Identification of KU-55933 as an anti-atherosclerosis compound by using a hemodynamic-based high-throughput drug screening platform

Several compounds have been used for atherosclerosis treatment, including clinical trials; however, no anti-atherosclerotic drugs based on hemodynamic force-mediated atherogenesis have been discovered. Our previous studies demonstrated that "small mothers against decapentaplegic homolog 1/5" (Smad1/5) is a convergent signaling molecule for chemical [e.g., bone morphogenetic proteins (BMPs)] and mechanical (e.g., disturbed flow) stimulations and hence may serve as a promising hemodynamic-based target for anti-atherosclerosis drug development. The goal of this study was to develop a high-throughput screening (HTS) platform to identify potential compounds that can inhibit disturbed flow- and BMP-induced Smad1/5 activation and atherosclerosis. Through HTS using a Smad1/5 downstream target inhibitor of DNA binding 1 (Id-1) as a luciferase reporter, we demonstrated that KU-55933 and Apicidin suppressed Id-1 expression in AD-293 cells. KU-55933 (10 μM), Apicidin (10 μM), and the combination of half doses of each [1/2(K + A)] inhibited disturbed flow- and BMP4-induced Smad1/5 activation in human vascular endothelial cells (ECs). KU-55933, Apicidin, and 1/2(K + A) treatments caused 50.6%, 47.4%, and 73.3% inhibitions of EC proliferation induced by disturbed flow, respectively, whereas EC inflammation was only suppressed by KU-55933 and 1/2(K + A), but not Apicidin alone. Administrations of KU-55933 and 1/2(K + A) to apolipoprotein E-deficient mice inhibited Smad1/5 activation in ECs in athero-susceptible regions, thereby suppressing endothelial proliferation and inflammation, with the attenuation of atherosclerotic lesions in these mice. A unique drug screening platform has been developed to demonstrate that KU-55933 and its combination with Apicidin are promising therapeutic compounds for atherosclerosis based on hemodynamic considerations.

Vinculin phosphorylation impairs vascular endothelial junctions promoting atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis preferentially develops in arterial branches and curvatures where vascular endothelium is exposed to disturbed flow. In this study, the effects of disturbed flow on the regulation of vascular endothelial phosphoproteins and their contribution to therapeutic application in atherogenesis were elucidated.

METHODS

Porcine models, large-scale phosphoproteomics, transgenic mice, and clinical specimens were used to discover novel site-specific phosphorylation alterations induced by disturbed flow in endothelial cells (ECs).

RESULTS

A large-scale phosphoproteomics analysis of native endothelium from disturbed (athero-susceptible) vs. pulsatile flow (athero-resistant) regions of porcine aortas led to the identification of a novel atherosclerosis-related phosphoprotein vinculin (VCL) with disturbed flow-induced phosphorylation at serine 721 (VCLS721p). The induction of VCLS721p was mediated by G-protein-coupled receptor kinase 2 (GRK2)S29p and resulted in an inactive form of VCL with a closed conformation, leading to the VE-cadherin/catenin complex disruption to enhance endothelial permeability and atherogenesis. The generation of novel apolipoprotein E-deficient (ApoE-/-) mice overexpressing S721-non-phosphorylatable VCL mutant in ECs confirmed the critical role of VCLS721p in promoting atherosclerosis. The administration of a GRK2 inhibitor to ApoE-/- mice suppressed plaque formation by inhibiting endothelial VCLS721p. Studies on clinical specimens from patients with coronary artery disease (CAD) revealed that endothelial VCLS721p is a critical clinicopathological biomarker for atherosclerosis progression and that serum VCLS721p level is a promising biomarker for CAD diagnosis.

CONCLUSIONS

The findings of this study indicate that endothelial VCLS721p is a valuable hemodynamic-based target for clinical assessment and treatment of vascular disorders resulting from atherosclerosis.

SOX4 is a novel phenotypic regulator of endothelial cells in atherosclerosis revealed by single-cell analysis

INTRODUCTION

Atherosclerotic complications represent the leading cause of cardiovascular mortality globally. Dysfunction of endothelial cells (ECs) often initiates the pathological events in atherosclerosis.

OBJECTIVES

In this study, we sought to investigate the transcriptional profile of atherosclerotic aortae, identify novel regulator in dysfunctional ECs and hence provide mechanistic insights into atherosclerotic progression.

METHODS

We applied single-cell RNA sequencing (scRNA-seq) on aortic cells from Western diet-fed apolipoprotein E-deficient (ApoE^-/-) mice to explore the transcriptional landscape and heterogeneity of dysfunctional ECs. In vivo validation of SOX4 upregulation in ECs were performed in atherosclerotic tissues, including mouse aortic tissues, human coronary arteries, and human renal arteries. Single-cell analysis on human aortic aneurysmal tissue was also performed. Downstream vascular abnormalities induced by EC-specific SOX4 overexpression, and upstream modulators of SOX4 were revealed by biochemical assays, immunostaining, and wire myography. Effects of shear stress on endothelial SOX4 expression was investigated by in vitro hemodynamic study.

RESULTS

Among the compendium of aortic cells, mesenchymal markers in ECs were significantly enriched. Two EC subsets were subsequently distinguished, as the 'endothelial-like' and 'mesenchymal-like' subsets. Conventional assays consistently identified SOX4 as a novel atherosclerotic marker in mouse and different human arteries, additional to a cancer marker. EC-specific SOX4 overexpression promoted atherogenesis and endothelial-to-mesenchymal transition (EndoMT). Importantly, hyperlipidemia-associated cytokines and oscillatory blood flow upregulated, whereas the anti-diabetic drug metformin pharmacologically suppressed SOX4 level in ECs.

CONCLUSION

Our study unravels SOX4 as a novel phenotypic regulator during endothelial dysfunction, which exacerbates atherogenesis. Our study also pinpoints hyperlipidemia-associated cytokines and oscillatory blood flow as endogenous SOX4 inducers, providing more therapeutic insights against atherosclerotic diseases.

Endothelial Yin Yang 1 Phosphorylation at S118 Induces Atherosclerosis Under Flow

Rationale: Disturbed flow occurring in arterial branches and curvatures induces vascular endothelial cell (EC) dysfunction and atherosclerosis. We postulated that disturbed flow plays important roles in modulating phosphoprotein expression profiles to regulate endothelial functions and atherogenesis. Objective: The goal of this study is to discover novel site-specific phosphorylation alterations induced by disturbed flow in ECs to contribute to atherosclerosis. Methods and Results: Quantitative phosphoproteomics analysis of ECs exposed to disturbed flow with low and oscillatory shear stress (OS, 0.5plusminus4 dynes/cm²) vs. pulsatile flow with high shear stress (PS, 124plusminus dynes/cm²) revealed that OS induces serine (S)118 phosphorylation of Yin Yang 1 (phospho-YY1^S118) in ECs. Elevated phospho-YY1^S118 level in ECs was further confirmed to be present in the disturbed flow regions in experimental animals and human atherosclerotic arteries. This disturbed flow-induced EC phospho-YY1^S118 is mediated by casein kinase 2α (CK2α) through its direct interaction with YY1. Yeast two-hybrid library screening and in situ proximity ligation assays demonstrate that phospho-YY1^S118 directly binds zinc finger with KRAB and SCAN domains 4 (ZKSCAN4) to induce promoter activity and gene expression of human double minute 2 (HDM2), which consequently induces EC proliferation through down-regulations of p53 and p21^CIP1. Administration of apolipoprotein E-deficient (ApoE^-/-) mice with CK2-specific inhibitor tetrabromocinnamic acid or atorvastatin inhibits atherosclerosis formation through down-regulations of EC phospho-YY1^S118 and HDM2. Generation of novel transgenic mice bearing EC-specific overexpression of S118-non-phosphorylatable mutant of YY1 in ApoE^-/- mice confirms the critical role of phospho-YY1^S118 in promoting atherosclerosis through EC HDM2. Conclusions: Our findings provide new insights into the mechanisms by which disturbed flow induces endothelial phospho-YY1^S118 to promote atherosclerosis, thus indicating phospho-YY1^S118 as a potential molecular target for atherosclerosis treatment.

Punicalagin Attenuates Disturbed Flow-Induced Vascular Dysfunction by Inhibiting Force-Specific Activation of Smad1/5

Background

Pathophysiological vascular remodeling in response to disturbed flow with low and oscillatory shear stress (OSS) plays important roles in atherosclerosis progression. Pomegranate extraction (PE) was reported having anti-atherogenic effects. However, whether it can exert a beneficial effect against disturbed flow-induced pathophysiological vascular remodeling to inhibit atherosclerosis remains unclear. The present study aims at investigating the anti-atherogenic effects of pomegranate peel polyphenols (PPP) extraction and its purified compound punicalagin (PU), as well as their protective effects on disturbed flow-induced vascular dysfunction and their underlying molecular mechanisms.

Methods

The anti-atherogenic effects of PPP/PU were examined on low-density lipoprotein receptor knockout mice fed with a high fat diet. The vaso-protective effects of PPP/PU were examined in rat aortas using myograph assay. A combination of in vivo experiments on rats and in vitro flow system with human endothelial cells (ECs) was used to investigate the pharmacological actions of PPP/PU on EC dysfunction induced by disturbed flow. In addition, the effects of PPP/PU on vascular smooth muscle cell (VSMC) dysfunction were also examined.

Results

PU is the effective component in PPP against atherosclerosis. PPP/PU evoked endothelium-dependent relaxation in rat aortas. PPP/PU inhibited the activation of Smad1/5 in the EC layers at post-stenotic regions of rat aortas exposed to disturbed flow with OSS. PPP/PU suppressed OSS-induced expression of cell cycle regulatory and pro-inflammatory genes in ECs. Moreover, PPP/PU inhibited inflammation-induced VSMC dysfunction.

Conclusion

PPP/PU protect against OSS-induced vascular remodeling through inhibiting force-specific activation of Smad1/5 in ECs and this mechanism contributes to their anti-atherogenic effects.

Mechanoresponsive Smad5 Enhances MiR-487a Processing to Promote Vascular Endothelial Proliferation in Response to Disturbed Flow

MicroRNAs (miRs) and bone morphogenetic protein receptor-specific Smads are mechano-responsive molecules that play vital roles in modulating endothelial cell (EC) functions in response to blood flow. However, the roles of interplay between these molecules in modulating EC functions under flows remain unclear. We elucidated the regulatory roles of the interplay between miR-487a and Smad5 in EC proliferation in response to different flow patterns. Microarray and quantitative RT-PCR showed that disturbed flow with low and oscillatory shear stress (OS, 0.5 ± 4 dynes/cm²) upregulates EC miR-487a in comparison to static controls and pulsatile shear stress (12 ± 4 dynes/cm²). MiR-487a expression was higher in ECs in the inner curvature (OS region) than the outer curvature of the rat aortic arch and thoracic aorta and also elevated in diseased human coronary arteries. MiR-487a expression was promoted by nuclear phospho-Smad5, which bound to primary-miR-487a to facilitate miR-487a processing. Algorithm prediction and luciferase reporter and argonaute 2-immunoprecipitation assays demonstrated that miR-487a binds to 3'UTR of CREB binding protein (CBP) and p53. Knockdown and overexpression of miR-487a decreased and increased, respectively, phospho-Rb and cyclin A expressions through CBP and p53. A BrdU incorporation assay showed that miR-487a enhanced EC proliferation under OS in vitro and in disturbed flow regions of experimentally stenosed rat abdominal aorta in vivo. These results demonstrate that disturbed flow with OS induces EC expression of miR-487a through its enhanced processing by activated-Smad5. MiR-487 inhibits its direct targets CBP and p53 to induce EC cycle progression and proliferation. Our findings suggest that EC miR-487 may serve as an important molecular target for intervention against disturbed flow-associated vascular disorders resulting from atherosclerosis.

Focal TLR4 activation mediates disturbed flow-induced endothelial inflammation

AIMS

Disturbed blood flow at arterial branches and curvatures modulates endothelial function and predisposes the region to endothelial inflammation and subsequent development of atherosclerotic lesions. Activation of the endothelial Toll-like receptors (TLRs), in particular TLR4, contributes to vascular inflammation. Therefore, we investigate whether TLR4 can sense disturbed flow (DF) to mediate the subsequent endothelial inflammation.

METHODS AND RESULTS

En face staining of endothelium revealed that TLR4 expression, activation, and its downstream inflammatory markers were elevated in mouse aortic arch compared with thoracic aorta, which were absent in Tlr4mut mice. Similar results were observed in the partial carotid ligation model where TLR4 signalling was activated in response to ligation-induced flow disturbance in mouse carotid arteries, and such effect was attenuated in Tlr4mut mice. DF in vitro increased TLR4 expression and activation in human endothelial cells (ECs) and promoted monocyte-EC adhesion, which were inhibited in TLR4-knockdown ECs. Among endogenous TLR4 ligands examined as candidate mediators of DF-induced TLR4 activation, fibronectin containing the extra domain A (FN-EDA) expressed by ECs was increased by DF and was revealed to directly interact with and activate TLR4.

CONCLUSION

Our findings demonstrate the indispensable role of TLR4 in DF-induced endothelial inflammation and pinpoint FN-EDA as the endogenous TLR4 activator in this scenario. This novel mechanism of vascular inflammation under DF condition may serve as a critical initiating step in atherogenesis.

Inhibition of miR-21 alleviated cardiac perivascular fibrosis via repressing EndMT in T1DM

In type 1 and type 2 diabetes mellitus, increased cardiac fibrosis, stiffness and associated diastolic dysfunction may be the earliest pathological phenomena in diabetic cardiomyopathy. Endothelial-mesenchymal transition (EndMT) in endothelia cells (ECs) is a critical cellular phenomenon that increases cardiac fibroblasts (CFs) and cardiac fibrosis in diabetic hearts. The purpose of this paper is to explore the molecular mechanism of miR-21 regulating EndMT and cardiac perivascular fibrosis in diabetic cardiomyopathy. In vivo, hyperglycaemia up-regulated the mRNA level of miR-21, aggravated cardiac dysfunction and collagen deposition. The condition was recovered by inhibition of miR-21 following with improving cardiac function and decreasing collagen deposition. miR-21 inhibition decreased cardiac perivascular fibrosis by suppressing EndMT and up-regulating SMAD7 whereas activating p-SMAD2 and p-SMAD3. In vitro, high glucose (HG) up-regulated miR-21 and induced EndMT in ECs, which was decreased by inhibition of miR-21. A highly conserved binding site of NF-κB located in miR-21 5'-UTR was identified. In ECs, SMAD7 is directly regulated by miR-21. In conclusion, the pathway of NF-κB/miR-21/SMAD7 regulated the process of EndMT in T1DM, in diabetic cardiomyopathy, which may be regarded as a potential clinical therapeutic target for cardiac perivascular fibrosis.

Atherosclerosis and flow: roles of epigenetic modulation in vascular endothelium

Background

Endothelial cell (EC) dysfunctions, including turnover enrichment, gap junction disruption, inflammation, and oxidation, play vital roles in the initiation of vascular disorders and atherosclerosis. Hemodynamic forces, i.e., atherprotective pulsatile (PS) and pro-atherogenic oscillatory shear stress (OS), can activate mechanotransduction to modulate EC function and dysfunction. This review summarizes current studies aiming to elucidate the roles of epigenetic factors, i.e., histone deacetylases (HDACs), non-coding RNAs, and DNA methyltransferases (DNMTs), in mechanotransduction to modulate hemodynamics-regulated EC function and dysfunction.

Main body of the abstract

OS enhances the expression and nuclear accumulation of class I and class II HDACs to induce EC dysfunction, i.e., proliferation, oxidation, and inflammation, whereas PS induces phosphorylation-dependent nuclear export of class II HDACs to inhibit EC dysfunction. PS induces overexpression of the class III HDAC Sirt1 to enhance nitric oxide (NO) production and prevent EC dysfunction. In addition, hemodynamic forces modulate the expression and acetylation of transcription factors, i.e., retinoic acid receptor α and krüppel-like factor-2, to transcriptionally regulate the expression of microRNAs (miRs). OS-modulated miRs, which stimulate proliferative, pro-inflammatory, and oxidative signaling, promote EC dysfunction, whereas PS-regulated miRs, which induce anti-proliferative, anti-inflammatory, and anti-oxidative signaling, inhibit EC dysfunction. PS also modulates the expression of long non-coding RNAs to influence EC function. i.e., turnover, aligmant, and migration. On the other hand, OS enhances the expression of DNMT-1 and -3a to induce EC dysfunction, i.e., proliferation, inflammation, and NO repression.

Conclusion

Overall, epigenetic factors play vital roles in modulating hemodynamic-directed EC dysfunction and vascular disorders, i.e., atherosclerosis. Understanding the detailed mechanisms through which epigenetic factors regulate hemodynamics-directed EC dysfunction and vascular disorders can help us to elucidate the pathogenic mechanisms of atherosclerosis and develop potential therapeutic strategies for atherosclerosis treatment.

Hemodynamics-Based Strategy of Using Retinoic Acid Receptor and Retinoid X Receptor Agonists to Induce MicroRNA-10a and Inhibit Atherosclerotic Lesion

The protocols in this chapter describe methods for identifying the functional roles of retinoic acid receptor (RAR) and retinoid X receptor (RXR) signaling in atherosclerosis and developing RARα/RXRα-specific agonists as hemodynamics-based therapeutic components for atherosclerosis treatment. In vitro cell culture flow system is used to elucidate the effects of different flow patterns and shear stresses, i.e., atherogenic oscillatory shear stress (OS) vs. atheroprotective pulsatile shear stress (PS), on RAR/RXR signaling and inflammatory responses in vascular endothelial cells (ECs). Western blotting, nuclear and cytoplasmic protein extraction, immunoprecipitation, and in situ proximity ligation assay are used to examine the expression, location, and association of RARs (i.e., RARα, RARβ, and RARγ) and RXRs (i.e., RXRα, RXRβ, and RXRγ) in ECs in response to OS vs. PS. Chromatin immunoprecipitation is used to examine the binding activity of RARα/RA-responsive elements (RARE). RT-microRNA (miR) quantitative real-time PCR and RT-PCR are used to detect the expressions of miR-10a and pro-inflammatory molecules, respectively. Specific siRNAs of RARα and RXRα, precursor miR-10a (PreR-10a), and antagomiR-10a (AMR-10a) are used to elucidate the regulatory roles of RARα, RXRα, and miR-10a in pro-inflammatory signaling in ECs. RARα/RXRα-specific agonists are used to induce miR-10a expression and inhibit OS-induced pro-inflammatory signaling in ECs in vitro. Apolipoprotein E-deficient (ApoE^-/-) mice are used as an atherosclerotic animal model. Administration of ApoE^-/- mice with RARα/RXRα-specific agonists results in inhibitions in atherosclerotic lesion formation. Co-administration of ApoE^-/- mice with RARα/RXRα agonists and AMR-10a is performed to identify the role of miR-10a in RARα/RXRα agonists-mediated inhibition in atherosclerotic lesions. Oil Red O staining and H&E staining are used to examine the levels of atherosclerotic lesions in the vessel wall. In situ miR hybridization and immunohistochemical staining are used to detect the expression of miR-10a and pro-inflammatory molecules and the infiltration of inflammatory cells in the vessel wall. RARα/RXRα-specific agonists are used to mimic the atheroprotective effects of PS to induce endothelial miR-10a and hence repress OS-induced pro-inflammatory signaling and atherosclerotic lesion formation in vivo. The results indicate that RAR/RXR-specific agonists have great potential to be developed as hemodynamics-based therapeutic components for atherosclerosis treatment.

MicroRNA-21 and Venous Neointimal Hyperplasia of Dialysis Vascular Access

BACKGROUND AND OBJECTIVES

There is increasing evidence that microRNAs (miRNAs) play crucial roles in the regulation of neointima formation. However, the translational evidence of the role of miRNAs in dialysis vascular access is limited.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

miRNA expression in tissues was assessed by using venous tissues harvested from ten patients on dialysis who received revision or removal surgery, and ten patients who were predialysis and received creation surgery of arteriovenous fistulas served as controls. To extend these findings, 60 patients who received angioplasty of dialysis access were enrolled and the levels of circulating miRNAs were determined before and 2 days after angioplasty. Clinical follow-up was continued monthly for 6 months. The primary outcome of angioplasty cohort was target lesion restenosis within 6 months after angioplasty.

RESULTS

In the surgery cohort, the expressions of miR-21, miR-130a, and miR-221 were upregulated in stenotic tissues, whereas those of miR-133 and miR-145 were downregulated. In situ hybridization revealed similar expression patterns of these miRNAs, localized predominantly in the neointima region. Twenty eight patients in the angioplasty cohort developed restenosis within 6 months. The levels of circulating miR-21, miR-130a, miR-221, miR-133, and miR-145 significantly increased 2 days after angioplasty. Kaplan-Meier plots showed that patients with an increase of miR-21 expression level >0.35 have a higher risk of patency loss (hazard ratio, 4.45; 95% confidence interval, 1.68 to 11.7). In a multivariable analysis, postangioplasty increase of miR-21 expression was independently associated with restenosis (hazard ratio, 1.20; 95% confidence interval, 1.07 to 1.35 per one unit increase of miR-21 expression level; P=0.001).

CONCLUSIONS

Certain miRNAs are differentially expressed in the stenotic venous segments of dialysis accesses. An increase in blood miR-21 level with angioplasty is associated with a higher risk of restenosis.

Induction of microRNA-10a using retinoic acid receptor-α and retinoid x receptor-α agonists inhibits atherosclerotic lesion formation

BACKGROUND AND AIMS

MicroRNA (miR)-10a is a shear-regulated miR with the lowest expression in vascular endothelial cells (ECs) in athero-susceptible regions with oscillatory shear stress (OS). The aim of this study is to elucidate the relationship between EC miR-10a and atherosclerosis and develop a hemodynamics-based strategy for atherosclerosis treatment.

METHODS

A combination of in vitro flow system and in vivo experimental animals was used to examine the functional roles of EC miR-10a and its clinical applications in atherosclerosis.

RESULTS

En face staining showed that EC miR-10a is down-regulated in the inner curvature (OS region) of aortic arch in rats. Co-administration with retinoic acid receptor-α (RARα)- and retinoid X receptor-α (RXRα)-specific agonists rescued EC miR-10a expression in this OS region. These effects of OS and RARα/RXRα-specific agonists on EC miR-10a expression were confirmed by the in vitro flow system, and were modulated by the RARα-histone deacetylases complex, with the consequent modulation in the downstream GATA6/vascular cell adhesion molecule (VCAM)-1 signaling cascade. Animal studies showed that miR-10a levels are decreased in both aortic endothelium of atherosclerotic lesions and blood plasma from apolipoprotein E-deficient (ApoE^-/-) mice. In vivo induction of EC miR-10a by administration of RARα/RXRα-specific agonists protects ApoE^-/- mice from atherosclerosis through inhibition of GATA6/VCAM-1 signaling and inflammatory cell infiltration.

CONCLUSIONS

Our findings indicate that down-regulation of miR-10a in aortic endothelium and blood serum is associated with atherosclerosis, and miR-10a has potential to be developed as diagnostic molecule for atherosclerosis. Moreover, EC miR-10a induction by RARα/RXRα-specific agonists is a potential hemodynamics-based strategy for atherosclerosis treatment.

Differential regulations of fibronectin and laminin in Smad2 activation in vascular endothelial cells in response to disturbed flow

BACKGROUND

Atherosclerosis occurs in arterial curvatures and branches, where the flow is disturbed with low and oscillatory shear stress (OSS). The remodeling and alterations of extracellular matrices (ECMs) and their composition is the critical step in atherogenesis. In this study, we investigated the effects of different ECM proteins on the regulation of mechanotransduction in vascular endothelial cells (ECs) in response to OSS.

METHODS

Through the experiments ranging from in vitro cell culture studies on effects of OSS on molecular signaling to in vivo examinations on clinical specimens from patients with coronary artery disease (CAD), we elucidated the roles of integrins and different ECMs, i.e., fibronectin (FN) and laminin (LM), in transforming growth factor (TGF)-β receptor (TβR)-mediated Smad2 activation and nuclear factor-κB (NF-κB) signaling in ECs in response to OSS and hence atherogenesis.

RESULTS

OSS at 0.5±12 dynes/cm² induces sustained increases in the association of types I and II TβRs with β1 and β3 integrins in ECs grown on FN, but it only transient increases in ECs grown on LM. OSS induces a sustained activation of Smad2 in ECs on FN, but only a transient activation of Smad2 in ECs on LM. OSS-activation of Smad2 in ECs on FN regulates downstream NF-κB signaling and pro-inflammatory gene expression through the activation of β1 integrin and its association with TβRs. In contrast, OSS induces transient activations of β1 and β3 integrins in ECs on LM, which associate with type I TβR to regulate Smad2 phosphorylation, resulting in transient induction of NF-κB and pro-inflammatory gene expression. In vivo investigations on diseased human coronary arteries from CAD patients revealed that Smad2 is highly activated in ECs of atherosclerotic lesions, which is accompanied by the concomitant increase of FN rather than LM in the EC layer and neointimal region of atherosclerotic lesions.

CONCLUSIONS

Our findings provide new insights into the mechanisms of how OSS regulates Smad2 signaling and pro-inflammatory genes through the complex signaling networks of integrins, TβRs, and ECMs, thus illustrating the molecular basis of regional pro-inflammatory activation within disturbed flow regions in the arterial tree.

Endothelial progenitors promote hepatocarcinoma intrahepatic metastasis through monocyte chemotactic protein-1 induction of microRNA-21

OBJECTIVES

Endothelial progenitor cells (EPCs) circulate with increased numbers in the peripheral blood of patients with highly-vascularised hepatocellular carcinoma (HCC) and contribute to angiogenesis and neovascularisation. We hypothesised that angiogenic EPCs, that is, colony forming unit-endothelial cells (CFU-ECs), and outgrowth EPCs, that is, endothelial colony-forming cells, may exert paracrine effects on the behaviours and metastatic capacities of human hepatoma cells.

DESIGN

Various molecular and functional approaches ranging from in vitro cell culture studies on molecular signalling to in vivo investigations on cell invasion and orthotropic transplantation models in mice and clinical specimens from patients with HCC were used.

RESULTS

Monocyte chemotactic protein-1 (MCP-1) was identified as a critical mediator released from CFU-ECs to contribute to the chemotaxis of Huh7 and Hep3B cells by inducing their microRNA-21 (miR-21) biogenesis through the C-C chemokine receptor-2/c-Jun N-terminal kinase/activator protein-1 signalling cascade. CFU-EC-induction of miR-21 in these cells activated their Rac1 and matrix metallopeptidase-9 by silencing Rho GTPase-activating protein-24 and tissue inhibitor of metalloproteinase-3, respectively, leading to increased cell mobility. MCP-1-induction of miR-21 induced epithelial-mesenchymal transformation of Huh7 cells in vitro and their intrahepatic metastatic capability in vivo. Moreover, increased numbers of MCP-1(+) EPCs and their positive correlations with miR-21 induction and metastatic stages in human HCC were found.

CONCLUSIONS

Our results provide new insights into the complexity of EPC-HCC interactions and indicate that anticancer therapies targeting either the MCP-1 released from angiogenic EPCs or the miR-21 biogenesis in HCC cells may prevent the malignant progression of primary tumours.

MicroRNA mediation of endothelial inflammatory response to smooth muscle cells and its inhibition by atheroprotective shear stress

RATIONALE

In atherosclerotic lesions, synthetic smooth muscle cells (sSMCs) induce aberrant microRNA (miR) profiles in endothelial cells (ECs) under flow stagnation. Increase in shear stress induces favorable miR modulation to mitigate sSMC-induced inflammation.

OBJECTIVE

To address the role of miRs in sSMC-induced EC inflammation and its inhibition by shear stress.

METHODS AND RESULTS

Coculturing ECs with sSMCs under static condition causes initial increases of 4 anti-inflammatory miRs (146a/708/451/98) in ECs followed by decreases below basal levels at 7 days; the increases for miR-146a/708 peaked at 24 hours and those for miR-451/98 lasted for only 6 to 12 hours. Shear stress (12 dynes/cm(2)) to cocultured ECs for 24 hours augments these 4 miR expressions. In vivo, these 4 miRs are highly expressed in neointimal ECs in injured arteries under physiological levels of flow, but not expressed under flow stagnation. MiR-146a, miR-708, miR-451, and miR-98 target interleukin-1 receptor-associated kinase, inhibitor of nuclear factor-κB kinase subunit-γ, interleukin-6 receptor, and conserved helix-loop-helix ubiquitous kinase, respectively, to inhibit nuclear factor-κB signaling, which exerts negative feedback control on the biogenesis of these miRs. Nuclear factor-E2-related factor (Nrf)-2 is critical for shear-induction of miR-146a in cocultured ECs. Silencing either Nrf-2 or miR-146a led to increased neointima formation of injured rat carotid artery under physiological levels of flow. Overexpressing miR-146a inhibits neointima formation of rat or mouse carotid artery induced by injury or flow cessation.

CONCLUSIONS

Nrf-2-mediated miR-146a expression is augmented by atheroprotective shear stress in ECs adjacent to sSMCs to inhibit neointima formation of injured arteries.

Protein kinase C-δ and -β coordinate flow-induced directionality and deformation of migratory human blood T-lymphocytes

T-lymphocyte migration under flow is critical for immune responses, but the mechanisms by which flow modulates the migratory behaviors of T-lymphocytes remain unclear. Human peripheral blood T-lymphocytes (PBTLs), when stimulated with phorbol 12-myristate 13-acetate (PMA), stretched their cell bodies dramatically and moved along the flow direction. In contrast, stromal cell-derived factor-1α-stimulated PBTLs deformed and migrated in a random manner. Here we elucidated the molecular mechanisms underlying flow-induced directionality and deformation of PMA-stimulated PBTLs. PMA primed PBTLs for polarization under flow, with protein kinase C (PKC)-δ enriched in the leading edge, PKC-βI in the microtubule organizing center, and PKC-βII in the uropod and peripheral region. PKC-δ regulated cell protrusions in the leading edge through Tiam1/Rac1/calmodulin, whereas PKC-β regulated RhoA/Rho-associated kinase activity and microtubule stability to modulate uropod contractility and detachment. Our findings indicate that PKC-δ and -β coordinate in the cell leading edge and uropod, respectively, to modulate the directionality and deformability of migratory T-lymphocytes under flow.

Regulation of fibrillar collagen-mediated smooth muscle cell proliferation in response to chemical stimuli by telomere reverse transcriptase through c-Myc

Human telomerase reverse transcriptase (hTERT) and oncogene c-Myc have been shown to regulate cell proliferation. Our previous studies demonstrated that fibrillar collagen mediates vascular smooth muscle cell (SMC) cycle progression and proliferation in response to platelet-derived growth factor (PDGF)-BB and interleukin (IL)-1β. However, whether hTERT and c-Myc are involved in these fibrillar collagen-mediated SMC responses remain unclear. The present study elucidated the regulatory role of hTERT and c-Myc in PDGF-BB/IL-1β-induced cell cycle progression in SMCs on fibrillar collagen and its underlying mechanisms. Our results showed that PDGF-BB and IL-1β exert synergistic effects to induce hTERT expression, but not its activity, in human arterial SMCs on fibrillar collagen. This PDGF-BB/IL-1β-induced up-regulation of hTERT contributes to cell cycle progression in SMCs through the up-regulation of cyclin-dependent kinase-6 and down-regulations of p27(KIP1) and p21(CIP1). In addition, PDGF-BB/IL-1β induces up-regulation of c-Myc in SMCs on fibrillar collagen; this response is mediated by the increased binding of hTERT, which can form complexes with TPP1 and hnRNPK, to the guanine-rich region of the c-Myc promoter and consequently contributes to cell cycle progression in SMCs on fibrillar collagen. Moreover, the PDGF-BB/IL-1β-induced hTERT and c-Myc expressions are regulated by phosphatidylinositol 3-kinase/Akt in SMCs on fibrillar collagen. Our findings provide insights into the mechanisms by which hTERT and c-Myc regulates SMC cell cycle progression and proliferation on fibrillar collagen in response to chemical stimuli.

Regulation of vascular smooth muscle cell turnover by endothelial cell-secreted microRNA-126: role of shear stress

RATIONALE

Endothelial microRNA-126 (miR-126) modulates vascular development and angiogenesis. However, its role in the regulation of smooth muscle cell (SMC) function is unknown.

OBJECTIVE

To elucidate the role of miR-126 secreted by endothelial cells (ECs) in regulating SMC turnover in vitro and in vivo, as well as the effects of shear stress on the regulation.

METHODS AND RESULTS

Coculture of SMCs with ECs or treatment of SMCs with conditioned media from static EC monoculture (EC-CM) increased SMC miR-126 level and SMC turnover; these effects were abolished by inhibition of endothelial miR-126 and by the application of laminar shear stress to ECs. SMC miR-126 did not increase when treated with EC-CM from ECs subjected to inhibition of miR biogenesis, or with CM from sheared ECs. Depletion of extracellular/secreted vesicles in EC-CM did not affect the increase of SMC miR-126 by EC-CM. Biotinylated miR-126 or FLAG (DYKDDDDK epitope)-tagged Argonaute2 transfected into ECs was detected in the cocultured or EC-CM-treated SMCs, indicating a direct EC-to-SMC transmission of miR-126 and Argonaute2. Endothelial miR-126 represses forkhead box O3, B-cell lymphoma 2, and insulin receptor substrate 1 mRNAs in the cocultured SMCs, suggesting the functional roles of the transmitted miR-126. Systemic depletion of miR-126 in mice inhibited neointimal lesion formation of carotid arteries induced by cessation of blood flow. Administration of EC-CM or miR-126 mitigated the inhibitory effect.

CONCLUSIONS

Endothelial miR-126 acts as a key intercellular mediator to increase SMC turnover, and its release is reduced by atheroprotective laminar shear stress.

Mechanical regulation of epigenetics in vascular biology and pathobiology

Vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) are constantly exposed to haemodynamic forces, including blood flow-induced fluid shear stress and cyclic stretch from blood pressure. These forces modulate vascular cell gene expression and function and, therefore, influence vascular physiology and pathophysiology in health and disease. Epigenetics, including DNA methylation, histone modification/chromatin remodelling and RNA-based machinery, refers to the study of heritable changes in gene expression that occur without changes in the DNA sequence. The role of haemodynamic force-induced epigenetic modifications in the regulation of vascular gene expression and function has recently been elucidated. This review provides an introduction to the epigenetic concepts that relate to vascular physiology and pathophysiology. Through the studies of gene expression, cell proliferation, angiogenesis, migration and pathophysiological states, we present a conceptual framework for understanding how mechanical force-induced epigenetic modifications work to control vascular gene expression and function and, hence, the development of vascular disorders. This research contributes to our knowledge of how the mechanical environment impacts the chromatin state of ECs and VSMCs and the consequent cellular behaviours.

Roles of microRNAs in atherosclerosis and restenosis

Atherosclerosis is commonly appreciated to represent a chronic inflammatory response of the vascular wall, and its complications cause high mortality in patients. Angioplasty with stent replacement is commonly performed in patients with atherosclerotic disease. However, the restenosis usually has a high incidence rate in angioplasty patients. Although the pathophysiological mechanisms underlying atherosclerosis and restenosis have been well established, new signaling molecules that control the progress of these pathologies have continuously been discovered. MicroRNAs (miRs) have recently emerged as a novel class of gene regulators that work via transcriptional degradation and translational inhibition or activation. Over 30% of genes in the cell can be directly regulated by miRs. Thus, miRs are recognized as crucial regulators in normal development, physiology and pathogenesis. Alterations of miR expression profiles have been revealed in diverse vascular diseases. A variety of functions of vascular cells, such as cell differentiation, contraction, migration, proliferation and inflammation that are involved in angiogenesis, neointimal formation and lipid metabolism underlying various vascular diseases, have been found to be regulated by miRs. This review summarizes current research progress and knowledge on the roles of miRs in regulating vascular cell function in atherosclerosis and restenosis. These discoveries are expected to present opportunities for clinical diagnostic and therapeutic approaches in vascular diseases resulting from atherosclerosis and restenosis.

β(2)-Integrin and Notch-1 differentially regulate CD34(+)CD31(+) cell plasticity in vascular niches

AIMS

The implication of circulating haematopoietic CD34(+) progenitors in the vasculature is unclear due to the lack of understanding of their characteristics and plasticity mediated by their cellular microenvironment. We investigated how vascular smooth muscle cells (SMCs) and their interactions with endothelial cells (ECs) affect the behaviour and plasticity of CD34(+)CD31(+) progenitors and the underlying mechanisms.

METHODS AND RESULTS

Human peripheral blood-derived CD34(+)CD31(+) cells were directly transplanted into injured arteries in vivo and co-cultured with ECs and SMCs in vitro. CD34(+)CD31(+) progenitors injected into wire-injured mouse arteries differentiate into ECs and macrophages in the neoendothelial layer and neointima, respectively. SMC-co-culture increases CD34(+)CD31(+) cell mobility and adhesion to and transmigration across ECs. Sorted CD34(+)CD31(+) progenitors that adhered to ECs co-cultured with SMCs have the capacity to form capillary-like structures in Matrigel and chimeric blood vessels in vivo. Sorted transmigrated progenitors give rise to macrophages with increased pro-angiogenic activity. These differentiations of CD34(+)CD31(+) progenitors into ECs and macrophages are mediated by β(2)-integrin and Notch-1, respectively. β(2)-Integrin and Notch-1 are activated by their counterligands, intercellular adhesion molecule-1 (ICAM-1) and jagged-1, which are highly expressed in the neoendothelium and neointima in injured arteries. Intra-arterial injection of β(2)-integrin-activated CD34(+)CD31(+) progenitors into wire-injured mouse arteries inhibits neointima formation.

CONCLUSION

Our findings indicate that the peripheral vascular niches composed of ECs and SMCs may predispose haematopoietic CD34(+)CD31(+) progenitors to differentiate into ECs and macrophages through the activations of the ICAM-1/β(2)-integrin and jagged-1/Notch-1 cascades, respectively.

Salvianolic acid B inhibits low-density lipoprotein oxidation and neointimal hyperplasia in endothelium-denuded hypercholesterolaemic rabbits

BACKGROUND

Atherosclerosis and restenosis are inflammatory responses involving free radicals and lipid peroxidation and may be prevented/cured by antioxidant-mediated lipid peroxidation inhibition. Salvianolic acid (Sal B), a water-soluble antioxidant obtained from a Chinese medicinal herb, is believed to have multiple preventive and therapeutic effects against human vascular diseases. In this study the in vitro and in vivo inhibitory effects of Sal B on oxidative stress were determined.

RESULTS

In human aortic endothelial cells (HAECs), Sal B reduced oxidative stress, inhibited low-density lipoprotein (LDL) oxidation and reduced oxidised LDL-induced cytotoxicity. Sal B inhibited Cu(2+) -induced LDL oxidation in vitro (with a potency 16.3 times that of probucol) and attenuated HAEC-mediated LDL oxidation as well as reactive oxygen species (ROS) production. In cholesterol-fed New Zealand White rabbits (with probucol as positive control), Sal B intake reduced Cu(2+) -induced LDL oxidation, lipid deposition in the thoracic aorta, intimal thickness of the aortic arch and thoracic aorta and neointimal formation in the abdominal aorta.

CONCLUSION

The data obtained in this study suggest that Sal B protects HAECs from oxidative injury-mediated cell death via inhibition of ROS production. The antioxidant activity of Sal B may help explain its efficacy in the treatment of vascular diseases.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Cobra CRISP functions as an inflammatory modulator via a novel Zn2+- and heparan sulfate-dependent transcriptional regulation of endothelial cell adhesion molecules

Cysteine-rich secretory proteins (CRISPs) have been identified as a toxin family in most animal venoms with biological functions mainly associated with the ion channel activity of cysteine-rich domain (CRD). CRISPs also bind to Zn(2+) at their N-terminal pathogenesis-related (PR-1) domain, but their function remains unknown. Interestingly, similar the Zn(2+)-binding site exists in all CRISP family, including those identified in a wide range of organisms. Here, we report that the CRISP from Naja atra (natrin) could induce expression of vascular endothelial cell adhesion molecules, i.e. intercellular adhesion molecule-1, vascular adhesion molecule-1, and E-selectin, to promote monocytic cell adhesion in a heparan sulfate (HS)- and Zn(2+)-dependent manner. Using specific inhibitors and small interfering RNAs, the activation mechanisms are shown to involve both mitogen-activated protein kinases and nuclear factor-κB. Biophysical characterization of natrin by using fluorescence, circular dichroism, and x-ray crystallographic methods further reveals the presence of two Zn(2+)-binding sites for natrin. The strong binding site is located near the putative Ser-His-Glu catalytic triad of the N-terminal domain. The weak binding site remains to be characterized, but it may modulate HS binding by enhancing its interaction with long chain HS. Our results strongly suggest that natrin may serve as an inflammatory modulator that could perturb the wound-healing process of the bitten victim by regulating adhesion molecule expression in endothelial cells. Our finding uncovers a new aspect of the biological role of CRISP family in immune response and is expected to facilitate future development of new therapeutic strategy for the envenomed victims.

Oscillatory flow-induced proliferation of osteoblast-like cells is mediated by alphavbeta3 and beta1 integrins through synergistic interactions of focal adhesion kinase and Shc with phosphatidylinositol 3-kinase and the Akt/mTOR/p70S6K pathway

Interstitial flow in and around bone tissue is oscillatory in nature and affects the mechanical microenvironment for bone cell growth and formation. We investigated the role of oscillatory shear stress (OSS) in modulating the proliferation of human osteoblast-like MG63 cells and its underlying mechanisms. Application of OSS (0.5 +/- 4 dynes/cm(2)) to MG63 cells induced sustained activation of phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR/p70S6K (p70S6 kinase) signaling cascades and hence cell proliferation, which was accompanied by increased expression of cyclins A and D1, cyclin-dependent protein kinases-2, -4, and -6, and bone formation-related genes (c-fos, Egr-1, and Cox-2) and decreased expression of p21(CIP1) and p27(KIP1). OSS-induced activation of PI3K/Akt/mTOR/p70S6K and cell proliferation were inhibited by specific antibodies or small interference RNAs of alpha(v)beta(3) and beta(1) integrins and by dominant-negative mutants of Shc (Shc-SH2) and focal adhesion kinase (FAK) (FAK(F397Y)). Co-immunoprecipitation assay showed that OSS induces sustained increases in association of Shc and FAK with alpha(v)beta(3) and beta(1) integrins and PI3K subunit p85, which were abolished by transfecting the cells with FAK(F397Y) or Shc-SH2. OSS also induced sustained activation of ERK, which was inhibited by the specific PI3K inhibitor LY294002 and was required for OSS-induced activation of mTOR/p70S6K and proliferation in MG63 cells. Our findings provide insights into the mechanisms by which OSS induces osteoblast-like cell proliferation through activation of alpha(v)beta(3) and beta(1) integrins and synergistic interactions of FAK and Shc with PI3K, leading to the modulation of downstream ERK and Akt/mTOR/p70S6K pathways.

The effects of fiber size on MG63 cells cultured with collagen based matrices

The behavior of human osteoblast-like MG63 cells cultured on electrospun collagen fibers of three different sizes (50-200 nm, 200-500 nm, and 500-1000 nm in diameter) were investigated. The growth of MG63 cells on all three electrospun collagen fibers are the same and about 70% higher than those cultured on monomeric collagen and tissue-culture polystyrene (TCPS). The migration speed of MG63 cells, on the other hand, decreased as the diameter of nanofibers increased. There were more distinct actin stress fibers formed in MG63 cells when the cells cultured on collagen substrates as compared with TCPS. In addition, MG63 cells displayed different adhesion and spreading patterns on different sizes of collagen fibers. Size variation of collagen nanofibers apparently has more impact on cell migration distance and cell morphology as compared with cell growth. It was demonstrated that collagen nanofibers promoted MG63 cell interaction with matrices by providing a suitably rough nanometer surface. The results of this study present important information for the development of collagen-based biomaterials.

BMP-4 induction of arrest and differentiation of osteoblast-like cells via p21 CIP1 and p27 KIP1 regulation

Cell cycle regulation by differentiation signals is critical for eukaryote development. We investigated the roles of bone morphogenetic protein (BMP)-4, an important stimulator of osteoblast differentiation and bone formation, in regulating cell cycle distribution in four osteoblast-like cell lines and mouse primary osteoblasts, and the underlying mechanisms. In all cells used, BMP-4 induced G(0)/G(1) arrest. The molecular basis of the BMP-4 effect was analyzed, and the presentation on molecular mechanism is focused on human MG63 cells. BMP-4 induced p21(CIP1) and p27(KIP1) expressions and hence cell differentiation but had no effects on the expressions of cyclins A, B1, D1, and E, cyclin-dependent protein kinase-2, -4, and -6. Using specific small interfering RNA (siRNA), we found that BMP-4-induced G(0)/G(1) arrest, and p21(CIP1) and p27(KIP1) expressions were mediated by BMP receptor type IA (BMPRIA)-specific Sma- and Mad-related protein (Smad)1/5. BMP-4 induced transient phosphorylations of ERK; transfection of MG63 cells with ERK2, but not ERK1, -specific siRNA inhibited the BMP-4-induced responses in MG63 cells. Pretreatment of MG63 cells with Arg-Gly-Asp-Ser, which blocks the cell-extracellular matrix interaction, or transfection with beta(3) integrin-specific siRNA inhibited BMP-4-induced ERK and Smad1/5 phosphorylations. BMP-4 induced transient increases in associations of beta(3)-integrin with focal adhesion kinase and Shc, the dominant-negative mutants of which inhibited BMP-4-induced ERK and Smad1/5 phosphorylations. Our results indicate that BMP-4 induces G(0)/G(1) arrest and hence differentiation in osteoblast-like cells through increased expressions of p21(CIP1) and p27(KIP1), which are mediated by BMPRIA-specific Smad1/5. The extracellular matrix/beta(3) integrin/ focal adhesion kinase/Shc/ERK2 signaling pathway is involved in these BMP-4-induced responses in osteoblast-like cells.

Shear stress induces synthetic-to-contractile phenotypic modulation in smooth muscle cells via peroxisome proliferator-activated receptor alpha/delta activations by prostacyclin released by sheared endothelial cells

RATIONALE

Phenotypic modulation of smooth muscle cells (SMCs), which are located in close proximity to endothelial cells (ECs), is critical in regulating vascular function. The role of flow-induced shear stress in the modulation of SMC phenotype has not been well defined.

OBJECTIVE

The objective was to elucidate the role of shear stress on ECs in modulating SMC phenotype and its underlying mechanism.

METHODS AND RESULTS

Application of shear stress (12 dyn/cm2) to ECs cocultured with SMCs modulated SMC phenotype from synthetic to contractile state, with upregulation of contractile markers, downregulation of proinflammatory genes, and decreased percentage of cells in the synthetic phase. Treating SMCs with media from sheared ECs induced peroxisome proliferator-activated receptor (PPAR)-alpha, -delta, and -gamma ligand binding activities; transfecting SMCs with specific small interfering (si)RNAs of PPAR-alpha and -delta, but not -gamma, inhibited shear induction of contractile markers. ECs exposed to shear stress released prostacyclin (PGI2). Transfecting ECs with PGI2 synthase-specific siRNA inhibited shear-induced activation of PPAR-alpha/delta, upregulation of contractile markers, downregulation of proinflammatory genes, and decrease in percentage of SMCs in synthetic phase. Mice with PPAR-alpha deficiency (compared with control littermates) showed altered SMC phenotype toward a synthetic state, with increased arterial contractility in response to angiotensin II.

CONCLUSIONS

These results indicate that laminar shear stress induces synthetic-to-contractile phenotypic modulation in SMCs through the activation of PPAR-alpha/delta by the EC-released PGI2. Our findings provide insights into the mechanisms underlying the EC-SMC interplays and the protective homeostatic function of laminar shear stress in modulating SMC phenotype.

Vascular endothelial responses to altered shear stress: pathologic implications for atherosclerosis

Atherosclerosis preferentially develops at branches and curvatures of the arterial tree, where blood flow is disturbed from a laminar pattern, and wall shear stress is non-uniform and has an irregular distribution. Vascular endothelial cells (ECs), which form an interface between the flowing blood and the vessel wall, are exposed to blood flow-induced shear stress. There is increasing evidence suggesting that laminar blood flow and sustained high shear stress modulate the expression of EC genes and proteins that function to protect against atherosclerosis; in contrast, disturbed blood flow and the associated low and reciprocating shear stress upregulate proatherosclerotic genes and proteins that promote development of atherosclerosis. Understanding of the effects of shear stress on ECs will provide mechanistic insights into its role in the pathogenesis of atherosclerosis. The aim of this review article is to summarize current findings on the effects of shear stress on ECs, in terms of their signal transduction, gene expression, structure, and function. These endothelial cellular responses have important relevance to understanding the pathophysiological effects of altered shear stress associated with atherosclerosis and thrombosis and their complications.

Synergism of biochemical and mechanical stimuli in the differentiation of human placenta-derived multipotent cells into endothelial cells

There have been intensive studies on the differentiation of endothelial progenitor cells (EPCs) into endothelial cells. We investigated the endothelial differentiation of placenta-derived multipotent cells (PDMCs), a population of CD34(-)/CD133(-)/Flk-1(-) cells. PDMCs were cultured in basal media or media containing endothelial growth factors (EGM), including vascular endothelial growth factor (VEGF), for 3 days and then subjected to shear stress of 6 or 12dyn/cm(2) for 24h. Culture of PDMCs in EGM under static conditions resulted in significant increases in VEGF receptor-1 (Flt-1) and receptor-2 (Flk-1) expression. Application of shear stress at 12dyn/cm(2) to these cells led to significant increases in their expression of von Willebrand Factor and platelet-endothelial cell adhesion molecule-1 at both the gene and protein levels. Shear stress at 6dyn/cm(2) had lesser effects. Uptakes of acetylated low-density lipoproteins as well as formation of tube-like structures on Matrigel were significantly increased after subjecting to shear stress of 12dyn/cm(2) for 24h. Our findings suggest that the combined use of endothelial growth factors and high shear stress is synergistic for the endothelial differentiation of PDMCs.

Photoluminescence of Si nanocrystallites and amorphous oxygen-containing si nanoparticles: the reversible effect of ambient atmosphere on luminescence

Si nanocrystallites of various sizes and oxygen-containing Si nanoparticles with different oxygen contents were prepared by vapor condensation. The Si nanocrystallites showed a visible light emission from 500 nm to 900 nm with the peak at 800 nm, and the intensity of photoluminescence increased with decreasing the particle size. This photoluminescence observed in vacuum could be quenched by air and hydrogen, and reappeared after the sample chamber was evacuated. The oxygen-containing Si nanoparticles consisting mainly of Si oxide were amorphous and had an average particle size of approximately 20 nm. Increasing the oxygen content of nanoparticles caused a blueshift of the absorption edge in the transmission spectra. A blue-green photoluminescence with two peaks at 500 nm and 800 nm was observed from these oxygen-containing Si nanoparticles. The luminescence intensity increased with the oxygen content of nanoparticles, and was very sensitive to the ambient atmosphere. Much lower intensity was observed in air, but higher intensity could be recovered in vacuum. Surface states and oxygen-induced luminescent centers were proposed to be responsible for the photoluminescence from the Si nanocrystallites and oxygen-containing Si nanoparticles, respectively. The reversible ambient effect in both cases could be explained by surface charge redistribution during the gas adsorption and desorption processes.

Leukocyte-endothelium interaction: measurement by laser tweezers force spectroscopy

Leukocyte adhesion to vascular endothelium is an initial step of many inflammatory diseases. Although the atomic force microscopy (AFM) measurements of leukocyte-endothelial interaction have been recently introduced. with cell adhesion force unbinding curves (CAFUC). We obtained pico-Newton force in the initial interaction between a single living THP-1 cell and HUVEC monolayer using a custom-built laser tweezers (LT) system. The measured quantities included the non-linear force-distance relationship, and the effect of yielding in cell detachment. It is possible to introduce a time scale into the LT cell-detachment experiments for further exploration and more detailed information on the viscoelastic properties of living cells.

Cell Migration Rate on Poly(ɛ-caprolactone)/Poly(ethylene glycol) Diblock Copolymers and Correlation with the Material Sliding Angle

The nanostructure of a biomaterial surface has strong influence on cell behavior. The migration of cells on nanostructured surfaces, however, has not been investigated so far. In this study, we used PCL/PEG diblock copolymers as model surfaces to examine the effect of nanoislands on migration of different cells, including fibroblasts and endothelial cells. The water sliding angle of the substrates was measured. The cell migration rate was examined under a real-time optical microscope. It was found that a greater cell migration rate correlated with the smaller sliding angle of the substrate.

Mechanisms of induction of endothelial cell E-selectin expression by smooth muscle cells and its inhibition by shear stress

E-selectin is a major adhesion molecule expressed by endothelial cells (ECs), which are exposed to shear stress and neighboring smooth muscle cells (SMCs). We investigated the mechanisms underlying the modulation of EC E-selectin expression by SMCs and shear stress. SMC coculture induced rapid and sustained increases in expression of E-selectin and phosphorylation of interleukin-1 (IL-1) receptor-associated kinase glycoprotein-130, as well as the downstream mitogen-activated protein kinases (MAPKs) and Akt. By using specific inhibitors, dominant-negative mutants, and small interfering RNA, we demonstrated that activations of c-Jun-NH(2)-terminal kinase (JNK) and p38 of the MAPK pathways are critical for the coculture-induced E-selectin expression. Gel shifting and chromatin immunoprecipitation assays showed that SMC coculture increased the nuclear factor-kappaB (NF-kappaB)-promoter binding activity in ECs; inhibition of NF-kappaB activation by p65-antisense, lactacystin, and N-acetyl-cysteine blocked the coculture-induced E-selectin promoter activity. Protein arrays and blocking assays using neutralizing antibodies demonstrated that IL-1beta and IL-6 produced by EC/SMC cocultures are major contributors to the coculture induction of EC signaling and E-selectin expression. Preshearing of ECs at 12 dynes/cm(2) inhibited the coculture-induced EC signaling and E-selectin expression. Our findings have elucidated the molecular mechanisms underlying the SMC induction of EC E-selectin expression and the shear stress protection against this SMC induction.

The inhibition of TNF-α-induced E-selectin expression in endothelial cells via the JNK/NF-κB pathways by highly N-acetylated chitooligosaccharides

Chitooligosaccharides (COS) have been shown to regulate various cellular and biological functions. However, the effect of COS on inflammatory responses of the cells remains unclear. We investigated the regulatory effect of highly N-acetylated COS (NACOS) on tumor necrosis factor-alpha (TNF-alpha)-induced endothelial cell (EC) E-selectin expression, which is crucial for leukocyte recruitment. ECs were kept as controls or pre-treated with NACOS for different times, and then stimulated with TNF-alpha for 4h. The results show that pre-treating ECs with NACOS inhibited the TNF-alpha-induced E-selectin expression in a dose- and time-dependent manner. This NACOS-mediated inhibition in E-selectin expression was regulated at the transcriptional level, but not due to changes in mRNA stability. Stimulation of ECs with TNF-alpha-induced rapid increases in the phosphorylation of their mitogen-activated protein kinases (MAPKs) [extracellular signal-regulated kinase (ERK), c-Jun-NH2-terminal kinase (JNK), and p38 MAPK]; the inhibitor for JNK (i.e., SP600125), but not those for ERK (i.e., PD98059) and p38 MAPK (i.e., SB203580), attenuated this TNF-alpha-induced E-selectin expression. Pre-treating ECs with NACOS inhibited the TNF-alpha-induced JNK activation, suggesting that JNK was involved in the inhibitory effect of NACOS on TNF-alpha-induced E-selectin expression. Pre-treating ECs with NACOS inhibited the TNF-alpha-induced p65 and p50 mRNA expressions. Gel shifting and chromatin immunoprecipitation assays showed that NACOS blocked the TNF-alpha-induced increases in the binding activity and in vivo promoter binding of nuclear factor-kappaB (NF-kappaB) in ECs. Our findings provide a molecular mechanism by which NACOS inhibit TNF-alpha-induced E-selectin expression in ECs, and a basis for using NACOS in pharmaceutical therapy against inflammation.

Directional shear flow and Rho activation prevent the endothelial cell apoptosis induced by micropatterned anisotropic geometry

To study the roles of anisotropic cell morphology and directionality of mechanical force in apoptosis, the spreading of human umbilical vein endothelial cells (HUVECs) was constrained by growing on micropatterned (MP) strips of fibronectin (FN, 20 microg/cm2) with widths of 15, 30, and 60 microm on silicone membrane. Cells on 30- and 60-microm strips, like cells on a nonpatterned (NP) surface coated with FN, showed clear actin stress fibers with anchoring spots of phosphorylated focal adhesion kinase (p-FAK) and no significant apoptosis. On 15-microm strips, cells had few stress fibers, no p-FAK, and significant apoptosis. After seeding for 12 h, the cells were subjected to pulsatile shear stress (12+/-4 dyn/cm2) parallel or perpendicular to MP strips, or kept under static condition. Parallel flow caused cell elongation with enhanced stress fibers and p-FAK, and a reduction in apoptosis, but perpendicular flow did not. The Rho inhibitory C3 exoenzyme abolished the effects of parallel flow. RhoV14, the constitutively active Rho, enhanced stress fibers and p-FAK, and prevented apoptosis of HUVECs on 15-microm strips under static condition. RhoV14 also reduced cell apoptosis under both parallel and perpendicular flows. Our results indicate that cell apoptosis can be modulated by changes in ECM micropatterning, anisotropic cell morphology, and mechanical forces. These extracellular microenvironment factors affect cell survival through alterations in Rho GTPase activity, stress fiber organization, and FAK phosphorylation.

Synergistic roles of platelet-derived growth factor-BB and interleukin-1beta in phenotypic modulation of human aortic smooth muscle cells

The phenotype of smooth muscle cells (SMCs) plays an important role in vascular function in health and disease. We investigated the mechanism of modulation of SMC phenotype (from contractile to synthetic) induced by the synergistic action of a growth factor (platelet-derived growth factor, PDGF-BB) and a cytokine (interleukin, IL-1beta). Human aortic SMCs grown on polymerized collagen showed high expression levels of contractile markers (smooth muscle alpha-actin, myosin heavy chain, and calponin). These levels were not significantly affected by PDGF-BB and IL-1beta individually, but decreased markedly after the combined usage of PDGF-BB and IL-1beta. PDGF/IL-1beta costimulation also induced a sustained phosphorylation of Akt and p70 ribosomal S6 kinase (p70S6K). The effects of PDGF/IL-1beta costimulation on contractile marker expression and Akt and p70S6K phosphorylation were blocked by the phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 and by adenovirus expressing a dominant-negative Akt, and they were mimicked by constitutively active Akt. PDGF-BB/IL-1beta induced a sustained phosphorylation of PDGF receptor (PDGFR)-beta and its association with IL-1 receptor (IL-1R1). Such activation and association of receptors were blocked by a PDGFR-beta neutralizing antibody (AF385), an IL-1R1 antagonist (IL-1ra), as well as a specific inhibitor of PDGFR-beta phosphorylation (AG1295); these agents also eliminated the PDGF-BB/IL-1beta-induced signaling and phenotypic modulation. PDGF-BB/IL-1beta inhibited the polymerized collagen-induced serum response factor DNA binding activity in the nucleus, and this effect was mediated by the PDGFR-beta/IL-1R1 association and phosphatidylinositol 3-kinase/Akt/p70S6K pathway. Our findings provide insights into the mechanism of SMC phenotypic modulation from contractile to synthetic, e.g., in atherosclerosis.

Shear stress regulates gene expression in vascular endothelial cells in response to tumor necrosis factor-alpha: a study of the transcription profile with complementary DNA microarray

We investigate the role of shear stress in regulating the gene expression in endothelial cells (ECs) in response to tumor necrosis factor-alpha (TNF-alpha). ECs were kept in static condition or pre-exposed to a high level (HSS, 20 dynes/cm2) or a low level of shear stress (LSS, 0.5 dynes/cm2) for 24 h, and TNF-alpha was added under static condition for 4 h. In static ECs, DNA microarray showed that TNF-alpha caused a significant increase in expression of 102 genes and a significant decrease in expression of 12 genes. Pre-shearing of ECs decreased the TNF-alpha-responsiveness of many pro-inflammatory, pro-coagulant, proliferative, and pro-apoptotic genes, whereas it increased the responsiveness of some antioxidant, anti-coagulant, and anti-apoptotic genes. LSS showed less regulatory effects than HSS on EC gene expression in response to TNF-alpha. The microarray data were confirmed by reverse-transcription polymerase chain reaction for 64 selected genes. Pre-shearing of ECs at HSS significantly inhibited the TNF-alpha-induced p65 and p50 mRNA expressions and nuclear factor-kappaB (NF-kappaB)-DNA binding activity. Inhibition of NF-kappaB activity with the p65-antisense or lactacystin under static condition blocked the expression of most of the genes that are TNF-alpha-inducible and shear stress-down-regulated. Our findings suggest that laminar shear stress serves protective functions against atherogenesis.

Phosphatidylinositol 3-kinase/Akt pathway is involved in transforming growth factor-beta1-induced phenotypic modulation of 10T1/2 cells to smooth muscle cells

Transforming growth factor-beta1 (TGF-beta1) is known to induce phenotypic modulation of mesenchymal cells to SMCs. However, the intracellular signals regulating induction of the SMC phenotype of mesenchymal cells have not been fully clarified. In the present study, we examined the role of the mitogen-activated protein kinase (MAPK) superfamily and phosphatidylinositol 3-kinase (PI3K)/Akt in the TGF-beta1-mediated phenotypic modulation of 10T1/2 mesenchymal cells to SMCs characterized by the expression of SMC-specific markers, including smooth muscle alpha-actin (SMalpha-actin), myosin heavy chain (SM-MHC), and protein 22-alpha (SM22alpha). The results showed the following: (1) TGF-beta1 induced SMalpha-actin and SM-MHC expressions in 10T1/2 cells in a time-dependent manner. (2) TGF-beta1 induced biphasic increases in extracellular signal-regulated kinase (ERK), p38 MAPK, c-Jun-NH2-terminal kinase (JNK), and Akt phosphorylation. (3) The inhibitor for PI3K/Akt (i.e., LY294002), but not those for MAPKs (i.e., SB203580, PD98059, and SP600125), attenuated the TGF-beta1-induced SMalpha-actin and SM-MHC expressions in 10T1/2 cells; in addition, transfection of 10T1/2 cells with the Akt-specific small interfering RNA (siRNA) significantly reduced their SMalpha-actin and SM-MHC expressions. (4) LY294002 and the Akt-specific siRNA inhibited the TGF-beta1-induced SM22alpha gene expression and promoter activity, suggesting that the TGF-beta1-induced gene expression was mediated by PI3K/Akt at the transcriptional level. (5) LY294002 inhibited the TGF-beta1-induced gene expression and DNA binding activity of serum response factor (SRF). These results indicate that TGF-beta1 is capable of inducing the SMC phenotype of 10T1/2 cells and that this induction is mediated through the PI3K/Akt signaling pathway.

Neutrophils, lymphocytes, and monocytes exhibit diverse behaviors in transendothelial and subendothelial migrations under coculture with smooth muscle cells in disturbed flow

Atherosclerosis develops at regions of the arterial tree exposed to disturbed flow. The early stage of atherogenesis involves the adhesion of leukocytes (white blood cells [WBCs]) to and their transmigration across endothelial cells (ECs), which are located in close proximity to smooth muscle cells (SMCs). We investigated the effects of EC/SMC coculture and disturbed flow on the adhesion and transmigration of 3 types of WBCs (neutrophils, peripheral blood lymphocytes [PBLs], and monocytes) using our vertical-step flow (VSF) chamber, in which ECs were cocultured with SMCs in collagen gels. Such coculture significantly increased the adhesion and transmigration of neutrophils, PBLs, and monocytes under VSF, particularly in the reattachment area, where the rolling velocity of WBCs and their transmigration time were decreased, as compared with the other areas. Neutrophils, PBLs, and monocytes showed different subendothelial migration patterns under VSF. Their movements were more random and shorter in distance in the reattachment area. Coculture of ECs and SMCs induced their expressions of adhesion molecules and chemokines, which contributed to the increased WBC adhesion and transmigration. Our findings provide insights into the mechanisms of WBC interaction with the vessel wall (composed of ECs and SMCs) under the complex flow environments found in regions of prevalence for atherogenesis.