Phosphorylation of endothelial nitric-oxide synthase regulates superoxide generation from the enzyme

MiR-497-5p regulates ox-LDL-induced dysfunction in vascular endothelial cells by targeting VEGFA/p38/MAPK pathway in atherosclerosis

Background

The impairment of endothelial cells triggered by oxidized low-density lipoprotein (ox-LDL) stands as a critical event in the advancement of atherosclerosis (AS). MiR-497-5p has been recognized as a potential predictor for AS, but its precise involvement in ox-LDL-induced endothelial cell dysfunction remains to be elucidated.

Methods

An in vitro AS cell model was established by exposing human umbilical vein endothelial cells (HUVECs) to 100 μg/mL ox-LDL for 24 h. The assessment of endothelial cell function included evaluating cell viability, caspase-3 activity, inflammatory factors, and oxidative markers. Molecular mechanisms were elucidated through quantitative real-time PCR, Western blot analysis, and luciferase reporter assays.

Results

Our investigation revealed that exposure to ox-LDL led to an upregulation in miR-497-5p and p-p38 levels, while downregulating the expression of vascular endothelial growth factor A (VEGFA) and phosphorylated (p)-endothelial nitric oxide synthase (p-eNOS) in HUVECs. Ox-LDL exposure resulted in decreased cell viability and angiogenic capacity, coupled with increased apoptosis, inflammation, and oxidative stress in HUVECs, partially mediated by the upregulation of miR-497-5p. We confirmed VEGFA as a direct target of miR-497-5p. Interfering with VEGFA expression significantly reversed the effects mediated by miR-497-5p silencing in HUVECs exposed to ox-LDL.

Conclusions

In summary, our findings demonstrate that miR-497-5p exacerbates ox-LDL-induced dysfunction in HUVECs through the activation of the p38/MAPK pathway, mediated by the targeting of VEGFA.

Differential superoxide production in phosphorylated neuronal nitric oxide synthase mu and alpha variants

Neuronal nitric oxide synthase (nNOS) is regulated by phosphorylation in vivo, yet the underlying biochemical mechanisms remain unclear, primarily due to difficulty in obtaining milligram quantities of phosphorylated nNOS protein; detailed spectroscopic and rapid kinetics investigations require purified protein samples at a concentration in the range of hundreds microM. Moreover, the functional diversity of the nNOS isoform is linked to its splice variants. Also of note is that determination of protein phosphorylation stoichiometry remains as a challenge. To address these issues, this study first expanded a recent genetic code expansion approach to produce phosphorylated rat nNOSμ and nNOSα holoproteins through site-specific incorporation of phosphoserine (pSer) at residues 1446 and 1412, respectively; this site is at the C-terminal tail region, a NOS-unique regulatory element. A quantitative mass spectrometric approach was then developed in-house to analyze unphosphorylated peptides in phosphatase-treated and -untreated phospho-nNOS proteins. The observed pSer-incorporation efficiency consistently exceeded 80%, showing high pSer-incorporation efficiency. Notably, EPR spin trapping results demonstrate that under l-arginine-depleted conditions, pSer1412 nNOSα presented a significant reduction in superoxide generation, whereas pSer1446 nNOSμ exhibited the opposite effect, compared to their unphosphorylated counterparts. This suggests that phosphorylation at the C-terminal tail has a regulatory effect on nNOS uncoupling that may differ between variant forms. Furthermore, the methodologies for incorporating pSer into large, complex protein and quantifying the percentage of phosphorylation in recombinant purified protein should be applicable to other protein systems.

Therapeutic Potential for Beta-3 Adrenoreceptor Agonists in Peripheral Arterial Disease and Diabetic Foot Ulcers

Annually, peripheral arterial disease is estimated to cost over USD 21 billion and diabetic foot disease an estimated at USD 9-13 billion. Mirabegron is a TGA-approved beta-3 adrenoreceptor agonist, shown to be safe and effective in the treatment of overactive bladder syndrome by stimulating bladder smooth muscle relaxation. In this review, we discuss the potential use of beta-3 adrenoreceptor agonists as therapeutic agents repurposed for peripheral arterial disease and diabetic foot ulcers. The development of both conditions is underpinned by the upregulation of oxidative stress pathways and consequential inflammation and hypoxia. In oxidative stress, there is an imbalance of reactive oxygen species and nitric oxide. Endothelial nitric oxide synthase becomes uncoupled in disease states, producing superoxide and worsening oxidative stress. Agonist stimulation of the beta-3 adrenoreceptor recouples and activates endothelial nitric oxide synthase, increasing the production of nitric oxide. This reduces circulating reactive oxygen species, thus decreasing redox modification and dysregulation of cellular proteins, causing downstream smooth muscle relaxation, improved endothelial function and increased angiogenesis. These mechanisms lead to endothelial repair in peripheral arterial disease and an enhanced perfusion in hypoxic tissue, which will likely improve the healing of chronic ulcers.

Metabolic reprogramming, oxidative stress, and pulmonary hypertension

Mitochondria are highly dynamic organelles essential for cell metabolism, growth, and function. It is becoming increasingly clear that endothelial cell dysfunction significantly contributes to the pathogenesis and vascular remodeling of various lung diseases, including pulmonary arterial hypertension (PAH), and that mitochondria are at the center of this dysfunction. The more we uncover the role mitochondria play in pulmonary vascular disease, the more apparent it becomes that multiple pathways are involved. To achieve effective treatments, we must understand how these pathways are dysregulated to be able to intervene therapeutically. We know that nitric oxide signaling, glucose metabolism, fatty acid oxidation, and the TCA cycle are abnormal in PAH, along with alterations in the mitochondrial membrane potential, proliferation, and apoptosis. However, these pathways are incompletely characterized in PAH, especially in endothelial cells, highlighting the urgent need for further research. This review summarizes what is currently known about how mitochondrial metabolism facilitates a metabolic shift in endothelial cells that induces vascular remodeling during PAH.

Calciprotein Particles Induce Endothelial Dysfunction by Impairing Endothelial Nitric Oxide Metabolism

BACKGROUND

Calciprotein particles (CPPs) are associated with the development of vascular calcifications in chronic kidney disease. The role of endothelial cells (ECs) in this process is unknown. Here, we investigated the interaction of CPPs and ECs, thereby focusing on endothelial nitric oxide metabolism and oxidative stress.

METHODS

CPPs were generated in calcium- and phosphate-enriched medium. Human umbilical vein endothelial cells were exposed to different concentrations of CPPs (0-100 µg/mL) for 24 or 72 hours. Ex vivo porcine coronary artery rings were used to measure endothelial cell-dependent vascular smooth muscle cell relaxation after CPP exposure. Serum samples from an early chronic kidney disease cohort (n=245) were analyzed for calcification propensity (measure for CPP formation) and nitrate and nitrite levels (NO_x).

RESULTS

CPP exposure for 24 hours reduced eNOS (endothelial nitric oxide synthase) mRNA expression and decreased nitrite production, indicating reduced nitric oxide bioavailability. Also, 24-hour CPP exposure caused increased mitochondria-derived superoxide generation, together with nitrotyrosine protein residue formation. Long-term (72 hours) exposure of human umbilical vein endothelial cells to CPPs induced eNOS uncoupling and decreased eNOS protein expression, indicating further impairment of the nitric oxide pathway. The ex vivo porcine coronary artery model showed a significant reduction in endothelial-dependent vascular smooth muscle cell relaxation after CPP exposure. A negative association was observed between NO_x levels and calcification propensity (r=-0.136; P=0.049) in sera of (early) chronic kidney disease patients.

CONCLUSIONS

CPPs cause endothelial cell dysfunction by impairing nitric oxide metabolism and generating oxidative stress. Our findings provide new evidence for direct effects of CPPs on ECs and pathways involved.

Flow-dependent shear stress affects the biological properties of pericyte-like cells isolated from human dental pulp

BACKGROUND

Human dental pulp stem cells represent a mesenchymal stem cell niche localized in the perivascular area of dental pulp and are characterized by low immunogenicity and immunomodulatory/anti-inflammatory properties. Pericytes, mural cells surrounding the endothelium of small vessels, regulate numerous functions including vessel growth, stabilization and permeability. It is well established that pericytes have a tight cross talk with endothelial cells in neoangiogenesis and vessel stabilization, which are regulated by different factors, i.e., microenvironment and flow-dependent shear stress. The aim of this study was to evaluate the effects of a pulsatile unidirectional flow in the presence or not of an inflammatory microenvironment on the biological properties of pericyte-like cells isolated from human dental pulp (hDPSCs).

METHODS

Human DPSCs were cultured under both static and dynamic conditions with or without pre-activated peripheral blood mononuclear cells (PBMCs). Pulsatile unidirectional flow shear stress was generated by using a specific peristaltic pump. The angiogenic potential and inflammatory properties of hDPSCs were evaluated through reverse phase protein microarrays (RPPA), confocal immunofluorescence and western blot analyses.

RESULTS

Our data showed that hDPSCs expressed the typical endothelial markers, which were up-regulated after endothelial induction, and were able to form tube-like structures. RPPA analyses revealed that these properties were modulated when a pulsatile unidirectional flow shear stress was applied to hDPSCs. Stem cells also revealed a downregulation of the immune-modulatory molecule PD-L1, in parallel with an up-regulation of the pro-inflammatory molecule NF-kB. Immune-modulatory properties of hDPSCs were also reduced after culture under flow-dependent shear stress and exposure to an inflammatory microenvironment. This evidence was strengthened by the detection of up-regulated levels of expression of pro-inflammatory cytokines in PBMCs.

CONCLUSIONS

In conclusion, the application of a pulsatile unidirectional flow shear stress induced a modulation of immunomodulatory/inflammatory properties of dental pulp pericyte-like cells.

LncRNA HOXA11-AS promotes vascular endothelial cell injury in atherosclerosis by regulating the miR-515-5p/ROCK1 axis

AIMS

Long non-coding RNA HOXA11-AS participated in heart disease. In this study, we aim to evaluate the potential roles of HOXA11-AS in atherosclerosis and its underlying mechanisms.

METHODS AND RESULTS

The expression levels of HOXA11-AS in ox-LDL-treated HUVECs and arch tissues of high-fat diet-fed ApoE^-/- mice (n = 10) were assessed by qRT-PCR. The effects of HOXA11-AS knockdown on the development of atherosclerosis were evaluated using in vitro and in vivo models. Luciferase reporter and RNA immunoprecipitation (RIP) assays verified the potential relationships between HOXA11-AS or ROCK1 and miR-515-5p. The interactive roles between HOXA11-AS and miR-515-5p and between miR-515-5p and ROCK1 were further characterized in ox-LDL-treated HUVECs. Our data showed that HOXA11-AS was significantly up-regulated (P < 0.001), whereas miR-515-5p was dramatically down-regulated in AS mice tissues (P < 0.001) and ox-LDL-treated HUVECs (P < 0.01). Ox-LDL could induce endothelial injuries by inhibiting cell proliferation (P < 0.001) and SOD synthesis (P < 0.001), promoting apoptosis (P < 0.01), ROS (P < 0.001), and MDA production (P < 0.001), increasing Bax (P < 0.001) and cleaved Caspase-3 (P < 0.001), and decreasing Bcl-2 (P < 0.001) and phosphorylated eNOS (P < 0.01). HOXA11-AS knockdown attenuated endothelial injuries via increasing eNOS phosphorylation. Luciferase assay and RIP results confirmed that miR-515-5p is directly bound to HOXA11-AS and ROCK1. HOXA11-AS promoted ox-LDL-induced HUVECs injury by directly inhibiting miR-515-5p from increasing ROCK1 expression and subsequently decreasing the expression and phosphorylation of eNOS. MiR-515-5p mimics could partially reverse the effects of HOXA11-AS knockdown.

CONCLUSIONS

HOXA11-AS contributed to atherosclerotic injuries by directly regulating the miR-515-5p/ROCK1 axis. This study provided new evidence that HOXA11-AS might be a candidate for atherosclerosis therapy.

Role of thioredoxin-interacting protein in mediating endothelial dysfunction in hypertension

Excessive oxidative stress is a major causative factor of endothelial dysfunction in hypertension. As an endogenous pro-oxidant, thioredoxin-interacting protein (TXNIP) contributes to oxidative damage in various tissues. The present study aimed to investigate the role of TXNIP in mediating endothelial dysfunction in hypertension. In vivo, an experimental model of acquired hypertension was established with two-kidney, one-clip (2K1C) surgery. The expression of TXNIP in the vascular endothelial cells of multiple vessels was significantly increased in hypertensive rats compared with sham-operated rats. Resveratrol, a TXNIP inhibitor, suppressed vascular oxidative damage and increased the expression and activity of eNOS in the aorta of hypertensive rats. Notably, impaired endothelium-dependent vasodilation was effectively improved by TXNIP inhibition in hypertensive rats. In vitro, we observed that Ang II increased the expression of TXNIP in primary human aortic endothelial cells (HAECs) and that TXNIP knockdown by RNA interference alleviated cellular oxidative stress damage and mitigated the impaired eNOS activation and intracellular nitric oxide (NO) production observed in Ang II-treated HAECs. However, inhibiting thioredoxin (TRX) with PX-12 completely blunted the protective effect of silencing TXNIP. In addition, TXNIP knockdown facilitated TRX expression and promoted TRX nuclear translocation to further activate AP1 and REF1. TRX overexpression exhibited favorable effects on eNOS/NO homeostasis in Ang II-treated HAECs. Thus, TXNIP contributes to oxidative stress and endothelial dysfunction in hypertension, and these effects are dependent on the antioxidant capacity of TRX, suggesting that targeting TXNIP may be a novel strategy for antihypertensive therapy.

Pathways of Microcirculatory Endothelial Dysfunction in Obstructive Sleep Apnea: A Comprehensive Ex Vivo Evaluation in Human Tissue

BACKGROUND

The mechanism and markers of cardiovascular disease (CVD) in obstructive sleep apnea (OSA) remain unknown. The microcirculation is the site of early changes in OSA patients who are free of CVD risk.

METHODS

Patients with newly diagnosed moderate to severe OSA (n = 7) were studied before and 12 weeks after intensive treatment with continuous positive airway pressure (CPAP), along with weight and age matched controls (n = 7). Microcirculatory vessels were isolated from gluteal biopsies and changes in critical functional genes were measured.

RESULTS

The following genes changed after 12 weeks of intensive CPAP therapy in the microcirculatory vessels: angiotensin receptor type 1 (AGTR-1) (11.6 (3.4) to 6 (0.8); P = 0.019); NADPH oxidase (NOX4) (0.85 (0.02) to 0.79 (0.11); P = 0.016); and dimethylarginine dimethylaminohydrolase (DDAH 1) (1 (0.31) to 0.55 (0.1); P = 0.028). Despite decreased nitric oxide (NO) availability as measured indirectly through brachial artery flow-mediated dilation, endothelial NO synthase (NOS3) did not change with CPAP. Other disease markers of OSA that changed with treatment in the microcirculation were endothelin, hypoxia inducible factor 1a, nuclear factor kappa B, interleukin-8, and interleukin-6.

CONCLUSIONS

In this ex vivo evaluation of the microcirculation of patients with OSA and no CVD risk, several pathways of CVD were activated supporting that OSA independently induces microcirculatory endothelial dysfunction and serving as disease-specific markers for future pharmacological targeting of OSA-related CVD risk. The findings support the role of renin-angiotensin activation and endothelial oxidative stress in the decreased microcirculatory NO availability in OSA.

Decreased NO production in endothelial cells exposed to plasma from ME/CFS patients

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease characterized by severe and persistent fatigue. Along with clinical studies showing endothelial dysfunction (ED) in a subset of ME/CFS patients, we have recently reported altered ED-related microRNAs in plasma from affected individuals. Inadequate nitric oxide (NO), mainly produced by the endothelial isoform of nitric oxide synthase (eNOS) in endothelial cells (ECs), is a major cause of ED. In this study, we hypothesized that plasma from that cohort of ME/CFS patients induces eNOS-related ED in vitro. To test this, we cultured human umbilical vein endothelial cells (HUVECs) in the presence of plasma from either ME/CFS patients (ME/CFS-plasma, n = 11) or healthy controls (HC-plasma, n = 12). Then, we measured the NO production in the absence and presence of tyrosine kinase and G protein-coupled receptors agonists (TKRs and GPCRs, respectively), well-known to activate eNOS in ECs. Our data showed that HUVECs incubated with ME/CFS-plasma produced less NO either in the absence or presence of eNOS activators compared to ones in presence of HC-plasma. Also, the NO production elicited by bradykinin, histamine, and acetylcholine (GPCRs agonists) was more affected than the one triggered by insulin (TKR agonist). Finally, inhibitory eNOS phosphorylation at Thr495 was higher in HUVECs treated with ME/CFS-plasma compared to the same treatment with HC-plasma. In conclusion, this study in vitro shows a decreased NO production in HUVECs exposed to plasma from ME/CFS patients, suggesting an unreported role of eNOS in the pathophysiology of this disease.

Electronic Cigarette Exposure Causes Vascular Endothelial Dysfunction Due to NADPH Oxidase Activation and eNOS Uncoupling

We recently reported a mouse model of chronic electronic cigarette (e-cig) exposure-induced cardiovascular pathology, where long-term exposure to e-cig vape (ECV) induces cardiac abnormalities, impairment of endothelial function, and systemic hypertension. Here, we delineate the underlying mechanisms of ECV-induced vascular endothelial dysfunction (VED), a central trigger of cardiovascular disease. C57/BL6 male mice were exposed to ECV generated from e-cig liquid containing 0, 6, or 24 mg/ml nicotine for 16 and 60 weeks. Time-dependent elevation in blood pressure and systemic vascular resistance were observed, along with an impairment of acetylcholine-induced aortic relaxation in ECV-exposed mice, compared to air-exposed control. Decreased intravascular nitric oxide (NO) levels and increased superoxide generation with elevated 3-nitrotyrosine levels in the aorta of ECV-exposed mice were observed, indicating that ECV-induced superoxide reacts with NO to generate cytotoxic peroxynitrite. Exposure increased NADPH oxidase expression, supporting its role in ECV-induced superoxide generation. Downregulation of endothelial nitric oxide synthase (eNOS) expression and Akt-dependent eNOS phosphorylation occurred in the aorta of ECV-exposed mice, indicating that exposure inhibited de novo NO synthesis. Following ECV exposure, the critical NOS cofactor tetrahydrobiopterin was decreased, with a concomitant loss of its salvage enzyme, dihydrofolate reductase. NADPH oxidase and NOS inhibitors abrogated ECV-induced superoxide generation in the aorta of ECV exposed mice. Together, our data demonstrate that ECV exposure activates NADPH oxidase and uncouples eNOS, causing a vicious cycle of superoxide generation and vascular oxidant stress that triggers VED and hypertension with predisposition to other cardiovascular disease.

Redox-Regulation of α-Globin in Vascular Physiology

Interest in the structure, function, and evolutionary relations of circulating and intracellular globins dates back more than 60 years to the first determination of the three-dimensional structure of these proteins. Non-erythrocytic globins have been implicated in circulatory control through reactions that couple nitric oxide (NO) signaling with cellular oxygen availability and redox status. Small artery endothelial cells (ECs) express free α-globin, which causes vasoconstriction by degrading NO. This reaction converts reduced (Fe2+) α-globin to the oxidized (Fe3+) form, which is unstable, cytotoxic, and unable to degrade NO. Therefore, (Fe3+) α-globin must be stabilized and recycled to (Fe2+) α-globin to reinitiate the catalytic cycle. The molecular chaperone α-hemoglobin-stabilizing protein (AHSP) binds (Fe3+) α-globin to inhibit its degradation and facilitate its reduction. The mechanisms that reduce (Fe3+) α-globin in ECs are unknown, although endothelial nitric oxide synthase (eNOS) and cytochrome b5 reductase (CyB5R3) with cytochrome b5 type A (CyB5a) can reduce (Fe3+) α-globin in solution. Here, we examine the expression and cellular localization of eNOS, CyB5a, and CyB5R3 in mouse arterial ECs and show that α-globin can be reduced by either of two independent redox systems, CyB5R3/CyB5a and eNOS. Together, our findings provide new insights into the regulation of blood vessel contractility.

Atrial nitroso-redox balance and refractoriness following on-pump cardiac surgery: a randomized trial of atorvastatin

AIMS

Systemic inflammation and increased activity of atrial NOX2-containing NADPH oxidases have been associated with the new onset of atrial fibrillation (AF) after cardiac surgery. In addition to lowering LDL-cholesterol, statins exert rapid anti-inflammatory and antioxidant effects, the clinical significance of which remains controversial.

METHODS AND RESULTS

We first assessed the impact of cardiac surgery and cardiopulmonary bypass (CPB) on atrial nitroso-redox balance by measuring NO synthase (NOS) and GTP cyclohydrolase-1 (GCH-1) activity, biopterin content, and superoxide production in paired samples of the right atrial appendage obtained before (PRE) and after CPB and reperfusion (POST) in 116 patients. The effect of perioperative treatment with atorvastatin (80 mg once daily) on these parameters, blood biomarkers, and the post-operative atrial effective refractory period (AERP) was then evaluated in a randomized, double-blind, placebo-controlled study in 80 patients undergoing cardiac surgery on CPB. CPB and reperfusion led to a significant increase in atrial superoxide production (74% CI 71-76%, n = 46 paired samples, P < 0.0001) and a reduction in atrial tetrahydrobiopterin (BH4) (34% CI 33-35%, n = 36 paired samples, P < 0.01), and in GCH-1 (56% CI 55-58%, n = 26 paired samples, P < 0.001) and NOS activity (58% CI 52-67%, n = 20 paired samples, P < 0.001). Perioperative atorvastatin treatment prevented the effect of CPB and reperfusion on all parameters but had no significant effect on the postoperative right AERP, troponin release, or NT-proBNP after cardiac surgery.

CONCLUSION

Perioperative statin therapy prevents post-reperfusion atrial nitroso-redox imbalance in patients undergoing on-pump cardiac surgery but has no significant impact on postoperative atrial refractoriness, perioperative myocardial injury, or markers of postoperative LV function.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT01780740.

Viable Allogeneic Mitochondria Transplantation Improves Gas Exchange and Alveolar-Capillary Permeability in Rats with Endotoxin-Induced Acute Lung Injuries

Background: Acute lung injuries (ALI) cause disruption of the alveolar-capillary barrier and is the leading cause of death in critically ill patients. This study tested the hypothesis that the administration of freshly isolated viable allogeneic mitochondria can prevent alveolar-capillary barrier injuries at the endothelial level, as mitochondrial dysfunction of the pulmonary endothelium is a critical aspect of ALI progression. Methods: ALI was induced by intratracheal lipopolysaccharide instillation (LPS, 1mg/kg) in anesthetized rats. Mitochondria (100 µg) were isolated from the freshly harvested soleus muscles of naïve rats and stained with a green fluorescence MitoTracker™ dyne. A mitochondria or placebo solution was randomly administered into the jugular veins of the rats at 2 h and 4 h after ALI induction. An arterial blood gas analysis was done 20 h later. The animals were then sacrificed and lung tissues were harvested for analysis. Results: An IVIS Spectrum imaging system was used to obtain ex vivo heart-lung block images and track the enhancement of MitoTracker™ fluorescence in the lungs. Mitochondria transplantation significantly improved arterial oxygen contents (PaO₂ and SaO₂) and reduced CO₂ tension in rats with ALI. Animals with mitochondrial transplants had significantly higher ATP concentrations in their lung tissues. Allogeneic mitochondria transplantation preserved alveolar-capillary barrier function, as shown by a reduction in protein levels in the bronchoalveolar lavage fluid and decreased extravasated Evans blue dyne and hemoglobin content in lung tissues. In addition, relaxation responses to acetylcholine and eNOS expression were potentiated in injured pulmonary arteries and inflammatory cells infiltration into lung tissue was reduced following mitochondrial transplantation. Conclusions: Transplantation of viable mitochondria protects the integrity of endothelial lining of the alveolar-capillary barrier, thereby improving gas exchange during the acute stages of endotoxin-induced ALI. However, the long-term effects of mitochondrial transplantation on pulmonary function recovery after ALI requires further investigation.

High Soluble Endoglin Levels Affect Aortic Vascular Function during Mice Aging

Endoglin is a 180 kDa transmembrane glycoprotein that was demonstrated to be present in two different endoglin forms, namely membrane endoglin (Eng) and soluble endoglin (sEng). Increased sEng levels in the circulation have been detected in atherosclerosis, arterial hypertension, and type II diabetes mellitus. Moreover, sEng was shown to aggravate endothelial dysfunction when combined with a high-fat diet, suggesting it might be a risk factor for the development of endothelial dysfunction in combination with other risk factors. Therefore, this study hypothesized that high sEng levels exposure for 12 months combined with aging (an essential risk factor of atherosclerosis development) would aggravate vascular function in mouse aorta. Male transgenic mice with high levels of human sEng in plasma (Sol-Eng⁺) and their age-matched male transgenic littermates that do not develop high soluble endoglin (Control) on a chow diet were used. The aging process was initiated to contribute to endothelial dysfunction/atherosclerosis development, and it lasted 12 months. Wire myograph analysis showed impairment contractility in the Sol-Eng⁺ group when compared to the control group after KCl and PGF_2α administration. Endothelium-dependent responsiveness to Ach was not significantly different between these groups. Western blot analysis revealed significantly decreased protein expression of Eng, p-eNOS, and ID1 expression in the Sol-Eng⁺ group compared to the control group suggesting reduced Eng signaling. In conclusion, we demonstrated for the first time that long-term exposure to high levels of sEng during aging results in alteration of vasoconstriction properties of the aorta, reduced eNOS phosphorylation, decreased Eng expression, and altered Eng signaling. These findings suggest that sEng can be considered a risk factor for the development of vascular dysfunction during aging and a potential therapeutical target for pharmacological intervention.

Ex vivo Akt inhibition reverses castration induced internal pudendal artery and penile endothelial dysfunction

AIMS

Androgen deprivation therapy is a common prostate cancer treatment which causes men to have castrate levels of testosterone. Unfortunately, most testosterone deficient patients will suffer severe erectile dysfunction (ED) and have no effective ED treatment options. Testosterone deficiency causes endothelial dysfunction and impairs penile vasodilation necessary to maintain an erection. Recent evidence demonstrates testosterone activates androgen receptors (AR) and generates nitric oxide (NO) through the Akt-endothelial NO synthase (eNOS) pathway; however, it remains unknown how castration impacts this signaling pathway.

MATERIALS AND METHODS

In this study, we used a surgically castrated rat model to determine how castration impacts ex vivo internal pudendal artery (IPA) and penile relaxation through the Akt-eNOS pathway.

KEY FINDINGS

Unlike systemic vasculature, castration causes significant IPA and penis endothelial dysfunction associated with a 50% AR reduction. Though testosterone and acetylcholine (ACh) both phosphorylate Akt and eNOS, castration did not affect testosterone-mediated IPA and penile Akt or eNOS phosphorylation. Surprisingly, castration increases ACh-mediated Akt and eNOS phosphorylation but reduces the eNOS dimer to monomer ratio. Akt inhibition using 10DEBC preserves IPA eNOS dimers. Functionally, 10DEBC reverses castration induced ex vivo IPA and penile endothelial dysfunction.

SIGNIFICANCE

These data demonstrate how castration uncouples eNOS and provide a novel strategy for improving endothelial-dependent relaxation necessary for an erection. Further studies are needed to determine if Akt inhibition may treat or even prevent ED in testosterone deficient prostate cancer survivors.

Rutaecarpine Increases Nitric Oxide Synthesis via eNOS Phosphorylation by TRPV1-Dependent CaMKII and CaMKKβ/AMPK Signaling Pathway in Human Endothelial Cells

Rutaecarpine (RUT) is a bioactive alkaloid isolated from the fruit of Evodia rutaecarpa that exerts a cellular protective effect. However, its protective effects on endothelial cells and its mechanism of action are still unclear. In this study, we demonstrated the effects of RUT on nitric oxide (NO) synthesis via endothelial nitric oxide synthase (eNOS) phosphorylation in endothelial cells and the underlying molecular mechanisms. RUT treatment promoted NO generation by increasing eNOS phosphorylation. Additionally, RUT induced an increase in intracellular Ca²⁺ concentration and phosphorylation of Ca²⁺/calmodulin-dependent protein kinase kinase β (CaMKKβ), AMP-activated protein kinase (AMPK), and Ca²⁺/calmodulin-dependent kinase II (CaMKII). Inhibition of transient receptor potential vanilloid type 1 (TRPV1) attenuated RUT-induced intracellular Ca²⁺ concentration and phosphorylation of CaMKII, CaMKKβ, AMPK, and eNOS. Treatment with KN-62 (a CaMKII inhibitor), Compound C (an AMPK inhibitor), and STO-609 (a CaMKKβ inhibitor) suppressed RUT-induced eNOS phosphorylation and NO generation. Interestingly, RUT attenuated the expression of ICAM-1 and VCAM-1 induced by TNF-α and inhibited the inflammation-related NF-κB signaling pathway. Taken together, these results suggest that RUT promotes NO synthesis and eNOS phosphorylation via the Ca²⁺/CaMKII and CaM/CaMKKβ/AMPK signaling pathways through TRPV1. These findings provide evidence that RUT prevents endothelial dysfunction and benefit cardiovascular health.

Potential Benefits of Berry Anthocyanins on Vascular Function

Cardiovascular disease (CVD), such as hypertension and atherosclerosis, is the leading cause of global death. Endothelial dysfunction (ED) is a strong predictor for most CVD making it a therapeutic target for both drug and nutrition interventions. It has been previously shown that polyphenols from wine and grape extracts possess vasodilator activities, due to the increased expression and phosphorylation of the endothelial nitric oxide synthase (eNOS), and consequent vasodilator nitric oxide (NO) production. This is vital in the prevention of ED, as NO production contributes to the maintenance of endothelial homeostasis. Moreover, polyphenols have the ability to inhibit reactive oxygen species (ROS), which can cause oxidative stress, as well as suppress the upregulation of inflammatory markers within the endothelium. However, while the majority of the research has focused on red wine, this has overshadowed the potential of other nutritional components for targeting ED, such as the use of berries. Berries are high in anthocyanin flavonoids a subtype of polyphenols with studies suggesting improved vascular function as a result of inducing NO production and reducing oxidative stress and inflammation. This review focuses on the protective effects of berries within the vasculature.

Potential Roles of Endoplasmic Reticulum Stress and Cellular Proteins Implicated in Diabesity

The role of the endoplasmic reticulum (ER) has evolved from protein synthesis, processing, and other secretory pathways to forming a foundation for lipid biosynthesis and other metabolic functions. Maintaining ER homeostasis is essential for normal cellular function and survival. An imbalance in the ER implied stressful conditions such as metabolic distress, which activates a protective process called unfolded protein response (UPR). This response is activated through some canonical branches of ER stress, i.e., the protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1α (IRE1α), and activating transcription factor 6 (ATF6). Therefore, chronic hyperglycemia, hyperinsulinemia, increased proinflammatory cytokines, and free fatty acids (FFAs) found in diabesity (a pathophysiological link between obesity and diabetes) could lead to ER stress. However, limited data exist regarding ER stress and its association with diabesity, particularly the implicated proteins and molecular mechanisms. Thus, this review highlights the role of ER stress in relation to some proteins involved in diabesity pathogenesis and provides insight into possible pathways that could serve as novel targets for therapeutic intervention.

Type I interferon activation and endothelial dysfunction in caveolin-1 insufficiency-associated pulmonary arterial hypertension

Interferonopathies, interferon (IFN)-α/β therapy, and caveolin-1 (CAV1) loss-of-function have all been associated with pulmonary arterial hypertension (PAH). Here, CAV1-silenced primary human pulmonary artery endothelial cells (PAECs) were proliferative and hypermigratory, with reduced cytoskeletal stress fibers. Signal transducers and activators of transcription (STAT) and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) were both constitutively activated in these cells, resulting in a type I IFN-biased inflammatory signature. Cav1 ^-/- mice that spontaneously develop pulmonary hypertension were found to have STAT1 and AKT activation in lung homogenates and increased circulating levels of CXCL10, a hallmark of IFN-mediated inflammation. PAH patients with CAV1 mutations also had elevated serum CXCL10 levels and their fibroblasts mirrored phenotypic and molecular features of CAV1-deficient PAECs. Moreover, immunofluorescence staining revealed endothelial CAV1 loss and STAT1 activation in the pulmonary arterioles of patients with idiopathic PAH, suggesting that this paradigm might not be limited to rare CAV1 frameshift mutations. While blocking JAK/STAT or AKT rescued aspects of CAV1 loss, only AKT inhibitors suppressed activation of both signaling pathways simultaneously. Silencing endothelial nitric oxide synthase (NOS3) prevented STAT1 and AKT activation induced by CAV1 loss, implicating CAV1/NOS3 uncoupling and NOS3 dysregulation in the inflammatory phenotype. Exogenous IFN reduced CAV1 expression, activated STAT1 and AKT, and altered the cytoskeleton of PAECs, implicating these mechanisms in PAH associated with autoimmune and autoinflammatory diseases, as well as IFN therapy. CAV1 insufficiency elicits an IFN inflammatory response that results in a dysfunctional endothelial cell phenotype and targeting this pathway may reduce pathologic vascular remodeling in PAH.

An isoform-specific pivot modulates the electron transfer between the flavin mononucleotide and heme centers in inducible nitric oxide synthase

Intraprotein interdomain electron transfer (IET) between the flavin mononucleotide (FMN) and heme centers is an obligatory step in nitric oxide synthase (NOS) enzymes. An isoform-specific pivotal region near Leu406 in the heme domain of human inducible NOS (iNOS) was proposed to mediate the FMN-heme domain-domain alignment (J Inorg Biochem 153:186-196, 2015). The FMN-heme IET rate is a measure of the interdomain FMN/heme complex formation. In this work, the FMN-heme IET kinetics in the wild type (wt) human iNOS oxygenase/FMN (oxyFMN) construct were directly measured by laser flash photolysis with added synthetic peptide related to the pivotal region, in comparison with the wt construct alone. The IET rates were decreased by the iNOS HKL peptide in a dose-saturable fashion, and the inhibitory effect was abolished by a single L406 → E mutation in the peptide. A similar trend in change of the NO synthesis activity of wt iNOS holoenzyme by the peptides was observed. These data, along with the kinetics and modeling results for the L406T and L406F mutant oxyFMN proteins, indicated that the Leu406 residue modulates the FMN-heme IET through hydrophobic interactions. Moreover, the IET rates were analyzed for the wt iNOS oxyFMN protein in the presence of nNOS or eNOS-derived peptide related to the equivalent pivotal heme domain site. These results together indicate that the isoform-specific pivotal region at the heme domain specifically interacts with the conserved FMN domain surface, to facilitate proper interdomain docking for the FMN-heme IET in NOS.

Pathobiology of ischiocavernosus and bulbospongiosus muscles in long-term diabetic male rats and its implication on erectile dysfunction

OBJECTIVE

To analyze pathobiology of ischiocavernosus (IC) and bulbospongiosus (BS) muscles in long-term diabetic male rats and its implication on erectile dysfunction (ED).

METHODS

Male rats were grouped into control and diabetic rats (received single injection of 60 mg/kg bw. of streptozotocin [STZ]). At 120th day, the animals were subjected to various analyses like serum hormone, penile reflex, electromyography of IC and BS muscles, after euthanasia IC and BS muscles were processed for morphological, histology, histometric analysis, immunostaining and immunoblotting synaptophysin, nNOS and NADPH diaphorase histochemistry.

RESULTS

Significant reduction in serum hormone level, penile reflex, reduced action potential or activity in both these muscles and wide range of histological alterations were observed in STZ rats. Muscles showed significant reduction in the diameter, volume and numerical density of the fiber in both muscles of STZ rats. Synaptophysin, nNOS and NADPH diaphorase were significantly reduced in diabetic animal IC and BS.

CONCLUSION

Severe neuromuscular circuitry alteration in IC and BS. Study concludes that degenerative changes in IC and BS may play a major role in ED in diabetic condition. Indicating diabetic-induced postsynaptic neuronal degeneration along with impaired motor action of the muscle and severe muscle degeneration affecting ED.

Preventing treatment failures in coronary artery disease: what can we learn from the biology of in-stent restenosis, vein graft failure, and internal thoracic arteries?

Coronary artery disease (CAD) remains one of the most important causes of morbidity and mortality worldwide, and the availability of percutaneous or surgical revascularization procedures significantly improves survival. However, both strategies are daunted by complications which limit long-term effectiveness. In-stent restenosis (ISR) is a major drawback for intracoronary stenting, while graft failure is the limiting factor for coronary artery bypass graft surgery (CABG), especially using veins. Conversely, internal thoracic artery (ITA) is known to maintain long-term patency in CABG. Understanding the biology and pathophysiology of ISR and vein graft failure (VGF) and mechanisms behind ITA resistance to failure is crucial to combat these complications in CAD treatment. This review intends to provide an overview of the biological mechanisms underlying stent and VGF and of the potential therapeutic strategy to prevent these complications. Interestingly, despite being different modalities of revascularization, mechanisms of failure of stent and saphenous vein grafts are very similar from the biological standpoint.

Chronic cigarette smoke exposure triggers a vicious cycle of leukocyte and endothelial-mediated oxidant stress that results in vascular dysfunction

Although there is a strong association between cigarette smoking exposure (CSE) and vascular endothelial dysfunction (VED), the underlying mechanisms by which CSE triggers VED remain unclear. Therefore, studies were performed to define these mechanisms using a chronic mouse model of cigarette smoking (CS)-induced cardiovascular disease mirroring that in humans. C57BL/6 male mice were subjected to CSE for up to 48 wk. CSE impaired acetylcholine (ACh)-induced relaxation of aortic and mesenteric segments and triggered hypertension, with mean arterial blood pressure at 32 and 48 wk of exposure of 122 ± 6 and 135 ± 5 mmHg compared with 99 ± 4 and 102 ± 6 mmHg, respectively, in air-exposed mice. CSE led to monocyte activation with superoxide generation in blood exiting the pulmonary circulation. Macrophage infiltration with concomitant increase in NADPH oxidase subunits p22^phox and gp91^phox was seen in aortas of CS-exposed mice at 16 wk, with further increase out to 48 wk. Associated with this, increased superoxide production was detected that decreased with Nox inhibition. Tetrahydrobiopterin was progressively depleted in CS-exposed mice but not in air-exposed controls, resulting in endothelial nitric oxide synthase (eNOS) uncoupling and secondary superoxide generation. CSE led to a time-dependent decrease in eNOS and Akt expression and phosphorylation. Overall, CSE induces vascular monocyte infiltration with increased NADPH oxidase-mediated reactive oxygen species generation and depletes the eNOS cofactor tetrahydrobiopterin, uncoupling eNOS and triggering a vicious cycle of oxidative stress with VED and hypertension. Our study provides important insights toward understanding the process by which smoking contributes to the genesis of cardiovascular disease and identifies biomarkers predictive of disease.NEW & NOTEWORTHY In a chronic model of smoking-induced cardiovascular disease, we define underlying mechanisms of smoking-induced vascular endothelial dysfunction (VED). Smoking exposure triggered VED and hypertension and led to vascular macrophage infiltration with concomitant increase in superoxide and NADPH oxidase levels as early as 16 wk of exposure. This oxidative stress was accompanied by tetrahydrobiopterin depletion, resulting in endothelial nitric oxide synthase uncoupling with further superoxide generation triggering a vicious cycle of oxidative stress and VED.

Electrical stimulation of the carotid sinus lowers arterial pressure and improves heart rate variability in L-NAME hypertensive conscious rats

We evaluated the effects of long-term (48 h) electrical stimulation of the carotid sinus (CS) in hypertensive rats. L-NAME-treated (10 days) Wistar rats were implanted with a catheter in the femoral artery and a miniaturized electrical stimulator attached to electrodes positioned around the left CS, encompassing the CS nerve. One day after implantation, arterial pressure (AP) was directly recorded in conscious animals for 60 min. Square pulses (1 ms, 3 V, 30 Hz) were applied intermittently (20/20 s ON/OFF) to the CS for 48 h. After the end of stimulation, AP was recorded again. Nonstimulated rats (control group) and rats without electrodes around the CS (sham-operated) were also studied. Next, the animals were decapitated, and segments of mesenteric resistance arteries were removed to study vascular function. After the stimulation period, AP was 16 ± 5 mmHg lower in the stimulated group, whereas sham-operated and control rats showed similar AP between the first and second recording periods. Heart rate variability (HRV) evaluated using time and frequency domain tools and a nonlinear approach (symbolic analysis) suggested that hypertensive rats with electrodes around the CS, stimulated or not, exhibited a shift in cardiac sympathovagal balance towards parasympathetic tone. The relaxation response to acetylcholine in endothelium-intact mesenteric arteries was enhanced in rats that underwent CS stimulation for 48 h. In conclusion, long-term CS stimulation is effective in reducing AP levels, improving HRV and increasing mesenteric vascular relaxation in L-NAME hypertensive rats. Moreover, only the presence of electrodes around the CS is effective in eliciting changes in HRV similar to those observed in stimulated rats.

Monosodium urate crystal interleukin-1β release is dependent on Toll-like receptor 4 and transient receptor potential V1 activation

OBJECTIVE

The present study aimed to elucidate the mechanisms involved in MSU-induced IL-1β release in a rodent animal model of acute gout arthritis.

METHODS

Painful (mechanical and thermal hypersensitivity, ongoing pain and arthritis score) and inflammatory (oedema, plasma extravasation, cell infiltration and IL-1β release) parameters were assessed several hours after intra-articular injection of MSU (100 µg/articulation) in wild-type or knockout mice for Toll-like receptor 4 (TLR4), inducible nitric oxide synthase (iNOS), transient receptor potential (TRP) V1 and the IL-1 receptor (IL-1R). Also, wild-type animals were treated with clodronate, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS) (TLR4 antagonist), spleen tyrosine kinase (SYK) inhibitor (iSYK), aminoguanidine (AMG, an iNOS inhibitor) or SB366791 (TRPV1 antagonist). Nitrite/nitrate and IL-1β levels were measured on the synovial fluid of wild-type mice, 2 h after intra-articular MSU injections, or medium from macrophages stimulated for MSU (1000 μg) for 2 h.

RESULTS

Intra-articular MSU injection caused robust nociception and severe inflammation from 2 up to 6 h after injection, which were prevented by the pre-treatment with clodronate, LPS-RS, iSYK, AMG and SB366791, or the genetic ablation of TLR4, iNOS, TRPV1 or IL-1R. MSU also increased nitrite/nitrate and IL-1β levels in the synovial fluid, which was prevented by clodronate, LPS-RS, iSYK and AMG, but not by SB366791. Similarly, MSU-stimulated peritoneal macrophages released nitric oxide, which was prevented by LPS-RS, iSYK and AMG, but not by SB366791, and released IL-1β, which was prevented by LPS-RS, iSYK, AMG and SB366791.

CONCLUSION

Our data indicate that MSU may activate TLR4, SYK, iNOS and TRPV1 to induce the release of IL-1β by macrophages, triggering nociception and inflammation during acute gout attack.

Dual Character of Reactive Oxygen, Nitrogen, and Halogen Species: Endogenous Sources, Interconversions and Neutralization

Oxidative stress resulting from accumulation of reactive oxygen, nitrogen, and halogen species (ROS, RNS, and RHS, respectively) causes the damage of cells and biomolecules. However, over the long evolutionary time, living organisms have developed the mechanisms for adaptation to oxidative stress conditions including the activity of the antioxidant system (AOS), which maintains low intracellular levels of RONS (ROS and RNS) and RHS. Moreover, living organisms have adapted to use low concentrations of these electrophiles for the regulation of cell functions through the reversible post-translational chemical modifications of redox-sensitive amino acid residues in intracellular effectors of signal transduction pathways (protein kinases and protein phosphatases), transcription factors, etc. An important fine-tuning mechanism that ensures involvement of RONS and RHS in the regulation of physiological processes is interconversion between different reactive species. This review focuses on the complex networks of interacting RONS and RHS types and their endogenous sources, such as NOX family of NADPH oxidases, complexes I and III of the mitochondrial electron transport chain, NO synthases, cytochrome P450-containing monooxygenase system, xanthine oxidoreductase, and myeloperoxidases. We highlight that kinetic parameters of reactions involving RONS and RHS determine the effects of these reactive species on cell functions. We also describe the functioning of enzymatic and non-enzymatic AOS components and the mechanisms of RONS and RHS scavenging under physiological conditions. We believe that analysis of interactions between RONS and relationships between different endogenous sources of these compounds will contribute to better understanding of their role in the maintenance of cell redox homeostasis as well as initiation and progression of diseases.

Sesamin Induces Endothelial Nitric Oxide Synthase Activation via Transient Receptor Potential Vanilloid Type 1

Sesamin, the most abundant lignan in sesame seed oil, has many biological activities. However, the underlying molecular mechanisms behind the regulatory effects of sesamin on endothelial nitric oxide synthase (eNOS) activity and nitric oxide (NO) generation in endothelial cells (ECs) remain unclear. Sesamin induced the intracellular level of NO and eNOS phosphorylation in ECs in a concentration- and time-dependent manner. Additionally, sesamin induced levels of intracellular calcium, leading to the phosphorylation of calmodulin-dependent protein kinase II (CaMKII) at Thr286, calcium/calmodulin-dependent protein kinase kinase beta (CaMKKβ) at Ser511, protein kinase A (PKA) at Thr197, Akt at Ser473, and AMP-activated protein kinase (AMPK) at Thr172. In particular, blocking of the transient receptor potential vanilloid type 1 (TRPV1) channel by capsazepine (TRPV1 antagonist), as well as TRPV1 knockdown via TRPV1 silencing RNA, abrogated sesamin-induced PKA, Akt, AMPK, CaMKII, CaMKKβ, and eNOS phosphorylation and NO level in ECs. Furthermore, sesamin inhibited TNF-α-induced NF-κB translocation, intercellular adhesion molecule-1 expression, and monocyte adhesion. Sesamin triggered eNOS activity and NO production via activation of TRPV1-calcium signaling, which involved the phosphorylation of PKA, CaMKII, CaMKKβ, Akt, and AMPK. Sesamin may be useful for treating or preventing the endothelial dysfunction correlated with cardiovascular diseases.

Inhibited Nitric Oxide Production of Human Endothelial Nitric Oxide Synthase by Nitrated and Oxygenated Polycyclic Aromatic Hydrocarbons

Nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) from the direct atmospheric emission or the degradation of parent PAHs are increasingly recognized because of their potential health risks. Herein, we investigated the effects of four NPAHs/OPAHs (1-NNAP, 9-NANT, 9,10-AQ, and 9-FLU) and their parent PAHs (NAP, ANT, and FLU) on endothelium function with regard to endothelial nitric oxide synthase (eNOS) and endothelium-derived nitric oxide (NO) production in human umbilical vein endothelial cells. The eNOS enzymatic activity and NO production were promoted by NAP, ANT, and FLU; however, eNOS activity was dropped by 52.8, 52.1, 52.5, and 44.5%, and NO production was decreased by 31.1, 50.3, 65.0, and 35.0% after 24 h exposure to 0.01 μM 1-NNAP, 9-NANT, 9,10-AQ, and 9-FLU, respectively. The mRNA expression of eNOS and protein expression of phosphorylated eNOS (Ser1177) were increased by three PAHs but decreased by four NPAHs/OPAHs. The 100 ns molecular dynamics simulations reveal the conformational alteration in the key propionate of heme upon the binding of NPAHs/OPAHs. Our findings provide the first in silico and in vitro evidence for the potential endothelial dysfunction of nitrated and oxygenated PAHs. The health risk implications of NPAHs/OPAHs and corresponding parent PAHs warrant further research.

Progesterone Protects Prefrontal Cortex in Rat Model of Permanent Bilateral Common Carotid Occlusion via Progesterone Receptors and Akt/Erk/eNOS

Sustained activation of pro-apoptotic signaling due to a sudden and prolonged disturbance of cerebral blood circulation governs the neurodegenerative processes in prefrontal cortex (PFC) of rats whose common carotid arteries are permanently occluded. The adequate neuroprotective therapy should minimize the activation of toxicity pathways and increase the activity of endogenous protective mechanisms. Several neuroprotectants have been proposed, including progesterone (P₄). However, the underlying mechanism of its action in PFC following permanent bilateral occlusion of common carotid arteries is not completely investigated. We, thus herein, tested the impact of post-ischemic P₄ treatment (1.7 mg/kg for seven consecutive days) on previously reported aberrant neuronal morphology and amount of DNA fragmentation, as well as the expression of progesterone receptors along with the key elements of Akt/Erk/eNOS signal transduction pathway (Bax, Bcl-2, cytochrome C, caspase 3, PARP, and the level of nitric oxide). The obtained results indicate that potential amelioration of histological changes in PFC might be associated with the absence of activation of Bax/caspase 3 signaling cascade and the decline of DNA fragmentation. The study also provides the evidence that P₄ treatment in repeated regiment of administration might be effective in neuronal protection against ischemic insult due to re-establishment of the compromised action of Akt/Erk/eNOS-mediated signaling pathway and the upregulation of progesterone receptors.

SUMO2 regulates vascular endothelial function and oxidative stress in mice

SUMOylation is a posttranslational modification of lysine residues. Modification of proteins by small ubiquitin-like modifiers (SUMO)1, -2, and -3 can achieve varied, and often unique, physiological and pathological effects. We looked for SUMO2-specific effects on vascular endothelial function. SUMO2 expression was upregulated in the aortic endothelium of hypercholesterolemic low-density lipoprotein receptor-deficient mice and was responsible for impairment of endothelium-dependent vasorelaxation in these mice. Moreover, overexpression of SUMO2 in aortas ex vivo, in cultured endothelial cells, and transgenically in the endothelium of mice increased vascular oxidative stress and impaired endothelium-dependent vasorelaxation. Conversely, inhibition of SUMO2 impaired physiological endothelium-dependent vasorelaxation in normocholesterolemic mice. These findings indicate that while endogenous SUMO2 is important in maintenance of normal endothelium-dependent vascular function, its upregulation impairs vascular homeostasis and contributes to hypercholesterolemia-induced endothelial dysfunction.

NEW & NOTEWORTHY Sumoylation is known to impair vascular function; however, the role of specific SUMOs in the regulation of vascular function is not known. Using multiple complementary approaches, we show that hyper-SUMO2ylation impairs vascular endothelial function and increases vascular oxidative stress, whereas endogenous SUMO2 is essential for maintenance of normal physiological function of the vascular endothelium.

Discordance between eNOS phosphorylation and activation revealed by multispectral imaging and chemogenetic methods

Nitric oxide (NO) synthesized by the endothelial isoform of nitric oxide synthase (eNOS) is a critical determinant of vascular homeostasis. However, the real-time detection of intracellular NO-a free radical gas-has been difficult, and surrogate markers for eNOS activation are widely utilized. eNOS phosphorylation can be easily measured in cells by probing immunoblots with phosphospecific antibodies. Here, we pursued multispectral imaging approaches using biosensors to visualize intracellular NO and Ca²⁺ and exploited chemogenetic approaches to define the relationships between NO synthesis and eNOS phosphorylation in cultured endothelial cells. We found that the G protein-coupled receptor agonists adenosine triphosphate (ATP) and histamine promoted rapid increases in eNOS phosphorylation, as did the receptor tyrosine kinase agonists insulin and Vascular Endothelial Growth Factor (VEGF). Histamine and ATP also promoted robust NO formation and increased intracellular Ca²⁺ By contrast, neither insulin nor VEGF caused any increase whatsoever in intracellular NO or Ca²⁺-despite eliciting strong eNOS phosphorylation responses. Our findings demonstrate an unexpected and striking discordance between receptor-modulated eNOS phosphorylation and NO formation in endothelial cells. Previous reports in which phosphorylation of eNOS has been studied as a surrogate for enzyme activation may need to be reassessed.

Akt phosphorylation of neuronal nitric oxide synthase regulates gastrointestinal motility in mouse ileum

Nitric oxide (NO) is a major inhibitory neurotransmitter that mediates nonadrenergic noncholinergic (NANC) signaling. Neuronal NO synthase (nNOS) is activated by Ca²⁺/calmodulin to produce NO, which causes smooth muscle relaxation to regulate physiologic tone. nNOS serine1412 (S1412) phosphorylation may reduce the activating Ca²⁺ requirement and sustain NO production. We developed and characterized a nonphosphorylatable nNOS^S1412A knock-in mouse and evaluated its enteric neurotransmission and gastrointestinal (GI) motility to understand the physiologic significance of nNOS S1412 phosphorylation. Electrical field stimulation (EFS) of wild-type (WT) mouse ileum induced nNOS S1412 phosphorylation that was blocked by tetrodotoxin and by inhibitors of the protein kinase Akt but not by PKA inhibitors. Low-frequency depolarization increased nNOS S1412 phosphorylation and relaxed WT ileum but only partially relaxed nNOS^S1412A ileum. At higher frequencies, nNOS S1412 had no effect. nNOS^S1412A ileum expressed less phosphodiesterase-5 and was more sensitive to relaxation by exogenous NO. Under non-NANC conditions, peristalsis and segmentation were faster in the nNOS^S1412A ileum. Together these findings show that neuronal depolarization stimulates enteric nNOS phosphorylation by Akt to promote normal GI motility. Thus, phosphorylation of nNOS S1412 is a significant regulatory mechanism for nitrergic neurotransmission in the gut.

Reduced caveolae density in arteries of SHR contributes to endothelial dysfunction and ROS production

Caveolae are plasma membrane invaginations enriched with high cholesterol and sphingolipid content; they also contain caveolin proteins in their structure. Endothelial nitric oxide synthase (eNOS), an enzyme that synthesizes nitric oxide (NO) by converting L-arginine to L-citrulline, is highly concentrated in plasma membrane caveolae. Hypertension is associated with decreased NO production and impaired endothelium-dependent relaxation. Understanding the molecular mechanisms that follow hypertension is important. For this study, we hypothesized that spontaneously hypertensive rat (SHR) vessels should have a smaller number of caveolae, and that the caveolae structure should be disrupted in these vessels. This should impair the eNOS function and diminish NO bioavailability. Therefore, we aimed to investigate caveolae integrity and density in SHR aortas and mesenteric arteries and the role played by caveolae in endothelium-dependent relaxation. We have been able to show the presence of caveolae-like structures in SHR aortas and mesenteric arteries. Increased phenylephrine-induced contractile response after treatment with dextrin was related to lower NO release. In addition, impaired acetylcholine-induced endothelium-dependent relaxation could be related to decreased caveolae density in SHR vessels. The most important finding of this study was that cholesterol depletion with dextrin induced eNOS phosphorylation at Serine¹¹⁷⁷ (Ser¹¹⁷⁷) and boosted reactive oxygen species (ROS) production in normotensive rat and SHR vessels, which suggested eNOS uncoupling. Dextrin plus L-NAME or BH₄ decreased ROS production in aorta and mesenteric arteries supernatant’s of both SHR and normotensive groups. Human umbilical vein endothelial cells (HUVECs) treated with dextrin confirmed eNOS uncoupling, as verified by the reduced eNOS dimer/monomer ratio. BH₄, L-arginine, or BH₄ plus L-arginine inhibited eNOS monomerization. All these results showed that caveolae structure and integrity are essential for endothelium-dependent relaxation. Additionally, a smaller number of caveolae is associated with hypertension. Finally, caveolae disruption promotes eNOS uncoupling in normotensive and hypertensive rat vessels and in HUVECs.

Use of Computational Biochemistry for Elucidating Molecular Mechanisms of Nitric Oxide Synthase

Nitric oxide (NO) is an essential signaling molecule in the regulation of multiple cellular processes. It is endogenously synthesized by NO synthase (NOS) as the product of L-arginine oxidation to L-citrulline, requiring NADPH, molecular oxygen, and a pterin cofactor. Two NOS isoforms are constitutively present in cells, nNOS and eNOS, and a third is inducible (iNOS). Despite their biological relevance, the details of their complex structural features and reactivity mechanisms are still unclear. In this review, we summarized the contribution of computational biochemistry to research on NOS molecular mechanisms. We described in detail its use in studying aspects of structure, dynamics and reactivity. We also focus on the numerous outstanding questions in the field that could benefit from more extensive computational investigations.

Sources of Vascular Nitric Oxide and Reactive Oxygen Species and Their Regulation

Nitric oxide (NO) is a small free radical with critical signaling roles in physiology and pathophysiology. The generation of sufficient NO levels to regulate the resistance of the blood vessels and hence the maintenance of adequate blood flow is critical to the healthy performance of the vasculature. A novel paradigm indicates that classical NO synthesis by dedicated NO synthases is supplemented by nitrite reduction pathways under hypoxia. At the same time, reactive oxygen species (ROS), which include superoxide and hydrogen peroxide, are produced in the vascular system for signaling purposes, as effectors of the immune response, or as byproducts of cellular metabolism. NO and ROS can be generated by distinct enzymes or by the same enzyme through alternate reduction and oxidation processes. The latter oxidoreductase systems include NO synthases, molybdopterin enzymes, and hemoglobins, which can form superoxide by reduction of molecular oxygen or NO by reduction of inorganic nitrite. Enzymatic uncoupling, changes in oxygen tension, and the concentration of coenzymes and reductants can modulate the NO/ROS production from these oxidoreductases and determine the redox balance in health and disease. The dysregulation of the mechanisms involved in the generation of NO and ROS is an important cause of cardiovascular disease and target for therapy. In this review we will present the biology of NO and ROS in the cardiovascular system, with special emphasis on their routes of formation and regulation, as well as the therapeutic challenges and opportunities for the management of NO and ROS in cardiovascular disease.

Role of Alcohol Oxidative Metabolism in Its Cardiovascular and Autonomic Effects

Several review articles have been published on the neurobehavioral actions of acetaldehyde and other ethanol metabolites as well as in major alcohol-related disorders such as cancer and liver and lung disease. However, very few reviews dealt with the role of alcohol metabolism in the adverse cardiac and autonomic effects of alcohol and their potential underlying mechanisms, particularly in vulnerable populations. In this chapter, following a brief overview of the dose-related favorable and adverse cardiovascular effects of alcohol, we discuss the role of ethanol metabolism in its adverse effects in the brainstem and heart. Notably, current knowledge dismisses a major role for acetaldehyde in the adverse autonomic and cardiac effects of alcohol because of its low tissue level in vivo. Contrary to these findings in men and male rodents, women and hypertensive individuals are more sensitive to the adverse cardiac effects of similar amounts of alcohol. To understand this discrepancy, we discuss the autonomic and cardiac effects of alcohol and its metabolite acetaldehyde in a model of hypertension, the spontaneously hypertensive rat (SHR) and female rats. We present evidence that enhanced catalase activity, which contributes to cardioprotection in hypertension (compensatory) and in the presence of estrogen (inherent), becomes detrimental due to catalase catalysis of alcohol metabolism to acetaldehyde. Noteworthy, studies in SHRs and in estrogen deprived or replete normotensive rats implicate acetaldehyde in triggering oxidative stress in autonomic nuclei and the heart via (i) the Akt/extracellular signal-regulated kinases (ERK)/nitric oxide synthase (NOS) cascade and (ii) estrogen receptor-alpha (ERα) mediation of the higher catalase activity, which generates higher ethanol-derived acetaldehyde in female heart. The latter is supported by the ability of ERα blockade or catalase inhibition to attenuate alcohol-evoked myocardial oxidative stress and dysfunction. More mechanistic studies are needed to further understand the mechanisms of this public health problem.

Generation and characterization of functional phosphoserine-incorporated neuronal nitric oxide synthase holoenzyme

Phosphorylation is an important pathway for the regulation of nitric oxide synthase (NOS) at the posttranslational level. However, the molecular underpinnings of NOS regulation by phosphorylations remain unclear to date, mainly because of the problems in making a good amount of active phospho-NOS proteins. Herein, we have established a system in which recombinant rat nNOS holoprotein can be produced with site-specific incorporation of phosphoserine (pSer) at residue 1412, using a specialized bacterial host strain for pSer incorporation. The pSer1412 nNOS protein demonstrates UV-Vis, far-UV CD and fluorescence spectral properties that are identical to those of nNOS overexpressed in other bacterial strains. The protein is also functional, possessing normal NO production and NADPH oxidation activities in the presence of abundant substrate L-Arg. Conversely, the rate of FMN-heme interdomain electron transfer (IET) in pSer1412 nNOS is considerably lower than that of wild-type (wt) nNOS, while the phosphomimetic S1142E mutant possesses similar electron transfer kinetics to that of wt. The successful incorporation and high yield of pSer1412 into rat nNOS and the significant change in the IET kinetics upon the phosphorylation demonstrate a highly useful method for incorporating native phosphorylation sites as a substantial improvement to commonly used phosphomimetics.

Selective Insulin-like Growth Factor Resistance Associated with Heart Hemorrhages and Poor Prognosis in a Novel Preclinical Model of the Hematopoietic Acute Radiation Syndrome

Although bone marrow aplasia has been considered for the past decades as the major contributor of radiation-induced blood disorders, cytopenias alone are insufficient to explain differences in the prevalence of bleeding. In this study, the minipig was used as a novel preclinical model of hematopoietic acute radiation syndrome to assess if factors other than platelet counts correlated with bleeding and survival. We sought to determine whether radiation affected the insulin-like growth factor-1 (IGF-1) pathway, a growth hormone with cardiovascular and radioprotective features. Gottingen and Sinclair minipigs were exposed to ionizing radiation at hematopoietic doses. The smaller Gottingen minipig strain was more sensitive to radiation; differences in IGF-1 levels were minimal, suggesting that increased sensitivity could depend on weak response to the hormone. Radiation caused IGF-1 selective resistance by inhibiting the anti-inflammatory anti-oxidative stress IRS/PI3K/Akt but not the pro-inflammatory MAPK kinase pathway, shifting IGF-1 signaling towards a pro-oxidant, pro-inflammatory environment. Selective IGF-1 resistance associated with hemorrhages in the heart, poor prognosis, increase in C-reactive protein and NADPH oxidase 2, uncoupling of endothelial nitric oxide synthase, inhibition of nitric oxide (NO) synthesis and imbalance between the vasodilator NO and the vasoconstrictor endothelin-1 molecules. Selective IGF-1 resistance is a novel mechanism of radiation injury, associated with a vicious cycle amplifying reactive oxygen species-induced damage, inflammation and endothelial dysfunction. In the presence of thrombocytopenia, selective inhibition of IGF-1 cardioprotective function may contribute to the development of hemostatic disorders. This finding may be particularly relevant for individuals with low IGF-1 activity, such as the elderly or those with cardiometabolic dysfunctions.

Deletion of endothelial arginase 1 does not improve vasomotor function in diabetic mice

Endothelial arginase 1 was ablated to assess whether this prevents hyperglycemia-induced endothelial dysfunction by improving arginine availability for nitric oxide production. Endothelial Arg1-deficient mice (Arg1-KOTie2 ) were generated by crossing Arg1fl/fl (controls) with Tie2Cretg/- mice and analyzed by immunohistochemistry, measurements of hemodynamics, and wire myography. Ablation was confirmed by immunohistochemistry. Mean arterial blood pressure was similar in conscious male control and Arg1-KOTie2 mice. Depletion of circulating arginine by intravenous infusion of arginase 1 or inhibition of nitric oxide synthase activity with L-NG -nitro-arginine methyl ester increased mean arterial pressure similarly in control (9 ± 2 and 34 ± 2 mmHg, respectively) and Arg1-KOTie2 mice (11 ± 3 and 38 ± 4 mmHg, respectively). Vasomotor responses were studied in isolated saphenous arteries of 12- and 34-week-old Arg1-KOTie2 and control animals by wire myography. Diabetes was induced in 10-week-old control and Arg1-KOTie2 mice with streptozotocin, and vasomotor responses were studied 10 weeks later. Optimal arterial diameter, contractile responses to phenylephrine, and relaxing responses to acetylcholine and sodium nitroprusside were similar in normoglycemic control and Arg1-KOTie2 mice. The relaxing response to acetylcholine was dependent on the availability of extracellular l-arginine. In the diabetic mice, arterial relaxation responses to endothelium-dependent hyperpolarization and to exogenous nitric oxide were impaired. The data show that endothelial ablation of arginase 1 in mice does not markedly modify smooth muscle and endothelial functions of a resistance artery under normo- and hyperglycemic conditions.

Deciphering mechanism of conformationally controlled electron transfer in nitric oxide synthases

Electron transfer is a fundamental process in life that is very often coupled to catalysis within redox enzymes through a stringent control of protein conformational movements. Mammalian nitric oxide synthase (NOS) proteins are redox flavo-hemoproteins consisting of multiple modular domains. The NOS enzyme is exquisitely regulated in vivo by its partner, the Ca2+ sensing protein calmodulin (CaM), to control production of nitric oxide (NO). The importance of functional domain motion in NOS regulation has been increasingly recognized. The significant size and flexibility of NOS is a tremendous challenge to the mechanistic studies. Herein recent applications of modern biophysical techniques to NOS problems have been critically analyzed. It is important to note that any current biophysical technique alone can only probe partial aspects of the conformational dynamics due to limitations in the technique itself and/or the sample preparations. It is necessary to combine the latest methods to comprehensively quantitate the key conformational aspects (conformational states and distribution, conformational change rates, and domain interacting interfaces) governing the electron transfer. This is to answer long-standing central questions about the NOS isoforms by defining how specific CaM-NOS interactions and regulatory elements underpin the distinct conformational behavior of the NOS isoform, which in turn determine unique electron transfer and NO synthesis properties. This review is not intended as comprehensive, but as a discussion of prospects that promise impact on important questions in the NOS enzymology field.

Cigarette smoke constituents cause endothelial nitric oxide synthase dysfunction and uncoupling due to depletion of tetrahydrobiopterin with degradation of GTP cyclohydrolase

Cigarette smoking (CS) is a well-established risk factor for cardiovascular disease (CVD). Endothelial dysfunction (ED) with loss of nitric oxide (NO) production is a central mechanism leading to the advent of CVD. Despite many prior studies of this major health problem, the exact mechanism by which CS induces ED is not well understood. This study examines the mechanism by which CS induces ED with altered endothelial NO synthase (eNOS) function in aortic endothelial cells (AECs). Exposure of AECs to cigarette smoke extract (CSE) resulted in a marked decrease in NO production with concomitant increase in superoxide (O2.-) generation and accumulation of 4-hydroxy-2-nonenal protein adducts. CSE exposure led to depletion of the essential eNOS cofactor tetrahydrobiopterin (BH4) as well as total biopterin levels and decreased the expression level of guanosine triphosphate cyclohydrolase (GTPCH), the rate limiting enzyme in BH4 biosynthesis. Moreover, exposure of AECs to CSE increased the level of ubiquitinated proteins and increased 26 S proteasomal activity in a concentration-dependent manner. Pre-treatment with MG132, a 26 S proteasome inhibitor, partially prevented CSE-induced loss of BH4, total biopterin, GTPCH, and increased NO production following CSE exposure, indicating a role of the ubiquitin-proteasome system in CSE-induced eNOS dysfunction. In conclusion, CSE-induced eNOS dysfunction and uncoupling occurs due to BH4 depletion with BH4de novo synthesis limited by diminished GTPCH expression.

Pathogenetic role of endothelial nitric oxide synthase uncoupling during lung ischaemia-reperfusion injury

OBJECTIVES

Ischaemia-reperfusion injury is a necessary part of organ transplantation and a key determinant of both acute and chronic graft failure. We have assessed the contribution of endothelial nitric oxide synthase (eNOS) and eNOS uncoupling to oxidative and nitrosative stress formation during lung ischaemia-reperfusion injury dependent on ischaemia time.

METHODS

Forty eNOS wild-type mice (eNOS +/+ ) and 40 eNOS knock-out mice (eNOS -/- ) received either a sham thoracotomy or 60 or 90 min of ischaemia, followed by 0, 1 or 24 h of reperfusion. Lung tissue was analysed with electron spin resonance for NO production and reactive oxygen species content. Protein nitrosation, eNOS and eNOS uncoupling were determined using western blotting. In peripheral blood, arterial blood gases were taken and reactive oxygen species content was determined.

RESULTS

eNOS +/+ mice had lower reactive oxygen species production in their peripheral circulation but worse blood gas values after 1 h of reperfusion. Lung tissue of eNOS -/- mice showed lower reactive oxygen species and NO production and lower protein nitrosation compared with wild-type mice. Longer ischaemia times result in more elaborate oxidative and nitrosative stress dependent on eNOS genotype. Structural eNOS uncoupling was present after 60 min of ischaemia but diminished after 90 min of ischaemia.

CONCLUSIONS

eNOS uncoupling may contribute to lung ischaemia-reperfusion injury and inflammation. This ultimately leads to worse clinical outcome. Stabilizing eNOS may therefore be a new approach to extend pulmonary graft survival.

ROS and RNS signalling: adaptive redox switches through oxidative/nitrosative protein modifications

Over the last decade, a dual character of cell response to oxidative stress, eustress versus distress, has become increasingly recognized. A growing body of evidence indicates that under physiological conditions, low concentrations of reactive oxygen and nitrogen species (RONS) maintained by the activity of endogenous antioxidant system (AOS) allow reversible oxidative/nitrosative modifications of key redox-sensitive residues in regulatory proteins. The reversibility of redox modifications such as Cys S-sulphenylation/S-glutathionylation/S-nitrosylation/S-persulphidation and disulphide bond formation, or Tyr nitration, which occur through electrophilic attack of RONS to nucleophilic groups in amino acid residues provides redox switches in the activities of signalling proteins. Key requirement for the involvement of the redox modifications in RONS signalling including ROS-MAPK, ROS-PI3K/Akt, and RNS-TNF-α/NF-kB signalling is their specificity provided by a residue microenvironment and reaction kinetics. Glutathione, glutathione peroxidases, peroxiredoxins, thioredoxin, glutathione reductases, and glutaredoxins modulate RONS level and cell signalling, while some of the modulators (glutathione, glutathione peroxidases and peroxiredoxins) are themselves targets for redox modifications. Additionally, gene expression, activities of transcription factors, and epigenetic pathways are also under redox regulation. The present review focuses on RONS sources (NADPH-oxidases, mitochondrial electron-transportation chain (ETC), nitric oxide synthase (NOS), etc.), and their cross-talks, which influence reversible redox modifications of proteins as physiological phenomenon attained by living cells during the evolution to control cell signalling in the oxygen-enriched environment. We discussed recent advances in investigation of mechanisms of protein redox modifications and adaptive redox switches such as MAPK/PI3K/PTEN, Nrf2/Keap1, and NF-κB/IκB, powerful regulators of numerous physiological processes, also implicated in various diseases.

Low shear stress induces vascular eNOS uncoupling via autophagy-mediated eNOS phosphorylation

Uncoupled endothelial nitric oxide synthase (eNOS) produces O₂^- instead of nitric oxide (NO). Earlier, we reported rapamycin, an autophagy inducer and inhibitor of cellular proliferation, attenuated low shear stress (SS) induced O₂^- production. Nevertheless, it is unclear whether autophagy plays a critical role in the regulation of eNOS uncoupling. Therefore, this study aimed to investigate the modulation of autophagy on eNOS uncoupling induced by low SS exposure. We found that low SS induced endothelial O₂^- burst, which was accompanied by reduced NO release. Furthermore, inhibition of eNOS by L-NAME conspicuously attenuated low SS-induced O₂^- releasing, indicating eNOS uncoupling. Autophagy markers such as LC3 II/I ratio, amount of Beclin1, as well as ULK1/Atg1 were increased during low SS exposure, whereas autophagic degradation of p62/SQSTM1 was markedly reduced, implying impaired autophagic flux. Interestingly, low SS-induced NO reduction could be reversed by rapamycin, WYE-354 or ATG5 overexpression vector via restoration of autophagic flux, but not by N-acetylcysteine or apocynin. eNOS uncoupling might be ascribed to autophagic flux blockade because phosphorylation of eNOS Thr495 by low SS or PMA stimulation was also regulated by autophagy. In contrast, eNOS acetylation was not found to be regulated by low SS and autophagy. Notably, although low SS had no influence on eNOS Ser1177 phosphorylation, whereas boosted eNOS Ser1177 phosphorylation by rapamycin were in favor of the eNOS recoupling through restoration of autophagic flux. Taken together, we reported a novel mechanism for regulation of eNOS uncoupling by low SS via autophagy-mediated eNOS phosphorylation, which is implicated in geometrical nature of atherogenesis.

Transgenic overexpression of GTP cyclohydrolase 1 in cardiomyocytes ameliorates post-infarction cardiac remodeling

GTP cyclohydrolase 1 (GCH1) and its product tetrahydrobiopterin play crucial roles in cardiovascular health and disease, yet the exact regulation and role of GCH1 in adverse cardiac remodeling after myocardial infarction are still enigmatic. Here we report that cardiac GCH1 is degraded in remodeled hearts after myocardial infarction, concomitant with increases in the thickness of interventricular septum, interstitial fibrosis, and phosphorylated p38 mitogen-activated protein kinase and decreases in left ventricular anterior wall thickness, cardiac contractility, tetrahydrobiopterin, the dimers of nitric oxide synthase, sarcoplasmic reticulum Ca²⁺ release, and the expression of sarcoplasmic reticulum Ca²⁺ handling proteins. Intriguingly, transgenic overexpression of GCH1 in cardiomyocytes reduces the thickness of interventricular septum and interstitial fibrosis and increases anterior wall thickness and cardiac contractility after infarction. Moreover, we show that GCH1 overexpression decreases phosphorylated p38 mitogen-activated protein kinase and elevates tetrahydrobiopterin levels, the dimerization and phosphorylation of neuronal nitric oxide synthase, sarcoplasmic reticulum Ca²⁺ release, and sarcoplasmic reticulum Ca²⁺ handling proteins in post-infarction remodeled hearts. Our results indicate that the pivotal role of GCH1 overexpression in post-infarction cardiac remodeling is attributable to preservation of neuronal nitric oxide synthase and sarcoplasmic reticulum Ca²⁺ handling proteins, and identify a new therapeutic target for cardiac remodeling after infarction.

Role of LPS-elicited signaling in triggering gastric mucosal inflammatory responses to H. pylori: modulatory effect of ghrelin

Infection with Helicobacter pylori is a primary culprit in the etiology of gastric disease, and its cell-wall lipopolysaccharide (LPS) is recognized as a potent endotoxin responsible for triggering a pattern of the mucosal inflammatory responses. The engagement by the LPS of gastric mucosal Toll-like receptor 4 (TLR4) leads to initiation of signal transduction events characterized by the activation of mitogen-activated protein kinase (MAPK) cascade, induction of phosphoinositide-specific phospholipase C (PLC)/protein kinase C (PKC)/phosphatidylinositol 3-kinase (PI3K) pathway, and up-regulation in Src/Akt. These signaling events in turn exert their influence over H. pylori-elicited excessive generation of NO and PGE2 caused by the disturbances in nitric oxide synthase and cyclooxygenase isozyme systems, increase in epidermal growth factor receptor transactivation, and the induction in matrix metalloproteinase-9 (MMP-9) release. Interestingly, the extent of gastric mucosal inflammatory response to H. pylori is influenced by a peptide hormone, ghrelin, the action of which relays on the growth hormone secretagogue receptor type 1a (GHS-R1a)-mediated mobilization of G-protein dependent transduction pathways. Yet, the signals triggered by TLR-4 activation as well as those arising through GHS-R1a stimulation converge at MAPK and PLC/PKC/PI3K pathways that form a key integration node for proinflammatory signals generated by H. pylori LPS as well as for those involved in modulation of inflammation by ghrelin. Hence, therapeutic targeting these signals' convergence and integration node could provide a novel and attractive opportunities for developing more effective treatments of H. pylori-related gastric disease.

Dual-Specificity Phosphatase 4 Overexpression in Cells Prevents Hypoxia/Reoxygenation-Induced Apoptosis via the Upregulation of eNOS

Mitogen-activated protein kinases (MAPKs) signaling cascades regulate several cellular functions, including differentiation, proliferation, survival, and apoptosis. The duration and magnitude of phosphorylation of these MAPKs are decisive determinants of their physiological functions. Dual-specificity phosphatases exert kinetic control over these signaling cascades. Previously, we demonstrated that DUSP4^−/− hearts sustain a larger infarct and have poor functional recovery, when isolated hearts were subjected to ischemia/reperfusion. Uncontrolled p38 activation and upregulation of Nox4 expression are the main effectors for this functional alteration. Here, dual-specificity phosphatase 4 (DUSP4) overexpression in endothelial cells was used to investigate the role of DUSP4 on the modulation of reactive oxygen species (ROS) generation and vascular function, when cells were subjected to hypoxia/reoxygenation (H/R) insult. Immunostaining with cleaved caspase-3 revealed that DUSP4 overexpression prevents caspase-3 activation and apoptosis after H/R. The beneficial effects occur via modulating p38 activity, increased NO bioavailability, and reduced oxidative stress. More importantly, DUSP4 overexpression upregulates eNOS protein expression (1.62 ± 0.33 versus 0.65 ± 0.16) during H/R-induced stress. NO is a critical small molecule involved in regulating vascular tone, vascular growth, platelet aggregation, and modulation of inflammation. The level of NO generation determined using DAF-2 fluorescence demonstrated that DUSP4 overexpression augments NO production and thus improves vascular function. The level of superoxide generated from cells after being subjected to H/R was determined using dihydroethidium-HPLC method. The results suggested that DUSP4 overexpression in cells decreases H/R-induced superoxide generation (1.56 ± 0.14 versus 1.19 ± 0.05) and thus reduces oxidant stress. This also correlates with the reduction in the total protein S-glutathionylation, an indicator of protein oxidation. These results further support our hypothesis that DUSP4 is an antioxidant gene and a key phosphatase in modulating MAPKs, especially p38, during oxidative stress, which regulates ROS generation and eNOS expression and thus protects against oxidant-induced injury or apoptosis. Overall, DUSP4 may serve as an excellent molecular target for the treatment of ischemic heart disease.