Overexpression of fetal human pigment epithelium-derived factor in Escherichia coli. A functionally active neurotrophic factor

Expression and production of pigment epithelium-derived factor (PEDF) and PEDF receptor variants from mammalian and bacterial cells

Human SERPINF1 gene codes for pigment epithelium-derived factor (PEDF), a secreted glycoprotein and member of the SERPIN superfamily. To obtain large amounts of recombinant PEDF proteins, we subcloned the coding sequence of human SERPINF1 mutated versions into the pCEP4 vector and generated stably transfected HEK.Ebna cells. The cells produced and secreted recombinant PEDF proteins into the culturing media. The recombinant PEDF proteins were purified by ion-exchange column chromatography and milligram amounts of highly purified protein were recovered. PEDF has affinity for PEDF-receptor (PEDF-R), a membrane-linked lipase encoded by the PNPLA2 gene. Recombinant PEDF-R truncated versions were obtained from Escherichia coli containing expression vectors with human PNPLA2 cDNAs with 3'end deletions and by induction with isopropyl β-d-1-thiogalactopyranoside. The bacterially derived PEDF-R proteins in insoluble inclusion bodies were solubilized with urea and purified by cation-exchange column chromatography. C-terminally truncated PEDF-R versions containing the ligand binding region retained the ability to bind PEDF. The data demonstrate that mammalian-derived recombinant PEDF and bacterially derived recombinant PEDF-R can be produced and purified in large amounts for further use in structural and biological studies.

Association of pigment epithelium derived factor expression with cancer progression and prognosis: a meta-analysis study

BACKGROUND

Pigment epithelium derived factor (PEDF) is a secreted protein that strongly suppresses angiogenesis and directly inhibits cancer cells proliferation. The differential expression of PEDF has been observed in multiple types of human tumors. However, it is unclear as to how PEDF expression is associated with cancer progression and if PEDF could serve as a prognostic marker for cancer patients.

METHODS

We performed a comprehensive search for the studies on PEDF expression in 14 top-ranked types of solid tumor cancer with the highest incidence. A systemic approach was used to screen for qualified studies and to extract data. Meta-analysis was performed to investigate if PEDF expression is associated with the TNM staging, tumor size, lymph node invasion, distal metastasis and pathological grade of tumor in a pan-cancer manner. A Kaplan-Meier curve was plotted with the digitally-reconstituted patient survival data to study the effect of PEDF expression on the prognosis of cancer patients.

RESULTS

A total of nine studies were selected, reviewed and analyzed. Meta-analysis suggested that decreased PEDF protein expression was associated with higher TNM staging (OR = 2.13, 95% CI: 1.61-2.81), larger tumor size (OR = 1.42, 95% CI: 1.1-1.84), larger possibility of lymph node invasion (OR = 1.68, 95% CI: 1.26-2.22) and higher pathological grade (OR = 1.6, 95% CI: 1.2-2.13). No correlation was found between PEDF expression and tumor distal metastasis, gender or age. In addition, low PEDF protein level in tumor tissue is correlated with shorter overall survival (P < 0.05).

CONCLUSIONS

Low PEDF protein expression in cancer is significantly associated with more advanced cancer progression and significantly poorer survival. The differential clinical outcome among patients with various PEDF expression suggests its prognostic value.

PEDF expression affects retinal endothelial cell proangiogenic properties through alterations in cell adhesive mechanisms

Pigment epithelium-derived factor (PEDF) is an endogenous inhibitor of angiogenesis. Although various ocular cell types including retinal endothelial cells (EC) produce PEDF, we know very little about cell autonomous effects of PEDF in these cell types. Here we determined how PEDF expression affects retinal EC proangiogenic properties. Retinal EC were prepared from wild-type (PEDF+/+) and PEDF-deficient (PEDF-/-) mice. The identity of EC was confirmed by staining for specific markers including vascular endothelial cadherin, CD31, and B4-lectin. Retinal EC also expressed VEGF receptor 1 and endoglin, as well as ICAM-1, ICAM-2, and VCAM-1. PEDF-/- retinal EC were more proliferative, less apoptotic when challenged with H2O2, less migratory, and less adherent compared with PEDF+/+ EC. These changes could be associated, at least in part, with increased levels of tenascin-C, fibronectin, thrombospondin-1 and collagen IV, and lower amounts of osteopontin. PEDF-/- EC also exhibited alterations in expression of a number of integrins including α2, αv, β1, β8, and αvβ3, and cell-cell adhesion molecules including CD31, zonula occluden-1, and occludin. These observations correlated with attenuation of capillary morphogenesis and increased levels of oxidative stress in PEDF-/- EC. PEDF-/- EC also produced lower levels of VEGF compared with PEDF+/+ cells. Thus, PEDF deficiency has a significant impact on retinal EC adhesion and migration, perhaps through altered production of extracellular matrix and junctional proteins in response to increased oxidative stress affecting their proangiogenic activity.

Intraocular Transplantation of E1A-Immortalized Retinal Precursor Cells

The purpose of this study was to examine the effect of the ocular environment on the survival, tumorigenicity, and phenotypic marker expression of immortalized retinal precursor cells transplanted into immunocompetent adult and neonatal Sprague–Dawley rats. E1A-NR.3, a rat immortalized retinal precursor cell culture, was used as an inexhaustible source of experimental graft material. These cells were prelabeled with the fluorescent marker diI (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) and transplanted intravitreally (50,000 cells per μL) into 11 adult and 31 neonatal Sprague–Dawley rat eyes. At 1 mo posttransplant, animals were sacrificed and retinal tissue sections examined histologically for the presence of grafted cells, signs of tumor formation, and retinal phenotypic marker expression. No obvious signs of tumor formation or rejection were seen in a total of 42 eyes in the immunocompetent hosts. Our results indicate that E1A-NR.3 cells survive at least 1 month in vivo, and can migrate from the vitreous into neuroretinal cell layers. Subpopulations of surviving grafted cells were seen to express photoreceptor markers rhodopsin and recoverin comparably between in vitro and in vivo conditions. However, the number of cells immunoreactive for vimentin and E1A decreased significantly under in vivo conditions. This report represents the first experimental intravitreal transplantation of E1A-immortalized retinal precursor cells into adult and neonatal rats. The intraocular location and environment appears to affect phenotypic expression of surviving grafted cells, especially with respect to vimentin and E1A expression. The fact that E1A-NR.3 cells survived intraocularly at least 1 mo without tumor formation suggests that the cells may continue to be useful for further in vivo studies of experimental retinal transplantation, and effects of histological location on retinal cell phenotype and histogenesis in immunocompetent hosts. © 1998 Elsevier Science Inc.

Molecular mechanisms of OLIG2 transcription factor in brain cancer

Oligodendrocyte lineage transcription factor 2 (OLIG2) plays a pivotal role in glioma development. Here we conducted a comprehensive study of the critical gene regulatory networks involving OLIG2. These include the networks responsible for OLIG2 expression, its translocation to nucleus, cell cycle, epigenetic regulation, and Rho-pathway interactions. We described positive feedback loops including OLIG2: loops of epigenetic regulation and loops involving receptor tyrosine kinases. These loops may be responsible for the prolonged oncogenic activity of OLIG2. The proposed schemes for epigenetic regulation of the gene networks involving OLIG2 are confirmed by patient survival (Kaplan-Meier) curves based on the cancer genome atlas (TCGA) datasets. Finally, we elucidate the Coherent-Gene Modules (CGMs) networks-framework of OLIG2 involvement in cancer. We showed that genes interacting with OLIG2 formed eight CGMs having a set of intermodular connections. We showed also that among the genes involved in these modules the most connected hub is EGFR, then, on lower level, HSP90 and CALM1, followed by three lower levels including epigenetic genes KDM1A and NCOR1. The genes on the six upper levels of the hierarchy are involved in interconnections of all eight CGMs and organize functionally defined gene-signaling subnetworks having specific functions. For example, CGM1 is involved in epigenetic control. CGM2 is significantly related to cell proliferation and differentiation. CGM3 includes a number of interconnected helix-loop-helix transcription factors (bHLH) including OLIG2. Many of these TFs are partially controlled by OLIG2. The CGM4 is involved in PDGF-related: angiogenesis, tumor cell proliferation and differentiation. These analyses provide testable hypotheses and approaches to inhibit OLIG2 pathway and relevant feed-forward and feedback loops to be interrogated. This broad approach can be applied to other TFs.

Pigment epithelium-derived factor (PEDF) normalizes matrix defects in iPSCs derived from Osteogenesis imperfecta Type VI

Osteogenesis imperfecta (OI) Type VI is characterized by a defect in bone mineralization, which results in multiple fractures early in life. Null mutations in the PEDF gene, Serpinf1, are the cause of OI VI. Whether PEDF restoration in a murine model of OI Type VI could improve bone mass and function was previously unknown. In Belinsky et al, we provided evidence that PEDF delivery enhanced bone mass and improved parameters of bone function in vivo. Further, we demonstrated that PEDF temporally inhibits Wnt signaling to enhance osteoblast differentiation. Here, we demonstrate that generation of induced pluripotent stem cells (iPSCs) from a PEDF null patient provides additional evidence for PEDF's role in regulating extracellular matrix proteins secreted from osteoblasts. PEDF null iPSCs have marked abnormalities in secreted matrix proteins, capturing a key feature of human OI Type VI, which were normalized by exogenous PEDF. Lastly, we place our recent findings within the broader context of PEDF biology and the developmental signaling pathways that are implicated in its actions.

Pigment epithelium-derived factor (PEDF) regulates metabolism and insulin secretion from a clonal rat pancreatic beta cell line BRIN-BD11 and mouse islets

Pigment epithelium-derived factor (PEDF) is a multifunctional glycoprotein, associated with lipid catabolism and insulin resistance. In the present study, PEDF increased chronic and acute insulin secretion in a clonal rat β-cell line BRIN-BD11, without alteration of glucose consumption. PEDF also stimulated insulin secretion from primary mouse islets. Seahorse flux analysis demonstrated that PEDF did not change mitochondrial respiration and glycolytic function. The cytosolic presence of the putative PEDF receptor - adipose triglyceride lipase (ATGL) - was identified, and ATGL associated stimulation of glycerol release was robustly enhanced by PEDF, while intracellular ATP levels increased. Addition of palmitate or ex vivo stimulation with inflammatory mediators induced β-cell dysfunction, effects not altered by the addition of PEDF. In conclusion, PEDF increased insulin secretion in BRIN-BD11 and islet cells, but had no impact on glucose metabolism. Thus elevated lipolysis and enhanced fatty acid availability may impact insulin secretion following PEDF receptor (ATGL) stimulation.

Protein biomarkers in Parkinson's disease: Focus on cerebrospinal fluid markers and synaptic proteins

Despite extensive research, to date, no validated biomarkers for PD have been found. This review seeks to summarize studies approaching the detection of biomarker candidates for PD and introduce promising ones in more detail, with special attention to synaptic proteins. To this end, we performed a PubMed search and included studies using proteomic tools (2-dimensional difference in gel electrophoresis and/or mass spectrometry) for the comparison of samples from PD and control patients. We found 27 studies reporting more than 500 differentially expressed proteins in which a total of 28 were detected in 2 and 17 in 3 or more independent studies, including posttranslationally modified proteins. In addition, of these 500 proteins, 25 were found to be brain specific, and 14 were enriched in synapses. Special attention was given to the applicability of the biomarker regarding sampling procedures, that is, using CSF/serum material for diagnosis. Furthermore, presynaptic proteins involved in vesicle membrane fusion seem to be interesting candidates for future analyses. Nonetheless, even though such promising biomarker candidates for PD exist, validation of these biomarkers in large-scale clinical studies is necessary to evaluate the diagnostic potential. © 2016 International Parkinson and Movement Disorder Society.

Pigment Epithelium-Derived Factor (PEDF) is a Determinant of Stem Cell Fate: Lessons from an Ultra-Rare Disease

PEDF is a secreted glycoprotein that is widely expressed by multiple organs. Numerous functional contributions have been attributed to PEDF with antiangiogenic, antitumor, anti-inflammatory, and neurotrophic properties among the most prominent. The discovery that null mutations in the PEDF gene results in Osteogenesis Imperfecta Type VI, a rare autosomal recessive bone disease characterized by multiple fractures, highlights a critical developmental function for this protein. This ultra-rare orphan disease has provided biological insights into previous studies that noted PEDF’s effects on various stem cell populations. In addition to bone development, PEDF modulates resident stem cell populations in the brain, muscle, and eye. Functional effects on human embryonic stem cells have also been demonstrated. An overview of recent advances in our understanding by which PEDF regulates stem cells and their potential clinical applications will be evaluated in this review.

Characterization of Regenerative Phenotype of Unrestricted Somatic Stem Cells (USSC) from Human Umbilical Cord Blood (hUCB) by Functional Secretome Analysis

Stem cell transplantation is a promising therapeutic strategy to enhance axonal regeneration after spinal cord injury. Unrestricted somatic stem cells (USSC) isolated from human umbilical cord blood is an attractive stem cell population available at GMP grade without any ethical concerns. It has been shown that USSC transplantation into acute injured rat spinal cords leads to axonal regrowth and significant locomotor recovery, yet lacking cell replacement. Instead, USSC secrete trophic factors enhancing neurite growth of primary cortical neurons in vitro. Here, we applied a functional secretome approach characterizing proteins secreted by USSC for the first time and validated candidate neurite growth promoting factors using primary cortical neurons in vitro. By mass spectrometric analysis and exhaustive bioinformatic interrogation we identified 1156 proteins representing the secretome of USSC. Using Gene Ontology we revealed that USSC secretome contains proteins involved in a number of relevant biological processes of nerve regeneration such as cell adhesion, cell motion, blood vessel formation, cytoskeleton organization and extracellular matrix organization. We found for instance that 31 well-known neurite growth promoting factors like, e.g. neuronal growth regulator 1, NDNF, SPARC, and PEDF span the whole abundance range of USSC secretome. By the means of primary cortical neurons in vitro assays we verified SPARC and PEDF as significantly involved in USSC mediated neurite growth and therewith underline their role in improved locomotor recovery after transplantation. From our data we are convinced that USSC are a valuable tool in regenerative medicine as USSC's secretome contains a comprehensive network of trophic factors supporting nerve regeneration not only by a single process but also maintained its regenerative phenotype by a multitude of relevant biological processes.

PEDF and its roles in physiological and pathological conditions: implication in diabetic and hypoxia-induced angiogenic diseases

Pigment epithelium-derived factor (PEDF) is a broadly expressed multifunctional member of the serine proteinase inhibitor (serpin) family. This widely studied protein plays critical roles in many physiological and pathophysiological processes, including neuroprotection, angiogenesis, fibrogenesis and inflammation. The present review summarizes the temporal and spatial distribution patterns of PEDF in a variety of developing and adult organs, and discusses its functions in maintaining physiological homoeostasis. The major focus of the present review is to discuss the implication of PEDF in diabetic and hypoxia-induced angiogenesis, and the pathways mediating PEDF's effects under these conditions. Furthermore, the regulatory mechanisms of PEDF expression, function and degradation are also reviewed. Finally, the therapeutic potential of PEDF as an anti-angiogenic drug is briefly summarized.

Effects of pigment epithelium derived factor (PEDF) on malignant peripheral nerve sheath tumours (MPNSTs)

Neurofibromatosis type 1 (NF1) is an inherited genetic disease affecting 1 in 3,500 individuals. A prominent feature of NF1 is the formation of benign tumours of the peripheral nerve sheath (neurofibromas). However, these can become malignant and form highly metastatic malignant peripheral nerve sheath tumours (MPNST), which are usually fatal despite aggressive surgery, chemotherapy, and radiotherapy. Recent studies have shown that pigment epithelium-derived factor (PEDF) can induce differentiation and inhibit angiogenesis in several kinds of tumours. The present study was designed to determine the in vitro and in vivo effects of PEDF on MPNST angiogenesis and tumour growth. PEDF inhibited proliferation and augmented apoptosis in S462 MPNST cells after 48 h of treatment in culture. In xenografts of S462 MPNST cells in athymic nude mice, PEDF suppressed MPNST tumour burden, due mainly to inhibition of angiogenesis. These results demonstrate for the first time inhibitory effects of PEDF on the growth of human MPNST via induction of anti-angiogenesis and apoptosis. Our results suggest that PEDF could be a novel approach for future therapeutic purposes against MPNST.

The many facets of PEDF in drug discovery and disease: a diamond in the rough or split personality disorder?

INTRODUCTION

Pigment epithelium-derived factor (PEDF) was discovered as a neurotrophic factor secreted by retinal pigment epithelial cells. A decade later, it re-emerged as a powerful angiogenesis inhibitor guarding ocular function. Since then, significant advances were made identifying PEDF's mechanisms, targets and biomedical applications.

AREAS COVERED

The authors review several methodologies that have generated significant new information about the potential of PEDF as a drug. Furthermore, the authors review and discuss mechanistic and structure-function analyses combined with the functional mapping of active fragments, which have yielded several short bioactive PEDF peptides. Additionally, the authors present functional studies in knockout animals and human correlates that have provided important information about conditions amenable to PEDF-based therapies.

EXPERT OPINION

Through its four known receptors, PEDF causes a wide range of cellular events vitally important for the organism, which include survival and differentiation, migration and invasion, lipid metabolism and stem cell maintenance. These processes are deregulated in multiple pathological conditions, including cancer, metabolic and cardiovascular disease. PEDF has been successfully used in countless preclinical models of these conditions and human correlates suggest a wide utility of PEDF-based drugs. The most significant clinical application of PEDF, to date, is its potential therapeutic use for age-related macular degeneration. Moreover, PEDF-based gene therapy has advanced to early stage clinical trials. PEDF active fragments have been mapped and used to design short peptide mimetics conferring distinct functions of PEDF, which may address specific clinical problems and become prototype drugs.

[Amyloid-like fibrils forming and fibroblasts destruction in Tenon's capsule in progressive myopia as a result of pigment epithelium derived factor resistance to restricted proteolysis]

We have shown previously the presence of full length (50 kD) and truncated proteolytic form (45 kD) of pigment epithelium derived factor (PEDF) in the eye Tenon's capsule in progressive myopia. The full length PEDF is prevalent in myopia that correlates with breach in collagen fibrils forming. Immunohistochemical analysis of Tenon's capsule with polyclonal antibodies to PEDF revealed PEDF in control group being exclusively inside fibroblasts, whereas in myopia, PEDF was distributed extracellularly as halo around blasted fibroblasts. By means of atomic force microscopy and immunodot analysis with anti amyloid fibrils antibodies the ability was studied of recombinant PEDF fragments to form fibrils. Only full length PEDF was shown to form amyloid like fibril structures, but not the truncated form. Accumulation offibrils results in fibroblasts destruction and might be the cause of changes in biochemical and morphological structure of Tenon's capsule observed in myopia.

The effects of PEDF on cancer biology: mechanisms of action and therapeutic potential

The potent actions of pigment epithelium-derived factor (PEDF) on tumour-associated cells, and its extracellular localization and secretion, stimulated research on this multifunctional serpin. Such studies have identified several PEDF receptors and downstream signalling pathways. Known cellular PEDF responses have expanded from the initial discovery that PEDF induces retinoblastoma cell differentiation to its anti-angiogenic, antitumorigenic and antimetastatic properties. Although the diversity of PEDF activities seems to be complex, they are consistent with the varied mechanisms that regulate this multimodal factor. If PEDF is to be used for cancer management, a deeper appreciation of its many functions and mechanisms of action is needed.

Retinal pigment epithelium, age-related macular degeneration and neurotrophic keratouveitis

Age-related macular degeneration (AMD) is the leading cause of impaired vision and blindness in the aging population. The aims of our studies were to identify qualitative and quantitative alterations in mitochondria in human retinal pigment epithelium (RPE) from AMD patients and controls and to test the protective effects of pigment epithelium-derived factor (PEDF), a known neurotrophic and antiangiogenic substance, against neurotrophic keratouveitis. Histopathological alterations were studied by means of morphometry, light and electron microscopy. Unexpectedly, morphometric data showed that the RPE alterations noted in AMD may also develop in normal aging, 10-15 years later than appearing in AMD patients. Reduced tear secretion, corneal ulceration and leukocytic infiltration were found in capsaicin (CAP)-treated rats, but this effect was significantly attenuated by PEDF. These findings suggest that PEDF accelerated the recovery of tear secretion and also prevented neurotrophic keratouveitis and vitreoretinal inflammation. PEDF may have a clinical application in inflammatory and neovascular diseases of the eye.

Alterations in protein regulators of neurodevelopment in the cerebrospinal fluid of infants with posthemorrhagic hydrocephalus of prematurity

Neurological outcomes of preterm infants with posthemorrhagic hydrocephalus are among the worst in newborn medicine. There remains no consensus regarding the diagnosis or treatment of posthemorrhagic hydrocephalus, and the pathological pathways leading to the adverse neurological sequelae are poorly understood. In the current study, we developed an innovative approach to simultaneously identify potential diagnostic markers of posthemorrhagic hydrocephalus and investigate novel pathways of posthemorrhagic hydrocephalus-related neurological disability. Tandem multi-affinity fractionation for specific removal of plasma proteins from the hemorrhagic cerebrospinal fluid samples was combined with high resolution label-free quantitative proteomics. Analysis of cerebrospinal fluid obtained from infants with posthemorrhagic hydrocephalus demonstrated marked differences in the levels of 438 proteins when compared with cerebrospinal fluid from age-matched control infants. Amyloid precursor protein, neural cell adhesion molecule-L1, neural cell adhesion molecule-1, brevican and other proteins with important roles in neurodevelopment showed profound elevations in posthemorrhagic hydrocephalus cerebrospinal fluid compared with control. Initiation of neurosurgical treatment of posthemorrhagic hydrocephalus resulted in resolution of these elevations. The results from this foundational study demonstrate the significant promise of tandem multi-affinity fractionation-proteomics in the identification and quantitation of protein mediators of neurodevelopment and neurological injury. More specifically, our results suggest that cerebrospinal fluid levels of proteins such as amyloid precursor protein or neural cell adhesion molecule-L1 should be investigated as potential diagnostic markers of posthemorrhagic hydrocephalus. Notably, dysregulation of the levels these and other proteins may directly affect ongoing neurodevelopmental processes in these preterm infants, providing an entirely new hypothesis for the developmental disability associated with posthemorrhagic hydrocephalus.

Expression of pigment epithelium-derived factor in human melanocytes and malignant melanoma cells and tissues: Is loss of pigment epithelium-derived factor associated with melanoma?

BACKGROUND

Pigment epithelium-derived factor (PEDF) was first isolated from the medium conditioned by human fetal retinal pigment epithelial cells and has been detected in a broad range of human fetal and adult tissues. Recent studies have indicated that PEDF activity is inhibitory to angiogenesis.

OBJECTIVE

To study the expression and distribution of pigment epithelium-derived factor (PEDF) in human melanocytes, malignant melanoma cells and tissues.

RESULTS

PEDF was expressed in human melanocytes. The expression of PEDF protein diminished in the following orders healthy skin, pigmented nevus and human malignant melanoma (p < 0.001). Both the expression of PEDF mRNA and protein was much lower or almost absent in the malignant melanoma cell line A375 than that in human melanocytes (p < 0.001).

METHODS

The expression and distribution of PEDF in human healthy skin, pigmented nevus and malignant melanoma were studied. The expression of PEDF mRNA in human melanocytes and malignant melanoma cell line A375 was measured by reverse transcription polymerase chain reaction (RT-PCR) and PEDF protein was detected by immunohistochemical method and Western blotting analysis.

CONCLUSION

The lack of PEDF expression may contribute to the pathogenesis of malignant melanoma.

Overexpression of pigment epithelium-derived factor inhibits retinal inflammation and neovascularization

Pigment epithelium-derived factor (PEDF) is a serine proteinase inhibitor with antiangiogenic activities. To investigate whether PEDF overexpression has an impact on ocular neovascularization in vivo, we generated PEDF transgenic (PEDF-Tg) mice that ubiquitously express human PEDF driven by the β-actin promoter. The PEDF-Tg mice under normal conditions did not show any abnormalities in retinal histologic findings or visual function. In contrast, PEDF-Tg animals with oxygen-induced retinopathy (OIR) developed significantly less severe retinal neovascularization compared with wild-type (Wt) mice with OIR. In addition, PEDF-Tg mice with OIR had significantly lower vascular leakage in the retina but higher occludin levels than the Wt mice with OIR, suggesting a protective effect on the blood-retinal barrier. Furthermore, retinal levels of proinflammatory factors were significantly lower in PEDF-Tg mice with OIR than in the Wt mice with OIR. In the laser-induced choroidal neovascularization (CNV) model, the CNV area was significantly smaller in the PEDF-Tg mice than in the Wt mice. Also, the laser burn-induced overexpression of proangiogenic and inflammatory factors was observed in the retina and retinal pigment epithelium of Wt mice but not in PEDF-Tg mice. Taken together, these results suggest that overexpression of PEDF inhibits retinal inflammation and neovascularization in both the OIR and laser-induced CNV models. The PEDF-Tg mice provide a useful model for studying the roles of angiogenic inhibitors in neovascular disorders such as diabetic retinopathy.

Production of recombinant serpins in Escherichia coli

Serpins represent a diverse family of proteins that are found in a wide range of organisms and cellular locations. In order to study them, most need to be produced recombinantly, as isolation from their source is not always possible. Due to their relatively uncomplicated structure (single domain, few posttranslational modifications), the serpins are usually amenable to expression in Escherichia coli, which offers a fast and cost-effective solution for the generation of large amounts of protein. This chapter outlines the general procedures used in the expression and subsequent purification of serpins in E. coli, with a particular focus on the methods used for antitrypsin, the archetypal member of the family.

Assays for the antiangiogenic and neurotrophic serpin pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a secreted serpin that exhibits a variety of interesting biological activities. The multifunctional PEDF has neurotrophic and antiangiogenic properties, and acts in retinal differentiation, survival, and maintenance. It is also antitumorigenic and antimetastatic, and has stem cell self-renewal properties. It is widely distributed in the human body and exists in abundance in the eye as a soluble extracellular glycoprotein. Its levels are altered in diseases characterized by retinopathies and angiogenesis. Its mechanisms of neuroprotection and angiogenesis are associated with receptor interactions at cell-surface interfaces and changes in protein expression. This serpin lacks demonstrable serine protease inhibitory activity, but has binding affinity to extracellular matrix components and cell-surface receptors. Here we describe purification protocols, methods to quantify PEDF, and determine interactions with specific molecules, as well as neurotrophic and angiogenesis assays for this multifunctional protein.

Codon preference optimization increases heterologous PEDF expression

Pigment epithelium-derived factor (PEDF) is widely known for its neurotrophic and antiangiogenic functions. Efficacy studies of PEDF in animal models are limited because of poor heterologous protein yields. Here, we redesigned the human PEDF gene to preferentially match codon frequencies of E coli without altering the amino acid sequence. Following de novo synthesis, codon optimized PEDF (coPEDF) and the wtPEDF genes were cloned into pET32a containing a 5′ thioredoxin sequence (Trx) and the recombinant Trx-coPEDF or Trx-wtPEDF fusion constructs expressed in native and two tRNA augmented E coli hosts - BL21-CodonPlus(DE3)-RIL and BL21-CodonPlus(DE3)-RP, carrying extra copies of tRNA^arg,ile,leu and tRNA^arg,pro genes , respectively. Trx-PEDF fusion proteins were isolated using Ni-NTA metal affinity chromatography and PEDF purified after cleavage with factor Xα. Protein purity and identity were confirmed by western blot, MALDI-TOF, and UV/CD spectral analyses. Expression of the synthetic gene was ∼3.4 fold greater (212.7 mg/g; 62.1 mg/g wet cells) and purified yields ∼4 fold greater (41.1 mg/g; 11.3 mg/g wet cell) than wtPEDF in the native host. A small increase in expression of both genes was observed in hosts supplemented with rare tRNA genes compared to the native host but expression of coPEDF was ∼3 fold greater than wtPEDF in both native and codon-bias-adjusted E coli strains. ΔGs at −3 to +50 of the Trx site of both fusion genes were −3.9 kcal/mol. Functionally, coPEDF was equally as effective as wtPEDF in reducing oxidative stress, promoting neurite outgrowth, and blocking endothelial tube formation. These findings suggest that while rare tRNA augmentation and mRNA folding energies can significantly contribute to increased protein expression, preferred codon usage, in this case, is advantageous to translational efficiency of biologically active PEDF in E coli. This strategy will undoubtedly fast forward studies to validate therapeutic utility of PEDF in vivo.

PEDF and GDNF are key regulators of photoreceptor development and retinal neurogenesis in reaggregates from chick embryonic retina

Here, role(s) of pigment epithelial-derived factor (PEDF) and glial-derived neurotrophic factor (GDNF) on photoreceptor development in three-dimensional reaggregates from the retinae of the E6 chick embryo (rosetted spheroids) was investigated. Fully dispersed cells were reaggregated under serum-reduced conditions and supplemented with 50 ng/ml PEDF alone or in combination with 50 ng/ml GDNF. The spheroids were analyzed for cell growth, differentiation, and death using proliferating cell nuclear antigen, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling, and other immunocytochemical stainings and semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) methods. PEDF strongly promoted synthesis of the messenger RNAs for blue and violet cone opsins and to a lesser extent on the red and green cone opsins. This correlated with an increase in the number of cone photoreceptors, as determined by the cone cell marker CERN906. Likewise, PEDF nearly completely inhibited rod differentiation, as detected by immunostaining with anti-rho4D2 and RT-PCR. Furthermore, PEDF accelerated proliferation of cells in the spheroids and inhibited apoptosis. As negative effects, PEDF inhibited the normal histotypic tissue formation of retinal aggregates and reduced the frequency of photoreceptor rosettes and IPL-like areas. Noticeably, supplementation of PEDF-treated cultures with GDNF reversed the effects of PEDF on spheroid morphology and on rod differentiation. This study establishes that PEDF strongly affects three-dimensional retinogenesis in vitro, most notably by inhibiting rod development and supporting proliferation and differentiation of cones, effects which are partially counteracted by GDNF.

Expression and purification of functional recombinant human pigment epithelium-derived factor (PEDF) secreted by the yeast Pichia pastoris

Pigment epithelium-derived factor (PEDF) combines neurotrophic, neuroprotective, anti-angiogenic, anti-tumor and neural stem cell self-renewal properties in a single molecule, making this protein a valuable potential therapeutic agent. We herein analyzed the expression of human recombinant full-length PEDF, and its N- and C-terminal regions (amino acids 1-243 and 195-418, respectively) in three mammalian cell lines (HEK-293T, COS-1, and 26HCMsv), and in the yeast Pichia pastoris. The highest production of recombinant PEDF was achieved in P. pastoris which secreted approximately 30 microg of full-length rPEDF, and 47 microg of C-terminal/ml of culture medium. Full-length rPEDF was purified by one-step Ni-chelating high-performance liquid chromatography, recovering almost 70% of secreted rPEDF with a purity of 98.6%. The C-terminal region of PEDF was isolated by low-pressure liquid chromatography, recovering around 4% of the recombinant molecule with a purity of 98%. The N-terminal region of PEDF was not secreted by any expression system assayed. The two isolated recombinant PEDF polypeptides inhibited in vitro endothelial cell migration, and full-length rPEDF also increased cerebellar granule cell survival, thus demonstrating their biological activity. These polypeptides can be used to investigate the therapeutic role of PEDF in cancer, neurodegenerative and ocular diseases, and stem cell-based therapies.

Changes in pigment epithelium-derived factor expression following kainic acid induced cerebellar lesion in rat

Pigment epithelium-derived factor (PEDF) is a potent and broad-acting neurotrophic factor that protects various types of cultured neurons against glutamate excitotoxicity and induced apoptosis. The expression pattern and functions of PEDF in the central nervous system (CNS) remain largely undetermined. In this study, we analyzed the spatial and temporal expression of PEDF in normal and kainic acid (KA)-induced lesioned rat cerebellum using immunoblotting, immunohistochemistry and fluorescent in situ hybridization techniques. In normal rat cerebellum, PEDF protein and mRNA were mostly confined and co-localized with calbindin-positive cells in the Purkinje cell layer of the cerebellum, but not with glial fibrillary acidic protein (GFAP)-, 2', 3'-cyclic nucleotide 3'-phosphodiesterase (CNPase)-, and isolectin B4-positive cells. Injection of KA into the right cellebellum caused severe loss of calbindin-positive Purkinje neurons, and an increased number of GFAP-positive astrocytes and isolectin B4-positive microglia was observed on the ipsilateral side of the lesioned cerebellum. Although the PEDF level on the ipsilateral side of the cerebellum was dramatically decreased 2 days after KA treatment, significantly elevation of PEDF levels was observed at 7 days. In agreement with these results, PEDF protein and PEDF mRNA expression were co-localized with GFAP-positive reactive astrocytes in the ipsilateral side 7 days after KA treatment. Although the mechanism by which PEDF is induced in reactive astrocytes remains unclear, the increase in PEDF expression in injured brain may form part of a compensation mechanism against neuronal degeneration.

Cancer gene therapy targeting angiogenesis: An updated Review

Since the relationship between angiogenesis and tumor growth was established by Folkman in 1971, scientists have made efforts exploring the possibilities in treating cancer by targeting angiogenesis. Inhibition of angiogenesis growth factors and administration of angiogenesis inhibitors are the basics of anti-angiogenesis therapy. Transfer of anti-angiogenesis genes has received attention recently not only because of the advancement of recombinant vectors, but also because of the localized and sustained expression of therapeutic gene product inside the tumor after gene transfer. This review provides the up-to-date information about the strategies and the vectors studied in the field of anti-angiogenesis cancer gene therapy.

Pigment epithelium-derived factor inhibits oxidative stress-induced cell death by activation of extracellular signal-regulated kinases in cultured retinal pigment epithelial cells

Oxidative stress-induced retinal pigment epithelial (RPE) cell death is involved in the pathogenesis of age-related macular degeneration (AMD). Pigment epithelium-derived factor (PEDF) is an anti-angiogenic/neurotropic dual functional factor, and recently it was also shown to mediate anti-oxidative action. In the present study, the influence of PEDF in hydrogen peroxide (H(2)O(2))-induced RPE cell death was investigated using nontransformed human RPE cell line (ARPE-19). The recombinant PEDF was purified from E. coli. The MTT cell viability assay showed that PEDF rescued ARPE-19 from H(2)O(2)-induced cell death in a dose- and time-dependent manner. Western blot analysis revealed that PEDF stimulated the extracellular signal-regulated kinases (ERK1/2) phosphorylation. The PEDF cytoprotective effect was significantly attenuated by the ERK1/2 inhibitor PD98059. In this study, we demonstrate that PEDF induces ERK1/2 phosphorylation and we further suggest that the ERK signal cascade contributes to RPE cell's cytoprotection against oxidative stress.

Novel method for expression and purification of human pigment epithelium-derived factor with biological activities in Escherichia coli

We developed a novel method for the expression and purification of recombinant human PEDF in Escherchia coli, and proved it to be simple, convenient, and cheap to obtain this protein with biological activity intact. Human PEDF gene, amplified by PCR from human retinal cNDA library, was cloned into the prokaryotic expression vector pET-22b(+). The recombinant pET-22b(+)/PEDF was expressed in E. coli strain BL21(DE3). The recombinant protein showed a molecular weight of about 50 kDa and was mainly in the form of inclusion bodies according to SDS-PAGE and Western blot analysis. The insoluble rPEDF was solublized from inclusion bodies by denaturation using 6 M urea, purified by His-tag affinity chromatography, and renatured to natural structure by dialysis in the presence of DTT. The rPEDF could cell-type-specifically inhibit HRCEC proliferation in a dose-dependent manner and induce HRCEC apoptosis.

Pigment epithelium-derived factor protects retinal pigment epithelium from oxidant-mediated barrier dysfunction

Retinal pigment epithelium (RPE) cells form a monolayer at the blood-retina barrier between the retina and choriocapillaries. The barrier function may be damaged by multiple stresses to the cell, including the repeated exposure to oxidants that are generated by photoreceptor cell turnover. The purpose of our study was to document the protective effect of pigment epithelium-derived factor (PEDF), a tropic factor produced by the RPE, on H(2)O(2)-induced RPE barrier dysfunction. When assayed by a FITC-labeled dextran transepithelial flux, the increased permeability of the RPE barrier (induced by H(2)O(2)) was prevented by PEDF pretreatment. To further explore the mechanism leading to this permeability change, we investigated the distribution of cytoskeleton and junctional proteins. The redistribution of the two junctional proteins occludin, and N-cadherin and actin reorganization in RPE, induced by H(2)O(2), can be prevented by PEDF pretreatment. PEDF can also prevent H(2)O(2)-induced stress kinase p38/27-kDa heat shock protein signaling which is known to mediate actin rearrangement. These findings indicated that PEDF can stabilize actin, maintain normal membrane occludin and N-cadherin structure, and preserve the barrier function of RPE cells against oxidative stress.

Variable phosphorylation states of pigment-epithelium-derived factor differentially regulate its function

The pigment epithelium-derived factor (PEDF) belongs to the family of noninhibitory serpins. Although originally identified in the eye, PEDF is widely expressed in other body regions including the plasma. This factor can act either as a neurotrophic or as an antiangiogenic factor, and we previously showed that the 2 effects of PEDF are regulated through phosphorylation by PKA and CK2. Here, we studied the interplay between the PKA and CK2 phosphorylation of PEDF, and found that a PEDF mutant mimicking the CK2-phosphorylated PEDF cannot be phosphorylated by PKA, while the mutant mimicking the PKA-phosphorylated PEDF is a good CK2 substrate. Using triple mutants that mimic the PKA- and CK2-phosphorylated and nonphosphorylated PEDF, we found that PEDF can induce several distinct cellular activities dependent on its phosphorylation. The mutant mimicking the accumulative PKA plus CK2 phosphorylation exhibited the strongest antiangiogenic and neurotrophic activities, while the mutants mimicking the individual phosphorylation site mutants had either a reduced activity or only one of these activities. Thus, differential phosphorylation induces variable effects of PEDF, and therefore contributes to the complexity of PEDF action. It is likely that the triple phosphomimetic mutant can be used to generate effective antiangiogenic or neurotrophic drugs.

Inductive expression and characterization analysis of Paralichthys olivaceus pigment epithelium-derived factor in a virally infected cell line

Pigment epithelium-derived factor (PEDF) is acknowledged to be a non-inhibitory member of the serine protease inhibitor (serpin) superfamily, with antiangiogenesis, and neuroprotective and immunoregulatory function, mainly in the tissues of nervous system. Here, A PEDF gene homolog, Paralichthys olivaceus PEDF (PoPEDF), was isolated from flounder embryonic cells (FEC) treated with UV-inactivated Grass carp hemorrhage virus (GCHV) and subsequently identified as a differentially expressed gene. The full length of PoPEDF cDNA is 1803bp with an open reading frame of 1212bp encoding a 403-amino-acid protein. This deduced protein contains an N-terminal signal peptide, a glycosylation site, a consensus serpin motif, and a 34-mer and a 44-mer fragment, all of which are very conserved in the PEDF family. PoPEDF gene exhibits a conserved exon-intron arrangement with 8 exons and 7 introns. This conserved evolutionary relationship was further confirmed by a phylogenetic analysis, where fish PEDFs and mammalian members formed a well-supported clade. Constitutive expression of PoPEDF was widely detected in many tissues. In response to UV-inactivated GCHV or poly(I:C), PEDF mRNA was upregulated in FEC cells with time. This is the first report on the transcriptional induction of PEDF in virally infected cells.

Pigment epithelium-derived factor induces pro-survival genes through cyclic AMP-responsive element binding protein and nuclear factor kappa B activation in rat cultured cerebellar granule cells: Implication for its neuroprotective effect

Pigment epithelium-derived factor (PEDF) protects immature cerebellar granule cell neurons (CGCs) against apoptosis induced by K+ and serum deprivation. However, the precise mechanism of this protection remains unknown. We recently reported that the transcription factor nuclear factor kappa B (NF-kappaB) is activated in PEDF-treated CGCs. Although it is well known that NF-kappaB blocks apoptotic cell death through the induction of pro-survival factors, the effects of PEDF on the expression of these factors are not fully understood. In this study, we employed the use of reverse transcriptase-polymerase chain reaction to analyze the gene expression of certain pro-survival genes and found that genes such as c-IAP1, c-IAP2, FLIPs, A1/Bfl-1 and Mn-SOD were induced in PEDF-treated neurons. On the other hand, no induction was observed of the pro-apoptotic Bcl-2 family members Bax and Bid at any time from 3 to 24 h following PEDF addition. Furthermore, phosphorylation of cyclic AMP-responsive element binding protein (CREB) and increment of nuclear cyclic AMP-response element (CRE)-like DNA binding were observed in PEDF-treated CGCs. The anti-apoptotic effect of PEDF was blocked by overexpression of dominant negative CREB or a mutated form of IkappaBalpha. These results suggested that induction of both CRE- and NF-kappaB-dependent genes is required for the observed neuroprotective effects of PEDF on CGCs.

The regulation of pro-inflammatory gene expression induced by pigment epithelium-derived factor in rat cultured microglial cells

Pigment epithelium-derived factor (PEDF) is a potent and broadly acting neurotrophic factor that protects various cultured neurons against apoptotic stimuli. To investigate whether PEDF acts not only on neurons, but also glial cells, we analyzed the effects of recombinant human PEDF (rhPEDF) on cytokine mRNA levels, transcription factors, and signal transduction pathways in cultured microglial cells. RT-PCR analysis revealed that pro-inflammatory genes such as IL-1beta, IL-6, and TNFalpha were induced in rhPEDF-treated cultured microglial cells. Furthermore, rapid phosphorylation of CREB protein had occurred in rhPEDF-treated neonatal astrocytes. Up-regulation of pro-inflammatory genes by rhPEDF was blocked by overexpression of dominant negative CREB or a mutated form of IkappaBalpha. These results suggest that the induction of pro-inflammatory genes by rhPEDF is mediated via activation of NF-kappaB or CREB in microglial cells. Taken together, these results demonstrate that PEDF is a multipotent factor, capable of affecting not only neurons, but also microglial cells, and suggests that it may act as a neuro-immune modulator in the rodent brain.

Production of active pigment epithelium-derived factor inE. coli

Human pigment epithelium-derived factor (PEDF), a neurotrophic factor, is the most potent natural inhibitor of angiogenesis. To produce the active PEDF, the gene coding for the human PEDF protein was expressed in E. coli. The rPEDF protein was expressed at 457 mg l-1 as a soluble protein. The yield of purified GST fusion protein was 14 mg l-1. Purified rPEDF inhibited tube formation in endothelial cells.

Pigment epithelium-derived factor induces the production of chemokines by rat microglia

Many studies have shown that pigment epithelium-derived factor (PEDF) has neurotrophic effects on retinal cells and hippocampal, spinal cord, and cerebellar granule cell neurons, but much less work has examined the effects of PEDF on glia. In this study, we show that PEDF changes microglial morphology within 1 h of exposure, to a more deactivated form, while having no effect on the expression of such activation markers as OX-42 and ED-1. In contrast, urea activates acid phosphatase, and PEDF blocks that activation. PEDF also activates NFkappaB, accompanied by the induction of mRNAs and proteins for the chemokines macrophage inflammatory protein-1alpha (MIP-1alpha, MIP-2, and MIP-3alpha. All the chemokines stimulate acid phosphatase activity, and high doses of MIP-2 and MIP-3alpha), alter the morphology of the microglia at 1 h after treatment. These results suggest that the use of PEDF for clinical treatments, such as for retinal neovascularization, brain injury, or ischemia, should be undertaken with caution because of the possibility of induction of inflammation caused by microglial or other immune cell migration in response to the chemokines induced by PEDF.

Pigment epithelium-derived factor induces pro-inflammatory genes in neonatal astrocytes through activation of NF-?B and CREB

Pigment epithelium-derived factor (PEDF) is a potent and broadly acting neurotrophic factor that protects neurons in various types of cultured neurons against glutamate excitotoxicity and induced-apoptosis. Some of the effects of PEDF reflect specific changes in gene expression, mediated via activation of the transcription factor NF-kappa B in neurons. To investigate whether PEDF also modulates gene expression in astrocytes, we employed the use of RT-PCR to analyze the gene expression of certain pro-inflammatory genes and found that genes such as IL-1 beta, IL-6, TNF-alpha, MIP1 alpha, and MIP3 alpha were induced in PEDF-treated cultured neonatal astrocytes, but not in adult astrocytes. Electrophoresis mobility shift assay (EMSA) revealed that a time- and dose-dependent increase of NF-kappa B- and AP-1-DNA binding activity was observed in PEDF-treated neonatal astrocytes. Furthermore, rapid phosphorylation of CREB protein had occurred in PEDF-treated neonatal astrocytes. Upregulation of pro-inflammatory and AP-1-related genes by PEDF was blocked by overexpression of dominant negative CREB or a mutated form of I kappa B alpha. These results suggest that the induction of pro-inflammatory genes is mediated via activation of NF-kappa B, AP-1, and CREB in neonatal astrocytes. Taken together, these results demonstrate that PEDF is a multipotent factor, capable of affecting not only neurons, but also neonatal astrocytes, and suggests that it may act as a neuroimmune modulator in the developmental brain.

Inhibition of glioma invasion by overexpression of pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a potent inhibitor of angiogenesis and an inducer of neural differentiation. We previously reported the loss of PEDF expression in glioma progression. In this study, we investigated whether PEDF overexpression could suppress glioma growth and invasion. Glioma cell line U251 was stably transfected with a full-length human PEDF expression vector. The expression and release of various cytokines and angiogenic factors into the medium were analyzed by real-time reverse transcription-polymerase chain reaction, enzyme-linked immunosorbent assay, and gelatin zymography. Apoptosis was checked by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling. Growth inhibition was evaluated by using the in vitro Matrigel invasion. Tumorigenicity was examined in vivo by subcutaneous xenotransplantation into severe combined immunodeficient mice. In U251 cells overexpressing PEDF, thrombospondin-1 protein was upregulated (5.3-fold more), but the production of vascular endothelial growth factor (VEGF) (1.8-fold less) and basic fibroblast growth factor (2.5-fold less) was lower than in cells transfected with the vector only. PEDF also downregulated the production of matrix metalloproteinase-9. Conditioned medium collected from the PEDF-transfected U251 cells showed a significant reduction of VEGF expression. In vitro invasiveness was reduced by approximately 40%. PEDF expression prevented the growth of transfected cells and caused a significant increase in the percentage of cells undergoing apoptosis (50.4% in PEDF-transfected cells). Furthermore, the size of xenotransplants was significantly smaller. In conclusion, PEDF overexpression decreased malignancy, and this might be attributed to the promotion of apoptosis and the regulation of expression of angiogenic effectors. Thus, treatment with PEDF may be useful in patients with malignant gliomas. However, the mechanism of apoptosis induction needs to be investigated.

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.

PEDF derived from glial Müller cells: a possible regulator of retinal angiogenesis

A precise balance between stimulators and inhibitors of angiogenesis, such as vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF), respectively, is essential for angiogenic homeostasis in ocular tissues. Retinal hypoxia is accompanied by some pathological conditions that may promote intraocular neovascularization. Here we demonstrate that retinal glial (Müller) cells express and release pigment epithelium-derived factor (PEDF). Decreasing oxygen concentrations cause strong attenuation of PEDF release resulting in enhanced VEGF/PEDF ratios. Exposure of Müller cells to VEGF suppressed PEDF release in a dose-dependent manner. This may represent a novel mechanism of ocular angiogenic homeostasis sufficient in the control of PEDF levels during normoxia or mild hypoxia but supplemented by other (hitherto unknown) mechanisms in cases of strong hypoxia. In spite of the enhanced VEGF/PEDF ratios resulting from hypoxia, conditioned media of Müller cells failed to stimulate additional proliferation of retinal endothelial cells. These findings suggest that in the ischemic retina, Müller cells generate a permissive condition for angiogenesis by secreting more VEGF and less PEDF, but the onset of retinal endothelial cell proliferation requires another triggering signal that remains to be identified.

In vitro studies of pigment epithelium-derived factor in human Schwann cells after treatment with axolemma-enriched fraction

Pigment epithelium-derived factor (PEDF) is a multifunctional protein with known anti-angiogenic and trophic properties, capable of promoting the survival and growth of Schwann cells (SC). Normal rat SCs and ganglioneuroma-derived human SCs secrete PEDF. The ability of normal SC to secrete a number of trophic factors is controlled by axonal contact. Normal human Schwann cells (HSC) and malignant peripheral nerve sheath tumors (MPNST) cell lines synthesize and secrete PEDF as determined by reverse transcription PCR analysis for PEDF mRNA, immunocytochemistry, and Western blot analysis for PEDF protein. Two MPNST cell lines secreted higher levels of PEDF than did HSC. A 90.3% decrease in PEDF mRNA and a 29.3% decrease in secreted PEDF were observed after treatment of HSC with axolemma-enriched fraction (AEF, 100 microg/ml), a neuronal membrane fraction of the axonal plasma membrane used with cultured SC to mimic axonal contact in vitro. PEDF levels remained unchanged, however, in MPNST-derived SC conditioned media under the same treatment paradigm. These results suggest that MPNST SC lose the ability to downregulate PEDF upon axonal contact, which is characteristic of HSC. The elevated PEDF levels expressed by MPNST cell lines may serve to promote their proliferation and survival.

Loss of EPC-1/PEDF expression during skin aging in vivo

EPC-1/PEDF (early population doubling level cDNA-1/retinal pigmented epithelium-derived factor) is a single-copy, quiescence-specific gene that is transcribed into a 1.5 kb mRNA and then translated into a 50 kDa secreted protein that is a potent inhibitor of angiogenesis. EPC-1 expression has been detected in a number of cultured cell lines, including lung and skin fibroblasts, retinal pigmented epithelial cells, and endometrial stromal fibroblasts. Furthermore, its expression has been shown to decline during replicative aging of these cells in culture. In this report, we describe our examination of the age-related changes in EPC-1 expression in situ in skin sections from donors of different ages. EPC-1 mRNA is detected primarily in the dermal layer of the skin and its expression declines with increasing donor age. This decline is statistically significant between young (less than 31 years old) and middle-aged (between 30 and 60 years old) donors, with the decline becoming less dramatic at older ages. This age-related decline in the expression of an angiogenic inhibitor contributes to the imbalance of angiogenic modulators that is observed during aging. In fact, this decline may reflect a compensatory change to help reverse the decline of angiogenesis marked by reduced abundance of microvessels. This downregulation of an angiogenesis inhibitor may, in turn, play a critical role in the development of diseases caused by abnormal vascularization. The potential role of the age-associated decline in EPC-1 expression in tissue remodeling and in the development of skin diseases with excessive angiogenesis may provide new insights into disease prevention.

Identification of the antivasopermeability effect of pigment epithelium-derived factor and its active site

Vascular permeability plays a key role in a wide array of life-threatening and sight-threatening diseases. Vascular endothelial growth factor can increase vascular permeability. Using a model system for nonproliferative diabetic retinopathy, we found that pigment epithelium-derived factor (PEDF) effectively abated vascular endothelial growth factor-induced vascular permeability. A 44-amino acid region of PEDF was sufficient to confer the antivasopermeability activity. Additionally, we identified four amino acids (glutamate-101, isoleucine-103, leucine-112, and serine-115) critical for this activity. PEDF, or a derivative, could potentially abate or restore vision loss from diabetic macular edema. Furthermore, PEDF may represent a superior therapeutic approach to sepsis-associated hypotension, nephrotic syndrome, and other sight-threatening and life-threatening diseases resulting from excessive vascular permeability.

Pigment epithelium-derived factor in the monkey retinal pigment epithelium and interphotoreceptor matrix: apical secretion and distribution

Pigment epithelium-derived factor (PEDF) is an extracellular protein derived from the retinal pigment epithelium (RPE), a tissue formed by polarized cells that release growth and trophic factors in a directional fashion. We have investigated the distribution and directional release of PEDF protein by the monkey RPE. We established primary cultures of monkey RPE cells that expressed the PEDF gene, and that synthesized and secreted the PEDF protein. Northern analysis of RPE cultures and monkey ocular tissues showed that PEDF transcripts were highly expressed in RPE as compared with several other monkey ocular tissues, being even more abundant in cultured cells than they were in the native RPE. The differentiated RPE cells in culture secreted protein that shared the immunological, biochemical and biological characteristics of PEDF. The overall PEDF levels in the RPE conditioned media reached 6.5 mg ml- after 8 days in culture (i.e. 1.1 pg of PEDF per RPE cell). RPE cells were cultivated on permeable supports as monolayers forming a barrier between apical and basal compartments. Apical and basal culture media were sampled at three or four-day intervals for 18 cycles, and the PEDF content was quantified. Most of the PEDF protein was significantly higher in the apical than in the basal medium (>4 times) at the initial recovery intervals, to be detected only in the apical medium at the latter intervals. In the native monkey eye, the concentration of soluble PEDF in the interphotoreceptor matrix (144 nM) was 7-fold and 25-fold greater than in vitreous and aqueous, respectively. PEDF was abundant in the interphotoreceptor matrix surrounding rod and cone outer segments, and was detectable at lower levels in the RPE as visualized by confocal microscopy. We concluded that PEDF synthesized by the RPE is secreted preferentially from the apical surface and is distributed apically to the RPE bordering the outer segments of photoreceptors. PEDF can be a useful marker for RPE polarization and differentiation. The polarization of RPE may be an important mechanism to control PEDF secretion and our results offer interesting possibilities on regulation of PEDF.

Treatment of cerebellar granule cell neurons with the neurotrophic factor pigment epithelium-derived factor in vitro enhances expression of other neurotrophic factors as well as cytokines and chemokines

Microarray analyses demonstrated that a variety of genes was affected by treatment of cerebellar granule cell neurons with the neurotrophic factor pigment epithelium-derived factor (PEDF). The genes for neurotrophins, glial cell-derived neurotrophic factor (GDNF), and their receptors were regulated differentially in immature versus mature neurons; however, nerve growth factor (NGF), neurotrophin (NT)-3, and GDNF did not contribute to the protective effect of PEDF. Brain-derived neurotrophic factor (BDNF) seemed capable of inducing apoptosis, because a blocking antibody enhanced the protective effect of PEDF. In addition, PEDF exposure also stimulated expression of several cytokine and chemokine genes. Removal of the less than 1% of microglia in the cultures by treatment with L-leucine methyl ester, combined with enzyme-linked immunosorbent assays (ELISAs), demonstrated that the cerebellar granule cells constitutively produce three chemokines, macrophage inflammatory protein (MIP)-1alpha, MIP-2, and MIP-3alpha, whose production is enhanced further by treatment with PEDF. Blocking antibodies to each of the chemokines was protective under control conditions, suggesting that they may contribute to the "natural" apoptosis occurring in the cultures, and enhanced the effects of PEDF. Although PEDF enhanced production of all three chemokines, the blocking antibodies did not increase its protective effect against induced apoptosis. These results suggest that although PEDF enhances expression of other neurotrophic factors or chemokines, it does not exert its neuroprotective effect on cerebellar granule cells through their production.

Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies

Age-related macular degeneration is the principal cause of registered legal blindness among those aged over 65 in the United States, western Europe, Australia, and Japan. Despite intensive research, the precise etiology of molecular events that underlie age-related macular degeneration is poorly understood. However, investigations on parallel fronts are addressing this prevalent public health problem. Sophisticated biochemical and biophysical techniques have refined our understanding of the pathobiology of drusen, geographic atrophy, and retinal pigment epithelial detachments. Epidemiological identification of risk factors has facilitated an intelligent search for underlying mechanisms and fueled clinical investigation of behavior modification. Gene searches have not only brought us to the cusp of identifying the culpable gene loci in age-related macular degeneration, but also localized genes responsible for other macular dystrophies. Recent and ongoing investigations, often cued by tumor biology, have revealed an important role for various growth factors, particularly in the neovascular form of the condition. Transgenic and knockout studies have provided important mechanistic insights into the development of choroidal neovascularization, the principal cause of vision loss in age-related macular degeneration. This in turn has culminated in preclinical and clinical trials of directed molecular interventions.

Secretion of pigment epithelium-derived factor. Mutagenic study

Pigment epithelium-derived factor (PEDF), a neurotrophic and antiangiogenic protein, is an extracellular component of the retinal interphotoreceptor matrix which has been shown to be secreted by human fetal retinal pigment epithelial cells. It belongs to the serpin superfamily and contains the typical exposed reactive center loop. The function of this loop is still unknown. In this study we used site-directed mutagenesis of the cDNA encoding PEDF to show that (a) truncation of the C-terminal tail (Pro415-Pro418) of PEDF, (b) deletion of the Pro373-Ala380 segment that resides within the reactive center loop of the protein, and (c) alanine substitution of amino-acid residues Asn391-Thr403 located within its hydrophobic core inhibit PEDF secretion, but not its transcription, by cells transfected with the various PEDF cDNAs. On the basis of the crystal structure of PEDF, these mutations are presumed to alter the protein conformation, suggesting that conservation of the 3D structure of PEDF is essential for its secretion. In addition, we show that replacement of Gly376 and Leu377 with alanine prevents PEDF secretion. As these two residues are located within the highly exposed segment of the reactive center loop, we propose a novel function for this loop in PEDF. Our results imply that the reactive center loop, specifically Gly376 and Leu377, is involved in the interaction of PEDF with components of the quality control system in the endoplasmic reticulum, thus ensuring its efficient secretion.

Mapping the type I collagen-binding site on pigment epithelium-derived factor. Implications for its antiangiogenic activity

Pigment epithelium-derived factor (PEDF), a neurotrophic and antiangiogenic serpin, is identified in tissues rich in collagen, e.g. cornea, vitreous, bone, and cartilage. We show that recombinant human PEDF formed complexes with collagens from the bovine cornea and vitreous. We have examined the direct binding of PEDF to collagen I and found that interactions were ionic in nature and occurred when PEDF and collagen I were both in solution, when either one was immobilized, or even when collagen I was denatured under reducing conditions. (125)I-PEDF bound to immobilized collagen I in a saturable fashion (K(D) = 123 nm). Compared with neurotrophic PEDF-derived peptides, ovalbumin and angiogenic inhibitors, only full-length PEDF competed efficiently with (125)I-PEDF for the binding to immobilized collagen I (EC(50) = 3 microg/ml). The collagen-binding region was analyzed using controlled proteolysis and chemically modified PEDF. Cleavage of the serpin exposed loop did not prevent binding to collagen I. Conjugation of lysines with fluorescein increased the collagen binding affinity. However, treatment of PEDF with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide abolished it, implicating the PEDF aspartic and/or glutamic acid residues in its interaction with collagen I. A negatively charged region on the surface of the PEDF molecule is rich in acidic residues (Glu(41), Glu(42), Glu(43), Asp(44), Asp(64), Asp(256), Asp(258), Glu(290), Glu(291), Glu(296), Asp(300), Glu(304)) available to interact directly with positively charged areas of collagen. This represents the first collagen-binding site described for a serpin, which in PEDF, is distinct from its heparin-binding region, neurotrophic active site, and its serpin exposed loop. The collagen-binding property of PEDF may play a role in surface localization and modulation of its antiangiogenic effects in the eye and bone.