Progression and regression of atherosclerosis in APOE3-Leiden transgenic mice: an immunohistochemical study

Liver-targeted Angptl4 silencing by antisense oligonucleotide treatment attenuates hyperlipidaemia and atherosclerosis development in APOE*3-Leiden.CETP mice

AIMS

Angiopoietin-like 3 (ANGPTL3) and 4 (ANGPTL4) inhibit lipoprotein lipase to regulate tissue fatty acid (FA) uptake from triglyceride (TG)-rich lipoproteins such as very low density lipoproteins (VLDL). While pharmacological inhibition of ANGPTL3 is being evaluated as a lipid-lowering strategy, systemic ANGPTL4 inhibition is not pursued due to adverse effects. This study aims to compare the therapeutic potential of liver-specific Angptl3 and Angptl4 silencing to attenuate hyperlipidemia and atherosclerosis development in APOE*3-Leiden.CETP mice, a well-established humanized model for lipoprotein metabolism.

METHODS AND RESULTS

Mice were subcutaneously injected twice per week with saline or liver-targeted antisense oligonucleotides against Angptl3, Angptl4, both, or a scrambled oligonucleotide. Plasma lipid levels, VLDL clearance, and hepatic VLDL production were determined, and atherosclerosis development was assessed. For toxicological evaluation, cynomolgus monkeys were treated with three dosages of liver-targeted ANGPTL4-silencing oligonucleotides. Liver-targeted Angptl4 silencing reduced plasma TGs (-48%) and total cholesterol (-56%), explained by higher VLDL-derived FA uptake by brown adipose tissue and lower VLDL production by the liver. Accordingly, Angptl4 silencing reduced atherosclerotic lesion size (-86%) and improved lesion stability. Hepatic Angptl3 silencing similarly attenuated hyperlipidemia and atherosclerosis development. While Angptl3 and Angptl4 silencing lowered plasma TGs in the refed and fasted state, respectively, combined Angptl3/4 silencing lowered plasma TGs independent of the nutritional state. In cynomolgus monkeys, anti-ANGPTL4 ASO treatment was well tolerated without adverse effects.

CONCLUSION

Liver-targeted Angptl4 silencing potently attenuates hyperlipidemia and atherosclerosis development in APOE*3-Leiden.CETP mice, and liver-targeted ANGPTL4 silencing is well tolerated in non-human primates. These data warrant further clinical development of liver-targeted ANGPTL4 silencing.

Nanomedicine for Diagnosis and Treatment of Atherosclerosis

With the changing disease spectrum, atherosclerosis has become increasingly prevalent worldwide and the associated diseases have emerged as the leading cause of death. Due to their fascinating physical, chemical, and biological characteristics, nanomaterials are regarded as a promising tool to tackle enormous challenges in medicine. The emerging discipline of nanomedicine has filled a huge application gap in the atherosclerotic field, ushering a new generation of diagnosis and treatment strategies. Herein, based on the essential pathogenic contributors of atherogenesis, as well as the distinct composition/structural characteristics, synthesis strategies, and surface design of nanoplatforms, the three major application branches (nanodiagnosis, nanotherapy, and nanotheranostic) of nanomedicine in atherosclerosis are elaborated. Then, state-of-art studies containing a sequence of representative and significant achievements are summarized in detail with an emphasis on the intrinsic interaction/relationship between nanomedicines and atherosclerosis. Particularly, attention is paid to the biosafety of nanomedicines, which aims to pave the way for future clinical translation of this burgeoning field. Finally, this comprehensive review is concluded by proposing unresolved key scientific issues and sharing the vision and expectation for the future, fully elucidating the closed loop from atherogenesis to the application paradigm of nanomedicines for advancing the early achievement of clinical applications.

Combined glucose-dependent insulinotropic polypeptide receptor and glucagon-like peptide-1 receptor agonism attenuates atherosclerosis severity in APOE*3-Leiden.CETP mice

BACKGROUND AND AIMS

Combined agonism of the glucose-dependent insulinotropic polypeptide receptor (GIPR) and the glucagon-like peptide-1 receptor (GLP1R) is superior to single GLP1R agonism in terms of glycemic control and lowering body weight in individuals with obesity and with or without type 2 diabetes mellitus. As both GIPR and GLP1R signaling have also been implicated in improving inflammatory responses and lipid handling, two crucial players in atherosclerosis development, here we aimed to investigate the effects of combined GIPR/GLP1R agonism in APOE*3-Leiden.CETP mice, a well-established mouse model for human-like lipoprotein metabolism and atherosclerosis development.

METHODS

Female APOE*3-Leiden.CETP mice were fed a Western-type diet (containing 16% fat and 0.15% cholesterol) to induce dyslipidemia, and received subcutaneous injections with either vehicle, a GIPR agonist (GIPFA-085), a GLP1R agonist (GLP-140) or both agonists. In the aortic root area, atherosclerosis development was assessed.

RESULTS

Combined GIPR/GLP1R agonism attenuated the development of severe atherosclerotic lesions, while single treatments only showed non-significant improvements. Mechanistically, combined GIPR/GLP1R agonism decreased markers of systemic low-grade inflammation. In addition, combined GIPR/GLP1R agonism markedly lowered plasma triglyceride (TG) levels as explained by reduced hepatic very-low-density lipoprotein (VLDL)-TG production as well as increased TG-derived fatty acid uptake by brown and white adipose tissue which was coupled to enhanced hepatic uptake of core VLDL remnants.

CONCLUSIONS

Combined GIPR/GLP1R agonism attenuates atherosclerosis severity by diminishing inflammation and increasing VLDL turnover. We anticipate that combined GIPR/GLP1R agonism is a promising strategy to lower cardiometabolic risk in humans.

The role of sialic acid-binding immunoglobulin-like-lectin-1 (siglec-1) in immunology and infectious disease

Siglec-1, also known as Sialoadhesin (Sn) and CD169 is highly conserved among vertebrates and with 17 immunoglobulin-like domains is Siglec-1 the largest member of the Siglec family. Expression of Siglec-1 is found primarily on dendritic cells (DCs), macrophages and interferon induced monocyte. The structure of Siglec-1 is unique among siglecs and its function as a receptor is also different compared to other receptors in this class as it contains the most extracellular domains out of all the siglecs. However, the ability of Siglec-1 to internalize antigens and to pass them on to lymphocytes by allowing dendritic cells and macrophages to act as antigen presenting cells, is the main reason that has granted Siglec-1's key role in multiple human disease states including atherosclerosis, coronary artery disease, autoimmune diseases, cell-cell signaling, immunology, and more importantly bacterial and viral infections. Enveloped viruses for example have been shown to manipulate Siglec-1 to increase their virulence by binding to sialic acids present on the virus glycoproteins allowing them to spread or evade immune response. Siglec-1 mediates dissemination of HIV-1 in activated tissues enhancing viral spread via infection of DC/T-cell synapses. Overall, the ability of Siglec-1 to bind a variety of target cells within the immune system such as erythrocytes, B-cells, CD8+ granulocytes and NK cells, highlights that Siglec-1 is a unique player in these essential processes.

ABCB5+ mesenchymal stromal cells therapy protects from hypoxia by restoring Ca2+ homeostasis in vitro and in vivo

BACKGROUND

Hypoxia in ischemic disease impairs Ca²⁺ homeostasis and may promote angiogenesis. The therapeutic efficacy of mesenchymal stromal cells (MSCs) in peripheral arterial occlusive disease is well established, yet its influence on cellular Ca²⁺ homeostasis remains to be elucidated. We addressed the influence of ATP-binding cassette subfamily B member 5 positive mesenchymal stromal cells (ABCB5⁺ MSCs) on Ca²⁺ homeostasis in hypoxic human umbilical vein endothelial cells (HUVECs) in vitro and in vivo.

METHODS

Hypoxia was induced in HUVECs by Cobalt (II) chloride (CoCl₂) or Deferoxamine (DFO). Dynamic changes in the cytosolic- and endoplasmic reticulum (ER) Ca²⁺ and changes in reactive oxygen species were assessed by appropriate fluorescence-based sensors. Metabolic activity, cell migration, and tube formation were assessed by standard assays. Acute-on-chronic ischemia in Apolipoprotein E knock-out (ApoE^-/-) mice was performed by double ligation of the right femoral artery (DFLA). ABCB5⁺ MSC cells were injected into the ischemic limb. Functional recovery after DFLA and histology of gastrocnemius and aorta were assessed.

RESULTS

Hypoxia-induced impairment of cytosolic and ER Ca²⁺ were restored by ABCB5⁺ MSCs or their conditioned medium. Similar was found for changes in intracellular ROS production, metabolic activity, migratory ability and tube formation. The restoration was paralleled by an increased expression of the Ca²⁺ transporter Sarco-/endoplasmic reticulum ATPase 2a (SERCA2a) and the phosphorylation of Phospholamban (PLN). In acute-on-chronic ischemia, ABCB5⁺ MSCs treated mice showed a higher microvascular density, increased SERCA2a expression and PLN phosphorylation relative to untreated controls.

CONCLUSIONS

ABCB5⁺ MSCs therapy can restore cellular Ca²⁺ homeostasis, which may beneficially affect the angiogenic function of endothelial cells under hypoxia in vitro and in vivo.

Endothelial ADAM10 controls cellular response to oxLDL and its deficiency exacerbates atherosclerosis with intraplaque hemorrhage and neovascularization in mice

Introduction

The transmembrane protease A Disintegrin And Metalloproteinase 10 (ADAM10) displays a "pattern regulatory function," by cleaving a range of membrane-bound proteins. In endothelium, it regulates barrier function, leukocyte recruitment and angiogenesis. Previously, we showed that ADAM10 is expressed in human atherosclerotic plaques and associated with neovascularization. In this study, we aimed to determine the causal relevance of endothelial ADAM10 in murine atherosclerosis development in vivo.

Methods and results

Endothelial Adam10 deficiency (Adam10 ^ecko ) in Western-type diet (WTD) fed mice rendered atherogenic by adeno-associated virus-mediated PCSK9 overexpression showed markedly increased atherosclerotic lesion formation. Additionally, Adam10 deficiency was associated with an increased necrotic core and concomitant reduction in plaque macrophage content. Strikingly, while intraplaque hemorrhage and neovascularization are rarely observed in aortic roots of atherosclerotic mice after 12 weeks of WTD feeding, a majority of plaques in both brachiocephalic artery and aortic root of Adam10^ecko mice contained these features, suggestive of major plaque destabilization. In vitro, ADAM10 knockdown in human coronary artery endothelial cells (HCAECs) blunted the shedding of lectin-like oxidized LDL (oxLDL) receptor-1 (LOX-1) and increased endothelial inflammatory responses to oxLDL as witnessed by upregulated ICAM-1, VCAM-1, CCL5, and CXCL1 expression (which was diminished when LOX-1 was silenced) as well as activation of pro-inflammatory signaling pathways. LOX-1 shedding appeared also reduced in vivo, as soluble LOX-1 levels in plasma of Adam10^ecko mice was significantly reduced compared to wildtypes.

Discussion

Collectively, these results demonstrate that endothelial ADAM10 is atheroprotective, most likely by limiting oxLDL-induced inflammation besides its known role in pathological neovascularization. Our findings create novel opportunities to develop therapeutics targeting atherosclerotic plaque progression and stability, but at the same time warrant caution when considering to use ADAM10 inhibitors for therapy in other diseases.

Survey of Approaches for Investigation of Atherosclerosis In Vivo

Although in vitro model systems are useful for investigation of atherosclerosis-associated processes, they represent simplification of complex events that occur in vivo, which involve interactions between many different cell types together with their environment. The use of animal model systems is important for more in-depth insights of the molecular mechanisms underlying atherosclerosis and for identifying potential targets for agents that can prevent plaque formation and even reverse existing disease. This chapter will provide a survey of such animal models and associated techniques that are routinely used for research of atherosclerosis in vivo.

Cannabinoid type 1 receptor inverse agonism attenuates dyslipidemia and atherosclerosis in APOE∗3-Leiden.CETP mice

Pharmacological blockade of the cannabinoid type 1 receptor, a G protein-coupled receptor expressed in the central nervous system and various peripheral tissues, reverses diet-induced obesity and dyslipidemia through the reduction of food intake and altered nutrient partitioning. This strategy is being explored for a number of therapeutic applications; however, its potency for the treatment of atherosclerotic cardiovascular disease via improvements in lipid metabolism remains unclear. Therefore, here, we aimed to investigate whether inhibition of the endocannabinoid system can attenuate atherosclerosis development through improvement of dyslipidemia. Lean, dyslipidemic female APOE∗3-Leiden.CETP transgenic mice were fed a Western-type diet supplemented with or without the cannabinoid type 1 receptor inverse agonist rimonabant (20 mg·kg body weight-1 day-1) for up to 20 weeks. Plasma lipids and bile acids were determined, and atherosclerotic lesions were scored in the aortic valve region. Rimonabant lowered plasma levels of triglyceride (TG) (-56%) and non-HDL-C (-19%) and increased HDL-C (+57%). These effects were explained by decreased VLDL-TG production (-52%) and accelerated VLDL-TG turnover accompanied by pronounced browning of white adipose tissue. In addition, rimonabant attenuated reverse cholesterol transport (-30%), increased plasma bile acid levels (+160%), and increased hepatic cholesterol accumulation (+88%). Importantly, rimonabant markedly lowered atherosclerotic lesion size (-64%), which coincided with decreased lesion severity (28% vs. 56% severe lesions) and which strongly correlated with non-HDL-C exposure (R2 = 0.60). Taken together, inhibition of the endocannabinoid system potently reverses dyslipidemia and prevents atherogenesis, even in the absence of obesity.

P300/CBP Associated Factor (PCAF) Deficiency Enhances Diet-Induced Atherosclerosis in ApoE3*Leiden Mice via Systemic Inhibition of Regulatory T Cells

Background: Inflammatory stimuli induced by NF-kB drive atherosclerotic lesion formation. The epigenetic P300/CBP associated factor (PCAF) post-transcriptionally acetylates FoxP3, which is required for regulatory T-cell (Treg) differentiation and immune modulation. We hypothesize that PCAF deficiency affects atherosclerosis via regulation of regulatory Tregs.

Method: ApoE3^*Leiden (n = 13) and ApoE3^*LeidenxPCAF^−/− (n = 13) were fed a high-fat diet (HFD) containing 1.25% cholesterol. Systemic FoxP3⁺ T cells were measured every 4 weeks by flow cytometry (n = 6). After 5-months of HFD, mice were euthanized, and hearts and blood were collected. IL-6 and TNFα concentrations were measured in plasma to identify systemic inflammatory responses. Compositional and morphometrical analyses were performed on the atherosclerotic lesions in the aortic sinuses.

Results: After 5 months of HFD, plasma cholesterol concentrations were not different for ApoE3^*LeidenxPCAF^−/− compared to ApoE3^*Leiden mice. Expression of FoxP3 by systemic CD4⁺ T cells decreased 1.8 fold in ApoE3^*LeidenxPCAF^−/− after 5 months HFD and remained significantly reduced after 5 months of HFD. Systemic TNFα and IL-6 concentrations were comparable, whereas the atherosclerotic lesion size in ApoE3^*LeidenxPCAF^−/− mice was increased by 28% compared to ApoE3^*Leiden mice. In atherosclerotic lesions, no differences were observed in macrophage differentiation or VSMC content, although a small increase in collagen was identified.

Conclusion: Our data show that PCAF deficiency resulted in a decrease in circulatory FoxP3⁺ regulatory T cells and ameliorated atherosclerotic lesions with no differences in systemic inflammation or macrophage differentiation in the atherosclerotic lesions. This suggests that PCAF regulates atherosclerosis via modulation of FoxP3⁺ regulatory T cell differentiation.

Central Role of Oxidative Stress in Age-Related Macular Degeneration: Evidence from a Review of the Molecular Mechanisms and Animal Models

Age-related macular degeneration (AMD) is a common cause of visual impairment in the elderly. There are very limited therapeutic options for AMD with the predominant therapies targeting vascular endothelial growth factor (VEGF) in the retina of patients afflicted with wet AMD. Hence, it is important to remind readers, especially those interested in AMD, about current studies that may help to develop novel therapies for other stages of AMD. This study, therefore, provides a comprehensive review of studies on human specimens as well as rodent models of the disease, to identify and analyze the molecular mechanisms behind AMD development and progression. The evaluation of this information highlights the central role that oxidative damage in the retina plays in contributing to major pathways, including inflammation and angiogenesis, found in the AMD phenotype. Following on the debate of oxidative stress as the earliest injury in the AMD pathogenesis, we demonstrated how the targeting of oxidative stress-associated pathways, such as autophagy and nuclear factor erythroid 2-related factor 2 (Nrf2) signaling, might be the futuristic direction to explore in the search of an effective treatment for AMD, as the dysregulation of these mechanisms is crucial to oxidative injury in the retina. In addition, animal models of AMD have been discussed in great detail, with their strengths and pitfalls included, to assist inform in the selection of suitable models for investigating any of the molecular mechanisms.

Atorvastatin Blocks Advanced Glycation End Products Induced Reduction in Macrophage Cholesterol Efflux Mediated With ATP-Binding Cassette Transporters G 1

BACKGROUND

There is accumulating evidence that the AGEs-RAGE interaction plays an important role in accelerated atherosclerosis in diabetes. Our previous study showed that the AGEs-RAGE axis can reduce the cholesterol efflux of THP-1 macrophages through suppression of the expression of ABCG1 and that statins can inhibit the expression of RAGE. However, the role of statins in recovering the cholesterol efflux of macrophages reduced by AGEs has not been assessed.

METHODS AND RESULTS

ApoE-/-mice and THP-1 macrophages were both treated by AGEs or AGEs combined with anti-RAGE antibody (only in THP-1 cells), ALT711 and atorvastatin separately. Cholesterol efflux of THP-1 macrophages and murine peritoneal macrophages was tested by fluorescence microplate technique. RT-PCR and western blot analysis were used to measure the expression of RAGE and molecules included in cholesterol efflux. After co-incubating with atorvastatin and AGEs, reduction in lipid accumulation in THP-1 macrophages and improvement of lesions complexity occurred compared with treating by AGEs only. Atorvastatin increased cholesterol efflux and ABCG1 expression of macrophages, which were reduced by AGEs, and decreased the expression of RAGE at the same time.

CONCLUSIONS

This study demonstrated that atorvastatin can recover the deleterious ABCG1-mediated cholesterol efflux induced by AGEs in THP-1 macrophages and murine peritoneal macrophages by downregulating RAGE expression. It may contribute to the protective action of atorvastatin in diabetic subjects with atherosclerosis.

Atherogenic LOX-1 signaling is controlled by SPPL2-mediated intramembrane proteolysis

The intramembrane proteases SPPL2a/b control pro-atherogenic signaling of membrane-bound proteolytic fragments derived from the oxLDL receptor LOX-1. In mice deficient for these proteases, plaque development and fibrosis is enhanced. This highlights SPPL2a/b as crucial players of a novel athero-protective mechanism, which is conserved in humans.

The lectin-like oxidized LDL receptor 1 (LOX-1) is a key player in the development of atherosclerosis. LOX-1 promotes endothelial activation and dysfunction by mediating uptake of oxidized LDL and inducing pro-atherogenic signaling. However, little is known about modulators of LOX-1–mediated responses. Here, we show that the function of LOX-1 is controlled proteolytically. Ectodomain shedding by the metalloprotease ADAM10 and lysosomal degradation generate membrane-bound N-terminal fragments (NTFs), which we identified as novel substrates of the intramembrane proteases signal peptide peptidase–like 2a and b (SPPL2a/b). SPPL2a/b control cellular LOX-1 NTF levels which, following self-association via their transmembrane domain, can activate MAP kinases in a ligand-independent manner. This leads to an up-regulation of several pro-atherogenic and pro-fibrotic targets including ICAM-1 and the connective tissue growth factor CTGF. Consequently, SPPL2a/b-deficient mice, which accumulate LOX-1 NTFs, develop larger and more advanced atherosclerotic plaques than controls. This identifies intramembrane proteolysis by SPPL2a/b as a novel atheroprotective mechanism via negative regulation of LOX-1 signaling.

Understanding the Impact of Dietary Cholesterol on Chronic Metabolic Diseases through Studies in Rodent Models

The development of certain chronic metabolic diseases has been attributed to elevated levels of dietary cholesterol. However, decades of research in animal models and humans have demonstrated a high complexity with respect to the impact of dietary cholesterol on the progression of these diseases. Thus, recent investigations in non-alcoholic fatty liver disease (NAFLD) point to dietary cholesterol as a key factor for the activation of inflammatory pathways underlying the transition from NAFLD to non-alcoholic steatohepatitis (NASH) and to hepatic carcinoma. Dietary cholesterol was initially thought to be the key factor for cardiovascular disease development, but its impact on the disease depends partly on the capacity to modulate plasmatic circulating low-density lipoprotein (LDL) cholesterol levels. These studies evidence a complex relationship between these chronic metabolic diseases and dietary cholesterol, which, in certain conditions, might promote metabolic complications. In this review, we summarize rodent studies that evaluate the impact of dietary cholesterol on these two prevalent chronic diseases and their relevance to human pathology.

Whole body and hematopoietic ADAM8 deficiency does not influence advanced atherosclerotic lesion development, despite its association with human plaque progression

Although A Disintegrin And Metalloproteinase 8 (ADAM8) is not crucial for tissue development and homeostasis, it has been implicated in various inflammatory diseases by regulating processes like immune cell recruitment and activation. ADAM8 expression has been associated with human atherosclerosis development and myocardial infarction, however a causal role of ADAM8 in atherosclerosis has not been investigated thus far. In this study, we examined the expression of ADAM8 in early and progressed human atherosclerotic lesions, in which ADAM8 was significantly upregulated in vulnerable lesions. In addition, ADAM8 expression was most prominent in the shoulder region of human atherosclerotic lesions, characterized by the abundance of foam cells. In mice, Adam8 was highly expressed in circulating neutrophils and in macrophages. Moreover, ADAM8 deficient mouse macrophages displayed reduced secretion of inflammatory mediators. Remarkably, however, neither hematopoietic nor whole-body ADAM8 deficiency in mice affected atherosclerotic lesion size. Additionally, except for an increase in granulocyte content in plaques of ADAM8 deficient mice, lesion morphology was unaffected. Taken together, whole body and hematopoietic ADAM8 does not contribute to advanced atherosclerotic plaque development, at least in female mice, although its expression might still be valuable as a diagnostic/prognostic biomarker to distinguish between stable and unstable lesions.

Tyrosine Kinase Inhibitors and Vascular Toxicity: Impetus for a Classification System?

The introduction of molecularly targeted therapies with tyrosine kinase inhibitors has revolutionized cancer therapy and has contributed to a steady decline in cancer-related mortality since the late 1990s. However, not only cardiac but also vascular toxicity has been reported for these agents, some as expected on-target effects (e.g., VEGF receptor inhibitors) and others as unanticipated events (e.g., BCR-Abl inhibitors). A sound understanding of these cardiovascular toxic effects is critical to advance mechanistic insight into vascular disease and clinical care. From a conceptual standpoint, there might be value in defining type I (permanent) and type II (transient) vascular toxicity. This review will focus on the tyrosine kinase inhibitors in current clinical use and their associated vascular side effects.

Losartan attenuates the coronary perivasculitis through its local and systemic anti-inflammatory properties in a murine model of Kawasaki disease

BACKGROUND

Kawasaki disease is a common systemic vasculitis that leads to coronary artery lesions. Besides its antihypertensive effects, losartan can modulate inflammation in cardiovascular disease. We examined whether losartan can attenuate coronary inflammation in a murine model of Kawasaki disease.

METHODS AND RESULTS

Five-wk-old C57/BL6J male mice were intraperitoneally injected with Lactobacillus casei cell wall extract to induce coronary inflammation and divided into four groups: placebo, intravenous immunoglobulin (IVIG), losartan, and IVIG+losartan. After 2 wk, mice were harvested. The coronary perivasculitis was significantly attenuated by losartan but not by IVIG alone, and further dramatic attenuation by IVIG+losartan was observed. The frequency of Lactobacillus casei cell wall extract-induced myocarditis (80%) was markedly lowered by losartan (22%) and IVIG+losartan (0%). Furthermore, interleukin (IL)-6 mRNA was markedly attenuated by IVIG+losartan. Serum levels of IL-6, TNF-α, MCP-1, and IL-10 after Lactobacillus casei cell wall extract injection were slightly decreased by IVIG or losartan. Moreover, IL-1β, IL-10, and MCP-1 levels were significantly decreased by IVIG+losartan.

CONCLUSION

The addition of losartan to IVIG strongly attenuated the severity of coronary perivasculitis and the incidence of myocarditis, along with suppressing systemic/local cytokines as well as the activated macrophage infiltration. Therefore, losartan may be a potentially useful additive drug for the acute phase of Kawasaki disease to minimize coronary artery lesions.

Adventitial lymphatic capillary expansion impacts on plaque T cell accumulation in atherosclerosis

During plaque progression, inflammatory cells progressively accumulate in the adventitia, paralleled by an increased presence of leaky vasa vasorum. We here show that next to vasa vasorum, also the adventitial lymphatic capillary bed is expanding during plaque development in humans and mouse models of atherosclerosis. Furthermore, we investigated the role of lymphatics in atherosclerosis progression. Dissection of plaque draining lymph node and lymphatic vessel in atherosclerotic ApoE^-/- mice aggravated plaque formation, which was accompanied by increased intimal and adventitial CD3⁺ T cell numbers. Likewise, inhibition of VEGF-C/D dependent lymphangiogenesis by AAV aided gene transfer of hVEGFR3-Ig fusion protein resulted in CD3⁺ T cell enrichment in plaque intima and adventitia. hVEGFR3-Ig gene transfer did not compromise adventitial lymphatic density, pointing to VEGF-C/D independent lymphangiogenesis. We were able to identify the CXCL12/CXCR4 axis, which has previously been shown to indirectly activate VEGFR3, as a likely pathway, in that its focal silencing attenuated lymphangiogenesis and augmented T cell presence. Taken together, our study not only shows profound, partly CXCL12/CXCR4 mediated, expansion of lymph capillaries in the adventitia of atherosclerotic plaque in humans and mice, but also is the first to attribute an important role of lymphatics in plaque T cell accumulation and development.

Dietary fatty acids on aortic root calcification in mice with metabolic syndrome

Metabolic syndrome (MetS) is associated with obesity, dyslipidemia, type 2 diabetes, and chronic low-grade inflammation.

Inhibition of siglec-1 by lentivirus mediated small interfering RNA attenuates atherogenesis in apoE-deficient mice

BACKGROUND

Siglec-1 is highly expressed on circulating monocytes and plaque macrophages in atherosclerotic patients, but the exact role of Siglec-1 in atherosclerosis has not been elucidated.

METHODS

Lentiviral vector containing small interfering RNA targeting Siglec-1 (Lv-shSiglec-1) or control vector (Lv-shNC) were injected intravenously into 6-week old Apoe^-/- mice. Then onset of atherosclerosis was observed.

RESULTS

Siglec-1 was highly expressed in aortic plaques and it can be down-regulated by Lv-shSiglec-1 injection. The plaque area and serum pro-inflammatory cytokine (IL-1β, IL-6, TNF-α and IL-17A) levels in Lv-shSiglec-1 mice were significantly lower than Lv-shNC mice, whereas IL-10 was higher. Moreover, plaque macrophages accumulation in aortic wall in Lv-shSiglec-1 mice was diminish, partly by decreased secretion of MCP-1/CXCL2 and CCR2/CXCR2 of aortas and monocytes, respectively. Furthermore, silencing of Siglec-1 can attenuate oxLDL uptake by peritoneal macrophages.

CONCLUSIONS

Inhibition of Siglec-1 can prevent atherosclerotic lesion formation by suppress monocytes-endothelial cells adhesion and macrophages accumulation.

TTC39B deficiency stabilizes LXR reducing both atherosclerosis and steatohepatitis

Cellular mechanisms that mediate steato-hepatitis, an increasingly prevalent condition in the Western world for which no therapies are available¹, are poorly understood. Despite the fact its synthetic agonists induce fatty liver, the Liver X receptor (LXR) transcription factor remains a target of interest because of its anti-atherogenic, cholesterol removal and anti-inflammatory activities. We discovered that tetratricopeptide repeat (TPR) domain protein 39B (Ttc39b, C9orf52) (T39), a high density lipoprotein (HDL) gene discovered in human genome wide association studies (GWAS)², promotes the ubiquitination and degradation of LXR. Chow-fed T39^-/- mice displayed increased HDL cholesterol levels associated with increased enterocyte ATP binding cassette transporter A1 (Abca1) expression and increased LXR protein without change in LXR mRNA. When challenged with a high fat/high cholesterol/bile salt (HF/HC/BS) diet, T39^-/- mice or mice with hepatocyte-specific T39 deficiency showed increased hepatic LXR protein and target gene expression, and unexpectedly protection from steato-hepatitis and death. Western Type Diet (WTD)-fed Low density lipoprotein receptor (Ldlr)^-/-T39^-/- mice showed decreased fatty liver, increased HDL, decreased LDL and reduced atherosclerosis. In addition to increasing hepatic Abcg5/8 expression and limiting dietary cholesterol absorption, T39 deficiency inhibited hepatic sterol regulatory element binding protein 1 (SREBP-1, ADD1) processing. This was explained by an increase in microsomal phospholipids containing polyunsaturated fatty acids (PUFA), linked to an LXRα-dependent increase in expression of enzymes mediating PC biosynthesis and incorporation of PUFA into phospholipids. The preservation of endogenous LXR protein activates a beneficial profile of gene expression that promotes cholesterol removal and inhibits lipogenesis. T39 inhibition could be an effective strategy for reducing both steato-hepatitis and atherosclerosis.

Myeloid A disintegrin and metalloproteinase domain 10 deficiency modulates atherosclerotic plaque composition by shifting the balance from inflammation toward fibrosis

A disintegrin and metalloproteinase domain 10 (ADAM10) is a metalloprotease involved in cleavage of various cell surface molecules, such as adhesion molecules, chemokines, and growth factor receptors. Although we have previously shown an association of ADAM10 expression with atherosclerotic plaque progression, a causal role of ADAM10 in atherosclerosis has not been investigated. Bone marrow from conditional knockout mice lacking Adam10 in the myeloid lineage or from littermate controls was transplanted into lethally irradiated low density lipoprotein receptor Ldlr(-/-) mice on an atherogenic diet. Myeloid Adam10 deficiency did not affect plaque size, but it increased plaque collagen content. Matrix metalloproteinase 9 and 13 expression and matrix metalloproteinase 2 gelatinase activity were significantly impaired in Adam10-deficient macrophages, whereas their capacity to stimulate collagen production was unchanged. Furthermore, relative macrophage content in advanced atherosclerotic lesions was decreased. In vitro, Adam10-deficient macrophages showed reduced migration toward monocyte chemoattractant protein-1 and transmigration through collagen. In addition, Adam10-deficient macrophages displayed increased anti-inflammatory phenotype with elevated IL-10, and reduced production of proinflammatory tumor necrosis factor, IL-12, and nitric oxide in response to lipopolysaccharide. These data suggest a critical role of Adam10 for leukocyte recruitment, inflammatory mediator production, and extracellular matrix degradation. Thereby, myeloid ADAM10 may play a causal role in modulating atherosclerotic plaque stability.

Hematopoietic α7 nicotinic acetylcholine receptor deficiency increases inflammation and platelet activation status, but does not aggravate atherosclerosis

BACKGROUND

The autonomic nervous system attenuates inflammation through activation of the α7 nicotinic acetylcholine receptor (α7nAChR), a pathway termed the cholinergic anti-inflammatory reflex. Interestingly, α7nAChR is expressed on immune cells and platelets, both of which play a crucial role in the development of atherosclerosis.

OBJECTIVE

To investigate the role of hematopoietic α7nAChR in inflammation and platelet function in atherosclerotic ldlr(-/-) mice and to identify its consequences for atherosclerotic lesion development.

METHODS

Bone marrow from α7nAChR(-/-) mice or wild-type littermates was transplanted into irradiated ldlr(-/-) mice. After a recovery period of 8 weeks, the mice were fed an atherogenic Western-type diet for 7 weeks.

RESULTS

Hematopoietic α7nAChR deficiency clearly increased the number of leukocytes in the peritoneum (2.6-fold, P < 0.001), blood (2.9-fold; P < 0.01), mesenteric lymph nodes (2.0-fold; P < 0.001) and spleen (2.2-fold; P < 0.01), indicative of an increased inflammatory status. Additionally, expression of inflammatory mediators was increased in peritoneal leukocytes (TNFα, 1.6-fold, P < 0.01; CRP, 1.8-fold, P < 0.01) as well as in the spleen (TNFα, 1.6-fold, P < 0.01). The lack of α7nAChR on platelets from these mice increased the expression of active integrin αIIb β3 upon stimulation by ADP (1.9-fold, P < 0.01), indicating increased activation status, while incubation of human platelets with an α7nAChR agonist decreased aggregation (-35%, P < 0.05). Despite the large effects of hematopoietic α7nAChR deficiency on inflammatory status and platelet function, it did not affect atherosclerosis development or composition of lesions.

CONCLUSIONS

Hematopoietic α7nAChR is important for attenuation of inflammatory responses and maintaining normal platelet reactivity, but loss of hematopoietic α7nAChR does not aggravate development of atherosclerosis.

Exendin-4 decreases liver inflammation and atherosclerosis development simultaneously by reducing macrophage infiltration

BACKGROUND AND PURPOSE

The aetiology of inflammation in the liver and vessel wall, leading to non-alcoholic steatohepatitis (NASH) and atherosclerosis, respectively, shares common mechanisms including macrophage infiltration. To treat both disorders simultaneously, it is highly important to tackle the inflammatory status. Exendin-4, a glucagon-like peptide-1 (GLP-1) receptor agonist, reduces hepatic steatosis and has been suggested to reduce atherosclerosis; however, its effects on liver inflammation are underexplored. Here, we tested the hypothesis that exendin-4 reduces inflammation in both the liver and vessel wall, and investigated the common underlying mechanism.

EXPERIMENTAL APPROACH

Female APOE*3-Leiden.CETP mice, a model with human-like lipoprotein metabolism, were fed a cholesterol-containing Western-type diet for 5 weeks to induce atherosclerosis and subsequently treated for 4 weeks with exendin-4.

KEY RESULTS

Exendin-4 modestly improved dyslipidaemia, but markedly decreased atherosclerotic lesion severity and area (-33%), accompanied by a reduction in monocyte adhesion to the vessel wall (-42%) and macrophage content in the plaque (-44%). Furthermore, exendin-4 reduced hepatic lipid content and inflammation as well as hepatic CD68⁺ (-18%) and F4/80⁺ (-25%) macrophage content. This was accompanied by less monocyte recruitment from the circulation as the Mac-1⁺ macrophage content was decreased (-36%). Finally, exendin-4 reduced hepatic chemokine expression in vivo and suppressed oxidized low-density lipoprotein accumulation in peritoneal macrophages in vitro, effects dependent on the GLP-1 receptor.

CONCLUSIONS AND IMPLICATIONS

Exendin-4 reduces inflammation in both the liver and vessel wall by reducing macrophage recruitment and activation. These data suggest that exendin-4 could be a valuable strategy to treat NASH and atherosclerosis simultaneously.

Both transient and continuous corticosterone excess inhibit atherosclerotic plaque formation in APOE*3-leiden.CETP mice

Introduction

The role of glucocorticoids in atherosclerosis development is not clearly established. Human studies show a clear association between glucocorticoid excess and cardiovascular disease, whereas most animal models indicate an inhibitory effect of glucocorticoids on atherosclerosis development. These animal models, however, neither reflect long-term glucocorticoid overexposure nor display human-like lipoprotein metabolism.

Aim

To investigate the effects of transient and continuous glucocorticoid excess on atherosclerosis development in a mouse model with human-like lipoprotein metabolism upon feeding a Western-type diet.

Methods

Pair-housed female APOE*3-Leiden.CETP (E3L.CETP) mice fed a Western-type containing 0.1% cholesterol for 20 weeks were given corticosterone (50 µg/ml) for either 5 (transient group) or 17 weeks (continuous group), or vehicle (control group) in the drinking water. At the end of the study, atherosclerosis severity, lesion area in the aortic root, the number of monocytes adhering to the endothelial wall and macrophage content of the plaque were measured.

Results

Corticosterone treatment increased body weight and food intake for the duration of the treatment and increased gonadal and subcutaneous white adipose tissue weight in transient group by +35% and +31%, and in the continuous group by +140% and 110%. Strikingly, both transient and continuous corticosterone treatment decreased total atherosclerotic lesion area by −39% without lowering plasma cholesterol levels. In addition, there was a decrease of −56% in macrophage content of the plaque with continuous corticosterone treatment, and a similar trend was present with the transient treatment.

Conclusion

Increased corticosterone exposure in mice with human-like lipoprotein metabolism has beneficial, long-lasting effects on atherosclerosis, but negatively affects body fat distribution by promoting fat accumulation in the long-term. This indicates that the increased atherosclerosis observed in humans in states of glucocorticoid excess may not be related to cortisol per se, but might be the result of complex indirect effects of cortisol.

Sialoadhesin - a macrophage-restricted marker of immunoregulation and inflammation

Sialoadhesin (Sn, also known as Siglec-1 and CD169) is a macrophage-restricted cell surface receptor that is conserved across mammals. Sn is a member of the sialic acid-binding IgG-like lectin (Siglec) family of proteins characterized by affinity to specifically sialylated ligands, and under normal conditions is expressed on subsets of macrophages in secondary lymphoid tissues, such as lymph node and spleen. However, Sn-positive macrophages can also be found in a variety of pathological conditions, including (autoimmune) inflammatory infiltrates and tumours. Sn has been shown to contribute to sialylated pathogen uptake, antigen presentation and lymphocyte proliferation, and to influence both immunity and tolerance. This review presents Sn as a macrophage-specific marker of inflammation and immunoregulation with the potential to becoming an important biomarker for immunologically active macrophages and a target for therapy.

Differential effects of drug interventions and dietary lifestyle in developing type 2 diabetes and complications: a systems biology analysis in LDLr-/- mice

Excess caloric intake leads to metabolic overload and is associated with development of type 2 diabetes (T2DM). Current disease management concentrates on risk factors of the disease such as blood glucose, however with limited success. We hypothesize that normalizing blood glucose levels by itself is insufficient to reduce the development of T2DM and complications, and that removal of the metabolic overload with dietary interventions may be more efficacious. We explored the efficacy and systems effects of pharmaceutical interventions versus dietary lifestyle intervention (DLI) in developing T2DM and complications. To mimic the situation in humans, high fat diet (HFD)-fed LDLr-/- mice with already established disease phenotype were treated with ten different drugs mixed into HFD or subjected to DLI (switch to low-fat chow), for 7 weeks. Interventions were compared to untreated reference mice kept on HFD or chow only. Although most of the drugs improved HFD-induced hyperglycemia, drugs only partially affected other risk factors and also had limited effect on disease progression towards microalbuminuria, hepatosteatosis and atherosclerosis. By contrast, DLI normalized T2DM risk factors, fully reversed hepatosteatosis and microalbuminuria, and tended to attenuate atherogenesis. The comprehensive beneficial effect of DLI was reflected by normalized metabolite profiles in plasma and liver. Analysis of disease pathways in liver confirmed reversion of the metabolic distortions with DLI. This study demonstrates that the pathogenesis of T2DM towards complications is reversible with DLI and highlights the differential effects of current pharmacotherapies and their limitation to resolve the disease.

Contribution of monocytes Siglec-1 in stimulating T cells proliferation and activation in atherosclerosis

OBJECTIVE

Atherosclerosis (AS) is widely accepted as an inflammatory disease and monocytes are particularly important in inflammatory immune responses. As an important biomarker of monocytes activation, Siglec-1 is highly expressed on circulating monocytes and atherosclerotic plaques of coronary artery disease (CAD) patients, but the exact role of Siglec-1 has not been elucidated.

METHODS

M-CSF, INF-α, IFN-γ, TNF-α and ox-LDL alone or in combination were used to stimulate Siglec-1 expression on monocytes, whereas small interfering RNA (si-RNA) or blocking antibody was used to down-regulate Siglec-1. Meanwhile, the role of Siglec-1 in chemokines secretion was determined. Then monocytes from CAD patients or healthy controls were cocultured with CD4+ or CD8+ T cells from a third healthy individual, and lymphocyte proliferation and activation were determined.

RESULTS

All the stimuluses could enhance Siglec-1 expression on monocytes in a dose-dependent manner, and M-CSF could synergistically stimulate Siglec-1 expression with ox-LDL. Moreover, the secretion of MCP-1, MIP-1α and MIP-2 were enhanced when Siglec-1 was up-regulated and down to normal level when Siglec-1 was blocked. More importantly, increased Siglec-1 expression on monocytes was related to the increased T cell proliferation and pro-inflammatory cytokines secretion in CAD patients. However, down-regulation of Siglec-1 could attenuate proliferation and activation of cocultured CD4+ and CD8+ T cells.

CONCLUSION

Siglec-1 can promote chemokines and pro-inflammatory cytokines secretion and influence the inflammatory process of AS.

Differentiation factors and cytokines in the atherosclerotic plaque micro-environment as a trigger for macrophage polarisation

The phenotype of macrophages in atherosclerotic lesions can vary dramatically, from a large lipid laden foam cell to a small inflammatory cell. Classically, the concept of macrophage heterogeneity discriminates between two extremes called either pro-inflammatory M1 macrophages or anti-inflammatory M2 macrophages. Polarisation of plaque macrophages is predominantly determined by the local micro-environment present in the atherosclerotic lesion and is rather more complex than typically described by the M1/M2 paradigm. In this review we will discuss the role of various polarising factors in regulating the phenotypical state of plaque macrophages. We will focus on two main levels of phenotype regulation, one determined by differentiation factors produced in the lesion and the other determined by T-cell-derived polarising cytokines. With foam cell formation being a key characteristic of macrophages during atherosclerosis initiation and progression, these polarisation factors will also be linked to lipid handling of macrophages.

Antibody binding to porcine sialoadhesin reduces phagocytic capacity without affecting other macrophage effector functions

Sialoadhesin (Sn) is a macrophage-restricted endocytic receptor involved in cell-cell, cell-matrix and cell-pathogen interactions. Recently, porcine Sn (pSn) was shown to be involved in signaling and lately Sn is gaining interest as a potential target for immunotherapy. However, little is known about the effect of ligand binding to Sn on macrophage effector functions. In this study, we tested the effect of antibody binding to pSn on macrophage viability, phagocytosis of microspheres, uptake and processing of soluble antigens, reactive oxygen/nitrogen species production, MHC I and MHC II cell surface expression and cytokine production. This was done by treatment of porcine primary alveolar macrophages with the pSn-specific mAb 41D3, or an isotype-matched control mAb. No significant effect on most effector functions under study was observed, except for a significant reduction of phagocytosis. Thus, antibody binding to pSn can downregulate phagocytosis, which could have implications on homeostasis, infectious and immune diseases, and immunotherapy.

Cannabinoid Receptor 2 Deficiency in Haematopoietic cells Aggravates Early Atherosclerosis in LDL Receptor Deficient Mice

OBJECTIVE

The cannabinoid receptor 2 (CB2) has been implicated to play a role in various inflammatory processes. Since atherosclerosis is currently considered a chronic inflammatory disease, we studied the effect of haematopoietic CB2 deficiency on atherosclerosis development.

METHODS AND RESULTS

To investigate the effect of CB2 deficiency in immune cells on atherogenesis in vivo, a bone marrow transplantation was performed in irradiated LDL receptor deficient mice (LDLr(-/-)), using CB2 deficient (CB2(-/-)) or wildtype (WT) donor mice. After 12 weeks on a high fat-high cholesterol diet, en face analysis showed that atherosclerosis in the aortic arch was significantly increased in CB2(-/-) transplanted animals (6.40 ± 3.21%) as compared to WT transplanted mice (3.85 ± 1.61%). Although the total lesion area in the aortic root was not significantly different between WT and CB2(-/-) transplanted mice (0.45 ± 0.13 mm(2) and 0.51 ± 0.17 mm(2), respectively), CB2(-/-) transplanted mice showed a significantly larger plaque area (0.13 ± 0.07 mm(2)) than WT transplanted mice (0.08 ± 0.05 mm(2)) in the aortic valve in which atherogenesis is in an earlier stage than in the other aortic valves.

CONCLUSIONS

Lack of endocannabinoid signaling via the CB2 receptor aggravates early atherosclerosis development in LDLr(-/-) mice, suggesting that CB2 specific activation may prevent the development of atherosclerosis.

Cholesterol diet and effect of long-term withdrawal on plaque development and composition in the thoracic aorta of New Zealand White rabbits

AIMS

Experimental study on plaque progression, regression and composition in atherosclerotic thoracic aorta of hypercholesterolemic rabbits after long-term withdrawal of cholesterol-enriched diet (CED).

METHODS

Rabbits were fed 2% cholesterol for 6 weeks followed by withdrawal periods for 15, 23, 34, 68, or 78 weeks. Cholesterol, triglyceride, and phospholipids levels in blood and cholesterol concentrations in aorta were quantified. Plaque size and cellularity, phenotype of macrophages and smooth muscle cells were (immuno)histomorphometrically analyzed in segments of the thoracic aorta.

RESULTS

After 6 weeks of CED, blood cholesterol levels were about 80-fold higher, whereas atherosclerosis and cholesterol content in the thoracic aorta were only minimally increased. However, the latter significantly increased within 15 weeks after cholesterol withdrawal, while serum cholesterol level was still 10-fold increased. Thereafter plaque area and cholesterol content remained almost unchanged until the end of the study despite a long-term normalization of serum cholesterol level after withdrawal of CED. Directly after 6 weeks of CED the densities of macrophages and apoptotic cells within plaques were highest, decreasing after cholesterol withdrawal, whereas, vice versa the density of smooth muscle cells (SMCs) significantly increased.

CONCLUSION

We suggest that atherosclerotic plaques respond to long-term withdrawal of CED by decrease in number and phenotype of macrophages and increase of SMCs without regression of the lesion size. The cellular changes are suggested to considerably contribute to higher plaque stability.

Ritonavir protects against the development of atherosclerosis in APOE*3-Leiden mice

OBJECTIVE

The use of the HIV-protease inhibitor ritonavir (RTV) is associated with induction of hypertriglyceridemia, which is a cardiovascular risk factor. Therefore, we investigated the effect of RTV on atherosclerosis development in APOE*3-Leiden transgenic mice, a model for human-like lipoprotein metabolism and atherosclerosis.

METHODS AND RESULTS

APOE*3-Leiden mice were fed a Western-type diet without or with RTV (35 mg/kg/day) for 19 weeks. RTV increased plasma TG levels throughout the study (approximately 2-fold; P<0.05). Despite these increased TG levels, RTV decreased the atherosclerotic lesion area in the aortic root (-57%; P<0.05), concomitant with reduced macrophage area (-72%; P<0.01) and decreased lesion severity. This could not be explained by reduced inflammatory markers in plasma (i.e. serum amyloid A, E-selectin and fibrinogen), nor by decreased lipid accumulation in macrophages or increased cholesterol efflux from macrophages, as assessed using peritoneal macrophages in vitro. Rather, whereas RTV did not affect plasma total cholesterol levels, RTV decreased (V)LDL-cholesterol and increased cholesterol in apoE-rich large HDL.

CONCLUSION

Despite inducing hypertriglyceridemia, RTV decreases atherosclerotic lesion area and severity, associated with decreased (V)LDL-cholesterol and increased atheroprotective apoE-rich large HDL.

Genome-wide mRNA expression analysis of hepatic adaptation to high-fat diets reveals switch from an inflammatory to steatotic transcriptional program

BACKGROUND

Excessive exposure to dietary fats is an important factor in the initiation of obesity and metabolic syndrome associated pathologies. The cellular processes associated with the onset and progression of diet-induced metabolic syndrome are insufficiently understood.

PRINCIPAL FINDINGS

To identify the mechanisms underlying the pathological changes associated with short and long-term exposure to excess dietary fat, hepatic gene expression of ApoE3Leiden mice fed chow and two types of high-fat (HF) diets was monitored using microarrays during a 16-week period. A functional characterization of 1663 HF-responsive genes reveals perturbations in lipid, cholesterol and oxidative metabolism, immune and inflammatory responses and stress-related pathways. The major changes in gene expression take place during the early (day 3) and late (week 12) phases of HF feeding. This is also associated with characteristic opposite regulation of many HF-affected pathways between these two phases. The most prominent switch occurs in the expression of inflammatory/immune pathways (early activation, late repression) and lipogenic/adipogenic pathways (early repression, late activation). Transcriptional network analysis identifies NF-kappaB, NEMO, Akt, PPARgamma and SREBP1 as the key controllers of these processes and suggests that direct regulatory interactions between these factors may govern the transition from early (stressed, inflammatory) to late (pathological, steatotic) hepatic adaptation to HF feeding. This transition observed by hepatic gene expression analysis is confirmed by expression of inflammatory proteins in plasma and the late increase in hepatic triglyceride content. In addition, the genes most predictive of fat accumulation in liver during 16-week high-fat feeding period are uncovered by regression analysis of hepatic gene expression and triglyceride levels.

CONCLUSIONS

The transition from an inflammatory to a steatotic transcriptional program, possibly driven by the reciprocal activation of NF-kappaB and PPARgamma regulators, emerges as the principal signature of the hepatic adaptation to excess dietary fat. These findings may be of essential interest for devising new strategies aiming to prevent the progression of high-fat diet induced pathologies.

Genomics and cardiovascular drug development

In the last half century, phenomenal advances have been made in understanding the pathophysiology of cardiovascular disease and in developing therapies to reduce cardiovascular risk. Nevertheless, cardiovascular disease remains the leading cause of death and morbidity in the industrialized world, with rapidly rising prevalence in developing countries, accounting for approximately 30% of all deaths worldwide. Since the initial availability of statin drugs in 1987, few novel cardiovascular therapies have emerged. Whereas statins reduce the mortality and morbidity from atherosclerotic heart disease by approximately 30%, the staggering 70% residual cardiovascular risk underscores the persistent need for novel therapies. Substantial advances in genomic research offer promise to greatly facilitate cardiovascular drug development. Over the past decade, often termed "the genomics revolution," such advancements as the emergence of genome-wide genotyping in humans, the industrialization of messenger ribonucleic acid expression profiling, and the maturation of proteomic and metabolomic methodologies have been made. In addition, the advancement of informatics to allow the intersection of multiple complex datasets has led to the field of systems biology. Genomic approaches are already being utilized to drive novel compound pipelines by helping with the identification and validation of novel targets. In the future, the study of genomics is expected to support biomarker discovery and development and the identification of responder patient segments. The focus of the present review is the application of genomics to the development of novel atherosclerosis therapies.

Siglecs as positive and negative regulators of the immune system

Siglecs (sialic acid-binding Ig-like lectins) are mainly expressed in the immune system. Sn (sialoadhesin) (siglec-1), CD22 (siglec-2) and siglec-15 are well conserved, whereas the CD33-related siglecs are undergoing rapid evolution, as reflected in large differences in repertoires among the different mammals studied so far. In the present paper, we review recent findings on the signalling properties of the CD33-related siglecs and discuss the emergence of both inhibitory and activating forms of this family. We also discuss how Sn may function as a positive regulator of adaptive immune responses and its emerging role as an induced macrophage pattern-recognition molecule for sialylated pathogens, especially enveloped viruses.

LXR agonist suppresses atherosclerotic lesion growth and promotes lesion regression in apoE*3Leiden mice: time course and mechanisms

The aim of this study was to define the anti-atherosclerotic role of liver-X-receptors (LXRs) under lesion progressive and lesion regressive conditions, to establish a temporal line of events, and to gain insights into the mechanisms underlying the anti-atherogenic potency of LXRs. We used apoE*3Leiden (E3L) mice to comprehensively and time-dependently dissect how T0901317, an LXR-agonist, inhibits initiation and progression of atherosclerotic lesions and regresses existing lipid- and macrophage-rich lesions. T0901317 suppresses lesion evolution and promotes lesion regression regarding lesion number, area, and severity. Quantitative plasma and vessel wall analyses corroborated by immunohistochemical evaluation of the aortic lesions revealed that under progressive (high-cholesterol diet) as well as regressive (cholesterol-free diet) conditions T0901317: i) significantly increases plasma triglyceride and total cholesterol levels; ii) does not affect the systemic inflammation marker, Serum amyloid A (SAA); iii) suppresses endothelial monocyte adhesion; and iv) induces the expression of the cholesterol efflux-related genes apolipoprotein E (apoE), ATP binding cassette (ABC) transporters ABCA1 and ABCG1. Furthermore, under progressive conditions, T0901317 suppresses the vascular inflammatory status (NF-kappaB) and the vascular expression of adhesion molecules [E-selectin, intercellular adhesion molecule (ICAM)-1, and CD44], lowers lesional macrophage accumulation, and blocks lesion evolution at the transition from lesional stage II to III. Under regressive conditions, T0901317 induces lesional macrophage disappearance and increases the expression of the chemokine receptor CCR7, a factor functionally required for regression. The LXR-agonist T0901317 retards vascular lesion development and promotes lesion regression at several levels. The findings support that vascular LXR is a potential anti-atherosclerotic target.

Two-photon microscopy on vital carotid arteries: imaging the relationship between collagen and inflammatory cells in atherosclerotic plaques

We used two-photon laser scanning microscopy (TPLSM) to demonstrate for the first time its potential in studying relational details at the cellular level of atherogenesis in intact, viable mouse carotid arteries. Isolated and mounted arteries of ApoE-/-mice, aged 15 or 21 weeks (7 and 13 weeks on western diet), were imaged after labeling with specific fluorescent markers for cell nuclei, inflammatory cells, collagen, and lipids. Data were compared with C57BL6/J mice fed a chow diet. Control vessels had intact endothelium without adhering blood cells or significant intimal collagen labeling. In ApoE-/-mice already at 15 weeks, inflammatory cells adhered to the endothelium and increased labeling of collagen was observed in tunica intima at both lesion-prone and non-lesion-prone sites, indicating endothelium activation. In plaques, internalized inflammatory cell density increased with age and plaque progression in tunicae adventitia and intima, but not media. In the whole plaque, aging or plaque progression did not alter the direct relationship between inflammatory cells and collagen. However, within the fibrous caps specifically, direct contact between inflammatory cells and collagen increased with age. This study demonstrates the potential of TPLSM in determining detailed information regarding the complex relationship between inflammatory cells and collagen during atherogenesis.

Torcetrapib does not reduce atherosclerosis beyond atorvastatin and induces more proinflammatory lesions than atorvastatin

BACKGROUND

Although cholesteryl ester transfer protein (CETP) inhibition is regarded as a promising strategy to reduce atherosclerosis by increasing high-density lipoprotein cholesterol, the CETP inhibitor torcetrapib given in addition to atorvastatin had no effect on atherosclerosis and even increased cardiovascular death in the recent Investigation of Lipid Level Management to Understand its Impact in Atherosclerotic Events trial. Therefore, we evaluated the antiatherogenic potential and adverse effects of torcetrapib in humanized APOE*3-Leiden.CETP (E3L.CETP) mice.

METHODS AND RESULTS

E3L.CETP mice were fed a cholesterol-rich diet without drugs or with torcetrapib (12 mg x kg(-1) x d(-1)), atorvastatin (2.8 mg x kg(-1) x d(-1)), or both for 14 weeks. Torcetrapib decreased CETP activity in both the absence and presence of atorvastatin (-74% and -73%, respectively; P<0.001). Torcetrapib decreased plasma cholesterol (-20%; P<0.01), albeit to a lesser extent than atorvastatin (-42%; P<0.001) or the combination of torcetrapib and atorvastatin (-40%; P<0.001). Torcetrapib increased high-density lipoprotein cholesterol in the absence (30%) and presence (34%) of atorvastatin. Torcetrapib and atorvastatin alone reduced atherosclerotic lesion size (-43% and -46%; P<0.05), but combination therapy did not reduce atherosclerosis compared with atorvastatin alone. Remarkably, compared with atorvastatin, torcetrapib enhanced monocyte recruitment and expression of monocyte chemoattractant protein-1 and resulted in lesions of a more inflammatory phenotype, as reflected by an increased macrophage content and reduced collagen content.

CONCLUSIONS

CETP inhibition by torcetrapib per se reduces atherosclerotic lesion size but does not enhance the antiatherogenic potential of atorvastatin. However, compared with atorvastatin, torcetrapib introduces lesions of a less stable phenotype.

Acute elevation of plasma PLTP activity strongly increases pre-existing atherosclerosis

OBJECTIVE

A transgenic mouse model was generated that allows conditional expression of human PLTP, based on the tetracycline-responsive gene system, to study the effects of an acute increase in plasma PLTP activity as may occur in inflammation.

METHODS AND RESULTS

The effects of an acute elevation of plasma PLTP activity on the metabolism of apolipoprotein B-containing lipoproteins and on diet-induced pre-existing atherosclerosis were determined in mice displaying a humanized lipoprotein profile (low-density lipoprotein receptor knockout background). Induced expression of PLTP strongly increases plasma VLDL levels in LDL receptor knockout mice, whereas VLDL secretion is not affected. The elevation in plasma triglyceride levels is explained by a PLTP-dependent inhibition of VLDL catabolism, which is caused, at least partly, by a decreased lipoprotein lipase activity. Together with the decreased plasma HDL levels, the acutely increased PLTP expression results in a highly atherogenic lipoprotein profile. Induction of PLTP expression leads to a further increase in size of pre-existing atherosclerotic lesions, even on a chow diet. In addition, the lesions contain more macrophages and less collagen relative to controls, suggesting a less stable lesion phenotype.

CONCLUSIONS

In conclusion, acute elevation of PLTP activity destabilizes atherosclerotic lesions and aggravates pre-existing atherosclerosis.

The Role of Immunity and Inflammation in the Progression of Atherosclerosis in Patients With HIV Infection

Background and Purpose— The initial steps of atherosclerosis and the entry of HIV into the cell share similar biological mechanisms. Therefore, our hypothesis is that the progression of atherosclerosis in patients with HIV infection can be influenced by variations in genes implicated in both processes.

Methods and Results— The progression of atherosclerosis over a 2-year follow-up period was measured as the combined carotid and femoral intima media thickness (IMT) in 141 patients with HIV infection. The ΔIMT (IMT follow-up −IMT baseline ) values were used to segregate patients as minimal progressors or regressors (lowest ΔIMT tertile), slow progressors (mid ΔIMT tertile), and rapid progressors (highest ΔIMT tertile). Mutations CCR-5Δ32, CCR-2 64I, MCP-1-2518G, SDF1-3′A, and CX3CR-1 (T280 mol/L and V249I) in the host DNA were determined. Mean age of the patients was 38.96 (SEM: 0.61) and 68.8% were male. The mean ΔIMT was 0.045 mm (0.01) per year, which represented a significant progression ( P <0.001) with respect to baseline values. Patients with minimal progression or regression had a significantly ( P =0.01) higher CD4 cell count than slow progressors and rapid progressors. Multivariate analyses indicated that age and total cholesterol were positively associated with IMT progression. In contrast, the CD4 cell count, the SDF1-3′A, and the CX3CR-1 249 I mutated alleles were associated with lesser IMT progression.

Conclusion— The course of atherosclerosis in patients with HIV infection is influenced by polymorphisms in the SDF1 and CX3CR1 genes by metabolic variables and by the CD4 cell count. These data would be of help in assessing therapeutic needs of these patients.

Angiotensin Inhibition Decreases Progression of Advanced Atherosclerosis and Stabilizes Established Atherosclerotic Plaques

Although increased extracellular matrix (ECM) is pathogenic in a variety of chronic tissue injuries, reduced and/or disrupted ECM may be detrimental in atherosclerosis and rather destabilize existing atherosclerotic lesions. This study therefore assessed the effects of angiotensin II (AngII) antagonism on ECM components of advanced atherosclerosis. Twenty-four-week-old apolipoprotein E-deficient mice were treated with the AngII antagonist losartan for 12 wk. Controls received water or hydralazine. AngII antagonism significantly reduced progression of established atherosclerosis, whereas hydralazine showed no benefit despite similar decrease in BP. Although there was no difference in the macrophage component, AngII antagonism increased the relative collagen portion of the lesions; lessened elastin fragmentation, increased the total elastin content of the aorta; and reduced the mRNA and activity/protein of the elastolytic proteases, cathepsin S, and metalloproteinase-9. Extracellular elastin degradation by cultured smooth muscle cells (SMC) was reduced by losartan, as was SMC invasion through an elastin gel barrier. Thus, AngII antagonism lessens progression of atherosclerosis, increases collagen, and preserves elastin components of ECM within the vascular lesions, which, at least in part, is modulated by effects on SMC. These effects not only decrease further expansion of advanced lesions but also stabilize the established atherosclerotic plaques and may underlie the decreased incidence of acute cardiovascular events that are observed in patients in whom AngII antagonism is begun after atherosclerosis is already established.

Trans-10, cis-12 conjugated linoleic acid causes inflammation and delipidation of white adipose tissue in mice: a microarray and histological analysis

A combined histological and microarray analysis of the white adipose tissue (WAT) of mice fed trans-10, cis-12 conjugated linoleic acid (t10c12 CLA) was performed to better define functional responses. Mice fed t10c12 CLA for 14 days lost 85% of WAT mass, 95% of adipocyte lipid droplet volume, and 15 or 47% of the number of adipocytes and total cells, respectively. Microarray profiling of replicated pools ( n = 2 per day × diet) of control and treated mice ( n = 140) at seven time points after 1–17 days of t10c12 CLA feeding found between 2,682 and 4,216 transcript levels changed by twofold or more. Transcript levels for genes involved in glucose and fatty acid import or biosynthesis were significantly reduced. Highly expressed transcripts for lipases were significantly reduced but still abundant. Increased levels of mRNAs for two key thermogenesis proteins, uncoupling protein 1 and carnitine palmitoyltransferase 1, may have increased energy expenditures. Significant reductions of mRNAs for major adipocyte regulatory factors, including peroxisome proliferator activated receptor-γ, sterol regulatory binding protein 1, CAAT/enhancer binding protein-α, and lipin 1 were correlated with the reduced transcript levels for key metabolic pathways in the WAT. A prolific inflammation response was indicated by the 2- to 100-fold induction of many cytokine transcripts, including those for IL-6, IL-1β, TNF ligands, and CXC family members, and an increased density of macrophages. The mRNA changes suggest that a combination of cell loss, increased energy expenditure, and residual transport of lipids out of the adipocytes may account for the cumulative mass loss observed.

Cholesteryl Ester Transfer Protein Decreases High-Density Lipoprotein and Severely Aggravates Atherosclerosis in APOE*3-Leiden Mice

Objective— The role of cholesteryl ester transfer protein (CETP) in the development of atherosclerosis is still undergoing debate. Therefore, we evaluated the effect of human CETP expression on atherosclerosis in APOE*3-Leiden ( E3L ) mice with a humanized lipoprotein profile.

Methods and Results— E3L mice were crossbred with human CETP transgenic mice. On a chow diet, CETP expression increased plasma total cholesterol (TC) (+43%; P <0.05). To evaluate the effects of CETP on the development of atherosclerosis, mice were fed a Western-type diet containing 0.25% cholesterol, leading to 4.3-fold elevated TC levels in both E3L and CETP.E3L mice ( P <0.01). On both diets, CETP expression shifted the distribution of cholesterol from high-density lipoprotein (HDL) toward very-low-density lipoprotein (VLDL)/low-density lipoprotein (LDL). Moreover, plasma of CETP.E3L mice had reduced capacity (−39%; P <0.05) to induce SR-BI–mediated cholesterol efflux from Fu5AH cells than plasma of E3L mice. After 19 weeks on the Western-type diet, CETP.E3L mice showed a 7.0-fold increased atherosclerotic lesion area in the aortic root compared with E3L mice ( P <0.0001).

Conclusions— CETP expression in E3L mice shifts the distribution of cholesterol from HDL to VLDL/LDL, reduces plasma-mediated SR-BI–dependent cholesterol efflux, and represents a clear pro-atherogenic factor in E3L mice. We anticipate that the CETP.E3L mouse will be a valuable model for the preclinical evaluation of HDL-raising interventions on atherosclerosis development.

The antigen recognized by MOMA-I is sialoadhesin

The monoclonal antibody MOMA-1 is a widely-used marker for marginal metallophilic macrophages in spleen and some other subsets of macrophages. The antigen recognized by MOMA-1 has yet to be characterized, but its expression pattern is similar to that of sialoadhesin (Sn, CD169, Siglec-1), a member of the sialic acid binding Ig-like lectin (Siglec) family. Using flow cytometry of Sn-transfected cells and staining of lymphoid tissue sections from Sn-deficient mice, we demonstrate here that the antigen recognized by MOMA-1 is Sn.