Bei Cheng

Chlamydia pneumoniae induces macrophage-derived foam cell formation via PPAR α and PPAR γ-dependent pathways

In the presence of low density lipoprotein (LDL), Chlamydia pneumoniae induces macrophage‐derived foam cell formation, a typical pathological feature of early atherosclerosis. However, its mechanism has not been fully understood. Peroxisome proliferator‐activated receptors (PPARs) are key regulators of macrophage lipid metabolism. This study therefore investigated the role that PPAR α and PPAR γ may play a role in C. pneumoniae‐induced foam cell formation. Oil Red O staining and Lipid mass quantification showed that LDL‐treated THP‐1 macrophages infected with high doses of C. pneumoniae (5 × 105 and 1 × 106 IFU) resulted in the large accumulation of lipid droplets and markedly increased the ratio of intracellular cholesteryl ester (CE) to total cholesterol (TC) (>50%). The results of RT‐PCR and Western blot indicated that C. pneumoniae infection dose‐dependently suppressed the expression of PPAR α and PPAR γ at mRNA and protein levels in LDL‐treated THP‐1 macrophages. PPAR α (fenofibrate) and PPAR γ (rosiglitazone) agonists, inhibited the accumulation of intracellular CE by C. pneumoniae in a dose‐dependent manner. Furthermore, C. pneumoniae‐induced foam cell formation was significantly suppressed by higher doses of fenofibrate (20 and 50 μM) and rosiglitazone (10 and 20 μM). These results first reveal that C. pneumoniae induces foam cell formation via PPAR α and PPAR γ‐dependent pathway, which may contribute to its pro‐atherogenic properties.

Chlamydia pneumoniae disturbs cholesterol homeostasis in human THP-1 macrophages via JNK-PPARγ dependent signal transduction pathways

Chlamydia pneumoniae (C. pneumoniae) induces macrophage-derived foam cell formation, a hallmark of early atherosclerosis, in the presence of low density lipoprotein (LDL). However, its mechanisms have yet to be elucidated. In this study we examined the effects of live, heat-killed and UV-inactivated C. pneumoniae on cholesterol metabolism in THP-1-derived macrophages and the role of c-Jun NH(2) terminal kinase (JNK), which may participate in the C. pneumoniae-induced disruption of intracellular cholesterol homeostasis. We investigated whether SP600125, a special JNK inhibitor, affects the expression of peroxisome proliferator-activated receptor gamma (PPARγ), and also its downstream target genes Acyl-CoA cholesterol acyltransferase-1 (ACAT1), ATP-binding cassette transporter A1 and G1 (ABCA1/G1) in human THP-1 macrophages infected with C. pneumoniae. In this paper we found that both live and inactivated C. pneumoniae infection induce intracellular cholesterol accumulation and foam cell formation. C. pneumoniae infection increased the expression of ACAT1 and decreased the expression of ABCA1/G1, all of which facilitated cholesterol accumulation and promoted macrophage-derived foam cell formation. However, these responses were attenuated by SP600125 in a dose-dependent manner. These results demonstrate for the first time that both live and inactivated C. pneumoniae infections disturb cholesterol homeostasis in human THP-1 macrophages and C. pneumoniae infection disturbs cholesterol homeostasis via JNK-PPARγ dependent signal transduction pathways.

Protective effect of Astragalus polysaccharides on ATP binding cassette transporter A1 in THP-1 derived foam cells exposed to tumor necrosis factor-alpha.

Astragalus polysaccharide (APS), the main extract from the traditional Chinese medicinal herb Astragalus membranaceus, has been reported to benefit the treatment of immune‐inflammatory diseases and metabolic disorders. In atherosclerotic plaques, proinflammatory cytokines exert adverse effects on lipids thereby aggravating atherosclerosis. Recent evidence shows that tumor necrosis factor‐alpha (TNF‐α) can down‐regulate the expression of ATP‐binding cassette transporter A1 (ABCA1), which plays a vital role in reverse cholesterol transport and determines the process of atherosclerosis. In the present study, the effects of APS on ABCA1 expression, cholesterol effluent rate and total cholesterol content of THP‐1 derived foam cells exposed to TNF‐α were investigated. Compared with the foam cells exposed to TNF‐α, ABCA1 expression was promoted in the presence of APS. Consequently the cholesterol effluent rate increased and the total cholesterol content decreased significantly. TNF‐α could enhance the activity of nuclear factor‐kappa B (NF‐κB) in the foam cells. This effect could be attenuated by APS. These findings suggest that APS could protect ABCA1 against the lesion of TNF‐α in THP‐1 derived foam cells, which may contribute to its antiatherosclerotic properties. Copyright

Chlamydia pneumoniae induces macrophage-derived foam cell formation by up-regulating acyl-coenzyme A: cholesterol acyltransferase 1

In macrophages, the accumulation of cholesteryl esters synthesized by acyl-coenzyme A: cholesterol acyltransferase 1(ACAT1) plays a crucial role in foam cell formation, a hallmark of early atherosclerotic lesions. It is suggested that Chlamydia pneumoniae (C. pneumoniae) induces foam cell formation. However, the mechanism of foam cell formation induced by C. pneumoniae has not been fully elucidated. In this study, we found that C. pneumoniae increased the expression of acyl-coenzyme A: cholesterol acyltransferase 1(ACAT1) mRNA and protein in a dose-dependent manner in THP-1-derived macrophages exposed to low density lipoprotein (LDL). In addition, C. pneumoniae dose-dependently suppressed the expression of peroxisome proliferator-activated receptor gamma (PPAR gamma) mRNA and protein. Rosiglitazone, a specific PPAR gamma agonist, not only dose-dependently alleviated the down-regulation of PPAR gamma expression by C. pneumoniae infection, but also dose-dependently inhibited the C. pneumoniae-induced ACAT1 expression. Furthermore, higher doses of rosiglitazone (10 and 20 microM) suppressed the C. pneumoniae-induced foam cell formation from morphological (Oil red O staining) and biochemical (zymochemistry method) criteria. These results first demonstrate that C. pneumoniae induces macrophage-derived foam cell formation by up-regulating ACAT1 expression via PPAR gamma-dependent pathway, which may contribute to its pro-atherogenic properties.

Insulin induces human acyl-coenzyme A: cholesterol acyltransferase1 gene expression via MAP kinases and CCAAT/enhancer-binding protein α.

Insulin resistance characterized by hyperinsulinemia is associated with increased risk of atherosclerosis. Acyl‐coenzyme A: cholesterol acyltransferase (ACAT) is an intracellular enzyme involved in cellular cholesterol homeostasis and in atherosclerotic foam cell formation. To investigate the relationship between hyperinsulinemia and atherosclerosis, we investigated whether insulin induced ACAT1 gene expression and found that insulin up‐regulated ACAT1 mRNA, protein and enzyme activity in human THP‐1 cells and THP‐1–derived macrophages. Moreover, luciferase assays revealed that insulin enhanced the ACAT1 gene P1 promoter activity but not the P7 promoter. To explore the molecular mechanisms involved, deletion analysis of the human ACAT1 P1 promoter revealed an insulin response element (IRE) upstream of the P1 promoter (from −603 to −580), EMSA experiments demonstrated that CCAAT/enhancer binding protein α(C/EBPα) bound to the P1 promoter IRE. Insulin‐induced ACAT1 upregulation was blocked by the presence of PD98059 (an inhibitor of extracellular signal‐regulated kinase, ERK) and SB203580 (an inhibitor of p38 mitogen‐activated protein kinase, p38MAPK) but not by Wortmannin (an inhibitor of phosphatidylinositol 3‐kinase, PI3K) or U73122 (an inhibitor of phospholipase C‐γ, PLCγ). These studies demonstrate that insulin promotes ACAT1 gene expression at the transcriptional level. The molecular mechanism of insulin action is mediated via interaction of the functional IRE upstream of the ACAT1 P1 promoter with C/EBPα and is MAPK‐dependent. J. Cell. Biochem. 114: 2188–2198, 2013.

MAPK-PPARα/γ signal transduction pathways are involved in Chlamydia pneumoniae-induced macrophage-derived foam cell formation.

Chlamydia pneumoniae (C. pneumoniae) is now widely accepted as an independent risk of atherosclerosis development. In this paper, our results showed that C. pneumoniae infection significantly increased the number of foam cells in LDL-treated THP-1 macrophages. C-Jun NH2 terminal kinase (JNK1/2) inhibitor SP600125 and extracellular signal-regulated kinase (ERK1/2) inhibitor PD98059 strongly inhibited C. pneumoniae-induced accumulation of lipid droplet, whereas p38 inhibitor SB203580 had no obvious effect on lipid accumulation. Furthermore, we found that C. pneumoniae not only stimulated the phosphorylation of Mitogen-activated protein kinase (MAPK) including JNK1/2, ERK1/2 and p38 but also down-regulated the expression of peroxisome proliferator-activated receptors (PPARγ and PPARα) at mRNA and protein levels. However, the phosphorylation of JNK1/2, ERK1/2 and p38 MAPK by C. pneumoniae was substantially reversed after PPARγ agonist (rosiglitazone) or PPARα agonist (fenofibrate) treatment while PPARγ inhibitor (GW9662) and PPARα antagonist (MK886) enhanced C. pneumoniae-induced phosphorylation of JNK1/2, ERK1/2 and p38. In addition, we demonstrated that C. pneumoniae-induced PPARγ and PPARα down-regulation were significantly suppressed by JNK1/2 inhibitor (SP600125) and ERK1/2 inhibitor (PD98059), but not p38 inhibitor (SB203580). These results first declare that MAPK-PPARα/γ reciprocal signal pathways are involved in C. pneumoniae, which induces foam cell formation, thus facilitating atherogenesis.

PTX3 Is Located at the Membrane of Late Apoptotic Macrophages and Mediates the Phagocytosis of Macrophages

Apoptotic macrophages are removed by neighboring phagocytes (efferocytosis), which is an important event in advanced atherosclerosis. Recent reports have elucidated some key molecular regulators in efferocytosis including complement C1q, MFGE8, and MERTK. However, it remains unknown whether the long pentraxin 3 (PTX3), which is an important molecule that is involved in apoptotic cell clearance in the immune response, plays a part in efferocytosis during advanced atherosclerosis. In this study, we modeled macrophage apoptosis in advanced plaques by incubating macrophages (peritoneal macrophages isolated from C57 mice) with free cholesterol (free cholesterol-induced apoptotic macrophages, FC-AMs). FC-AMs were added to a monolayer of fresh phagocytes to study the engulfment response. We observed that PTX3 was mainly located at the membrane of late apoptotic macrophages. The anti-PTX3 monoclonal Ab 16B5 inhibited the engulfment of late apoptotic macrophages by phagocytes in a dose-dependent manner (from 14.63% inhibition at 5 μg/ml to 26.19% inhibition at 50 μg/ml). These results suggest that PTX3 located at the membrane of late apoptotic macrophages mediates their phagocytosis by phagocytes in a cell model of advanced atherosclerosis.

Ghrelin inhibits foam cell formation via simultaneously down-regulating the expression of acyl-coenzyme A:cholesterol acyltransferase 1 and up-regulating adenosine triphosphate-binding cassette transporter A1

BACKGROUND Ghrelin, an endogenous ligand of the growth hormone secretagogue receptor (GHS-R), revealed cardioprotective effects in both experimental models and human. There is far less information on the mechanisms that produce antiatherogenic effects. We assessed the expression of acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT-1) and adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1), which have been implicated in regulating cellular cholesterol homeostasis and therefore play critical roles in foam cell formation, in THP-1-derived foam cells in the presence of various concentration of ghrelin. METHODS After 48 h of culture in the presence of phorbol myristate acetate, THP-1 monocytes differentiated to macrophages. After another 24 h of culture with ox-LDL, the differentiated cells transformed to foam cells. Different concentrations of ghrelin and other intervention factors were added, respectively. The expression of ACAT-1 and ABCA1 was detected by a technique in molecular biology. The content of cellular cholesterol was measured by zymochemistry via a fluorospectrophotometer. RESULTS Ghrelin could down-regulate the expression of ACAT-1 and up-regulate the expression of ABCA1 in a dose-dependent manner simultaneously. Ghrelin also decreased cellular cholesterol content and increased cholesterol efflux. These effects could be abolished by the specific antagonist of GHS-R and a peroxisome proliferator-activated receptor γ (PPARγ)-specific inhibitor, respectively. CONCLUSIONS The results suggest that ghrelin inhibited foam cell formation via simultaneously down-regulating the expression of ACAT-1 and up-regulating ABCA1. Those effects may be achieved via pathways involving GHS-R and PPARγ.

RTEF-1 protects against oxidative damage induced by H2O2 in human umbilical vein endothelial cells through Klotho activation

Oxidative stress is a main risk factor of vascular aging, which may lead to age-associated diseases. Related transcriptional enhancer factor-1 (RTEF-1) has been suggested to regulate many genes expression which are involved in the endothelial angiogenesis and vasodilation. However, whether RTEF-1 has a direct role in anti-oxidation and what specific genes are involved in RTEF-1-driven anti-oxidation have not been elucidated. In this study, we found that overexpressing RTEF-1 in H2O2-treated human umbilical vein endothelial cells decreased senescence-associated-β-galactosidase (SA-β-gal)-positive cells and G0/G1 cells population. The expressions of p53 and p21 were decreased in H2O2-treated RTEF-1 o/e human umbilical vein endothelial cells. However, specific small interfering RNA of RTEF-1 totally reversed the anti-oxidation effect of RTEF-1 and inhibited RTEF-1-induced decreased p53 and p21 expressions. It demonstrated that RTEF-1 could protect cells from H2O2-induced oxidative damage. In addition, we demonstrated that RTEF-1 could up-regulate Klotho gene expression and activate its promoter. Furthermore, Klotho small interfering RNA significantly blocked RTEF-1-driven endothelial cell protection from H2O2-induced oxidative damage and increased p53 and p21 expressions. These results reveal that RTEF-1 is a potential anti-oxidation gene and can prevent H2O2-induced endothelial cell oxidative damage by activating Klotho.

Pentraxin 3 (PTX3) promoter methylation associated with PTX3 plasma levels and neutrophil to lymphocyte ratio in coronary artery disease

Background Pentraxin 3 (PTX3) is expressed in the heart under inflammatory conditions and plays an important role in atherogenesis. Patients with increased PTX3 levels may suffer from higher rates of cardiac events. Regulation of specific genes by promoter methylation is important in atherogenesis. The factors influencing PTX3 levels and the association between epigenetics and PTX3 levels have not been investigated. Methods Blood samples were collected from 64 patients admitted to the Department of Cardiology, 35 who had coronary artery disease (CAD), and 29 who were CAD-free. Plasma levels of PTX3 were measured by ELISA. PTX3 promoter methylation was evaluated via methyl-specific PCR. The severity of coronary artery lesion was evaluated by angiography. Results The level of PTX3 promoter methylation in the CAD group was 62.69% ± 20.57%, significantly lower than that of the CAD-free group, which was 72.45% ± 11.84% (P = 0.03). Lower PTX3 promoter methylation levels in the CAD group were associated with higher plasma PTX3 concentrations (r = −0.29, P = 0.02). Furthermore, lower PTX3 promoter methylation levels were associated with higher neutrophil to lymphocyte ratio (NLR) in men (r = −0.58, P = 0.002). Conclusions The present study provides new evidence that methylation of the PTX3 promoter is associated with PTX3 plasma levels and NLR in coronary artery disease. This study also shows that modification of epigenetics by chronic inflammation might be a significant molecular mechanism in the atherosclerotic processes that influence plasma PTX3 concentrations.