The matricellular protein CCN1 controls retinal angiogenesis by targeting VEGF, Src homology 2 domain phosphatase-1 and Notch signaling

Cellular communication network factor 1 promotes retinal leakage in diabetic retinopathy via inducing neutrophil stasis and neutrophil extracellular traps extrusion

BACKGROUND

Diabetic retinopathy (DR) is a major cause of blindness and is characterized by dysfunction of the retinal microvasculature. Neutrophil stasis, resulting in retinal inflammation and the occlusion of retinal microvessels, is a key mechanism driving DR. These plugging neutrophils subsequently release neutrophil extracellular traps (NETs), which further disrupts the retinal vasculature. Nevertheless, the primary catalyst for NETs extrusion in the retinal microenvironment under diabetic conditions remains unidentified. In recent studies, cellular communication network factor 1 (CCN1) has emerged as a central molecule modulating inflammation in pathological settings. Additionally, our previous research has shed light on the pathogenic role of CCN1 in maintaining endothelial integrity. However, the precise role of CCN1 in microvascular occlusion and its potential interaction with neutrophils in diabetic retinopathy have not yet been investigated.

METHODS

We first examined the circulating level of CCN1 and NETs in our study cohort and analyzed related clinical parameters. To further evaluate the effects of CCN1 in vivo, we used recombinant CCN1 protein and CCN1 overexpression for gain-of-function, and CCN1 knockdown for loss-of-function by intravitreal injection in diabetic mice. The underlying mechanisms were further validated on human and mouse primary neutrophils and dHL60 cells.

RESULTS

We detected increases in CCN1 and neutrophil elastase in the plasma of DR patients and the retinas of diabetic mice. CCN1 gain-of-function in the retina resulted in neutrophil stasis, NETs extrusion, capillary degeneration, and retinal leakage. Pre-treatment with DNase I to reduce NETs effectively eliminated CCN1-induced retinal leakage. Notably, both CCN1 knockdown and DNase I treatment rescued the retinal leakage in the context of diabetes. In vitro, CCN1 promoted adherence, migration, and NETs extrusion of neutrophils.

CONCLUSION

In this study, we uncover that CCN1 contributed to retinal inflammation, vessel occlusion and leakage by recruiting neutrophils and triggering NETs extrusion under diabetic conditions. Notably, manipulating CCN1 was able to hold therapeutic promise for the treatment of diabetic retinopathy.

CCN-Hippo YAP signaling in vision and its role in neuronal, glial and vascular cell function and behavior

The retina is a highly specialized tissue composed of a network of neurons, glia, and vascular and epithelial cells; all working together to coordinate and transduce visual signals to the brain. The retinal extracellular matrix (ECM) shapes the structural environment in the retina but also supplies resident cells with proper chemical and mechanical signals to regulate cell function and behavior and maintain tissue homeostasis. As such, the ECM affects virtually all aspects of retina development, function and pathology. ECM-derived regulatory cues influence intracellular signaling and cell function. Reversibly, changes in intracellular signaling programs result in alteration of the ECM and downstream ECM-mediated signaling network. Our functional studies in vitro, genetic studies in mice, and multi omics analyses have provided evidence that a subset of ECM proteins referred to as cellular communication network (CCN) affects several aspects of retinal neuronal and vascular development and function. Retinal progenitor, glia and vascular cells are major sources of CCN proteins particularly CCN1 and CCN2. We found that expression of the CCN1 and CCN2 genes is dependent on the activity of YAP, the core component of the hippo-YAP signaling pathway. Central to the Hippo pathway is a conserved cascade of inhibitory kinases that regulate the activity of YAP, the final transducer of this pathway. Reversibly, YAP expression and/or activity is dependent on CCN1 and CCN2 downstream signaling, which creates a positive or negative feedforward loop driving developmental processes (e.g., neurogenesis, gliogenesis, angiogenesis, barriergenesis) and, when dysregulated, disease progression in a range of retinal neurovascular disorders. Here we describe mechanistic hints involving the CCN-Hippo-YAP regulatory axis in retina development and function. This regulatory pathway represents an opportunity for targeted therapies in neurovascular and neurodegenerative diseases. The CCN-YAP regulatory loop in development and pathology.

Andrographolide suppresses hypoxia-induced embryonic hyaloid vascular system development through HIF-1a/VEGFR2 signaling pathway

Introduction

Ocular abnormalities and the development of retinal vasculature may cause postnatal retinopathy. In the past decade, tremendous progress has been made in identifying the mechanisms that regulate retina vasculature. However, the means of regulating embryonic hyaloid vasculature development is largely unknown. This study aims to determine whether and how andrographolide regulates embryonic hyaloid vasculature development.

Methods

Murine embryonic retinas were used in this study. Whole mount isolectin B4 (IB4) staining, hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC), and immunofluorescence staining (IF) were performed to determine whether andrographolide is critical for embryonic hyaloid vasculature development. BrdU incorporation assay, Boyden chamber migration assay, spheroid sprouting assay, and Matrigel-based tube formation assay were performed to evaluate whether andrographolide regulates the proliferation and migration of vascular endothelial cells. Molecular docking simulation and Co-immunoprecipitation assay were used to observe protein interaction.

Results

Hypoxia conditions exist in murine embryonic retinas. Hypoxia induces HIF-1a expression; high-expressed HIF-1a interacts with VEGFR2, resulting in the activation of the VEGF signaling pathway. Andrographolide suppresses hypoxia-induced HIF-1a expression and, at least in part, interrupts the interaction between HIF-1a and VEGFR2, causing inhibiting endothelial proliferation and migration, eventually inhibiting embryonic hyaloid vasculature development.

Conclusion

Our data demonstrated that andrographolide plays a critical role in regulating embryonic hyaloid vasculature development.

Atomic Force Microscopy-Based Measurements of Retinal Microvessel Stiffness in Mice with Endothelial-Specific Deletion of CCN1

Vascular stiffness is an independent predictor of human vascular diseases and is linked to ischemia, diabetes, high blood pressure, hyperlipidemia, and/or aging. Blood vessel stiffening increases owing to changes in the microscale architecture and/or content of extracellular, cytoskeletal, and nuclear matrix proteins. These alterations, while best appreciated in large blood vessels, also gradually occur in the microvasculature and play an important role in the initiation and progression of numerous microangiopathies including diabetic retinopathy. Although macroscopic measurements of arterial stiffness by pulse wave velocity are often used for clinical diagnosis, stiffness changes of intact microvessels and their causative factors have not been characterized. Herein, we describe the use of atomic force microscopy (AFM) to determine stiffness of mouse retinal capillaries and assess its regulation by the cellular communication network (CCN) 1, a stiffness-sensitive gene-encoded matricellular protein. AFM yields reproducible measurements of retinal capillary stiffness in lightly fixed freshly isolated retinal flat mounts. AFM measurements also show significant changes in compliance properties of the retinal microvasculature of mice with endothelial-specific deletion of CCN1, indicating that CCN1 expression, or lack thereof, affects the mechanical properties of microvascular cells in vivo. Thus, AFM has the force sensitivity and the spatial resolution necessary to measure the local modulus of retinal capillaries in situ and eventually to investigate microvascular compliance heterogeneities as key components of disease pathogenesis.

The Role Vascular Endothelial Growth Factor, Control Glycemic, Lipid Profile, and Hypoxia-inducible Factor 1-Alpha at Type 2 Diabetic Patients in North Sumatera, Indonesia

BACKGROUND: Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder whose prevalence continues to increase worldwide. Chronic hyperglycemia increases the area of hypoxia that can be measured by markers of hypoxia-inducible factor 1-alpha (HIF-1α) and endothelial cell damage by vascular endothelial growth factor (VEGF) secretion and the association of the course of diabetes mellitus, dyslipidemia is also a risk factor that can aggravate the condition. diabetes mellitus. AIM: The aim of this study was to correlate VEGF with HIF-1α and other metabolic markers in T2DM. METHODS: Examination such as blood pressure, height, and body mass index, and duration of diabetes were recorded. Laboratory examination like blood sugar levels and glycated hemoglobin (Hba1C) levels, lipid profile such as cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglycerides were evaluated by Paramitha Laboratory Clinic and VEGF and HIF-1α we examined by ELISA methods in the Integrated laboratory of Medical Faculty, Universitas Sumatera Utara. The study was done by cross-sectional analytic methods, among 135 patients with T2DM who were admitted from the various primary health-care centers in Medan city and surrounding areas in North Sumatera. The inclusion criteria of the samples were all the patients diagnosed with T2DM, both the sexes, and the exclusion criteria of the samples with T1DM and severe disease. The data of the samples were processed using a computer with the SPSS program. RESULTS: There was a positive significant correlation between VEGF with HIF-1α, with a strong correlation, and found a negative correlation between VEGF with fasting blood sugar and HDL (p < 0.005). CONCLUSION: By finding strongly and positive correlation between VEGF and HIF-1α, the samples of menunjukkan bahwa peningkatan konsentrasi VEGF meningkat selaras dengan peningkatan konsentrasi dari HIF-1α _dan ini menunjukkan bahwa proses angiogenesis pada sample sedang berlangsung sebagai mekanisme kompensasi pertahanan vascular.

Diabetes Promotes Retinal Vascular Endothelial Cell Injury by Inducing CCN1 Expression

Purpose: Diabetic retinopathy (DR) is one of the most common diabetic microvascular complications. However, the pathogenesis of DR has not yet been fully elucidated. This study aimed to discover novel and key molecules involved in the pathogenesis of DR, which could potentially be targets for therapeutic DR intervention.

Methods: To identify potential genes involved in the pathogenesis of DR, we analyzed the public database of neovascular membranes (NVMs) from patients with proliferative diabetic retinopathy (PDR) and healthy controls (HCs) (GSE102485, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE102485). Further, we compared these findings by performing RNA-sequencing analysis of peripheral blood mononuclear cells (PBMC) from patients with DR, control patients with non-complicated diabetes mellitus (DMC), and HCs. To determine the critical role of candidate genes in DR, knockdown or knockout was performed in human retinal vascular endothelial cells (HRVECs). The oxidative stress pathway, as well as tight junction integrity, was analyzed.

Results: Transcriptional profiles showed distinct patterns between the NVMs of patients with DR and those of the HCs. Those genes enriched in either extracellular matrix (ECM)-receptor interaction or focal adhesion pathways were considerably upregulated. Both pathways were important for maintaining the integrity of retinal vascular structure and function. Importantly, the gene encoding the matricellular protein CCN1, a key gene in cell physiology, was differentially expressed in both pathways. Knockdown of CCN1 by small interfering RNA (siRNA) or knockout of CCN1 by the CRISPR-Cas9 technique in HRVECs significantly increased the levels of VE-cadherin, reduced the level of NADPH oxidase 4 (NOX4), and inhibited the generation of reactive oxygen species (ROS).

Conclusion: The present study identifies CCN1 as an important regulator in the pathogenesis of DR. Increased expression of CCN1 stimulates oxidative stress and disrupts tight junction integrity in endothelial cells by inducing NOX4. Thus, targeting the CCN1/NOX4 axis provides a therapeutic strategy for treating DR by alleviating endothelial cell injury.

Notch Signaling in the Bone Marrow Lymphopoietic Niche

Lifelong mammalian hematopoiesis requires continuous generation of mature blood cells that originate from Hematopoietic Stem and Progenitor Cells (HSPCs) situated in the post-natal Bone Marrow (BM). The BM microenvironment is inherently complex and extensive studies have been devoted to identifying the niche that maintains HSPC homeostasis and supports hematopoietic potential. The Notch signaling pathway is required for the emergence of the definitive Hematopoietic Stem Cell (HSC) during embryonic development, but its role in BM HSC homeostasis is convoluted. Recent work has begun to explore novel roles for the Notch signaling pathway in downstream progenitor populations. In this review, we will focus an important role for Notch signaling in the establishment of a T cell primed sub-population of Common Lymphoid Progenitors (CLPs). Given that its activation mechanism relies primarily on cell-to-cell contact, Notch signaling is an ideal means to investigate and define a novel BM lymphopoietic niche. We will discuss how new genetic model systems indicate a pre-thymic, BM-specific role for Notch activation in early T cell development and what this means to the paradigm of lymphoid lineage commitment. Lastly, we will examine how leukemic T-cell acute lymphoblastic leukemia (T-ALL) blasts take advantage of Notch and downstream lymphoid signals in the pathological BM niche.

Endothelial YAP/TAZ Signaling in Angiogenesis and Tumor Vasculature

Solid tumors are dependent on vascularization for their growth. The hypoxic, stiff, and pro-angiogenic tumor microenvironment induces angiogenesis, giving rise to an immature, proliferative, and permeable vasculature. The tumor vessels promote tumor metastasis and complicate delivery of anti-cancer therapies. In many types of tumors, YAP/TAZ activation is correlated with increased levels of angiogenesis. In addition, endothelial YAP/TAZ activation is important for the formation of new blood and lymphatic vessels during development. Oncogenic activation of YAP/TAZ in tumor cell growth and invasion has been studied in great detail, however the role of YAP/TAZ within the tumor endothelium remains insufficiently understood, which complicates therapeutic strategies aimed at targeting YAP/TAZ in cancer. Here, we overview the upstream signals from the tumor microenvironment that control endothelial YAP/TAZ activation and explore the role of their downstream targets in driving tumor angiogenesis. We further discuss the potential for anti-cancer treatments and vascular normalization strategies to improve tumor therapies.

Notch in mechanotransduction - from molecular mechanosensitivity to tissue mechanostasis

Tissue development and homeostasis are controlled by mechanical cues. Perturbation of the mechanical equilibrium triggers restoration of mechanostasis through changes in cell behavior, while defects in these restorative mechanisms lead to mechanopathologies, for example, osteoporosis, myopathies, fibrosis or cardiovascular disease. Therefore, sensing mechanical cues and integrating them with the biomolecular cell fate machinery is essential for the maintenance of health. The Notch signaling pathway regulates cell and tissue fate in nearly all tissues. Notch activation is directly and indirectly mechanosensitive, and regulation of Notch signaling, and consequently cell fate, is integral to the cellular response to mechanical cues. Fully understanding the dynamic relationship between molecular signaling, tissue mechanics and tissue remodeling is challenging. To address this challenge, engineered microtissues and computational models play an increasingly large role. In this Review, we propose that Notch takes on the role of a 'mechanostat', maintaining the mechanical equilibrium of tissues. We discuss the reciprocal role of Notch in the regulation of tissue mechanics, with an emphasis on cardiovascular tissues, and the potential of computational and engineering approaches to unravel the complex dynamic relationship between mechanics and signaling in the maintenance of cell and tissue mechanostasis.

A CTGF-YAP Regulatory Pathway Is Essential for Angiogenesis and Barriergenesis in the Retina

Connective tissue growth factor (CTGF) or cellular communication network 2 (CCN2) is a matricellular protein essential for normal embryonic development and tissue repair. CTGF exhibits cell- and context-dependent activities, but CTGF function in vascular development and barrier function is unknown. We show that endothelial cells (ECs) are one of the major cellular sources of CTGF in the developing and adult retinal vasculature. Mice lacking CTGF expression either globally or specifically in ECs exhibit impaired vascular cell growth and morphogenesis and blood barrier breakdown. The global molecular signature of CTGF includes cytoskeletal and extracellular matrix protein, growth factor, and transcriptional co-regulator genes such as yes-associated protein (YAP). YAP, itself a transcriptional activator of CTGF, mediates several CTGF-controlled angiogenic and barriergenic transcriptional programs. Re-expression of YAP rescues, at least partially, angiogenesis and barriergenesis in CTGF mutant mouse retinas. Thus, the CTGF-YAP regulatory loop is integral to retinal vascular development and barrier function.

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CTGF has a strong and persistent expression in the retinal vasculature

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Mice lacking CTGF exhibit defects in angiogenesis and blood barrier integrity

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CTGF-targeted genes include matrix, growth, and transcription co-factors like YAP

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YAP re-expression partly rescues angiogenic and barriergenic defects of CTGF loss

Eyeing the Extracellular Matrix in Vascular Development and Microvascular Diseases and Bridging the Divide between Vascular Mechanics and Function

The extracellular matrix (ECM) is critical in all aspects of vascular development and health: supporting cell anchorage, providing structure, organization and mechanical stability, and serving as a sink for growth factors and sustained survival signals. Abnormal changes in ECM protein expression, organization, and/or properties, and the ensuing changes in vascular compliance affect vasodilator responses, microvascular pressure transmission, and collateral perfusion. The changes in microvascular compliance are independent factors initiating, driving, and/or exacerbating a plethora of microvascular diseases of the eye including diabetic retinopathy (DR) and vitreoretinopathy, retinopathy of prematurity (ROP), wet age-related macular degeneration (AMD), and neovascular glaucoma. Congruently, one of the major challenges with most vascular regenerative therapies utilizing localized growth factor, endothelial progenitor, or genetically engineered cell delivery, is the regeneration of blood vessels with physiological compliance properties. Interestingly, vascular cells sense physical forces, including the stiffness of their ECM, through mechanosensitive integrins, their associated proteins and the actomyosin cytoskeleton, which generates biochemical signals that culminate in a rapid expression of matricellular proteins such as cellular communication network 1 (CCN1) and CCN2 (aka connective tissue growth factor or CTGF). Loss or gain of function of these proteins alters genetic programs of cell growth, ECM biosynthesis, and intercellular signaling, that culminate in changes in cell behavior, polarization, and barrier function. In particular, the function of the matricellular protein CCN2/CTGF is critical during retinal vessel development and regeneration wherein new blood vessels form and invest a preformed avascular neural retina following putative gradients of matrix stiffness. These observations underscore the need for further in-depth characterization of the ECM-derived cues that dictate structural and functional properties of the microvasculature, along with the development of new therapeutic strategies addressing the ECM-dependent regulation of pathophysiological stiffening of blood vessels in ischemic retinopathies.

CYR61/CCN1 expression in resected pancreatic ductal adenocarcinoma: A retrospective pilot study of the interaction between the tumors and their surrounding microenvironment

BACKGROUND

CCN1 is an extracellular matrix-associated protein thought to be implicated in tumor-stromal interaction in several solid tumors. The aim of our pilot study was to evaluate the correlation between CCN1 expression in stromal cells, pancreatic intraepithelial neoplasia (PanIN) and pancreatic ductal adenocarcinoma cells in resected pancreatic ductal adenocarcinoma (PDAC) specimens, and correlate that clinically.

METHODS

A total of 42 paraffin-embedded PDAC tumor specimens were stained for CCN1 and evaluated via immunohistochemical (IHC) analysis. Statistical analysis was performed to correlate between CCN1 expression profiles in tumor tissues and clinicopathological parameters of patients.

RESULTS

Our results showed CCN1 (CYR61) gene was highly expressed in PDAC tissues relative to other organ specific tumor tissues. Also, moderate and overexpression of CCN1 in PanIN was associated with PanIN grade 3 tissues. A statistically significant association was found between PanIN CCN1 scores on one hand and cancer stage, cancer grade, and CCN1 expression among ductal tumor cells and adjacent stromal cells on the other hand.

DISCUSSION

The associations demonstrated suggest that CCN1 might be contributing to a substantial role in the interaction between the pancreatic tumors on one hand and their surrounding microenvironment and their precursors on the other hand; hence, it might serve as a potential therapeutic target for PDAC.

A Practical Guide to the Automated Analysis of Vascular Growth, Maturation and Injury in the Brain

The distinct organization of the brain's vasculature ensures the adequate delivery of oxygen and nutrients during development and adulthood. Acute and chronic pathological changes of the vascular system have been implicated in many neurological disorders including stroke and dementia. Here, we describe a fast, automated method that allows the highly reproducible, quantitative assessment of distinct vascular parameters and their changes based on the open source software Fiji (ImageJ). In particular, we developed a practical guide to reliably measure aspects of growth, repair and maturation of the brain's vasculature during development and neurovascular disease in mice and humans. The script can be used to assess the effects of different external factors including pharmacological treatments or disease states. Moreover, the procedure is expandable to blood vessels of other organs and vascular in vitro models.

Pro-metastatic functions of Notch signaling is mediated by CYR61 in breast cells

Metastasis is the main cause of cancer related deaths, and unfolding the molecular mechanisms underlying metastatic progression is critical for the development of novel therapeutic approaches. Notch is one of the key signaling pathways involved in breast tumorigenesis and metastasis. Notch activation induces pro-metastatic processes such as migration, invasion and epithelial to mesenchymal transition (EMT). However, molecular mediators working downstream of Notch in these processes are not fully elucidated. CYR61 is a secreted protein implicated in metastasis, and its inhibition by a monoclonal antibody suppresses metastasis in xenograft breast tumors, indicating the clinical importance of CYR61 targeting. Here, we aimed to investigate whether CYR61 works downstream of Notch in inducing pro-metastatic phenotypes in breast cells. We showed that CYR61 expression is positively regulated by Notch activity in breast cells. Notch1-induced migration, invasion and anchorage independent growth of a normal breast cell line, MCF10A, were abrogated by CYR61 silencing. Furthermore, upregulation of core EMT markers upon Notch1-activation was impaired in the absence of CYR61. However, reduced migration and invasion of highly metastatic cell line, MDA MB 231, cells upon Notch inhibition was not dependent on CYR61 downregulation. In conclusion, we showed that in normal breast cell line MCF10A, CYR61 is a mediator of Notch1-induced pro-metastatic phenotypes partly via induction of EMT. Our results imply CYR61 as a prominent therapeutic candidate for a subpopulation of breast tumors with high Notch activity.

CCN1-Yes-Associated Protein Feedback Loop Regulates Physiological and Pathological Angiogenesis

Cellular communication network factor 1 (CCN1) is a dynamically expressed, matricellular protein required for vascular development and tissue repair. The CCN1 gene is a presumed target of Yes-associated protein (YAP), a transcriptional coactivator that regulates cell growth and organ size. Herein, we demonstrate that the CCN1 promoter is indeed a direct genomic target of YAP in endothelial cells (ECs) of new blood vessel sprouts and that YAP deficiency in mice downregulates CCN1 and alters cytoskeletal and mitogenic gene expression. Interestingly, CCN1 overexpression in cultured ECs inactivates YAP in a negative feedback and causes its nuclear exclusion. Accordingly, EC-specific deletion of the CCN1 gene in mice mimics a YAP gain-of-function phenotype, characterized by EC hyperproliferation and blood vessel enlargement. CCN1 brings about its effect by providing cells with a soft compliant matrix that creates YAP-repressive cytoskeletal states. Concordantly, pharmacological inhibition of cell stiffness recapitulates the CCN1 deletion vascular phenotype. Furthermore, adeno-associated virus-mediated expression of CCN1 reversed the pathology of YAP hyperactivation and the subsequent aberrant growth of blood vessels in mice with ischemic retinopathy. Our studies unravel a new paradigm of functional interaction between CCN1 and YAP and underscore the significance of their interplay in the pathogenesis of neovascular diseases.

CCN1 interlinks integrin and hippo pathway to autoregulate tip cell activity

CCN1 (CYR61) stimulates active angiogenesis in various tumours, although the mechanism is largely unknown. Here, we report that CCN1 is a key regulator of endothelial tip cell activity in angiogenesis. Microvessel networks and directional vascular cell migration patterns were deformed in ccn1-knockdown zebrafish embryos. CCN1 activated VEGFR2 and downstream MAPK/PI3K signalling pathways, YAP/TAZ, as well as Rho effector mDia1 to enhance tip cell activity and CCN1 itself. VEGFR2 interacted with integrin αvβ3 through CCN1. Integrin αvβ3 inhibitor repressed tip cell number and sprouting in postnatal retinas from endothelial cell-specific Ccn1 transgenic mice, and allograft tumours in Ccn1 transgenic mice showed hyperactive vascular sprouting. Cancer patients with high CCN1 expression have poor survival outcomes and positive correlation with ITGAV and ITGB3 and high YAP/WWTR1. Thus, our data underscore the positive feedback regulation of tip cells by CCN1 through integrin αvβ3/VEGFR2 and increased YAP/TAZ activity, suggesting a promising therapeutic intervention for pathological angiogenesis.

Caught between a "Rho" and a hard place: are CCN1/CYR61 and CCN2/CTGF the arbiters of microvascular stiffness?

The extracellular matrix (ECM) is a deformable dynamic structure that dictates the behavior, function and integrity of blood vessels. The composition, density, chemistry and architecture of major globular and fibrillar proteins of the matrisome regulate the mechanical properties of the vasculature (i.e., stiffness/compliance). ECM proteins are linked via integrins to a protein adhesome directly connected to the actin cytoskeleton and various downstream signaling pathways that enable the cells to respond to external stimuli in a coordinated manner and maintain optimal tissue stiffness. However, cardiovascular risk factors such as diabetes, dyslipidemia, hypertension, ischemia and aging compromise the mechanical balance of the vascular wall. Stiffening of large blood vessels is associated with well-known qualitative and quantitative changes of fibrillar and fibrous macromolecules of the vascular matrisome. However, the mechanical properties of the thin-walled microvasculature are essentially defined by components of the subendothelial matrix. Cellular communication network (CCN) 1 and 2 proteins (aka Cyr61 and CTGF, respectively) of the CCN protein family localize in and act on the pericellular matrix of microvessels and constitute primary candidate markers and regulators of microvascular compliance. CCN1 and CCN2 bind various integrin and non-integrin receptors and initiate signaling pathways that regulate connective tissue remodeling and response to injury, the associated mechanoresponse of vascular cells, and the subsequent inflammatory response. The CCN1 and CCN2 genes are themselves responsive to mechanical stimuli in vascular cells, wherein mechanotransduction signaling converges into the common Rho GTPase pathway, which promotes actomyosin-based contractility and cellular stiffening. However, CCN1 and CCN2 each exhibit unique functional attributes in these processes. A better understanding of their synergistic or antagonistic effects on the maintenance (or loss) of microvascular compliance in physiological and pathological situations will assist more broadly based studies of their functional properties and translational value.

Transplantation of human endometrial perivascular cells with elevated CYR61 expression induces angiogenesis and promotes repair of a full-thickness uterine injury in rat

Background

Disruptions of angiogenesis can have a significant effect on the healing of uterine scars. Human endometrial perivascular cells (CD146+PDGFRβ+) function as stem cells in the endometrium. Cysteine-rich angiogenic inducer 61 (CYR61) plays an important role in vascular development. The purpose of this study was to observe the effects of the transplantation of human endometrial perivascular cells (En-PSCs) overexpressing CYR61 on structural and functional regeneration in rat models of partial full-thickness uterine excision.

Methods

We first sorted human En-PSCs from endometrial single-cell suspensions by flow cytometry. Human En-PSCs expressing low or high levels of CYR61 were then generated via transfection with a CYR61-specific small interfering ribonucleic acid (si-CYR61) construct or overexpression plasmid. To establish a rat model of uterine injury, a subset of uterine wall was then resected from each uterine horn in experimental animals. Female rats were randomly assigned to five groups, including a sham-operated group and four repair groups that received either PBS loaded on a collagen scaffold (collagen/PBS), En-PSCs loaded on a collagen scaffold (collagen/En-PSCs), En-PSCs with low CYR61 expression loaded on a collagen scaffold (collagen/si-CYR61 En-PSCs), and En-PSCs overexpressing CYR61 loaded on a collagen scaffold (collagen/ov-CYR61 En-PSCs). These indicated constructs were sutured in the injured uterine area to replace the excised segment. On days 30 and 90 after transplantation, a subset of rats in each group was sacrificed, and uterine tissue was recovered and serially sectioned. Hematoxylin and eosin staining and immunohistochemical staining were then performed. Finally, the remaining rats of each group were mated with fertile male rats on day 90 for a 2-week period.

Results

Sorted En-PSCs expressed all recognized markers of mesenchymal stem cells (MSCs), including CD10, CD13, CD44, CD73, CD90, and CD105, and exhibited differentiation potential toward adipocytes, osteoblasts, and neuron-like cells. Compared with En-PSCs and En-PSCs with low CYR61 expression, En-PSCs with elevated CYR61 expression enhanced angiogenesis by in vitro co-culture assays. At day 90 after transplantation, blood vessel density in the collagen/ov-CYR61 En-PSCs group (11.667 ± 1.287) was greater than that in the collagen/En-PSCs group (7.167 ± 0.672) (P < 0.05) and the collagen/si-CYR61 En-PSCs group (3.750 ± 0.906) (P < 0.0001). Pregnancy rates differed among groups, from 40% in the collagen/PBS group to 80% in the collagen/En-PSCs group, 12.5% in the collagen/si-CYR61 En-PSCs group, and 80% in the collagen/ov-CYR61 En-PSCs group. In addition, four embryos were evident in the injured uterine horns of the collagen/ov-CYR61 En-PSCs group, while no embryos were identified in the injured uterine horns of the collagen/PBS group.

Conclusions

The results showed that CYR61 plays an important role in angiogenesis. Collagen/ov-CYR61 En-PSCs promoted endometrial and myometrial regeneration and induced neovascular regeneration in injured rat uteri. The pregnancy rate of rats treated with transplantation of collagen/En-PSCs or collagen/ov-CYR61 En-PSCs was improved. Moreover, the number of embryos implantation on the injured area in uterus was increased after transplantation of collagen/ov-CYR61 En-PSCs.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1272-3) contains supplementary material, which is available to authorized users.

Identification of Cysteine-Rich Angiogenic Inducer 61 as a Potential Antifibrotic and Proangiogenic Mediator in Scleroderma

OBJECTIVE

We previously identified CYR61 as a histone deacetylase 5 (HDAC-5)-repressed gene in systemic sclerosis (SSc; scleroderma) endothelial cells (ECs). When overexpressed, cysteine-rich angiogenic inducer 61 (CYR-61) promoted angiogenesis in SSc ECs. This study was undertaken to examine the role of CYR-61 in fibrosis and determine the mechanisms involved in CYR-61-mediated angiogenesis in SSc.

METHODS

Dermal ECs and fibroblasts were isolated from biopsy specimens from healthy subjects and patients with SSc. CYR-61 level was determined by quantitative polymerase chain reaction, Western blotting, and enzyme-linked immunosorbent assay. CYR-61 was overexpressed using a CYR61 vector or knocked down using small interfering RNA, and functional and mechanistic studies were then conducted in fibroblasts and ECs.

RESULTS

Lower CYR61 messenger RNA levels were observed in dermal fibroblasts and ECs from SSc patients than in those from healthy controls. In SSc fibroblasts, overexpression of CYR-61 led to significant reduction in the expression of profibrotic genes, including COL1A1 (P = 0.002) and ACTA2 (P = 0.04), and an increase in the expression of matrix-degrading genes, including MMP1 (P = 0.002) and MMP3 (P =0.004), and proangiogenic VEGF (P = 0.03). The antifibrotic effect of CYR-61 was further demonstrated by delay in wound healing, inhibition of gel contraction, inactivation of the transforming growth factor β pathway, and early superoxide production associated with senescence in SSc fibroblasts. In SSc ECs, overexpression of CYR-61 led to increased production of vascular endothelial cell growth factor. The proangiogenic effects of CYR-61 were mediated by signaling through αvβ3 receptors and downstream activation of AMP-activated protein kinase, AKT, and the endothelial cell nitric oxide synthase/nitric oxide pathway system.

CONCLUSION

CYR-61, which is epigenetically regulated by HDAC-5, is a potent antifibrotic and proangiogenic mediator in SSc. Therapeutic intervention to promote CYR-61 activity or increase CYR-61 levels might be of benefit in SSc.

Functional Vascular Tissue Engineering Inspired by Matricellular Proteins

Modern regenerative medicine, and tissue engineering specifically, has benefited from a greater appreciation of the native extracellular matrix (ECM). Fibronectin, collagen, and elastin have entered the tissue engineer's toolkit; however, as fully decellularized biomaterials have come to the forefront in vascular engineering it has become apparent that the ECM is comprised of more than just fibronectin, collagen, and elastin, and that cell-instructive molecules known as matricellular proteins are critical for desired outcomes. In brief, matricellular proteins are ECM constituents that contrast with the canonical structural proteins of the ECM in that their primary role is to interact with the cell. Of late, matricellular genes have been linked to diseases including connective tissue disorders, cardiovascular disease, and cancer. Despite the range of biological activities, this class of biomolecules has not been actively used in the field of regenerative medicine. The intent of this review is to bring matricellular proteins into wider use in the context of vascular tissue engineering. Matricellular proteins orchestrate the formation of new collagen and elastin fibers that have proper mechanical properties-these will be essential components for a fully biological small diameter tissue engineered vascular graft (TEVG). Matricellular proteins also regulate the initiation of thrombosis via fibrin deposition and platelet activation, and the clearance of thrombus when it is no longer needed-proper regulation of thrombosis will be critical for maintaining patency of a TEVG after implantation. Matricellular proteins regulate the adhesion, migration, and proliferation of endothelial cells-all are biological functions that will be critical for formation of a thrombus-resistant endothelium within a TEVG. Lastly, matricellular proteins regulate the adhesion, migration, proliferation, and activation of smooth muscle cells-proper control of these biological activities will be critical for a TEVG that recellularizes and resists neointimal formation/stenosis. We review all of these functions for matricellular proteins here, in addition to reviewing the few studies that have been performed at the intersection of matricellular protein biology and vascular tissue engineering.

The endothelial tip-stalk cell selection and shuffling during angiogenesis

Angiogenesis is a critical, fine-tuned, multi-staged biological process. Tip-stalk cell selection and shuffling are the building blocks of sprouting angiogenesis. Accumulated evidences show that tip-stalk cell selection and shuffling are regulated by a variety of physical, chemical and biological factors, especially the interaction among multiple genes, their products and environments. The classic Notch-VEGFR, Slit-Robo, ECM-binding integrin, semaphorin and CCN family play important roles in tip-stalk cell selection and shuffling. In this review, we outline the progress and prospect in the mechanism and the roles of the various molecules and related signaling pathways in endothelial tip-stalk cell selection and shuffling. In the future, the regulators of tip-stalk cell selection and shuffling would be the potential markers and targets for angiogenesis.

Abscisic acid - an anti-angiogenic phytohormone that modulates the phenotypical plasticity of endothelial cells and macrophages

Abscisic acid (ABA) has shown anti-inflammatory and immunoregulatory properties in preclinical models of diabetes and inflammation. Herein, we studied the effects of ABA on angiogenesis, a strictly controlled process that, when dysregulated, leads to severe angiogenic disorders including vascular overgrowth, exudation, cellular inflammation and organ dysfunction. By using a 3D sprouting assay, we show that ABA effectively inhibits migration, growth and expansion of endothelial tubes without affecting cell viability. Analyses of the retinal vasculature in developing normoxic and hyperoxic mice challenged by oxygen toxicity reveal that exogenously administered ABA stunts the development and regeneration of blood vessels. In these models, ABA downregulates endothelial cell (EC)-specific growth and migratory genes, interferes with tip and stalk cell specification, and hinders the function of filopodial protrusions required for precise guidance of vascular sprouts. In addition, ABA skews macrophage polarization towards the M1 phenotype characterized by anti-angiogenic marker expression. In accordance with this, ABA treatment accelerates macrophage-induced programmed regression of fetal blood vessels. These findings reveal protective functions of ABA against neovascular growth through modulation of EC and macrophage plasticity, suggesting the potential utility of ABA as a treatment in vasoproliferative diseases.

The matricellular protein CCN1 in tissue injury repair

The expression of Ccn1 (Cyr61) is essential for cardiovascular development during embryogenesis, whereas in adulthood it is associated with inflammation, wound healing, injury repair, and related pathologies including fibrosis and cancer. Recent studies have found that CCN1 plays a critical role in promoting wound healing and tissue repair. Mechanistically, CCN1 functions through direct interaction with specific integrin receptors expressed in various cell types in the wound tissue microenvironment to coordinate diverse cellular functions for repair. Here we briefly summarize the current knowledge on the functions of CCN1 in tissue injury repair and discuss pertinent unanswered questions.

CCN1/Cyr61 enhances the function of hepatic stellate cells in promoting the progression of hepatocellular carcinoma

Hepatic stellate cells (HSCs) are the main extracellular matrix (ECM)-producing cells in liver fibrosis. Activated HSCs stimulate the proliferation and migration of hepatocellular carcinoma (HCC) cells. Cysteine-rich 61 (CCN1/Cyr61) is an ECM protein. Our previous studies demonstrated that the expression of CCN1 was significantly higher in benign hepatic cirrhosis tissue and cancer-adjacent hepatic cirrhosis tissues. CCN1 is a target gene of β-catenin in HCC and promotes the proliferation of HCC cells. The present study aimed to examine whether CCN1 can activate HSCs and affect the function of activated HSCs in promoting the progression of HCC. CCN1 expression was determined during the progression of liver fibrosis in a mouse model. LX-2 cells, which were infected with adenoviruses AdCCN1 or AdRFP, and HepG2 cells were co-cultured or subcutaneously co-implanted into in nude mice. MTT assay, Crystal Violet staining, Boyden chamber, matrigel invasion and monolayer scratch assays were used to analyze the proliferation, migration and invasion capability of HepG2 cells. Xenograft sizes were measured and histological analyses were performed by hematoxylin and eosin, immunohistochemical, immunefluorescence and Sirius Red staining. It was demonstrated that the expression of CCN1 was continually increased in liver fibrosis and the that expression may be correlated with the progression of liver fibrosis. CCN1 affected the function of LX-2 and enhanced the effect of LX-2 on promoting the viability, migration and invasion of HepG2 cells in vitro. CCN1 enhanced the effect of LX-2 on promoting the growth of HepG2 xenografts in vivo. CCN1 also affected the function of activated HSCs and regulated the formation of the xenograft microenvironment, including fibrogenesis and angiogenesis, which are beneficial for the progression of HCC. These findings demonstrated that CCN1 may be involved in the progression of the hepatic cirrhosis-HCC axis through regulating HSCs.

Recombinant CCN1 prevents hyperoxia-induced lung injury in neonatal rats

BackgroundCystein-rich protein 61 (Cyr61/CCN1) is a member of the CCN family of matricellular proteins that has an important role in tissue development and remodeling. However, the role of CCN1 in the pathogenesis of bronchopulmonary dysplasia (BPD) is unknown. Accordingly, we have investigated the effects of CCN1 on a hyperoxia-induced lung injury model in neonatal rats.MethodsIn experiment 1, newborn rats were randomized to room air (RA) or 85% oxygen (O₂) for 7 or 14 days, and we assessed the expression of CCN1. In experiment 2, rat pups were exposed to RA or O₂ and received placebo or recombinant CCN1 by daily intraperitoneal injection for 10 days. The effects of CCN1 on hyperoxia-induced lung inflammation, alveolar and vascular development, vascular remodeling, and right ventricular hypertrophy (RVH) were observed.ResultsIn experiment 1, hyperoxia downregulated CCN1 expression. In experiment 2, treatment with recombinant CCN1 significantly decreased macrophage and neutrophil infiltration, reduced inflammasome activation, increased alveolar and vascular development, and reduced vascular remodeling and RVH in the hyperoxic animals.ConclusionThese results demonstrate that hyperoxia-induced lung injury is associated with downregulated basal CCN1 expression, and treatment with CCN1 can largely reverse hyperoxic injury.

Hypoxia and Redox Signaling on Extracellular Matrix Remodeling: From Mechanisms to Pathological Implications

SIGNIFICANCE

The extracellular matrix (ECM) is an essential modulator of cell behavior that influences tissue organization. It has a strong relevance in homeostasis and translational implications for human disease. In addition to ECM structural proteins, matricellular proteins are important regulators of the ECM that are involved in a myriad of different pathologies. Recent Advances: Biochemical studies, animal models, and study of human diseases have contributed to the knowledge of molecular mechanisms involved in remodeling of the ECM, both in homeostasis and disease. Some of them might help in the development of new therapeutic strategies. This review aims to review what is known about some of the most studied matricellular proteins and their regulation by hypoxia and redox signaling, as well as the pathological implications of such regulation.

CRITICAL ISSUES

Matricellular proteins have complex regulatory functions and are modulated by hypoxia and redox signaling through diverse mechanisms, in some cases with controversial effects that can be cell or tissue specific and context dependent. Therefore, a better understanding of these regulatory processes would be of great benefit and will open new avenues of considerable therapeutic potential.

FUTURE DIRECTIONS

Characterizing the specific molecular mechanisms that modulate matricellular proteins in pathological processes that involve hypoxia and redox signaling warrants additional consideration to harness the potential therapeutic value of these regulatory proteins. Antioxid. Redox Signal. 27, 802-822.

Tumor matrix stiffness promotes metastatic cancer cell interaction with the endothelium

Tumor progression alters the composition and physical properties of the extracellular matrix. Particularly, increased matrix stiffness has profound effects on tumor growth and metastasis. While endothelial cells are key players in cancer progression, the influence of tumor stiffness on the endothelium and the impact on metastasis is unknown. Through quantitative mass spectrometry, we find that the matricellular protein CCN1/CYR61 is highly regulated by stiffness in endothelial cells. We show that stiffness-induced CCN1 activates β-catenin nuclear translocation and signaling and that this contributes to upregulate N-cadherin levels on the surface of the endothelium, in vitro This facilitates N-cadherin-dependent cancer cell-endothelium interaction. Using intravital imaging, we show that knockout of Ccn1 in endothelial cells inhibits melanoma cancer cell binding to the blood vessels, a critical step in cancer cell transit through the vasculature to metastasize. Targeting stiffness-induced changes in the vasculature, such as CCN1, is therefore a potential yet unappreciated mechanism to impair metastasis.

Interplay between CCN1 and Wnt5a in endothelial cells and pericytes determines the angiogenic outcome in a model of ischemic retinopathy

CYR61-CTGF-NOV (CCN)1 is a dynamically expressed extracellular matrix (ECM) protein with critical functions in cardiovascular development and tissue repair. Angiogenic endothelial cells (ECs) are a major cellular source of CCN1 which, once secreted, associates with the ECM and the cell surface and tightly controls the bidirectional flow of information between cells and the surrounding matrix. Endothelium-specific CCN1 deletion in mice using a cre/lox strategy induces EC hyperplasia and causes blood vessels to coalesce into large flat hyperplastic sinuses with no distinctive hierarchical organization. This is consistent with the role of CCN1 as a negative feedback regulator of vascular endothelial growth factor (VEGF) receptor activation. In the mouse model of oxygen-induced retinopathy (OIR), pericytes become the predominant CCN1 producing cells. Pericyte-specific deletion of CCN1 significantly decreases pathological retinal neovascularization following OIR. CCN1 induces the expression of the non-canonical Wnt5a in pericyte but not in EC cultures. In turn, exogenous Wnt5a inhibits CCN1 gene expression, induces EC proliferation and increases hypersprouting. Concordantly, treatment of mice with TNP470, a non-canonical Wnt5a inhibitor, reestablishes endothelial expression of CCN1 and significantly decreases pathological neovascular growth in OIR. Our data highlight the significance of CCN1-EC and CCN1-pericyte communication signals in driving physiological and pathological angiogenesis.

Slit2 suppresses endothelial cell proliferation and migration by inhibiting the VEGF-Notch signaling pathway

Slit homolog 2 (Slit2) is distributed in various tissues and participates in numerous cellular processes; however, the role of Slit2 in the regulation of angiogenesis remains controversial, since it has previously been reported to exert proangiogenic and antiangiogenic activities. The present study aimed to investigate the effects of Slit2 on vascular endothelial cell proliferation and migration in vitro, and to reveal the possible underlying signaling pathway. Aortic endothelial cells were isolated from Sprague Dawley rats and cultured. Cell proliferation assay, cell migration assay, immunocytochemistry and small interfering RNA transfection were subsequently performed. The results demonstrated that exogenous Slit2 administration markedly suppressed TNF-α-induced endothelial cell proliferation and migration in vitro. In addition, TNF-α application upregulated the protein expression levels of vascular endothelial growth factor (VEGF) and Notch in RAECs, whereas Slit2 administration downregulated VEGF and Notch expression in RAECs cultured in TNF-α conditioned medium. Further studies indicated that knockdown of VEGF suppressed the effects of TNF-α on the induction of RAEC proliferation and migration. VEGF knockdown-induced inhibition of RAEC proliferation and migration in TNF-α conditioned medium was also achieved without Slit2 administration. Furthermore, VEGF knockdown markedly decreased Notch1 and Notch2 expression. These results indicated that Slit2 suppresses TNF-α-induced vascular endothelial cell proliferation and migration in vitro by inhibiting the VEGF-Notch signaling pathway. Therefore, Slit2 may inhibit the proliferation and migration of endothelial cells during vascular development.

Analysis of CCN Protein Expression and Activities in Vasoproliferative Retinopathies

The retina is a complex neurovascular structure that conveys light/visual image through the optic nerve to the visual cortex of the brain. Neuronal and vascular activities in the retina are physically and functionally intertwined, and vascular alterations are consequential to the proper function of the entire visual system. In particular, alteration of the structure and barrier function of the retinal vasculature is commonly associated with the development of vasoproliferative ischemic retinopathy, a set of clinically well-defined chronic ocular microvascular complications causing blindness in all age groups. Experimentally, the retinal tissue provides researchers with a convenient, easily accessible, and directly observable model suitable to investigate whether and how newly identified genes regulate vascular development and regeneration. The six mammalian CCN gene-encoded proteins are part of an extracellular network of bioactive molecules that regulate various aspects of organ system development and diseases. Whether and how these molecules regulate the fundamental aspects of blood vessel development and pathology and subsequently the neurovascular link in the retina are open-ended questions. Sophisticated methods have been developed to gain insight into the pathogenesis of retinal vasculopathy. This chapter describes several useful methodologies and animal models to investigate the regulation and potential relevance of the CCN proteins in vasoproliferative diseases of the retina.

CCN1 Promotes VEGF Production in Osteoblasts and Induces Endothelial Progenitor Cell Angiogenesis by Inhibiting miR-126 Expression in Rheumatoid Arthritis

Angiogenesis is the formation of new capillaries from preexisting vasculature. The perpetuation of angiogenesis plays a critical role in the pathogenesis of various disease states including rheumatoid arthritis (RA). Cysteine-rich 61 (Cyr61 or CCN1) is an important proinflammatory cytokine in RA. Here, we investigated the role of CCN1 in angiogenesis associated with vascular endothelial growth factor (VEGF) production and osteoblasts. We found higher expression of CCN1 and VEGF in synovial fluid from RA patients compared with healthy controls. CCN1 induced VEGF expression in osteoblasts and increased endothelial progenitor cells (EPCs) angiogenesis by inhibiting miR-126 via the protein kinase C-alpha (PKC-α) signaling pathway. CCN1 knockdown inhibited angiogenesis in both in vitro and in vivo models. Inhibition of CCN1 expression with lentiviral vectors expressing short hairpin RNA (shRNA) ameliorated articular swelling, cartilage erosion, and angiogenesis in the ankle joint of mice with collagen-induced arthritis (CIA). Our study is the first to describe how CCN1 promotes VEGF expression in osteoblasts and increased EPCs angiogenesis in RA disease. CCN1 may serve as a potential target for RA treatment. © 2016 American Society for Bone and Mineral Research.

Modulation of VEGF receptor 2 signaling by protein phosphatases

Phosphorylation of serines, threonines, and tyrosines is a central event in signal transduction cascades in eukaryotic cells. The phosphorylation state of any particular protein reflects a balance of activity between kinases and phosphatases. Kinase biology has been exhaustively studied and is reasonably well understood, however, much less is known about phosphatases. A large body of evidence now shows that protein phosphatases do not behave as indiscriminate signal terminators, but can function both as negative or positive regulators of specific signaling pathways. Genetic models have also shown that different protein phosphatases play precise biological roles in health and disease. Finally, genome sequencing has unveiled the existence of many protein phosphatases and associated regulatory subunits comparable in number to kinases. A wide variety of roles for protein phosphatase roles have been recently described in the context of cancer, diabetes, hereditary disorders and other diseases. In particular, there have been several recent advances in our understanding of phosphatases involved in regulation of vascular endothelial growth factor receptor 2 (VEGFR2) signaling. The receptor is the principal signaling molecule mediating a wide spectrum of VEGF signal and, thus, is of paramount significance in a wide variety of diseases ranging from cancer to cardiovascular to ophthalmic. This review focuses on the current knowledge about protein phosphatases' regulation of VEGFR2 signaling and how these enzymes can modulate its biological effects.

Extracellular Matrix, a Hard Player in Angiogenesis

The extracellular matrix (ECM) is a complex network of proteins, glycoproteins, proteoglycans, and polysaccharides. Through multiple interactions with each other and the cell surface receptors, not only the ECM determines the physical and mechanical properties of the tissues, but also profoundly influences cell behavior and many physiological and pathological processes. One of the functions that have been extensively explored is its impingement on angiogenesis. The strong impact of the ECM in this context is both direct and indirect by virtue of its ability to interact and/or store several growth factors and cytokines. The aim of this review is to provide some examples of the complex molecular mechanisms that are elicited by these molecules in promoting or weakening the angiogenic processes. The scenario is intricate, since matrix remodeling often generates fragments displaying opposite effects compared to those exerted by the whole molecules. Thus, the balance will tilt towards angiogenesis or angiostasis depending on the relative expression of pro- or anti-angiogenetic molecules/fragments composing the matrix of a given tissue. One of the vital aspects of this field of research is that, for its endogenous nature, the ECM can be viewed as a reservoir to draw from for the development of new more efficacious therapies to treat angiogenesis-dependent pathologies.

Notch: A multi-functional integrating system of microenvironmental signals

The Notch signaling cascade is an evolutionarily ancient system that allows cells to interact with their microenvironmental neighbors through direct cell-cell interactions, thereby directing a variety of developmental processes. Recent research is discovering that Notch signaling is also responsive to a broad variety of stimuli beyond cell-cell interactions, including: ECM composition, crosstalk with other signaling systems, shear stress, hypoxia, and hyperglycemia. Given this emerging understanding of Notch responsiveness to microenvironmental conditions, it appears that the classical view of Notch as a mechanism enabling cell-cell interactions, is only a part of a broader function to integrate microenvironmental cues. In this review, we summarize and discuss published data supporting the idea that the full function of Notch signaling is to serve as an integrator of microenvironmental signals thus allowing cells to sense and respond to a multitude of conditions around them.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

Emerging roles of CCN proteins in vascular development and pathology

The CCN family of proteins consists of 6 members (CCN1-CCN6) that share conserved functional domains. These matricellular proteins interact with growth factors, extracellular matrix (ECM) proteins, cell surface integrins and other receptors to promote ECM-intracellular signaling. This signaling leads to propagation of a variety of cellular actions, including adhesion, invasion, migration and proliferation within several cell types, including epithelial, endothelial and smooth muscle cells. Though CCNs share significant homology, the function of each is unique due to distinct and cell specific expression patterns. Thus, their correct spatial and temporal expressions are critical during embryonic development, wound healing, angiogenesis and fibrosis. Disruption of these patterns leads to severe development disorders and contributes to the pathological progression of cancers, vascular diseases and chronic inflammatory diseases such as colitis, rheumatoid arthritis and atherosclerosis. While the effects of CCNs are diverse, this review will focus on the role of CCNs within the vasculature during development and in vascular diseases.

Regulating the regulators of angiogenesis by CCN1 and taking it up a Notch

CCN1 is encoded by an extracellular matrix protein-gene that is essential for the proper development of the cardiovascular system and the control of angiogenesis, inflammation, progenitor cell lineage commitment and extracellular matrix protein remodeling during the adult life. High-precision genetic models of tissue-specific gene deletion demonstrated a pivotal role of CCN1 in providing positional information to angiogenic endothelial cells (ECs) during the outgrowth and maturation of nascent blood vessel sprouts, fine-controlling Notch-dependent inter-endothelial cell communications and mediating interaction with inflammatory cells. Some of these pleiotropic activities of CCN1 are unique among proteins of the extracellular matrix. Thus, CCN1 represents a model molecule for investigating and unraveling novel aspects of extracellular protein signaling in vascular development and diseases.

VEGF-mediated NF-κB activation protects PC12 cells from damage induced by hypoxia

Neuronal apoptosis is a contributing cause of disability and death in cerebral ischemia. Nuclear factor-κB (NF-κB) may become a potential therapeutic target for hypoxic/ischemic neuron damage because NF-κB is inactivated after hypoxia exposure. Vascular endothelial growth factor (VEGF) has been found to improve neurological function recovery in cerebral ischemic injury although the exact molecular mechanisms that underlie the neuroprotective function of VEGF remain largely unknown. Here we defined the mechanism by which VEGF antagonized neuron-like PC12 cells apoptosis induced by hypoxia mimetic agent cobalt chloride (CoCl2) is through restoration of NF-κB activity. Depletion of VEGF with small interfering RNA (siRNA) in PC12 cells conferred CoCl2-induced cytotoxicity which was mitigated by VEGF administration. Treatment of PC12 cells with VEGF attenuated the CoCl2-induced cytotoxicity in both dose- and time-dependent manner. Mechanistically, VEGF increased IκBα phosphorylation and ubiquitination, promoted P65 nuclear translocation as well as upregulated XIAP and CCND1 expression. Meanwhile, VEGF administration reversed the dysregulation of IκBα phosphorylation and ubiquitination, P65 nuclear translocation as well as XIAP and CCND1 expression induced by CoCl2. Notably, the VEGF-dependent cytoprotection was abolished by pretreatment with BAY 11-7085, a specific inhibitor of NF-κB. Our data suggest that VEGF/NF-κB signalling pathway represents an adaptive mechanism that protects neural cells against hypoxic damage.

Eyeing the Cyr61/CTGF/NOV (CCN) group of genes in development and diseases: highlights of their structural likenesses and functional dissimilarities

“CCN” is an acronym referring to the first letter of each of the first three members of this original group of mammalian functionally and phylogenetically distinct extracellular matrix (ECM) proteins [i.e., cysteine-rich 61 (CYR61), connective tissue growth factor (CTGF), and nephroblastoma-overexpressed (NOV)]. Although “CCN” genes are unlikely to have arisen from a common ancestral gene, their encoded proteins share multimodular structures in which most cysteine residues are strictly conserved in their positions within several structural motifs. The CCN genes can be subdivided into members developmentally indispensable for embryonic viability (e.g., CCN1, 2 and 5), each assuming unique tissue-specific functions, and members not essential for embryonic development (e.g., CCN3, 4 and 6), probably due to a balance of functional redundancy and specialization during evolution. The temporo-spatial regulation of the CCN genes and the structural information contained within the sequences of their encoded proteins reflect diversity in their context and tissue-specific functions. Genetic association studies and experimental anomalies, replicated in various animal models, have shown that altered CCN gene structure or expression is associated with “injury” stimuli—whether mechanical (e.g., trauma, shear stress) or chemical (e.g., ischemia, hyperglycemia, hyperlipidemia, inflammation). Consequently, increased organ-specific susceptibility to structural damages ensues. These data underscore the critical functions of CCN proteins in the dynamics of tissue repair and regeneration and in the compensatory responses preceding organ failure. A better understanding of the regulation and mode of action of each CCN member will be useful in developing specific gain- or loss-of-function strategies for therapeutic purposes.

Single and Compound Knock-outs of MicroRNA (miRNA)-155 and Its Angiogenic Gene Target CCN1 in Mice Alter Vascular and Neovascular Growth in the Retina via Resident Microglia

The response of the retina to ischemic insult typically leads to aberrant retinal neovascularization, a major cause of blindness. The epigenetic regulation of angiogenic gene expression by miRNAs provides new prospects for their therapeutic utility in retinal neovascularization. Here, we focus on miR-155, a microRNA functionally important in inflammation, which is of paramount importance in the pathogenesis of retinal neovascularization. Whereas constitutive miR-155-deficiency in mice results in mild vascular defects, forced expression of miR-155 causes endothelial hyperplasia and increases microglia count and activation. The mouse model of oxygen-induced retinopathy, which recapitulates ischemia-induced aberrant neovessel growth, is characterized by increased expression of miR-155 and localized areas of microglia activation. Interestingly, miR-155 deficiency in mice reduces microglial activation, curtails abnormal vessel growth, and allows for rapid normalization of the retinal vasculature following ischemic insult. miR-155 binds to the 3'-UTR and represses the expression of the CCN1 gene, which encodes an extracellular matrix-associated integrin-binding protein that both promotes physiological angiogenesis and harnesses growth factor-induced abnormal angiogenic responses. Single CCN1 deficiency or double CCN1 and miR-155 knock-out in mice causes retinal vascular malformations typical of faulty maturation, mimicking the vascular alterations of miR-155 gain of function. During development, the miR-155/CCN1 regulatory axis balances the proangiogenic and proinflammatory activities of microglia to allow for their function as guideposts for sprout fusion and anastomosis. Under ischemic conditions, dysregulated miR-155 and CCN1 expression increases the inflammatory load and microglial activation, prompting aberrant angiogenic responses. Thus, miR-155 functions in tandem with CCN1 to modulate inflammation-induced vascular homeostasis and repair.