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Keire PA, Bressler SL, Lemire JM, Edris B, Rubin BP, Rahmani M, McManus BM, van de Rijn M, Wight TN. A role for versican in the development of leiomyosarcoma. J Biol Chem 2014; 289:34089-103. [PMID: 25320080 DOI: 10.1074/jbc.m114.607168] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Leiomyosarcoma (LMS) is a mesenchymal cancer that occurs throughout the body. Although LMS is easily recognized histopathologically, the cause of the disease remains unknown. Versican, an extracellular matrix proteoglycan, increases in LMS. Microarray analyses of 80 LMSs and 24 leiomyomas showed a significant elevated expression of versican in human LMS versus benign leiomyomas. To explore the importance of versican in this smooth muscle cell tumor, we used versican-directed siRNA to knock down versican expression in a LMS human cell line, SK-LMS-1. Decreased versican expression was accompanied by slower rates of LMS cell proliferation and migration, increased adhesion, and decreased accumulation of the extracellular matrix macromolecule hyaluronan. Addition of purified versican to cells expressing versican siRNA restored cell proliferation to the level of LMS controls, increased the pericellular coat and the retention of hyaluronan, and decreased cell adhesion in a dose-dependent manner. The presence of versican was not only synergistic with hyaluronan in increasing cell proliferation, but the depletion of versican decreased hyaluronan synthase expression and decreased the retention of hyaluronan. When LMS cells stably expressing versican siRNA were injected into nude mice, the resulting tumors displayed significantly less versican and hyaluronan staining, had lower volumes, and had reduced levels of mitosis as compared with controls. Collectively, these results suggest a role for using versican as a point of control in the management and treatment of LMS.
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Bogdani M, Johnson PY, Potter-Perigo S, Nagy N, Day AJ, Bollyky PL, Wight TN. Hyaluronan and hyaluronan-binding proteins accumulate in both human type 1 diabetic islets and lymphoid tissues and associate with inflammatory cells in insulitis. Diabetes 2014; 63:2727-43. [PMID: 24677718 PMCID: PMC4113060 DOI: 10.2337/db13-1658] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Hyaluronan (HA) is an extracellular matrix glycosaminoglycan that is present in pancreatic islets, but little is known about its involvement in the development of human type 1 diabetes (T1D). We have evaluated whether pancreatic islets and lymphoid tissues of T1D and nondiabetic organ donors differ in the amount and distribution of HA and HA-binding proteins (hyaladherins), such as inter-α-inhibitor (IαI), versican, and tumor necrosis factor-stimulated gene-6 (TSG-6). HA was dramatically increased both within the islet and outside the islet endocrine cells, juxtaposed to islet microvessels in T1D. In addition, HA was prominent surrounding immune cells in areas of insulitis. IαI and versican were present in HA-rich areas of islets, and both molecules accumulated in diabetic islets and regions exhibiting insulitis. TSG-6 was observed within the islet endocrine cells and in inflammatory infiltrates. These patterns were only observed in tissues from younger donors with disease duration of <10 years. Furthermore, HA and IαI amassed in follicular germinal centers and in T-cell areas in lymph nodes and spleens in T1D patients compared with control subjects. Our observations highlight potential roles for HA and hyaladherins in the pathogenesis of diabetes.
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Merrilees MJ, Falk BA, Zuo N, Dickinson ME, May BCH, Wight TN. Use of versican variant V3 and versican antisense expression to engineer cultured human skin containing increased content of insoluble elastin. J Tissue Eng Regen Med 2014; 11:295-305. [PMID: 24945362 DOI: 10.1002/term.1913] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 02/24/2014] [Accepted: 04/20/2014] [Indexed: 12/22/2022]
Abstract
Skin substitutes for repair of dermal wounds are deficient in functional elastic fibres. We report that the content of insoluble elastin in the dermis of cultured human skin can be increased though the use of two approaches that enhance elastogenesis by dermal fibroblasts, forced expression of versican variant V3, which lacks glycosaminoglycan (GAG) chains, and forced expression of versican antisense to decrease levels of versican variant V1 with GAG chains. Human dermal fibroblasts transduced with V3 or anti-versican were cultured under standard conditions over a period of 4 weeks to produce dermal sheets, with growth enhanced though multiple seedings for the first 3 weeks. Human keratinocytes, cultured in supplemented media, were added to the 4-week dermal sheets and the skin layer cultured for a further week. At 5 weeks, keratinocytes were multilayered and differentiated, with desmosome junctions thoughout and keratin deposits in the upper squamous layers. The dermal layer was composed of layered fibroblasts surrounded by extracellular matrix of collagen bundles and, in control cultures, small scattered elastin deposits. Forced expression of V3 and versican antisense slowed growth, decreased versican V1 expression, increased tropoelastin expression and/or the deposition of large aggregates of insoluble elastin in the dermal layer, and increased tissue stiffness, as measured by nano-indentation. Skin sheets were also cultured on Endoform Dermal Template™, the biodegradable wound dressing made from the lamina propria of sheep foregut. Skin structure and the enhanced deposition of elastin by forced expression of V3 and anti-versican were preserved on this supportive substrate. Copyright © 2014 John Wiley & Sons, Ltd.
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Reeves SR, Kolstad T, Lien TY, Elliott M, Ziegler SF, Wight TN, Debley JS. Asthmatic airway epithelial cells differentially regulate fibroblast expression of extracellular matrix components. J Allergy Clin Immunol 2014; 134:663-670.e1. [PMID: 24875618 DOI: 10.1016/j.jaci.2014.04.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Revised: 04/06/2014] [Accepted: 04/11/2014] [Indexed: 02/06/2023]
Abstract
BACKGROUND Airway remodeling might explain lung function decline among asthmatic children. Extracellular matrix (ECM) deposition by human lung fibroblasts (HLFs) is implicated in airway remodeling. Airway epithelial cell (AEC) signaling might regulate HLF ECM expression. OBJECTIVES We sought to determine whether AECs from asthmatic children differentially regulate HLF expression of ECM constituents. METHODS Primary AECs were obtained from well-characterized atopic asthmatic (n = 10) and healthy (n = 10) children intubated during anesthesia for an elective surgical procedure. AECs were differentiated at an air-liquid interface for 3 weeks and then cocultured with HLFs from a healthy child for 96 hours. Collagen I (COL1A1), collagen III (COL3A1), hyaluronan synthase (HAS) 2, and fibronectin expression by HLFs and prostaglandin E2 synthase (PGE2S) expression by AECs were assessed by using RT-PCR. TGF-β1 and TGF-β2 concentrations in media were measured by using ELISA. RESULTS COL1A1 and COL3A1 expression by HLFs cocultured with AECs from asthmatic patients was greater than that by HLFs cocultured with AECs from healthy subjects (2.2-fold, P < .02; 10.8-fold, P < .02). HAS2 expression by HLFs cocultured with AECs from asthmatic patients was 2.5-fold higher than that by HLFs cocultured with AECs from healthy subjects (P < .002). Fibronectin expression by HLFs cocultured with AECs from asthmatic patients was significantly greater than that by HLFs alone. TGF-β2 activity was increased in cocultures of HLFs with AECs from asthmatic patients (P < .05), whereas PGES2 was downregulated in AEC-HLF cocultures (2.2-fold, P < .006). CONCLUSIONS HLFs cocultured with AECs from asthmatic patients showed differential expression of the ECM constituents COL1A1 and COL3A1 and HAS2 compared with HLFs cocultured with AECs from healthy subjects. These findings support a role for altered ECM production in asthmatic airway remodeling, possibly regulated by unbalanced AEC signaling.
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Kang I, Yoon DW, Braun KR, Wight TN. Expression of versican V3 by arterial smooth muscle cells alters tumor growth factor β (TGFβ)-, epidermal growth factor (EGF)-, and nuclear factor κB (NFκB)-dependent signaling pathways, creating a microenvironment that resists monocyte adhesion. J Biol Chem 2014; 289:15393-404. [PMID: 24719328 DOI: 10.1074/jbc.m113.544338] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Monocyte/macrophage accumulation plays a critical role during progression of cardiovascular diseases, such as atherosclerosis. Our previous studies demonstrated that retrovirally mediated expression of the versican V3 splice variant (V3) by arterial smooth muscle cells (ASMCs) decreases monocyte adhesion in vitro and macrophage accumulation in a model of lipid-induced neointimal formation in vivo. We now demonstrate that V3-expressing ASMCs resist monocyte adhesion by altering the composition of the microenvironment surrounding the cells by affecting multiple signaling pathways. Reduction of monocyte adhesion to V3-expressing ASMCs is due to the generation of an extracellular matrix enriched in elastic fibers and depleted in hyaluronan, and reduction of the proinflammatory cell surface vascular cell adhesion molecule 1 (VCAM1). Blocking these changes reverses the protective effect of V3 on monocyte adhesion. The enhanced elastogenesis induced by V3 expression is mediated by TGFβ signaling, whereas the reduction in hyaluronan cable formation induced by V3 expression is mediated by the blockade of epidermal growth factor receptor and NFκB activation pathways. In addition, expression of V3 by ASMCs induced a marked decrease in NFκB-responsive proinflammatory cell surface molecules that mediate monocyte adhesion, such as VCAM1. Overall, these results indicate that V3 expression by ASMCs creates a microenvironment resistant to monocyte adhesion via differentially regulating multiple signaling pathways.
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Chang MY, Tanino Y, Vidova V, Kinsella MG, Chan CK, Johnson PY, Wight TN, Frevert CW. Reprint of: A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease. Matrix Biol 2014; 35:162-73. [PMID: 24727035 PMCID: PMC4096977 DOI: 10.1016/j.matbio.2014.04.003] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 01/21/2014] [Accepted: 01/21/2014] [Indexed: 01/08/2023]
Abstract
The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.
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Chang MY, Tanino Y, Vidova V, Kinsella MG, Chan CK, Johnson PY, Wight TN, Frevert CW. A rapid increase in macrophage-derived versican and hyaluronan in infectious lung disease. Matrix Biol 2014; 34:1-12. [PMID: 24472738 DOI: 10.1016/j.matbio.2014.01.011] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2013] [Revised: 01/21/2014] [Accepted: 01/21/2014] [Indexed: 02/08/2023]
Abstract
The goals of this study were to characterize the changes in chondroitin sulfate proteoglycans and hyaluronan in lungs in acute response to gram-negative bacterial infection and to identify cellular components responsible for these changes. Mice were treated with intratracheal (IT) live Escherichia coli, E. coli lipopolysaccharide (LPS), or PBS. Both E. coli and LPS caused rapid selective increases in mRNA expression of versican and hyaluronan synthase (Has) isoforms 1 and 2 associated with increased immunohistochemical and histochemical staining for versican and hyaluronan in the lungs. Versican was associated with a subset of alveolar macrophages. To examine whether macrophages contribute to versican and hyaluronan accumulation, in vitro studies with primary cultures of bone marrow-derived and alveolar macrophages were performed. Unstimulated macrophages expressed very low levels of versican and hyaluronan synthase mRNA, with no detectible versican protein or hyaluronan product. Stimulation with LPS caused rapid increases in versican mRNA and protein, a rapid increase in Has1 mRNA, and concomitant inhibition of hyaluronidases 1 and 2, the major hyaluronan degrading enzymes. Hyaluronan could be detected following chloroquine pre-treatment, indicating rapid turnover and degradation of hyaluronan by macrophages. In addition, the effects of LPS, the M1 macrophage classical activation agonist, were compared to those of IL-4/IL-13 or IL-10, the M2a and M2c alternative activation agonists, respectively. Versican and Has1 increased only in response to M1 activation. Finally, the up-regulation of versican and Has1 in the whole lungs of wild-type mice following IT LPS was completely abrogated in TLR-4(-/-) mice. These findings suggest that versican and hyaluronan synthesis may play an important role in the innate immune response to gram-negative lung infection.
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Obika M, Vernon RB, Gooden MD, Braun KR, Chan CK, Wight TN. ADAMTS-4 and biglycan are expressed at high levels and co-localize to podosomes during endothelial cell tubulogenesis in vitro. J Histochem Cytochem 2013; 62:34-49. [PMID: 24051360 DOI: 10.1369/0022155413507727] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Proteolysis of the extracellular matrix influences vascular growth. We examined the expression of ADAMTS-1, -4, and -5 metalloproteinases and their proteoglycan substrates versican, decorin, and biglycan as human umbilical vein endothelial cells (HUVECs) formed tubes within type I collagen gels in vitro. Tubulogenic and control HUVEC cultures expressed low levels of ADAMTS-1 and -5 mRNAs, but ADAMTS-4 mRNA was relatively abundant and was significantly elevated (as was ADAMTS-4 protein) in tubulogenic cultures versus controls. Immunocytochemistry revealed ADAMTS-4 in f-actin- and cortactin-positive podosome-like puncta in single cells and mature tubes. Tubulogenic and control cultures expressed low levels of versican and decorin mRNAs; however, peak levels of biglycan mRNA were 400- and 16,000-fold that of versican and decorin, respectively. Biglycan mRNA was highest at 3 hr, declined steadily through day 7 and, at 12 hr and beyond, was significantly lower in tubulogenic cultures than in controls. Western blots of extracellular matrix from tubulogenic cultures contained bands corresponding to biglycan and its cleavage products. By immunocytochemistry, biglycan was found in the pericellular matrix surrounding endothelial tubes and in cell-associated puncta that co-localized with ADAMTS-4 and cortactin. Collectively, our results suggest that ADAMTS-4 and its substrate biglycan are involved in tubulogenesis by endothelial cells.
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Viola M, Bartolini B, Vigetti D, Karousou E, Moretto P, Deleonibus S, Sawamura T, Wight TN, Hascall VC, De Luca G, Passi A. Oxidized low density lipoprotein (LDL) affects hyaluronan synthesis in human aortic smooth muscle cells. J Biol Chem 2013; 288:29595-603. [PMID: 23979132 DOI: 10.1074/jbc.m113.508341] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Thickening of the vessel in response to high low density lipoprotein(s) (LDL) levels is a hallmark of atherosclerosis, characterized by increased hyaluronan (HA) deposition in the neointima. Human native LDL trapped within the arterial wall undergoes modifications such as oxidation (oxLDL). The aim of our study is to elucidate the link between internalization of oxLDL and HA production in vitro, using human aortic smooth muscle cells. LDL were used at an effective protein concentration of 20-50 μg/ml, which allowed 80% cell viability. HA content in the medium of untreated cells was 28.9 ± 3.7 nmol HA-disaccharide/cell and increased after oxLDL treatment to 53.9 ± 5.6. OxLDL treatments doubled the transcripts of HA synthase HAS2 and HAS3. Accumulated HA stimulated migration of aortic smooth muscle cells and monocyte adhesiveness to extracellular matrix. The effects induced by oxLDL were inhibited by blocking LOX-1 scavenger receptor with a specific antibody (10 μg/ml). The cholesterol moiety of LDL has an important role in HA accumulation because cholesterol-free oxLDL failed to induce HA synthesis. Nevertheless, cholesterol-free oxLDL and unmodified cholesterol (20 μg/ml) induce only HAS3 transcription, whereas 22,oxysterol affects both HAS2 and HAS3. Moreover, HA deposition was associated with higher expression of endoplasmic reticulum stress markers (CHOP and GRP78). Our data suggest that HA synthesis can be induced in response to specific oxidized sterol-related species delivered through oxLDL.
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85
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Wilson CL, Gough PJ, Chang CA, Chan CK, Frey JM, Liu Y, Braun KR, Chin MT, Wight TN, Raines EW. Endothelial deletion of ADAM17 in mice results in defective remodeling of the semilunar valves and cardiac dysfunction in adults. Mech Dev 2013; 130:272-89. [PMID: 23354118 DOI: 10.1016/j.mod.2013.01.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2012] [Revised: 12/21/2012] [Accepted: 01/07/2013] [Indexed: 12/24/2022]
Abstract
Global inactivation of the metalloproteinase ADAM17 during mouse development results in perinatal lethality and abnormalities of the heart, including late embryonic cardiomegaly and thickened semilunar and atrioventricular valves. These defects have been attributed in part to a lack of ADAM17-mediated processing of HB-EGF, as absence of soluble HB-EGF results in similar phenotypes. Because valvular mesenchymal cells are largely derived from cardiac endothelial cells, we generated mice with a floxed Adam17 allele and crossed these animals with Tie2-Cre transgenics to focus on the role of endothelial ADAM17 in valvulogenesis. We find that although hearts from late-stage embryos with ablation of endothelial ADAM17 appear normal, an increase in valve size and cell number is evident, but only in the semilunar cusps. Unlike Hbegf(-/-) valves, ADAM17-null semilunar valves do not differ from controls in acute cell proliferation at embryonic day 14.5 (E14.5), suggesting compensatory processing of HB-EGF. However, levels of the proteoglycan versican are significantly reduced in mutant hearts early in valve remodeling (E12.5). After birth, aortic valve cusps from mutants are not only hyperplastic but also show expansion of the glycosaminoglycan-rich component, with the majority of adults exhibiting aberrant compartmentalization of versican and increased deposition of collagen. The inability of mutant outflow valve precursors to transition into fully mature cusps is associated with decreased postnatal viability, progressive cardiomegaly, and systolic dysfunction. Together, our data indicate that ADAM17 is required in valvular endothelial cells for regulating cell content as well as extracellular matrix composition and organization in semilunar valve remodeling and homeostasis.
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Ayars AG, Altman LC, Potter-Perigo S, Radford K, Wight TN, Nair P. Sputum hyaluronan and versican in severe eosinophilic asthma. Int Arch Allergy Immunol 2012; 161:65-73. [PMID: 23257685 DOI: 10.1159/000343031] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2012] [Accepted: 08/27/2012] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND We examined levels of hyaluronan, a matrix glycosaminoglycan and versican, a matrix proteoglycan, in the sputum of asthmatics treated with mepolizumab (anti-IL-5 monoclonal antibody) versus placebo to evaluate the utility of these measurements as possible biomarkers of asthma control and airway remodeling. METHODS Patients with severe, prednisone-dependent asthma received either mepolizumab or placebo as described in a previously published randomized, double-blind, placebo-controlled study. We measured hyaluronan and versican levels by enzyme-linked immunosorbent assay in sputum collected before and after the 16-week treatment phase. Patients underwent a predefined prednisone tapering schedule if they remained exacerbation free, and sputum eosinophil percentage, asthma control questionnaire (ACQ) and spirometry were monitored. RESULTS After 6 months of mepolizumab therapy and prednisone tapering, there was a significant increase in sputum hyaluronan in the placebo group compared with baseline (p = 0.003). In contrast, there was a significant decrease in sputum hyaluronan in the active treatment group compared with placebo (p = 0.007), which correlated with improvements in percent forced expiratory volume in 1 s (FEV1%) (p = 0.001) and ACQ scores (p = 0.009) as well as a decrease in sputum eosinophils (p = 0.02). There was a nonsignificant increase in sputum versican in the placebo group (p = 0.16), a decrease in the mepolizumab group (p = 0.13) and a significant inverse correlation between versican reduction and FEV1% improvement (p = 0.03). CONCLUSIONS Sputum hyaluronan values are reduced with mepolizumab therapy and correlate with improved clinical and spirometry values, suggesting this measurement may serve as a noninvasive biomarker of asthma control.
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Rutnam ZJ, Wight TN, Yang BB. miRNAs regulate expression and function of extracellular matrix molecules. Matrix Biol 2012; 32:74-85. [PMID: 23159731 DOI: 10.1016/j.matbio.2012.11.003] [Citation(s) in RCA: 86] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 10/17/2012] [Accepted: 10/18/2012] [Indexed: 12/19/2022]
Abstract
MicroRNAs (miRNAs) are a family of small non-coding RNA molecules that are made up of 18-25 nucleotides that function in post-transcriptional gene regulation. The expression of miRNAs is highly conserved and essential in regulating many cellular processes including formation, maintenance and the remodelling of the extracellular matrix (ECM). In this review, we examine different ECM molecules and the miRNAs involved in regulating their abundance and how these changes influence cell phenotype. For example, miRNAs and their target messenger RNAs (mRNAs) are involved in cell adhesion, by regulating the synthesis and turnover of key ECM adhesion molecules and their receptors including cadherins, integrins and other non-integrin ECM receptors. Other miRNAs regulate the abundance of cytokines and growth factors which in turn stimulate cells to synthesize and secrete specialized ECMs. For example, miR-125a/b and miR-146a and their downstream target mRNAs influence the production of the epidermal growth factor family which has a significant impact on the nature of the ECM formed. miRNAs affect structural ECM proteins important in the assembly, composition and organization of the ECM. Proteins such as collagen, fibronectin, versican, and nephronectin are targeted by several miRNAs. miRNAs can also control the expression of proteins such as matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs), which are involved in ECM remodelling and are important for tissue development, cell motility and wound healing. It has become clear that many different miRNAs control the balance in ECM composition that determines normal tissue function and alterations in the expression of these miRNAs can lead to pathological consequences.
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Bollyky PL, Bogdani M, Bollyky JB, Hull RL, Wight TN. The role of hyaluronan and the extracellular matrix in islet inflammation and immune regulation. Curr Diab Rep 2012; 12:471-80. [PMID: 22810951 PMCID: PMC3432646 DOI: 10.1007/s11892-012-0297-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Type 1 diabetes (T1D) is a disease that in most individuals results from autoimmune attack of a single tissue type, the pancreatic islet. A fundamental, unanswered question in T1D pathogenesis is how the islet tissue environment influences immune regulation. This crosstalk is likely to be communicated through the extracellular matrix (ECM). Here, we review what is known about the ECM in insulitis and examine how the tissue environment is synchronized with immune regulation. In particular, we focus on the role of hyaluronan (HA) and its interactions with Foxp3+ regulatory T-cells (Treg). We propose that HA is a "keystone molecule" in the inflammatory milieu and that HA, together with its associated binding proteins and receptors, is an appropriate point of entry for investigations into how ECM influences immune regulation in the islet.
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Reed MJ, Damodarasamy M, Chan CK, Johnson MNR, Wight TN, Vernon RB. Cleavage of hyaluronan is impaired in aged dermal wounds. Matrix Biol 2012; 32:45-51. [PMID: 23022999 DOI: 10.1016/j.matbio.2012.09.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2012] [Revised: 09/18/2012] [Accepted: 09/19/2012] [Indexed: 10/27/2022]
Abstract
Changes in extracellular matrix (ECM) are one of many components that contribute to impaired wound healing in aging. This study examined the effect of age on the glycosaminoglycan hyaluronan (HA) in normal and wounded dermis from young (4-6 month-old) and aged (22-24 month-old) mice. HA content and size were similar in the normal dermis of young and aged mice. Dermal explants labeled with [(3)H]-glucosamine showed decreased generation of smaller forms of HA in aged explants relative to young explants. Aged mice exhibited delayed wound repair compared with young mice with the greatest differential at 5 days. Expression of hyaluronan synthase (HAS) 2 and 3, and hyaluronidase (HYAL) 1-3 mRNA in wounds of young and aged mice was similar. There was a trend toward a decreased HYAL protein expression in aged wound dermis, which was accompanied by changes in detectable HYAL activity. Total HA content was similar in young and aged wound dermis. There was significantly less HA in the lower MW range (~250 kDa and smaller) in 5-day wound dermis, but not in 9-day wound dermis, from aged mice relative to young mice. We propose that decreased cleavage of HA is an additional component of impaired dermal wound healing in aging.
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Hull RL, Peters MJ, Perigo SP, Chan CK, Wight TN, Kinsella MG. Overall sulfation of heparan sulfate from pancreatic islet β-TC3 cells increases maximal fibril formation but does not determine binding to the amyloidogenic peptide islet amyloid polypeptide. J Biol Chem 2012; 287:37154-64. [PMID: 22936797 DOI: 10.1074/jbc.m112.409847] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Islet amyloid, a pathologic feature of type 2 diabetes, contains the islet β-cell peptide islet amyloid polypeptide (IAPP) as its unique amyloidogenic component. Islet amyloid also contains heparan sulfate proteoglycans (HSPGs) that may contribute to amyloid formation by binding IAPP via their heparan sulfate (HS) chains. We hypothesized that β-cells produce HS that bind IAPP via regions of highly sulfated disaccharides. Unexpectedly, HS from the β-cell line β-TC3 contained fewer regions of highly sulfated disaccharides compared with control normal murine mammary gland (NMuMG) cells. The proportion of HS that bound IAPP was similar in both cell lines (∼65%). The sulfation pattern of IAPP-bound versus non-bound HS from β-TC3 cells was similar. In contrast, IAPP-bound HS from NMuMG cells contained frequent highly sulfated regions, whereas the non-bound material demonstrated fewer sulfated regions. Fibril formation from IAPP was stimulated equally by IAPP-bound β-TC3 HS, non-bound β-TC3 HS, and non-bound NMuMG HS but was stimulated to a greater extent by the highly sulfated IAPP-bound NMuMG HS. Desulfation of HS decreased the ability of both β-TC3 and NMuMG HS to stimulate IAPP maximal fibril formation, but desulfated HS from both cell types still accelerated fibril formation relative to IAPP alone. In summary, neither binding to nor acceleration of fibril formation from the amyloidogenic peptide IAPP is dependent on overall sulfation in HS synthesized by β-TC3 cells. This information will be important in determining approaches to reduce HS-IAPP interactions and ultimately prevent islet amyloid formation and its toxic effects in type 2 diabetes.
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Hull RL, Johnson PY, Braun KR, Day AJ, Wight TN. Hyaluronan and hyaluronan binding proteins are normal components of mouse pancreatic islets and are differentially expressed by islet endocrine cell types. J Histochem Cytochem 2012; 60:749-60. [PMID: 22821669 PMCID: PMC3524560 DOI: 10.1369/0022155412457048] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The pancreatic islet comprises endocrine, vascular, and neuronal cells. Signaling among these cell types is critical for islet function. The extracellular matrix (ECM) is a key regulator of cell-cell signals, and while some islet ECM components have been identified, much remains unknown regarding its composition. We investigated whether hyaluronan, a common ECM component that may mediate inflammatory events, and molecules that bind hyaluronan such as versican, tumor necrosis factor-stimulated gene 6 (TSG-6), and components of inter-α-trypsin inhibitor (IαI), heavy chains 1 and 2 (ITIH1/ITIH2), and bikunin, are normally produced in the pancreatic islet. Mouse pancreata and isolated islets were obtained for microscopy (with both paraformaldehyde and Carnoy's fixation) and mRNA. Hyaluronan was present predominantly in the peri-islet ECM, and hyaluronan synthase isoforms 1 and 3 were also expressed in islets. Versican was produced in α cells; TSG-6 in α and β cells; bikunin in α, β, and δ cells; and ITIH1/ITIH2 predominantly in β cells. Our findings demonstrate that hyaluronan, versican, TSG-6, and IαI are normal islet components and that different islet endocrine cell types contribute these ECM components. Thus, dysfunction of either α or β cells likely alters islet ECM composition and could thereby further disrupt islet function.
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92
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Tanino Y, Chang MY, Wang X, Gill SE, Skerrett S, McGuire JK, Sato S, Nikaido T, Kojima T, Munakata M, Mongovin S, Parks WC, Martin TR, Wight TN, Frevert CW. Syndecan-4 regulates early neutrophil migration and pulmonary inflammation in response to lipopolysaccharide. Am J Respir Cell Mol Biol 2012; 47:196-202. [PMID: 22427536 DOI: 10.1165/rcmb.2011-0294oc] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Proteoglycans (PGs) and their associated glycosaminoglycan side chains are effectors of inflammation, but little is known about changes to the composition of PGs in response to lung infection or injury. The goals of this study were to identify changes to heparan sulfate PGs in a mouse model of gram-negative pneumonia, to identify the Toll-like receptor adaptor molecules responsible for these changes, and to determine the role of the heparan sulfate PG in the innate immune response in the lungs. We treated mice with intratracheal LPS, a component of the cell wall of gram-negative bacteria, to model gram-negative pneumonia. Mice treated with intratracheal LPS had a rapid and selective increase in syndecan-4 mRNA that was regulated through MyD88-dependent mechanisms, whereas expression of several other PGs was not affected. To determine the role of syndecan-4 in the inflammatory response, we exposed mice deficient in syndecan-4 to LPS and found a significant increase in neutrophil numbers and amounts of CXC-chemokines and total protein in bronchoalveolar lavage fluid. In studies performed in vitro, macrophages and epithelial cells treated with LPS had increased expression of syndecan-4. Studies performed using BEAS-2B cells showed that pretreatment with heparin and syndecan-4 decreased the expression of CXCL8 mRNA in response to LPS and TNF-α. These findings indicate that the early inflammatory response to LPS involves marked up-regulation of syndecan-4, which functions to limit the extent of pulmonary inflammation and lung injury.
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93
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Chang MY, Chan CK, Braun KR, Green PS, O'Brien KD, Chait A, Day AJ, Wight TN. Monocyte-to-macrophage differentiation: synthesis and secretion of a complex extracellular matrix. J Biol Chem 2012; 287:14122-35. [PMID: 22351750 PMCID: PMC3340194 DOI: 10.1074/jbc.m111.324988] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Although monocyte- and macrophage-derived molecules are known to promote extracellular matrix (ECM) disruption and destabilization, it is less appreciated that they also synthesize molecules contributing to ECM formation, stabilization, and function. We have identified and characterized the synthesis of proteoglycans and related proteins, some not previously known to be associated with macrophages. Proteoglycan extracts of [35S]sulfate- and 35S-trans amino acid-radiolabeled culture media from THP-1 monocytes induced to differentiate by treatment with phorbol myristate acetate revealed three major proteins of ∼25, 90, and 100 kDa following chondroitin ABC lyase digestion. The 25-kDa protein was predominant for monocytes, whereas the 90- and 100-kDa proteins were predominant for macrophages. Tandem mass spectrometry identified (i) the 25-kDa core protein as serglycin, (ii) the 90-kDa core protein as inter-α-inhibitor heavy chain 2 (IαIHC2), and (iii) the 100-kDa core as amyloid precursor-like protein 2 (APLP2). Differentiation was also associated with (i) a >500-fold increase in mRNA for TNF-stimulated gene-6, an essential cofactor for heavy chain-mediated matrix stabilization; (ii) a >800-fold increase in mRNA for HAS2, which is responsible for hyaluronan synthesis; and (iii) a 3-fold increase in mRNA for versican, which interacts with hyaluronan. Biochemical evidence is also presented for an IαIHC2-APLP2 complex, and immunohistochemical staining of human atherosclerotic lesions demonstrates similar staining patterns for APLP2 and IαIHC2 with macrophages, whereas serglycin localizes to the underlying glycosaminoglycan-rich region. These findings indicate that macrophages synthesize many of the molecules participating in ECM formation and function, suggesting a novel role for these molecules in the differentiation of macrophages in the development of atherosclerosis.
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Wight TN, Potter-Perigo S. The extracellular matrix: an active or passive player in fibrosis? Am J Physiol Gastrointest Liver Physiol 2011; 301:G950-5. [PMID: 21512158 PMCID: PMC3233785 DOI: 10.1152/ajpgi.00132.2011] [Citation(s) in RCA: 181] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Fibrosis is characterized by excessive accumulation of collagen and other extracellular matrix (ECM) components, and this process has been likened to aberrant wound healing. The early phases of wound healing involve the formation of a provisional ECM containing fibrin, fibrinogen, and fibronectin. Fibroblasts occupy this matrix and proliferate in response to activators elaborated by leukocytes that have migrated into the wound and are retained by the ECM. This coincides with the appearance of the myofibroblast, a specialized form of fibroblast whose differentiation is primarily driven by cytokines, such as transforming growth factor-β (TGF-β), and by mechanical tension. When these signals are reduced, as when TGF-β secretion is reduced, or as in scar shrinkage, myofibroblasts undergo apoptosis, resulting in a collagen-rich, cell-poor scar. Retention of myofibroblasts in fibrosis has been described as the result of imbalanced cytokine signaling, especially with respect to levels of activated TGF-β. ECM components can regulate myofibroblast persistence directly, since this phenotype is dependent on extracellular hyaluronan, tenascin-C, and the fibronectin splice variant containing the "extra domain A," and also, indirectly, through retention of TGF-β-secreting cells such as eosinophils. Thus the ECM is actively involved in both cellular and extracellular events that lead to fibrosis. Targeting components of the ECM as cells respond to injury and inflammatory stimuli holds promise as a means to avoid development of fibrosis and direct the wound-healing process toward reestablishment of a healthy equilibrium.
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95
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Evanko SP, Potter-Perigo S, Bollyky PL, Nepom GT, Wight TN. Hyaluronan and versican in the control of human T-lymphocyte adhesion and migration. Matrix Biol 2011; 31:90-100. [PMID: 22155153 DOI: 10.1016/j.matbio.2011.10.004] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2011] [Revised: 10/10/2011] [Accepted: 10/31/2011] [Indexed: 12/13/2022]
Abstract
The ability of lymphocytes to migrate freely through connective tissues is vital to efficient immune function. How the extracellular matrix (ECM) may affect T-cell adhesion and migration is not well understood. We have examined the adhesion and migration of activated human T-lymphocytes on ECM made by fibroblast-like synoviocytes and lung fibroblasts. These cells were minimally interactive until treated with a viral mimetic, Poly I:C. This treatment promoted myofibroblast formation and engendered a higher-order structured ECM, rich in versican and hyaluronan, to which T-cells avidly adhered in a hyaluronidase-sensitive manner. This Poly I:C-induced matrix impeded T-cell spreading and migration on and through synoviocyte monolayers, while hyaluronidase treatment or adding versican antibody during matrix formation reversed the effect on T-cell migration. Hyaluronidase also reversed the spread myofibroblast morphology. These data suggest that the viscous hyaluronan- and versican-rich matrix binds and constrains T-lymphocytes. Using purified matrix components and solid state matrices of defined composition, we uncovered a role for versican in modulating hyaluronan-T-cell interactions. Versican prevented T-cell binding to soluble hyaluronan, as well as the amoeboid shape change on hyaluronan-coated dishes and T-cell penetration of collagen gels. Together, these data suggest that hyaluronan and versican play a role in T-cell trafficking and function in inflamed tissues.
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Harten IA, Zahr RS, Lemire JM, Machan JT, Moses MA, Doiron RJ, Curatolo AS, Rothman FG, Wight TN, Toole BP, Gordon LB. Age-dependent loss of MMP-3 in Hutchinson-Gilford progeria syndrome. J Gerontol A Biol Sci Med Sci 2011; 66:1201-7. [PMID: 21852285 DOI: 10.1093/gerona/glr137] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Hutchinson-Gilford progeria syndrome (HGPS) is a rare, progressive segmental premature aging disease that includes scleroderma-like skin, progressive joint contracture, and atherosclerosis. Affected individuals die prematurely of heart attacks or strokes. Extracellular matrix dysregulation is implicated as a factor in disease progression. We analyzed messenger RNA and protein levels for matrix metalloproteinases (MMPs)-2,-3, and -9 in HGPS primary human dermal fibroblasts using real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and gelatin zymography. MMP-3 messenger RNA and protein levels decreased significantly with increasing donor age in HGPS fibroblasts but not in controls. MMP-2 messenger RNA also showed a donor age-dependent decrease in HGPS fibroblasts, but levels of secreted protein were unchanged. MMP-9 was similar in HGPS and control cultures. The decreased MMP-3 may represent a shift in the inherent extracellular matrix-degrading proteolytic balance in favor of matrix deposition in HGPS. This metalloproteinase has the potential to serve as a biomarker of therapeutic efficacy when assessing treatments for HGPS.
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Chiba T, Chang MY, Wang S, Wight TN, McMillen TS, Oram JF, Vaisar T, Heinecke JW, De Beer FC, De Beer MC, Chait A. Serum amyloid A facilitates the binding of high-density lipoprotein from mice injected with lipopolysaccharide to vascular proteoglycans. Arterioscler Thromb Vasc Biol 2011; 31:1326-32. [PMID: 21474830 DOI: 10.1161/atvbaha.111.226159] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Levels of serum amyloid A (SAA), an acute-phase protein carried on high-density lipoprotein (HDL), increase in inflammatory states and are associated with increased risk of cardiovascular disease. HDL colocalizes with vascular proteoglycans in atherosclerotic lesions. However, its major apolipoprotein, apolipoprotein A-I, has no proteoglycan-binding domains. Therefore, we investigated whether SAA, which has proteoglycan-binding domains, plays a role in HDL retention by proteoglycans. METHODS AND RESULTS HDL from control mice and mice deficient in both SAA1.1 and SAA2.1 (SAA knockout mice) injected with bacterial lipopolysaccharide (LPS) was studied. SAA mRNA expression in the liver and plasma levels of SAA increased dramatically in C57BL/6 mice after LPS administration, although HDL cholesterol did not change. Fast protein liquid chromatography analysis showed most of the SAA to be in HDL. Mass spectrometric analysis indicated that HDL from LPS-injected control mice had high levels of SAA1.1/2.1 and reduced levels of apolipoprotein A-I. HDL from LPS-injected control mice demonstrated high-affinity binding to biglycan relative to normal mouse HDL. In contrast, HDL from LPS-injected SAA knockout mice showed very little binding to biglycan, consistent with SAA facilitating the binding of HDL to vascular proteoglycans. CONCLUSION SAA enrichment of HDL under inflammatory conditions plays an important role in the binding of HDL to vascular proteoglycans.
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Merrilees MJ, Beaumont BW, Braun KR, Thomas AC, Kang I, Hinek A, Passi A, Wight TN. Neointima formed by arterial smooth muscle cells expressing versican variant V3 is resistant to lipid and macrophage accumulation. Arterioscler Thromb Vasc Biol 2011; 31:1309-16. [PMID: 21441139 DOI: 10.1161/atvbaha.111.225573] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
OBJECTIVE Extracellular matrix (ECM) of neointima formed following angioplasty contains elevated levels of versican, loosely arranged collagen, and fragmented deposits of elastin, features associated with lipid and macrophage accumulation. ECM with a low versican content, compact structure, and increased elastic fiber content can be achieved by expression of versican variant V3, which lacks chondroitin sulfate glycosaminoglycans. We hypothesized that V3-expressing arterial smooth muscle cells (ASMC) can be used to form a neointima resistant to lipid and macrophage accumulation associated with hypercholesterolemia. METHODS AND RESULTS ASMC transduced with V3 cDNA were seeded into ballooned rabbit carotid arteries, and animals were fed a chow diet for 4 weeks, followed by a cholesterol-enriched diet for 4 weeks, achieving plasma cholesterol levels of 20 to 25 mmol/L. V3 neointimae at 8 weeks were compact, multilayered, and elastin enriched. They were significantly thinner (57%) than control neointimae; contained significantly more elastin (118%), less collagen (22%), and less lipid (76%); and showed significantly reduced macrophage infiltration (85%). Mechanistic studies demonstrated that oxidized low-density lipoprotein stimulated the formation of a monocyte-binding ECM, which was inhibited in the presence of V3 expressing ASMC. CONCLUSION These results demonstrate that expression of V3 in vessel wall creates an elastin-rich neointimal matrix that in the presence of hyperlipidemia is resistant to lipid deposition and macrophage accumulation.
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Fu Y, Nagy JA, Brown LF, Shih SC, Johnson PY, Chan CK, Dvorak HF, Wight TN. Proteolytic cleavage of versican and involvement of ADAMTS-1 in VEGF-A/VPF-induced pathological angiogenesis. J Histochem Cytochem 2011; 59:463-73. [PMID: 21411713 DOI: 10.1369/0022155411401748] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Malignant tumors and chronic inflammatory diseases induce angiogenesis by overexpressing vascular endothelial growth factor A (VEGF-A/VPF). VEGF-A-induced pathological angiogenesis can be mimicked in immunoincompetent mice with an adenoviral vector expressing VEGF-A(164) (Ad-VEGF-A(164)). The initial step is generation of greatly enlarged "mother" vessels (MV) from preexisting normal venules by a process involving degradation of their rigid basement membranes. Immunohistochemical and Western blot analyses revealed that versican, an extracellular matrix component in the basement membranes of venules, is degraded early in the course of MV formation, resulting in the appearance of a versican N-terminal DPEAAE fragment associated with MV endothelial cells. The protease ADAMTS-1, known to cleave versican near its N terminus to generate DPEAAE, is also upregulated by VEGF-A in parallel with MV formation and localizes to the endothelium of the developing MV. The authors also show that MMP-15 (MT-2 MMP), a protease that activates ADAMTS-1, is upregulated by VEGF-A in endothelial cells in vitro and in vivo. These data suggest VEGF-A initiates MV formation, in part, by inducing the expression of endothelial cell proteases such as ADAMTS-1 and MMP-15 that act in concert to degrade venular basement membrane versican. Thus, versican is actively processed during the early course of VEGF-A-induced pathological angiogenesis.
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Tillinghast EK, Townley MA, Wight TN, Uhlenbruck G, Janssen E. The Adhesive Glycoprotein of the Orb Web of Argiope Aurantia (Araneae, Araneidae). ACTA ACUST UNITED AC 2011. [DOI: 10.1557/proc-292-9] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
AbstractA phosphorylated, glycoprotein preparation has been obtained from orb webs of the araneid spider Argiope aurantia. This preparation probably contains proteins from more than one gland type, but resolution of these proteins has not yet been achieved. Nevertheless, a major component appears to be the adhesive glycoprotein(s) from the adhesive spiral. A product of the aggregate glands, this glycoprotein(s) occurs as discrete nodules along the core fibers of the adhesive spiral, within the viscid, aqueous droplets.The glycoprotein preparation has a high apparent molecular weight (> 200 kDa) and is polydisperse. The only monosaccharide constituent identified by gas-liquid chromatography or in lectin studies is N-acetylgalactosamine and this is at least primarily O-linked to threonine. By electron microscopy, linear, unbranched and apparently flexible filaments are observed. Phosphorylated serine and threonine residues are present in the preparation and glycine, proline and threonine together account for about 57 mole % of the preparation's amino acid content. Thus, in some, but not all, respects, this glycoprotein preparation is reminiscent of a secretory mucin.
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