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. Author manuscript; available in PMC: 2022 Oct 1.
Published in final edited form as: Curr Opin Lipidol. 2021 Oct 1;32(5):293–300. doi: 10.1097/MOL.0000000000000778

Metabolic regulation of macrophage proliferation and function in atherosclerosis

Michael T Patterson 1, Jesse W Williams 1,2
PMCID: PMC8416794  NIHMSID: NIHMS1727028  PMID: 34334628

Abstract

Purpose of Review-

Macrophage accumulation within atherosclerotic plaque is a primary driver of disease progression. However, recent advances in both phenotypic and functional heterogeneity of these cells have allowed for improved insight into potential regulation of macrophage function within lesions. In this review, we will discuss recent insights on macrophage heterogeneity, lipid processing, metabolism, and proliferation in atherosclerosis. Furthermore, we will identify outstanding questions in the field that are pertinent to future studies.

Recent Findings-

With the recent development of single cell RNA sequencing (scRNA-seq), several studies have highlighted the diverse macrophage populations within plaques, including pro-inflammatory, anti-inflammatory, lipid loaded and tissue resident macrophages. Furthermore, new data has suggested that differential activation of metabolic pathways, including glycolysis and fatty acid oxidation, may play a key role in determining function. Recent works have highlighted that different populations retain varying capacity to undergo proliferation; regulating the proliferation pathway may be highly effective in reducing plaque in advanced lesions.

Summary-

Macrophage populations within atherosclerosis are highly heterogeneous; differences in cytokine production, lipid handling, metabolism, and proliferation are seen between subpopulations. Understanding the basic cellular mechanisms that drive this heterogeneity will allow for the development of highly specific disease modulating agents to combat atherosclerosis.

Keywords: Atherosclerosis, Macrophage, Metabolism, Proliferation

Introduction

Cardiovascular disease (CVD) remains the leading cause of mortality in the US and world, representing approximately 1 out of every 3 deaths [1]. Despite major advancements in combating disease such as increased disease detection, effective cholesterol lowering therapeutics, and a reduction in some high-risk behaviors such as smoking, the impact of CVD has expanded worldwide. A primary driver of CVD is atherosclerotic plaque formation in the mid- and large-sized arteries. The hallmark of atherosclerosis pathogenesis is the deposition of low-density lipoprotein particles (LDL) into arterial walls, forming what is termed a fatty streak. LDL particles are modified within the artery intima, often yielding oxidized LDL (oxLDL), which promotes endothelial activation and atherogenesis. These steps ultimately result in enhanced local and systemic inflammation though the recruitment of circulating immune cells—both innate and adaptive. This inflammatory cascade is driven by monocyte derived macrophages and local tissue resident macrophages which engulf LDL and constitute a major proportion of the plaque’s cellular makeup. Macrophages that take up large quantities of LDL and store it in the form of lipid droplets are referred to as foamy macrophages, a term associated with their foam-like morphology. Continued blood monocyte recruitment and intraplaque proliferation maintain plaque-associated macrophages as plaque expands and additional cell types enter the lesions [2]. Atherosclerotic lesion expansion leads to increased arterial stiffening, altered blood flow, and extra cellular matrix remodeling, which cumulatively elevates risk for downstream pathologic events like stenosis or rupture.

Within plaque, macrophages perform highly regulated cellular processes, including lipid uptake, storage, efferocytosis, and metabolic rewiring, all of which have been extensively studied. However, the diversity of macrophage populations within plaques, including both pro- and anti-inflammatory subsets, is only recently being appreciated. The dynamics of plaque expansion, through monocyte recruitment, regulation of cell death, or local plaque proliferation, and how it relates to macrophage diversity remains to be fully understood. Deciphering how these basic cellular mechanisms affect macrophages are of particular clinical relevance, given that pre-clinical and clinical data suggest that suppressing inflammation [3, 4] and blunting local macrophage proliferation [5] are potential effective therapeutic options in CVD.

Plaque Macrophage Diversity

Initial studies aimed at identifying the makeup of atherosclerotic plaques found that the primary cell type present in the lesion core are macrophages, while the fibrous cap is dominated by smooth muscle and other stromal cells [6]. However, the development of single cell genomics and proteomics has allowed for a more in-depth exploration of cellular diversity in atherosclerosis [7], and dramatically expanded our understanding of macrophage heterogeneity within lesions. Multiple studies performed scRNA-seq on murine and human atherosclerotic plaques and have identified several unique macrophage subsets including inflammatory, foamy, and tissue resident populations [8–12]. Figure 1 depicts macrophage diversity within atherosclerotic lesions derived from recent gene expression and functional studies. It was previously believed that foamy cells were the major producers of proinflammatory cytokines within a plaque given that oxLDL treatment would augment macrophage inflammatory responses in vitro. However, when macrophages were pre-loaded with lipid to generate foamy-like cells the macrophages were resistant to activation [13, 14], suggesting that it was possible plaque associated foamy macrophages were not the inflammatory culprit within lesions [13, 14]. In our prior study [9], we validated this possibility by utilizing a fluorescent lipid-staining approach in tandem with florescence activated cell sorting (FACS) which allowed for the separation of lipid-loaded (foamy) and non-lipid loaded (nonfoamy) macrophages from established atherosclerotic plaque. Bulk RNA-seq and scRNA-seq data uncovered that foamy cells are not major producers of proinflammatory cytokines, but rather nonfoamy macrophages expressed high transcript levels of known inflammatory genes such as Il-1β. These data also described gene expression levels comparing foamy macrophages and foamy smooth-muscle cells. Together, these results suggest that drivers of inflammation may be mediated through the nonfoamy macrophages, and that studies focused at understanding the generation and maintenance of these cells may lead to beneficial treatments.

Figure 1.

Figure 1.

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Arterial macrophage subpopulations in steady state and atherosclerosis.

The aorta has two established resident macrophage populations (upper half), adventitia and intima (MacAIR) associated macrophages that are present in steady state and during atherosclerosis progression. Adventitia macrophages promote artery homeostasis, whereas MacAIR cells promote early lesion inflammation and foamy cell formation during lesion initiation. Atherosclerotic plaque possesses an array of macrophage subtypes. Foamy macrophages have cytoplasmic lipid droplets and fail to express inflammatory cytokines. Reparative macrophages are responsive to IL-4 signaling to promote and anti-inflammatory response. Inflammatory macrophages are nonfoamy cells that have inflammasome activation signature and release of IL-1β.

Tissue resident macrophage is a term referring to populations that can maintain self-renewal in tissues, independent of the necessity of additional progenitor cells like monocytes [15]. While often derived from yolk-sac or embryonic origins, it is now understood that this is not a requirement for generating a tissue-resident population. To date, two tissue resident macrophage populations have been identified in the murine aorta and are localized to distinct regions prone to plaque formation-- the adventitia and the intima (Figure 1). Each of these populations influences arterial disease. Ensan et al [16] originally defined the tissue resident macrophages present in the adventitia of nascent mouse aortas. Using lineage tracking methods, they found that this subset was derived both embryonically from CX3CR1+ precursors and postnatally from circulating monocytes [16]. Further characterization of this subset found that they highly express Lyve1 and play a role in regulating arterial stiffness through cross talk with smooth muscle cells [17]. Interestingly, a recent report [18] extended the prior work to suggest that embryonically derived adventitia resident macrophages proliferate locally in response to angiotensin II driven inflammation and adopt a tissue reparative transcription response. This work highlights that despite continued ability to recruit new monocyte derived macrophages to the adventitia, tissue resident cells show an enhanced wound healing response, suggesting that macrophage ontogeny or prior immune experience shapes function.

Moreover, aorta intima resident macrophages (MacAIR) were originally described by the Steinman and Cybulsky groups as myeloid lineage cells localizing to regions of turbulent flow and prone to atherosclerotic plaque formation [19–24]. The cells were initially proposed as dendritic cells based on expression of traditional markers CD11c and MHC II [19] and suggested to have abilities to present antigen to T cells. Yet, they were also observed to perform a number of macrophage restricted functions, including lipid uptake in the artery wall following HFD feeding [21]. Our recent work expanded these important observations by utilizing scRNA-seq profiling and fate-mapping animal model approaches to allow for fluorescent tracking of cell subsets [8]. We defined gene expression programs associated with MacAIR specification and described their development and steady state maintenance programs. In contrast to adventitia macrophages, MacAIR are derived exclusively from circulating monocytes at birth and were shown to play a role in early plaque development [8].

A recent study integrating multiple mouse scRNA-seq datasets which highlighted the diversity of plaque macrophages and identified 4 major macrophage populations and 2 major monocyte populations conserved across 9 experiments [25]. These populations include Trem2+ foamy macrophages, IL-1β+ inflammatory macrophages, CXCL4+ resident adventitia macrophages, interferon inducible macrophages (INFICs), canonical monocytes and 2 mixed monocyte/dendritic cell populations [25]. Building on this work, Zernecke et al. [26] took a similar approach and integrated scRNA-seq experiments from both human and mouse atherosclerotic plaques and further elucidated macrophage subsets. In this study, the authors found that multiple populations existed within these four major macrophage subsets in murine plaques, including CD209hi and CD209lo adventitia resident macrophages, NLRP3hi and MHCIIhi inflammatory macrophages, Trem2+ Slamf9hi and Trem2+ Gpnmbhi foamy cells (the latter corresponding to MacAIR) and rare populations like small peritoneal macrophages [27] and INFICs. Using cross-species data integration, they found that human atherosclerotic plaques display macrophage populations that transcriptionally resemble mouse subsets, including Lyve1+ adventitia macrophages, Trem2+ foamy macrophages, INFICs, and inflammatory macrophages.

Macrophage Lipid Handling and Metabolism

Early pioneering work in macrophage biology showed that lesional macrophages take up lipid by scavenger receptors, primarily CD36, SR-A1 and SR-B1, via endocytosis and pinocytosis [28, 29]. Under normal conditions, engulfed lipoproteins are hydrolyzed to free cholesterol within lysosomes and either esterified in the endoplasmic reticulum and stored or effluxed and transferred to high density lipoprotein (HDL) particles via ABC transporters in a process called reverse cholesterol transport [30]. However, in atherosclerotic plaque macrophages, this process is overwhelmed, and esterified cholesterol is stored in large lipid droplets giving foamy macrophages their bloated appearance. Interestingly, later studies highlighted the atheroprotective role of ABC transporters in macrophages, showing that deletion of these proteins lead to increased oxidative stress [31] and proliferation [32], suggesting that activation of this pathway may be useful therapeutically to revitalize foamy cell function. Furthermore, plaque macrophages highly express the lipid sensing molecule Trem2, which has been implicated in coordinating metabolic homeostasis of both liver [33] and adipose tissue [34] macrophages and protecting against non-alcoholic fatty liver disease associated sepsis [33] and obesity [34]. Given this, we believe that modulation of Trem2 signaling could alter macrophage function within plaques and be a potential target for pharmacologic intervention in atherosclerosis.

Upon binding of scavenger receptors and uptake of lipid, macrophages undergo global transcriptional changes that alter cell phenotype and function. In a recent study, Zhang et al. [35] elucidated a potential link between lipid uptake and macrophage function though activation of the small GTPase Rheb. In this work, the authors found that Rheb was activated in macrophages treated with ox-LDL and in atherosclerotic plaques, and downstream activation of Rheb leads to increased lipid uptake, inflammatory cytokine transcription and proliferation [35]. In a similar study, You et al [36]. explored the role of the sorting nexin SNX10 in atherosclerosis and found that SNX10 deletion in ApoE−/ mice led to decreased plaque size, altered lipid uptake and anti-inflammatory phenotype. Interestingly, they found that SNX10 deletion decreased expression of CD36, which requires SNX10-Lyn AKT signaling for expression, and attenuation of this pathway increased nuclear translocation of the transcription factor TFEB, which ultimately drove metabolic rewiring leading to anti-inflammatory phenotype [36].

Under inflammatory conditions, macrophages shift their metabolism toward glycolysis and away from oxidative phosphorylation [37, 38]. To meet the increased demand for glucose, macrophages upregulate the glucose transporter GLUT1c [39]. This upregulation of glucose transport in macrophages allowed the original in vivo studies into the metabolic pathways involved in atherosclerosis by using positron emission tomography to detect the accumulation of the glucose analog 18F-fluoro-2-deoxy-d-glucose (18F-FDG) within plaques. These studies showed that there was a significant increase of glucose uptake within lesions that had lipid-rich necrotic cores, suggesting that glycolysis is an important fuel source for plaque macrophages [40, 41]. Overexpression studies demonstrated elevated glucose uptake and enhance metabolism, yet no expansion of atherosclerotic disease or inflammatory cytokine were associate. This suggests that excess glucose uptake alone is insufficient to drive inflammatory responses in vivo [42]. Further studies into the role of glucose uptake in atherosclerosis explored GLUT1 deletion in the context of ApoE−/− and found decreased plaque size, primarily due to blunted myelopoiesis which decreased monocyte trafficking to plaques [43]. However, once taken up, the intracellular utilization of glucose through glycolysis or pentose phosphate pathway have yet to be formally delineated. Recently, a study [44] using multi-isotope imaging mass spectrometry in LDLR−/− mice elucidated the potential interplay between proliferation and glycolysis. This group found that proliferating cells preferentially take up radiolabeled glucose [44], suggesting that glucose plays a role in both promoting monocyte differentiation and driving macrophage proliferation. Furthermore, it is well documented that increased glycolytic flux leads to induction of inflammation [37], implying that alteration of glycolytic drivers could modulate atherogenesis. Analysis of advanced human plaques found altered metabolic profiles associating elevated inflammatory cytokine production with glycolysis [45]. In accordance with this hypothesis, van Leent et al. [46] found that the protein Prosaposin (Psap), a lysosomal protease, modulates glycolysis and inflammatory responses in atherosclerosis. In this work, they found that Psap was induced upon mTOR signaling, and deletion led to decreased plaque inflammation and attenuated glucose flux and oxidative phosphorylation [46]. Moreover, C-reactive protein (CRP), an acute phase protein elevated in CVD, was associated with driving glycolytic flux and proinflammatory cytokine production [47], further suggesting that altered glycolysis modulates inflammation in atherosclerosis. Finally, was shown that phagocytic engulfment of dead cells by macrophages (termed efferocytosis) can trigger upregulation of Glut1 and activation of aerobic glycolysis and this activation can lead to the release of lactate which can modulate the local microenvironment toward a more anti-inflammatory phenotype. These findings challenge the idea that upregulation of glycolysis is strictly pro-inflammatory and suggest that a deeper understanding of macrophage glycolysis in inflammation is necessary [48, 49].

Though the data suggests that myeloid glycolytic flux plays an important role in the pathogenesis of atherosclerosis, other signaling molecules may synergize with glucose to regulate an anti-atherogenic metabolic state. IL-4, a cytokine involved in anti-inflammatory responses and proliferative potential of macrophages [50, 51], has been found to be an inducer of fatty acid oxidation (FAO) through induction of STAT6 and PGC1β [52]. Building on these observations, Zhang et al. [53] found that non-inflammatory efferocytosis, provided fuel for driving metabolic signatures associated with FAO. This increase in FAO activated IL-10 transcription, leading to tissue repair after myocardial infarction [53], suggests that FAO could be an inducer of anti-inflammatory responses in the similar setting of atherosclerosis. Interestingly, ATP citrate lyase (Acly), an enzyme that promotes fatty acid and cholesterol biosynthesis, was recently found to drive plaque instability through alteration of fatty acid metabolism [54]. The authors found that deletion of Acly deregulated fatty acid and cholesterol biosynthesis, leading to increased efferocytosis and ultimately increased plaque stability [54]. Taken together, it stands to reason that deregulated fatty acid biosynthesis drives an increased need for metabolic fuel that could be met by increased efferocytosis and FAO, boosting anti-inflammatory responses. While macrophage metabolism plays an important role in atherosclerosis, specific mechanisms utilized by plaque associated populations, and whether they can be harnessed to regulate disease outcome remains to be elucidated.

Proliferation

Plaque macrophages receive several proatherogenic signals that promote survival and lesion growth [55]. Mouse studies have highlighted that macrophages not only survive and take up residence in the aorta, but also proliferate robustly [56, 57]. Surprisingly, subsequent investigation into the macrophage dynamics within plaques suggested that lipid laden foam cells were the primary proliferative subset, despite their lipid filled, bloated cytoplasm [58]. The concept that macrophages proliferate within a plaque ultimately led to the question whether intraplaque proliferation or continued monocyte recruitment was the major driver of plaque expansion. Robbins et al. [59] found that macrophages turn over rapidly in advanced plaques of ApoE−/− mice and that replenishment of macrophages primarily depends on local proliferation. This study attributed signaling through SR-A1 as the trigger for macrophage expansion and further plaque expansion. The relevance of inhibiting local macrophage proliferation could be seen through studies targeting cyclin-dependent kinase pathways [60, 61]. Yet, understanding mechanisms that promote or regulate proliferation within atherosclerotic lesions has been difficult.

Recent work exploring the function of MacAIR has found that this population is the first to adopt a foamy cell phenotype at sites of plaque formation and initiate plaque growth through promoting circulating monocyte recruitment [8]. Interestingly, these cells had limited proliferative capacity during atherosclerosis and required circulating monocyte replenishment to expand their niche and plaque growth, suggesting that early disease may be dominated by monocyte recruitment rather than macrophage proliferation. Recent human data has supported the relevance of monocyte recruitment in atherosclerosis through correlation of increased blood monocyte counts to an increased risk of developing CVD [62, 63]. Overall, these studies suggest that early plaque development may be driven by circulating monocyte recruitment, while later plaque expansion is driven by macrophage proliferation. This switch from recruitment to proliferation appears to coincide with the size of lesions and may be a result of limited access from circulating cells. Monocytes fail to penetrate deep within lesions of advanced plaques in mouse studies [64]. Thus, when monocyte recruitment is unable to replace macrophages deep within lesions, it seems reasonable to consider that proliferation is an alternative that becomes more favorable. However, mechanisms driving the switch from monocyte recruitment to macrophage proliferation remains to be understood and should be a goal of subsequent study.

Mechanisms regulating macrophage proliferation within plaques are driven by cytokines, growth factors, and ox-LDL [65]. Macrophage colony stimulating growth factor 1 (CSF-1) and granulocyte/macrophage stimulating growth factor (GM-CSF) are key regulators of macrophage development and proliferation during inflammation [66]; and both have been implicated in atherosclerosis development [67–69]. Deficiency of CSF-1 decreases plaque size of Ldlr−/− mice [67] and later studies attributed decreased plaque size, in part, to increased macrophage apoptosis [70]. A recent study [71] detailed the effects of cell specific deletion of CSF-1 on the development of atherosclerosis and found that macrophage proliferation was highly dependent on local, not systemic CSF-1 production. Furthermore, using cell-type restricted mouse models, they found that the primary producers of CSF-1 driving macrophage proliferation are smooth muscle cells and fibroblasts [71]. While cell extrinsic drivers of cell division may be major players in atherosclerosis development, it is now being appreciated that macrophage intrinsic pathways may play a role in driving proliferation within a plaque. One such example is clonal hematopoiesis, which is the development of somatic mutations in hematopoietic stem cells (HSPC), typically with age, that leads to selective proliferation of a single clone of cells. Clonal hematopoiesis has been identified as an independent risk factor for having a myocardial infarction [72, 73]; and mouse studies using Tet2-deficient and Dnmt3a-mutant mice two common HSPC mutations that lead to clonal hematopoiesis, found accelerated development of atherosclerosis and heart failure [74]. Recently [75], it was shown that the common somatic mutation Jak2VF, increased macrophage proliferation within plaque and led to increased necrotic core formation. Interestingly, this study found that the mechanism of this phenotype was through activation of the non-canonical AIM2 inflammasome due to increased DNA replication stress [75].

Given the vital role of macrophage proliferation in plaque growth, attempts to target macrophage turnover clinically has drawn attention. Statins, the gold standard for the prevention of atherosclerosis, primarily work by inhibiting cholesterol production and downregulating LDL receptors. However, more recent data have suggested that mechanisms are independent of lipid lowering, such as inhibition of inflammation [76], decreased monocyte recruitment [77], and blunted macrophage proliferation [78]. Härdtner et al. [79] defined a potential macrophage proliferation dependent mechanism of statins through which decreased serum LDL and local lipid contents in the plaque lead to decreased macrophage proliferation within established plaques, independent of monocyte recruitment. This study built on the hypothesis that macrophage proliferation is a key driver of late plaque expansion by suggesting that lipid uptake is a key component of cell division and highlighted the effect statin treatment has on macrophage proliferation. How statins affect early plaque development, either through decreased proliferation or blunting monocyte recruitment, remains to be understood, and is a clinically relevant question that could inform future treatment methods. Moreover, the use of nanoparticles to selectively deliver agents to sites of plaques to blunt macrophage proliferation has been tested preclinically with some success. Engineered high density lipoprotein nanoparticles loaded with simvastatin employed in ApoE−/− hypercholesteremic mice significantly decreased plaque size, highlighting the potential therapeutic efficacy of targeting intraplaque macrophage proliferation [5]. A newer study using a similar approach found that biomimetic nanoparticles loaded with rapamycin, a potent antiproliferative and anti-inflammatory agent, rapidly decreased both macrophage proliferation and secretion of proinflammatory cytokines, suggesting that targeting both macrophage proliferation and inflammation could be used acutely to stabilize plaques [80].

Conclusions

Recent large-scale clinical trials have validated the role of inflammation in promoting CVD and shown important proof-of-concept that targeting inflammatory pathways can show beneficial effects beyond standard of care cholesterol management [3, 4]. Expanding our understanding of inflammatory pathways, particularly in the macrophage lineage, may uncover unique disease-specific mechanisms that may allow for safer approaches to controlling disease progression. Importantly, consideration should be given to metabolic parameters that may modify lipid handling and inflammatory states of plaque associated macrophages. Candidates for these pathways include the regulation of lipid uptake and metabolism associated with foamy macrophage formations, recruitment of monocytes that may undergo activation toward inflammatory pathways, and regulation of proliferating macrophages within lesions. Ultimately, progress toward understanding these molecular pathways may lead to identification and translation into disease-specific targets that may be produce the next group of immune-modulatory therapies.

Key Points.

  • Macrophage subsets within atherosclerotic plaques are genetically diverse.

  • Metabolic factors regulate macrophage activation and function within atherosclerotic plaque.

  • Proliferation of plaque associated macrophages may play a dual role in driving disease progression and regression.

Acknowledgements

We would like to thank Dr. Stoyan Ivanov for contributions to the preparation of this article.

Financial Support and Sponsorship

This work was supported by a grant from the National Institutes of Health, R00 HL138163.

Footnotes

Conflicts of Interest

Authors declare no conflicts of interest exist.

References

  • [1].Benjamin EJ, Muntner P, Alonso A et al. Heart Disease and Stroke Statistics-2019 Update: A Report From the American Heart Association. Circulation 2019; 139:e56–e528. [DOI] [PubMed] [Google Scholar]
  • [2].Kim KW, Ivanov S, Williams JW. Monocyte Recruitment, Specification, and Function in Atherosclerosis. Cells 2020; 10. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [3].Ridker PM, Everett BM, Thuren T et al. Antiinflammatory Therapy with Canakinumab for Atherosclerotic Disease. N Engl J Med 2017; 377:1119–1131. [DOI] [PubMed] [Google Scholar]
  • [4].Tardif JC, Kouz S, Waters DD et al. Efficacy and Safety of Low-Dose Colchicine after Myocardial Infarction. N Engl J Med 2019; 381:2497–2505. [DOI] [PubMed] [Google Scholar]
  • [5].Tang J, Lobatto ME, Hassing L et al. Inhibiting macrophage proliferation suppresses atherosclerotic plaque inflammation. Sci Adv 2015; 1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [6].Jonasson L, Holm J, Skalli O et al. Regional Accumulations of T-Cells, Macrophages, and Smooth-Muscle Cells in the Human Atherosclerotic Plaque. Arteriosclerosis 1986; 6:131–138. [DOI] [PubMed] [Google Scholar]
  • [7].Williams JW, Winkels H, Durant CP et al. Single Cell RNA Sequencing in Atherosclerosis Research. Circ Res 2020; 126:1112–1126. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [8].Williams JW, Zaitsev K, Kim KW et al. Limited proliferation capacity of aortic intima resident macrophages requires monocyte recruitment for atherosclerotic plaque progression. Nat Immunol 2020; 21:1194–1204. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [9].Kim K, Shim D, Lee JS et al. Transcriptome Analysis Reveals Nonfoamy Rather Than Foamy Plaque Macrophages Are Proinflammatory in Atherosclerotic Murine Models. Circ Res 2018; 123:1127–1142. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [10].Cochain C, Vafadarnejad E, Arampatzi P et al. Single-Cell RNA-Seq Reveals the Transcriptional Landscape and Heterogeneity of Aortic Macrophages in Murine Atherosclerosis. Circ Res 2018; 122:1661–1674. [DOI] [PubMed] [Google Scholar]
  • [11].Winkels H, Ehinger E, Vassallo M et al. Atlas of the Immune Cell Repertoire in Mouse Atherosclerosis Defined by Single-Cell RNA-Sequencing and Mass Cytometry. Circ Res 2018; 122:1675–1688. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [12].Fernandez DM, Rahman AH, Fernandez NF et al. Single-cell immune landscape of human atherosclerotic plaques. Nat Med 2019; 25:1576–1588. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [13].Jongstra-Bilen J, Zhang CX, Wisnicki T et al. Oxidized Low-Density Lipoprotein Loading of Macrophages Downregulates TLR-Induced Proinflammatory Responses in a Gene-Specific and Temporal Manner through Transcriptional Control. J Immunol 2017; 199:2149–2157. [DOI] [PubMed] [Google Scholar]
  • [14].Spann NJ, Garmire LX, McDonald JG et al. Regulated accumulation of desmosterol integrates macrophage lipid metabolism and inflammatory responses. Cell 2012; 151:138–152. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [15].Williams JW, Giannarelli C, Rahman A et al. Macrophage Biology, Classification, and Phenotype in Cardiovascular Disease: JACC Macrophage in CVD Series (Part 1). J Am Coll Cardiol 2018; 72:2166–2180. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [16].Ensan S, Li A, Besla R et al. Self-renewing resident arterial macrophages arise from embryonic CX3CR1(+) precursors and circulating monocytes immediately after birth. Nature Immunology 2016; 17:159–168. [DOI] [PubMed] [Google Scholar]
  • [17].Lim HY, Lim SY, Tan CK et al. Hyaluronan Receptor LYVE-1-Expressing Macrophages Maintain Arterial Tone through Hyaluronan-Mediated Regulation of Smooth Muscle Cell Collagen(vol 49, 326, 2018). Immunity 2018; 49:1191–1191. [DOI] [PubMed] [Google Scholar]
  • [18].Weinberger T, Esfandyari D, Messerer D et al. Ontogeny of arterial macrophages defines their functions in homeostasis and inflammation. Nat Commun 2020; 11. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This article performed ontogenic analysis of adventia macropahges in steady state and following AngII-mediated vascular inflammation. They find the macrophage origin from embryonic precursors may enhave proliferative potential compared to monocyte-derived adventitia macrophages.
  • [19].Choi JH, Do Y, Cheong C et al. Identification of antigen-presenting dendritic cells in mouse aorta and cardiac valves. J Exp Med 2009; 206:497–505. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [20].Choi JH, Cheong C, Dandamudi DB et al. Flt3 signaling-dependent dendritic cells protect against atherosclerosis. Immunity 2011; 35:819–831. [DOI] [PubMed] [Google Scholar]
  • [21].Paulson KE, Zhu SN, Chen M et al. Resident intimal dendritic cells accumulate lipid and contribute to the initiation of atherosclerosis. Circ Res 2010; 106:383–390. [DOI] [PubMed] [Google Scholar]
  • [22].Hsu YW, Hsu FF, Chiang MT et al. Siglec-E retards atherosclerosis by inhibiting CD36-mediated foam cell formation. J Biomed Sci 2021; 28. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [23].Zhu SN, Chen M, Jongstra-Bilen J, Cybulsky MI. GM-CSF regulates intimal cell proliferation in nascent atherosclerotic lesions. J Exp Med 2009; 206:2141–2149. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [24].Jongstra-Bilen J, Haidari M, Zhu SN et al. Low-grade chronic inflammation in regions of the normal mouse arterial intima predisposed to atherosclerosis. J Exp Med 2006; 203:2073–2083. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [25].Zernecke A, Winkels H, Cochain C et al. Meta-Analysis of Leukocyte Diversity in Atherosclerotic Mouse Aortas. Circulation Research 2020; 127:402–426. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This is the first study to integrate multiple published scRNA-seq datasets from all stages of disease progression to develop a unified atlas for cell heterogeneity.
  • [26].Alma Zernecke F E, Tobias Weinberger, Christian Schulz, Klaus Ley, Antoine-Emmanuel Saliba, Clément Cochain. integrated scrna-seq analysis identifies conserved transcriptomic features of mononuclear phagocytes in mouse and human atherosclerosis. BioRxiv 2021. [Google Scholar]
  • [27].Kim KW, Williams JW, Wang YT et al. MHC II+ resident peritoneal and pleural macrophages rely on IRF4 for development from circulating monocytes. J Exp Med 2016; 213:1951–1959. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [28].Berberian PA, Fowler S. The subcellular biochemistry of human arterial lesions. I. Biochemical constituents and marker enzymes in diseased and unaffected portions of human aortic specimens. Exp Mol Pathol 1979; 30:27–40. [DOI] [PubMed] [Google Scholar]
  • [29].Kunjathoor VV, Febbraio M, Podrez EA et al. Scavenger receptors class A-I/II and CD36 are the principal receptors responsible for the uptake of modified low density lipoprotein leading to lipid loading in macrophages. J Biol Chem 2002; 277:49982–49988. [DOI] [PubMed] [Google Scholar]
  • [30].Tall AR, Yvan-Charvet L. Cholesterol, inflammation and innate immunity. Nature Reviews Immunology 2015; 15:104–116. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [31].Yvan-Charvet L, Pagler TA, Seimon TA et al. ABCA1 and ABCG1 protect against oxidative stress-induced macrophage apoptosis during efferocytosis. Circ Res 2010; 106:1861–1869. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [32].Yvan-Charvet L, Pagler T, Gautier EL et al. ATP-binding cassette transporters and HDL suppress hematopoietic stem cell proliferation. Science 2010; 328:1689–1693. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [33].Hou J, Zhang J, Cui P et al. TREM2 sustains macrophage-hepatocyte metabolic coordination in nonalcoholic fatty liver disease and sepsis. J Clin Invest 2021; 131. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [34].Jaitin DA, Adlung L, Thaiss CA et al. Lipid-Associated Macrophages Control Metabolic Homeostasis in a Trem2-Dependent Manner. Cell 2019; 178:686–698 e614. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [35].Zhang Q, Hu J, Wu Y et al. Rheb (Ras Homolog Enriched in Brain 1) Deficiency in Mature Macrophages Prevents Atherosclerosis by Repressing Macrophage Proliferation, Inflammation, and Lipid Uptake. Arterioscler Thromb Vasc Biol 2019; 39:1787–1801. [DOI] [PubMed] [Google Scholar]
  • [36].You Y, Bao WL, Zhang SL et al. Sorting Nexin 10 Mediates Metabolic Reprogramming of Macrophages in Atherosclerosis Through the Lyn-Dependent TFEB Signaling Pathway. Circ Res 2020; 127:534–549. [DOI] [PubMed] [Google Scholar]
  • [37].Tabas I, Bornfeldt KE. Intracellular and Intercellular Aspects of Macrophage Immunometabolism in Atherosclerosis. Circ Res 2020; 126:1209–1227. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [38].Gallerand Alexandre S MI, Merlin Johanna, Guinamard Rodolphe R., Yvan-Charvet Laurent, Ivanov Stoyan Myeloid Cell Diversity and Impact of Metabolic Cues during Atherosclerosis. Immunometabolism 2020; e200028:2. [Google Scholar]
  • [39].Fukuzumi M, Shinomiya H, Shimizu Y et al. Endotoxin-induced enhancement of glucose influx into murine peritoneal macrophages via GLUT1. Infect Immun 1996; 64:108–112. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [40].Silvera SS, Aidi HE, Rudd JH et al. Multimodality imaging of atherosclerotic plaque activity and composition using FDG-PET/CT and MRI in carotid and femoral arteries. Atherosclerosis 2009; 207:139–143. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [41].Masteling MG, Zeebregts CJ, Tio RA et al. High-resolution imaging of human atherosclerotic carotid plaques with micro 18F-FDG PET scanning exploring plaque vulnerability. J Nucl Cardiol 2011; 18:1066–1075. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [42].Nishizawa T, Kanter JE, Kramer F et al. Testing the role of myeloid cell glucose flux in inflammation and atherosclerosis. Cell Rep 2014; 7:356–365. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [43].Sarrazy V, Viaud M, Westerterp M et al. Disruption of Glut1 in Hematopoietic Stem Cells Prevents Myelopoiesis and Enhanced Glucose Flux in Atheromatous Plaques of ApoE(−/−) Mice. Circ Res 2016; 118:1062–1077. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [44].Guillermier C, Doherty SP, Whitney AG et al. Imaging mass spectrometry reveals heterogeneity of proliferation and metabolism in atherosclerosis. JCI Insight 2019; 4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [45].Tomas L, Edsfeldt A, Mollet IG et al. Altered metabolism distinguishes high-risk from stable carotid atherosclerotic plaques. Eur Heart J 2018; 39:2301–2310. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [46].van Leent MMT, Beldman TJ, Toner YC et al. Prosaposin mediates inflammation in atherosclerosis. Sci Transl Med 2021; 13. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [47].Newling M, Sritharan L, van der Ham AJ et al. C-Reactive Protein Promotes Inflammation through Fc gamma R-Induced Glycolytic Reprogramming of Human Macrophages. Journal of Immunology 2019; 203:225–235. [DOI] [PubMed] [Google Scholar]
  • [48].Morioka S, Perry JSA, Raymond MH et al. Efferocytosis induces a novel SLC program to promote glucose uptake and lactate release. Nature 2018; 563:714–718. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [49].Freemerman AJ, Zhao L, Pingili AK et al. Myeloid Slc2a1-Deficient Murine Model Revealed Macrophage Activation and Metabolic Phenotype Are Fueled by GLUT1. J Immunol 2019; 202:1265–1286. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [50].Weinstock A, Rahman K, Yaacov O et al. Wnt signaling enhances macrophage responses to IL-4 and promotes resolution of atherosclerosis. Elife 2021; 10. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This article shows that WNT-deficiency enhanced sensitivity to anti-inflammatory signals within plaque macrophages, which is sufficient to accelerate atherosclerosis resolution.
  • [51].King VL, Szilvassy SJ, Daugherty A. Interleukin-4 deficiency decreases atherosclerotic lesion formation in a site-specific manner in female LDL receptor−/− mice. Arterioscler Thromb Vasc Biol 2002; 22:456–461. [DOI] [PubMed] [Google Scholar]
  • [52].Vats D, Mukundan L, Odegaard JI et al. Oxidative metabolism and PGC-1 beta attenuate macrophage-mediated inflammation. Cell Metab 2006; 4:255–255. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [53].Zhang S, Weinberg S, DeBerge M et al. Efferocytosis Fuels Requirements of Fatty Acid Oxidation and the Electron Transport Chain to Polarize Macrophages for Tissue Repair. Cell Metab 2019; 29:443-+. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [54].Baardman J, Verberk SGS, van der Velden S et al. Macrophage ATP citrate lyase deficiency stabilizes atherosclerotic plaques. Nat Commun 2020; 11:6296. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [55].Hansson GK, Libby P. The immune response in atherosclerosis: a double-edged sword. Nat Rev Immunol 2006; 6:508–519. [DOI] [PubMed] [Google Scholar]
  • [56].Lutgens E, de Muinck ED, Kitslaar PJ et al. Biphasic pattern of cell turnover characterizes the progression from fatty streaks to ruptured human atherosclerotic plaques. Cardiovasc Res 1999; 41:473–479. [DOI] [PubMed] [Google Scholar]
  • [57].Gordon D, Reidy MA, Benditt EP, Schwartz SM. Cell proliferation in human coronary arteries. Proc Natl Acad Sci U S A 1990; 87:4600–4604. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [58].Lessner SM, Prado HL, Waller EK, Galis ZS. Atherosclerotic lesions grow through recruitment and proliferation of circulating monocytes in a murine model. Am J Pathol 2002; 160:2145–2155. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [59].Robbins CS, Hilgendorf I, Weber GF et al. Local proliferation dominates lesional macrophage accumulation in atherosclerosis. Nat Med 2013; 19:1166–1172. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [60].Kuo CL, Murphy AJ, Sayers S et al. Cdkn2a is an atherosclerosis modifier locus that regulates monocyte/macrophage proliferation. Arterioscler Thromb Vasc Biol 2011; 31:2483–2492. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [61].Yamada S, Senokuchi T, Matsumura T et al. Inhibition of Local Macrophage Growth Ameliorates Focal Inflammation and Suppresses Atherosclerosis. Arterioscler Thromb Vasc Biol 2018; 38:994–1006. [DOI] [PubMed] [Google Scholar]
  • [62].Zeynalova S, Bucksch K, Scholz M et al. Monocyte subtype counts are associated with 10-year cardiovascular disease risk as determined by the Framingham Risk Score among subjects of the LIFE-Adult study. PLoS One 2021; 16:e0247480. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [63].Swirski FK, Libby P, Aikawa E et al. Ly-6Chi monocytes dominate hypercholesterolemia-associated monocytosis and give rise to macrophages in atheromata. J Clin Invest 2007; 117:195–205. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [64].Williams JW, Martel C, Potteaux S et al. Limited Macrophage Positional Dynamics in Progressing or Regressing Murine Atherosclerotic Plaques-Brief Report. Arterioscler Thromb Vasc Biol 2018; 38:1702–1710. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This article defines aorta intima resident macrophages (MacAIR) in the steady state and describes gene expression programs associated with residency in the artery intima in diseased and non-diseased settings. Fate mapping experiments also show that local macropahge proliferation was insufficient to support MacAIR presence into later stages of disease.
  • [65].Andres V, Pello OM, Silvestre-Roig C. Macrophage proliferation and apoptosis in atherosclerosis. Curr Opin Lipidol 2012; 23:429–438. [DOI] [PubMed] [Google Scholar]
  • [66].Tang J, Frey JM, Wilson CL et al. Neutrophil and Macrophage Cell Surface Colony-Stimulating Factor 1 Shed by ADAM17 Drives Mouse Macrophage Proliferation in Acute and Chronic Inflammation. Mol Cell Biol 2018; 38. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [67].Rajavashisth T, Qiao JH, Tripathi S et al. Heterozygous osteopetrotic (op) mutation reduces atherosclerosis in LDL receptor- deficient mice. J Clin Invest 1998; 101:2702–2710. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [68].Qiao JH, Tripathi J, Mishra NK et al. Role of macrophage colony-stimulating factor in atherosclerosis: studies of osteopetrotic mice. Am J Pathol 1997; 150:1687–1699. [PMC free article] [PubMed] [Google Scholar]
  • [69].Rajavashisth TB, Andalibi A, Territo MC et al. Induction of endothelial cell expression of granulocyte and macrophage colony-stimulating factors by modified low-density lipoproteins. Nature 1990; 344:254–257. [DOI] [PubMed] [Google Scholar]
  • [70].Shaposhnik Z, Wang X, Lusis AJ. Arterial colony stimulating factor-1 influences atherosclerotic lesions by regulating monocyte migration and apoptosis. J Lipid Res 2010; 51:1962–1970. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [71].Sinha SK, Miikeda A, Fouladian Z et al. Local M-CSF (Macrophage Colony-Stimulating Factor) Expression Regulates Macrophage Proliferation and Apoptosis in Atherosclerosis. Arterioscler Thromb Vasc Biol 2021; 41:220–233. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [72].Jaiswal S, Natarajan P, Silver AJ et al. Clonal Hematopoiesis and Risk of Atherosclerotic Cardiovascular Disease. N Engl J Med 2017; 377:111–121. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [73].Jung C, Evans MA, Walsh K. Genetics of age-related clonal hematopoiesis and atherosclerotic cardiovascular disease. Curr Opin Cardiol 2020; 35:219–225. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [74].Fuster JJ, MacLauchlan S, Zuriaga MA et al. Clonal hematopoiesis associated with TET2 deficiency accelerates atherosclerosis development in mice. Science 2017; 355:842–847. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [75].Fidler TP, Xue C, Yalcinkaya M et al. The AIM2 inflammasome exacerbates atherosclerosis in clonal haematopoiesis. Nature 2021. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This article defines the role of well known clonal hematopoiesis mutation in Jak2 in regulating macrophages activation status in models of atherosclerosis. They define new associations in DNA-sensing and activation through the AIM2 inflammasome and mechanistic links to local macrophage proliferation.
  • [76].Kinlay S Low-density lipoprotein-dependent and -independent effects of cholesterol-lowering therapies on C-reactive protein: a meta-analysis. J Am Coll Cardiol 2007; 49:2003–2009. [DOI] [PubMed] [Google Scholar]
  • [77].Verschuren L, Kleemann R, Offerman EH et al. Effect of low dose atorvastatin versus diet-induced cholesterol lowering on atherosclerotic lesion progression and inflammation in apolipoprotein E*3-Leiden transgenic mice. Arterioscler Thromb Vasc Biol 2005; 25:161–167. [DOI] [PubMed] [Google Scholar]
  • [78].Jain MK, Ridker PM. Anti-inflammatory effects of statins: clinical evidence and basic mechanisms. Nat Rev Drug Discov 2005; 4:977–987. [DOI] [PubMed] [Google Scholar]
  • [79].Hardtner C, Kornemann J, Krebs K et al. Inhibition of macrophage proliferation dominates plaque regression in response to cholesterol lowering. Basic Res Cardiol 2020; 115:78. [DOI] [PMC free article] [PubMed] [Google Scholar]; *This article addressed the necessity of macrophage proliferation during atherosclerosis regresson models, defining a necessity for SR-A1 and local macrophage proliferation for normal resolution kinetics.
  • [80].Boada C, Zinger A, Tsao C et al. Rapamycin-Loaded Biomimetic Nanoparticles Reverse Vascular Inflammation. Circ Res 2020; 126:25–37. [DOI] [PubMed] [Google Scholar]

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