Toll-like receptor-4 modulates survival by induction of left ventricular remodeling after myocardial infarction in mice

The Influence of Metabolic Risk Factors on the Inflammatory Response Triggered by Myocardial Infarction: Bridging Pathophysiology to Treatment

Myocardial infarction (MI) sets off a complex inflammatory cascade that is crucial for effective cardiac healing and scar formation. Yet, if this response becomes excessive or uncontrolled, it can lead to cardiovascular complications. This review aims to provide a comprehensive overview of the tightly regulated local inflammatory response triggered in the early post-MI phase involving cardiomyocytes, (myo)fibroblasts, endothelial cells, and infiltrating immune cells. Next, we explore how the bone marrow and extramedullary hematopoiesis (such as in the spleen) contribute to sustaining immune cell supply at a cardiac level. Lastly, we discuss recent findings on how metabolic cardiovascular risk factors, including hypercholesterolemia, hypertriglyceridemia, diabetes, and hypertension, disrupt this immunological response and explore the potential modulatory effects of lifestyle habits and pharmacological interventions. Understanding how different metabolic risk factors influence the inflammatory response triggered by MI and unraveling the underlying molecular and cellular mechanisms may pave the way for developing personalized therapeutic approaches based on the patient's metabolic profile. Similarly, delving deeper into the impact of lifestyle modifications on the inflammatory response post-MI is crucial. These insights may enable the adoption of more effective strategies to manage post-MI inflammation and improve cardiovascular health outcomes in a holistic manner.

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.

Immunomodulation and immunopharmacology in heart failure

The immune system is intimately involved in the pathophysiology of heart failure. However, it is currently underused as a therapeutic target in the clinical setting. Moreover, the development of novel immunomodulatory therapies and their investigation for the treatment of patients with heart failure are hampered by the fact that currently used, evidence-based treatments for heart failure exert multiple immunomodulatory effects. In this Review, we discuss current knowledge on how evidence-based treatments for heart failure affect the immune system in addition to their primary mechanism of action, both to inform practising physicians about these pleiotropic actions and to create a framework for the development and application of future immunomodulatory therapies. We also delineate which subpopulations of patients with heart failure might benefit from immunomodulatory treatments. Furthermore, we summarize completed and ongoing clinical trials that assess immunomodulatory treatments in heart failure and present several therapeutic targets that could be investigated in the future. Lastly, we provide future directions to leverage the immunomodulatory potential of existing treatments and to foster the investigation of novel immunomodulatory therapeutics.

Toll-like Receptors as Pro-Thrombotic Drivers in Viral Infections: A Narrative Review

Toll-like receptors (TLRs) have a critical role in the pathogenesis and disease course of viral infections. The induced pro-inflammatory responses result in the disturbance of the endovascular surface layer and impair vascular homeostasis. The injury of the vessel wall further promotes pro-thrombotic and pro-coagulatory processes, eventually leading to micro-vessel plugging and tissue necrosis. Moreover, TLRs have a direct role in the sensing of viruses and platelet activation. TLR-mediated upregulation of von Willebrand factor release and neutrophil, as well as macrophage extra-cellular trap formation, further contribute to (micro-) thrombotic processes during inflammation. The following review focuses on TLR signaling pathways of TLRs expressed in humans provoking pro-thrombotic responses, which determine patient outcome during viral infections, especially in those with cardiovascular diseases.

The Impacts of Animal-Based Diets in Cardiovascular Disease Development: A Cellular and Physiological Overview

Cardiovascular disease (CVD) is the leading cause of death in the United States, and diet plays an instrumental role in CVD development. Plant-based diets have been strongly tied to a reduction in CVD incidence. In contrast, animal food consumption may increase CVD risk. While increased serum low-density lipoprotein (LDL) cholesterol concentrations are an established risk factor which may partially explain the positive association with animal foods and CVD, numerous other biochemical factors are also at play. Thus, the aim of this review is to summarize the major cellular and molecular effects of animal food consumption in relation to CVD development. Animal-food-centered diets may (1) increase cardiovascular toll-like receptor (TLR) signaling, due to increased serum endotoxins and oxidized LDL cholesterol, (2) increase cardiovascular lipotoxicity, (3) increase renin-angiotensin system components and subsequent angiotensin II type-1 receptor (AT1R) signaling and (4) increase serum trimethylamine-N-oxide concentrations. These nutritionally mediated factors independently increase cardiovascular oxidative stress and inflammation and are all independently tied to CVD development. Public policy efforts should continue to advocate for the consumption of a mostly plant-based diet, with the minimization of animal-based foods.

Metagenomic sequencing of human cardiac tissue reveals Microbial RNA which correlates with Toll-like receptor-associated inflammation in patients with heart disease

Cardiovascular disease (CVD) is strongly associated with chronic low-grade inflammation, involving activated Toll-like receptors and their downstream cellular machinery. Moreover, CVD and other related inflammatory conditions are associated with infiltration of bacteria and viruses originating from distant body sites. Thus, in this study we aimed to map the presence of microbes in the myocardium of patients with heart disease that we previously found to display upregulated Toll-like receptor signaling. We performed metagenomics analysis of atrial cardiac tissue from patients undergoing coronary artery bypass grafting (CABG) or aortic valve replacement (AVR) and compared with atrial cardiac tissue from organ donors. A total of 119 species of bacteria and seven species of virus were detected in the cardiac tissue. RNA expression of five bacterial species were increased in the patient group of which L. kefiranofaciens correlated positively with cardiac Toll-like receptor-associated inflammation. Interaction network analysis revealed four main gene set clusters involving cell growth and proliferation, Notch signaling, G protein signaling and cell communication in association with L. kefiranofaciens RNA expression. Taken together, intracardial expression of L. kefiranofaciens RNA correlates with pro-inflammatory markers in the diseased cardiac atrium and may have an effect on specific signaling processes important for cell growth, proliferation and cell communication.

CRISPR-Cas9 editing of TLR4 to improve the outcome of cardiac cell therapy

Inflammation and fibrosis limit the reparative properties of human mesenchymal stromal cells (hMSCs). We hypothesized that disrupting the toll-like receptor 4 (TLR4) gene would switch hMSCs toward a reparative phenotype and improve the outcome of cell therapy for infarct repair. We developed and optimized an improved electroporation protocol for CRISPR-Cas9 gene editing. This protocol achieved a 68% success rate when applied to isolated hMSCs from the heart and epicardial fat of patients with ischemic heart disease. While cell editing lowered TLR4 expression in hMSCs, it did not affect classical markers of hMSCs, proliferation, and migration rate. Protein mass spectrometry analysis revealed that edited cells secreted fewer proteins involved in inflammation. Analysis of biological processes revealed that TLR4 editing reduced processes linked to inflammation and extracellular organization. Furthermore, edited cells expressed less NF-ƙB and secreted lower amounts of extracellular vesicles and pro-inflammatory and pro-fibrotic cytokines than unedited hMSCs. Cell therapy with both edited and unedited hMSCs improved survival, left ventricular remodeling, and cardiac function after myocardial infarction (MI) in mice. Postmortem histologic analysis revealed clusters of edited cells that survived in the scar tissue 28 days after MI. Morphometric analysis showed that implantation of edited cells increased the area of myocardial islands in the scar tissue, reduced the occurrence of transmural scar, increased scar thickness, and decreased expansion index. We show, for the first time, that CRISPR-Cas9-based disruption of the TLR4-gene reduces pro-inflammatory polarization of hMSCs and improves infarct healing and remodeling in mice. Our results provide a new approach to improving the outcomes of cell therapy for cardiovascular diseases.

Beneficial effect of TLR4 blockade by a specific aptamer antagonist after acute myocardial infarction

Experimental evidence indicates that the control of the inflammatory response after myocardial infarction is a key strategy to reduce cardiac injury. Cellular damage after blood flow restoration in the heart promotes sterile inflammation through the release of molecules that activate pattern recognition receptors, among which TLR4 is the most prominent. Transient regulation of TLR4 activity has been considered one of the potential therapeutic interventions with greater projection towards the clinic. In this regard, the characterization of an aptamer (4FT) that acts as a selective antagonist for human TLR4 has been investigated in isolated macrophages from different species and in a rat model of cardiac ischemia/reperfusion (I/R). The binding kinetics and biological responses of murine and human macrophages treated with 4FT show great affinity and significant inhibition of TLR4 signaling including the NF-κB pathway and the LPS-dependent increase in the plasma membrane currents (Kv currents). In the rat model of I/R, administration of 4FT following reoxygenation shows amelioration of cardiac injury function and markers, a process that is significantly enhanced when the second dose of 4FT is administered 24 h after reperfusion of the heart. Parameters such as cardiac injury biomarkers, infiltration of circulating inflammatory cells, and the expression of genes associated with the inflammatory onset are significantly reduced. In addition, the expression of anti-inflammatory genes, such as IL-10, and pro-resolution molecules, such as resolvin D1 are enhanced after 4FT administration. These results indicate that targeting TLR4 with 4FT offers new therapeutic opportunities to prevent cardiac dysfunction after infarction.

Impact of myeloid differentiation protein 1 on cardiovascular disease

Cardiovascular disease remains the leading cause of disability and mortality worldwide and a significant global burden. Many lines of evidence suggest complex remodeling responses to cardiovascular disease, such as myocardial ischemia, hypertension and valve disease, which lead to poor clinical outcomes, including heart failure, arrhythmia and sudden cardiac death (SCD). The mechanisms underlying cardiac remodeling are closely related to reactive oxygen species (ROS) and inflammation. Myeloid differentiation protein 1 (MD1) is a secreted glycoprotein known as lymphocyte antigen 86. The complex of MD1 and radioprotective 105 (RP105) is an important regulator of inflammation and is involved in the modulation of vascular remodeling and atherosclerotic plaque development. A recent study suggested that the expression of MD1 in hypertrophic cardiomyopathy (HCM) patients is decreased compared with that in donor hearts. Therefore, MD1 may play an important role in the pathological processes of cardiovascular disease and have potential clinical value. Here, this review aims to discuss the current knowledge regarding the role of MD1 in the regulation of cardiac pathophysiology.

Protective effects of Dapagliflozin on the vulnerability of ventricular arrhythmia in rats with pulmonary artery hypertension induced by monocrotaline

Monocrotaline (MCT)-induced pulmonary artery hypertension (PAH) has been reported to cause right heart failure (RHF). Moreover, Right heart diseases have been determined to cause ventricular arrhythmia (VA). So we can conclude that MCT-induced PAH increases the incidence of VA. In addition, Previous studies have determined the benefits of Dapagliflozin (DA) on the cardiac system, but the responses of MCT-induced RHF to DA are not fully reported. So the present study sought to evaluate the effects of DA on the MCT-induced PAH. A dose intraperitoneal injection of MCT (60 mg/kg) was carried out to induce a rat model with PAH. DA (60 mg/l) was administered for 4 weeks following MCT injection. Echocardiography, body weight, blood pressure, blood glucose, electrophysiological study, and Western blot were performed. Four weeks after the MCT injection, MCT-treated rats decreased body weight, blood glucose and blood pressure. In addition, MCT caused the formation of PAH and RHF. Moreover, MCT-induced PAH rats increased the incidence of VA, prolonged action potential duration (APD), and shortened effective refractory period (ERP). Additionally, PAH rats significantly prevented the activated expressions of Ion channel proteins such as potassium channel (Kv1.5, Kv2.1, Kv4.2, Kv4.3) and L-type Ca channel (Cav1.2). As we expected, these changes above in PAH rats were reversed when DA was administered. Mechanistically, DA significantly reduced the levels of toll-like receptor (TLR4), the nuclear factor kappa B (NF-κB) in MCT-treated rats. In conclusion, these findings determine that DA reduces the vulnerability of VA in PAH rats through the TLR4/NF-κB signaling pathway.

Markedly reduced myocardial expression of γ-protocadherins and long non-coding RNAs in patients with heart disease

BACKGROUND

Adverse cardiac remodeling and tissue damage following heart disease is strongly associated with chronic low grade inflammation. The mechanisms underlying persisting inflammatory signals are not fully understood, but may involve defective and/or non-responsive transcriptional and post-transcriptional regulatory mechanisms. In the current study, we aimed to identify novel mediators and pathways involved in processes associated with inflammation in the development and maintenance of cardiac disease.

METHODS AND RESULTS

We performed RNA sequencing analysis of cardiac tissue from patients undergoing coronary artery bypass grafting (CABG) or aortic valve replacement (AVR) and compared with control tissue from multi-organ donors. Our results confirmed previous findings of a marked upregulated inflammatory state, but more importantly, we found pronounced reduction of non-protein coding genes, particularly long non-coding RNAs (lncRNA), including several lncRNAs known to be associated with inflammation and/or cardiovascular disease. In addition, Gene Set Enrichment Analysis revealed markedly downregulated microRNA pathways, resulting in aberrant expression of other genes, particularly γ-protocadherins.

CONCLUSIONS

Our data suggest that aberrant expression of non-coding gene regulators comprise crucial keys in the progression of heart disease, and may be pivotal for chronic low grade inflammation associated with cardiac dysfunction. By unmasking atypical γ-protocadherin expression as a prospective genetic biomarker of myocardial dysfunction, our study provides new insight into the complex molecular framework of heart disease. Creating new approaches to modify non-coding gene regulators, such as those identified in the current study, may define novel strategies to shift γ-protocadherin expression, thereby normalizing part of the molecular architecture associated with heart disease.

TLR4 deletion increases basal energy expenditure and attenuates heart apoptosis and ER stress but mitigates the training-induced cardiac function and performance improvement

Strategies capable of attenuating TLR4 can attenuate metabolic processes such as inflammation, endoplasmic reticulum (ER) stress, and apoptosis in the body. Physical exercise has been a cornerstone in suppressing inflammation and dysmetabolic outcomes caused by TRL4 activation. Thus, the present study aimed to evaluate the effects of a chronic physical exercise protocol on the TLR4 expression and its repercussion in the inflammation, ER stress, and apoptosis pathways in mice hearts. Echocardiogram, RT-qPCR, immunoblotting, and histological techniques were used to evaluate the left ventricle of wild-type (WT) and Tlr4 knockout (TLR4 KO) mice submitted to a 4-week physical exercise protocol. Moreover, we performed a bioinformatics analysis to expand the relationship of Tlr4 mRNA in the heart with inflammation, ER stress, and apoptosis-related genes of several isogenic strains of BXD mice. The TLR4 KO mice had higher energy expenditure and heart rate in the control state but lower activation of apoptosis and ER stress pathways. The bioinformatics analysis reinforced these data. In the exercised state, the WT mice improved performance and cardiac function. However, these responses were blunted in the KO group. In conclusion, TLR4 has an essential role in the inhibition of apoptosis and ER stress pathways, as well as in the training-induced beneficial adaptations.

Diagnostic Value of sST2 in Cardiovascular Diseases: A Systematic Review and Meta-Analysis

Biomarkers such as B-type natriuretic peptide (BNP), N-terminal pro-BNP (NT-proBNP), cardiac troponin (cTn), and CK-MB contribute significantly to the diagnosis of cardiovascular disease (CVD). Recent studies have demonstrated that suppression of tumorigenicity 2 (ST2) is associated with CVD, but a meta-analysis of ST2 levels in different CVDs has yet to be conducted. Therefore, the present study aimed to investigate soluble ST2 (sST2) levels in patients with ischemic heart disease (IHD), myocardial infarction (MI), and heart failure (HF). A total of 1,425 studies were searched across four databases, of which 16 studies were included in the meta-analysis. The Newcastle-Ottawa Quality Assessment Scale (NOS) values of all 16 studies were ≥7. The meta-analysis results indicated that the sST2 level was not correlated with IHD (standard mean difference [SMD] = 0.58, 95% confidence interval [95% CI] = 0.00 to 1.16, p = 0.05) or MI (weighted mean difference [WMD] = 0.17, 95% CI = -0.22 to 0.55, p = 0.40) but was significantly associated with HF (WMD = 0.21, 95% CI = 0.04 to 0.38, p = 0.02; I ² = 99%, p < 0.00001). sST2 levels did not differ significantly between patients with IHD or MI and healthy individuals; however, we believe that ST2 could be used as an auxiliary diagnostic biomarker of HF.

The Role of MIF in Hepatic Function, Oxidative Stress, and Inflammation in Thioacetamide-induced Liver Injury in Mice: Protective Effects of Betaine

BACKGROUND

Macrophage migration inhibitory factor (MIF) is a multipotent cytokine that contributes to the inflammatory response to chemical liver injury. This cytokine exhibits pro- and anti-inflammatory effects depending on the etiology and stage of liver disease.

OBJECTIVE

Our study aimed to investigate the role of MIF in oxidative stress and inflammation in the liver, and modulatory effects of betaine on MIF in thioacetamide (TAA)-induced chronic hepatic damage in mice.

METHODS

The experiment was performed on wild type and knockout MIF-/- C57BL/6 mice. They were divided into the following groups: control; Bet-group that received betaine (2% wt/v dissolved in drinking water); MIF-/- mice group; MIF-/-+Bet; TAA-group that received TAA (200 mg/kg b.w.), intraperitoneally, 3x/week/8 weeks); TAA+Bet; MIF-/-+TAA, and MIF-/-+TAA+Bet. In TAA- and Bet-treated groups, animals received the same doses. After eight weeks of treatment, blood samples were collected for biochemical analysis, and liver specimens were prepared for the assessment of parameters of oxidative stress and inflammation.

RESULTS

In MIF-/-mice, TAA reduced transaminases, γ-glutamyltranspeptidase, bilirubin, malondialdehyde (MDA), oxidative protein products (AOPP), total oxidant status (TOS), C-reactive protein (CRP), IL-6, IFN-γ, and increased thiols and total antioxidant status (TAS). Betaine attenuated the mechanism of MIF and mediated effects in TAA-induced liver injury, reducing transaminases, γ-glutamyltranspeptidase, bilirubin, MDA, AOPP, TOS, CRP, IL-6, IFN-g, and increasing thiols.

CONCLUSION

MIF is a mediator in hepatotoxic, pro-oxidative, and proinflammatoryeffects of TAA-induced liver injury. MIF-targeted therapy can potentially mitigate oxidative stress and inflammation in the liver, but the exact mechanism of its action requires further investigation. Betaine increases anti-oxidative defense and attenuates hepatotoxic effects of MIF, suggesting that betaine can be used for the prevention and treatment of liver damage.

Post-ischemic Myocardial Inflammatory Response: A Complex and Dynamic Process Susceptible to Immunomodulatory Therapies

Following acute occlusion of a coronary artery causing myocardial ischemia and implementing first-line treatment involving rapid reperfusion, a dynamic and balanced inflammatory response is initiated to repair and remove damaged cells. Paradoxically, restoration of myocardial blood flow exacerbates cell damage as a result of myocardial ischemia-reperfusion (MI-R) injury, which eventually provokes accelerated apoptosis. In the end, the infarct size still corresponds to the subsequent risk of developing heart failure. Therefore, true understanding of the mechanisms regarding MI-R injury, and its contribution to cell damage and cell death, are of the utmost importance in the search for successful therapeutic interventions to finally prevent the onset of heart failure. This review focuses on the role of innate immunity, chemokines, cytokines, and inflammatory cells in all three overlapping phases following experimental, mainly murine, MI-R injury known as the inflammatory, reparative, and maturation phase. It provides a complete state-of-the-art overview including most current research of all post-ischemic processes and phases and additionally summarizes the use of immunomodulatory therapies translated into clinical practice.

Berry-Derived Polyphenols in Cardiovascular Pathologies: Mechanisms of Disease and the Role of Diet and Sex

Cardiovascular disease (CVD) prevalence, pathogenesis, and manifestation is differentially influenced by biological sex. Berry polyphenols target several signaling pathways pertinent to CVD development, including inflammation, oxidative stress, and cardiac and vascular remodeling, and there are innate differences in these pathways that also vary by sex. There is limited research systematically investigating sex differences in berry polyphenol effects on these pathways, but there are fundamental findings at this time that suggest a sex-specific effect. This review will detail mechanisms within these pathological pathways, how they differ by sex, and how they may be individually targeted by berry polyphenols in a sex-specific manner. Because of the substantial polyphenolic profile of berries, berry consumption represents a promising interventional tool in the treatment and prevention of CVD in both sexes, but the mechanisms in which they function within each sex may vary.

Modulation of the acute defence reaction by eplerenone prevents cardiac disease progression in viral myocarditis

Aims

Left ventricular (LV) dysfunction in viral myocarditis is attributed to myocardial inflammation and fibrosis, inducing acute and long‐time cardiac damage. Interventions are not established. On the basis of the link between inflammation, fibrosis, aldosterone, and extracellular matrix regulation, we aimed to investigate the effect of an early intervention with the mineralocorticoid receptor antagonist (MRA) eplerenone on cardiac remodelling in a murine model of persistent coxsackievirus B3 (CVB3)‐induced myocarditis.

Methods and results

SWR/J mice were infected with 5 × 10⁴ plaque‐forming units of CVB3 (Nancy strain) and daily treated either with eplerenone (200 mg/kg body weight) or with placebo starting from Day 1. At Day 8 or 28 post infection, mice were haemodynamically characterized and subsequently sacrificed for immunohistological and molecular biology analyses. Eplerenone did not influence CVB3 load. Already at Day 8, 1.8‐fold (P < 0.05), 1.4‐fold (P < 0.05), 3.2‐fold (P < 0.01), and 2.1‐fold (P < 0.001) reduction in LV intercellular adhesion molecule 1 expression, presence of monocytes/macrophages, oxidative stress, and apoptosis, respectively, was observed in eplerenone‐treated vs. untreated CVB3‐infected mice. In vitro, eplerenone led to 1.4‐fold (P < 0.01) and 1.2‐fold (P < 0.01) less CVB3‐induced cardiomyocyte oxidative stress and apoptosis. Furthermore, collagen production was 1.1‐fold (P < 0.05) decreased in cardiac fibroblasts cultured with medium of eplerenone‐treated vs. untreated CVB3‐infected HL‐1 cardiomyocytes. These ameliorations were in vivo translated into prevention of cardiac fibrosis, as shown by 1.4‐fold (P < 0.01) and 2.1‐fold (P < 0.001) lower collagen content in the LV of eplerenone‐treated vs. untreated CVB3‐infected mice at Days 8 and 28, respectively. This resulted in an early and long‐lasting improvement of LV dimension and function, as indicated by reduced LV end‐systolic volume and end‐diastolic volume, and an increase in LV contractility (dP/dt_max) and LV relaxation (dP/dt_min), respectively (P < 0.05).

Conclusions

Early intervention with the MRA eplerenone modulates the acute host and defence reaction and prevents cardiac disease progression in experimental CVB3‐induced myocarditis without aggravation of viral load. The findings advocate for an initiation of therapy of viral myocarditis as early as possible, even before the onset of inflammation‐induced myocardial dysfunction. This may also have implications for coronavirus disease‐19 therapy.

Exendin-4 Attenuates Remodeling in the Remote Myocardium of Rats After an Acute Myocardial Infarction by Activating β-Arrestin-2, Protein Phosphatase 2A, and Glycogen Synthase Kinase-3 and Inhibiting β-Catenin

PURPOSE

This study tested if the protective anti-remodeling effect of GLP-1 agonist Exendin-4 after an acute myocardial infarction (MI) in rats involves inhibition of the Wnt1/β-catenin signaling pathway.

METHODS

Rats were divided into sham, sham + Exendin-4 (10 μg/day, i.p), MI, and MI + Exendin-4. MI was introduced to rats by permanent left anterior descending coronary artery (LAD) ligation.

RESULTS

On day 7 post-infraction, MI rats showed LV dysfunction with higher serum levels of cardiac markers. Their remote myocardia showed increased mRNA and protein levels of collagen I/III with higher levels of reactive oxygen species (ROS) and inflammatory cytokines, as well as protein levels of Wnt1, phospho-Akt, transforming growth factor (TGF-β1), Smad, phospho-Smad3, α-SMA, caspase-3, and Bax. They also showed higher protein levels of phospho-glycogen synthase kinase-3β (p-GSK3β), as well as total, phosphorylated, and nuclear β-catenin with a concomitant decrease in the levels of cyclic adenosine monophosphate (cAMP), mRNA of manganese superoxide dismutase (MnSOD), and protein levels of Bcl-2, β-arrestin-2, and protein phosphatase-2 (PP2A). Administration of Exendin-4 to MI rats reduced the infarct size and reversed the aforementioned signaling molecules without altering protein levels of TGF-1β and Wnt1 or Akt activation. Interestingly, Exendin-4 increased mRNA levels of MnSOD, protein levels of β-arrestin-2 and PP2A, and β-catenin phosphorylation but reduced the phosphorylation of GSK3β and Smad3, and total β-catenin levels in the LV of control rats.

CONCLUSION

Exendin-4 inhibits the remodeling in the remote myocardium of rats following acute MI by attenuating β-catenin activation and activating β-arrestin-2, PP2A, and GSK3β. Graphical Abstract A graphical abstract that illustrates the mechanisms by which Exendin-4 inhibits cardiac remodeling in remote myocardium of left ventricle MI-induced rats. Mechanisms are assumed to occur in the cardiomyocytes and/or other resident cells such as fibroblast. Β-catenin activation and nuclear translocation are associated with increased synthesis of inflammatory cytokines and transforming growth factor β-1 (TGF-β1). GSK3β is inhibited by phosphorylation at Ser⁹. Under normal conditions, β-catenin is degraded in the cytoplasm by the active GSK3β-dependent degradation complex (un-phosphorylated) which usually phosphorylates β-catenin at Ser^33/37/Thr⁴¹. After MI, TGF-β1, and Wnt 1 levels are significantly increased, the overproduction of Wnt1 induces β-catenin stabilization and nuclear translocation through increasing the phosphorylation of disheveled (DVL) protein which in turn phosphorylates and inhibits GSK3β. TGF-β1 stimulates the phosphorylation of Smad-3 and subsequent nuclear translocation to activate the transcription of collage 1/III and α-smooth muscle actin (α-SMA). Besides, TGF-β1 stabilizes cytoplasmic β-catenin levels indirectly by phosphorylation of Akt at Thr³⁰⁸-induced inhibition of GSK3β by increasing phosphorylation of Ser⁹. Exendin-4, and possibly through G protein-coupled receptors (GPCRs), increases levels of cAMP and upregulates β-arrestin-2 levels. Both can result in a positive inotropic effect. Besides, β-arrestin-2 can stimulate PP2A to dephosphorylation Smad3 (inhibition) and GSK3β (activation), thus reduces fibrosis and prevents the activation of β-catenin and collagen deposition.

Mesenchymal stromal cell-derived exosomes attenuate myocardial ischaemia-reperfusion injury through miR-182-regulated macrophage polarization

AIMS

Mesenchymal stromal cells (MSCs) gradually become attractive candidates for cardiac inflammation modulation, yet understanding of the mechanism remains elusive. Strikingly, recent studies indicated that exosomes secreted by MSCs might be a novel mechanism for the beneficial effect of MSCs transplantation after myocardial infarction. We therefore explored the role of MSC-derived exosomes (MSC-Exo) in the immunomodulation of macrophages after myocardial ischaemia/reperfusion (I/R) and its implications in cardiac injury repair.

METHODS AND RESULTS

Exosomes were isolated from the supernatant of MSCs using gradient centrifugation method. Administration of MSC-Exo to mice through intramyocardial injection after myocardial I/R reduced infarct size and alleviated inflammation level in heart and serum. Systemic depletion of macrophages with clodronate liposomes abolished the curative effects of MSC-Exo. MSC-Exo modified the polarization of M1 macrophages to M2 macrophages both in vivo and in vitro. miRNA sequencing of MSC-Exo and bioinformatics analysis implicated miR-182 as a potent candidate mediator of macrophage polarization and toll-like receptor 4 (TLR4) as a downstream target. Diminishing miR-182 in MSC-Exo partially attenuated its modulation of macrophage polarization. Likewise, knock down of TLR4 also conferred cardioprotective efficacy and reduced inflammation level in a mouse model of myocardial I/R.

CONCLUSION

Our data indicate that MSC-Exo attenuates myocardial I/R injury in mice via shuttling miR-182 that modifies the polarization status of macrophages. This study sheds new light on the application of MSC-Exo as a potential therapeutic tool for myocardial I/R injury.

Dietary natural products as epigenetic modifiers in aging-associated inflammation and disease

Covering: up to 2020Chronic, low-grade inflammation is linked to aging and has been termed "inflammaging". Inflammaging is considered a key contributor to the development of metabolic dysfunction and a broad spectrum of diseases or disorders including declines in brain and heart function. Genome-wide association studies (GWAS) coupled with epigenome-wide association studies (EWAS) have shown the importance of diet in the development of chronic and age-related diseases. Moreover, dietary interventions e.g. caloric restriction can attenuate inflammation to delay and/or prevent these diseases. Common themes in these studies entail the use of phytochemicals (plant-derived compounds) or the production of short chain fatty acids (SCFAs) as epigenetic modifiers of DNA and histone proteins. Epigenetic modifications are dynamically regulated and as such, serve as potential therapeutic targets for the treatment or prevention of age-related disease. In this review, we will focus on the role for natural products that include phytochemicals and short chain fatty acids (SCFAs) as regulators of these epigenetic adaptations. Specifically, we discuss regulators of methylation, acetylation and acylation, in the protection from chronic inflammation driven metabolic dysfunction and deterioration of neurocognitive and cardiac function.

Targeting Inflammation by Flavonoids: Novel Therapeutic Strategy for Metabolic Disorders

A balanced metabolic profile is essential for normal human physiological activities. Disproportions in nutrition give rise to imbalances in metabolism that are associated with aberrant immune function and an elevated risk for inflammatory-associated disorders. Inflammation is a complex process, and numerous mediators affect inflammation-mediated disorders. The available clinical modalities do not effectively address the underlying diseases but rather relieve the symptoms. Therefore, novel targeted agents have the potential to normalize the metabolic system and, thus, provide meaningful therapy to the underlying disorder. In this connection, polyphenols, the well-known and extensively studied phytochemical moieties, were evaluated for their effective role in the restoration of metabolism via various mechanistic signaling pathways. The various flavonoids that we observed in this comprehensive review interfere with the metabolic events that induce inflammation. The mechanisms via which the polyphenols, in particular flavonoids, act provide a promising treatment option for inflammatory disorders. However, detailed clinical studies of such molecules are required to decide their clinical fate.

Toll-like receptor-mediated inflammation markers are strongly induced in heart tissue in patients with cardiac disease under both ischemic and non-ischemic conditions

BACKGROUND

A sustained low grade inflammatory state is a recognized feature of various diseases, including cardiovascular disease. This state of chronic inflammation involves activation of Toll-like receptor (TLR) signaling. However, little is known regarding the genetic profile of TLR components in cardiac tissue from patients with cardiac disease.

METHODS

In this study we investigated the genetic profile of 84 TLR markers in a unique set of cardiac tissue from patients that had undergone either coronary artery bypass grafting (CABG) or aortic valve replacement (AVR). In addition, we compared the gene data from the cardiac tissue with the same gene profile in blood as well as circulating cytokines to elucidate possible targets in blood that could be used to estimate the inflammatory state of the heart in cardiac disease.

RESULTS

We found a marked upregulation of TLR-induced inflammation in cardiac tissue from both patient groups compared to healthy controls. The inflammation appeared to be primarily mediated through TLR1, 3, 7, 8 and 10, resulting in a marked induction of mediators of the innate immune response. Furthermore, the gene expression data in combination with unbiased multivariate analysis suggested a difference in inflammatory response in ischemic cardiac tissue compared to non-ischemic cardiac tissue. Serum levels of IL-13 were significantly elevated in both CABG and AVR patients compared to controls, whereas other cytokines did not appear to coincide with cardiac TLR-induced inflammation.

CONCLUSIONS

We propose that cardiac disease in humans may be mediated by local cardiac TLR signaling under both ischemic and non-ischemic conditions.

The impact of age on cardiac function and extracellular matrix component expression in adverse post-infarction remodeling in mice

The aim of this study was to describe the potential associations of the expression of matricellular components in adverse post-infarction remodeling of the geriatric heart. In male geriatric (OM, age: 18 months) and young (YM, age: 11 weeks) OF1 mice myocardial infarction (MI) was induced by permanent ligation of the left anterior descending coronary artery. Cardiac function was evaluated by MRI. Plasma and myocardial tissue samples were collected 3d, 7d, and 32d post-MI. Age and MI were associated with impaired cardiac function accompanied by left-ventricular (LV) dilatation. mRNA expression of MMP-2 (7d: p < 0.05), TIMP-1 (7d: p < 0.05), TIMP-2 (7d: p < 0.05), Collagen-1 (3d and 7d: p < 0.05) and Collagen-3 (7d: p < 0.05) in LV non-infarcted myocardium was significantly higher in YM than in OM after MI. MMP-9 activity in plasma was increased in OM after MI (3d: p < 0.01). Tenascin-C protein levels assessed by ELISA were decreased in OM as compared to YM after MI in plasma (3d: p < 0.001, 7d: p < 0.05) and LV non-infarcted myocardium (7d: p < 0.01). Dysregulation in ECM components in non-infarcted LV might be associated and contribute to adverse LV remodeling and impaired cardiac function. Thus, targeting ECM might be a potential therapeutic approach to enhance cardiac function in geriatric patients following MI.

Recent advances of adapter proteins in the regulation of heart diseases

Heart diseases are major causes of mortality. Cardiac hypertrophy, myocardial infarction (MI), viral cardiomyopathy, ischemic and reperfusion (I/R) heart injury finally lead to heart failure and death. Insulin and IGF1 signal pathways play key roles in normal cardiomyocyte growth and physiological cardiac hypertrophy while inflammatory signal pathway is associated with pathological cardiac hypertrophy, MI, viral cardiomyopathy, I/R heart injury, and heart failure. Adapter proteins are the major family proteins, which transduce signals from insulin, IGF1, or cytokine receptors to the downstream pathways and have been shown to regulate variety of heart diseases. Here, we summarized the recent advances in understanding the physiological and pathological roles of adapter proteins in heart failure.

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.

The innate immune system in chronic cardiomyopathy: a European Society of Cardiology (ESC) scientific statement from the Working Group on Myocardial Function of the ESC

Activation of the immune system in heart failure (HF) has been recognized for over 20 years. Initially, experimental studies demonstrated a maladaptive role of the immune system. However, several phase III trials failed to show beneficial effects in HF with therapies directed against an immune activation. Preclinical studies today describe positive and negative effects of immune activation in HF. These different effects depend on timing and aetiology of HF. Therefore, herein we give a detailed review on immune mechanisms and their importance for the development of HF with a special focus on commonalities and differences between different forms of cardiomyopathies. The role of the immune system in ischaemic, hypertensive, diabetic, toxic, viral, genetic, peripartum, and autoimmune cardiomyopathy is discussed in depth. Overall, initial damage to the heart leads to disease specific activation of the immune system whereas in the chronic phase of HF overlapping mechanisms occur in different aetiologies.

Inflammation - Cause or Consequence of Heart Failure or Both?

PURPOSE OF REVIEW

With the intention to summarize the currently available evidence on the pathophysiological relevance of inflammation in heart failure, this review addresses the question whether inflammation is a cause or consequence of heart failure, or both.

RECENT FINDINGS

This review discusses the diversity (sterile, para-inflammation, chronic inflammation) and sources of inflammation and gives an overview of how inflammation (local versus systemic) can trigger heart failure. On the other hand, the review is outlined how heart failure-associated wall stress and signals released by stressed, malfunctioning, or dead cells (DAMPs: e.g., mitochondrial DNA, ATP, S100A8, matricellular proteins) induce cardiac sterile inflammation and how heart failure provokes inflammation in various peripheral tissues in a direct (inflammatory) and indirect (hemodynamic) manner. The crosstalk between the heart and peripheral organs (bone marrow, spleen, gut, adipose tissue) is outlined and the importance of neurohormonal mechanisms including the renin angiotensin aldosteron system and the ß-adrenergic nervous system in inflammation and heart failure is discussed. Inflammation and heart failure are strongly interconnected and mutually reinforce each other. This indicates the difficulty to counteract inflammation and heart failure once this chronic vicious circle has started and points out the need to control the inflammatory process at an early stage avoiding chronic inflammation and heart failure. The diversity of inflammation further addresses the need for a tailored characterization of inflammation enabling differentiation of inflammation and subsequent target-specific strategies. It is expected that the characterization of the systemic and/or cardiac immune profile will be part of precision medicine in the future of cardiology.

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.

Dexmedetomidine Protects Cardiomyocytes against Hypoxia/Reoxygenation Injury by Suppressing TLR4-MyD88-NF-κB Signaling

OBJECTIVE

We previously reported that dexmedetomidine (DEX) offers cardioprotection against ischemia/reperfusion injury in rats. Here, we evaluated the role of toll-like receptors 4- (TLR4-) myeloid differentiation primary response 88- (MyD88-) nuclear factor-kappa B (NF-κB) signaling in DEX-mediated protection of cardiomyocytes using in vitro models of hypoxia/reoxygenation (H/R).

METHODS

The experiments were carried out in H9C2 cells and in primary neonatal rat cardiomyocytes. Cells pretreated with vehicle or DEX were exposed to hypoxia for 1 h followed by reoxygenation for 12 h. We analyzed cell viability and lactate dehydrogenase (LDH) activity and measured tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1β mRNA levels, TLR4, MyD88, and nuclear NF-κB p65 protein expression and NF-κB p65 nuclear localization. TLR4 knock-down by TLR4 siRNA transfection and overexpression by TLR4 DNA transfection were used to further confirm our findings.

RESULTS

DEX protected against H/R-induced cell damage and inflammation, as evidenced by increased cell survival rates, decreased LDH activity, and decreased TNF-α, IL-6, and IL-1β mRNA levels, as well as TLR4 and NF-κB protein expression. TLR4 knock-down partially prevented cell damage following H/R injury, while overexpression of TLR4 abolished the DEX-mediated protective effects.

CONCLUSIONS

DEX pretreatment protects rat cardiomyocytes against H/R injury. This effect is partly mediated by TLR4 suppression via TLR4-MyD88-NF-κB signaling.

Protective effects of triptolide on TLR4 mediated autoimmune and inflammatory response induced myocardial fibrosis in diabetic cardiomyopathy

ETHNOPHARMACOLOGICAL RELEVANCE

Triptolide is a most important active ingredient extracted from traditional Chinese medicine Tripterygium, which has been widely used to treat glomerulonephritis as well as immune-mediated disorders, likely for its immunosuppressive, anti-proliferative and anti-inflammatory effects.

AIM OF THE STUDY

In this study, we have investigated the potential protective effects of triptolide against diabetic cardiomyopathy (DCM) by regulating immune system, attenuating inflammatory response, thus resulting in decreased cardiac fibrosis and improved left ventricle function.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly divided into 5 groups: normal group, diabetic group and diabetic rats treated with triptolide (50, 100, or 200μg/kg/day resp) for 8 weeks. Cardiac function was performed by echocardiography and histopathology of the hearts was examined with HE, Masson staining and scanning electron microscopy. Immune regulation mediator, macrophage infiltration, inflammatory response and cardiac fibrosis related cytokines were measured by RT-PCR, Western blot and Immunohistochemistry staining.

RESULTS

In the diabetic group, the expressions of TLR4 and NF-κB p65 were both up-regulated, which was associated with increased pro-inflammatory cytokines, coupled with cardiac fibrosis and impaired left ventricular function. Interestingly, pathological structure and function of left ventricle were both significantly improved in the triptolide treated groups. Furthermore, the immune mediator TLR4, downstream activator NF-κB p65, macrophage infiltration (CD68+), pro-inflammatory cytokines (TNF-α, IL-1β), cell adhesion molecule (VCAM-1) and chemokine (MCP-1) were significantly suppressed when treated with medium and high dosage triptolide compared with the diabetic group. Moreover, cardiac fibrosis pathway including α-SMA, TGF-β1, vimentin and collagen accumulations were observed significantly decreased in the triptolide treated groups.

CONCLUSIONS

Our data demonstrated that the protective effects of triptolide against DCM might attribute to inhibition of TLR4-induced NF-κB/IL-1β immune pathway, suppression of NF-κB/TNF-α/VCAM-1 inflammatory pathway and down-regulation of TGF-β1/α-SMA/Vimentin fibrosis pathway.

Inflammatory processes in cardiovascular disease: a route to targeted therapies

Inflammatory processes are firmly established as central to the development and complications of cardiovascular diseases. Elevated levels of inflammatory markers have been shown to be predictive of future cardiovascular events. The specific targeting of these processes in experimental models has been shown to attenuate myocardial and arterial injury, reduce disease progression, and promote healing. However, the translation of these observations and the demonstration of clear efficacy in clinical practice have been disappointing. A major limitation might be that tools currently used to measure 'inflammation' are insufficiently precise and do not provide information about disease site and activity, or discriminate between functionally important activation pathways. The challenge, therefore, is to make measures of inflammation that are more meaningful, and which can guide specific targeted therapies. In this Review, we consider the roles of inflammatory processes in the related pathologies of atherosclerosis and acute myocardial infarction, by providing an evaluation of the known and emerging inflammatory pathways. We highlight contemporary techniques to characterize and quantify inflammation, and consider how they might be used to guide specific treatments. Finally, we discuss emerging opportunities in the field, including their current limitations and challenges that are the focus of ongoing study.

A novel 72-kDa leukocyte-derived osteoglycin enhances the activation of toll-like receptor 4 and exacerbates cardiac inflammation during viral myocarditis

Background

Viral myocarditis can severely damage the myocardium through excessive infiltration of immune cells. Osteoglycin (OGN) is part of the small leucine-rich repeat proteoglycan (SLRP) family. SLRP’s may affect inflammatory and fibrotic processes, but the implication of OGN in cardiac inflammation and the resulting injury upon viral myocarditis is unknown.

Methods and results

This study uncovered a previously unidentified 72-kDa variant of OGN that is predominant in cardiac human and mouse samples of viral myocarditis. Its absence in mice significantly decreased cardiac inflammation and injury in Coxsackievirus-B3-induced myocarditis. It also delayed mortality in lipopolysaccharide-induced endotoxemia going along with a reduced systemic production of pro-inflammatory cytokines. This 72-kDa OGN is expressed in the cell membrane of circulating and resident cardiac macrophages and neutrophils. Co-immunoprecipitation and OGN siRNA experiments revealed that this 72-kDa variant activates the toll-like receptor-4 (TLR4) with a concomitant increase in IL-6, TNF-α, IL-1β, and IL-12 expression. This immune cell activation by OGN occurred via MyD88 and increased phosphorylation of c-jun. Finally, the 72-kDa chondroitin sulfate is the result of O-linked glycosylation of the 32-kDa protein core of OGN. In contrast, the 34-kDa dermatan sulfate-OGN, involved in collagen cross linking, was also the result of O-linked glycosylation.

Conclusion

The current study discovered a novel 72-kDa chondroitin sulfate-OGN that is specific for innate immune cells. This variant is able to bind and activate TLR4. The absence of OGN decreases cytokine production by both circulating and cardiac leukocytes upon (systemic) LPS exposure, and reduces cardiac inflammation and injury in viral myocarditis.

Electronic supplementary material

The online version of this article (doi:10.1007/s00018-016-2423-7) contains supplementary material, which is available to authorized users.

Toll-like receptors in the pathogenesis of pulmonary fibrosis

Pulmonary fibrosis (PF) constitutes the end stage of a broad range of heterogeneous interstitial lung diseases, characterized by the destruction of the pulmonary parenchyma, deposition of extracellular matrix and dramatic changes in the phenotype of both fibroblasts and alveolar epithelial cells. More than 200 causes of pulmonary fibrosis have been identified so far, yet the most common form is idiopathic pulmonary fibrosis (IPF). IPF is a lethal lung disorder of unknown etiology with a gradually increasing worldwide incidence and a median survival of 3-5 years from the time of diagnosis. Despite intense research efforts, the pathogenesis remains elusive and no effective treatment is available. Accumulating body of evidence suggests an abnormal wound healing response followed by extracellular matrix deposition, destruction of lung architecture, ultimately leading to respiratory failure. The contribution of immune system in lung fibrogenesis had been largely underscored due to the absence of response to immunosuppressive agents; however, the premise that lung fibrosis has an immunologic background has been recently revived. Toll-like receptors (TLRs) are pattern recognition receptors (PRRs), which link innate and adaptive immune response and regulate wound healing. TLRs promote tissue repair or fibrosis in many disease settings including lung fibrosis, albeit with profound differences depending on the cellular microenvironment. This review summarizes the current state of knowledge regarding the mechanistic implications between TLRs and lung fibrosis and highlights the therapeutic potential of targeting TLR signaling at the ligand or receptor level.

Oxidized Low-Density Lipoprotein Induces Apoptosis in Cultured Neonatal Rat Cardiomyocytes by Modulating the TLR4/NF-κB Pathway

This study was designed to investigate the apoptosis induced by oxidized low-density lipoprotein (ox-LDL) in cultured neonatal rat cardiomyocytes and explore the possible mechanisms. We evaluated whether ox-LDL-induced apoptosis depended in part on the activation of toll-like receptor-4(TLR4)/Nuclear factor κB (NF-κB) signaling pathway. Cells were cultivated with and without ox-LDL. Cell apoptosis was evaluated by flow cytometry. Immunofluorescence, western blot analysis and quantitative real-time polymerase chain reaction (qRT-PCR) were conducted to assess protein or mRNA expressions. Resatorvid (TAK-242), an exogenous synthetic antagonist for TLR4, was used to inhibit TLR4 signal transduction. Dose- and time-dependent apoptotic index of cardiomyocytes occurred after ox-LDL treatment. Incubation of cardiomyocytes with ox-LDL (50 μg/mL) for 24 hours increased TLR4 and NF-κB expressions significantly. Decrease of Bcl-2/Bax protein ratio, activation of caspase-3 and 9 were also detected. Ox-LDL-induced cardiomyocyte apoptosis, TLR4 and NF-κB expressions were attenuated by pretreatment with TAK-242. In conclusion, our findings indicate that the apoptosis induced by ox-LDL in cultured neonatal rat cardiomyocytes at least in part by modulating the TLR4/NF-κB signaling pathway.

Deletion of Apoptosis Inhibitor of Macrophage (AIM)/CD5L Attenuates the Inflammatory Response and Infarct Size in Acute Myocardial Infarction

Background

An excessive inflammatory response after myocardial infarction (MI) increases myocardial injury. The toll‐like receptor (TLR)‐4 is activated by the recognition of endogenous ligands and is proinflammatory when there is myocardial tissue injury. The apoptosis inhibitor of the macrophage (AIM) is known to provoke an efflux of saturated free fatty acids (FFA) due to lipolysis, which causes inflammation via the TLR‐4 pathway. Therefore, this study investigated the hypothesis that AIM causes a proinflammatory response after MI.

Methods and Results

The left anterior descending coronary artery was ligated to induce MI in both AIM‐knockout (AIM^−/−) and wild‐type (WT) mice. After 3 days, the inflammatory response from activation of the TLR‐4/NFκB pathway was assessed, and infarct size was measured by staining with triphenyltetrazolium chloride. In addition, left ventricular remodeling was examined after 28 days. Although the area at risk was similar between AIM^−/− and WT mice, the infarct size was significantly smaller in AIM^−/− mice (P=0.02). The heart weight–to–body weight ratio and myocardial fibrosis were also decreased in the AIM^−/− mice, and the 28‐day survival rate was improved (P<0.01). With the reduction of plasma FFA in AIM^−/− mice, myocardial IRAK4 and NFκB activity were decreased (all P<0.05). Moreover, there was a reduction in myeloperoxidase activity and inducible nitric oxide synthase as part of the inflammatory response (P<0.01, P=0.03, respectively). Furthermore, NFκB DNA‐binding activation via TLR‐4, neutrophil infiltration, and inflammatory mediators were decreased in AIM^−/− mice.

Conclusions

The deletion of AIM reduced the inflammatory response and infarct size and improved survival after myocardial infarction.

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.

Emerging roles of innate immune signaling and toll-like receptors in fibrosis and systemic sclerosis

Pathological fibrosis is a distinguishing hallmark of systemic sclerosis (SSc) as well as a number of more common conditions. Fibrosis is a complex and dynamic process associated with immune dysregulation, vasculopathy, and uncontrolled extracellular matrix production leading to intractable scar formation in the skin and internal organs. Persistent or recurrent chemical, infectious, mechanical, or autoimmune injury in genetically predisposed individuals causes sustained fibroblasts activation. Innate immune signaling via toll-like receptors (TLRs) is increasingly recognized as a key player driving the persistent fibrotic response in SSc. In particular, expression of TLR4 as well as its endogenous ligands are elevated in lesional tissue from patients with SSc. Ligand-induced TLR4 activation elicits potent stimulatory effects on fibrotic gene expression and myofibroblast differentiation. Furthermore, TLR4 appears to sensitize fibroblasts to the profibrotic stimulatory effect of transforming growth factor-β. This review highlights recent advances and emerging paradigms for understanding the regulation, complex functional roles, and therapeutic potential of TLRs in SSc pathogenesis.

Cardiac fibroblasts as sentinel cells in cardiac tissue: Receptors, signaling pathways and cellular functions

Cardiac fibroblasts (CF) not only modulate extracellular matrix (ECM) proteins homeostasis, but also respond to chemical and mechanical signals. CF express a variety of receptors through which they modulate the proliferation/cell death, autophagy, adhesion, migration, turnover of ECM, expression of cytokines, chemokines, growth factors and differentiation into cardiac myofibroblasts (CMF). Differentiation of CF to CMF involves changes in the expression levels of various receptors, as well as, changes in cell phenotype and their associated functions. CF and CMF express the β2-adrenergic receptor, and its stimulation activates PKA and EPAC proteins, which differentially modulate the CF and CMF functions mentioned above. CF and CMF also express different levels of Angiotensin II receptors, in particular, AT1R activation increases collagen synthesis and cell proliferation, but its overexpression activates apoptosis. CF and CMF express different levels of B1 and B2 kinin receptors, whose stimulation by their respective agonists activates common signaling transduction pathways that decrease the synthesis and secretion of collagen through nitric oxide and prostacyclin I2 secretion. Besides these classical functions, CF can also participate in the inflammatory response of cardiac repair, through the expression of receptors commonly associated to immune cells such as Toll like receptor 4, NLRP3 and interferon receptor. The activation by their respective agonists modulates the cellular functions already described and the release of cytokines and chemokines. Thus, CF and CMF act as sentinel cells responding to a plethora of stimulus, modifying their own behavior, and that of neighboring cells.

Toll-interacting protein contributes to mortality following myocardial infarction through promoting inflammation and apoptosis

BACKGROUND AND PURPOSE

Toll-interacting protein (Tollip) is an endogenous inhibitor of toll-like receptors, a superfamily that plays a pivotal role in various pathological conditions, including myocardial infarction (MI). However, the exact role of Tollip in MI remains unknown.

EXPERIMENTAL APPROACH

MI models were established in Tollip knockout (KO) mice, mice with cardiac-specific overexpression of human Tollip gene and in their Tollip(+/+) and non-transgenic controls respectively. The effects of Tollip on MI were evaluated by mortality, infarct size and cardiac function. Hypoxia-induced cardiomyocyte damage was investigated in vitro to confirm the role of Tollip in heart damage.

KEY RESULTS

Tollip expression was dramatically up-regulated in human ischaemic hearts and infarcted mice hearts. MI-induced mortality, infarct size and cardiac dysfunction were decreased in Tollip-KO mice compared with Tollip(+/+) controls. Ischaemic hearts from Tollip-KO mice exhibited decreased inflammatory cell infiltration and reduced NF-κB activation. Tollip depletion also alleviated myocardial apoptosis by down-regulating pro-apoptotic protein levels and up-regulating anti-apoptotic protein expressions in infarct border zone. Conversely, MI effects were exacerbated in mice with cardiac-specific Tollip overexpression. This aggravated MI injury by Tollip in vivo was confirmed with in vitro assays. Inhibition of Akt signalling was associated with the detrimental effects of Tollip on MI injury; activation of Akt largely reversed the deleterious effects of Tollip on MI-induced cardiomyocyte death.

CONCLUSIONS AND IMPLICATIONS

Tollip promotes inflammatory and apoptotic responses after MI, leading to increased mortality and aggravated cardiac dysfunction. These findings suggest that Tollip may serve as a novel therapeutic target for the treatment of MI.

Matrine pretreatment improves cardiac function in rats with diabetic cardiomyopathy via suppressing ROS/TLR-4 signaling pathway

AIM

Matrine is an alkaloid from Sophora alopecuroides L, which has shown a variety of pharmacological activities and potential therapeutic value in cardiovascular diseases. In this study we examined the protective effects of matrine against diabetic cardiomyopathy (DCM) in rats.

METHODS

Male SD rats were injected with streptozotocin (STZ) to induce DCM. One group of DCM rats was pretreated with matrine (200 mg·kg(-1)·d(-1), po) for 10 consecutive days before STZ injection. Left ventricular function was evaluated using invasive hemodynamic examination, and myocardiac apoptosis was assessed. Primary rat myocytes were used for in vitro experiments. Intracellular ROS generation, MDA content and GPx activity were determined. Real-time PCR and Western blotting were performed to detect the expression of relevant mRNAs and proteins.

RESULTS

DCM rats exhibited abnormally elevated non-fasting blood glucose levels at 4 weeks after STZ injection, and LV function impairment at 16 weeks. The cardiac tissues of DCM rats showed markedly increased apoptosis, excessive ROS production, and activation of TLR-4/MyD-88/caspase-8/caspase-3 signaling. Pretreatment with matrine significantly decreased non-fasting blood glucose levels and improved LV function in DCM rats, which were associated with reducing apoptosis and ROS production, and suppressing TLR-4/MyD-88/caspase-8/caspase-3 signaling in cardiac tissues. Incubation in a high-glucose medium induced oxidative stress and activation of TLR-4/MyD-88 signaling in cultured myocytes in vitro, which were significantly attenuated by pretreatment with N-acetylcysteine.

CONCLUSION

Excessive ROS production in DCM activates the TLR-4/MyD-88 signaling, resulting in cardiomyocyte apoptosis, whereas pretreatment with matrine improves cardiac function via suppressing ROS/TLR-4 signaling pathway.

Independent roles of the priming and the triggering of the NLRP3 inflammasome in the heart

AIMS

The NLRP3 inflammasome is activated in the ischaemic heart promoting caspase-1 activation, inflammation, and cell death. Ischaemic injury establishes both a priming signal (transcription of inflammasome components) and a trigger (NLRP3 activation). Whether NLRP3 activation, without priming, induces cardiac dysfunction and/or failure is unknown. The aim of this study was to assess the independent and complementary roles of the priming and the triggering signals in the heart, in the absence of ischaemia or myocardial injury.

METHODS AND RESULTS

We used mice with mutant NLRP3 (constitutively active), NLRP3-A350V, under the control of tamoxifen-driven expression of the Cre recombinase (Nlrp3-A350V/CreT mice). The mice were treated for 10 days with tamoxifen before measuring the activity of caspase-1, the effector enzyme in the inflammasome. Tamoxifen treatment induced the inflammasome in the spleen but not in the heart, despite expression of the mutant NLRP3-A350V. The components of the inflammasome were significantly less expressed in the heart compared with the spleen. Subclinical low-dose lipopolysaccharide (LPS; 2 mg/kg) in Nlrp3-A350V/CreT mice induced the expression of the components of the inflammasome (priming), measured using real-time PCR and western blot, leading to the formation of an active inflammasome (caspase-1 activation) in the heart and LV systolic dysfunction while low-dose LPS was insufficient to induce LV systolic dysfunction in wild-type mice (all P < 0.01 for mutant vs. wild-type mice).

CONCLUSION

The signalling pathway governing the inflammasome formation in the heart requires a priming signal in order for an active NLRP3 to induce caspase-1 activation and LV dysfunction.

Role of toll-like receptors in myocardial infarction

Toll-like receptors (TLRs) play a pivotal role in both innate and adaptive immunity, and TLRs recognize invading pathogens through molecular pattern recognition, and ultimately lead to the activation of transcription factors and inflammatory responses. Myocardial infarction leads to changes in the remodeling of the left ventricle of the heart, and the degree and type of remodeling provides important diagnostic information for the therapeutic management of ischemic heart disease. Innate immune takes a most important role in myocardial infarction. There are some studies reporting that TLRs play an important role in the myocardial infarction. The literatures were searched extensively and this review was performed to review the role of TLRs in myocardial infarction.

Toll-like receptor-4 is upregulated in plaque debris of patients with acute coronary syndrome more than Toll-like receptor-2

Atherosclerosis is a dise ase characterized by inflammation in the arterial wall. Atherogenesis is dependent on the innate immune response involving activation of Toll-like receptors (TLRs) and the expression of inflammatory proteins, those may lead to acute coronary syndrome (ACS). We investigated the expression level of TLR-4 in ACS, as compared with TLR-2 and patients with stable angina. Fifty-eight consecutive patients who underwent primary percutaneous coronary intervention (PCI, n = 29) because of ACS and elective PCI (n = 29) because of stable angina using a filter-device distal protection device system were prospectively analyzed. mRNA levels of TLR-2 and TLR-4 in debris containing various inflammatory tissues entrapped in the filter device were altogether analyzed using real-time PCR. There were no significant differences in age, sex distribution, between stable angina and ACS groups. TLR-4 expression levels were higher in patients with ACS than in patients with stable angina. TLR-4 might play a more important role than TLR-2 in atherogenesis, especially in ACS.

Innate immune receptors in heart failure: Side effect or potential therapeutic target?

Heart failure (HF) is a leading cause of mortality and morbidity in western countries and occasions major expenses for public health systems. Although optimal medical treatment is widely available according to current guidelines, the prognosis of patients with HF is still poor. Despite the etiology of the disease, increased systemic or cardiac activation of the innate immune system is well documented in several types of HF. In some cases there is evidence of an association between innate immune activation and clinical outcome of patients with this disease. However, the few large trials conducted with the use of anti-inflammatory medication in HF have not revealed its benefits. Thus, greater understanding of the relationship between alteration in the immune system and development and progression of HF is urgently necessary: prior to designing therapeutic interventions that target pathological inflammatory processes in preventing harmful cardiac effects of immune modulatory therapy. In this regard, relatively recently discovered receptors of the innate immune system, i.e., namely toll-like receptors (TLRs) and nod-like receptors (NLRs)-are the focus of intense cardiovascular research. These receptors are main up-stream regulators of cytokine activation. This review will focus on current knowledge of the role of TLRs and NLRs, as well as on downstream cytokine activation, and will discuss potential therapeutic implications.

Cardioprotective effect of carvedilol: inhibition of apoptosis in H9c2 cardiomyocytes via the TLR4/NF-κB pathway following ischemia/reperfusion injury

Carvedilol is a non-selective β-blocker used in the treatment of cardiovascular disease, including myocardial ischemia. The aim of the present study was to investigate the molecular mechanisms underlying the effects of carvedilol on simulated ischemia/reperfusion (SI/R)-induced cardiomyocyte apoptosis in vitro. H9c2 cardiomyocytes were incubated with either a vehicle or an ischemic buffer during hypoxia followed by reoxygenation with or without carvedilol. In two additional groups, toll-like receptor 4 (TLR4) and nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) were inhibited by a TLR4 antibody and pyrrolidine dithiocarbamate, respectively. The results revealed that carvedilol markedly decreased SI/R-induced apoptosis in a concentration-dependent manner, as demonstrated by flow-cytometric analysis. This effect was shown to be associated with an increase in the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X (Bax) protein ratio and concurrent reductions in the expression levels of TLR4 and NF-κB. These results suggest that carvedilol provides significant cardioprotection against SI/R-induced injury in H9c2 cardiomyocytes, an effect likely to be mediated through the TLR4/NF-κB signaling pathway.

Stiffness of left ventricular cardiac fibroblasts is associated with ventricular dilation in patients with recent-onset nonischemic and nonvalvular cardiomyopathy

BACKGROUND

Ventricular dilation is known as a pivotal predictor in recent-onset cardiomyopathy (ROCM), but its pathophysiology is not fully understood. In the present study we investigated whether single-cell stiffness of right and left ventricular-derived fibroblasts has an effect on cardiac phenotype in patients with ROCM.

METHODS AND RESULTS

Patients with endomyocardial biopsy-proven ROCM were included (n=10). Primary cardiac fibroblasts (CFBs) were cultured from left and right ventricular endomyocardial biopsies and their single-cell stiffness was analyzed by quantification of Young's modulus using colloidal probe atomic force microscopy. Cardiac fibrosis was analyzed by Masson's trichrome staining. CFBs from the left ventricle showed significantly decreased stiffness when compared with CFBs from the right ventricle, indexed by decreased stiffness (Young's modulus 3,374±389 vs. 4,837±690 Pa; P<0.05). Young's modulus of CFBs derived from the left ventricle correlated negatively with the left ventricular end-diastolic dimension derived from 2-dimensional echocardiography (R(2)=0.77; P<0.01). Neither left nor right ventricular fibrosis correlated with the respective ventricular dimensions.

CONCLUSIONS

Our data suggest that a decrease in single-cell stiffness of left ventricular fibroblasts could trigger left ventricular dilation in patients with ROCM. This implies a new potential mechanism for the ventricular dilation with this disease.

Effect of carvedilol on cardiomyocyte apoptosis in a rat model of myocardial infarction: a role for toll-like receptor 4

OBJECTIVES

Toll-like receptor 4 (TLR4) is crucial in cardiomyocyte apoptosis induced by myocardial infarction (MI) and carvedilol has been reported to have anti-apoptotic effects. We hypothesized that the effects of this agent are in part mediated through TLR4 signaling pathways.

MATERIALS AND METHODS

A total of 48 rats were randomized to the following groups before surgery: sham-operated group (n = 8), MI group (n = 10) and three carvedilol-treatment groups (n = 30, 2 mg/kg, 10 mg/kg and 30 mg/kg). Sham and MI groups were given vehicle and carvedilol groups received different dose carvedilol, by direct gastric gavage for 7 days. On the 4(th) day of drug or vehicle administration, MI model was produced by ligating the left anterior descending coronary artery. On day 3 after MI, apoptosis was assessed by TdT-UTP nick-end assay; the levels of expression of Bax, Bcl-2, TLR4 and nuclear factor-κB (NF-κB) in infarcted myocardium were analyzed by immunohistochemistry.

RESULTS

Carvedilol ameliorated MI-induced apoptosis in a dose-dependent manner. In parallel, carvedilol also decreased the ratio of Bax to Bcl-2, the expression of TLR4 and NF-κB induced by MI. The extent of apoptosis and Bax-Bcl-2 ratio was strongly correlated with the TLR4 levels.

CONCLUSION

This study suggests that the short-term administration of carvedilol can significantly alleviate cardiomyocyte apoptosis in the infarcted myocardium probably by inhibiting the excessive expression of TLR4 and NF-κB induced by infarction.