TLR2 ligands induce cardioprotection against ischaemia/reperfusion injury through a PI3K/Akt-dependent mechanism

Lipopolysaccharide Induces Trained Innate Immune Tolerance in the Heart Through Interferon Signaling in a Model of Stress-Induced Cardiomyopathy

Background

Although the ability of the heart to adapt to environmental stress has been studied extensively, the molecular and cellular mechanisms responsible for cardioprotection are not yet fully understood.

Methods

We administered Toll-like receptor (TLR) agonists or a diluent to wild-type mice and assessed their potential to induce cardiac protection against injury from a high intraperitoneal dose of isoproterenol (ISO) administered 7 days later. Cardioprotective effects were analyzed through serum cardiac troponin I levels, immune cell profiling via flow cytometry, echocardiography, and multiomic single-nuclei RNA and ATAC sequencing.

Results

Pretreatment with the TLR4 agonist lipopolysaccharide (LPS), but not TLR1/2 or TLR3 agonists, conferred cardioprotection against ISO, as demonstrated by reduced cardiac troponin I leakage, decreased inflammation, preservation of cardiac structure and function, and improved survival. Remarkably, LPS-induced tolerance was reversed by β-glucan treatment. Multiomic analysis showed that LPS-tolerized hearts had greater chromatin accessibility and upregulated gene expression compared to hearts treated with LPS and β-glucan (reverse-tolerized). The LPS tolerance was associated with upregulation of interferon response pathways across various cell types, including cardiac myocytes and stromal cells. Blocking both type 1 and type 2 interferon signaling eliminated LPS-induced tolerance against ISO, while pretreatment with recombinant type 1 and 2 interferons conferred cardiac protection. Multiomic sequencing further revealed enhanced cytoprotective signaling in interferon-treated hearts. Analysis of cell-cell communication networks indicated increased autocrine signaling by cardiac myocytes, as well as greater paracrine signaling between stromal cells and myeloid cells, in LPS-tolerized versus reverse-tolerized hearts.

Conclusions

LPS pretreatment confers cardiac protection against ISO-induced injury through TLR4 mediated type 1 and 2 interferon signaling, consistent with trained innate immune tolerance. The observation that LPS-induced protection in cardiac myocytes involves both cell-autonomous and non-cell-autonomous mechanisms underscores the complexity of innate immune tolerance in the heart, warranting further investigation into this cardioprotective phenotype.

Clinical Perspective

What is new?: The Toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS) confers cardiac protection against isoproterenol-mediated injury in a manner consistent with trained innate immune tolerance, which is reversed by β-glucan treatment.Activation of type 1 and 2 interferon signaling, which is downstream of Toll-like receptor 4, is necessary and sufficient for LPS-induced cardiac protection.LPS-tolerized hearts show heightened autocrine signaling by cardiac myocytes and, to a greater degree, increased cell-cell communication between cardiac myocytes and stromal and myeloid cells compared to reverse-tolerized hearts.What are the clinical implications?: TLR4 and interferon signaling play key roles in the establishment of cardiac protection and LPS-induced trained innate immune tolerance.The protective effects of LPS are mediated by cell-autonomous and non-cell-autonomous mechanisms, suggesting that a deeper understanding of the molecular and cellular signatures of innate immune tolerance is required for the development of targeted approaches to modulate trained innate immunity, and consequently cytoprotection, in the heart.

Sulfate-Reducing Bacteria Induce Pro-Inflammatory TNF-α and iNOS via PI3K/Akt Pathway in a TLR 2-Dependent Manner

Desulfovibrio, resident gut sulfate-reducing bacteria (SRB), are found to overgrow in diseases such as inflammatory bowel disease and Parkinson's disease. They activate a pro-inflammatory response, suggesting that Desulfovibrio may play a causal role in inflammation. Class I phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway regulates key events in the inflammatory response to infection. Dysfunctional PI3K/Akt signaling is linked to numerous diseases. Bacterial-induced PI3K/Akt pathway may be activated downstream of toll-like receptor (TLR) signaling. Here, we tested the hypothesis that Desulfovibrio vulgaris (DSV) may induce tumor necrosis factor alpha (TNF-α) and inducible nitric oxide synthase (iNOS) expression via PI3K/Akt in a TLR 2-dependent manner. RAW 264.7 macrophages were infected with DSV, and protein expression of p-Akt, p-p70S6K, p-NF-κB, p-IkB, TNF-α, and iNOS was measured. We found that DSV induced these proteins in a time-dependent manner. Heat-killed and live DSV, but not bacterial culture supernatant or a probiotic Lactobacillus plantarum, significantly caused PI3K/AKT/TNF/iNOS activation. LY294002, a PI3K/Akt signaling inhibitor, and TL2-C29, a TLR 2 antagonist, inhibited DSV-induced PI3K/AKT pathway. Thus, DSV induces pro-inflammatory TNF-α and iNOS via PI3K/Akt pathway in a TLR 2-dependent manner. Taken together, our study identifies a novel mechanism by which SRB such as Desulfovibrio may trigger inflammation in diseases associated with SRB overgrowth.

Neuronal substance P drives metastasis through an extracellular RNA-TLR7 axis

Tumour innervation is associated with worse patient outcomes in multiple cancers1,2, which suggests that it may regulate metastasis. Here we observed that highly metastatic mouse mammary tumours acquired more innervation than did less-metastatic tumours. This enhanced innervation was driven by expression of the axon-guidance molecule SLIT2 in tumour vasculature. Breast cancer cells induced spontaneous calcium activity in sensory neurons and elicited release of the neuropeptide substance P (SP). Using three-dimensional co-cultures and in vivo models, we found that neuronal SP promoted breast tumour growth, invasion and metastasis. Moreover, patient tumours with elevated SP exhibited enhanced lymph node metastatic spread. SP acted on tumoral tachykinin receptors (TACR1) to drive death of a small population of TACR1high cancer cells. Single-stranded RNAs (ssRNAs) released from dying cells acted on neighbouring tumoural Toll-like receptor 7 (TLR7) to non-canonically activate a prometastatic gene expression program. This SP- and ssRNA-induced Tlr7 gene expression signature was associated with reduced breast cancer survival outcomes. Therapeutic targeting of this neuro-cancer axis with the TACR1 antagonist aprepitant, an approved anti-nausea drug, suppressed breast cancer growth and metastasis in multiple models. Our findings reveal that tumour-induced hyperactivation of sensory neurons regulates multiple aspects of metastatic progression in breast cancer through a therapeutically targetable neuropeptide/extracellular ssRNA sensing axis.

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.

Pseudomonas plecoglossicida fliP gene affects the immune response of Epinephelus fuscoguttatus ♀×Epinephelus lanceolatus ♂ to infection

Pseudomonas plecoglossicida is a pathogen that causes visceral white spot disease in a variety of teleosts. The protein encoded by fliP gene is involved in the assembly of bacterial flagella, which plays a vital role in bacterial pathogenicity. However, the roles of the fliP gene on the host immune response remain unclear. Here, we compared the pathogenicity of fliP gene-deleted (ΔfliP) strain, fliP gene-complemented (C-ΔfliP) strain and wild-type (NZBD9) strain of P. plecoglossicida to hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂), and explored the impacts of fliP gene on the immune response of hybrid grouper to P. plecoglossicida infection by using RNA-seq. In this study, the grouper in the ΔfliP strain-infected group had a 30% higher survival rate than those in the NZBD9 strain-infected group. In addition, the deletion of fliP gene decreased bacterial load in the spleen, intestine, liver as well as head kidney of hybrid grouper and the tissues damage were weakened. Moreover, the infection of hybrid grouper spleen by the ΔfliP strain induced 1,189 differential expression genes compared with the counterpart infected by NZBD9 strain. KEGG enrichment analysis showed that 9 immune-related pathways, 5 signal transduction pathways, and 3 signaling molecules and interaction pathways were significantly enriched. qRT-PCR analysis revealed that the ΔfliP strain mainly up-regulated the expression of inflammation related genes (IL-6, IL-12, IL-1β, IL-10, CXCL8, CXCL10) and immune regulation related genes (TLR2, P65, MyD88, P85, AKT), but down-regulated the expression of cell death related genes (FoxO1, Bim, PLK2 and LDHA) during infection. Based on the above results, fliP gene contributed to the pathogenicity of P. plecoglossicida to hybrid grouper (E. fuscoguttatus ♀ × E. lanceolatus ♂), deletion of fliP gene promoted the inflammation and immune response of hybrid grouper to P. plecoglossicida infection, which accelerating host clearance of pathogen and reducing tissue damages.

Inhibition of the NLRP3 Inflammasome Activation/Assembly through the Activation of the PI3K Pathway by Naloxone Protects Neural Stem Cells from Ischemic Condition

Naloxone is a well-known opioid antagonist and has been suggested to have neuroprotective effects in cerebral ischemia. We investigated whether naloxone exhibits anti-inflammatory and neuroprotective effects in neural stem cells (NSCs) injured by oxygen-glucose deprivation (OGD), whether it affects the NOD-like receptor protein 3 (NLRP3) inflammasome activation/assembly, and whether the role of the phosphatidylinositol 3-kinase (PI3K) pathway is important in the control of NLRP3 inflammasome activation/assembly by naloxone. Primary cultured NSCs were subjected to OGD and treated with different concentrations of naloxone. Cell viability, proliferation, and the intracellular signaling proteins associated with the PI3K pathway and NLRP3 inflammasome activation/assembly were evaluated in OGD-injured NSCs. OGD significantly reduced survival, proliferation, and migration and increased apoptosis of NSCs. However, treatment with naloxone significantly restored survival, proliferation, and migration and decreased apoptosis of NSCs. Moreover, OGD markedly increased NLRP3 inflammasome activation/assembly and cleaved caspase-1 and interleukin-1β levels in NSCs, but naloxone significantly attenuated these effects. These neuroprotective and anti-inflammatory effects of naloxone were eliminated when cells were treated with PI3K inhibitors. Our results suggest that NLRP3 inflammasome is a potential therapeutic target and that naloxone reduces ischemic injury in NSCs by inhibiting NLRP3 inflammasome activation/assembly mediated by the activation of the PI3K signaling pathway.

Cardioprotective effect of epigallocatechin gallate in myocardial ischemia/reperfusion injury and myocardial infarction: a meta-analysis in preclinical animal studies

This meta-analysis aims to determine the efficacy of Epigallocatechin gallate (EGCG) in the treatment of myocardial ischemia-reperfusion injury (MIRI) and summarize the mechanisms involved. Literature from six databases including Web of Science, PubMed, Embase, China National Knowledge Infrastructure (CNKI), Wan-Fang database, and VIP database (VIP) were systematically searched. All the analysis were conducted by R. Twenty-five eligible studies involving 443 animals were included in this meta-analysis. The results indicated that compared to controls, EGCG exerts a cardioprotective effect by reducing myocardial infarct size (SMD = -4.06; 95% CI: -5.17, -2.94; P < 0.01; I2 = 77%). The funnel plot revealed publication bias. Moreover, EGCG significantly improves cardiac function, serum myocardial injury enzyme, and oxidative stress levels in MIRI animal models. This meta-analysis demonstrates that EGCG exhibits therapeutic promise in animal models of MIRI. However, further validation is still needed in large animal models and large clinical studies.

The Role of ncRNAs in Cardiac Infarction and Regeneration

Myocardial infarction is the most prevalent cardiovascular disease worldwide, and it is defined as cardiomyocyte cell death due to a lack of oxygen supply. Such a temporary absence of oxygen supply, or ischemia, leads to extensive cardiomyocyte cell death in the affected myocardium. Notably, reactive oxygen species are generated during the reperfusion process, driving a novel wave of cell death. Consequently, the inflammatory process starts, followed by fibrotic scar formation. Limiting inflammation and resolving the fibrotic scar are essential biological processes with respect to providing a favorable environment for cardiac regeneration that is only achieved in a limited number of species. Distinct inductive signals and transcriptional regulatory factors are key components that modulate cardiac injury and regeneration. Over the last decade, the impact of non-coding RNAs has begun to be addressed in many cellular and pathological processes including myocardial infarction and regeneration. Herein, we provide a state-of-the-art review of the current functional role of diverse non-coding RNAs, particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), in different biological processes involved in cardiac injury as well as in distinct experimental models of cardiac regeneration.

Lactate promotes endothelial-to-mesenchymal transition via Snail1 lactylation after myocardial infarction

High levels of lactate are positively associated with the prognosis and mortality in patients with heart attack. Endothelial-to-mesenchymal transition (EndoMT) plays an important role in cardiac fibrosis. Here, we report that lactate exerts a previously unknown function that increases cardiac fibrosis and exacerbates cardiac dysfunction by promoting EndoMT following myocardial infarction (MI). Treatment of endothelial cells with lactate disrupts endothelial cell function and induces mesenchymal-like function following hypoxia by activating the TGF-β/Smad2 pathway. Mechanistically, lactate induces an association between CBP/p300 and Snail1, leading to lactylation of Snail1, a TGF-β transcription factor, through lactate transporter monocarboxylate transporter (MCT)-dependent signaling. Inhibiting Snail1 diminishes lactate-induced EndoMT and TGF-β/Smad2 activation after hypoxia/MI. The MCT inhibitor CHC mitigates lactate-induced EndoMT and Snail1 lactylation. Silence of MCT1 compromises lactate-promoted cardiac dysfunction and EndoMT after MI. We conclude that lactate acts as an important molecule that up-regulates cardiac EndoMT after MI via induction of Snail1 lactylation.

Exercise training maintains cardiovascular health: signaling pathways involved and potential therapeutics

Exercise training has been widely recognized as a healthy lifestyle as well as an effective non-drug therapeutic strategy for cardiovascular diseases (CVD). Functional and mechanistic studies that employ animal exercise models as well as observational and interventional cohort studies with human participants, have contributed considerably in delineating the essential signaling pathways by which exercise promotes cardiovascular fitness and health. First, this review summarizes the beneficial impact of exercise on multiple aspects of cardiovascular health. We then discuss in detail the signaling pathways mediating exercise's benefits for cardiovascular health. The exercise-regulated signaling cascades have been shown to confer myocardial protection and drive systemic adaptations. The signaling molecules that are necessary for exercise-induced physiological cardiac hypertrophy have the potential to attenuate myocardial injury and reverse cardiac remodeling. Exercise-regulated noncoding RNAs and their associated signaling pathways are also discussed in detail for their roles and mechanisms in exercise-induced cardioprotective effects. Moreover, we address the exercise-mediated signaling pathways and molecules that can serve as potential therapeutic targets ranging from pharmacological approaches to gene therapies in CVD. We also discuss multiple factors that influence exercise's effect and highlight the importance and need for further investigations regarding the exercise-regulated molecules as therapeutic targets and biomarkers for CVD as well as the cross talk between the heart and other tissues or organs during exercise. We conclude that a deep understanding of the signaling pathways involved in exercise's benefits for cardiovascular health will undoubtedly contribute to the identification and development of novel therapeutic targets and strategies for CVD.

Clinical assessment and molecular mechanism of the upregulation of Toll-like receptor 2 (TLR2) in myocardial infarction

Objective

The prevalence and mortality of cardiovascular diseases remain ranked first worldwide. Myocardial infarction (MI) is the central cause of death from cardiovascular diseases, seriously endangering human health. The clinical implication of toll-like receptor 2 (TLR2) remains contradictory, and its mechanism is still unknown. Hence, the objective of this study was to elucidate the clinical value and molecular mechanism of TLR2 in MI.

Methods

All high-throughput datasets and eligible literature were screened, and the expression levels of TLR2 were collected from the MI. The integrated expression level of TLR2 was displayed by calculating the standardized mean difference (SMD) and the area under the curve (AUC) of the summary receiver operating characteristic curve (sROC). The related TLR2 genes were sent for pathway analyses by gene ontology (GO), Kyoto encyclopedia of genes and genome (KEGG), and disease ontology (DO). Single-cell RNA-seq was applied to ascertain the molecular mechanism of TLR2 in MI.

Results

Nine microarrays and four reported data were available to calculate the comprehensive expression level of TLR2 in MI, including 325 cases of MI and 306 cases of controls. The SMD was 2.55 (95% CI = 1.35–3.75), and the AUC was 0.76 (95% CI = 0.72–0.79), indicating the upregulation of TLR2 in MI. The related TLR2 genes were primarily enriched in the pathways of atherosclerosis, arteriosclerotic cardiovascular disease, and arteriosclerosis, suggesting the clinical role of TLR2 in the progression of MI. Afterward, TLR2 was upregulated in myeloid cells in MI.

Conclusions

TLR2 may have a crucial role in progressing from coronary atherosclerosis to MI. The upregulation of TLR2 may have a favorable screening value for MI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02754-y.

Potential therapeutic strategies for myocardial infarction: the role of Toll-like receptors

Myocardial infarction (MI) is a life-threatening condition among patients with cardiovascular diseases. MI increases the risk of stroke and heart failure and is a leading cause of morbidity and mortality worldwide. Several genetic and epigenetic factors contribute to the development of MI, suggesting that further understanding of the pathomechanism of MI might help in the early management and treatment of this disease. Toll-like receptors (TLRs) are well-known members of the pattern recognition receptor (PRR) family and contribute to both adaptive and innate immunity. Collectively, studies suggest that TLRs have a cardioprotective effect. However, prolonged TLR activation in the response to signals generated by damage-associated molecular patterns (DAMPs) results in the release of inflammatory cytokines and contributes to the development and exacerbation of myocardial inflammation, MI, ischemia-reperfusion injury, myocarditis, and heart failure. The objective of this review is to discuss and summarize the association of TLRs with MI, highlighting their therapeutic potential for the development of advanced TLR-targeted therapies for MI.

Poly(I:C) attenuates myocardial ischemia/reperfusion injury by restoring autophagic function

Polyinosinic-polycytidylic acid (poly(I:C)) is the agonist of Toll-like receptor 3 (TLR3), which participates in innate immune responses under the condition of myocardial ischemia/reperfusion injury (MIRI). It has been shown that poly(I:C) exhibited cardioprotective activities through the PI3K/Akt pathway, which is the main signal transduction pathway during autophagy. However, the precise mechanism by whether poly(I:C) regulates autophagy remains poorly understood. Thus, this study was designed to investigate the therapeutic effect of poly(I:C) against MIRI and the underlying pathway connection with autophagy. We demonstrated that 1.25 and 5 mg/kg poly(I:C) preconditioning significantly reduced myocardial infarct size and cardiac dysfunction. Moreover, poly(I:C) significantly promoted cell survival by restoring autophagy flux and then regulating it to an adequate level Increased autophagy protein Beclin1 and LC3II together with p62 degradation after additional chloroquine. In addition, mRFP-GFP-LC3 adenoviruses exhibited autophagy activity in neonatal rat cardiac myocytes (NRCMs). Mechanistically, poly(I:C) activated the PI3K/AKT/mTOR pathway to induce autophagy, which was abolished by LY294002 (PI3K antagonist), rapamycin (autophagy activator and mTOR inhibitor), or 3-methyladenine (autophagy inhibitor), suggesting either inhibition of the PI3K/Akt/mTOR pathway or autophagy activity interrupt the beneficial effect of poly(I:C) preconditioning. In conclusion, poly(I:C) promotes cardiomyocyte survival from ischemia/reperfusion injury by regulating autophagy via the PI3K/Akt/mTOR pathway.

Reactive oxygen species-based nanomaterials for the treatment of myocardial ischemia reperfusion injuries

Interventional coronary reperfusion strategies are widely adopted to treat acute myocardial infarction, but morbidity and mortality of acute myocardial infarction are still high. Reperfusion injuries are inevitable due to the generation of reactive oxygen species (ROS) and apoptosis of cardiac muscle cells. However, many antioxidant and anti-inflammatory drugs are largely limited by pharmacokinetics and route of administration, such as short half-life, low stability, low bioavailability, and side effects for treatment myocardial ischemia reperfusion injury. Therefore, it is necessary to develop effective drugs and technologies to address this issue. Fortunately, nanotherapies have demonstrated great opportunities for treating myocardial ischemia reperfusion injury. Compared with traditional drugs, nanodrugs can effectively increase the therapeutic effect and reduces side effects by improving pharmacokinetic and pharmacodynamic properties due to nanodrugs’ size, shape, and material characteristics. In this review, the biology of ROS and molecular mechanisms of myocardial ischemia reperfusion injury are discussed. Furthermore, we summarized the applications of ROS-based nanoparticles, highlighting the latest achievements of nanotechnology researches for the treatment of myocardial ischemia reperfusion injury.

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Cardiovascular diseases are the leading cause of death worldwide. Researches of the myocardial infarction pathology and development of new treatments have very important scientific significance in the biomedical field.

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Many nanomaterials have shown amazing therapeutic effects to reduce myocardial damage by eliminating ROS.

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Nanomaterials effectively reduced myocardial damage through eliminating ROS from NOXs, M-ETC, M-Ca²⁺, M-mPTP, and RIRR.

New Cardiomyokine Reduces Myocardial Ischemia/Reperfusion Injury by PI3K-AKT Pathway Via a Putative KDEL-Receptor Binding

Background CDNF (cerebral dopamine neurotrophic factor) belongs to a new family of neurotrophic factors that exert systemic beneficial effects beyond the brain. Little is known about the role of CDNF in the cardiac context. Herein we investigated the effects of CDNF under endoplasmic reticulum-stress conditions using cardiomyocytes (humans and mice) and isolated rat hearts, as well as in rats subjected to ischemia/reperfusion (I/R). Methods and Results We showed that CDNF is secreted by cardiomyocytes stressed by thapsigargin and by isolated hearts subjected to I/R. Recombinant CDNF (exoCDNF) protected human and mouse cardiomyocytes against endoplasmic reticulum stress and restored the calcium transient. In isolated hearts subjected to I/R, exoCDNF avoided mitochondrial impairment and reduced the infarct area to 19% when administered before ischemia and to 25% when administered at the beginning of reperfusion, compared with an infarct area of 42% in the untreated I/R group. This protection was completely abrogated by AKT (protein kinase B) inhibitor. Heptapeptides containing the KDEL sequence, which binds to the KDEL-R (KDEL receptor), abolished exoCDNF beneficial effects, suggesting the participation of KDEL-R in this cardioprotection. CDNF administered intraperitoneally to rats decreased the infarct area in an in vivo model of I/R (from an infarct area of ≈44% in the I/R group to an infarct area of ≈27%). Moreover, a shorter version of CDNF, which lacks the last 4 residues (CDNF-ΔKTEL) and thus allows CDNF binding to KDEL-R, presented no cardioprotective activity in isolated hearts. Conclusions This is the first study to propose CDNF as a new cardiomyokine that induces cardioprotection via KDEL receptor binding and PI3K/AKT activation.

Pre- and Post-Conditioning of the Heart: An Overview of Cardioprotective Signaling Pathways

Since the discovery of ischemic pre- and post-conditioning, more than 30 years ago, the knowledge about the mechanisms and signaling pathways involved in these processes has significantly increased. In clinical practice, on the other hand, such advancement has yet to be seen. This article provides an overview of ischemic pre-, post-, remote, and pharmacological conditioning related to the heart. In addition, we reviewed the cardioprotective signaling pathways and therapeutic agents involved in the above-mentioned processes, aiming to provide a comprehensive evaluation of the advancements in the field. The advancements made over the last decades cannot be ignored and with the exponential growth in techniques and applications. The future of pre- and post-conditioning is promising.

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

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

RP105 plays a cardioprotective role in myocardial ischemia reperfusion injury by regulating the Toll‑like receptor 2/4 signaling pathways

The revascularization of blood vessels after myocardial infarction can lead to serious myocardial damage. Previous studies showed that radioprotective 105 kDa protein (RP105) is a specific negative regulator of myocardial ischemia reperfusion injury (MIRI). RP105 can modulate the Toll‑like receptor (TLR)2/TLR4 signaling pathways. However, the synergistic effect of TLR2/4 regulated by RP105 during MIRI requires further investigation. To determine this effect, a MIRI model was established in rats in the present study. The expression of RP105 was depleted by transfecting RP105‑siRNA and then detected using western blotting. Furthermore, the myocardium tissue was stained with the hematoxylin and eosin staining. Knockdown of RP105 promoted the activity of serum myocardial enzymes during MIRI and increased myocardial infarction. The present results indicated that knockdown of RP105 activated the TLR2/4 signaling pathway by modulating the myeloid differentiation primary response 88 and NF‑κB signaling pathways. Furthermore, decreased expression of RP105 promoted myocardial cell apoptosis, which induced the damage of myocardial ischemic reperfusion. The present results suggested both TLR2 and TLR4 as key targets of RP105, thus RP105 may be a promising candidate to facilitate the development of novel therapeutic strategies for MIRI.

Rutin Prevents LTA Induced Oxidative Changes in H9c2 Cells

Lipoteichoic acid (LTA), a component of Gram-positive bacteria cell walls is involved in infective endocarditis (IE), a life-threatening disease. We evaluated for the first time, whether flavonoid rutin (quercetin-3-rutinoside) can block LTA-induced pro-inflammatory response and reactive oxygen species (ROS) production, and reduction of antioxidant enzymes. We found that rutin suppresses LTA effects on the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase, as well as the pro-inflammatory enzyme cyclooxygenase-2, preventing phosphorylation of the mitogen-activated protein kinases (MAPKs), p38, and c-Jun N-terminal kinase, and the increase of ROS production induced by LTA. Taken together, these findings suggest that rutin prevents oxidative damage, inflammation, and MAPKs activation induced by LTA. Rutin may exert a protective effect in IE. These data provide novel insights for future use of rutin to prevent the mechanisms of LTA-related pathogenesis, inflammatory processes, and antioxidant enzyme levels in diseases such as IE.

Overexpression of GATA4 enhances the antiapoptotic effect of exosomes secreted from cardiac colony-forming unit fibroblasts via miRNA221-mediated targeting of the PTEN/PI3K/AKT signaling pathway

Background

GATA4 is an early cardiac-specific transcription factor, and endogenous GATA4-positive cells play a critical role in cardioprotection after myocardial injury. As functional paracrine units of therapeutic cells, exosomes can partially reproduce the reparative properties of their parental cells. Here, we investigated the cardioprotective capabilities of exosomes derived from cardiac colony-forming unit fibroblasts (cCFU-Fs) overexpressing GATA4 (cCFU-Fs^GATA4) and the underlying mechanism through which these exosomes use microRNA (miRNA) delivery to regulate target proteins in myocardial infarction (MI).

Methods

Exosomes were harvested from cCFU-Fs by ultracentrifugation. miRNA arrays were performed to determine differential miRNA expression between exosomes derived from cCFU-Fs^GATA4 (GATA4-Exo) and control cCFU-Fs (NC-Exo). A dual-luciferase reporter assay confirmed that miR221 directly targets the 3′ untranslated region (UTR) of the phosphatase and tensin homolog on chromosome ten (PTEN) gene. Cardiac function and myocardial infarct size were evaluated by echocardiography and Masson trichrome staining, respectively.

Results

Compared with NC-Exo, GATA4-Exo increased the survival and reduced the apoptosis of H9c2 cells. Direct intramyocardial transplantation of GATA4-Exo at the border of the ischemic region following ligation of the left anterior descending (LAD) coronary artery significantly restored cardiac contractile function and reduced infarct size. Microarray analysis revealed significantly increased miR221 expression in GATA4-Exo. qPCR confirmed higher miR221 levels in H9c2 cells treated with GATA4-Exo than in those treated with NC-Exo. miR221 mimic-transfected H9c2 cells demonstrated a significantly higher survival rate following exposure to hypoxic conditions than those transfected with miR221 inhibitor. A dual-luciferase reporter gene assay confirmed the PTEN gene as a target of miR221. Western blot analysis showed that H9c2 cells treated with GATA4-Exo exhibited lower PTEN protein expression and higher p-Akt expression.

Conclusion

GATA4 overexpression enhances the protective effect of cCFU-F-derived exosomes on myocardial ischemic injury. In terms of the mechanism, it is at least partly due to the miR221 transferred by GATA4-Exo, which inhibits PTEN expression, activates the phosphatidylinositol 3 kinase (PI3K)/AKT signaling pathway, and subsequently alleviates apoptosis of myocardial cells (CMs).

NLRP3 Inflammasome in Cardioprotective Signaling

The NLRP3 inflammasome may contribute to infarct development during acute cardiac ischemia-reperfusion (IR). Because infarct size strongly correlates with the degree of heart failure in the long term, therapies that reduce reperfusion injury are still needed as first primary care against heart failure development. Inhibition of the NLRP3 inflammasome is currently viewed as such a potential therapy. However, previous research studies directed at inhibition of various inflammatory pathways in acute cardiac IR injury were often disappointing. This is because inflammation is a double-edged sword, detrimental when hyperactive, but beneficial at lower activity, with activity critically dependent on time of reperfusion and cellular location. Moreover, several inflammatory mediators can also mediate cardioprotective signaling. It is reasonable that this also applies to the NLRP3 inflammasome, although current literature has mainly focused on its detrimental effects in the context of acute cardiac IR. Therefore, in this review, we focus on beneficial, cardioprotective properties of the NLRP3 inflammasome and its components NLRP3, ASC, and caspase-1. The results show that (1) NLRP3 deficiency prevents cardioprotection in isolated heart by ischemic preconditioning and in vivo heart by TLR2 activation, associated with impaired STAT3 or Akt signaling, respectively; (2) ASC deficiency also prevents in vivo TLR2-mediated protection; and (3) caspase-1 inhibition results in decreased infarction but impaired protection through the Akt pathway during mild ischemic insults. In conclusion, the NLRP3 inflammasome is not only detrimental, it can also be involved in cardioprotective signaling, thus fueling the future challenge to acquire a full understanding of NLRP3 inflammasome role in cardiac IR before embarking on clinical trials using NLRP3 inhibitors.

Ischemic postconditioning attenuates the inflammatory response in ischemia/reperfusion myocardium by upregulating miR‑499 and inhibiting TLR2 activation

Toll-like receptor 2 (TLR2)-mediated myocardial inflammation serves an important role in promoting myocardial ischemic/reperfusion (I/R) injury. Previous studies have shown that miR-499 is critical for cardioprotection after ischemic postconditioning (IPostC). Therefore, the present study evaluated the protective effect of IPostC on the myocardium by inhibiting TLR2, and also assessed the involvement of microRNA (miR)-499. Rat hearts were subjected to 30 min of ischemia and 2 h of reperfusion. The IPostC was 3 cycles of 30 sec of reperfusion and 30 sec of re-occlusion prior to reperfusion. In total, 90 rats were randomly divided into six groups (n=15 per group): Sham; I/R; IPostC; miR-499 negative control adeno-associated virus (AAV) vectors + IPostC; miR-499 inhibitor AAV vectors + IPostC; and miR-499 mimic AAV vectors + IPostC. It was identified that IPostC significantly decreased the I/R-induced cardiomyocyte apoptotic index (29.4±2.03% in IPostC vs. 42.64±2.27% in I/R; P<0.05) and myocardial infarct size (48.53±2.49% in IPostC vs. 66.52±3.1% in I/R; P<0.05). Moreover, these beneficial effects were accompanied by increased miR-499 expression levels (as demonstrated by reverse transcription-quantitative PCR) in the myocardial tissue and decreased TLR2, protein kinase C (PKC), interleukin (IL)-1β and IL-6 expression levels (as demonstrated by western blotting and ELISA) in the myocardium and serum. The results indicated that IPostC + miR-499 mimics significantly inhibited inflammation and the PKC signaling pathway and enhanced the anti-inflammatory and anti-apoptotic effects of IPostC. However, IPostC + miR-499 inhibitors had the opposite effect. Therefore, it was speculated that IPostC may have a miR-499-dependent cardioprotective effect. The present results suggested that miR-499 may be involved in IPostC-mediated ischemic cardioprotection, which may occur via local and systemic TLR2 inhibition, subsequent inhibition of the PKC signaling pathway and a decrease in inflammatory cytokine release, including IL-1β and IL-6. Moreover, these effects will ultimately lead to a decrease in the myocardial apoptotic index and myocardial infarct size via the induction of the anti-apoptotic protein Bcl-2, and inhibition of the pro-apoptotic protein Bax in myocardium.

TLR (Toll-Like Receptor) 4 Antagonism Prevents Left Ventricular Hypertrophy and Dysfunction Caused by Neonatal Hyperoxia Exposure in Rats

Preterm birth is associated with proinflammatory conditions and alterations in adult cardiac shape and function. Neonatal exposure to high oxygen, a rat model of prematurity-related conditions, leads to cardiac remodeling, fibrosis, and dysfunction. TLR (Toll-like receptor) 4 signaling is a critical link between oxidative stress, inflammation, and the pathogenesis of cardiovascular diseases. The current study sought to investigate the role of TLR4 signaling in neonatal oxygen-induced cardiomyopathy. Male Sprague-Dawley pups were kept in 80% oxygen or room air from day 3 to 10 of life and treated with TLR4 antagonist lipopolysaccharide from the photosynthetic bacterium Rhodobacter sphaeroides(LPS-RS) or saline. Echocardiography was performed at 4, 7, and 12 weeks. At 12 weeks, intraarterial blood pressure was measured before euthanization for histological and biochemical analyses. At day 10, cardiac TLR4, Il (interleukin) 18, and Il1β expression were increased in oxygen-exposed compared with room air controls. At 4 weeks, compared with room air-saline, saline-, but not LPS-RS treated-, oxygen-exposed animals, exhibited increased left ventricle mass index, reduced ejection fraction, and cardiac output index. Findings were similar at 7 and 12 weeks. LPS-RS did not influence echocardiography in 12 weeks room air animals. Systolic blood pressure was higher in saline- but not LPS-RS treated-oxygen-exposed animals compared with room air-saline and -LPS-RS controls. LPS-RS prevented cardiac fibrosis and cardiomyocytes hypertrophy, the increased TLR4, Myd88, and Il18 gene expression, TRIF expression, and CD68+ macrophages infiltration associated with neonatal oxygen exposure, without impact in room air rats. This study indicates that neonatal exposure to high oxygen programs TLR4 activation, which contributes to cardiac remodeling and dysfunction.

Melatonin Attenuates Acute Pancreatitis-Induced Liver Damage Through Akt-Dependent PPAR-γ Pathway

BACKGROUND

Despite melatonin treatment diminishes inflammatory mediator production and improves organ injury after acute pancreatitis (AP), the mechanisms remain unknown. This study explores whether melatonin improves liver damage after AP through protein kinase B (Akt)-dependent peroxisome proliferator activated receptor (PPAR)-γ pathway.

METHODS

Male Sprague-Dawley rats were subjected to cerulein-induced AP. Animals were treated with vehicle, melatonin, and melatonin plus phosphoinositide 3-kinase (PI3K)/Akt inhibitor wortmannin 1 h following the onset of AP. Various indicators and targeted proteins were checked at 8 h in the sham and AP groups.

RESULTS

At 8 h after AP, serum alanine aminotransferase/aspartate aminotransferase levels, histopathology score of hepatic injury, liver myeloperoxidase activity, and proinflammatory cytokine production were significantly increased and liver tissue adenosine triphosphate concentration was lower compared with shams. AP resulted in a marked decrease in liver Akt phosphorylation and PPAR-γ expression in comparison with the shams (relative density, 0.442 ± 0.037 versus. 1.098 ± 0.069 and 0.390 ± 0.041 versus ± 1.080 0.063, respectively). Melatonin normalized AP-induced reduction in liver tissue Akt activation (1.098 ± 0.054) and PPAR-γ expression (1.145 ± 0.083) as well as attenuated the increase in liver injury markers and proinflammatory mediator levels, which was abolished by coadministration of wortmannin.

CONCLUSIONS

Collectively, our findings suggest that melatonin improves AP-induced liver damage in rats, at least in part, via Akt-dependent PPAR-γ pathway.

Impact of miR-223-3p and miR-2909 on inflammatory factors IL-6, IL-1ß, and TNF-α, and the TLR4/TLR2/NF-κB/STAT3 signaling pathway induced by lipopolysaccharide in human adipose stem cells

MicroRNAs (miRNAs) are small non-coding RNA molecules that play an important role in the regulation of gene expression related to inflammatory responses. Human adipose stem cells are characterized by pluripotent differentiation potential and isolated from adipose tissues. These cells regulate inflammation mainly by interacting with immune cells and affecting the secretion of immune factors; details of this interaction are currently unknown. In the current study, we successfully established an acute inflammation model and a chronic inflammation model involving adipose stem cells. We used high-throughput miRNA microarray analysis to identify miRNAs that were significantly (p < 0.05) differentially expressed during both acute and chronic inflammation. Lipopolysaccharide (LPS) significantly (p < 0.05) reduced the expression of miR-223-3P and miR-2909, while promoting the production of pro-inflammatory cytokines, interleukin (IL) 6, IL-1β, and tumor necrosis factor (TNF)-α via the Toll-like receptor (TLR) 4/TLR2/nuclear factor (NF)-κB/signal transducer and activator of transcription (STAT) 3 signaling pathway in human adipose stem cells. Further, miR-223-3P expression was significantly (p < 0.05) reduced in human adipose stem cells during activation by IL-6 stimulation. The inducible down-regulation of miR-223-3P resulted in the activation of STAT3, which was directly targeted by miR-223-3P. STAT3 directly targeted TLR4 and TLR2, promoting the production of the pro-inflammatory cytokine, IL-6, and formed a positive feedback loop to regulate IL-6 levels. Similarly, TNF-α significantly (p < 0.05) increased the expression of miR-223-3p, with LPS and TLR4/TLR2/NF-κB/STAT3 forming a negative feedback loop to regulate TNF-α levels. In addition, miR-2909, which depends on NF-κB, targeted Krueppel-like factor (KLF) 4 to regulate the levels of pro-inflammatory cytokines, IL-6, IL-1β, and TNF-α. We conclude that miR-223-3p and miR-2909 form a complex regulatory network with pro-inflammatory factors and signaling pathways in adipose stem cells stimulated by LPS. These findings will inform the development of therapies against autoimmune and inflammatory diseases.

Exogenous IL-19 attenuates acute ischaemic injury and improves survival in male mice with myocardial infarction

BACKGROUND AND PURPOSE

Myocardial infarction (MI) is one of the leading causes of death in China and often results in the development of heart failure. In this work, we tested the therapeutic role of Interleukin-19 (IL-19) in mice with MI and investigated the underlying molecular mechanism.

EXPERIMENTAL APPROACH

Mice were subjected to MI by ligation of left anterior descending coronary artery (LAD) and treated with IL-19 (10ng g^-1 ; i.p.).

KEY RESULTS

Protein expression of IL-19 and its receptor in myocardium were upregulated 24 hrs post-MI in male mice. IL-19 treatment decreased infarct and apoptosis in myocardium, accompanied by enhanced haem oxygenase-1 (HO-1) activities and reduced malondialdehyde (MDA) formation. Pretreatment with IL-19 upregulated HO-1 expression in cultured neonatal mouse ventricular myocytes and attenuated oxygen-glucose deprivation (OGD)-induced injuries in vitro. Furthermore, IL-19 preserved cardiac function and improved survival of mice with MI. IL-19 reduced inflammatory infiltrates and suppressed formation of TNF-α, IL-1β, and IL-6. More importantly, IL-19 inhibited polarization toward proinflammatory M1 macrophages and stimulated M2 macrophage polarization in myocardium of mice with MI. IL-19 enhanced protein levels of vascular endothelial growth factor (VEGF) and promoted angiogenesis in myocardium of mice with MI. In addition, IL-19 treatment increased DNA-binding of the transcription factor STAT3 in myocardium of mice with MI.

CONCLUSIONS AND IMPLICATIONS

Treatment with exogenous IL-19 attenuated acute ischemic injury and improved survival of mice with MI. The mechanisms underlying these effects involved induction of HO-1, M2 macrophage polarization, angiogenesis, and STAT3 activation.

Cyanidin attenuates Aβ25-35-induced neuroinflammation by suppressing NF-κB activity downstream of TLR4/NOX4 in human neuroblastoma cells

Cyanidin is polyphenolic pigment found in plants. We have previously demonstrated that cyanidin protects nerve cells against Aβ_25-35-induced toxicity by decreasing oxidative stress and attenuating apoptosis mediated by both the mitochondrial apoptotic pathway and the ER stress pathway. To further elucidate the molecular mechanisms underlying the neuroprotective effects of cyanidin, we investigated the effects of cyanidin on neuroinflammation mediated by the TLR4/NOX4 pathway in Aβ_25-35-treated human neuroblastoma cell line (SK-N-SH). SK-N-SH cells were exposed to Aβ_25-35 (10 μmol/L) for 24 h. Pretreatment with cyanidin (20 μmol/L) or NAC (20 μmol/L) strongly inhibited the NF-κB signaling pathway in the cells evidenced by suppressing the degradation of IκBα, translocation of the p65 subunit of NF-κB from the cytoplasm to the nucleus, and thereby reducing the expression of iNOS protein and the production of NO. Furthermore, pretreatment with cyanidin greatly promoted the translocation of the Nrf2 protein from the cytoplasm to the nucleus; upregulating cytoprotective enzymes, including HO-1, NQO-1 and GCLC; and increased the activity of SOD enzymes. Pretreatment with cyanidin also decreased the expression of TLR4, directly improved intracellular ROS levels and regulated the activity of inflammation-related downstream pathways including NO production and SOD activity through TLR4/NOX4 signaling. These results demonstrate that TLR4 is a primary receptor in SK-N-SH cells, by which Aβ_25-35 triggers neuroinflammation, and cyanidin attenuates Aβ-induced inflammation and ROS production mediated by the TLR4/NOX4 pathway, suggesting that inhibition of TLR4 by cyanidin could be beneficial in preventing neuronal cell death in the process of Alzheimer's disease.

MicroRNA-214 protects against hypoxia/reoxygenation induced cell damage and myocardial ischemia/reperfusion injury via suppression of PTEN and Bim1 expression

BACKGROUND

Myocardial apoptosis plays an important role in myocardial ischemia/reperfusion (I/R) injury. Activation of PI3K/Akt signaling protects the myocardium from I/R injury. This study investigated the role of miR-214 in hypoxia/reoxygenation (H/R)-induced cell damage in vitro and myocardial I/R injury in vivo.

METHODS AND RESULTS

H9C2 cardiomyoblasts were transfected with lentivirus expressing miR-214 (LmiR-214) or lentivirus expressing scrambled miR-control (LmiR-control) respectively, to establish cell lines of LmiR-214 and LmiR-control. The cells were subjected to hypoxia for 4 h followed by reoxygenation for 24 h. Transfection of LmiR-214 suppresses PTEN expression, significantly increases the levels of Akt phosphorylation, markedly attenuates LDH release, and enhances the viability of the cells subjected to H/R. In vivo transfection of mouse hearts with LmiR-214 significantly attenuates I/R induced cardiac dysfunction and reduces I/R-induced myocardial infarct size. LmiR-214 transfection significantly attenuates I/R-induced myocardial apoptosis and caspase-3/7 and caspase-8 activity. Increased expression of miR-214 by transfection of LmiR-214 suppresses PTEN expression, increases the levels of phosphorylated Akt, represses Bim1 expression and induces Bad phosphorylation in the myocardium. In addition, in vitro data shows transfection of miR-214 mimics to H9C2 cells suppresses the expression and translocation of Bim1 from cytosol to mitochondria and induces Bad phosphorylation.

CONCLUSIONS

Our in vitro and in vivo data suggests that miR-214 protects cells from H/R induced damage and attenuates I/R induced myocardial injury. The mechanisms involve activation of PI3K/Akt signaling by targeting PTEN expression, induction of Bad phosphorylation, and suppression of Bim1 expression, resulting in decreases in I/R-induced myocardial apoptosis.

The role and difference of TLR2 and TLR4 in rhabdomyolysis induced acute kidney injury in mice

To investigate the role of toll like receptors (TLRs) 2 and 4 in rhabdomyolysis (RM)-related acute kidney injury (AKI). Wild-type (WT) mice and TLR2 knockout (TLR2^-/-) or TLR4 knockout (TLR4^-/-) mice were injected with either saline (sham) or glycerin (to induce RM-related AKI). Samples were collected for detection of 0 h 24 h (Cr) creatinine, urea nitrogen (BUN), creatine kinase (CK), and PAS staining of renal tissues. Serum Cr and BUN level was significantly increased in TLR2^-/- and TLR4^-/-AKI groups more than those in the control group and the WT mice in AKI group. TLR4^-/-AKI group Cr, BUN level, and the pathological damage was lightest. The expression levels of signal transduction proteins in TLR2^-/- and TLR4^-/-AKI group were higher than in the control group, but was lower than that in the wild AKI group, with the TLR4^-/-AKI group having the lowest levels. The expression level of inflammatory factor mRNA in TLR2^-/- and TLR4^-/-AKI groups was higher than that in control group, but was lower than that in wild AKI group, with TLR4^-/-AKI group displaying lowest levels. Knockout of TLRs 2 and 4 decreased kidney inflammation and improved RM-related AKI.

CRISPR-Cas9 mediated gene knockout in human coronary artery endothelial cells reveals a pro-inflammatory role of TLR2

Endothelial inflammatory responses promote the development and progression of atherosclerosis. It was reported that Toll-like receptors 2 (TLR2) is associated with endothelial inflammation. However, the effect of TLR2 on inflammatory responses in human coronary artery endothelial cells (HCAECs) remains largely unknown. Here, we tested the hypothesis that TLR2 can enhance inflammatory reactions in HCAECs after stimulated by TLR2 agonist. First, we used CRISPR-Cas9 technology to knockout TLR2 gene in HCAECs. Then, TLR2-KO and wild type HCAECs were treated with TLR2 agonist peptidoglycan (PGN). The expression levels of intercellular cell adhesion molecule-1 (ICAM-1), interleukin-6 (IL-6), and interleukin-8 (IL-8) were analyzed by real-time PCR, Western blot, and ELISA. The expression status of myeloid differentiation primary response gene 88 (MyD88), phosphorylated IRAK-1 (pIRAK-1) and phosphorylated NF-κB (pNF-κB) were detected by Western blot. Our results show that after treated with TLR2 agonist, the expression levels of ICAM-1, IL-6, and IL-8 were downregulated in TLR2-KO cells compared to those of wild type cells. Further, Western blots of MyD88, pIRAK-1, and pNF-κB show that the expression levels of these pro-inflammatory molecules were much lower in TLR2-KO cells compared to that of wild type cells by stimulating with TLR2 agonist. We suggest that TLR2 may affect inflammatory reaction in HCAECs by introducing pro-inflammatory molecules like MyD88, pIRAK-1, and pNF-κB.

Systemic TLR2 Antibody Application in Renal Ischaemia and Reperfusion Injury Decreases AKT Phosphorylation and Increases Apoptosis in the Mouse Kidney

Acute kidney injury remains an important cause of renal dysfunction. In this context, Toll-like receptors have been demonstrated to play a critical role in the induction of innate and inflammatory responses. Among these, Toll-like receptor 2 (TLR2) is constitutively expressed in tubular epithelial cells (TECs) of the kidney and is also known to mediate ischaemia reperfusion (IR) injury. Adult male C57BL/6JRj mice were randomized into seven groups (n = 8): a non-operative control group (CTRL) and six interventional groups in which mice were subjected to a 30 min. bilateral renal ischaemia. Immediately before reperfusion, mice were treated either with saline or with TLR2 antibody (clone T2.5) and harvested after ischaemia and reperfusion for 3, 24 and 48 hr. Analysed kidney homogenates of TLR2 antibody-treated mice displayed significantly decreased levels of TLR2 protein after 3 hr of IR compared to saline-treated mice. Accordingly, the degree of AKT phosphorylation was significantly decreased after 3 hr of IR compared to saline-treated animals. TUNEL staining revealed significantly higher apoptosis rates in TLR2 antibody-treated animals compared to saline-treated mice after 3 and 24 hr of IR. Further, a positive correlation between TLR2 protein expression and phosphorylation of AKT as well as a negative correlation with the number of TUNEL-positive cells could be observed. Inhibition of TLR2 and its signalling pathway by a single application of TLR2 antibody results in reduced phosphorylation of AKT and consecutively increased apoptosis.

Cardioprotective Effects of HuoxueAnshen Recipe against Myocardial Injuries Induced by Sleep Deprivation in Rats

Background. Traditional Chinese Medicine is extensively used in China and HuoxueAnshen Recipe (HAR) was formulated according to its method in treating CHD accompanied with insomnia in clinic. However, there are few studies related to the effect of HAR on myocardial injury and sleep disorders. Purpose. To investigate the effects of HAR on sleep deprivation- (SD-) induced myocardial I/R injury. Methods. Male Wistar rats receiving a daily gavage of HAR or vehicle were exposed to SD intervention while control rats had normal sleep. Then all rats were exposed to myocardial I/R. Hormone, vascular endothelial, and inflammatory related factors were detected before and after I/R, while cardiac injury, cardiac function, myocardial infarct size, and apoptosis were detected after I/R. Results. Levels of neuropeptide Y, vascular endothelial and inflammatory related factors were significantly increased while melatonin was decreased in vehicle-treated SD rats but not in HAR-treated SD rats after SD. In addition, cardiac injury, cardiac dysfunction, myocardial infarct size, and myocardial apoptosis were deteriorated in vehicle-treated SD rats but were ameliorated in HAR-treated SD rats after I/R. Conclusion. HAR not only improved SD-induced hormone disorders, inflammation, and endothelial dysfunction, but also alleviated I/R injury, which supports protective usage in CHD and psychocardiology.

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.

Cobalt chloride induces RhoA/ROCK activation and remodeling effect in H9c2 cardiomyoblasts: Involvement of PI3K/Akt and MAPK pathways

Chronic heart failure is a serious complication of myocardial infarction, one of the major causes of death worldwide that often leads to adverse cardiac hypertrophy and poor prognosis. Hypoxia-induced cardiac tissue remodeling is considered an important underlying etiology. This study aimed to delineate the signaling profiles of RhoA/ROCK, PI3K/Akt, and MAPK and their involvement in regulation of remodeling events in cultured H9c2 cardiomyoblast cells. In addition to its growth-suppressive effect, the hypoxia-mimetic chemical, cobalt chloride (CoCl₂) significantly induced RhoA kinase activation as revealed by increased MBS phosphorylation and ROCK1/2 expression in H9c2 cells. CoCl₂ treatment up-regulated type I collagen and MMP-9, but did not affect MMP-2, implicating its role in tissue remodeling. Kinetic signal profiling study showed that CoCl₂ also elicited Smad2 hyperphosphorylation and its nuclear translocation in the absence of TGF-β1. In addition, CoCl₂ activated Akt-, ERK1/2-, JNK-, and p38 MAPK-mediated signaling pathways. Kinase inhibition experiments demonstrated that hydroxyfasudil, a RhoA kinase inhibitor, significantly blocked the CoCl₂- and lysophosphatidic acid-evoked Smad2 phosphorylation and overexpression of type I collagen and MMP-9, and that PI3K and ERK interplayed with RhoA and its downstream Smad2 signaling cascade. In conclusion, this study demonstrated that RhoA/ROCK, PI3K/Akt, and MAPK pathways are mechanistically involved in the CoCl₂-stimulated tissue remodeling in H9c2 cardiomyoblast cells. Targeting signaling mediators might be used to mitigate hypoxia-related Smad2 phosphorylation and cardiac remodeling events in ischemic cardiomyopathy.

Biological Effect of Licochalcone C on the Regulation of PI3K/Akt/eNOS and NF-κB/iNOS/NO Signaling Pathways in H9c2 Cells in Response to LPS Stimulation

Polyphenols compounds are a group molecules present in many plants. They have antioxidant properties and can also be helpful in the management of sepsis. Licochalcone C (LicoC), a constituent of Glycyrrhiza glabra, has various biological and pharmacological properties. In saying this, the effect of LicoC on the inflammatory response that characterizes septic myocardial dysfunction is poorly understood. The aim of this study was to determine whether LicoC exhibits anti-inflammatory properties on H9c2 cells that are stimulated with lipopolysaccharide. Our results have shown that LicoC treatment represses nuclear factor-κB (NF-κB) translocation and several downstream molecules, such as inducible nitric oxide synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). Moreover, LicoC has upregulated the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/endothelial nitric oxide synthase (eNOS) signaling pathway. Finally, 2-(4-Morpholinyl)-8-phenyl-1(4H)-benzopyran-4-one hydrochloride (LY294002), a specific PI3K inhibitor, blocked the protective effects of LicoC. These findings indicate that LicoC plays a pivotal role in cardiac dysfunction in sepsis-induced inflammation.

Involvement of Toll Like Receptor 2 Signaling in Secondary Injury during Experimental Diffuse Axonal Injury in Rats

Treatment of diffuse axonal injury (DAI) remains challenging in clinical practice due to the unclear pathophysiological mechanism. Uncontrolled, excessive inflammation is one of the most recognized mechanisms that contribute to the secondary injury after DAI. Toll like receptor 2 (TLR2) is highlighted for the initiation of a vicious self-propagating inflammatory circle. However, the role and detailed mechanism of TLR2 in secondary injury is yet mostly unknown. In this study, we demonstrated the expression of TLR2 levels in cortex, corpus callosum, and internal capsule and the localization of TLR2 in neurons and glial cells in rat DAI models. Intracerebral knockdown of TLR2 significantly downregulated TLR2 expression, attenuated cortical apoptosis, lessened glial response, and reduced the secondary axonal and neuronal injury in the cortex by inhibiting phosphorylation of mitogen-activated protein kinases (MAPK) including Erk, JNK, and p38, translocation of NF-κB p65 from the cytoplasm to the nucleus, and decreasing levels of proinflammatory cytokines including interleukin-6, interleukin-1β, and tumor necrosis factor-α. On the contrary, administration of TLR2 agonist to DAI rats achieved an opposite effect. Collectively, we demonstrated that TLR2 was involved in mediating secondary injury after DAI by inducing inflammation via the MAPK and NF-κB pathways.

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

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

The cytoprotective effect of biglycan core protein involves Toll-like receptor 4 signaling in cardiomyocytes

AIMS

Exogenously administered biglycan (core protein with high-molecular weight glycosaminoglycan chains) has been shown to protect neonatal cardiomyocytes against simulated ischemia/reperfusion injury (SI/R), however, the mechanism of action is not clear. In this study we aimed to investigate, which structural component of biglycan is responsible for its cardiocytoprotective effect and to further explore the molecular mechanisms involved in the cytoprotection.

METHODS AND RESULTS

A pilot study was conducted to demonstrate that both native (glycanated) and deglycanated biglycan can attenuate cell death induced by SI/R in a dose-dependent manner in primary neonatal cardiomyocytes isolated from Wistar rats. In separate experiments, we have shown that similarly to glycanated biglycan, recombinant human biglycan core protein (rhBGNc) protects cardiomyocytes against SI/R injury. In contrast, the glycosaminoglycan component dermatan sulfate had no significant effect on cell viability, while chondroitin sulfate further enhanced cell death induced by SI/R. Treatment of cardiomyocytes with rhBGNc reverses the effect of SI/R upon markers of necrosis, apoptosis, mitochondrial membrane potential, and autophagy. We have also shown that pharmacological blockade of Toll-like receptor 4 (TLR4) signaling or its downstream mediators (IRAK1/4, ERK, JNK and p38 MAP kinases) abolished the cytoprotective effect of rhBGNc against SI/R injury. Pretreatment of cardiomyocytes with rhBGNc for 20h resulted in increased Akt phosphorylation and NO production without having significant effect on phosphorylation of ERK1/2, STAT3, and on the production of superoxide. Treatment over 10min and 1h with rhBGNc increased ERK1 phosphorylation, while the SI/R-induced increase in superoxide production was attenuated by rhBGNc. Blockade of NO synthesis also prevented the cardiocytoprotective effect of rhBGNc.

CONCLUSIONS

The core protein of exogenous biglycan protects myocardial cells from SI/R injury via TLR4-mediated mechanisms involving activation of ERK, JNK and p38 MAP kinases and increased NO production. The cytoprotective effect of rhBGNc is due to modulation of SI/R-induced changes in necrosis, apoptosis and autophagy.

Epigallocatechin gallate exerts protective effects against myocardial ischemia/reperfusion injury through the PI3K/Akt pathway-mediated inhibition of apoptosis and the restoration of the autophagic flux

Epigallocatechin gallate (EGCG), a polyphenol derived from green tea, exhibits a wide range of biological activities, including antioxidant, atherosclerosis and antitumor activities. In this study, the cardioprotective effects of EGCG on myocardial ischemia/reperfusion (I/R) injury in rats and the underlying mechanisms were investigated. A rat model of I/R injury was established by ligating the left anterior descending coronary artery for 30 min, followed by reperfusion for 2 h. The levels of I/R-induced creatine kinase-MB (CK-MB) and the release of lactate dehydrogenase (LDH), as well as the infarct size, cardiomyocyte apoptosis and cardiac functional impairment were examined and compared. Western blot analysis was carried out to elucidate the potential molecular mechanisms of action of EGCG. The results revealed that EGCG post-conditioning significantly decreased the levels of CK-MB and the release of LDH, reduced the myocardial infarct size, decreased the apoptotic rate and partially preserved heart function. Furthermore, EGCG decreased the expression of cleaved caspase-3 concomitantly with the upregulation of PI3K, and the phosphorylation of Akt and endothelial nitric oxide synthase (eNOS). It also inhibited I/R-induced overautophagy and promoted the clearance of autophagosomes, as evidenced by a decrease in the ratio of microtubule-associated protein 1 light chain 3 (LC3)-II/LC3-I, the downregulation of Beclin1, Atg5 and p62, and the upregulation of active cathepsin D. Additionally, we observed an increase in the phosphorylation levels of the mammalian target of rapamycin (mTOR) following treatment with EGCG. Taken together, the findings of this study demonstrate that, EGCG post-conditioning alleviates myocardial I/R injury by inhibiting apoptosis and restoring the autophagic flux, which is associated with several targets of the PI3K/Akt signaling pathway.

Heat-killed Staphylococcus aureus reduces atherosclerosis by inducing anti-inflammatory macrophages

BACKGROUND

Staphylococcus aureus cell wall components can induce IL-10 responses by immune cells, which may be atheroprotective. Therefore, in this study, we investigated whether heat-killed S. aureus (HK-SA) could inhibit the development of atherosclerosis.

METHODS

Atherosclerosis-susceptible LDL receptor-deficient mice were administered intraperitoneal HK-SA twice weekly and fed a Western-type diet for 6 weeks.

RESULTS

HK-SA administration resulted in a 1.6-fold increase in IL-10 production by peritoneal macrophages and splenocytes, and a 12-fold increase in serum IL-10 levels. Moreover, aortic plaque ICAM-1, VCAM-1 and CCL2 expression levels were significantly downregulated by on average 40%. HK-SA-treated mice had reduced numbers of inflammatory Ly-6C(hi) monocytes as well as Th1 and Th17 cells in the circulation and spleen, respectively. Attenuated leucocyte recruitment resulted in a significant inhibition of macrophage and T cell infiltration in atherosclerotic plaques, culminating in a significant 34% reduction in the development of atherosclerosis. To determine the effects of intraperitoneal HK-SA treatment, we stimulated macrophages with HK-SA in vitro. This resulted in a significant toll-like receptor 2 (TLR2)-dependent increase in IL-10, arginase-1, iNOS, TNF-α, PD-L1, CCL22 and indoleamine 2,3-dioxygenase expression. It was found that phosphoinositide 3-kinase crucially determined the balance of pro- and anti-inflammatory gene expression. The HK-SA-induced macrophage phenotype resembled M2b-like immunoregulatory macrophages.

CONCLUSIONS

We have shown that HK-SA treatment induces strong anti-inflammatory IL-10 responses by macrophages, which are largely dependent on TLR2 and PI3K, and protects against the development of atherosclerosis. Commensalism with S. aureus could thus reduce cardiovascular events.

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.

NLRP3 inflammasome activation during myocardial ischemia reperfusion is cardioprotective

BACKGROUND

The innate immune receptor NLRP3 recognizes tissue damage and initiates inflammatory processes through formation multiprotein complexes with the adaptor protein ASC and caspase-1, i.e. NLRP3 inflammasomes, which through cleavage of pro-IL-1β mediates release of bioactive IL-1β. We hypothesized that NLRP3 mediates tissue damage during acute myocardial infarction (MI) and sought to investigate the mechanisms herein in an experimental MI model in mice.

METHODS AND RESULTS

The left coronary artery (LCA) of WT, NLRP3(-/-) and ASC(-/-) mice of both genders was ligated for 30 min followed by 3 or 24 h reperfusion. For pre-conditioning studies, the TLR2 agonist Pam3CSK4 or PBS was injected intraperitoneally 60 min prior to LCA ligation. For mechanistic investigations, blood plasmas and left ventricle tissues were collected, and a hypothesis-driven selection of protein or mRNA targets was investigated. Surprisingly, hearts from NLRP3-deficient mice featured larger infarct size than WT mice (p = 0.0048). In general, there were only modest changes with no significant pattern in myocardial infiltration of neutrophils and macrophages and systemic and myocardial cytokine expression between the three genotypes. Preconditioning with the TLR2 agonist Pam3CSK4 induced Akt phosphorylation and reduced infarct size in WT but not NLRP3 -or ASC -deficient hearts.

CONCLUSION

Absence of NLRP3 results in increased myocardial infarct size after in vivo ischemia reperfusion, seemingly due to dysfunction of the cardioprotective RISK pathway. Our data imply that NLRP3 contributes to cardio-protection during I/R and do not support a role for NLRP3 or ASC inhibition in the management of acute MI including revascularization therapy.

Attenuation of cardiac dysfunction and remodeling of myocardial infarction by microRNA-130a are mediated by suppression of PTEN and activation of PI3K dependent signaling

OBJECTIVE

Activation of PI3K/Akt signaling protects the myocardium from ischemia/reperfusion injury. MicroRNAs have been demonstrated to play an important role in the regulation of gene expression at the post-transcriptional level. In this study, we examined whether miR-130a will attenuate cardiac dysfunction and remodeling after myocardial infarction (MI) via PI3K/Akt dependent mechanism.

APPROACHES AND RESULTS

To determine the role of miR-130a in the proliferation and migration of endothelial cells, HUVECs were transfected with miR-130a mimics before the cells were subjected to scratch-induced wound injury. Transfection of miR-130a mimics stimulated the migration of endothelial cells into the wound area and increased phospho-Akt levels. To examine the effect of miR-130a on cardiac dysfunction and remodeling after MI, Lentivirus expressing miR-130a (LmiR-130a) was delivered into mouse hearts seven days before the mice were subjected to MI. Cardiac function was assessed by echocardiography before and for up to 21 days after MI. Ejection fraction (EF%) and fractional shortening (FS%) in the LmiR-130a transfected MI hearts were significantly greater than in LmiR-control and untransfected control MI groups. LmiR-130a transfection increased capillary number and VEGF expression, and decreased collagen deposition in the infarcted myocardium. Importantly, LmiR-130a transfection significantly suppressed PTEN expression and increased the levels of phosphorylated Akt in the myocardium. However, treatment of LmiR-130a-transfected mice with LY294002, a PI3K inhibitor, completely abolished miR-130a-induced attenuation of cardiac dysfunction after MI.

CONCLUSIONS

miR-130a plays a critical role in attenuation of cardiac dysfunction and remodeling after MI. The mechanisms involve activation of PI3K/Akt signaling via suppression of PTEN expression.

Peptidoglycan Up-Regulates CXCL8 Expression via Multiple Pathways in Monocytes/Macrophages

Peptidoglycan (PG), the gram positive bacterial pathogen-associated molecular patterns (PAMP), is detected in a high proportion in macrophage-rich atheromatous regions, and expression of chemokine CXCL8, which triggers monocyte arrest on early atherosclerotic endothelium, is elevated in monocytes/macrophages in human atherosclerotic lesion. The aim of this study was to investigate whether PG induced CXCL8 expression in the cell type and to determine cellular signaling pathways involved in that process. Exposure of THP-1 cell, human monocyte/macrophage cell line, to PG not only enhanced CXCL8 release but also profoundly induced il8 gene transcription. PG-induced release of CXCL8 and induction of il8 gene transcription were blocked by OxPAPC, an inhibitor of TLR-2/4 and TLR4, but not by polymyxin B, an inhibitor of LPS. PG-mediated CXCL8 release was significantly attenuated by inhibitors of PI3K-Akt-mTOR pathways. PKC inhibitors, MAPK inhibitors, and ROS quenchers also significantly attenuated expression of CXCL8. The present study proposes that PG contributes to inflammatory reaction and progression of atherosclerosis by inducing CXCL8 expression in monocytes/macrophages, and that TLR-2, PI3K-Akt-mTOR, PKC, ROS, and MAPK are actively involved in the process.

TLR4 Deters Perfusion Recovery and Upregulates Toll-like Receptor 2 (TLR2) in Ischemic Skeletal Muscle and Endothelial Cells

Toll-like receptors (TLRs) play an important role in regulating muscle regeneration and angiogenesis in response to ischemia. TLR2 knockout mice exhibit pronounced skeletal muscle necrosis and abnormal vessel architecture after femoral artery ligation, suggesting that TLR2 signaling is protective during ischemia. TLR4, an important receptor in inflammatory signaling, has been shown to regulate TLR2 expression in other systems. We hypothesize that a similar relationship between TLR4 and TLR2 may exist in hindlimb ischemia in which TLR4 upregulates TLR2, a mediator of angiogenesis and perfusion recovery. We examined the expression of TLR2 in unstimulated and in TLR-agonist treated endothelial cells (ECs). TLR2 expression (low in control ECs) was upregulated by lipopolysaccharide, the danger signal high mobility group box-1, and hypoxia in a TLR4-dependent manner. Endothelial tube formation on Matrigel as well as EC permeability was assessed as in vitro measures of angiogenesis. Time-lapse imaging demonstrated that ECs lacking TLR4 formed more tubes, whereas TLR2 knockdown ECs exhibited attenuated tube formation. TLR2 also mediated EC permeability, an initial step during angiogenesis, in response to high-mobility group box-1 (HMGB1) that is released by cells during hypoxic injury. In vivo, ischemia-induced upregulation of TLR2 required intact TLR4 signaling that mediated systemic inflammation, as measured by local and systemic IL-6 levels. Similar to our in vitro findings, vascular density and limb perfusion were both enhanced in the absence of TLR4 signaling, but not if TLR2 was deleted. These findings indicate that TLR2, in the absence of TLR4, improves angiogenesis and perfusion recovery in response to ischemia.