Evidence that the death of macrophage foam cells contributes to the lipid core of atheroma

Oxidized LDL regulates efferocytosis through the CD36-PKM2-mtROS pathway

Macrophage efferocytosis, the process by which phagocytes engulf and remove apoptotic cells (ACs), plays a critical role in maintaining tissue homeostasis. Efficient efferocytosis prevents secondary necrosis, mitigates chronic inflammation, and impedes atherosclerosis progression. However, the regulatory mechanisms of efferocytosis under atherogenic conditions remain poorly understood. We previously demonstrated that oxidized LDL (oxLDL), an atherogenic lipoprotein, induces mitochondrial reactive oxygen species (mtROS) in macrophages via CD36. In this study, we demonstrate that macrophage mtROS facilitate continual efferocytosis through a positive feedback mechanism. However, oxLDL disrupts continual efferocytosis by dysregulating the internalization of ACs. This disruption is mediated by an overproduction of mtROS. Mechanistically, oxLDL/CD36 signaling promotes the translocation of cytosolic PKM2 to mitochondria, facilitated by the chaperone GRP75. Mitochondrial PKM2 then binds to Complex III of the electron transport chain, inducing mtROS production. This study elucidates a novel regulatory mechanism of efferocytosis in atherosclerosis, providing potential therapeutic targets for intervention.

SUMMARY

Macrophages clear apoptotic cells through a process called efferocytosis, which involves mitochondrial ROS. However, the atherogenic oxidized LDL overstimulates mitochondrial ROS via the CD36-PKM2 pathway, disrupting continual efferocytosis. This finding elucidates a novel molecular mechanism that explains defects in efferocytosis, driving atherosclerosis progression.

Is the suppression of CD36 a promising way for atherosclerosis therapy?

Atherosclerosis is the main underlying pathology of many cardiovascular diseases and is marked by plaque formation in the artery wall. It has posed a serious threat to the health of people all over the world. CD36 acts as a significant regulator of lipid homeostasis, which is closely associated with the onset and progression of atherosclerosis and may be a new therapeutic target. The abnormal overexpression of CD36 facilitates lipid accumulation, foam cell formation, inflammation, endothelial apoptosis, and thrombosis. Numerous natural products and lipid-lowering agents are found to target the suppression of CD36 or inhibit the upregulation of CD36 to prevent and treat atherosclerosis. Here, the structure, expression regulation and function of CD36 in atherosclerosis and its related pharmacological therapies are reviewed. This review highlights the importance of drugs targeting CD36 suppression in the treatment and prevention of atherosclerosis, in order to develop new therapeutic strategies and potential anti-atherosclerotic drugs both preclinically and clinically.

Drug screen identifies verteporfin as a regulator of lipid metabolism in macrophage foam cells

Arterial macrophage foam cells are filled with cholesterol ester (CE) stored in cytosolic lipid droplets (LDs). Foam cells are central players in progression of atherosclerosis as regulators of lipid metabolism and inflammation, two major driving forces of atherosclerosis development. Thus, foam cells are considered plausible targets for intervention in atherosclerosis. However, a compound that directly regulates the lipid metabolism of LDs in the arterial foam cells has not yet been identified. In this study, we screened compounds that inhibit macrophage foam cell formation using a library of 2697 FDA-approved drugs. From the foam cells generated via loading of human oxidized low-density lipoprotein (oxLDL), we found 21 and 6 compounds that reduced and enhanced accumulations of lipids respectively. Among them, verteporfin most significantly reduced oxLDL-induced foam cell formation whereas it did not display a significant impact on foam cell formation induced by fatty acid. Mechanistically our data demonstrate that verteporfin acts via inhibition of oxLDL association with macrophages, reducing accumulation of CE. Interestingly, while other drugs that reduced foam cell formation did not have impact on pre-existing foam cells, verteporfin treatment significantly reduced their total lipids, CE, and pro-inflammatory gene expression. Together, our study identifies verteporfin as a novel regulator of foam cell lipid metabolism and inflammation and a potential compound for intervention in atherosclerosis.

Membrane Cholesterol Interactions with Proteins in Hypercholesterolemia-Induced Endothelial Dysfunction

PURPOSE OF REVIEW

The goal of this review is to highlight work identifying mechanisms driving hypercholesterolemia-mediated endothelial dysfunction. We specifically focus on cholesterol-protein interactions and address specific questions related to the impact of hypercholesterolemia on cellular cholesterol and vascular endothelial function. We describe key approaches used to determine the effects of cholesterol-protein interactions in mediating endothelial dysfunction under dyslipidemic conditions.

RECENT FINDINGS

The benefits of removing the cholesterol surplus on endothelial function in models of hypercholesterolemia is clear. However, specific mechanisms driving cholesterol-induced endothelial dysfunction need to be determined. In this review, we detail the latest findings describing cholesterol-mediated endothelial dysfunction, highlighting our studies indicating that cholesterol suppresses endothelial Kir2.1 channels as a major underlying mechanism. The findings detailed in this review support the targeting of cholesterol-induced suppression of proteins in restoring endothelial function in dyslipidemic conditions. The identification of similar mechanisms regarding other cholesterol-endothelial protein interactions is warranted.

Loss of Macrophage mTORC2 Drives Atherosclerosis via FoxO1 and IL-1β Signaling

BACKGROUND

The mTOR (mechanistic target of rapamycin) pathway is a complex signaling cascade that regulates cellular growth, proliferation, metabolism, and survival. Although activation of mTOR signaling has been linked to atherosclerosis, its direct role in lesion progression and in plaque macrophages remains poorly understood. We previously demonstrated that mTORC1 (mTOR complex 1) activation promotes atherogenesis through inhibition of autophagy and increased apoptosis in macrophages.

METHODS

Using macrophage-specific Rictor- and mTOR-deficient mice, we now dissect the distinct functions of mTORC2 pathways in atherogenesis.

RESULTS

In contrast to the atheroprotective effect seen with blockade of macrophage mTORC1, macrophage-specific mTORC2-deficient mice exhibit an atherogenic phenotype, with larger, more complex lesions and increased cell death. In cultured macrophages, we show that mTORC2 signaling inhibits the FoxO1 (forkhead box protein O1) transcription factor, leading to suppression of proinflammatory pathways, especially the inflammasome/IL (interleukin)-1β response, a key mediator of vascular inflammation and atherosclerosis. In addition, administration of FoxO1 inhibitors efficiently rescued the proinflammatory response caused by mTORC2 deficiency both in vitro and in vivo. Interestingly, collective deletion of macrophage mTOR, which ablates mTORC1- and mTORC2-dependent pathways, leads to minimal change in plaque size or complexity, reflecting the balanced yet opposing roles of these signaling arms.

CONCLUSIONS

Our data provide the first mechanistic details of macrophage mTOR signaling in atherosclerosis and suggest that therapeutic measures aimed at modulating mTOR need to account for its dichotomous functions.

Identification of key upregulated genes involved in foam cell formation and the modulatory role of statin therapy

BACKGROUND

We aimed to investigate the possible effect of statins on important genes/proteins involved in foam cell formation.

METHODS

The gene expression profile of the GSE9874, GSE54666, and GSE7138from the Omnibus database were usedto identify genes involved in foam cell formation. The protein-protein interaction (PPI) network and MCODE analysis of the intersection of three databases were analyzed. We used molecular docking analysis to investigate the possible interaction of different statins with the overexpressed hub genes obtained from PPI analysis.

RESULTS

The intersection among the three datasets showed 54 upregulated and 26 down-regulated genes. The most critical overexpressed genes/proteins obtained as hub genes included: G6PD, NPC1, ABCA1, ABCG1, PGD, PLIN2, PPAP2B, and TXNRD1 based on PPI analysis. Functional enrichment analysis of 81 intersection DEGs at the biological process level focusing on the cholesterol metabolic process, secondary alcohol biosynthetic process and the cholesterol biosynthetic process. Under cellular components, the analysis confirmed that these 81 intersection DEGs were mainly applied in endoplasmic reticulum membrane, lysosome and lytic vacuole. The molecular functions were identified as sterol binding, oxidoreductase activity and NADP binding. The molecular docking showed that all statins appear to affect important protein targets overexpressed in foam cell formation. However, lipophilic statins, especially pitavastatin and lovastatin, had a greater effect than hydrophilic statins. The most significant protein target of all the overexpressed genes interacting with all statin types was ABCA1.

CONCLUSION

The effect of lipophilic statins was shown for several critical proteins in foam cell formation.

miR-126 promotes M1 to M2 macrophage phenotype switching via VEGFA and KLF4

Background

Macrophage polarization and microRNA play crucial roles in the development of atherosclerosis (AS). The M1 macrophage phenotype contributes to the formation of plaques, while the M2 macrophage phenotype resolves inflammation and promotes tissue repair. MiR-126 has been found to play a role in regulating macrophage polarization in the context of AS. However, the exact mechanism of miR-126 requires further research.

Methods

The foam cell model was established by stimulating THP-1 with oxidized low-density lipoprotein (ox-LDL). We transfected foam cells with miR-126 mimic and its negative control. The transfection of miR-126 was implemented by riboFECT CP transfection kit. The levels of miR-126 and M1/M2 associated genes in foam cells were quantified using reverse transcription-quantitative PCR (RT-qPCR). Additionally, the expressions of CD86+ and CD206+ cells in foam cells were determined by flow cytometry. Western blotting and RT-qPCR were used to determine the protein and mRNA levels of the vascular endothelial growth factor A (VEGFA) and the transcriptional regulator Krüppel-like factor 4 (KLF4), respectively. Additionally, we detected endothelial cell migration after co-culturing endothelial cells and macrophages. MG-132 was used to indirectly activate the expression of VEGFA, and the expression of KLF4 was also evaluated.

Results

The activation of apoptosis and production of foam cells were boosted by the addition of ox-LDL. We transfected foam cells with miR-126 mimic and its negative control and observed that miR-126 greatly suppressed foam cell development and inhibited phagocytosis. Moreover, it caused pro-inflammatory M1 macrophages to switch to the anti-inflammatory M2 phenotype. This was reflected by the increase in anti-inflammatory gene expression and the decrease in pro-inflammatory gene expression. Additionally, miR-126 dramatically decreased the expressions of VEGFA and KLF4. The protein-protein interaction network analysis showed a significantly high correlation between miR-126, VEGFA, and KLF4. MiR-126 may also promote EC migration by activating macrophage PPAR γ expression and effectively suppressing macrophage inflammation. MG-132 indirectly activated the expression of VEGFA, and the expression of KLF4 also significantly increased, which indicates a direct or indirect relationship between VEGFA and KLF4.

Conclusion

Our study shows that miR-126 can reverse ox-LDL-mediated phagocytosis and apoptosis in macrophages. Consequently, the potential role of miR-126 was manifested in regulating macrophage function and promoting vascular endothelial migration.

The emerging role of pyroptosis-related inflammasome pathway in atherosclerosis

Atherosclerosis (AS), a chronic sterile inflammatory disorder, is one of the leading causes of mortality worldwide. The dysfunction and unnatural death of plaque cells, including vascular endothelial cells (VEC), macrophages, and vascular smooth muscle cells (VSMC), are crucial factors in the progression of AS. Pyroptosis was described as a form of cell death at least two decades ago. It is featured by plasma membrane swelling and rupture, cell lysis, and consequent robust release of cytosolic contents and pro-inflammatory mediators, including interleukin-1β (IL-1β), IL-18, and high mobility group box 1 (HMGB1). Pyroptosis of plaque cells is commonly observed in the initiation and development of AS, and the levels of pyroptosis-related proteins are positively correlated with plaque instability, indicating the crucial contribution of pyroptosis to atherogenesis. Furthermore, studies have also identified some candidate anti-atherogenic agents targeting plaque cell pyroptosis. Herein, we summarize the research progress in understating (1) the discovery and definition of pyroptosis; (2) the characterization and molecular mechanisms of pyroptosis; (3) the regulatory mechanisms of pyroptosis in VEC, macrophage, and VSMC, as well as their potential role in AS progression, aimed at providing therapeutic targets for the prevention and treatment of AS.

Cholesterol crystals and atherosclerotic plaque instability: Therapeutic potential of Eicosapentaenoic acid

Atherosclerotic plaques associated with acute coronary syndromes (ACS), i.e. culprit lesions, frequently feature a ruptured fibrous cap with thrombotic complications. On imaging, these plaques exhibit a low attenuation, lipid-rich, necrotic core containing cholesterol crystals and are inherently unstable. Indeed, cholesterol crystals are causally associated with plaque vulnerability in vivo; their formation results from spontaneous self-assembly of cholesterol molecules. Cholesterol homeostasis is a central determinant of the physicochemical conditions leading to crystal formation, which are favored by elevated membrane free cholesterol content in plaque endothelial cells, smooth muscle cells, monocyte-derived macrophages, and foam cells, and equally by lipid oxidation. Emerging evidence from imaging trials in patients with coronary heart disease has highlighted the impact of intervention involving the omega-3 fatty acid, eicosapentaenoic acid (EPA), on vulnerable, low attenuation atherosclerotic plaques. Thus, EPA decreased features associated with unstable plaque by increasing fibrous cap thickness in statin-treated patients, by reducing lipid volume and equally attenuating intraplaque inflammation. Importantly, atherosclerotic plaques rapidly incorporate EPA; indeed, a high content of EPA in plaque tissue is associated with decreased plaque inflammation and increased stability. These findings are entirely consistent with the major reduction seen in cardiovascular events in the REDUCE-IT trial, in which high dose EPA was administered as its esterified precursor, icosapent ethyl (IPE); moreover, clinical benefit was proportional to circulating EPA levels. Eicosapentaenoic acid is efficiently incorporated into phospholipids, where it modulates cholesterol-enriched domains in cell membranes through physicochemical lipid interactions and changes in rates of lipid oxidation. Indeed, biophysical analyses indicate that EPA exists in an extended conformation in membranes, thereby enhancing normal cholesterol distribution while reducing propagation of free radicals. Such effects mitigate cholesterol aggregation and crystal formation. In addition to its favorable effect on cholesterol domain structure, EPA/IPE exerts pleiotropic actions, including antithrombotic, antiplatelet, anti-inflammatory, and proresolving effects, whose plaque-stabilizing potential cannot be excluded. Docosahexaenoic acid is distinguished from EPA by a higher degree of unsaturation and longer carbon chain length; DHA is thus predisposed to changes in its conformation with ensuing increase in membrane lipid fluidity and promotion of cholesterol aggregation into discrete domains. Such distinct molecular effects between EPA and DHA are pronounced under conditions of high cellular cholesterol content and oxidative stress. This review will focus on the formation and role of cholesterol monohydrate crystals in destabilizing atherosclerotic plaques, and on the potential of EPA as a therapeutic agent to attenuate the formation of deleterious cholesterol membrane domains and of cholesterol crystals. Such a therapeutic approach may translate to enhanced plaque stability and ultimately to reduction in cardiovascular risk.

K-80003 Inhibition of Macrophage Apoptosis and Necrotic Core Development in Atherosclerotic Vulnerable Plaques

PURPOSE

Macrophage apoptosis coupled with a defective phagocytic clearance of the apoptotic cells promotes plaque necrosis in advanced atherosclerosis, which causes acute atherothrombotic vascular disease. Nonsteroidal anti-inflammatory drug sulindac derivative K-80003 treatment was previously reported to dramatically attenuate atherosclerotic plaque progression and destabilization. However, the underlying mechanisms are not fully understood. This study aimed to determine the role of K-80003 on macrophage apoptosis and elucidate the underlying mechanism.

METHODS

The mouse model of vulnerable carotid plaque in ApoE-/- mice was developed in vivo. Consequently, mice were randomly grouped into two study groups: the control group and the K-80003 group (30 mg/kg/day). Samples of carotid arteries were collected to determine atherosclerotic necrotic core area, cellular apoptosis, and oxidative stress. The effects of K-80003 on RAW264.7 macrophage apoptosis, oxidative stress, and autophagic flux were also examined in vitro.

RESULTS

K-80003 significantly suppressed necrotic core formation and inhibited cellular apoptosis of vulnerable plaques. K-80003 can also inhibit 7-ketocholesterol-induced macrophage apoptosis in vitro. Furthermore, K-80003 inhibited intraplaque cellular apoptosis mainly through the suppression of oxidative stress, which is a key cause of advanced lesional macrophage apoptosis. Mechanistically, K-80003 prevented 7-ketocholesterol-induced impairment of autophagic flux in macrophages, evidenced by the decreased LC3II and SQSTM1/p62 expression, GFP-RFP-LC3 cancellation upon K-80003 treatment.

CONCLUSION

Inhibition of macrophage apoptosis and necrotic core formation by autophagy-mediated reduction of oxidative stress is one mechanism of the suppression of plaque progression and destabilization by K-80003.

Case Report: Next Generation Sequencing in Clinical Practice–A Real Tool for Ending the Protracted Diagnostic Odyssey

We reported a case of sitosterolemia, which is a rare genetic disease, characterized by increased plant sterol absorption and great heterogeneity of clinical manifestations. Our patient was initially referred to the lipid clinic due to high cholesterol levels and premature cardiovascular disease. Diagnosis of familial hypercholesterolemia was established in accordance with the Dutch Lipid Clinic Network criteria. Next-generation sequencing was later performed, which revealed a nonsense mutation in the ABCG8 gene, which led to the diagnosis of sitosterolemia. The aim of our report is to demonstrate, how genetic testing helped to make the correct diagnosis and to explain many of the patient's health problems, which etiology remained unclear for many years.

Phage Display Preparation of Specific Polypeptides in Atherosclerotic Foam Cells

Atherosclerosis and related complications are the most common causes of death in modern societies. Macrophage-derived foam cells play critical roles in the initiation and progression of atherosclerosis. Effective, rapid, and instrument-independent detection in the early stage of chronic atherosclerosis progression could provide an opportunity for early intervention and treatment. Therefore, as a starting point, in this study, we aimed to isolate and prepare foam cell-specific polypeptides using a phage display platform. The six target polypeptides, which were acquired in this study, were evaluated by ELISA and showed strong specificity with foam cells. Streptavidin coupled quantum dots (QDs) were used as fluorescence developing agents, and images of biotin-modified polypeptides specifically binding with foam cells were clearly observed. The polypeptides obtained in this study could lay the foundation for developing a rapid detection kit for early atherosclerosis lesions and could provide new materials for research on the mechanisms of foam cell formation and the development of blocking drugs.

The regulation of Ero1-alpha in homocysteine-induced macrophage apoptosis and vulnerable plaque formation in atherosclerosis

BACKGROUND AND AIMS

Hyperhomocysteinemia (HHcy) is an independent risk factor for atherosclerosis and plaque vulnerability. Macrophage apoptosis mediated by endoplasmic reticulum (ER) stress plays an important role in the pathogenesis of HHcy-aggravated atherosclerosis. Endoplasmic reticulum oxidoreductase 1α (Ero1α) is critical for ER stress-induced apoptosis. We hypothesized that Ero1α may contribute to ER-stress induced macrophage apoptosis and plaque stability in advanced atherosclerotic lesions by HHcy.

METHODS

Apoe^-/- mice were maintained on drinking water containing homocysteine (Hcy, 1.8 g/L) to establish HHcy atherosclerotic models. The role of Ero1α in atherosclerotic plaque stability, macrophage apoptosis and ER stress were monitored in the plaque of aortic roots in HHcy Apoe^-/- mice with or without silence or overexpression of Ero1α through lentivirus. Mouse peritoneal macrophages were used to confirm the regulation of Ero1α on ER stress dependent apoptosis in the presence of HHcy.

RESULTS

Atherosclerotic plaque vulnerability and macrophage apoptosis were promoted in Apoe^-/- mice by high Hcy diet, accompanied by the upregulation of Ero1α expression and ER stress. Inhibition of Ero1α prevented macrophage apoptosis and atherosclerotic plaque vulnerability, and vice versa. Consistently, in mouse peritoneal macrophages, ER stress and apoptosis were attenuated by Ero1α deficiency, but enhanced by Ero1α overexpression.

CONCLUSIONS

Hcy, via upregulation of Ero1α expression, activates ER stress-dependent macrophage apoptosis to promote vulnerable plaque formation in atherosclerosis. Ero1α may be a potential therapeutic target for atherosclerosis induced by Hcy.

Midkine: A multifaceted driver of atherosclerosis

Atherosclerosis constitutes the pathological basis of life-threatening events, including heart attack and stroke. Midkine is a heparin-binding growth factor and forms a small protein family with pleiotrophin. Under inflammatory or hypoxic conditions, midkine expression is up-regulated. Upon binding to its receptors, midkine can activate multiple signal pathways to regulate cell survival and migration, epithelial-to-mesenchymal transition, and oncogenesis. Circulating midkine levels are significantly increased in patients with essential hypertension, obesity or severe peripheral artery disease. Importantly, midkine exerts a proatherogenic effect by altering multiple pathophysiological processes involving atherogenesis, including macrophage lipid accumulation, vascular inflammation, neointima formation, insulin resistance and macrophage apoptosis. Midkine represents a potential therapeutic target for atherosclerosis-associated diseases. This review described the structure characteristics, expression patterns and signal transduction pathways of midkine with an emphasis on its role in atherosclerosis.

Suppression of apoptosis in vascular endothelial cell, the promising way for natural medicines to treat atherosclerosis

Atherosclerosis, a chronic multifactorial disease, is closely related to the development of cardiovascular diseases and is one of the predominant causes of death worldwide. Normal vascular endothelial cells play an important role in maintaining vascular homeostasis and inhibiting atherosclerosis by regulating vascular tension, preventing thrombosis and regulating inflammation. Currently, accumulating evidence has revealed that endothelial cell apoptosis is the first step of atherosclerosis. Excess apoptosis of endothelial cells induced by risk factors for atherosclerosis is a preliminary event in atherosclerosis development and might be a target for preventing and treating atherosclerosis. Interestingly, accumulating evidence shows that natural medicines have great potential to treat atherosclerosis by inhibiting endothelial cell apoptosis. Therefore, this paper reviewed current studies on the inhibitory effect of natural medicines on endothelial cell apoptosis and summarized the risk factors that may induce endothelial cell apoptosis, including oxidized low-density lipoprotein (ox-LDL), reactive oxygen species (ROS), angiotensin II (Ang II), tumor necrosis factor-α (TNF-α), homocysteine (Hcy) and lipopolysaccharide (LPS). We expect this review to highlight the importance of natural medicines, including extracts and monomers, in the treatment of atherosclerosis by inhibiting endothelial cell apoptosis and provide a foundation for the development of potential antiatherosclerotic drugs from natural medicines.

Cholesterol-Induced Phenotypic Modulation of Smooth Muscle Cells to Macrophage/Fibroblast-like Cells Is Driven by an Unfolded Protein Response

OBJECTIVE

Vascular smooth muscle cells (SMCs) dedifferentiate and initiate expression of macrophage markers with cholesterol exposure. This phenotypic switching is dependent on the transcription factor Klf4 (Krüppel-like factor 4). We investigated the molecular pathway by which cholesterol induces SMC phenotypic switching. Approach and Results: With exposure to free cholesterol, SMCs decrease expression of contractile markers, activate Klf4, and upregulate a subset of macrophage and fibroblast markers characteristic of modulated SMCs that appear with atherosclerotic plaque formation. These phenotypic changes are associated with activation of all 3 pathways of the endoplasmic reticulum unfolded protein response (UPR), Perk (protein kinase RNA-like endoplasmic reticulum kinase), Ire (inositol-requiring enzyme) 1α, and Atf (activating transcription factor) 6. Blocking the movement of cholesterol from the plasma membrane to the endoplasmic reticulum prevents free cholesterol-induced UPR, Klf4 activation, and upregulation of the majority of macrophage and fibroblast markers. Cholesterol-induced phenotypic switching is also prevented by global UPR inhibition or specific inhibition of Perk signaling. Exposure to chemical UPR inducers, tunicamycin and thapsigargin, is sufficient to induce these same phenotypic transitions. Finally, analysis of published single-cell RNA sequencing data during atherosclerotic plaque formation in hyperlipidemic mice provides preliminary in vivo evidence of a role of UPR activation in modulated SMCs.

CONCLUSIONS

Our data demonstrate that UPR is necessary and sufficient to drive phenotypic switching of SMCs to cells that resemble modulated SMCs found in atherosclerotic plaques. Preventing a UPR in hyperlipidemic mice diminishes atherosclerotic burden, and our data suggest that preventing SMC transition to dedifferentiated cells expressing macrophage and fibroblast markers contributes to this decreased plaque burden.

MicroRNA sequences modulating inflammation and lipid accumulation in macrophage “foam” cells: Implications for atherosclerosis

Accumulation of macrophage “foam” cells, laden with cholesterol and cholesteryl ester, within the intima of large arteries, is a hallmark of early “fatty streak” lesions which can progress to complex, multicellular atheromatous plaques, involving lipoproteins from the bloodstream and cells of the innate and adaptive immune response. Sterol accumulation triggers induction of genes encoding proteins mediating the atheroprotective cholesterol efflux pathway. Within the arterial intima, however, this mechanism is overwhelmed, leading to distinct changes in macrophage phenotype and inflammatory status. Over the last decade marked gains have been made in understanding of the epigenetic landscape which influence macrophage function, and in particular the importance of small non-coding micro-RNA (miRNA) sequences in this context. This review identifies some of the miRNA sequences which play a key role in regulating “foam” cell formation and atherogenesis, highlighting sequences involved in cholesterol accumulation, those influencing inflammation in sterol-loaded cells, and novel sequences and pathways which may offer new strategies to influence macrophage function within atherosclerotic lesions.

Diversity of macrophage phenotypes and responses in atherosclerosis

The presence of macrophages within the plaque is a defining hallmark of atherosclerosis. Macrophages are exposed to various microenvironments such as oxidized lipids and cytokines which effect their phenotypic differentiation and activation. Classically, macrophages have been divided into two groups: M1 and M2 macrophages induced by T-helper 1 and T-helper 2 cytokines, respectively. However, for a decade, greater phenotypic heterogeneity and plasticity of these cells have since been reported in various models. In addition to M1 and M2 macrophage phenotypes, the concept of additional macrophage phenotypes such as M (Hb), Mox, and M4 has emerged. Understanding the mechanisms and functions of distinct phenotype of macrophages can lead to determination of their potential role in atherosclerotic plaque pathogenesis. However, there are still many unresolved controversies regarding their phenotype and function with respect to atherosclerosis. Here, we summarize and focus on the differential subtypes of macrophages in atherosclerotic plaques and their differing functional roles based upon microenvironments such as lipid, intraplaque hemorrhage, and plaque regression.

IFN Regulatory Factor 1 Mediates Macrophage Pyroptosis Induced by Oxidized Low-Density Lipoprotein in Patients with Acute Coronary Syndrome

Background

Atherosclerosis (AS) is recognized as a chronic inflammatory disease. It is caused by the interaction between inflammatory cells such as macrophages, dendritic cells, and lipoproteins. Evidence has revealed that macrophage pyroptosis in lesion contributes to the formation of the necrotic core and thinning of the fibrous cap, which plays crucial roles in the onset of acute coronary syndrome (ACS). IFN regulatory factor 1 (IRF-1) is a pleiotropic transcription factor involved in various immune processes and cell death. We propose that IRF-1 may be implicated in macrophage pyroptosis in the pathogenesis of AS and ACS.

Methods

Patients with stable angina, unstable angina, acute myocardial infarction, and clinical presentation of chest pain were enrolled. The expression of IRF-1 in human PBMC-derived macrophages was analyzed. Then, overexpression and inhibition of IRF-1 was performed in macrophages from patients with ACS to explore the possible role and mechanism of IRF-1 involvement in macrophage pyroptosis.

Results

The expression of IRF-1 in macrophages was upregulated in ACS patients. The overexpression or inhibition of IRF-1 effectively modulated caspase-1 activation, as well as macrophage lysis, expression of gasdermin D-N (GSDMD-N), production of IL-1β and IL-18, and activation of NLRP3-ASC inflammasome, which were all inhibited by caspase-1 inhibitor. Further experiments revealed that pyroptosis and the downstream inflammatory response in AS induced by IRF-1 is a process that is dependent on reactive oxygen species (ROS) generation.

Conclusion

Our observations suggest that IRF-1 potently activates ox-LDL-induced macrophage pyroptosis and may play an important role in AS and ACS.

Etosis, rather than apoptosis or cell proliferation, typifies thrombus progression - An immunohistochemical study of coronary aspirates

Background

Coronary thrombosis is a process with unpredictable clinical outcome. Changes of thrombus composition overtime influence tissue repair and stabilization. We investigated rates of cell deaths and cell proliferation at different time points after initiation of thrombosis.

Methods

Thrombectomy aspirates of 55 myocardial infarction patients were selected and histomorphologically classified as fresh (25), lytic (25), partially fibrocellular (10), completely fibrocellular (10). Paraffin sections were immunostained with anti-(cleaved) caspase-3/Casp3 (apoptosis), Citrullinated histone/CitH 3 (etosis), C-reactive protein/CRP and Ki67 (proliferation) in combination with either Feulgen counterstaining (DNA) or cell markers for granulocytes, macrophages, SMCs, platelets and endothelium. Rates of apoptosis, etosis and proliferation were measured as a percentage of total number of immunopositive pixels versus total number of DNA positive pixels, while co-localization with cell markers was assessed by digital image analysis.

Results

Positive staining of CitH3 was observed more frequently (93%) than Casp3 (70%), Ki67 (79%) or CRP (59%) (p < 0.05). Moreover, rate of etosis, found in granulocytes and macrophages, differed significantly among thrombi of different age, being higher in lytic (12.82) than in fresh (8.52) and late-organized (2.75) (p < 0.05). Such differences were not observed for the rates of apoptosis or cell proliferation related to thrombus age. CRP staining was present in fresh, lytic and organized thrombi, but did not reliably identify necrotic areas.

Conclusions

Different patterns of cell death and cell proliferation are noticed during progression of coronary thrombus overtime, but with significant differences for only etosis. Etosis could potentially serve as a biomarker for thrombus instability with clinical significance.

Age-Related Changes in Immune Cells of the Human Cochlea

Age-related hearing loss is a chronic degenerative disorder affecting one in two individuals above the age of 75. Current population projections predict a steady climb in the number of older individuals making the search for interventions to prevent or reverse this disorder even more critical. There is growing acceptance that aberrant activity of resident or infiltrating immune cells, such as macrophages, is a major factor contributing to the onset and progression of age-related degenerative diseases. However, how macrophage populations and their functionally-driven morphological characteristics change with age in the human cochlea remains largely unknown. In this study, we employed immunohistochemical approaches along with confocal and super-resolution imaging, three-dimensional reconstructions, and quantitative analysis to determine age-related changes in macrophage numbers and morphology as well as interactions with other cell-types and structures of the auditory nerve and lateral wall in the human cochlea. In the cochlea of human ears from young and middle aged adults those macrophages in the auditory nerve assumed a worm-like structure in contrast to those in the spiral ligament or associated with the dense microvascular network in the stria vascularis which exhibited a highly ramified morphology. Macrophages in both the auditory nerve and cochlear lateral wall showed morphological alterations with age. The population of activated macrophages in the auditory nerve increased in cochleas obtained from older donors. Dual-immunohistochemical staining with macrophage, myelin, and neuronal markers revealed increased interactions of macrophages with the glial and neuronal components of the aged auditory nerve. These findings implicate the involvement of abnormal macrophage-glia interactions in age-related physiological and pathological alterations in the human cochlea. There is clearly a need to further investigate the contribution of macrophage-associated inflammatory dysregulation in human presbyacusis.

Accelerated Atherosclerosis in Rheumatoid Arthritis: Mechanisms and Treatment

Background:

Rheumatoid arthritis (RA) is a chronic systemic autoimmune inflammatory disorder that increases the risk of developing cardiovascular disease. There is accumulating evidence that the RA disease state accelerates the formation of atherosclerotic plaques. Treatments for RA improve joint symptomatology and may reduce inflammation, but consideration of their effects on the cardiovascular system is generally low priority.

Objective:

Since cardiovascular disease is the leading cause of mortality in RA patients, the impact of RA therapies on atherosclerosis is an area in need of attention and the focus of this review.

Results:

The drugs used to treat RA may be analgesics, conventional disease-modifying anti-rheumatic drugs, and/or biologics, including antibodies against the cytokine tumor necrosis factor-α. Pain relievers such as nonselective non-steroidal anti-inflammatory drugs and cyclooxygenase inhibitors may adversely affect lipid metabolism and cyclooxygenase inhibitors have been associated with increased adverse cardiovascular events, such as myocardial infarction and stroke. Methotrexate, the anchor disease-modifying anti-rheumatic drug in RA treatment has multiple atheroprotective advantages and is often combined with other therapies. Biologic inhibitors of tumor necrosis factor-α may be beneficial in preventing cardiovascular disease because tumor necrosis factor-α promotes the initiation and progression of atherosclerosis. However, some studies show a worsening of the lipid profile in RA with blockade of this cytokine, leading to higher total cholesterol and triglycerides.

Conclusion:

Greater understanding of the pharmacologic activity of RA treatments on the atherosclerotic process may lead to improved care, addressing both damages to the joints and heart.

Oxytocin: Potential to mitigate cardiovascular risk

Cardiovascular disease (CVD) remains the leading cause of death worldwide, despite multiple treatment options. In addition to elevated lipid levels, oxidative stress and inflammation are key factors driving atherogenesis and CVD. New strategies are required to mitigate risk and most urgently for statin-intolerant patients. The neuropeptide hormone oxytocin, synthesized in the brain hypothalamus, is worthy of consideration as a CVD ancillary treatment because it moderates factors directly linked to atherosclerotic CVD such as inflammation, weight gain, food intake and insulin resistance. Though initially studied for its contribution to parturition and lactation, oxytocin participates in social attachment and bonding, associative learning, memory and stress responses. Oxytocin has shown promise in animal models of atherosclerosis and in some human studies as well. A number of properties of oxytocin make it a candidate CVD treatment. Oxytocin not only lowers fat mass and cytokine levels, but also improves glucose tolerance, lowers blood pressure and relieves anxiety. Further, it has an important role in communication in the gut-brain axis that makes it a promising treatment for obesity and type 2 diabetes. Oxytocin acts through its receptor which is a class I G-protein-coupled receptor present in cells of the vascular system including the heart and arteries. While oxytocin is not used for heart disease at present, residual CVD risk remains in a substantial portion of patients despite multidrug regimens, leaving open the possibility of using the endogenous nonapeptide as an adjunct therapy. This review discusses the possible role for oxytocin in human CVD prevention and treatment.

Endothelial cell apoptosis and the role of endothelial cell-derived extracellular vesicles in the progression of atherosclerosis

To maintain physiological homeostasis, cell turnover occurs every day in the body via a form of programmed cell death called apoptosis. During apoptosis, cells undergo distinct morphological changes culminating in the disassembly of the dying cell into smaller fragments known as apoptotic bodies (ApoBDs). Dysregulation of apoptosis is associated with diseases including infection, cancer and atherosclerosis. Although the development of atherosclerosis is largely attributed to the accumulation of lipids and inflammatory debris in vessel walls, it is also associated with apoptosis of macrophages, smooth muscle cells (SMCs) and endothelial cells. During cellular activation and apoptosis, endothelial cells can release several types of membrane-bound extracellular vesicles (EVs) including exosomes, microvesicles (MVs)/microparticles and ApoBDs. Emerging evidence in the field suggests that these endothelial cell-derived EVs (EndoEVs) can contribute to intercellular communication during the development of atherosclerosis via the transfer of cellular contents such as protein and microRNA, which may prevent or promote disease progression depending on the context. This review provides an up-to-date overview of the known causes and consequences of endothelial cell death during atherosclerosis along with highlighting current methodological approaches to studying EndoEVs and the potential roles of EndoEVs in atherosclerosis development.

Extracellular traps derived from macrophages, mast cells, eosinophils and neutrophils are generated in a time-dependent manner during atherothrombosis

Extracellular traps generated by neutrophils contribute to thrombus progression in coronary atherosclerotic plaques. It is not known whether other inflammatory cell types in coronary atherosclerotic plaque or thrombus also release extracellular traps. We investigated their formation by macrophages, mast cells, and eosinophils in human coronary atherosclerosis, and in relation to the age of thrombus of myocardial infarction patients. Coronary arteries with thrombosed or intact plaques were retrieved from patients who died from myocardial infarction. In addition, thrombectomy specimens from patients with myocardial infarction were classified histologically as fresh, lytic or organised. Neutrophil and macrophage extracellular traps were identified using sequential triple immunostaining of CD68, myeloperoxidase, and citrullinated histone H3. Eosinophil and mast cell extracellular traps were visualised using double immunostaining for eosinophil major basic protein or tryptase, respectively, and citrullinated histone H3. Single‐ and double‐stained immunopositive cells in the plaque, adjacent adventitia, and thrombus were counted. All types of leucocyte‐derived extracellular traps were present in all thrombosed plaques, and in all types of the in vivo‐derived thrombi, but only to a much lower extent in intact plaques. Neutrophil traps, followed by macrophage traps, were the most prominent types in the autopsy series of atherothrombotic plaques, including the adventitia adjacent to thrombosed plaques. In contrast, macrophage traps were more numerous than neutrophil traps in intact plaques (lipid cores) and organised thrombi. Mast cell and eosinophil extracellular traps were also present, but sparse in all instances. In conclusion, not only neutrophils but also macrophages, eosinophils, and mast cells are sources of etosis involved in evolving coronary thrombosis. Neutrophil traps dominate numerically in early thrombosis and macrophage traps in late (organising) thrombosis, implying that together they span all the stages of thrombus progression and maturation. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Inhibition of microRNA-17-5p reduces the inflammation and lipid accumulation, and up-regulates ATP-binding cassette transporterA1 in atherosclerosis

Atherosclerosis (AS) is a chronic inflammatory disease of the arterial wall. Macrophages are considered to be closely associated with the development and progression of AS. However, the precise mechanism of miR-17-5p in the macrophages under AS remains incompletely clarified. This study investigated the regulatory effect of miR-17-5p on the inflammation and lipid accumulation in mouse macrophages both in vivo and in vitro. It was found that miR-17-5p was highly expressed with lowered ATP-binding cassette transporterA1 (ABCA1) level in the peripheral blood leucocytes (PBLs) of AS patients. Moreover, the level of miR-17-5p was up-regulated in the macrophages of ApoE^-/- mice fed with a high-cholesterol diet. Furthermore, we injected miR-17-5p antagomir into AS mice or transfected miR-17-5p inhibitors into mouse macrophage RAW264.7 cells. Results showed that downregulation of miR-17-5p significantly reduced the production of inflammatory cytokines, inhibited the lipid accumulation and up-regulated ABCA1, and activated peroxisome proliferator-activated receptor (PPAR) γ/Liver X receptor (LXR) α signaling pathway. Additionally, ABCA1 was found to be a target of miR-17-5p by directly binding to 3'-untranslated region (3'-UTR) of its mRNA. Our study indicates a novel regulatory mechanism for miR-17-5p by interacting with ABCA1, which could be a therapy-target for the treatment of AS.

The role of non-resolving inflammation in atherosclerosis

Non-resolving inflammation drives the development of clinically dangerous atherosclerotic lesions by promoting sustained plaque inflammation, large necrotic cores, thin fibrous caps, and thrombosis. Resolution of inflammation is not merely a passive return to homeostasis, but rather an active process mediated by specific molecules, including fatty acid-derived specialized pro-resolving mediators (SPMs). In advanced atherosclerosis, there is an imbalance between levels of SPMs and proinflammatory lipid mediators, which results in sustained leukocyte influx into lesions, inflammatory macrophage polarization, and impaired efferocytosis. In animal models of advanced atherosclerosis, restoration of SPMs limits plaque progression by suppressing inflammation, enhancing efferocytosis, and promoting an increase in collagen cap thickness. This Review discusses the roles of non-resolving inflammation in atherosclerosis and highlights the unique therapeutic potential of SPMs in blocking the progression of clinically dangerous plaques.

Where Does Inflammation Fit?

PURPOSE OF REVIEW

This review focuses on the complex relationship between inflammation and the onset of acute coronary syndrome and heart failure.

RECENT FINDINGS

In the last few years, two important lines of research brought new and essential information to light in the pathogenesis of acute coronary syndrome: a) the understanding of the immune mediate mechanisms of inflammation in Ischemic Heart Disease (IHD) and b) evidence that the inflammatory mechanisms associated with atherosclerosis and its complications can be modulated by anti-inflammatory molecules. A large amount of data also suggests that inflammation is a major component in the development and exacerbation of heart failure (HF), in a symbiotic relationship. In particular, recent evidence underlies peculiar aspects of the phenomenon: oxidative stress and autophagy; DAMPS and TLR-4 signaling activation; different macrophages lineage and the contribution of NLRP-3 inflammasome; adaptive immune system. A possible explanation that could unify the pathogenic mechanism of these different conditions is the rising evidence that increased bowel permeability may allow translation of gut microbioma product into the circulation. These findings clearly establish the role of inflammation as the great trigger for two of the major cardiovascular causes of death and morbidity. Further studies are needed, to better clarify the issue and to define more targeted approaches to reduce pathological inflammation while preserving the physiological one.

Functional diversity of macrophages in vascular biology and disease

Atherosclerosis is a multifactorial chronic inflammatory disease and is largely responsible for cardiovascular disease, the most common cause of global mortality. The hallmark of atherogenesis is immune activation following lipid accumulation in the arterial wall. In particular, macrophages play a non-redundant role in both the progression and regression of inflammation in the atherosclerotic lesion. Macrophages are remarkably heterogeneous phagocytes that perform versatile functions in health and disease. Their functional diversity in vascular biology is only partially mapped. Targeting macrophages is often highlighted as a therapeutic approach for cancer, metabolic and inflammatory diseases. Future strategies for therapeutic intervention in atherosclerosis may benefit from attempts to reduce local proliferation of pro-inflammatory macrophage subsets or enhance resolution of inflammation. Thus, characterisation of macrophage subsets during atherosclerosis would empower clinical interventions. Therefore, it would be of fundamental importance to understand how pathological factors modulate macrophage activity in order to exploit their use in the treatment of atherosclerosis and other diseases.

D4F alleviates macrophage-derived foam cell apoptosis by inhibiting the NF-κB-dependent Fas/FasL pathway

This study was designed to explore the protective effect of D4F, an apolipoprotein A-I mimetic peptide, on nuclear factor-κB (NF-κB)-dependent Fas/Fas ligand (FasL) pathway-mediated apoptosis in macrophages induced by oxidized low-density lipoprotein (ox-LDL). Our results showed that ox-LDL induced apoptosis, NF-κB P65 nuclear translocation and the upregulation of Fas/FasL pathway-related proteins, including Fas, FasL, Fas-associated death domain proteins (FADD), caspase-8 and caspase-3 in RAW264.7 macrophages, whereas silencing of Fas blocked ox-LDL-induced macrophage apoptosis. Furthermore, silencing of P65 attenuated macrophage apoptosis and the upregulation of Fas caused by ox-LDL, whereas P65 expression was not significantly affected by treatment with Fas siRNA. D4F attenuated the reduction of cell viability and the increase in lactate dehydrogenase leakage and apoptosis. Additionally, D4F inhibited ox-LDL-induced P65 nuclear translocation and upregulation of Fas/FasL pathway-related proteins in RAW264.7 cells and in atherosclerotic lesions of apoE^-/- mice. However, Jo2, a Fas-activating monoclonal antibody, reversed the inhibitory effect of D4F on ox-LDL-induced cell apoptosis and upregulation of Fas, FasL and FADD. These data indicate that NF-κB mediates Fas/FasL pathway activation and apoptosis in macrophages induced by ox-LDL and that D4F protects macrophages from ox-LDL-induced apoptosis by suppressing the activation of NF-κB and the Fas/FasL pathway.

Liraglutide attenuates atherosclerosis via inhibiting ER-induced macrophage derived microvesicles production in T2DM rats

BACKGROUND

We investigated the effects of liraglutide on the formation and progression of atherosclerosis in type 2 diabetes mellitus (T2DM) rats.

METHODS

Sprague-Dawley rats were divided into control group, diabetes group and liraglutide treated group. The T2DM rats model with atherosclerosis were induced by high fat diet followed small dosage streptozotocin injection. Body weight and blood glucose levels were monitored once a week for 3 months and then the rats were sacrificed.Peripheral blood and aorta tissues were collected for further biochemical and pathological estimation respectively. Moreover, immunohistochemistry staining was used to detect the infiltration of macrophages and cell apoptosis in tissue samples. The amount of microvesicles of atherosclerotic plaques was determined by ELISA. Western blot was applied to detect the protein expressions of CHOP, GRP78 and caspase-3 in tissue samples. The mRNA expressions of SREBP-1c and FAS were detected by RT-PCR.

RESULTS

The rat model of diabetic atherosclerosis was established successfully. Compared with the control group, glucose, triglycerides, total cholesterol, AST, ALT, BUN, fasting insulin and homeostatic model assessment insulin resistance levels in peripheral blood were significantly increased in the diabetes group. While, these indicators in the liraglutide group were significantly lower than that in the diabetes group. Moreover, the atherosclerotic plaques were observed in the rats of diabetes group but not remarkable in the liraglutide group. The ratio between aorta intima and media thickness was significantly greater in the diabetes group than that in the liraglutide group. Compared with the diabetes group, the infiltration and apoptosis of macrophages were milder in the liraglutide group. The expressions of CD68, caspase-3, CHOP and GRP78 in aorta tissue samples were significantly downregulated in the liraglutide group than that in the diabetes group. Furthermore, the microvesicles of aorta tissues in the liraglutide group were significantly decreased than that in the diabetes group. The mRNA expressions of SREBP-1c and FAS were lower in the liraglutide group than that in the diabetes group.

CONCLUSION

Liraglutide attenuates diabetic atherosclerosis by inhibition of ER stress and subsequent macrophage apoptosis and microvesicles production in T2DM rats.

2016 Russell Ross Memorial Lecture in Vascular Biology: Molecular-Cellular Mechanisms in the Progression of Atherosclerosis

Atherosclerosis is initiated by the subendothelial accumulation of apoB-lipoproteins, which initiates a sterile inflammatory response dominated by monocyte-macrophages but including all classes of innate and adaptive immune cells. These inflammatory cells, together with proliferating smooth muscle cells and extracellular matrix, promote the formation of subendothelial lesions or plaques. In the vast majority of cases, these lesions do not cause serious clinical symptoms, which is due in part to a resolution-repair response that limits tissue damage. However, a deadly minority of lesions progress to the point where they can trigger acute lumenal thrombosis, which may then cause unstable angina, myocardial infarction, sudden cardiac death, or stroke. Many of these clinically dangerous lesions have hallmarks of defective inflammation resolution, including defective clearance of dead cells (efferocytosis), necrosis, a defective scar response, and decreased levels of lipid mediators of the resolution response. Efferocytosis is both an effector arm of the resolution response and an inducer of resolution mediators, and thus its defect in advanced atherosclerosis amplifies plaque progression. Preclinical causation/treatment studies have demonstrated that replacement therapy with exogenously administered resolving mediators can improve lesional efferocytosis and prevent plaque progression. Work in this area has the potential to potentiate the cardiovascular benefits of apoB-lipoprotein-lowering therapy.

Phosphorylation of CHOP (C/EBP Homologous Protein) by the AMP-Activated Protein Kinase Alpha 1 in Macrophages Promotes CHOP Degradation and Reduces Injury-Induced Neointimal Disruption In Vivo

RATIONALE

Elevated levels of CHOP (C/EBP homologous protein), a member of the C/EBP transcription factor family, in advanced atherosclerotic plaques is reported to be associated with atherosclerotic plaque rupture in humans. However, the molecular mechanism by which CHOP accumulation occurs is poorly defined.

OBJECTIVE

The aim of this study was to investigate if (1) macrophage AMPK (AMP-activated protein kinase) regulates cellular CHOP accumulation and (2) whole-body Ampk deletion leads to neointimal disruption.

METHODS AND RESULTS

In isolated or cultured macrophages, Ampkα1 deletion markedly increased apoptosis and CHOP, whereas pharmacological activation of AMPK dramatically reduced CHOP protein level via promoting CHOP degradation by proteasome. In addition, cotransfection of Chop-specific siRNA, but not control siRNA, markedly reduced apoptosis in macrophages transfected with Ampkα1-specific siRNA. Mechanistically, AMPKα1 was found to coimmunoprecipitate with CHOP and phosphorylate CHOP at serine 30. Furthermore, serine 30 phosphorylation of CHOP triggered its ubiquitination and proteasomal degradation. In a mouse model of plaque stability, deletion of Ampkα1 but not Ampkα2 promoted injury-induced neointimal disruption. This was paralleled by increased CHOP expression and apoptosis in vivo. Finally, transfection of Chop-specific siRNA but not control siRNA reduced both CHOP level and injury-induced neointimal disruption in vivo.

CONCLUSIONS

Our results indicate that AMPKα1 mediates CHOP ubiquitination and proteasomal degradation in macrophages by promoting the phosphorylation of CHOP at serine 30. We conclude that AMPKα1 might be a valid therapeutic target in preventing atherosclerotic vulnerable plaque formation.

A Comparative Study of Coronary Atherosclerosis in Young and Old

INTRODUCTION

Atherosclerotic coronary artery disease is an important cause of sudden and unexpected deaths in the young people. It is assumed that thrombosis and plaque hemorrhage are commonly associated with sudden deaths from coronary atherosclerosis in the young. In this study, we compared the histological patterns of atherosclerosis in young and old populations to see whether an association exists between the histological pattern of atherosclerosis in the young and thrombosis or plaque hemorrhage.

METHODS AND RESULTS

All autopsy cases of coronary atherosclerosis in young people (aged younger than 40 years) in comparison with an equal number of randomly selected older people (older than 65 years) over a period of 4 and a half years in the Provincial Forensic Pathology Unit of the Ontario Forensic Pathology Service in Toronto, Canada, were reviewed to characterize the gross and histologic appearance. There were 28 cases of atherosclerosis in young people ("the young"). Twenty-three (82%) of the young had eccentric atherosclerosis compared with 11 (39%) of the old. An inflammatory response was seen in all 28 (100%) of the young in comparison with 17 (61%) of the old. Thirteen (47%) of the young compared with 3 (11%) of the old had thrombosis, whereas 9 (32%) of the young and 17 (61%) of the old had plaque hemorrhage. Pultaceous debris was the principal component in 11 atherosclerotic plaques (39%) in the young, followed by foam cells in 7 (25%). In the older group, pultaceous debris was the principal component in 18 (64%) followed by dense fibrous tissue in 5 (18%).

CONCLUSIONS

The morphology in coronary atherosclerosis of the young is significantly different from the old. Coronary atherosclerosis in the young commonly shows an eccentric distribution with associated inflammation. Thrombosis is commoner among the young, whereas plaque hemorrhage is commoner among the old.

The role of macrophage transcription factor MafB in atherosclerotic plaque stability

BACKGROUND AND AIMS

Macrophage differentiation is associated with the development of atherosclerosis and plaque vulnerability and is regulated by transcription factor MafB. We previously reported that MafB attenuates macrophage apoptosis, which is associated with atherosclerotic plaque instability. The aim of this study was to elucidate the role of MafB in the progression of atherosclerotic plaque.

METHODS

We generated macrophage-specific dominant-negative (DN) MafB transgenic mice and intercrossed DN-MafB mice with apolipoprotein E (ApoE) knockout (KO) mice.

RESULTS

There was no significant difference in advanced atherosclerotic lesion area between DN-MafB/ApoE KO mice and littermate control ApoE KO mice 9 weeks after high-cholesterol diet. However, DN-MafB/ApoE KO mice showed significantly larger necrotic cores and lower collagen content in atherosclerotic plaques than ApoE KO mice. Although there was no difference in intraplaque macrophage infiltration and efferocytosis, DN-MafB/ApoE KO mice showed significantly more apoptotic macrophages at the plaque edges than did ApoE KO mice. Real-time PCR analysis revealed that peritoneal macrophages of DN-MafB/ApoE KO mice had a greater increase in matrix metalloproteinase-9 and mRNA expression of inflammatory/M1 macrophage markers (tissue necrosis factor-α, interleukin-6, CD11c, and p47phox) after lipopolysaccharide stimulation than those of ApoE KO mice.

CONCLUSION

Macrophage-specific inhibition of MafB may destabilize atherosclerotic plaques in advanced lesions.

Protocatechuic Acid Prevents oxLDL-Induced Apoptosis by Activating JNK/Nrf2 Survival Signals in Macrophages

Protocatechuic acid (PCA), one of the main metabolites of complex polyphenols, exerts numerous biological activities including antiapoptotic, anti-inflammatory, and antiatherosclerotic effects. Oxidised LDL have atherogenic properties by damaging arterial wall cells and inducing p53-dependent apoptosis in macrophages. This study was aimed at defining the molecular mechanism responsible for the protective effects of PCA against oxidative and proapoptotic damage exerted by oxLDL in J774 A.1 macrophages. We found that the presence of PCA in cells treated with oxLDL completely inhibited the p53-dependent apoptosis induced by oxLDL. PCA decreased oxLDL-induced ROS overproduction and in particular prevented the early increase of ROS. This decrease seemed to be the main signal responsible for maintaining the intracellular redox homeostasis hindering the activation of p53 induced by ROS, p38MAPK, and PKCδ. Consequently the overexpression of the proapoptotic p53-target genes such as p66Shc protein did not occur. Finally, we demonstrated that PCA induced the activation of JNK, which, in turn, determined the increase of nuclear Nrf2, leading to inhibition of the early ROS overproduction. We concluded that the antiapoptotic mechanism of PCA was most likely related to the activation of the JNK-mediated survival signals that strengthen the cellular antioxidant defences rather than to the PCA antioxidant power.

Lipid-induced epigenomic changes in human macrophages identify a coronary artery disease-associated variant that regulates PPAP2B Expression through Altered C/EBP-beta binding

Genome-wide association studies (GWAS) have identified over 40 loci that affect risk of coronary artery disease (CAD) and the causal mechanisms at the majority of loci are unknown. Recent studies have suggested that many causal GWAS variants influence disease through altered transcriptional regulation in disease-relevant cell types. We explored changes in transcriptional regulation during a key pathophysiological event in CAD, the environmental lipid-induced transformation of macrophages to lipid-laden foam cells. We used a combination of open chromatin mapping with formaldehyde-assisted isolation of regulatory elements (FAIRE-seq) and enhancer and transcription factor mapping using chromatin immuno-precipitation (ChIP-seq) in primary human macrophages before and after exposure to atherogenic oxidized low-density lipoprotein (oxLDL), with resultant foam cell formation. OxLDL-induced foam cell formation was associated with changes in a subset of open chromatin and active enhancer sites that strongly correlated with expression changes of nearby genes. OxLDL-regulated enhancers were enriched for several transcription factors including C/EBP-beta, which has no previously documented role in foam cell formation. OxLDL exposure up-regulated C/EBP-beta expression and increased genomic binding events, most prominently around genes involved in inflammatory response pathways. Variants at CAD-associated loci were significantly and specifically enriched in the subset of chromatin sites altered by oxLDL exposure, including rs72664324 in an oxLDL-induced enhancer at the PPAP2B locus. OxLDL increased C/EBP beta binding to this site and C/EBP beta binding and enhancer activity were stronger with the protective A allele of rs72664324. In addition, expression of the PPAP2B protein product LPP3 was present in foam cells in human atherosclerotic plaques and oxLDL exposure up-regulated LPP3 in macrophages resulting in increased degradation of pro-inflammatory mediators. Our results demonstrate a genetic mechanism contributing to CAD risk at the PPAP2B locus and highlight the value of studying epigenetic changes in disease processes involving pathogenic environmental stimuli.

Coronary artery disease is a complex disease where over 40 genomic loci contributing to genetic risk have been identified. However, identifying the precise variants, genomic elements and genes that mediate this risk at each locus has proved challenging. We hypothesized that some genetic risk variants may influence a key step in development of coronary artery disease, which occurs when macrophages encounter environmentally-derived lipid. These cells take up lipid and accumulate in atherosclerotic plaques in the walls of blood vessels where they contribute to the inflammatory atherosclerotic disease process. Therefore, we studied the effects of this lipid exposure on the genomic activity of these cells. Environmental lipid exposure triggered changes in transcriptional regulation and gene expression. Variants at coronary artery disease risk loci were enriched for genomic regions altered by lipid exposure. We studied one such risk variant rs72664324 in detail and found that it altered binding of the C/EBP-beta transcription factor and altered expression of the PPAP2B gene. PPAP2B encodes an enzyme that degrades pro-inflammatory substances. Our study demonstrates a hitherto unknown genetic mechanism underlying atherosclerotic heart disease and demonstrates the value of studying changes in transcriptional regulation in key disease processes involving environmental influences.

Inflammation and its resolution as determinants of acute coronary syndromes

Inflammation contributes to many of the characteristics of plaques implicated in the pathogenesis of acute coronary syndromes. Moreover, inflammatory pathways not only regulate the properties of plaques that precipitate acute coronary syndromes but also modulate the clinical consequences of the thrombotic complications of atherosclerosis. This synthesis will provide an update on the fundamental mechanisms of inflammatory responses that govern acute coronary syndromes and also highlight the ongoing balance between proinflammatory mechanisms and endogenous pathways that can promote the resolution of inflammation. An appreciation of the countervailing mechanisms that modulate inflammation in relation to acute coronary syndromes enriches our fundamental understanding of the pathophysiology of this important manifestation of atherosclerosis. In addition, these insights provide glimpses into potential novel therapeutic interventions to forestall this ultimate complication of the disease.

A peripheral blood gene expression score is associated with plaque volume and phenotype by intravascular ultrasound with radiofrequency backscatter analysis: results from the ATLANTA study

BACKGROUND

A composite, peripheral gene expression score based on quantitative RNA-measurements has been validated for detecting stenosis against invasive coronary X-ray angiography. IVUS/VH has been validated for quantitative measurements of coronary plaque volume and composition and has been shown to be predictive of outcomes and treatment effects. The correlation between peripheral gene expression and coronary plaque composition by intravascular ultrasound with radiofrequency backscatter (IVUS/VH) is unknown.

METHODS

Peripheral blood gene expression score (GES) was prospectively measured in 18 patients undergoing IVUS/VH. Plaque volume and composition [fibrous tissue (FI), fibro-fatty tissue (FF), necrotic core (NC) and dense calcium (DC)] were quantified in 3 dimensions in all plaques within the entire pullback. The relationship to GES was assessed by Spearman rank correlation.

RESULTS

Mean age was 61.1±8.6 years; 67% were male. 1,158 mm of coronary anatomy was imaged by IVUS/VH. Using a validated scale of 1-40, mean GES was 21.6±9.4. GES was associated with plaque volume (R(2)=0.55; P=0.018), NC volume (R(2)=0.56; P=0.015), DC volume (R(2)=0.60; P=0.007), and non-calcified plaque volume (R(2)=0.50; P=0.036) by Spearman rank correlation.

CONCLUSIONS

In this preliminary report, increased GES was associated with higher plaque volume and a more vulnerable plaque phenotype as evidenced by NC and DC. This composite GES is not only associated with obstructive coronary disease, but also with higher plaque volume and vulnerable phenotype.

Pyroptosis: an inflammatory cell death implicates in atherosclerosis

Cell death and inflammation are the fundamental biological processes in both normal physiology and pathology. Apoptosis is the most well-studied process of cell death, but there are also many other forms of cell death such as necrosis, autophagy and pyroptosis. Cell death could be observed throughout atherosclerosis and plays an important role in determining the fate of atherosclerotic lesion. Inflammation, the primary response of innate immunity, is considered essential in initiating and driving atherosclerosis. Apoptosis and autophagy had been reported in atherosclerosis, however, the mechanism of cell death involved in atherosclerosis still remain largely unknown. Cell death and inflammation are inextricably linked with their effectors modulating the process of atherosclerosis. Therefore, we proposed hypothesis that pyroptosis, an inflammatory form of cell death, may be implicated in atherosclerosis and play an important role in lesion instability.

Oxidized low density lipoprotein induced caspase-1 mediated pyroptotic cell death in macrophages: implication in lesion instability?

BACKGROUND

Macrophage death in advanced lesion has been confirmed to play an important role in plaque instability. However, the mechanism underlying lesion macrophage death still remains largely unknown.

METHODS AND RESULTS

Immunohistochemistry showed that caspase-1 activated in advanced lesion and co-located with macrophages and TUNEL positive reaction. In in-vitro experiments showed that ox-LDL induced caspase-1 activation and this activation was required for ox-LDL induced macrophages lysis, IL-1β and IL-18 production as well as DNA fragmentation. Mechanism experiments showed that CD36 and NLRP3/caspase-1/pathway involved in ox-LDL induced macrophage pyroptosis.

CONCLUSION

Our study here identified a novel cell death, pyroptosis in ox-LDL induced human macrophage, which may be implicated in lesion macrophages death and play an important role in lesion instability.

Localization of oxidized low-density lipoprotein and its relation to plaque morphology in human coronary artery

OBJECTIVES

Oxidized low-density lipoprotein (oxLDL) plays a key role in the formation of atherosclerotic plaques. However, its localization in human coronary arterial wall is not well understood. The present study was performed to visualize deposition sites and patterns of native oxLDL and their relation to plaque morphology in human coronary artery.

METHODS

Evans blue dye (EB) elicits a violet fluorescence by excitation at 345-nm and emission at 420-nm, and a reddish-brown fluorescence by excitation at 470-nm and emission at 515-nm characteristic of oxLDL only. Therefore, native oxLDL in excised human coronary artery were investigated by color fluorescent microscopy (CFM) using EB as a biomarker.

RESULTS

(1) By luminal surface scan with CFM, the % incidence of oxLDL in 38 normal segments, 41 white plaques and 32 yellow plaques that were classified by conventional angioscopy, was respectively 26, 44 and 94, indicating significantly (p<0.05) higher incidence in the latter than the former two groups. Distribution pattern was classified as patchy, diffuse and web-like. Web-like pattern was observed only in yellow plaques with necrotic core. (2) By transected surface scan, oxLDL deposited within superficial layer in normal segments and diffusely within both superficial and deep layers in white and yellow plaques. In yellow plaques with necrotic core, oxLDL deposited not only in the marginal zone of the necrotic core but also in the fibrous cap.

CONCLUSION

Taken into consideration of the well-known process of coronary plaque growth, the results suggest that oxLDL begins to deposit in human coronary artery wall before plaque formation and increasingly deposits with plaque growth, exhibiting different deposition sites and patterns depending on morphological changes.