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

Serum proteome analysis identifies a potential biomarker for axial psoriatic arthritis

BACKGROUND

To identify potential serum biomarkers for differentiating between axial psoriatic arthritis (axPsA) and peripheral psoriatic arthritis (pPsA).

METHODS

Serum samples were collected from patients with PsA to create a biomarker discovery cohort and a verification cohort. Patients with PsA were classified into axial or peripheral subtypes based on imaging criteria. Untargeted proteomics technology was used in the discovery phase to screen for biomarkers, and candidate biomarkers were evaluated using enzyme-linked immunosorbent assay (ELISA) in the verification phase.

RESULTS

We identified 45 significantly differentially expressed proteins (DEPs) between axPsA (n = 20) and pPsA (n = 20) with liquid chromatography-mass spectrometry. Among these DEPs, serum pigment epithelium-derived factor (PEDF) was identified as a candidate biomarker using the Boruta algorithm and lasso regression. Results of ELISA further confirmed that the level of serum PEDF expression was significantly higher in axPsA (n = 37) than in pPsA (n = 51) at the verification cohort (37.9 ± 10.1 vs. 30.5 ± 8.9 μg/mL, p < 0.001). Receiver operating characteristics analysis showed that PEDF had an area under the curve (AUC) of 0.72. Serum PEDF was positively correlated with body mass index and C-reactive protein. Additionally, there was a tendency towards a positive correlation between PEDF and the Bath Ankylosing Spondylitis Disease Activity Index.

CONCLUSIONS

This study provided a comprehensive characterization of the proteome in axPsA and pPsA and identified a candidate biomarker, PEDF, that may contribute to early diagnosis for axPsA.

Knockdown of DAPK1 inhibits IL-1β-induced inflammation and cartilage degradation in human chondrocytes by modulating the PEDF-mediated NF-κB and NLRP3 inflammasome pathway

Osteoarthritis (OA) is a common joint disease that is characterized by inflammation and cartilage degradation. Death-associated protein kinase 1 (DAPK1) is a multi-domain serine/threonine kinase and has been reported to be involved in the progression of OA. However, its role and mechanism in OA remain unclear. Here, we found the expression of DAPK1 in OA cartilage tissues was higher than that in normal cartilage tissues. The expression of DAPK1 in chondrocytes was up-regulated by IL-1β. Knockdown of DAPK1 promoted cell viability and anti-apoptotic protein expression, while it inhibited the apoptosis rate and pro-apoptotic protein expressions in IL-1β-induced chondrocytes. In addition, DAPK1 inhibition reduced the levels of inflammatory cytokines and expressions of matrix metalloproteinases (MMPs), and increased the expressions of collagen II and aggrecan. The data of mechanistic investigation indicated that the expression of pigment epithelium-derived factor (PEDF) was positively regulated by DAPK1. Overexpression of PEDF attenuated the effects of DAPK1 knockdown on IL-1β-induced cell viability, apoptosis, inflammation, and cartilage degradation. Furthermore, PEDF overexpression restored the activity of the NF-κB pathway and NLRP3 inflammasome after DAPK1 knockdown. Collectively, down-regulation of DAPK1 inhibited IL-1β-induced inflammation and cartilage degradation via the PEDF-mediated NF-κB and NLRP3 inflammasome pathways.

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.

Oxyresveratrol Reduces the Migration of Human Osteosarcoma Cell U2OS via Attenuating STAT3 Activation

Objective: Osteosarcoma is a malignant tumor with high metastatic properties that are associated with increased mortality and poor prognosis. Therefore, it is crucial to develop an effective treatment for metastatic osteosarcoma. Oxyresveratrol (ORES), derived from mulberry twigs and fruits, has antitumor effects. However, it remains unknown whether ORES inhibits osteosarcoma metastasis. In this study, we determined the inhibitory effect of ORES on osteosarcoma metastasis. Key Findings: ORES attenuated the migration of U2OS cells, dose-dependently increased E-cadherin expression, and reduced N-cadherin expression in U2OS cells, indicating that ORES can inhibit epithelial–mesenchymal transition (EMT) in osteosarcoma cells. Furthermore, ORES inhibited the expression of Twist, which is associated with the downregulation of STAT3 phosphorylation. IL-6-induced STAT3 phosphorylation rescues the inhibitory effect of ORES on U2OS metastasis. Summary: Our results indicate that ORES is a potential therapeutic agent for metastatic osteosarcoma. ORES inhibits osteosarcoma cell migration by reducing EMT formation.

Quantitative proteomic study reveals differential expression of matricellular proteins between fibrous dysplasia and cemento-ossifying fibroma pathogenesis

BACKGROUND

Fibrous dysplasia (FD) and cemento-ossifying fibroma (COF) are the most common gnathic fibro-osseous lesions. These diseases exhibit remarkable overlap of several clinicopathological aspects and differential diagnosis depends on the combination of histopathological, radiographic and clinical aspects. Their molecular landscape remain poorly characterized and herein we assessed their proteomic and phosphoproteomic profiles.

METHODS

The quantitative differences in protein profile of FD and COF were assessed by proteomic and phosphoproteomic analyses of formalin-fixed paraffin-embedded tissue samples. Pathway enrichment analyses with differentialy regulated proteins were performed.

RESULTS

FD and COF exhibited differential regulation of pathways related to extracellular matrix organization, cell adhesion, and platelet and erythrocytes activities. Additionally, these lesions demonstrated distinct abundance of proteins involved in osteoblastic differentiation and tumorigenesis and differential abundance of phosphorylation of Ser61 of Yes-associated protein 1 (YAP1).

CONCLUSIONS

In summary, despite the morphological similarity between these diseases, our results demonstrated that COF and DF present numerous quantitative differences in their proteomic profiles.These findings suggest that these fibro-osseous lesions trigger distinct molecular mechanisms during their pathogenesis. Moreover, some proteins identified in our analysis could serve as potential biomarkers for differential diagnosis of these diseases after further validation.

The m6A Methyltransferase METTL3 Is Functionally Implicated in DLBCL Development by Regulating m6A Modification in PEDF

Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of lymphoma, whose treatment still has a major challenge of achieving a satisfactory curative effect. The underlying mechanisms also have not been fully illustrated. N⁶-Methyladenosine (m6A) has been identified as the most prevalent internal modification of mRNAs present in eukaryotes, which is involved in the pathogenesis of cancers. It remains unclear how m6A mRNA methylation is functionally linked to the pathogenesis of DLBCL. In this study, we sought to explore the roles of METTL3 on DLBCL development. The results showed that m6A level for RNA methylation and the expression level of METTL3 were upregulated in DLBCL tissues and cell lines. Functionally, downregulated METTL3 expression in DLBCL cells inhibited the cell proliferation ability. Further mechanism analysis indicated that METTL3 knockdown abates the m6A methylation and total mRNA level of pigment epithelium-derived factor (PEDF). However, Wnt/β-catenin signaling was not thus activated. Overexpressed PEDF abrogates the inhibition of cell proliferation in DLBCL cells that is caused by METTL3 silence. In summary, the above-mentioned results demonstrated that the METTL3 promotes DLBCL progression by regulating the m6A level of PEDF.

Pigment epithelium-derived factor (PEDF) and PEDF-receptor in the adult mouse brain: Differential spatial/temporal localization pattern

Pigment epithelium-derived factor (PEDF) is a multifunctional protein which was initially described in the retina, although it is also present in other tissues. It functions as an antioxidant agent promoting neuronal survival. Recently, a PEDF receptor has shown an elevated binding affinity for PEDF. There are no relevant data regarding the distribution of both proteins in the brain, therefore the main goal of this work was to investigate the spatiotemporal presence of PEDF and PEDFR in the adult mouse brain, and to determine the PEDF blood level in mouse and human. The localization of both proteins was analyzed by different experimental methods such as immunohistochemistry, western-blotting, and also by enzyme-linked immunosorbent assay. Differential expression was found in some telencephalic structures and positive signals for both proteins were detected in the cerebellum. The magnitude of the PEDFR labeling pattern was higher than PEDF and included some cortical and subventricular areas. Age-dependent changes in intensity of both protein immunoreactions were found in the cortical and hippocampal areas with greater reactivity between 4 and 8 months of age, whilst others, like the subventricular zones, these differences were more evident for PEDFR. Although ubiquitous presence was not found in the brain for these two proteins, their relevant functions must not be underestimated. It has been described that PEDF plays an important role in neuroprotection and data provided in the present work represents the first extensive study to understand the relevance of these two proteins in specific brain areas.

Therapeutic Potential of Pigment Epithelium-derived Factor in Cancer

Pigment epithelium-derived factor (PEDF) is one of the serine protease inhibitors with multifunctional properties, which is produced by various types of organs and tissues. There is an accumulating body of evidence that PEDF plays an important role in the maintenance of tissue homeostasis. Indeed, PEDF not only works as an endogenous inhibitor of angiogenesis, but also suppresses oxidative stress, inflammatory and thrombotic reactions in cell culture systems, animal models, and humans. Furthermore, we, along with others, have found that PEDF inhibits proliferation of, and induces apoptotic cell death in, numerous kinds of tumors. In addition, circulating as well as tumor expression levels of PEDF have been inversely associated with tumor growth and metastasis. These observations suggest that supplementation of PEDF proteins and/or enhancement of endogenous PEDF expression could be a novel therapeutic strategy for the treatment of cancer. Therefore, in this paper, we review the effects of PEDF on diverse types of cancer, and discuss its therapeutic perspectives.

Guinea fowl eggshell quantitative proteomics yield new findings related to its unique structural characteristics and superior mechanical properties

The Guinea fowl eggshell is a bioceramic material with the remarkable mechanical property of being twice as strong as the chicken eggshell. Both eggshells are composed of 95% calcite and 3.5% organic matrix, which control its structural organization. Chicken eggshell is made of columnar calcite crystals arranged vertically. In the Guinea fowl, the same structure is observed in its inner half, followed by a dramatic change in crystal size and orientation in the outer region. Guinea fowl eggshell is thicker than chicken eggshell. Both structure and shell thickness confer a superior resistance to breakage compared to eggshells of other bird species. To understand the underlying mechanisms controlling the structural organization of this highly resistant material, we used quantitative proteomics to analyze the protein composition of the Guinea fowl eggshell organic matrix at key stages of the biomineralization process. We identified 149 proteins, which were compared to other bird eggshell proteomes and analyzed their potential functions. Among the 149 proteins, 9 are unique to Guinea fowl, some are involved in the control of the calcite precipitation (Lysozyme, Ovocleidin-17-like, Ovocleidin-116 and Ovalbumin), 61 are only found in the zone of microstructure shift and 17 are more abundant in this zone. SIGNIFICANCE: The avian eggshell is a critical physical barrier to protect the contents of this autonomous reproductive enclosure from physical and microbial assault. The Guinea fowl (Numida meleagris) eggshell exhibits a unique microstructure (texture), which confers exceptional mechanical properties compared to eggshells of other species. In order to understand the mechanisms that regulate formation of this texture in the Guinea fowl eggshell, we performed comparative quantitative proteomics at key stages of shell mineralization and particularly during the dramatic shift in shell microstructure. We demonstrate that the Guinea fowl eggshell proteome comprises 149 proteins, of which 61 were specifically associated with the change in size and orientation of calcite crystals. Comparative proteomics analysis with eggshell of other bird species leads to new insights into the biomineralization process. Moreover, our data represents a list of organic compounds as potential additives to regulate material design for industrial fabrication of ceramics. This information also provides molecular markers for efficient genomic selection of chicken strains to lay eggs with improved shell mechanical properties for enhanced food safety.

Pigment epithelium-derived factor inhibits adipogenesis in 3T3-L1 adipocytes and protects against high-fat diet-induced obesity and metabolic disorders in mice

Obesity is a major cause of metabolic syndrome and type II diabetes, and it presents with metabolic disorders, such as hyperglycemia, hyperlipidemia, and insulin resistance. Pigment epithelium-derived factor (PEDF), a protein isolated from retinal pigment epithelial cells, has multiple functions, including neuronal protection, antineoplastic effects, and anti-inflammatory activity. The aim of this study is to investigate the antiobesity effects of PEDF. The antiobesity effects of PEDF on fat accumulation, inflammation, energy expenditure, insulin resistance, and obesity-related physiological parameters and protein levels were assessed in high-fat diet (HFD)-induced obese mice in vivo and in 3T3-L1 adipocytes, palmitate (PA)-treated HepG2 cells, and C2C12 myotubes in vitro. In an in vivo assay, PEDF effectively decreased body weight gain, white adipose tissue mass, and inflammation and improved insulin resistance, dyslipidemia, and hyperglycemia in HFD-induced mice. In liver tissue, PEDF decreased lipid accumulation and fibrosis. In an in vitro assay, PEDF diminished the differentiation of 3T3-L1 preadipocytes. We also determined that PEDF promoted lipolysis and prolonged cell cycle progression, through the mTOR-S6K pathway and downstream transcription factors, such as peroxisome proliferator-activated receptor gamma, CCAAT/enhancer-binding protein α (CEBP-α), and CEBP-β. In addition, PEDF decreased reactive oxygen species production in PA-induced HepG2 cells and improved glucose uptake ability in PA-induced HepG2 cells and C2C12 myotubes. In the present study, PEDF protected against HFD-induced obesity and metabolic disorders in mice, inhibited adipogenesis, and improved insulin resistance. These results provide a new potential treatment for obesity in the future.