Angiogenesis: initiation and control

Milestones in tumor vascularization and its therapeutic targeting

Research into the mechanisms and manifestations of solid tumor vascularization was launched more than 50 years ago with the proposition and experimental demonstrations that angiogenesis is instrumental for tumor growth and was, therefore, a promising therapeutic target. The biological knowledge and therapeutic insights forthcoming have been remarkable, punctuated by new concepts, many of which were not foreseen in the early decades. This article presents a perspective on tumor vascularization and its therapeutic targeting but does not portray a historical timeline. Rather, we highlight eight conceptual milestones, integrating initial discoveries and recent progress and posing open questions for the future.

Cellular heterogeneity and stem cells of vascular endothelial cells in blood vessel formation and homeostasis: Insights from single-cell RNA sequencing

Vascular endothelial cells (ECs) that constitute the inner surface of blood vessels are essential for new vessel formation and organ homeostasis. ECs display remarkable phenotypic heterogeneity across different organs and the vascular tree during angiogenesis and homeostasis. Recent advances in single cell RNA sequencing (scRNA-seq) technologies have allowed a new understanding of EC heterogeneity in both mice and humans. In particular, scRNA-seq has identified new molecular signatures for arterial, venous and capillary ECs in different organs, as well as previously unrecognized specialized EC subtypes, such as the aerocytes localized in the alveolar capillaries of the lung. scRNA-seq has also revealed the gene expression profiles of specialized tissue-resident EC subtypes that are capable of clonal expansion and contribute to adult angiogenesis, a process of new vessel formation from the pre-existing vasculature. These specialized tissue-resident ECs have been identified in various different mouse tissues, including aortic endothelium, liver, heart, lung, skin, skeletal muscle, retina, choroid, and brain. Transcription factors and signaling pathways have also been identified in the specialized tissue-resident ECs that control angiogenesis. Furthermore, scRNA-seq has also documented responses of ECs in diseases such as cancer, age-related macular degeneration, Alzheimer's disease, atherosclerosis, and myocardial infarction. These new findings revealed by scRNA-seq have the potential to provide new therapeutic targets for different diseases associated with blood vessels. In this article, we summarize recent advances in the understanding of the vascular endothelial cell heterogeneity and endothelial stem cells associated with angiogenesis and homeostasis in mice and humans, and we discuss future prospects for the application of scRNA-seq technology.

The impact of aging and physical training on angiogenesis in the musculoskeletal system

Angiogenesis is the physiological process of capillary growth. It is strictly regulated by the balanced activity of agents that promote the formation of capillaries (pro-angiogenic factors) on the one hand and inhibit their growth on the other hand (anti-angiogenic factors). Capillary rarefaction and insufficient angiogenesis are some of the main causes that limit blood flow during aging, whereas physical training is a potent non-pharmacological method to intensify capillary growth in the musculoskeletal system. The main purpose of this study is to present the current state of knowledge concerning the key signalling molecules implicated in the regulation of skeletal muscle and bone angiogenesis during aging and physical training.

Adipose Tissue Development Relies on Coordinated Extracellular Matrix Remodeling, Angiogenesis, and Adipogenesis

Despite developing prenatally, the adipose tissue is unique in its ability to undergo drastic growth even after reaching its mature size. This development and subsequent maintenance rely on the proper coordination between the vascular niche and the adipose compartment. In this review, the process of adipose tissue development is broken down to explain (1) the ultrastructural matrix remodeling that is undertaken during simultaneous adipogenesis and angiogenesis, (2) the paracrine crosstalk involved during adipose development, (3) the mechanical regulators involved in adipose growth, and (4) the proteolytic and paracrine oversight for matrix remodeling during adipose development. It is crucial to gain a better understanding of the complex relationships that exist between adipose tissue and the vasculature during tissue development to provide insights into the pathological tissue expansion of obesity and to develop improved soft-tissue reconstruction techniques.

Identification of CD157-Positive Vascular Endothelial Stem Cells in Mouse Retinal and Choroidal Vessels: Fluorescence-Activated Cell Sorting Analysis

Purpose

CD157 (also known as Bst1) positive vascular endothelial stem cells (VESCs), which contribute to vascular regeneration, have been recently identified in mouse organs, including the retinas, brain, liver, lungs, heart, and skin. However, VESCs have not been identified in the choroid. The purpose of this study was to identify VESCs in choroidal vessels and to establish the protocol to isolate retinal and choroidal VESCs.

Methods

We established an efficient protocol to create single-cell suspensions from freshly isolated mouse retina and choroid by enzymatic digestion using dispase, collagenase, and type II collagenase. CD157-positive VESCs, defined as CD31⁺CD45⁻CD157⁺ cells, were sorted using fluorescence-activated cell sorting (FACS).

Results

In mouse retina, among CD31⁺CD45⁻ endothelial cells (ECs), 1.6 ± 0.2% were CD157-positive VESCs, based on FACS analysis. In mouse choroid, among CD31⁺CD45⁻ ECs, 4.5 ± 0.4% were VESCs. The CD157-positive VESCs generated a higher number of EC networks compared with CD157-negative non-VESCs under vascular endothelial growth factor (VEGF) in vitro cultures. The EC network area, defined as the ratio of the CD31-positive area to the total area in each field, was 4.21 ± 0.39% (retinal VESCs) and 0.27 ± 0.12% (retinal non-VESCs), respectively (P < 0.01). The EC network area was 8.59 ± 0.78% (choroidal VESCs) and 0.14 ± 0.04% (choroidal non-VESCs), respectively (P < 0.01). The VESCs were located in large blood vessels but not in the capillaries.

Conclusions

We confirmed distinct populations of CD157-positive VESCs in both mouse retina and choroid. VESCs are located in large vessels and have the proliferative potential. The current results may open new avenues for the research and treatment of ocular vascular diseases.

The Fundamental Contribution of Judah Folkman in the Setting of Angiogenesis Assays

Judah Folkman (1933-2008) made seminal discoveries on the mechanisms of angiogenesis which have opened a field of investigation worldwide. This chapter summarizes the fundamental contribution of Folkman in the setting of angiogenesis assays in vivo and in vitro.

Vascular Heterogeneity With a Special Focus on the Hepatic Microenvironment

Utilizing single-cell sequencing, recent studies were able to analyze at a greater resolution the heterogeneity of the vasculature and its complex composition in different tissues. Differing subpopulations have been detected, distinguishable only by their transcriptome. Designed to provide further insight into the heterogeneity of the functional vascular tissue, endothelial cells have been the main target of those studies. This review aims to present a synopsis of the variability of the different vascular beds, their endothelial variety, and the supporting cells that allow the vessels to serve their various purposes. Firstly, we are going to chart vascular tissue heterogeneity on a cellular level, describing endothelial diversity as well as stromal microenvironmental variety and interaction in a physiological setting. Secondly, we will summarize the current knowledge of pathological vessel formation in the context of cancer. Conventional anti-tumor therapeutic targets as well as anti-angiogenetic therapy is frequently limited by poor response of the tumor tissue. Reasons for moderate response and resistance to treatment can be found through different drivers of angiogenesis, different mechanisms of blood supply, but also in poorly understood tissue diversity. Based on this, we are comparing how pathologies alter the normal structure of vascular tissues highlighting the involved mechanisms. Lastly, illustrating the concept above, we will focus on the hepatic microenvironment, an organ of frequent metastatic spreading (e.g., from colorectal, breast, and lung cancers). We will address how the hepatic vasculature usually develops and subsequently we will describe how common liver metastases vary in their vasculature and the way they supply themselves (e.g., angiogenesis versus vessel co-option).

Expression and clinical implication of cyclooxygenase-2 and E-cadherin in oral squamous cell carcinomas

Epithelial-Mesenchymal Transition (EMT) and angiogenesis are crucial events for development of aggressive and often fatal Oral Squamous Cell Carcinomas (OSCCs). Both promote cancer progression and metastasis development, but while the former induces the loss of E-cadherin expression and, hence cadherin switching; the latter produces hematic blood vessel neo-formation and contribute to OSCC cell growth, tumor mass development, and dissemination. Cyclooxygenase-2 (COX-2) has an important role, not only in angiogenic mechanisms, but also in favoring cancer invasion. Indeed it decreases the expression of E-cadherin and leads to phenotypic changes in epithelial cells (EMT) enhancing their carcinogenic potential. Our aim is to evaluate the interplay between E-cadherin cytoplasmic delocalization, COX-2 up-regulation and COX-2 induced neo-angiogenesis in 120 cases of OSCC. We have analyzed the distribution and the number of neo-formed endothelial buds surrounding infiltrating cells that express COX-2, as well as the neo-formed vessels in chronic inflammatory infiltrate, which surround the tumor. A double immunostaining method was employed in order to verify co-localization of endothelial cell marker (CD34) and COX-2. IHC has also been used to assess E-cadherin expression. Our data demonstrate that the OSCC cells, which lose membranous E-cadherin staining, acquiring a cytoplasmic delocalization, overexpress COX-2. Moreover, we find a new CD34+ vessel formation (sprouting angiogenesis). Only basaloid type of OSCC showes low level of COX-2 expression together with very low level of neo-angiogenesis and consequent tumor necrosis. The well-known anti-metastatic effect of certain COX-2 inhibitors suggests that these molecules might have clinical utility in the management of advanced cancers.

Single-Cell RNA Sequencing Maps Endothelial Metabolic Plasticity in Pathological Angiogenesis

Endothelial cell (EC) metabolism is an emerging target for anti-angiogenic therapy in tumor angiogenesis and choroidal neovascularization (CNV), but little is known about individual EC metabolic transcriptomes. By single-cell RNA sequencing 28,337 murine choroidal ECs (CECs) and sprouting CNV-ECs, we constructed a taxonomy to characterize their heterogeneity. Comparison with murine lung tumor ECs (TECs) revealed congruent marker gene expression by distinct EC phenotypes across tissues and diseases, suggesting similar angiogenic mechanisms. Trajectory inference predicted that differentiation of venous to angiogenic ECs was accompanied by metabolic transcriptome plasticity. ECs displayed metabolic transcriptome heterogeneity during cell-cycle progression and in quiescence. Hypothesizing that conserved genes are important, we used an integrated analysis, based on congruent transcriptome analysis, CEC-tailored genome-scale metabolic modeling, and gene expression meta-analysis in cross-species datasets, followed by in vitro and in vivo validation, to identify SQLE and ALDH18A1 as previously unknown metabolic angiogenic targets.

CYP4A/20-HETE regulates ischemia-induced neovascularization via its actions on endothelial progenitor and preexisting endothelial cells

20-Hydroxyeicosatetraenoic acid (20-HETE) was recently identified as a novel contributor of ischemia-induced neovascularization based on the key observation that pharmacological interferences of CYP4A/20-HETE decrease ischemic neovascularization. The objective of the present study is to examine whether the underlying cellular mechanisms involve endothelial progenitor cells (EPCs) and preexisting endothelial cells (ECs). We found that ischemia leads to a time-dependent increase of cyp4a12 expression and 20-HETE production, which are endothelial in origin, using immunofluorescent microscopy, Western blot analysis, and LC-MS/MS. This is accompanied by increases in the tissue stromal cell-derived factor-1α (SDF-1α) expressions as well as SDF-1α plasma levels, EPC mobilization from bone marrow, and subsequent homing to ischemic tissues. Pharmacological interferences of CYP4A/20-HETE with a 20-HETE synthesis inhibitor, dibromo-dodecenyl-methylsulfimide (DDMS), or a 20-HETE antagonist, N-(20-hydroxyeicosa-6(Z), 15(Z)-dienoyl) glycine (6, 15-20-HEDGE), significantly attenuated these increases. Importantly, we also determined that 20-HETE plays a novel role in maintaining EPC functions and increasing the expression of Oct4, Sox2, and Nanog, which are indicative of increased progenitor cell stemness. Flow cytometric analysis revealed that pharmacological interferences of CYP4A/20-HETE decrease the EPC population in culture, whereas 20-HETE increases the cultured EPC population. Furthermore, ischemia also markedly increased the proliferation, oxidative stress, and ICAM-1 expression in the preexisting EC in the hindlimb gracilis muscles. We found that these increases were markedly negated by DDMS and 6, 15-20-HEDGE. Taken together, CYP4A/20-HETE regulates ischemia-induced compensatory neovascularization via its combined actions on promoting EPC and local preexisting EC responses that are associated with increased neovascularization. NEW & NOTEWORTHY CYP4A/20-hydroxyeicosatetraenoic acid (20-HETE) was recently discovered as a novel contributor of ischemia-induced neovascularization. However, the underlying molecular and cellular mechanisms are completely unknown. Here, we show that CYP4A/20-HETE regulates the ischemic neovascularization process via its combined actions on both endothelial progenitor cells (EPCs) and preexisting endothelial cells. Moreover, this is the first study, to the best of our knowledge, that associates CYP4A/20-HETE with EPC differentiation and stemness.

Potential roles of tumor-derived exosomes in angiogenesis

INTRODUCTION

Tumor-derived exosomes (TEX) and their role in tumor progression by accelerating angiogenesis are of great current interest. A better understanding of the mechanisms underlying TEX-blood vessels cross-talk may lead to improvements in current diagnosis, prognosis and treatment of cancer. Areas covered: For solid tumors, an adequate blood supply is of critical importance for their development, growth and metastasis. TEX, virus-size vesicles which circulate freely throughout body fluids and accumulate in the tumor microenvironment (TME), have been recognized as a new contributor to angiogenesis. TEX serve as a communication system between the tumor and various normal cells and are responsible for functional reprogramming of these cells. The molecular and genetic cargos that TEX deliver to the recipient cells involved in angiogenesis promote its induction and progression. The targeted inhibition of TEX pro-angiogenic functions might be a novel therapeutic approach for control of tumor progression. Expert opinion: TEX circulating in body fluids of cancer patients carry a complex molecular and genetic cargo and are responsible for phenotypic and functional reprogramming of endothelial cells and other normal cells residing in the TME.

Synergistic Effects of Nanodrug, Ultrasound Hyperthermia, and Thermal Ablation on Solid Tumors-An Animal Study

OBJECTIVE

Delivery barriers of nanodrug in large tumors due to heterogeneous blood supply, elevated interstitial pressure, and long transport distances can degrade the efficacy of cancer treatment. In this study, we proposed a therapeutic strategy to improve the tumor growth inhibition by injecting pegylated liposomal doxorubicin (PLD), and then applying a short time of ultrasound hyperthermia (HT) on the entire solid tumor, and inflicting ultrasound thermal ablation (Ab) in the low-perfused tumor region.

METHODS

BALB/c female mice with an average weight of 20 g were adopted and murine breast cancer cells 4T1 were subcutaneously implanted into the flank. A 1.0-MHz planar and a 0.47-MHz focused ultrasound transducers were used, respectively, for the HT and Ab treatment.

RESULTS

For a PLD dose of 5 mg/kg, the PLD + HT(42 °C, 10 min) group caused a significant decrease in the tumor size as compared with the control and the PLD group, but there were no significant differences between the PLD + HT group and the PLD + Ab(56 °C, 49 s) + HT group. For a PLD dose of 3 mg/kg, the tumor sizes among the four groups were mutually significant. The level of reduction in tumor was PLD + Ab + HT > PLD + HT > PLD > control.

CONCLUSION

The combination of anticancer nanodrug and ultrasound thermal treatment could remarkably suppress cancer tumor growth with a minimum compromise of side effects.

SIGNIFICANCE

The strategy of using thermal Ab in locations that are not reached by nanodrug with mild HT shows a promising potential for the entire tumor treatment.

L-arginine and arginine ethyl ester enhance proliferation of endothelial cells and preadipocytes - how an arginine ethyl ester-releasing biomaterial could support endothelial cell growth in tissue engineering

Adipose tissue engineering is a promising solution for the reconstruction of soft tissue defects. An insufficient neovascularisation within the scaffolds that leads to necrosis and tissue loss is still a major shortcoming of current tissue engineering attempts. Biomaterials, which release angiogenic factors such as L-arginine, could overcome this challenge by supporting the neovascularisation of the constructs. L-arginine is insoluble in organic solvents and thus cannot be incorporated into commonly used polymers in contrast to its ethyl ester. Here, we compared the effects of arginine and its ethyl ester on endothelial cells and preadipocytes, and generated an arginine ethyl ester-releasing, angiogenic polymer. We cultivated adipose tissue-derived endothelial cells and preadipocytes in arginine-free medium supplemented with L-arginine or L-arginine ethyl ester and assayed the proliferation rate and the degree of adipogenic differentiation, respectively. Additionally, we prepared arginine ethyl ester-releasing poly(D,L-lactide) foils, and investigated their impact on endothelial cell proliferation. We could demonstrate that arginine ethyl ester like arginine significantly increased the proliferation of endothelial cells and preadipocytes without inhibiting an induced adipogenic conversion of the preadipocytes. Further, we could show that the arginine ethyl ester-releasing polymer significantly increased endothelial cell growth. The present data are helpful guidance for generating angiogenic biomaterials that promote endothelial cell growth, and thereby could support neovascularisation within tissue engineering approaches.

In vitro analysis of the anticancer properties of scorpion venom in colorectal and breast cancer cell lines

Scorpion venom contains various types of proteins and peptides that are able to act as inhibitors of neurotransmitter molecules. This is achieved primarily via the inhibition of ion channels. In addition, scorpion venom has been demonstrated to exhibit anticancer properties in prostate and breast cancer, as well as leukemia. The anticancer properties of scorpion venom are due to its inhibitory effect on matrix metalloproteinase (MMP) activity, which leads to reduced motility and invasion in tumor cells. The inhibitory effects of venom on MMPs additionally lead to a reduction in the metastatic potential of malignant tumors. In the present study, the effect of venom obtained from a local serpentarium facility was examined in colorectal and breast cancer cell lines. Cell motility and clonogenic survival assays revealed a significant decrease (60-90%) in cell motility and colony formation, two significant hallmarks of cancer survival, following treatment with various concentrations of venom. These results were in agreement with previous studies demonstrating the anticancer activity of scorpion venom. In conclusion, the venom utilized at the Research Center of Prince Sultan Military Medical City Hospital (Riyadh, Saudi Arabia) possesses significant anticancer potential against colorectal and breast cancer cell lines.

Moringa oleifera as an Anti-Cancer Agent against Breast and Colorectal Cancer Cell Lines

In this study we investigated the anti-cancer effect of Moringa oleifera leaves, bark and seed extracts. When tested against MDA-MB-231 and HCT-8 cancer cell lines, the extracts of leaves and bark showed remarkable anti-cancer properties while surprisingly, seed extracts exhibited hardly any such properties. Cell survival was significantly low in both cells lines when treated with leaves and bark extracts. Furthermore, a striking reduction (about 70–90%) in colony formation as well as cell motility was observed upon treatment with leaves and bark. Additionally, apoptosis assay performed on these treated breast and colorectal cancer lines showed a remarkable increase in the number of apoptotic cells; with a 7 fold increase in MD-MB-231 to an increase of several fold in colorectal cancer cell lines. However, no significant apoptotic cells were detected upon seeds extract treatment. Moreover, the cell cycle distribution showed a G2/M enrichment (about 2–3 fold) indicating that these extracts effectively arrest the cell progression at the G2/M phase. The GC-MS analyses of these extracts revealed numerous known anti-cancer compounds, namely eugenol, isopropyl isothiocynate, D-allose, and hexadeconoic acid ethyl ester, all of which possess long chain hydrocarbons, sugar moiety and an aromatic ring. This suggests that the anti-cancer properties of Moringa oleifera could be attributed to the bioactive compounds present in the extracts from this plant. This is a novel study because no report has yet been cited on the effectiveness of Moringa extracts obtained in the locally grown environment as an anti-cancer agent against breast and colorectal cancers. Our study is the first of its kind to evaluate the anti-malignant properties of Moringa not only in leaves but also in bark. These findings suggest that both the leaf and bark extracts of Moringa collected from the Saudi Arabian region possess anti-cancer activity that can be used to develop new drugs for treatment of breast and colorectal cancers.

Concentration-Dependent Vascularization of Adipose Stromal Vascular Fraction Cells

Adipose-derived stromal vascular fraction (SVF) cells have been shown to self-associate to form vascular structures under both in vitro and in vivo conditions. The angiogenic (new vessels from existing vessels) and vasculogenic (new vessels through self-assembly) potential of the SVF cell population may provide a cell source for directly treating (i.e., point of care without further cell isolation) ischemic tissues. However the correct dosage of adipose SVF cells required to achieve a functional vasculature has not been established. Accordingly, in vitro and in vivo dose response assays were performed evaluating the SVF cell vasculogenic potential. Serial dilutions of freshly isolated rat adipose SVF cells were plated on growth factor reduced Matrigel and vasculogenesis, assessed as cellular tube-like network assembly, was quantified after 3 days of culture. This in vitro vasculogenesis assay indicated that rat SVF cells reached maximum network length at a concentration of 2.5 × 10(5) cells/ml and network maintained at the higher concentrations tested. The same concentrations of rat and human SVF cells were used to evaluate vasculogenesis in vivo. SVF cells were incorporated into collagen gels and subcutaneously implanted into Rag1 immunodeficient mice. The 3D confocal images of harvested constructs were evaluated to quantify dose dependency of SVF cell vasculogenesis potential. Rat- and human-derived SVF cells yielded a maximum vasculogenic potential at 1 × 10(6) and 4 × 10(6) cells/ml, respectively. No adverse reactions (e.g., toxicity, necrosis, tumor formation) were observed at any concentration tested. In conclusion, the vasculogenic potential of adipose-derived SVF cell populations is dose dependent.

Vasostatin inhibits VEGF-induced endothelial cell proliferation, tube formation and induces cell apoptosis under oxygen deprivation

Anti-angiogenesis treatment has been a promising new form of cancer therapy. Endothelial cells are critical for vascular homeostasis and play important roles in angiogenesis, vascular and tissue remodeling. Vasostatin, the 180 amino acid N-terminal fragment of the calreticulin protein, is reported to be a potent endogenous inhibitor of angiogenesis, suppressing tumor growth. However, the mechanism of these effects has not been sufficiently investigated. This study was performed to investigate the possible mechanism of vasostatin effects on primary cultured human umbilical vein endothelial cells (HUVEC). We found that vasostatin could inhibit the cell viability of HUVEC and induce cell apoptosis through mitochondrial pathways via activation of caspase-3 under oxygen deprivation conditions. Meanwhile, vasostatin also inhibited vascular endothelial growth factor-induced proliferation and tube formation of HUVEC. The possible mechanism of vasostatin-inhibited proliferation of HUVEC could be through down-regulation of endothelial nitric oxide synthase. These findings suggest that vasostatin could regulate endothelial cell function and might be used in anti-angiogenesis treatment.

Current understanding of molecular and cellular mechanisms in fibroplasia and angiogenesis during acute wound healing

Cutaneous wound healing ultimately functions to facilitate barrier restoration following injury-induced loss of skin integrity. It is an evolutionarily conserved, multi-cellular, multi-molecular process involving co-ordinated inter-play between complex signalling networks. Cellular proliferation is recognised as the third stage of this sequence. Within this phase, fibroplasia and angiogenesis are co-dependent processes which must be successfully completed in order to form an evolving extracellular matrix and granulation tissue. The resultant structures guide cellular infiltration, differentiation and secretory profile within the wound environment and consequently have major influence on the success or failure of wound healing. This review integrates in vitro, animal and human in vivo studies, to provide up to date descriptions of molecular and cellular interactions involved in fibroplasia and angiogenesis. Significant molecular networks include adhesion molecules, proteinases, cytokines and chemokines as well as a plethora of growth factors. These signals are produced by, and affect behaviour of, cells including fibroblasts, fibrocytes, keratinocytes, endothelial cells and inflammatory cells resulting in significant cellular phenotypic and functional plasticity, as well as controlling composition and remodelling of structural proteins including collagen and fibronectin. The interdependent relationship between angiogenesis and fibroplasia relies on dynamic reciprocity between cellular components, matrix proteins and bioactive molecules. Unbalanced regulation of any one component can have significant consequences resulting in delayed healing, chronic wounds or abnormal scar formation. Greater understanding of angiogenic and fibroplastic mechanisms underlying chronic wound pathogenesis has identified novel therapeutic targets and enabled development of improved treatment strategies including topical growth factors and skin substitutes.

Adipose tissue angiogenesis: impact on obesity and type-2 diabetes

The growth and function of tissues are critically dependent on their vascularization. Adipose tissue is capable of expanding many-fold during adulthood, therefore requiring the formation of new vasculature to supply growing and proliferating adipocytes. The expansion of the vasculature in adipose tissue occurs through angiogenesis, where new blood vessels develop from those pre-existing within the tissue. Inappropriate angiogenesis may underlie adipose tissue dysfunction in obesity, which in turn increases type-2 diabetes risk. In addition, genetic and developmental factors involved in vascular patterning may define the size and expandability of diverse adipose tissue depots, which are also associated with type-2 diabetes risk. Moreover, the adipose tissue vasculature appears to be the niche for pre-adipocyte precursors, and factors that affect angiogenesis may directly impact the generation of new adipocytes. Here we review recent advances on the basic mechanisms of angiogenesis, and on the role of angiogenesis in adipose tissue development and obesity. A substantial amount of data points to a deficit in adipose tissue angiogenesis as a contributing factor to insulin resistance and metabolic disease in obesity. These emerging findings support the concept of the adipose tissue vasculature as a source of new targets for metabolic disease therapies. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Angiogenic inhibition in high-grade gliomas: past, present and future

High-grade gliomas, especially glioblastoma (GBM), are among the most aggressive and vascularized tumors. Angiogenesis plays a significant role in tumor growth and survival, and thus offers a target for anticancer treatment. Bevacizumab, a humanized monoclonal antibody against VEGF, was approved by the US FDA as a single agent for the treatment of recurrent glioblastoma. Significant radiographic response and progression-free survival were seen with bevacizumab treatment. However, benefits to overall survival remain undetermined. Other antiangiogenic strategies targeting VEGF, VEGF receptor (VEGFR) and other angiogenic factors have also been examined. Tumor progression after antiangiogenic treatment is inevitable, and effective salvage therapy is yet to be identified. Mechanisms of resistance to antiangiogenic therapy include activation of alternative proangiogenic pathways and increased tumor invasion. Strategies targeting these escape mechanisms are currently being investigated. The use of antiangiogenic drugs is generally well tolerated, although rare and potentially life-threatening adverse effects have been identified. With the striking antipermeability effect of anti-VEGF inhibitors, assessment of true tumor response has become a challenge. The Response Assessment in Neuro-Oncology Working Group has developed new criteria for clinical trials in patients with high-grade glioma. Identification of neuroimaging advances and biologic markers will greatly enhance treatment strategies for these patients.

Modification of smoke toxicant yields alters the effects of cigarette smoke extracts on endothelial migration: an in vitro study using a cardiovascular disease model

Endothelial damage plays a key role in atherosclerosis and this is impacted upon by numerous risk factors including cigarette smoking. A potential measure to reduce the cardiovascular burden associated with smoking is to reduce smoke toxicant exposure. In an in vitro endothelial damage repair assay, endothelial cell migration was inhibited by cigarette smoke particulate matter (PM) generated from several cigarette types. This inhibition was reduced when cells were exposed to PM from an experimental cigarette with reduced smoke toxicant levels. As a number of toxicants induce oxidative stress and since oxidative stress may link cigarette smoke and endothelial damage, we hypothesized that PM effects were dependent on elevated cellular oxidants. However, although PM-induced cellular oxidant production could be inhibited by ascorbic acid or n-acetylcysteine, both these antioxidants were without effect on migration responses to PM. Furthermore, reactive oxygen species production, as indicated by dihydroethidium fluorescence, was not different in cells exposed to smoke from cigarettes with different toxicant levels. In summary, our data demonstrate that a cardiovascular disease-related biological response may be modified when cells are exposed to smoke containing different levels of toxicants. This appeared independent of the induction of oxidative stress.

The human brain intracerebral microvascular system: development and structure

The capillary from the meningeal inner pial lamella play a crucial role in the development and structural organization of the cerebral cortex extrinsic and intrinsic microvascular compartments. Only pial capillaries are capable of perforating through the cortex external glial limiting membrane (EGLM) to enter into the nervous tissue, although incapable of perforating the membrane to exit the brain. Circulatory dynamics and functional demands determine which capillaries become arterial and which capillaries become venous. The perforation of the cortex EGLM by pial capillaries is a complex process characterized by three fundamental stages: (1) pial capillary contact with the EGLM with fusion of vascular and glial basal laminae at the contact site, (2) endothelial cell filopodium penetration through the fussed laminae with the formation of a funnel between them that accompanies it into the nervous tissue while remaining open to the meningeal interstitium and, (3) penetration of the whole capillary carrying the open funnel with it and establishing an extravascular Virchow-Robin Compartment (V-RC) that maintains the perforating vessel extrinsic (outside) the nervous tissue through its entire length. The V-RC is walled internally by the vascular basal lamina and externally by the basal lamina of joined glial cells endfeet. The VRC outer glial wall appear as an extension of the cortex superficial EGLM. All the perforating vessels within the V-RCs constitute the cerebral cortex extrinsic microvascular compartment. These perforating vessels are the only one capable of responding to inflammatory insults. The V-RC remains open (for life) to the meningeal interstitium permitting the exchanges of fluid and of cells between brain and meninges. The V-RC function as the brain sole drainage (prelymphatic) system in both physiological as well as pathological situations. During cortical development, capillaries emerge from the perforating vessels, by endothelial cells growing sprouts analogous to their angiogenesis, entering into their corresponding V-RCs. These new capillaries to enter into the nervous tissue must perforate through the V-RC outer glial wall, a process analogous to the original perforation of the cortex EGLM by pial capillaries. These emerging capillaries are incapable of reentering the V-RCs and/or perforating vessels. As the new capillary enters into the nervous tissue, it becomes surrounded by glial endfeet and carries a single basal lamina (possibly glial). Capillaries emerging from contiguous perforators establish an anastomotic plexus between them, by mechanisms still poorly understood. The capillaries of this anastomotic plexus constitute the cerebral cortex intrinsic microvascular compartment and together constitute the so-called blood-brain-barrier. The intrinsic capillaries are changing and readapting continuously, by both active angiogenesis and reabsorption, to the gray matter neurons developmental and functional needs. The brain intrinsic capillaries are among the most active microvessels of the human body. Unresolved developmental and functional aspects concerning the cerebral cortex intrinsic capillary plexus need to be further investigated.

The nitric oxide system--cure for shortcomings in adipose tissue engineering?

Adipose tissue engineering aims to grow fat tissue for soft tissue reconstruction after tumour resection or trauma. However, insufficient progenitor cell differentiation and poor vascularization compromise the generation of clinically applicable adipose tissue. The desired process of neo-adipogenesis seems to be difficult to mimic, even though it takes place in all of us, inevitably and rapidly, as soon as we start consuming high-caloric diets. It has previously been proposed that inflammation and its key regulator, nitric oxide (NO), may play a relevant part in neo-adipogenesis. We here discuss how a controlled activation of the nitric oxide system on various levels may represent a cure for several current shortcomings in adipose tissue engineering.

20-HETE in neovascularization

Cytochrome P450 4A/F (CYP4A/F) converts arachidonic acid (AA) to 20-HETE by ω-hydroxylation. The contribution of 20-HETE to the regulation of myogenic response, blood pressure, and mitogenic actions has been well summarized. This review focuses on the emerging role of 20-HETE in physiological and pathological vascularization. 20-HETE has been shown to regulate vascular smooth muscle cells (VSMC) and endothelial cells (EC) by affecting their proliferation, migration, survival, and tube formation. Furthermore, the proliferation, migration, secretion of proangiogenic molecules (such as HIF-1α, VEGF, SDF-1α), and tube formation of endothelial progenitor cells (EPC) are stimulated by 20-HETE. These effects are mediated through c-Src- and EGFR-mediated downstream signaling pathways, including MAPK and PI3K/Akt pathways, eNOS uncoupling, and NOX/ROS system activation. Therefore, the CYP4A/F-20-HETE system may be a therapeutic target for the treatment of abnormal angiogenic diseases.

Increased glomerular filtration rate in early metabolic syndrome is associated with renal adiposity and microvascular proliferation

Metabolic syndrome (MetS) is associated with glomerular hyperfiltration and is a risk factor for chronic kidney disease, but the underlying mechanisms are poorly defined. This study tested the hypothesis that increased glomerular filtration rate (GFR) in early MetS is associated with renal adiposity and microvascular proliferation. Twelve MetS-prone Ossabaw pigs were randomized to 10 wk of a standard (lean, n = 6) or atherogenic (MetS, n = 6) diet. Kidney hemodynamics and function, perirenal fat volume, and tubular dynamics were assessed in vivo by multidetector computed tomography (CT) and blood oxygen level-dependent (BOLD)-MRI. Microvascular architecture was assessed ex vivo with micro-CT. Candidate injury mechanisms were evaluated in kidney tissue by Western blotting and histology. Basal GFR, renal blood flow, and renal cortical perfusion and volume were elevated in the MetS group. Perirenal and kidney tissue fat, proximal-nephron intratubular fluid concentration, and endothelial nitric oxide synthase expression were increased in MetS. GFR levels correlated with tissue triglyceride levels. Elevated spatial density of 20- to 40-μm cortical microvessels was accompanied by mild oxidative stress, inflammation, and with proximal tubular vacuolization. Medullary size and perfusion were relatively preserved, and BOLD-MRI showed intact medullary tubular response to furosemide. Increased GFR in early MetS is associated with renal adiposity and microvascular proliferation, which involve mainly the renal cortex and precede significant activation of oxidative stress and inflammation. Renal adiposity and proliferative microvessels may represent novel therapeutic targets for preserving renal function in early MetS.

Molecular control of vascular development in the zebrafish

The zebrafish is emerging as a novel model for the study of embryonic vascular development. In this review we summarize the advantages of this intriguing experimental system and the advances in our understanding of the molecular control of vascular development it has allowed.

Angiopoietin 1 reduces rat follicular atresia mediated by apoptosis through the PI3K/Akt pathway

The aim of this study was to determine the effect of the local inhibition of ANGPT1 on steroid production, proliferation and apoptosis of ovarian follicular cells and on the PI3K/AKT pathway. We also examined the effect of ANGPTs on follicular cell apoptosis and proliferation in early antral follicles (EAFs) in culture. Follicular cells expressing PCNA decreased after ANGPT1 Ab treatment. Moreover, ANGPT1 inhibition increased the levels of active caspase 3 and androsterone, but decreased estradiol, AKT phosphorylation and the area of smooth muscle cell actin. In cultured EAFs from prepubertal rats treated with diethylstilbestrol (DES), ANGPT1 increased PCNA and decreased apoptosis while ANGPT2 reversed these effects. These results show that ANGPT1 alters steroidogenesis, reduces ovarian apoptosis, and stimulates cell proliferation in antral follicles. ANGPT1 may exert these roles by regulating ovarian vascular stability and/or by a direct effect on follicular cells, possibly involving the PI3K/AKT pathway.

Complex spinal-paraspinal fast-flow lesions in CLOVES syndrome: analysis of clinical and imaging findings in 6 patients

CLOVES syndrome is a complex disorder of congenital lipomatous overgrowth, vascular malformations, epidermal nevi, and skeletal/scoliosis/spinal anomalies. We report the occurrence of spinal-paraspinal fast-flow lesions within or adjacent to the truncal overgrowth or a cutaneous birthmark in 6 patients with CLOVES syndrome.

Morphologic characterization of osteosarcoma growth on the chick chorioallantoic membrane

Background

The chick chorio-allantoic membrane (CAM) assay is a commonly used method for studying angiogenic or anti-angiogenic activities in vivo. The ease of access allows direct monitoring of tumour growth by biomicroscopy and the possibility to screen many samples in an inexpensive way. The CAM model provides a powerful tool to study effects of molecules, which interfere with physiological angiogenesis, or experimental tumours derived from cancer cell lines. We therefore screened eight osteosarcoma cell lines for their ability to form vascularized tumours on the CAM.

Findings

We implanted 3-5 million cells of human osteosarcoma lines (HOS, MG63, MNNG-HOS, OST, SAOS, SJSA1, U2OS, ZK58) on the CAM at day 10 of embryonic development. Tumour growth was monitored by in vivo biomicroscopy at different time points and tumours were fixed in paraformaldehyde seven days after cell grafting. The tissue was observed, photographed and selected cases were further analyzed using standard histology.

From the eight cell lines the MNNG-HOS, U2OS and SAOS were able to form solid tumours when grafted on the CAM. The MNNG-HOS tumours showed the most reliable and consistent growth and were able to penetrate the chorionic epithelium, grow in the CAM stroma and induce a strong angiogenic response.

Conclusions

Our results show that the CAM assay is a useful tool for studying osteosarcoma growth. The model provides an excellent alternative to current rodent models and could serve as a preclinical screening assay for anticancer molecules. It might increase the speed and efficacy of the development of new drugs for the treatment of osteosarcoma.

Vascular morphogenesis in the zebrafish embryo

During embryonic development, the vertebrate vasculature is undergoing vast growth and remodeling. Blood vessels can be formed by a wide spectrum of different morphogenetic mechanisms, such as budding, cord hollowing, cell hollowing, cell wrapping and intussusception. Here, we describe the vascular morphogenesis that occurs in the early zebrafish embryo. We discuss the diversity of morphogenetic mechanisms that contribute to vessel assembly, angiogenic sprouting and tube formation in different blood vessels and how some of these complex cell behaviors are regulated by molecular pathways.

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

Tumour angiogenesis: its mechanism and therapeutic implications in malignant gliomas

Angiogenesis is a key event in the progression of malignant gliomas. The presence of microvascular proliferation leads to the histological diagnosis of glioblastoma multiforme. Tumour angiogenesis involves multiple cellular processes including endothelial cell proliferation, migration, reorganisation of extracellular matrix and tube formation. These processes are regulated by numerous pro-angiogenic and anti-angiogenic growth factors. Angiogenesis inhibitors have been developed to interrupt the angiogenic process at the growth factor, receptor tyrosine kinase and intracellular kinase levels. Other anti-angiogenic therapies alter the immune response and endogeneous angiogenesis inhibitor levels. Most anti-angiogenic therapies for malignant gliomas are in Phase I/II trials and only modest efficacies are reported for monotherapies. The greatest potential for angiogenesis inhibitors may lie in their ability to combine safely with chemotherapy and radiotherapy.

Angiogenesis in adipose tissue

Angiogenesis is required for the growth and expansion of both healthy and pathological tissues. The plasticity of the adipose tissue is reflected by its remarkable ability to expand or to reduce in size throughout the adult lifespan. We, and others, have recently shown that expansion of fat mass is dependent on angiogenesis, and suppression of angiogenesis might provide a novel therapeutic approach for prevention and treatment of obesity. Here, we outline two technical procedures for assessment of angiogenesis in adipose tissues.

A review of clinical and molecular prognostic factors in osteosarcoma

Traditional prognostic determinants in osteosarcoma have included demographics (age, sex), tumour size, site, stage, and the response to chemotherapy. Many of these are determined using varying techniques and units of measurement, which can make comparison between studies difficult. The absence of survival difference between limb sparing surgery and amputation has been repeatedly demonstrated in primary disease, and even in the setting of pathological fracture. On the other hand, there is still some controversy over the existence of increased local recurrence for limb-sparing surgery, and the implications of this. Commonly used prognostic determinants such as metastases, and response to chemotherapy enable a high degree of prognostic accuracy but usually at a late stage in the course of disease. Leading on from this, there is a need to uncover molecular pathways with specific influence over osteosarcoma progression to facilitate earlier treatment changes. Some important pathways are already being defined, for example the association of CXCR4 with metastases on presentation, the likelihood of doxorubicin resistance with positive P-glycoprotein, and the reduced survival prediction of over expressed survivin. It is anticipated that the future of osteosarcoma treatment will involve treatment tailored to the molecular profile of tumours at diagnosis, adjuvant therapy directed towards dysfunctional molecular pathways rather than the use of cytotoxics, and a more standardised approach to the measurement of clinical prognostic factors.

Vascularization and Improved In Vivo Survival of VEGF-Secreting Cells Microencapsulated in HEMA-MMA

Vascularization caused by encapsulated cells engineered to secrete vascular endothelial growth factor (VEGF) improved the in vivo survival of the encapsulated cells in a syngeneic mouse Matrigel plug model. Murine fibroblast cells (L929) were engineered to secrete recombinant human vascular endothelial growth factor (rhVEGF(165)). Transfected and nontransfected L929 cells were microencapsulated in a 75:25 hydroxyethyl methacrylate-methyl methacrylate (HEMA-MMA) copolymer. Capsules containing transfected cells induced vascularization in vivo at 1 and 3 weeks postimplantation. In histological sections, a significant positive correlation was seen between the number of capsules and blood vessel density for VEGF-secreting cell capsule implants. New vessels, many positively stained for smooth muscle cells and pericytes, were seen surrounding these VEGF-secreting cell capsule explants. Few vessels were seen in nontransfected L929 capsule implants. The viability of transfected and nontransfected encapsulated cells was assessed on explantation. Although the viability of all encapsulated cells decreased at both 1 and 3 weeks, encapsulated VEGF-secreting cells retained more of the viability than did encapsulated nontransfected control cells. Genetically modified cells promoted vascularization in this context and appeared to enhance the viability of the encapsulated cells, although the extent of the functional benefit was less than expected. Additional effort is required to enhance the benefit, to quantify it, and to understand further the host response to HEMA-MMA microencapsulated cells and tissue constructs, more generally.

Glycine as a potent anti-angiogenic nutrient for tumor growth

Accumulating lines of evidence suggest a possibility that glycine is useful as an immuno-modulating amino acid. Glycine most likely prevents the lipopolysaccharide (LPS)-induced elevation of intracellular Ca(2+) concentration in Kupffer cells, thereby minimizing LPS receptor signaling and cytokine production. Moreover, it was reported that dietary glycine inhibits the growth of tumors. Vascular endothelial growth factor (VEGF) plays a critical role in cancer progression by promoting new blood vessel formation. Activation of VEGF receptor has been shown to result in activation of phospholipase C-gamma and increases in intracellular Ca(2+) concentration. The VEGF-induced cell proliferation is dependent on intracellular Ca(2+) concentration. The effects of glycine on VEGF-induced increases in intracellular Ca(2+) concentration in endothelial cell line (CPA) were studied. The VEGF increased intracellular Ca(2+) concentration rapidly, but glycine blunted increases in intracellular Ca(2+) concentration due to VEGF. Further, the inhibitory effects of glycine were prevented by low concentrations of strychnine (1 micromol/L) or incubation with chloride-free buffer. Moreover, glycine increased influx of radiolabeled chloride into CPA cells approximately 10-fold. Furthermore, mRNA 92% identical to the beta-subunit of the glycine-gated chloride channel from spinal cord was identified in endothelial cells using reverse transcription-polymerase chain reaction. Finally, glycine significantly diminished serum-stimulated proliferation and migration of endothelial cells. These data indicate that the inhibitory effect of glycine on growth and migration of endothelial cells is due to activation of a glycine-gated chloride channel. This hyperpolarizes the cell membrane and blocks influx of Ca(2+), thereby minimizing growth factor-mediated signaling. Therefore, glycine can be used not only for treatment of inflammation, but also for chemoprevention and treatment of carcinoma.

Spackling the crack: stabilizing human fibroblast growth factor-1 by targeting the N and C terminus beta-strand interactions

The beta-trefoil protein human fibroblast growth factor-1 (FGF-1) is made up of a six-stranded antiparallel beta-barrel closed off on one end by three beta-hairpins, thus exhibiting a 3-fold axis of structural symmetry. The N and C terminus beta-strands hydrogen bond to each other and their interaction is postulated from both NMR and X-ray structure data to be important in folding and stability. Specific mutations within the adjacent N and C terminus beta-strands of FGF-1 are shown to provide a substantial increase in stability. This increase is largely correlated with an increased folding rate constant, and with a smaller but significant decrease in the unfolding rate constant. A series of stabilizing mutations are subsequently combined and result in a doubling of the DeltaG value of unfolding. When taken in the context of previous studies of stabilizing mutations, the results indicate that although FGF-1 is known for generally poor thermal stability, the beta-trefoil architecture appears capable of substantial thermal stability. Targeting stabilizing mutations within the N and C terminus beta-strand interactions of a beta-barrel architecture may be a generally useful approach to increase protein stability. Such stabilized mutations of FGF-1 are shown to exhibit significant increases in effective mitogenic potency, and may prove useful as "second generation" forms of FGF-1 for application in angiogenic therapy.

Induction of directional sprouting angiogenesis by matrix gradients

The fate of any tissue engineering implant relies upon an adequate oxygen and nutrients supply throughout the cellular construct and, hence, by the ability of the scaffold to induce and guide vascular ingrowth. However, implant vascularization is usually an uncontrolled process that takes several weeks. In this work, we assessed the feasibility of controlling vascular sprout rate and direction within three-dimensional collagen-hyaluronic acid semi-interpenetrated networks by modulating the spatial distribution of the matricellular cues. Results indicated that increasing amount of hyaluronic acid (HA) within the matrix led to a progressive inhibition of sprouting. In HA-rich matrices, the sprout number and the propagation rate showed a 2.7- and 4-fold reduction, respectively, compared to collagen matrices. Furthermore, by creating HA gradients within the collagen network, we were able to direct and enhance the sprouting rate. This study provides an experimental platform for controlling vascularization of engineered tissues.

Intratumoral VEGF and FGF1 administration alters tumor growth, vascular density, oxygenation, and expression of MCP-1 and interleukins

The biological and physiological effects of exogenous FGF 1 and VEGF were measured using the KHT murine fibrosarcoma tumor model. Tumor-bearing C3H mice were treated intratumorally with either one or six daily doses of 6 microg/mouse FGF1, VEGF, or saline. Tumors were excised 24 hrs after the final injection. Compared to controls, only FGF1 treatment significantly increased tumor weight and size, and only in the 6 dose group. Both FGF1 and VEGF administration (6 dose) decreased tumor cell hypoxia as detected by EF5 uptake: 85% +/- 5% for FGF1 and 82% +/- 6% for VEGF versus 100% +/- 6% for controls. Decreased tumor cell EF5 staining, however, was not associated with changes in numbers of structural or angiogenic vessels. DiOC7 staining showed a slight decrease in perfused vessel numbers in tumors treated with daily VEGF. Intratumoral injections of FGF1 or VEGF also slightly decreased the tumor tissue chemokine MCP-1, interleukins (IL-1beta, IL-6, and IL-18) mRNA expression, and increased NFkappaB binding without altering Ap-1 binding of IkappaB protein expression. In summary, single pulse exposures of tumors to angiogenic factors had little or no effects on tumor growth or perfusion, while daily exposures stimulated tumor growth through improved tumor oxygenation. This improved vascular function occurs without an increase in vascular density.

Pathophysiology of acute wound healing

Wound healing is a complex process that can be divided into at least 3 continuous and overlapping processes: an inflammatory reaction, a proliferative process leading to tissue restoration, and, eventually, tissue remodeling. Wound healing processes are strictly regulated by multiple growth factors and cytokines released at the wound site. Although the desirable final result of coordinated healing would be the formation of tissue with a similar structure and comparable functions as with intact skin, regeneration is uncommon (with notable exceptions such as early fetal healing); healing however results in a structurally and functionally satisfactory but not identical outcome. Alterations that disrupt controlled healing processes would extend tissue damage and repair. The pathobiologic states may lead to chronic or nonhealing wounds or excessive fibrosis.

Recombined DNA vaccines encoding calreticulin linked to HPV6bE7 enhance immune response and inhibit angiogenic activity in B16 melanoma mouse model expressing HPV 6bE7 antigen

Calreticulin (CRT) has been reported to have an effect of upregulating MHC class I presentation as well as inhibiting angiogenesis in vitro and in vivo. Combination of dual mechanisms of enhanced immunogenicity of human papillomavirus (HPV) 6bE7 antigen and antiangiogenesis may be introduced in the strategy of vaccines against condyloma acuminatum (CA) resulting from HPV infection. Therefore, we constructed DNA vaccines by employing different lengths of CRT chimerically linked to a model antigen HPV6bE7 and investigated the immunological and antiangiogenic effects of these vaccines in a B16 melanoma model that express HPV6bE7 antigen. Our results showed that vaccination with CRT180/HPV6bE7 or CRT120/HPV6bE7 enhanced the presence of CD8(+) T cells and TCRgammadelta T cells in vivo, increased the specific lysis activity against E7-expressing cells and secretion levels of IL-2 and IFN-gamma by activating T cells in vitro significantly. Moreover, recombined CRT180 or CRT120 with HPV6bE7 vaccines could elicit a more efficient E7-specific immune response than HPV6bE7 alone. The similarity of immunological enhancement of CRT180/HPV6bE7 and CRT120/HPV6bE7 implies that the immunologically active region mainly exist in fragment 1-120 aa. Furthermore, CRT180/HPV6bE7 and CRT180 displayed remarkable superiority over CRT120/HPV6bE7 in vivo angiogenesis assay, suggesting that the antiangiogenic activity of CRT resides in a domain between aa 120 and 180. Vaccination with CRT180/HPV6bE7 generated the best protective effect of delaying tumor formation and reduction of tumor size in tumor growth inhibition experiment among all DNA constructs. Therefore, CRT180/HPV6bE7 vaccine may enhance the immunological response to HPV6bE7 and inhibit angiogenesis. This construct may be useful in preventing HPV-associated dermatosis and may be developed as a promising strategy to control CA.

Current and future pharmacological intervention for diabetic retinopathy

Diabetic retinopathy (DR) is a potentially visually devastating complication of chronic hyperglycaemia. Prospective, randomised clinical trials have delineated the standard prevention protocols, including intensive glycaemic, blood pressure, and lipid control, and laser photocoagulation treatment for neovascularisation and clinically significant macular oedema. However, despite these interventions, vision loss from DR still occurs at an alarming rate. Researchers have directed their efforts towards better understanding the specific biological and chemical changes occurring in DR to develop more targeted pharmacological prevention and treatment strategies. This review of diabetic retinopathy will primarily detail the therapies in development at present, including aldose reductase inhibitors, advanced glycosylation end product inhibitors, antioxidants, supplemental oxygen, growth factor modulators including vascular endothelial growth factor inhibitors and protein kinase C inhibitors, extracellular matrix modifiers including corticosteroids, and vitreous modulators. The experimental therapies alter several different pathways that lead to DR. Future research will further delineate these pathways, and therapy is likely to involve arresting several different promoters of DR.

The influence of fluid shear stress on the remodeling of the embryonic primary capillary plexus

The primary capillary plexus in early yolk sacs is remodeled into matured vitelline vessels aligned in the direction of blood flow at the onset of cardiac contraction. We hypothesized that the influence of fluid shear stress on cellular behaviors may be an underlying mechanism by which some existing capillary channels remain open while others are closed during remodeling. Using a recently developed E-Tmod knock-out/lacZ knock-in mouse model, we showed that erythroblasts exhibited rheological properties similar to those of a viscous cell suspension. In contrast, the non-erythroblast (NE) cells, which attach among themselves within the yolk sac, are capable of lamellipodia extension and cell migration. Isolated NE cells in a parallel-plate flow chamber exposed to fluid shear stress, however, ceased lamellipodia extension. Such response may minimize NE cell migration into domains exposed to fluid shear stress. A two-dimensional mathematical model incorporating these cellular behaviors demonstrated that shear stress created by the blood flow initiated by the embryonic heart contraction might be needed for the remodeling of primary capillary plexus.

Pigment epithelium-derived factor (PEDF)-induced apoptosis and inhibition of vascular endothelial growth factor (VEGF) expression in MG63 human osteosarcoma cells

Pigment epithelium-derived factor (PEDF) has been shown to be the most potent inhibitor of angiogenesis in the mammalian eye, thus suggesting that loss of PEDF is involved in angiogenic eye diseases such as proliferative diabetic retinopathy. Angiogenesis is required for tumor growth and progression as well. We, along with others, have recently found that PEDF could inhibit growth of melanoma and hepatocellular carcinoma in nude mice through its anti-angiogenic effects on tumor endothelial cells. However, the possibility of the direct effect of PEDF on tumor cells has remained. In this study, we investigated the effects of PEDF on growth and vascular endothelial growth factor (VEGF) expression in MG63 human cultured osteosarcoma cells. PEDF decreased viable cell number as well as DNA synthesis in MG63 cells in a dose-dependent manner. Furthermore, PEDF was found to increase caspase-3/7 activity and to subsequently induce apoptotic cell death in MG63 cells. PEDF also inhibited VEGF expression in MG63 cells at both mRNA and protein levels. Our present study provides novel beneficial aspects of PEDF on osteosarcoma cells; one is induction of apoptotic cell death of tumor cells, and the other is the suppression of VEGF expression, which would lead to inhibition of tumor angiogenesis. PEDF therefore might be a promising therapeutic agent for treatment of patients with osteosarcoma.

Modulation of tumor endothelial cell marker 7 expression during endothelial cell capillary morphogenesis

Angiogenesis, the process of new blood vessel formation from preexisting capillaries, is a multistep process. The principle cell type in this process is endothelial cells which are required to undergo proliferation, migration, differentiation, and coalescence into cord-like structures with a central lumen. However, the molecular and cellular mechanisms that regulate this process require further investigation. In this study, we have used the fibrin/fibrinogen-based three-dimensional culture to enrich for primary cultured mouse aortic endothelial cells, and to induce endothelial cell capillary morphogenesis. We found among all the cell surface markers examined that only TEM7 expression was up-regulated upon endothelial cells capillary morphogenesis. In addition, inhibition of capillary morphogenesis by serum stimulation completely blocked TEM7 expression. In contrast, stimulation of endothelial cell capillary morphogenesis with PMA enhanced TEM7 expression. Furthermore, incubation of endothelial cells with a recombinant extracellular domain of TEM7 blocked capillary morphogenesis in three-dimensional cultures. These results suggest that TEM7 is a novel protein whose cell surface expression is essential during endothelial cell capillary morphogenesis.

IQGAP1 regulates reactive oxygen species-dependent endothelial cell migration through interacting with Nox2

OBJECTIVE

Endothelial cell (EC) migration is a key event for repair process after vascular injury and angiogenesis. EC migration is regulated by reorganization of the actin cytoskeleton at the leading edge and localized production of reactive oxygen species (ROS) at the site of injury. However, underlying mechanisms are unclear. We reported that IQGAP1, an actin binding scaffold protein, mediates VEGF-induced activation of gp91phox (Nox2)-dependent NAD(P)H oxidase and EC migration. We thus hypothesized that Nox2 and IQGAP1 may play important roles in ROS-dependent EC migration in response to injury.

METHODS AND RESULTS

Using a monolayer scratch assay with confluent ECs, we show that ROS production is increased at the margin of scratch area and Nox2 translocates to the leading edge, where it colocalizes and associates with both actin and IQGAP1 in migrating ECs. Knockdown of IQGAP1 using siRNA and inhibition of the actin cytoskeleton blocked scratch injury-induced H2O2 production, Nox2 translocation and its interaction with actin, and EC migration toward the injured site.

CONCLUSIONS

These suggest that IQGAP1 may function to link Nox2 to actin at the leading edge, thereby facilitating ROS production at the site of injury, which may contribute to EC migration.

Blood and lymph vessels in embryonic tumors

Formation of embryonic blood and lymph vessels is mediated by different steps of vasculogenesis and angiogenesis. The vascular endothelial growth factor family (VEGF) as well as the VEGF-receptors on the surface of blood endothelial cells and lymph endothelial cells are responsible for both processes. In addition to the embryonic development of the vessel systems, the interactions of angiogenesis factors and receptors are also present in solid tumors. Embryonic tumors in children offer an interesting target for new substances developed for anti-angiogenesis. Some data on the role of blood vessels and anti-blood-angiogenesis are available on embryonic tumors. However, studies of lymph-angiogenesis are not found and anti-lymph-angiogenesis is not at all examined in embryonic tumors. This review gives an overview of the challenging field of angiogenesis and anti-angiogenesis of both blood and lymph vessels with a focus on embryonic tumors.