Angiopoietin-like protein 2 promotes chronic adipose tissue inflammation and obesity-related systemic insulin resistance

Association of serum angiopoietin-like protein 2 with carotid intima-media thickness in subjects with type 2 diabetes

BACKGROUND

Although recent animal studies have suggested that angiopoietin-like protein 2 (ANGPTL2), a novel inflammatory adipokine, is likely to be involved in the pathogenesis of atherosclerosis, in rodents, little is known regarding whether serum ANGPTL2 level is also associated with atherosclerosis in humans, especially in patients with type 2 diabetes. The aim of this study was to investigate whether serum ANGPTL2 concentration is associated with atherosclerosis by measuring carotid intima-media thickness (IMT) in subjects with type 2 diabetes without previous history of cardiovascular diseases. In addition, we examined the clinical and biochemical variables associated with serum ANGPLT2 concentration.

METHODS

We measured the circulating ANGPTL2 level in 166 subjects (92 men and 74 women; mean age of 60.0 years) with type 2 diabetes. Measurements of carotid IMT were performed in all subjects.

RESULTS

Serum ANGPTL2 concentration was positively correlated with carotid IMT (r = 0.220, p = 0.004). In multiple linear regression, serum ANGPTL2 concentration was independently associated with increased carotid IMT along with older age, male gender, and higher systolic blood pressure. Higher levels of hemoglobin A1c and high-sensitivity C-reactive protein were significantly associated with elevated serum ANGPTL2 concentration in subjects with type 2 diabetes.

CONCLUSIONS

Serum ANGPTL2 concentration was significantly and positively associated with carotid atherosclerosis in patients with type 2 diabetes, suggesting that ANGPTL2 may be important in the atherosclerosis in humans.

ANGPTL2 increases bone metastasis of breast cancer cells through enhancing CXCR4 signaling

Bone metastasis of breast cancer cells is a major concern, as it causes increased morbidity and mortality in patients. Bone tissue-derived CXCL12 preferentially recruits breast cancer cells expressing CXCR4 to bone metastatic sites. Thus, understanding how CXCR4 expression is regulated in breast cancer cells could suggest approaches to decrease bone metastasis of breast tumor cells. Here, we show that tumor cell-derived angiopoietin-like protein 2 (ANGPTL2) increases responsiveness of breast cancer cells to CXCL12 by promoting up-regulation of CXCR4 in those cells. In addition, we used a xenograft mouse model established by intracardiac injection of tumor cells to show that ANGPTL2 knockdown in breast cancer cells attenuates tumor cell responsiveness to CXCL12 by decreasing CXCR4 expression in those cells, thereby decreasing bone metastasis. Finally, we found that ANGPTL2 and CXCR4 expression levels within primary tumor tissues from breast cancer patients are positively correlated. We conclude that tumor cell-derived ANGPTL2 may increase bone metastasis by enhancing breast tumor cell responsiveness to CXCL12 signaling through up-regulation of tumor cell CXCR4 expression. These findings may suggest novel therapeutic approaches to treat metastatic breast cancer.

Angiopoietin-like protein 2 promotes inflammatory conditions in the ligamentum flavum in the pathogenesis of lumbar spinal canal stenosis by activating interleukin-6 expression

PURPOSE

Chronic inflammation is thought to cause ligamentum flavum (LF) degeneration and hypertrophy in lumbar spinal canal stenosis (LSCS). Angiopoietin-like protein 2 (Angptl2) is highly expressed in hypertrophied LF. Because Angptl2 regulates interleukin-6 (IL-6) expression in various tissues, we investigated whether IL-6 is expressed in hypertrophied LF and, if so, does Angptl2 induce IL-6 expression in LF fibroblasts.

METHODS

LF tissue was obtained from LSCS patients and non-LSCS patients. Polymerase chain reaction (PCR) for Angptl2 and IL-6 genes and immunohistochemistry for IL-6 protein were performed in LF tissue. Fibroblasts from LF tissue were used for in vitro experiments. Expression of integrin α5β1 (an Angptl2 receptor) and Angptl2 binding to receptors on LF fibroblasts were examined by fluorescence-activated cell sorter analysis and cell adhesion assays. After Angptl2 recombinant protein treatment, NF-κB activation and IL-6 expression in LF fibroblasts were investigated by immunocytochemistry, PCR, and enzyme-linked immunosorbent assay.

RESULTS

IL-6 mRNA expression was increased in hypertrophied LF tissue from LSCS patients and positively correlated with LF thickness and Angptl2 mRNA expression. IL-6 protein was highly expressed in LF fibroblasts in hypertrophied LF tissue. In vitro experiments demonstrated integrin α5β1 expression on LF fibroblasts and Angptl2 binding to cells via receptors. Angptl2 stimulation promoted NF-κB nuclear translocation and induced IL-6 expression and secretion in LF fibroblasts.

CONCLUSIONS

Angptl2 promotes inflammation in LF tissue by activating IL-6 expression, leading to LF degeneration and hypertrophy.

Knockdown of angiopoietin like-2 protects against angiotensin II-induced cerebral endothelial dysfunction in mice

Angiopoietin like-2 (angptl2) is a circulating pro-inflammatory and pro-oxidative protein, but its role in regulating cerebral endothelial function remains unknown. We hypothesized that in mice knockdown (KD) of angptl2, cerebral endothelial function would be protected against ANG II-induced damage. Subcutaneous infusion of ANG II (200 ng·kg−1·min−1, n = 15) or saline ( n = 15) was performed in 20-wk-old angptl2 KD mice and wild-type (WT) littermates for 14 days. In saline-treated KD and WT mice, the amplitude and the sensitivity of ACh-induced dilations of isolated cerebral arteries were similar. However, while endothelial nitric oxide (NO) synthase (eNOS)-derived O2−/H2O2 contributed to dilation in WT mice, eNOS-derived NO ( P < 0.05) was involved in KD mice. ANG II induced cerebral endothelial dysfunction only in WT mice ( P < 0.05), which was reversed ( P < 0.05) by either N-acetyl-l-cysteine, apocynin, gp91ds-tat, or indomethacin, suggesting the contribution of reactive oxygen species from Nox2 and Cox-derived contractile factors. In KD mice treated with ANG II, endothelial function was preserved, likely via Nox-derived H2O2, sensitive to apocynin and PEG-catalase ( P < 0.05), but not to gp91ds-tat. In the aorta, relaxation similarly and essentially depended on NO; endothelial function was maintained after ANG II infusion in all groups, but apocynin significantly reduced aortic relaxation in KD mice ( P < 0.05). Protein expression levels of Nox1/2 in cerebral arteries were similar among all groups, but that of Nox4 was greater ( P < 0.05) in saline-treated KD mice. In conclusion, knockdown of angptl2 may be protective against ANG II-induced cerebral endothelial dysfunction; it favors the production of NO, likely increasing endothelial cell resistance to stress, and permits the expression of an alternative vasodilatory Nox pathway.

Angiopoietin-like proteins stimulate HSPC development through interaction with notch receptor signaling

Angiopoietin-like proteins (angptls) are capable of ex vivo expansion of mouse and human hematopoietic stem and progenitor cells (HSPCs). Despite this intriguing ability, their mechanism is unknown. In this study, we show that angptl2 overexpression is sufficient to expand definitive HSPCs in zebrafish embryos. Angptl1/2 are required for definitive hematopoiesis and vascular specification of the hemogenic endothelium. The loss-of-function phenotype is reminiscent of the notch mutant mindbomb (mib), and a strong genetic interaction occurs between angptls and notch. Overexpressing angptl2 rescues mib while overexpressing notch rescues angptl1/2 morphants. Gene expression studies in ANGPTL2-stimulated CD34(+) cells showed a strong MYC activation signature and myc overexpression in angptl1/2 morphants or mib restored HSPCs formation. ANGPTL2 can increase NOTCH activation in cultured cells and ANGPTL receptor interacted with NOTCH to regulate NOTCH cleavage. Together our data provide insight to the angptl-mediated notch activation through receptor interaction and subsequent activation of myc targets.

GDC-0152 attenuates the malignant progression of osteosarcoma promoted by ANGPTL2 via PI3K/AKT but not p38MAPK signaling pathway

Angiopoietin-like protein 2 (ANGPTL2) plays an important role in inflammatory carcinogenesis and tumor metastasis. The compound GDC-0152 is a peptidomimetic small molecule antagonist of inhibitor of apoptosis (IAP) proteins with antitumor activity. However, the interaction between ANGPTL2 and GDC-0152 has not been studied. It has been proven that ANGPTL2 promotes metastasis of osteosarcoma. Therefore, in the present study, the effect of GDC-0152 on the malignant progression of osteosarcoma promoted by ANGPTL2 was investigated. Human osteosarcoma cell line SaOS2 cells were pre-treated or non-treated with GDC-0152 and then exposed to recombinant human ANGPTL2. The viability of SaOS2 cells was determined by MTT assay, the migration of SaOS2 cells was analyzed by chamber migration assay kit, and the SaOS2 cell apoptosis was determined by fluorescence-activated cell sorting (FACS) and nuclear staining. Treatment with ANGPTL2 increased SaOS2 cell growth and migration and decreased cell apoptosis. The increased cell growth and decreased cell apoptosis were significantly attenuated in SaOS2 cells receiving GDC-0152. However, the ANGPTL2-increased SaOS2 cell migration was not inhibited by GDC-0152 treatment. Furthermore, western blot analysis showed that the activation of phosphatidyl inositol 3-kinase (PI3K) (p85), PI3K (p110), protein kinase B (Akt) (Ser473), Akt (Thr308) and p38 mitogen-activated protein kinase (p38MAPK) were upregulated by ANGPTL2. Quantitative real-time polymerase chain reaction (qTR-PCR) and gelatin zymography showed that the mRNA expression and activity of matrix metalloproteinase-9 (MMP-9) and matrix metalloproteinase-2 (MMP-2) were also increased by ANGPTL2. The upregulated activation of PI3K and Akt were significantly suppressed by the treatment of GDC-0152. In contrast, GDC-0152 did not suppress ANGPTL2-induced p38MAPK phosphorylation, MMP-9/MMP-2 mRNA expression or MMP-9/MMP-2 activity. Taken together, these data indicate that GDC-0152 attenuates the malignant progression of osteosarcoma promoted by ANGPTL2 via PI3K/AKT but not p38MAPK signaling pathway. The present study indicated a novel therapeutic strategy to inhibit tumor growth by indirectly preventing ANGPTL2 signaling.

ANGPTL2 promotes tumor metastasis in hepatocellular carcinoma

BACKGROUND AND AIM

Angiopoietin-like protein 2 (ANGPTL2) plays various roles in metabolism, vascular biology, inflammation, and tumor metastasis, but little is known about its function in human hepatocellular carcinoma (HCC) metastasis. This study aimed to further explore the function of ANGPTL2 on migration and invasion of liver cancer cells.

METHODS

Quantitative real-time polymerase chain reaction, Western blotting, immunohistochemistry, transwell migration, and invasion assays were performed to clarify the function of ANGPTL2 in the regulation of cell migration and invasion in human HCC.

RESULTS

In HCC patients, ANGPTL2 expression was higher in HCC tissues compared with matched noncancerous liver tissues. And the ANGPTL2 levels of HCC tissues positively correlated with intrahepatic metastasis in HCC patients. Overexpression of ANGPTL2 significantly increased migration and invasion of HCC cells in vitro, and promoted intrahepatic and distal pulmonary metastasis in vivo, while knockdown of endogenous ANGPTL2 resulted in a reduced migration and invasion in vitro. Colony formation assay and 3-(4,5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed ANGPTL2 did not affect cell proliferation in vitro, whereas overexpression of ANGPTL2 promoted tumor formation in xenograft animal model.

CONCLUSIONS

Our findings show that ANGPTL2 drives human HCC metastasis and provides a potential therapeutic target for HCC treatment.

Angiopoietin-like 7 is an anti-angiogenic protein required to prevent vascularization of the cornea

Purpose

We sought to identify the anti-angiogenic molecule expressed in corneal keratocytes that is responsible for maintaining the avascularity of the cornea.

Methods

Human umbilical vein endothelial cells (HUVECs) were cultured with either human dermal fibroblasts or with human corneal keratocytes under serum-free conditions. The areas that exhibited blood vessel formation were estimated by immunostaining the cultures with an antitibody against CD31, a blood vessel marker. We also performed microarray gene-expression analysis and selected one molecule, angiopoietin-like 7 (ANGPTL7) for further functional studies conducted with the keratocytes and in vivo in mice.

Results

Areas showing blood vessel formation in normal serum-free medium were conditions were markedly smaller when HUVECs were co-cultured with corneal keratocytes than when they were co-cultured with the dermal fibroblasts under the same conditions. Microarray analysis revealed that ANGPTL7 expression was higher in keratocytes than in dermal fibroblasts. In vitro, inhibiting ANGPTL7 expression by using a specific siRNA led to greater tube formation than did the transfection of cells with a control siRNA, and this increase in tube formation was abolished when recombinant ANGPTL7 protein was added to the cultures. In vivo, intrastromal injections of an ANGPTL7 PshRNA into the avascular corneal stroma of mice resulted in the growth of blood vessels.

Conclusions

ANGPTL7, which is abundantly expressed in keratocytes, plays a major role in maintaining corneal avascularity and transparency.

Angiopoietin-Like Protein 2 Acts as a Novel Biomarker for Diagnosis and Prognosis in Patients with Esophageal Cancer

BACKGROUND

Angiopoietin-like protein 2 (ANGPTL2) mediates chronic inflammation. Tumor cell-derived ANGPTL2 promotes tumor invasion and angiogenesis. Overexpression of ANGPTL2 in tumor cells is associated with tumor progression and has been recognized in lung, breast, colon, and gastric cancer. However, to our knowledge the functional and clinical significance of ANGPTL2 expression has not been investigated in patients with esophageal cancer (EC).

METHODS

First, in vitro assays were performed for functional analysis of ANGPTL2 using small interfering RNA. Next, ANGPTL2 expression in EC tissues (n = 71) was evaluated by immunohistochemistry (IHC in patients with EC (n = 71). Finally, serum ANGPLT2 levels from patients with EC (n = 71) and healthy controls (n = 35) were evaluated using enzyme-linked immunosorbent assay.

RESULTS

Knockdown of ANGPTL2 expression decreased the proliferative, invasive, and migration capacity in EC cell lines. ANGPTL2 expression in EC tissues was significantly elevated in patients with a high T stage, squamous cell carcinoma, and high TNM stage. Patients with high ANGPTL2 expression had significantly poorer overall and disease-free survival than those with low expression. Furthermore, high ANGPTL2 expression in EC tissues was an independent predictive marker for a poor prognosis. On the other hand, the serum ANGPTL2 level in patients with EC was significantly higher than that in healthy controls, and allowed for highly accurate discrimination between patients with and without EC. However, no significant association between serum ANGPTL2 levels and clinicopathological findings was observed in patients with EC.

CONCLUSIONS

We have demonstrated novel evidence for the clinical significance of ANGPTL2 as a biomarker in patients with EC.

Angiopoietin-like protein 2 induces androgen-independent and malignant behavior in human prostate cancer cells

Angiopoietin-like proteins (ANGPTLs), which comprise 7 members (ANGPTL1-ANGPTL7), structurally resemble angiopoietins. We investigated the roles of ANGPTLs in the acquisition of androgen independence and the malignant behavior of human prostate cancer cells. Expression of ANGPTL messenger RNA (mRNA) and proteins were ascertained using RT-qPCR and western blot analysis in human prostate cancer cell lines. Androgen‑dependent LNCaP and androgen-independent LNCaP/AI cells, respectively, were cultured in fetal bovine and charcoal-stripped medium. Cell proliferation, androgen dependence, migration and invasion, respectively, were examined under the overexpression and knockdown of ANGPTL2 by transfection of ANGPTL2 cDNA and its small‑interfering RNA (siRNA). The effects of exogenous ANGPTL2 and blocking of its receptor, integrin α5β1, were also investigated. Human prostate cancer cell lines predominantly expressed ANGPTL2 among the members. Interrupting ANGPTL2 expression with siRNA suppressed the proliferation, migration and invasion of LNCaP cells. LNCaP/AI cells showed a higher ANGPTL2 expression than that of LNCaP cells. Furthermore, siRNA led to apoptosis of LNCaP/AI cells. The ANGPTL2-overexpressing LNCaP cells markedly increased proliferation, epithelial-to-mesenchymal transition (EMT) and malignant behavior in androgen‑deprived medium. The migration rates were increased depending on the concentration of ANGPTL2 recombinant protein and were inhibited by anti-integrin α5β1 antibodies. To the best of our knowledge, this is the first study to elucidate the expression of ANGPTL2 in human prostate cancer cells. ANGPTL2 may be important in the acquisition of androgen independency and tumor progression of prostate cancer in an autocrine and/or paracrine manner via the integrin α5β1 receptor. Targeting ANGPTL2 may therefore be an efficacious therapeutic modality for prostate cancer.

Angiopoietin-like protein 2 is a potential biomarker for gastric cancer

Globally, gastric cancer is one of the most common types of cancer and is the second leading cause of cancer‑induced mortality. Early detection of gastric cancer is able to contribute to a reduction of its mortality. For early detection, more specific and sensitive biomarkers than the classic biomarkers, including carcinoembryonic antigen, carbohydrate antigen 19‑9 and C‑reactive protein, are required. The present study focused on the evaluation of the potential of angiopoietin‑like protein 2 (ANGPTL2) as a novel biomarker for gastric cancer. The expression levels of ANGPTL2 in undifferentiated and differentiated gastric cancer cell lines (HGC‑27 and MKN7, respectively) were therefore investigated. Additionally, ANGPTL2 levels in the serum of gastric cancer patients were compared with those of healthy individuals to evaluate the possibility of the protein as a predictive biomarker for gastric cancer. It was established that the expression levels of ANGPTL2 mRNA and protein were higher in undifferentiated HGC‑27 cells than those in differentiated MKN7 cells. In a patient study, it was indicated that the levels of ANGPTL2 in the serum of gastric cancer patients were higher than those in healthy controls. The diagnostic performance of ANGPTL2 was assessed by constructing a receiver operating characteristic (ROC) curve and was evaluated by calculating the area under each ROC curve (AUC). For the discrimination of patients with gastric cancer from healthy individuals, the AUC for ANGPTL2 was 0.774 (P=0.005) (95% confidence interval, 0.615‑0.933). These results suggested that ANGPTL2 was a potential biomarker for gastric cancer.

Co-expression of immunoglobulin-like transcript 4 and angiopoietin-like proteins in human non-small cell lung cancer

The development of strategies for the inhibition of non‑small cell lung cancer (NSCLC) progression and metastasis have been mainly unsuccessful, in part due to insufficient mechanistic understanding of the disease. In the current study, the critical role of the co‑expression of immunoglobulin‑like transcript 4 (ILT4) and its ligands, angiopoietin‑like proteins (ANGPTLs), in the development of NSCLC was demonstrated. ILT4 and ANGPTL2 or ANGPTL5 were found to be co‑expressed in the five NSCLC cell lines that were investigated at the mRNA and protein level. Upon up‑ or downregulation of ILT4, the expression of ANGPTL2 was increased or reduced, respectively, while the expression of ANGPTL5 was unaffected. The co‑expression of ILT4 and ANGPTL2/ANGPTL5 was detected in human primary NSCLC tissues using immunohistochemical analysis. In total, 114 lung cancer specimens were included in the study; high expression of ILT4, ANGPTL2 and ANGPTL5 was observed in 58.8, 45.6 and 55.3%, respectively. The expression of ILT4 was found to be significantly correlated with a high expression level of ANGPTL2 (R=0.466, P=0.004); however, it was not correlated with the expression of ANGPTL5 (R=0.142, P=0.131). In ILT4‑positive samples, cases with ANGPTL2‑positive expression levels presented greater levels of lymph node metastasis (P=0.011) and shorter overall survival times (P=0.045). In addition, cases with ANGPTL5‑positive expression presented poor overall survival rates (P=0.040). By contrast, in the ILT4‑negative cases, no statistically significant differences were identified in the overall survival rates between samples with high and low expression of ANGPTL2 or ANGPTL5. In conclusion, the present study demonstrated the presence of interaction among ILT4 and ANGPTLs, which may be important in NSCLC progression. Therefore, the blockade of ANGPTLs or ILT4 may be an effective therapeutic approach for NSCLC treatment.

Angiopoietin-like-2: a multifaceted protein with physiological and pathophysiological properties

Angptl2 is a multifaceted protein, displaying both physiological and pathological functions, in which scientific and clinical interest is growing exponentially within the past few years. Its physiological functions are not well understood, but angptl2 was first acknowledged for its pro-angiogenic and antiapoptotic capacities. In addition, angptl2 can be considered a growth factor, since it increases survival and expansion of hematopoietic stem cells and may promote vasculogenesis. Finally, angptl2 has an important, but largely unrecognised, physiological role: in the cytosol, angptl2 binds to type 1A angiotensin II receptors and induces their recycling, with recovery of the receptor signal functions. Despite these important physiological properties, angptl2 is better acknowledged for its deleterious pro-inflammatory properties and its contribution in multiple chronic diseases such as cancer, diabetes, atherosclerosis, metabolic disorders and many other chronic diseases. This review aims at presenting an updated description of both the beneficial and deleterious biological properties of angptl2, in addition to its molecular signalling pathways and transcriptional regulation. The multiplicity of diseases in which angptl2 contributes makes it a new highly relevant clinical therapeutic target.

Reprogramming suppresses premature senescence phenotypes of Werner syndrome cells and maintains chromosomal stability over long-term culture

Werner syndrome (WS) is a premature aging disorder characterized by chromosomal instability and cancer predisposition. Mutations in WRN are responsible for the disease and cause telomere dysfunction, resulting in accelerated aging. Recent studies have revealed that cells from WS patients can be successfully reprogrammed into induced pluripotent stem cells (iPSCs). In the present study, we describe the effects of long-term culture on WS iPSCs, which acquired and maintained infinite proliferative potential for self-renewal over 2 years. After long-term cultures, WS iPSCs exhibited stable undifferentiated states and differentiation capacity, and premature upregulation of senescence-associated genes in WS cells was completely suppressed in WS iPSCs despite WRN deficiency. WS iPSCs also showed recapitulation of the phenotypes during differentiation. Furthermore, karyotype analysis indicated that WS iPSCs were stable, and half of the descendant clones had chromosomal profiles that were similar to those of parental cells. These unexpected properties might be achieved by induced expression of endogenous telomerase gene during reprogramming, which trigger telomerase reactivation leading to suppression of both replicative senescence and telomere dysfunction in WS cells. These findings demonstrated that reprogramming suppressed premature senescence phenotypes in WS cells and WS iPSCs could lead to chromosomal stability over the long term. WS iPSCs will provide opportunities to identify affected lineages in WS and to develop a new strategy for the treatment of WS.

Angiopoietin-like protein 2 renders colorectal cancer cells resistant to chemotherapy by activating spleen tyrosine kinase-phosphoinositide 3-kinase-dependent anti-apoptotic signaling

Angiopoietin-like protein 2 (ANGPTL2) plays an important role in inflammatory carcinogenesis and tumor metastasis by activating tumor angiogenesis and tumor cell chemotaxis and invasiveness. However, it is unclear whether ANGPTL2 expression has an effect on tumor cell survival. Here, we explored that possibility by determining whether ANGPTL2 expression altered survival of human colorectal cancer cell lines treated with antineoplastic drugs. To do so, we generated SW480 cells expressing ANGPTL2 (SW480/ANGPTL2) and control (SW480/Ctrl) cells. Apoptosis induced by antineoplastic drug treatment was significantly decreased in SW480/ANGPTL2 compared to control cells. Expression of anti-apoptotic BCL-2 family genes was upregulated in SW480/ANGPTL2 compared to SW480/Ctrl cells. To assess signaling downstream of ANGPTL2 underlying this effect, we carried out RNA sequencing analysis of SW480/ANGPTL2 and SW480/Ctrl cells. That analysis, combined with in vitro experiments, indicated that Syk-PI3K signaling induced expression of BCL-2 family genes in SW480/ANGPTL2 cells. Furthermore, ANGPTL2 increased its own expression in a feedback loop by activating the spleen tyrosine kinase–nuclear factor of activated T cells (Syk–NFAT) pathway. Finally, we observed a correlation between higher ANGPTL2 expression in primary unresectable tumors from colorectal cancer patients who underwent chemotherapy with a lower objective response rate. These findings suggest that attenuating ANGPTL2 signaling in tumor cells may block tumor cell resistance to antineoplastic therapies.

Elevated serum angiopoietin-like protein 2 correlates with the metastatic properties of colorectal cancer: a serum biomarker for early diagnosis and recurrence

PURPOSE

Angiopoietin-like protein 2 (ANGPTL2) is a mediator of chronic inflammation and inflammatory carcinogenesis. The biologic and clinical significance of ANGPTL2 remains unknown in human cancer. Therefore, we investigated the function of ANGPTL2 and evaluated its clinical significance in both primary tumors and matched sera in patients with colorectal cancer.

EXPERIMENTAL DESIGN

A colorectal cancer cell line was transfected with siRNA against ANGPTL2 for the assessment of its function. We examined ANGPTL2 expression in colorectal cancer tissues (n = 195) by immunohistochemistry. Finally, we screened serum ANGPTL2 levels from 32 colorectal cancers and 23 normal controls (NC), and validated these results in serum samples obtained from 195 colorectal cancers and 45 NCs by ELISA.

RESULTS

Knockdown of ANGPTL2 in vitro significantly inhibited cell proliferation, migration, and invasion, whereas it enhanced anoikis. ANGPTL2 was overexpressed in colorectal cancer tissues, and was significantly associated with advanced T stage, lymph node, and liver metastasis. Likewise, serum ANGPTL2 levels in colorectal cancers were significantly higher than NCs (P < 0.01), and allowed distinguishing of colorectal cancers from NCs with high accuracy (AUC = 0.837). The subsequent validation step confirmed that serum ANGPTL2 levels in colorectal cancers were significantly higher than in NCs (P < 0.0001), and had a high AUC value (0.885) for distinguishing colorectal cancers from NCs. High serum ANGPTL2 was significantly associated with advanced T stage, lymph node and liver metastasis, early relapse, and poor prognosis in colorectal cancers.

CONCLUSION

Serum ANGPTL2 is a novel diagnostic and recurrence-predictive biomarker in patients with colorectal cancer.

Serum ANGPTL2 levels reflect clinical features of breast cancer patients: implications for the pathogenesis of breast cancer metastasis

INTRODUCTION

Breast cancer is a leading cause of cancer-related death in women worldwide, and its metastasis is a major cause of disease mortality. Therefore, identification of the mechanisms underlying breast cancer metastasis is crucial for the development of therapeutic and diagnostic strategies. Our recent study of immunodeficient female mice transplanted with MDA-MB231 breast cancer cells demonstrated that tumor cell-derived angiopoietin-like protein 2 (ANGPTL2) accelerates metastasis through both increasing tumor cell migration in an autocrine/paracrine manner, and enhancing tumor angiogenesis. To determine whether ANGPTL2 contributes to its clinical pathogenesis, we asked whether serum ANGPTL2 levels reflect the clinical features of breast cancer progression.

METHODS

We monitored the levels of secreted ANGPTL2 in supernatants of cultured proliferating MDA-MB231 cells. We also determined whether the circulating ANGPTL2 levels were positively correlated with cancer progression in an in vivo breast cancer xenograft model using MDA-MB231 cells. Finally, we investigated whether serum ANGPTL2 levels were associated with clinical features in breast cancer patients.

RESULTS

Both in vitro and in vivo experiments showed that the levels of ANGPTL2 secreted from breast cancer cells increased with cell proliferation and cancer progression. Serum ANGPTL2 levels in patients with metastatic breast cancer were significantly higher than those in healthy subjects or in patients with ductal carcinoma in situ or non-metastatic invasive ductal carcinoma. Serum ANGPTL2 levels in patients negative for estrogen receptors and progesterone receptors, particularly triple-negative cases, reflected histological grades.

CONCLUSIONS

These findings suggest that serum ANGPTL2 levels in breast cancer patients could represent a potential marker of breast cancer metastasis.

Angiopoietin-like protein 2 negatively regulated by microRNA-25 contributes to the malignant progression of colorectal cancer

Angiopoietin-like protein 2 (ANGPTL2) is associated with tumor progression while dysregulation of its expression has been observed in various types of cancer. However, the expression and role of ANGPTL2 remain exclusive in colorectal cancer (CRC). In the present study, we determined the expression levels of ANGPTL2 in CRC tissues and cells. The roles of ANGPTL2 and miR-25 in the migration and invasion of CRC SW620 and HCT-116 cells were also investigated using transwell assays or scratch wound assays. The results showed that ANGPTL2 increased with metastatic progression. Increased ANGPTL2 and decreased microRNA-25 (miR-25) expression were found to coexist in CRC. The functional studies revealed that knockdown of ANGPTL2 reduced colony formation, and the invasive and migratory abilities of human CRC SW620 and HCT-116 cells. Similarly, overexpression of miR-25 resulted in reduced colony formation, invasion and migration in both cell lines. The overexpression of miR-25 led to a decreased ANGPTL2 mRNA and protein expression, whereas the downregulation of miR-25 resulted in increased ANGPTL2 mRNA and protein expression, in SW620 and HCT-116 cells. miR-25 directly targeted ANGPTL2 by binding to its 3'‑UTR, as determined by the dual luciferase reporter assay. To the best of our know-ledge, the results of this study suggest for the first time that the abnormal upregulation of ANGPTL2 in CRC is associated with miR-25 downregulation. Additionally, miR-25‑mediated ANGPTL2 promoted the malignant progression of CRC. The present study provides evidence supporting ANGPTL2 and miR-25 as diagnostic or therapeutic targets for CRC.

Lack of angiopoietin-like-2 expression limits the metabolic stress induced by a high-fat diet and maintains endothelial function in mice

Background

Angiopoietin‐like‐2 (angptl2) is produced by several cell types including endothelial cells, adipocytes and macrophages, and contributes to the inflammatory process in cardiovascular diseases. We hypothesized that angptl2 impairs endothelial function, and that lowering angptl2 levels protects the endothelium against high‐fat diet (HFD)‐induced fat accumulation and hypercholesterolemia.

Methods and Results

Acute recombinant angptl2 reduced (P<0.05) acetylcholine‐mediated vasodilation of isolated wild‐type (WT) mouse femoral artery, an effect reversed (P<0.05) by the antioxidant N‐acetylcysteine. Accordingly, in angptl2 knockdown (KD) mice, ACh‐mediated endothelium‐dependent vasodilation was greater (P<0.05) than in WT mice. In arteries from KD mice, prostacyclin contributed to the overall dilation unlike in WT mice. After a 3‐month HFD, overall vasodilation was not altered, but dissecting out the endothelial intrinsic pathways revealed that NO production was reduced in arteries isolated from HFD‐fed WT mice (P<0.05), while NO release was maintained in KD mice. Similarly, endothelium‐derived hyperpolarizing factor (EDHF) was preserved in mesenteric arteries from HFD‐fed KD mice but not in those from WT mice. Finally, the HFD increased (P<0.05) total cholesterol–to–high‐density lipoprotein ratios, low‐density lipoprotein–to–high‐density lipoprotein ratios, and leptin levels in WT mice only, while glycemia remained similar in the 2 strains. KD mice displayed less triglyceride accumulation in the liver (P<0.05 versus WT), and adipocyte diameters in mesenteric and epididymal white adipose tissues were smaller (P<0.05) in KD than in WT fed an HFD, while inflammatory gene expression increased (P<0.05) in the fat of WT mice only.

Conclusions

Lack of angptl2 expression limits the metabolic stress induced by an HFD and maintains endothelial function in mice.

Cloning, expression and purification of functionally active human angiopoietin-like protein 2

Angiopoietin-like protein 2 (Angptl2) is a secreted glycoprotein that has been implicated in angiogenesis, inflammation and atherosclerosis as well as enhancing the survival of human hematopoietic stem cells. Glycosylation of Angptl2 is required for biological activity and studies of angiopoietin-like protein 2 have been hindered by the lack of a source for the mature form of this protein. We describe a system that permits purification of the glycosylated form of human Angptl2 from conditioned media of stably transfected HEK 293 cells. To facilitate purification while retaining the integrity of Angptl2's endogenous N-terminal secretion signal peptide, GST was fused downstream of the Angptl2 coding sequence. Secreted Angptl2-GST was purified using a one-step glutathione-affinity purification scheme. The purity and identity of the resulting protein were confirmed by SDS-PAGE, immunoblotting, and mass spectrometry. N-Glycosidase treatment reduced the apparent molecular mass of Angptl2-GST on SDS-PAGE, confirming its glycosylation state. Purified human Angptl2-GST stimulated both HUVEC migration and microtubule formation in vitro. The yield of Angptl2-GST obtained was in quantities suitable for multiple applications including functional in vitro and in vivo assays.

Angiopoietin-like proteins 3, 4 and 8: regulating lipid metabolism and providing new hope for metabolic syndrome

Angiopoietin-like proteins (ANGPTLs) are a group of eight proteins that share structural similarity to the members of the angiopoietin protein family. ANGPTL3 plays a vital role in the regulation of the plasma levels of triglyceride and cholesterol, mainly via reversible inhibition of the lipoprotein lipase activity. ANGPTL4, which functions as a homo-oligomer different from ANGPTL3 and ANGPTL8, not only regulates the plasma levels of triglyceride and prevents the uptake of dietary lipids into adipose tissues but also inhibits intravascular lipolysis. ANGPTL8 (also called betatrophin) has been identified as an important factor in regulating the triglyceride levels and adipose tissue mass as well as in replenishing the adipose tissue triglyceride store. ANGPTL8 acts together with ANGPTL3 to regulate the lipid metabolism, and ANGPTL8 promotes cleavage of ANGPTL3 to augment the activity of ANGPTL3. In addition, ANGPTL8 promotes proliferation of pancreatic β-cells and enhances insulin secretion. The properties of ANGPTLs in regulating the lipid metabolism suggest their application in the target therapy for metabolic syndrome. As ANGPTLs are regulated by several factors and may be involved in certain specific pathways of lipid metabolism, designing drugs that target ANGPTLs or factors regulating ANGPTLs may be an efficient approach to treat metabolic syndrome.

Effects of the Angiotensin receptor blocker olmesartan on adipocyte hypertrophy and function in mice with metabolic disorders

In the present study, we examined the therapeutic effects of olmesartan, an angiotensin II (Ang II) type 1 receptor (AT1R)-specific blocker, in genetically obese diabetic KKAy mice, a model of human metabolic disorders with visceral obesity, with a focus on an olmesartan effect on the adipose tissue. Olmesartan treatment (3 mg/kg per day) for 4 weeks significantly lowered systolic blood pressure but did not affect body weight during the study period in KKAy mice. However, there were three interesting findings possibly related to the pleiotropic effects of olmesartan on adipose tissue in KKAy mice: (1) an inhibitory effect on adipocyte hypertrophy, (2) a suppressive effect on IL-6 gene expression, and (3) an ameliorating effect on oxidative stress. On the other hand, olmesartan exerted no evident influence on the adipose tissue expression of AT1R-associated protein (ATRAP), which is a molecule interacting with AT1R so as to inhibit pathological AT1R activation and is suggested to be an emerging molecular target in metabolic disorders with visceral obesity. Collectively, these results suggest that the blood pressure lowering effect of olmesartan in KKAy mice is associated with an improvement in adipocyte, including suppression of adipocyte hypertrophy and inhibition of the adipose IL-6-oxidative stress axis. Further study is needed to clarify the functional role of adipose ATRAP in the pleiotropic effects of olmesartan.

Diverse roles of ANGPTL2 in physiology and pathophysiology

Stresses based on aging and lifestyle can cause tissue damage. Repair of damage by tissue remodeling is often meditated by communications between parenchymal and stromal cells via cell-cell contact or humoral factors. However, loss of tissue homeostasis leads to chronic inflammation and pathological tissue remodeling. Angiopoietin-like protein 2 (ANGPTL2) maintains tissue homeostasis by promoting adaptive inflammation and subsequent tissue reconstruction, whereas excess ANGPTL2 activation induced by prolonged stress promotes breakdown of tissue homeostasis due to chronic inflammation and irreversible tissue remodeling, promoting development of various metabolic diseases. Thus, it is important to define how ANGPTL2 signaling is regulated in order to understand mechanisms underlying disease development. Here, we focus on ANGPTL2 function in physiology and pathophysiology.

Obesity and its metabolic complications: the role of adipokines and the relationship between obesity, inflammation, insulin resistance, dyslipidemia and nonalcoholic fatty liver disease

Accumulating evidence indicates that obesity is closely associated with an increased risk of metabolic diseases such as insulin resistance, type 2 diabetes, dyslipidemia and nonalcoholic fatty liver disease. Obesity results from an imbalance between food intake and energy expenditure, which leads to an excessive accumulation of adipose tissue. Adipose tissue is now recognized not only as a main site of storage of excess energy derived from food intake but also as an endocrine organ. The expansion of adipose tissue produces a number of bioactive substances, known as adipocytokines or adipokines, which trigger chronic low-grade inflammation and interact with a range of processes in many different organs. Although the precise mechanisms are still unclear, dysregulated production or secretion of these adipokines caused by excess adipose tissue and adipose tissue dysfunction can contribute to the development of obesity-related metabolic diseases. In this review, we focus on the role of several adipokines associated with obesity and the potential impact on obesity-related metabolic diseases. Multiple lines evidence provides valuable insights into the roles of adipokines in the development of obesity and its metabolic complications. Further research is still required to fully understand the mechanisms underlying the metabolic actions of a few newly identified adipokines.

Adipokines: a link between obesity and cardiovascular disease

Obesity is a risk factor for various cardiovascular diseases including hypertension, atherosclerosis, and myocardial infarction. Recent studies aimed at understanding the microenvironment of adipose tissue and its impact on systemic metabolism have shed light on the pathogenesis of obesity-linked cardiovascular diseases. Adipose tissue functions as an endocrine organ by secreting multiple immune-modulatory proteins known as adipokines. Obesity leads to increased expression of pro-inflammatory adipokines and diminished expression of anti-inflammatory adipokines, resulting in the development of a chronic, low-grade inflammatory state. This adipokine imbalance is thought to be a key event in promoting both systemic metabolic dysfunction and cardiovascular disease. This review will focus on the adipose tissue microenvironment and the role of adipokines in modulating systemic inflammatory responses that contribute to cardiovascular disease.

Role of Endothelial Cell–Derived Angptl2 in Vascular Inflammation Leading to Endothelial Dysfunction and Atherosclerosis Progression

Objective—

Cardiovascular disease (CVD), the most common morbidity resulting from atherosclerosis, remains a frequent cause of death. Efforts to develop effective therapeutic strategies have focused on vascular inflammation as a critical pathology driving atherosclerosis progression. Nonetheless, molecular mechanisms underlying this activity remain unclear. Here, we ask whether angiopoietin-like protein 2 (Angptl2), a proinflammatory protein, contributes to vascular inflammation that promotes atherosclerosis progression.

Approach and Results—

Histological analysis revealed abundant Angptl2 expression in endothelial cells and macrophages infiltrating atheromatous plaques in patients with cardiovascular disease. Angptl2 knockout in apolipoprotein E–deficient mice ( ApoE −/− / Angptl2 −/− ) attenuated atherosclerosis progression by decreasing the number of macrophages infiltrating atheromatous plaques, reducing vascular inflammation. Bone marrow transplantation experiments showed that Angptl2 deficiency in endothelial cells attenuated atherosclerosis development. Conversely, ApoE −/− mice crossed with transgenic mice expressing Angptl2 driven by the Tie2 promoter ( ApoE −/− /Tie2- Angptl2 Tg), which drives Angptl2 expression in endothelial cells but not monocytes/macrophages, showed accelerated plaque formation and vascular inflammation because of increased numbers of infiltrated macrophages in atheromatous plaques. Tie2- Angptl2 Tg mice alone did not develop plaques but exhibited endothelium-dependent vasodilatory dysfunction, likely because of decreased production of endothelial cell–derived nitric oxide. Conversely, Angptl2 −/− mice exhibited less severe endothelial dysfunction than did wild-type mice when fed a high-fat diet. In vitro, Angptl2 activated proinflammatory nuclear factor-κB signaling in endothelial cells and increased monocyte/macrophage chemotaxis.

Conclusions—

Endothelial cell–derived Angptl2 accelerates vascular inflammation by activating proinflammatory signaling in endothelial cells and increasing macrophage infiltration, leading to endothelial dysfunction and atherosclerosis progression.

Prolyl-4-hydroxylase domain 3 (PHD3) is a critical terminator for cell survival of macrophages under stress conditions

On a molecular level, cells sense changes in oxygen availability through the PHDs, which regulate the protein stability of the α-subunit of the transcription factor HIF. Especially, PHD3 has been additionally associated with apoptotic cell death. We hypothesized that PHD3 plays a role in cell-fate decisions in macrophages. Therefore, myeloid-specific PHD3(-/-) mice were created and analyzed. PHD3(-/-) BMDM showed no altered HIF-1α or HIF-2α stabilization or increased HIF target gene expression in normoxia or hypoxia. Macrophage M1 and M2 polarization was unchanged likewise. Compared with macrophages from WT littermates, PHD3(-/-) BMDM exhibited a significant reduction in TUNEL-positive cells after serum withdrawal or treatment with stauro and SNAP. Under the same conditions, PHD3(-/-) BMDM also showed less Annexin V staining, which is representative for membrane disruption, and indicated a reduced early apoptosis. In an unbiased transcriptome screen, we found that Angptl2 expression was reduced in PHD3(-/-) BMDM under stress conditions. Addition of rAngptl2 rescued the antiapoptotic phenotype, demonstrating that it is involved in the PHD3-mediated response toward apoptotic stimuli in macrophages.

Angiopoietin-like protein 2 regulates endothelial colony forming cell vasculogenesis

Angiopoietin-like 2 (ANGPTL2) has been reported to induce sprouting angiogenesis; however, its role in vasculogenesis, the de novo lumenization of endothelial cells (EC), remains unexplored. We sought to investigate the potential role of ANGPTL2 in regulating human cord blood derived endothelial colony forming cell (ECFC) vasculogenesis through siRNA mediated inhibition of ANGPTL2 gene expression. We found that ECFCs in which ANGPTL2 was diminished displayed a threefold decrease in in vitro lumenal area whereas addition of exogenous ANGPTL2 protein domains to ECFCs lead to increased lumen formation within a 3 dimensional (3D) collagen assay of vasculogenesis. ECFC migration was attenuated by 36 % via ANGPTL2 knockdown (KD) although proliferation and apoptosis were not affected. We subsequently found that c-Jun NH2-terminal kinase (JNK), but not ERK1/2, phosphorylation was decreased upon ANGPTL2 KD, and expression of membrane type 1 matrix metalloproteinase (MT1-MMP), known to be regulated by JNK and a critical regulator of EC migration and 3D lumen formation, was decreased in lumenized structures in vitro derived from ANGPTL2 silenced ECFCs. Treatment of ECFCs in 3D collagen matrices with either a JNK inhibitor or exogenous rhTIMP-3 (an inhibitor of MT1-MMP activity) resulted in a similar phenotype of decreased vascular lumen formation as observed with ANGPTL2 KD, whereas stimulation of JNK activity increased vasculogenesis. Based on gene silencing, pharmacologic, cellular, and biochemical approaches, we conclude that ANGPTL2 positively regulates ECFC vascular lumen formation likely through its effects on migration and in part by activating JNK and increasing MT1-MMP expression.

The secreted protein ANGPTL2 promotes metastasis of osteosarcoma cells through integrin α5β1, p38 MAPK, and matrix metalloproteinases

The tumor microenvironment can enhance the invasive capacity of tumor cells. We showed that expression of angiopoietin-like protein 2 (ANGPTL2) in osteosarcoma (OS) cell lines increased and the methylation of its promoter decreased with time when grown as xenografts in mice compared with culture. Compared with cells grown in normal culture conditions, the expression of genes encoding DNA demethylation-related enzymes increased in tumor cells implanted into mice or grown in hypoxic, serum-starved culture conditions. ANGPTL2 expression in OS cell lines correlated with increased tumor metastasis and decreased animal survival by promoting tumor cell intravasation mediated by the integrin α5β1, p38 mitogen-activated protein kinase, and matrix metalloproteinases. The tolloid-like 1 (TLL1) protease cleaved ANGPTL2 into fragments in vitro that did not enhance tumor progression when overexpressed in xenografts. Expression of TLL1 was weak in OS patient tumors, suggesting that ANGPTL2 may not be efficiently cleaved upon secretion from OS cells. These findings demonstrate that preventing ANGPTL2 signaling stimulated by the tumor microenvironment could inhibit tumor cell migration and metastasis.

Angiopoietin-like protein 2 induced by mechanical stress accelerates degeneration and hypertrophy of the ligamentum flavum in lumbar spinal canal stenosis

Chronic inflammation and subsequent fibrosis induced by mechanical stress play an important role in ligamentum flavum (LF) hypertrophy and degeneration in patients with lumbar spinal canal stenosis (LSCS). Angiopoietin-like protein 2 (Angptl2) is a chronic inflammatory mediator induced under various pathological conditions and increases the expression of TGF-β1, which is a well-characterized mediator in LF hypertrophy. We investigated whether Angptl2 is induced by mechanical stress, and whether it contributes to LF hypertrophy and degeneration by activating the TGF-β1 signaling cascade. In this study, we investigated human LF tissue and LF fibroblasts isolated from patients who underwent lumbar surgery. We found that Angptl2 was abundantly expressed in fibroblasts of hypertrophied LF tissues at both the mRNA and protein levels. This expression was not only positively correlated with LF thickness and degeneration but also positively correlated with lumbar segmental motion. Our in vitro experiments with fibroblasts from hypertrophied LF tissue revealed that mechanical stretching stress increases the expression and secretion of Angptl2 via activation of calcineurin/NFAT pathways. In hypertrophied LF tissue, expression of TGF-β1 mRNA was also increased and TGF-β1/Smad signaling was activated. Angptl2 expression in LF tissue was positively correlated with the expression of TGF-β1 mRNA, suggesting cooperation between Angptl2 and TGF-β1 in the pathogenesis of LF hypertrophy. In vitro experiments revealed that Angptl2 increased levels of TGF-β1 and its receptors, and also activated TGF-β1/Smad signaling. Mechanical stretching stress increased TGF-β1 mRNA expression, which was partially attenuated by treatment with a calcineurin/NFAT inhibitor or Angptl2 siRNA, indicating that induction of TGF-β1 expression by mechanical stretching stress is partially mediated by Angptl2. We conclude that expression of Angptl2 induced by mechanical stress in LF fibroblasts promotes LF tissue degeneration by activation of TGF-β1/Smad signaling, which results in LF hypertrophy in patients with LSCS.

Angiopoietin-like proteins: a comprehensive look

Angiopoietin-like proteins (ANGPTLs) are a family of proteins structurally similar to the angiopoietins. To date, eight ANGPTLs have been discovered, namely ANGPTL1 to ANGPTL8. Emerging evidence implies a key role for ANGPTLs in the regulation of a plethora of physiological and pathophysiological processes. Most of the ANGPTLs exhibit multibiological properties, including established functional roles in lipid and glucose metabolism, inflammation, hematopoiesis, and cancer. This report represents a systematic and updated appraisal of this class of proteins, focusing on the main features of each ANGPTL.

Effects of Ang II receptor blocker irbesartan on adipose tissue function in mice with metabolic disorders

Recent studies indicate that the functional renin-angiotensin system (RAS) exists in the adipose tissue. The adipose tissue RAS is proposed in the pathophysiology of metabolic disorders. In the present study, we examined therapeutic effects of irbesartan, an angiotensin II (Ang II) type 1 receptor (AT1R)-specific blocker, in genetically obese diabetic KKAy mice, a model of human metabolic disorders without any dietary loading, with our focus on the analysis on possible effect of irbesartan on the adipose tissue. The treatment with irbesartan significantly lowered systolic blood pressure with a concomitant decrease in body weight in KKAy mice. In addition, irbesartan significantly decreased the adipose leptin mRNA expression and tended to decrease IL-6 mRNA expression in the adipose tissue of KKAy mice. Furthermore irbesartan preserved the adipose gene expression of AT1R-associated protein (ATRAP), an endogenous inhibitory molecule of tissue AT1R signaling, with a concomitant tendency of up-regulation of adipose tissue ATRAP/AT1R ratio. Collectively, these results suggest that the irbesartan-induced beneficial suppressive effect on the leptin-IL-6 axis in the adipose tissue in KKAy mice is partly mediated by a trend of up-regulation of the adipose ATRAP/AT1R ratio as one of pleiotropic effects of irbesartan.

Angiopoietin-like protein 2 accelerates carcinogenesis by activating chronic inflammation and oxidative stress

Chronic inflammation has received much attention as a risk factor for carcinogenesis. We recently reported that Angiopoietin-like protein 2 (Angptl2) facilitates inflammatory carcinogenesis and metastasis in a chemically induced squamous cell carcinoma (SCC) of the skin mouse model. In particular, we demonstrated that Angptl2-induced inflammation enhanced susceptibility of skin tissues to "preneoplastic change" and "malignant conversion" in SCC development; however, mechanisms underlying this activity remain unclear. Using this model, we now report that transgenic mice overexpressing Angptl2 in skin epithelial cells (K14-Angptl2 Tg mice) show enhanced oxidative stress in these tissues. Conversely, in the context of this model, Angptl2 knockout (KO) mice show significantly decreased oxidative stress in skin tissue as well as a lower incidence of SCC compared with wild-type mice. In the chemically induced SCC model, treatment of K14-Angptl2 Tg mice with the antioxidant N-acetyl cysteine (NAC) significantly reduced oxidative stress in skin tissue and the frequency of SCC development. Interestingly, K14-Angptl2 Tg mice in the model also showed significantly decreased expression of mRNA encoding the DNA mismatch repair enzyme Msh2 compared with wild-type mice and increased methylation of the Msh2 promoter in skin tissues. Msh2 expression in skin tissues of Tg mice was significantly increased by NAC treatment, as was Msh2 promoter demethylation. Overall, this study strongly suggests that the inflammatory mediator Angptl2 accelerates chemically induced carcinogenesis through increased oxidative stress and decreased Msh2 expression in skin tissue.

IMPLICATIONS

Angptl2-induced inflammation increases susceptibility to microenvironmental changes, allowing increased oxidative stress and decreased Msh2 expression; therefore, Angptl2 might be a target to develop new strategies to antagonize these activities in premalignant tissue.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Angiotensin receptor-binding protein ATRAP/Agtrap inhibits metabolic dysfunction with visceral obesity

BACKGROUND

Metabolic disorders with visceral obesity have become a major medical problem associated with the development of hypertension, type 2 diabetes, and dyslipidemia and, ultimately, life-threatening cardiovascular and renal diseases. Adipose tissue dysfunction has been proposed as the cause of visceral obesity-related metabolic disorders, moving the tissue toward a proinflammatory phenotype.

METHODS AND RESULTS

Here we first report that adipose tissues from patients and mice with metabolic disorders exhibit decreased expression of ATRAP/Agtrap, which is a specific binding modulator of the angiotensin II type 1 receptor, despite its abundant expression in adipose tissues from normal human and control mice. Subsequently, to examine a functional role of ATRAP in the pathophysiology of metabolic disorders, we produced homozygous ATRAP deficient (Agtrap(-/-)) mice, which exhibited largely normal physiological phenotype at baseline. Under dietary high fat loading, Agtrap(-/-) mice displayed systemic metabolic dysfunction, characterized by an increased accumulation of pad fat, hypertension, dyslipidemia, and insulin resistance, along with adipose tissue inflammation. Conversely, subcutaneous transplantation of donor fat pads overexpressing ATRAP derived from Agtrap transgenic mice to Agtrap(-/-) recipient mice improved the systemic metabolic dysfunction.

CONCLUSIONS

These results demonstrate that Agtrap(-/-) mice are an effective model of metabolic disorders with visceral obesity and constitute evidence that ATRAP plays a protective role against insulin resistance, suggesting a new therapeutic target in metabolic disorders. Identification of ATRAP as a novel receptor binding modulator of adipose tissue inflammation not only has cardiovascular significance but may have generalized implication in the regulation of tissue function.

CTLA-4Ig immunotherapy of obesity-induced insulin resistance by manipulation of macrophage polarization in adipose tissues

It has been established that obesity alters the metabolic and endocrine function of adipose tissue and, together with accumulation of adipose tissue macrophages, contributes to insulin resistance. Although numerous studies have reported that shifting the polarization of macrophages from M1 to M2 can alleviate adipose tissue inflammation, manipulation of macrophage polarization has not been considered as a specific therapy. Here, we determined whether cytotoxic T-lymphocyte-associated antigen-4IgG1 (CTLA-4Ig) can ameliorate insulin resistance by induction of macrophages from proinflammatory M1 to anti-inflammatory M2 polarization in the adipose tissues of high fat diet-induced insulin-resistant mice. CTLA4-Ig treatment prevented insulin resistance by changing gene expression to M2 polarization, which increased the levels of arginase 1. Furthermore, flow cytometric analysis confirmed the alteration of polarization from CD11c (M1)- to CD206 (M2)-positive cells. Concomitantly, CTLA-4Ig treatment resulted in weight reductions of epididymal and subcutaneous adipose tissues, which may be closely related to overexpression of apoptosis inhibitors in macrophages. Moreover, proinflammatory cytokine and chemokine levels decreased significantly. In contrast, CCAAT enhancer binding protein α, peroxisome proliferator-activated receptor γ, and adiponectin expression increased significantly in subcutaneous adipose tissue. This novel mechanism of CTLA-4lg immunotherapy may lead to an ideal anti-obesity/inflammation/insulin resistance agent.

The angiotensin II AT1 receptor-associated protein Arap1 is involved in sepsis-induced hypotension

Introduction

Hypotension in septic patients results from hypovolemia, vasodilatation and hyporeactivity to vasoconstrictors, such as angiotensin II. The AT1 receptor-associated protein 1 (Arap1) is expressed in vascular smooth muscle cells and increases the surface expression of the AT1-receptor in vitro. We hypothesized that dysregulation of Arap1 may contribute to vascular hyporeactivity to angiotensin II during endotoxemia.

Methods

Arap1-deficient mice were used to assess the role of Arap1 in sepsis-induced hypotension. The isolated perfused kidney was used as an in vitro model to determine the relevance of Arap1 for vascular resistance and sensitivity to angiotensin II.

Results

During endotoxemia, mean arterial blood pressure (MAP) decreased in both genotypes, with the time course of sepsis-induced hypotension being markedly accelerated in Arap1-/- compared to +/+ mice. However, baseline MAP was similar in Arap1-/- and wildtype mice (102 ± 2 vs.103 ± 2 mmHg; telemetry measurements; n = 10; P = 0.66). Following lipopolysaccharide (LPS) injections (3 mg/kg), Arap1 expression was successively down-regulated in the wildtype mice, reaching levels below 10% of baseline expression. The endotoxemia-related decline in Arap1 expression could be recapitulated in cultured mesangial cells by incubation with pro-inflammatory cytokines, such as tumor necrosis factor α and interferon γ. Plasma renin concentration was increased in Arap1-/- mice compared to wildtype mice (66 ± 6 vs. 41 ± 4 ng AngI/ml/h; n = 23; P = 0.001), presumably contributing to preserved MAP under baseline conditions. The sensitivity of the vasculature to angiotensin II was reduced in Arap1-/- compared to +/+ mice, as determined in the isolated perfused kidney.

Conclusions

Our data suggest that down-regulation of Arap1 expression during sepsis contributes to the development of hypotension by causing reduced vascular sensitivity to angiotensin II.

Serum Angptl2 levels are independently associated with albuminuria in type 2 diabetes

BACKGROUND

Elevated serum Angptl2 levels are positively associated with the development of type 2 diabetes. We investigated whether serum Angptl2 levels are associated with diabetic nephropathy in patients with type 2 diabetes.

METHODS

Two hundred and thirty patients with type 2 diabetes and 63 healthy controls participated in this cross-sectional study. Subjects with type 2 diabetes were divided into three groups using urinary albumin-to-creatinine ratio (ACR): a normoalbuminuric group (n=57), a microalbuminuric group (n=130) and a macroalbuminuria group (n=43). Serum Angptl2 concentrations were measured by enzyme-linked immunosorbent assay.

RESULTS

Median serum (interquartile range) Angptl2 levels in control subjects and patients with type 2 diabetes with normoalbuminuria, microalbuminuria and macroalbuminuria were 24.03 (16.3-33.45), 36.14 (27.91-43.07), 44.6 (37.47-49.92), 50.19 (45.95-60.13)ng/ml (p<0.01) respectively. Angptl2 levels correlated with urinary ACR in participants with type 2 diabetes (r=0.38, p<0.01). Significant intercorrelations of Angptl2 were found with age, duration of diabetes, and fasting plasma glucose. After adjustment for significant covariates, albuminuria was still significantly associated with Angptl2 levels in type 2 diabetes (r=0.31, p<0.01).

CONCLUSIONS

Angptl2 levels are elevated in patients with type 2 diabetes with an independent association between increasing Angptl2 levels and increasing levels of albuminuria. This suggests a possible role of Angptl2 in progressive nephropathy in patients with type 2 diabetes.

Angiopoietin-like 2 promotes atherogenesis in mice

BACKGROUND

Angiopoietin like-2 (angptl2), a proinflammatory protein, is overexpressed in endothelial cells (ECs) from patients with coronary artery disease (CAD). Whether angptl2 contributes to atherogenesis is unknown. We tested the hypothesis that angptl2 promotes inflammation and leukocyte adhesion onto ECs, thereby accelerating atherogenesis in preatherosclerotic dyslipidemic mice.

METHODS AND RESULTS

In ECs freshly isolated from the aorta, basal expression of TNF-α and IL-6 mRNA was higher in 3-month-old severely dyslipidemic mice (LDLr(-/-); hApoB100(+/+) [ATX]) than in control healthy wild-type (WT) mice (P<0.05) and was increased in both groups by exogenous angptl2 (100 nmol/L). Angptl2 stimulated the adhesion of leukocytes ex vivo on the native aortic endothelium of ATX, but not WT mice, in association with higher expression of ICAM-1 and P-selectin in ECs (P<0.05). Antibodies against these endothelial adhesion molecules prevented leukocyte adhesion. Intravenous administration of angptl2 for 1 month in preatherosclerotic 3-month-old ATX mice increased (P<0.05) total cholesterol and LDL-cholesterol levels, strongly induced (P<0.05) the expression of endothelial proinflammatory cytokines and adhesion molecules while accelerating atherosclerotic lesion formation by 10-fold (P<0.05). Plasma and aortic tissue levels of angptl2 increased (P<0.05) with age and were higher in 6- and 12-month-old ATX mice than in age-matched WT mice. Angptl2 accumulated to high levels in the atherosclerotic lesions (P<0.05). Finally, angptl2 was greatly expressed (P<0.05) in ECs cultured from CAD patients, and circulating angptl2 levels were 6-fold higher in CAD patients compared with age-matched healthy volunteers.

CONCLUSIONS

Angptl2 contributes to the pathogenesis of atherosclerosis.

Association of serum angiopoietin-like protein 2 and epinephrine levels in metabolically healthy but obese individuals: In vitro and in vivo evidence

In the present study, we explored the association of serum angiopoietin-like protein 2 (ANGPTL2) levels with insulin sensitivity and serum epinephrine levels in metabolically healthy but obese (MHO) subjects. We also investigated the effects of epinephrine on ANGPTL2 expression in adipocytes in vitro. We examined the metabolic characteristics and serum ANGPTL2 and epinephrine levels in 100 non-diabetic obese postmenopausal women. Subjects were classified as MHO (n=25) or at-risk (n=25) based on the upper and lower quartiles of insulin sensitivity, respectively. Differentiated 3T3-L1 adipocytes were treated with increasing doses of epinephrine (10, 30 and 50 nM) in the presence or absence of phentolamine (10 μM), propranolol (0.3 μM), LY294002 (50 μM) or protein kinase A inhibitor fragment 6-22 amide (PKAI, 1 mM) for 24 h. We observed that serum ANGPTL2 levels were negatively correlated with insulin sensitivity (r=-0.23, P=0.021) and serum epinephrine level (r=-0.62, P<0.001) in the study subjects, with the MHO subjects displaying significantly lower serum ANGPTL2 and higher serum epinephrine levels than the at-risk subjects. Epinephrine reduced the ANGPTL2 mRNA and protein levels in differentiated 3T3-L1 adipocytes in a dose-dependent manner. Propranolol and PKAI were able to eliminate this reduction in ANGPTL2 levels whereas phentolamine and LY294002 were not. The in vitro findings indicated that epinephrine decreased ANGPTL expression at the mRNA and protein levels via the β-adrenoceptors and the PKA signaling pathway. This study suggests that β-receptor activation helps to maintain the metabolic profile of MHO individuals and prevent type 2 diabetes mellitus (T2DM) by decreasing serum ANGPTL2 levels.

Targeted deletion of fibrinogen like protein 1 reveals a novel role in energy substrate utilization

Fibrinogen like protein 1(Fgl1) is a secreted protein with mitogenic activity on primary hepatocytes. Fgl1 is expressed in the liver and its expression is enhanced following acute liver injury. In animals with acute liver failure, administration of recombinant Fgl1 results in decreased mortality supporting the notion that Fgl1 stimulates hepatocyte proliferation and/or protects hepatocytes from injury. However, because Fgl1 is secreted and detected in the plasma, it is possible that the role of Fgl1 extends far beyond its effect on hepatocytes. In this study, we show that Fgl1 is additionally expressed in brown adipose tissue. We find that signals elaborated following liver injury also enhance the expression of Fgl1 in brown adipose tissue suggesting that there is a cross talk between the injured liver and adipose tissues. To identify extra hepatic effects, we generated Fgl1 deficient mice. These mice exhibit a phenotype suggestive of a global metabolic defect: Fgl1 null mice are heavier than wild type mates, have abnormal plasma lipid profiles, fasting hyperglycemia with enhanced gluconeogenesis and exhibit differences in white and brown adipose tissue morphology when compared to wild types. Because Fgl1 shares structural similarity to Angiopoietin like factors 2, 3, 4 and 6 which regulate lipid metabolism and energy utilization, we postulate that Fgl1 is a member of an emerging group of proteins with key roles in metabolism and liver regeneration.

A molecular clock regulates angiopoietin-like protein 2 expression

Various physiological and behavioral processes exhibit circadian rhythmicity. These rhythms are usually maintained by negative feedback loops of core clock genes, namely, CLOCK, BMAL, PER, and CRY. Recently, dysfunction in the circadian clock has been recognized as an important foundation for the pathophysiology of lifestyle-related diseases, such as obesity, cardiovascular disease, and some cancers. We have reported that angiopoietin-like protein 2 (ANGPTL2) contributes to the pathogenesis of these lifestyle-related diseases by inducing chronic inflammation. However, molecular mechanisms underlying regulation of ANGPTL2 expression are poorly understood. Here, we assess circadian rhythmicity of ANGPTL2 expression in various mouse tissues. We observed that ANGPTL2 rhythmicity was similar to that of the PER2 gene, which is regulated by the CLOCK/BMAL1 complex. Promoter activity of the human ANGPTL2 gene was significantly induced by CLOCK and BMAL1, an induction markedly attenuated by CRY co-expression. We also identified functional E-boxes in the ANGPTL2 promoter and observed occupancy of these sites by endogenous CLOCK in human osteosarcoma cells. Furthermore, Cry-deficient mice exhibited arrhythmic Angptl2 expression. Taken together, these data suggest that periodic expression of ANGPTL2 is regulated by a molecular clock.

Angiopoietin-like protein 1 suppresses SLUG to inhibit cancer cell motility

Angiopoietin-like protein 1 (ANGPTL1) is a potent regulator of angiogenesis. Growing evidence suggests that ANGPTL family proteins not only target endothelial cells but also affect tumor cell behavior. In a screen of 102 patients with lung cancer, we found that ANGPTL1 expression was inversely correlated with invasion, lymph node metastasis, and poor clinical outcomes. ANGPTL1 suppressed the migratory, invasive, and metastatic capabilities of lung and breast cancer cell lines in vitro and reduced metastasis in mice injected with cancer cell lines overexpressing ANGPTL1. Ectopic expression of ANGPTL1 suppressed the epithelial-to-mesenchymal transition (EMT) by reducing the expression of the zinc-finger protein SLUG. A microRNA screen revealed that ANGPTL1 suppressed SLUG by inducing expression of miR-630 in an integrin α(1)β(1)/FAK/ERK/SP1 pathway-dependent manner. These results demonstrate that ANGPTL1 represses lung cancer cell motility by abrogating the expression of the EMT mediator SLUG.