TGF-β1 induces COX-2 expression and PGE2 synthesis through MAPK and PI3K pathways in human mesangial cells

Emergence of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin axis in transforming growth factor-β-induced epithelial-mesenchymal transition

During development and in pathological contexts such as fibrosis and cancer progression, epithelial cells can initiate a complex transcriptional reprogramming, accompanied by dramatic morphological changes, in a process named 'epithelial-mesenchymal transition' (EMT). In this transition, epithelial cells lose their epithelial characteristics to acquire mesenchymal properties and increased motile and invasive behavior. Transforming growth factor-β (TGF-β) has emerged as a major inducer of EMT through activation of downstream signaling pathways, including Smad and non-Smad signaling pathways. Among the non-Smad pathways, increasing evidence is emerging that the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin axis plays a major role in TGF-β-induced EMT, notably through the regulation of translation and cell invasion. Pharmacological inhibitors of the phosphoinositide 3-kinase-Akt-mammalian target of rapamycin pathway may therefore represent an opportunity to selectively target essential aspects of TGF-β-induced EMT and provide an approach to prevent cancer cell dissemination toward metastasis, without the need to fully inactivate TGF-β signaling.

Connective tissue growth factor induction by lysophosphatidic acid requires transactivation of transforming growth factor type β receptors and the JNK pathway

Transforming growth factor β (TGF-β) is a very strong pro-fibrotic factor which mediates its action, at least in part, through the expression of connective tissue growth factor (CTGF/CCN2). Along with these cytokines, the involvement of phospholipids in wound healing and the development of fibrosis has been revealed. Among them, lysophosphatidic acid (LPA) is a novel, potent regulator of wound healing and fibrosis that has diverse effects on many types of cells. We decided to evaluate the effect of LPA together with TGF-β on CTGF expression. We found that myoblasts treated with LPA and TGF-β1 produced an additive effect on CTGF expression. In the absence of TGF-β, the induction of CTGF expression by LPA was abolished by a dominant negative form of the TGF-β receptor type II (TGF-βRII) and by the use of SB 431542, a specific inhibitor of the serine/threonine kinase activity of TGF-βRI, suggesting that CTGF induction is dependent on LPA and requires active TGF-βRs. Moreover, we show that LPA requires Smad-2/3 proteins for the induction of CTGF expression, but not their phosphorylation or their nuclear translocation. The requirement of TGF-βRI for LPA mediated-effects is differential, since treatment of myoblasts with LPA in the presence of SB 431542 abolished the induction of stress fibers but not the induction of proliferation. Finally, we demonstrated that CTGF induction in response to LPA requires the activation of JNK, but not ERK, signaling pathways. The JNK requirement is independent of TGF-βRI-mediated activity. These novel results for the mechanism of action of LPA and TGF-β are important for understanding the role of pro-fibrotic growth factors and phospholipids involved in wound healing and related diseases.

Conditional beta-catenin loss in mice promotes chemical hepatocarcinogenesis: role of oxidative stress and platelet-derived growth factor receptor alpha/phosphoinositide 3-kinase signaling

Activation of beta-catenin, the central effector of the canonical Wnt pathway and a recognized oncogene, has been implicated in hepatocellular carcinoma. We examined N-nitrosodiethylamine (DEN)-induced tumorigenesis in hepatic beta-catenin conditional knockout mice (beta-cat KO). Male beta-cat KO and age- and sex-matched littermate controls were given a single intraperitoneal DEN injection and followed for 6-12 months for hepatic tumors. Hepatic tumors were characterized for histology, proliferation, apoptosis, oxidative stress, and specific proteins by way of western blot, immunohistochemistry, and coprecipitation studies. For in vivo tumor intervention studies, specific inhibitors were administered intraperitoneally or through drinking water. Intriguingly, beta-cat KO mice showed a paradoxical increase in susceptibility to DEN-induced tumorigenesis. This accelerated tumorigenesis is due to increased injury and inflammation, unrestricted oxidative stress, fibrosis, and compensatory increase in hepatocyte proliferation secondary to platelet-derived growth factor receptor alpha (PDGFRalpha)/phosphoinositide 3-kinase (PIK3CA)/Akt activation and c-Myc overexpression. In vitro suppression of beta-catenin expression in hepatoma cells led to enhanced PDGFRalpha expression, which was abrogated in the presence of nuclear factor kappaB (NF-kappaB) inhibitor. Daily treatment of 6-month-old DEN-exposed beta-cat KO with PDGFRalpha inhibitor dramatically reduced tumor numbers and size. Inclusion of N-acetyl-L-cysteine, a known antioxidant and NF-kappaB inhibitor, in the drinking water led to complete abolition of tumorigenesis in DEN-exposed beta-cat KO.

CONCLUSION

Loss of beta-catenin impairs the liver's ability to counteract DEN-induced oxidative stress and enhances tumorigenesis through PDGFRalpha/PIK3CA/Akt signaling. Blockade of PDGFRalpha or oxidative stress dramatically affects beta-catenin-deficient tumorigenesis. Also, hepatoma cells use PDGFRalpha/PIK3CA signaling as an escape mechanism following beta-catenin suppression, and their sequential suppression profoundly impedes tumor proliferation.

Adult Dirofilaria immitis excretory/secretory antigens upregulate the production of prostaglandin E2 and downregulate monocyte transmigration in an "in vitro" model of vascular endothelial cell cultures

Canine and feline cardiopulmonary dirofilariosis caused by Dirofilaria immitis is a chronic and potentially fatal disease. Adult worms live in the pulmonary arteries of infected immunocompetent hosts for years. The aim of the present study is the identification of the influence of the metabolic products (excretory/secretory antigens, DiE/S) of D. immitis on the vascular endothelial cells, because the vascular endothelium interplays in a direct manner with the parasite and their products. For this purpose, HAAE-1 vascular endothelial cells were treated with DiE/S, using non-treated cultures as negative controls. Significant increases in the COX-2, 5-LO expression and PGE(2) level were detected in the treated cells compared with the control cells. Moreover, DiE/S decreases monocyte transmigrations across vascular endothelial cell monolayers. Treatment with DiE/S does not have a cytotoxic effect and do not alter apoptosis, necrosis or cell cycle of vascular endothelial cells. These results suggest that the DiE/S stimulates the production of mediators and mechanisms that favor the survival of the parasite, in vascular endothelial cells, contributing to restrict vascular and lung damages in the infected host, without altering the basic physiologic processes of endothelial cells.

Inflammation and EMT: an alliance towards organ fibrosis and cancer progression

Recent advances in our understanding of the molecular pathways that govern the association of inflammation with organ fibrosis and cancer point to the epithelial to mesenchymal transition (EMT) as the common link in the progression of these devastating diseases. The EMT is a crucial process in the development of different tissues in the embryo and its reactivation in the adult may be regarded as a physiological attempt to control inflammatory responses and to 'heal' damaged tissue. However, in pathological contexts such as in tumours or during the development of organ fibrosis, this healing response adopts a sinister nature, steering these diseases towards metastasis and organ failure. Importantly, the chronic inflammatory microenvironment common to fibrotic and cancer cells emerges as a decisive factor in the induction of the pathological EMT.

TGF-beta-induced epithelial to mesenchymal transition

During development and in the context of different morphogenetic events, epithelial cells undergo a process called epithelial to mesenchymal transition or transdifferentiation (EMT). In this process, the cells lose their epithelial characteristics, including their polarity and specialized cell-cell contacts, and acquire a migratory behavior, allowing them to move away from their epithelial cell community and to integrate into surrounding tissue, even at remote locations. EMT illustrates the differentiation plasticity during development and is complemented by another process, called mesenchymal to epithelial transition (MET). While being an integral process during development, EMT is also recapitulated under pathological conditions, prominently in fibrosis and in invasion and metastasis of carcinomas. Accordingly, EMT is considered as an important step in tumor progression. TGF-beta signaling has been shown to play an important role in EMT. In fact, adding TGF-beta to epithelial cells in culture is a convenient way to induce EMT in various epithelial cells. Although much less characterized, epithelial plasticity can also be regulated by TGF-beta-related bone morphogenetic proteins (BMPs), and BMPs have been shown to induce EMT or MET depending on the developmental context. In this review, we will discuss the induction of EMT in response to TGF-beta, and focus on the underlying signaling and transcription mechanisms.

Leptin induces functional activation of cyclooxygenase-2 through JAK2/STAT3, MAPK/ERK, and PI3K/AKT pathways in human endometrial cancer cells

Hyperleptinemia is a common feature of obese women who have a higher risk of endometrial cancer than women with normal weights, and epidemiologic studies have suggested a correlation between obesity and endometrial carcinoma. Therefore, understanding of the molecular mechanism involved in leptin signaling transduction is important in endometrial cancer prevention and treatment. In this study, both isoforms of the leptin receptor (Ob-R), the long form (Ob-Rb) and short form (Ob-Ra), were detected as being expressed in six endometrial cancer cell lines with various differentiation status by western blotting, and Ob-Ra was found to be more abundant than Ob-Rb in these cells. Moreover, the expressions of both isoforms were inversely correlated with histoprognostic grading. We also showed that leptin stimulated cell proliferation and induced activations of signal transducers and activators of transcription 3 (STAT3), extracellular signal-regulated kinase (ERK1/2), AKT, and cyclooxygenase (COX)-2 in endometrial cancer cells dose-dependently by [(3)H] thymidine incorporation assay and western blotting. Leptin-stimulation resulted in increased expression of COX-2 mRNA and prostaglandin E2 (PGE2) production of endometrial cancer cells by reverse transcription-polymerase chain reaction and enzyme immunoassay, respectively, which was effectively blocked by pharmacological inhibitors of Janus tyrosine kinase 2 (JAK2), AG490; of mitogen-activated protein kinase (MAPK) kinase, U0126; of phosphatidylinositol 3-kinase (PI3K), LY294002; and of COX-2, NS398. These results suggest that leptin promotes cell proliferation of endometrial cancer cells via the aforementioned multiple signal-transduction pathways. Leptin-induced functional activation of COX-2 is JAK2/STAT3-, MAPK/ERK-, and PI3K/AKT-dependent, indicating that COX-2 may be a critical factor of endometrial carcinogenesis in obesity.

Cell Defence and Survival

Central to immune defence mechanisms is the role of transcription factor nuclear factor kappa B (NF-kB). This is a complex biochemical topic with ever more controls revealed. NF-kB determines the production of proinflammatory cytokines and chemokines. Pharmacologists step in with possible means of control. Other systems involved in defence include the cyclooxygenase 2 (Cox-2) enzyme and perioxisome proliferator-activated receptors. Insulin receptor activation needs to be seen in context. The mTOR system directs uptake of nutrients by cells. mTOR is suppressed by rapamycin, whose usage is now quite considerable in the control of transplant rejection.

Dirofilaria immitis and Wolbachia-derived antigens: its effect on endothelial mammal cells

Antigens of both Dirofilaria immitis and Wolbachia symbiont bacteria are implicated in the inflammatory pathology of heartworm infection. The aim of the present study was to compare the stimulatory capacity of in vitro cultures of vascular endothelial cells by the adult somatic antigens of D. immitis (DiSA) and the recombinant form of the Wolbachia surface protein (rWSP), during the first 24h of stimulation. Our results indicate a different stimulatory activity of the two antigens. Both the DiSA and rWSP stimulate the production of the enzymes responsible of the arachidonic acid metabolism, cyclooxygenase-2, 5-lipoxygenase (5-LO), and leukotriene B4. Only DiSA stimulates the production of prostaglandin E2. Related to the adhesion molecules, the DiSA stimulates the expression of intercellular adhesion molecule-1 (ICAM-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1), whereas rWSP stimulates ICAM-1, PECAM-1, and vascular cell adhesion molecule-1 (VCAM-1). Expression of E-cadherin and vascular endothelial growth factor also were stimulated by rWSP. Neither of the two antigens altered the basic physiological mechanisms of endothelial cells, such as cell proliferation, cell cycle, or apoptosis. The biological and pathological significance of these finding are discussed.

Vascular endothelial cell activation by adult Dirofilaria immitis antigens

Dirofilaria immitis is the causal agent of cardiopulmonary dirofilariosis (heartworm disease). Adult worms lodge in the pulmonary arteries and right ventricle, thus vascular endothelium is exposed to high concentrations of Dirofilaria antigenic products. Heartworm disease habitually develops as a chronic foreseeable pathology. Moreover, the simultaneous death of many adult worms, naturally or induced by a filaricide treatment, can cause acute thromboembolisms and endarteritis. To better understand the effects of the massive death of D. immitis adult worms on the blood vessel endothelium, we cultured vascular endothelial cells in the presence or absence of an antigenic extract of D. immitis adult worms (DiSA). The parasite products increased the expression of enzymes and the synthesis of eicosanoids related to inflammation, such as COX-2, 5-LO, PGE(2) and LTB(4). The expression of ICAM-1 and PECAM-1 adhesion molecules and endothelial and inducible Nitric Oxide Synthases (eNOS and iNOS) was also increased in cultures treated with DiSA. Nevertheless, DiSA decreased endothelial permeability and does not alter both proliferation and apoptosis. These results suggest that the somatic extract of D. immitis adult worms stimulate inflammatory mechanisms in endothelial cells, without altering their basic physiologic processes.

Screening of senescence-associated genes with specific DNA array reveals the role of IGFBP-3 in premature senescence of human diploid fibroblasts

Repeated exposures to sublethal concentrations of tert-butylhydroperoxide and ethanol trigger premature senescence of WI-38 human diploid fibroblasts. We found 16 replicative senescence-related genes with similar alterations in expression level in replicative senescence and two models of stress-induced premature senescence. Among these genes was IGFBP-3. Using a siRNA approach, we showed that IGFBP-3 regulates the appearance of several biomarkers of senescence after repeated exposures of WI-38 fibroblasts to tert-butylhydroperoxide and ethanol.

Mifepristone attenuates human chorionic gonadotropin–induced extracellular signal–regulated kinase 1/2 phosphorylation, cyclooxygenase-2, and prostaglandin E2 production in human granulosa luteal cells

OBJECTIVE

To elucidate the role of RU486 in regulating the function of granulosa luteal cells and its possible involvement in ovarian dysfunction.

DESIGN

An in vitro study.

SETTING

University hospital.

PATIENT(S)

Our subjects were women under the age of 40 who were unable to get pregnant as a result of male-factor infertility.

INTERVENTION(S)

HCG and RU486 were added to cultured granulosa luteal cells; after incubation for 12 hours, the harvested cells were subjected to total mRNA and protein measurements.

MAIN OUTCOME MEASURE(S)

Reverse transcriptase-polymerase chain reaction, immunoblot assay, immunocytochemistry, and enzyme immunoassay were performed.

RESULT(S)

RU486 attenuates hCG-induced cyclooxygenase-2 (COX-2) mRNA and protein expression and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and decreases the hCG-induced prostaglandin E2 (PGE2) production in a dose-dependent manner. RU486 treatment had no significant effect on COX-1 mRNA expression.

CONCLUSION(S)

Treatments using gonadotropins are able to induce ERK1/2 phosphorylation resulting in increased COX-2 protein expression and prostaglandin synthesis. RU486 attenuates the activation of ERK1/2, decreases the expression of COX-2, and affects PGE2 production by inhibiting hCG-induced COX-2 expression.

Intracisternal administration of transforming growth factor-β evokes fever through the induction of cyclooxygenase-2 in brain endothelial cells

Transforming growth factor-β (TGF-β), a pleiotropic cytokine, regulates cell proliferation, differentiation, and apoptosis, and plays a key role in development and tissue homeostasis. TGF-β functions as an anti-inflammatory cytokine because it suppresses microglia and B-lymphocyte functions, as well as the production of proinflammatory cytokines. However, we previously demonstrated that the intracisternal administration of TGF-β induces fever like that produced by proinflammatory cytokines. In this study, we investigated the mechanism of TGF-β-induced fever. The intracisternal administration of TGF-β increased body temperature in a dose-dependent manner. Pretreatment with cyclooxygenase-2 (COX-2)-selective inhibitor significantly suppressed TGF-β-induced fever. COX-2 is known as one of the rate-limiting enzymes of the PGE2 synthesis pathway, suggesting that fever induced by TGF-β is COX-2 and PGE2 dependent. TGF-β increased PGE2 levels in cerebrospinal fluid and increased the expression of COX-2 in the brain. Double immunostaining of COX-2 and von Willebrand factor (vWF, an endothelial cell marker) revealed that COX-2-expressing cells were mainly endothelial cells. Although not all COX-2-immunoreactive cells express TGF-β receptor, some COX-2-immunoreactive cells express activin receptor-like kinase-1 (ALK-1, an endothelial cell-specific TGF-β receptor), suggesting that TGF-β directly or indirectly acts on endothelial cells to induce COX-2 expression. These findings suggest a novel function of TGF-β as a proinflammatory cytokine in the central nervous system.

Microparticles stimulate the synthesis of prostaglandin E(2) via induction of cyclooxygenase 2 and microsomal prostaglandin E synthase 1

OBJECTIVE

Microparticles are small vesicles that are released from activated or dying cells and that occur abundantly in the synovial fluid of patients with rheumatoid arthritis (RA). The goal of these studies was to elucidate the mechanisms by which microparticles activate synovial fibroblasts to express a proinflammatory phenotype.

METHODS

Microparticles from monocytes and T cells were isolated by differential centrifugation. Synovial fibroblasts were cocultured with increasing numbers of microparticles. Gene expression was analyzed by real-time polymerase chain reaction and confirmed by Western blotting and enzyme immunoassay. Arachidonic acid labeled with tritium was used to study the transport of biologically active lipids by microparticles. The roles of NF-kappaB and activator protein 1 (AP-1) signaling were analyzed with electrophoretic mobility shift assay and transfection with small interfering RNA and IkappaB expression vectors.

RESULTS

Microparticles strongly induced the synthesis of cyclooxygenase 2 (COX-2), microsomal prostaglandin E synthase 1 (mPGES-1), and prostaglandin E(2) (PGE(2)). In contrast, no up-regulation of COX-1, mPGES-2, cytosolic PGES, or phospholipase A(2) was observed. The induction of PGE(2) was blocked by selective inhibition of COX-2. Microparticles activated NF-kappaB, AP-1, p38, and JNK signaling in synovial fibroblasts. Inhibition of NF-kappaB, AP-1, and JNK signaling reduced the stimulatory effects. Arachidonic acid was transported from leukocytes to fibroblasts by microparticles. Arachidonic acid derived from microparticles was converted to PGE(2) by synovial fibroblasts.

CONCLUSION

These results demonstrate that microparticles up-regulate the production of PGE(2) in synovial fibroblasts by inducing COX-2 and mPGES-1. These data provide evidence for a novel mechanism by which microparticles may contribute to inflammation and pain in RA.

Sevoflurane-mediated TGF-beta1 signaling in renal proximal tubule cells

Several volatile anesthetics, including sevoflurane, protect against renal ischemia-reperfusion injury in vivo by reducing necrosis and inflammation. Furthermore, in cultured renal tubule cells, sevoflurane directly induced the phosphorylation of the cytoprotective kinases (ERK and Akt), upregulated 70-kDa heat shock protein (HSP70), and attenuated nuclear translocation of the proinflammatory transcription factor NF-kappaB. It has been shown that sevoflurane increases the release of transforming growth factor-beta1 (TGF-beta1) in human proximal tubule (HK-2) cells via externalization of plasma membrane phosphatidylserine (PS), and this increase in TGF-beta1 protected HK-2 cells against hydrogen peroxide-mediated necrosis. In this study, we aimed to determine whether the sevoflurane-mediated phosphorylation of ERK and Akt, induction of HSP70, and reduction in NF-kappaB activation are due to TGF-beta1 receptor-mediated signaling after PS externalization in HK-2 cells. Exogenous TGF-beta1 and a liposome mixture containing PS mimicked sevoflurane-mediated ERK and Akt phosphorylation and HSP70 induction in HK-2 cells. Sevoflurane and TGF-beta1 caused the nuclear translocation of the SMAD3 transcription factor in HK-2 cells. Furthermore, a neutralizing TGF-beta1 antibody or exogenous annexin V to bind PS prevented sevoflurane-induced ERK and Akt phosphorylation and HSP70 induction in HK-2 cells. Finally, a TGF-beta1 antibody and annexin V attenuated the reduction in nuclear translocation of NF-kappaB by sevoflurane. Therefore, we demonstrate in this study that sevoflurane-mediated cytoprotective and anti-inflammatory effects in HK-2 cells are at least partially due to the externalization of PS and activation of TGF-beta1 signaling pathways.

Role of TGF-beta and PGE2 in T cell responses during Plasmodium yoelii infection

During an acute blood-stage malaria infection, T cell responses to malaria and other bystander antigens are inhibited. Plasmodium infection induces strong cytokine responses that facilitate parasite clearance but may interfere with T cell functions, as some of the soluble immune mediators induced are also general inhibitors of T cell responses. Using a malaria mouse model, we have analyzed the cytokines produced by dendritic cells in response to P. yoelii infection that have potential T cell inhibitory activity. We found that during acute infection DC migrate to the spleen and secrete TGF-beta, prostaglandin E2 (PGE2) and IL-10. We have analyzed the role of these general T cell inhibitors in a particular T cell response of evident importance in malaria infections: the CD8+ T cells generated against the liver-stage of the disease. During blood-stage infection, inhibition of the activity of TGF-beta and PGE2 restores the CD8+ T cell responses generated by sporozoites, increasing protection against re-infection. Our findings suggest that the strong cytokine response induced by blood-stage P. yoelii infection affects host T cell responses, inhibiting protective CD8+ T cells against the liver-stage of the disease.

Effect of adenosine in extracellular matrix synthesis in human and rat mesangial cells

Adenosine (ADO) is an intermediary metabolite of adenosine trisphosphate degradation and a vasoactive mediator. We showed previously that ADO induces contraction and proliferation in rat mesangial cells by a mechanism involving A1 and A2 receptors. The studies concerning the effect of ADO on extracellular matrix (ECM) accumulation in mesangial cells are scarce. The purpose of our study was to evaluate the effect of ADO and the effect of the selective stimulation of A1 and A2 ADO receptors on the expression of ECM components fibronectin and collagen type I, in human and rat renal mesangial cells. Cultured human and rat renal mesangial cells were subjected to selective stimulation of A1 and A2 ADO receptors for 24 and 48 h. Fibronectin and collagen type I expression was evaluated by Western blot; total collagen synthesis was measured by [3H]-proline incorporation into collagen proteins. ADO, A1 and A2 receptor stimulation induce increases in fibronectin expression in rat mesangial cells, and A1 receptor stimulation partially inhibits fibronectin expression in serum-stimulated rat mesangial cells, without any effect in human mesangial cells. A2 receptor stimulation reduces collagen type I expression in serum-stimulated mesangial cells. Neither ADO nor A1 or A2 receptor stimulation induce significant changes in total collagen synthesis. These data suggest that ADO is not a major regulator of ECM synthesis in rat and human mesangial cells.

TGF-beta1 release by volatile anesthetics mediates protection against renal proximal tubule cell necrosis

BACKGROUND/AIMS

We have previously demonstrated that clinically utilized volatile anesthetics protect against renal ischemia reperfusion injury in rats in vivo and reduce necrosis in vitro via activation of ERK and Akt and by upregulating HSP70. In this study, we further deciphered the upstream cellular signaling mechanism(s) of volatile anesthetic-mediated antinecrotic effects in vitro. We hypothesized that volatile anesthetics perturb the structure of the plasma membrane lipid bilayer, causing externalization of phosphatidylserine (PS) to the outer surface on renal tubule cells leading to the increased generation of transforming growth factor-beta1 (TGF-beta1), a cytokine with antinecrotic properties.

METHODS AND RESULTS

In human proximal tubule (HK-2) cell culture, 16-hour exposure to volatile anesthetics (isoflurane, halothane, sevoflurane) caused membrane externalization of PS detected by positive annexin-V staining and increased the release of TGF-beta1 into the cell culture media. Exogenous TGF-beta1 induced protection and neutralizing TGF-beta1 antibody prevented the cytoprotection by volatile anesthetics against hydrogen peroxide-induced HK-2 cell necrosis.

CONCLUSIONS

Volatile anesthetics induce a cytoprotective signaling cascade in proximal tubule cells via membrane externalization of PS initiating TGF-beta1-mediated cytoprotection.

A novel modulatory mechanism of transforming growth factor-beta signaling through decorin and LRP-1

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that signals to the nucleus through cell surface transmembrane receptors with serine/threonine kinase activity and cytoplasmic effectors, including Smad proteins. Here we describe two novel modulators of this pathway, lipoprotein-receptor related protein (LRP-1) and decorin. Decorin null (Dcn null) myoblasts showed a diminished TGF-beta response that is restored by decorin re-expression. Importantly, this reactivation occurs without changes in the binding to TGF-beta receptors, Smad protein phosphorylation, or Smad-4 nuclear translocation. In wild type myoblasts, inhibition of decorin binding to LRP-1 and depletion of LRP-1 inhibited TGF-beta response to levels similar to those observed in Dcn null myoblasts. Re-expression of decorin in Dcn null myoblasts cannot restore TGF-beta response if the Smad pathway or phosphatidylinositol 3-kinase activity is inhibited, suggesting that this LRP-1-decorin modulatory pathway requires activation of the Smad pathway by TGF-beta and involves phosphatidylinositol 3-kinase activity. This work unveils a new regulatory mechanism for TGF-beta signaling by decorin and LRP-1.

Gene expression fingerprinting for human hereditary hemorrhagic telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is an autosomal dominant vascular disorder characterized by telangiectases and internal arteriovenous malformations. It is caused by mutations in elements of the transforming growth factor-beta (TGF-beta) receptor complex: endoglin, a co-receptor, responsible for HHT1, or ALK1 (activin receptor-like kinase 1), a type I receptor leading to HHT2. Recently, we have established cultures of HHT endothelial cells, primary targets of the disease. These cells showed deficient TGF-beta signaling and angiogenesis, representing a useful human model to study the molecular mechanism of this disease. To understand the pathogenic mechanism underlying HHT, we have used total RNA probes to compare HHT versus non-HHT cells by expression microarrays. This work represents a systematic study to identify target genes affected in HHT cells. Given the similarity of symptoms in HHT1 and HHT2, special interest has been put on the identification of common targets for both HHT types. As a result, 277 downregulated and 63 upregulated genes were identified in HHT versus control cells. These genes are involved in biological processes relevant to the HHT pathology, such as angiogenesis, cytoskeleton, cell migration, proliferation and NO synthesis. The type of misregulated genes found in HHT endothelial cells lead us to propose a model of HHT pathogenesis, opening new perspectives to understand this disorder. Moreover, as the disease is originated by mutations in proteins of the TGF-beta receptor complex, these results may be useful to find out targets of the TGF-beta pathway in endothelium.

Endothelial progenitor cells stimulate cerebrovascular production of prostacyclin by paracrine activation of cyclooxygenase-2

In the present study we hypothesized that endothelial progenitor cells (EPCs) enhance production of vasoprotective substances in cerebral arteries. Isolated mononuclear cells from rabbit peripheral blood were cultured in endothelial growth medium (EGM-2) for 7 days to yield EPCs. Rabbit basilar arteries were exposed to autologous EPCs ( approximately 5x10(5) cells) in vitro or in vivo. Twenty-four hours after intracisternal delivery of autologous EPCs, basilar arteries were isolated and expression of vasoregulatory proteins, production of prostacyclin (PGI(2)), and cAMP were determined. Arteries transplanted with EPCs demonstrated increased protein expression of cyclooxygenase-2 and PGI(2) in adventitia, media, and endothelium. Furthermore, production of PGI(2) and arterial content of cAMP, second messenger for PGI(2), were significantly augmented after transplantation of EPCs. In contrast, production of thromboxane A(2) was significantly reduced, whereas production of prostaglandin E(2) remained unchanged. The increased production of PGI(2) and arterial content of cAMP were inhibited only by a selective cyclooxygenase-2 inhibitor, NS-398. In vitro or in vivo treatment of basilar artery with conditioned media from EPCs also caused increase in cyclooxygenase-2 and PGI(2) synthase protein expression associated with elevation of cAMP. Our results suggest that in cerebral arteries, paracrine effect of EPCs promotes vasoprotection by increasing PGI(2) production and intracellular concentration of cAMP. This effect appears to be mediated by activation of arachidonic acid metabolism via stimulation of cyclooxygenase-2/PGI(2) synthase pathway.