Blocking TLR2 activity diminishes and stabilizes advanced atherosclerotic lesions in apolipoprotein E-deficient mice

TAX1BP1/A20 inhibited TLR2-NF-κB activation to induce tolerant expression of IL-6 in endothelial cells

The inflammatory cascadedriven by interleukin-6 (IL-6) plays a crucial role in the initiation and progression of chronic inflammatory conditions such as atherosclerosis. Research has demonstrated that prolonged exposure to inflammatory stimuli leads to the development of "immune tolerance" in specialized immune cells such as monocytes and macrophages, serving as a mechanism to prevent tissue damage and curb the inflammatory cascade. However, our recent investigation revealed that immune tolerance did not effectively regulate the production of IL-6 in human umbilical vein endothelial cells (HUVECs) when stimulated by a Toll-like receptor 2 (TLR2) ligand Pam3CSK4, which is a potent activator of the pro-inflammatory transcription factor NF-κB. Furthermore, the negative regulator of NF-κB signaling, A20, was ineffective in suppressing TLR2-induced IL-6 synthesis in this context. Notably, all A20 auxiliary molecules, with the exception of TAX1BP1, were found to be significantly expressed in HUVECs. DNA methylation in TAX1BP1 was confirmed in GEO database. According to the information provided, it is hypothesized that altered DNA methylation in HUVECs could potentially lead to decreased expression of TAX1BP1, thereby impeding A20's capacity to modulate continuous activation of the TLR2-NF-κB pathway. This may consequently lead to unregulated production of IL-6, evading immune tolerance mechanisms. Subsequent investigations suggested that demethylating TAX1BP1 could enhance its expression, potentially reducing the endogenous IL-6 levels induced by repeated TLR2 stimulation and restoring A20's inhibitory role in NF-κB signaling. Additionally, over-expression of TAX1BP1 coulddecrease the production of atherosclerosis-associated cytokines like IL-6, MCP-1, ICAM-1, and VCAM-1, while increasing NO release following repeated Pam3cks4 stimulation, along with enhanced co-localization of TAX1BP1 and A20. These findings indicate that inducing immune tolerance in endothelial cells may effectively suppress endogenous IL-6 production and halt the IL-6-mediated inflammatory cascade, with TAX1BP1/A20 identified as crucial components in this process.These insights provide novel perspectives and potential targets for therapeutic strategies in inflammatoryimmunological disorders involving the overproduction of IL-6.

Anti-Inflammatory Oxysterol, Oxy210, Inhibits Atherosclerosis in Hyperlipidemic Mice and Inflammatory Responses of Vascular Cells

BACKGROUND AND AIMS

We previously reported that Oxy210, an oxysterol-based drug candidate, exhibits antifibrotic and anti-inflammatory properties. We also showed that, in mice, it ameliorates hepatic hallmarks of non-alcoholic steatohepatitis (NASH), including inflammation and fibrosis, and reduces adipose tissue inflammation. Here, we aim to investigate the effects of Oxy210 on atherosclerosis, an inflammatory disease of the large arteries that is linked to NASH in epidemiologic studies, shares many of the same risk factors, and is the major cause of mortality in people with NASH.

METHODS

Oxy210 was studied in vivo in APOE*3-Leiden.CETP mice, a humanized mouse model for both NASH and atherosclerosis, in which symptoms are induced by consumption of a high fat, high cholesterol "Western" diet (WD). Oxy210 was also studied in vitro using two cell types that are important in atherogenesis: human aortic endothelial cells (HAECs) and macrophages treated with atherogenic and inflammatory agents.

RESULTS

Oxy210 reduced atherosclerotic lesion formation by more than 50% in hyperlipidemic mice fed the WD for 16 weeks. This was accompanied by reduced plasma cholesterol levels and reduced macrophages in lesions. In HAECs and macrophages, Oxy210 reduced the expression of key inflammatory markers associated with atherosclerosis, including interleukin-1 beta (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), chemokine (C-C motif) ligand 2 (CCL2), vascular cell adhesion molecule-1 (VCAM-1), and E-Selectin. In addition, cholesterol efflux was significantly enhanced in macrophages treated with Oxy210.

CONCLUSIONS

These findings suggest that Oxy210 could be a drug candidate for targeting both NASH and atherosclerosis, as well as chronic inflammation associated with the manifestations of metabolic syndrome.

Analysis of Immune and Inflammation Characteristics of Atherosclerosis from Different Sample Sources

Background

Atherosclerosis is the predominant cause of cardiovascular diseases. Existing studies suggest that the development of atherosclerosis is closely related to inflammation and immunity, but whether there are differences and similarities between atherosclerosis occurring at different sites is still unknown. We elucidated the pathological characteristics of peripheral vascular diseases by using bioinformatic analyses on immune cells and inflammation-related gene expression in atherosclerotic arteries and plaques.

Methods

Eight data sets regarding atherosclerosis were downloaded from the Gene Expression Omnibus database. Human immune genes were obtained from the IMMPORT website. The samples were scored and divided into high- and low-immune groups. Then the samples were analysed using weighted gene co-expression network analysis, while the modules were analysed using functional enrichment. The protein–protein interaction network was constructed using the STRING and Cytoscape databases. The hub immune genes were screened, and the correlation between hub immune genes and immune cells was analysed.

Results

Immune cells and their functions were significantly different during atherosclerosis development. The infiltration proportion of immune cells was approximately similar in samples from different sources of patients with carotid atherosclerosis. However, the sensitivity of lower extremity atherosclerosis samples to immune cells is lower than that of carotid atherosclerosis samples.The samples from the plaque and artery were mainly infiltrated by macrophages, T cells and mast cells. After immune cells were assessed, resting NK cells, activated mast cells and M0 macrophages were found to be key immune cells in atherosclerosis and plaque formation. In addition, CCL4, TLR2, IL1B and PTPRC were considered to be immune marker genes in atherosclerosis development. Conclusion. Bioinformatic data analysis confirms the essential role of immune cells in cardiovascular diseases, and also indicates some differences of immune and inflammation characteristics of atherosclerosis between carotid and lower extremity arteries.

Therapeutic Effect of Schistosoma japonicum Cystatin on Atherosclerotic Renal Damage

Atherosclerosis is a chronic inflammation of the arterial vessel wall driven by lipid metabolism disorders. Although helminthic infection and their derivatives have been identified to attenuate the chronic inflammatory diseases, the immunomodulatory effect of recombinant Schistosoma japonicum cystatin (rSj-Cys) on metabolic diseases and atherosclerosis has not been reported. In this study, we investigated the therapeutic efficacy of rSj-Cys on atherosclerotic renal damage and explored the related immunological mechanism. The results demonstrated that treatment with rSj-Cys significantly reduced body weight gain, hyperlipidemia, and atherosclerosis induced by the high-fat diet in apoE^–/– mice. The treatment of rSj-Cys also significantly improved kidney functions through promoting macrophage polarization from M1 to M2, therefore inhibiting M1 macrophage–induced inflammation. The possible mechanism underlying the regulatory effect of rSj-Cys on reducing atherosclerosis and atherosclerotic renal damage is that rSj-Cys stimulates regulatory T cell and M2 macrophage polarization that produce regulatory cytokines, such as interleukin 10 and transforming growth factor β. The therapeutic effect of rSj-Cys on atherosclerotic renal damage is possibly through inhibiting the activation of TLR2/Myd88 signaling pathway. The results in this study provide evidence for the first time that Schistosoma-derived cystatin could be developed as a therapeutic agent to treat lipid metabolism disorder and atherosclerosis that threats million lives around the world.

Regulatory T Cell-Related Gene Biomarkers in the Deterioration of Atherosclerosis

Background: Regulatory T cells (Tregs) have shown to be protective against the development of atherosclerosis, a major pathological cause for cardiovascular events. Here, we aim to explore the roles of Tregs-related genes in atherosclerosis deterioration. Methods and Results: We downloaded the gene expression profile of 29 atherosclerotic samples from the Gene Expression Omnibus database with an accession number of GSE28829. The abundance of Tregs estimated by the CIBERSORT algorithm was negatively correlated with the atherosclerotic stage. Using the limma test and correlation analysis, a total of 159 differentially expressed Tregs-related genes (DETregRGs) between early and advanced atherosclerotic plaques were documented. Functional annotation analysis using the DAVID tool indicated that the DETregRGs were mainly enriched in inflammatory responses, immune-related mechanisms, and pathways such as complement and coagulation cascades, platelet activation, leukocyte trans-endothelial migration, vascular smooth muscle contraction, and so on. A protein-protein interaction network of the DETregRGs was then constructed, and five hub genes (PTPRC, C3AR1, CD53, TLR2, and CCR1) were derived from the network with node degrees ≥20. The expression patterns of these hub DETregRGs were further validated in several independent datasets. Finally, a single sample scoring method was used to build a gene signature for the five DETregRGs, which could distinguish patients with myocardial infarction from those with stable coronary disease. Conclusion: The results of this study will improve our understanding about the Tregs-associated molecular mechanisms in the progression of atherosclerosis and facilitate the discovery of novel biomarkers for acute cardiovascular events.

The Anti-Inflammatory Effect of Taurine on Cardiovascular Disease

Taurine is a non-protein amino acid that is expressed in the majority of animal tissues. With its unique sulfonic acid makeup, taurine influences cellular functions, including osmoregulation, antioxidation, ion movement modulation, and conjugation of bile acids. Taurine exerts anti-inflammatory effects that improve diabetes and has shown benefits to the cardiovascular system, possibly by inhibition of the renin angiotensin system. The beneficial effects of taurine are reviewed.

The Role of Toll-like Receptors in Atherothrombotic Cardiovascular Disease

Toll-like receptors (TLRs) are dominant components of the innate immune system. Activated by both pathogen-associated molecular patterns and damage-associated molecular patterns, TLRs underpin the pathology of numerous inflammation related diseases that include not only immune diseases, but also cardiovascular disease (CVD), diabetes, obesity, and cancers. Growing evidence has demonstrated that TLRs are involved in multiple cardiovascular pathophysiologies, such as atherosclerosis and hypertension. Specifically, a trial called the Canakinumab Anti-inflammatory Thrombosis Outcomes Study showed the use of an antibody that neutralizes interleukin-1β, reduces the recurrence of cardiovascular events, demonstrating inflammation as a therapeutic target and also the research value of targeting the TLR system in CVD. In this review, we provide an update of the interplay between TLR signaling, inflammatory mediators, and atherothrombosis, with an aim to identify new therapeutic targets for atherothrombotic CVD.

Mechanisms of erosion of atherosclerotic plaques

PURPOSE OF REVIEW

The present review explores the mechanisms of superficial intimal erosion, a common cause of thrombotic complications of atherosclerosis.

RECENT FINDINGS

Human coronary artery atheroma that give rise to thrombosis because of erosion differ diametrically from those associated with fibrous cap rupture. Eroded lesions characteristically contain few inflammatory cells, abundant extracellular matrix, and neutrophil extracellular traps (NETs). Innate immune mechanisms such as engagement of Toll-like receptor 2 (TLR2) on cultured endothelial cells can impair their viability, attachment, and ability to recover a wound. Hyaluronan fragments may serve as endogenous TLR2 ligands. Mouse experiments demonstrate that flow disturbance in arteries with neointimas tailored to resemble features of human eroded plaques disturbs endothelial cell barrier function, impairs endothelial cell viability, recruits neutrophils, and provokes endothelial cells desquamation, NET formation, and thrombosis in a TLR2-dependent manner.

SUMMARY

Mechanisms of erosion have received much less attention than those that provoke plaque rupture. Intensive statin treatment changes the characteristic of plaques that render them less susceptible to rupture. Thus, erosion may contribute importantly to the current residual burden of risk. Understanding the mechanisms of erosion may inform the development and deployment of novel therapies to combat the remaining atherothrombotic risk in the statin era.

Vitamin K2 can suppress the expression of Toll-like receptor 2 (TLR2) and TLR4, and inhibit calcification of aortic intima in ApoE-/- mice as well as smooth muscle cells

Background and objectives Vascular calcification is a common complication in atherosclerosis. Accumulating evidence showed that Toll-like receptors (TLRs) mediate pro-inflammatory and atherosclerosis. Recent studies demonstrated that vascular calcification is one of the detrimental effects of vitamin K (Vit K) antagonists. However, the effects of Vit K on the expression of TLR2 and 4 and intimal calcification in artery remained unidentified. Methods and results Eighteen ApoE^-/- mice were randomly divided into model group, Vit K-treated group, and control group. The mice of model and Vit K-treated group were fed with high-fat diet, while control group mice were fed with normal diet. Mice of Vit K-treated group were administered orally with vitamin K2 (40 mg.kg^-1.day^-1) for 12 weeks. Twelve weeks later the aortic sections of mice were acquired and stained with hematoxylin and eosin and von Kossa, respectively. Calcium content and activity of alkaline phosphatase (ALP) at aortic tissues were measured. The expression levels of TLR2 and TLR4 in aorta sections were detected by immunohistochemisty and RT-PCR, respectively. The effects of Vit K on cellular calcification were further studied in A7r5 SMCs. Results demonstrated that high-fat diet induced typical atherosclerosis with intimal calcification in ApoE^-/- mice, while in Vit K-treated group atherosclerosis and calcium deposits were not serious; Vit K2 also inhibited cellular calcification in A7r5 SMCs. Quantitative analysis showed that calcium and ALP activity at aortic tissues in the Vit K-treated mice were significantly lower than that of the model group ( P < 0.01); Compared to the control group, the expression levels of TLR2 and TLR4 in the model group were significantly higher ( P < 0.05), while in Vit K-treated group the levels of TLR2 and 4 were significantly lower than that in the model group. Furthermore, the content of calcium was positively related to the expression levels of TLR2 and TLR4 mRNA at aortic tissues ( r = 0.77 and r = 0.79, respectively, both P < 0.001). Conclusion VitK2 can inhibit intimal calcification of aortic artery induced by high-fat diet in ApoE^-/- mice and A7r5 SMCs calcification induced by β-sodium glycerophosphate, and meanwhile can reduce the expression of TLR2 and TLR4. These results suggested that the effects of VitK2 on vascular calcification may be associated with the expression of TLR2 and TLR4.

The influence of AICAR - direct activator of AMP-activated protein kinase (AMPK) - on liver proteome in apoE-knockout mice

There is a growing body of evidence that altered functioning of apoE may aggravate cellular energy homeostasis and stress response, leading to oxidative stress, mitochondrial dysfunction, endoplasmic reticulum (ER) stress and inflammation, leading to hypercholesterolemia, dyslipidemia, liver steatosis and neurodegeneration. One of the key cellular responses to mitochondria and ER-stress related processes and cellular energy imbalance is AMP-activated protein kinase (AMPK), considered as a cellular master energy sensor and critical regulator of mitochondrial homeostasis. The aim of our study was to use differential proteomics and transcriptomics approach to elucidate the effect of direct AMPK activator AICAR on liver proteome in apoE^-/- mice - experimental model of atherosclerosis and moderate nonalcoholic steatosis. We applied Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) labeling and two-dimensional chromatography coupled with mass spectrometry (2DLC-MS/MS) MudPIT strategy, as well as RT-PCR to investigate the changes in mitochondrial and cytosolic proteins and transcripts expression in 6-month old AICAR-treated apoE^-/-. AICAR elicited induction of proteins related to mitochondrial β-oxidation, protein degradation and energy producing pathways (i.a. tricarboxylic acid cycle members and mitochondrial adenylate kinase 2). On the other hand, AICAR repressed inflammatory and pro-apoptotic markers in the apoE^-/- mice liver, alongside reduction in several peroxisomal proteins, possibly suggesting induction of anti-oxidative pexophagy.

Toll-like receptor 7 deficiency protects apolipoprotein E-deficient mice from diet-induced atherosclerosis

Toll-like receptor 7 (TLR7) mediates autoantigen and viral RNA-induced cytokine production. Increased TLR7 expression in human atherosclerotic lesions suggests its involvement in atherogenesis. Here we demonstrated TLR7 expression in macrophages, smooth muscle cells (SMCs), and endothelial cells from mouse atherosclerotic lesions. To test a direct participation of TLR7 in atherosclerosis, we crossbred TLR7-deficient (Tlr7 ^-/-) mice with apolipoprotein E-deficient (Apoe ^-/-) mice and produced Apoe ^-/- Tlr7 ^-/- and Apoe ^-/- Tlr7 ^+/+ littermates, followed by feeding them an atherogenic diet to produce atherosclerosis. Compared to Apoe ^-/- Tlr7 ^+/+ mice, Apoe ^-/- Tlr7 ^-/- mice showed reduced aortic arch and sinus lesion areas. Reduced atherosclerosis in Apoe ^-/- Tlr7 ^-/- mice did not affect lesion macrophage-positive area and CD4⁺ T-cell number per lesion area, but reduced lesion expression of inflammatory markers major histocompatibility complex-class II and IL6, lesion matrix-degrading proteases cathepsin S and matrix metalloproteinase-9, and systemic serum amyloid A levels. TLR7 deficiency also reduced aortic arch SMC loss and lesion intima and media cell apoptosis. However, TLR7 deficiency did not affect aortic wall elastin fragmentation and collagen contents, or plasma lipoproteins. Therefore, TLR7 contributes to atherogenesis in Apoe ^-/- mice by regulating lesion and systemic inflammation. A TLR7 antagonist may mitigate atherosclerosis.

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.

Anti-apoA-1 auto-antibodies increase mouse atherosclerotic plaque vulnerability, myocardial necrosis and mortality triggering TLR2 and TLR4

Auto-antibodies to apolipoprotein A-1 (anti-apoA-1 IgG) were shown to promote inflammation and atherogenesis, possibly through innate immune receptors signalling. Here, we aimed at investigating the role of Toll-like receptors (TLR) 2 and 4 on anti-apoA-1 IgG-induced atherosclerotic plaque vulnerability, myocardial necrosis and mortality in mice. Adult male apolipoprotein E knockout (ApoE)-/- (n=72), TLR2-/-ApoE-/- (n=36) and TLR4-/-Apo-/- (n=28) mice were intravenously injected with 50 µg/mouse of endotoxin-free polyclonal anti-apoA-1 IgG or control isotype IgG (CTL IgG) every two weeks for 16 weeks. Atherosclerotic plaque size and vulnerability were assessed by histology. Myocardial ischaemia and necrosis, respectively, were determined by electrocardiographic (ECG) changes assessed by telemetry and serum troponin I (cTnI) measurements. Impact on survival was assessed by Kaplan-Meier analyses. In ApoE-/- mice, anti-apoA-1 IgG passive immunisation enhanced histological features of atherosclerotic plaque vulnerability (increase in neutrophil and MMP-9 and reduction in collagen content), induced a substantial cTnI elevation (p=0.001), and increased mortality rate by 23 % (LogRank, p=0.04) when compared to CTL IgG. On a subgroup of ApoE-/- mice equipped with telemetry (n=4), a significant ST-segment depression was noted in anti-apoA-1 IgG-treated mice when compared to CTL IgG recipients (p< 0.001), and an acute ST-segment elevation myocardial infarction preceding mouse death was observed in one case. The deleterious effects of anti-apoA-1 IgG on atherosclerotic plaque vulnerability, myocardial necrosis and death were partially reversed in TLR2-/-ApoE-/- and TLR4-/-ApoE-/- backgrounds. In conclusion, anti-apoA-1 auto-antibodies seem to be active mediators of atherosclerotic plaque vulnerability, myocardial necrosis, and mortality in mice through TLR2- and TLR4-mediated pathways.

Inflammation and hypertension: new understandings and potential therapeutic targets

Research studying the role of inflammation in hypertension and cardiovascular disease has flourished in recent years; however, the exact mechanisms by which the activated immune cells lead to the development and maintenance of hypertension remain to be elucidated. The objectives of this brief review are to summarize and discuss the most recent findings in the field, with special emphasis on potential therapeutics to treat or prevent hypertension. This review will cover novel immune cell subtypes recently associated to the disease including the novel role of cytokines, toll-like receptors, and inflammasomes in hypertension.

TLR4 rs1927911, but not TLR2 rs5743708, is associated with atherosclerotic cerebral infarction in the Southern Han population: a case-control study

The objective of this study was to explore the association of toll-like receptor (TLR) 4 rs1927911 and TLR2 rs5743708 with atherosclerotic cerebral infarction (ACI) and their effects on blood pressure, fasting blood glucose, and blood lipids in the Han population of Hunan Province. TLR4 rs1927911 and TLR2 rs5743708 were detected by polymerase chain reaction and restriction fragment length polymorphism in 170 patients with ACI and 149 healthy controls. Our results indicated that the genotype and allele frequencies of TLR4 rs1927911 were significantly different between ACI patients and controls, whereas those of TLR2 rs5743708 were not significantly different between the 2 groups. For TLR4 rs1927911, blood pressure, fasting blood sugar, and serum lipid levels were not significantly different among different genotypes in the ACI and control groups. The rs1927911 polymorphism of the TLR4 gene may be a risk factor for ACI in the Southern Han population of Hunan Province; however, it may not be associated with blood pressure, fasting blood sugar, or blood lipids.