Angiopoietin-like-4 is a potential angiogenic mediator in arthritis

Suppression of angiopoietin-like 4 reprograms endothelial cell metabolism and inhibits angiogenesis

Angiopoietin-like 4 (ANGPTL4) is known to regulate various cellular and systemic functions. However, its cell-specific role in endothelial cells (ECs) function and metabolic homeostasis remains to be elucidated. Here, using endothelial-specific Angptl4 knock-out mice (Angptl4iΔEC), and transcriptomics and metabolic flux analysis, we demonstrate that ANGPTL4 is required for maintaining EC metabolic function vital for vascular permeability and angiogenesis. Knockdown of ANGPTL4 in ECs promotes lipase-mediated lipoprotein lipolysis, which results in increased fatty acid (FA) uptake and oxidation. This is also paralleled by a decrease in proper glucose utilization for angiogenic activation of ECs. Mice with endothelial-specific deletion of Angptl4 showed decreased pathological neovascularization with stable vessel structures characterized by increased pericyte coverage and reduced permeability. Together, our study denotes the role of endothelial-ANGPTL4 in regulating cellular metabolism and angiogenic functions of EC.

Silencing of Angiopoietin-Like Protein 4 (Angptl4) Decreases Inflammation, Extracellular Matrix Degradation, and Apoptosis in Osteoarthritis via the Sirtuin 1/NF-κB Pathway

Osteoarthritis (OA) is a frequently observed condition in aged people. OA cartilage is characterized by chondrocyte apoptosis, chondrocyte inflammation, and hyperactive catabolism of extracellular matrix. However, the specific molecular mechanisms remain unclear. Recent data has shown that Angptl4, a multifunctional cytokine, is involved in the regulation of inflammatory and apoptosis responses in different tissues. This study is aimed at defining the role of Angptl4 in the development of OA. We employed X-ray analysis, safranin O-fast green (S-O) staining, and hematoxylin staining to evaluate histomorphological characteristics in the knee joint of mice. Real-time quantitative polymerase chain reaction, Western blot assays, immunofluorescence staining, and enzyme-linked immunosorbent assays (ELISA) were performed to analyze the changes in gene and protein expression. Mechanically, our data demonstrated that Angptl4 knockdown improved the degradation of extracellular matrix and reduced TNF-α-mediated chondrocyte inflammation and apoptosis by suppressing sirtuin 1/NF-κB signaling pathway. In addition, animal studies showed that the suppression of Angptl4 expression might alleviate OA development. In conclusion, our findings revealed the underlying mechanisms of Angptl4 regulation in chondrocytes and its potential value in the treatment of OA.

ANGPTL2 Promotes Inflammation via Integrin α5β1 in Chondrocytes

BACKGROUND

Angiopoietin-like protein 2 (ANGPTL2) is a secreted molecule with numerous physiologic and pathologic functions, for example, in angiogenesis, hematopoiesis, and tumorigenesis. Although recent studies implicated ANGPTL2 in chronic inflammation in mouse peritoneal macrophages, human ligamentum flavum fibroblasts, and human retinal microvascular endothelial cells, the mechanism underlying ANGPTL2-associated inflammation in chondrocytes remains unclear. Therefore, it was investigated whether ANGPTL2 is expressed in or functions in chondrocytes.

METHODS

Expression of ANGPTL2 and its receptor, integrin α5β1 were examined over time in ATDC5 cells using real-time RT-PCR (reverse transcription-polymerase chain reaction) analysis. ATDC5 cells were then incubated with or without ANGPTL2 for 3 hours, and expression of the IL-1β, TNF-α, COX-2, aggrecanase (ADAMTS)-5, matrix metalloproteinase (MMP)-3, and MMP-13 genes were examined using real-time RT-PCR. Additionally, phosphorylation of ERK, JNK, p38, Akt, and NF-κB was examined by western blotting. Furthermore, it was also investigated for the effect of anti-integrin α₅β₁ antibody on the expression of inflammatory markers and intracellular signaling pathways.

RESULTS

ANGPTL2 induced the phosphorylation of all 3 MAPKs, Akt, and NF-κB and dramatically upregulated the expression of inflammation-related factor genes. Inhibiting the activation of integrin α5β1 suppressed these reactions.

CONCLUSION

ANGPTL2 may induce inflammatory factors by stimulating the integrin α5β1/MAPKs, Akt, and NF-κB signaling pathway.

ANGPTL4: a multifunctional protein involved in metabolism and vascular homeostasis

PURPOSE OF REVIEW

Since the first discovery of Angiopoetin-like 4 (ANGPTL4) in 2000, the involvement of ANGPTL4 in different aspects of lipid metabolism and vascular biology has emerged as an important research field. In this review, we summarize the fundamental roles of ANGPTL4 in regulating metabolic and nonmetabolic functions and their implication in lipid metabolism and with several aspects of vascular function and dysfunction.

RECENT FINDINGS

ANGPTL4 is a secreted glycoprotein with a physiological role in lipid metabolism and a predominant expression in adipose tissue and liver. ANGPTL4 inhibits the activity of lipoprotein lipase and thereby promotes an increase in circulating triglyceride levels. Therefore, ANGPTL4 has been highly scrutinized as a potential therapeutic target. Further involvement of ANGPTL4 has been shown to occur in tumorigenesis, angiogenesis, vascular permeability and stem cell regulation, which opens new opportunities of using ANGPTL4 as potential therapeutic targets for other pathophysiological conditions.

SUMMARY

Further determination of ANGPTL4 regulatory circuits and defining specific molecular events that mediate its biological effects remain key to future ANGPTL4-based therapeutic applications in different disease settings. Many new and unanticipated roles of ANGPTL4 in the control of cell-specific functions will assist clinicians and researchers in developing potential therapeutic applications.

Dual functional nanoparticles containing SOX duo and ANGPT4 shRNA for osteoarthritis treatment

In our previous studies, we found that adult stem cells transfected with sex-determining region Y-box (SOX)-9, -6 and -5 genes (SOX trio) enhanced chondrogenesis and suppressed the progression of osteoarthritis (OA). The inhibition of angiopoietin-like 4 (ANGPT4) is known to reduce levels of cartilage damaging enzymes, such as, matrix metalloproteinases (MMPs). In this study, we designed nanoparticles comprising dexamethasone-conjugated polyethylenimine (_DEX PEI) complexed with minicircle plasmid (MC) harboring SOX duo (SOX-9, -6) and ANGPTL4 small hairpin RNA (shANG) [_MC SOX9/6/shANG] in the expectation that transfection of these nanoparticles would enhance chondrogenesis of stem cells and suppress inflammation in OA. Adipose-derived stem cells (ADSCs) transfected with _MC SOX9/6/shANG (_MC SOX9/6/shANG-tADSCs) showed significantly higher expressions of COL2 gene and protein than _MC SOX9/6-transfected ADSCs (_MC SOX9/6-tADSCs) during in vitro chondrogenesis while both enhanced chondrogenesis in the absence of growth factor addition as compared with negative controls. Furthermore, the expressions of MMP13 and MMP3 genes were significantly more diminished in _MC SOX9/6/shANG-tADSCs than in _MC SOX9/6-tADSCs. In vivo experiments using surgically-induced OA rats showed _MC SOX9/6/shANG-tADSC-treated rats had significantly lower levels of cyclooxygenase (COX-2) and MMP13 in synovial fluids than _MC SOX9/6-tADSC-treated rats, but no significant difference was observed between them in histological appearances. Both groups showed significantly less joint destruction than control groups did. These results demonstrate that dual functional nanoparticles containing SOX duo and ANGPT4 shRNA enhance chondrogenesis of ADSCs and suppress inflammation in OA. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:234-242, 2020.

Sema4D/PlexinB1 promotes endothelial differentiation of dental pulp stem cells via activation of AKT and ERK1/2 signaling

Inducing of dental pulp stem cells (DPSCs) into endothelial cells (ECs) to prevascularize pulp tissue constructs may offer a novel and viable approach for enhancing pulp regeneration. However, there are numerous challenges in current methods for the acquisition of sufficient translational ECs. It was known that Sema4D/PlexinB1 signaling exerts profound effects on enhancing vascular endothelial growth factor (VEGF) secretion and angiogenesis. Whether Sema4D/PlexinB1 could regulate endothelial differentiation of DPSCs is not yet investigated. In this study, when DPSCs were treated with Sema4D (2 μg/mL), ECs-specific (VEGFR1, VEGFR2, CD31, and vWF), and angiogenic genes and proteins were significantly upregulated. The induced ECs exhibited similar endothelial vessel formation ability to that of human umbilical vein endothelial cells (HUVECs). Furthermore, phosphorylation of AKT increased dramatically within 5 minutes (from 0.93 to 21.8), while p-ERK1/2 was moderately elevated (from 0.94 to 2.65). In summary, our results demonstrated that Sema4D/PlexinB1 signaling induces endothelial differentiation of DPSCs. The interactions of Sema4D, VEGF, ANGPTL4, ANG1, and HIF-1α may play a crucial role in mediating the differentiation process.

A review of the multifunctionality of angiopoietin-like 4 in eye disease

Angiopoietin-like protein 4 (ANGPTL4) is a multifunctional cytokine regulating vascular permeability, angiogenesis, and inflammation. Dysregulations in these responses contribute to the pathogenesis of ischemic retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinal vein occlusion, and sickle cell retinopathy (SCR). However, the role of ANGPTL4 in these diseases remains controversial. Here, we summarize the functional mechanisms of ANGPTL4 in several diseases. We highlight original studies that provide detailed data about the mechanisms of action for ANGPTL4, its applications as a diagnostic or prognostic biomarker, and its use as a potential therapeutic target. Taken together, the discussions in this review will help us gain a better understanding of the molecular mechanisms by which ANGPTL4 functions in eye disease and will provide directions for future research.

Angiopoietin-Like Proteins in Angiogenesis, Inflammation and Cancer

Altered expression of secreted factors by tumor cells or cells of the tumor microenvironment is a key event in cancer development and progression. In the last decade, emerging evidences supported the autocrine and paracrine activity of the members of the Angiopoietin-like (ANGPTL) protein family in angiogenesis, inflammation and in the regulation of different steps of carcinogenesis and metastasis development. Thus, ANGPTL proteins become attractive either as prognostic or predictive biomarkers, or as novel target for cancer treatment. Here, we outline the current knowledge about the functions of the ANGPTL proteins in angiogenesis, cancer progression and metastasis. Moreover, we discuss the most recent evidences sustaining their role as prognostic or predictive biomarkers for cancer therapy. Although the role of ANGPTL proteins in cancer has not been fully elucidated, increasing evidence suggest their key effects in the proliferative and invasive properties of cancer cells. Moreover, given the common overexpression of ANGPTL proteins in several aggressive solid tumors, and their role in tumor cells and cells of the tumor microenvironment, the field of research about ANGPTL proteins network may highlight new potential targets for the development of future therapeutic strategies.

ANGPTL-4 induces diabetic retinal inflammation by activating Profilin-1

Diabetic retinopathy (DR), the most common cause of irreversible blindness in working-age adults, results in central vision loss that is caused by microvascular damage to the inner lining of the back of the eye, the retina. The aim of this work was to assess the temporal relationships between angiopoietin-like protein-4 (ANGPTL-4), a novel adipocytokine factor, and diabetic retinal inflammation and microvascular dysfunction. The downstream pathway(s) and upstream mediator(s) of ANGPTL-4 were then determined under high glucose (HG) conditions. Diabetic rats and control animals were randomly assigned to receive hypoxia inducible factor-1 alpha (HIF-1α) blockade (doxorubicin or shRNA) or vehicle for 8 weeks. Human retinal microvascular endothelial cells (HRMECs) were incubated with normal or high glucose, with or without blockade or recombinant proteins, for ANGPTL-4, HIF-1α, and vascular endothelial growth factor (VEGF). The levels of ANGPTL-4, profilin-1, HIF-1α, VEGF, interleukin 1 beta (IL-1β), IL-6, and intercellular adherent molecule 1 (ICAM-1) in the rat retinas and HRMEC extracts were examined by Western blotting and real-time RT-PCR. The levels of ANGPTL-4, profilin-1, HIF-1α, and VEGF protein and mRNA were significantly higher in the diabetic rats and HG-exposed HRMECs. ANGPTL-4 was a potent modulator of increased inflammation, permeability, and angiogenesis via activation of the profilin-1 signaling pathway. Our results showed that ANGPTL-4 upregulation was induced by HG, which was dependent on HIF-1α activation that was also triggered by HG, both in vivo and in vitro. Our results suggest that targeting ANGPTL-4, alone or in combination with profilin-1, may be an effective therapeutic strategy and diagnostic screening biomarker for proliferative diabetic retinopathy and other vitreous-retinal inflammatory diseases.

Angiopoietin-like 4: A molecular link between insulin resistance and rheumatoid arthritis

Recent evidence suggests that common factor(s) or molecule(s) might regulate lipid and glucose metabolism, inflammation, and bone and cartilage degeneration. These findings may be particularly relevant for cases of rheumatoid arthritis, in which chronic inflammation occurs in an autoimmune context and causes the degradation of articular joints as well as insulin resistance and cardiovascular complications. Candidates for this common regulatory system include signals mediated by peroxisome proliferator-activated regulator and its response factor, angiopoietin-like 4. The expression and bioactivity of angiopoietin-like 4, an adipocytokine that was originally reported to have an angiogenic function, have been detected not only in the vascular system and adipose tissue but also in rheumatoid joints. An essential role for angiopoietin-like 4 has been established in dyslipidemia, and recent reports indicate that it may modulate bone and cartilage catabolism in rheumatoid arthritis. The enhanced expression of angiopoietin-like 4 in rheumatoid arthritis may explain the occurrence of insulin resistance, cardiovascular risk, and joint destruction, thereby suggesting that this molecule could be a potential target for anti-rheumatoid arthritis strategies. This review describes recent research on the role of angiopoietin-like 4 in chronic inflammatory conditions and rheumatoid arthritis, as well as potential therapeutic candidates. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:939-943, 2017.

Angiopoietin-like 4 Mediates Colonic Inflammation by Regulating Chemokine Transcript Stability via Tristetraprolin

Many gastrointestinal diseases exhibit a protracted and aggravated inflammatory response that can lead to hypercytokinaemia, culminating in extensive tissue damage. Recently, angiopoietin-like 4 (ANGPTL4) has been implicated in many inflammation-associated diseases. However, how ANGPTL4 regulates colonic inflammation remains unclear. Herein, we show that ANGPTL4 deficiency in mice (ANGPTL4^−/−) exacerbated colonic inflammation induced by dextran sulfate sodium (DSS) or stearic acid. Microbiota was similar between the two genotypes prior DSS challenge. A microarray gene expression profile of the colon from DSS-treated ANGPTL4^−/− mice was enriched for genes involved in leukocyte migration and infiltration, and showed a close association to inflamed ulcerative colitis (UC), whereas the profile from ANGPTL4^+/+ littermates resembled that of non-inflamed UC biopsies. Bone marrow transplantation demonstrates the intrinsic role of colonic ANGPTL4 in regulating leukocyte infiltration during DSS-induced inflammation. Using immortalized human colon epithelial cells, we revealed that the ANGPTL4-mediated upregulation of tristetraprolin expression operates through CREB and NF-κB transcription factors, which in turn, regulates the stability of chemokines. Together, our findings suggest that ANGPTL4 protects against acute colonic inflammation and that its absence exacerbates the severity of inflammation. Our findings emphasize the importance of ANGPTL4 as a novel target for therapy in regulating and attenuating inflammation.

Nuclear receptors regulate lipid metabolism and oxidative stress markers in chondrocytes

Abstract

Joint homeostasis failure can result in osteoarthritis (OA). Currently, there are no treatments to alter disease progression in OA, but targeting early changes in cellular behavior has great potential. Recent data show that nuclear receptors contribute to the pathogenesis of OA and could be viable therapeutic targets, but their molecular mechanisms in cartilage are incompletely understood. This study examines global changes in gene expression after treatment with agonists for four nuclear receptor implicated in OA (LXR, PPARδ, PPARγ, and RXR). Murine articular chondrocytes were treated with agonists for LXR, PPARδ, PPARγ, or RXR and underwent microarray, qPCR, and cellular lipid analyses to evaluate changes in gene expression and lipid profile. Immunohistochemistry was conducted to compare two differentially expressed targets (Txnip, Gsta4) in control and cartilage-specific PPARδ knockout mice subjected to surgical destabilization of the medial meniscus (DMM). Nuclear receptor agonists induced different gene expression profiles with many responses affecting lipid metabolism. LXR activation downregulated gene expression of proteases involved in OA, whereas RXR agonism decreased expression of ECM components and increased expression of Mmp13. Functional assays indicate increases in cell triglyceride accumulation after PPARγ, LXR, and RXR agonism but a decrease after PPARδ agonism. PPARδ and RXR downregulate the antioxidant Gsta4, and PPARδ upregulates Txnip. Wild-type, but not PPARδ-deficient mice, display increased staining for Txnip after DMM. Collectively, these data demonstrate that nuclear receptor activation in chondrocytes primarily affects lipid metabolism. In the case of PPARδ, this change might lead to increased oxidative stress, possibly contributing to OA-associated changes.

Key message

Nuclear receptors regulate metabolic genes in chondrocytes.

Nuclear receptors affect triglyceride levels.

PPARδ mediates regulation of oxidative stress markers.

Nuclear receptors are promising therapeutic targets for osteoarthritis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-016-1501-5) contains supplementary material, which is available to authorized users.

Multiple Roles of Angiopoietin-Like 4 in Osteolytic Disease

Hypoxia and the hypoxia-inducible factor (HIF) transcription factor drive pathological bone loss in conditions including rheumatoid arthritis (RA), osteoarthritis, osteoporosis, primary bone tumours, and bone metastatic cancer. There is therefore considerable interest in determining the function(s) of HIF-induced genes in these pathologies. Angiopoietin-like 4 (ANGPTL4) is an adipose-derived, HIF-1α- and PPARγ-induced gene that was originally discovered as an endocrine and autocrine/paracrine regulator of lipid metabolism. Given the inverse relationship between bone adiposity and fracture risk, ANGPTL4 might be considered a good candidate for mediating the downstream effects of HIF-1α relevant to osteolytic disease. This review will consider the possible roles of ANGPTL4 in regulation of osteoclast-mediated bone resorption, cartilage degradation, angiogenesis, and inflammation, focusing on results obtained in the study of RA. Possible roles in other musculoskeletal pathologies will also be discussed. This will highlight ANGPTL4 as a regulator of multiple disease processes, which could represent a novel therapeutic target in osteolytic musculoskeletal disease.

Angiopoietin-like 4 promotes angiogenesis in the tendon and is increased in cyclically loaded tendon fibroblasts

KEY POINTS

Angiopoietin-like 4 (ANGPTL4) modulates tendon neovascularization. Cyclic loading stimulates the activity of transforming growth factor-β and hypoxia-inducible factor 1α and thereby increases the expression and release of ANGPTL4 from human tendon cells. Targeting ANGPTL4 and its regulatory pathways is a potential avenue for regulating tendon vascularization to improve tendon healing or adaptation.

ABSTRACT

The mechanisms that regulate angiogenic activity in injured or mechanically loaded tendons are poorly understood. The present study examined the potential role of angiopoietin-like 4 (ANGPTL4) in the angiogenic response of tendons subjected to repetitive mechanical loading or injury. Cyclic stretching of human tendon fibroblasts stimulated the expression and release of ANGPTL4 protein via transforming growth factor-β (TGF-β) and hypoxia-inducible factor 1α (HIF-1α) signalling, and the released ANGPTL4 was pro-angiogenic. Angiogenic activity was increased following ANGPTL4 injection into mouse patellar tendons, whereas the patellar tendons of ANGPTL4 knockout mice displayed reduced angiogenesis following injury. In human rotator cuff tendons, the expression of ANGPTL4 was correlated with the density of tendon endothelial cells. To our knowledge, this is the first study characterizing a role of ANGPTL4 in the tendon. ANGPTL4 may assist in the regulation of vascularity in the injured or mechanically loaded tendon. TGF-β and HIF-1α comprise two signalling pathways that modulate the expression of ANGPTL4 by mechanically stimulated tendon fibroblasts and, in the future, these could be manipulated to influence tendon healing or adaptation.

ANGPTL4 Correlates with NSCLC Progression and Regulates Epithelial-Mesenchymal Transition via ERK Pathway

Purpose Lung cancer remains the leading cause of cancer deaths with intricate mechanisms. In the present study, we evaluated the clinical significance and biological role of ANGPTL4 in non-small cell lung cancer (NSCLC), the most common lung cancer subtype. Methods Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) was used for examining the mRNA level of ANGPTL4 in NSCLC tissues and adjacent non-tumor tissues, NSCLC cell lines, and the immortalized human bronchial epithelial cell line HBE, respectively. A tissue microarray was used for analyzing the relationship between ANGPTL4 expression and the clinicopathological parameters of NSCLC patients. Commercial lentivirus expressing shRNAs was used for silencing ANGPTL4. Cell Counting Kit-8 (CCK-8) was employed for evaluating the cell proliferation ability and transwell with or without matrigel was used for cell migration and invasion assay. Results As the result, ANGPTL4 was over-expressed in NSCLC tissues compared with benign lung tissues. Silencing ANGPTL4 expression strongly inhibited the proliferation, migration, and invasion of A549 and H520 cells, which was in accordance with the increase of epithelial marker E-cadherin and decrease of mesenchymal marker vimentin. By screening the ERK, AKT, EGFR, and STAT3 pathways, we found that cell growth, migration, and invasion arrest induced by loss of ANGPTL4 expression was partially attributable to down-regulation of ERK signaling. Conclusion These results suggested that ANGPTL4 was essential for proliferation and metastasis of lung cancer cells and might serve as a novel target for the treatment of lung cancer.

ANGPTL-4 correlates with vascular endothelial growth factor in patients with proliferative diabetic retinopathy

PURPOSE

To investigate the relationship between angiopoietin-like protein 4 (ANGPTL-4) and vascular endothelial growth factor (VEGF) in the serum and vitreous of eyes in patients with proliferative diabetic retinopathy (PDR).

METHODS

Thirty-five eyes of 35 patients with PDR, 20 eyes of 20 patients with non-proliferative diabetic retinopathy, 20 eyes of 20 patients with diabetes but no diabetic retinopathy, and 14 eyes of 14 nondiabetic patients with an idiopathic macular hole (IMH) were recruited from Shanghai First People's Hospital. The ANGPTL-4 and VEGF concentrations were determined using enzyme-linked immunosorbent assays. Group means were compared using one-way analysis of variance with GraphPad Prism 4.0 and SPSS ver. 17.0. The research followed the tenets of the Declaration of Helsinki.

RESULTS

The ANGPTL-4 and VEGF levels were significantly higher in the vitreous and serum of patients with PDR compared with patients with IMH. There were significant correlations between the ANGPTL-4 and VEGF levels in the vitreous and serum of patients with PDR. The vitreous and serum ANGPTL-4 levels were also significantly correlated in patients with PDR. The ANGPTL-4 in both the vitreous and serum correlated with the serum triglyceride and high-density lipoprotein cholesterol levels.

CONCLUSIONS

The ANGPTL-4 levels were markedly elevated and the ANGPTL-4 expression was directly correlated with the VEGF expression in the vitreous and serum of patients with PDR. The vitreous and serum ANGPTL-4 levels were also significantly correlated with serum lipids in patients with PDR. Our results suggest that the ANGPTL-4 may be used as a new therapeutic target for the treatment of PDR.

Distinctive pro-inflammatory gene signatures induced in articular chondrocytes by oncostatin M and IL-6 are regulated by Suppressor of Cytokine Signaling-3

OBJECTIVE

To describe gene expression in murine chondrocytes stimulated with IL-6 family cytokines and the impact of deleting Suppressor of Cytokine Signaling-3 (SOCS-3) in this cell type.

METHOD

Primary chondrocytes were isolated from wild type and SOCS-3-deficient (Socs3(Δ/Δcol2)) mice and stimulated with oncostatin M (OSM), IL-6 plus the soluble IL-6 receptor (IL-6/sIL-6R), IL-11 or leukemia inhibitory factor (LIF) for 4 h. Total RNA was extracted and gene expression was evaluated by microarray analysis. Validation of the microarray results was performed using Taqman probes on RNA derived from chondrocytes stimulated for 1, 2, 4 or 8 h. Gene ontology was characterized using DAVID (database for annotation, visualization and integrated discovery).

RESULTS

Multiple genes, including Bcl3, Junb, Tgm1, Angptl4 and Lrg1, were upregulated in chondrocytes stimulated with each gp130 cytokine. The gene transcription profile in response to OSM stimulation was pro-inflammatory and was highly correlated to IL-6/sIL-6R, rather than IL-11 or LIF. In the absence of SOCS-3, OSM and IL-6/sIL-6R stimulation induced an interferon (IFN)-like gene signature, including expression of IL-31ra and S100a9.

CONCLUSION

While each gp130 cytokine induced a transcriptional response in chondrocytes, OSM- and IL-6/sIL-6R were the most potent members of this cytokine family. SOCS-3 plays an important regulatory role in this cell type, as it does in hematopoietic cells. Our results provide new insights into a hierarchy of gp130-induced transcriptional responses in chondrocytes that is normally restrained by SOCS-3 and suggest therapeutic inhibition of OSM may have benefit over and above antagonism of IL-6 during inflammatory arthritis.

Expression of phosphocitrate-targeted genes in osteoarthritis menisci

Phosphocitrate (PC) inhibited calcium crystal-associated osteoarthritis (OA) in Hartley guinea pigs. However, the molecular mechanisms remain elusive. This study sought to determine PC targeted genes and the expression of select PC targeted genes in OA menisci to test hypothesis that PC exerts its disease modifying activity in part by reversing abnormal expressions of genes involved in OA. We found that PC downregulated the expression of numerous genes classified in immune response, inflammatory response, and angiogenesis, including chemokine (C-C motif) ligand 5, Fc fragment of IgG, low affinity IIIb receptor (FCGR3B), and leukocyte immunoglobulin-like receptor, subfamily B member 3 (LILRB3). In contrast, PC upregulated the expression of many genes classified in skeletal development, including collagen type II alpha1, fibroblast growth factor receptor 3 (FGFR3), and SRY- (sex determining region Y-) box 9 (SOX-9). Immunohistochemical examinations revealed higher levels of FCGR3B and LILRB3 and lower level of SOX-9 in OA menisci. These findings indicate that OA is a disease associated with immune system activation and decreased expression of SOX-9 gene in OA menisci. PC exerts its disease modifying activity on OA, at least in part, by targeting immune system activation and the production of extracellular matrix and selecting chondroprotective proteins.

Angiopoietin-like 4 is over-expressed in rheumatoid arthritis patients: association with pathological bone resorption

INTRODUCTION

Osteoclasts are responsible for the bone loss associated with rheumatoid arthritis (RA). The secreted adipokine angiopoietin-like 4 (ANGPTL4) specifically increases osteoclast-mediated bone resorption. We have investigated expression of ANGPTL4 and its regulatory transcription factor, hypoxia-inducible factor-1 alpha (HIF-1α), in osteoclasts and other cells within rheumatoid synovium. We have also examined whether circulating levels of ANGPTL4 differ in RA patients compared with that in normal controls or patients with osteoarthritis (OA).

RESULTS

Immunohistochemical analysis revealed that bone-apposing osteoclasts within the rheumatoid synovium express both ANGPTL4 and HIF-1α. ANGPTL4 was also strongly expressed in synovial lining cells, endothelial cells, stromal cells, CD68+ macrophages and plasma cells within RA synovium. Little ANGPTL4 was evident in normal synovial tissue. This reflected the over-expression of HIF-1α in rheumatoid versus normal synovial tissue. The concentration of ANGPTL4 was higher in both the serum and the synovial fluid of RA patients than in patients with OA or normal controls. High serum ANGPTL4 associated with elevated levels of the serum marker of bone resorption, receptor activator for nuclear factor κB ligand (RANKL).

CONCLUSIONS

Over-expression of ANGPTL4 in multiple cell types within the rheumatoid synovium potentially provides a local pool of ANGPTL4 to stimulate osteoclast-mediated bone resorption in RA. Additionally, correlation of high serum ANGPTL4 with circulating RANKL suggests that ANGPTL4 may represent a novel marker for bone destruction in RA.

Thymidine phosphorylase regulates the expression of CXCL10 in rheumatoid arthritis fibroblast-like synoviocytes

OBJECTIVE

Thymidine phosphorylase (TP) in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) is induced by tumor necrosis factor α (TNFα) and other cytokines that have been reported to be major inflammation mediators in RA. We previously demonstrated that TP plays an important role in angiogenesis and tumor growth, invasion, and metastasis. The aim of this study was to investigate whether the role of TP in the pathogenesis of RA is similar to its role in tumors.

METHODS

In FLS obtained from 2 patients with RA, the expression of TP, interferon-γ (IFNγ)-inducible protein 10 (CXCL10), and other cytokines was measured by quantitative real-time polymerase chain reaction, immunoblotting, and enzyme-linked immunosorbent assays. Microarray analysis was performed using FLS transfected with TYMP complementary DNA and treated with a TP inhibitor.

RESULTS

The expression of TP in FLS was up-regulated by TNFα, interleukin-1β (IL-1β), IL-17, IFNγ, and lipopolysaccharide. Microarray analysis of FLS overexpressing TP identified CXCL10 as a thymidine phosphorylase-related gene. The expression of CXCL10 was induced by TNFα, and this induction was suppressed by TYMP small interfering RNA and TP inhibitor. Furthermore, the combination of TNFα and IFNγ synergistically augmented the expression of TP and CXCL10. TP-induced CXCL10 expression was suppressed by the antioxidant EUK-8. In the synovial tissue of patients with RA, TP levels were significantly correlated with CXCL10 expression.

CONCLUSION

The combination of TNFα and IFNγ strongly induced the expression of thymidine phosphorylase in RA FLS. The induction of thymidine phosphorylase enhanced the expression of CXCL10, which may contribute to the Th1 phenotype and bone destruction observed in RA.

Involvement of angiopoietin-like 4 in matrix remodeling during chondrogenic differentiation of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are considered for cartilage engineering given their ability to differentiate into chondrocytes. Chondrogenic differentiation of MSCs is currently triggered by micromass culture in the presence of a member of the TGF-β superfamily. However, the main constituents of the cartilaginous matrix, aggrecan and type II collagen, are degraded at the end of the differentiation process through induction of matrix metallopeptidase (MMP)13. We hypothesized that MSCs undergoing chondrogenic differentiation produce an intermediate cytokine that triggers this matrix remodeling. Analysis of transcriptomic data identified angiopoietin-like 4 (ANGPTL4) as one of the most strongly up-regulated gene encoding a secreted factor during TGF-β-induced chondrogenesis. To gain insight into the role of ANGPTL4 during chondrogenesis, we used recombinant ANGPTL4 as well as a RNA interference approach. Addition of exogenous ANGPTL4 during the course of TGF-β-induced differentiation reduced the mRNA levels of aggrecan and type II collagen, although it increased those of MMP1 and MMP13. Accordingly, deposition of aggrecan and total collagens was diminished, whereas release of MMP1 and MMP13 was increased. Conversely, transfection of MSCs with an siRNA targeting ANGPTL4 prior to induction of chondrogenesis increased expression of type II collagen and aggrecan, whereas it repressed that of MMP1, MMP3, and MMP13. A neutralizing antibody against integrin αVβ5, a known receptor for ANGPTL4, mimicked some of the effects observed after siRNA-mediated ANGPTL4 silencing. Our data provide evidence that ANGPTL4 promotes cartilage matrix remodeling by inhibiting expression of its two key components and by up-regulating the level of certain MMPs.

Skeletal actions of fasting-induced adipose factor (FIAF)

Several adipokines are known to influence skeletal metabolism. Fasting-induced adipose factor (FIAF) is an adipokine that gives rise to 2 further peptides in vivo, the N-terminal coiled-coil domain (FIAF(CCD)) and C-terminal fibrinogen-like domain (FIAF(FLD)). The skeletal action of these peptides is still uncertain. Our results show that FIAF(CCD) is a potent inhibitor of osteoclastogenesis and function, as seen in mouse bone marrow and RAW264.7 cell cultures, and in a resorption assay using isolated primary mature osteoclasts. The inhibitory effects at 500 ng/mL were approximately 90%, 50% and 90%, respectively, in these assays. FIAF(CCD) also stimulated osteoblast mitogenesis by approximately 30% at this concentration. In comparison, FIAF(FLD) was only active in decreasing osteoblast mitogenesis, and intact FIAF had no effect in any of these assays. In murine bone marrow cultures, FIAF(CCD) reduced the expression of macrophage colony-stimulating factor (M-CSF), nuclear factor of activated T-cells c1 (NFATc1) and dendritic cell-specific transmembrane protein (DC-STAMP), and to lesser extent suppressed the expression of connective tissue growth factor (CTGF). FIAF(CCD) also decreased expression of M-CSF and CTGF in stromal/osteoblastic ST2 cells. Its effect on receptor activator of nuclear factor κB (RANKL) and osteoprotegerin expression in bone marrow was not consistent with its inhibitory action on osteoclastogenesis, but it decreased RANKL expression in ST2 cells. In RAW264.7 cell cultures, FIAF(CCD) significantly reduced the expression of NFATc1 and DC-STAMP. In conclusion, FIAF(CCD) inhibits osteoclast differentiation and function in vitro and decreases expression of genes encoding key osteoclastogenic factors such as M-CSF, CTGF, NFATc1, and DC-STAMP. FIAF(CCD)'s action on osteoclasts may be independent of the RANKL/osteoprotegerin pathway. These results suggest a novel mechanism by which adipose tissue may regulate bone resorption and skeletal health.

Hypoxic retinal Muller cells promote vascular permeability by HIF-1-dependent up-regulation of angiopoietin-like 4

Vision loss from ischemic retinopathies commonly results from the accumulation of fluid in the inner retina [macular edema (ME)]. Although the precise events that lead to the development of ME remain under debate, growing evidence supports a role for an ischemia-induced hyperpermeability state regulated, in part, by VEGF. Monthly treatment with anti-VEGF therapies is effective for the treatment of ME but results in a major improvement in vision in a minority of patients, underscoring the need to identify additional therapeutic targets. Using the oxygen-induced retinopathy mouse model for ischemic retinopathy, we provide evidence showing that hypoxic Müller cells promote vascular permeability by stabilizing hypoxia-inducible factor-1α (HIF-1α) and secreting angiogenic cytokines. Blocking HIF-1α translation with digoxin inhibits the promotion of endothelial cell permeability in vitro and retinal edema in vivo. Interestingly, Müller cells require HIF--but not VEGF--to promote vascular permeability, suggesting that other HIF-dependent factors may contribute to the development of ME. Using gene expression analysis, we identify angiopoietin-like 4 (ANGPTL4) as a cytokine up-regulated by HIF-1 in hypoxic Müller cells in vitro and the ischemic inner retina in vivo. ANGPTL4 is critical and sufficient to promote vessel permeability by hypoxic Müller cells. Immunohistochemical analysis of retinal tissue from patients with diabetic eye disease shows that HIF-1α and ANGPTL4 localize to ischemic Müller cells. Our results suggest that ANGPTL4 may play an important role in promoting vessel permeability in ischemic retinopathies and could be an important target for the treatment of ME.

Gene expression profiling of articular cartilage reveals functional pathways and networks of candidate genes for osteochondrosis in pigs

Osteochondrosis (OC) is a joint disorder that frequently causes leg weakness in growing pigs, resulting in welfare problems and economic losses. We aimed to detect molecular pathways relevant to the emergence of the disease and to identify candidate genes for the liability to the disorder. Therefore, we compared microarray-based expression patterns of articular cartilage with (n=11) and without (n=11) histologically diagnosed OC lesions obtained from discordant sib-pairs. A total of 1,564 genes were found with different transcript abundance [differentially expressed (DE) genes] at q≤0.05. To further identify candidate genes, we integrated data from quantitative trait loci (QTL) and genome-wide association (GWA) studies with the expression analysis. We detected 317 DE genes within the QTL confidence intervals, of which 26 DE genes also overlapped GWA regions. Ingenuity Pathway Analysis suggests a pathogenic role of immune response, angiogenesis, and synthesis of extracellular matrix pathways for OC. These processes could facilitate the emergence of defects. But they may also promote the degradation of articular cartilage and the worsening of the disease. A functional network was derived that comprised genes with functional and positional clues of their role in bone and cartilage metabolisms and development, including extracellular matrix genes (e.g., LOX, OGN, and ASPN), angiogenesis genes (e.g., ANGPTL4 and PDGFA), and immune response genes (e.g., ICAM1, AZGP1, C1QB, C1QC, PDE4B, and CDA). The study identified molecular processes linked to OC and several genes with positional, genetic-statistical, and functional evidence for their role in the emergence of articular cartilage lesions and the liability to OC.

Effect of angiopoietin-like protein 4 on rat pulmonary microvascular endothelial cells exposed to LPS

Pulmonary microvascular endothelial cells (PMVECs) possess highly proliferative and angiogenic capacities and are localized at the critical interface between the blood and microvessel wall; they are the primary targets of inflammatory cytokines during lung inflammation. Angiopoietin-like protein 4 (Angptl4) is a circulating protein that has recently been im-plicated in the regulation of angiogenesis and metastasis. This study aimed to investigate the effect of Angptl4 on rat PMVECs (RPMVECs) exposed to lipopolysaccharide (LPS). The cell culture was stimulated with LPS. Total Angptl4 cDNA was obtained from Source BioScience. The PCR product was cloned into the pcDNA3.1-eGFP or the pcDNA3.1‑eGFP‑Angptl4 vector, which were then transfected into the RPMVECs using SuperFect transfection reagent. The Angptl4 mRNA levels, protein levels and cell morphology of the RPMVECs in the experimental groups were detected using real time-PCR, western blot analysis, MTT assay, ELISA and confocal microscopy methods, respective-ly. The Angptl4 expression vector, pcDNA3.1‑eGFP-Angptl4, was successfully constructed. The Angptl4 mRNA level in the LPS-pcDNA3.1-eGFP-transfected group (blank control) was slightly increased and was significantly higher in the experimental group compared with the empty vector and blank control group with significant differences. Pro-apoptotic caspase-8, -9 and Bax protein were inhibited, while p-AKT/AKT and p-Mek1/2 protein expression was also decreased. The rosiglitazone group had significantly decreased levels of the inflammatory cytokine, tumor necrosis factor (TNF)-α (P<0.01). The overexpression of Angptl4 inhibited the LPS-induced increase in the permeability of the RPMVECs, which was associated with the depolymerization of central F-actin in the RPMVECs. In conclusion, our study demonstrates that the overexpression of Angptl4 exerts protective, anti-inflammatory and anti-angiogenic effects. It re-presents a novel therapeutic target gene for the treatment of acute lung injury induced by LPS.

Angiopoietin-like protein 4 (ANGPTL4) is induced by high glucose in retinal pigment epithelial cells and exhibits potent angiogenic activity on retinal endothelial cells

PURPOSE

Hyperglycaemia has been identified as major risk factor for diabetic retinopathy (DR). It is widely accepted that the progression of DR is mainly due to a local imbalance of pro- versus anti-angiogenic factors in the retina. In this study, we investigated whether retinal pigment epithelial (RPE) cells produced pro-angiogenic factors under high glucose (HG) conditions in vitro.

METHODS

Cultured human retinal endothelial (RE) cells were exposed to conditioned medium from retinal pigment epithelium cells (ARPE-19) grown in HG medium and assessed for tube formation. Based on the expression profiles of ARPE-19, we investigated whether ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions using cultured human RE cells as the test system for experiments with recombinant protein, conditioned medium from ARPE-19 and RNA interference (RNAi).

RESULTS

The conditioned medium from ARPE-19 cultured under HG conditions promoted tube formation of cultured human RE cells. GeneChip analysis showed that ANGPTL4 was one of the highest upregulated genes under HG conditions. In addition, recombinant ANGPTL4 promoted all of the elements of angiogenesis in human RE cells in vitro. The results of experiments using conditioned medium from ARPE-19 combined with RNAi demonstrated that ANGPTL4 was a major angiogenic factor released from ARPE-19 under HG conditions.

CONCLUSIONS

ANGPTL4 was induced by high glucose in RPE cells and exhibited potent angiogenic activity on RE cells. Our results are unique and may potentially add a new candidate to the long list of molecules involved in diabetic retinopathy.

ANGPTL4 is a secreted tumor suppressor that inhibits angiogenesis

Tumor suppressors with extracellular function are likely to have advantages as targets for cancer therapy, but few are known. Here, we focused on angiopoietin-like 4 (ANGPTL4), which is a secreted glycoprotein involved in lipoprotein metabolism and angiogenesis, is methylation-silenced in human cancers, but has unclear roles in cancer development and progression. We found a deletion mutation in its coiled-coil domain at its N-terminal in human gastric cancers, in addition to hypermethylation of the ANGPTL4 promoter CpG islands. Forced expression of wild-type ANGPTL4, but not ANGPTL4 with the deletion, at physiological levels markedly suppressed in vivo tumorigenicity and tumor angiogenesis, indicating that the latter caused the former. Tumor-derived ANGPTL4 suppressed in vitro vascular tube formation and proliferation of human umbilical vascular endothelial cells, partly due to suppression of ERK signaling. These showed that ANGPTL4 is a genetically and epigenetically inactivated secreted tumor suppressor that inhibits tumor angiogenesis.

Epidermal growth factor receptor variant type III markedly accelerates angiogenesis and tumor growth via inducing c-myc mediated angiopoietin-like 4 expression in malignant glioma

Background

Expression of the constitutively activated mutant EGFR variant III (EGFRvIII), the most common mutation in glioblastoma multiforme (GBMs), has been clinically correlated with tumor proliferation, invasion, and angiogenesis. In this study, we examined the role of EGFRvIII on the tumor microenvironment, especially on angiogenesis.

Methods

To study the role of EGFRvIII in tumor angiogenesis, we prepared LN229 glioblastoma transfected with enhanced green fluorescent protein (EGFP), wild-type EGFR, or EGFRvIII (LN229-WT or -vIII), and examined tumor growth and microvessel density in the tumors. Additionally, the potential angiogenic factors were identified by real-time PCR analysis, and the functions in LN229-vIII cells were examined.

Results

LN229-vIII cells showed more aggressive tumor growth and higher vascularity as compared to LN229-WT cells in vivo, although there was no significant difference in the cell growth rates in vitro. We next investigated the expression of 60 angiogenesis-related factors to clarify the mechanisms underlying the difference in vascularity between tumor xenografts of LN229-vIII and LN229-WT. We found that the mRNA and protein expressions of angiopoietin-like 4 (Angptl4), a secreted protein involved in angiogenesis and metabolism regulation, were significantly induced by EGFRvIII overexpression, both in vitro and in vivo. Constitutive knockdown of Angptl4 in LN229-vIII using shRNA significantly decreased the microvessel density in the tumor xenografts and suppressed tumor growth. To clarify the regulatory mechanisms of Angptl4 by EGFRvIII, we analyzed the signaling pathways and transcription factors by pharmacological inhibition and RNA interference. U0126, an ERK signal inhibitor dramatically suppressed Angptl4 expression. The transcription factor c-Myc, which is regulated by ERK, was activated in the LN229-vIII cells and knockdown of c-Myc using siRNA also attenuated Angptl4 expression in the LN229-vIII cells. Furthermore, chromatin immunoprecipitation (ChIP) assay revealed increased recruitment of c-Myc to the promoter region of Angptl4 in the LN229-vIII cells.

Conclusions

In summary, we demonstrated that EGFRvIII induces Angptl4 expression through the ERK/c-Myc pathway and promotes tumor angiogenesis in malignant gliomas.

Molecular hierarchy of heparin-binding EGF-like growth factor-regulated angiogenesis in triple-negative breast cancer

Heparin-binding EGF-like growth factor (HB-EGF) is one of several proangiogenic factors and represents a possible therapeutic target for patients with triple-negative breast cancer (TNBC). However, the role of HB-EGF in promoting tumor aggressiveness in TNBC remains unclear. To investigate specific genes and pathways involved in TNBC tumorigenesis, we profiled gene expression changes in two TNBC cell lines under two-dimensional culture (2DC) and three-dimensional culture (3DC) and in a tumor xenograft model. We identified simultaneous upregulation of HB-EGF, VEGFA, and angiopoietin-like 4 (ANGPTL4) in 3DC and tumor xenografts, compared with 2DC. We show that HB-EGF regulates the expression of VEGFA or ANGPTL4 via transcriptional regulation of hypoxia-inducible factor-1α and NF-κB. Furthermore, suppression of VEGFA or ANGPTL4 expression enhanced HB-EGF expression, highlighting a unique regulatory loop underlying this angiogenesis network. Targeted knockdown of HB-EGF significantly suppressed tumor formation in a TNBC xenograft model, compared with individual knockdown of either VEGFA or ANGPTL4, by reducing the expression of both VEGFA and ANGPTL4. In patients with TNBC, VEGFA or ANGPTL4 expression was also significantly correlated with HB-EGF expression. Low concentrations of exogenously added HB-EGF strongly activated the proliferation of endothelial cells, tube formation, and vascular permeability in blood vessels, in a similar fashion to high doses of VEGFA and ANGPTL4. Taken together, these results suggest that HB-EGF plays a pivotal role in the acquisition of tumor aggressiveness in TNBC by orchestrating a molecular hierarchy regulating tumor angiogenesis.

Differential effects of Th1 versus Th2 cytokines in combination with hypoxia on HIFs and angiogenesis in RA

Introduction

Hypoxia and T-helper cell 1 (Th1) cytokine-driven inflammation are key features of rheumatoid arthritis (RA) and contribute to disease pathogenesis by promoting angiogenesis. The objective of our study was to characterise the angiogenic gene signature of RA fibroblast-like synoviocytes (FLS) in response to hypoxia, as well as Th1 and T-helper cell 2 (Th2) cytokines, and in particular to dissect out effects of combined hypoxia and cytokines on hypoxia inducible transcription factors (HIFs) and angiogenesis.

Methods

Human angiogenesis PCR arrays were used to screen cDNA from RA FLS exposed to hypoxia (1% oxygen) or dimethyloxalylglycine, which stabilises HIFs. The involvement of HIF isoforms in generating the angiogenic signature of RA FLS stimulated with hypoxia and/or cytokines was investigated using a DNA-binding assay and RNA interference. The angiogenic potential of conditioned media from hypoxia-treated and/or cytokine-treated RA FLS was measured using an in vitro endothelial-based assay.

Results

Expression of 12 angiogenic genes was significantly altered in RA FLS exposed to hypoxia, and seven of these were changed by dimethyloxalylglycine, including ephrin A3 (EFNA3), vascular endothelial growth factor (VEGF), adipokines angiopoietin-like (ANGPTL)-4 and leptin. These four proangiogenic genes were dependent on HIF-1 in hypoxia to various degrees: EFNA3 >ANGPTL-4 >VEGF >leptin. The Th1 cytokines TNFα and IL-1β induced HIF-1 but not HIF-2 transcription as well as activity, and this effect was additive with hypoxia. In contrast, Th2 cytokines had no effect on HIFs. IL-1β synergised with hypoxia to upregulate EFNA3 and VEGF in a HIF-1-dependent fashion but, despite strongly inducing HIF-1, TNFα suppressed adipokine expression and had minimal effect on EFNA3. Supernatants from RA FLS subjected to hypoxia and TNFα induced fewer endothelial tubules than those from FLS subjected to TNFα or hypoxia alone, despite high VEGF protein levels. The Th2 cytokine IL-4 strongly induced ANGPTL-4 and angiogenesis by normoxic FLS and synergised with hypoxia to induce further proangiogenic activity.

Conclusion

The present work demonstrates that Th1 cytokines in combination with hypoxia are not sufficient to induce angiogenic activity by RA FLS despite HIF-1 activation and VEGF production. In contrast, Th2 cytokines induce angiogenic activity in normoxia and hypoxia, despite their inability to activate HIFs, highlighting the complex relationships between hypoxia, angiogenesis and inflammation in RA.

Early transcriptional pattern of angiogenesis induced by EGCG treatment in cervical tumour cells

The major green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) has been shown to exhibit antitumour activities in several tumour models. One of the possible mechanisms by which EGCG can inhibit cancer progression is through the modulation of angiogenesis signalling cascade. The tumour cells’ ability to tightly adhere to endothelium is a very important process in the metastatic process, because once disseminated into the bloodstream the tumour cells must re-establish adhesive connections to endothelium in order to extravasate into the target tissues. In this study, we investigated the anti-angiogenic effects of EGCG treatment (10 μM) on human cervical tumour cells (HeLa) by evaluating the changes in the expression pattern of 84 genes known to be involved in the angiogenesis process. Transcriptional analysis revealed 11 genes to be differentially expressed and was further validated by measuring the induced biological effects. Our results show that EGCG treatment not only leads to the down-regulation of genes involved in the stimulation of proliferation, adhesion and motility as well as invasion processes, but also to the up-regulation of several genes known to have antagonist effects. We observed reduced proliferation rates, adhesion and spreading ability as well as invasiveness of HeLa tumour cells upon treatment, which suggest that EGCG might be an important anti-angiogenic therapeutic approach in cervical cancers.

Hypoxia-inducible factor 1 alpha-activated angiopoietin-like protein 4 contributes to tumor metastasis via vascular cell adhesion molecule-1/integrin β1 signaling in human hepatocellular carcinoma

Angiopoietin-like protein 4 (ANGPTL4) plays complex and often contradictory roles in vascular biology and tumor metastasis, but little is known about its function in hepatocellular carcinoma (HCC) metastasis. In the present study, we showed that hypoxia-inducible factor 1α (HIF-1α) directly up-regulates ANGPTL4, and its stableness positively correlates with ANGPTL4 expression in HCC tissue. Overexpression of ANGPTL4 significantly increased HCC cell transendothelial migration in vitro and intrahepatic and distal pulmonary metastasis in vivo, whereas silencing ANGPTL4 expression or treatment with a neutralizing antibody specific for ANGPTL4 protein resulted in a reduced transendothelial migration. We also found that serum ANGPTL4 is higher in HCC patients, compared to healthy control, and correlates with intrahepatic metastasis and histological grade. Further, secreted ANGPTL4 promotes transendothelial migration and metastasis of HCC cells in vitro and in vivo through the up-regulation of vascular cell adhesion molecule-1 (VCAM-1) of human umbilical vein endothelial cells and the activation of the VCAM-1/integrin β1 axis.

CONCLUSION

ANGPTL4 is a target gene of HIF-1α and acts as an important regulator in the metastasis of HCC. Serum ANGPTL4 correlates with tumor progression and metastasis and might be used to indicate prognosis in HCC patients.

Docosahexaenoic acid stimulates tube formation in first trimester trophoblast cells, HTR8/SVneo

Angiogenesis is a key factor in the placentation process and vascular remodeling that involves several growth factors such as vascular endothelial growth factor (VEGF) and angiopoietin-like protein 4 (ANGPTL4). PPARs are involved in the placentation process but not much information is available on whether their ligands such as fatty acids have any effects on these processes. We therefore investigated the effect of fatty acids (arachidonic acid, 20:4 n-6(ARA), eicosapentaenoic acid, 20:5 n-3(EPA), docosahexaenoic acid, 22:6 n-3 (DHA) and oleic acid, 18:1 n-9 (OA)) on tube formation (as a measure of angiogenesis) on matrigel in the first trimester trophoblast cells, HTR8/SVneo. In addition we also investigated the effects of fatty acids on expression of genes involved in angiogenesis (VEGF and ANGPTL4) and lipid metabolism in these cells. Gene expression was determined after incubating these cells with different fatty acids for 24 h using real-time qRT-PCR, whereas VEGF and ANGPTL4 proteins were measured by respective ELISA kits. Of all the fatty acids tested, DHA increased tube formation to the greatest extent. DHA-induced increase in tube length was 583%, 247% and 70% over control, OA and EPA, respectively (p < 0.05). In addition, DHA stimulated cell proliferation by 150% of these cells. Of all fatty acids investigated, only DHA stimulated VEGF mRNA expression and protein secretion compared with control. Unlike DHA, other fatty acids (OA, EPA, ARA) stimulated ANGPTL4 mRNA expression and protein secretion in these cells. An inhibitor of VEGF decreased DHA stimulated tube formation in these cells. Altogether these data indicate that DHA may potently influence the placentation process by stimulating tube formation and this effect may be mediated in part via VEGF in first trimester trophoblast cells.

Proteolytic processing of angiopoietin-like protein 4 by proprotein convertases modulates its inhibitory effects on lipoprotein lipase activity

Angiopoietin-like protein 4 (ANGPTL4) has been associated with a variety of diseases. It is known as an endogenous inhibitor of lipoprotein lipase (LPL), and it modulates lipid deposition and energy homeostasis. ANGPTL4 is cleaved by unidentified protease(s), and the biological importance of this cleavage event is not fully understood with respect to its inhibitory effect on LPL activity. Here, we show that ANGPTL4 appears on the cell surface as the full-length form, where it can be released by heparin treatment in culture and in vivo. ANGPTL4 protein is then proteolytically cleaved into several forms by proprotein convertases (PCs). Several PCs, including furin, PC5/6, paired basic amino acid-cleaving enzyme 4, and PC7, are able to cleave human ANGPTL4 at a consensus site. PC-specific inhibitors block the processing of ANGPTL4. Blockage of ANGPTL4 cleavage reduces its inhibitory effects on LPL activity and decreases its ability to raise plasma triglyceride levels. In summary, the cleavage of ANGPTL4 by these PCs modulates its inhibitory effect on LPL activity.

Hypoxia-inducible factor regulates osteoclast-mediated bone resorption: role of angiopoietin-like 4

Hypoxia and the hypoxia-inducible factor (HIF) transcription factor regulate angiogenic-osteogenic coupling and osteoclast-mediated bone resorption. To determine how HIF might coordinate osteoclast and osteoblast function, we studied angiopoietin-like 4 (ANGPTL4), the top HIF target gene in an Illumina HumanWG-6 v3.0 48k array of normoxic vs. hypoxic osteoclasts differentiated from human CD14⁺ monocytes (14.3-fold induction, P<0.0004). ANGPTL4 mRNA and protein were induced by 24 h at 2% O₂ in human primary osteoclasts, monocytes, and osteoblasts. ANGPTL4 protein was observed by immunofluorescence in osteoclasts and osteoblasts in vivo. Normoxic inducers of HIF (CoCl₂, desferrioxamine, and l-mimosine) and 100 ng/ml ANGPTL4 stimulated osteoclastic resorption 2- to 3-fold in assays of lacunar dentine resorption, without affecting osteoclast viability. Isoform-specific HIF-1α small interfering RNA ablated hypoxic induction of ANGPTL4 and of resorption, which was rescued by addition of exogenous ANGPTL4 (P<0.001). In the osteoblastic Saos2 cell line, ANGPTL4 caused a dose-dependent increase in proliferation (P<0.01, 100 ng/ml) and, at lower doses (1–25 ng/ml), mineralization. These results demonstrate that HIF is sufficient to enhance osteoclast-mediated bone resorption and that ANGPTL4 can compensate for HIF-1α deficiency with respect to stimulation of osteoclast activity and also augments osteoblast proliferation and differentiation.—Knowles, H. J., Cleton-Jansen, A.-M., Korsching, E., and Athanasou, N.A. Hypoxia-inducible factor regulates osteoclast-mediated bone resorption: role of angiopoietin-like 4.

Viral G protein-coupled receptor up-regulates Angiopoietin-like 4 promoting angiogenesis and vascular permeability in Kaposi's sarcoma

Kaposi's sarcoma (KS) is an enigmatic vascular tumor thought to be a consequence of dysregulated expression of the human herpesvirus-8 (HHV-8 or KSHV)-encoded G protein-coupled receptor (vGPCR). Indeed, transgenic animals expressing vGPCR manifest vascular tumors histologically identical to human KS, with expression of the viral receptor limited to a few cells, suggestive of a paracrine mechanism for vGPCR tumorigenesis. Both human and vGPCR experimental KS lesions are characterized by prominent angiogenesis and vascular permeability attributed to the release of angiogenic molecules, most notably vascular endothelial growth factor. However, the relative contribution of these paracrine mediators to the angiogenic and exudative phenotype of KS lesions remains unclear. Here we show that vGPCR up-regulation of Angiopoietin-like 4 (ANGPTL4) plays a prominent role in promoting the angiogenesis and vessel permeability observed in KS. Indeed, ANGPTL4 expression is a hallmark of vGPCR experimental and human KS lesions. Inhibition of ANGPTL4 effectively blocks vGPCR promotion of the angiogenic switch and vascular leakage in vitro and tumorigenesis in vivo. These observations suggest that ANGPTL4 is a previously unrecognized target for the treatment of patients with KS. As angiogenesis and increased vessel permeability are common themes in all solid tumors, these findings may have a broad impact on our understanding and treatment of cancer.

Regulation of the angiopoietin-Tie ligand-receptor system with a novel splice variant of Tie1 reduces the severity of murine arthritis

OBJECTIVES

To determine the function of the angiopoietin (Ang)-Tie ligand-receptor system, and to assess the effect of Tie1-751, a naturally occurring extracellular domain of the Tie1 receptor derived by alternative splicing, in an in vivo model of RA.

METHODS

In the murine CIA model, expression of endogenous Ang1, Ang2, Tie1 and Tie2 in whole paws was analysed by quantitative RT-PCR. To assess the effect of inhibition of the Ang-Tie axis, Tie1-751 was expressed and fused to the Fc fragment of human IgG1. The effect of Tie1-751-Fc on human umbilical vein endothelial cell (HUVEC) cytoprotection and migration in response to Ang1, either alone or in combination with VEGF, was investigated. Furthermore, an in vitro angiogenesis assay was used to determine the effect of Tie1-751-Fc on Ang1-mediated angiogenesis. Finally, Tie1-751-Fc was administered in CIA, and the effects on clinical disease and joint architecture of hind foot specimens were determined.

RESULTS

Gene expression levels of Ang1, Ang2, and receptors Tie1 and Tie2 in whole paws were significantly increased during the progression of arthritis. Tie1-751-Fc significantly inhibited HUVEC cytoprotection and migration in response to Ang1 alone, or Ang1 in combination with VEGF. Tie1-751-Fc also significantly inhibited angiogenesis induced by a combination of Ang1 plus VEGF. Finally, Tie1-751-Fc, when administered intra-peritoneally to arthritic mice, reduced clinical signs of arthritis, damage to joint architecture and infiltration of blood vessels into the synovium.

CONCLUSIONS

Our data demonstrate that the Ang-Tie ligand-receptor system is dysregulated in CIA. Tie1-751, a novel splice variant of the Tie1 receptor, inhibits Ang1/VEGF signalling, suggesting that Ang inhibition may be of therapeutic benefit in inflammatory arthritis.

Synoviocyte-derived angiopoietin-like protein 2 contributes to synovial chronic inflammation in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by symmetrical polyarticular synovitis of the diarthrodial joints. Several proinflammatory cytokines derived from both infiltrating inflammatory cells and activated resident cells within the RA joint play a fundamental role in the processes that cause inflammation. However, anticytokine treatment is beneficial but not curative, the effects are only partial, and nonresponses are common. Therefore, an effort has been made to identify other key regulators of inflammation in articular structures to develop new therapies to suppress synovial inflammation and joint destruction in RA. Adipose tissue-derived angiopoietin-like protein 2 (Angptl2) activates an inflammatory cascade in endothelial cells and induces chemotaxis of monocytes/macrophages in obesity, resulting in initiation and propagation of inflammation within adipose tissues and obesity-related metabolic diseases. Angptl2 mRNA and protein are abundantly expressed in hyperplastic rheumatoid synovium of RA patients, especially in fibroblast-like and macrophage-like synoviocytes, but not in B and T lymphocytes. Angptl2 concentration in joints of RA patients was also significantly increased in comparison with patients with osteoarthritis, which in comparison with RA represents a significantly lower inflammatory grade form of arthritis. Notably, Angptl2 promoted increased chemotactic activities of CD14+CD16- monocytes from synovial fluid of RA patients. Therefore, Angptl2 acts as an important rheumatoid synovium-derived inflammatory mediator in RA pathogenesis.

Activating peroxisome proliferator-activated receptor gamma mutant promotes tumor growth in vivo by enhancing angiogenesis

Peroxisome proliferator-activated receptor gamma (PPARgamma) is expressed in a variety of cancer cells. The addition of ligand activates the receptor by inducing a conformational change in the receptor, which can be recapitulated by mutation. To investigate the role of activated PPARgamma signaling in breast cancer, we compared the function of a constitutively active PPARgamma (PgammaCA) mutant with the wild-type PPARgamma in ErbB2-induced mammary tumorigenesis in vivo. Tumor cells transduced with either PPARgamma or PgammaCA were implanted into immunocompetent FVB mice. Enhanced tumor growth was observed in PgammaCA-transduced cells, which was associated with increased angiogenesis and endothelial stem cells as evidenced by increased number of cells stained with von Willebrand factor, c-Kit, CD133, and CD31. Genome-wide expression profiling identified a group of genes within the angiogenesis pathway, including Angptl4, as targets of activated PPARgamma; PgammaCA also induced Angptl4 protein secretion in ErbB2-transformed mammary epithelial cells. Angptl4 promoted vascular endothelial cell migration; conversely, immunodepletion of Angptl4 reduced PgammaCA-mediated cellular migration. Collectively, these studies suggest that activated PPARgamma induces Angptl4 to promote tumor growth through enhanced angiogenesis in vivo.

Induction of ANGPTL4 expression in human airway smooth muscle cells by PMA through activation of PKC and MAPK pathways

In this study, we demonstrate that protein kinase C (PKC) activators, including phorbol-12-myristate-13-acetate (PMA), 1,2-dioctanoyl-sn-glycerol (DOG), and platelet-derived growth factor alpha are potent inducers of angiopoietin-like protein 4 (ANGPTL4) expression in several normal lung cell types and carcinoma cell lines. In human airway smooth muscle (HASM) cells induction of ANGPTL4 expression is observed as early as 2 h after the addition of PMA. PMA also increases the level of ANGPTL4 protein released in the medium. PKC inhibitors Ro31-8820 and Gö6983 greatly inhibit the induction of ANGPTL4 mRNA by PMA suggesting that this up-regulation involves activation of PKC. Knockdown of several PKCs by corresponding siRNAs suggest a role for PKCalpha. PMA does not activate MAPK p38 and p38 inhibitors have little effect on the induction of ANGPTL4 indicating that p38 is not involved in the regulation of ANGPTL4 by PMA. In contrast, treatment of HASM by PMA induces phosphorylation and activation of Ra, MEK1/2, ERK1/2, JNK, Elk-1, and c-Jun. The Ras inhibitor manumycin A, the MEK1/2 inhibitor U0126, and the JNK inhibitor SP600125, greatly reduce the increase in ANGPTL4 expression by PMA. Knockdown of MEK1/2 and JNK1/2 expression by corresponding siRNAs inhibits the induction of ANGPTL4. Our observations suggest that the induction of ANGPTL4 by PMA in HASM involves the activation of PKC, ERK, and JNK pathways. This induction may play a role in tissue remodeling during lung injury and be implicated in several lung pathologies.

Angiopoietins and Angiopoietin-Like Proteins in Angiogenesis

Vascular network formation requires several endothelial cell growth factors. These factors have a potent angiogenic effect, and their precise coordination is essential for vascular development. Among them, angiopoietins function through the Tie2 receptor, whose signaling is critical to regulate vascular stabilization and remodeling. It has been reported that the angiopoietin/Tie2 signal is involved in survival and migration of endothelial cells and regulates vascular remodeling and maintenance of vascular integrity. More recent studies demonstrate that angiopoietin/Tie2 signaling is also required for lymphangiogenesis. The authors and several other groups have identified six angiopoietin-like proteins (Angptls) containing a coiled-coil domain and a fibrinogen-like domain, both of which are characteristic of angiopoietins. Interestingly, Angptls also function in angiogenesis through regulating survival and migration of endothelial cells, although Angptls do not bind the angiopoietin receptor Tie2. Currently, Angptls are orphan ligands, but they have been reported to have pleiotropic effects not only on vascular cells but also on metabolism and tumor biology. Here, the authors review current findings relating to the roles of angiopoietins and Angptls in vascular biology and discuss molecular mechanisms relevant to these factors and angiogenesis.

A mouse mammary gland involution mRNA signature identifies biological pathways potentially associated with breast cancer metastasis

Mouse mammary gland involution resembles a wound healing response with suppressed inflammation. Wound healing and inflammation are also associated with tumour development, and a 'wound-healing' gene expression signature can predict metastasis formation and survival. Recent studies have shown that an involuting mammary gland stroma can promote metastasis. It could therefore be hypothesised that gene expression signatures from an involuting mouse mammary gland may provide new insights into the physiological pathways that promote breast cancer progression. Indeed, using the HOPACH clustering method, the human orthologues of genes that were differentially regulated at day 3 of mammary gland involution and showed prolonged expression throughout the first 4 days of involution distinguished breast cancers in the NKI 295 breast cancer dataset with low and high metastatic activity. Most strikingly, genes associated with copper ion homeostasis and with HIF-1 promoter binding sites were the most over-represented, linking this signature to hypoxia. Further, six out of the ten mRNAs with strongest up-regulation in cancers with poor survival code for secreted factors, identifying potential candidates that may be involved in stromal/matrix-enhanced metastasis formation/breast cancer development. This method therefore identified biological processes that occur during mammary gland involution, which may be critical in promoting breast cancer metastasis that could form a basis for future investigation, and supports a role for copper in breast cancer development.

Caloric restriction and exercise increase plasma ANGPTL4 levels in humans via elevated free fatty acids

OBJECTIVE

Plasma lipoprotein levels are determined by the balance between lipoprotein production and clearance. Recently, angiopoietin-like protein 4 (ANGPTL4) was uncovered as a novel endocrine factor that potently raises plasma triglyceride levels by inhibiting triglyceride clearance. However, very little is known about ANGPTL4 in human. Here we set out to identify physiological determinants of plasma ANGPTL4 levels in humans, focusing on the effect of energy restriction and plasma FFAs.

METHODS AND RESULTS

We developed an ELISA for quantitative measurement of ANGPTL4 in human plasma. Using this assay we found major variations in baseline plasma ANGPTL4 levels between individuals. Within an individual, plasma ANGPTL4 levels remain stable throughout the day but increase significantly in response to long-term fasting, chronic caloric restriction, and endurance exercise. Intralipid injection as well as treatment with a beta-adrenergic agonist, both of which lead to elevated plasma FFA levels, increased plasma ANGPTL4 levels compared to control treatment. Fatty acids markedly induced ANGPTL4 gene expression in rat hepatoma FAO cells, human primary myocytes, and mouse intestinal MSIE cells.

CONCLUSIONS

In conclusion, our results show that plasma ANGPTL4 levels are increased by fasting, caloric restriction, and exercise, which is likely mediated by elevated plasma FFAs.