Regulation of endothelial and myocardial NO synthesis by multi-site eNOS phosphorylation

The Far Side of Vascular Injury

Substances historically thought to cause direct vascular injury in laboratory animals are a heterogeneous group of toxic agents with varied mechanisms of action. Morphologically, the reviewed agents can be broadly categorized into those targeting endothelial cell (ECs) and those targeting smooth muscle cells (SMCs). Anticancer drugs, immunosuppressants, and heavy metals are targeting primarily ECs while allylamine, β-aminopropionitrile, and mitogen-activated protein kinase kinase inhibitors affect mainly SMCs. It is now recognized that the pathogenicity of some of these agents is often mediated through intermediary events, particularly vasoconstriction. There are clear similarities in the clinical and microscopic findings associated with many of these agents in animals and man, allowing the use of animal models to investigate mechanisms and pathogenesis. The molecular pathogenic mechanisms and comparative morphology in animals and humans will be reviewed.

Liposomal tetrahydrobiopterin preserves eNOS coupling in the post-ischemic heart conferring in vivo cardioprotection

Tetrahydrobiopterin (BH4) is an essential cofactor of nitric oxide synthase (NOS), and reduced BH4 availability leads to endothelial NOS (eNOS) uncoupling and increased reactive oxygen species (ROS) generation. Questions remain regarding the functional state of eNOS and role of BH4 availability in the process of in vivo myocardial ischemia-reperfusion (I/R) injury. Rats were subjected to 60min of in vivo left coronary artery occlusion and varying periods of reperfusion with or without pre-ischemic liposomal BH4 supplementation (1mg/kg, iv). Myocardial infarction was correlated with cardiac BH4 content, eNOS protein level, NOS enzyme activity, and ROS generation. In the vehicle group, 60-min ischemia drastically reduced myocardial BH4 content in the area at risk (AAR) compared to non-ischemic (NI) area and the level remained lower during early reperfusion followed by recovery after 24-h reperfusion. Total eNOS, activated eNOS protein level (eNOS Ser1177 phosphorylation) and NOS activity were also significantly reduced during ischemia and/or early reperfusion, but recovered after 24-h reperfusion. With liposomal BH4 treatment, BH4 levels were identical in the AAR and NI area during ischemia and/or early reperfusion, and were significantly higher than with vehicle. BH4 pre-treatment preserved eNOS Ser1177 phosphorylation and NOS activity in the AAR, and significantly reduced myocardial ROS generation and infarction compared to vehicle. These findings provide direct evidence that in vivo I/R induces eNOS dysfunction secondary to BH4 depletion, and that pre-ischemic liposomal BH4 administration preserves eNOS function conferring cardioprotection with reduced oxidative stress.

Pterostilbene, an Active Constituent of Blueberries, Stimulates Nitric Oxide Production via Activation of Endothelial Nitric Oxide Synthase in Human Umbilical Vein Endothelial Cells

Endothelial dysfunction, a key process in development of cardiovascular diseases, is largely due to reduced nitric oxide (NO) derived from endothelial NO synthase (eNOS). Resveratrol has been reported to stimulate NO production via estrogen receptor α (ERα) activation in endothelial cells. Here, we investigated whether two natural methylated analogs of resveratrol, pterostilbene (Pts) and trans-3,5,4'-trimethoxystilbene (TMS), similarly to resveratrol, could influence endothelial NO release in human umbilical vein endothelial cells (HUVECs). In HUVECs exposed to Pts or TMS, NO production and phosphorylation of eNOS, protein kinase B (Akt), and ERα were measured by using a fluorimetric NO assay kit and Western blot analysis, respectively. Dimethylated Pts, but not trimethylated TMS, stimulated dose-dependent NO production via eNOS phosphorylation. Pts also stimulated dose-dependent phosphorylation of Akt, but not of ERα. NO production and eNOS phosphorylation in response to Pts were significantly abolished by the phosphoinositide 3-kinase (PI3K)/Akt inhibitor LY294002, but not by the ERα antagonist ICI182780. Our results suggest that Pts, but not TMS, is capable of inducing eNOS phosphorylation and the subsequent NO release, presumably, by activating PI3K/Akt pathway. The potential efficacy of Pts, an active constituent of blueberries, may aid in the prevention of cardiovascular diseases characterized by endothelial dysfunction.

The Sirt1 activator SRT1720 attenuates angiotensin II-induced atherosclerosis in apoE⁻/⁻ mice through inhibiting vascular inflammatory response

Activation of the silent mating type information regulation 2 homolog 1 (SIRT1) has been shown consistent antiinflammatory function. However, little information is available on the function of SIRT1 during Angiotensin II (AngII)-induced atherosclerosis. Here we report atheroprotective effects of sirt1 activation in a model of AngII-accelerated atherosclerosis, characterized by suppression pro-inflammatory transcription factors Nuclear transcription factor (NF)-κB and Signal Transducers and Activators of Transcription. (STAT) signaling pathway, and atherosclerotic lesion macrophage content. In this model, administration of the SIRT1 agonist SRT1720 substantially attenuated AngII-accelerated atherosclerosis with decreasing blood pressure and inhibited NF-κB and STAT3 activation, which was associated with suppression of inflammatory factor and atherogenic gene expression in the artery. In vitro studies demonstrated similar changes in AngII-treated VSMCs and macrophages: SIRT1 activation inhibited the expression levels of proinflammatory factor. These studies uncover crucial proinflammatory mechanisms of AngII and highlight actions of SIRT1 activation to inhibit AngII signaling, which is atheroprotective.

MicroRNA-765 influences arterial stiffness through modulating apelin expression

The present study aims to discover single nucleotide polymorphisms (SNPs) at the apelin gene (APLN) in relation to arterial stiffness, and to explore its molecular mechanisms. A two-step genetic association study was conducted using 799 and 937 subjects in the screening and validation data, respectively. Four tagging SNPs of APLN were tested. SNP rs3115757 was significantly associated with stiffness parameters (β, Ep and PWV) in women, but not in men. The function of rs3115757 was tagged by rs3115758 which is located in miR-765 binding site in the 3' untranslated region of APLN. The reporter assay confirmed that different alleles of rs3115758 interfered with miR-765 binding and then modified APLN expression. Over-expression of miR-765 in endothelial cells decreased mRNA and protein levels of APLN, which further inhibited the phosphorylation of eNOS and ERK/Akt/AMPK signaling. Collectively, our data showed that rs3115758 accounts for the susceptibility of arterial stiffening through miR-765-induced APLN repression.

The F-BAR Protein NOSTRIN Dictates the Localization of the Muscarinic M3 Receptor and Regulates Cardiovascular Function

Rationale:

Endothelial dysfunction is an early event in cardiovascular disease and characterized by reduced production of nitric oxide (NO). The F-BAR protein NO synthase traffic inducer (NOSTRIN) is an interaction partner of endothelial NO synthase and modulates its subcellular localization, but the role of NOSTRIN in pathophysiology in vivo is unclear.

Objective:

We analyzed the consequences of deleting the NOSTRIN gene in endothelial cells on NO production and cardiovascular function in vivo using NOSTRIN knockout mice.

Methods and Results:

The levels of NO and cGMP were significantly reduced in mice with endothelial cell–specific deletion of the NOSTRIN gene resulting in diastolic heart dysfunction. In addition, systemic blood pressure was increased, and myograph measurements indicated an impaired acetylcholine-induced relaxation of isolated aortic rings and resistance arteries. We found that the muscarinic acetylcholine receptor subtype M3 (M3R) interacted directly with NOSTRIN, and the latter was necessary for correct localization of the M3R at the plasma membrane in murine aorta. In the absence of NOSTRIN, the acetylcholine-induced increase in intracellular Ca 2+ in primary endothelial cells was abolished. Moreover, the activating phosphorylation and Golgi translocation of endothelial NO synthase in response to the M3R agonist carbachol were diminished.

Conclusions:

NOSTRIN is crucial for the localization and function of the M3R and NO production. The loss of NOSTRIN in mice leads to endothelial dysfunction, increased blood pressure, and diastolic heart failure.

Cross-talk Between Nitrate-Nitrite-NO and NO Synthase Pathways in Control of Vascular NO Homeostasis

AIMS

Inorganic nitrate and nitrite from endogenous and dietary sources have emerged as alternative substrates for nitric oxide (NO) formation in addition to the classic L-arginine NO synthase (NOS)-dependent pathway. Here, we investigated a potential cross-talk between these two pathways in the regulation of vascular function.

RESULTS

Long-term dietary supplementation with sodium nitrate (0.1 and 1 mmol kg(-1) day(-1)) in rats caused a reversible dose-dependent reduction in phosphorylated endothelial NOS (eNOS) (Ser1177) in aorta and a concomitant increase in phosphorylation at Thr495. Moreover, eNOS-dependent vascular responses were attenuated in vessels harvested from nitrate-treated mice or when nitrite was acutely added to control vessels. The citrulline-to-arginine ratio in plasma, as a measure of eNOS activity, was reduced in nitrate-treated rodents. Telemetry measurements revealed that a low dietary nitrate dose reduced blood pressure, whereas a higher dose was associated with a paradoxical elevation. Finally, plasma cyclic guanosine monophosphate increased in mice that were treated with a low dietary nitrate dose and decreased with a higher dose.

INNOVATION AND CONCLUSIONS

These results demonstrate the existence of a cross-talk between the nitrate-nitrite-NO pathway and the NOS-dependent pathway in control of vascular NO homeostasis.

Salidroside improves endothelial function and alleviates atherosclerosis by activating a mitochondria-related AMPK/PI3K/Akt/eNOS pathway

Salidroside (SAL) is a phenylpropanoid glycoside isolated from the medicinal plant Rhodiola rosea. A recent study has reported that SAL can efficiently decrease atherosclerotic plaque formation in low-density lipoprotein receptor-deficient mice. This study was to investigate the molecular mechanism of antiatherogenic effects of SAL. Given the importance of endothelial nitric oxide synthase (eNOS) in atherosclerosis, we sought to elucidate whether SAL could stimulate eNOS activation and also to explore its upstream signaling pathway. Six-week old apoE(-/-) male mice were fed a high-fat diet for 8weeks and then were administered with SAL for another 8weeks. SAL significantly improved endothelial function associated with increasing eNOS activation, thus reduced the atherosclerotic lesion area. SAL increased eNOS-Ser1177 phosphorylation and decreased eNOS-Thr495 phosphorylation, indicative of eNOS activation in endothelium. The aortic sinus lesions in SAL treated mice displayed reduced inflammation. SAL significantly activated AMP-activated protein kinase (AMPK). Both AMPK inhibitor and AMPK small interfering RNA (siRNA) abolished SAL-induced Akt-Ser473 and eNOS-Ser1177 phosphorylation. In contrast, LY294002, the PI3k/Akt pathway inhibitor, abolished SAL-induced phosphorylation and expression of eNOS. High performance liquid chromatography (HPLC) analysis revealed that SAL decreased cellular ATP content and increased the cellular AMP/ATP ratio, which was associated with the activation of AMPK. SAL was found to decrease the mitochondrial membrane potential (ΔΨm), which is a likely consequence of reduced ATP production. The action of SAL to reduce atherosclerotic lesion formation may at least be attributed to its effect on improving endothelial function by promoting nitric oxide (NO) production, which was associated with mitochondrial depolarization and subsequent activation of the AMPK/PI3K/Akt/eNOS pathway. Taken together, our data described the effects of SAL on mitochondria, which played critical roles in improving endothelial function in atherosclerosis.

Long-lasting partnership between insulin resistance and endothelial dysfunction: role of metabolic memory

BACKGROUND AND PURPOSE

The persistence of deleterious effects of hyperglycaemia even after glucose normalization is referred to as 'metabolic memory'. However, similar persistent effects of the metabolic consequences of a high fat diet (HFD) have not been described.

EXPERIMENTAL APPROACH

Rats were given a normal pellet diet (NPD) or a HFD for 3 months. The animals from the HFD group were then returned to the NPD to observe the long-term effects of insulin resistance. Endothelial dysfunction was assessed by carbachol-mediated vasorelaxation and eNOS phosphorylation.

KEY RESULTS

As expected, HFD consumption resulted in insulin resistance and endothelial dysfunction. Phosphorylation of eNOS at S1177 was decreased in HFD rats, compared with that in the NPD group. Rats on 3 months of HFD showed glucose intolerance and impaired insulin sensitivity and were then switched back to NPD (REV group) . Levels of cholesterol and triglyceride, and adiposity returned to normal in REV rats. However, endothelium-dependent vascular responses to carbachol which were impaired in HFD rats, continued to be impaired in REV rats. Similarly, decreased eNOS phosphorylation after HFD was not improved after 1 or 6 months of REV.

CONCLUSIONS AND IMPLICATIONS

Our data indicate that returning to NPD did not improve the insulin sensitivity or the endothelial dysfunction induced by HFD. Although some biochemical parameters responsible for insulin resistance and endothelial dysfunction were normalized, molecular and vascular abnormalities, involving NO, persisted for several months, highlighting the long-lasting effects of metabolic memory.

Role of the bradykinin B2 receptor in a rat model of local heart irradiation

PURPOSE

Radiation-induced heart disease (RIHD) is a delayed effect of radiotherapy for cancers of the chest, such as breast, esophageal, and lung. Kinins are small peptides with cardioprotective properties. We previously used a rat model that lacks the precursor kininogen to demonstrate that kinins are involved in RIHD. Here, we examined the role of the kinin B2 receptor (B2R) in early radiation-induced signaling in the heart.

MATERIALS AND METHODS

Male Brown Norway rats received the B2R-selective antagonist HOE-140 (icatibant) via osmotic minipump from 5 days before until 4 weeks after 21 Gy local heart irradiation. At 4 weeks, signaling events were measured in left ventricular homogenates and nuclear extracts using western blotting and real-time polymerase chain reaction. Numbers of CD68-positive (monocytes/macrophages), CD2-positive (T-lymphocytes), and mast cells were measured using immunohistochemistry.

RESULTS

Radiation-induced c-Jun phosphorylation and nuclear translocation were enhanced by HOE-140. HOE-140 did not modify endothelial nitric oxide synthase (eNOS) phosphorylation or alter numbers of CD2-positive or mast cells, but enhanced CD68-positive cell counts in irradiated hearts.

CONCLUSIONS

B2R signaling may regulate monocyte/macrophage infiltration and c-Jun signals in the irradiated heart. Although eNOS is a main target for kinins, the B2R may not regulate eNOS phosphorylation in response to radiation.

Critical regulators of endothelial cell functions: for a change being alternative

SIGNIFICANCE

The endothelium regulates vessel dilation and constriction, balances hemostasis, and inhibits thrombosis. In addition, pro- and anti-angiogenic molecules orchestrate proliferation, survival, and migration of endothelial cells. Regulation of all these processes requires fine-tuning of signaling pathways, which can easily be tricked into running the opposite direction when exogenous or endogenous signals get out of hand. Surprisingly, some critical regulators of physiological endothelial functions can turn malicious by mere alternative splicing, leading to the expression of protein isoforms with opposite functions.

RECENT ADVANCES

While reviewing the evidence of alternative splicing on cellular physiology, it became evident that expression of splice factors and their activities are regulated by externally triggered signaling cascades. Furthermore, genome-wide identification of RNA-binding sites of splicing regulatory proteins now offer a glimpse into the splicing code responsible for alternative splicing of molecules regulating endothelial functions.

CRITICAL ISSUES

Due to the constantly growing number of transcript and protein isoforms, it will become more and more important to identify and characterize all transcripts and proteins regulating endothelial cell functions. One critical issue will be a non-ambiguous nomenclature to keep consistency throughout different laboratories.

FUTURE DIRECTIONS

RNA-deep sequencing focusing on exon-exon junction needs to more reliably identify alternative splicing events combined with functional analyses that will uncover more splice variants contributing to or inhibiting proper endothelial functions. In addition, understanding the signals mediating alternative splicing and its regulation might allow us to derive new strategies to preserve endothelial function by suppressing or upregulating specific protein isoforms. Antioxid. Redox Signal. 22, 1212-1229.

Sustained release nitrite therapy results in myocardial protection in a porcine model of metabolic syndrome with peripheral vascular disease

Metabolic syndrome (MetS) reduces endothelial nitric oxide (NO) bioavailability and exacerbates vascular dysfunction in patients with preexisting vascular diseases. Nitrite, a storage form of NO, can mediate vascular function during pathological conditions when endogenous NO is reduced. The aims of the present study were to characterize the effects of severe MetS and obesity on dyslipidemia, myocardial oxidative stress, and endothelial NO synthase (eNOS) regulation in the obese Ossabaw swine (OS) model and to examine the effects of a novel, sustained-release formulation of sodium nitrite (SR-nitrite) on coronary vascular reactivity and myocardial redox status in obese OS subjected to critical limb ischemia (CLI). After 6 mo of an atherogenic diet, obese OS displayed a MetS phenotype. Obese OS had decreased eNOS functionality and NO bioavailability. In addition, obese OS exhibited increased oxidative stress and a significant reduction in antioxidant enzymes. The efficacy of SR-nitrite therapy was examined in obese OS subjected to CLI. After 3 wk of treatment, SR-nitrite (80 mg · kg(-1) · day(-1) bid po) increased myocardial nitrite levels and eNOS function. Treatment with SR-nitrite reduced myocardial oxidative stress while increasing myocardial antioxidant capacity. Ex vivo assessment of vascular reactivity of left anterior descending coronary artery segments demonstrated marked improvement in vasoreactivity to sodium nitroprusside but not to substance P and bradykinin in SR-nitrite-treated animals compared with placebo-treated animals. In conclusion, in a clinically relevant, large-animal model of MetS and CLI, treatment with SR-nitrite enhanced myocardial NO bioavailability, attenuated oxidative stress, and improved ex vivo coronary artery vasorelaxation.

Amyloid β peptide-induced inhibition of endothelial nitric oxide production involves oxidative stress-mediated constitutive eNOS/HSP90 interaction and disruption of agonist-mediated Akt activation

BACKGROUND

Amyloid β (Aβ)-induced vascular dysfunction significantly contributes to the pathogenesis of Alzheimer's disease (AD). Aβ is known to impair endothelial nitric oxide synthase (eNOS) activity, thus inhibiting endothelial nitric oxide production (NO).

METHOD

In this study, we investigated Aβ-effects on heat shock protein 90 (HSP90) interaction with eNOS and Akt in cultured vascular endothelial cells and also explored the role of oxidative stress in this process.

RESULTS

Treatments of endothelial cells (EC) with Aβ promoted the constitutive association of HSP90 with eNOS but abrogated agonist (vascular endothelial growth factor (VEGF))-mediated HSP90 interaction with Akt. This effect resulted in blockade of agonist-mediated phosphorylation of Akt and eNOS at serine 1179. Furthermore, Aβ stimulated the production of reactive oxygen species in endothelial cells and concomitant treatments of the cells with the antioxidant N-acetyl-cysteine (NAC) prevented Aβ effects in promoting HSP90/eNOS interaction and rescued agonist-mediated Akt and eNOS phosphorylation.

CONCLUSIONS

The obtained data support the hypothesis that oxidative damage caused by Aβ results in altered interaction of HSP90 with Akt and eNOS, therefore promoting vascular dysfunction. This mechanism, by contributing to Aβ-mediated blockade of nitric oxide production, may significantly contribute to the cognitive impairment seen in AD patients.

Regulation of eNOS enzyme activity by posttranslational modification

The regulation of endothelial NO synthase (eNOS) employs multiple different cellular control mechanisms impinging on level and activity of the enzyme. This review aims at summarizing the current knowledge on the posttranslational modifications of eNOS, including acylation, nitrosylation, phosphorylation, acetylation, glycosylation and glutathionylation. Sites, mediators and impact on enzyme localization and activity of the single modifications will be discussed. Moreover, interdependence, cooperativity and competition between the different posttranslational modifications will be elaborated with special emphasis on the susceptibility of eNOS to metabolic cues.

Renal endothelial dysfunction in diabetic nephropathy

Endothelial dysfunction has been posited to play an important role in the pathogenesis of diabetic nephropathy (DN). Due to the heterogeneity of endothelial cells (ECs), it is difficult to generalize about endothelial responses to diabetic stimuli. At present, there are limited techniques fordirectly measuring EC function in vivo, so diagnosis of endothelial disorders still largely depends on indirect assessment of mediators arising from EC injury. In the kidney microcirculation, both afferent and efferent arteries, arterioles and glomerular endothelial cells (GEnC) have all been implicated as targets of diabetic injury. Both hyperglycemia per se, as well as the metabolic consequences of glucose dysregulation, are thought to lead to endothelial cell dysfunction. In this regard, endothelial nitric oxide synthase (eNOS) plays a central role in EC dysfunction. Impaired eNOS activity can occur at numerous levels, including enzyme uncoupling, post-translational modifications, internalization and decreased expression. Reduced nitric oxide (NO) bioavailability exacerbates oxidative stress, further promoting endothelial dysfunction and injury. The injured ECs may then function as active signal transducers of metabolic, hemodynamic and inflammatory factors that modify the function and morphology of the vessel wall and interact with adjacent cells, which may activate a cascade of inflammatory and proliferative and profibrotic responses in progressive DN. Both pharmacological approaches and potential regenerative therapies hold promise for restoration of impaired endothelial cells in diabetic nephropathy.

Association of six genetic variants with myocardial infarction

Although various genes that confer susceptibility to myocardial infarction (MI) have been identified for Caucasian populations in genome-wide association studies (GWAS), genetic variants related to this condition in Japanese individuals have not been identified definitively. The aim of the present study was to examine an association of MI in Japanese individuals with 29 polymorphisms identified as susceptibility loci for MI or coronary artery disease in Caucasian populations by meta-analyses of GWAS. The study subjects comprised 1,824 subjects with MI and 2,329 controls. Genotypes of the polymorphisms were determined by Luminex bead-based multiplex assay. To compensate for multiple comparisons, we adopted the criterion of a false discovery rate (FDR) of <0.05 for statistical significance for association. Comparisons of allele frequencies by the χ(2) test revealed that rs9369640 of the phosphatase and actin regulator 1 gene (PHACTR1, FDR=0.0007), rs4977574 of the CDKN2B antisense RNA 1 gene (CDKN2B-AS1, FDR=0.0038), rs264 of the lipoprotein lipase gene (LPL, FDR=0.0061), rs599839 of the proline/serine-rich coiled-coil 1 gene (PSRC1, FDR=0.0118), rs9319428 of the fms-related tyrosine kinase 1 gene (FLT1, FDR=0.0118) and rs12413409 of the cyclin and CBS domain divalent metal cation transport mediator 2 gene (CNNM2, FDR=0.0300) were significantly associated with MI. Multivariate logistic regression analysis with adjustment for covariates revealed that rs9369640 (P=0.0005; odds ratio, 0.89), rs4977574 (P=0.0001; odds ratio, 1.50), rs264 (P=0.0405; odds ratio, 0.85), rs599839 (P=0.0003; odds ratio, 0.68), rs9319428 (P=0.0155; odds ratio, 1.20) and rs12413409 (P=0.0076; odds ratio, 0.66) were significantly (P<0.05) associated with MI. PHACTR1, CDKN2B-AS1, LPL, PSRC1, FLT1 and CNNM2 may thus be susceptibility loci for MI in Japanese individuals.

Sprint interval and moderate-intensity continuous training have equal benefits on aerobic capacity, insulin sensitivity, muscle capillarisation and endothelial eNOS/NAD(P)Hoxidase protein ratio in obese men

KEY POINTS

Skeletal muscle capillary density and vasoreactivity are reduced in obesity, due to reduced nitric oxide bioavailability. Sprint interval training (SIT) has been proposed as a time efficient alternative to moderate-intensity continuous training (MICT), but its effect on the skeletal muscle microvasculature has not been studied in obese individuals. We observed that SIT and MICT led to equal increases in capillarisation and endothelial eNOS content, while reducing endothelial NOX2 content in microvessels of young obese men. We conclude that SIT is equally effective at improving skeletal muscle capillarisation and endothelial enzyme balance, while being a time efficient alternative to traditional MICT.

ABSTRACT

Sprint interval training (SIT) has been proposed as a time efficient alternative to moderate-intensity continuous training (MICT), leading to similar improvements in skeletal muscle capillary density and microvascular function in young healthy humans. In this study we made the first comparisons of the muscle microvascular response to SIT and MICT in an obese population. Sixteen young obese men (age 25 ± 1 years, BMI 34.8 ± 0.9 kg m(-2) ) were randomly assigned to 4 weeks of MICT (40-60 min cycling at ∼65% V̇O2 peak , 5 times per week) or constant load SIT (4-7 constant workload intervals of 200% Wmax 3 times per week). Muscle biopsies were taken before and after training from the m. vastus lateralis to measure muscle microvascular endothelial eNOS content, eNOS serine(1177) phosphorylation, NOX2 content and capillarisation using quantitative immunofluorescence microscopy. Maximal aerobic capacity (V̇O2 peak ), whole body insulin sensitivity and arterial stiffness were also assessed. SIT and MICT increased skeletal muscle microvascular eNOS content and eNOS ser(1177) phosphorylation in terminal arterioles and capillaries (P < 0.05), but the latter effect was eliminated when normalised to eNOS content (P = 0.217). SIT and MICT also reduced microvascular endothelial NOX2 content (P < 0.05) and both increased capillary density and capillary-fibre perimeter exchange index (P < 0.05). In parallel, SIT and MICT increased V̇O2 peak (P < 0.05) and whole body insulin sensitivity (P < 0.05), and reduced central artery stiffness (P < 0.05). As no significant differences were observed between SIT and MICT it is concluded that SIT is a time efficient alternative to MICT to improve aerobic capacity, insulin sensitivity and muscle capillarisation and endothelial eNOS/NAD(P)Hoxidase protein ratio in young obese men.

Transient carotid ischemia as a remote conditioning stimulus for myocardial protection in anesthetized rabbits: Insights into intracellular signaling

BACKGROUND

We investigated the effectiveness of perconditioning (Perc) applied at different time points along with the role of RISK, SAFE, STAT5 and eNOS pathways.

METHODS AND RESULTS

Anesthetized rabbits were subjected to 30-min ischemia/3-hour reperfusion. Perc, consisted of 4 cycles of 1-min ischemia/reperfusion, was applied in the carotid artery at different time points. Perc was started and ended during ischemia, started during ischemia and ended at the beginning of reperfusion, started at the end of ischemia and ended at reperfusion and started and ended during reperfusion. The PI3K inhibitor wortmannin, or the JAK-2 inhibitor AG490, was also applied and the infarct size was assessed. In another series assigned to the previous groups, the phosphorylation of Akt, PI3K, ERKs1/2, GSK3β, STAT3, and STAT5 was evaluated. All Perc groups had smaller infarction compared to those without Perc, independently of PI3K or JAK-2 inhibition. STAT5 was the only molecule that was phosphorylated in parallel with cardioprotection. Since Src and angiotensin II mediate the STAT5 pathway, we administered the Scr inhibitor PP1 and the angiotensin II receptor antagonist valsartan. PP1 and valsartan prevented STAT5 phosphorylation, but did not abrogate the effect of Perc. Furthermore, the NOS inhibitor L-NAME was administered and abrogated the infarct size limiting effect of Perc. In parallel, the expression of cleaved caspase-3 was elevated only in the control and Perc-A-L-NAME groups.

CONCLUSION

Perc reduces infarction independently of RISK, SAFE and STAT5 pathways. Src kinase and angiotensin II play a predominant role in STAT5 activation. eNOS may protect the myocardium through inhibition of apoptosis.

The volatile oil of Nardostachyos Radix et Rhizoma induces endothelial nitric oxide synthase activity in HUVEC cells

Nardostahyos Radix et Rhizoma (NRR; the root and rhizome of Nardostachys jatamansi DC.) is a widely used medicinal herb. Historically, NRR is being used for the treatment of cardiovascular and neurological diseases. To search for active ingredients of NRR, we investigated the vascular benefit of NRR volatile oil in (i) the vasodilation in rat aorta ring, and (ii) the release of nitric oxide (NO) and the phosphorylation of endothelial NO synthase (eNOS) in cultured human umbilical vein endothelial cells (HUVECs). By measuring the fluorescence signal in cultures, application of NRR volatile oil resulted in a rapid activation of NO release as well as the phosphorylation of eNOS: both inductions were markedly reduced by L-NAME. In parallel, the phosphorylation level of Akt kinase was markedly increased by the oil treatment, which was partially attenuated by PI3K/Akt inhibitor LY294002. This inhibitor also blocked the NRR-induced NO production and eNOS phosphorylation. In HUVECs, application of NRR volatile oil elevated the intracellular Ca(2+) level, and BAPTA-AM, a Ca(2+) chelator, reduced the Ca(2+) surge: the blockage were also applied to NRR-induced eNOS phosphorylation and NO production. These findings suggested the volatile oil of NRR was the major ingredient in triggering the vascular dilatation, and which was mediated via the NO production.

Molecular physiopathology of obesity-related diseases: multi-organ integration by GRK2

Obesity is a worldwide problem that has reached epidemic proportions both in developed and developing countries. The excessive accumulation of fat poses a risk to health since it favours the development of metabolic alterations including insulin resistance and tissue inflammation, which further contribute to the progress of the complex pathological scenario observed in the obese. In this review we put together the different outcomes of fat accumulation and insulin resistance in the main insulin-responsive tissues, and discuss the role of some of the key molecular routes that control disease progression both in an organ-specific and also in a more systemic manner. In particular, we focus on the importance of studying the integrated regulation of different organs and pathways that contribute to the global pathophysiology of this condition with a specific emphasis on the role of emerging key molecular nodes such as the G protein-coupled receptor kinase 2 (GRK2) signalling hub.

Alpha-lipoic acid activates eNOS through activation of PI3-kinase/Akt signaling pathway

BACKGROUND

Lipoic acid (LA) exerts therapeutic effects on cardiovascular diseases. However, the mechanisms underlying these therapeutic effects remain elusive. Endothelial nitric oxide synthase (eNOS) plays a critical role in cardiovascular homeostasis. LA was shown to potently activate PI3-kinase/Akt pathway, and the latter is critical in the regulation of eNOS activity. In the present study, we test the hypothesis that LA improves endothelial function through PI3-kinase/Akt-mediated eNOS activation.

METHODS AND RESULTS

Western blot analysis showed that LA time- and dose-dependently induced phosphorylation of Akt and eNOS in human umbilical vein endothelial cells (HUVECs). Both PI3-kinase and Akt inhibitors abolished LA-induced eNOS phosphorylation, indicating that LA induces eNOS phosphorylation through the PI3-kinase/Akt pathway. This increase in eNOS phosphorylation was paralleled by an increase in NO release by HUVECs, supporting its relevance in eNOS activity regulation. Myograph analysis revealed that LA relaxed phenylephrine-induced contraction. Endothelium removal and NOS inhibition by L-NAME abolished this vasodilator action of LA, and Akt but not AMPK inhibition significantly reduced the vasodilator action of LA, indicating that it is mediated by PI3-kinase/Akt pathway-dependent activation of eNOS. Consistent with in vitro results, intraperitoneal injection with LA significantly increased plasma nitrite and nitrate levels in C57Bl/6j mice.

CONCLUSIONS

LA activates eNOS through a PI3-kinase/Akt signaling pathway-dependent mechanism, offering a potential molecular basis for the therapeutic effects of LA on cardiovascular diseases.

Mechanistic analysis of nonoxygenated hypothermic machine perfusion's protection on warm ischemic kidney uncovers greater eNOS phosphorylation and vasodilation

Protection of endothelial cell function may explain the benefits of nonoxygenated hypothermic machine perfusion (MP) for marginal kidney preservation. However, this hypothesis remains to be tested with a preclinical model. We postulated that MP protects the nitric oxide (NO) signaling pathway, altered by static cold storage (CS), and improves renal circulation recovery compared to CS. The endothelium releases the vasodilator NO in response to flow via either increased endothelial NO synthase (eNOS) expression (KLF2-dependent) or activation of eNOS by phosphorylation (via Akt, PKA or AMPK). Using a porcine model of kidney transplantation, including 1 h of warm ischemia and preserved 24 h by CS or MP (n=5), we reported that MP did not alter the cortical levels of KLF2 and eNOS at the end of preservation, but significantly increased eNOS activating phosphorylation compared to CS. eNOS phosphorylation appeared AMPK-dependent and was concomitant to an increased NO-dependent vasodilation of renal arteries measured, ex situ, at the end of preservation. In vivo, laser Doppler showed that cortical microcirculation was improved at reperfusion in MP kidneys. In conclusion, we demonstrate for the first time, in a large-animal model, that MP protects the NO signaling pathway, confirming the value of MP for marginal kidney preservation.

Valproic acid increases NO production via the SH-PTP1-CDK5-eNOS-Ser(116) signaling cascade in endothelial cells and mice

Valproic acid (VPA) with its inhibitory activity of histone deacetylase has been used in the treatment of epilepsy and bipolar disorder associated with cerebrovascular dysfunction. Because nitric oxide (NO) produced by endothelial NO synthase (eNOS) plays a role in the maintenance of vascular function, NO is likely to mediate VPA׳s drug effect, but its effect on NO production remains controversial. We investigated whether and how VPA regulates NO production in bovine aortic endothelial cells (BAECs) and mice. VPA increased NO production in BAECs, which was accompanied by a decrease in phosphorylation of eNOS at serine 116 (eNOS-Ser(116)) and cyclin-dependent kinase 5 at tyrosine 15 (CDK5-Tyr(15)). Ectopic expression of p25, a CDK5 activator, restored the VPA-inhibited eNOS-Ser(116) phosphorylation. In silico analysis revealed that the CDK5-Tyr(15) residue might be a substrate for SH2 domain-containing protein tyrosine phosphatase 1 (SH-PTP1), and CDK5 actually interacted with SH-PTP1. VPA increased SH-PTP1 expression and its activity. Stibogluconate, a specific SH-PTP1 inhibitor, reversed the VPA-inhibited phosphorylation of CDK5-Tyr(15) and eNOS-Ser(116). Knockdown of SH-PTP1 using small interfering RNA also reversed all the observed effects of VPA. Finally, both serum NO level and acetylcholine-induced aortic relaxation increased in VPA-medicated male mice. These increases were accompanied by increased SH-PTP1 expression and decreased phosphorylation of CDK5-Tyr(15) and eNOS-Ser(116) in mouse aortas. In conclusion, VPA increases NO production by inhibiting the CDK5-Tyr(15)-eNOS-Ser(116) phosphorylation axis; this process is mediated by SH-PTP1. VPA may be useful in the treatment of NO-related cerebrocardiovascular diseases.

Association of a transcription factor 21 gene polymorphism with hypertension

Various loci and genes that confer susceptibility to coronary artery disease (CAD) have been identified mainly in Caucasian populations by genome-wide association studies (GWASs). As hypertension is a major risk factor for CAD, certain polymorphisms may contribute to the genetic susceptibility to CAD through affecting the predisposition to hypertension. The aim of the present study was to examine a possible association of hypertension with 29 single-nucleotide polymorphisms (SNPs) previously identified by meta-analyses of GWASs as susceptibility loci for CAD. Study subjects comprised of 5,460 individuals (3,348 subjects with hypertension and 2,112 controls). The genotypes of SNPs were determined by the multiplex bead-based Luminex assay. The χ² test revealed that genotype distributions and allele frequencies for rs12190287 of the transcription factor 21 gene (TCF21) and rs1122608 of the SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a, member 4 gene (SMARCA4) were significantly (P<0.05) associated with hypertension. Allele frequencies for rs9369640 of the phosphatase and actin regulator 1 gene (PHACTR1) and genotype distributions for rs599839 of the proline/serine-rich coiled-coil 1 gene (PSRC1) were also significantly associated with hypertension. Multivariable logistic regression analysis with adjustment for age, gender, body mass index and smoking status revealed that rs12190287 of TCF21 (P=0.0014; recessive model; odds ratio, 1.21) was significantly associated with hypertension, and the C allele represented a risk factor for this condition. Similar analyses revealed that rs1122608 of SMARCA4 (P=0.0305; dominant model; odds ratio, 0.86), rs9369640 of PHACTR1 (P=0.0119; dominant model; odds ratio, 0.82) and rs599839 of PSRC1 (P=0.0248; dominant model; odds ratio, 0.84) were also related to hypertension, with the minor T, C and G alleles, respectively, being protective against this condition. Thus, the present results indicate that rs12190287 (G→C) of TCF21 is a susceptibility locus for hypertension.

A novel ACE2 activator reduces monocrotaline-induced pulmonary hypertension by suppressing the JAK/STAT and TGF-β cascades with restored caveolin-1 expression

INTRODUCTION

Pulmonary hypertension (PH) is characterized by increased pressure in the pulmonary artery and right ventricular hypertrophy (RVH). Recently, angiotensin-converting enzyme 2 (ACE2), which converts angiotensin (Ang) II into Ang-(1-7), was shown to inhibit experimental PH. Here we identified a novel ACE2 activator and investigated how the compound reduced monocrotaline (MCT)-induced PH.

METHODS

To induce PH, Sprague-Dawley rats were injected subcutaneously with MCT, followed by the continuous administration of NCP-2454, an ACE2 activator, using osmotic pumps. Pulmonary arterial compliance was monitored every week until 4 weeks post-injection (wpi). RVH and lung remodeling was evaluated using lung tissue at 4 wpi.

RESULTS

NCP-2454 upregulated the production of Ang-(1-7) when incubated with ACE2 and Ang II. Notably, a continuous infusion of NCP-2454 significantly improved pulmonary arterial compliance, right ventricular systolic pressure, and RVH in MCT-treated rats. Interestingly, NCP-2454 increased the relative expression of ACE2 and MAS mRNA in lung tissue, especially in MCT-treated rats. In addition, the compound inhibited the MCT-induced overexpression of transforming growth factor β, phosphorylation of signal transducer and activator of transcription-3 (STAT3), and interleukin-6 production. The compound also restored the expression of caveolin-1 (Cav-1), which negatively regulates the Janus kinase-STAT signaling cascade.

CONCLUSIONS

NCP-2454 prevented MCT-induced PH by suppressing intracellular inflammatory cascades, an upstream molecular change of which is the disruption of Cav-1 expression.

Endothelial nitric oxide synthase is regulated by ERK phosphorylation at Ser602

eNOS (endothelial nitric oxide synthase) contains a MAPK (mitogen-activated protein kinase)-binding site associated with a major eNOS control element. Purified ERK (extracellular-signal-regulated kinase) phosphorylates eNOS with a stoichiometry of 2–3 phosphates per eNOS monomer. Phosphorylation decreases NO synthesis and cytochrome c reductase activity. Three sites of phosphorylation were detected by MS. All sites matched the SP and TP MAPK (mitogen-activated protein kinase) phosphorylation motif. Ser⁶⁰² lies at the N-terminal edge of the 42-residue eNOS AI (autoinhibitory) element. The pentabasic MAPK-binding site lies at the opposite end of the AI, and other critical regulatory features are between them. Thr⁴⁶ and Ser⁵⁸ are located in a flexible region associated with the N terminus of the oxygenase domain. In contrast with PKC (protein kinase C), phosphorylation by ERK did not significantly interfere with CaM (calmodulin) binding as analysed by optical biosensing. Instead, ERK phosphorylation favours a state in which FMN and FAD are in close association and prevents conformational changes that expose reduced FMN to acceptors. The close associations between control sites in a few regions of the molecule suggest that control of signal generation is modulated by multiple inputs interacting directly on the surface of eNOS via overlapping binding domains and tightly grouped targets.

17-β Oestradiol prevents cardiovascular dysfunction in post-menopausal metabolic syndrome by affecting SIRT1/AMPK/H3 acetylation

BACKGROUND AND PURPOSE

Oestrogen therapy is known to induce cardioprotection in post-menopausal metabolic syndrome (PMS). Hence, we investigated the effect of 17-β oestradiol (E2) on functional responses to angiotensin II and cardiovascular dysfunction in a rat model of PMS.

EXPERIMENTAL APPROACH

PMS was induced in ovariectomized rats by feeding a high-fat diet for 10 weeks. Isometric tension responses of aortic rings to angiotensin II were recorded using an isometric force transducer. TUNEL assay and immunoblotting was performed to assess apoptosis and protein expression respectively in PMS.

KEY RESULTS

Endothelial dysfunction in PMS was characterized by enhanced angiotensin II-induced contractile responses and impaired endothelial dependent vasodilatation. This was associated with an increased protein expression of AT1 receptors in the aorta and heart in PMS. PMS induced cardiac apoptosis by activating Bax and PARP protein expression. These changes were associated with a down-regulation in the expression of silent information regulation 2 homologue (SIRT1)/P-AMP-activated PK (AMPK) and increased H3 acetylation in aorta and heart. E2 partially suppressed angiotensin II-induced contractions, restored the protein expression of SIRT1/P-AMPK and suppressed H3 acetylation. The role of SIRT1/AMPK was further highlighted by administration of sirtinol and compound C (ex vivo), which enhanced angiotensin II contractile responses and ablated the protective effect of E2 on PMS.

CONCLUSION AND IMPLICATIONS

Our results provide novel mechanisms for PMS-induced cardiovascular dysfunction involving SIRT1/AMPK/ histone H3 acetylation, which was prevented by E2. The study suggests that therapies targeting SIRT1/AMPK/epigenetic modifications may be beneficial in reducing the risk of cardiovascular disorders.

Protection after stroke: cellular effectors of neurovascular unit integrity

Neurological disorders are prevalent worldwide. Cerebrovascular diseases (CVDs), which account for 55% of all neurological diseases, are the leading cause of permanent disability, cognitive and motor disorders and dementia. Stroke affects the function and structure of blood-brain barrier, the loss of cerebral blood flow regulation, oxidative stress, inflammation and the loss of neural connections. Currently, no gold standard treatments are available outside the acute therapeutic window to improve outcome in stroke patients. Some promising candidate targets have been identified for the improvement of long-term recovery after stroke, such as Rho GTPases, cell adhesion proteins, kinases, and phosphatases. Previous studies by our lab indicated that Rho GTPases (Rac and RhoA) are involved in both tissue damage and survival, as these proteins are essential for the morphology and movement of neurons, astrocytes and endothelial cells, thus playing a critical role in the balance between cell survival and death. Treatment with a pharmacological inhibitor of RhoA/ROCK blocks the activation of the neurodegeneration cascade. In addition, Rac and synaptic adhesion proteins (p120 catenin and N-catenin) play critical roles in protection against cerebral infarction and in recovery by supporting the neurovascular unit and cytoskeletal remodeling activity to maintain the integrity of the brain parenchyma. Interestingly, neuroprotective agents, such as atorvastatin, and CDK5 silencing after cerebral ischemia and in a glutamate-induced excitotoxicity model may act on the same cellular effectors to recover neurovascular unit integrity. Therefore, future efforts must focus on individually targeting the structural and functional roles of each effector of neurovascular unit and the interactions in neural and non-neural cells in the post-ischemic brain and address how to promote the recovery or prevent the loss of homeostasis in the short, medium and long term.

Association between phosphatase related gene variants and coronary artery disease: case-control study and meta-analysis

Recent studies showed that the serum alkaline phosphatase is an independent predictor of the coronary artery disease (CAD). In this work, we aimed to summarize the association between three phosphatase related single nucleotide polymorphisms (rs12526453, rs11066301 and rs3828329) and the risk of CAD in Han Chinese. Our results showed that the rs3828329 of the ACP1 gene was closely related to the risk of CAD in Han Chinese (OR = 1.45, p = 0.0006). This significant association of rs3828329 with CAD was only found in the females (Additive model: OR = 1.80, p = 0.001; dominant model: OR = 1.69, p = 0.03; recessive model: OR = 1.96, p = 0.0008). Moreover, rs3828329 was likely to exert its effect in females aged 65 years and older (OR = 2.27, p = 0.001). Further meta-analyses showed that the rs12526453 of PHACTR11 gene (OR = 1.14, p < 0.0001, random-effect method) and the rs11066301 of PTPN11 gene (OR = 1.15, p < 0.0001, fixed-effects method) were associated with CAD risk in multiple populations. Our results showed that the polymorphisms rs12526453 and rs11066301 are significantly associated with the CAD risk in multiple populations. The rs3828329 of ACP1 gene is also a risk factor of CAD in Han Chinese females aged 65 years and older.

The N-terminal portion of autoinhibitory element modulates human endothelial nitric-oxide synthase activity through coordinated controls of phosphorylation at Thr495 and Ser1177

NO production catalysed by eNOS (endothelial nitric-oxide synthase) plays an important role in the cardiovascular system. A variety of agonists activate eNOS through the Ser1177 phosphorylation concomitant with Thr495 dephosphorylation, resulting in increased ·NO production with a basal level of calcium. To date, the underlying mechanism remains unclear. We have previously demonstrated that perturbation of the AIE (autoinhibitory element) in the FMN-binding subdomain can also lead to eNOS activation with a basal level of calcium, implying that the AIE might regulate eNOS activation through modulating phosphorylation at Thr495 and Ser1177. Here we generated stable clones in HEK-293 (human embryonic kidney 293) cells with a series of deletion mutants in both the AIE (Δ594-604, Δ605-612 and Δ626-634) and the C-terminal tail (Δ14; deletion of 1164-1177). The expression of Δ594-604 and Δ605-612 mutants in non-stimulated HEK-293 cells substantially increased nitrate/nitrite release into the culture medium; the other two mutants, Δ626-634 and Δ1164-1177, displayed no significant difference when compared with WTeNOS (wild-type eNOS). Intriguingly, mutant Δ594-604 showed close correlation between Ser1177 phosphorylation and Thr495 dephosphorylation, and NO production. Our results have indicated that N-terminal portion of AIE (residues 594-604) regulates eNOS activity through coordinated phosphorylation on Ser1177 and Thr495.

Echinocystic acid, isolated from Gleditsia sinensis fruit, protects endothelial progenitor cells from damage caused by oxLDL via the Akt/eNOS pathway

AIMS

Our previous studies revealed that echinocystic acid (EA) showed obvious attenuation of atherosclerosis in rabbits fed a high-fat diet. However, the underlying mechanisms remain to be elucidated. Considering the importance of endothelial progenitor cells (EPCs) in atherosclerosis, we hypothesise that EPCs may be one of the targets for the anti-atherosclerotic potential of EA.

MAIN METHODS

After in vitro cultivation, EPCs were exposed to 100 μg/mL of oxidised low-density lipoprotein (oxLDL) and incubated with or without EA (5 and 20 μM) for 48 h. An additional two groups of EPCs (oxLDL+20 μM EA) were pre-treated with either wortmannin, an inhibitor of the phosphoinositide 3-kinase (PI3K) pathway, or nitro-l-arginine methyl ester (l-NAME), an endothelial nitric oxide synthase (eNOS)-specific inhibitor. Assessment of EPC apoptosis, adhesion, migration, and nitric oxide (NO) release was performed using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) staining, cell counting, caspase-3 activity assay, transwell chamber assay, and Griess reagent, respectively. The protein expression of protein kinase B (Akt) and eNOS was detected using Western blot.

KEY FINDINGS

Treatment of EPCs with oxLDL induced significant apoptosis and impaired adhesion, migration, and NO production. The deleterious effects of oxLDL on EPCs were attenuated by EA. However, when EPCs were pre-treated with wortmannin or l-NAME, the effects of EA were abrogated. Additionally, oxLDL significantly down-regulated eNOS protein expression as well as repression of eNOS and Akt phosphorylation.

SIGNIFICANCE

The inhibitory effect of oxLDL on Akt/eNOS phosphorylation was attenuated by EA. Taken together, the results indicate that EA protects EPCs from damage caused by oxLDL via the Akt/eNOS pathway.

Upregulation of caveolin-1 contributes to aggravated high-salt diet-induced endothelial dysfunction and hypertension in type 1 diabetic rats

AIMS

Endothelial dysfunction and hypertension is more common in individuals with diabetes than in the general population. This study was aimed to investigate the underlying mechanisms responsible for endothelial dysfunction of type 1 diabetic rats fed with high-salt diet.

MAIN METHODS

Type 1 diabetes (DM) was induced by intraperitoneal injection of streptozotocin (70 mg·kg(-1)). Normal or diabetic rats were randomly fed high-salt food (HS, 8% NaCl) or standard food (CON) for 6 weeks.

KEY FINDINGS

Both HS (143±10 mmHg) and DM+HS (169±11 mmHg) groups displayed significantly higher systolic blood pressure than those in the CON group (112±12 mmHg, P<0.01). DM+HS rats exhibited more pronounced impairment of vasorelaxation to acetylcholine and insulin compared with either DM or HS. Akt/endothelial nitric oxide synthase (eNOS) phosphorylation levels and nitric oxide (NO) concentration in DM+HS were significantly lower than in DM. The levels of caveolin-1 (cav-1) in DM+HS were significantly higher than that in DM and HS. Co-immunoprecipitation results showed increased interaction between cav-1 and eNOS in the DM+HS group. In the presence of cav-1 small interfering RNA (siRNA), eNOS phosphorylations in human umbilical vein endothelial cells (HUVEC) were significantly increased compared with control siRNA. Cav-1 was slightly but not significantly lower in HUVEC cultured with high glucose and high-salt buffer solution and pretreated with wortmannin or l-nitro-arginine methyl ester.

SIGNIFICANCE

Impaired endothelial Akt activation and increased cav-1 expression and resultant decreased eNOS activation contributes to aggravated high-salt diet-induced endothelial dysfunction and hypertension in DM rats.

Resveratrol ameliorates low shear stress‑induced oxidative stress by suppressing ERK/eNOS‑Thr495 in endothelial cells

Fluid shear stress has been revealed to differentially regulate endothelial nitric oxide synthase (eNOS) distribution in vessels. eNOS, a key enzyme in controlling nitric oxide (NO) release, has a crucial role in mediating oxidative stress, and resveratrol (RSV)‑mediated eNOS also attenuates oxidative damage and suppresses endothelial dysfunction. To observe the protective effect of RSV on low shear stress (LSS)‑induced oxidative damage and the potential mechanisms involved, a parallel‑plate flow chamber, which imposed a low level of stress of 2 dynes/cm2 to cells, was employed. Reactive oxygen species (ROS), NO and apoptotic cells were examined in LSS‑treated endothelial cells (ECs) with or without RSV. Western blot analysis was used to examine LSS‑regulated eNOS‑Ser1177, Thr495 and Ser633, which were tightly associated with NO release. To further determine the underlying signaling pathways involved, extracellular signal‑regulated kinase (ERK), a possible upstream target of eNOS‑Thr495, was investigated, followed by examination of eNOS‑Thr495 in ERK‑inhibited cells. Additionally, eNOS mRNA expression levels were analyzed in cells challenged with LSS. The results revealed that RSV markedly decreased LSS‑induced oxidative damage in ECs. Furthermore, eNOS‑Ser1177 and Thr495 as well as phospho‑ERK were time‑dependently activated by LSS. The ERK inhibitor deactivated eNOS‑Thr495, which was accompanied by increased intracellular superoxide dismutase (SOD) levels. Of note, the activation effect of LSS on ERK/eNOS was markedly eliminated by RSV. In conclusion, RSV exerts antioxidant effects by suppressing LSS-activated ERK/eNOS and may provide a potential therapeutic target for atherosclerosis.

Urocortin 2 stimulates nitric oxide production in ventricular myocytes via Akt- and PKA-mediated phosphorylation of eNOS at serine 1177

Urocortin 2 (Ucn2) is a cardioactive peptide exhibiting beneficial effects in normal and failing heart. In cardiomyocytes, it elicits cAMP- and Ca(2+)-dependent positive inotropic and lusitropic effects. We tested the hypothesis that, in addition, Ucn2 activates cardiac nitric oxide (NO) signaling and elucidated the underlying signaling pathways and mechanisms. In isolated rabbit ventricular myocytes, Ucn2 caused concentration- and time-dependent increases in phosphorylation of Akt (Ser473, Thr308), endothelial NO synthase (eNOS) (Ser1177), and ERK1/2 (Thr202/Tyr204). ERK1/2 phosphorylation, but not Akt and eNOS phosphorylation, was suppressed by inhibition of MEK1/2. Increased Akt phosphorylation resulted in increased Akt kinase activity and was mediated by corticotropin-releasing factor 2 (CRF2) receptors (astressin-2B sensitive). Inhibition of phosphatidylinositol 3-kinase (PI3K) diminished both Akt as well as eNOS phosphorylation mediated by Ucn2. Inhibition of protein kinase A (PKA) reduced Ucn2-induced phosphorylation of eNOS but did not affect the increase in phosphorylation of Akt. Conversely, direct receptor-independent elevation of cAMP via forskolin increased phosphorylation of eNOS but not of Akt. Ucn2 increased intracellular NO concentration ([NO]i), [cGMP], [cAMP], and cell shortening. Inhibition of eNOS suppressed the increases in [NO]i and cell shortening. When both PI3K-Akt and cAMP-PKA signaling were inhibited, the Ucn2-induced increases in [NO]i and cell shortening were attenuated. Thus, in rabbit ventricular myocytes, Ucn2 causes activation of cAMP-PKA, PI3K-Akt, and MEK1/2-ERK1/2 signaling. The MEK1/2-ERK1/2 pathway is not required for stimulation of NO signaling in these cells. The other two pathways, cAMP-PKA and PI3K-Akt, converge on eNOS phosphorylation at Ser1177 and result in pronounced and sustained cellular NO production with subsequent stimulation of cGMP signaling.

Endothelial caveolar subcellular domain regulation of endothelial nitric oxide synthase

Complex regulatory processes alter the activity of endothelial nitric oxide synthase (eNOS) leading to nitric oxide (NO) production by endothelial cells under various physiological states. These complex processes require specific subcellular eNOS partitioning between plasma membrane caveolar domains and non-caveolar compartments. Translocation of eNOS from the plasma membrane to intracellular compartments is important for eNOS activation and subsequent NO biosynthesis. We present data reviewing and interpreting information regarding: (i) the coupling of endothelial plasma membrane receptor systems in the caveolar structure relative to eNOS trafficking; (ii) how eNOS trafficking relates to specific protein-protein interactions for inactivation and activation of eNOS; and (iii) how these complex mechanisms confer specific subcellular location relative to eNOS multisite phosphorylation and signalling. Dysfunction in the regulation of eNOS activation may contribute to several disease states, in particular gestational endothelial abnormalities (pre-eclampsia, gestational diabetes etc.), that have life-long deleterious health consequences that predispose the offspring to develop hypertensive disease, Type 2 diabetes and adiposity.

Perivascular adipose tissue inhibits endothelial function of rat aortas via caveolin-1

Perivascular adipose tissue (PVAT)-derived factors have been proposed to play an important role in the pathogenesis of atherosclerosis. Caveolin-1 (Cav-1), occupying the calcium/calmodulin binding site of endothelial NO synthase (eNOS) and then inhibiting nitric oxide (NO) production, is also involved in the development of atherosclerosis. Thus, we investigated whether PVAT regulated vascular tone via Cav-1 and/or endothelial NO pathways. Isometric tension studies were carried out in isolated thoracic aortas from Wistar rats in the presence and absence of PVAT. Concentration-response curves of phenylephrine, acetylcholine, and sodium nitroprusside were illustrated to examine the vascular reactivity and endothelial function. The protein expressions of eNOS and Cav-1 were also examined in aortic homogenates. Our results demonstrated that PVAT significantly enhanced vasoconstriction and inhibited vasodilatation via endothelium-dependent mechanism. The aortic NO production was diminished after PVAT treatment, whereas protein expression and activity of eNOS were not significantly affected. In addition, Cav-1 protein expression was significantly increased in aortas with PVAT transfer. Furthermore, a caveolae depleter methyl-β-cyclodextrin abolished the effect of PVAT on the enhancement of vasoconstriction, and reversed the impairment of aortic NO production. In conclusion, unknown factor(s) released from PVAT may inhibit endothelial NO production and induce vasocontraction via an increase of Cav-1 protein expression.

β3-Adrenoreceptor stimulation protects against myocardial infarction injury via eNOS and nNOS activation

β3-adrenergic receptor (AR) and the downstream signaling, nitric oxide synthase (NOS) isoforms, have been emerged as novel modulators of heart function and even potential therapeutic targets for cardiovascular diseases. However, it is not known whether β3-AR plays cardioprotective effects against myocardial infarction (MI) injury. Therefore, the present study was designed to determine the effects of β3-AR on MI injury and to elucidate the underlying mechanism. MI model was constructed by left anterior descending (LAD) artery ligation. Animals were administrated with β3-AR agonist BRL37344 (BRL) or β3-AR inhibitor SR59230A (SR) respectively at 0.1 mg/kg/hour one day after MI operation. The scar area, cardiac function and the apoptosis of myocardial were assessed by Masson's trichrome stain, echocardiography and TUNEL assay respectively. Western blot analysis was performed to elucidate the expressions of target proteins. β3-AR activation with BRL administration significantly attenuated fibrosis and decreased scar area after MI. Moreover, BRL also preserved heart function, and reduced the apoptosis of cardiomyocyte induced by MI. Furthermore, BRL treatment altered the phosphorylation status of endothelial NOS (eNOS) and increased the expression of neuronal NOS (nNOS). These results suggested that β3-AR stimulation has a substantial effect on recovery of heart function. In addition, the activations of both eNOS and nNOS may be associated with the cardiac protective effects of β3-AR.

[Regulation of uterine blood flow. II. Functions of estrogen and estrogen receptor α/β in genomic and non-genomic actions of the uterine endothelium]

Pregnancy is marked by changes and cardiovascular adaptations that are important for the maintenance and growth of the placenta and fetus. During this period, the uterine vascular adaptations manifest changes that can be classified as short or long term and they related to adaptations for vasodilation, angiogenic or remodeling. Estrogen and the classical estrogen receptors (ERs), ER-α and ER-β, have been shown to be partially responsible for facilitating this dramatic increase in uterine blood flow needed during pregnancy. This literature review discusses the basis for structural diversity and functional selectivity of ERs by estrogen, the role of ERs on the genomic and non-genomic effects in endothelial cells of uterine arteries (UAEC). These themes integrate scientific knowledge about the molecular regulation of UAEC to maintain the physiological increase in uteroplacental perfusion observed during normal pregnancy.

Vascular relaxation induced by C-type natriuretic peptide involves the ca2+/NO-synthase/NO pathway

AIMS

C-type natriuretic peptide (CNP) and nitric oxide (NO) are endothelium-derived factors that play important roles in the regulation of vascular tone and arterial blood pressure. We hypothesized that NO produced by the endothelial NO-synthase (NOS-3) contributes to the relaxation induced by CNP in isolated rat aorta via activation of endothelial NPR-C receptor. Therefore, the aim of this study was to investigate the putative contribution of NO through NPR-C activation in the CNP induced relaxation in isolated conductance artery.

MAIN METHODS

Concentration-effect curves for CNP were constructed in aortic rings isolated from rats. Confocal microscopy was used to analyze the cytosolic calcium mobilization induced by CNP. The phosphorylation of the residue Ser1177 of NOS was analyzed by Western blot and the expression and localization of NPR-C receptors was analyzed by immunohistochemistry.

KEY FINDINGS

CNP was less potent in inducing relaxation in denuded endothelium aortic rings than in intact ones. L-NAME attenuated the potency of CNP and similar results were obtained in the presence of hydroxocobalamin, an intracellular NO0 scavenger. CNP did not change the phosphorylation of Ser1177, the activation site of NOS-3, when compared with control. The addition of CNP produced an increase in [Ca2+]c in endothelial cells and a decrease in [Ca2+]c in vascular smooth muscle cells. The NPR-C-receptors are expressed in endothelial and adventitial rat aortas.

SIGNIFICANCE

These results suggest that CNP-induced relaxation in intact aorta isolated from rats involves NO production due to [Ca2+]c increase in endothelial cells possibly through NPR-C activation expressed in these cells. The present study provides a breakthrough in the understanding of the close relationship between the vascular actions of nitric oxide and CNP.

Osteocalcin attenuates high fat diet-induced impairment of endothelium-dependent relaxation through Akt/eNOS-dependent pathway

Background

Recent studies have demonstrated a protective effect of osteocalcin (OCN) on glucose homeostasis and metabolic syndrome. However, its role in vascular function remains unknown. This study investigated the contribution of OCN to the pathogenesis of endothelial dysfunction in the thoracic aorta of apolipoprotein E-deficient (ApoE-KO) mice.

Methods

Eight-week-old ApoE–KO mice were given chow or high fat diet (HFD) for 12 weeks with or without daily intraperitoneal injection of OCN. Intraperitoneal glucose tolerance test (IPGTT), insulin tolerance test (ITT),measurement of serum lipid profiles and blood pressure were carried out. Endothelium-dependent relaxation (EDR) was measured by wire myography. Human umbilical vein endothelial cells (HUVECs) were used to study the role of OCN on eNOS levels in vitro. PI3K inhibitor (LY294002) and Akt inhibitor V were used ex-vivo to determine whether PI3K/Akt/eNOS contributes to the beneficial effect of OCN for the vascular or not.

Results

Daily injections of OCN can significantly improve lipid metabolism, glucose tolerance and insulin sensitivity in ApoE-KO mice. In ApoE-KO mice fed with HFD, the OCN-treated mice displayed an improved acetylcholine-stimulated EDR compared to the vehicle-treated group. In addition, compared to vehicle-treated HUVECs, OCN-treated HUVECs displayed increased activation of the Akt-eNOS signaling pathway, as evidenced by significantly higher levels of phosphorylated Akt and eNOS. Furthermore, a similar beneficial effect of OCN on thoracic aorta was observed using ex vivo organ culture of isolated mouse aortic segment. However, this effect was attenuated upon co-incubation with PI3K inhibitor or Akt inhibitor V.

Conclusions

Our study demonstrates that OCN has an endothelial-protective effect in atherosclerosis through mediating the PI3K/Akt/eNOS signaling pathway.

The role of eNOS phosphorylation in causing drug-induced vascular injury

Previously we found that regulation of eNOS is an important part of the pathogenic process of Drug-induced vascular injury (DIVI) for PDE4i. The aims of the current study were to examine the phosphorylation of eNOS in mesentery versus aorta at known regulatory sites across DIVI-inducing drug classes and to compare changes across species. We found that phosphorylation at S615 in rats was elevated 35-fold 2 hr after the last dose of CI-1044 in mesentery versus 3-fold in aorta. Immunoprecipitation studies revealed that many of the upstream regulators of eNOS activation were associated with eNOS in 1 or more signalosome complexes. Next rats were treated with drugs from 4 other classes known to cause DIVI. Each drug was given alone and in combination with SIN-1 (NO donor) or L-NAME (eNOS inhibitor), and the level of eNOS phosphorylation in mesentery and aorta tissue was correlated with the extent of vascular injury and measured serum nitrite. Drugs or combinations produced altered serum nitrite levels as well as vascular injury score in the mesentery. The results suggested that phosphorylation of S615 may be associated with DIVI activity. Studies with the species-specific A2A adenosine agonist CI-947 in rats versus primates showed a similar pattern.

Vitamin D protects human endothelial cells from oxidative stress through the autophagic and survival pathways

CONTEXT

Recently, vitamin D (VitD) has been recognized as increasingly importance in many cellular functions of several tissues and organs other than bone. In particular, VitD showed important beneficial effects in the cardiovascular system. Although the relationship among VitD, endothelium, and cardiovascular disease is well established, little is known about the antioxidant effect of VitD.

OBJECTIVE

Our objective was to study the intracellular pathways activated by VitD in cultured human umbilical vein endothelial cells undergoing oxidative stress.

DESIGN

Nitric oxide production, cell viability, reactive oxygen species, the mitochondrial permeability transition pore, membrane potential, and caspase-3 activity were measured during oxidative stress induced by administration of 200 μM hydrogen peroxide for 20 minutes. Experiments were repeated in the presence of specific vitamin D receptor ligand ZK191784.

RESULTS

Pretreatment with VitD alone or in combination with ZK191784 is able to reduce the apoptosis-related gene expression, involving both intrinsic and extrinsic pathways. At the same time, it has been shown the activation of pro-autophagic beclin 1 and the phosphorylation of ERK1/2 and Akt, indicating a modulation between apoptosis and autophagy. Moreover, VitD alone or in combination with ZK191784 is able to prevent the loss of mitochondrial potential and the consequent cytochrome C release and caspase activation.

CONCLUSIONS

The present study shows that VitD may prevent endothelial cell death through modulation of the interplay between apoptosis and autophagy. This effect is obtained by inhibiting superoxide anion generation, maintaining mitochondria function and cell viability, activating survival kinases, and inducing NO production.

Low-molecular-weight fucoidan protects endothelial function and ameliorates basal hypertension in diabetic Goto-Kakizaki rats

Endothelial dysfunction, characterized by impairment of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) bioavailability, has been implicated in diabetic cardiovascular pathogenesis. In this study, low-molecular-weight fucoidan (LMWF), which has multiple biological activities including anti-inflammatory and anti-oxidative properties, was investigated for its protective effect against endothelial dysfunction in Goto-Kakizaki type 2 diabetic rats. LMWF (50, 100, or 200 mg/kg/day) or probucol (100 mg/kg/day) were given to diabetic rats for 12 weeks. Basal blood pressure, acetylcholine- or flow-mediated relaxation of mesenteric and paw arteries, endothelium-dependent dilation of aorta, eNOS phosphorylation, and NO production were measured using laser Doppler flowmetry, force myograph, hematoxylin and eosin staining, western blot analysis, and an NO assay. We found that LMWF robustly ameliorated the basal hypertension and impairment of endothelium-dependent relaxation in the aorta, as well as mesenteric and paw arteries in diabetic rats. In addition, the reduction in eNOS phosphorylation at Ser1177, eNOS expression, and NO production because of diabetes were partially reversed by LMWF treatment. However, probucol, a lipid-modifying drug with antioxidant properties, displayed only mild effects. Moreover, LMWF induced, in a dose-dependent manner, endothelium-dependent vasodilation and eNOS phosphorylation at Ser1177 in normal aorta, and also promoted Ser1177 phosphorylation and NO synthesis in primary cultured vasoendothelial cells. Thus, these data demonstrate for the first time that fucoidan protects vasoendothelial function and reduces basal blood pressure in type 2 diabetes rats via, at least in part, preservation of eNOS function. Fucoidan is therefore a potential candidate drug for protection of endothelium in diabetic cardiovascular complications.