisms of vascular remodeling in hypertension and the protective mechanisms of aerobic exercise against vascular remodeling during the pathological process of hypertension. The main focus is on the mechanisms of oxidative stress and inflammation in the pathological condition of hypertension and vascular phenotypic transformation induced by the trilaminar structure of vascular endothelial cells, smooth muscle cells and extracellular matrix, and the peripheral adipose layer of the vasculature. To further explore the possible mechanisms by which aerobic exercise ameliorates vascular remodeling in the pathological process of hypertension through anti-proliferative, anti-inflammatory, antioxidant and thus inhibiting vascular phenotypic transformation. It provides a new perspective to reveal the intervention targets of vascular remodeling for the prevention and treatment of hypertension and its complications.

CFTR limits F-actin formation and promotes morphological alignment with flow in human lung microvascular endothelial cells

Micro- and macrovascular endothelial dysfunction in response to shear stress has been observed in cystic fibrosis (CF), and has been associated with inflammation and oxidative stress. We tested the hypothesis that the cystic fibrosis transmembrane conductance regulator (CFTR) regulates endothelial actin cytoskeleton dynamics and cellular alignment in response to flow. Human lung microvascular endothelial cells (HLMVEC) were cultured with either the CFTR inhibitor GlyH-101 (20 µM) or CFTRinh-172 (20 µM), tumor necrosis factor (TNF)-α (10 ng/ml) or a vehicle control (0.1% dimethyl sulfoxide) during 24 and 48 h of exposure to shear stress (11.1 dynes/cm2 ) or under static control conditions. Cellular morphology and filamentous actin (F-actin) were assessed using immunocytochemistry. [Nitrite] and endothelin-1 ([ET-1]) were determined in cell culture supernatant by ozone-based chemiluminescence and ELISA, respectively. Treatment of HLMVECs with both CFTR inhibitors prevented alignment of HLMVEC in the direction of flow after 24 and 48 h of shear stress, compared to vehicle control (both p < 0.05). Treatment with TNF-α significantly increased total F-actin after 24 h versus control (p < 0.05), an effect that was independent of shear stress. GlyH-101 significantly increased F-actin after 24 h of shear stress versus control (p < 0.05), with a significant (p < 0.05) reduction in cortical F-actin under both static and flow conditions. Shear stress decreased [ET-1] after 24 h (p < 0.05) and increased [nitrite] after 48 h (p < 0.05), but neither [nitrite] nor [ET-1] was affected by GlyH-101 (p > 0.05). CFTR appears to limit cytosolic actin polymerization, while maintaining a cortical rim actin distribution that is important for maintaining barrier integrity and promoting alignment with flow, without effects on endothelial nitrite or ET-1 production.

Abnormal Flow Dynamics Result in Low Wall Shear Stress and High Oscillatory Shear Index in Abdominal Aortic Dilatation: Initial in vivo Assessment with 4D-flow MRI

PURPOSE

To characterize the non-laminar flow dynamics and resultant decreased wall shear stress (WSS) and high oscillatory shear index (OSI) of the infrarenal abdominal aortic dilatation, cardiac phase-resolved 3D phase-contrast MRI (4D-flow MRI) was performed.

METHODS

The prospective single-arm study was approved by the Institutional Review Board and included 18 subjects (median 67.5 years) with the dilated infrarenal aorta (median diameter 35 mm). 4D-flow MRI was conducted on a 1.5T MRI system. On 3D streamline images, laminar and non-laminar (i.e., vortex or helical) flow patterns were visually assessed both for the dilated aorta and for the undilated upstream aorta. Cardiac phase-resolved flow velocities, WSS and OSI, were also measured for the dilated aorta and the upstream undilated aorta.

RESULTS

Non-laminar flow represented by vortex or helical flow was more frequent and overt in the dilated aorta than in the undilated upstream aorta (P < 0.0156) with a very good interobserver agreement (weighted kappa: 0.82-1.0). The WSS was lower, and the OSI was higher on the dilated aortic wall compared with the proximal undilated segments. In mid-systole, mean spatially-averaged WSS was 0.20 ± 0.016 Pa for the dilated aorta vs. 0.68 ± 0.071 Pa for undilated upstream aorta (P < 0.0001), and OSI on the dilated aortic wall was 0.093 ± 0.010 vs. 0.041 ± 0.0089 (P = 0.013). The maximum values and the amplitudes of the WSS at the dilated aorta were inversely proportional to the ratio of dilated/undilated aortic diameter (r = -0.694, P = 0.0014).

CONCLUSION

4D-flow can characterize abnormal non-laminar flow dynamics within the dilated aorta in vivo. The wall of the infrarenal aortic dilatation is continuously and increasingly affected by atherogenic stimuli due to the flow disturbances represented by vortex or helical flow, which is reflected by lower WSS and higher OSI.

Macitentan in the treatment of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an uncommon but lethal and progressive disease in which prostacyclin, nitric oxide and endothelin-1 pathways are disturbed and contribute to the pathophysiology of this disease. Endothelin receptor antagonists are a class of drugs that have been approved as PAH therapy. Macitentan is a lipophilic, tissue specific, dual receptor antagonist with a higher potency than bosentan and a reduced risk of hepatic injury. Macitentan has shown a reduction in morbidity and mortality due to PAH at long-term follow-up and improvements in hemodynamics, exercise capacity and functional class at the short term. Its main adverse events are nasopharyngitis, bronchitis and an increased risk of anemia. We review the clinical data of macitentan and its use in PAH.

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

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The Effects of Exercise, Aspirin, and Celecoxib in an Atherogenic Environment

INTRODUCTION

Optimal vascular function is a hallmark of cardiovascular health. Specifically, the balance of vasoconstricting and vasodilating substances is recognized as a marker of vascular health. One of the greatest challenges to vascular health and vasodilatory balance is tumor necrosis factor alpha (TNFα)-mediated inflammation. Uncovering effective strategies that maintain a vascular environment that is more vasodilatory and antithrombotic in the face of an inflammatory challenge is favorable.

PURPOSE

To test the ability of various antithrombotic and provasodilatory treatments, as well as combinations thereof, to prevent unfavorable changes in markers of endothelial dysfunction in human umbilical vein endothelial cells when presented with an inflammatory challenge.

METHODS

Human umbilical vein endothelial cells were pretreated with exercise-like levels of laminar shear stress (LSS), aspirin, celecoxib, and their combination before a TNFα challenge. Western blot analysis as well as colorimetric assays were used to determine levels of endothelial nitric oxide synthase (eNOS) and prostacyclin (6-keto PGF1α)/thromboxane (TXB2) metabolite ratio, respectively.

RESULTS

Neither aspirin nor celecoxib were effective in preventing TNFα-induced reduction in eNOS. Further, aspirin was unable to maintain baseline levels of prostacyclin/thromboxane ratio in the face of the inflammatory challenge. Laminar shear stress, aspirin/LSS combination, and celecoxib/LSS combination were all able to prevent TNFα-induced alterations in eNOS levels and prostacyclin/thromboxane ratio.

CONCLUSIONS

Effective strategies to maintain a healthy endothelium, and therefore resistance vessel health, need to include exercise-levels of shear stress to be effective.

Endothelin and the heart in health and diseases

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

Deciphering transcriptional regulation in human embryonic stem cells specified towards a trophoblast fate

Differentiated human embryonic stem cells (hESC) continue to provide a model for studying early trophoblast cells (TB), but many questions have been raised regarding their true identity. Therefore, we carried out a global and unbiased analysis on previously published transcriptomic profiles for hESC differentiated to TB by means of bone morphogenetic protein-4 and inhibitors of activin A and fibroblast growth factor-2 signaling (BAP treatment). Our results confirm that BAP treated hESC (ESCd) lack a mesoderm signature and are a subtype of placental cells unlike those present at term. ESCd display a high level of expression of genes implicated in migration and invasion compared to commonly used, immortalized TB cell lines and primary cells from term placenta. Co-expression network analysis also identified gene modules involved in cell migration and adhesion, processes that are likely critical during the beginning stages of placentation. Finally, protein-protein interaction analysis predicted several additional genes that may play important roles in early stages of placental development. Together, our analyses provide novel insights into the transcriptional programs that are active in ESCd.

Involvement of the metabolic sensor GPR81 in cardiovascular control

GPR81 is a receptor for the metabolic intermediate lactate with an established role in regulating adipocyte lipolysis. Potentially novel GPR81 agonists were identified that suppressed fasting plasma free fatty acid levels in rodents and in addition improved insulin sensitivity in mouse models of insulin resistance and diabetes. Unexpectedly, the agonists simultaneously induced hypertension in rodents, including wild-type, but not GPR81-deficient mice. Detailed cardiovascular studies in anesthetized dogs showed that the pressor effect was associated with heterogenous effects on vascular resistance among the measured tissues: increasing in the kidney while remaining unchanged in hindlimb and heart. Studies in rats revealed that the pressor effect could be blocked, and the renal resistance effect at least partially blocked, with pharmacological antagonism of endothelin receptors. In situ hybridization localized GPR81 to the microcirculation, notably afferent arterioles of the kidney. In conclusion, these results provide evidence for a potentially novel role of GPR81 agonism in blood pressure control and regulation of renal vascular resistance including modulation of a known vasoeffector mechanism, the endothelin system. In addition, support is provided for the concept of fatty acid lowering as a means of improving insulin sensitivity.

A novel antihypertension agent, sargachromenol D from marine brown algae, Sargassum siliquastrum, exerts dual action as an L-type Ca2+ channel blocker and endothelin A/B2 receptor antagonist

We isolated the novel vasoactive marine natural products, (5E,10E)-14-hydroxy-2,6,10-trimethylpentadeca-5,10-dien-4-one (4) and sargachromenol D (5), from Sargassum siliquastrum collected from the coast of the East Sea in South Korea by using activity-guided HPLC purification. The compounds effectively dilated depolarization (50mMK+)-induced basilar artery contraction with EC50 values of 3.52±0.42 and 1.62±0.63μM, respectively, but only sargachromenol D (5) showed a vasodilatory effect on endothelin-1 (ET-1)-induced basilar artery contraction (EC50=9.8±0.6μM). These results indicated that sargachromenol D (5) could act as a dual antagonist of l-type Ca2+ channel and endothelin A/B2 receptors. Moreover, sargachromenol D (5) lowered blood pressure in spontaneous hypertensive rats (SHRs) 2h after oral treatment at a dose of 80mg/kg dose and the effect was maintained for 24h. Based on our ex vivo and in vivo experiments, we propose that sargachromenol D (5) is a strong candidate for the treatment of hypertension that is not controlled by conventional drugs, in particular, severe-, type II diabetes-, salt-sensitive, and metabolic disease-induced hypertension.

Inflammation and myointimal hyperplasia. Correlation with hemodynamic forces

OBJECTIVES

The aim of our study was to correlate flow dynamics and the release of inflammatory cytokines Interleukin 1, 2, 6, TNF (Tumour Necrosis Factor) alfa, both in vitro and in vivo.

MATERIALS AND METHODS

Endothelial cells were exposed to laminar flow (6dyne/cm²) in an in vitro circulatory system and the release of Interleukin 1, 2, 6 and TNF alfa was quantified by ELISA. Interleukin 1, 2, 6 and TNF alfa release was also assessed in vein grafts implanted in the arterial circulation of Lewis rats. Arterial vein grafts were explanted at different time intervals from 3days to 12weeks after surgery. Vein grafts implanted in the arterial circulation for 4weeks, were re implanted in the venous circulation of syngenic Lewis rats, and the release of Interleukin 1, 2, 6 and TNF alfa, was assessed in an organ culture. Six vein grafts (4 occluded, 2 patent) implanted in humans as femorodistal bypass were examined for the presence of myointimal hyperplasia and perigraft inflammatory cells.

RESULTS

In vitro, endothelial cells exposed to laminar flow released an increased amount of Interleukin 1, 2, 6 and TNF alfa in comparison to endothelial cells not exposed to flow. In experimental vein grafts implanted in the arterial circulation there was an increased release of inflammatory cytokines associated to inflammatory changes in the adventitia. Once the vein grafts were re implanted in the venous circulation, the release of these cytokines diminished, while the inflammatory changes in the adventitia regressed.

CONCLUSIONS

Increased shear stress induces release of cytokines and inflammatory changes in the adventitia. These inflammatory changes can contribute to plaque progression and to un stable plaque. These findings support the use of anti-inflammatory therapy in patients prone to develop atherosclerosis and in those who had arterial reconstructive surgery.

A novel hydrodynamic approach of drag-reducing polymers to improve left ventricular hypertrophy and aortic remodeling in spontaneously hypertensive rats

Drag-reducing polymers (DRPs), when added in minute concentrations, have been shown to decrease peripheral vascular resistance. In this study, the effect of DRPs on the hypertension-induced left ventricular hypertrophy and aortic remodeling was evaluated in spontaneously hypertensive rats (SHR). Male SHR and age-matched Wistar rats were divided into four groups and received intravenous injection of normal saline (NS) or DRPs. Body weight (BW), heart rate (HR) and systolic blood pressure (SBP) were measured. Echocardiography was used to evaluate the changes in left ventricle (LV) function and global wall motion. The LV and aorta were stained by hematoxylin and eosin. Cell size of cardiomyocytes and aortic medial thickness were evaluated for each section. The expression of endothelin-1 (ET-1) of LV and aorta was examined by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and immunohistochemistry. There was no significant difference in the increase of SBP among SHR + NS, SHR + 10DRP and SHR + 20DRP groups. SHR + NS group had markedly smaller left ventricular end-systolic diameter and left ventricular end-diastolic diameter but bigger anterior and posterior systolic wall thicknesses, while there was no significant difference in fractional shortening and ejection fraction. The cross-sectional areas (CSAs) of cardiomyocytes and the medial thickness of the aorta in SHR + 10 (ppm) DRP and SHR + 20 (ppm) DRP groups were significantly reduced compared with SHR + NS group. The expression of ET-1 in SHR + 10DRP and SHR + 20DRP groups was significantly attenuated. These results suggest that chronic treatment with DRPs can protect against left ventricular hypertrophy and aortic remodeling. DRPs may offer a new approach to the treatment of left ventricular hypertrophy and aortic remodeling caused by hypertension.

Enhanced cryopreservation of MSCs in microfluidic bioreactor by regulated shear flow

Cell-matrix systems can be stored for longer period of time by means of cryopreservation. Cell-matrix and cell-cell interaction has been found to be critical in a number of basic biological processes. Tissue structure maintenance, cell secretary activity, cellular migration, and cell-cell communication all exist because of the presence of cell interactions. This complex and co-ordinated interaction between cellular constituents, extracellular matrix and adjacent cells has been identified as a significant contributor in the overall co-ordination of tissue. The prime objective of this investigation is to evaluate the effects of shear-stress and cell-substrate interaction in successful recovery of adherent human mesenchymal-stem-cells (hMSCs). A customized microfluidic bioreactor has been used for the purpose. We have measured the changes in focal-point-adhesion (FPAs) by changing induced shear stress inside the bioreactor. The findings indicate that with increase in shear stress, FPAs increases between substrate and MSCs. Further, experimental results show that increased FPAs (4e-3 μbar) enhances the cellular survivability of adherent MSCs. Probably, for the first time involvement of focal point interaction in the outcome of cryopreservation of MSCs has been clarified, and it proved a potentially new approach for modification of cryopreservation protocol by up-regulating focal point of cells to improve its clinical application.

Deep transcriptomic profiling reveals the similarity between endothelial cells cultured under static and oscillatory shear stress conditions

Atherosclerosis is a multifactorial disease that preferentially develops in specific regions in the arterial tree. This characteristic is mainly attributed to the unique pattern of hemodynamic shear stress in vivo. High laminar shear stress (LS) found in straight lumen exerts athero-protective effects. Low or oscillatory shear stress (OS) present in regions of lesser curvature and arterial bifurcations predisposes arterial intima to atherosclerosis. Shear stress-regulated endothelial function plays an important role in the process of atherosclerosis. Most in vitro research studies focusing on the molecular mechanisms of endothelial function are performed in endothelial cells (ECs) under cultured static (ST) condition. Some findings, however, are not recapitulated in subsequent translational studies, mostly likely due to the missing biomechanical milieu. Here, we profiled the whole transcriptome of primary human coronary arterial endothelial cells (HCAECs) under different shear stress conditions with RNA sequencing. Among 16,313 well-expressed genes, we detected 8,177 that were differentially expressed in OS vs. LS conditions and 9,369 in ST vs. LS conditions. Notably, only 1,618 were differentially expressed in OS vs. ST conditions. Hierarchical clustering of ECs demonstrated a strong similarity between ECs under OS and ST conditions at the transcriptome level. Subsequent pairwise heat mapping and principal component analysis gave further weight to the similarity. At the individual gene level, expressional analysis of representative well-known genes as well as novel genes showed a comparable amount at mRNA and protein levels in ECs under ST and OS conditions. In conclusion, the present work compared the whole transcriptome of HCAECs under different shear stress conditions at the transcriptome level as well as at the individual gene level. We found that cultured ECs are significantly different from those under LS conditions. Thus using cells under ST conditions is unlikely to elucidate endothelial physiology. Given the revealed high similarities of the endothelial transcriptome under OS and ST conditions, it may be helpful to understand the underlying mechanisms of OS-induced endothelial dysfunction from static cultured endothelial studies.

Stop chronic kidney disease progression: Time is approaching

Progression of chronic kidney disease (CKD) is inevitable. However, the last decade has witnessed tremendous achievements in this field. Today we are optimistic; the dream of withholding this progression is about to be realistic. The recent discoveries in the field of CKD management involved most of the individual diseases leading the patients to end-stage renal disease. Most of these advances involved patients suffering diabetic kidney disease, chronic glomerulonephritis, polycystic kidney disease, renal amyloidosis and chronic tubulointerstitial disease. The chronic systemic inflammatory status and increased oxidative stress were also investigated. This inflammatory status influences the anti-senescence Klotho gene expression. The role of Klotho in CKD progression together with its therapeutic value are explored. The role of gut as a major source of inflammation, the pathogenesis of intestinal mucosal barrier damage, the role of intestinal alkaline phosphatase and the dietary and therapeutic implications add a novel therapeutic tool to delay CKD progression.

Vascular endothelium - Gatekeeper of vessel health

The vascular endothelium is an interface between the blood stream and the vessel wall. Changes in this single cell layer of the artery wall are believed of primary importance in the pathogenesis of vascular disease/atherosclerosis. The endothelium responds to humoral, neural and especially hemodynamic stimuli and regulates platelet function, inflammatory responses, vascular smooth muscle cell growth and migration, in addition to modulating vascular tone by synthesizing and releasing vasoactive substances. Compromised endothelial function contributes to the pathogenesis of cardiovascular disease; endothelial 'dysfunction' is associated with risk factors, correlates with disease progression, and predicts cardiovascular events. Therapies for atherosclerosis have been developed, therefore, that are directed towards improving endothelial function.

Adaptive phenotypic modulation of human arterial endothelial cells to fluid shear stress-encoded signals: modulation by phosphodiesterase 4D-VE-cadherin signalling

Although cAMP-signalling regulates numerous functions of vascular endothelial cells (VECs), including their ability to impact vascular resistance in response to changes in blood flow dynamics, few of the mechanisms underlying these effects have yet to be described. In addition to forming stable adherens junctions (AJs) in static VEC cultures, VE-cadherin (VECAD) has emerged as a critical component in a key mechanosensor responsible for linking altered blood flow dynamics and the VEC-mediated control of vascular resistance. Previously, a cAMP phosphodiesterase, PDE4D, was shown to coordinate the VEC permeability limiting effects of cAMP-elevating agents in human arterial VECs (HAECs). Herein, we report that PDE4D acts to allow cAMP-elevating agents to regulate VECADs' role as a sensor of flow-associated fluid shear stress (FSS)-encoded information in HAECs. Thus, we report that PDE4 activity is increased in HAECs exposed to laminar FSS and that this effect contributes to controlling how FSS impacts the morphological and gene expression changes in HAECs exposed to flow. More specifically, we report that PDE4D regulates the efficiency with which VECAD, within its mechanosensor, controls VEGFR2 and Akt activities. Indeed, we show that PDE4D knockdown (KD) significantly blunts responses of HAECs to levels of FSS characteristically found in areas of the vasculature in which stenosis is prevalent. We propose that this effect may provide a new therapeutic avenue in modulating VEC behaviour at these sites by promoting an adaptive and vasculo-protective phenotype.

An In Vitro Cynomolgus Vascular Surrogate System for Preclinical Drug Assessment and Human Translation

Objectives—

The predictive value of animal and in vitro systems for drug development is limited, particularly for nonhuman primate studies as it is difficult to deduce the drug mechanism of action. We describe the development of an in vitro cynomolgus macaque vascular system that reflects the in vivo biology of healthy, atheroprone, or advanced inflammatory cardiovascular disease conditions.

Approach and Results—

We compare the responses of the in vitro human and cynomolgus vascular systems to 4 statins. Although statins exert beneficial pleiotropic effects on the human vasculature, the mechanism of action is difficult to investigate at the tissue level. Using RNA sequencing, we quantified the response to statins and report that most statins significantly increased the expression of genes that promote vascular health while suppressing inflammatory cytokine gene expression. Applying computational pathway analytics, we identified statin-regulated biological themes, independent of cholesterol lowering, that provide mechanisms for off-target effects, including thrombosis, cell cycle regulation, glycogen metabolism, and ethanol degradation.

Conclusions—

The cynomolgus vascular system described herein mimics the baseline and inflammatory regional biology of the human vasculature, including statin responsiveness, and provides mechanistic insight not achievable in vivo.

Synthesis of alkylsulfonyl and substituted benzenesulfonyl curcumin mimics as dual antagonist of L-type Ca(2+) channel and endothelin A/B2 receptor

We synthesized a library of curcumin mimics with diverse alkylsulfonyl and substituted benzenesulfonyl modifications through a simple addition reaction of important intermediate, 1-(3-Amino-phenyl)-3-(4-hydroxy-3-methoxy-phenyl)-propenone (10), with various sulfonyl chloride reactants and then tested their vasodilatation effect on depolarization (50 mM K(+))- and endothelin-1 (ET-1)-induced basilar artery contraction. Generally, curcumin mimics with aromatic sulfonyl groups showed stronger vasodilation effect than alkyl sulfonylated curcumin mimics. Among the tested compounds, six curcumin mimics (11g, 11h, 11i, 11j, 11l, and 11s) in a depolarization-induced vasoconstriction and seven compounds (11g, 11h, 11i, 11j, 11l, 11p, and 11s) in an ET-1-induced vasoconstriction showed strong vasodilation effect. Based on their biological properties, synthetic curcumin mimics can act as dual antagonist scaffold of L-type Ca(2+) channel and endothelin A/B2 receptor in vascular smooth muscle cells. In particular, compounds 11g and 11s are promising novel drug candidates to treat hypertension related to the overexpression of L-type Ca(2+) channels and ET peptides/receptors-mediated cardiovascular diseases.

Hydrostatic pressure and shear stress affect endothelin-1 and nitric oxide release by endothelial cells in bioreactors

Abundant experimental evidence demonstrates that endothelial cells are sensitive to flow; however, the effect of fluid pressure or pressure gradients that are used to drive viscous flow is not well understood. There are two principal physical forces exerted on the blood vessel wall by the passage of intra-luminal blood: pressure and shear. To analyze the effects of pressure and shear independently, these two stresses were applied to cultured cells in two different types of bioreactors: a pressure-controlled bioreactor and a laminar flow bioreactor, in which controlled levels of pressure or shear stress, respectively, can be generated. Using these bioreactor systems, endothelin-1 (ET-1) and nitric oxide (NO) release from human umbilical vein endothelial cells were measured under various shear stress and pressure conditions. Compared to the controls, a decrease of ET-1 production by the cells cultured in both bioreactors was observed, whereas NO synthesis was up-regulated in cells under shear stress, but was not modulated by hydrostatic pressure. These results show that the two hemodynamic forces acting on blood vessels affect endothelial cell function in different ways, and that both should be considered when planning in vitro experiments in the presence of flow. Understanding the individual and synergic effects of the two forces could provide important insights into physiological and pathological processes involved in vascular remodeling and adaptation.

The cerebral vasculature as a therapeutic target for neurological disorders and the role of shear stress in vascular homeostatis and pathophysiology

It is widely accepted that vascular mechanisms are involved in the genesis of many neurological disorders. In particular, blood-brain barrier (BBB) dysfunction has been related to the severity of Alzheimer's disease, encephalopathy due to meningitis, multiple sclerosis, HIV-associated encephalopathy, epilepsy, gliomas and metastatic brain tumors. The BBB may constitute an important therapeutic target to protect neurons after CNS diseases. Both in vivo and in vitro, the functional phenotype of vascular endothelium is dynamically responsive to circulating cytokines, growth factors and puslatile blood flow (shear stress). Shear stress can play a critical role in vascular homeostasis and pathophysiology; it is a major regulator of remodeling in developed blood vessels and in blood vessels affected by atherosclerotic lesions. The physiological fluid mechanic stimulus, shear stress, could be considered to be an important 'differentiative' stimulus capable of modulating endothelial phenotype in vivo. Endothelial cells undergo cell cycle arrest after exposure to physiological levels of shear stress. As for mature endothelial cells, in which flow mediated shear stress may play a role in the induction, progression and/or prevention of atherosclerosis by changing their function, stress may play a role in endothelial cell differentiation from hemopoietic stem cells and/or from embryonic stem cells. Stem cells may be used to repair vascular damage, including loss of EC, due to a variety of diseases (e.g. myocardial neovascularization by adult bone marrow derived angioblasts). In the brain, it was proposed that neuron-producing stem cells may be used to treat Alzheimer's disease, paralysis, etc. Surprisingly, very few investigators are exploring the use of endothelial precursors to revert or prevent cerebrovascular disease. This review summarizes the most recent data related to cerebral vasculature as a therapeutic target for neurological disorders and the role of shear stress in blood-brain barrier homeostasis and pathophysiology.

Immune and inflammatory role in renal disease

Chronic and acute renal diseases, irrespective of the initiating cause, have inflammation and immune system activation as a common underlying mechanism. The purpose of this review is to provide a broad overview of immune cells and inflammatory proteins that contribute to the pathogenesis of renal disease, and to discuss some of the physiological changes that occur in the kidney as a result of immune system activation. An overview of common forms of acute and chronic renal disease is provided, followed by a discussion of common therapies that have anti-inflammatory or immunosuppressive effects in the treatment of renal disease.

Slow receptor dissociation kinetics differentiate macitentan from other endothelin receptor antagonists in pulmonary arterial smooth muscle cells

Two endothelin receptor antagonists (ERAs), bosentan and ambrisentan, are currently approved for the treatment of pulmonary arterial hypertension (PAH), a devastating disease involving an activated endothelin system and aberrant contraction and proliferation of pulmonary arterial smooth muscle cells (PASMC). The novel ERA macitentan has recently concluded testing in a Phase III morbidity/mortality clinical trial in PAH patients. Since the association and dissociation rates of G protein-coupled receptor antagonists can influence their pharmacological activity in vivo, we used human PASMC to characterize inhibitory potency and receptor inhibition kinetics of macitentan, ambrisentan and bosentan using calcium release and inositol-1-phosphate (IP(1)) assays. In calcium release assays macitentan, ambrisentan and bosentan were highly potent ERAs with K(b) values of 0.14 nM, 0.12 nM and 1.1 nM, respectively. Macitentan, but not ambrisentan and bosentan, displayed slow apparent receptor association kinetics as evidenced by increased antagonistic potency upon prolongation of antagonist pre-incubation times. In compound washout experiments, macitentan displayed a significantly lower receptor dissociation rate and longer receptor occupancy half-life (ROt(1/2)) compared to bosentan and ambrisentan (ROt(1/2):17 minutes versus 70 seconds and 40 seconds, respectively). Because of its lower dissociation rate macitentan behaved as an insurmountable antagonist in calcium release and IP(1) assays, and unlike bosentan and ambrisentan it blocked endothelin receptor activation across a wide range of endothelin-1 (ET-1) concentrations. However, prolongation of the ET-1 stimulation time beyond ROt(1/2) rendered macitentan a surmountable antagonist, revealing its competitive binding mode. Bosentan and ambrisentan behaved as surmountable antagonists irrespective of the assay duration and they lacked inhibitory activity at high ET-1 concentrations. Thus, macitentan is a competitive ERA with significantly slower receptor dissociation kinetics than the currently approved ERAs. Slow dissociation caused insurmountable antagonism in functional PASMC-based assays and this could contribute to an enhanced pharmacological activity of macitentan in ET-1-dependent pathologies.

Slow receptor dissociation kinetics differentiate macitentan from other endothelin receptor antagonists in pulmonary arterial smooth muscle cells

Two endothelin receptor antagonists (ERAs), bosentan and ambrisentan, are currently approved for the treatment of pulmonary arterial hypertension (PAH), a devastating disease involving an activated endothelin system and aberrant contraction and proliferation of pulmonary arterial smooth muscle cells (PASMC). The novel ERA macitentan has recently concluded testing in a Phase III morbidity/mortality clinical trial in PAH patients. Since the association and dissociation rates of G protein-coupled receptor antagonists can influence their pharmacological activity in vivo, we used human PASMC to characterize inhibitory potency and receptor inhibition kinetics of macitentan, ambrisentan and bosentan using calcium release and inositol-1-phosphate (IP₁) assays. In calcium release assays macitentan, ambrisentan and bosentan were highly potent ERAs with K_b values of 0.14 nM, 0.12 nM and 1.1 nM, respectively. Macitentan, but not ambrisentan and bosentan, displayed slow apparent receptor association kinetics as evidenced by increased antagonistic potency upon prolongation of antagonist pre-incubation times. In compound washout experiments, macitentan displayed a significantly lower receptor dissociation rate and longer receptor occupancy half-life (ROt_1/2) compared to bosentan and ambrisentan (ROt_1/2∶17 minutes versus 70 seconds and 40 seconds, respectively). Because of its lower dissociation rate macitentan behaved as an insurmountable antagonist in calcium release and IP₁ assays, and unlike bosentan and ambrisentan it blocked endothelin receptor activation across a wide range of endothelin-1 (ET-1) concentrations. However, prolongation of the ET-1 stimulation time beyond ROt_1/2 rendered macitentan a surmountable antagonist, revealing its competitive binding mode. Bosentan and ambrisentan behaved as surmountable antagonists irrespective of the assay duration and they lacked inhibitory activity at high ET-1 concentrations. Thus, macitentan is a competitive ERA with significantly slower receptor dissociation kinetics than the currently approved ERAs. Slow dissociation caused insurmountable antagonism in functional PASMC-based assays and this could contribute to an enhanced pharmacological activity of macitentan in ET-1-dependent pathologies.

The endothelin axis in uterine leiomyomas: new insights

The endothelin axis, comprising endothelin-1 (ET-1) and its receptors (ETA and ETB), is involved in the pathophysiology of different human tumors. Here we review conventional approaches and gene expression profiling indicating the association of ET-1 and its cognate receptors with human and rat leiomyomas, the most common benign tumors of myometrium. Specifically, ET-1/ETA interactions affect human and rat leiomyoma cell proliferation through protein kinase C and mitogen-activated protein kinase-dependent signaling pathways. Recent experiments demonstrate that the ET-1 axis exerts a potent antiapoptotic effect involving sphingolipid metabolism and prostaglandin-endoperoxide synthase 2/prostaglandin system in the rat Eker leiomyoma tumor-derived ELT3 cell line. Evidence supports that steroid hormones, growth factors, and extracellular matrix are key regulators of the leiomyoma growth. Interestingly, the ET-1 axis is under steroid hormones and can cooperate with these growth factors. Therefore, ET-1 alone or in association with these factors could contribute to the complex regulation of uterine tumor growth, such as proliferation, survival, and extracellular matrix production. This review summarizes current knowledge and emerging data on ET-1 in uterine leiomyoma pathology.

Mechanotransduction of shear in the endothelium: basic studies and clinical implications

The endothelium plays an integral role in the development and progression of atherosclerosis. Hemodynamic forces, particularly shear stress, have a powerful influence on endothelial phenotype and function; however, there is no clear consensus on how endothelial cells sense shear. Nevertheless, multiple endothelial cell signal transduction pathways are activated when exposed to shear stress in vitro. The type of shear, laminar or oscillatory, impacts which signal transduction pathways are initiated as well as which subsequent genes are up- or down-regulated, thereby influencing endothelial phenotype and function. Recently, human studies have examined the impact of shear stress and different shear patterns at rest and during exercise on endothelial function. Current evidence supports the theory that augmented exercise-induced shear stress contributes to improved endothelial function following acute exercise and exercise training, whereas retrograde shear initiates vascular dysfunction. The purpose of this review is to examine the current theories on how endothelial cells sense shear stress, to provide an overview on shear stress-induced signal transduction pathways and subsequent gene expression, and to review the current literature pertaining to shear stress and shear patterns at rest as well as during exercise in humans and the related effects on endothelial function.

A flexible bioreactor system for constructing in vitro tissue and organ models

To develop in vitro models of cells, tissues and organs we have designed and realized a series of cell culture chambers. Each chamber is purpose designed to simulate a particular feature of the in vivo environment. The bioreactor system is user friendly, and the chambers are easy to produce, sterilize and assemble. In addition they can be connected together to simulate inter-organ or tissue cross-talk. Here we discuss the design philosophy of the bioreactor system and then describe its construction. Preliminary results of validation tests obtained with hepatocytes and endothelial cells are also reported. The results show that endothelial cells are extremely sensitive to small levels of shear stress and that the presence of heterotypic signals from endothelial cells enhances the endogenous metabolic function of hepatocytes.

The interaction between endothelin-1 and nitric oxide in the vasculature: new perspectives

Nitric oxide (NO) and endothelin-1 (ET-1) are natural counterparts in vascular function, and it is becoming increasingly clear that an imbalance between these two mediators is a characteristic of endothelial dysfunction and is important in the progression of vascular disease. Here, we review classical and more recent data that suggest that ET-1 should be regarded as an essential component of NO signaling. In particular, we review evidence of the role of ET-1 in models of acute and chronic NO synthase blockade. Furthermore, we discuss the possible mechanisms by which NO modulates ET-1 activity. On the basis of these studies, we suggest that NO tonically inhibits ET-1 function, and in conditions of diminished NO bioavailability, the deleterious effects of unmitigated ET-1 actions result in vasoconstriction and eventually lead to vascular remodeling and dysfunction.

Flow regulation of collecting duct endothelin-1 production

Collecting duct (CD) endothelin-1 (ET-1) is an important autocrine inhibitor of CD Na(+) reabsorption. Salt loading is thought to increase CD ET-1 production; however, definitive evidence of this, as well as understanding of the mechanisms transducing this effect, is lacking. Tubule fluid flow increases in response to Na(+) loading; hence, we studied flow modulation of CD ET-1 production. Three days of a high-salt diet increased mouse and rat inner medullary CD (IMCD) ET-1 mRNA expression. Acute furosemide infusion increased urinary ET-1 excretion in anesthetized rats. Primary cultures of mouse or rat IMCD detached in response to flow using a closed perfusion chamber, consequently a CD cell line (mpkCCDcl4) was examined. Flow increased ET-1 mRNA at shear stress rates exceeding 1 dyne/cm(2), with the maximal effect seen between 2 and 10 dyne/cm(2). Induction of ET-1 mRNA was first evident after 1 h, and most apparent after 2 h, of flow. Inhibition of calmodulin or dihydropyridine-sensitive Ca(2+) channels did not alter the flow response; however, chelation of intracellular Ca(2+) or removal of extracellular Ca(2+) largely prevented flow-stimulated ET-1 mRNA accumulation. Downregulation of protein kinase C (PKC) using phorbol 12-myristate 13-acetate, or PKC inhibition with calphostin C, markedly reduced flow-stimulated ET-1 mRNA levels. Flow-stimulated ET-1 mRNA accumulation was abolished by inhibition of phospholipase C (PLC). Taken together, these data indicate that flow increases CD ET-1 production and this is dependent on extracellular and intracellular Ca(2+), PKC, and PLC. These studies suggest a novel pathway for coupling alterations in extracellular fluid volume to CD ET-1 production and ultimately control of CD Na(+) reabsorption.

Hemodynamic forces in endothelial dysfunction and vascular aging

Aging is a key risk factor associated with the onset of cardiovascular disease. Notably, vascular aging and cardiovascular disease are both associated with endothelial dysfunction, or a marked decrease in production and bioavailability the vasodilator of nitric oxide (NO). As a result of decreased nitric oxide availability, aging vessels often exhibit endothelial cell senescence and increased oxidative stress. One of the most potent activators of NO production is fluid shear stress produced by blood flow. Interestingly, age-related decrease in NO production partially results from endothelial insensitivity to shear stress. While the endothelial cell response to fluid shear stress has been well characterized in recent years, the exact mechanisms of how the mechanical force of fluid shear stress is converted into intracellular biochemical signals are relatively unknown. Therefore, gaining a better knowledge of mechanosignaling events in endothelial cells may prove to be beneficial for developing potential therapies for cardiovascular diseases.

Endothelin-1 gene regulation

Over two decades of research have demonstrated that the peptide hormone endothelin-1 (ET-1) plays multiple, complex roles in cardiovascular, neural, pulmonary, reproductive, and renal physiology. Differential and tissue-specific production of ET-1 must be tightly regulated in order to preserve these biologically diverse actions. The primary mechanism thought to control ET-1 bioavailability is the rate of transcription from the ET-1 gene (edn1). Studies conducted on a variety of cell types have identified key transcription factors that govern edn1 expression. With few exceptions, the cis-acting elements bound by these factors have been mapped in the edn1 regulatory region. Recent evidence has revealed new roles for some factors originally believed to regulate edn1 in a tissue or hormone-specific manner. In addition, other mechanisms involved in epigenetic regulation and mRNA stability have emerged as important processes for regulated edn1 expression. The goal of this review is to provide a comprehensive overview of the specific factors and signaling systems that govern edn1 activity at the molecular level.

Molecular mechanisms responsible for the atheroprotective effects of laminar shear stress

The endothelium lining the inner surface of blood vessels of the cardiovascular system is constantly exposed to hemodynamic shear stress. The interaction between endothelial cells and hemodynamic shear stress has critical implications for atherosclerosis. Regions of arterial narrowing, curvatures, and bifurcations are especially susceptible to atherosclerotic lesion formation. In such areas, endothelial cells experience low, or oscillatory, shear stress. Corresponding changes in endothelial cell structure and function make them susceptible to the initiation and development of atherosclerosis. In contrast, blood flow with high laminar shear stress activates signal transductions as well as gene and protein expressions that play important roles in vascular homeostasis. In response to laminar shear stress, the release of vasoactive substances such as nitric oxide and prostacyclin decreases permeability to plasma lipoproteins as well as the adhesion of leukocytes, and inhibits smooth muscle cell proliferation and migration. In summary, different flow patterns directly determine endothelial cell morphology, metabolism, and inflammatory phenotype through signal transduction and gene and protein expression. Thus, high laminar shear stress plays a key role in the prevention of atherosclerosis through its regulation of vascular tone and long-term maintenance of the integrity and function of endothelial cells.

Vascular endothelial responses to altered shear stress: pathologic implications for atherosclerosis

Atherosclerosis preferentially develops at branches and curvatures of the arterial tree, where blood flow is disturbed from a laminar pattern, and wall shear stress is non-uniform and has an irregular distribution. Vascular endothelial cells (ECs), which form an interface between the flowing blood and the vessel wall, are exposed to blood flow-induced shear stress. There is increasing evidence suggesting that laminar blood flow and sustained high shear stress modulate the expression of EC genes and proteins that function to protect against atherosclerosis; in contrast, disturbed blood flow and the associated low and reciprocating shear stress upregulate proatherosclerotic genes and proteins that promote development of atherosclerosis. Understanding of the effects of shear stress on ECs will provide mechanistic insights into its role in the pathogenesis of atherosclerosis. The aim of this review article is to summarize current findings on the effects of shear stress on ECs, in terms of their signal transduction, gene expression, structure, and function. These endothelial cellular responses have important relevance to understanding the pathophysiological effects of altered shear stress associated with atherosclerosis and thrombosis and their complications.

Endothelin receptor B-mediated induction of c-jun and AP-1 in response to shear stress in human endothelial cellsThis article is one of a selection of papers published in the special issue (part 2 of 2) on Forefronts in Endothelin

In vivo, endothelial cells are constantly exposed to shear stress by flowing blood. Short-term exposure of endothelial cells to shear stress has been shown to induce endothelin-1 release. It is currently unknown, however, whether this shear stress-dependent endothelin-1 release affects the expression and activity of transcription factors. In this study, primary cultures of human endothelial cells from the umbilical vein were exposed to laminar shear stress in a cone-and-plate viscometer. Laminar shear stress for 30 min induced a 2-fold increase in mRNA expression of c-jun , but not c-fos, in human endothelial cells. Blockade of endothelin receptor subtype B (ETB) with BQ788 prevented this shear stress-dependent induction of c-jun expression. The induction of c-jun by shear stress involved protein kinase C and endothelial NO synthase. In addition, exposure of endothelial cells to arterial laminar shear stress for 1 h increased the binding of transcription factor AP-1 to its consensus sequence by 1.7-fold in electrophoretic mobility shift assays. This induction was also mediated by an ETB-dependent pathway. Supershift analysis supports an AP-1 complex containing c-jun, but not c-fos, in human endothelial cells. In conclusion, our data suggest endothelin-1-mediated induction of c-jun expression and activation of AP-1 (possibly as a c-jun homodimer) by laminar shear stress in human endothelial cells.

Activation of ETB receptors regulates the abundance of ET-1 mRNA in vascular endothelial cells

BACKGROUND AND PURPOSE

The factors that influence the cellular levels of endothelin-1 (ET-1) include transcription, mRNA localization, stability and translation, post-translational maturation of preproET-1 and degradation of ET-1. We investigated the regulation of ET-1 mRNA abundance by extracellular ET-1 in porcine aortic endothelial cells (PAECs).

EXPERIMENTAL APPROACH

Passsage one cultures of PAECs were incubated in starving medium in the presence or absence of ET-1 and antagonists or pharmacological inhibitors. PreproET-1 mRNA, endothelin-1 promoter activity, Erk and p38 MAPK activation were determined.

KEY RESULTS

Exogenous ET-1 reduced cellular ET-1 mRNA content: a reduction of 10 000-fold was observed after 4 h. ET-1 simultaneously reduced the stability of ET-1 mRNA and increased the loading of RNA Polymerase II at the endothelin-1 promoter. In the absence of exogenous ET-1, the ETB-selective antagonist, BQ788, increased ET-1 mRNA. An ETA-selective antagonist had no effect. ET-1 mRNA returned to control levels within 24 h. Whereas activation of p38 MAPK induced by ET-1 peaked at 30 min and returned to control levels within 90 min, Erk1/2 remained active after 4 h of stimulation. Inhibition of p38 MAPK prevented the ET-1-induced decrease in ET-1 mRNA. In contrast, Erk1/2 inhibition increased ET-1 mRNA. Similarly, inhibition of receptor internalization increased ET-1 mRNA in the presence or absence of exogenous ET-1.

CONCLUSIONS AND IMPLICATIONS

These results suggest that extracellular ET-1 regulates the abundance of ET-1 mRNA in PAECs, in an ETB receptor-dependent manner, by modulating both mRNA stability and transcription via mechanisms involving receptor endocytosis and both ERK and p38 MAPK pathways.

Calcium regulation of endothelin-1 synthesis in rat inner medullary collecting duct

Collecting duct-derived endothelin-1 (ET-1) reduces blood pressure and inhibits Na and water reabsorption. Collecting duct ET-1 production is increased by volume expansion; however, the mechanism by which this occurs is unknown. We hypothesized that intracellular calcium, which is likely to be increased by volume expansion, regulates collecting duct ET-1 synthesis. Rat inner medullary collecting ducts (IMCD) were studied in primary culture. ET-1 release was decreased by 50–70% after chelation of intracellular calcium (BAPTA) or inhibition of CaM (W7) or CaMK (KN-93). These agents reduced ET-1 mRNA to a similar degree. CaM inhibition did not affect ET-1 mRNA stability. Transfection of IMCD with rat ET-1 promoter-luciferase constructs revealed maximal activity within 1.7 kb 5′ to the transcription start site; 5, 20, 35, and 90% of this activity were in the 0.08-, 0.37-, 1.0-, and 3.0-kb promoter regions, respectively. W7 markedly inhibited activity of the 3.0-kb but not 0.37- or 1.0-kb promoter regions. In contrast, W7 did not affect ET-1 release by rat aortic endothelial cells. Furthermore, transfected endothelial cells had maximal activity in the 0.37-kb region (as compared with the 1.7- and 3.0-kb regions), whereas W-7 had no effect on the activity of any of these promoter regions. In summary, IMCD ET-1 synthesis is regulated by calcium/CaM/CaMK-dependent pathways. The calcium/CaM-sensitive pathway is active in IMCD, but not endothelial cells. This suggests that IMCD-specific enhancer elements exist within the ET-1 promoter that confer unique calcium responsiveness.

Arterial adaptations to chronic changes in haemodynamic function: coupling vasomotor tone to structural remodelling

Healthy mature arteries are usually extremely quiescent tissues with cell proliferation rates much below 1%/day and with extracellular matrix constituents exhibiting half-lives of years to decades. However, chronic physiological or pathological changes in haemodynamic function elicit arterial remodelling processes that may involve substantial tissue synthesis, degradation or turnover. Although these remodelling processes accommodate changing demands placed upon the cardiovascular system by physiological adaptations, they can compromise further perfusion in the context of arterial occlusive disease and they entrench hypertension and may exacerbate its progression. Recent findings indicate that some of the most important such remodelling responses involve the integrated effects of persistently altered vascular tone that feed into restructuring responses, with common signalling pathways frequently interacting in the control of both phases of the response. Current efforts to define these signals and their targets may provide new directions for therapeutic interventions to treat important vascular disorders.

Role of Krüppel-Like Transcription Factors in Endothelial Biology

Krüppel-like factors are members of the zinc finger family of transcription factors that have been implicated as playing key roles in regulating cellular differentiation and tissue development. Studies over the past several years support an important role for this family of factors in vascular biology. This review summarizes the role of Krüppel-like factors in endothelial cell biology.

Induction of the plasminogen activator system by mechanical stimulation of human bronchial epithelial cells

Mechanical stimulation of the airway epithelium, as would occur during bronchoconstriction, is a potent stimulus and can activate profibrotic pathways. We used DNA microarray technology to examine gene expression in compressed normal human bronchial epithelial cells (NHBE). Compressive stress applied continuously over an 8-h period to NHBE cells led to the upregulation of several families of genes, including a family of plasminogen-related genes that were previously not known to be regulated in this system. Real-time PCR demonstrated a peak increase in gene expression of 8.0-fold for urokinase plasminogen activator (uPA), 16.2-fold for urokinase plasminogen activator receptor (uPAR), 4.2-fold for plasminogen activator inhibitor-1 (PAI-1), and 3.9-fold for tissue plasminogen activator (tPA). Compressive stress also increased uPA protein levels in the cell lysates (112.0 versus 82.0 ng/ml, P = 0.0004), and increased uPA (4.7 versus 3.3 ng/ml, P = 0.02), uPAR (1.3 versus 0.86 ng/ml, P = 0.007), and PAI-1 (50 versus 36 ng/ml, P = 0.006) protein levels in cell culture media. Functional studies demonstrated increased urokinase-dependent plasmin generation in compression-stimulated cells (0.0090 versus 0.0033 OD/min, P = 0.03). In addition, compression led to increased activation of matrix metalloproteinase (MMP)-9 and MMP-2 in a urokinase-dependent manner. In postmortem human lung tissue, we observed an increase in epithelial uPA and uPAR immunostaining in the airways of two patients who died in status asthmaticus compared with minimal immunoreactivity noted in airways from seven lung donors without asthma. Together these observations suggest an integrated response of airway epithelial cells to mechanical stimulation, acting through the plasminogen-activating system to modify the airway microenvironment.

Role of small GTPases in endothelial cytoskeletal dynamics and the shear stress response

Fluid shear stress caused by blood flow is a major determinant of vascular remodeling and arterial tone and can lead to development of atherosclerosis. The endothelial monolayer in vivo acts as a signal transduction interface for hemodynamic forces; these forces determine the shape, cytoskeletal organization, and function of endothelial cells, allowing the vessels to cope with physiological or pathological conditions. The Ras superfamily of GTPases have been revealed to be master regulators of many cellular activities. In particular, the GTPases RhoA, Rac1, and Cdc42 are known to regulate cell shape changes through effects on the cytoskeleton, but their ability to influence polarity, microtubule dynamics, and transcription factor activity is just as significant. Shear stress modulates the activity of small GTPases, which are critical for both cytoskeletal reorganization and changes in gene expression in response to shear stress. The goal of this article is to review what is known about Ras and more so about Rho GTPases in mechanotransduction and the responses of cells to fluid flow. Several distinct signaling pathways can be coordinately activated by flow, and small GTPases are strongly implicated in some of them; thus possible connections will be explored and a unifying hypothesis offered.

Wall shear stress--an important determinant of endothelial cell function and structure--in the arterial system in vivo. Discrepancies with theory

It has been well established that wall shear stress is an important determinant of endothelial cell function and gene expression as well as of its structure. There is increasing evidence that low wall shear stress, as present in artery bifurcations opposite to the flow divider where atherosclerotic lesions preferentially originate, expresses an atherogenic endothelial gene profile. Besides, wall shear stress regulates arterial diameter by modifying the release of vasoactive mediators by endothelial cells. Most of the studies on the influence of wall shear stress on endothelial cell function and structure have been performed in vitro, generally exposing endothelial cells from different vascular regions to an average wall shear stress level calculated according to Poiseuille's law, which does not hold for the in vivo situation, assuming wall shear stress to be constant along the arterial tree. Also in vivo wall shear stress has been determined based upon theory, assuming the velocity profile in arteries to be parabolic, which is generally not the case. Wall shear stress has been calculated, because of the lack of techniques to assess wall shear stress in vivo. In recent years, techniques have been developed to accurately assess velocity profiles in arterioles, using fluorescently labeled particles as flow tracers, and non-invasively in large arteries by means of ultrasound or magnetic resonance imaging. Wall shear rate is derived from the in vivo recorded velocity profiles and wall shear stress is estimated as the product of wall shear rate and plasma viscosity in arterioles and whole blood viscosity in large arteries. In this review, we will discuss wall shear stress in vivo, paying attention to its assessment and especially to the results obtained in both arterioles and large arteries. The limitations of the methods currently in use are discussed as well. The data obtained in the arterial system in vivo are compared with the theoretically predicted ones, and the consequences of values deviating from theory for in vitro studies are considered. Applications of wall shear stress as in flow-mediated arterial dilation, clinically in use to assess endothelial cell (dys)function, are also addressed. This review starts with some background considerations and some theoretical aspects.

Toward a Unified Theory of Renal Progression

Various disciplines within nephrology investigate the mechanisms by which kidneys fail. Progress in the areas of glomerular hemodynamics, proteinuria, tubular biology, interstitial nephritis, fibroblast formation, and fibrosis have added kernels of information that together support a unified theory of renal progression. Prevention of progression to end-stage disease has largely focused on control of systemic and glomerular hypertension. Current success in delaying a decline in glomerular filtration rate underlines the promise of a more comprehensive approach. New knowledge about the cell biology of progression also suggests that other adjunctive therapies may be possible. We describe the progress and highlight those spheres where new-targeted interventions may arise.