Characterization of fluorescent NBD-cholesterol efflux in THP-1-derived macrophages

CTRP9 prevents atherosclerosis progression through changing autophagic status of macrophages by activating USP22 mediated-de-ubiquitination on Sirt1 in vitro

BACKGROUND

Atherosclerosis (AS) is commonly regarded as a key driver accounted for the leading causes of morbidity and mortality among cardiovascular and cerebrovascular diseases. A growing body of evidence indicates that autophagy in macrophages involved in AS might be a potential therapeutic target. C1q/TNF-related protein 9 (CTRP9) has been proven to delay the progression of cardiovascular diseases. However, the relations between CTRP9 and Sirt1, as well as their effects on macrophages autophagy have not been fully explored.

METHODS

Macrophages were differentiated from mononuclear cells collected from peripheral blood samples of healthy donors. The in vitro AS models were constructed by ox-LDL treatment. Cell viability was determined by CCK-8 assay. Immunofluorescence assay of LC3 was implemented for evaluating autophagy activity. Oil Red O staining was performed for lipid accumulation detection. ELISA, cholesterol concentration assay and cholesterol efflux analysis were conducted using commercial kits. Cycloheximide assay was implemented for revealing protein stability. RT-qPCR was used for mRNA expression detection, and western blotting was performed for protein level monitoring.

RESULTS

CTRP9 attenuated impaired cell viability, autophagy inhibition and increased lipid accumulation induced by ox-LDL. Moreover, CTRP9 maintained Sirt1 protein level through enhancing its stability through de-ubiquitination, which was mediated by upregulated USP22 level. CRTP9 exerted its protective role in promoting autophagy and reducing lipid accumulation through the USP22/Sirt1 axis.

CONCLUSION

Collectively, CTRP9 alleviates lipid accumulation and facilitated the macrophages autophagy by upregulating USP22 level and maintaining Sirt1 protein expression, thereby exerting a protective role in AS progression in vitro.

Essential oil from Fructus Alpinia zerumbet ameliorates atherosclerosis by activating PPARγ-LXRα-ABCA1/G1 signaling pathway

BACKGROUND

Atherosclerosis (AS) is a progressive chronic disease. Currently, cardiovascular diseases (CVDs) caused by AS is responsible for the global increased mortality. Yanshanjiang as miao herb in Guizhou of China is the dried and ripe fruit of Fructus Alpinia zerumbet. Accumulated evidences have confirmed that Yanshanjiang could ameliorate CVDs, including AS. Nevertheless, its effect and mechanism on AS are still largely unknown.

PURPOSE

To investigate the role of essential oil from Fructus Alpinia zerumbet (EOFAZ) on AS, and the potential mechanism.

METHODS

A high-fat diet (HFD) ApoE-/- mice model of AS and a oxLDL-induced model of macrophage-derived foam cells (MFCs) were reproduced to investigate the pharmacological properties of EOFAZ on AS in vivo and foam cell formation in vitro, respectively. The underlying mechanisms of EOFAZ were investigated using Network pharmacology and molecular docking. EOFAZ effect on PPARγ protein stability was measured using a cellular thermal shift assay (CETSA). Pharmacological agonists and inhibitors and gene interventions were employed for clarifying EOFAZ's potential mechanism.

RESULTS

EOFAZ attenuated AS progression in HFD ApoE-/- mice. This attenuation was manifested by the reduced aortic intima plaque development, increased collagen content in aortic plaques, notable improvement in lipid profiles, and decreased levels of inflammatory factors. Moreover, EOFAZ inhibited the formation of MFCs by enhancing cholesterol efflux through activiting the PPARγ-LXRα-ABCA1/G1 pathway. Interestingly, the pharmacological knockdown of PPARγ impaired the beneficial effects of EOFAZ on MFCs. Additionally, our results indicated that EOFAZ reduced the ubiquitination degradation of PPARγ, and the chemical composition of EOFAZ directly bound to the PPARγ protein, thereby increasing its stability. Finally, PPARγ knockdown mitigated the protective effects of EOFAZ on AS in HFD ApoE-/- mice.

CONCLUSION

These findings represent the first confirmation of EOFAZ's in vivo anti-atherosclerotic effects in ApoE-/- mice. Mechanistically, its chemical constituents can directly bind to PPARγ protein, enhancing its stability, while reducing PPARγ ubiquitination degradation, thereby inhibiting foam cell formation via activation of the PPARγ-LXRα-ABCA1/G1 pathway. Simultaneously, EOFAZ could ameliorates blood lipid metabolism and inflammatory microenvironment, thus synergistically exerting its anti-atherosclerotic effects.

PLK1 promotes cholesterol efflux and alleviates atherosclerosis by up-regulating ABCA1 and ABCG1 expression via the AMPK/PPARγ/LXRα pathway

Polo-like kinase 1 (PLK1) is a serine/threonine kinase involving lipid metabolism and cardiovascular disease. However, its role in atherogenesis has yet to be determined. The aim of this study was to observe the impact of PLK1 on macrophage lipid accumulation and atherosclerosis development and to explore the underlying mechanisms. We found a significant reduction of PLK1 expression in lipid-loaded macrophages and atherosclerosis model mice. Lentivirus-mediated overexpression of PLK1 promoted cholesterol efflux and inhibited lipid accumulation in THP-1 macrophage-derived foam cells. Mechanistic analysis revealed that PLK1 stimulated the phosphorylation of AMP-activated protein kinase (AMPK), leading to activation of the peroxisome proliferator-activated receptor γ (PPARγ)/liver X receptor α (LXRα) pathway and up-regulation of ATP binding cassette transporter A1 (ABCA1) and ABCG1 expression. Injection of lentiviral vector expressing PLK1 increased reverse cholesterol transport, improved plasma lipid profiles and decreased atherosclerotic lesion area in apoE-deficient mice fed a Western diet. PLK1 overexpression also facilitated AMPK and HSL phosphorylation and enhanced the expression of PPARγ, LXRα, ABCA1, ABCG1 and LPL in the aorta. In summary, these data suggest that PLK1 inhibits macrophage lipid accumulation and mitigates atherosclerosis by promoting ABCA1- and ABCG1-dependent cholesterol efflux via the AMPK/PPARγ/LXRα pathway.

Defects in a liver-bone axis contribute to hepatic osteodystrophy disease progression

Hepatic osteodystrophy (HOD) is a metabolic bone disease that is often associated with chronic liver disease and is marked by bone loss. Here, we demonstrate that hepatic expression of the phosphatase PP2Acα is upregulated during HOD, leading to the downregulation of expression of the hepatokine lecithin-cholesterol acyltransferase (LCAT). Loss of LCAT function markedly exacerbates the bone loss phenotype of HOD in mice. In addition, we found that alterations in cholesterol levels are involved in the regulation of osteoblast and osteoclast activities. We also found that LCAT improves liver function and relieves liver fibrosis in the mouse HOD model by promoting reversal of cholesterol transport from the bone to the liver. In summary, defects in a liver-bone axis occur during HOD that can be targeted to ameliorate disease progression.

High levels of oxidized fatty acids in HDL impair the antioxidant function of HDL in patients with diabetes

AIMS

Previous studies demonstrate that the antioxidant functions of high-density lipoprotein (HDL) are impaired in diabetic patients. The composition of HDL plays an important role in maintaining the normal functionality of HDL. In this study, we compared the levels of oxidized fatty acids in HDL from diabetic subjects and non-diabetic healthy controls, aiming to investigate the role of oxidized fatty acids in the antioxidant property of HDL.

METHODS

HDL was isolated from healthy subjects (n=6) and patients with diabetes (n=6, hemoglobin A1c ≥ 9%, fasting glucose ≥ 7 mmol/L) using a dextran sulfate precipitation method. Cholesterol efflux capacity mediated by HDL was measured on THP-1 derived macrophages. The antioxidant capacity of HDL was evaluated with dichlorofluorescein-based cellular assay in human aortic endothelial cells. Oxidized fatty acids in HDL were determined by liquid chromatography-tandem mass spectrometry. The correlations between the levels of oxidized fatty acids in HDL and the endothelial oxidant index in cells treated with HDLs were analyzed through Pearson's correlation analyses, and the effects of oxidized fatty acids on the antioxidant function of HDL were verified in vitro.

RESULTS

The cholesterol efflux capacity of HDL and the circulating HDL-cholesterol were similar in diabetic patients and healthy controls, whereas the antioxidant capacity of HDL was significantly decreased in diabetic patients. There were higher levels of oxidized fatty acids in HDL isolated from diabetic patients, which were strongly positively correlated with the oxidant index of cells treated with HDLs. The addition of a mixture of oxidized fatty acids significantly disturbed the antioxidant activity of HDL from healthy controls, while the apolipoprotein A-I mimetic peptide D-4F could restore the antioxidant function of HDL from diabetic patients.

CONCLUSION

HDL from diabetic patients displayed substantially impaired antioxidant activity compared to HDL from healthy subjects, which is highly correlated with the increased oxidized fatty acids levels in HDL.

Spectrally and Time-Resolved Fluorescence Imaging of 22-NBD-Cholesterol in Human Peripheral Blood Mononuclear Cells in Chronic Kidney Disease Patients

The interaction of the fluorescent probe 22-NBD-cholesterol with membranes of human peripheral blood mononuclear cells (PBMC) was tested by time- and spectrally resolved fluorescence imaging to monitor the disturbance of lipid metabolism in chronic kidney disease (CKD) and its treatment with statins. Blood samples from healthy volunteers (HV) and CKD patients, either treated or untreated with statins, were compared. Spectral imaging was done using confocal microscopy at 16 spectral channels in response to 458 nm excitation. Time-resolved imaging was achieved by time-correlated single photon counting (TCSPC) following excitation at 475 nm. The fluorescence of 22-NBD-cholesterol was mostly integrated into plasmatic membrane and/or intracellular membrane but was missing from the nuclear region. The presence of two distinct spectral forms of 22-NBD-cholesterol was uncovered, with significant variations between studied groups. In addition, two fluorescence lifetime components were unmasked, changing in CKD patients treated with statins. The gathered results indicate that 22-NBD-cholesterol may serve as a tool to study changes in the lipid metabolism of patients with CKD to monitor the effect of statin treatment.

Stearoyl-CoA desaturase-1 impairs the reparative properties of macrophages and microglia in the brain

Failure of remyelination underlies the progressive nature of demyelinating diseases such as multiple sclerosis. Macrophages and microglia are crucially involved in the formation and repair of demyelinated lesions. Here we show that myelin uptake temporarily skewed these phagocytes toward a disease-resolving phenotype, while sustained intracellular accumulation of myelin induced a lesion-promoting phenotype. This phenotypic shift was controlled by stearoyl-CoA desaturase-1 (SCD1), an enzyme responsible for the desaturation of saturated fatty acids. Monounsaturated fatty acids generated by SCD1 reduced the surface abundance of the cholesterol efflux transporter ABCA1, which in turn promoted lipid accumulation and induced an inflammatory phagocyte phenotype. Pharmacological inhibition or phagocyte-specific deficiency of Scd1 accelerated remyelination ex vivo and in vivo. These findings identify SCD1 as a novel therapeutic target to promote remyelination.

Role of Neutral Sphingomyelinase-2 (NSM 2) in the Control of T Cell Plasma Membrane Lipid Composition and Cholesterol Homeostasis

The activity of neutral sphingomyelinase-2 (NSM2) to catalyze the conversion of sphingomyelin (SM) to ceramide and phosphocholine at the cytosolic leaflet of plasma membrane (PM) is important in T cell receptor (TCR) signaling. We recently identified PKCζ as a major NSM2 downstream effector which regulates microtubular polarization. It remained, however, unclear to what extent NSM2 activity affected overall composition of PM lipids and downstream effector lipids in antigen stimulated T cells. Here, we provide a detailed lipidomics analyses on PM fractions isolated from TCR stimulated wild type and NSM2 deficient (ΔNSM) Jurkat T cells. This revealed that in addition to that of sphingolipids, NSM2 depletion also affected concentrations of many other lipids. In particular, NSM2 ablation resulted in increase of lyso-phosphatidylcholine (LPC) and lyso-phosphatidylethanolamine (LPE) which both govern PM biophysical properties. Crucially, TCR dependent upregulation of the important T cell signaling lipid diacylglycerol (DAG), which is fundamental for activation of conventional and novel PKCs, was abolished in ΔNSM cells. Moreover, NSM2 activity was found to play an important role in PM cholesterol transport to the endoplasmic reticulum (ER) and production of cholesteryl esters (CE) there. Most importantly, CE accumulation was essential to sustain human T cell proliferation. Accordingly, inhibition of CE generating enzymes, the cholesterol acetyltransferases ACAT1/SOAT1 and ACAT2/SOAT2, impaired TCR driven expansion of both CD4⁺ and CD8⁺ T cells. In summary, our study reveals an important role of NSM2 in regulating T cell functions by its multiple effects on PM lipids and cholesterol homeostasis.

Oligomeric proanthocyanidins and epigallocatechin gallate aggravate autophagy of foam cells through the activation of Class III PI3K/Beclin1-complex mediated cholesterol efflux

Foam cells are specialized types of cells which predominate the necrotic core of atherosclerotic plaque. Recently, autophagy-mediated cholesterol efflux from foam cells has been proposed as a beneficial therapy for atherosclerosis. The purpose of this study was to delineate the underlying molecular mechanism of oligomeric proanthocyanidins (OPC) and epigallocatechin gallate (EGCG) induced autophagy of foam cells and associated cholesterol efflux. The oxidized low-density lipoprotein induced foam cells demonstrated impaired autophagy flux through the downregulated expressions of LC3BII/LC3BI, autophagy related gene-5, Class III phosphoinositide 3 kinase (Class III PI3K), Beclin1, ABCA1, and ABCG1 with concomitant increase in the expressions of protein 62, Class I phosphoinositide 3 kinase, Akt, and mammalian target of rapamycin. However, these effects were significantly abolished by treatment with OPC and EGCG through activation of autophagy flux via Class III PI3K/Beclin1 and with upregulated expression of transporter proteins ABCA1 and ABCG1. Furthermore, the cholesterol efflux process in the foam cells was activated by lysosomal acid lipase and cathepsin D facilitated lipolysis of lipid droplets. Taken together, our data demonstrate that OPC and EGCG treatment stimulated the coordinated activation of autophagy and cholesterol efflux through Class III PI3K/Beclin1 pathway in foam cells, suggesting a promising therapeutic strategy against atherosclerosis.

Association Between ApoA-I (Apolipoprotein A-I) Immune Complexes and Adverse Cardiovascular Events-Brief Report

OBJECTIVE

The immune response is linked to the progression of atherosclerotic cardiovascular disease (CVD). Free autoantibodies targeting ApoA-I (apolipoprotein A-I) have been identified as a component of the inflammatory milieu in patients and have a moderate association with CVD progression. Based on the presence of these antibodies and the high concentration of circulating ApoA-I, we hypothesized that antibodies bound to ApoA-I as an immune complex would be predictive of incident adverse CVD outcomes. Approach and Results: The presence of ApoA-I/IgG immune complexes (ICs) in plasma was confirmed by ELISA in 3 subject cohorts. Characterization of the protein components of ApoAI/IgG ICs indicate that ICs are not correlated with total ApoA-I concentration and are enriched in the anti-inflammatory subclass, IgG4, relative to total plasma IgG (>30% versus 6%). In 359 patients with coronary artery disease (CAD), there were 71 incident adverse CVD events (death, myocardial infarction, and stroke) during a median 4.1-year follow-up. In Cox proportional hazard regression analysis, low levels of ApoA-I/IgG ICs were independent predictors of adverse cardiovascular outcomes after adjustment for age, sex, diabetes mellitus, estimated glomerular filtration rate, presence of obstructive CAD, heart failure, total cholesterol, and HDL (high-density lipoprotein) cholesterol (adjusted hazard ratio of 1.90 [95% CI, 1.03-3.49; P=0.038] between the lowest and the highest tertiles).

CONCLUSIONS

Low levels of ApoA-I/IgG ICs are associated with an increased risk of adverse events in patients with CAD, raising their potential to be used as a biomarker to predict CVD progression.

MicroRNA-23a-5p promotes atherosclerotic plaque progression and vulnerability by repressing ATP-binding cassette transporter A1/G1 in macrophages

Disruption of carotid vulnerable atherosclerotic plaque is responsible for acute ischemic stroke (AIS) and the early detection and intervention approach are greatly limited. Undertaking a microarray of microRNAs (miRNAs) in the plasma of AIS patients with carotid vulnerable plaques, miR-23a-5p was markedly elevated and was positively correlated with the plaque progression and vulnerability. Correspondingly, we found that miR-23a-5p expression was significantly increased in both plasma and macrophages from atherosclerosis mice. Bioinformatics analysis and in vitro knockdown experiments identified that ATP-binding cassette transporter A1/G1 as a novel target of miR-23a-5p. Luciferase reporter assays showed that miR-23a-5p repressed the 3' untranslated regions (UTR) activity of ABCA1/G1. Moreover, functional analyses demonstrated that transfection of miR-23a-5p inhibitor enhanced cholesterol efflux and decreased foam cell formation through upregulating ABCA1/G1 expression levels. Furthermore, long term in vivo systemically delivered miR-23a-5p antagomir significantly increased ABCA1/G1 expression in the aorta of ApoE^-/- mice. Importantly, the miR-23a-5p antagomir therapy significantly reduced atherosclerosis progression and promoted plaque stability. Our observations indicate that miR-23a-5p promotes macrophage-derived foam cell formation and might be a key regulator contributing to atherosclerotic plaque progression and vulnerability.

DBZ (Danshensu Bingpian Zhi), a Novel Natural Compound Derivative, Attenuates Atherosclerosis in Apolipoprotein E-Deficient Mice

BACKGROUND

DBZ (Danshensu Bingpian Zhi), a synthetic derivative of a natural compound found in traditional Chinese medicine, has been reported to suppress lipopolysaccharide-induced macrophage activation and lipid accumulation in vitro. The aim of this study was to assess whether DBZ could attenuate atherosclerosis at early and advanced stages.

METHODS AND RESULTS

The effects of DBZ on the development of atherosclerosis were studied using apolipoprotein E-deficient (apoE-/-) mice. For early treatment, 5-week-old apoE-/- mice were fed a Western diet and treated daily by oral gavage with or without DBZ or atorvastatin for 10 weeks. For advanced treatment, 5-week-old apoE-/- mice were fed a Western diet for 10 weeks to induce atherosclerosis, and then they were randomly divided into 4 groups and subjected to the treatment of vehicle, 20 mg/kg per day DBZ, 40 mg/kg per day DBZ, or 10 mg/kg per day atorvastatin for the subsequent 10 weeks. We showed that early treatment of apoE-/- mice with DBZ markedly reduced atherosclerotic lesion formation by inhibiting inflammation and decreasing macrophage infiltration into the vessel wall. Treatment with DBZ also attenuated the progression of preestablished diet-induced atherosclerotic plaques in apoE-/- mice. In addition, we showed that DBZ may affect LXR (liver X receptor) function and that treatment of macrophages with DBZ suppressed lipopolysaccharide-stimulated cell migration and oxidized low-density lipoprotein-induced foam cell formation.

CONCLUSIONS

DBZ potentially has antiatherosclerotic effects that involve the inhibition of inflammation, macrophage migration, leukocyte adhesion, and foam cell formation. These results suggest that DBZ may be used as a therapeutic agent for the prevention and treatment of atherosclerosis.

Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE-/- mice

Recently, we demonstrated that heat shock protein (HSP)-27 is protective against the development of experimental atherosclerosis, reducing plaque cholesterol content by more than 30%. Moreover, elevated HSP-27 levels are predictive of relative freedom from clinical cardiovascular events. HSP-27 signaling occurs via the activation of NF-κB, which induces a marked up-regulation in expression of granulocyte-monocyte colony-stimulating factor (GM-CSF), a cytokine that is known to alter ABC transporters involved in reverse cholesterol transport (RCT). Therefore, we hypothesized that HSP-27-derived GM-CSF has a potent role in impeding plaque formation by promoting macrophage RCT and sought to better characterize this pathway. Treatment of THP-1 cells, RAW-Blue cells, and primary macrophages with recombinant HSP-27 resulted in NF-κB activation via TLR-4 and was inhibited by various pharmacologic blockers of this pathway. Moreover, HSP-27-induced upregulation of GM-CSF expression was dependent on TLR-4 signaling. Recombinant (r)HSP-27 treatment of ApoE^-/- female (but not male) mice for 4 wk yielded reductions in plaque area and cholesterol clefts of 33 and 47%, respectively, with no effect on GM-CSF^-/-ApoE^-/- mice. With 12 wk of rHSP-27 treatment, both female and male mice showed reductions in plaque burden (55 and 42%, respectively) and a 60% reduction in necrotic core area but no treatment effect in GM-CSF^-/-ApoE^-/- mice. In vitro functional studies revealed that HSP-27 enhanced the expression of ABCA1 and ABCG1, as well as facilitated cholesterol efflux in vitro by ∼10%. These novel findings establish a paradigm for HSP-27-mediated RCT and set the stage for the development of HSP-27 atheroprotective therapeutics.-Pulakazhi Venu, V. K., Adijiang, A., Seibert, T., Chen, Y.-X., Shi, C., Batulan, Z., O'Brien, E. R. Heat shock protein 27-derived atheroprotection involves reverse cholesterol transport that is dependent on GM-CSF to maintain ABCA1 and ABCG1 expression in ApoE^-/- mice.

The ACAT2 expression of human leukocytes is responsible for the excretion of lipoproteins containing cholesteryl/steryl esters

Acyl-coenzymeA:cholesterol acyltransferase 2 (ACAT2) is abundantly expressed in intestine and fetal liver of healthy human. Our previous studies have shown that in monocytic cells the low-level expression of human ACAT2 gene with specific CpG-hypomethylated promoter is regulated by the CCAAT/enhancer binding protein (C/EBP) transcription factors. In this study, we further report that the ACAT2 gene expression is attributable to the C/EBPs in the human leukocytes and correlated with the excretion of fluorescent lipoproteins containing the ACAT2-catalyzed NBD22-steryl esters. Moreover, this lipoprotein excretion can be inhibited by the ACAT2 isoform-selective inhibitor pyripyropene A (PPPA) in a dose-dependent manner, and employed to determine the half maximum inhibitory concentration (IC50) values of PPPA. Significantly, it is found that the differentiation-inducing factor all-trans retinoic acid, but not the proinflammatory cytokine tumor necrosis factor-α, enhances this ACAT2-dependent lipoprotein excretion. These data demonstrate that the ACAT2 expression of human leukocytes is responsible for the excretion of lipoproteins containing cholesteryl/steryl esters (CE/SE), and suggest that the excretion of lipoproteins containing the ACAT2-catalyzed CS/SE may avoid cytotoxicity through decreasing the excess intracellular cholesterols/sterols (especially various oxysterols), which is essential for the action of the human leukocytes.