Regulation of factors controlling angiogenesis in liver development: a role for PEDF in the formation and maintenance of normal vasculature

Pigment Epithelial-Derived Factor in Pancreatic and Liver Cancers-From Inflammation to Cancer

Gastrointestinal (GI) cancers are among the leading causes of mortality worldwide. Despite the emergence of new possibilities that offer hope regarding the successful treatment of these cancers, they still represent a significant global health burden. These cancers can arise from various cell types within the gastrointestinal tract and may exhibit different characteristics, behaviors, and treatment approaches. Both the prognosis and the outcomes of GI treatment remain problematic because these tumors are primarily diagnosed in advanced clinical stages. Current biomarkers exhibit limited sensitivity and specificity. Therefore, when developing strategies for the diagnosis and treatment of GI cancers, it is of fundamental importance to discover new biomarkers capable of addressing the challenges of early-stage diagnosis and the presence of lymph node metastases. Pigment epithelial-derived factor (PEDF) has garnered interest due to its inhibitory effects on the migration and proliferation of cancer cells. This protein has been suggested to be involved in various inflammation-related diseases, including cancer, through various mechanisms. It was also observed that reducing the level of PEDF is sufficient to trigger an inflammatory response. This suggests that PEDF is an endogenous anti-inflammatory factor. Overall, PEDF is a versatile protein with diverse biological functions that span across different tissues and organ systems. Its multifaceted activities make it an intriguing target for therapeutic interventions in various diseases, including cancer, neurodegeneration, and metabolic disorders. This review, for the first time, summarizes the role of PEDF in the pathogenesis of selected GI cancers and its potential utility in early diagnosis, prognosis, and therapeutic strategies for this malignancy.

Receptors that bind to PEDF and their therapeutic roles in retinal diseases

Retinal neovascular, neurodegenerative, and inflammatory diseases represented by diabetic retinopathy are the main types of blinding eye disorders that continually cause the increased burden worldwide. Pigment epithelium-derived factor (PEDF) is an endogenous factor with multiple effects including neurotrophic activity, anti-angiogenesis, anti-tumorigenesis, and anti-inflammatory activity. PEDF activity depends on the interaction with the proteins on the cell surface. At present, seven independent receptors, including adipose triglyceride lipase, laminin receptor, lipoprotein receptor-related protein, plexin domain-containing 1, plexin domain-containing 2, F1-ATP synthase, and vascular endothelial growth factor receptor 2, have been demonstrated and confirmed to be high affinity receptors for PEDF. Understanding the interactions between PEDF and PEDF receptors, their roles in normal cellular metabolism and the response the initiate in disease will be accommodating for elucidating the ways in which inflammation, angiogenesis, and neurodegeneration exacerbate disease pathology. In this review, we firstly introduce PEDF receptors comprehensively, focusing particularly on their expression pattern, ligands, related diseases, and signal transduction pathways, respectively. We also discuss the interactive ways of PEDF and receptors to expand the prospective understanding of PEDF receptors in the diagnosis and treatment of retinal diseases.

PEDF is an endogenous inhibitor of VEGF-R2 angiogenesis signaling in endothelial cells

Pigment epithelium derived factor (PEDF), an endogenous inhibitor of angiogenesis, targets the growth of aberrant blood vessels in many tissues, including the eye. In this study we show that PEDF prevented early mitogenic signals of vascular endothelial growth factor (VEGF-A) in primate retinal endothelial cells, blocking proliferation, migration and tube formation. PEDF inhibited the phosphorylation and activation of five major downstream VEGF-A signaling partners, namely phosphoinositide-3-OH Kinase (PI3K), AKT, FAK, Src (Y416), and PLC-γ. It did so by binding to the extracellular domain of VEGF-R2, blocking VEGF-A-induced tyrosine phosphorylation (Tyr 951 and Tyr 1175), and inhibiting VEGF-R2 receptor kinase activity. PEDF had no effect on the transcription or translation of VEGF-R2 in cultured HUVECs. PEDF also bound to the extracellular domain of VEGF-R1. We conclude that PEDF blocks the growth of new blood vessels, in part, by reducing VEGF-A activation of its key mitogenic receptor, VEGF-R2, and by preventing its downstream signals in endothelial cells.

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.

Pigment Epithelium-Derived Factor Affects Angiogenesis in Celiac Disease

OBJECTIVE

Recent studies have demonstrated that angiogenesis is impaired in patients with celiac disease (CD). In this study, we evaluated the levels of the novel antiangiogenic factor pigment epithelium-derived factor (PEDF) in CD patients.

METHODS

Eighty-four patients were included in the study; 71 patients with CD and 13 healthy controls. In the CD patient cohort, there were 21 newly diagnosed patients, 19 with adherence to a gluten-free diet and 31 practicing no adherence to this diet. The PEDF levels were measured using enzyme-linked immunosorbent assays.

RESULTS

The data revealed that celiac patients had higher levels of PEDF than did healthy controls. PEDF levels were not significantly different among the three CD groups. Additionally, the PEDF levels were not correlated with tissue transglutaminase IgA or IgG.

CONCLUSIONS

Our data indicate that PEDF levels are significantly higher in CD patients than those in the healthy controls. This result suggests that PEDF negatively affects angiogenesis in CD. Although we did not observe any differences of PEDF levels among celiac patients, additional studies including more patients could clarify this issue.

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.

Polymorphisms in PEDF linked with the susceptibility to age-related macular degeneration: A case-control study

To study the relationship between pigment epithelium-derived factor (PEDF) rs1136287, rs1894286 polymorphisms and the risk of age-related macular degeneration (AMD) in northern Chinese populations.The study was carried out on case-control methods. Ninety-six patients with AMD and 98 health controls were recruited who were matched with the former by age and gender, rs1136287 and rs1894286 were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Hardy-Weinberg equilibrium (HWE) was also checked by χ test. The distribution frequencies of genotype, allele, and haplotype were calculated by direct counting method. The genotype, allele, and haplotype distribution differences between the case and control groups were analyzed by chi-square test, and odds ratio (OR) and 95% confidence interval (CI) was used to express the relative risk of AMD in northern Chinese populations. The linkage disequilibrium (LD) and haplotype analyses were conducted with Haploview software.The genotype and allele distribution frequencies in rs1136287 were obviously between in cases and controls (P < .05). TT genotype might lead to 3.24 times risk of AMD occurrence compared with CC genotype (OR = 3.24, 95% CI = 1.26-8.32), and C allele also played an increased risk role in the attack of AMD (OR = 1.58, 95% CI = 1.06-2.38). The T-C haplotype frequency of rs1136287-rs1894286 in PEDF were significantly correlated to the increased susceptibility to AMD (OR = 1.57, 95% CI = 1.02-2.40).The rs1136287 polymorphism in PEDF may be related to the occurrence risk of AMD. Additionally, a haplotype is also a non-ignorable risk factor.

Pigment epithelium-derived factor: a key mediator in bone homeostasis and potential for bone regenerative therapy

Objectives

Pigment epithelium-derived factor (PEDF), a multifunctional endogenous glycoprotein, has a very wide range of biological actions, notably in bone homeostasis. The question has been raised regarding the place of PEDF in the treatment of bone disorders and osteosarcoma, and its potential for tumour growth suppression.

Methods

The PubMed database was used to compile this review.

Key findings

Pigment epithelium-derived factor's actions in osteoid tissues include promoting mesenchymal stem cell commitment to osteoblasts, increasing matrix mineralisation, and promoting osteoblast proliferation. It shows potential to improve therapeutic outcomes in treatment of multiple cancer types and regrowth of bone after trauma or resection in animal studies. PEDF may possibly have a reduced adverse effect profile compared with current osteo-regenerative treatments; however, there is currently very limited evidence regarding the safety or efficacy in human models.

Summary

Pigment epithelium-derived factor is very active within the body, particularly in osseous tissue, and its physiological actions give it potential for treatment of both bone disorders and multiple tumour types. Further research is needed to ascertain the adverse effects and safety profile of PEDF as a therapeutic agent.

Pigment Epithelium-Derived Factor Plays a Role in Alzheimer's Disease by Negatively Regulating Aβ42

Alzheimer's disease (AD) is the most common cause of dementia. Pigment epithelium-derived factor (PEDF), a unique neurotrophic protein, decreases with aging. Previous reports have conflicted regarding whether the PEDF concentration is altered in AD patients. In addition, the effect of PEDF on AD has not been documented. Here, we tested serum samples of 31 AD patients and 271 normal controls. We found that compared to PEDF levels in young and middle-aged control subjects, PEDF levels were reduced in old-aged controls and even more so in AD patients. Furthermore, we verified that PEDF expression was much lower and amyloid β-protein (Aβ)42 expression was much higher in senescence-accelerated mouse prone 8 (SAMP8) strain mice than in senescence-accelerated mouse resistant 1 (SAMR1) control strain mice. Accordingly, high levels of Aβ42 were also observed in PEDF knockout (KO) mice. PEDF notably reduced cognitive impairment in the Morris water maze (MWM) and significantly downregulated Aβ42 in SAMP8 mice. Mechanistically, PEDF downregulated presenilin-1 (PS1) expression by inhibiting the c-Jun N-terminal kinase (JNK) pathway. Taken together, our findings demonstrate for the first time that PEDF negatively regulates Aβ42 and that PEDF deficiency with aging might play a crucial role in the development of AD.

The stem cell regulator PEDF is dispensable for maintenance and function of hematopoietic stem cells

Pigment epithelium derived factor (PEDF), a ubiquitously expressed 50 kDa secreted glycoprotein, was recently discovered to regulate self-renewal of neural stem cells and have a supportive effect on human embryonic stem cell growth. Here, we analyzed expression of PEDF in the murine hematopoietic stem cell (HSC) compartments and found that PEDF is highly expressed in primary long-term HSCs. Therefore, we characterized the hematopoietic system in a knockout mouse model for PEDF and using this model we surprisingly found that PEDF is dispensable for HSC regulation. PEDF knockout mice exhibit normal hematopoiesis in steady state conditions and the absence of PEDF lead to normal regeneration capacity in a serial competitive transplantation setting. Additionally, PEDF-deficient cells exhibit unaltered lineage distribution upon serial transplantations. When human cord blood stem and progenitor cells were cultured in media supplemented with recombinant PEDF they did not show changes in growth potential. Taken together, we report that PEDF is not a critical regulatory factor for HSC function during regeneration in vivo or growth of human stem/progenitor cells in vitro.

Time Course and Quantification of Pancreatic Islet Revasculariztion following Intraportal Transplantation

A large proportion of islets are lost after transplantation partly due to a lack of functional vasculature. Islets revascularize from host tissue but the process takes up to 2 weeks and has been suggested to result in reduced vascular density in engrafted islets. We describe a method for observing and quantifying the revascularization of intraportally transplanted islets that includes number, density, and branching of islet capillaries. Syngeneic islets were transplanted selectively into the two right posterior lobes of the liver of adult Lewis rats. Sections of the livers were dual stained for insulin and Bandeiraea simplicifolia and analyzed for islet morphology, area, and vascular density from day 0 to day 14 posttransplant and compared to native islets. Vascular density was 1431 ± 75.7 vessels/mm2 in native islets and fell to 325.3 ± 30.8 vessels/mm2 (p < 0.001) by day 1 posttransplant and subsequently increased until day 14 when it was significantly higher than in native islets (2612.5 ± 107.8 vessels/mm2, p < 0.001). The percentage of islet area occupied by vascular space was 9.1 ± 0.9% in native islets. After falling to 2.3 ± 0.3% (p < 0.001) 1 day posttransplant this rose to supranormal levels (21.5 ± 0.8%, p < 0.001) by day 14. The index of capillary branching was 0.771 ± 0.017 in native islets and fell to 0.465 ± 0.02 (p = 0.001) by day 3 but returned to native values by day 7 posttransplantation (0.726 ± 0.03). This technique provides a robust method for tracking and quantifying the revascularization of intraportally transplanted islets, which should enable the comparison of different strategies aimed at accelerating islet revascularization.

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.

Bayesian phylogeny analysis of vertebrate serpins illustrates evolutionary conservation of the intron and indels based six groups classification system from lampreys for ∼500 MY

The serpin superfamily is characterized by proteins that fold into a conserved tertiary structure and exploits a sophisticated and irreversible suicide-mechanism of inhibition. Vertebrate serpins are classified into six groups (V1-V6), based on three independent biological features-genomic organization, diagnostic amino acid sites and rare indels. However, this classification system was based on the limited number of mammalian genomes available. In this study, several non-mammalian genomes are used to validate this classification system using the powerful Bayesian phylogenetic method. This method supports the intron and indel based vertebrate classification and proves that serpins have been maintained from lampreys to humans for about 500 MY. Lampreys have fewer than 10 serpins, which expand into 36 serpins in humans. The two expanding groups V1 and V2 have SERPINB1/SERPINB6 and SERPINA8/SERPIND1 as the ancestral serpins, respectively. Large clusters of serpins are formed by local duplications of these serpins in tetrapod genomes. Interestingly, the ancestral HCII/SERPIND1 locus (nested within PIK4CA) possesses group V4 serpin (A2APL1, homolog of α 2-AP/SERPINF2) of lampreys; hence, pointing to the fact that group V4 might have originated from group V2. Additionally in this study, details of the phylogenetic history and genomic characteristics of vertebrate serpins are revisited.

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.

PEDF improves cardiac function in rats with acute myocardial infarction via inhibiting vascular permeability and cardiomyocyte apoptosis

Pigment epithelium-derived factor (PEDF) is a pleiotropic gene with anti-inflammatory, antioxidant and anti-angiogenic properties. However, recent reports about the effects of PEDF on cardiomyocytes are controversial, and it is not known whether and how PEDF acts to inhibit hypoxic or ischemic endothelial injury in the heart. In the present study, adult Sprague-Dawley rat models of acute myocardial infarction (AMI) were surgically established. PEDF-small interfering RNA (siRNA)-lentivirus (PEDF-RNAi-LV) or PEDF-LV was delivered into the myocardium along the infarct border to knockdown or overexpress PEDF, respectively. Vascular permeability, cardiomyocyte apoptosis, myocardial infarct size and animal cardiac function were analyzed. We also evaluated PEDF’s effect on the suppression of the endothelial permeability and cardiomyocyte apoptosis under hypoxia in vitro. The results indicated that PEDF significantly suppressed the vascular permeability and inhibited hypoxia-induced endothelial permeability through PPARγ-dependent tight junction (TJ) production. PEDF protected cardiomyocytes against ischemia or hypoxia-induced cell apoptosis both in vivo and in vitro via preventing the activation of caspase-3. We also found that PEDF significantly reduced myocardial infarct size and enhanced cardiac function in rats with AMI. These data suggest that PEDF could protect cardiac function from ischemic injury, at least by means of reducing vascular permeability, cardiomyocyte apoptosis and myocardial infarct size.

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.

Cellular and molecular basis of liver development

Liver is a prime organ responsible for synthesis, metabolism, and detoxification. The organ is endodermal in origin and its development is regulated by temporal, complex, and finely balanced cellular and molecular interactions that dictate its origin, growth, and maturation. We discuss the relevance of endoderm patterning, which truly is the first step toward mapping of domains that will give rise to specific organs. Once foregut patterning is completed, certain cells within the foregut endoderm gain competence in the form of expression of certain transcription factors that allow them to respond to certain inductive signals. Hepatic specification is then a result of such inductive signals, which often emanate from the surrounding mesenchyme. During hepatic specification bipotential hepatic stem cells or hepatoblasts become apparent and undergo expansion, which results in a visible liver primordium during the stage of hepatic morphogenesis. Hepatoblasts next differentiate into either hepatocytes or cholangiocytes. The expansion and differentiation is regulated by cellular and molecular interactions between hepatoblasts and mesenchymal cells including sinusoidal endothelial cells, stellate cells, and also innate hematopoietic elements. Further maturation of hepatocytes and cholangiocytes continues during late hepatic development as a function of various growth factors. At this time, liver gains architectural novelty in the form of zonality and at cellular level acquires polarity. A comprehensive elucidation of such finely tuned developmental cues have been the basis of transdifferentiation of various types of stem cells to hepatocyte-like cells for purposes of understanding health and disease and for therapeutic applications.

Significance of plasma levels of pigment epithelium-derived factor as determined by multidetector row computed tomography in patients with mild chronic kidney disease and/or coronary artery disease

Little is known about the association between plasma levels of pigment epithelium-derived factor (PEDF), coronary artery disease (CAD) and/or chronic kidney disease (CKD). This study evaluated 289 consecutive patients with chest pain or at least one coronary risk factor who underwent coronary angiography using multidetector row computed tomography (MDCT). Presence of CAD and CKD, CAD severity (i.e. number of significantly stenosed coronary vessels, described as vessel disease [VD]), coronary calcification scores, visceral fat area (VFA), subcutaneous fat area on MDCT, and metabolic biomarkers were recorded. PEDF levels correlated significantly with sex, VFA, CKD presence/hyperuricaemia and high-density lipoprotein cholesterol levels. PEDF levels were closely associated with CKD and were significantly higher in CKD patients than in non-CKD patients, regardless of the presence of CAD. CKD patients with two-VD or three-VD had higher plasma PEDF levels than non-CKD patients with two-VD or three-VD. It is concluded that PEDF may be associated with CKD regardless of the presence of CAD.

Alzheimer's disease and non-demented high pathology control nonagenarians: comparing and contrasting the biochemistry of cognitively successful aging

The amyloid cascade hypothesis provides an economical mechanistic explanation for Alzheimer's disease (AD) dementia and correlated neuropathology. However, some nonagenarian individuals (high pathology controls, HPC) remain cognitively intact while enduring high amyloid plaque loads for decades. If amyloid accumulation is the prime instigator of neurotoxicity and dementia, specific protective mechanisms must enable these HPC to evade cognitive decline. We evaluated the neuropathological and biochemical differences existing between non-demented (ND)-HPC and an age-matched cohort with AD dementia. The ND-HPC selected for our study were clinically assessed as ND and possessed high amyloid plaque burdens. ELISA and Western blot analyses were used to quantify a group of proteins related to APP/Aβ/tau metabolism and other neurotrophic and inflammation-related molecules that have been found to be altered in neurodegenerative disorders and are pivotal to brain homeostasis and mental health. The molecules assumed to be critical in AD dementia, such as soluble or insoluble Aβ40, Aβ42 and tau were quantified by ELISA. Interestingly, only Aβ42 demonstrated a significant increase in ND-HPC when compared to the AD group. The vascular amyloid load which was not used in the selection of cases, was on the average almost 2-fold greater in AD than the ND-HPC, suggesting that a higher degree of microvascular dysfunction and perfusion compromise was present in the demented cohort. Neurofibrillary tangles were less frequent in the frontal cortices of ND-HPC. Biochemical findings included elevated vascular endothelial growth factor, apolipoprotein E and the neuroprotective factor S100B in ND-HPC, while anti-angiogenic pigment epithelium derived factor levels were lower. The lack of clear Aβ-related pathological/biochemical demarcation between AD and ND-HPC suggests that in addition to amyloid plaques other factors, such as neurofibrillary tangle density and vascular integrity, must play important roles in cognitive failure.

Pigment epithelium-derived factor (PEDF) interacts with transportin SR2, and active nuclear import is facilitated by a novel nuclear localization motif

PEDF (Pigment epithelium-derived factor) is a non-inhibitory member of the serpin gene family (serpinF1) that displays neurotrophic and anti-angiogenic properties. PEDF contains a secretion signal sequence, but although originally regarded as a secreted extracellular protein, endogenous PEDF is found in the cytoplasm and nucleus of several mammalian cell types. In this study we employed a yeast two-hybrid interaction trap screen to identify transportin-SR2, a member of the importin-β family of nuclear transport karyopherins, as a putative PEDF binding partner. The interaction was supported in vitro by GST-pulldown and co-immunoprecipitation. Following transfection of HEK293 cells with GFP-tagged PEDF the protein was predominantly localised to the nucleus, suggesting that active import of PEDF occurs. A motif (YxxYRVRS) shared by PEDF and the unrelated transportin-SR2 substrate, RNA binding motif protein 4b, was identified and we investigated its potential as a nuclear localization signal (NLS) sequence. Site-directed mutagenesis of this helix A motif in PEDF resulted in a GFP-tagged mutant protein being excluded from the nucleus, and mutation of two arginine residues (R67, R69) was sufficient to abolish nuclear import and PEDF interaction with transportin-SR2. These results suggest a novel NLS and mechanism for serpinF1 nuclear import, which may be critical for anti-angiogenic and neurotrophic function.

Identification of a novel inhibitor of the canonical Wnt pathway

Wnt signaling is known to regulate multiple processes including angiogenesis, inflammation, and fibrosis. Here, we identified a novel inhibitor of the Wnt pathway, pigment epithelium-derived factor (PEDF), a multifunctional serine proteinase inhibitor. Both overexpression of PEDF in transgenic mice and administration of PEDF protein attenuated Wnt signaling induced by retinal ischemia. Furthermore, PEDF knockdown by small interfering RNA (siRNA) and PEDF knockout in PEDF(-/-) mice induced activation of Wnt signaling. PEDF bound to LRP6, a Wnt coreceptor, with high affinity (K(d) [dissociation constant] of 3.7 nM) and blocked the Wnt signaling induced by Wnt ligand. The physical interaction of PEDF with LRP6 was confirmed by a coprecipitation assay, which showed that PEDF bound to LRP6 at the E1E2 domain. In addition, binding of PEDF to LRP6 blocked Wnt ligand-induced LRP6-Frizzled receptor dimerization, an essential step in Wnt signaling. These results suggest that PEDF is an endogenous antagonist of LRP6, and blocking Wnt signaling may represent a novel mechanism for its protective effects against diabetic retinopathy.

Sinusoid development and morphogenesis may be stimulated by VEGF-Flk-1 signaling during fetal mouse liver development

Early morphogenesis of hepatic sinusoids was histochemically and experimentally analyzed, and the importance of VEGF-Flk-1 signaling in the vascular development was examined during murine liver organogenesis. FITC-gelatin injection experiments into young murine fetuses demonstrated that all primitive sinusoidal structures were confluent with portal and central veins, suggesting that hepatic vessel development may occur via angiogenesis. At 12.5-14.5 days of gestation, VEGF receptors designated Flk-1, especially their mature form, were highly expressed in endothelial cells of primitive sinusoidal structures and highly phosphorylated on their tyrosine residues. At the same time, VEGF was also detected in hepatoblasts/hepatocytes, hemopoietic cells, and megakaryocytes of the whole liver parenchyma. Furthermore, the addition of VEGF to E12.5 liver cell cultures significantly induced the growth and branching morphogenesis of sinusoidal endothelial cells. Therefore, VEGF-Flk-1 signaling may play an important role in the growth and morphogenesis of primitive sinusoids during fetal liver development.

Pigment epithelium-derived factor (PEDF) as a therapeutic target in cardiovascular disease

In this review we discuss the role of pigment epithelium-derived factor (PEDF) as a possible new target molecule to therapeutically influence cardiovascular disease. PEDF is a multifunctional, pleiotropic protein with antiangiogenic, antitumorigenic, antioxidant, anti-inflammatory, antithrombotic, neurotrophic and neuroprotective properties. First identified in retinal pigment epithelium cells, it is expressed in various tissues throughout the body such as the eye, liver and adipose tissue. Recently PEDF has also been characterized in the heart. PEDF has been suggested to have a protective role in atherosclerosis, the main cause of coronary heart disease, myocardial infarction and heart failure due to its anti-inflammatory, antioxidant and antithrombotic effects in the vessel wall and platelets. Additionally PEDF has strong antiangiogenic effects by inducing apoptosis in endothelial cells and by regulating the expression of other angiogenic factors. Therefore blocking of PEDF locally for example in ischemic tissue in the heart might favour angiogenesis, induce neovascularization and lead to increased perfusion of the injured tissue. On the other hand, local overexpression of PEDF restricted to atherosclerotic lesions might block angiogenesis, inflammation and thrombosis at these sites and thus counteract destabilization and rupture of the lesion otherwise caused by inflammatory activation and excessive angiogenesis and inhibit subsequent thrombus formation.

'Loss of pigment epithelium-derived factor enables migration, invasion and metastatic spread of human melanoma'

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). Here, we show that PEDF expression is high in melanocytes, but it is lost during malignant progression of human melanoma. Using a high-throughput analysis of the data from microarray studies of molecular profiling of human melanoma, we found that PEDF expression is lost in highly invasive melanomas. In paired cell lines established from the same lesion but representing the high and low extremes of malignant potential, abundant PEDF expression was restricted to the poorly aggressive counterparts. We used RNA interference to directly address the functional consequences of PEDF silencing. PEDF knockdown in poorly aggressive melanoma cell lines augmented migration, invasion and vasculogenic mimicry, which translated into an increased in vivo metastatic potential. PEDF interference also significantly enhanced the migratory and invasive capability of normal melanocytes and moderately increased their proliferative potential. Our results show that loss of PEDF enables melanoma cells to acquire an invasive phenotype and, therefore, modulation of this multifunctional factor could be critical for the malignant progression of human melanoma.

Constitutive overexpression of pigment epithelium-derived factor inhibition of ocular melanoma growth and metastasis

PURPOSE

Pigment epithelium-derived factor (PEDF) is known to be an angiogenesis suppressor and to have antitumor effects. This study investigates whether constitutive overexpression of PEDF inhibits the growth and hepatic micrometastasis of ocular melanoma.

METHODS

Real-time RT-PCR was used to detect endogenous PEDF expression in human uveal melanoma cell lines and mouse melanoma cells. A lentiviral vector containing a mouse PEDF expression sequence was constructed and transduced into mouse melanoma cells in vitro. Transgene expression was assessed by Western blot analysis. Angiogenesis and transendothelial migration assays were performed in constitutively stable PEDF-overexpressing cells and transduced lentiviral vector control cells. The size and microvessel density of the ocular tumor and the number of hepatic micrometastasis were compared between the mice inoculated with PEDF-overexpressing tumor cells and those mice with the control cell line.

RESULTS

Four human uveal melanoma and three mouse melanoma cell lines were found to express PEDF mRNA. Endogenous overexpressing PEDF melanoma cells lost the ability to migrate and form tubes in vitro. In the animal experiment, the size of the ocular melanoma and the number of hepatic micrometastasis were decreased and microvessel density was also reduced in mice inoculated with constitutively overexpressing PEDF melanoma cells.

CONCLUSIONS

Lentivirus-mediated gene transfer of PEDF decreased the growth of ocular melanoma and its hepatic micrometastasis in a mouse ocular melanoma model. Dual antitumor/antiangiogenic activities of PEDF suggest that PEDF gene therapy may be considered an approach for the treatment of ocular melanoma.

Characterization of PEDF: a multi-functional serpin family protein

Pigment epithelium-derived factor (PEDF) is a 50 kDa secreted glycoprotein that belongs to the non-inhibitory serpin family group. PEDF has been described as a natural angiogenesis inhibitor with neurotrophic and immune-modulation properties; it balances angiogenesis in the eye and blocks tumor progression. The mechanisms underlying most of these events are not completely clear; however, it appears that PEDF acts via multiple high affinity ligands and cell receptors. In this review article, we will summarize the current knowledge on the biochemical properties of PEDF and its receptors, the multimodal activities of PEDF and finally address the therapeutic potential of PEDF in treating angiogenesis-, neurodegeneration- and inflammation-related diseases.

Regulating the angiogenic balance in tissues

A balance between angiogenesis inducers and inhibitors in the microenvironment controls the rate of new blood vessel formation. We hypothesized that fibroblasts, an important cellular constituent of the tissue stroma, secrete molecules that contribute to this balance. We further hypothesized that fibroblasts secrete molecules that promote angiogenesis when they are in a proliferative state and molecules that inhibit angiogenesis when they are not actively cycling (quiescent). Microarray analysis revealed that angiogenesis inducers and inhibitors are regulated as fibroblasts transition into a quiescent state and reenter the cell cycle in response to changes in serum. To assess whether changes in transcript levels result in changes in the levels of secreted proteins, we collected conditioned medium from proliferating and quiescent fibroblasts and performed immunoblotting for selected proteins. Secreted protein levels of the angiogenesis inhibitor pigment epithelium derived factor (PEDF) were higher in quiescent than proliferating fibroblasts. Conversely, proliferating fibroblasts secreted increased levels of the angiogenesis inducer vascular endothelial growth factor-C (VEGF-C). For the angiogenesis inhibitor thrombospondin-2, quiescent cells secreted a prominent 160 kDa form in addition to the 200 kDa form secreted by proliferating and restimulated fibroblasts. Using immunohistochemistry we discovered that fibroblasts surround blood vessels and that the angiogenesis inhibitor PEDF is expressed by quiescent fibroblasts in uterine tissue, supporting a role for PEDF in maintaining quiescence of the vasculature. This work takes a new approach to the study of angiogenesis by examining the expression of multiple angiogenesis regulators secreted from a key stromal cell, the fibroblast.

Increased serum pigment epithelium-derived factor is associated with microvascular complications, vascular stiffness and inflammation in Type 1 diabetes

AIMS

To determine in Type 1 diabetes patients if levels of pigment epithelium-derived factor (PEDF), an anti-angiogenic, anti-inflammatory and antioxidant factor, are increased in individuals with complications and positively related to vascular and renal dysfunction, body mass index, glycated haemoglobin, lipids, inflammation and oxidative stress.

METHODS

Serum PEDF levels were measured by ELISA in a cross-sectional study of 123 Type 1 diabetic patients (71 without and 52 with microvascular complications) and 31 non-diabetic control subjects. PEDF associations with complication status, pulse-wave analysis and biochemical results were explored.

RESULTS

PEDF levels [geometric mean (95% CI)] were increased in patients with complications 8.2 (7.0-9.6) microg/ml, vs. complication-free patients [5.3 (4.7-6.0) microg/ml, P < 0.001] and control subjects [5.3 (4.6-6.1) microg/ml, P < 0.001; anova between three groups, P < 0.001], but did not differ significantly between control subjects and complication-free patients (P > 0.05). In diabetes, PEDF levels correlated (all P < 0.001) with systolic blood pressure (r = 0.317), pulse pressure (r = 0.337), small artery elasticity (r = -0.269), glycated haemoglobin (r = 0.245), body mass index (r = 0.362), renal dysfunction [including serum creatinine (r = 0.491), cystatin C (r = 0.500)], triglycerides (r = 0.367), and inflammation [including log(e)C-reactive protein (CRP; r = 0.329), and soluble vascular cell adhesion molecule-1 (r = 0.363)]. Age, blood urea nitrogen, systolic blood pressure, pulse pressure and log(e)CRP correlated with PEDF levels in control subjects (all P < 0.04). PEDF levels were not significantly correlated with measures of oxidative stress: isoprostanes, oxidized low-density lipoprotein or paraoxonase-1 activity. On stepwise linear regression analysis (all subjects), independent determinants of PEDF levels were renal function, triglycerides, inflammation, small artery elasticity and age (r(2) = 0.427).

CONCLUSIONS

In Type 1 diabetes, serum PEDF levels are associated with microvascular complications, poor vascular health, hyperglycaemia, adiposity and inflammation.

Curcumin as an inhibitor of angiogenesis

Angiogenesis, the formation of new blood vessels from host vasculature, is critical for tumor growth and metastases. -Curcumin, a novel small-molecular-weight compound, has been shown to inhibit carcinogenesis in different organs and the common link between these actions is its antiangiogenic effect. Curcumin is a direct inhibitor of angiogenesis and also downregulates various proangiogenic proteins like vascular endothelial growth factor and basic fibroblast growth factor. Curcumin's antiangiogenic effect is also in part due to its inhibitory effect on signal transduction pathways, including those involving protein kinase C and the transcription factors NF-kappaB and AP-1. Curcumin has an inhibitory effect on two groups of proteinases involved in angiogenesis that are the members of the matrix metalloproteinase family and the urokinase plasminogen activator family. Cell adhesion molecules are upregulated in active angiogenesis and curcumin can block'this effect, adding further dimensions to curcumin's antiangiogenic effect. Curcumin shows a dose-dependent inhibition on tumor necrosis factor, a versatile cytokine, which has its effect on angiogenesis through the signal transduction pathways, expression of proangiogenic factors, and cell adhesion molecules. Curcumin's effect on the overall process of angiogenesis compounds its enormous potential as an antiangiogenic drug.

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.

Inhibition of orthotopic osteosarcoma growth and metastasis by multitargeted antitumor activities of pigment epithelium-derived factor

Osteosarcoma is major cause of cancer-related death in the pediatric age group, and this is due to the development of pulmonary metastases that fail to be eradicated with current treatment regimes. Although there have been significant improvements in the long-term survival of such patients, 25-50% with initially non-metastatic disease, subsequently develop metastases and this remains the major cause of death for these patients. In this study, we report the multimodal activity of pigment epithelium-derived factor (PEDF) in inhibiting osteosarcoma growth, angiogenesis and metastasis. In vitro, we found that administration of recombinant PEDF (rPEDF) on two osteosarcoma cell lines (rat UMR 106-01 and human SaOS-2) significantly reduced tumor cell proliferation and increased apoptosis, as well as decreased cell invasion, angiogenesis, and increased adhesion to collagen type-1. Administration of rPEDF upregulated the mRNA expression of phenotypic osteoblast differentiation markers (ALP, pro-alpha(1) collagen and osteocalcin) in a pre-osteoblastic cell line, UMR 201, and also increased mineralized nodule formation in both UMR 106-01 and SaOS-2. In vivo, rPEDF dramatically suppressed primary osteosarcoma growth and the development of macroscopic pulmonary metastases in an orthotopic model of human osteosarcoma (SaOS-2). Interestingly, no activity was seen in tumors grown subcutaneously, suggesting a paracrine interaction between PEDF and the bone microenvironment. Preliminary pharmacoevaluation studies demonstrated rPEDF stability within media containing serum and osteosarcoma cells, and no gross systemic toxicity was observed in vivo with rPEDF administration. These results suggest that PEDF is emerging as an attractive and clinically appealing drug candidate for the treatment of osteosarcoma.

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.

Gene transfer of pigment epithelium-derived factor suppresses tumor growth and angiogenesis in a hepatoblastoma xenograft model

Normal hepatocytes express pigment epithelium-derived factor (PEDF), an endogenous antiangiogenic factor. We hypothesized that decreased PEDF expression may be one mechanism driving hepatoblastoma growth, and in vivo gene transfer of PEDF could suppress neovascularization and limit tumor growth. PEDF functional activity was determined in vitro using endothelial cell migration assays and in vivo using a subcutaneous tumor model. HUH-6 human hepatoblastoma tumors were treated with hybrid adenoviral/adeno-associated viral expression vectors for PEDF (Hyb-PEDF, n = 4) or beta-galactosidase (Hyb-betagal, n = 4) daily for 4 d. Mitotic figures, microvascular density (MVD), PEDF, and VEGF expression were assessed. Hyb-PEDF treatment inhibited in vivo tumor growth (p < 0.008) and decreased MVD (p < 0.001), the number of mitotic figures (p < 0.001), and VEGF expression when compared with Hyb-betagal-treated tumors. HUH-6 expression of PEDF was dramatically reduced when cultured under hypoxic conditions and also when grown in vivo, and the addition of neutralizing anti-PEDF antibody increased the already high baseline angiogenic activity of the HUH-6 cell secretions in vitro (p < 0.04). PEDF is an important endogenous regulator of the liver vasculature. Augmenting intra-tumoral PEDF levels inhibits tumor growth by reducing angiogenesis and VEGF expression. Potent inhibitors of angiogenesis, such as PEDF, may be an effective alternative treatment for children with hepatoblastoma.

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.

Comparative proteomics of cerebrospinal fluid in neuropathologically-confirmed Alzheimer's disease and non-demented elderly subjects

OBJECTIVES

Diagnostic tests able to reveal Alzheimer's disease (AD) in living patients before cognitive ability is destroyed are urgently needed. Such tests must distinguish AD from other dementia causes, as well as differentiate subtle changes associated with normal aging from true pathology emergence. A single biomarker offering such diagnostic and prognostic capacities has eluded identification. Therefore, a valuable test for AD is likely to be based on a specific pattern of change in a set of proteins, rather than a single protein.

METHODS

We examined pooled cerebrospinal fluid (CSF) samples obtained from neuropathologically-confirmed AD (n=43) and non-demented control subjects (n=43) using 2-dimensional gel electrophoresis (2DE) proteomic methodology to detect differentially expressed proteins. Proteins exhibiting expression level differences between the pools were recovered and identified using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry.

RESULTS

Five differentially-expressed proteins with potential roles in amyloid-beta metabolism and vascular and brain physiology [apolipoprotein A-1 (Apo A-1), cathepsin D (CatD), hemopexin (HPX), transthyretin (TTR), and two pigment epithelium-derived factor (PEDF) isoforms] were identified. Apo A-1, CatD and TTR were significantly reduced in the AD pool sample, while HPX and the PEDF isoforms were increased in AD CSF.

DISCUSSION

These results suggest that multi-factor proteomic pattern analysis of the CSF may provide a means to diagnose and assess AD.

Vasohibin is up-regulated by VEGF in the retina and suppresses VEGF receptor 2 and retinal neovascularization

Vasohibin is a recently identified protein that is up-regulated in cultured vascular endothelial cells by vascular endothelial growth factor and fibroblast growth factor 2. It inhibits endothelial cell migration, proliferation, and tube formation, and suppresses angiogenesis in chick chorioallantoic membrane, after subcutaneous implantation of matrigel, and in a tumor xenograft model. This has led to the hypothesis that vasohibin functions as a negative feedback inhibitor of angiogenesis. In this study, we tested that hypothesis in a well-characterized model of retinal neovascularization. In ischemic retina, increased expression of VEGF was accompanied by elevation of vasohibin mRNA and blocking of the increase in vegf mRNA with vegf siRNA significantly attenuated the rise in vasohibin mRNA. In transgenic mice in which the rhodopsin promoter drives expression of VEGF in the retina, there was also a significant increase in vasohibin mRNA. In mice with ischemic retinopathy, there was increased expression of vasohibin in vascular endothelial cells, and vasohibin knockdown caused an increase in neovascularization. Conversely, intraocular injection of recombinant vasohibin or an adenoviral vector containing a vasohibin expression cassette strongly suppressed retinal neovascularization in mice with ischemic retinopathy. Knockdown of vasohibin mRNA in ischemic retina had no significant effect on vegf or vegf receptor 1 mRNA levels but caused a significant elevation in the level of vegf receptor 2 mRNA. These data support the hypothesis that vasohibin acts as a negative feedback regulator of neovascularization in the retina and suggest that suppression of VEGF receptor 2 may play some role in mediating its activity.

A novel technique to specifically analyze the secretome of cells and tissues

The secretome of cells and tissues may reflect a broad variety of pathological conditions and thus represents a rich source of biomarkers. The identity of secreted proteins, usually isolated from cell supernatants or body fluids, is hardly accessible by direct proteome analysis, because these proteins are often masked by high amounts of proteins actually not secreted by the investigated cells. Here, we present a novel method for the specific detection of proteins secreted by human tissue specimen as well as cultured cells and chose liver as a model. The method is based on the metabolic labelling of proteins synthesized during a limited incubation period. Then, the cell supernatant is filtered, precipitated, and subjected to two-dimensional gel electrophoresis. Whereas fluorography detected a large number of proteins derived from residual plasma and dead cells, the autoradiographs selectively displayed genuinely secreted proteins. We demonstrate the feasibility of this approach by means of the secretomes of the hepatocellular carcinoma-derived cell line HepG2 and human liver slices. The selective identification of cell- and tissue-specific protein secretion profiles may help to identify novel sets of biomarkers for wide clinical applications.

Expression of angiogenesis factors in human umbilical vein endothelial cells and their regulation by PEDF

The VEGFs and FGF-2 stimulate angiogenesis. Pigment epithelium-derived factor (PEDF) and thrombospondin-1 (TSP-1) strongly inhibit angiogenesis. Human umbilical vein endothelial cells (HUVECs) expressed VEGF-A, -B, -C, the VEGF receptors R1, R2, and R3, PEDF, FGF-2, and TSP-1, but VEGF-D transcripts were barely detectable. Hypoxia reduced the transcript levels of VEGF-C and its cognate receptor, VEGF-R3. PEDF blocked the effect of CoCl(2) on these two factors. The expression of VEGF-A and -B as well as VEGF-R1 and VEGF-R2 remained unchanged after exposure to hypoxia, PEDF, or both. There was a marked reduction in TSP-1 transcripts in CoCl(2) treated cultures and PEDF blocked this reduction. PEDF induced a small increase in FGF-2 transcripts in HUVECs, but there was no change in FGF-2 expression in HUVECs exposed to hypoxia or hypoxia plus PEDF. PEDF may control neovascularization, in part, by restoring the negative effects of hypoxia on the expression of a potent angiogenesis inhibitor, TSP-1. PEDF may also modulate vascular leakage by maintaining the transcriptional levels of the vascular homeostasis factors, VEGF-C and VEGF-R3 in hypoxic conditions.