the role of damps and pamps in inflammation-mediated · increasing inflammation and in the...
TRANSCRIPT
Draft
The Role of DAMPs and PAMPs in Inflammation-mediated
Vulnerability of Atherosclerotic Plaques
Journal: Canadian Journal of Physiology and Pharmacology
Manuscript ID cjpp-2016-0664.R2
Manuscript Type: Review
Date Submitted by the Author: 29-Dec-2016
Complete List of Authors: Rai, Vikrant; Creighton University School of Medicine, Department of Clinical & Translational Science Agrawal, Devendra; Creighton University School of Medicine, Department of Clinical & Translational Science
Is the invited manuscript for consideration in a Special
Issue?:
IACS Sherbrooke 2016 special issue Part 2
Keyword: Inflammation, Atherosclerotic Plaque, DAMPs, PAMPs, Plaque Vulnerability
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
1
The Role of DAMPs and PAMPs in Inflammation-mediated Vulnerability of Atherosclerotic
Plaques
Vikrant Rai and Devendra K. Agrawal
Department of Clinical and Translational Science, Creighton University School of Medicine,
Omaha, NE 68178
*Corresponding author
Devendra K. Agrawal, Ph.D. (Biochem), Ph.D. (Med. Sciences), MBA, MS (ITM), FAAAAI,
FAHA, FAPS, FIACS
Professor and Chairman, Department of Clinical & Translational Science
The Peekie Nash Carpenter Endowed Chair in Medicine
Senior Associate Dean for Clinical & Translational Research
Creighton University School of Medicine
CRISS II Room 510, 2500 California Plaza
Omaha, NE, 68178, USA
Tel: (402) 280-2938
Fax: (402) 280-1421
E-mail: [email protected]
Running title: DAMPs, PAMPs and plaque vulnerability
Page 1 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
2
Abstract
Atherosclerosis is a chronic inflammatory disease resulting in the formation of the
atherosclerotic plaque. Plaque formation starts with the inflammation in fatty streak and
progress through atheroma, atheromatous plaque, and fibroatheroma leading to
development of stable plaque. Hypercholesterolemia, dyslipidemia, hyperglycemia are the
risk factors for atherosclerosis. Inflammation, infection with viruses and bacteria, and
dysregulation in the endothelial and vascular smooth muscle cells leads to advanced plaque
formation. Death of the cells in the intima due to inflammation results in secretion of
damage-associated molecular patterns (DAMPs) such as high mobility group box 1 (HMGB1),
receptor for advanced glycation end products (RAGE), alarmins (S100A8, S100A9, S100A12,
and oxidized low-density lipoproteins), and infection with pathogens leads to secretion of
pathogen-associated molecular patterns (PAMPs) such as lipopolysaccharides, lipoteichoic
acids, and peptidoglycans. DAMPs and PAMPs further activate the inflammatory surface
receptors such as TREM-1 and TLRs and downstream signaling kinases and transcription
factors leading to increased secretion of pro-inflammatory cytokines such as tumor necrosis
factor (TNF)-α, interleukin (IL)-1β, IL-6, and interferon (IFN)-γ and matrix metalloproteinases
(MMPs). These mediators and cytokines along with MMPs render the plaque vulnerable for
rupture leading to ischemic events. In this review, we have discussed the role of DAMPs and
PAMPs in association with inflammation-mediated plaque vulnerability.
Keywords: Inflammation; Atherosclerotic arterial plaque; DAMPs; PAMPs; Oxidized-LDL;
Plaque vulnerability
Page 2 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
3
1. Introduction
Atherosclerosis, a chronic disease characterized by the deposition of excessive lipids
in the arterial intima is associated with inflammation, hyperglycemia, hyperlipidemia, and
dysregulation of the angiotensin system (Xu et al. 2016). Aggregation and oxidation of the
deposited lipids in the intima leads to the generation of modified lipid moieties (minimally-
oxidized lipid, oxLDL) further causing the chronic stimulation of the innate and adaptive
immune response. Induction of endothelial cells and vascular smooth muscle cells leads to
expression of adhesion molecules, chemoattractants, and growth factors. Interaction of
these factors with receptors on monocytes results in homing, migration, and differentiation
of these monocytes into macrophages and dendritic cells, and secretion of pro-
inflammatory cytokines involving the toll-like receptors (TLRs) (Bentzon et al. 2014) (Figure
1).
Atherosclerotic plaques consist of thick sclerotic collagen-rich fibrous cap and a lipid-
rich atheromatous mass. Increases in plaque size, intra ‑ and extracellular lipid
accumulation, intra-plaque rupture, and inflammation renders the stable plaque unstable.
Vulnerable plaques are described as the plaque prone to rupture and susceptible for
thrombus formation and ischemic events (Butcovan et al. 2016). Infiltration of the
inflammatory cells and secretion of the pro-inflammatory cytokines enhances the immune
response and inflammation in the plaque. Increased level of inflammation in the plaque has
been associated with plaque vulnerability (Ridker and Luscher 2014). Vulnerable plaques
are characterized by the presence of a thin inflamed fibrous cap, a lipid core, necrotic core,
increased neovascularization, inflammation, changes in vessel media and adventitia,
intraplaque hemorrhage, and positive vascular remodeling (Otsuka et al. 2014; Virmani et al.
Page 3 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
4
2006). Further, the serum inflammatory markers and the oxidized LDL, cholesterol,
apolipoprotein B, homocysteine levels and the matrix metalloproteinases (MMPs) levels
have been discussed as the serum markers of vulnerabilities (Benedek et al. 2016; Chan and
Watts 2006; Koening et al. 2011; Minamisawa et al. 2016; Mittal et al. 2014; Sreckovic et al.
2016).
Increased inflammation and lipid accumulation render the plaque unstable. Exposure
of the macrophages to apoptotic bodies and necrosis in the plaque resulting in the necrotic
core formation leads to the release of damage-associated molecular patterns (DAMPs) such
as high mobility group box 1 (HMGB1). Increased HMGB1 and pro-inflammatory cytokines
secreted from pro-inflammatory cells feedbacks the cycle and further increases the pro-
inflammatory cytokines and HMGB1 (Butcovan et al. 2016). Increased HMGB1 enhances the
inflammation through TLRs, receptor for advanced glycation end products (RAGE), triggering
receptors expressed on myeloid cells (TREM)-1, and increased pro-inflammatory cytokines
production such as interleukin (IL)-6, IL-1β (beta), and tumor necrosis factor alpha (TNF-α)
(Andersson and Tracey 2011; Pelham and Agrawal 2014) (Figure 2). Since increased
inflammation renders the stable plaque unstable; these mediators of inflammation may play
a potential role in vulnerability of atherosclerotic plaque. The role of TREM-1 and TLRs
involving NF-κB and pro-inflammatory cytokines TNF-α in the pathogenesis of unstable
plaque has been documented (Gargiulo et al. 2015; Rai et al. 2016; Rao et al. 2016a; 2016b).
Along with inflammation, the role of infection of the arterial intima and the presence
of viruses and bacteria and their products has been discussed in association with the plaque
development, progression and vulnerability (Lanter et al. 2014; Rosenfeld and Campbell
2011; Zimmer et al. 2015). Inflammation of the intima leads to damage of the endothelial
Page 4 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
5
and vascular smooth muscle cells and production of DAMPs such as HMGB-1, RAGE,
endogenous receptor ligand for advanced glycation end products (EN-RAGE), and alarmins
(calgranulins). The deposition of the lipids and oxLDL causes activation of innate and
adaptive immunity leading to increased production of inflammatory cytokines and homing
of inflammatory cells. Infection of the arterial intima with viruses and bacteria results in the
production of pathogen-associated molecular patterns (PAMPs), such as lipopolysaccharides
(LPS), peptidoglycans, and lipoteichoic acid (Chen et al. 2013; Kim et al. 2013; Thankam et al.
2016) (Figures 2 and 3). Here, we have discussed the role of DAMPs and PAMPs and their
interaction with inflammatory mediators in the pathogenesis of inflammation-mediated
plaque vulnerability.
2. Damage-associated molecular Patterns
2.1 High Mobility Group Box 1
HMGB1 is a highly conserved protein released by the injured or necrotic cells, and by
the immune cells in response to inflammation and infection (Andersson and Tracey 2011).
HMGB1 plays a role in sterile infection as well as in infectious inflammation. Exposure of the
monocytes, macrophages, dendritic cells, endothelial cells, and platelets to pro-
inflammatory cytokines such as TNF-α, IL-1β, and interferon-gamma (IFN-γ), microbe-
associated molecular patterns (MAMPs), and PAMPs leads to the secretion of DAMPs such
as HMGB-1. Further, the secretion of HMGB-1 is increased by a feed-forward loop by the
secreted HMGB-1, and due the damage and apoptosis of the cells in intima and exposure of
the monocytes with apoptotic bodies (Andersson and Tracey 2011). Increased HMGB-1
induces the production of inflammatory cytokines (IFN-γ, TNF-α, IL-1β, IL-6) contributing a
potential role in the progression of atherosclerosis and plaque vulnerability (Su et al. 2015)
Page 5 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
6
(Figure 2). The development of advanced plaque in the rabbit model of atherosclerosis with
the administration of HMGB-1 and TNF-α suggests the role of pro-inflammatory cytokines
and HMGB-1 in increasing the inflammation and development of advanced plaque (Kim et
al. 2016).
Metabolic syndrome, a low-grade chronic inflammatory state, affects 35% of US
adults and consists of increased blood pressure, high blood sugar, excess body fat around
the waist, and abnormal cholesterol or triglyceride levels. It is associated with increased risk
for cardiovascular disease, and increased expression of the pathogen recognition receptors,
toll-like receptors (TLRs). The increased levels of TLRs (TLR2 and 4) may be due to the
increased circulating levels of PAMP-binding proteins (soluble CD14 and lipopolysaccharide
binding protein), and the DAMPs (HMGB-1) (Jialal et al. 2014; Jialal et al. 2015). The
increased levels of DAMPs and PAMPs contribute to TLRs mediated pro-inflammatory
response, a major factor associated with the pathogenesis of atherosclerosis.
Hypercholesterolemia promotes pro-inflammatory cytokine production and plaque
destabilization by inducing IL-1β, IL-8, TNF-α, S100A8, S100A12 (ENRAGE), and MMP1
through Syk/PI3K and NF-κB signaling (Corr et al. 2016; Gargiulo et al. 2015) (Figures 2 and
3). Hyperglycemia regulates the release of HMGB-1 from leukocytes which facilitates the
thrombus formation (Yamashita et al. 2012). Activated platelets have a potential role in
increasing inflammation and in the development; progression and transition of stable to
unstable plaque and binding of HMGB-1 with platelets involving RAGE further enhance the
inflammation and progression of plaque (Ahrens et al. 2015).
Increased HMGB-1 is associated with induction of matrix metalloproteinases (MMPs)
and matrix degradation resulting in collagen loss and blockade of HMGB-1 results in
Page 6 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
7
decreased inflammation and MMP activity (Kohno et al. 2012). Increased MMP activity is
associated with plaque vulnerability and blocking MMPs may be a novel strategy and a
promising target for stabilizing vulnerable plaques in patients with carotid stenosis (Rao, et
al. 2014). Further, the TREM-1 (Rao et al. 2016a) and TLR4 (Gargiulo et al. 2015) mediated
regulation of MMPs via TNF-α in carotid plaque vulnerability, and the role of TREM-1,
HMGB-1 and RAGE axis in inflammation has been discussed (Thankam et al. 2016)
suggesting the association of these mediators in inflammation mediated plaque
vulnerability.
2.2 Receptor for Advanced Glycation End-products
RAGE is a pattern recognition receptor and mediates the innate immune response.
RAGE in expressed on immune cells, T and B-lymphocytes, and dendritic cells, and is
involved in immediate inflammatory responses. The ligand for the RAGE is advanced
glycation end products (Kierdorf and Fritz 2013). The non-enzymatic reaction between
reducing sugars with free amino groups on proteins, lipids, or nucleic acids results in the
formation of a heterogeneous group of complex structures called as advanced glycation end
products (AGEs). Further, glucose and (or) fructose metabolism intermediate derived
glyceraldehydes-derived AGEs are called as toxic AGEs (TAGE) and play a role in
development and progression of plaque (Takeuchi 2016). AGE formation and accumulation,
a normal process of aging is accelerated by hyperglycemia in diabetes making it a major risk
factor for atherosclerosis (Xu et al. 2016). Increased concentration of AGEs, oxidative stress,
and inflammation facilitates the lipid deposition leading to development and progression of
atherosclerosis (Figure 2). AGEs play a potential role in the pathogenesis of atherosclerosis
via engagement with RAGE present on the various cells found in the atherosclerotic lesion.
Page 7 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
8
The binding of the AGEs (commonly carboxymethyl lysine and methylglyoxal-derived
hydroimidazolone-1) with RAGE results in increased monocyte activation and macrophage
migration, thereby increasing the inflammation in the arterial wall (Heier et al. 2015)
(Figures 2 and 3). Further, AGEs-RAGE engagement also increases the lipid accumulation in
macrophages by regulating cholesterol uptake, esterification, and efflux, thereby increasing
the foam cells and atherogenesis (Xu et al. 2016).
RAGE also increases the lipid deposition and foam cell formation in smooth muscle
cells by smooth muscle cell priming and increasing the uptake of minimally oxidized low-
density lipoprotein (Chellan et al. 2016). Further, as discussed earlier, increased deposition
of lipids, oxidative stress, and inflammation are the characteristics of unstable plaque. RAGE
being a mediator of these factors plays a potential role in the destabilization of plaque.
Vascular smooth muscle cell and endothelial cell dysfunctions are associated with
atherogenesis and unstable plaque, and RAGE plays a role in AGEs-induced vascular smooth
muscle cell (VSMC) dysfunction (Nam et al. 2016). This suggests that RAGE is a potential
mediator of plaque vulnerability.
Endothelial dysfunction is associated with atheroma formation. Endothelial
progenitor cells are essential for re-endothelialization and neovascularization, and the
paucity and dysfunction of these cells have been associated with the pathogenesis of
atherosclerosis (Chen et al. 2016; Yamashita et al. 2012). Hyperactivity of JNK signaling
pathway mediated by AGEs-RAGE engagement results in increased reactive oxygen species
and oxidative stress leading to cellular apoptosis and inhibition of cell proliferation (Chen et
al. 2016). The transition of stable to unstable plaque is also mediated by increased
inflammation by homing of inflammatory cells and pro-inflammatory cytokines.
Page 8 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
9
Inflammatory mediators such as HMGB1, TLRs, TREM-1, S100A8, S100A9, and S100A12 play
a potential role in increasing inflammation through inflammatory cytokines in the plaque,
thereby increasing the vulnerability (Oesterle and Bowman 2015) (Figures 2 and 3).
RAGE is the receptor for not only AGEs, HMGB-1 (Bangert et al. 2016), TLRs
(Medeiros et al. 2014), and TREM-1 (Zysset et al. 2016) but also for the calcium binding
S100/calgranulin proteins (S100A8, S100A9, and S100A12) (Oesterle and Bowman 2015),
and plays a potential role in inflammation-induced atherosclerosis and destabilization of
plaque (Figure 3). This suggests that RAGE axis is a mediator for inflammation-induced
development and progression of plaque as well as instability. Further, it has also been
documented that soluble RAGE (sRAGE) works as the decoy receptor and decrease the RAGE
signaling, thereby decreasing the inflammation. Increasing levels of sRAGE have been
associated with the protective effect on inflammation but not on arterial wall thickness and
stiffness, suggesting a potential therapeutic target and the role of RAGE in plaque
vulnerability (Heier et al. 2015).
2.3 EN-RAGE (S100A12)
EN-RAGE is a member of the S100 protein (calcium-binding proteins) family (Foell et
al. 2003). EN-RAGE is an endogenously produced inflammatory ligand of the RAGE and Toll-
like receptor 4 and endogenous receptor ligand for AGEs. The binding of RAGE with EN-
RAGE activates inflammatory cascades involving NF-κB and inflammatory cytokines
mediating inflammation and atherosclerosis (Ligthart et al. 2014). The significant association
between the increased levels of S100A12 and atherosclerotic cardiovascular disease
(Shiotsu et al. 2011) and with carotid atherosclerosis (Abbas et al. 2012) has been reported.
Page 9 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
10
Abbas et al. (2012) reported the association of the highest increase in S100A12 plasma
levels with early symptoms (2 months), whereas only the modest increase in
S100A8/S100A9 plasma levels at 2 to 6 months but not later. The increased mRNA levels of
S100A8, S100A9, and S100A12 were also associated with the carotid plaque development.
Further, the TLR2 and TLR4 activation increases the mRNA expression of S100A8, S100A9,
and S10012 and increases the release of interleukin-1β and interferon -γ from thrombin-
activated platelets leading to significantly enhanced expression of S100A12 (Figure 3). This
suggests the pathogenic role of S100A12 in association with other inflammatory mediators
in the early phase of development.
However, the pleiotropic role of S10012A has also been reported. Higher levels of
S100A12 were found to be associated with plaque rupture and percutaneous coronary
intervention, but no stimulation of pro-inflammatory cytokines and inhibition of MMP-2,
MMP-9, and MMP-3 via Zn2+
sequestration suggest the protective role of S100A12 in
advanced atherosclerotic plaque (Goyette et al. 2009). Contrarily, reduced amount of
infiltrating inflammatory cells, diminished intimal and medial vascular calcification, smaller
necrotic cores, normalization of RAGE expression and delayed type hypersensitivity with a
S100 protein binding immuno-modulatory compound (ABR-215757) by attenuating the
S100A12 expression suggest its protective role on plaque instability, but atherogenic role of
S100A12 (Yan et al. 2013). Furthermore, the strong association between neutrophil-derived
human S100A12 with the increased risk of coronary heart disease suggests the potential
role of S100A12 in atherosclerosis and plaque vulnerability (Ligthart et al. 2014; Liu et al.
2014).
2.4 Alarmins
Page 10 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
11
2.4.1 S100A8 and S100A9 (calgranulins)
Alarmins S100A8 and S100A9 are the members of calcium-binding protein family
calgranulins. S100A8 and S100A9 are markers of inflammation, and play a potential role in
the pathogenesis of various inflammatory diseases (Vogl et al. 2014). In inflammatory states,
S100A8 and S100A9 are expressed primarily by myeloid cells such as dendritic cells and by
non-myeloid cells such as endothelial cells and vascular smooth muscle cells (VSMCs), and
modulate the inflammatory processes through TLR4 and RAGE (Figure 3). LPS increases the
expression of S100A8 and S100A9 in VSMCs. Increased levels of S100A8 and S100A9 have
been associated with increased cardiovascular events and atherosclerosis (Averill et al.
2012). The accumulation of AGEs is associated with the increase in S100A8, S100A9, and IL-
1β expression thereby increasing the inflammation (Nakajima et al. 2015). Further, the
increased expression of S100A8 and S100A9 on monocytes, macrophages, and the human
arterial wall has been associated with atherogenesis and rupture prone-plaque (Ionita et al.
2009; McCormick et al. 2005). Increased levels of S100A8 and S100A9 in the area of
atherosclerotic plaque and thrombus are believed to be derived from the activated platelets
(Lood et al. 2016).
Unstable plaque is characterized by the thin fibrous cap. Thinning of the fibrous cap
is mediated by the degradation of the collagen content of the extracellular matrix by the
matrix metalloproteinases (MMPs) resulting in plaque rupture and ischemic events (Butoi et
al. 2016; Newby 2015; Rao et al. 2015). Further, it has also been documented that S100A8
and S100A9 are the inducers of MMPs (Moz et al. 2016; Schelbergen et al. 2012; van Lent et
al. 2012) (Figure 3). Hence, increased alarmins with age and inflammation in the arterial
plaque may induce MMPs and may mediate the collagen loss and plaque rupture. These
Page 11 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
12
results suggest that S100A8 and S100A9 increases inflammation and induces MMPs
mediating thinning of the fibrous cap and plaque rupture. Higher levels of these alarmins
have been correlated with plaque rupture (Ionita et al. 2009; Schiopu and Cotoi 2013; Xia et
al. 2016). However, studies have also reported that S100A8 and S100A9 inhibit MMPs
(Isaksen and Fagerhol 2001) and may suppress innate immune response in dendritic cells
(Averill et al. 2011). Therefore, further studies are needed to correlate the level of alarmins
and MMPs activation in stable plaque rendering them unstable. Furthermore, higher levels
of alarmins have been associated with plaque vulnerability, and studies are needed to
determine the predictive power of alarmins in at-risk patients (Averill et al. 2011; Ionita et
al. 2009; Isaksen and Fagerhol 2001; Schiopu and Cotoi 2013; Xia et al. 2016).
2.4.2 Oxidized low-density lipoprotein (oxLDL)
Oxidized LDL is a marker of cardiovascular disease and correlates with its risk and
severity (Fraley and Tsimikas 2006). The oxLDL increases the accumulation of cholesterol
within the foam cells of atherosclerotic lesions (Itabe et al. 2011). Oxidized-LDL enhances
the endothelial dysfunction and foam cell formation and increases the atherogenesis
involving the monocytes, macrophages, and mast cells through increased secretion of TNF-α
and histamine (Chen and Khismatullin 2015; Cipolletta et al. 2005; Singh et al. 2002; Zhu et
al. 2005). Mast cell granules also increase the development of foam cell by its binding with
LDL and increasing the uptake of LDL by macrophage. Reduced progression of
atherosclerosis, lipid deposition, and recruitment of T-lymphocyte and macrophage into the
plaque in LDLr and mast cell-deficient (LDLr−/−
KitW-sh/W-sh
) mouse (Sun et al. 2007) suggest
the role of mast cell-LDL interaction in the progression of atherosclerosis. These studies also
suggest that mast cell deficiency markedly reduces the progression of atherosclerosis. The
Page 12 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
13
co-activation of macrophage and mast cell by higher circulating levels of oxLDL enhances the
risk of atherosclerosis (Chen and Khismatullin 2015). Since oxLDL can be formed in the liver
as well as in the atherosclerotic lesion, the circulating oxLDL and the oxLDL produced in the
plaque affect the plaque vulnerability differently (Itabe et al. 2011). Niccoli et al. (2007)
reported that neither oxLDL (recognized by monoclonal antibody mAb-4E6) nor
malondialdehyde-modified LDL (recognized by monoclonal antibody mAb-1H11) in the
plaque plays a role in plaque instability; however circulating oxLDL may play a role in plaque
vulnerability. Similar to oxLDL, oxidized-cholesterol was also found to be more
hypercholesterolemic and atherogenic than cholesterol in hamster (Ng et al. 2008).
Hypercholesterolemia, dyslipidemia, and inflammation are risk factor for
atherosclerosis and plaque vulnerability (Gupta et al. 2016). Dyslipidemia is also associated
with the increased expression of inflammatory mediator TREM-1 in advanced plaque (Zysset
et al. 2016). Further, increased TREM-1 expression is associated with unstable plaque and
plaque vulnerability. This suggests that dyslipidemia enhances the inflammation in plaque
through increased surface expression of TREM-1 leading to increased monocytes homing,
production of pro-atherogenic or pro-inflammatory cytokines, and foam cell formation, and
thus enhanced the plaque vulnerability (Rai et al. 2016; Rao et al. 2016a; Zysset et al. 2016)
(Figures 2 and 3). Increased expression of TREM-1 on matured dendritic cells has been
correlated with plaque instability (Rai et al. 2016), and DCs and activated T cells have been
co-localized in atherosclerotic plaque. Further, suppression of the atherogenic potential of
the oxLDL induced DCs and limitation of the pro-inflammatory cytokine (TNF-α, IL-1β, and IL-
6) production with statins suggest the role of oxLDL in atherogenesis and plaque
vulnerability (Frostegard et al. 2016). Similarly, decreased expression of TNF-α and oxLDL-
Page 13 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
14
induced inflammatory cytokines with soluble-TREM-1 suggests the potential role of TREM-1
and oxLDL in coronary artery disease and atherosclerosis (Dai et al. 2016).
TREM-1 amplifies the TLR4 signaling and enhances the inflammation and immune
reaction (Pelham and Agrawal 2014). TLRs participate in lipid deposition and enhanced
inflammation in atherogenesis. The expression of TREM-1 and TLR4 in macrophage can be
increased by oxLDL leading to increased pro-inflammatory cytokine production. Inhibition of
TREM-1 with short-hairpin RNA and synthetic polypeptide LP-17 leads to decreased
secretion of pro-inflammatory cytokines, suggesting the potential role of oxLDL induced
TREM-1 and TLR4 in atherosclerotic plaque development, progression, and vulnerability (Li
et al. 2016). The role of oxLDL mediated TLR4 activation in macrophages, and association of
increased expression of TLR4 with increased inflammation suggests the correlation of TLR4,
oxLDL, inflammation, and atherosclerosis (Xu et al. 2001). Since, increased expression of
inflammatory mediators (TREM-1, TLRs, and inflammatory cytokines), dyslipidemia, and
inflammation is also associated with unstable plaque; activation of TLR4 with oxLDL may be
correlated with plaque vulnerability (Miller 2005; Rai et al. 2016; Rao et al. 2016a; 2016b).
3. Pathogen Associated Molecular Patterns
Along with inflammation, infection of the intima may also play a role in the
development, progression and plaque destabilization. The presence of bacteria and viruses
in the atherosclerotic area has been documented (Lanter et al. 2014; Rosenfeld and
Campbell 2011; Zimmer et al. 2015). Direct infection of vascular cells, production of
endotoxins, modulating the immune response, secretion of pro-inflammatory cytokines or
acute phase proteins, destruction of the intima or activation of the mediators of
inflammation by these viruses and bacteria are the possible mechanism contributing to
Page 14 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
15
atherogenesis (Lanter et al. 2014; Rosenfeld and Campbell 2011; Zimmer et al. 2015).
Further, the presence of bacteria as biofilm proximal to the internal elastic lamina and in
association with fibrous tissue has been found, and rupture or dispersion of this biofilm is
associated with the increased propensity of plaque rupture (Lanter et al. 2014). Chronic
inflammation plays a potential role in atherogenesis and increased inflammation in the
plaque induces the plaque instability. HMGB-1 secretion from the necrotic core and by
positive feedback enhances this process through secretion of the pro-inflammatory
cytokines. HMGB-1 expression and release can also be increased by bacterial endotoxins
lipopolysaccharide, a known pathogen-associated molecular patterns (PAMPs) (Chen et al.
2013). As discussed above, the interaction of HMGB-1 with TREM-1, TLRs, and RAGE result
in increased secretion of pro-inflammatory cytokines, inflammation, and plaque
vulnerability. Further LPS exposure increases expression of HMGB-1 and inflammation
rendering the plaque more vulnerable (Jaw et al. 2016) (Figure 3). Increased TREM-1
expression on macrophages with LPS, TLR4 mediated TREM-1 expression, LPS mediated
increased TLRs expression, and involvement of HMGB1-RAGE axis and LPS binding protein in
increasing inflammation suggests the potential role of LPS in enhancing the expression of
inflammatory mediators (Arts et al. 2011; Huebener et al. 2015; Murakami et al. 2007; Park
and Lee 2013; Pelham and Agrawal 2014; Wu et al. 2012) (Figure 3). Since these mediators
are involved in the pathogenesis of plaque instability, LPS may play a potential in plaque
destabilization.
An aberrant vascular smooth muscle proliferation result in plaque formation,
however, VSMCs regeneration is essential for the repair of the plaque area (Bennett et al.
2016). Reduced regenerating power of VSMCs renders the plaque unstable and is a
Page 15 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
16
characteristic feature of unstable plaque. VSMCs apoptosis, cell senescence, and VSMC-
derived macrophage-like cells may promote inflammation, progression, and destabilization
of the plaque (Bennett et al. 2016). VSMCs associated plaque progression and instability is
mediated by the DNA damage products called double-stranded breaks, which promotes cell
senescence, apoptosis, and inflammation (Bennett et al. 2016; Gray et al. 2015). Activation
of Na+/H
+ exchanger-1 by LPS via Ca
2+/calpain results in apoptosis of VSMCs apoptosis and
atherosclerosis and inhibition of Na+/H
+ exchanger-1 leads to attenuation of LPS-accelerated
atherosclerosis and promotes plaque stability, suggesting the potential role of LPS in plaque
destabilization (Li et al. 2014).
Rupture of the plaque is mediated by the destruction of the extracellular membrane
by MMPs (Newby 2008). Newby (2015) reviewed the role of MMPs in atherosclerosis and
concluded the stabilizing effect of MMPs on intimal thickening leading to plaque
stabilization, as well as the destabilizing effect on the plaque by extracellular matrix and
collagen degradation (Newby 2008; Newby 2015). Further, LPS induced stimulation of
monocytes and production of MMP-1 and MMP-9 has been documented in association with
the ischemic events and plaque destabilization (Speidl et al. 2004). Furthermore, both TLR4
and TREM-1 are mediators of inflammation and the role of LPS in enhancing the MMP-9
expression through TLR/NF-κB stimulation, and TREM-1 expression through TLR4 dependent
pathway, in the context of atherosclerosis has been reported (Li et al. 2012; Zheng et al.
2010). The correlation of increased expression of MMP-1, and MMP-9, TREM-1, and
decreased expression of collagen I and collagen III through involvement of TNF-α, epidermal
growth factor, Ets-1, NF-kB, p38-MAPK, JNK-MAPK, and PI3K in relation to plaque
destabilization has also been documented (Rao et al. 2014; Rao et al. 2015; Rao et al. 2016a)
Page 16 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
17
(Figure 3). These results suggest the potential role of LPS in carotid plaque destabilization
via stimulation of these mediators of inflammation.
The role of PAPMs such as lipoteichoic acid and peptidoglycans has also been
discussed in the literature in relation to the atherogenesis and the plaque vulnerability (Kim
et al. 2013; Laman et al. 2002; Schoneveld et al. 2005). Lipoteichoic acid suppresses the LPS
induced inflammation in the plaque by attenuating the expression of MMP-9, COX-2, Bax,
HSP27, TLR4 and CCR7 through downregulation of NF-κB along with inhibiting the
monocyte/macrophage infiltration (Kim et al. 2013). Peptidoglycan present in
atherosclerotic plaque is a functional LPS analog which induces pro-inflammatory cytokine
production and MMPs via binding to CD14 on macrophages. Significantly increased numbers
of the peptidoglycan positive cells have been correlated with the vulnerable plaque (Laman
et al. 2002). Peptidoglycan stimulates TLR2 and enhances the inflammation and plaque
vulnerability (Schoneveld et al. 2005). Further, amplification of mRNA and protein
expression of IL-6, TLR2 and TLR4 increased the secretion of IL-6, IL-8, and nuclear
translocation of NF-κB in the human umbilical vein endothelial cells incubated with LPS,
lipoteichoic acid, or peptidoglycan in the presence of histamine (Jehle et al. 2000; Talreja et
al. 2004). These findings suggest a synergy between PAMPs and endogenously secreted
histamine in activating the endothelial cells resulting in enhanced production of
inflammatory cytokines (Jehle et al. 2000; Talreja et al. 2004) (Figures 2 and 3).
Endothelial dysfunction plays a crucial role in plaque development and vulnerability
(Raveendran et al. 2011; Tan et al. 2007). In response to increased inflammation,
endothelial cells may also enhance secretion of the inflammatory cytokines and activation of
mediators of inflammation, thereby contributing to plaque progression and rupture
Page 17 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
18
(Raveendran et al. 2011; Tan et al. 2007). The synergy between endogenously released
histamine and LPS in increasing the inflammation via increased mRNA expression of H1
receptors resulting in increased production of prostaglandin I2, prostaglandin E2 and IL-6 by
endothelial cells has been reported. This effect was partly attributed to histamine-induced
expression of TLR4 (Raveendran et al. 2011) (Figures 2 and 3). Production of prostaglandin
I2 and prostaglandin E2 can also be increased by stimulating the cyclooxygenase-2 through
LPS and histamine (Tan et al. 2007). These studies suggest that histamine release in
endothelial cells increases inflammation and may contribute to plaque vulnerability. The
role of flagellin-induced activation of NADPH oxidase-4 involving TLR5 and production of
hydrogen peroxide has been discussed. This lead to increased secretion of pro-inflammatory
cytokines and adhesion molecule leading to increased inflammation, reduction in the
adhesion and transendothelial migration of monocytes, and atherosclerosis (Kim et al.
2016). Since monocytes and macrophages play a potential role in inducing inflammation and
plaque destabilization, flagellin-induced inflammation may play a potential role in plaque
vulnerability (Kim et al. 2016).
4. Conclusion
Atherosclerotic plaque development, progression, and vulnerability are affected by
inflammation and infection by viruses and bacteria and their products. Inflammation and
infection in the fatty streak result in homing of inflammatory cells, increased apoptosis and
necrosis, and increased lipid deposition leading to secretion of DAMPs and PAMPs, and
inflammatory cytokines involving surface receptors and downstream signaling molecules
(Lanter et al. 2014; Rosenfeld and Campbell 2011; Thankam et al. 2016; Zimmer et al. 2015)
Increased secretion of the inflammatory cytokines and matrix metalloproteinases mediate
Page 18 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
19
the transition of stable plaque to unstable, thus increasing the plaque vulnerability (Rao et
al. 2014; Rao et al. 2016a; Rao et al. 2016b). As discussed, these mediators of inflammation
serve as the markers for the assessment of the extent of plaque vulnerability as well as
potential therapeutic targets for the vulnerable plaque. Decreased secretion of
inflammatory cytokines and morphological features of unstable plaque with blocking
HMGB1, the use of sRAGE and sTREM1, and TREM-1 blocking with LP17 and short hairpin
RNA suggest the potential therapeutic options. The pleiotropic effect of EN-RAGE and oxLDL
(plaque vs. circulatory), differential expression of S100A12 and S100A8/A9 with time has
been discussed but needs further research. Further understanding the effect of DAMPs and
PAMPs on VSMCs and endothelial cells, analyzing the protective effect of lipoteichoic acid
by attenuating LPS action, and elaborating the effects of plaque and circulatory oxLDL would
be therapeutically beneficial.
Acknowledgement
This work was supported by research grants R01 HL112597, R01 HL116042, and R01
HL120659 to DK Agrawal from the National Heart, Lung and Blood Institute, National
Institutes of Health, USA. The content of this review article is solely the responsibility of the
authors and does not necessarily represent the official views of the National Institutes of
Health.
Financial and competing interests’ disclosure
The authors have no other relevant affiliations or financial involvement with any
organization or entity with financial interest or financial conflict with the subject matter or
Page 19 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
20
materials discussed in the manuscript apart from those disclosed. No writing assistance was
utilized in the production of this manuscript.
References
Abbas, A., Aukrust, P., Dahl, T.B., Bjerkeli, V., Sagen, E.B., Michelsen, A., et al. 2012. High
levels of S100A12 are associated with recent plaque symptomatology in patients with
carotid atherosclerosis. Stroke, 43(5): 1347-53. PMID: 22382154 doi:
10.1161/STROKEAHA.111.642256
Ahrens, I., Chen, Y.C., Topcic, D., Bode, M., Haenel, D., Hagemeyer, C.E., et al. 2015. HMGB1
binds to activated platelets via the receptor for advanced glycation end products and is
present in platelet rich human coronary artery thrombi. Thromb. Haemost. 114(5): 994-
1003. PMID: 26202300 doi: 10.1160/TH14-12-1073
Andersson, U. and Tracey, K. J. 2011. HMGB1 is a therapeutic target for sterile inflammation
and infection. Annu. Rev. Immunol. 29: 139-162. PMID: 21219181 doi: 10.1146/annurev-
immunol-030409-101323
Arts, R. J., Joosten, L.A., Dinarello, C.A., Kullberg, B.J., van der Meer, J.W., and Netea, M.G.
2011. TREM-1 interaction with the LPS/TLR4 receptor complex. Eur. Cytokine Netw.
22(1): 11-14. PMID: 21393102 doi: 10.1684/ecn.2011.0274
Averill, M. M., Barnhart, S., Becker, L., Li, X., Heinecke, J.W., Leboeuf, R.C., et al. 2011.
S100A9 differentially modifies phenotypic states of neutrophils, macrophages, and
dendritic cells: implications for atherosclerosis and adipose tissue inflammation.
Circulation, 123(11): 1216-1226. PMID: 21382888 doi:
10.1161/CIRCULATIONAHA.110.985523
Page 20 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
21
Averill, M. M., Kerkhoff, C., and Bornfeldt, K.E. 2012. S100A8 and S100A9 in cardiovascular
biology and disease. Arterioscler. Thromb. Vasc. Biol. 32(2): 223-229. PMID: 22095980
doi: 10.1161/ATVBAHA.111.236927
Bangert, A., Andrassy, M., Muller, A.M., Bockstahler, M., Fischer, A., Volz, C.H., et al. 2016.
Critical role of RAGE and HMGB1 in inflammatory heart disease. Proc. Natl. Acad. Sci. U S
A 113(2): E155-64. PMID: 26715748 doi: 10.1073/pnas.1522288113
Benedek, T., Maurovich-Horváth, P., Ferdinandy, P., and Merkely, B. 2016. The Use of
Biomarkers for the Early Detection of Vulnerable Atherosclerotic Plaques and Vulnerable
Patients. A Review. J. Cardiovasc. Emergencies, 2(3): 106-113. doi: 10.1515/jce-2016-
0017
Bennett, M. R., Sinha, S., and Owens, G.K. 2016. Vascular Smooth Muscle Cells in
Atherosclerosis. Circ. Res. 118(4): 692-702. PMID: 26892967 doi:
10.1161/CIRCRESAHA.115.306361
Bentzon, J.F., Otsuka, F., Virmani, R., and Falk, E. 2014. Mechanisms of plaque formation and
rupture. Circ. Res. 114(12): 1852-1866. PMID: 24902970 doi:
10.1161/CIRCRESAHA.114.302721
Butcovan, D., Mocanu, V., Baran, D., Ciurescu, D., and Tinica, G. 2016. Assessment of
vulnerable and unstable carotid atherosclerotic plaques on endarterectomy specimens.
Exp. Ther. Med. 11(5): 2028-2032. PMID: 27168846 doi: 10.3892/etm.2016.3096
Butoi, E., Gan, A.M., Tucureanu, M.M., Stan, D., Macarie, R.D., Constantinescu, C., et al.
2016. Cross-talk between macrophages and smooth muscle cells impairs collagen and
metalloprotease synthesis and promotes angiogenesis. Biochim. Biophys. Acta. 1863(7
Pt A): 1568-1578. PMID: 27060293 doi: 10.1016/j.bbamcr.2016.04.001
Page 21 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
22
Chan, D.C., and Watts, G.F. 2006. Apolipoproteins as markers and managers of coronary
risk. QJ Med 99:277-287. PMID: 16504986 doi: 10.1093/qjmed/hcl027.
Chellan, B., Reardon, C.A., Getz, G.S., and Hofmann Bowman, M.A. 2016. Enzymatically
Modified Low-Density Lipoprotein Promotes Foam Cell Formation in Smooth Muscle
Cells via Macropinocytosis and Enhances Receptor-Mediated Uptake of Oxidized Low-
Density Lipoprotein. Arterioscler. Thromb. Vasc. Biol. 36(6): 1101-1113. PMID: 27079883
doi: 10.1161/ATVBAHA.116.307306
Chen, C. and Khismatullin, D. B. 2015. Oxidized low-density lipoprotein contributes to
atherogenesis via co-activation of macrophages and mast cells. PLoS One, 10(3):
e0123088. PMID: 25811595 doi: 10.1371/journal.pone.0123088
Chen, D., Bellussi, L.M., Passali, D., and Chen, L. 2013. LPS may enhance expression and
release of HMGB1 in human nasal epithelial cells in vitro. Acta. Otorhinolaryngol. Ital.
33(6): 398-404. PMID: 24376296 PMCID: PMC3870446
Chen, J., Jing, J., Yu, S., Song, M., Tan, H., Cui, B., et al. 2016. Advanced glycation
endproducts induce apoptosis of endothelial progenitor cells by activating receptor
RAGE and NADPH oxidase/JNK signaling axis. Am. J. Transl. Res. 8(5): 2169-2178. PMID:
27347324 PMCID: PMC4891429
Cipolletta, C., Ryan, K.E., Hanna, E.V., and Trimble, E.R. 2005. Activation of peripheral blood
CD14+ monocytes occurs in diabetes. Diabetes, 54(9):2779-86. PMID: 16123369 doi.
10.2337/diabetes.54.9.2779
Corr, E. M., Corr, E.M., Cunningham, C.C., and Dunne, A. 2016. Cholesterol crystals activate
Syk and PI3 kinase in human macrophages and dendritic cells. Atherosclerosis, 251: 197-
205. PMID: 27356299 doi: 10.1016/j.atherosclerosis.2016.06.035
Page 22 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
23
Dai, D., Xiong, W., Fan, Q., Wang, H., Chen, Q., Shen, W., et al. 2016. "Association of
decreased serum sTREM-1 level with the severity of coronary artery disease: Inhibitory
effect of sTREM-1 on TNF-alpha- and oxLDL-induced inflammatory reactions in
endothelial cells." Medicine (Baltimore) 95(37): e4693. PMID: 27631216 doi:
10.1097/MD.0000000000004693
Fraley, A. E., and Tsimikas, S. 2006. Clinical applications of circulating oxidized low-density
lipoprotein biomarkers in cardiovascular disease. Curr. Opin. Lipidol. 17(5):502-9. PMID:
16960498 DOI: 10.1097/01.mol.0000245255.40634.b5
Foell , D., Kane, D., Bresnihan, B., Vogl, T., Nacken, W., Sorg, C., Fitzgerald, O., and Roth, J.
2003. Expression of the pro-inflammatory protein S100A12 (EN-RAGE) in rheumatoid
and psoriatic arthritis. Rheumatology (Oxford), 42(11):1383-9. PMID: 12832707 DOI:
10.1093/rheumatology/keg385
Frostegard, J., Zhang, Y., Sun, J., Yan, K., and Liu, A. 2016. Oxidized Low-Density Lipoprotein
(OxLDL)-Treated Dendritic Cells Promote Activation of T Cells in Human Atherosclerotic
Plaque and Blood, Which Is Repressed by Statins: microRNA let-7c Is Integral to the
Effect. J. Am. Heart. Assoc. 5(9). PMID: 27650878 pii: e003976. doi:
10.1161/JAHA.116.003976.
Gargiulo, S., Gamba, P., Testa, G., Rossin, D., Biasi, F., Poli, G., et al. 2015. Relation between
TLR4/NF-kappaB signaling pathway activation by 27-hydroxycholesterol and 4-
hydroxynonenal, and atherosclerotic plaque instability. Aging Cell, 14(4): 569-581. PMID:
25757594 doi: 10.1111/acel.12322
Goyette, J., Yan, W.X., Yamen, E., Chung, Y.M., Lim, S.Y., Hsu, K., et al. 2009. Pleiotropic roles
of S100A12 in coronary atherosclerotic plaque formation and rupture. J. Immunol.
183(1): 593-603. PMID: 19542470 doi: 10.4049/jimmunol.0900373
Page 23 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
24
Gray, K., Kumar, S., Figg, N., Harrison, J., Baker, L., Mercer, J., et al. 2015. Effects of DNA
damage in smooth muscle cells in atherosclerosis. Circ. Res. 116(5): 816-826. PMID:
25524056 doi: 10.1161/CIRCRESAHA.116.304921
Gupta, G.K., Agrawal, T., Rai, V., Del Core, M.G., Hunter, W.J. 3rd, and Agrawal, D.K. 2016.
Vitamin D Supplementation Reduces Intimal Hyperplasia and Restenosis following
Coronary Intervention in Atherosclerotic Swine. PLoS One, 11(6):e0156857. doi:
10.1371/journal.pone.0156857. PMID: 27271180
Heier, M., Margeirsdottir, H.D., Gaarder, M., Stensaeth, K.H., Brunborg, C., Torjesen, P.A., et
al. 2015. Soluble RAGE and atherosclerosis in youth with type 1 diabetes: a 5-year
follow-up study. Cardiovasc. Diabetol. 14: 126. PMID: 26408307 doi: 10.1186/s12933-
015-0292-2
Huebener, P., Pradere, J.P., Hernandez, C., Gwak, G.Y., Caviglia, J.M., Mu, X., et al. 2015. The
HMGB1/RAGE axis triggers neutrophil-mediated injury amplification following necrosis.
J. Clin. Invest. 125(2): 539-550. PMID: 25562324 doi: 10.1172/JCI76887
Ionita, M. G., Vink, A., Dijke, I.E., Laman, J.D., Peeters, W., van der Kraak, P.H., et al. 2009.
High levels of myeloid-related protein 14 in human atherosclerotic plaques correlate
with the characteristics of rupture-prone lesions. Arterioscler. Thromb. Vasc. Biol. 29(8):
1220-1227. PMID: 19520974 doi: 10.1161/ATVBAHA.109.190314
Isaksen, B. and Fagerhol, M. K. 2001. Calprotectin inhibits matrix metalloproteinases by
sequestration of zinc. Mol. Pathol. 54(5): 289-292. PMID: 11577169 PMCID:
PMC1187084
Itabe, H., Obama, T., and Kato, R. 2011. The Dynamics of Oxidized LDL during Atherogenesis.
J. Lipids, 2011: 418313. PMID: 21660303 doi: 10.1155/2011/418313
Page 24 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
25
Jaw, J. E., Tsuruta, M., Oh, Y., Schipilow, J., Hirano, Y., Ngan, D.A., et al. 2016. Lung exposure
to lipopolysaccharide causes atherosclerotic plaque destabilisation. Eur. Respir. J. 48(1):
205-215. PMID: 27009170 doi: 10.1183/13993003.00972-2015
Jehle, A. B., Li, Y., Stechschulte, A. C., Stechschulte, D. J., and Dileepan, K.N. 2000. Endotoxin
and mast cell granule proteases synergistically activate human coronary artery
endothelial cells to generate interleukin-6 and interleukin-8. J. Interferon Cytokine Res.
20(4):361-8. PMID: 10805370 doi: 10.1089/107999000312298
Jialal, I., Devaraj, S., Bettaieb, A., Ha, F., and Adams-Huet, B. 2015. Increased adipose tissue
secretion of Fetuin-A, lipopolysaccharide-binding protein and high-mobility group box
protein 1 in metabolic syndrome. Atherosclerosis, 241(1): 130-137. PMID: 25978344 doi:
10.1016/j.atherosclerosis.2015.04.814
Jialal, I., Rajamani, U., Adams-Huet, B., and Kaur, H. 2014. Circulating pathogen-associated
molecular pattern - binding proteins and High Mobility Group Box protein 1 in nascent
metabolic syndrome: implications for cellular Toll-like receptor activity. Atherosclerosis,
236(1): 182-187. PMID: 25063948 doi: 10.1016/j.atherosclerosis.2014.06.022
Kierdorf , K. and Fritz, G. 2013. RAGE regulation and signaling in inflammation and beyond. J.
Leukoc. Biol. 94(1):55-68. doi: 10.1189/jlb.1012519. PMID: 23543766
Kim, J., Seo, M., Kim, S.K., and Bae, Y.S. 2016. Flagellin-induced NADPH oxidase 4 activation
is involved in atherosclerosis. Sci. Rep. 6: 25437. PMID: 27146088 doi:
10.1038/srep25437
Kim, J. S., Lee, S.G., Oh, J., Park, S., Park, S.I., Hong, S.Y., et al. 2016. Development of
Advanced Atherosclerotic Plaque by Injection of Inflammatory Proteins in a Rabbit Iliac
Artery Model. Yonsei Med. J. 57(5): 1095-1105. PMID: 27401639 doi:
10.3349/ymj.2016.57.5.1095
Page 25 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
26
Kim, J. Y., Kim, H., Jung, B.J., Kim, N.R., Park, J.E., and Chung, D.K. 2013. Lipoteichoic acid
isolated from Lactobacillus plantarum suppresses LPS-mediated atherosclerotic plaque
inflammation. Mol. Cells, 35(2): 115-124. PMID: 23456333 doi: 10.1007/s10059-013-
2190-3
Koening, W., Karakas, M., Zierer, A., Herder, C., Baumert, J., Meisinger, C., and Thorand, B.
2011. Oxidized LDL and the Risk of Coronary Heart Disease: Results from the
MONICA/KORA Augsburg Study. Clin. Chem. 57:1196-200. PMID: 21697499 doi:
10.1373/clinchem.2011.165134.
Kohno, T., Anzai, T., Kaneko, H., Sugano, Y., Shimizu, H., and Shimoda, M., et al. 2012. High-
mobility group box 1 protein blockade suppresses development of abdominal aortic
aneurysm. J. Cardiol. 59(3): 299-306. PMID: 22365948 doi: 10.1016/j.jjcc.2012.01.007
Laman, J. D., Schoneveld, A.H., Moll, F.L., van Meurs, M., and Pasterkamp, G. 2002.
Significance of peptidoglycan, a proinflammatory bacterial antigen in atherosclerotic
arteries and its association with vulnerable plaques. Am. J. Cardiol. 90(2): 119-123.
PMID: 12106839 http://dx.doi.org/10.1016/S0002-9149(02)02432-3
Lanter, B. B., Sauer, K., and Davies, D.G. 2014. Bacteria present in carotid arterial plaques
are found as biofilm deposits which may contribute to enhanced risk of plaque rupture.
MBio. 5(3): e01206-01214. PMID: 24917599 doi: 10.1128/mBio.01206-14
Li, H., Hong, F., Pan, S., Lei, L., and Yan, F. 2016. Silencing Triggering Receptors Expressed on
Myeloid Cells-1 Impaired the Inflammatory Response to Oxidized Low-Density
Lipoprotein in Macrophages. Inflammation, 39(1): 199-208. PMID: 26277357 doi:
10.1007/s10753-015-0239-5
Page 26 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
27
Li, H., Xu, H., and Sun, B. 2012. Lipopolysaccharide regulates MMP-9 expression through
TLR4/NF-kappaB signaling in human arterial smooth muscle cells. Mol. Med. Rep. 6(4):
774-778. PMID: 22842850 doi: 10.3892/mmr.2012.1010
Li, J. F., Chen, S., Feng, J.D., Zhang, M.Y., and Liu, X.X. 2014. Probucol via inhibition of NHE1
attenuates LPS-accelerated atherosclerosis and promotes plaque stability in vivo. Exp.
Mol. Pathol. 96(2): 250-256. PMID: 24594116 doi: 10.1016/j.yexmp.2014.02.010
Ligthart, S., Sedaghat, S., Ikram, M.A., Hofman, A., Franco, O.H., and Dehghan. A. 2014. EN-
RAGE: a novel inflammatory marker for incident coronary heart disease. Arterioscler.
Thromb. Vasc. Biol. 34(12): 2695-2699. PMID: 25341801 doi:
10.1161/ATVBAHA.114.304306
Liu, J., Ren, Y.G., Zhang, L.H., Tong, Y.W., and Kang, L. 2014. Serum S100A12 concentrations
are correlated with angiographic coronary lesion complexity in patients with coronary
artery disease. Scand. J. Clin. Lab. Invest. 74(2): 149-154. PMID: 24341566 doi:
10.3109/00365513.2013.864786
Lood, C., Tyden, H., Gullstrand, B., Jonsen, A., Kallberg, E., Morgelin, M., et al. 2016. Platelet-
Derived S100A8/A9 and Cardiovascular Disease in Systemic Lupus Erythematosus.
Arthritis Rheumatol. 68(8): 1970-1980. PMID: 26946461 doi: 10.1002/art.39656
McCormick, M. M., Rahimi, F., Bobryshev, Y.V., Gaus, K., Zreiqat, H., Cai, H., et al. 2005.
S100A8 and S100A9 in human arterial wall. Implications for atherogenesis. J. Biol. Chem.
280(50): 41521-41529. PMID: 16216873 doi: 10.1074/jbc.M509442200
Medeiros, M. C., Frasnelli, S.C., Bastos Ade, S., Orrico, S.R., Rossa, C, Jr. 2014. Modulation of
cell proliferation, survival and gene expression by RAGE and TLR signaling in cells of the
innate and adaptive immune response: role of p38 MAPK and NF-κB. J. Appl. Oral Sci.
22(3): 185-193. PMID: 25025559 PMCID: PMC4072269
Page 27 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
28
Miller, Y. I. 2005. Toll-like receptors and atherosclerosis: oxidized LDL as an endogenous
Toll-like receptor ligand. Future Cardiol. 1(6): 785-792. PMID: 19804052 doi:
10.2217/14796678.1.6.785
Minamisawa, M., Motoki ,H., Izawa, A., Kashima, Y., Hioki, H., Abe, N., et al. 2016.
Comparison of Inflammatory Biomarkers in Outpatients With Prior Myocardial
Infarction. Int. Heart J. 57:11-17. doi: 10.1536/ ihj.15-197. PMID: 26742699
Mittal, B., Mishra, A., Srivastava, A., Kumar, S., and Garg, N. 2014. Matrix metalloproteinases
in coronary artery disease. Adv. Clin. Chem. 64:1-72. PMID: 24938016
Moz, S., Basso, D., Padoan, A., Bozzato, D., Fogar, P., Zambon, C.F., et al. 2016. Blood
expression of matrix metalloproteinases 8 and 9 and of their inducers S100A8 and
S100A9 supports diagnosis and prognosis of PDAC-associated diabetes mellitus. Clin.
Chim. Acta. 456: 24-30. PMID: 26923392 doi: 10.1016/j.cca.2016.02.018
Murakami, Y., Kohsaka, H., Kitasato, H., and Akahoshi, T. 2007. Lipopolysaccharide-induced
up-regulation of triggering receptor expressed on myeloid cells-1 expression on
macrophages is regulated by endogenous prostaglandin E2. J. Immunol. 178(2): 1144-
1150. PMID: 17202378 doi: 10.4049/jimmunol.178.2.1144
Nakajima, Y., Inagaki, Y., Kido, J., and Nagata, T. 2015. Advanced glycation end products
increase expression of S100A8 and A9 via RAGE-MAPK in rat dental pulp cells. Oral Dis.
21(3): 328-334. PMID: 25098709 doi: 10.1111/odi.12280
Nam, M. H., Son, W.R., Lee, Y.S., and Lee, K.W. 2016. Glycolaldehyde-derived advanced
glycation end products (glycol-AGEs)-induced vascular smooth muscle cell dysfunction is
regulated by the AGES-receptor (RAGE) axis in endothelium. Cell Commun. Adhes. 22(2-
6):67-78 PMID: 27602595 doi: 10.1080/15419061.2016.1225196
Page 28 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
29
Newby, A. C. 2008. Metalloproteinase expression in monocytes and macrophages and its
relationship to atherosclerotic plaque instability. Arterioscler.Thromb.Vasc.Biol. 28(12):
2108-2114. PMID: 18772495 doi: 10.1161/ATVBAHA.108.173898
Newby, A. C. 2015. Metalloproteinases promote plaque rupture and myocardial infarction:
A persuasive concept waiting for clinical translation. Matrix Biol. 44-46: 157-166. PMID:
25636537 doi: 10.1016/j.matbio.2015.01.015
Ng, C. H., Qiang Yao, X., Huang, Y., and Chen, Z.Y. 2008. Oxidised cholesterol is more
hypercholesterolaemic and atherogenic than non-oxidised cholesterol in hamsters. Br. J.
Nutr. 99(4): 749-755. PMID: 17916278 doi: 10.1017/S0007114507842784
Niccoli, G., Mongiardo, R., Lanza, G.A., Ricco, A., Burzotta, F., Trani, C., et al. 2007. The
complex link between oxidised low-density lipoprotein and unstable angina. J.
Cardiovasc. Med. (Hagerstown), 8(5): 387-391. PMID: 17443110 doi:
10.2459/01.JCM.0000268127.36295.04
Oesterle, A. and Bowman, M. A. 2015. S100A12 and the S100/Calgranulins: Emerging
Biomarkers for Atherosclerosis and Possibly Therapeutic Targets. Arterioscler. Thromb.
Vasc. Biol. 35(12): 2496-2507. PMID: 26515415 doi: 10.1161/ATVBAHA.115.302072
Otsuka, F., Joner, M., Prati, F., Virmani, R., and Narula, J. 2014. Clinical classification of
plaque morphology in coronary disease. Nat. Rev. Cardiol. 11(7): 379-389. PMID:
24776706 doi: 10.1038/nrcardio.2014.62
Park, B. S. and Lee, J. O. 2013. Recognition of lipopolysaccharide pattern by TLR4 complexes.
Exp. Mol. Med. 45: e66. PMID: 24310172 doi: 10.1038/emm.2013.97
Pelham, C. J. and Agrawal, D. K. 2014. Emerging roles for triggering receptor expressed on
myeloid cells receptor family signaling in inflammatory diseases. Expert Rev. Clin.
Immunol. 10(2): 243-256. PMID: 24325404 doi: 10.1586/1744666X.2014.866519
Page 29 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
30
Rai, V., Rao, V.H., Shao, Z., and Agrawal, D.K. 2016. Dendritic Cells Expressing Triggering
Receptor Expressed on Myeloid Cells-1 Correlate with Plaque Stability in Symptomatic
and Asymptomatic Patients with Carotid Stenosis. PLoS One, 11(5): e0154802. PMID:
27148736 doi: 10.1371/journal.pone.0154802
Rao, V. H., Kansal, V., Stoupa, S., and Agrawal, D.K. 2014. MMP-1 and MMP-9 regulate
epidermal growth factor-dependent collagen loss in human carotid plaque smooth
muscle cells. Physiol. Rep. 2(2): e00224. PMID: 24744893 doi: 10.1002/phy2.224
Rao, V. H., Rai, V., Stoupa, S., and Agrawal, D.K. 2015. Blockade of Ets-1 attenuates
epidermal growth factor-dependent collagen loss in human carotid plaque smooth
muscle cells. Am. J Physiol. Heart Circ. Physiol. 309(6): H1075-1086. PMID: 26254334 doi:
10.1152/ajpheart.00378.2015
Rao, V. H., Rai, V., Stoupa, S., Subramanian, S., and Agrawal, D.K. 2016a. Tumor necrosis
factor-alpha regulates triggering receptor expressed on myeloid cells-1-dependent
matrix metalloproteinases in the carotid plaques of symptomatic patients with carotid
stenosis. Atherosclerosis, 248: 160-169. PMID: 27017522 doi:
10.1016/j.atherosclerosis.2016.03.021.
Rao, V.H., Rai, V., Stoupa, S., Subramanian, S., and Agrawal, D.K. 2016b. Data on TREM-1
activation destabilizing carotid plaques. Data Brief, 8: 230-234. PMID: 27331093 doi:
10.1016/j.dib.2016.05.047
Raveendran, V.V., Tan, X., Sweeney, M. E., Levant, B., Slusser, J., Stechschulte, D.J., and
Dileepan, K. N. 2011. Lipopolysaccharide induces H1 receptor expression and enhances
histamine responsiveness in human coronary artery endothelial cells. Immunology,
132(4):578-88. PMID: 21255012 doi: 10.1111/j.1365-2567.2010.03403.x.
Page 30 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
31
Ridker, P. M. and Luscher, T. F. 2014. Anti-inflammatory therapies for cardiovascular
disease. Eur. Heart J. 35(27): 1782-1791. PMID: 24864079 doi:
10.1093/eurheartj/ehu203
Rosenfeld, M. E. and Campbell, L. A. 2011. Pathogens and atherosclerosis: update on the
potential contribution of multiple infectious organisms to the pathogenesis of
atherosclerosis. Thromb. Haemost. 106(5): 858-867. PMID: 22012133 doi:
10.1160/TH11-06-0392
Schelbergen, R. F., Blom, A.B., van den Bosch, M.H., Sloetjes, A., Abdollahi-Roodsaz, S.,
Schreurs, B.W., et al. 2012. Alarmins S100A8 and S100A9 elicit a catabolic effect in
human osteoarthritic chondrocytes that is dependent on Toll-like receptor 4. Arthritis
Rheum. 64(5): 1477-1487. PMID: 22012133 doi: 10.1160/TH11-06-0392
Schiopu, A. and Cotoi, O. S. 2013. S100A8 and S100A9: DAMPs at the crossroads between
innate immunity, traditional risk factors, and cardiovascular disease. Mediators Inflamm.
2013: 828354. PMID: 24453429 doi: 10.1155/2013/828354
Schoneveld, A. H., Oude Nijhuis, M.M., van Middelaar, B., Laman, J.D., de Kleijn, D.P., and
Pasterkamp, G. 2005. Toll-like receptor 2 stimulation induces intimal hyperplasia and
atherosclerotic lesion development. Cardiovasc. Res. 66(1): 162-169. PMID: 15769459
doi: 10.1016/j.cardiores.2004.12.016
Shiotsu, Y., Mori, Y., Nishimura, M., Sakoda, C., Tokoro, T., Hatta, T., et al. 2011. Plasma
S100A12 level is associated with cardiovascular disease in hemodialysis patients. Clin. J.
Am. Soc. Nephrol. 6(4): 718-723. PMID: 21258041 doi: 10.2215/CJN.08310910
Singh, R.B., Mengi, S.A., Xu, Y.J., Arneja, A.S., and Dhalla, N.S. 2002. Pathogenesis of
atherosclerosis: A multifactorial process. Exp. Clin. Cardiol. 7(1): 40–53. PMID: 19644578
Page 31 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
32
Smith, D.D., Tan, X., Raveendran,V. V., Tawfik,O., Stechschulte,D. J., and Dileepan, K. N.
2012. Mast cell deficiency attenuates progression of atherosclerosis and hepatic
steatosis in apolipoprotein E-null mice. Am. J. Physiol. Heart Circ. Physiol. 302(12):
H2612–H2621. doi: 10.1152/ajpheart.00879.2011 PMCID: PMC3378258
Speidl, W. S., Toller, W.G., Kaun, C., Weiss, T.W., Pfaffenberger, S., Kastl, S.P., et al. 2004.
Catecholamines potentiate LPS-induced expression of MMP-1 and MMP-9 in human
monocytes and in the human monocytic cell line U937: possible implications for peri-
operative plaque instability. FASEB J. 18(3): 603-605. PMID: 14715701 doi:
10.1096/fj.03-0454fje
Sreckovic, B., Sreckovic, V.D., Soldatovic, I., Colak, E., Sumarac-Dumanovic, M., Janeski, H. et
al. 2016. Homocysteine is a marker for metabolic syndrome and atherosclerosis.
Diabetes Metab. Syndr. PMID: 27600468 doi: 10.1016/j.dsx.2016.08.026.
Su, Z., Lu, H., Jiang, H., Zhu, H., Li, Z., Zhang, P., et al. 2015. IFN-gamma-producing Th17 cells
bias by HMGB1-T-bet/RUNX3 axis might contribute to progression of coronary artery
atherosclerosis. Atherosclerosis, 243(2): 421-428. PMID: 26520896 doi:
10.1016/j.atherosclerosis.2015.09.037
Sun, J., Sukhova. G. K., Wolters, P. J., Yang, M., Kitamoto, S., Libby, P., MacFarlane, L. A.,
Mallen-St Clair, J., and Shi, G. P. 2007. Mast cells promote atherosclerosis by releasing
proinflammatory cytokines. Nat. Med. 13: 719–724 [PubMed: 17546038] DOI:
10.1038/nm1601
Takeuchi, M. 2016. Serum Levels of Toxic AGEs (TAGE) May Be a Promising Novel Biomarker
for the Onset/Progression of Lifestyle-Related Diseases. Diagnostics (Basel), 6(2). PMID:
27338481 doi: 10.3390/diagnostics6020023
Page 32 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
33
Talreja, J., Kabir, M. H., B Filla, M., Stechschulte, D. J., and Dileepan, K.N. 2004 Histamine
induces Toll-like receptor 2 and 4 expression in endothelial cells and enhances sensitivity
to Gram-positive and Gram-negative bacterial cell wall components. Immunology,
113(2):224-33. PMID: 15379983 doi: 10.1111/j.1365-2567.2004.01946.x
Tan, X., Essengue, S., Talreja, J., Reese, J., Stechschulte, D. J., and Dileepan, K. N. 2007.
Histamine directly and synergistically with lipopolysaccharide stimulates
cyclooxygenase-2 expression and prostaglandin I(2) and E(2) production in human
coronary artery endothelial cells. J. Immunol. 179(11):7899-906. PMID: 18025237
doi: 10.4049/jimmunol.179.11.7899
Thankam, F. G., Dilisio, M.F., Dietz, N.E., and Agrawal, D.K. 2016. TREM-1, HMGB1 and RAGE
in the Shoulder Tendon: Dual Mechanisms for Inflammation Based on the Coincidence of
Glenohumeral Arthritis. PLoS One, 11(10): e0165492. PMID: 27792788 doi:
10.1371/journal.pone.0165492
van Lent, P. L., Blom, A.B., Schelbergen, R.F., Sloetjes, A., Lafeber, F.P., Lems, W.F., et al.
2012. Active involvement of alarmins S100A8 and S100A9 in the regulation of synovial
activation and joint destruction during mouse and human osteoarthritis. Arthritis
Rheum. 64(5): 1466-1476. PMID: 22143922 doi: 10.1002/art.34315
Virmani, R., Burke, A.P., Farb, A., and Kolodgie, F.D. 2006. Pathology of the vulnerable
plaque. J. Am. Coll. Cardiol. 47(8 Suppl): C13-18. PMID: 16631505 doi:
10.1016/j.jacc.2005.10.065
Vogl, T., Eisenblatter, M., Voller, T., Zenker, S., Hermann, S., van Lent, P., et al. 2014. Alarmin
S100A8/S100A9 as a biomarker for molecular imaging of local inflammatory activity.
Nat. Commun. 5: 4593. PMID: 25098555 doi: 10.1038/ncomms5593
Page 33 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
34
Wu, C. X., Sun, H., Liu, Q., Guo, H., and Gong, J.P. 2012. LPS induces HMGB1 relocation and
release by activating the NF-kappaB-CBP signal transduction pathway in the murine
macrophage-like cell line RAW264.7. J. Surg. Res. 175(1): 88-100. PMID: 21571302 doi:
10.1016/j.jss.2011.02.026
Xia, G. L., Wang, Y.K., and Huang, Z.Q. 2016. The Correlation of Serum Myeloid-Related
Protein-8/14 and Eosinophil Cationic Protein in Patients with Coronary Artery Disease.
Biomed. Res. Int. 2016: 4980251. PMID: 27022611 doi: 10.1155/2016/4980251
Xu, L., Wang, Y.R., Li, P.C., and Feng, B. 2016. Advanced glycation end products increase
lipids accumulation in macrophages through upregulation of receptor of advanced
glycation end products: increasing uptake, esterification and decreasing efflux of
cholesterol. Lipids Health Dis. 15(1): 161. PMID: 27644038 doi: 10.1186/s12944-016-
0334-0
Xu, X. H., Shah, P.K., Faure, E., Equils, O., Thomas, L., Fishbein, M.C., et al. 2001. Toll-like
receptor-4 is expressed by macrophages in murine and human lipid-rich atherosclerotic
plaques and upregulated by oxidized LDL. Circulation, 104(25): 3103-3108. PMID:
11748108 http://dx.doi.org/10.1161/hc5001.100631
Yamashita, A., Nishihira, K., Matsuura, Y., Ito, T., Kawahara, K., Hatakeyama, K., et al. 2012.
Paucity of CD34-positive cells and increased expression of high-mobility group box 1 in
coronary thrombus with type 2 diabetes mellitus. Atherosclerosis, 224(2): 511-514.
PMID: 22862965 doi: 10.1016/j.atherosclerosis.2012.07.027
Yan, L., Bjork, P., Butuc, R., Gawdzik, J., Earley, J., Kim, G., et al. 2013. Beneficial effects of
quinoline-3-carboxamide (ABR-215757) on atherosclerotic plaque morphology in
S100A12 transgenic ApoE null mice. Atherosclerosis, 228(1): 69-79. PMID: 23497784 doi:
10.1016/j.atherosclerosis.2013.02.023
Page 34 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
35
Zheng, H., Heiderscheidt, C.A., Joo, M., Gao, X., Knezevic, N., Mehta, D., et al. 2010. MYD88-
dependent and -independent activation of TREM-1 via specific TLR ligands. Eur. J.
Immunol. 40(1): 162-171. PMID: 19904768 doi: 10.1002/eji.200839156
Zhu, Y., Liao, H., Xie, X., Yuan, Y., Lee, T.S., Wang, N., Wang, X., Shyy, J.Y., and Stemerman,
M.B. 2005. Oxidized LDL downregulates ATP-binding cassette transporter-1 in human
vascular endothelial cells via inhibiting liver X receptor (LXR). Cardiovasc. Res. 68(3):425-
32. PMID: 16099444 DOI: 10.1016/j.cardiores.2005.07.003
Zimmer, S., Grebe,A., and Latz, E. 2015. Danger signaling in atherosclerosis. Circ. Res. 116(2):
323-340. PMID: 25593277 doi: 10.1161/CIRCRESAHA.116.301135
Zysset, D., Weber, B., Rihs, S., Brasseit, J., Freigang, S., Riether, C., et al. 2016. TREM-1 links
dyslipidemia to inflammation and lipid deposition in atherosclerosis. Nat. Commun. 7:
13151. PMID: 27762264 doi: 10.1038/ncomms13151
Page 35 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
36
Figure legend
Figure 1: Pathogenesis of the development of atherosclerotic plaque. Fatty streaks are the
initial lesions in the process. The inflammation and oxidative stress in the fatty streaks and
lipid deposits lead to the formation of atheroma with increased VSMCs proliferation and
homing of inflammatory cells. Innate immune response results in the production of
inflammatory cytokines and increased inflammation in atheroma. Apoptosis and necrosis of
the cells result in secretion of damage associated molecular patterns (DAMPs), which
further activate the inflammatory mediators resulting in the formation of necrotic core.
Thus, atheroma progresses through atheromatous plaque to fibro-atheromatous plaque
with increased inflammation and inflammatory cytokines. This leads to thining of fibrous
cap, endothelial dysfunction, angiogenesis, VSMCs proliferation and collagen damage
resulting in the destabilization of the plaque to become unstable.
oxLDL - Minimally oxidized-low density lipoproteins; RBCs - red blood cells, VSMCs -
vascular smooth muscle cells.
Figure 2: Progression of atherosclerotic plaque. Increased deposition of the oxLDL and
AGEs induces the innate immune response resulting in increased homing of inflammatory
cells and secretion of inflammatory cytokines, such as IL-6, TNF-α, IFN-γ and IL-1β, leading to
formation of apoptotic bodies and necrotic core and enhanced inflammation in plaque area.
LPS, bacterial endotoxins and endogenously released substance such as histamine also
enhance inflammatory cytokines and other mediators of inflammation. HMGB-1 released
from these dying cells activates the inflammatory cascade through TREM-1, TRLs and RAGE
leading to enhanced inflammation, inflammatory cytokine secretion, activation of MMPs,
collagen loss, angiogenesis and hemorrhage. VSMCs proliferation, calcification, necrotic core
Page 36 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
37
and thining of the fibrous cap render the plaque vulnerable to rupture. AGEs - Advanced
glycation end products, HMGB-1 - high mobility group box-1, IL-6 – interleukin-6, IL-1β –
interleukin-1 beta, IFN-γ- interferon-gamma, LPS - lipopolysaccharides, ox-LDL - minimally
oxidized-low density lipoproteins, MMPs - matrix metalloproteinases, RAGE - receptor for
advanced glycation end products, TREM-1 - triggering receptor expressed on myeloid cells,
TLRs - toll-like receptors, TNF-α - tumor necrosis factor- alpha, and VSMCs - vascular smooth
muscle cells.
Figure 3: Role of DAMPs and PAMPs in inflammation-mediated plaque vulnerability.
HMGB1 secreted from necrotic cells and from the interaction of apoptotic bodies with
inflammatory cells interacts with RAGE, TREM-1 and TLRs to activate them. Activation of
these inflammatory receptors initiates a downstream signaling pathway involving NF-κB
resulting in increased secretion of inflammatory cytokines such as IL-6, TNF-α, IFN-γ and IL-
1β. This leads to further increased inflammation, activation of MMPs, collagen loss and
plaque rupture. Accumulation and oxidation of AGEs and their interaction with RAGE and
EN-RAGE, and accumulation of alarmins S100A8 and S100A9 and interaction with TLRs
enhance inflammatotory cytokine production and plaque vulnerability. LPS-induced HMGB-
1, TREM-1, TLRs, and alarmins and peptidoglycans-induced activation of TLRs also increase
inflammatory cytokines and plaque vulnerability. AGEs - Advanced glycation end products,
EN-RAGE - endogenous receptor for advanced glycation end products, ECM - extra cellular
matrix, HMGB-1 - high mobility group box1, IFN-γ - interferon gamma, IL-6 - interleukin-6, IL-
1β - interleukin- 1beta, LPS - lipopolysaccharides, MMPs - matrix metalloproteinases, oxLDL
- minimally oxidized lo density lipoprotein, NF-kB - nuclear-factor kappa beta, RAGE -
Page 37 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
38
receptor for advanced glycation end products, TLRs - toll-like receptors, TREM1 - triggering
receptor expressed on myeloid cell1, TNF-α - tumor necrosis factor alpha.
Page 38 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
Apoptotic cell
Adhesion molecules, chemoattractants, and growth factors
Angiogenesis
Endothelial cell
Foam cells
Hemorrhage
Lipids
Monocyte
Macrophages
Necrotic core
oxLDL
Platelets
RBCs
Thrombus
VSMCs
Fatty Streak
Atheroma Atheromatous
plaque
Fibro-atheromatous
plaque
Ruptured
plaque
↑VSMCs
proliferation
↑ Homing of inflammatory cell and secretion of
inflammatory cytokines
Endothelial dysfunction, VSMCs proliferation, impaired repair
and plaque rupture
oxLDL accumulation, release of
chemoattractant and growth factors
Increased inflammation, necrotic core formation,
angiogenesis, and hemorrhage
Page 39 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
Fatty Streak
Atheroma
Atheromatous
plaque
Fibro-atheromatous
plaque
Ruptured
plaque
Deposition and oxidation of lipids (oxLDL) and AGEs
Activation of innate and adaptive immunity
Release of adhesion molecules, chemoattractant and growth factors
Increased homing of inflammatory cells
(monocyte/macrophage)
Apoptosis and necrosis
↑inflammatory cytokines (IL-6, TNF-α, IL-1β, etc.)
↑HMGB-1
Stages of plaque development
Pathogenesis of plaque development and rupture
Activation of inflammatory surface receptors (RAGE, TREM-1, TLR2/4) on
macrophages, endothelial cells and VSMCs
Increased inflammatory cytokines, MMPs, necrotic
core formation, angiogenesis, hemorrhage
Collagen damage, thinning of fibrous cap, calcification,
hemorrhage
LPS/endotoxin/ endogenous substances
Page 40 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology
Draft
LPS
HMGB1
TREM
-1
TLR
s
RAGE
↑ NF-κB
↑ Inflammatory cytokines (TNF-α, IL-1β, IL6, IL-8, IFN-γ)
↑ Plaque vulnerability
↑ MMPs
AGEs
Collagen and ECM degradation
Cytoplasmic Kinases S100A8 and
S100A9
Lipids
Apoptotic bodies
oxLDL
Vascular smooth
muscle cells
Macrophage
Foam cells
Monocytes
Apoptotic cells
Hemorrhage
Necrotic core
Peptidoglycans
Bacteria
↑ MMPs
Page 41 of 41
https://mc06.manuscriptcentral.com/cjpp-pubs
Canadian Journal of Physiology and Pharmacology