Platelet-derived growth factor (PDGF)-C, a PDGF family member with a vascular endothelial growth factor-like structure

Platelet-derived growth factor (PDGF)-C is a novel member of the PDGF family that binds to PDGF alphaalpha and alphabeta receptors. The growth factor domain of PDGF-C (GFD-PDGF-C) was expressed in high yields in Escherichia coli and was purified and refolded from inclusion bodies obtaining a biologically active growth factor with dimeric structure. The GFD-PDGF-C contains 12 cysteine residues, and Ellman assay analysis indicates that it contains three intramonomeric disulfide bonds, which is in accordance with GFD-PDGF-C being a member of the cystine knot superfamily of growth factors. The recombinant GFD-PDGF-C was characterized by CD, fluorescence, NMR, and infrared spectroscopy. Together, our data indicate that GFD-PDGF-C is a highly thermostable protein that contains mostly beta-sheet secondary structure and some (6%) alpha-helix structure. The structural model of PDGF-C, obtained by homology-based molecular modeling using the structural representatives of this family of growth factors, shows that GFD-PDGF-C has a higher structural homology to the vascular endothelial growth factor than to PDGF-B. The modeled structure can give further insights into the function and specificity of this molecule.

Angiopoietins and Tie-2 expression in angiogenesis and proliferation of human hepatocellular carcinoma

Human hepatocellular carcinoma (HCC) is a hypervascular tumor but the mechanisms underlying the process of angiogenesis are not fully understood. Angiopoietins (Ang) have been recently identified as ligands for Tie-2 receptor and are thought to be important factors in vascular maturation and stability during angiogenesis. In this study, we investigated the expression of Ang-1, Ang-2, Tie-2, and vascular endothelial growth factor (VEGF) in surgically resected specimens from 46 patients with HCC to determine their potential role in tumor angiogenesis and its progression. VEGF messenger RNA (mRNA) was significantly up-regulated in HCC compared to normal liver tissue from patients with hepatic metastases. No differences were found between HCC and adjacent liver tissue. Meanwhile, Ang-2 mRNA expression in HCC was significantly increased when compared to adjacent liver tissue. On the other hand, Ang-1 and Tie-2 mRNA expression in HCC was not different from that in adjacent liver tissue. Immunohistochemical staining also showed increased Ang-2 protein in HCC. Furthermore, a high Ang-2/1 mRNA ratio in HCC was closely associated with tumor portal vein invasion, tumor diameter, and the microvessel density level as assessed by CD34 immunostaining. With regard to prognosis, the survival time for patients in the high Ang-2/1 mRNA ratio group was significantly poorer when compared with the low Ang-2/1 mRNA ratio group. In conclusion, an increased expression of Ang-2/1 in the presence of VEGF may play a critical role in promoting tumor angiogenesis and progression in human HCC.

Angiogenic growth factor expression in rat skeletal muscle in response to exercise training

Angiogenesis occurs in skeletal muscle in response to exercise training. To gain insight into the regulation of this process, we evaluated the mRNA expression of factors implicated in angiogenesis over the course of a training program. We studied sedentary control (n = 17) rats and both sedentary (n = 18) and exercise-trained (n = 48) rats with bilateral femoral artery ligation. Training consisted of treadmill exercise (4 times/day, 1-24 days). Basal mRNA expression in sedentary control muscle was inversely related to muscle vascularity. Angiogenesis was histologically evident in trained white gastrocnemius muscle by day 12. Training produced initial three- to sixfold increases in VEGF, VEGF receptors (KDR and Flt), the angiopoietin receptor (Tie-2), and endothelial nitric oxide synthase mRNA, which dissipated before the increase in capillarity, and a substantial (30- to 50-fold) but transient upregulation of monocyte chemoattractant protein 1 mRNA. These results emphasize the importance of early events in regulating angiogenesis. However, we observed a sustained elevation of the angiopoietin 2-to-angiopoietin 1 ratio, suggesting continued vascular destabilization. The response to exercise was (in general) tempered in high-oxidative muscles. These findings place importance on cellular events coupled to the onset of angiogenesis.

Inhibition of rat corneal angiogenesis by a nuclease-resistant RNA aptamer specific for angiopoietin-2

Angiopoietin-2 (Ang2) appears to be a naturally occurring antagonist of the endothelial receptor tyrosine kinase Tie2, an important regulator of vascular stability. Destabilization of the endothelium by Ang2 is believed to potentiate the actions of proangiogenic growth factors. To investigate the specific role of Ang2 in the adult vasculature, we generated a nuclease-resistant RNA aptamer that binds and inhibits Ang2 but not the related Tie2 agonist, angiopoietin-1. Local delivery of this aptamer but not a partially scrambled mutant aptamer inhibited basic fibroblast growth factor-mediated neovascularization in the rat corneal micropocket angiogenesis assay. These in vivo data directly demonstrate that a specific inhibitor of Ang2 can act as an antiangiogenic agent.

[Induction of angiogenesis in ischemic myocardium by adenovirus mediated angiopoietin-1 gene transfer, an experimental study]

OBJECTIVE

To investigate the effect on angiogenesis in ischemic myocardium of adenovirus mediated angiopoietin-1 gene transfer.

METHODS

Ang-1 cDNA was obtained from human spleen by RT-PCR and then cotransfected into 293 host cells together with Adv5-CAG, E1 and E3 substituted adenovirus genome, thus constructing recombinant adenovirus Adv5-CAG/Ang-1. Recombinant adenovirus Adv5-CAG/LacZ containing LacZ gene was constructed too. Thirty six male New Zealand white rabbits were randomly divided into 3 group of 12 rabbits: DMEM group, Ang-1 group, and LacZ group and underwent high-positioned double-ligation of the left anterior descending coronary artery and then myocardial injection of DMEM, Adv5-CAG/Ang-1, or Adv5-CAG/LacZ respectively. Fourteen days after the operation 2 rabbits in each group were killed, the myocardial tissues where injected was given were taken to detect the expression of Ang-1 by RT-PCR. Coronary angiography was conducted 28 days postoperatively upon 5 rabbits in each group to observe the angiogenesis in the ischemic myocardium. Five rabbits in each group were killed at the 14 th and 28 th postoperative days to observe the capillary density by immunohistochemical staining.

RESULTS

The Ang-1 cDNA cloned in the laboratory was 1,515 bp in length containing the signal peptide structure in accordance with the report in literature. Fourteen days after operation, Ang-1 gene was positive in the myocardium of Ang-1 group and negative in the other 2 groups. New vessel formation was obvious at the 28 th postoperative day in the Ang-1 group and not in the other 2 groups. Capillary density increased after operation in all 3 groups, however, more significant in the Ang-1 group, especially 28 days after.

CONCLUSION

Adenovirus-mediated angiopoietin-1 gene effectively promotes the neovascularization in ischemic myocardium of rabbits.

Pseudogenization of the tumor-growth promoter angiogenin in a leaf-eating monkey

Physiological functions of human genes may be studied by gene-knockout experiments in model organisms such as the mouse. This strategy relies on the existence of one-to-one gene orthology between the human and mouse. When lineage-specific gene duplication occurs and paralogous genes share a certain degree of functional redundancy, knockout mice may not provide accurate functional information on human genes. Angiogenin is a small protein that stimulates blood-vessel growth and promotes tumor development. Humans and related primates only have one angiogenin gene, while mice have three paralogous genes. This makes it difficult to generate angiogenin-knockout mice and even more difficult to interpret the genotype-phenotype relation from such animals should they be generated. We here show that in the douc langur (Pygathrix nemaeus), an Asian leaf-eating colobine monkey, the single-copy angiogenin gene has a one-nucleotide deletion in the sixth codon of the mature peptide, generating a premature stop codon. This nucleotide deletion is found in five unrelated individuals sequenced, and therefore is likely to have been fixed in the species. Five colobine species that are closely related to the douc langur have intact angiogenin genes, suggesting that the pseudogenization event was recent and unique to the douc langur lineage. This natural knockout experiment suggests that primate angiogenin is dispensable even in the wild. Further physiological studies of douc langurs may offer additional information on the role of this cancer-related gene in normal physiology of primates, including humans. Our findings also provide a strong case for the importance of evolutionary analysis in biomedical studies of gene functions.

Evidence for hypoxia-induced neuronal-to-chromaffin metaplasia in neuroblastoma

We present evidence that in neuroblastoma, a pediatric malignancy of embryonal sympathetic origin, hypoxia, underlies a phenotypic switch from a primitive neuronal to a chromaffin cell type. This conclusion is based on morphological and molecular data on 116 clinical tumors and is supported by data on the phenotypic effects of hypoxia on neuroblastoma cell lines when studied in monolayer culture and as tumor xenografts. In the clinical material, extensive chromaffin features were seen in regions of chronic tumor hypoxia. This was the exclusive form of intra-tumoral maturation of stroma-poor tumors and was also seen in stroma-rich tumors, either exclusively or in combination with ganglion-like cells. In neuroblastoma cell lines, hypoxia induced changes in gene expression associated with the chromaffin features observed in vivo. We therefore propose tumor hypoxia as a major cue determining phenotype in sympathetic tumors of neuroblastic origin. Because it appears to be reversible upon reoxygenation in monolayer culture, we suggest the term metaplasia for the phenomenon.

Mast cell-mediated stimulation of angiogenesis: cooperative interaction between A2B and A3 adenosine receptors

Adenosine is released during tissue injury, ischemia and tumor growth, and promotes angiogenesis. Because mast cells accumulate in the proximity of new blood vessel development, we examined if they may contribute to adenosine-induced angiogenesis. We found that HMC-1 human mast cells express A2A, A2B, and A3 adenosine receptors. The adenosine agonist NECA (100 micromol/L) increased interleukin-8 (IL-8), vascular endothelial growth factor (VEGF), and angiopoietin-2 mRNA expression. NECA-induced secretion of IL-8 and VEGF was verified by ELISA. A2B receptors mediate VEGF and IL-8 secretion because neither CGS21680 (selective A2A agonist) nor IB-MECA (selective A3 agonist) produced this effect, and it was inhibited by the selective A2B antagonist IPDX but not by the selective A2A antagonist SCH58261 or the selective A3 antagonist MRS1191. In contrast, the selective A3 agonist IB-MECA (EC50 1 nmol/L) stimulated angiopoietin-2 expression. Conditioned media from NECA-activated HMC-1 stimulated human umbilical vein endothelial cell proliferation and migration, and induced capillary tube formation. Capillary formation induced by mast cell-conditioned media was maximal if both HMC-1 A2B and A3 receptors were activated, whereas activation of A2B receptor alone was less effective. Thus, adenosine A2B and A3 receptors act in a functional cooperative fashion to promote angiogenesis by a paracrine mechanism involving the differential expression and secretion of angiogenic factors from human mast cells.

Angiopoietin-1 protects against the development of cardiac allograft arteriosclerosis

BACKGROUND

Angiopoietin (Ang)-1 is an angiogenic growth factor that counteracts the permeability and proinflammatory effects of vascular endothelial growth factor and other proinflammatory cytokines. Recently, we demonstrated that vascular endothelial growth factor enhances cardiac allograft arteriosclerosis. Here, we studied the roles of Ang1, its natural antagonist Ang2, and their receptor Tie2 in rat cardiac allograft arteriosclerosis.

METHODS AND RESULTS

Heterotopic cardiac allografts and syngrafts were transplanted from Dark Agouti (DA) to Wistar-Furth rats and from DA to DA rats, respectively. Immunohistochemistry disclosed that only a few mesenchymal cells expressed Ang1 in normal hearts and syngrafts, whereas no immunoreactivity was found in cardiac allografts undergoing chronic rejection. Ang2 and Tie2 immunoreactivity was induced mainly in capillaries and postcapillary venules in chronic allografts when compared with syngeneic controls, but no immunoreactivity was found in arterial endothelium. Intracoronary perfusion of cardiac allografts with a clinical-grade adenoviral vector encoding human Ang1 (Ad.Ang1) protected against the development of allograft arteriosclerosis. Ad.Ang1 perfusion reduced Ang2 expression in microcirculation, the numbers of graft-infiltrating leukocytes, and the level of immunoactivation and interstitial fibrosis, as well as both the incidence and intensity of intimal lesions. Ad.Ang1 perfusion also increased CD34+ stem cell counts in peripheral blood.

CONCLUSIONS

Our findings suggest that the antiinflammatory properties of Ang1 may offer an entirely new therapeutic approach to prevent cardiac allograft arteriosclerosis.

Effects of five commonly used glucocorticoids on haemangioma in vitro

1. High-dose systemic or intralesional steroids are the first-line pharmacological treatments for haemangioma. However, the mechanism of action of steroids is unknown. Using the in vitro model developed by us, the present study examined some of the effects of five commonly used glucocorticoids on haemangioma biopsies taken from two patients. 2. At 12 micro mol/L, triamcinolone and dexamethasone consistently exhibited capillary growth inhibition, whereas methylprednisolone displayed an inhibitory effect during the first 7 days of culture. At this concentration, inhibition of capillary growth was observed in betamethasone-treated cultures derived from one patient but not in those derived from the other. However, hydrocortisone had a negligible effect on capillary growth. 3. Transcription of various factors considered important for haemangioma development were studied by reverse transcription-polymerase chain reaction. Neither vascular endothelial growth factor nor fibroblast growth factor-2 played a vital role in steroid-induced inhibition of capillary growth. All glucocorticoids induced a marked decrease of interleukin (IL)-6 transcripts. 4. Capillary growth inhibition in cultures treated with all glucocorticoids, except triamcinolone, was associated with an increased transcription of clusterin/apolipoprotein J (clust/apoJ), an apoptotic gene. There was increased transcription of mitochondrial cytochrome (cyt) b in the inhibited cultures resulting from triamcinolone, dexamethasone or methylprednisolone treatment that was associated with capillary growth inhibition, suggesting an important role of mitochondria in glucocorticoid-induced regression of haemangioma. 5. Our results indicate that glucocorticoids may modulate haemangiogenesis via an upregulation of cyt b, clust/apoJ and/or IL-6. The variable effects of different glucocorticoids on one or more of these factors may explain the interindividual variation in the in vivo response of haemangioma to the steroids.

Expression of genes regulating angiogenesis in human circulating hematopoietic cord blood CD34+/CD133+ cells

OBJECTIVES

Human CD34+ cells represent a heterogeneous population of immature cells which may differentiate to various cell types. The aim of the study was to determine angiogenesis regulating genes expression in CD34+ cells, their subpopulations, and during their differentiation induced by hematopoietic growth factors.

MATERIAL AND METHODS

We have measured the expression of angiogenesis regulating genes angiopoietin-1 (Ang-1), angiopoietin-1 (Ang-2) and their receptor Tie-2, vascular endothelial growth factor (VEGF) and its receptors VEGFR-1 and VEGFR-2 in sorted population of CD34+ and CD34+/CD133+ cells from human cord blood and bone marrow, and in their differentiating progeny, using real time reverse transcriptase polymerase chain reaction. The hematopoietic differentiation of CD34+ cells was induced in semisolid or liquid differentiation supporting media containing appropriate hematopoietic growth factors.

RESULTS

A higher expression of Ang-1, Ang-2, and Tie-2 mRNAs was detected in CD34+/CD133+ cord blood cells as compared with CD34-/CD133- fraction, but no expression of these genes was detected in burst-forming unit erythroid (BFU-E) nor colony-forming unit granulocyte macrophage (CFU-GM) colonies. The level of Ang-1 and Tie-2 mRNAs, but not that of Ang-2 mRNA gradually decreased during a 14-d incubation of cord blood CD34+ cells in a liquid culture. A significantly higher expression of VEGF mRNA was in BFU-E as compared with CFU-GM cell colonies and CD34+/CD133+ cells. VEGFR-1 mRNA was equally expressed in CD34+/CD133+ and CD34-/CD133- cells as well as in BFU-E and CFU-GM colonies. Expression of VEGFR-2 mRNA was detected at the borderline of method sensitivity only in CD34+/CD133+ cells.

CONCLUSION

CD34+/CD133+ cord blood cells express Ang-1, Ang-2 and VEGF as well as their receptor mRNAs, suggesting a role of these cells in regulation both angiopoiesis and hematopoiesis.

Glomerular-specific alterations of VEGF-A expression lead to distinct congenital and acquired renal diseases

Kidney disease affects over 20 million people in the United States alone. Although the causes of renal failure are diverse, the glomerular filtration barrier is often the target of injury. Dysregulation of VEGF expression within the glomerulus has been demonstrated in a wide range of primary and acquired renal diseases, although the significance of these changes is unknown. In the glomerulus, VEGF-A is highly expressed in podocytes that make up a major portion of the barrier between the blood and urinary spaces. In this paper, we show that glomerular-selective deletion or overexpression of VEGF-A leads to glomerular disease in mice. Podocyte-specific heterozygosity for VEGF-A resulted in renal disease by 2.5 weeks of age, characterized by proteinuria and endotheliosis, the renal lesion seen in preeclampsia. Homozygous deletion of VEGF-A in glomeruli resulted in perinatal lethality. Mutant kidneys failed to develop a filtration barrier due to defects in endothelial cell migration, differentiation, and survival. In contrast, podocyte-specific overexpression of the VEGF-164 isoform led to a striking collapsing glomerulopathy, the lesion seen in HIV-associated nephropathy. Our data demonstrate that tight regulation of VEGF-A signaling is critical for establishment and maintenance of the glomerular filtration barrier and strongly supports a pivotal role for VEGF-A in renal disease.

A quantitative gene expression study suggests a role for angiopoietins in focal nodular hyperplasia

BACKGROUND AND AIMS

Although the pathogenesis of focal nodular hyperplasia (FNH) of the liver remains unclear, a vascular mechanism has been suspected. To gain insight into the pathogenesis of FNH, we performed a large-scale quantitative study of gene expression in FNH.

METHODS

Quantitative expression level of 209 selected genes was assessed using real-time reverse-transcription polymerase chain reaction in 14 cases of FNH and compared with their expression level in 13 cases of liver cirrhosis, 4 adenomas, and 15 hepatocellular carcinomas.

RESULTS

Among the 7 genes, the expression of which was significantly up-regulated or down-regulated in FNH, the most informative markers for the diagnosis of FNH as assessed using the receiving operative curve and area under the curve (AUC) were angiopoietin-1 (Ang-1; AUC, 0.82) and angiopoietin-2 (Ang-2; AUC, 0.80). These 2 genes are involved in the regulation of vasculogenesis. In FNH, Ang-1 was significantly up-regulated, Ang-2 was down-regulated, and the Ang-1/Ang-2 ratio was highly and specifically increased in FNH compared with normal liver or other groups of lesions (FNH, 15.2-fold increase; HCC, 2.78; adenoma, 2.28; cirrhosis, 1.92; P < 0.01 for FNH vs. all groups, analysis of variance). Tie-2 messenger RNA, the receptor of Ang-1 and Ang-2, was detected at the same level in FNH as in normal liver. Ang-1 protein was detected on Western blot of FNH and expressed by endothelial cells of dystrophic vessels and sinusoids as shown by immunohistochemistry.

CONCLUSIONS

A specific increase of Ang-1/Ang-2 ratio in FNH, in the presence of the functional Tie-2 receptor, might be involved in the formation of hyperplastic and dystrophic vessels of FNH.

Aldose reductase inhibitor fidarestat prevents retinal oxidative stress and vascular endothelial growth factor overexpression in streptozotocin-diabetic rats

The study addressed the role for aldose reductase (AR) in 1) retinal oxidative stress and vascular endothelial growth factor (VEGF) overexpression in early diabetes, and 2) high glucose-induced oxidative stress in retinal endothelial cells. In vivo experiments were performed on control rats and diabetic rats treated with or without low or high dose of the AR inhibitor (ARI) fidarestat (2 or 16 mg. kg(-1). day(-1)). In vitro studies were performed on bovine retinal endothelial cells (BREC) cultured in either 5 or 30 mmol/l glucose with or without 1 micro mol/l fidarestat. Intracellular reactive oxygen species were assessed using the 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (H(2)DCFDA) probe and flow cytometry. Both low and high doses of fidarestat (i.e., the doses that partially and completely inhibited sorbitol pathway hyperactivity) arrested diabetes-induced retinal lipid peroxidation. This was achieved due to upregulation of the key antioxidative defense enzyme activities rather than changes in reduced glutathione, oxidized glutathione, ascorbate and dehydroascorbate concentrations, and the glutathione and ascorbate redox states. Diabetes-associated 2.1-fold VEGF protein overexpression (enzyme-linked immunosorbent assay; ELISA) was dose-dependently prevented by fidarestat, whereas total VEGF mRNA and VEGF-164 mRNA (RT-PCR) abundance were not affected by either diabetes or the ARI. In BREC, fidarestat corrected hyperglycemia-induced increase in H(2)DCFDA fluorescence but not oxidative stress caused by three different pro-oxidants in normoglycemic conditions. In conclusion, increased AR activity contributes to retinal oxidative stress and VEGF protein overexpression in early diabetes. The findings justify the rationale for evaluation of fidarestat on diabetic retinopathy.

Elevated glucose inhibits VEGF-A-mediated endocardial cushion formation: modulation by PECAM-1 and MMP-2

Atrioventricular (AV) septal defects resulting from aberrant endocardial cushion (EC) formation are observed at increased rates in infants of diabetic mothers. EC formation occurs via an epithelial-mesenchymal transformation (EMT), involving transformation of endocardial cells into mesenchymal cells, migration, and invasion into extracellular matrix. Here, we report that elevated glucose inhibits EMT by reducing myocardial vascular endothelial growth factor A (VEGF-A). This effect is reversed with exogenous recombinant mouse VEGF-A165, whereas addition of soluble VEGF receptor-1 blocks EMT. We show that disruption of EMT is associated with persistence of platelet endothelial cell adhesion molecule-1 (PECAM-1) and decreased matrix metalloproteinase-2 (MMP-2) expression. These findings correlate with retention of a nontransformed endocardial sheet and lack of invasion. The MMP inhibitor GM6001 blocks invasion, whereas explants from PECAM-1 deficient mice exhibit MMP-2 induction and normal EMT in high glucose. PECAM-1-negative endothelial cells are highly motile and express more MMP-2 than do PECAM-1-positive endothelial cells. During EMT, loss of PECAM-1 similarly promotes single cell motility and MMP-2 expression. Our findings suggest that high glucose-induced inhibition of AV cushion morphogenesis results from decreased myocardial VEGF-A expression and is, in part, mediated by persistent endocardial cell PECAM-1 expression and failure to up-regulate MMP-2 expression.

Inhibition of breast carcinoma and trophoblast cell invasiveness by vascular endothelial growth factor

Vascular endothelial growth factor (VEGF) is a potent endothelial cell mitogen and angiogenic growth factor that enhances endothelial cell invasion through the extracellular matrix (ECM). While various cell types express VEGF receptors, little is known about the biological actions of VEGF on nonendothelial cells. Therefore, the main objective of the present study was to determine the effect of VEGF on the in vitro invasiveness and proliferation of human MDA-MB-231 breast carcinoma cells and human HTR-8/SVneo trophoblast cells. Reverse-transcriptase polymerase chain reaction analysis demonstrated the presence of transcripts encoding VEGF receptors (VEGFR) -1, -2, and -3 as well as neuropilins-1 and -2 in the trophoblast cells, and the presence of transcripts encoding VEGFR-2 and neuropilins-1 and -2 in the breast carcinoma cells. Both cell lines also expressed transcripts for VEGF-A, -B, -C and -D, as well as for placenta growth factor (PlGF). Although incubation with exogenous VEGF-A(165) or VEGF-A(121) did not affect the rate of proliferation of either the trophoblast or the breast carcinoma cells, incubation with these molecules reduced their ability to invade through reconstituted ECM (Matrigel). The effect of VEGF-A(165) on the invasiveness of both cell lines was inhibited by the inclusion of a neutralizing antibody to VEGF. Exogenous VEGF-A(165) also decreased the cell surface expression of the urokinase-type plasminogen activator (a molecule required for invasion) by the breast carcinoma and trophoblast cells. These results indicate that the biological actions of VEGF on certain cell types may differ from the effects of this molecule on vascular endothelial cells, and therefore are relevant to angiogenesis-based therapies.

Signaling molecules in nonfamilial pulmonary hypertension

BACKGROUND

Biochemical, genetic, and clinical evidence indicates that smooth-muscle proliferation around small pulmonary vessels is an essential part of the pathogenesis of pulmonary hypertension. Mutations in the bone morphogenetic protein receptor type 2 (BMPR2) have been linked to familial cases of pulmonary hypertension, but the molecular basis of the common nonfamilial forms is unknown.

METHODS

We evaluated the pattern of expression of angiopoietin-1, a protein involved in the recruitment of smooth-muscle cells around blood vessels; TIE2, the endothelial-specific receptor for angiopoietin-1; and bone morphogenetic protein receptor type 1A (BMPR1A) and BMPR2 in lung-biopsy specimens from patients with pulmonary hypertension and from normotensive control patients. The effect of angiopoietin-1 on the modulation of BMPR expression was also evaluated in subcultures of human pulmonary arteriolar endothelial cells.

RESULTS

The expression of angiopoietin-1 messenger RNA and the protein itself and the phosphorylation of TIE2 were strongly up-regulated in the lungs of patients with various forms of pulmonary hypertension, correlating directly with the severity of disease. A mechanistic link between familial and acquired pulmonary hypertension was demonstrated by the finding that angiopoietin-1 shuts off the expression of BMPR1A, a transmembrane protein required for BMPR2 signaling, in pulmonary arteriolar endothelial cells. Similarly, we found that the expression of BMPR1A was severely reduced in the lungs of patients with various forms of acquired as well as primary nonfamilial pulmonary hypertension.

CONCLUSIONS

These findings suggest that all forms of pulmonary hypertension are linked by defects in the signaling pathway involving angiopoietin-1, TIE2, BMPR1A, and BMPR2 and consequently identify specific molecular targets for therapeutic intervention.

Angiopoietins, growth factors, and vascular morphology in early arthritis

OBJECTIVE

To examine angiogenic growth factors in patients with early, untreated inflammatory arthritides and controls.

METHODS

Synovial membrane (SM) infiltrate and Ang1, Ang2, and vascular endothelial growth factor (VEGF) mRNA and protein expression were examined using immunohistochemistry and in situ hybridization. Synovial fluid (SF) VEGF, transforming growth factor-beta (TGF-beta 1), and tumor necrosis factor-alpha (TNF-alpha) protein were measured by ELISA. Vascular morphology was assessed at arthroscopy.

RESULTS

Ang2 mRNA and protein expression was observed in early psoriatic arthritis (PsA) and rheumatoid arthritis (RA) SM. Expression of Ang2 and VEGF was significantly greater in early PsA SM and correlated strongly. SF VEGF and TGF-beta 1 concentrations were also significantly higher in early PsA compared to RA. Distinct vascular morphology, with tortuous vessels in PsA, correlated with microscopic vascular scores (r = 0.54, p = 0.005) and VEGF levels (r = 0.51, p = 0.01). Ang1 mRNA and protein expression was observed, but concentrations were markedly lower than for Ang2 and VEGF. Clinical disease activity, SM infiltration, and SF TNF-alpha concentrations were similar in both groups.

CONCLUSION

This is the first report of angiopoietin expression in early inflammatory arthritis. There is a close relationship between angiopoietins, VEGF, TGF-beta, and vascular morphology. There is differential angiogenesis at an early stage of inflammation, with major pathogenic and therapeutic implications.

Proteinuria and vascular changes after renal irradiation: the role of reactive oxygen species (ROS) and vascular endothelial growth factor (Vegf)

Proteinuria occurs in all degrees of radiation nephropathy and can be present without other symptoms. In this study, radiation-induced proteinuria in C3H mice demonstrated a clear dose-response relationship and was apparent before the onset of significant structural vascular changes and decreases in renal function. This suggests that proteinuria is not a secondary event due to loss of the vascular structure. In an attempt to ameliorate radiation-induced proteinuria and progressive renal failure, two factors were studied. The influence of reactive oxygen species (ROS), which are generated by infiltrating neutrophils and mediate proteinuria in models of acute glomerular injury, was the first to be investigated. Short-term administration of the reactive oxygen scavengers superoxide dismutase (SOD) and catalase did not reverse an established radiation-induced proteinuria. Continuous administration of the antioxidant N-acetylcysteine (NAC) also failed to inhibit this proteinuria. However, since no direct assessment of the impact of these interventions on renal redox status was made, the putative role of ROS in radiation-induced proteinuria and nephropathy remains undefined. The second factor studied was vascular endothelial growth factor (Vegf), which is suggested to be involved in glomerular vessel permeability and the development of proteinuria in some models of renal disease. Northern blot analysis of mRNA from whole kidneys did not demonstrate any increased expression of Vegf after irradiation. There was also no change in the ratio of the different Vegf isoforms (PCR analysis), either in the whole kidney or in isolated glomeruli. No significant role for Vegf was identified for radiation-induced vascular changes or proteinuria, although post-transcriptional changes cannot be excluded.

Detection of gene expression of vascular endothelial growth factor and flk-1 in the renal glomeruli of the normal rat kidney using the laser microdissection system

The recent development of the laser microdissection (LMD) technique enables one to target particular tissues or cells for gene or protein analyses. The purpose of this study was to detect local mRNA expression of vascular endothelial growth factor (VEGF) and its receptor, flk-1, in the glomeruli of normal rat kidneys using the LMD system. Frozen sections of the kidney of 8-week-old male Wistar rats were made. The glomeruli were dissected from the frozen sections with the LMD system, and total RNA was extracted from 200 glomeruli in each kidney. Reverse-transcription polymerase chain reaction (RT-PCR) revealed the local mRNA expression of three isoforms of VEGF, flk-1 and GAPDH in the glomeruli. Moreover, the real-time PCR was performed to evaluate the experimental condition for quantification of VEGF and flk-1 mRNA expression using this system, and the results showed that at least 10 glomeruli might be needed for quantifying local VEGF mRNA expression. However, cDNA from 200 glomeruli was not enough for quantitative evaluation of flk-1 mRNA with this system. These results demonstrate the reproducibility of the analysis of mRNA expression in the renal glomeruli using the LMD system and also suggest that the application of the LMD technique will provide information to further our understanding of the mechanisms involved in kidney diseases.

Angiopoietin-1 is expressed in the synovium of patients with rheumatoid arthritis and is induced by tumour necrosis factor alpha

OBJECTIVES

To examine the potential role of the angiogenic growth factor angiopoietin-1 (Ang-1) in inflammatory arthritis.

METHODS

Eighteen synovial tissue samples were obtained from 17 patients with a clinical diagnosis of rheumatoid arthritis (RA) and compared with six synovial tissue samples from six patients with osteoarthritis (OA). Ang-1 expression in synovial tissues was determined by immunohistochemistry and in situ hybridisation. Ang-1 mRNA and protein expression were also examined by northern blot analysis and enzyme linked immunosorbent assay (ELISA) in cultured synovial fibroblasts and human umbilical vein endothelial cells (HUVECs) before and after treatment with tumour necrosis factor (TNF)alpha.

RESULTS

Ang-1 protein expression was detected by immunohistochemistry in 16/18 RA synovial tissue samples. Ang-1 protein was frequently observed in the synovial lining layer and in cells within the sublining synovial tissue, in both perivascular areas and in areas remote from vessels. In contrast, Ang-1 was only weakly detected in these sites in OA samples. Ang-1 mRNA and protein were also expressed in cultured synovial fibroblasts derived from patients with RA. In addition, induction of Ang-1 mRNA and protein was observed by northern blot analysis and ELISA after stimulation of RA synovial fibroblasts, but not HUVECs, with the proinflammatory cytokine TNF alpha.

CONCLUSIONS

Ang-1 mRNA and protein are expressed in the synovium of patients with RA, and are up regulated in synovial fibroblasts by TNF alpha. Ang-1 may therefore be an important regulator of angiogenesis in inflammatory arthritis.

17alpha-estradiol-induced VEGF-A expression in rat pituitary tumor cells is mediated through ER independent but PI3K-Akt dependent signaling pathway

17alpha-E(2), a weak estrogen exhibited both agonistic and antagonistic effects, and caused a time- and dose-dependent induction of VEGF-A mRNA expression in GH3 rat pituitary tumor cells. This effect was unaffected by the presence of the pure estrogen receptor antagonist ICI 182,780 but was specifically blocked by a protein synthesis inhibitor puromycin. Inhibition of phosphatidylinositol-3 kinase (PI3K) activity by wortmannin decreased the effect of 17alpha-E(2) on VEGF-A mRNA expression. This inhibitor also blocked the increase in phosphorylation of Akt induced by exposure to 17alpha-E(2). In contrast, exposure to the MAP kinase inhibitor, U0126, had no impact on 17alpha-E(2)-induced VEGF-A mRNA expression. Taken together, these studies indicate that like potent estrogens 17alpha-E(2) up-regulates VEGF-A mRNA expression in estrogen responsive GH3 rat pituitary tumor cells, but this induction is not mediated through a classical estrogen receptor pathway. PI3K-Akt signaling pathway is required for the induction of VEGF-A mRNA in GH3 cells by 17alpha-E(2).

Expression of angiogenic factors including VEGFs and the effects of hypoxia and thalidomide on human myeloma cells

Angiogenic factors are major causes of tumor progression in hematological malignancies, particularly multiple myeloma, as well as solid tumors. The introduction of thalidomide as an anti-angiogenic agent in myeloma treatment has demonstrated the importance of angiogenic factors in the progression of myeloma. However, the direct effects of angiogenic factors, particularly VEGFs, hypoxia, and thalidomide, on myeloma cells are not been documented. In this study, we demonstrate increased expression and production levels of VEGF in myeloma compared to non-myelomatous hematological lines, resistance to hypoxia and enhancement of VEGF-A production by hypoxia in myeloma, and direct growth inhibition of myeloma cells due to apoptosis and G1 arrest caused by TNFalpha upregulation induced by thalidomide. These findings may encourage the clinical use of anti-angiogenic agents for their cytostatic effects and the prevention of progression.

Cellular dysfunction in the diabetic fibroblast: impairment in migration, vascular endothelial growth factor production, and response to hypoxia

Although it is known that systemic diseases such as diabetes result in impaired wound healing, the mechanism for this impairment is not understood. Because fibroblasts are essential for wound repair, we compared the in vitro behavior of fibroblasts cultured from diabetic, leptin receptor-deficient (db/db) mice with wild-type fibroblasts from mice of the same genetic background in processes important during tissue repair. Adult diabetic mouse fibroblast migration exhibited a 75% reduction in migration compared to normal fibroblasts (P < 0.001) and was not significantly stimulated by hypoxia (1% O(2)), whereas wild-type fibroblast migration was up-regulated nearly twofold in hypoxic conditions (P < 0.05). Diabetic fibroblasts produced twice the amount of pro-matrix metalloproteinase-9 as normal fibroblasts, as measured by both gelatin zymography and enzyme-linked immunosorbent assay (P < 0.05). Adult diabetic fibroblasts exhibited a sevenfold impairment in vascular endothelial growth factor (VEGF) production (4.5 +/- 1.3 pg/ml versus 34.8 +/- 3.3 pg/ml, P < 0.001) compared to wild-type fibroblasts. Moreover, wild-type fibroblast production of VEGF increased threefold in response to hypoxia, whereas diabetic fibroblast production of VEGF was not up-regulated in hypoxic conditions (P < 0.001). To address the question whether these differences resulted from chronic hyperglycemia or absence of the leptin receptor, fibroblasts were harvested from newborn db/db mice before the onset of diabetes (4 to 5 weeks old). These fibroblasts showed no impairments in VEGF production under basal or hypoxic conditions, confirming that the results from db/db fibroblasts in mature mice resulted from the diabetic state and were not because of alterations in the leptin-leptin receptor axis. Markers of cellular viability including proliferation and senescence were not significantly different between diabetic and wild-type fibroblasts. We conclude that, in vitro, diabetic fibroblasts show selective impairments in discrete cellular processes critical for tissue repair including cellular migration, VEGF production, and the response to hypoxia. The VEGF abnormalities developed concurrently with the onset of hyperglycemia and were not seen in normoglycemic, leptin receptor-deficient db/db mice. These observations support a role for fibroblast dysfunction in the impaired wound healing observed in human diabetics, and also suggest a mechanism for the poor clinical outcomes that occur after ischemic injury in diabetic patients.

Omega-3 fatty acids: implications for the treatment of tumor-associated inflammation

Our in vivo and in vitro studies using omega-3 fatty acids (FA) have provided insight into the biological effects and mechanisms of their anti-inflammatory action(s). The implications for this research are profound because there are few nutritional therapies available that have the potential to be clinically effective in malignancies and other chronic inflammatory conditions as omega-3 FA. In this summary of experiments the biological effects of omega-3 FA are discussed and the potential mechanisms of action presented.