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Volumn 111, Issue 11, 2014, Pages 2326-2337

Effects of shear stress pattern and magnitude on mesenchymal transformation and invasion of aortic valve endothelial cells

Author keywords

3D culture; Endothelial to mesenchymal transformation; Inflammation; Side specific

Indexed keywords

BIOREACTORS; BLOOD VESSELS; CELL ENGINEERING; CELLS; CYTOLOGY; GENE EXPRESSION; HEMODYNAMICS; PATHOLOGY; PHYSIOLOGICAL MODELS; PHYSIOLOGY; SHEAR FLOW; SHEAR STRESS; TISSUE; TISSUE ENGINEERING;

EID: 84925248678     PISSN: 00063592     EISSN: 10970290     Source Type: Journal    
DOI: 10.1002/bit.25291     Document Type: Article
Times cited : (115)

References (53)
  • 2
    • 0036372929 scopus 로고    scopus 로고
    • Gene expression profiling of human aortic endothelial cells exposed to disturbed flow and steady laminar flow
    • Brooks AR, Lelkes PI, Rubanyi GM. 2002. Gene expression profiling of human aortic endothelial cells exposed to disturbed flow and steady laminar flow. Physiol Genomics 9(1):27-41.
    • (2002) Physiol Genomics , vol.9 , Issue.1 , pp. 27-41
    • Brooks, A.R.1    Lelkes, P.I.2    Rubanyi, G.M.3
  • 3
    • 1842431062 scopus 로고    scopus 로고
    • Gene expression profiling of vascular endothelial cells exposed to fluid mechanical forces: Relevance for focal susceptibility to atherosclerosis
    • Brooks AR, Lelkes PI, Rubanyi GM. 2004. Gene expression profiling of vascular endothelial cells exposed to fluid mechanical forces: Relevance for focal susceptibility to atherosclerosis. Endothelium 11(1):45-57.
    • (2004) Endothelium , vol.11 , Issue.1 , pp. 45-57
    • Brooks, A.R.1    Lelkes, P.I.2    Rubanyi, G.M.3
  • 4
    • 79957869196 scopus 로고    scopus 로고
    • Aortic valve disease and treatment: The need for naturally engineered solutions
    • Butcher JT, Mahler GJ, Hockaday LA. 2011. Aortic valve disease and treatment: The need for naturally engineered solutions. Adv Drug Deliv Rev 63(4-5):242-268.
    • (2011) Adv Drug Deliv Rev , vol.63 , Issue.4-5 , pp. 242-268
    • Butcher, J.T.1    Mahler, G.J.2    Hockaday, L.A.3
  • 5
    • 33646564670 scopus 로고    scopus 로고
    • Valvular endothelial cells regulate the phenotype of interstitial cells in co-culture: Effects of steady shear stress
    • Butcher JT, Nerem RM. 2006. Valvular endothelial cells regulate the phenotype of interstitial cells in co-culture: Effects of steady shear stress. Tissue Eng 12(4):905-915.
    • (2006) Tissue Eng , vol.12 , Issue.4 , pp. 905-915
    • Butcher, J.T.1    Nerem, R.M.2
  • 6
    • 34547593732 scopus 로고    scopus 로고
    • Valvular endothelial cells and the mechanoregulation of valvular pathology
    • Butcher JT, Nerem RM. 2007. Valvular endothelial cells and the mechanoregulation of valvular pathology. Philos Trans R Soc Lond B Biol Sci 362(1484):1445-1457.
    • (2007) Philos Trans R Soc Lond B Biol Sci , vol.362 , Issue.1484 , pp. 1445-1457
    • Butcher, J.T.1    Nerem, R.M.2
  • 7
    • 3943101416 scopus 로고    scopus 로고
    • Unique morphology and focal adhesion development of valvular endothelial cells in static and fluid flow environments
    • Butcher JT, Penrod AM, Garcia AJ, Nerem RM. 2004. Unique morphology and focal adhesion development of valvular endothelial cells in static and fluid flow environments. Arterioscler Thromb Vasc Biol 24(8):1429-1434.
    • (2004) Arterioscler Thromb Vasc Biol , vol.24 , Issue.8 , pp. 1429-1434
    • Butcher, J.T.1    Penrod, A.M.2    Garcia, A.J.3    Nerem, R.M.4
  • 8
    • 33644831129 scopus 로고    scopus 로고
    • Transcriptional profiles of valvular and vascular endothelial cells reveal phenotypic differences: Influence of shear stress
    • Butcher JT, Tressel S, Johnson T, Turner D, Sorescu G, Jo H, Nerem RM. 2006. Transcriptional profiles of valvular and vascular endothelial cells reveal phenotypic differences: Influence of shear stress. Arterioscler Thromb Vasc Biol 26(1):69-77.
    • (2006) Arterioscler Thromb Vasc Biol , vol.26 , Issue.1 , pp. 69-77
    • Butcher, J.T.1    Tressel, S.2    Johnson, T.3    Turner, D.4    Sorescu, G.5    Jo, H.6    Nerem, R.M.7
  • 9
    • 0032559834 scopus 로고    scopus 로고
    • Oscillatory shear stress stimulates adhesion molecule expression in cultured human endothelium
    • Chappell DC, Varner SE, Nerem RM, Medford RM, Alexander RW. 1998. Oscillatory shear stress stimulates adhesion molecule expression in cultured human endothelium. Circ Res 82(5):532-539.
    • (1998) Circ Res , vol.82 , Issue.5 , pp. 532-539
    • Chappell, D.C.1    Varner, S.E.2    Nerem, R.M.3    Medford, R.M.4    Alexander, R.W.5
  • 10
    • 84879935337 scopus 로고    scopus 로고
    • Cardiac-like flow generator for long-term imaging of endothelial cell responses to circulatory pulsatile flow at microscale
    • Chen H, Cornwell J, Zhang H, Lim T, Resurreccion R, Port T, Rosengarten G, Nordon RE. 2013a. Cardiac-like flow generator for long-term imaging of endothelial cell responses to circulatory pulsatile flow at microscale. Lab Chip 13(15):2999-3007.
    • (2013) Lab Chip , vol.13 , Issue.15 , pp. 2999-3007
    • Chen, H.1    Cornwell, J.2    Zhang, H.3    Lim, T.4    Resurreccion, R.5    Port, T.6    Rosengarten, G.7    Nordon, R.E.8
  • 11
    • 84878635008 scopus 로고    scopus 로고
    • A 3D microfluidic platform incorporating methacrylated gelatin hydrogels to study physiological cardiovascular cell-cell interactions
    • Chen MB, Srigunapalan S, Wheeler AR, Simmons CA. 2013b. A 3D microfluidic platform incorporating methacrylated gelatin hydrogels to study physiological cardiovascular cell-cell interactions. Lab Chip 13(13):2591-2598.
    • (2013) Lab Chip , vol.13 , Issue.13 , pp. 2591-2598
    • Chen, M.B.1    Srigunapalan, S.2    Wheeler, A.R.3    Simmons, C.A.4
  • 12
    • 78751652828 scopus 로고    scopus 로고
    • Effects of disturbed flow on vascular endothelium: Pathophysiological basis and clinical perspectives
    • Chiu J-J, Chien S. 2011. Effects of disturbed flow on vascular endothelium: Pathophysiological basis and clinical perspectives. Physiol Rev 91(1):327-387.
    • (2011) Physiol Rev , vol.91 , Issue.1 , pp. 327-387
    • Chiu, J.-J.1    Chien, S.2
  • 14
    • 0026497093 scopus 로고
    • Anatomy of aortic heart valve leaflets: The influence of glutaraldehyde fixation on function
    • Suppl 1
    • Christie GW. 1992. Anatomy of aortic heart valve leaflets: The influence of glutaraldehyde fixation on function. Eur J Cardiothorac Surg 6(Suppl 1):S25-S33.
    • (1992) Eur J Cardiothorac Surg , vol.6 , pp. S25-S33
    • Christie, G.W.1
  • 16
    • 0032104153 scopus 로고    scopus 로고
    • Oscillatory and steady laminar shear stress differentially affect human endothelial redox state: Role of a superoxide-producing NADH oxidase
    • De Keulenaer GW, Chappell DC, Ishizaka N, Nerem RM, Alexander RW, Griendling KK. 1998. Oscillatory and steady laminar shear stress differentially affect human endothelial redox state: Role of a superoxide-producing NADH oxidase. Circ Res 82(10):1094-1101.
    • (1998) Circ Res , vol.82 , Issue.10 , pp. 1094-1101
    • De Keulenaer, G.W.1    Chappell, D.C.2    Ishizaka, N.3    Nerem, R.M.4    Alexander, R.W.5    Griendling, K.K.6
  • 18
    • 80355133049 scopus 로고    scopus 로고
    • Isolation of valvular endothelial cells
    • e2158)
    • Gould RA, Butcher JT. 2010. Isolation of valvular endothelial cells. J Vis Exp 46(e2158):doi: 10.3791/2158
    • (2010) J Vis Exp , vol.46
    • Gould, R.A.1    Butcher, J.T.2
  • 21
    • 0022449843 scopus 로고
    • Correlation of endothelial cell shape and wall shear stress in a stenosed dog aorta
    • Levesque MJ, Liepsch D, Moravec S, Nerem RM. 1986. Correlation of endothelial cell shape and wall shear stress in a stenosed dog aorta. Arteriosclerosis 6(2):220-229.
    • (1986) Arteriosclerosis , vol.6 , Issue.2 , pp. 220-229
    • Levesque, M.J.1    Liepsch, D.2    Moravec, S.3    Nerem, R.M.4
  • 23
    • 84871737124 scopus 로고    scopus 로고
    • Inflammatory cytokines promote mesenchymal transformation in embryonic and adult valve endothelial cells
    • Mahler GJ, Farrar EJ, Butcher JT. 2013. Inflammatory cytokines promote mesenchymal transformation in embryonic and adult valve endothelial cells. Arterioscler Thromb Vasc Biol 33:121-130.
    • (2013) Arterioscler Thromb Vasc Biol , vol.33 , pp. 121-130
    • Mahler, G.J.1    Farrar, E.J.2    Butcher, J.T.3
  • 24
    • 80355143988 scopus 로고    scopus 로고
    • Isolation and culture of avian embryonic valvular progenitor cells
    • e2159
    • Mahler GJ, Gould RA, Butcher JT. 2010. Isolation and culture of avian embryonic valvular progenitor cells. J Vis Exp 44(e2159):doi: 10.3791/2159
    • (2010) J Vis Exp , vol.44
    • Mahler, G.J.1    Gould, R.A.2    Butcher, J.T.3
  • 25
    • 0033485806 scopus 로고    scopus 로고
    • Hemodynamic shear stress and its role in atherosclerosis
    • Malek AM, Alper SL, Izumo S. 1999. Hemodynamic shear stress and its role in atherosclerosis. JAMA 282(21):2035-2042.
    • (1999) JAMA , vol.282 , Issue.21 , pp. 2035-2042
    • Malek, A.M.1    Alper, S.L.2    Izumo, S.3
  • 26
    • 0017355845 scopus 로고
    • Structural development of endocardial cushions
    • Markwald RR, Fitzharris TP, Manasek FJ. 1977. Structural development of endocardial cushions. Am J Anat 148(1):85-119.
    • (1977) Am J Anat , vol.148 , Issue.1 , pp. 85-119
    • Markwald, R.R.1    Fitzharris, T.P.2    Manasek, F.J.3
  • 27
    • 0016590595 scopus 로고
    • Sturctural analysis of endocardial cytodifferentiation
    • Markwald RR, Fitzharris TP, Smith WN. 1975. Sturctural analysis of endocardial cytodifferentiation. Dev Biol 42(1):160-180.
    • (1975) Dev Biol , vol.42 , Issue.1 , pp. 160-180
    • Markwald, R.R.1    Fitzharris, T.P.2    Smith, W.N.3
  • 28
    • 0034641588 scopus 로고    scopus 로고
    • Are atherosclerotic processes involved in aortic-valve calcification
    • Mohler ER III. 2000. Are atherosclerotic processes involved in aortic-valve calcification? Lancet 356(9229):524-525.
    • (2000) Lancet , vol.356 , Issue.9229 , pp. 524-525
    • Mohler, E.R.1
  • 29
    • 9344271129 scopus 로고    scopus 로고
    • Mechanisms of aortic valve calcification
    • A6
    • Mohler ER III. 2004. Mechanisms of aortic valve calcification. Am J Cardiol 94(11):1396-1402, A6.
    • (2004) Am J Cardiol , vol.94 , Issue.11 , pp. 1396-1402
    • Mohler, E.R.1
  • 31
    • 80053630634 scopus 로고    scopus 로고
    • (Micro)managing the mechanical microenvironment
    • Moraes C, Sun Y, Simmons CA. 2011. (Micro)managing the mechanical microenvironment. Integr Biol 3(10):959-971.
    • (2011) Integr Biol , vol.3 , Issue.10 , pp. 959-971
    • Moraes, C.1    Sun, Y.2    Simmons, C.A.3
  • 32
    • 0031011870 scopus 로고    scopus 로고
    • Expression of smooth muscle alpha-actin in mesenchymal cells during formation of avian endocardial cushion tissue: A role for transforming growth factor b3
    • Nakajima Y, Mironov V, Yamagishi T, Nakamura H, Markwald RR. 1997. Expression of smooth muscle alpha-actin in mesenchymal cells during formation of avian endocardial cushion tissue: A role for transforming growth factor b3. Dev Dyn 209(3):296-309.
    • (1997) Dev Dyn , vol.209 , Issue.3 , pp. 296-309
    • Nakajima, Y.1    Mironov, V.2    Yamagishi, T.3    Nakamura, H.4    Markwald, R.R.5
  • 33
    • 0023492256 scopus 로고
    • Flush mounted hot film anemometer measurement of wall shear stress distal to a tri-leaflet valve for Newtonian and non-Newtonian blood analog fluids
    • Nandy S, Tarbell JM. 1987. Flush mounted hot film anemometer measurement of wall shear stress distal to a tri-leaflet valve for Newtonian and non-Newtonian blood analog fluids. Biorheology 24(5):483-500.
    • (1987) Biorheology , vol.24 , Issue.5 , pp. 483-500
    • Nandy, S.1    Tarbell, J.M.2
  • 34
    • 33750520931 scopus 로고    scopus 로고
    • Matrix-specific suppression of integrin activation in shear stress signaling
    • Orr AW, Ginsberg MH, Shattil SJ, Deckmyn H, Schwartz MA. 2006. Matrix-specific suppression of integrin activation in shear stress signaling. Mol Biol Cell 17(11):4686-4697.
    • (2006) Mol Biol Cell , vol.17 , Issue.11 , pp. 4686-4697
    • Orr, A.W.1    Ginsberg, M.H.2    Shattil, S.J.3    Deckmyn, H.4    Schwartz, M.A.5
  • 35
    • 0034800126 scopus 로고    scopus 로고
    • Aortic valve endothelial cells undergo transforming growth factor-b-mediated and non-transforming growth factor-b-mediated transdifferentiation in vitro
    • Paranya G, Vineberg S, Dvorin E, Kaushal S, Roth SJ, Rabkin E, Schoen FJ, Bischoff J. 2001. Aortic valve endothelial cells undergo transforming growth factor-b-mediated and non-transforming growth factor-b-mediated transdifferentiation in vitro. Am J Pathol 159(4):1335-1343.
    • (2001) Am J Pathol , vol.159 , Issue.4 , pp. 1335-1343
    • Paranya, G.1    Vineberg, S.2    Dvorin, E.3    Kaushal, S.4    Roth, S.J.5    Rabkin, E.6    Schoen, F.J.7    Bischoff, J.8
  • 37
    • 0021919134 scopus 로고
    • Surface responses of aortic valve endothelia from diet-induced, hypercholesterolemic rabbits
    • Sarphie TG. 1985. Surface responses of aortic valve endothelia from diet-induced, hypercholesterolemic rabbits. Atherosclerosis 54(3):283-299.
    • (1985) Atherosclerosis , vol.54 , Issue.3 , pp. 283-299
    • Sarphie, T.G.1
  • 38
    • 84863205849 scopus 로고    scopus 로고
    • NIH Image to ImageJ: 25 years of image analysis
    • Schneider CA, Rasband WS, Eliceiri KW. 2012. NIH Image to ImageJ: 25 years of image analysis. Nat Methods 9(7):671-675.
    • (2012) Nat Methods , vol.9 , Issue.7 , pp. 671-675
    • Schneider, C.A.1    Rasband, W.S.2    Eliceiri, K.W.3
  • 39
    • 0019454624 scopus 로고
    • Tissue and cell renewal in the natural aortic valve of rats: An autoradiographic study
    • Schneider PJ, Deck JD. 1981. Tissue and cell renewal in the natural aortic valve of rats: An autoradiographic study. Cardiovasc Res 15(4):181-189.
    • (1981) Cardiovasc Res , vol.15 , Issue.4 , pp. 181-189
    • Schneider, P.J.1    Deck, J.D.2
  • 40
    • 84867185117 scopus 로고    scopus 로고
    • A novel technique for quantifying mouse heart valve leaflet stiffness with atomic force microscopy
    • Sewell-Loftin MK, Brown CB, Baldwin HS, Merryman WD. 2012. A novel technique for quantifying mouse heart valve leaflet stiffness with atomic force microscopy. J Heart Valve Dis 21(4):513-520.
    • (2012) J Heart Valve Dis , vol.21 , Issue.4 , pp. 513-520
    • Sewell-Loftin, M.K.1    Brown, C.B.2    Baldwin, H.S.3    Merryman, W.D.4
  • 41
    • 70350442774 scopus 로고    scopus 로고
    • Integrated microfluidic chip for endothelial cells culture and analysis exposed to a pulsatile and oscillatory shear stress
    • Shao J, Wu L, Wu J, Zheng Y, Zhao H, Jin Q, Zhao J. 2009. Integrated microfluidic chip for endothelial cells culture and analysis exposed to a pulsatile and oscillatory shear stress. Lab Chip 9(21):3118-3125.
    • (2009) Lab Chip , vol.9 , Issue.21 , pp. 3118-3125
    • Shao, J.1    Wu, L.2    Wu, J.3    Zheng, Y.4    Zhao, H.5    Jin, Q.6    Zhao, J.7
  • 42
    • 6344283050 scopus 로고    scopus 로고
    • Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress induces monocyte adhesion by stimulating reactive oxygen species production from a Nox1-based NADPH oxidase
    • Sorescu GP, Song H, Tressel SL, Hwang J, Dikalov S, Smith DA, Boyd NL, Platt MO, Lassegue B, Griendling KK, Jo H. 2004. Bone morphogenic protein 4 produced in endothelial cells by oscillatory shear stress induces monocyte adhesion by stimulating reactive oxygen species production from a Nox1-based NADPH oxidase. Circ Res 95(8):773-779.
    • (2004) Circ Res , vol.95 , Issue.8 , pp. 773-779
    • Sorescu, G.P.1    Song, H.2    Tressel, S.L.3    Hwang, J.4    Dikalov, S.5    Smith, D.A.6    Boyd, N.L.7    Platt, M.O.8    Lassegue, B.9    Griendling, K.K.10    Jo, H.11
  • 43
    • 59449104824 scopus 로고    scopus 로고
    • Altered shear stress stimulates upregulation of endothelial VCAM-1 and ICAM-1 in a BMP-4 and TGF-b1-dependent pathway
    • Sucosky P, Balachandran K, Elhammali A, Jo H, Yoganathan AP. 2009. Altered shear stress stimulates upregulation of endothelial VCAM-1 and ICAM-1 in a BMP-4 and TGF-b1-dependent pathway. Arterioscler Thromb Vasc Biol 29(2):254-260.
    • (2009) Arterioscler Thromb Vasc Biol , vol.29 , Issue.2 , pp. 254-260
    • Sucosky, P.1    Balachandran, K.2    Elhammali, A.3    Jo, H.4    Yoganathan, A.P.5
  • 44
    • 0035119612 scopus 로고    scopus 로고
    • Messenger-RNA expression of matrix metalloproteinases, tissue inhibitors of metalloproteinases, and transcription factors in rheumatic synovial cells under mechanical stimuli
    • Sun HB, Yokota H. 2001. Messenger-RNA expression of matrix metalloproteinases, tissue inhibitors of metalloproteinases, and transcription factors in rheumatic synovial cells under mechanical stimuli. Bone 28(3):303-309.
    • (2001) Bone , vol.28 , Issue.3 , pp. 303-309
    • Sun, H.B.1    Yokota, H.2
  • 45
    • 84857489355 scopus 로고    scopus 로고
    • TGF-{beta} Signaling in endothelial-to-mesenchymal transition: The role of shear stress and primary cilia
    • ten Dijke P, Egorova AD, Goumans M-JTH, Poelmann RE, Hierck BP. 2012. TGF-{beta} Signaling in endothelial-to-mesenchymal transition: The role of shear stress and primary cilia. Sci Signal 5(212):pt2.
    • (2012) Sci Signal , vol.5 , Issue.212 , pp. pt2
    • ten Dijke, P.1    Egorova, A.D.2    Goumans, M.-J.3    Poelmann, R.E.4    Hierck, B.P.5
  • 47
    • 0345055316 scopus 로고    scopus 로고
    • The role of elastin in aortic valve mechanics
    • Vesely I. 1997. The role of elastin in aortic valve mechanics. J Biomech 31(2):115-123.
    • (1997) J Biomech , vol.31 , Issue.2 , pp. 115-123
    • Vesely, I.1
  • 48
    • 0026575408 scopus 로고
    • Micromechanics of the fibrosa and the ventricularis in aortic valve leaflets
    • Vesely I, Noseworthy R. 1992. Micromechanics of the fibrosa and the ventricularis in aortic valve leaflets. J Biomech 25(1):101-113.
    • (1992) J Biomech , vol.25 , Issue.1 , pp. 101-113
    • Vesely, I.1    Noseworthy, R.2
  • 49
    • 52649129923 scopus 로고    scopus 로고
    • Design, fabrication and implementation of a novel multi-parameter control microfluidic platform for three-dimensional cell culture and real-time imaging
    • Vickerman V, Blundo J, Chung S, Kamm R. 2008. Design, fabrication and implementation of a novel multi-parameter control microfluidic platform for three-dimensional cell culture and real-time imaging. Lab Chip 8(9):1468-1477.
    • (2008) Lab Chip , vol.8 , Issue.9 , pp. 1468-1477
    • Vickerman, V.1    Blundo, J.2    Chung, S.3    Kamm, R.4
  • 50
    • 0033159718 scopus 로고    scopus 로고
    • Estimation of the shear stress on the surface of an aortic valve leaflet
    • Weston MW, LaBorde DV, Yoganathan AP. 1999. Estimation of the shear stress on the surface of an aortic valve leaflet. Ann Biomed Eng 27(4):572-579.
    • (1999) Ann Biomed Eng , vol.27 , Issue.4 , pp. 572-579
    • Weston, M.W.1    LaBorde, D.V.2    Yoganathan, A.P.3
  • 51
    • 84859897858 scopus 로고    scopus 로고
    • Experimental measurement of dynamic fluid shear stress on the aortic surface of the aortic valve leaflet
    • Yap C, Saikrishnan N, Tamilselvan G, Yoganathan A. 2012a. Experimental measurement of dynamic fluid shear stress on the aortic surface of the aortic valve leaflet. Biomech Model Mechanobiol 11(1-2):171-182.
    • (2012) Biomech Model Mechanobiol , vol.11 , Issue.1-2 , pp. 171-182
    • Yap, C.1    Saikrishnan, N.2    Tamilselvan, G.3    Yoganathan, A.4
  • 52
    • 84859889118 scopus 로고    scopus 로고
    • Experimental measurement of dynamic fluid shear stress on the ventricular surface of the aortic valve leaflet
    • Yap C, Saikrishnan N, Yoganathan A. 2012b. Experimental measurement of dynamic fluid shear stress on the ventricular surface of the aortic valve leaflet. Biomech Model Mechanobiol 11(1-2):231-244.
    • (2012) Biomech Model Mechanobiol , vol.11 , Issue.1-2 , pp. 231-244
    • Yap, C.1    Saikrishnan, N.2    Yoganathan, A.3
  • 53
    • 79251613628 scopus 로고    scopus 로고
    • Measurement of layer-specific mechanical properties in multilayered biomaterials by micropipette aspiration
    • Zhao R, Sider KL, Simmons CA. 2011. Measurement of layer-specific mechanical properties in multilayered biomaterials by micropipette aspiration. Acta Biomater 7(3):1220-1227.
    • (2011) Acta Biomater , vol.7 , Issue.3 , pp. 1220-1227
    • Zhao, R.1    Sider, K.L.2    Simmons, C.A.3


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