The normal cellular prion protein and its possible role in angiogenesis.

Cellular Prion Protein (PrPc) is a ubiquitous glycoprotein present on the surface of endothelial cells. Resting vascular endothelial cells show minimum expression of PrPc and can constitutively release PrPc. PrPc participates in cell survival, differentiation and angiogenesis. During development, neonatal brain endothelial cells transiently express PrPc. Our group recently reported upregulation of PrPc in microvessels from ischemic brain regions in stroke patients. Ischemia/hypoxia induces PrPc expression through the activation of extracellular signal-regulated kinase (ERK). All these data suggest that PrPc plays an important role in angiogenic responses. In addition, PrPc participates in cellular function in the central nervous system, since PrPc is also highly expressed in neurons. PrPc binds copper, suggesting a role in copper metabolism. PrPc also protects cells against oxidative stress and it seems to be involved in neuroprotection. Several studies have demonstrated that PrPc prevents cells from apoptosis and subsequent tissue damage. Moreover, PrPc plays an important role in the immune response. Here, we review the multiple functions of PrPc with a special attention to its recently reported role in angiogenesis.

Dynamin and perforin are associated with neovascularisation in advanced carotid plaques.

Intimal plaque neovascularization is associated with the development of symptomatic disease and thrombosis, with new 'leaky' fragile microvessels prone to haemorrhage. Perforin or pore forming protein is involved in vascular cell death by forming pores in target cells. Enzymes, in particular, granzyme B are secreted by immune infiltrates present in inflammatory plaque regions and have been shown to induce endothelial cell apoptosis. Similarly, dynamin-2 is a GTPase which mediates oxidised low density lipoprotein-induced apoptosis and is also required for granzyme B-mediated exocytosis and apoptosis. Our pilot studies identified increased expression of these proteins in complicated atherosclerotic plaques. Here we demonstrate by immunohistochemistry that both proteins are over-expressed in angiogenic regions of complicated carotid plaques. Dynamin-2 was extensively localised around microvessels and in immune infiltrating cells whilst perforin was localised in immune infiltrating cells, endothelial cells and smooth muscle cells. Over-expression of these proteins may contribute to plaque destabilisation by increasing cellular apoptosis in vulnerable atherosclerotic plaques.

Changes in Hyaluronan Metabolism and RHAMM Receptor Expression Accompany Formation of Complicated Carotid Lesions and May be Pro-Angiogenic Mediators of Intimal Neovessel Growth.

Previous studies have shown that changes in expression of the glycosaminoglycan, hyaluronan (HA) were associated with erosion in areas of post-mortem coronary artery liable to rupture. Angiogenesis is an important feature of ulcerating haemorrhagic plaques prone to rupture. HA is a glycosaminoglycan known to possess potent angiogenic properties on metabolism to oligosaccharides of HA (o-HA) in the presence of hyaluronidase (HYAL) enzymes. In this study, we have examined HA receptor and HYAL enzyme expression in a series of carotid artery specimens used as vascular transplants and exhibiting various stages of atherosclerotic lesions as determined by anatomo-pathology. Our results demonstrated dramatically increased expression of HYAL-1 in regions of inflammation associated with complicated plaques. Receptor for HA-mediated motility (RHAMM), which is known to be important in transducing angiogenic signals in vascular endothelium, was strongly expressed on intimal blood vessels from complicated lesions but almost absent from other regions including adventitial vessels. Metabolism of HA, together with up-regulation of RHAMM in complicated plaque lesions might be partly responsible for over-production of leaky neovessels and predisposition to plaque rupture.

A microarray study of gene and protein regulation in human and rat brain following middle cerebral artery occlusion.

BACKGROUND: Altered gene expression is an important feature of ischemic cerebral injury and affects proteins of many functional classes. We have used microarrays to investigate the changes in gene expression at various times after middle cerebral artery occlusion in human and rat brain. RESULTS: Our results demonstrated a significant difference in the number of genes affected and the time-course of expression between the two cases. The total number of deregulated genes in the rat was 335 versus 126 in the human, while, of 393 overlapping genes between the two array sets, 184 were changed only in the rat and 36 in the human with a total of 41 genes deregulated in both cases. Interestingly, the mean fold changes were much higher in the human. The expression of novel genes, including p21-activated kinase 1 (PAK1), matrix metalloproteinase 11 (MMP11) and integrase interactor 1, was further analyzed by RT-PCR, Western blotting and immunohistochemistry. Strong neuronal staining was seen for PAK1 and MMP11. CONCLUSION: Our findings confirmed previous studies reporting that gene expression screening can detect known and unknown transcriptional features of stroke and highlight the importance of research using human brain tissue in the search for novel therapeutic agents.

Expression of cyclin-dependent kinase 5 mRNA and protein in the human brain following acute ischemic stroke.

Neuronal cell death after brain ischemia may be regulated by activation of cyclin-dependent kinase 5 (Cdk5). In this study, expression of Cdk5 and its activator p35/p25 was examined in human post-mortem stroke tissue and in human cerebral cortical fetal neurons and human brain microvascular endothelial cells exposed to oxygen-glucose deficiency and reperfusion. The majority of patients demonstrated increased expression of Cdk5 and p-Cdk5 in stroke-affected tissue, with about a third showing increased p35 and p25 cleaved fragment as determined by Western blotting. An increase in Cdk5-, p-Cdk5- and p35-positive neurons and microvessels occurred in stroke-affected regions of patients. Staining of neurons became irregular and clumped in the cytoplasm, and nuclear translocation occurred, with colocalization of p35 and Cdk5. Association of Cdk5 with nuclear damage was demonstrated by coexpression of nuclear Cdk5 in TUNEL-positive neurons and microvessels in peri-infarcted regions. In vitro studies showed up-regulation and/or nuclear translocation of Cdk5, p-Cdk5 and p35 in neurons and endothelial cells subjected to oxygen-glucose deficiency, and strong staining was associated with propidium iodide positive nuclei, an indicator of cellular damage. These results provide new evidence for a role of Cdk5 in the events associated with response to ischemic injury in humans.

Cellular prion protein is increased in the plasma and peri-infarcted brain tissue after acute stroke.

The physiologic properties of the normal cellular prion protein (PrP(C)) have not been established fully, although recent evidence showed its upregulation in cerebral ischaemia. Using patients, animal models, and in vitro studies we aimed to identify in detail the expression and localization of PrP(C) in ischemic stroke. Patients in acute phase of ischaemic stroke had increased plasma levels of circulating PrP(C) as compared to healthy age- and gender-matched controls (3.1 +/- 1.4 vs. 1.9 +/- 0.7 ng/ml, P = 0.002). Immunohistochemistry showed increased expression of PrP(C) in the soma of peri-infarcted neurones as well as in the endothelial cells (EC) of micro-vessels and inflammatory cells in peri-infarcted brain tissue from patients who survived for 2-34 days after an initial stroke. The same pattern was repeated 1-48 hr after MCAO. RT-PCR showed increased gene expression of PrP(C) by human foetal neurons (HFN) after 12 hr of oxygen glucose deprivation (OGD), which remained increased after 24 hr reperfusion. Western blotting confirmed that protein expression was similarly upregulated, and fluorescent labeling showed a notable increase in peri-nuclear and axonal PrP(C) staining intensity. Increased plasma PrP(C) seems to reflect endogenous expression in acute stroke-affected brain tissue. Increased cellular expression in peri-infarcted regions may influence hypoxia-induced cell damage, although the effects on EC survival and angiogenesis remain to be elucidated.

A comparative study of neovascularisation in atherosclerotic plaques using CD31, CD105 and TGF beta 1.

OBJECTIVES: This study aims to identify plaque neovascularisation using antibodies to CD31, CD105 and TGFbeta1, and to compare their patterns of expression. METHODS: Tissue expression of CD31, CD105 and TGFbeta1 was examined immunohistologically in atherosclerotic plaques from 53 patients who had undergone carotid endarterectomy and in 10 controls. RESULTS: CD31 was observed in a proportion of the microvessels within atheroma. The expression of CD105 was barely visible in normal arteries, but was markedly enhanced in atherosclerotic plaques. The vast majority of the microvessels in atheroma were positive for CD105 with pronounced expression around the periphery of the lipid core. In consecutive sections, microvessels showing negative staining for CD31 were positive for CD105. Although TGFbeta1 was seen in the thickened intima, it was more strongly expressed in well-formed fibrous plaques. Consecutive sections showed that some microvessels were stained by both CD105 and TGFbeta1, but in certain areas microvessels were exclusively CD105 positive. CONCLUSIONS: These observations highlight the distinctive expression patterns of CD31, CD105 and TGFbeta1, suggesting their specific roles in the development of atherosclerotic plaques. CD105 is almost universally expressed in microvessels within the atheroma and is therefore a better vascular marker than CD31 and TGFbeta1for assessing neovascularisation in atherosclerotic plaques.

Concomitant cell growth and differentiation are dependent on erbB1 and integrin activation in an autonomously surviving colon adenocarcinoma: involvement of autocrine amphiregulin secretion.

In normal colon epithelium, cell proliferation is followed by cell differentiation. The purpose of this work was to investigate, in the HT29-D4 colon adenocarcinoma cell line, the occurrence of a temporal sequence of changes in cell proliferation and differentiation, the role of autocrine EGF family ligands and to determine which transduction pathway(s) are involved in these processes. In a medium lacking both growth factor and serum, HT29-D4 cells secreted amphiregulin (AR), which was shown to be strongly involved in cell adhesion, growth and differentiation. In the main, integrins alpha2beta1 and alphavbeta6 intervened in these processes. Using tyrphostins, it was demonstrated that AR involvement was mediated through the ErbB1/ERK1,2 and ErbB1/FAK pathways. These signalling molecules were directly involved in pRb inhibition and, thus, in cyclin A expression. Concomitantly, colon differentiation markers were also expressed. Furthermore, terminal cell maturation resulted in a colon absorptive cell with strong polarisation, the growth of which was inhibited by tyrphostin and an ERK1,2 inhibitor. It was concluded that in a colon adenocarcinoma, cell proliferation and differentiation can occur concomitantly and that these deregulated processes are controlled by autocrine secretion through the ErbB1/ERK1,2 and FAK pathways.

Can angiogenesis be exploited to improve stroke outcome? Mechanisms and therapeutic potential.

Recent developments in our understanding of the pathophysiological events that follow acute ischaemic stroke suggest an important role for angiogenesis which, through new blood vessel formation, results in improved collateral circulation and may impact on the medium-to-long term recovery of patients. Future treatment regimens may focus on optimization of this process in the ischaemic boundary zones or 'penumbra' region adjacent to the infarct, where partially affected neurons exposed to intermediate perfusion levels have the capability of survival if perfusion is maintained or normalized. In this review, we present evidence that angiogenesis is a key feature of ischaemic stroke recovery and neuronal post-stroke re-organization, examine the signalling mechanisms through which it occurs, and describe the therapeutic potential of treatments aimed at stimulating revascularization and neuroprotection after stroke.

Preparation of tissue-specific monoclonal antibodies using purified endothelial membrane proteins from biotinylated pulmonary vasculature of rhesus monkey.

In the present study, we perfused the rhesus lung vascular bed in situ with sulfo-NHS-LC-Biotin to biotinylate its luminal surface membrane proteins. After homogenization, dialysis, and affinity chromatography, biotinylated endothelial membrane proteins were successfully isolated and characterized as enriched endothelial membrane proteins with no contamination of intracellular proteins. When they were used as immunogens to develop monoclonal antibodies (MAbs), three MAbs--TX111, TX112, and TX113--were obtained. Among them, TX111 was demonstrated to specifically bind to rhesus lung tissue by Western blotting and enzymelinked immunosorbent assay (ELISA)--that is, positively stained capillary endothelium of rhesus lung. The molecular weight of the corresponding antigen for TX111 was approximately 70 kDa under reducing conditions. TX111 also reacted with human lung homogenate, but not with rat lung homogenate. These results suggest that (1) the biotinylation method is applicable for isolating endothelial proteins in situ from large animals; (2) anti-human protein MAbs are likely to be obtained using monkey proteins; and (3) TX111 is potentially useful for pulmonary vascular targeting.

Expression of basic fibroblast growth factor mRNA and protein in the human brain following ischaemic stroke.

Our previous work has demonstrated that angiogenesis occurs in the damaged brain tissue of patients surviving acute ischaemic stroke and increased microvessel density in the penumbra is associated with longer patient survival. The brain is one of the richest sources of FGF-2 and several studies have noted its angiogenic and neuroprotective effects in the nervous system. These findings led us to investigate the expression and localisation of both FGF-2 mRNA and protein in brain tissue collected within 12 h of death from 10 patients who survived for between 24 h and 43 days after acute stroke caused by thrombosis or embolus. Western blot analysis demonstrated increased FGF-2 protein expression in both grey and white matter in the infarcted core and the penumbra region compared to the normal contralateral hemisphere of all 10 patients studied. Using indirect immunoperoxidase staining of paraffin embedded sections, we observed the presence of FGF-2 in neurones, astrocytes, macrophages and endothelial cells. In situ hybridisation was used to localise and quantify mRNA expression in ischaemic brain tissue of the same 10 patients. The expression of FGF-2 in the penumbra of all patients was significantly raised compared with infarcted tissue and normal-looking contralateral hemisphere. In addition, serum FGF-2 was significantly increased between 1 and 14 days (P<0.001) in many patients with both ischaemic stroke (n=28) and intra-cerebral haemorrhage (n=16) compared with age-matched control subjects undergoing routine medical examinations (n=20). We suggest that up-regulation of FGF-2 is one of the mechanisms that leads to angiogenesis and neuro-protection in the penumbra region after acute stroke in man.

A novel method to isolate and map endothelial membrane proteins from pulmonary vasculature.

Vascular endothelium has attracted extensive attention due to its important role in many physiological and pathological processes. Many methods have been developed to study the components and their functions in vascular endothelium. Here we report a novel approach to investigate vascular endothelium using normal rat lungs as the model. We perfused lung vascular beds with sulfosuccinimidyl-6-(biotinamido) hexanoate, a biotin analog, to label endothelial membrane proteins. The biotinylated proteins were isolated from lung homogenate with immobilized monomeric avidin and confirmed to be highly pure endothelial membrane proteins with little contamination of intracellular proteins. These biotinylated proteins were used as immunogens for development of monoclonal antibodies. Indeed, newly generated monoclonal antibodies have revealed different expression patterns of proteins across tissues. Some proteins were found highly specifically expressed to capillary vessels of pulmonary vasculature. This method has also been proven useful for investigating vasculature of other organs, as this study explored.

CD105 inhibits transforming growth factor-beta-Smad3 signalling.

CD105 (endoglin) is an important component of the transforming growth factor-beta (TGF-beta) receptor complex and is highly expressed in endothelial cells in tissues undergoing angiogenesis such as healing wounds, infarcts and in a wide range of tumours. In an attempt to understand the molecular mechanism by which CD105 exerts its effects on angiogenesis by modulating TGF-beta1 signalling, in this preliminary communication, CD105 transfected rat myoblasts were utilized as an in vitro model. Overexpression of CD105 in these transfectants antagonised TGF-beta1-mediated inhibition of cell proliferation and reduced TGF-beta1-mediated p3TP-Lux (PAI-1 promoter) luciferase activity. It also reduced (CAGA)12-Luc luciferase activity in response to TGF-beta1. The CAGA sequence is specific for Smad3/4 binding, implying that CD105 is involved in inhibition of TGF-beta1/Smad3 signalling. Furthermore, CD105 overexpression reduced serine phosphorylation of Smad3 and inhibited subsequent nuclear translocation of Smad3. CD105 resulted in high phosphorylation of JNK1, which is able to activate c-Jun. c-Jun is known to inhibit Smad3 transcriptional activity on CAGA sites, suggesting that CD105 may also inhibit Smad3 signalling through JNK1.

Overexpression of CD105 in rat myoblasts: role of CD105 in cell attachment, spreading and survival.

CD105 is a receptor for transforming growth factor-beta but it is also considered to be involved in cellular functions such as cell adhesion and migration. Using CD105 transfected rat myoblasts, we have investigated the role of CD105 in cell adhesion, spreading, growth and migration. CD105 transfected myoblasts expressed abundant CD105, which was preferentially located within focal adhesion sites. These cells took on a bipolar morphology whereas mock cells remained polygonal or rounded, and when wounded, CD105 expressing cells realigned their long axis prior to migrating and migrated as a cohort of cells. CD105 expression promoted cellular attachment, spreading, survival and growth in serum-free conditions and each of these parameters could be inhibited by a RGD-containing peptide but not a RAD-containing peptide. Mock-transfected cells could not attach, spread or grow under these conditions. Attachment, spreading and growth in CD105 expressing cells could be promoted by the addition of a monoclonal antibody against CD105. Expression of CD105 resulted in the phosphorylation of JNK1 but had no effect on beta1 integrin expression. From this preliminary study, we conclude that in addition to acting as a transforming growth factor-beta receptor, CD105 has an important role in cell adhesion, migration and survival.

TNF alpha down-regulates CD105 expression in vascular endothelial cells: a comparative study with TGF beta 1.

The vascular endothelium participates in angiogenesis, inflammation and the immune response, which are modulated by vasoactive cytokines such as tumour necrosis factor-alpha (TNF alpha) and transforming growth factor-beta 1 (TGF beta 1). CD105 is a component of the TGF beta receptor complex and is abundantly expressed in activated/injured endothelium where it is implicated in multiple cellular processes. Up-regulation of CD105 in synovial cells of rheumatoid arthritis and psoriatic lesions implies a possible role in the pathogenesis of such inflammatory disorders. The pro-inflammatory cytokine, TNF alpha, and anti-inflammatory cytokine, TGF beta 1, regulate multiple cellular processes such as proliferation, differentiation and apoptosis. Our hypothesis is that CD105 gene expression in endothelial cells is regulated by the multifunctional cytokines TNF alpha and TGF beta 1. By using human dermal microvascular endothelial cells the present study has shown that long-term treatment with TNF alpha (0.1-5 ng/ml) elicited a concentration- and time-dependent significant suppression (over 50% reduction) in CD105 protein levels. The observations that no significant alterations in the CD105 mRNA levels or in the CD105 promoter activity were found and that the potent inhibitor of NF kappa B, PDTC, did not affect the TNF alpha action suggest that CD105 down-regulation by TNF alpha is not at the transcriptional level. In contrast to TNF alpha, TGF beta 1 significantly elevated CD105 protein and mRNA expression (approximately 2-fold increase) through activation of its promoter activity. From these data we conclude that TNF alpha and TGF beta 1 exert opposing effects on CD105 expression in human vascular endothelial cells and that CD105 is enmeshed in the network of signal pathways modulating multiple cellular functions.

Three-dimensional structure and survival of newly formed blood vessels after focal cerebral ischemia.

Penumbra tissue becomes highly angiogenic after ischaemic stroke in man, and the re-establishment of a functional vasculature might be beneficial to patients. Unilateral ischaemia was induced in male Sprague-Dawley rats by permanent occlusion of the distal left middle cerebral artery (MCAO). Animals with stroke were kept alive for 1, 7, 14, 21 or 28 days after which time they were terminally anaesthetized. Vascular casts of infarcted areas, analyzed by scanning electron microscopy demonstrated that radially arranged neocortical arterioles and venules lost their regular patterns within one day of occlusion, and soon afterwards started to form a very dense network of anastomosing microvessels. At 1 week, vascular budding was visible at many sites. The smallest microvessels (4-10 microm) formed connections with the surrounding proliferating vessels similar to those in the normal brain. Survival of microvascular endothelial cells (ECs) was studied by double labeling of tissue sections using immunohistochemistry and antibodies to caspase-3, and TUNEL staining for apoptotic cells. ECs demonstrated intensive staining for caspase-3 and also staining by TUNEL, particularly near the infarct border, 14 days post-MCAO. These data support the hypothesis that growing blood vessels in ischaemic tissue form new connections, the pattern of which is similar to that in normal rat brain, but different to those formed in growing tumours. This normal growth pattern might be essential in future therapies involving induction of vascularization and neuroprotection to enhance long-term survival of the penumbra.

CD105 prevents apoptosis in hypoxic endothelial cells.

CD105, a marker of endothelial cells, is abundantly expressed in tissues undergoing angiogenesis and is a receptor for transforming growth factorbeta. The pivotal role of CD105 in the vascular system was demonstrated by the severe vascular defects that occur in CD105-knockout mice, but the exact mechanisms for CD105 regulation of vascular development have not been fully elucidated. In light of the function of CD105 and the importance of hypoxia in neovascularisation, we speculated that CD105 is involved in hypoxia-initiated angiogenesis. Using tissue-cultured human microvascular endothelial cells, we have investigated the effects of hypoxic stress on CD105 gene expression. Hypoxia induced a significant increase in membrane-bound and secreted CD105 protein levels. CD105 mRNA and promoter activity were also markedly elevated, the latter returning to the basal level after 16 hours of hypoxic stress. Hypoxia induced cell cycle arrest at the G0/G1 phases and massive cell apoptosis after 24 hours through a reduction in the Bcl-2 to Bax ratio, downregulation of Bcl-XL and Mcl-1, and upregulation of caspase-3 and caspase-8. The consequence of CD105 upregulation was revealed using an antisense approach and a TUNEL assay. Suppression of CD105 increased cell apoptosis under hypoxic stress in the absence of TGFbeta1. Furthermore, hypoxia and TGFbeta1 synergistically induced apoptosis in the CD105-deficient cells but not in the control cells. We conclude that hypoxia is a potent stimulus for CD105 gene expression in vascular endothelial cells, which in turn attenuates cell apoptosis and thus contributes to angiogenesis.

Increased intrathecal levels of the angiogenic factors VEGF and TGF-beta in Alzheimer's disease and vascular dementia.

The aim of the present study was to investigate, in patients with Alzheimer's disease (AD), and vascular dementia (VAD), patterns of local release of vascular endothelial growth factor (VEGF) and transforming growth factor-beta (TGF-beta), two cytokines having a pivotal role in hypoxia-induced angiogenesis. The intrathecal levels of these molecules were related to the clinical severity of these diseases and to the intrathecal levels of beta-amyloid protein. Significantly increased cerebrospinal fluid (CSF) levels of both VEGF and TGF-beta were observed in 20 patients with AD and in 26 patients with VAD compared to healthy controls. Interestingly, there was significant correlation between the CSF levels of TGF-beta and VEGF in all the individuals studied. Our study demonstrates, both in patients with AD and in patients with VAD, an intrathecal production of VEGF, a cytokine which plays a pivotal role in angiogenesis. These results suggest that vascular factors might not only play a role in the pathogenesis of VAD but also in the pathogenesis of AD. In addition, we show in AD and VAD an intrathecal production of TGF-beta, a cytokine exerting on one hand anti-inflammatory and angiogenic properties, but on the other promoting amyloidogenesis.