Is there a role for cardiomyocyte toll-like receptor 4 in endotoxemia?

Long noncoding RNA MCM3AP-AS1 attenuates sepsis-induced cardiomyopathy by improving inflammation, oxidative stress, and mitochondrial function through mediating the miR-501-3p/CADM1/STAT3 axis

Oxidative stress and inflammation are highly important for sepsis-mediated myocardial damage. The long noncoding RNA (lncRNA) MCM3AP-AS1 is involved in inflammatory diseases, but its function in acute myocardial injury during sepsis has not been fully elucidated. LPS and cecal ligation and puncture (CLP) were used to construct in vitro and in vivo sepsis-induced myocardial damage models, respectively. qRT-PCR was used to evaluate alterations in MCM3AP-AS1 and miR-501-3p alterations. After the MCM3AP-AS1 and miR-501-3p knockdown or overexpression models were established, the viability, apoptosis, inflammation, oxidative stress, and mitochondrial function of the myocardial cells were examined. Dual luciferase activity assay, RNA immunoprecipitation, and fluorescence in situ hybridization (FISH) confirmed the correlation among MCM3AP-AS1, miR-501-3p, and CADM1. Previous studies revealed that MCM3AP-AS1 was downregulated in sepsis patients, myocardial cells treated with LPS, and in the CLP mouse sepsis model, whereas miR-501-3p expression was increased. MCM3AP-AS1 overexpression hampered myocardial damage mediated by LPS and abated inflammation, oxidative stress, and mitochondrial dysfunction in myocardial cells and THP-1 cells. In contrast, MCM3AP-AS1 knockdown or miR-501-3p overexpression promoted all the effects of LPS. In vivo, MCM3AP-AS1 overexpression increased the survival rate of CLP mice; ameliorated myocardial injury; decreased the levels of TNF-α, IL-1β, IL-6, iNOS, COX2, ICAM1, VCAM1, PGE2, and MDA; and increased the levels of SOD, GSH-PX, Nrf2, and HO-1. Mechanistic studies demonstrated that MCM3AP-AS1 acted as a competitive endogenous RNA to repress miR-501-3p, enhance CADM1 expression, and dampen STAT3/nuclear factor-kappaB (NF-κB) activation. MCM3AP-AS1 suppresses myocardial injury elicited by sepsis by mediating the miR-501-3p/CADM1/STAT3/NF-κB axis.

Songorine promotes cardiac mitochondrial biogenesis via Nrf2 induction during sepsis

Septic cardiomyopathy is characterized by impaired contractive function with mitochondrial dysregulation. Songorine is a typical active C₂₀-diterpene alkaloid from the lateral root of Aconitum carmichaelii, which has been used for the treatment of heart failure. This study investigated the protective role of songorine in septic heart injury from the aspect of mitochondrial biogenesis. Songorine (10, 50 mg/kg) protected cardiac contractive function against endotoxin insult in mice with Nrf2 induction. In cardiomyocytes, lipopolysaccharide (LPS) evoked mitochondrial reactive oxygen species (ROS) production and redistributed STIM1 to interact with Orai1 for the formation of calcium release-activated calcium (CRAC) channels, mediating calcium influx, which were prevented by songorine, likely due to ROS suppression. Songorine activated Nrf2 by promoting Keap1 degradation, having a contribution to enhancing antioxidant defenses. When LPS shifted metabolism away from mitochondrial oxidative phosphorylation (OXPHOS) in cardiomyocytes, songorine upregulated mitochondrial genes involved in fatty acid β-oxidation, tricarboxylic acid (TCA) cycle and electron transport chain in a manner dependent on Nrf2, resultantly protecting the capability of OXPHOS. Songorine increased luciferase report gene activities of nuclear respiratory factor-1 (Nrf1) and mitochondrial transcription factor A (Tfam) dependently on Nrf2, indicative of the regulation of Nrf2/ARE and NRF1 signaling cascades. Songorine promoted PGC-1α binding to Nrf2, and the cooperation was required for songorine to activate Nrf2/ARE and NRF1 for the control of mitochondrial quality and quantity. In support, the beneficial effects of songorine on cardioprotection and mitochondrial biogenesis were diminished by cardiac Nrf2 deficiency in mice subjected to LPS challenge. Taken together, these results showed that Nrf2 transcriptionally promoted mitochondrial biogenesis in cooperation with PGC-1α. Songorine activated Nrf2/ARE and NRF1 signaling cascades to rescue cardiomyocytes from endotoxin insult, suggesting that protection of mitochondrial biogenesis was a way for pharmacological intervention to prevent septic heart injury.

•

Mitochondrial ROS increased calcium influx through CRAC channels.

•

Nrf2 interacted with PGC-1α to regulate mitochondrial biogenesis.

•

Songorine activated Nrf2 by promoting Keap1 degradation.

•

Songorine regulated Nrf2/ARE and PGC-1α cascades to protect cardiac function.

Lipopolysaccharide Activates Toll-Like Receptor 4 and Prevents Cardiac Fibroblast-to-Myofibroblast Differentiation

Bacterial lipopolysaccharide (LPS) is a known ligand of Toll-like receptor 4 (TLR4) which is expressed in cardiac fibroblasts (CF). Differentiation of CF to cardiac myofibroblasts (CMF) is induced by transforming growth factor-β1 (TGF-β1), increasing alpha-smooth muscle actin (α-SMA) expression. In endothelial cells, an antagonist effect between LPS-induced signaling and canonical TGF-β1 signaling was described; however, it has not been studied whether in CF and CMF the expression of α-SMA induced by TGF-β1 is antagonized by LPS and the mechanism involved. In adult rat CF and CMF, α-SMA, ERK1/2, Akt, NF-κβ, Smad3, and Smad7 protein levels were determined by western blot, TGF-β isoforms by ELISA, and α-SMA stress fibers by immunocytochemistry. CF and CMF secrete the three TGF-β isoforms, and the secretion levels of TGF-β2 was affected by LPS treatment. In CF, LPS treatment decreased the protein levels of α-SMA, and this effect was prevented by TAK-242 (TLR4 inhibitor) and LY294002 (Akt inhibitor), but not by BAY 11-7082 (NF-κβ inhibitor) and PD98059 (ERK1/2 inhibitor). TGF-β1 increased α-SMA protein levels in CF, and LPS prevented partially this effect. In addition, in CMF α-SMA protein levels were decreased by LPS treatment, which was abolished by TAK-242. Finally, in CF LPS decreased the p-Smad3 phosphorylation and increased the Smad7 protein levels. LPS treatment prevents the CF-to-CMF differentiation and reverses the CMF phenotype induced by TGF-β1, through decreasing p-Smad3 and increasing Smad7 protein levels.

The Role of Endotoxin in the Setting of Cardiorenal Syndrome Type 5

Lipopolysaccharide or endotoxin, the major cell wall component of gram-negative bacteria, plays a pivotal role in the pathogenesis of sepsis. It is able to activate the host defense system through the interaction with Toll-like receptor 4, thus triggering pro-inflammatory mechanisms. When the production of inflammatory mediators becomes uncontrolled and excessive, septic shock develops with multiple organ dysfunction, such as myocardial and renal impairment, which are hallmarks of cardiorenal syndrome type 5. In this review, we will analyze the role of endotoxin in the pathogenesis of sepsis, its effects on cardiac and renal interactions in the setting of cardiorenal syndrome type 5 and the possible use of extracorporeal therapies in this clinical condition.

Sepsis-Induced Cardiomyopathy: Mechanisms and Treatments

Sepsis is a lethal syndrome with a high incidence and a weighty economy burden. The pathophysiology of sepsis includes inflammation, immune dysfunction, and dysfunction of coagulation, while sepsis-induced cardiomyopathy (SIC), defined as a global but reversible dysfunction of both sides of the heart induced by sepsis, plays a significant role in all of the aspects above in the pathogenesis of sepsis. The complex pathogenesis of SIC involves a combination of dysregulation of inflammatory mediators, mitochondrial dysfunction, oxidative stress, disorder of calcium regulation, autonomic nervous system dysregulation, and endothelial dysfunction. The treatments for SIC include the signal pathway intervention, Chinese traditional medicine, and other specific therapy. Here, we reviewed the latest literatures on the mechanisms and treatments of SIC and hope to provide further insights to researchers and create a new road for the therapy of sepsis.

Potential phytoestrogen alternatives exert cardio-protective mechanisms via estrogen receptors

The 17 beta-estradiol (E2) is a sex hormone that is most abundant and most active estrogen in premenopausal women. The importance of E2 in providing cardioprotection and reducing the occurrence of heart disease in women of reproductive age has been well recognized. There are three subtype of estrogen receptors (ERs), including ERα, ERβ and GPR30 have been identified and accumulating evidence reveal their roles on E2-mediated genomic and nongenomic pathway in cardiomyocytes against various cardiac insults. In this review, we focus on the estrogen and ERs mediated signaling pathways in cardiomyocytes that determines cardio-protection against various stresses and further discuss the clinical implication of ERs and phytoestrogens. Further we provide some insights on phytoeostrogens which may play as alternatives in estrogen replacement therapies.

Endotoxin Effects on Cardiac and Renal Functions and Cardiorenal Syndromes

Gram-negative sepsis is a major cause of morbidity and mortality in critical ill patients. Recent findings in molecular biology and in signaling pathways have enhanced our understanding of its pathogenesis and opened up opportunities of innovative therapeutic approaches. Endotoxin plays a pivotal role in the pathogenesis of multi-organ dysfunction in the setting of gram-negative sepsis. Indeed, heart and kidney impairments seem to be induced by the release of circulating pro-inflammatory and pro-apoptotic mediators triggered by endotoxin interaction with immune cells. These molecules are responsible for cellular apoptosis, autophagy, cell cycle arrest, and microRNAs activation. Therefore, the early identification of sepsis-associated acute kidney injury and heart dysfunction may improve the patient clinical outcome. In this report, we will consider the role of endotoxin in the pathogenesis of sepsis, its effects on both cardiac and renal functions, and the interactions between these 2 systems in the setting of cardiorenal syndromes (CRS), particularly in CRS type 5. Finally, we will discuss the possible role of extracorporeal therapies in reducing endotoxin levels.

Enhanced monocyte chemoattractant protein-1 production in aging mice exaggerates cardiac depression during endotoxemia

Introduction

Endotoxemia and the systemic inflammatory response syndrome have a significant impact on post-surgery outcome, particularly in the elderly. The cytokine response to endotoxin is altered by aging. We tested the hypothesis that vulnerability to endotoxemic cardiac depression increases with aging due to age-related augmentation of myocardial inflammatory responses.

Methods

Adult (4 to 6 months) and old (20 to 22 months) C57/BL6 mice were treated with endotoxin (0.5 mg/kg, iv). Left ventricle (LV) function was assessed using a microcatheter system. Chemokines and cytokines in plasma and myocardium were analyzed by enzyme-linked immunosorbent assay (ELISA). Mononuclear cells in the myocardium were examined using immunofluorescence staining.

Results

Old mice displayed worse LV function (cardiac output: 3.0 ± 0.2 mL/min versus 4.4 ± 0.3 mL/min in adult mice) following endotoxin treatment. The exaggerated cardiac depression in old mice was associated with higher levels of monocyte chemoattractant protein-1 (MCP-1) and keratinocyte chemoattractant (KC) in plasma and myocardium, greater myocardial accumulation of mononuclear cells, and greater levels of tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β) and interleukin 6 (IL-6) in plasma and myocardium. Neutralization of MCP-1 resulted in greater reductions in myocardial mononuclear cell accumulation and cytokine production, and greater improvement in LV function in old mice while neutralization of KC had a minimal effect on LV function.

Conclusion

Old mice have enhanced inflammatory responses to endotoxemia that lead to exaggerated cardiac functional depression. MCP-1 promotes myocardial mononuclear cell accumulation and cardiodepressant cytokines production, and plays an important role in the endotoxemic cardiomyopathy in old mice. The findings suggest that special attention is needed to protect the heart in the elderly with endotoxemia.

Toll-like receptor 4 stimulation initiates an inflammatory response that decreases cardiomyocyte contractility

Toll-like receptors (TLRs) have been identified as primary innate immune receptors for the recognition of pathogen-associated molecular patterns by immune cells, initiating a primary response toward invading pathogens and recruitment of the adaptive immune response. TLRs, especially Toll-like receptor 4 (TLR4), can also be stimulated by host-derived molecules and are expressed in the cardiovascular system, thus acting as a possible key link between cardiovascular diseases and the immune system. TLR4 is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia. We used wild-type (WT) mice, TLR4-deficient (TLR4-knockout [ko]) mice, and chimeras that underwent myeloablative bone marrow transplantation to dissociate between TLR4 expression in the heart (TLR4-ko/WT) and the immunohematopoietic system (WT/TLR4-ko). Following lipopolysaccharide (LPS) challenge (septic shock model) or coronary artery ligation, myocardial ischemia (MI) model, we found WT/TLR4-ko mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of interleukin-1β and tumor necrosis factor-α, and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. The cardiac function of TLR4-ko or WT/TLR4-ko mice was less affected by LPS and demonstrated reduced suppression by MI compared with WT. These results suggest that TLR4 expressed in the cardiomyocytes plays a key role in this acute phenomenon.

Cyclic stretch enhances the expression of toll-like receptor 4 gene in cultured cardiomyocytes via p38 MAP kinase and NF-kappaB pathway

Background

Toll-like receptor 4 (TLR4) plays an important role in innate immunity. The role of TLR4 in stretched cardiomyocytes is not known. We sought to investigate whether mechanical stretch could regulate TLR4 expression, as well as the possible molecular mechanisms and signal pathways mediating the expression of TLR4 by cyclic mechanical stretch in cardiomyocytes.

Methods

Neonatal Wistar rat cardiomyocytes grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation at 60 cycles/min. Western blot, real-time polymerase chain reaction, and promoter activity assay were performed. In vitro monocyte adhesion to stretched myocyte was detected.

Results

Cyclic stretch significantly increased TLR4 protein and mRNA expression after 2 h to 24 h of stretch. Addition of SB203580, TNF-α antibody, and p38α MAP kinase siRNA 30 min before stretch inhibited the induction of TLR4 protein. Cyclic stretch increased, while SB203580 abolished the phosphorylated p38 protein. Gel shifting assay showed significant increase of DNA-protein binding activity of NF-κB after stretch and SB203580 abolished the DNA-protein binding activity induced by cyclic stretch. DNA-binding complexes induced by cyclic stretch could be supershifted by p65 monoclonal antibody. Cyclic stretch increased TLR4 promoter activity while SB203580 and NF-κB siRNA decreased TLR4 promoter activity. Cyclic stretch increased adhesion of monocyte to cardiomyocytes while SB203580, TNF-α antibody, and TLR4 siRNA attenuated the adherence of monocyte. TNF-α and Ang II significantly increased TLR4 protein expression. Addition of losartan, TNF-α antibody, or p38α siRNA 30 min before Ang II and TNF-α stimulation significantly blocked the increase of TLR4 protein by AngII and TNF-α.

Conclusions

Cyclic mechanical stretch enhances TLR4 expression in cultured rat neonatal cardiomyocytes. The stretch-induced TLR4 is mediated through activation of p38 MAP kinase and NF-κB pathways. TLR4 up-regulation by cyclic stretch increases monocyte adherence.

Betaine inhibits Toll-like receptor 4 expression in rats with ethanol-induced liver injury

AIM: To test whether ethanol feeding could induce Toll-like receptor 4 (TLR4) responses, assess the hepatoprotective effect of betaine and its inhibitive effect on TLR4 in animal models of alcoholic liver injury.

METHODS: Forty-eight female Sprague-Dawley rats were randomly divided into four groups as control, model, low and high dose betaine groups. Except control group, all rats were fed with high fat-containing diet plus ethanol and fish oil gavages for 8 wk. Betaine was administered intragastrically after exposure of ethanol for 4 wk. The changes of liver histology were examined. The expression of TLR4 mRNA and protein was detected by RT-PCR and Western blotting, respectively. The serum aminotransferase activity [alanine transarninase (ALT), aspartate aminotransferase (AST)], serum endotoxin, and liver inflammatory factors [tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-18 (IL-18)] were also assayed.

RESULTS: Compared with control group, rats of model group developed marked liver injury, accompanied by an increase of ALT (159.41 ± 7.74 U/L vs 59.47 ± 2.34 U/L, P < 0.0001), AST (248.25 ± 1.40 U/L vs 116.89 ± 3.48 U/L, P < 0.0001), endotoxin (135.37 ± 30.17 ng/L vs 44.15 ± 7.54 ng/L, P < 0.0001), TNF-α (20.81 ± 8.58 pg/mL vs 9.34 ± 2.57 pg/mL, P = 0.0003), IFN-γ (30.18 ± 7.60 pg/mL vs 16.86 ± 9.49 pg/mL, P = 0.0039) and IL-18 (40.99 ± 8.25 pg/mL vs 19.73 ± 9.31 pg/mL, P = 0.0001). At the same time, the expression of TLR4 mRNA and protein was markedly induced in the liver after chronic ethanol consumption (1.45 ± 0.07 vs 0.44 ± 0.04, P < 0.0001; 1.83 ± 0.13 vs 0.56 ± 0.08, P < 0.0001). Compared with model group, betaine feeding resulted in significant decreases of ALT (64.93 ± 6.06 U/L vs 159.41 ± 7.74 U/L, P < 0.0001), AST (188.73 ± 1.11 U/L vs 248.25 ± 1.40 U/L, P < 0.0001), endotoxin (61.80 ± 12.56 ng/L vs 135.37 ± 30.17 ng/L, P < 0.0001), TNF-α (9.79 ± 1.32 pg/mL vs 20.81 ± 8.58 pg/mL, P = 0.0003), IFN-γ (18.02 ± 5.96 pg/mL vs 30.18 ± 7.60 pg/mL, P = 0.0008) and IL-18 (18.23 ± 7.01 pg/mL vs 40.99 ± 8.25 pg/mL, P < 0.0001). Betaine also improved liver steatosis. The expression levels of TLR4 mRNA or protein in liver tissues were significantly lowered (0.62 ± 0.04 vs 1.45 ± 0.07, P < 0.0001; and 0.65 ± 0.06 vs 1.83 ± 0.13, P < 0.0001). There was a statistical difference of TLR4 mRNA and protein expression between high- and low-dose betaine groups (0.62 ± 0.04 vs 0.73 ± 0.05, P < 0.0001, and 0.65 ± 0.06 vs 0.81 ± 0.09, P < 0.0001).

CONCLUSION: Betaine can prevent the alcohol-induced liver injury effectively and improve the liver function. The expression of TLR4 increases significantly in ethanol-fed rats and betaine administration can inhibit TLR4 expression.

Sepsis and the heart

Septic shock, the most severe complication of sepsis, accounts for approximately 10% of all admissions to intensive care. Our understanding of its complex pathophysiology remains incomplete but clearly involves stimulation of the immune system with subsequent inflammation and microvascular dysfunction. Cardiovascular dysfunction is pronounced and characterized by elements of hypovolaemic, cytotoxic, and distributive shock. In addition, significant myocardial depression is commonly observed. This septic cardiomyopathy is characterized by biventricular impairment of intrinsic myocardial contractility, with a subsequent reduction in left ventricular (LV) ejection fraction and LV stroke work index. This review details the myocardial dysfunction observed in adult septic shock, and discusses the underlying pathophysiology. The utility of using the regulatory protein troponin for the detection of myocardial dysfunction is also considered. Finally, options for the management of sepsis-induced LV hypokinesia are discussed, including the use of levosimendan.