Treatment Of Human Aortic Endothelial Cells Research Articles

Abstract 131: Phosphoproteomics Analysis Reveals That Angiotensin-(1-5) Inhibits MTOR Signalling Pathway In Endothelial Cells

Introduction: Our group demonstrated that Angiotensin-(1-5) [Ang-(1-5)] is a biologically active component of the protective arm of the Renin-Angiotensin System (RAS), displaying high efficacy towards the AT 2 R. However, signaling mechanisms for Ang-(1-5) in vitro are still unknown. Objective: To characterize Ang-(1-5) signaling signature in human aortic endothelial cells. Methods: Human aortic endothelial cells (HAEC) were stimulated with Ang-(1-5) (1μM) for 1, 3, 5 or 20 minutes. Proteins were isolated, digested and labeled with TMTpro TM 16-plex. Phosphorylation changes of proteins in response to Ang-(1-5) treatment were analyzed by mass spectrometry. Raw data were processed in Proteome Discoverer. General bioinformatic analysis was performed in R Studios and functional analysis was performed with DAVID and Cytoscape. Validation of phosphoproteomics data was performed by western blot in HAEC treated with Ang-(1-5) (1μM) for 1, 3, 5 or 20 minutes. Results: Treatment of HAEC with Ang-(1-5) significantly modified the phosphorylation status of 831 proteins at 1799 residues, majority of these being dephosphorylated (1079). Functional bioinformatic analysis revealed a cluster of proteins involved in cell cycle and cell division regulation. Upon further analysis, we observed that Ang-(1-5) led to dephosphorylation of residues of CLIP-170 (Ser 195 , Ser 200 , Ser 204 ), 4EBP1 (Ser 65 ), S6K1 (Ser 447 ) and ribosomal S6 protein (Ser 244 , Ser 247 ), suggesting an inhibitory effect on mTOR activity. Western blot analysis confirmed the inhibitory effect of Ang-(1-5) on mTOR signaling, as a significant dephosphorylation of Ser 65 -4EBP1 [% vs. CT = 69.9%] and Thr 389 -S6K1 [% vs. CT = 43.7%] was observed at all timepoints tested. These effects were AT 2 R-mediated, since PD123319 prevented dephosphorylation of Ser 65 -4EBP1 and Thr 389 -S6K1 driven by Ang-(1-5). Conclusion: This study provides an in-depth analysis of Ang-(1-5) signaling patterns in HAEC. The overall similarity of Ang-(1-5) and C21 intracellular signaling further supports that Ang-(1-5) is a hormone of the protective RAS. Since inhibition of mTOR in endothelial cells is known as an anti-senescence mechanism, further investigations are needed to confirm an anti-senescence effect of Ang-(1-5).

PS-BPB04-6: PROOF OF BIOLOGICAL ACTIVITY AND EXPLORATION OF EARLY SIGNALING EVENTS OF ANGIOTENSIN-(1–5)

Introduction: Recombinant human ACE2 increases the circulating levels of angiotensin-(1–5) [Ang-(1–5)], a peptide thus far regarded as biologically inactive. Since ACE2 is a central component of the protective RAS, we hypothesized that Ang-(1–5) is a new biologically active peptide within this hormonal system. Objective: To investigate biological activity and signaling mechanisms of Ang-(1–5). Methods: In order to show a biological effect and to test whether Ang-(1–5) signals through the AT2-receptor (AT2R), nitric oxide (NO) release was measured by DAF-FM fluorescence in AT2R transfected (AT2R-CHO) or non-transfected (NT-CHO) CHO cells, treated with Ang-(1–5) or C21 (AT2R agonist, positive control) (0.1 nM to 10 μM) for 15 minutes. Vehicle (cell media) treated cells served as negative control. To investigate Ang-(1–5) signaling patterns, human aortic endothelial cells (HAEC) were treated with vehicle or Ang-(1–5) (1 μM) for 1, 3, 5 or 20 minutes. Proteins were harvested, digested and labeled with TMTpro-16plex. Phosphopeptide enrichment was carried out by TiO2. Samples were subjected to LC-MS/MS analysis and the resulting mass spectra were searched against the human SwissProt database. Results: Ang-(1–5) induced a concentration-dependent increase in NO production in AT2-CHO cells (Emax: 65.60 ± 14.02%), thus proving its biological activity. Ang-(1–5) had 69% higher efficacy than the established AT2R agonist C21 (Emax: 38.76 ± 10.24%). Ang-(1–5) seems to signal through the AT2R, because effects on NO release were absent in NT-CHO cells. Treatment of HAEC with Ang-(1–5) significantly modified the phosphorylation status of 831 proteins at 1799 residues. The majority of residues (1079) were dephosphorylated while 729 residues were phosphorylated. Changes in protein phosphorylation in response to Ang-(1–5) occurred at all investigated time points, most of them after 20 minutes. Functional bioinformatic analysis revealed a cluster of proteins involved in cell cycle and cell division regulation. Conclusion: This study provides evidence that Ang-(1–5) is an endogenous AT2R agonist with high efficacy towards the AT2R. The early signaling phosphorylation pattern resembles those of other protective RAS agonists, such as C21 and Ang-(1–7).

Sox13 is a novel flow-sensitive transcription factor that prevents inflammation by repressing chemokine expression in endothelial cells.

Atherosclerosis is a chronic inflammatory disease and occurs preferentially in arterial regions exposed to disturbed blood flow (d-flow) while the stable flow (s-flow) regions are spared. D-flow induces endothelial inflammation and atherosclerosis by regulating endothelial gene expression partly through the flow-sensitive transcription factors (FSTFs). Most FSTFs, including the well-known Kruppel-like factors KLF2 and KLF4, have been identified from in vitro studies using cultured endothelial cells (ECs). Since many flow-sensitive genes and pathways are lost or dysregulated in ECs during culture, we hypothesized that many important FSTFs in ECs in vivo have not been identified. We tested the hypothesis by analyzing our recent gene array and single-cell RNA sequencing (scRNAseq) and chromatin accessibility sequencing (scATACseq) datasets generated using the mouse partial carotid ligation model. From the analyses, we identified 30 FSTFs, including the expected KLF2/4 and novel FSTFs. They were further validated in mouse arteries in vivo and cultured human aortic ECs (HAECs). These results revealed 8 FSTFs, SOX4, SOX13, SIX2, ZBTB46, CEBPβ, NFIL3, KLF2, and KLF4, that are conserved in mice and humans in vivo and in vitro. We selected SOX13 for further studies because of its robust flow-sensitive regulation, preferential expression in ECs, and unknown flow-dependent function. We found that siRNA-mediated knockdown of SOX13 increased endothelial inflammatory responses even under the unidirectional laminar shear stress (ULS, mimicking s-flow) condition. To understand the underlying mechanisms, we conducted an RNAseq study in HAECs treated with SOX13 siRNA under shear conditions (ULS vs. oscillatory shear mimicking d-flow). We found 94 downregulated and 40 upregulated genes that changed in a shear- and SOX13-dependent manner. Several cytokines, including CXCL10 and CCL5, were the most strongly upregulated genes in HAECs treated with SOX13 siRNA. The robust induction of CXCL10 and CCL5 was further validated by qPCR and ELISA in HAECs. Moreover, the treatment of HAECs with Met-CCL5, a specific CCL5 receptor antagonist, prevented the endothelial inflammation responses induced by siSOX13. In addition, SOX13 overexpression prevented the endothelial inflammation responses. In summary, SOX13 is a novel conserved FSTF, which represses the expression of pro-inflammatory chemokines in ECs under s-flow. Reduction of endothelial SOX13 triggers chemokine expression and inflammatory responses, a major proatherogenic pathway.

Abstract 116: Proof Of Biological Activity And Exploration Of Early Signaling Events Of Angiotensin-(1-5)

Introduction: Recombinant human ACE2 increases the circulating levels of angiotensin-(1-5) [Ang-(1-5)], a peptide thus far regarded as biologically inactive. Since ACE2 is a central component of the protective RAS, we hypothesized that Ang-(1-5) is a new biologically active peptide within this hormonal system. Objective: To investigate biological activity and signaling mechanisms of Ang-(1-5). Methods: In order to show a biological effect and to test whether Ang-(1-5) signals through the AT 2 -receptor (AT 2 R), nitric oxide (NO) release was measured by DAF-FM fluorescence in AT 2 R transfected (AT 2 R-CHO) or non-transfected (NT-CHO) CHO cells, treated with Ang-(1-5) or C21 (AT 2 R agonist, positive control) (0.1nM to 10μM) for 15 minutes. Vehicle (cell media) treated cells served as negative control. To investigate Ang-(1-5) signaling patterns, human aortic endothelial cells (HAEC) were treated with vehicle or Ang-(1-5) (1μM) for 1, 3, 5 or 20 minutes. Proteins were harvested, digested and labeled with TMTpro-16plex. Phosphopeptide enrichment was carried out by TiO 2 . Samples were subjected to LC-MS/MS analysis and the resulting mass spectra were searched against the human SwissProt database. Results: Ang-(1-5) induced a concentration-dependent increase in NO production in AT 2 -CHO cells (E max : 65.60 ± 14.02%), thus proving its biological activity. Ang-(1-5) had 69% higher efficacy than the established AT 2 R agonist C21 (E max : 38.76 ± 10.24%). Ang-(1-5) seems to signal through the AT 2 R, because effects on NO release were absent in NT-CHO cells. Treatment of HAEC with Ang-(1-5) significantly modified the phosphorylation status of 831 proteins at 1799 residues. The majority of residues (1079) were dephosphorylated while 729 residues were phosphorylated. Changes in protein phosphorylation in response to Ang-(1-5) occurred at all investigated time points, most of them after 20 minutes. Functional bioinformatic analysis revealed a cluster of proteins involved in cell cycle and cell division regulation. Conclusion: This study provides evidence that Ang-(1-5) is an endogenous AT 2 R agonist with high efficacy towards the AT 2 R. The early signaling phosphorylation pattern resembles those of other protective RAS agonists, such as C21 and Ang-(1-7).

Abstract P3130: Role Of The Placenta-derived Extracellular Vesicle-cargo Protein, Vasorin In Vascular Dysfunction In Preeclampsia

Background: We recently demonstrated that placenta-derived extracellular vesicles (pEVs) cargo play a role in vascular dysfunction in patients with severe preeclampsia (sPE). We focused our follow up studies on a novel protein vasorin (VASN) that has not as yet been studied in PE. Here, we hypothesize that decreased VASN in EVs cargo plays a significant role in the regulation of vascular endothelial proliferation and function in sPE. Methods: We manipulated VASN by overexpression and knockdown in human aortic endothelial cells (HAEC) and in murine aortic vascular rings (MVR) using adenoviral vectors encoding VASN (AD-VASN) or VASN shRNA (AD-shVASN), respectively. VASN levels in EVs, in HAEC and in MVR with/wo adenoviral overexpression or knockdown of VASN was done by western blotting. Migration of HAEC was studied by a scratch and repair migration assay and contractile function of MVR was assessed by wire myography. A PE-like vascular dysfunction was produced in timed pregnant mice by intravenous injection of an adenoviral vector encoding the short form of FMS-like tyrosine kinase 1 (sFLT-1) on embryonic day 10.5 (E10.5) of pregnancy. Plasma from sFLT-1 -injected and control untreated (UT) mice were collected on E15.5,E17.5 and E19.5. Results: We confirmed our findings with proteomics and using western blotting we detected a significant reduction in VASN levels in both urinary and plasma-derived EVs in sPE patients when compared to normotensive. Moreover, we detected a time-dependent significant reduction of VASN in EVs from plasma of sFLT-1 injected mice whereas UT mice exhibited a time-dependent increase of VASN. Western blotting also confirmed over-expression and knock down of VASN in HAEC and in MVR treated with AD-VASN and AD-shVASN, respectively. Treatment of HAEC with EVs from sPE, but not by EVs from NTP inhibited migration, and pretreatment with AD-VASN but not with AD-shVASN rescued migration upon treatment with EVs from PE. Treatment of MVR with EVs from sPE, but not by EVs from NTP inhibited acetylcholine (ACh)-induced vasorelaxation. Pretreatment with AD-VASN, but not with AD-shVASN rescued ACh-induced vasorelaxation upon treatment with EVs from sPE. Conclusion: Over-expression of VASN using adenoviral vectors rescued inhibitory effects of EVs from sPE on migration of HAEC and ACh-induced vasorelaxation in MVR, suggesting that reduced VASN content in EVs from sPE plays a mechanistic role in vascular dysfunction observed in sPE.

Circular RNA circ_0090231 promotes atherosclerosis in vitro by enhancing NLR family pyrin domain containing 3-mediated pyroptosis of endothelial cells

ABSTRACT Atherosclerosis (AS) is an inflammatory disease caused by multiple factors. Multiple circRNAs are involved in the development of AS. The present study focusses on delineating the role of circ_0090231 in AS. Human aortic endothelial cells (HAECs) were treated with oxidized low-density lipoprotein (ox-LDL) to construct an in vitro AS model. Real-time quantitative polymerase-chain reaction (RT-qPCR) was used to detect the levels of circ_0090231, IL-1β, and IL-18 transcripts. CircRNA/target gene interactions were predicted using StarBase and TargetScan and confirmed using an RNA pull-down assay and dual-luciferase reporter assay. Further, 3-(4,5)-dimethylthiahiazo(−2)-3,5-diphenytetrazoliumromide (MTT) and lactate dehydrogenase (LDH) release assays were performed to evaluate cell viability and damage in the AS model, respectively. Cell pyroptosis and protein expression were determined using flow cytometry and western blotting respectively. The treatment of HAECs with ox-LDL not only led to significant increase in the levels of circ_0090231 but also resulted in improved cell viability as well as reduced cell injury and pyroptosis as compared to that in non-treated cells. The circ_0090231 was also identified to function as a sponge for miR-635, knockdown of which reverses the effects of circ_0090231 inhibition. Furthermore, our results revealed that levels of NLRP3, a miR-635 target, are not only augmented in the AS model but its overexpression also weakens the miR-635 regulatory effects in the AS development. Taken together, the circ_0090231/miR-635/NLRP3 axis affects the development of AS by regulating cell pyroptosis, thus providing new insights into the mechanism of AS development.

Decursin inhibits the oxidation of low-density lipoprotein and protects human aortic endothelial cells against oxidative damage

Atherosclerosis is the pathological basis of cardiovascular diseases (CVDs) which are the leading cause of death worldwide. The pathogenesis of atherosclerosis itself is complex. Low-density lipoprotein (LDL) oxidation has been shown to increase lipid peroxide levels in arterial wall of atherosclerosis lesion site. Decursin is a coumarin with a range of pharmacological effects. The present study investigated the inhibitory effect of decursin on LDL oxidation, and its protective effect against oxidative damage in human aortic endothelial cells (HAECs). Two models of oxidative damage were used in this study: Cu2+-induced LDL oxidative damage and 2,2'-azobis-2-methyl-propanimidyl, dihydrochloride (AAPH)-induced oxidative damage of HAECs. The inhibitory effect of decursin on LDL oxidation, and its protective effect on oxidative damage of HAECs were determined. The results showed that the level of thiobarbituric acid reactive substances (TBARS) was significantly increased by Cu2+, but was significantly and concentration-dependently reduced after treatment with decursin (p < 0.05). There were only a few viable cells in AAPH-treated group, but treatment with decursin led to significant, time- and concentration-dependent increases in their viability (p < 0.05). The AAPH-induced oxidative damage significantly increased the activity of lactate dehydrogenase (LDH) and level of reactive oxygen species (ROS), but significantly reduced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) (p < 0.05). However, treatment of HAECs with decursin significantly and concentration-dependently reduced the LDH activity and level of ROS, but significantly increased the activities of SOD and GPx, concentration-dependently (p < 0.05). It also significantly and concentration-dependently reduced apoptosis induced by AAPH (p < 0.05). These results show that decursin effectively inhibits LDL oxidation induced by Cu2+, and protects HAECs from oxidative damage caused by AAPH in vitro via a mechanism involving activation of SOD and GPx.

RANKL treatment of vascular endothelial cells leading to paracrine pro-calcific signaling involves ROS production.

Numerous studies have highlighted the causal link between over-production of reactive oxygen species (ROS) and cardiovascular complications such as vascular calcification (VC). Receptor-activator of nuclear factor-κB ligand (RANKL) has previously been shown to act on endothelial cells, eliciting the production/release of paracrine pro-calcific signals that act, in-turn, upon underlying vascular smooth muscle cells (VSMCs) to induce osteoblastic differentiation and VC. A role for endothelial ROS signaling in this process has not been established however. In the current paper, we investigate the possibility that RANKL leads to ROS signaling within the endothelial layer as part of the RANKL-driven VC signaling cascade. Human aortic endothelial cells (HAECs) were treated with RANKL (25ng/ml, 72h) and monitored for ROS production, in parallel with various pro-calcific signaling indices. Antioxidant co-treatments included TRAIL (5ng/ml), apocynin (10mM) and N-acetylcysteine (5mM). Treatment of HAECs with RANKL-induced robust ROS production. This surge could be partially attenuated by TRAIL and strongly attenuated by apocynin and N-acetylcysteine. RANKL also elicited a range of signaling events in HAECs that we have previously demonstrated are coupled to osteoblastic differentiation in underlying VSMCs. These include non-canonical NF-κB/p52 activation, elevated BMP-2 release and increased alkaline phosphatase (ALP) enzyme activity (cellular and extracellular). Importantly, these RANKL-induced signaling events could be completely prevented by co-treatment of HAECs with antioxidants. In summary, RANKL elicits ROS generation in HAECs with direct consequences for generation of paracrine pro-calcific signals known to effect calcification in underlying VSMCs.

Elevated methylation of cyclin dependent kinase inhibitor 2B contributes to the risk of coronary heart disease in women.

Cyclin dependent kinase inhibitor 2B (CDKN2B) encodes a cyclin-dependent kinase inhibitor that may enhance the formation of atherosclerotic plaques. The aim of the present study was to investigate the contribution of CDKN2B promoter methylation on the risk of coronary heart disease (CHD). The present results indicated a significant association between increased CDKN2B methylation and the risk of CHD (adjusted P=0.043). A breakdown analysis according to sex demonstrated that CDKN2B methylation was significantly associated with the risk of CHD in women (adjusted P=0.010), but not in men. A further breakdown analysis by age indicated a significant association of CHD in the women >60 years (P=0.024). Luciferase reporter gene assay results indicated that the CDKN2B promoter fragment significantly enhanced luciferase activity (P<0.001). In addition, CDKN2B transcription was significantly enhanced following treatment with 5-aza-2′-deoxycytidine methylation inhibitor in human aortic endothelial cells (HAEC) and human primary coronary artery smooth muscle cells (HPCASMC; P<0.05 and P<0.01), but not in 293 cells. Notably, estrogen treatment reduced CDKN2B methylation of several CpGs and significantly increased CDKN2B gene expression levels in HAEC, HPCASMC and 293 cells (P<0.05 and P<0.01). Additionally, treatment of HAEC and HPCASMC with simvastatin and γ-carboxy-L-glutamic acid reduced CDKN2B promoter methylation and increased CDKN2B transcription concomitantly. The present study suggests that CDKN2B promoter methylation may be associated with sex dimorphism in the pathogenesis of CHD.

Abstract 212: Chronic Systemic Inflammation Accelerates Endothelial Cholesterol Crystal Formation and Lysosomal Dysfunction

Objective: Atherogenesis is an inflammatory process accelerated in psoriasis, a chronic inflammatory skin disease associated with premature cardiovascular diseases (CVD). Cholesterol crystal (CC) formation is implicated at onset and progression of atherosclerotic CVD, and we have recently shown CC formation to be upregulated in a murine model of psoriasis-related atherosclerosis. Therefore, we investigated inflammatory CC production in this psoriasis mouse model and also using psoriasis patient derived samples. Methods: K14-Rac1V12 psoriasis mouse aortas were examined for CC formation and structural abnormalities, such as subendothelial spaces, via electron microscopy and histology. Human aortic endothelial cells (HAoEC) were stimulated with sera from healthy and psoriatic volunteers (n=5 each), inflammatory markers TNFα+IFNγ, LDL or combination of TNFα+IFNγ+LDL. The effect on CC formation and lysosomal function was determined by advanced microscopy and flow cytometry. HAoECs were also treated with TNFα+IFNγ+LDL combined with β-cyclodextrin (CD), a stimulant for cholesterol release from cells, and analyzed for CC formation and lysosomal function. Results: Psoriatic mouse aortas showed enlarged subendothelial spaces and 40% increased CC formation under normolipidemic conditions compared to littermate controls. Treatment of HAoECs with psoriasis patient-sera (severe skin disease, low CVD risk score) or TNFα+IFNγ+LDL showed a 2-fold increase in CC formation and 30% increased lysosomal frequency compared to controls. Despite an increase in lysosome frequency, TNFα+IFNγ+LDL treatment decreased overall pH-related lysosomal activity. CD treatment diminished TNFα+IFNγ+LDL-induced CC formation (compared to vehicle), and restored lysosomal function without affecting lysosome frequency. Conclusion: Psoriasis mice displayed accelerated CC formation in the absence of hyperlipidemic conditions suggesting chronic systemic inflammation accelerates CC formation in vivo and in vitro , accompanied by lysosomal dysfunction in ECs. These findings suggest that dyslipidemia and systemic inflammation in psoriasis are important contributors to early atherogenesis and should be treatment targets for CVD risk mitigation.

Structure-activity relationship for toxicity of α-pyrrolidinophenones in human aortic endothelial cells

In this study, we found that exposure of 20 μM α-pyrrolidinooctanophenone (α-POP), a new synthetic cathinone, time- and dose-dependently reduced viability of human aortic endothelial (HAE) cells, and the 50% lethal concentration (LC50) for α-POP in its 48-h treatment was 15.6 μM. In addition, the LC50 comparison of α-POP and α-pyrrolidinoheptanophenone (α-PHPP) toxicity against ten human cells exhibited that vascular (HAE and human aortic smooth muscle) and bronchial epithelial BEAS-2B cells were more susceptible to the cytotoxicity than neuronal (SK-N-SH and A172), gastrointestinal (DLD1 and MKN45), hepatic HepG2, renal HEK293 and pulmonary A549 cells. The results suggest that abuse of the lipophilic α-pyrrolidinophenones (PPs), such as α-POP and α-PHPP, is more likely to cause damage to the vascular, respiratory and central nervous systems. Structure-activity relationship study of 18 PPs with different alkyl chain lengths and substituents revealed that the endothelial cell toxicity depends on the alkyl chain length (α-POP > α-PHPP > PPs with shorter chains), and the presence of 4′-fluoro or 3′,4′-methylenedioxy group on α-POP and α-PHPP increased the cytotoxicity. In order to understand the cytotoxic mechanism of α-POP and F-α-POP that showed the most potent toxicity, the contribution of reactive oxygen species (ROS) production, caspase-3 activation and DNA fragmentation were investigated. The treatment of HAE cells with α-POP or F-α-POP resulted in remarkable ROS production, and the ROS production and apoptotic events were significantly prevented by pretreating the cells with an antioxidant N-acetyl-l-cysteine, suggesting that ROS-dependent signaling is primarily responsible for endothelial cell apoptosis elicited by the lipophilic synthetic cathinones.

Aspalatone Prevents VEGF-Induced Lipid Peroxidation, Migration, Tube Formation, and Dysfunction of Human Aortic Endothelial Cells.

Although aspalatone (acetylsalicylic acid maltol ester) is recognized as an antithrombotic agent with antioxidative and antiplatelet potential; its efficacy in preventing endothelial dysfunction is not known. In this study, we examined the antiangiogenic, antioxidative, and anti-inflammatory effect of aspalatone in human aortic endothelial cells (HAECs). Specifically, the effect of aspalatone on VEGF-induced HAECs growth, migration, tube formation, and levels of lipid peroxidation-derived malondialdehyde (MDA) was examined. Our results indicate that the treatment of HAECs with aspalatone decreased VEGF-induced cell migration, tube formation, and levels of MDA. Aspalatone also inhibited VEGF-induced decrease in the expression of eNOS and increase in the expression of iNOS, ICAM-1, and VCAM-1. Aspalatone also prevented the VEGF-induced adhesion of monocytes to endothelial cells. Furthermore, aspalatone also prevented VEGF-induced release of inflammatory markers such as Angiopoietin-2, Leptin, EGF, G-CSF, HB-EGF, and HGF in HAECs. Thus, our results suggest that aspalatone could be used to prevent endothelial dysfunction, an important process in the pathophysiology of cardiovascular diseases.

Complement-Mediated Enhancement of Monocyte Adhesion to Endothelial Cells by HLA Antibodies, and Blockade by a Specific Inhibitor of the Classical Complement Cascade, TNT003.

BackgroundAntibody-mediated rejection (AMR) of most solid organs is characterized by evidence of complement activation and/or intragraft macrophages (C4d + and CD68+ biopsies). We previously demonstrated that crosslinking of HLA I by antibodies triggered endothelial activation and monocyte adhesion. We hypothesized that activation of the classical complement pathway at the endothelial cell surface by HLA antibodies would enhance monocyte adhesion through soluble split product generation, in parallel with direct endothelial activation downstream of HLA signaling.MethodsPrimary human aortic endothelial cells (HAEC) were stimulated with HLA class I antibodies in the presence of intact human serum complement. C3a and C5a generation, endothelial P-selectin expression, and adhesion of human primary and immortalized monocytes (Mono Mac 6) were measured. Alternatively, HAEC or monocytes were directly stimulated with purified C3a or C5a. Classical complement activation was inhibited by pretreatment of complement with an anti-C1s antibody (TNT003).ResultsTreatment of HAEC with HLA antibody and human complement increased the formation of C3a and C5a. Monocyte recruitment by human HLA antibodies was enhanced in the presence of intact human serum complement or purified C3a or C5a. Specific inhibition of the classical complement pathway using TNT003 or C1q-depleted serum significantly reduced adhesion of monocytes in the presence of human complement.ConclusionsDespite persistent endothelial viability in the presence of HLA antibodies and complement, upstream complement anaphylatoxin production exacerbates endothelial exocytosis and leukocyte recruitment. Upstream inhibition of classical complement may be therapeutic to dampen mononuclear cell recruitment and endothelial activation characteristic of microvascular inflammation during AMR.

OR37 Antibody ligation of Hla B*44:03 fails to stimulate endothelial cell proliferation due to a failure to recruit integrin beta4

Aim Antibody-mediated rejection (AMR) is an important clinical problem after solid organ transplantation. Recipients producing posttransplant HLA antibodies (Ab) are at a higher risk for acute and chronic AMR. Notably, not all patients producing post-transplant Ab develop AMR. We postulated that distinct HLA class I alleles may differ in their capacity to transduce signals. Our previous data showed that HLA-B*44:03 was less efficient than other B locus molecules, including B*44:02, to stimulate signal transduction networks in endothelial cells (EC) despite having a similar binding capacity. We tested the hypothesis that failure of B*44:03 to stimulate signal transduction and EC proliferation was due to its inability to recruit integrin β 4. Method Primary human aortic EC (HAEC) were stimulated with human HLA-B12 allele specific mAb, and phosphorylation of signaling proteins was detected by Western Blot. For protein:protein complex formation, HAEC were stimulated with F(ab’)2 fragment of anti-HLA class I (HLA I) mAb W6/32 or mouse IgG as a control. Cell lysates were immunoprecipitated with a mouse anti-HLA-B12 mAb recognizing both B*44:02 and B*44:03 alleles and complex formation between class I and integrin β 4 was detected by Western Blot. Gene silencing was determined with siRNA transfection. EC proliferation was measured by BrdU incorporation and analyzed by flow cytometry. Results Treatment of HAEC with anti-B12 mAb stimulated a increase in phosphorylation of Src, mTOR, ERK and Akt in B*44:02, but not in B*44:03 HAEC. Co-immunoprecipitation experiments showed complex formation between HLA I and integrin β 4 in B*44:02 HAEC, but not in HAEC carrying B*44:03. Furthermore, transfection of EC with integrin β 4 siRNA inhibited HLA-B12 mAb-induced protein phosphorylation and cell proliferation. Conclusions Our results demonstrate that HAEC carrying B*44:03 fail to transduce proliferative signals because they are unable to recruit integrin β 4 into a signaling complex. Disrupting complex formation between integrin β 4 and HLA I may provide a new therapeutic target to prevent AMR.

Abstract 130: Hypercholesterolemia Suppresses Carotid Artery Endothelial NOS3 Expression via Epigenetic Mechanisms

Objective: One of the first clinically detectable changes in the vasculature during atherogenesis is the accumulation of cholesterol within the vessel wall. Hypercholesterolemia is characterized by dysfunctional endothelial-dependent vessel relaxation and impaired NOS3 function. Since DNA methylation at gene promoter regions strongly suppresses gene expression, we postulated that high-fat/high-cholesterol diet suppresses endothelial NOS3 through promoter DNA methylation. Methods: Domestic male pigs were fed control diet (CD) or isocaloric high fat and high cholesterol diet (HC; 12% fat and 1.5% cholesterol) for 2, 4, 8 or 12 weeks prior to tissue collection. Furthermore, to determine the effects of risk factor withdrawal, an additional group of swine received HC for 12 weeks and then CD for 8 weeks; a control group received HC continuously for 20 weeks. Endothelial cells were harvested from common carotid aorta. In parallel in vitro studies, cultured human aortic endothelial cells (HAEC) were treated with human LDL, GW3956 (LXR agonist) and RG108 (DNA methyltransferase [DNMT] inhibitor). In cells from both sources, DNA methylation at the NOS3 promoter was measured using methylation specific pyro sequencing, and endothelial gene expression was measured using RT PCR. Results: HC diet increased plasma cholesterol level from 75 mg/dl on CD to a plateau of about 540 mg/dl within 2 weeks. Endothelial NOS3 expression was significantly reduced (71±9 % of CD) after 4 weeks of HC, a level sustained at subsequent time points. Withdrawal of HC for 8 weeks did not recover NOS3 expression. After 12-week HC, the NOS3 promoter was hypermethylated. Withdrawal of HC did not reverse NOS3 promoter methylation. In vitro treatment of HAEC with human LDL (200 mg/dl total cholesterol) or GW3956 (5μM) suppressed NOS3 mRNA to 50% and 30% respectively, suggesting that LXR/RXR is involved in suppression of NOS3. Nitric oxide production was consistently suppressed by GW3959. Both could be reversed through inhibition of DNMTs by RG108. Conclusions: DNA methylation and LXR/RXR pathway can mediate the HC-suppression of endothelial NOS3. The study identifies novel pharmaceutical targets in treating endothelial dysfunction. Crosstalk between these pathways is under investigation.

Ramipril protects the endothelium from high glucose-induced dysfunction through CaMKKβ/AMPK and heme oxygenase-1 activation.

This study aims to investigate the effects of ramipril (RPL) on endothelial dysfunction associated with diabetes mellitus using cultured human aortic endothelial cells (HAECs) and a type 2 diabetic animal model. The effect of RPL on vasodilatory function in fat-fed, streptozotocin-treated rats was assessed. RPL treatment of 8 weeks alleviated insulin resistance and inhibited the decrease in endothelium-dependent vasodilation in diabetic rats. RPL treatment also reduced serum advanced glycation end products (AGE) concentration and rat aorta reactive oxygen species formation and increased aorta endothelium heme oxygenase-1 (HO-1) expression. Exposure of HAECs to high concentrations of glucose induced prolonged oxidative stress, apoptosis, and accumulation of AGEs. These effects were abolished by incubation of ramiprilat (RPT), the active metabolite of RPL. However, treatment of HAECs with STO-609, a CaMKKβ (Ca(2+)/calmodulin-dependent protein kinase kinase-β) inhibitor; compound C, an AMPK (AMP-activated protein kinase) inhibitor; and Zn(II)PPIX, a selective HO-1 inhibitor, blocked these beneficial effects of RPT. In addition, RPT increased nuclear factor erythroid 2-related factor-2 (Nrf-2) nuclear translocation and activation in a CaMKKβ/AMPK pathway-dependent manner, leading to increased expression of the Nrf-2-regulated antioxidant enzyme, HO-1. The inhibition of CaMKKβ or AMPK by pharmaceutical approach ablated RPT-induced HO-1 expression. Taken together, RPL ameliorates insulin resistance and endothelial dysfunction in diabetes via reducing oxidative stress. These effects are mediated by RPL activation of CaMKK-β, which in turn activates the AMPK-Nrf-2-HO-1 pathway for enhanced endothelial function.

Multi-walled carbon nanotube directed gene and protein expression in cultured human aortic endothelial cells is influenced by suspension medium

The use and production of multi-walled carbon nanotubes (MWCNTs) have significantly increased over the last decade due to their versatility in numerous applications. Their unique physical and chemical properties make them desirable for various biomedical applications, but the same properties also raise concerns about their safety to human health, particularly at the cellular level. The vascular endothelium could be exposed to nanomaterials either by direct intravenous administration in nanomedicine or by translocation following inhalational exposure in an occupational setting. We hypothesized that direct exposure to MWCNTs will increase the expression of inflammatory markers in human aortic endothelial cells (HAEC). We also investigated the effect of the route of exposure on activation by changing the suspension medium of the MWCNTs. HAEC were treated in vitro with MWCNTs (1 or 10μg/cm2) suspended in either cell culture medium [(M)-MWCNTs] or 10% clinical grade pulmonary surfactant [(S)-MWCNTs]. The zeta potential of the (S)-MWCNTs was significantly more negative than the (M)-MWCNTs suggesting a more stable suspension. Treatment of HAEC with (S)-MWCNTs; as compared to (M)-MWCNTs resulted in a significantly higher up-regulation of mRNA transcripts for cell adhesion molecules VCAM1, SELE, ICAM1 and the chemokine CCL2. Time dependent changes in VCAM1 and CCL2 protein levels were confirmed by immunofluorescence, flow cytometry and ELISA. A label free quantitative mass spectrometry proteomic analysis was utilized to compare protein expression patterns between the two suspensions of MWCNTs. We identified significant expression changes in >200 unique proteins in MWCNT treated HAEC. However, the two suspensions of MWCNTs resulted in different protein expression patterns with the eIF2 pathway as the only common pathway identified between the two suspensions. These data suggest that direct exposure to MWCNTs induces acute inflammatory and protein expression changes in HAEC, which is influenced by the type of media used for suspension of MWCNTs and their resulting zeta potential.

Abstract 358: Cyclic Strain-Induced Release of Thrombomodulin from Human Aortic Endothelial Cells

Introduction: Loss of thrombomodulin (TM), a cofactor in the protein C anti-coagulant pathway, through a combination of reduced TM expression and elevated TM release, is a key feature of endothelial dysfunction leading to vascular diseases. Reduction in endothelial TM levels for example is viewed as a major cause of cyclic strain-induced early vein graft failure. In this respect, our understanding of the mechanistic relationship between vessel stretch and TM expression/release in endothelial cells is very limited, with a particular shortage of in vitro models. In this study, we investigated how cyclic circumferential strain negatively regulates thrombomodulin levels in human aortic endothelial cells (HAECs) in vitro. Methods: A Flexercell® Tension-Plus™ FX-4000T™ system (Flexcell International Corp., Hillsborough, NC) was routinely employed to subject HAECs to equibiaxial cyclic strain over a range of doses (0, 2.5 and 7.5% stretch; 60 cycles/min; cardiac waveform) and times (0-48 hours). TM expression was analyzed via Western blotting and qRT-PCR, whilst TM release was monitored by ELISA. Results: (i) Cyclic strain of HAECs led to significant force- and time-dependent reductions in TM expression (mRNA and protein) in conjunction with elevated TM release into media; (ii) Inclusion of either GM6001 (25 μM) or apocynin (10 mM) into strain experiments to block MMP-2/9 and NADPH oxidase activities, respectively, had no effect on strain-induced TM release; (iii) Control studies demonstrated that treatment of HAECs with neither TNF-α (0, 10, 100 ng/ml) nor oxLDL (10, 50, 145.7 μg/ml) increased TM release from HAECs - however, oxLDL treatment was found to dose-dependently potentiate cyclic-strain-induced TM release. Conclusions: Cyclic strain negatively regulates TM levels in endothelial cells in vitro. Moreover, release of TM from HAECs does not appear to involve the strain-dependent induction of either MMP-2/9 proteolytic activity or NADPH oxidase-dependent superoxide production. Finally, the cyclic strain-induced release of TM appears to be potentiated by inflammatory atherogenic conditions such as high oxLDL levels.

Angiopoeitin-2 modulates Survivin expression in OxLDL-induced endothelial cell apoptosis

Angiopoeitin-2 (Ang-2) antagonizes Angiopeitin-1 (Ang-1)-mediated Tie-2 signaling. Ang-1 is reported to up-regulate anti-apoptotic Survivin expression. Here, we investigated the interplay between Ang-2 and Survivin in response to oxidized low density lipoprotein (OxLDL)-induced apoptosis. We demonstrate that treatment of human aortic endothelial cells (HAEC) with 100μg/ml of OxLDL down-regulated Ang-2 expression as early as 4h after treatment and persisted up to 24h (p<0.05, n=3), but did not down-regulate Survivin until the 24h point. Further, treatment of HAEC with recombinant Ang-2 up-regulated Survivin expression (at Ang-2 ⩾200ng/ml, p<0.05, n=3) and attenuated the OxLDL-mediated down-regulation of Survivin (p<0.05, n=3). Knockdown of Ang-2 further down-regulated Survivin expression, whereas over-expression of Survivin attenuated OxLDL-induced HAEC apoptosis (p<0.05, n=3). Hence, Ang-2 mediated Survivin expression in response to OxLDL-induced endothelial apoptosis.

Protein Kinase A-α Directly Phosphorylates FoxO1 in Vascular Endothelial Cells to Regulate Expression of Vascular Cellular Adhesion Molecule-1 mRNA

FoxO1, a forkhead box O class transcription factor, is abundant in insulin-responsive tissues. Akt, downstream from phosphatidylinositol 3-kinase in insulin signaling, phosphorylates FoxO1 at Thr(24), Ser(256), and Ser(319), negatively regulating its function. We previously reported that dehydroepiandrosterone-stimulated phosphorylation of FoxO1 in endothelial cells requires cAMP-dependent protein kinase α (PKA-α). Therefore, we hypothesized that FoxO1 is a novel direct substrate for PKA-α. Using an immune complex kinase assay with [γ-(32)P]ATP, purified PKA-α directly phosphorylated wild-type FoxO1 but not FoxO1-AAA (mutant with alanine substitutions at known Akt phosphorylation sites). Phosphorylation of wild-type FoxO1 (but not FoxO1-AAA) was detectable using phospho-specific antibodies. Similar results were obtained using purified GST-FoxO1 protein as the substrate. Thus, FoxO1 is a direct substrate for PKA-α in vitro. In bovine aortic endothelial cells, interaction between endogenous PKA-α and endogenous FoxO1 was detected by co-immunoprecipitation. In human aortic endothelial cells (HAEC), pretreatment with H89 (PKA inhibitor) or siRNA knockdown of PKA-α decreased forskolin- or prostaglandin E(2)-stimulated phosphorylation of FoxO1. In HAEC transfected with a FoxO-promoter luciferase reporter, co-expression of the catalytic domain of PKA-α, catalytically inactive mutant PKA-α, or siRNA against PKA-α caused corresponding increases or decreases in transactivation of the FoxO promoter. Expression of vascular cellular adhesion molecule-1 mRNA, up-regulated by FoxO1 in endothelial cells, was enhanced by siRNA knockdown of PKA-α or treatment of HAEC with the PKA inhibitor H89. Adhesion of monocytes to endothelial cells was enhanced by H89 treatment or overexpression of FoxO1-AAA, similar to effects of TNF-α treatment. We conclude that FoxO1 is a novel physiological substrate for PKA-α in vascular endothelial cells.