Endothelial cell regulation by transforming growth factor-beta

Alterations of transcriptome expression, cell cycle, and mitochondrial superoxide reveal foetal endothelial dysfunction in Saudi women with gestational diabetes mellitus

Gestational diabetes mellitus (GDM) affects one in four Saudi women and is associated with high risks of cardiovascular diseases in both the mother and foetus. It is believed that endothelial cells (ECs) dysfunction initiates these diabetic complications. In this study, differences in the transcriptome profiles, cell cycle distribution, and mitochondrial superoxide (MTS) between human umbilical vein endothelial cells (HUVECs) from GDM patients and those from healthy (control) subjects were analysed. Transcriptome profiles were generated using high-density expression microarray. The selected four altered genes were validated using qRT-PCR. MTS and cell cycle were analysed by flow cytometry. A total of 84 altered genes were identified, comprising 52 upregulated and 32 downregulated genes in GDM.HUVECs. Our selection of the four interested altered genes (TGFB2, KITLG, NEK7, and IGFBP5) was based on the functional network analysis, which revealed that these altered genes are belonging to the highest enrichment score associated with cellular function and proliferation; all of which may contribute to ECs dysfunction. The cell cycle revealed an increased percentage of cells in the G2/M phase in GDM.HUVECs, indicating cell cycle arrest. In addition, we found that GDM.HUVECs had increased MTS generation. In conclusion, GDM induces persistent impairment of the biological functions of foetal ECs, as evidenced by analyses of transcriptome profiles, cell cycle, and MTS even after ECs culture in vitro for several passages under normal glucose conditions.

TGF-β1 polymorphism increases the risk of bleeding complications in patients on oral anticoagulant after cardiac valve replacement

Although an elevated INR is highly associated with an increased risk of warfarin-associated bleeding, it has been reported that some patients also experience bleeding complications at therapeutic INRs. TGF-β1 polymorphisms has been reported to cause vascular malformations, resulting in bleeding complications, but there are few published genetic studies regarding bleeding complications in patients on warfarin therapy. This study aimed to determine if there is an association between transforming growth factor beta-1 (TGF-β1) polymorphisms and bleeding complications in patients who maintain international normalized ratios (INRs) of 2.0-3.0 with warfarin therapy after cardiac valve replacement. Eleven single nucleotide polymorphis (SNPs) of TGF-β1 (rs1800469, rs2241718, rs4803455, rs2241717, rs2241716, rs2241715, rs2241714, rs11083616, rs2317130, rs747857, and rs1982073) were analyzed. Univariate and multivariable analyses were conducted to evaluate the associations between genetic polymorphisms and bleeding risk. Attributable risk and the number needed to genotype (NNG) were calculated to identify the potential clinical value of genotyping. A discrimination of model was assessed via an analysis of the area under the receiver operating curve (AUROC). To test the model's goodness of fit, a Hosmer-Lemeshow test was performed. Of 142 patients, 21 experienced bleeding complications. Among analyzed single nucleotide polymorphis (SNPs) of TGF-β1 (rs1800469, rs2241718, rs4803455, rs2241717, rs2241716, rs2241715, rs2241714, rs11083616, rs2317130, rs747857, and rs1982073), AA genotype carriers in rs2241718 had about 5.5 times more bleeding complications than those with the G allele after adjusting for other confounders. The attributable risk and NNG for rs2241718 were 81.9% and 57.8, respectively. The presence of atrial fibrillation and myocardial infarction increased bleeding complications 3.9- and 9.8-fold, compared with those without atrial fibrillation and myocardial infarction, respectively. Bleeding complications during warfarin therapy in patients with mechanical heart valves were associated with TGF-β1 polymorphisms as well as atrial fibrillation and myocardial infarction.

Epithelial-mesenchymal transition of the retinal pigment epithelium causes choriocapillaris atrophy

Epithelial-to-mesenchymal transition (EMT) of the retinal pigment epithelium (RPE) is commonly observed at sites of choroidal neovascularization in patients suffering from age-related macular degeneration. To learn in an experimental model how RPE EMT affects the biology of the choroidal vasculature, we studied transgenic mice (βB1-TGF-β1) with ocular overexpression of transforming growth factor-β1 (TGF-β1). RPE EMT was detectable at postnatal day (P)1 and included marked structural and functional alterations such as loss of the outer blood-retina barrier and reduced mRNA expression of the RPE-characteristic molecules Rlbp1, Rpe65, Rbp1 and Vegfa. Moreover, vascular endothelial growth factor (VEGF) was not detectable by immunohistochemistry at the RPE/choroid interface, while RPE cells stained intensely for α-smooth muscle actin. The choriocapillaris, the characteristic choroidal capillary network adjacent to the RPE, developed normally and was not obviously changed in embryonic transgenic eyes but was absent at P1 indicating its atrophy. At around the same time, photoreceptors stopped to differentiate and photoreceptor apoptosis was abundant in the second week of life. Structural changes were also seen in the retinal vasculature of transgenic animals, which did not form intraretinal vessels, and the hyaloid vasculature, which did not regress. In addition, the amounts of retinal HIF-1α and its mRNA were markedly reduced. We conclude that high amounts of active TGF-β1 in the mouse eye cause transdifferentiation of the RPE to a mesenchymal phenotype. The loss of epithelial differentiation leads to the diminished synthesis of RPE-characteristic molecules including that of VEGF. Lack of RPE-derived VEGF causes atrophy of the choriocapillaris, a scenario that disrupts photoreceptor differentiation and finally results in photoreceptor apoptosis. Lack of retinal vessel formation and of hyaloid vessel regression might be caused by the decrease in the metabolic requirements of the neuroretina leading to low amounts of retinal HIF-1α. In summary, our data indicate that failure of RPE differentiation may well precede and cause atrophy of the choriocapillaris. In contrast, RPE EMT is not sufficient to cause choroidal neovascularization.

Pericyte contractility controls endothelial cell cycle progression and sprouting: insights into angiogenic switch mechanics

Microvascular stability and regulation of capillary tonus are regulated by pericytes and their interactions with endothelial cells (EC). While the RhoA/Rho kinase (ROCK) pathway has been implicated in modulation of pericyte contractility, in part via regulation of the myosin light chain phosphatase (MLCP), the mechanisms linking Rho GTPase activity with actomyosin-based contraction and the cytoskeleton are equivocal. Recently, the myosin phosphatase-RhoA-interacting protein (MRIP) was shown to mediate the RhoA/ROCK-directed MLCP inactivation in vascular smooth muscle. Here we report that MRIP directly interacts with the β-actin-specific capping protein βcap73. Furthermore, manipulation of MRIP expression influences pericyte contractility, with MRIP silencing inducing cytoskeletal remodeling and cellular hypertrophy. MRIP knockdown induces a repositioning of βcap73 from the leading edge to stress fibers; thus MRIP-silenced pericytes increase F-actin-driven cell spreading twofold. These hypertrophied and cytoskeleton-enriched pericytes demonstrate a 2.2-fold increase in contractility upon MRIP knockdown when cells are plated on a deformable substrate. In turn, silencing pericyte MRIP significantly affects EC cycle progression and angiogenic activation. When MRIP-silenced pericytes are cocultured with capillary EC, there is a 2.0-fold increase in EC cycle entry. Furthermore, in three-dimensional models of injury and repair, silencing pericyte MRIP results in a 1.6-fold elevation of total tube area due to EC network formation and increased angiogenic sprouting. The pivotal role of MRIP expression in governing pericyte contractile phenotype and endothelial growth should lend important new insights into how chemomechanical signaling pathways control the "angiogenic switch" and pathological angiogenic induction.

Signal transduction in vasculogenesis and developmental angiogenesis

The vasculature is a highly specialized organ that functions in a number of key physiological tasks including the transport of oxygen and nutrients to tissues. Formation of the vascular system is an essential and rate-limiting step in development and occurs primarily through two main mechanisms, vasculogenesis and angiogenesis. Both vasculogenesis, the de novo formation of vessels, and angiogenesis, the growth of new vessels from pre-existing vessels by sprouting, are complex processes that are mediated by the precise coordination of multiple cell types to form and remodel the vascular system. A host of signaling molecules and their interaction with specific receptors are central to activating and modulating vessel formation. This review article summarizes the current state of research involving signaling molecules that have been demonstrated to function in the regulation of vasculogenesis and angiogenesis, as well as molecules known to play a role in vessel maturation, hypoxia-driven angiogenesis and arterial-venous specification.

Microvascular modifications in diabetic retinopathy

Patients struggling with diabetes are at elevated risks for several sight-threatening diseases, including proliferative diabetic retinopathy (DR). DR manifests in two stages: first, the retinal microvasculature is compromised and capillary degeneration occurs; subsequently, an over-compensatory angiogenic response is initiated. Early changes in the retinal microcirculation include disruptions in blood flow, thickening of basement membrane, eventual loss of mural cells, and the genesis of acellular capillaries. Endothelial apoptosis and capillary dropout lead to a hypoxic inner retina, alterations in growth factors, and upregulation of inflammatory mediators. With disease progression, pathologic angiogenesis generates abnormal preretinal microvessels. Current therapies, which include panretinal photocoagulation and vitrectomy, have remained unaltered for several decades. With several exciting preclinical advances, emergent technologies and innovative cellular targets may offer newfound hope for developing "next-generation" interventional or preventive clinical approaches that will significantly advance current standards of care and clinical outcomes.

High-throughput flow cytometry purification of transduced progenitors expressing defined levels of vascular endothelial growth factor induces controlled angiogenesis in vivo

Delivery of therapeutic genes by genetically modified progenitors is a powerful tool for regenerative medicine. However, many proteins remain localized within or around the expressing cell, and heterogeneous expression levels can lead to reduced efficacy or increased toxicity. For example, the matrix-binding vascular endothelial growth factor (VEGF) can induce normal, stable, and functional angiogenesis or aberrant angioma growth depending on its level of expression in the microenvironment around each producing cell, and not on its total dose. To overcome this limitation, we developed a flow cytometry-based method to rapidly purify transduced cells expressing desired levels of a therapeutic transgene. Primary mouse myoblasts were transduced with a bicistronic retrovirus expressing VEGF linked to a nonfunctional, truncated form of the syngenic molecule CD8a. By using a clonal population uniformly expressing a known VEGF level as a reference, cells producing similar VEGF amounts were rapidly sorted from the primary population on the basis of their CD8a fluorescence intensity. A single round of sorting with a suitably designed gate yielded a purified population that induced robust, normal, and stable angiogenesis, and completely avoided angioma growth, which was instead always caused by the heterogeneous parent population. This clinically applicable high-throughput technique allowed the delivery of highly controlled VEGF levels in vivo, leading to significantly improved safety without compromising efficacy. Furthermore, when applied to other suitable progenitor populations, this technique could help overcome a significant obstacle in the development of safe and efficacious vascularization strategies in the fields of regenerative medicine and tissue engineering.

Activation of TGF-beta1 through up-regulation of TSP-1 by retinoic acid in retinal pigment epithelial cells

PURPOSE

Retinoic acid (RA) affects the activation of transforming growth factor-beta 1 (TGF-beta1) in a variety of cells. We have previously shown that thrombospondin-1 (TSP-1) expression in retinal pigment epithelial (RPE) cells is up-regulated by RA. Since TSP-1 activates TGF-beta1, we investigated whether RA stimulates the activation of TGF-beta1 through up-regulation of TSP-1 in RPE cells.

METHODS

Human RPE cells were cultured with RA or TSP-1. The active form of TGF-beta1 in the culture medium was measured by enzyme-linked immunosorbent assay.

RESULTS

The active form of TGF-beta1 was increased dose-dependently by RA or TSP-1. The activation of TGF-beta1 by RA was significantly hampered by an anti-TSP-1 antibody. Also, antibodies against integrins alphavbeta3 and alphavbeta5 inhibited the activation of TGF-beta1.

CONCLUSIONS

These findings suggest that, in RPE cells, RA increases the activation of TGF-beta1 via up-regulation of TSP-1, and integrins such as alphavbeta3 and alphavbeta5 are essential in this activation step.

Prostate cancer cells regulate growth and differentiation of bone marrow endothelial cells through TGFbeta and its receptor, TGFbetaRII

BACKGROUND

The underlying mechanisms permitting prostate cancer bone metastasis are poorly understood. We previously showed that the highly metastatic prostate cancer cell line, PC-3, inhibits bone marrow endothelial (HBME-1) cell growth in collagen gels and induces them to differentiate into cords, resembling angiogenesis in vivo.

METHODS

cDNA microarray analysis was performed to identify cytokines responsible for the effects of PC-3 cells on HBME-1 cells. Cytokine and neutralizing antibody studies were done to further investigate specific angiogenic factors, such as transforming growth factor beta (TGFbeta). TGFbeta RNA and protein were detected by real-time RT-PCR and enzyme-linked immunosorbent assay (ELISA) analysis to measure their production by prostate cancer cell lines. Conditioned media experiments using TGFbeta neutralizing antibodies were used to analyze TGFbeta activation by prostate cancer cells.

RESULTS

PC-3 conditioned media altered the expression of several TGFbeta-regulated or -associated genes in HBME-1 cells. Low concentrations of TGFbeta cytokines inhibited HBME-1 cell growth to a similar level as PC-3 conditioned media and partially induced differentiation. Inhibitors and neutralizing antibodies directed against TGFbeta isoforms and TGFbeta receptor type 2 (TGFbetaRII) reversed the growth inhibition of HBME-1 cells conferred by PC-3 conditioned media. Yet, only TGFbetaRII neutralizing antibodies significantly inhibited HBME-1 differentiation. Also, prostate cancer cell lines produced low levels of TGFbeta RNA and protein, and were shown to activate serum-derived TGFbeta.

CONCLUSIONS

These results suggest that prostate cancer cells mediate growth inhibition and differentiation of bone marrow endothelial cells both through production and activation of TGFbeta as well as alteration of TGFbetaRII-mediated signal transduction. This could contribute to the establishment and growth of bone metastases.

Reactive oxygen species production via NADPH oxidase mediates TGF-beta-induced cytoskeletal alterations in endothelial cells

Cytoskeletal alterations in endothelial cells have been linked to nitric oxide generation and cell-cell interactions. Transforming growth factor (TGF)-beta has been described to affect cytoskeletal rearrangement in numerous cell types; however, the underlying pathway is unclear. In the present study, we found that human umbilical vein endothelial cells (HUVEC) have marked cytoskeletal alterations with short-term TGF-beta treatment resulting in filipodia formation and F-actin assembly. The cytoskeletal alterations were blocked by the novel TGF-beta type I receptor/ALK5 kinase inhibitor (SB-505124) but not by the p38 kinase inhibitor (SB-203580). TGF-beta also induced marked stimulation of reactive oxygen species (ROS) within 5 min of TGF-beta exposure. TGF-beta stimulation of ROS was mediated by the NAPDH oxidase homolog Nox4 as DPI, an inhibitor of NADPH oxidase, and dominant-negative Nox4 adenovirus blocked ROS production. Finally, inhibition of ROS with ROS scavengers or dominant-negative Nox4 blocked the TGF-beta effect on cytoskeleton changes in endothelial cells. In conclusion, our studies show for the first time that TGF-beta-induced ROS production in human endothelial cells is via Nox4 and that TGF-beta alteration of cytoskeleton in HUVEC is mediated via a Nox4-dependent pathway.

The transforming growth factor-beta family members bone morphogenetic protein-2 and macrophage inhibitory cytokine-1 as mediators of the antiangiogenic activity of N-(4-hydroxyphenyl)retinamide

PURPOSE

Tumor growth appears to be an angiogenesis-dependent process. N-(4-hydroxyphenyl)retinamide (fenretinide; 4HPR) has been found to inhibit and/or prevent tumor growth under diverse conditions. Although 4HPR is antiangiogenic, the molecular mechanisms of this effect remain largely unknown.

EXPERIMENTAL DESIGN

Endothelial cells were treated with 4HPR in vitro to study the effects on migration, invasion, and organization, as well as gene expression by microarray and quantitative PCR studies. In vivo angiogenesis was evaluated in the Matrigel model.

RESULTS

4HPR treatment substantially modified the biological activities of endothelial cells, repressing their capacity to migrate, invade, and organize into capillary-like structures. The inhibition of invasion induced by 4HPR was also associated with decreased activities of the metalloproteases matrix metalloproteinase-2 and CD13/APN. Using oligonucleotide microarrays, we observed that bone morphogenetic protein-2 and macrophage inhibitory cytokine-1, two multifunctional cytokines of the transforming growth factor-beta family that regulate the growth, differentiation, apoptosis, and matrix accumulation of a variety of cells, are up-regulated in vitro by 4HPR. Both these molecules specifically inhibited endothelial cell growth, migration, and invasion in vitro and suppressed angiogenesis in the Matrigel plug assay in vivo. Blocking antibodies to bone morphogenetic protein-2 were able to reverse the suppressive effects of 4HPR in vitro and in vivo.

CONCLUSIONS

These data support the conclusion that 4HPR inhibits tumor growth by repression of new vessel growth and identify novel points of regulation of angiogenesis in transforming growth factor-beta family proteins.

Rat liver sinusoidal endothelial cell phenotype is maintained by paracrine and autocrine regulation

The phenotypic features of liver sinusoidal endothelial cells (SEC), open fenestrae in sieve plates and lack of a basement membrane, are lost with capillarization. The current study examines localization of CD31 as a marker for the dedifferentiated, nonfenestrated SEC and examines regulation of SEC phenotype in vitro. CD31 localization in SEC was examined by confocal microscopy and immunogold-scanning electron microscopy. SEC cultured for 1 day express CD31 in the cytoplasm, whereas after 3 days, CD31 is also expressed on cell-cell junctions. Immunogold-scanning electron microscopy confirmed the absence of CD31 surface expression on fenestrated SEC 1 day after isolation and demonstrated the appearance of CD31 surface expression on SEC that had lost fenestration after 3 days in culture. SEC isolated from fibrotic liver do show increased expression of CD31 on the cell surface. Coculture with either hepatocytes or stellate cells prevents CD31 surface expression, and this effect does not require heterotypic contact. The paracrine effect of hepatocytes or stellate cells on SEC phenotype is abolished with anti-VEGF antibody and is reproduced by addition of VEGF to SEC cultured alone. VEGF stimulates SEC production of nitric oxide. NG-nitro-L-arginine methyl ester blocked the paracrine effect of hepatocytes or stellate cells on SEC phenotype and blocked the ability of VEGF to preserve the phenotype of SEC cultured alone. In conclusion, surface expression of CD31 is a marker of a dedifferentiated, nonfenestrated SEC. The VEGF-mediated paracrine effect of hepatocytes or stellate cells on maintenance of SEC phenotype requires autocrine production of nitric oxide by SEC.

Signaling pathways in vascular development

The vasculature is one of the most important and complex organs in the mammalian body. The first functional organ to form during embryonic development, the intricately branched network of endothelial and supporting periendothelial cells is essential for the transportation of oxygen and nutrients to and the removal of waste products from the tissues. Serious disruptions in the formation of the vascular network are lethal early in post-implantation development, while the maintenance of vessel integrity and the control of vessel physiology and hemodynamics have important consequences throughout embryonic and adult life. A full understanding of the signaling pathways of vascular development is important not just for understanding normal development but because of the importance of reactivation of angiogenic pathways in disease states. Clinically there is a need to develop therapies to promote new blood vessel formation in situations of severe tissue ischemia, such as coronary heart disease. In addition, there is considerable interest in developing angiogenic inhibitors to block the new vessel growth that solid tumors promote in host tissue to enhance their own growth. Already studies on the signaling pathways of normal vascular development have provided new targets for therapeutic intervention in both situations. Further understanding of the complexities of the pathways should help refine such strategies.

Tubedown-1 in remodeling of the developing vitreal vasculature in vivo and regulation of capillary outgrowth in vitro

Tubedown-1 (tbdn-1) is a mammalian homologue of the N-terminal acetyltransferase subunit NAT1 of Saccharomyces cerevisiae and copurifies with an acetyltransferase activity. Tbdn-1 expression in endothelial cells becomes downregulated during the formation of capillary-like structures in vitro and is regulated in vivo in a manner which suggests a functional role in dampening blood vessel development. Here we show that tbdn-1 is expressed highly in the vitreal vascular network (tunica vasculosa lentis and vasa hyaloidea propria) during the pruning and remodeling phases of this transient structure. The vitreal blood vessels of mice harboring a targeted inactivation of TGF-beta2 fail to remodel and abnormally accumulate, a phenomenon reminiscent of the ocular pathology resembling persistent fetal vasculature (PFV) in humans. Since suppression of normal tbdn-1 expression has been previously observed in retinal vessel proliferation, we analyzed vitreal vascular changes and tbdn-1 expression in TGF-beta2(-/-) eyes. The nuclei of vitreal vessel endothelial cells in TGF-beta2(-/-) eyes express proliferating cell nuclear antigen (PCNA) and exhibit increased levels of active (P42/44)mitogen-activated protein kinase (phospho-(P42/44)MAPK), characteristics consistent with proliferative endothelial cells. In contrast to normal vitreal vessels, collagen IV expression exhibited a disorganized pattern in the TGF-beta2(-/-) vitreal vessels, suggesting vessel disorganization and possibly a breakdown of vessel basal laminae. Moreover, vitreal vessels of TGF-beta2(-/-) mice lack expression of pericyte markers (CD13, alpha smooth muscle actin) and show ultrastructural changes consistent with pericyte degeneration. The accumulating vitreal blood vessels of TGF-beta2(-/-) mice, while maintaining expression of the endothelial marker von Willebrand Factor, show a significant decrease in the expression of tbdn-1. We addressed the functional role of tbdn-1 in the regulation of vitreal blood vessels using an in vitro model of choroid-retina capillary outgrowth. Clones of the RF/6A fetal choroid-retina endothelial cell line showing suppression of tbdn-1 levels after overexpression of an antisense TBDN-1 cDNA display a significant increase in the formation of capillary-like structures in vitro compared with controls. These findings suggest that tbdn-1 inhibits capillary-like formation in vitro and may serve to dampen vitreal blood vessel formation preceding the regression of the vitreal vasculature during development. Our results also suggest that tbdn-1 may participate with TGF-beta2 in regulating normal development of the vitreal vasculature.

Angiogenesis of the blood-brain barrier in vitro and the function of cerebral pericytes

Cerebral pericytes constitute an essential component of the blood-brain barrier (BBB) and are involved in blood vessel assembly. Recently, we reported on the induction of a BBB-specific enzyme expressed by cerebral pericytes (pericytic aminopeptidase N/pAPN) in coculture with cerebral endothelial cells. We completed this in vitro BBB system by adding astrocytes to these mixed cultures of endothelial cells and pericytes. Under these triculture conditions, endothelial cells and pericytes reorganize into capillary-like structures (CLSs). Capillary formation can also be achieved by the application of transforming growth factor beta 1 (TGF-b1) in the culture medium of endothelial-pericyte cultures lacking astrocytes. In contrast to the effect achieved by astrocytes, pericytes did not assemble with endothelial cells. In both cases (application of astrocytes or TGF-b1), endothelial cells underwent apoptosis. However, endothelial cells that form CLSs in the presence of pericytes appeared to be resistant to induction of apoptosis. On the basis of these observations, we concluded that astrocytes have a profound influence on the morphogenetic events underlying the organization of the vessel wall; that the effect of TGF-b1 is different from the astrocytic effect because it lacks induction of endothelial-pericyte association; and that pericytes stabilize CLSs formed by endothelial cells in coculture with astrocytes.

Angiogenesis as a target for gastric cancer

BACKGROUND

The growth of solid tumors and the formation of metastases depend on angiogenesis. Both tumor cells and host cells secrete a variety of factors to stimulate angiogenesis.

METHODS

We investigated the expression of angiogenic factors in gastric cancer in vitro and in vivo.

RESULTS

The expression of one of the angiogenic factors, vascular endothelial growth factor antigen, in gastric cancer cells can thus serve as a pertinent predictive factor for hematogenous invasion or metastasis, in addition to having prognostic value. The presence of micrometastasis in bone marrow was closely related to vascular endothelial growth factor positivity and microvessel density in the primary gastric cancer. In in vivo experiments antiangiogenic agents with cytotoxic anticancer drugs formed a highly effective modulator combination for the treatment of the Lewis lung carcinoma against primary and metastatic disease.

CONCLUSIONS

Antiangiogenic agents may thus be valuable for long-term administration to maintain tumor dormancy because drug resistance does not develop, and these agents have a sustained effect. As a target, antiangiogenic therapy may therefore be potentially able to prolong survival time of patients with gastric cancer.

Growth factors in glioma angiogenesis: FGFs, PDGF, EGF, and TGFs

It has become well accepted that solid tumors must create a vascular system for nutrient delivery and waste removal in order to grow appreciably. This process, angiogenesis, is critical to the progression of gliomas, with vascular changes accompanying the advancement of these tumors. The cascade of events in this process of blood vessel formation involves a complex interplay between tumor cells, endothelial cells, and their surrounding basement membranes in which enzymatic degradation of surrounding ground substance and subsequent endothelial cell migration, proliferation, and tube formation occurs. It is likely that a host of growth factors is responsible for mediating these key events. To date, a role for Vascular Endothelial Growth Factor (VEGF) in glioma angiogenesis has been convincingly demonstrated. This review explores the contribution of other growth factors--Fibroblast Growth Factors (FGFs), Platelet-Derived Growth Factor (PDGF), Epidermal Growth Factor (EGF), and Transforming Growth Factors (TGFs)--to glioma angiogenesis. These growth factors may influence glioma angiogenesis by directly stimulating endothelial cell proliferation, by mediating the expression of key proteases on endothelial cells necessary for angiogenesis, or by regulating the expression of VEGF and of each other.

Differential gene expression by endothelial cells in distinct angiogenic states

Angiogenesis is a complex process that can be regarded as a series of sequential events comprising a variety of tissue cells. The major problem when studying angiogenesis in vitro is the lack of a model system mimicking the various aspects of the process in vivo. In this study we have used two in vitro models, each representing different and distinct aspects of angiogenesis. Differentially expressed genes in the two culture forms were identified using the suppression subtractive hybridization technique to prepare subtracted cDNA libraries. This was followed by a differential hybridization screen to pick up overexpressed clones. Using comparative multiplex RT-PCR we confirmed the differential expression and showed differences up to 14-fold. We identified a broad range of genes already known to play an important role during angiogenesis like Flt1 or TIE2. Furthermore several known genes are put into the context of endothelial cell differentiation, which up to now have not been described as being relevant to angiogenesis, like NrCAM, Claudin14, BMP-6, PEA-15 and PINCH. With ADAMTS4 and hADAMTS1/METH-1 we further extended the set of matrix metalloproteases expressed and regulated by endothelial cells.

Glucose-mediated regulation of transforming growth factor-beta (TGF-beta) and TGF-beta receptors in human retinal endothelial cells

PURPOSE

Diabetic retinopathy is a micro-angiopathy affecting predominantly small vessels of the retina. Clinical trials have demonstrated a strong association between tight glucose control and a reduction in the incidence and the severity of diabetic retinopathy. Transforming growth factor beta (TGF-beta) is involved in the control of endothelial cell proliferation, adhesion, and deposition of extracellular matrix, thus TGF-beta may play a role in the control of endothelial cell proliferation seen in the disease. We wished to investigate the regulation of transforming growth factor beta and its receptors (type I and II) in human retinal endothelial cells exposed to a range of glucose concentrations.

METHODS

Human retinal endothelial cells were isolated from donor eyes, cultured in vitro and exposed to a range of glucose concentrations (0-25 mmol/l). TGF-beta protein and mRNA levels were determined by ELISA and Northern analysis, respectively. The binding affinities and TGF-beta receptor numbers were defined using a binding assay.

RESULTS

Northern hybridisation and ELISA showed that after 8 hours, the level of TGF-beta mRNA and protein was significantly higher at 15mmol/l compared to 5, 20 or 25mmol/ l. Binding assays showed that for high glucose (25 mmol/l), human retinal endothelial cells express a population of TGF-beta receptors with higher affinity for its ligand than at 5 or 15 mmol/l.

CONCLUSIONS

These results demonstrate that glucose regulates TGF-beta mRNA and protein production and also TGF-beta receptor expression in human retinal endothelial cells. Thus, the glucose-mediated changes that occur in diabetic patients may expose human retinal endothelial cells to potential angiogenic factors which may influence disease progression.

Normoxic wound fluid contains high levels of vascular endothelial growth factor

OBJECTIVE

To examine the temporal integration of vascular endothelial growth factor (VEGF), which has been shown to be present in wound fluid, with the putatively related processes of wound fluid oxygen content, wound angiogenesis, and granulation tissue formation.

SUMMARY BACKGROUND DATA

During cutaneous wound repair, new tissue formation starts with reepithelialization and is followed by granulation tissue formation, including neutrophil and macrophage accumulation, fibroblast ingrowth, matrix deposition, and angiogenesis. Because angiogenesis and increased vascular permeability are characteristic features of wound healing, VEGF may play an important role in tissue repair.

METHODS

A ventral hernia, surgically created in the abdominal wall of female swine, was repaired using silicone sheeting and skin closure. Over time, a fluid-filled wound compartment formed, bounded by subcutaneous tissue and omentum. Ultrasonography was performed serially to examine the anatomy and dimensions of the subcutaneous tissue and wound compartment. Serial wound fluid samples, obtained by percutaneous aspiration, were analyzed for PO2, PCO2, pH, and growth factor concentrations.

RESULTS

Three independent assays demonstrate that VEGF protein is present at substantially elevated levels in a wound fluid associated with the formation of abdominal granulation tissue. However, the wound fluid is not hypoxic at any time. Serial sampling reveals that transforming growth factor beta-1 protein appears in the wound fluid before VEGF.

CONCLUSIONS

The results suggest that VEGF is a prominent regulator of wound angiogenesis and vessel permeability. A factor other than hypoxia, perhaps the earlier appearance of another growth factor, transforming growth factor beta-1, may positively regulate VEGF appearance in the wound fluid.

Immunodetection and characterisation of soluble CD105-TGFbeta complexes

CD105 (endoglin) is a receptor for transforming growth factor beta (TGFbeta). Although methods to measure soluble forms of TGFbeta and CD105 have been published, no assay is available to quantify the receptor-ligand complexes. We describe both an indirect enzyme-linked immunosorbent assay for the quantitation of soluble CD105-TGFbeta1 and the characterization of the complexes by immunoprecipitation and immunoblotting. Mab E9, specifically reactive with CD105, was utilised as the capture reagent in the ELISA system. Detection of complexes was achieved using chicken antibody against TGFbeta1 and the subsequent detection of bound antibody demonstrated by the addition of anti-species antiserum conjugated to horseradish peroxidase (HRP). By using enhanced chemiluminescence and optimised antibodies, the assay was made sufficiently sensitive and reproducible to detect low levels of circulating complexes. Whether the assay had any practical applications was evaluated in breast cancer patients. Plasma levels of CD105-TGFbeta1 were significantly elevated in 59 patients with breast cancer compared to 52 age matched normal women (p < 0.001). Immunoprecipitation using a rabbit anti-CD105 antibody, which reacts with both dimeric and monomeric CD105, and immunoblotting showed that three molecular forms of CD105-TGFbeta1 complexes > 200, 195, and 125 kDa existed in the plasma. We believe these represent the oligomer, dimer and probably the protease degraded form of CD105 complexed to TGFbeta1. The resistance to hypertonic solution, SDS and heat treatment suggested that the soluble CD105-TGFbeta1 complex may be linked by covalent bonds. The measurement of CD105-TGFbeta complexes in the circulation may have important clinical applications not only in cancer but also in patients with other angiogenic diseases such as rheumatoid arthritis, myocardial infarction and stroke.

Growth factors reverse the impaired sprouting of microvessels from aged mice

Aging is accompanied by impaired angiogenesis and deficient expression of several angiogenic growth factors. To test the hypothesis that replacement of these factors would improve angiogenesis in aged animals, we cultured microvessels derived from the epididymal fat pad of aged and young mice ("aged" and "young" microvessels) in three-dimensional collagen gels for 2 weeks and measured their sprouting (formation of branch points) in response to fetal bovine serum (FBS), endothelial cell growth supplement (ECGS), and the specific growth factors transforming growth factor-beta1 (TGF-beta1), vascular endothelial growth factor (VEGF), insulin-like growth factor-1 (IGF-1), and basic fibroblast growth factor (bFGF). In the presence of culture medium with 1% FBS (Minimal medium), sprouting of aged microvessels was significantly less than sprouting of young microvessels. The addition of high levels of FBS and ECGS to Minimal medium enhanced the sprouting of microvessels from aged mice to a greater degree than that of young mice, such that the difference between the two age groups was no longer significant. Formation of branch points by aged microvessels was also significantly increased by Minimal medium supplemented with TGF-beta1, bFGF, IGF-1, or VEGF (listed in order of highest to lowest stimulation). Sprouts generated in the presence of VEGF possessed a particularly high percentage of endothelial cells. Mitomycin C did not diminish the degree of sprouting induced by TGF-beta1, VEGF, or IGF-1, a result indicating that early stages of angiogenesis, including formation of branch points, do not require cell division. From our findings in vitro, we propose that age-related deficiencies in angiogenesis in vivo are likely to be due, in part, to a decrease in angiogenic growth factors in the extracellular milieu.

Mammary carcinoma cells over-expressing tissue inhibitor of metalloproteinases-1 show enhanced vascular endothelial growth factor expression

The tissue inhibitor of metalloproteinases-1 (TIMP-1) has at least 2 independent functions, i.e., regulation of matrix metalloproteinases and erythroid-potentiating activity. We investigated the effects of TIMP-1 over-expression on tumor growth, using cloned lines derived from a TIMP-1-transfected rat breast carcinoma cell line. The in vitro growth rate of the TIMP-1-transfected clones was indistinguishable from that of the control. In contrast, the highest TIMP-1-producing clone (159.0 ng/ml), designated as T-H, formed 4.6-fold larger s.c. tumors than did the control after 14 days. Tumors derived from an intermediate TIMP-1-producing clone (45.4 ng/ml), designated as T-M, were 1.9-fold larger than the control. TIMP-1 over-expression was associated with increased vascular endothelial growth factor (VEGF) expression, vascularization and proliferative activity of the s.c. tumors. Similar to the rat breast carcinoma cells, transfection of TIMP-1 cDNA into the human breast carcinoma cell line MCF-7 resulted in up-regulation of VEGF, with a linear relationship between TIMP-1 and VEGF production in 9 cell clones examined. There was, however, no change in VEGF expression when the rat and human breast carcinoma cell lines were exposed to exogenous recombinant TIMP-1. Our findings suggest that over-expression of TIMP-1 confers growth advantage on breast carcinoma cells in vivo and that up-regulation of VEGF expression may play an important role in this TIMP-1-mediated, growth-stimulating effect.

Mutant endoglin in hereditary hemorrhagic telangiectasia type 1 is transiently expressed intracellularly and is not a dominant negative

Endoglin (CD105), a component of the TGF-beta 1 receptor complex, is the target gene for the dominantly inherited vascular disorder hereditary hemorrhagic telangiectasia type 1 (HHT1). We have identified a novel endoglin splice site mutation, leading to an in-frame deletion of exon 3, in a new-born from a family with HHT. Expression of normal and mutant endoglin proteins was analyzed in umbilical vein endothelial cells from this baby and in activated monocytes from the affected father. In both samples, only normal dimeric endoglin (160 kD) was observed at the cell surface, at 50% of control levels. Despite an intact transmembrane region, mutant protein was only detectable by metabolic labeling, as an intracellular homodimer of 130 kD. In monocytes from three clinically affected HHT1 patients, with known mutations creating premature stop codons in exons 8 and 10, surface endoglin was also reduced by half and no mutant was detected. Overexpression into COS-1 cells of endoglin cDNA truncated in exons 7 and 11, revealed their intracellular expression, inability to be secreted and to form heterodimers at the cell surface. These results indicate that mutated forms of endoglin are transiently expressed intracellularly and not likely to act as dominant negative proteins, as proposed previously. A reduction in the level of functional endoglin is thus involved in the generation of HHT1, and associated arteriovenous malformations.

Angiogenic factors expressed by human prostatic cell lines: effect on endothelial cell growth in vitro

BACKGROUND

Antiangiogenic therapy for prostatic cancer should offer additional ways of combating tumor progression. Knowledge of the possible angiogenic factors expressed by prostate cancer cell lines would therefore assist in the design and testing of such potential treatments.

METHODS

Changes in the proliferation and morphology of several endothelial cell lines (BAEC, HUVEC, and BACE) in response to either coculturing with human prostatic cell lines or culturing with conditioned medium derived from these lines were assessed.

RESULTS

Proliferation of BAEC cells was significantly stimulated by conditioned media from DU145, LNCaP, and DuPro-1, and also by coculture with LNCaP and DuPro-1. Growth of HUVEC cells was significantly increased with conditioned media from LNCaP, Ten12, and PC3, and by coculture with DU145 and DuPro-1. FGF2 supplementation is required for BACE growth in vitro, and only conditioned medium from Ten12 cells, which produce the highest levels of this growth factor, significantly increased cell numbers. BACE growth, however, was stimulated in coculture experiments with DU145, DuPro-1, PC3, and LNCaP. Morphological changes were only observed in the BAEC and BACE cells when cultured with conditioned media.

CONCLUSIONS

Prostatic carcinoma cell lines express a variety of angiogenic substances, including FGF2, which can stimulate endothelial cell proliferation in vitro, but this response may be modified by the prostatic-cell expression of other factors such as TGF alpha and TGF beta.

TGF-beta and the endothelium during immune injury

During immune injury, activation of endothelial cells by inflammatory cytokines stimulates leukocyte adhesion to the endothelium, turns the endothelium from an anticoagulant surface to one that is frankly procoagulant, and results in the release of vasoactive mediators and growth factors. Cytokine activation of endothelial cells also results in increased endothelial cell TGF-beta 1 synthesis and enhanced activation of latent TGF-beta, the latter involving a shift of plasmin production from the apical to subendothelial surface. In cytokine-stimulated endothelial cells, TGF-beta hinders leukocyte adhesion and transmigration via inhibition of IL-8 and E-selectin expression. TGF-beta also profoundly diminishes cytokine-stimulated inducible nitric oxide synthase production and instead augments endothelial nitric oxide synthase expression. Thus, some of the TGF-beta actions on endothelium during immune activation can viewed as immunosuppressive. TGF-beta also influences mechanisms of vascular remodeling during the healing phase of immune injury. It stimulates PDGF-B synthesis by endothelial cells, causes bFGF release from subendothelial matrix, and promotes VEGF synthesis by non-endothelial cells. Together these mediators control angiogenesis, a critical component of the vascular repair phenomenon. Further, endothelial cell derived PDGF-B and bFGF influence the proliferation and migration of neighboring cells. Thus, endothelial cells and TGF-beta actions on the endothelium play important roles both during the initial phase of immune injury and during the later remodeling phase.

Transforming growth factor-beta: vasculogenesis, angiogenesis, and vessel wall integrity

Genetic studies have recently revealed a role for transforming growth factor-beta-1 (TGF-beta 1) and its receptors (TGF-beta Rs I and II as well as endoglin) in embryonic vascular assembly and in the establishment and maintenance of vessel wall integrity. The purpose of this review is threefold: first, to reassess previous studies on TGF-beta and endothelium in the light of these recent findings; second, to describe some of the well-established as well as controversial issues concerning TGF-beta and its regulatory role in angiogenesis; and third, to explore the notion of "context' with respect to TGF-beta and endothelial cell function. Although the focus of this review will be on the endothelium, other vascular wall cells are also likely to be important in the pathogenesis of the vascular lesions revealed by genetic studies.

Transforming growth factor-beta receptor expression on endothelial cells: heterogeneity of type III receptor expression

Recent studies of whole animal responses have defined a role for circulating TGF-beta in the preservation and stabilization of microvascular endothelial function (Lefer et al. [1993] Proc. Natl. Acad. Sci. U.S.A., 90:1018-1022; Pfister et al. [1992] J. Exp. Med., 176:265-269). In order to determine which TGF-beta receptor types are responsible for this endothelial cell responsiveness, we used an affinity-labeling technique with 125I-TGF-beta 1 and -beta 2 to characterize TGF-beta receptors on five different endothelial cell cultures: early passage bovine lung and rat epididymal fat pad microvascular endothelial cells (BLMEC and REEC), established endothelial cell lines from bovine adrenal medulla capillaries (EJG), fetal bovine heart (FBHE), and bovine pulmonary artery (CPAE). Since it is known that endothelial cells from different parts of the vasculature vary with respect to cell surface antigen expression (McCarthy et al. [1991] Trends Pharmacol. Sci., 12:462-467; Augustin et al. [1994] Bioessays, 16:901-906), it is important to compare TGF-beta receptor expression on microvascular and macrovascular endothelial cells. We observed 85 kDa and 200-400 kDa labeled receptor bands and analyzed their relationship to the cloned Type II and III receptors using peptide antibodies. We used dithiothreitol and phosphoinositol-phospholipase C pretreatments to establish whether the 65 kDa labeled band which we observed corresponded to the Type I receptor or a glycophosphotidylinositol-linked binding protein. The results demonstrated that microvascular but not macrovascular endothelial cells express high levels of the Type III receptor. This differential expression of the Type III receptor indicates that distinct anatomical segments of the vasculature have distinct TGF-beta receptor profiles. The presence of the Type III receptor on micro- but not macrovascular endothelial cells may account for the reportedly different potency of TGF-beta 1 and TGF-beta 2 on these two endothelial cell types. Analysis of the 85 kDa and 65 kDa affinity-labeled bands revealed that all the endothelial cells express the Type II receptor and a band consistent with the presence of a dithiothreitol-sensitive Type I receptor. Two isoform-specific phosphoinositol-phospholipase C releasable TGF-beta binding proteins were also detected: a 60 kDa protein on one micro- (EJG) and one macro- (FBHE) vascular endothelial cell line and a 150/180 kDa protein on the macrovascular cell lines (FBHE and CPAE). These studies emphasize the heterogeneous nature of endothelial cells and underline the importance of using microvascular endothelial cells when examining TGF-beta responses related to microvascular function.

Specific binding of endocrine transforming growth factor-beta 1 to vascular endothelium

The presentation of recombinant biologically active 125I-TGF-beta 1 via the bloodstream to potential target cells in mice and rats was evaluated by quantitative light and electron microscope radioautography. Specificity was evaluated by in vivo competition with excess unlabeled TGF-beta 1, and integrity of the ligand at the binding site was demonstrated by trichloroacetic acid precipitation after extraction from tissues. The distribution of radiolabel at 2.5, 15, 30, 45, and 60 min after 125I-TGF-beta 1 injection revealed radiolabel principally over microvasculature endothelium but at times > 2.5 min over endothelial endocytic components indicative of internalization. Nonspecific binding of 125I-TGF-beta 1 to the apex of the proximal convoluted tubule of the kidney indicated it as the likely site of rapid clearance of TGF-beta 1 from the circulation, while a comparison of the binding of 125I-TGF-beta 1 (endothelial) to that of 125I-TGF-beta 1 complexed with alpha 2-macroglobulin-methylamine (liver parenchyma) indicated that clearance of TGF-beta 1 complexed alpha 2-macroglobulin was likely via the hepatic alpha 2-macroglobulin receptor. The endothelial TGF-beta receptors uncovered here are likely involved in the local regulatory mechanism of leukocyte and monocyte adhesion and tissue infiltration regulated by endocrine TGF-beta 1.

Oxygen modulates production of bFGF and TGF-beta by retinal cells in vitro

Vasoproliferative retinopathies result from retinal capillary non-perfusion and consequent inner retinal hypoxia. However, it is not known whether oxygen mediates vasoproliferation directly (at the nuclear level) or indirectly by regulating the production of growth factors. We have investigated the effect of oxygen on the production of basic fibroblast growth factor and transforming-growth-factor-beta by a variety of retinal cell types in culture. Confluent cultures were maintained for 48 hr under varying oxygen tensions ranging from 135 to 18 mmHg. A reduction in basic fibroblast growth factor levels was observed in the cell lysates and extracellular matrix from retinal microvascular endothelial cell, retinal microvascular pericyte and retinal pigment epithelial cell cultures when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Levels of basic fibroblast growth factor in conditioned media from microvascular endothelial and retinal pigment epithelial cell cultures also decreased when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Total transforming-growth-factor-beta (and specifically isoforms 1 and 2) in the conditioned media from all three cell types was similarly modulated by oxygen i.e. it decreased as the oxygen tension of the medium was reduced from 135 to 18 mmHg. In contrast, the steady state messenger RNA levels for both basic fibroblast growth factor and transforming-growth-factor-beta 1 genes in RPE cells increased significantly when the oxygen tension of the medium was reduced from 135 to 18 mmHg. These results support the putative role of oxygen in influencing the balance of growth factors during the development of preretinal new vessels.

The role of vascular permeability factor and basic fibroblast growth factor in tumor angiogenesis

In the last decade a considerable amount of research has been dedicated to studying the process of angiogenesis. In the field of tumor biology angiogenesis is a relevant subject of investigation as well, since newly formed blood vessels are required for the growth of tumors and provide an exit route for metastasizing tumor cells. In this review we discuss some aspects of tumor angiogenesis with emphasis on the role that growth factors bFGF and VPF play in this process. A number of biochemical characteristics and biological properties of the two factors and their receptors are reviewed, and the expression of bFGF and VPF in both normal tissues and in tumors is discussed. Finally, we speculate on the use of bFGF and VPF expression as a diagnostic parameter and on possible clinical applications.

Fibronectin, laminin, vitronectin and their receptors at newly-formed capillaries in proliferative diabetic retinopathy

Proliferative diabetic retinopathy (PDR) is characterized by intraocular formation of fibroglial vascularized tissue by active vasoproliferative mechanisms. Using immunocytochemistry, we have studied changes in the distribution pattern of fibronectin (FN), laminin (LN), vitronectin (VN) and their receptors in the newly-formed capillaries of PDR. In intraocular vascularized tissue of PDR patients, FN was present on both luminal and basal surfaces of endothelial cells, and was diffusely distributed in the interpericyte space. LN was also associated with the interpericyte space. VN was occasionally detected on the luminal capillary side, but was frequent in the basal aspect of the endothelium in the interpericyte space, where it was colocalized with FN. Beta-1 subunit complex receptors were detected on the luminal side, while alpha v beta 3 integrin was identified on both sides, more so in the luminal than in the basal endothelial domain. By slot-blotting techniques and densitometric analysis, increased concentrations of intravitreous FN and VN were found in PDR in comparison with normal samples. These results suggest that FN, VN and LN have a key role in the structural arrangement of newly formed capillaries in PDR, and that receptor expression could be involved in events of endothelial cell adhesion and proliferation.

Localization of heparin-binding EGF-like growth factor in the smooth muscle cells and macrophages of human atherosclerotic plaques

Heparin-binding EGF-like growth factor (HB-EGF) is a potent chemoattractant and mitogen for smooth muscle cells (SMC) in culture. To elucidate whether HB-EGF is implicated in the pathogenesis of human atherosclerosis, we examined immunohistochemical localization of HB-EGF in human aortic walls and atherosclerotic plaques. The medial SMC of the aorta in babies and children synthesized HB-EGF protein, while the number of SMC producing HB-EGF was dramatically decreased in young and middle-aged adults. In atherosclerotic plaques, however, marked production of HB-EGF protein was detected in SMC and macrophages of the plaques. Furthermore, EGF receptors, to which HB-EGF is known to bind, were detected in plaque SMC. These data suggest that HB-EGF may be implicated in the migration and proliferation of SMC that occurs in the normal development of arterial walls, and in the formation of atherosclerotic plaques.

Tumor metastasis: current biologic concepts and their implications for control of residual disease

Metastatic disease presents an important obstacle to curative cancer therapy. This article reviews cancer biology concepts relevant to the pathogenesis of tumor metastasis and their implications for the surgical oncologist seeking to control or eradicate metastatic disease.

Monoclonal antibodies that recognize the type-2 activin receptor, ACTR2

Monoclonal antibodies (MAbs) were raised in mice against a bacterial fusion protein composed of the intracellular serine/threonine kinase domain of the type-2 activin receptor, ACTR2, fused to glutathione S-transferase. Three MAbs with high affinity toward the ACTR2 kinase domain were isolated, one of which recognized specifically ACTR2 expressed transiently in vascular endothelial cells. These reagents should be of use in the elucidation of mechanisms of transmembrane signaling by this member of the emerging receptor serine threonine kinase family.

Tumor invasion, proteolysis, and angiogenesis

In this review, some of the current literature on the regulation of proteolysis and angiogenesis during tumor invasion is discussed. Due to the critical location of brain tumors, an understanding of tumor cell interactions with the local environment is particularly relevant. Tissue breakdown during tumor invasion is associated with proteolytic activity, mediated by tumor cells, and surrounding host cells. This review covers two classes of proteinases and inhibitors that have commonly been associated with tumor invasion i.e., plasminogen activator (PA)/plasmin and matrix metalloproteinases (MMP) with special emphasis on the MMP inhibitors, TIMP-1 and TIMP-2. At different steps of the metastatic process, tumor cells interact with endothelial cells. Tumor cells also stimulate the formation of new vessels through the expression of specific angiogenic molecules. At least eight angiogenic molecules have been purified, sequenced and cloned, four of which are discussed here. Regulation of angiogenic activity has been the focus of intense studies recently, and a wide range of synthetic and natural angiogenesis inhibitors have been discovered. Targeting of angiogenic molecules and tumor vasculature may prove useful in future cancer therapeutic strategies.

Cell-cell signaling between adult rat ventricular myocytes and cardiac microvascular endothelial cells in heterotypic primary culture

It is unclear whether signaling between endothelial cells and muscle cells within ventricular myocardium, known to be important during cardiac development, remains physiologically relevant in the adult heart. Also, the mechanisms regulating the synthesis and activation of locally acting autacoids such as endothelins, cytokines known to have potent effects on contractile function and gene expression in cardiac myocytes, are unknown, as their cells of origin within ventricular muscle. Microvascular endothelial cells isolated from ventricular tissue of adult rats do not express endothelins constitutively. However, the appearance of preproendothelin mRNA can be increased in cardiac microvascular endothelial cells by heterotypic primary culture with adult rat ventricular myocytes. Cell-cell contact, or at least close apposition, appears to be necessary to increase preproendothelin mRNA, as medium conditioned by ventricular myocytes alone was ineffective when applied to monocultures of microvascular endothelial cells. The level of TGF beta precursor mRNA is also markedly increased in microvascular endothelial cells in coculture and precedes the appearance of endothelin precursor transcripts. In coculture, TGF beta acts as an autocrine cytokine, increasing endothelin precursor mRNA and inhibiting the rate of microvascular endothelial cell proliferation. This regulation of endothelial cell phenotype in heterotypic primary cultures suggests that dynamic, reciprocal cell-cell signaling may also be occurring between microvascular endothelium and ventricular myocytes in vivo.

The pathogenesis of atherosclerosis: a perspective for the 1990s

Atherosclerosis, the principal cause of heart attack, stroke and gangrene of the extremities, is responsible for 50% of all mortality in the USA, Europe and Japan. The lesions result from an excessive, inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. A large number of growth factors, cytokines and vasoregulatory molecules participate in this process. Our ability to control the expression of genes encoding these molecules and to target specific cell types provides opportunities to develop new diagnostic and therapeutic agents to induce the regression of the lesions and, possibly, to prevent their formation.