Intussusceptive lymphangiogenesis in vascular transformation of lymph node sinuses

Numerous lymphatic anastomosing channels in the lymph nodes are the most demonstrative finding of the rare lesion termed “vascular transformation of lymph node sinuses” (VTS). The mechanism of lymphatic vessel formation in VTS has not been studied. Vessel intussusception contributes to vascular expansion, and intraluminal pillars/posts, interstitial tissue structures or larger pillars (ITSs) and folds are the hallmarks of this process in blood vessels. The aim of this work is to assess whether these hallmarks of intussusception occur in VTS lymphatic vessels, indicating intussusceptive lymphangiogenesis. For this purpose, specimens of five cases of VTS were used for serial histological sections, immunohistochemistry and immunofluorescence in confocal microscopy, which enabled us to demonstrate the 3D image that defines the pillars. The studies showed a) meshworks of lymphatic vessels, which form complex loops, resembling sinuses of lymph nodes, b) presence of intralymphatic pillars, ITSs and folds, with a cover of lymphatic endothelial cells expressing podoplanin and a varying-sized connective core (e.g. collagen), and c) increase of vessel meshwork and linear arrangement, splitting and fusion of ITSs, pillars and folds, with remodelling and segmentation. In conclusion, the development of lymphatic vessel loops, ITSs, pillars and folds with segmentation in VTS supports intussusceptive lymphangiogenesis. This mechanism of intussusception is of interest because it participates in VTS histogenesis, contributes to general knowledge of intussusceptive lymphangiogenesis, which has received less attention than intussusception in blood vessels, and provides a basis for further studies in other lymphatic conditions.     

THE ROLE OF VASCULAR ENDOTHELIAL GROWTH FACTOR IN A MURINE CHRONIC GRANULOMATOUS TISSUE AIR POUCH MODEL OF ANGIOGENESIS

Chronic granulomatous inflammation may be considered an angiogenic-dependent process. Recently it has been demonstrated that vascular endothelial growth factor (VEGF) or vascular permeability factor is essential for tumour angiogenesis. Its role in inflammation-mediated angiogenesis has yet to be determined. In this study, the murine chronic granulomatous air pouch model was used to investigate the role of VEGF in angiogenesis. Animals were treated twice weekly with 10 μ g per animal of neutralizing antibody to rh VEGF and the vascularity and granuloma dry weight were assessed after 7 days. This resulted in significant suppression of both angiogenesis and granuloma dry weight. Western blot analysis demonstrated the presence of VEGF; the levels of protein paralleled the angiogenic response. These results demonstrate for the first time that VEGF may be an important regulator of angiogenesis in inflammation.     

A new mechanism for pillar formation during tumor-induced intussusceptive angiogenesis: inverse sprouting

One of the hallmarks of intussusceptive angiogenesis is the development of intraluminal connective tissue pillars. The exact mechanism of pillar formation has not yet been elucidated. By using electron and confocal microscopy, we observed intraluminal nascent pillars that contain a collagen bundle covered by endothelial cells (ECs) in the vasculature of experimental tumors. We proposed a new mechanism for the development of these pillars. First, intraluminal endothelial bridges are formed. Second, localized dissolution of the basement membrane occurs and a bridging EC attaches to a collagen bundle in the underlying connective tissue. A pulling force is then exerted by the actin cytoskeleton of the ECs via specific attachment points, which contain vinculin, to the collagen bundle, resulting in suction and subsequent transport of the collagen bundle into and through the vessel lumen. Third, the pillar matures through the immigration of connective tissue cells and the deposition of new collagenous connective tissue. The proposed simple mechanism generates a connection between the processes of endothelial bridging and intussusceptive angiogenesis and identifies the source of the force behind pillar formation. Moreover, it ensures the rapid formation of pillars from pre-existing building blocks and the maintenance of EC polarity. To describe it, we coined the term inverse sprouting.     

Intussusceptive microvascular growth in human glioma

Intussusceptive microvascular growth (IMG), which occurs by splitting of the existing vasculature by transluminal pillars or transendothelial bridges, has been demonstrated in several tumors such as colon and mammary carcinomas, melanoma and B-cell non-Hodgkin’s lymphomas. In this study, we have correlated in human glioma the extent of angiogenesis, evaluated as microvascular density, the immunoreactivity of tumor cells to vascular endothelial growth factor (VEGF), vessel diameter and IMG to the tumor stage. Results demonstrate for the first time a relationship in human glioma progression between angiogenesis, VEGF immunoreactivity of tumor cells, vessel diameter and the number of connections of intraluminal tissue folds with the opposite vascular wall, expression of IMG and suggest that IMG could be a mechanism of compensatory vascular growth occurring in human glioma. The advantages are that (1) blood vessels are generated more rapidly; (2) it is energetically and metabolically more economic; (3) the capillaries thereby formed are less leaky.     

体外仿生三维血管生成微流控芯片的构建

目的在微流控芯片上构建模拟人体血管的三维血管管道,实现管道间的物质交换,并形成有自主出芽功能的血管,为血管生成相关的疾病机制研究、药物筛选等提供良好的平台工具。方法利用微流控技术,采用被动进样方式,使人体脐静脉内皮细胞(human umbilical vein endothelial cells,HUVEC)在微流控芯片上自主贴壁生长形成三维血管管腔,构建体外仿生三维单管道血管和双管道血管芯片。在此基础上,开展对血管响应刺激因子出芽的功能的验证实验。结果体外仿生的双管道芯片的构建成功率达80%以上。在血管管道,内皮细胞无需借助外力支撑,在芯片上自主形成直径300μm±50μm,细胞分布均匀的、类似体内血管的三维血管管腔;物质通过模拟体内的扩散过程达到血管管道,使血管管腔响应物质刺激而出现功能性的血管出芽。结论体外仿生三维血管微流控芯片在体外实现了体内血管的结构与功能,模拟了体内物质扩散对血管生成的影响,可以用于生理过程中血管生成的体外动态观察。     

Intussusceptive angiogenesis: its emergence, its characteristics, and its significance.

This review shall familiarize the reader with the various aspects of intussusceptive angiogenesis (IA). The basic event in IA is the formation of transvascular tissue pillars. Depending on location, timing, and frequency of pillar emergence, the IA process has different outcomes. In capillaries, a primary IA function is to expand the capillary bed in size and complexity (intussusceptive microvascular growth). It represents an alternative to capillary sprouting. Highly ordered pillar formation in a developing capillary network leads to the formation of vascular trees (intussusceptive arborization). In small arteries and veins, pillar formation at the vessels' branching angles leads either to remodeling of the branching geometry or even to vascular pruning (intussusceptive branching remodeling). It appears essential that future angiogenic research considers always both phenomena, sprouting and intussusception. Vascularization of tissues, organs, and tumors rely heavily on both mechanisms; neglecting one or the other would obscure our understanding of the angiogenesis process.     

Inflammation‐Induced Intussusceptive Angiogenesis in Murine Colitis

Intussusceptive angiogenesis is a morphogenetic process that forms new blood vessels by the division of a single blood vessel into two lumens. Here, we show that this process of intraluminal division participates in the inflammation‐induced neovascularization associated with chemically induced murine colitis. In studies of both acute (4–7 days) and chronic (28–31 days) colitis, intravital microscopy of intravascular tracers demonstrated a twofold reduction in blood flow velocity. In the acute colitis model, the decreased velocity was associated with marked dilatation of the mucosal plexus. In contrast, chronic inflammation was associated with normal caliber vessels and duplication (and triplication) of the quasi‐polygonal mucosal plexus. Scanning electron microscopy (SEM) of intravascular corrosion casts suggested that pillar formation and septation, previously linked to the morphogenetic process of intussusceptive angiogenesis, were present within days of the onset of inflammation. Four weeks after the onset of inflammation, SEM of vascular corrosion casts demonstrated replication of the mucosal plexus without significant evidence of sprouting angiogenesis. These data suggest that mucosal capillaries have comparable aggregate cross‐sectional area in acute and chronic colitis; however, there is a significant increase in functional capillary density in chronic colitis. We conclude that intussusceptive angiogenesis is a fundamental mechanism of microvascular adaptation to prolonged inflammation. Anat Rec, 2010. © 2010 Wiley‐Liss, Inc.     

Pre-hatch lung development in the ostrich

We studied development of the ostrich lung using light microscopy as well as electron microscopy techniques. At E24, the lung comprised a few epithelial tubes, interspersed with abundant mesenchyme with scattered profiles of incipient blood vessels. Between E24 and E39, the epithelial thickness was reduced by 90% from 13.5 ± 0.41 μm to 1.33 ± 0.014 μm (mean ± SD, respectively). Atria were evident at E32, and by E35, the first portions of the blood-gas barrier (BGB) measuring 3.41 ± 1.12 μm were encountered. Gas exchange tissue was well formed by E39 with atria, infundibulae, air capillaries and a mature blood-gas barrier (BGB). BGB formation proceeded through the complex processes of secarecytosis and peremerecytosis, which entailed decapitation of epithelial cells by cutting or pinching off respectively and by E39, the BGB was thin at 2.21 ± 1.21 μm. Vascular remodeling by intussusceptive angiogenesis was a late stage process mediated by intraluminal pillars in the pulmonary vasculature.     

Ultrastructural changes in blood vessels in epidermal growth factor treated experimental cutaneous wound model

This study investigates the impact of epidermal growth factor (EGF) on blood vessels, specifically on the development of intussusceptive angiogenesis in cutaneous wound healing. Excisional wounds were formed on both sides of the medulla spinalis in dorsal location of the rats. The control and EGF-treated groups were divided into two groups with respect to sacrifice day: 5 d and 7 d. EGF was topically applied to the EGF-treated group once a day. The wound tissue was removed from rats, embedded in araldite and paraffin, and then examined under transmission electron and light microscopes. The ultrastructural signs of intussusceptive angiogenesis, such as intraluminal protrusion of endothelial cells and formation of the contact zone of opposite endothelial cells, were observed in the wound. Our statistical analyses, based on light microscopy observations, also confirm that EGF treatment induces intussusceptive angiogenesis. Moreover, we found that induction of EGF impact on intussusceptive angiogenesis is higher on the 7th day of treatment than on the 5th day. This implies that the duration of EGF treatment is important. This research clarifies the effects of EGF on the vessels and proves that EGF induces intussusceptive angiogenesis, being a newer model with respect to sprouting type.     

Intravascular pillars and pruning in the extraembryonic vessels of chick embryos

To investigate the local mechanical forces associated with intravascular pillars and vessel pruning, we studied the conducting vessels in the extraembryonic circulation of the chick embryo. During the development days 13–17, intravascular pillars and blood flow parameters were identified using fluorescent vascular tracers and digital time‐series video reconstructions. The geometry of selected vessels was confirmed by corrosion casting and scanning electron microscopy. Computational simulations of pruning vessels suggested that serial pillars form along pre‐existing velocity streamlines; blood pressure demonstrated no obvious spatial relationship with the intravascular pillars. Modeling a Reynolds number of 0.03 produced 4 pillars at approximately 20‐μm intervals matching the observed periodicity. In contrast, a Reynolds number of 0.06 produced only 2 pillars at approximately 63‐μm intervals. Our modeling data indicated that the combination of wall shear stress and gradient of shear predicted the location, direction, and periodicity of developing pillars. Developmental Dynamics 240:1335–1343, 2011. © 2011 Wiley‐Liss, Inc.     

The phenotype of the human materno-fetal endothelial barrier: molecular occupancy of paracellular junctions dictate permeability and angiogenic plasticity

In vitro models predict that molecular occupancy of endothelial junctions may regulate both barrier function and angiogenesis. Whether this is true in human vascular beds undergoing physiological angiogenesis has not been shown. This review presents data which demonstrate there are two distinct junctional phenotypes, 'activated' and 'stable', present in the vascular tree of the human placenta taken from two distinct highly angiogenic gestational periods (first and last trimester). Stability is conferred by the presence of occludin in tight junctions and plakoglobin in adherens junctions. Their localization may be influenced by vascular endothelial growth factor and angiopoietins 1 and 2 that have a similar temporal and site-specific differential expression. The junctional phenotypes are reversible, as shown in studies with endothelial cells isolated from placental microvessels and grown in the presence/absence of cAMP-enhancing agents. Reductions in protein levels and loss of junctional localization of adhesion molecules result in increased permeability to macromolecules, whilst up-regulation and re-targeting of these molecules inhibit cell proliferation and increase transendothelial resistance. These studies suggest junctional adhesion molecules can regulate physiological angiogenesis and vascular re-modelling. Moreover, the activated junctional phenotype of placental microvessels allows them to participate in increased growth and proliferation. This junctional immaturity appears to be at the expense of barrier function resulting in sites of maximal materno-fetal solute exchange.     

Vascular system of intramural leiomyomata revealed by corrosion casting and scanning electron microscopy

BACKGROUND: The vascular system of leiomyomata, the most common benign tumours in women, is an important factor controlling development and growth of the tumour. It has not been, however, investigated morphologically using the best currently available technique, corrosion casting combined with scanning electron microscopy. METHODS: Myomatous uteri collected upon autopsy were perfused via afferent vessels with fixative followed by Mercox resin and corroded after polymerization of the resin. The obtained vascular casts visualizing all vessels including capillaries were examined using scanning electron microscopy. RESULTS: The smallest (1-3 mm) fibroids were avascular, in larger ones (<1 cm) a few small vessels invaded the lesion from the periphery. The largest tumours (>1 cm) contained irregular networks of blood vessels with density similar to or lower than that of normal myometrium. Such tumours were surrounded by an extremely dense vascular layer ('vascular capsule') which was the source of larger vessels supplying and draining the tumour. CONCLUSIONS: During development of leiomyoma, the pre-existing blood vessels undergo regression and new vessels invade the tumour from the periphery, where intense angiogenesis, probably promoted by growth factors secreted by the tumour, leads to the formation of a 'vascular capsule' responsible for supply of blood to the growing tumour.     

Hemodynamic Changes in Splanchnic Blood Vessels in Portal Hypertension

Portal hypertension (PHT) is associated with a hyperdynamic state characterized by a high cardiac output, increased total blood volume, and a decreased splanchnic vascular resistance. This splanchnic vasodilation is a result of an important increase in local and systemic vasodilators (nitric oxide, carbon monoxide, prostacyclin, endocannabinoids, and so on), the presence of a splanchnic vascular hyporesponsiveness toward vasoconstrictors, and the development of mesenteric angiogenesis. All these mechanisms will be discussed in this review. To decompress the portal circulation in PHT, portosystemic collaterals will develop. The presence of these portosystemic shunts are responsible for major complications of PHT, namely bleeding from gastrointestinal varices, encephalopathy, and sepsis. Until recently, it was accepted that the formation of collaterals was due to opening of preexisting vascular channels, however, recent data suggest also the role of vascular remodeling and angiogenesis. These points are also discussed in detail. Anat Rec, 291:699–713, 2008. © 2008 Wiley‐Liss, Inc.     

水通道蛋白与肿瘤血管新生

肿瘤血管新生对于肿瘤的生长具有重要作用。水通道蛋白在肿瘤组织中常出现表达异常，并且可以促进肿瘤血管的新生及包括肿瘤血管内皮在内的多种细胞的迁移，与此同时，水通道蛋白与肿瘤血管的高通透性有关，这可能是肿瘤组织对水通道蛋白缺失具有较高敏感性的原因。鉴于水通道蛋白对于肿瘤特别是肿瘤血管新生的影响，其抑制剂可能成为新的肿瘤治疗的目标靶点。     

The vasculature in rheumatoid arthritis: cause or consequence?

The expansion of the synovial lining of joints in rheumatoid arthritis (RA) necessitates an increase in the vascular supply to the synovium, to cope with the increased requirement for oxygen and nutrients. New blood vessel formation –'angiogenesis'– is recognized as a key event in the formation and maintenance of the pannus in RA, suggesting that targeting blood vessels in RA may be an effective future therapeutic strategy. Although many pro-angiogenic factors have been demonstrated to be expressed in RA synovium, vascular endothelial growth factor (VEGF) has been demonstrated to a have a central involvement in the angiogenic process in RA. Nevertheless, it is unclear whether angiogenesis – whether driven by VEGF and/or other factors – should be considered as a 'cause' or 'consequence' of disease. This ongoing 'chicken vs. egg' debate is difficult, as even the success of angiogenesis inhibition in models of RA does not provide a direct answer to the question. This review will focus on the role of the vasculature in RA, and the contribution of different angiogenic factors in promoting disease. Although no data regarding the effectiveness of anti-angiogenic therapy in RA have been reported to date, the blockade of angiogenesis nevertheless looks to be a promising therapeutic avenue.     

Vascularization of rat pituitary autografts

Pituitary autotransplantation eliminates direct vascular contact between the hypothalamus and the adenohypophysis, and enables us to study the role of the hypothalamus in regulating adenohypophysial endocrine activity. The aim of this study was to investigate vascularization of the pituitary autografts. Three-month-old male Wistar rats were hypophysectomized, and their adenohypophyses were autotransplanted under the renal capsule. The animals were killed 3 weeks after autotransplantation. The grafts were removed and studied by using histology, immunohistochemistry and transmission electron microscopy. In the central portion of the grafts, organizing necrosis was apparent. The peripheral portion of the graft contained all adenohypophysial cell types, with a predominance of lactotrophs. Vascular endothelial growth factor and hypoxia-inducible factor were expressed in the graft mainly in the perinecrotic areas. Several capillaries inside the grafts were lined by continuous unfenestrated epithelium, while others were lined by fenestrated endothelium, suggesting that neovascularization is the result of two processes: ingrowths of capillaries from the renal capsule to the graft, and neoformation of capillaries from pre-existing adenohypophysial vessels. In conclusion, hypoxia seems to be an important factor in the vascularization of pituitary autografts. Mediated via hypoxia-inducible factor, hypoxia stimulates vascular endothelial growth factor secretion, which plays a crucial role in angiogenesis.     

Angiogenesis dependent characteristics of tumor observed on rabbit VX2 hepatic carcinoma

Objective: To evaluate angiogenesis dependent characteristics of carcinoma proliferation, metastasis and to found if there is tumor vascularity architecture defect. Methods: 36 rabbits were random divided into 2 groups: Experimental group: 18 rabbits liver were implanted with VX₂ tumor by surgery operation; Control group: 18 experimental rabbits performed the same surgery operation without tumor implantation, the course of tumor growth and blood vessel invasion was observed by autopsy. One slide was used for hematoxylin-eosin (HE) staining, one slide was used for elastic fiber staining by Victoria blue and Ponceau’s histochemical staining, and one slide was used for vascular endothelial cell immunohistochemical staining with biotinylated-ulex europaeus agglutinin I (UEA I); all three slides were observed under an optical microscopic. One additional slide was systematically observed by electron microscopy. SPSS 19.0 software was used for the statistical analyses of the data. Results: The tumor grew acceleration after tumor angiogenesis, volume of original tumors was correlated with vascular caliber. The central tumor found necrosis without enough blood supply while tumor grew rapidly after tumor angiogenesis. The tumor infiltrated into liver blood sinus, blood vessels in hepatic interstitial tissue, the liver capsular vein and important organs metastasis such as lungs, kidneys, abdominal cavity caused rabbits died. The average vascular density count of 18 experimental rabbits under 400 times light microscope were 43.17 ± 8.68/vessels/High Power Field; Tumor vascular diameter all within 200 μm. Vascular elastic fiber staining presented tumor blood vessels internal, external elastic plate intact, vascular endothelial cells organelles of tumor were integrity without endothelial cells architecture defect found by pathologic observation. Conclusion: Proliferation and metastasis of rabbit VX₂ hepatic carcinoma was correlated with tumor angiogenesis and no tumor vascular architecture defect was found by pathologic observation, it need further exploration by other methods.     

Tenascin-C Expression in Ultrastructurally Defined Angiogenic and Vasculogenic Lesions

Tenascin-C (TN) is an extracellular matrix glycoprotein expressed during embryogenesis. Its distribution is restricted in normal adult tissues and is upregulated in tumors and inflammatory conditions. Twenty-five specimens were studied, including 7 reactive vascular lesions (6 cases of granulation tissue and 1 case of bacillary angiomatosis), and 18 vascular tumors (6 angiosarcomas, 7 hemangioendotheliomas, and 5 AIDS-related nodular type Kaposi's sarcomas). Formalin fixed-paraffin-embedded tissues were stained with monoclonal antibody to TN (DAKO) and with MIB-1 (AMAC). Heterogeneous expression of TN immunoreactivity was seen in all cases, with a diffuse pattern in bacillary angiomatosis and most granulation tissue cases and a focal pattern in angiosarcoma and most hemangioendothelioma cases. Kaposi's sarcoma cases showed both a focal and diffuse pattern of distribution. In most cases proliferation indices (PI) did not correlate with TN expression. Electron microscopy demonstrated active angiogenesis in bacillary angiomatosis and granulation tissue and vasculogenesis in angiosarcoma and hemangioendothelioma. The study demonstrated positive TN expression in reactive lesions with angiogenesis (granulation tissue and bacillary angiomatosis) and neoplastic lesions showing vasculogenesis (angiosarcoma and hemangioendothelioma), although with a different pattern of distribution. These results suggest that TN might be an important extracellular matrix glycoprotein in angiogenesis and vasculogenesis.     

Aquaporin‐1 expression in the chick embryo chorioallantoic membrane

The chick embryo chorioallantoic membrane (CAM) is commonly used in vivo to study both angiogenesis and anti‐angiogenesis. Rapid membrane water transport is mediated by a family of molecular water channels, called aquaporins (AQPs), which have been identified in the epithelial and endothelial cells of higher vertebrates. AQP1, expressed in adsorptive and secretory epithelia, is also expressed in endothelial cells of capillaries and arteries. Its mRNA has been found in vascular smooth muscle cells (VSMCs) of arteries and capillaries, as well as in a subset of VSMCs of human atherosclerotic plaques. This study investigated the developmental expression of AQP1 in the chick CAM by Western blot and immunohistochemistry. Western blot results show that a major nonglycosylated band was observed with electrophoretic mobility of approximately 28 kDa in the three developmental stages examined. Immunohistochemistry data demonstrate that AQP1 was clearly expressed in the ectodermal and endodermal epithelia, the vascular endothelium, and the VSMCs. Because little information is available on the behavior of microvessel AQP1 during angiogenesis in normal and pathological conditions, our data relative to the pattern of expression of AQP1 in CAM blood vessels in normal conditions may be considered a useful tool to further investigate its modifications in several experimental conditions implying a stimulation or an inhibition of angiogenesis in the CAM assay. Anat Rec 268:85–89, 2002. © 2002 Wiley‐Liss, Inc.