Chimera analysis supports a predominant role of PDGFRbeta in promoting smooth-muscle cell chemotaxis after arterial injury

Oxidative stress: An essential factor in the process of arteriovenous fistula failure

For more than half a century, arteriovenous fistula (AVFs) has been recognized as a lifeline for patients requiring hemodialysis (HD). With its higher long-term patency rate and lower probability of complications, AVF is strongly recommended by guidelines in different areas as the first choice for vascular access for HD patients, and its proportion of application is gradually increasing. Despite technological improvements and advances in the standards of postoperative care, many deficiencies are still encountered in the use of AVF related to its high incidence of failure due to unsuccessful maturation to adequately support HD and the development of neointimal hyperplasia (NIH), which narrows the AVF lumen. AVF failure is linked to the activation and migration of vascular cells and the remodeling of the extracellular matrix, where complex interactions between cytokines, adhesion molecules, and inflammatory mediators lead to poor adaptive remodeling. Oxidative stress also plays a vital role in AVF failure, and a growing amount of data suggest a link between AVF failure and oxidative stress. In this review, we summarize the present understanding of the pathophysiology of AVF failure. Furthermore, we focus on the relation between oxidative stress and AVF dysfunction. Finally, we discuss potential therapies for addressing AVF failure based on targeting oxidative stress.

Direct Impact of Human Platelets on the Development of Transplant Arteriosclerosis

BACKGROUND

Platelets play an important role in the pathogenesis of inflammatory and proliferative vascular changes. The aim of this study was to investigate whether human platelets are able to induce transplant arteriosclerosis in a humanized C57/Bl6-Rag2-/-γc-/- mouse xenograft model.

METHODS

Nonactivated and in vitro-activated human platelets were analyzed and phenotyped for surface markers by flow cytometry. Side branches of human mammary arteries were implanted into the infrarenal aorta of recipients, followed by daily application of human platelets and histological analyzed on day 30 after transplantation.

RESULTS

Human platelets collected by apheresis had low levels of platelet activation markers. However, after in vitro activation, expression was markedly increased. Sixty minutes after injection in recipient mice, nonactivated human platelets become significantly activated. Increased adhesion of platelets to the vascular endothelium was detected by in vivo fluorescence microscopy. After intravenous injection of nonactivated or activated platelets, human xenografts showed pronounced intimal proliferation. Immunohistological analysis showed that the group treated with activated human platelets exhibited significantly increased intragraft protein expression of intracellular adhesion molecule-1 and platelet-derived growth factor receptor beta and smooth muscle cell migration into the neointima.

CONCLUSIONS

These data demonstrate that an isolated daily application of both in vivo- and in vitro-activated human platelets results in the development of transplant arteriosclerosis in a humanized mouse transplantation model.

CFTR Suppresses Neointimal Formation Through Attenuating Proliferation and Migration of Aortic Smooth Muscle Cells

ABSTRACT

Cystic fibrosis transmembrane conductance regulator (CFTR) plays important roles in arterial functions and the fate of cells. To further understand its function in vascular remodeling, we examined whether CFTR directly regulates platelet-derived growth factor-BB (PDGF-BB)-stimulated vascular smooth muscle cells (VSMCs) proliferation and migration, as well as the balloon injury-induced neointimal formation. The CFTR adenoviral gene delivery was used to evaluate the effects of CFTR on neointimal formation in a rat model of carotid artery balloon injury. The roles of CFTR in PDGF-BB-stimulated VSMC proliferation and migration were detected by mitochondrial tetrazolium assay, wound healing assay, transwell chamber method, western blot, and qPCR. We found that CFTR expression was declined in injured rat carotid arteries, while adenoviral overexpression of CFTR in vivo attenuated neointimal formation in carotid arteries. CFTR overexpression inhibited PDGF-BB-induced VSMC proliferation and migration, whereas CFTR silencing caused the opposite results. Mechanistically, CFTR suppressed the phosphorylation of PDGF receptor β, serum and glucocorticoid-inducible kinase 1, JNK, p38 and ERK induced by PDGF-BB, and the increased mRNA expression of matrix metalloproteinase-9 and MMP2 induced by PDGF-BB. In conclusion, our results indicated that CFTR may attenuate neointimal formation by suppressing PDGF-BB-induced activation of serum and glucocorticoid-inducible kinase 1 and the JNK/p38/ERK signaling pathway.

Phenotypic switch of smooth muscle cells in paediatric chronic intestinal pseudo-obstruction syndrome

Smooth Muscle Cells (SMC) are unique amongst all muscle cells in their capacity to modulate their phenotype. Indeed, SMCs do not terminally differentiate but instead harbour a remarkable capacity to dedifferentiate, switching between a quiescent contractile state and a highly proliferative and migratory phenotype, a quality often associated to SMC dysfunction. However, phenotypic plasticity remains poorly examined in the field of gastroenterology in particular in pathologies in which gut motor activity is impaired. Here, we assessed SMC status in biopsies of infants with chronic intestinal pseudo-obstruction (CIPO) syndrome, a life-threatening intestinal motility disorder. We showed that CIPO-SMCs harbour a decreased level of contractile markers. This phenotype is accompanied by an increase in Platelet-Derived Growth Factor Receptor-alpha (PDGFRA) expression. We showed that this modulation occurs without origin-related differences in CIPO circular and longitudinal-derived SMCs. As we characterized PDGFRA as a marker of digestive mesenchymal progenitors during embryogenesis, our results suggest a phenotypic switch of the CIPO-SMC towards an undifferentiated stage. The development of CIPO-SMC culture and the characterization of SMC phenotypic switch should enable us to design therapeutic approaches to promote SMC differentiation in CIPO.

Reactive Oxygen Species: Modulators of Phenotypic Switch of Vascular Smooth Muscle Cells

Reactive oxygen species (ROS) are natural byproducts of oxygen metabolism in the cell. At physiological levels, they play a vital role in cell signaling. However, high ROS levels cause oxidative stress, which is implicated in cardiovascular diseases (CVD) such as atherosclerosis, hypertension, and restenosis after angioplasty. Despite the great amount of research conducted to identify the role of ROS in CVD, the image is still far from being complete. A common event in CVD pathophysiology is the switch of vascular smooth muscle cells (VSMCs) from a contractile to a synthetic phenotype. Interestingly, oxidative stress is a major contributor to this phenotypic switch. In this review, we focus on the effect of ROS on the hallmarks of VSMC phenotypic switch, particularly proliferation and migration. In addition, we speculate on the underlying molecular mechanisms of these cellular events. Along these lines, the impact of ROS on the expression of contractile markers of VSMCs is discussed in depth. We conclude by commenting on the efficiency of antioxidants as CVD therapies.

Nilotinib attenuates endothelial dysfunction and liver damage in high-cholesterol-fed rabbits

Nilotinib is an oral potent tyrosine kinase inhibitor that has diverse biological activities. However, its effects on hypercholesterolemia and associated disorders have not been studied yet. The present study explored the effect of nilotinib on atherosclerosis progression, endothelial dysfunction, and hyperlipidemia-associated hepatic injury in high-cholesterol (HC)-fed rabbits. Rabbits were classified into four groups: control, nilotinib, HC, and HC + nilotinib groups. Rabbits were fed either a regular diet or an HC-enriched diet for 8 weeks. By the end of the eighth week, blood and tissue samples were obtained for biochemical, histological, immunohistochemical, and in vitro analyses. Results indicated that the HC diet induced a significant elevation in the serum lipid parameters (triglycerides, total cholesterol, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol), lactate dehydrogenase, and nitric oxide content. Endothelial dysfunction was evident through the impairment of acetylcholine-induced relaxation of isolated aortas and the histopathological lesions of the aortic specimen. Moreover, HC significantly increased serum malondialdehyde. Liver damage was clear through increase in serum transaminases and alkaline phosphatase, and it was further supported by histopathological examination. HC increased the expression of platelet-derived growth factor receptor (PDGFR)-B in both aorta and liver tissues. Interestingly, nilotinib administration retarded atherosclerosis progression and attenuated all of the aforementioned parameters. These data suggest that nilotinib may counteract atherosclerosis development, vascular dysfunction, and hepatic damage in HC-fed rabbits through interfering with PDGF-B.

Redox regulation of vascular remodeling

Vascular remodeling is a dynamic process of structural and functional changes in response to biochemical and biomechanical signals in a complex in vivo milieu. While inherently adaptive, dysregulation leads to maladaptive remodeling. Reactive oxygen species participate in homeostatic cell signaling in tightly regulated- and compartmentalized cellular circuits. It is well established that perturbations in oxidation-reduction (redox) homeostasis can lead to a state of oxidative-, and more recently, reductive stress. We provide an overview of the redox signaling in the vasculature and review the role of oxidative- and reductive stress in maladaptive vascular remodeling. Particular emphasis has been placed on essential processes that determine phenotype modulation, migration and fate of the main cell types in the vessel wall. Recent advances in systems biology and the translational opportunities they may provide to specifically target the redox pathways driving pathological vascular remodeling are discussed.

The matricellular protein Cyr61 is a key mediator of platelet-derived growth factor-induced cell migration

Platelet-derived growth factor (PDGF), a potent chemoattractant, induces cell migration via the MAPK and PI3K/Akt pathways. However, the downstream mediators are still elusive. In particular, the role of extracellular mediators is largely unknown. In this study, we identified the matricellular protein Cyr61, which is de novo synthesized in response to PDGF stimulation, as the key downstream mediator of the ERK and JNK pathways, independent of the p38 MAPK and AKT pathways, and, thereby, it mediates PDGF-induced smooth muscle cell migration but not proliferation. Our results revealed that, when Cyr61 was newly synthesized by PDGF, it was promptly translocated to the extracellular matrix and physically interacted with the plasma membrane integrins α6β1 and αvβ3. We further demonstrate that Cyr61 and integrins are integral components of the PDGF signaling pathway via an "outside-in" signaling route to activate intracellular focal adhesion kinase (FAK), leading to cell migration. Therefore, this study provides the first evidence that the PDGF-induced endogenous extracellular matrix component Cyr61 is a key mediator in modulating cell migration by connecting intracellular PDGF-ERK and JNK signals with integrin/FAK signaling. Therefore, extracellular Cyr61 convergence with growth factor signaling and integrin/FAK signaling is a new concept of growth factor-induced cell migration. The discovered signaling pathway may represent an important therapeutic target in growth factor-mediated cell migration/invasion-related vascular diseases and tumorigenesis.

Mitochondrial fission induced by platelet-derived growth factor regulates vascular smooth muscle cell bioenergetics and cell proliferation

Vascular smooth muscle cells (VSMCs) develop a highly proliferative and synthetic phenotype in arterial diseases. Because such phenotypic changes are likely integrated with the energetic state of the cell, we hypothesized that changes in cellular metabolism regulate VSMC plasticity. VSMCs were exposed to platelet-derived growth factor-BB (PDGF) and changes in mitochondrial morphology, proliferation, contractile protein expression, and mitochondrial metabolism were examined. Exposure of VSMCs to PDGF resulted in mitochondrial fragmentation and a 50% decrease in the abundance of mitofusin 2. Synthetic VSMCs demonstrated a 20% decrease in glucose oxidation, which was accompanied by an increase in fatty acid oxidation. Results of mitochondrial function assays in permeabilized cells showed few changes due to PDGF treatment in mitochondrial respiratory chain capacity and coupling. Treatment of VSMCs with Mdivi-1—an inhibitor of mitochondrial fission—inhibited PDGF-induced mitochondrial fragmentation by 50% and abolished increases in cell proliferation; however, it failed to prevent PDGF-mediated activation of autophagy and removal of contractile proteins. In addition, treatment with Mdivi-1 reversed changes in fatty acid and glucose oxidation associated with the synthetic phenotype. These results suggest that changes in mitochondrial morphology and bioenergetics underlie the hyperproliferative features of the synthetic VSMC phenotype, but do not affect the degradation of contractile proteins. Mitochondrial fragmentation occurring during the transition to the synthetic phenotype could be a therapeutic target for hyperproliferative vascular disorders.

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PDGF promotes mitochondrial fragmentation in vascular smooth muscle cells.

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PDGF increases metabolic reliance on fatty acids.

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Mitochondrial fragmentation regulates proliferation and bioenergetics.

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PDGF-induced bioenergetic and autophagic responses regulate de-differentiation.

PDGF-mediated autophagy regulates vascular smooth muscle cell phenotype and resistance to oxidative stress

Vascular injury and chronic arterial diseases result in exposure of VSMCs (vascular smooth muscle cells) to increased concentrations of growth factors. The mechanisms by which growth factors trigger VSMC phenotype transitions remain unclear. Because cellular reprogramming initiated by growth factors requires not only the induction of genes involved in cell proliferation, but also the removal of contractile proteins, we hypothesized that autophagy is an essential modulator of VSMC phenotype. Treatment of VSMCs with PDGF (platelet-derived growth factor)-BB resulted in decreased expression of the contractile phenotype markers calponin and α-smooth muscle actin and up-regulation of the synthetic phenotype markers osteopontin and vimentin. Autophagy, as assessed by LC3 (microtubule-associated protein light chain 3 α; also known as MAP1LC3A)-II abundance, LC3 puncta formation and electron microscopy, was activated by PDGF exposure. Inhibition of autophagy with 3-methyladenine, spautin-1 or bafilomycin stabilized the contractile phenotype. In particular, spautin-1 stabilized α-smooth muscle cell actin and calponin in PDGF-treated cells and prevented actin filament disorganization, diminished production of extracellular matrix, and abrogated VSMC hyperproliferation and migration. Treatment of cells with PDGF prevented protein damage and cell death caused by exposure to the lipid peroxidation product 4-hydroxynonenal. The results of the present study demonstrate a distinct form of autophagy induced by PDGF that is essential for attaining the synthetic phenotype and for survival under the conditions of high oxidative stress found to occur in vascular lesions.

Tissue transglutaminase promotes PDGF/PDGFR-mediated signaling and responses in vascular smooth muscle cells

Although the pivotal role of platelet derived growth factor (PDGF)-mediated signaling in vascular diseases was demonstrated, the pathophysiological mechanisms driving its over-activation remain incompletely understood. Tissue transglutaminase (tTG) is a multifunctional protein expressed in the vasculature, including smooth muscle cells (SMCs), and implicated in several vascular pathologies. The goal of this study is to define the regulation of PDGF-BB/PDGFRβ-induced signaling pathways and cell responses by tTG in vascular SMCs. We find that in human aortic SMCs, shRNA-mediated depletion and over-expression of tTG reveals its ability to down-regulate PDGFRβ levels and induce receptor clustering. In these cells, tTG specifically amplifies the activation of PDGFRβ and its multiple downstream signaling targets in response to PDGF-BB. Furthermore, tTG promotes dedifferentiation and increases survival, proliferation, and migration of human aortic SMCs mediated by this growth factor. Finally, PDGF-BB stimulates tTG expression in human aortic SMCs in culture and in the blood vessels in response to injury. Together, our results show that tTG in vascular SMCs acts as a principal enhancer within the PDGF-BB/PDGFRβ signaling axis involved in phenotypic modulation of these cells, thereby suggesting a novel role for this protein in the progression of vascular diseases.

Characterization of Pdgfrb-Cre transgenic mice reveals reduction of ROSA26 reporter activity in remodeling arteries

With the intention to modulate gene expression in vascular mural cells of remodeling vessels, we generated and characterized transgenic mouse lines with Cre recombinase under the control of the platelet-derived growth factor receptor-β promoter, referred to as Tg(Pdgfrb-Cre)(35Vli) . Transgenic mice were crossed with the Gt(ROSA)26Sor(tm1Sor) strain and examined for Cre activation by β-galactosidase activity, which was compared with endogenous Pdgfrb expression. In addition, Pdgfrb-Cre mice were used to drive expression of a conditional myc-tagged Cthrc1 transgene. There was good overlap of β-galactosidase activity with endogenous Pdgfrb immunoreactivity. However, dedifferentiation of vascular mural cells induced by carotid artery ligation revealed a dramatic discrepancy between ROSA26 reporter activity and Pdgfrb promoter driven Cre dependent myc-tagged Cthrc1 transgene expression. Our studies demonstrate the capability of the Pdgfrb-Cre mouse to drive conditional transgene expression as a result of prior Cre-mediated recombination in tissues known to express endogenous Pdgfrb. In addition, the study shows that ROSA26 promoter driven reporter mice are not suitable for lineage marking of smooth muscle in remodeling blood vessels.

Mouse chimeras as a system to investigate development, cell and tissue function, disease mechanisms and organ regeneration

Chimeras are organisms composed of at least two genetically distinct cell lineages originating from different zygotes. In the laboratory, mouse chimeras can be produced experimentally; various techniques allow combining different early stage mouse embryos with each other or with pluripotent stem cells. Identification of the progeny of the different lineages in chimeras permits to follow cell fate and function, enabling correlation of genotype with phenotype. Mouse chimeras have become a tool to investigate critical developmental processes, including cell specification, differentiation, patterning, and the function of specific genes. In addition, chimeras can also be generated to address biological processes in the adult, including mechanisms underlying diseases or tissue repair and regeneration. This review summarizes the different types of chimeras and how they have been generated and provides examples of how mouse chimeras offer a unique and powerful system to investigate questions pertaining to cell and tissue function in the developing and adult organism.

Redox control of vascular smooth muscle migration

Vascular smooth muscle cell migration is important during vascular development and contributes to lesion formation in the adult vasculature. The mechanisms regulating migration of this cell type are therefore of great interest. Recent work has shown that reactive oxygen species (ROS) derived from NADPH oxidases are important mediators of promigratory signaling pathways. ROS regulate the intracellular signals responsible for lamellipodia formation, actin cytoskeleton remodeling, focal adhesion turnover, and contraction of the cell body. In addition, they contribute to matrix remodeling, a critical step to initiate and support vascular smooth muscle cell motility. Despite these recent advances in our understanding of the redox mechanisms that contribute to migration, additional work is needed to evaluate fully the potential of ROS-sensitive molecular signals as therapeutic targets to prevent inappropriate smooth muscle cell migration.

Integrin-linked kinase functions as a downstream signal of platelet-derived growth factor to regulate actin polymerization and vascular smooth muscle cell migration

Background

Vascular smooth muscle cell migration and accumulation in response to growth factors extensively contribute to the development of intimal thickening within the vessel wall. Cumulative evidence has shown that actin cytoskeleton polymerization and rearrangement are critical steps during cellular spreading and migration. Integrin-linked kinase, an intracellular serine/threonine kinase, is a cytoplasmic interactor of integrin beta-1 and beta-3 receptors regulating cell-cell and/or cell-extracellular matrix interaction, cell contraction, extracellular matrix modification, and cell spreading and migration in response to various stimuli. However, the regulatory role of ILK during vascular smooth muscle cell migration and the importance of integrin signaling in occlusive vascular diseases are not yet fully elucidated.

Results

In the present study, we report that integrin-linked kinase controls mouse aortic smooth muscle cell migration in response to platelet-derived growth factor. We have also identified p38 mitogen activated protein kinase as a downstream signaling pathway of the integrin-linked kinase that regulates platelet-derived growth factor-induced actin polymerization and smooth muscle cell migration.

Conclusion

This study will provide new insights into the potential therapeutic value of modulating integrin signaling in an attempt to block or delay smooth muscle cell migration and the progression of vascular diseases.

Metallothionein enhances angiogenesis and arteriogenesis by modulating smooth muscle cell and macrophage function

OBJECTIVE

In a previous study we identified metallothionein (MT) as a candidate gene potentially influencing collaterogenesis. In this investigation, we determined the effect of MT on collaterogenesis and examined the mechanisms contributing to the effects we found.

METHODS AND RESULTS

Collateral blood flow recovery was assessed using laser Doppler perfusion imaging, and angiogenesis was measured using a Matrigel plug assay. Smooth muscle cells were isolated from MT knockout (KO) mice for functional assays. Gene expression of matrix metalloproteinase-9, platelet-derived growth factor, vascular endothelial growth factor, and Fat cadherin in smooth muscle cells was measured by real-time polymerase chain reaction, and protein levels of vascular endothelial growth factor and matrix metalloproteinase-9 were determined using enzyme-linked immunosorbent assay and Western blot. CD11b(+) macrophages were tested for invasiveness using a real-time impedance assay. Both flow recovery and angiogenesis were impaired in MT KO mice. Proliferation, migration, and invasion were decreased in MT KO smooth muscle cells, and matrix metalloproteinase-9, platelet-derived growth factor, and vascular endothelial growth factor expression were also decreased, whereas FAT-1 cadherin expression was elevated. MT KO CD11b(+) cells were more invasive than wild-type cells.

CONCLUSIONS

MT plays an important role in collateral flow recovery and angiogenesis, an activity that appears to be mediated, in part, by the effects of MT on the functionality of 3 cell types essential for these processes: endothelial cells, smooth muscle cells, and macrophages.

Role of platelet-derived growth factors in physiology and medicine

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have served as prototypes for growth factor and receptor tyrosine kinase function for more than 25 years. Studies of PDGFs and PDGFRs in animal development have revealed roles for PDGFR-alpha signaling in gastrulation and in the development of the cranial and cardiac neural crest, gonads, lung, intestine, skin, CNS, and skeleton. Similarly, roles for PDGFR-beta signaling have been established in blood vessel formation and early hematopoiesis. PDGF signaling is implicated in a range of diseases. Autocrine activation of PDGF signaling pathways is involved in certain gliomas, sarcomas, and leukemias. Paracrine PDGF signaling is commonly observed in epithelial cancers, where it triggers stromal recruitment and may be involved in epithelial-mesenchymal transition, thereby affecting tumor growth, angiogenesis, invasion, and metastasis. PDGFs drive pathological mesenchymal responses in vascular disorders such as atherosclerosis, restenosis, pulmonary hypertension, and retinal diseases, as well as in fibrotic diseases, including pulmonary fibrosis, liver cirrhosis, scleroderma, glomerulosclerosis, and cardiac fibrosis. We review basic aspects of the PDGF ligands and receptors, their developmental and pathological functions, principles of their pharmacological inhibition, and results using PDGF pathway-inhibitory or stimulatory drugs in preclinical and clinical contexts.

High glucose-induced upregulation of Rho/Rho-kinase via platelet-derived growth factor receptor-beta increases migration of aortic smooth muscle cells

Small GTPase Rho and Rho-kinase, the target protein of Rho, play an important role in atherosclerosis. In diabetic macroangiopathy, one of the major pathogenic changes is the migration of vascular smooth muscle cells (SMCs). Platelet-derived growth factor (PDGF) is known to stimulate the migration of SMCs. In the current study, we have investigated the involvement of the Rho/Rho-kinase pathway in the increased migration of cultured human aortic SMCs under a high glucose condition. PDGF stimulated the activation and the protein level of Rho. The protein level of PDGF receptor-beta (PDGFR-beta) was increased under the high glucose condition concomitant with the increased protein level and activation of Rho. The increased protein level and activity of Rho were suppressed by an anti-PDGF neutralizing antibody or a PDGFR-beta inhibitor, AG1433, under the high glucose condition. Furthermore, high glucose significantly increased the migration of SMCs. A specific inhibitor of Rho-kinase, Y-27632, or anti-PDGF neutralizing antibody inhibited increased migration of SMCs under the high glucose condition. The protein levels of Rho were increased in aortae of diabetic rats, which were abolished by the treatment of Imatinib, the inhibitor of PDGFR. These observations indicate that the upregulation of the PDGFR-beta / Rho / Rho-kinase pathway increases the migration of SMCs under the high glucose condition. The inhibition of Rho/Rho-kinase may be a new target for the treatment of diabetic macroangiopathy.

Progenitor cells and vascular disease

Vascular progenitor cells have been the focus of much attention in recent years; both from the point of view of their pathophysiological roles and their potential as therapeutic agents. However, there is as yet no definitive description of either endothelial or vascular smooth muscle progenitor cells. Cells with the ability to differentiate into mature endothelial and vascular smooth muscle reportedly reside within a number of different tissues, including bone marrow, spleen, cardiac muscle, skeletal muscle and adipose tissue. Within these niches, vascular progenitor cells remain quiescent, until mobilized in response to injury or disease. Once mobilized, these progenitor cells enter the circulation and migrate to sites of damage, where they contribute to the remodelling process. It is generally perceived that endothelial progenitors are reparative, acting to restore vascular homeostasis, while smooth muscle progenitors contribute to pathological changes. Indeed, the number of circulating endothelial progenitor cells inversely correlates with exposure to cardiovascular risk factors and numbers of animal models and human studies have demonstrated therapeutic roles for endothelial progenitor cells, which can be enhanced by manipulating them to overexpress vasculo-protective genes. It remains to be determined whether smooth muscle progenitor cells, which are less well studied than their endothelial counterparts, can likewise be manipulated to achieve therapeutic benefit. This review outlines our current understanding of endothelial and smooth muscle progenitor cell biology, their roles in vascular disease and their potential as therapeutic agents.

The cell cycle: a critical therapeutic target to prevent vascular proliferative disease

Percutaneous coronary intervention is the preferred revascularization approach for most patients with coronary artery disease. However, this strategy is limited by renarrowing of the vessel by neointimal hyperplasia within the stent lumen (in-stent restenosis). Vascular smooth muscle cell proliferation is a major component in this healing process. This process is mediated by multiple cytokines and growth factors, which share a common pathway in inducing cell proliferation: the cell cycle. The cell cycle is highly regulated by numerous mechanisms ensuring orderly and coordinated cell division. The present review discusses current concepts related to regulation of the cell cycle and new therapeutic options that target aspects of the cell cycle.

Pharmacological inhibition of the vitronectin receptor abrogates PDGF-BB-induced hepatic stellate cell migration and activation in vitro

BACKGROUND/AIMS

Activated hepatic stellate cells (HSC) play a central role in the development of liver fibrosis. Platelet-derived growth factor (PDGF)-BB and the integrin alphavbeta3 mediate mesenchymal cell migration and proliferation. However, their contribution and interaction during fibrogenic activation of HSC remains unclear. To this aim we investigated if PDFGF-BB and alphavbeta3 interact, and how far small molecular inhibitors of alphavbeta3 modulate PDGF-BB and serum-induced migration, proliferation and fibrogenic activation of HSC.

METHODS

Rat and human HSC were subjected to migration and proliferation assays in the presence or absence of a peptide or a nonpeptide alphavbeta3 inhibitor. Activation of mitogen-activated protein kinases (ERK1/2, p38), Akt, focal adhesion kinase (FAK), paxillin and beta3 integrin was evaluated by phospho-specific Western blotting. Fibrosis related transcripts were determined by quantitative real-time PCR.

RESULTS

PDGF-BB-stimulated HSC migration which was blocked dose-dependently by the alphavbeta3 antagonists, with complete inhibition at 10(-6)M. alphavbeta3 blockage did not affect cell viability or proliferation, while it decreased phosphorylation of FAK, paxillin, beta3 integrin and p38, but not of ERK1/2 or Akt. alphavbeta3 inhibition led to downregulation of certain profibrogenic transcripts, while it upregulated fibrolytic MMP-13 mRNA.

CONCLUSIONS

Inhibition of integrin alphavbeta3 leads to abrogation of migration of HSC stimulated with PDGF-BB and to an antifibrogenic gene expression pattern.

Antagonism of platelet‐derived growth factor by perivascular gene transfer attenuates adventitial cell migration after vascular injury: new tricks for old dogs?

Migration of adventitial fibroblasts contributes to vascular remodeling after angioplasty. This study has used perivascular gene transfer of a truncated platelet-derived growth factor PDGF receptor (PDGFXR) to investigate whether antagonism of PDGF signaling alters adventitial cell migration after balloon injury in rat carotid arteries. Adenoviruses coordinating expression of beta-galactosidase (LacZ) and PDGFXR or LacZ and green fluorescent protein (GFP) were applied to the perivascular surface of arteries and balloon injury performed 4 days later. Vessels were excised at 3, 7, and 14 days to determine morphology and gene expression. Uninjured arteries only expressed LacZ positive cells in the adventitial compartment; however, after injury in LacZ and GFP transfected arteries, LacZ positive cells contributed to the population of cells within the media and neointima at 7-14 days. Overexpression of PDGFXR and LacZ resulted in a significant reduction in the number of LacZ labeled cells in the neointima after vascular injury, concomitant with reduced remodeling, collagen content, expression of matrix metalloproteinase-2, and increased levels of tissue inhibitors of metalloproteinase-1 and -2. We provide evidence that perivascular antagonism of PDGF attenuates remodeling and contribution of adventitial fibroblasts to neointima formation after balloon angioplasty. Perivascular gene transfer may represent a therapeutic strategy to reduce the incidence of restenosis.

Modulation of Smooth Muscle Cell Migration by Members of the Low-Density Lipoprotein Receptor Family

Low-density lipoprotein receptor family members (LRs) play a key role in the catabolism of many membrane-associated proteins, such as complexes between proteinases and their receptors, in addition to being involved in lipoprotein metabolism as suspected by the hitherto well-established functions of low-density lipoprotein receptor, in a variety of tissues. Recent studies using receptor-deficient or -overexpressing animals and cells have suggested that certain LRs are important regulators of the migration (and proliferation) of vascular smooth muscle cells (SMCs). LR expression is markedly induced in intimal or medial SMCs during the formation of atherosclerotic lesions. Because LRs can modulate the activity of the urokinase-type plasminogen activator (uPA) receptor and possibly of the platelet-derived growth factor (PDGF) receptor, LRs may influence the migration of SMCs through functional modulation of these membrane receptors. Therefore, SMC migration may be regulated by time-restricted expression of LRs. In agreement with the concept of functional interaction between LRs and membrane signaling receptors, a negative regulator of uPA receptor protein catabolism, LR11, has been identified. Statins modulate the PDGF-induced migration of intimal SMCs via the LR11/uPA receptor cascade. Selective modification of the LRs/uPA receptor/PDGF receptor systems in SMCs may be important for suppression of atherosclerotic plaque formation as well as for preventing intimal thickening after angioplasty.

Drug-Eluting Coronary Stents

The introduction and widespread use of coronary stents have been the most important advancement in the percutaneous treatment of coronary artery disease since the introduction of balloon angioplasty. Coronary artery stents reduce the rate of angiographic and clinical restenosis compared to balloon angioplasty. This angiographic restenosis was further reduced with the introduction of drug-eluting stents and hence further reduction in the frequency of major adverse cardiac events. Herein we present a comprehensive and up-to-date review about the use of drug-eluting stents in the treatment of coronary artery disease.

Stimulation of vascular smooth muscle cell migration by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a well known proinflammatory factor that influences the migration and proliferation of various cell types, predominantly monocytes and macrophages. Recent evidence suggests an important role for MIF in the progression of atherosclerosis and restenosis. For this reason, we studied the effect of MIF on platelet-derived growth factor-BB (PDGF-BB)-induced migration and PDGF receptor protein expression in vascular smooth muscle cells (VSMCs). Furthermore, the possibility of MIF influencing the migration of VSMCs was investigated. Our results show that short-term incubation of MIF is able to enhance PDGF-BB-induced migration. Long-term incubation decreases PDGF-BB-induced migration, but preserves a short-term stimulatory effect. These effects are not regulated at the level of PDGF receptor protein expression. MIF also acts as a chemoattractant for VSMCs, with a maximum response at 15 ng/ml. In contrast, the proliferation of VSMCs was unaffected by MIF. We conclude that MIF has a biphasic effect on VSMC migration. It remains unclear whether this effect is direct or involves the secretion of unidentified promigratory factors. Exogenous MIF does not stimulate VSMC proliferation; however, a role for MIF in proliferation cannot be fully ruled out. In view of the known key contributions of macrophage-derived MIF and VSMCs, the observed effects may well play a role in the progression of atherosclerosis and restenosis.

Vascular progenitor cells: origin and mechanisms of mobilization, differentiation, integration, and vasculogenesis

The recent discovery of progenitor cells in peripheral blood that can differentiate into endothelial or vascular smooth muscle cells has led to the re-evaluation of many traditionally held beliefs about vascular biology. Most notably, concepts of vascular regeneration and repair, previously considered limited to the proliferation of existing differentiated cells within vascular tissue, have been expanded to include the potential for postnatal vasculogenesis. These cells have since been identified in the bone marrow, heart, skeletal muscle, and other peripheral tissues, including the vasculature itself. The significance of these cells lies not only in developing our understanding of normal vascular biology, but also in the insights they may provide into vascular diseases such as atherosclerosis. In addition, a potential role in therapeutics has already been explored in early clinical trials in humans. The mechanisms underlying the mobilization, target tissue integration, differentiation, and the observed therapeutic benefits of these cells are now being elucidated. It is these mechanisms, and the current understanding of the lineage of these cells, that constitutes the focus of this review.

Caveolin-1 expression by means of p38beta mitogen-activated protein kinase mediates the antiproliferative effect of carbon monoxide

During vascular injury, the proliferation and migration of smooth muscle cells leads to characteristic neointima formation, which can be exacerbated by genetic depletion of caveolin-1 or heme oxygenase 1 (HO-1), and inhibited by carbon monoxide (CO), a by-product of heme oxygenase 1 activity. CO inhibited smooth muscle cell proliferation by activating p38 mitogen-activated protein kinase (MAPK) and p21(Waf1/Cip1). Exposure to CO increased caveolin-1 expression in neointimal lesions of injured aorta and in vitro by activating guanylyl cyclase and p38 MAPK. p38beta-/- fibroblasts did not induce caveolin-1 in response to CO, and exhibited a diminished basal caveolin-1 expression, which was restored by p38beta gene transfer. p38beta MAPK down-regulated extracellular signal-regulated protein kinase 1/2 (ERK-1/2), which can repress caveolin-1 transcription. Genetic depletion of caveolin-1 abolished the antiproliferative effect of CO. Thus, we demonstrate that CO, by activating p38beta MAPK, up-regulates caveolin-1, which acts as a tumor suppressor protein that mediates the growth inhibitory properties of this gas.

PDGF signaling in cells and mice

Since its discovery over three decades ago, platelet-derived growth factor (PDGF) has been a model system for learning how growth factors regulate biological processes. For the first several decades investigators used cells grown in tissue culture. More recently, PDGF signaling has also been investigated in mice. This review outlines the advances in these two systems, and highlights some of the directions for future investigation.

PDGF and cardiovascular disease

Platelet-derived growth factor (PDGF) was identified in a search for serum factors that stimulate smooth muscle cell (SMC) proliferation. During the development of lesions of atherosclerosis that can ultimately lead to vessel occlusion, SMC are stimulated by inflammatory factors to migrate from their normal location in the media. They accumulate within the forming lesion where they contribute to lesion expansion by proliferation and deposition of extracellular matrix. Different genetic manipulations in vascular cells combined with various inhibitory strategies have provided strong evidence for PDGF playing a prominent role in the migration of SMC into the neointima following acute injury and in atherosclerosis. Other activities of PDGF identified in vivo suggest additional functions for PDGF in the pathogenesis of cardiovascular disease.

Essential role of protein kinase G and decreased cytoplasmic Ca2+ levels in NO-induced inhibition of rat aortic smooth muscle cell motility

Hyperinsulinemia is a major risk factor for the development of vascular disease. We have reported that insulin increases the motility of vascular smooth muscle cells via a hydrogen peroxide-mediated mechanism and that nitric oxide (NO) attenuates insulin-induced motility via a cGMP-mediated mechanism. Events downstream of cGMP elevation have not yet been investigated. The aim of our study was to test the hypothesis that antimotogenic effects of NO and cGMP in cultured rat aortic smooth muscle cells are mediated via PKG, followed by reduction of cytoplasmic Ca(2+) levels and increased protein tyrosine phosphatase-proline, glutamate, serine, and threonine activity, leading to suppression of agonist-induced elevation of hydrogen peroxide levels and cell motility. Treatment of primary cultures with adenovirus expressing PKG-1alpha mimicked NO-induced inhibition of insulin-elicited hydrogen peroxide elevation and cell motility, whereas treatment with the pharmacological PKG inhibitor Rp-8-bromo-3',5'-cyclic monophosphorothioate (Rp-8-Br-cGMPS) rescued the stimulatory effects of insulin that were suppressed by NO donor. Treatment of cells with insulin failed to increase cytoplasmic Ca(2+) levels, whereas NO donor decreased cytoplasmic Ca(2+) levels in the presence or absence of insulin. Treatment of cells with the Ca(2+) chelator BAPTA mimicked the effects of PKG and the NO donor and increased the activity of PTP-PEST. Finally, treatment with a dominant negative allele of PTP-PEST reversed the inhibitory effect of BAPTA on cell motility and hydrogen peroxide elevation. We conclude that NO-induced inhibition of cell motility occurs via PKG-mediated reduction of basal cytoplasmic Ca(2+) levels, followed by increased PTP-PEST activity, leading to decreased hydrogen peroxide levels and reduced cell motility.