In vivo angiogenic phenotype of endothelial cells and pericytes induced by vascular endothelial growth factor-A

Whole-exome sequencing in moyamoya patients of Northern-European origin identifies gene variants involved in Nitric Oxide metabolism: A pilot study

Introduction

Moyamoya disease (MMD) is a chronic cerebrovascular steno-occlusive disease of largely unknown etiology. Variants in the RNF213 gene are strongly associated with MMD in East-Asia. In MMD patients of Northern-European origin, no predominant susceptibility variants have been identified so far.

Research question

Are there specific candidate genes associated with MMD of Northern-European origin, including the known RNF213 gene? Can we establish a hypothesis for MMD phenotype and associated genetic variants identified for further research?

Material and methods

Adult patients of Northern-European origin, treated surgically for MMD at Oslo University Hospital between October 2018 to January 2019 were asked to participate. WES was performed, with subsequent bioinformatic analysis and variant filtering. The selected candidate genes were either previously reported in MMD or known to be involved in angiogenesis. The variant filtering was based on variant type, location, population frequency, and predicted impact on protein function.

Results

Analysis of WES data revealed nine variants of interest in eight genes. Five of those encode proteins involved in nitric oxide (NO) metabolism: NOS3, NR4A3, ITGAV, GRB7 and AGXT2. In the AGXT2 gene, a de novo variant was detected, not previously described in MMD. None harboured the p.R4810K missense variant in the RNF213 gene known to be associated with MMD in East-Asian patients.

Discussion and conclusion

Our findings suggest a role for NO regulation pathways in Northern-European MMD and introduce AGXT2 as a new susceptibility gene. This pilot study warrants replication in larger patient cohorts and further functional investigations.

Anti-angiogenic collagen IV-derived peptide target engagement with αvβ3 and α5β1 in ocular neovascularization models

AXT107, a collagen-derived peptide that binds integrins αvβ3 and α5β1 with high affinity, suppresses vascular endothelial growth factor (VEGF) signaling, promotes angiopoietin 2-induced Tie2 activation, and suppresses neovascularization (NV) and vascular leakage. Immunohistochemical staining for αvβ3 and α5β1 was markedly increased in NV compared with normal retinal vessels. After intravitreous injection of AXT107, there was no staining with an anti-AXT107 antibody on normal vessels but robust staining of NV that co-localized with αvβ3 and α5β1. Likewise, after intravitreous injection, fluorescein amidite-labeled AXT107 co-localized with αvβ3 and α5β1 on NV but not normal vessels. AXT107 also co-localized with αv and α5 at cell-cell junctions of human umbilical vein endothelial cells (HUVECs). AXT107-integrin binding was demonstrated by ex vivo cross-linking/pull-down experiments. These data support the hypothesis that AXT107 therapeutic activity is mediated through binding αvβ3 and α5β1 which are markedly upregulated on endothelial cells in NV providing selective targeting of diseased vessels which has therapeutic and safety benefits.

Evidence for oligodendrocyte progenitor cell heterogeneity in the adult mouse brain

Oligodendrocyte progenitor cells (OPCs) account for approximately 5% of the adult brain and have been historically studied for their role in myelination. In the adult brain, OPCs maintain their proliferative capacity and ability to differentiate into oligodendrocytes throughout adulthood, even though relatively few mature oligodendrocytes are produced post-developmental myelination. Recent work has begun to demonstrate that OPCs likely perform multiple functions in both homeostasis and disease and can significantly impact behavioral phenotypes such as food intake and depressive symptoms. However, the exact mechanisms through which OPCs might influence brain function remain unclear. The first step in further exploration of OPC function is to profile the transcriptional repertoire and assess the heterogeneity of adult OPCs. In this work, we demonstrate that adult OPCs are transcriptionally diverse and separate into two distinct populations in the homeostatic brain. These two groups show distinct transcriptional signatures and enrichment of biological processes unique to individual OPC populations. We have validated these OPC populations using multiple methods, including multiplex RNA in situ hybridization and RNA flow cytometry. This study provides an important resource that profiles the transcriptome of adult OPCs and will provide a toolbox for further investigation into novel OPC functions.

Quantitative Assessment of the Apical and Basolateral Membrane Expression of VEGFR2 and NRP2 in VEGF-A-stimulated Cultured Human Umbilical Vein Endothelial Cells

Endothelial cells (ECs) form a precisely regulated polarized monolayer in capillary walls. Vascular endothelial growth factor-A (VEGF-A) induces endothelial hyperpermeability, and VEGF-A applied to the basolateral side, but not the apical side, has been shown to be a strong barrier disruptor in blood-retinal barrier ECs. We show here that VEGF-A presented to the basolateral side of human umbilical vein ECs (HUVECs) induces higher permeability than apical stimulation, which is similar to results obtained with bovine retinal ECs. We investigated with immunocytochemistry and confocal imaging the distribution of VEGF receptor-2 (VEGFR2) and neuropilin-2 (NRP2) in perinuclear apical and basolateral membrane domains. Orthogonal z-sections of cultured HUVECs were obtained, and the fluorescence intensity at the apical and basolateral membrane compartments was measured. We found that VEGFR2 and NRP2 are evenly distributed throughout perinuclear apical and basolateral membrane compartments in unstimulated HUVECs grown on Transwell inserts, whereas basolateral VEGF-A stimulation induces a shift toward basolateral VEGFR2 and NRP2 localization. When HUVECs were grown on coverslips, the distribution of VEGFR2 and NRP2 across the perinuclear apical and basolateral membrane domains was different. Our findings demonstrate that HUVECs dynamically regulate VEGFR2 and NRP2 localization on membrane microdomains, depending on growth conditions and the polarity of VEGF-A stimulation.

Challenging Management of Neovascular Glaucoma to Achieve the Best Visual Outcome

Neovascular glaucoma (NVG) resulting from ischemic insults caused by various diseases, such as proliferative diabetic retinopathy and central vein occlusion, remains a challenging situation. This case report aims to describe the complex management of NVG, resulting from diabetic retinopathy, to achieve the best visual outcome. A 47-year-old male presented with poor visual acuity of both eyes. His right eye was inoperable. Ahmed valve implantation with intraoperative intravitreal bevacizumab injection was performed in his left eye. Panretinal photocoagulation was performed serially after phacoemulsification. However, intraocular pressure was found to be raised, thus necessitating 5-fluorouracil needling bleb revision and administration of intracameral bevacizumab injection. During 15 months of follow-up we were able to achieve the best visual outcome possible in this patient. Comprehensive management of NVG should be implemented with a multidisciplinary approach.

Overview of Crosstalk Between Multiple Factor of Transcytosis in Blood Brain Barrier

Blood brain barrier (BBB) conserves unique regulatory system to maintain barrier tightness while allowing adequate transport between neurovascular units. This mechanism possess a challenge for drug delivery, while abnormality may result in pathogenesis. Communication between vascular and neural system is mediated through paracellular and transcellular (transcytosis) pathway. Transcytosis itself showed dependency with various components, focusing on caveolae-mediated. Among several factors, intense communication between endothelial cells, pericytes, and astrocytes is the key for a normal development. Regulatory signaling pathway such as VEGF, Notch, S1P, PDGFβ, Ang/Tie, and TGF-β showed interaction with the transcytosis steps. Recent discoveries showed exploration of various factors which has been proven to interact with one of the process of transcytosis, either endocytosis, endosomal rearrangement, or exocytosis. As well as providing a hypothetical regulatory pathway between each factors, specifically miRNA, mechanical stress, various cytokines, physicochemical, basement membrane and junctions remodeling, and crosstalk between developmental regulatory pathways. Finally, various hypotheses and probable crosstalk between each factors will be expressed, to point out relevant research application (Drug therapy design and BBB-on-a-chip) and unexplored terrain.

[Fibrinolytics: from the thrombolysis to the processes of blood vessels growth and remodeling, neurogenesis, carcinogenesis and fibrosis]

One of the most outstanding scientific achievements in the thrombolysis is the development and administration of fibrinolysin - the first Soviet drug that lyses blood clots. Intracoronary administration of fibrinolysin reduced the mortality of patients with myocardial infarction by almost 20%. For his work in this field Yevgeny Chazov was awarded the Lenin Prize in 1982. Over the next decades, under his leadership, the Cardiology Center established scientific and clinical laboratories that created new generations of drugs based on fibrinolytics for treating patients with myocardial infarction, restoration of blood flow in ischemic tissue, and also studying the mechanisms of remodeling of blood vessels involving the fibrinolysis system. It have been found new mechanisms of regulation of the navigation of blood vessels and nerves growth, tumor growth and its metastasis with the participation of the fibrinolysis system proteins. The review reports the role of the fibrinolysis system in the thrombolysis, blood vessels growth and remodeling, neurogenesis, carcinogenesis and fibrosis. The article is dedicated to the 90th anniversary of academician E.I. Chazov.

The uPAR System as a Potential Therapeutic Target in the Diseased Eye

Dysregulation of vascular networks is characteristic of eye diseases associated with retinal cell degeneration and visual loss. Visual impairment is also the consequence of photoreceptor degeneration in inherited eye diseases with a major inflammatory component, but without angiogenic profile. Among the pathways with high impact on vascular/degenerative diseases of the eye, a central role is played by a system formed by the ligand urokinase-type plasminogen activator (uPA) and its receptor uPAR. The uPAR system, although extensively investigated in tumors, still remains a key issue in vascular diseases of the eye and even less studied in inherited retinal pathologies such as retinitis pigmantosa (RP). Its spectrum of action has been extended far beyond a classical pro-angiogenic function and has emerged as a central actor in inflammation. Preclinical studies in more prevalent eye diseases characterized by neovascular formation, as in retinopathy of prematurity, wet macular degeneration and rubeosis iridis or vasopermeability excess as in diabetic retinopathy, suggest a critical role of increased uPAR signaling indicating the potentiality of its modulation to counteract neovessel formation and microvascular dysfunction. The additional observation that the uPAR system plays a major role in RP by limiting the inflammatory cascade triggered by rod degeneration rises further questions about its role in the diseased eye.

Myocardial Telocyte-Like Cells: A Review Including New Evidence

Telocytes (TCs) are a controversial cell type characterized by the presence of a particular kind of prolongations, known as telopodes, which are long, thin, and moniliform. A number of attempts has been made to establish the molecular phenotype of cardiac TCs (i.e., expression of c-kit, CD34, vimentin, PDGRFα, PDGRFβ, etc.). We designed an immunohistochemical study involving cardiac tissue samples obtained from 10 cadavers with the aim of determining whether there are TC-like interstitial cells that populate the interstitial space other than the mural microvascular cells. We applied the markers for CD31, CD34, PDGRFα, CD117/c-kit, and α-smooth muscle actin (α-SMA). We found that, in relation to two-dimensional cuts, the endothelial tubes could be misidentified as TC-like cells, the difference being the positive identification of endothelial lumina. Moreover, we found that cardiac pericytes express PDGRFα, CD117/c-kit, and α-SMA, and that they could also be misidentified as TCs when using light microscopy. We reviewed the respective values of the previously identified markers for achieving a clear-cut identification of cardiac TCs, highlighting the critical lack of specificity.

Dynamic, heterogeneous endothelial Tie2 expression and capillary blood flow during microvascular remodeling

Microvascular endothelial cell heterogeneity and its relationship to hemodynamics remains poorly understood due to a lack of sufficient methods to examine these parameters in vivo at high resolution throughout an angiogenic network. The availability of surrogate markers for functional vascular proteins, such as green fluorescent protein, enables expression in individual cells to be followed over time using confocal microscopy, while photoacoustic microscopy enables dynamic measurement of blood flow across the network with capillary-level resolution. We combined these two non-invasive imaging modalities in order to spatially and temporally analyze biochemical and biomechanical drivers of angiogenesis in murine corneal neovessels. By stimulating corneal angiogenesis with an alkali burn in Tie2-GFP fluorescent-reporter mice, we evaluated how onset of blood flow and surgically-altered blood flow affects Tie2-GFP expression. Our study establishes a novel platform for analyzing heterogeneous blood flow and fluorescent reporter protein expression across a dynamic microvascular network in an adult mammal.

The Hepatic Lymphatic Vascular System: Structure, Function, Markers, and Lymphangiogenesis

The lymphatic vascular system has been minimally explored in the liver despite its essential functions including maintenance of tissue fluid homeostasis. The discovery of specific markers for lymphatic endothelial cells has advanced the study of lymphatics by methods including imaging, cell isolation, and transgenic animal models and has resulted in rapid progress in lymphatic vascular research during the last decade. These studies have yielded concrete evidence that lymphatic vessel dysfunction plays an important role in the pathogenesis of many diseases. This article reviews the current knowledge of the structure, function, and markers of the hepatic lymphatic vascular system as well as factors associated with hepatic lymphangiogenesis and compares liver lymphatics with those in other tissues.

Pleiotropic action of CpG-ODN on endothelium and macrophages attenuates angiogenesis through distinct pathways

There is an integral relationship between vascular cells and leukocytes in supporting healthy tissue homeostasis. Furthermore, activation of these two cellular components is key for tissue repair following injury. Toll-like receptors (TLRs) play a role in innate immunity defending the organism against infection, but their contribution to angiogenesis remains unclear. Here we used synthetic TLR9 agonists, cytosine-phosphate-guanosine oligodeoxynucleotides (CpG-ODN), to investigate the role of TLR9 in vascular pathophysiology and identify potential therapeutic translation. We demonstrate that CpG-ODN stimulates inflammation yet inhibits angiogenesis. Regulation of angiogenesis by CpG-ODN is pervasive and tissue non-specific. Further, we noted that synthetic CpG-ODN requires backbone phosphorothioate but not TLR9 activation to render and maintain endothelial stalk cells quiescent. CpG-ODN pre-treated endothelial cells enhance macrophage migration but restrain pericyte mobilisation. CpG-ODN attenuation of angiogenesis, however, remains TLR9-dependent, as inhibition is lost in TLR9 deficient mice. Additionally, CpG-ODNs induce an M1 macrophage phenotype that restricts angiogenesis. The effects mediated by CpG-ODNs can therefore modulate both endothelial cells and macrophages through distinct pathways, providing potential therapeutic application in ocular vascular disease.

Tumor-Priming Smoothened Inhibitor Enhances Deposition and Efficacy of Cytotoxic Nanoparticles in a Pancreatic Cancer Model

Most pancreatic adenocarcinoma patients present with unresectable disease and benefit little from chemotherapy. Poor tumor perfusion and vascular permeability limit drug deposition. Previous work showed that Smoothened inhibitors of hedgehog signaling (sHHI) promote neovascularization in spontaneous mouse models of pancreatic cancer (PaCA) and enhance tumor permeability to low-molecular weight compounds. Here, we tested the hypothesis that sHHI can enhance tumor deposition and efficacy of drug-containing nanoparticles consisting of 80 to 100 nm sterically-stabilized liposomes (SSL) containing doxorubicin (SSL-DXR). SCID mice bearing low-passage patient-derived PaCA xenografts (PDX) were pretreated p.o. for 10 days with 40 mg/kg/d NVP-LDE225 (erismodegib), followed by i.v. SSL-DXR. Microvessel density, permeability, perfusion, and morphology were compared with untreated controls, as was SSL deposition and therapeutic efficacy. The sHHI alone affected tumor growth minimally, but markedly increased extravasation of nanoparticles into adenocarcinoma cell-enriched regions of the tumor. Immunostaining showed that sHHI treatment decreased pericyte coverage (α-SMA(+)) of CD31(+) vascular endothelium structures, and increased the abundance of endothelium-poor (CD31(-)) basement membrane structures (collagen IV(+)), suggesting increased immature microvessels. SSL-DXR (15 mg/kg) administered after sHHI pretreatment arrested tumor volume progression and decreased tumor perfusion/permeability, suggesting an initial vascular pruning response. Compared with controls, one cycle of 10-day sHHI pretreatment followed by 6 mg/kg SSL-DXR doubled median tumor progression time. Three cycles of treatment with sHHI and SSL-DXR, with a 10-day between-cycle drug holiday, nearly tripled median tumor progression time. Based upon these data, short-term sHHI treatment sequenced with nanoparticulate drug carriers constitutes a potential strategy to enhance efficacy of pancreatic cancer therapy.

Pericytes contribute to the disruption of the cerebral endothelial barrier via increasing VEGF expression: implications for stroke

Disruption of the blood-brain barrier (BBB) integrity occurring during the early onset of stroke is not only a consequence of, but also contributes to the further progression of stroke. Although it has been well documented that brain microvascular endothelial cells and astrocytes play a critical role in the maintenance of BBB integrity, pericytes, sandwiched between endothelial cells and astrocytes, remain poorly studied in the pathogenesis of stroke. Our findings demonstrated that treatment of human brain microvascular pericytes with sodium cyanide (NaCN) and glucose deprivation resulted in increased expression of vascular endothelial growth factor (VEGF) via the activation of tyrosine kinase Src, with downstream activation of mitogen activated protein kinase and PI3K/Akt pathways and subsequent translocation of NF-κB into the nucleus. Conditioned medium from NaCN-treated pericytes led to increased permeability of endothelial cells, and this effect was significantly inhibited by VEGF-neutralizing antibody. The in vivo relevance of these findings was further corroborated in the stroke model of mice wherein the mice, demonstrated disruption of the BBB integrity and concomitant increase in the expression of VEGF in the brain tissue as well as in the isolated microvessel. These findings thus suggest the role of pericyte-derived VEGF in modulating increased permeability of BBB during stroke. Understanding the regulation of VEGF expression could open new avenues for the development of potential therapeutic targets for stroke and other neurological disease.

Therapeutic efficacy of a novel non-peptide αvβ3 integrin antagonist for pathological retinal angiogenesis in mice

αvβ3 integrin has been reported as a promising therapeutic target for angiogenesis. In the present study, we tested the antiangiogenic activity of 3-[3-(6-guanidino-1-oxoisoindolin-2-yl) propanamido]-3-(pyridin-3-yl) propanoic acid dihydrochloride (GOPPP), a novel non-peptide αvβ3 antagonist. Both human umbilical vein endothelial cells (HUVECs) and a mouse model of oxygen-induced retinopathy (OIR) were investigated separately. HUVEC adhesion, proliferation, migration, ERK1/2 and Akt phosphorylation were assessed. C57BL/6 mice were used for the studies in the OIR model. After exposure to 75% oxygen from postnatal day (PD) 7 to PD12, the mice were returned to room air, and GOPPP was intravitreally administered on PD12. Retinal neovascularization was evaluated on PD17. Hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) protein levels and ERK1/2 phosphorylation were determined by Western blot analysis of retina proteins. GOPPP significantly inhibited the pro-angiogenic effects of vitronectin on HUVECs, including adhesion, proliferation, and migration, and inhibited ERK1/2 and Akt phosphorylation. Retinal neovascularization in the OIR model was significantly suppressed by intravitreal administration of 50 ng GOPPP. The pro-angiogenic factors HIF-1α and VEGF induced by hypoxia were significantly inhibited by GOPPP in OIR mice. GOPPP administration also inhibited ERK1/2 phosphorylation in the OIR model. These results indicate that GOPPP, a novel αvβ3 integrin antagonist, may have potential for the treatment of pathological retinal angiogenesis.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.

Molecular analysis of blood-retinal barrier loss in the Akimba mouse, a model of advanced diabetic retinopathy

The molecular mechanisms of vascular leakage in diabetic macular edema and proliferative retinopathy are poorly understood, mainly due to the lack of reliable in vivo models. The Akimba (Ins2(Akita)VEGF(+/-)) mouse model combines retinal neovascularization with hyperglycemia, and in contrast to other models, displays the majority of signs of advanced clinical diabetic retinopathy (DR). To study the molecular mechanism that underlies the breakdown of the blood-retinal barrier (BRB) in diabetic macular edema and proliferative diabetic retinopathy, we investigated the retinal vasculature of Akimba and its parental mice Kimba (trVEGF029) and Akita (Ins2(Akita)). Quantitative PCR, immunohistochemistry and fluorescein angiography were used to characterize the retinal vasculature with special reference to the inner BRB. Correlations between the degree of fluorescein leakage and retinal gene expression were tested by calculating the Spearman's correlation coefficient. Fluorescein leakage demonstrating BRB loss was observed in Kimba and Akimba, but not in Akita or wild type mice. In Kimba and Akimba mice fluorescein leakage was associated with focal angiogenesis and correlated significantly with Plvap gene expression. PLVAP is an endothelial cell-specific protein that is absent in intact blood-retinal barrier, but its expression significantly increases in pathological conditions such as DR. Furthermore, in Akimba mice BRB disruption was linked to decreased expression of endothelial junction proteins, pericyte dropout and vessel loss. Despite fluorescein leakage, no alteration in BRB protein levels or pericyte coverage was detected in retinas of Kimba mice. In summary, our data not only demonstrate that hyperglycemia sensitizes retinal vasculature to the effects of VEGF, leading to more severe microvascular changes, but also confirm an important role of PLVAP in the regulation of BRB permeability.

Innovations in studying in vivo cell behavior and pharmacology in complex tissues--microvascular endothelial cells in the spotlight

Many studies on the molecular control underlying normal cell behavior and cellular responses to disease stimuli and pharmacological intervention are conducted in single-cell culture systems, while the read-out of cellular engagement in disease and responsiveness to drugs in vivo is often based on overall tissue responses. As the majority of drugs under development aim to specifically interact with molecular targets in subsets of cells in complex tissues, this approach poses a major experimental discrepancy that prevents successful development of new therapeutics. In this review, we address the shortcomings of the use of artificial (single) cell systems and of whole tissue analyses in creating a better understanding of cell engagement in disease and of the true effects of drugs. We focus on microvascular endothelial cells that actively engage in a wide range of physiological and pathological processes. We propose a new strategy in which in vivo molecular control of cells is studied directly in the diseased endothelium instead of at a (far) distance from the site where drugs have to act, thereby accounting for tissue-controlled cell responses. The strategy uses laser microdissection-based enrichment of microvascular endothelium which, when combined with transcriptome and (phospho)proteome analyses, provides a factual view on their status in their complex microenvironment. Combining this with miniaturized sample handling using microfluidic devices enables handling the minute sample input that results from this strategy. The multidisciplinary approach proposed will enable compartmentalized analysis of cell behavior and drug effects in complex tissue to become widely implemented in daily biomedical research and drug development practice.

Not all MSCs can act as pericytes: functional in vitro assays to distinguish pericytes from other mesenchymal stem cells in angiogenesis

Pericytes play a crucial role in angiogenesis and vascular maintenance. They can be readily identified in vivo and isolated as CD146(+)CD34(-) cells from various tissues. Whether these and other markers reliably identify pericytes in vitro is unclear. CD146(+)CD34(-) selected cells exhibit multilineage potential. Thus, their perivascular location might represent a stem cell niche. This has spurred assumptions that not only all pericytes are mesenchymal stromal cells (MSCs), but also that all MSCs can act as pericytes. Considering this hypothesis, we developed functional assays by confronting test cells with endothelial cultures based on matrigel assay, spheroid sprouting, and cord formation. We calibrated these assays first with commercial cell lines [CD146(+)CD34(-) placenta-derived pericytes (Pl-Prc), bone marrow (bm)MSCs and fibroblasts]. We then functionally compared the angiogenic abilities of CD146(+)CD34(-)selected bmMSCs with CD146(-) selected bmMSCs from fresh human bm aspirates. We show here that only CD146(+)CD34(-) selected Pl-Prc and CD146(+)CD34(-) selected bmMSCs maintain endothelial tubular networks on matrigel and improve endothelial sprout morphology. CD146(-) selected bmMSCs neither showed these abilities, nor did they attain pericyte function despite progressive CD146 expression once passaged. Thus, cell culture conditions appear to influence expression of this and other reported pericyte markers significantly without correlation to function. The newly developed assays, therefore, promise to close a gap in the in vitro identification of pericytes via function. Indeed, our functional data suggest that pericytes represent a subpopulation of MSCs in bm with a specialized role in vascular biology. However, these functions are not inherent to all MSCs.

Immunohistochemical localization and characterization of putative mesenchymal stem cell markers in the retinal capillary network of rodents

Perivascular cells of microvascular niches are the prime candidates for being a reservoire of mesenchymal stem cell (MSC)-like cells in many tissues and organs that could serve as a potential source of cells and a target of novel cell-based therapeutic approaches. In the present study, by utilising typical markers of pericytes (neuronal-glial antigen 2, NG2, a chondroitin sulphate proteoglycan) and those of MSCs (CD146 and CD105) and primitive pluripotent cells (sex-determining region Y-box 2, Sox2), the phenotypic traits and the distribution of murine and rat retinal perivascular cells were investigated in situ. Our findings indicate that retinal microvessels of juvenile rodents are highly covered by NG2-positive branching processes of pericytic (perivascular) cells that are less prominent in mature capillary networks of the adult retina. In the adult rodent retinal vascular bed, NG2 labeling is mainly confined to membranes of the cell body resulting in a pearl-chain-like distribution along the vessels. Retinal pericytes, which were identified by their morphology and NG2 expression, simultaneously express CD146. Furthermore, CD146-positive cells located at small arteriole-to-capillary branching points appear more intensely stained than elsewhere. Evidence for a differential expression of the two markers around capillaries that would hint at a clonal heterogeneity among pericytic cells, however, is lacking. In contrast, the expression of CD105 is exclusively restricted to vascular endothelial cells and Sox2 is detected neither in perivascular nor in endothelial cells. In dissociated retinal cultures, however, simultaneous expression of NG2 and CD105 was observed. Collectively, our data indicate that vascular wall resident retinal pericytes share some phenotypic features (i.e. CD146 expression) with archetypal MSCs, which is even more striking in dissociated retinal cultures (i.e. CD105 expression). These findings might have implications for the treatment of retinal pathologies.

Molecular basis of the inner blood-retinal barrier and its breakdown in diabetic macular edema and other pathological conditions

Breakdown of the inner endothelial blood-retinal barrier (BRB), as occurs in diabetic retinopathy, age-related macular degeneration, retinal vein occlusions, uveitis and other chronic retinal diseases, results in vasogenic edema and neural tissue damage, causing loss of vision. The central mechanism of altered BRB function is a change in the permeability characteristics of retinal endothelial cells caused by elevated levels of growth factors, cytokines, advanced glycation end products, inflammation, hyperglycemia and loss of pericytes. Subsequently, paracellular but also transcellular transport across the retinal vascular wall increases via opening of endothelial intercellular junctions and qualitative and quantitative changes in endothelial caveolar transcellular transport, respectively. Functional changes in pericytes and astrocytes, as well as structural changes in the composition of the endothelial glycocalyx and the basal lamina around BRB endothelium further facilitate BRB leakage. As Starling's rules apply, active transcellular transport of plasma proteins by the BRB endothelial cells causing increased interstitial osmotic pressure is probably the main factor in the formation of macular edema. The understanding of the complex cellular and molecular processes involved in BRB leakage has grown rapidly in recent years. Although appropriate animal models for human conditions like diabetic macular edema are lacking, these insights have provided tools for rational design of drugs aimed at restoring the BRB as well as for design of effective transport of drugs across the BRB, to treat the chronic retinal diseases such as diabetic macular edema that affect the quality-of-life of millions of patients.

Endothelial tip cells in ocular angiogenesis: potential target for anti-angiogenesis therapy

Endothelial tip cells are leading cells at the tips of vascular sprouts coordinating multiple processes during angiogenesis. In the developing retina, tip cells play a tightly controlled, timely role in angiogenesis. In contrast, excessive numbers of tip cells are a characteristic of the chaotic pathological blood vessels in proliferative retinopathies. Tip cells control adjacent endothelial cells in a hierarchical manner to form the stalk of the sprouting vessel, using, among others, the VEGF-DLL-Notch signaling pathway, and recruit pericytes. Tip cells are guided toward avascular areas by signals from the local extracellular matrix that are released by cells from the neuroretina such as astrocytes. Recently, tip cells were identified in endothelial cell cultures, enabling identification of novel molecular markers and mechanisms involved in tip cell biology. These mechanisms are relevant for understanding proliferative retinopathies. Agents that primarily target tip cells can block pathological angiogenesis in the retina efficiently and safely without adverse effects. A striking example is platelet-derived growth factor, which was recently shown to be an efficacious additional target in the treatment of retinal neovascularization. Here we discuss these and other tip cell-based strategies with respect to their potential to treat patients with ocular diseases dominated by neovascularization.

Pericytes promote selective vessel regression to regulate vascular patterning

Blood vessel networks form in a 2-step process of sprouting angiogenesis followed by selective branch regression and stabilization of remaining vessels. Pericytes are known to function in stabilizing blood vessels, but their role in vascular sprouting and selective vessel regression is poorly understood. The endosialin (CD248) receptor is expressed by pericytes associated with newly forming but not stable quiescent vessels. In the present study, we used the Endosialin(-/-) mouse as a means to uncover novel roles for pericytes during the process of vascular network formation. We demonstrate in a postnatal retina model that Endosialin(-/-) mice have normal vascular sprouting but are defective in selective vessel regression, leading to increased vessel density. Examination of the Endosialin(-/-) mouse tumor vasculature revealed an equivalent phenotype, indicating that pericytes perform a hitherto unidentified function to promote vessel destabilization and regression in vivo in both physiologic and pathologic angiogenesis. Mechanistically, Endosialin(-/-) mice have no defect in pericyte recruitment. Rather, endosialin binding to an endothelial associated, but not a pericyte associated, basement membrane component induces endothelial cell apoptosis and detachment. The results of the present study advance our understanding of pericyte biology and pericyte/endothelial cell cooperation during vascular patterning and have implications for the design of both pro- and antiangiogenic therapies.

Prematurely elevating estradiol in early baboon pregnancy suppresses uterine artery remodeling and expression of extravillous placental vascular endothelial growth factor and α1β1 and α5β1 integrins

We previously showed that advancing the increase in estradiol levels from the second to the first third of baboon pregnancy suppressed placental extravillous trophoblast (EVT) invasion and remodeling of the uterine spiral arteries. Cell culture studies show that vascular endothelial cell growth factor (VEGF) plays a central role in regulating EVT migration and remodeling of the uterine spiral arteries by increasing the expression/action of certain integrins that control extracellular matrix remodeling. To test the hypothesis that the estradiol-induced reduction in vessel remodeling in baboons is associated with an alteration in VEGF and integrin expression, extravillous placental VEGF and integrin expression was determined on d 60 of gestation (term is 184 d) in baboons in which uterine artery transformation was suppressed by maternal estradiol administration on d 25-59. EVT uterine spiral artery invasion was 5-fold lower (P < 0.01), and VEGF protein expression, quantified by in situ proximity ligation assay, was 50% lower (P < 0.05) in the placenta anchoring villi of estradiol-treated than in untreated baboons. α1β1 and α5β1 mRNA levels in cells isolated by laser capture microdissection from the anchoring villi and cytotrophoblastic shell of estradiol-treated baboons were over 2-fold (P < 0.01) and 40% (P < 0.05) lower, respectively, than in untreated animals. In contrast, placental extravillous αvβ3 mRNA expression was unaltered by estradiol treatment. In summary, extravillous placental expression of VEGF and α1β1 and α5β1 integrins was decreased in a cell- and integrin-specific manner in baboons in which EVT invasion and remodeling of the uterine spiral arteries were suppressed by prematurely elevating estradiol levels in early pregnancy. We propose that estrogen normally controls the extent to which the uterine arteries are transformed by placental EVT in primate pregnancy by regulating expression of VEGF and particular integrin extracellular remodeling molecules that mediate this process.

Vascular endothelial growth factor receptor 2 inhibition in-vivo affects tumor vasculature in a tumor type-dependent way and downregulates vascular endothelial growth factor receptor 2 protein without a prominent role for miR-296

The precise molecular effects that antiangiogenic drugs exert on tumor vasculature remain to be poorly understood. We therefore set out to investigate the molecular and architectural changes that occur in the vasculature of two different tumor types that both respond to vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor therapy. Mice bearing Lewis lung carcinoma (LLC) or B16.F10 melanoma were treated with vandetanib (ZD6474), a VEGFR2/epidermal growth factor receptor (EGFR)/REarranged during Transfection (RET) kinase inhibitor, resulting in a significant 80% reduction in tumor outgrowth. Although in LLC the vascular density was not affected by vandetanib treatment, it was significantly decreased in B16.F10. In LLC, vandetanib treatment induced a shift in vascular gene expression toward stabilization, as demonstrated by upregulation of Tie2 and N-cadherin and downregulation of Ang2 and integrin β3. In contrast, only eNOS and P-selectin responded to vandetanib treatment in B16.F10 vasculature. Strikingly, vandetanib reduced protein expression of VEGFR2 in both models, whereas mRNA remained unaffected. Analysis of miR-296 expression allowed us to exclude a role for the recently proposed microRNA-296 in VEGFR2 posttranslational control in LLC and B16.F10 in vivo. Our data demonstrate that VEGFR2/EGFR inhibition through vandetanib slows down both LLC and B16.F10 tumor growth. Yet, the underlying molecular changes in the vasculature that orchestrate the antitumor effect differ between tumor types. Importantly, in both models, vandetanib treatment induced loss of its pharmacological target, which was not directly related to miR-296 expression. Validation of our observations in tumor biopsies from VEGFR2 inhibitor-treated patients will be essential to unravel the effects of VEGFR2 inhibitor therapy on tumor vasculature in relation to therapeutic efficacy.

Pericytes on the tumor vasculature: jekyll or hyde?

The induction of tumor vasculature, known as the 'angiogenic switch', is a rate-limiting step in tumor progression. Normal blood vessels are composed of two distinct cell types: endothelial cells which form the channel through which blood flows, and mural cells, the pericytes and smooth muscle cells which serve to support and stabilize the endothelium. Most functional studies have focused on the responses of endothelial cells to pro-angiogenic stimuli; however, there is mounting evidence that the supporting mural cells, particularly pericytes, may play key regulatory roles in both promoting vessel growth as well as terminating vessel growth to generate a mature, quiescent vasculature. Tumor vessels are characterized by numerous structural and functional abnormalities, including altered association between endothelial cells and pericytes. These dysfunctional, unstable vessels contribute to hypoxia, interstitial fluid pressure, and enhanced susceptibility to metastatic invasion. Increasing evidence points to the pericyte as a critical regulator of endothelial activation and subsequent vessel development, stability, and function. Here we discuss both the stimulatory and inhibitory effects of pericytes on the vasculature and the possible utilization of vessel normalization as a therapeutic strategy to combat cancer.

CD34 marks angiogenic tip cells in human vascular endothelial cell cultures

The functional shift of quiescent endothelial cells into tip cells that migrate and stalk cells that proliferate is a key event during sprouting angiogenesis. We previously showed that the sialomucin CD34 is expressed in a small subset of cultured endothelial cells and that these cells extend filopodia: a hallmark of tip cells in vivo. In the present study, we characterized endothelial cells expressing CD34 in endothelial monolayers in vitro. We found that CD34-positive human umbilical vein endothelial cells show low proliferation activity and increased mRNA expression of all known tip cell markers, as compared to CD34-negative cells. Genome-wide mRNA profiling analysis of CD34-positive endothelial cells demonstrated enrichment for biological functions related to angiogenesis and migration, whereas CD34-negative cells were enriched for functions related to proliferation. In addition, we found an increase or decrease of CD34-positive cells in vitro upon exposure to stimuli that enhance or limit the number of tip cells in vivo, respectively. Our findings suggest cells with virtually all known properties of tip cells are present in vascular endothelial cell cultures and that they can be isolated based on expression of CD34. This novel strategy may open alternative avenues for future studies of molecular processes and functions in tip cells in angiogenesis.

Differential proliferation rhythm of neural progenitor and oligodendrocyte precursor cells in the young adult hippocampus

Oligodendrocyte precursor cells (OPCs) are a unique type of glial cells that function as oligodendrocyte progenitors while constantly proliferating in the normal condition from rodents to humans. However, the functional roles they play in the adult brain are largely unknown. In this study, we focus on the manner of OPC proliferation in the hippocampus of the young adult mice. Here we report that there are oscillatory dynamics in OPC proliferation that differ from neurogenesis in the subgranular zone (SGZ); the former showed S-phase and M-phase peaks in the resting and active periods, respectively, while the latter only exhibited M-phase peak in the active period. There is coincidence between different modes of proliferation and expression of cyclin proteins that are crucial for cell cycle; cyclin D1 is expressed in OPCs, while cyclin D2 is observed in neural stem cells. Similar to neurogenesis, the proliferation of hippocampal OPCs was enhanced by voluntary exercise that leads to an increase in neuronal activity in the hippocampus. These data suggest an intriguing control of OPC proliferation in the hippocampus.

The impact of pericytes on the blood-brain barrier integrity depends critically on the pericyte differentiation stage

The blood-brain barrier consists of the cerebral microvascular endothelium, pericytes, astrocytes and neurons. In this study we analyzed the differentiation stage dependent influence of primary porcine brain capillary pericytes on the barrier integrity of primary porcine brain capillary endothelial cells. At first, we were able to induce two distinct differentiation stages of the primary pericytes in vitro. TGFβ treated pericytes expressed more α-SMA and actin while desmin, vimentin and nestin expression was decreased when compared to bFGF induced cells. Further analysis of α-SMA revealed that most of the pericytes differentiated with TGFβ expressed functional α-SMA while only few cells expressed functional α-SMA in the presence of bFGF. In addition the permeability factors VEGF, MMP-2 and MMP-9 were higher secreted by the α-SMA positive phenotype indicating a proangiogenic role of this TGFβ induced pericyte differentiation stage. Higher level of VEGF, MMP-2 and MMP-9 were as well detected in the TGFβ pretreated pericyte coculture with endothelial cells when compared to the influence of the bFGF pretreated pericytes. The TEER measurement of the barrier integrity of endothelial cells revealed that bFGF induced α-SMA negative pericytes stabilize the barrier integrity while α-SMA positive pericytes differentiated by TGFβ decrease the barrier integrity. These results together reveal the potential of pericytes to regulate the endothelial barrier integrity in a differentiation stage dependant pathway.

Regulation of the blood-brain barrier integrity by pericytes via matrix metalloproteinases mediated activation of vascular endothelial growth factor in vitro

The blood-brain barrier consists of the cerebral microvascular endothelium, pericytes, astrocytes, and neurons. In this study, we analyzed the influence of primary porcine brain capillary pericytes on the barrier integrity of primary porcine brain capillary endothelial cells in a species-consistent in vitro coculture model. We were able to show a barrier integrity-decreasing impact of pericytes by transendothelial electrical resistance (TEER) and (14)C-sucrose permeability measurements. The morphology analysis revealed serrated cell borders and a shift of the endothelial morphology towards a cobblestone shape under the influence of pericytes. The analysis of the two major barrier integrity modulators vascular endothelial growth factor (VEGF) and matrix metalloproteinases (MMPs) displayed higher MMP activity and higher levels VEGF, MMP-2, and MMP-9 in the coculture, whereas VEGF levels were decreased by the MMP inhibitor GM6001, indicating a complex interplay of both. Inhibition experiments with neutralizing VEGF antibody and GM6001 increased the TEER, which proves the involvement of VEGF and MMPs in the barrier-decreasing process. Analysis of occludin yielded decreased protein content and discontinuous expression at the endothelial cell borders under the influence of pericytes. These results together reveal the potential of pericytes to regulate the endothelial barrier integrity via MMPs and VEGF.

Laminin alpha4-null mutant mice develop chronic kidney disease with persistent overexpression of platelet-derived growth factor

Each extracellular matrix compartment in the kidney has a unique composition, with regional specificity in the expression of various laminin isoforms. Although null mutations in the majority of laminin chains lead to specific developmental abnormalities in the kidney, Lama4-/- mice have progressive glomerular and tubulointerstitial fibrosis. These mice have a significant increase in expression of platelet-derived growth factor (PDGF)-BB, PDGF-DD, and PDGF receptor beta in association with immature glomerular and peritubular capillaries. In addition, mesangial cell exposure to alpha4-containing laminins, but not other isoforms, results in down-regulation of PDGF receptor mRNA and protein, suggesting a direct effect of LN411/LN421 on vessel maturation. Given the known role of overexpression of PDGF-BB and PDGF-DD on glomerular and tubulointerstitial fibrosis, these data suggest that failure of laminin alpha4-mediated down-regulation of PDGF activity contributes to the progressive renal lesions in this animal model. Given the recent demonstration that individuals with laminin alpha4 mutations develop cardiomyopathy, these findings may be relevant to kidney disease in humans.

Expression of intermediate filament nestin in blood vessels of neural and non-neural tissues

Our previous findings performed in rat tissues demonstrated that intermediate filament nestin is expressed in endothelial cells of newly formed blood vessels of developing organs and neural transplants. The aim of the present study was to identify other cellular markers expressed in nestin-positive (nestin+) blood vessels. To reach this goal we performed double immunofluorescent study to co-localize nestin with endothelium-specific markers (CD31, CD34 II, vimentin) or markers of perivascular cells (GFAP, SMA) in paraffin-embedded sections of normal human brain tissue, low- and high-grade gliomas, postinfarcted heart and samples of non-neural tumours. Our findings documented that all the samples examined contained blood vessels with different ratio of nestin+ endothelial cells. Double immunostaining provided unambiguous evidence that endothelial cells expressed nestin and allowed them to distinguish from other nestin+ elements (perivascular astrocytic endfeet, undifferentiated tumour cells, smooth muscle cells and pericytes). Nestin+ endothelium was not confined only to newly formed capillaries but was also observed in blood vessels of larger calibres, frequently in arterioles and venules. We conclude that nestin represents a reliable vascular marker that is expressed in endothelial cells. Elevation of nestin expression likely corresponds to reorganization of intermediate filament network in the cytoskeleton of endothelial cells in the course of their maturation or adaptation to changes in growing tissues.

Treatment of retinal diseases with VEGF antagonists

Diabetic retinopathy (DR) and age-related macular degeneration (AMD) are the most prevalent causes of blindness in the Western world. The pathogenesis of neovascularization and vascular leakage, both hallmarks of these diseases, appears to have one common denominator: vascular endothelial growth factor (VEGF). Since the recent introduction of anti-VEGF therapy, intravitreal injections with these agents have become standard care in neovascular AMD, and have been found to be a valuable additional treatment strategy in several other vascular retinal diseases. This review provides an overview of the history of anti-VEGF treatment in the eye, its rationale, its efficacy, and its potential drawbacks.

Markers for microscopic imaging of lymphangiogenesis and angiogenesis

Imaging of lymphangiogenesis and angiogenesis requires robust and unambiguous markers of lymphatic and blood vessels. Although much progress has been made in recent years in identifying molecules specifically expressed on lymphatic and blood vessels, no perfect marker has been found that works reliably in all species, tissues, vascular beds, and in all physiological and pathologic conditions. The heterogeneity of expression of markers in both blood and lymphatic vessels reflects underlying differences in the phenotype of endothelial cells. Use of only one marker can lead to misleading interpretations, but these pitfalls can usually be avoided by use of multiple markers and three-dimensional whole-mount preparations. LYVE-1, VEGFR-3, Prox1, and podoplanin are among the most useful markers for microscopic imaging of lymphatic vessels, but, depending on histologic location, each marker can be expressed by other cell types, including vascular endothelial cells. Other markers, including CD31, junctional proteins, and receptors, such as VEGF-2, are shared by lymphatic and blood vessels.

Iodine deficiency induces a thyroid stimulating hormone-independent early phase of microvascular reshaping in the thyroid

Expansion of the thyroid microvasculature is the earliest event during goiter formation, always occurring before thyrocyte proliferation; however, the precise mechanisms governing this physiological angiogenesis are not well understood. Using reverse transcriptase-polymerase chain reaction and immunohistochemistry to measure gene expression and laser Doppler to measure blood flow in an animal model of goitrogenesis, we show that thyroid angiogenesis occurred into two successive phases. The first phase lasted a week and involved vascular activation; this process was thyroid-stimulating hormone (TSH)-independent and was directly triggered by expression of vascular endothelial growth factor (VEGF) by thyrocytes as soon as the intracellular iodine content decreased. This early reaction was followed by an increase in thyroid blood flow and endothelial cell proliferation, both of which were mediated by VEGF and inhibited by VEGF-blocking antibodies. The second, angiogenic, phase was TSH-dependent and was activated as TSH levels increased. This phase involved substantial up-regulation of the major proangiogenic factors VEGF-A, fibroblast growth factor-2, angiopoietin 1, and NG2 as well as their receptors Flk-1/VEGFR2, Flt-1/VEGFR1, and Tie-2. In conclusion, goiter-associated angiogenesis promotes thyroid adaptation to iodine deficiency. Specifically, as soon as the iodine supply is limited, thyrocytes produce proangiogenic signals that elicit early TSH-independent microvascular activation; if iodine deficiency persists, TSH plasma levels increase, triggering the second angiogenic phase that supports thyrocyte proliferation.

Studies with an orally bioavailable alpha V integrin antagonist in animal models of ocular vasculopathy: retinal neovascularization in mice and retinal vascular permeability in diabetic rats

The alpha(V) integrins are key receptors involved in mediating cell migration and angiogenesis. In age-related macular degeneration (AMD) and diabetic retinopathy, angiogenesis plays a critical role in the loss of vision. These ocular vasculopathies might be treatable with a suitable alpha(V) antagonist, and an oral drug would offer a distinct advantage over current therapies. (3,S,beta,S)-1,2,3,4-Tetrahydro-beta-[[1-[1-oxo-3-(1,5,6,7-tetrahydro-1,8-naphthyridin-2-yl)propyl]-4-piperidinyl]methyl]-3-quinolinepropanoic acid (JNJ-26076713) is a potent, orally bioavailable, nonpeptide alpha(V) antagonist derived from the arginine-glycine-asparagine binding motif in the matrix protein ligands (e.g., vitronectin). This compound inhibits alpha(V)beta(3) and alpha(V)beta(5) binding to vitronectin in the low nanomolar range, it has excellent selectivity over integrins alpha(IIb)beta(3) and alpha(5)beta(1), and it prevents adhesion to human, rat, and mouse endothelial cells. JNJ-26076713 blocks cell migration induced by vascular endothelial growth factor, fibroblast growth factor (FGF), and serum, and angiogenesis induced by FGF in the chick chorioallantoic membrane model. JNJ-26076713 is the first alpha(V) antagonist reported to inhibit retinal neovascularization in an oxygen-induced model of retinopathy of prematurity after oral administration. In diabetic rats, orally administered JNJ-26076713 markedly inhibits retinal vascular permeability, a key early event in diabetic macular edema and AMD. Given this profile, JNJ-26076713 represents a potential therapeutic candidate for the treatment of age-related macular degeneration, macular edema, and proliferative diabetic retinopathy.

Endothelial stomatal and fenestral diaphragms in normal vessels and angiogenesis

Vascular endothelium lines the entire cardiovascular system where performs a series of vital functions including the control of microvascular permeability, coagulation inflammation, vascular tone as well as the formation of new vessels via vasculogenesis and angiogenesis in normal and disease states. Normal endothelium consists of heterogeneous populations of cells differentiated according to the vascular bed and segment of the vascular tree where they occur. One of the cardinal features is the expression of specific subcellular structures such as plas-malemmal vesicles or caveolae, transendothelial channels, vesiculo-vacuolar organelles, endothelial pockets and fenestrae, whose presence define several endothelial morphological types. A less explored observation is the differential expression of such structures in diverse settings of angiogenesis. This review will focus on the latest developments on the components, structure and function of these specific endothelial structures in normal endothelium as well as in diverse settings of angiogenesis.

An intimate interplay between precocious, migrating pericytes and endothelial cells governs human fetal brain angiogenesis

In order to better understand the process of angiogenesis in the developing human brain, we have examined the spatial relationship and relative contributions of endothelial cells and pericytes, the two primary cell types involved in vessel growth, together with their relation with the vascular basement membrane. Pericytes were immunolocalized through use of the specific markers nerve/glial antigen 2 (NG2) proteoglycan, endosialin (CD248) and the platelet-derived growth factor receptor beta (PDGFR-beta), while endothelial cells were identified by the pan-endothelial marker CD31 and the blood brain barrier (BBB)-specific markers claudin-5 and glucose transporter isoform 1 (GLUT-1). The quantitative analysis demonstrates that microvessels of the fetal human telencephalon are characterized by a continuous layer of activated/angiogenic NG2 pericytes, which tightly invest endothelial cells and participate in the earliest stages of vessel growth. Immunolabelling with anti-active matrix metalloproteinase-2 (aMMP-2) and anti-collagen type IV antibodies revealed that aMMP-2 producing endothelial cells and pericytes are both associated with the vascular basement membrane during vessel sprouting. Detailed localization of the two vascular cell types during angiogenesis suggests that growing microvessels of the human telencephalon are formed by a pericyte-driven angiogenic process in which the endothelial cells are preceded and guided by migrating pericytes during organization of the growing vessel wall.

Clinicopathological significance of stromal variables: angiogenesis, lymphangiogenesis, inflammatory infiltration, MMP and PINCH in colorectal carcinomas

Cancer research has mainly focused on alterations of genes and proteins in cancer cells themselves that result in either gain-of-function in oncogenes or loss-of-function in tumour-suppressor genes. However, stromal variables within or around tumours, including blood and lymph vessels, stromal cells and various proteins, have also important impacts on tumour development and progression. It has been shown that disruption of stromal-epithelial interactions influences cellular proliferation, differentiation, death, motility, genomic integrity, angiogenesis, and other phenotypes in various tissues. Moreover, stromal variables are also critical to therapy in cancer patients. In this review, we mainly focus on the clinicopathological significance of stromal variables including angiogenesis, lymphangiogenesis, inflammatory infiltration, matrix metalloproteinase (MMP), and the particularly interesting new cysteine-histidine rich protein (PINCH) in colorectal cancer (CRC).

Pericytes from human non-small cell lung carcinomas: An attractive target for anti-angiogenic therapy

Anti-angiogenic strategies have largely focused on endothelial cells and progenitors. However, pericytes are also an important component of vasculature. Perivascular cells from normal tissues have been widely reported, yet have not been extensively studied from human tumors. We have investigated pericytes from tumors of patients with lung cancer, the leader of cancer-related deaths in both men and women. Antibodies and magnetic beads were used to isolate cells from non-small cell lung carcinomas (NSCLC). The morphology of the pericytes was distinct with multiple elongated cytoplasmic extensions. Molecular expression of angiogenic genes was quantified by RT-PCR. Flow cytometric analysis shows that NSCLC pericytes express antigens such NG2 and VEGFR1 and present the ganglioside 3G5. The value of pericytes as models of tumor vasculature was demonstrated in cell-culture-based angiogenesis assays such as tube formation and proliferation. Results show that pericytes from some NSCLC but not all were able to maintain tubes networks on Matrigel. Pericyte function can be influenced by angiogenic growth factors or anti-angiogenic agents. Pericytes displayed invasive action against NSCLC clusters in the absence of other cell types. Perivascular cells contribute to the progression of disease and are an attractive target for anti-angiogenic therapy.