Keishi Miyata

Angiopoietin-like Protein 2 Promotes Chronic Adipose Tissue Inflammation and Obesity-Related Systemic Insulin Resistance

Recent studies of obesity have provided new insights into the mechanisms underlying insulin resistance and metabolic dysregulation. Numerous efforts have been made to identify key regulators of obesity-linked adipose tissue inflammation and insulin resistance. We found that angiopoietin-like protein 2 (Angptl2) was secreted by adipose tissue and that its circulating level was closely related to adiposity, systemic insulin resistance, and inflammation in both mice and humans. Angptl2 activated an inflammatory cascade in endothelial cells via integrin signaling and induced chemotaxis of monocytes/macrophages. Constitutive Angptl2 activation in vivo induced inflammation of the vasculature characterized by abundant attachment of leukocytes to the vessel walls and increased permeability. Angptl2 deletion ameliorated adipose tissue inflammation and systemic insulin resistance in diet-induced obese mice. Conversely, Angptl2 overexpression in adipose tissue caused local inflammation and systemic insulin resistance in nonobese mice. Thus, Angptl2 is a key adipocyte-derived inflammatory mediator that links obesity to systemic insulin resistance.

Genetic variants at the 9p21 locus contribute to atherosclerosis through modulation of ANRIL and CDKN2A/B

UNLABELLED Genome-wide association studies (GWAS) have identified genetic variants contributing to the risk of cardiovascular disease (CVD) at the chromosome 9p21 locus. The CVD-associated region is adjacent to the two cyclin dependent kinase inhibitors (CDKN)2A and 2B and the last exons of the non-coding RNA, ANRIL. It is still not clear which of or how these transcripts are involved in the pathogenesis of atherosclerosis. OBJECTIVE We assessed the hypothesis that 9p21 locus polymorphisms influence the expression of the transcripts in the region (ANRIL, CDKN2A/B) and that these transcripts contribute to atherogenesis through the modulation of proliferation in VSMC. METHODS We genotyped 18 SNPs (r(2)<0.8 and MAF>0.05) across the region of interest: CDKN2A/B and ANRIL, encompassing the CVD-associated region. RNA and DNA were extracted from the blood of 57 volunteers (69-72 years old). Carotid ultrasound was performed in 56 subjects. CDKN2A/B and ANRIL (exons 1-2 and 17-18) expression was measured employing RT-PCR. Gene expression and cell growth were evaluated in cultured VSMC after the siRNA-mediated knock-down of ANRIL. RESULTS The risk alleles for atherosclerosis-related phenotypes were consistently associated with a lower expression of ANRIL when evaluating exons 1-2. Common carotid artery stenosis was associated with a significantly lower (P<0.01) expression of ANRIL (exons 1-2). ANRIL knock-down in VSMC caused significant variation in expression of CDKN2A/B (P<0.05) and reduction of cell growth (P<0.05) in vitro. CONCLUSION Disease-associated SNPs at the 9p21 locus predominantly affect the expression of ANRIL. Overall, our results suggest that several CVD-associated SNPs in the 9p21 locus affect the expression of ANRIL, which, in turn modulate cell growth, possibly via CDKN2A/B regulation.

Activated Endocannabinoid System in Coronary Artery Disease and Antiinflammatory Effects of Cannabinoid 1 Receptor Blockade on Macrophages

Background— Cannabinoid 1 (CB1) receptor blockade with rimonabant represents a clinical therapeutic strategy for obesity. Recently, the role of the endocannabinoid system has been described in peripheral organs. We sought to determine whether the endocannabinoid system could be involved in human atherosclerosis and whether CB1 receptor blockade could modulate proinflammatory activity in macrophages. Methods and Results— mRNA expression levels of CB1 receptor in coronary atherectomy samples were significantly higher in patients with unstable angina than in those with stable angina (3.62±2.96-fold; n=7; P<0.05). Immunoreactive area analysis of the coronary artery showed that CB1 receptor expression was greater in lipid-rich atheromatous plaques than in fibrous plaques, especially in CD68 macrophages (9.5±1.2% versus 0.6±0.6%; n=5; P<0.01). Levels of blood endocannabinoids were significantly higher in patients with coronary artery disease (n=20) than those without coronary artery disease (n=20) (median [interquartile range]: anandamide, 1.048 pmol/mL [0.687 to 1.387 pmol/mL] versus 0.537 pmol/mL [0.468 to 0.857 pmol/mL], P<0.01; 2-arachidonoyl glycerol, 13.30 pmol/mL [6.65 to 16.21 pmol/mL] versus 7.67 pmol/mL [6.39 to 10.03 pmol/mL], P<0.05). In cultured macrophages, expression of CB1 receptor was significantly increased during monocyte-macrophage differentiation (1.78±0.13-fold; n=6; P<0.01). CB1 receptor blockade in macrophages induced a significant increase in cytosolic cAMP (29.9±13.0%; n=4; P<0.01), inhibited phosphorylation of c-Jun N-terminal kinase (−19.1±12.6%, n=4; P<0.05), and resulted in a significant decrease in the production of proinflammatory mediators (interleukin-1β, −28.9±10.9%; interleukin-6, −24.8±7.6%; interleukin-8, −22.7±5.2%; tumor necrosis factor-α, −13.6±4.8%; matrix metalloproteinase-9, −16.4±3.8%; n=4 to 8; P<0.01). Conclusions— Patients with coronary artery disease demonstrated the activation of the endocannabinoid system with elevated levels of blood endocannabinoids and increased expression of CB1 receptor in coronary atheroma. CB1 receptor blockade exhibited antiinflammatory effects on macrophages, which might provide beneficial effects on atherogenesis.

The Endoplasmic Reticulum Stress-C/EBP Homologous Protein Pathway-Mediated Apoptosis in Macrophages Contributes to the Instability of Atherosclerotic Plaques

Objective—To elucidate whether and how the endoplasmic reticulum (ER) stress-C/EBP homologous protein (CHOP) pathway in macrophages is involved in the rupture of atherosclerotic plaques. Methods and Results—Increases in macrophage-derived foam cell death in coronary atherosclerotic plaques cause the plaque to become vulnerable, thus resulting in acute coronary syndrome. The ER stress–CHOP/growth arrest and DNA damage-inducible gene-153 (GADD153) pathway is induced in the macrophage-derived cells in atherosclerotic lesions and is involved in plaque formation. However, the role of CHOP in the final stage of atherosclerosis has not been fully elucidated. Many CHOP-expressing macrophages showed apoptosis in advanced ruptured atherosclerotic lesions in wild-type mice, whereas few apoptotic cells were observed in Chop−/− mice. The rupture of atherosclerotic plaques was significantly reduced in high cholesterol–fed Chop−/−/Apoe−/− mice compared with Chop+/+/Apoe−/− mice. Furthermore, using mice that underwent bone marrow transplantation, we showed that expression of CHOP in macrophages significantly contributes to the formation of ruptures. By using primary cultured macrophages, we further showed that unesterified free cholesterol derived from incorporated denatured low-density lipoprotein was accumulated in the ER and induced ER stress-mediated apoptosis in a CHOP-Bcl2-associated X protein (Bax) pathway-dependent manner. Conclusion—The ER stress-CHOP-Bax–mediated apoptosis in macrophages contributes to the instability of atherosclerotic plaques.

Macrophage-derived AIM Is endocytosed into adipocytes and decreases lipid droplets via inhibition of fatty acid synthase activity

Macrophages infiltrate adipose tissue in obesity and are involved in the induction of inflammation, thereby contributing to the development of obesity-associated metabolic disorders. Here, we show that the macrophage-derived soluble protein AIM is endocytosed into adipocytes via CD36. Within adipocytes, AIM associates with cytosolic fatty acid synthase (FAS), thereby decreasing FAS activity. This decreases lipid droplet size, stimulating the efflux of free fatty acids and glycerol from adipocytes. As an additional consequence of FAS inhibition, AIM prevents preadipocyte maturation. In vivo, the increase in adipocyte size and fat weight induced by high-fat diet (HFD) was accelerated in AIM-deficient (AIM(-)(/-)) mice compared to AIM(+/+) mice. Moreover, injection of recombinant AIM in AIM(-)(/-) mice suppresses the increase in fat mass induced by HFD. Interestingly, metabolic rates are comparable in AIM(-)(/-) and AIM(+/+) mice, suggesting that AIM specifically influences adipocyte status. Thus, this AIM function in adipocytes may be physiologically relevant to obesity progression.

Distinct Roles of Ephrin-B2 Forward and EphB4 Reverse Signaling in Endothelial Cells

Objective—The transmembrane ligand ephrin-B2 and its receptor tyrosine kinase EphB4 are specifically expressed on arterial and venous endothelial cells, respectively, and bidirectional signals mediated by both proteins play an important role in vascular development. However, how such bidirectional signals are required for cell-cell adhesion or repulsion remains unclear. Methods and Results—Using a cell line and sorted primary endothelial cells, we show that ephrin-B2 forward signaling through the EphB4 receptor inhibits cell adhesion, whereas EphB4 reverse signaling by the transmembrane ephrin-B2 ligand does not. Cell migration is also inhibited on immobilized ephrin-B2-Fc but not on EphB4-Fc protein. Conclusions—Ephrin-B2 forward signaling and EphB4 reverse signaling differentially affect cell adhesion and migration between arterial and venous endothelial cells.

Angiopoietin-like Protein 2 Is an Important Facilitator of Inflammatory Carcinogenesis and Metastasis

Chronic inflammation plays important roles at different stages of cancer development, including carcinogenesis, tumor invasion, and metastasis, but molecular mechanisms linking inflammation to cancer development have not been fully clarified. Here, we report that expression of angiopoietin-like protein 2 (Angptl2), recently identified as a chronic inflammation mediator, is highly correlated with the frequency of carcinogenesis in a chemically induced skin squamous cell carcinoma (SCC) mouse model. Furthermore, Angptl2 expression in SCC is highly correlated with the frequency of tumor cell metastasis to distant secondary organs and lymph nodes. When SCC was induced in transgenic mice expressing Angptl2 in skin epithelial cells, epithelial-to-mesenchymal transitions in SCC as well as tumor angiogenesis and lymphangiogenesis were significantly increased, resulting in increased tumor cell metastasis and shortened survival compared with wild-type mice. Conversely, in a chemically induced SCC mouse model, carcinogenesis and metastasis were markedly attenuated in Angptl2 knockout mice, resulting in extended survival compared with wild-type mice. Overall, we propose that Angptl2 contributes to increased carcinogenesis and metastasis and represents a novel target to antagonize these pathologies.

Tumor cell-derived angiopoietin-like protein ANGPTL2 is a critical driver of metastasis

Strategies to inhibit metastasis have been mainly unsuccessful in part due to insufficient mechanistic understanding. Here, we report evidence of critical role for the angiopoietin-like protein 2 (ANGPTL2) in metastatic progression. In mice, Angptl2 has been implicated in inflammatory carcinogenesis but it has not been studied in human tumors. In patients with lung cancer, elevated levels of ANGPTL2 expression in tumor cells within the primary tumor were associated with a reduction in the period of disease-free survival after surgical resection. Transcription factors NFATc, ATF2, and c-Jun upregulated in aggressive tumor cells promoted increased Angptl2 expression. Most notably, tumor cell-derived ANGPTL2 increased in vitro motility and invasion in an autocrine/paracrine manner, conferring an aggressive metastatic tumor phenotype. In xenograft mouse models, tumor cell-derived ANGPTL2 accelerated metastasis and shortened survival whereas attenuating ANGPTL2 expression in tumor cells-blunted metastasis and extended survival. Overall, our findings showed that tumor cell-derived ANGPTL2 drives metastasis and provided an initial proof of concept for blockade of its action as a strategy to antagonize the metastatic process.

Macrophage-Derived Angiopoietin-Like Protein 2 Accelerates Development of Abdominal Aortic Aneurysm

Objective—Recently, we reported that angiopoietin-like protein 2 (Angptl2) functions in various chronic inflammatory diseases. In the present study, we asked whether Angptl2 and its associated chronic inflammation contribute to abdominal aortic aneurysm (AAA). Methods and Results—Immunohistochemistry revealed that Angptl2 is abundantly expressed in infiltrating macrophages within the vessel wall of patients with AAA and in a CaCl2-induced AAA mouse model. When Angptl2-deficient mice were used in the mouse model, they showed decreased AAA development compared with wild-type mice, as evidenced by reduction in aneurysmal size, less severe destruction of vessel structure, and lower expression of proinflammatory cytokines and matrix metalloproteinase-9. However, no difference in the number of infiltrating macrophages within the aortic aneurysmal vessel wall was observed between genotypes. AAA development was also significantly suppressed in wild-type mice that underwent Angptl2-deficient bone marrow transplantation. Expression levels of proinflammatory cytokines and metalloproteinase-9 in Angptl2-deficient macrophages were significantly decreased, and those decreases were rescued by treatment of Angptl2 deficient macrophages with exogenous Angptl2. Conclusion—Macrophage-derived Angptl2 contributes to AAA development by inducing inflammation and degradation of extracellular matrix in the vessel wall, suggesting that targeting the Angptl2-induced inflammatory axis in macrophages could represent a new strategy for AAA therapy.

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.