eNOS Activity In Endothelial Cells Research Articles

Abstract 690: Circulating Proteomics And Endothelial Cell Phenotype In Patients With Type 2 Diabetes Mellitus (T2DM)

Patients with T2DM display endothelial dysfunction that predicts cardiovascular risk. We have previously demonstrated reduced eNOS activation in endothelial cells (ECs) isolated from patients with T2DM. We sought to identify drivers of EC dysfunction using a combination of proteomic and transcriptomic approaches by measuring: serum O-link cardiovascular panels II and III along with insulin-mediated eNOS phosphorylation and miRNA profiling (NextGen sequencing) in isolated ECs. In 69 patients (37 with T2DM and 32 age- and sex-similar non-T2DM controls) proteomic analysis identified 35 upregulated and 6 downregulated (FDR p<0.05) proteins that included metabolic, vascular and fluid homeostasis, immune and apoptosis related biomarkers. Several biomarkers related to the degree of insulin-mediated eNOS phosphorylation in isolated EC: (renin r= -0.38, p=0.004, chymotrypsin C r= 0.37, p=0.006, paraoxinase 3, r= 0.35, p=0.009, lipoprotein lipase r= 0.34, p=0.01, superoxide dismutase 2 r= 0.31, p=0.02 and adrenomedullin r= -0.27, p=0.049). In a subset of 10 patients (5/group), we confirmed expression of EC-specific miRNA in ECs purified by CD144 microbeads. Comparing patients with T2DM and controls we found 6 upregulated and 7 downregulated miRNAs (FDR P<0.05). Ingenuity Pathway Analysis shows that these miRNAs are involved in the regulation of inflammation, glucose metabolism, stress signaling and cell cycle pathways. Further we found overlap of differentially expressed miRNA with predicted regulation of biomarkers that were altered in T2DM including: miR-4326 and miR-1270 regulate TNFRSF10A and ALCAM, while, miR-4433-5p and miR-342-3p are involved in regulation of superoxide dismutase 2. Our findings demonstrate that an association of circulating biomarkers particularly those that relate to fluid metabolism and oxidative stress with altered endothelial cell signaling in patients with T2DM. Further we have early evidence of altered non-coding miRNA expression in ECs in T2DM that may be related to inflammation and oxidative stress. Ongoing studies are evaluating the functional implications of altered miRNA expression in regulating vascular function in patients with T2DM.

Vasodilatory Effect of Guanxinning Tablet on Rabbit Thoracic Aorta is Modulated by Both Endothelium-Dependent and -Independent Mechanism.

Vasodilatory therapy plays an important role in the treatment of cardiovascular diseases, especially hypertension and coronary heart disease. Previous research found that Guanxinning tablet (GXNT), a traditional Chinese compound preparation composed of Salvia miltiorrhiza (Danshen) and Ligusticum chuanxiong (Chuanxiong), increase blood flow in the arteries, but whether vasodilation plays a role in this effect remains unclear. Here, we found that GXNT significantly alleviated the vasoconstriction of isolated rabbit thoracic aorta induced by phenylephrine (PE), norepinephrine (NE), and KCl in a dose-dependent manner with or without endothelial cells (ECs). Changes in calcium ion levels in vascular smooth muscle cells (VSMCs) showed that both intracellular calcium release and extracellular calcium influx through receptor-dependent calcium channel (ROC) declined with GXNT treatment. Experiments to examine potassium channels suggested that endothelium-denuded vessels were also regulated by calcium-activated potassium channels (Kca) and ATP-related potassium channels (KATP) but not voltage-gated potassium channels (kv) and inward rectifying potassium channels (KIR). For endothelium-intact vessels, the nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) contents in vascular tissue obviously increased after GXNT treatment, and pretreatment with the NO synthase inhibitor Nw-nitro-L-arginine methyl ester (L-NAME) or guanylyl cyclase inhibitor methylthionine chloride (MB) significantly inhibited vasodilation. An assessment of NO-related pathway protein expression revealed that GXNT enhanced the expression of phosphorylated endothelial NO synthase (eNOS) in a dose-dependent manner but had no effect on total eNOS, p-Akt, Akt, or PI3K levels in human umbilical vein ECs (HUVECs). In addition to PI3K/AKT signaling, Ca2+/calmodulin (CaM)-Ca2+/CaM-dependent protein kinase II (CaMKII) signaling is a major signal transduction pathway involved in eNOS activation in ECs. Further results showed that free calcium ion levels were decreased in HUVECs with GXNT treatment, accompanied by an increase in p-CaMKII expression, implying an increase in the Ca2+/CaM-Ca2+/CaMKII cascade. Taken together, these findings suggest that the GXNT may have exerted their vasodilative effect by activating the endothelial CaMKII/eNOS signaling pathway in endothelium-intact rings and calcium-related ion channels in endothelium-denuded vessels.

Arginase II protein regulates Parkin-dependent p32 degradation that contributes to Ca2+-dependent eNOS activation in endothelial cells.

AimsArginase II (ArgII) plays a key role in the regulation of Ca2+ between the cytosol and mitochondria in a p32-dependent manner. p32 contributes to endothelial nitric oxide synthase (eNOS) activation through the Ca2+/CaMKII/AMPK/p38MAPK/Akt signalling cascade. Therefore, we investigated a novel function of ArgII in the regulation of p32 stability.Methods and resultsmRNA levels were measured by quantitative reverse transcription-PCR, and protein levels and activation were confirmed by western blot analysis. Ca2+ concentrations were measured by FACS analysis and a vascular tension assay was performed. ArgII bound to p32, and ArgII protein knockdown using siArgII facilitated the ubiquitin-dependent proteasomal degradation of p32. β-lactone, a proteasome inhibitor, inhibited the p32 degradation associated with endothelial dysfunction in a Ca2+-dependent manner. The amino acids Lys154, Lys 180, and Lys220 of the p32 protein were identified as putative ubiquitination sites. When these sites were mutated, p32 was resistant to degradation in the presence of siArgII, and endothelial function was impaired. Knockdown of Pink/Parkin as an E3-ubiquitin ligase with siRNAs resulted in increased p32, decreased [Ca2+]c, and attenuated CaMKII-dependent eNOS activation by siArgII. siArgII-dependent Parkin activation was attenuated by KN93, a CaMKII inhibitor. Knockdown of ArgII mRNA and its gene, but not inhibition of its activity, accelerated the interaction between p32 and Parkin and reduced p32 levels. In aortas of ArgII−/− mice, p32 levels were reduced by activated Parkin and inhibition of CaMKII attenuated Parkin-dependent p32 lysis. siParkin blunted the phosphorylation of the activated CaMKII/AMPK/p38MAPK/Akt/eNOS signalling cascade. However, ApoE−/− mice fed a high-cholesterol diet had greater ArgII activity, significantly attenuated phosphorylation of Parkin, and increased p32 levels. Incubation with siArgII augmented p32 ubiquitination through Parkin activation, and induced signalling cascade activation.ConclusionThe results suggest a novel function for ArgII protein in Parkin-dependent ubiquitination of p32 that is associated with Ca2+-mediated eNOS activation in endothelial cells.

Ecklonia cava Extract and Its Derivative Dieckol Promote Vasodilation by Modulating Calcium Signaling and PI3K/AKT/eNOS Pathway in In Vitro and In Vivo Models.

Nitric oxide (NO), an endothelial-derived relaxing factor synthesized by endothelial nitric oxide synthase (eNOS) in endothelial cells, enhances vasodilation by modulating vascular tone. The calcium concentration critically influences eNOS activation in endothelial cells. Thus, modulation of calcium-dependent signaling pathways may be a potential therapeutic strategy to enhance vasodilation. Marine algae reportedly possess protective effects against cardiovascular disorders, including hypertension and vascular dysfunction; however, the underlying molecular signaling pathways remain elusive. In the present study, we extracted and isolated dieckol from Ecklonia cava and investigated calcium transit-enhanced vasodilation. Calcium modulation via the well-known M3 muscarinic acetylcholine receptor (AchM3R), which is linked to NO formation, was investigated and the vasodilatory effect of dieckol was verified. Our results indicated that dieckol effectively promoted NO generation via the PI3K/Akt/eNOS axis and calcium transients influenced by AchM3R. We also treated Tg(flk: EGFP) transgenic zebrafish with dieckol to assess its vasodilatory effect. Dieckol promoted vasodilation by enlarging the dorsal aorta diameter, thus regulating blood flow velocity. In conclusion, our findings suggest that dieckol modulates calcium transit through AchM3R, increases endothelial-dependent NO production, and efficiently enhances vasodilation. Thus, E. cava and its derivative, dieckol, can be considered as potential natural vasodilators.

Shear stress regulates eNOS signaling in human umbilical vein endothelial cells via SRB1-PI3KAP1 pathway

Background: The occurrence and development of atherosclerosis are closely related to shear stress on the endothelial cells. However, related molecular mechanisms of controlling mechanical signal transduction in endothelial cells remain largely unknown. Aim of the Study: To obtain this goal, here, a parallel-plate flow chamber was used to impose laminar shear stress (8.4 dyne/cm2 ) on endothelial cells for 0 minute (min), 10 min, 30 min, 60 min, and 120 min. Subjects and Methods: The RNA interference was employed to down-regulate scavenger receptor class B1 (SRB1) and LY294002 was performed to block the phosphorylation status of the phosphoinositide 3-kinase pathway. Then, the cell status was observed under the microscope, followed by detection of phosphorylated phosphoinositide 3-kinase (PI3K), p38, extracellular signal-regulated protein kinases 1 and 2 and the binding activities of activator protein 1, nuclear factorκB and endothelial nitric oxide synthase (eNOs) by western blot. The results showed that shear stress (8.4 dyne/cm2 ) for 60 min induced obvious cell morphologic changes. Meanwhile, PI3K phosphorylation and eNOS expression were significantly increased by shear stress while reversed by SRB1 si-RNA and LY294002. Additionally, shear stress caused the enhanced binding activity of nuclear transcription factor activator protein 1 (AP-1) to DNA from 10 to 120 min, while only at 30 and 60 min for NF-κB. After treatment with SRB1 si-RNA and LY294002 inhibitor, the binding activities of AP-1 and DNA was significantly decreased, however, there was no effect on NF-κB binding activity. Results: Therefore, SRB1 plays a crucial role in mediating shear stress-induced eNOS activation in endothelial cells via PI3K-AP1 pathway. These findings will provide an important understanding of shear stress-induced cell alterations in clinic detection

Cacao Polyphenols Potentiate Anti-Platelet Effect of Endothelial Cells and Ameliorate Hypercoagulatory States Associated with Hypercholesterolemia.

Platelets are related to the formation of blood clots that play a crucial role in thrombosis and other cardiovascular diseases. Cocoa, derived from Theobroma cocoa, has been widely used as functional food for improving cardiovascular health. In the present study, the direct and indirect effects of cacao polyphenols (CPs) were investigated on human platelet aggregation associated with endothelial cells (ECs) senescence. In addition, the effect of CPs on high-fat diet- (HFD-) induced hypercoagulatory states in rats was evaluated. CPs directly inhibited the human platelet aggregation induced by thromboxane analogue, U46619, and treatment of CPs on senescent endothelial cells markedly restored inhibitory effect of ECs on platelet aggregation. Nitric oxide (NO) from ECs is known as modulator of platelet aggregation and CPs increased eNOS activity in ECs and coronary artery. In animal model, increased TG level induced by high fat diet (HFD) was significantly decreased by CPs administration. In addition, the HFD animal had shorter bleeding time, and CPs administration attenuated the HFD-induced changes. Taken together, the present study indicates that CPs have potent anti-platelet effects most likely by direct and indirect effect via ECs and have the potential for lowering the risk of cardiovascular disease-related hypercoagulation due to hypercholesterolemia.

Phosphorylation inactivation of endothelial nitric oxide synthesis in pulmonary arterial hypertension.

The impairment of vasodilator nitric oxide (NO) production is well accepted as a typical marker of endothelial dysfunction in vascular diseases, including in the pathophysiology of pulmonary arterial hypertension (PAH), but the molecular mechanisms accounting for loss of NO production are unknown. We hypothesized that low NO production by pulmonary arterial endothelial cells in PAH is due to inactivation of NO synthase (eNOS) by aberrant phosphorylation of the protein. To test the hypothesis, we evaluated eNOS levels, dimerization, and phosphorylation in the vascular endothelial cells and lungs of patients with PAH compared with controls. In mechanistic studies, eNOS activity in endothelial cells in PAH lungs was found to be inhibited due to phosphorylation at T495. Evidence pointed to greater phosphorylation/activation of protein kinase C (PKC) α and its greater association with eNOS as the source of greater phosphorylation at T495. The presence of greater amounts of pT495-eNOS in plexiform lesions in lungs of patients with PAH confirmed the pathobiological mechanism in vivo. Transfection of the activating mutation of eNOS (T495A/S1177D) restored NO production in PAH cells. Pharmacological blockade of PKC activity by β-blocker also restored NO formation by PAH cells, identifying one mechanism by which β-blockers may benefit PAH and cardiovascular diseases through recovery of endothelial functions.

TNFα reduces eNOS activity in endothelial cells through serine 116 phosphorylation and Pin1 binding: Confirmation of a direct, inhibitory interaction of Pin1 with eNOS

Production of NO by the endothelial nitric oxide synthase (eNOS) has a major role in blood pressure control and suppression of atherosclerosis. In a previous study, we presented evidence implicating the Pin1 prolyl isomerase in negative modulation of eNOS activity in bovine aortic endothelial cells (BAECs). Pin1 recognizes phosphoserine/phosphothreonine–proline motifs in target proteins and catalyzes prolyl isomerization at the peptide bond. In the present study, we show, first, with purified proteins, that Pin1 binds to eNOS directly via the Pin1 WW domain. Binding is enhanced by mimicking phosphorylation of eNOS at S116. Interaction of Pin1 with eNOS markedly reduces eNOS enzymatic activity. Second, in BAECs, we show that TNFα induces ERK 1/2-mediated S116 phosphorylation of eNOS, accompanied by Pin1 binding. TNFα treatment of BAECs results in a reduction in NO release from the cells in a manner that depends on the activities of both Pin1 and ERK 1/2. Evidence is also presented that this mechanism of eNOS regulation cannot occur in rat and mouse cells because there is no proline residue in the mouse and rat amino acid sequences adjacent to the putative phosphorylation site. Moreover, we find that phosphorylation of this site is not detectable in mouse eNOS.

PECAM1 regulates flow-mediated Gab1 tyrosine phosphorylation and signaling

Endothelial dysfunction, characterized by impaired activation of endothelial nitric oxide (NO) synthase (eNOS) and ensued decrease of NO production, is a common mechanism of various cardiovascular pathologies, including hypertension and atherosclerosis. Laminar blood flow-mediated specific signaling cascades modulate vascular endothelial cells (ECs) structure and functions. We have previously shown that flow-stimulated Gab1 (Grb2-associated binder-1) tyrosine phosphorylation mediates eNOS activation in ECs, which in part confers laminar flow atheroprotective action. However, the molecular mechanisms whereby flow regulates Gab1 tyrosine phosphorylation and its downstream signaling events remain unclear. Here we show that platelet endothelial cell adhesion molecule-1 (PECAM1), a key molecule in an endothelial mechanosensing complex, specifically mediates Gab1 tyrosine phosphorylation and its downstream Akt and eNOS activation in ECs upon flow rather than hepatocyte growth factor (HGF) stimulation. Small interfering RNA (siRNA) targeting PECAM1 abolished flow- but not HGF-induced Gab1 tyrosine phosphorylation and Akt, eNOS activation as well as Gab1 membrane translocation. Protein-tyrosine phosphatase SHP2, which has been shown to interact with Gab1, was involved in flow signaling and HGF signaling, as SHP2 siRNA diminished the flow- and HGF-induced Gab1 tyrosine phosphorylation, membrane localization and downstream signaling. Pharmacological inhibition of PI3K decreased flow-, but not HGF-mediated Gab1 phosphorylation and membrane localization as well as eNOS activation. Finally, we observed that flow-mediated Gab1 and eNOS phosphorylation in vivo induced by voluntary wheel running was reduced in PECAM1 knockout mice. These results demonstrate a specific role of PECAM1 in flow-mediated Gab1 tyrosine phosphorylation and eNOS signaling in ECs.

Abstract 12231: PECAM1 is Essential for Flow-mediated Gab1 Tyrosine Phosphorylation and Signaling in vitro and in vivo

Introduction: Impaired activation of endothelial nitric oxide (NO) synthase (eNOS) and ensued NO production is a common mechanism of various cardiovascular pathologies, including hypertension and atherosclerosis. Specific signaling cascades, generated by vascular endothelial cells (ECs) in response to laminar flow, modulate EC structure and functions, NO production in particular. We have previously shown that flow-stimulated Gab1 (Grb2-associated binder-1) tyrosine phosphorylation mediates eNOS activation. However, the upstream mechanism that regulates Gab1 tyrosine phosphorylation remains unclear. Hypothesis: We hypothesized that platelet endothelial cell adhesion molecule-1 (PECAM1), a key molecule in an endothelial mechanosensing complex, specifically mediates Gab1 tyrosine phosphorylation and its downstream Akt and eNOS activation in ECs upon flow rather than hepatocyte growth factor (HGF) stimulation. Methods: Western blot, en face staining and voluntary wheel running. Results: Small interfering RNA (siRNA) targeting PECAM1 abolished flow- but not HGF-induced Gab1 tyrosine phosphorylation and Akt, eNOS activation as well as Gab1 membrane translocation. Protein-tyrosine phosphatase SHP2, which has been shown to interact with Gab1, was involved in a flow signaling pathway as well as HGF-induced signaling, as SHP2 siRNA diminished the flow- and HGF-induced Gab1 tyrosine phosphorylation, membrane localization and downstream signaling. Pharmacological inhibition of PI3K by LY294002 decreased flow, but not HGF-mediated Gab1 phosphorylation and membrane localization as well as eNOS activation. Finally, we observed that flow-mediated Gab1 and eNOS phosphorylation in vivo induced by voluntary wheel running was reduced in PECAM1 knockout mice. Conclusions: These results demonstrate a specific role of PECAM1 in flow-mediated Gab1 tyrosine phosphorylation and eNOS signaling in ECs

Effect of 3,4-dihydroxyacetophenone on endothelial dysfunction in streptozotocin-induced rats with type 2 diabetes.

This study investigated whether 3,4-Dihydroxyacetophenone (DHAP) could improve endothelial function in streptozotocin-induced type 2 diabetic rats. Sprague-Dawley rats were randomly divided into control, diabetic, and diabetic DHAP-treated animals. After treatment with DHAP for 8 weeks, endothelial function was determined by measuring endothelium-dependent vasodilatation (EDV) of the thoracic aorta. Endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) production in endothelial cells and nuclear transcription factor kappa B (NF-κB) expression and superoxide anion production in the aorta were determined. DHAP treatment reduced serum levels of triglycerides, cholesterol, malondialdehyde, and tumor necrosis factor α, and enhanced serum adiponectin levels. Endothelium-dependent vasodilatation was significantly attenuated in rats with diabetes and increased significantly after DHAP treatment. NO levels and eNOS activity in endothelial cells were significantly reduced, and NF-κB activation and superoxide production increased in rats with diabetes compared with the control group. DHAP treatment enhanced NO levels and eNOS activity and decreased NF-κB activation and superoxide production. These findings suggest that DHAP could improve endothelial function in streptozotocin-induced type 2 diabetic rats. The mechanism may be related to the enhancement of eNOS activity and NO production by reducing plasma lipid levels, oxidative stress, and inflammatory activity.

209 Beta-catenin Functions as an Endogenous Negative Regulator of Endothelial Nitric Oxide Synthase Function

IntroductionNitric oxide (NO) derived from endothelial NO synthase (eNOS) has multiple anti-atherogenic actions in the vasculature. eNOS activity is controlled by association with a number of regulatory proteins. We here...

Abstract 516: Altered Autophagy Contributes to Endothelial Dysfunction in Human Diabetes Mellitus

Diabetes is associated with increased oxidative stress and decreased nitric oxide (NO) bioactivity in the vasculature. Autophagy is a critical multistep pathway that eliminates oxidatively damaged proteins and organelles from the cell. Emerging evidence implicates impaired autophagy in a variety of non-vascular tissues that contributes to the pathogenesis of diabetes in experimental models. We hypothesized that impaired autophagy contributes to endothelial dysfunction associated with type 2 diabetes mellitus in humans. We measured vascular function and markers of autophagy in freshly isolated endothelial cells from patients with diabetes (n=41) and non-diabetic controls (n=41). Diabetes was associated with endothelial dysfunction characterized by lower brachial artery flow-mediated dilation. Endothelial cells from diabetic patients displayed no differences in LC3 puncta compared to those from controls but had higher levels of endothelial p62 (p=0.004), a protein that accumulates with reduced autophagic flux. In endothelial cells from controls, the autophagy inhibitor bafilomycin impaired eNOS activation, confirming that intact autophagy is necessary for NO signaling. Global activation of autophagy with spermidine reversed endothelial dysfunction in cultured endothelial cells exposed to high glucose (p=0.007). In regard to mechanism of impairment, the autophagy initiator rapamycin failed to improve eNOS activation in endothelial cells from diabetics. Further, expression of beclin-1, a key contributor to autophagosome formation, was similar in diabetics and controls, arguing against impaired initiation of autophagy. In endothelial cells from diabetics, blocking the terminal step of autophagy with bafilomycin led to a further accumulation of p62 (P=0.01), suggesting intact but insufficient levels of autophagy. Lamp2a, which facilitates the merger of autophagosomes and lysosomes, was higher in diabetic cells, possibly reflecting a compensatory response to reduced flux. Collectively, these findings provide evidence for inadequate autophagic flux in endothelial cells from diabetic patients that contributes to endothelial dysfunction and may be a target for therapy of diabetic vascular disease.

Enhanced activation of NAD(P)H

Guanosine 5'-triphosphate cyclohydrolase-1 (GTPCH-1) is a rate-limiting enzyme in de-novo synthesis of tetrahydrobiopterin (BH4), an essential cofactor for endothelial nitric oxide synthase (eNOS) coupling. Adenosine 5'-monophosphate-activated protein kinase (AMPK) is crucial for GTPCH-1 preservation, and tumor suppressor kinase liver kinase B1 (LKB1), an upstream kinase of AMPK, is activated by NAD-dependent class III histone deacetylase sirtuin 1 (SIRT1)-mediated deacetylation. β-Lapachone has been shown to increase cellular NAD/NADH ratio via quinone oxidoreductase 1 (NQO1) activation. In this study, we have evaluated whether β-lapachone-induced NQO1 activation modulates blood pressure (BP) through preservation of GTPCH-1 in a hypertensive animal model. Spontaneously hypertensive rats (SHRs), primary aortic endothelial cells, and endothelial cell line were used to investigate the hypotensive effect of β-lapachone and its action mechanism. β-Lapachone treatment dramatically lowered BP and vascular tension in SHRs and induced eNOS activation in endothelial cells. Consistent with these effects, β-lapachone treatment also elevated levels of both aortic cGMP and plasma nitric oxide in SHRs. Meanwhile, β-lapachone-treated SHRs showed significantly increased levels of aortic NAD, LKB1 deacetylation, and AMPK Thr phosphorylation followed by increased GTPCH-1 and tetrahydrobiopterin/dihydrobiopterin ratio. In-vitro study revealed that AMPK inhibition by overexpression of dominant-negative AMPK nearly abolished GTPCH-1 protein conservation. Enhanced LKB1 deacetylation and AMPK activation were also elicited by β-lapachone in endothelial cells. However, inhibition of LKB1 deacetylation by blocking of NQO1 or SIRT1 blunted AMPK activation by β-lapachone. This is the first study demonstrating that eNOS coupling can be regulated by NQO1 activation via LKB1/AMPK/GTPCH-1 modulation, which is possibly correlated with relieving hypertension. These findings provide strong evidence to suggest that NQO1 might be a new therapeutic target for hypertension.

Obligatory Role for Endothelial Heparan Sulphate Proteoglycans and Caveolae Internalization in Catestatin-Dependent eNOS Activation

The chromogranin-A peptide catestatin modulates a wide range of processes, such as cardiovascular functions, innate immunity, inflammation, and metabolism. We recently found that the cardiac antiadrenergic action of catestatin requires a PI3K-dependent NO release from endothelial cells, although the receptor involved is yet to be identified. In the present work, based on the cationic properties of catestatin, we tested the hypothesis of its interaction with membrane heparan sulphate proteoglycans, resulting in the activation of a caveolae-dependent endocytosis. Experiments were performed on bovine aortic endothelial cells. Endocytotic vesicles trafficking was quantified by confocal microscopy using a water-soluble membrane dye; catestatin colocalization with heparan sulphate proteoglycans and caveolin 1 internalization were studied by fluorimetric measurements in live cells. Modulation of the catestatin-dependent eNOS activation was assessed by immunofluorescence and immunoblot analysis. Our results demonstrate that catestatin (5 nM) colocalizes with heparan sulphate proteoglycans and induces a remarkable increase in the caveolae-dependent endocytosis and caveolin 1 internalization, which were significantly reduced by both heparinase and wortmannin. Moreover, catestatin was unable to induce Ser1179 eNOS phosphorylation after pretreatments with heparinase and methyl-β-cyclodextrin. Taken together, these results highlight the obligatory role for proteoglycans and caveolae internalization in the catestatin-dependent eNOS activation in endothelial cells.

(−)‐Epicatechin induces calcium and translocation independent eNOS activation in endothelial cells via AKT/HSP90

The consumption of cacao‐derived products provides beneficial cardiovascular effects. Vascular actions of cocoa are related to enhanced nitric oxide (NO) production. These actions can be reproduced by the administration of the flavanol (−)‐epicatechin (EPI). EPI is capable of inducing the synthesis of NO via endothelial NO synthase (eNOS) activation in human coronary artery endothelial cells (HCAEC) through PI3K/AKT/PKA and Ca2+‐CaM/CaMKII pathways. To further understand the mechanisms behind the vascular action of EPI, we investigated the effects of Ca2+ depletion on eNOS translocation, as well as on its activation/phosphorylation. Results demonstrate that under Ca2+‐free conditions, EPI (but not BK) is capable of inducing NO production through eNOS phosphorylation. EPI‐induced translocation of eNOS from the plasmalemma was abolished upon Ca2+ depletion. Thus, under these conditions, EPI can stimulate NO synthesis independent of calmodulin binding to eNOS and of its translocation into the cytoplasm. EPI is able to induce AKT activation as well as the physical association of HSP90‐eNOS. We also examined the effects of EPI on the NO/cGMP/vasodilator‐stimulated phosphoprotein (VASP) pathway in isolated Ca2+‐deprived canine mesenteric arteries. EPI induces the activation of the vasorelaxation‐related pathway and the effects were blocked by nitro‐L‐arginine methyl ester (L‐NAME). Results indicate that EPI can uniquely modulate endothelial responses independently of calcium.

ER stress induction increases NADPH oxidase and reduces eNOS activity in endothelial cells

Cardiovascular diseases are associated with endoplasmic reticulum (ER) stress. We have demonstrated that induction of ER stress in C57BL/6J, by the injection of tunicamycin, impairs vascular endothelium‐dependent relaxation (unpublished data).In this study, we aimed to determine the mechanism by which ER stress reduces nitric oxide synthase activity.We incubated mice primary coronary arterioles endothelial cells with tunicamycin (1 ug/mL) for 6 h in the presence or absence of two ER stress inhibitors (Tudca, 500 ug/mL and PBA, 10 mM). Tunycamicin increased the expression of phosphorylated PERK and eIF2alpha, CHOP and ATF6, which were reduced with ER stress inhibitors. The induction of ER stress enhanced NADPH oxidase activity and Nox1/Nox4 mRNA levels associated with an increase of reactive oxygen species, which were reduced by ER stress inhibitors. Phosphorylated eNOS expression was reduced with tunicamycin and rescued by ER stress inhibition. The transfection of endothelial cells with a reporter plasmid containing the eNOS promoter revealed that ER stress induction reduced eNOS promoter activity by 50%, which was rescued by ER stress inhibition.ConclusionER stress enhances oxidative stress and reduces eNOS promoter activity and phosphorylated eNOS, which are responsible for endothelial dysfunction.

β Common receptor integrates the erythropoietin signaling in activation of endothelial nitric oxide synthase

Erythropoietin (EPO), the key hormone for erythropoiesis, also increases nitric oxide (NO) bioavailability in endothelial cells (ECs), yet the definitive mechanisms are not fully understood. Increasing evidence has demonstrated that β common receptor (βCR) plays a crucial role in EPO-mediated non-hematopoietic effects. We investigated the role of βCR in EPO-induced endothelial NO synthase (eNOS) activation in bovine aortic ECs (BAECs) and the molecular mechanisms involved. Results of confocal microscopy and immunoprecipitation analyses revealed that βCR was colocalized and interacted with EPO receptor (EPOR) in ECs. Inhibition of βCR or EPOR by neutralizing antibodies or small interfering RNA abolished the EPO-induced NO production. Additionally, blockage of βCR abrogated the EPO-induced increase in the phosphorylation of eNOS, Akt, Src, or Janus kinase 2 (JAK2). Immunoprecipitation analysis revealed that treatment with EPO increased the interaction between βCR and eNOS, which was suppressed by inhibition of Src, JAK2, or Akt signaling with specific pharmacological inhibitors. Furthermore, EPO-induced EC proliferation, migration, and tube formation were blocked by pretreatment with βCR antibody and Src, JAK2, or PI3K/Akt inhibitors. Moreover, in vivo experiments showed that EPO increased the level of phosphorylated eNOS, Src, JAK2, and Akt, as well as βCR-eNOS association in aortas and promoted the angiogenesis in Matrigel plug, which was diminished by βCR or EPOR neutralizing antibodies. Our findings suggest that βCR may play an integrative role in the EPO signaling-mediated activation of eNOS in ECs.

Effects of cold exposure and shear stress on endothelial nitric oxide synthase activation

Endothelial nitric oxide synthase (eNOS) is the primary enzyme that produces nitric oxide (NO), which plays an important role in blood vessel relaxation. eNOS activation is stimulated by various mechanical forces, such as shear stress. Several studies have shown that local cooling of the human finger causes strong vasoconstriction, followed after several minutes by cold-induced vasodilation (CIVD). However, the role played by endothelial cells (ECs) in blood vessel regulation in respond to cold temperatures is not fully understood. In this study, we found that low temperature alone does not significantly increase or decrease eNOS activation in ECs. We further found that the combination of shear stress with temperature change leads to a significant increase in eNOS activation at 37°C and 28°C, and a decrease at 4°C. These results show that ECs play an important role in blood vessel regulation under shear stress and low temperature.

Caveolin‐1 Phosphorylation Negatively Regulates eNOS Activity in Endothelial Cells

Endothelial nitric oxide synthase (eNOS) activity is regulated by phosphorylation, Ca2+ ‐calmodulin, and interaction with caveolin‐1 (Cav‐1). However, the mechanism by which Cav‐1 negatively regulates eNOS activity following stimulation is not clear. Here, we examined the kinetics of eNOS activation (phosphorylation and NO production) and binding to Cav‐1 in endothelial cells and mouse lung homogenates following addition of Ca2+ ionophore A23187. Ca2+increased Src, Akt, Cav‐1, and eNOS phosphorylation and NO production within minutes which returned to baseline levels within 30 min. We observed an increase in eNOS association (co‐IP) with Cav‐1 following stimulation which was blocked by NOS inhibitor L‐NAME and Src inhibitor PP2. Furthermore, siRNA‐mediated knockdown of Cav‐1 potentiated eNOS phosphorylation whereas depletion of eNOS blocked the increase in Src activity and Cav‐1 phosphorylation. FRET between Cav‐1‐YFP and eNOS‐CFP in co‐transfected CHO cells significantly increased after stimulation. Moreover, in co‐transfected HEK293 cells, WT and phospho‐mimicking S1179D‐ eNOS but not phospho‐defective S1179A‐ eNOS co‐IP'd with WT and phospho‐mimicking Y14D‐Cav‐1 but not phospho‐defective Y14F‐Cav‐1 mutant. These data suggest that Ca2+‐dependent activation of eNOS induces Cav‐1 phosphorylation via Src which in turn binds to eNOS and negatively regulates its activity. Supported by NIH HL071626 and HL060678.