Functional role for toll-like receptors in atherosclerosis and arterial remodeling

Preeclampsia and coronary plaque erosion: Manifestations of endothelial dysfunction resulting in cardiovascular events in women

Atherosclerosis is the major underlying pathology of cardiovascular disease (CVD). The risk for CVD is increased in women with a history of preeclampsia. Multiple studies have indicated that accelerated atherosclerosis underlies this increased CVD risk. Furthermore, it has been suggested that endothelial dysfunction and inflammation play an important role in the increased CVD risk of women with preeclampsia. Rupture or erosion of atherosclerotic plaques can induce the formation of thrombi that underlie the onset of acute clinical CVD such as myocardial infarction and stroke. In relatively young women, cardiovascular events are mainly due to plaque erosions. Eroded plaques have a distinct morphology compared to ruptured plaques, but have been understudied as a substrate for CVD. The currently available evidence points towards lesions with features of stability such as high collagen content and smooth muscle cells and with distinct mechanisms that further promote the pro-thrombotic environment such as Toll Like Receptor (TLR) signaling and endothelial apoptosis. These suggested mechanisms, that point to endothelial dysfunction and intimal thickening, may also play a role in preeclampsia. Pregnancy is considered a stress test for the cardiovascular system with preeclampsia as an additional pathological substrate for earlier manifestation of vascular disease. This review provides a summary of the possible common mechanisms involved in preeclampsia and accelerated atherosclerosis in young females and highlights plaque erosion as a likely substrate for CVD events in women with a history of preeclampsia.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Toll-like receptors mediating vascular malfunction: Lessons from receptor subtypes

Toll-like receptors (TLR) are a subfamily of pattern recognition receptors (PRR) implicated in a variety of vascular abnormalities. However, the pathophysiological role and the interplay between different TLR-mediated innate and adaptive immune responses during the development of vascular diseases remain largely unspecified. TLR are widely distributed in both immune and nonimmune cells in the blood vessel wall. The expressions and locations of TLR are dynamically regulated in response to distinct molecular patterns derived from pathogens or damaged host cells. As a result, the outcome of TLR signaling is agonist- and cell type-dependent. A better understanding of discrete TLR signaling pathways in the vasculature will provide unprecedented opportunities for the discovery of novel therapies in many inflammatory vascular diseases. The present brief review discusses the role of individual TLR in controlling cellular functions of the vascular system, by focusing on the inflammatory responses within the blood vessel wall which contribute to the development of hypertension and atherosclerosis.

Relation between TLR4/NF-κB signaling pathway activation by 27-hydroxycholesterol and 4-hydroxynonenal, and atherosclerotic plaque instability

It is now thought that atherosclerosis, although due to increased plasma lipids, is mainly the consequence of a complicated inflammatory process, with immune responses at the different stages of plaque development. Increasing evidence points to a significant role of Toll-like receptor 4 (TLR4), a key player in innate immunity, in the pathogenesis of atherosclerosis. This study aimed to determine the effects on TLR4 activation of two reactive oxidized lipids carried by oxidized low-density lipoproteins, the oxysterol 27-hydroxycholesterol (27-OH) and the aldehyde 4-hydroxynonenal (HNE), both of which accumulate in atherosclerotic plaques and play a key role in the pathogenesis of atherosclerosis. Secondarily, it examined their potential involvement in mediating inflammation and extracellular matrix degradation, the hallmarks of high-risk atherosclerotic unstable plaques. In human promonocytic U937 cells, both 27-OH and HNE were found to enhance cell release of IL-8, IL-1β, and TNF-α and to upregulate matrix metalloproteinase-9 (MMP-9) via TLR4/NF-κB-dependent pathway; these actions may sustain the inflammatory response and matrix degradation that lead to atherosclerotic plaque instability and to their rupture. Using specific antibodies, it was also demonstrated that these inflammatory cytokines increase MMP-9 upregulation, thus enhancing the release of this matrix-degrading enzyme by macrophage cells and contributing to plaque instability. These innovative results suggest that, by accumulating in atherosclerotic plaques, the two oxidized lipids may contribute to plaque instability and rupture. They appear to do so by sustaining the release of inflammatory molecules and MMP-9 by inflammatory and immune cells, for example, macrophages, through activation of TLR4 and its NF-κB downstream signaling.

TLR4 is a critical regulator of angiotensin II-induced vascular remodeling: the roles of extracellular SOD and NADPH oxidase

Toll-like receptor 4 (TLR4) and angiotensin II (AngII) induce vascular remodeling through the production of reactive oxygen species (ROS). AngII has also been shown to increase antioxidant enzyme extracellular superoxide dismutase (ecSOD). However, the roles of TLR4 in Ang II-induced ROS production, vascular remodeling and hypertension remain unknown. Mice lacking TLR4 function showed significant inhibition of vascular remodeling in response to chronic AngII infusion, with no impact on blood pressure. The increases in ROS level and NADPH oxidase activity in response to AngII infusion were markedly blunted in TLR4-deficient mice. Similar effects were observed in wild-type (WT) mice treated with a sub-depressor dose of the AT1 receptor antagonist irbesartan, which had no effects on TLR4-deficient mice. Intriguingly, the AngII infusion-induced increases in ecSOD activity and expression were rather enhanced in TLR4-deficient mice compared with WT mice, whereas the expression of the proinflammatory chemokine MCP-1 was decreased. Importantly, AngII-induced vascular remodeling was positively correlated with NADPH oxidase activity, ROS levels and MCP-1 expression levels. Notably, chronic norepinephrine infusion, which elevates blood pressure without increasing ROS production, did not induce significant vascular remodeling in WT mice. Taken together, these findings suggest that ROS elevation is required for accelerating vascular remodeling but not for hypertensive effects in this model. We demonstrated that TLR4 plays a pivotal role in regulating AngII-induced vascular ROS levels by inhibiting the expression and activity of the antioxidant enzyme ecSOD, as well as by activating NADPH oxidase, which enhances inflammation to facilitate the progression of vascular remodeling.

Infections and autoimmunity: role of human cytomegalovirus in autoimmune endothelial cell damage

Molecular mimicry between infectious agents and normal human host cell proteins represents one of the possible mechanisms responsible for autoimmunity. Among infectious agents, human cytomegalovirus (HCMV) is an ideal candidate for involvement in autoimmune disorders because of its lifelong persistence through periods of reactivation and latency and because of the extensive manipulation of innate and adaptive immunity. HCMV has been implicated in the pathogenesis of vascular damage in systemic sclerosis (SSc) and atherosclerosis. Based on our data, which demonstrate a cause-and-effect relationship between HCMV and endothelial cell aggression in SSc and atherosclerosis, we propose that immune responses to particular HCMV proteins may result in autoaggression through a mechanism of molecular mimicry of normally expressed endothelial cell surface molecules.

Sphingosine 1-phosphate induced anti-atherogenic and atheroprotective M2 macrophage polarization through IL-4

Sphingosine 1-phosphate (S1P) has been implicated in anti-atherogenic properties of high-density lipoproteins. However, the roles and signaling of S1P in macrophages, the main contributor to atherosclerosis, have not been well studied. Furthermore, pro-inflammatory M1 and anti-inflammatory M2 macrophage phenotypes may influence the development of atherosclerosis. Therefore, we investigated the effects of S1P on macrophage phenotypes, especially on M2 polarization and its signaling in relation to the anti-atherogenic properties of S1P. It was found that S1P induced anti-inflammatory M2 polarization via IL-4 secretion and its signaling, and induced IL-4Rα and IL-2Rγ. In addition, down-stream signalings, such as, stat-6 phosphorylation, SOCS1 induction, and SOCS3 suppression were also observed in macrophages in response to S1P. Furthermore, S1P-induced ERK activation, and the inhibitions of p38 MAPK and JNK were found to be key signals for IL-4 induction. Moreover, the anti-atherogenic effect of S1P in HDL was confirmed by the observation that oxidized LDL-induced lipid accumulation was attenuated in S1P-treated M2 macrophages. Furthermore, the atheroprotective effect of S1P was demonstrated by its anti-apoptotic effect on S1P-treated macrophages. The present study shows that S1P-induced M2 polarization of macrophages could be mediated via IL-4 signaling, and suggests that M2 polarization by S1P is responsible for the anti-atherogenic and atheroprotective properties of high-density lipoproteins in vivo.

Can the TLR-4-mediated signaling pathway be "a key inflammatory promoter for sporadic TAA"?

Thoracic aorta shows with advancing age various changes and a progressive deterioration in structure and function. As a result, vascular remodeling (VR) and medial degeneration (MD) occur as pathological entities responsible principally for the sporadic TAA onset. Little is known about their genetic, molecular, and cellular mechanisms. Recent evidence is proposing the strong role of a chronic immune/inflammatory process in their evocation and progression. Thus, we evaluated the potential role of Toll like receptor- (TLR-) 4-mediated signaling pathway and its polymorphisms in sporadic TAA. Genetic, immunohistochemical, and biochemical analyses were assessed. Interestingly, the rs4986790 TLR4 polymorphism confers a higher susceptibility for sporadic TAA (OR = 14.4, P = 0.0008) and it represents, together with rs1799752 ACE, rs3918242 MMP-9, and rs2285053 MMP-2 SNPs, an independent sporadic TAA risk factor. In consistency with these data, a significant association was observed between their combined risk genotype and sporadic TAA. Cases bearing this risk genotype showed higher systemic inflammatory mediator levels, significant inflammatory/immune infiltrate, a typical MD phenotype, lower telomere length, and positive correlations with histopatological abnormalities, hypertension, smoking, and ageing. Thus, TLR4 pathway should seem to have a key role in sporadic TAA. It might represent a potential useful tool for preventing and monitoring sporadic TAA and developing personalized treatments.

Biliverdin modulates the expression of C5aR in response to endotoxin in part via mTOR signaling

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Biliverdin mitigates LPS-dependent C5aR expression in macrophages in part via mTOR.

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Biliverdin promotes phosphorylation of Akt and PS6.

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Biliverdin decreases LPS-mediated induction of C5aR-associated cytokines.

Macrophages play a crucial role in the maintenance and resolution of inflammation and express a number of pro- and anti-inflammatory molecules in response to stressors. Among them, the complement receptor 5a (C5aR) plays an integral role in the development of inflammatory disorders. Biliverdin and bilirubin, products of heme catabolism, exert anti-inflammatory effects and inhibit complement activation. Here, we define the effects of biliverdin on C5aR expression in macrophages and the roles of Akt and mammalian target of rapamycin (mTOR) in these responses. Biliverdin administration inhibited lipopolysaccharide (LPS)-induced C5aR expression (without altering basal expression), an effect partially blocked by rapamycin, an inhibitor of mTOR signaling. Biliverdin also reduced LPS-dependent expression of the pro-inflammatory cytokines TNF-α and IL-6. Collectively, these data indicate that biliverdin regulates LPS-mediated expression of C5aR via the mTOR pathway, revealing an additional mechanism underlying biliverdin’s anti-inflammatory effects.

Lack of the Toll-Like Receptor 4 Gene Polymorphisms Asp299Gly and Thr399ile in a Chinese Population

The toll-like receptor 4 (TLR4), predominantly known for its role as an important mediator of immune reactions, is expressed in atherosclerotic lesions. Atherosclerosis resulting in cerebral or carotid arterial stenosis/occlusion plays the most important role in the occurrence of cerebral infarction (CI), and thus TLR4 polymorphisms may influence formation of atherosclerosis and the development of CI. This study was aimed to detect two commonly reported Asp299Gly and Thr399Ile polymorphisms in TLR4 gene in Hunan Han Chinese and their possible relationship with CI. By using the method of polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), the polymorphisms TLR4, Asp299Gly and Thr399Ile, were determined in 366 CI patients and 200 controls from Changsha area of Hunan Province. Carotid intima-media thickness (CIMT) also was detected by Bmode ultrasonography. Our results suggested both the TLR4, Asp299Gly and Thr399Ile, genetic polymorphisms were not observed in all subjects from Hunan Changsha. Therefore, we speculate they might not be an important factor in the development of CI in the Chinese.

Islet endothelial activation and oxidative stress gene expression is reduced by IL-1Ra treatment in the type 2 diabetic GK rat

Background

Inflammation followed by fibrosis is a component of islet dysfunction in both rodent and human type 2 diabetes. Because islet inflammation may originate from endothelial cells, we assessed the expression of selected genes involved in endothelial cell activation in islets from a spontaneous model of type 2 diabetes, the Goto-Kakizaki (GK) rat. We also examined islet endotheliuml/oxidative stress (OS)/inflammation-related gene expression, islet vascularization and fibrosis after treatment with the interleukin-1 (IL-1) receptor antagonist (IL-1Ra).

Methodology/Principal Findings

Gene expression was analyzed by quantitative RT-PCR on islets isolated from 10-week-old diabetic GK and control Wistar rats. Furthermore, GK rats were treated s.c twice daily with IL-1Ra (Kineret, Amgen, 100 mg/kg/day) or saline, from 4 weeks of age onwards (onset of diabetes). Four weeks later, islet gene analysis and pancreas immunochemistry were performed. Thirty-two genes were selected encoding molecules involved in endothelial cell activation, particularly fibrinolysis, vascular tone, OS, angiogenesis and also inflammation. All genes except those encoding angiotensinogen and epoxide hydrolase (that were decreased), and 12-lipoxygenase and vascular endothelial growth factor (that showed no change), were significantly up-regulated in GK islets. After IL-1Ra treatment of GK rats in vivo, most selected genes implied in endothelium/OS/immune cells/fibrosis were significantly down-regulated. IL-1Ra also improved islet vascularization, reduced fibrosis and ameliorated glycemia.

Conclusions/Significance

GK rat islets have increased mRNA expression of markers of early islet endothelial cell activation, possibly triggered by several metabolic factors, and also some defense mechanisms. The beneficial effect of IL-1Ra on most islet endothelial/OS/immune cells/fibrosis parameters analyzed highlights a major endothelial-related role for IL-1 in GK islet alterations. Thus, metabolically-altered islet endothelium might affect the β-cell microenvironment and contribute to progressive type 2 diabetic β-cell dysfunction in GK rats. Counteracting islet endothelial cell inflammation might be one way to ameliorate/prevent β-cell dysfunction in type 2 diabetes.

TLR4 polymorphisms and ageing: implications for the pathophysiology of age-related diseases

INTRODUCTION

Innate immunity provides a first line of host defense against infection by recognizing and killing microbes while simultaneously activating an instructive immune response. Toll-like receptors (TLRs) are principal mediators of rapid microbial recognition and function mainly by detection of pathogen-associated molecular patterns that do not exist in the host. Recognition of their ligands leads to a series of signaling events resulting in acute host responses, involved in killing pathogens.

DISCUSSION

We describe the involvement of TLR4 polymorphisms in ageing, and in particular in age-related diseases, suggesting the crucial role of molecules of innate immunity in pathophysiology of these diseases. Hence, we observed that pro-inflammatory alleles may be related to unsuccessful ageing, such as Alzheimer's disease, prostate cancer, and atherosclerosis; in contrast, the control of inflammation by anti-inflammatory alleles may result in increased longevity and successful ageing. Finally, a possible therapeutic approach to delay age-related diseases is outlined.

Toll-like receptor modulation: a novel therapeutic strategy in cardiovascular disease?

BACKGROUND

Toll-like receptors (TLRs) have been recently recognised as primary receptors in the innate immune system. Apart from initiating a prompt immune response against invading pathogens, TLRs are also considered to be an important link between innate immunity, inflammation and a variety of clinical disorders, including cardiovascular diseases. TLR signalling manipulation with novel drugs could offer important opportunities for cardiovascular disease modification.

OBJECTIVE

To present the latest knowledge supporting the involvement of TLRs in the pathogenesis and progress of cardiovascular diseases and explore the role of TLRs as potential targets for therapeutic intervention in cardiovascular territory.

METHODS

A review of the literature documenting implication of TLR signalling in cardiovascular disorders. Current progress in TLR-targeting drug development and the potential role of such a treatment strategy in cardiovascular disorders are discussed.

CONCLUSIONS

A growing body of evidence supports a role for TLRs in cardiovascular disease initiation and progression. Altering TLR signalling with novel drugs could be a beneficial therapeutic strategy for patients with cardiovascular disorders.

Functional consequences of toll-like receptor 4 polymorphisms

Toll-like receptor 4 (TLR4) is an important pathogen recognition receptor that recognizes mainly lipopolysaccharide (LPS) of Gram-negative bacteria, but also structures from fungal and mycobacterial pathogens, as well as endogenous ligands. Two nonsynonymous polymorphisms of TLR4, Asp299Gly and Thr399Ile, have been suggested to alter the function of the receptor. Some, but not all, studies have proposed that these polymorphisms lead to reduced cytokine response and increased susceptibility to Gram-negative infections. In this review, we compare studies that assessed the effect of the Asp299Gly and Thr399Ile polymorphisms on susceptibility to Gram-negative infections and examine the phenotypic consequences of these polymorphisms. In addition, we review the geographical distribution of TLR4 polymorphisms and present a model for evolutionary pressures on the TLR4 genetic make-up.

Selective attenuation of Toll-like receptor 2 signalling may explain the atheroprotective effect of sphingosine 1-phosphate

AIMS

Vascular inflammation is a major atherogenic factor and Toll-like receptor (TLR) 2 ligands, including bacterial and serum lipoproteins, seem to be involved in atherogenesis. On this basis, we analysed the effect of lipoproteins and different lipid components on TLR2-dependent signalling.

METHODS AND RESULTS

In TLR2-transfected human embryonic kidney 293 cells and human monocytes, oxidized low-density lipoproteins inhibited nuclear factor (NF)-kappaB-driven transcriptional activity and chemokine gene expression in response to TLR2 ligands. Sphingosine 1-phosphate (S1P) and oxidized palmitoyl-arachidonoyl-phosphatidylcholine, but not lipoprotein-carried lysophospholipids, inhibited TLR2 activation. Silencing experiments in TLR2-transfected 293 cells showed that the S1P-mediated attenuation effect is mediated by S1P receptors type 1 and type 2. To address the physiological significance of these findings, additional experiments were performed in human peripheral blood monocytes and monocyte-derived macrophages. In both cell types, S1P selectively attenuated TLR2 signalling, as NF-kappaB and extracellular signal-regulated kinase activation, but not c-Jun amino terminal kinase phosphorylation, were inhibited by physiologically relevant concentrations of S1P. Moreover, the attenuation of TLR2 signalling was partially reverted by pharmacological inhibition of phosphoinositide 3-kinase (PI3K) and Ras pathways. In addition, S1P inhibited the chemokine gene expression elicited by TLR2, but not by TLR4 ligands.

CONCLUSION

These findings disclose a cross-talk mechanism between lipoprotein components and TLR in which engagement of S1P receptors exert selective attenuation of TLR2-dependent activation via PI3K and Ras signalling. A corollary to these data is that the negative cross-talk of S1P receptors and TLR2 signalling might be involved in the atheroprotective effects of S1P.

Expression of Toll-like receptor 4 in the basilar artery after experimental subarachnoid hemorrhage in rabbits: a preliminary study

Inflammation and immunity play a crucial role in the pathogenesis of cerebral vasospasm after subarachnoid hemorrhage (SAH). Recently, a growing body of evidence indicates that Toll-like receptor (TLR) 4 is vital for inflammation and immunity. Therefore, this study aimed to detect the expression of TLR4 in the basilar artery in a rabbit SAH model and to clarify the potential role of TLR4 in cerebral vasospasm. A total of 48 rabbits were randomly divided into four groups: control group; day 3, day 5, and day 7 groups. Day 3, day 5, and day 7 groups were all SAH groups. The animals in day 3, day 5 and day 7 groups were subjected to injection of autologous blood into cisterna magna twice on day 0 and day 2 and were killed on days 3, 5, and 7, respectively. Cross-sectional area of basilar artery was measured and the TLR4 expression was assessed by immunohistochemistry and Western blot analysis. The basilar arteries exhibited vasospasm after SAH and became more severe on day 3 and 5. The elevated expression of TLR4 was detected after SAH and peaked on day 3 and 5. TLR4 is increasingly expressed in a parallel time course to the development of cerebral vasospasm in a rabbit experimental model of SAH.

Endothelial cells' activation and apoptosis induced by a subset of antibodies against human cytomegalovirus: relevance to the pathogenesis of atherosclerosis

BACKGROUND

Human cytomegalovirus (hCMV) is involved in the pathogenesis of atherosclerosis. We have previously shown in patients with atherosclerosis that antibodies directed against the hCMV-derived proteins US28 and UL122 are able to induce endothelial cell damage and apoptosis of non-stressed endothelial cells through cross-rection with normally expressed surface molecules. Our aim was to dissect the molecular basis of such interaction and to investigate mechanisms linking innate immunity to atherosclerosis.

METHODOLOGY/PRINCIPAL FINDINGS

We analysed the gene expression profiles in endothelial cells stimulated with antibodies affinity-purified against either the UL122 or the US28 peptides using the microarray technology. Microarray results were validated by quantitative PCR and by detection of proteins in the medium. Supernatant of endothelial cells incubated with antibodies was analysed also for the presence of Heat Shock Protein (HSP)60 and was used to assess stimulation of Toll-Like Receptor-4 (TLR4). Antibodies against UL122 and US28 induced the expression of genes encoding for adhesion molecules, chemokines, growth factors and molecules involved in the apoptotis process together with other genes known to be involved in the initiation and progression of the atherosclerotic process. HSP60 was released in the medium of cells incubated with anti-US28 antibodies and was able to engage TLR4.

CONCLUSIONS/SIGNIFICANCE

Antibodies directed against hCMV modulate the expression of genes coding for molecules involved in activation and apoptosis of endothelial cells, processes known to play a pivotal role in the pathogenesis of atherosclerosis. Moreover, endothelial cells exposed to such antibodies express HSP60 on the cell surface and release HSP60 in the medium able to activate TLR4. These data confirm that antibodies directed against hCMV-derived proteins US28 and UL122 purified from patients with coronary artery disease induce endothelial cell damage and support the hypothesis that hCMV infection may play a crucial role in mediating the atherosclerotic process.

Sirolimus blocks the accumulation of hyaluronan (HA) by arterial smooth muscle cells and reduces monocyte adhesion to the ECM

Sirolimus (SRL), an inhibitor of human arterial smooth muscle cell (ASMC) proliferation and migration, prevents in-stent restenosis (ISR). Little is known about the effect of SRL on the extracellular matrix (ECM) component, hyaluronan, a key macromolecule in neointimal hyperplasia and inflammation. In this study, we investigated SRL regulation of the synthesis of hyaluronan by cultured human ASMC and the effect of SRL on hyaluronan mediated monocyte adhesion to the ECM. Hyaluronan production on a per cell basis was significantly inhibited by SRL at 4 days and remained so through 10 days. This reduction was correlated with reduced levels of hyaluronan synthase mRNAs while hyaluronan degradation rates were unchanged. Poly I:C, a viral mimetic, caused increased hyaluronan accumulation by ASMC cell layers and this increase was inhibited by SRL. The inhibition was paralleled by a reduction in hyaluronan-dependent monocyte adhesion to the ECM. This study demonstrates that SRL not only regulates the proliferation of ASMC but reduces the production of hyaluronan by these cells. This alteration in ECM composition results in reduced monocyte adhesion to the ECM in cultures of ASMC. Alterations in hyaluronan accumulation may contribute to the inhibition of ISR that is achieved by SRL.

Oxidized low-density lipoprotein correlates positively with toll-like receptor 2 and interferon regulatory factor-1 and inversely with superoxide dismutase-1 expression: studies in hypercholesterolemic swine and THP-1 cells

BACKGROUND

Oxidized low-density lipoprotein (LDL) is associated with cardiovascular disease. Macrophages contribute to LDL oxidation, and oxidized LDL (oxLDL) affects macrophage function. We searched for the strongest gene correlates of oxLDL in macrophages in coronary plaques and studied the effect of oxLDL on their expression in THP-1 cells.

METHODS AND RESULTS

Gene expression in macrophages isolated from coronary plaque macrophages from hypercholesterolemic swine was measured on Agilent Human cDNA microarrays. Compared with a universal reference, 1653 transcripts were deregulated. The expression of 11 genes correlated positively and the expression of 5 genes correlated negatively with plaque oxLDL. Interferon regulatory factor-1 (IRF1; R2 = 0.69) and toll-like receptor 2 (TLR2; R2 = 0.18) were the strongest positive correlates of oxLDL. Superoxide dismutase 1 (SOD1) was the strongest inverse correlate of oxLDL (R2 = 0.57). Immunohistochemical analysis showed colocalization of IRF1, TLR2, and SOD1 protein in macrophages and confirmed the RNA expression data. OxLDL-induced foam cell formation in THP-1 macrophages was associated with increased expression of IRF1 and TLR2 and decreased expression of SOD1.

CONCLUSIONS

Our data support the hypothesis that oxLDL is a proinflammatory stimulus that induces the expression of TLR2 and IRF1, 2 important gene regulators of innate immune response, and inhibits the expression of the antioxidant SOD1.

Sequence variants of Toll-like receptor 4 and susceptibility to prostate cancer

Chronic inflammation has been hypothesized to be a risk factor for prostate cancer. The Toll-like receptor 4 (TLR4) presents the bacterial lipopolysaccharide (LPS), which interacts with ligand-binding protein and CD14 (LPS receptor) and activates expression of inflammatory genes through nuclear factor-kappaB and mitogen-activated protein kinase signaling. A previous case-control study found a modest association of a polymorphism in the TLR4 gene [11381G/C, GG versus GC/CC: odds ratio (OR), 1.26] with risk of prostate cancer. We assessed if sequence variants of TLR4 were associated with the risk of prostate cancer. In a nested case-control design within the Health Professionals Follow-up Study, we identified 700 participants with prostate cancer diagnosed after they had provided a blood specimen in 1993 and before January 2000. Controls were 700 age-matched men without prostate cancer who had had a prostate-specific antigen test after providing a blood specimen. We genotyped 16 common (>5%) single nucleotide polymorphisms (SNP) discovered in a resequencing study spanning TLR4 to test for association between sequence variation in TLR4 and prostate cancer. Homozygosity for the variant alleles of eight SNPs was associated with a statistically significantly lower risk of prostate cancer (TLR4_1893, TLR4_2032, TLR4_2437, TLR4_7764, TLR4_11912, TLR4_16649, TLR4_17050, and TLR4_17923), but the TLR4_15844 polymorphism corresponding to 11381G/C was not associated with prostate cancer (GG versus CG/CC: OR, 1.01; 95% confidence interval, 0.79-1.29). Six common haplotypes (cumulative frequency, 81%) were observed; the global test for association between haplotypes and prostate cancer was statistically significant (chi(2) = 14.8 on 6 degrees of freedom; P = 0.02). Two common haplotypes were statistically significantly associated with altered risk of prostate cancer. Inherited polymorphisms of the innate immune gene TLR4 are associated with risk of prostate cancer.

Defects in regulation of local immune responses resulting in atherosclerosis

Atherosclerosis is nowadays generally accepted as an inflammatory disease but the mechanism of its origin and development have not yet been fully clarified. The present review focuses on the role of the local immune system as one of the key players in the pathogenesis of the complex process. Its part represented by vascular-associated lymphoid tissue (VALT) within the arterial wall participates directly in the vascular wall's homeostatis. Its inordinate activation during ontogenic development of an individual, this formerly defensive and physiologic mechanism transform into a pathological process resulting in an impairing inflammation. Hsp60, CRP and oxidized or otherwise modified LDL are serious candidates for triggering these pathological changes. The principal role is played by anti-Hsp60 antibodies and by shear stress originating on the surface of endothelium due to blood flow. The experimental and clinical data supporting this immunological hypothesis of atherosclerosis are discussed.

Porphyromonas gingivalis fimbria-dependent activation of inflammatory genes in human aortic endothelial cells

Epidemiological and pathological studies have suggested that infection with the oral pathogen Porphyromonas gingivalis can potentiate atherosclerosis and human coronary heart disease. Furthermore, infection with invasive, but not noninvasive P. gingivalis has been demonstrated to accelerate atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice and to accelerate local inflammatory responses in aortic tissue. In the present study, using high-density oligonucleotide microarrays, we have defined the gene expression profile of human aortic endothelial cells (HAEC) after infection with invasive and noninvasive P. gingivalis. After infection of HAEC with invasive P. gingivalis strain 381, we observed the upregulation of 68 genes. Genes coding for the cytokines Gro2 and Gro3; the adhesion molecules intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule (VCAM)-1, and ELAM-1 (E-selectin); the chemokine interleukin-8 (IL-8); and the proinflammatory molecules IL-6 and cyclooxygenase-2 were among the most highly upregulated genes in P. gingivalis 381-infected HAEC compared to uninfected HAEC control. Increased mRNA levels for signaling molecules, transcriptional regulators, and cell surface receptors were also observed. Of note, only 4 of these 68 genes were also upregulated in HAEC infected with the noninvasive P. gingivalis fimA mutant. Reverse transcription-PCR, enzyme-linked immunosorbent assay, and fluorescence-activated cell sorting analysis confirmed the expression of ICAM-1, VCAM-1, E-/P-selectins, IL-6, and IL-8 in HAEC infected with invasive P. gingivalis. We also demonstrated that increased expression of ICAM-1 and VCAM-1 in aortic tissue of ApoE(-/-) mice orally challenged with invasive P. gingivalis but not with the noninvasive P. gingivalis fimA mutant by immunohistochemical analysis. Taken together, these results demonstrate that P. gingivalis fimbria-mediated invasion upregulates inflammatory gene expression in HAEC and in aortic tissue and indicates that invasive P. gingivalis infection accelerates inflammatory responses directly in the aorta.

Adipocyte fatty acid-binding protein expression and lipid accumulation are increased during activation of murine macrophages by toll-like receptor agonists

OBJECTIVE

Toll-like receptors (TLRs) recognize pathogens and mediate signaling pathways important for host defense. Recent studies implicate TLR polymorphisms in atherosclerosis risk in humans. Adipocyte fatty acid-binding protein (aP2) is present in macrophages and has an important role in atherosclerotic plaque development. We investigated aP2 expression in RAW 264.7 cells treated with lipopolysaccharide (LPS) and other TLR agonists and assessed lipid accumulation in these activated murine macrophages.

METHODS AND RESULTS

Stimulation with LPS, a TLR4 ligand, resulted in a 56-fold increase in aP2 mRNA expression, and zymosan, a TLR2 ligand, induced an approximately 1500-fold increase. Polyinosine: polycytidylic acid (poly I:C), a TLR3 ligand, led to a 9-fold increase. Levels of aP2 protein were significantly increased in LPS or zymosan-treated macrophages compared with control or poly I:C-treated cells. In addition, the cholesteryl ester content of LPS or zymosan-treated macrophages was approximately 5-fold greater in the presence of low-density lipoprotein, and triglyceride content was approximately 2-fold greater in the absence of exogenous lipid than control or poly I:C-treated cells.

CONCLUSIONS

Expression of macrophage aP2 is induced on TLR activation and parallels increases in cholesteryl ester and triglyceride levels. These results provide a molecular link between the known roles of TLR and aP2 in foam cell formation.