TLR signaling: an emerging bridge from innate immunity to atherogenesis

Wolbachia-induced inhibition of O'nyong nyong virus in Anopheles mosquitoes is mediated by Toll signaling and modulated by cholesterol

Enhanced host immunity and competition for metabolic resources are two main competing hypotheses for the mechanism of Wolbachia-mediated pathogen inhibition in arthropods. Using an Anopheles mosquito - somatic Wolbachia infection - O'nyong nyong virus (ONNV) model, we demonstrate that the mechanism underpinning Wolbachia-mediated virus inhibition is up-regulation of the Toll innate immune pathway. However, the viral inhibitory properties of Wolbachia were abolished by cholesterol supplementation. This result was due to Wolbachia-dependent cholesterol-mediated suppression of Toll signaling rather than competition for cholesterol between Wolbachia and virus. The inhibitory effect of cholesterol was specific to Wolbachia-infected Anopheles mosquitoes and cells. These data indicate that both Wolbachia and cholesterol influence Toll immune signaling in Anopheles mosquitoes in a complex manner and provide a functional link between the host immunity and metabolic competition hypotheses for explaining Wolbachia-mediated pathogen interference in mosquitoes. In addition, these results provide a mechanistic understanding of the mode of action of Wolbachia-induced pathogen blocking in Anophelines, which is critical to evaluate the long-term efficacy of control strategies for malaria and Anopheles-transmitted arboviruses.

Therapeutic Targeting of TLR4 for Inflammation, Infection, and Cancer: A Perspective for Disaccharide Lipid A Mimetics

The Toll-like receptor 4 (TLR4) signaling pathway plays a central role in the prompt defense against infectious challenge and provides immediate response to Gram-negative bacterial infection. The TLR4/MD-2 complex can sense and respond to various pathogen-associated molecular patterns (PAMPs) with bacterial lipopolysaccharide (LPS) being the most potent and the most frequently occurring activator of the TLR4-mediated inflammation. TLR4 is believed to be both a friend and foe since improperly regulated TLR4 signaling can result in the overactivation of immune responses leading to sepsis, acute lung injury, or pathologic chronic inflammation involved in cancer and autoimmune disease. TLR4 is also considered a legitimate target for vaccine adjuvant development since its activation can boost the adaptive immune responses. The dual action of the TLR4 complex justifies the efforts in the development of both TLR4 antagonists as antisepsis drug candidates or remedies for chronic inflammatory diseases and TLR4 agonists as vaccine adjuvants or immunotherapeutics. In this review, we provide a brief overview of the biochemical evidences for possible pharmacologic applications of TLR4 ligands as therapeutics and report our systematic studies on the design, synthesis, and immunobiological evaluation of carbohydrate-based TLR4 antagonists with nanomolar affinity for MD-2 as well as disaccharide-based TLR4 agonists with picomolar affinity for the TLR4/MD-2 complex.

The Role of APOE and NF-κB in Alzheimer’s Disease

Apolipoprotein E (APOE) has three different isoforms, with APOE4 carriers representing a major risk factor for the development of Alzheimer’s disease (AD). AD is the most common form of dementia, and is a relentlessly progressive disorder that afflicts the aged, characterized by severe memory loss. Presently, AD does not have a cure, increasing the urgency for the development of novel therapeutics for the prevention/treatment of AD. The APOE4 isoform is associated with many pathological mechanisms, such as increased neuroinflammation and a reduction in β-amyloid (Aβ) clearance. The accumulation of Aβ plaques in the brain is a hallmark of AD. The presence of APOE4 can increase neuroinflammation via overactivation of the nuclear factor kappa B (NF-κB) pathway. The NF-κB pathway is a family of transcription factors involved with regulating over 400 genes involved with inflammation. AD is associated with sustained inflammation and an overactivation of the NF-κB pathway. Therefore, targeting the APOE4 isoform and suppressing the NF-κB pathway using anti-inflammatory compounds may result in the development of novel therapeutics for the prevention/treatment of AD.

The role of Helicobacter cinaedi in the development of atherosclerosis

Helicobacter cinaedi (H. cinaedi) is a Gram-negative curved motile rod that causes bloodstream or enteric infections. It was suggested that H. cinaedi was involved in the progression of atherosclerosis. We aimed to investigate the presence of H. cinaedi DNA using a nested-polymerase chain reaction (PCR) in atheroma plaques from patients with atherosclerosis-induced vascular diseases. A total of 129 patients diagnosed with valvular heart disease due to atherosclerosis and 146 patients with non-atherosclerotic post-stenotic dilatation were included as the patient and the control groups, respectively. The ATCC BA847 H. cinaedi strain was used as the positive control for the nested-PCR method. We investigated H. cinaedi DNA in our study groups using the nested-PCR method and detected only six H. cinaedi DNA (4.65%) in the 129 atherosclerotic patient group. We detected significant difference between patient and control groups with respect to the presence of H. cinaedi on the basis of Fischer’s exact test (p = 0.010) by univariate analysis. Age (OR: 1.042, p = 0.016), total cholesterol (≥200 mg/dL) (OR: 1.849, p = 0.0001), and high-density lipoprotein (≥50 mg/dL) (OR: 0.745, p = 0.039) levels were detected as independent variables for the risk of atherosclerosis development in the patient group. The presence of H. cinaedi was not detected as an independent variable in a multivariate analysis. Previous studies suggested that H. cinaedi-induced oral infections might translocate to vascular tissue and induce chronic inflammation in the aorta, which subsequently may lead to atherosclerotic plaque formation. In conclusion, we could not suggest that there is a causal relationship between H. cinaedi and the development of atherosclerosis. However, age (OR: 1.042), total cholesterol (≥200 mg/dL, OR: 1.849), and high-density lipoprotein (≥50 mg/dL, OR: 0.745, as protective) levels have a significant role in the pathogenesis of atherosclerosis development. We also suggest that the presence of H. cinaedi may contribute to the risk of atherosclerosis development due to the univariate comparison result.

Inhibition of the Renin-Angiotensin System Reduces Gene Expression of Inflammatory Mediators in Adipose Tissue Independent of Energy Balance

Obesity is a growing health problem worldwide. The renin-angiotensin system (RAS) is present in adipose tissue, and evidence suggests that it is involved in both diet-induced obesity and the inflammation associated with obesity. The present experiments determined the effect of (1) different angiotensin-converting enzyme (ACE) inhibitors (captopril, perindopril, enalapril) and angiotensin receptor blockers (ARBs: telmisartan, losartan) on adiposity of mice fed a high-fat diet for 28 days (2); acute treatment with the ACE-inhibitor captopril on gene expression of inflammatory markers in mice fed a high-fat diet (HFD); and (3) short-term (2 days) and chronic (28 days) treatment of ACE-inhibition on energy expenditure (EE) and energy balance in mice fed HFD ad libitum (AL), as well as receiving HFD limited to the amount of calories eaten by controls (pair-fed (PF) group). Body weight, food intake, adiposity and plasma leptin were lower in ACE inhibitor or ARB-treated groups over 28 days compared with HFD untreated mice. Short-term treatment with captopril led to increased EE relative to the level in the PF group. After 28 days, EE was lower in both captopril-treated and PF mice compared with AL, but the effect was greater in the captopril-treated group. Adiponectin was elevated in captopril-treated mice, but not in PF mice, after both 2 and 28 days. Additionally, acute RAS blockade in HFD-fed mice reduced mRNA expression for MCP-1, IL-6, TLR4, and leptin in adipose tissue relative to values in untreated groups. These data demonstrate that ACE inhibition and angiotensin receptor blockade reduce food intake to produce weight loss and suggest that the anti-inflammatory effects of ACE inhibition may be independent of weight loss.

Protective role of TIRAP functional variant against development of coronary artery disease

Coronary artery disease (CAD) is the leading cause of sudden death worldwide. Inflammation is proved to be an important player in development of the CAD. Inflammation is directly regulated by the Toll like receptors (TLRs). Susceptibility of CAD is influenced by genetic variations within TLRs and the proteins involved in its signaling cascade. The TIRAP/MAL {TIR domain containing adaptor protein / MyD88 (myeloid differentiation primary response gene 88) adaptor-like} exhibits maximum genetic variations of all adaptor proteins involved in TLR signaling cascade. Susceptibility to a number of diseases can be influenced due to presence of S180L single nucleotide polymorphism (SNP) of TIRAP/MAL. This study was conducted to investigate the functional role of this well characterized S180L polymorphism on susceptibility to CAD among Pakistani patients. A total of 146 Pakistani CAD patients and 147 controls were genotyped by Amplification Refractory Mutation System-Polymerase Chain Reaction (ARMS-PCR) and the data was analyzed by using 2-tailed Chi square (x2 ) test. The p value ≤ 0.05 was considered to be significant. Significantly high frequency of homozygous L180L genotype was observed among healthy subjects as compared to the CAD patients [24 (16%) vs 7 (5%); x2 11.85; p = 0.003]. Moreover, the allele frequency of the minor allele; 180L was observed to be significantly higher among controls than the CAD patients, having same direction of association [156 (53%) vs 131 (45%); OR (95% CI) = 0.7198 (0.520-0.996); p < 0.05). Our results indicate that protective effect of L180L; a coding variant of TIRAP/MAL against CAD is discernible.

MicroRNA-20a-3p regulates the host immune response to facilitate the mycobacterium tuberculosis infection by targeting IKKβ/NF-κB pathway

BACKGROUND

Mycobacterium tuberculosis (M.tb) has evolved to utilize different mechanisms to evade the host immune response. Several microRNAs (miRNAs) have been found to regulate innate immune response in M.tb replication and infection, but the roles and detailed molecular mechanisms of miRNAs in M.tb infection remain to be clarified.

METHODS

Previously published dataset GSE94007 from GEO database was used for screening differential-expressed miRNAs, and a significant up-regulated miR-20a-3p was chosen for further investigation. Cells were transfected with miR-20a-3p mimics, inhibitors, IKKβ siRNA, or their controls to verify the role of miR-20a-3p and IKKβ in M.tb infection and host immune response. IL-β, IL-6 and TNF-α contents in supernatant were measured by ELISA kits. The expression level of IKKβ/NF-κB pathway were also detected by western blot.

RESULTS

We found that miR-20a-3p was dose-and time-dependently increased during M.tb infection. Subsequently, our results demonstrated that upregulation of miR-20a-3p promoted intracellular growth of bacterial, and suppressed the release of proinflammatory cytokines in both M.tb-infected RAW264.7 and BMDM cells, while downregulation of miR-20a-3p had an opposite effect. Moreover, miR-20a-3p suppressed the activity of NF-κB pathway by directly targeting IKKβ, resulting in the suppression of pro-inflammatory cytokines, attenuation of immune response and promotion of M.tb survival.

CONCLUSION

Our findings uncover a role of miR-20a-3p and its target IKKβ in regulating M.tb induced immune responses and provide a better understanding of pathogenesis of M.tb infection.

Bacterial Lipoteichoic Acid Attenuates Toll-Like Receptor Dependent Dendritic Cells Activation and Inflammatory Response

Toll-like receptor (TLR) signaling is an indispensable factor in immune cells activation. Many TLR ligands have been identified, and were characterized the immunological functions such as inflammatory cytokine production in immune cells. However, the anti-inflammatory response in TLR ligand-mediated manner is poorly understood. In this report, we show that bacterial lipoteichoic acid (LTA), which is a TLR2 ligand from gram-positive bacteria including Staphylococcus aureus (S. aureus), suppresses TLR-mediated inflammatory response in dendritic cells (DCs). The TLR ligand-induced Tumor Necrosis Factor-alpha (TNF-α) production was suppressed in the bone marrow derived dendritic cells (BMDCs) by co-treatment of LTA. The cellular activation, which was characterized as upregulations of CD80, CD86 and major histocompatibility complex II (MHC II) expression, was also suppressed in the TLR ligand stimulated BMDCs in the presence of LTA. While LTA itself didn’t induced both TNF-α production and upregulation of cell surface markers. The LTA mediated immunosuppressive function was abolished by TLR2 blocking in lipopolysaccharide (LPS)-stimulated BMDCs. Furthermore, LTA also showed the immunosuppressive function in the generation of IFN-γ+CD4+ T (Th1) cells by attenuation of antigen presenting activity in the BMDCs. In the imiquimod (IMQ)-induced acute skin inflammation, LTA suppressed the inflammation by downregulation of the activation in skin accumulated DCs. Thus, LTA is a TLR2 dependent immunological suppressor against inflammatory response induced by other TLR ligands in the DCs.

Anti-inflammatory Action of Statins in Cardiovascular Disease: the Role of Inflammasome and Toll-Like Receptor Pathways

Atherosclerosis is one type of cardiovascular disease (CVD) in which activation of the NLRP3 inflammasome and toll-like receptor (TLR) pathways is implicated. One of the most effective treatments for atherosclerosis is the use of statin medications. Recent studies have indicated that statins, in addition to their lipid-lowering effects, exert inhibitory and/or stimulatory effects on the NLRP3 inflammasome and TLRs. Some of the statins lead to activation of the inflammasome and subsequently cause secretion of IL-1β and IL-18. Thus, these actions may further aggravate the disease. On the other hand, some statins cause inhibition of the inflammasome or TLRs and along with lipid-lowering, help to improve the disease by reducing inflammation. In this article, we discuss these contradictory studies and the mechanisms of action of statins on the NLRP3 inflammasome and TLR pathways. The dose-dependent effects of statins on the NLRP3 complex are related to their chemistry, pharmacokinetic properties, and danger signals. Lipophilic statins have more pleiotropic effects on the NLRP3 complex in comparison to hydrophilic statins. Statins can suppress TLR4/MyD88/NF-ĸB signaling and cause an immune response shift to an anti-inflammatory response. Furthermore, statins inhibit the NF-ĸB pathway by decreasing the expression of TLRs 2 and 4. Statins are cost-effective drugs, which should have a continued future in the treatment of atherosclerosis due to both their immune-modulating and lipid-lowering effects.

S100 family proteins in inflammation and beyond

The S100 family proteins possess a variety of intracellular and extracellular functions. They interact with multiple receptors and signal transducers to regulate pathways that govern inflammation, cell differentiation, proliferation, energy metabolism, apoptosis, calcium homeostasis, cell cytoskeleton and microbial resistance. S100 proteins are also emerging as novel diagnostic markers for identifying and monitoring various diseases. Strategies aimed at targeting S100-mediated signaling pathways hold a great potential in developing novel therapeutics for multiple diseases. In this chapter, we aim to summarize the current knowledge about the role of S100 family proteins in health and disease with a major focus on their role in inflammatory conditions.

Genital Chlamydia infection in hyperlipidemic mouse models exacerbates atherosclerosis

BACKGROUND AND AIMS

Atherosclerosis is a chronic inflammatory disease, and recent studies have shown that infection at remote sites can contribute to the progression of atherosclerosis in hyperlipidemic mouse models. In this report, we tested the hypothesis that genital Chlamydia infection could accelerate the onset and progression of atherosclerosis.

METHODS

Apolipoprotein E (Apoe^-/-) and LDL receptor knockout (Ldlr^-/-) mice on a high-fat diet were infected intra-vaginally with Chlamydia muridarum. Atherosclerotic lesions on the aortic sinuses and in the descending aorta were assessed at 8-weeks post-infection. Systemic, macrophage, and vascular site inflammatory responses were assessed and quantified.

RESULTS

Compared to the uninfected groups, infected Apoe^-/- and Ldlr^-/- mice developed significantly more atherosclerotic lesions in the aortic sinus and in the descending aorta. Increased lesions were associated with higher circulating levels of serum amyloid A-1, IL-1β, TNF-α, and increased VCAM-1 expression in the aortic sinus, suggesting an association with inflammatory responses observed during C. muridarum infection. Genital infection courses were similar in Apoe^-/-, Ldlr^-/-, and wild type mice. Further, Apoe^-/- mice developed severe uterine pathology with increased dilatations. Apoe-deficiency also augmented cytokine/chemokine response in C. muridarum infected macrophages, suggesting that the difference in macrophage response could have contributed to the genital pathology in Apoe^-/- mice.

CONCLUSIONS

Overall, these studies demonstrate that genital Chlamydia infection exacerbates atherosclerotic lesions in hyperlipidemic mouse and suggest a novel role for Apoe in full recovery of uterine anatomy after chlamydial infection.

Chlamydia and Lipids Engage a Common Signaling Pathway That Promotes Atherogenesis

BACKGROUND

Recent studies indicate that Toll-like receptor 4 (TLR4) and myeloid differentiation factor 88 (MyD88) signaling promote the development of high fat diet-induced atherosclerosis in hypercholesterolemic mice.

OBJECTIVES

The authors investigated the role of TLR4/MyD88 signaling in hematopoietic and stromal cells in the development and infection-mediated acceleration of atherosclerosis.

METHODS

The authors generated bone marrow chimeras between wild-type and Tlr4^-/- mice, as well as wild-type and Myd88^-/- mice. All mice were on the Apoe^-/- background and fed high fat diet. The authors infected the chimeric mice with C. pneumoniae (CP) and fed them high fat diet.

RESULTS

Aortic sinus plaques and lipid content were significantly reduced in Apoe^-/- mice that received Tlr4^-/-or Myd88^-/- bone marrow compared with control animals despite similar cholesterol levels. Similarly, Tlr4 or Myd88 deficiency in stromal cells also led to a reduction in the lesion area and lipid in aortic sinus plaques. MyD88 expression only in CD11c+ dendritic cells (myeloid cells) in cells was sufficient in otherwise MyD88-deficient mice to induce CP infection-mediated acceleration of atherosclerosis, underlining the key role of MyD88 in CD11c+ dendritic cells (myeloid cells). Whereas CP infection markedly accelerated atherosclerosis in TLR4- or MyD88-positive chimeras, CP infection had a minimal effect on atherosclerosis in TLR4- or MyD88-deficient mice (either in the hematopoietic or stromal cell compartments).

CONCLUSIONS

The authors show that both CP infection and metabolic stress associated with dyslipidemia use the same innate immune response pathway, utilizing TLR4/MyD88 signaling, with similar relative contributions in bone marrow-derived hematopoietic cells and in stromal cells. Further studies are required to understand this intricate and complex cross talk among innate and adaptive immune systems in various conditions to more effectively design dendritic cell-mediated atheroprotective vaccines and other therapeutic strategies.

Anti-inflammatory activity of small-molecule antagonists of Toll-like receptor 2 (TLR2) in mice

Toll-like receptor 2 (TLR2) is currently investigated as a potential therapeutic target in diseases with underlying inflammation like sepsis and arthritis. We reported the discovery, by virtual screening and biological testing, of eight TLR2 antagonists (AT1-AT8) which showed TLR2-inhibitory activity in human cells (Murgueitio et al., 2014). In this study, we have deepened in the mechanism of action and selectivity (TLR2/1 or TLR2/6) of those compounds in mouse primary cells and in vivo. The antagonists reduced, in a dose-dependent way the TNFα production (e.g. AT5 IC₅₀ 7.4 μM) and also reduced the nitric oxide (NO) formation in mouse bone marrow-derived macrophages (BMDM). Treatment of BMDM with the antagonists showed that downstream of TLR2, MAPKs phosphorylation and IkBα degradation was reduced. Notably, in a mouse model of tri-acylated lipopeptide (Pam3CSK4)-induced inflammation, AT5 attenuated the TNFα and IL-6 inflammatory response. Further, the effect of AT5 in the stimulation of BMDM by the endogenous alarmin HMGB1 was investigated. Our results indicate that AT4-AT7 and, particularly AT5 appear as good starting points for the development of inhibitors targeting TLR2 in inflammatory disorders.

Analysis of host Toll-like receptor 3 and RIG-I-like receptor gene expression in patients with abdominal aortic aneurysm

OBJECTIVE

Abdominal aortic aneurysm (AAA) is a vascular disease relatively common in the elderly population. Although some events that contribute to the development and progression of AAA are known, there are limited data examining the association of Toll-like receptor 3 (TLR3) and RIG-I-like receptor expression with the pathogenesis of AAAs. In this study, we investigated the gene and protein expression of TLR3 and RIG-I-like receptors (RIG-I and MDA5) in aortic wall and blood of AAA patients and examined the relationship between their expression and immune response.

METHODS

Total RNA was extracted from aortic wall tissues and blood samples collected from 20 patients with AAA and blood samples of 17 healthy volunteers without aortic aneurysm. To evaluate the DDX58 (RIG-I), IFIH1 (MDA5), and TLR3 gene expression level, quantitative real-time polymerase chain reaction was used. Extracellular cytokine and pattern recognition receptor levels were quantified by enzyme-linked immunosorbent assays.

RESULTS

TLR3, RIG-I, and MDA5 were constitutively expressed in both aortic tissues and blood samples from AAA patients and healthy volunteers. In patients with AAA, higher TLR3 expression in aortic tissues than in blood was found (P = .004). The DDX58 messenger RNA expression was higher in blood of patients with AAA compared with healthy subjects (P = .021). A significantly higher level of plasma interleukin 4 was noticed in patients with AAA than in healthy individuals (P = .008).

CONCLUSIONS

This study suggests that RIG-I and TLR3 seem to be important factors in the pathogenesis of AAA.

Induced carotid atherosclerosis in lupus mice

Fas knockout (Fas^-/-) mice are a model for systemic lupus erythematosus (SLE) -like autoimmune syndromes. We aimed to induce atherosclerosis (AS) in Fas^-/- mice. Sixteen male Fas^-/- mice were included in the study, sex-matched C57B6/L (B6) and apolipoprotein E-knockout (ApoE^-/-) mice were negative and positive AS controls, respectively. A silica collar was placed around the right carotid artery of each mouse to induce AS development. All mice were fed a 24-week high-fat diet, and investigated for AS lesions. We also compared the levels of blood lipid and glucose, serum tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), anti-nuclear antibody (ANA) and anti-double-stranded deoxyribonucleic acid (anti-dsDNA) antibody in Fas^-/- mice with those in B6 or ApoE^-/- mice. All ApoE^-/- and 6 Fas^-/- but no B6 mice showed atherogenesis in right carotid artery. The carotid plaque contains more collagen and less lipid in Fas^-/- than ApoE^-/- mice. The levels of blood glucose, serum TNF-α, IL-6, ANA, and anti-dsDNA antibody were significantly higher in Fas^-/- mice than those in B6 mice, the levels of serum TNF-α and blood glucose were significantly higher and the level of blood lipid was significantly lower in Fas^-/- mice than those in ApoE^-/- mice. Therefore, carotid AS can develop in Fas^-/- mice. Fas^-/- mice display higher levels of serum IL-6, TNF-α, ANA, and anti-dsDNA than B6 mice, higher levels of serum TNF-α and blood glucose and lower level of blood lipid than ApoE^-/- mice, and less lipid and more collagen in AS plaque than ApoE^-/- mice.

Role of toll-like receptor 4 Asp299Gly polymorphism in the development of cardiovascular diseases in HIV-infected patients

OBJECTIVE

Cardiovascular diseases (CVDs) are one of the main causes of morbimortality in HIV-infected patients on suppressive antiretroviral therapy. The objective of this work was to evaluate the role of single nucleotide polymorphisms (SNPs) in lipopolysaccharide (LPS) Toll-like receptor 4 (TLR4) and CVDs occurrence in HIV-infected patients. Additionally, the functional consequences of carrying these SNPs were analyzed.

METHODS

The association of TLR4 SNPs, Asp299Gly/Thr399Ile with CVDs occurrence was analyzed using multivariate logistic regression models. Clinical, immunological, and traditional cardiovascular risk factors were used as covariates. The monocyte phenotype and response were assessed by multiparametric flow cytometry comparing carriers with noncarriers of this SNP.

RESULTS

Asp299Gly SNP, assayed in 253 HIV-infected patients, was independently associated with the occurrence of CVDs after adjusting for CD4+ T-cell nadir, HCV-coinfection, bacterial pneumonia, diabetes mellitus, and traditional cardiovascular risk factors [odds ratio (confidence interval 95%) = 3.672 (1.061-12.712), P = 0.04). Carriers of Asp299Gly SNP showed higher percentage of patrolling and intermediate monocytes producing a proinflammatory combination of cytokines compared with noncarriers (P = 0.037 and P = 0.046, respectively). Intermediate monocyte subset levels correlated with soluble interleukin-6 levels only in carriers (r = 0.89; P = 0.01).

CONCLUSION

TLR4 Asp299Gly polymorphism is independently associated with the occurrence of CVDs in HIV-infected patients. The proinflammatory profile associated to this variant could be involved in the development of atherosclerotic pathologies.

Pycnogenol Reduces Toll-Like Receptor 4 Signaling Pathway-Mediated Atherosclerosis Formation in Apolipoprotein E-Deficient Mice

Pycnogenol (PYC) is an extract from French maritime pine bark. Its antioxidative and anti-inflammatory effects have been shown to be beneficial for atherosclerosis. Here, we tested whether PYC could suppress high cholesterol and fat diet (HCD)-induced atherosclerosis formation in apolipoprotein E (apoE)-deficient mice. In our study, PYC suppressed oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation in peritoneal macrophages. Apolipoprotein E-deficient mice were orally administered PYC or a control solvent for ten weeks, and these mice were fed a standard diet or high cholesterol and fat diet during the latter eight weeks. Pycnogenol markedly decreased the size of atherosclerotic lesions induced by high cholesterol and fat diet compared with the nontreated controls. In addition, TLR4 expression in aortic sinus was stimulated by high cholesterol and fat diet feeding and was significantly reduced by PYC. A mechanistic analysis indicated that lipopolysaccharide (LPS) significantly increased expression of fatty acid binding protein (aP2) and macrophage scavenger receptor class A (SR-A), which were blocked by a JNK inhibitor. Furthermore, PYC inhibited the lipopolysaccharide-induced upregulation of aP2 and scavenger receptor class A via the JNK pathway. In conclusion, PYC administration effectively attenuates atherosclerosis through the TLR4-JNK pathway. Our results suggest that PYC could be a potential prophylaxis or treatment for atherosclerosis in humans.

Perpetual change: autophagy, the endothelium, and response to vascular injury

Current studies of vascular health, aging, and autophagy emphasize how the endothelium adapts to stress and contributes to disease. The endothelium is far from an inert barrier to blood-borne cells, pathogens, and chemical signals; rather, it actively translates circulating mediators into tissue responses, changing rapidly in response to physiologic stressors. Macroautophagy-the cellular ingestion of effete organelles and protein aggregates to provide anabolic substrates to fuel bioenergetics in times of stress-plays an important role in endothelial cell homeostasis, vascular remodeling, and disease. These roles include regulating vascular tone, sustaining or limiting cell survival, and contributing to the development of atherosclerosis secondary to infection, inflammation, and angiogenesis. Autophagy modulates these critical functions of the endothelium in a dynamic and perpetual response to tissue and intravascular cues.

Immunohistochemical characterization of Toll-like receptor 2 in gut epithelial cells and macrophages of goldfish Carassius auratus fed with a high-cholesterol diet

Toll-like receptors (TLRs) are a group of pattern recognition molecules that play a crucial role in innate immunity. The structural conservation of the archaic TLR system suggests that the regulation of the immune response might be similar in fish and mammals. Several TLRs (TLR-1, -2, and -4) are expressed by activated macrophages, "foam cells" in human atherosclerotic lesions. To date, 20 different TLRs were identified in more than a dozen different fish species. In this study we found that feeding goldfish, Carrassius auratus, a high-cholesterol diet (HCD) resulted macrophage foam cell formation in the intestinal tissues. The expression of TLR2 has been found in foam cells and in the cytoplasm of enterocytes, however the staining was more intense at the apical surface of polarized intestinal epithelial cells and in the lamina propria. In the intestinal epithelial cells and in the lamina propria cells of the control fish the TLR2 was expressed at low levels. The intestinal epithelium is directly involved in the mucosal immune response through its expression of proinflammatory genes, release of inflammatory cytokines, and recruitment of inflammatory cells.

The role of Toll-like receptor 4 in high-glucose-induced inflammatory and fibrosis markers in human peritoneal mesothelial cells. Int Urol Nephrol. 2017;49:171-181. [PMID: 27722989 DOI: 10.1007/s11255-016-1430-9]

PURPOSE

High glucose stimulates peritoneal inflammation and extracellular matrix accumulation in human peritoneal mesothelial cells (HPMCs). However, the roles of Toll-like receptor 4 (TLR4) and TLR2 in high-glucose-induced inflammation and fibrosis in peritoneal dialysis (PD) remain unclear. This study aimed to evaluate the effect of high glucose on TLR2 and TLR4 expression in HPMCs and to assess their impact on peritoneal inflammatory and fibrosis markers.

METHODS

Using cultured HPMCs, TLRs expression by high-glucose (50 mM) stimulation was assessed by quantitative real-time PCR. The association of reactive oxygen species (ROS) in high-glucose-induced TLR2 and TLR4 expression was measured by 2',7'-dichlorodihydrofluorescein diacetate staining with or without ROS inhibitor. In addition, the role of TLR2 and TLR4 on high-glucose-induced inflammatory and fibrosis markers including chemoattractant protein-1 (MCP-1), NF-κB, alpha-smooth muscle actin (α-SMA), transforming growth factor-β (TGF-ß), and fibronectin was evaluated after inhibition of TLR2 and TLR4 by small-interfering RNA (siRNA) or anti-TLR4/TLR2 antibodies, respectively.

RESULTS

High glucose induced TLR1, TLR2, and TLR4 mRNAs expressions. High-glucose-induced TLR4 and TLR2 mRNAs were associated partly with the generation of ROS. Inhibition of TLR4 attenuated the high-glucose-induced expression of MCP-1 mRNA and protein, MyD88 mRNA, nuclear NF-κB p65 protein, TGF-β, fibronectin, and α-SMA mRNA and protein. However, inhibition of TLR2 did not change the expression of MCP-1 mRNA and protein.

CONCLUSIONS

High glucose induces inflammatory and fibrosis markers in HPMCs partly through the TLR4/MyD88/NF-κB signaling pathway rather than TLR2. Therefore, TLR4 might be a therapeutic target for ameliorating peritoneal inflammation and fibrosis in PD.

Flagellin-induced NADPH oxidase 4 activation is involved in atherosclerosis

It is widely accepted that bacterial infection-mediated inflammation facilitates development of atherosclerosis by activating toll-like receptor (TLR) signaling system. We reasoned that NADPH oxidases (Nox), required for TLR-mediated inflammatory response, are involved in atherogenesis. Here, we show that the activation of Nox4 through TLR5 regulates the inflammation of the endothelium and in atherogenesis. Flagellin-induced interaction between the COOH region of Nox4 and the TIR domain of TLR5 led to H2O2 generation, which in turn promoted the secretion of pro-inflammatory cytokines including IL-8, as well as the expression of ICAM-1 in human aortic endothelial cells (HAECs). Knockdown of the Nox4 in HAECs resulted in attenuated expressions of IL-8 and ICAM-1 leading to a reduction in the adhesion and trans-endothelial migration of monocytes. Challenge of recombinant FliC (rFliC) to the ApoE KO mice with high-fat diet (HFD) resulted in significantly increased atherosclerotic plaque sizes compared to the saline-injected mice. However, an injection of rFliC into the Nox4ApoE DKO mice with HFDs failed to generate atherosclerotic plaque, suggesting that Nox4 deficiency resulted in significant protections against rFliC-mediated atherogenesis. We conclude that TLR5-dependent Nox4 activation and subsequent H2O2 generation play critical roles for the development of atherosclerosis.

Is Western Diet-Induced Nonalcoholic Steatohepatitis in Ldlr-/- Mice Reversible?

Background

Nonalcoholic fatty liver disease (NAFLD) is a major public health burden in western societies. The progressive form of NAFLD, nonalcoholic steatohepatitis (NASH), is characterized by hepatosteatosis, inflammation, oxidative stress, and hepatic damage that can progress to fibrosis and cirrhosis; risk factors for hepatocellular carcinoma. Given the scope of NASH, validating treatment protocols (i.e., low fat diets and weight loss) is imperative.

Methods

We evaluated the efficacy of two diets, a non-purified chow (NP) and purified (low-fat low-cholesterol, LFLC) diet to reverse western diet (WD)-induced NASH and fibrosis in Ldlr^-/- mice.

Results

Mice fed WD for 22–24 weeks developed robust hepatosteatosis with mild fibrosis, while mice maintained on the WD an additional 7–8 weeks developed NASH with moderate fibrosis. Returning WD-fed mice to the NP or LFLC diets significantly reduced body weight and plasma markers of metabolic syndrome (dyslipidemia, hyperglycemia) and hepatic gene expression markers of inflammation (Mcp1), oxidative stress (Nox2), fibrosis (Col1A, LoxL2, Timp1) and collagen crosslinking (hydroxyproline). Time course analyses established that plasma triglycerides and hepatic Col1A1 mRNA were rapidly reduced following the switch from the WD to the LFLC diet. However, hepatic triglyceride content and fibrosis did not return to normal levels 8 weeks after the change to the LFLC diet. Time course studies further revealed a strong association (r² ≥ 0.52) between plasma markers of inflammation (TLR2 activators) and hepatic fibrosis markers (Col1A, Timp1, LoxL2). Inflammation and fibrosis markers were inversely associated (r² ≥ 0.32) with diet-induced changes in hepatic ω3 and ω6 polyunsaturated fatty acids (PUFA) content.

Conclusion

These studies establish a temporal link between plasma markers of inflammation and hepatic PUFA and fibrosis. Low-fat low-cholesterol diets promote reversal of many, but not all, features associated with WD-induced NASH and fibrosis in Ldlr^-/- mice.

Toll-like receptor 4-induced endoplasmic reticulum stress contributes to impairment of vasodilator action of insulin

Impairment of vasodilator action of insulin is associated with endothelial dysfunction and insulin resistance. Activation of Toll-like receptor 4 (TLR4) induces proinflammatory response and endoplasmic reticulum (ER) stress. Saturated fatty acids (SFA) activate TLR4, which induces ER stress and endothelial dysfunction. Therefore, we determined whether TLR4-mediated ER stress is an obligatory step mediating SFA-induced endothelial dysfunction. Palmitate stimulated proinflammatory responses and ER stress, and this was suppressed by knockdown of TLR4 in primary human aortic endothelial cells (HAEC). Next, we examined the role of TLR4 in vasodilatory responses in intact vessels isolated from wild-type (WT, C57BL/6) and TLR4-KO mice after feeding high-fat (HFD) or normal chow diet (NCD) for 12 wk. Arterioles isolated from HFD WT mice exhibited impaired insulin-stimulated vasodilation compared with arterioles isolated from NCD WT mice. Deficiency of TLR4 was protective from HFD-induced impairment of insulin-stimulated vasodilation. There were no differences in acetylcholine (Ach)- or sodium nitroprusside (SNP)-stimulated vasodilation between the two groups. Furthermore, we examined whether ER stress is involved in SFA-induced impairment of vasodilator actions of insulin. Infusion of palmitate showed the impairment of vasodilatory response to insulin, which was ameliorated by coinfusion with tauroursodeoxycholic acid (TUDCA), an ER stress suppressor. Taken together, the results suggest that TLR4-induced ER stress may be an obligatory step mediating the SFA-mediated endothelial dysfunction.

Undiagnosed airflow limitation is common in patients with coronary artery disease and associated with cardiac stress

BACKGROUND AND OBJECTIVE

Smoking is a common risk factor for coronary artery disease (CAD) and chronic obstructive pulmonary disease (COPD). We evaluated the prevalence of undiagnosed COPD in patients with CAD and assessed the relationship between airflow obstruction and markers of cardiac stress.

METHODS

We recruited prospectively consecutive patients aged >40 years without known history of chronic lung disease (e.g. asthma, COPD, bronchiectasis) who had undergone percutaneous coronary intervention (PCI) for obstructive CAD between August 2009 and October 2010. Spirometry was performed and serum ST2, a novel biomarker of cardiomyocyte stress and fibrosis, was measured by enzyme-linked immunosorbent assay.

RESULTS

Among 475 subjects (mean age 64 ± 9.7, range 42-85 years, 87.2% males, 58.5% current or ex-smokers) who underwent spirometry, 51 (10.7%) had undiagnosed airflow obstruction with FEV1 /FVC ratio <70%. Of these 51 subjects, 14 (2.9%), 23 (4.8%) and 14 (2.9%) had FEV1 ≥80, 50-80 and 30-50% predicted normal, respectively. ST2 level was measured in all the subjects with undiagnosed airflow obstruction and in 290 subjects with normal lung function. There was no significant difference in left ventricular ejection fraction on echocardiogram between subjects with and without airflow obstruction. Patients with severe airflow obstruction had a higher level of cardiac stress marker ST2 than those with mild and moderate airflow obstruction (rho = -0.214, P ≤ 0.001).

CONCLUSION

Undiagnosed airflow obstruction is common among patients with CAD who have undergone PCI. Severity of airflow limitation is associated with increasing cardiac stress.

Genetics ignite focus on microglial inflammation in Alzheimer's disease

In the past five years, a series of large-scale genetic studies have revealed novel risk factors for Alzheimer’s disease (AD). Analyses of these risk factors have focused attention upon the role of immune processes in AD, specifically microglial function. In this review, we discuss interpretation of genetic studies.  We then focus upon six genes implicated by AD genetics that impact microglial function: TREM2, CD33, CR1, ABCA7, SHIP1, and APOE. We review the literature regarding the biological functions of these six proteins and their putative role in AD pathogenesis. We then present a model for how these factors may interact to modulate microglial function in AD.

TRIF adaptor signaling is important in abdominal aortic aneurysm formation

OBJECTIVE

Abdominal aortic aneurysm (AAA) is characterized by inflammation, loss of smooth muscle cells (SMCs), and degradation of the extracellular matrix in the vessel wall. Innate immune receptors such as Toll-like receptors (TLRs) were recently shown to regulate immunological processes leading to the formation and progression of atherosclerotic plaques as well as to other cardiovascular pathologies. Our aim was to investigate whether blockage of TLR signaling, under the control of TIR domain-containing adaptor protein including IFN-β (TRIF), could inhibit the inflammatory response and AAA development in mice.

RESULTS

In human AAA, an increased TLR3 and TLR4 expression in association with macrophages and T lymphocytes was demonstrated with immunohistochemical analysis. Angiotensin (Ang) II-induced aneurysm formation was significantly reduced by 30% in ApoE(-/-)Trif(-/-) mice compared to ApoE(-/-) mice. Morphologically, AngII-infused ApoE(-/-)Trif(-/-) mice had a more intact cellular and extracellular matrix while ApoE(-/-) mice infused with AngII displayed an increased medial thickness associated with aortic dissection, thrombus formation, and a more disorganized vessel wall. Gene expression analysis of the abdominal aorta revealed a profound decrease of the inflammatory genes CD68 (P < 0.05), CD11b (P < 0.05), and TNF-α (P < 0.05) and the protease gene MMP-12 (P < 0.01) in ApoE(-/-)Trif(-/-) mice compared to ApoE(-/-) mice infused with AngII.

CONCLUSION

Our results suggest that signaling through TRIF is important for the inflammatory response of AngII-induced AAA and that blockage of the TRIF pathway reduces vascular inflammation and protects against AAA formation.

Antagonism of toll-like receptor 2 attenuates the formation and progression of abdominal aortic aneurysm

Abdominal aortic aneurysm (AAA) is an inflammatory vascular disorder with high mortality. Accumulating evidence shows that toll-like receptor 2 (TLR2) plays a critical role in the regulation of wound-repairing process after tissue injury. We wondered if TLR2 signaling contributed to the pathogenesis of AAA and that targeting TLR2 would attenuate AAA development and progression. In this study, enhanced expression of TLR2 and its ligands were observed in human AAA tissue. Neutralization of TLR2 protected against AAA development and caused established AAA to regress in mouse models of AAA. In addition, TLR2-deficient mice also failed to develop AAA. The prophylactic and therapeutic effects of blocking TLR2 were accompanied by a significant resolution of inflammation and vascular remodeling, as indicated by the decreased expression or activity of MMP-2/9, α-SMA, inflammatory cytokines, and transcription factors NF-κB, AP-1 and STAT1/3 in AAA tissue. Mechanistically, blocking TLR2 decreased the expression and interaction of TLR2 and several endogenous ligands, which diminished chronic inflammation and vascular remodeling in the vascular tissue of AAA. Our studies indicate that the interactions between TLR2 and its endogenous ligands contribute to the pathogenesis of AAA and that targeting TLR2 offers great potential toward the development of therapeutic agents against AAA.

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.

Sensing and responding to cytosolic viruses invasions: An orchestra of kaleidoscopic ubiquitinations

Ubiquitin is a versatile molecular signature that modulates diverse cellular processes via proteasome-dependent and proteasome-independent mechanisms. The covalent and/or non-covalent binding of mono-ubiquitin and/or poly-ubiquitin chains to a target protein broadens the dynamic and functional spectra for signal integration. Different linkages of poly-ubiquitin chains determine specific physiological or pathological functions of target proteins. Accumulating evidences has revealed the essential roles of ubiquitination in orchestrating the host defenses against cytosolic RNA or DNA from viral infections. In this review, we summarize the current progress regarding the understanding of ubiquitin-mediated regulation of the RIG-I and STING antiviral signaling pathways and discuss certain critical issues that remain to be resolved in future studies.

Adiponectin as a potential biomarker of vascular disease

The increasing prevalence of diabetes and its complications heralds an alarming situation worldwide. Obesity-associated changes in circulating adiponectin concentrations have the capacity to predict insulin sensitivity and are a link between obesity and a number of vascular diseases. One obvious consequence of obesity is a decrease in circulating levels of adiponectin, which are associated with cardiovascular disorders and associated vascular comorbidities. Human and animal studies have demonstrated decreased adiponectin to be an independent risk factor for cardiovascular disease. However, in animal studies, increased circulating adiponectin alleviates obesity-induced endothelial dysfunction and hypertension, and also prevents atherosclerosis, myocardial infarction, and diabetic cardiac tissue disorders. Further, metabolism of a number of foods and medications are affected by induction of adiponectin. Adiponectin has beneficial effects on cardiovascular cells via its antidiabetic, anti-inflammatory, antioxidant, antiapoptotic, antiatherogenic, vasodilatory, and antithrombotic activity, and consequently has a favorable effect on cardiac and vascular health. Understanding the molecular mechanisms underlying the regulation of adiponectin secretion and signaling is critical for designing new therapeutic strategies. This review summarizes the recent evidence for the physiological role and clinical significance of adiponectin in vascular health, identification of the receptor and post-receptor signaling events related to the protective effects of the adiponectin system on vascular compartments, and its potential use as a target for therapeutic intervention in vascular disease.

Periodontal innate immune mechanisms relevant to atherosclerosis

Atherosclerosis is a common cardiovascular disease in the USA where it is a leading cause of illness and death. Atherosclerosis is the most common cause for heart attack and stroke. Most commonly, people develop atherosclerosis as a result of diabetes, genetic risk factors, high blood pressure, a high-fat diet, obesity, high blood cholesterol levels, and smoking. However, a sizable number of patients suffering from atherosclerosis do not harbor the classical risk factors. Ongoing infections have been suggested to play a role in this process. Periodontal disease is perhaps the most common chronic infection in adults with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between periodontal infection and atherosclerosis. This review focuses on exploring the molecular consequences of infection by pathogens that exacerbate atherosclerosis, with the focus on infections by the periodontal bacterium Porphyromonas gingivalis as a running example.

Regulation of cigarette smoke-induced toll-like receptor 4 expression by peroxisome proliferator-activated receptor-gamma agonists in bronchial epithelial cells

BACKGROUND AND OBJECTIVE

This study was designed to determine the effects of peroxisome proliferator-activated receptor-gamma (PPARγ) on airway inflammatory response to cigarette smoke (CS) exposure.

METHODS

For the in vivo experiments, 50 male Wistar rats were randomly assigned to one of four groups and were exposed to CS and pretreatment with a PPARγ agonist, rosiglitazone or a vehicle (saline). PPARγ antagonist bisphenol A diglycidyl ether (BADGE) or saline was administered before rosiglitazone treatment. Leukotriene B4 (LTB4) and interleukin-8 (IL-8) were measured by enzyme-linked immunosorbent assay. PPARγ and toll-like receptor 4 (TLR4) expression levels were assessed by immunohistochemistry and real-time polymerase chain reaction. For the in vitro experiments, human bronchial epithelial cells were stimulated with CS or phosphate buffer saline, pretreated with PPARγ agonist rosiglitazone or 15-deoxy-(Δ12,14)-PG J2 before CS exposure. BADGE was administered prior to the agonist treatment. PPARγ, TLR4 and inhibitor of κB (IκBα) expression levels were assessed by Western bot.

RESULTS

CS exposure decreased PPARγ expression, as well as increased IL-8, LTB4 and TLR4 expression levels in bronchial epithelial cells in vivo and in vitro. Moreover, PPARγ ligands counteracted CS-induced airway inflammation by reducing IL-8 and LTB4 expression levels that are associated with TLR4 and nuclear factor-kappa B (NF-κB).

CONCLUSION

CS exposure increased the pro-inflammatory activity of bronchial epithelial cells by affecting PPARγ expression. Moreover, PPARγ may play a significant role as a modulator of the TLR4-dependent inflammatory pathway through NF-κB in bronchial epithelial cells.

Tenascin-C is increased in atherothrombotic stroke patients and has an anti-inflammatory effect in the human carotid artery

Tenascin-C (Tn-C) is an endogenous ligand of toll-like receptor-4 (TLR-4); a key signalling molecule associated with chronic inflammatory conditions. Both Tn-C and TLR-4 are increased in unstable human atheroma, but their effects on local inflammatory conditions have not been investigated. The aim of the present study was to investigate the association and functional implications of Tn-C/TLR-4 signalling in large artery atherosclerotic stroke. Plasma Tn-C was measured by ELISA and found to be higher in recent stroke patients (n = 336; median 12.77 µg/mL, inter-quartile range 10.23-15.74 µg/mL) than in controls (n = 321; median 11.31 µg/mL, inter-quartile range 8.89-13.90 µg/mL), P < 0.001. Plasma Tn-C was also independently positively associated with stroke (odds ratio for highest Tn-C quartile 2.27, 95% confidence interval 1.37-3.76). Assessment of Tn-C associated chronic cytokine secretion was performed in vitro using paired, human, macroscopically disease matched, carotid atheroma tissue biopsies obtained from five patients undergoing carotid endarterectomy. A 4-day incubation with specific Tn-C blocking antibodies (Abs) increased secretion of TLR-4-associated cytokines, interleukin (IL)-8, IL-1β, tumour necrosis factor and C-C motif chemokine (CCL)3 and expression of TLR-4 in the tissue. These results suggest with Tn-C blockade another endogenous TLR-4 ligand upregulates TLR-4 expression and subsequent cytokine secretion. Titration of the Tn-C Abs also dose dependently increased secretion of IL-6, IL-8, IL-1β, and CCL3 in mixed, healthy, primary vascular cell culture. In summary, circulating concentrations of Tn-C are higher in patients with a recent history of atherosclerotic stroke and may play an anti-inflammatory role by reducing pro-inflammatory cytokine release from atheroma.

Apolipoprotein E-knockout mice on high-fat diet show autoimmune injury on kidney and aorta

BACKGROUND

Apolipoprotein E-knockout (ApoE(-/-)) mice is a classic model of atherosclerosis. We have found that ApoE(-/-) mice showed splenomegaly, higher titers of serum anti-nuclear antibody (ANA) and anti-dsDNA antibody compared with C57B6/L (B6) mice. However, whether ApoE(-/-) mice show autoimmune injury remains unclear.

METHODS AND RESULTS

Six females and six males in each group, ApoE(-/)(-), Fas(-/-) and B6 mice, were used in this study. The titers of serum ANA, anti-dsDNA antibody and creatinine and urine protein were measured by ELISA after 4 months of high-fat diet. The spleen weight and the glomerular area were determined. The expressions of IgG, C3 and macrophage in kidney and atherosclerotic plaque were detected by immunostaining followed by morphometric analysis. Similar to the characteristics of Fas(-/-) mice, a model of systemic lupus erythematosus (SLE), ApoE(-/-) mice, especially female, displayed significant increases of spleen weight and glomerular area when compared to B6 mice. Also, elevated titers of serum ANA, anti-dsDNA antibody and creatinine and urine protein. Moreover, the expressions of IgG, C3 and macrophage in glomeruli and aortic plaques were found in ApoE(-/-) mice. In addition, the IgG and C3 expressions in glomeruli and plaques significantly increased (or a trend of increase) in female ApoE(-/-) mice compared with males.

CONCLUSIONS

Apolipoprotein E-knockout mice on high-fat diet show autoimmune injury on kidney and aorta.

Toll-like receptor 4 mediates endothelial cell activation through NF-κB but is not associated with endothelial dysfunction in patients with rheumatoid arthritis

OBJECTIVE

To investigate the effects of TLR4 antagonism on human endothelial cells activation and cytokine expression, and whether the Asp299Gly TLR4 polymorphism is associated with better endothelial function in patients with rheumatoid arthritis (RA).

METHODS

Human aortic endothelial cells (HAECs) were treated with lipopolysaccharide (LPS), OxPAPC, and free fatty acids (FFA) at baseline and after incubation with the TLR4 antagonist eritoran (E5564). Cytokine expression was assessed by quantitative real-time PCR. In vivo endothelial function was assessed as brachial artery flow-mediated dilation (FMD) in RA patients with the wild type gene (aa) and with the Asp299Gly TLR4 polymorphic variant (ag).

RESULTS

In HAEC, TLR4 antagonism with eritoran inhibited LPS-induced mRNA expression of IL-6, IL-8, TNFα, CCL-2, VCAM and ICAM (P<0.05 for all) and inhibited Ox-PAPC-induced mRNA expression of IL-8 (P<0.05) and IL-6, albeit not to a statistically significant level (p = 0.07). In contrast, eritoran did not affect FFA-induced mRNA expression of IL-6 (P>0.05). In 30 patients with RA (15 with the ag allele) undergoing measurement of FMD, no differences in FMD and plasma levels of IL-6, IL-8, VCAM, and ICAM were found between the aa and the ag phenotype (P>0.05 for all).

CONCLUSIONS

TLR4 signaling in endothelial cells may be triggered by LPS and oxidized phospholipids, leading to endothelial activation and inflammation, which are inhibited by eritoran. Our in vivo investigation, however, does not support an association between the Asp299Gly TLR4 polymorphism and improved endothelium-dependent vasodilator function in patients with RA. Further study is needed to better understand the potential role of TLR4 on endothelial dysfunction in this and other patient populations.

Pathogen sensing pathways in human embryonic stem cell derived-endothelial cells: role of NOD1 receptors

Human embryonic stem cell-derived endothelial cells (hESC-EC), as well as other stem cell derived endothelial cells, have a range of applications in cardiovascular research and disease treatment. Endothelial cells sense Gram-negative bacteria via the pattern recognition receptors (PRR) Toll-like receptor (TLR)-4 and nucleotide-binding oligomerisation domain-containing protein (NOD)-1. These pathways are important in terms of sensing infection, but TLR4 is also associated with vascular inflammation and atherosclerosis. Here, we have compared TLR4 and NOD1 responses in hESC-EC with those of endothelial cells derived from other stem cells and with human umbilical vein endothelial cells (HUVEC). HUVEC, endothelial cells derived from blood progenitors (blood outgrowth endothelial cells; BOEC), and from induced pluripotent stem cells all displayed both a TLR4 and NOD1 response. However, hESC-EC had no TLR4 function, but did have functional NOD1 receptors. In vivo conditioning in nude rats did not confer TLR4 expression in hESC-EC. Despite having no TLR4 function, hESC-EC sensed Gram-negative bacteria, a response that was found to be mediated by NOD1 and the associated RIP2 signalling pathways. Thus, hESC-EC are TLR4 deficient but respond to bacteria via NOD1. This data suggests that hESC-EC may be protected from unwanted TLR4-mediated vascular inflammation, thus offering a potential therapeutic advantage.

The Chloroform Fraction of Carpinus tschonoskii Leaves Inhibits the Production of Inflammatory Mediators in HaCaT Keratinocytes and RAW264.7 Macrophages

Inflammation is the immune system’s response to infection and injury-related disorders, and is related to pro-inflammatory factors (NO, PGE₂, cytokines, etc.) produced by inflammatory cells. Atopic dermatitis (AD) is a representative inflammatory skin disease that is characterized by increasing serum levels of inflammatory chemokines, including macrophage-derived chemokine (MDC). Carpinus tschonoskii is a member of the genus Carpinus. We investigated the anti-inflammatory activity of C. tschonoskii by studying the effects of various solvent fractions prepared from its leaves on inflammatory mediators in HaCaT and RAW264.7 cells. We found that the chloroform fraction of C. tschonoskii inhibited MDC at both the protein and mRNA levels in HaCaT cells, acting via the inhibition of STAT1 in the IFN-γ signaling pathway. In addition, the chloroform fraction significantly suppressed the expression of inflammatory factors induced by lipopolysaccharide stimulation, except COX-2 and TNF-α. These results suggest that the chloroform fraction of C. tschonoskii leaves may include a component with potential anti-inflammatory activity.

Toll-like receptor 4 gene polymorphisms and acute coronary syndrome: no association in a Mexican population

OBJECTIVE

The objective of this study was to establish the role of the TLR-4 gene polymorphisms in individuals in risk of developing ACS.

METHODS

The study included 457 Mexican patients with ACS and 283 control individuals. The TLR-4 Asp299Gly and TLR-4 Thr399Ile single nucleotide polymorphisms were genotyped using 5' exonuclease TaqMan genotyping assays on an 7900HT Fast real-time PCR system according to manufacturer's instructions (Applied Biosystems, Foster City, USA).

RESULTS

The results obtained in this study showed that the frequency of the two polymorphisms (TLR-4 Asp299Gly and TLR-4 Thr399Ile) studied were similar between patients with ACS and healthy controls. Multiple logistic regression analysis showed that the largest risk factor for ACS development was given by smoking (11.88-fold increased risk), hypertension (4.32-fold increased risk), type II diabetes (3.44-fold increased risk), gender (2.32-fold increased risk), and dyslipidemia (1.52-fold increased risk).

CONCLUSION

The Asp299Gly and Thr399Ile polymorphisms were not associated with susceptibility to ACS in the Mexican population.

Toll-like receptor 4 gene Asp299Gly polymorphism in ischemic cerebrovascular disease: a meta-analysis

Epidemiological studies have evaluated the association between Toll-like receptor 4 (TLR4) gene Asp299Gly (rs4986790) polymorphism and the risk of ischemic cerebrovascular disease, but the results are inconsistent. In an effort to clarify earlier inconclusive results, a meta-analysis was performed. We searched the PubMed, Web of Science, Embase, Cochrane database, Clinicaltrials.gov, Current Controlled Trials, CNKI, CBMdisc, Chinese Clinical Trial Registry and Google Scholar until up to 20 July 2013. Additionally, hand searching of the references of identified articles was performed. Original observational studies investigating the association between TLR4 gene Asp299Gly polymorphism and ischemic cerebrovascular disease risk were included. All statistical analyses were performed using Stata 11.0. The search strategy identified 1038 potentially relevant articles, seven of which were included in the final meta-analysis, covering a total of 1767 cases and 2785 controls. Overall, no significant association was found between TLR4 gene Asp299Gly polymorphism and ischemic cerebrovascular disease risk (for G allele versus A allele: OR = 0.95, 95% CI = 0.75-1.21, p = 0.69; for G/G+A/G versus A/A: OR = 0.96, 95% CI = 0.75-1.22, p = 0.73). In addition, the similar results were obtained in the sensitivity analysis based on studies with the high quality. In summary, the present meta-analysis indicates that TLR4 gene Asp299Gly polymorphism is not associated with increased ischemic cerebrovascular disease risk.

Contributions of pulmonary hypertension to HIV-related cardiac dysfunction

BACKGROUND/AIM

To evaluate the prevalence of pulmonary hypertension among patients living with HIV/AIDS and to determine its contribution to cardiac dysfunction.

METHOD

A hospital based cross sectional study was carried out over a 6-month period at the Jos University Teaching Hospital. The subjects were 200 confirmed HIV positive patients, ≥18 years of age who consented to the study. Physical examination, laboratory investigations, 2 dimensional and Doppler echocardiography were conducted on the subjects.

RESULTS

The mean age of the patients was 38 ± 9 years, and there were 142 females (71%). Females were younger, mean age 36 ± 8 years versus 41 ± 10 years for males (p-value <0.01). The median CD4 cell count was 312 cells/μl, there were no homosexual or intravenous drug user among the subjects. Eight of the subjects had pulmonary hypertension, with a case prevalence of 4%, and this had no relationship to CD4 cell count. Both systolic and diastolic functions were worse in subjects with pulmonary hypertension, with a negative correlation between mean pulmonary arterial systolic pressure (mPASP) and parameters like ejection fraction (r = -0.28, p-value 0.0003), fractional shortening (r = -0.21, p-value 0.003), deceleration time (r = -0.13. p-value 0.09).

CONCLUSION

Immune-suppression affects the cardiac function adversely and coexisting pulmonary hypertension contributes to poor systolic and diastolic function in affected patients. The subtle nature of presentation of pulmonary hypertension and other cardiac dysfunctions in HIV/AIDS patients demand a high-index of suspicion and early intervention if detected, to ensure better care for these emerging threats to our patients.

Saturated fatty acid palmitate aggravates neointima formation by promoting smooth muscle phenotypic modulation

OBJECTIVE

Obesity is a major risk factor of atherosclerotic cardiovascular disease. Circulating free fatty acid levels are known to be elevated in obese individuals and, along with dietary saturated fatty acids, are known to associate with cardiovascular events. However, little is known about the molecular mechanisms by which free fatty acids are linked to cardiovascular disease.

APPROACH AND RESULTS

We found that administration of palmitate, a major saturated free fatty acid, to mice markedly aggravated neointima formation induced by carotid artery ligation and that the neointima primarily consisted of phenotypically modulated smooth muscle cells (SMCs). In cultured SMCs, palmitate-induced phenotypic modulation was characterized by downregulation of SMC differentiation markers, such as SM α-actin and SM-myosin heavy chain, and upregulation of mediators involved in inflammation and remodeling of the vessel wall, such as platelet-derived growth factor B and matrix metalloproteinases. We also found that palmitate induced the expression of proinflammatory genes via a novel toll-like receptor 4/myeloid differentiation primary response 88/nuclear factor-κB/NADPH oxidase 1/reactive oxygen species signaling pathway: nuclear factor-κB was activated by palmitate via toll-like receptor 4 and its adapter, MyD88, and once active, it transactivated Nox1, encoding NADPH oxidase 1, a major reactive oxygen species generator in SMCs. Pharmacological inhibition and small interfering RNA-mediated knockdown of the components of this signaling pathway mitigated the palmitate-induced upregulation of proinflammatory genes. More importantly, Myd88 knockout mice were resistant to palmitate-induced exacerbation of neointima formation.

CONCLUSIONS

Palmitate seems to promote neointima formation by inducing inflammatory phenotypes in SMCs.

Reconstituted high-density lipoprotein modulates activation of human leukocytes

An anti-inflammatory effect of reconstituted High Density Lipoprotein (rHDL) has been demonstrated in atherosclerosis and in sepsis models. An increase of adhesion molecules as well as tissue factor expression on endothelial cells in response to inflammatory or danger signals are attenuated by the treatment with rHDL. Here we show the inhibitory effect of rHDL on the activation of human leukocytes in a whole blood assay as well as on monocyte-derived human dendritic cells (DC). Multiplex analysis of human whole blood showed that phytohaemagglutinin (PHA)-induced secretion of the cytokines IL-1β, IL-1RA, IL-2R, IL-6, IL-7, IL-12(p40), IL-15 and IFN-α was inhibited. Furthermore, an inhibitory effect on the production of the chemokines CCL-2, CCL-4, CCL-5, CXCL-9 and CXCL-10 was observed. Activation of granulocytes and CD14+ monocytes by PHA is inhibited dose-dependently by rHDL shown as decreased up-regulation of ICAM-1 surface expression. In addition, we found a strong inhibitory effect of rHDL on toll-like receptor 2 (TLR2)- and TLR4-mediated maturation of DC. Treatment of DC with rHDL prevented the up-regulation of cell surface molecules CD80, CD83 and CD86 and it inhibited the TLR-driven activation of inflammatory transcription factor NF-κB. These findings suggest that rHDL prevents activation of crucial cellular players of cellular immunity and could therefore be a useful reagent to impede inflammation as well as the link between innate and adaptive immunity.

Periodontal innate immune mechanisms relevant to obesity

Obesity affects over 35% of the adult population of the USA, and obesity-related illnesses have emerged as the leading cause of preventable death worldwide, according to the World Health Organization. Obesity's secondary morbidities include increased risk of cardiovascular disease, type II diabetes, and cancer, in addition to increased occurrence and severity of infections. Sedentary lifestyle and weight gain caused by consumption of a high-fat diet contribute to the development of obesity, with individuals having a body mass index (BMI) score > 30 being considered obese. Genetic models of obesity (ob/ob mice, db/db mice, and fa/fa rats) have been insufficient to study human obesity because of the overall lack of genetic causes for obesity in human populations. To date, the diet-induced obese (DIO) mouse model best serves research studies relevant to human health. Periodontal disease presents with a wide range of clinical variability and severity. Research in the past decade has shed substantial light on both the initiating infectious agents and host immunological responses in periodontal disease. Up to 46% of the general population harbors the microorganism(s) associated with periodontal disease, although many are able to limit the progression of periodontal disease or even clear the organism(s) if infected. In the last decade, several epidemiological studies have found an association between obesity and increased incidence of periodontal disease. This review focuses on exploring the immunological consequences of obesity that exacerbate effects of infection by pathogens, with focus on infection by the periodontal bacterium Porphyromonas gingivalis as a running example.

Effect of different degrees of impaired glucose metabolism on the expression of inflammatory markers in monocytes of patients with atherosclerosis

Inflammatory markers are elevated in type 2 diabetic patients (DP) and may predict the development of type 2 diabetes. Our aims were to analyze differences in the expression of inflammatory and immunological molecules between DP and healthy subjects and to investigate whether glycemic control might prevent the overexpression of inflammatory markers in DP. Twenty-two DP with advanced atherosclerosis and eight healthy blood donors were included. DP were classified as well (HbA1c ≤ 6.5) or poorly controlled (HbA1c > 6.5). In "in vitro" studies, monocytes were exposed to low (5.5 mM) or high glucose (26 mM) concentrations in the absence or presence of insulin. Expression profiling of 14 inflammatory genes was analyzed using TLDA analysis. "In vivo" results show that monocytes from DP had increased levels of monocyte chemoattractant protein (MCP-1) and interleukin 6 (IL6) and lower levels of Toll-like receptor 2 (TLR2) mRNA than healthy subjects. Well-controlled DP had lower levels of IL-6 than poorly controlled DP, suggesting that glycemic control may prevent IL6 mRNA alterations associated with diabetes. "In vitro" results demonstrate that glucose directly and significantly induced MCP-1 and IL6 and reduced TLR2 mRNA expression. Insulin at high dose (100 IU/ml) dramatically enhanced the upregulatory effects of glucose on MCP-1 and IL-6 and reduced per se TLR2 mRNA expression. MCP-1, IL-6 and TLR2 are key inflammatory players altered in monocytes from type 2 DP. Both hyperinsulinemia and hyperglycemia contribute to alter the expression of these genes. The glycemic control only significantly prevented IL6 overexpression in this group of patients.

Expression and activity of the TLR4/NF-κB signaling pathway in mouse intestine following administration of a short-term high-fat diet

Insulin resistance in obesity is associated with chronic systemic low-grade inflammation. Although it has been shown that Toll-like receptor 4 (TLR4) in the liver, muscle and adipose tissue plays an important role in obesity-associated inflammation and insulin resistance, the effect of TLR4 activation in the intestine has not been investigated. The aim of this study was to explore the activation of the mouse intestinal TLR4/NF-κB signaling pathway following the administration of a short-term high-fat diet, as well as the function of the signaling pathway in the local enteric inflammatory response. The effect of the high-fat diet on TLR4 activation, NF-κB and phosphorylated IκB (PIκB) activity, and tumor necrosis factor (TNF)-α and IL-6 expression in the intestinal tissues of diet-induced obese C57BL/6 mice was investigated. The results demonstrated that the high-fat diet induced TLR4 mRNA and protein expression in intestinal tissues. TLR4/NF-κB signaling pathway activation gradually increased as the number of days of high-fat diet administration increased, and peaked on day 7. Additionally, activation of the signaling pathway reduced PIκB expression levels and increased TNF-α and IL-6 expression levels in intestinal tissues. Our results demonstrated that a short-term high-fat diet induces activation of the TLR4/NF-κB signaling pathway in intestinal tissues, which causes local intestinal low-grade inflammation. These data improve our understanding of the molecular events involved in intestinal low-grade inflammation, which may be the triggering factor for chronic systemic low-grade inflammation.

Toll-like receptors and human disease: lessons from single nucleotide polymorphisms

Toll-like receptors (TLRs), a large group of proteins which recognize various pathogen-associated molecular patterns, are critical for the normal function of the innate immune system. Following their discovery many single nucleotide polymorphisms within TLRs and components of their signaling machinery have been discovered and subsequently implicated in a wide range of human diseases including atherosclerosis, sepsis, asthma, and immunodeficiency. This review discusses the effect of genetic variation on TLR function and how they may precipitate disease.