Toll-like receptors 2-deficient mice are protected against postischemic coronary endothelial dysfunction

The Role of TLRs in Obesity and Its Related Metabolic Disorders

Obesity affects the adaptability of adipose tissue (AT), impairing its ability to regulate energy and metabolism. Obesity is associated with many metabolic disorders, including dyslipidemia, hypertension, sleep disorders, non-alcoholic liver disease, and some types of cancer. Toll-like receptors (TLRs) are important in obesity and related metabolic disorders. TLRs are pattern-recognizing receptors (PRRs) involved in the innate immune system and recognize pathogen-associated molecular patterns (PAMPs) and endogenous ligands. TLRs, especially TLR2 and TLR4, are activated by fatty acids, endotoxins, and other ligands. TLR2 and TLR4 activation triggers inflammatory responses. Chronic inflammation driven by TLR activation is a hallmark of obesity and metabolic diseases. The inflammatory response triggered by TLR activation alters insulin signaling, contributing to insulin resistance, a key feature of metabolic syndrome and type 2 diabetes. Modulation of TLR activity through lifestyle changes (diet and exercise), obesity surgery, and pharmacological agents is under study as a possible therapeutic approach to controlling obesity and its complications.

Repair of the Infarcted Heart: Cellular Effectors, Molecular Mechanisms and Therapeutic Opportunities

The adult mammalian heart has limited endogenous regenerative capacity and heals through the activation of inflammatory and fibrogenic cascades that ultimately result in the formation of a scar. After infarction, massive cardiomyocyte death releases a broad range of damage-associated molecular patterns that initiate both myocardial and systemic inflammatory responses. TLRs (toll-like receptors) and NLRs (NOD-like receptors) recognize damage-associated molecular patterns (DAMPs) and transduce downstream proinflammatory signals, leading to upregulation of cytokines (such as interleukin-1, TNF-α [tumor necrosis factor-α], and interleukin-6) and chemokines (such as CCL2 [CC chemokine ligand 2]) and recruitment of neutrophils, monocytes, and lymphocytes. Expansion and diversification of cardiac macrophages in the infarcted heart play a major role in the clearance of the infarct from dead cells and the subsequent stimulation of reparative pathways. Efferocytosis triggers the induction and release of anti-inflammatory mediators that restrain the inflammatory reaction and set the stage for the activation of reparative fibroblasts and vascular cells. Growth factor-mediated pathways, neurohumoral cascades, and matricellular proteins deposited in the provisional matrix stimulate fibroblast activation and proliferation and myofibroblast conversion. Deposition of a well-organized collagen-based extracellular matrix network protects the heart from catastrophic rupture and attenuates ventricular dilation. Scar maturation requires stimulation of endogenous signals that inhibit fibroblast activity and prevent excessive fibrosis. Moreover, in the mature scar, infarct neovessels acquire a mural cell coat that contributes to the stabilization of the microvascular network. Excessive, prolonged, or dysregulated inflammatory or fibrogenic cascades accentuate adverse remodeling and dysfunction. Moreover, inflammatory leukocytes and fibroblasts can contribute to arrhythmogenesis. Inflammatory and fibrogenic pathways may be promising therapeutic targets to attenuate heart failure progression and inhibit arrhythmia generation in patients surviving myocardial infarction.

NTPDase1/CD39 Ectonucleotidase Is Necessary for Normal Arterial Diameter Adaptation to Flow

NTPDase1/CD39, the major vascular ectonucleotidase, exerts thrombo-immunoregulatory function by controlling endothelial P2 receptor activation. Despite the well-described release of ATP from endothelial cells, few data are available regarding the potential role of CD39 as a regulator of arterial diameter. We thus investigated the contribution of CD39 in short-term diameter adaptation and long-term arterial remodeling in response to flow using Entpd1-/- male mice. Compared to wild-type littermates, endothelial-dependent relaxation was modified in Entpd1-/- mice. Specifically, the vasorelaxation in response to ATP was potentiated in both conductance (aorta) and small resistance (mesenteric and coronary) arteries. By contrast, the relaxing responses to acetylcholine were supra-normalized in thoracic aortas while decreased in resistance arteries from Entpd1-/- mice. Acute flow-mediated dilation, measured via pressure myography, was dramatically diminished and outward remodeling induced by in vivo chronic increased shear stress was altered in the mesenteric resistance arteries isolated from Entpd1-/- mice compared to wild-types. Finally, changes in vascular reactivity in Entpd1-/- mice were also evidenced by a decrease in the coronary output measured in isolated perfused hearts compared to the wild-type mice. Our results highlight a key regulatory role for purinergic signaling and CD39 in endothelium-dependent short- and long-term arterial diameter adaptation to increased flow.

Peli1 deletion in macrophages attenuates myocardial ischemia/reperfusion injury by suppressing M1 polarization

The polarization of macrophages to the M1 or M2 phenotype has a pivotal role in inflammatory response following myocardial ischemia/reperfusion injury. Peli1, an E3 ubiquitin ligase, is closely associated with inflammation and autoimmunity as an important regulatory protein in the Toll-like receptor signaling pathway. We aimed to explore the function of Peli1 in macrophage polarization under myocardial ischemia/reperfusion injury and elucidate the possible mechanisms. We show here that Peli1 is upregulated in peripheral blood mononuclear cells from patients with myocardial ischemia/reperfusion, which is correlated with myocardial injury and cardiac dysfunction. We also found that the proportion of M1 macrophages was reduced and myocardial infarct size was decreased, paralleling improvement of cardiac function in mice with Peli1 deletion in hematopoietic cells or macrophages. Macrophage Peli1 deletion lessened M1 polarization and reduced the migratory ability in vitro. Mechanistically, Peli1 contributed to M1 polarization by promoting K63-linked ubiquitination and nuclear translocation of IRF5. Moreover, Peli1 deficiency in macrophages reduced the apoptosis of cardiomyocytes in vivo and in vitro. Together, our study demonstrates that Peli1 deficiency in macrophages suppresses macrophage M1 polarization and alleviates myocardial ischemia/reperfusion injury by inhibiting the nuclear translocation of IRF5, which may serve as a potential intervention target for myocardial ischemia/reperfusion injury.

Neonatal asphyxia as an inflammatory disease: Reactive oxygen species and cytokines

Neonatologists resuscitate asphyxiated neonates by every available means, including positive ventilation, oxygen therapy, and drugs. Asphyxiated neonates sometimes present symptoms that mimic those of inflammation, such as fever and edema. The main pathophysiology of the asphyxia is inflammation caused by hypoxic-ischemic reperfusion. At birth or in the perinatal period, neonates may suffer several, hypoxic insults, which can activate inflammatory cells and inflammatory mediator production leading to the release of larger quantities of reactive oxygen species (ROS). This in turn triggers the production of oxygen stress-induced high mobility group box-1 (HMGB-1), an endogenous damage-associated molecular patterns (DAMPs) protein bound to toll-like receptor (TLR) -4, which activates nuclear factor-kappa B (NF-κB), resulting in the production of excess inflammatory mediators. ROS and inflammatory mediators are produced not only in activated inflammatory cells but also in non-immune cells, such as endothelial cells. Hypothermia inhibits pro-inflammatory mediators. A combination therapy of hypothermia and medications, such as erythropoietin and melatonin, is attracting attention now. These medications have both anti-oxidant and anti-inflammatory effects. As the inflammatory response and oxidative stress play a critical role in the pathophysiology of neonatal asphyxia, these drugs may contribute to improving patient outcomes.

Macrophages in myocardial infarction

The heart contains a population of resident macrophages that markedly expands following injury through recruitment of monocytes and through proliferation of macrophages. In myocardial infarction, macrophages have been implicated in both injurious and reparative responses. In coronary atherosclerotic lesions, macrophages have been implicated in disease progression and in the pathogenesis of plaque rupture. Following myocardial infarction, resident macrophages contribute to initiation and regulation of the inflammatory response. Phagocytosis and efferocytosis are major functions of macrophages during the inflammatory phase of infarct healing, and mediate phenotypic changes, leading to acquisition of an anti-inflammatory macrophage phenotype. Infarct macrophages respond to changes in the cytokine content and extracellular matrix composition of their environment and secrete fibrogenic and angiogenic mediators, playing a central role in repair of the infarcted heart. Macrophages may also play a role in scar maturation and may contribute to chronic adverse remodeling of noninfarcted segments. Single cell studies have revealed a remarkable heterogeneity of macrophage populations in infarcted hearts; however, the relations between transcriptomic profiles and functional properties remain poorly defined. This review manuscript discusses the fate, mechanisms of expansion and activation, and role of macrophages in the infarcted heart. Considering their critical role in injury, repair, and remodeling, macrophages are important, but challenging, targets for therapeutic interventions in myocardial infarction.

Ferroptosis and its role in cardiomyopathy

Heart disease is the leading cause of death worldwide. Cardiomyopathy is a disease characterized by the heart muscle damage, resulting heart in a structurally and functionally change, as well as heart failure and sudden cardiac death. The key pathogenic factor of cardiomyopathy is the loss of cardiomyocytes, but the related molecular mechanisms remain unclear. Ferroptosis is a newly discovered regulated form of cell death, characterized by iron accumulation and lipid peroxidation during cell death. Recent studies have shown that ferroptosis plays an important regulatory roles in the occurrence and development of many heart diseases such as myocardial ischemia/reperfusion injury, cardiomyopathy and heart failure. However, the systemic association of ferroptosis and cardiomyopathy remains largely unknown and needs to be elucidated. In this review, we provide an overview of the molecular mechanisms of ferroptosis and its role in individual cardiomyopathies, highlight that targeting ferroptosis maybe a potential therapeutic strategy for cardiomyopathy therapy in the future.

TLR2 and TLR4 Modulate Mouse Ileal Motility by the Interaction with Muscarinic and Nicotinic Receptors

Irritable bowel syndrome (IBS) is a chronic functional bowel disorder characterized by intestinal dysmotility. Changes in intestinal microbiota (dysbiosis) can lead to alterations in neuro-muscular functions in the gut. Toll-like receptors (TLRs) 2 and 4 recognize intestinal bacteria and are involved in the motor response induced by gastrointestinal (GI) neurotransmitters. Acetylcholine (ACh) is a well-known neurotransmitter involved in the regulation of GI motility. This study aimed to evaluate the role of TLR2 and TLR4 in the intestinal motor-response induced by ACh in the mouse ileum, as well as the expression and function of the muscarinic and nicotinic ACh receptors. Muscle contractility studies showed that the contractions induced by ACh were significantly lower in TLR2^−/− and TLR4^−/− with respect to WT mice. In WT mice, the contractions induced by ACh were reduced in the presence of AF-DX AF-DX 116 (a muscarinic ACh receptor (mAChR) M2 antagonist), 4-DAMP (a mAChR M3 antagonist), mecamylamine (a nicotinic AChR receptor (nAChR) α3β4 antagonist) and α-bungarotoxin (a nAChR α7 antagonist). In TLR2^−/− mice, the contractions induced by ACh were increased by AF-DX 116 and mecamylamine. In TLR4^−/− mice, the contractions induced by ACh were reduced by α-bungarotoxin and 4-DAMP. The mRNA and protein expressions of M3 and α3 receptors were diminished in the ileum from TLR2^−/− and TLR4^−/− with respect to WT mice. However, the levels of mRNA and protein of β4 were diminished only in TLR4^−/− but not in TLR2^−/− mice. In conclusion, our results show that TLR2 and TLR4 modulates the motor responses to ACh in the mouse ileum. TLR2 acts on muscarinic M2 and M3 and nicotinic α3β4 ACh receptors, while TLR4 acts on muscarinic M3 and nicotinic α3β4 and α7 ACh receptors.

Reperfusion Cardiac Injury: Receptors and the Signaling Mechanisms

It has been documented that Ca2+ overload and increased production of reactive oxygen species play a significant role in reperfusion injury (RI) of cardiomyocytes. Ischemia/reperfusion induces cell death as a result of necrosis, necroptosis, apoptosis, and possibly autophagy, pyroptosis and ferroptosis. It has also been demonstrated that the NLRP3 inflammasome is involved in RI of the heart. An increase in adrenergic system activity during the restoration of coronary perfusion negatively affected cardiac resistance to RI. Toll-like receptors are involved in RI of the heart. Angiotensin II and endothelin-1 aggravated ischemic/reperfusion injury of the heart. Activation of neutrophils, monocytes, CD4+ T-cells and platelets contributes to cardiac ischemia/reperfusion injury. Our review outlines the role of these factors in reperfusion cardiac injury.

Sex Effect on Cardiac Damage in Mice With Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system. Recent clinical study suggested that MS patient exhibited acute heart failure. Further, 12-lead electrocardiographic study showed a longer QTc interval in both MS patient and experimental autoimmune encephalomyelitis (EAE) Lewis rat. However, there is limited study regarding the effect of sex on cardiac injury in EAE. To our knowledge, sex effect on cardiac damage in mice with EAE has not yet been published. Herein, we examined the role of the immune system in mediating cardiac dysfunction after EAE in female and male mice. Neurological function was subsequently evaluated and cardiac function was assessed by echocardiography at multiple time points after EAE. EAE mice exhibited severe neurological deficit and significant cardiac dysfunction, including decreased left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) at 1 and 2 months after EAE induction. Meanwhile male EAE presented increased expression of the oxidative stress (e.g., nicotinamaide adenine dinucleotide phosphate oxidase-2; NOX-2) in heart, as well as cardiac hypertrophy, increased left ventricle (LV) mass and more severe cardiac fibrosis compared with male control mice. In addition, male EAE mice showed significantly increased cardiac canonical inflammatory mediator (e.g., monocyte chemoattractant protein-1; MCP-1, transforming growth factor-β; TGF-β and toll-like receptor 2; TLR-2) compared with female EAE mice at 2 months after EAE induction. In conclusion, EAE increases inflammatory factor expression and aggravates cardiac dysfunction in male mice compared with female mice, which may contribute to different cardiac outcome in EAE mice.

Integrated Weighted Gene Co-expression Network Analysis Identified That TLR2 and CD40 Are Related to Coronary Artery Disease

The current research attempted to identify possible hub genes and pathways of coronary artery disease (CAD) and to detect the possible mechanisms. Array data from GSE90074 were downloaded from the Gene Expression Omnibus (GEO) database. Integrated weighted gene co-expression network analysis (WGCNA) was performed to analyze the gene module and clinical characteristics. Gene Ontology annotation (GO), Disease Ontology (DO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed by clusterProfiler and the DOSE package in R. A protein-protein interaction (PPI) network was established using Cytoscape software, and significant modules were analyzed using Molecular Complex Detection (MCODE) to identify hub genes. Then, further functional validation of hub genes in other microarrays and population samples was performed, and survival analysis was performed to investigate the prognosis. A total of 660 genes were located in three modules and associated with CAD. GO functions identified 484 biological processes, 39 cellular components, and 22 molecular functions with an adjusted P < 0.05. In total, 38 pathways were enriched in KEGG pathway analysis, and 147 DO items were identified with an adjusted P < 0.05 (false discovery rate, FDR set at < 0.05). There was a total of four modules with a score > 10 after PPI network analysis using the MCODE app, and two hub genes (TLR2 and CD14) were identified. Then, we validated the information from the GSE60993 dataset using the GSE59867 dataset and population samples, and we found that these two genes were associated with plaque vulnerability. These two genes varied at different time points after myocardial infarction, and both of them had the lowest prognosis of heart failure when they were expressed at low levels. We performed an integrated WGCNA and validated that TLR2 and CD14 were closely associated with the severity of coronary artery disease, plaque instability and the prognosis of heart failure after myocardial infarction.

Poly(I:C) preconditioning protects the heart against myocardial ischemia/reperfusion injury through TLR3/PI3K/Akt-dependent pathway

Emerging evidence suggests that Toll-like receptors (TLRs) ligands pretreatment may play a vital role in the progress of myocardial ischemia/reperfusion (I/R) injury. As the ligand of TLR3, polyinosinic-polycytidylic acid (poly(I:C)), a synthetic double-stranded RNA, whether its preconditioning can exhibit a cardioprotective phenotype remains unknown. Here, we report the protective effect of poly(I:C) pretreatment in acute myocardial I/R injury by activating TLR3/PI3K/Akt signaling pathway. Poly(I:C) pretreatment leads to a significant reduction of infarct size, improvement of cardiac function, and downregulation of inflammatory cytokines and apoptotic molecules compared with controls. Subsequently, our data demonstrate that phosphorylation of TLR3 tyrosine residue and its interaction with PI3K is enhanced, and protein levels of phospho-PI3K and phospho-Akt are both increased after poly(I:C) pretreatment, while knock out of TLR3 suppresses the cardioprotection of poly(I:C) preconditioning through a decreased activation of PI3K/Akt signaling. Moreover, inhibition of p85 PI3K by the administration of LY294002 in vivo and knockdown of Akt by siRNA in vitro significantly abolish poly(I:C) preconditioning-induced cardioprotective effect. In conclusion, our results reveal that poly(I:C) preconditioning exhibits essential protection in myocardial I/R injury via its modulation of TLR3, and the downstream PI3K/Akt signaling, which may provide a potential pharmacologic target for perioperative cardioprotection.

Rapid Lipid Modification of Endothelial Cell Membranes in Cardiac Ischemia/Reperfusion Injury: a Novel Therapeutic Strategy to Reduce Infarct Size

PURPOSE

Plasma membranes constitute a gathering point for lipids and signaling proteins. Lipids are known to regulate the location and activity of signaling proteins under physiological and pathophysiological conditions. Membrane lipid therapies (MLTs) that gradually modify lipid content of plasma membranes have been developed to treat chronic disease; however, no MLTs have been developed to treat acute conditions such as reperfusion injury following myocardial infarction (MI) and percutaneous coronary intervention (PCI). A fusogenic nanoliposome (FNL) that rapidly incorporates exogenous unsaturated lipids into endothelial cell (EC) membranes was developed to attenuate reperfusion-induced protein signaling. We hypothesized that administration of intracoronary (IC) FNL-MLT interferes with EC membrane protein signaling, leading to reduced microvascular dysfunction and infarct size (IS).

METHODS

Using a myocardial ischemia/reperfusion swine model, the efficacy of FNL-MLT in reducing IS following a 60-min coronary artery occlusion was tested. Animals were randomized to receive IC Ringer's lactate solution with or without 10 mg/mL/min of FNLs for 10 min prior to reperfusion (n = 6 per group).

RESULTS

The IC FNL-MLT reduced IS (25.45 ± 16.4% vs. 49.7 ± 14.1%, P < 0.02) and enhanced regional myocardial blood flow (RMBF) in the ischemic zone at 15 min of reperfusion (2.13 ± 1.48 mL/min/g vs. 0.70 ± 0.43 mL/min/g, P < 0.001). The total cumulative plasma levels of the cardiac injury biomarker cardiac troponin I (cTnI) were trending downward but were not significant (999.3 ± 38.7 ng/mL vs. 1456.5 ± 64.8 ng/mL, P = 0.1867). However, plasma levels of heart-specific fatty acid binding protein (hFABP), another injury biomarker, were reduced at 2 h of reperfusion (70.3 ± 38.0 ng/mL vs. 137.3 ± 58.2 ng/mL, P = 0.0115).  CONCLUSION: The IC FNL-MLT reduced IS compared to vehicle in this swine model. The FNL-MLT maybe a promising adjuvant to PCI in the treatment of acute MI.

Myocardial infarction biomarker discovery with integrated gene expression, pathways and biological networks analysis

Myocardial infarction (MI) is the most prevalent coronary heart disease caused by the complex molecular interactions between multiple genes and environment. Here, we aim to identify potential biomarkers for the disease development and for prognosis of MI. We have used gene expression dataset (GSE66360) generated from 51 healthy controls and 49 patients experiencing acute MI and analyzed the differentially expressed genes (DEGs), protein-protein interactions (PPI), gene network-clusters to annotate the candidate pathways relevant to MI pathogenesis. Bioinformatic analysis revealed 810 DEGs. Their functional annotations have captured several MI targeting biological processes and pathways like immune response, inflammation and platelets degranulation. PPI network identify seventeen hub and bottleneck genes, whose involvement in MI was further confirmed by DisGeNET database. OpenTarget Platform reveal unique bottleneck genes as potential target for MI. Our findings identify several potential biomarkers associated with early stage MI providing a new insight into molecular mechanism underlying the disease.

Toll-Like Receptors Contribute to Sex Differences in Blood Pressure Regulation

Toll-like receptors (TLRs) play an important role in the innate immune system, and recently, they have been shown to be involved in the regulation of blood pressure. The incidence of hypertension is higher in men, and it increases in postmenopausal women. In fact, premenopausal women are protected from cardiovascular disease compared with age-matched men, and it is well established that this protective effect is lost with menopause. However, the molecular mechanisms underlying this protection in women are unknown. Whether or not it could be related to differential activation of the innate immune system remains to be elucidated. This review focuses on (1) the differences between men and women in TLR activation and (2) whether TLR activation may influence the regulation of blood pressure in a sex-dependent manner.

Sterile inflammation in thoracic transplantation

The life-saving benefits of organ transplantation can be thwarted by allograft dysfunction due to both infectious and sterile inflammation post-surgery. Sterile inflammation can occur after necrotic cell death due to the release of endogenous ligands [such as damage-associated molecular patterns (DAMPs) and alarmins], which perpetuate inflammation and ongoing cellular injury via various signaling cascades. Ischemia-reperfusion injury (IRI) is a significant contributor to sterile inflammation after organ transplantation and is associated with detrimental short- and long-term outcomes. While the vicious cycle of sterile inflammation and cellular injury is remarkably consistent amongst different organs and even species, we have begun understanding its mechanistic basis only over the last few decades. This understanding has resulted in the developments of novel, yet non-specific therapies for mitigating IRI-induced graft damage, albeit with moderate results. Thus, further understanding of the mechanisms underlying sterile inflammation after transplantation is critical for identifying personalized therapies to prevent or interrupt this vicious cycle and mitigating allograft dysfunction. In this review, we identify common and distinct pathways of post-transplant sterile inflammation across both heart and lung transplantation that can potentially be targeted.

Astragaloside IV protects human cardiomyocytes from hypoxia/reoxygenation injury by regulating miR-101a

Astragaloside IV (AS/IV) is one of the extracted components from the traditional Chinese medicine Astragalus which has been demonstrated to have potential capacity for anti-inflammation activity and for treating cardiovascular disease. Our purpose was to determine the function and underlying molecular mechanism of AS/IV in hypoxia/reoxygenation (H/R) injured in cardiomyocytes. Differentially expressed genes (DEGs) were screened using bioinformatic analysis, and the molecular targeting relationship was verified by the dual-luciferase report system. H/R injured cardiomyocytes were employed to explore the effect of AS/IV. QRT-PCR and Western blot analysis were applied to detect the expression of mRNA and proteins, respectively. Additionally, superoxide dismutase (SOD), lactic dehydrogenase (LDH) and MDA (malondialdehyde) levels were detected to determine the oxidative damage. Cell viability was assessed by CCK-8, and flow cytometry was used to evaluate cell apoptosis ratio. TGFBR1 and TLR2 were selected as DEGs. Additionally, AS/IV could enhance cell proliferation and upregulated miR-101a expression, which suppressed TGFBR1 and TLR2 expression in H/R injured cardiomyocytes. Moreover, the results of Western blot exhibited that the downstream genes (p-ERK and p-p38) in the MAPK signaling pathway were suppressed, which meant AS/IV could inhibit this pathway in H/R injured cardiomyocytes. Overall, this study demonstrated AS/IV could attenuate H/R injury in human cardiomyocytes via the miR-101a/TGFBR1/TLR2/MAPK signaling pathway axis, which means that it could serve as a possible alternate for H/R treatment.

Targeting Extracellular Heat Shock Protein 70 Ameliorates Doxorubicin-Induced Heart Failure Through Resolution of Toll-Like Receptor 2-Mediated Myocardial Inflammation

Background

Heart failure (HF) is one of the most significant causes of morbidity and mortality for the cardiovascular risk population. We found previously that extracellular HSP70 (heat shock protein) is an important trigger in cardiac hypertrophy and fibrosis, which are associated with the development of heart dysfunction. However, the potential role of HSP70 in response to HF and whether it could be a target for the therapy of HF remain unknown.

Methods and Results

An HF mouse model was generated by a single IP injection of doxorubicin at a dose of 15 mg/kg. Ten days later, these mice were treated with an HSP70 neutralizing antibody for 5 times. We observed that doxorubicin treatment increased circulating HSP70 and expression of HSP70 in myocardium and promoted its extracellular release in the heart. Blocking extracellular HSP70 activity by its antibody significantly ameliorated doxorubicin‐induced left ventricular dilation and dysfunction, which was accompanied by a significant inhibition of cardiac fibrosis. The cardioprotective effect of the anti‐HSP70 antibody was largely attributed to its ability to promote the resolution of myocardial inflammation, as evidenced by its suppression of the toll‐like receptor 2–associated signaling cascade and modulation of the intracellular distribution of the p50 and p65 subunits of nuclear factor‐κB.

Conclusions

Extracellular HSP70 serves as a noninfectious inflammatory factor in the development of HF, and blocking extracellular HSP70 activity may provide potential therapeutic benefits for the treatment of HF.

Nanoparticle incorporating Toll-like receptor 4 inhibitor attenuates myocardial ischaemia-reperfusion injury by inhibiting monocyte-mediated inflammation in mice

AIMS

Myocardial ischaemia-reperfusion (IR) injury hampers the therapeutic effect of revascularization in patients with acute myocardial infarction (AMI). Innate immunity for damage-associated protein patterns promotes the process of IR injury; however, the blockade of Toll-like receptor 4 (TLR4) in myocardial IR injury has not been translated into clinical practice. Therefore, we aimed to examine whether the nanoparticle-mediated administration of TAK-242, a chemical inhibitor of TLR4, attenuates myocardial IR injury in a clinically feasible protocol in a mouse model.

METHODS AND RESULTS

We have prepared poly-(lactic-co-glycolic acid) nanoparticles containing TAK-242 (TAK-242-NP). TAK-242-NP significantly enhanced the drug delivery to monocytes/macrophages in the spleen, blood, and the heart in mice. Intravenous administration of TAK-242-NP (containing 1.0 or 3.0 mg/kg TAK-242) at the time of reperfusion decreased the infarct size, but the TAK-242 solution did not even when administered at a dosage of 10.0 mg/kg. TAK-242-NP inhibited the recruitment of Ly-6Chigh monocytes to the heart, which was accompanied by decreased circulating HMGB1, and NF-κB activation and cytokine expressions in the heart. TAK-242-NP did not decrease the infarct size further in TLR4-deficient mice, confirming the TLR4-specific mechanism in the effects of TAK-242-NP. Furthermore, TAK-242-NP did not decrease the infarct size further in CCR2-deficient mice, suggesting that monocyte/macrophage-mediated inflammation is the primary therapeutic target of TAK-242-NP.

CONCLUSION

The nanoparticle-mediated delivery of TAK-242-NP represent a novel and clinical feasible strategy in patients undergone coronary revascularization for AMI by regulating TLR4-dependent monocytes/macrophages-mediated inflammation.

Toll-like receptors 2 and 6 mediate apoptosis and inflammation in ischemic skeletal myotubes

Critical limb ischemia (CLI) is associated with skeletal muscle damage. However, the pathophysiology of the muscle damage is poorly understood. Toll-like receptors (TLR) have been attributed to play a role in ischemia-induced tissue damage but their role in skeletal muscle damage in CLI is unknown. TLR2 and TLR6 expression was found to be upregulated in skeletal muscle of patients with CLI. In vitro, ischemia led to upregulation of TLR2 and TLR6 by myotubes, and activation of the downstream TLR signaling pathway. Ischemia-induced activation of the TLR signaling pathway led to secretion of the pro-inflammatory cytokine interleukin-6 and muscle apoptosis, which were abrogated by neutralising TLR2 and TLR6 antibodies. Our study demonstrates that TLR2 and TLR6 are upregulated in ischemic muscle and play a role in ischemia-induced muscle damage. Thus, manipulating the TLR pathway locally may be of potential therapeutic benefit.

Targeting HMGB1 ameliorates cardiac fibrosis through restoring TLR2-mediated autophagy suppression in myocardial fibroblasts

BACKGROUND

Extracellular high-mobility group box 1 (HMGB1) has been identified as playing a critical role in the pathogenesis of tissue fibrosis. However, the underlying mechanism of its involvement in cardiac fibrosis is still not well-defined. Here, we aim to investigate whether toll-like receptor 2 (TLR2) contributes to the extracellular HMGB1-mediated development and progression of cardiac fibrosis.

METHODS

A mouse model of cardiac fibrosis was induced by subcutaneous injection of isoproterenol (ISO). Glycyrrhizic acid (GA), an inhibitor of HMGB1 derived from natural products, was simultaneously administered by intraperitoneal injection. Echocardiography, H&E and Sirius red staining were used to evaluate cardiac function and fibrosis. The myocardial expression of autophagy-associated proteins was examined using immunoblotting. Cardiac fibroblasts were treated with different concentrations of HMGB1 to examine the expression levels of α-SMA, collagen I and autophagy markers. Interactions of HMGB1/TLR2 and α-SMA/p62 were examined by immunoprecipitation and immunofluorescence.

RESULTS

ISO-treated mice showed characteristic cardiac fibrosis, increased expression and co-localization of HMGB1 and TLR2, as well as impaired autophagic signals in myocardial tissues, which could be prevented by silencing TLR2. Exogenous administration of HMGB1 blocked the autophagic flux in fibroblasts, which caused extensive accumulation of collagen I and α-SMA. In addition, cardiac fibrosis was alleviated by GA treatment through abrogating the interaction between HMGB1 and TLR2.

CONCLUSIONS

Our study suggests that the interaction between TLR2 and HMGB1 contributes to the pathogenesis of cardiac fibrosis via suppressing fibroblast autophagy, and that inhibiting HMGB1 with GA provides therapeutic benefits for the treatment of fibroproliferative heart diseases.

Toll-like receptor 2 deficiency hyperactivates the FoxO1 transcription factor and induces aging-associated cardiac dysfunction in mice

Toll-like receptors (TLRs) are a family of pattern-recognition receptors involved in innate immunity. Previous studies have shown that TLR2 inhibition protects the heart from acute stress, including myocardial infarction and doxorubicin-induced cardiotoxicity in animal models. However, the role of TLR2 in the development of aging-associated heart failure is not known. In this work, we studied aging-associated changes in structure and function of TLR2-deficient mice hearts. Whereas young TLR2-KO mice did not develop marked cardiac dysfunction, 8- and 12-month-old TLR2-KO mice exhibited spontaneous adverse cardiac remodeling and cardiac dysfunction in an age-dependent manner. The hearts of the 8-month-old TLR2-KO mice had increased fibrosis, cell death, and reactivation of fetal genes. Moreover, TLR2-KO hearts displayed reduced infiltration by macrophages, increased numbers of myofibroblasts and atrophic cardiomyocytes, and higher levels of the atrophy-related ubiquitin ligases MuRF-1 and atrogin-1. Mechanistically, TLR2 deficiency impaired the PI3K/Akt signaling pathway, leading to hyperactivation of the transcription factor Forkhead box protein O1 (FoxO1) and, in turn, to elevated expression of FoxO target genes involved in the regulation of muscle wasting and cell death. AS1842856-mediated chemical inhibition of FoxO1 reduced the expression of the atrophy-related ubiquitin ligases and significantly reversed the adverse cardiac remodeling while improving the contractile functions in the TLR2-KO mice. Interestingly, TLR2 levels decreased in hearts of older mice, and the activation of TLR1/2 signaling improved cardiac functions in these mice. These findings suggest that TLR2 signaling is essential for protecting the heart against aging-associated adverse remodeling and contractile dysfunction in mice.

The effects of aspirin and ticagrelor on Toll-like receptor (TLR)-mediated platelet activation: results of a randomized, cross-over trial

Platelet activation underlies the pathology of an acute myocardial infarction (AMI), and dual antiplatelet therapy (DAPT) is administered post-AMI to limit this activation. Platelets express Toll-like receptors (TLRs) 1, 2, and 4 and become potently activated in response to TLR2/1 and TLR4 stimulation. However, it is unknown whether antiplatelet agents can protect against platelet activation via these TLR pathways. This study aimed to determine the extent to which TLR-mediated platelet activation can be inhibited by currently used antiplatelet agents. Ten healthy subjects were enrolled into a single-blinded randomized cross-over trial. Subjects received either aspirin monotherapy or DAPT (aspirin in combination with ticagrelor) for 1 week, were washed out, and crossed over to the other drug regimen. Platelet activation was assessed in response to Pam3CSK4 (a TLR2/1 agonist) and lipopolysaccharide (LPS; a TLR4 agonist) at baseline and after each antiplatelet drug regimen. Platelet-surface expression of CD62p and PAC1 by flow cytometry was measured as markers of platelet activation. At baseline, expression of CD62p and PAC1 increased significantly in response to high-dose LPS and in a dose-dependent manner in response to Pam3CSK4. Aspirin monotherapy did not inhibit platelet activation in response to any TLR agonist tested. DAPT with aspirin and ticagrelor only modestly inhibited expression of both activation markers in response to high doses of Pam3CSK4 and LPS. However, incubation with these TLR agonists led to substantial platelet activation despite treatment with these anti-platelet agents. Platelet-TLR2/1 and platelet-TLR4 represent intact on-treatment platelet activation pathways, which may contribute to on-going platelet activation post-AMI.

Inflammatory Response During Myocardial Infarction

The occlusion of a coronary artery by a thrombus generated on a ruptured atherosclerotic plaque has been pursued in the last decades as a determining event for the clinical outcome after myocardial infarction (MI). Yet, MI causes a cell death wave front, which triggers an inflammatory response to clear cellular debris, and which in excess can double the myocardial lesion and influence the clinical prognosis in the short and long term. Accordingly, proper, timely regulated inflammatory response has now been considered a second pivotal player in cardiac recovery after MI justifying the search for pharmacological strategies to modulate inflammatory effectors. This chapter reviews the key events and the main effectors of inflammation after myocardial ischemic insult, as well as the contribution of this phenomenon to the progression of atherosclerosis.

Retracted Article: Chrysin attenuates myocardial ischemia–reperfusion injury by inhibiting myocardial inflammation

The aim of this study was to investigate the effects of chrysin (CH) on myocardial ischemia–reperfusion injury. Cytokines were reduced by CH in coronary artery occlusion-induced rats and also in H9C2 cells. The ST segment was also restored by CH. Triphenyltetrazolium chloride (TTC) staining and pathological analysis showed that CH could alleviate myocardial injury. Results in H9C2 cells showed that CH improved heart injury in hypoxia/reoxygenation (H/R) of H9C2 cells. In addition, the expressions of the HMGB1-related inflammation pathway in rats and H9C2 cells were significantly decreased by CH. The present study shows the protective effects of CH on myocardial injury via inflammation.

The aim of this study was to investigate the effects of chrysin (CH) on myocardial ischemia–reperfusion injury.

Insights into innate immune signalling in controlling cardiac remodelling

Canonical innate immune signalling involves complex cascades: multiple germline-encoded pattern recognition receptors rapidly recognize pathogen-associated or damage-associated molecular patterns to induce the production of cytokines, which bind to their corresponding receptors to orchestrate subsequent host defense phases. Inflammation is a healthy response to pathogenic signals, which are typically rapid and specific, and they terminate once the threat has passed. However, excessive activation or suppression of innate immune or inflammatory responses can lead to considerable human suffering, such as cardiac remodelling. Interestingly, recent studies have revealed that innate immune molecules in the parenchymal cells of the heart influence cardiac homeostasis not only by directly regulating innate immune responses but also through reprogrammed signalling pathways, which are independent of conventional innate immune signalling. Elucidating 'innate immune signalling reprogramming' events will help us better understand the functions of innate immune molecules and, moreover, the pathogenesis of cardiac diseases.

Mechanisms of erosion of atherosclerotic plaques

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Redox regulation of cardiovascular inflammation - Immunomodulatory function of mitochondrial and Nox-derived reactive oxygen and nitrogen species

Oxidative stress is a major hallmark of cardiovascular diseases although a causal link was so far not proven by large clinical trials. However, there is a close association between oxidative stress and inflammation and increasing evidence for a causal role of (low-grade) inflammation for the onset and progression of cardiovascular diseases, which may serve as the missing link between oxidative stress and cardiovascular morbidity and mortality. With the present review we would like to highlight the multiple redox regulated pathways in inflammation, discuss the sources of reactive oxygen and nitrogen species that are of interest for these processes and finally discuss the importance of angiotensin II (AT-II) as a trigger of cardiovascular inflammation and the initiation and progression of cardiovascular diseases.

Glycyrrhizin Ameliorate Ischemia Reperfusion Lung Injury through Downregulate TLR2 Signaling Cascade in Alveolar Macrophages

This experiment was conducted to study whether pretreatment with Glycyrrhizin (GL) could ameliorate ischemia-reperfusion (I/R) lung injury and investigate the mechanisms of its protective effects in a mice model. Six-eight weeks male BALB/C mice were randomly assigned to four groups (n = 6): Control, Glycyrrhizin, I/R and I/R+Glycyrrhizin. Lung I/R was achieved by clamping the left hilus pulmonis. GL (200 mg/kg) was injected intraperitoneally 30 min before anesthesia. Measurement of pathohistological lung injury score, pulmonary permeability, isolated alveolar macrophages, inflammatory mediators, TLR2 and its downstream factors (MyD88, NF-κB) were performed. The results were as anticipated. Pathohistological evaluation indicated that GL significantly ameliorated I/R-induced lung injury, pulmonary permeability and edema. Pretreatment with GL significantly inhibited I/R-induced inflammation in lung tissues and BALF. In addition, GL significantly decreased I/R-induced isolated alveolar macrophages and suppressed I/R-induced expression of TLR2 and its downstream factors in lung tissues and alveolar macrophages. Collectively, our data indicated that pretreatment with GL could ameliorate I/R lung injury. The mechanisms of its protective effects might be inhibit I/R-induced inflammatory response through downregulate TLR2 signaling cascade in alveolar macrophages.

Hypomethylation of the Toll-like receptor-2 gene increases the risk of essential hypertension

Studies on the etiology of essential hypertension (EH) have demonstrated that chronic inflammation contributes to the onset and development of elevated blood pressure. Toll‑like receptors (TLRs), important immune receptors, serve a role in chronic inflammation and are associated with EH. In the present study, 96 patients with EH, and 96 age‑ and sex‑matched healthy controls were recruited, and eight cytosine‑phosphate‑guanine (CpG) dinucleotides (CpG1‑8) were analyzed using bisulfite pyrosequencing technology. It was observed that the methylation levels of all of the eight CpG dinucleotides were decreased in the EH group compared with the control group; however, only CpG1 (2.83±1.34 vs. 3.44±1.75; P=0.009), CpG6 (3.58±3.64 vs. 8.30±4.13; P<0.001) and CpG8 (8.91±5.32 vs. 11.33±3.87; P<0.001) were significantly different, as demonstrated by paired t‑test analysis. In addition, logistic regression analysis demonstrated that CpG6 hypomethylation was a risk factor of EH (odds ratio=1.10; adjusted P=0.009), and CpG6 methylation level was observed to be negatively correlated with systolic blood pressure (r=‑0.304; P<0.001) and diastolic blood pressure (r=‑0.329; P<0.001). Additionally, receiver operating characteristic curve analysis demonstrated that a methylation level of 7.5% for CpG6 (area under the curve, 0.834; P<0.001) was an appropriate threshold value to predict the risk of EH. With generalized multifactor dimensionality reduction, a potential gene‑gene interaction between CpG6 and CpG8 (P=0.001), and gene‑environment interactions between smoking, alcohol consumption, CpG6, CpG7 and CpG8 (P=0.011), were observed. In conclusion, the results of the present study demonstrated that hypomethylation of the TLR2 promoter, particularly CpG6, was associated with the risk of EH in this population. Additionally, a gene‑gene interaction between CpG6 and CpG8, and interactions between environmental factors, including smoking and alcohol consumption, and CpG6, CpG7 and CpG8, may be associated with the risk of EH.

The Biological Basis for Cardiac Repair After Myocardial Infarction: From Inflammation to Fibrosis

In adult mammals, massive sudden loss of cardiomyocytes after infarction overwhelms the limited regenerative capacity of the myocardium, resulting in the formation of a collagen-based scar. Necrotic cells release danger signals, activating innate immune pathways and triggering an intense inflammatory response. Stimulation of toll-like receptor signaling and complement activation induces expression of proinflammatory cytokines (such as interleukin-1 and tumor necrosis factor-α) and chemokines (such as monocyte chemoattractant protein-1/ chemokine (C-C motif) ligand 2 [CCL2]). Inflammatory signals promote adhesive interactions between leukocytes and endothelial cells, leading to extravasation of neutrophils and monocytes. As infiltrating leukocytes clear the infarct from dead cells, mediators repressing inflammation are released, and anti-inflammatory mononuclear cell subsets predominate. Suppression of the inflammatory response is associated with activation of reparative cells. Fibroblasts proliferate, undergo myofibroblast transdifferentiation, and deposit large amounts of extracellular matrix proteins maintaining the structural integrity of the infarcted ventricle. The renin-angiotensin-aldosterone system and members of the transforming growth factor-β family play an important role in activation of infarct myofibroblasts. Maturation of the scar follows, as a network of cross-linked collagenous matrix is formed and granulation tissue cells become apoptotic. This review discusses the cellular effectors and molecular signals regulating the inflammatory and reparative response after myocardial infarction. Dysregulation of immune pathways, impaired suppression of postinfarction inflammation, perturbed spatial containment of the inflammatory response, and overactive fibrosis may cause adverse remodeling in patients with infarction contributing to the pathogenesis of heart failure. Therapeutic modulation of the inflammatory and reparative response may hold promise for the prevention of postinfarction heart failure.

Inflammation and metabolic cardiomyopathy

Excessive feeding is associated with an increase in the incidence of chronic metabolic diseases, such as obesity, insulin resistance, and type 2 diabetes. Metabolic disturbance induces chronic low-grade inflammation in metabolically-important organs, such as the liver and adipose tissue. Many of the inflammatory signalling pathways are directly triggered by nutrients. The pro-inflammatory mediators in adipocytes and macrophages infiltrating adipose tissue promote both local and systemic pro-inflammatory status. Metabolic cardiomyopathy is a chronic metabolic disease characterized by structural and functional alterations and interstitial fibrosis without coronary artery disease or hypertension. In the early stage of metabolic cardiomyopathy, metabolic disturbance is not accompanied by substantial changes in myocardial structure and cardiac function. However, metabolic disturbance induces subcellular low-grade inflammation in the heart, and in turn, subcellular component abnormalities, such as oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, and impaired calcium handling, leading to impaired myocardial relaxation. In the advanced stage, the vicious cycle of subcellular component abnormalities, inflammatory cell infiltration, and neurohumoral activation induces cardiomyocyte injury and death, and cardiac fibrosis, resulting in impairment of both diastolic and systolic functions. This review discusses some recent advances in understanding involvement of inflammation in metabolic cardiomyopathy.

Stanniocalcin-1 attenuates ischemic cardiac injury and response of differentiating monocytes/macrophages to inflammatory stimuli

Stanniocalcin-1 (STC-1) is a multifunctional glycoprotein with antioxidant and anti-inflammatory properties. Ischemic myocardial necrosis generates "danger" signals that perpetuate detrimental inflammatory reactions often involving monocyte recruitment and their subsequent differentiation into proinflammatory macrophages. Therefore, we evaluated the effects of recombinant STC-1 (rSTC-1) on monocyte phenotype and in a mouse model of myocardial infarction. Using an established protocol to differentiate human monocytes into macrophages, we demonstrated that rSTC-1 did not alter morphology of the differentiated cells, toll-like receptor (TLR) 4 expression, or expression of the myeloid cell marker CD11b. However, rSTC-1 treatment before differentiation attenuated the rise in the expression of CD14, a TLR4 coreceptor and pathogen sensor that propagates innate immune responses, and suppressed levels of inflammatory cytokines produced by the differentiated cells in response to the CD14-TLR4 ligand lipopolysaccharide. Moreover, rSTC-1 treatment reduced CD14 expression in monocytes stimulated with endogenous danger signals. Interestingly, the effects of rSTC-1 on CD14 expression were not reproduced by a superoxide dismutase mimetic. In mice with induced myocardial infarcts, intravenous administration of rSTC-1 decreased CD14 expression in the heart as well as levels of tumor necrosis factor alpha, C-X-C motif ligand 2, interleukin 1 beta, and myeloperoxidase. It also suppressed the formation of scar tissue while enhancing cardiac function. The data suggests that one of the beneficial effects of STC-1 might be attributed to suppression of CD14 on recruited monocytes and macrophages that limits their inflammatory response. STC-1 may be a promising therapy to protect the heart and other tissues from ischemic injury.

The Role of TLR2, TLR4, and TLR9 in the Pathogenesis of Atherosclerosis

Toll-like receptors (TLRs) are key players in the pathogenesis of inflammatory conditions including coronary arterial disease (CAD). They are expressed by a variety of immune cells where they recognize pathogen-associated molecular patterns (PAMPs). TLRs recruit adaptor molecules, including myeloid differentiation primary response protein (MYD88) and TIRF-related adaptor protein (TRAM), to mediate activation of MAPKs and NF-kappa B pathways. They are associated with the development of CAD through various mechanisms. TLR4 is expressed in lipid-rich and atherosclerotic plaques. In TLR2^−/− and TLR4^−/− mice, atherosclerosis-associated inflammation was diminished. Moreover, TLR2 and TLR4 may induce expression of Wnt5a in advanced staged atheromatous plaque leading to activation of the inflammatory processes. TLR9 is activated by CpG motifs in nucleic acids and have been implicated in macrophage activation and the uptake of oxLDL from the circulation. Furthermore, TLR9 also stimulates interferon-α (INF-α) secretion and increases cytotoxic activity of CD4⁺ T-cells towards coronary artery tunica media smooth muscle cells. This review outlines the pathophysiological role of TLR2, TLR4, and TLR9 in atherosclerosis, focusing on evidence from animal models of the disease.

Assessment of endothelial damage and cardiac injury in a mouse model mimicking thrombotic thrombocytopenic purpura

Essentials Endothelial injury is thought to be a key event in thrombotic thrombocytopenic purpura (TTP). Endothelial and cardiac damages were assessed in a model of TTP using ADAMTS-13 knockout mice. Damages of cardiac perfusion and function were associated with nitric oxide pathway alteration. Endothelial dysfunction constitutes a critical event in TTP development and cardiac injury.

SUMMARY

Background Cardiac alterations represent a major cause of mortality in patients with thrombotic thrombocytopenic purpura (TTP). Endothelial injury remains poorly defined, but seems to be a key initiating event leading to the formation of platelet-rich thrombi in TTP patients. Objectives To assess the changes in endothelial function and the induced cardiac damage in a mouse model of TTP. Patients/methods We used an animal model in which TTP-like symptoms are triggered by injection of 2000 units kg-1 of recombinant von Willebrand factor in ADAMTS-13 knockout mice. Results These mice developed TTP-like symptoms, i.e. severe thrombocytopenia, schistocytosis, and anemia. On day 2, magnetic resonance imaging demonstrated a decrease in left ventricular perfusion associated with alteration of left ventricular ejection fraction, fractional shortening, and cardiac output, suggesting early systolic dysfunction. This was associated with decrease in endothelium-mediated relaxation responses to acetylcholine in mesenteric and coronary arteries, demonstrating severe early endothelial dysfunction. In parallel, we showed decreased cardiac expression of endothelial nitric oxide (NO) synthase and increased expression of antioxidant enzymes, suggesting alteration of the NO pathway. At this time, cardiac immunohistochemistry revealed an increase in the expression of VCAM-1 and E-selectin. Conclusion This study provides evidence that the heart is a sensitive target organ in TTP, and shows, for the first time, strong mesenteric and coronary endothelial dysfunction in an induced-TTP model. The mechanisms incriminated are the occurrence of a pro-oxidant state, and proadhesive and proinflammatory phenotypes. This previously largely unrecognized vascular dysfunction may represent an important contributor to the systemic organ failure occurring in TTP.

TLR2 Regulates Complement-Mediated Inflammation Induced by Blood Loss During Hemorrhage

Hemorrhagic shock resulting from blood loss directs the majority of the blood to the vital organs, dramatically reducing blood flow to the intestines and resulting in damage and inflammation. The excessive intestinal inflammatory response includes pro-inflammatory cytokines and complement activation, although the mechanism is not clear. Toll-like receptors play a vital role in the innate immune response and toll-like receptor 2 (TLR2) is required for intestinal ischemia/reperfusion-induced injury. We hypothesized that TLR2 plays an integral role in the intestinal inflammatory response after hemorrhage and subjected C57Bl/6 wild-type and Tlr2(-/-) mice to atraumatic loss of ∼30% total blood volume. Two hours after blood removal, the intestinal injury and inflammation were assessed. We demonstrate that compared with wild-type control mice, Tlr2(-/-) mice sustain less intestinal damage and inflammation. Importantly, TLR2 regulated eicosanoid and complement activation and IL-12 and TNFα secretions, indicating interactions between TLR2 and complement in response to significant blood loss.

Inflammation and Inflammatory Cells in Myocardial Infarction and Reperfusion Injury: A Double-Edged Sword

Myocardial infarction (MI) is the most common cause of cardiac injury, and subsequent reperfusion further enhances the activation of innate and adaptive immune responses and cell death programs. Therefore, inflammation and inflammatory cell infiltration are the hallmarks of MI and reperfusion injury. Ischemic cardiac injury activates the innate immune response via toll-like receptors and upregulates chemokine and cytokine expressions in the infarcted heart. The recruitment of inflammatory cells is a dynamic and superbly orchestrated process. Sequential infiltration of the injured myocardium with neutrophils, monocytes and their descendant macrophages, dendritic cells, and lymphocytes contributes to the initiation and resolution of inflammation, infarct healing, angiogenesis, and ventricular remodeling. Both detrimental effects and a beneficial role in the pathophysiology of MI and reperfusion injury may be attributed to the subset heterogeneity and functional diversity of these inflammatory cells.

Modulation of Macrophage Polarization and HMGB1-TLR2/TLR4 Cascade Plays a Crucial Role for Cardiac Remodeling in Senescence-Accelerated Prone Mice

The aim of this study was to investigate the role of macrophage polarization in aging heart. Macrophage differentiation is pathogenically linked to many inflammatory and immune disorders. It is often preceded by myocardial inflammation, which is characterized by increased cardiac damage and pro-inflammatory cytokine levels. Therefore, we investigated the hypothesis that senescence accelerated-prone (SAMP8) mice cardiac tissue would develop macrophage polarization compared with senescence-resistant control (SAMR1) mice. Both SAMP8 and SAMR1 mice were sacrificed when they became six month old. We evaluated, histo-pathological changes and modifications in protein expression by Western blotting and immuno-histochemical staining for M1 and M2 macrophage markers, high mobility group protein (HMG)B1 and its cascade proteins, pro-inflammatory factors and inflammatory cytokines in cardiac tissue. We observed significant upregulation of HMGB1, toll-like receptor (TLR)2, TLR4, nuclear factor (NF)κB p65, tumor necrosis factor (TNF)α, cyclooxygenase (COX)2, interferon (IFN)γ, interleukin (IL)-1β, IL-6 and M1 like macrophage specific marker cluster of differentiation (CD)68 expressions in SAMP8 heart. In contrast, M2 macrophage specific marker CD36, and IL-10 expressions were down-regulated in SAMP8 mice. The results from the study demonstrated that, HMGB1-TLR2/TLR4 signaling cascade and induction of phenotypic switching to M1 macrophage polarization in SAMP8 mice heart would be one of the possible reasons behind the cardiac dysfunction and thus it could become an important therapeutic target to improve the age related cardiac dysfunction.

Modulation of endothelial function by Toll like receptors

Endothelial cells (EC) are able to actively control vascular permeability, coagulation, blood pressure and angiogenesis. Most recently, a role for endothelial cells in the immune response has been described. Therefore, the endothelium has a dual role controlling homeostasis but also being the first line for host defence and tissue damage repair thanks to its ability to mount an inflammatory response. Endothelial cells have been shown to express pattern-recognition receptors (PRR) including Toll-like receptors (TLR) that are activated in response to stimuli within the bloodstream including pathogens and damage signals. TLRs are strategic mediators of the immune response in endothelial cells but they also regulate the angiogenic process critical for tissue repair. Nevertheless, endothelial activation and angiogenesis can contribute to some pathologies. Thus, inappropriate endothelial activation, also known as endothelial dysfunction, through TLRs contributes to tissue damage during autoimmune and inflammatory diseases such as atherosclerosis, hypertension, ischemia and diabetes associated cardiovascular diseases. Also TLR induced angiogenesis is required for the growth of some tumors, atherosclerosis and rheumatoid arthritis, among others. In this review we discuss the importance of various TLRs in modulating the activation of endothelial cells and their importance in immunity to infection and vascular disease as well as their potential as therapeutic targets.

The role of toll like receptors in giant cell arteritis

GCA is a common primary systemic vasculitis that results in granulomatous inflammation of medium to large arteries. Both innate and adaptive immune mechanisms combine to drive intimal hyperplasia, luminal stenosis and ultimately occlusion. While the pathogenesis of GCA is incompletely understood, the activation of resident adventitial dendritic cells via toll like receptors (TLRs) appears to be a crucial inciting event. Here we explore the role of TLRs in the pathogenesis of GCA, including their effects on dendritic cell and T cell activation and recruitment, putative infectious triggers for GCA and the potential of TLR inhibition as a novel therapeutic strategy in GCA.

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

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

Inflammatory and fibrotic responses of cardiac fibroblasts to myocardial damage associated molecular patterns (DAMPs)

Cardiac fibroblasts (CF) are well-established as key regulators of extracellular matrix (ECM) turnover in the context of myocardial remodelling and fibrosis. Recently, this cell type has also been shown to act as a sensor of myocardial damage by detecting and responding to damage-associated molecular patterns (DAMPs) upregulated with cardiac injury. CF express a range of innate immunity pattern recognition receptors (TLRs, NLRs, IL-1R1, RAGE) that are stimulated by a host of different DAMPs that are evident in the injured or remodelling myocardium. These include intracellular molecules released by necrotic cells (heat shock proteins, high mobility group box 1 protein, S100 proteins), proinflammatory cytokines (interleukin-1α), specific ECM molecules up-regulated in response to tissue injury (fibronectin-EDA, tenascin-C) or molecules modified by a pathological environment (advanced glycation end product-modified proteins observed with diabetes). DAMP receptor activation on fibroblasts is coupled to altered cellular function including changes in proliferation, migration, myofibroblast transdifferentiation, ECM turnover and production of fibrotic and inflammatory paracrine factors, which directly impact on the heart's ability to respond to injury. This review gives an overview of the important role played by CF in responding to myocardial DAMPs and how the DAMP/CF axis could be exploited experimentally and therapeutically.

Extracellular RNA facilitates hypoxia-induced leukocyte adhesion and infiltration in the lung through TLR3-IFN-γ-STAT1 signaling pathway

Endogenous ligands released from dying cells, including extracellular RNA (eRNA), cause TLR activation, which is associated with inflammation and vascular diseases. However, the importance of this response in acute hypoxia (AH) remains unexplored. Here, we observed eRNA-mediated TLR3 activation during exposure of mice to AH in the absence of exogenous viral stimuli. RNaseA treatment diminished AH-induced expression of IFN and cell adhesion molecules (CAMs) and myeloid cell infiltration in the lung, and TLR3 gene silencing or neutralization with antibodies markedly attenuated AH- or poly I:C-induced IFN and CAM expression and leukocyte adhesion (LA) and myeloid cell infiltration in the lung. However, RNaseA treatment or TLR3 gene silencing failed to alter AH-induced cell death and proliferation in lung vasculature. Furthermore, IFN-γ--but not IFN-α--regulated AH-induced CAM expression and LA. Treatment with RNaseA, TLR3 siRNA, neutralizing antibodies, or a STAT1 inhibitor substantially decreased AH- and poly I:C-induced STAT1 phosphorylation, CAM expression, and myeloid cell infiltration, suggesting a central role for STAT1 phosphorylation in AH-induced LA and infiltration. We conclude that eRNA activates TLR3 and facilitates, through in vivo IFN-γ-STAT1 signaling, AH-induced leukocyte infiltration in the lung. Thus, RNaseA might provide a therapeutic alternative for patients with lung diseases.

Implication of pattern-recognition receptors in cardiovascular diseases

SIGNIFICANCE

Pattern-recognition receptors (PRRs) are a family of receptors that are used to detect pathogen-associated molecular patterns or damage-associated molecular patterns, which initiate immune responses to resolve infections and repair damaged tissues. Abnormalities in PRR activation will unavoidably lead to excessive inflammation.

RECENT ADVANCES

Although multiple pathophysiological processes are involved in cardiovascular disease, recent studies have highlighted the importance of innate PRRs, in particular, Toll-like receptors and nucleotide-binding oligomerization domain-like receptors, in mediating inflammatory responses and cardiovascular function.

CRITICAL ISSUES

The functional roles and regulatory mechanisms of PRRs in cardiovascular diseases are still largely unknown. In particular, controversies exist on the certainty of these detrimental or beneficial effects of some PRRs in different diseased states or different experimental animal models.

FUTURE DIRECTIONS

Considering that the molecular mechanisms for individual PRR to regulate cellular function are complex and multiple PRRs are activated simultaneously or synergistically, a better understanding of the function of individual PRRs and the interplay of PRRs will provide unexpected opportunities to develop new therapies for cardiovascular disease by modulation of an innate immune system.