Regulatory effects of platelet-derived growth factor-AA homodimer on migration of vascular smooth muscle cells

Cellular Prion protein moonlights vascular smooth muscle cell fate: Surveilled by trophoblast cells

Uterine spiral artery remodeling (uSAR) is a hallmark of hemochorial placentation. Compromised uSAR leads to adverse pregnancy outcomes. Salient developmental events involved in uSAR are active areas of research and include (a) trophendothelial cell invasion into the spiral arteries, selected demise of endothelial cells; (b) de-differentiation of vascular smooth muscle cells (VSMC); and (c) migration and/or death of VSMCs surrounding spiral arteries. Here we demonstrated that cellular prion (PRNP) is expressed in the rat metrial gland, the entry point of spiral arteries with the highest expression on E16.5, the day at which trophoblast invasion peaks. PRNP is expressed in VSMCs that drift away from the arterial wall. RNA interference of Prnp functionally restricted migration and invasion of rat VSMCs. Furthermore, PRNP interacted with two migration-promoting factors, focal adhesion kinase (FAK) and platelet-derived growth factor receptor-β (PDGFR-β), forming a ter-molecular complex in both the metrial gland and A7r5 cells. The presence of multiple putative binding site of odd skipped related-1 (OSR1) transcription factor on the Prnp promoter was observed using in silico promoter analysis. Ectopic overexpression of OSR1 increased, and knockdown of OSR1 decreased expression of PRNP in VSMCs. Coculture of VSMCs with rat primary trophoblast cells decreased the levels of OSR1 and PRNP. Interestingly, PRNP knockdown led to apoptotic death in ~9% of VSMCs and activated extrinsic apoptotic pathways. PRNP interacts with TRAIL-receptor DR4 and protects VSMCs from TRAIL-mediated apoptosis. These results highlight the biological functions of PRNP in VSMC cell-fate determination during uteroplacental development, an important determinant of healthy pregnancy outcome.

Parainfectious cerebral vasculopathy complicating bacterial meningitis: Acute-short lived vasospasm followed by delayed-long lasting vasculitis

Bacterial meningitis is a serious, life-threatening infection of the meninges. Several radiological studies highlight prominent structural alterations occurring in the cerebral vasculature, leading to significant cerebrovascular consequences during bacterial meningitis. Beginning with reflexive arterial vasospasm , cerebrovascular disease during bacterial meningitis proceeds through a orderly sequence of arterial vasculitis with inflammatory cell infiltration, medial smooth muscle migration and proliferation, medial necrosis, adventitial fibrosis and eventual intimal stenosis. As such, this review focuses on changes occurring within cerebral arteries during disease progression, highlighting the various structural modifications occurring in the arterial vessels that contribute to disturbances in cerebral hemodynamics and, ultimately, cerebrovascular consequences during bacterial meningitis.

The Mechanisms of Restenosis and Relevance to Next Generation Stent Design

Stents are lifesaving mechanical devices that re-establish essential blood flow to the coronary circulation after significant vessel occlusion due to coronary vessel disease or thrombolytic blockade. Improvements in stent surface engineering over the last 20 years have seen significant reductions in complications arising due to restenosis and thrombosis. However, under certain conditions such as diabetes mellitus (DM), the incidence of stent-mediated complications remains 2–4-fold higher than seen in non-diabetic patients. The stents with the largest market share are designed to target the mechanisms behind neointimal hyperplasia (NIH) through anti-proliferative drugs that prevent the formation of a neointima by halting the cell cycle of vascular smooth muscle cells (VSMCs). Thrombosis is treated through dual anti-platelet therapy (DAPT), which is the continual use of aspirin and a P2Y₁₂ inhibitor for 6–12 months. While the most common stents currently in use are reasonably effective at treating these complications, there is still significant room for improvement. Recently, inflammation and redox stress have been identified as major contributing factors that increase the risk of stent-related complications following percutaneous coronary intervention (PCI). The aim of this review is to examine the mechanisms behind inflammation and redox stress through the lens of PCI and its complications and to establish whether tailored targeting of these key mechanistic pathways offers improved outcomes for patients, particularly those where stent placement remains vulnerable to complications. In summary, our review highlights the most recent and promising research being undertaken in understanding the mechanisms of redox biology and inflammation in the context of stent design. We emphasize the benefits of a targeted mechanistic approach to decrease all-cause mortality, even in patients with diabetes.

Dual Role of CREB in The Regulation of VSMC Proliferation: Mode of Activation Determines Pro- or Anti-Mitogenic Function

Vascular smooth muscle cell (VSMC) proliferation has been implicated in the development of restenosis after angioplasty, vein graft intimal thickening and atherogenesis. We investigated the mechanisms underlying positive and negative regulation of VSMC proliferation by the transcription factor cyclic AMP response element binding protein (CREB). Incubation with the cAMP elevating stimuli, adenosine, prostacyclin mimetics or low levels of forksolin activated CREB without changing CREB phosphorylation on serine-133 but induced nuclear translocation of the CREB co-factors CRTC-2 and CRTC-3. Overexpression of CRTC-2 or -3 significantly increased CREB activity and inhibited VSMC proliferation, whereas CRTC-2/3 silencing inhibited CREB activity and reversed the anti-mitogenic effects of adenosine A2B receptor agonists. By contrast, stimulation with serum or PDGF_BB significantly increased CREB activity, dependent on increased CREB phosphorylation at serine-133 but not on CRTC-2/3 activation. CREB silencing significantly inhibited basal and PDGF induced proliferation. These data demonstrate that cAMP activation of CREB, which is CRTC2/3 dependent and serine-133 independent, is anti-mitogenic. Growth factor activation of CREB, which is serine-133-dependent and CRTC2/3 independent, is pro-mitogenic. Hence, CREB plays a dual role in the regulation of VSMC proliferation with the mode of activation determining its pro- or anti-mitogenic function.

Divergent Regulation of Actin Dynamics and Megakaryoblastic Leukemia-1 and -2 (Mkl1/2) by cAMP in Endothelial and Smooth Muscle Cells

Proliferation and migration of vascular smooth muscle cells (VSMCs) or endothelial cell (ECs) promote or inhibit, respectively, restenosis after angioplasty, vein graft intimal thickening and atherogenesis. Here we investigated the effects of cAMP-induced cytoskeletal remodelling on the serum response factor (SRF) co-factors Megakaryoblastic Leukemia-1 and -2 (MKL1 and MKL2) and their role in controlling VSMC and EC proliferation and migration. Elevation of cAMP using forskolin, dibutyryl-cAMP (db-cAMP), BAY60-6583 or Cicaprost induced rapid cytoskeleton remodelling and inhibited proliferation and migration in VSMCs but not EC. Furthermore, elevated cAMP inhibited mitogen-induced nuclear-translocation of MKL1 and MKL2 in VSMCs but not ECs. Forskolin also significantly inhibited serum response factor (SRF)-dependent reporter gene (SRE-LUC) activity and mRNA expression of pro-proliferative and pro-migratory MKL1/2 target genes in VSMCs but not in ECs. In ECs, MKL1 was constitutively nuclear and MKL2 cytoplasmic, irrespective of mitogens or cAMP. Pharmacological or siRNA inhibition of MKL1 significantly inhibited the proliferation and migration of VSMC and EC. Our new data identifies and important contribution of MKL1/2 to explaining the strikingly different response of VSMCs and ECs to cAMP elevation. Elucidation of these pathways promises to identify targets for specific inhibition of VSMC migration and proliferation.

The Hippo pathway mediates inhibition of vascular smooth muscle cell proliferation by cAMP

AIMS

Inhibition of vascular smooth muscle cell (VSMC) proliferation by intracellular cAMP prevents excessive neointima formation and hence angioplasty restenosis and vein-graft failure. These protective effects are mediated via actin-cytoskeleton remodelling and subsequent regulation of gene expression by mechanisms that are incompletely understood. Here we investigated the role of components of the growth-regulatory Hippo pathway, specifically the transcription factor TEAD and its co-factors YAP and TAZ in VSMC.

METHODS AND RESULTS

Elevation of cAMP using forskolin, dibutyryl-cAMP or the physiological agonists, Cicaprost or adenosine, significantly increased phosphorylation and nuclear export YAP and TAZ and inhibited TEAD-luciferase report gene activity. Similar effects were obtained by inhibiting RhoA activity with C3-transferase, its downstream kinase, ROCK, with Y27632, or actin-polymerisation with Latrunculin-B. Conversely, expression of constitutively-active RhoA reversed the inhibitory effects of forskolin on TEAD-luciferase. Forskolin significantly inhibited the mRNA expression of the pro-mitogenic genes, CCN1, CTGF, c-MYC and TGFB2 and this was reversed by expression of constitutively-active YAP or TAZ phospho-mutants. Inhibition of YAP and TAZ function with RNAi or Verteporfin significantly reduced VSMC proliferation. Furthermore, the anti-mitogenic effects of forskolin were reversed by overexpression of constitutively-active YAP or TAZ.

CONCLUSION

Taken together, these data demonstrate that cAMP-induced actin-cytoskeleton remodelling inhibits YAP/TAZ-TEAD dependent expression of pro-mitogenic genes in VSMC. This mechanism contributes novel insight into the anti-mitogenic effects of cAMP in VSMC and suggests a new target for intervention.

cAMP-induced actin cytoskeleton remodelling inhibits MKL1-dependent expression of the chemotactic and pro-proliferative factor, CCN1

Elevation of intracellular cAMP concentration has numerous vascular protective effects that are in part mediated via actin cytoskeleton-remodelling and subsequent regulation of gene expression. However, the mechanisms are incompletely understood. Here we investigated whether cAMP-induced actin-cytoskeleton remodelling modulates VSMC behaviour by inhibiting expression of CCN1. In cultured rat VSMC, CCN1-silencing significantly inhibited BrdU incorporation and migration in a wound healing assay. Recombinant CCN1 enhanced chemotaxis in a Boyden chamber. Adding db-cAMP, or elevating cAMP using forskolin, significantly inhibited CCN1 mRNA and protein expression in vitro; transcriptional regulation was demonstrated by measuring pre-spliced CCN1 mRNA and CCN1-promoter activity. Forskolin also inhibited CCN1 expression in balloon injured rat carotid arteries in vivo. Inhibiting RhoA activity, which regulates actin-polymerisation, by cAMP-elevation or pharmacologically with C3-transferase, or inhibiting its downstream kinase, ROCK, with Y27632, significantly inhibited CCN1 expression. Conversely, expression of constitutively active RhoA reversed the inhibitory effects of forskolin on CCN1 mRNA. Furthermore, CCN1 mRNA levels were significantly decreased by inhibiting actin-polymerisation with latrunculin B or increased by stimulating actin-polymerisation with Jasplakinolide. We next tested the role of the actin-dependent SRF co-factor, MKL1, in CCN1 expression. Forskolin inhibited nuclear translocation of MKL1 and binding of MKL1 to the CCN1 promoter. Constitutively-active MKL1 enhanced basal promoter activity of wild-type but not SRE-mutated CCN1; and prevented forskolin inhibition. Furthermore, pharmacological MKL-inhibition with CCG-1423 significantly inhibited CCN1 promoter activity as well as mRNA and protein expression. Our data demonstrates that cAMP-induced actin-cytoskeleton remodelling regulates expression of CCN1 through MKL1: it highlights a novel cAMP-dependent mechanism controlling VSMC behaviour.

Regulation of arterial blood pressure by Akt1-dependent vascular relaxation

Endothelial cell-dependent vascular relaxation plays an important role in the regulation of blood pressure. Here, we show that stimulation of vascular endothelial cells with platelet-derived growth factor (PDGF) results in vascular relaxation through Akt1-dependent activation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production. Stimulation of both human umbilical artery endothelial cells and abdominal aortic vessels with PDGF induced NO production. PDGF-dependent production of NO was completely abolished by inhibition of phosphatidylinositol 3-kinase with wortmannin (100 nM). Stimulation of aortic vessels with PDGF resulted in the activation of Akt phosphorylation and eNOS phosphorylation: however, eNOS phosphorylation and production of NO were abolished in aortic vessels of mice lacking Akt1. PDGF strongly induced vascular relaxation in the presence of endothelium, and inhibition of NO production by N-nitro-L: -arginine-methyl ester completely blocked PDGF-dependent vascular relaxation. In addition, PDGF-dependent relaxation was completely abolished by inhibition of PI3K with wortmannin (100 nM). Furthermore, vessels from Akt1 heterozygotes showed normal relaxation after PDGF stimulation, whereas vessels from Akt1 knockout littermates did not respond to PDGF stimulation. Finally, administration of PDGF (5 ng/ml) significantly lowered blood pressure in Akt1 heterozygotes, whereas a blood pressure-lowering effect was not observed in Akt1 knockout littermates. These results suggest that Akt1 regulates blood pressure through regulation of vascular relaxation by eNOS phosphorylation and subsequent production of NO.

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.

Disruption of PDGFRalpha-initiated PI3K activation and migration of somite derivatives leads to spina bifida

Spina bifida, or failure of the vertebrae to close at the midline, is a common congenital malformation in humans that is often synonymous with neural tube defects (NTDs). However, it is likely that other etiologies exist. Genetic disruption of platelet-derived growth factor receptor (PDGFR) alpha results in spina bifida, but the underlying mechanism has not been identified. To elucidate the cause of this birth defect in PDGFRalpha mutant embryos, we examined the developmental processes involved in vertebrae formation. Exposure of chick embryos to the PDGFR inhibitor imatinib mesylate resulted in spina bifida in the absence of NTDs. We next examined embryos with a tissue-specific deletion of the receptor. We found that loss of the receptor from chondrocytes did not recapitulate the spina bifida phenotype. By contrast, loss of the receptor from all sclerotome and dermatome derivatives or disruption of PDGFRalpha-driven phosphatidyl-inositol 3' kinase (PI3K) activity resulted in spina bifida. Furthermore, we identified a migration defect in the sclerotome as the cause of the abnormal vertebral development. We found that primary cells from these mice exhibited defects in PAK1 activation and paxillin localization. Taken together, these results indicate that PDGFRalpha downstream effectors, especially PI3K, are essential for cell migration of a somite-derived dorsal mesenchyme and disruption of receptor signaling in these cells leads to spina bifida.

The primary cilium coordinates signaling pathways in cell cycle control and migration during development and tissue repair

Cell cycle control and migration are critical processes during development and maintenance of tissue functions. Recently, primary cilia were shown to take part in coordination of the signaling pathways that control these cellular processes in human health and disease. In this review, we present an overview of the function of primary cilia and the centrosome in the signaling pathways that regulate cell cycle control and migration with focus on ciliary signaling via platelet-derived growth factor receptor alpha (PDGFRalpha). We also consider how the primary cilium and the centrosome interact with the extracellular matrix, coordinate Wnt signaling, and modulate cytoskeletal changes that impinge on both cell cycle control and cell migration.

Mechanisms of vascular smooth muscle cell migration

Smooth muscle cell migration occurs during vascular development, in response to vascular injury, and during atherogenesis. Many proximal signals and signal transduction pathways activated during migration have been identified, as well as components of the cellular machinery that affect cell movement. In this review, a summary of promigratory and antimigratory molecules belonging to diverse chemical and functional families is presented, along with a summary of key signaling events mediating migration. Extracellular molecules that modulate migration include small biogenic amines, peptide growth factors, cytokines, extracellular matrix components, and drugs used in cardiovascular medicine. Promigratory stimuli activate signal transduction cascades that trigger remodeling of the cytoskeleton, change the adhesiveness of the cell to the matrix, and activate motor proteins. This review focuses on the signaling pathways and effector proteins regulated by promigratory and antimigratory molecules. Prominent pathways include phosphatidylinositol 3-kinases, calcium-dependent protein kinases, Rho-activated protein kinase, p21-activated protein kinases, LIM kinase, and mitogen-activated protein kinases. Important downstream targets include myosin II motors, actin capping and severing proteins, formins, profilin, cofilin, and the actin-related protein-2/3 complex. Actin filament remodeling, focal contact remodeling, and molecular motors are coordinated to cause cells to migrate along gradients of chemical cues, matrix adhesiveness, or matrix stiffness. The result is recruitment of cells to areas where the vessel wall is being remodeled. Vessel wall remodeling can be antagonized by common cardiovascular drugs that act in part by inhibiting vascular smooth muscle cell migration. Several therapeutically important drugs act by inhibiting cell cycle progression, which may reduce the population of migrating cells.

A novel “sandwich” assay for quantifying chemo-regulated cell migration within 3-dimensional matrices: Wound healing cytokines exhibit distinct motogenic activities compared to the transmembrane assay

The extracellular matrix profoundly affects cellular response to soluble motogens. In view of this critical aspect of matrix functionality, we have developed a novel assay to quantify chemo-regulated cell migration within biologically relevant 3-dimensional matrices. In this "sandwich" assay, target cells are plated at the interface between an upper and lower matrix compartment, either in the presence of an isotropic (uniform) or anisotropic (gradient) spatial distribution of test motogen. Cell migration in response to the different conditions is ascertained by quantifying their subsequent disposition within the upper and lower matrix compartments. The objective of this study has been to compare the motogenic activities of platelet-derived growth factor (PDGF-AB) and transforming growth factor-beta isoforms (TGF-beta1, -beta2 and -beta3) in the sandwich assay and the commonly employed transmembrane assay. As previously reported, dermal fibroblasts exhibited a motogenic response to isotropic and anisotropic distributions of all tested cytokines in the transmembrane assay. In contrast, only PDGF-AB and TGF-beta3 were active in the sandwich assay, each eliciting directionally unbiased (symmetrical) migration into the upper and lower type I collagen matrices in response to an isotropic cytokine distribution and a directionally biased response to an anisotropic distribution. TGF-beta1 and -beta2 were completely devoid of motogenic activity. These results are consistent with the reported differential bioactivities of PDGF and TGF-beta3 compared to TGF-beta1 and -beta2 in animal models of wound healing and suggest that the sandwich assay provides a means of obtaining physiologically relevant data regarding chemo-regulated cell migration.

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.

Shear stress-stimulated endothelial cells induce smooth muscle cell chemotaxis via platelet-derived growth factor-BB and interleukin-1alpha

OBJECTIVE

Vascular smooth muscle cell (SMC) migration is critical to the development of atherosclerosis and neointimal hyperplasia. Hemodynamic forces such as shear stress and cyclic strain stimulate endothelial cell signal-transduction pathways, resulting in the secretion of several factors, including SMC chemoattractants such as platelet-derived growth factor (PDGF). We hypothesized that mechanical forces stimulate endothelial cells to secrete SMC chemoattractants to induce migration via the mitogen-activated protein kinase (MAPK) pathway.

METHODS

Bovine aortic endothelial cells were exposed to shear stress, cyclic strain, or static conditions for 16 hours. The resulting conditioned medium was used as a SMC chemoattractant in a Boyden chamber. Activation of SMC extracellular signal-regulated protein kinase 1/2 (ERK1/2) was assessed by Western blot analysis. Pathways were inhibited with anti-PDGF-BB or anti-interleukin-1alpha (IL-1alpha) antibodies, or the ERK1/2 upstream pathway inhibitor PD98059.

RESULTS

Conditioned medium from endothelial cells exposed to shear stress corresponding to arterial levels of shear stress stimulated SMC migration but lower levels of shear stress or cyclic strain did not. Both PDGF-BB and IL-1alpha were secreted into the conditioned medium by endothelial cells stimulated with shear stress. Both PDGF-BB and IL-1alpha stimulated SMC chemotaxis but were not synergistic, and both stimulated SMC ERK1/2 phosphorylation. Inhibition of PDGF-BB or IL-1alpha inhibited SMC chemotaxis and ERK1/2 phosphorylation.

CONCLUSION

Shear stress stimulates endothelial cells to secrete several SMC chemoattractants, including PDGF-BB and IL-1alpha; both PDGF-BB and IL-1alpha stimulate SMC chemotaxis via the ERK1/2 signal-transduction pathway. These results suggest that the response to vascular injury may have a common pathway amenable to pharmacologic manipulation.

CLINICAL RELEVANCE

One difficulty in the pharmacologic treatment of atherosclerosis or neointimal hyperplasia leading to restenosis is the multiplicity of activated pathways and thus potential treatment targets. This study demonstrates that shear stress, a hemodynamic force that may be a biologically relevant stimulus to induce vascular pathology, stimulates endothelial cells to secrete PDGF-BB and IL-1alpha. Both of these mediators stimulate the SMC ERK1/2 pathway to induce migration, a critical event in the pathogenesis of atherosclerosis and neointimal hyperplasia. Therefore, this study suggests a relevant common target pathway in SMC that is amenable to manipulation for clinical treatment.

Urokinase-induced signaling in human vascular smooth muscle cells is mediated by PDGFR-beta

Urokinase (uPA)-induced signaling in human vascular smooth muscle cells (VSMC) elicits important cellular functional responses, such as cell migration and proliferation. However, how intracellular signaling is linked to glycolipid-anchored uPA receptor (uPAR) is unknown. We provide evidence that uPAR activation by uPA induces its association with platelet-derived growth factor receptor (PDGFR)-beta. The interaction results in PDGF-independent PDGFR-beta activation by phosphorylation of cytoplasmic tyrosine kinase domains and receptor dimerization. Association of the receptors as well as the tyrosine kinase activity of PDGFR-beta are decisive in mediating uPA-induced downstream signaling that regulates VSMC migration and proliferation. These findings provide a molecular basis for mechanisms VSMC use to induce uPAR- and PDGFR-directed signaling. The processes may be relevant to VSMC function and vascular remodeling.

Shear stress inhibits smooth muscle cell migration via nitric oxide-mediated downregulation of matrix metalloproteinase-2 activity

Vascular smooth muscle cell (SMC) migration is a hallmark of intimal hyperplasia (IH), the progression of which is affected by hemodynamic conditions at the diseased site. The realization that SMCs are exposed to blood flow in both denuded vessels (direct blood flow) and intact vessels (interstitial blood flow) motivated this study of the effects of fluid flow shear stress (SS) on SMC migration. Rat aortic SMCs were seeded onto Matrigel-coated cell culture inserts, and their migratory activity toward PDGF-BB when exposed to SS in a rotating disk apparatus was quantified. Four hours of either 10 or 20 dyn/cm2 SS significantly inhibited SMC migration to the bottom side of the insert. This inhibition was associated with downregulation of SMC matrix metalloproteinase (MMP)-2 activation. Four hours of 10 dyn/cm2 SS also drastically increased SMC production of NO. A NO synthase inhibitor (N(G)-nitro-L-arginine methyl ester; 100 microM) abolished the shear-induced increase in SMC NO production as well as the inhibition of migration and MMP-2 activity. A NO donor (S-nitroso-N-acetyl-penicillamine; 500 microM) suppressed SMC migration via the reduction of both total and active MMP-2 levels. Addition of 10 microM MMP-2 inhibitor I to inserts significantly reduced SMC migration. Western blots showed no effect of 4 h of 20 dyn/cm2 SS on SMC production of PDGF-AA, another chemical known to suppress SMC migration. Thus it appears that SS acts to suppress SMC migration by upregulating the cellular production of NO, which in turn inhibits MMP-2 activity.

Embryonic mouse testis development: role of platelet derived growth factor (PDGF-BB)

Platelet-derived growth factors (PDGFs) are paracrine growth factors mediating epithelial-mesenchymal interactions and exerting multiple biological activities which include cell proliferation, motility, and differentiation. As previously demonstrated, PDGFs act during embryonic development and recently, by culturing male genital ridges, we have demonstrated that PDGF-BB is able to support in vitro testicular cord formation. In the present paper, we report that PDGF-BB is present during embryonic testis development and, in organ culture, induces cord formation although with reduced diameters compared with the cords formed in the genital ridges cultured in the presence of HGF. Moreover we have analyzed the roles exerted by this growth factor during the morphogenesis of the testis. We demonstrate by immunohistochemical experiments that PDGF-BB and its receptors are synthesized by the male UGRs isolated from 11.5 and 13.5 dpc embryos and by Western blot that the factor is secreted in a biologically active form by testicular cells isolated from 13.5 dpc embryos. The biological roles of the factor have also been studied and we demonstrate that PDGF-BB acts as a migratory factor for male mesonephric cells whose migration is a male specific event necessary for a normal testicular morphogenesis. In addition we demonstrate that during testicular development, PDGF-BB induces testicular cell proliferation being in this way responsible for the increase in size of the testis. Finally we demonstrate that PDGF-BB is able to reorganize dissociated testicular cells inducing the formation of large cellular aggregates. However the structures formed in vitro under PDGF-BB stimulation never had a cord-like morphology similar to the cord-like structures formed in the presence of HGF (Ricci et al., 2002, Mech Dev 118:19-28), suggesting that this factor does not act as a morphogenetic factor during testicular development. All together the data presented in this paper demonstrate that PDGF-BB and its receptors (alpha- and beta-subunits) are present during the crucial ages of embryonic mouse testis morphogenesis and indicate the multiple roles exerted by this factor during the development of the male gonad.

Epidermal Growth Factor Induces Fibroblast Contractility and Motility via a Protein Kinase C δ-dependent Pathway

Myosin-based cell contractile force is considered to be a critical process in cell motility. However, for epidermal growth factor (EGF)-induced fibroblast migration, molecular links between EGF receptor (EGFR) activation and force generation have not been clarified. Herein, we demonstrate that EGF stimulation increases myosin light chain (MLC) phosphorylation, a marker for contractile force, concomitant with protein kinase C (PKC) activity in mouse fibroblasts expressing human EGFR constructs. Interestingly, PKCdelta is the most strongly phosphorylated isoform, and the preferential PKCdelta inhibitor rottlerin largely prevented EGF-induced phosphorylation of PKC substrates and MARCKS. The pathway through which EGFR activates PKCdelta is suggested by the fact that the MEK-1 inhibitor U0126 and the phosphatidylinositol 3-kinase inhibitor LY294002 had no effect on PKCdelta activation, whereas lack of PLCgamma signaling resulted in delayed PKCdelta activation. EGF-enhanced MLC phosphorylation was prevented by a specific MLC kinase inhibitor ML-7 and the PKC inhibitors chelerythrine chloride and rottlerin. Further indicating that PKCdelta is required, a dominant-negative PKCdelta construct or RNAi-mediated PKCdelta depletion also prevented MLC phosphorylation. In the absence of PLC signaling, MLC phosphorylation and cell force generation were delayed similarly to PKCdelta activation. All of the interventions that blocked PKCdelta activation or MLC phosphorylation abrogated EGF-induced cell contractile force generation and motility. Our results suggest that PKCdelta activation is responsible for a major part of EGF-induced fibroblast contractile force generation. Hence, we identify here a new pathway helping to govern cell motility, with PLC signaling playing a role in activation of PKCdelta to promote the acute phase of EGF-induced MLC activation.

Estrogen regulates insulin-like growth factor 1, platelet-derived growth factor A and B, and their receptors in the vascular wall

BACKGROUND

Peptide growth factors induce vascular smooth muscle cell (SMC) proliferation and migration after vascular injury, leading to arterial stenosis. Estrogen provides vasculoprotective effects by regulating endothelial and vascular SMC function.

METHODS

We performed aortic denudations in male Wistar rats. One group received 17beta-estradiol, 0.25 mg/kg per day subcutaneously, and the other group vehicle. Growth factor and receptor mRNA in the aorta wall was quantitated at 15 minutes, 3 days, and 7 days after denudation. Western blotting and immunohistochemistry were used to quantify and localize the protein.

RESULTS

Aortic injury caused SMC proliferation in the intima and media, indicated by an increase in the number of intimal nuclei and area. Quantitative reverse-transcriptase polymerase chain reaction and Western blotting showed concomitant up-regulation of insulin-like growth factor (IGF)-1, platelet-derived growth factor (PDGF)-B, and PDGF-receptor (R)alpha. 17beta-estradiol significantly inhibited SMC proliferation and intimal thickening. Similarly, estrogen administration completely suppressed IGF-1 mRNA (P=0.004) and protein but had no effect on IGF-1R. Estrogen had virtually no effect on PDGF-A mRNA or protein levels; however, on day 7, it inhibited PDGF-Ralpha mRNA by 74% (P=0.005) and protein by 67%. On day 7, it also inhibited PDGF-B mRNA expression by 36% (P=0.04) but had little effect on protein. PDGF-Rbeta expression was unaffected by estrogen. Estradiol treatment reduced immunoreactivity of IGF-1, PDGF-A, PDGF-Ralpha, and PDGF-B in vascular lesions, whereas no changes were seen with respect to IGF-1R and PDGF-Rbeta.

CONCLUSIONS

Our findings demonstrate that estrogen regulates IGF-1, PDGF-A, PDGF-B, and PDGF-Ralpha, which may be related to the vasculoprotective effect of estrogen, but has no effect on IGF-1R or PDGF-Rbeta.

The role of estrogen in cardiovascular disease

Cardiovascular disease is the number one cause of death among women, accounting for nearly 50% of female deaths. Statistics show that women on average develop cardiovascular disease 10 to 15 years later in life than men, and that the risk may increase after menopause. This observation has led to much speculation as to what physiological change(s) associated with menopause is responsible for the higher risk of atherosclerosis. Estrogen, with its potential as a cardioprotective agent and as an immunomodulator of the inflammatory response in atherosclerosis, has received the most attention. Understanding the mechanisms that lead to these differences may allow beneficial therapeutic intervention to enhance this effect in females and evoke this protection in males. This review will do the following: (1) characterize mechanisms of atherosclerosis, (2) explore the role of estrogen-replacement therapy, (3) define the effect of gender on inflammation, (4) compare and contrast the effects of estrogen and testosterone on endothelial functional, and (5) suggest mechanistic based therapeutic opportunities.

Effect of deposited lipids in atheromatous lesions on the migration of vascular smooth muscle cells

In advanced atherosclerotic lesions, a decrease in smooth muscle cells is observed in the cap tissue. This causes the thinning of the cap, and may lead to plaque rupture. We studied the effect of deposited lipids on the migration of vascular smooth muscle cells, and identified the main cause of the effect. The lipids were extracted from atherosclerotic lesions in the human aorta at autopsy, and separated into three fractions with a Sep-Pak ODS cartridge. Then, each fraction was added to the lower part of a chemotaxis chamber, and cultured vascular smooth muscle cells to the upper part. After 4 hours incubation, the cells that had migrated to the opposite side were counted. The oxysterol-rich fraction (10 microg/ml) inhibited the migration, whereas the cholesterol ester and free cholesterol fractions did not. Finally, we tested the pure oxysterols, 7-ketocholesterol and 27-hydroxycholesterol. Both inhibited migration, whereas the free cholesterol and cholesterol ester did not. Oxysterols generated in the lipid pool might inhibit the migration of smooth muscle cells.

Pleiotropic activity of hepatocyte growth factor during embryonic mouse testis development

The hepatocyte growth factor (HGF) is a pleiotropic cytokine whose action is mediated by c-met, a glycoproteic receptor with tyrosine kinase activity which transduces its multiple biological activities including cell proliferation, motility and differentiation. During embryonic development HGF acts as a morphogenetic factor as previously demonstrated for metanephric and lung development. Recently, culturing male genital ridges, we demonstrated that HGF is able to support in vitro testicular cord formation. In the present paper we report the expression pattern of the HGF gene during embryonic testis development and the multiple roles exerted by this factor during the morphogenesis of this organ. Northern blot analysis reveals a positive signal in urogenital ridges isolated from 11.5 days post coitum (dpc) embryos and in testes isolated from 13.5 and 15.5 dpc male embryos. On the contrary HGF mRNA is undetectable in ovaries isolated from 13.5 and 15.5 dpc embryos. Moreover, we demonstrate that HGF is synthesized and secreted by the male gonad and is biologically active. These data indicate a male specific biological function of HGF during embryonic gonadal development. This hypothesis is supported by the in vitro demonstration that HGF acts as a migratory factor for male mesonephric cells which is a male specific event. In addition we demonstrate that during testicular development, HGF acts as a morphogenetic factor able to reorganize dissociated testicular cells which, under HGF stimulation, form a tridimensional network of cord-like structures. Finally, we demonstrate that HGF induces testicular cell proliferation in this way being responsible for the size increase of the testis. All together the data presented in this paper demonstrate that HGF is expressed during the embryonic development of the testis and clarify the multiple roles exerted by this factor during the morphogenesis of the male gonad.

Blockade of platelet-derived growth factor receptor-beta pathway induces apoptosis of vascular endothelial cells and disrupts glomerular capillary formation in neonatal mice

Platelet-derived growth factor (PDGF), a potent chemotactic and proliferation factor for mesenchymal-derived cells, has been demonstrated to play critical roles in kidney development. Two receptors for PDGF, PDGFR-alpha and PDGFR-beta, have been identified and we previously analyzed the effects of blockade of PDGFR-alpha signal in neonatal mice. In the current study, we examined the role of PDGFR-beta in glomerular development by blocking PDGFR-beta signal in neonatal mice by administration of antagonistic anti-PDGFR-beta monoclonal antibody. Unlike the mice injected with anti-PDGFR-alpha antibody, the mice injected daily with anti-PDGFR-beta antibody could be kept alive at least for 2 weeks after birth but showed severe disruption of the glomerular structure, whereas no apparent deformation was observed in the collecting ducts. In the disrupted glomeruli, the number of the mesangial cells was reduced markedly. Electron microscopic analysis and immunohistochemical studies with terminal deoxynucleotidyl transferase nick-end labeling staining revealed that the capillary endothelial cells of the glomeruli in the outer cortex region underwent apoptosis. However, the glomeruli located near the medulla were less affected. Because PDGFR-beta is not expressed in the endothelial cells, the effects of the blockade of PDGFR-beta might have caused glomerular endothelial cell apoptosis by inducing the loss of mesangial cells and/or pericytes.

Metalloprotease inhibitor blocks angiotensin II-induced migration through inhibition of epidermal growth factor receptor transactivation

In vascular smooth muscle cells (VSMCs), angiotensin II (AngII) induces transactivation of the EGF receptor (EGFR) which involves a metalloprotease that stimulates processing of heparin-binding EGF from its precursor. However, the identity and pharmacological sensitivity of the metalloprotease remain unclear. Here, we screened the effects of several metalloprotease inhibitors on AngII-induced EGFR transactivation in VSMCs. We found that an N-phenylsulfonyl-hydroxamic acid derivative [2R-[(4-biphenylsulfonyl)amino]-N-hydroxy-3-phenylpropinamide] (BiPS), previously known as matrix metalloprotease (MMP)-2/9 inhibitor, markedly inhibited AngII-induced EGFR transactivation, whereas the MMP-2 or -9 inhibition by other MMP inhibitors failed to block the transactivation. BiPS markedly inhibited AngII-induced ERK activation and protein synthesis without affecting AngII-induced intracellular Ca2+ elevation. VSMC migration induced by AngII was also inhibited not only by an EGFR inhibitor but also by BiPS. Thus, BiPS is a specific candidate to block AngII-induced EGFR transactivation and subsequent growth and migration of VSMCs, suggesting its potency to prevent vascular remodeling.

Inhibition of vascular smooth muscle cell migration by cytochrome p450 epoxygenase-derived eicosanoids

Vascular smooth muscle cell (SMC) migration and proliferation contribute to neointimal hyperplasia and restenosis after vascular injury. The epoxyeicosatrienoic acids (EETs), which are products of cytochrome P450 (CYP) epoxygenases, possess vasodilatory, antiinflammatory, and fibrinolytic properties. To determine whether these compounds also possess antimigratory and antiproliferative properties, we stimulated rat aortic SMCs with either 20% serum or platelet-derived growth factor (PDGF-BB, 20 ng/mL). In a concentration-dependent manner, treatment with EETs, particularly 11,12-EET, inhibited SMC migration through a modified transwell filter by 53% to 60%. EETs, however, have no inhibitory effects on PDGF-stimulated SMC proliferation. Adenoviral-mediated overexpression of the CYP isoform, CYP2J2, in SMCs also inhibited serum- and PDGF-induced SMC migration by 32% and 26%, respectively; both effects of which were reversed by the CYP inhibitors SKF525A or clotrimazole, but not by the K(Ca) channel blocker, charybdotoxin, or the cyclooxygenase inhibitor, diclofenac. The effect of EETs correlated with increases in intracellular cAMP levels. Indeed, forskolin and 8-bromo-cAMP exert similar inhibitory effects on SMC migration as 11,12-EET and the effects of 11,12-EET were blocked by cAMP and protein kinase A (PKA) inhibitors. These findings indicate that EETs possess antimigratory effects on SMCs through the cAMP-PKA pathway and suggest that CYP epoxygenase-derived eicosanoids may play important roles in vascular disease and remodeling.

Different effects of high and low shear stress on platelet-derived growth factor isoform release by endothelial cells: consequences for smooth muscle cell migration

In the present study, we analyzed the effect of conditioned media (CM) from bovine aortic endothelial cells exposed to laminar shear stress (SS) of 5 dyne/cm2 (SS5) or 15 dyne/cm2 (SS15) for 16 hours on smooth muscle cell (SMC) migration. In response to CM from bovine aortic endothelial cells exposed to SS5 (CMSS5) and SS15 (CMSS15), migration was 45 +/- 5.5 and 30 +/- 1.5 cells per field, respectively (P<0.05). Similar results were obtained with SS of 2 versus 20 dyne/cm2 and also when SS of 5 and 15 dyne/cm2 lasted 24 hours. Platelet-derived growth factor (PDGF)-AA levels in CMSS5 and CMSS15 were 9 +/- 7 and 18 +/- 5 ng/10(6) cells for 16 hours, respectively (P<0.05); PDGF-BB levels in CMSS5 and CMSS15 were 38 +/- 10 and 53 +/- 10 ng/10(6) cells for 16 hours, respectively (P<0.05). PDGF receptor alpha (PDGFRalpha) and PDGF receptor beta (PDGFRbeta) in SMCs were phosphorylated by CMSS15>CMSS5. In response to CMSS15, a neutralizing antibody against PDGF-AA enhanced SMC migration to a level comparable to that of CMSS5; in contrast, antibodies against PDGF-BB abolished SMC migration. Transfection of SMCs with a dominant-negative PDGFRalpha or PDGFRbeta increased or inhibited, respectively, SMC migration in response to CMSS15. Overexpression of wild-type PDGFRalpha inhibited SMC migration in response to CMSS5, CMSS15, or recombinant PDGF-BB (P<0.001). These results suggest that the ability of high SS to inhibit arterial wall thickening in vivo may be related to enhanced activation of PDGFRalpha in SMCs by PDGF isoforms secreted by the endothelium.

Inhibitory effect of prostaglandin E 1 on intimal thickening caused by poor runoff conditions in the canine autologous vein grafts

The efficacy of ONO-1608, a newly developed liposomal formulation of prostaglandin E 1 prodrug, was evaluated on intimal hyperplasia of experimental canine autologous vein grafts under distal poor runoff conditions. The femoral vein was implanted into the femoral artery, preparing a distal poor runoff canine model. After 4 weeks of preparing the poor runoff model, the femoral vein was implanted into the femoral artery. They were then divided into two groups consisting of the control group and the ONO-1608 group. At 4 weeks, the grafts were harvested and intimal hyperplasia of the graft was measured with an ocular cytometer. Intimal cell proliferation was determined by bromodeoxyuridine incorporation 2 weeks after surgery. In addition, the effect of ONO-1608 on the proliferation of platelet-derived growth factor (PDGF)-stimulated human aortic smooth muscle cells (HASMCs) in culture was also investigated. At 4 weeks, the degree of intimal hyperplasia of the graft in the ONO-1608 group was significantly less than that of the control group. The bromodeoxyuridine labeling index 2 weeks after grafting was significantly lower in the ONO-1608 group compared with that in the control group. In addition, ONO-1608 significantly inhibited the proliferation of PDGF-stimulated HASMCs in culture. These results demonstrate the efficacy of ONO-1608 in reducing the degree of intimal hyperplasia of canine autogenous vein grafts under poor runoff conditions. The mechanism of reducing the intimal hyperplasia may be that ONO-1608 inhibited PDGF-stimulated proliferation of the smooth muscle cell. These results suggest that the administration of ONO-1608 may be beneficial in patients who have undergone gone arterial reconstruction.

Differential effects of protein kinase C on human vascular smooth muscle cell proliferation and migration

Vascular smooth muscle cell (SMC) migration and proliferation contribute to intimal hyperplasia, and protein kinase C (PKC) may be required for both events. In this report, we investigated the role of PKC in proliferation and migration of SMC derived from the human saphenous vein. Activation of PKC by phorbol-12,13-dibutyrate (PDBu) or (-)-indolactam [(-)-ILV] increases SMC proliferation. Downregulation of PKC activity by prolonged incubation with phorbol ester or inhibition of PKC with chelerythrine in SMC diminished agonist-stimulated proliferation. In contrast, stimulation of PKC with PDBu or (-)-ILV inhibited basal and agonist-induced SMC chemotaxis. Moreover, downregulation of PKC or inhibition with chelerythrine accentuated migration. We postulated that the inhibitory effect of PKC on SMC chemotaxis was mediated through cAMP-dependent protein kinase (protein kinase A, PKA). In support of this hypothesis, we found that activation of PKC in SMC stimulated PKA activity. The cAMP agonist forskolin significantly inhibited SMC chemotaxis. Furthermore, the inhibitory effect of PKC on SMC chemotaxis was completely reversed by cAMP or PKA inhibitors. In search of the PKC isotype(s) underlying these differential effects of PKC in SMC, we identified eight isotypes expressed in human SMC. Only PKC-alpha, -beta I, -delta, and -epsilon were eliminated by downregulation, suggesting that one or more of these four enzymes facilitate the observed phorbol ester-dependent effects of PKC in SMC. In summary, we found that PKC activation enhances proliferation but inhibits migration of human vascular SMC. These differential effect of PKC on vascular cells appears to be mediated through PKC-alpha, -beta I, -delta, and/or -epsilon.

Defibrinogenating effect of batroxobin (Defibrase®) in rats and inhibition of migration of human vascular smooth muscle cells by the plasma of batroxobin-treated rats in vitro

The defibrinogenating effect of batroxobin (Defibrase) in male Wistar rats and the inhibitory effects of the plasma of batroxobin-treated rats on the migration of human vascular smooth muscle cells (SMCs) were investigated in vitro. At 1 h after a single intravenous injection of 3.0, 10.0 or 30.0 BU/kg batroxobin (ten rats in each group), the fibrinogen levels in the plasma of the rats decreased to 88.3, 66.2 and 16.5%, respectively, of that in the plasma of control saline-treated rats (261.0+/-26.7 mg/dl). When the plasma from the batroxobin-treated rats was added to Dulbecco's modified Eagle's medium at a concentration of 0.2% for a vascular SMC migration assay and incubated in a modified Boyden's chamber system at 37 degrees C for 24 h, significant inhibitory effects on vascular SMC migration were observed in the 10.0 (P<0.05) and 30.0 BU/kg (P<0.01) batroxobin-treated rats. The plasma of batroxobin-treated rats as well as standard rat fibrinogen induced vascular SMC migration in a fibrinogen content-dependent manner except the plasma of the 30.0 BU/kg batroxobin-treated rats. Moreover, the rat serum (0.1 approximately 5.0%) did not show any activity on vascular SMC migration in the present experimental system. These results indicate that the plasma fibrinogen significantly influences vascular SMC migration, and that the inhibitory effect of the plasma of batroxobin-treated rats on vascular SMC migration is related to the defibrinogenating action of batroxobin in vivo.

The two PDGF receptors maintain conserved signaling in vivo despite divergent embryological functions

Gene targeting studies have indicated that the two receptors for PDGF, alpha and beta, direct unique functions during development. Distinct ligand affinities, patterns of gene expression, and/or mechanisms of signal relay may account for functional specificity of the two PDGF receptor isoforms. To distinguish between these factors, we have created two complementary lines of knockin mice in which the intracellular signaling domains of one PDGFR have been removed and replaced by those of the other PDGFR. While both lines demonstrated substantial rescue of normal development, substitution of the PDGFbetaR signaling domains with those of the PDGFalphaR resulted in varying degrees of vascular disease. This observation provides a framework for discussing the evolution of receptor tyrosine kinase functional specificity.

The chemotactic and mitogenic effects of platelet-derived growth factor-BB on rat aorta smooth muscle cells are inhibited by basic fibroblast growth factor

In response to endovascular injury, platelet-derived growth factor-BB (PDGF-BB) and basic fibroblast growth factor (bFGF) are released locally and modulate vascular smooth muscle cells (SMC) proliferation and migration within the vascular wall. The aim of the present in vitro study was to determine how rat aorta SMC respond to the simultaneous exposure to PDGF-BB and bFGF. In a modified Boyden chamber assay bFGF exhibited a dose-dependent effect to inhibit the chemotactic action of PDGF-BB. A comparable result was observed in proliferation assays. In contrast, MIP-1 beta, epidermal growth factor (EGF), fibronectin and acidic FGF (aFGF) did not inhibit the chemotactic effect of PDGF-BB. Denatured bFGF did not exert an inhibitory effect and neutralizing antibodies either to bFGF or to bFGF-receptor abolished the inhibition observed in the presence of bFGF. The role played by PDGF receptor alpha (PDGF-Ralpha) was investigated in PDGF-Ralpha-dominant negative-transfected SMC, by selectively blocking PDGF-BB-binding to PDGF-Ralpha with neomycin, by neutralizing PDGF-Ralpha with a monoclonal antibody and by selectively stimulating PDGF-Ralpha with PDGF-AA; in all cases the effect of bFGF to inhibit PDGF-BB-directed SMC migration was abolished. These in vitro studies show that bFGF significantly inhibits PDGF-BB-induced SMC migration and proliferation and that this effect is mediated by both PDGF-Ralpha and bFGF receptor.

The migratory response to platelet-derived growth factor of smooth muscle cells isolated from synthetic vascular grafts in a canine model

OBJECTIVE

Previous studies on smooth muscle cells (SMCs) harvested from implanted synthetic grafts demonstrate increased production of platelet-derived growth factor (PDGF) but decreased proliferative response compared with aortic SMCs. The purpose of this study was to determine the migratory response of graft versus aortic SMCs.

METHODS

Thoracoabdominal grafts were implanted in beagles. The SMCs were harvested from the graft and infrarenal aorta. Migration was determined with the use of a razor-scrape assay and computerized image analysis.

RESULTS

The mean distance migrated and the number of cells that migrated were greater in graft SMCs at baseline (185 +/- 18 micrometer and 108 +/- 17 cells) compared with aortic cells (110 +/- 10 micrometer and 42 +/- 5 cells)(P <.05). Baseline differences persisted after treatment with antibodies to PDGF. The addition of PDGF (10 ng/mL) resulted in increased migration in both graft (229 +/- 23 micrometer and 146 +/- 20 cells) and aortic SMCs (130 +/- 9 micrometer and 70 +/- 5 cells) compared with baseline (P <.05). The relative increase in response to PDGF was similar between the two groups (P = not significant).

CONCLUSIONS

Graft SMCs differ phenotypically from aortic SMCs; they exhibit increased basal migration that is independent of autocrine stimulation by PDGF. In contrast to their blunted proliferative response, graft SMCs have a similar migratory response to PDGF compared with aortic SMCs.

Effect of platelet-derived growth factor receptor-alpha and -beta blockade on flow-induced neointimal formation in endothelialized baboon vascular grafts

The growth of neointima and neointimal smooth muscle cells in baboon polytetrafluoroethylene grafts is regulated by blood flow. Because neointimal smooth muscle cells express both platelet-derived growth factor receptor-alpha and -beta (PDGFR-alpha and -beta), we designed this study to test the hypothesis that inhibiting either PDGFR-alpha or PDGFR-beta with a specific mouse/human chimeric antibody will modulate flow-induced neointimal formation. Bilateral aortoiliac grafts and distal femoral arteriovenous fistulae were placed in 17 baboons. After 8 weeks, 1 arteriovenous fistulae was ligated, normalizing flow through the ipsilateral graft while maintaining high flow in the contralateral graft. The experimental groups received a blocking antibody to PDGFR-alpha (Ab-PDGFR-alpha; 10 mg/kg; n=5) or PDGFR-beta (Ab-PDGFR-beta; 10 mg/kg; n=6) by pulsed intravenous administration 30 minutes before ligation and at 4, 8, 15, and 22 days after ligation. Controls received carrier medium alone (n=8). Serum antibody concentrations were followed. Grafts were harvested after 28 days and analyzed by videomorphometry. Serum Ab-PDGFR-alpha concentrations fell rapidly after day 7 to 0, whereas serum Ab-PDGFR-beta concentrations were maintained at the target levels (>50 microg/mL). Compared with controls (3.7+/-0.3), the ratio of the intimal areas (normalized flow/high flow) was significantly reduced in Ab-PDGFR-beta (1.2+/-0.2, P<0.01) but not in Ab-PDGFR-alpha (2.2+/-0.4). Ab-PDGFR-alpha decreased significantly the overall smooth muscle cell nuclear density of the neointima (P<0.01) compared with either the control or Ab-PDGFR-beta treated groups. PDGFR-beta is necessary for flow-induced neointimal formation in prosthetic grafts. Targeting PDGFR-beta may be an effective pharmacological strategy for suppressing graft neointimal development.

Platelets and restenosis

Restenosis is currently the major limitation of percutaneous transluminal coronary angioplasty (PTCA). Factors such as elastic recoil, migration of vascular smooth muscle cells from media to intima, neointimal proliferation and vascular remodeling underly the restenotic process. Presently there is no effective therapy available for restenosis. The role of platelets in the development of thrombosis and abrupt closure after PTCA is well recognized. However, the effects of platelets in PTCA extend well beyond the early phase. Although antiplatelet agents such as glycoprotein IIb/IIIa antagonists have been reported to reduce target vessel revascularization, major unresolved controversies still exist. This report reviews the potential role of platelets in restenosis. Various drugs, successfully tested in experimental studies and in a small number of human studies, that inhibit the effect of platelets on the restenotic process are also reviewed.

Novel method for the quantitative assessment of cell migration: a study on the motility of rabbit anterior cruciate (ACL) and medial collateral ligament (MCL) cells

A novel method of quantitating cell migration has been proposed for the potential utilization of tissue engineered scaffolds. Applying Alt's conservation law to describe the motion of first passage ACL and MCL cells, we have developed a quantitative method to assess innate differences in the motility of cells from these two ligamentous tissues. In this study, first passage ACL and MCL cells were cultured from four mature New Zealand white rabbits. One side of the cell monolayer was scraped completely away to create a wound model. The cell moved into the cell-free area, and cell density profiles were analyzed at 6 h and 12 h. Values of the random motility coefficient (mu) were then estimated by curve fitting the 6 h and 12 h data to a mathematical model, derived from the conservation law of cell flux. During 6 h of incubation in medium supplemented with 1% FBS, MCL cells (mu(MCL) = 4.63 +/- 0.65 X 10(-6) mm(2)/sec) were significantly (p < 0.05) more mobile than ACL cells (mu(ACL) = 2.51 +/- 0.31 X 10(-6) mm(2)/sec). At 12 h, the MCL cells also appeared to move faster (mu(ACL) = 4.39 +/- 0.63 X 10(-6) mm(2)/sec, mu(MCL) = 6.59 +/- 1.47 X 10(-6) mm(2)/sec), but the difference was not statistically significant (p = 0.18). Exposure of the cells to growth factors PDGF-BB or bFGF for 6 h had no significant effect on the migration of the ACL and MCL cells. However, exposure of the ACL cells (p < 0.05) and the MCL cells (p = 0.19) to 1 ng/mL of PDGFBB for 12 h enhanced their migration. Incubation with a high concentration (100 ng/mL) of PDGF-BB or bFGF at concentrations tested (1 or 100 ng/mL) for 12 h, produced little or no migratory stimulation on these ligament cells. Our findings support the previous qualitative observations made by numerous investigators. The novel methodology developed in this study may provide a basis for tissue engineering, and the results may be applied to tissue reconstruction techniques of the knee ligaments.

Cyclic AMP inhibited proliferation of human aortic vascular smooth muscle cells, accompanied by induction of p53 and p21

Although cAMP is an important second messenger that plays a pivotal role in the regulation of platelet aggregation and dilatation of blood vessels, little is known about the action of cAMP on the growth of vascular smooth muscle cells (VSMCs). Thus, we initially studied the effects of cAMP accumulation by using various cAMP stimulants, including a phosphodiesterase type 3 inhibitor (cilostazol) on human aortic VSMC growth. Accumulation of cAMP inhibited the platelet-derived growth factor (PDGF)-stimulated VSMC growth in a dose-dependent manner (P<0.01), whereas PDGF significantly stimulated the growth of human VSMCs. Thus, we focused on the role of cell cycle regulatory genes, especially on a negative regulator, an anti-oncogene, p53. The protein of p53 was potentiated by cilostazol as well as forskolin and 8-bromo-cAMP, whereas PDGF decreased p53 expression. Upregulation of p53 protein by cAMP was further confirmed by the observation that the decrease in p21, a p53-inducible protein, by PDGF was significantly attenuated by cilostazol in a dose-dependent manner (P<0.01). These results revealed that accumulation of cAMP inhibited VSMC proliferation, which was at least in part due to an increase in p53-p21 expression. Because p53 and p21 have been reported to induce apoptosis, we examined apoptotic cells for cAMP accumulation. Incubation of VSMCs with cilostazol resulted in a significant increase in apoptotic cells in a dose-dependent manner compared with vehicle treatment as assessed by nuclear chromatic morphology (P<0.01); forskolin also stimulated apoptotic cells. Consistent with nuclear staining, DNA fragmentation in VSMCs treated with forskolin as well as 8-bromo-cAMP and cilostazol was significantly increased compared with DNA fragmentation in VSMCs treated with vehicle, whereas PDGF significantly decreased the rate of DNA fragmentation (P<0.01). Overall, these results demonstrated that cAMP inhibited the proliferation of human aortic VSMCs, accompanied by p53-p21-mediated apoptosis. Analogues of cAMP that have direct inhibitory effects on VSMC proliferation can be considered as potential antiproliferative drugs against VSMC growth.

Tumor invasion: role of growth factor-induced cell motility

Cancer progression to the invasive and metastatic stage represents the most formidable barrier to successful treatment. To develop rational therapies, we must determine the molecular bases of these transitions. Cell motility is one of the defining characteristics of invasive tumors, enabling tumors to migrate into adjacent tissues or transmigrate limiting basement membranes and extracellular matrices. Invasive tumor cells have been demonstrated to present dysregulated cell motility in response to extracellular signals from growth factors and cytokines. Recent findings suggest that this growth factor receptor-mediated motility is one of the most common aberrations in tumor cells leading to invasiveness and represents a cellular behavior distinct from-adhesion-related haptokinetic and haptotactic migration. This review focuses on the emerging understanding of the biochemical and biophysical foundations of growth factor-induced cell motility and tumor cell invasiveness, and the implications for development of targeted agents, with particular emphasis on signaling from the epidermal growth factor (EGF) and hepatocyte growth factor (HGF) receptors, as these have most often been associated with tumor invasion. The nascent models highlight the roles of various intracellular signaling pathways including phospholipase C-gamma (PLC gamma), phosphatidylinositol (PI)3'-kinase, mitogen-activated protein (MAP) kinase, and actin cytoskeleton-related events. Development of novel agents against tumor invasion will require not only a detailed appreciation of the biochemical regulatory elements of motility but also a paradigm shift in our approach to and assessment of cancer therapy.

Identification of the Receptor-associated Signaling Enzymes That Are Required for Platelet-derived Growth Factor-AA-dependent Chemotaxis and DNA Synthesis

Activation of the platelet-derived growth factor (PDGF) alpha receptor (alphaPDGFR) leads to cell migration and DNA synthesis. These events are preceded by the ligand-induced tyrosine phosphorylation of the receptor and its association with SH2-containing signaling enzymes including Src family members (Src), the phosphotyrosine phosphatase SHP-2, phosphatidylinositol 3-kinase (PI3K), and phospholipase C-gamma1 (PLCgamma). In this study, we sought to systematically evaluate the relative roles of the signaling enzymes that are recruited to the alphaPDGFR for DNA synthesis and cell migration. Our approach was to generate and characterize tyrosine to phenylalanine alphaPDGFR mutants that failed to associate with one or more of the above listed signaling enzymes. In a 3T3-like cell line (Ph cells), PDGF-dependent DNA synthesis was strictly dependent on only one of the receptor-associated proteins, PI3K. In contrast, multiple signaling enzymes were required for maximal chemotaxis, as receptors unable to associate with either Src, PI3K, or PLCgamma initiated chemotaxis to 4, 47, or 56% of the wild-type level, respectively. Furthermore, coexpression of mutant receptors revealed that these signaling enzymes do not need to be on the same receptor for a cell to respond chemotactically to PDGF. We conclude that for the alphaPDGFR, PI3K plays a major role in initiating DNA synthesis, whereas PI3K, PLCgamma, and especially Src are required for chemotaxis.

Platelet-derived growth factor inhibits platelet activation in heparinized whole blood

We previously have demonstrated that human platelets have functionally active platelet-derived growth factor alpha-receptors. Studies with gel-filtered platelets showed that an autocrine inhibition pathway is transduced through this tyrosine kinase receptor during platelet activation. The physiological significance of this inhibitory effect of platelet-derived growth factor on gel-filtered platelets activation is, however, not known. In the present study, we investigated whether platelet-derived growth factor inhibits platelet activation under more physiological conditions in heparinized whole blood, which represents a more physiological condition than gel-filtered platelets. Using flow cytometric assays, we demonstrate here that platelet-derived growth factor inhibits thrombin-, thrombin receptor agonist peptide SFLLRN-, and collagen-induced platelet aggregation and shedding of platelet-derived microparticles from the platelet plasma membrane during platelet aggregation in stirred heparinized whole blood. The inhibitory effect of platelet-derived growth factor was dose dependent. However, under nonaggregating conditions (no stirring), we could not demonstrate any significant effect of platelet-derived growth factor on thrombin- and thrombin receptor agonist peptide-induced platelet surface expression of P-selectin. Our results demonstrate that platelet-derived growth factor appears to be a true antithrombotic agent only under aggregating conditions in heparinized whole blood.

Evidence for distinct signaling properties and biological responses induced by the PDGF receptor alpha and beta subtypes

Platelet-derived growth factor (PDGF) acts as a potent mitogen, chemoattractant and survival factor for mesenchymal cells. In addition to its importance in mammalian development, PDGF plays a critical role in physiological repair mechanisms and in the pathogenesis of various proliferative diseases. The biological effects of PDGF are initiated via two related receptor tyrosine kinases, termed alpha and betaPDGF receptors. Recent observations provide increasing evidence for distinct roles of the two PDGF receptor subtypes in both embryogenesis and disease formation. Moreover, characterization of the signal relay mechanisms indicates, that the alpha and betaPDGF receptors are not identical in their ability to bind intracellular effector molecules. Furthermore, the two PDGF receptors initiate overlapping, yet distinct signal transduction pathways. These differences may account for some of the variabilities in biological responses resulting from activation of these two receptors.

Signal transduction via platelet-derived growth factor receptors

Platelet-derived growth factor (PDGF) exerts its stimulatory effects on cell growth and motility by binding to two related protein tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation, allowing binding and activation of cytoplasmic SH2-domain containing signal transduction molecules. Thereby, a number of different signaling pathways are initiated leading to cell growth, actin reorganization migration and differentiation. Recent observations suggest that extensive cross-talk occurs between different signaling pathways, and that stimulatory signals are modulated by inhibitory signals arising in parallel.

Heparan sulfate proteoglycans mediate a potent inhibitory signal for migration of vascular smooth muscle cells

Migration of vascular smooth muscle cells (SMCs) is a key step in vascular remodeling and formation of pathological lesions in diseased arteries and may be controlled by extracellular matrix (ECM) and by factors that regulate ECM composition, such as platelet-derived growth factor (PDGF). In culture, PDGF-AB and -BB enhance but PDGF-AA (although having no effect alone) suppresses SMC migration stimulated by other PDGF isoforms. To determine whether the migration-inhibitory mechanism of PDGF-AA was mediated by ECM composition, we examined baboon SMC migration in a Boyden chamber assay using filters coated with different ECM proteins. PDGF-AA suppressed the PDGF-BB-induced migration of baboon SMCs on a filter coated with basement membrane proteins (Matrigel) and fibronectin but failed to inhibit cell migration on a type I collagen (Vitrogen)-coated filter. Fibronectin and fibronectin fragments that contain heparin-binding domains permitted PDGF-AA inhibition of cell migration, but a fragment lacking heparin-binding domains did not. Treatment of SMCs with heparin lyases II and III, but not with chondroitin ABC lyase, diminished the PDGF-AA-mediated inhibition of migration. PDGF-AA stimulated accumulation of proteoglycan (PG) in the cell layer more potently than did PDGF-BB, whereas the turnover of cell layer PG was unaffected by either PDGF-AA or -BB. Northern blot analysis revealed that PDGF-AA increased syndecan-1 mRNA expression more than did PDGF-BB, whereas both PDGF isoforms decreased perlecan expression. The changes in cell migration and PG synthesis induced by PDGF-AA were accompanied by changes in the morphology of SMCs. PDGF-AA dramatically induced the spreading of SMCs, whereas the heparin lyase treatment of PDGF-AA-stimulated cultures diminished cell spreading. The data suggest that PDGF-AA selectively modifies heparan sulfate PG accumulation on SMCs and thereby influences the interactions of SMCs with heparin-binding ECM proteins. These interactions, in turn, generate signals that suppress SMC migration.

Platelet-derived growth factor-BB, insulin-like growth factor-I, and phorbol ester activate different signaling pathways for stimulation of vascular smooth muscle cell migration

Vascular smooth muscle cell (VSMC) migration is an important process in the development of vascular occlusive disease. To investigate mitogen regulation of VSMC migration, a cell-layer-scrape assay was used to measure migration 20 h after stimulation of VSMC with platelet-derived growth factor-BB (PDGF-BB), insulin-like growth factor I (IGF-I), or phorbol 12-myristate 13-acetate (PMA). The contributions of cell proliferation were eliminated by treatment of VSMC with hydroxyurea, which suppressed DNA synthesis.PDGF-BB stimulated VSMC migration 2.5-fold, while PMA and IGF-I stimulated migration 1.7- and 1.5-fold, respectively. The importance of protein kinase C (PKC), ERK, and phosphoinositide-3' kinase (PI3 kinase) in mitogen-stimulated migration was investigated, using specific inhibitors of these signaling molecules. PDGF-BB-stimulated migration was inhibited by the general PKC inhibitor RO 31-8220 (40%), the MEK inhibitor PD98059 (31%), and the PI3 kinase inhibitor wortmannin (22%) but not by PMA-induced downregulation of conventional and novel PKC isoforms. IGF-I-stimulated migration was inhibited by RO 31-8220 (34%) and wortmannin (37%) but was much less affected by PD98059 (19%) or PKC downregulation (10%). PMA-stimulated migration was inhibited by RO 31-8220 (53%), PD98059 (50%), wortmannin (45%), and PKC downregulation (47%). Western analysis confirmed that ERK was strongly activated by PDGF-BB and PMA but not by IGF-I. To examine potential in vivo negative regulators of VSMC migration, we analyzed the ability of heparin, an analogue of heparan sulfate, and TGFbeta to attenuate mitogen-stimulated migration. Heparin but not TGFbeta inhibited VSMC migration stimulated by all three mitogens. Delayed-addition experiments showed that RO 31-8220 retained substantial inhibitory activity even if added 3 h after PMA or IGF-I stimulation and 5 h after PDGF-BB addition, suggesting that sustained PKC activation is important for migration. The MEK inhibitor retained some effectiveness for 5 h after PDGF-BB stimulation but only 1 h after PMA addition. Western analysis showed ERK activation was transient after PMA treatment but sustained for 6 h after PDGF-BB treatment. Heparin strongly inhibited migration even if added 5-7 h after mitogen stimulation, suggesting that heparin may inhibit both short- and long-term signals necessary for migration. The present studies indicate that PMA and IGF-I activate a limited number of second messengers resulting in moderate stimulation of migration; in contrast PDGF-BB stimulates multiple signaling pathways resulting in strong stimulation of migration and lessened sensitivity to inhibitory signals.

Differences in cellular responses to mitogens in arterial smooth muscle cells derived from patients with moyamoya disease

BACKGROUND AND PURPOSE

Moyamoya disease is a progressive cerebrovascular occlusive disease affecting primarily children. The etiology remains unknown. We examined the chemotactic and proliferative activities of inflammatory cell products from arterial smooth muscle cells (SMCs) derived from moyamoya patients and compared them with those from control subjects.

METHODS

We used 12 SMC strains from moyamoya patients and eight from control subjects. SMC migration was examined in a micro chemotaxis chamber. DNA synthesis was measured by an immunoperoxidase technique.

RESULTS

Platelet-derived growth factor (PDGF)-BB markedly stimulated cell migration and DNA synthesis in control SMCs. PDGF-AA stimulated only DNA synthesis in control SMCs. In moyamoya SMCs, PDGF-AA and PDGF-BB stimulated cell migration but not DNA synthesis. Basic fibroblast growth factor had little migratory activity but stimulated DNA synthesis in moyamoya SMCs and control SMCs. Conversely, hepatocyte growth factor stimulated cell migration but not DNA synthesis in moyamoya SMCs and control SMCs. In contrast, interleukin-1 beta (IL-1 beta) significantly stimulated the migration and DNA synthesis of control SMCs, while it inhibited moyamoya SMC migration. The levels of IL-1 beta-induced nitric oxide production did not differ between moyamoya SMCs and control SMCs, suggesting that IL-1 beta inhibits the migration of moyamoya SMCs through a nitric oxide-independent pathway.

CONCLUSIONS

The differences in responses to PDGF and IL-1 in moyamoya SMCs are involved in the mechanism by which intimal thickening develops in moyamoya disease.

Synergistic inhibition of vascular smooth muscle cell migration by phosphodiesterase 3 and phosphodiesterase 4 inhibitors

Cyclic nucleotide phosphodiesterases (PDEs) hydrolyze cAMP or cGMP and terminate their signaling. Two important families of PDEs that regulate cAMP signaling in cardiovascular tissues are the cGMP-inhibited PDEs (PDE3) and the cAMP-specific PDEs (PDE4). In this study, we have used a combination of an in vitro motility assay and a sensitive method for the measurement of cAMP in order to determine the relative roles of PDE3 and of PDE4 in the regulation of cAMP-mediated inhibition of VSMC migration. Our data demonstrate that forskolin, an activator of adenylyl cyclases, causes concentration-dependent inhibition of platelet-derived growth factor-induced VSMC migration. Incubation of cultured VSMCs with a PDE4-selective inhibitor, Ro 20-1724, markedly potentiated both the antimigratory effect and the increase in cAMP caused by forskolin. Cilostamide, a PDE3-selective compound, did not affect either the antimigratory activity of forskolin or its ability to increase cAMP. Cilostamide and Ro 20-1724 interacted synergistically to potentiate the inhibition of VSMC migration by forskolin and caused a supra-additive increase in cAMP. These data are consistent with an important role for both PDE3 and PDE4 in the regulation of cAMP-mediated inhibition of VSMC migration.

Amino-terminal fragment (1-34) of parathyroid hormone-related protein inhibits migration and proliferation of cultured vascular smooth muscle cells

We investigated the effects of amino-terminal fragment (1-34) of parathyroid hormone-related protein [PTHrP-(1-34)] on the migration and proliferation of vascular smooth muscle cells (VSMCs). Cultured VSMCs (5-9th passage) obtained from the aortas of male Wistar rats were used in this study. Migration of VSMCs was assessed using a modified Boyden's chamber. Proliferation of VSMCs was evaluated by measuring [3H]thymidine incorporation and counting cell numbers. PTHrP-(1-34) inhibited 10% fetal bovine serum (FBS)-induced increase in migration of VSMCs (61% of control at 1 micromol/l) in a concentration-dependent manner. PTHrP-(1-34) also inhibited 5% FBS-induced increase in [3H]thymidine incorporation (37% of control at 1 micromol/l) and cell number of VSMCs (33% of control at 1 micromol/l) in a concentration-dependent manner. Parathyroid hormone (PTH)-(1-34) inhibited the migration and DNA synthesis of VSMCs to a similar extent. PTHrP-(7-34), a PTH/PTHrP receptor antagonist, significantly inhibited these effects of PTHrP and PTH. PTHrP-(1-34) also inhibited platelet-derived growth factor-BB (5 ng/ml)-induced migration and DNA synthesis of VSMCs. These findings suggest that PTHrP-(1-34) inhibits the migration and proliferation of VSMCs through PTH/PTHrP receptors.

Quantitation of platelet-derived growth factor receptors in human arterial smooth muscle cells in vitro

Platelet-derived growth factor (PDGF) is suggested to play an important role in the development of atherosclerosis as a migratory and mitogenic stimulus to arterial smooth muscle cells (ASMCs). Stimulated and unstimulated ASMCs were studied with respect to PDGF receptor (PDGF-R) mRNA and protein expression. Quantitative RT-PCR was developed for simultaneous evaluation of both PDGF-R alpha and -R beta mRNA expression and a quantitative ELISA for estimation of corresponding PDGF-R subunits. On the mRNA level, the overall PDGF-R beta expression was approximately 100 times lower than that of PDGF-R alpha. Furthermore, although PDGF-R alpha mRNA levels were high irrespective of hASMC phenotype, PDGF-R beta mRNA was influenced by serum stimulation with lower copy numbers in proliferating and confluent cells compared with quiescent cells. On the protein level, quiescent hASMCs expressed 10 times more PDGF-R beta than PDGF-R alpha. Serum stimulation decreased cell surface PDGF-Rs, with most prominent loss of PDGF-R alpha (ELISA and immunohistochemistry). Our results suggest a differential regulatory pattern for PDGF-R alpha and -R beta and are compatible with the usage of alternative promoters for regulation of -R alpha expression. Further, it seems that the number of available receptor subunits is not the only determinant of variations in cell stimulation with different PDGF isoforms.