Macrophages and Foam Cells: Brief Overview of Their Role, Linkage, and Targeting Potential in Atherosclerosis

Atherosclerosis is still one of the main causes of death around the globe. This condition leads to various life-threatening cardiovascular complications. However, no effective preventive measures are known apart from lifestyle corrections, and no cure has been developed. Despite numerous studies in the field of atherogenesis, there are still huge gaps in already poor understanding of mechanisms that underlie the disease. Inflammation and lipid metabolism violations are undoubtedly the key players, but many other factors, such as oxidative stress, endothelial dysfunction, contribute to the pathogenesis of atherosclerosis. This overview is focusing on the role of macrophages in atherogenesis, which are at the same time a part of the inflammatory response, and also tightly linked to the foam cell formation, thus taking part in both crucial for atherogenesis processes. Being essentially involved in atherosclerosis development, macrophages and foam cells have attracted attention as a promising target for therapeutic approaches.

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Foam Cells as Therapeutic Targets in Atherosclerosis with a Focus on the Regulatory Roles of Non-Coding RNAs

International Journal of Molecular Sciences ◽

10.3390/ijms22052529 ◽

2021 ◽

Vol 22 (5) ◽

pp. 2529

Author(s):

Amin Javadifar ◽

Sahar Rastgoo ◽

Maciej Banach ◽

Tannaz Jamialahmadi ◽

Thomas P. Johnston ◽

...

Keyword(s):

Lipid Metabolism ◽

Foam Cell ◽

Cell Formation ◽

Foam Cells ◽

Foam Cell Formation ◽

Special Focus ◽

Lipid Uptake ◽

Therapeutic Goals ◽

Expression Of Genes

Atherosclerosis is a major cause of human cardiovascular disease, which is the leading cause of mortality around the world. Various physiological and pathological processes are involved, including chronic inflammation, dysregulation of lipid metabolism, development of an environment characterized by oxidative stress and improper immune responses. Accordingly, the expansion of novel targets for the treatment of atherosclerosis is necessary. In this study, we focus on the role of foam cells in the development of atherosclerosis. The specific therapeutic goals associated with each stage in the formation of foam cells and the development of atherosclerosis will be considered. Processing and metabolism of cholesterol in the macrophage is one of the main steps in foam cell formation. Cholesterol processing involves lipid uptake, cholesterol esterification and cholesterol efflux, which ultimately leads to cholesterol equilibrium in the macrophage. Recently, many preclinical studies have appeared concerning the role of non-encoding RNAs in the formation of atherosclerotic lesions. Non-encoding RNAs, especially microRNAs, are considered regulators of lipid metabolism by affecting the expression of genes involved in the uptake (e.g., CD36 and LOX1) esterification (ACAT1) and efflux (ABCA1, ABCG1) of cholesterol. They are also able to regulate inflammatory pathways, produce cytokines and mediate foam cell apoptosis. We have reviewed important preclinical evidence of their therapeutic targeting in atherosclerosis, with a special focus on foam cell formation.

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Myeloid-specific deficiency of pregnane X receptor decreases atherosclerosis in LDL receptor-deficient mice

The Journal of Lipid Research ◽

10.1194/jlr.ra119000122 ◽

2020 ◽

Vol 61 (5) ◽

pp. 696-706

Author(s):

Yipeng Sui ◽

Zhaojie Meng ◽

Se-Hyung Park ◽

Weiwei Lu ◽

Christopher Livelo ◽

...

Keyword(s):

Foam Cell ◽

Cell Formation ◽

Ldl Receptor ◽

Plasma Lipid ◽

Pregnane X Receptor ◽

Foam Cell Formation ◽

Lipid Uptake ◽

Atherosclerosis Development

The pregnane X receptor (PXR) is a nuclear receptor that can be activated by numerous drugs and xenobiotic chemicals. PXR thereby functions as a xenobiotic sensor to coordinately regulate host responses to xenobiotics by transcriptionally regulating many genes involved in xenobiotic metabolism. We have previously reported that PXR has pro-atherogenic effects in animal models, but how PXR contributes to atherosclerosis development in different tissues or cell types remains elusive. In this study, we generated an LDL receptor-deficient mouse model with myeloid-specific PXR deficiency (PXRΔMyeLDLR−/−) to elucidate the role of macrophage PXR signaling in atherogenesis. The myeloid PXR deficiency did not affect metabolic phenotypes and plasma lipid profiles, but PXRΔMyeLDLR−/− mice had significantly decreased atherosclerosis at both aortic root and brachiocephalic arteries compared with control littermates. Interestingly, the PXR deletion did not affect macrophage adhesion and migration properties, but reduced lipid accumulation and foam cell formation in the macrophages. PXR deficiency also led to decreased expression of the scavenger receptor CD36 and impaired lipid uptake in macrophages of the PXRΔMyeLDLR−/− mice. Further, RNA-Seq analysis indicated that treatment with a prototypical PXR ligand affects the expression of many atherosclerosis-related genes in macrophages in vitro. These findings reveal a pivotal role of myeloid PXR signaling in atherosclerosis development and suggest that PXR may be a potential therapeutic target in atherosclerosis management.

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Epac1 (Exchange Protein Directly Activated by cAMP 1) Upregulates LOX-1 (Oxidized Low-Density Lipoprotein Receptor 1) to Promote Foam Cell Formation and Atherosclerosis Development

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvbaha.119.314238 ◽

2020 ◽

Vol 40 (12) ◽

Author(s):

William G. Robichaux ◽

Fang C. Mei ◽

Wenli Yang ◽

Hui Wang ◽

Hua Sun ◽

...

Keyword(s):

Bone Marrow ◽

Foam Cell ◽

Cell Formation ◽

Foam Cell Formation ◽

Low Density ◽

Lipid Uptake ◽

Wild Type ◽

Ldl Uptake ◽

Atherosclerosis Development

Objective: The cAMP second messenger system, a major stress-response pathway, plays essential roles in normal cardiovascular functions and in pathogenesis of heart diseases. Here, we test the hypothesis that the Epac1 (exchange protein directly activated by cAMP 1) acts as a major downstream effector of cAMP signaling to promote atherogenesis and represents a novel therapeutic target. Approach and Results: To ascertain Epac1’s function in atherosclerosis development, a triple knockout mouse model ( LTe ) was generated by crossing Epac1 −/− mice with atherosclerosis-prone LDb mice lacking both Ldlr and Apobec1 . Deletion of Epac1 led to a significant reduction of atherosclerotic lesion formation as measured by postmortem staining, accompanied by attenuated macrophage/foam cell infiltrations within atherosclerotic plaques as determined by immunofluorescence staining in LTe animals compared with LDb littermates. Primary bone marrow–derived macrophages were isolated from Epac1-null and wild-type mice to investigate the role of Epac1 in lipid uptake and foam cell formation. ox-LDLs (oxidized low-density lipoproteins) stimulation of bone marrow–derived macrophages led to elevated intracellular cAMP and Epac1 levels, whereas an Epac-specific agonist, increased lipid accumulation in wild-type, but not Epac1-null, bone marrow–derived macrophages. Mechanistically, Epac1 acts through PKC (protein kinase C) to upregulate LOX-1 (ox-LDL receptor 1), a major scavenger receptor for ox-LDL uptake, exerting a feedforward mechanism with ox-LDL to increase lipid uptake and propel foam cell formation and atherogenesis. Conclusions: Our study demonstrates a fundamental role of cAMP/Epac1 signaling in vascular remodeling by promoting ox-LDL uptake and foam cell formation during atherosclerosis lesion development. Therefore, Epac1 represents a promising, unexplored therapeutic target for atherosclerosis.

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The Potential of Fluocinolone Acetonide to Mitigate Inflammation and Lipid Accumulation in 2D and 3D Foam Cell Cultures

BioMed Research International ◽

10.1155/2018/3739251 ◽

2018 ◽

Vol 2018 ◽

pp. 1-11

Author(s):

Luong T. H. Nguyen ◽

Aristo Muktabar ◽

Jinkai Tang ◽

Yee Shan Wong ◽

Colby S. Thaxton ◽

...

Keyword(s):

Lipid Accumulation ◽

Foam Cell ◽

Cell Formation ◽

Foam Cells ◽

Fluocinolone Acetonide ◽

Major Adverse Cardiovascular Events ◽

Foam Cell Formation ◽

Fetal Bovine ◽

Atherosclerosis Development ◽

2D And 3D

Inflammation plays an important role in all stages of atherosclerosis development. Therefore, the use of anti-inflammatory drugs could reduce the risk of major adverse cardiovascular events due to atherosclerosis. Herein, we explored the capacity of fluocinolone acetonide (FA), a glucocorticoid (GC), in modulating foam cell formation and response. Human THP-1 derived foam cells were produced using 100 μg/mL oxidized low-density lipoproteins (OxLDL) and fetal bovine serum (1 and 10%). 2D cultures of these cells were treated with FA (0.1, 1, 10, and 50 μg/mL) in comparison with dexamethasone (Dex). Results showed that treatment with 0.1 and 1 μg/mL FA and Dex improved foam cell survival. FA and Dex also inhibited inflammatory cytokine (CD14, M-CSF, MIP-3α, and TNF-α) secretion. Notably, at the concentration of 1 μg/mL, both FA and Dex reduced cholesteryl ester accumulation. Compared to Dex, FA was significantly better in reducing lipid accumulation at the therapeutic concentrations of 1 and 10 μg/mL. In a novel 3D foam cell spheroid model, FA was shown to be more effective than Dex in diminishing lipid accumulation, at the concentration of 0.1 μg/mL. Taken together, FA was demonstrated to be effective in preventing both lipid accumulation and inflammation in foam cells.

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Periodontal Pathogens Promote Foam Cell Formation by Blocking Lipid Efflux

Journal of Dental Research ◽

10.1177/00220345211008811 ◽

2021 ◽

pp. 002203452110088

Author(s):

J.H. Rho ◽

H.J. Kim ◽

J.Y. Joo ◽

J.Y. Lee ◽

J.H. Lee ◽

...

Keyword(s):

Foam Cell ◽

Experimental Studies ◽

Cell Formation ◽

Foam Cells ◽

Periodontal Pathogen ◽

Lipid Homeostasis ◽

Foam Cell Formation ◽

Periodontal Pathogens ◽

Oil Red O

Foam cells are one of the major cellular components of atherosclerotic plaques, within which the trace of periodontal pathogens has also been identified in recent studies. In line with these findings, the correlation between periodontitis and atherosclerotic cardiovascular incidences has been repetitively supported by evidence from a number of experimental studies. However, the direct role of periodontal pathogens in altered cellular signaling underlying such cardiovascular events has not been clearly defined. To determine the role of periodontal pathogens in the pathogenesis of atherosclerosis, especially in the evolution of macrophages into foam cells, we monitored the pattern of lipid accumulation within macrophages in the presence of periodontal pathogens, followed by characterization of these lipids and investigation of major molecules involved in lipid homeostasis. The cells were stained with the lipophilic fluorescent dye BODIPY 493/503 and Oil Red O to characterize the lipid profile. The amounts of Oil Red O–positive droplets, representing neutral lipids, as well as fluorescent lipid aggregates were prominently increased in periodontal pathogen–infected macrophages. Subsequent analysis allowed us to locate the accumulated lipids in the endoplasmic reticulum. In addition, the levels of cholesteryl ester in periodontal pathogen–infected macrophages were increased, implying disrupted lipid homeostasis. Further investigations to delineate the key messengers and regulatory factors involved in the altered lipid homeostasis have revealed alterations in cholesterol efflux–related enzymes, such as ABCG1 and CYP46A1, as contributors to foam cell formation, and increased Ca2+ signaling and reactive oxygen species (ROS) production as key events underlying disrupted lipid homeostasis. Consistently, a treatment of periodontal pathogen–infected macrophages with ROS inhibitors and nifedipine attenuated the accumulation of lipid droplets, further confirming periodontal pathogen–induced alterations in Ca2+ and ROS signaling and the subsequent dysregulation of lipid homeostasis as key regulatory events underlying the evolution of macrophages into foam cells.

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Dynamic Role of Macrophage Sub Types for Development of Atherosclerosis and Potential Use of Herbal Immunomodulators as Imminent Therapeutic Strategy

Cardiovascular & Hematological Agents in Medicinal Chemistry ◽

10.2174/1871525718666201217163207 ◽

2020 ◽

Vol 18 ◽

Author(s):

Parimalanandhini Duraisamy ◽

Sangeetha Ravi ◽

Mahalakshmi Krishnan ◽

Catherene M. Livya ◽

Beulaja Manikandan ◽

...

Keyword(s):

Foam Cell ◽

Cell Formation ◽

Atherosclerotic Lesion ◽

Foam Cell Formation ◽

Atherosclerosis Progression ◽

Proinflammatory Mediators ◽

M1 Macrophage ◽

Tnf Α ◽

Inflammatory Site

: Atherosclerosis, a major contributor to cardiovascular disease is a global alarm causing mortality worldwide. Being a progressive disease in the arteries, it mainly causes recruitment of monocytes to the inflammatory sites and subside pathological conditions. Monocyte-derived macrophage mainly acts in foam cell formation by engorging the LDL molecules, oxidizes it into Ox-LDL and leads to plaque deposit development. Macrophages in general differentiate, proliferate and undergo apoptosis at the inflammatory site. Frequently two subtypes of macrophages M1 and M2 has to act crucially in balancing the micro-environmental conditions of endothelial cells in arteries. The productions of proinflammatory mediators like IL-1, IL-6, TNF-α by M1 macrophage has atherogenic properties majorly produced during the early progression of atherosclerotic plaques. To counteract cytokine productions and M1-M2 balance, secondary metabolites (phytochemicals) from plants act as a therapeutic agent in alleviating atherosclerosis progression. This review summarizes the fundamental role of the macrophage in atherosclerotic lesion formation along with its plasticity characteristic as well as recent therapeutic strategies using herbal components and anti-inflammatory cytokines as potential immunomodulators.

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Abstract 3691: Deletion of Suppressor Of Cytokine Signaling-1 in a Murine Model of Atherosclerosis Results in a Lethal Systemic Inflammation

Circulation ◽

10.1161/circ.118.suppl_18.s_467-c ◽

2008 ◽

Vol 118 (suppl_18) ◽

Author(s):

Christina Grothusen ◽

Harald Schuett ◽

Stefan Lumpe ◽

Andre Bleich ◽

Silke Glage ◽

...

Keyword(s):

Foam Cell ◽

Low Density Lipoprotein ◽

Cell Formation ◽

Density Lipoprotein ◽

Foam Cell Formation ◽

Cytokine Signaling ◽

Suppressor Of Cytokine Signaling ◽

The Impact

Introduction: Atherosclerosis is a chronic inflammatory disease of the cardiovascular system which may result in myocardial infarction and sudden cardiac death. While the role of pro-inflammatory signaling pathways in atherogenesis has been well characterized, the impact of their negative regulators, e.g. suppressor of cytokine signaling (SOCS)-1 remains to be elucidated. Deficiency of SOCS-1 leads to death 3 weeks post-partum due to an overwhelming inflammation caused by an uncontrolled signalling of interferon-gamma (IFNγ). This phenotype can be rescued by generating recombination activating gene (rag)-2, SOCS-1 double knock out (KO) mice lacking mature lymphocytes, the major source of IFNγ. Since the role of SOCS-1 during atherogenesis is unknown, we investigated the impact of a systemic SOCS-1 deficiency in the low-density lipoprotein receptor (ldlr) KO model of atherosclerosis. Material and Methods: socs-1 −/− /rag-2 −/− deficient mice were crossed with ldlr-KO animals. Mice were kept under sterile conditions on a normal chow diet. For in-vitro analyses, murine socs-1 −/− macrophages were stimulated with native low density lipoprotein (nLDL) or oxidized (ox)LDL. SOCS-1 expression was determined by quantitative PCR and western blot. Foam cell formation was determined by Oil red O staining. Results: socs-1 −/− /rag-2 −/− /ldlr −/− mice were born according to mendelian law. Tripel-KO mice showed a reduced weight and size, were more sensitive to bacterial infections and died within 120 days (N=17). Histological analyses revealed a systemic, necrotic, inflammation in Tripel-KO mice. All other genotypes developed no phenotype. In-vitro observations revealed that SOCS-1 mRNA and protein is upregulated in response to stimulation with oxLDL but not with nLDL. Foam cell formation of socs-1 −/− macrophages was increased compared to controls. Conclusion: SOCS-1 seemingly controls critical steps of atherogenesis by modulating foam cell formation in response to stimulation with oxLDL. SOCS-1 deficiency in the ldlr-KO mouse leads to a lethal inflammation. These observations suggest a critical role for SOCS-1 in the regulation of early inflammatory responses in atherogenesis.

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Abstract 57: The Epigenetic Enzyme Kdm6b Controls the Pro-Fibrotic Transcriptome Signature of Foam Cells

Arteriosclerosis Thrombosis and Vascular Biology ◽

10.1161/atvb.37.suppl_1.57 ◽

2017 ◽

Vol 37 (suppl_1) ◽

Author(s):

Annette E Neele ◽

Koen H Prange ◽

Marten A Hoeksema ◽

Saskia van der Velden ◽

Tina Lucas ◽

...

Keyword(s):

Foam Cell ◽

Smooth Muscle Actin ◽

Cell Formation ◽

Atherosclerotic Lesion ◽

Foam Cells ◽

Foam Cell Formation ◽

Cell Phenotype ◽

Sequencing Analysis ◽

Dependent Manner ◽

Alpha Smooth Muscle Actin

Aim: Foam cells are a key hallmark of atherosclerotic lesion formation. Within the atherosclerotic lesion macrophages scavenge modified lipoproteins and thereby acquire their foam cell characteristics. Besides their foam cell phenotype, macrophages can have specific inflammation regulatory functions in atherosclerotic lesions. Epigenetic pathways are crucial for monocyte to macrophage differentiation and activation. The H3K27 demethylase Kdm6b (also known as Jmjd3) is regulated in response to various triggers and regulates several modes of macrophage activation. Given the crucial role of macrophage foam cells in atherosclerosis, we here studied Kdm6b in peritoneal foam cells in order to identify regulated pathways. Material and Methods: A myeloid deficient Kdm6b mice (LysMCre-Kdm6b fl/fl ) was generated and bone marrow of Kdm6b wt or Kdm6b del mice was transplanted to irradiated Ldlr -/- mice which were fed a high fat diet for 9 weeks to induce foam cell formation. Peritoneal foam cells from Kdm6b del or Kdm6b wt mice were isolated and used for RNA-sequencing analysis. Results: Among the list of downregulated genes many genes involving fibrosis were affected in Kdm6b deficient foam cells including Collagen genes ( Col1a1 , Col1a2 ), Alpha smooth muscle actin ( Acta2 ) and Fibronectin-1 ( Fn1 ). Pathway analysis on downregulated genes ( P -value < 0.05) indicated that pathways involved in epithelial to mesenchymaltransition (EMT) ( q- value=10 -13 ) and extracellular matrix organization ( q- value=10 -4 ) were significantly downregulated. Pro-fibrotic pathways were thus strongly suppressed in Kdm6b deleted foam cells. Analysis of published datasets of foam cells showed that foam cell formation induces these pro-fibrotic characteristics. Overlay of both data sets indicated that fibrotic genes which are induced upon foam cell formation, are reduced in the absence of Kdm6b. These data suggest that foam cell formation induces a pro-fibrotic gene signature in a Kdm6b-dependent manner. Conclusion: We identified Kdm6b as a novel regulator of the pro-fibrotic signature of peritoneal foam cells.

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Signaling Pathways and Key Genes Involved in Regulation of foam Cell Formation in Atherosclerosis

Cells ◽

10.3390/cells9030584 ◽

2020 ◽

Vol 9 (3) ◽

pp. 584 ◽

Cited By ~ 16

Author(s):

Anastasia V. Poznyak ◽

Wei-Kai Wu ◽

Alexandra A. Melnichenko ◽

Reinhard Wetzker ◽

Vasily Sukhorukov ◽

...

Keyword(s):

Foam Cell ◽

Low Density Lipoprotein ◽

Cell Formation ◽

Density Lipoprotein ◽

Foam Cells ◽

Foam Cell Formation ◽

Beneficial Effects ◽

Complex Process ◽

Experimental Therapies ◽

Inflammatory Drugs

Atherosclerosis is associated with acute cardiovascular conditions, such as ischemic heart disease, myocardial infarction, and stroke, and is the leading cause of morbidity and mortality worldwide. Our understanding of atherosclerosis and the processes triggering its initiation is constantly improving, and, during the last few decades, many pathological processes related to this disease have been investigated in detail. For example, atherosclerosis has been considered to be a chronic inflammation triggered by the injury of the arterial wall. However, recent works showed that atherogenesis is a more complex process involving not only the immune system, but also resident cells of the vessel wall, genetic factors, altered hemodynamics, and changes in lipid metabolism. In this review, we focus on foam cells that are crucial for atherosclerosis lesion formation. It has been demonstrated that the formation of foam cells is induced by modified low-density lipoprotein (LDL). The beneficial effects of the majority of therapeutic strategies with generalized action, such as the use of anti-inflammatory drugs or antioxidants, were not confirmed by clinical studies. However, the experimental therapies targeting certain stages of atherosclerosis, among which are lipid accumulation, were shown to be more effective. This emphasizes the relevance of future detailed investigation of atherogenesis and the importance of new therapies development.

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Role of Monocytes in Atherogenesis

Physiological Reviews ◽

10.1152/physrev.00005.2003 ◽

2003 ◽

Vol 83 (4) ◽

pp. 1069-1112 ◽

Cited By ~ 262

Author(s):

BJARNE ØSTERUD ◽

EIRIK BJØRKLID

Keyword(s):

Growth Factors ◽

Foam Cell ◽

Cell Formation ◽

Lipid Peroxides ◽

Transgenic Animals ◽

Foam Cell Formation ◽

Cellular Interactions ◽

Adhesive Molecules ◽

Inflammatory System

Østerud, Bjarne, and Eirik Bjørklid. Role of Monocytes in Atherogenesis. Physiol Rev 83: 1069-1112, 2003; 10.1152/physrev.00005.2003.—This review focuses on the role of monocytes in the early phase of atherogenesis, before foam cell formation. An emerging consensus underscores the importance of the cellular inflammatory system in atherogenesis. Initiation of the process apparently hinges on accumulating low-density lipoproteins (LDL) undergoing oxidation and glycation, providing stimuli for the release of monocyte attracting chemokines and for the upregulation of endothelial adhesive molecules. These conditions favor monocyte transmigration to the intima, where chemically modified, aggregated, or proteoglycan- or antibody-complexed LDL may be endocytotically internalized via scavenger receptors present on the emergent macrophage surface. The differentiating monocytes in concert with T lymphocytes exert a modulating effect on lipoproteins. These events propagate a series of reactions entailing generation of lipid peroxides and expression of chemokines, adhesion molecules, cytokines, and growth factors, thereby sustaining an ongoing inflammatory process leading ultimately to lesion formation. New data emerging from studies using transgenic animals, notably mice, have provided novel insights into many of the cellular interactions and signaling mechanisms involving monocytes/macrophages in the atherogenic processes. A number of these studies, focusing on mechanisms for monocyte activation and the roles of adhesive molecules, chemokines, cytokines and growth factors, are addressed in this review.

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