Oxidant resistant human apolipoprotein A-I functions similarly to the unmodified human isoform in delaying atherosclerosis progression and promoting atherosclerosis regression in hyperlipidemic mice

Background

Transgenic overexpression of apolipoprotein A-I (apoA1) has been shown to delay atherosclerosis lesion progression and promote lesion regression in mouse models; however, apoA1 is subject to oxidation by myeloperoxidase (MPO) and loss of function. The activity of oxidant resistant human apoA1 was compared to unmodified human apoA1 in mouse models of atherosclerosis progression and regression.

Methods and results

Human apoA1 and the MPO oxidant resistant 4WF isoform transgenic mice were bred to LDL receptor deficient (LDLr KO) mice and fed a western-type diet. High level expression of these human apoA1 isoforms did not lead to increased HDL-cholesterol levels on the LDLr KO background. In males and females, lesion progression was studied over time, and both apoA1 and 4WF transgenic mice vs. LDLr KO mice had significant and similar delayed lesion progression and reduced non-HDL cholesterol. Using time points with equivalent lesion areas, lesion regression was initiated by feeding the mice a low-fat control diet containing a microsomal triglyceride transfer protein inhibitor for 7 weeks. Lesions regressed more in the male apoA1 and 4WF transgenics vs. the LDLr KO, but the 4WF isoform was not superior to the unmodified isoform in promoting lesion regression.

Conclusions

Both human apoA1 and the 4WF MPO oxidant resistant apoA1 isoform delayed lesion progression and promoted lesion regression in LDLr KO mice, with more pronounced effects in males than females; moreover, the 4WF isoform functioned similarly to the unmodified human apoA1 isoform.

Soat1 mediates the mouse strain effects on cholesterol loading-induced endoplasmic reticulum stress and CHOP expression in macrophages

We previously demonstrated that AKR vs. DBA/2 mouse bone marrow derived macrophages have higher levels of free cholesterol and lower levels of esterified cholesterol after cholesterol loading, and that AKR, but not DBA/2, macrophages induced C/EBP homologous protein (CHOP) expression after cholesterol loading. We earlier determined that the free and esterified cholesterol level effect is due to a truncation in the sterol O-acyltransferase 1 (Soat1) gene, encoding acetyl-coenzyme A acetyltransferase 1 (ACAT1). Here we examined the mechanism for the differential induction of CHOP by cholesterol loading. CHOP was induced in both strains after incubation with tunicamycin, indicating both strains have competent endoplasmic reticulum stress pathways. CHOP was induced when DBA/2 macrophages were cholesterol loaded in the presence of an ACAT inhibitor, indicating that the difference in free cholesterol levels were responsible for this strain effect. This finding was confirmed in macrophages derived from DBA/2 embryonic stem cells. Cholesterol loading of Soat1 gene edited cells, mimicking the AKR allele, led to increased free cholesterol levels and restored CHOP induction. The upstream pathway of free cholesterol induced endoplasmic reticulum stress was investigated; and, RNA-dependent protein kinase-like endoplasmic reticulum kinase (PERK) and inositol-requiring enzyme 1 α protein kinase (IRE1α) pathways were required for maximal CHOP expression.

Microscopic imaging as a tool to target spatial and temporal extraction of bioactive compounds through ultrasound intensification

Unravelling a chain of events in ultrasound-assisted extraction (UAE) of bioactive compounds from plants has to start with a detailed description of destructuration at macroscopic and microscopic scale. The present work aims to study the impacts and interactions of UAE on the extreme complexity and diversity of plants structures. Three plant species were selected for their difference in specialized structures and their spatial distribution of secondary metabolites: bitter orange leaf (C. aurantium L.), blackcurrant leaf (R. nigrum L.), and artichoke leaf (C. scolymus L.). Different microscopic techniques (Cyto-histochemistry, stereomicroscopic analysis, Scanning Electron Microscopy (SEM)) have been used to understand the complexity of plant structures and to highlight ultrasound-induced impacts especially on metabolites storage structures, with a neat comparison with conventional "silent" extraction procedure. The main results indicate that spatial UAE impacts are strongly related to plant structures' properties (morphology, thickness, etc.) and particularly to the nature and the chemical constitution of their storage specialized structures. From a temporal point of view, for all studied leaves, observed mechanisms followed a special order according to structures and their mechanical resistance level to ultrasound (US) treatment. Microscopic mapping of metabolites and structures should be considered as a decision tool during UAE to target intensification process.

Correction: Interleukin-22-deficiency and microbiota contribute to the exacerbation of Toxoplasma gondii-induced intestinal inflammation

The original version of this Article omitted the author Dr Mathias Chamaillard from the l'Institut de Pasteur, Lille, France. This has been corrected in both the PDF and HTML versions of the Article.

Interleukin-22-deficiency and microbiota contribute to the exacerbation of Toxoplasma gondii-induced intestinal inflammation

Upon oral infection with Toxoplasma gondii cysts (76 K strain) tachyzoites are released into the intestinal lumen and cross the epithelial barrier causing damage and acute intestinal inflammation in C57BL/6 (B6) mice. Here we investigated the role of microbiota and IL-22 in T.gondii-induced small intestinal inflammation. Oral T.gondii infection in B6 mice causes inflammation with IFNγ and IL-22 production. In IL-22-deficient mice, T.gondii infection augments the Th1 driven inflammation. Deficiency in either IL-22bp, the soluble IL-22 receptor or Reg3γ, an IL-22-dependent antimicrobial lectin/peptide, did not reduce inflammation. Under germ-free conditions, T.gondii-induced inflammation was reduced in correlation with parasite load. But intestinal inflammation is still present in germ-free mice, at low level, in the lamina propria, independently of IL-22 expression. Exacerbated intestinal inflammation driven by absence of IL-22 appears to be independent of IL-22 deficiency associated-dysbiosis as similar inflammation was observed after fecal transplantation of IL-22-/- or WT microbiota to germ-free-WT mice. Our results suggest cooperation between parasite and intestinal microbiota in small intestine inflammation development and endogenous IL-22 seems to exert a protective role independently of its effect on the microbiota. In conclusion, IL-22 participates in T.gondii induced acute small intestinal inflammation independently of microbiota and Reg3γ.

Histo-cytochemistry and scanning electron microscopy for studying spatial and temporal extraction of metabolites induced by ultrasound. Towards chain detexturation mechanism

There are more than 1300 articles in scientific literature dealing with positive impacts of Ultrasound-Assisted Extraction (UAE) such as reduction of extraction time, diminution of solvent and energy used, enhancement in yield and even selectivity, intensification of diffusion, and eliminating wastes. This present study aims to understand what are the mechanism(s) behind these positive impacts which will help to design a decision tool for UAE of natural products. Different microscopic observations (Scanning Electron Microscopy (SEM), Environmental Scanning Electron Microscopy (e-SEM), Cyto-histochemistry) have been used for spacial and temporal localization of metabolites in rosemary leaves, which is one of the most studied and most important plant for its antioxidant metabolites used in food industry, during conventional and ultrasound extraction. The study permits to highlight that ultrasound impacted rosemary leaves not by a single or different mechanisms in function of ultrasound power, as described by previous studies, but by a chain detexturation mechanism in a special order: local erosion, shear forces, sonoporation, fragmentation, capillary effect, and detexturation. These detexturation impacts followed a special order during ultrasound treatment leading at the end to the total detexturation of rosemary leaves. These mechanisms and detexturation impacts were identified in glandular trichomes, non-glandular-trichomes and the layer adaxial and abaxial cuticle. Modelling metabolites diffusion phenomenon during conventional and ultrasound extraction with the second Fick's law allowed the estimation of diffusivities and solvent penetration into the inner tissues and in meantime to accelerate the release of valuable metabolites.

Consideration of Sex Differences in Design and Reporting of Experimental Arterial Pathology Studies-Statement From ATVB Council

There are many differences in arterial diseases between men and women, including prevalence, clinical manifestations, treatments, and prognosis. The new policy of the National Institutes of Health, which requires the inclusion of sex as a biological variable for preclinical studies, aims to foster new mechanistic insights and to enhance our understanding of sex differences in human diseases. The purpose of this statement is to suggest guidelines for designing and reporting sex as a biological variable in animal models of atherosclerosis, thoracic and abdominal aortic aneurysms, and peripheral arterial disease. We briefly review sex differences of these human diseases and their animal models, followed by suggestions on experimental design and reporting of animal studies for these vascular pathologies.

Quantitative Trait Locus Mapping of Macrophage Cholesterol Metabolism and CRISPR/Cas9 Editing Implicate an ACAT1 Truncation as a Causal Modifier Variant

OBJECTIVE

Cholesterol metabolism is a dynamic process involving intracellular trafficking, cholesterol esterification, and cholesterol ester hydrolysis. Our objective was to identify genes that regulate macrophage cholesterol metabolism.

APPROACHES AND RESULTS

We performed quantitative trait loci mapping of free and esterified cholesterol levels and the ratio of esterified to free cholesterol in acetylated low-density lipoprotein-loaded bone marrow-derived macrophages from an AKR×DBA/2 strain intercross. Ten distinct cholesterol modifier loci were identified, and bioinformatics was used to prioritize candidate genes. The strongest locus was located on distal chromosome 1, which we named Mcmm1 (macrophage cholesterol metabolism modifier 1). This locus harbors the Soat1 (sterol O-acyltransferase 1) gene, encoding Acyl-coenzyme A:cholesterol acyltransferase 1 (ACAT1), which esterifies free cholesterol. The parental AKR strain has an exon 2 deletion in Soat1, which leads to a 33 amino acid N-terminal truncation in ACAT1. CRISPR/Cas9 editing of DBA/2 embryonic stem cells was performed to replicate the AKR strain Soat1 exon 2 deletion, while leaving the remainder of the genome unaltered. DBA/2 stem cells and stem cells heterozygous and homozygous for the Soat1 exon 2 deletion were differentiated into macrophages and loaded with acetylated low-density lipoprotein. DBA/2 stem cell-derived macrophages accumulated less free cholesterol and more esterified cholesterol relative to cells heterozygous and homozygous for the Soat1 exon 2 deletion.

CONCLUSIONS

A Soat1 deletion present in AKR mice, and resultant N-terminal ACAT1 truncation, was confirmed to be a significant modifier of macrophage cholesterol metabolism. Other Mcmm loci candidate genes were prioritized via bioinformatics.

Abstract 171: Lysosomal Response Tocholesterol Loading is Altered in DBA/2 Mouse Foam Cells Which May Explain Impairedautolysosome Formation and Lipid Droplets Clearance

In a previous study, we identified autolysosome formation as the limiting step for turnover of cholesterol esters in lipid droplets of macrophage foam cells from the athero-sensitive DBA/2 strain compared to the athero-resistant AKR mouse strain. As autophagosome formation was similar in these two strains, we hypothesized that the lysosomal response to acetylated LDL (AcLDL) loading may be defective in DBA/2 vs. AKR foam cells. For all our studies, we cultured AKR and DBA/2 macrophages with or without AcLDL for 24h. AcLDL loaded DBA/2 vs. AKR cells exhibited a 40 to 50% decrease in lysosome number as measured by staining cells with Lysotracker or an anti-Lamp1 antibody, respectively. Lysosomal degradation capacity was assayed by cell incubation with Alexa647-DQ-ovalbumin, and we observed that AcLDL loading led to a 15% decrease in lysosomal capacity in DBA/2 foam cells (p<0.001) while it had no effect in AKR cells. Also, unloaded and loaded AKR cells had higher degradation capacity than DBA/2 cells (31% and 43%, respectively, p<0.001) which couldn’t be explained by a change in lysosomal pH. As the transcription factor TFEB is a key regulator for lysosome biogenesis and function, we analyzed TFEB protein expression by western blot. Upon loading, TFEB was increased in AKR (48%) but not DBA/2 cells leading to a 45% higher TFEB level in AKR vs. DBA/2 foam cells (p<0.05). AKR and DBA/2 macrophages were labeled with a TFEB antibody and the nucleus to cytoplasm fluorescence intensity ratio was assessed. AcLDL loading led to a 37% increase in TFEB nuclear localization in AKR foam cells vs. unloaded cells (p<0.001) with no effect in DBA/2 macrophages. These results were confirmed by western blot after cellular fractionation. In conclusion, we found that DBA/2 vs. AKR foam cells have altered TFEB processing that may explain decreased lysosome number and function and impaired autolysosome formation in DBA/2 cells.

Abstract 649: Knockout of the Ath26 Quantitative Trait Locus Candidate Gene Cyp4f13 Decreases Atherosclerosis in DBA/2 ApoE-Deficient Mice

We previously identified the atherosclerosis modifying Ath26 quantitative trait locus (QTL) on mouse chr. 17 from intercrosses of apoE-/- mice on the AKR and DBA/2 background, where the DBA/2 allele is associated with larger lesions. The aim of our study was to identify causal genes responsible for Ath26 . Here we report confirmation of the Ath26 QTL in female AKR.DBAchr17 congenic mice, where inheriting 2 DBA/2 vs. AKR alleles at this locus resulted in ~5x larger lesions (p<0.001 by ANOVA posttest). We identified Cyp4f13 as a candidate gene in this locus from gene expression microarray data of bone marrow derived macrophages from individual F2 mice, where Cyp4f13 expression had the strongest correlation with lesion area of all expressed genes (r=0.46, p<0.0001, n=114). We obtained Cyp4f13 knockout (KO) embryonic stem cells and created KO mice that we backcrossed on the DBA/2 apoE-/- background. We bred male and female DBA/2 apoE-/- mice that were wild type (WT), hemizygous (HET), or KO for the Cyp4f13 gene. Chow diet fed mice were euthanized at 16 weeks of age. There were no significant differences in body weight, plasma total cholesterol or HDL-C among the 3 genotypes in either sex. Cross section lesion areas in the aortic root were not normally distributed and analyzed with non-parametric statistics. In male mice the lesions areas were smaller in the HET and KO vs. WT mice, and since the HET and KO mice had ~ equivalent lesions, we combined these two groups and found a significant 35 % decrease in median lesion area vs. WT mice (P=0.03, two-tailed Mann-Whitney test, HET+KO n=42, WT n=11). In female mice, lesions were 50% smaller in the HET and KO vs. WT mice (P=0.001, HET+KO n=31, WT n=17). Cyp4f13 belongs to the Cyp4F gene family containing 9 members in mice, 8 of which are clustered on chr. 17. Cyp4F proteins hydroxylate the omega carbon on arachadonic acid forming 20-HETE, and also hydroxylate leukotriene B4 (LTB4). Liver microsomes from Cyp4f13 HET mice had decreased 20-HETE forming activity vs. WT mice. 20-HETE and/or LTB4 metabolism may regulate inflammation and contribute to atherogenesis. We conclude that Cyp4f13 is an atherosclerosis modifier gene that may be partially responsible for the Ath26 QTL on chr. 17.

Abstract 550: TFEB Expression, Turnover, and Nuclear Localization are Altered in DBA/2 Mouse Macrophages Associated With Impaired Autolysosome Formation and Lipid Droplet Clearance

In a previous study, we identified autolysosome formation as the limiting step for turnover of cholesterol esters in lipid droplets of macrophage foam cells from the atherosclerosis sensitive DBA/2 strain compared to the atherosclerosis resistant AKR mouse strain. As autophagosome formation was similar in these two strains, we wanted to evaluate the role of lysosomes in autolysosome formation in AKR and DBA/2 cells. For all our studies, we cultured AKR and DBA/2 bone marrow-derived macrophages with or without acetylated LDL (AcLDL) for 24h. Lysosome function and number, assessed by flow cytometry on Lysotracker red DND-99 (LyT) labeled cells, was not affected by AcLDL loading in AKR and DBA/2 cells. However, in both unloaded and loaded conditions, DBA/2 cells exhibited a 30 to 50% lower LyT intensity suggesting that they have intrinsically decreased lysosome number/function. Lysosomal degradation capacity was assayed by incubation with DQ-ovalbumin and we observed a 27% decrease in lysosome function in DBA/2 vs. AKR foam cells (p<0.01). The impairment of lysosomal degradation was confirmed by 44.8% decreased levels of cathepsin L mature form in DBA/2 vs. AKR foam cells (p<0.05). As the transcription factor TFEB is a key regulator for lysosome biogenesis and function, we studied this factor in our system. First, we analyzed TFEB protein expression by western blot. Upon cholesterol loading, TFEB was induced in AKR (48%, p<0.01) but not DBA/2 cells leading to a 45% higher TFEB levels in AKR vs. DBA/2 foam cells (p<0.05). A preliminary evaluation of TFEB turnover by western blot also revealed that, upon loading, TFEB half-life is twice as long in AKR vs. DBA/2 macrophages (10.1h and 4.8h, respectively). Finally, we investigated TFEB nuclear translocation by immunofluorescence. AKR and DBA/2 macrophages were labeled with an antibody against TFEB and the percentage of TFEB positive nuclei was assessed. After 24h AcLDL loading, only 26% of DBA/2 nuclei contained TFEB vs. 48% for AKR nuclei (p=0.0002 by Fisher’s exact test). In conclusion, we found that DBA/2 vs. AKR foam cells have altered TFEB processing that may explain the altered lysosome number and function. This may result in the autolysosome formation defect in the DBA/2 foam cells.

Free-cholesterol-mediated autophagy of ORMDL1 stimulates sphingomyelin biosynthesis

Cholesterol confers unique biophysical properties to the plasma membrane bilayer that are essential for maintaining optimal membrane fluidity, which in turn regulate multiple physiological functions required to promote cellular integrity and viability. Conversely, excessive cholesterol causes pathological conditions such as atherosclerosis that can lead to heart attacks. Human atheroma macrophages carry a large burden of free cholesterol (FC) in addition to cholesterol esters. It is recognized that sterols can modulate the levels of other lipids to attain lipid homeostasis; thus, excess FC may play a role in modulating compensatory sphingolipid pathways. Recent studies have shown that excess lipids can cause ER stress and apoptosis. In contrast, autophagy may play a protective role by clearing excess lipids from macrophage foam cell lipid droplets. Interestingly, a macrophage study using a TLR4-specifc agonist showed that de novo sphingolipid biosynthesis is essential for autophagy induction, suggesting links between sphingolipid biosynthesis and autophagy. While the role of autophagy in removing excess lipids has been the focus of many studies, its role in fine-tuning cellular lipid homeostasis remains largely unexplored.

Abstract 536: Lysosome Insufficiency in Atherosclerosis Prone DBA/2 Mouse Macrophages Associated With Impaired Autolysosome Formation and Lipid Drop Clearance

In a previous study, we identified autolysosome formation as the limiting step for turnover of cholesterol esters in lipid droplets of macrophage foam cells from the atherosclerosis sensitive DBA/2 strain compared to the atherosclerosis resistant AKR mouse strain. As autophagosome formation was similar in these two strains, we wanted to evaluate the role of lysosome biogenesis and function on autolysosome formation in AKR and DBA/2 cells. The transcription factor TFEB is a key regulator for lysosome biogenesis and function that positively regulates the expression of lysosomal enzymes and structural proteins, and controls lysosomes number. For all our studies, we cultured AKR and DBA/2 macrophages with or without acetylated LDL (AcLDL) for 24h. First, we analyzed TFEB protein expression by western blot. Upon loading, TFEB was increased in AKR (48%, p<0.01) but not DBA/2 cells leading to a 45% higher TFEB level in AKR vs. DBA/2 foam cells (p<0.05), suggesting that lysosome number and function may be impaired in DBA/2 foam cells. To assess lysosome function and number, cells were labeled with Lysotracker red DND-99 (LyT) and analyzed by flow cytometry. We found that AcLDL loading did not affect LyT intensity. However, in both unloaded and loaded conditions, DBA/2 cells exhibited a 30 to 50% lower LyT intensity suggesting that they have intrinsically decreased lysosome number/function. Lysosomal degradation capacity was assayed by incubation with DQ-ovalbumin and we observed a 27% decrease in lysosome function in DBA/2 vs. AKR foam cells (p<0.01). In addition, upon loading, the mature form of cathepsin L was increased in AKR (43%, p<0.05) but not DBA/2 cells. Together these data suggest an impairment of lysosomal degradation capacity in DBA/2 foam cells. Finally, we investigated the role of TPC2, a lysosomal membrane protein which over expression has been previously linked to a defect in autolysosome formation. We found that upon AcLDL loading TPC2 protein levels were increased by 35% in DBA/2 cells, which are defective in autolysosome formation, while they were unchanged in AKR cells. In conclusion, we found that DBA/2 vs. AKR foam cells express more TPC2 and have fewer and/or dysfunctional lysosomes that may explain the autolysosome formation defect in these cells.

A₁ adenosine receptor deficiency or inhibition reduces atherosclerotic lesions in apolipoprotein E deficient mice

AIMS

The goal of this study was to determine whether the A1 adenosine receptor (AR) plays a role in atherosclerosis development and to explore its potential mechanisms.

METHODS AND RESULTS

Double knockout (DKO) mice, deficient in the genes encoding A1 AR and apolipoprotein E (apoE), demonstrated reduced atherosclerotic lesions in aortic arch (en face), aortic root, and innominate arteries when compared with apoE-deficient mice (APOE-KO) of the same age. Treating APOE-KO with an A1 AR antagonist (DPCPX) also led to a concentration-dependent reduction in lesions. The total plasma cholesterol and triglyceride levels were not different between DKO and APOE-KO; however, higher triglyceride was observed in DKO fed a high-fat diet. DKO also had higher body weights than APOE-KO. Plasma cytokine concentrations (IL-5, IL-6, and IL-13) were significantly lower in DKO. Proliferating cell nuclear antigen expression was also significantly reduced in the aorta from DKO. Despite smaller lesions in DKO, the composition of the innominate artery lesion and cholesterol loading and efflux from bone marrow-derived macrophages of DKO were not different from APOE-KO.

CONCLUSION

The A1 AR may play a role in the development of atherosclerosis, possibly due to its pro-inflammatory and mitogenic properties.

Ribosomal protein L13a deficiency in macrophages promotes atherosclerosis by limiting translation control-dependent retardation of inflammation

OBJECTIVE

Unresolved inflammatory response of macrophages plays a pivotal role in the pathogenesis of atherosclerosis. Previously we showed that ribosomal protein L13a-dependent translational silencing suppresses the synthesis of a cohort of inflammatory proteins in monocytes and macrophages. We also found that genetic abrogation of L13a expression in macrophages significantly compromised the resolution of inflammation in a mouse model of lipopolysaccharide-induced endotoxemia. However, its function in the pathogenesis of atherosclerosis is not known. Here, we examine whether L13a in macrophage has a protective role against high-fat diet-induced atherosclerosis.

APPROACH AND RESULTS

We bred the macrophage-specific L13a knockout mice L13a Flox(+/+) Cre(+/+) onto apolipoprotein E-deficient background and generated the experimental double knockout mice L13a Flox(+/+) Cre(+/+) apolipoprotein E deficient (apoE(-/-)). L13a Flox(+/+) Cre(-/-) mice on apolipoprotein E-deficient background were used as controls. Control and knockout mice were subjected to high-fat diet for 10 weeks. Evaluation of aortic sinus sections and entire aorta by en face showed significantly higher atherosclerosis in the knockout mice. Severity of atherosclerosis in knockout mice was accompanied by thinning of the smooth muscle cell layer in the media, larger macrophage area in the intimal plaque region and higher plasma levels of inflammatory cytokines. In addition, macrophages isolated from knockout mice had higher polyribosomal abundance of several target mRNAs, thus showing defect in translation control.

CONCLUSIONS

Our data demonstrate that loss of L13a in macrophages increases susceptibility to atherosclerosis in apolipoprotein E-deficient mice, revealing an important role of L13a-dependent translational control as an endogenous protection mechanism against atherosclerosis.

Transcriptome analysis of genes regulated by cholesterol loading in two strains of mouse macrophages associates lysosome pathway and ER stress response with atherosclerosis susceptibility

Cholesterol loaded macrophages in the arterial intima are the earliest histological evidence of atherosclerosis. Studies of mouse models of atherosclerosis have shown that the strain background can have a significant effect on lesion development. We have previously shown that DBA/2 ApoE(-/-) mice have aortic root lesions 10-fold larger than AKR ApoE(-/-) mice. The current study analyzes the response to cholesterol loading of macrophages from these two strains. Macrophages from the atherosclerosis susceptible DBA/2 strain had significantly higher levels of total and esterified cholesterol compared to atherosclerosis resistant AKR macrophages, while free cholesterol levels were higher in AKR cells. Gene expression profiles were obtained and data were analyzed for strain, cholesterol loading, and strain-cholesterol loading interaction effects by a fitted linear model. Pathway and transcriptional motif enrichment were identified by gene set enrichment analysis. In addition to observed strain differences in basal gene expression, we identified many transcripts whose expression was significantly altered in response to cholesterol loading, including P2ry13 and P2ry14, Trib3, Hyal1, Vegfa, Ccr5, Ly6a, and Ifit3. Eight pathways were significantly enriched in transcripts regulated by cholesterol loading, among which the lysosome and cytokine-cytokine receptor interaction pathways had the highest number of significantly regulated transcripts. Of the differentially regulated transcripts with a strain-cholesterol loading interaction effect, we identified three genes known to participate in the endoplasmic reticulum (ER) stress response, Ddit3, Trib3 and Atf4. These three transcripts were highly up-regulated by cholesterol in AKR and either down-regulated or unchanged in loaded DBA/2 macrophages, thus associating a robust ER stress response with atherosclerosis resistance. We identified significant transcripts with strain, loading, or strain-loading interaction effect that reside within previously described quantitative trait loci as atherosclerosis modifier candidate genes. In conclusion, we characterized several strain and cholesterol induced differences that may lead to new insights into cellular cholesterol metabolism and atherosclerosis.

Physiological difference in autophagic flux in macrophages from 2 mouse strains regulates cholesterol ester metabolism

OBJECTIVE

DBA/2 apoE(-/-) mice have ≈10-fold larger lesions than AKR apoE(-/-) mice. The objective of this study was to determine whether macrophages from these 2 strains had altered cholesterol metabolism that might play a role in their divergent atherosclerosis susceptibility.

APPROACH AND RESULTS

AKR and DBA/2 macrophages incubated with acetylated low-density lipoprotein resulted in higher cholesterol ester (CE) and lower free cholesterol accumulation in the DBA/2 cells. However, these strains had equivalent acetylated low-density lipoprotein uptake and cholesterol esterification activity. Cholesterol efflux from unloaded cells to apolipoprotein A-I or high-density lipoprotein was similar in the 2 strains. However, on acetylated low-density lipoprotein loading, cholesterol efflux was impaired in the DBA/2 cells, but this impairment was corrected by loading in the presence of an inhibitor of cholesterol esterification. Thus, the cholesterol efflux capabilities are similar in these strains, but there seemed to be a defect in lipid droplet-stored CE mobilization in DBA/2 cells. Lalistat 1, a specific inhibitor of lysosomal acid lipase, completely blocked the hydrolysis of lipid droplet-stored CE, implying that lipid droplet autophagy is responsible for CE turnover in these cells. CE turnover was 2-fold slower in DBA/2 versus AKR cells. Autophagic flux, estimated by a fluorescent light chain 3-II reporter and the increase in p62 levels after chloroquine treatment, was higher in AKR versus DBA/2 macrophages, which had an apparent decrease in autophagosome fusion with lysosomes. When autophagy was activated by amino acid starvation, CE levels decreased in DBA/2 cells.

CONCLUSIONS

Physiological regulation of autophagy in macrophages controls CE accumulation and may modify atherosclerosis susceptibility.

Dysregulation of cholesterol homeostasis in human prostate cancer through loss of ABCA1

Recent epidemiologic data show that low serum cholesterol level as well as statin use is associated with a decreased risk of developing aggressive or advanced prostate cancer, suggesting a role for cholesterol in aggressive prostate cancer development. Intracellular cholesterol promotes prostate cancer progression as a substrate for de novo androgen synthesis and through regulation of AKT signaling. By conducting next-generation sequencing-based DNA methylome analysis, we have discovered marked hypermethylation at the promoter of the major cellular cholesterol efflux transporter, ABCA1, in LNCaP prostate cancer cells. ABCA1 promoter hypermethylation renders the promoter unresponsive to transactivation and leads to elevated cholesterol levels in LNCaP. ABCA1 promoter hypermethylation is enriched in intermediate- to high-grade prostate cancers and not detectable in benign prostate. Remarkably, ABCA1 downregulation is evident in all prostate cancers examined, and expression levels are inversely correlated with Gleason grade. Our results suggest that cancer-specific ABCA1 hypermethylation and loss of protein expression direct high intracellular cholesterol levels and hence contribute to an environment conducive to tumor progression.

Abstract 516: Strain-Specific Differences in Transcriptome Regulation by Cholesterol Loading in Macrophages from AKR and DBA/2 ApoE-Deficient Mice

Background: Macrophages are a key cell type in atherogenesis as upon cholesterol loading they become foam cells in the arterial intima that provide the earliest histological evidence of atherosclerosis. Thus, atherosclerosis can be viewed as a disease caused by a combination of elevated cholesterol and inflammation.

Methods and Results: We studied the cholesterol loading response of apoE -/- macrophages from atherosclerosis resistant (AKR) and atherosclerosis susceptible (DBA/2) strains. Bone marrow macrophages (BMM) from male and female mice were treated ex vivo with or without AcLDL and whole genome transcriptome data was obtained using Illumina expression microarrays. Transcriptome data were analyzed in gender-specific and combined manners using the Limma R package. Probe data were fitted to a linear model with strain, gender, and cholesterol loading as additive variables to delineate the strain:loading interaction effect. We identified 790 transcripts with a significant strain:loading interaction effect, suggesting that the response to AcLDL was altered in BMM between the two strains. For example the Cd274 gene was up regulated by cholesterol loading in AKR, while down regulated in DBA/2 (p=1.4E-09). Gene enrichment analysis was performed using the Romer R package. The strain:loading differentially regulated transcripts were found to be significantly enriched in sterol regulatory element binding protein (SREBP)-motif-containing genes, which contain binding sites for the SREBP-1a and SREBP-1c transcription factors within 1000 bp of their transcription start site. Nuclear SREBP was found abundantly only in unloaded cells from both strains. The SREBP-motif-containing geneset was significantly enriched in transcripts that were down-regulated in loaded DBA/2 BMM relative to the other samples. We also identified many SREBP-motif associated genes that were up regulated upon cholesterol loading, suggesting a novel function for SREBP as a transcriptional repressor in unloaded macrophages.

Conclusions: Transcriptome profiling can yield insights into strain differences in cholesterol loading and atherosclerosis susceptibility. The SREBP pathway may be alternatively regulated in atherosclerosis resistant and susceptible strains.

Abstract 284: Cholesterol Handling in Bone Marrow--Derived Macrophages from Apoe-Deficient AKR and DBA/2 Mice

It has been demonstrated in humans that about 50% of the susceptibility to atherosclerosis is heritable. Therefore, it is not surprising that mice from distinct genetic backgrounds present different susceptibility to atherosclerosis. For example, apoE -/- DBA/2 mice have aortic root atherosclerosis lesion areas >10-fold larger than apoE -/- AKR mice. In order to better understand the mechanisms underlying this difference, we studied cholesterol metabolism in bone marrow-derived macrophages from these two strains. In the unloaded state, macrophages from both strains had equivalent amounts of total, esterified, and free cholesterol (TC, CE, and FC, respectively). Cells were loaded with acetylated low density lipoproteins (AcLDL) for 48h and DBA/2 macrophages had 36% higher TC (p<0.0001) vs. AKR macrophages, mainly due to 72% higher CE accumulation (p<0.0001). In contrast the loaded DBA/2 macrophages had 6% lower FC than the AKR macrophages (p<0.05). No difference was seen in AcLDL uptake or acetyl-coenzyme A acyltransferase (ACAT) activity between the two strains. When cells were loaded with AcLDL, the DBA/2 cells released cholesterol less efficiently than the AKR cells to apoAI (18% lower, p=0.01) or HDL (25% lower, p=0.001). However when the loading was performed in presence of ACAT inhibitor, blocking the formation of CE, the efflux from the two strains was equivalent suggesting a blockage of CE hydrolysis in DBA/2 cells. In loaded cells, when a 24h chase period was done in presence of ACAT inhibitor to prevent cholesterol re-esterification, the CE was reduce by 69% in AKR cells (t 1/2 = 47h) compared to chase without inhibitor while it was only reduced by 42% in DBA/2 cells (t 1/2 = 101h). Furthermore, when lalistat, an inhibitor of lysosomal acid lipase (LAL), and ACAT inhibitor were added during the chase, CE levels were equivalent to the one observed in chase without any inhibitors, suggesting that CE hydrolysis occurs primarily in the lysosome. In conclusion, our data support the hypothesis that DBA/2 cells accumulate more CE than AKR cells due to a defect in CE hydrolysis by LAL. Autophagy has been recently described as the pathway in macrophages by which lipid droplets can be delivered to the lysosome, and we are investigating the role of this pathway in our cells.

Abstract 3133: Regulatory sequences of the ATP-Binding Cassette Transporter A1 gene are hypermethylated in prostate cancer resulting in loss of gene expression

Introduction/Objective: Cholesterol homeostasis is altered in prostate cancer resulting in increased levels of cholesteryl esters and free cholesterol, but the mechanism behind these perturbations is not complete understood. We examine the role of DNA methylation in the regulation of ABCA1 expression. Methods: Genome wide methylation analysis using MBD-isolated Genome Sequencing (MiGS) was performed on the normal prostate epithelial cell line PrEC, the prostate cancer cell lines LNCaP and DU 145, 3 benign prostate specimens obtained from radical cystoprostatectomy, and 6 prostate cancer specimens obtained from radical prostatectomy. Bisulfite genomic sequencing was performed on the ABCA1 CpG island in PrEC and LNCaP to verify the methylation patterns discovered by MiGS. Real time RT-PCR was performed to assess ABCA1 mRNA levels in PrEC and LNCaP. LNCaP was treated with 5-aza-2′-deoxycytidine (5-aza), the LXR agonist T0901317, or a combination of the two drugs; and ABCA1 CpG island methylation was assessed by methylation-specific PCR (MSP) and gene expression was assessed by real time RT-PCR. Results: MiGS analysis revealed that ABCA1 CpG island methylation was present in LNCaP and 6 prostate cancer specimens but not PrEC, DU 145, or 3 benign prostate specimens. Bisulfite genomic sequencing primers were used to amplify fragments from the CpG island spanning −404 to +1,301 of the ABCA1 gene. LNCaP showed dense methylation in the entire region while PrEC showed only minimal methylation from −236 to −404. Real time RT-PCR revealed that there was 10-fold more ABCA1 mRNA in PrEC when compared with LNCaP. Treatment of LNCaP with 10µM T0901317 for 24 hours increased ABCA1 mRNA to 14 fold above untreated LNCaP without detectable changes in DNA methylation. Treatment with 5µM 5-aza for 1 week increased ABCA1 mRNA to 50 fold above control and resulted in loss of DNA methylation in the ABCA1 CpG island as detected by MSP. The combination of 5µM 5-aza and 10µM T0901317 increased ABCA1 mRNA expression in LNCaP to 320 fold above control. Conclusions: ABCA1 is hypermethylated in a subset of prostate cancers, but not normal prostate, resulting in loss of gene expression. Therapeutic strategies aimed at reducing intracellular cholesterol content solely by inhibiting HMG-CoA reductase may be hindered by this acquired deficiency in cholesterol export.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3133. doi:1538-7445.AM2012-3133

The critical role of IL-1 receptor-associated kinase 4-mediated NF-κB activation in modified low-density lipoprotein-induced inflammatory gene expression and atherosclerosis

Exciting discoveries related to IL-1R/TLR signaling in the development of atherosclerosis plaque have triggered intense interest in the molecular mechanisms by which innate immune signaling modulates the onset and development of atherosclerosis. Previous studies have clearly shown the definitive role of proinflammatory cytokine IL-1 in the development of atherosclerosis. Recent studies have provided direct evidence supporting a link between innate immunity and atherogenesis. Although it is still controversial about whether infectious pathogens contribute to cardiovascular diseases, direct genetic evidence indicates the importance of IL-1R/TLR signaling in atherogenesis. In this study, we examined the role of IL-1R-associated kinase 4 (IRAK4) kinase activity in modified low-density lipoprotein (LDL)-mediated signaling using bone marrow-derived macrophage as well as an in vivo model of atherosclerosis. First, we found that the IRAK4 kinase activity was required for modified LDL-induced NF-κB activation and expression of a subset of proinflammatory genes but not for the activation of MAPKs in bone marrow-derived macrophage. IRAK4 kinase-inactive knockin (IRAK4KI) mice were bred onto ApoE(-/-) mice to generate IRAK4KI/ApoE(-/-) mice. Importantly, the aortic sinus lesion formation was impaired in IRAK4KI/ApoE(-/-) mice compared with that in ApoE(-/-) mice. Furthermore, proinflammatory cytokine production was reduced in the aortic sinus region of IRAK4KI/ApoE(-/-) mice compared with that in ApoE(-/-) mice. Taken together, our results indicate that the IRAK4 kinase plays an important role in modified LDL-mediated signaling and the development of atherosclerosis, suggesting that pharmacological inhibition of IRAK4 kinase activity might be a feasible approach in the development of antiatherosclerosis drugs.

A simple and sensitive enzymatic method for cholesterol quantification in macrophages and foam cells

A precise and sensitive method for measuring cellular free and esterified cholesterol is required in order to perform studies of macrophage cholesterol loading, metabolism, storage, and efflux. Until now, the use of an enzymatic cholesterol assay, commonly used for aqueous phase plasma cholesterol assays, has not been optimized for use with solid phase samples such as cells, due to inefficient solubilization of total cholesterol in enzyme compatible solvents. We present an efficient solubilization protocol compatible with an enzymatic cholesterol assay that does not require chemical saponification or chromatographic separation. Another issue with enzyme compatible solvents is the presence of endogenous peroxides that interfere with the enzymatic cholesterol assay. We overcame this obstacle by pretreatment of the reaction solution with the enzyme catalase, which consumed endogenous peroxides resulting in reduced background and increased sensitivity in our method. Finally, we demonstrated that this method for cholesterol quantification in macrophages yields results that are comparable to those measured by stable isotope dilution gas chromatography with mass spectrometry detection. In conclusion, we describe a sensitive, simple, and high-throughput enzymatic method to quantify cholesterol in complex matrices such as cells.

Dynamin is involved in endolysosomal cholesterol delivery to the endoplasmic reticulum: role in cholesterol homeostasis

Cholesterol is one of the most essential membrane components in mammalian cells and plays a critical role in several cellular functions. It is now established that intracellular cholesterol transport contributes to the regulation of cellular cholesterol homeostasis by mechanisms that are yet poorly defined. In this study, we examined the role of clathrin- and dynamin-dependent trafficking on the regulatory machinery involved in cholesterol homeostasis. Thus, expression levels of three major sterol-sensitive genes, that is sterol-regulatory element binding protein 2 (SREBP-2), hydroxymethylglutaryl-coenzyme A (HMGCoA) reductase and low-density lipoprotein (LDL) receptor, were monitored to study the cell response to the addition of LDL-derived cholesterol. We found that inhibition of clathrin-dependent endocytosis had no effect on the intracellular distribution of cholesterol and the regulation of sterol-sensitive genes. In contrast, inhibition of dynamin activity resulted in the lack of regulation of SREBP-2, HMGCoA reductase and LDL receptor genes. Immunolocalization studies along with the measure of free and esterified cholesterol indicated that dynamin inactivation led to the accumulation of free cholesterol (FC) within the late endosomal (LE)/lysosomal compartment resulting in insufficient delivery of regulatory cholesterol to the endoplasmic reticulum (ER) where the transcriptional control of sterol-sensitive genes occurs. Our data therefore indicate that dynamin plays a critical role in the delivery of cholesterol from the LE/lysosomal network to the ER and highlight the importance of LE trafficking in cholesterol homeostasis.

Enhanced efflux of cholesterol from ABCA1-expressing macrophages to serum from type IV hypertriglyceridemic subjects

Since elevated plasma triglycerides (TGs) are an independent cardiovascular risk factor, we have compared the cholesterol efflux potential of sera from asymptomatic hypertriglyceridemic (HTG) type IIb, type IV or normolipidemic (NLP) individuals using two different cell systems. In both type IIb and IV HTG, the efflux of cholesterol from SR-BI-rich Fu5AH cells was similar to that obtained with NLP. The maintenance of efflux efficiency in spite of reduced HDL-cholesterol levels can be mainly attributed to the relative enrichment of HDL with phospholipid. In the J774 macrophage cell system, pretreatment with cAMP, which upregulates ABCA1, induced a markedly higher increase in efflux to type IV sera compared with type IIb or NLP. In addition, type IV sera exhibited two-fold higher pre-beta HDL relative concentration (percentage of total apo AI) compared with NLP. Moreover, positive correlations were established between ABCA1-mediated efflux and the serum pre-beta HDL levels or TG concentrations. Thus, the hyperTGemia is associated with a higher fraction of apo AI recovered as pre-beta HDL which appear to be partly responsible for enhanced efflux obtained upon the cAMP stimulation of J774 cells. In conclusion, we demonstrated for the first time that the ABCA1-expressing J774 cell system is responsive to the percent of apo AI present in human serum as pre-beta HDL. Our results suggest that high-plasma TG, accompanied by low HDL may not result in an impaired cholesterol efflux capacity.

Characterization of polymorphic structure of SREBP-2 gene: role in atherosclerosis

Sterol regulatory element binding proteins (SREBPs) are membrane-bound transcription factors that control the metabolism of cholesterol and fatty acids in mammalian cells. We postulated that polymorphisms (SNPs) in SREBP-2 gene might influence lipid parameters and the risk of coronary atherosclerosis. PCR-SSCP analysis and direct sequencing of DNA from 64 asymptomatic hypercholesterolemic men revealed seven genetic SREBP-2 SNPs. The genotype distribution of four of these SNPs (1668G>T, 1784G>C, 3474T>C and 3705C>T), and their influence on plasma lipid values and clinical parameters was studied in 655 asymptomatic men previously selected for the presence of at least one cardiovascular risk factor (hypertension, hypercholesterolemia, tobacco consumption). No significant relation was found with lipid parameters but there was a significant association between the 1784G>C polymorphism and intima-media thickness (IMT) measured in 497 subjects. Thus, a common variation in the SREBP-2 gene is related with early-stage carotid atherosclerosis in subjects with a risk of cardiovascular events without detectable change in plasma lipid levels.

Biomarker assessments in asbestos-exposed workers as indicators for selective prevention of mesothelioma or bronchogenic carcinoma: rationale and practical implementations

In the first part of this study we have shown how the serum levels of four selected tumour markers, namely tissue polypeptide antigen (TPA), carcino-embryonic antigen (CEA), hyaluronic acid (HA) and ferritin, display patterns characteristic of mesothelioma (M) or bronchogenic carcinoma (BC) in asbestos-exposed workers, and we hypothesize that the differences in marker patterns correspond to differences in carcinogenesis mechanisms. In a preliminary study, we found these specific marker patterns in 5/19 exposed workers of whom only one demonstrated any radiological signs of disease. Thus these specific marker patterns may be early events, occurring long (possibly years) before the classical radiological signs of exposure to asbestos. Accordingly they afford an optimal opportunity for prevention which should be adapted to the carcinogenesis mechanism as it is revealed by the marker pattern; it is aimed at antagonizing free radical carcinogenesis in all persons with TPA levels in excess of 100 U/l or Ferritin in excess of 400 ng/ml, and at inhibiting chemical carcinogenesis in those having elevated CEA levels (over 3 ng/ml). The mechanisms involved in these inhibitory processes are described and discussed, as well as the practical implementations that proceed from them. A prevention trial is now being started among 300 active and retired workers of an asbestos-cement works in northern France; the design of the study is presented. This prevention programme should be maintained over many years and holds a strong potential for reducing the untoward effects of exposure to asbestos.

Biomarker assessments in asbestos-exposed workers as indicators for selective prevention of mesothelioma or bronchogenic carcinoma: rationale and practical implementations

Asbestos-associated malignancies are one of the major industrial hazards of recent decades and will continue to be so until beyond the end of the century. It has been estimated that, in the United States alone, there will be 131,200 cancer deaths as a result of asbestos exposure. At present the early lesions are detected radiologically, by which time intervention is no longer effective. The aim of this study was to test the value of a battery of serum biomarkers in the early detection of malignancy and in distinguishing between the early stages of mesothelioma and bronchogenic carcinoma. Many of the biomarkers had no discriminating value but on the basis of four such markers (namely TPA, CEA, HA and ferritin) it has been possible to distinguish between the late stages of the two malignancies and asbestosis. The results are discussed in terms of their possible application to the detection of early pre-malignant lesions in a screened population of asbestos-exposed persons, with the aim of attempting to prevent cancer death in such early detected cases.

[Effects of isosorbide dinitrate injection on acute myocardial infarction. A haemodynamic and gamma-angiographic study (author's transl)]

The haemodynamic and gamma-angiographic effects of isosorbide dinitrate (ISDN) injection were evaluated in 18 patients with recent myocardial infarction by measuring diastolic (DPAP) and systolic (SPAP) pulmonary artery pressures, diastolic (DAP) and systolic (SAP) systemic arterial pressures, cardiac index (CI) and heart rate (HR). Total ejection fraction (EF) was measured by radionuclide angiography. Within the first hour of treatment, there was a significant fall in DPAP (from 25.11 +/- 6.5 to 18.3 +/- 6 mmHg), SPAP (from 47 +/- 11.5 to 36.6 +/- 10 mmHg) and SAP (from 140 +/- 27.8 to 123 +/- 20 mmHg). Changes in DAP, CI and HR were not significant. The drug produced a significant increase in EF (from 32.6 +/- 15 to 35.3 +/- 15 p. cent). On the basis of these results the patients could be divided into three categories: -- Group I patients (n = 5) with EF greater than 45, in whom the haemodynamic effects (fall in DRAP from 20.8 +/- 4.2 to 16.3 +/- 3 mmHg) and the gamma-angiographic effects (increase in EF from 53.8 +/- 6 to 58.6 +/- 3 p. cent) were favourable. -- Group II patients (n = 5) with EF less than 40, in whom the haemodynamic effects (fall in DRAP from 29 +/- 8.5 to 17.8 +/- 6 mmHg) and the gamma-angiographic effects (increase in EF from 23 +/- 9 to 34 +/- 7 p. cent) were still favourable. -- Group III patients (n = 8) with low EF, in whom there were no significant changes in haemodynamic effects (DPAP from 25.3 +/- 3 to 23.4 +/- 5 mmHg) and gamma-angiographic effects (EF from 26 +/- 6 to 25 +/- 5 p. cent). This group corresponds to cases with very extensive necrosis of unfavourable outcome (4 deaths). One may therefore consider that the lack of effectiveness of ISDN in subjects with left ventricular failure and low EF is of poor prognosis and requires more aggressive therapy.