Angiogenesis and Atherosclerosis
1999; Lippincott Williams & Wilkins; Volume: 100; Issue: 8 Linguagem: Inglês
10.1161/01.cir.100.8.783
ISSN1524-4539
AutoresRoy L. Silverstein, Ralph L. Nachman,
Tópico(s)Kruppel-like factors research
ResumoHomeCirculationVol. 100, No. 8Angiogenesis and Atherosclerosis Free AccessEditorialPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessEditorialPDF/EPUBAngiogenesis and Atherosclerosis The Mandate Broadens Roy L. Silverstein and Ralph L. Nachman Roy L. SilversteinRoy L. Silverstein From Weill Medical College of Cornell University, Department of Medicine, Division of Hematology/Medical Oncology, New York, NY. and Ralph L. NachmanRalph L. Nachman From Weill Medical College of Cornell University, Department of Medicine, Division of Hematology/Medical Oncology, New York, NY. Originally published24 Aug 1999https://doi.org/10.1161/01.CIR.100.8.783Circulation. 1999;100:783–785Among the most exciting developments in vascular medicine is the targeting of specific molecular regulators of blood vessel growth and development for therapeutic benefit. Angiogenesis, whether physiological, such as occurs during embryogenesis, or pathological, such as occurs during wound healing and tumor progression, requires a highly coordinated series of events that includes endothelial cell proliferation, migration, tube and lumen formation, and in some cases, recruitment of smooth muscle and other adventitial cells. A large number of studies in cellular systems and animal models have led to identification and characterization of specific factors that can either stimulate or inhibit angiogenesis.1 These studies were mainly stimulated by Folkman's hypothesis that tumor growth beyond a few millimeters requires recruitment and formation of a new microcirculation, and thus, that blood vessel–directed therapy might be effective in treating cancer. Translational research has now been initiated by several groups to test the hypothesis that local delivery of angiogenic agents, such as vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF), by various strategies, including viral vectors, naked DNA, or purified recombinant proteins, may improve blood flow to ischemic tissues in patients with advanced atherosclerosis. In some cases, preliminary data have been reported and appear promising.2Specific antiangiogenic therapies are also now in the clinical-trial stage for a broadening group of common diseases, including cancer, macular degeneration, and rheumatoid arthritis. Recent studies in rodent models suggest that antiangiogenic agents may limit adipose mass in hereditary obesity and may slow progression of atheroma.3 The latter result, reported in the April 6, 1999, issue of Circulation, showed that atheromatous lesions beyond a certain size, like malignant tumors, contain an increased number of vasa vasorum and that 2 different angiogenesis inhibitors, the fumagillin analogue TNP-470 or endostatin, a proteolytic fragment of collagen XVIII, when delivered over a 16-week period, decreased lesion progression in apolipoprotein E null mice fed a cholesterol-rich "western" diet. The effect was most obvious in lesions of an intermediate age, but it was dramatic (70% to 85% reduction in plaque area). These studies substantiate the hypothesis published 15 years ago that neovascularization by vasa vasorum in coronary vessels contributes to atherogenesis.4In the current issue of Circulation, Chen et al5 have identified a new therapeutic target for vascular disease that may relate to the same biological regulatory mechanisms that control angiogenesis. They show that a specific neutralizing monoclonal antibody directed against thrombospondin-1 (TSP-1) improved "healing" of a balloon-injured rat carotid artery. The antibody was delivered locally into the lumen at the time of the injury and then by constant infusion into the vessel wall adventitia for 2 to 4 weeks. The authors documented successful delivery of the antibody into the vessel wall by immunohistochemical techniques and demonstrated a statistically significant increased rate of reendothelialization in the treated arteries along with a decrease in the ratio of intima-to-media thickness. These effects were associated with an increased number of proliferating cells at the lumen (presumably migrating endothelial cells) and a decreased number of proliferating cells in the media (presumably smooth muscle cells).So what is TSP-1, and why should targeting this molecule lead to accelerated reendothelialization and reduced neointima formation? TSP-1 is a 450 000-Da matrix glycoprotein6 of long-standing interest to vascular biologists because of its pattern of expression and its ability to modulate many important vascular cell functions. It is present in large amounts in platelet α-granules, from which it is secreted at sites of platelet activation. It is also made and secreted by endothelial cells and smooth muscle cells in a highly regulated manner. Its expression is rapidly and dramatically upregulated in response to vascular injury or exposure of cells to platelet-derived growth factor (PDGF) or bFGF; thus, it is present in large amounts in atheroma and in the matrix of a balloon-injured vessel. Of most relevance to angiogenesis and repair of arterial balloon injury are the observations that TSP-1 is a highly potent inhibitor of angiogenesis in vivo and is capable of blocking capillary endothelial cell proliferation, migration, and tube formation induced by angiogenic factors.7 It also enhances smooth muscle proliferation and migration in response to PDGF.6 Antibodies to TSP-1 thus could potentially augment the endothelial cell migration and proliferation necessary for reendothelialization while blocking the smooth muscle cell migration and proliferation associated with accelerated restenosis.The biology of TSP-1, however, is complex, and the effects seen in response to delivery of anti–TSP-1 into an injured vessel are likely to be much more complicated than those described above. TSP-1 interacts with many matrix constituents,6 including heparan sulfate proteoglycans, fibronectin, and collagen, and probably plays a role in matrix stability and remodeling. Evidence from TSP-1 null mice suggests that this is particularly important in bone matrix, but the role of TSP-1 in vascular wound matrix remodeling and stability has not yet been well characterized. TSP-1 can also interact with several specific cellular adhesion receptors, including CD36,8 αv-integrins,9 heparan sulfate proteoglycans, and integrin-associated protein (IAP; CD47).10 It can function as an adhesion molecule, promoting tumor cell–matrix interactions9 and platelet aggregation, but it also has antiadhesive properties for some cells, leading, for example, to disruption of endothelial cell focal adhesion plaques. On macrophages, TSP-1 mediates recognition and phagocytosis of apoptotic leukocytes, thus participating in the later stages of the inflammatory response and limiting proinflammatory influences.11 TSP-1 interacts with several proteases, including plasminogen, urokinase, thrombin, cathepsin, and elastase, promoting plasmin generation6 but inhibiting cathepsin. It also binds transforming growth factor-β (TGF-β) with high affinity and can efficiently convert the latent form into the active form.12 This latter effect is probably very important in vascular injury responses. TGF-β is a highly active cytokine and, like TSP-1, is also found in large amounts in injured vessels. It promotes collagen production and matrix deposition by vascular cells, regulates plasmin generation, and has many important anti-inflammatory properties. Studies of the TGF-β null mouse and the TSP-1 null mouse have shown, in fact, that the 2 phenotypes are similar and that TSP-1 is the critical in vivo activator of TGF-β.12Two critical questions arise from these observations. How can a single molecule effect so many disparate functions, and to which of the many functions attributable to TSP-1 can the "healing" effects of anti–TSP-1 treatment be ascribed? The answer to the first question is the most straightforward and relates directly to the structural organization of the protein. TSP-1 is a homotrimeric protein structurally organized as a series of discrete modules in linear array6 (Figure). The most N-terminal of these modules is a domain responsible for heparin binding and for disulfide bond–dependent trimerization of the TSP monomers. Immediately adjacent to the heparin binding domain is a cysteine-rich region with homology to procollagen. After that are 3 copies of a domain called the type I repeat, sequences of 50 to 54 amino acids that are homologous to malaria proteins and properdin. Adjacent to this region are 3 copies of type II repeats bearing epidermal growth factor–like homology, and after that are 7 type III repeats bearing homology to calcium binding sites in many other proteins. These are followed by a unique globular carboxy-terminal domain. Studies using protease digestion, monoclonal antibodies, synthetic peptides, and recombinant TSP-1 fragments have shown that each of these domains is responsible for specific functions. Thus, the apparently contradictory studies showing that TSP-1 has both proadhesive and antiadhesive properties are explained by the existence of multiple TSP-1 cellular adhesion receptors, each with specificity for a different TSP domain (Figure) and each with its own unique pattern of cellular expression. The TSP type I repeats contain the amino acid sequence CSVTCG, which has been shown to mediate binding to CD36.13 The last type III repeat contains the integrin binding domain, RGDA,9 and the carboxy-terminal domain contains the binding site for IAP.10 The TGF-β binding and activation domain also appears to be in the type I repeats, but it is not known whether it is identical to the CSVTCG sequence required for CD36 binding.The CD36–TSP-1 interaction is particularly relevant to angiogenesis and vascular biology. CD36 is an 88 000-Da glycoprotein expressed on platelets, macrophages, adipocytes, and certain specialized epithelia (retinal pigment and breast).1415 It too is a complex multifunctional protein, serving as a scavenger receptor on macrophages for oxidized LDL and apoptotic cells1617 and as a fatty acid transporter on adipocytes and muscle.18 On endothelium, its expression is limited to microvessels, the vessels from which new vessels arise during an angiogenic response. CD36 is the receptor that mediates some of the antiangiogenic properties of TSP-1. Studies by Bouck and colleagues, collaborating with our group,19 have shown that blockade of the TSP-1–CD36 interaction with recombinant CD36 peptides or inhibitory antibodies blocked the ability of TSP-1 to inhibit endothelial cell proliferation, migration, and tube formation. Synthetic peptides from the type I TSP repeat or from related sequences in other molecules have been shown to bind CD36 and to inhibit angiogenesis. Furthermore, transfection of CD36 cDNA into TSP-1–unresponsive macrovascular endothelial cells conferred responsiveness to TSP-1 in in vitro angiogenesis assays. Studies on a CD36 null mouse generated in our laboratory have shown that angiogenesis is not inhibited by TSP-1 in an in vivo corneal angiogenesis assay. A second region of the TSP-1 molecule from the procollagen homology domain also has antiangiogenic activity, implicating TSP-1–matrix interactions in angiogenesis as well. Although αv-integrins have been implicated in endothelial cell survival and apoptosis, the integrin binding region of TSP-1 has not been shown to have antiangiogenic activity.The question of which of the many functions attributable to TSP-1 is responsible for the healing effects of anti–TSP-1 treatment is a more difficult one. There are 2 pieces of evidence suggesting that CD36 might not be involved. If, in fact, the cells responsible for reendothelialization are migrating in from the periphery of the injury, they are not likely to express CD36. Macrovascular endothelial cells, such as in the carotid artery, are CD36 negative. Second, the monoclonal antibody used by Chen et al,5 C6.7, recognizes the carboxy-terminal IAP binding domain on TSP-1, not the CD36 binding region in the type I repeats. IAP is a membrane-spanning protein shown to modulate integrin function and signaling on vascular cells.10 C6.7 can block chemotaxis and spreading of endothelial cells on RGD-containing substrates, presumably by blocking the ability of TSP-1 to mediate IAP-dependent integrin activation. On the other hand, recent studies20 suggest the existence of a circulating pool of endothelial cell progenitors with high angiogenic potential. If reendothelialization is mediated in part by homing of these cells to the lesion, with subsequent proliferation and differentiation, it is possible that TSP could function by blocking these phenomena in a CD36-dependent manner. Also, although C6.7 does not recognize the type I repeat, it might interfere with CD36 binding and function by steric effects. Thus, although the studies by Chen et al5 are intriguing, significantly more characterization at the molecular level will be required to determine whether the observed effects are due to antiendothelial proliferation/migration activities, pro–smooth muscle cell proliferation activities, TGF-β activation, integrin interactions, IAP interactions, matrix stability, protease activity, or even effects on macrophage activation.The provocative preliminary studies published in Circulation this year by Chen et al5 and Moulton et al3 may help in defining the precise clinical scenarios suitable for proangiogenesis- or antiangiogenesis-based therapies for patients with atherosclerosis. The use of antiangiogenic therapies to halt progression of lesions is exciting and logical but may be limited by a restricted temporal window of opportunity and, in certain circumstances such as angioplasty, may be associated with exacerbating restenosis after balloon angioplasty. The use of proangiogenic factors as an in vivo bypass strategy is equally logical and is supported by intriguing preliminary data. On the basis of studies similar to the one reported by Chen et al,5 this strategy might also be of benefit for the angiogenesis-related process of reendothelialization of a balloon-injured artery. In this regard, TSP-1 might be an attractive therapeutic target because of its additional effects on smooth muscle cells, TGF-β, and the inflammatory response, which could limit the exaggerated proliferative responses in the vessel wall that lead to accelerated restenosis. The caveats of these studies include the potential risk of promoting plaque instability and lesion progression if, as suggested by Barger et al4 and others and as supported by the recent studies of Moulton et al,3 neovascularization in the lesion is proatherosclerotic. It is possible that as we learn more about the mechanisms of the arterial healing effects of TSP-1, "designer" molecules based on structure/function relationships could be developed to maximize the therapeutic effects of TSP-1 while minimizing potential negative effects.The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.Download figureDownload PowerPoint Figure 1. Domain structure of TSP-1.FootnotesCorrespondence to Roy L. Silverstein, MD, Weill Medical College of Cornell University, Department of Medicine, Division of Hematology/Medical Oncology, 1300 York Ave, Room C606, New York, NY 10021. E-mail [email protected] References 1 Hanahan D, Folkman J. Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis. Cell.1996; 86:353–364.CrossrefMedlineGoogle Scholar2 Isner JM, Pieczek A, Schainfeld R, Blair R, Haley L, Asahara T, Rosenfield K, Razvi S, Walsh K, Symes JF. Clinical evidence of angiogenesis after arterial gene transfer of phVEGF165 in patient with ischaemic limb. Lancet.1996; 348:370–374.CrossrefMedlineGoogle Scholar3 Moulton KS, Heller E, Konerding MA, Flynn E, Palinski W, Folkman J. Angiogenesis inhibitors endostatin or TNP-470 reduce intimal neovascularization and plaque growth in apolipoprotein E-deficient mice. Circulation.1999; 99:1726–1732.CrossrefMedlineGoogle Scholar4 Barger AC, Beeuwkes R, Lainet L, Silverman KJ. Hypothesis: vasa vasorum and neovascularization of human coronary arteries. N Engl J Med.1984; 310:175–177.CrossrefMedlineGoogle Scholar5 Chen D, Asahara T, Krasinski K, Witzenbichler B, Yang J, Magner M, Kearney M, Frazier WA, Isner JM, Andrés V. Antibody blockade of thrombospondin-1 accelerates reendothelialization and reduces neointima formation in balloon-injured rat carotid artery. Circulation.1999; 100:849–854.CrossrefMedlineGoogle Scholar6 Bornstein P. Thrombospondins: structure and regulation of expression. FASEB J.1992; 6:3290–3299.CrossrefMedlineGoogle Scholar7 Good DJ, Polverini PJ, Rastinejad F, Le Beau MM, Lemons RS, Frazier WA, Bouck NP. A tumor suppressor dependent inhibitor of angiogenesis is immunologically and functionally indistinguishable from a fragment of thrombospondin. Proc Natl Acad Sci U S A.1990; 87:6624–6628.CrossrefMedlineGoogle Scholar8 Asch AS, Barnwell J, Silverstein RL, Nachman RL. Isolation of the thrombospondin membrane receptor. J Clin Invest.1987; 79:1054–1061.CrossrefMedlineGoogle Scholar9 Lawler J, Weinstein R, Hynes RO. Cell attachment to thrombospondin: the role of RGD, calcium, and integrin receptors. J Cell Biol.1988; 107:2351–2361.CrossrefMedlineGoogle Scholar10 Chung J, Gao A-G, Frazier WA. Thrombospondin acts via integrin-associated protein to activate the platelet integrin αIIBβ3. J Biol Chem.1997; 272:14740–14746.CrossrefMedlineGoogle Scholar11 Savill J, Hogg N. Thrombospondin cooperates with CD36 and the vitronectin receptor in macrophage recognition of neutrophils undergoing apoptosis. J Clin Invest.1992; 90:1513–1522.CrossrefMedlineGoogle Scholar12 Crawford SE, Stellmach V, Murphy-Ullrich JE, Ribeiro SMF, Lawler J, Hynes RO, Boivin GP, Bouck N. Thrombospondin-1 is a major activator of TGF-β1 in vivo. Cell.1998; 93:1159–1170.CrossrefMedlineGoogle Scholar13 Catimel B, Leung LLK, El-Ghissasi H, Mercier N, McGregor J. Human platelet glycoprotein IIIb binds to thrombospondin fragments bearing the C-terminal region, and/or the type I repeats (CSVTCG motif), but not to the N-terminal heparin-binding region. Biochem J.1992; 284:231–236.CrossrefMedlineGoogle Scholar14 Greenwalt DE, Lipsky RH, Ockenhouse CF, Ikeda H, Tandon N, Jamieson GA. Membrane glycoprotein CD36: a review of its roles in adherence, signal transduction, and transfusion medicine. Blood.1992; 80:1105–1115.CrossrefMedlineGoogle Scholar15 Ryeom S, Sparrow J, Silverstein RL. CD36 participates in the phagocytosis of rod outer segments on retinal pigment epithelium. J Cell Sci.1996; 109:387–395.CrossrefMedlineGoogle Scholar16 Endemann G, Stanton LW, Madden KS, Bryant CM, White RT, Protter AA. CD36 is a receptor for oxidized low density lipoprotein. J Biol Chem.1993; 268:11811–11816.CrossrefMedlineGoogle Scholar17 Ren Y, Silverstein RL, Allen J, Savill J. CD36 gene transfer confers capacity for phagocytosis of cells undergoing apoptosis. J Exp Med.1995; 181:1857–1862.CrossrefMedlineGoogle Scholar18 Abumrad N, El-Maghrabi MR, Amri E, Lopez E, Grimaldi P. Cloning of a rat adipocyte membrane protein implicated in binding or transport of long-chain fatty acids that is induced during preadipocyte differentiation. J Biol Chem.1993; 268:17665–17668.CrossrefMedlineGoogle Scholar19 Dawson DW, Pearce SFA, Zhong R, Silverstein RL, Frazier WA, Bouck NP. CD36 mediates the inhibitory effects of thrombospondin-1 on endothelial cells. J Cell Biol.1997; 138:707–717.CrossrefMedlineGoogle Scholar20 Asahara T, Murohara T, Sullivan A, Silver M, van der Zee R, Witzenbichler B, Schatteman G, Isner JM. Isolation of putative progenitor endothelial cells for angiogenesis. Science.1997; 275:965–967.Google Scholar Previous Back to top Next FiguresReferencesRelatedDetailsCited By Singh S and Gautam A (2019) Upregulated LOX-1 Receptor: Key Player of the Pathogenesis of Atherosclerosis, Current Atherosclerosis Reports, 10.1007/s11883-019-0801-y, 21:10, Online publication date: 1-Oct-2019. Tsai S, Wang J, Liao W, Hsu Y, Lin C, Liao M, Huang P and Lin S (2018) Fucoidan attenuates angiotensin II-induced abdominal aortic aneurysms through the inhibition of c-Jun N-terminal kinase and nuclear factor κB activation, Journal of Vascular Surgery, 10.1016/j.jvs.2017.09.042, 68:6, (72S-81S.e1), Online publication date: 1-Dec-2018. 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Zimmerman M, Selzman C, Raeburn C, Calkins C, Barsness K and Harken A (2001) Clinical Applications of Cardiovascular Angiogenesis, Journal of Cardiac Surgery, 10.1111/j.1540-8191.2001.tb00555.x, 16:6, (490-497), Online publication date: 1-Nov-2001. Hida K, Wada J, Zhang H, Hiragushi K, Tsuchiyama Y, Shikata K and Makino H (2000) Identification of genes specifically expressed in the accumulated visceral adipose tissue of OLETF rats, Journal of Lipid Research, 10.1016/S0022-2275(20)31994-5, 41:10, (1615-1622), Online publication date: 1-Oct-2000. August 24, 1999Vol 100, Issue 8 Advertisement Article InformationMetrics Copyright © 1999 by American Heart Associationhttps://doi.org/10.1161/01.CIR.100.8.783 Originally publishedAugust 24, 1999 Keywordscell adhesion moleculesangiogenesisrestenosisEditorialsatherosclerosisPDF download Advertisement
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