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

DLC1 promotes mechanotransductive feedback for YAP via RhoGAP-mediated focal adhesion turnover

Angiogenesis is a tightly controlled dynamic process demanding a delicate equilibrium between pro-angiogenic signals and factors that promote vascular stability. The spatiotemporal activation of the transcriptional co-factors YAP (herein referring to YAP1) and TAZ (also known WWTR1), collectively denoted YAP/TAZ, is crucial to allow for efficient collective endothelial migration in angiogenesis. The focal adhesion protein deleted-in-liver-cancer-1 (DLC1) was recently described as a transcriptional downstream target of YAP/TAZ in endothelial cells. In this study, we uncover a negative feedback loop between DLC1 expression and YAP activity during collective migration and sprouting angiogenesis. In particular, our study demonstrates that signaling via the RhoGAP domain of DLC1 reduces nuclear localization of YAP and its transcriptional activity. Moreover, the RhoGAP activity of DLC1 is essential for YAP-mediated cellular processes, including the regulation of focal adhesion turnover, traction forces, and sprouting angiogenesis. We show that DLC1 restricts intracellular cytoskeletal tension by inhibiting Rho signaling at the basal adhesion plane, consequently reducing nuclear YAP localization. Collectively, these findings underscore the significance of DLC1 expression levels and its function in mitigating intracellular tension as a pivotal mechanotransductive feedback mechanism that finely tunes YAP activity throughout the process of sprouting angiogenesis.

The influence of microenvironment stiffness on endothelial cell fate: Implication for occurrence and progression of atherosclerosis

Atherosclerosis, the primary cause of cardiovascular diseases (CVDs), is characterized by phenotypic changes in fibrous proliferation, chronic inflammation and lipid accumulation mediated by vascular endothelial cells (ECs) and vascular smooth muscle cells (SMCs) which are correlated with the stiffening and ectopic remodeling of local extracellular matrix (ECM). The native residents, ECs and SMCs, are not only affected by various chemical factors including inflammatory mediators and chemokines, but also by a range of physical stimuli, such as shear stress and ECM stiffness, presented in the microenvironmental niche. Especially, ECs, as a semi-selective barrier, can sense mechanical forces, respond quickly to changes in mechanical loading and provide context-specific adaptive responses to restore homeostasis. However, blood arteries undergo stiffening and lose their elasticity with age. Reports have shown that the ECM stiffening could influence EC fate by changing the cell adhesion, spreading, proliferation, cell to cell contact, migration and even communication with SMCs. The cell behaviour changes mediated by ECM stiffening are dependent on the activation of a signaling cascade of mechanoperception and mechanotransduction. Although the substantial evidence directly indicates the importance of ECM stiffening on the native ECs, the understanding about this complex interplay is still largely limited. In this review, we systematically summarize the roles of ECM stiffening on the behaviours of endothelial cells and elucidate the underlying details in biological mechanism, aiming to provide the process of how ECs integrate ECM mechanics and the highlights for bioaffinity of tissue-specific engineered scaffolds.

CCN1 expression is regulated by mechanical stimuli in tendons

Tendon overuse injuries are common, but the processes that govern tendon response to mechanical load are not fully understood. A series of experiments of in vitro and in vivo experiments was devised to study to the relationship between mechanical stimuli and the matricellular protein Cellular Communication Network Factor 1 (CCN1) in tenocytes and tendons. First, human and murine tenocytes were subjected to cyclic uniaxial loading in order to evaluate changes in CCN1 gene expression as a response to mechanical stimuli. Then, baseline Ccn1 gene expression in different murine tendons (Achilles, patellar, forearm, and tail) was examined. Finally, changes in Ccn1 expression after in vivo unloading experiments were examined. It was found that CCN1 expression significantly increased in both human and murine tenocytes at 5 and 10% cyclical uniaxial strain, while 2.5% strain did not have any effect on CCN1 expression. At baseline, the Achilles, patellar, and forearm tendons had higher expression levels of Ccn1 as compared to tail tendons. Twenty-four hours of immobilization of the hind-limb resulted in a significant decrease in Ccn1 expression in both the Achilles and patellar tendons. In summary, CCN1 expression is up-regulated in tenocytes subjected to mechanical load and down-regulated by loss of mechanical load in tendons. These results show that CCN1 expression in tendons is at least partially regulated by mechanical stimuli.

CCN proteins: opportunities for clinical studies-a personal perspective

The diverse members of the CCN family now designated as CCN1(CYR61), CCN2 (CTGF), CCN3(NOV), CCN4(WISP1), CCN5(WISP2), CCN6(WISP3) are a conserved matricellular family of proteins exhibiting a spectrum of functional properties throughout all organs in the body. Interaction with cell membrane receptors such as integrins trigger intracellular signaling pathways. Proteolytically cleaved fragments (constituting the active domains) can be transported to the nucleus and perform transcriptional relevant functional activities. Notably, as also found in other protein families some members act opposite to others creating a system of functionally relevant checks and balances. It has become apparent that these proteins are secreted into the circulation, are quantifiable, and can serve as disease biomarkers. How they might also serve as homeostatic regulators is just becoming appreciated. In this review I have attempted to highlight the most recent evidence under the subcategories of cancer and non-cancer relevant that could lead to potential therapeutic approaches or ideas that can be factored into clinical advances. I have added my own personal perspective on feasibility.

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.

Knockdown SENP1 Suppressed the Angiogenic Potential of Mesenchymal Stem Cells by Impacting CXCR4-Regulated MRTF-A SUMOylation and CCN1 Expression

The angiogenic potential of mesenchymal stem cells (MSCs) is critical for adult vascular regeneration and repair, which is regulated by various growth factors and cytokines. In the current study, we report that knockdown SUMO-specific peptidase 1 (SENP1) stimulated the SUMOylation of MRTF-A and prevented its translocation into the nucleus, leading to downregulation of the cytokine and angiogenic factor CCN1, which significantly impacted MSC-mediated angiogenesis and cell migration. Further studies showed that SENP1 knockdown also suppressed the expression of a chemokine receptor CXCR4, and overexpression of CXCR4 could partially abrogate MRTF-A SUMOylation and reestablish the CCN1 level. Mutation analysis confirmed that SUMOylation occurred on three lysine residues (Lys-499, Lys-576, and Lys-624) of MRTF-A. In addition, SENP1 knockdown abolished the synergistic co-activation of CCN1 between MRTF-A and histone acetyltransferase p300 by suppressing acetylation on histone3K9, histone3K14, and histone4. These results revealed an important signaling pathway to regulate MSC differentiation and angiogenesis by MRTF-A SUMOylation involving cytokine/chemokine activities mediated by CCN1 and CXCR4, which may potentially impact a variety of cellular processes such as revascularization, wound healing, and progression of cancer.

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.

Senescent hepatic stellate cells promote liver regeneration through IL-6 and ligands of CXCR2

Senescent cells have long been associated with deleterious effects in aging-related pathologies, although recent studies have uncovered their beneficial roles in certain contexts, such as wound healing. We have found that hepatic stellate cells (HSCs) underwent senescence within 2 days after 2/3 partial hepatectomy (PHx) in young (2–3 months old) mice, and the elimination of these senescent cells by using the senolytic drug ABT263 or by using a genetic mouse model impaired liver regeneration. Senescent HSCs secrete IL-6 and CXCR2 ligands as part of the senescence-associated secretory phenotype, which induces multiple signaling pathways to stimulate liver regeneration. IL-6 activates STAT3, induces Yes-associated protein (YAP) activation through SRC family kinases, and synergizes with CXCL2 to activate ERK1/2 to stimulate hepatocyte proliferation. The administration of either IL-6 or CXCL2 partially restored liver regeneration in mice with senescent cell elimination, and the combination of both fully restored liver weight recovery. Furthermore, the matricellular protein central communication network factor 1 (CCN1, previously called CYR61) was rapidly elevated in response to PHx and induced HSC senescence. Knockin mice expressing a mutant CCN1 unable to bind integrin α₆β₁ were deficient in senescent cells and liver regeneration after PHx. Thus, HSC senescence, largely induced by CCN1, is a programmed response to PHx and plays a critical role in liver regeneration through signaling pathways activated by IL-6 and ligands of CXCR2.

CCN1 interacts with integrins to regulate intestinal stem cell proliferation and differentiation

Intestinal stem cells (ISCs) at the crypt base contribute to intestinal homeostasis through a balance between self-renewal and differentiation. However, the molecular mechanisms regulating this homeostatic balance remain elusive. Here we show that the matricellular protein CCN1/CYR61 coordinately regulates ISC proliferation and differentiation through distinct pathways emanating from CCN1 interaction with integrins α_vβ₃/α_vβ₅. Mice that delete Ccn1 in Lgr5 + ISCs or express mutant CCN1 unable to bind integrins α_vβ₃/α_vβ₅ exhibited exuberant ISC expansion and enhanced differentiation into secretory cells at the expense of absorptive enterocytes in the small intestine, leading to nutrient malabsorption. Analysis of crypt organoids revealed that through integrins α_vβ₃/α_vβ₅, CCN1 induces NF-κB-dependent Jag1 expression to regulate Notch activation for differentiation and promotes Src-mediated YAP activation and Dkk1 expression to control Wnt signaling for proliferation. Moreover, CCN1 and YAP amplify the activities of each other in a regulatory loop. These findings establish CCN1 as a niche factor in the intestinal crypts, providing insights into how matrix signaling exerts overarching control of ISC homeostasis.

Intestinal stem cells contribute to homeostasis through a balance between self-renewal and differentiation. Here the authors show that CCN1 is an intestinal stem cell niche factor that activates integrin αvβ3/αvβ5 signaling to regulate proliferation and differentiation through distinct downstream pathways.

G-quadruplexes Stabilization Upregulates CCN1 and Accelerates Aging in Cultured Cerebral Endothelial Cells

Senescence in the cerebral endothelium has been proposed as a mechanism that can drive dysfunction of the cerebral vasculature, which precedes vascular dementia. Cysteine-rich angiogenic inducer 61 (Cyr61/CCN1) is a matricellular protein secreted by cerebral endothelial cells (CEC). CCN1 induces senescence in fibroblasts. However, whether CCN1 contributes to senescence in CEC and how this is regulated requires further study. Aging has been associated with the formation of four-stranded Guanine-quadruplexes (G4s) in G-rich motifs of DNA and RNA. Stabilization of the G4 structures regulates transcription and translation either by upregulation or downregulation depending on the gene target. Previously, we showed that aged mice treated with a G4-stabilizing compound had enhanced senescence-associated (SA) phenotypes in their brains, and these mice exhibited enhanced cognitive deficits. A sequence in the 3'-UTR of the human CCN1 mRNA has the ability to fold into G4s in vitro. We hypothesize that G4 stabilization regulates CCN1 in cultured primary CEC and induces endothelial senescence. We used cerebral microvessel fractions and cultured primary CEC from young (4-months old, m/o) and aged (18-m/o) mice to determine CCN1 levels. SA phenotypes were determined by high-resolution fluorescence microscopy in cultured primary CEC, and we used Thioflavin T to recognize RNA-G4s for fluorescence spectra. We found that cultured CEC from aged mice exhibited enhanced levels of SA phenotypes, and higher levels of CCN1 and G4 stabilization. In cultured CEC, CCN1 induced SA phenotypes, such as SA β-galactosidase activity, and double-strand DNA damage. Furthermore, CCN1 levels were upregulated by a G4 ligand, and a G-rich motif in the 3'-UTR of the Ccn1 mRNA was folded into a G4. In conclusion, we demonstrate that CCN1 can induce senescence in cultured primary CEC, and we provide evidence that G4 stabilization is a novel mechanism regulating the SASP component CCN1.

Mechanosensing by TRPV4 mediates stiffness-induced foreign body response and giant cell formation

Implantation of biomaterials or devices into soft tissue often leads to the development of the foreign body response (FBR), an inflammatory condition that can cause implant failure, tissue injury, and death of the patient. Macrophages accumulate and fuse to generate destructive foreign body giant cells (FBGCs) at the tissue-implant interface, leading to the development of fibrous scar tissue around the implant that is generated by myofibroblasts. We previously showed that the FBR in vivo and FBGC formation in vitro require transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel. Here, we report that TRPV4 was required specifically for the FBR induced by implant stiffness independently of biochemical cues and for intracellular stiffening that promotes FBGC formation in vitro. TRPV4 deficiency reduced collagen deposition and the accumulation of macrophages, FBGCs, and myofibroblasts at stiff, but not soft, implants in vivo and inhibited macrophage-induced differentiation of wild-type fibroblasts into myofibroblasts in vitro. Atomic force microscopy demonstrated that TRPV4 was required for implant-adjacent tissue stiffening in vivo and for cytoskeletal remodeling and intracellular stiffening induced by fusogenic cytokines in vitro. Together, these data suggest a mechanism whereby a reciprocal functional interaction between TRPV4 and substrate stiffness leads to cytoskeletal remodeling and cellular force generation to promote FBGC formation during the FBR.

Yes-Associated Protein in Atherosclerosis and Related Complications: A Potential Therapeutic Target That Requires Further Exploration

Atherosclerosis and its complications diseases remain leading causes of cardiovascular morbidity and mortality, bringing a massive burden on public health worldwide. Atherosclerosis is recognized as chronic inflammation, and involves several highly correlated processes, including lipid metabolism dysfunction, endothelial cell dysfunction, inflammation, oxidative stress, vascular smooth muscle cell activation, platelet activation, thrombosis, altered matrix metabolism, and vascular remodeling. Within the past few decades, accumulating evidence has shown that the Yes-associated protein (YAP), the major effector of the Hippo pathway, can play a crucial role in pathogenesis and development of atherosclerosis. Activation of YAP-related pathways, which are induced by alerting flow pattern and matrix stiffness among others, can regulate processes including vascular endothelial cell dysfunction, monocyte infiltration, and smooth muscle cell migration, which contribute to atherosclerotic lesion formation. Further, YAP potentially modulates atherosclerotic complications such as vascular calcification and intraplaque hemorrhage, which require further investigation. Here, we summarized the relevant literature to outline current findings detailing the relationship between of YAP and atherosclerosis and highlight areas for future research.

Cumulus cells of euploid versus whole chromosome 21 aneuploid embryos reveal differentially expressed genes

RESEARCH QUESTION

Can cumulus cells be used as a non-invasive target for the study of determinants of preimplantation embryo quality?

DESIGN

Cumulus cells were collected from monosomy 21, trisomy 21 and euploid embryos and subjected to RNA sequencing analysis and real-time polymerase chain reaction assays. The differential gene expression was analysed for different comparisons.

RESULTS

A total of 3122 genes in monosomy 21 cumulus cells and 19 genes in trisomy 21 cumulus cells were differentially expressed compared with euploid cumulus cells. Thirteen of these genes were differentially expressed in both monosomy and trisomy 21, compared with euploid, including disheveled segment polarity protein 2 (DVL2), cellular communication network factor 1 (CCN1/CYR61) and serum response factor (SRF), which have been previously implicated in embryo developmental competence. In addition, ingenuity pathway analysis revealed cell-cell contact function to be affected in both monosomy and trisomy 21 cumulus cells.

CONCLUSIONS

These findings support the use of cumulus cell gene expression analysis for the development of biomarkers evaluating oocyte quality for patients undergoing fertility preservation of oocytes.

Functional Role of miR-155 in the Pathogenesis of Diabetes Mellitus and Its Complications

Substantial evidence indicates that microRNA-155 (miR-155) plays a crucial role in the pathogenesis of diabetes mellitus (DM) and its complications. A number of clinical studies reported low serum levels of miR-155 in patients with type 2 diabetes (T2D). Preclinical studies revealed that miR-155 partakes in the phenotypic switch of cells within the islets of Langerhans under metabolic stress. Moreover, miR-155 was shown to regulate insulin sensitivity in liver, adipose tissue, and skeletal muscle. Dysregulation of miR-155 expression was also shown to predict the development of nephropathy, neuropathy, and retinopathy in DM. Here, we systematically describe the reports investigating the role of miR-155 in DM and its complications. We also discuss the recent results from in vivo and in vitro models of type 1 diabetes (T1D) and T2D, discussing the differences between clinical and preclinical studies and shedding light on the molecular pathways mediated by miR-155 in different tissues affected by DM.

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.

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

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.