Leading Edge
Review
Atherosclerosis: Recent developments
Johan L.M. Bjo¨ rkegren1,2,* and Aldons J. Lusis3,*
1Department of Genetics and Genomic Sciences, Division of Cardiology, Department of Medicine, Icahn School of Medicine at Mount Sinai,
New York, NY 10029, USA
2Department of Medicine, Huddinge, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden
3Department of Medicine/Division of Cardiology, Department of Microbiology, Immunology and Molecular Genetics, Department of Human
Genetics, A2-237 Center for the Health Sciences, University of California, Los Angeles, Los Angeles, CA USA
*Correspondence: johan.bjorkegren@mssm.edu (J.L.M.B.), jlusis@mednet.ucla.edu (A.J.L.)
https://doi.org/10.1016/j.cell.2022.04.004
SUMMARY
Atherosclerosis is an inﬂammatory disease of the large arteries that is the major cause of cardiovascular disease
(CVD) and stroke. Here, we review the current understanding of the molecular, cellular, genetic, and
environmental contributions to atherosclerosis, from both individual pathway and systems perspectives.
We place an emphasis on recent developments, some of which have yielded unexpected biology, including
previously unknown heterogeneity of inﬂammatory and smooth muscle cells in atherosclerotic lesions, roles
for senescence and clonal hematopoiesis, and links to the gut microbiome.
INTRODUCTION
Atherosclerosis or coronary artery disease (CAD) is the most
common form of cardiovascular disease (CVD) where the main
component is lipid accumulation and inﬂammation of the large
arteries, which eventually may lead to its clinical complications,
myocardial infarction (MI) and stroke. As a disease of slow progression,
clinically signiﬁcant atherosclerosis occurs primarily
in older individuals and, despite declining incidence in some
countries, remains the leading cause of mortality worldwide.
Atherosclerotic lesions are characterized by a lifetime long accumulation
and transformation of lipids, inﬂammatory cells, smooth
muscle cells, and necrotic cell debris in the intimal space underneath
a monolayer of endothelial cells (ECs) that line the interior
vessel wall. Typically, lesion growth can reduce blood ﬂow in the
lumen by >50% and may cause angina particularly during
exercise or stress. Lesions can become unstable and rupture,
particularly if they have fatty and inﬂammatory composition. If
this occurs in the coronary arteries, it can result in a local clot
that may completely obstruct the blood ﬂow to cause an MI.
Alternatively, the clot can escape the heart and travel to the brain
where it may cause a stroke.
Recently, there have been major advances in the understanding
of molecular and cellular interactions in atherosclerosis.
These include previously unknown cellular heterogeneity in
atherosclerotic lesions revealed through single-cell RNA
sequencing (scRNA-seq). There has also been recognition that
processes that occur during aging, such as senescence and
clonal hematopoiesis, likely play an important role. Also, the links
between the gut microbiome and atherosclerosis are becoming
increasingly clear. Substantial progress continues to be made in
the systems understanding of the interplay of genetic and environmental
risk factors of atherosclerosis and its relationship to
cardiometabolic traits. Finally, there have been exciting advances
in the diagnostic and therapeutic arena.
This review provides an overview of the disease with an
emphasis on recent developments. We ﬁrst discuss the growth
of atherosclerotic lesions, from initiation to advanced lesions
and aging. This is followed by a discussion of genetic approaches
and the major genetic and environmental risk factors
for the disease. We conclude with a discussion of clinical aspects
and future directions. Due to limitations in the length of
the review, we largely refer to recent reviews rather than original
articles except for recent major events.
LESION INITIATION AND GROWTH
The vessel wall consists of a monolayer of EC that border the
luminal blood ﬂow. Underlying this is a largely acellular layer consisting
of glycosaminoglycans and collagen, termed the ‘‘intima.’’
Next are layers of smooth muscle cells (SMC), termed
the ‘‘media,’’ and ﬁnally, a ﬁbrous layer termed the ‘‘adventitia.’’
Atherosclerosis is initiated in large part by the accumulation of
certain plasma lipoproteins, including low-density lipoproteins
(LDLs) and remnants of triglyceride-rich lipoproteins, in the
intimal region of the vessel. This results in an activation of the
overlying EC by a still poorly understood mechanism but likely
involving the generation of proinﬂammatory oxidized lipids.
Blood monocytes then bind to endothelial adhesion molecules,
enter the intima, and differentiate to macrophages. These, in
turn, can take up the lipoproteins, giving rise to cholesterol ester
engorged ‘‘foam cells’’ (Figure 1). In this section, we discuss the
cell types and molecular interactions involved in lesion initiation.
Endothelial cells (ECs)
As outlined in Figure 1, ECs form a single cell layer connected by
tight junctions separating the blood from the vessel wall.
Under conditions of disturbed blood ﬂow, the ECs and their tight
junctions become ‘‘leaky,’’ which promotes the uptake of
plasma LDL and TG-rich lipoproteins either by trans-endothelial
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This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
transport or diffusion at the cell-cell junctions (Zhang et al.,
2018). The subsequent activation of the ECs occurs in response
to oxidation of lipoprotein lipids and other inﬂammatory mediators,
resulting in the expression of P-selectin, E-selectin,
VACM1, and ICAM1 that promotes the adhesion of monocytes,
other leukocytes, and chemotactic factors such as CCR2 and
CCR5 (Gimbrone and Garcia-Cardena, 2016). Disturbed blood
ﬂow can also trigger erosion, an alternative mechanism of EC
dysfunction. It is caused by the TLR2-dependent EC apoptosis
and secretion of IL-8, leading to neutrophil recruitment, activation,
and release of neutrophil extracellular traps, which aggravate
the injury of the EC layer and may lead to thrombus formation
(Luo et al., 2021).
Shear stress and lipid accumulation
Atherosclerosis tends to occur in regions of arteries such as bifurcations
that exhibit turbulent blood ﬂow as compared with laminar
ﬂow. Turbulent ﬂow changes the cellular alignment of ECs and increases
their permeability to large molecules. Multiple pathways
underlying this response have been identiﬁed, including BMPTGFb,
WNT, and Notch (Souilhol et al., 2020). As a result of the
increased permeability, certain lipoproteins accumulate in the
intimal region, in part by interaction with the intimal glycosaminoglycans
(Bore´n and Williams, 2016). Once trapped in this way, LDL
and triglyceride-rich remnant lipoproteins can become aggregated
and chemically modiﬁed (Figure 1).
Lipid oxidation and inﬂammation
A large body of evidence has suggested that the oxidation of
lipids in lipoproteins trapped in the vessel wall produce proinﬂammatory
species, leading to leukocyte recruitment and
inﬂammation. For example, treatment of EC with oxidized
phospholipids or oxidized LDL induces the expression of adheFigure
1. Development of fatty streak
lesions
Lipoproteins enter the intima at of sites of shear
stress. The lipoproteins then aggregate and
become oxidized and otherwise modiﬁed, resulting
in the activation of the overlying EC to express
adhesion and chemotactic molecules for monocytes.
The monocytes enter the intima, differentiate
to macrophages, and take up modiﬁed
lipoproteins to give rise to foam cells. The size of
the intima is exaggerated in the ﬁgure.
sion molecules and chemotactic factors
(Figure 1). Despite this, direct proof for
this hypothesis has been difﬁcult to
obtain, and the fact that antioxidant drugs
have failed to reduce atherosclerosis has
caused some to conclude that alternative
mechanisms, such as aggregated LDL,
are the triggers for inﬂammation (Libby,
2021). However, studies showing that
transgenic expression of a natural antibody
to oxidized phospholipids suppresses
lesions in mice argues in favor
of the lipid oxidation hypothesis in atherosclerosis
(Que et al., 2018). Lipoproteins
can also undergo oxidation in the lysosomes of macrophages,
resulting in the release of lipid oxidation products. Inhibition of
such oxidation by the antioxidant cysteamine blocked and
even reversed lesion development in LDL receptor null mice (Ahmad
et al., 2021). The lipid oxidation product octanol was
recently shown to bind to olfactory receptor 2 in vascular macrophages,
activating the NLRP3 inﬂammasome and inducing interleukin
1b. Targeting the receptor reduced atherosclerosis and
boosting octanol levels increased it (Orecchioni et al., 2022).
Studies have also suggested that lipid oxidation in the intestine
may contribute to systemic inﬂammation and atherosclerosis
(Mukherjee et al., 2022).
Monocytes, macrophages, and foam cells
Monocytes are recruited to the vessel wall in response
to the expression adhesion molecules and chemotactic proteins
by EC. Upon entering the intimal region, these differentiate into
macrophages in response to locally produced M-CSF and other
cytokines (Figure 1). Mouse studies suggest that the abundance
of macrophages in early lesions is determined by recruitment
but that in more advanced lesions it results largely from macrophage
proliferation (Robbins et al., 2013). Macrophages
contribute very importantly to lesion progression as evidenced
by the fact that M-CSF null mice on a hypercholesterolemic background
are almost entirely resistant to lesion development. Native
LDL is not taken up by macrophages but must ﬁrst be modiﬁed by
oxidation or aggregation. Lesional macrophages can take up such
‘‘modiﬁed’’ intimal lipoproteins through scavenger receptors or
phagocytosis of aggregated lipoproteins to give rise to cholesterol
engorged macrophages or ‘‘foam cells.’’ Although foam cells can
efﬂux cholesterol using the transporters ABCA1 and ABCG1, they
frequently undergo apoptosis or necrosis to give rise to a growing
‘‘necrotic core’’ consisting of cholesterol esters, cholesterol
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crystals, and cell debris that increases the likelihood of lesion
rupture. Macrophages also undergo metabolic transitions during
the various stages of atherosclerosis that can, in turn, affect their
functions (Tabas and Bornfeldt, 2020).
ADVANCED ATHEROSCLEROTIC LESIONS
Following initiation, lipids and foam cells continue to accumulate,
and other leukocytes, particularly T cells, enter the lesion and
interact with macrophages. Over time, the foam cells die to
give rise to necrotic cores consisting of cell debris and cholesterol.
Also, SMC transform from a contractile to a proliferate state
and migrate to the region underlying the EC to form a ‘‘ﬁbrous
cap’’ that protects the lesion from rupture. SMC can also differentiate
into macrophage-like cells that give rise to foam cells and
bone-like cells that deposit calcium phosphate mineral. Although
lesions can grow sufﬁciently large to impede the ﬂow of blood,
the most clinically signiﬁcant event is a MI resulting from the formation
of a clot triggered by lesion rupture or endothelial erosion
(Figures 2 and 3). In this section, we discuss the roles of SMC and
lymphocytes in lesion progression as well as processes inﬂuencing
inﬂammation, calciﬁcation, and lesion stability. Finally,
we discuss the use of single-cell sequencing to examine cellular
heterogeneity in lesions.
Smooth muscle cells
During lesion growth, SMC in the media transform from a contractile
to a proliferative state and migrate into the intima. Over
time, the intimal SMC secrete an extracellular matrix consisting
largely of collagen to give rise to a protective (against rupture)
ﬁbrous cap (Figure 2). Relatively few migration-competent
SMC enter the intima and then undergo clonal expansion followed
by redifferentiation into contractile SMC. Lineage tracing
studies have shown that these cells can undergo trans-differentiation
into macrophage-like and osteochondrogenic descendants
(Alencar et al., 2020; Pan et al., 2020). The macrophageFigure
2. Development of atherosclerosis
lesions
Macrophages proliferate in response to M-CSF,
and foam cells are engulfed by macrophages, a
process known as efferocytosis. SMC transform
to a proliferative state, migrate to the endothelial
region, and secrete collagen to give rise to a
‘‘ﬁbrous cap.’’ SMC can also transform into macrophage-like
cells that take up lipid to give rise to
foam cells. T and B cells also enter the lesion and
interact with other cell types to promote or retard
lesion development.
like SMC can take up lipid to give rise to
foam cells that can undergo apoptosis
and suppressed efferocytosis to give
rise to secondary necrosis and inﬂammation.
SMC can also acquire cholesterol
from nearby macrophage foam cells by
a recently described pathway involving
membrane-derived particles (He et al.,
2018). It has been estimated that in animal
models, SMC-derived foam cells could account for as much as
50% of lesional foam cells (Basatemur et al., 2019). SMC also
produce macrophage colony stimulation factor (M-CSF) that
drives the proliferation of macrophages in lesions. The osteochondrocytes
can give rise to calciﬁcation granules that can subsequently
coalesce to produce calcium nodules (Basatemur
et al., 2019).
T lymphocytes
Adaptive as well as innate immunity drives the chronic inﬂammation
of atherosclerosis, and several classes of T cells impact disease
progression (Roy et al., 2022). T cells are present at all
stages of atherosclerosis, and their inﬁltration is mediated by
chemokine receptors (CCR5 and CXCR6) and ligands (CCL5
and CXCL16). T cells can activate as well as suppress immune
activation and can help B cells to produce antibodies. Most
abundant in lesions are TH1 interferon g secreting cells, promoting
plaque growth and instability. Treg cells express anti-inﬂammatory
cytokines (IL-10 and TGFb), promote macrophage
efferocytosis, and show a negative correlation with atherosclerosis.
TH2 cells express IL-5 and IL-13, both of which are protective.
T cells as well as B cells are activated by antigens present in
lesions, and dendritic cells that have acquired atherosclerosis
antigens can leave the lesion and stimulate responses elsewhere
(Proto et al., 2018; Roy et al., 2022).
B lymphocytes
B cells participate in local and systemic immune responses that
contribute to the chronic inﬂammation in atherosclerosis
(Sage et al., 2019). They are derived from bone marrow progenitors
and mature in the spleen. Each B cell produces a unique B
cell receptor that recognizes a speciﬁc antigen, triggering
transformation into antibody producing plasma cells. Both antiatherogenic
and proatherogenic B cell subsets have been identiﬁed.
Some B cells produce ‘‘natural’’ antibodies that bind oxidized
epitopes present in oxidized lipoproteins and necrotic debris,
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thereby inhibiting inﬂammation. Antibodies to a number of antigens,
including LDL, oxidized LDL, apolipoprotein B (the major
protein of LDL), and pathogens such as cytomegalovirus, are
associated with atherosclerosis. Recent studies indicate that
elevated levels of the IgE immunoglobulins, which can stimulate
proinﬂammatory responses in macrophages, are signiﬁcantly
associated with increased atherosclerosis. B cell autoimmunity
can also contribute to atherosclerosis; for example, some mouse
models of lupus show increased atherosclerosis (Sage
et al., 2019).
Hematopoiesis
Substantial evidence indicates that increased hematopoiesis,
the process involved in replenishing blood cells, promotes
atherosclerosis. Hematopoiesis and circulating leukocytes are
increased in response to smoking, stress, and a poor diet and
are reduced by exercise and elevated high-density lipoproteins
(HDL) levels. Recent studies in mice and humans support a
causal relationship between increased hematopoiesis, clonal
hematopoiesis, and atherosclerosis (Heyde et al., 2021). Hyperlipidemia
appears to promote hematopoiesis in part by its effects
on cholesterol efﬂux pathways and is inhibited by the functions of
ABCA1, ABCG1, and HDL (Schloss et al., 2020). SREBP2 and
Notch signaling also appear to be involved in the regulation of
hematopoiesis (Gu et al., 2019).
Efferocytosis and resolution
Efferocytosis is the process by which apoptotic cells are cleared,
thereby preventing secondary necrosis and inﬂammation. It is
mediated primarily by macrophages that engulf the dying cells
and is important in reducing the growth of necrotic cores
(Figure 2) (Doran et al., 2020). Resolution is an active process
aimed at the restoration of tissue integrity and function during
Figure 3. Advanced atherosclerotic lesions
Foam cells and other cells die to give rise to
cholesterol-rich necrotic cores. Calciﬁcation
frequently occurs in the intima or media. Lesions
can rupture or EC can erode to stimulate the formation
of a thrombus, possibly resulting in an MI or
stroke.
inﬂammation. It involves a functional
switch from proinﬂammatory to antiinﬂammatory
macrophages and is mediated
by certain lipids (known as
resolvins and lipoxins), proteins, and nitric
oxide (Ba¨ ck et al., 2019). Recent studies
indicate that efferocytosis can promote
noninﬂammatory macrophage proliferation
and contribute to tissue resolution
(Gerlach et al., 2021).
Calciﬁcation
Coronary calciﬁcation occurs with the
development of advanced lesions and
can be assessed by various imaging modalities.
It can occur in both the intimal
and medial layers and may be associated with increased plaque
stability. It begins with very small matrix vesicles that originate
from apoptotic SMCs and macrophages. These coalesce into
larger masses over time, generally near the necrotic core, and
eventually form calciﬁed sheets (Figure 3). Bone-related proteins,
such as BMP-1, BMP-4, and matrix GLA protein, are often
expressed in such regions (Basatemur et al., 2019; Mori
et al., 2018).
Fibrous cap
Advanced lesions contain a layer of ﬁbrous connective tissue,
termed the ﬁbrous cap, that lies next to the EC layer. It is
composed of collagen, elastin, and bundles of SMC as well as
macrophages and lymphocytes. It was previously thought that
nearly all the cells that produce extracellular matrix in the cap
are derived from SMC. Recent experiments, however, suggest
that a signiﬁcant fraction of these cells are derived from EC or
macrophages that have undergone endothelial-to-mesenchymal
transition or macrophage-to-mesenchymal transition
(Newman et al., 2021).
Lesion stability
A MI usually occurs when a lesion ruptures, triggering the formation
of a blood clot (Figure 3). ‘‘Vulnerable plaques’’ are more a
function of their composition than size. Fibrous lesions with thick
ﬁbrous caps tend to be more stable than fatty, inﬂammatory lesions.
A number of factors have been identiﬁed that affect lesion
stability, including SMC and EC cell senescence. Macrophages
appear to contribute to plaque destabilization by amplifying
inﬂammation and producing proteases that attack the ﬁbrous
cap. MI can also occur as a result of endothelial erosion
(Figure 3). Neutrophils, although rare in lesions, appear to promote
endothelial erosion via neutrophil traps and secretion of
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matrix metalloproteinases (Libby, 2021). A recent study showed
that oxidized lipids promote the formation of neutrophil extracellular
traps and accelerate carotid artery thrombosis in a mouse
model (Dou et al., 2021).
Cell heterogeneity and plasticity
Historically, a major challenge to atherosclerosis researchers
has been the heterogeneity of arterial wall cell types involved in
this process. In recent single-cell RNA-seq studies, it has
become increasingly clear that these cellular phenotypes are
highly plastic, transforming along with the progression of atherosclerosis.
For instance, arterial wall SMC-derived cells were
shown to exhibit substantial phenotypic plasticity, transforming
into osteogenic-like cells during late-stage atherosclerosis plaque
formation in both mice and humans (Alencar et al., 2020).
Similarly, it was demonstrated that SMCs transitioned to an intermediate
cell state with multipotent differentiation capacity,
including proatherogenic macrophage-like, and ﬁbrochondrocyte-like
cells, and, athero-protectively, reverting back to the
original SMC phenotype. Retinoic acid signaling associated
with symptomatic atherosclerosis was shown to regulate the
state of intermediate SMCs in humans (Pan et al., 2020). In
another study including human coronary arteries, TCF21, a
CAD risk gene identiﬁed by genome-wide association studies
(GWAS), was shown to regulate SMC plasticity in a CAD-protective
role (Wirka et al., 2019).
Besides SMCs, the single-celllandscape of immune cells and in
part EC in atherosclerosis has recently been studied both in humans(Fernandezet
al., 2019) andmice (Winkels et al., 2018). Early
on, 13 distinct myeloid cell populations were identiﬁed in mouse
aortas where resident-like macrophages were found in both
healthy and atherosclerotic aortas, whereas monocytes, monocyte-derived
dendritic cells, and 2 populations of macrophages
were almost exclusively detectable in atherosclerotic aortas,
comprising inﬂammatory macrophages expressing TREM2 (Cochain
et al., 2018). These results were largely conﬁrmed in human
carotid plaques and additionally provided evidence for endothelial-mesenchymal
transition and a decline in CD4+ and CD8+
cell cytotoxicity (Depuydt et al., 2020). Somewhat in contrast, it
was shown that carotid plaques from symptomatic patients
were characterized by a distinct subset of CD4+ T cells that
were activated and differentiated (Fernandez et al., 2019).
More recently, single-nucleus chromatin accessibility proﬁling
(i.e., ‘‘snATAC-seq’’) of human atherosclerotic lesions was used
to investigate cell type-speciﬁc patterns of cis-regulatory elements
and to understand how transcription factors establishing
cell identity may interact with genetic risk variants identiﬁed by
GWAS of CAD. The authors found that CAD-associated genetic
variants were particularly enriched in endothelial and SMC-speciﬁc
open chromatin. Then, by performing genome-wide experimental
ﬁne-mapping of these CAD variants using epigenetic
quantitative trait loci analysis in primary human aortic EC
and self-transcribing active regulatory region sequencing
(STARR-seq) in SMC, they were able to identify potential causal
single-nucleotide polymorphisms (SNPs) and associated target
genes for over 30 established CAD loci (O¨ rd et al., 2021). Using
a similar approach, the CAD GWAS candidate gene, ATF3,
was recently identiﬁed as a repressor of SMC transitioning, promoting
vascular inﬂammation (Wang et al., 2021).
ANIMAL MODELS
Most of the biological understanding of mechanisms underlying
CAD derives from studies of animal models. Historically, the primary
animal models for atherosclerosis were rabbits and hamsters,
as those develop signiﬁcant atherosclerotic lesions when
placed on high-fat, high-cholesterol diets. However, because
of their much greater utility for genetics studies, mice have
become the most widely used models for atherosclerosis and
its risk factors. In particular, engineered mice exhibiting high
LDL/VLDL-cholesterol levels (such as LDL receptor deﬁcient or
apolipoprotein E deﬁcient mice) are primarily employed for validation
of human candidate genes, studies of environmental interactions,
drug studies, and gene discovery (Daugherty et al.,
2017). Recently, overexpression of PCSK9 using an adenoassociated
virus vector has become widely used since it avoids the
necessity of breeding engineered genes onto a hyperlipidemic
background (Goettsch et al., 2016). At present, nearly 1,000
genes have been studied in such mouse models using gene targeting,
overexpression, or drug treatments. Different strains of
mice exhibit over 100-fold variation in atherosclerosis when
hyperlipidemia is induced by genetic perturbation, and this variation
has also been exploited to identify genes and pathways
(von Scheidt et al., 2017).
The development of atherosclerotic lesions in hyperlipidemic
mice is similar to that observed in pathologic studies of the
human disease, including lipid accumulation in the intima, monocyte
recruitment, and foam cell formation, followed by SMC proliferation
and the formation of a ﬁbrous cap. In addition to monocytes,
T lymphocytes are recruited to the lesions, and in certain
genetic backgrounds, intimal and medial calciﬁcation occurs.
However, the mouse models rarely show evidence of lesion
rupture, a particularly signiﬁcant point since about three quarters
of heart attacks result from plaque rupture followed by thrombosis
(von Scheidt et al., 2017). Other, specialized hyperlipidemic
models, such as one involving dual ligation of the right
coronary artery, lead to locally predeﬁned plaque instability
and rupture with characteristics of human unstable plaques
(Noonan et al., 2022). Apart from pathology, the mouse models
show consistency with atherosclerosis risk factors such as
LDL levels, HDL levels, hypertension, smoking, diabetes, renal
failure, arthritis, lupus, aging, distress, air pollution, the metabolite
TMAO derived from gut bacteria, and physical activity. Moreover,
an analysis of the pathways contributing to atherosclerosis
based on human GWAS genes (see below) and mouse engineered
genes shows a considerable overlap (von Scheidt
et al., 2017).
AGING AND ATHEROSCLEROSIS
Atherosclerosis is largely a disease of the elderly, with most MI or
strokes occurring in individuals over 55 years of age (Tyrrell and
Goldstein, 2021). There are, however, some early onset forms,
such as familial hypercholesterolemia (FH) or very rare disorders
such as Hutchinson-Gilford progeria. In this section, we discuss
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three relatively recently discovered processes in aging that
contribute to atherosclerosis.
Clonal hematopoiesis and leukocytosis
Circulating blood cells are derived from hundreds of hematopoietic
stem cells (HSC), and thus, a somatic mutation in a stem cell
will generally be found in a tiny fraction of blood cells. ‘‘Clonal hematopoiesis’’
refers to the expansion of an HSC in response to a
mutation that gives rise to blood cell ‘‘clones’’ abundant in the
circulation (Bick et al., 2020). Clonal hematopoiesis, relatively
common in older individuals, is strongly associated with atherosclerosis
(Jaiswal et al., 2017). One likely explanation for the
association is increased hematopoiesis, which will statistically
increase the likelihood of developing mutations impacting HSC
proliferation, since mutations tend to occur during replication
(Heyde et al., 2021). A second explanation is that the clones,
particularly monocytes and neutrophils, are more proinﬂammatory,
promoting lesion growth. Experimental evidence in mice
suggests that certain common clonal mutations contribute to
increased inﬂammation and atherosclerosis. For example, the
TET2 clonal mutation increases macrophage IL-6 expression (Fidler
et al., 2021; Tyrrell and Goldstein, 2021) (Figure 4).
Senescence
Cellular senescence of EC and SMC as well as macrophages has
been implicated in lesion growth, inﬂammation, and stability
(Grootaert et al., 2021; Kotla et al., 2019). Senescence can be
triggered by oxidative stress, DNA damage, and replicative
exhaustion. It exerts both beneﬁcial and detrimental effects. It
protects against cancer and promotes tissue repair, but senescent
cells in aging tissues have been causally linked to degenerFigure
4. Aging and atherosclerosis
The ﬁgure depictsthree pro-atherogenic events that
often occur with aging: the development of clonal
hematopoiesis, senescence, and immunoaging.
Clonal hematopoiesis can be viewed as a vicious
cycle in which hematopoiesis is stimulated by
certain atherosclerosis risk factors which, along with
aging, increase the chance of somatic mutations
that lead to stem cell clones with a proliferative
advantage, The increased hematopoiesis results
in leukocytosis and the clones that emerge
may exhibit pro-inﬂammatory properies, thereby
enhancing lesion growth. Evidence for cellular
senescence has been observed for a number of cell
types in atherosclerotic lesions in mice. Such cells
release a variety of cytokines and immune modulators
(senescence-associated secreting proteins,
SASP) that act inﬂame or kill nearby cells. The
chronic inﬂammation that often accompanies aging,
known as immunoaging is associated with M1
macrophages that express pro-inﬂammatory cytokines
and the ectoenzyme CD38 that can degrade
NAD+
are involved in immunoaging.
ation and dysfunction. Senescent cells
act on the surrounding cells by secreting
a variety of inﬂammatory cytokines, immune
modulators, and proteases, collectively
termed the senescence-associated
secretory phenotype (SASP) (Figure 4).
Senescent cells can be eliminated pharmacologically
using ‘‘senolytic’’ drugs
such as ABT263 that target BCL-2 family members. In atherosclerosis,
senescent cells contribute to the degeneration of the
ﬁbrous cap, important in preventing plaque rupture, and senolytic
clearance restored SMC numbers and cap thickness (Childs
et al., 2021). SIRT6, a member of the sirtuin family of class III histone
deacetylases protects SMC in lesions from senescence
through inhibition of telomere damage (Grootaert et al., 2021).
Inﬂammaging
Chronic, low-grade inﬂammation frequently develops with
advanced age in the absence of infection and contributes to
age-related pathologies such as atherosclerosis. It can have
profound effects on systemic functions such as lipid and glucose
metabolism. Among the features of aging are increased macrophage
abundance and altered polarization. Recent studies suggest
that M1-like macrophages, in addition to senescent cells,
may be a major source of proinﬂammatory cytokines such as
IL-1beta, IL-6, and TNF and increased activation of NLRP3 during
aging (Covarrubias et al., 2021). NAD+
levels decline with
aging, and a number of recent studies have shown that NAD+
supplements that restore NAD+
levels are protective of metabolic
and cardiovascular dysfunctions in aging. One of the mechanisms
leading to reduced levels NAD+
levels is the enhanced
expression in proinﬂammatory macrophages of CD38, an ectoenzyme
exposed by MI-like macrophages that hydrolyzes
NAD+
(Abdellatif et al., 2021) (Figure 4).
GENETICS OF ATHEROSCLEROSIS
It has been said that ‘‘genetics is to biology as mathematics is to
physics,’’ and genetic studies have proven key to understanding
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atherosclerosis. A substantial fraction of atherosclerosis, about
40%, can be attributed to genetic variations. Genetic studies
of rare Mendelian disorders, such as FH and, more recently,
PCSK9 mutations, have revealed novel mechanisms or have
led to important therapeutic advances. Recent exome
sequencing studies of large numbers of individuals have the potential
to identify additional rare variants with large effect sizes
for atherosclerosis and related traits (Backman et al., 2021).
However, the vast majority of the heritable component consists
of the combined effects of many genes, each contributing a
small fraction to overall susceptibility (Figure 5). Although such
variants individually contribute a small fraction of risk, they
have substantial effects acting jointly to regulate may downstream
genes that are linked in biologic networks. In this section,
we review studies of common genetic variations, including sex
differences, that contribute to the common forms of atherosclerosis
and systems genetics approaches that integrate molecular
and clinical traits.
Common genetic variations
GWAS of CAD have been critical in identifying loci harboring
genes that contribute to common, complex forms of the disease.
As of this writing, over 200 loci have been identiﬁed for CAD using
very large cohorts and meta-analyses, including
CARDIOGRAM and UK BIOBANK that are primarily of European
ancestry as well as a large Japanese cohort (Erdmann et al.,
2018; Koyama et al., 2020) (Figure 5). Together, however, these
loci explain less than half of the heritable component of disease,
indicating that many additional genes remain to be identiﬁed.
Although some variants with large effect sizes (ODDs ratios in
the range of 2) have been identiﬁed, most loci have very modest
effects and are not individually useful for risk assessment. The
most signiﬁcant common genetic variant affecting atherosclerosis
regulates the expression of a long noncoding RNA termed
ANRIL. Many long noncoding RNAs and microRNAs have now
been identiﬁed that inﬂuence processes relevant to atherosclerosis
(Pierce and Feinberg, 2020). A large fraction of the candidate
genes at the loci associated with CVD risk have now been
validated, primarily using mouse models, and have provided
new insights into disease. Most but not all of the genes ﬁt into
several canonical pathways that provide a picture of the mechanistic
underpinnings of the disease (Figure 5). Hundreds of genetic
loci have also been identiﬁed for traits that contribute to
atherosclerosis, such as plasma lipids, hypertension, and diabetes
(Cabrera et al., 2019; Graham et al., 2021; Mahajan
et al., 2018). Most such loci do not overlap with those for CAD,
presumably because the effect sizes for CAD become too small
to detect in even very large studies. Most of the interactions in
atherosclerosis and other complex traits appear to be additive,
Figure 5. Genetic factors contributing to atherosclerosis suscepti-
bility
GWAS studies of CVD have identiﬁed about 200 loci that contain candidate
genes that ﬁt into several risk categories as indicated, although a large number
of genes do not as yet ﬁt into any known category. GWAS loci for CVD risk
factors, including plasma lipid levels (Graham et al., 2021), hypertension
(Cabrera et al., 2019), and diabetes (Mahajan et al., 2018), have each identiﬁed
hundreds of additional, largely nonoverlapping loci. Figure adapted from
Erdmann et al. (2018).
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although nonadditive interactions are hard to detect in human
studies.
Sex differences
Atherosclerosis is sexually dimorphic in incidence and complications.
Younger women are relatively protected from the disease,
but by the seventh decade, the incidence of MI surpasses that of
men (Man et al., 2020). Sex hormones play a major role, but
recent studies indicate that genes on the sex chromosomes
are also important. Thus, using data from the UK Biobank, it
was found that a certain Y chromosome haplotype, containing
the UTY gene, increases cardiovascular risk (Eales et al.,
2019). Also, studies in mice revealed signiﬁcant sex-based effects
on atherosclerosis of X chromosome genes that escape
X-inactivation (AlSiraj et al., 2019).
Systems genetics
High-throughput approaches capable of assessing global epigenetic
marks and global transcript, protein, and metabolite levels
can be incorporated into genetic studies to provide evidence of
causality and underlying mechanisms. Such approaches have
been particularly informative in mice where relevant tissues
can be accessed, the environment can be controlled, and experimental
validation is possible (Seldin et al., 2019). One of the difﬁculties
of applying a ‘‘systems genetics’’ approach in humans is
the lack of access to relevant tissues, although blood samples
have proven very informative for investigation of metabolites
and circulating miRNAs in relationship to CAD (Nikpay et al.,
2019). The GTEx consortium has performed RNA-seq on samples
of many tissues from hundreds of random donors and identiﬁed
loci regulating gene expression, known as expression
quantitative trait loci or eQTL (Kim-Hellmuth et al., 2020). The
DNA polymorphisms regulating gene expression at the loci can
then be examined in GWAS or case-control studies of atherosclerosis.
One particularly useful resource for CVD studies is
STARNET (the Stockholm-Tartu Atherosclerosis Reverse
Network Engineering Task study) , a RNA-seq resource of
atherosclerosis-relevant tissues, including tissue biopsies from
the atherosclerotic aortic wall, mammary artery, liver, skeletal
muscle, as well as abdominal and subcutaneous fat obtained
from living donors undergoing open breast surgery (Franze´ n
et al., 2016). The resource now includes 1,300 individuals with
established CAD and >400 controls veriﬁed to be CAD free. In
addition to providing detailed information about the genetics of
gene expression or protein levels, STARNET has been used to
model atherosclerosis in the form of biologic networks acting
both within and across metabolic tissues driving atherosclerosis
in the arterial wall (Koplev et al., 2022). Very large epidemiologic
studies that incorporate sequencing and multiomics analyses
are being mined for novel insights in CAD as well as other diseases.
For example, it was recently found in the UK Biobank
data that serum HDL-cholesterol and apolipoprotein AI levels
are signiﬁcantly associated with SARS-CoV-2 infection (Hilser
et al., 2021). Omics-level analyses have been performed on the
cultured EC and SMC derived from the ‘‘trimmings’’ of aortas
of donor hearts obtained from heart transplantation operations.
Cultures obtained from about 100–150 donors have been subjected
to global transcriptomic and epigenetic analyses. Thousands
of eQTL have have been identiﬁed, some of which regulate
candidates at GWAS loci or traits measured in vitro such as SMC
mobility or the tendency to calcify (Aherrahrou et al., 2020) or EC
responses to cytokines (Stolze et al., 2020).
TRADITIONAL RISK FACTORS WITH A STRONG
GENETIC COMPONENT
In this section, we review recent developments for the most signiﬁcant
traditional CVD risk factors that have large genetic components.
A number of additional risk factors, not discussed here,
include systemic inﬂammatory disorders (such as lupus and
arthritis), renal failure, increased thrombosis, obesity, and type
1 diabetes.
Lipoprotein metabolism
Plasma lipoprotein levels constitute the major risk factor for
atherosclerosis. Lipids are transported through the circulation
as complexes with proteins, termed lipoproteins. Triglyceriderich
chylomicrons and very-low-density lipoproteins (VLDL) are
secreted by the intestine and liver, respectively, and are acted
upon by lipases to produce remnants and LDL. Their primary
function is to deliver triglycerides to peripheral tissues as a
source of energy. High density lipoproteins (HDL) are also
secreted by liver and intestine and undergo a variety of transformations
in the circulation. Among the functions of HDL are to
mediate the transport of cholesterol from peripheral tissues to
liver, termed reverse cholesterol transport. Plasma lipoprotein
levels are determined by many genetic factors (nearly 1,500 individual
GWAS signals) as well as important environmental factors
(Graham et al., 2021).
LDL consists of a single major polypeptide, apolipoprotein B
(ApoB) and a cargo of cholesterol esters bounded by a phospholipid
monolayer. The levels of LDL, the major cholesterol carrying
lipoprotein in humans, have long been known to contribute to
atherosclerosis. Studies of FH, a dominant Mendelian disorder
characterized by very high levels of LDL and increased atherosclerosis,
have been particularly informative in dissecting
cholesterol metabolism. The most common forms result from
mutations of the LDL receptor, responsible of removal of LDL
from the circulation through recognition of ApoB. Recent studies
have identiﬁed a number of novel genes contributing to LDL receptor
function, the most signiﬁcant being the secreted protein,
PCSK9, that regulates the turnover of the LDL receptor (Gupta
et al., 2020).
Lp(a) is an LDL-like particle differing from LDL by the addition
of a protein termed apolipoprotein (a) that is disulﬁde bridged to
ApoB. Its levels are controlled largely by alleles of the apolipoprotein(a)
gene locus and are resistant to statin therapy. High
Lp(a) levels are associated with increased CAD and valve calciﬁcation.
Lp(a) appears to be more atherogenic than LDL,
possibly because the particles transport oxidized phospholipids
(Que et al., 2018).
HDL levels are negatively associated with atherosclerosis, and
it had been assumed that HDL directly protect against the disease.
A causal relationship, however, has been challenged
based on the failure of drugs that raise HDL-cholesterol to protect
and Mendelian randomization (MR) studies showing that
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genetic variations that affect HDL-cholesterol levels, such as
variants of endothelial lipase, do not have a signiﬁcant impact
on atherosclerosis. On the other hand, since HDL particles are
heterogeneous, it may be that only certain HDL species are protective
and that HDL-cholesterol levels are a poor measure of the
protective species. For example, a recent study showed that
HDL produced by the intestine are functionally distinct from
liver-derived HDL in that they protect the liver, and perhaps the
vessel wall, from gut-derived lipopolysaccharide (LPS) (Han
et al., 2021). Also, MR can be confounded by pleiotropy, the
ability of genetic variants to affect multiple traits. For example,
variants that affect plasma lipids can also impact other traits
associated with atherosclerosis, such as diabetes. Two recent
MR studies, in contrast to the original reports, concluded that
HDL levels are independently associated with CAD (Thomas
et al., 2021). One of these studies examined subtypes of HDL
and concluded that although small and medium-sized HDL are
protective, large HDL may be proatherogenic (Zhao et al., 2021).
Triglyceride-rich lipoprotein levels are positively associated
with atherosclerosis, but the relationship was previously thought
to be indirect, resulting from interactions with HDL metabolism.
This was supported by the fact that certain disorders with greatly
elevated plasma triglyceride levels, such as lipoprotein lipase
deﬁciency, exhibit modest increases in atherosclerosis. More
recent genetic studies, however, suggest that certain triglyceride-rich
lipoproteins do indeed directly promote atherosclerosis
(Liu et al., 2017).
Hypertension
Elevated blood pressure is a major risk factor of CAD and stroke,
with many environmental and genetic contributions. Very large
meta-analyses have identiﬁed over 500 independent loci associated
with one or more blood pressure traits (Giri et al., 2019).
Despite being a well-established independent risk factor for
atherosclerosis, the mechanism by which hypertension accelerates
CAD has remained elusive. A recent study shed light on this
important issue by demonstrating that increased pressure per se
facilitates coronary atherosclerosis, independent of humoral
changes associated with hypertension, by increasing smooth
muscle cell activity and intimal accumulation of LDLs (Al-Mashhadi
et al., 2021).
Diabetes
Type 2 diabetes results from environmental and genetic interactions
(Mahajan et al., 2018). It has become very common with the
epidemic of obesity and is strongly associated with CAD,
although the underlying mechanisms are poorly understood. Diabetics
often exhibit metabolic syndrome, a cluster of traits
including insulin resistance, obesity, hypertension, and elevated
LDL levels, all of which contribute independently to atherosclerosis.
The dysregulation of blood sugar in diabetes may exacerbate
atherosclerosis through a range of mechanisms including
LDL modiﬁcation, formation of advanced glycation end-products
(AGE), oxidative stress, vascular regulation of microRNA
levels, and epigenetics (Poznyak et al., 2020). A recent study
showed that hyperglycemia promotes proinﬂammatory gene
expression in macrophages and that this persists following
transplantation into normoglycemic mice, resulting in increased
atherosclerosis (Edgar et al., 2021).
ENVIRONMENTAL RISK FACTORS
Environment appears to play a major role in atherosclerosis as
evidenced by the fact that modiﬁcations to lifestyle choices
and shifts in cultural practices can greatly alter CAD risk despite
the same genetic background. For example, CAD mortality rates
in Beijing, China, increased by 50% for men and 27% for women
because of environmental changes between 1984 and 1999. In
addition to the ‘‘traditional’’ risk factors, factors such as circadian
rhythm, altitude, and seasons can inﬂuence disease susceptibility
(Bhatnagar, 2017). Genetic factors undoubtedly
interact with environmental factors, but such interactions remain
poorly understood in humans.
Nutrition and obesity
Unhealthy diets contribute to many of the traditional risk factors
such as LDL levels, triglyceride levels, diabetes mellitus, and hypertension.
In surveys, about 50% of young adults and 31% of
older adults have reported poor diets (Benjamin et al., 2018).
CAD risk is affected by diet composition independent of energy
content; for example, in one study, replacement of 5% of energy
from saturated fat with unsaturated fat was associated with a
42% reduction in CAD risk (Bhatnagar, 2017). Apart from effects
on obesity and plasma lipids, certain dietary constituents can be
metabolized by intestinal bacteria into metabolites that affect
atherosclerosis or diabetes (see below). A number of recent
studies indicate that diet can importantly affect immunity and
inﬂammation (Schloss et al., 2020). A recent study showed that
a subset of T cells in the intestine function to modulate systemic
metabolism. Knockout mice for b7 integrin lack these cells and
are resistant to obesity, hypertension, diabetes, and atherosclerosis
when fed a high-fat, high-sugar diet (He et al., 2019).
Exercise and physical activity
Physical activity has been associated with a reduced risk of CAD.
Potential mediators include improved glucose tolerance,
reduced plasma lipids, increased anti-inﬂammatory pathways,
and reduced obesity. In contrast to stress, exercise appears to
dampen hematopoiesis and reduce circulating monocytes and
neutrophils in both humans and mice (Figure 4) (Schloss et al.,
2020). One mechanism by which exercise mediates hematopoiesis
and immune function involves leptin signaling. In mice,
running decreased leptin production and reduced signaling to
stromal cells in the bone marrow niche, elevating CXCL12, a
stem cell quiescence-promoting factor. ATAC sequencing (a
measure of accessible chromatin) of hematopoietic cells
revealed that running induced lasting epigenetic changes that
persisted after exercise was stopped. Despite the reduced leukocytes,
running mice were better able to respond to sepsis,
supporting other studies that found improved anti-inﬂammatory
effects with increased physical activity (Frodermann et al., 2019).
Sleep and stress
Long-term lack of sleep associates with a number of diseases,
including CAD (Domı´nguez et al., 2019). A recent study on sleep
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fragmentation in mice indicates that one mechanism involves
increased hematopoiesis and circulating myeloid cells (Figure 3).
Sleep-deprived mice on a hyperlipidemic background had larger
atherosclerotic plaques with more macrophages than controls.
They also exhibited reduced levels of hypocretin, a hormone produced
by the hypothalamus that regulates arousal and appetite.
It was shown that one function of hypocretin is to suppress hematopoiesis
by binding to a receptor on preneutrophils in bone
marrow that results in suppression of M-CSF, an activator of
macrophage growth. Sleep-fragmented mice that were given
hypocretin did not show an increase in hematopoiesis or
atherosclerosis, conﬁrming the brain-bone marrow-lesion axis
(McAlpine et al., 2019).
In common with poor sleep, chronic stress causes monocytosis
and neutrophilia in mice and humans. Stressors are processed
by the amygdala and hypothalamus, triggering the
sympathetic nervous system to increase catecholamine production,
which then signals through b-adrenergic receptors on stromal
and other bone marrow cells to increase hematopoiesis.
Stress also stimulates glucocorticoid secretion from adrenal
glands via the limbic-hypothalamic-pituitary-adrenal axis. This
may accelerate atherosclerosis, since prolonged corticosteroid
therapy is associated with CAD (Schloss et al., 2020).
Smoking
Although smoking increases the risk of cancer and respiratory diseases,
nearly half of the premature mortality associated with
smoking is because of CAD. Smokers have a 2-fold higher risk
of CAD and even light smokers have about a 2-fold higher risk
of MI. Meta-analyses of many studies showed that smoking increases
LDL and blood pressure but that these do not account
for most of the risk (Bhatnagar, 2017). The use of e-cigarettes is
spreading, and a recent study found that e-cigarettes exert intermediate
effects on lipid peroxidation and antioxidant defenses as
compared with tobacco smoke, indicating that they promote
inﬂammation and carry potential risk for CAD (Gupta et al., 2021).
Pollution
Most air pollution is a mixture of aerosols containing both particles
and gases. It has been estimated that it contributes to about
7 million premature deaths per year. There is evidence for effects
of air pollution on dyslipidemia, endothelial dysfunction, platelet
activation, atherosclerosis, and lesion stability. Under controlled
conditions in animal models, increased exposure to concentrated
ambient particles increases atherogenesis, insulin resistance,
and thrombosis (Bhatnagar, 2017). A recent study in
animal models showed that diesel exhaust induces mitochondrial
dysfunction and hyperlipidemia (Yin et al., 2019).
Intestinal microbiota
The human intestine harbors trillions of bacteria, fungi, and viruses
(collectively termed ‘‘microbiota’’) that play an important
role in a healthy ecosystem. The bacteria, in particular, help
digest food, stimulate the immune system, and produce unique
metabolites that can enter the host’s circulation. At birth, individuals
acquire their microbes from their mothers and other family
members, and these are modulated by many factors, including
diet, drugs, pollution, exercise, disease, host genetic factors,
and aging. The composition of the microbiota is relatively constant
in most individuals, but there are striking differences between
individuals. Epidemiological studies have revealed strong
associations between the composition of the gut microbiota and
numerous diseases, including CAD, but the causal relationships
are largely unknown (Jie et al., 2017).
Microbial metabolites have emerged as particularly signiﬁcant
mediators of atherosclerosis. The most signiﬁcant identiﬁed thus
far is trimethylamine N-oxide (TMAO), produced by hepatic oxidation
of trimethylamine, a metabolite derived from bacterial metabolism
of choline and carnitine. Individuals who consume diets
rich in choline or carnitine, or who have kidney disease, have
elevated levels of TMAO. TMAO appears to promote atherosclerosis
by increasing platelet reactivity and vascular inﬂammation
(Tang et al., 2019). Short-chain fatty acids, produced by anerobic
fermentation of undigested ﬁbers, are absorbed through the portal
circulation and modulate blood pressure and inﬂammatory functions.
A study in mice demonstrated that Roseburia intestinalis
could reduce atherosclerosis through production of the shortchain
fatty acid butyrate (Kasahara et al., 2018).
Alcohol consumption
Text: Based on observational studies, it has been assumed that
modest alcohol consumption has cardiovascular beneﬁts. A
recent study applied Mendelian randomization (MR), a technique
that uses natural genetic variation as a proxy for exposure, to the
UK Biobank cohort to evaluate cardiovascular risks at different
levels of consumption (Biddinger et al. 2022). The authors
concluded that the apparent protection with modest consumption
was the result of confounding lifestyle factors and that
CAD and elevated blood pressure increased exponentially at
higher levels of consumption.
Infections
Bacterial and viral infections have long been associated with
atherosclerosis. Recent large epidemiological studies of patients
infected with SARS-CoV-2 have revealed striking postinfection
increases in the incidence of a variety of CVD (Xie et al., 2022).
Conclusions
Understanding how environmental factors contribute is perhaps
the most signiﬁcant knowledge gap in CAD. Human studies are
greatly complicated by the difﬁculty of controlling or measuring
the environment over many years. For this reason, studies in animal
models are likely to be crucial in closing the gap. Some large
efforts are underway to understand the underlying mechanisms.
For example, MOTRPAC is a U.S. national consortium that aims
to understand the molecular transducers of exercise. There are
also large population studies of relationships of gut microbes
and their metabolites to obesity, diabetes, and CAD (Sanna
et al., 2022).
TOWARD PRECISION MEDICINE AND NOVEL
THERAPIES
Atherosclerotic lesions develop over a lifetime and are largely
irreversible, although some studies suggest that lipid-rich lesions
can exhibit some regression. Therefore, the clinically most
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important goals are prevention and early diagnosis. The advances
in understanding the disease as well as technical developments
have created many opportunities for the development
of novel medical applications.
Precision medicine
There is increasing recognition that preventive measures are
required to deal with the problem of atherosclerosis. Although
the 30-day mortality of MI has been greatly reduced, this has resulted
in increased numbers of heart failure patients. Current
clinical evaluation of atherosclerosis risk is based largely on
‘‘traditional’’ risk factors (see above) and on imaging techniques.
Nontraditional risk factors such as TMAO levels, IgE levels, or the
plasma proteome (Williams et al., 2019) are not yet widely
analyzed but could be incorporated into diagnosis. With the
identiﬁcation of hundreds of genetic loci contributing to disease,
polygenic genetic risk scores based on high-density genotyping
have the potential to predict risk of CAD or risk of development of
very high LDL-cholesterol early in life (Aragam and Natarajan,
2020; Hindy et al., 2020). In elderly where CAD is already manifested,
the plasma proteome (3–5,000 proteins), reﬂecting both
genetic and environmental factors, is emerging as a highly relevant
source to detect obstructive CAD (Williams et al., 2019).
Targeting lipid metabolism
Since plasma LDL, Lp(a), and triglyceride-rich lipoproteins are
important drivers of atherosclerosis, many efforts have been
directed at reducing their levels. Statins inhibit HMG-CoA reductase,
the rate limiting enzyme in cholesterol synthesis, and thereby
increase levels of LDL receptor in the liver. They are widely used
and effective at lowering LDL levels. Statins can, however, have
signiﬁcant side effects, such as muscle weakness, and can also
contribute to type 2 diabetes. Ezetimibe, an inhibitor of the
NPC1L1 transporter responsible for cholesterol absorption in the
small intestine, is an alternative. Another alternative is to administer
neutralizing antibodies for the secreted protease PCSK9
that downregulates the LDL receptor by blocking its recycling.
PCSK9 inhibition decreased major cardiovascular events in large
randomized trials (Pasta et al., 2020). High Lp(a) is among the
strongest common genetic factors for CAD (see above), and it is
relatively resistant to statin treatment. A highly speciﬁc antisense
oligonucleotide directed to hepatocytes was recently examined
in a randomized trial of 286 patients with established CAD. The
treatment resulted in dose-dependent decreases in Lp(a) of up
to 80% with no signiﬁcant adverse events, and larger clinical trials
to study functional impacts are underway (Tsimikas et al., 2020).
Targeting inﬂammation and the immune system
The potential for infection has limited efforts to treat atherosclerosis
by modulating inﬂammatory aspects. However, the
CANTOS clinical trial that targeted IL-1b with neutralizing antibodies
in patients with CAD showed a signiﬁcant 15% reduction
in risk of MI and stroke, with only a small increase in infection rates
(Libby, 2021). Also, nanotechnologies targeting macrophages
have been proposed for both diagnostic and therapeutic applications
(Chen et al., 2022). Based on their roles in atherosclerosis,
therapies that modulate system and T lymphocytes show considerable
promise. Among the approaches being considered are B
cell depletion using the drug rituximab, used to treat arthritis,
and omalizumab, used to treat asthma. Another approach is to
boost protective B cell or T cell responses using vaccination. For
example,vaccination trialswithapolipoproteinB peptidesshowed
positive results in preclinical tests (Roy et al., 2022; Sage
et al., 2019).
Targeting the genome
The development of CRISPR-based technologies has enabled
speciﬁc and permanent edits to the genome. The main issues
are delivery to the cells of interest and potential off-target effects.
CRISPR technology has now been used to treat sickle cell anemia
and certain eye disorders, and there are potential applications
in atherosclerosis such as reduction of cholesterol levels.
The most straightforward application is to eliminate expression
of a deleterious gene, and an obvious target in cholesterol metabolism
is the PCSK9 protein that promotes turnover of the LDL
receptor. In one study, lipid nanoparticles were used to deliver
CRISPR base editors to liver in cynomolgus monkeys, resulting
in near-complete knockdown of PCSK9 expression in the liver
after a single injection with concomitant reduction of LDLcholesterol
by 60%. The change remained stable, providing a
‘‘one and done’’ advantage as compared with antibody-based
reduction of PCSK9 that require repeated injections (Musunuru
et al., 2021). Related to this, it may be possible to increase
expression of desirable genes using editing or delivery of
mRNA with approaches similar to those employed in certain
SARS-COV-2 vaccines. Although the editing of the germ line is
now feasible, several biological as well as ethical issues remain,
and it certainly will not be employed in the near future.
Targeting aging
There is evidence that certain mutations common in clonal hematopoiesis
have proinﬂammatory properties, raising the possibility
that they can be targeted (Fidler et al., 2021). Accumulating
evidence suggests that macrophages are important in the systemic
inﬂammation that often occurs in aging, and hence, targeting
macrophage immunometabolism to modulate functions and
polarization is a therapeutic strategy that could be explored (Covarrubias
et al., 2021). As discussed above, there is evidence of
the involvement of senescence in atherosclerosis, at least in
mice. Senolytics, drugs that kill senescent cells, have shown
great promise in animal models of diabetes and other disorders.
A recent study showed that chimeric antigen receptor (CAR)
T cells that target senescent cells can also be effective senolytic
agents (Amor et al., 2020).
Targeting gut microbiota
The potential for modulating gut microbiota as a CAD therapeutic
target is being actively explored. Probiotics and prebiotics are
commonly taken, but whether they directly inﬂuence overall microbial
composition in humans is unclear. Dietary modulation
can clearly affect the levels of circulating microbial metabolites;
for example, plant-based diets reduce TMAO levels and increase
short-chain fatty acid levels (Tang et al., 2019). Inhibitors of the
bacterial lyases that produce TMA have been developed and
are highly effective in suppressing TMAO levels in animal models
(Roberts et al., 2018).
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A HOLISTIC "TOP-DOWN" UNDERSTANDING
A coherent understanding of atherosclerosis will entail integration
of the various genetic and environmental factors and
cross-tissue circuits contributing to the disease. Toward this
end, a top-down, systemic network view (Bjo¨ rkegren et al.,
2015; Franze´ n et al., 2016) of the combined high-dimensional,
multiorgan metabolic processes that perturb the biology of the
arterial wall leading to atherosclerosis is now gradually emerging
(Koplev et al., 2022). Unlike GWAS, these systems studies are
based on the integration of clinical phenotypes, DNA genotypes,
and ‘‘DNA activity’’ measures such as RNA-seq data aiming to
infer models of gene-regulatory networks. Simultaneously
considering the activity of thousands of genes across multiple
disease-relevant organs, these models incorporate multiple genetic
risk loci and candidate pathways, such as those identiﬁed
by GWAS, combined with inﬂuences exerted by environmental
risk factors, such as smoking and lifestyle (Figure 6). To build
these models, individual genes are ﬁrst linked based on their
similarity of expression across samples or individuals resulting
in modules of coexpressed genes. Such coexpression modules
have been shown to be evolutionary conserved and reﬂect pathophysiological
states relevant to clinical phenotypes. Next, by
applying Bayesian algorithms that consider prior causal information
inherent in the coexpression modules such as gene expression-regulatory
SNPs and transcription factors, the direction of
gene-gene interactions in the coexpression modules can be assessed,
transforming them into gene-regulatory coexpression
networks (GRNs). The information about directions of genegene
interactions in these GRNs is essential, primarily because
it allows the identiﬁcation of key driver genes. These genes
tend to be located at the top of the hierarchy, regulating many
downstream genes in the GRN. Perturbation experiments of
Figure 6. Gene activity across multiple organs
is used to infer network models
Gene-regulatory coexpression networks (GRNs)
capturing genetic (inherited) and environmental
risk variation organize genes within and across
tissues in groups of biological processes and
molecular functions that are relevant to the etiology
of coronary atherosclerosis. Together, GRNs may
provide a mechanistic framework in which isolated
candidate pathways and genetic risk loci can be
understood from a broader molecular multiorgan
context. Such a framework may be important to
fulﬁll the promises of precision medicine. Adopted
from STARNET.MSSM.EDU (Koplev et al., 2022).
key driver genes using in vivo model systems
has demonstrated their efﬁcacy in
modulating the activity of entire GRNs
as well as downstream phenotypes,
including atherosclerosis. This latter characteristic
has prompted the term ‘‘key
disease driver’’ and the notion that these
genes may be realistic targets for novel interventions.
Such approaches may also
be useful in deﬁning molecular signals in
blood that mirror network activity associated
with obstructive CAD/atherosclerosis in people who are at
risk of a heart attack or stroke. The usefulness of systems approaches
was recently highlighted by Hartman et al. (2021)
who used network and key driver biology to elucidate sex differences
in the complex etiology of atherosclerosis.
THE ROAD AHEAD
The last 5 or 10 years have seen remarkable advances in the
understanding of atherosclerosis. Important advances have
also occurred on the clinical front, with the introduction of several
new therapeutic approaches. Despite the great progress, there
are many challenges in moving forward. Among many knowledge
gaps are the following: How does lipid accumulation in
the subendothelial space promote inﬂammation? What are the
roles of the dozens of genes identiﬁed by GWAS that do not ﬁt
into any causal category? How important is cellular senescence
in the human disease? How do diabetes, hypertension, and kidney
disease promote atherosclerosis? What mechanisms
contribute to the protective effects of exercise? What factors
protect women against early forms of atherosclerosis? One
key to addressing these questions will be increasingly sophisticated
technologies that allow measurement of gene activity at
the level of the genome across disease-relevant tissues, down
to open chromatin in single cells of atherosclerotic lesions.
Also, combining ‘‘top down’’ (i.e., systems) and ‘‘bottom up’’
(i.e., pathways) approaches will be important for the development
of therapies that target multiple facets of atherosclerosis
and that can be tailored to the needs of individual patients in
line with the promise of precision medicine. The chances of
such therapeutic strategies will likely depend on identifying individuals
at risk early on, and noninvasive diagnostics will undoubtedly
be a central theme of future study.
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ACKNOWLEDGMENTS
We thank our colleagues and students for discussions. A.J.L. particularly
thanks Alan Fogelman for introducing him to atherosclerosis research and
supporting him through the years. J.B. thanks Anders Hamsten for introducing
him to the ﬁeld of genetics and support in his early career. We thank Rosa Chen
for help in the preparation of this manuscript. Our research was supported by
funds from the National Institutes of Health (HL144651, HL147883, and
HL148110) (A.J.L.), the American Heart Association and the Leducq Foundation
(A.J.L., J.B.), and the Swedish Research Council (2018-02529) and Swedish
Heart Lung Foundation (20170265) (J.B.).
DECLARATION OF INTERESTS
The authors have no competing interests.
REFERENCES
Abdellatif, M., Sedej, S., and Kroemer, G. (2021). NAD(+) metabolism in cardiac
health, aging, and disease. Circulation 144, 1795–1817.
Aherrahrou, R., Guo, L., Nagraj, V.P., Aguhob, A., Hinkle, J., Chen, L., Yuhl
Soh, J., Lue, D., Alencar, G.F., Boltjes, A., et al. (2020). Genetic regulation of
atherosclerosis-relevant phenotypes in human vascular smooth muscle cells.
Circ. Res. 127, 1552–1565.
Ahmad, F., Mitchell, R.D., Houben, T., Palo, A., Yadati, T., Parnell, A.J., Patel,
K., Shiri-Sverdlov, R., and Leake, D.S. (2021). Cysteamine decreases low-density
lipoprotein oxidation, causes regression of atherosclerosis, and improves
liver and muscle function in low-density lipoprotein receptor-deﬁcient mice.
J. Am. Heart Assoc. 10, e017524.
Alencar, G.F., Owsiany, K.M., Karnewar, S., Sukhavasi, K., Mocci, G., Nguyen,
A.T., Williams, C.M., Shamsuzzaman, S., Mokry, M., Henderson, C.A., et al.
(2020). Stem cell pluripotency genes Klf4 and Oct4 regulate complex SMC
phenotypic changes critical in late-stage atherosclerotic lesion pathogenesis.
Circulation 142, 2045–2059.
Al-Mashhadi, R.H., Al-Mashhadi, A.L., Nasr, Z.P., Mortensen, M.B., Lewis,
E.A., Camafeita, E., Ravlo, K., Al-Mashhadi, Z., Kjær, D.W., Palmfeldt, J.,
et al. (2021). Local pressure drives low-density lipoprotein accumulation and
coronary atherosclerosis in hypertensive minipigs. J. Am. Coll. Cardiol. 77,
575–589.
AlSiraj, Y., Chen, X., Thatcher, S.E., Temel, R.E., Cai, L., Blalock, E., Katz, W.,
Ali, H.M., Petriello, M., Deng, P., et al. (2019). XX sex chromosome complement
promotes atherosclerosis in mice. Nat. Commun. 10, 2631.
Amor, C., Feucht, J., Leibold, J., Ho, Y.J., Zhu, C., Alonso-Curbelo, D., Mansilla-Soto,
J., Boyer, J.A., Li, X., Giavridis, T., et al. (2020). Senolytic CAR
T cells reverse senescence-associated pathologies. Nature 583, 127–132.
Aragam, K.G., and Natarajan, P. (2020). Polygenic scores to assess atherosclerotic
cardiovascular disease risk: clinical perspectives and basic implications.
Circ. Res. 126, 1159–1177.
Ba¨ ck, M., Yurdagul, A., Jr., Tabas, I., O¨ o¨ rni, K., and Kovanen, P.T. (2019).
Inﬂammation and its resolution in atherosclerosis: mediators and therapeutic
opportunities. Nat. Rev. Cardiol. 16, 389–406.
Backman, J.D., Li, A.H., Marcketta, A., Sun, D., Mbatchou, J., Kessler, M.D.,
Benner, C., Liu, D., Locke, A.E., Balasubramanian, S., et al. (2021). Exome
sequencing and analysis of 454,787 UK Biobank participants. Nature 599,
628–634.
Basatemur, G.L., Jørgensen, H.F., Clarke, M.C.H., Bennett, M.R., and Mallat,
Z. (2019). Vascular smooth muscle cells in atherosclerosis. Nat. Rev. Cardiol.
16, 727–744.
Benjamin, E.J., Virani, S.S., Callaway, C.W., Chamberlain, A.M., Chang, A.R.,
Cheng, S., Chiuve, S.E., Cushman, M., Delling, F.N., Deo, R., et al. (2018).
Heart disease and stroke statistics-2018 update: a report from the American
Heart Association. Circulation 137, e67–e492.
Bhatnagar, A. (2017). Environmental determinants of cardiovascular disease.
Circ. Res. 121, 162–180.
Bick, A.G., Weinstock, J.S., Nandakumar, S.K., Fulco, C.P., Bao, E.L., Zekavat,
S.M., Szeto, M.D., Liao, X., Leventhal, M.J., Nasser, J., et al. (2020). Inherited
causes of clonal haematopoiesis in 97,691 whole genomes. Nature
586, 763–768.
Biddinger, K.J., Emdin, C.A., Haas, M.E., Wang, M., Hindy, G., Ellinor, P.T., Kathiresan,
S., Khera, A.V., and Krishna, G.A. (2022). Association of habitual
alcohol intake with risk of cardiovascular disease. JAMA Netw Open 5,
e223849. https://doi.org/10.1001/jamanetworkopen.2022.3849.
Bjo¨ rkegren, J.L.M., Kovacic, J.C., Dudley, J.T., and Schadt, E.E. (2015).
Genome-wide signiﬁcant loci: how important are they? Systems genetics to
understand heritability of coronary artery disease and other common complex
disorders. J. Am. Coll. Cardiol. 65, 830–845.
Bore´ n, J., and Williams, K.J. (2016). The central role of arterial retention of
cholesterol-rich apolipoprotein-B-containing lipoproteins in the pathogenesis
of atherosclerosis: a triumph of simplicity. Curr. Opin. Lipidol. 27, 473–483.
Cabrera, C.P., Ng, F.L., Nicholls, H.L., Gupta, A., Barnes, M.R., Munroe, P.B.,
and Caulﬁeld, M.J. (2019). Over 1000 genetic loci inﬂuencing blood pressure
with multiple systems and tissues implicated. Hum. Mol. Genet. 28,
R151–R161.
Chen, W., Schilperoort, M., Cao, Y., Shi, J., Tabas, I., and Tao, W. (2022).
Macrophage-targeted nanomedicine for the diagnosis and treatment of
atherosclerosis. Nat. Rev. Cardiol. 19, 228–249.
Childs, B.G., Zhang, C., Shuja, F., Sturmlechner, I., Trewartha, S., Fierro Velasco,
R., Baker, D., Li, H., and van Deursen, J.M. (2021). Senescent cells suppress
innate smooth muscle cell repair functions in atherosclerosis. Nat Aging
1, 698–714.
Cochain, C., Vafadarnejad, E., Arampatzi, P., Pelisek, J., Winkels, H., Ley, K.,
Wolf, D., Saliba, A.E., and Zernecke, A. (2018). Single-cell RNA-Seq reveals
the transcriptional landscape and heterogeneity of aortic macrophages in
murine atherosclerosis. Circ. Res. 122, 1661–1674.
Covarrubias, A.J., Perrone, R., Grozio, A., and Verdin, E. (2021). NAD(+) metabolism
and its roles in cellular processes during ageing. Nat. Rev. Mol. Cell
Biol. 22, 119–141.
Daugherty, A., Tall, A.R., Daemen, M.J.A.P., Falk, E., Fisher, E.A., Garcı´a-Carden˜
a, G., Lusis, A.J., Owens, A.P., 3rd, Rosenfeld, M.E., Virmani, R., et al.
(2017). Recommendation on design, execution, and reporting of animal
atherosclerosis studies: a scientiﬁc statement from the American Heart Association.
Arterioscler. Thromb. Vasc. Biol. 37, e131–e157.
Depuydt, M.A.C., Prange, K.H.M., Slenders, L., O¨ rd, T., Elbersen, D., Boltjes,
A., de Jager, S.C.A., Asselbergs, F.W., de Borst, G.J., Aavik, E., et al. (2020).
Microanatomy of the human atherosclerotic plaque by single-cell transcriptomics.
Circ. Res. 127, 1437–1455.
Domı´nguez, F., Fuster, V., Ferna´ ndez-Alvira, J.M., Ferna´ ndez-Friera, L., Lo´ pez-Melgar,
B., Blanco-Rojo, R., Ferna´ ndez-Ortiz, A., Garcı´a-Pavı´a, P.,
Sanz, J., Mendiguren, J.M., et al. (2019). Association of sleep duration and
quality with subclinical atherosclerosis. J. Am. Coll. Cardiol. 73, 134–144.
Doran, A.C., Yurdagul, A., Jr., and Tabas, I. (2020). Efferocytosis in health and
disease. Nat. Rev. Immunol. 20, 254–267.
Dou, H., Kotini, A., Liu, W., Fidler, T., Endo-Umeda, K., Sun, X., Olszewska, M.,
Xiao, T., Abramowicz, S., Yalcinkaya, M., et al. (2021). Oxidized phospholipids
promote NETosis and arterial thrombosis in LNK(SH2B3) deﬁciency. Circulation
144, 1940–1954.
Eales, J.M., Maan, A.A., Xu, X., Michoel, T., Hallast, P., Batini, C., Zadik, D.,
Prestes, P.R., Molina, E., Denniff, M., et al. (2019). Human Y chromosome exerts
pleiotropic effects on susceptibility to atherosclerosis. Arterioscler.
Thromb. Vasc. Biol. 39, 2386–2401.
Edgar, L., Akbar, N., Braithwaite, A.T., Krausgruber, T., Gallart-Ayala, H.,
Bailey, J., Corbin, A.L., Khoyratty, T.E., Chai, J.T., Alkhalil, M., et al. (2021).
ll
OPEN ACCESS
1642 Cell 185, May 12, 2022
Review
Hyperglycemia induces trained immunity in macrophages and their precursors
and promotes atherosclerosis. Circulation 144, 961–982.
Erdmann, J., Kessler, T., Munoz Venegas, L., and Schunkert, H. (2018). A
decade of genome-wide association studies for coronary artery disease: the
challenges ahead. Cardiovasc. Res. 114, 1241–1257.
Fernandez, D.M., Rahman, A.H., Fernandez, N.F., Chudnovskiy, A., Amir, E.D.,
Amadori, L., Khan, N.S., Wong, C.K., Shamailova, R., Hill, C.A., et al. (2019).
Single-cell immune landscape of human atherosclerotic plaques. Nat. Med.
25, 1576–1588.
Fidler, T.P., Xue, C., Yalcinkaya, M., Hardaway, B., Abramowicz, S., Xiao, T.,
Liu, W., Thomas, D.G., Hajebrahimi, M.A., Pircher, J., et al. (2021). The AIM2
inﬂammasome exacerbates atherosclerosis in clonal haematopoiesis. Nature
592, 296–301.
Franze´ n, O., Ermel, R., Cohain, A., Akers, N.K., Di Narzo, A., Talukdar, H.A.,
Foroughi-Asl, H., Giambartolomei, C., Fullard, J.F., Sukhavasi, K., et al.
(2016). Cardiometabolic risk loci share downstream cis- and trans-gene regulation
across tissues and diseases. Science 353, 827–830.
Frodermann, V., Rohde, D., Courties, G., Severe, N., Schloss, M.J., Amatullah,
H., McAlpine, C.S., Cremer, S., Hoyer, F.F., Ji, F., et al. (2019). Exercise reduces
inﬂammatory cell production and cardiovascular inﬂammation via instruction
of hematopoietic progenitor cells. Nat. Med. 25, 1761–1771.
Gerlach, B.D., Ampomah, P.B., Yurdagul, A., Jr., Liu, C., Lauring, M.C., Wang,
X., Kasikara, C., Kong, N., Shi, J., Tao, W., and Tabas, I. (2021). Efferocytosis
induces macrophage proliferation to help resolve tissue injury. Cell Metab. 33,
2445–2463.e8.
Gimbrone, M.A., Jr., and Garcı´a-Carden˜ a, G. (2016). Endothelial cell dysfunction
and the pathobiology of atherosclerosis. Circ. Res. 118, 620–636.
Giri, A., Hellwege, J.N., Keaton, J.M., Park, J., Qiu, C., Warren, H.R., Torstenson,
E.S., Kovesdy, C.P., Sun, Y.V., Wilson, O.D., et al. (2019). Trans-ethnic association
study of blood pressure determinants in over 750,000 individuals.
Nat. Genet. 51, 51–62.
Goettsch, C., Hutcheson, J.D., Hagita, S., Rogers, M.A., Creager, M.D., Pham,
T., Choi, J., Mlynarchik, A.K., Pieper, B., Kjolby, M., et al. (2016). A single injection
of gain-of-function mutant PCSK9 adeno-associated virus vector induces
cardiovascular calciﬁcation in mice with no genetic modiﬁcation. Atherosclerosis
251, 109–118.
Graham, S.E., Clarke, S.L., Wu, K.H., Kanoni, S., Zajac, G.J.M., Ramdas, S.,
Surakka, I., Ntalla, I., Vedantam, S., Winkler, T.W., et al. (2021). The power
of genetic diversity in genome-wide association studies of lipids. Nature
600, 675–679.
Grootaert, M.O.J., Finigan, A., Figg, N.L., Uryga, A.K., and Bennett, M.R.
(2021). SIRT6 protects smooth muscle cells from senescence and reduces
atherosclerosis. Circ. Res. 128, 474–491.
Gu, Q., Yang, X., Lv, J., Zhang, J., Xia, B., Kim, J.D., Wang, R., Xiong, F., Meng,
S., Clements, T.P., et al. (2019). AIBP-mediated cholesterol efﬂux instructs hematopoietic
stem and progenitor cell fate. Science 363, 1085–1088.
Gupta, M., Blumenthal, C., Chatterjee, S., Bandyopadhyay, D., Jain, V., Lavie,
C.J., Virani, S.S., Ray, K.K., Aronow, W.S., and Ghosh, R.K. (2020). Novel
emerging therapies in atherosclerosis targeting lipid metabolism. Expert
Opin. Investig. Drugs 29, 611–622.
Gupta, R., Lin, Y., Luna, K., Logue, A., Yoon, A.J., Haptonstall, K.P., Moheimani,
R., Choroomi, Y., Nguyen, K., Tran, E., et al. (2021). Electronic and tobacco
cigarettes alter polyunsaturated fatty acids and oxidative biomarkers.
Circ. Res. 129, 514–526.
Han, Y.H., Onufer, E.J., Huang, L.H., Sprung, R.W., Davidson, W.S., Czepielewski,
R.S., Wohltmann, M., Sorci-Thomas, M.G., Warner, B.W., and Randolph,
G.J. (2021). Enterically derived high-density lipoprotein restrains liver
injury through the portal vein. Science 373, eabe6729.
Hartman, R.J.G., Owsiany, K., Ma, Lijiang, Koplev, S., Hao, K., Slenders, L.,
Civelek, M., Mokry, M., Covacic, J.C., Paterkamp, G., et al. (2021). Sex-Stratiﬁed
Gene Regulatory Networks Reveal Female Key Driver Genes of Atherosclerosis
Involved in Smooth Muscle Cell Phenotype Switching. Circulation
143, 713–726. https://doi.org/10.1161/CIRCULATIONAHA.120.051231.
He, C., Hu, X., Weston, T.A., Jung, R.S., Sandhu, J., Huang, S., Heizer, P., Kim,
J., Ellison, R., Xu, J., et al. (2018). Macrophages release plasma membranederived
particles rich in accessible cholesterol. Proc. Natl. Acad. Sci. USA
115, E8499–E8508.
He, S., Kahles, F., Rattik, S., Nairz, M., McAlpine, C.S., Anzai, A., Selgrade, D.,
Fenn, A.M., Chan, C.T., Mindur, J.E., et al. (2019). Gut intraepithelial T cells
calibrate metabolism and accelerate cardiovascular disease. Nature 566,
115–119.
Heyde, A., Rohde, D., McAlpine, C.S., Zhang, S., Hoyer, F.F., Gerold, J.M.,
Cheek, D., Iwamoto, Y., Schloss, M.J., Vandoorne, K., et al. (2021). Increased
stem cell proliferation in atherosclerosis accelerates clonal hematopoiesis.
Cell 184, 1348–1361.e22.
Hilser, J.R., Han, Y., Biswas, S., Gukasyan, J., Cai, Z., Zhu, R., Tang, W.H.W.,
Deb, A., Lusis, A.J., Hartiala, J.A., and Allayee, H. (2021). Association of serum
HDL-cholesterol and apolipoprotein A1 levels with risk of severe SARS-CoV-2
infection. J. Lipid Res. 62, 100061.
Hindy, G., Aragam, K.G., Ng, K., Chafﬁn, M., Lotta, L.A., Baras, A., Genetics
Center, Regeneron, Drake, I., Orho-Melander, M., Melander, O., et al. (2020).
Genome-wide polygenic score, clinical risk factors, and long-term trajectories
of coronary artery disease. Arterioscler. Thromb. Vasc. Biol. 40, 2738–2746.
Jaiswal, S., Natarajan, P., Silver, A.J., Gibson, C.J., Bick, A.G., Shvartz, E.,
McConkey, M., Gupta, N., Gabriel, S., Ardissino, D., et al. (2017). Clonal hematopoiesis
and risk of atherosclerotic cardiovascular disease. N. Engl. J. Med.
377, 111–121.
Jie, Z., Xia, H., Zhong, S.L., Feng, Q., Li, S., Liang, S., Zhong, H., Liu, Z., Gao,
Y., Zhao, H., et al. (2017). The gut microbiome in atherosclerotic cardiovascular
disease. Nat. Commun. 8, 845.
Kasahara, K., Krautkramer, K.A., Org, E., Romano, K.A., Kerby, R.L., Vivas,
E.I., Mehrabian, M., Denu, J.M., Ba¨ ckhed, F., Lusis, A.J., and Rey, F.E.
(2018). Interactions between Roseburia intestinalis and diet modulate atherogenesis
in a murine model. Nat. Microbiol. 3, 1461–1471.
Kim-Hellmuth, S., Aguet, F., Oliva, M., Mun˜ oz-Aguirre, M., Kasela, S., Wucher,
V., Castel, S.E., Hamel, A.R., Vin˜ uela, A., Roberts, A.L., et al. (2020). Cell typespeciﬁc
genetic regulation of gene expression across human tissues. Science
369, eaaz8528.
Koplev, S., Seldin, M., Sukhavasi, K., Ermel, R., Pang, S., Zeng, L., Bankier, S.,
di Narzo, A., Cheng, H., Meda, V., et al. (2022). A mechanistic framework for
cardiometabolic and coronary artery diseases. Nat. Cardiovasc. Res. 1,
85–100.
Kotla, S., Vu, H.T., Ko, K.A., Wang, Y., Imanishi, M., Heo, K.S., Fujii, Y.,
Thomas, T.N., Gi, Y.J., Mazhar, H., et al. (2019). Endothelial senescence is
induced by phosphorylation and nuclear export of telomeric repeat binding
factor 2-interacting protein. JCI Insight 4, e124867.
Koyama, S., Ito, K., Terao, C., Akiyama, M., Horikoshi, M., Momozawa, Y.,
Matsunaga, H., Ieki, H., Ozaki, K., Onouchi, Y., et al. (2020). Population-speciﬁc
and trans-ancestry genome-wide analyses identify distinct and shared
genetic risk loci for coronary artery disease. Nat. Genet. 52, 1169–1177.
Libby, P. (2021). The changing landscape of atherosclerosis. Nature 592,
524–533.
Liu, D.J., Peloso, G.M., Yu, H., Butterworth, A.S., Wang, X., Mahajan, A., Saleheen,
D., Emdin, C., Alam, D., Alves, A.C., et al. (2017). Exome-wide association
study of plasma lipids in >300,000 individuals. Nat. Genet. 49, 1758–1766.
Luo, X., Lv, Y., Bai, X., Qi, J., Weng, X., Liu, S., Bao, X., Jia, H., and Yu, B.
(2021). Plaque erosion: a distinctive pathological mechanism of acute coronary
syndrome. Front. Cardiovasc. Med. 8, 711453.
Mahajan, A., Taliun, D., Thurner, M., Robertson, N.R., Torres, J.M., Rayner,
N.W., Payne, A.J., Steinthorsdottir, V., Scott, R.A., Grarup, N., et al. (2018).
Fine-mapping type 2 diabetes loci to single-variant resolution using high-
ll
OPEN ACCESS
Cell 185, May 12, 2022 1643
Review
density imputation and islet-speciﬁc epigenome maps. Nat. Genet. 50,
1505–1513.
Man, J.J., Beckman, J.A., and Jaffe, I.Z. (2020). Sex as a biological variable in
atherosclerosis. Circ. Res. 126, 1297–1319.
McAlpine, C.S., Kiss, M.G., Rattik, S., He, S., Vassalli, A., Valet, C., Anzai, A.,
Chan, C.T., Mindur, J.E., Kahles, F., et al. (2019). Sleep modulates haematopoiesis
and protects against atherosclerosis. Nature 566, 383–387.
Mori, H., Torii, S., Kutyna, M., Sakamoto, A., Finn, A.V., and Virmani, R. (2018).
Coronary artery calciﬁcation and its progression: what does it really mean?
JACC Cardiovasc. Imaging 11, 127–142.
Mukherjee, P., Chattopadhyay, A., Grijalva, V., Dorreh, N., Lagishetty, V., Jacobs,
J.P., Clifford, B.L., Vallim, T., Mack, J.J., Navab, M., et al. (2022).
Oxidized phospholipids cause changes in jejunum mucus that induce dysbiosis
and systemic inﬂammation. J. Lipid Res. 63, 100153.
Musunuru, K., Chadwick, A.C., Mizoguchi, T., Garcia, S.P., DeNizio, J.E., Reiss,
C.W., Wang, K., Iyer, S., Dutta, C., Clendaniel, V., et al. (2021). In vivo
CRISPR base editing of PCSK9 durably lowers cholesterol in primates. Nature
593, 429–434.
Newman, A.A.C., Serbulea, V., Baylis, R.A., Shankman, L.S., Bradley, X., Alencar,
G.F., Owsiany, K., Deaton, R.A., Karnewar, S., Shamsuzzaman, S., et al.
(2021). Multiple cell types contribute to the atherosclerotic lesion ﬁbrous cap
by PDGFRbeta and bioenergetic mechanisms. Nat. Metab. 3, 166–181.
Nikpay, M., Beehler, K., Valsesia, A., Hager, J., Harper, M.E., Dent, R., and
McPherson, R. (2019). Genome-wide identiﬁcation of circulating-miRNA
expression quantitative trait loci reveals the role of several miRNAs in the regulation
of cardiometabolic phenotypes. Cardiovasc. Res. 115, 1629–1645.
Noonan, J., Bobik, A., and Peter, K. (2022). The tandem stenosis mouse
model: towards understanding, imaging, and preventing atherosclerotic plaque
instability and rupture. Br. J. Pharmacol. 179, 979–997.
O¨ rd, T., O˜ unap, K., Stolze, L.K., Aherrahrou, R., Nurminen, V., Toropainen, A.,
Selvarajan, I., Lo¨ nnberg, T., Aavik, E., Yla¨ -Herttuala, S., et al. (2021). Single-cell
epigenomics and functional ﬁne-mapping of atherosclerosis GWAS loci. Circ.
Res. 129, 240–258.
Orecchioni, M., Kobiyama, K., Winkels, H., Ghosheh, Y., McArdle, S., Mikulski,
Z., Kiosses, W.B., Fan, Z., Wen, L., Jung, Y., et al. (2022). Olfactory receptor 2
in vascular macrophages drives atherosclerosis by NLRP3-dependent IL-1
production. Science 375, 214–221.
Pan, H., Xue, C., Auerbach, B.J., Fan, J., Bashore, A.C., Cui, J., Yang, D.Y.,
Trignano, S.B., Liu, W., Shi, J., et al. (2020). Single-cell genomics reveals a
novel cell state during smooth muscle cell phenotypic switching and potential
therapeutic targets for atherosclerosis in mouse and human. Circulation 142,
2060–2075.
Pasta, A., Cremonini, A.L., Pisciotta, L., Buscaglia, A., Porto, I., Barra, F., Ferrero,
S., Brunelli, C., and Rosa, G.M. (2020). PCSK9 inhibitors for treating hypercholesterolemia.
Expert Opin. Pharmacother. 21, 353–363.
Pierce, J.B., and Feinberg, M.W. (2020). Long noncoding RNAs in atherosclerosis
and vascular injury: pathobiology, biomarkers, and targets for therapy.
Arterioscler. Thromb. Vasc. Biol. 40, 2002–2017.
Poznyak, A., Grechko, A.V., Poggio, P., Myasoedova, V.A., Alﬁeri, V., and Orekhov,
A.N. (2020). The diabetes mellitus-atherosclerosis connection: the role
of lipid and glucose metabolism and chronic inﬂammation. Int. J. Mol. Sci.
21, 1835.
Proto, J.D., Doran, A.C., Gusarova, G., Yurdagul, A., Jr., Sozen, E., Subramanian,
M., Islam, M.N., Rymond, C.C., Du, J., Hook, J., et al. (2018). Regulatory
T cells promote macrophage efferocytosis during inﬂammation resolution. Immunity
49, 666–677.e6.
Que, X., Hung, M.Y., Yeang, C., Gonen, A., Prohaska, T.A., Sun, X., Diehl, C.,
Ma¨ a¨ tta¨ , A., Gaddis, D.E., Bowden, K., et al. (2018). Oxidized phospholipids are
proinﬂammatory and proatherogenic in hypercholesterolaemic mice. Nature
558, 301–306.
Robbins, C.S., Hilgendorf, I., Weber, G.F., Theurl, I., Iwamoto, Y., Figueiredo,
J.L., Gorbatov, R., Sukhova, G.K., Gerhardt, L.M., Smyth, D., et al. (2013).
Local proliferation dominates lesional macrophage accumulation in atherosclerosis.
Nat. Med. 19, 1166–1172.
Roberts, A.B., Gu, X., Buffa, J.A., Hurd, A.G., Wang, Z., Zhu, W., Gupta, N.,
Skye, S.M., Cody, D.B., Levison, B.S., et al. (2018). Development of a gut
microbe-targeted nonlethal therapeutic to inhibit thrombosis potential. Nat.
Med. 24, 1407–1417.
Roy, P., Orecchioni, M., and Ley, K. (2022). How the immune system shapes
atherosclerosis: roles of innate and adaptive immunity. Nat. Rev. Immunol.
ahead of print 22, 251–265.
Sage, A.P., Tsiantoulas, D., Binder, C.J., and Mallat, Z. (2019). The role of B
cells in atherosclerosis. Nat. Rev. Cardiol. 16, 180–196.
Sanna, S., Kurilshikov, A., van der Graaf, A., Fu, J., and Zhernakova, A. (2022).
Challenges and future directions for studying effects of host genetics on the
gut microbiome. Nat. Genet. 54, 100–106.
Schloss, M.J., Swirski, F.K., and Nahrendorf, M. (2020). Modiﬁable cardiovascular
risk, hematopoiesis, and innate immunity. Circ. Res. 126, 1242–1259.
Seldin, M., Yang, X., and Lusis, A.J. (2019). Systems genetics applications in
metabolism research. Nat. Metab. 1, 1038–1050.
Souilhol, C., Serbanovic-Canic, J., Fragiadaki, M., Chico, T.J., Ridger, V., Roddie,
H., and Evans, P.C. (2020). Endothelial responses to shear stress in
atherosclerosis: a novel role for developmental genes. Nat. Rev. Cardiol. 17,
52–63.
Stolze, L.K., Conklin, A.C., Whalen, M.B., Lo´ pez Rodrı´guez, M., O˜ unap, K.,
Selvarajan, I., Toropainen, A., O¨ rd, T., Li, J., Eshghi, A., et al. (2020). Systems
genetics in human endothelial cells identiﬁes non-coding variants modifying
enhancers, expression, and complex disease traits. Am. J. Hum. Genet.
106, 748–763.
Tabas, I., and Bornfeldt, K.E. (2020). Intracellular and intercellular aspects of
macrophage immunometabolism in atherosclerosis. Circ. Res. 126,
1209–1227.
Tang, W.H.W., Ba¨ ckhed, F., Landmesser, U., and Hazen, S.L. (2019). Intestinal
microbiota in cardiovascular health and disease: JACC State-of-the-art review.
J. Am. Coll. Cardiol. 73, 2089–2105.
Thomas, D.G., Wei, Y., and Tall, A.R. (2021). Lipid and metabolic syndrome
traits in coronary artery disease: a Mendelian randomization study. J. Lipid
Res. 62, 100044.
Tsimikas, S., Gordts, P.L.S.M., Nora, C., Yeang, C., and Witztum, J.L. (2020).
Statin therapy increases lipoprotein(a) levels. Eur. Heart J. 41, 2275–2284.
Tyrrell, D.J., and Goldstein, D.R. (2021). Ageing and atherosclerosis: vascular
intrinsic and extrinsic factors and potential role of IL-6. Nat. Rev. Cardiol. 18,
58–68.
von Scheidt, M., Zhao, Y., Kurt, Z., Pan, C., Zeng, L., Yang, X., Schunkert, H.,
and Lusis, A.J. (2017). Applications and limitations of mouse models for understanding
human atherosclerosis. Cell Metab. 25, 248–261.
Wang, Y., Gao, H., Wang, F., Ye, Z., Mokry, M., Turner, A.W., Ye, J., Koplev, S.,
Luo, L., Alsaigh, T., et al. (2021). Dynamic changes in chromatin accessibility
are associated with the atherogenic transitioning of vascular smooth muscle
cells. Cardiovasc. Res. Online ahead of print. https://doi.org/10.1093/cvr/
cvab347.
Williams, S.A., Kivimaki, M., Langenberg, C., Hingorani, A.D., Casas, J.P.,
Bouchard, C., Jonasson, C., Sarzynski, M.A., Shipley, M.J., Alexander, L.,
et al. (2019). Plasma protein patterns as comprehensive indicators of health.
Nat. Med. 25, 1851–1857.
Winkels, H., Ehinger, E., Vassallo, M., Buscher, K., Dinh, H.Q., Kobiyama, K.,
Hamers, A.A.J., Cochain, C., Vafadarnejad, E., Saliba, A.E., et al. (2018). Atlas
of the immune cell repertoire in mouse atherosclerosis deﬁned by single-cell
RNA-sequencing and mass cytometry. Circ. Res. 122, 1675–1688.
Wirka, R.C., Wagh, D., Paik, D.T., Pjanic, M., Nguyen, T., Miller, C.L., Kundu,
R., Nagao, M., Coller, J., Koyano, T.K., et al. (2019). Atheroprotective roles
ll
OPEN ACCESS
1644 Cell 185, May 12, 2022
Review
of smooth muscle cell phenotypic modulation and the TCF21 disease gene as
revealed by single-cell analysis. Nat. Med. 25, 1280–1289.
Xie, Y., Xu, E., Bowe, B., and Al-Aly, Z. (2022). Long-term cardiovascular outcomes
of COVID-19. Nat. Med. 28, 583–590.
Yin, F., Gupta, R., Vergnes, L., Driscoll, W.S., Ricks, J., Ramanathan, G.,
Stewart, J.A., Shih, D.M., Faull, K.F., Beaven, S.W., et al. (2019).
Diesel exhaust induces mitochondrial dysfunction, hyperlipidemia, and liver
steatosis. Arterioscler. Thromb. Vasc. Biol. 39, 1776–1786.
Zhang, X., Sessa, W.C., and Ferna´ ndez-Hernando, C. (2018). Endothelial
transcytosis of lipoproteins in atherosclerosis. Front. Cardiovasc. Med. 5, 130.
Zhao, Q., Wang, J., Miao, Z., Zhang, N.R., Hennessy, S., Small, D.S., and
Rader, D.J. (2021). A Mendelian randomization study of the role of lipoprotein
subfractions in coronary artery disease. eLife 10, e58361.
ll
OPEN ACCESS
Cell 185, May 12, 2022 1645
Review