Expression In Vascular Endothelium Research Articles

Eicosapentaenoic acid (EPA) treatment increased the ratio to arachidonic (EPA/AA) and reduced adhesion molecule expression in vascular endothelium during inflammation

Abstract Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Amarin Pharmaceutical, Inc. Elucida Research LLC. Background Omega-3 fatty acid (n3-FA) treatment reduces cardiovascular (CV) risk in relation to circulating EPA/AA ratios. Treatment with icosapent ethyl (IPE), a highly purified EPA formulation, increased the EPA/AA ratio in treated patients (MARINE, ANCHOR). Unlike mixed n3-FA formulations, IPE reduced a composite of CV events in high-risk patients (REDUCE-IT) in relation to on-treatment EPA levels. These benefits of EPA may result in part from effects on vascular endothelial function and fatty acid content during inflammation. Purpose We measured the effect of EPA on human endothelial cells (HUVECs) during inflammatory activation, monitoring the release of soluble intercellular adhesion molecule-1 (sICAM-1) and changes in fatty acid content. Methods HUVECs were challenged with IL-6 (12 ng/mL) for 2 hours and then treated with EPA (40 µM) or vehicle for 24 hours. Total protein content was measured in cell lysates. Total fatty acids were extracted and derivatized using methanol containing 14% boron trifluoride to form fatty acid methyl esters (FAME). Gas chromatography measured total fatty acid content from C14-C24 and normalized to total protein. Levels of sICAM-1 were measured in cell supernatant using immunochemistry. Results EPA treatment increased the EPA/AA ratio by >20-fold compared to IL-6 treatment alone (1.55 ± 0.11 vs. 0.07 ± 0.003, p<0.001). The increased EPA/AA ratio correlated with EPA and docosapentaenoic acid (DPA) levels in lysates, which increased by 19-fold (26.71 ± 1.28 vs. 1.28 ± 0.05 mg/g protein, p<0.001) and 4-fold (29.42 ± 1.91 vs. 6.17 ± 0.36 mg/g protein, p<0.001), respectively, compared to IL-6. While IL-6 treatment increased sICAM-1 release (83%, p<0.001), subsequent treatment with EPA reduced sICAM-1 release by 39% (p<0.001). Conclusion In human ECs, EPA increased the EPA/AA ratio along with other n3-FAs under conditions of inflammation. Changes in the EPA/AA ratio correlated with reductions in sICAM-1 release with IL-6 exposure. As on-treatment EPA levels predict reduced CV risk, these direct vascular benefits of EPA may contribute to reduced CV risk observed in outcome trials.

Erianin alleviated liver steatosis by enhancing Nrf2-mediated VE-cadherin expression in vascular endothelium

Non-alcoholic fatty liver disease (NAFLD) is emerging as the most common chronic liver disease and is closely associated with metabolic syndrome. Endothelial dysfunction was involved in many metabolic diseases, but the concrete participation of hepatic vascular endothelial dysfunction in liver steatosis that is an early stage of NAFLD is still unclear. In this study, the formation of liver steatosis and the elevation of serum insulin content were observed accompanying with the decreased vascular endothelial cadherin (VE-cadherin) expression in hepatic vessels from db/db mice, Goto-Kakizaki (GK) and high-fat diet (HFD)-fed rats. Liver steatosis was obviously enhanced in mice after the application of VE-cadherin neutralizing antibody. In vitro results showed that insulin decreased VE-cadherin expression and caused endothelial barrier breakdown. Furthermore, the alteration of VE-cadherin expression was found to be positively related with the transcriptional activation of nuclear erythroid 2-related factor 2 (Nrf2), and chromatin immunoprecipitation (ChIP) assay displayed that Nrf2 could directly regulate VE-cadherin expression. Insulin reduced Nrf2 activation by decreasing sequestosome-1 (p62/SQSTM1) expression downstream of insulin receptor. Moreover, the p300-mediated Nrf2 acetylation was weakened by enhancing the competitive binding of transcription factor GATA-binding protein 4 (GATA4) to p300. Finally, we found that erianin, a natural compound, could promote VE-cadherin expression by inducing Nrf2 activation, thereby alleviating liver steatosis in GK rats. Our results suggest that hepatic vascular endothelial dysfunction owing to the VE-cadherin deficiency dependent on the reduced Nrf2 activation promoted liver steatosis, and erianin alleviated liver steatosis through enhancing Nrf2-mediated VE-cadherin expression.

Aggrecan accumulates at sites of increased pulmonary arterial pressure in idiopathic pulmonary arterial hypertension.

Expansion of extracellular matrix occurs in all stages of pulmonary angiopathy associated with pulmonary arterial hypertension (PAH). In systemic arteries, dysregulation and accumulation of the large chondroitin-sulfate proteoglycan aggrecan is associated with swelling and disruption of vessel wall homeostasis. Whether aggrecan is present in pulmonary arteries, and its potential roles in PAH, has not been thoroughly investigated. Here, lung tissue from 11 patients with idiopathic PAH was imaged using synchrotron radiation phase-contrast microcomputed tomography (TOMCAT beamline, Swiss Light Source). Immunohistochemistry for aggrecan core protein in subsequently sectioned lung tissue demonstrated accumulation in PAH compared with failed donor lung controls. RNAscope in situ hybridization indicated ACAN expression in vascular endothelium and smooth muscle cells. Based on qualitative histological analysis, aggrecan localizes to cellular, rather than fibrotic or collagenous, lesions. Interestingly, ADAMTS15, a potential aggrecanase, was upregulated in pulmonary arteries in PAH. Aligning traditional histological analysis with three-dimensional renderings of pulmonary arteries from synchrotron imaging identified aggrecan in lumen-reducing lesions containing loose, cell-rich connective tissue, at sites of intrapulmonary bronchopulmonary shunting, and at sites of presumed elevated pulmonary blood pressure. Our findings suggest that ACAN expression may be an early response to injury in pulmonary angiopathy and supports recent work showing that dysregulation of aggrecan turnover is a hallmark of arterial adaptations to altered hemodynamics. Whether cause or effect, aggrecan and aggrecanase regulation in PAH are potential therapeutic targets.

Abstract P1069: Integrin Linked Kinase Controls Human Valve Endotelial Cells Pro-osteogenic Activation In A TFG-b/NO Dependent Manner

Calcific aortic valve disease (CAVD) is expected in the aging population. CAVD physiopathology arises from endothelial dysfunction leading to lipid accumulation, inflammation, and osteogenic transformation. Many studies suggest that valve endothelial cells (VECs) undergoing EndMT may differentiate into osteoblastic interstitial cells. We previously showed that Integrin linked kinase (ILK) regulates vasomotor function by preventing endothelial nitric oxide synthase uncoupling. ILK expression in vascular endothelium plays an essential cardioprotective role. Moreover, we have found a significant negative correlation between human valve protein levels of ILK and the osteogenic marker Runx2 and BMP2 in 70 patients with calcific aortic stenosis, a higher decrease at the endothelial level. We hypothesized that Endothelial ILK plays a protective role in human valve endothelial cells osteogenic transition. Isolation of human valve endothelial cells from the aortic (aortic hVECs) and ventricular sides (ventricular hVECs) show a specific ILK decrease in the aortic hVECs from calcific compared to non-calcified valve (p<0.05). Silencing ILK expression in hVECs decreased NO production and increased ROS (Reactive Oxygen Species) production as early as 72 hours. After five days of silencing ILK, hVEC express myofibroblast markers SM22a, α-SMA, MMP12, MMP9, and SNAI 1 while losing the endothelial markers (CD31, and vWF (p<0.01). ILK silenced hVECs (siILK-hVECs) express the osteogenic marker RunX2 indicating osteogenic differentiation and developed calcified nodules. Cell treatment with Noggin, a BMP2 antagonist, did not reverse the increase of Runx2, thus excluding the implication of the BMP2/RUNX2 axis. However, silk-hVECs showed an increase in phosphorylated-SMAD 2, suggesting a TFG-β -dependent mechanism. Treatment of siILK-hVECs with the NO donor DETA-NO decreased Smad 2 activation and RunX2. Moreover, DETA-NO treated siILK hVECs cultured in pro-osteogenic media did not develop calcification. Collectively, our results point to a crucial role of ILK in keeping human valve endothelial cell phenotype preventing valve calcification in a Nitric Oxide-TFGβ1 dependent manner. Financed by the Regional European fund “a way to achieve Europe.” JCCM SBPLY/19/180501/000055S and ISCIII PI20/00930

The LOX-1 receptor ectopically expressed in the liver alleviates atherosclerosis by clearing Ox-LDL from the circulation

ObjectiveOxidized Low-Density-Lipoprotein (Ox-LDL) is the core factor in the development of atherosclerosis. However, there are few therapies aimed at eliminating Ox-LDL. Here in this study, we investigate whether the ectopically expression of the lectin-like oxidized low density lipoprotein receptor (LOX-1) in the liver could lead to the elimination of circulating Ox-LDL and prevent the deposition in the vascular wall, thereby alleviating the progression of atherosclerosis.MethodsApolipoprotein E-deficient (ApoE−/−) mice were randomly divided into three groups, the control group, the AAV8-TBG-eGFP group (eGFP group) and AAV8-TBG-LOX-1 group (LOX-1 group). In the LOX-1 group, mice received an injection of virus dilution AAV8-TBG-LOX-1 (1.16 × 1011 virus genome (v.g)/animal/100 μl). The mice in the control group and eGFP group received the same amount of sterile saline and AAV8-TBG-eGFP virus dilution injections. The expression of LOX-1 in the liver was detected by immunofluorescent, western blot and immunohistochemistry. The safety of the virus was assessed by hematoxylin–eosin (H&E) staining, blood biochemical analyses and immunofluorescent. The function of LOX-1 in the liver was detected by the co-localization of LOX-1 and Dil-labeled Ox-LDL (Dil-Ox-LDL) under laser scanning confocal microscope. The extent of Ox-LDL in plasma was detected by ELISA. Changes in blood lipids were assessed through blood biochemical analysis. The progression of atherosclerotic lesions was detected by Oil red O staining. And the expression of Vascular Cell Adhesion Molecule-1 (VCAM-1) in endothelial cells and the extent and migration of macrophages in atherosclerotic plaque were detected by immunofluorescence staining. The protein expression in liver was assessed by qRT-PCR and western blot.ResultsThe expression of LOX-1 was stable in liver within 4 weeks. Ectopically expressed LOX-1 in the liver phagocytosed and degraded Ox-LDL and reduced Ox-LDL from circulation but did not have a significant effect on blood lipid levels. After the expression of LOX-1 in liver, Ox-LDL can be cleared by the hepatocytes, thereby reducing VCAM-1 expression in vascular endothelium and the migration of macrophages in plaques, and eventually alleviating the progression of atherosclerosis. Functional expression of LOX-1 in hepatocytes may facilitate the metabolic clearance of Ox-LDL by upregulating the expression of ATP-binding cassette G5 and G8 (ABCG5/G8), which is the primary neutral sterol transporter in hepatobiliary and transintestinal cholesterol excretion.ConclusionEctopic liver-specific expression of LOX-1 receptor alleviates the progression of atherosclerosis by clearing Ox-LDL from circulation.

Abstract 13243: Integrin Linked Kinase Expression in Human Valvular Endothelial Cells Plays a Protective Role in Calcific Aortic Valve Disease

Introduction: Calcific aortic valve disease (CAVD) is the most common valvular heart disease in the aging population. CAVD is a highly active ossification process originated in valvular interstitial cells which differentiate towards an osteoblastic phenotype. However, the role of valvular endothelial cells in CAVD has not been fully explored. We previously demonstrated that ILK expression in vascular endothelium plays an essential cardioprotective role. Hypothesis: Endothelial ILK plays a protective role in human valvular endothelial cells osteogenesis. Methods and Results: Human aortic valves were obtained from 52 patients with calcific aortic stenosis compared with 16 non-calcified aortic valves and ILK levels were analyzed. Our study showed a significant relationship between the degree of AV calcification and decreased ILK expression detected by IHQ and qPCR (p< 0,013). Moreover, decreased ILK expression correlated with BMP2 and Runx2, two markers of valvular calcification (p<0.01). Human valvular endothelial cells (hVECs) isolated from non-calcified controls display the ability to calcify when cultured in pro-calcifiying conditions and ILK levels were unaffected by the pro-calcifiying conditions. However, silencing ILK expression in hVECs resulted in decreased NO production, increased expression of calcific disease markers Runx2, BMP2, and osteopontin. ILK silencing in hVECs induced calcium deposition, determined by alizarin red staining, when cultured in pro-calcifiying conditions. Thus, our results suggest that decreased ILK expression could promote endothelial to osteogenic phenotype transition. Restoring nitric oxide levels by DETA-NONOate treatment in ILK silenced hVEC was able to reverse those effects partially. Conclusions: Collectively, our results point to a crucial role of ILK in maintaining human valve endothelial cell function preventing valvular calcification.

Endothelium-specific deletion of amyloid-β precursor protein exacerbates endothelial dysfunction induced by aging.

The physiological function of amyloid precursor protein (APP) in the control of endothelial function during aging is unclear. Aortas of young (4-6 months old) and aged (23-26 months old) wild-type (WT) and endothelium-specific APP-deficient (eAPP−/−) mice were used to study aging-induced changes in vascular phenotype. Unexpectedly, aging significantly increased protein expression of APP in aortas of WT mice but not in aortas of eAPP−/− mice thereby demonstrating selective upregulation APP expression in vascular endothelium of aged aortas. Most notably, endothelial dysfunction (impairment of endothelium-dependent relaxations) induced by aging was significantly exacerbated in aged eAPP−/− mice aortas as compared to age-matched WT mice. Consistent with this observations, endothelial nitric oxide synthase (eNOS) protein expression was significantly decreased in aged eAPP−/− mice as compared to age matched WT mice. In addition, protein expression of cyclooxygenase 2 and release of prostaglandins were significantly increased in both aged WT and eAPP−/− mice. Notably, treatment with cyclooxygenase inhibitor, indomethacin, normalized endothelium-dependent relaxations in aged WT mice, but not in aged eAPP−/− mice. In aggregate, our findings support the concept that aging-induced upregulation of APP in vascular endothelium is an adaptive response designed to protect and preserve expression and function of eNOS.

Tubeimoside I improves endothelial function in sepsis via activation of SIRT3

Sepsis is life-threatening organ dysfunction caused by a deregulated host response to infection. Endothelial dysfunction is the initial factor leading to organ dysfunction and it is associated with increased mortality. There is no effective drug to treat sepsis-induced endothelial dysfunction. In this study, we detected a favorable effect of tubeimoside I (TBM) in ameliorating sepsis-induced endothelial dysfunction. To unveil the mechanism how TBM protects against sepsis-induced endothelial dysfunction, we examined TBM's effects on oxidative stress and apoptosis both in vivo and in vitro. TBM treatment alleviated oxidative stress by decreasing NOX2 and Ac-SOD2/SOD2 and decreased apoptosis by inhibiting cleaved caspse3 and Bax/Bcl-2. Notably, sepsis induced a significant decrease of SIRT3 expression in vascular endothelium, while TBM treatment reversed SIRT3 expression. To clarify whether TBM provides protection via SIRT3, we knockdown SIRT3 using siRNA before TBM treatment. Then, the cytoprotective effects of TBM were largely abolished by siSIRT3. This suggests that SIRT3 plays an essential role in TBM's endothelial protective effects and TBM might be a potential drug candidate to treat sepsis-induced endothelial dysfunction.The authors show that intraperitoneal injection of tubeimoside I (TBM) alleviates the endothelial dysfunction caused by sepsis. Their results suggest that TBM functions by reducing oxidative stress and apoptosis via SIRT3, an NAD-dependent deacetylase. TBM is therefore a promising new therapeutic agent against sepsis-induced endothelial dysfunction.

Long non-coding RNA Meg3 deficiency impairs glucose homeostasis and insulin signaling by inducing cellular senescence of hepatic endothelium in obesity

Obesity-induced insulin resistance is a risk factor for diabetes and cardiovascular disease. However, the mechanisms underlying endothelial senescence in obesity, and how it impacts obesity-induced insulin resistance remain incompletely understood. In this study, transcriptome analysis revealed that the long non-coding RNA (lncRNA) Maternally expressed gene 3 (Meg3) is one of the top differentially expressed lncRNAs in the vascular endothelium in diet-induced obese mice. Meg3 knockdown induces cellular senescence of endothelial cells characterized by increased senescence-associated β–galactosidase activity, increased levels of endogenous superoxide, impaired mitochondrial structure and function, and impaired autophagy. Moreover, Meg3 knockdown causes cellular senescence of hepatic endothelium in diet-induced obese mice. Furthermore, Meg3 expression is elevated in human nonalcoholic fatty livers and nonalcoholic steatohepatitis livers, which positively correlates with the expression of CDKN2A encoding p16, an important hallmark of cellular senescence. Meg3 knockdown potentiates obesity-induced insulin resistance and impairs glucose homeostasis. Insulin signaling is reduced by Meg3 knockdown in the liver and, to a lesser extent, in the skeletal muscle, but not in the visceral fat of obese mice. We found that the attenuation of cellular senescence of hepatic endothelium by ablating p53 expression in vascular endothelium can restore impaired glucose homeostasis and insulin signaling in obesity. In conclusion, our data demonstrate that cellular senescence of hepatic endothelium promotes obesity-induced insulin resistance, which is tightly regulated by the expression of Meg3. Our results suggest that manipulation of Meg3 expression may represent a novel approach to managing obesity-associated hepatic endothelial senescence and insulin resistance.

Role of thrombomodulin expression on hematopoietic stem cells

BackgroundActivation of protease‐activated receptor 1 (PAR1) by either thrombin or activated protein C (aPC) differentially regulate the quiescence and bone marrow (BM) retention of hematopoietic stem cells (HSC). Murine HSC co‐express THBD, PAR1, and endothelial protein C receptor (EPCR), suggesting that HSC sustain quiescence in a quasi‐cell autonomous manner due to the binding of thrombin present in the microenvironment to THBD, activation of EPCR‐bound protein C by the thrombin‐THBD‐complex, and subsequent activation of PAR1 by the aPC‐EPCR complex. ObjectiveTo determine the role of THBD expression on HSC for sustaining stem cell quiescence and BM retention under homeostatic conditions. MethodsHematopoietic stem cell function was analyzed in mice with constitutive or temporally controlled complete THBD‐deficiency by flow cytometry, functional assays, and single cell RNA profiling. ResultsTHBD was expressed in mouse, but not human, HSC, progenitors, and immature B cells. Expression in vascular endothelium was conserved in humans' BM. Mice with constitutive THBD deficiency had a normal peripheral blood profile, altered BM morphology, reduced numbers of progenitors and immature B cells, pronounced extramedullary hematopoiesis, increased HSC frequency, and marginally altered transcriptionally defined HSC stemness. Transplantation experiments indicated near normal engraftment and repopulating ability of THBD‐deficient HSC. Transgenic aPC supplementation normalized BM histopathology and HSC abundance, and partially restored transcriptional stemness, but had no effect on B cell progenitors and extramedullary hematopoiesis. Temporally controlled THBD gene ablation in adult mice did not cause the above abnormalities. ConclusionTHBD expression on HSPC has minor effects on homeostatic hematopoiesis in mice, and is not conserved in humans.

Abstract 217: Coronary Artery Disease Locus 1p32.2 Harbors a Flow-Sensitive Endothelial Enhancer that Regulates PLPP3

Genome-wide association studies (GWAS) have identified chromosome 1p32.2 as one of the loci most strongly associated with coronary artery disease (CAD) susceptibility; however, the causal mechanism related to this CAD locus remains poorly understood. A unique feature of atherosclerotic vascular disease such as CAD is that atherosclerosis develops preferentially at arterial sites of curvature, branching, and bifurcation where endothelial cells are activated by disturbed blood flow. Recent investigations by us and others strongly implicate PhosphoLipid PhosPhatase 3 (PLPP3, also known as PhosPhatidic-Acid-Phosphatase-type-2B/ PPAP2B or Lipid Phosphate Phosphohydrolase/LPP3) as the causal gene at this locus. PLPP3 encodes an enzyme that suppresses endothelial inflammation and promotes monolayer integrity by hydrolyzing the bioactive lipid lysophosphatidic acid (LPA). Our studies demonstrated that PLPP3 is significantly reduced in vascular endothelium exposed to disturbed flow in vitro and in vivo, as the result of increased miR-92a and reduced KLF2, when compared to cells subjected to unidirectional blood flow. In addition, CAD risk allele at rs17114036 located in 1p32.2 locus is associated with reduced PLPP3 expression in an endothelium-specific manner, shown by expression quantitative trait locus (eQTL). Employing Transposase-Accessible Chromatin using Sequencing (ATAC-Seq), ChIP-Seq, CRISPR/Cas9-based genome editing, luciferase reporters, and allelic imbalance assays, we report here that CAD SNP rs17114036 is located in an endothelial enhancer that is dynamically activated by athero-protective unidirectional flow and deletion of this enhancer causatively reduces PLPP3 expression in vascular endothelium. In addition, CAD risk allele at rs17114036 is associated with reduced activity of this enhancer and its response to unidirectional flow. These results described a new molecular mechanism by which human genetic variance and mechano-transduction converge on critical vascular functions related to atherosclerosis. Moreover, we have engineered innovative polymeric nano-carriers that preferentially target inflamed endothelium and deliver therapeutic nucleotides that intervene in miR92a-PLPP3 signaling in animal models of atherosclerosis.

Salt-induced Na+/K+-ATPase-α/β expression involves soluble adenylyl cyclase in endothelial cells.

High dietary salt intake may lead to vascular stiffness, which predicts cardiovascular diseases such as heart failure, and myocardial and cerebral infarctions as well as renal impairment. The vascular endothelium is a primary target for deleterious salt effects leading to dysfunction and endothelial stiffness. We hypothesize that the Ca2+- and bicarbonate-activated soluble adenylyl cyclase (sAC) contributes to Na+/K+-ATPase expression regulation in vascular endothelial cells and is an important regulator of endothelial stiffness. In vitro stimulation of vascular endothelial cells with high sodium (150mM Na+)-induced Na+/K+-ATPase-α and Na+/K+-ATPase-β protein expression determined by western blot. Promoter analyses revealed increased cAMP response element (CRE)-mediated Na+/K+-ATPase-α transcriptional activity under high sodium concentrations. Inhibition of sAC by the specific inhibitor KH7 or siRNA reduced the sodium effects. Flame photometry revealed increased intracellular sodium concentrations in response to high sodium stimulations, which were paralleled by elevated ATP levels. Using atomic force microscopy, a nano-technique that measures cellular stiffness and deformability, we detected significant endothelial stiffening under increased sodium concentrations, which was prevented by inhibition of sAC using KH7 and Na+/K+-ATPase using ouabain. Furthermore, analysis of primary aortic endothelial cells in an in vitro aging model revealed an impaired Na+/K+-ATPase-α sodium response and elevated intracellular sodium levels with cellular aging. We conclude that sAC mediates sodium-induced Na+/K+-ATPase expression in vascular endothelium and is an important regulator of endothelial stiffness. The reactivity of Na+/K+-ATPase-α expression regulation in response to high sodium seems to be impaired in aging endothelial cells and might be a component of endothelial dysfunction.

Cystathionine γ-lyase protects vascular endothelium: a role for inhibition of histone deacetylase 6.

Endothelial cystathionine γ-lyase (CSEγ) contributes to cardiovascular homeostasis, mainly through production of H2S. However, the molecular mechanisms that control CSEγ gene expression in the endothelium during cardiovascular diseases are unclear. The aim of the current study is to determine the role of specific histone deacetylases (HDACs) in the regulation of endothelial CSEγ. Reduced CSEγ mRNA expression and protein abundance were observed in human aortic endothelial cells (HAEC) exposed to oxidized LDL (OxLDL) and in aortas from atherogenic apolipoprotein E knockout (ApoE-/-) mice fed a high-fat diet compared with controls. Intact murine aortic rings exposed to OxLDL (50 μg/ml) for 24 h exhibited impaired endothelium-dependent vasorelaxation that was blocked by CSEγ overexpression or the H2S donor NaHS. CSEγ expression was upregulated by pan-HDAC inhibitors and by class II-specific HDAC inhibitors, but not by other class-specific inhibitors. The HDAC6 selective inhibitor tubacin and HDAC6-specific siRNA increased CSEγ expression and blocked OxLDL-mediated reductions in endothelial CSEγ expression and CSEγ promoter activity, indicating that HDAC6 is a specific regulator of CSEγ expression. Consistent with this finding, HDAC6 mRNA, protein expression, and activity were upregulated in OxLDL-exposed HAEC, but not in human aortic smooth muscle cells. HDAC6 protein levels in aortas from high-fat diet-fed ApoE-/- mice were comparable to those in controls, whereas HDAC6 activity was robustly upregulated. Together, our findings indicate that HDAC6 is upregulated by atherogenic stimuli via posttranslational modifications and is a critical regulator of CSEγ expression in vascular endothelium. Inhibition of HDAC6 activity may improve endothelial function and prevent or reverse the development of atherosclerosis.NEW & NOTEWORTHY Oxidative injury to endothelial cells by oxidized LDL reduced cystathionine γ-lyase (CSEγ) expression and H2S production, leading to endothelial dysfunction, which was prevented by histone deacetylase 6 (HDAC6) inhibition. Our data suggest HDAC6 as a novel therapeutic target to prevent the development of atherosclerosis.

Expression and Processing of Amyloid Precursor Protein in Vascular Endothelium.

Amyloid precursor protein (APP) is evolutionary conserved protein expressed in endothelial cells of cerebral and peripheral arteries. In this review, we discuss mechanisms responsible for expression and proteolytic cleavage of APP in endothelial cells. We focus on physiological and pathological implications of APP expression in vascular endothelium.

Functional inhibition of urea transporter UT-B enhances endothelial-dependent vasodilatation and lowers blood pressure via L-arginine-endothelial nitric oxide synthase-nitric oxide pathway.

Mammalian urea transporters (UTs), UT-A and UT-B, are best known for their role in urine concentration. UT-B is especially distributed in multiple extrarenal tissues with abundant expression in vascular endothelium, but little is known about its role in vascular function. The present study investigated the physiological significance of UT-B in regulating vasorelaxations and blood pressure. UT-B deletion in mice or treatment with UT-B inhibitor PU-14 in Wistar-Kyoto rats (WKYs) and spontaneous hypertensive rats (SHRs) reduced blood pressure. Acetylcholine-induced vasorelaxation was significantly augmented in aortas from UT-B null mice. PU-14 concentration-dependently produced endothelium-dependent relaxations in thoracic aortas and mesenteric arteries from both mice and rats and the relaxations were abolished by Nω-nitro-L-arginine methyl ester. Both expression and phosphorylation of endothelial nitric oxide synthase (eNOS) were up-regulated and expression of arginase I was down-regulated when UT-B was inhibited both in vivo and in vitro. PU-14 induced endothelium-dependent relaxations to a similar degree in aortas from 12 weeks old SHRs or WKYs. In summary, here we report for the first time that inhibition of UT-B plays an important role in regulating vasorelaxations and blood pressure via up-regulation of L-arginine-eNOS-NO pathway, and it may become another potential therapeutic target for the treatment of hypertension.

Toll-like receptor 10 expression in chicken, cattle, pig, dog, and rat lungs

Toll-like receptors (TLRs) are conserved immune receptors that play critical roles in innate immunity and are known as “gate keepers” of immune system. TLR10 is identified as type 1 plasma membrane protein but the identity of its ligand remains unclear. Till date, no data are available on tissue and cell specific expression of TLR10 in normal and inflamed lungs of domestic animal species, and rat, which is commonly used as a model to study human diseases. We characterized a commercially available TLR10 antibody for use in cattle, pig, dog, chicken, and rat. Western blotting of total lung protein extracts from cattle, dog, pig and chicken showed a band of 85–100kDa, which is similar to the molecular weight of TLR10. The immuno-histochemical and immuno-electron microscopic data show TLR10 expression in vascular endothelium and smooth muscles in lungs of control and inflamed animals. Further, we found that expression of TLR10 in bovine neutrophils is altered upon treatment with Escherichia coli lipopolysaccharide. These data show TLR10 expression in the lungs of these mammalian species and that activation of bovine neutrophils alters the expression of TLR10.

Ammonia Stimulates Heme Oxygenase‐1 Gene Expression in Human Endothelial Cells

Ammonia is continuously generated during cell metabolism via the catabolism of purines, pyrimidines and polyamines, and deamination of amino acids. Although endothelial cells (ECs) produce substantial amounts of ammonia, the role of this gas in ECs is not known. Since heme oxygenase‐1 (HO‐1) is an important regulator of EC function, we investigated whether ammonia modulates the expression of HO‐1 in cultured human umbilical vein ECs. Treatment of ECs with ammonia, given as ammonium chloride or ammonium hydroxide, stimulated a concentration‐ and time‐dependent increase in HO‐1 protein. A significant rise in HO‐1 protein was first detected after 4 hours and levels progressively increased over 24 hours of ammonia exposure. Ammonia‐mediated increases in HO‐1 protein expression were paralleled by significant elevations in HO‐1 mRNA. The induction of HO‐1 by ammonia was dependent on de novo RNA synthesis since it was blocked by the transcriptional inhibitor actinomycin D. Ammonia also stimulated a rapid and sustained increase in the production of reactive oxygen species (ROS) beginning one hour after ammonia administration. However, incubation of ECs with the antioxidant N‐acetyl‐L‐cysteine prevented the formation of ROS and blocked the induction of HO‐1 by ammonia. In conclusion, this study found that ammonia stimulates HO‐1 gene expression in vascular endothelium via a transcriptional‐ and redox‐sensitive pathway. The ability of ammonia to induce HO‐1 may provide a potential mechanism by which this gas regulates EC function. Supported by NIH grant HL59976.

Toll‐like receptor 10 Expression in Chicken, Cattle, Pig, Dog, and Rat Lungs

Toll‐like receptors (TLRs) are conserved immune receptors that play critical roles in innate immunity and are known as “gate keepers” of immune system. TLR10 is identified as type 1 plasma membrane protein but the identity of its ligand remains unclear. Till date, no data available on tissue and cell specific expression of TLR10 in normal and inflamed lungs of domestic animal species, and rat, which is commonly used as a model to study human diseases. First, we used homologous sequence alignment of published sequences of TLR10 from cattle, pig, dog, chicken and rat and the peptide alignment with antibody sequence to determine that a commercially available TLR10 antibody may be suitable for detection of TLR10. Western blotting of total lung protein extracts from cattle, dog, pig and chicken showed a band in 85‐ 100kDa region indicating the TLR10 protein. The immunohistochemistry, immunoelectron microscopy and confocal microscopy data show TLR10 expression in vascular endothelium and smooth muscle actin of control and inflamed animals. Further, we detected that basal expression of TLR10 in bovine neutrophil is altered upon treatment with E. coli lipopolysaccharide. These data show TLR10 expression in the lungs of these mammalian species and that activation of bovine neutrophils alters the expression of TLR10

Lymphoid neogenesis in skin of human hand, nonhuman primate, and rat vascularized composite allografts.

The mechanisms of skin rejection in vascularized composite allotransplantation (VCA) remain incompletely understood. The formation of tertiary lymphoid organs (TLO) in hand transplantation has been recently described. We assess this phenomenon in experimental and clinical VCA rejection. Skin biopsies of human (n=187), nonhuman primate (n=11), and rat (n=15) VCAs were analyzed for presence of TLO. A comprehensive immunohistochemical assessment (characterization of the cell infiltrate, expression of adhesion molecules) including staining for peripheral node addressin (PNAd) was performed and correlated with rejection and time post-transplantation. TLO were identified in human, nonhuman primate, and rat skin samples. Expression of PNAd was increased in the endothelium of vessels upon rejection in human skin (P=0.003) and correlated with B- and T-lymphocyte numbers and LFA-1 expression. PNAd expression was observed at all time-points after transplantation and increased significantly after year 5. In nonhuman primate skin, PNAd expression was found during inflammatory conditions early and late after transplantation. In rat skin, PNAd expression was strongly associated with acute rejection and time post-transplantation. Lymphoid neogenesis and TLO formation can be uniformly found in experimental and human VCA. PNAd expression in vascular endothelium correlates with skin rejection and T- and B-cell infiltration.

Cell Density Impacts Epigenetic Regulation of Cytokine-Induced E-Selectin Gene Expression in Vascular Endothelium

Growing evidence suggests that the phenotype of endothelial cells during angiogenesis differs from that of quiescent endothelial cells, although little is known regarding the difference in the susceptibility to inflammation between both the conditions. Here, we assessed the inflammatory response in sparse and confluent endothelial cell monolayers. To obtain sparse and confluent monolayers, human umbilical vein endothelial cells were seeded at a density of 7.3×103 cells/cm2 and 29.2×103 cells/cm2, respectively, followed by culturing for 36 h and stimulation with tumor necrosis factor α. The levels of tumor necrosis factor α-induced E-selectin protein and mRNA expression were higher in the confluent monolayer than in the sparse monolayer. The phosphorylation of c-jun N-terminal kinase and p38 mitogen-activated protein kinase or nuclear factor-κB activation was not involved in this phenomenon. A chromatin immunoprecipitation assay of the E-selectin promoter using an anti-acetyl-histone H3 antibody showed that the E-selectin promoter was highly and specifically acetylated in the confluent monolayer after tumor necrosis factor α activation. Furthermore, chromatin accessibility real-time PCR showed that the chromatin accessibility at the E-selectin promoter was higher in the confluent monolayer than in the sparse monolayer. Our data suggest that the inflammatory response may change during blood vessel maturation via epigenetic mechanisms that affect the accessibility of chromatin.