MyD88-dependent nuclear factor-κB activation is involved in fibrinogen-induced hypertrophic response of cardiomyocytes

The gut microbiota-inflammation-HFpEF axis: deciphering the role of gut microbiota dysregulation in the pathogenesis and management of HFpEF

Heart failure with preserved left ventricular ejection fraction (HFpEF) is a disease that affects multiple organs throughout the body, accounting for over 50% of heart failure cases. HFpEF has a significant impact on individuals' life expectancy and quality of life, but the exact pathogenesis remains unclear. Emerging evidence implicates low-grade systemic inflammation as a crucial role in the onset and progression of HFpEF. Gut microbiota dysregulation and associated metabolites alteration, including short-chain fatty acids, trimethylamine N-oxides, amino acids, and bile acids can exacerbate chronic systemic inflammatory responses and potentially contribute to HFpEF. In light of these findings, we propose the hypothesis of a "gut microbiota-inflammation-HFpEF axis", positing that the interplay within this axis could be a crucial factor in the development and progression of HFpEF. This review focuses on the role of gut microbiota dysregulation-induced inflammation in HFpEF's etiology. It explores the potential mechanisms linking dysregulation of the gut microbiota to cardiac dysfunction and evaluates the therapeutic potential of restoring gut microbiota balance in mitigating HFpEF severity. The objective is to offer novel insights and strategies for the management of HFpEF.

Fibroblast-specific MyD88-dependent signaling aggravates inflammation and cardiac dysfunction in the MI heart

BACKGROUND

Excessive fibrosis and chronic inflammation are vital to adverse cardiac remodeling of the MI heart. The crosstalk of fibroblasts (FBs) (primary drivers of fibrosis) and immune cells (that govern inflammation) is critical for the repair and remodeling of the injured heart. However, the molecular mechanisms through which FBs communicate with immune cells are poorly understood. In the MI heart, substantial cardiac cell damage releases alarmins, which trigger an immune response through the TLR/MyD88 pathway. The role of MyD88-dependent signaling is well characterized in immune cell biology. However, the role of FB-derived MyD88 signaling in MI heart injury is unknown.

OBJECTIVE

To define the role of FB-MyD88 in MI pathology.

METHODS AND RESULTS

MyD88 was deleted from fibroblasts or myofibroblasts with tamoxifen-inducible Tcf21- or Postn- promoter-driven Cre recombinase. Control and MyD88 KO mice were subjected to permanent LAD ligation (MI injury), and cardiac parameters were evaluated. Additionally, co-culture experiments and chemokine profiling were conducted to identify mechanisms facilitating FB-immune cell crosstalk. FB-specific MyD88 deletion restricted MI-induced adverse cardiac remodeling and cardiac dysfunction. Surprisingly, FB-specific MyD88 deletion reduced myeloid cell recruitment and molecular markers of chronic inflammation in the KO heart. The mechanistic studies confirmed that MyD88 is required for the activation of NF-κB in FBs. Additionally, co-culture experiments demonstrated that FB-MyD88 facilitates immune cell crosstalk through chemokines and promotes an inflammatory gene program.

CONCLUSION

These findings suggest that FB-MyD88 promotes MI-induced chronic inflammation and cardiac dysfunction. Therefore, targeting MyD88 could serve as a potential therapeutic strategy.

HNF4α ubiquitination mediated by Peli1 impairs FAO and accelerates pressure overload-induced myocardial hypertrophy

Impaired fatty acid oxidation (FAO) is a prominent feature of metabolic remodeling observed in pathological myocardial hypertrophy. Hepatocyte nuclear factor 4alpha (HNF4α) is closely associated with FAO in both cellular processes and disease conditions. Pellino 1 (Peli1), an E3 ligase containing a RING-like domain, plays a crucial role in catalyzing polyubiquitination of various substrates. In this study, we aimed to investigate the involvement of HNF4α and its ubiquitination, facilitated by Peli1, in FAO during pressure overload-induced cardiac hypertrophy. Peli1 systemic knockout mice (Peli1KO) display improved myocardial hypertrophy and cardiac function following transverse aortic constriction (TAC). RNA-seq analysis revealed that changes in gene expression related to lipid metabolism caused by TAC were reversed in Peli1KO mice. Importantly, both HNF4α and its downstream genes involved in FAO showed a significant increase in Peli1KO mice. We further used the antagonist BI6015 to inhibit HNF4α and delivered rAAV9-HNF4α to elevate myocardial HNF4α level, and confirmed that HNF4α inhibits the development of cardiac hypertrophy after TAC and is essential for the enhancement of FAO mediated by Peli1 knockout. In vitro experiments using BODIPY incorporation and FAO stress assay demonstrated that HNF4α enhances FAO in cardiomyocytes stimulated with angiotension II (Ang II), while Peli1 suppresses the effect of HNF4α. Mechanistically, immunoprecipitation and mass spectrometry analyses confirmed that Peli1 binds to HNF4α via its RING-like domain and promotes HNF4α ubiquitination at residues K307 and K309. These findings shed light on the underlying mechanisms contributing to impaired FAO and offer valuable insights into a promising therapeutic strategy for addressing pathological cardiac hypertrophy.

Ginsenoside Re inhibits myocardial fibrosis by regulating miR-489/myd88/NF-κB pathway

Background

Myocardial fibrosis (MF) is an advanced pathological manifestation of many cardiovascular diseases, which can induce heart failure and malignant arrhythmias. However, the current treatment of MF lacks specific drugs. Ginsenoside Re has anti-MF effect in rat, but its mechanism is still not clear. Therefore, we investigated the anti-MF effect of ginsenoside Re by constructing mouse acute myocardial infarction (AMI) model and AngⅡ induced cardiac fibroblasts (CFs) model.

Methods

The anti-MF effect of miR-489 was investigated by transfection of miR-489 mimic and inhibitor in CFs. Effect of ginsenoside Re on MF and its related mechanisms were investigated by ultrasonographic, ELISA, histopathologic staining, transwell test, immunofluorescence, Western blot and qPCR in the mouse model of AMI and the AngⅡ-induced CFs model.

Results

MiR-489 decreased the expression of α-SMA, collagenⅠ, collagen Ⅲ and myd88, and inhibited the phosphorylation of NF-κB p65 in normal CFs and CFs treated with AngⅡ. Ginsenoside Re could improve cardiac function, inhibit collagen deposition and CFs migration, promote the transcription of miR-489, and reduce the expression of myd88 and the phosphorylation of NF-κB p65.

Conclusion

MiR-489 can effectively inhibit the pathological process of MF, and the mechanism is at least partly related to the regulation of myd88/NF-κB pathway. Ginsenoside Re can ameliorate AMI and AngⅡ induced MF, and the mechanism is at least partially related to the regulation of miR-489/myd88/NF-κB signaling pathway. Therefore, miR-489 may be a potential target of anti-MF and ginsenoside Re may be an effective drug for the treatment of MF.

Toll-like receptors in cardiac hypertrophy

Toll-like receptors (TLRs) are a family of pattern recognition receptors (PRRs) that can identify pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). TLRs play an important role in the innate immune response, leading to acute and chronic inflammation. Cardiac hypertrophy, an important cardiac remodeling phenotype during cardiovascular disease, contributes to the development of heart failure. In previous decades, many studies have reported that TLR-mediated inflammation was involved in the induction of myocardium hypertrophic remodeling, suggesting that targeting TLR signaling might be an effective strategy against pathological cardiac hypertrophy. Thus, it is necessary to study the mechanisms underlying TLR functions in cardiac hypertrophy. In this review, we summarized key findings of TLR signaling in cardiac hypertrophy.

Cardiomyocyte-specific Peli1 contributes to the pressure overload-induced cardiac fibrosis through miR-494-3p-dependent exosomal communication

Cardiac fibrosis is an essential pathological process in pressure overload (PO)-induced heart failure. Recently, myocyte-fibroblast communication is proven to be critical in heart failure, in which, pathological growth of cardiomyocytes (CMs) may promote fibrosis via miRNAs-containing exosomes (Exos). Peli1 regulates the activation of NF-κB and AP-1, which has been demonstrated to engage in miRNA transcription in cardiomyocytes. Therefore, we hypothesized that Peli1 in CMs regulates the activation of cardiac fibroblasts (CFs) through an exosomal miRNA-mediated paracrine mechanism, thereby promoting cardiac fibrosis. We found that CM-conditional deletion of Peli1 improved PO-induced cardiac fibrosis. Moreover, Exos from mechanical stretch (MS)-induced WT CMs (WT MS-Exos) promote activation of CFs, Peli1^-/- MS-Exos reversed it. Furthermore, miRNA microarray and qPCR analysis showed that miR-494-3p was increased in WT MS-Exos while being down regulated in Peli1^-/- MS-Exos. Mechanistically, Peli1 promoted miR-494-3p expression via NF-κB/AP-1 in CMs, and then miR-494-3p induced CFs activation by inhibiting PTEN and amplifying the phosphorylation of AKT, SMAD2/3, and ERK. Collectively, our study suggests that CMs Peli1 contributes to myocardial fibrosis via CMs-derived miR-494-3p-enriched exosomes under PO, and provides a potential exosomal miRNA-based therapy for cardiac fibrosis.

MyD88: At the heart of inflammatory signaling and cardiovascular disease

Cardiovascular disease is a leading cause of death worldwide and is associated with systemic inflammation. In depth study of the cell-specific signaling mechanisms mediating the inflammatory response is vital to improving anti-inflammatory therapies that reduce mortality and morbidity. Cellular damage in the cardiovascular system results in the release of damage associated molecular patterns (DAMPs), also known as "alarmins," which activate myeloid cells through the adaptor protein myeloid differentiation primary response 88 (MyD88). MyD88 is broadly expressed in most cell types of the immune and cardiovascular systems, and its role often differs in a cardiovascular disease context and cell specific manner. Herein we review what is known about MyD88 in the setting of a variety of cardiovascular diseases, discussing cell specific functions and the relative contributions of MyD88-dependent vs. independent alarmin triggered inflammatory signaling. The widespread involvement of these pathways in cardiovascular disease, and their largely unexplored complexity, sets the stage for future in depth mechanistic studies that may place MyD88 in both immune and non-immune cell types as an attractive target for therapeutic intervention in cardiovascular disease.

Role of TLR4/MyD88 Signaling Pathway in the Occurrence and Development of Uremia-Induced Myocardial Hypertrophy and Possible Mechanism

The morbidity and mortality of cardiovascular disease (CVD) are relatively high. Studies have shown that most patients with chronic kidney disease (CKD) die from cardiovascular complications. Clinically, the pathophysiological state in which heart disease and kidney disease are causal and influence each other is called cardiorenal syndrome (CRS). Myocardial hypertrophy is the key stage of the heart structure changing from reversible to irreversible. It is an important pathophysiological basis for heart failure. Therefore, this study intends to start with the end-stage uremic phase of CKD to construct an animal model of uremia in rats to study the relationship between uremia, TLR4/MyD88 signaling pathway, and myocardial hypertrophy. The results showed that the uremic rats showed slow weight gain and were thinner. At 12 weeks (w), the serum creatinine and urea nitrogen of the uremic rats increased, and the global hypertrophy index increased. Detecting the expression of Toll-like receptor 4 (TLR4) and myeloid differentiation factor (MyD88) in blood samples of rats, we found that the expression of TLR4 and MyD88 increased at 12 w in the uremia group; pathological observation showed that at 4 weeks of uremia model rats, renal tissue compensatory hypertrophy, renal fibrous membrane proliferation, renal parenchyma atrophy, a large number of fibrous proliferation and inflammatory cell infiltration in the interstitium, and protein casts in the renal tubules were observed. Myocardial cells were obviously hypertrophy and disordered. At 12 w, renal tubules were obviously expanded, the epithelium was flat, the brush border disappeared, and the interstitial fibrous connective tissue of the myocardial tissue was proliferated. The detection of TLR4 and MyD88 in kidney tissue and myocardial tissue revealed that the positive expression of TLR4 and MyD88 gradually increased over time. Therefore, the final result of the study is that uremia can gradually lead to myocardial hypertrophy and TLR4 and MyD88 are highly expressed in serum, kidney, and myocardial tissues of uremic rats, suggesting that TLR4 and MyD88 may be related to the degree of uremic disease and the myocardium caused by it. Hypertrophy is related.

LncRNA AK020546 protects against cardiac ischemia-reperfusion injury by sponging miR-350-3p

Long non-coding RNAs (lncRNAs) have been implicated in the development of cardiovascular diseases. We observed that lncRNA AK020546 was downregulated following ischemia/reperfusion injury to the myocardium and following H2O2 treatment in H9c2 cardiomyocytes. In vivo and in vitro studies showed that AK020546 overexpression attenuated the size of the ischemic area, reduced apoptosis among H9c2 cardiomyocytes, and suppressed the release of reactive oxygen species, lactic acid dehydrogenase, and malondialdehyde. AK020546 served as a competing endogenous RNA for miR-350-3p and activated the miR-350-3p target gene ErbB3. MiR-350-3p overexpression reversed the effects of AK020546 on oxidative stress injury and apoptosis in H9c2 cardiomyocytes. Moreover, ErbB3 knockdown alleviated the effects of AK020546 on the expression of ErbB3, Bcl-2, phosphorylated AKT, cleaved Caspase 3, and phosphorylated Bad. These findings suggest lncRNA AK020546 protects against ischemia/reperfusion and oxidative stress injury by sequestering miR-350-3p and activating ErbB3, which highlights its potential as a therapeutic target for ischemic heart diseases.

Key Player in Cardiac Hypertrophy, Emphasizing the Role of Toll-Like Receptor 4

Toll-like receptor 4 (TLR4), a key pattern recognition receptor, initiates the innate immune response and leads to chronic and acute inflammation. In the past decades, accumulating evidence has implicated TLR4-mediated inflammatory response in regulation of myocardium hypertrophic remodeling, indicating that regulation of the TLR4 signaling pathway may be an effective strategy for managing cardiac hypertrophy's pathophysiology. Given TLR4's significance, it is imperative to review the molecular mechanisms and roles underlying TLR4 signaling in cardiac hypertrophy. Here, we comprehensively review the current knowledge of TLR4-mediated inflammatory response and its interaction ligands and co-receptors, as well as activation of various intracellular signaling. We also describe the associated roles in promoting immune cell infiltration and inflammatory mediator secretion, that ultimately cause cardiac hypertrophy. Finally, we provide examples of some of the most promising drugs and new technologies that have the potential to attenuate TLR4-mediated inflammatory response and prevent or reverse the ominous cardiac hypertrophy outcomes.

Blockade of c-Src Within the Paraventricular Nucleus Attenuates Inflammatory Cytokines and Oxidative Stress in the Mechanism of the TLR4 Signal Pathway in Salt-Induced Hypertension

Toll-like receptor 4 (TLR4) and cellular Src (c-Src) are closely associated with inflammatory cytokines and oxidative stress in hypertension, so we designed this study to explore the exact role of c-Src in the mechanism of action of the TLR4 signaling pathway in salt-induced hypertension. Salt-sensitive rats were given a high salt diet for 10 weeks to induce hypertension. This resulted in higher levels of TLR4, activated c-Src, pro-inflammatory cytokines, oxidative stress, and arterial pressure. Infusion of a TLR4 blocker into the hypothalamic paraventricular nucleus (PVN) decreased the activated c-Src, while microinjection of a c-Src inhibitor attenuated the PVN levels of nuclear factor-kappa B, pro-inflammatory cytokines, and oxidative stress. Our findings suggest that a long-term high-salt diet increases TLR4 expression in the PVN and this promotes the activation of c-Src, which upregulates the expression of pro-inflammatory cytokines and results in the overproduction of reactive oxygen species. Therefore, inhibiting central c-Src activity may be a new target for treating hypertension.

Dihydromyricetin Attenuates Inflammation through TLR4/NF-kappaB Pathway

Microglia plays a complex role in neuroinflammation, which has been implicated in neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease. This study aims to explore the effect and mechanism of Dihydromyricetin (DHM) on lipopolysaccharide (LPS)-induced inflammation in microglial BV-2 cells. Cell viability was measured by 3-[4,5-dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide (MTT) assay. The pro-inflammatory mediators and cytokines including interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α); inducible nitric oxide synthase (iNOS); and cyclooxygenase 2 (COX-2) were measured by enzyme-linked immunosorbent assay (ELISA) and/or quantitative real-time PCR (qRT-PCR). The expression of p-p65, p-IκBα, toll-like receptor 4 (TLR4), and myeloid differentiation primary response 88 (MyD88) were analyzed by western blot. The present study showed that DHM treatment alleviated LPS-induced viability reduction, suppressed the mRNA levels of IL-6, IL-1β and TNF-α, inhibited the mRNA and protein expression of iNOS and COX-2, and attenuated the activation of NF-кB and TLR4 signaling in a concentration-dependent manner. In conclusion, DHM exerts an anti-inflammatory effect on LPS-induced BV-2 microglial cells, possibly through TRL4/NF-κB signaling pathway.

Long non-coding RNAs in the failing heart and vasculature

Following completion of the human genome, it became evident that the majority of our DNA is transcribed into non-coding RNAs (ncRNAs) instead of protein-coding messenger RNA. Deciphering the function of these ncRNAs, including both small- and long ncRNAs (lncRNAs), is an emerging field of research. LncRNAs have been associated with many disorders and a number have been identified as key regulators in the development and progression of disease, including cardiovascular disease (CVD). CVD causes millions of deaths worldwide, annually. Risk factors include coronary artery disease, high blood pressure and ageing. In this review, we will focus on the roles of lncRNAs in the cellular and molecular processes that underlie the development of CVD: cardiomyocyte hypertrophy, fibrosis, inflammation, vascular disease and ageing. Finally, we discuss the biomarker and therapeutic potential of lncRNAs.

Targeting toll-like receptor 4 signalling pathways: can therapeutics pay the toll for hypertension?

The immune system plays a prominent role in the initiation and maintenance of hypertension. The innate immune system, via toll-like receptors (TLRs), identifies distinct signatures of invading microbes and damage-associated molecular patterns and triggers a chain of downstream signalling cascades, leading to secretion of pro-inflammatory cytokines and shaping the adaptive immune response. Over the past decade, a dysfunctional TLR-mediated response, particularly via TLR4, has been suggested to support a chronic inflammatory state in hypertension, inducing deleterious local and systemic effects in host cells and tissues and contributing to disease progression. While the underlying mechanisms triggering TLR4 need further research, evidence suggests that sustained elevations in BP disrupt homeostasis, releasing endogenous TLR4 ligands in hypertension. In this review, we discuss the emerging role of TLR4 in the pathogenesis of hypertension and whether targeting this receptor and its signalling pathways could offer a therapeutic strategy for management of this multifaceted disease. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Dihydrotanshinone I Attenuates Atherosclerosis in ApoE-Deficient Mice: Role of NOX4/NF-κB Mediated Lectin-Like Oxidized LDL Receptor-1 (LOX-1) of the Endothelium

Dihydrotanshinone I (DHT) is a natural compound extracted from Salvia miltiorrhiza Bunge which has been widely used for treating cardiovascular diseases. However, its role in atherosclerosis remains unclear. In this study, the effect of DHT on atherosclerosis were investigated using apolipoprotein E-deficient (ApoE^-/-) mice and endothelial cells. In lipopolysaccharide (LPS)-stimulated human umbilical vein endothelial cells (HUVECs), DHT (10 nM) decreased lectin-like ox-LDL receptor-1 (LOX-1) and NADPH oxidase 4 (NOX4) expression, reactive oxygen species (ROS) production, NF-κB nuclear translocation, ox-LDL endocytosis and monocytes adhesion. Silence NOX4 inhibited LPS-induced LOX-1 expression, NF-κB nuclear translocation, ox-LDL endocytosis and monocytes adhesion. In ApoE^-/- mice fed with an atherogenic diet, DHT (10 and 25 mg kg^-1) significantly attenuated atherosclerotic plaque formation, altered serum lipid profile, decreased oxidative stress and shrunk necrotic core areas. The enhanced expression of LOX-1, NOX4, and NF-κB in aorta was also dramatically inhibited by DHT. In conclusion, these results suggested that DHT showed anti-atherosclerotic activity through inhibition of LOX-1 mediated by NOX4/NF-κB signaling pathways both in vitro and in vivo. This finding suggested that DHT might be used as a potential vascular protective candidate for the treatment of atherosclerosis.

Tlr2 deficiency does not limit the development of left ventricular hypertrophy in a model of transverse aortic constriction induced pressure overload

Background

Toll-like receptors (TLRs) are involved in a variety of cardiovascular disorders, including septic cardiomyopathy, ischemia/reperfusion, heart failure, and cardiac hypertrophy. Previous research revealed that TLR4 promotes cardiac hypertrophy in vivo. Therefore, we investigated whether TLR2 is also involved in the development of cardiac hypertrophy.

Methods

Tlr2 deficient and wild type mice were subjected to transverse aortic constriction (TAC) or sham operation procedure. Left ventricular, heart and lung weights as well as hemodynamic parameters were determined after 3, 14 or 28 days. Real-time RT PCR was used to evaluate left ventricular gene expression. Protein content was determined via ELISA.

Results

TAC increased systolic left ventricular pressure, contraction and relaxations velocities as well as the heart weight in both genotypes. Tlr2 deficiency significantly enhanced cardiac hypertrophy after 14 and 28 days of TAC. Left ventricular end-diastolic pressure and heart rate increased in Tlr2^−/− TAC mice only. Fourteen days of TAC led to a significant elevation of ANP, BNP, TGFβ and TLR4 mRNA levels in Tlr2^−/− left ventricular tissue.

Conclusion

These data suggest that Tlr2 deficiency may promote the development of cardiac hypertrophy and ventricular remodeling after transverse aortic constriction.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Tlr4 Deficiency Protects against Cardiac Pressure Overload Induced Hyperinflammation

Transverse aortic constriction provokes a pro-inflammatory reaction and results in cardiac hypertrophy. Endogenous ligands contribute to cardiac hypertrophy via toll-like receptor (TLR)-4 binding. A lack of TLR4 signaling diminishes hypertrophy and inflammation. Wild type mice undergoing aortic constriction respond to a lipopolysaccharide second-hit stimulus with hyperinflammation. The objective of this study was to assess whether other second-hit challenges utilizing TLR ligands provoke a comparable inflammatory reaction, and to find out whether this response is absent in TLR4 deficient mice. Assuming that cardiac stress alters the expression of pattern recognition receptors we analyzed the effects of transverse aortic constriction and second-hit virulence factor treatment on TLR expression, as well as cytokine regulation. Wild type and Tlr4-/- mice were subjected to three days of TAC and subsequently confronted with gram-positive TLR2 ligand lipoteichoic acid (LTA, 15 mg/g bodyweight) or synthetic CpG-oligodesoxynucleotide 1668 thioate (20 nmol/kg bodyweight, 30 min after D-galactosamin desensitization) signaling via TLR9. Hemodynamic measurements and organ preservation were performed 6 h after stimulation. Indeed, the study revealed a robust enhancement of LTA induced pattern recognition receptor and cytokine mRNA expression and a LTA-dependent reduction of hemodynamic pressure in TAC wild type mice. Second-Hit treatment with CpG-ODNs led to similar results. However, second-hit effects were abolished in Tlr4-/- mice. In total, these data indicate for the first time that cardiac stress increases the inflammatory response towards both, gram-negative and gram-positive, TLR ligands as well as bacterial DNA. The decrease of the inflammatory response upon TLR2 and -9 ligand challenge in TAC Tlr4-/- mice demonstrates that a lack of TLR4 signaling does not only prevent left ventricular hypertrophy but also protects the mice from a cardiac stress induced hyperinflammatory reaction.

Conditional knockout of prolyl hydroxylase domain protein 2 attenuates high fat-diet-induced cardiac dysfunction in mice

Oxygen sensor prolyl hydroxylases (PHDs) play important roles in the regulation of HIF-α and cell metabolisms. This study was designed to investigate the direct role of PHD2 in high fat-diet (HFD)-induced cardiac dysfunction. In HFD fed mice, PHD2 expression was increased without significant changes in PHD1 and PHD3 levels in the heart. This was accompanied by a significant upregulation of myeloid differentiation factor 88 (MYD88) and NF-κB. To explore the role of PHD2 in HFD-induced cardiac dysfunction, PHD2 conditional knockout mice were fed a HFD for 16 weeks. Intriguingly, knockout of PHD2 significantly reduced MYD88 and NF-κb expression in HFD mouse hearts. Moreover, knockout of PHD2 inhibited TNFα and ICAM-1 expression, and reduced cell apoptosis and macrophage infiltration in HFD mice. This was accompanied by a significant improvement of cardiac function. Most importantly, conditional knockout of PHD2 at late stage in HFD mice significantly improved glucose tolerance and reversed cardiac dysfunction. Our studies demonstrate that PHD2 activity is a critical contributor to the HFD-induced cardiac dysfunction. Inhibition of PHD2 attenuates HFD-induced cardiac dysfunction by a mechanism involving suppression of MYD88/NF-κb pathway and inflammation.

Toll-like receptor 4 inhibition reduces vascular inflammation in spontaneously hypertensive rats

AIMS

Hypertension is associated with increased levels of circulating cytokines and recent studies have shown that innate immunity contributes to hypertension. The mechanisms which hypertension stimulates immune response remain unclear, but may involve formation of neo-antigens that activate the immune system. Toll like receptor 4 (TLR4) is an innate immune receptor that binds a wide spectrum of exogenous (lipopolysaccharide) and endogenous ligands. TLR4 signaling leads to activation of nuclear factor kappa B (NFκB) and transcription of genes involved in inflammatory response. We previously demonstrated that TLR4 blockade reduces blood pressure and the augmented vascular contractility in spontaneously hypertensive rats (SHR). Here we hypothesized that inhibition of TLR4 ameliorates the vascular inflammatory process by a NFκB signaling pathway.

MAIN METHODS

SHR and Wistar rats were treated with anti-TLR4 antibody (1μg/day) or unspecific IgG for 15days (i.p.).

KEY FINDINGS

Anti-TLR4 treatment decreased production of reactive oxygen species and expression of IL-6 cytokine in mesenteric resistance arteries from SHR, when compared with IgG-treated SHR. Anti-TLR4 treatment also abolished the increased vascular reactivity to noradrenaline observed in IgG-treated SHR, as described before, and inhibition of NFκB decreased noradrenaline responses only in IgG-treated SHR. Mesenteric arteries from SHR treated with anti-TLR4 displayed decreased expression of MyD88, but not TRIF, key molecules in TLR4 signaling. Phosphorylation of p38 and NF-κB p65 were decreased in arteries from anti-TLR4-treated SHR versus IgG-treated SHR.

SIGNIFICANCE

Together, these results suggest that TLR4 is a key player in hypertension and vascular inflammatory process by a NFκB signaling pathway.

The long noncoding RNA CHRF regulates cardiac hypertrophy by targeting miR-489

RATIONALE

Sustained cardiac hypertrophy is often accompanied by maladaptive cardiac remodeling leading to decreased compliance and increased risk for heart failure. Maladaptive hypertrophy is considered to be a therapeutic target for heart failure. MicroRNAs (miRNAs) and long noncoding RNAs (lncRNAs) have various biological functions and have been extensively investigated in past years.

OBJECTIVE

We identified miR-489 and lncRNAs (cardiac hypertrophy related factor, CHRF) from hypertrophic cardiomyocytes. Here, we tested the hypothesis that miR-489 and CHRF can participate in the regulation of cardiac hypertrophy in vivo and in vitro.

METHODS AND RESULTS

A microarray was performed to analyze miRNAs in response to angiotensin II treatment, and we found miR-489 was substantially reduced. Enforced expression of miR-489 in cardiomyocytes and transgenic overexpression of miR-489 both exhibited reduced hypertrophic response on angiotensin II treatment. We identified myeloid differentiation primary response gene 88 (Myd88) as a miR-489 target to mediate the function of miR-489 in cardiac hypertrophy. Knockdown of Myd88 in cardiomyocytes and Myd88-knockout mice both showed attenuated hypertrophic responses. Furthermore, we explored the molecular mechanism by which miR-489 expression is regulated and found that an lncRNA that we named CHRF acts as an endogenous sponge of miR-489, which downregulates miR-489 expression levels. CHRF is able to directly bind to miR-489 and regulate Myd88 expression and hypertrophy.

CONCLUSIONS

Our present study reveals a novel cardiac hypertrophy regulating model that is composed of CHRF, miR-489, and Myd88. The modulation of their levels may provide a new approach for tackling cardiac hypertrophy.

Activation of hypoxia-inducible factor-2 in adipocytes results in pathological cardiac hypertrophy

Background

Obesity can cause structural and functional abnormalities of the heart via complex but largely undefined mechanisms. Emerging evidence has shown that obesity results in reduced oxygen concentrations, or hypoxia, in adipose tissue. We hypothesized that the adipocyte hypoxia‐signaling pathway plays an essential role in the development of obesity‐associated cardiomyopathy.

Methods and Results

Using a mouse model in which the hypoxia‐inducible factor (HIF) pathway is activated by deletion of the von Hippel–Lindau gene specifically in adipocytes, we found that mice with adipocyte–von Hippel–Lindau deletion developed lethal cardiac hypertrophy. HIF activation in adipocytes results in overexpression of key cardiomyopathy‐associated genes in adipose tissue, increased serum levels of several proinflammatory cytokines including interleukin‐1β and monocyte chemotactic protein‐1, and activation of nuclear factor–κB and nuclear factor of activated T cells in the heart. Interestingly, genetic deletion of Hif2a, but not Hif1a, was able to rescue cardiac hypertrophy and abrogate adipose inflammation.

Conclusion

We have discovered a previously uncharacterized mechanism underlying a critical and direct role of the adipocyte HIF‐2 transcription factor in the development of adipose inflammation and pathological cardiac hypertrophy.

Toll-like receptors and damage-associated molecular patterns: novel links between inflammation and hypertension

Low-grade systemic inflammation is a common manifestation of hypertension; however, the exact mechanisms that initiate this pathophysiological response, thereby contributing to further increases in blood pressure, are not well understood. Aberrant vascular inflammation and reactivity via activation of the innate immune system may be the first step in the pathogenesis of hypertension. One of the functions of the innate immune system is to recognize and respond to danger. Danger signals can arise from not only pathogenic stimuli but also endogenous molecules released following cell injury and/or death [damage-associated molecular patterns (DAMPs)]. In the short-term, activation of the innate immune system is beneficial in the vasculature by providing cytoprotective mechanisms and facilitating tissue repair following injury or infection. However, sustained or excessive immune system activation, such as in autoimmune diseases, may be deleterious and can lead to maladaptive, irreversible changes to vascular structure and function. An initial source of DAMPs that enter the circulation to activate the innate immune system could arise from modest elevations in peripheral vascular resistance. These stimuli could subsequently lead to ischemic- or pressure-induced events aggravating further cell injury and/or death, providing more DAMPs for innate immune system activation. This review will address and critically evaluate the current literature on the role of the innate immune system in hypertension pathogenesis. The role of Toll-like receptor activation on somatic cells of the vasculature in response to the release of DAMPs and the consequences of this activation on inflammation, vasoreactivity, and vascular remodeling will be specifically discussed.

Priming with synthetic oligonucleotides attenuates pressure overload-induced inflammation and cardiac hypertrophy in mice

AIMS

Inflammation and Toll-like receptor (TLR) signalling have been linked to the development of cardiac hypertrophy following transverse aortic constriction (TAC). In the present study, we investigated whether pre-treatment with the synthetic TLR9 ligands 1668-thioate or 1612-thioate modulates the progression of TAC-induced cardiac inflammation and hypertrophy.

METHODS AND RESULTS

C57BL/6N-mice were pre-treated with 1668-thioate, 1612-thioate (0.25 nmol/g, i.p.), or phosphate-buffered saline 16 h prior to TAC or sham surgery. Heart-weight/body-weight ratio (HW/BW), cardiomyocyte cell size, cellular macrophage accumulation, myofibroblast differentiation, and collagen deposition were investigated for up to 28 days. Cardiac function was monitored using a pressure-volume catheter and M-mode echocardiography. Inflammatory gene expression in the heart was analysed via gene array, while the time course of mRNA expression of key inflammatory mediators was assessed via RT-qPCR. TAC increased the HW/BW ratio and cardiomyocyte cell size and induced macrophage accumulation, myofibroblast differentiation, and collagen deposition. These changes were accompanied by cardiac inflammation and a significant loss of left ventricular function. Pre-treatment with cytosine-phosphate-guanine (CpG)-containing 1668-thioate attenuated the inflammatory response, the progression of cardiac hypertrophy, and cardiac remodelling, which resulted in a prolonged preservation of left ventricular function. These changes were induced to a smaller extent by the use of the non-CG-containing oligodeoxynucleotide 1612-thioate.

CONCLUSION

Pre-treatment with 1668-thioate attenuated cardiac hypertrophy following pressure overload, possibly by modifying the hypertrophy-induced inflammatory response, thereby reducing cardiac growth and fibrosis as well as delaying loss of cardiac function.

The toll-like receptor 4-antagonist eritoran reduces murine cardiac hypertrophy

AIMS

Toll-like receptor 4 (TLR4) recognizes lipopolysaccharides and endogenous ligands released after organ injury. Deficiency of TLR4 attenuates the development of left ventricular hypertrophy after transverse aortic constriction (TAC) in mice. We hypothesized that application of the TLR4 antagonist eritoran may also reduce cardiac hypertrophy after TAC surgery.

METHODS AND RESULTS

A catheter was implanted into the jugular vein of C57BL/6 mice to allow repeated administration of eritoran (5 mg/kg body weight) or placebo. Three days after TAC or sham surgery, heart weights were determined and cardiac tissue underwent mRNA and protein quantification. The TAC placebo group exhibited a significant increase in left ventricular weight, left ventricular weight/tibia length, and left ventricular/body weight ratio compared with the sham and TAC eritoran groups. Natriuretic peptide mRNA was elevated significantly only in TAC placebo mice. Transverse aortic constriction surgery led to a distinct increase in interleukin (IL)-1β and IL-6 mRNA and protein expression in the placebo but not the eritoran group. In contrast, IL-10 was significantly increased in both eritoran groups independent from TAC. Matrix metalloproteinase zymographic activity was highest in TAC placebo animals.

CONCLUSION

Application of the TLR4 antagonist eritoran attenuates the development of cardiac hypertrophy possibly by a reduction in inflammatory and increase in anti-inflammatory cytokines.

The TIR/BB-loop mimetic AS-1 prevents cardiac hypertrophy by inhibiting IL-1R-mediated MyD88-dependent signaling

Activation of NF-κB contributes to cardiac hypertrophy and the interleukin-1 receptor (IL-1R)-mediated MyD88-dependent signaling pathway predominately activates NF-κB. Recent studies have shown that the TIR/BB-Loop mimetic (AS-1) disrupted the interaction of MyD88 with the IL-1R, resulting in blunting of NF-κB activation. We have examined the effects of AS-1 on the IL-1β-induced hypertrophic response using cultured neonatal cardiac myocytes in vitro and transverse aortic constriction (TAC) pressure overload-induced cardiac hypertrophy in vivo. Neonatal cardiac myocytes were treated with AS-1 15 min prior to IL-1β stimulation for 24 h. AS-1 treatment significantly attenuated IL-1β-induced hypertrophic responses of cardiac myocytes. In vivo experiments showed that AS-1 administration prevented cardiac hypertrophy and dysfunction induced by pressure overload. AS-1 administration disrupted the interaction of IL-1R with MyD88 in the pressure overloaded hearts and prevented activation of NF-κB. In addition, AS-1 prevented increases in activation of the MAPK pathway (p38 and p-ERK) in TAC-induced hypertrophic hearts. Our data suggest that the IL-1R-mediated MyD88-dependent signaling pathway plays a role in the development of cardiac hypertrophy and AS-1 attenuation of cardiac hypertrophy is mediated by blocking the interaction between IL-1R and MyD88, resulting in decreased NF-κB binding activity and decreased MAPK activation.

Endogenous ligands of TLR2 and TLR4: agonists or assistants?

The mammalian TLRs serve as key sensors of PAMPs, such as bacterial LPS, lipopeptides, and flagellins, which are present in microbial cells but not host cells. TLRs have therefore been considered to play a central role in the discrimination between "self" and "non-self". However, since the discovery of their microbial ligands, many studies have provided evidence that host-derived molecules may also stimulate TLR2- or TLR4-dependent signaling. To date, more than 20 of these endogenous TLR ligands have been proposed, which have tended to fall into the categories of released intracellular proteins, ECM components, oxidatively modified lipids, and other soluble mediators. This review aims to summarize the evidence supporting the intrinsic TLR-stimulating capacity of each of these proposed endogenous ligands with a particular emphasis on the measures taken to exclude contaminating LPS and lipopeptides from experimental systems. The emerging evidence that many of these molecules may be more accurately described as PAMP-binding molecules (PBMs) or PAMP-sensitizing molecules (PSMs), rather than genuine ligands of TLR2 or TLR4, is also summarized. The relevance of this possibility to the pathogenesis of chronic inflammatory diseases, tumor surveillance, and autoimmunity is discussed.