Promote Endothelial Cells Proliferation Research Articles

Inhibition effect of tacrolimus and platelet-derived growth factor-BB on restenosis after vascular intimal injury

Excessive proliferation and migration of vascular smooth muscle cells(VSMCs) and delayed proliferation and migration of endothelial cells(ECs) were the main cause of restenosis after endovascular interventional therapy. Since tacrolimus has proved to be more sensitive to inhibiting VSMCs’ proliferation,and platelet-derived growth factor-BB(PDGF-BB) benefitted ECs’ and VSMCs’ proliferation, this study was aimed to identify combined effect of tacrolimus and PDGF-BB, investigate any mechanisms underneath and demonstrate combined effect of two drugs in vivo. As the results showed we confirmed differential effect of PDGF-BB and tacrolimus on ECs and VSMCs. On the concentration level of 2–5μg/ml tacrolimus plus 10ng/ml PDGF-BB, combination of drugs could effectively promote ECs proliferation and migration, and meanwhile inhibit VSMCs proliferation and migration, and the inhibition of p-mTOR’s expression within VSMCs played an important role in this differentiated effect. Raising concentration level of PDGF-BB would weaken inhibitory effect of tacrolimus on both kinds of cell. For injured intima, the mix solution of two drugs could promote intima healing and suppress excessive intimal hyperplasia.

Shear stress induces endothelial-to-mesenchymal transition via the transcription factor Snail

Blood flow influences atherosclerosis by generating wall shear stress, which alters endothelial cell (EC) physiology. Low shear stress induces dedifferentiation of EC through a process termed endothelial-to-mesenchymal transition (EndMT). The mechanisms underlying shear stress-regulation of EndMT are uncertain. Here we investigated the role of the transcription factor Snail in low shear stress-induced EndMT. Studies of cultured EC exposed to flow revealed that low shear stress induced Snail expression. Using gene silencing it was demonstrated that Snail positively regulated the expression of EndMT markers (Slug, N-cadherin, α-SMA) in EC exposed to low shear stress. Gene silencing also revealed that Snail enhanced the permeability of endothelial monolayers to macromolecules by promoting EC proliferation and migration. En face staining of the murine aorta or carotid arteries modified with flow-altering cuffs demonstrated that Snail was expressed preferentially at low shear stress sites that are predisposed to atherosclerosis. Snail was also expressed in EC overlying atherosclerotic plaques in coronary arteries from patients with ischemic heart disease implying a role in human arterial disease. We conclude that Snail is an essential driver of EndMT under low shear stress conditions and may promote early atherogenesis by enhancing vascular permeability.

Smooth Muscle Cell Proangiogenic Phenotype Induced by Cyclopentenyl Cytosine Promotes Endothelial Cell Proliferation and Migration

Vascular smooth muscle cells (SMCs) and endothelial cells (ECs) are in close contact with blood vessels. SMC phenotypes can be altered during pathological vascular remodeling. However, how SMC phenotypes affect EC properties remains largely unknown. In this study, we found that PDGF-BB-induced synthetic SMCs suppressed EC proliferation and migration while exhibiting increased expression of anti-angiogenic factors, such as endostatin, and decreased pro-angiogenic factors, including CXC motif ligand 1 (CXCL1). Cyclopentenyl cytosine (CPEC), a CTP synthase inhibitor that has been reported previously to inhibit SMC proliferation and injury-induced neointima formation, induced SMC redifferentiation. Interestingly, CPEC-conditioned SMC culture medium promoted EC proliferation and migration because of an increase in CXCL1 along with decreased endostatin production in SMCs. Addition of recombinant endostatin protein or blockade of CXCL1 with a neutralizing antibody suppressed the EC proliferation and migration induced by CPEC-conditioned SMC medium. Mechanistically, CPEC functions as a cytosine derivate to stimulate adenosine receptors A1 and A2a, which further activate downstream cAMP and Akt signaling, leading to the phosphorylation of cAMP response element binding protein and, consequently, SMC redifferentiation. These data provided proof of a novel concept that synthetic SMC exhibits an anti-angiogenic SMC phenotype, whereas contractile SMC shows a pro-angiogenic phenotype. CPEC appears to be a potent stimulator for switching the anti-angiogenic SMC phenotype to the pro-angiogenic phenotype, which may be essential for CPEC to accelerate re-endothelialization for vascular repair during injury-induced vascular wall remodeling.

Flow-dependent YAP/TAZ activities regulate endothelial phenotypes and atherosclerosis

The focal nature of atherosclerotic lesions suggests an important role of local hemodynamic environment. Recent studies have demonstrated significant roles of Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) in mediating mechanotransduction and vascular homeostasis. The objective of this study is to investigate the functional role of YAP/TAZ in the flow regulation of atheroprone endothelial phenotypes and the consequential development of atherosclerotic lesions. We found that exposure of cultured endothelial cells (ECs) to the atheroprone disturbed flow resulted in YAP/TAZ activation and translocation into EC nucleus to up-regulate the target genes, including cysteine-rich angiogenic inducer 61 (CYR61), connective tissue growth factor (CTGF), and ankyrin repeat domain 1 (ANKRD1). In contrast, the athero-protective laminar flow suppressed YAP/TAZ activities. En face analysis of mouse arteries demonstrated an increased nuclear localization of YAP/TAZ and elevated levels of the target genes in the endothelium in atheroprone areas compared with athero-protective areas. YAP/TAZ knockdown significantly attenuated the disturbed flow induction of EC proliferative and proinflammatory phenotypes, whereas overexpression of constitutively active YAP was sufficient to promote EC proliferation and inflammation. In addition, treatment with statin, an antiatherosclerotic drug, inhibited YAP/TAZ activities to diminish the disturbed flow-induced proliferation and inflammation. In vivo blockade of YAP/TAZ translation by morpholino oligos significantly reduced endothelial inflammation and the size of atherosclerotic lesions. Our results demonstrate a critical role of the activation of YAP/TAZ by disturbed flow in promoting atheroprone phenotypes and atherosclerotic lesion development. Therefore, inhibition of YAP/TAZ activation is a promising athero-protective therapeutic strategy.

The effects of nerve growth factor on endothelial cells seeded on different titanium surfaces

Angiogenesis is critical for peri-implant bone regeneration and osseointegration. Endothelial cells (ECs) play an important role in angiogenesis during the early stage of bone formation. Nerve growth factor (NGF) is also reported to function as an angiogenic growth factor. The effects of NGF on ECs seeded on titanium surfaces are unclear. This study was done to investigate the influence of NGF on peri-implant angiogenesis in vitro and in vivo. We used two different titanium surfaces. ECs seeded on these surfaces were treated with indicated concentrations of NGF or vascular endothelial growth factor (VEGF). Proliferation, differentiation, morphological features, and amounts attached were assessed. Chicken embryo chorioallantoic membrane (CAM) was adopted to evaluate the effect of NGF in vivo. The results showed that NGF could promote EC proliferation on both titanium surfaces (F1d=2.083, P=0.156; F3d=30.857, P=0.0002; F5d=4.440, P=0.041; F7d=11.065, P=0.001). NGF and the SLA surface upregulated mRNA of NGF, TrkA, and p75 expression (FNGF=11.941, P=0.003; FTrkA=28.514, P=0.004; Fp75=7.725, P=0.01). In vivo, the supernatants of the NGF-treated group could promote neovascularization in CAM (F=17.662, P=0.009). This study demonstrated that NGF could enhance EC proliferation, gene expression on different titanium surfaces, and neovascularization in CAM. This provides novel information in relation to the promotion of early dental implant osseointegration.

Biocompatibility of Ir/Ti-oxide coatings: Interaction with platelets, endothelial and smooth muscle cells

Applying surface coatings on a biomedical implant is a promising modification technique which can enhance the implant's biocompatibility via controlling blood constituents- or/and cell-surface interaction. In this study, the influence of composition of IrxTi1−x-oxide coatings (x=0, 0.2, 0.4, 0.6, 0.8, 1) formed on a titanium (Ti) substrate on the responses of platelets, endothelial cells (ECs) and smooth muscle cells (SMCs) was investigated. The results showed that a significant decrease in platelet adhesion and activation was obtained on Ir0.2Ti0.8-oxide and Ir0.4Ti0.6-oxide coatings, rendering the surfaces more blood compatible, in comparison to the control (316L stainless steel, 316L-SS) and other coating compositions. Further, a substantial increase in the EC/SMC surface count ratio after 4h of cell attachment to the Ir0.2Ti0.8-oxide and Ir0.4Ti0.6-oxide coatings, relative to the 316L-SS control and the other coating compositions, indicated high potential of these coatings for the enhancement of surface endothelialization. This indicates the capability of the corresponding coating compositions to promote EC proliferation on the surface, while inhibiting that of SMCs, which is important in cardiovascular stents applications.

EGFL7 polymorphism to predict tumor response in metastatic colorectal cancer (mCRC) patients (pts) treated with FOLFIRI and bevacizumab (BV).

3565 Background: Angiogenesis involves endothelial cell (EC) sprouting, proliferation, and differentiation and recruitment of mural cells to stabilize new vessels. The proteins Epidermal Growth Factor Domain-Like 7 (EGFL-7) and Activin Receptor-like Kinase 1 (ALK1) play critical roles. EC-secreted EGFL7 antagonizes Notch to promote EC proliferation, sprouting, and motility. EGFL7 also regulates mural cell recruitment and extracellular matrix deposition. ALK1 is an EC-restricted TGF-β Type 1 receptor with downstream repression of Vascular Endothelial Growth Factor (VEGF) signaling. ALK1 also promotes pericyte-EC adhesion. EGFL7 or ALK1 inhibition enhances antitumor efficacy when combined with BV in murine models. Both are overexpressed in many cancers and may be critical for efficacy of anti-VEGF therapy. We tested whether EGFL7 (rs1051851, rs2297538) and ALK1 polymorphisms (rs2293094, rs11169953, rs706819) will predict efficacy of BV-based therapy in mCRC pts. Methods: Genomic DNA was extracted from peripheral whole blood samples from 455 mCRC pts treated with first-line BV and FOLFIRI. SNPs were analyzed by PCR-based direct DNA sequencing and evaluated for association with tumor response rate (RR), overall survival (OS), and progression free survival (PFS). Results: Male/female: 272/183; median age: 62 (range: 25-81); median PFS and median OS: 10.9 (95%CI: 10.1-11.6) and 29.9 (95%CI: 25.9-34.6) months, respectively; response to therapy: 59% (215 pts); median follow-up:23.6 (range: 1.8-60.4) months. Pts carrying the EGFL7 rs1051851 G/G alleles had a 62% RR versus 56% in pts with A/G and 29% in patients with A/A (p=0.0130, Cochran-Armitage trend test). The result remained significant after adjustment for baseline pt characteristics (p=0.026, Multivariable logistic regression test). There was no statistically significant association between tested polymorphisms and OS or PFS. Conclusions: The EGFL7 SNP rs1051851 may predict tumor response in mCRC pts treated with FOLFIRI and BV. To our knowledge, this is the first study demonstrating predictive significance of genetic variations in EGFL7. Prospective validation of this study is warranted.

BMP receptor-integrin interaction mediates responses of vascular endothelial Smad1/5 and proliferation to disturbed flow

Vascular endothelial cells (ECs) are constantly exposed to blood flow-induced shear stress. Our previous study demonstrated that disturbed flow with low and oscillatory shear stress (OSS) induces bone morphogenetic protein receptor (BMPR)-specific Smad1/5 activation in ECs, but the underlying mechanisms and the in vivo functional role of Smad1/5 remain unclear. Here we elucidated the molecular mechanisms by which OSS activates EC Smad1/5 and its in vivo functional role. Lentiviral Smad5-specific short hairpin RNA (Lenti-shSmad5) was constructed and intra-arterially injected into the lumen of stenosed abdominal aorta in bromodeoxyuridine-infused rats. Co-immunoprecipitation and in situ proximity ligation assays were performed on ECs exposed to OSS (0.5±4 dynes/cm(2) ) in a parallel-plate flow chamber to investigate BMPR-integrin interactions and their regulatory role in OSS-activation of EC Smad1/5. Intra-arterial administration of Lenti-shSmad5 inhibited bromodeoxyuridine uptake of ECs at post-stenotic sites, where disturbed flow with OSS occurs. OSS induced sustained BMPRIB-αv β3 integrin association in ECs, which was mediated by the intracytoplasmic kinase domain of BMPRII and subsequently activated the Shc/focal adhesion kinase (FAK)/extracellular signal-regulated kinase (ERK) cascade, leading to Smad1/5 activation. This OSS-activation of Smad1/5 induced its association with and activation of runt-related transcription factor-2 (Runx2), leading to activations of mammalian target of rapamycin (mTOR) and p70S6 kinase (p70S6K), a pathway critical for EC proliferation in response to OSS. Oscillatory shear stress induces synergistic interactions between specific BMPRs and integrin to activate Smad1/5 through the Shc/FAK/ERK pathway, which leads to the activation of the Runx2/mTOR/p70S6K pathway to promote EC proliferation.

Early growth response protein 1 promotes restenosis by upregulating intercellular adhesion molecule-1 in vein graft.

Objectives. To verify the relationship between Egr-1 and vein graft restenosis and investigate the related mechanisms. Methods. Mouse vein graft models were established in Egr-1 knockout (KO) and wild-type (WT) mice. The vein grafts in the mice were taken for pathological examination and immunohistochemical analysis. The endothelial cells (ECs) were stimulated by using a computer-controlled cyclic stress unit. BrdU staining and PCR were used to detect ECs proliferation activity and Egr-1 and ICAM-1 mRNA expression, respectively. Western-blot analysis was also used to detect expression of Egr-1 and intercellular adhesion molecule-1 (ICAM-1) proteins. Results. The lumens of vein grafts in Egr-1 KO mice were wider than in WT mice. ECs proliferation after mechanical stretch stimulation was suppressed by Egr-1 knockout (P < 0.05). Both in vein grafts and ECs from WT mice after mechanical stretch stimulation, mRNA expression and protein of Egr-1 and ICAM-1 showed increases (P < 0.05). However, ICAM-1 expression was significantly suppressed in ECs from Egr-1 knockout mice (P < 0.05). Conclusions. Egr-1 may promote ECs proliferation and result in vein graft restenosis by upregulating the expression of ICAM-1. As a key factor of vein graft restenosis, it could be a target for the prevention of restenosis after CABG surgery.

Diabetic HDL is dysfunctional in stimulating endothelial cell migration and proliferation due to down regulation of SR-BI expression.

BackgroundDiabetic HDL had diminished capacity to stimulate endothelial cell (EC) proliferation, migration, and adhesion to extracellular matrix. The mechanism of such dysfunction is poorly understood and we therefore sought to determine the mechanistic features of diabetic HDL dysfunction.Methodology/Principal FindingsWe found that the dysfunction of diabetic HDL on human umbilical vein endothelial cells (HUVECs) was associated with the down regulation of the HDL receptor protein, SR-BI. Akt-phosphorylation in HUVECs was induced in a biphasic manner by normal HDL. While diabetic HDL induced Akt phosphorylation normally after 20 minutes, the phosphorylation observed 24 hours after diabetic HDL treatment was reduced. To determine the role of SR-BI down regulation on diminished EC responses of diabetic HDL, Mouse aortic endothelial cells (MAECs) were isolated from wild type and SR-BI (−/−) mice, and treated with normal and diabetic HDL. The proliferative and migratory effects of normal HDL on wild type MAECs were greatly diminished in SR-BI (−/−) cells. In contrast, response to diabetic HDL was impaired in both types suggesting diminished effectiveness of diabetic HDL on EC proliferation and migration might be due to the down regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL’s capacity to activate Akt chronically.Conclusions/SignificanceDiabetic HDL was dysfunctional in promoting EC proliferation, migration, and adhesion to matrix which was associated with the down-regulation of SR-BI. Additionally, SR-BI down regulation diminishes diabetic HDL’s capacity to activate Akt chronically.

Brain-Derived Neurotrophic Factor Promotes Tumorigenesis via Induction of Neovascularization: Implication in Hepatocellular Carcinoma

Brain-derived neurotrophic factor (BDNF) has emerged as a novel angiogenic factor, and yet its impact on tumorigenesis is unclear. This study aimed at investigating the roles of BDNF in angiogenesis and tumor development. BDNF was overexpressed in a mouse endothelial cell (EC) line by stable transfection, and angiogenic properties of the transfectants were assessed. Microarray analysis was employed to explore the molecular pathways. The impact of modulating BDNF levels in two mouse EC lines on tumorigenic potential of a transformed mouse liver cell line was evaluated by an in vivo cotransplantation model. BDNF and tropomyosin receptor kinase B (TrkB) protein levels were determined in 50 pairs of human hepatocellular carcinoma (HCC) tissues by Western blotting and immunohistochemistry. Survival analysis was carried out to determine their clinical significance. Overexpression of BDNF could promote EC proliferation, migration, invasion, and survival. Microarray and molecular studies showed that RhoA, caspase-9, caspase-3, growth arrest specific 6, and VEGF could mediate BDNF/TrkB-induced angiogenesis. The cotransplantation experiment showed that high BDNF-expressing ECs could facilitate tumor angiogenesis and growth, whereas knockdown of BDNF by short hairpin RNAs impaired such effects. Furthermore, examination on human HCC tissues revealed upregulation of BDNF and TrkB protein levels in 46.0% and 33.3% of the cases studied, respectively. Immunohistochemistry disclosed strong BDNF reactivity in both tumor and endothelial cells. High TrkB expression was associated with shorter overall survival. BDNF/TrkB system was crucial for tumor angiogenesis and growth, which may represent a potential target for antiangiogenic therapy in HCC.

Abstract 5586: Catestatin Induces Therapeutic Neovascularization by Induction of Angiogenesis and Incorporation of Endothelial Progenitor Cells

Introduction Catestatin (Cat), a biologically active fragment of Chromogranin A was described as a nicotinic antagonist inhibiting catecholamine release. Recently, also other biological effects for this peptide were described like release of histamine or activation during cutaneous wounds. We found that Cat induces chemotaxis on a variety of cells including endothelial cells (EC) and therefore hypothesized that Cat might act as a novel angiogenic cytokine. Results To investigate the effect of Cat on EC differentiation into vascular structures in vitro , we performed a matrigel tube formation assay using different concentrations of Cat. Cat at 10 −9 M was most effective in promoting tube formation (rel. tube form. 1.77+/−0.08 vs. ctr.; n=4, P&lt;0.01). This effect could be blocked by a Cat antibody (Ab) (0.87 +/−0.1 vs. ctr; n=4, P&lt;0.01 vs. Cat). Additionally, Cat dose-dependently induced chemotaxis of EC (rel. chemotact. index 10 −9 M: 1.67+/−0.03 vs. ctr; n=6, P&lt;0.01) and promoted EC proliferation as measured by cell numbers of starved EC (rel. cell number 10 −9 M: 1.86 +/−0.13 vs. ctr., n=4, P&lt;0.01; Cat-Ab 0.97+/−0.06 vs. ctr; n=4, P&lt;0.05 vs. Cat). Western blot analysis revealed stimulation of ERK and AKT by 10 −9 M Cat indicating activation of these signal transduction pathways. We also tested for angiogenic effects in vivo by using 3 different mouse models. In the mouse cornea neovascularization model Cat induced significant growth of new blood vessels. In the unilateral limb ischemia model injection of Cat (10 μ g every other day for 2 weeks) into adductor muscles increased capillary (475+/−31 vs. 303+/−28/mm 2 ; n=7, P=0.003) and arteriole (10.1+/−0.8 vs. 5.2+/−1.0/mm 2 ; n=7, P=0.001) density, and accelerated perfusion recovery as shown by LDPI (LDPI ratio ischemic/control leg after 28 days of ischemia) 0.94 vs. 0.74; n=10, P=0.009. Moreover, Cat treated mice showed more incorporated EPC in ischemic limbs using the actin-GFP bone marrow transplant model (21.7+/−2.2 vs. 9.6+/−2.1; n=6, P&lt;0.001). Conclusion In summary our observations demonstrate that Cat therapy induces angiogenesis, arteriogenesis and vasculogenesis in the hind-limb ischemia model suggesting that Cat might be a promising agent for therapeutic angiogenesis in peripheral arterial disease.

G-CSF exerts dual effects on endothelial cells—Opposing actions of direct eNOS induction versus indirect CRP elevation

Granulocyte-colony stimulating factor (G-CSF) has been shown to have protective effects in the heart and brain. However, it may also be involved in the acute inflammatory response which may be harmful. The effects of G-CSF on endothelial cells (ECs) and the vasculature are mostly unknown. To study the possible dual effects of G-CSF on ECs, we investigated whether G-CSF induces release of C-reactive protein (CRP) by hepatocytes and whether the direct beneficial effects of G-CSF could protect ECs from the detrimental effects of CRP. G-CSF treatment significantly induced monocytes to produce IL-6, and culture supernatants of G-CSF-stimulated monocytes induced CRP production in hepatocytes. On the other hand, G-CSF directly promoted EC proliferation and migration and reversed the deleterious effects of CRP. In mechanistic analyses, G-CSF increased not only the protein expression of endothelial nitric oxide synthase (eNOS), but also its transcription. Furthermore, it enhanced eNOS phosphorylation and activation, leading to increased production of NO. Thus, G-CSF reversed the attenuated production of NO by CRP. These effects of G-CSF on eNOS transcription, translation, and activation were blunted by the PI3K inhibitor, suggesting that EC protective effects of G-CSF were associated with the activation of the Akt/eNOS pathway. In conclusion, although G-CSF induces an inflammatory reaction leading to CRP production, it has direct beneficial effects protecting ECs from the deleterious effects of CRP through activation of Akt/eNOS pathway, leading to an increase in NO production. Our data suggests that G-CSF may exert dual opposing effects on endothelial cells.

Abstract 327: NADPH Oxidase-dependent Signaling Involved In Endothelial Cell Survival And Proliferation: Role Of Nox2 And Nox4

Objective: Endothelial cells (EC) produce a variety of reactive oxygen species (ROS) which act as mediators of signaling for proliferation, migration, differentiation and cell death. The major source of ROS in EC at rest is the NADPH oxidase enzyme complex. We aimed to determine the roles of the Nox2 and Nox4 catalytic subunits of NADPH oxidase in proliferation and survival of human microvascular endothelial cells (HMEC-1). Methods: Intracellular superoxide was measured by dihydroethidium fluorescence and lucigenin chemiluminescence, and total ROS by dichlorodihydrofluorescein-diacetate assay. Nox4 and Nox2 protein expression was measured by Western blot, and cell proliferation was quantitated by trypan blue exclusion and a tetrazolium-based MTS assay. EC survival was measured by caspase3/7 activity. Results: The expression of Nox4 (but not Nox2) protein, superoxide and total ROS, were all significantly higher (P &lt; 0.05, N = 4) under proliferative conditions (sparse culture or serum addition) than in quiescent (dense culture or serum-starved) cells. Suppression of NADPH oxidase-derived ROS with specific siRNA significantly reduced cell proliferation as shown below. Under proliferative conditions phosphorylation of ERK and Akt were increased. Suppression of Nox4-derived ROS production reduced the phosphorylation of both ERK and Akt, whereas suppression of Nox2 reduced only Akt phosphorylation. Further, suppression of Nox2, but not Nox4, significantly activated caspase3/7 (P &lt; 0.05, N = 4). Thus Nox4-derived ROS act to promote proliferation of EC via ERK and Akt signaling, whereas Nox2 prevents apoptotic signaling via Akt and caspase3/7. Conclusion: Nox isoform-derived ROS act via distinct signaling pathways to promote EC proliferation and survival. Selective modulation of Nox-type NADPH oxidase could be a useful approach for blocking angiogenesis or for therapeutic angiogenesis in chronic ischemia or tissue engineering.

Pravastatin Induces Rat Aortic Endothelial Cell Proliferation and Migration via Activation of PI3K/Akt/mTOR/p70 S6 Kinase Signaling

The HMG-CoA reductase inhibitors (statins) have been shown to exert several vascular protective effects that are not related to changes in cholesterol profile, and these effects of statins are partly caused by the activation of angiogenesis. Endothelial cell (EC) proliferation and migration are crucial events for angiogenesis and statins are known to enhance these events. However, the molecular mechanism by which statins promote EC proliferation and migration is not fully understood. In this study, we show Akt and its downstream target mammalian target of rapamycin (mTOR) play an important role in pravastatin-induced EC proliferation and migration. We found that pravastatin significantly enhanced the proliferation and migration of rat aortic endothelial cells (rAECs). The addition of pravastatin to rAECs resulted in rapid phosphorylation of Akt and p70 S6 kinase (p70S6K). LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), blocked both Akt and p70S6K phosphorylation, whereas rapamycin, a specific inhibitor of mTOR, suppressed only p70S6K phosphorylation induced by pravastatin. Furthermore, both LY294002 and rapamycin inhibited pravastatin-induced rAEC proliferation and migration. Taken together, our findings indicate that pravastatin activates PI3K/Akt/mTOR /p70S6K signaling in this sequential manner and this pathway contributes to pravastatin-induced rAEC proliferation and migration.

Soluble Guanylyl Cyclase Activation Promotes Angiogenesis

Soluble guanylyl cyclase (sGC) is a cGMP-generating enzyme carrying a heme prosthetic group that functions as a nitric oxide (NO) sensor. sGC is present in most cells types, including the vascular endothelium, where its biological functions remain largely unexplored. Herein, we have investigated the role of sGC in angiogenesis and angiogenesis-related properties of endothelial cells (EC). Initially, we determined that sGC was present and enzymatically active in the chicken chorioallantoic membrane (CAM) during the days of maximal angiogenesis. In the CAM, inhibition of endogenous sGC inhibited neovascularization, whereas activation promoted neovessel formation. Using zebrafish as a model for vascular development, we did not detect any effect on vasculogenesis upon sGC blockade, but we did observe an abnormal angiogenic response involving the cranial and intersegmental vessels, as well as the posterior cardinal vein. In vitro, pharmacological activation of sGC or adenovirus-mediated sGC gene transfer promoted EC proliferation and migration, whereas sGC inhibition blocked tube-like network formation. In addition, sGC inhibition blocked the migratory response to vascular EC growth factor. Cells infected with sGC-expressing adenoviruses exhibited increased extracellular signal-regulated kinase 1/2 and p38 MAPK activation that was sensitive to sGC inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, suggesting that these mitogen-activated protein kinases are downstream effectors of sGC in EC. A functional role for p38 in cGMP-stimulated migration was demonstrated using SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole]; pharmacological inhibition of p38 attenuated BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine] and sGC overexpression-induced EC mobilization. We conclude that sGC activation promotes the expression of angiogenesis-related properties by EC and that sGC might represent a novel target to modulate neovessel formation.

Multiply attenuated, self-inactivating lentiviral vectors efficiently transduce human coronary artery cells in vitro and rat arteries in vivo

Endothelial cells (ECs) in normal vessels are poorly transducible by retroviral vectors, which require cell division for gene transduction. Among retroviruses, lentiviruses have the unique ability to integrate their genome into the chromatin of nondividing cells. Here we show that multiply attenuated, self-inactivating, lentiviral vectors transduce both proliferating and growth-arrested human umbilical vein ECs (HUVECs), human coronary artery ECs (HCAECs), and human coronary artery smooth muscle cells (HCASMCs), with high efficacy. Lentiviral vectors containing the enhanced green fluorescence protein (EGFP) transgene driven by either the cytomegalovirus or the elongation factor-1α promoter, but not the phosphoglycerate kinase promoter, directed high-level EGFP expression in endothelial and smooth muscle cells. The endothelium-specific Tie2 promoter also directed transgene expression in ECs. Re-insertion of cis-acting sequences from pol of human immunodeficiency virus type 1 (HIV-1) into the vectors improved transgene expression. A lentiviral vector containing the vascular endothelial growth factor transgene promoted EC proliferation and sprouting in vitro. In vivo gene transfer was studied by lumenal infusion of vector containing solutions into rat carotid arteries. Lentivirus-mediated EGFP gene transfer was observed in ~5% of ECs. Lentiviral vectors containing the LacZ transgene achieved detectable β-galactosidase activity in rat arteries, albeit at a lower level compared with adenoviral vectors. This difference was mainly due to the lower concentration of lentiviral vector preparations. Lentivirus-mediated gene transfer was associated with minimal neointimal hyperplasia and scant inflammatory cell infiltrates in the media and adventitia. These observations indicate that lentiviral vectors may be useful for genetic modifications of vascular cells in vitro and in vivo.