Effects of active and negative mutants of Ras on rat arterial neointima formation

Endothelial mechanobiology

Lining the luminal surface of the vasculature, endothelial cells (ECs) are in direct contact with and differentially respond to hemodynamic forces depending on their anatomic location. Pulsatile shear stress (PS) is defined by laminar flow and is predominantly located in straight vascular regions, while disturbed or oscillatory shear stress (OS) is localized to branch points and bifurcations. Such flow patterns have become a central focus of vascular diseases, such as atherosclerosis, because the focal distribution of endothelial dysfunction corresponds to regions exposed to OS, whereas endothelial homeostasis is maintained in regions defined by PS. Deciphering the mechanotransduction events that occur in ECs in response to differential flow patterns has required the innovation of multidisciplinary approaches in both in vitro and in vivo systems. The results from these studies have identified a multitude of shear stress-regulated molecular networks in the endothelium that are implicated in health and disease. This review outlines the significance of scientific findings generated in collaboration with Dr. Shu Chien.

Delivery of viral vectors for gene therapy in intimal hyperplasia and restenosis in atherosclerotic swine

Cardiovascular diseases including atherosclerosis are a major financial and health burden globally. Inflammation associated with atherosclerosis results in the development of plaques that can rupture causing thrombosis, stroke, or death. The most widely used treatment for the removal of atherosclerotic plaques is percutaneous transluminal coronary angioplasty (PTCA) with or without stenting. Although this is a safer and minimally invasive method, restenosis and intimal hyperplasia after interventional procedure remains a major hurdle and more refined approaches are needed. Studies in large animal models such as pigs have facilitated a greater understanding of the underlying mechanisms of the disease and provided novel targets for therapeutic intervention. In pre-clinical studies, viral vector gene therapy has emerged as a promising option for the reduction and/or prevention of restenosis and intimal hyperplasia. Although studies in animal models have generated promising results, clinical trials have yet to prove the clinical efficacy of gene therapy in coronary artery diseases. In this review, we examined and critically reviewed the most recent advances in viral vector gene therapy obtained from studies using porcine model of atherosclerosis.

Gene Therapy for the Extension of Vein Graft Patency: A Review

The mainstay of treatment for long-segment small-vessel chronic occlusive disease not amenable to endovascular intervention remains surgical bypass grafting using autologous vein. The procedure is largely successful and the immediate operative results almost always favorable. However, the lifespan of a given vein graft is highly variable, and less than 50% will remain primarily patent after 5 years. The slow process of graft malfunction is a result of the vein's chronic maladaptive response to the systemic arterial environment, its primary component being the uncontrolled proliferation of vascular smooth muscle cells (SMCs). It has recently been suggested that this response might be attenuated through pre-implantation genetic modification of the vein, so-called gene therapy for the extension of vein graft patency. Gene therapy seems particularly well suited for the prevention or postponement of vein graft failure since: (1) the stimulation of SMC proliferation appears to largely be an early and transient process, matching the kinetics of current gene transfer technology; (2) most veins are relatively normal and free of disease at the time of bypass allowing for effective gene transfer using a variety of systems; and (3) the target tissue is directly accessible during operation because manipulation and irrigation of the vein is part of the normal workflow of the surgical procedure. This review briefly summarizes the current knowledge of the incidence and basic mechanisms of vein graft failure, the vector systems and molecular targets that have been proposed as possible pre-treatments, the results of experimental genetic modification of vein grafts, and the few available clinical studies of gene therapy for vascular proliferative disorders.

Deletion of Methionine Sulfoxide Reductase A Does Not Affect Atherothrombosis but Promotes Neointimal Hyperplasia and Extracellular Signal-Regulated Kinase 1/2 Signaling

OBJECTIVE

Emerging evidence suggests that methionine oxidation can directly affect protein function and may be linked to cardiovascular disease. The objective of this study was to define the role of the methionine sulfoxide reductase A (MsrA) in models of vascular disease and identify its signaling pathways.

APPROACH AND RESULTS

MsrA was readily identified in all layers of the vascular wall in human and murine arteries. Deletion of the MsrA gene did not affect atherosclerotic lesion area in apolipoprotein E-deficient mice and had no significant effect on susceptibility to experimental thrombosis after photochemical injury. In contrast, the neointimal area after vascular injury caused by complete ligation of the common carotid artery was significantly greater in MsrA-deficient than in control mice. In aortic vascular smooth muscle cells lacking MsrA, cell proliferation was significantly increased because of accelerated G1/S transition. In parallel, cyclin D1 protein and cdk4/cyclin D1 complex formation and activity were increased in MsrA-deficient vascular smooth muscle cell, leading to enhanced retinoblastoma protein phosphorylation and transcription of E2F. Finally, MsrA-deficient vascular smooth muscle cell exhibited greater activation of extracellular signal-regulated kinase 1/2 that was caused by increased activity of the Ras/Raf/mitogen-activated protein kinase signaling pathway.

CONCLUSIONS

Our findings implicate MsrA as a negative regulator of vascular smooth muscle cell proliferation and neointimal hyperplasia after vascular injury through control of the Ras/Raf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase 1/2 signaling pathway.

Ras ssDNA aptamer inhibits vascular smooth muscle cell proliferation and migration through MAPK and PI3K pathways

Proliferation and migration of vascular smooth muscle cells (VSMCs) mediated by Ras proteins are crucial in restenosis following percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG). In this study, a novel, single-stranded DNA (ssDNA) aptamer designated as Ras-a1 with high affinity and specificity to human Ras protein was isolated using systematic evolution of ligands by exponential enrichment. Ras-a1 was delivered into VSMCs by electroporation using one square waveform of 200 V for 20 msec. Proliferation of VSMCs was determined using a cell counting kit‑8 assay, which revealed the maximal inhibitory rate (40%) was obtained at 24 h after Ras-a1 transfection. The migration of VSMCs, determined using a Transwell assay, was significantly inhibited in Rasa1 cells in a time-dependent manner. To investigate the potential mechanisms of transfected Ras-a1 on the migration and proliferation of VSMCs, the phosphorylation of MEK1/2, ERK1/2, and Akt was determined using western blot analysis, which showed that a marked downregulation was observed in the phosphorylation of MEK1/2, ERK1/2, and Akt following the delivery of Ras-a1. This result demonstrated that Ras-a1 inhibits the proliferation and migration of VSMCs by inhibiting the phosphorylation of Ras and interrupting signal transduction in the Ras‑MEK1/2‑ERK1/2 and phosphoinositide-3 kinase/Akt pathways. The novel Ras protein-targeted ssDNA aptamer selected may be applicable for the prevention of restenosis after PCI and CABG.

In vitro selection and identification of ssDNA aptamers recognizing the Ras protein

The aim of this study was to develop high-affinity single-stranded DNA (ssDNA) aptamers that can selectively recognize the protein Ras and can be used as preventive and therapeutic agents for restenosis occurring after coronary surgery or angioplasty. For this purpose, we used the systematic evolution of ligands by exponential enrichment (SELEX) technique, also known as in vitro selection. Using this technique, ssDNA aptamers recognizing the Ras protein were obtained from a synthesized random ssDNA library in vitro. The binding rate and affinity of each aptamer pool, isolated in successive rounds of selection, were measured using ELISA, and the finally selected aptamer pool was cloned and sequenced. The binding affinities of each aptamer in this pool were measured. Their primary and secondary structures were analyzed using the DNAMAN 5.29 software, and the relationship between these structures and corresponding binding affinities was analyzed. The rate of aptamer pool binding to the Ras protein gradually increased from 2.4 to 34.5% along the selection process. Optical density (OD) and equilibrium dissociation constant (Kd) measurements showed that OD gradually increased from 0.220 to 1.080 and Kd decreased from 51.5 to 18.3 nM. The 11th pool of aptamers was selected based on these analyses, and cloning and sequencing of individual aptamers was performed. Secondary structure analysis revealed different conformations, but of a single type: stem‑loop. The aptamer Ra1 showed the highest affinity, with a measured OD of 1.213 and an estimated Kd of 15.3 nM. The binding affinity of the aptamer Ra1 to Ras was dose-dependent. In conclusion, high‑affinity ssDNA aptamers recognizing the Ras protein have been successfully selected. These aptamers may serve in the future as preventive and/or therapeutic agents for restenosis occurring after coronary surgery or angioplasty.

Ras-Mek-Erk signaling regulates Nf1 heterozygous neointima formation

Neurofibromatosis type 1 (NF1) results from mutations in the NF1 tumor-suppressor gene, which encodes neurofibromin, a negative regulator of diverse Ras signaling cascades. Arterial stenosis is a nonneoplastic manifestation of NF1 that predisposes some patients to debilitating morbidity and sudden death. Recent murine studies demonstrate that Nf1 heterozygosity (Nf1(+/-)) in monocytes/macrophages significantly enhances intimal proliferation after arterial injury. However, the downstream Ras effector pathway responsible for this phenotype is unknown. Based on in vitro assays demonstrating enhanced extracellular signal-related kinase (Erk) signaling in Nf1(+/-) macrophages and vascular smooth muscle cells and in vivo evidence of Erk amplification without alteration of phosphatidylinositol 3-kinase signaling in Nf1(+/-) neointimas, we tested the hypothesis that Ras-Erk signaling regulates intimal proliferation in a murine model of NF1 arterial stenosis. By using a well-established in vivo model of inflammatory cell migration and standard cell culture, neurofibromin-deficient macrophages demonstrate enhanced sensitivity to growth factor stimulation in vivo and in vitro, which is significantly diminished in the presence of PD0325901, a specific inhibitor of Ras-Erk signaling in phase 2 clinical trials for cancer. After carotid artery injury, Nf1(+/-) mice demonstrated increased intimal proliferation compared with wild-type mice. Daily administration of PD0325901 significantly reduced Nf1(+/-) neointima formation to levels of wild-type mice. These studies identify the Ras-Erk pathway in neurofibromin-deficient macrophages as the aberrant pathway responsible for enhanced neointima formation.

Heterozygous inactivation of the Nf1 gene in myeloid cells enhances neointima formation via a rosuvastatin-sensitive cellular pathway

Mutations in the NF1 tumor suppressor gene cause Neurofibromatosis type 1 (NF1). Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity. Some NF1 patients develop cardiovascular disease, which represents an underrecognized disease complication and contributes to excess morbidity and mortality. Specifically, NF1 patients develop arterial occlusion resulting in tissue ischemia and sudden death. Murine studies demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) in bone marrow cells enhances neointima formation following arterial injury. Macrophages infiltrate Nf1(+/-) neointimas, and NF1 patients have increased circulating inflammatory monocytes in their peripheral blood. Therefore, we tested the hypothesis that heterozygous inactivation of Nf1 in myeloid cells is sufficient for neointima formation. Specific ablation of a single copy of the Nf1 gene in myeloid cells alone mobilizes a discrete pro-inflammatory murine monocyte population via a cell autonomous and gene-dosage dependent mechanism. Furthermore, lineage-restricted heterozygous inactivation of Nf1 in myeloid cells is sufficient to reproduce the enhanced neointima formation observed in Nf1(+/-) mice when compared with wild-type controls, and homozygous inactivation of Nf1 in myeloid cells amplified the degree of arterial stenosis after arterial injury. Treatment of Nf1(+/-) mice with rosuvastatin, a stain with anti-inflammatory properties, significantly reduced neointima formation when compared with control. These studies identify neurofibromin-deficient myeloid cells as critical cellular effectors of Nf1(+/-) neointima formation and propose a potential therapeutic for NF1 cardiovascular disease.

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.

Exploring the molecular mechanisms of OSU-03012 on vascular smooth muscle cell proliferation

Restenosis is resulted from the proliferation and migration of vascular smooth muscle cells (VSMCs) from the arterial media into the intima within the vessel lumen following percutaneous transluminal coronary angioplasty (PTCA). OSU-03012, a synthetic compound (2-amino-N-{4-[5-(2-phenanthrenyl)-3-(trifluoromethyl)-1H-pyrazol-1-yl]-phenyl} acetamide) acting as a PDK-1 inhibitor, is used as an apoptosis-promoting anticancer drug. However, whether OSU-03012 can inhibit VSMC proliferation and migration following PTCA remains unclear. In this study, we used A10 smooth muscle cells cultured in 10% FBS for stimulating proliferation and evaluated the inhibitory effects of OSU-03012 on cell proliferation and migration. The data demonstrated that OSU-03012 dose-dependently inhibited A10 cell proliferation examined by Trypan blue, MTT and morphological alteration assays, and inhibited the levels of proliferation-related proteins, proliferating cell nuclear antigen (PCNA), phosphorylated ERK examined by western blotting. Additionally, 10 μM OSU-03012 also enhanced apoptosis examined using DAPI assay by regulating apoptosis-related proteins. Furthermore, compared with the control group, A10 cells treated with 10 μM OSU-03012 showed a lower number of migrating cells examined by Boyden Chamber assay, and a dose-dependently reduced NFκB-dependent and interferon-stimulated response element (ISRE) promoter luciferase activities, implying the anti-migration and anti-inflammation effects of OSU03012. Taken together, this study provides insights into the pharmacological mechanisms of OSU-03012 in preventing smooth muscle cell proliferation, migration, and inflammation supporting the novel discovery of OSU-03012 as an adjuvant therapy for balloon injury-induced restenosis.

Basic Science Review: Statin Therapy-Part I: The Pleiotropic Effects of Statins in Cardiovascular Disease

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA-reductase) inhibitors, otherwise known as statins, are currently the medical treatment of choice for hypercholesterolemia. Hypercholesterolemia is a known risk factor for cardiovascular disease, and statin therapy has led to a significant reduction in morbidity and mortality from adverse cardiac events, stroke, and peripheral arterial disease. In addition to achieving a therapeutic decrease in serum cholesterol levels, statin therapy appears to promote other effects that are independent of changes in serum cholesterol. These ‘‘pleiotropic’’ effects include attenuation of vascular inflammation, improved endothelial cell function, stabilization of atherosclerotic plaque, decreased vascular smooth muscle cell migration and proliferation, and inhibition of platelet aggregation. This article is part I of a 2-part review, and it focuses on the pleiotropic effects of statins at the cellular level.

Nf1+/- mice have increased neointima formation via hyperactivation of a Gleevec sensitive molecular pathway

Neurofibromatosis type I (NF1) is a genetic disorder caused by mutations in the NF1 tumor suppressor gene. Neurofibromin is encoded by NF1 and functions as a negative regulator of Ras activity. Somatic mutations in the residual normal NF1 allele within cancers of NF1 patients is consistent with NF1 functioning as a tumor-suppressor. However, the prevalent non-malignant manifestations of NF1, including learning and bone disorders emphasize the importance of dissecting the cellular and biochemical effects of NF1 haploinsufficiency in multiple cell lineages. One of the least studied complications of NF1 involves cardiovascular disorders, including arterial occlusions that result in cerebral and visceral infarcts. NF1 vasculopathy is characterized by vascular smooth muscle cell (VSMC) accumulation in the intima area of vessels resulting in lumen occlusion. We recently showed that Nf1 haploinsufficiency increases VSMC proliferation and migration via hyperactivation of the Ras-Erk pathway, which is a signaling axis directly linked to neointima formation in diverse animal models of vasculopathy. Given this observation, we tested whether heterozygosity of Nf1 would lead to vaso-occlusive disease in genetically engineered mice in vivo. Strikingly, Nf1+/- mice have increased neointima formation, excessive vessel wall cell proliferation and Erk activation after vascular injury in vivo. Further, this effect is directly dependent on a Gleevec sensitive molecular pathway. Therefore, these studies establish an Nf1 model of vasculopathy, which mirrors features of human NF1 vaso-occlusive disease, identifies a potential therapeutic target and provides a platform to further dissect the effect of Nf1 haploinsufficiency in cardiovascular disease.

Neurofibromin is a novel regulator of RAS-induced signals in primary vascular smooth muscle cells

Neurofibromatosis type I (NF1) is a genetic disorder caused by mutations in the NF1 tumor suppressor gene. Neurofibromin is encoded by NF1 and functions as a negative regulator of Ras activity. NF1 patients develop renal artery stenosis and arterial occlusions resulting in cerebral and visceral infarcts. Further, NF1 patients develop vascular neurofibromas where tumor vessels are invested in a dense pericyte sheath. Although it is well established that aberrations in Ras signaling lead to human malignancies, emerging data generated in genetically engineered mouse models now implicate perturbations in the Ras signaling axis in vascular smooth muscular cells (VSMCs) as central to the initiation and progression of neointimal hyperplasia and arterial stenosis. Despite these observations, the function of neurofibromin in regulating VSMC function and how Ras signals are terminated in VSMCs is virtually unknown. Utilizing VSMCs harvested from Nf1+/- mice and primary human neurofibromin-deficient VSMCs, we identify a discrete Ras effector pathway, which is tightly regulated by neurofibromin to limit VSMC proliferation and migration. Thus, these studies identify neurofibromin as a novel regulator of Ras activity in VSMCs and provide a framework for understanding cardiovascular disease in NF1 patients and a mechanism by which Ras signals are attenuated for maintaining VSMC homeostasis in blood vessel walls.

Integrins regulate VE-cadherin and catenins: dependence of this regulation on Src, but not on Ras

Adhesions of cells to extracellular matrix and adjacent cells are mediated by integrins and VE-cadherin, respectively. Although these adhesion processes play crucial roles in vascular cell migration and angiogenesis, it remains unclear as to how they are coordinated to regulate cellular functions. We report here that integrin engagement by treating bovine endothelial aortic cell monolayers with beads coated with fibronectin (Fn) led to disruption of the VE-cadherin-containing adherens junctions. This disruption was accompanied by increases of tyrosine phosphorylation of beta-catenin, gamma-catenin, and p120ctn, as well as the dissociation of alpha-catenin and gamma-catenin from VE-cadherin. We applied a membrane-targeted Src reporter based on the fluorescence resonance energy transfer technique to visualize the dynamic Src activation at subcellular levels in live cells. The integrin engagement induced by Fn-coated beads caused the activation of Src around the beads and at adherens junctions, which are subsequently disrupted. The inhibition of Src with PP1 blocked the effects of integrin engagement on adherens junctions. Although Ras can also modulate adherens junctions, the resulting patterns of phosphorylation and association of junction proteins were distinct from those induced by integrin engagement. The inhibition of Ras by RasN17 did not rescue the disruption of adherens junctions induced by integrin engagement or by Src activation. Integrin engagement by Fn-coated beads also induced a significant alteration of cortical actin filaments at adherens junctions. The results indicate that integrin engagement disrupts VE-cadherin-containing adherens junctions via the activation of Src, but not Ras, possibly as a result of modulation of the actin network.

R-Ras is a global regulator of vascular regeneration that suppresses intimal hyperplasia and tumor angiogenesis

R-Ras is a small GTPase of the Ras family that regulates cell survival and integrin activity. Despite a number of in vitro studies, the in vivo function of R-Ras remains unclear. Here, we used R-Ras-null mice to explore the in vivo function of this small GTPase. Our results show a role for R-Ras as a regulator of vascular differentiation that primarily affects the remodeling of blood vessels. We show that R-Ras-null mice, although otherwise phenotypically normal, mount excessive vascular responses. We found that in vivo R-Ras expression is largely confined to fully differentiated smooth muscle cells, including those of blood vessels, and to endothelial cells. Challenging the R-Ras-null mice with arterial injury or tumor implantation showed exaggerated neointimal thickening in response to the injury and increased angiogenesis in the tumors. In wild-type mice, R-Ras expression was greatly reduced in hyperplastic neointimal smooth muscle cells and in angiogenic endothelial cells. Forced expression of activated R-Ras suppressed mitogenic and invasive activities of growth factor-stimulated vascular cells. These results establish an unexpected role for R-Ras in blood vessel homeostasis and suggest that R-Ras signaling may offer a target for therapeutic intervention in vascular diseases.

The molecular mechanism of actinomycin D in preventing neointimal formation in rat carotid arteries after balloon injury

The pathological mechanism of restenosis is primarily attributed to excessive proliferation of vascular smooth muscle cells (SMC). Actinomycin D has been regarded as a potential candidate to prevent balloon injury-induced neointimal formation. To explore its molecular mechanism in regulating cell proliferation, we first showed that actinomycin D markedly reduced the SMC proliferation via the inhibition of BrdU incorporation at 80 nM. This was further supported by the G1-phase arrest using a flowcytometric analysis. Actinomycin D was extremely potent with an inhibitory concentration IC50 at 0.4 nM, whereas the lethal dose LD50 was at 260 microM. In an in vivo study, the pluronic gel containing 80 nM and 80 microM actinomycin D was applied topically to surround the rat carotid adventitia; the thickness of neointima was substantially reduced (45 and 55%, respectively). The protein expression levels of proliferating cell nuclear antigen (PCNA), focal adhesion kinase (FAK), and Raf were all suppressed by actinomycin D. Extracellular signal-regulated kinases (Erk) involved in cell-cycle arrest were found to increase by actinomycin D. These observations provide a detailed mechanism of actinomycin D in preventing cell proliferation thus as a potential intervention for restenosis.

Pharmacological treatment for prevention of restenosis

Coronary artery disease (CAD) is the leading cause of mortality and morbidity among adults in the Western world. Coronary artery bypass grafting and percutaneous coronary interventions (PCI) have gained widespread acceptance for the treatment of symptomatic CAD. There has been an explosive growth worldwide in the utilisation of PCI, such as balloon angioplasty and stenting, which now accounts for over 50% of coronary revascularisation. Despite the popularity of PCI, the problem of recurrent narrowing of the dilated artery (restenosis) continues to vex investigators. In recent years, significant advances have occurred in the understanding of restenosis. Two processes seem to contribute to restenosis: remodelling (vessel size changes) and intimal hyperplasia (vascular smooth muscle cell [VSMC] proliferation and extracellular matrix [ECM] deposition). Despite considerable efforts, pharmacological approaches to decrease restenosis have been largely unsuccessful and the only currently applied modality to reduce the restenosis rate is stenting. However, stenting only prevents remodelling and does not inhibit intimal hyperplasia. Several potential targets for inhibiting restenosis are currently under investigation including platelet activation, the coagulation cascade, VSMC proliferation and migration, and ECM synthesis. In addition, new approaches for local drug therapy, such as drug eluting stents, are currently being evaluated in preclinical and clinical studies. In this article, we critically review the current status of drugs that are being evaluated for restenosis at various stages of development (in vitro, preclinical animal models and human trials).

Myocyte protection by 10 kD heat shock protein (Hsp10) involves the mobile loop and attenuation of the Ras GTP-ase pathway

Heat shock proteins (hsp), hsp60 and hsp10, are involved in the folding of imported mitochondrial proteins and the refolding of denatured proteins after stress. We examined whether hsp10 can reduce myocyte death by its mitochondrial function or by interacting with cytoplasmic signaling pathways. Overexpression of hsp10 by adenoviral infection decreased myocyte death induced by hydrogen peroxide, sodium cyanide, and simulated ischemia and reoxygenation (SI/RO). We generated an adenoviral vector coding for a temperature-sensitive mutant hsp10 protein (P34H), incapable of cooperatively refolding denatured malate dehydrogenase with hsp60. Overexpression of the hsp10 mutant potentiated SI/RO-induced myocyte death. Analysis of electron transport chain function revealed increased Complex I capacity with hsp10 overexpression, whereas hsp10(P34H) overexpression decreased Complex II capacity. Hsp10 overexpression preserved both Complex I and II function after SI/RO. Examination of the Ras GTP-ase signaling pathway indicated that inhibition of Ras was required for protection by hsp10. Constitutive activation of Ras abolished the effects afforded by hsp10 and hsp10(P34H). Hsp10 overexpression inactivated Raf, ERK, and p90Ribosomal kinase (p90RSK) before and after SI/RO. Our results suggest that complex mechanisms are involved in the protection by hsp10 against SI/RO-induced myocyte death. This mechanism may involve the hsp10 mobile loop and attenuation of the Ras GTP-ase signaling pathway.

Molecular and mechanical bases of focal lipid accumulation in arterial wall

Mechanical forces such as shear stress can modulate gene and protein expressions and hence cellular functions by activating membrane sensors and intracellular signaling. Using cultured endothelial cells, we have shown that laminar shear stress causes a transient increase in monocyte chemotactic protein-1 (MCP-1) expression, which involves the Ras-MAP kinase signaling pathway. We have demonstrated that integrins and the vascular endothelial growth factor receptor Flk-1 can sense shear stress, with integrins being upstream to Flk-1. Other possible membrane components involved in the sensing of shear stress include G-protein coupled receptors, intercellular junction proteins, membrane glycocalyx, and the lipid bilayer. Mechano-transduction involves the participation of a multitude of sensors, signaling molecules, and genes. Microarray analysis has demonstrated that shear stress can upregulate and downregulate different genes. Sustained shear stress downregulates atherogenic genes (e.g., MCP-1 and the genes that facilitate lipid accumulation) and upregulates growth-arrest genes. In contrast, disturbed flow observed at branch points and simulated in step-flow channels causes sustained activation of MCP-1 and the genes facilitating cell turnover and lipid accumulation. These findings provide a molecular basis for the explanation of the preferential localization of atherosclerotic lesions at regions of disturbed flow, such as the arterial branch points. The combination of mechanics and biology (from molecules-cells to organs-systems) can help to elucidate the physiological processes of mechano-chemical transduction and improving the methods of the management of important clinical conditions such as coronary artery disease.

Grb2 is required for the development of neointima in response to vascular injury

OBJECTIVE

Neointima formation occurs in arteries in response to mechanical or chemical injury and is responsible for substantial morbidity. In this work, the role of the intracellular linker protein Grb2 in the pathogenesis of neointima formation was examined. Grb2 is a critical signaling protein that facilitates the activation of the small GTPase ras by receptor tyrosine kinases.

METHODS AND RESULTS

Cultured rat aortic smooth muscle cells were treated with an antisense morpholino to Grb2 and these cells showed a reduced proliferative response to platelet-derived growth factor stimulation. Grb2-/- mice do not survive embryonic development. Grb2+/- mice appear normal at birth and are fertile but have defective signaling in several tissues. Cultured smooth muscle cells derived from Grb2+/- mice grew at a much slower rate than cells derived from Grb2+/+ mice. Grb2+/- and Grb2+/+ mice were subjected to carotid injury. After 21 days, Grb2+/+ mice developed robust neointima formation that, in some cases, resulted in an occlusive lesion. In contrast, Grb2+/- mice were resistant to the development of neointima

CONCLUSIONS

Grb2 is an essential component of the signaling cascade resulting in neointima formation after arterial injury.

Signal transduction in matrix contraction and the migration of vascular smooth muscle cells in three-dimensional matrix

The interaction of vascular smooth muscle cells (SMCs) and extracellular matrix plays important roles in vascular remodeling. We investigated the signaling pathways involved in SMC-induced matrix contraction and SMC migration in three-dimensional (3D) collagen matrix. Matrix contraction is inhibited by the disruption of actin filaments but not microtubules. Therefore, we investigated the roles of signaling pathways related to actin filaments in matrix contraction. SMC-induced matrix contraction was markedly blocked (-80%) by inhibiting the Rho-p160ROCK pathway and myosin light chain kinase, and was decreased to a lesser extent (30-40%) by a negative mutant of Rac and inhibitors of phosphatidylinositol 3-kinase (PI 3-kinase) or p38 mitogen-activated protein kinase (MAPK), but it was not affected by the inhibition of Ras and Cdc42-Wiskott-Aldrich syndrome protein (WASP) pathways. Inhibition of extracellular-signal-regulated kinase (ERK) decreased SMC-induced matrix contraction by only 15%. The migration speed and persistence of SMCs in the 3D matrix were decreased by the inhibition of p160ROCK, PI 3-kinase, p38 MAPK or WASP to different extents, and p160ROCK inhibitor had the strongest inhibitory effect. Our results suggest that the SMC-induced matrix contraction and the migration of SMCs in 3D matrix share some signaling pathways leading to force generation at cell-matrix adhesions and that various signaling pathways have different relative importance in the regulations of these processes in SMCs.

A chemically modified dextran inhibits smooth muscle cell growth in vitro and intimal in stent hyperplasia in vivo

PURPOSE

Intimal smooth muscle cell (SMC) hyperplasia is a main component of the arterial wall response to injury. We have investigated the capacity of a water-soluble nonanticoagulant functionalized dextran (E9) in inhibition of SMC growth in vitro and in vivo.

METHODS

E9 was obtained with chemical substitutions with anionic and hydrophobic groups on the dextran backbone. SMC proliferation (cell counting, thymidine uptake, cell cycle analysis) was followed in culture in the presence of E9. Western blot analysis against phosphorylated mitogen-activated protein kinase (MAPK), extracellular signal-regulated protein kinase 1/2, and assessment of MAPK activity on serum-stimulated SMCs also were investigated. Binding/displacement experiments, electron microscopy, and cell fractionations were used to follow the binding and internalization of radiolabeled and fluorescentlabeled E9. New Zealand white rabbit iliac arteries were injured with balloon dilatation and stent deployment. Animals were treated for 14 days with saline solution or E9 (5 mg/kg injected subcutaneously, twice daily). Morphometric analyses were carried out in each group (n = 6 arteries, 18 sections).

RESULTS

Nonanticoagulant E9 inhibited SMC proliferation in vitro. Tyrosine phosphorylation of MAPK 1/2 and MAPK activity were inhibited with E9 within 5 minutes of incubation. The binding and rapid cytoplasmic internalization of the synthetic compound was evidenced, but, in contrast to heparin, we did not detect any nuclear localization of the antiproliferative E9. In the in vivo model, qualitative modifications of neointimal structure with a thinner fibrocellular neointima were noticed after E9 treatment. Morphometric analyses of stented arteries in E9-treated animals indicated an important reduction (P <.01) of intimal growth: 33% and 45% for intimal area and intima/media ratio, respectively.

CONCLUSION

Cytoplasmic internalization of the synthetic polysaccharide correlated to the SMC growth inhibition that involved the MAPK pathway. In vivo inhibition of intimal instent hyperplasia with this nonanticoagulant derived dextran is shown providing a new candidate for a potential selective treatment of SMC proliferation.

Inhibition of neointimal formation in porcine coronary artery by a Ras mutant

BACKGROUND

Therapeutic approaches to reduce the neointimal formation caused by balloon injury have been focused mainly on experimental models of restenosis in the rat carotid artery. However, restenosis in rat carotid artery may not replicate the coronary arterial responses to injury in larger animals and humans.

METHODS

In this study, we used pig coronary arteries as an animal model to evaluate the preventive effects of a virus-mediated dominant negative mutant RasN17 on balloon injury-induced restenosis. The viral particles were delivered to the balloon-injured coronary arteries via a dispatch catheter to keep the virus in a confined arterial segment for 10 min to reach optimal transfection. Six weeks after balloon injury, the pigs were sacrificed and the left anterior descending arteries were isolated for histological analysis.

RESULTS

Neointima formation was prominent in the group receiving balloon injury as compared with the uninjured controls. A remodeling process with migration of collagen was also found in the injured coronary arteries. The application of AdRasN17 led to a 56% decrease in neointima formation and a 75% increase in lumen size, as compared with the balloon-injured vessels treated with AdLacZ control.

CONCLUSIONS

These results suggest that AdRasN17 is an effective therapeutic gene in preventing balloon injury-induced neointimal formation in pig coronary arteries.

LDL-activated p38 in endothelial cells is mediated by Ras

Endothelial dysfunction is a major atherogenic proinflammatory event. LDL causes the activation and phenotypic changes of cultured vascular endothelial cells (ECs). We previously reported that LDL activates c-Jun and AP-1 in ECs. In this study, we demonstrated that p38-ATF-2 is activated by LDL in human ECs and that this activation is mediated by Ras. When ECs are incubated with LDL in pathophysiological concentrations, the p38-mediated ATF-2 phosphorylation and ATF-2 transactivation are increased in a time- and dose-dependent manner. To elucidate the upstream mechanism in LDL-activated p38 in ECs, we demonstrate that LDL increases Ras translocation from the cytoplasm to the cellular membrane, with concurrent increases in Ras binding activity to GST-Raf-1. Overexpression of RasN17, a dominant negative mutant of Ras, attenuates the LDL-induced increases in (1) phosphorylation of ATF-2, (2) phosphorylation of c-Jun, (3) AP-1 binding, and (4) AP-1-driven luciferase activity. To study the effect of p38 in the regulation of an LDL targeting gene, we show that a specific p38 inhibitor attenuates LDL-induced E-selectin at the mRNA level. Thus, LDL activates both p38 and JNK signaling pathways through Ras activation, and furthermore, these events may play an important role in LDL-induced endothelial activation.