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Xuewei Zhu,
Marlena M Westcott,
Xin Bi,
Mingxia Liu,
Kymberly M Gowdy,
Jeongmin Seo,
Qiang Cao,
Abraham K Gebre,
Michael B Fessler,
Elizabeth M Hiltbold,
John S Parks
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ABSTRACT: Rationale: ATP-binding cassette transporter A1 (ABCA1) plays a critical role in eliminating excess free cholesterol (FC) from tissues by effluxing cellular FC and phospholipids to lipid-poor apolipoprotein A-I. Macrophage ABCA1 also dampens pro-inflammatory MyD88-dependent Toll-like receptor signaling by reducing cellular membrane FC and lipid raft content, indicating a role of ABCA1 in innate immunity. However, whether ABCA1 expression has a role in regulating macrophage function in vivo is unknown. Objective: We investigated whether macrophage ABCA1 expression impacts host defense function, including microbial killing and chemotaxis. Methods and Results: Myeloid cell-specific ABCA1 knockout (MSKO) vs. wild type (WT) mice were infected with Listeria monocytogenes (Lm) for 36h or 72h before sacrifice. Lm-induced monocytosis was similar for WT and MSKO mice; however, MSKO mice were more resistant to Lm infection, with significantly less body weight loss, less Lm burden in liver and spleen, and less hepatic damage 3 days post infection. In addition, Lm-infected MSKO mouse livers had: 1) greater MCP-1 and MIP-2 expression, 2) more monocyte/macrophage infiltration, 3) less neutral lipid accumulation, and 4) diminished expression of lipogenic genes. MSKO macrophages showed enhanced chemotaxis toward chemokines in vitro and increased migration from peritoneum in response to LPS in vivo. Lm infection of WT macrophages markedly reduced expression of ABCA1 protein as well as other cholesterol export proteins (such as ABCG1 and apoE). Conclusions: Myeloid-specific ABCA1 deletion favors host response to and clearance of Lm. Macrophage Lm infection reduces expression of cholesterol export proteins, suggesting that diminished cholesterol efflux enhances innate immune function of macrophages.
Circulation Research 09/2012; · 9.49 Impact Factor
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ABSTRACT: Fish oil, containing omega-3 fatty acids, attenuates atherosclerosis. We hypothesized that omega-3 fatty acid-enriched oils are atheroprotective through alteration of monocyte subsets and their trafficking into atherosclerotic lesions.
Low-density lipoprotein receptor knockout and apolipoprotein E(-/-) mice were fed diets containing 10% (calories) palm oil and 0.2% cholesterol, supplemented with an additional 10% palm oil, echium oil (containing 18:4 n-3), or fish oil. Compared with palm oil-fed low-density lipoprotein receptor knockout mice, echium oil and fish oil significantly reduced plasma cholesterol, splenic Ly6C(hi) monocytosis by ≈50%, atherosclerosis by 40% to 70%, monocyte trafficking into the aortic root by ≈50%, and atherosclerotic lesion macrophage content by 30% to 44%. In contrast, atherosclerosis and monocyte trafficking into the artery wall was not altered by omega-3 fatty acids in apolipoprotein E(-/-) mice; however, Ly6C(hi) splenic monocytes positively correlated with aortic root intimal area across all diet groups. In apolipoprotein E(-/-) mice, fish oil reduced the percentage of blood Ly6C(hi) monocytes, despite an average 2-fold higher plasma cholesterol relative to palm oil.
The presence of splenic Ly6C(hi) monocytes parallels the appearance of atherosclerotic disease in both low-density lipoprotein receptor knockout and apolipoprotein E(-/-) mice. Furthermore, omega-3 fatty acids favorably alter monocyte subsets independently from effects on plasma cholesterol and reduce monocyte recruitment into atherosclerotic lesions.
Arteriosclerosis Thrombosis and Vascular Biology 07/2012; 32(9):2122-30. · 6.37 Impact Factor
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Mary G Sorci-Thomas,
John S Owen,
Brian Fulp,
Shaila Bhat, Xuewei Zhu,
John S Parks,
Dharika Shah,
W Gray Jerome,
Mark Gerelus,
Manal Zabalawi,
Michael J Thomas
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ABSTRACT: This report details the lipid composition of nascent HDL (nHDL) particles formed by the action of the ATP binding cassette transporter A1 (ABCA1) on apolipoprotein A-I (apoA-I). nHDL particles of different size (average diameters of ∼ 12, 10, 7.5, and <6 nm) and composition were purified by size-exclusion chromatography. Electron microscopy suggested that the nHDL were mostly spheroidal. The proportions of the principal nHDL lipids, free cholesterol, glycerophosphocholine, and sphingomyelin were similar to that of lipid rafts, suggesting that the lipid originated from a raft-like region of the cell. Smaller amounts of glucosylceramides, cholesteryl esters, and other glycerophospholipid classes were also present. The largest particles, ∼ 12 nm and 10 nm diameter, contained ∼ 43% free cholesterol, 2-3% cholesteryl ester, and three apoA-I molecules. Using chemical cross-linking chemistry combined with mass spectrometry, we found that three molecules of apoA-I in the ∼ 9-14 nm nHDL adopted a belt-like conformation. The smaller (7.5 nm diameter) spheroidal nHDL particles carried 30% free cholesterol and two molecules of apoA-I in a twisted, antiparallel, double-belt conformation. Overall, these new data offer fresh insights into the biogenesis and structural constraints involved in forming nascent HDL from ABCA1.
The Journal of Lipid Research 06/2012; 53(9):1890-909. · 5.56 Impact Factor
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ABSTRACT: High-density lipoprotein (HDL) levels are inversely associated with coronary heart disease due to HDL's ability to transport excess cholesterol in arterial macrophages to the liver for excretion [i.e., reverse cholesterol transport (RCT)]. However, recent advances highlight additional atheroprotective roles for HDL beyond bulk cholesterol removal from cells through RCT. By promoting cellular free cholesterol (FC) efflux, HDL and its apolipoproteins (apoA-I and apoE) decrease plasma membrane FC and lipid raft content in immune and hematopoietic stem cells, decreasing inflammatory and cell proliferation signaling pathways. HDL and apoA-I also dampen inflammatory signaling pathways independent of cellular FC efflux. In addition, HDL lipid and protein cargo provide protection against parasitic and bacterial infection, endothelial damage, and oxidant toxicity. Here, current knowledge is reviewed regarding the role of HDL and its apolipoproteins in regulating cellular cholesterol homeostasis, highlighting recent advances on novel functions and mechanisms by which HDLs regulate inflammation and hematopoiesis.
Annual Review of Nutrition 04/2012; 32:161-82. · 9.45 Impact Factor
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Yun-Hee Youm,
Thirumala-Devi Kanneganti,
Bolormaa Vandanmagsar, Xuewei Zhu,
Anthony Ravussin,
Ayinuer Adijiang,
John S Owen,
Michael J Thomas,
Joseph Francis,
John S Parks,
Vishwa Deep Dixit
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ABSTRACT: The collapse of thymic stromal cell microenvironment with age and resultant inability of the thymus to produce naive T cells contributes to lower immune-surveillance in the elderly. Here we show that age-related increase in 'lipotoxic danger signals' such as free cholesterol (FC) and ceramides, leads to thymic caspase-1 activation via the Nlrp3 inflammasome. Elimination of Nlrp3 and Asc, a critical adaptor required for inflammasome assembly, reduces age-related thymic atrophy and results in an increase in cortical thymic epithelial cells, T cell progenitors and maintenance of T cell repertoire diversity. Using a mouse model of irradiation and hematopoietic stem cell transplantation (HSCT), we show that deletion of the Nlrp3 inflammasome accelerates T cell reconstitution and immune recovery in middle-aged animals. Collectively, these data demonstrate that lowering inflammasome-dependent caspase-1 activation increases thymic lymphopoiesis and suggest that Nlrp3 inflammasome inhibitors may aid the re-establishment of a diverse T cell repertoire in middle-aged or elderly patients undergoing HSCT.
Cell reports. 01/2012; 1(1):56-68.
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ABSTRACT: The previous studies in our laboratory revealed that seven cysteine mutants of apolipoprotein A-I (apoA-I) have different structural features and biological activities in vitro and in vivo. To investigate the potential cardioprotective effects of apolipoprotein A-I(N74C) [apoA-I(N74C)], we examined the anti-inflammatory, antioxidant, and antiatherosclerotic effects of this cysteine mutant in a rapid atherosclerosis model induced by perivascular carotid collar placement in apoE⁻/⁻ mice. Lipid-free apoA-I(N74C) showed a significant increased antioxidant potency in low density lipoprotein (LDL) oxidation in vitro and reduced intracellular lipid accumulation in THP-1-derived macrophages, relative to wild-type apoA-I (apoA-Iwt). Mice injected with recombinant HDL (rHDL) reconstituted with apoA-I(N74C) (named rHDL74) through tail veins (40 mg/kg of body weight, three injections) had a significant lower level of serum interleukin-6 (IL-6) and enhanced serum antioxidation compared with mice receiving rHDL reconstituted with apoA-Iwt (named rHDLwt). Moreover, compared with rHDLwt, the rHDL74 in vivo injection resulted in a significant decrease in plaque size, ratio of aorta intima to media, arterial remodeling, and macrophage content in lesions. In summary, intravenous injection with rHDL74 reconstituted with apoA-I cysteine mutant apoA-I (N74C) dramatically delays the development of atherosclerosis induced by perivascular carotid collar placement and reduces vascular remodeling in the carotid artery in apoE⁻/⁻ mice.
The Journal of Lipid Research 12/2010; 51(12):3434-42. · 5.56 Impact Factor
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ABSTRACT: We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.
The Journal of Lipid Research 11/2010; 51(11):3196-206. · 5.56 Impact Factor
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ABSTRACT: Crosstalk exists in mammalian cells between cholesterol trafficking and innate immune signaling. Apolipoprotein A-I (apoA-I), a serum apolipoprotein that induces antiatherogenic efflux of macrophage cholesterol, is widely described as anti-inflammatory because it neutralizes bacterial lipopolysaccharide. Conversely, lipopolysaccharide-induced inflammation is proatherogenic. However, whether innate immunity plays an endogenous, physiological role in host cholesterol homeostasis in the absence of infection is undetermined. We report that apoA-I signals in the macrophage through Toll-like receptor (TLR)2, TLR4, and CD14, utilizing myeloid differentiation primary response protein 88 (MyD88)-dependent and -independent pathways, to activate nuclear factor-kappaB and induce cytokines. MyD88 plays a critical role in reverse cholesterol transport in vitro and in vivo, in part through promoting ATP-binding cassette A1 transporter upregulation. Taken together, this work identifies apoA-I as an endogenous stimulus of innate immunity that couples cholesterol trafficking to inflammation through MyD88 and identifies innate immunity as a physiologic signal in cholesterol homeostasis.
Cell metabolism 06/2010; 11(6):493-502. · 17.35 Impact Factor
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J Mark Brown,
Soonkyu Chung,
Janet K Sawyer,
Chiara Degirolamo,
Heather M Alger,
Tam M Nguyen, Xuewei Zhu,
My-Ngan Duong,
Amanda L Brown,
Caleb Lord,
Ramesh Shah,
Matthew A Davis,
Kathryn Kelley,
Martha D Wilson,
Jennifer Madenspacher,
Michael B Fessler,
John S Parks,
Lawrence L Rudel
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ABSTRACT: Stearoyl-CoA desaturase 1 (SCD1) is a critical regulator of energy metabolism and inflammation. We have previously reported that inhibition of SCD1 in hyperlipidemic mice fed a saturated fatty acid (SFA)-enriched diet prevented development of the metabolic syndrome, yet surprisingly promoted severe atherosclerosis. In this study we tested whether dietary fish oil supplementation could prevent the accelerated atherosclerosis caused by SCD1 inhibition.
LDLr(-/-), ApoB(100/100) mice were fed diets enriched in saturated fat or fish oil in conjunction with antisense oligonucleotide (ASO) treatment to inhibit SCD1. As previously reported, in SFA-fed mice, SCD1 inhibition dramatically protected against development of the metabolic syndrome, yet promoted atherosclerosis. In contrast, in mice fed fish oil, SCD1 inhibition did not result in augmented macrophage inflammatory response or severe atherosclerosis. In fact, the combined therapy of dietary fish oil and SCD1 ASO treatment effectively prevented both the metabolic syndrome and atherosclerosis.
SCD1 ASO treatment in conjunction with dietary fish oil supplementation is an effective combination therapy to comprehensively combat the metabolic syndrome and atherosclerosis in mice.
Arteriosclerosis Thrombosis and Vascular Biology 10/2009; 30(1):24-30. · 6.37 Impact Factor
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J Mark Brown,
Soonkyu Chung,
Janet K Sawyer,
Chiara Degirolamo,
Heather M Alger,
Tam Nguyen, Xuewei Zhu,
My-Ngan Duong,
Amanda L Wibley,
Ramesh Shah,
Matthew A Davis,
Kathryn Kelley,
Martha D Wilson,
Carol Kent,
John S Parks,
Lawrence L Rudel
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ABSTRACT: Stearoyl-coenzyme A desaturase 1 (SCD1) is a well-known enhancer of the metabolic syndrome. The purpose of the present study was to investigate the role of SCD1 in lipoprotein metabolism and atherosclerosis progression.
Antisense oligonucleotides were used to inhibit SCD1 in a mouse model of hyperlipidemia and atherosclerosis (LDLr(-/-)Apob(100/100)). In agreement with previous reports, inhibition of SCD1 protected against diet-induced obesity, insulin resistance, and hepatic steatosis. Unexpectedly, however, SCD1 inhibition strongly promoted aortic atherosclerosis, which could not be reversed by dietary oleate. Further analyses revealed that SCD1 inhibition promoted accumulation of saturated fatty acids in plasma and tissues and reduced plasma triglyceride, yet had little impact on low-density lipoprotein cholesterol. Because dietary saturated fatty acids have been shown to promote inflammation through toll-like receptor 4, we examined macrophage toll-like receptor 4 function. Interestingly, SCD1 inhibition resulted in alterations in macrophage membrane lipid composition and marked hypersensitivity to toll-like receptor 4 agonists.
This study demonstrates that atherosclerosis can occur independently of obesity and insulin resistance and argues against SCD1 inhibition as a safe therapeutic target for the metabolic syndrome.
Circulation 10/2008; 118(14):1467-75. · 14.74 Impact Factor
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ABSTRACT: HDL has been shown to be able to neutralize the toxicity of lipopolysaccharide (LPS). Our previous study (J. Lipid Res. 2005. 46: 1303-1311) characterized the properties of secondary structure and in vitro functions of different cysteine mutants of apolipoprotein A-I. Here, we reconstituted recombinant HDLs (named rHDLwt, rHDL52, rHDL74, rHDL107, rHDL129, rHDL173, rHDL195, and rHDL228) by mixing wild type or those mutants with dipalmitoyl phosphatidylcholine and examined their in vivo effects on LPS-induced endotoxemia in mice. Our results showed that 24 h after injection, mice receiving rHDL74 or rHDL52 had a significant decrease of plasma tumor necrosis factor alpha (TNF-alpha) and interleukin-1beta (IL-1beta), compared with control mice receiving either saline or rHDLwt (P < 0.05). Administration of rHDL74 to mice injected with LPS also led to a decrease of plasma IL-6, protection of lung against acute injury, and attenuation of endotoxin-induced clinical symptoms in mice, compared with controls injected with LPS only. However, injection of rHDL228 significantly increased plasma concentration of TNF-alpha and exacerbated LPS-induced lung injury. In summary, compared with rHDLwt, rHDL74 and rHDL52 exhibit higher anti-inflammation capabilities, whereas rHDL228 shows hyper-proinflammation by exacerbating LPS-induced endotoxemia in mice.
The Journal of Lipid Research 08/2008; 49(8):1640-5. · 5.56 Impact Factor
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Xuewei Zhu,
Ji-Young Lee,
Jenelle M Timmins,
J Mark Brown,
Elena Boudyguina,
Anny Mulya,
Abraham K Gebre,
Mark C Willingham,
Elizabeth M Hiltbold,
Nilamadhab Mishra,
Nobuyo Maeda,
John S Parks
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ABSTRACT: Macrophage-specific Abca1 knock-out (Abca1(-)(M)(/-)(M)) mice were generated to determine the role of macrophage ABCA1 expression in plasma lipoprotein concentrations and the innate immune response of macrophages. Plasma lipid and lipoprotein concentrations in chow-fed Abca1(-)(M)(/-)(M) and wild-type (WT) mice were indistinguishable. Compared with WT macrophages, Abca1(-)(M)(/-)(M) macrophages had a >95% reduction in ABCA1 protein, failed to efflux lipid to apoA-I, and had a significant increase in free cholesterol (FC) and membrane lipid rafts without induction of endoplasmic reticulum stress. Lipopolysaccharide (LPS)-treated Abca1(-)(M)(/-)(M) macrophages exhibited enhanced expression of pro-inflammatory cytokines and increased activation of the NF-kappaB and MAPK pathways, which could be diminished by silencing MyD88 or by chemical inhibition of NF-kappaB or MAPK. In vivo LPS injection also resulted in a higher pro-inflammatory response in Abca1(-)(M)(/-)(M) mice compared with WT mice. Furthermore, cholesterol depletion of macrophages with methyl-beta-cyclodextrin normalized FC content between the two genotypes and their response to LPS; cholesterol repletion of macrophages resulted in increased cellular FC accumulation and enhanced cellular response to LPS. Our results suggest that macrophage ABCA1 expression may protect against atherosclerosis by facilitating the net removal of excess lipid from macrophages and dampening pro-inflammatory MyD88-dependent signaling pathways by reduction of cell membrane FC and lipid raft content.
Journal of Biological Chemistry 06/2008; 283(34):22930-41. · 4.77 Impact Factor
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ABSTRACT: Abstract Angiogenesis plays an important role in normal physiology of blood vessel growth, but can contribute to the pathogenesis of diseases, such as cancer. A new anti-angiogenic recombinant kringle protein, composed of the fused domains of human apolipoprotein(a) carboxyl-terminal kringle IV-10 and kringle V, was expressed in Pichia pastoris and human colorectal carcinoma (HCT 116) cells to investigate its influence on angiogenesis and tumor growth. The mature recombinant protein exhibited the characteristic features of kringle-containing proteins (glycosylation and disulfide bond formation) and, when added to cultures of human umbilical vein endothelial cell, resulted in a 31% decrease in proliferation relative to untreated controls (p<0.05). The neo-angiogenesis was diminished by 63% in chick embryos treated with 10 mug recombinant protein compared with 7% for phosphate buffer solution-treated embryos (p<0.01). Transfection of a kringle IV-10-kringle V fusion protein construct into HCT 116 cells decreased tumorigenesis and inhibited tumor growth in vivo without affecting tumor cell proliferation. HCT 116 cells that expressed recombinant protein displayed a much lower relative growth ratio of 8% (p<0.01) against the control tumor cells. From these results, we conclude that human apolipoprotein(a) carboxyl-terminal kringle IV-10-kringle V fusion protein is an effective inhibitor of angiogenesis and angiogenesis-dependent tumor growth.
Biological Chemistry 02/2008; 389(2):135-41. · 2.96 Impact Factor
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ABSTRACT: ApoAV, a newly discovered apolipoprotein, plays a key role in human triglyceride homeostasis; however, the structure-function correlation of apoAV is not clearly understood. To explore the relationship, wild type and six deletion mutants, that is (AV (Delta(1-51)), AV (Delta(51-128)), AV (Delta(132-188)), AV (Delta(192-238)), AV (Delta(246-299)), AV (Delta(301-343))), of human apoAV expressed in Escherichia coli were studied. All the deleted regions together encompass almost the entire 343 amino acid sequence of wild type apoAV. Circular dichroism spectroscopy showed that the alpha helical content of lipid-free wild type apoAV was 46%. In comparison with wild type apoAV, AV (Delta(192-238)) and AV (Delta(301-343)) displayed significantly decreased lipid binding activities, confirming the importance of these two regions in lipid binding function of apoAV. While, the LPL activation function of apoAV remarkably impaired after deletion of residues 192-238. These findings suggested that the domain (192-238) is absolutely necessary for apoAV in lipid binding and lipoprotein lipase activation.
Chemistry and Physics of Lipids 10/2006; 143(1-2):22-8. · 2.57 Impact Factor
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ABSTRACT: Apolipoprotein A-I(Milano) (A-I(M)) (R173C), a natural mutant of human apolipoprotein A-I (apoA-I), and five other cysteine variants of apoA-I at residues 52 (S52C), 74 (N74C), 107 (K107C), 129 (G129C), and 195 (K195C) were generated. Cysteine residues were incorporated in each of the various helices at the same helical wheel position as for the substitution in A-I(M). The secondary structural properties of the monomeric mutants, their abilities to bind lipid and to promote cholesterol efflux from THP-1 macrophages, and the possibility of antiperoxidation were investigated. Results showed that the alpha helical contents of all of the cysteine mutants were similar to that of wild-type apoA-I (wtapoA-I). The cysteine variant of A-I(M) at residue 173 [A-I(M)(R173C)] exhibited weakened structural stability, whereas A-I(G129C) a more stable structure than wtapoA-I. A-I(G129C) and A-I(K195C) exhibited significantly impaired capabilities to bind lipid compared with wtapoA-I. A-I(K107C) possessed a higher capacity to promote cholesterol efflux from macrophages than wtapoA-I, and A-I(M)(R173C) and A-I(K195C) exhibited an impaired efflux capability. Neither A-I(M)(R173C) nor any other cysteine mutant could resist oxidation against lipoxygenase. In summary, in spite of the similar mutant position on the helix, these variants exhibited different structural features or biological activities, suggesting the potential influence of the local environment of mutations on the whole polypeptide chain.
The Journal of Lipid Research 07/2005; 46(6):1303-11. · 5.56 Impact Factor
