Endothelial Cell Interactions Research Articles

Uric acid promotes chemokine and adhesion molecule production in vascular endothelium via nuclear factor-kappa B signaling

Background and aimsHyperuricemia is an important risk factor for atherosclerosis, yet the potential mechanisms are not well understood. Migration and adhesion of leukocytes to endothelial cells play key roles in initiation and development of atherosclerosis. We investigated monocyte–endothelial cell interactions and potential signaling pathways under uric acid (UA)-stimulated conditions. Methods and resultsPrimary human umbilical vein endothelial cells (HUVECs) were cultured and exposed to different concentrations of UA for various periods. Experimental hyperuricemia rat models were established. Expression of chemoattractant protein-1 (MCP-1), interleukin 8 (IL-8), vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) were evaluated. Monocyte–endothelial cell interactions were elucidated by chemotaxis and adhesion assays, and nuclear factor-kappa B (NF-κB) pathway was studied using fluorescent microscopy and electrophoretic mobility shift assay. Results showed that high concentration of UA stimulated generation of chemokines and adhesion molecules in ex vivo and in vivo experiments. Migration and adhesion of human monocytic leukemia cell line THP-1 cells to HUVECs were promoted and activated NF-κB was significantly increased. UA-induced responses were ameliorated by organic anion transporter inhibitor probenecid and NF-κB inhibitor BAY11-7082. It was also observed that human endothelial cells expressed urate transporter-1, which was not regulated by UA. ConclusionHigh concentration of UA exerts unfavorable effects directly on vascular endothelium via the NF-κB signaling pathway, the process of which requires intracellular uptake of UA.

Abstract 056: Integrative Genomic Analysis Unravels Novel Pathways And Key Regulatory Networks In Blood Pressure

Blood pressure (BP) is a highly heritable trait and hypertension is a major risk factor for cardiovascular diseases. Recent genome-wide association studies (GWAS) have implicated a number of susceptibility loci for systolic (SBP) and diastolic (DBP) blood pressure. However, these loci together only explain 1% of the BP variability and the underlying mechanisms remain elusive. In this study, we utilized an integrative genomics approach that leveraged multiple genetic and genomic datasets including 1) GWAS from CHARGE (The Cohorts for Heart and Aging Research in Genomic Epidemiology) Consortium for DBP and SBP, 2) expression quantitative trait loci (eQTLs) from genetics of gene expression studies of human tissues related to hypertension (such as peripheral blood, whole blood, human aortic endothelial cells, and adipose tissue), 3) knowledge-driven biological pathways, and 4) data-driven regulatory gene networks. The integration of these diverse data sources enabled tissue-specific investigations on whether the genetic variants associated with BP concentrated on specific parts of gene regulatory networks, termed as “subnetworks”, and whether novel key regulators in the subnetworks could be identified based on data-driven network topology. We identified 10 and 8 subnetworks for DBP and SBP respectively. Among these, subnetworks associated with ion homeostasis, ALK in cardiac myocytes, B cell receptor signaling, and Regulation of Insulin Secretion, were shared between DBP and SBP. More interestingly, we detected tissue-specific pathways, for example, L1CAM interactions in aortic endothelial cells and Leukocyte transendothelial migration in adipose. Among the trait-specific subnetworks, those involved in megakaryocyte development and cytoskeleton remodeling were found to be SBP-specific while GAB1 signalosome subnetwork was DBP-specific. Finally, by utilizing the gene-gene relationships revealed by the network architecture, we detected key regulator genes, both known (e.g. COL1A1, KL, and OSR1) and novel (e.g. EFEMP1, and CRABP2), in these blood pressure subnetworks. Our results shed lights on the complex mechanisms underlying blood pressure and highlight potential novel targets for hypertension and cardiovascular diseases.

Nestin involvement in tissue injury and cancer--a potential tumor marker?

In eukaryotic cells, the cytoskeleton contains three major filamentous components: actin microfilaments, microtubules and intermediate filaments. Nestin represents one of the class VI intermediate filament proteins. Clinical and molecular analyses have revealed substantial information regarding the presence of Nestin in cells with progenitor or stem cell properties. During tissue injury Nestin is expressed in cells with progenitor cell-like properties. These cells may serve as a tissue reserve and, as such, may contribute to tissue repair. Based on currently available data, Nestin also appears to be implicated in two oncogenic processes. First, Nestin has been found to be expressed in cancer stem-like cells and poorly differentiated cancer cells and, as such, Nestin is thought to contribute to the aggressive behavior of these cells. Second, Nestin has been found to be involved in tumor angiogenesis through an interaction of cancer cells and blood vessel endothelial cells and, as such, Nestin is thought to facilitate tumor growth. We conclude that Nestin may serve as a promising tumor marker and as a potential therapeutic target amenable to tumor suppression and angiogenesis inhibition.

Brain-targeted delivery of docetaxel by glutathione-coated nanoparticles for brain cancer.

Gliomas are some of the most aggressive types of cancers but the blood-brain barrier acts as an obstacle to therapeutic intervention in brain-related diseases. The blood-brain barrier blocks the permeation of potentially toxic compounds into neural tissue through the interactions of brain endothelial cells with glial cells (astrocytes and pericytes) which induce the formation of tight junctions in endothelial cells lining the blood capillaries. In the present study, we characterize a glutathione-coated docetaxel-loaded PEG-PLGA nanoparticle, show its in vitro drug release data along with cytotoxicity data in C6 and RG2 cells, and investigate its trans-blood-brain barrier permeation through the establishment of a Transwell cellular co-culture. We show that the docetaxel-loaded nanoparticle's size enables its trans-blood-brain barrier permeation; the nanoparticle exhibits a steady, sustained release of docetaxel; the drug is able to induce cell death in glioma models; and the glutathione-coated nanoparticle is able to permeate through the Transwell in vitro blood-brain barrier model.

Glycobiology of ocular angiogenesis

Ocular neovascularization can affect almost all the tissues of the eye: the cornea, the iris, the retina, and the choroid. Pathological neovascularization is the underlying cause of vision loss in common ocular conditions such as diabetic retinopathy, retinopathy of prematurity and age-related macular neovascularization. Glycosylation is the most common covalent posttranslational modification of proteins in mammalian cells. A growing body of evidence demonstrates that glycosylation influences the process of angiogenesis and impacts activation, proliferation, and migration of endothelial cells as well as the interaction of angiogenic endothelial cells with other cell types necessary to form blood vessels. Recent studies have provided evidence that members of the galectin class of β-galactoside-binding proteins modulate angiogenesis by novel carbohydrate-based recognition systems involving interactions between glycans of angiogenic cell surface receptors and galectins. This review discusses the significance of glycosylation and the role of galectins in the pathogenesis of ocular neovascularization.

Mechanisms of vasculogenesis in 3D fibrin matrices mediated by the interaction of adipose-derived stem cells and endothelial cells.

Vascularization of tissue-engineered constructs is essential to provide sufficient nutrient supply and hemostasis after implantation into target sites. Co-cultures of adipose-derived stem cells (ASC) with outgrowth endothelial cells (OEC) in fibrin gels were shown to provide an effective possibility to induce vasculogenesis in vitro. However, the mechanisms of the interaction between these two cell types remain unclear so far. The aim of this study was to evaluate differences of direct and indirect stimulation of ASC-induced vasculogenesis, the influence of ASC on network stabilization and molecular mechanisms involved in vascular structure formation. Endothelial cells (EC) were embedded in fibrin gels either containing non-coated or ASC-coated microcarrier beads as well as ASC alone. Moreover, EC-seeded constructs incubated with ASC-conditioned medium were used in addition to constructs with ASC seeded on top. Vascular network formation was visualized by green fluorescent protein expressing cells or immunostaining for CD31 and quantified. RT-qPCR of cells derived from co-cultures in fibrin was performed to evaluate changes in the expression of EC marker genes during the first week of culture. Moreover, angiogenesis-related protein levels were measured by performing angiogenesis proteome profiler arrays. The results demonstrate that proximity of endothelial cells and ASC is required for network formation and ASC stabilize EC networks by developing pericyte characteristics. We further showed that ASC induce controlled vessel growth by secreting pro-angiogenic and regulatory proteins. This study reveals angiogenic protein profiles involved in EC/ASC interactions in fibrin matrices and confirms the usability of OEC/ASC co-cultures for autologous vascular tissue engineering.

Regulation of methylglyoxal-elicited leukocyte recruitment by endothelial SGK1/GSK3 signaling

Excessive levels of the glycolysis metabolite methylglyoxal (MG) elicit enhanced expression of adhesion molecules which foster leukocyte–endothelial cell interactions. The signaling mechanisms involved remain elusive. To address this, we investigated the signal transduction of leukocyte- and endothelial-expressed phosphoinositide 3-kinase (PI3K) effector kinases glycogen synthase kinase 3 (GSK3) and serum- and glucocorticoid-inducible kinase 1 (SGK1) in the regulation of MG-elicited leukocyte recruitment. Using intravital microscopy of mouse cremasteric microvasculature, we demonstrate that GSK3 inhibitors lithium and SB216763 mitigate MG-elicited leukocyte recruitment and microvascular hyperpermeability. In SVEC4-10EE2 endothelial cells, but not in neutrophils, MG transiently activates GSK3 by reducing inhibitory phospho-GSK3α/β (Ser21/9) which parallels decrease of phospho-Akt at early time points (<30min). At later time points (≥1h), MG induces GSK3 deactivation which is dissipated by siRNA silencing of SGK. MG treatment potentiates endothelial SGK1 mRNA, total SGK1, phospho-SGK1 and phospho-NDRG1. The SGK1 inhibitor GSK650394 attenuates MG-elicited leukocyte recruitment. Pharmacological inhibition or silencing endothelial GSK3 or SGK attenuates MG-triggered nuclear factor (NF)-κB activity. Furthermore, silencing SGK blunts MG-triggered redox-sensitive phosphorylation of endothelial transcription factor CREB. Inhibition of SGK1 or GSK3 mitigates the expression of endothelial adhesion molecules P- and E-selectins and ICAM-1. Moreover, SGK1-dependent CREB activation participates in MG-elicited ICAM-1 upregulation. We conclude that temporal activation of endothelial SGK1 and GSK3 is decisive in MG-elicited upregulation of transcription factors, adhesion molecule expression, and leukocyte-vascular endothelium interactions. This novel signaling pathway may link excessive MG levels in vivo to inflammation, thus, unraveling potential therapeutic targets.

Engineered three-dimensional microfluidic device for interrogating cell-cell interactions in the tumor microenvironment.

Stromal cells in the tumor microenvironment play a key role in the metastatic properties of a tumor. It is recognized that cancer-associated fibroblasts (CAFs) and endothelial cells secrete factors capable of influencing tumor cell migration into the blood or lymphatic vessels. We developed a microfluidic device that can be used to image the interactions between stromal cells and tumor cell spheroids in a three dimensional (3D) microenvironment while enabling external control of interstitial flow at an interface, which supports endothelial cells. The apparatus couples a 200-μm channel with a semicircular well to mimic the interface of a blood vessel with the stroma, and the design allows for visualization of the interactions of interstitial flow, endothelial cells, leukocytes, and fibroblasts with the tumor cells. We observed that normal tissue-associated fibroblasts (NAFs) contribute to the "single file" pattern of migration of tumor cells from the spheroid in the 3D microenvironment. In contrast, CAFs induce a rapid dispersion of tumor cells out of the spheroid with migration into the 3D matrix. Moreover, treatment of tumor spheroid cultures with the chemokine CXCL12 mimics the effect of the CAFs, resulting in similar patterns of dispersal of the tumor cells from the spheroid. Conversely, addition of CXCL12 to co-cultures of NAFs with tumor spheroids did not mimic the effects observed with CAF co-cultures, suggesting that NAFs produce factors that stabilize the tumor spheroids to reduce their migration in response to CXCL12.

We have contact: endothelial cell-smooth muscle cell interactions.

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

Contribution of the vascular bone marrow niche to leukemia progression

Leukemia arises from leukemic stem cells, which reside within the bone marrow occupying two different stem cells niches: the endosteal and the vascular niche. The maintenance of leukemic stem cells requires complex regulation mediated by many intrinsic and extrinsic signals provided by their niche cells. The interaction of leukemic and endothelial cells can occur either via direct contact through cell adhesion molecules such as selectins or integrins or signals can be transmitted by chemokines or cytokines of which stromal cell-derived factor 1 represents the most studied. Experimental studies provide evidence that targeting molecules involved in the interaction of leukemic and endothelial cells might represent a promising therapeutic target. Indeed, first clinical trials considering this concept are currently under investigation.

Liver sinusoidal endothelial cell-mediated CD8 T cell priming depends on co-inhibitory signal integration over time.

The initiation of adaptive immunity requires cell-to-cell contact between T cells and antigen-presenting cells. Together with immediate TCR signal transduction, the formation of an immune synapse (IS) is one of the earliest events detected during T cell activation. Here, we show that interaction of liver sinusoidal endothelial cells (LSEC) with naive CD8 T cells, which induces CD8 T cells without immediate effector function, is characterized by a multi-focal type IS. The co-inhibitory molecule B7H1, which is pivotal for the development of non-responsive LSEC-primed T cells, did not alter IS structure or TCRβ/CD11a cluster size or density, indicating that IS form does not determine the outcome of LSEC-mediated T cell activation. Instead, PD-1 signaling during CD8 T cell priming by LSEC repressed IL-2 production as well as sustained CD25 expression. When acting during the first 24 h of LSEC/CD8 T cell interaction, CD28 co-stimulation inhibited the induction of non-responsive LSEC-primed T cells. However, after more than 36 h of PD-1 signaling, CD28 co-stimulation failed to rescue effector function in LSEC-primed T cells. Together, these data show that during LSEC-mediated T cell priming, integration of co-inhibitory PD-1 signaling over time turns on a program for CD8 T cell development, that cannot be overturned by co-stimulatory signals.

Therapeutic translation in acute kidney injury: the epithelial/endothelial axis.

Acute kidney injury (AKI) remains a major clinical event with rising incidence, severity, and cost; it now has a morbidity and mortality exceeding acute myocardial infarction. There is also a documented conversion to and acceleration of chronic kidney disease to end-stage renal disease. The multifactorial nature of AKI etiologies and pathophysiology and the lack of diagnostic techniques have hindered translation of preclinical success. An evolving understanding of epithelial, endothelial, and inflammatory cell interactions and individualization of care will result in the eventual development of effective therapeutic strategies. This review focuses on epithelial and endothelial injury mediators, interactions, and targets for therapy.

Simvastatin reduces leucocyte– and platelet–endothelial cell interaction in murine antigen-induced arthritis in vivo

Objectives: The use of statins in the prevention and treatment of cardiovascular diseases is well established. Their use as anti-inflammatory and immunomodulatory agents in the treatment of rheumatoid arthritis (RA) has also been investigated, with several clinical and experimental studies indicating an anti-inflammatory effect of statins for RA, but other studies showing no effect or even the opposite. The current study was designed to examine the effect of simvastatin in an in vivo murine model of arthritis using intravital microscopy.Method: We assigned four groups (n = 7, female C57Bl6 mice), two with and two without antigen-induced arthritis (AiA), from which one of the non-AiA groups and one of the AiA groups were treated with simvastatin 40 mg/kg i.p. daily for 14 consecutive days after induction of arthritis. Platelet– and leucocyte–endothelial cell interaction was assessed by measurement of rolling and adherent fluorescence-labelled platelets and leucocytes, functional capillary density (FCD) was evaluated, and knee joint diameter was determined as a clinical parameter.Results: In arthritic mice treated with simvastatin, a significant reduction in platelet– and leucocyte–endothelial cell interaction was observed in comparison to arthritic mice treated with vehicle. In addition, a significant reduction in FCD was seen in arthritic mice treated with simvastatin, along with a reduction in knee joint swelling of the AiA mice.Conclusions: Treatment of AiA mice with simvastatin showed significant reductions in platelet– and leucocyte–endothelial cell interactions, in FCD, and in the swelling of the knee joint. These results support the hypothesis of the anti-inflammatory effects of statins in the treatment of RA.

Characterization of dielectrophoresis-aligned nanofibrous silk fibroin–chitosan scaffold and its interactions with endothelial cells for tissue engineering applications

Aligned three-dimensional nanofibrous silk fibroin–chitosan (eSFCS) scaffolds were fabricated using dielectrophoresis (DEP) by investigating the effects of alternating current frequency, the presence of ions, the SF:CS ratio and the post-DEP freezing temperature. Scaffolds were characterized with polarized light microscopy to analyze SF polymer chain alignment, atomic force microscopy (AFM) to measure the apparent elastic modulus, and scanning electron microscopy and AFM to analyze scaffold topography. The interaction of human umbilical vein endothelial cells (HUVECs) with eSFCS scaffolds was assessed using immunostaining to assess cell patterning and AFM to measure the apparent elastic modulus of the cells. The eSFCS (50:50) samples prepared at 10MHz with NaCl had the highest percentage of aligned area as compared to other conditions. As DEP frequency increased from 100kHz to 10MHz, fibril sizes decreased significantly. eSFCS (50:50) scaffolds fabricated at 10MHz in the presence of 5mM NaCl had a fibril size of 77.96±4.69nm and an apparent elastic modulus of 39.9±22.4kPa. HUVECs on eSFCS scaffolds formed aligned and branched capillary-like vascular structures. The elastic modulus of HUVEC cultured on eSFCS was 6.36±2.37kPa. DEP is a potential tool for fabrication of SFCS scaffolds with aligned nanofibrous structures that can guide vasculature in tissue engineering and repair.

Remote ischemic preconditioning differentially affects NADPH oxidase isoforms during hepatic ischemia–reperfusion

AimsWe investigated the function of major superoxide-generating enzymes after remote ischemic preconditioning (IPC) and hepatic ischemia–reperfusion (IR), with the specific aim of assessing the importance of the most relevant NADPH oxidase (NOX) isoforms, NOX2 and NOX4, in the mechanism of action. Main methods60-min partial liver ischemia was induced in Sprague–Dawley rats in the presence or absence of remote IPC (2×10-min limb IR), and hepatic microcirculatory variables were determined through intravital video microscopy and lightguide spectrophotometry during reperfusion. Inflammatory enzyme activities (myeloperoxidase (MPO) and xanthine oxidoreductase (XOR)), cytokine production (TNF-α and HMGB-1), liver necroenzyme levels (AST, ALT and LDH) and NOX2 and NOX4 protein expression changes (Western blot analysis) were assayed biochemically. Key findingsIn this setting, remote IPC significantly decreased the IR-induced hepatic NOX2 expression, but the NOX4 expression remained unchanged. The remote IPC provided significant, but incomplete protection against the leukocyte–endothelial cell interactions and flow deterioration. Hepatocellular damage (AST, ALT and LDH release), cytokine levels, and XOR and MPO activities also diminished. SignificanceRemote IPC limited the IR-induced microcirculatory dysfunction, but the protective effect did not affect all NOX homologs (at least not NOX4). The residual damage and inflammatory activation could well be linked to the unchanging NOX4 activity.

The Endothelin-Integrin Axis Is Involved in Macrophage-induced Breast Cancer Cell Chemotactic Interactions with Endothelial Cells

Elevated macrophage infiltration in tumor tissues is associated with breast cancer metastasis. Cancer cell migration/invasion toward angiogenic microvasculature is a key step in metastatic spread. We therefore studied how macrophages stimulated breast cancer cell interactions with endothelial cells. Macrophages produced cytokines, such as interleukin-8 and tumor necrosis factor-α, to stimulate endothelin (ET) and ET receptor (ETR) expression in breast cancer cells and human umbilical vascular endothelial cells (HUVECs). ET-1 was induced to a greater extent from HUVECs than from breast cancer cells, resulting in a density difference that facilitated cancer cell chemotaxis toward HUVECs. Macrophages also stimulated breast cancer cell adhesion to HUVECs and transendothelial migration, which were repressed by ET-1 antibody or ETR inhibitors. The ET axis induced integrins, such as αV and β1, and their counterligands, such as intercellular adhesion molecule-2 and P-selectin, in breast cancer cells and HUVECs, and antibodies against these integrins efficiently suppressed macrophage-stimulated breast cancer cell interactions with HUVECs. ET-1 induced Ets-like kinase-1 (Elk-1), signal transducer and activator of transcription-3 (STAT-3), and nuclear factor-κB (NF-κB) phosphorylation in breast cancer cells. The use of inhibitors to prevent their phosphorylation or ectopic overexpression of dominant-negative IκBα perturbed ET-1-induced integrin αV and integrin β1 expression. The physical associations of these three transcriptional factors with the gene promoters of the two integrins were furthermore evidenced by a chromatin immunoprecipitation assay. Finally, our mouse orthotopic tumor model revealed an ET axis-mediated lung metastasis of macrophage-stimulated breast cancer cells, suggesting that the ET axis was involved in macrophage-enhanced breast cancer cell endothelial interactions.

Aberrant Presentation of HPA-Reactive Carbohydrates Implies Selectin-Independent Metastasis Formation in Human Prostate Cancer

To investigate the impact of prostate cancer cell surface glycosylation as part of the tumor cell-endothelial cell interaction in prostate cancer metastasis. Glycosyltransferase expression was profiled in metastasis-derived prostate cancer cell lines and compared with primary epithelium. Prostate cancer cells were examined for HPA- and selectin-binding and adhesion to endothelium. Spontaneous metastasis xenograft models were established to test the lectin HPA-binding sites as a marker of metastatic competence and to evaluate E-selectin-binding sites in vivo. The importance of selectins for metastasis formation was analyzed using Sele(-/-)/Selp(-/-) mice. The clinical relevance of HPA- and E-selectin-binding sites in prostate cancer was determined. Glycosyltransferases involved in the synthesis of common HPA-binding sites are downregulated in prostate cancer cells. An absence of HPA-reactive carbohydrates specifically indicates spontaneous metastatic spread of prostate cancer xenografts in vivo and a poor prognosis of patients with prostate cancer. HPA-binding sites decrease in lymph node metastases compared with corresponding primary tumors. Common selectin ligands are absent on prostate cancer cells, which do not adhere to recombinant selectins or endothelium under shear stress in vitro. Spontaneous metastasis formation is largely independent of selectins in vivo. E-selectin-binding sites are detectable in only 2% of patients with prostate cancer without prognostic significance. Prostate cancer is characterized by an inverse functional and prognostic importance of HPA-binding sites compared with other adenocarcinomas. Accordingly, this study surprisingly shows that the selectin-selectin ligand axis, which is essential for extravasation and thus metastasis formation in several malignancies, can be circumvented in prostate cancer.

Not simply misshapen red cells: multimolecular and cellular events in sickle vaso-occlusion.

Thromboinflammatory diseases result from the interactions of vascular endothelial cells, inflammatory cells, and platelets with cellular adhesion molecules, plasma proteins, and lipids. Tipping the balance toward a prothrombotic, proinflammatory phenotype results from multicellular activation signals. In this issue of the JCI, Li et al. explore the regulation of heterotypic neutrophil-platelet contacts in response to TNF-α-induced venular inflammation with relevance to sickle cell disease (SCD).

Heparan Sulfates Mediate the Interaction between Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1) and the Gαq/11 Subunits of Heterotrimeric G Proteins

The endothelial cell-cell junction has emerged as a major cell signaling structure that responds to shear stress by eliciting the activation of signaling pathways. Platelet endothelial cell adhesion molecule-1 (PECAM-1) and heterotrimeric G protein subunits Gαq and 11 (Gαq/11) are junctional proteins that have been independently proposed as mechanosensors. Our previous findings suggest that they form a mechanosensitive junctional complex that discriminates between different flow profiles. The nature of the PECAM-1·Gαq/11 interaction is still unclear although it is likely an indirect association. Here, we investigated the role of heparan sulfates (HS) in mediating this interaction and in regulating downstream signaling in response to flow. Co-immunoprecipitation studies show that PECAM-1·Gαq/11 binding is dramatically decreased by competitive inhibition with heparin, pharmacological inhibition with the HS antagonist surfen, and enzymatic removal of HS chains with heparinase III treatment as well as by site-directed mutagenesis of basic residues within the extracellular domain of PECAM-1. Using an in situ proximity ligation assay, we show that endogenous PECAM-1·Gαq/11 interactions in endothelial cells are disrupted by both competitive inhibition and HS degradation. Furthermore, we identified the heparan sulfate proteoglycan syndecan-1 in complexes with PECAM-1 that are rapidly decreased in response to flow. Finally, we demonstrate that flow-induced Akt activation is attenuated in endothelial cells in which PECAM-1 was knocked down and reconstituted with a binding mutant. Taken together, our results indicate that the PECAM-1·Gαq/11 mechanosensitive complex contains an endogenous heparan sulfate proteoglycan with HS chains that is critical for junctional complex assembly and regulating the flow response.

Islet Microenvironment, Modulated by Vascular Endothelial Growth Factor-A Signaling, Promotes β Cell Regeneration

Pancreatic islet endocrine cell and endothelial cell (EC) interactions mediated by vascular endothelial growth factor-A (VEGF-A) signaling are important for islet differentiation and the formation of highly vascularized islets. To dissect how VEGF-A signaling modulates intra-islet vasculature, islet microenvironment, and β cell mass, we transiently increased VEGF-A production by β cells. VEGF-A induction dramatically increased the number of intra-islet ECs but led to β cell loss. After withdrawal of the VEGF-A stimulus, β cell mass, function, and islet structure normalized as a result of a robust, but transient, burst in proliferation of pre-existing β cells. Bone marrow-derived macrophages (MΦs) recruited to the site of β cell injury were crucial for the β cell proliferation, which was independent of pancreatic location and circulating factors such as glucose. Identification of the signals responsible for the proliferation of adult, terminally differentiated β cells will improve strategies aimed at β cell regeneration and expansion.