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Objective: We sought to determine how endothelial cell (EC) expression of the activating k-Ras (kirsten rat sarcoma 2 viral oncogene homolog) mutation, k-RasV12, affects their ability to form lumens and tubes and interact with pericytes during capillary assembly Approach and Results: Using defined bioassays where human ECs undergo observable tubulogenesis, sprouting behavior, pericyte recruitment to EC-lined tubes, and pericyte-induced EC basement membrane deposition, we assessed the impact of EC k-RasV12 expression on these critical processes that are necessary for proper capillary network formation. This mutation, which is frequently seen in human ECs within brain arteriovenous malformations, was found to markedly accentuate EC lumen formation mechanisms, with strongly accelerated intracellular vacuole formation, vacuole fusion, and lumen expansion and with reduced sprouting behavior, leading to excessively widened tube networks compared with control ECs. These abnormal tubes demonstrate strong reductions in pericyte recruitment and pericyte-induced EC basement membranes compared with controls, with deficiencies in fibronectin, collagen type IV, and perlecan deposition. Analyses of signaling during tube formation from these k-RasV12 ECs reveals strong enhancement of Src (Src proto-oncogene, non-receptor tyrosine kinase), Pak2 (P21 [RAC1 (Rac family small GTPase 1)] activated kinase 2), b-Raf (v-raf murine sarcoma viral oncogene homolog B1), Erk (extracellular signal–related kinase), and Akt (AK strain transforming) activation and increased expression of PKCε (protein kinase C epsilon), MT1-MMP (membrane-type 1 matrix metalloproteinase), acetylated tubulin and CDCP1 (CUB domain-containing protein 1; most are known EC lumen regulators). Pharmacological blockade of MT1-MMP, Src, Pak, Raf, Mek (mitogen-activated protein kinase) kinases, Cdc42 (cell division cycle 42)/Rac1, and Notch markedly interferes with lumen and tube formation from these ECs. Conclusions: Overall, this novel work demonstrates that EC expression of k-RasV12 disrupts capillary assembly due to markedly excessive lumen formation coupled with strongly reduced pericyte recruitment and basement membrane deposition, which are critical pathogenic features predisposing the vasculature to develop arteriovenous malformations.

Whether alterations in the microtubule cytoskeleton affect the ability of endothelial cells (ECs) to sprout and form branching networks of tubes was investigated in this study. Bioassays of human EC tubulogenesis, where both sprouting behavior and lumen formation can be rigorously evaluated, were used to demonstrate that addition of the microtubule-stabilizing drugs, paclitaxel, docetaxel, ixabepilone, and epothilone B, completely interferes with EC tip cells and sprouting behavior, while allowing for EC lumen formation. In bioassays mimicking vasculogenesis using single or aggregated ECs, these drugs induce ring-like lumens from single cells or cyst-like spherical lumens from multicellular aggregates with no evidence of EC sprouting behavior. Remarkably, treatment of these cultures with a low dose of the microtubule-destabilizing drug, vinblastine, led to an identical result, with complete blockade of EC sprouting, but allowing for EC lumen formation. Administration of paclitaxel in vivo markedly interfered with angiogenic sprouting behavior in developing mouse retina, providing corroboration. These findings reveal novel biological activities for pharmacologic agents that are widely utilized in multidrug chemotherapeutic regimens for the treatment of human malignant cancers. Overall, this work demonstrates that manipulation of microtubule stability selectively interferes with the ability of ECs to sprout, a necessary step to initiate and form branched capillary tube networks.

The extracellular matrix represents a critical regulator of tissue vascularization during embryonic development and postnatal life. In this perspective, we present key information and concepts that focus on how the extracellular matrix controls capillary assembly, maturation, and stabilization, and, in addition, contributes to tissue stability and health. In particular, we present and discuss mechanistic details underlying (1) the role of the extracellular matrix in controlling different steps of vascular morphogenesis, (2) the ability of endothelial cells (ECs) and pericytes to coassemble into elongated and narrow capillary EC-lined tubes with associated pericytes and basement membrane matrices, and (3) the identification of specific growth factor combinations ("factors") and peptides as well as coordinated "factor" and extracellular matrix receptor signaling pathways that are required to form stabilized capillary networks.

Objective: In this work, we have sought to define growth factor requirements and the signaling basis for different stages of human vascular morphogenesis and maturation. Approach and Results: Using a serum-free model of endothelial cell (EC) tube morphogenesis in 3-dimensional collagen matrices that depends on a 5 growth factor combination, SCF (stem cell factor), IL (interleukin)-3, SDF (stromal-derived factor)-1α, FGF (fibroblast growth factor)-2, and insulin (factors), we demonstrate that VEGF (vascular endothelial growth factor) pretreatment of ECs for 8 hours (ie, VEGF priming) leads to marked increases in the EC response to the factors which includes; EC tip cells, EC tubulogenesis, pericyte recruitment and proliferation, and basement membrane deposition. VEGF priming requires VEGFR2, and the effect of VEGFR2 is selective to the priming response and does not affect factor-dependent tubulogenesis in the absence of priming. Key molecule and signaling requirements for VEGF priming include RhoA, Rock1 (Rho-kinase), PKCα (protein kinase C α), and PKD2 (protein kinase D2). siRNA suppression or pharmacological blockade of these molecules and signaling pathways interfere with the ability of VEGF to act as an upstream primer of downstream factor-dependent EC tube formation as well as pericyte recruitment. VEGF priming was also associated with the formation of actin stress fibers, activation of focal adhesion components, upregulation of the EC factor receptors, c-Kit, IL-3Rα, and CXCR4 (C-X-C chemokine receptor type 4), and upregulation of EC-derived PDGF (platelet-derived growth factor)-BB, PDGF-DD, and HB-EGF (heparin-binding epidermal growth factor) which collectively affect pericyte recruitment and proliferation. Conclusions: Overall, this study defines a signaling signature for a separable upstream VEGF priming step, which can activate ECs to respond to downstream factors that are necessary to form branching tube networks with associated mural cells.

Objective: We sought to identify and investigate the functional role of the major endothelial cell (EC)-derived factors that control pericyte recruitment to EC tubes and pericyte-induced tube maturation during capillary network formation. Approach and Results: We identify PDGF (platelet-derived growth factor)-BB, PDGF-DD, ET (endothelin)-1, TGF (transforming growth factor)-β, and HB-EGF (heparin-binding epidermal growth factor), as the key individual and combined regulators of pericyte assembly around EC tubes. Using novel pericyte only assays, we demonstrate that PDGF-BB, PDGF-DD, and ET-1 are the primary direct drivers of pericyte invasion. Their addition to pericytes induces invasion as if ECs were present. In contrast, TGF-β and HB-EGF have minimal ability to directly stimulate pericyte invasion. In contrast, TGF-β1 can act as an upstream pericyte primer to stimulate invasion in response to PDGFs and ET-1. HB-EGF stimulates pericyte proliferation along with PDGFs and ET-1. Using EC-pericyte cocultures, individual, or combined blockade of these EC-derived factors, or their pericyte receptors, using neutralizing antibodies or chemical inhibitors, respectively, interferes with pericyte recruitment and proliferation. As individual factors, PDGF-BB and ET-1 have the strongest impact on these events. However, when the blocking reagents are combined to interfere with each of the above factors or their receptors, more dramatic and profound blockade of pericyte recruitment, proliferation, and pericyte-induced basement membrane deposition occurs. Under these conditions, ECs form tubes that become much wider and less elongated as if pericytes were absent. Conclusions: Overall, these new studies define and characterize a functional role for key EC-derived factors controlling pericyte recruitment, proliferation, and pericyte-induced basement membrane deposition during capillary network assembly.

Anti-angiogenic therapies have generated significant interest for their potential to combat tumor growth. However, tumor overproduction of pro-angiogenic ligands can overcome these therapies, hampering success of this approach. To circumvent this problem, we target the resynthesis of phosphoinositides consumed during intracellular transduction of pro-angiogenic signals in endothelial cells (EC), thus harnessing the tumor’s own production of excess stimulatory ligands to deplete adjacent ECs of the capacity to respond to these signals. Using zebrafish and human endothelial cells in vitro, we show ECs deficient in CDP-diacylglycerol synthase 2 are uniquely sensitive to increased vascular endothelial growth factor (VEGF) stimulation due to a reduced capacity to re-synthesize phosphoinositides, including phosphatidylinositol-(4,5)-bisphosphate (PIP2), resulting in VEGF-exacerbated defects in angiogenesis and angiogenic signaling. Using murine tumor allograft models, we show that systemic or EC specific suppression of phosphoinositide recycling results in reduced tumor growth and tumor angiogenesis. Our results suggest inhibition of phosphoinositide recycling provides a useful anti-angiogenic approach., Tumors can overproduce pro-angiogenic ligands overcoming currently approved anti-angiogenic therapies and hindering their success. Here, the authors show that targeting phosphoinositide recycling during tumor angiogenesis harnesses the tumor’s own production of angiogenic ligands to deplete adjacent endothelial cells of the capacity to respond to these signals.

Objective: In this work, we examine the molecular basis for capillary tube regression and identify key proregressive factors, signaling pathways, and pharmacological antagonists of this process. Approach and Results: We demonstrate that the proinflammatory mediators, IL (interleukin)-1β, TNF (tumor necrosis factor) α, and thrombin, singly and in combination, are potent regulators of capillary tube regression in vitro. These proregressive factors, when added to endothelial cell–pericyte cocultures, led to selective loss of endothelial cell-lined tube networks, with retention and proliferation of pericytes despite the marked destruction of adjacent capillary tubes. Moreover, treatment of macrophages with the TLR (toll-like receptor) agonists Pam3CSK4 and lipopolysaccharide generates conditioned media with marked proregressive activity, that is completely blocked by a combination of neutralizing antibodies directed to IL-1β and TNFα but not to other factors. The same combination of blocking antibodies, as well as the anti-inflammatory cytokine IL-10, interfere with macrophage-dependent hyaloid vasculature regression in mice suggesting that proinflammatory cytokine signaling regulates capillary regression in vivo. In addition, we identified a capillary regression signaling signature in endothelial cells downstream of these proregressive agents that is characterized by increased levels of ICAM-1 (intercellular adhesion molecule-1), phospho-p38, and phospho-MLC2 (myosin light chain-2) and decreased levels of phospho-Pak2, acetylated tubulin, phospho-cofilin, and pro-caspase3. Finally, we identified combinations of pharmacological agents (ie, FIST and FISTSB) that markedly rescue the proregressive activities of IL-1β, TNFα, and thrombin, individually and in combination. Conclusions: Overall, these new studies demonstrate that the major proinflammatory mediators, IL-1β, TNFα, and thrombin, are key regulators of capillary tube regression—a critical pathological process regulating human disease.

Title of referenced paper: Solar energy at birth and human lifespan, Journal of Photochemistry & Photobiology B 186 (2018)59–68.This paper uses National Center for Health Statistics (NCHS) death data collected from 1979- 2013, inclusive, and average monthly solar intensity as measured by sunspot number collected from the National Oceanic and Atmospheric Administration (NOAA) from 1900–2013, inclusive. Keywords: Ultraviolet radiation, Human lifespan, Sunspot number, Solar energy, Multiple sclerosis, Epigenetics

In this brief communication, we propose the concept that capillary regression may represent a primary pathogenic process underlying COVID-19 infection, particularly in the serious and life-threatening manifestations of the disease. We suggest that the marked elevations of pro-inflammatory mediators that are observed in these seriously ill patients may directly induce capillary regression and endothelial cell (EC) loss. Recent autopsy studies are demonstrating EC loss leading to widespread microthrombi and associated tissue damage. Recent work has indicated that interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNFα), and thrombin, individually and in combination, can potently cause capillary tube regression in experimental models in vitro and in vivo. Other pro-inflammatory mediators including interferon gamma (IFNγ), interleukin-4 (IL-4), and interleukin-13 (IL-13) were also shown to be pro-regressive and could be relevant mediators in COVID-19 patients. Interestingly, combinations of pharmacologic agents were identified that reduced capillary regression and protected capillary tube networks against these pro-inflammatory mediators. Such an approach might be an important therapeutic option going forward to treat key disease states where capillary regression plays a major underlying pathogenic role. Finally, if capillary regression is occurring in response to these pro-inflammatory mediators during COVID-19 infection, we suggest that combinations of blocking agents directed to these key pro-regressive mediators might be necessary to appropriately treat patients.

Here, we examine known GTPase regulators of vesicle trafficking events to assess whether they affect endothelial cell (EC) lumen and tube formation. We identify novel roles for the small GTPases Rab3A, Rab3B, Rab8A, Rab11A, Rab27A, RalA, RalB and caveolin-1 in co-regulating membrane trafficking events that control EC lumen and tube formation. siRNA suppression of individual GTPases such as Rab3A, Rab8A, and RalB markedly inhibit tubulogenesis, while greater blockade is observed with combinations of siRNAs such as Rab3A and Rab3B, Rab8A and Rab11A, and RalA and RalB. These combinations of siRNAs also disrupt very early events in lumen formation including the formation of intracellular vacuoles. In contrast, knockdown of the endocytosis regulator, Rab5A, fails to inhibit EC tube formation. Confocal microscopy and real-time videos reveal that caveolin-1 strongly labels intracellular vacuoles and localizes to the EC apical surface as they fuse to form the luminal membrane. In contrast, Cdc42 and Rab11A localize to a perinuclear, subapical region where intracellular vacuoles accumulate and fuse during lumen formation. Our new data demonstrates that EC tubulogenesis is coordinated by a series of small GTPases to control polarized membrane trafficking events to generate, deliver, and fuse caveolin-1-labeled vacuoles to create the apical membrane surface.

Purpose The purpose of this paper is to examine the role of UVR at birth and its relationship to lifespan and determine whether there are significant differential effects on sex and race. We test if variation in UVR, as determined by solar cycles (long-term variation), is related to survival as measured by age at death. Methods The data used 78 million death records from the National Center for Health Statistics (NCHS) from 1979 to 2013 with accidents, suicides, and war casualties deleted resulted in ~63 million records. Records of persons ≤ 47 years old were also scrubbed because we could not show an effect on lifespan based upon the intensity of solar energy as reflected by sunspot number (SSN). This we hypothesize is due to the protective effect of the hormones associated with growth and reproduction. Also selected were persons afflicted with multiple sclerosis (MS). Results Males of all races born with a UVR intensity as estimated by sunspot number (SSN) ≤ 90 had an average lifespan of 74.4 years, for females of all races, 78.1 years; males born with >90 had an average lifespan of 66.3 years, for females of all races, 70.2 years, resulting in a lifespan decrease of 8.1 years for males and 8.5 years for females. For African-American males born ≤ 90 SSN, 70.8 years and for >90 SSN, 62.5 years, an 8.3-year decrease; similarly, for African-American females ≤ 90 SSN, 75.0, for >90 SSN, 65.4 years, a 9.6-year decrease. Higher solar energy at birth had an adverse effect on human lifespan. We also found that there were twice as many persons with MS born in >80–90 SSN as in the general population. Conclusions There is a statistically significant inverse relationship between exposure to solar energy at birth and average human lifespan. Solar energy by some mechanism alters the epigenome at birth, but the effect of higher solar energy becomes apparent after the age of natural selection.

The formation of new blood vessels, or angiogenesis, is a complex process that plays important roles in growth and development, tissue and organ regeneration, as well as numerous pathological conditions. Angiogenesis undergoes multiple discrete steps that can be individually evaluated and quantified by a large number of bioassays. These independent assessments hold advantages but also have limitations. This article describes in vivo, ex vivo, and in vitro bioassays that are available for the evaluation of angiogenesis and highlights critical aspects that are relevant for their execution and proper interpretation. As such, this collaborative work is the first edition of consensus guidelines on angiogenesis bioassays to serve for current and future reference. Fil: Nowak Sliwinska, Patrycja. Université of Lausanne; Suiza. Univeristé of Geneve; Suiza Fil: Alitalo, Kari. Katholikie Universiteit Leuven; Bélgica Fil: Allen, Elizabeth. Katholikie Universiteit Leuven; Bélgica Fil: Anisimov, Andrey. Katholikie Universiteit Leuven; Bélgica Fil: Aplin, Alfred C.. University of Washington; Estados Unidos Fil: Auerbach, Robert. University of Wisconsin; Estados Unidos Fil: Augustin, Hellmut G.. Heidelberg University; Alemania. German Cancer Consortium; Alemania Fil: Bates, David O.. University of Nottingham; Reino Unido Fil: Beijnum, Judy R. van. Cancer Center Amsterdam; Países Bajos Fil: Bender, R. Hugh F.. University of California; Estados Unidos Fil: Bergers, Gabriele. Katholikie Universiteit Leuven; Bélgica Fil: Bikfalvi, Andreas. Universite de Bordeaux; Francia Fil: Bischoff, Joyce. Harvard Medical School; Estados Unidos Fil: Böck, Barbara C.. Heidelberg University; Alemania. German Cancer Consortium; Alemania Fil: Brooks, Peter C.. Maine Medical Center Research Institute; Estados Unidos Fil: Bussolino, Federico. Università di Torino; Italia. Candiolo Cancer Institute; Italia Fil: Cakir, Bertan. Harvard Medical School; Estados Unidos Fil: Carmeliet, Peter. Katholikie Universiteit Leuven; Bélgica Fil: Castranova, Daniel. Harvard Medical School; Estados Unidos Fil: Cimpean, Anca M.. Victor Babes University of Medicine and Pharmacy; Rumania Fil: Cleaver, Ondine. University Of Texas At Brownsville; Estados Unidos Fil: Coukos, George. Universida de Lausanne; Suiza Fil: Davis, George E.. University of Missouri; Estados Unidos Fil: De Palma, Michele. Swiss Federal Institute of Technology; Suiza Fil: Dimberg, Anna. Uppsala University; Suiza Fil: Dings, Ruud P. M.. University of Arkansas for Medical Sciences; Estados Unidos Fil: Djonov, Valentin. University of Bern; Suiza Fil: Dudley, Andrew C.. University of Virginia; Estados Unidos Fil: Dufton, Neil P.. Imperial College London; Reino Unido Fil: Fendt, Sarah-Maria. VIB Center for Cancer Biology; Bélgica Fil: Ferrara, Napoleone. University of California at San Diego; Estados Unidos Fil: Fruttiger, Marcus. University College London; Estados Unidos Fil: Fukumura, Dai. Harvard Medical School; Estados Unidos Fil: Ghesquière, Bart. Harvard Medical School; Estados Unidos Fil: Gong, Yan. Harvard Medical School; Estados Unidos Fil: Griffin, Robert J.. VIB Center for Cancer Biology; Bélgica Fil: Harris, Adrian L.. University of Oxford; Reino Unido Fil: Hughes, Christopher C. W.. University of California at Irvine; Estados Unidos Fil: Hultgren, Nan W.. University of California at Irvine; Estados Unidos Fil: Iruela-Arispe, M. Luisa. University of California at Los Angeles; Estados Unidos Fil: Irving, Melita. Universida de Lausanne; Suiza Fil: Maidana, Agostina Jainen. Harvard Medical School; Estados Unidos Fil: Kalluri, Raghu. Texas A&M University; Estados Unidos Fil: Kalucka, Joanna. Katholikie Universiteit Leuven; Bélgica Fil: Kerbel, Robert S.. University of Toronto; Canadá Fil: Kitajewski, Jan. University of Illinois; Estados Unidos Fil: Klaassen, Ingeborg. University of Amsterdam; Países Bajos Fil: Kleinmann, Hynda K.. The George Washington University; Estados Unidos Fil: Koolwijk, Pieter. Fondation Asile des Aveugles; Suiza. Universida de Lausanne; Suiza Fil: Kuczynski, Elisabeth. University of Toronto; Canadá Fil: Kwak, Brenda R.. University of Geneva; Suiza Fil: Koen, Marien. HistoGeneX; Bélgica Fil: Melero Martin, Juan M.. University of Liège; Bélgica Fil: Munn, Lance L.. Harvard Medical School; Estados Unidos Fil: Nicosia, Roberto F.. VA Puget Sound Health Care System; Estados Unidos Fil: Noel, Agnes. University of Liège; Bélgica Fil: Nurro, Jussi. University of Eastern Finland; Finlandia Fil: Olsson, Anna-Karin. Uppsala University; Suiza Fil: Petrova, Tatiana V.. Ludwig Institute for Cancer Research Lausanne; Suiza Fil: Pietras, Kristian. Division of Translational Cancer Research; Suecia Fil: Pili, Roberto. Indiana University Simon Cancer Center; Estados Unidos Fil: Pollard, Jeffrey W.. University of Edinburgh; Reino Unido Fil: Post, Mark J.. Maastricht University; Países Bajos Fil: Quax, Paul H. A.. Einthoven Laboratory for Experimental Vascular Medicine; Países Bajos Fil: Rabinovich, Gabriel Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Biológica; Argentina Fil: Raica, Marius. Victor Babes University of Medicine and Pharmacy; Rumania Fil: Randi, Anna M.. Imperial College London; Reino Unido Fil: Ribatti, Domenico. Università degli Studi di Bari; Italia Fil: Ruegg, Curzio. University of Fribourg; Suiza Fil: Schlingemann, Reinier O.. University of Amsterdam; Países Bajos Fil: Schulte Merker, Stefan. Institute of Cardiovascular Organogenesis and Regeneration; Alemania Fil: Smith, Lois E. H.. Harvard Medical School; Estados Unidos Fil: Song, Jonathan W.. Ohio State University; Estados Unidos Fil: Stacker, Steven A.. University of Melbourne; Australia Fil: Stalin, Jimmy. Institute of Cardiovascular Organogenesis and Regeneration; Alemania Fil: Stratman, Amber N.. National Institutes of Health; Estados Unidos Fil: Van de Velde, Maureen. University of Liège; Bélgica Fil: van Hinsbergh, Victor W. M.. Universida de Lausanne; Suiza Fil: Vermeulen, Peter B.. HistoGeneX; Bélgica. University of Antwerp; Bélgica Fil: Waltenberger, Johannes. University of Münster; Alemania Fil: Weinstein, Brant M.. National Institutes of Health; Estados Unidos Fil: Xin, Hong. University of California at San Diego; Estados Unidos Fil: Yetkin Arik, Bahar. University of Amsterdam; Países Bajos Fil: Yla Herttuala, Seppo. University of Eastern Finland; Finlandia Fil: Yoder, Mervin C.. Indiana University; Estados Unidos Fil: Griffioen, Arjan W.. VU University Medical Center; Países Bajos

Ig-GAD2, an antigen-specific immune modulator, requires bone marrow (BM) cell transfer in order to restore beta (β)-cell formation and induce recovery from established type 1 diabetes (T1D). The BM cells provide endothelial precursor cells (EPCs) that give rise to islet resident endothelial cells (ECs). This study shows that, during development of T1D, the immune attack causes collateral damage to the islet vascular network. The EPC-derived ECs repair and restore islet blood vessel integrity. In addition, β-cell genetic tracing indicates that the newly formed β-cells originate from residual β-cells that escaped the immune attack and, unexpectedly, from β-cell precursors. This indicates that the rejuvenated islet microenvironment invigorates formation of new β-cells not only from residual β-cells but also from precursor cells. This is twofold significant from the perspective of precursor cells as a safe reserve for restoration of β-cell mass and its promise for therapy of T1D long after diagnosis.

Cardiovascular function depends on patent, continuous and stable blood vessel formation by endothelial cells (ECs). Blood vessel development initiates by vasculogenesis, as ECs coalesce into linear aggregates and organize to form central lumens that allow blood flow. Molecular mechanisms underlying in vivo vascular ‘tubulogenesis’ are only beginning to be unraveled. We previously showed that the GTPase-interacting protein called Rasip1 is required for the formation of continuous vascular lumens in the early embryo. Rasip1−/− ECs exhibit loss of proper cell polarity and cell shape, disrupted localization of EC-EC junctions and defects in adhesion of ECs to extracellular matrix (ECM). In vitro studies showed that Rasip1 depletion in cultured ECs blocked tubulogenesis. Whether Rasip1 is required in blood vessels after their initial formation remained unclear. Here, we show that Rasip1 is essential for vessel formation and maintenance in the embryo, but not in quiescent adult vessels. Rasip1 is also required for angiogenesis in three models of blood vessel growth: in vitro matrix invasion, retinal blood vessel growth and Directed In vivo Angiogenesis Assays (DIVAA). Rasip1 is thus necessary in growing embryonic blood vessels, postnatal angiogenic sprouting and remodeling, but is dispensable for maintenance of established blood vessels, making it a potential anti-angiogenic therapeutic target.

Here, we describe highly reproducible methods to investigate human EC invasion and sprouting behavior in 3D collagen matrices. Two assay models are presented whereby ECs are induced to sprout from a monolayer surface or from aggregated ECs suspended within a collagen gel matrix. In each case, the assays are performed using serum-free defined media containing a combination of five growth factors (Factors): FGF-2, SCF, IL-3, SDF-1α, and insulin. In both models, marked EC sprouting occurs with leading EC tip cells over a 12-24 h period. To illustrate their utility, we present data showing the influence of various pharmacologic inhibitors directed to membrane-type matrix metalloproteinases (MT-MMPs), protein kinase C alpha (PKCα), Src family kinases, and Notch-dependent signaling. Marked inhibition of sprouting is observed after blockade of MT-MMPs and PKCα, while strong increases in sprouting and EC tip cell number is observed following blockade of Src kinases, Notch signaling or both. Interestingly, the increased sprouting behavior observed following Src or Notch blockade directly correlates with a loss in the ability of ECs to form lumens. These defined in vitro assay models allow for a genetic and signaling dissection of EC tip cells vs. lumen forming ECs, which are both necessary for the formation of branching networks of tubes during vascular morphogenic events.

Although major progress in our understanding of the genes and mechanisms that regulate lymphatic vasculature development has been made, we still do not know how lumen formation and maintenance occurs. Here, we identify the Ras-interacting protein Rasip1 as a key player in this process. We show that lymphatic endothelial cell-specific Rasip1-deficient mouse embryos exhibit enlarged and blood-filled lymphatics at embryonic day 14.5. These vessels have patent lumens with disorganized junctions. Later on, as those vessels become fragmented and lumens collapse, cell junctions become irregular. In addition, Rasip1 deletion at later stages impairs lymphatic valve formation. We determined that Rasip1 is essential for lymphatic lumen maintenance during embryonic development by regulating junction integrity, as Rasip1 loss results in reduced levels of junction molecules and defective cytoskeleton organization in vitro and in vivo. We determined that Rasip1 regulates Cdc42 activity, as deletion of Cdc42 results in similar phenotypes to those seen following the loss of Rasip1. Furthermore, ectopic Cdc42 expression rescues the phenotypes in Rasip1-deficient lymphatic endothelial cells, supporting the suggestion that Rasip1 regulates Cdc42 activity to regulate cell junctions and cytoskeleton organization, which are both activities required for lymphatic lumen maintenance.

Here, we describe highly reproducible methods to investigate human EC invasion and sprouting behavior in 3D collagen matrices. Two assay models are presented whereby ECs are induced to sprout from a monolayer surface or from aggregated ECs suspended within a collagen gel matrix. In each case, the assays are performed using serum-free defined media containing a combination of five growth factors (Factors): FGF-2, SCF, IL-3, SDF-1α, and insulin. In both models, marked EC sprouting occurs with leading EC tip cells over a 12-24 h period. To illustrate their utility, we present data showing the influence of various pharmacologic inhibitors directed to membrane-type matrix metalloproteinases (MT-MMPs), protein kinase C alpha (PKCα), Src family kinases, and Notch-dependent signaling. Marked inhibition of sprouting is observed after blockade of MT-MMPs and PKCα, while strong increases in sprouting and EC tip cell number is observed following blockade of Src kinases, Notch signaling or both. Interestingly, the increased sprouting behavior observed following Src or Notch blockade directly correlates with a loss in the ability of ECs to form lumens. These defined in vitro assay models allow for a genetic and signaling dissection of EC tip cells vs. lumen forming ECs, which are both necessary for the formation of branching networks of tubes during vascular morphogenic events.

Studies over many years reveal a critical role for extracellular matrices, matrix metalloproteinases, key small GTPases, and defined growth factors in the molecular control of vascular tube morphogenesis and stabilization in three-dimensional (3D) tissue environments. Key interactions involve endothelial cells (ECs) and pericytes which co-assemble to affect vessel formation, remodeling and stabilization events during development and postnatal life. The EC tube formation process results in the creation of networks of proteolytically generated vascular guidance tunnels. These tunnels are physical matrix spaces that regulate vascular tube remodeling and represent matrix conduits into which pericytes are recruited, to allow dynamic and polarized cell-cell interactions with ECs. EC-pericyte interactions regulate vascular basement membrane matrix assembly, a necessary step for endothelial tube maturation and stabilization. ECs form tube networks and tunnels in 3D extracellular matrices in a manner dependent on integrins; membrane-type metalloproteinases; small GTPases including Cdc42, Rac isoforms, k-Ras, and Rap1b; and key downstream effectors of these GTPases. In addition, human EC tubulogenesis requires a defined five-growth factor combination including stem cell factor (SCF), interleukin-3 (IL-3), stromal-derived factor-1 alpha (SDF-1α), fibroblast growth factor-2 (FGF-2), and insulin (Factors). These Factors are necessary to integrate signal transduction cascades to form human EC tube networks and attract pericytes [through EC-derived platelet-derived growth factor (PDGF)-BB and heparin-binding epidermal growth factor (HB-EGF)] to control vessel maturation events.

Variation in annual abundance of 50 widespread moths in England and Wales was assessed from the area under the log10(moth count + 1) versus time curve (abundance index) for adult moth count data reported between 2003 and 2013 to the UK and Ireland Garden Moth Scheme; a citizen science project. Associations between abundance index and the abundance index of the previous generation, with inward migration, and with UK Met Office data for rainfall, mean temperature and sunshine were sought by multiple linear regression. Sixty-eight generations from univoltine or bivoltine species were analysed with a median range in abundance index between equivalent generations of 98 %. Significant (P

Talin (tln) binds and activates integrins to couple extracellular matrix–bound integrins to the cytoskeleton; however, its role in heart development is not well characterized. We identified the defective gene and the resulting cardiovascular phenotypes in zebrafish tln1fl02k mutants. The ethylnitrosourea-induced fl02k mutant showed heart failure, brain hemorrhage, and diminished cardiac and vessel lumens at 52 h post fertilization. Positional cloning revealed a nonsense mutation of tln1 in this mutant. tln1, but neither tln2 nor -2a, was dominantly expressed in the heart and vessels. Unlike tln1 and -2 in the mouse heart, the unique tln1 expression in the heart enabled us, for the first time, to determine the critical roles of Tln1 in the maintenance of cardiac sarcomeric Z-disks and endothelial/endocardial cell integrity, partly through regulating F-actin networks in zebrafish. The similar expression profiles of tln1 and integrin β1b (itgb1b) and synergistic function of the 2 genes revealed that itgb1b is a potential partner for tln1 in the stabilization of cardiac Z-disks and vessel lumens. Taken together, the results of this work suggest that Tln1-mediated Itgβ1b plays a crucial role in maintaining cardiac sarcomeric Z-disks and endothelial/endocardial cell integrity in zebrafish and may also help to gain molecular insights into congenital heart diseases.—Wu, Q., Zhang, J., Koh, W., Yu, Q., Zhu, X., Amsterdam, A., Davis, G. E., Arnaout, M. A., Xiong, J.-W. Talin1 is required for cardiac Z-disk stabilization and endothelial integrity in zebrafish.

This review addresses fundamental mechanisms underlying how capillaries form in three-dimensional extracellular matrices and how endothelial cells (ECs) and pericytes co-assemble to form capillary networks. In addition to playing a critical role in supplying oxygen and nutrients to tissues, recent work suggests that blood vessels supply important signals to facilitate tissue development. Here, we hypothesize that another major function of capillaries is to supply signals to suppress major disease mechanisms including inflammation, infection, thrombosis, hemorrhage, edema, ischemic injury, fibrosis, autoimmune disease, and tumor growth/ progression. Capillary dysfunction plays a key pathogenic role in many human diseases, and thus, this suppressing function may be attenuated and central toward the initiation and progression of disease. We describe how capillaries form through creation of EC-lined tube networks and vascular guidance tunnels in 3D extracellular matrices. Pericytes recruit to the abluminal EC tube surface within these tunnel spaces, and work together to assemble the vascular basement membrane matrix. These processes occur under serum-free conditions in 3D collagen or fibrin matrices and in response to five key growth factors which are stem cell factor, interleukin-3, stromal-derived factor-1α, fibroblast growth factor-2, and insulin. In addition, we identified a key role for EC-derived platelet-derived growth factor-BB and heparin-binding epidermal growth factor in pericyte recruitment and proliferation to promote EC-pericyte tube co-assembly and vascular basement membrane matrix deposition. A molecular understanding of capillary morphogenesis and maturation should lead to novel therapeutic strategies to repair capillary dysfunction in major human disease contexts including cancer and diabetes.

Here we examine the question of how endothelial cells (ECs) develop their apical membrane surface domain during lumen and tube formation. We demonstrate marked apical membrane targeting of activated Src kinases to this apical domain during early and late stages of this process. Immunostaining for phosphotyrosine or phospho-Src reveals apical membrane staining in intracellular vacuoles initially. This is then followed by vacuole to vacuole fusion events to generate an apical luminal membrane, which is similarly decorated with activated phospho-Src kinases. Functional blockade of Src kinases completely blocks EC lumen and tube formation, whether this occurs during vasculogenic tube assembly or angiogenic sprouting events. Multiple Src kinases participate in this apical membrane formation process and siRNA suppression of Src, Fyn and Yes, but not Lyn, blocks EC lumen formation. We also demonstrate strong apical targeting of Src-GFP and Fyn-GFP fusion proteins and increasing their expression enhances lumen formation. Finally, we show that Src- and Fyn-associated vacuoles track and fuse along a subapically polarized microtubule cytoskeleton, which is highly acetylated. These vacuoles generate the apical luminal membrane in a stereotypically polarized, perinuclear position. Overall, our study identifies a critical role for Src kinases in creating and decorating the EC apical membrane surface during early and late stages of lumen and tube formation, a central event in the molecular control of vascular morphogenesis.

This study aimed to form microvessels in fibrin gels, which is of interest both for studying the fundamental cell-matrix interactions as well as for tissue engineering purposes, and to align the microvessels, which would provide natural inlet and outlet sides for perfusion. The data reported here demonstrate the formation of highly interconnected microvessels in fibrin gel under defined medium conditions and the ability to align them using two methods, both of which involved anchoring the gel at both ends to constrain the cell-induced compaction. The first method used only defined medium and resulted in moderate alignment. The second method used defined and serum-containing media sequentially to achieve high levels of microvessel alignment.

Vascular tube morphogenesis requires the establishment of endothelial cell (EC) apical-basal polarity in three-dimensional (3D) extracellular matrices. To date, there is little understanding of how EC polarity is controlled during these highly dynamic and rapid morphogenic events. We show that the microtubule tip complex proteins, end binding 1 (EB1), p150(Glued), and Clasp1, control human EC tube formation by (1) inducing microtubule assembly and asymmetric cytoskeletal polarization, whereby acetylated and detyrosinated tubulins distribute in a subapical membrane location and filamentous actin distributes basally; (2) increasing tubulin posttranslational modifications, including required acetylation events; and (3) regulating an EC lumen signaling cascade that involves membrane type 1 matrix metallopatrinase (MT1-MMP)-dependent proteolysis as well as Pak, Raf, and Erk kinases. Another regulator of this process is the microtubule stabilizing protein, tau, which binds p150(Glued) and similarly affects EC lumen formation by controlling the levels of acetylated and detyrosinated tubulins. Increased expression of the tubulin deacetylases, sirtuin 2, and histone deacetylase 6 (HDAC6), blocks EC tube formation and cytoskeletal polarization, while siRNA suppression of these deacetylases stimulates these events. Overall, this work reveals a fundamental role for microtubule tip complex proteins in coordinating microtubule assembly, posttranslational modifications including acetylation, and apical-basal cytoskeletal polarization to control the developing apical membrane surface during blood vessel tubulogenesis in 3D matrix environments.

Rationale: Vascular tubulogenesis is essential to cardiovascular development. Within initial vascular cords of endothelial cells, apical membranes are established and become cleared of cell–cell junctions, thereby allowing continuous central lumens to open. Rasip1 (Ras-interacting protein 1) is required for apical junction clearance, as well as for regulation of Rho GTPase (enzyme that hydrolyzes GTP) activity. However, it remains unknown how activities of different Rho GTPases are coordinated by Rasip1 to direct tubulogenesis. Objective: The aim of this study is to determine the mechanisms downstream of Rasip1 that drive vascular tubulogenesis. Methods and Results: Using conditional mouse mutant models and pharmacological approaches, we dissect GTPase pathways downstream of Rasip1. We show that clearance of endothelial cell apical junctions during vascular tubulogenesis depends on Rasip1, as well as the GTPase Cdc42 (cell division control protein 42 homolog) and the kinase Pak4 (serine/threonine-protein kinase 4). Genetic deletion of Rasip1 or Cdc42, or inhibition of Pak4, all blocks endothelial cell tubulogenesis. By contrast, inactivation of RhoA (Ras homologue gene family member A) signaling leads to vessel overexpansion, implicating actomyosin contractility in control of lumen diameter. Interestingly, blocking activity of NMII (nonmuscle myosin II) either before, or after, lumen morphogenesis results in dramatically different tubulogenesis phenotypes, suggesting time-dependent roles. Conclusions: Rasip1 controls different pools of GTPases, which in turn regulate different pools of NMII to coordinate junction clearance (remodeling) and actomyosin contractility during vascular tubulogenesis. Rasip1 promotes activity of Cdc42 to activate Pak4, which in turn activates NMII, clearing apical junctions. Once lumens open, Rasip1 suppresses actomyosin contractility via inhibition of RhoA by Arhgap29, allowing controlled expansion of vessel lumens during embryonic growth. These findings elucidate the stepwise processes regulated by Rasip1 through downstream Rho GTPases and NMII.

GH receptor (GHR) binds GH at the cell surface via its extracellular domain and initiates intracellular signal transduction, resulting in important anabolic and metabolic actions. GH signaling is subject to dynamic regulation, which in part is exerted by modulation of cell surface GHR levels. Constitutive and inducible metalloprotease-mediated cleavage of GHR regulate GHR abundance and thereby modulate GH action. We previously demonstrated that GHR proteolysis is catalyzed by the TNF-α converting enzyme (TACE; ADAM17). Tissue inhibitors of metalloproteases-3 (TIMP3) is a natural specific inhibitor of TACE, although mechanisms underlying this inhibition are not yet fully understood. In the current study, we use two model cell lines to examine the relationships between cellular TACE, TIMP3 expression, GHR metalloproteolysis, and GH sensitivity. These two cell lines exhibited markedly different sensitivity to inducible GHR proteolysis, which correlated directly to their relative levels of mature TACE vs unprocessed TACE precursor and indirectly to their levels of cellular TIMP3. Our results implicate TIMP3 as a modulator of cell surface GHR abundance and the ability of GH to promote cellular signaling; these modulatory effects may be conferred by endogenous TIMP3 expression as well as exogenous TIMP3 exposure. Furthermore, our analysis suggests that TIMP3, in addition to regulating the activity of TACE, may also modulate the maturation of TACE, thereby affecting the abundance of the active form of the enzyme.

During capillary network formation, ECs establish interconnecting tubes with defined lumens that reside within vascular guidance tunnels (physical spaces generated during EC tubulogenesis). Pericytes are recruited to EC tubes within these tunnels and capillary basement membrane deposition occurs to facilitate tube maturation. Here, we discuss molecular mechanisms controlling EC tubulogenesis demonstrating the involvement of integrins, MT1-MMP, extracellular matrix, Cdc42, Rac1, Rac2, k-Ras, Rap1b, and key downstream effectors including Pak2, Pak4, IQGAP1, MRCKβ, and Rasip1. These molecules activate kinase cascades controlling EC tube formation, in conjunction with growth factor receptor signaling, which involve PKCɛ, Src family, Raf, Mek, and Erk kinases. These molecules and signaling cascades stimulate EC lumen and tube formation by: regulating MT-MMP-dependent lumen expansion and vascular guidance tunnel formation; generation of intracellular vacuoles/vesicles to create EC apical membranes; and establishing cytoskeletal polarity with acetylated tubulin distributed subapically (and F-actin basally) to facilitate vacuole trafficking/fusion in a polarized, perinuclear region. Using defined serum-free models, we have demonstrated that human EC tubulogenesis and EC-pericyte tube coassembly requires five exogenously applied growth factors which are SCF, IL-3, SDF-1α, FGF-2, and insulin (Factors). Also, we have demonstrated that EC-derived PDGF-BB and HB-EGF are necessary for pericytes to proliferate, recruit to tubes, and induce basement membrane assembly. Finally, we have shown that VEGF fails to directly stimulate EC tubulogenesis. In contrast, it acts as an upstream EC primer of downstream "Factor"-induced tubulogenic and EC-pericyte tube coassembly by upregulating c-Kit, IL-3Rα, and CXCR4 as well as PDGF-BB and HB-EGF expression.

Understanding the mechanisms that regulate angiogenesis and translating these into effective therapies are of enormous scientific and clinical interests. In this report, we demonstrate the central role of CDP-diacylglycerol synthetase (CDS) in the regulation of VEGFA signaling and angiogenesis. CDS activity maintains phosphoinositide 4,5 bisphosphate (PIP2) availability through resynthesis of phosphoinositides, whereas VEGFA, mainly through phospholipase Cγ1, consumes PIP2 for signal transduction. Loss of CDS2, 1 of 2 vertebrate CDS enzymes, results in vascular-specific defects in zebrafish in vivo and failure of VEGFA-induced angiogenesis in endothelial cells in vitro. Absence of CDS2 also results in reduced arterial differentiation and reduced angiogenic signaling. CDS2 deficit-caused phenotypes can be successfully rescued by artificial elevation of PIP2 levels, and excess PIP2 or increased CDS2 activity can promote excess angiogenesis. These results suggest that availability of CDS-controlled resynthesis of phosphoinositides is essential for angiogenesis.

Kidney pericytes are progenitors of scar-forming interstitial myofibroblasts that appear after injury. The function of kidney pericytes as microvascular cells and how these cells detach from peritubular capillaries and migrate to the interstitial space, however, are poorly understood. Here, we used an unbiased approach to identify genes in kidney pericytes relevant to detachment and differentiation in response to injury in vivo, with a particular focus on genes regulating proteolytic activity and angiogenesis. Kidney pericytes rapidly activated expression of a disintegrin and metalloprotease with thrombospondin motifs-1 (ADAMTS1) and downregulated its inhibitor, tissue inhibitor of metalloproteinase 3 (TIMP3) in response to injury. Similarly to brain pericytes, kidney pericytes bound to and stabilized capillary tube networks in three-dimensional gels and inhibited metalloproteolytic activity and angiogenic signaling in endothelial cells. In contrast, myofibroblasts did not have these vascular stabilizing functions despite their derivation from kidney pericytes. Pericyte-derived TIMP3 stabilized and ADAMTS1 destabilized the capillary tubular networks. Furthermore, mice deficient in Timp3 had a spontaneous microvascular phenotype in the kidney resulting from overactivated pericytes and were more susceptible to injury-stimulated microvascular rarefaction with an exuberant fibrotic response. Taken together, these data support functions for kidney pericytes in microvascular stability, highlight central roles for regulators of extracellular proteolytic activity in capillary homoeostasis, and identify ADAMTS1 as a marker of activation of kidney pericytes.

Extracellular matrix synthesis and deposition surrounding the developing vasculature are critical for vessel remodeling and maturation events. Although the basement membrane is an integral structure underlying endothelial cells (ECs), few studies, until recently, have been performed to understand its formation in this context. In this review article, we highlight new data demonstrating a corequirement for ECs and pericytes to properly deposit and assemble vascular basement membranes during morphogenic events. In EC only cultures or under conditions whereby pericyte recruitment is blocked, there is a lack of basement membrane assembly, decreased vessel stability (with increased susceptibility to pro-regressive stimuli), and increased EC tube widths (a marker of dysfunctional EC-pericyte interactions). ECs and pericytes both contribute basement membrane components and, furthermore, both cells induce the expression of particular components as well as integrins that recognize them. The EC-derived factors—platelet derived growth factor-BB and heparin binding-epidermal growth factor—are both critical for pericyte recruitment to EC tubes and concomitant vascular basement membrane formationin vitroandin vivo. Thus, heterotypic EC-pericyte interactions play a fundamental role in vascular basement membrane matrix deposition, a critical tube maturation event that is altered in key disease states such as diabetes and cancer.

Considerable progress has been made toward a molecular understanding of how cells form lumen and tube structures in three-dimensional (3D) extracellular matrices (ECM). This progress has occurred through work performed with endothelial and epithelial cell models using both in vitro and in vivo approaches. Despite the apparent similarities between endothelial and epithelial cell lumen and tube formation mechanisms, there are clear distinctions that directly relate to their functional differences. This review will focus on endothelial cell (EC) lumen formation mechanisms which control blood vessel formation during development and postnatal life. Of great interest is that an EC lumen signaling complex has been identified which controls human EC lumen and tube formation in 3D matrices and which coordinates integrin-ECM contacts, cell surface proteolysis, cytoskeletal rearrangements, and cell polarity. This complex consists of the collagen-binding integrin α2β1, the collagen-degrading membrane-type 1 matrix metalloproteinase (MT1-MMP), junction adhesion molecule (Jam)C, JamB, polarity proteins Par3 and Par6b, and the Rho GTPase Cdc42-GTP. These interacting proteins are necessary to stimulate 3D matrix-specific signaling events (including activation of protein kinase cascades that regulate the actin and microtubule cytoskeletons) to control the formation of EC lumens and tube networks. Also, EC lumen formation is directly coupled to the generation of vascular guidance tunnels, enzymatically generated ECM conduits that facilitate EC tube remodeling and maturation. Mural cells such as pericytes are recruited along EC tubes within these tunnel spaces to control ECM remodeling events resulting in vascular basement membrane matrix assembly, a key step in tube maturation and stabilization.

ERG is a member of the ETS transcription factor family that is highly enriched in endothelial cells (ECs). To further define the role of ERG in regulating EC function, we evaluated the effect of ERG knock-down on EC lumen formation in 3D collagen matrices. Blockade of ERG using siRNA completely interferes with EC lumen formation. Quantitative PCR (QPCR) was used to identify potential downstream gene targets of ERG. In particular, we identified RhoJ as the Rho GTPase family member that is closely related to Cdc42 as a target of ERG. Knockdown of ERG expression in ECs led to a 75% reduction in the expression of RhoJ. Chromatin immunoprecipitation and transactivation studies demonstrated that ERG could bind to functional sites in the proximal promoter of the RhoJ gene. Knock-down of RhoJ similarly resulted in a marked reduction in the ability of ECs to form lumens. Suppression of either ERG or RhoJ during EC lumen formation was associated with a marked increase in RhoA activation and a decrease in Rac1 and Cdc42 activation and their downstream effectors. Finally, in contrast to other Rho GTPases, RhoJ exhibits a highly EC-restricted expression pattern in several different tissues, including the brain, heart, lung, and liver.

Here, we demonstrate a novel, direct-acting, and synergistic role for 3 hematopoietic stem cell cytokines: stem cell factor, interleukin-3, and stromal derived factor-1α, in controlling human endothelial cell (EC) tube morphogenesis, sprouting, and pericyte-induced tube maturation under defined serum-free conditions in 3-dimensional matrices. Angiogenic cytokines such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) alone or VEGF/FGF combinations do not support these responses. In contrast, VEGF and FGF prime EC responses to hematopoietic cytokines via up-regulation of c-Kit, IL-3Rα, and C-X-C chemokine receptor type 4 from either human ECs or embryonic quail vessel explants. In support of these findings, EC Runx1 is demonstrated to be critical in coordinating vascular morphogenic responses by controlling hematopoietic cytokine receptor expression. Combined blockade of hematopoietic cytokines or their receptors in vivo leads to blockade of developmental vascularization in quail embryos manifested by vascular hemorrhage and disrupted vascular remodeling events in multiple tissue beds. This work demonstrates a unique role for hematopoietic stem cell cytokines in vascular tube morphogenesis and sprouting and further demonstrates a novel upstream priming role for VEGF and FGF to facilitate the action of promorphogenic hematopoietic cytokines.

SummaryCardiovascular function depends on patent blood vessel formation by endothelial cells (ECs). However, the mechanisms underlying vascular “tubulogenesis” are only beginning to be unraveled. We show that endothelial tubulogenesis requires the Ras interacting protein 1, Rasip1, and its binding partner, the RhoGAP Arhgap29. Mice lacking Rasip1 fail to form patent lumens in all blood vessels, including the early endocardial tube. Rasipl null angioblasts fail to properly localize the polarity determinant Par3 and display defective cell polarity, resulting in mislocalized junctional complexes and loss of adhesion to extracellular matrix (ECM). Similarly, depletion of either Rasip1 or Arhgap29 in cultured ECs blocks in vitro lumen formation, fundamentally alters the cytoskeleton, and reduces integrin-dependent adhesion to ECM. These defects result from increased RhoA/ROCK/myosin II activity and blockade of Cdc42 and Rac1 signaling. This study identifies Rasip1 as a unique, endothelial-specific regulator of Rho GTPase signaling, which is essential for blood vessel morphogenesis.

Proteinases play a key role during angiogenesis and have been implicated in vascular morphogenesis, stabilization and regression. Major advances have identified specific proteinases and their inhibitors that separately control these processes. Relevant proteinases include cell surface or soluble metalloproteinases, serine proteinases and cathepsins that affect these events and a critical issue concerns how these proteinases are balanced by their inhibitors to affect tissue vascularization. Importantly, heterotypic communication of endothelial cells with vessel supporting cells such as pericytes controls proteinase and inhibitor expression to regulate these processes.

This review addresses new concepts related to the importance of how cells within the cardiovascular system respond to matricryptic sites generated from the extracellular matrix (ECM) following tissue injury. A model is presented whereby matricryptic sites exposed from the ECM result in activation of multiple cell surface receptors including integrins, scavenger receptors, and toll-like receptors which together are hypothesized to coactivate downstream signaling pathways which alter cell behaviors following tissue injury. Of great interest are the relationships between matricryptic fragments of ECM called matricryptins and other stimuli that activate cells during injury states such as released components from cells (DNA, RNA, cytoskeletal components such as actin) or products from infectious agents in innate immunity responses. These types of cell activating molecules, which are composed of repeating molecular elements, are known to interact with pattern recognition receptors that (i) are expressed from cell surfaces, (ii) are released from cells following tissue injury, or (iii) circulate as components of plasma. Thus, cell recognition of matricryptic sites from the ECM appears to be an important component of a broad cell and tissue sensory system to detect and respond to environmental cues generated following varied types of tissue injury.

We show that endothelial cell (EC)–generated vascular guidance tunnels (ie, matrix spaces created during tube formation) serve as conduits for the recruitment and motility of pericytes along EC ablumenal surfaces to facilitate vessel maturation events, including vascular basement membrane matrix assembly and restriction of EC tube diameter. During quail development, pericyte recruitment along microvascular tubes directly correlates with vascular basement membrane matrix deposition. Pericyte recruitment to EC tubes leads to specific induction of fibronectin and nidogen-1 (ie, matrix-bridging proteins that link together basement membrane components) as well as perlecan and laminin isoforms. Coincident with these events, up-regulation of integrins, α5β1, α3β1, α6β1, and α1β1, which bind fibronectin, nidogens, laminin isoforms, and collagen type IV, occurs in EC-pericyte cocultures, but not EC-only cultures. Integrin-blocking antibodies to these receptors, disruption of fibronectin matrix assembly, and small interfering RNA suppression of pericyte tissue inhibitor of metalloproteinase (TIMP)-3 (a known regulator of vascular tube stabilization) all lead to decreased EC basement membrane, resulting in increased vessel lumen diameter, a key indicator of dysfunctional EC-pericyte interactions. Thus, pericyte recruitment to EC-lined tubes during vasculogenesis is a stimulatory event controlling vascular basement membrane matrix assembly, a fundamental maturation step regulating the transition from vascular morphogenesis to stabilization.

Skeletal muscle repair and regeneration requires the activity of satellite cells, a population of myogenic stem cells scattered throughout the tissue and activated to proliferate and differentiate in response to myotrauma or disease. While it seems likely that satellite cells would need to navigate local muscle tissue to reach damaged areas, relatively little data on such motility exist, and most studies have been with immortalized cell lines. We find that primary satellite cells are significantly more motile than myoblast cell lines, and that adhesion to laminin promotes primary cell motility more than fourfold over other substrates. Using timelapse videomicroscopy to assess satellite cell motility on single living myofibers, we have identified a requirement for the laminin-binding integrin α7β1 in satellite cell motility, as well as a role for hepatocyte growth factor in promoting directional persistence. The extensive migratory behavior of satellite cells resident on muscle fibers suggests caution when determining, based on fixed specimens, whether adjacent cells are daughters from the same mother cell. We also observed more persistent long-term contact between individual satellite cells than has been previously supposed, potential cell-cell attractive and repulsive interactions, and migration between host myofibers. Based on such activity, we assayed for expression of “pathfinding” cues, and found that satellite cells express multiple guidance ligands and receptors. Together, these data suggest that satellite cell migration in vivo may be more extensive than currently thought, and could be regulated by combinations of signals, including adhesive haptotaxis, soluble factors, and guidance cues.

In this study, we present data showing that Cdc42-dependent lumen formation by endothelial cells (ECs) in three-dimensional (3D) collagen matrices involves coordinated signaling by PKCepsilon in conjunction with the Src-family kinases (SFKs) Src and Yes. Activated SFKs interact with Cdc42 in multiprotein signaling complexes that require PKCepsilon during this process. Src and Yes are differentially expressed during EC lumen formation and siRNA suppression of either kinase, but not Fyn or Lyn, results in significant inhibition of EC lumen formation. Concurrent with Cdc42 activation, PKCepsilon- and SFK-dependent signaling converge to activate p21-activated kinase (Pak)2 and Pak4 in steps that are also required for EC lumen formation. Pak2 and Pak4 further activate two Raf kinases, B-Raf and C-Raf, leading to ERK1 and ERK2 (ERK1/2) activation, which all seem to be necessary for EC lumen formation. This work reveals a multicomponent kinase signaling pathway downstream of integrin-matrix interactions and Cdc42 activation involving PKCepsilon, Src, Yes, Pak2, Pak4, B-Raf, C-Raf and ERK1/2 to control EC lumen formation in 3D collagen matrices.

The formation of vascular lumens by endothelial cells is a critical step in the angiogenic process that occurs during invasion and growth of the incipient vascular sprout. Once a lumen is established, capillaries are rapidly exposed to the physical forces associated with the flow of blood which, together with genetic information, regulate the ultimate size of inner vessel diameter. Here we review the recent literature on vascular lumen formation and compare it to lumen formation in other epithelial systems. We also discuss the regulation of lumen diameter after vascular morphogenesis has been completed.