Hydrogen peroxide regulation of bovine endothelin-converting enzyme-1

Post-injury Inhibition of Endothelin-1 Dependent Renal Vasoregulation Mitigates Rhabdomyolysis-Induced Acute Kidney Injury

In patients with rhabdomyolysis, the overwhelming release of myoglobin into the circulation is the primary cause of kidney injury. Myoglobin causes direct kidney injury as well as severe renal vasoconstriction. An increase in renal vascular resistance (RVR) results in renal blood flow (RBF) and glomerular filtration rate (GFR) reduction, tubular injury, and acute kidney injury (AKI). The mechanisms that underlie rhabdomyolysis-induced AKI are not fully understood but may involve the local production of vasoactive mediators in the kidney. Studies have shown that myoglobin stimulates endothelin-1 (ET-1) production in glomerular mesangial cells. Circulating ET-1 is also increased in rats subjected to glycerol-induced rhabdomyolysis. However, the upstream mechanisms of ET-1 production and downstream effectors of ET-1 actions in rhabdomyolysis-induced AKI remain unclear. Vasoactive ET-1 is generated by ET converting enzyme 1 (ECE-1)-induced proteolytic processing of inactive big ET to biologically active peptides. The downstream ion channel effectors of ET-1-induced vasoregulation include the transient receptor potential cation channel, subfamily C member 3 (TRPC3). This study demonstrates that glycerol-induced rhabdomyolysis in Wistar rats promotes ECE-1-dependent ET-1 production, RVR increase, GFR decrease, and AKI. Rhabdomyolysis-induced increases in RVR and AKI in the rats were attenuated by post-injury pharmacological inhibition of ECE-1, ET receptors, and TRPC3 channels. CRISPR/Cas9-mediated knockout of TRPC3 channels attenuated ET-1-induced renal vascular reactivity and rhabdomyolysis-induced AKI. These findings suggest that ECE-1-driven ET-1 production and downstream activation of TRPC3-dependent renal vasoconstriction contribute to rhabdomyolysis-induced AKI. Hence, post-injury inhibition of ET-1-mediated renal vasoregulation may provide therapeutic targets for rhabdomyolysis-induced AKI.

Induction of reactive oxygen species by mechanical stretch drives endothelin production in neonatal pig renal epithelial cells

Vasoactive endothelin (ET) is generated by ET converting enzyme (ECE)-induced proteolytic processing of pro-molecule big ET to biologically active peptides. H2O2 has been shown to increase the expression of ECE1 via transactivation of its promoter. The present study demonstrates that H2O2 triggered ECE1-dependent ET1-3 production in neonatal pig proximal tubule (PT) epithelial cells. A uniaxial stretch of PT cells decreased catalase, increased NADPH oxidase (NOX)2 and NOX4, and increased H2O2 levels. Stretch also increased cellular ECE1, an effect reversed by EUK-134 (a synthetic superoxide dismutase/catalase mimetic), NOX inhibitor apocynin, and siRNA-mediated knockdown of NOX2 and NOX4. Short-term unilateral ureteral obstruction (UUO), an inducer of renal tubular cell stretch and oxidative stress, increased renal ET1-3 generation and vascular resistance (RVR) in neonatal pigs. Despite removing the obstruction, UUO-induced increase in RVR persisted, resulting in early acute kidney injury (AKI). ET receptor (ETR)-operated Ca2+ entry in renal microvascular smooth muscle (SM) via transient receptor potential channel 3 (TRPC3) channels reduced renal blood flow and increased RVR. Although acute reversible UUO (rUUO) did not change protein expression levels of ETR and TRPC3 in renal microvessels, inhibition of ECE1, ETR, and TRPC3 protected against renal hypoperfusion, RVR increase, and early AKI. These data suggest that mechanical stretch-driven oxyradical generation stimulates ET production in neonatal pig renal epithelial cells. ET activates renal microvascular SM TRPC3, leading to persistent vasoconstriction and reduction in renal blood flow. These mechanisms may underlie rUUO-induced renal insufficiency in infants.

Cyclosporine A induces endothelin-converting enzyme-1: Studies in vivo and in vitro

AIM

Cyclosporine A (CsA) induces renal vasoconstriction and hypoxia and enhances the expression of endothelin-1 (ET-1) pro-hormone (pre-pro-ET-1), plausibly leading to a feed-forward loop of renal vasoconstriction, hypoxia and enhanced synthesis of the potent vasoconstrictor ET-1. Endothelin-converting enzyme (ECE)-1 cleaves big endothelin to generate endothelin (ET)-1 and is upregulated by hypoxia via hypoxia-inducible factor (HIF). We hypothesized that in addition to the direct induction of ET-1 synthesis, CsA might also intensify renal ECE-1 expression, thus contributing to enhanced ET-1 synthesis following CsA.

METHODS

CsA was administered to Sprague Dawley rats (120 mg/kg/SC) for 4 days, and renal HIF and ECE-1 expression were assessed with Western blots and immunostaining. Human umbilical vein endothelial cells (HUVEC) and proximal tubular cell line (HK-2) were subjected to CsA, and ECE-1 induction was evaluated using real-time mRNA PCR and Western blots.

RESULTS

Cyclosporine A intensified renal parenchymal ECE-1 expression in the rat kidney, particularly in distal nephron segments, along with renal hypoxia (detected by pimonidazole adducts) and HIF expression, in line with our recent observations showing episodic hypoxia in mice subjected to CsA. Furthermore, in cultured normoxic HUVEC and HK-2 cells, CsA dose-dependently induced both pre-pro-ET-1 and ECE-1 mRNA and protein expression, with enhanced ET-1 generation.

CONCLUSION

CsA induces ECE-1 via both hypoxic and non-hypoxic pathways. ECE-1 may contribute to increased renal ET-1 generation following CsA, participating in a feed-forward loop of renal parenchymal hypoxia and ET synthesis.

TRAF3IP2 mediates high glucose-induced endothelin-1 production as well as endothelin-1-induced inflammation in endothelial cells

Hyperglycemia-induced production of endothelin (ET)-1 is a hallmark of endothelial dysfunction in diabetes. Although the detrimental vascular effects of increased ET-1 are well known, the molecular mechanisms regulating endothelial synthesis of ET-1 in the setting of diabetes remain largely unidentified. Here, we show that adapter molecule TRAF3 interacting protein 2 (TRAF3IP2) mediates high glucose-induced ET-1 production in endothelial cells and ET-1-mediated endothelial cell inflammation. Specifically, we found that high glucose upregulated TRAF3IP2 in human aortic endothelial cells, which subsequently led to activation of JNK and IKKβ. shRNA-mediated silencing of TRAF3IP2, JNK1, or IKKβ abrogated high-glucose-induced ET-converting enzyme 1 expression and ET-1 production. Likewise, overexpression of TRAF3IP2, in the absence of high glucose, led to activation of JNK and IKKβ as well as increased ET-1 production. Furthermore, ET-1 transcriptionally upregulated TRAF3IP2, and this upregulation was prevented by pharmacological inhibition of ET-1 receptor B using BQ-788, or inhibition of NADPH oxidase-derived reactive oxygen species using gp91ds-tat and GKT137831. Notably, we found that knockdown of TRAF3IP2 abolished ET-1-induced proinflammatory and adhesion molecule (IL-1β, TNF-α, monocyte chemoattractant protein 1, ICAM-1, VCAM-1, and E-selectin) expression and monocyte adhesion to endothelial cells. Finally, we report that TRAF3IP2 is upregulated and colocalized with CD31, an endothelial marker, in the aorta of diabetic mice. Collectively, findings from the present study identify endothelial TRAF3IP2 as a potential new therapeutic target to suppress ET-1 production and associated vascular complications in diabetes. NEW & NOTEWORTHY This study provides the first evidence that the adapter molecule TRAF3 interacting protein 2 mediates high glucose-induced production of endothelin-1 by endothelial cells as well as endothelin-1-mediated endothelial cell inflammation. The findings presented herein suggest that TRAF3 interacting protein 2 may be an important therapeutic target in diabetic vasculopathy characterized by excess endothelin-1 production.

Hyperphosphatemia induces senescence in human endothelial cells by increasing endothelin-1 production

Hyperphosphatemia is related to some pathologies, affecting vascular cell behavior. This work analyzes whether high concentration of extracellular phosphate induces endothelial senescence through up‐regulation of endothelin‐1 (ET‐1), exploring the mechanisms involved. The phosphate donor β‐glycerophosphate (BGP) in human endothelial cells increased ET‐1 production, endothelin‐converting enzyme‐1 (ECE‐1) protein, and mRNA expression, which depend on the AP‐1 activation through ROS production. In parallel, BGP also induced endothelial senescence by increasing p16 expression and the senescence‐associated β‐galactosidase (SA‐ß‐GAL) activity. ET‐1 itself was able to induce endothelial senescence, increasing p16 expression and SA‐ß‐GAL activity. In addition, senescence induced by BGP was blocked when different ET‐1 system antagonists were used. BGP increased ROS production at short times, and the presence of antioxidants prevented the effect of BGP on AP1 activation, ECE‐1 expression, and endothelial senescence. These findings were confirmed in vivo with two animal models in which phosphate serum levels were increased: seven/eight nephrectomized rats as chronic kidney disease models fed on a high phosphate diet and aged mice. Both models showed hyperphosphatemia, higher levels of ET‐1, and up‐regulation in aortic ECE‐1, suggesting a direct relationship between hyperphosphatemia and ET‐1. Present results point to a new and relevant role of hyperphosphatemia on the regulation of ET‐1 system and senescence induction at endothelial level, both in endothelial cells and aorta from two animal models. The mechanism involved showed a higher ROS production, which probably activates AP‐1 transcription factor and, as a result, ECE‐1 expression, increasing ET‐1 synthesis, which in consequence induces endothelial senescence.

Glucose Oxidase Induces Cellular Senescence in Immortal Renal Cells through ILK by Downregulating Klotho Gene Expression

Cellular senescence can be prematurely induced by oxidative stress involved in aging. In this work, we were searching for novel intermediaries in oxidative stress-induced senescence, focusing our interest on integrin-linked kinase (ILK), a scaffold protein at cell-extracellular matrix (ECM) adhesion sites, and on the Klotho gene. Cultured renal cells were treated with glucose oxidase (GOx) for long time periods. GOx induced senescence, increasing senescence associated β-galactosidase activity and the expression of p16. In parallel, GOx increased ILK protein expression and activity. Ectopic overexpression of ILK in cells increased p16 expression, even in the absence of GOx, whereas downregulation of ILK inhibited the increase in p16 due to oxidative stress. Additionally, GOx reduced Klotho gene expression and cells overexpressing Klotho protein did not undergo senescence after GOx addition. We demonstrated a direct link between ILK and Klotho since silencing ILK expression in cells and mice increases Klotho expression and reduces p53 and p16 expression in renal cortex. In conclusion, oxidative stress induces cellular senescence in kidney cells by increasing ILK protein expression and activity, which in turn reduces Klotho expression. We hereby present ILK as a novel downregulator of Klotho gene expression.

The active form of vitamin D, calcitriol, induces a complex dual upregulation of endothelin and nitric oxide in cultured endothelial cells

Despite the presence of vitamin D receptor (VDR) in endothelial cells, the effect of vitamin D on endothelial function is unknown. An unbalanced production of vasoactive endothelial factors such as nitric oxide (NO) or endothelin-1 (ET-1) results in endothelial dysfunction, which can alter the normal cardiovascular function. Present experiments were devoted to assess the effect of active vitamin D (calcitriol) on the synthesis of endothelial vasoactive factors. The results were that, in cells, calcitriol increased ET-1 and NO productions, which were measured by ELISA and fluorimetric assay, respectively. Calcitriol also increased endothelin-converting enzyme-1 (ECE-1) and endothelial-nitric oxide synthase (eNOS) activities, their mRNA (qPCR), their protein expressions (Western-blot), and their promoter activities (transfection assays). Calcitriol did not change prepro-ET-1 mRNA. The effect was specific to VDR activation because when VDR was silenced by siRNA, the observed effects disappeared. Mechanisms involved in each upregulation differed. ECE-1 upregulation depended on AP-1 activation, whereas eNOS upregulation depended directly on VDR activation. To evaluate the in vivo consequences of acute calcitriol treatment, normal Wistar rats were treated with a single ip injection of 400 ng/kg calcitriol and euthanized 24 h later. Results confirmed those observed in cells, that production and expression of both factors were increased by calcitriol. Besides, calcitriol-treated rats showed a slight rise in mean blood pressure, which decreased when pretreated with FR-901533, an ECE-1 antagonist. We conclude that calcitriol increases the synthesis of both ET-1 and NO in endothelial cells. However, the ET-1 upregulation seems to be biologically more relevant, as animals acutely treated with calcitriol show slight increases in blood pressure.

Endothelin-converting enzyme is a plausible target gene for hypoxia-inducible factor

Renal endothelin-converting enzyme (ECE)-1 is induced in experimental diabetes and following radiocontrast administration, conditions characterized by renal hypoxia, hypoxia-inducible factor (HIF) stabilization, and enhanced endothelin synthesis. Here we tested whether ECE-1 might be a HIF-target gene in vitro and in vivo. ECE-1 transcription and expression increased in cultured vascular endothelial and proximal tubular cell lines, subject to hypoxia, to mimosine or cobalt chloride. These interventions are known to stabilize HIF signaling by inhibition of HIF-prolyl hydroxylases. In rats, HIF-prolyl-hydroxylase inhibition by mimosine or FG-4497 increased HIF-1α immunostaining in renal tubules, principally in distal nephron segments. This was associated with markedly enhanced ECE-1 protein expression, predominantly in the renal medulla. A progressive and dramatic increase in ECE-1 immunostaining over time, in parallel with enhanced HIF expression, was also noted in conditional von Hippel-Lindau knockout mice. Since HIF and STAT3 are cross-stimulated, we triggered HIF expression by STAT3 activation in mice, transfected by or injected with a chimeric IL-6/IL-6-receptor protein, and found a similar pattern of enhanced ECE-1 expression. Chromatin immunoprecipitation sequence (ChIP-seq) and PCR analysis in hypoxic endothelial cells identified HIF binding at the ECE-1 promoter and intron regions. Thus, our findings suggest that ECE-1 may be a novel HIF-target gene.

Reactive oxygen species in pulmonary vascular remodeling

The pathogenesis of pulmonary hypertension is a complex multifactorial process that involves the remodeling of pulmonary arteries. This remodeling process encompasses concentric medial thickening of small arterioles, neomuscularization of previously nonmuscular capillary-like vessels, and structural wall changes in larger pulmonary arteries. The pulmonary arterial muscularization is characterized by vascular smooth muscle cell hyperplasia and hypertrophy. In addition, in uncontrolled pulmonary hypertension, the clonal expansion of apoptosis-resistant endothelial cells leads to the formation of plexiform lesions. Based upon a large number of studies in animal models, the three major stimuli that drive the vascular remodeling process are inflammation, shear stress, and hypoxia. Although, the precise mechanisms by which these stimuli impair pulmonary vascular function and structure are unknown, reactive oxygen species (ROS)-mediated oxidative damage appears to play an important role. ROS are highly reactive due to their unpaired valence shell electron. Oxidative damage occurs when the production of ROS exceeds the quenching capacity of the antioxidant mechanisms of the cell. ROS can be produced from complexes in the cell membrane (nicotinamide adenine dinucleotide phosphate-oxidase), cellular organelles (peroxisomes and mitochondria), and in the cytoplasm (xanthine oxidase). Furthermore, low levels of tetrahydrobiopterin (BH4) and L-arginine the rate limiting cofactor and substrate for endothelial nitric oxide synthase (eNOS), can cause the uncoupling of eNOS, resulting in decreased NO production and increased ROS production. This review will focus on the ROS generation systems, scavenger antioxidants, and oxidative stress associated alterations in vascular remodeling in pulmonary hypertension.

Integrin-linked kinase mediates the hydrogen peroxide-dependent transforming growth factor-β1 up-regulation

Transforming growth factor type-β1 (TGF-β1) has been recognized as a central mediator in many pathological events related to extracellular matrix (ECM) proteins accumulation, where their locally increased expression has been implicated in the fibrosis process of numerous organs, including glomerular fibrosis in the kidney. We and others have reported the TGF-β1 synthesis regulation by reactive oxygen species (ROS), and moreover we also described the implication of integrin-linked kinase (ILK) in the AP-1-dependent TGF-β1 up-regulation. Thus, we propose here that hydrogen peroxide (H2O2)-dependent TGF-β1 regulation may be mediated by ILK activation. First we confirmed the increase in TGF-β1 expression in human mesangial cells (HMC) after treatment with H2O2 or with an alternative H2O2-generating system such as the glucose-oxidase enzyme (GOX). By using immunoblotting, immunofluorescence, and ELISA techniques, we demonstrate that extracellular H2O2 up-regulates TGF-β1 transcription, as well as increases TGF-β1 promoter activity. Furthermore, catalase-decreased intracellular H2O2 abolished TGF-β1 up-regulation. The use of pharmacological inhibitors as well as knockdown of ILK with small interfering RNA (siRNA) demonstrated the implication of a PI3K/ILK/AKT/ERK MAPK signaling pathway axis in the H2O2-induced TGF-β1 overexpression. Finally, we explored the physiological relevance of these findings by treating HMC with angiotensin II, a known stimuli of H2O2 synthesis. Our results confirm the relevance of previous findings after a more physiological stimulus. In summary, our results provide evidence that ILK activity changes may act as a mechanism in response to different stimuli such as H2O2 in the induced TGF-β1 up-regulation in pathological or even physiological conditions.

Nitric oxide decreases the expression of endothelin-converting enzyme-1 through mRNA destabilization

OBJECTIVE

Endothelial function depends on the equilibrium in the synthesis of vasoactive endothelial factors. It is well known that endothelin and nitric oxide (NO) exhibit reciprocal regulation. We assessed the ability of NO to regulate endothelin-converting enzyme-1 (ECE-1) expression in vascular endothelial cells.

METHODS AND RESULTS

Bovine aortic endothelial cells were incubated with 2 different NO donors as well as with a cyclic-GMP analog, dibutyryl-cGMP (dB-cGMP). ECE-1 protein content and mRNA expression were evaluated by Western blot and Northern blot, respectively, promoter activity by transfection experiments, ECE-1 activity by ELISA, and cGMP production by radioimmunoassay. Both NO donors decreased ECE-1 protein content, mRNA expression, and ECE-1 activity. ODQ, an inhibitor of soluble guanylyl cyclase, blocked those effects. NO donors raised cGMP levels, and dB-cGMP mimicked their effects on ECE-1 expression, which were blocked by KT5823, a nonspecific PKG inhibitor. The changes on ECE-1 expression were due to a destabilization on 3'-untranslated region (3'-UTR) of this mRNA, because the activity of a luciferase reporter construct containing the 3'-UTR of the ECE-1 gene was reduced by dB-cGMP in a PKG-dependent manner. The biological relevance of this regulation was confirmed in bovine aortic endothelial cells coincubated with macrophages in the presence of lipopolysaccharide, in eNOS-deficient mice, and in Wistar rats treated with NO donors. In every case, an inverse relationship was observed between NO and ECE-1 protein content.

CONCLUSION

Our results support that NO regulates ECE-1 expression through a cGMP/PKG-dependent regulatory mechanism at the post-transcriptional level via the 3'-UTR of the ECE-1 gene.

Structure-activity relationship of resveratrol and its analogue, 4,4'-dihydroxy-trans-stilbene, toward the endothelin axis in human endothelial cells

Resveratrol inhibits endothelin-1, a vascular tension regulator. We synthesized the resveratrol analogue 4,4'-dihydroxy-trans-stilbene with 2 hydroxyl groups in the 4 and 4' position to obtain a molecule more active than resveratrol (3,4',5-trihydroxy-trans-stilbene). The results demonstrate that 4,4'-dihydroxy-trans-stilbene led to a significant decrease in total endothelin-1 secretion and in endothelin-1 messenger RNA (mRNA) levels in human endothelial cells. In addition, resveratrol and its analogue decreased endothelin-converting enzyme-1 mRNA levels and further reduced the activity of the enzyme. 4,4'-dihydroxy-trans-stilbene was more active than resveratrol because the new molecule exerted greater activity at the level of endothelin synthesis and conversion, even at a lower concentration. Although 4,4'-dihydroxy-trans-stilbene and resveratrol inhibited formation of reactive oxygen species and lipid peroxidation, the treatment of cells with different oxidant agents did not modify the endothelin-1 release. This finding suggests that the inhibition of endothelin-1 secretion is independent of the antioxidant properties of the 2 compounds. On the basis of these results, the resveratrol analogue 4,4'-dihydroxy-trans-stilbene could be a promising chemopreventive agent against cardiovascular diseases.

Impaired amyloid β-degrading enzymes in brain of streptozotocin-induced diabetic rats

Enzymes that degrade the amyloid β-peptide (Aβ) are important regulators of cerebral Aβ levels. High level of Aβ was found in the brain of diabetic patients and diabetic animals. Aim of the study was to investigate whether activities of Aβ-degrading enzymes neprilysin (NEP), endothelin-converting enzyme 1 (ECE-1) and insulin-degrading enzyme (IDE) were impaired in the brain of diabetic rats. Diabetes was induced in rats by ip administration of 65 mg/kg streptozotocin. The temporal cortex and hippocampus were obtained for activity and mRNA level assays of the three enzymes on the 35th day after induction. ECE-1 activity was significantly decreased both in the hippocampus and cortex of diabetic rats, while for IDE significantly lower activity occurred only in the cortex. NEP activity was slightly decreased in both brain regions. The hippocampus of diabetic rats showed significant decrease in mRNA levels of NEP and ECE-1 and moderate increase in IDE mRNA level. The cortex of diabetic rats showed slight decrease in mRNA levels of the three enzymes. The results indicated that the three Aβ-degrading enzymes were damaged to different extents in the brain of diabetic rats, and impairment of ECE-1 and IDE partly contributed to the elevated Aβ(1-40) levels in brain of diabetic rats.

The peptidase inhibitor CGS-26303 increases endothelin converting enzyme-1 expression in endothelial cells through accumulation of big endothelin-1

BACKGROUND AND PURPOSE

CGS-26303 inhibits endothelin converting enzyme (ECE)-1 more specifically than phosphoramidon. We have studied the effect of CGS-26303 on ECE-1 expression in bovine aortic endothelial cells.

METHODS

ECE-1 activity and big endothelin (ET)-1 levels were measured by ELISA, ECE-1 expression using western and northern blot and promoter activity using transfection assays.

KEY RESULTS

ECE-1 activity was completely inhibited by CGS-26303 25 microM and phosphoramidon 100 microM. CGS-26303 and phosphoramidon, though not thiorphan, a neutral endopeptidase (NEP) inhibitor, stimulated ECE-1 expression in cells (maximal effect at 16 h, 25 microM). Cycloheximide abolished that effect. CGS-26303 induced ECE-1 mRNA expression and ECE-1 promoter activity. CGS-35066, a selective ECE-1 inhibitor, mimicked the effects of CGS-26303, suggesting that the effect was specific to ECE-1 inhibition. Big ET-1 accumulated in the cells and in the supernatants after CGS-26303 treatment. Neither exogenously added ET-1 nor the blockade of their receptors with bosentan modified ECE-1 protein. When big ET-1 was added to cells, significant increases in ECE-1 protein content and ECE-1 promoter activity were found. Bosentan did not block those effects. CGS-26303 did not modify prepro-ET-1 expression. CGS-26303 and big ET-1 induced the same effects in human endothelial cells, at lower doses.

CONCLUSIONS

These results suggest that the accumulation of big ET-1 is responsible for the effects of CGS-26303 on ECE-1 and they did not depend on NEP blockade. Changes in ECE-1 protein after the administration of CGS-26303 could lead to a decreased response in long-term treatments.

Mice Deficient in Telomerase Activity Develop Hypertension Because of an Excess of Endothelin Production

Background— Telomere shortening has been related to vascular dysfunction and hypertension. In the present study, we analyzed the influence of telomerase deficiency and telomere shortening on arterial pressure (AP).

Methods and Results— AP was evaluated in 6-month-old mice lacking the RNA component of the telomerase ( terc −/− ) at the first generation and third generation (G3). First generation and G3 mice showed higher AP than wild-type (WT) mice. To analyze the mechanisms involved, mean AP and vascular resistance in response to vasoactive substances were measured in G3 and WT mice. These mice showed similar responses to acetylcholine, N G -nitro- l -arginine methyl ester, angiotensin II, and losartan administration. Mean AP did not increase after endothelin-1 (ET-1) administration in G3 mice, but it did in WT animals. Bosentan treatment decreased mean AP only in G3 mice. Serum and urine concentrations of ET-1 were higher in terc −/− than in WT mice. Endothelin-converting enzyme (ECE-1) mRNA expression was higher in terc −/− animals than in the WT group. FR901533, an ECE antagonist, decreased blood pressure in conscious G3 mice. Studies in mouse embryonic fibroblasts from G3 mice suggest that ECE-1 overexpression could be mediated by reactive oxygen species in an AP-1–dependent mechanism, in which some kinases such as PI3-kinase, Akt, erk1/2, and Jun Kinase could be involved. An increased activity of nicotinamide adenine dinucleotide phosphate oxidase seems to be the main source of reactive oxygen species.

Conclusions— Mice lacking telomerase activity show hypertension as a result of an increase in plasma ET-1 levels, which is a consequence of ECE-1 overexpression. A direct link between telomerase activity and hypertension is reported.

PKCepsilon increases endothelin converting enzyme activity and reduces amyloid plaque pathology in transgenic mice

Deposition of plaques containing amyloid beta (Abeta) peptides is a neuropathological hallmark of Alzheimer's disease (AD). Here we demonstrate that neuronal overexpression of the epsilon isozyme of PKC decreases Abeta levels, plaque burden, and plaque-associated neuritic dystrophy and reactive astrocytosis in transgenic mice expressing familial AD-mutant forms of the human amyloid precursor protein (APP). Compared with APP singly transgenic mice, APP/PKCepsilon doubly transgenic mice had decreased Abeta levels but showed no evidence for altered cleavage of APP. Instead, PKCepsilon overexpression selectively increased the activity of endothelin-converting enzyme, which degrades Abeta. The activities of other Abeta-degrading enzymes, insulin degrading enzyme and neprilysin, were unchanged. These results indicate that increased neuronal PKCepsilon activity can promote Abeta clearance and reduce AD neuropathology through increased endothelin-converting enzyme activity.

Reduced endothelin converting enzyme-1 and endothelin-3 mRNA in the developing bowel of male mice may increase expressivity and penetrance of Hirschsprung disease–like distal intestinal aganglionosis

Hirschsprung disease (distal intestinal aganglionosis, HSCR) is a multigenic disorder with incomplete penetrance, variable expressivity, and a strong male gender bias. Recent studies demonstrated that these genetic patterns arise because gene interactions determine whether enteric nervous system (ENS) precursors successfully proliferate and migrate into the distal bowel. We now demonstrate that male gender bias in the extent of distal intestinal aganglionosis occurs in mice with Ret dominant-negative mutations (RetDN) that mimic human HSCR. We hypothesized that male gender bias could result from reduced expression of a gene already known to be essential for ENS development. Using quantitative real-time polymerase chain reaction (PCR) we demonstrated reduced levels of endothelin converting enzyme-1 and endothelin-3 mRNA in the male mouse bowel at the time that ENS precursors migrate into the colon. Other HSCR-associated genes are expressed at comparable levels in male and female mice. Testosterone and Mullerian inhibiting substance had no deleterious effect on ENS precursor development, but adding EDN3 peptide to E11.5 male RetDN heterozygous mouse gut explants in organ culture significantly increased the rate of ENS precursor migration through the bowel.

Endothelin-1 activation of JAK2 in vascular smooth muscle cells involves NAD(P)H oxidase-derived reactive oxygen species

Endothelin-1 (ET-1) and JAK2 are both implicated in diabetic complications. Therefore, we investigated whether ET-1 differentially activates JAK2 under conditions of normal (5 mM) and high (25 mM) glucose. We tested the hypothesis that reactive oxygen species mediate the activation of JAK2 in response to ET-1. In rat aortic vascular smooth muscle cells (VSMC), ET-1 (10 (- 7) M, 5 min) stimulated the activation of JAK2, which was further enhanced under high glucose conditions. Allopurinol (xanthine oxidase inhibitor, 1 microM) and l-NAME (nitric oxide synthase inhibitor, 1 mM) had no effect on ET-1-induced JAK2 activation, while apocynin (NAD(P)H oxidase inhibitor 100 microM) resulted in a significant inhibition of ET-1-induced JAK2 and MAPK activation. Overexpression of SOD did not inhibit ET-1-induced activation of JAK2, but catalase (50 units/mL) treatment resulted in complete inhibition. In vivo administration of apocynin (1.5 mM) resulted in a significant decrease ( 50%), while the ETA receptor antagonist ABT-627 completely inhibited phosphorylation of JAK2 in aortae from STZ-induced diabetic rats. Additionally, DHE staining of aortic sections was significantly reduced in diabetic rats treated with ABT-627. These data suggest that in VSMC, ET-1 via the ETA receptor, utilizes NAD(P)H oxidase to activate JAK2.

Vascular endothelin in hypertension

Endothelins are powerful vasoconstrictor peptides that also play numerous other functions in many different organs. Endothelin-1 (ET-1) is the most abundant and important of this family of peptides in blood vessels. Production of ET-1 is increased in the endothelium and the kidney in salt-dependent models of hypertension (e.g.: DOCA-salt rats and Dahl salt-sensitive rats, in salt-loaded SHR-SP, in angiotensin II-infused and in diabetic rats). ET-1 elicits an inflammatory response by increasing oxidant stress in the vascular wall, which induces vascular remodeling and endothelial dysfunction found in the hypertensive models that exhibit an endothelin-mediated component. Endothelin receptor antagonism reduces blood pressure and vascular hypertrophic remodeling present in these hypertensive models. Patients with stage 2 hypertension have enhanced vascular expression of ET-1. Endothelin receptor antagonists lower blood pressure in hypertensive patients. They could become therapeutic agents for prevention of target organ damage in hypertension and in type 2 diabetes, chronic renal failure and congestive heart failure. Side effects of endothelin receptor blockers have prevented up to the present their development for these indications. New endothelin antagonists devoid of these side effects, or alternatively inhibitors of the endothelin converting enzymes that generate ET-1 may in the future become available to block the endothelin system. However, to date endothelin antagonists have been approved only for the treatment of primary pulmonary hypertension, a rapidly fatal condition in which the endothelin system plays an important role and endothelin antagonists exert favorable effects.

Activation of the JAK/STAT pathway in vascular smooth muscle by serotonin

Serotonin (5-hydroxytryptamine, 5-HT) is a vasoconstrictor and mitogen whose levels are elevated in diabetes. Previous studies have shown the presence of 5-HT2A, 5-HT2B, and 5-HT1B receptors in vascular smooth muscle cells (VSMCs). There are currently no data regarding 5-HT2B and 5-HT1B receptor activation of the JAK/STAT pathway in VSMCs and resultant potential alterations in 5-HT signaling in diabetes. Therefore, we tested the hypothesis that 5-HT differentially activates the JAK/STAT pathway in VSMCs under conditions of normal (5 mM) and high (25 mM) glucose. Treatment of rat VSMCs with 5-HT (10(-6) M) resulted in time-dependent activation ( approximately 2-fold) of JAK2, JAK1, and STAT1, but not STAT3 (maximal at 5 min, returned to baseline by 30 min). The 5-HT2B receptor agonist BW723C86 and the 5-HT1B receptor agonist CGS12066A (10(-9)-10(-5) M, 5-min stimulation) did not activate the JAK/STAT pathway. Treatment with the 5-HT2A receptor antagonist ketanserin (10 nM) inhibited JAK2 activation by 5-HT. Treatment of streptozotocin-induced diabetic rats with ketanserin (5 mg.kg-1.day-1) reduced activation of JAK2 and STAT1 but not STAT3 in endothelium-denuded thoracic aorta in vivo. 5-HT (10(-6) M) treatment resulted in increased cell proliferation and increased DNA synthesis, which were inhibited by the JAK2 inhibitor AG490. Further studies with apocynin, diphenyleneiodonium chloride, catalase, and virally transfected superoxide dismutase had no effect at either glucose concentration on activation of the JAK/STAT pathway by 5-HT. Therefore, we conclude that 5-HT activates JAK2, JAK1, and STAT1 via the 5-HT2A receptors in a reactive oxygen species-independent manner under both normal and high glucose conditions.

Angiotensin II and endothelin-1 regulate MAP kinases through different redox-dependent mechanisms in human vascular smooth muscle cells

OBJECTIVE

The role of reactive oxygen species (ROS) in mitogen-activated protein kinase (MAPK) signaling by angiotensin (Ang) II and endothelin-1 (ET-1) in human vascular smooth muscle cells (VSMC) was investigated.

DESIGN

VSMCs were derived from resistance arteries from healthy subjects. MAPK activity was assessed using phospho-specific antibodies. ROS generation was measured by CMH2DCFDA fluorescence and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity by lucigenin chemiluminescence.

RESULTS

Ang II and ET-1 increased MAPK phosphorylation (P < 0.01). Pre-treatment with Tiron and Tempol, *O2 scavengers, attenuated agonist-stimulated phosphorylation of p38MAPK, c-Jun N-terminal kinases (JNK) and ERK5, but not of ERK1/2 (extracellular signal-regulated kinases). Apocynin and diphenylene iodinium (DPI), NAD(P)H oxidase inhibitors, decreased Ang II-induced responses 60-70%. ET-1-mediated MAPK phosphorylation was unaffected by apocynin but was reduced (> 50%) by thenoyltrifluoroacetone (TIFT) and carboxyl cyanide-m-chlorophenylhydrazone (CCCP), mitochondrial inhibitors. Allopurinol and N-nitro-l-arginine methyl ester (l-NAME), xanthine oxidase and nitric oxide synthase (NOS) inhibitors, respectively, did not influence MAPK activation. Intracellular ROS generation, was increased by Ang II and ET-1 (P < 0.01). DPI inhibited Ang II- but not ET-1-mediated ROS production. Expression of p22phox and p47phox and activation of NAD(P)H oxidase were increased by Ang II but not by ET-1. CCCP and TIFT significantly attenuated ET-1-mediated ROS formation (P < 0.05), without influencing Ang II effects.

CONCLUSIONS

Ang II activates p38MAPK, JNK and ERK5 primarily through NAD(P)H oxidase-generated ROS. ET-1 stimulates these kinases via redox-sensitive processes that involve mitochondrial-derived ROS. These data suggest that redox-dependent activation of MAPKs by Ang II and ET-1 occur through distinct ROS-generating systems that could contribute to differential signaling by these agonists in VSMCs.