Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol

Long Non-Coding RNAs Link Oxidized Low-Density Lipoprotein With the Inflammatory Response of Macrophages in Atherogenesis

Atherosclerosis is characterized as a chronic inflammatory response to cholesterol deposition in arteries. Low-density lipoprotein (LDL), especially the oxidized form (ox-LDL), plays a crucial role in the occurrence and development of atherosclerosis by inducing endothelial cell (EC) dysfunction, attracting monocyte-derived macrophages, and promoting chronic inflammation. However, the mechanisms linking cholesterol accumulation with inflammation in macrophage foam cells are poorly understood. Long non-coding RNAs (lncRNAs) are a group of non-protein-coding RNAs longer than 200 nucleotides and are found to regulate the progress of atherosclerosis. Recently, many lncRNAs interfering with cholesterol deposition or inflammation were identified, which might help elucidate their underlying molecular mechanism or be used as novel therapeutic targets. In this review, we summarize and highlight the role of lncRNAs linking cholesterol (mainly ox-LDL) accumulation with inflammation in macrophages during the process of atherosclerosis.

Association of cholesterol uptake capacity, a novel indicator for HDL functionality, and coronary plaque properties: An optical coherence tomography-based observational study

BACKGROUND

Cholesterol efflux from atherosclerotic lesion is a key function of high-density lipoprotein (HDL). Recently, we established a simple, high-throughput, cell-free assay to evaluate the capacity of HDL to accept additional cholesterol, which is herein referred to as "cholesterol uptake capacity (CUC)".

OBJECTIVE

To clarify the cross-sectional relationship between CUC and coronary plaque properties.

METHODS

We enrolled 135 patients to measure CUC and assess the morphological features of angiographic stenosis by optical coherence tomography (OCT). We estimated the extent of the lipid-rich plaque by multiplying the mean lipid arc by lipid length (lipid index). The extent of the OCT-detected macrophage accumulation in the target plaque was semi-quantitatively estimated using a grading system.

RESULTS

Lipid-rich plaque lesions were identified in 125 patients (92.6%). CUC was inversely associated with the lipid index (R = -0.348, P < 0.0001). In addition, CUC was also inversely associated with macrophage score (R = -0.327, P < 0.0001). Conversely, neither circulating levels of HDL cholesterol nor apoA1 showed a similar relationship.

CONCLUSIONS

We demonstrated that CUC was inversely related to lipid-rich plaque burden and the extent of macrophage accumulation, suggesting that CUC could be useful for cardiovascular risk stratification.

Selenium alleviates lipopolysaccharide-induced endometritisviaregulating the recruitment of TLR4 into lipid rafts in mice

Selenium (Se) is an essential trace element for living organisms and plays diverse biological roles.

Saikosaponin A protects chickens against pullorum disease via modulation of cholesterol

The worsening problem of antibiotic resistance prompts the need for alternative strategies that do not directly target bacteria. Virulent Salmonella pullorum strains can invade macrophages and lead to a systemic infection. Saikosaponin A (SSa), a bioactive saponin isolated from Radix bupleuri, has been demonstrated to exhibit anti-inflammatory, hepatoprotective, and cholesterol regulatory activity. The aim of this study was to investigate the effects of SSa on Salmonella-induced pullorum disease in chickens and clarify the possible mechanism. A S. pullorum-induced pullorum disease chicken model was used to confirm the protective effect of SSa in vivo. The model of HD11 cells infected with S. pullorum was used to investigate the molecular mechanism of SSa in vitro. In vivo, SSa prolonged the survival time and decreased the liver bacterial burdens in the pullorum disease model. In vitro, SSa dose-dependently suppressed the invasion of HD11 cells by S. pullorum. SSa depleted cholesterol in the lipid rafts, disrupted the formation of lipid rafts, and promoted the transcription of LXRα, ABCA1, and ABCG1. Moreover, the addition of water-soluble cholesterol and inhibition of LXRα with the LXRα antagonist geranylgeranyl pyrophosphate reversed the inhibitory effects of SSa on the invasion of HD11 cells by S. pullorum. In conclusion, the protective effect of SSa against S. pullorum infection is associated with the upregulation of the LXRα-ABCG1/ABCA1 pathway, which results in a decrease in cholesterol in the lipid rafts of HD11 cells, thereby suppressing the invasion of HD11 cells by S. pullorum. These results validate SSa as a host-target drug for the prevention of bacterial diseases, including those caused by S. pullorum.

Anti-Inflammatory Effects of HDL (High-Density Lipoprotein) in Macrophages Predominate Over Proinflammatory Effects in Atherosclerotic Plaques

OBJECTIVE

HDL (high-density lipoprotein) infusion reduces atherosclerosis in animal models and is being evaluated as a treatment in humans. Studies have shown either anti- or proinflammatory effects of HDL in macrophages, and there is no consensus on the underlying mechanisms. Here, we interrogate the effects of HDL on inflammatory gene expression in macrophages. Approach and Results: We cultured bone marrow-derived macrophages, treated them with reconstituted HDL or HDL isolated from APOA1^Tg;Ldlr^-/- mice, and challenged them with lipopolysaccharide. Transcriptional profiling showed that HDL exerts a broad anti-inflammatory effect on lipopolysaccharide-induced genes and proinflammatory effect in a subset of genes enriched for chemokines. Cholesterol removal by POPC (1-palmitoyl-2-oleoyl-glycero-3-phosphocholine) liposomes or β-methylcyclodextrin mimicked both pro- and anti-inflammatory effects of HDL, whereas cholesterol loading by POPC/cholesterol-liposomes or acetylated LDL (low-density lipoprotein) before HDL attenuated these effects, indicating that these responses are mediated by cholesterol efflux. While early anti-inflammatory effects reflect reduced TLR (Toll-like receptor) 4 levels, late anti-inflammatory effects are due to reduced IFN (interferon) receptor signaling. Proinflammatory effects occur late and represent a modified endoplasmic reticulum stress response, mediated by IRE1a (inositol-requiring enzyme 1a)/ASK1 (apoptosis signal-regulating kinase 1)/p38 MAPK (p38 mitogen-activated protein kinase) signaling, that occurs under conditions of extreme cholesterol depletion. To investigate the effects of HDL on inflammatory gene expression in myeloid cells in atherosclerotic lesions, we injected reconstituted HDL into Apoe^-/- or Ldlr^-/- mice fed a Western-type diet. Reconstituted HDL infusions produced anti-inflammatory effects in lesion macrophages without any evidence of proinflammatory effects.

CONCLUSIONS

Reconstituted HDL infusions in hypercholesterolemic atherosclerotic mice produced anti-inflammatory effects in lesion macrophages suggesting a beneficial therapeutic effect of HDL in vivo.

Myeloid Acat1/Soat1 KO attenuates pro-inflammatory responses in macrophages and protects against atherosclerosis in a model of advanced lesions

Cholesterol esters are a key ingredient of foamy cells in atherosclerotic lesions; their formation is catalyzed by two enzymes: acyl-CoA:cholesterol acyltransferases (ACATs; also called sterol O-acyltransferases, or SOATs) ACAT1 and ACAT2. ACAT1 is present in all body cells and is the major isoenzyme in macrophages. Whether blocking ACAT1 benefits atherosclerosis has been under debate for more than a decade. Previously, our laboratory developed a myeloid-specific Acat1 knockout (KO) mouse (Acat1 ^-M/-M), devoid of ACAT1 only in macrophages, microglia, and neutrophils. In previous work using the ApoE KO (ApoE ^-/-) mouse model for early lesions, Acat1 ^-M/-M significantly reduced lesion macrophage content and suppressed atherosclerosis progression. In advanced lesions, cholesterol crystals become a prominent feature. Here we evaluated the effects of Acat1 ^-M/-M in the ApoE KO mouse model for more advanced lesions and found that mice lacking myeloid Acat1 had significantly reduced lesion cholesterol crystal contents. Acat1 ^-M/-M also significantly reduced lesion size and macrophage content without increasing apoptotic cell death. Cell culture studies showed that inhibiting ACAT1 in macrophages caused cells to produce less proinflammatory responses upon cholesterol loading by acetyl low-density lipoprotein. In advanced lesions, Acat1 ^-M/-M reduced but did not eliminate foamy cells. In advanced plaques isolated from ApoE ^-/- mice, immunostainings showed that both ACAT1 and ACAT2 are present. In cell culture, both enzymes are present in macrophages and smooth muscle cells and contribute to cholesterol ester biosynthesis. Overall, our results support the notion that targeting ACAT1 or targeting both ACAT1 and ACAT2 in macrophages is a novel strategy to treat advanced lesions.

Macrophage Rewiring by Nutrient Associated PI3K Dependent Pathways

Class 1 Phosphoinositide-3-Kinases (PI3Ks) have been widely studied and mediate essential roles in cellular proliferation, chemotaxis, insulin sensitivity, and immunity. Here, we provide a comprehensive overview of how macrophage expressed PI3Ks and their downstream pathways orchestrate responses to metabolic stimuli and nutrients, polarizing macrophages, shaping their cellular identity and function. Particular emphasis will be given to adipose tissue macrophages, crucial players of insulin resistance and chronic metabolically triggered inflammation during obesity. An understanding of PI3K dependent wiring of macrophage responses is important as this is involved in various diseases ranging from obesity, type 2 diabetes to chronic inflammatory disease.

Toll-like receptor mediated inflammation requires FASN-dependent MYD88 palmitoylation

Toll-like receptor (TLR)/myeloid differentiation primary response protein (MYD88) signaling aggravates sepsis by impairing neutrophil migration to infection sites. However, the role of intracellular fatty acids in TLR/MYD88 signaling is unclear. Here, inhibition of fatty acid synthase by C75 improved neutrophil chemotaxis and increased the survival of mice with sepsis in cecal ligation puncture and lipopolysaccharide-induced septic shock models. C75 specifically blocked TLR/MYD88 signaling in neutrophils. Treatment with GSK2194069 that targets a different domain of fatty acid synthase, did not block TLR signaling or MYD88 palmitoylation. De novo fatty acid synthesis and CD36-mediated exogenous fatty acid incorporation contributed to MYD88 palmitoylation. The binding of IRAK4 to the MYD88 intermediate domain and downstream signal activation required MYD88 palmitoylation at cysteine 113. MYD88 was palmitoylated by ZDHHC6, and ZDHHC6 knockdown decreased MYD88 palmitoylation and TLR/MYD88 activation upon lipopolysaccharide stimulus. Thus, intracellular saturated fatty acid-dependent palmitoylation of MYD88 by ZDHHC6 is a therapeutic target of sepsis.

The cooperative induction of macrophage activation by fucoidan derived from Cladosiphon okamuranus and β-glucan derived from Saccharomyces cerevisiae

The present study investigated immune stimulatory effects of Cladosiphon okamuranus-derived fucoidan to activate murine macrophage-like cell line RAW264, and the functional relationship with zymosan, a Saccharomyces cerevisiae-derived β-glucan. The production of nitric oxide (NO) and tumor necrosis factor-α (TNF-α) in RAW264 cells were remarkably enhanced in the presence of 10 μg/mL fucoidan, and the stimulatory effects of fucoidan were maximally augmented in combinational treatment with 500 ng/mL zymosan, whereas any TLR ligands had no those effects. Confocal microscopic analyses suggested that fucoidan bound on plasma membrane, and it was estimated that some cell surface molecules acted as receptor for fucoidan because cytochalasin D, an inhibitor of phagocytosis, did not affect the immune enhancing activities, whereas methyl-β-cyclodextrin (MβCD), a general agent for disruption of lipid rafts, diminished that. Furthermore, it was revealed that the additive effects of zymosan on the immune activation with fucoidan was thought to be mediated by dectin-1 based on the results with dectin-1-knockdown RAW264 cells. All of results suggested that fucoidan and some kinds of β-glucan would cooperatively reinforce the activity of innate immune cells via interactive receptor crosstalk.

Exposure to PM2.5 affects blood lipid levels in asthmatic rats through notch signaling pathway

BACKGROUND

Epidemiological studies have confirmed atmospheric PM_2.5 could affect asthma, and dyslipidemia may be related to pathogenesis of asthma. Recent studies show Notch ligands had lipid combination domains which are responsible for regulating lipid levels. However, the effect of PM_2.5 on asthmatic rats' lipid levels and the role of Notch signaling pathway is unclear.

METHODS

Rats were treat with ovalbumin (OVA) to establish asthma models. Notch signaling pathway inhibitor (DAPT) was injected intraperitoneally. Asthmatic and healthy rats were exposed to different concentrations of PM_2.5. Lung tissues were collected and the expression of Hes1 protein was detected by Western Blot. Blood samples were collected to detect the serum lipid levels.

RESULTS

Hes1 expression levels in healthy and asthma pathway inhibition groups were lower than those in control groups. Compared with control group, rats exposed to PM_2.5 in middle and high dose, the levels of TG and TC were decreased. Similar results were observed after exposure to the same concentration of PM_2.5 in asthmatic rats. Rats, which were exposed to PM_2.5 after being established the asthma model successfully, could exhibit more significant dyslipidemia than those with direct exposure. After Notch signaling pathway inhibited, TC and LDL in asthma pathway inhibition group were lower than those in healthy group.

CONCLUSIONS

PM_2.5 can affect the lipid levels of asthmatic rats through the Notch signaling pathway.

SREBF1/MicroRNA-33b Axis Exhibits Potent Effect on Unstable Atherosclerotic Plaque Formation In Vivo

Objective- Atherosclerosis is a common disease caused by a variety of metabolic and inflammatory disturbances. MicroRNA (miR)-33a within SREBF2 (sterol regulatory element-binding factor 2) is a potent target for treatment of atherosclerosis through regulating both aspects; however, the involvement of miR-33b within SREBF1 remains largely unknown. Although their host genes difference could lead to functional divergence of miR-33a/b, we cannot dissect the roles of miR-33a/b in vivo because of lack of miR-33b sequences in mice, unlike human. Approach and Results- Here, we analyzed the development of atherosclerosis using miR-33b knock-in humanized mice under apolipoprotein E-deficient background. MiR-33b is prominent both in human and mice on atheroprone condition. MiR-33b reduced serum high-density lipoprotein cholesterol levels and systemic reverse cholesterol transport. MiR-33b knock-in macrophages showed less cholesterol efflux capacity and higher inflammatory state via regulating lipid rafts. Thus, miR-33b promotes vulnerable atherosclerotic plaque formation. Furthermore, bone marrow transplantation experiments strengthen proatherogenic roles of macrophage miR-33b. Conclusions- Our data demonstrated critical roles of SREBF1-miR-33b axis on both lipid profiles and macrophage phenotype remodeling and indicate that miR-33b is a promising target for treating atherosclerosis.

Miltefosine increases macrophage cholesterol release and inhibits NLRP3-inflammasome assembly and IL-1β release

Miltefosine is an FDA approved oral drug for treating cutaneous and visceral leishmaniasis. Leishmania is a flagellated protozoa, which infects and differentiates in macrophages. Here, we studied the effects of Miltefosine on macrophage's lipid homeostasis, autophagy, and NLRP3 inflammasome assembly/activity. Miltefosine treatment conferred multiple effects on macrophage lipid homeostasis leading to increased cholesterol release from cells, increased lipid-raft disruption, decreased phosphatidylserine (PS) flip from the cell-surface, and redistribution of phosphatidylinositol 4,5-bisphosphate (PIP2) from the plasma membrane to actin rich regions in the cells. Enhanced basal autophagy, lipophagy and mitophagy was observed in cells treated with Miltefosine vs. control. Miltefosine treated cells showed marked increased in phosphorylation of kinases involved in autophagy induction such as; Adenosine monophosphate-activated protein kinase (AMPK) and Unc-51 like autophagy activating kinase (ULK1). The Toll like receptor (TLR) signaling pathway was blunted by Miltefosine treatment, resulting in decreased TLR4 recruitment to cell-surface and ~75% reduction in LPS induced pro-IL-1β mRNA levels. Miltefosine reduced endotoxin-mediated mitochondrial reactive oxygen species and protected the mitochondrial membrane potential. Miltefosine treatment induced mitophagy and dampened NLRP3 inflammasome assembly. Collectively, our data shows that Miltefosine induced ABCA1 mediated cholesterol release, induced AMPK phosphorylation and mitophagy, while dampening NLRP3 inflammasome assembly and IL-1β release.

Exosomes containing HIV protein Nef reorganize lipid rafts potentiating inflammatory response in bystander cells

HIV infection has a profound effect on “bystander” cells causing metabolic co-morbidities. This may be mediated by exosomes secreted by HIV-infected cells and containing viral factors. Here we show that exosomes containing HIV-1 protein Nef (exNef) are rapidly taken up by macrophages releasing Nef into the cell interior. This caused down-regulation of ABCA1, reduction of cholesterol efflux and sharp elevation of the abundance of lipid rafts through reduced activation of small GTPase Cdc42 and decreased actin polymerization. Changes in rafts led to re-localization of TLR4 and TREM-1 to rafts, phosphorylation of ERK1/2, activation of NLRP3 inflammasome, and increased secretion of pro-inflammatory cytokines. The effects of exNef on lipid rafts and on inflammation were reversed by overexpression of a constitutively active mutant of Cdc42. Similar effects were observed in macrophages treated with exosomes produced by HIV-infected cells or isolated from plasma of HIV-infected subjects, but not with exosomes from cells and subjects infected with ΔNef-HIV or uninfected subjects. Mice injected with exNef exhibited monocytosis, reduced ABCA1 in macrophages, increased raft abundance in monocytes and augmented inflammation. Thus, Nef-containing exosomes potentiated pro-inflammatory response by inducing changes in cholesterol metabolism and reorganizing lipid rafts. These mechanisms may contribute to HIV-associated metabolic co-morbidities.

HIV infects only a limited repertoire of cells expressing HIV receptors. Nevertheless, co-morbidities of HIV infection, such as atherosclerosis, dementia, renal impairment, myocardial pathology, abnormal haematopoiesis and others, involve dysfunction of cells that can not be infected by HIV. These co-morbidities persist even after successful application of antiretroviral therapy, when no virus is found in the blood. Many co-morbidities of HIV have a common element in their pathogenesis, impairment of cholesterol metabolism. In this study we show that HIV protein Nef released from infected cells in extracellular vesicles is taken up by un-infected (‘bystander’) cells impairing cholesterol metabolism in these cells. This impairment causes formation of excessive lipid rafts, re-localization of the inflammatory receptors into rafts, and triggers inflammation. These mechanisms may contribute to HIV-associated metabolic co-morbidities. Our work demonstrates how a single viral factor released from infected cells into circulation may cause a pleiotropy of pathogenic responses.

Impaired Cholesterol-Uptake Capacity of HDL Might Promote Target-Lesion Revascularization by Inducing Neoatherosclerosis After Stent Implantation

Background We evaluated the importance of high-density lipoprotein (HDL) functionality for target-lesion revascularization in patients treated with coronary stents using a rapid cell-free assay system to evaluate the functional capacity of HDL to accept additional cholesterol (cholesterol-uptake capacity; CUC). Methods and Results From an optical coherence tomography (OCT) registry of patients treated with coronary stents, 207 patients were enrolled and their HDL was functionally evaluated by measuring the CUC. Follow-up OCT was performed (median duration, 24.5 months after stenting) to evaluate the presence of neoatherosclerosis. Clinical follow-up was performed to assess target-lesion revascularization for a median duration of 42.3 months after stent implantation. Neoatherosclerosis was identified in 37 patients (17.9%). Multivariate logistic regression analysis revealed that a decreased CUC was independently associated with neoatherosclerosis (odds ratio, 0.799; P<0.001). The CUC showed a significant inverse correlation with incidence of target-lesion revascularization (odds ratio, 0.887; P=0.003) and with lipid accumulation inside stents, suggesting that neoatherosclerosis contributes to the association between CUC and target-lesion revascularization. Conclusions Impaired HDL functionality, detected as decreased CUC, might lead to future stent failure by provoking atherogenic changes of the neointima within stents. Both quantitative and qualitative assessments of HDL might enable the improved prediction of clinical outcomes after stent implantation.

Biological mechanisms and related natural modulators of liver X receptor in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming a worldwide health problem, but no approved medical treatment exists so far. Nuclear receptors are one of the drug targets for nonalcoholic steatohepatitis (NASH). Among them, liver X receptor (LXR) has been studied in recent years in tumors, metabolic diseases and inflammatory diseases, but its physiological and pharmacological effects in the treatment of NASH are controversial. Activation of LXR has the potential to modulate cholesterol homeostasis, induce anti-inflammatory effects and increase insulin sensitivity, but liver lipid deposition and hypertriglyceridemia are also increased. Inhibition of liver LXR transcriptional activity in the context of NAFLD can effectively alleviate hepatic steatosis, inflammation, and fibrosis but elevates the risk of potential cardiovascular disease. The contradictory pharmacodynamic effects of LXR in the treatment of NASH increase the difficulty of developing targeted drugs. Moreover, natural compounds play an important part in drug development, and in recent years, some natural compounds have been reported to treat NAFLD by acting on LXR or LXR pathways with fewer adverse reactions, presenting a promising therapeutic prospect. In this review, we discuss the mechanisms of LXR in NASH and summarize the natural products reported to modulate NAFLD via LXR or the LXR pathway, offering an alternative approach for LXR-related drug development in NAFLD.

Gender Dictates the Relationship between Serum Lipids and Leukocyte Counts in the National Health and Nutrition Examination Survey 1999⁻2004

Dyslipidemias and leukocytosis are associated with cardiovascular disease and immune disorders. Mechanistic studies have shown lipoprotein metabolism to play a significant role in the regulation of atherosclerosis development and leukocyte activation, whereas lipid-lowering treatments have been shown to exert beneficial anti-inflammatory and immunomodulatory effects in clinical trials. However, the relationship between clinical markers of lipid metabolism and leukocyte counts has not been extensively evaluated at the population level. We aimed to determine whether clinical blood lipid measures are associated with leukocyte counts in the general U.S. population represented in the National Health and Nutrition Examination Survey (NHANES) 1999–2004, and whether differences exist between men and women (n = 5647). We observed a strong positive linear trend between serum triglycerides vs. blood lymphocyte and basophil counts in both men and women, whereas a positive trend between monocytes vs. triglycerides and lymphocytes vs. total cholesterol and LDL-cholesterol (LDL-C) was only detected in women. Conversely, HDL-C was inversely associated with a greater number of leukocyte subsets in men, whereas inverse trends between HDL-C vs. lymphocytes were observed in both men and women. In multiple regression models, a 10% increase in total cholesterol, LDL-C, and triglycerides was associated with a predicted 1.6%, 0.6%, and 1.4% increase in blood lymphocyte counts in women, respectively, whereas no relationship was observed in men. In both men and women, a 10% increase in triglycerides was additionally associated with higher lymphocyte, neutrophil, and basophil counts, whereas 10% increases in HDL-cholesterol were associated with significantly lower lymphocyte, neutrophil, eosinophil, and basophil counts in men, in addition to lower lymphocyte and monocyte counts in women. These findings suggest that clinical lipid markers may be used to predict blood leukocyte distributions, and that a gender-specific relationship exists between distinct classes of serum lipids and immune cell subsets.

Interaction between an ATP-Binding Cassette A1 (ABCA1) Variant and Egg Consumption for the Risk of Ischemic Stroke and Carotid Atherosclerosis: a Family-Based Study in the Chinese Population

Aims: ATP-binding cassette A1 (ABCA1) plays an important role in reducing the risk of stroke. Egg is the major source of dietary cholesterol and is known to be associated with the risk of stroke and atherosclerosis. We aimed to assess the effects of interaction between an ABCA1 variant (rs2066715) and egg consumption on the risk of ischemic stroke (IS), carotid plaque, and carotid-intima media thickness (CIMT) in the Chinese population.

Methods: In total, 5869 subjects (including 1213 IS cases) across 1128 families were enrolled and divided into two groups based on the median egg consumption (4 eggs per week). In the analyses for the presence of carotid plaque and CIMT, 3171 out of 4656 IS-free controls without self-reported history of coronary heart disease and lipid-lowering medications were included. Multilevel logistic regression models were used to model the genetic association of rs2066715 with the risk of IS, and mixed-effect linear regression for the genetic association of rs2066715 with carotid plaque, and CIMT. The gene-by-egg cross-product term was included in the regression model for interaction analysis.

Results: We found that rs2066715 was associated with the increased risk of carotid plaque among those who consumed < 4 eggs per week after adjustment (odds ratio [95% confidence interval]: 1.61 [1.08, 2.39], P = 0.019). A significant effect of interaction between rs2066715 and egg consumption on the risk of carotid plaque was identified (P = 0.011).

Conclusion: rs2066715 was found to interact with egg consumption in modifying the risk of carotid plaque in the Chinese population.

ABCA1 Overexpression in Endothelial Cells In Vitro Enhances ApoAI-Mediated Cholesterol Efflux and Decreases Inflammation

Atherosclerosis, a disease of blood vessels, is driven by cholesterol accumulation and inflammation. Gene therapy that removes cholesterol from blood vessels and decreases inflammation is a promising approach for prevention and treatment of atherosclerosis. In previous work, we reported that helper-dependent adenoviral (HDAd) overexpression of apolipoprotein A-I (apoAI) in endothelial cells (ECs) increases cholesterol efflux in vitro and reduces atherosclerosis in vivo. However, the effect of HDAdApoAI on atherosclerosis is partial. To improve this therapy, we considered concurrent overexpression of ATP-binding cassette subfamily A, member 1 (ABCA1), a protein that is required for apoAI-mediated cholesterol efflux. Before attempting combined apoAI/ABCA1 gene therapy, we tested whether an HDAd that expresses ABCA1 (HDAdABCA1) increases EC cholesterol efflux, whether increased cholesterol efflux alters normal EC physiology, and whether ABCA1 overexpression in ECs has anti-inflammatory effects. HDAdABCA1 increased EC ABCA1 protein (∼3-fold; p < 0.001) and apoAI-mediated cholesterol efflux (2.3-fold; p = 0.007). Under basal culture conditions, ABCA1 overexpression did not alter EC proliferation, metabolism, migration, apoptosis, nitric oxide production, or inflammatory gene expression. However, in serum-starved, apoAI-treated EC, ABCA1 overexpression had anti-inflammatory effects: decreased inflammatory gene expression (∼50%; p ≤ 0.02 for interleukin [IL]-6, tumor necrosis factor [TNF]-α, and vascular cell adhesion protein-1); reduced lipid-raft Toll-like receptor 4 (80%; p = 0.001); and a trend towards increased nitric oxide production (∼55%; p = 0.1). In ECs stimulated with lipopolysaccharide, ABCA1 overexpression markedly decreased inflammatory gene expression (∼90% for IL-6 and TNF-α; p < 0.001). Therefore, EC ABCA1 overexpression has no toxic effects and counteracts the two key drivers of atherosclerosis: cholesterol accumulation and inflammation. In vivo testing of HDAdABCA1 is warranted.

Leucine-rich repeats and calponin homology containing 4 (Lrch4) regulates the innate immune response

Toll-like receptors (TLRs) are pathogen-recognition receptors that trigger the innate immune response. Recent reports have identified accessory proteins that provide essential support to TLR function through ligand delivery and receptor trafficking. Herein, we introduce leucine-rich repeats (LRRs) and calponin homology containing 4 (Lrch4) as a novel TLR accessory protein. Lrch4 is a membrane protein with nine LRRs in its predicted ectodomain. It is widely expressed across murine tissues and has two expression variants that are both regulated by lipopolysaccharide (LPS). Predictive modeling indicates that Lrch4 LRRs conform to the horseshoe-shaped structure typical of LRRs in pathogen-recognition receptors and that the best structural match in the protein database is to the variable lymphocyte receptor of the jawless vertebrate hagfish. Silencing Lrch4 attenuates cytokine induction by LPS and multiple other TLR ligands and dampens the in vivo innate immune response. Lrch4 promotes proper docking of LPS in lipid raft membrane microdomains. We provide evidence that this is through regulation of lipid rafts as Lrch4 silencing reduces cell surface gangliosides, a metric of raft abundance, as well as expression and surface display of CD14, a raft-resident LPS co-receptor. Taken together, we identify Lrch4 as a broad-spanning regulator of the innate immune response and a potential molecular target in inflammatory disease.

Apolipoprotein A1 mimetic peptide ATI-5261 reverses arterial stiffness at late pregnancy and early postpartum in a COMT-/- mouse model of preeclampsia

Background

Preeclampsia (PE) is a serious maternal complication during pregnancy. Associated arterial stiffness in PE patients leads to increased risks of cardiovascular diseases later in life. Cholesterol efflux capacity, especially ATP binding cassette transporter A1 (ABCA1) dependent capacity, has been proposed to be a likely mediator of arterial stiffness. In the present study, we aimed to evaluate the effect of an apolipoprotein A1 mimetic peptide ATI-5261 on arterial stiffness in a mouse model of PE.

Methods

Pregnant COMT^-/- mice were randomized to receive vehicle or ATI-5261 (30 mg/kg per day) via subcutaneous injection from gestational days (GD) 10.5 to GD 18.5 or to 10 days postpartum. Pregnant C57BL/6 J mice received vehicle during paralleled periods were served as normal controls.

Results

COMT^-/- mice displayed maternal hypertension and proteinuria during pregnancy. Carotid-femoral pulse wave velocity (PWV) was increased at GD 18.5 and 10 days postpartum. ATI-5261 treatment in COMT^-/- mice significantly reduced PWV and partially normalized impaired ex vivo vascular function at late pregnancy and early postpartum. ATI-5261 treatment also increased serum ABCA1 concentrations and cholesterol efflux capacity, as well as ABCA1 expressions in the placenta. Pup weights, crown to rump lengths and abdominal circumferences were reduced in COMT^-/- mice. Treatment with ATI-5261 did not alter these fetal measurements but significantly reduced placental weights and increased fetal to placental ratios in COMT^-/- mice.

Conclusion

ATI-5261 reversed arterial stiffness at late pregnancy and early postpartum in a COMT^-/- mouse model of PE and may be a potential therapy for arterial stiffness associated with PE.

A New Frontier in Immunometabolism. Cholesterol in Lung Health and Disease

The lung has a unique relationship to cholesterol that is shaped by its singular physiology. On the one hand, the lungs receive the full cardiac output and have a predominant dependence on plasma lipoprotein uptake for their cholesterol supply. On the other hand, surfactant lipids, including cholesterol, are continually susceptible to oxidation owing to direct environmental exposure and must be cleared or recycled because of the very narrow biophysical mandates placed upon surfactant lipid composition. Interestingly, increased lipid-laden macrophage "foam cells" have been noted in a wide range of human lung pathologies. This suggests that lipid dysregulation may be a unifying and perhaps contributory event in chronic lung disease pathogenesis. Recent studies have shown that perturbations in intracellular cholesterol trafficking critically modify the immune response of macrophages and other cells. This minireview discusses literature that has begun to demonstrate the importance of regulated cholesterol traffic through the lung to pulmonary immunity, inflammation, and fibrosis. This emerging recognition of coupling between immunity and lipid homeostasis in the lung presents potentially transformative concepts for understanding lung disease and may also offer novel and exciting avenues for therapeutic development.

Dynamics of Plasma Lipidome in Progression to Islet Autoimmunity and Type 1 Diabetes - Type 1 Diabetes Prediction and Prevention Study (DIPP)

Type 1 diabetes (T1D) is one of the most prevalent autoimmune diseases among children in Western countries. Earlier metabolomics studies suggest that T1D is preceded by dysregulation of lipid metabolism. Here we used a lipidomics approach to analyze molecular lipids in a prospective series of 428 plasma samples from 40 children who progressed to T1D (PT1D), 40 children who developed at least a single islet autoantibody but did not progress to T1D during the follow-up (P1Ab) and 40 matched controls (CTR). Sphingomyelins were found to be persistently downregulated in PT1D when compared to the P1Ab and CTR groups. Triacylglycerols and phosphatidylcholines were mainly downregulated in PT1D as compared to P1Ab at the age of 3 months. Our study suggests that distinct lipidomic signatures characterize children who progressed to islet autoimmunity or overt T1D, which may be helpful in the identification of at-risk children before the initiation of autoimmunity.

Environmental Signals Influencing Myeloid Cell Metabolism and Function in Diabetes

The environment induces metabolic reprogramming of immune cells via specific signaling pathways. Recent studies have revealed that changes in cell metabolism affect key immune cell functions including cytokine production and migration. In diabetes, these functions are either insufficiently or excessively activated, translating into diabetes-associated complications, including increased susceptibility to infection and accelerated cardiovascular disease. Diabetes alters the abundance of environmental signals, including glucose, insulin, and lipids. Subsequently, changes in environmental signals drive metabolic reprogramming, impair immune cell function, and ultimately contribute to diabetes-associated complications. We review here recent studies on changes in innate immune cell metabolism, especially in myeloid cells, that are driven by environmental signals relevant to diabetes, and discuss therapeutic perspectives of targeting metabolism of immune cells in diabetes.

Lower High-Density Lipoproteins Levels During Human Immunodeficiency Virus Type 1 Infection Are Associated With Increased Inflammatory Markers and Disease Progression

Introduction

High-density lipoproteins (HDL) are responsible for the efflux and transport of cholesterol from peripheral tissues to the liver. In addition, HDL can modulate various immunological mechanisms, including the inflammatory response. Inflammasomes are multiprotein complexes that have been reported to be activated during human immunodeficiency virus type 1 (HIV-1) infection, thus contributing to immune hyperactivation, which is the main pathogenic mechanism of HIV-1 progression. However, the relationship between HDL and inflammasomes in the context of HIV-1 infection is unclear. Therefore, this research aims to explore the association between HDL and the components of the inflammatory response during HIV-1 infection.

Methodology

A cross-sectional study, including 36 HIV-1-infected individuals without antiretroviral treatment and 36 healthy controls matched by sex and age, was conducted. Viral load, CD4+ T-cell counts, serum HDL, and C-reactive protein (CRP) were quantified. Serum cytokine levels, including IL-1β, IL-6, and IL-18, were assessed by ELISA. The inflammasome-related genes in peripheral blood mononuclear cells were determined by quantitative real-time PCR.

Results

HIV-1-infected individuals showed a significant decrease in HDL levels, particularly those subjects with higher viral load and lower CD4+ T-cell counts. Moreover, upregulation of inflammasome-related genes (NLRP3, AIM2, ASC, IL-1β, and IL-18) was observed, notably in those HIV-1-infected individuals with higher viral loads (above 5,000 copies/mL). Serum levels of IL-6 and CRP were also elevated in HIV-1-infected individuals. Significant negative correlations between HDL and the mRNA of NLRP3, AIM2, ASC, IL-1β, and IL-18, as well as viral load and CRP were observed in HIV-1-infected individuals. Likewise, a significant positive correlation between HDL and CD4+ T-cell counts was found.

Conclusion

In summary, our results indicate that HDL might modulate the expression of several key components of the inflammasomes during HIV-1 infection, suggesting a novel role of HDL in modifying the inflammatory state and consequently, the progression of HIV-1 infection.

Impact of Dietary Cholesterol on the Pathophysiology of Infectious and Autoimmune Disease

Cellular cholesterol metabolism, lipid raft formation, and lipoprotein interactions contribute to the regulation of immune-mediated inflammation and response to pathogens. Lipid pathways have been implicated in the pathogenesis of bacterial and viral infections, whereas altered lipid metabolism may contribute to immune dysfunction in autoimmune diseases, such as systemic lupus erythematosus, multiple sclerosis, and rheumatoid arthritis. Interestingly, dietary cholesterol may exert protective or detrimental effects on risk, progression, and treatment of different infectious and autoimmune diseases, although current findings suggest that these effects are variable across populations and different diseases. Research evaluating the effects of dietary cholesterol, often provided by eggs or as a component of Western-style diets, demonstrates that cholesterol-rich dietary patterns affect markers of immune inflammation and cellular cholesterol metabolism, while additionally modulating lipoprotein profiles and functional properties of HDL. Further, cholesterol-rich diets appear to differentially impact immunomodulatory lipid pathways across human populations of variable metabolic status, suggesting that these complex mechanisms may underlie the relationship between dietary cholesterol and immunity. Given the Dietary Guidelines for Americans 2015⁻2020 revision to no longer include limitations on dietary cholesterol, evaluation of dietary cholesterol recommendations beyond the context of cardiovascular disease risk is particularly timely. This review provides a comprehensive and comparative analysis of significant and controversial studies on the role of dietary cholesterol and lipid metabolism in the pathophysiology of infectious disease and autoimmune disorders, highlighting the need for further investigation in this developing area of research.

Regulation of macrophage immunometabolism in atherosclerosis

After activation, cells of the myeloid lineage undergo robust metabolic transitions, as well as discrete epigenetic changes, that can dictate both ongoing and future inflammatory responses. In atherosclerosis, in which macrophages play central roles in the initiation, growth, and ultimately rupture of arterial plaques, altered metabolism is a key feature that dictates macrophage function and subsequent disease progression. This Review explores how factors central to the plaque microenvironment (for example, altered cholesterol metabolism, oxidative stress, hypoxia, apoptotic and necrotic cells, and hyperglycemia) shape the metabolic rewiring of macrophages in atherosclerosis as well as how these metabolic shifts in turn alter macrophage immune-effector and tissue-reparative functions. Finally, this overview offers insight into the challenges and opportunities of harnessing metabolism to modulate aberrant macrophage responses in disease.

Cholesterol-dependent cytolysins impair pro-inflammatory macrophage responses

Necrotizing soft tissue infections are lethal polymicrobial infections. Two key microbes that cause necrotizing soft tissue infections are Streptococcus pyogenes and Clostridium perfringens. These pathogens evade innate immunity using multiple virulence factors, including cholesterol-dependent cytolysins (CDCs). CDCs are resisted by mammalian cells through the sequestration and shedding of pores during intrinsic membrane repair. One hypothesis is that vesicle shedding promotes immune evasion by concomitantly eliminating key signaling proteins present in cholesterol-rich microdomains. To test this hypothesis, murine macrophages were challenged with sublytic CDC doses. CDCs suppressed LPS or IFNγ-stimulated TNFα production and CD69 and CD86 surface expression. This suppression was cell intrinsic. Two membrane repair pathways, patch repair and intrinsic repair, might mediate TNFα suppression. However, patch repair did not correlate with TNFα suppression. Intrinsic repair partially contributed to macrophage dysfunction because TLR4 and the IFNγR were partially shed following CDC challenge. Intrinsic repair was not sufficient for suppression, because pore formation was also required. These findings suggest that even when CDCs fail to kill cells, they may impair innate immune signaling responses dependent on cholesterol-rich microdomains. This is one potential mechanism to explain the lethality of S. pyogenes and C. perfringens during necrotizing soft tissue infections.

Taraxasterol Inhibits LPS-Induced Inflammatory Response in BV2 Microglia Cells by Activating LXRα

Neuroinflammation plays a critical role in the development of neurodegenerative diseases. Taraxasterol, a pentacyclic-triterpene isolated from Taraxacum officinale, has been reported to have anti-inflammatory effect. The aim of this study was to investigate the anti-inflammatory effects and mechanism of taraxasterol in LPS-stimulated BV2 microglia cells. BV2 microglia cells were treated with taraxasterol 12 h before LPS stimulation. The effects of taraxasterol on LPS-induced TNF-α and IL-1β production were detected by ELISA. The effects of taraxasterol on LXRα, ABCA1, TLR4, and NF-κB expression were detected by western blot analysis. The results showed that taraxasterol dose-dependently inhibited LPS-induced TNF-α and IL-1β production and NF-κB activation. Taraxasterol also disrupted the formation of lipid rafts and inhibited translocation of TLR4 into lipid rafts. Furthermore, taraxasterol was found to activate LXRα-ABCA1 signaling pathway which induces cholesterol efflux from cells. In addition, our results showed that the anti-inflammatory effect of taraxasterol was attenuated by transfection with LXRα siRNA. In conclusion, these results suggested that taraxasterol inhibits LPS-induced inflammatory response in BV2 microglia cells by activating LXRα-ABCA1 signaling pathway.

Hepatocyte ABCA1 Deletion Impairs Liver Insulin Signaling and Lipogenesis

Plasma membrane (PM) free cholesterol (FC) is emerging as an important modulator of signal transduction. Here, we show that hepatocyte-specific knockout (HSKO) of the cellular FC exporter, ATP-binding cassette transporter A1 (ABCA1), leads to decreased PM FC content and defective trafficking of lysosomal FC to the PM. Compared with controls, chow-fed HSKO mice had reduced hepatic (1) insulin-stimulated Akt phosphorylation, (2) activation of the lipogenic transcription factor Sterol Regulatory Element Binding Protein (SREBP)-1c, and (3) lipogenic gene expression. Consequently, Western-type diet-fed HSKO mice were protected from steatosis. Surprisingly, HSKO mice had intact glucose metabolism; they showed normal gluconeogenic gene suppression in response to re-feeding and normal glucose and insulin tolerance. We conclude that: (1) ABCA1 maintains optimal hepatocyte PM FC, through intracellular FC trafficking, for efficient insulin signaling; and (2) hepatocyte ABCA1 deletion produces a form of selective insulin resistance so that lipogenesis is suppressed but glucose metabolism remains normal.

Adipose-Derived Exosomes Exert Proatherogenic Effects by Regulating Macrophage Foam Cell Formation and Polarization

Background

Obesity is causally associated with atherosclerosis, and adipose tissue (AT)–derived exosomes may be implicated in the metabolic complications of obesity. However, the precise role of AT‐exosomes in atherogenesis remains unclear. We herein aimed to assess the effect of AT‐exosomes on macrophage foam cell formation and polarization and subsequent atherosclerosis development.

Methods and Results

Four types of exosomes isolated from the supernatants of ex vivo subcutaneous AT and visceral AT (VAT) explants that were derived from wild‐type mice and high‐fat diet (HFD)–induced obese mice were effectively taken up by RAW264.7 macrophages. Both treatment with wild‐type VAT exosomes and HFD‐VAT exosomes, but not subcutaneous AT exosomes, markedly facilitated macrophage foam cell generation through the downregulation of ATP‐binding cassette transporter (ABCA1 and ABCG1)–mediated cholesterol efflux. Decreased expression of liver X receptor‐α was also observed. Among the 4 types of exosomes, only HFD‐VAT exosomes significantly induced M1 phenotype transition and proinflammatory cytokine (tumor necrosis factor α and interleukin 6) secretion in RAW264.7 macrophages, which was accompanied by increased phosphorylation of NF‐κB‐p65 but not the cellular expression of NF‐κB‐p65 or IκB‐α. Furthermore, systematic intravenous injection of HFD‐VAT exosomes profoundly exacerbated atherosclerosis in hyperlipidemic apolipoprotein E–deficient mice, as indicated by the M1 marker (CD16/32 and inducible nitric oxide synthase)–positive areas and the Oil Red O/Sudan IV–stained area, without affecting the plasma lipid profile and body weight.

Conclusions

This study demonstrated a proatherosclerotic role for HFD‐VAT exosomes, which is exerted by regulating macrophage foam cell formation and polarization, indicating a novel link between AT and atherosclerosis in the context of obesity.

An unexpected link between fatty acid synthase and cholesterol synthesis in proinflammatory macrophage activation

Different immune activation states require distinct metabolic features and activities in immune cells. For instance, inhibition of fatty acid synthase (FASN), which catalyzes the synthesis of long-chain fatty acids, prevents the proinflammatory response in macrophages; however, the precise role of this enzyme in this response remains poorly defined. Consistent with previous studies, we found here that FASN is essential for lipopolysaccharide-induced, Toll-like receptor (TLR)-mediated macrophage activation. Interestingly, only agents that block FASN upstream of acetoacetyl-CoA synthesis, including the well-characterized FASN inhibitor C75, inhibited TLR4 signaling, while those acting downstream had no effect. We found that acetoacetyl-CoA could overcome C75's inhibitory effect, whereas other FASN metabolites, including palmitate, did not prevent C75-mediated inhibition. This suggested an unexpected role for acetoacetyl-CoA in inflammation that is independent of its role in palmitate synthesis. Our evidence further suggested that acetoacetyl-CoA arising from FASN activity promotes cholesterol production, indicating a surprising link between fatty acid synthesis and cholesterol synthesis. We further demonstrate that this process is required for TLR4 to enter lipid rafts and facilitate TLR4 signaling. In conclusion, we have uncovered an unexpected link between FASN and cholesterol synthesis that appears to be required for TLR signal transduction and proinflammatory macrophage activation.

The Interplay of Lipids, Lipoproteins, and Immunity in Atherosclerosis

PURPOSE OF REVIEW

Atherosclerosis is an inflammatory disorder of the arterial wall, in which several players contribute to the onset and progression of the disease. Besides the well-established role of lipids, specifically cholesterol, and immune cell activation, new insights on the molecular mechanisms underlying the atherogenic process have emerged.

RECENT FINDINGS

Meta-inflammation, a condition of low-grade immune response caused by metabolic dysregulation, immunological memory of innate immune cells (referred to as "trained immunity"), cholesterol homeostasis in dendritic cells, and immunometabolism, i.e., the interplay between immunological and metabolic processes, have all emerged as new actors during atherogenesis. These observations reinforced the interest in directly targeting inflammation to reduce cardiovascular disease. The novel acquisitions in pathophysiology of atherosclerosis reinforce the tight link between lipids, inflammation, and immune response, and support the benefit of targeting LDL-C as well as inflammation to decrease the CVD burden. How this will translate into the clinic will depend on the balance between costs (monoclonal antibodies either to PCSK9 or to IL-1ß), side effects (increased incidence of death due to infections for anti-IL-1ß antibody), and the benefits for patients at high CVD risk.

Saikosaponin a inhibits LPS-induced inflammatory response by inducing liver X receptor alpha activation in primary mouse macrophages

The aim of this study was to investigate the effects of SSa on LPS-induced endotoxemia in mice and clarify the possible mechanism. An LPS-induced endotoxemia mouse model was used to confirm the anti-inflammatory activity of SSa in vivo. The primary mouse macrophages were used to investigate the molecular mechanism and targets of SSa in vitro. In vivo, the results showed that SSa improved survival during lethal endotoxemia. In vitro, our results showed that SSa dose-dependently inhibited the expression of TNF-α, IL-6, IL-1β, IFN-β-and RANTES in LPS-stimulated primary mouse macrophages. Western blot analysis showed that SSa suppressed LPS-induced NF-κB and IRF3 activation. Furthermore, SSa disrupted the formation of lipid rafts by depleting cholesterol and inhibited TLR4 translocation into lipid rafts. Moreover, SSa activated LXRα, ABCA1 and ABCG1. Silencing LXRα abrogated the effect of SSa. In conclusion, the anti-inflammatory effects of SSa is associated with activating LXRα dependent cholesterol efflux pathway which result in disrupting lipid rafts by depleting cholesterol and reducing translocation of TLR4 to lipid rafts, thereby attenuating LPS mediated inflammatory response.

The role of adiponectin and adipolin as anti-inflammatory adipokines in the formation of macrophage foam cells and their association with cardiovascular diseases

Obesity is one of the major public health concerns that is closely associated with obesity-related disorders such as type 2 diabetes mellitus (T2DM), hypertension, and atherosclerosis. Atherosclerosis is a chronic disease characterized by excess cholesterol deposition in the arterial intima and the formation of foam cells. Adipocytokines or adipokines are secreted by the adipose tissue as endocrine glands; adiponectin and adipolin are among these adipokines that are associated with obese and insulin-resistant phenotypes. Adipolin and adiponectin are cytokines that exert substantial impact on obesity, progression of atherosclerosis, insulin resistance, and glucose metabolism. In this paper, we review the formation of macrophage foam cells, which are associated with atherosclerosis, and the macrophage mechanism, which includes uptake, esterification, and release. We also summarize current information on adipose tissue-derived hormone and energy homeostasis in obesity. Finally, the role of adipokines, e.g., adipoline and adiponectin, in regulating metabolic, cardiovascular diseases is discussed.

Macrophages and lipid metabolism

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The transcriptional signature of Kupffer cells & Alveolar macrophages are enriched for lipid metabolism genes.

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Lipid metabolism may control macrophage phenotype.

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Dysregulated lipid metabolism in macrophages contributes to disease pathology.

Distinct macrophage populations throughout the body display highly heterogeneous transcriptional and epigenetic programs. Recent research has highlighted that these profiles enable the different macrophage populations to perform distinct functions as required in their tissue of residence, in addition to the prototypical macrophage functions such as in innate immunity. These ‘extra’ tissue-specific functions have been termed accessory functions. One such putative accessory function is lipid metabolism, with macrophages in the lung and liver in particular being associated with this function. As it is now appreciated that cell metabolism not only provides energy but also greatly influences the phenotype and function of the cell, here we review how lipid metabolism affects macrophage phenotype and function and the specific roles played by macrophages in the pathogenesis of lipid-related diseases. In addition, we highlight the current questions limiting our understanding of the role of macrophages in lipid metabolism.

Targeted Deletion of Adipocyte Abca1 (ATP-Binding Cassette Transporter A1) Impairs Diet-Induced Obesity

OBJECTIVE

Adipose tissue cholesterol increases with adipocyte triglyceride content and size during development of obesity. However, how adipocyte cholesterol affects adipocyte function is poorly understood. The aim of this study was to evaluate the role of the cellular cholesterol exporter, Abca1 (ATP-binding cassette transporter A1), on adipose tissue function during diet-induced obesity.

APPROACH AND RESULTS

Adiponectin Cre recombinase transgenic mice were crossed with Abca1^flox/flox mice to generate ASKO (adipocyte-specific Abca1 knockout) mice. Control and ASKO mice were then fed a high-fat, high-cholesterol (45% calories as fat and 0.2% cholesterol) diet for 16 weeks. Compared with control mice, ASKO mice had a 2-fold increase in adipocyte plasma membrane cholesterol content and significantly lower body weight, epididymal fat pad weight, and adipocyte size. ASKO versus control adipose tissue had decreased PPARγ (peroxisome proliferator-activated receptor γ) and CCAAT/enhancer-binding protein expression, nuclear SREBP1 (sterol regulatory element-binding protein 1) protein, lipogenesis, and triglyceride accretion but similar Akt activation after acute insulin stimulation. Acute siRNA-mediated Abca1 silencing during 3T3L1 adipocyte differentiation reduced adipocyte Abca1 and PPARγ protein expression and triglyceride content. Systemic stimulated triglyceride lipolysis and glucose homeostasis were similar between control and ASKO mice.

CONCLUSIONS

Adipocyte Abca1 is a key regulator of adipocyte lipogenesis and lipid accretion, likely because of increased adipose tissue membrane cholesterol, resulting in decreased activation of lipogenic transcription factors PPARγ and SREBP1.

Immunometabolic Signaling Pathways Contribute to Macrophage and Dendritic Cell Function

Understanding of antigen-presenting cell (APC) participation in tissue inflammation and metabolism has advanced through numerous studies using systems biology approaches. Previously unrecognized connections between these research areas have been elucidated in the context of inflammatory disease involving innate and adaptive immune responses. A new conceptual framework bridges APC biology, metabolism, and cytokines in the generation of effective T-cell responses. Exploring these connections is paramount to addressing the rising tide of multi-organ system diseases, particularly chronic diseases associated with metabolic syndrome, infection, and cancer. Focused research in these areas will aid the development of strategies to harness and manipulate innate immunology to improve vaccine development, anti-viral, anti-inflammatory, and anti-tumor therapies. This review highlights recent advances in APC "immunometabolism" specifically related to chronic viral and metabolic disease in humans. The goal of this review is to develop an abridged and consolidated outlook on recent thematic updates to APC immunometabolism in the areas of regulation and crosstalk between metabolic and inflammatory signaling and the integrated stress response and how these signals dictate APC function in providing T-cell activation Signal 3.

Inhibition of miR-361-5p suppressed pulmonary artery smooth muscle cell survival and migration by targeting ABCA1 and inhibiting the JAK2/STAT3 pathway

MicroRNAs play a crucial role in the progression of pulmonary arterial hypertension (PAH). The aim of this study was to investigate the effect of miR-361-5p on the proliferation, migration and apoptosis of pulmonary artery smooth muscle cells (PASMCs) that under the treatment of hypoxia and explore the underlying mechanisms. The results proved that hypoxia noticeably up-regulated the expression of miR-361-5p in PASMCs in comparison to the normoxia-treated cells, while TNF-α and IL-6 stimulation had no obvious effects on miR-361-5p level. Hypoxia induced miR-361-5p elevation in a HIF-1α-dependent manner. Inhibition of miR-361-5p dramatically inhibited hypoxia-induced cell proliferation and migration. miR-361-5p inhibition also rescued hypoxia exposure caused suppression of PASMCs apoptosis. In addition, the results showed that ABCA1 was a direct target of miR-361-5p and was down-regulated in hypoxia-induced PASMCs. Hypoxia and TNF-α or IL-6 stimulation significantly inhibited ABCA1 expression. In addition, overexpression of ABCA1 enhanced the effect of miR-361-5p on hPASMCs. Furthermore, the inhibition of miR-361-5p significantly down-regulated the expression level of p-JAK2 and p-STAT3. In conclusion, it may suggest that the suppression of miR-361-5p suppressed PASMC survival and migration by targeting ABCA1 and inhibiting the JAK2/STAT3 pathway.

[Bidirectional regulation of Pam3CSK4?induced inflammatory response by ATP?binding cassette transporter A1 knockdown in mouse mononuclear macrophages in vitro]

OBJECTIVE

To investigate the regulatory effect of ATP?binding cassette transporter A1 (ABCA1) knockdown on inflammatory response induced by Pam3CSK4 in mouse mononuclear macrophage RAW264.7 cell line.

METHODS

A mouse mononuclear macrophage RAW264.7 cell line with stable ABCA1 knockdown was constructed and stimulated with Toll?like receptor 2 (TLR2) ligand Pam3CSK4, and the changes in the transcriptional levels of the proinflammatory and anti-inflammatory cytokines were analyzed in this cell model.

RESULTS

In RAW264.7 cells, ABCA1 knockdown significantly up-regulated Pam3CSK4 stimulation?induced expressions of IL?1β, TNF?α and IL?6 and also enhanced the expression of transcription factor cAMP?dependent transcription factor 3 (ATF3) without obviously affecting the expressions of the transcription factors ATF1, ATF2, ATF4 or ATF5.

CONCLUSION

ABCA1 knockdown in macrophages may have both proinflammatory and anti?inflammatory effects. ABCA1 knockdown up?regulates the transcription of ATF3 possibly through a mechanism that is different from that for the other members of the ATF protein family.

LRP1 integrates murine macrophage cholesterol homeostasis and inflammatory responses in atherosclerosis

Low-density lipoprotein receptor-related protein 1 (LRP1) is a multifunctional cell surface receptor with diverse physiological roles, ranging from cellular uptake of lipoproteins and other cargo by endocytosis to sensor of the extracellular environment and integrator of a wide range of signaling mechanisms. As a chylomicron remnant receptor, LRP1 controls systemic lipid metabolism in concert with the LDL receptor in the liver, whereas in smooth muscle cells (SMC) LRP1 functions as a co-receptor for TGFβ and PDGFRβ in reverse cholesterol transport and the maintenance of vascular wall integrity. Here we used a knockin mouse model to uncover a novel atheroprotective role for LRP1 in macrophages where tyrosine phosphorylation of an NPxY motif in its intracellular domain initiates a signaling cascade along an LRP1/SHC1/PI3K/AKT/PPARγ/LXR axis to regulate and integrate cellular cholesterol homeostasis through the expression of the major cholesterol exporter ABCA1 with apoptotic cell removal and inflammatory responses.

Targeting nuclear receptors for the treatment of fatty liver disease

Ligand-activated nuclear receptors, including peroxisome proliferator-activated receptor alpha (PPARα), pregnane X receptor, and constitutive androstane receptor, were first identified as key regulators of the responses against chemical toxicants. However, numerous studies using mouse disease models and human samples have revealed critical roles for these receptors and others, such as PPARβ/δ, PPARγ, farnesoid X receptor (FXR), and liver X receptor (LXR), in maintaining nutrient/energy homeostasis in part through modulation of the gut-liver-adipose axis. Recently, disorders associated with disrupted nutrient/energy homeostasis, e.g., obesity, metabolic syndrome, and non-alcoholic fatty liver disease (NAFLD), are increasing worldwide. Notably, in NAFLD, a progressive subtype exists, designated as non-alcoholic steatohepatitis (NASH) that is characterized by typical histological features resembling alcoholic steatohepatitis (ASH), and NASH/ASH are recognized as major causes of hepatitis virus-unrelated liver cirrhosis and hepatocellular carcinoma. Since hepatic steatosis is basically caused by an imbalance between fat/energy influx and utilization, abnormal signaling of these nuclear receptors contribute to the pathogenesis of fatty liver disease. Standard therapeutic interventions have not been fully established for fatty liver disease, but some new agents that activate or inhibit nuclear receptor signaling have shown promise as possible therapeutic targets. In this review, we summarize recent findings on the roles of nuclear receptors in fatty liver disease and discuss future perspectives to develop promising pharmacological strategies targeting nuclear receptors for NAFLD/NASH.

Myeloid-specific genetic ablation of ATP-binding cassette transporter ABCA1 is protective against cancer

Increased circulating levels of apolipoprotein A-I (apoA-I), the major protein of high-density lipoprotein (HDL), by genetic manipulation or infusion, protects against melanoma growth and metastasis. Herein, we explored potential roles in melanoma tumorigenesis for host scavenger receptor class B, type 1 (SR-B1), and ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1), all mediators of apoA-I and HDL sterol and lipid transport function. In a syngeneic murine melanoma tumor model, B16F10, mice with global deletion of SR-B1 expression exhibited increased plasma HDL cholesterol (HDLc) levels and decreased tumor volume, indicating host SR-B1 does not directly contribute to HDL-associated anti-tumor activity. In mice with myeloid-specific loss of ABCA1 (Abca1-M/-M ; A1-M/-M), tumor growth was inhibited by ∼4.8-fold relative to wild type (WT) animals. Abcg1-M/-M (G1-M/-M) animals were also protected by 2.5-fold relative to WT, with no further inhibition of tumor growth in Abca1/Abcg1 myeloid-specific double knockout animals (DKO). Analyses of tumor-infiltrating immune cells revealed a correlation between tumor protection and decreased presence of the immune suppressive myeloid-derived suppressor cell (MDSC) subsets, Ly-6G+Ly-6CLo and Ly-6GnegLy-6CHi cells. The growth of the syngeneic MB49 murine bladder cancer cells was also inhibited in A1-M/-M mice. Collectively, our studies provide further evidence for an immune modulatory role for cholesterol homeostasis pathways in cancer.

C1q/Tumor necrosis factor-related protein-3 protects macrophages against LPS-induced lipid accumulation, inflammation and phenotype transition via PPARγ and TLR4-mediated pathways

Macrophage inflammation and foam cell formation are critical events during the initiation and development of atherosclerosis (AS). C1q/tumor necrosis factor-related protein-3 (CTRP3) is a novel adipokine with anti-inflammatory and cardioprotection properties; however, little is known regarding the influence of CTRP3 on AS. As macrophages play a key role in AS, this study investigated the effects of CTRP3 on macrophage lipid metabolism, inflammatory reactions, and phenotype transition, as well as underlying mechanisms, to reveal the relationship between CTRP3 and AS. CTRP3 reduced the number of lipid droplets, lowered cholesteryl ester (CE), total cholesterol (TC), and free cholesterol (FC) levels, reduced the CE/TC ratio, and dose-dependently inhibited TNFα, IL-6, MCP-1, MMP-9 and IL-1β release in lipopolysaccharide (LPS)-stimulated THP-1 macrophages and mouse peritoneal macrophages. Pretreatment with CTRP3 effectively increased macrophage transformation to M2 macrophages rather than M1 macrophages. Western blotting showed that the specific NF-κB pathway inhibitor ammonium pyrrolidine dithiocarbamate (PDTC) or siRNA targeting PPARγ/LXRα markedly strengthened or abolished the above-mentioned effects of CTRP3, respectively. These results show that CTRP3 inhibits TLR4-NF-κB pro-inflammatory pathways but activates the PPARγ-LXRα-ABCA1/ABCG1 cholesterol efflux pathway. Taken together, CTRP3 participates in anti-lipid accumulation, anti-inflammation and macrophage phenotype conversion via the TLR4-NF-κB and PPARγ-LXRα-ABCA1/ABCG1 pathways and, thus, may have anti-atherosclerotic properties.