Pigment epithelium-derived factor (PEDF) binds to glycosaminoglycans: analysis of the binding site

Unravelling the Impact of Cyclic Mechanical Stretch in Keratoconus-A Transcriptomic Profiling Study

Biomechanical and molecular stresses may contribute to the pathogenesis of keratoconus (KC). We aimed to profile the transcriptomic changes in healthy primary human corneal (HCF) and KC-derived cells (HKC) combined with TGFβ1 treatment and cyclic mechanical stretch (CMS), mimicking the pathophysiological condition in KC. HCFs (n = 4) and HKCs (n = 4) were cultured in flexible-bottom collagen-coated 6-well plates treated with 0, 5, and 10 ng/mL of TGFβ1 with or without 15% CMS (1 cycle/s, 24 h) using a computer-controlled Flexcell FX-6000T Tension system. We used stranded total RNA-Seq to profile expression changes in 48 HCF/HKC samples (100 bp PE, 70-90 million reads per sample), followed by bioinformatics analysis using an established pipeline with Partek Flow software. A multi-factor ANOVA model, including KC, TGFβ1 treatment, and CMS, was used to identify differentially expressed genes (DEGs, |fold change| ≥ 1.5, FDR ≤ 0.1, CPM ≥ 10 in ≥1 sample) in HKCs (n = 24) vs. HCFs (n = 24) and those responsive to TGFβ1 and/or CMS. PANTHER classification system and the DAVID bioinformatics resources were used to identify significantly enriched pathways (FDR ≤ 0.05). Using multi-factorial ANOVA analyses, 479 DEGs were identified in HKCs vs. HCFs including TGFβ1 treatment and CMS as cofactors. Among these DEGs, 199 KC-altered genes were responsive to TGFβ1, thirteen were responsive to CMS, and six were responsive to TGFβ1 and CMS. Pathway analyses using PANTHER and DAVID indicated the enrichment of genes involved in numerous KC-relevant functions, including but not limited to degradation of extracellular matrix, inflammatory response, apoptotic processes, WNT signaling, collagen fibril organization, and cytoskeletal structure organization. TGFβ1-responsive KC DEGs were also enriched in these. CMS-responsive KC-altered genes such as OBSCN, CLU, HDAC5, AK4, ITGA10, and F2RL1 were identified. Some KC-altered genes, such as CLU and F2RL1, were identified to be responsive to both TGFβ1 and CMS. For the first time, our multi-factorial RNA-Seq study has identified many KC-relevant genes and pathways in HKCs with TGFβ1 treatment under CMS, suggesting a potential role of TGFβ1 and biomechanical stretch in KC development.

Pigment epithelium-derived factor downregulation in oestrogen receptor positive breast cancer bone metastases is associated with menopause

Pigment epithelium-derived factor (PEDF) has a critical role in bone development and anti-tumour function in breast cancer (BC). As the expression and role of PEDF in BC bone metastases is unknown, we aimed to characterise PEDF in primary and metastatic BC. Subcellular PEDF localisation was semi-quantitatively analysed via immunohistochemistry in patient-matched, archived formalin-fixed paraffin-embedded primary BC and liver, lung, and decalcified bone metastases specimens. PEDF localisation was evaluated in 23 metastatic BC patients diagnosed with ER+, human epidermal growth factor receptor-2 (HER2) negative BC or TNBC. Cytoplasmic (p = 0.019) and membrane (p = 0.048) PEDF was lower in bone metastases compared to primary ER+/HER2- BC. In contrast, nuclear PEDF scores were higher in metastases compared to primary TNBC (p = 0.027), and increased membrane PEDF in metastatic tissue had improved disease-free interval (p = 0.016). Nuclear PEDF was decreased in bone metastases compared to primary ER+//HER2- BC in post-menopausal patients (p = 0.029). These novel findings indicate PEDF plays a role in clinical BC metastasis. Significantly lower PEDF levels in the post-menopausal compared to pre-menopausal setting suggests future PEDF research may have greater clinical importance in the post-menopausal ER+/HER2- BC population.

NFκB-Mediated Mechanisms Drive PEDF Expression and Function in Pre- and Post-Menopausal Oestrogen Levels in Breast Cancer

Pigment epithelium-derived factor (PEDF) protein regulates normal bone, with anti-tumour roles in bone and breast cancer (BC). Pre- and post-menopausal oestrogen levels may regulate PEDF expression and function in BC, though the mechanisms behind this remain unknown. In this study, in vitro models simulating pre- and post-menopausal bone microenvironments were used to evaluate if PEDF regulates pro-metastatic biomarker expression and downstream functional effects on BC cells. PEDF treatment reduced phosphorylated-nuclear factor-κB p65 subunit (p-NFκB-p65), tumour necrosis factor-α (TNFα), C-X-C chemokine receptor type-4 (CXCR4), and urokinase plasminogen activator receptor (uPAR) in oestrogen receptor (ER)+/human epidermal growth factor receptor-2 (HER2)- BC cells under post-menopausal oestrogen conditions. In triple negative BC (TNBC) cells, PEDF treatment reduced pNFκB-p65 and uPAR expression under pre-menopausal oestrogen conditions. A potential reciprocal regulatory axis between p-NFκB-65 and PEDF in BC was identified, which was BC subtype-specific and differentially regulated by menopausal oestrogen conditions. The effects of PEDF treatment and NFκB inhibition on BC cell function under menopausal conditions were also compared. PEDF treatment exhibited superior anti-viability effects, while combined PEDF and NFκB-p65 inhibitor treatment was superior in reducing BC cell colony formation in a subtype-specific manner. Lastly, immunohistochemical evaluation of p-NFκB-p65 and PEDF expression in human BC and bone metastases specimens revealed an inverse correlation between nuclear PEDF and NFκB expression in bone metastases. We propose that menopausal status is associated with a PEDF/NFκB reciprocal regulatory axis, which drives PEDF expression and anti-metastatic function in a subtype-specific manner. Altogether, our findings identify pre-menopausal TNBC and post-menopausal ER+/HER2- BC patients as target populations for future PEDF research.

Pigment epithelium-derived factor modulates periodontal homeostasis in mice and induces osteogenic differentiation of human periodontal ligament fibroblasts

AIM

The aim of this study was to investigate the influence of pigment epithelium-derived factor (PEDF) on periodontal homeostasis in mice and the osteogenic differentiation of human periodontal ligament fibroblasts (PDLFs).

MATERIALS AND METHODS

Micro-computed tomography and histology were performed to compare the alveolar bone volume, density, and bone-related markers between PEDF-deficient (PEDF^-/-) and wild-type (WT) mice. Furthermore, after recombinant human PEDF treatment, the PDLF viability and osteogenic differentiation were examined using the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity assay, Von Kossa staining, Alizarin red staining, real-time quantitative polymerase chain reaction (qRT-PCR), and immunoblotting.

RESULTS

The alveolar bone volume and density of PEDF^-/- mice were significantly lower than those of the WT mice. Higher receptor activator for nuclear factor-κB ligand (RANKL) expression and lower osteoprotegerin (OPG) expression levels were observed in the PEDF^-/- group. Moreover, PEDF treatment did not affect the PDLF proliferation. PEDF dose-dependently improved mineral deposition. Compared with the control group, 250 ng/mL PEDF promoted OPG mRNA expression in PDLFs on Day 3 but inhibited RANKL, Wnt5a, GSK3b mRNA, and non-phosphorylated β-catenin protein expression. However, 250 ng/mL PEDF had no significant effect on the expression of Wnt3a. On Day 7, after culture with 250 ng/mL PEDF in osteogenic medium, the ALP and RUNX2 protein levels were upregulated. VEGF protein expression was reduced in a dose-dependent manner after PEDF stimulation. The PEDF protein expression increased as the osteogenic induction time increased.

CONCLUSION

PEDF gene knockout suppresses periodontal homeostasis in mice, and PEDF treatment induces PDLF osteogenic differentiation in vitro.

Stage II of Chronic Kidney Disease—A Tipping Point in Disease Progression?

Chronic kidney disease (CKD) is the progressive loss of renal function. Although advances have been made in understanding the progression of CKD, key molecular events in complex pathophysiological mechanisms that mark each stage of renal failure remain largely unknown. Changes in plasma protein profiles in different disease stages are important for identification of early diagnostic markers and potential therapeutic targets. The goal of this study was to determine the molecular profile of each CKD stage (from 1 to 5), aiming to specifically point out markedly expressed or downregulated proteins. We performed a cross-sectional shotgun-proteomic study of pooled plasma across CKD stages and compared them to healthy controls. After sample pooling and heparin-column purification we analysed proteomes from healthy to CKD stage 1 through 5 participants’ plasma by liquid-chromatography/mass-spectrometry. We identified 453 proteins across all study groups. Our results indicate that key events, which may later affect the course of disease progression and the overall pathophysiological background, are most pronounced in CKD stage 2, with an emphasis on inflammation, lipoprotein metabolism, angiogenesis and tissue regeneration. We hypothesize that CKD stage 2 is the tipping point in disease progression and a suitable point in disease course for the development of therapeutic solutions.

Pigment epithelium-derived factor engineered to increase glycosaminoglycan affinity while maintaining bioactivity

Pigment epithelium-derived factor (PEDF) is a secreted protein that is essential in tissue homeostasis and is involved in multiple functions in the eye, such as antiangiogenesis and neuroprotection. However, short retention in the retinal microenvironment can limit its therapeutic effects. In this study, we modified the amino acid sequence of PEDF to increase its affinity for heparin and hyaluronic acid (HA), which are negatively charged extracellular matrix (ECM) molecules. HA is the major component of the vitreous humor. We selectively converted neutral or anionic residues into cationic residues to obtain engineered PEDF (ePEDF). Using in vitro binding assays, we demonstrate that ePEDF had higher affinity for heparin and HA than wild-type PEDF (wtPEDF). ePEDF exhibited antiangiogenic and retinal survival bioactivities. It inhibited endothelial cell proliferation and tube formation in vitro. In an ex vivo model mimicking retinal degeneration, ePEDF protected photoreceptors from cell death. The findings suggest that protein engineering is an approach to develop active PEDF with higher ECM affinity to potentially improve its retention in the retina microenvironment and in turn make it a more efficient therapeutic drug for retinal diseases.

Association of overhydration and serum pigment epithelium-derived factor with CKD progression in diabetic kidney disease: A prospective cohort study

AIM

Little is known about whether overhydration (OH), measured using bioimpedance assay (BIA), is associated with CKD progression in patients with type 2 diabetes mellitus (T2DM). We hypothesised that OH was a predictor, and pigment epithelium-derived factor (PEDF) was a modifiable risk factor of CKD progression.

METHODS

We conducted a prospective cohort study of 1,065 patients with clinically euvolemic T2DM who attended the diabetes centre in a tertiary hospital or primary care clinic. CKD progression was defined as a combination of the worsening of the KDIGO defined CKD category by eGFR and a ≥25% decline in eGFR compared to baseline.

RESULTS

Patients with T2DM in the highest tertile of OH and relative OH (OH/ extracellular water > 7%) were positively associated with CKD progression (hazard ratio [HR] 1.45 [95% confidence interval (CI) 1.14-1.85; p = 0.003 and HR 1.29 [95%CI 1.05-1.59; p = 0.017]). There were positive associations between PEDF and CKD progression (β = 1.10; p = 0.001) and between OH and CKD progression (β = 0.21; p = 0.036). OH remained positively associated with CKD progression mediated by PEDF.

CONCLUSIONS

OH is an independent risk factor for CKD progression in patients with T2DM. Our study supports the novel definition of PEDF as a positive mediator between OH and CKD progression.

Injectable in-situ gel depot system for targeted delivery of biologics to the retina

In current clinical settings, frequent intravitreal (IVT) injections of anti-vascular endothelial growth factors are used due to their short in-vivo half-life and rapid clearance from the back of the eye. The IVT injections are associated with pain, risk of infection, retinal detachment, and financial burden. Biologics molecules can undergo physical, chemical, and enzymatic degradation during formulation development and in the biological environment. Moreover, the complex ocular structures also act as a rate-limiting barrier for these biologics. Thus, delivering stable and clinically relevant biologics concentration to the back of the eye is still a challenge. Compare to other drug delivery platforms, injectable in-situ gelling depot systems (IISGDs) have emerged as an effective system for biologics delivery. In this review, we have discussed various biologics used in ocular therapeutics and their associated challenges. Different routes of delivery and associated tissue barriers are also discussed. Different types of IISGDs developed to date for biologics delivery to the back of the eye were also covered. To conclude, various critical parameters related to the formulation development process and injectable depot systems that need careful consideration and further investigations were highlighted.

Spatiotemporal regulation of PEDF signaling by type I collagen remodeling

Dynamic remodeling of the extracellular matrix affects many cellular processes, either directly or indirectly, through the regulation of soluble ligands; however, the mechanistic details of this process remain largely unknown. Here we propose that type I collagen remodeling regulates the receptor-binding activity of pigment epithelium-derived factor (PEDF), a widely expressed secreted glycoprotein that has multiple important biological functions in tissue and organ homeostasis. We determined the crystal structure of PEDF in complex with a disulfide cross-linked heterotrimeric collagen peptide, in which the α(I) chain segments-each containing the respective PEDF-binding region (residues 930 to 938)-are assembled with an α2α1α1 staggered configuration. The complex structure revealed that PEDF specifically interacts with a unique amphiphilic sequence, KGHRGFSGL, of the type I collagen α1 chain, with its proposed receptor-binding sites buried extensively. Molecular docking demonstrated that the PEDF-binding surface of type I collagen contains the cross-link-susceptible Lys930 residue of the α1 chain and provides a good foothold for stable docking with the α1(I) N-telopeptide of an adjacent triple helix in the fibril. Therefore, the binding surface is completely inaccessible if intermolecular crosslinking between two crosslink-susceptible lysyl residues, Lys9 in the N-telopeptide and Lys930, is present. These structural analyses demonstrate that PEDF molecules, once sequestered around newly synthesized pericellular collagen fibrils, are gradually liberated as collagen crosslinking increases, making them accessible for interaction with their target cell surface receptors in a spatiotemporally regulated manner.

Pigment Epithelium-Derived Factor as a Possible Treatment Agent for Choroidal Neovascularization

Choroidal neovascularization (CNV) is a sight-threatening disease and is characterized by the formation of pathological neovascularization in the choroid which extends into the subretinal space. Exudative age-related macular degeneration (AMD) is the formation of CNV in the macular area which leads to irreversible blindness. Continuous leakage and hemorrhage of the CNV lesion may eventually result in scarring or later fibrosis, which could result in photoreceptor cell atrophy. The current strategy for treating CNV is the use of antivascular endothelial growth factor (VEGF) agents. Many studies have demonstrated the efficacy of intravitreal anti-VEGF therapy. Other studies have also reported the side effects of single anti-VEGF treatment. And long-term inhibition of a single system may result in collateral damage to other visual elements. Pigment epithelium-derived factor (PEDF) is a 50 kDa protein that was first isolated from the conditioned medium of human RPE cells. PEDF has both antiangiogenesis and neuroprotective functions for photoreceptor cells. It may be a potential ocular antiangiogenic agent. This review outlines the distribution of PEDF in the eye, the mechanism of antiangiogenesis, the protective effect on the retina, and the relationship between PEDF and VEGF.

The role of pigment epithelium-derived factor in protecting against cellular stress

Since its discovery as a neurotrophic factor in retinal pigmented epithelium cells in the late 1980s, there has been an increase in understanding of the role that pigment epithelium-derived factor (PEDF) plays in cellular functions. PEDF plays an important role in mediating cellular protection during exposure to oxidative stress and inflammation by preventing stress-induced angiogenesis and apoptosis. PEDF acts to reduce oxidative stress by promoting mitochondrial stability and by regulating the expression of enzymes involved in ROS accumulation and clearance. PEDF protects against the negative effects of oxidative stress by regulating cell survival pathways and the expression of inflammatory and proangiogenic mediators. PEDF-mediated cellular protection may be of clinical importance in diseases characterised by oxidative stress, chronic inflammation and pathological neovascularization, indicating that targeting PEDF may be a potential focus for therapeutic interventions in chronic diseases. In this review, we provide a historical perspective on the discoveries of PEDF interactions and functions, and discuss recent in vitro, in vivo and clinical findings to provide a current summary of the important protective effects following cellular exposure to stress stimuli and future clinical potential of PEDF.

Pigment epithelium-derived factor in lipid metabolic disorders

Pigment epithelium-derived factor (PEDF) is a secreted glycoprotein that has anti-angiogenic, anti-proliferative, neurotrophic and immunomodulatory properties. PEDF has recently emerged as a critical metabolic regulatory protein since the discovery of its modulatory activities in the lipolytic pathway by binding to adipose triglyceride lipase (ATGL). Despite being beneficial in maintaining the homeostasis of hepatic lipid accumulation, PEDF has been uncovered an unfavorable role associated with insulin resistance. The molecular events that connect these two apparent distinct observations have been controversial and remained largely unknown. Therefore in this short review, we attempt to summarize the current findings of PEDF regarding its lipid metabolic functions and provide perspectives in identifying PEDF as a potential therapeutic target in lipid disorders.

The effects of pigment epithelium-derived factor on atherosclerosis: putative mechanisms of the process

Cardiovascular disease (CVD) is a leading cause of death worldwide. Atherosclerosis is believed to be the major cause of CVD, characterized by atherosclerotic lesion formation and plaque disruption. Although remarkable advances in understanding the mechanisms of atherosclerosis have been made, the application of these theories is still limited in the prevention and treatment of atherosclerosis. Therefore, novel and effective strategies to treat high-risk patients with atherosclerosis require further development. Pigment epithelium-derived factor (PEDF), a glycoprotein with anti-inflammatory, anti-oxidant, anti-angiogenic, anti-thrombotic and anti-tumorigenic properties, is of considerable interest in the prevention of atherosclerosis. Accumulating research has suggested that PEDF exerts beneficial effects on atherosclerotic lesions and CVD patients. Our group, along with colleagues, has demonstrated that PEDF may be associated with acute coronary syndrome (ACS), and that the polymorphisms of rs8075977 of PEDF are correlated with coronary artery disease (CAD). Moreover, we have explored the anti-atherosclerosis mechanisms of PEDF, showing that oxidized-low density lipoprotein (ox-LDL) reduced PEDF concentrations through the upregulation of reactive oxygen species (ROS), and that D-4F can protect endothelial cells against ox-LDL-induced injury by preventing the downregulation of PEDF. Additionally, PEDF might alleviate endothelial injury by inhibiting the Wnt/β-catenin pathway. These data suggest that PEDF may be a novel therapeutic target for the treatment of atherosclerosis. In this review, we will summarize the role of PEDF in the development of atherosclerosis, focusing on endothelial dysfunction, inflammation, oxidative stress, angiogenesis and cell proliferation. We will also discuss its promising therapeutic implications for atherosclerosis.

So you think computational approaches to understanding glycosaminoglycan-protein interactions are too dry and too rigid? Think again!

Glycosaminoglycans (GAGs) play key roles in virtually all biologic responses through their interaction with proteins. A major challenge in understanding these roles is their massive structural complexity. Computational approaches are extremely useful in navigating this bottleneck and, in some cases, the only avenue to gain comprehensive insight. We discuss the state-of-the-art on computational approaches and present a flowchart to help answer most basic, and some advanced, questions on GAG-protein interactions. For example, firstly, does my protein bind to GAGs?; secondly, where does the GAG bind?; thirdly, does my protein preferentially recognize a particular GAG type?; fourthly, what is the most optimal GAG chain length?; fifthly, what is the structure of the most favored GAG sequence?; and finally, is my GAG-protein system 'specific', 'non-specific', or a combination of both? Recent advances show the field is now poised to enable a non-computational researcher perform advanced experiments through the availability of various tools and online servers.

Pigment Epithelium-Derived Factor (PEDF) mediates cartilage matrix loss in an age-dependent manner under inflammatory conditions

Background

Inflammation is a major cause of cartilage destruction and leads to the imbalance of metabolic activities in the arthritic joint. Pigment epithelium-derived factor (PEDF) has been reported to have both pro- and anti-inflammatory activities in various cell types and to be upregulated in the arthritic joint, but its role in joint destruction is unclear. Our aim was to investigate the role of PEDF in cartilage degeneration under inflammatory conditions.

Methods

PEDF was ectopically expressed in primary human articular chondrocytes, and catabolic gene expression and protein secretion in response to the pro-inflammatory cytokine interleukin 1 beta (IL-1β) were evaluated. Metatarsal bones from PEDF-deficient and wild type mice were cultured in the presence or absence of IL-1β. Cartilage matrix integrity and matrix metalloproteinases MMP-1, MMP-3, and MMP-13 were evaluated. PEDF-deficient and wild type mice were evaluated in the monosodium iodoacetate (MIA) inflammatory joint destruction animal model to determine the role of PEDF in inflammatory arthritis in vivo. Student’s t-tests and Mann–Whitney tests were employed where appropriate, for parametric and non-parametric data, respectively.

Results

We showed that PEDF protein levels were higher in human osteoarthritis samples compared to normal samples. We demonstrated that ectopic PEDF expression in primary human articular chondrocytes exacerbated catabolic gene expression in the presence of IL-1β. In whole bone organ cultures, IL-1β induced MMP-1, MMP-3 and MMP-13 protein production, and caused significant cartilage matrix loss. Interestingly, Toluidine Blue staining showed that PEDF-deficient bones from 29 week old animals, but not 10 week old animals, had reduced matrix loss in response to IL-1β compared to their wild type counterparts. In addition, PEDF-deficiency in 29 week old animals preserved matrix integrity and protected against cell loss in the MIA joint destruction model in vivo.

Conclusion

We conclude that PEDF exacerbates cartilage degeneration in an age-dependent manner under an inflammatory setting. This is the first study identifying a specific role for PEDF in joint inflammation and highlights the multi-faceted activities of PEDF.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-017-1410-y) contains supplementary material, which is available to authorized users.

Anti-tumor effects of pigment epithelium-derived factor (PEDF): implication for cancer therapy. A mini-review

Pigment epithelium-derived factor (PEDF) is a secreted glycoprotein and a non-inhibitory member of the serine protease inhibitor (serpin) family. It is widely expressed in human fetal and adult tissues but its expression decreases with age and in malignant tissues. The main anti-cancer activities of PEDF derive from its dual effects, either indirectly on the tumor microenvironment (indirect antitumor action) or directly on the tumor itself (direct antitumor influence). The indirect antitumor activities of PEDF were uncovered from the early findings that it stimulates retinoblastoma cell differentiation and that additionally it possesses anti-angiogenic, anti-tumorigenic and anti-metastatic properties. The mechanisms of its direct antitumor effect, however, have not been fully elucidated. This review highlights recent progress in our understanding of the multifunctional activities of PEDF and, in particular, its anti-cancer signaling mechanisms. Additionally, we discuss the possibility of using novel phosphaplatin compounds that can upregulate PEDF expression as a chemotherapy for cancer treatment.

Pressure-Induced Alterations in PEDF and PEDF-R Expression: Implications for Neuroprotective Signaling in Glaucoma

Introduction

Alterations in neuron-glia signaling are implicated in glaucoma, a neurodegenerative disease characterized by retinal ganglion cell (RGC) death. Pigment epithelium derived factor (PEDF) is a secreted protein with potential neuroprotective qualities in retinal disease, including chronic ocular hypertension. Here we sought to determine whether moderate, short-term elevations in IOP alter PEDF signaling and whether pressure-induced PEDF signaling directly impacts RGC apoptosis.

Methods

In retina from naïve mice and mice with unilateral, microbead-induced glaucoma, we examined expression and cell type-specific localization of PEDF and its receptor (PEDF-R), using quantitative PCR and immunohistochemistry. Using primary cultures of purified RGCs and Müller cells, we examined cell type-specific expression of PEDF in response to 48 hours of elevated hydrostatic pressure, using multiplex ELISA and immunocytochemistry. We also measured pressure-induced apoptosis of RGCs in the presence or absence of atglistatin, a potent and selective inhibitor of PEDF-R, and recombinant PEDF, using TUNEL assays.

Results

PEDF and PEDF-R are constitutively expressed in naïve retina, primarily in the ganglion cell and nerve fiber layers. Elevated IOP increases PEDF and PEDF-R expression, particularly associated with RGCs and Müller cells. Elevated pressure in vitro increased PEDF secretion by 6-fold in RGCs and trended towards an increase in expression by Müller cells, as compared to ambient pressure. This was accompanied by changes in the subcellular localization of PEDF-R in both cell types. Inhibition of PEDF signaling with atglistatin increased pressure-induced apoptosis in RGCs and treatment with recombinant PEDF inhibited pressure-induced apoptosis, both in a dose-dependent manner.

Conclusion

Our findings suggest that moderate, short-term elevations in IOP promote PEDF signaling via up-regulation of both PEDF and PEDF-R. Based on in vivo and in vitro studies, this PEDF signaling likely arises from both Müller cells and RGCs, and has the potential to directly inhibit RGC apoptosis.

Small Retinoprotective Peptides Reveal a Receptor-binding Region on Pigment Epithelium-derived Factor

The cytoprotective effects of pigment epithelium-derived factor (PEDF) require interactions between an as of a yet undefined region with a distinct ectodomain on the PEDF receptor (PEDF-R). Here we characterized the area in PEDF that interacts with PEDF-R to promote photoreceptor survival. Molecular docking studies suggested that the ligand binding site of PEDF-R interacts with the neurotrophic region of PEDF (44-mer, positions 78-121). Binding assays demonstrated that PEDF-R bound the 44-mer peptide. Moreover, peptide P1 from the PEDF-R ectodomain had affinity for the 44-mer and a shorter fragment within it, 17-mer (positions 98-114). Single residue substitutions to alanine along the 17-mer sequence were designed and tested for binding and biological activity. Altered 17-mer[R99A] did not bind to the P1 peptide, whereas 17-mer[H105A] had higher affinity than the unmodified 17-mer. Peptides 17-mer, 17-mer[H105A], and 44-mer exhibited cytoprotective effects in cultured retina R28 cells. Intravitreal injections of these peptides and PEDF in the rd1 mouse model of retinal degeneration decreased the numbers of dying photoreceptors, 17-mer[H105A] being most effective. The blocking peptide P1 hindered their protective effects both in retina cells and in vivo. Thus, in addition to demonstrating that the region composed of positions 98-114 of PEDF contains critical residues for PEDF-R interaction that mediates survival effects, the findings reveal distinct small PEDF fragments with neurotrophic effects on photoreceptors.

Quantitative proteomics provides new insights into chicken eggshell matrix protein functions during the primary events of mineralisation and the active calcification phase

Eggshell is a bioceramic composed of 95% calcium carbonate mineral and 3.5% organic matrix. Its structural organisation is controlled by its organic matrix. We have used quantitative proteomics to study four key stages of shell mineralisation: 1) widespread deposition of amorphous calcium carbonate (ACC), 2) ACC transformation into crystalline calcite aggregates, 3) formation of larger calcite crystal units and 4) development of a columnar structure with preferential calcite crystal orientation. This approach explored the distribution of 216 shell matrix proteins found at the four stages. Variations in abundance according to these calcification events were observed for 175 proteins. A putative function related to the mineralisation process was predicted by bioinformatics for 77 of them and was further characterised. We confirmed the important role of lysozyme, ovotransferrin, ovocleidin-17 and ovocleidin-116 for shell calcification process, characterised major calcium binding proteins (EDIL3, ALB, MFGE8, NUCB2), and described novel proteoglycans core proteins (GPC4, HAPLN3). We suggest that OVAL and OC-17 play a role in the stabilisation of ACC. Finally, we report proteins involved in the regulation of proteins driving the mineralisation. They correspond to numerous molecular chaperones including CLU, PPIB and OCX21, protease and protease inhibitors including OVM and CST3, and regulators of phosphorylation.

Pigment epithelium-derived factor as a multifunctional regulator of wound healing

During dermal wound repair, hypoxia-driven proliferation results in dense but highly permeable, disorganized microvascular networks, similar to those in solid tumors. Concurrently, activated dermal fibroblasts generate an angiopermissive, provisional extracellular matrix (ECM). Unlike cancers, wounds naturally resolve via blood vessel regression and ECM maturation, which are essential for reestablishing tissue homeostasis. Mechanisms guiding wound resolution are poorly understood; one candidate regulator is pigment epithelium-derived factor (PEDF), a secreted glycoprotein. PEDF is a potent antiangiogenic in models of pathological angiogenesis and a promising cancer and cardiovascular disease therapeutic, but little is known about its physiological function. To examine the roles of PEDF in physiological wound repair, we used a reproducible model of excisional skin wound healing in BALB/c mice. We show that PEDF is abundant in unwounded and healing skin, is produced primarily by dermal fibroblasts, binds to resident microvascular endothelial cells, and accumulates in dermal ECM and epidermis. PEDF transcript and protein levels were low during the inflammatory and proliferative phases of healing but increased in quantity and colocalization with microvasculature during wound resolution. Local antibody inhibition of endogenous PEDF delayed vessel regression and collagen maturation during the remodeling phase. Treatment of wounds with intradermal injections of exogenous, recombinant PEDF inhibited nascent angiogenesis by repressing endothelial proliferation, promoted vascular integrity and function, and increased collagen maturity. These results demonstrate that PEDF contributes to the resolution of healing wounds by causing regression of immature blood vessels and stimulating maturation of the vascular microenvironment, thus promoting a return to tissue homeostasis after injury.

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.

Quantitative proteomics and bioinformatic analysis provide new insight into protein function during avian eggshell biomineralization

Gallus gallus eggshell is a bioceramic composed of 95% calcium carbonate in calcitic form and 3.5% extracellular organic matrix. The calcification process occurs in the uterine fluid where biomineralization follows a temporal sequence corresponding to the initiation, growth and termination stages of crystal growth. Eggshell texture and its ultrastructure are regulated by organic matrix proteins, which control mineralization process and influence the eggshell biomechanical properties. We performed proteomic qualitative analyses and identified 308 uterine fluid proteins. Quantitative analysis showed differential abundances at the three stages of shell biomineralization for 64 of them. Cluster analysis revealed a first group of proteins related to mineralization and mainly present at the onset of calcification including OVOT, OVAL, OC-17, and two novel calcium binding proteins (EDIL3, MFGE8). A second group of proteins mainly present at the initiation and termination of shell formation was potentially involved in the regulation of the activity of the uterine fluid proteins (e.g. molecular chaperones, folding proteins, proteases and protease inhibitors). OCX21, a protein highly concentrated in the fluid and the shell, belongs to this group. A third group equally represented at all stages of shell mineralization corresponded to antibacterial proteins that could protect the forming egg against microbial invasion.

BIOLOGICAL SIGNIFICANCE

The calcitic avian eggshell protects the developing embryo and, moreover, ensures that the nutritious table egg remains free of pathogens. The eggshell is formed by nucleation upon a fibrous scaffold (the eggshell membranes) followed by an interaction between the growing mineral crystals and the shell organic matrix. This interaction leads to a highly ordered shell microstructure and texture which contribute to its exceptional mechanical properties. Shell mineralization occurs in three distinct phases of calcification (initiation, growth and termination), which are associated with distinct populations of matrix proteins that are secreted into the acellular uterine fluid as modulators of the process. The recent development of high-throughput methods has led to the identification of many proteins in the shell, but little is known concerning their role in shell formation. In order to determine precisely the importance of particular proteins relative to eggshell mineralization, this project used qualitative and quantitative proteomics of the uterine fluid constituents, coupled with bioinformatic analysis, to predict the functional role of proteins secreted at each of the three main stages of shell calcification. Besides its relevance to food production and to hen reproduction, eggshell calcification is furthermore a relevant model for studying calcium carbonate biomineralization on a two-dimensional membrane support. Better understanding of this process will provide insight into the fabrication of ceramics at ambient pressure and temperature.

Pigment epithelium-derived factor (PEDF) inhibits breast cancer metastasis by down-regulating fibronectin

Pigment epithelium-derived factor (PEDF) plays an important role in the tumor growth and metastasis inhibition. It has been reported that PEDF expression is significantly reduced in breast cancer, and associated with disease progression and poor patient outcome. However, the exact mechanism of PEDF on breast cancer metastasis including liver and lung metastasis remains unclear. The present study aims to reveal the impact of PEDF on breast cancer. The orthotopic tumor mice model inoculated by MDA-MB-231 cells stably expressing PEDF or control cells was used to assess liver and lung metastasis of breast cancer. In vitro, migration and invasion experiments were used to detect the metastatic abilities of MDA-MB-231 and SKBR3 breast cancer cells with or without overexpression of PEDF. The metastatic-related molecules including EMT makers, fibronectin, and p-AKT and p-ERK were detected by qRT-PCR, Western blot, and Fluorescent immunocytochemistry. PEDF significantly inhibited breast cancer growth and metastasis in vivo and in vitro. Mechanically, PEDF inhibited breast cancer cell migration and invasion by down-regulating fibronectin and subsequent MMP2/MMP9 reduction via p-ERK and p-AKT signaling pathways. However, PEDF had no effect on EMT conversion in the breast cancer cells which was usually involved in cancer metastasis. Furthermore, the study showed that laminin receptor mediated the down-regulation of fibronectin by PEDF. These results reported for the first time that PEDF inhibited breast cancer metastasis by down-regulating fibronectin via laminin receptor/AKT/ERK pathway. Our findings demonstrated PEDF as a dual effector in limiting breast cancer growth and metastasis and highlighted a new avenue to block breast cancer progression.

The association study of plasma levels of pigment epithelium-derived factor with acute coronary syndrome in the chinese han population

OBJECTS

To investigate the relationship between plasma levels of pigment epithelium-derived factor (PEDF) and acute coronary syndrome (ACS) in the Chinese Han population.

METHODS

Plasma PEDF levels were measured in 200 consecutive ACS patients and 160 age- and sex-matched healthy control subjects. Logistic regression analysis was performed to determine whether PEDF was an independently protective factor against ACS. All ACS patients were followed up for 6 months and the short-term major adverse cardiovascular events (MACE) were obtained: cardiac death and recurrent angina.

RESULTS

The ACS patients showed notably lower plasma PEDF levels relative to the control group (7.31 ± 2.21 vs. 8.44 ± 2.13 μg/ml, respectively, p = 0.001). Logistic regression analysis revealed that PEDF had a significant protective effect against ACS (OR = 0.76, 95% CI 0.623-0.935, p = 0.01). After 6 months of follow-up, we found that the mean PEDF concentration of the patients with short-term MACE was lower than the patients without (6.05 ± 2.18 vs. 7.52 ± 2.07 µg/ml, p = 0.031). The Kaplan-Meier survival curves suggested that patients with plasma PEDF levels <7.00 µg/ml showed a lower survival trend than those in the higher group, but the difference was not significant (p = 0.477).

CONCLUSIONS

Our study indicates that plasma PEDF levels are significantly lower in ACS patients than in controls, and lower PEDF levels are further associated with adverse cardiac outcomes after ACS.

Pigment epithelium-derived factor (PEDF) prevents retinal cell death via PEDF Receptor (PEDF-R): identification of a functional ligand binding site

The extracellular pigment epithelium-derived factor (PEDF) displays retina survival activity by interacting with receptor proteins on cell surfaces. We have previously reported that PEDF binds and stimulates PEDF receptor (PEDF-R), a transmembrane phospholipase. However, the PEDF binding site of PEDF-R and its involvement in survival activity have not been identified. The purpose of this work is to identify a biologically relevant ligand-binding site on PEDF-R. PEDF bound the PEDF-R ectodomain L4 (Leu(159)-Met(325)) with affinity similar to the full-length PEDF-R (Met(1)-Leu(504)). Binding assays using synthetic peptides spanning L4 showed that PEDF selectively bound E5b (Ile(193)-Leu(232)) and P1 (Thr(210)-Leu(249)) peptides. Recombinant C-terminal truncated PEDF-R4 (Met(1)-Leu(232)) and internally truncated PEDF-R and PEDF-R4 (ΔHis(203)-Leu(232)) retained phospholipase activity of the full-length PEDF-R. However, PEDF-R polypeptides without the His(203)-Leu(232) region lost the PEDF affinity that stimulated their enzymatic activity. Cell surface labeling showed that PEDF-R is present in the plasma membranes of retina cells. Using siRNA to selectively knock down PEDF-R in retina cells, we demonstrated that PEDF-R is essential for PEDF-mediated cell survival and antiapoptotic activities. Furthermore, preincubation of PEDF with P1 and E5b peptides blocked the PEDF·PEDF-R-mediated retina cell survival activity, implying that peptide binding to PEDF excluded ligand-receptor interactions on the cell surface. Our findings establish that PEDF-R is required for the survival and antiapoptotic effects of PEDF on retina cells and has determinants for PEDF binding within its L4 ectodomain that are critical for enzymatic stimulation.

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.

Loss of pigment epithelium-derived factor: a novel mechanism for the development of endocrine resistance in breast cancer

INTRODUCTION

Despite the benefits of endocrine therapies such as tamoxifen and aromatase inhibitors in treating estrogen receptor (ER) alpha-positive breast cancer, many tumors eventually become resistant. The molecular mechanisms governing resistance remain largely unknown. Pigment epithelium-derived factor (PEDF) is a multifunctional secreted glycoprotein that displays broad anti-tumor activity based on dual targeting of the tumor microenvironment (anti-angiogenic action) and the tumor cells (direct anti-tumor action). Recent studies indicate that PEDF expression is significantly reduced in several tumor types, including breast cancer, and that its reduction is associated with disease progression and poor patient outcome. In the current study, we investigated the role of PEDF in the development of endocrine resistance in breast cancer.

METHODS

PEDF mRNA and protein levels were measured in several endocrine-resistant breast cancer cell lines including MCF-7:5C, MCF-7:2A, and BT474 and in endocrine-sensitive cell lines MCF-7, T47D, and ZR-75-1 using real-time PCR and western blot analyses. Tissue microarray analysis and immunohistochemistry were used to assess the PEDF protein level in tamoxifen-resistant breast tumors versus primary tumors. Lentiviruses were used to stably express PEDF in endocrine-resistant breast cancer cell lines to determine their sensitivity to tamoxifen following PEDF re-expression.

RESULTS

We found that PEDF mRNA and protein levels were dramatically reduced in endocrine-resistant MCF-7:5C, MCF-7:2A, and BT474 breast cancer cells compared with endocrine-sensitive MCF-7, T47D, and ZR-75-1 cells, and that loss of PEDF was associated with enhanced expression of pSer167ERα and the receptor tyrosine kinase rearranged during transfection (RET). Importantly, we found that silencing endogenous PEDF in tamoxifen-sensitive MCF-7 and T47D breast cancer cells conferred tamoxifen resistance whereas re-expression of PEDF in endocrine-resistant MCF-7:5C and MCF-7:2A cells restored their sensitivity to tamoxifen in vitro and in vivo through suppression of RET. Lastly, tissue microarray studies revealed that PEDF protein was reduced in ~52.4% of recurrence tumors (31 out of 59 samples) and loss of PEDF was associated with disease progression and poor patient outcome.

CONCLUSION

Overall, these findings suggest that PEDF silencing might be a novel mechanism for the development of endocrine resistance in breast cancer and that PEDF expression might be a predictive marker of endocrine sensitivity.

Identification of pigment epithelium-derived factor protein forms with distinct activities on tumor cell lines

Purpose. Pigment epithelium-derived factor (PEDF) is a multifunctional serpin. The purpose of this study is to identify PEDF protein forms and investigate their biological activities on tumor cell lines. Methods. Recombinant human PEDF proteins were purified by cation- and anion-exchange column chromatography. They were subjected to SDS-PAGE, IEF, deglycosylation, heparin affinity chromatography, and limited proteolysis. Cell viability, real-time electrical impedance of cells, and wound healing assays were performed using bladder and breast cancer cell lines, rat retinal R28, and human ARPE-19 cells. Results. Two PEDF protein peaks were identified after anion-exchange column chromatography: PEDF-1 eluting with lower ionic strength than PEDF-2. PEDF-1 had higher pI value and lower apparent molecular weight than PEDF-2. Both PEDF forms were glycosylated, bound to heparin, and had identical patterns by limited proteolysis. However, PEDF-2 emerged as being highly potent in lowering cell viability in all tumor cell lines tested, and in inhibiting tumor and ARPE-19 cell migration. In contrast, PEDF-1 minimally affected tumor cell viability and cell migration but protected R28 cells against death caused by serum starvation. Conclusion. Two distinct biochemical forms of PEDF varying in overall charge have distinct biological effects on tumor cell viability and migration. The existence of PEDF forms may explain the multifunctional modality of PEDF.

Inhibition of tumor cell surface ATP synthesis by pigment epithelium-derived factor: implications for antitumor activity

Recently, we have shown that the antiangiogenic pigment epithelium-derived factor (PEDF) can bind the catalytic β-subunit of F1-ATP synthase and inhibit endothelial cell surface ATP synthase activity. This factor can additionally restrict tumor growth, invasion and metastasis, and can directly induce death on several tumor cell types. Active cell surface ATP synthase is also present in certain tumor cells and its ATP product is considered a stimulus for tumor growth. The present study aimed to elucidate the biological implications of the interactions between the extracellular PEDF and tumor cell surface ATP synthase. Incubation of T24 human urinary bladder carcinoma cells in media containing human recombinant PEDF protein for 48-96 h dramatically decreased cell viability in a concentration-dependent fashion as monitored by real-time cell impedance with a microelectronic system, microscopic imaging and biomarkers of live cells. Intact tumor cells exhibited cell surface ATP synthesis activity, which was inhibited by piceatannol, a specific inhibitor of F1/F0-ATP synthase. Immunoblotting revealed that the β subunit of F1-ATP synthase was present in plasma membrane fractions of these cells. Interestingly, pre-incubation of tumor cells with PEDF inhibited the activity of cell surface ATP synthase in a concentration-dependent fashion. The PEDF-derived peptide 34-mer decreased tumor cell viability and inhibited extracellular ATP synthesis to the same extent as full-length PEDF. Moreover, ATP additions attenuated both the PEDF-mediated decrease in tumor cell viability and the inhibition of endothelial cell tube formation. The results lead to conclude that PEDF is a novel inhibitor of tumor cell surface ATP synthase activity that exhibits a cytotoxic effect on tumor cells, and that the structural determinants for these properties are within the peptide region 34-mer of the PEDF polypeptide. The data strongly suggest a role for the interaction between the 34-mer region of PEDF and tumor cell-surface ATP synthase in promoting tumor cell death.

Trans-scleral delivery of macromolecules

Non-invasive drug delivery to the posterior segment of the eye represents an important unmet medical need, and trans-scleral delivery could be an interesting solution. This review analyses the possibility of trans-scleral drug delivery for high molecular weight compounds, such as proteins and genetic material, which currently represent the most innovative and efficacious molecules for the treatment of many diseases of the posterior segment of the eye. The paper reviews all the barriers, both static and dynamic, involved in trans-scleral administration of drugs, trying to elucidate the role of each of them in the specific case of macromolecules. Delivery systems to sustain drug release and enhancing strategies to improve trans-scleral penetration are also described. Finally, the review approaches the use of computational models as a screening tool to evaluate the feasibility of trans-scleral administration for macromolecules.

Pigment epithelium-derived factor (PEDF) shares binding sites in collagen with heparin/heparan sulfate proteoglycans

Pigment epithelium-derived factor (PEDF) is a collagen-binding protein that is abundantly distributed in various tissues, including the eye. It exhibits various biological functions, such as anti-angiogenic, neurotrophic, and neuroprotective activities. PEDF also interacts with extracellular matrix components such as collagen, heparan sulfate proteoglycans (HSPGs), and hyaluronan. The collagen-binding property has been elucidated to be important for the anti-angiogenic activity in vivo (Hosomichi, J., Yasui, N., Koide, T., Soma, K., and Morita, I. (2005) Biochem. Biophys. Res. Commun. 335, 756-761). Here, we investigated the collagen recognition mechanism by PEDF. We first narrowed down candidate PEDF-binding sequences by taking advantage of previously reported structural requirements in collagen. Subsequent searches for PEDF-binding sequences employing synthetic collagen-like peptides resulted in the identification of one of the critical binding sites for PEDF, human α1(I)(929-938) (IKGHRGFSGL). Further analysis revealed that the collagen recognition by PEDF is sequence- and conformation-specific, and the high affinity binding motif is KGXRGFXGL in the triple helix. The PEDF-binding motif significantly overlapped with the heparin/HSPG-binding motif, KGHRG(F/Y). The interaction of PEDF with collagen I was specifically competed with by heparin but not by chondroitin sulfate-C or hyaluronan. The binding sequences for PEDF and heparin/HSPG also overlapped with the covalent cross-linking sites between collagen molecules. These findings imply a functional relationship between PEDF and HSPGs during angiogenesis, and the interaction of these molecules is regulated by collagen modifications.

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.

The applied biochemistry of PEDF and implications for tissue homeostasis

Pigment epithelium-derived factor (PEDF) is an endogenously produced glycoprotein with a spectrum of biological roles across diverse pathologies. Recent research has focused on the biochemical properties of PEDF and its associated receptors. This review discusses the recent developments in PEDF biochemistry and how this new knowledge will help progress our understanding of PEDF as a molecular mediator for anti-angiogenesis and -tumorigenesis. Additionally, pathophysiological roles for PEDF in healing and tissue homeostasis are being revealed and our enhanced understanding of the interactions between PEDF and its receptors may yet prove useful in propelling PEDF towards clinical application.

Pigment epithelium-derived factor binds to cell-surface F(1)-ATP synthase

Pigment epithelium-derived factor (PEDF), a potent blocker of angiogenesis in vivo, and of endothelial cell migration and tubule formation, binds with high affinity to an as yet unknown protein on the surfaces of endothelial cells. Given that protein fingerprinting suggested a match of a approximately 60 kDa PEDF-binding protein in bovine retina with Bos taurus F(1)-ATP synthase beta-subunit, and that F(1)F(o)-ATP synthase components have been identified recently as cell-surface receptors, we examined the direct binding of PEDF to F(1). Size-exclusion ultrafiltration assays showed that recombinant human PEDF formed a complex with recombinant yeast F(1). Real-time binding as determined by surface plasmon resonance demonstrated that yeast F(1) interacted specifically and reversibly with human PEDF. Kinetic evaluations revealed high binding affinity for PEDF, in agreement with PEDF affinities for endothelial cell surfaces. PEDF blocked interactions between F(1) and angiostatin, another antiangiogenic factor, suggesting overlapping PEDF-binding and angiostatin-binding sites on F(1). Surfaces of endothelial cells exhibited affinity for PEDF-binding proteins of approximately 60 kDa. Antibodies to F(1)beta-subunit specifically captured PEDF-binding components in endothelial plasma membranes. The extracellular ATP synthesis activity of endothelial cells was examined in the presence of PEDF. PEDF significantly reduced the amount of extracellular ATP produced by endothelial cells, in agreement with direct interactions between cell-surface ATP synthase and PEDF. In addition to demonstrating that PEDF binds to cell-surface F(1), these results show that PEDF is a ligand for endothelial cell-surface F(1)F(o)-ATP synthase. They suggest that PEDF-mediated inhibition of ATP synthase may form part of the biochemical mechanisms by which PEDF exerts its antiangiogenic activity.

Effects of human recombinant PEDF protein and PEDF-derived peptide 34-mer on choroidal neovascularization

PURPOSE

Pigment epithelium-derived factor (PEDF) is a serpin with antiangiogenic properties. Previously, the authors showed that PEDF injected into the subconjunctiva reaches the choroid. Here, they examined the effects of PEDF polypeptide fragments on vessel sprouting and on choroidal neovascularization (CNV) after subconjunctival administration.

METHODS

Recombinant human PEDF (rhuPEDF) was cleaved at its serpin-exposed loop by limited chymotrypsin proteolysis. Synthetic PEDF peptides 34-mer (Asp(44)-Asn(77)) and 44-mer (Val(78)-Thr(121)) were used. Ex vivo chick aortic vessel sprouting assays were performed. CNV was induced in rats by laser injury of Bruch's membrane. Daily subconjunctival injections (0.01-10 pmol/d protein) were performed for 5 days starting at day of injury or at the seventh day after injury. New vessel volumes were quantified using optical sections of choroid/RPE flat-mounts labeled with isolectin-Ib4. PEDF distribution was evaluated by immunofluorescence of choroid/RPE/retina cross-sections.

RESULTS

Full-length rhuPEDF, cleaved rhuPEDF, or peptide 34-mer exhibited ex vivo antiangiogenic activity, but peptide 44-mer was inefficient. PEDF immunostaining around CNV lesions diminished after laser injury. Subconjunctival administration of rhuPEDF or 34-mer at 0.1 pmol/d decreased CNV lesion volumes by 52% and 47%, respectively, whereas those of 44-mer were similar to vehicle injections. Doses of 0.1 and 1 pmol/d rhuPEDF decreased fully developed CNV complex volumes by 45% and 50%, respectively, compared with vehicle injections.

CONCLUSIONS

A functional region for the inhibition of vessel sprouting and CNV resides within the 34-mer region of PEDF. Furthermore, subconjunctival administration of optimal range dosages of rhuPEDF or 34-mer can suppress and regress rat CNV lesions, demonstrating that these agents reach the choroid/RPE complex as functionally active molecules.

Laminin receptor involvement in the anti-angiogenic activity of pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is a multifunctional protein with neurotrophic, anti-oxidative, and anti-inflammatory properties. It is also one of the most potent endogenous inhibitors of angiogenesis, playing an important role in restricting tumor growth, invasion, and metastasis. Studies show that PEDF binds to cell surface proteins, but little is known about how it exerts its effects. Recently, research identified phospholipase A(2)/nutrin/patatin-like phospholipase domain-containing 2 as one PEDF receptor. To identify other receptors, we performed yeast two-hybrid screening using PEDF as bait and discovered that the non-integrin 37/67-kDa laminin receptor (LR) is another PEDF receptor. Co-immunoprecipitation, His tag pulldown, and surface plasmon resonance assays confirmed the interaction between PEDF and LR. Using the yeast two-hybrid method, we further restricted the LR-interacting domain on PEDF to a 34-amino acid (aa) peptide (aa 44-77) and the PEDF-interacting domain on LR to a 91-aa fragment (aa 120-210). A 25-mer peptide named P46 (aa 46-70), derived from 34-mer, interacts with LR in surface plasmon resonance assays and binds to endothelial cell (EC) membranes. This peptide induces EC apoptosis and inhibits EC migration, tube-like network formation in vitro, and retinal angiogenesis ex vivo, like PEDF. Our results suggest that LR is a real PEDF receptor that mediates PEDF angiogenesis inhibition.

Pigment epithelium-derived factor binds to hyaluronan. Mapping of a hyaluronan binding site

Pigment epithelium-derived factor (PEDF) is a multifunctional serpin with antitumorigenic, antimetastatic, and differentiating activities. PEDF is found within tissues rich in the glycosaminoglycan hyaluronan (HA), and its amino acid sequence contains putative HA-binding motifs. We show that PEDF coprecipitation with glycosaminoglycans in media conditioned by human retinoblastoma Y-79 cells decreased after pretreatments with hyaluronidase, implying an association between HA and PEDF. Direct binding of human recombinant PEDF to highly purified HA was demonstrated by coprecipitation in the presence of cetylpyridinium chloride. Binding of PEDF to HA was concentration-dependent and saturable. The PEDF-HA interactions were sensitive to increasing NaCl concentrations, indicating an ionic nature of these interactions and having affinity higher than PEDF-heparin. Competition assays showed that PEDF can bind heparin and HA simultaneously. PEDF chemically modified with fluorescein retained the capacity for interacting with HA but lacked heparin affinity, suggesting one or more distinct HA-binding regions on PEDF. The HA-binding region was examined by site-directed mutagenesis. Single-point and cumulative alterations at basic residues within the putative HA-binding motif K189A/K191A/R194A/K197A drastically reduced the HA-binding activity without affecting heparin- or collagen I binding of PEDF. Cumulative alterations at sites critical for heparin binding (K146A/K147A/R149A) decreased HA affinity but not collagen I binding. Thus these clusters of basic residues (BXBXXBXXB and BX3AB2XB motifs) in PEDF are functional regions for binding HA. In the spatial PEDF structure they are located in distinct areas away from the collagen-binding site. The HA-binding activity of PEDF may contribute to deposition in the extracellular matrix and to its reported antitumor/antimetastatic effects.

Establishment of a human in vitro model of the outer blood-retinal barrier

The outer blood-retinal barrier is composed of a monolayer of retinal pigment epithelium, Bruch's membrane and the choriocapillaris which is fenestrated. Endothelial proliferation and breaching of Bruch's membrane leads to the neovascular form of age-related macula degeneration (ARMD). The aim of this study was to generate an in vitro model that mimics more faithfully the phenotype of the choriocapillaris and the trilayer architecture in vitro. A trilayer culture model was generated with retinal pigment epithelium (ARPE-19) cell cultures on the epithelial surface of amniotic membrane and with human umbilical vein-derived endothelial cells on the other surface. A control model for the effect of retinal pigment epithelium on endothelial changes was generated with corneal epithelial cells replacing the ARPE-19. Both human umbilical vein-derived endothelial and ARPE-19 cells formed confluent monolayers on respective surfaces of the amnion. The human umbilical vein-derived endothelial cells in the trilayer became fenestrated when co-cultured with the ARPE-19 cells, but not with corneal epithelial cells, or when grown as monolayers on the amnion, showing a loss of fidelity of origin in the presence of ARPE-19 cells. These cells also revealed VE-cadherin and ZO-1 at cell-cell contacts from 24 h in the trilayer. The tight junctional molecules, occludin and ZO-1, were localized to cell-cell contact regions in the retinal pigment epithelium, both in the monolayer and in the trilayer system. Permeability of the trilayer was tested by using fluorescein and fluorescein-conjugated tracers under flow. At 72 h the trilayer severely restricted transfer of sodium fluorescein (NaF) (ten-fold reduction) whilst transfer of a 4 kDa FITC-conjugated dextran was virtually occluded, confirming a restrictive barrier. Ultrastructural studies showed the retinal pigment epithelium monolayer was polarized with microvilli present on the apical surface. Paracellular clefts showed numerous tight junctional-like appositions, similar to that seen on amnion alone. This study demonstrates that ARPE-19 and human umbilical vein-derived endothelial cells can be co-cultured on the amniotic membrane and that the resultant cross-talk leads to formation of a fenestrated endothelium, whilst maintaining a polarized restrictive epithelial layer. The fenestrated endothelial phenotype achieved in this human in vitro trilayer model is a first and offers an outer-retinal barrier which approaches the in vivo state and has potential for studies into induced junctional disruption, endothelial proliferation and migration: features of ARMD.

Balance of vascular endothelial growth factor and pigment epithelial growth factor prior to development of proliferative vitreoretinopathy

BACKGROUND

Pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) are imbalanced in eyes with proliferative diabetic retinopathy or proliferative vitreoretinopathy (PVR). It is not known whether such an imbalance is already present in early PVR stages. We therefore analyzed VEGF and PEDF concentrations in subretinal fluids prior to PVR development.

METHODS

A large number (n = 137) of subretinal fluid samples were obtained at the time of scleral buckling surgery for rhegmatogenous retinal detachment (RRD). Thirty patients developed PVR within 6 months after surgery. One hundred and seven patients undergoing the same surgery but without complications served as controls. Furthermore, vitreous from 16 patients with macular hole or pucker (MHP) served as reference for baseline intraocular concentrations. PEDF and VEGF concentrations were measured by commercial ELISAs.

RESULTS

PEDF levels were substantially higher (9.6 microg/ml) compared to MHP vitreous (0.3 microg/ml, p < 0.001). VEGF levels were also higher (RRD: 0.07 ng/ml; MHP: 0.01 ng/ml, p < 0.05). Subretinal concentrations were not significantly different between PVR and control RRD patients.

CONCLUSIONS

Although both VEGF and PEDF are increased at first surgery for RRD, they do not predict PVR development later on. The high PEDF concentrations and its known antiangiogenic activity suggest a protective role against neovascularization.

Expression of pigment-epithelium-derived factor during kidney development and aging

Inhibitors and stimulators of endothelial cell growth are essential for the coordination of blood vessel formation during organ growth and development. In the adult kidney, one of the major inhibitors of angiogenesis is pigment-epithelium-derived factor (PEDF). We have analyzed the expression and distribution of PEDF during various stages of renal development and aging with particular emphasis on the formation of functional glomeruli. We show that PEDF gene expression and protein levels in the kidney significantly increase with age. We have detected PEDF in the mesenchyme and endothelial cells at all developmental stages studied, in all regions of the nephrogenic zone in which the formation of new blood vessels is associated with the development of nephrons and collecting ducts, and in mature podocytes in the adult kidney. Our results are the first to suggest that PEDF is important in early renal postnatal development, that it could be relevant to the maturation of glomerular function and the filtration barrier formed by these cells, and that it may serve as an anti-angiogenic modulator during kidney development.

Heparin Binding Induces a Conformational Change in Pigment Epithelium-derived Factor

Pigment epithelium-derived factor (PEDF) is a noninhibitory serpin found in plasma and in the extracellular space. The protein is involved in different biological processes including cell differentiation and survival. In addition, it is a potent inhibitor of angiogenesis. The function is likely associated with binding to cell surface receptors in a heparin-dependent way (Alberdi, E. M., Weldon, J. E., and Becerra, S. P. (2003) BMC Biochem. 4, 1). We have investigated the structural basis for this observation and show that heparin induces a conformational change in the vicinity of Lys(178). This structural change was evident both when binding to intact heparin and specific heparin-derived oligosaccharides at physiological conditions or simply when exposing PEDF to low ionic strength. Binding to other glycosaminoglycans, heparin-derived oligosaccharides smaller than hexadecasaccharides (dp16), or type I collagen did not affect the structure of PEDF. The conformational change is likely to expose the epitope involved in binding to the receptor and thus regulates the interactions with cell surface receptors.

Identification of a lipase-linked cell membrane receptor for pigment epithelium-derived factor

Pigment epithelium-derived factor (PEDF) is an extracellular multifunctional protein belonging to the serpin superfamily with demonstrable neurotrophic, gliastatic, neuronotrophic, antiangiogenic, and antitumorigenic properties. We have previously provided biochemical evidence for high affinity PEDF-binding sites and proteins in plasma membranes of retina, retinoblastoma, and CNS cells. This study was designed to reveal a receptor involved in the biological activities of PEDF. Using a yeast two-hybrid screening, we identified a novel gene from pigment epithelium of the human retina that codes for a PEDF-binding partner, which we term PEDF-R. The derived polypeptide has putative transmembrane, intracellular and extracellular regions, and a phospholipase domain. Recently, PEDF-R (TTS-2.2/independent phospholipase A(2) (PLA(2))zeta and mouse desnutrin/ATGL) has been described in adipose cells as a member of the new calcium-independent PLA(2)/nutrin/patatin-like phospholipase domain-containing 2 (PNPLA2) family that possesses triglyceride lipase and acylglycerol transacylase activities. Here we describe the PEDF-R gene expression in the retina and its heterologous expression by bacterial and eukaryotic systems, and we demonstrate that its protein product has specific and high binding affinity for PEDF, has a potent phospholipase A(2) activity that liberates fatty acids, and is associated with eukaryotic cell membranes. Most importantly, PEDF binding stimulates the enzymatic phospholipase A(2) activity of PEDF-R. In conclusion, we have identified a novel PEDF-R gene in the retina for a phospholipase-linked membrane protein with high affinity for PEDF, suggesting a molecular pathway by which ligand/receptor interaction on the cell surface could generate a cellular signal.

PEDF: a potential molecular therapeutic target with multiple anti-cancer activities

Pigment epithelium-derived factor (PEDF) is an endogenously produced protein that is widely expressed throughout the human body, and exhibits multiple and varied biological activities. Already established as a potent anti-angiogenic molecule, PEDF has recently shown promise as a potential anti-tumour agent, causing both direct and indirect tumour suppression. Here, we explore the unique anti-tumour properties of PEDF and discuss its role as an effective anti-angiogenic, anti-proliferative and pro-differentiation factor. We also discuss the prospects for PEDF therapy and the need for a closer evaluation of issues such as delivery, stability and potential toxicity.

Pigment epithelium-derived factor: a multimodal tumor inhibitor

Pigment epithelium-derived factor (PEDF), a noninhibitory member of the serine protease inhibitor (serpin) family, is a well-known potent endogenous inhibitor of angiogenesis. It has been known for years to be aberrantly expressed in ocular disorders, but in recent years, down-regulation has been shown to be prevalent in a range of cancers as well. This review describes the trimodal anticancer activities of this interesting protein: antiangiogenesis, apoptosis-mediated tumor suppression, and tumor cell differentiation. The key to successful antitumor therapy with this protein is the ability to synthesize the recombinant form of the protein (or its active shortened forms) and deliver at therapeutic doses or alternatively to use gene transfer technology to prolong the effect in vivo. Although there is a substantial amount of work carried out at the preclinical stage with this protein, more groundwork has to be done before PEDF is tested against cancer in clinical trials.

What is the role of the vasculature in the neural stem cell niche?

Evaluation of: Ramirez-Castillejo C, Sanchez-Sanchez F, Andreu-Agullo C et al.: Pigment epithelium-derived factor is a niche signal for neural stem cell renewal. Nat. Neurosci. 9(3), 331–339 (2006) [3] . Vascular cells are essential components of the cytoarchitecture of multiple stem cell niches, although their exact role(s) in mediating cell–cell, cell–matrix or paracrine interactions are not clearly defined. In the neural stem cell niche, vascular endothelial cells are thought to secrete soluble factors and extracellular matrix proteins that can modulate the proliferation and potential of neural stem cells and progenitors within their microenvironment. Current studies, such as those reported by Ramirez-Castillejo and colleagues focus on elucidating the molecular regulation of neural stem cell phenotype and function by one such endothelial cell-derived effector, pigment epithelium-derived factor. This work and its implications are discussed herein.

Expression of pigment epithelium-derived factor and vascular endothelial growth factor in fibrovascular membranes from patients with proliferative diabetic retinopathy

PURPOSE

The expression of pigment epithelium-derived factor (PEDF), a strong inhibitor of angiogenesis, has not been examined in human ocular fibrovascular membranes, to the best of our knowledge. The purpose of this study was to determine whether PEDF is expressed in the fibrovascular membranes in eyes of patients with proliferative diabetic retinopathy (PDR), and to compare the expression of PEDF with that of vascular endothelial growth factor (VEGF).

METHODS

The expression of PEDF and VEGF in the fibrovascular membranes excised during vitreous surgery in eight cases of PDR was determined by immunohistochemistry.

RESULTS

VEGF was strongly expressed in the endothelial cells of newly formed vessels in the fibrovascular membranes. In contrast, PEDF was weakly expressed in the endothelial cells and was prominently expressed in the extracellular matrix and fibrous tissue surrounding the new vessels.

CONCLUSIONS

Our results suggest that PEDF, along with VEGF, may modulate the formation of fibrovascular membranes in patients with PDR.