Tie2 is tied at the cell-cell contacts and to extracellular matrix by angiopoietin-1

In Vitro Study of Thymosin Beta 4 Promoting Transplanted Fat Survival by Regulating Adipose-Derived Stem Cells

BACKGROUND

Autologous fat grafting (AFG) has emerged as a highly sought-after plastic surgery procedure, although its success has been hampered by the uncertain fat survival rate. Current evidence suggests that adipose-derived stem cells (ADSCs) may contribute to fat retention in AFG. In previous studies, it was confirmed that thymosin beta 4 (Tβ4) could enhance fat survival in vivo, although the precise mechanism remains unclear.

METHODS

ADSCs were isolated from patients undergoing liposuction and their proliferation, apoptosis, anti-apoptosis, and migration were analyzed under Tβ4 stimulation using cell counting kit-8, flow cytometry, wound healing assay, and real-time quantitative PCR. The mRNA levels of genes relating to angiogenesis and Hippo signaling were also determined.

RESULTS

Tβ4 at 100 ng/mL (p-value = 0.0171) and 1000 ng/mL (p-value = 0.0054) significantly increased ADSC proliferation from day 1 compared to the control group (0 ng/mL). In addition, the mRNA levels of proliferation-associated genes were elevated in the Tβ4 group. Furthermore, Tβ4 enhanced the anti-apoptotic ability of ADSCs when stimulated with Tβ4 and an apoptotic induction reagent (0 ng/mL vs. 1000 ng/mL, p-value = 0.011). Crucially, the mRNA expression levels of angiogenesis-related genes and critical genes in the Hippo pathway were affected by Tβ4 in ADSCs.

CONCLUSIONS

Tβ4 enhances adipose viability in AFG via facilitating ADSC proliferation and reducing apoptosis, and acts as a crucial positive regulator of ADSC-associated angiogenesis. Additionally, Tβ4 could be accountable for the phenotypic adjustment of ADSCs by regulating the Hippo pathway.

NO LEVEL ASSIGNED

This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Pioneering therapies for post-infarction angiogenesis: Insight into molecular mechanisms and preclinical studies

Acute myocardial infarction (MI), despite significant progress in its treatment, remains a leading cause of chronic heart failure and cardiovascular events such as cardiac arrest. Promoting angiogenesis in the myocardial tissue after MI to restore blood flow in the ischemic and hypoxic tissue is considered an effective treatment strategy. The repair of the myocardial tissue post-MI involves a robust angiogenic response, with mechanisms involved including endothelial cell proliferation and migration, capillary growth, changes in the extracellular matrix, and stabilization of pericytes for neovascularization. In this review, we provide a detailed overview of six key pathways in angiogenesis post-MI: the PI3K/Akt/mTOR signaling pathway, the Notch signaling pathway, the Wnt/β-catenin signaling pathway, the Hippo signaling pathway, the Sonic Hedgehog signaling pathway, and the JAK/STAT signaling pathway. We also discuss novel therapeutic approaches targeting these pathways, including drug therapy, gene therapy, protein therapy, cell therapy, and extracellular vesicle therapy. A comprehensive understanding of these key pathways and their targeted therapies will aid in our understanding of the pathological and physiological mechanisms of angiogenesis after MI and the development and application of new treatment strategies.

Modulation of the Host Response as a Therapeutic Strategy in Severe Lung Infections

Respiratory pathogens such as influenza and SARS-CoV-2 can cause severe lung infections leading to acute respiratory distress syndrome (ARDS). The pathophysiology of ARDS includes an excessive host immune response, lung epithelial and endothelial cell death and loss of the epithelial and endothelial barrier integrity, culminating in pulmonary oedema and respiratory failure. Traditional approaches for the treatment of respiratory infections include drugs that exert direct anti-pathogen effects (e.g., antivirals). However, such agents are typically ineffective or insufficient after the development of ARDS. Modulation of the host response has emerged as a promising alternative therapeutic approach to mitigate damage to the host for the treatment of respiratory infections; in principle, this strategy should also be less susceptible to the development of pathogen resistance. In this review, we discuss different host-targeting strategies against pathogen-induced ARDS. Developing therapeutics that enhance the host response is a pathogen-agnostic approach that will help prepare for the next pandemic.

Lipedema: Insights into Morphology, Pathophysiology, and Challenges

Lipedema is an adipofascial disorder that almost exclusively affects women. Lipedema leads to chronic pain, swelling, and other discomforts due to the bilateral and asymmetrical expansion of subcutaneous adipose tissue. Although various distinctive morphological characteristics, such as the hyperproliferation of fat cells, fibrosis, and inflammation, have been characterized in the progression of lipedema, the mechanisms underlying these changes have not yet been fully investigated. In addition, it is challenging to reduce the excessive fat in lipedema patients using conventional weight-loss techniques, such as lifestyle (diet and exercise) changes, bariatric surgery, and pharmacological interventions. Therefore, lipedema patients also go through additional psychosocial distress in the absence of permanent treatment. Research to understand the pathology of lipedema is still in its infancy, but promising markers derived from exosome, cytokine, lipidomic, and metabolomic profiling studies suggest a condition distinct from obesity and lymphedema. Although genetics seems to be a substantial cause of lipedema, due to the small number of patients involved in such studies, the extrapolation of data at a broader scale is challenging. With the current lack of etiology-guided treatments for lipedema, the discovery of new promising biomarkers could provide potential solutions to combat this complex disease. This review aims to address the morphological phenotype of lipedema fat, as well as its unclear pathophysiology, with a primary emphasis on excessive interstitial fluid, extracellular matrix remodeling, and lymphatic and vasculature dysfunction. The potential mechanisms, genetic implications, and proposed biomarkers for lipedema are further discussed in detail. Finally, we mention the challenges related to lipedema and emphasize the prospects of technological interventions to benefit the lipedema community in the future.

In Vivo Targeting of the Neurovascular Unit: Challenges and Advancements

The blood-brain barrier (BBB) is essential for the homeostasis of the central nervous system (CNS). Functions of the BBB are performed by the neurovascular unit (NVU), which consists of endothelial cells, pericytes, astrocytes, microglia, basement membrane, and neurons. NVU cells interact closely and together are responsible for neurovascular coupling, BBB integrity, and transendothelial fluid transport. Studies have shown that NVU dysfunction is implicated in several acute and chronic neurological diseases, including Alzheimer's disease, multiple sclerosis, and stroke. The mechanisms of NVU disruption remain poorly understood, partially due to difficulties in selective targeting of NVU cells. In this review, we discuss the relative merits of available protein markers and drivers of the NVU along with recent advancements that have been made in the field to increase efficiency and specificity of NVU research.

Integrin-specific hydrogels for growth factor-free vasculogenesis

Integrin-binding biomaterials have been extensively evaluated for their capacity to enable de novo formation of capillary-like structures/vessels, ultimately supporting neovascularization in vivo. Yet, the role of integrins as vascular initiators in engineered materials is still not well understood. Here, we show that αvβ3 integrin-specific 3D matrices were able to retain PECAM1⁺ cells from the stromal vascular fraction (SVF) of adipose tissue, triggering vasculogenesis in vitro in the absence of extrinsic growth factors. Our results suggest that αvβ3-RGD-driven signaling in the formation of capillary-like structures prevents the activation of the caspase 8 pathway and activates the FAK/paxillin pathway, both responsible for endothelial cells (ECs) survival and migration. We also show that prevascularized αvβ3 integrin-specific constructs inosculate with the host vascular system fostering in vivo neovascularization. Overall, this work demonstrates the ability of the biomaterial to trigger vasculogenesis in an integrin-specific manner, by activating essential pathways for EC survival and migration within a self-regulatory growth factor microenvironment. This strategy represents an improvement to current vascularization routes for Tissue Engineering constructs, potentially enhancing their clinical applicability.

Transplantation of 3D bio-printed cardiac mesh improves cardiac function and vessel formation via ANGPT1/Tie2 pathway in rats with acute myocardial infarction

A novel tissue engineering strategy using 3D bio-print technology has become a promising therapeutic method for acute myocardial infarction (AMI) in an animal model. However, the application of 3D bio-printed tissue remains limited due to poor graft survival. Therefore, it is a scientific priority to enhance graft survival by precisely adjusting the 3D environment of encapsulated cells. In this study, novel transplantable 3D cardiac mesh (cMesh) tissue with a porous mesh structure was presented using human cardiomyocytes, human cardiac fibroblasts, and gelatin-methacryloyl-collagen hydrogel. Cardiomyocytes and cardiac fibroblasts were well spreaded. The cardiomyocytes were connected with a gap junction channel in bio-printed cMesh and a 3D cardiac patch with an aggregated structure. Porous cMesh demonstrated structural advantages by increased phosphorylation of mTOR, AKT, and ERK signals associated with cell survival. Transplanted cMesh in rats with AMI improved long-term graft survival, vessel formation, and stabilization, reduced fibrosis, increased left ventricle thickness, and enhanced cardiac function. Our results suggest that porous cMesh provides structural advantages and a positive therapeutic effect in an AMI animal model.

Human urine-derived stem cell-derived exosomal miR-21-5p promotes neurogenesis to attenuate Rett syndrome via the EPha4/TEK axis

Rett syndrome (RTT) is a rare neurodevelopmental disorder that results in multiple disabilities. Exosomal microRNA (miRs) from urine-derived stem cells (USCs) have been shown to induce neurogenesis and aid in functional recovery from brain ischemia. In the present study, we sought to determine whether that exosomal miR-21-5p from USCs could promote early neural formation in a model of RTT. USCs were isolated and evaluated by flow cytometry. Exosomes were analyzed by transmission electron microscopy, tunable resistive pulse sensing (TRPS), and western blotting. PKH26 fluorescent dyes were used to observe intake of exosomes in vivo and in vitro. An RTT mouse model was treated with exosomes for behavioral studies. Dual-luciferase report gene assays were conducted to evaluate the relationship between miR-21-5p and Eph receptor A4 (EphA4). In vitro, treatment with exosomes from human urine-derived stem cells (USC-Exos) increased the percentage of neuron-specific class III beta-tubulin (Tuj1)+ nerve cells as well as the transcription levels of β-III tubulin and doublecortin (DCX). A higher level of miR-21-5p was observed in USC-Exos, which promoted differentiation in NSCs by targeting the EPha4/TEK axis. In vivo, exosomal miR-21-5p improved the behavior, motor coordination, and cognitive ability of mice, facilitated the differentiation of NSCs in the subventricular zone of the lateral ventricle and promoted a marked rise in the number of DCX+ cells. Our data provide evidence that exosomal miR-21-5p from human USCs facilitate early nerve formation by regulating the EPha4/TEK axis.

Novel angiogenesis strategy to ameliorate pulmonary hypertension

OBJECTIVE

To select a suitable combination of classic angiogenic and vascular stabilization factors to improve the proliferation and maturity of neovascularization of lung tissue in a rat pulmonary arterial hypertension (PAH) model.

METHODS

PAH rat model was established by intraperitoneal injection of monocrotaline. Proangiogenic factors hepatocyte growth factor (HGF) and vascular endothelial growth factor (VEGF), as well as vascular stabilization factors angiopoietin-1 (Ang-1), platelet-derived growth factor, and transforming growth factor-beta were transfected by pairs into the lung tissue of rats with PAH through lentivirus. Four weeks later, pulmonary artery angiography and hemodynamic parameters were determined to testify the remission of PAH. Immunofluorescence staining and Western blot were performed to investigate the structure and function of neovascularization.

RESULTS

The pulmonary artery pressure and weight index of the right ventricle in HGF+Ang-1 and VEGF+Ang-1 groups were significantly decreased compared with vehicle group. The contrast medium filling time and right pulmonary artery root diameter were also significantly decreased. In addition, the maturity and perfusion of neovascularization in HGF+Ang-1 and VEGF+Ang-1 groups were promoted compared to vehicle group, and vascular leakage was reduced. Finally, the adherens junction integrity of vascular endothelial cells in HGF+Ang-1 and VEGF+Ang-1 combinations was upregulated compared with other combinations.

CONCLUSIONS

HGF+Ang-1 transfection and VEGF+Ang-1 transfection alleviate PAH by promoting maturation and stability of new blood vessels, which may be potential candidates for PAH treatment.

EphA4/Tie2 crosstalk regulates leptomeningeal collateral remodeling following ischemic stroke

Leptomeningeal anastomoses or pial collateral vessels play a critical role in cerebral blood flow (CBF) restoration following ischemic stroke. The magnitude of this adaptive response is postulated to be controlled by the endothelium, although the underlying molecular mechanisms remain under investigation. Here we demonstrated that endothelial genetic deletion, using EphA4fl/fl/Tie2-Cre and EphA4fl/fl/VeCahderin-CreERT2 mice and vessel painting strategies, implicated EphA4 receptor tyrosine kinase as a major suppressor of pial collateral remodeling, CBF, and functional recovery following permanent middle cerebral artery occlusion. Pial collateral remodeling is limited by the crosstalk between EphA4-Tie2 signaling in vascular endothelial cells, which is mediated through p-Akt regulation. Furthermore, peptide inhibition of EphA4 resulted in acceleration of the pial arteriogenic response. Our findings demonstrate that EphA4 is a negative regulator of Tie2 receptor signaling, which limits pial collateral arteriogenesis following cerebrovascular occlusion. Therapeutic targeting of EphA4 and/or Tie2 represents an attractive new strategy for improving collateral function, neural tissue health, and functional recovery following ischemic stroke.

Intravitreal AAV2.COMP-Ang1 Attenuates Deep Capillary Plexus Expansion in the Aged Diabetic Mouse Retina

Purpose

We determine whether intravitreal angiopoietin-1 combined with the short coiled-coil domain of cartilage oligomeric matrix protein by adeno-associated viral serotype 2 (AAV2.COMP-Ang1) delivery following the onset of vascular damage could rescue or repair damaged vascular beds and attenuate neuronal atrophy and dysfunction in the retinas of aged diabetic mice.

Methods

AAV2.COMP-Ang1 was bilaterally injected into the vitreous of 6-month-old male Ins2Akita mice. Age-matched controls consisted of uninjected C57BL/6J and Ins2Akita males, and of Ins2Akita males injected with PBS or AAV2.REPORTER (AcGFP or LacZ). Retinal thickness and visual acuity were measured in vivo at baseline and at the 10.5-month endpoint. Ex vivo vascular parameters were measured from retinal flat mounts, and Western blot was used to detect protein expression.

Results

All three Ins2Akita control groups showed significantly increased deep vascular density at 10.5 months compared to uninjected C57BL/6J retinas (as measured by vessel area, length, lacunarity, and number of junctions). In contrast, deep microvascular density of Ins2Akita retinas treated with AAV2.COMP-Ang1 was more similar to uninjected C57BL/6J retinas for all parameters. However, no significant improvement in retinal thinning or diabetic retinopathy-associated visual loss was found in treated diabetic retinas.

Conclusions

Deep retinal microvasculature of diabetic Ins2Akita eyes shows late stage changes consistent with disorganized vascular proliferation. We show that intravitreally injected AAV2.COMP-Ang1 blocks this increase in deep microvascularity, even when administered subsequent to development of the first detectable vascular defects. However, improving vascular normalization did not attenuate neuroretinal degeneration or loss of visual acuity. Therefore, additional interventions are required to address neurodegenerative changes that are already underway.

Pericytes Contribute to Dysfunction in a Human 3D Model of Placental Microvasculature through VEGF-Ang-Tie2 Signaling

Placental vasculopathies are associated with a number of pregnancy-related diseases, including pre-eclampsia (PE)-a leading cause of maternal-fetal morbidity and mortality worldwide. Placental presentations of PE are associated with endothelial dysfunction, reduced vessel perfusion, white blood cell infiltration, and altered production of angiogenic factors within the placenta (a candidate mechanism). Despite maintaining vascular quiescence in other tissues, how pericytes contribute to vascular growth and signaling in the placenta remains unknown. Here, pericytes are hypothesized to play a detrimental role in the pathogenesis of placental vascular growth. A perfusable triculture model is developed, consisting of human endothelial cells, fibroblasts, and pericytes, capable of recapitulating growth and remodeling in a system that mimics inflamed placental microvessels. Placental pericytes are shown to contribute to growth restriction of microvessels over time, an effect that is strongly regulated by vascular endothelial growth factor and Angiopoietin/Tie2 signaling. Furthermore, this model is capable of recapitulating essential processes including tumor necrosis factor alpha (TNFα)-mediated vascular leakage and leukocyte infiltration, both important aspects associated with placental PE. This placental vascular model highlights that an imbalance in endothelial-pericyte crosstalk can play a critical role in the development of vascular pathology and associated diseases.

Sodium nitroprusside prevents the detrimental effects of glucose on the neurovascular unit and behaviour in zebrafish

Diabetes is associated with dysfunction of the neurovascular unit, although the mechanisms of this are incompletely understood and currently no treatment exists to prevent these negative effects. We previously found that the nitric oxide (NO) donor sodium nitroprusside (SNP) prevents the detrimental effect of glucose on neurovascular coupling in zebrafish. We therefore sought to establish the wider effects of glucose exposure on both the neurovascular unit and on behaviour in zebrafish, and the ability of SNP to prevent these. We incubated 4-days post-fertilisation (dpf) zebrafish embryos in 20 mM glucose or mannitol for 5 days until 9 dpf, with or without 0.1 mM SNP co-treatment for 24 h (8-9 dpf), and quantified vascular NO reactivity, vascular mural cell number, expression of a klf2a reporter, glial fibrillary acidic protein (GFAP) and transient receptor potential cation channel subfamily V member 4 (TRPV4), as well as spontaneous neuronal activation at 9 dpf, all in the optic tectum. We also assessed the effect on light/dark preference and locomotory characteristics during free-swimming studies. We find that glucose exposure significantly reduced NO reactivity, klf2a reporter expression, vascular mural cell number and TRPV4 expression, while significantly increasing spontaneous neuronal activation and GFAP expression (all in the optic tectum). Furthermore, when we examined larval behaviour, we found that glucose exposure significantly altered light/dark preference and high and low speed locomotion while in light. Co-treatment with SNP reversed all these molecular and behavioural effects of glucose exposure. Our findings comprehensively describe the negative effects of glucose exposure on the vascular anatomy, molecular phenotype and function of the optic tectum, and on whole-organism behaviour. We also show that SNP or other NO donors may represent a therapeutic strategy to ameliorate the complications of diabetes on the neurovascular unit.This article has an associated First Person interview with the first author of the paper.

Angiopoietin-1 accelerates restoration of endothelial cell barrier integrity from nanoparticle-induced leakiness

Nanoparticles (NPs) have been widely used in biomedical field for therapeutic treatments, drug carriers, and bio-imaging agent. Recent studies have highlighted the possibility of utilizing inorganic NPs in inducing endothelial leakiness through endothelial remodeling to promote drug transport across the barrier. However, an uncontrolled and persistent leakiness could lead to promiscuous transport of molecules and cells across the barrier, highlighting the pressing need to control the timely recovery from endothelial cell leakiness. Herein, we show that angiopoietin-1 (Ang1) could promote recovery of human microvascular endothelial cells (HMVECs) from titanium dioxide nanoparticle (TiO₂ NPs)-induced endothelial leakiness. Ang1 is known as an anti-permeability growth factor which forms complexes with its receptor Tie2 at the cell-to-cell junctions. We find that the introduction of Ang1 not only accelerates the recovery of NP-induced endothelial leakiness (NanoEL) but also promotes cell rigidity by increasing tubulin acetylation, thereby remodels the endothelial cells to further mitigate the effects of NP exposure through the activation of the Akt pathway. Using in vitro metastasis model, we further show that HMVECs treated with TiO₂ NPs followed by Ang1 could reduce migration of human skin cancer A431 cells across the endothelial barrier. In summary, Ang1 plays important roles in promoting the recovery of endothelial cell leakiness and endothelial stability through a mechano-transduction pathway and shows great potential as key modulator that allows material scientist to regulate endothelial leakiness induced by NPs.

Methods to label, image, and analyze the complex structural architectures of microvascular networks

Microvascular networks play key roles in oxygen transport and nutrient delivery to meet the varied and dynamic metabolic needs of different tissues throughout the body, and their spatial architectures of interconnected blood vessel segments are highly complex. Moreover, functional adaptations of the microcirculation enabled by structural adaptations in microvascular network architecture are required for development, wound healing, and often invoked in disease conditions, including the top eight causes of death in the Unites States. Effective characterization of microvascular network architectures is not only limited by the available techniques to visualize microvessels but also reliant on the available quantitative metrics that accurately delineate between spatial patterns in altered networks. In this review, we survey models used for studying the microvasculature, methods to label and image microvessels, and the metrics and software packages used to quantify microvascular networks. These programs have provided researchers with invaluable tools, yet we estimate that they have collectively attained low adoption rates, possibly due to limitations with basic validation, segmentation performance, and nonstandard sets of quantification metrics. To address these existing constraints, we discuss opportunities to improve effectiveness, rigor, and reproducibility of microvascular network quantification to better serve the current and future needs of microvascular research.

Angiopoietin/Tie2 Axis Regulates the Age-at-Injury Cerebrovascular Response to Traumatic Brain Injury

Although age-at-injury influences chronic recovery from traumatic brain injury (TBI), the differential effects of age on early outcome remain understudied. Using a male murine model of moderate contusion injury, we investigated the underlying mechanism(s) regulating the distinct response between juvenile and adult TBI. We demonstrate similar biomechanical and physical properties of naive juvenile and adult brains. However, following controlled cortical impact (CCI), juvenile mice displayed reduced cortical lesion formation, cell death, and behavioral deficits at 4 and 14 d. Analysis of high-resolution laser Doppler imaging showed a similar loss of cerebral blood flow (CBF) in the ipsilateral cortex at 3 and 24 h post-CCI, whereas juvenile mice showed enhanced subsequent restoration at 2-4 d compared with adults. These findings correlated with reduced blood-brain barrier (BBB) disruption and increased perilesional vessel density. To address whether an age-dependent endothelial cell (EC) response affects vessel stability and tissue outcome, we magnetically isolated CD31⁺ ECs from sham and injured cortices and evaluated mRNA expression. Interestingly, we found increased transcripts for BBB stability-related genes and reduced expression of BBB-disrupting genes in juveniles compared with adults. These differences were concomitant with significant changes in miRNA-21-5p and miR-148a levels. Accompanying these findings was robust GFAP immunoreactivity, which was not resolved by day 35. Importantly, pharmacological inhibition of EC-specific Tie2 signaling abolished the juvenile protective effects. These findings shed new mechanistic light on the divergent effects that age plays on acute TBI outcome that are both spatial and temporal dependent.SIGNIFICANCE STATEMENT Although a clear "window of susceptibility" exists in the developing brain that could deter typical developmental trajectories if exposed to trauma, a number of preclinical models have demonstrated evidence of early recovery in younger patients. Our findings further demonstrate acute neuroprotection and improved restoration of cerebral blood flow in juvenile mice subjected to cortical contusion injury compared with adults. We also demonstrate a novel role for endothelial cell-specific Tie2 signaling in this age-related response, which is known to promote barrier stability, is heightened in the injured juvenile vasculature, and may be exploited for therapeutic interventions across the age spectrum following traumatic brain injury.

Delineating Pro-Angiogenic Myeloid Cells in Cancer Therapy

Recent evidence suggests that myeloid cells are critical in cancer development and therapy resistance processes. Pharmacological targeting of tumor-associated myeloid cells is an emerging approach among upcoming immune therapies. Surprisingly, myeloid cells are heterogeneous, including a subset of the myeloid cell displaying angiogenic properties in solid tumors. There is an urgent need to delineate angiogenic myeloid cell populations in order to facilitate specific targeting of protumor myeloid cells among heterogeneous pool. This review article is intended to compile all the relevant information in the literature for improved understanding of angiogenic myeloid cells and their role in tumor refractoriness to cancer therapy.

Biological Features of Bone Marrow Mesenchymal Stromal Cells in Childhood Acute Lymphoblastic Leukemia

Objective:

Mesenchymal stromal cells (MSCs) have a supportive role in hematopoiesis and as components of the bone marrow (BM) microenvironment may present alterations during acute lymphoblastic leukemia (ALL) and be affected by chemotherapeutic agents. We examined the biological and functional characteristics of MSCs in ALL diagnosis and treatment and their effect on MSC qualitative properties.

Materials and Methods:

Immunophenotypic characterization, evaluation of clonogenicity, and proliferative capacity were measured. Apoptotic features, cell-cycle analysis, and stromal cell-derived factor 1α and angiopoietin-1 levels in MSC supernatant at diagnosis and in different phases of treatment were assessed. Chemotherapy was administered according to the Berlin-Frankfurt-Munster-2000 protocol. BM samples from children with solid tumors without BM involvement were used as the control group.

Results:

The morphology, the immunophenotypic profile, and the apoptotic characteristics of the MSCs were not affected by leukemia. The secretion of factors involved in the trafficking of hematopoietic cells in the BM seems to be upregulated at diagnosis in comparison to the treatment phases. MSCs are influenced by the disease in terms of their functional characteristics such as clonogenicity and proliferation rate. These effects cease as soon as treatment is initiated. Chemotherapy does not seem to exert any effect on any of the MSC features examined.

Conclusion:

MSCs from children with ALL are affected by their interaction with the leukemic environment, but this phenomenon ceases upon treatment initiation, while no effect is observed by chemotherapy itself.

Multimodal Genetic Approach for Molecular Imaging of Vasculature in a Mouse Model of Melanoma

PURPOSE

In this study, we evaluated a genetic approach for in vivo multimodal molecular imaging of vasculature in a mouse model of melanoma.

PROCEDURES

We used a novel transgenic mouse, Ts-Biotag, that genetically biotinylates vascular endothelial cells. After inoculating these mice with B16 melanoma cells, we selectively targeted endothelial cells with (strept)avidinated contrast agents to achieve multimodal contrast enhancement of Tie2-expressing blood vessels during tumor progression.

RESULTS

This genetic targeting system provided selective labeling of tumor vasculature and showed in vivo binding of avidinated probes with high specificity and sensitivity using microscopy, near infrared, ultrasound, and magnetic resonance imaging. We further demonstrated the feasibility of conducting longitudinal three-dimensional (3D) targeted imaging studies to dynamically assess changes in vascular Tie2 from early to advanced tumor stages.

CONCLUSIONS

Our results validated the Ts-Biotag mouse as a multimodal targeted imaging system with the potential to provide spatio-temporal information about dynamic changes in vasculature during tumor progression.

Angiopoetin-2 Signals Do Not Mediate the Hypervascularization of Islets in Type 2 Diabetes

AIMS

Changes in the islet vasculature have been implicated in the regulation of β-cell survival and function during the progression to type 2 diabetes (T2D). Failure of the β-cell to compensate for the increased insulin demand in obesity eventually leads to diabetes; as a result of the complex interplay of genetic and environmental factors (e.g. ongoing inflammation within the islets) and impaired vascular function. The Angiopoietin/Tie (Ang/Tie) angiogenic system maintains vasculature and is closely related to organ inflammation and angiogenesis. In this study we aimed to identify whether the vessel area within the islets changes in diabetes and whether such changes would be triggered by the Tie-antagonist Ang-2.

METHODS

Immunohistochemical and qPCR analyses to follow islet vascularization and Ang/Tie levels were performed in human pancreatic autopsies and isolated human and mouse islets. The effect of Ang-2 was assessed in β-cell-specific Ang-2 overexpressing mice during high fat diet (HFD) feeding.

RESULTS

Islet vessel area was increased in autopsy pancreases from patients with T2D. The vessel markers Tie-1, Tie-2 and CD31 were upregulated in mouse islets upon HFD feeding from 8 to 24 weeks. Ang-2 was transiently upregulated in mouse islets at 8 weeks of HFD and under glucolipotoxic conditions (22.2 mM glucose/ 0.5 mM palmitate) in vitro in human and mouse islets, in contrast to its downregulation by cytokines (IL-1β, IFN-ɣ and TNF-α). Ang-1 on the other hand was oppositely regulated, with a significant loss under glucolipotoxic condition, a trend to reduce in islets from patients with T2D and an upregulation by cytokines. Modulation of such changes in Ang-2 by its overexpression or the inhibition of its receptor Tie-2 impaired β-cell function at basal conditions but protected islets from cytokine induced apoptosis. In vivo, β-cell-specific Ang-2 overexpression in mice induced hypervascularization under normal diet but contrastingly led to hypovascularized islets in response to HFD together with increased apoptosis and reduced β-cell mass.

CONCLUSIONS

Islet hypervascularization occurs in T2D. A balanced expression of the Ang1/Ang2 system is important for islet physiology. Ang-2 prevents β-cell mass and islet vascular adaptation in response to HFD feeding with no major influence on glucose homeostasis.

Angiopoietin receptor TEK mutations underlie primary congenital glaucoma with variable expressivity

Primary congenital glaucoma (PCG) is a devastating eye disease and an important cause of childhood blindness worldwide. In PCG, defects in the anterior chamber aqueous humor outflow structures of the eye result in elevated intraocular pressure (IOP); however, the genes and molecular mechanisms involved in the etiology of these defects have not been fully characterized. Previously, we observed PCG-like phenotypes in transgenic mice that lack functional angiopoietin-TEK signaling. Herein, we identified rare TEK variants in 10 of 189 unrelated PCG families and demonstrated that each mutation results in haploinsufficiency due to protein loss of function. Multiple cellular mechanisms were responsible for the loss of protein function resulting from individual TEK variants, including an absence of normal protein production, protein aggregate formation, enhanced proteasomal degradation, altered subcellular localization, and reduced responsiveness to ligand stimulation. Further, in mice, hemizygosity for Tek led to the formation of severely hypomorphic Schlemm's canal and trabecular meshwork, as well as elevated IOP, demonstrating that anterior chamber vascular development is sensitive to Tek gene dosage and the resulting decrease in angiopoietin-TEK signaling. Collectively, these results identify TEK mutations in patients with PCG that likely underlie disease and are transmitted in an autosomal dominant pattern with variable expressivity.

Angiopoietin-1 facilitates recovery of hematopoiesis in radiated mice

Angiopoietin-1 (Ang-1) plays a critical role in the regulation of endothelial cell survival and vascular maturation and stability. However, its role in hematopoiesis is not clear. Here, we determined effect of Ang-1 on the recovery of hematopoiesis in radiated mice. By injecting an Ang-1 plasmid, we found that Ang-1 was preferentially expressed in bone marrow (BM) of femur from radiated mice. This injection resulted in elevated blood counts and serum VEGF level. The blockade in S phase of cell cycle in mouse BM stromal cells following radiation was attenuated by injection of Ang-1 plasmid. In addition, injection of Ang-1 plasmid attenuated the radiation-mediated inhibition of Tie2 expression. Furthermore, through analyzing Notch1 expression, we found that injection of Ang-1 plasmid increased Notch mRNA expression in radiated mice. In conclusion, these findings suggest that Ang-1 facilitates the recovery of hematopoiesis in radiated mice with the involvement of Notch signaling pathway.

Runx1 downregulates stem cell and megakaryocytic transcription programs that support niche interactions

Disrupting mutations of the RUNX1 gene are found in 10% of patients with myelodysplasia (MDS) and 30% of patients with acute myeloid leukemia (AML). Previous studies have revealed an increase in hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells in conditional Runx1-knockout (KO) mice, but the molecular mechanism is unresolved. We investigated the myeloid progenitor (MP) compartment in KO mice, arguing that disruptions at the HSC/MPP level may be amplified in downstream cells. We demonstrate that the MP compartment is increased by more than fivefold in Runx1 KO mice, with a prominent skewing toward megakaryocyte (Meg) progenitors. Runx1-deficient granulocyte-macrophage progenitors are characterized by increased cloning capacity, impaired development into mature cells, and HSC and Meg transcription signatures. An HSC/MPP subpopulation expressing Meg markers was also increased in Runx1-deficient mice. Rescue experiments coupled with transcriptome analysis and Runx1 DNA-binding assays demonstrated that granulocytic/monocytic (G/M) commitment is marked by Runx1 suppression of genes encoding adherence and motility proteins (Tek, Jam3, Plxnc1, Pcdh7, and Selp) that support HSC-Meg interactions with the BM niche. In vitro assays confirmed that enforced Tek expression in HSCs/MPPs increases Meg output. Interestingly, besides this key repressor function of Runx1 to control lineage decisions and cell numbers in progenitors, our study also revealed a critical activating function in erythroblast differentiation, in addition to its known importance in Meg and G/M maturation. Thus both repressor and activator functions of Runx1 at multiple hematopoietic stages and lineages likely contribute to the tumor suppressor activity in MDS and AML.

[Changes of angiopoietin 1 expression in G-CSF induced hematopoietic stem progenitor cells mobilization]

目的

探讨G-CSF诱导的造血干／祖细胞（HSPC）动员过程中血管生成素1(Ang1)在小鼠骨髓的表达变化及导致其变化的机制。

方法

采用流式细胞术检测小鼠动员前及动员后外周血Lin⁻Sca1⁺cKit⁺(LSK)细胞比例变化，并应用ELISA、免疫组化、RQ-PCR等方法检测G-CSF动员不同时间点小鼠外周血和骨髓标本，观察Ang1、骨钙素（OCN）基因及蛋白水平变化，显微镜下计数骨髓标本成骨细胞数量。

结果

G-CSF动员5 d小鼠外周血LSK细胞比例为（0.61±0.05)%，相对于对照组的(0.04±0.01)%显著增高(P<0.05)；稳态小鼠OCN及Ang1 mRNA在骨内膜细胞表达高于骨髓有核细胞；动员后骨内膜细胞OCN及Ang1 mRNA相对表达量对照组（28.64±8.61及2.84±0.95)、G-CSF动员3 d组（12.55±7.06及0.93±0.30）及动员5 d组（4.75±1.62及0.92±0.22）均下降；动员后骨内膜成骨细胞数量显著减少，骨髓组织Ang1蛋白表达下降；对照组、动员3 d及5 d组外周血OCN及Ang1浓度分别为（24.11±3.17）及（2.24±0.52)ng/ml、(9.96±2.16）及（1.21±0.38)ng/ml和（8.43±2.62）及(0.90±0.24) ng/ml，动员3 d及5 d组均明显低于对照组，差异均有统计学意义(P值均<0.05)。

结论

在G-CSF介导的HSPC动员过程中，骨髓微环境中成骨细胞数量下降、功能减低，进而导致骨髓Ang1表达下降，导致骨髓对HSPC的趋化和黏附能力下降，有利于HSPC动员的发生。

Evaluating the Impact of Human Amnion Epithelial Cells on Angiogenesis

The effects of human amnion epithelial cells (hAECs) on angiogenesis remain controversial. It is yet unknown if the presence of inflammation and/or gestational age of hAEC donors have an impact on angiogenesis. In this study, we examined the differences between term and preterm hAECs on angiogenesis in vitro and in vivo. Conditioned media from term hAECs induced the formation of longer huVEC tubules on Matrigel. Both term and preterm hAECs expressed VEGFA, PDGFB, ANGPT1, and FOXC1, which significantly increased after TNFα and IFNγ stimulation. In the presence of TNFα and IFNγ, coculture with term hAECs reduced gene transcription of Tie-2 and Foxc1 in huVECs, while coculture with preterm hAECs increased gene transcription of PDGFRα and PDGFRβ and reduced gene transcription of FOXC1 in huVECs. In vivo assessment of angiogenesis using vWF immunostaining revealed that hAEC treatment decreased angiogenesis in a bleomycin model of lung fibrosis but increased angiogenesis in a neonatal model of hyperoxia-induced lung injury. In summary, our findings suggested that the impact of hAECs on angiogenesis may be influenced by the presence of inflammation and underlying pathology.

A murine toolbox for imaging the neurovascular unit

The neurovascular unit (NVU) coordinates many essential functions in the brain including blood flow control, nutrient delivery, and maintenance of BBB integrity. These functions are the result of a cellular and molecular interplay that we are just beginning to understand. Cells of the NVU can now be investigated in the intact brain through the combined use of high-resolution in vivo imaging and non-invasive molecular tools to observe and manipulate cell function. Mouse lines that target transgene expression to cells of the NVU will be of great value in future work. However, a detailed evaluation of target cell specificity and expression pattern within the brain is required for many existing lines. The purpose of this review was to catalog mouse lines available to cerebrovascular biologists and to discuss their utility and limitations in future imaging studies.

Regulation of Angiogenic Functions by Angiopoietins through Calcium-Dependent Signaling Pathways

Angiopoietins are vascular factors essential for blood vessel assembly and correct organization and maturation. This study describes a novel calcium-dependent machinery activated through Angiopoietin-1/2-Tie receptor system in HUVECs monolayer. Both cytokines were found to elicit intracellular calcium mobilization. Targeting intracellular Ca²⁺ signaling, antagonizing IP₃ with 2-APB or cADPR with 8Br-cADPR, was found to modulate in vitro angiogenic responses to Angiopoietins in a specific way. 2-APB and 8Br-cADPR impaired the phosphorylation of AKT and FAK induced by Ang-1 and Ang-2. On the other hand, phosphorylation of ERK1/2 and p38, as well as cell proliferation, was not affected by either inhibitor. The ability of ECs to migrate following Angs stimulation, evaluated by “scratch assay,” was reduced by either 2-APB or 8Br-cADPR following Ang-2 stimulation and only slightly affected by 2-APB in cells stimulated with Ang-1. These results identify a novel calcium-dependent machinery involved in the complex interplay regulating angiogenic processes showing that IP₃- and cADPR-induced Ca²⁺ release specifically regulates distinct Angs-mediated angiogenic steps.

Controlled protein delivery in the generation of microvascular networks

Rapid induction and stabilization of new microvascular networks is essential for the proper functioning of engineered tissues. Many efforts to achieve this goal have used proangiogenic proteins-such as vascular endothelial growth factors-to induce the formation of new microvessels. These proteins have demonstrated promise in improving vascularization, but it is also clear that the spatial and temporal presentation of these signals is important for achieving proper vascular function. Delivery systems that present proteins in a localized and sustained manner, can promote the formation and stabilization of microvascular networks by precisely presenting proangiogenic proteins at desired locations, and for specified durations. Further, these systems allow for some control over the sequence of release of multiple proteins, and it has become clear that such coordination is critical for the development of fully functional and mature vascular structures. This review focuses on the actions of proangiogenic proteins and the innovations in controlled release technologies that precisely deliver these to stimulate microvascular network formation and stabilization.

Angiopoietin-2 in Bone Marrow milieu promotes Multiple Myeloma-associated angiogenesis

Angiopoietin-2 (Ang-2) is involved in angiogenesis in both solid and hematological malignancies. In Multiple Myeloma (MM), serum Ang-2 correlates with disease progression and response to therapy. To address the patho-physiologic role of Ang-2 in MM associated angiogenesis, we used sera from patients with active MM, which contained significantly higher levels of the molecule, compared to those from patients with smoldering MM and Monoclonal Gammopathy of Undetermined Significance. MM Bone Marrow (BM) sera with high Ang-2 concentration specifically contributed to endothelial cell (EC) activation, while Ang-1 containing sera maintained EC stabilization. The functional dichotomy of Ang-1 and Ang-2 was confirmed by the triggering of distinctive signaling pathways down-stream the common Tie-2 receptor, i.e., the Akt or the ERK- phosphorylation pathway. Notably, Ang-2 but not VEGF serum levels correlated with BM micro-vessel density, further underscoring the key role of Ang-2 in angiogenesis. Western Blot, RT-PCR and immunocytochemistry identified MMEC as the major source of Ang-2, at variance with MM cells and CD14(+) BM monocytes. These data suggest that Ang-2 produced in the BM milieu may contribute to MM angiogenesis and suggest that the molecule can be further exploited both as angiogenesis biomarker and as a potential therapeutic target.

Inhibition of tyrosine kinase receptor Tie2 reverts HCV-induced hepatic stellate cell activation

Background

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease (CLD) and is frequently linked to intrahepatic microvascular disorders. Activation of hepatic stellate cells (HSC) is a central event in liver damage, due to their contribution to hepatic renewal and to the development of fibrosis and hepatocarcinoma. During the progression of CLDs, HSC attempt to restore injured tissue by stimulating repair processes, such as fibrosis and angiogenesis. Because HSC express the key vascular receptor Tie2, among other angiogenic receptors and mediators, we analyzed its involvement in the development of CLD.

Methods

Tie2 expression was monitored in HSC cultures that were exposed to media from HCV-expressing cells (replicons). The effects of Tie2 blockade on HSC activation by either neutralizing antibody or specific signaling inhibitors were also examined.

Results

Media from HCV-replicons enhanced HSC activation and invasion and upregulated Tie2 expression. Notably, the blockade of Tie2 receptor (by a specific neutralizing antibody) or signaling (by selective AKT and MAPK inhibitors) significantly reduced alpha-smooth muscle actin (α-SMA) expression and the invasive potential of HCV-conditioned HSC.

Conclusions

These findings ascribe a novel profibrogenic function to Tie2 receptor in the progression of chronic hepatitis C, highlighting the significance of its dysregulation in the evolution of CLDs and its potential as a novel therapeutic target.

Thyroid hormone induces sprouting angiogenesis in adult heart of hypothyroid mice through the PDGF-Akt pathway

Study of physiological angiogenesis and associated signalling mechanisms in adult heart has been limited by the lack of a robust animal model. We investigated thyroid hormone-induced sprouting angiogenesis and the underlying mechanism. Hypothyroidism was induced in C57BL/6J mice by feeding with propylthiouracil (PTU). One year of PTU treatment induced heart failure. Both 12 weeks- (young) and 1 year-PTU (middle age) treatment caused a remarkable capillary rarefaction observed in capillary density. Three-day Triiodothyronine (T3) treatment significantly induced cardiac capillary growth in hypothyroid mice. In cultured left ventricle (LV) tissues from PTU-treated mice, T3 also induced robust sprouting angiogenesis where pericyte-wrapped endothelial cells formed tubes. The in vitro T3 angiogenic response was similar in mice pre-treated with PTU for periods ranging from 1.5 to 12 months. Besides bFGF and VEGF₁₆₄, PDGF-BB was the most robust angiogenic growth factor, which stimulated notable sprouting angiogenesis in cultured hypothyroid LV tissues with increasing potency, but had little effect on tissues from euthyroid mice. T3 treatment significantly increased PDGF receptor beta (PDGFR-β) protein levels in hypothyroid heart. PDGFR inhibitors blocked the action of T3 both on sprouting angiogenesis in cultured LV tissue and on capillary growth in vivo. In addition, activation of Akt signalling mediated in T3-induced angiogenesis was blocked by PDGFR inhibitor and neutralizing antibody. Our results suggest that hypothyroidism leads to cardiac microvascular impairment and rarefaction with increased sensitivity to angiogenic growth factors. T3-induced cardiac sprouting angiogenesis in adult hypothyroid mice was associated with PDGF-BB, PDGFR-β and downstream activation of Akt.

Expression of angiopoietin-TIE system components in angiosarcoma

Angiosarcoma is an aggressive malignancy of endothelial differentiation. Potential roles of the endothelial angiopoietin-tunica interna endothelial cell kinase (ANGPT-TIE) system in angiosarcoma diagnosis, pathogenesis, prognosis and treatment are undefined. To examine the expression and prognostic significance of angiopoietin-1, angiopoietin-2, TIE1 and TEK (TIE2) proteins in angiosarcoma, we immunohistochemically evaluated clinically annotated human angiosarcoma samples. Correlations of protein expression with overall survival and pathological features were explored. The cohort included 51 patients diagnosed with angiosarcoma at the age of 30-86 years (median 67). The 5-year overall survival was 45% with a median of 26 months. Moderate to strong expression of angiopoietin-1, TIE1 and TEK (TIE2) was identified in the majority of angiosarcomas and moderate to strong expression of angiopoietin-2 was observed in 42% of angiosarcomas. Increased angiopoietin-1 expression correlated with improved survival. Non-significant trends toward longer survival were also observed with increased TIE1 and TEK (TIE2) expression. Increased expression of angiopoietin-2, TIE1 and TEK (TIE2) was associated with vasoformative architecture. No differences in expression of these proteins were observed when patients were segregated by age, gender, presence or absence of metastases at diagnosis, primary tumor location, radiation association or the presence of necrosis. We conclude that components of the ANGPT-TIE system are commonly expressed in angiosarcomas. Reduced expression of these proteins is associated with non-vasoformative and clinically more aggressive lesions.

Formation of a PKCζ/β-catenin complex in endothelial cells promotes angiopoietin-1-induced collective directional migration and angiogenic sprouting

Angiogenic sprouting requires that cell-cell contacts be maintained during migration of endothelial cells. Angiopoietin-1 (Ang-1) and vascular endothelial growth factor act oppositely on endothelial cell junctions. We found that Ang-1 promotes collective and directional migration and, in contrast to VEGF, induces the formation of a complex formed of atypical protein kinase C (PKC)-ζ and β-catenin at cell-cell junctions and at the leading edge of migrating endothelial cells. This complex brings Par3, Par6, and adherens junction proteins at the front of migrating cells to locally activate Rac1 in response to Ang-1. The colocalization of PKCζ and β-catenin at leading edge along with PKCζ-dependent stabilization of cell-cell contacts promotes directed and collective endothelial cell migration. Consistent with these results, down-regulation of PKCζ in endothelial cells alters Ang-1-induced sprouting in vitro and knockdown in developing zebrafish results in intersegmental vessel defects caused by a perturbed directionality of tip cells and by loss of cell contacts between tip and stalk cells. These results reveal that PKCζ and β-catenin function in a complex at adherens junctions and at the leading edge of migrating endothelial cells to modulate collective and directional migration during angiogenesis.

Efficacy of Tie2 receptor antagonism in angiosarcoma

Angiosarcomas are malignant endothelial cell tumors with few effective systemic treatments. Despite a unique endothelial origin, molecular candidates for targeted therapeutic intervention have been elusive. In this study, we explored the tunica internal endothelial cell kinase 2 (Tie2) receptor as a potential therapeutic target in angiosarcoma. Human angiosarcomas from diverse sites were shown to be universally immunoreactive for Tie2. Tie2 and vascular endothelial growth factor receptor (VEGFR) antagonists inhibited SVR and MS1-VEGF angiosarcoma cell survival in vitro. In the high-grade SVR cell line, Tie2 and VEGF antagonists inhibited cell survival synergistically, whereas effects were largely additive in the low-grade MS1-VEGF cell line. Xenograft modeling using these cell lines closely recapitulated the human disease. In vivo, Tie2 and VEGFR inhibition resulted in significant angiosarcoma growth delay. The combination proved more effective than either agent alone. Tie2 inhibition seemed to elicit tumor growth delay through increased tumor cell apoptosis, whereas VEGFR inhibition reduced tumor growth by lowering tumor cell proliferation. These data identify Tie2 antagonism as a potential novel, targeted therapy for angiosarcomas and provide a foundation for further investigation of Tie2 inhibition, alone and in combinations, in the management of this disease.

Novel genetic approach for in vivo vascular imaging in mice

RATIONALE

The formation and maintenance of a functional vasculature is essential for normal embryonic development, and genetic changes that affect the vasculature underlie pathogenesis in many human diseases. In vivo imaging in mouse models is required to understand the full complexity of mammalian vascular formation, which is a dynamic and 3-dimensional process. Optical microscopy of genetically expressed fluorescent reporter proteins offers high resolution but limited depth of penetration in vivo. Conversely, there are a plethora of molecular probes for alternative in vivo vascular imaging modalities, but few options for genetic control of contrast enhancement.

OBJECTIVE

To develop a reporter system for multimodal imaging of genetic processes involved in mammalian vascular biology.

METHODS AND RESULTS

To approach this problem, we developed an optimal tagging system based on Biotag-BirA technology. In the resulting Biotag reporter system, coexpression of 2 interacting proteins results in biotin labeling of cell membranes, thus enabling multimodal imaging with "avidinated" probes. To assess this approach for in vivo imaging, we generated transgenic mice that expressed the Biotag-BirA transgene from a minimal Tie2 promoter. A variety of imaging methods were used to show the utility of this approach for quantitative analysis in embryonic and adult models of vascular development, using intravascular injection of avidinated probes for near infrared, ultrasound, and magnetic resonance imaging.

CONCLUSIONS

The present results demonstrate the versatility of the Biotag system for studies of vascular biology in genetically engineered mice, providing a robust approach for multimodal in vivo imaging of genetic processes in the vasculature.

Peripheral blood monocyte subsets predict antiviral response in chronic hepatitis C

BACKGROUND

Hepatitis C virus infection evolves into chronic progressive liver disease in a significant percentage of patients. Monocytes constitute a diverse group of myeloid cells that mediate innate and adaptive immune response. In addition to proinflammatory CD16+ monocytes, a Tie-2+ subgroup - Tie-2 expressing monocytes (TEMs) - that has robust proangiogenic potential has been recently defined.

AIM

To study the heterogeneity of peripheral blood monocytes in chronic hepatitis C (CHC) patients and to examine their proposed pathophysiological roles on disease progression and response to antiviral therapy.

METHODS

We studied CD16+ and Tie-2+ peripheral monocyte subpopulations in 21 healthy subjects and 39 CHC patients in various stages of disease and responses to antiviral treatment using flow cytometry. Expression profiles of proangiogenic and tissue remodelling factors in monocyte supernatants were measured using ELISA and protein arrays. Intrahepatic expression of CD14, CD31 and Tie-2 was analysed using immunofluorescence.

RESULTS

Increases of certain peripheral monocyte subsets were observed in the blood of CHC patients, wherein those cells with proinflammatory (CD16+) or proangiogenic (TEMs) potential expanded (P < 0.005, both). Notably, TEMs were significantly increased in nonresponders, particularly those with lower CD16 expression. In addition, many angiogenic factors were differentially expressed by peripheral monocytes from control or CHC patients, such as angiopoietin-1 and angiogenin (P < 0.05). Interestingly, intrahepatic TEMs were distinguished within portal infiltrates of CHC patients.

CONCLUSIONS

These findings suggest for the first time the relevance of peripheral monocytes phenotypes for the achievement of response to treatment. Hence, the study of monocyte subset regulation might effect improved CHC prognoses and adjuvant therapies.

Complementary vascular and matrix regulatory pathways underlie the beneficial mechanism of action of sorafenib in liver fibrosis

Paracrine signaling between hepatic stellate cells (HSCs) and liver endothelial cells (LECs) modulates fibrogenesis, angiogenesis, and portal hypertension. However, mechanisms regulating these processes are not fully defined. Sorafenib is a receptor tyrosine kinase inhibitor that blocks growth factor signaling in tumor cells but also displays important and not yet fully characterized effects on liver nonparenchymal cells including HSCs and LECs. The aim of this study was to test the hypothesis that sorafenib influences paracrine signaling between HSCs and LECs and thereby regulates matrix and vascular changes associated with chronic liver injury. Complementary magnetic resonance elastography, micro-computed tomography, and histochemical analyses indicate that sorafenib attenuates the changes in both matrix and vascular compartments that occur in response to bile duct ligation-induced liver injury in rats. Cell biology studies demonstrate that sorafenib markedly reduces cell-cell apposition and junctional complexes, thus reducing the proximity typically observed between these sinusoidal barrier cells. At the molecular level, sorafenib down-regulates angiopoietin-1 and fibronectin, both released by HSCs in a manner dependent on the transcription factor Kruppel-like factor 6 , suggesting that this pathway underlies both matrix and vascular changes associated with chronic liver disease.

CONCLUSION

Collectively, the results of this study demonstrate that sorafenib inhibits both matrix restructuring and vascular remodeling that accompany chronic liver diseases and characterize cell and molecular mechanisms underlying this effect. These data may help to refine future therapies for advanced gastrointestinal and liver diseases characterized by abundant fibrosis and neovascularization.

Circulating angiopoietins-1 and -2, angiopoietin receptor Tie-2 and vascular endothelial growth factor-A as biomarkers of acute myocardial infarction: a prospective nested case-control study

Background

Angiogenesis is up-regulated in myocardial ischemia. However, limited data exist assessing the value of circulating angiogenic biomarkers in predicting future incidence of acute myocardial infarction (AMI). Our aim was to examine the association between circulating levels of markers of angiogenesis with risk of incident acute myocardial infarction (AMI) in men and women.

Methods

We performed a case-control study (nested within a large cohort of persons receiving care within Kaiser Permanente of Northern California) including 695 AMI cases and 690 controls individually matched on age, gender and race/ethnicity.

Results

Median [inter-quartile range] serum concentrations of vascular endothelial growth factor-A (VEGF-A; 260 [252] vs. 235 [224] pg/mL; p = 0.01) and angiopoietin-2 (Ang-2; 1.18 [0.66] vs. 1.05 [0.58] ng/mL; p < 0.0001) were significantly higher in AMI cases than in controls. By contrast, endothelium-specific receptor tyrosine kinase (Tie-2; 14.2 [3.7] vs. 14.0 [3.1] ng/mL; p = 0.07) and angiopoietin-1 levels (Ang-1; 33.1 [13.6] vs. 32.5 [12.7] ng/mL; p = 0.52) did not differ significantly by case-control status. After adjustment for educational attainment, hypertension, diabetes, smoking, alcohol consumption, body mass index, LDL-C, HDL-C, triglycerides and C-reactive protein, each increment of 1 unit of Ang-2 as a Z score was associated with 1.17-fold (95 percent confidence interval, 1.02 to 1.35) increased odds of AMI, and the upper quartile of Ang-2, relative to the lowest quartile, was associated with 1.63-fold (95 percent confidence interval, 1.09 to 2.45) increased odds of AMI.

Conclusions

Our data support a role of Ang-2 as a biomarker of incident AMI independent of traditional risk factors.

Activated protein C enhances human keratinocyte barrier integrity via sequential activation of epidermal growth factor receptor and Tie2

Keratinocytes play a critical role in maintaining epidermal barrier function. Activated protein C (APC), a natural anticoagulant with anti-inflammatory and endothelial barrier protective properties, significantly increased the barrier impedance of keratinocyte monolayers, measured by electric cell substrate impedance sensing and FITC-dextran flux. In response to APC, Tie2, a tyrosine kinase receptor, was rapidly activated within 30 min, and relocated to cell-cell contacts. APC also increased junction proteins zona occludens, claudin-1 and VE-cadherin. Inhibition of Tie2 by its peptide inhibitor or small interfering RNA abolished the barrier protective effect of APC. Interestingly, APC did not activate Tie2 through its major ligand, angiopoietin-1, but instead acted by binding to endothelial protein C receptor, cleaving protease-activated receptor-1 and transactivating EGF receptor. Furthermore, when activation of Akt, but not ERK, was inhibited, the barrier protective effect of APC on keratinocytes was abolished. Thus, APC activates Tie2, via a mechanism requiring, in sequential order, the receptors, endothelial protein C receptor, protease-activated receptor-1, and EGF receptor, which selectively enhances the PI3K/Akt signaling to enhance junctional complexes and reduce keratinocyte permeability.

Zebrafish Tie-2 shares a redundant role with Tie-1 in heart development and regulates vessel integrity

Tie-2 is a member of the receptor tyrosine kinase family and is required for vascular remodeling and maintenance of mammalian vessel integrity. A number of mutations in the human TIE2 gene have been identified in patients suffering from cutaneomucosal venous malformations and ventricular septal defects. How exactly Tie-2 signaling pathways play different roles in both vascular development and vascular stability is unknown. We have generated a zebrafish line carrying a stop mutation in the kinase domain of the Tie-2 receptor. Mutant embryos lack Tie-2 protein, but do not display any defect in heart and vessel development. Simultaneous loss of Tie-1 and Tie-2, however, leads to a cardiac phenotype. Our study shows that Tie-1 and Tie-2 are not required for early heart development, yet they have redundant roles for the maintenance of endocardial-myocardial connection in later stages. Tie-2 and its ligand Angiopoietin-1 have also been reported to play an important role in vessel stability. We used atorvastatin and simvastatin, drugs that cause bleeding in wild-type zebrafish larvae, to challenge vessel stability in tie-2 mutants. Interestingly, recent clinical studies have reported hemorrhagic stroke as a side effect of atorvastatin treatment. Exposure of embryos to statins revealed that tie-2 mutants are significantly protected from statin-induced bleeding. Furthermore, tie-2 mutants became less resistant to bleeding after VE-cadherin knockdown. Taken together, these data show that atorvastatin affects vessel stability through Tie-2, and that VE-cadherin and Tie-2 act in concert to allow vessel remodeling while playing a role in vessel stability. Our study introduces an additional vertebrate model to study in vivo the function of Tie-2 in development and disease.

Targeting the ANGPT-TIE2 pathway in malignancy

Angiopoietins (ANGPTs) are ligands of the endothelial cell receptor TIE2 and have crucial roles in the tumour angiogenic switch. Increased expression of ANGPT2 relative to ANGPT1 in tumours correlates with poor prognosis. The biological effects of the ANGPT-TIE system are context dependent, which brings into question what the best strategy is to target this pathway. This Review presents an encompassing picture of what we know about this important axis in tumour biology. The various options for therapeutic intervention are discussed to identify the best path forwards.