Cell-cell interactions in vascular development

Human iPSC-derived mesodermal progenitor cells preserve their vasculogenesis potential after extrusion and form hierarchically organized blood vessels

Post-fabrication formation of a proper vasculature remains an unresolved challenge in bioprinting. Established strategies focus on the supply of the fabricated structure with nutrients and oxygen and either rely on the mere formation of a channel system using fugitive inks or additionally use mature endothelial cells and/or peri-endothelial cells such as smooth muscle cells for the formation of blood vesselsin vitro.Functional vessels, however, exhibit a hierarchical organization and multilayered wall structure that is important for their function. Human induced pluripotent stem cell-derived mesodermal progenitor cells (hiMPCs) have been shown to possess the capacity to form blood vesselsin vitro, but have so far not been assessed for their applicability in bioprinting processes. Here, we demonstrate that hiMPCs, after formulation into an alginate/collagen type I bioink and subsequent extrusion, retain their ability to give rise to the formation of complex vessels that display a hierarchical network in a process that mimics the embryonic steps of vessel formation during vasculogenesis. Histological evaluations at different time points of extrusion revealed the initial formation of spheres, followed by lumen formation and further structural maturation as evidenced by building a multilayered vessel wall and a vascular network. These findings are supported by immunostainings for endothelial and peri-endothelial cell markers as well as electron microscopic analyses at the ultrastructural level. Moreover, endothelial cells in capillary-like vessel structures deposited a basement membrane-like matrix at the basal side between the vessel wall and the alginate-collagen matrix. After transplantation of the printed constructs into the chicken chorioallantoic membrane (CAM) the printed vessels connected to the CAM blood vessels and get perfusedin vivo. These results evidence the applicability and great potential of hiMPCs for the bioprinting of vascular structures mimicking the basic morphogenetic steps ofde novovessel formation during embryogenesis.

In-depth bioinformatic study of the cadherin 5 interactome in patients with thoracic aortic aneurysm unveils 8 novel biomarkers

OBJECTIVES

Thoracic aortic aneurysm (TAA) is characterized by the dilation of the aorta and is associated with poor prognosis if not diagnosed and treated early. In this context, the identification of biomarkers regarding the TAA diagnosis, monitoring and prognosis is crucial. The purpose of the current study was to investigate the differential gene expression profile of the cadherin 5 (CDH5 or VE-Cadherin) gene network in patients with TAA, to propose novel biomarkers.

METHODS

In silico techniques were used to construct the interactome of the CDH5 network, identify the differentially expressed genes (DEGs) in TAA as compared to healthy controls, and uncover the related molecular functions and the regulating miRNAs.

RESULTS

Transcriptomic data of one microarray dataset were included, incorporating 43 TAA and 43 control samples. Eight DEGs were identified; 7 were up-regulated and 1 was down-regulated. A molecular signature of 8 genes (CDH5; Calcitonin Receptor-Like Receptor-CALCRL; Activin A Receptor-Like Type 1-ACVRL1, Tryptophanyl-TRNA Synthetase 1-WARS; Junction Plakoglobin-JUP, Protein Tyrosine Phosphatase Receptor Type J-PTPRJ, Purinergic Receptor P2X 4-P2RX4, Kinase Insert Domain Receptor-KDR) were identified as biomarkers associated with TAA. PTPRJ was associated with excellent discrimination and calibration in predicting TAA presentation. Positive correlations were reported regarding the expression of CDH5-CALCRL, CDH5-ACVRL1, CDH5-WARS and CDH5-PTPRJ. Finally, gene set enrichment analysis indicated the molecular functions and miRNA families (hsa-miR-296-5p, hsa-miR-6836-5p, hsa-miR-6132, hsa-miR-27a-5p and hsa-miR-6773-5p) relevant to the 8 biomarkers.

CONCLUSIONS

These outcomes propose an 8-gene molecular panel associated with TAA.

Facilitated self-assembly of a prevascularized dermal/epidermal collagen scaffold

Introduction: Resurfacing complex full thickness wounds requires free tissue transfer which creates donor site morbidity. We describe a method to fabricate a skin flap equivalent with a hierarchical microvascular network. Materials & methods: We fabricated a flap of skin-like tissue containing a hierarchical vascular network by sacrificing Pluronic^® F127 macrofibers and interwoven microfibers within collagen encapsulating human pericytes and fibroblasts. Channels were seeded with smooth muscle and endothelial cells. Constructs were topically seeded with keratinocytes. Results: After 28 days in culture, multiphoton microscopy revealed a hierarchical interconnected network of macro- and micro-vessels; larger vessels (>100 μm) were lined with a monolayer endothelial neointima and a subendothelial smooth muscle neomedia. Neoangiogenic sprouts formed in the collagen protodermis and pericytes self-assembled around both fabricated vessels and neoangiogenic sprouts. Conclusion: We fabricated a prevascularized scaffold containing a hierarchical 3D network of interconnected macro- and microchannels within a collagen protodermis subjacent to an overlying protoepidermis with the potential for recipient microvascular anastomosis.

Bicuspid Aortic Valve and Endothelial Dysfunction: Current Evidence and Potential Therapeutic Targets

Bicuspid aortic valve (BAV), the most frequent congenital heart malformation, is characterized by the presence of a two-leaflet aortic valve instead of a three-leaflet one. BAV disease progression is associated with valvular dysfunction (in the form of stenosis or regurgitation) and aortopathy, which can lead to aneurysm and aortic dissection. This morphological abnormality modifies valve dynamics and promotes eccentric blood flow, which gives rise to alterations of the flow pattern and wall shear stress (WSS) of the ascending aorta. Recently, evidence of endothelial dysfunction (ED) in BAV disease has emerged. Different studies have addressed a reduced endothelial functionality by analyzing various molecular biomarkers and cellular parameters in BAV patients. Some authors have found impaired functionality of circulating endothelial progenitors in these patients, associating it with valvular dysfunction and aortic dilation. Others focused on systemic endothelial function by measuring artery flow-mediated dilation (FMD), showing a reduced FMD in BAV individuals. Novel biomarkers like increased endothelial microparticles (EMP), which are related to ED, have also been discovered in BAV patients. Finally, latest studies indicate that in BAV, endothelial-to-mesenchymal transition (EndoMT) may also be de-regulated, which could be caused by genetic, hemodynamic alterations, or both. Different hypothesis about the pathology of ED in BAV are nowadays being debated. Some authors blamed this impaired functionality just on genetic abnormalities, which could lead to a pathological aorta. Nevertheless, thanks to the development of new and high-resolution imaging techniques like 4D flow MRI, hemodynamics has gained great attention. Based on latest studies, alterations in blood flow seem to cause proper modification of the endothelial cells (ECs) function and morphology. It also seems to be associated with aortic dilation and decreased vasodilators expression, like nitric oxide (NO). Although nowadays ED in BAV has been reported by many, it is not clear which its main cause may be. Comprehending the pathways that promote ED and its relevance in BAV could help further understand and maybe prevent the serious consequences of this disease. This review will discuss the ED present in BAV, focusing on the latest evidence, biomarkers for ED and potential therapeutic targets (Figure 1).

Heart regeneration with human pluripotent stem cells: Prospects and challenges

Cardiovascular disease, ranging from congenital heart disease to adult myocardial infarction, is the leading cause of death worldwide. In pursuit of reliable cardiovascular regenerative medicine, human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer plenty of potential cell-based applications. HPSCs are capable of proliferating indefinitely in an undifferentiated state, and are also pluripotent, being able to differentiate into virtually any somatic cell types given specific stepwise cues, thus representing an unlimited source to generate functional cardiovascular cells for heart regeneration. Here we recapitulated current advances in developing efficient protocols to generate hPSC-derived cardiovascular cell lineages, including cardiomyocytes, endothelial cells, and epicardial cells. We also discussed applications of hPSC-derived cells in combination with compatible bioactive materials, promising trials of cell transplantation in animal models of myocardial infarction, and potential hurdles to bring us closer to the ultimate goal of cell-based heart repair.

•

HPSCs hold tremendous therapeutic potential for treating CVDs.

•

HPSCs could differentiate into multiple cardiovascular cell lineages.

•

Transplantation of hPSC-derived cardiovascular cells and biomaterials shows promising results, but challenges still remain.

Bioprinting Approaches to Engineering Vascularized 3D Cardiac Tissues

PURPOSE OF REVIEW

3D bioprinting technologies hold significant promise for the generation of engineered cardiac tissue and translational applications in medicine. To generate a clinically relevant sized tissue, the provisioning of a perfusable vascular network that provides nutrients to cells in the tissue is a major challenge. This review summarizes the recent vascularization strategies for engineering 3D cardiac tissues.

RECENT FINDINGS

Considerable steps towards the generation of macroscopic sizes for engineered cardiac tissue with efficient vascular networks have been made within the past few years. Achieving a compact tissue with enough cardiomyocytes to provide functionality remains a challenging task. Achieving perfusion in engineered constructs with media that contain oxygen and nutrients at a clinically relevant tissue sizes remains the next frontier in tissue engineering. The provisioning of a functional vasculature is necessary for maintaining a high cell viability and functionality in engineered cardiac tissues. Several recent studies have shown the ability to generate tissues up to a centimeter scale with a perfusable vascular network. Future challenges include improving cell density and tissue size. This requires the close collaboration of a multidisciplinary teams of investigators to overcome complex challenges in order to achieve success.

Topical axitinib is a potent inhibitor of corneal neovascularization

BACKGROUND

This study evaluated the effects of topically applied axitinib, a tyrosine kinase inhibitor, in an experimental model of corneal neovascularization (CNV).

METHODS

A total of 48 New Zealand rabbits were used. CNV was induced by placing five silk sutures in the upper cornea of one eye per rabbit. Rabbits were randomized into four groups (12 rabbits each): 0.9% saline (control group), 0.02 mg/mL axitinib, 0.35 mg/mL axitinib and 0.5 mg/mL axitinib groups. All treatments were administered three times daily for 14 days. Photographs were taken using a slit lamp on days 7 and 14. The area of neovascularization was measured in mm2 , as the percentage of total corneal area and as the percentage of corneal surface covered by sutures (SCS).

RESULTS

On day 14, the CNV area in the control group (31.50 ± 7.47 mm2 ; 115.00 ± 22.55% of the corneal SCS) was larger than that in the 0.02 mg/mL axitinib group (19.20 ± 8.92 mm2 ; 73.89 ± 34.98%), the 0.35 mg/mL axitinib group (8.83 ± 3.92 mm2 ; 31.90 ± 13.59%) and the 0.5 mg/mL axitinib group (5.12 ± 3.97 mm2 ; 18.38 ± 13.65%). Compared with saline, CNV was inhibited 39.04% by 0.02 mg/mL axitinib, 71.96% by 0.35 mg/mL axitinib and 84.73% by 0.5 mg/mL axitinib.

CONCLUSION

Topical administration of the three axitinib concentrations inhibited CNV in rabbits, blocking both vascular endothelial growth factor and platelet-derived growth factor pathways. Axitinib at 0.5 mg/mL induced profound inhibition of corneal angiogenesis.

The dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin ameliorates retinal endothelial cell dysfunction triggered by inflammation

Diabetic retinopathy is considered a low-grade chronic inflammatory disease and several inflammatory molecules, including tumor necrosis factor (TNF)-α, are known to play a major role in the degeneration of retinal capillaries. Previous studies have reported that sitagliptin, a DPP-4 inhibitor, prevents the increase in blood-retinal barrier (BRB) permeability and inhibits the tight junction disassembly induced by diabetes.

AIM

Our goal was to investigate whether sitagliptin is able to prevent retinal endothelial cells (EC) dysfunction triggered by the pro-inflammatory cytokine TNF-α.

MAIN METHODS

The effects of TNF-α and/or sitagliptin on primary cultures of bovine retinal EC were tested. The EC monolayer permeability was analyzed by using 70 kDa rhodamine isothiocyanate (RITC) dextran. The cellular distribution profile of claudin-5 was examined by immunofluorescence staining, and DPP-4 activity was evaluated by using a fluorogenic substrate. Cell viability was assessed by MTT assay, and cell proliferation by the BrdU incorporation assay. Retinal EC migration and angiogenesis were evaluated by a scratch assay and a capillary tube formation in matrigel assay, respectively.

KEY FINDINGS

TNF-α increased the permeability of EC monolayer and induced the loss of claudin-5 immunostaining at the cell borders. This impairment was associated with decreased migration and capillary morphogenesis of retinal EC. Sitagliptin was unable to prevent the effect of TNF-α on EC permeability. However, it decreased DPP-4 activity in bovine retinal EC exposed to TNF-α, without affecting cell viability. Moreover, sitagliptin enhanced the migration and capillary morphogenesis in bovine retinal EC challenged with TNF-α.

SIGNIFICANCE

These results suggest that sitagliptin is able to positively modulate vascular EC function under conditions of retinal inflammation.

Engineered 3D vascular and neuronal networks in a microfluidic platform

Neurovascular coupling plays a key role in the pathogenesis of neurodegenerative disorders including motor neuron disease (MND). In vitro models provide an opportunity to understand the pathogenesis of MND, and offer the potential for drug screening. Here, we describe a new 3D microvascular and neuronal network model in a microfluidic platform to investigate interactions between these two systems. Both 3D networks were established by co-culturing human embryonic stem (ES)-derived MN spheroids and endothelial cells (ECs) in microfluidic devices. Co-culture with ECs improves neurite elongation and neuronal connectivity as measured by Ca2+ oscillation. This improvement was regulated not only by paracrine signals such as brain-derived neurotrophic factor secreted by ECs but also through direct cell-cell interactions via the delta-notch pathway, promoting neuron differentiation and neuroprotection. Bi-directional signaling was observed in that the neural networks also affected vascular network formation under perfusion culture. This in vitro model could enable investigations of neuro-vascular coupling, essential to understanding the pathogenesis of neurodegenerative diseases including MNDs such as amyotrophic lateral sclerosis.

Telomere Biology and Thoracic Aortic Aneurysm

Ascending aortic aneurysms are mostly asymptomatic and present a great risk of aortic dissection or perforation. Consequently, ascending aortic aneurysms are a source of lethality with increased age. Biological aging results in progressive attrition of telomeres, which are the repetitive DNA sequences at the end of chromosomes. These telomeres play an important role in protection of genomic DNA from end-to-end fusions. Telomere maintenance and telomere attrition-associated senescence of endothelial and smooth muscle cells have been indicated to be part of the pathogenesis of degenerative vascular diseases. This systematic review provides an overview of telomeres, telomere-associated proteins and telomerase to the formation and progression of aneurysms of the thoracic ascending aorta. A better understanding of telomere regulation in the vascular pathology might provide new therapeutic approaches. Measurements of telomere length and telomerase activity could be potential prognostic biomarkers for increased risk of death in elderly patients suffering from an aortic aneurysm.

Thymosin β4: Roles in Development, Repair, and Engineering of the Cardiovascular System

The burden of cardiovascular disease is a growing worldwide issue that demands attention. While many clinical trials are ongoing to test therapies for treating the heart after myocardial infarction (MI) and heart failure, there are few options doctors able to currently give patients to repair the heart. This eventually leads to decreased ventricular contractility and increased systemic disease, including vascular disorders that could result in stroke. Small peptides such as thymosin β4 (Tβ4) are upregulated in the cardiovascular niche during fetal development and after injuries such as MI, providing increased neovasculogenesis and paracrine signals for endogenous stem cell recruitment to aid in wound repair. New research is looking into the effects of in vivo administration of Tβ4 through injections and coatings on implants, as well as its effect on cell differentiation. Results so far demonstrate Tβ4 administration leads to robust increases in angiogenesis and wound healing in the heart after MI and the brain after stroke, and can differentiate adult stem cells toward the cardiac lineage for implantation to the heart to increase contractility and survival. Future work, some of which is currently in clinical trials, will demonstrate the in vivo effect of these therapies on human patients, with the goal of helping the millions of people worldwide affected by cardiovascular disease.

Axitinib inhibits retinal and choroidal neovascularization in in vitro and in vivo models

Age-related Macular Degeneration (AMD) is the leading cause of visual impairment and blindness in the elderly in developed countries. Neovascular/exudative (wet) AMD is the aggressive form of AMD and can involve choroidal neovascularization and vascular leakage. Anti-vascular endothelial growth factor (anti-VEGF) medications have significantly improved treatment of wet-AMD. However, only approximately 40% of patients obtain full benefit from anti-VEGF therapy and the medications are given by intravitreal injection. Axitinib, a small molecule multi-receptor tyrosine kinase inhibitor used for the treatment of advanced renal cell carcinoma, is taken orally and inhibits VEGF activity by blocking VEGF receptors. Axitinib also has the advantage of blocking platelet derived growth factor (PDGF) receptors which play a role in neovascularization. Using in vitro human retinal microvascular endothelial cells (HRMVECs), human brain vascular pericytes (HBVRs), 3D co-culture vessel sprout assay, and in vivo laser induced rat choroidal neovascularization (CNV) models, the effect of axitinib on neovascularization was evaluated. Axitinib inhibited neovascularization better than anti-VEGF and/or anti-hPDGF-B mAb in the in vitro models demonstrating that combined inhibition of both VEGF and PDGF pathways may be synergistic in treating wet-AMD. Additionally, axitinib showed good efficacy at a low dose (0.875 mg/day) in laser-induced CNV model in rats. In conclusion our data shows that axitinib, an inhibitor of VEGF and PDGF-B pathways may be useful in ameliorating wet-AMD therapy.

Phenotypic and Functional Changes of Endothelial and Smooth Muscle Cells in Thoracic Aortic Aneurysms

Thoracic aortic aneurysm develops as a result of complex series of events that alter the cellular structure and the composition of the extracellular matrix of the aortic wall. The purpose of the present work was to study the cellular functions of endothelial and smooth muscle cells from the patients with aneurysms of the thoracic aorta. We studied endothelial and smooth muscle cells from aneurysms in patients with bicuspid aortic valve and with tricuspid aortic valve. The expression of key markers of endothelial (CD31, vWF, and VE-cadherin) and smooth muscle (SMA, SM22α, calponin, and vimentin) cells as well extracellular matrix and MMP activity was studied as well as and apoptosis and cell proliferation. Expression of functional markers of endothelial and smooth muscle cells was reduced in patient cells. Cellular proliferation, migration, and synthesis of extracellular matrix proteins are attenuated in the cells of the patients. We show for the first time that aortic endothelial cell phenotype is changed in the thoracic aortic aneurysms compared to normal aortic wall. In conclusion both endothelial and smooth muscle cells from aneurysms of the ascending aorta have downregulated specific cellular markers and altered functional properties, such as growth rate, apoptosis induction, and extracellular matrix synthesis.

Notch signaling governs phenotypic modulation of smooth muscle cells

A feature of vascular smooth muscle cells is their unique ability to exist in multiple phenotypes permitting a broad range of functions that include contraction, proliferation, or synthesis and secretion of extracellular matrix. Although it is known that these phenotypes can be overlapping, the mechanisms that regulate phenotypic modulation are still unclear. Given that endothelial cells are known to convey signals to smooth muscle cells that govern their activities within the vasculature; we sought to better define how endothelial cells regulate phenotypic changes of smooth muscle cells in coculture conditions. Using human aortic smooth muscle cells, we show that endothelial cells promote an increase in a differentiated/contractile phenotype while decreasing proliferation. Analysis of the synthetic phenotype demonstrates that endothelial cells also increase collagen synthesis and secretion. Characterization of pathways important for these endothelial cell-dependent phenotypes reveal that Notch signaling plays an important role in the establishment of these smooth muscle properties. These data highlight the ability of endothelial cells to control phenotypic modulation in a unique and previously undefined manner.

We have contact: endothelial cell-smooth muscle cell interactions

Blood vessels are composed of two primary cell types, endothelial cells and smooth muscle cells, each providing a unique contribution to vessel function. Signaling between these two cell types is essential for maintaining tone in mature vessels, and their communication is critical during development, and for repair and remodeling associated with blood vessel growth. This review will highlight the pathways that endothelial cells and smooth muscle cells utilize to communicate during vessel formation and discuss how disruptions in these pathways contribute to disease.

Rectifying cancer drug discovery through network pharmacology

In spite of the expensive preclinical testing, the consistent failure to translate many promising targeted drugs from the laboratory bench to the clinic raises the question of whether the single-pathway drug-discovery strategies offer the correct perspective. As revealed by network biology, cancers harbor robust biological networks that are inherently resistant to changes, such as those induced by drugs with very narrow mechanisms of action. Therefore, network pharmacology strategies, the treatment of cancer by modulating more than one target, are needed. Different promiscuous approaches targeting multiple avenues within cancer-associated networks, such as the pleiotropic natural products, are emerging. Nevertheless, there is a long way before such 'proof-of-concept strategies' can be successfully applied in the clinical setting. This article provides a perspective on the current challenges in drug discovery, the reasons for high failure rates and how network pharmacology can aid the successful design of agents against cancer.

Diverse functions of kindlin/fermitin proteins during embryonic development in Xenopus laevis

The kindlin/fermitin family includes three proteins involved in regulating integrin ligand-binding activity and adhesion. Loss-of-function mutations in kindlins1 and 3 have been implicated in Kindler Syndrome and Leukocyte Adhesion Deficiency III (LAD-III) respectively, whereas kindlin2 null mice are embryonic lethal. Post translational regulation of cell-cell and cell-ECM adhesion has long been presumed to be important for morphogenesis, however, few specific examples of activation-dependent changes in adhesion molecule function in normal development have been reported. In this study, antisense morpholinos were used to reduce expression of individual kindlins in Xenopus laevis embryos in order to investigate their roles in early development. Kindlin1 knockdown resulted in developmental delays, gross malformations of the gut and eventual lethality by tadpole stages. Kindlin2 morphant embryos displayed late stage defects in vascular maintenance and angiogenic branching consistent with kindlin2 loss of function in the mouse. Antisense morpholinos were also used to deplete maternal kindlin2 protein in oocytes and eggs. Embryos lacking maternal kindlin2 arrested at early cleavage stages due to failures in cytokinesis. Kindlin3 morphant phenotypes included defects in epidermal ciliary beating and partial paralysis at tailbud stages but these embryos recovered eventually as morpholino levels decayed. These results indicate a remarkably diverse range of kindlin functions in vertebrate development.

Targeting cardiac fibroblasts to treat fibrosis of the heart: focus on HDACs

Cardiac fibrosis is implicated in numerous physiologic and pathologic conditions, including scar formation, heart failure and cardiac arrhythmias. However the specific cells and signaling pathways mediating this process are poorly understood. Lysine acetylation of nucleosomal histone tails is an important mechanism for the regulation of gene expression. Additionally, proteomic studies have revealed that thousands of proteins in all cellular compartments are subject to reversible lysine acetylation, and thus it is becoming clear that this post-translational modification will rival phosphorylation in terms of biological import. Acetyl groups are conjugated to lysine by histone acetyltransferases (HATs) and removed from lysine by histone deacetylases (HDACs). Recent studies have shown that pharmacologic agents that alter lysine acetylation by targeting HDACs have the remarkable ability to block pathological fibrosis. Here, we review the current understanding of cardiac fibroblasts and the fibrogenic process with respect to the roles of lysine acetylation in the control of disease-related cardiac fibrosis. Potential for small molecule HDAC inhibitors as anti-fibrotic therapeutics that target cardiac fibroblasts is highlighted. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium."

Peroxynitrite upregulates angiogenic factors VEGF-A, BFGF, and HIF-1α in human corneal limbal epithelial cells

PURPOSE

Corneal neovascularization (NV) is a sight-threatening condition often associated with infection, inflammation, prolonged contact lens use, corneal burns, and acute corneal graft rejection. Macrophages recruited to the cornea release nitric oxide (NO) and superoxide anion (O2(-)), which react together to form the highly toxic molecule peroxynitrite (ONOO(-)). The role of ONOO(-) in upregulating multiple angiogenic factors in cultured human corneal limbal epithelial (HCLE) cells was investigated.

METHODS

Human corneal limbal epithelial cells were incubated with 500 μM of ONOO(-) donor for various times. VEGF-A, BFGF, and hypoxic-inducible factor-alpha (HIF-1α) were investigated via Western blot and RT-PCR was performed for VEGF. Functional assays using human umbilical vein endothelial cells (HUVEC) used conditioned media from ONOO(-)-exposed HCLE cells. Secreted VEGF from conditioned media was detected and analyzed using ELISA.

RESULTS

Increased angiogenic factors were observed as early as 4 hours after HCLE exposure to ONOO(-). HIF-1 expression was seen at 4, 6, and 8 hours post-ONOO(-) exposure (P < 0.05). BFGF expression was elevated at 4 hours and peaked at 8 hours after treatment with ONOO(-) (P < 0.005). Increased VEGF-A gene expression was observed at 6 and 8 hours post-ONOO(-) treatment. Functional assays using conditioned media showed increased HUVEC migration and tube formation.

CONCLUSIONS

Exposure to elevated extracellular concentrations of ONOO(-) results in upregulation of angiogenic factors in HCLE cells. It is possible that, in the setting of inflammation or infection, that exposure to ONOO(-) could be one contributor to the complex initiators of corneal NV. Validation in vivo would identify an additional potential control point for corneal NV.

Control of perfusable microvascular network morphology using a multiculture microfluidic system

The mechanical and biochemical microenvironment influences the morphological characteristics of microvascular networks (MVNs) formed by endothelial cells (ECs) undergoing the process of vasculogenesis. The objective of this study was to quantify the role of individual factors in determining key network parameters in an effort to construct a set of design principles for engineering vascular networks with prescribed morphologies. To achieve this goal, we developed a multiculture microfluidic platform enabling precise control over paracrine signaling, cell-seeding densities, and hydrogel mechanical properties. Human umbilical vein endothelial cells (HUVECs) were seeded in fibrin gels and cultured alongside human lung fibroblasts (HLFs). The engineered vessels formed in our device contained patent, perfusable lumens. Communication between the two cell types was found to be critical in avoiding network regression and maintaining stable morphology beyond 4 days. The number of branches, average branch length, percent vascularized area, and average vessel diameter were found to depend uniquely on several input parameters. Importantly, multiple inputs were found to control any given output network parameter. For example, the vessel diameter can be decreased either by applying angiogenic growth factors--vascular endothelial growth factor (VEGF) and sphingosine-1-phsophate (S1P)--or by increasing the fibrinogen concentration in the hydrogel. These findings introduce control into the design of MVNs with specified morphological properties for tissue-specific engineering applications.

Dynamic cell-cell and cell-ECM interactions in the heart

Recent studies have placed an increasing amount of emphasis on the cardiovascular system and understanding how the heart and its vasculature can be regenerated following pathological stresses, such as hypertension and myocardial infarction. The remodeling process involves the permanent cellular constituents of the heart including myocytes, fibroblasts, endothelial cells, pericytes, smooth muscle cells and stem cells. It also includes transient cell populations, such as immune cells (e.g. lymphocytes, mast cells and macrophages) and circulating stem cells. Following injury, there are dramatic shifts in the various cardiac cell populations that can affect cell-cell and cell-extracellular matrix interactions and cardiac function. Cardiac fibroblasts are a key component in normal heart function, as well as during the remodeling process through dynamic cell-cell interactions and synthesis and degradation of the extracellular matrix. Fibroblasts dynamically interact with the various cardiac cell populations through mechanical, chemical (autocrine and/or paracrine) and electrophysiological means to alter gene and protein expression, cellular processes and ultimately cardiac function. Better understanding these cell-cell and cell-extracellular matrix interactions and their biological consequences should provide novel therapeutic targets for the treatment of heart disease. In this review we discuss the nature of these interactions and the importance of these interactions in maintaining normal heart function, as well as their role in the cardiac remodeling process. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium."

Troponin T3 expression in skeletal and smooth muscle is required for growth and postnatal survival: characterization of Tnnt3(tm2a(KOMP)Wtsi) mice

The troponin complex, which consists of three regulatory proteins (troponin C, troponin I, and troponin T), is known to regulate muscle contraction in skeletal and cardiac muscle, but its role in smooth muscle remains controversial. Troponin T3 (TnnT3) is a fast skeletal muscle troponin believed to be expressed only in skeletal muscle cells. To determine the in vivo function and tissue-specific expression of Tnnt3, we obtained the heterozygous Tnnt3+/flox/lacZ mice from Knockout Mouse Project (KOMP) Repository. Tnnt3(lacZ/+) mice are smaller than their WT littermates throughout development but do not display any gross phenotypes. Tnnt3(lacZ/lacZ) embryos are smaller than heterozygotes and die shortly after birth. Histology revealed hemorrhagic tissue in Tnnt3(lacZ/lacZ) liver and kidney, which was not present in Tnnt3(lacZ/+) or WT, but no other gross tissue abnormalities. X-gal staining for Tnnt3 promoter-driven lacZ transgene expression revealed positive staining in skeletal muscle and diaphragm and smooth muscle cells located in the aorta, bladder, and bronchus. Collectively, these findings suggest that troponins are expressed in smooth muscle and are required for normal growth and breathing for postnatal survival. Moreover, future studies with this mouse model can explore TnnT3 function in adult muscle function using the conditional-inducible gene deletion approach

Inflammatory cytokine-specific alterations in retinal endothelial cell function

Diabetic retinopathy (DR) is recognized as a chronic low-grade inflammatory disease. Retinal microvascular cell dysfunction and loss play an important role in the pathogenesis of DR. However, the basic mechanisms underlying the development and progression of DR are poorly understood. Many recent studies indicate that increased production of inflammatory factors either systemically and/or locally, is strongly associated with vascular dysfunction during diabetes. Here we sought to determine the specific impact of different inflammatory mediators on retinal endothelial cell (EC) function. Inflammatory mediators TNF-α and IL-1β attenuated the migration and capillary morphogenesis of retinal EC. These dysfunctions were associated with an increased production of reactive oxygen species, expression of inducible nitric oxide synthase, and production of total nitrate/nitrite. Incubation of retinal EC with TNF-α and IL-1β altered VE-cadherin localization, as well as the expression of other junctional proteins. In addition, TNF-α and IL-1β also altered the production of various ECM proteins including osteopontin, collagen IV, and tenascin-C. Mechanistically, these changes were concomitant with the activation of the mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) signaling pathways. In contrast, incubation of retinal EC with MCP-1 minimally affected their migratory, junctional, and ECM properties. Together our results indicate that the presence of inflammatory mediators in diabetes may have specific and significant impact on vascular cell function, and contribute to the pathogenesis of DR.

Intercellular transfer of P-glycoprotein from the drug resistant human bladder cancer cell line BIU-87 does not require cell-to-cell contact

PURPOSE

The efflux activity of transmembrane P-glycoprotein prevents various therapeutic drugs from reaching lethal concentrations in cancer cells, resulting in multidrug resistance. We investigated whether drug resistant bladder cancer cells could transfer functional P-glycoprotein to sensitive parental cells.

MATERIALS AND METHODS

Drug sensitive BIU-87 bladder cancer cells were co-cultured for 48 hours with BIU-87/ADM, a doxorubicin resistant derivative of the same cell line, in a Transwell® system that prevented cell-to-cell contact. The presence of P-glycoprotein in recipient cell membranes was established using fluorescein isothiocyanate, laser scanning confocal microscopy and Western blot. P-glycoprotein mRNA levels were compared between cell types. Rhodamine 123 efflux assay was done to confirm that P-glycoprotein was biologically active.

RESULTS

The amount of P-glycoprotein protein in BIU-87 cells co-cultured with BIU-87/ADM was significantly higher than in BIU-87 cells (0.44 vs 0.25) and BIU-87/H33342 cells (0.44 vs 0.26, each p <0.001), indicating P-glycoprotein transfer. P-glycoprotein mRNA expression was significantly higher in BIU-87/ADM cells than in co-cultured BIU-87 cells (1.28 vs 0.30), BIU-87/H33342 (0.28) and BIU-87 cells (0.25, each p <0.001), ruling out a genetic mechanism. After 30 minutes of efflux, rhodamine 123 fluorescence intensity was significantly lower in BIU-87/ADM cells (5.55 vs 51.45, p = 0.004) and co-cultured BIU-87 cells than in BIU-87 cells (14.22 vs 51.45, p <0.001), indicating that P-glycoprotein was functional.

CONCLUSIONS

Bladder cancer cells can acquire functional P-glycoprotein through a nongenetic mechanism that does not require direct cell contact. This mechanism is consistent with a microparticle mediated process.

Engineering of in vitro 3D capillary beds by self-directed angiogenic sprouting

In recent years, microfluidic systems have been used to study fundamental aspects of angiogenesis through the patterning of single-layered, linear or geometric vascular channels. In vivo, however, capillaries exist in complex, three-dimensional (3D) networks, and angiogenic sprouting occurs with a degree of unpredictability in all x,y,z planes. The ability to generate capillary beds in vitro that can support thick, biological tissues remains a key challenge to the regeneration of vital organs. Here, we report the engineering of 3D capillary beds in an in vitro microfluidic platform that is comprised of a biocompatible collagen I gel supported by a mechanical framework of alginate beads. The engineered vessels have patent lumens, form robust ∼1.5 mm capillary networks across the devices, and support the perfusion of 1 µm fluorescent beads through them. In addition, the alginate beads offer a modular method to encapsulate and co-culture cells that either promote angiogenesis or require perfusion for cell viability in engineered tissue constructs. This laboratory-constructed vascular supply may be clinically significant for the engineering of capillary beds and higher order biological tissues in a scalable and modular manner.

Endothelialization approaches for viable engineered tissues

One of the main limitation in obtaining thick, 3-dimensional viable engineered constructs is the inability to provide a sufficient and functional blood vessel system essential for the in vitro survival and the in vivo integration of the construct. Different strategies have been proposed to simulate the ingrowth of new blood vessels into engineered tissue, such as the use of growth factors, fabrication scaffold technologies, in vivo prevascularization and cell-based strategies, and it has been demonstrated that endothelial cells play a central role in the neovascularization process and in the control of blood vessel function. In particular, different "environmental" settings (origin, presence of supporting cells, biomaterial surface, presence of hemodynamic forces) strongly influence endothelial cell function, angiogenic potential and the in vivo formation of durable vessels. This review provides an overview of the different techniques developed so far for the vascularization of tissue-engineered constructs (with their advantages and pitfalls), focusing the attention on the recent development in the cell-based vascularization strategy and the in vivo applications.

Wnt-4 potently inhibits capillary outgrowth from rat aorta in 3D culture

Regulation of angiogenesis involves tight cell-to-cell and cell-to-extracellular-matrix interactions. Various reports demonstrate that the Wnt signaling pathways participate in this regulation. Using a three-dimensional aortic ring culture combined with an ex vivo retroviral infection approach, we evaluated the effects of two Wnt growth factors, Wnt-1 and Wnt-4, on the formation and growth of new capillaries. Our results show that Wnt-1 had no effect, whereas Wnt-4 was a potent inhibitor of capillary outgrowth in vitro.

Microvascular guidance: a challenge to support the development of vascularised tissue engineering construct

The guidance of endothelial cell organization into a capillary network has been a long-standing challenge in tissue engineering. Some research efforts have been made to develop methods to promote capillary networks inside engineered tissue constructs. Capillary and vascular networks that would mimic blood microvessel function can be used to subsequently facilitate oxygen and nutrient transfer as well as waste removal. Vascularization of engineering tissue construct is one of the most favorable strategies to overpass nutrient and oxygen supply limitation, which is often the major hurdle in developing thick and complex tissue and artificial organ. This paper addresses recent advances and future challenges in developing three-dimensional culture systems to promote tissue construct vascularization allowing mimicking blood microvessel development and function encountered in vivo. Bioreactors systems that have been used to create fully vascularized functional tissue constructs will also be outlined.

Vascular complications and diabetes: current therapies and future challenges

Diabetic retinal complications, including macular edema (DME) and proliferative diabetic retinopathy (PDR), are the leading cause of new cases of blindness among adults aged 20–74. Chronic hyperglycemia, considered the underlying cause of diabetic retinopathy, is thought to act first through violation of the pericyte-endothelial coupling. Disruption of microvascular integrity leads to pathologic consequences including hypoxia-induced imbalance in vascular endothelial growth factor (VEGF) signaling. Several anti-VEGF medications are in clinical trials for use in arresting retinal angiogenesis arising from DME and PDR. Although a review of current clinical trials shows promising results, the lack of large prospective studies, head-to-head therapeutic comparisons, and potential long-term and systemic adverse events give cause for optimistic caution. Alternative therapies including targeting pathogenic specific angiogenesis and mural-cell-based therapeutics may offer innovative solutions for currently intractable clinical problems. This paper describes the mechanisms behind diabetic retinal complications, current research supporting anti-VEGF medications, and future therapeutic directions.

Vascular endothelial growth factor (VEGF) isoform regulation of early forebrain development

This work was designed to determine the role of the vascular endothelial growth factor A (VEGF) isoforms during early neuroepithelial development in the mammalian central nervous system (CNS), specifically in the forebrain. An emerging model of interdependence between neural and vascular systems includes VEGF, with its dual roles as a potent angiogenesis factor and neural regulator. Although a number of studies have implicated VEGF in CNS development, little is known about the role that the different VEGF isoforms play in early neurogenesis. We used a mouse model of disrupted VEGF isoform expression that eliminates the predominant brain isoform, VEGF164, and expresses only the diffusible form, VEGF120. We tested the hypothesis that VEGF164 plays a key role in controlling neural precursor populations in developing cortex. We used microarray analysis to compare gene expression differences between wild type and VEGF120 mice at E9.5, the primitive stem cell stage of the neuroepithelium. We quantified changes in PHH3-positive nuclei, neural stem cell markers (Pax6 and nestin) and the Tbr2-positive intermediate progenitors at E11.5 when the neural precursor population is expanding rapidly. Absence of VEGF164 (and VEGF188) leads to reduced proliferation without an apparent effect on the number of Tbr2-positive cells. There is a corresponding reduction in the number of mitotic spindles that are oriented parallel to the ventricular surface relative to those with a vertical or oblique angle. These results support a role for the VEGF isoforms in supporting the neural precursor population of the early neuroepithelium.

Endothelial cells downregulate apolipoprotein D expression in mural cells through paracrine secretion and Notch signaling

Endothelial and mural cell interactions are vitally important for proper formation and function of blood vessels. These two cell types communicate to regulate multiple aspects of vessel function. In studying genes regulated by this interaction, we identified apolipoprotein D (APOD) as one gene that is downregulated in mural cells by coculture with endothelial cells. APOD is a secreted glycoprotein that has been implicated in governing stress response, lipid metabolism, and aging. Moreover, APOD is known to regulate smooth muscle cells and is found in abundance within atherosclerotic lesions. Our data show that the regulation of APOD in mural cells is bimodal. Paracrine secretion by endothelial cells causes partial downregulation of APOD expression. Additionally, cell contact-dependent Notch signaling plays a role. NOTCH3 on mural cells promotes the downregulation of APOD, possibly through interaction with the JAGGED-1 ligand on endothelial cells. Our results show that NOTCH3 contributes to the downregulation of APOD and by itself is sufficient to attenuate APOD transcript expression. In examining the consequence of decreased APOD expression in mural cells, we show that APOD negatively regulates cell adhesion. APOD attenuates adhesion by reducing focal contacts; however, it has no effect on stress fiber formation. These data reveal a novel mechanism in which endothelial cells control neighboring mural cells through the downregulation of APOD, which, in turn, influences mural cell function by modulating adhesion.

Calpain- and talin-dependent control of microvascular pericyte contractility and cellular stiffness

Pericytes surround capillary endothelial cells and exert contractile forces modulating microvascular tone and endothelial growth. We previously described pericyte contractile phenotype to be Rho GTPase- and α-smooth muscle actin (αSMA)-dependent. However, mechanisms mediating adhesion-dependent shape changes and contractile force transduction remain largely equivocal. We now report that the neutral cysteine protease, calpain, modulates pericyte contractility and cellular stiffness via talin, an integrin-binding and F-actin associating protein. Digital imaging and quantitative analyses of living cells reveal significant perturbations in contractile force transduction detected via deformation of silicone substrata, as well as perturbations of mechanical stiffness in cellular contractile subdomains quantified via atomic force microscope (AFM)-enabled nanoindentation. Pericytes overexpressing GFP-tagged talin show significantly enhanced contractility (~two-fold), which is mitigated when either the calpain-cleavage resistant mutant talin L432G or vinculin are expressed. Moreover, the cell-penetrating, calpain-specific inhibitor termed CALPASTAT reverses talin-enhanced, but not Rho GTP-dependent, contractility. Interestingly, our analysis revealed that CALPASTAT, but not its inactive mutant, alters contractile cell-driven substrata deformations while increasing mechanical stiffness of subcellular contractile regions of these pericytes. Altogether, our results reveal that calpain-dependent cleavage of talin modulates cell contractile dynamics, which in pericytes may prove instrumental in controlling normal capillary function or microvascular pathophysiology.

Roles of sphingosine-1-phosphate signaling in angiogenesis

Sphingosine-1-phosphate (S1P) is a blood-borne lipid mediator with pleiotropic biological activities. S1P acts via the specific cell surface G-protein-coupled receptors, S1P_1-5. S1P₁ and S1P₂ were originally identified from vascular endothelial cells (ECs) and smooth muscle cells, respectively. Emerging evidence shows that S1P plays crucial roles in the regulation of vascular functions, including vascular formation, barrier protection and vascular tone via S1P₁, S1P₂ and S1P₃. In particular, S1P regulates vascular formation through multiple mechanisms; S1P exerts both positive and negative effects on angiogenesis and vascular maturation. The positive and negative effects of S1P are mediated by S1P₁ and S1P₂, respectively. These effects of S1P₁ and S1P₂ are probably mediated by the S1P receptors expressed in multiple cell types including ECs and bone-marrow-derived cells. The receptor-subtype-specific, distinct effects of S1P favor the development of novel therapeutic tactics for antitumor angiogenesis in cancer and therapeutic angiogenesis in ischemic diseases.

Efficient in vivo vascularization of tissue-engineering scaffolds

The success of tissue engineering depends on the rapid and efficient formation of a functional blood vasculature. Adult blood vessels comprise endothelial cells and perivascular mural cells that assemble into patent tubules ensheathed by a basement membrane during angiogenesis. Using individual vessel components, we characterized intra-scaffold microvessel self-assembly efficiency in a physiological in vivo tissue engineering implant context. Primary human microvascular endothelial and vascular smooth muscle cells were seeded at different ratios in poly-L-lactic acid (PLLA) scaffolds enriched with basement membrane proteins (Matrigel) and implanted subcutaneously into immunocompromised mice. Temporal intra-scaffold microvessel formation, anastomosis and perfusion were monitored by immunohistochemical, flow cytometric and in vivo multiphoton fluorescence microscopy analysis. Vascularization in the tissue-engineering context was strongly enhanced in implants seeded with a complete complement of blood vessel components: human microvascular endothelial and vascular smooth muscle cells in vivo assembled a patent microvasculature within Matrigel-enriched PLLA scaffolds that anastomosed with the host circulation during the first week of implantation. Multiphoton fluorescence angiographic analysis of the intra-scaffold microcirculation showed a uniform, branched microvascular network. 3D image reconstruction analysis of human pulmonary artery smooth muscle cell (hPASMC) distribution within vascularized implants was non-random and displayed a preferential perivascular localization. Hence, efficient microvessel self-assembly, anastomosis and establishment of a functional microvasculture in the native hypoxic in vivo tissue engineering context is promoted by providing a complete set of vascular components.

Tumor cell-derived PDGF-B potentiates mouse mesenchymal stem cells-pericytes transition and recruitment through an interaction with NRP-1

Background

New blood vessel formation, or angiogenic switch, is an essential event in the development of solid tumors and their metastatic growth. Tumor blood vessel formation and remodeling is a complex and multi-step processes. The differentiation and recruitment of mural cells including vascular smooth muscle cells and pericytes are essential steps in tumor angiogenesis. However, the role of tumor cells in differentiation and recruitment of mural cells has not yet been fully elucidated. This study focuses on the role of human tumor cells in governing the differentiation of mouse mesenchymal stem cells (MSCs) to pericytes and their recruitment in the tumor angiogenesis process.

Results

We show that C3H/10T1/2 mouse embryonic mesenchymal stem cells, under the influence of different tumor cell-derived conditioned media, differentiate into mature pericytes. These differentiated pericytes, in turn, are recruited to bind with capillary-like networks formed by endothelial cells on the matrigel under in vitro conditions and recruited to bind with blood vessels on gel-foam under in vivo conditions. The degree of recruitment of pericytes into in vitro neo-angiogenesis is tumor cell phenotype specific. Interestingly, invasive cells recruit less pericytes as compared to non-invasive cells. We identified tumor cell-secreted platelet-derived growth factor-B (PDGF-B) as a crucial factor controlling the differentiation and recruitment processes through an interaction with neuropilin-1 (NRP-1) in mesenchymal stem cells.

Conclusion

These new insights into the roles of tumor cell-secreted PDGF-B-NRP-1 signaling in MSCs-fate determination may help to develop new antiangiogenic strategies to prevent the tumor growth and metastasis and result in more effective cancer therapies.

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.

S1P(2), the G protein-coupled receptor for sphingosine-1-phosphate, negatively regulates tumor angiogenesis and tumor growth in vivo in mice

Sphingosine-1-phosphate (S1P) has been implicated in tumor angiogenesis by acting through the G(i)-coupled chemotactic receptor S1P(1). Here, we report that the distinct receptor S1P(2) is responsible for mediating the G(12/13)/Rho-dependent inhibitory effects of S1P on Akt, Rac, and cell migration, thereby negatively regulating tumor angiogenesis and tumor growth. By using S1P(2)(LacZ/+) mice, we found that S1P(2) was expressed in both tumor and normal blood vessels in many organs, in both endothelial cells (EC) and vascular smooth muscle cells, as well as in tumor-associated, CD11b-positive bone marrow-derived cells (BMDC). Lewis lung carcinoma or B16 melanoma cells implanted in S1P(2)-deficient (S1P(2)(-/-)) mice displayed accelerated tumor growth and angiogenesis with enhanced association of vascular smooth muscle cells and pericytes. S1P(2)(-/-) ECs exhibited enhanced Rac activity, Akt phosphorylation, cell migration, proliferation, and tube formation in vitro. Coinjection of S1P(2)(-/-) ECs and tumor cells into wild-type mice also produced a relative enhancement of tumor growth and angiogenesis in vivo. S1P(2)(-/-) mice were also more efficient at recruiting CD11b-positive BMDCs into tumors compared with wild-type siblings. Bone marrow chimera experiments revealed that S1P(2) acted in BMDCs to promote tumor growth and angiogenesis. Our results indicate that, in contrast to endothelial S1P(1), which stimulates tumor angiogenesis, S1P(2) on ECs and BMDCs mediates a potent inhibition of tumor angiogenesis, suggesting a novel therapeutic tactic for anticancer treatment.

Cardiac fibroblast: the renaissance cell

The permanent cellular constituents of the heart include cardiac fibroblasts, myocytes, endothelial cells, and vascular smooth muscle cells. Previous studies have demonstrated that there are undulating changes in cardiac cell populations during embryonic development, through neonatal development and into the adult. Transient cell populations include lymphocytes, mast cells, and macrophages, which can interact with these permanent cell types to affect cardiac function. It has also been observed that there are marked differences in the makeup of the cardiac cell populations depending on the species, which may be important when examining myocardial remodeling. Current dogma states that the fibroblast makes up the largest cell population of the heart; however, this appears to vary for different species, especially mice. Cardiac fibroblasts play a critical role in maintaining normal cardiac function, as well as in cardiac remodeling during pathological conditions such as myocardial infarct and hypertension. These cells have numerous functions, including synthesis and deposition of extracellular matrix, cell-cell communication with myocytes, cell-cell signaling with other fibroblasts, as well as with endothelial cells. These contacts affect the electrophysiological properties, secretion of growth factors and cytokines, as well as potentiating blood vessel formation. Although a plethora of information is known about several of these processes, relatively little is understood about fibroblasts and their role in angiogenesis during development or cardiac remodeling. In this review, we provide insight into the various properties of cardiac fibroblasts that helps illustrate their importance in maintaining proper cardiac function, as well as their critical role in the remodeling heart.

The pericyte: cellular regulator of microvascular blood flow

The vascular system - through its development, response to injury, and remodeling during disease - constitutes one of the key organ systems sustaining normal human physiology; conversely, its dysregulation also underlies multiple pathophysiologic processes. Regulation of vascular endothelial cell function requires the integration of complex signals via multiple cell types, including arterial smooth muscle, capillary and post-capillary pericytes, and other perivascular cells such as glial and immune cells. Here, we focus on the pericyte and its roles in microvascular remodeling, reviewing current concepts in microvascular pathophysiology and offering new insights into the specific roles that pericyte-dependent signaling pathways may play in modulating endothelial growth and microvascular tone during pathologic angiogenesis and essential hypertension.

Attenuation of proliferation and migration of retinal pericytes in the absence of thrombospondin-1

Perivascular supporting cells, including vascular smooth muscle cells (VSMCs) and pericytes (PCs), provide instructive signals to adjacent endothelial cells helping to maintain vascular homeostasis. These signals are provided through direct contact and by the release of soluble factors by these cells. Thrombospondin (TSP)1 is a matricellular protein and an autocrine factor for VSMCs. TSP1 activity, along with that of PDGF, regulates VSMC proliferation and migration. However, the manner in which TSP1 and PDGF impact retinal PC function requires further investigation. In the present study, we describe, for the first time, the isolation and culture of retinal PCs from wild-type (TSP1(+/+)) and TSP1-deficient (TSP1(-/-)) immortomice. We showed that these cells express early and mature markers of PCs, including NG2, PDGF receptor-beta, and smooth muscle actin as well as desmin, calbindin, and mesenchymal stem cell markers. These cells were successfully passaged and maintained in culture for several months without significant loss of expression of these markers. TSP1(+/+) PCs proliferated at a faster rate compared with TSP1(-/-) PCs. In addition, TSP1(+/+) PCs, like VSMCs, responded to PDGF-BB with enhanced migration and proliferation. In contrast, TSP1(-/-) PCs failed to respond to the promigratory and proliferative activity of PDGF-BB. This may be attributed, at least in part, to the limited interaction of PDGF-BB with TSP1 in null cells, which is essential for PDGF proliferative and migratory action. We observed no significant differences in the rates of apoptosis in these cells. TSP1(-/-) PCs were also less adherent, expressed increased levels of TSP2 and fibronectin, and had decreased amounts of N-cadherin and alpha(v)beta(3)-integrin on their surface. Thus, TSP1 plays a significant role in retinal PC proliferation and migration impacting retinal vascular development and homeostasis.

An optimized three-dimensional in vitro model for the analysis of angiogenesis

Angiogenesis is the formation of new blood vessels from the existing vasculature. It is a multistage process in which activated endothelial cells (EC) degrade basement membrane, sprout from the parent vessel, migrate, proliferate, align, undergo tube formation, and eventually branch and anastomose with adjacent vessels. Here we describe a three-dimensional in vitro assay that reproduces each of these steps. Human umbilical vein endothelial cells (HUVEC) are cultured on microcarrier beads, which are then embedded in a fibrin gel. Fibroblasts cultured on top of the gel provide factors that synergize with bFGF and VEGF to promote optimal sprouting and tube formation. Sprouts appear around day 2, lumen formation begins at day 4, and at day 10 an extensive anastomosing network of capillary-like tubes is established. The EC express a similar complement of genes as angiogenic EC in vivo and undergo identical morphologic changes during tube formation. This model, therefore, recapitulates in vivo angiogenesis in several critical aspects and provides a system that is easy to manipulate genetically, can be visualized in real time, and allows for easy purification of angiogenic EC for downstream analysis.

Oncologic trogocytosis of an original stromal cells induces chemoresistance of ovarian tumours

BACKGROUND

The microenvironment plays a major role in the onset and progression of metastasis. Epithelial ovarian cancer (EOC) tends to metastasize to the peritoneal cavity where interactions within the microenvironment might lead to chemoresistance. Mesothelial cells are important actors of the peritoneal homeostasis; we determined their role in the acquisition of chemoresistance of ovarian tumours.

METHODOLOGY/PRINCIPAL FINDINGS

We isolated an original type of stromal cells, referred to as "Hospicells" from ascitis of patients with ovarian carcinosis using limiting dilution. We studied their ability to confer chemoresistance through heterocellular interactions. These stromal cells displayed a new phenotype with positive immunostaining for CD9, CD10, CD29, CD146, CD166 and Multi drug resistance protein. They preferentially interacted with epithelial ovarian cancer cells. This interaction induced chemoresistance to platin and taxans with the implication of multi-drug resistance proteins. This contact enabled EOC cells to capture patches of the Hospicells membrane through oncologic trogocytosis, therefore acquiring their functional P-gp proteins and thus developing chemoresistance. Presence of Hospicells on ovarian cancer tissue micro-array from patients with neo-adjuvant chemotherapy was also significantly associated to chemoresistance.

CONCLUSIONS/SIGNIFICANCE

This is the first report of trogocytosis occurring between a cancer cell and an original type of stromal cell. This interaction induced autonomous acquisition of chemoresistance. The presence of stromal cells within patient's tumour might be predictive of chemoresistance. The specific interaction between cancer cells and stromal cells might be targeted during chemotherapy.

Expression of the fast twitch troponin complex, fTnT, fTnI and fTnC, in vascular smooth muscle

It is generally believed that proteins of the troponin complex are not expressed in smooth muscle. We have directly assayed for expression of troponin transcripts in mouse vascular smooth muscle and found that troponin sequences normally associated with fast twitch skeletal muscle (fTnT, fTnI, fTnC) were present at significant levels in the thoracic aorta. In situ hybridization experiments demonstrated that fTnT, fTnI and fTnC transcripts were expressed in the smooth muscle layer of mouse blood vessels of all sizes. Protein blot analysis using rat tissue showed that at least two members of the troponin complex, Troponin T and Troponin I, were translated in vascular smooth muscle of the aorta. Finally, immuno-fluorescence microscopy of rat aortic smooth muscle revealed that TnT and TnI are localized in a unique pattern, coincident with the distribution of tropomyosin. It seems likely therefore, that a complete troponin complex is expressed in vascular smooth muscle and is associated with the contractile machinery of the cell. These observations raise the possibility that troponins play a role in regulation of smooth muscle function.

Differential gene expression in a coculture model of angiogenesis reveals modulation of select pathways and a role for Notch signaling

Communication between endothelial and mural cells (smooth muscle cells, pericytes, and fibroblasts) can dictate blood vessel size and shape during angiogenesis, and control the functional aspects of mature blood vessels, by determining things such as contractile properties. The ability of these different cell types to regulate each other's activities led us to ask how their interactions directly modulate gene expression. To address this, we utilized a three-dimensional model of angiogenesis and screened for genes whose expression was altered under coculture conditions. Using a BeadChip array, we identified 323 genes that were uniquely regulated when endothelial cells and mural cells (fibroblasts) were cultured together. Data mining tools revealed that differential expression of genes from the integrin, blood coagulation, and angiogenesis pathways were overrepresented in coculture conditions. Scans of the promoters of these differentially modulated genes identified a multitude of conserved C promoter binding factor (CBF)1/CSL elements, implicating Notch signaling in their regulation. Accordingly, inhibition of the Notch pathway with gamma-secretase inhibitor DAPT or NOTCH3-specific small interfering RNA blocked the coculture-induced regulation of several of these genes in fibroblasts. These data show that coculturing of endothelial cells and fibroblasts causes profound changes in gene expression and suggest that Notch signaling is a critical mediator of the resultant transcription.

Emerging pulmonary vasculature lacks fate specification

Lung morphogenesis requires precise coordination between branching morphogenesis and vascularization to generate distal airways capable of supporting respiration at the cell-cell interface. The specific origins and types of blood vessels that initially form in the lung, however, remain obscure. Herein, we definitively show that during the early phases of lung development [i.e., embryonic day (E) 11.5], functional vessels, replete with blood flow, are restricted to the mesenchyme, distal to the epithelium. However, by day E14.5, and in response to epithelial-derived VEGF signals, functional vessels extend from the mesenchyme to the epithelial interface. Moreover, these vessels reside adjacent to multipotent mesenchymal stromal cells that likely play a regulatory role in this process. As well as and distinct from the systemic vasculature, immunostaining for EphrinB2 and EphB4 revealed that arterial and venous identity is not distinguishable in emergent pulmonary vasculature. Collectively, this study provides evidence that lung vascularization initially originates in the mesenchyme, distal to the epithelium, and that arterial-venous specification does not exist in the early lung. At a mechanistic level, we show that basilar epithelial VEGF prompts endothelial cells to move toward the epithelium where they undergo morphogenesis during the proliferative, canalicular stage. Thus our findings challenge existing notions of vascular origin and identity during development.