Release In Endothelial Cells Research Articles

Uncovering the mechanisms of host mitochondrial cardiolipin release in syphilis: Insights from human microvascular endothelial cells

The release of host mitochondrial cardiolipin is believed to be the main factor that contributes to the production of anti-cardiolipin antibodies in syphilis. However, the precise mechanism by which mitochondria release cardiolipin in this context remains elusive. This study aimed to elucidate the mechanisms underlying mitochondrial cardiolipin release in syphilis. We conducted a cardiolipin quantitative assay and immunofluorescence analysis to detect mitochondrial cardiolipin release in human microvascular endothelial cells (HMEC-1), with and without Treponema pallidum (Tp) infection. Furthermore, we explored apoptosis, a key mechanism for mitochondrial cardiolipin release. The potential mediator molecules were then analyzed through RNA-sequence and subsequently validated using in vitro knockout techniques mediated by CRISPR-Cas9 and pathway-specific inhibitors. Our findings confirm that live-Tp is capable of initiating the release of mitochondrial cardiolipin, whereas inactivated-Tp does not exhibit this capability. Additionally, apoptosis detection further supports the notion that the release of mitochondrial cardiolipin occurs independently of apoptosis. The RNA-sequencing results indicated that microtubule-associated protein2 (MAP2), an axonogenesis and dendrite development gene, was up-regulated in HMEC-1 treated with Tp, which was further confirmed in syphilitic lesions by immunofluorescence. Notably, genetic knockout of MAP2 inhibited Tp-induced mitochondrial cardiolipin release in HMEC-1. Mechanically, Tp-infection regulated MAP2 expression via the MEK-ERK-HES1 pathway, and MEK/ERK phosphorylation inhibitors effectively block Tp-induced mitochondrial cardiolipin release. This study demonstrated that the infection of live-Tp enhanced the expression of MAP2 via the MEK-ERK-HES1 pathway, thereby contributing to our understanding of the role of anti-cardiolipin antibodies in the diagnosis of syphilis.

Circulating Extracellular Vesicles Are Elevated with Prediabetes and Adversely Affect Cerebral Endothelial Nitric Oxide and Endothelin-1 Production

Experimental and clinical studies indicate that a proatherogenic endothelial phenotype develops in the prediabetic, hyperglycemic state providing the platform for accelerated vascular disease with prediabetes and, in turn, type 2 diabetes. Prediabetes (fasting plasma glucose concentrations: 100-125 mg/dL) is associated with an increased risk of stroke. Circulating endothelial cell-derived microvesicles (EMVs) are now recognized as both a biomarker and mediator of vascular health and disease. In fact, EMVs have been shown to be involved in the pathogenesis of cerebrovascular dysfunction leading to increased stroke risk. Circulating EMVs are elevated in adults with prediabetes; whether EMVs associated with the prediabetic state promote endothelial abnormalities known to increase stroke risk is unknown. The experimental aim of this study was to determine the effect of EMVs isolated from adults with prediabetes on brain endothelial cell nitric oxide (NO) and endothelin (ET)-1 production. Circulating EMVs (CD144-PE) were isolated (flow cytometry) from 20 mid-life adults (age:44-69 yr): 10 normoglycemic (NG; 8M/2F; age: 55±2 yr; BMI: 25.7±0.8 kg/m2; fasting plasma glucose: 87±2 mg/dL) and 10 prediabetic (PreD: 8M/2F; 55±2 yr; 27.1±1.5 kg/m2; 107±2 mg/dL). Human cerebral microvascular endothelial cells (hCMECs) were cultured and separately treated with EMVs from each subject. Expression of intracellular proteins of interest was determined by capillary electrophoresis immunoassay. Circulating EMV concentrations were significantly higher (~65%) in PreD vs NG (180±25 vs 110±13 EMV/μL) and significantly associated with plasma glucose concentrations (r=0.48; P=0.03). Phosphorylation is the primary posttranslational modification regulating eNOS enzyme activity. Phosphorylation of Ser1177 confers the greatest activation of eNOS; whereas, phosphorylation at Thr495 reduces eNOS activation. Expression of p-eNOS (Ser1177) was lower (47.6±2.6 vs 58.6±3.5 AU; P=0.02) and p-eNOS (Thr495) higher (82.6±4.4 vs 31.1±2.5 AU; p<0.001) in cells treated with EMVs from PreD vs NG. Concordantly, NO production was ~20% lower (6.0±0.2 vs 7.2±0.4 μmol/L; p<0.05) in cells treated with EMVs from PreD adults. PreD-associated EMVs also significantly increased (~25-70%) the expression of Big ET-1 (804.4±47.7 vs 656.7±30.7 AU) and endothelin converting enzyme (290.0±24.6 vs 169.6±19.0 AU) as well as ET-1 production (30.2±4.3 vs 24.2±2.0 pg/mL) in hCMECs. In summary, EMVs harvested from adults with PreD reduced endothelial nitric oxide synthase (eNOS) activation and NO production and increased ET-1 synthesis and release in brain endothelial cells in vitro. Increased risk and incidence of stroke associated with prediabetes may be mediated by circulating EMVs. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Effect of Circulating Extracellular Vesicles from Adults with Spinal Cord Injury on Pulmonary Artery Endothelial Cell Function

Spinal cord injury (SCI) is associated with an increased risk and prevalence of cardiopulmonary and cerebrovascular disease-related morbidity and mortality. Despite an improved understanding of the neurological and physical consequences associated with SCI, factors that initiate, promote and accelerate cardiopulmonary disease are poorly understood. It has become apparent that the increased incidence of pulmonary disorders in adults with chronic SCI is not solely due to worsening of traditional risk factors, but also involves ill-defined factors. Several studies have implicated circulating endothelial cell-derived microvesicles (EMVs) in the etiology of cardiopulmonary diseases. We have previously reported that circulating EMVs are elevated in adults with chronic SCI and the expression of their microRNA cargo promotes disease. Reduction in pulmonary nitric oxide (NO) bioavailability and increased endothelin (ET)-1 production underly many cardiopulmonary disorders associated with SCI. The experimental aim of this study was to determine the effect of EMVs isolated from adults with chronic tetraplegic SCI on pulmonary endothelial cell NO and ET-1 production. As part of an ongoing study, circulating EMVs (CD144-PE) were isolated (flow cytometry) from 7 non-injured adults (all male; age: 38±4 yr) and 7 motor complete SCI adults with tetraplegic SCI (male; 44±5 yr). All subjects were free of overt cardiometabolic disease. Human pulmonary artery endothelial cells (HPAECs) were cultured and separately treated with EMVs from each subject for 24 hr. Expression of intracellular NO and ET-1 proteins of interest was determined by capillary electrophoresis immunoassay. Circulating EMV concentrations were significantly higher (~200%) in SCI vs non-injured (154±36 vs 54±7 EMV/μL). Expression of p-eNOS (Ser1177), the primary activation site for eNOS, was ~30% lower (96.0±2.3 vs 140.7±8.9 AU; p<0.01) and p-eNOS (Thr495), primary inhibitory site, ~40% higher (40.7±1.7 vs 28.8±3.1 AU; p<0.01) in cells treated with EMVs from SCI vs non-injured. As a result, NO production was ~20% lower (6.5±0.3 vs 8.3±0.7 μmol/L; P=0.03) in HPAECs treated with EMVs from adults with SCI. SCI-associated EMVs also significantly increased (~70%) the expression of Big ET-1 (60.6±3.6 vs 36.1±2.7 AU) resulting in enhanced endothelial ET-1 production (884.0±22.9 vs 778.7±18.0 pg/mL). In conclusion, EMVs harvested from adults with SCI markedly reduced eNOS activation and NO production and increased ET-1 synthesis and release in pulmonary endothelial cells in vitro. Circulating EMVs represent a potential mechanistic factor underlying pulmonary disorders and increased disease risk with SCI. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Indole-3-Propionic Acid, a Gut Microbiota-Derived Tryptophan Metabolite, Promotes Endothelial Dysfunction Impairing Purinergic-Induced Nitric Oxide Release in Endothelial Cells.

Different gut microbiota-derived metabolites influence cardiovascular function, and, among all, the role of indole-3-propionic acid (IPA), from tryptophan metabolism, shows controversial effects. The aim of this study was to evaluate its role in endothelial dysfunction. IPA effects were studied on bovine aortic endothelial cells (BAE-1). First, IPA cytotoxicity was evaluated by an MTS assay. Then, the levels of intracellular reactive oxygen species (ROS) were evaluated by a microplate reader or fluorescence microscopy with the CellROX® Green probe, and nitric oxide (NO) production was studied by fluorescence microscopy with the DAR4M-AM probe after acute or chronic treatment. Finally, immunoblotting analysis for endothelial nitric oxide synthase (eNOS) phosphorylation (p-eNOS) was performed. In BAE-1, IPA was not cytotoxic, except for the highest concentration (5 mM) after 48 h of treatment, and it showed neither oxidant nor antioxidant activity. However, the physiological concentration of IPA (1 μM) significantly reduced NO released by adenosine triphosphate (ATP)-stimulated BAE-1. These last data were confirmed by Western blot analysis, where IPA induced a significant reduction in p-eNOS in purinergic-stimulated BAE-1. Given these data, we can speculate that IPA negatively affects the physiological control of vascular tone by impairing the endothelial NO release induced by purinergic stimulation. These results represent a starting point for understanding the mechanisms underlying the relationship between gut microbiota metabolites and cardiometabolic health.

Lysosomal TRPML1 triggers global Ca2+ signals and nitric oxide release in human cerebrovascular endothelial cells.

Lysosomal Ca2+ signaling is emerging as a crucial regulator of endothelial Ca2+ dynamics. Ca2+ release from the acidic vesicles in response to extracellular stimulation is usually promoted via Two Pore Channels (TPCs) and is amplified by endoplasmic reticulum (ER)-embedded inositol-1,3,4-trisphosphate (InsP3) receptors and ryanodine receptors. Emerging evidence suggests that sub-cellular Ca2+ signals in vascular endothelial cells can also be generated by the Transient Receptor Potential Mucolipin 1 channel (TRPML1) channel, which controls vesicle trafficking, autophagy and gene expression. Herein, we adopted a multidisciplinary approach, including live cell imaging, pharmacological manipulation, and gene targeting, revealing that TRPML1 protein is expressed and triggers global Ca2+ signals in the human brain microvascular endothelial cell line, hCMEC/D3. The direct stimulation of TRPML1 with both the synthetic agonist, ML-SA1, and the endogenous ligand phosphatidylinositol 3,5-bisphosphate (PI(3,5)P2) induced a significant increase in [Ca2+]i, that was reduced by pharmacological blockade and genetic silencing of TRPML1. In addition, TRPML1-mediated lysosomal Ca2+ release was sustained both by lysosomal Ca2+ release and ER Ca2+- release through inositol-1,4,5-trisphophate receptors and store-operated Ca2+ entry. Notably, interfering with TRPML1-mediated lysosomal Ca2+ mobilization led to a decrease in the free ER Ca2+ concentration. Imaging of DAF-FM fluorescence revealed that TRPML1 stimulation could also induce a significant Ca2+-dependent increase in nitric oxide concentration. Finally, the pharmacological and genetic blockade of TRPML1 impaired ATP-induced intracellular Ca2+ release and NO production. These findings, therefore, shed novel light on the mechanisms whereby the lysosomal Ca2+ store can shape endothelial Ca2+ signaling and Ca2+-dependent functions in vascular endothelial cells.

Allyl Isothiocianate Induces Ca2+ Signals and Nitric Oxide Release by Inducing Reactive Oxygen Species Production in the Human Cerebrovascular Endothelial Cell Line hCMEC/D3.

Nitric oxide (NO) represents a crucial mediator to regulate cerebral blood flow (CBF) in the human brain both under basal conditions and in response to somatosensory stimulation. An increase in intracellular Ca2+ concentrations ([Ca2+]i) stimulates the endothelial NO synthase to produce NO in human cerebrovascular endothelial cells. Therefore, targeting the endothelial ion channel machinery could represent a promising strategy to rescue endothelial NO signalling in traumatic brain injury and neurodegenerative disorders. Allyl isothiocyanate (AITC), a major active constituent of cruciferous vegetables, was found to increase CBF in non-human preclinical models, but it is still unknown whether it stimulates NO release in human brain capillary endothelial cells. In the present investigation, we showed that AITC evoked a Ca2+-dependent NO release in the human cerebrovascular endothelial cell line, hCMEC/D3. The Ca2+ response to AITC was shaped by both intra- and extracellular Ca2+ sources, although it was insensitive to the pharmacological blockade of transient receptor potential ankyrin 1, which is regarded to be among the main molecular targets of AITC. In accord, AITC failed to induce transmembrane currents or to elicit membrane hyperpolarization, although NS309, a selective opener of the small- and intermediate-conductance Ca2+-activated K+ channels, induced a significant membrane hyperpolarization. The AITC-evoked Ca2+ signal was triggered by the production of cytosolic, but not mitochondrial, reactive oxygen species (ROS), and was supported by store-operated Ca2+ entry (SOCE). Conversely, the Ca2+ response to AITC did not require Ca2+ mobilization from the endoplasmic reticulum, lysosomes or mitochondria. However, pharmacological manipulation revealed that AITC-dependent ROS generation inhibited plasma membrane Ca2+-ATPase (PMCA) activity, thereby attenuating Ca2+ removal across the plasma membrane and resulting in a sustained increase in [Ca2+]i. In accord, the AITC-evoked NO release was driven by ROS generation and required ROS-dependent inhibition of PMCA activity. These data suggest that AITC could be exploited to restore NO signalling and restore CBF in brain disorders that feature neurovascular dysfunction.

Vasoprotective effects of NOX4 are mediated via polymerase and transient receptor potential melastatin 2 cation channels in endothelial cells.

NOX4 activation has been implicated to have vasoprotective and blood pressure (BP)-lowering effects. Molecular mechanisms underlying this are unclear, but NOX4-induced regulation of the redox-sensitive Ca2+ channel TRPM2 and effects on endothelial nitric oxide synthase (eNOS)-nitric oxide signalling may be important. Wild-type and LinA3, renin-expressing hypertensive mice, were crossed with NOX4 knockout mice. Vascular function was measured by myography. Generation of superoxide (O2-) and hydrogen peroxide (H2O2) were assessed by lucigenin and amplex red, respectively, and Ca2+ influx by Cal-520 fluorescence in rat aortic endothelial cells (RAEC). BP was increased in NOX4KO, LinA3 and LinA3/NOX4KO mice. This was associated with endothelial dysfunction and vascular remodelling, with exaggerated effects in NOX4KO groups. The TRPM2 activator, ADPR, improved vascular relaxation in LinA3/NOX4KO mice, an effect recapitulated by H2O2. Inhibition of PARP and TRPM2 with olaparib and 2-APB, respectively, recapitulated endothelial dysfunction in NOX4KO. In endothelial cells, Ang II increased H2O2 generation and Ca2+ influx, effects reduced by TRPM2 siRNA, TRPM2 inhibitors (8-br-cADPR, 2-APB), olaparib and GKT137831 (NOX4 inhibitor). Ang II-induced eNOS activation was blocked by NOX4 and TRPM2 siRNA, GKT137831, PEG-catalase and 8-br-cADPR. Our findings indicate that NOX4-induced H2O2 production activates PARP/TRPM2, Ca2+ influx, eNOS activation and nitric oxide release in endothelial cells. NOX4 deficiency impairs Ca2+ homeostasis leading to endothelial dysfunction, an effect exacerbated in hypertension. We define a novel pathway linking endothelial NOX4/H2O2 to eNOS/nitric oxide through PARP/TRPM2/Ca2+. This vasoprotective pathway is perturbed when NOX4 is downregulated and may have significance in conditions associated with endothelial dysfunction, including hypertension.

Pregnancy-Specific Glycoprotein 9 Enhances Store-Operated Calcium Entry and Nitric Oxide Release in Human Umbilical Vein Endothelial Cells

We explored changes in pregnancy-specific glycoprotein 9 (PSG9) levels in the serum of patients with preeclampsia and the effects and underlying mechanisms of PSG9 effects on calcium (Ca2+) homeostasis and nitric oxide (NO) release in human umbilical vein endothelial cells (HUVECs). Western blotting was used to detect protein expression levels, and an NO fluorescence probe was used to examine NO production. Intracellular Ca2+ concentrations were measured using a Ca2+-sensitive fluorescent dye under a fluorescence microscope. Compared with those in healthy pregnant women, serum PSG9 levels were significantly decreased in patients with preeclampsia. PSG9 (0.1 μg/mL) treatment of HUVECs significantly enhanced the expression levels of store-operated calcium entry (SOCE) channel proteins Orai1 and Orai2, but not Orai3, and of endothelial nitric oxide synthase (eNOS) and NO production. Pretreatment with an inhibitor of SOCE (BTP2) abolished PSG9-enhanced Orai1, Orai2, and eNOS expression levels and NO production in HUVECs. The mechanisms underlying SOCE that were PSG9 enhanced in HUVECs appear to involve the Ca2+/eNOS/NO signaling pathway. These findings suggest that serum PSG9 levels may be a potential biomarker for monitoring the occurrence or development of preeclampsia in pregnancy and that PSG9 may be a potential therapeutic target for the treatment of preeclampsia.

Cell-Based Biological Markers for Blood-Enriching Chinese Herbs: Erythropoietin Production in HepG2 Cells and Nitric Oxide Release in Human Umbilical Vein Endothelial Cells (HUVECs)

Cell-Based Biological Markers for Blood-Enriching Chinese Herbs: Erythropoietin Production in HepG2 Cells and Nitric Oxide Release in Human Umbilical Vein Endothelial Cells (HUVECs)

Live imaging of nitric oxide release in vascular endothelial cells in response to mechanical stimuli on an organ chip

Abstract Background Nitric oxide (NO), released from vascular endothelial cells in response to mechanical stimuli, regulates cardiac contractility and are also involved in the prevention of the development of cardiac hypertrophy. Purpose To establish an experimental system for live observation of NO release in response to mechanical stimuli on an organ chip. Methods Organ chips, which we used for the development of a heart-on-a-chip in the previous study [1], were used. We seeded 300,000 human umbilical vein endothelial cells on a stretchable elastic membrane coated with Matrigel of a chip channel. Shear stress was applied to the cells by increasing flow rate of a peristaltic pump connected to the chip channel (Figure 1A). Pressure stimulus was applied by hydrostatic pressure. Stretch stimulus was applied by suction to the side ports of a chip using an electric syringe pump (Figure 1B). Cells were stained with 10 μM 4,5-diaminofluorescein diacetate for fluorescent live NO imaging. Results Monolayers of the endothelial cells formed intercellular junctions confirmed by CD31 staining (Figure 1C, yellow). Apparent permeability, which was measured by Texas red dye (MW 3000), was maintained at a low level of ∼3x10–6 cm/s until day 30, suggested the formation of robust intercellular junction. When the endothelial cells were subjected to a pressure stimulus of 60 mmHg for 60 s, NO release was observed that lasted for >2 minutes (Figure 2A). A peak value of 1.46±1.08 (mean ± standard deviation) times the baseline was observed 271 s after the beginning of the pressure stimulus (n=251 cells). When the cells were subjected to a 1% stretch for 60 s, a peak value of 1.29±0.33 times the baseline was observed 105 s after the beginning of the stretch stimulus (Figure 2B). A shear stress of 0.01 dyn/cm2 hardly increased NO release (1.20±0.27 times the baseline, Figure 2C). Conclusion The system for live NO imaging in vascular endothelial cells in response to mechanical stimuli was established using organ-on-a-chip. The heart-on-a-chip with endothelial cells will be useful in elucidating the effects of mechanical stimulus such as hypertension on the contractile function and the remodeling of the heart. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Japan Society for the Promotion of Science

Biogenesis and release of endothelial extracellular vesicles: Morphological aspects

BackgroundCell-cell communication through extracellular vesicles (EVs) including exosomes, microvesicles and apoptotic bodies has been shown to be important in physiological homoeostasis as well as pathological processes such as atherosclerosis. However, while the cellular machinery controlling EV formation and composition has been studied during the past decade, less is known about the morphological process of their formation and release. MethodsUsing different electron microscopic approaches including transmission-, scanning-, immun-, and serial block face electron microscopy we studied the morphogenetic events of EV formation and release. We analysed the different steps of EV formation and release in cultured myocardial endothelial (MyEnd) and aortic endothelial (AoEnd) cell lines under serum starvation and under inflammatory conditions. ResultsWe show that in a narrow time frame, the number of active cells and microvesicle (MV) producing cells increased in dependence of time spent in cultivation and additional stimulation by TNF-α. However, MV secretion was a highly heterogeneous process which couldn´t be seen in all cells cultivated under the same conditions. Release of MVs could be observed all over the cells’ surface with no preferred release site. While no single specific microscopic approach applied was sufficient to provide a comprehensive analysis of EV biogenesis, we show that the limitations of one technique could be compensated by the qualities of the respective other applied techniques, thus enabling us to provide a detailed ultrastructural analysis of MV and exosome biogenesis. Surprisingly, exosome release in endothelial cells occurred via a yet undescribed process indicating that MVBs were incorporated into a novel distinct cellular compartment covered by fenestrated endothelium before exosome release. Lastly, we could show that TNF-α stimulation of AoEnd cells leads not only to the upregulation of CD44 in parental cells, but also to incorporation of CD44 into the membranes of generated MVs and exosomes. ConclusionsTaken together, our data contribute to a better understanding of biogenesis and release of EVs. We conclude that under inflammatory conditions, EVs can mediate the transfer of CD44 from endothelial cells to target cells at distant sites including vessel wall cells and this could be a mechanism by which MVs may change the and thus contribute to the development and progression of atherosclerotic lesions.

The involvement of H2S/NO pathways in the DHEA induced relaxation

Dehydroepiandrosterone (DHEA) is a precursor of androgen and estrogen hormones, and it is synthesized in the adrenal cortex. His levels have an age-dependent decline and low levels of DHEA were associated with cardiovascular disease. DHEA causes nitric oxide (NO) release in bovine aortic endothelial cells (BAEC) independently from estrogen and androgen receptors. Hydrogen sulfide (H2S) is the other important gasotransmitter in vascular homeostasis. Little is known about the mechanism of action driven by DHEA at the vascular level. In particular, the involvement of H2S/NO pathways in the DHEA induced relaxation has been investigated. Functional studies on CD1 mice aorta were used to perform a cumulative concentration curve of DHEA on a stable tone of phenylephrine. To investigate the mechanism(s) of action we used inhibitors of the androgen receptor, of the enzyme synthesis NO and H2S, and a blocker of KATP channel (target of H2S). Furthermore, we incubated the aorta with DHEA to measure H2S level. Finally, we treated BAEC with DHEA to measure H2S and NO levels at different times of incubation. We found that the relaxation induced by DHEA was partially dependent on the endothelium and this effect was mediated by either H2S and NO. Moreover, the relaxation did not involve the androgen receptor. Finally, the stimulation of H2S production by DHEA was fast both in aorta and in BAEC ( Fig. 1 ). These data bring new information on the mechanism(s) of action of DHEA in the vasculature and supports its protective role not only through NO but also through H2S synthesis.

Trimethylamine N-Oxide (TMAO) Impairs Purinergic Induced Intracellular Calcium Increase and Nitric Oxide Release in Endothelial Cells.

Trimethylamine N-oxide (TMAO) is a diet derived compound directly introduced through foodstuff, or endogenously synthesized from its precursors, primarily choline, L-carnitine, and ergothioneine. New evidence outlines high TMAO plasma concentrations in patients with overt cardiovascular disease, but its direct role in pathological development is still controversial. The purpose of the study was to evaluate the role of TMAO in affecting key intracellular factors involved in endothelial dysfunction development, such as reactive oxygen species, mitochondrial health, calcium balance, and nitric oxide release using bovine aortic endothelial cells (BAE-1). Cell viability and oxidative stress indicators were monitored after acute and prolonged TMAO treatment. The role of TMAO in interfering with the physiological purinergic vasodilatory mechanism after ATP stimulation was defined through measurements of the rise of intracellular calcium, nitric oxide release, and eNOS phosphorylation at Ser1179 (eNOSSer1179). TMAO was not cytotoxic for BAE-1 and it did not induce the rise of reactive oxygen species and impairment of mitochondrial membrane potential, either in the basal condition or in the presence of a stressor. In contrast, TMAO modified the purinergic response affecting intracellular ATP-induced calcium increase, nitric oxide release, and eNOSSer1179. Results obtained suggest a possible implication of TMAO in impairing the endothelial-dependent vasodilatory mechanism.

Novel indolic AMPK modulators induce vasodilatation through activation of the AMPK\u2013eNOS\u2013NO pathway

Endothelial adenosine monophosphate-activated protein kinase (AMPK) plays a critical role in the regulation of vascular tone through stimulating nitric oxide (NO) release in endothelial cells. Since obesity leads to endothelial dysfunction and AMPK dysregulation, AMPK activation might be an important strategy to restore vascular function in cardiometabolic alterations. Here, we report the identification of a novel AMPK modulator, the indolic derivative IND6, which shows affinity for AMPKα1β1γ1, the primary AMPK isoform in human EA.Hy926 endothelial cells. IND6 shows inhibitory action of the enzymatic activity in vitro, but increases the levels of p-Thr174AMPK, p-Ser1177eNOS and p-Ser79ACC in EA.Hy926. This paradoxical finding might be explained by the ability of IND6 to act as a mixed-type inhibitor, but also to promote the enzyme activation by adopting two distinct binding modes at the ADaM site. Moreover, functional assays reveal that IND6 increased the eNOS-dependent production of NO and elicited a concentration-dependent vasodilation of endothelium-intact rat aorta due to AMPK and eNOS activation, demonstrating a functional activation of the AMPK–eNOS–NO endothelial pathway. This kinase inhibition profile, combined with the paradoxical AMPK activation in cells and arteries, suggests that these new chemical entities may constitute a valuable starting point for the development of new AMPK modulators with therapeutic potential for the treatment of vascular complications associated with obesity.

High magnesium mitigates the vasoconstriction mediated by different types of calcium influx from monocrotaline-induced pulmonary hypertensive rats.

What is the central question of this study? What is the involvement of Mg2+ in mitigating the vasoconstriction in pulmonary arteries and smaller pulmonary arteries in the monocrotaline-induced pulmonary arterial hypertension (MCT-PAH) rat model? What are the main finding and its importance? Both store-operated Ca2+ entry- and receptor-operated Ca2+ entry-mediated vasoconstriction were enhanced in the MCT-PAH model. High magnesium inhibited vasoconstriction by directly antagonizing Ca2+ and increasing NO release, and this was more notable in smaller pulmonary arteries. Increased extracellular magnesium concentration has been shown to attenuate the endothelin-1-induced contractile response via the release of nitric oxide (NO) from the endothelium in proximal pulmonary arteries (PAs) of chronic hypoxic mice. Here, we further examined the involvement of Mg2+ in the inhibition of vasoconstriction in PAs and distal smaller pulmonary arteries (sPAs) in a monocrotaline-induced pulmonary arterial hypertension (MCT-PAH) rat model. The data showed that in control rats vasoconstriction in sPAs is more intense than that in PAs. In MCT-PAH rats, store-operated Ca2+ entry (SOCE)- and receptor-operated Ca2+ entry (ROCE)-mediated contraction were significantly strengthened. However, there was no upregulation of the vasoconstriction mediated by voltage-dependent calcium entry (VDCE). Furthermore, high magnesium greatly inhibited VDCE-mediated contraction in PAs rather than sPAs, which was the opposite of the ROCE-mediated contraction. Moreover, monocrotaline pretreatment partly eliminated the endothelium-dependent vasodilatation in PAs, which in sPAs, however, was still promoted by magnesium due to the increased NO release in pulmonary microvascular endothelial cells (PMVECs). In conclusion, the findings suggest that both SOCE- and ROCE-mediated vasoconstriction in the MCT-PAH model are enhanced, especially in sPAs. The inhibitory effect of high magnesium on vasoconstriction can be achieved partly by its direct role as a Ca2+ antagonist and partly by increasing NO release in PMVECs.

Propofol Causes Sustained Ca2+ Elevation in Endothelial Cells by Stimulating Ryanodine Receptor and Suppressing Plasmalemmal Ca2+ Pump.

Propofol, a general anesthetic administered intravenously, may cause pain at the injection site. The pain is in part due to irritation of vascular endothelial cells. We here investigated the effects of propofol on Ca2+ transport and pain mediator release in human umbilical vein endothelial cells (EA.hy926). Propofol mobilized Ca2+ from cyclopiazonic acid (CPA)-dischargeable pool but did not cause Ca2+ release from the lysosomal Ca2+ stores. Propofol-elicited Ca2+ release was suppressed by 100 μM ryanodine, suggesting the participation of ryanodine receptor channels. Propofol did not affect ATP-triggered Ca2+ release but abolished the Ca2+ influx triggered by ATP; in addition, propofol also suppressed store-operated Ca2+ entry elicited by CPA. Ca2+ clearance during CPA-induced Ca2+ discharge was unaffected by a low Na+ (50 mM) extracellular solution, but strongly suppressed by 5 mM La3+ (an inhibitor of plasmalemmal Ca2+ pump), suggesting Ca2+ extrusion was predominantly through the plasmalemmal Ca2+ pump. Propofol mimicked the effect of La3+ in suppressing Ca2+ clearance. Propofol also stimulated release of pain mediators, namely, reactive oxygen species and bradykinin. Our data suggest propofol elicited Ca2+ release and repressed Ca2+ clearance, causing a sustained cytosolic [Ca2+]i elevation. The latter may cause reactive oxygen species and bradykinin release, resulting in pain.

Nitric oxide regulates adhesiveness, invasiveness, and migration of anoikis-resistant endothelial cells.

Anoikis is a type of apoptosis that occurs in response to the loss of adhesion to the extracellular matrix (ECM). Anoikis resistance is a critical mechanism in cancer and contributes to tumor metastasis. Nitric oxide (NO) is frequently upregulated in the tumor area and is considered an important player in cancer metastasis. The aim of this study was to evaluate the effect of NO on adhesiveness, invasiveness, and migration of anoikis-resistant endothelial cells. Here, we report that anoikis-resistant endothelial cells overexpress endothelial nitric oxide synthase. The inhibition of NO release in anoikis-resistant endothelial cells was able to decrease adhesiveness to fibronectin, laminin, and collagen IV. This was accompanied by an increase in cell invasiveness and migration. Furthermore, anoikis-resistant cell lines displayed a decrease in fibronectin and collagen IV protein expression after L-NAME treatment. These alterations in adhesiveness and invasiveness were the consequence of MMP-2 up-regulation observed after NO release inhibition. The decrease in NO levels was able to down-regulate the activating transcription factor 3 (ATF3) protein expression. ATF3 represses MMP-2 gene expression by antagonizing p53-dependent trans-activation of the MMP-2 promoter. We speculate that the increased release of NO by anoikis-resistant endothelial cells acted as a response to restrict the MMP-2 action, interfering in MMP-2 gene expression via ATF3 regulation. The up-regulation of nitric oxide by anoikis-resistant endothelial cells is an important response to restrict tumorigenic behavior. Without this mechanism, invasiveness and migration potential would be even higher, as shown after L-NAME treatment.

Pinitol Protects Against Ox-Low-Density Lipoprotein-Induced Endothelial Inflammation and Monocytes Attachment.

Atherosclerosis is a cardiovascular disease that affects a majority of people around the world at old age. Atherosclerosis is slow to develop and challenging to treat. Endothelial dysfunction caused by oxidative stress, inflammation, and other pathological factors drives the process of atherogenesis. LOX-1 is one of the main scavenging receptors for oxidized low-density lipoprotein (ox-LDL) and contributes to atherogenesis by inducing overproduction of reactive oxygen species, increased expression of proinflammatory cytokines, and secretion of cellular adhesion molecules. In addition, activation of LOX-1 inhibits the expression of KLF2, a key protective factor against atherosclerosis. In this study, we investigated the effects of pinitol, and naturally occurring cyclic polyol, on endothelial dysfunction induced by ox-LDL. Our findings show that pinitol revealed a good safety profile, as evidenced by reducing lactate dehydrogenase release in human aortic endothelial cells. In our experiments, pinitol reduced the production of reactive oxygen species and expression of IL-6 and monocyte chemoattractant protein-1 induced by ox-LDL. Pinitol also significantly reduced the attachment of THP-1 monocytes to endothelial cells via downregulation of vascular cellular adhesion molecule-1 and E-selectin. Importantly, we found that pinitol reduced the expression of LOX-1 induced by ox-LDL and rescued the expression of KLF2, which is dependent on ERK5 expression. Together, our findings provide notable evidence that pinitol may have potential implication in the prevention and treatment of atherosclerosis.

Activation of the Constitutive Androstane Receptor Inhibits Leukocyte Adhesiveness to Dysfunctional Endothelium.

Leukocyte cell recruitment into the vascular subendothelium constitutes an early event in the atherogenic process. As the effect of the constitutive androstane receptor (CAR) on leukocyte recruitment and endothelial dysfunction is poorly understood, this study investigated whether the role of CAR activation can affect this response and the underlying mechanisms involved. Under physiological flow conditions, TNFα-induced endothelial adhesion of human leukocyte cells was concentration-dependently inhibited by preincubation of human umbilical arterial endothelial cells with the selective human CAR ligand CITCO. CAR agonism also prevented TNFα induced VCAM-1 expression, as well as MCP-1/CCL-2 and RANTES/CCL-5 release in endothelial cells. Suppression of CAR expression with a small interfering RNA abrogated the inhibitory effects of CITCO on these responses. Furthermore, CITCO increased interaction of CAR with Retinoid X Receptor (RXR) and reduced TNFα-induced p38-MAPK/NF-κB activation. In vivo, using intravital microscopy in the mouse cremasteric microcirculation treatment with the selective mouse CAR ligand TCPOBOP inhibited TNFα-induced leukocyte rolling flux, adhesion, and emigration and decreased VCAM-1 in endothelium. These results reveal that CAR agonists can inhibit the initial inflammatory response that precedes the atherogenic process by targeting different steps in the leukocyte recruitment cascade. Therefore, CAR agonists may constitute a new therapeutic tool in controlling cardiovascular disease-associated inflammatory processes.

NMDA receptors elicit flux-independent intracellular Ca2+ signals via metabotropic glutamate receptors and flux-dependent nitric oxide release in human brain microvascular endothelial cells

The excitatory neurotransmitter glutamate gates post-synaptic N-methyl-d-aspartate (NMDA) receptors (NMDARs) to mediate extracellular Ca2+ entry and stimulate neuronal nitric oxide (NO) synthase to release NO and trigger neurovascular coupling (NVC). Neuronal and glial NMDARs may also operate in a flux-independent manner, although it is unclear whether their non-ionotropic mode of action is involved in NVC. Recently, endothelial NMDARs were found to trigger Ca2+-dependent NO production and induce NVC, but the underlying mode of signaling remains elusive. Herein, we report that GluN1 protein, as well as GluN2C and GluN3B transcripts and proteins, were expressed and that NMDA did not elicit inward currents, but induced a dose-dependent increase in intracellular Ca2+ concentration ([Ca2+]i) in the human brain microvascular endothelial cell line, hCMEC/D3. A multidisciplinary approach, including live cell imaging, whole-cell patch-clamp recordings, pharmacological manipulation and gene targeting, revealed that NMDARs increase the [Ca2+]i in a flux-independent manner in hCMEC/D3 cells. The Ca2+ response to NMDA was triggered by endogenous Ca2+ release from the endoplasmic reticulum and the lysosomal Ca2+ stores and sustained by store-operated Ca2+ entry. Unexpectedly, pharmacological and genetic blockade of mGluR1 and mGluR5 dramatically impaired NMDARs-mediated Ca2+ signals. These findings indicate that NMDARs may increase the endothelial [Ca2+]i in a flux-independent manner via group 1 mGluRs. However, imaging of DAF-FM fluorescence revealed that NMDARs may also induce Ca2+-dependent NO release by signaling in a flux-dependent manner. These findings, therefore, shed novel light on the mechanisms whereby brain microvascular endothelium decodes glutamatergic signaling and regulates NVC.