High-density Lipoprotein In Macrophages Research Articles

Phosphatidylserine enhances anti-inflammatory effects of reconstituted HDL in macrophages via distinct intracellular pathways.

Phosphatidylserine (PS) is a minor phospholipid constituent of high-density lipoprotein (HDL) that exhibits potent anti-inflammatory activity. It remains indeterminate whether PS incorporation can enhance anti-inflammatory effects of reconstituted HDL (rHDL). Human macrophages were treated with rHDL containing phosphatidylcholine alone (PC-rHDL) or PC and PS (PC/PS-rHDL). Interleukin (IL)-6secretion and expression was more strongly inhibited by PC/PS-rHDL than PC-rHDL in both tumor necrosis factor (TNF)-α- and lipopolysaccharide (LPS)-stimulated macrophages. siRNA experiments revealed that the enhanced anti-inflammatory effects of PC/PS-rHDL required scavenger receptor class B type I (SR-BI). Furthermore, PC/PS-rHDL induced a greater increase in Akt1/2/3 phosphorylation than PC-rHDL. In addition, PC/PS but not PC-rHDL decreased the abundance of plasma membrane lipid rafts and p38mitogen-activated protein kinase (p38MAPK) phosphorylation. Finally, when these rHDL formulations were administered to dyslipidemic low-density lipoprotein (LDL)-receptor knockout mice fed a high-cholesterol diet, circulating IL-6levels were significantly reduced only in PC/PS-rHDL-treated mice. In parallel, enhanced Akt1/2/3 phosphorylation by PC/PS-rHDL was observed in the mouse aortic tissue using immunohistochemistry. We concluded that the incorporation of PS into rHDLs enhanced their anti-inflammatory activity by modulating Akt1/2/3- and p38MAPK-mediated signaling through SR-BI in stimulated macrophages. These data identify PS as a potent anti-inflammatory component capable of enhancing therapeutic potential of rHDL-based therapy.

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

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 APOA1Tg;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. Reconstituted HDL infusions in hypercholesterolemic atherosclerotic mice produced anti-inflammatory effects in lesion macrophages suggesting a beneficial therapeutic effect of HDL in vivo.

Modification of HDL by reactive aldehydes alters select cardioprotective functions of HDL in macrophages.

While increased levels of high-density lipoprotein (HDL)-cholesterol correlate with protection against cardiovascular disease, recent findings demonstrate that HDL function, rather than HDL-cholesterol levels, may be a better indicator of cardiovascular risk. One mechanism by which HDL function can be compromised is through modification by reactive aldehydes such as acrolein (Acro), 4-hydroxynonenal, and malondialdehyde (MDA). In this study, we tested the hypothesis that modification of HDL with reactive aldehydes would impair HDL's athero-protective functions in macrophages. Compared to native HDL, Acro- and MDA-modified HDL have impaired abilities to promote migration of primary peritoneal macrophages isolated from C57BL6/J mice. Incubation of macrophages with MDA-HDL also led to an increased ability to generate reactive oxygen species. Our studies revealed that the changes in HDL function following aldehyde modification are likely not through activation of canonical nuclear factor-kappa B signaling pathways. Consistent with this finding, treatment of either noncholesterol-loaded macrophages or foam cells with modified forms of HDL does not lead to significant changes in expression levels of inflammatory markers. Importantly, our data also demonstrate that changes in HDL function are dependent on the type of modification present on the HDL particle. Our findings suggest that modification of HDL with reactive aldehydes can impair some, but not all, of HDL's athero-protective functions in macrophages.

Novel Mechanism of Regulation of the 5-lipoxygenase/leukotriene B4 Pathway by High-Density Lipoprotein in Macrophages

Novel Mechanism of Regulation of the 5-lipoxygenase/leukotriene B4 Pathway by High-Density Lipoprotein in Macrophages

Novel mechanism of regulation of the 5-lipoxygenase/leukotriene B4 pathway by high-density lipoprotein in macrophages

High-density lipoprotein (HDL) interacts with various cells, particularly macrophages, in functional cell-HDL interactions. Here, we found that HDL protein quality and lipid quality play critical roles in HDL functions. HDL fractions from healthy volunteers (HDLHealthy) and patients with recurrent coronary atherosclerotic disease (HDLCAD) were prepared. To analyse functional HDL-macrophage interactions, macrophages were co-incubated with each HDL, and lipid mediator production was assessed by liquid chromatography/mass spectrometry-based metabololipidomics. HDLHealthy treatment attenuated the pro-inflammatory lipid mediator production, particularly that of leukotriene (LT) B4, and this treatment enhanced lipoxin (LX) B4 and resolvin (Rv) E2 production. HDLHealthy treatment enhanced the proteasome-mediated degradation of the LTB4-producing enzyme 5-lipoxygenase (LO) in activated macrophages; however, HDLCAD did not show these anti-inflammatory effects. HDLHealthy was engulfed by macrophages via clathrin-mediated endocytosis, which was a critical step in 5-LO/LTB4 regulation. We also found that HDLCAD showed higher levels of the LTB4-producing enzymes and thus promoted LTB4 production from HDLCAD. In addition, LTB4 attenuated HDL endocytosis, HDL-mediated 5-LO degradation in macrophages, and HDL-derived augmentation of macrophage phagocytosis. These results indicated that local LTB4 produced de novo from HDLCAD regulates HDL-macrophage functional interactions and plays critical roles in dysfunctional, inflammatory HDL characteristics.

9-cis β-Carotene Increased Cholesterol Efflux to HDL in Macrophages.

Cholesterol efflux from macrophages is a key process in reverse cholesterol transport and, therefore, might inhibit atherogenesis. 9-cis-β-carotene (9-cis-βc) is a precursor for 9-cis-retinoic-acid (9-cis-RA), which regulates macrophage cholesterol efflux. Our objective was to assess whether 9-cis-βc increases macrophage cholesterol efflux and induces the expression of cholesterol transporters. Enrichment of a mouse diet with βc from the alga Dunaliella led to βc accumulation in peritoneal macrophages. 9-cis-βc increased the mRNA levels of CYP26B1, an enzyme that regulates RA cellular levels, indicating the formation of RA from βc in RAW264.7 macrophages. Furthermore, 9-cis-βc, as well as all-trans-βc, significantly increased cholesterol efflux to high-density lipoprotein (HDL) by 50% in RAW264.7 macrophages. Likewise, food fortification with 9-cis-βc augmented cholesterol efflux from macrophages ex vivo. 9-cis-βc increased both the mRNA and protein levels of ABCA1 and apolipoprotein E (APOE) and the mRNA level of ABCG1. Our study shows, for the first time, that 9-cis-βc from the diet accumulates in peritoneal macrophages and increases cholesterol efflux to HDL. These effects might be ascribed to transcriptional induction of ABCA1, ABCG1, and APOE. These results highlight the beneficial effect of βc in inhibition of atherosclerosis by improving cholesterol efflux from macrophages.

Anti-Inflammatory Effects of High-Density Lipoprotein Through Activating Transcription Factor 3

High-density lipoprotein (HDL) cholesterol levels are inversely proportional to the risk of atherosclerosis. However, the evidence that raising HDL per se will reduce atherosclerosis and thereby cardiovascular events remains controversial, and mechanisms of putative HDL-mediated atheroprotection remain unclear. In addition to canonical role of HDL in mobilizing excess cholesterol from arterial wall macrophages (the first step in reverse cholesterol transport), there is compelling evidence to support the anti-inflammatory effects of HDL, both dependent and independent of its cholesterol transport capacities.1 Macrophages serve as important orchestrators of inflammation at the intersection of immunity, metabolism, and cardiovascular diseases. Yet anti-inflammatory effects of HDL in macrophages are less well understood. In a recent issue of Nature Immunology , De Nardo et al2 report that anti-inflammatory effects of HDL in macrophages are mediated through the induction of activating transcription factor 3 (ATF3), an ancient transcriptional modulator that provides negative feedback on toll-like receptor (TLR) innate immune signaling. The authors first describe that pretreatment with both native HDL and reconstituted HDL (apoA-I and phospholipids) inhibited cytokine production by multiple distinct TLR ligands in murine bone marrow–derived macrophages (BMDM), human peripheral blood mononuclear cells, and TLR ligand–treated mice, an in vivo model of acute inflammation and liver injury. Although HDL is known to interact and neutralize the TLR4 ligand lipopolysaccharide directly, the authors showed that HDL did not interact with TLR1/2 ligands (Pam3CSK4) and the TLR9 ligand (CpG DNA) and did not directly modulate TLR1/2/9 activation, signaling transduction (eg, …

63 : Investigating the anti-inflammatory effects of HDL in macrophages

Elevated levels of High Density Lipoprotein (HDL) are correlated with decreased risk of cardiovascular disease. Much of this effect is attributed to the efflux of cellular cholesterol to HDL, reducing foam cell formation and atherosclerosis progression. HDL also has remarkable anti-inflammatory properties, for instance it can down-regulate adhesion molecule expression on endothelial cells, which may interfere with immune cell recruitment. Considering the important role of macrophages and Toll Like Receptors (TLRs) in sterile inflammatory conditions such as atherosclerosis, we directly investigated the effect of HDL on macrophage activation by TLR ligands. Here we show that HDL protects against TLR-driven, macrophage mediated liver damage in vivo and macrophage cytokine secretion in vitro. HDL does not affect upstream TLR signaling, but rather inhibits pro-inflammatory gene expression at the transcriptional level. Microarray analysis revealed that HDL strongly modulates macrophage transcription, and we identified ATF3, a transcriptional repressor of the CREB family of basic leucine zipper transcription factors, as a key mediator of HDL’s effects. HDL treatment increases ATF3 expression both in vitro and in vivo and increases occupancy of ATF3 at the promoters of its target genes. Consistent with these findings, the anti-inflammatory effects of HDL on TLR-mediated cytokine expression is lost in ATF3−/− macrophages. This work identifies a new biology for HDL as an inducer of the transcriptional modulator ATF3 and presents an opportunity to exploit endogenous molecules for therapeutic potential.

マクロファージにおけるＨＤＬの細胞内動態 トランス側ゴルジ装置との関連

High density lipoprotein (HDL) is known to participate in the removal of free cholesterol from cholesterol-loaded cultured macrophages. To provide some morphological evidence to this phenomenon, endocytic uptake and intracellular pathway of HDL in rat petironeal macrophages were investigated at the electron microscopic level. A horseradish peroxidase conjugate of HDL (HDL-HRP) showed specific binding to coated pits of the plasma membrane on the incubation with the cells at 4°C. When the cells were warmed to 37°C for various periods, HDL-HRP was internalized and delivered through coated vesicles and tubulo-vesicular system to endosomes at the periphery of cytoplasm. Further incubation revealed the distribution in endosomes of the Golgi region as well as trans-Golgi vesiceles, followed by resecretion out of the cells. Thus, these results disclosed the unique endocytosis -resecretion pathway of HDL in macrophages that we call HDL pathway. In addition, comparing the intracellular pathway of transferrin by the same approach, transferrin-HRP conjugates showed their indistinguishable movement through trans-Golgi vesicles from that of HDL.Trans-Golgi system has recently been emphasized to play an important role in receptor recycling as well as membrane sorting (Pastan & Willingham). In the light of the present findings, we believe that HDL shares the same fate as transferrin through this compartment. Furthermore, it could be postulated that cholesterol transport from cholesterolloaded macrophages to HDL molecule might occur in this unique HDL pathway.