RAGE and TLRs as Key Targets for Antiatherosclerotic Therapy

Pathological role of RAGE underlying progression of various diseases: its potential as biomarker and therapeutic target

The receptor for advanced glycation end products (RAGE) is a multi-ligand receptor with several structural types, performing a myriad of molecular mechanisms. The RAGE-ligand interactions play important roles in maintaining latent chronic inflammation, and oxidative damage underlying various pathological conditions like metabolic syndrome (MetS), neurodegenerative diseases, stroke, cardiovascular disorders, pulmonary disorders, cancer and infections. RAGE is thoroughly explored in knockout animals and human trials, targeted by small molecule inhibitors, peptides, diet, and natural compounds. But it is yet to be incorporated in the mainstream management of any ailment. This review performs an appraisal of the pathological mechanisms influenced by RAGE to uncover its prospects as a biomarker while also assessing its power to become a promising therapeutic target.

Inhibition of Toll-like Receptors Alters Macrophage Cholesterol Efflux and Foam Cell Formation

Arterial macrophage cholesterol accumulation and impaired cholesterol efflux lead to foam cell formation and the development of atherosclerosis. Modified lipoproteins interact with toll-like receptors (TLR), causing an increased inflammatory response and altered cholesterol homeostasis. We aimed to determine the effects of TLR antagonists on cholesterol efflux and foam cell formation in human macrophages. Stimulated monocytes were treated with TLR antagonists (MIP2), and the cholesterol efflux transporter expression and foam cell formation were analyzed. The administration of MIP2 attenuated the foam cell formation induced by lipopolysaccharides (LPS) and oxidized low-density lipoproteins (ox-LDL) in stimulated THP-1 cells (p < 0.001). The expression of ATP-binding cassette transporters A (ABCA)-1, ABCG-1, scavenger receptor (SR)-B1, liver X receptor (LXR)-α, and peroxisome proliferator-activated receptor (PPAR)-γ mRNA and proteins were increased (p < 0.001) following MIP2 administration. A concentration-dependent decrease in the phosphorylation of p65, p38, and JNK was also observed following MIP2 administration. Moreover, an inhibition of p65 phosphorylation enhanced the expression of ABCA1, ABCG1, SR-B1, and LXR-α. TLR inhibition promoted the cholesterol efflux pathway by increasing the expression of ABCA-1, ABCG-1, and SR-B1, thereby reducing foam cell formation. Our results suggest a potential role of the p65/NF-kB/LXR-α/ABCA1 axis in TLR-mediated cholesterol homeostasis.

Paracrine Signals in Calcified Conditioned Media Elicited Differential Responses in Primary Aortic Vascular Smooth Muscle Cells and in Adventitial Fibroblasts

Our goal was to determine if paracrine signals from different aortic layers can impact other cell types in the diabetic microenvironment, specifically medial vascular smooth muscle cells (VSMCs) and adventitial fibroblasts (AFBs). The diabetic hyperglycemic aorta undergoes mineral dysregulation, causing cells to be more responsive to chemical messengers eliciting vascular calcification. Advanced glycation end-products (AGEs)/AGE receptors (RAGEs) signaling has been implicated in diabetes-mediated vascular calcification. To elucidate responses shared between cell types, pre-conditioned calcified media from diabetic and non-diabetic VSMCs and AFBs were collected to treat cultured murine diabetic, non-diabetic, diabetic RAGE knockout (RKO), and non-diabetic RKO VSMCs and AFBs. Calcium assays, western blots, and semi-quantitative cytokine/chemokine profile kits were used to determine signaling responses. VSMCs responded to non-diabetic more than diabetic AFB calcified pre-conditioned media. AFB calcification was not significantly altered when VSMC pre-conditioned media was used. No significant changes in VSMCs signaling markers due to treatments were reported; however, genotypic differences existed. Losses in AFB α-smooth muscle actin were observed with diabetic pre-conditioned VSMC media treatment. Superoxide dismutase-2 (SOD-2) increased with non-diabetic calcified + AGE pre-conditioned VSMC media, while same treatment decreased diabetic AFBs levels. Overall, non-diabetic and diabetic pre-conditioned media elicited different responses from VSMCs and AFBs.

Chronic E-Cigarette Use Impairs Endothelial Function on the Physiological and Cellular Levels

BACKGROUND

The harmful vascular effects of smoking are well established, but the effects of chronic use of electronic cigarettes (e-cigarettes) on endothelial function are less understood. We hypothesized that e-cigarette use causes changes in blood milieu that impair endothelial function.

METHODS

Endothelial function was measured in chronic e-cigarette users, chronic cigarette smokers, and nonusers. We measured effects of participants' sera, or e-cigarette aerosol condensate, on NO and H2O2 release and cell permeability in cultured endothelial cells (ECs).

RESULTS

E-cigarette users and smokers had lower flow-mediated dilation (FMD) than nonusers. Sera from e-cigarette users and smokers reduced VEGF (vascular endothelial growth factor)-induced NO secretion by ECs relative to nonuser sera, without significant reduction in endothelial NO synthase mRNA or protein levels. E-cigarette user sera caused increased endothelial release of H2O2, and more permeability than nonuser sera. E-cigarette users and smokers exhibited changes in circulating biomarkers of inflammation, thrombosis, and cell adhesion relative to nonusers, but with distinct profiles. E-cigarette user sera had higher concentrations of the receptor for advanced glycation end products (RAGE) ligands S100A8 and HMGB1 (high mobility group box 1) than smoker and nonuser sera, and receptor for advanced glycation end product inhibition reduced permeability induced by e-cigarette user sera but did not affect NO production.

CONCLUSIONS

Chronic vaping and smoking both impair FMD and cause changes in the blood that inhibit endothelial NO release. Vaping, but not smoking, causes changes in the blood that increase microvascular endothelial permeability and may have a vaping-specific effect on intracellular oxidative state. Our results suggest a role for RAGE in e-cigarette-induced changes in endothelial function.

Therapeutic potential of traditional Chinese medicine in atherosclerosis: A review

Atherosclerosis is the onset of endothelial cell damage and is characterized by abnormal accumulation of fibrinogen and lipid in large and middle arteries. Recent researches indicate that traditional Chinese medicine including Notoginseng Radix et Rhizoma, Astragali Radix, Salviae Miltiorrhizae Radix et Rhizoma, Ginseng Radix et Rhizoma, Fructus Crataegi, Glycyrrhizae Radix et Rhizoma, Polygoni Multiflori Radix, Fructus Lycii, and Coptidis Rhizoma have therapeutic effects on atherosclerosis. Furthermore, the pharmacological roles of these kinds of traditional Chinese medicine in atherosclerosis refer to endothelial function influences, cell proliferation and migration, platelet aggregation, thrombus formation, oxidative stress, inflammation, angiogenesis, apoptosis, autophagy, lipid metabolism, and the gut microbiome. Traditional Chinese medicine may serve as potential and effective anti-atherosclerosis drugs. However, a critical study has shown that Notoginseng Radix et Rhizoma may also have toxic effects including pustules, fever, and elevate circulating neutrophil count. Further high-quality studies are still required to determine the clinical safety and efficacy of traditional Chinese medicine and its active ingredients.

Modulatory role of atorvastatin against high-fat diet and zymosan-induced activation of TLR2/NF-ƙB signaling pathway in C57BL/6 mice

OBJECTIVES

Accumulated evidence provides a strong connection between the immune system and vascular inflammation. The innate immune system's main sensors are toll-like receptors (TLRs). Zymosan (Zym), a fungal product, induces an inflammatory response via activating TLR2 of the immune system. Atorvastatin, a potent statin, possesses pleiotropic effects including immunomodulatory, lipid-lowering, and anti-inflammatory. Therefore, the current study aimed to evaluate the protective role of atorvastatin against a high-fat diet (HFD) and Zym-induced vascular inflammation in C57BL/6 mice via modulation of TLR2/NF-ƙB signaling pathway.

MATERIALS AND METHODS

In silico study was conducted to confirm the binding affinity of atorvastatin against TLR2. Under in vivo study, mice were divided into four groups: Normal control: normal standard chow-diet fed for 30 days + Zym vehicle (sterile PBS, 5 mg/ml on 8th day); HFD (30 days) + Zym (80 mg/kg, IP, on 8th day); HFD/Zym + atorvastatin vehicle (0.5% CMC, p.o., from 10th to 30th day); HFD/Zym + atorvastatin (3.6 mg/kg, p.o., from 10th to 30th day).

RESULTS

Atorvastatin treatment along with HFD and Zym inhibited vascular inflammation by suppressing the levels of aortic TLR2, cardiac NF-ƙB and decrease in serum TNF-α and IL-6. Further, there was an increase in hepatic LDLR levels, resulting in a decrease in serum LDL-C and an increase in HDL-C levels. Histopathological examination of the aorta showed a reduction in plaque accumulation with the atorvastatin-treated group as compared with HFD and Zym-treated group.

CONCLUSION

Atorvastatin attenuates vascular inflammation mediated by HFD and Zym through suppression of TLR2, NF-ƙB, TNF-α, IL-6, and upregulation of LDLR levels.

RAGE Differentially Altered in vitro Responses in Vascular Smooth Muscle Cells and Adventitial Fibroblasts in Diabetes-Induced Vascular Calcification

The Advanced Glycation End-Products (AGE)/Receptor for AGEs (RAGE) signaling pathway exacerbates diabetes-mediated vascular calcification (VC) in vascular smooth muscle cells (VSMCs). Other cell types are involved in VC, such as adventitial fibroblasts (AFBs). We hope to elucidate some of the mechanisms responsible for differential signaling in diabetes-mediated VC with this work. This work utilizes RAGE knockout animals and in vitro calcification to measure calcification and protein responses. Our calcification data revealed that VSMCs calcification was AGE/RAGE dependent, yet AFBs calcification was not an AGE-mediated RAGE response. Protein expression data showed VSMCs lost their phenotype marker, α-smooth muscle actin, and had a higher RAGE expression over non-diabetics. RAGE knockout (RKO) VSMCs did not show changes in phenotype markers. P38 MAPK, a downstream RAGE-associated signaling molecule, had significantly increased activation with calcification in both diabetic and diabetic RKO VSMCs. AFBs showed a loss in myofibroblast marker, α-SMA, due to calcification treatment. RAGE expression decreased in calcified diabetic AFBs, and P38 MAPK activation significantly increased in diabetic and diabetic RKO AFBs. These findings point to potentially an alternate receptor mediating the calcification response in the absence of RAGE. Overall, VSMCs and AFBs respond differently to calcification and the application of AGEs.

Role of Atypical Chemokines and Chemokine Receptors Pathways in the Pathogenesis of COPD

Chronic obstructive pulmonary disease (COPD) represents a heightened inflammatory response in the lung generally resulting from tobacco smoking-induced recruitment and activation of inflammatory cells and/or activation of lower airway structural cells. Several mediators can modulate activation and recruitment of these cells, particularly those belonging to the chemokines (conventional and atypical) family. There is emerging evidence for complex roles of atypical chemokines and their receptors (such as high mobility group box 1 (HMGB1), antimicrobial peptides, receptor for advanced glycosylation end products (RAGE) or toll-like receptors (TLRs)) in the pathogenesis of COPD, both in the stable disease and during exacerbations. Modulators of these pathways represent potential novel therapies for COPD and many are now in preclinical development. Inhibition of only a single atypical chemokine or receptor may not block inflammatory processes because there is redundancy in this network. However, there are many animal studies that encourage studies for modulating the atypical chemokine network in COPD. Thus, few pharmaceutical companies maintain a significant interest in developing agents that target these molecules as potential antiinflammatory drugs. Antibody-based (biological) and small molecule drug (SMD)-based therapies targeting atypical chemokines and/or their receptors are mostly at the preclinical stage and their progression to clinical trials is eagerly awaited. These agents will most likely enhance our knowledge about the role of atypical chemokines in COPD pathophysiology and thereby improve COPD management.

Calcium-Binding Protein S100A4 Is Upregulated in Carotid Atherosclerotic Plaques and Contributes to Expansive Remodeling

Background

Carotid plaques with expansive arterial remodeling are closely related to cerebral ischemic events. Although S100A4 (S100 calcium‐binding protein A4) is expressed in atherosclerotic lesions, its role in atherosclerotic plaque progression remains unknown. In this study, we examined the association between carotid arterial expansive remodeling and S100A4 expression.

Methods and Results

Preoperative high‐resolution magnetic resonance imaging was used to assess luminal stenosis and vascular remodeling in patients undergoing carotid endarterectomy. To examine murine carotid atherosclerosis, we induced experimental lesions by flow cessation in apolipoprotein E‐deficient mice fed a high‐fat diet. The role of S100A4 in plaque formation and smooth muscle cell proliferation was investigated in vivo and in vitro, respectively. Human carotid arterial expansive remodeling showed positive correlations with the expression of S100A4, MMP2, and MMP9. S100A4 mRNA levels were positively correlated with those of MMP2, MMP9, and MMP13. S100A4 was expressed in vascular smooth muscle cells (VSMCs) and VSMC‐derived foam cells in the plaque shoulder and marginal areas. S100A4 expression increased concomitantly with plaque formation in our animal model. Exogenous recombinant S100A4 protein enhanced the levels of Mmp2, Mmp9, and Mmp13 and the cell proliferation ability in VSMCs. A chemotaxis assay indicated that extracellular S100A4 functions as a chemoattractant for VSMCs.

Conclusions

S100A4 expression was elevated in human carotid plaques and showed a positive correlation with the degree of expansive remodeling. S100A4‐positive VSMC‐derived cells are considered to play an important role in carotid expansive remodeling.

Matrix Metalloproteinases as Biomarkers of Atherosclerotic Plaque Instability

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases responsible for tissue remodeling and degradation of extracellular matrix (ECM) proteins. MMPs may modulate various cellular and signaling pathways in atherosclerosis responsible for progression and rupture of atherosclerotic plaques. The effect of MMPs polymorphisms and the expression of MMPs in both the atherosclerotic plaque and plasma was shown. They are independent predictors of atherosclerotic plaque instability in stable coronary heart disease (CHD) patients. Increased levels of MMPs in patients with advanced cardiovascular disease (CAD) and acute coronary syndrome (ACS) was associated with future risk of cardiovascular events. These data confirm that MMPs may be biomarkers in plaque instability as they target in potential drug therapies for atherosclerosis. They provide important prognostic information, independent of traditional risk factors, and may turn out to be useful in improving risk stratification.

Associations of Innate and Adaptive Immune Cell Subsets With Incident Type 2 Diabetes Risk: The MESA Study

OBJECTIVE

Cell-mediated immunity is implicated in glucose homeostasis and insulin resistance. Whether the levels of innate and adaptive immune cells in peripheral blood are risk factors for incident type 2 diabetes (T2D) remains unknown. We hypothesized that the proportions of naive, memory, CD28-, Th17, and T regulatory CD4+ cells would be associated with incident T2D. In secondary analyses, we evaluated the relationships of 28 additional immune cell phenotypes with T2D.

DESIGN

Immune cell phenotypes (n = 33) were measured by flow cytometry using cryopreserved cells collected from 1113 participants of the Multi-Ethnic Study of Atherosclerosis (MESA) at the baseline examination (2000-2002). Cox proportional hazards models were used to evaluate associations of immune cell phenotypes with incident T2D over a median follow-up of 9.1 years, adjusted for age, sex, race/ethnicity, educational status, and body mass index.

RESULTS

Incident T2D was observed for 120 participants. None of the cell phenotypes included in the primary hypotheses were significantly associated with T2D (all P > 0.05). Among the secondary immune cells studied, a higher proportion of CD19+CD27+ B cells was associated with a reduced risk of T2D (hazard ratio: 0.72 (95% confidence interval: 0.56, 0.93), per 1-standard deviation (16%) increase). This association was no longer significant after correction for the multiple cell phenotypes tested (P > 0.0015).

CONCLUSIONS

Our results suggest that the frequencies of several subsets of monocytes, innate lymphocytes, and CD4+ and CD8+ T cells in circulating blood are not related to the future onset of T2D. Higher levels of CD19+CD27+ B cells may be associated with decreased T2D risk.

TLRs and RAGE are elevated in carotid plaques from patients with moderate-to-severe obstructive sleep apnea syndrome

Background

There is growing evidence that obstructive sleep apnea (OSA) promotes vascular endothelial dysfunction and atherogenesis. Pathways that mediate this pathology may include Toll-like receptors (TLRs) and receptor for advanced glycation end products (RAGE) which play a significant role in proinflammatory processes. The aim of this study was to measure the expression of the above-mentioned receptors in relation to OSA severity in carotid plaques obtained during open endarterectomy.

Methods

This prospective study included patients with a sleep study prior to surgery and a plaque specimen obtained during standard open endarterectomy. Immunohistochemistry of TLR2, TLR4, TLR7, TLR9, RAGE, HMGB1, and NF-κB was performed on atherosclerotic plaques from carotid arteries of patients with and without OSA.

Results

There were 46 patients (22 women, mean age 73.2 ± 1.3 years): 14 control patients, 13 with mild, 11 with moderate, and 8 with severe OSA. The expression of all TLRs and RAGE increased proportionately with increasing OSA severity. The largest differences between patients with severe OSA and no OSA were found for TLR2 (2.88 ± 0.35 vs. 1.27 ± 0.47, p < 0.001), TLR4 (2.88 ± 0.35 vs. 1.64 ± 0.5, p < 0.001), TLR9 (2.38 ± 0.52 vs. 1.45 ± 0.52, p < 0.01), and RAGE (2.5 ± 0.53 vs. 1.82 ± 0.6, p < 0.05).

Conclusion

TLR2, TLR4, TLR9, and RAGE expression was significantly increased in carotid plaques of patients with moderate-to-severe OSA when compared with control patients with no OSA and those with mild OSA. TLR and RAGE-mediated pathways may play a significant role in OSA-dependent atherogenesis.

The receptor for advanced glycation end-products (RAGE) is an important pattern recognition receptor (PRR) for inflammaging

The receptor for advanced glycation end-products (RAGE) was initially characterized and named for its ability to bind to advanced glycation end-products (AGEs) that form upon the irreversible and non-enzymatic interaction between nucleophiles, such as lysine, and carbonyl compounds, such as reducing sugars. The concentrations of AGEs are known to increase in conditions such as diabetes, as well as during ageing. However, it is now widely accepted that RAGE binds with numerous ligands, many of which can be defined as pathogen-associated molecular patterns (PAMPs) or damage-associated molecular patterns (DAMPs). The interaction between RAGE and its ligands mainly results in a pro-inflammatory response, and can lead to stress events often favouring mitochondrial dysfunction or cellular senescence. Thus, RAGE should be considered as a pattern recognition receptor (PRR), similar to those that regulate innate immunity. Innate immunity itself plays a central role in inflammaging, the chronic low-grade and sterile inflammation that increases with age and is a potentially important contributory factor in ageing. Consequently, and in addition to the age-related accumulation of PAMPs and DAMPs and increases in pro-inflammatory cytokines from senescent cells and damaged cells, PRRs are therefore important in inflammaging. We suggest here that, through its interconnection with immunity, senescence, mitochondrial dysfunction and inflammasome activation, RAGE is a key contributor to inflammaging and that the pro-longevity effects seen upon blocking RAGE, or upon its deletion, are thus the result of reduced inflammaging.