Pigment epithelium-derived factor: neurotrophic activity and identification as a member of the serine protease inhibitor gene family.

Cultured pigment epithelial cells of the fetal human retina secrete a protein, pigment epithelium-derived factor (PEDF), that induces a neuronal phenotype in cultured human retinoblastoma cells. Morphological changes include the induction of an extensive neurite meshwork and the establishment of corona-like cellular aggregates surrounding a central lumen. The differentiated cells also show increases in the expression of neuron-specific enolase and the 200-kDa neurofilament subunit. Amino acid and DNA sequence data demonstrate that PEDF belongs to the serine protease inhibitor (serpin) family. The PEDF gene contains a typical signal-peptide sequence, initiator methionine codon, and polyadenylylation signal and matches the size of other members of the serpin superfamily (e.g., alpha 1-antitrypsin). It lacks homology, however, at the putative serpin reactive center. Thus, PEDF could exert a paracrine effect in the embryonic retina, influencing neuronal differentiation by a mechanism that does not involve classic inhibition of serine protease activity.     

RETRACTED ARTICLE: PEDF inhibits VEGF- and EPO- induced angiogenesis in retinal endothelial cells through interruption of PI3K/Akt phosphorylation

Retinal angiogenesis in diabetes may lead to visual impairment and even irreversible blindness in people of working age group worldwide. The main pathological feature of proliferative diabetic retinopathy (PDR) is hypoxia, and overproduction of growth factors like vascular endothelial growth factor (VEGF) and erythropoietin (Epo). This results in pathological proliferation of retinal endothelial cells (RECs), leading to new vessel formation (angiogenesis). Inhibition of angiogenesis is a promising strategy for treatment of PDR and other retinal neovascular disorders. Pigment epithelium-derived factor (PEDF), a 50-kDa protein secreted by retinal pigment epithelium, inhibits the growth of new blood vessel induced in the eye in a variety of ways with a yet elusive mechanism. Here, we investigated the possible mechanism by which PEDF inhibits VEGF- and Epo-induced angiogenic effects in RECs is mediated through PI3K/Akt pathway. PEDF treatment induced the apoptosis in RECs by activating caspase-3 and DNA fragmentation. We found a dose-dependent increase in cell survival with VEGF or Epo, which was attenuated in the presence of PEDF. In addition, PEDF significantly (P < 0.05) inhibited migration and in vitro tube formation in RECs in the presence of VEGF as like PI3K/Akt inhibitor. Of interest, PEDF effectively abrogated VEGF-mediated phosphorylation of PI3K/Akt. Further studies using RECs transfected with constitutively active and dominant-negative forms of Akt suggest that PEDF could inhibit VEGF- and also Epo-induced angiogenesis by disruption of PI3K/Akt signaling.     

色素上皮衍生因子与糖尿病视网膜病变

色素上皮衍生因子(PEDF)来源于人视网膜色素上皮细胞,是眼内有效的血管生成抑制剂,对保持正常眼组织透明无血管的状态有重要作用。PEDF能对抗多种促血管生成因子,有针对性地抑制病理性血管生成,延缓糖尿病视网膜病变的进展,发挥保护作用。同时,PEDF在眼部浓度降低可增加糖尿病视网膜病变的危险。其作用机制仍在探索中。外源性应用PEDF及进行基因治疗对眼部血管增生性疾病具有显著疗效。因此,深入研究可能会发现PEDF治疗临床血管增生性疾病更广泛的作用。     

Extracellular phosphorylation converts pigment epithelium-derived factor from a neurotrophic to an antiangiogenic factor

The pigment epithelium-derived factor (PEDF) belongs to the superfamily of serine protease inhibitors (serpin). There have been 2 distinct functions attributed to this factor, which can act either as a neurotrophic or as an antiangiogenic factor. Besides its localization in the eye, PEDF was recently reported to be present also in human plasma. We found that PEDF purified from plasma is a phosphoprotein, which is extracellularly phosphorylated by protein kinase CK2 (CK2) and to a lesser degree, intracellularly, by protein kinase A (PKA). CK2 phosphorylates PEDF on 2 main residues, Ser24 and Ser114, and PKA phosphorylates PEDF on one residue only, Ser227. The physiologic relevance of these phosphorylations was determined using phosphorylation site mutants. We found that both CK2 and PKA phosphorylations of PEDF markedly affect its physiologic function. The fully CK2 phosphorylation site mutant S24, 114E abolished PEDF neurotrophic activity but enhanced its antiangiogenic activity, while the PKA phosphorylation site mutant S227E reduced PEDF antiangiogenic activity. This is a novel role of extracellular phosphorylation that is shown here to completely change the nature of PEDF from a neutrophic to an antiangiogenic factor.     

Pigment epithelium-derived factor inhibits leptin-induced angiogenesis by suppressing vascular endothelial growth factor gene expression through anti-oxidative properties

Leptin, a circulating hormone secreted mainly from adipose tissues, is involved in the control of body weight. Recently, leptin was found to be an angiogenic factor, and its vitreous levels are associated with angiogenic eye diseases such as proliferative diabetic retinopathy. However, the molecular mechanism for leptin-elicited angiogenesis remains to be elucidated. Pigment epithelium-derived factor (PEDF) has been shown to be the most potent natural inhibitor of angiogenesis in the mammalian eye, and its levels in the vitreous were decreased in angiogenic eye diseases. In this study, we investigated whether and how PEDF could inhibit the leptin-induced DNA synthesis in microvascular endothelial cells (EC), a key step of angiogenesis. Leptin significantly increased intracellular reactive oxygen species (ROS) generation in microvascular EC. PEDF was found to inhibit the leptin-induced ROS generation in EC. An anti-oxidant, N-acetylcysteine, or PEDF completely prevented the leptin-induced upregulation of vascular endothelial growth factor (VEGF) mRNA levels as well as any increase in DNA synthesis in microvascular EC. Polyclonal antibodies against human VEGF were also found to completely inhibit DNA synthesis in leptin-exposed EC. The present study suggests that leptin could elicit angiogenesis through autocrine VEGF production via intracellular ROS generation. PEDF may block the angiogenic effects of leptin through its anti-oxidative properties.     

Pigment-epithelium-derived factor (PEDF) inhibits angiotensin-II-induced vascular endothelial growth factor (VEGF) expression in MOLT-3 T cells through anti-oxidative properties

Angiotensin II (Ang II), the dominant effector of the renin-angiotensin system, elicits numerous inflammatory-proliferative responses, thereby being involved in angiogenesis. T cells play an important role in angiogenesis as well by delivering vascular endothelial growth factor (VEGF) to inflammatory sites. Since we have previously shown that pigment-epithelium-derived factor (PEDF) blocks the Ang II signaling in endothelial cells, we studied here whether PEDF could inhibit the Ang-II-induced VEGF expression in MOLT-3 T and examined the potential mechanism of PEDF inhibitory effects. Ang II significantly up-regulated VEGF mRNA levels in MOLT-3 T cells, which was inhibited by PEDF or olmesartan, an Ang II type 1 receptor blocker. PEDF blocked the Ang-II-induced reactive oxygen species (ROS) generation in MOLT-3 T cells. Furthermore, H(2)O(2) was found to up-regulate VEGF mRNA levels in MOLT-3 T cells in a dose-dependent manner. These results demonstrate that PEDF could inhibit the Ang-II-induced VEGF expression in MOLT-3 T cells via suppression of ROS generation. Blockade by PEDF of VEGF expression in T cells may become a novel therapeutic target for pathological angiogenesis.     

Pigment epithelium–derived factor down regulates hyperglycemia-induced apoptosis via PI3K/Akt activation in goat retinal pericytes

Pigment epithelium–derived factor (PEDF) is a well-known protease inhibitor for angiogenesis in the eye, suggesting that loss of PEDF in eye is implicated in the pathogenesis of proliferative diabetic retinopathy. Since the role of PEDF in diabetic retinopathy is unclear, the effect of PEDF on different types of cells constituting the blood vessel has to be checked. Here, we have investigated the effects of PEDF under hyperglycemic conditions in retinal pericytes, isolated from goat’s eye and used to analyze the signaling pathway involved. High glucose increased the apoptotic cell death and intracellular reactive oxygen species generation, which was blocked on the addition of PEDF. PEDF was found to inhibit the apoptotic cell death and protect the cells via activating the PI3K/Akt pathway, which was analyzed with dominant negative Akt and constitutively active Akt–transfected cells. These results demonstrate that PEDF protects pericytes against the high glucose–induced apoptosis and dysfunction.     

Pigment epithelium-derived factor in idiopathic pulmonary fibrosis: a role in aberrant angiogenesis

Pigment epithelium-derived factor (PEDF) is a 50-kD protein with angiostatic and neurotrophic activities that regulates vascular development within the eye. PEDF expression was increased in the lungs of patients with idiopathic pulmonary fibrosis (IPF) based on microarray analyses. Angiogenesis has been implicated in the pathogenesis of fibrotic lung diseases, we therefore hypothesized that regional abnormalities in vascularization occur in IPF as a result of an imbalance between PEDF and vascular endothelial growth factor. We demonstrated that vascular density is regionally decreased in IPF within the fibroblastic foci, and that within these areas PEDF was increased, whereas vascular endothelial growth factor was decreased. PEDF colocalized with the fibrogenic cytokine, transforming growth factor (TGF)-beta 1, particularly within the fibrotic interstitium and the fibroblastic focus, and prominently within the epithelium directly overlying the fibroblastic focus. This suggested that TGF-beta 1 might regulate PEDF expression. Using 3T3-L1 fibroblasts and human lung fibroblasts, we showed that PEDF was indeed a TGF-beta 1 target gene. Collectively, our findings implicate PEDF as a regulator of pulmonary angiogenesis and an important mediator in IPF.     

Elevated serum levels of pigment epithelium-derived factor in the metabolic syndrome

CONTEXT: Pigment epithelium-derived factor (PEDF), a potent inhibitor of angiogenesis with neuronal differentiating activity, inhibits endothelial cell injury in vitro, thus suggesting the involvement of PEDF in atherosclerosis. Therefore, elucidating the relationship between serum levels of PEDF and coronary risk factors could provide a clue to understanding the pathophysiological role of PEDF in vivo. OBJECTIVE: We examined whether serum levels of PEDF were associated with risk factors for coronary artery disease. DESIGN: The study was designed as a cross-sectional study. Setting: The study was set within the general community. PATIENTS OR OTHER PARTICIPANTS: A total of 196 general Japanese residents (age 65.7 +/- 9.3 yr; 71 males and 125 females) without clinical evidence of coronary or peripheral arterial occlusive diseases were enrolled in this study. RESULTS: PEDF showed a normal distribution, ranging from 8-24 microg/ml, with a mean of 14.6 +/- 3.2 microg/ml. Multivariate analyses revealed that uric acid (P < 0.001), waist circumference (P = 0.009), insulin (P = 0.019), and triglycerides (P = 0.028) were significant independent determinants of serum PEDF levels. Age- and uric acid-adjusted PEDF levels were significantly higher (P = 0.048 for men and P = 0.007 for women) in proportion to the accumulation of the number of the components of the metabolic syndrome. CONCLUSIONS: The present study reveals that serum levels of PEDF are strongly associated with the metabolic syndrome. Our results suggest that serum PEDF levels may be elevated as a counter-system in the metabolic syndrome.     

Pigment epithelium-derived factor inhibits oxidative stress-induced apoptosis and dysfunction of cultured retinal pericytes

Pigment epithelium-derived factor (PEDF) is a potent inhibitor of angiogenesis in the mammalian eye, suggesting that loss of PEDF is implicated in the pathogenesis of proliferative diabetic retinopathy. However, a role for PEDF in early diabetic retinopathy remains to be elucidated. Since oxidative stress is thought to be involved in pericyte loss and dysfunction, one of the changes characteristic of early diabetic retinopathy, we investigated whether and how PEDF could protect cultured retinal pericyte against oxidative stress injury. High glucose (30 mM) increased intracellular reactive oxygen species (ROS) generation in pericytes, which was completely blocked by PEDF. High glucose or H2O2 was found to induce growth retardation and apoptotic cell death of pericytes. PEDF completely restored these cytopathic effects on pericytes. An increased ratio of bax to bcl-2 mRNA level with subsequent activation of caspase-3 was observed in high-glucose- or H2O2-exposed pericytes, which was also completely prevented by PEDF. PEDF significantly increased glutathione peroxidase (GPx) mRNA levels and activity in pericytes. Further, PEDF was found to completely inhibit high-glucose- or H2O2-induced increase in a mRNA ratio of angiopoietin-2 to angiopoietin-1 and up-regulation of VEGF mRNA levels in pericytes. PEDF mRNA levels themselves were down-regulated in high-glucose- or H2O2-exposed pericytes. These results demonstrate that PEDF protects against high-glucose- or H2O2-induced pericyte apoptosis and dysfunction through its anti-oxidative properties via GPx induction. Our present study suggests that substitution of PEDF proteins might be a promising therapeutic strategy for treatment of patients with early diabetic retinopathy.     

Evaluation of protein pigment epithelium-derived factor (PEDF) and microvessel density (MVD) as prognostic indicators in breast cancer

Purpose  

Angiogenesis, which plays an important role in tumor growth and metastasis, is regulated by a balance between angiogenic stimulators and inhibitors. Pigment epithelium-derived factor (PEDF), a secreted glycoprotein is an important inhibitor of angiogenesis. Although the precise mechanisms by which PEDF exerts its actions remain poorly understood, there is growing evidence supporting the role of PEDF as a candidate antitumor agent. In this study, we investigated the role of PEDF in breast cancer.     

Pigment epithelium-derived factor (PEDF) prevents diabetes- or advanced glycation end products (AGE)-elicited retinal leukostasis

Pigment epithelium-derived factor (PEDF) is the most potent inhibitor of angiogenesis in the mammalian eye, suggesting that PEDF may protect against proliferative diabetic retinopathy. However, a role for PEDF in early diabetic retinopathy remains to be elucidated. Leukocyte adhesion to retinal capillary endothelium (leukostasis) is a critical event in early diabetic retinopathy, whose process is mainly mediated by intercellular adhesion molecule-1 (ICAM-1). We investigated here whether PEDF could prevent diabetes- or advanced glycation end products (AGE)-elicited retinal leukostasis by suppressing ICAM-1 expression. Immunohistochemistry of 8-hydroxydeoxyguanosine (8-OHdG), an oxidative stress marker, showed intense staining in the nuclei of cells in the inner and outer plexiform layers of streptozotocin-induced diabetic rat retinas. Administration of PEDF or pyridoxal phosphate, an AGE inhibitor, decreased retinal levels of 8-OHdG and subsequently suppressed ICAM-1 gene expression and retinal leukostasis in diabetic rats. Further, intravenous administration of AGE to normal rats increased ICAM-1 gene expression and retinal leukostasis, which were blocked by PEDF. PEDF also inhibited the AGE-induced T cell adhesion to microvascular endothelial cells by suppressing ICAM-1 expression. These results demonstrated that PEDF inhibited diabetes- or AGE-elicited retinal leukostasis by suppressing ICAM-1. Our present study suggests that PEDF may play a protective role against early diabetic retinopathy by attenuating the deleterious effect of AGE.     

PEDF-derived peptide inhibits corneal angiogenesis by suppressing VEGF expression

Pigment epithelium-derived factor (PEDF) a glycoprotein that belongs to the superfamily of serine protease inhibitors, has been recently shown to be the most potent inhibitor of angiogenesis in the mammalian eye. However, which active domain of PEDF protein could be involved in its anti-angiogenic properties remains unknown. Therefore, in this study, we examined which PEDF-derived synthetic peptides could inhibit corneal neovascularization induced by chemical cauterization in vivo. Rats treated with topical application of PEDF protein had 31% less corneal neovascularization at day 7 after the injury than phosphate-buffered saline (PBS)-treated rats. P5-2 and P5-3 peptides (residues 388-393 and 394-400 of PEDF protein, respectively) significantly suppressed the corneal neovascularization after chemical cauterization at day 7, and its anti-angiogenic potential was almost equal to that of full-length PEDF protein. Further, full-length PEDF protein and P5-3 peptide significantly decreased 8-hydroxy-2'-deoxyguanosine and vascular endothelial growth factor (VEGF) levels in the corneal. Our present study suggests that PEDF-derived synthetic peptide, P5-3 could inhibit the corneal neovascularization induced by chemical cauterization in rats by suppressing VEGF expression via its anti-oxidative properties.     

Prevention of ischemia-induced retinopathy by the natural ocular antiangiogenic agent pigment epithelium-derived factor

Aberrant blood vessel growth in the retina that underlies the pathology of proliferative diabetic retinopathy and retinopathy of prematurity is the result of the ischemia-driven disruption of the normally antiangiogenic environment of the retina. In this study, we show that a potent inhibitor of angiogenesis found naturally in the normal eye, pigment epithelium-derived growth factor (PEDF), inhibits such aberrant blood vessel growth in a murine model of ischemia-induced retinopathy. Inhibition was proportional to dose and systemic delivery of recombinant protein at daily doses as low as 2.2 mg/kg could prevent aberrant endothelial cells from crossing the inner limiting membrane. PEDF appeared to inhibit angiogenesis by causing apoptosis of activated endothelial cells, because it induced apoptosis in cultured endothelial cells and an 8-fold increase in apoptotic endothelial cells could be detected in situ when the ischemic retinas of PEDF-treated animals were compared with vehicle-treated controls. The ability of low doses of PEDF to curtail aberrant growth of ocular endothelial cells without overt harm to retinal morphology suggests that this natural protein may be beneficial in the treatment of a variety of retinal vasculopathies.     

色素上皮衍生因子抑制人肝癌裸鼠移植瘤生长

目的 观察人色素上皮衍生因子(PEDF)对血管生成的抑制作用,探讨PEDF在肝癌基因治疗中的应用前景. 方法构建色素上皮衍生因子慢病毒表达质粒pLenti-PEDF,经293T细胞包装,收集病毒上清液,感染肝癌细胞株HepG2.收集各组细胞的条件培养基,通过Westernblot分析各组细胞PEDF的表达情况,并通过人脐静脉血管内皮细胞增殖及迁移试验研究其体外生物学活性.人肝癌细胞HepG2移植到裸鼠皮下,研究Lenti-PEDF病毒对肝癌移植瘤生长的抑制作用,逆转录聚合酶链反应检测肿瘤组织中PEDF mRNA表达.多组间均数比较采用单因素方差分析,组间两两比较采用LSD法.结果 限制性内切酶酶切分析和测序结果均表明成功构建了PEDF慢病毒表达载体,以293T细胞包装的重组慢病毒能够高效感染肝癌细胞,肝痛细胞感染重组慢病毒后可高效表达PEDF并分泌到培养上清液中.体外研究结果表明,重组PEDF可明显抑制人脐静脉血管内皮细胞的增殖及迁移,抑制率分别达29%和48%,与空白对照组相比,差异有统计学意义(P值均<0.01).Lenti-PEDF病毒能明显抑制人肝癌裸鼠皮下移植瘤的生长(P<0.01).瘤内注射Lenti-PEDF病毒21 d后,逆转录聚合酶链反应在肿瘤组织检测到PEDF mRNA的过表达.结论 本研究初步提示PEDF能有效遏制肿瘤的血管生成和肿瘤生长,为肝癌的基因治疗提供了一条新的思路.     

Angiotensinogen and its cleaved derivatives inhibit angiogenesis

The members of the serine protease inhibitor (serpin) family, which share a common tertiary structure and a role as serin protease inhibitors, are involved in a variety of newly discovered functions. For example, antithrombin III exerts a strong antiangiogenic activity. Angiotensinogen, the renin substrate, has a folded structure and is a member of the noninhibitory serpin subfamily. Two other noninhibitory serpins, maspin and pigment epithelium-derived factor, have antiangiogenic properties. We investigated the antiangiogenic effect of angiotensinogen and 2 related compounds: (1) des(angiotensin I)angiotensinogen, the product of angiotensinogen cleavage by renin, and (2) the reactive center loop-cleaved angiotensinogen, which is produced after selective and limited proteolysis by the protease V8. We used well-established in vitro (endothelial cell proliferation and migration, and capillary-like tube formation on Matrigel) and in vivo (the chick chorioallantoic membrane assay) models of angiogenesis to evaluate the antiangiogenic activities of these 3 related molecules. Our data demonstrated that these compounds exerted a clear and equipotent antiangiogenic effect, thus attributing a novel function to angiotensinogen and des(angiotensin I)angiotensinogen, for which no function was previously known.     

Plasma concentration of pigment epithelium-derived factor in patients with diabetic retinopathy

CONTEXT: Pigment epithelium-derived factor (PEDF) is a strong inhibitor of angiogenesis. Eyes with diabetic retinopathy have low levels of ocular PEDF; however, the PEDF levels in the blood of diabetics have still not been determined. OBJECTIVES: Our objective was to determine the plasma levels of PEDF in diabetic patients and to determine the relationship with the stage of the diabetic retinopathy. DESIGN AND SETTING: This study was designed as a cross-sectional, institutional study. PATIENTS OR OTHER PARTICIPANTS: A total of 145 Japanese were studied; 112 had type 2 diabetes mellitus, and 33 were healthy controls. INTERVENTION: There was no intervention. MAIN OUTCOME MEASURES: The plasma level of PEDF was measured by ELISA, and the stage of diabetic retinopathy was determined by ophthalmic examinations. Clinical systemic status of diabetic patients was also examined. RESULTS: The plasma PEDF level in diabetic patients (6.68 +/- 0.54 microg/ml; mean +/- sem) was significantly higher than that in controls (4.38 +/- 0.59 microg/ml, P = 0.03), and the level was especially high in patients with proliferative diabetic retinopathy (7.78 +/- 0.98 microg/ml; n = 45; P = 0.005). The gender (P = 0.03), blood urea nitrogen (P = 0.005), and triglycerides (P = 0.04) were significant and independent determinants of plasma PEDF levels in diabetic patients. CONCLUSIONS: The PEDF level in the plasma was significantly elevated in diabetic patients, especially those with proliferative diabetic retinopathy. High levels of PEDF in the plasma may be related to the progression of diabetic retinopathy.     

Antiangiogenic antithrombin

Angiogenesis is critical for several physiologic and pathophysiologic processes, and several angiogenesis inhibitors are now in clinical trials for the treatment of cancer. Antithrombin is a member of the serpin family of proteins and functions as an inhibitor of thrombin and other enzymes involved in the clotting cascade. While studying the inhibition of tumor growth by tumor mass in a human small cell lung cancer model, we discovered that the cleaved conformation of antithrombin has potent antiangiogenic and antitumor activity. The stable locked and latent forms of intact antithrombin, which are substantially similar in conformation to the cleaved form of the molecule, also inhibit angiogenesis and tumor growth in vivo and act selectively upon endothelial cells and the tumor vasculature. The intact native molecule does not have this effect. The discovery of antiangiogenic antithrombin provides further evidence that the clotting and fibrinolytic pathways are directly related to the regulation of angiogenesis. As for other endogenous angiogenesis inhibitors, the precise mechanism of action for antiangiogenic antithrombin has not been defined, but several studies now suggest that it may target the endothelial cell at multiple levels resulting in a profound blockade of the angiogenic cascade. In this paper, an overview of the angiogenesis inhibitor antiangiogenic antithrombin and a summary of the pertinent literature are provided.