Visualization of Pulse-Wave Velocity on Arterial Wall of Mice Through High-Frequency Ultrafast Doppler Imaging.

Arterial pulse-wave velocity (PWV) is widely used in clinical applications to assess cardiovascular diseases. Ultrasound methods have been proposed for estimating regional PWV in human arteries. Furthermore, high-frequency ultrasound (HFUS) has been applied to perform preclinical small-animal PWV measurements; however, electrocardiogram (ECG)-gated retrospective imaging is required to achieve high-frame-rate imaging, which might be affected by arrhythmia-related problems. In this article, HFUS PWV mapping based on 40-MHz ultrafast HFUS imaging is proposed to visualize PWV on mouse carotid artery to measure arterial stiffness without ECG gating. In contrast to most other studies that used cross-correlation methods to detect arterial motion, ultrafast Doppler imaging was applied in this study to measure arterial wall velocity for PWV estimations. The performance of the proposed HFUS PWV mapping method was verified using a polyvinyl alcohol (PVA) phantom with various freeze-thaw cycles. Small-animal studies were then performed in wild-type (WT) mice and in apolipoprotein E knockout (ApoE KO) mice that were fed a high-fat diet (for 16 and 24 weeks). The Young's modulus of the PVA phantom measured through HFUS PWV mapping was 15.3 ± 0.81, 20.8 ± 0.32, and 32.2 ± 1.11 kPa for three, four, and five freeze-thaw cycles, respectively, and the corresponding measurement biases (relative to theoretical values) were 1.59%, 6.41%, and 5.73%, respectively. In the mouse study, the average PWVs were 2.0 ± 0.26, 3.3 ± 0.45, and 4.1 ± 0.22 m/s for 16-week WT, 16-week ApoE KO, and 24-week ApoE KO mice, respectively. The PWVs of ApoE KO mice increased during the high-fat diet feeding period. HFUS PWV mapping was used to visualize the regional stiffness of mouse artery, and a histology confirmed that the plaque formation in the bifurcation region increased the regional PWV. All the results indicate that the proposed HFUS PWV mapping method is a convenient tool for investigating arterial properties in preclinical small-animal studies.

The regulation and functions of the matricellular CCN proteins induced by shear stress.

Shear stress is a frictional drag generated by the flow of fluid, such as blood or interstitial fluid, and plays a critical role in regulating cellular gene expression and functional phenotype. The matricellular CCN family proteins are dynamically regulated by shear stress of different flow patterns, and their expression significantly alters the microenvironment of cells. Secreted CCN proteins mainly bind to several cell surface integrin receptors to mediate their diverse functions in regulating cell survival, function, and behavior. Gene-knockout studies indicate major functions of CCN proteins in the cardiovascular and skeletal systems, the two primary systems in which CCN expressions are regulated by shear stress. In the cardiovascular system, the endothelium is directly exposed to vascular shear stress. Unidirectional laminar blood flow generates laminar shear stress, which promotes a mature endothelial phenotype and upregulates anti-inflammatory CCN3 expression. In contrast, disturbed flow generates oscillatory shear stress, which induces endothelial dysfunction through the induction of CCN1 and CCN2. Shear-induced CCN1 binds to integrin α6ß1 and promotes superoxide production, NF-κB activation, and inflammatory gene expression in endothelial cells. Although the interaction between shear stress and CCN4-6 is not clear, CCN 4 exhibits a proinflammatory property and CCN5 inhibits vascular cell growth and migration. The crucial roles of CCN proteins in cardiovascular development, homeostasis, and disease are evident but not fully understood. In the skeletal system, mechanical loading on bone generates shear stress from interstitial fluid in the lacuna-canalicular system and promotes osteoblast differentiation and bone formation. CCN1 and CCN2 are induced and potentially mediate fluid shear stress mechanosensing in osteocytes. However, the exact roles of interstitial shear stress-induced CCN1 and CCN2 in bone are still not clear. In contrast to other CCN family proteins, CCN3 inhibits osteoblast differentiation, although its regulation by interstitial shear stress in osteocytes has not been reported. The induction of CCN proteins by shear stress in bone and their functions remain largely unknown and merit further investigation. This review discusses the expression and functions of CCN proteins regulated by shear stress in physiological conditions, diseases, and cell culture models. The roles between CCN family proteins can be compensatory or counteractive in tissue remodeling and homeostasis.

Estimation of Mouse Carotid Arterial Wall Shear Stress Using High-Frequency Ultrasound Imaging.

Wall shear stress (WSS) is a crucial hemodynamic factor that promotes atherosclerosis (plaque) development in arteries; although the relationship between WSS and arterial atherosclerosis has been explored in many animal studies, it is not fully understood. No suitable tool, however, exists for rapidly estimating dynamic WSS in small-animal studies. This study proposes a 40-MHz high-frequency ultrasound (HFUS) imaging system for dynamic WSS estimation based on mouse carotid artery blood flow velocity gradient measurements by vector Doppler imaging (VDI). Aliasing reduces the accuracy of Doppler measurements, which can be prevented by increasing the imaging frame rate. Conventionally, imaging is performed at two tilted angles by alternating between the angles; in the proposed method, the frame rate was doubled by imaging at each tilted angle sequentially and by then temporally aligning the sequences based on pulsatile flow characteristics. Velocity estimation using this method had low errors for both a steady-flow straight-tube and pulsatile flow 60%-stenosis phantom. The method was tested for wild-type (WT) C57BL/6 mice at 16 weeks old and apolipoprotein E knockout (ApoE KO) mice at 16 and 24 weeks old; differences in time-averaged and oscillatory WSS were observed, and histology confirmed that the 24-week ApoE KO mice with the highest oscillatory WSS had the greatest plaque formation. The proposed HFUS WSS imaging method can predict the location and extent of plaque development; thus, this method is useful for small-animal studies investigating the WSS effect on atherosclerotic plaque development.

Shear-Regulated Extracellular Microenvironments and Endothelial Cell Surface Integrin Receptors Intertwine in Atherosclerosis.

Mechanical forces imposed by blood flow shear stress directly modulate endothelial gene expression and functional phenotype. The production of extracellular matrix proteins and corresponding cell-surface integrin receptors in arterial endothelial cells is intricately regulated by blood flow patterns. Laminar blood flow promotes mature and atheroresistant endothelial phenotype, while disturbed flow induces dysfunctional and atheroprone endothelial responses. Here, we discuss how hemodynamic changes orchestrate the remodeling of extracellular microenvironments and the expression profile of the integrin receptors in endothelial cells leading to oxidative stress and inflammation. Targeting the interaction between matrix proteins and their corresponding integrins is a potential therapeutic approach for atherosclerosis.

BDNF reverses aging-related microglial activation.

BACKGROUND: Excessive microglial activation is implicated in the pathogenesis of various age-related neurodegenerative diseases. In addition to neurons, brain-derived neurotrophic factor (BDNF) and its receptor TrkB are also expressed in microglia. However, the direct effect of BDNF on age-related microglial activation has rarely been investigated. METHODS: We began to address this question by examining the effect of age on microglial activation and the BDNF-TrkB pathway in mice. By using pharmacological and genetic approaches, the roles of BDNF and downstream signaling pathways in microglial activation and related neurotoxicity were examined in microglial cell line and primary microglial cells. RESULTS: We showed that microglial activation was evident in the brains of aged mice. The levels of BDNF and TrkB in microglia decreased with age and negatively correlated with their activation statuses in mice during aging. Interestingly, aging-related microglial activation could be reversed by chronic, subcutaneous perfusion of BDNF. Peripheral lipopolysaccharide (LPS) injection-induced microglial activation could be reduced by local supplement of BDNF, while shTrkB induced local microglial activation in naïve mice. In cultured microglial cell line and primary microglial cells, BDNF inhibited LPS-induced microglial activation, including morphological changes, activations of p38, JNK, and NF-кB, and productions of proinflammatory cytokines. These effects were blocked by shTrkB. BDNF induced activations of ErK and CREB which then competed with LPS-induced activation of NF-кB for binding to a common coactivator, CREB-binding protein. CONCLUSIONS: Decreasing BDNF-TrkB signaling during aging favors microglial activation, while upregulation BDNF signaling inhibits microglial activation via the TrkB-Erk-CREB pathway.

CCN1 triggers adaptive autophagy in cardiomyocytes to curb its apoptotic activities.

Autophagy occurs at basal levels for cellular homeostasis under normal conditions and is increased in response to nutrient starvation or stress to ensure cell survival. However, excessive autophagy can be deleterious to cardiomyocytes. CCN1/Cyr61, a matricellular protein, is expressed in the stressed heart to induce cardiomyopathy. The role of autophagy in CCN1-associated cardiotoxicity was not clear. Here, we found that autophagy was induced in the myocardium of the isoproterenol (ISO; 100 mg/kg/day for 5 days; s.c.) treated mice, where CCN1 expression is colocalized. The knock-in mice carrying an integrin α6ß1-binding-defective mutant allele Ccn1-dm were resistant to the ISO-induced cardiac injury and autophagy. Our in vitro studies demonstrated that CCN1 dose- and time-dependently induced GFP-LC3-labeled autophagosome formation in rat cardiomyoblast H9c2 cells. The formation of autolysosomes in response to CCN1 (5 µg/ml; 3 h) treatment was identified by the acridine orange staining. The autophagy induction was confirmed by the elevated protein levels of Beclin 1, Atg5, and LC3-II, and the decrease of p62. Inhibition of autophagy by 3-methyladenine or by silencing Atg5 gene enabled CCN1-induced apoptosis in H9c2 cells, suggesting a protective role of autophagy. CCN1 binds to integrin α6ß1 to induce autophagy through reactive oxygen species, and the activation of ERK and JNK. Furthermore, mitophagy was observed after CCN1 treatment for the clearance of depolarized mitochondria. Together, these results demonstrated that autophagy is induced in response to CCN1/α6ß1 signaling in cardiomyocytes to alleviate CCN1-associated cardiotoxicity.

Shear-Induced CCN1 Promotes Atheroprone Endothelial Phenotypes and Atherosclerosis.

BACKGROUND: Atherosclerosis occurs preferentially at the blood vessels encountering blood flow turbulence. The matricellular protein CCN1 is induced in endothelial cells by disturbed flow, and is expressed in advanced atherosclerotic lesions in patients and in the Apoe-/- mouse model. The role of CCN1 in atherosclerosis remains undefined. METHODS: To assess the function of CCN1 in vivo, knock-in mice carrying the integrin α6ß1-binding-defective mutant allele Ccn1-dm on the Apoe-/- background were tested in an atherosclerosis model generated by carotid artery ligation. Additionally, CCN1-regulated functional phenotypes of human umbilical vein endothelial cells, or primary mouse aortic endothelial cells isolated from wild-type and Ccn1 dm/dm mice, were investigated in the in vitro shear stress experiments under unidirectional laminar shear stress (12 dyn/cm2) versus oscillatory shear stress (±5 dyn/cm2) conditions. RESULTS: We found that Ccn1 expression was upregulated in the arterial endothelium 3 days after ligation before any detectable structural changes, and intensified with the progression of atherosclerotic lesions. Compared with Apoe-/- controls, Ccn1 dm/dm/ Apoe-/- mice were remarkably resistant to ligation-induced plaque formation (n=6). These mice exhibited lower oxidative stress, expression of endothelin-1 and monocyte chemoattractant protein-1, and monocyte homing. CCN1/α6ß1 critically mediated flow-induced activation of the pleiotropic transcription factor nuclear factor-κB and therefore the induction of atheroprone gene expression in the mouse arterial endothelium after ligation (n=6), or in cultured human umbilical vein endothelial cells or primary mouse aortic endothelial cells exposed to oscillatory shear stress (n=3 in triplicate). Interestingly, the activation of nuclear factor-κB by CCN1/α6ß1 signaling prompted more production of CCN1 and α6ß1. Blocking CCN1-α6ß1 binding by the Ccn1-dm mutation or by T1 peptide (derived from an α6ß1-binding sequence of CCN1) disrupted the positive-feedback regulation between CCN1/α6ß1 and nuclear factor-κB, and prevented flow-induced atheroprone phenotypic alterations in endothelial cells or atherosclerosis in mice. CONCLUSIONS: These data demonstrate a causative role of CCN1 in atherosclerosis via modulating endothelial phenotypes. CCN1 binds to its receptor integrin α6ß1 to activate nuclear factor-κB, thereby instigating a vicious circle to persistently promote atherogenesis. T1, a peptide antagonist selectively targeting CCN1-α6ß1, can be further optimized for developing T1-mimetics to treat atherosclerosis.

Ganoderma Triterpenoids Exert Antiatherogenic Effects in Mice by Alleviating Disturbed Flow-Induced Oxidative Stress and Inflammation.

Ganoderma mushrooms, used in traditional Chinese medicine to promote health and longevity, have become widely accepted as herbal supplements. Ganoderma lucidum (GL), a commonly seen ganoderma species, is commercially cultivated under controlled conditions for more consistent chemical composition. The medicinal properties of GL are attributable to its antioxidant and anti-inflammatory activities. We intended to assess the effect of GL in atherosclerosis, an arterial condition associated with chronic oxidative stress and inflammation, using a carotid-artery-ligation mouse model. Flow turbulence created in the ligated artery induces oxidative stress and neointimal hyperplasia, a feature of early atherogenesis. Daily oral GL prevented neointimal thickening 2 weeks after ligation. Moreover, the ganoderma triterpenoid (GT) crude extract isolated from GL abolished ligation-induced neointima formation. Mechanistically, endothelial dysfunction was observed 3 days after ligation before any structural changes could be detected. GTs alleviated the oxidative stress and restored the atheroresistent status of endothelium by inhibiting the induction of a series of atherogenic factors, including endothelin-1, von Willebrand factor, and monocyte chemoattractant protein-1 after 3-day ligation. The anti-inflammatory activity of GTs was tested in cultured human umbilical vein endothelial cells (HUVECs) exposed to disturbed flow in an in vitro perfusion system. GTs abolished the induction of proinflammatory VCAM-1, TNF-α, and IL-6 by oscillatory shear stress. Moreover, the antioxidant activity of GTs was tested in HUVECs against the insult of H2O2. GTs dissipated the cellular superoxide accumulation imposed by H2O2, thereby mitigating H2O2-induced cell damage and proatherogenic response. Our results revealed the atheroprotective properties of ganoderma mushrooms and identified triterpenoids as the critical constituents for those effects. GTs prevent atherogenesis by eliminating disturbed flow-induced oxidative stress and inflammation.

Matricellular protein CCN1 mediates doxorubicin-induced cardiomyopathy in mice.

Doxorubicin (DOX) is an effective chemotherapeutic agent however its clinical use is limited by its cumulative cardiotoxicity. Matricellular protein CCN1 mediates work-overload-induced cardiac injury. We aimed to assess the role of CCN1 in DOX-associated cardiomyopathy. Here we discovered CCN1 expression in the myocardium 1 day after DOX treatment (15 mg/kg; i.p.) in mice. Whereas CCN1 synergizes with Fas ligand (FasL) to induce cardiomyocyte apoptosis, we found that FasL was also induced by DOX in the heart. To assess the function of CCN1 in vivo, knockin mice (Ccn1dm/dm) expressing an a6ß1-binding defective CCN1 mutant were treated with a single dose of DOX (15 mg/kg; i.p.). Compared with wild-type mice, Ccn1dm/dm mice were resistant to DOX-induced cardiac injury and dysfunction 14 days after injection. Using rat cardiomyoblast H9c2 cells, we demonstrated that DOX induced reactive oxygen species accumulation to upregulate CCN1 and FasL expression. CCN1 mediated DOX cardiotoxicity by engaging integrin a6ß1 to promote p38 mitogen-activated protein kinase activation and the release of mitochondrial Smac and HtrA2 to cytosol, thereby counteracting the inhibition of XIAP and facilitating apoptosis. In summary, CCN1 critically mediates DOX-induced cardiotoxicity. Disrupting CCN1/a6ß1 engagement abolishes DOX-associated cardiomyopathy in mice.

CCN1 enables Fas ligand-induced apoptosis in cardiomyoblast H9c2 cells by disrupting caspase inhibitor XIAP.

Cell proliferation from pre-existing cardiomyocytes is a major source of cells for normal mammalian myocardial renewal or for regeneration after myocardial injury. These proliferative cardiomyocytes may act differently from the postmitotic cardiomyocytes in a stressed heart. Extracellular matrix molecule CCN1 is produced to promote Fas ligand (FasL)-induced cardiomyocyte apoptosis in mice with stress-induced cardiac injury. We aimed to investigate the effect of CCN1 on the proliferative cardiomyocytes. We used rat embryonic cardiomyoblast H9c2 cells to study the cardiotoxicity of CCN1. We found that FasL dose-dependently increased the X-linked inhibitor of apoptosis protein (XIAP) levels to prevent the progression of apoptosis in H9c2 cells. CCN1, though it did not induce apoptosis by itself, sensitized H9c2 cells to FasL-induced apoptosis. CCN1 functions by engaging its cell-surface receptor integrin α6ß1 and elevating reactive oxygen species levels, which leads to mitogen-activated protein kinase p38 activation, cytosolic Bax translocation to mitochondria, and the release of mitochondrial Smac and HtrA2 to cytosol. These elevated cytosolic Smac and HtrA2 dismantle the inhibition of XIAP, thereby facilitating the activation of caspase-3 and the apoptosis-induced by FasL. In summary, we demonstrated a novel mechanism underlying the resistance of cardiomyoblasts to FasL-induced apoptosis, and the pro-apoptotic function of CCN1 by disrupting this resistance.

Sesame oil therapeutically ameliorates cardiac hypertrophy by regulating hypokalemia in hypertensive rats.

BACKGROUND: Hypokalemia and hypertension are common manifestations of preclinical cardiovascular conditions that have a predictive value for cardiovascular morbidity and mortality. Cardiac hypertrophy, an important risk factor in heart failure, is attributed to long-term hypokalemia and hypertension. Sesame oil is rich in nutrients and possesses potent antihypertensive activities. METHODS: We investigated the therapeutic potential of sesame oil using a hypertensive model created by subcutaneously injecting deoxycorticosterone acetate (DOCA; 15 mg/mL/kg in mineral oil; twice weekly for 5 weeks) and supplementing with 1% sodium chloride drinking water (DOCA/salt) to uninephrectomized rats. Sesame oil was administered by oral gavage (0.5 or 1 mL/kg/d for 7 days) after 4 weeks of DOCA/salt treatment. Systolic blood pressure (SBP) and diastolic blood pressure (DBP), electrocardiography (ECG), and K(+) and Mg(2+) levels were assessed 24 hours after the last dose of sesame oil. Heart tissue was collected for histologic analysis. RESULTS: Sesame oil effectively reduced the SBP/DBP and ECG abnormalities and increased the serum levels of K(+) and Mg(2+) while limiting the urinary excretion of K(+) in DOCA/salt-induced hypertensive rats. In addition, sesame oil decreased the heart mass, the thickness of the left ventricle, and the diameter of cardiomyocytes, indicating the regression of left ventricular hypertrophy in the hypertensive rats. CONCLUSION: We demonstrate that sesame oil therapeutically ameliorates cardiac hypertrophy by regulating hypokalemia in hypertensive rats.

The triterpenoids of Ganoderma tsugae prevent stress-induced myocardial injury in mice.

Ganoderma mushrooms (Lingzhi in Chinese) have well-documented health benefits. Ganoderma tsugae (G. tsugae), one of the ganoderma species, has been commercially cultivated as a dietary supplement. Because G. tsugae has high antioxidant activity and because oxidative stress is often associated with cardiac injury, we hypothesized that G. tsugae protects against cardiac injury by alleviating oxidative stress. We tested the hypothesis using a work-overload-induced myocardial injury model created by challenging mice with isoproterenol (ISO). Remarkably, oral G. tsugae protected the mice from ISO-induced myocardial injury. Moreover, the triterpenoid fraction of G. tsugae, composed of a mixture of nine structurally related ganoderic acids (GAs), provided cardioprotection by inhibiting the ISO-induced expression of Fas/Fas ligand, oxidative stress, and apoptosis. The antioxidant activity of GAs was tested in cultured cardio-myoblast H9c2 cells against the insult of H2O2. GAs dissipated the cellular reactive oxygen species imposed by H2O2 and prevented cell death. Our findings uncovered the cardioprotective activity of G. tsugae and identified GAs as the bioactive components against cardiac insults.

Extracellular matrix protein CCN1 regulates cardiomyocyte apoptosis in mice with stress-induced cardiac injury.

AIMS: Expression of extracellular matrix protein CCN1 is induced in end-stage ischaemic cardiomyopathy in humans, and after cardiac ischaemia and reperfusion in experimental animal models. Despite its well-documented angiogenic activities, CCN1 increases the cytotoxicities of the tumour necrosis factor family cytokines, which promotes apoptosis in fibroblasts. We aimed to determine the physiological function of CCN1 in an injured heart. METHODS AND RESULTS: To assess the function of CCN1 in vivo, knock-in mice carrying the apoptosis-defective mutant allele Ccn1-dm were tested in an isoproterenol (ISO)-induced myocardial injury model (100 mg/kg/day of sc injected ISO for 5 days). Compared with wild-type mice, Ccn1(dm/dm) mice were remarkably resistant to ISO-induced cardiac injury; they showed no post-treatment cardiomyocyte apoptosis or myocardial tissue damage. ISO cardiotoxicity was dependent on Fas ligand (FasL) and its downstream signalling. Using primary cultures of cardiomyocytes isolated from rats, we demonstrated that CCN1 sensitized FasL-mediated apoptosis by engaging its cell-surface receptor integrin α6ß1 and up-regulating intracellular reactive oxygen species (ROS), which activated mitogen-activated protein kinase p38, and increased cell-surface Fas expression. CONCLUSION: CCN1 is a critical pathophysiological regulator that mediates cardiomyocyte apoptosis during work-overload-induced cardiac injury. CCN1 increases cellular susceptibility to Fas-induced apoptosis by increasing ROS and cell-surface Fas expression.

Sesamol attenuates isoproterenol-induced acute myocardial infarction via inhibition of matrix metalloproteinase-2 and -9 expression in rats.

BACKGROUND/AIMS: The protective role of sesamol and its possible action against isoproterenol-induced myocardial injury and infarction is unknown. We tested the hypothesis that sesamol's protection against myocardial infarction is associated with the inhibition of matrix metalloproteinase (MMP)-2 and MMP-9. METHODS: Four groups of experimental rats were subcutaneously injected with sesamol (0, 1, 3, or 10 mg/kg) and then, 2 h later, intraperitoneally injected with isoproterenol (100 mg/kg 24 h apart on 2 consecutive days) to induce myocardial infarction. Control rats were treated with saline only. Blood pressure (BP), heart rate (HR), and electrocardiography (ECG) wave durations, serum creatine phosphokinase isoenzymes (CKMB), lactate dehydrogenase (LDH), myocardial histology, MMP-2, and MMP-9 were assessed 24 h after the last dose of isoproterenol was given. RESULTS: BP was lower, and HR, ECG wave durations, CKMB, LDH, myocardial injury, MMP-2, and MMP-9 levels were higher in experimental rats than in control rats. BP was significantly higher, and all the other parameters were significantly lower in the rats treated with sesamol than in those treated with isoproterenol only. CONCLUSIONS: Sesamol effectively prevented myocardial infarction, at least in part, by controlling proteolytic activities and the expression of MMP-2 and -9 in isoproterenol-treated rats.

The matricellular protein CCN1 is essential for cardiac development.

The matricellular protein CCN1 (formerly named CYR61) regulates cell adhesion, migration, proliferation, survival, and differentiation through binding to integrin receptors and heparan sulfate proteoglycans. Here we show that Ccn1-null mice are impaired in cardiac valvuloseptal morphogenesis, resulting in severe atrioventricular septal defects (AVSD). Remarkably, haploinsufficiency for Ccn1 also results in delayed formation of the ventricular septum in the embryo and persistent ostium primum atrial septal defects (ASD) in approximately 20% of adults. Mechanistically, Ccn1 is not required for epithelial-to-mesenchymal transformation or cell proliferation and differentiation in the endocardial cushion tissue. However, Ccn1 deficiency leads to precocious apoptosis in the atrial junction of the cushion tissue and impaired gelatinase activities in the muscular component of the interventricular septum at embryonic day 12.5, when fusion between the endocardial cushion tissue and the atrial and ventricular septa occurs, indicating that these defects may underlie the observed AVSD. Moreover, human CCN1 maps to 1p21-p31, the chromosomal location of an AVSD susceptibility gene. Together, these results provide evidence that deficiency in matrix signaling can lead to autosomal dominant AVSD, identify Ccn1(+/-) mice as a genetic model for ostium primum ASD, and implicate CCN1 as a candidate gene for AVSD in humans.

CYR61 (CCN1) is essential for placental development and vascular integrity.

CYR61 (CCN1) is a member of the CCN family of secreted matricellular proteins that includes connective tissue growth factor (CCN2), NOV (CCN3), WISP-1 (CCN4), WISP-2 (CCN5), and WISP-3 (CCN6). First identified as the product of a growth factor-inducible immediate-early gene, CYR61 is an extracellular matrix-associated angiogenic inducer that functions as a ligand of integrin receptors to promote cell adhesion, migration, and proliferation. Aberrant expression of Cyr61 is associated with breast cancer, wound healing, and vascular diseases such as atherosclerosis and restenosis. To understand the functions of CYR61 during development, we have disrupted the Cyr61 gene in mice. We show here that Cyr61-null mice suffer embryonic death: approximately 30% succumbed to a failure in chorioallantoic fusion, and the reminder perished due to placental vascular insufficiency and compromised vessel integrity. These findings establish CYR61 as a novel and essential regulator of vascular development. CYR61 deficiency results in a specific defect in vessel bifurcation (nonsprouting angiogenesis) at the chorioallantoic junction, leading to an undervascularization of the placenta without affecting differentiation of the labyrinthine syncytiotrophoblasts. This unique phenotype is correlated with impaired Vegf-C expression in the allantoic mesoderm, suggesting that CYR61-regulated expression of Vegf-C plays a role in vessel bifurcation. The genetic and molecular basis of vessel bifurcation is presently unknown, and these findings provide new insight into this aspect of angiogenesis.