CD11cHi monocyte-derived macrophages are a major cellular compartment infected by Mycobacterium tuberculosis.

During tuberculosis, lung myeloid cells have two opposing roles: they are an intracellular niche occupied by Mycobacterium tuberculosis, and they restrict bacterial replication. Lung myeloid cells from mice infected with yellow-fluorescent protein expressing M. tuberculosis were analyzed by flow cytometry and transcriptional profiling to identify the cell types infected and their response to infection. CD14, CD38, and Abca1 were expressed more highly by infected alveolar macrophages and CD11cHi monocyte-derived cells compared to uninfected cells. CD14, CD38, and Abca1 "triple positive" (TP) cells had not only the highest infection rates and bacterial loads, but also a strong interferon-γ signature and nitric oxide synthetase-2 production indicating recognition by T cells. Despite evidence of T cell recognition and appropriate activation, these TP macrophages are a cellular compartment occupied by M. tuberculosis long-term. Defining the niche where M. tuberculosis resists elimination promises to provide insight into why inducing sterilizing immunity is a formidable challenge.

MicroRNA-33 Regulates the Innate Immune Response via ATP Binding Cassette Transporter-mediated Remodeling of Membrane Microdomains.

MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression by promoting degradation and/or repressing translation of specific target mRNAs. Several miRNAs have been identified that regulate the amplitude of the innate immune response by directly targeting Toll-like receptor (TLR) pathway members and/or cytokines. miR-33a and miR-33b (the latter present in primates but absent in rodents and lower species) are located in introns of the sterol regulatory element-binding protein (SREBP)-encoding genes and control cholesterol/lipid homeostasis in concert with their host gene products. These miRNAs regulate macrophage cholesterol by targeting the lipid efflux transporters ATP binding cassette (ABC)A1 and ABCG1. We and others have previously reported that Abca1(-/-) and Abcg1(-/-) macrophages have increased TLR proinflammatory responses due to augmented lipid raft cholesterol. Given this, we hypothesized that miR-33 would augment TLR signaling in macrophages via a raft cholesterol-dependent mechanism. Herein, we report that multiple TLR ligands down-regulate miR-33 in murine macrophages. In the case of lipopolysaccharide, this is a delayed, Toll/interleukin-1 receptor (TIR) domain-containing adapter-inducing interferon-ß-dependent response that also down-regulates Srebf-2, the host gene for miR-33. miR-33 augments macrophage lipid rafts and enhances proinflammatory cytokine induction and NF-κB activation by LPS. This occurs through an ABCA1- and ABCG1-dependent mechanism and is reversible by interventions upon raft cholesterol and by ABC transporter-inducing liver X receptor agonists. Taken together, these findings extend the purview of miR-33, identifying it as an indirect regulator of innate immunity that mediates bidirectional cross-talk between lipid homeostasis and inflammation.

Macrophages engulfing apoptotic cells produce nonclassical retinoids to enhance their phagocytic capacity.

Previous work in our laboratory has shown that transglutaminase 2 (TG2) acting as a coreceptor for integrin ß3 is required for proper phagocytosis of apoptotic cells. In the absence of TG2, systemic lupus erythematosus-like autoimmunity develops in mice, similarly to other mice characterized by a deficiency in the clearance of apoptotic cells. In this study, we demonstrate that increasing TG2 expression alone in wild-type macrophages is not sufficient to enhance engulfment. However, during engulfment, the lipid content of the apoptotic cells triggers the lipid-sensing receptor liver X receptor (LXR), which in response upregulates the expression of the phagocytic receptor Mer tyrosine kinase and the phagocytosis-related ABCA1, and that of retinaldehyde dehydrogenases leading to the synthesis of a nonclassical retinoid. Based on our retinoid analysis, this compound might be a dihydro-retinoic acid derivative. The novel retinoid then contributes to the upregulation of further phagocytic receptors including TG2 by ligating retinoic acid receptors. Inhibition of retinoid synthesis prevents the enhanced phagocytic uptake induced by LXR ligation. Our data indicate that stimulation of LXR enhances the engulfment of apoptotic cells via regulating directly and indirectly the expression of a range of phagocytosis-related molecules, and its signaling pathway involves the synthesis of a nonclassical retinoid. We propose that retinoids could be used for enhancing the phagocytic capacity of macrophages in diseases such as systemic lupus erythematosus, where impaired phagocytosis of apoptotic cells plays a role in the pathogenesis of the disease.

ATP-binding cassette transporter 1 attenuates ovalbumin-induced neutrophilic airway inflammation.

Apolipoprotein A-I (apoA-I) is an important component of high-density lipoprotein particles that mediates reverse cholesterol transport out of cells by interacting with the ATP-binding cassette transporter 1 (ABCA1). apoA-I has also been shown to attenuate neutrophilic airway inflammation in experimental ovalbumin (OVA)-induced asthma by reducing the expression of granulocyte colony-stimulating factor (G-CSF). Here, we hypothesized that overexpression of the ABCA1 transporter might similarly attenuate OVA-induced neutrophilic airway inflammation. Tie2-human ABCA1 (hABCA1) mice expressing human ABCA1 under the control of the Tie2 promoter, which is primarily expressed by vascular endothelial cells, but can also be expressed by macrophages, received daily intranasal OVA challenges, 5 d/wk for 5 weeks. OVA-challenged Tie2-hABCA1 mice had significant reductions in total bronchoalveolar lavage fluid (BALF) cells that reflected a decrease in neutrophils, as well as reductions in peribronchial inflammation, OVA-specific IgE levels, and airway epithelial thickness. The reduced airway neutrophilia in OVA-challenged Tie2-hABCA1 mice was associated with significant decreases in G-CSF protein levels in pulmonary vascular endothelial cells, alveolar macrophages, and BALF. Intranasal administration of recombinant murine G-CSF to OVA-challenged Tie2-hABCA1 mice for 5 days increased BALF neutrophils to a level comparable to that of OVA-challenged wild-type mice. We conclude that ABCA1 suppresses OVA-induced airway neutrophilia by reducing G-CSF production by vascular endothelial cells and alveolar macrophages. These findings suggest that ABCA1 expressed by vascular endothelial cells and alveolar macrophages may play important roles in attenuating the severity of neutrophilic airway inflammation in asthma.

Caprylic Acid Improves Lipid Metabolism, Suppresses the Inflammatory Response and Activates the ABCA1/p-JAK2/p-STAT3 Signaling Pathway in C57BL/6J Mice and RAW264.7 Cells.

OBJECTIVE: This study aimed to investigate the effects of caprylic acid (C8:0) on lipid metabolism and inflammation, and examine the mechanisms underlying these effects in mice and cells. METHODS: Fifty-six 6-week-old male C57BL/6J mice were randomly allocated to four groups fed a high-fat diet (HFD) without or with 2% C8:0, palmitic acid (C16:0) or eicosapentaenoic acid (EPA). RAW246.7 cells were randomly divided into five groups: normal, lipopolysaccharide (LPS), LPS+C8:0, LPS+EPA and LPS+cAMP. The serum lipid profiles, inflammatory biomolecules, and ABCA1 and JAK2/STAT3 mRNA and protein expression were measured. RESULTS: C8:0 decreased TC and LDL-C, and increased the HDL-C/LDL-C ratio after injection of LPS. Without LPS, it decreased TC in mice ( P < 0.05). Moreover, C8:0 decreased the inflammatory response after LPS treatment in both mice and cells ( P < 0.05). Mechanistic investigations in C57BL/6J mouse aortas after injection of LPS indicated that C8:0 resulted in higher ABCA1 and JAK2/STAT3 expression than that with HFD, C16:0 and EPA, and resulted in lower TNF-α, NF-κB mRNA expression than that with HFD ( P < 0.05). In RAW 264.7 cells, C8:0 resulted in lower expression of pNF-κBP65 than that in the LPS group, and higher protein expression of ABCA1, p-JAK2 and p-STAT3 than that in the LPS and LPS+cAMP groups ( P < 0.05). CONCLUSION: Our studies demonstrated that C8:0 may play an important role in lipid metabolism and the inflammatory response, and the mechanism may be associated with ABCA1 and the p-JAK2/p-STAT3 signaling pathway.

trans-Chalcone prevents insulin resistance and hepatic inflammation and also promotes hepatic cholesterol efflux in high-fat diet-fed rats: modulation of miR-34a-, miR-451-, and miR-33a-related pathways.

Insulin resistance and inflammation are strongly linked to non-alcoholic fatty liver disease (NAFLD) as a feature of the metabolic syndrome. Furthermore, the role of dysregulation of miR-34a, miR-451, and miR-33a in pathogenesis and progression of NAFLD has been identified. trans-Chalcone is a simple chalcone with anti-diabetic and anti-inflammatory activities. However, to the best of our knowledge, miRNA-dependent mechanisms of these protective effects under pathologic conditions are not understood. Thus, this study, for the first time, aimed to evaluate the effects of trans-Chalcone on miR-34a, miR-451, and miR-33a signaling pathways in the liver of high-fat (HF) emulsion-fed rats. To this aim, twenty-one rats were randomly and equally divided into three groups: control, which was gavaged with 10% tween 80; HF, which was gavaged with HF emulsion and 10% tween 80; and HF + trans-Chalcone (HF + TC), which was gavaged with HF emulsion and trans-Chalcone. Then, circulating levels of glucose and insulin were measured and used for the calculation of HOMA-IR. Hepatic expression levels of miR-34a, miR-451, miR-33a, SIRT1, and ABCA1 and also protein levels of ABCA1 and IL-8 were assayed. In this study, trans-chalcone increased hepatic cholesterol efflux and prevented insulin resistance and liver inflammation in HF emulsion-fed rats. These protective effects were modulated through the down-regulation of miR-34a and its associated elevation of SIRT1, the up-regulation of miR-451 which was associated with a reduction in IL-8, and the inhibition of miR-33a which was related to the elevation of ABCA1 in the liver of HF emulsion-fed rats. Therefore, trans-Chalcone exerts its beneficial effects by targeting hepatic miR-34a-, miR-451-, and miR-33a-related pathways.

Activation of liver X receptors inhibit LPS-induced inflammatory response in primary bovine mammary epithelial cells.

Liver X Receptors (LXRs) belong to the nuclear receptor superfamily, have been reported that activation of LXRs with synthetic ligands has anti-inflammatory effects in various inflammatory diseases. This study aims at investigating the effects of T0901317 (T0), a synthetic LXRs ligand, on lipopolysaccharide (LPS)-stimulated primary bovine mammary epithelial cells (bMECs). BMECs were stimulated by LPS in the presence or absence of T0. The results showed that treatment with T0 significantly inhibited LPS-induced tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and interleukin-6 (IL-6) expression. LPS-induced NF-κB activation was also suppressed by T0. Furthermore, T0 was found to inhibit the translocation of TLR4 to lipid rafts. T0 could activate ATP-binding cassette transporter A1 (ABCA1) dependent pathway which induced cholesterol efflux from cells and disrupted the formation of lipid rafts. Thus, based on those findings we proposed that LXRs agonist might become a novel therapeutic target for inflammation.

Cholesterol Accumulation in Dendritic Cells Links the Inflammasome to Acquired Immunity.

Autoimmune diseases such as systemic lupus erythematosus (SLE) are associated with increased cardiovascular disease and reduced plasma high-density lipoprotein (HDL) levels. HDL mediates cholesterol efflux from immune cells via the ATP binding cassette transporters A1 and G1 (ABCA1/G1). The significance of impaired cholesterol efflux pathways in autoimmunity is unknown. We observed that Abca1/g1-deficient mice develop enlarged lymph nodes (LNs) and glomerulonephritis suggestive of SLE. This lupus-like phenotype was recapitulated in mice with knockouts of Abca1/g1 in dendritic cells (DCs), but not in macrophages or T cells. DC-Abca1/g1 deficiency increased LN and splenic CD11b+ DCs, which displayed cholesterol accumulation and inflammasome activation, increased cell surface levels of the granulocyte macrophage-colony stimulating factor receptor, and enhanced inflammatory cytokine secretion. Consequently, DC-Abca1/g1 deficiency enhanced T cell activation and Th1 and Th17 cell polarization. Nlrp3 inflammasome deficiency diminished the enlarged LNs and enhanced Th1 cell polarization. These findings identify an essential role of DC cholesterol efflux pathways in maintaining immune tolerance.

Impact of TLR 2, TLR 4-activation on the Expression of ABCA1 and ABCG1 in Raw Cells.

Toll-like receptors (TLR) activation is thought to modulate the macrophage cholesterol efflux and contribute to the atherosclerosis progression; however, the precise pathophysiological mechanism remains unclear. We investigated the effects of TLR2- and TLR4-activation on the expression of the ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 in a mouse macrophage cell line, Raw 264.7. Both TLR2- and TLR4-activation upregulated the expression of ABCA1 mRNA but downregulated that of ABCG1 mRNA. These alterations may be mainly regulated by the following 3 cascades: (1) the TLR/myeloid differentiation primary-response protein 88/Liver X receptor pathway, which upregulated the ABCA1 mRNA; (2) NF-κB pathway, which downregulated the ABCG1 mRNA, and (3) the p38 pathway, which upregulated and stabilized ABCA1 mRNA. These cascades are involved in a complex crosstalk and result in the upregulation of ABCA1 mRNA without a change in ABCA1 protein and the down-regulation of ABCG1 mRNA leading to the increase in ABCG1 protein. These alterations, especially the induction of ABCG1 protein, may be closely involved with the development of atherosclerosis.

Caprylic Acid Improves Lipid Metabolism, Suppresses the Inflammatory Response and Activates the ABCA1/p-JAK2/p-STAT3 Signaling Pathway in C57BL/6J Mice and RAW264.7 Cells / 生物医学与环境科学（英文）

OBJECTIVE@#This study aimed to investigate the effects of caprylic acid (C8:0) on lipid metabolism and inflammation, and examine the mechanisms underlying these effects in mice and cells.@*METHODS@#Fifty-six 6-week-old male C57BL/6J mice were randomly allocated to four groups fed a high-fat diet (HFD) without or with 2% C8:0, palmitic acid (C16:0) or eicosapentaenoic acid (EPA). RAW246.7 cells were randomly divided into five groups: normal, lipopolysaccharide (LPS), LPS+C8:0, LPS+EPA and LPS+cAMP. The serum lipid profiles, inflammatory biomolecules, and ABCA1 and JAK2/STAT3 mRNA and protein expression were measured.@*RESULTS@#C8:0 decreased TC and LDL-C, and increased the HDL-C/LDL-C ratio after injection of LPS. Without LPS, it decreased TC in mice ( P < 0.05). Moreover, C8:0 decreased the inflammatory response after LPS treatment in both mice and cells ( P < 0.05). Mechanistic investigations in C57BL/6J mouse aortas after injection of LPS indicated that C8:0 resulted in higher ABCA1 and JAK2/STAT3 expression than that with HFD, C16:0 and EPA, and resulted in lower TNF-α, NF-κB mRNA expression than that with HFD ( P < 0.05). In RAW 264.7 cells, C8:0 resulted in lower expression of pNF-κBP65 than that in the LPS group, and higher protein expression of ABCA1, p-JAK2 and p-STAT3 than that in the LPS and LPS+cAMP groups ( P < 0.05).@*CONCLUSION@#Our studies demonstrated that C8:0 may play an important role in lipid metabolism and the inflammatory response, and the mechanism may be associated with ABCA1 and the p-JAK2/p-STAT3 signaling pathway.

The A's Have It: Developing Apolipoprotein A-I Mimetic Peptides Into a Novel Treatment for Asthma.

New treatments are needed for patients with asthma who are refractory to standard therapies, such as individuals with a phenotype of "type 2-low" inflammation. This important clinical problem could potentially be addressed by the development of apolipoprotein A-I (apoA-I) mimetic peptides. ApoA-I interacts with its cellular receptor, the ATP-binding cassette subfamily A, member 1 (ABCA1), to facilitate cholesterol efflux out of cells to form nascent high-density lipoprotein particles. The ability of the apoA-I/ABCA1 pathway to promote cholesterol efflux from cells that mediate adaptive immunity, such as antigen-presenting cells, can attenuate their function. Data from experimental murine models have shown that the apoA-I/ABCA1 pathway can reduce neutrophilic airway inflammation, primarily by suppressing the production of granulocyte-colony stimulating factor. Furthermore, administration of apoA-I mimetic peptides to experimental murine models of allergic asthma has decreased both neutrophilic and eosinophilic airway inflammation, as well as airway hyperresponsiveness and mucous cell metaplasia. Higher serum levels of apoA-I have also been associated with less severe airflow obstruction in patients with asthma. Collectively, these results suggest that the apoA-I/ABCA1 pathway may have a protective effect in asthma, and support the concept of advancing inhaled apoA-I mimetic peptides to clinical trials that can assess their safety and effectiveness. Thus, we propose that the development of inhaled apoA-I mimetic peptides as a new treatment could represent a clinical advance for patients with severe asthma who are unresponsive to other therapies.

HDL does not influence the polarization of human monocytes toward an alternative phenotype.

BACKGROUND: Macrophages are crucial cells in the pathogenesis of atherosclerosis. Macrophages are plastic cells which can switch from a classical pro-inflammatory M1 to an alternative anti-inflammatory M2 macrophage phenotype, depending on the environmental stimuli. Because high-density lipoprotein (HDL) cholesterol levels are inversely correlated to cardiovascular disease and since HDL displays anti-inflammatory properties, we investigated whether HDL can affect alternative macrophage differentiation of primary human monocytes in the presence of interleukin (IL)-4, a M2 macrophage polarization driver, in vitro and ex vivo. METHODS AND RESULTS: M2 macrophages are highly responsive to HDL stimulation, since the expression of pentraxin 3 (PTX3), a well known HDL target gene, is induced by HDL more strongly in M2 macrophages than in control unpolarized resting macrophages (RM). As expected, the expression of M2 markers, such as Mannose Receptor (MR), CD200 Receptor (CD200R), Coagulation factor XIII A1 (F13A1), IL-1 receptor antagonist (IL-1RA) and IL10, was induced in IL-4 polarized M2 macrophages compared to RM. However, incubation with HDL added in vitro did not modulate the gene expression of M2 macrophage polarization markers. Moreover, monocytes isolated from subjects with genetically low HDL levels, carrying ABCA1 or LCAT mutations, differentiated ex vivo into M2 macrophages without any difference in the alternative macrophage marker expression profile. CONCLUSIONS: These in vitro and ex vivo results indicate that, contrary to mouse macrophages, HDL does not influence macrophage M2 polarization of human monocyte-derived macrophages. Thus, the anti-inflammatory properties of HDL in humans are probably not related to the enhancement of the M2 macrophage phenotype.