Aortic Sinus Lesion Area Research Articles

Abstract 3078: Free Fatty Acid Receptor 4: An Emerging Target To Reduce Atherosclerosis

Free fatty acid receptor 4 (FFAR4) has recently emerged as a target for preventing CVD through its ability to reduce macrophage foam cell formation and inflammation. We have shown that activation of FFAR4 by synthetic agonists decreases foam cell formation, whereas deficiency of FFAR4 increases foam cell formation. Building on these data, we hypothesized that FFAR4 would protect against atherosclerotic plaque formation in vivo . To test this hypothesis, we generated global FFAR4 knockout mice on an apoE-deficient background. Male and female apoE/FFAR4 double knockout mice (n=20) and their apoE knockout controls (n=20) were fed a Western diet (42% calories from fat and 0.2% cholesterol) for 16 weeks. We collected weekly body weights and fasting plasma samples from mice at 0, 8, and 16 weeks to measure triglyceride and cholesterol levels. At the end of the 16-week study, atherosclerotic plaque severity was determined by analyzing the aortic sinus lesion area of the heart and the en-face lesion area of the aortic arch. In both the male and female mice, we observed no differences in weekly body weights or lipid levels between the apoE knockout and apoE/FFAR4 double knockout mice. In our first cohort of male mice (n=10), the two genotypes showed no difference in the aortic sinus lesion area. However, male apoE/FFAR4 double knockout mice had a statistically significant (p=0.039) 1.4-fold increase in total aortic arch lesion area compared to FFAR4-deficient mice. While female mice (n=9) showed no differences in atherosclerotic plaque in the aortic sinus and aortic arch between the two genotypes, they did present with 1.7-fold (p=0.002) and 2-fold increases (p=0.009) in aortic sinus lesion area and aortic arch lesion area, respectively, as compared to male mice. Based on analysis of an initial set of mice, our data support a protective role for FFAR4 in the development of atherosclerotic plaque formation in male mice, and our findings may have uncovered a new therapeutic target against atherosclerosis.

Abstract 2052: Macrophage-specific Ripk1 Knockdown Reduces Macrophage Inflammation And Atherosclerosis Progression In Ldlr -/- Mice.

Background: Chronic activation of the innate immune system drives inflammation and contributes to atherosclerosis. Pro-inflammatory agents (oxidised LDL, IL-1β) drive lesional inflammation and development, whereas anti-inflammatory agents (IL-10, HDL, Apolipoprotein-AI), promote an anti-inflammatory milieu and resolution. RIPK1 (Receptor interacting protein kinase 1) is a master regulatory gene that decides whether a cell undergoes inflammation, apoptosis and/or necroptosis, depending on its phosphorylation or ubiquitination status. We have previously observed that RIPK1 gene expression is increased in both endothelial cells and macrophages in early atherosclerotic lesions (Karunakaran et al, Circulation 2022). Here, we seek to determine whether macrophage-specific RIPK1 contributes to atherosclerosis. Methods: Given that Ripk1 -/- mice are lethal, we performed bone marrow (BM) transplants of Ripk1 +/- and wild-type (wt) littermate BM into female and male Ldlr -/- mice (n=8-12/grp) and mice were fed a western diet for 12-16 wks. In vitro experiments were performed in BM derived macrophages from wt and Ripk1 +/- mice. Results: Ldlr -/- mice recipient of Ripk1 +/- BM and western diet feeding for 12 or 16 wk had a marked reduction in aortic sinus lesion area (68.9% and 49.7% respectively, p<0.05) compared to their wt controls. Preliminary analysis show that there is a reduction in lesional macrophage area in Ripk1 +/- BM recipient Ldlr -/- mice relative to control (0.02±0.01 vs 0.01±0.006mm, p<0.01), suggesting that macrophage infiltration was reduced. Interestingly, anti-inflammatory agents, including recombinant IL10, IL13 (both 100ng/ml), Apolipoprotein-AI and discoidal HDL (both 500ug/mL) markedly reduced macrophage Ripk1 expression in vitro (by ~50%, p<0.05), likely reducing Ripk1-dependent inflammation and promoting an anti-inflammatory milieu. Current mechanistic studies are investigating the transcriptional regulator, STAT3, as a key regulator of Ripk1 expression. Conclusion: We identified macrophage-RIPK1 as a central driver of atherosclerosis. These timely studies highlight the therapeutic potential of dampening Ripk1 overexpression, as opposed to the detrimental abolishment of Ripk1, in treating atherosclerosis.

Atheroprotective and atheroregressive potential of azapeptide derivatives of GHRP-6 as selective CD36 ligands in apolipoprotein E-deficient mice

Background and aimsScavenger receptor class B member 3, also known as cluster of differentiation-36 (CD36) receptor, is involved in the uptake and accumulation of modified lipoprotein in macrophages, driving atherosclerosis progression. Azapeptide analogs of growth hormone-releasing peptide-6 (GHRP-6) have been developed as selective CD36 ligands and evaluated for their anti-atherosclerotic properties in apoe−/− mice. MethodsFrom 4 to 19 weeks of age, male apoe−/− mice were fed a high fat high cholesterol (HFHC) diet, then switched to normal chow and treated daily with 300 nmol/kg of MPE-001 ([aza-Tyr4]-GHRP-6) or MPE-003 ([aza-(N,N-diallylaminobut-2-ynyl)Gly4]-GHRP-6) for 9 weeks. In another protocol, mice were fed a HFHC diet throughout the study. ResultsAzapeptides decreased lesion progression in the aortic arch and reduced aortic sinus lesion areas below pre-existing lesions levels in apoe−/− mice which were switched to chow diet. In mice fed a HFHC throughout the study, azapeptides reduced lesion progression in the aortic vessel and sinus. The anti-atherosclerotic effect of azapeptides was associated with a reduced ratio of iNOS+/CD206+ macrophages within lesions, and lowered plasma inflammatory cytokine levels. Monocytes from azapeptide-treated mice showed altered mitochondrial oxygen consumption rates, consistent with an M2-like phenotype. These effects were dependent on CD36, and not observed in apoe−/−cd36−/− mice. ConclusionsAzapeptides MPE-001 and MPE-003 diminished aortic lesion progression and reduced, below pre-existing levels, lesions in the aortic sinus of atherosclerotic mice. A relative increase of M2-like macrophages was observed in lesions, associated with reduced systemic inflammation. Development of CD36-selective azapeptide ligands merits consideration for treating atherosclerotic disease.

CEMIP regulates the proliferation and migration of vascular smooth muscle cells in atherosclerosis through the WNT-beta-catenin signaling pathway.

In this study we investigated the regulatory role of cell-migration-inducing and hyaluronan-binding protein (CEMIP) in the proliferation and migration of vascular smooth muscle cells (VSMCs). The mRNA and protein levels of CEMIP were upregulated in the plasma samples from patients with atherosclerosis, and in VSMCs stimulated with platelet-derived growth factor-BB (PDGF-BB), compared with plasma from healthy subjects and untreated VSMCs. Silencing CEMIP suppressed PDGF-BB-induced cell migration and proliferation in VSMCs, as determined using a Cell Counting Kit-8 assays, 5-ethynyl-2'-deocyuridine (EDU) assays, flow cytometry, wound healing assays, and Transwell assays. Overexpression of CEMIP promoted the proliferation and migration of VSMCs via activation of the Wnt-β-catenin signaling pathway and the upregulation of its target genes, including matrix metalloproteinase-2, matrix metalloproteinase-7, cyclin D1, and c-myc, whereas CEMIP deficiency showed the opposite effects. The knockdown of CEMIP in ApoE-/- mice by intravenous injection of lentiviral vector expressing si-CEMIP protected against high-fat-diet-induced atherosclerosis, as shown by the reduced aortic lesion areas, aortic sinus lesion areas, and the concentration of blood lipids compared with mice normally expressing CEMIP. These results demonstrated that CEMIP regulates the proliferation and migration of VSMCs in atherosclerosis by activating the WNT-β-catenin signaling pathway, which suggests the therapeutic potential of CEMIP for the management of atherosclerosis.

Abstract 623: Activating Liver X Receptors Alters Endothelial Progenitor Cell Differentiation and Enhances the Release of Factors that Reduce Atherosclerosis

The liver x receptors (LXRα/β) are nuclear receptors that are highly expressed in macrophages and endothelial progenitor cells (EPCs). EPCs are bone marrow (BM) derived cells that facilitate endothelial repair through the secretion of factors. The importance of LXRs in preventing atherosclerosis has been attributed to promoting cholesterol efflux from macrophages. However, a role for EPCs in the LXR response has not been explored. We hypothesized that LXR activation in EPCs contributes to their anti-atherogenic effects by preventing endothelial activation during atherogenesis. In the Lxr -/- mice, circulating EPCs were decreased by 27% compared to WT, while myeloid populations were increased. Isolated hematopoietic stem cells treated with LXR agonist (1μM GW3965) ex vivo showed a 36% increase in the number of EPC colonies formed, while myeloid colonies were decreased by 25%. GW3965 treatment during EPC differentiation resulted in a 76% decrease in endothelial lineage marker ( Cd144 and Vegfr2 ) expression. To investigate endothelial cell activation, activated human umbilical vein endothelial cells were incubated with the conditioned media (CM) from GW3965-treated WT EPCs, which reduced THP-1 monocyte adhesion by 36% compared to the CM from vehicle treatment. To determine the effects of the EPC-derived CM in vivo , Ldlr -/- mice were injected with concentrated CM bi-weekly over an 8-week period, which decreased aortic sinus lesion area by 52% compared to the media control injections. Taken together, the loss of LXRs perturbed hematopoietic balance in vivo , while the activation of LXRs were associated with enhanced ex vivo EPC formation. Furthermore, LXR activation altered EPC differentiation and secretome resulting in decreased in vitro endothelial-monocyte adhesion. When administered to atherosclerotic-prone mice, these secreted factors reduced lesion formation in the aortic sinus. These data suggest that LXRs reduce the development of atherosclerosis in part through the release of EPC-derived factors that can reduce endothelial activation.

Toll-like receptor 7 deficiency protects apolipoprotein E-deficient mice from diet-induced atherosclerosis

Toll-like receptor 7 (TLR7) mediates autoantigen and viral RNA-induced cytokine production. Increased TLR7 expression in human atherosclerotic lesions suggests its involvement in atherogenesis. Here we demonstrated TLR7 expression in macrophages, smooth muscle cells (SMCs), and endothelial cells from mouse atherosclerotic lesions. To test a direct participation of TLR7 in atherosclerosis, we crossbred TLR7-deficient (Tlr7−/−) mice with apolipoprotein E-deficient (Apoe−/−) mice and produced Apoe−/−Tlr7−/− and Apoe−/−Tlr7+/+ littermates, followed by feeding them an atherogenic diet to produce atherosclerosis. Compared to Apoe−/−Tlr7+/+ mice, Apoe−/−Tlr7−/− mice showed reduced aortic arch and sinus lesion areas. Reduced atherosclerosis in Apoe−/−Tlr7−/− mice did not affect lesion macrophage-positive area and CD4+ T-cell number per lesion area, but reduced lesion expression of inflammatory markers major histocompatibility complex-class II and IL6, lesion matrix-degrading proteases cathepsin S and matrix metalloproteinase-9, and systemic serum amyloid A levels. TLR7 deficiency also reduced aortic arch SMC loss and lesion intima and media cell apoptosis. However, TLR7 deficiency did not affect aortic wall elastin fragmentation and collagen contents, or plasma lipoproteins. Therefore, TLR7 contributes to atherogenesis in Apoe−/− mice by regulating lesion and systemic inflammation. A TLR7 antagonist may mitigate atherosclerosis.

Effect of miR-467b on atherosclerosis of rats.

To observe the effect of miR-467b on the atherosclerosis (AS) of rats with apolipoprotein E (ApoE) gene knockout (ApoE(-/-)). ApoE(-/-) rats were fed with high fat and high cholesterol diet and were randomly divided into group A, group B and group C, with 10 rats in each group. Group A: rats were injected with ApoE agonist through the caudal vein; group B: rats were injected with ApoE antagonist through the caudal vein; group C: as negative control group. Enzyme oxidation method was used to detect the blood lipid levels of rats. Western blotting method was used to detect the aortic lipoprotein lipase (LPL) expression levels of rats. HE staining and oil red O staining were performed to observe the AS lesions and lipid accumulation state. Compared with group C, blood lipid level, aortic intima and aortic sinus lipid accumulation area ratio, aortic sinus lesion area and LPL expression level in group A significantly reduced; while blood lipid level, aortic intima and aortic sinus lipid accumulation area ratio, aortic sinus lesion area, and LPL expression level in group B significantly increased, with the statistical difference (P<0.05). miR-467b can alleviate the AS lesions of ApoE(-/-) rats, and its inhibiting effect on AS may be related to LPL expression.

Macrophage Mitochondrial Energy Status Regulates Cholesterol Efflux and Is Enhanced by Anti-miR33 in Atherosclerosis

Therapeutically targeting macrophage reverse cholesterol transport is a promising approach to treat atherosclerosis. Macrophage energy metabolism can significantly influence macrophage phenotype, but how this is controlled in foam cells is not known. Bioinformatic pathway analysis predicts that miR-33 represses a cluster of genes controlling cellular energy metabolism that may be important in macrophage cholesterol efflux. We hypothesized that cellular energy status can influence cholesterol efflux from macrophages, and that miR-33 reduces cholesterol efflux via repression of mitochondrial energy metabolism pathways. In this study, we demonstrated that macrophage cholesterol efflux is regulated by mitochondrial ATP production, and that miR-33 controls a network of genes that synchronize mitochondrial function. Inhibition of mitochondrial ATP synthase markedly reduces macrophage cholesterol efflux capacity, and anti-miR33 required fully functional mitochondria to enhance ABCA1-mediated cholesterol efflux. Specifically, anti-miR33 derepressed the novel target genes PGC-1α, PDK4, and SLC25A25 and boosted mitochondrial respiration and production of ATP. Treatment of atherosclerotic Apoe(-/-) mice with anti-miR33 oligonucleotides reduced aortic sinus lesion area compared with controls, despite no changes in high-density lipoprotein cholesterol or other circulating lipids. Expression of miR-33a/b was markedly increased in human carotid atherosclerotic plaques compared with normal arteries, and there was a concomitant decrease in mitochondrial regulatory genes PGC-1α, SLC25A25, NRF1, and TFAM, suggesting these genes are associated with advanced atherosclerosis in humans. This study demonstrates that anti-miR33 therapy derepresses genes that enhance mitochondrial respiration and ATP production, which in conjunction with increased ABCA1 expression, works to promote macrophage cholesterol efflux and reduce atherosclerosis.

Macrophage mitochondrial energy status regulates cholesterol efflux and is enhanced by anti‐miR33 in atherosclerosis

Therapeutically targeting macrophage reverse cholesterol transport is a promising approach to treat atherosclerosis and miR‐33 has emerged as novel regulator of cholesterol homeostasis. Cellular energy status can significantly influence macrophage function, and bioinformatic analysis predicts that miR‐33 represses a cluster of genes controlling energy metabolism that may contribute to macrophage cholesterol efflux. We hypothesize that miR‐33 represses mitochondria metabolic pathways to reduce cholesterol efflux. Here, we show that macrophage cholesterol efflux is regulated by mitochondrial ATP production and that miR‐33 controls a network of genes that synchronize mitochondrial function. Macrophage cholesterol efflux capacity was markedly reduced by ATP synthase inhibition, confirming the importance of mitochondria in the efflux of excess cholesterol. Specifically, anti‐miR33 derepressed the novel target genes PGC‐1α, PDK4 and SLC25A25 and boosted mitochondrial respiration and ATP production, and mitochondrial respiration was key to the pro‐efflux effects of anti‐miR33. Anti‐miR33 therapy in atherosclerotic Apoe‐/‐ mice reduced aortic sinus lesion area, despite no changes in HDL‐C. Also, this therapy increased expression of mitochondrial target genes in vivo, suggesting that the regulation of mitochondrial genetic networks occur in atherosclerotic lesions.ConclusionWe showed that anti‐miR33 therapy de‐represses genes that enhance mitochondrial respiration and ATP production, which in conjunction with increased ABCA1 expression, promotes macrophage cholesterol efflux and reduces atherosclerosis.

Abstract 262: Anti-miR33 Therapy Promotes PGC1α Expression, Mitochondrial Function and Immunometabolic Pathways in Macrophages in Atherosclerosis

Macrophage foam cells are central to atherosclerotic plaque formation and therapies that increase macrophage cholesterol efflux remain an attractive yet elusive target. Therapeutically inhibiting microRNA-33, a critical regulator of lipid metabolism, increases circulating HDL and reduces atherosclerosis. However, the precise molecular mechanisms that regulate these beneficial effects are unknown. Thus, we sought to uncover novel gene networks regulated by miR33 that may contribute to atherosclerosis. Results: Microarray analysis of macrophages from anti-miR33 treated Ldlr-/- mice revealed several novel miR33 target genes that were de-repressed. Among these genes was PPARγ coactivator 1α (PGC1α), a crucial gene that controls cellular energy homeostasis and mitochondrial metabolism. 3’UTR luciferase assays verified that PGC1α is a specific and direct target of miR33. Macrophages transfected with miR33 mimics or anti-miR33 had decreased or increased PGC1α mRNA and protein respectively. Bioinformatic pathway analysis predicted that in addition to PGC1α, miR33 also regulates multiple mitochondrial proteins, such as pyruvate dehydrogenase kinase 4 (PDK4), solute carrier 25 A25 (SLC25A25) and Acyl-CoA Dehydrogenase (ACADSB). Anti-miR33 treatment of macrophages increases PDK4, SLC25A25 and ACADSB mRNA expression, validating these genes as miR33 targets. Seahorse XF Flux Analyzer studies show that macrophages treated with anti-miR33 have increased basal and maximal oxygen consumption rates, confirming that anti-miR33 therapy impacts positively on mitochondrial respiration and function. miR33 inhibition increased macrophage cholesterol efflux, which was abolished by oligomycin- a mitochondrial respiration inhibitor. This suggests that miR33 regulates cholesterol efflux at least in part by regulating mitochondrial function. Lastly, western-diet-fed apoE-/- mice treated with anti-miR33 injections (10mg/kg) for 8 weeks had a marked reduction in aortic sinus lesion area relative to control (p≤0.05), despite no change in HDL levels. Conclusion: Anti-miR33 therapy can positively impact on mitochondrial function, promoting macrophage cholesterol efflux and may contribute to HDL-independent anti-atherosclerotic effects.

Apolipoprotein A–V modulates multiple atherogenic mechanisms in a mouse model of disturbed clearance of triglyceride-rich lipoproteins

ObjectiveApolipoprotein A–V plays an important role in reducing plasma triglyceride levels. We hypothesized that expression of apoA–V would inhibit atherogenesis in apoE−/− mice fed chow diet which is a known model of hypercholesterolemia. Our aim was to study this protective effect and to explore possible mechanisms. Methods and resultsApoA–V+/+ApoE−/− mice expressing human apolipoprotein A–V (hapoA–V) were generated and compared to apoE−/− mice. Atherosclerotic aortic sinus lesion area was 70% smaller in hapoA–V+/+apoE−/−. This was accompanied by a 58% reduction in lesion macrophage content. Furthermore, advanced atherosclerotic lesions in hapoA–V+/+apoE−/− mice showed features of a more stable plaque, manifested by 59% and 37% higher collagen and α-actin content, respectively. Plasma triglyceride and cholesterol levels in hapoA–V+/+apoE−/− mice were 47% and 33% lower, respectively. These were associated with a 33% reduction in very low density lipoprotein triglyceride production and 2-fold acceleration in triglyceride-rich lipoprotein clearance in hapoA–V+/+apoE−/− mice. In addition, hapoA–V+/+apoE−/− mice showed enhanced insulin sensitivity (25% and 15% improvement in glucose tolerance and insulin responsiveness, respectively). Finally, hapoA–V+/+apoE−/− displayed a milder systemic inflammatory response compared to apoE−/− mice, manifested by 22%, 65% and 15% lower plasma levels of TNFα, IL-1β and IL-6, respectively. ConclusionsWe showed that human apolipoprotein A–V is a potent modulator of atherosclerosis in mice through multiple modes of action. These findings may identify apoA–V as a potential therapeutic target for treatment of atherosclerosis.

Interleukin-1 receptor type-1 in non-hematopoietic cells is the target for the pro-atherogenic effects of interleukin-1 in apoE-deficient mice

ObjectivesInterleukin (IL)-1 produced by vascular and bone marrow-derived cells exerts proinflammatory effects in these cell types by binding to IL-1 receptor type-1 (IL-1R1). We have previously shown that bone marrow-derived IL-1α and IL-1β are critical for atherogenesis in apoE knockout (KO) mice. The aim of the present study was to investigate whether IL-1R1 on vascular wall resident or bone marrow-derived cells mediates IL-1's effects in atherogenesis. Methods and resultsWe generated apoE−/−/IL-1R1−/− double knockout (DKO) mice and created radiation chimeras. Aortic sinus lesion area was 20–47% lower in DKO compared to apoE KO mice with similar plasma lipids. The production of IL-1α and IL-1β upon stimulation with LPS was not altered in IL-1R1−/− compared to IL-1R1+/+ peritoneal macrophages. DKO mice transplanted with IL-1R1+/+ bone marrow-derived cells had reduced (48%) aortic sinus lesion compared to apoE KO mice while specific deficiency of IL-1R1 in bone marrow-derived cells did not attenuate atherosclerosis. The mRNA levels of genes that promote macrophage recruitment to the vascular wall, namely CD68, VCAM-1, ICAM-1 and MCP-1 were lower in aortas from DKO compared to apoE KO mice. Finally, blockade of IL-1R1 with IL-1R antagonist (IL-1Ra) resulted in complete abrogation of IL-1β-induced expression of adhesion and chemotactic molecules and IL-1α, in isolated human umbilical vein endothelial cells (HUVEC). ConclusionsVascular wall resident cells are the main targets for the pro-atherogenic effects of bone marrow-derived IL-1 through IL-1R1, partly by induction of adhesion and chemotactic molecules in endothelial cells.

Oral administration of L-mR18L, a single domain cationic amphipathic helical peptide, inhibits lesion formation in ApoE null mice

We have shown that Ac-hE18A-NH₂, a dual-domain cationic apolipoprotein-mimetic peptide, reduces plasma cholesterol levels in dyslipidemic mice. Two single-domain cationic peptides based on the lytic class L peptide 18L were developed to test the hypothesis that a single-domain cationic amphipathic peptide can reduce atherosclerosis in apolipoprotein (apo)E null mice when orally administered. To incorporate anti-inflammatory properties, aromatic residues were clustered in the nonpolar face similar to peptide 4F, resulting in modified 18L (m18L). To reduce lytic properties, the Lys residues of 18L were replaced with Arg with the resulting peptide called modified R18L (mR18L). Biophysical studies showed that mR18L had stronger interactions with lipids than did m18L. Peptide mR18L was also more effective than m18L in promoting LDL uptake by HepG2 cells. ApoE null mice received normal chow or chow containing m18L or mR18L for six weeks. A significant reduction in plasma cholesterol and aortic sinus lesion area was seen only in the mR18L group. Plasma from mice administered mR18L, unlike those from the control and m18L groups, did not enhance monocyte adhesion to endothelial cells. Thus oral administration of mR18L reduces plasma cholesterol and lesion formation and inhibits monocyte adhesion.

A novel method for oral delivery of apolipoprotein mimetic peptides synthesized from all L-amino acids

Administered subcutaneously, D-4F or L-4F are equally efficacious, but only D-4F is orally efficacious because of digestion of L-4F by gut proteases. Orally administering niclosamide (a chlorinated salicylanilide used as a molluscicide, antihelminthic, and lampricide) in temporal proximity to oral L-4F (but not niclosamide alone) in apoE null mice resulted in significant improvement (P < 0.001) in the HDL-inflammatory index (HII), which measures the ability of HDL to inhibit LDL-induced monocyte chemotactic activity in endothelial cell cultures. Oral administration of L-[113-122]apoJ with niclosamide also resulted in significant improvement (P < 0.001) in HII. Oral administration of niclosamide and L-4F together with pravastatin to female apoE null mice at 9.5 months of age for six months significantly reduced aortic sinus lesion area (P = 0.02), en face lesion area (P = 0.033), and macrophage lesion area (P = 0.02) compared with pretreatment, indicating lesion regression. In contrast, lesions were significantly larger in mice receiving only niclosamide and pravastatin or L-4F and pravastatin (P < 0.001). In vitro niclosamide and L-4F tightly associated rendering the peptide resistant to trypsin digestion. Niclosamide itself did not inhibit trypsin activity. The combination of niclosamide with apolipoprotein mimetic peptides appears to be a promising method for oral delivery of these peptides.

Plasma S-Adenosylhomocysteine Is a Better Biomarker of Atherosclerosis Than Homocysteine in Apolipoprotein E-Deficient Mice Fed High Dietary Methionine ,

Homocysteine (Hcy) and S-adenosylhomocysteine (AdoHcy) are critical intermediates of methionine metabolism. To investigate which, if either, of these compounds is more closely related to atherosclerosis, we fed 5 groups of apolipoprotein E (apoE)-deficient mice different diets for 8 wk to induce changes in their plasma Hcy and AdoHcy concentrations. These included an AIN-93G control diet (C), this C diet supplemented with methionine (M), the M diet deficient in folates, vitamin B-6, and vitamin B-12 (M−V), this M diet supplemented with these B vitamins (M+V), and a C diet deficient in B vitamins (C−V). Compared with controls, mice fed the C−V diet had a moderate elevation in their plasma total Hcy (tHcy) levels; however, their plasma AdoHcy concentration and atherosclerotic lesion areas were not different. In contrast, the mice fed the M+V diet had larger atherosclerotic lesion areas and elevated plasma AdoHcy concentrations but their plasma tHcy concentration did not differ from that of the group C mice. The plasma AdoHcy concentration and aortic sinus lesion areas were positively correlated (r = 0.866; P < 0.001). We observed a negative correlation between the plasma AdoHcy concentration and both the DNA methyltransferase activity (r = −0.792; P < 0.001) and global DNA methylation status (r = −0.824; P < 0.001) in the aortic tissue. Hence, our study suggests that plasma AdoHcy is a better biomarker of atherosclerosis than Hcy and may accelerate the development of atherosclerotic lesions in apoE-deficient mice that have been fed a high methionine diet. The mechanisms underlying this effect may be related to the AdoHcy-mediated inhibition of DNA methylation in the aortic tissue.

Expression of the Lystbeige mutation is atheroprotective in chow-fed apolipoprotein E-deficient mice

Lyst(beige) mice crossed with hyperlipidemic low density lipoprotein receptor-deficient mice (BgLDLr(-/-)) display increased lesion area and a more stable lesion morphology. To verify that the beige phenotype is not unique to LDLr(-/-) mice, we examined atherosclerosis in beige, apolipoprotein E-deficient mutant mice (BgApoE(-/-)). Severe diet-induced hyperlipidemia in BgApoE(-/-) mice resulted in increased aortic sinus lesion areas compared with controls. Minimal aortic lesions were observed in both genotypes on a chow diet. Nevertheless, BgApoE(-/-) mice displayed drastically reduced aortic sinus lesion growth. Reconstitution with bone marrow (BM) from green fluorescent protein mice created chimeric animals that allowed for the identification of donor-derived cells within lesions. Expressing the beige mutation exclusively in BM-derived cells had no impact on plaque development, yet the beige mutation in all cells except the BM-derived cells led to significantly larger aortic sinus lesion areas. Both mRNA and secreted protein levels of monocyte chemoattractant protein 1 were altered in quiescent and phorbol ester-stimulated cultured macrophages, vascular smooth muscle cells, and aortic endothelial cells isolated from BgApoE(-/-) mice. Thus, expression of the beige mutation in all cell types involved in lesion development contributed to atheroprotection in chow-fed ApoE(-/-) mice.

Endogenous angiotensin II enhances atherogenesis in apoprotein E-deficient mice with renovascular hypertension through activation of vascular smooth muscle cells

Renovascular hypertension is one of the most important risk factors in the development of atherosclerosis. However, very little is known about the role of angiotensin II (AII), a key regulator of blood pressure homeostasis, on renovascular hypertension-associated atherogenesis. To study a possible role of AII on atherogenesis, we generated apoE-deficient hypertensive mice with either normal or increased AII production by applying 1-kidney, 1-clip (1K1C) or 2-kidney, 1-clip (2K1C) operation, respectively. Hypertension was successfully achieved in both mice groups, and was persistent for 8 weeks. Atherosclerosis quantification showed a marked increase in lesion area in aortic sinus of 2K1C mice as compared with 1K1C mice, suggesting a potential role of endogenous AII on atherogenesis. In the immunohistochemical analysis, induction of renovascular hypertension with 2K1C for 8 weeks led to an enhanced accumulation of macrophages in the aortic sinus, which was accompanied by a parallel increase in scavenger receptor A (SRA) expression on the macrophages. In in vitro experiments, although treatment of cells with increasing concentrations of AII (0.1 to 10 μM) affects neither SRA expression nor oxLDL uptake by macrophages, conditioned media (CM) derived from AII-stimulated vascular smooth muscle cells (VSMC) increased macrophage uptake of oxLDL in association with an enhanced expression of SRA on the macrophages. These findings suggest that the increased generation of AII in renovascular hypertension may initiate and promote atherosclerosis by activation of VSMC.

Differential role and tissue specificity of interleukin-1α gene expression in atherogenesis and lipid metabolism

Objective We examined the role of IL-1α and IL-1β expressed by bone marrow-derived cells in atherogenesis and lipid metabolism. Methods and results We first studied the effect of atherogenic diet on wild-type C57BL/6 IL-1α or IL-1β deficient mice. IL-1α KO resulted in a comparatively higher total cholesterol levels, compared to WT and IL-1β KO mice (398 ± 10; 266 ± 19; 223 ± 13 mg/dl, respectively, p < 0.001), due to higher non-HDL cholesterol. Nevertheless, aortic sinus lesion area was 56% lower in IL-1α KO ( p < 0.05) and 50% lower in IL-1β KO ( p = 0.08), compared to WT mice. Likewise, SAA levels in IL-1α KO mice were markedly lower compared to WT and IL-1β KO mice (31 ± 14; 220 ± 33 and 106 ± 39 μg/ml, respectively, p < 0.001). To study the specific role of bone marrow-derived IL-1, irradiated C57BL/6 mice were transplanted with either IL-1+/+, IL-1α−/− or IL-1β−/− bone marrow cells. Despite similar lipoprotein levels, aortic sinus lesion area was 59% lower in IL-1α−/− transplanted ( p < 0.05) compared to IL-1+/+ transplanted mice. Lesion area in IL-1β -/- was 33% lower than in IL-1+/+ recipient mice, but it was not statistically significant. Conclusion We demonstrated that early lesion formation is accelerated specifically by bone marrow-derived IL-1α. Furthermore, we showed that the expression of IL-1α in cells other than the bone marrow plays a significant role in non-HDL cholesterol metabolism.

Prothrombotic Effects of Hyperhomocysteinemia and Hypercholesterolemia in ApoE-Deficient Mice

We tested the hypothesis that hyperhomocysteinemia and hypercholesterolemia promote arterial thrombosis in mice. Male apolipoprotein E (Apoe)-deficient mice were fed one of four diets: control, hyperhomocysteinemic (HH), high fat (HF), or high fat/hyperhomocysteinemic (HF/HH). Total cholesterol was elevated 2-fold with the HF or HF/HH diets compared with the control or HH diets (P<0.001). Plasma total homocysteine (tHcy) was elevated (12 to 15 micromol/L) with the HH or HF/HH diets compared with the control or HF diets (4 to 6 micromol/L; P<0.001). Aortic sinus lesion area correlated strongly with total cholesterol (P<0.001) but was independent of tHcy. At 12 weeks of age, the time to thrombotic occlusion of the carotid artery after photochemical injury was >50% shorter in mice fed the HF diets, with or without hyperhomocysteinemia, compared with the control diet (P<0.05). At 24 weeks of age, carotid artery thrombosis was also accelerated in mice fed the HH diet (P<0.05). Endothelium-dependent nitric oxide-mediated relaxation of carotid artery rings was impaired in mice fed the HF, HH, or HF/HH diets compared with the control diet (P<0.05). Hyperhomocysteinemia and hypercholesterolemia, alone or in combination, produce endothelial dysfunction and increased susceptibility to thrombosis in Apoe-deficient mice.

Homozygous disruption of Pctp modulates atherosclerosis in apolipoprotein E-deficient mice

Phosphatidylcholine transfer protein (PC-TP) is a cytosolic phospholipid binding protein and a member of the steroidogenic acute regulatory-related transfer domain superfamily. Its tissue distribution includes liver and macrophages. PC-TP regulates hepatic lipid metabolism, and its absence in cholesterol-loaded macrophages is associated with reduced ATP binding cassette transporter A1-mediated lipid efflux and increased susceptibility to apoptosis induced by unesterified cholesterol. To explore a role for PC-TP in atherosclerosis, we prepared PC-TP-deficient/apolipoprotein E-deficient (Pctp(-/-)/Apoe(-/-)) mice and littermate Apoe(-/-) controls. At 16 weeks, atherosclerosis was increased in chow-fed male, but not female, Pctp(-/-)/Apoe(-/-) mice. This effect was associated with increases in plasma lipid concentrations. By contrast, no differences in atherosclerosis were observed between male or female Pctp(-/-)/Apoe(-/-) mice and Apoe(-/-) controls fed a Western-type diet for 16 weeks. At 24 weeks, atherosclerosis in chow-fed male Pctp(-/-)/Apoe(-/-) mice tended to be reduced in proportion to plasma cholesterol. The attenuation of atherosclerosis in female Pctp(-/-)/Apoe(-/-) mice fed chow or the Western-type diet for 24 weeks was not attributable to changes in plasma cholesterol or triglyceride concentrations. These findings suggest that PC-TP modulates the development of atherosclerosis, in part by regulating plasma lipid concentrations.