Angiopoietin 1, PDGF-B, and TGF-beta gene regulation in endothelial cell and smooth muscle cell interaction

Microvascular destabilization and intricated network of the cytokines in diabetic retinopathy: from the perspective of cellular and molecular components

Microvascular destabilization is the primary cause of the inner blood-retinal barrier (iBRB) breakdown and increased vascular leakage in diabetic retinopathy (DR). Microvascular destabilization results from the combinational effects of increased levels of growth factors and cytokines, involvement of inflammation, and the changed cell-to-cell interactions, especially the loss of endothelial cells and pericytes, due to hyperglycemia and hypoxia. As the manifestation of microvascular destabilization, the fluid transports via paracellular and transcellular routes increase due to the disruption of endothelial intercellular junctional complexes and/or the altered caveolar transcellular transport across the retinal vascular endothelium. With diabetes progression, the functional and the structural changes of the iBRB components, including the cellular and noncellular components, further facilitate and aggravate microvascular destabilization, resulting in macular edema, the neuroretinal damage and the dysfunction of retinal inner neurovascular unit (iNVU). Although there have been considerable recent advances towards a better understanding of the complex cellular and molecular network underlying the microvascular destabilization, some still remain to be fully elucidated. Recent data indicate that targeting the intricate signaling pathways may allow to against the microvascular destabilization. Therefore, efforts have been made to better clarify the cellular and molecular mechanisms that are involved in the microvascular destabilization in DR. In this review, we discuss: (1) the brief introduction of DR and microvascular destabilization; (2) the cellular and molecular components of iBRB and iNVU, and the breakdown of iBRB; (3) the matrix and cell-to-cell contacts to maintain microvascular stabilization, including the endothelial glycocalyx, basement membrane, and various cell-cell interactions; (4) the molecular mechanisms mediated cell-cell contacts and vascular cell death; (5) the altered cytokines and signaling pathways as well as the intricate network of the cytokines involved in microvascular destabilization. This comprehensive review aimed to provide the insights for microvascular destabilization by targeting the key molecules or specific iBRB cells, thus restoring the function and structure of iBRB and iNVU, to treat DR.

An overview of the molecular and clinical significance of the angiopoietin system in leukemia

The angiogenesis efficacy in solid tumors and hematological malignancies has been identified for more than twenty years. Although the exact role of angiogenesis in leukemia as a common hematological malignancy has not yet been extensively studied, its effect is demonstrated on the initiation and maintenance of a favorable microenvironment for leukemia cell proliferation. The angiopoietin family is a defined molecular mediator for angiogenesis, which contributes to vascular permeability and angiogenesis initiation. They participate in the angiogenesis process by binding to tyrosine kinase receptors (Tie) on endothelial cells. Considering the role of angiogenesis in leukemia development and the crucial effects of the Ang-Tie system in angiogenesis regulation, many studies have focused on the correlation between the Ang-Tie system and leukemia diagnosis, monitoring, and treatment. In this study, we reviewed the Ang-Tie system's potential diagnostic and therapeutic effects in different types of leukemia in the gene expression level analysis approach. The angiopoietin family context-dependent manner prevents us from defining its actual function in leukemia, emphasizing the need for more comprehensive studies.

Diminished schwann cell repair responses play a role in delayed diabetes-associated wound healing

Diabetes mellitus is the most common metabolic disease associated with impaired wound healing. Recently, Schwann cells (SCs), the glia of the peripheral nervous system, have been suggested to accelerate normal skin wound healing. However, the roles of SCs in diabetic wound healing are not fully understood. In this study, Full-thickness wounds were made in the dorsal skin of C57/B6 mice and db/db (diabetic) mice. Tissue samples were collected at different time points, and immunohistochemical and immunofluorescence analyses were performed to detect markers of de-differentiated SCs, including myelin basic protein, Sox 10, p75, c-Jun, and Ki67. In addition, in vitro experiments were performed using rat SC (RSC96) and murine fibroblast (L929) cell lines to examine the effects of high glucose conditions (50 mM) on the de-differentiation of SCs and the paracrine effects of SCs on myofibroblast formation. Here, we found that, compared with that in normal mice, wound healing was delayed and SCs failed to rapidly activate a repair program after skin wound injury in diabetic mice. Furthermore, we found that SCs from diabetic mice displayed functional impairments in cell de-differentiation, cell-cycle re-entry, and cell migration. In vitro, hyperglycemia impaired RSC 96 cell de-differentiation, cell-cycle re-entry, and cell migration, as well as their paracrine effects on myofibroblast formation, including the secretion of TGF-β and Timp1. These results suggest that delayed wound healing in diabetes is due in part to a diminished SC repair response and attenuated paracrine effects on myofibroblast formation.

Increased angiogenesis parallels cardiac tissue remodelling in experimental acute Trypanosoma cruzi infection

BACKGROUND

Angiogenesis has been implicated in tissue injury in several noninfectious diseases, but its role in Chagas disease (CD) physiopathology is unclear.

OBJECTIVES

The present study aimed to investigate the effect of Trypanosoma cruzi infection on cardiac angiogenesis during the acute phase of experimental CD.

METHODS

The signalling pathway involved in blood vessel formation and cardiac remodelling was evaluated in Swiss Webster mice infected with the Y strain of T. cruzi. The levels of molecules involved in the regulation of angiogenesis, such as vascular endothelial growth factor-A (VEGF-A), Flk-1, phosphorylated extracellular-signal-regulated protein kinase (pERK), hypoxia-inducible factor-1α (HIF-1α), CD31, α-smooth muscle actin (α-SMA) and also the blood vessel growth were analysed during T. cruzi infection. Hearts were analysed using conventional histopathology, immunohistochemistry and western blotting.

FINDINGS

In this study, our data demonstrate that T. cruzi acute infection in mice induces exacerbated angiogenesis in the heart and parallels cardiac remodelling. In comparison with noninfected controls, the cardiac tissue of T. cruzi-infected mice presented higher levels of (i) HIF-1α, VEGF-A, Flk-1 and pERK; (ii) angiogenesis; (iii) α-SMA+ cells in the tissue; and (iv) collagen -1 deposition around blood vessels and infiltrating throughout the myocardium.

MAIN CONCLUSIONS

We observed cardiac angiogenesis during acute experimental T. cruzi infection parallels cardiac inflammation and remodelling.

Cellular loci involved in the development of brain arteriovenous malformations

Brain arteriovenous malformations (bAVMs) are abnormal vessels that are prone to rupture, causing life-threatening intracranial bleeding. The mechanism of bAVM formation is poorly understood. Nevertheless, animal studies revealed that gene mutation in endothelial cells (ECs) and angiogenic stimulation are necessary for bAVM initiation. Evidence collected through analyzing bAVM specimens of human and mouse models indicate that cells other than ECs also are involved in bAVM pathogenesis. Both human and mouse bAVMs vessels showed lower mural cell-coverage, suggesting a role of pericytes and vascular smooth muscle cells (vSMCs) in bAVM pathogenesis. Perivascular astrocytes also are important in maintaining cerebral vascular function and take part in bAVM development. Furthermore, higher inflammatory cytokines in bAVM tissue and blood demonstrate the contribution of inflammatory cells in bAVM progression, and rupture. The goal of this paper is to provide our current understanding of the roles of different cellular loci in bAVM pathogenesis.

Diverse roles of tumor-stromal PDGFB-to-PDGFRβ signaling in breast cancer growth and metastasis

Over the last couple of decades, it has become increasingly apparent that the tumor microenvironment (TME) mediates every step of cancer progression and solid tumors are only able to metastasize with a permissive TME. This intricate interaction of cancer cells with their surrounding TME, or stroma, is becoming more understood with an ever greater knowledge of tumor-stromal signaling pairs such as platelet-derived growth factors (PDGF) and their cognate receptors. We and others have focused our research efforts on understanding how tumor-derived PDGFB activates platelet-derived growth factor receptor beta (PDGFRβ) signaling specifically in the breast cancer TME. In this chapter, we broadly discuss PDGF and PDGFR expression patterns and signaling in normal physiology and breast cancer. We then detail the expansive roles played by the PDGFB-to-PDGFRβ signaling pathway in modulating breast tumor growth and metastasis with a focus on specific cellular populations within the TME, which are responsive to tumor-derived PDGFB. Given the increasingly appreciated importance of PDGFB-to-PDGFRβ signaling in breast cancer progression, specifically in promoting metastasis, we end by discussing how therapeutic targeting of PDGFB-to-PDGFRβ signaling holds great promise for improving current breast cancer treatment strategies.

Targeting Tie2 in the Tumor Microenvironment: From Angiogenesis to Dissemination

Simple Summary

The dissemination of cancer cells from their original location to distant organs where they grow, a process called metastasis, causes more than 90% of cancer deaths. The identification of the molecular mechanisms of metastasis and the development of anti-metastatic therapies are essential to increase patient survival. In recent years, targeting the tumor microenvironment has become a promising avenue to prevent both tumor growth and metastasis. As the tumor microenvironment contains not only cancer cells but also blood vessels, immune cells, and other non-cancerous cells, it is naïve to think that therapy only affects a single cell type in this complex environment. Here we review the importance, and ways to inhibit the function, of one therapeutic target: the receptor Tie2. Tie2 is a receptor present on the cell surface of several cell types within the tumor microenvironment and regulates tumor angiogenesis, growth, and metastasis to distant organs.

Abstract

The Tie2 receptor tyrosine kinase is expressed in vascular endothelial cells, tumor-associated macrophages, and tumor cells and has been a major focus of research in therapies targeting the tumor microenvironment. The most extensively studied Tie2 ligands are Angiopoietin 1 and 2 (Ang1, Ang2). Ang1 plays a critical role in vessel maturation, endothelial cell migration, and survival. Ang2, depending on the context, may function to disrupt connections between the endothelial cells and perivascular cells, promoting vascular regression. However, in the presence of VEGF-A, Ang2 instead promotes angiogenesis. Tie2-expressing macrophages play a critical role in both tumor angiogenesis and the dissemination of tumor cells from the primary tumor to secondary sites. Therefore, Ang-Tie2 signaling functions as an angiogenic switch during tumor progression and metastasis. Here we review the recent advances and complexities of targeting Tie2 signaling in the tumor microenvironment as a possible anti-angiogenic, and anti-metastatic, therapy and describe its use in combination with chemotherapy.

Microvascular cells: A special focus on heterogeneity of pericytes in diabetes associated complications

Pericytes (PC) are microvascular mural cells that make specific cell-to-cell contacts with the endothelial cells (EC). These cells are obligatory constituents of the microvessels including the retinal vasculature and they serve as regulators of vascular development, stabilization, maturation and remodeling. During early stages of diabetic retinopathy (DR), apoptotic loss of PC surrounding the retinal vasculature occurs. This may lead to reduced vessel stability, the onset of EC apoptosis, and subsequent retinal ischemia leading to angiogenesis and eventually, severe vision loss due to late proliferative diabetic retinopathy (PDR). Similarly, diabetic nephropathy (DN) is a chronic kidney disease due to hyperglycemia that particularly affects renal PC. Chronic high blood glucose level causes migration of peritubular PC away from the capillary into the interstitial space, which destabilizes the micro vessels, resulting in microvascular rarefaction. In both diabetes associated complications, the identification of specific biomarkers is necessary to stabilize the PC at an early stage. This review largely covers the importance of PC towards the pathogenesis of diabetes associated complications, and their heterogeneity in healthy and angiogenic vasculature.

AKT/FOXO1 axis links cross-talking of endothelial cell and pericyte in TIE2-mutated venous malformations

Background

Venous malformations (VMs), most of which associated with activating mutations in the endothelial cells (ECs) tyrosine kinase receptor TIE2, are characterized by dilated and immature veins with scarce smooth muscle cells (SMCs) coverage. However, the underlying mechanism of interaction between ECs and SMCs responsible for VMs has not been fully understood.

Methods

Here, we screened 5 patients with TIE2-L914F mutation who were diagnosed with VMs by SNP sequencing, and we compared the expression of platelet-derived growth factor beta (PDGFB) and α-SMA in TIE2 mutant veins and normal veins by immunohistochemistry. In vitro, we generated TIE2-L914F-expressing human umbilical vein endothelial cells (HUVECs) and performed BrdU, CCK-8, transwell and tube formation experiments on none-transfected and transfected ECs. Then we investigated the effects of rapamycin (RAPA) on cellular characteristics. Next we established a co-culture system and investigated the role of AKT/FOXO1/PDGFB in regulating cross-talking of mutant ECs and SMCs.

Results

VMs with TIE2-L914F mutation showed lower expression of PDGFB and α-SMA than normal veins. TIE2 mutant ECs revealed enhanced cell viability and motility, and decreased tube formation, whereas these phenotypes could be reversed by rapamycin. Mechanically, RAPA ameliorated the physiological function of mutant ECs by inhibiting AKT-mTOR pathway, but also facilitated the nuclear location of FOXO1 and the expression of PDGFB in mutant ECs, and then improved paracrine interactions between ECs and SMCs. Moreover, TIE2 mutant ECs strongly accelerated the transition of SMCs from contractile phenotype to synthetic phenotype, whereas RAPA could prevent the phenotype transition of SMCs.

Conclusions

Our data demonstrate a previously unknown mechanistic linkage of AKT-mTOR/FOXO1 pathway between mutant ECs and SMCs in modulating venous dysmorphogenesis, and AKT/FOXO1 axis might be a potential therapeutic target for the recovery of TIE2-mutation causing VMs.

Nonselective alpha-/beta- AR antagonists can inhibit pericyte proliferation, migration, and secretion in vitro

It has been reported that the beta-adrenergic receptor blocker (propranolol) and the a-adrenergic receptor (AR) blocker (phentolamine) both can inhibit human endothelial cell (EC) angiogenesis in vitro. However, it is unknown whether this inhibition also acts on pericytes. The present study aimed to determine how pericytes react to treatment with an a-/β- AR blocker. In the study, cell proliferation assays and scratch assay were performed to assess the effect of phentolamine or propranolol on cell proliferation and migration. Western blot and ELISA were employed to determine changes in VEGF-A and Ang-1 expression levels. The results indicated that the nonselective a-/β- AR blocker inhibited the proliferation, migration, and secretion of pericytes. The use of the nonselective a-/β- AR blocker might have an impact on vascularization and vascular maturation. Our research suggests the rational use of nonselective a-/β- AR blockers to treat angiogenesis-dependent diseases.

GM-CSF ameliorates microvascular barrier integrity via pericyte-derived Ang-1 in wound healing

Skin wound healing involves complex coordinated interactions of cells, tissues, and mediators. Maintaining microvascular barrier integrity is one of the key events for endothelial homeostasis during wound healing. Vasodilation is observed after vasoconstriction, which causes blood vessels to become porous, facilitates leukocyte infiltration and aids angiogenesis at the wound-area, postinjury. Eventually, vessel integrity has to be reestablished for vascular maturation. Numerous studies have found that granulocyte macrophage colony-stimulating factor (GM-CSF) accelerates wound healing by inducing recruitment of repair cells into the injury area and releases of cytokines. However, whether GM-CSF is involving in the maintaining of microvascular barrier integrity and the underlying mechanism remain still unclear. Aim of this study was to investigate the effects of GM-CSF on modulation of microvascular permeability in wound healing and underlying mechanisms. Wound closure and microvascular leakage was investigated using a full-thickness skin wound mouse model after GM-CSF intervention. The endothelial permeability was measured by Evans blue assay in vivo and in vitro endothelium/pericyte co-culture system using a FITC-Dextran permeability assay. To identify the source of angiopoietin-1 (Ang-1), double staining is used in vivo and ELISA and qPCR are used in vitro. To determine the specific effect of Ang-1 on GM-CSF maintaining microvascular stabilization, Ang-1 siRNA was applied to inhibit Ang-1 production in vivo and in vitro. Wound closure was significantly accelerated and microvascular leakage was ameliorated after GM-CSF treatment in mouse wound sites. GM-CSF decreased endothelial permeability through tightening endothelial junctions and increased Ang-1 protein level that was derived by perictye. Furthermore, applications of siRNAAng-1 inhibited GM-CSF mediated protection of microvascular barrier integrity both in vivo and in vitro. Our data indicate that GM-CSF ameliorates microvascular barrier integrity via pericyte-derived Ang-1 during wound healing.

Role of lipids and intraplaque hypoxia in the formation of neovascularization in atherosclerosis

According to the current paradigm, chronic vascular inflammation plays a central role in the pathogenesis of atherosclerosis. The plaque progression is typically completed with rupture and subsequent acute cardiovascular complications. Previously, the role of adventitial vasa vasorum in atherogenesis was underestimated. However, investigators then revealed that vasa vasorum neovascularization can be observed when no clinical manifestation of atherosclerosis is present. Vasa vasorum is involved in various proatherogenic processes such as intimal accumulation of inflammatory leukocytes, intimal thickening, necrotic core formation, intraplaque haemorrhage, lesion rupture and atherothrombosis. Due to the destabilizing action of the intraplaque microenvironment, lesional vasa vasorum neovessels experience serious defects and abnormalities during development that leads to their immaturity, fragility and leakage. Indeed, intraplaque neovessels are a main cause of intraplaque haemorrhage. Visualization techniques showed that presence of neovascularization/haemorrhage can serve as a good indicator of lesion instability and higher risk of rupture. Vasa vasorum density is a strong predictor of acute cardiovascular events such as sudden death, myocardial infarction and stroke. At present, arterial vasa vasorum neovascularization is under intensive investigation along with development of therapeutic tools focused on the control of formation of vasa vasorum neovessels in order to prevent plaque haemorrhage/rupture and thromboembolism. KEY MESSAGE Neovascularization plays an important role in atherosclerosis, being involved in unstable plaque formation. Presence of neovascularization and haemorrhage indicates plaque instability and risk of rupture. Various imaging techniques are available to study neovascularization.

Pericytes in diabetes-associated vascular disease

Pericytes are mural cells that support and stabilise the microvasculature, and are present in all vascular beds. Pericyte-endothelial cell crosstalk is essential in both remodelling and quiescent vasculature, and this complex interaction is often disrupted in disease states. Pericyte loss is believed to be an early hallmark of diabetes-associated microvascular disease, including retinopathy and nephropathy. Here we review the current literature defining pericyte biology in the context of diabetes-associated vascular disease, with a particular focus on whether pericytes contribute actively to disease progression. We also speculate regarding the role of pericytes in the recovery from macrovascular complications, such as critical limb ischaemia. It becomes clear that dysfunctional pericytes are likely to actively induce disease progression by causing vasoconstriction and basement membrane thickening, resulting in tissue ischaemia. Moreover, their altered interactions with endothelial cells are likely to cause abnormal and inadequate neovascularisation in diverse vascular beds. Further research is needed to identify mechanisms by which pericyte function is altered by diabetes, with a view to developing therapeutic approaches that normalise vascular function and remodelling.

ER Alpha Rapid Signaling Is Required for Estrogen Induced Proliferation and Migration of Vascular Endothelial Cells

Estrogen promotes the proliferation and migration of vascular endothelial cells (ECs), which likely underlies its ability to accelerate re-endothelialization and reduce adverse remodeling after vascular injury. In previous studies, we have shown that the protective effects of E2 (the active endogenous form of estrogen) in vascular injury require the estrogen receptor alpha (ERα). ERα transduces the effects of estrogen via a classical DNA binding, "genomic" signaling pathway and via a more recently-described "rapid" signaling pathway that is mediated by a subset of ERα localized to the cell membrane. However, which of these pathways mediates the effects of estrogen on endothelial cells is poorly understood. Here we identify a triple point mutant version of ERα (KRR ERα) that is specifically defective in rapid signaling, but is competent to regulate transcription through the "genomic" pathway. We find that in ECs expressing wild type ERα, E2 regulates many genes involved in cell migration and proliferation, promotes EC migration and proliferation, and also blocks the adhesion of monocytes to ECs. ECs expressing KRR mutant ERα, however, lack all of these responses. These observations establish KRR ERα as a novel tool that could greatly facilitate future studies into the vascular and non-vascular functions of ERα rapid signaling. Further, they support that rapid signaling through ERα is essential for many of the transcriptional and physiological responses of ECs to E2, and that ERα rapid signaling in ECs, in vivo, may be critical for the vasculoprotective and anti-inflammatory effects of estrogen.

(2-Hydroxypropyl)-β-Cyclodextrin Is a New Angiogenic Molecule for Therapeutic Angiogenesis

Background

Peripheral artery disease (PAD), which is caused by atherosclerosis, results in progressive narrowing and occlusion of the peripheral arteries and inhibits blood flow to the lower extremities. Therapeutic angiogenesis is a promising strategy for treating ischemia caused by PAD. Nitric oxide (NO) has been shown to be a key mediator of angiogenesis. It has been demonstrated that β-cyclodextrincan stimulate vessel growth in rabbit corneas. In this study, we assessed the mechanism of action and therapeutic potential of a new angiogenic molecule, (2-hydroxypropyl)-β-cyclodextrin (2HP-β-CD).

Methods and Results

2HP-β-CD significantly increased vascular endothelial growth factor A (VEGF-A) and platelet-derived growth factor BB (PDGF-BB) peptides in human umbilical vein endothelial cells (HUVECs) and also increased basic fibroblast growth factor (bFGF) peptide in human aortic smooth muscle cells (HASMCs). 2HP-β-CD stimulated both proliferation and migration of HUVECs in an endothelial nitric oxide synthase (eNOS)/NO-dependent manner, whereas NO was found to be involved in proliferation, but not migration, of HASMCs. In a unilateral hindlimb ischemia model in mice, 2HP-β-CD injections not only promoted blood flow recovery and increased microvessel densities in ischemic muscle, but also promoted coverage of the vessels with smooth muscle cells, thus stabilizing the vessels. Administration of 2HP-β-CD increased the expression of several angiogenic factors, including VEGF-A, PDGF-BB and transforming growth factor beta-1 (TGF-β1) in ischemic muscle. Injections of 2HP-β-CD also stimulated protein kinase B and extracellular regulated protein kinases (ERK), leading to an increase in phosphorylation of eNOS in ischemic muscle. Treatment with the NOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME), showed that stimulation of blood flow induced by 2HP-β-CD was partially dependent on NO.

Conclusions

Therapeutic angiogenesis by 2HP-β-CD may be beneficial to patients with PAD.

PI3K at the crossroads of tumor angiogenesis signaling pathways

Tumors need blood vessels for their growth, thus providing the rationale for antiangiogenic therapy in cancer treatment. However, intrinsic and acquired resistance and low response rates have turned out to be major limitations of antiangiogenic therapy. This emphasizes the need to further understand how the vasculature in cancer can be targeted. Although endothelial cells (ECs) rely on multiple growth factors and cytokines to grow, antiangiogenic therapies have mainly centered on targeting vascular endothelial growth factor (VEGF). Phosphoinositide 3-kinases (PI3Ks) form a family of 8 isoenzymes with non-redundant functions in normal biology and cancer. The subgroup of class I PI3Ks are situated at the crossroad of a plethora of proangiogenic signals and control cell growth, survival, motility, and metabolism. These isoenzymes have pleiotropic roles in the tumor microenvironment, including cell-autonomous functions in ECs, underscoring the complexity of targeting this pathway in cancer. Here, we describe how the PI3K axis influences angiogenesis in different cell compartments and summarize the diversity of vascular responses to PI3K inhibition. Targeting PI3K signaling by isoform-selective inhibitors, together with readjusting the current doses below the maximum tolerated dose, may improve clinical responses to class I PI3K anticancer agents.

Genetic variations in angiopoietin and pericyte pathways and clinical outcome in patients with resected colorectal liver metastases

BACKGROUND

Genes involved in the angiopoietin and pericyte pathways may become escape mechanisms under antivascular endothelial growth factor (anti-VEGF) therapy. The authors investigated whether variations within genes in these pathways are associated with clinical outcome in patients with colorectal liver metastases who undergo liver resection and receive perioperative, bevacizumab-based chemotherapy.

METHODS

Single nucleotide polymorphisms (SNPs) in 9 genes (angiopoietin-1 [ANGPT1]; ANGPT2; TEK tyrosine kinase, endothelial [TEK]; platelet-derived growth factor β [PDGFB]; β-type platelet-derived growth factor receptor [PDGFRB]; insulin-like growth factor 1 [IGF1]; transforming growth factor β1 [TGFB1]; RalA binding protein 1 [RALBP1]; and regulator of G-protein signaling 5 [RGS5]) were analyzed in samples of genomic DNA from 149 patients and were evaluated for associations with clinical outcome.

RESULTS

RALBP1 reference SNP 329007 (rs329007) A>G resulted in a significant difference in recurrence-free survival (A/A genotype, 14.0 months; A/G or G/G genotype, 9.2 months; hazard ratio [HR], 1.60; P = .024). PDGFB rs1800818 A>G was associated with 3-year overall survival rates (A/A genotype, 78%; A/G genotype, 69%; [HR 1.37]; G/G genotype, 53%; [HR 2.12]; P = .048). In multivariate analysis, RALBP1 rs329007 A>G remained significant (HR, 1.99; P = .002). PDGFB rs1800818 A>G and RALBP1 rs329007 A>G were correlated with radiologic response (A/A or A/G genotype, 86%; G/G genotype, 71% [P = .042]; A/A genotype, 78%; A/G or G/G genotype, 94% [P = .018], respectively). RALBP1 rs329007 A>G demonstrated significantly different rates of histologic response (A/A genotype: major histologic response, 35%; partial histologic response, 34%; no histologic response, 30%; A/G or G/G genotype: 46%, 13%, and 41%, respectively; P = .029). Recursive partitioning analysis revealed that ANGPT2 rs2442599 T>C and RALBP1 rs329007 A>G were the main SNPs that predicted histologic response and recurrence-free survival, whereas PDGFB rs1800818 A>G was the leading SNP that predicted overall survival. ANGPT2 rs2916702 C>T and rs2442631 G>A were significantly associated with the probability of achieving a cure.

CONCLUSIONS

The current data suggest that variations in genes involved in the angiopoietin and pericyte pathways may be predictive and/or prognostic biomarkers in patients with resected colorectal liver metastases who receive bevacizumab-based chemotherapy.

Akt1 activity regulates vessel maturation in a tissue engineering model of angiogenesis

Akt kinase is a central signal transduction node that integrates extracellular cues that regulate cell migratory, proliferative, and morphological functions during angiogenesis. However, how Akt activity is modulated and contributes to subsequent vessel maturation is unclear. In this study we investigated the role of Akt1 in vessel maturation using human dermal microvascular endothelial cells (HDMVECs) expressing constitutively active and hemiphosphorylated Akt1 epi-alleles with graded kinase activity. HDMVECs expressing Akt1 epi-alleles were analyzed in vivo in a tissue engineering setting using a model of angiogenesis comprising cell-seeded poly-L-lactic acid scaffolds implanted subcutaneously into NOD/SCID murine hosts. The resultant intraimplant microvasculature was quantified for vascular parameters, including vessel diameter, perfusion, vascular density, and pericyte coverage. We found that constitutive Akt1 kinase activity in implanted HDMVECs correlated with loss of neovasculature function. Further, we found that the presence of coimplanted vascular smooth muscle cells (vSMCs) in the implants failed to promote blood vessel growth and maturation in a graded, Akt1 kinase activity-dependent manner. These results indicate that constitutive Akt1 activity disrupts the normal blood vessel growth and maturation. Therefore, we suggest that a downregulation of Akt1 activity is necessary for vSMC-induced maturation of newly formed blood vessels to occur.

Cell communication in a coculture system consisting of outgrowth endothelial cells and primary osteoblasts

Bone tissue is a highly vascularized and dynamic system with a complex construction. In order to develop a construct for implant purposes in bone tissue engineering, a proper understanding of the complex dependencies between different cells and cell types would provide further insight into the highly regulated processes during bone repair, namely, angiogenesis and osteogenesis, and might result in sufficiently equipped constructs to be beneficial to patients and thereby accomplish their task. This study is based on an in vitro coculture model consisting of outgrowth endothelial cells and primary osteoblasts and is currently being used in different studies of bone repair processes with special regard to angiogenesis and osteogenesis. Coculture systems of OECs and pOBs positively influence the angiogenic potential of endothelial cells by inducing the formation of angiogenic structures in long-term cultures. Although many studies have focused on cell communication, there are still numerous aspects which remain poorly understood. Therefore, the aim of this study is to investigate certain growth factors and cell communication molecules that are important during bone repair processes. Selected growth factors like VEGF, angiopoietins, BMPs, and IGFs were investigated during angiogenesis and osteogenesis and their expression in the cultures was observed and compared after one and four weeks of cultivation. In addition, to gain a better understanding on the origin of different growth factors, both direct and indirect coculture strategies were employed. Another important focus of this study was to investigate the role of “gap junctions,” small protein pores which connect adjacent cells. With these bridges cells are able to exchange signal molecules, growth factors, and other important mediators. It could be shown that connexins, the gap junction proteins, were located around cell nuclei, where they await their transport to the cell membrane. In addition, areas in which two cells formed gap junctions were found.

Developmental and tumoral vascularization is regulated by G protein-coupled receptor kinase 2

Tumor vessel dysfunction is a pivotal event in cancer progression. Using an in vivo neovascularization model, we identified G protein-coupled receptor kinase 2 (GRK2) as a key angiogenesis regulator. An impaired angiogenic response involving immature vessels was observed in mice hemizygous for Grk2 or in animals with endothelium-specific Grk2 silencing. ECs isolated from these animals displayed intrinsic alterations in migration, TGF-β signaling, and formation of tubular networks. Remarkably, an altered pattern of vessel growth and maturation was detected in postnatal retinas from endothelium-specific Grk2 knockout animals. Mouse embryos with systemic or endothelium-selective Grk2 ablation had marked vascular malformations involving impaired recruitment of mural cells. Moreover, decreased endothelial Grk2 dosage accelerated tumor growth in mice, along with reduced pericyte vessel coverage and enhanced macrophage infiltration, and this transformed environment promoted decreased GRK2 in ECs and human breast cancer vessels. Our study suggests that GRK2 downregulation is a relevant event in the tumoral angiogenic switch.

Multifarious functions of PDGFs and PDGFRs in tumor growth and metastasis

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) are frequently expressed in various tumors and their expression levels correlate with tumor growth, invasiveness, drug resistance, and poor clinical outcomes. Emerging experimental evidence demonstrates that PDGFs exhibit multiple functions in modulation of tumor growth, metastasis, and the tumor microenvironment by targeting malignant cells, vascular cells, and stromal cells. Understanding PDGF-PDGFR-mediated molecular signaling may provide new mechanistic rationales for optimizing current cancer therapies and the development of future novel therapeutic modalities.

Transplantation of modified human adipose derived stromal cells expressing VEGF165 results in more efficient angiogenic response in ischemic skeletal muscle

Background

Modified cell-based angiogenic therapy has become a promising novel strategy for ischemic heart and limb diseases. Most studies focused on myoblast, endothelial cell progenitors or bone marrow mesenchymal stromal cells transplantation. Yet adipose-derived stromal cells (in contrast to bone marrow) are abundantly available and can be easily harvested during surgery or liposuction. Due to high paracrine activity and availability ADSCs appear to be a preferable cell type for cardiovascular therapy. Still neither genetic modification of human ADSC nor in vivo therapeutic potential of modified ADSC have been thoroughly studied. Presented work is sought to evaluate angiogenic efficacy of modified ADSCs transplantation to ischemic tissue.

Materials and methods

Human ADSCs were transduced using recombinant adeno-associated virus (rAAV) serotype 2 encoding human VEGF165. The influence of genetic modification on functional properties of ADSCs and their angiogenic potential in animal models were studied.

Results

We obtained AAV-modified ADSC with substantially increased secretion of VEGF (VEGF-ADSCs). Transduced ADSCs retained their adipogenic and osteogenic differentiation capacities and adhesion properties. The level of angiopoetin-1 mRNA was significantly increased in VEGF-ADSC compared to unmodified cells yet expression of FGF-2, HGF and urokinase did not change. Using matrigel implant model in mice it was shown that VEGF-ADSC substantially stimulated implant vascularization with paralleling increase of capillaries and arterioles. In murine hind limb ischemia test we found significant reperfusion and revascularization after intramuscular transplantation of VEGF-ADSC compared to controls with no evidence of angioma formation.

Conclusions

Transplantation of AAV-VEGF- gene modified hADSC resulted in stronger therapeutic effects in the ischemic skeletal muscle and may be a promising clinical treatment for therapeutic angiogenesis.

Local Transplantation of Ex Vivo Expanded Bone Marrow-Derived CD34-Positive Cells Accelerates Fracture Healing

Transplantation of bone marrow (BM) CD34+ cells, an endothelial/hematopoietic progenitor-enriched cell population, has shown therapeutic efficiency in the treatment of ischemic diseases enhancing neovascularization. However, the number of CD34+ cells obtained from bone marrow is not sufficient for routine clinical application. To overcome this issue, we developed a more efficient and clinically applicable CD34+ cell expansion method. Seven-day ex vivo expansion culture of BM CD34+ cells with a cocktail of five growth factors containing VEGF, SCF, IL-6, Flt-3 ligand, and TPO resulted in reproducible more than 20-fold increase in cell number. The favorable effect of the local transplantation of culture expanded (cEx)-BM CD34+ cells on rat unhealing fractures was equivalent or higher than that of nonexpanded (fresh) BM CD34+ cells exhibiting sufficient therapeutic outcome with frequent vasculogenic/osteogenic differentiation of transplanted cEx-BM CD34+ cells and fresh BM CD34+ cells as well as intrinsic enhancement of angiogenesis/osteogenesis at the treated fracture sites. Specifically, cEx-BM CD34+ cell treatment demonstrated the best blood flow recovery at fracture sites compared with the nonexpanded BM CD34+ cells. In vitro, cEx-BM CD34+ cells showed higher colony/tube-forming capacity than nonexpanded BM CD34+ cells. Both cells demonstrated differentiation potential into osteoblasts. Since fresh BM CD34+ cells can be easily collected from fracture sites at the time of primary operation and stored for future use, autologous cEx-BM CD34+ cell transplantation would be not only a simple but also a promising therapeutic strategy for unhealing fractures in the field of orthopedic trauma surgery.

The effects of Ang-1, IL-8 and TGF-β1 on the pathogenesis of COPD

Chronic obstructive pulmonary disease (COPD) is a prevalent smoking-related disease for which no disease‑altering therapies currently exist. Airway remodeling is one of the most important mechanisms in the pathogenesis of COPD and is triggered by chronic inflammation mediated by angiopoietin-1 (Ang-1), interleukin-8 (IL-8) and transforming growth factor-β1 (TGF-β1). The aim of this study was to investigate the effects of Ang-1, IL-8 and TGF-β1 on the pathogenesis of COPD. Forty-two COPD patients and 10 healthy adults (group A) were included in this study. We divided the 42 patients into 4 groups (groups B-E) according to the severity of the disease. We investigated the levels of Ang-1, IL-8 and TGF-β1 and the levels of pulmonary function (PF) in the stable and acute phases of COPD by enzyme-linked immunosorbent assay. We found statistically significant differences in the expression levels of Ang-1, IL-8 and TGF-β1 between the stable and acute phases in groups B-E. We found statistically significant differences in the expression levels of Ang-1 among all groups in the stable phase. In addition, there were statistically significant differences in the expression levels of TGF-β1 among all groups. There were statistically significant differences in the expression levels of IL-8 between group A and the other groups in the stable phase. Furthermore, in groups C-E we found higher correlations between Ang-1 and the forced expiratory volume in one second of forced vital capacity (FVC) [FEV1(%)] and FEV1/FVC(%) than between TGF-β1 and FEV1(%) and FEV1/FVC(%). We conclude that the blood vessel factor is more closely related to the pathogenesis of COPD.

Transforming growth factor-beta1 induces microvascular abnormalities through a down-modulation of neural cell adhesion molecule in human hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a very angiogenic and malignant cancer. Conventional chemotherapy is poorly effective because of the abnormal structural organization of HCC-infiltrating vessels. In previous work, we demonstrated that HCC angiogenesis is driven by transforming growth factor beta-1(TGF-β1)/CD105 axis, stimulating liver-derived microvascular endothelial cells (Ld-MECs) migration. As TGF-β1 also affects mural cells (MCs) recruitment and maturation, we asked whether it may contribute to HCC-induced vascular abnormalities. HCC and adjacent non-neoplastic liver (nNL) biopsies obtained from 12 patients were analyzed by immunohistochemistry for angiogenic markers CD105, TGF-β1, CD44 and vascular endothelial growth factor-a (VEGFa) and for MC markers NG2, α-smooth muscle actin (αSMA) and neural cell adhesion molecule (NCAM). The same markers were also investigated by immunocytochemistry on cultured HCC-derived stromal cells (HCC-StCs) and nNL-derived StCs (nNL-StCs) isolated from the same liver biopsies. Angiogenic factors released by StCs were analyzed by ELISA and the interaction between StCs and Ld-MECs by adhesion assay. Compared with nNL, HCC biopsies showed increased angiogenic markers and αSMA that was localized in vessels. By contrast, NG2 and NCAM were substantially localized in tumor cells but absent in vessels and stroma. Cultured HCC-StCs showed less expression of NG2, αSMA and NCAM. They also demonstrated a lower capacity to release angiogenic factors and adhered on Ld-MECs. HCC-StCs and nNL-StCs treated with TGF-β1 or with of HepG2 (a human hepatoma cell line) derived conditioned medium (CM), down-modulated NCAM expression, whereas anti-NCAM antibodies significantly reduced the adhesion of StCs to Ld-MECs. By further blocking TGF-β1 with anti-TGF-β1 antibodies or with Ly-364947 (a specific inhibitor TGF-β1-receptor) adhesion to Ld-MECs and NCAM expression respectively was partially restored. TGF-β1 contributes to HCC-induced vascular alterations by affecting the interaction between HCC-StCs and Ld-MECs through a down-modulation of NCAM expression.

Angiopoietins in angiogenesis

Tie-1 and Tie-2 tyrosine kinase receptors are expressed specifically on vascular endothelial cells and on a certain subtype of macrophages implicated in angiogenesis, thus, they have been a major focus of angiogenesis research. Tie-1 and Tie-2 are essential for vascular maturation during developmental, physiological and pathological angiogenesis. Angiopoietin 1-4 (Ang-1-4) have been identified as bona fide ligands of the Tie-2 receptor, while Tie-1 remains an orphan receptor which is able to heterodimerize with Tie-2 and to modulate Tie-2 signal transduction. The most exhaustively studied angiopoietins are Ang-1 and Ang-2. Ang-1 is a critical player in vessel maturation and it mediates migration, adhesion and survival of endothelial cells. Ang-2 disrupts the connections between the endothelium and perivascular cells and promotes cell death and vascular regression. Yet, in conjunction with VEGF, Ang-2 promotes neo-vascularization. Hence, angiopoietins exert crucial roles in the angiogenic switch during tumor progression, and increased expression of Ang-2 relative to Ang-1 in tumors correlates with poor prognosis. Its central role in the regulation of physiological and pathological angiogenesis makes the angiopoietin/Tie signaling pathway a therapeutically attractive target for the treatment of vascular disease and cancer.

Molecular control of angiopoietin signalling

The angiopoietins act through the endothelial receptor tyrosine kinase Tie2 to regulate vessel maturation in angiogenesis and control quiescence and stability of established vessels. The activating ligand, Ang1 (angiopoietin-1), is constitutively expressed by perivascular cells, and the ability of endothelial cells to respond to the ligand is controlled at the level of the Ang1 receptor. This receptor interacts with the related protein Tie1 on the cell surface, and Tie1 inhibits Ang1 signalling through Tie2. The responsiveness of endothelium to Ang1 is determined by the relative levels of Tie2 and the inhibitory co-receptor Tie1 in the cells. Tie1 undergoes regulated ectodomain cleavage which is stimulated by a range of factors including VEGF (vascular endothelial growth factor), inflammatory cytokines and changes in shear stress. Ectodomain cleavage of Tie1 relieves inhibition of Tie2 and enhances Ang1 signalling. This mechanism regulates Ang1 signalling without requiring changes in the level of the ligand and allows Ang1 signalling to be co-ordinated with other signals in the cellular environment. Regulation of signalling at the level of receptor responsiveness may be an important adaptation in systems in which an activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.

Msx genes define a population of mural cell precursors required for head blood vessel maturation

Vessels are primarily formed from an inner endothelial layer that is secondarily covered by mural cells, namely vascular smooth muscle cells (VSMCs) in arteries and veins and pericytes in capillaries and veinules. We previously showed that, in the mouse embryo, Msx1(lacZ) and Msx2(lacZ) are expressed in mural cells and in a few endothelial cells. To unravel the role of Msx genes in vascular development, we have inactivated the two Msx genes specifically in mural cells by combining the Msx1(lacZ), Msx2(lox) and Sm22α-Cre alleles. Optical projection tomography demonstrated abnormal branching of the cephalic vessels in E11.5 mutant embryos. The carotid and vertebral arteries showed an increase in caliber that was related to reduced vascular smooth muscle coverage. Taking advantage of a newly constructed Msx1(CreERT2) allele, we demonstrated by lineage tracing that the primary defect lies in a population of VSMC precursors. The abnormal phenotype that ensues is a consequence of impaired BMP signaling in the VSMC precursors that leads to downregulation of the metalloprotease 2 (Mmp2) and Mmp9 genes, which are essential for cell migration and integration into the mural layer. Improper coverage by VSMCs secondarily leads to incomplete maturation of the endothelial layer. Our results demonstrate that both Msx1 and Msx2 are required for the recruitment of a population of neural crest-derived VSMCs.

Pericyte requirement for anti-leak action of angiopoietin-1 and vascular remodeling in sustained inflammation

Blood vessel leakiness is an early, transient event in acute inflammation but can also persist as vessels undergo remodeling in sustained inflammation. Angiopoietin/Tie2 signaling can reduce the leakiness through changes in endothelial cells. The role of pericytes in this action has been unknown. We used the selective PDGF-B-blocking oligonucleotide aptamer AX102 to determine whether disruption of pericyte-endothelial crosstalk alters vascular leakiness or remodeling in the airways of mice under four different conditions: i) baseline, ii) acute inflammation induced by bradykinin, iii) sustained inflammation after 7-day infection by the respiratory pathogen Mycoplasma pulmonis, or iv) leakage after bradykinin challenge in the presence of vascular stabilization by the angiopoietin-1 (Ang1) mimic COMP-Ang1 for 7 days. AX102 reduced pericyte coverage but did not alter the leakage of microspheres from tracheal blood vessels at baseline or after bradykinin; however, AX102 exaggerated leakage at 7 days after M. pulmonis infection and increased vascular remodeling and disease severity at 14 days. AX102 also abolished the antileakage effect of COMP-Ang1 at 7 days. Together, these findings show that pericyte contributions to endothelial stability have greater dependence on PDGF-B during the development of sustained inflammation, when pericyte dynamics accompany vascular remodeling, than under baseline conditions or in acute inflammation. The findings also show that the antileakage action of Ang1 requires PDGF-dependent actions of pericytes in maintaining endothelial stability.

Paracrine modulation of cholangiocyte serotonin synthesis orchestrates biliary remodeling in adults

Paracrine signaling between cholangiocytes and stromal cells regulates biliary remodeling. Cholangiocytes have neuroepithelial characteristics and serotonin receptor agonists inhibit their growth, but whether they are capable of serotonin biosynthesis is unknown. We hypothesized that cholangiocytes synthesize serotonin and that cross talk between liver myofibroblasts (MF) and cholangiocytes regulates this process to influence biliary remodeling. Transwell cultures of cholangiocytes ± MF, and tryptophan hydroxylase-2 knockin (TPH2KI) mice with an inactivating mutation of the neuronal tryptophan hydroxylase (TPH) isoform, TPH2, were evaluated. Results in the cell culture models confirm that cholangiocytes have serotonin receptors and demonstrate for the first time that these cells express TPH2 and produce serotonin, which autoinhibits their growth but stimulates MF production of TGF-β(1). Increased TGF-β(1), in turn, counteracts autocrine inhibition of cholangiocyte growth by repressing cholangiocyte TPH2 expression. Studies of TPH2KI mice confirm that TPH2-mediated production of serotonin plays an important role in remodeling damaged bile ducts because mice with decreased TPH2 function have reduced biliary serotonin levels and exhibit excessive cholangiocyte proliferation, accumulation of aberrant ductules and liver progenitors, and increased liver fibrosis after bile duct ligation. This new evidence that cholangiocytes express the so-called neuronal isoform of TPH, synthesize serotonin de novo, and deploy serotonin as an autocrine/paracrine signal to regulate regeneration of the biliary tree complements earlier work that revealed that passive release of serotonin from platelets stimulates hepatocyte proliferation. Given the prevalent use of serotonin-modulating drugs, these findings have potentially important implications for recovery from various types of liver damage.

Sp1-dependent activation of HDAC7 is required for platelet-derived growth factor-BB-induced smooth muscle cell differentiation from stem cells

We have previously demonstrated that histone deacetylase 7 (HDAC7) expression and splicing play an important role in smooth muscle cell (SMC) differentiation from embryonic stem (ES) cells, but the molecular mechanisms of increased HDAC7 expression during SMC differentiation are currently unknown. In this study, we found that platelet-derived growth factor-BB (PDGF-BB) induced a 3-fold increase in the transcripts of HDAC7 in differentiating ES cells. Importantly, our data also revealed that PDGF-BB regulated HDAC7 expression not through phosphorylation of HDAC7 but through transcriptional activation. By dissecting its promoters with progressive deletion analysis, we identified the sequence between -343 and -292 bp in the 5'-flanking region of the Hdac7 gene promoter as the minimal PDGF-BB-responsive element, which contains one binding site for the transcription factor, specificity protein 1 (Sp1). Mutation of the Sp1 site within this PDGF-BB-responsive element abolished PDGF-BB-induced HDAC7 activity. PDGF-BB treatment enhanced Sp1 binding to the Hdac7 promoter in differentiated SMCs in vivo as demonstrated by the chromatin immunoprecipitation assay. Moreover, we also demonstrated that knockdown of Sp1 abrogated PDGF-BB-induced HDAC7 up-regulation and SMC differentiation gene expression in differentiating ES cells, although enforced expression of Sp1 alone was sufficient to increase the activity of the Hdac7 promoter and expression levels of SMC differentiation genes. Importantly, we further demonstrated that HDAC7 was required for Sp1-induced SMC differentiation of gene expression. Our data suggest that Sp1 plays an important role in the regulation of Hdac7 gene expression in SMC differentiation from ES cells. These findings provide novel molecular insights into the regulation of HDAC7 and enhance our knowledge in SMC differentiation and vessel formation during embryonic development.

Angiopoietins, abdominal aortic aneurysm and atherosclerosis

Abdominal aortic aneurysm (AAA) and atherosclerosis are common causes of mortality and morbidity in an aging population. Angiogenesis is believed to contribute to the development and progression of these diseases. Angiopoietins (angpts) are known to be important regulators of angiogenesis. Angpts can also influence inflammation and have been shown to possess both pro-atherosclerotic and atheroprotective effects. This review explores the potential roles that the angpts play in the development and progression of AAA and atherosclerosis.

The expression of angiopoietin-1 and -2 in the endometrium of women with abnormal bleeding induced by an intra-uterine device

This study identified differences in expression of angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) in the endometrium of 33 women with abnormal bleeding induced by an intra-uterine device (IUD; 23 proliferative phase, 10 secretory phase) compared with 28 control samples from normal endometria in women without an IUD fitted (12 proliferative phase, 16 secretory phase). Expression of Ang-1, Ang-2 and endothelial cell-specific tyrosine kinase receptor-2 (Tie-2) mRNA was detected by reverse transcription-polymerase chain reaction (RT-PCR), and Ang-1 and Ang-2 protein levels were detected by immunohistochemistry. The RT-PCR results showed significantly decreased Ang-1 expression in the endometrium from IUD patients during both phases compared with the control women. Expression of Tie-2 mRNA and the Ang-1:Ang-2 mRNA ratio were also significantly decreased in endometria from IUD patients in the secretory phase compared with the control women. Immunohistochemical analysis showed elevated Ang-2 protein levels in secretory phase endometrium from IUD patients compared with the control women. These results suggest that the angiopoietin/Tie-2 system promotes vascular remodelling in the endometrium and that changes in the expression of Ang-1, Ang-2 and Tie-2 may contribute to abnormal uterine bleeding in some IUD users.

Expression and release of angiopoietin-1 from human neutrophils: intracellular mechanisms

We recently demonstrated that Tie2 receptor activation on human neutrophils by both angiopoietins (Ang1 and Ang2) promoted platelet-activating factor synthesis, beta(2)-integrin activation, and cell migration. Herein, we wanted to assess if human neutrophils express angiopoietins and further delineate their mechanisms of release. Employing Reverse transcriptase-polymerase chain reaction, Real time quantitative transcriptase-polymerase chain reaction, FACScan analysis and ELISA approaches, we observed that neutrophils express Ang1 but not Ang2. For each condition, vascular endothelial growth factor (VEGF) detection was performed as positive control. Using nitrogen cavitation, we observed that Ang1 is localized in the cytosolic fraction whereas VEGF is found in beta-granules. Treatment of neutrophils with phorbol myristate acetate (PMA), N-Formyl-Met-Leu-Phe (fMLP) and tumor necrosis factor-alpha (TNF-alpha) induced VEGF release. Maximal effect was observed with PMA (80 nM) stimulation inducing a complete release of VEGF content (565 +/- 100 pg/ml; 6 x 10(6) neutrophils), corresponding to a 18.9-fold increase as compared to phosphate buffer saline (PBS) treated neutrophils. By contrast, only a treatment with PMA (80 nM) induced Ang1 release. PMA treatment induced also a complete release of Ang1 (661 +/- 148 pg/ml; 6 x 10(6) neutrophils), corresponding to 2.8-fold increase as compared to PBS-treated neutrophils. In both cases, PMA-mediated release of VEGF and Ang1 was nearly maximal by 15 min. Finally, we observed that the induction of Ang1 release was calcium-independent whereas VEGF release was not. These data demonstrate the capacity of human neutrophils to synthesize Ang1, which is stored and released differently as compared to VEGF. These data suggest a different cascade of events regarding the distribution of selected growth factors during inflammation and angiogenesis.

PLATELET-DERIVED GROWTH FACTOR, TRANSFORMING GROWTH FACTOR-β, AND CONNECTIVE TISSUE GROWTH FACTOR IN A PORCINE BRONCHIAL MODEL OF OBLITERATIVE BRONCHIOLITIS

The expression of platelet-derived growth factor (PDGF), transforming growth factor (TGF)-beta, and connective tissue growth factor (CTGF) and the effect of imatinib, an agent inhibiting PDGF receptors, were assessed in a porcine bronchial transplantation model of obliterative bronchiolitis (OB). Up-regulation of PDGF-A, PDGF receptors alpha and beta, and TGF-beta expression occurred in allografts, whereas PDGF-B and CTGF expression was similar in allo- and autografts. Imatinib modified the inflammatory responses and expression patterns of PDGF-A and PDGF receptors. This study further confirms PDGF and TGF-beta as mediators of OB and supports the concept of the importance of the pathways signaled through PDGF receptors in post-transplant OB.

Platelet-derived growth factor and transforming growth factor-beta modulate the expression of matrix metalloproteinases and migratory function of human airway smooth muscle cells

BACKGROUND

Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) have been suggested to be involved in the pathogenesis of asthma. Their expression in airway smooth muscle (ASM) cells could be involved in collagen turnover and migration of these cells and thus may contribute to airway remodelling.

OBJECTIVE

To examine the effect of pro-fibrotic growth factors TGF-beta and platelet-derived growth factor (PDGF) on the expression of MMPs/TIMPs in cultured human ASM cells and to examine the role of MMP in the migration of ASM cells.

METHODS

ASM cells were stimulated with TGF-beta and/or PDGF. Expression and activity of MMP-1, MMP-2, MMP-3, TIMP-1 and TIMP-2 were evaluated by quantitative RT-PCR, Western blot and zymography. Modified Boyden-chamber migration assay was performed to investigate the effect of secreted MMP-3 and TIMP-1 on ASM-cell migration.

RESULTS

PDGF strongly up-regulated the expression of MMP-1 at mRNA and protein levels. PDGF, when combined with TGF-beta, caused synergistic up-regulation of MMP-3. TIMP-1 was additively up-regulated by TGF-beta and PDGF. These growth factors had no effect on the expression of MMP-2 and TIMP-2. U0126, an extracellular signal-regulated kinase (ERK) pathway inhibitor, inhibited the up-regulation of MMP-1 by PDGF. The synergistic/additive up-regulation of MMP-3 and TIMP-1 was inhibited by U0126 and SB431542, a Smad pathway inhibitor. Supernatant from ASM cells in which MMP-3 production was knocked down by RNA interference showed a decreased migratory effect on ASM cells, whereas supernatant from cells with suppressed TIMP-1 expression resulted in increased migration.

CONCLUSION

Our results suggest that PDGF with/without TGF-beta could facilitate migration of ASM cells by modification of MMP-TIMP balance through the ERK pathway.

The role of the Angiopoietins in vascular morphogenesis

The Angiopoietin/Tie system acts as a vascular specific ligand/receptor system to control endothelial cell survival and vascular maturation. The Angiopoietin family includes four ligands (Angiopoietin-1, Angiopoietin-2 and Angiopoietin-3/4) and two corresponding tyrosine kinase receptors (Tie1 and Tie2). Ang-1 and Ang-2 are specific ligands of Tie2 binding the receptor with similar affinity. Tie2 activation promotes vessel assembly and maturation by mediating survival signals for endothelial cells and regulating the recruitment of mural cells. Ang-1 acts in a paracrine agonistic manner inducing Tie2 phosphorylation and subsequent vessel stabilization. In contrast, Ang-2 is produced by endothelial cells and acts as an autocrine antagonist of Ang-1-mediated Tie2 activation. Ang-2 thereby primes the vascular endothelium to exogenous cytokines and induces vascular destabilization at higher concentrations. Ang-2 is strongly expressed in the vasculature of many tumors and it has been suggested that Ang-2 may act synergistically with other cytokines such as vascular endothelial growth factor to promote tumor-associated angiogenesis and tumor progression. The better mechanistic understanding of the Ang/Tie system is gradually paving the way toward the rationale exploitation of this vascular signaling system as a therapeutic target for neoplastic and non-neoplastic diseases.

Splicing of HDAC7 modulates the SRF-myocardin complex during stem-cell differentiation towards smooth muscle cells

Histone deacetylases (HDACs) have a central role in the regulation of gene expression. Here we investigated whether HDAC7 has an impact on embryonic stem (ES) cell differentiation into smooth muscle cells (SMCs). ES cells were seeded on collagen-IV-coated flasks and cultured in the absence of leukemia inhibitory factor in differentiation medium to induce SMC differentiation. Western blots and double-immunofluorescence staining demonstrated that HDAC7 has a parallel expression pattern with SMC marker genes. In ex vivo culture of embryonic cells from SM22-LacZ transgenic mice, overexpression of HDAC7 significantly increased beta-galactosidase-positive cell numbers and enzyme activity, indicating its crucial role in SMC differentiation during embryonic development. We found that HDAC7 undergoes alternative splicing during ES cell differentiation. Platelet-derived growth factor enhanced ES cell differentiation into SMCs through upregulation of HDAC7 splicing. Further experiments revealed that HDAC7 splicing induced SMC differentiation through modulation of the SRF-myocardin complex. These findings suggest that HDAC7 splicing is important for SMC differentiation and vessel formation in embryonic development.

Beta-adrenergic receptor regulation of growth factor protein levels in human choroidal endothelial cells

Remodeling of the choroidal vasculature is a prominent factor in age-related macular degeneration. While many of the growth factors involved in this vascular remodeling are known, their regulation remains much less so. The hypothesis of the present study was that stimulation of human choroidal endothelial cells with the beta-adrenergic receptor agonist isoproterenol would lead to an increase in pigment epithelial derived factor (PEDF) and angiopoietin 1 (Ang1), markers of a stable vasculature. Protein levels of PEDF and Ang1 were significantly increased following stimulation with isoproterenol. However, isoproterenol also significantly increased protein levels of vascular endothelial cell growth factor, which is active during vasculature remodeling. These data suggest that beta-adrenergic receptor agonists are likely upstream of a number of growth factors implicated in ocular disease and have multiple effects on choroidal endothelial cells. Modulation of this signaling in the choroid may offer a new avenue for therapeutics.

Reduction of Calponin h1 expression in human colon cancer blood vessels

AIMS

Calponin h1 (CN) is a differentiation marker of smooth muscle cells that has been reported to be down-regulated in the blood vessels of several human tumors. In this study, we examined CN expression in blood vessels in relation to the clinical and pathological features of colon cancer tissue samples.

METHODS

Fifty-six patients who had undergone colectomy for colon cancer were examined. To assess patients' disease-free survival, those who had metastasis at the time of surgical operation were excluded. Immunohistochemistry was performed by the indirect immunoperoxidase method, using serial sections made from formalin fixed and paraffin embedded tissue blocks.

RESULTS

We found that the expression of vascular CN in the peripheral region of colon cancer tissues was significantly reduced in association with tumor progression, lymphatic invasion, vascular invasion and recurrence. This reduction of CN indicated not only a decrease of pericytes and/or smooth muscle cells in tumor vessels, but also the immaturity of those cells, since CN down-regulation occurred even in alpha-smooth muscle actin-positive cells. The down-regulation of CN in vessels in the peripheral region of tumor tissues was inversely associated with the expression of VEGF (vascular endothelial growth factor), seemingly advantageous to angiogenesis.

CONCLUSION

The down-regulation of CN expression in colon cancer vasculature evaluated by immunohistochemistry may be useful in conjunction with conventional staging procedures to predict more reliable outcome and to select therapeutic treatment.

Angiopoietin-1 protects against airway inflammation and hyperreactivity in asthma

RATIONALE

The angiopoietins (Ang) comprise a family of growth factors mainly known for their role in blood vessel formation and remodeling. The best-studied member, Ang-1, exhibits antiapoptotic and antiinflammatory effects. Although the involvement of Ang-1 in angiogenesis is well recognized, little information exists about its role in respiratory physiology and disease. On the basis of its ability to inhibit vascular permeability, adhesion molecule expression, and cytokine production, we hypothesized that Ang-1 administration might exert a protective role in asthma.

OBJECTIVES

To determine changes in the expression of Ang and to assess the ability of Ang-1 to prevent the histologic, biochemical, and functional changes observed in an animal model of asthma.

METHODS

To test our hypothesis, a model of allergic airway disease that develops after ovalbumin (OVA) sensitization and challenge was used.

MEASUREMENTS AND MAIN RESULTS

Ang-1 expression was reduced at the mRNA and protein levels in lung tissue of mice sensitized and challenged with OVA, leading to reduced Tie2 phosphorylation. Intranasal Ang-1 treatment prevented the OVA-induced eosinophilic lung infiltration, attenuated the increase in IL-5 and IL-13, and reduced eotaxin and vascular cell adhesion molecule 1 expression. These antiinflammatory actions of Ang-1 coincided with higher levels of IkappaB and decreased nuclear factor-kappaB binding activity. More importantly, Ang-1 reversed the OVA-induced increase in tissue resistance and elastance, improving lung function.

CONCLUSIONS

We conclude that Ang-1 levels are decreased in asthma and that administration of Ang-1 might be of therapeutic value because it prevents the increased responsiveness of the airways to constrictors and ameliorates inflammation.

Platelet-derived growth factor BB modulates PCNA protein synthesis partially through the transforming growth factor beta signalling pathway in vascular smooth muscle cells

PDGF-BB (Platelet-derived growth factor BB) and TGF-β1(transforming growth factor β1) are important growth factors in the modulation of vascular smooth muscle cell (VSMC) proliferation and PCNA (proliferating cell nuclear antigen) expression in VSMCs. PCNA expresses at a high level in proliferating cells. The present study aims to assess the effects of PDGF-BB-induced overexpression of TGF-β1 on PCNA in VSMCs. The downstream proteins of the TGF-β signalling system in VSMCs, including TGF-β type I receptor (ALK-5 in VSMCs), Smurf2, Smad2, pSmad2/3, Smad4, and Smad7, were also investigated. Our results revealed that PDGF-BB significantly increased the expressions of TGF-β1 and PCNA, and the increase in PCNA can be partially inhibited by neutralizing anti-TGF-β1 antibody. Furthermore, PDGF-BB increased the expression of ALK-5, Smurf2, pSmad2/3, and Smad4, but lowered the levels of Smad2 and Smad7; these alterations were partially restored by neutralizing anti-TGF-β1 antibody. These findings suggest that PDGF-BB promotes PCNA expression in VSMCs partially through TGF-β1 overexpression, and that the TGF-β signalling system involves the molecular mechanism of PDGF-BB in VSMCs.

Pericytes: gatekeepers in tumour cell metastasis?

Tumour cells use two major routes to spread during metastasis, e.g. lymph vessels and blood vessels within or surrounding the primary tumour. The growth rate of the primary tumour often correlates with the quantity of new blood vessels that form within the tumour. However, qualitative abnormalities of the tumour vasculature profoundly affect the perfusion of the primary tumour and the escape of tumour cells into the circulation. In this paper, we review recent evidence for a novel role of the supporting mural cells in limiting blood-borne metastasis.