Ординатура / Офтальмология / Английские материалы / Retinal and Choroidal Angiogenesis_Penn_2008

growth factor in an in vitro quantitative microcarrier-based three-dimensional fibrin angiogenesis system, World J. Gastroenterol. 10, 2524-2528 (2004).

39.Y. Hata, S. L. Rook, and L. P. Aiello, Basic fibroblast growth factor induces expression of VEGF receptor KDR through a protein kinase C and p44/42 mitogen-activated protein kinase-dependent pathway, Diabetes 48, 1145-1155 (1999).

40.B. Nico, G. de Falco, A. Vacca, L. Roncali, and D. Ribatti, In vivo absence of synergism between fibroblast growth factor-2 and vascular endothelial growth factor, J. Hematother. Stem Cell Res. 10, 905-912 (2001).

41.L. E. H. Smith, W. Shen, C. Perruzzi, S. Soker, F. Kinose, X. Xu, G. Robinson, S. Driver,

J.Bischoff, B. Zhang, J. M. Schaeffer, and D. R. Senger, Regulation of vascular endothelial growth factor-dependent retinal neovascularization by insulin-like growth factor-1 receptor, Nat. Med. 5, 1390-1395 (1999).

42.R. O. Dull, J. Yuan, Y. S. Chang, J. Tarbell, R. K. Jain, and L. L. Munn, Kinetics of placenta growth factor/vascular endothelial growth factor synergy in endothelial hydraulic conductivity and proliferation, Microvasc. Res. 61, 203-210 (2001).

43.M. S. Pepper, S. J. Mandriota, M. Jeltsch, V. Kumar, and K. Alitalo, Vascular endothelial growth factor (VEGF)-C synergizes with basic fibroblast growth factor and VEGF in the induction of angiogenesis in vitro and alters endothelial cell extracellular proteolytic activity, J. Cell. Physiol. 177, 439-452 (1998).

44.Y. G. Yao, H. S. Yang, Z. C. Cao, J. Danielsson, and E. J. Duh, Upregulation of placental growth factor by vascular endothelial growth factor via a post-transcriptional mechanism, FEBS Lett. 579, 1227-1234 (2005).

45.L. Xue and H. P. Greisler, Angiogenic effect of fibroblast growth factor-1 and vascular endothelial growth factor and their synergism in a novel in vitro quantitative fibrin-based 3-dimensional angiogenesis system, Surgery 132, 259-267 (2002).

46.E. Van Belle, B. Witzenbichler, D. Chen, M. Silver, L. Chang, R. Schwall, and J. M. Isner, Potentiated angiogenic effect of scatter factor/hepatocyte growth factor via induction of vascular endothelial growth factor. The case for paracrine amplification of angiogenesis, Circulation 97, 381-390 (1998).

47.M. E. Gerritsen, J. E. Tomlinson, C. Zlot, M. Ziman, and S. Hwang, Using gene expression profiling to identify the molecular basis of the synergistic actions of hepatocyte growth factor and vascular endothelial growth factor in human endothelial cells, Br. J. Pharmacol. 140, 595-610 (2003).

48.M. Beilmann, G. Birk, and M. C. Lenter, Human primary co-culture angiogenesis assay reveals additive stimulation and different angiogenic properties of VEGF and HGF, Cytokine 26, 178-185 (2004).

49.X. Xin, S. Yang, G. Ingle, C. Zlot, L. Rangell, J. Kowalski, R. Schwall, N. Ferrara, and

M.E. Gerritsen, Hepatocyte growth factor enhances vascular endothelial growth factorinduced angiogenesis in vitro and in vivo, Am. J. Pathol. 158 (3), 1111-1120 (2001).

50.X. Xiao, J. Liu, and M. Sheng, Synergistic effect of estrogen and VEGF on the proliferation of hemangioma vascular endothelial cells, J. Pediatr. Surg. 39, 1107-1110 (2004).

51.I. Kryszek, A. Lange, P. Mottram, X. Alvarez, P. Cheng, M. Hogan, L. Moons, S. Wei,

L.Zou, V. Machelon, D. Emilie, M. Terrassa, A. Lackner, T. J. Curiel, P. Carmeliet, and

W.Zou, CXCL12 and vascular endothelial growth factor synergistically induce neoangiogenesis in human ovarian cancers, Cancer Res. 65, 465-472 (2005).

52.H. L. Brooks, Jr., S. Caballero, Jr., C. K. Newell, R. L. Steinmetz, D. Watson, M. S. Segal,

J.K. Harrison, E. W. Scott, and M. B. Grant, Vitreous levels of vascular endothelial growth factor and stromal-derived factor 1 in patients with diabetic retinopathy and

cystoid macular edema before and after intraocular injection of triamcinolone, Arch. Ophthalmol. 122, 1801-1807 (2004).

53.J. M. Butler, S. M. Guthrie, M. Koc, A. Afzal, S. Caballero, H. L. Brooks, R. N. Mames,

M.S. Segal, M. B. Grant, and E. W. Scott, SDF-1 is both necessary and sufficient to promote proliferative retinopathy, J. Clin. Invest. 115, 86-93 (2005).

54.Y. Oshima, T. Deering, S. Oshima, H. Nambu, P. S. Reddy, M. Kaleko, S. Connelly,

S.F. Hackett, and P. A. Campochiaro, Angiopoietin-2 enhances retinal vessel sensitivity to vascular endothelial growth factor, J. Cell. Physiol. 199, 412-417 (2004).

55.R. P. Visconti, C. D. Richardson, and T. N. Sato, Orchestration of angiogenesis and arteriovenous contribution by angiopoietins and vascular endothelial growth factor (VEGF), Proc. Natl. Acad. Sci. USA 99, 8219-8224 (2002).

56.K. G. Shyu, H. Chang, and J. M. Isner, Synergistic effect of angiopoietin-1 and vascular endothelial growth factor on neoangiogenesis in hypercholesterolemic rabbit model with acute hindlimb ischemia, Life Sci. 73, 563-579 (2003).

57.N. Arsic, L. Zentilin, S. Zacchigna, D. Santoro, G. Stanta, A. Salvi, G. Sinagra, and

M.Giacca, Induction of functional neovascularization by combined VEGF and angiopoietin-1 gene transfer using AAV vectors, Mol. Ther. 7, 450-459 (2003).

58.H. Hutchings, M. Maitre-Boube, J. Tombran-Tink, and J. Plouët, Pigment epitheliumderived factor exerts opposite effects on endothelial cells of different phenotypes,

Biochem. Biophys. Res. Commun. 294, 764-769 (2002).

59.M. Guan, C. P. Pang, H. F. Yam, K. F. Cheung, W. W. Liu, and Y. Lu, Inhibition of glioma invasion by overexpression of pigment epithelium-derived factor, Cancer Gene Ther. 11, 325-332 (2004).

60.E. J. Duh, H. S. Yang, I. Suzuma, M. Miyagi, E. Youngman, K. Mori, M. Katai, L. Yan,

K.Suzuma, K. West, S. Davarya, P. Tong, P. Gehlbach, J. Pearlman, J. W. Crabb, L. P. Aiello,

P.A. Campochiaro, and D. J. Zack, Pigment epithelium-derived factor suppresses ischemia-induced retinal neovascularization and VEGF-induced migration and growth,

Invest. Ophthalmol. Vis. Sci. 43, 821-829 (2002).

61.K. Takenaka, S. I. Yamagishi, Y. Jinnouchi, K. Nakamura, T. Matsui, and T. Imaizumi, Pigment epithelium-derived factor (PEDF)-induced apoptosis and inhibition of vascular endothelial growth factor (VEGF) expression in MG63 human osteosarcoma cells, Life Sci. 77 (25), 3231-3241 (2005).

62.C. K. Chan, L. N. Pham, J. Zhou, C. Spee, S. J. Ryan, and D. R. Hinton, Differential expression of proand antiangiogenic factors in mouse strain-dependent hypoxia-induced retinal neovascularization, Lab. Invest. 85, 721-733 (2005).

63.F. Ishikawa, K. Miyazono, U. Hellman, H. Drexler, C. Wernstedt, K. Hagiwara,

K.Usuki, F. Takaku, W. Risau, and C. H. Heldin, Identification of angiogenic activity and the cloning and expression of platelet-derived endothelial cell growth factor, Nature 338, 557-562 (1989).

64.W. Risau, H. Drexler, V. Mironov, A. Smits, A. Siegbahn, K. Funa, and C. H. Heldin, Platelet-derived growth factor is angiogenic in vivo, Growth Factors 7, 261-266 (1992).

65.X. Li, M. Tjwa, L. Moons, P. Fons, A. Noel, A. Ny, J. M. Zhou, J. Lennartsson, H. Li,

A.Luttun, A. Ponten, L. Devy, A. Bouche, H. Oh, A. Manderveld, S. Blacher, D. Communi,

P.Savi, F. Bono, M. Dewerchin, J. M. Foidart, M. Autiero, J. M. Herbert, D. Collen,

C.H. Heldin, U. Eriksson, and P. Carmeliet, Revascularization of ischemic tissues by PDGF-CC via effects on endothelial cells and their progenitors, J. Clin. Invest. 115, 118-127 (2005).

66.X. Hao, A. Månsson-Broberg, T. Gustaffson, K. H. Grinnemo, P. Blomberg, A. J. Siddiqui,

E.Wärdell, and C. Sylvén, Angiogenic effects of dual gene transfer of bFGF and PDGF-

BBafter myocardial infarction, Biochem. Biophys. Res. Commun. 315, 1058-1063 (2004).

67.F. De Marchis, D. Ribatti, C. Giampietri, A. Lentini, D. Faraone, M. Scoccianti,

M.C. Capogrossi, and A. Facchiano, Platelet-derived growth factor inhibits basic fibroblast growth factor angiogenic properties in vitro and in vivo through its D receptor, Blood 99, 2045-2053 (2002).

68.J. L. Wilkinson-Berka, S. Babic, T. de Gooyer, A. W. Stitt, K. Jaworski, L. G. T. Ong,

D.J. Kelly, and R. E. Gilbert, Inhibition of platelet-derived growth factor promotes pericyte loss and angiogenesis in ischemic retinopathy, Am. J. Pathol. 164, 1263-1273 (2004).

69.H. Ozaki, N. Okamoto, S. Ortega, M. Chang, K. Ozaki, S. Sadda, M. A. Vinores,

N.Derevjanik, D. J. Zack, C. Basilico, and P. A. Campochiaro, Basic fibroblast growth factor is neither necessary nor sufficient for the development of retinal neovascularization, Am. J. Pathol. 153, 757-765 (1998).

70.S. J. Reich, J. Fosnot, A. Kuroki, W. Tang, X. Yang, A. M. Maguire, J. Bennett, and

M.J. Tolentino, Small interfering RNA (siRNA) targeting VEGF effectively inhibits ocular neovascularization in a mouse model, Mol. Vis. 9, 210-216 (2003).

71.T. Tobe, S. Ortega, J. D. Luna, H. Ozaki, N. Okamoto, N. L. Derevjanik, S. A. Vinores,

C. Basilico, and P. A. Campochiaro, Targeted disruption of the FGF2 gene does not prevent choroidal neovascularization in a murine model, Am. J. Pathol. 153, 1641-1646 (1998).

72.L. N. Ramoshebi and U. Ripamonti, Osteogenic protein-1, a bone morphogenetic protein, induces angiogenesis in the chick chorioallantoic membrane and synergizes with basic fibroblast growth factor and transforming growth factor-E1, Anat. Rec. 259, 97-107 (2000).

73.Y. M. Lee, M. H. Bae, O. H. Lee, E. J. Moon, C. K. Moon, W. H. Kim, and K. W. Kim, Synergistic induction of in vivo angiogenesis by the combination of insulin-like growth factor-II and epidermal growth factor, Oncol. Rep. 12, 843-848 (2004).

74.G. Thurston, Role of angiopoietins and Tie receptor tyrosine kinases in angiogenesis and lymphangiogenesis, Cell Tissue Res. 314, 61-68 (2003).

75.J. W. Distler, A. Hirth, M. Kurowska-Stolarska, R. E. Gay, S. Gay, and O. Distler, Angiogenic and angiostatic factors in the molecular control of angiogenesis, Q. J. Nucl. Med. 47, 149-161 (2003).

76.C. D. Ley, M. W. B. Olsen, E. L. Lund, and P. E. G. Kristjansen, Angiogenic synergy of bFGF and VEGF is antagonized by angiopoietin-2 in a modified in vivo Matrigel assay, Microvasc. Res. 68, 161-168 (2004).

77.M. Onimaru, Y. Yonemitsu, M. Tanii, K. Nakagawa, I. Masaki, S. Okano, H. Ishibashi,

K.Shirasuna, M. Hasegawa, and K. Sueishi, Fibroblast growth factor-2 gene transfer can stimulate hepatocyte growth factor expression irrespective of hypoxia-mediated downregulation in ischemic limbs, Circ. Res. 91, 923-930 (2002).

78.R. Castellon, S. Caballero, H. K. Hamdi, S. R. Atilano, A. M. Aoki, R. W. Tarnuzzer,

M.C. Kenney, M. B. Grant, and A. V. Ljubimov, Effects of tenascin-C on normal and diabetic retinal endothelial cells in culture, Invest. Ophthalmol. Vis. Sci. 43, 2758-2766 (2002).

79.K. Tanaka, N. Hiraiwa, H. Hashimoto, Y. Yamazaki, and M. Kusakabe, Tenascin-C regulates angiogenesis in tumor through the regulation of vascular endothelial growth factor expression, Int. J. Cancer 108, 31-40 (2004).

80.P. Nyberg, L. Xie, and R. Kalluri, Endogenous inhibitors of angiogenesis, Cancer Res. 65, 3967-3979 (2005).

81.J. Dixelius, L. Jacobsson, E. Genersch, S. Bohman, P. Ekblom, and L. Claesson-Welsh, Laminin-1 promotes angiogenesis in synergy with fibroblast growth factor by distinct

regulation of the gene and protein expression profile in endothelial cells, J. Biol. Chem. 279, 23766-23772 (2004).

82.J. Sottile, Regulation of angiogenesis by extracellular matrix, Biochim. Biophys. Acta. 1654, 13-22 (2004).

83.Y. Yokoyama, M. Dhanabal, A. W. Griffioen, V. P. Sukhatme, and S. Ramakrishnan,

Synergy between angiostatin and endostatin: inhibition of ovarian cancer growth, Cancer Res. 60, 2190-2196 (2000).

84. S. Filleur, A. Courtin, S. Ait-Si-Ali, J. Guglielmi, C. Merle, A. Harel-Bellan,

P.Clézardin, and F. Cabon, SiRNA-mediated inhibition of vascular endothelial growth factor severely limits tumor resistance to antiangiogenic thrombospondin-1 and slows tumor vascularization and growth, Cancer Res. 63, 3919-3922 (2003).

85.M. Nozaki, E. Sakurai, B. J. Raisler, J. Z. Baffi, J. Witta, Y. Ogura, R. A. Brekken,

E.H. Sage, B. K. Ambati, and J. Ambati, Loss of SPARC-mediated VEGFR-1 suppression after injury reveals a novel antiangiogenic activity of VEGF-A, J. Clin. Invest. 116, 422-429 (2006).

86.N. Ortéga, H. Hutchings, and J. Plouët, Signal relays in the VEGF system, Front. Biosci. 4, D141-D152 (1999).

87.S. Rakhit, S. Pyne, and N. J. Pyne, The platelet-derived growth factor receptor stimulation of p42/p44 mitogen-activated protein kinase in airway smooth muscle involves a G-protein-mediated tyrosine phosphorylation of Gab1, Mol. Pharmacol. 58, 413-420 (2000).

88.M. A. Lawlor and P. Rotwein, Coordinate control of muscle cell survival by distinct insulin-like growth factor activated signaling pathways, J. Cell Biol. 151, 1131-1140 (2000).

89.J. Woolard, W. Y. Wang, H. S. Bevan, Y. Qiu, L. Morbidelli, R. O. Pritchard-Jones, T. G. Cui,

M.Sugiono, E. Waine, R. Perrin, R. Foster, J. Digby-Bell, J. D. Shields, C. E. Whittles,

R. E. Mushens, D. A. Gillatt, M. Ziche, S. J. Harper, and D. O. Bates, VEGF165b, an inhibitory vascular endothelial growth factor splice variant. Mechanism of action, in vivo effect on angiogenesis and endogenous protein expression, Cancer Res. 64, 7822-7835 (2004).

90.J. Schoenfeld, K. Lessan, N. A. Johnson, D. S. Charnock-Jones, A. Evans, E. Vourvouhaki,

L.Scott, R. Stephens, T. C. Freeman, S. A. Saidi, B. Tom, G. C. Weston, P. Rogers,

S.K. Smith, and C. G. Print, Bioinformatic analysis of primary endothelial cell gene array data illustrated by the analysis of transcriptome changes in endothelial cells exposed to VEGF-A and PlGF, Angiogenesis 7, 143-156 (2004).

91.E. I. Cline, S. Bicciato, C. DiBello, and M. W. Lingen, Prediction of in vivo synergistic activity of antiangiogenic compounds by gene expression profiling, Cancer Res. 62, 7143-7148 (2002).

92.R. L. Bilton and G. W. Booker, The subtle side to hypoxia inducible factor (HIFD) regulation, Eur. J. Biochem. 270, 791-798 (2003).

93.B. D. Kelly, S. F. Hackett, K. Hirota, Y. Oshima, Z. Cai, S. Berg-Dixon, A. Rowan,

Z.Yan, P. A. Campochiaro, and G. L. Semenza, Cell type-specific regulation of angiogenic growth factor gene expression and induction of angiogenesis in nonischemic tissue by a constitutively active form of hypoxia-inducible factor 1, Circ. Res. 93, 1074-1081 (2003).

94.T. H. Patel, H. Kimura, C. R. Weiss, G. L. Semenza, and L. V. Hofmann, Constitutively active HIF-1D improves perfusion and arterial remodeling in an endovascular model of limb ischemia, Cardiovasc. Res. 68 (1), 144-154 (2005).

95.B. Wang, Y. Zou, H. Li, H. Yan, J. S. Pan, and Z. L. Yuan, Genistein inhibited retinal neovascularization and expression of vascular endothelial growth factor and hypoxia

inducible factor 1alpha in a mouse model of oxygen-induced retinopathy, J. Ocul. Pharmacol. Ther. 21, 107-113 (2005).

96.A. V. Ljubimov, S. Caballero, A. M. Aoki, L. A. Pinna, M. B. Grant, and R. Castellon, Involvement of protein kinase CK2 in angiogenesis and retinal neovascularization, Invest. Ophthalmol. Vis. Sci. 45, 4583-4591 (2004).

97.D. Mottet, S. P. Ruys, C. Demazy, M. Raes, and C. Michiels, Role for casein kinase 2 in the regulation of HIF-1 activity, Int. J. Cancer 117, 764-774 (2005).

98.A. Baldysiak-Figiel, G. K. Lang, J. Kampmeier, and G. E. Lang, Octreotide prevents growth factor-induced proliferation of bovine retinal endothelial cells under hypoxia,

J.Endocrinol. 180, 417-424 (2004).

99.M. B. Grant, R. N. Mames, C. Fitzgerald, K. M. Hazariwala, R. Cooper-DeHoff,

S.Caballero, and K. S. Estes, The efficacy of octreotide in the therapy of severe nonproliferative and early proliferative diabetic retinopathy: a randomized controlled study, Diabetes Care 23, 504-509 (2000).

100.A. A. Kramerov, M. Saghizadeh, H. Pan, A. Kabosova, M. Montenarh, K. Ahmed,

J.S. Penn, C. K. Chan, D. R. Hinton, M. B. Grant, and A. V. Ljubimov, Expression of protein kinase CK2 in astroglial cells of normal and neovascularized retina, Am. J. Pathol. 168, 1722-1736 (2006).

101.N. Jo, C. Mailhos, M. Ju, E. Cheung, J. Bradley, K. Nishijima, G. S. Robinson,

A.P. Adamis, and D. T. Shima, Inhibition of platelet-derived growth factor B signaling enhances the efficacy of anti-vascular endothelial growth factor therapy in multiple models of ocular neovascularization, Am. J. Pathol. 168, 2036-2053 (2006).

102.R. S. Kerbel, J. Yu, J. Tran, S. Man, A. Viloria-Petit, G. Klement, B. L. Coomber, and

J.Rak, Possible mechanisms of acquired resistance to anti-angiogenic drugs: Implications for the use of combination therapy approaches, Cancer Metastasis Revs. 20, 79-86 (2001).

Chapter 17

PIGMENT EPITHELIUM-DERIVED FACTOR AND ANGIOGENESIS

Therapeutic Implications

Juan Amaral and S. Patricia Becerra

Laboratory of Retinal Cell and Molecular Biology, National Eye Institute, National Institutes of Health, Bethesda, Maryland

1.INTRODUCTION

The development, morphogenesis and survival of the neural and vascular retina rely on growth, trophic and survival factors derived mostly from the adjacent retinal pigment epithelium (RPE). The RPE secretes pigment epithelium-derived factor (PEDF), which promotes neuronal differentiation

311

J.S. Penn (ed.), Retinal and Choroidal Angiogenesis, 311–337.

© Springer Science+Business Media B.V. 2008

and survival in the retina. More importantly, PEDF inhibits retinal and choroidal angiogenesis.1 This interesting factor is deposited extracellularly in ocular compartments where it is a protector and barrier for vessel intrusion from the choroid into the neural retina. Its importance in the development, maintenance, and function of the retina is evident in animal models for inherited and light-induced retinal degeneration, ischemiainduced retina and laser-induced choroidal neovascularization, as well as in the inverse correlation between levels of PEDF protein in patients with diabetic retinopathy (DR), age-related macular degeneration (AMD) and progression of disease.2-10 PEDF also protects neurons of the central nervous system (CNS) and prevents tumor growth and angiogenesis, broadening its effects to other systems (see below). These observations have increased interest in the use of PEDF for treatment of a diverse array of diseases involving defective neuronal differentiation, insufficient cell survival, pathological new blood vessel formation (as in retinitis pigmentosa, DR, and AMD). It has also been applied to diseases outside of the eye such as amyotrophic lateral sclerosis and rheumatoid arthritis, as well as in the prevention of tumor growth.

The main focus of this review will be to evaluate the effects of PEDF in angiogenic models (in vitro and in vivo), the different approaches for its delivery, and how these can be applied to treat choroidal and retinal neovascularization.

2.PEDF, A MEMBER OF THE SERPIN FAMILY

Knowledge of the structure of a polypeptide contributes to the understanding of its function. Much of the information accumulated to date originates from the PEDF cDNA sequence, identified by Steele et al.11 The human PEDF mRNA is ~1.5 kb in length, and analyses of its cDNA sequence predict that human PEDF is a unique gene and a member of the serine protease inhibitor (serpin) supergene family. Its longest open reading frame of 418 codons encodes a 46-kDa polypeptide with an asparagine glycosylation site at position 285-287 (Asn-Leu-Thr) and an N- terminal signal peptide associated with secreted proteins. The translated product has the expected molecular weight and undergoes modifications before and/or during secretion that include one Asn glycosylation, the loss of 20 N-terminal amino acids, and, in some cases, phosphorylation and/or N-acetylation or other post-translational modification at its N-terminal residue. The mature PEDF is a diffusible monomeric glycoprotein with an apparent molecular weight of ~50,000 on SDS-PAGE and a molecular radius not larger than 3.05 nm.12-15 It has an isoelectric point of 7.2-7.8,

and, depending on the pH of its vehicle, it has affinity for anionic or cationic resins and biomolecules such as glycosaminoglycans or collagens.14,16-18 These biochemical characteristics of PEDF are conserved across species.

The role of PEDF as a serpin has been investigated. The serpins are a family of serine proteinase inhibitors that share the same overall tertiary structure consisting of three β-sheets surrounded by eight α-helices.19-21 The prototype is α1-antitrypsin or α1-proteinase inhibitor. This shared structure is also maintained in several members of the family with no known inhibitory function (e.g., ovalbumin, angiotensinogen, and maspin). The serpin structure confers on these proteins a globular conformation with a hinge region or exposed loop susceptible to proteolytic cleavage and located proximal to the C-terminal end of their sequences. In inhibitory serpins, the exposed loop constitutes the reactive center that is recognized by its target protease as the best substrate. Upon binding, the serpin and protease form a complex, preventing further proteolytic activity. Although the human PEDF polypeptide shares only 27% primary sequence homology with α1-antitrypsin, it has conserved 90% of the amino acid residues in α1-antitrypsin that are necessary for maintaining the tertiary structural integrity of serpins. X-ray crystallography confirms that the folded protein conformation of PEDF is that of a serpin.22 Crystal structures of human PEDF and the serpin prototype are shown in Figure 1 to illustrate its similarities. However, in spite of these similarities and unlike most serpins, PEDF does not behave as an inhibitor of serine proteases, it does not form complexes with serine proteases, and it does not undergo the typical serpin stress-relaxed conformational change upon cleavage of its serpin exposed loop.23 Thus, PEDF belongs to the noninhibitory subgroup of the serpin family.

Several serpins share biological activities with PEDF; however, sequence identity among them remains at only ~30%. Examples include glia-derived nexin/protease nexin-I, (GDN/PN-I), a neurite outgrowth factor for neuroblastoma cells that acts by inhibiting thrombin. Antithrombin III, angiostatin, maspin, and plasminogen activator inhibitor- I exhibit anti-angiogenic properties, but little is known about their mechanisms of action.

Figure 17-1. Structures of human PEDF and alpha-1-antitrypsin as obtained from the PDB depositions 1MV and 1QMB, respectively. In inhibitory serpins, the target protease cleaves the bond between amino acids at positions P1-P1’ within the reactive center loop (RCL or serpin exposed loop). Thereafter, the serpin undergoes a conformational change and complexes with the protease, preventing it from further activity. Position P2 corresponds to the amino acid one position upstream from P1.

3.PEDF, A NEUROTROPHIC FACTOR

There are several lines of evidence for the establishment of PEDF as a multipotent neurotrophic factor that acts on various types of neurons (see Table 1). PEDF has a potent neuronal differentiating activity in established cell lines from human retinoblastoma tumor.24-26 It protects rat retinal neurons from hydrogen peroxide–induced cell death in culture27 and has a morphogenetic effect on photoreceptor neurons of Xenopus laevis.28 The neurotrophic effects of PEDF have also been demonstrated in vivo. PEDF transiently delays the death of photoreceptor cells in mouse models of retinitis pigmentosa, retinal degeneration (rd/rd), and retinal degeneration

slow (rds/rds) mice.29 It also protects rat photoreceptor cells from light damage30,31 and the inner retina and retina ganglion cells from ischemia-

reperfusion injury.32 In addition to its effects on retina cells, PEDF has