Toll-like receptor 4, nitric oxide, and myocardial depression in endotoxemia

Glucan phosphate attenuates myocardial HMGB1 translocation in severe sepsis through inhibiting NF-κB activation

Myocardial dysfunction is a major consequence of septic shock and contributes to the high mortality of sepsis. High-mobility group box 1 (HMGB1) serves as a late mediator of lethality in sepsis. We have reported that glucan phosphate (GP) attenuates cardiac dysfunction and increases survival in cecal ligation and puncture (CLP)-induced septic mice. In the present study, we examined the effect of GP on HMGB1 translocation from the nucleus to the cytoplasm in the myocardium of septic mice. GP was administered to mice 1 h before induction of CLP. Sham-operated mice served as control. The levels of HMGB1, Toll-like receptor 4 (TLR4), and NF-κB binding activity were examined. In an in vitro study, H9C2 cardiomyoblasts were treated with lipopolysaccharide (LPS) in the presence or absence of GP. H9C2 cells were also transfected with Ad5-IκBα mutant, a super repressor of NF-κB activity, before LPS stimulation. CLP significantly increased the levels of HMGB1, TLR4, and NF-κB binding activity in the myocardium. In contrast, GP administration attenuated CLP-induced HMGB1 translocation from the nucleus to the cytoplasm and reduced CLP-induced increases in TLR4 and NF-κB activity in the myocardium. In vitro studies showed that GP prevented LPS-induced HMGB1 translocation and NF-κB binding activity. Blocking NF-κB binding activity by Ad5-IκBα attenuated LPS-induced HMGB1 translocation. GP administration also reduced the LPS-stimulated interaction of HMGB1 with TLR4. These data suggest that attenuation of HMGB1 translocation by GP is mediated through inhibition of NF-κB activation in CLP-induced sepsis and that activation of NF-κB is required for HMGB1 translocation.

MCP-1-induced protein attenuates endotoxin-induced myocardial dysfunction by suppressing cardiac NF-кB activation via inhibition of IкB kinase activation

Myocardial contractile dysfunction is a major consequence of septic shock, which is mainly mediated by nuclear factor-kappa B (NF-кB)-dependent production of inflammatory mediators in the heart. A novel zinc-finger protein, MCP-1-induced protein (MCPIP), is thought to have NF-кB inhibitory activity in certain cell cultures, but its pathophysiological consequence in vivo remains undefined. This study aims to clarify whether the anti-inflammatory potency of MCPIP contribute to amelioration of septic myocardial inflammation and dysfunction in vivo. Transgenic mice (TG) with cardiac-specific expression of MCPIP and their littermate wild-type (WT) controls were challenged with Escherichia coli LPS (10mg/kg ip) and myocardial function was assessed 18 h later using echocardiography. LPS administration markedly deteriorated myocardial contractile function evidenced by reduction of the percentage of left ventricular fractional shortening, which was significantly attenuated by myocardial expression of MCPIP. MCPIP TG mice exhibited a markedly reduced myocardial inflammatory cytokines, less of iNOS expression and peroxynitrite formation, decreased caspase-3/7 activities and apoptotic cell death compared with LPS-treated WT mice. Activation of cardiac NF-кB observed in LPS-challenged WT mice was suppressed by the presence of MCPIP, as evidenced by decreased phosphorylation of IкB kinase (IKKα/β), reduced degradation of the cytosolic IкBα, and decreased nuclear translocation of NF-кB p65 subunit and its target DNA-binding activity. These results suggest that MCPIP has therapeutic values to protect heart from inflammatory pathologies, possibly through inhibition of IкB kinase complex, leading to blockade of NF-кB activation, and subsequently, attenuation of the proinflammatory state and nitrosative stress in the myocardium.

Systemically administered ligands of Toll-like receptor 2, -4, and -9 induce distinct inflammatory responses in the murine lung

Objective. To determine whether systemically administered TLR ligands differentially modulate pulmonary inflammation. Methods. Equipotent doses of LPS (20 mg/kg), CpG-ODN (1668-thioat 1 nmol/g), or LTA (15 mg/kg) were determined via TNF activity assay. C57BL/6 mice were challenged intraperitoneally. Pulmonary NFκB activation (2 h) and gene expression/activity of key inflammatory mediators (4 h) were monitored. Results. All TLR ligands induced NFκB. LPS increased the expression of TLR2, 6, and the cytokines IL-1αβ, TNF-α, IL-6, and IL-12p35/p40, CpG-ODN raised TLR6, TNF-α, and IL12p40. LTA had no effect. Additionally, LPS increased the chemokines MIP-1α/β, MIP-2, TCA-3, eotaxin, and IP-10, while CpG-ODN and LTA did not. Myeloperoxidase activity was highest after LPS stimulation. MMP1, 3, 8, and 9 were upregulated by LPS, MMP2, 8 by CpG-ODN and MMP2 and 9 by LTA. TIMPs were induced only by LPS. MMP-2/-9 induction correlated with their zymographic activities. Conclusion. Pulmonary susceptibility to systemic inflammation was highest after LPS, intermediate after CpG-ODN, and lowest after LTA challenge.

Mitochondrial function and dysfunction in sepsis

Mitochondria are the key source of cellular ATP and their structure and function are markedly affected by pathophysiologic processes associated with the host's response to invading pathogens. In particular, the highly reactive compound peroxynitrite, generated by the reaction of nitric oxide and superoxide anions, inhibits mitochondrial enzymes and damages lipids, proteins, and nucleic acids. Enhanced oxidative stress induces DNA strand breaks that are repaired by activation of poly(ADP-ribose)polymerase (PARP). This process consumes large amounts of nicotinamide adenine dinucleotide (NAD(+)) leading to cellular NAD(+) depletion that impairs flux of reducing equivalents into the respiratory chain and also further promotes inflammation. In experimental studies, novel therapeutic strategies that aim to ameliorate the host's pathogen response or to modulate intracellular signaling events related to oxidative stress protected mitochondrial function and preserved cellular respiration ultimately leading to improved organ function.

Salvage effect of E5564, Toll-like receptor 4 antagonist on d-galactosamine and lipopolysaccharide-induced acute liver failure in rats

BACKGROUND AND AIMS

The transmembrane protein Toll-like receptor 4 (TLR4), which exists mainly in macrophages such as Kupffer cells of the liver, plays an important role in recognizing and mediating macrophage activation and pro-inflammatory cytokine release. Activation of the pro-inflammatory cytokine cascade, including tumor necrosis factor-alpha (TNF-alpha), has a pivotal role in the progression of severe liver injury. D-galactosamine (GalN) and lipopolysaccharide (LPS)-induced liver injury in rats is an experimental model of fulminant hepatic failure, where TNF-alpha plays a central role in the progression of liver injury. E5564, a synthetic analogue of the lipid A component of endotoxin, inhibits endotoxin-stimulated inflammation and is under study for patients with sepsis. In the present study, we sought to explore the salvage effect of TLR4 antagonist E5564 on GalN+LPS-induced acute liver failure (ALF) in rats.

METHODS

ALF was induced in male Wistar rats by the intraperitoneal injection of GalN (500 mg/kg) and LPS (50 microg/kg). Immediately after GalN+LPS injection, rats were treated with intravenous injection of E5564 (3 mg/kg). The cumulative survival rates of GalN+LPS-induced ALF rats were compared between those with and without E5564 treatment.

RESULTS

The intravenous injection of E5564 reduced the elevation of serum total bilirubin, aspartate aminotransferase, alanine aminotransferase and TNF-alpha levels in rats at 3 h after GalN+LPS injection, and improved the survival rate of GalN+LPS-induced ALF rats at 24 h (8% vs 43%).

CONCLUSIONS

TLR4 antagonist E5564 reduced GalN+LPS-induced acute liver injury in rats and improved the overall survival rate of GalN+LPS-induced ALF rats. It may contribute to the treatment of ALF through blocking endotoxin-induced TNF-alpha overproduction of macrophages.

Toll-like receptor 4 modulation as a strategy to treat sepsis

Despite a decrease in mortality over the last decade, sepsis remains the tenth leading causes of death in western countries and one of the most common cause of death in intensive care units. The recent discovery of Toll-like receptors and their downstream signalling pathways allowed us to better understand the pathophysiology of sepsis-related disorders. Particular attention has been paid to Toll-like receptor 4, the receptor for Gram-negative bacteria outer membrane lipopolysaccharide or endotoxin. Since most of the clinical trial targeting single inflammatory cytokine in the treatment of sepsis failed, therapeutic targeting of Toll-like receptor 4, because of its central role, looks promising. The purpose of this paper is to focus on the recent data of various drugs targeting TLR4 expression and pathway and their potential role as adjunctive therapy in severe sepsis and septic shock.

Cardiomyocyte Toll-like receptor 4 is involved in heart dysfunction following septic shock or myocardial ischemia

Toll-like receptors are expressed in immune cells and cardiac muscle. We examined whether the cardiac Toll-like receptor 4 (TLR4) is involved in the acute myocardial dysfunction caused by septic shock and myocardial ischemia (MI). We used wild type mice (WT), TLR4 deficient (TLR4-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). Mice were injected with lipopolysaccharide (LPS) (septic shock model) or subjected to coronary artery ligation (MI model) and tested in vivo and ex vivo, for function, histopathology proinflammatory cytokine and TLR4 expression. WT mice challenged with LPS or MI displayed reduced cardiac function, increased myocardial levels of IL-1 beta and TNF-alpha and upregulation of mRNA encoding TLR4 prior to myocardial leukocyte infiltration. TLR4 deficient mice sustained significantly smaller infarctions as compared to control mice at comparable areas at risk. The cardiac function of TLR4-ko mice was not affected by LPS and demonstrated reduced suppression by MI compared to WT. Chimeras deficient in myocardial TLR4 were resistant to suppression induced by LPS and the heart function was less depressed, compared to the TLR4-ko, following MI in the acute phase (4h). In contrast, hearts of chimeras deficient in immunohematopoietic TLR4 expression were suppressed both by LPS and MI, exhibiting increased myocardial cytokine levels, similar to WT mice. We concluded that cardiac function of TLR4-ko mice and chimeric mice expressing TLR4 in the immunohematopoietic system, but not in the heart, revealed resistance to LPS and reduced cardiac depression following MI, suggesting that TLR4 expressed by the cardiomyocytes themselves plays a key role in this acute phenomenon.

Extracellular heat shock protein 60, cardiac myocytes, and apoptosis

RATIONALE

Previously, we have found that changes in the location of intracellular heat shock protein (HSP)60 are associated with apoptosis. HSP60 has been reported to be a ligand of toll-like receptor (TLR)-4.

OBJECTIVE

We hypothesized that extracellular HSP60 (exHSP60) would mediate apoptosis via TLR4.

METHODS AND RESULTS

Adult rat cardiac myocytes were treated with HSP60, either recombinant human or with HSP60 purified from the media of injured rat cardiac myocytes. ExHSP60 induced apoptosis in cardiac myocytes, as detected by increased caspase 3 activity and increased DNA fragmentation. Apoptosis could be reduced by blocking antibodies to TLR4 and by nuclear factor kappaB binding decoys, but not completely inhibited, even though similar treatment blocked lipopolysaccharide-induced apoptosis. Three distinct controls showed no evidence for involvement of a ligand other than exHSP60 in the mediation of apoptosis.

CONCLUSIONS

This is the first report of HSP60-induced apoptosis via the TLRs. HSP60-mediated activation of TLR4 may be a mechanism of myocyte loss in heart failure, where HSP60 has been detected in the plasma.

Postischemic vascular permeability requires both TLR-2 and TLR-4, but only TLR-2 mediates the transendothelial migration of leukocytes

Ischemia-reperfusion (I/R) activates innate immunity involving Toll-like receptor (TLR) 2 and TLR-4 signaling. Leukocyte migration and vascular permeability contribute to postischemic tissue damage. We hypothesized that TLR-2 and TLR-4 directly mediate leukocyte migration and vascular permeability during I/R. We used in vivo microscopy on postischemic murine cremaster muscle to quantify leukocyte adhesion as well as transendothelial and interstitial migration in sham-operated wild-type mice and in wild-type, TLR-2(-/-), and TLR-4-mutant mice 30 and 120 min after I/R. Alterations in fluorescein isothiocyanate-dextran leakage across cremasteric venules were determined as a measure of endothelial permeability. I/R-induced leukocyte adhesion in TLR-2(-/-) and TLR-4-mutant mice was comparable to that in wild-type mice. The number of transmigrated leukocytes was increased upon I/R in wild-type mice as compared with the sham-operated group. In contrast, leukocyte transmigration was significantly attenuated in TLR-2(-/-) but not in TLR-4-mutant mice. Motility and polarization of interstitially migrating leukocytes did not significantly differ in TLR-2(-/-) and TLR-4-mutant mice from wild-type mice. Postischemic vascular leakage was significantly lower in both TLR-2(-/-) and TLR-4-mutant than in wild-type mice. We conclude that both TLR-2 signaling and TLR-4 signaling enhance postischemic vascular permeability and that TLR-2 has additional effects on the transendothelial migration of leukocytes at the postischemic vascular wall.

Lipopolysaccharide preconditioning enhances the efficacy of mesenchymal stem cells transplantation in a rat model of acute myocardial infarction

Background

Mesenchymal stem cells (MSCs)-based regenerative therapy is currently regarded as an alternative approach to salvage the acute myocardial infarcted hearts. However, the efficiency of MSCs transplantation is limited by lower survival rate of engrafted MSCs. In previous study, we found that 1.0 μg/ml Lipopolysaccharide (LPS) could protect MSCs against apoptosis induced by oxidative stress and meanwhile enhance the proliferation of MSCs. Therefore, in the present study, we firstly preconditioned MSCs with 1.0 μg/ml LPS, then transplanted MSCs into ischemic myocardium, and observed the survival and cardiac protective capacity of MSCs in a rat model of acute myocardial infarction. Furthermore, we tried to explore the underlying mechanisms and the role of Toll-like receptor-4 (TLR4) in the signal pathway of LPS-induced cardiac protection.

Methods and results

Acute myocardial infarction model was developed by left anterior descending coronary artery ligation. 60 rats were divided into 4 groups randomly and given an intramyocardial injection of one of the following treatments: 30 μl PBS (control group), 3 × 10⁶ wild MSCs/30 μl (wMSCs group), 3 × 10⁶ LPS-preconditioned wild MSCs/30 μl (LPS-wMSCs group), or 3 × 10⁶ LPS-preconditioned TLR4 gene deleted MSCs/30 μl (LPS-tMSCs group). After 3 weeks, LPS-preconditioned wild MSCs transplantation ameliorated cardiac function and reduced fibrosis of infarcted myocardium. Vascular density was markedly increased in LPS-wMSCs group compared with other three groups. Survival rate of engrafted MSCs was elevated and apoptosis of myocardium was reduced in infarcted heart. Expression of vascular endothelial growth factor (VEGF) and phospho-Akt was increased in the infarcted myocardium after transplantation of LPS-preconditioned MSCs.

Conclusion

LPS preconditioning enhanced survival of engrafted MSCs, stimulated expression of VEGF and activated PI3K/Akt pathway. LPS preconditioning before MSCs transplantation resulted in superior therapeutic neovascularization and recovery of cardiac function. LPS preconditioning provided a novel strategy in maximizing biologic and functional properties of MSCs.

Phenylmethimazole decreases Toll-like receptor 3 and noncanonical Wnt5a expression in pancreatic cancer and melanoma together with tumor cell growth and migration

PURPOSE

To evaluate whether (a) Wnt5a expression in pancreatic cancer and malignant melanoma cells might be associated with constitutive levels of Toll-like receptor 3 (TLR3) and/or TLR3 signaling; (b) phenylmethimazole (C10), a novel TLR signaling inhibitor, could decrease constitutive Wnt5a and TLR3 levels together with cell growth and migration; and (c) the efficacy of C10 as a potential inhibitor of pancreatic cancer and malignant melanoma cell growth in vivo.

EXPERIMENTAL DESIGN

We used a variety of molecular biology techniques including but not limited to PCR, Western blotting, and ELISA to evaluate the presence of constitutively activated TLR3/Wnt5a expression and signaling. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-based technology and scratch assays were used to evaluate inhibition of cell growth and migration, respectively. TLR3 regulation of cell growth was confirmed using small interfering RNA technology. Nude and severe combined immunodeficient mice were implanted with human pancreatic cancer and/or melanoma cells and the effects of C10 on tumor growth were evaluated.

RESULTS

We show that constitutive TLR3 expression is associated with constitutive Wnt5a in human pancreatic cancer and malignant melanoma cell lines, that C10 can decrease constitutive TLR3/Wnt5a expression and signaling, suggesting that they are interrelated signal systems, and that C10 inhibits growth and migration in both of these cancer cell lines. We also report that C10 is effective at inhibiting human pancreatic cancer and malignant melanoma tumor growth in vivo in nude or severe combined immunodeficient mice and associate this with inhibition of signal transducers and activators of transcription 3 activation.

CONCLUSIONS

C10 may have potential therapeutic applicability in pancreatic cancer and malignant melanoma.

Alterations in the cardiac inflammatory response to burn trauma in mice lacking a functional Toll-like receptor 4 gene

Our group and others have previously shown that Toll-like receptor 4 (TLR-4) inactivation prevents burn-induced myocardial contractile dysfunction; however, the molecular mechanisms that are involved in this cardioprotection are not well defined. This present study examines the involvement of TLR-4 in the cardiac inflammatory response to thermal insult. C3H/HeJ (TLR-4 mutant mice) and C3H/HeN wild-type (WT) mice were subjected to either a sham burn or 40% full-thickness burn injury and were fluid resuscitated with lactated Ringer using the Parkland formula. Mice (n = 7-9 per group) were killed at 2, 4, or 24 h postsham or burn, and heart tissue was harvested. Immunoblotting was performed to evaluate phosphorylated p38 mitogen-activated protein kinase (MAPK), nuclear p50, and cytoplasmic p50. Nuclear factor-kappaB was also characterized via electrophoretic mobility shift assay. Systemic and cardiac myocyte secretion of TNF-alpha, IL-1 beta, IL-6, and IL-10 were measured by enzyme-linked immunosorbent assay. Burn injury in WT mice promoted myocardial inflammatory signaling that included increased expression of phosphorylated p38 MAPK, nuclear p50, and increased cardiac myocyte secretion of cytokines. Systemic cytokines were also increased in WT animals, although not to the extent of the myocardial cytokine expression. Toll-like receptor 4 inactivation resulted in an attenuation of several burn-induced responses, including phosphorylation of p38 MAPK, nuclear translocation of nuclear factor-kappaB, and cytokine secretion. These data suggest that burn injury initiates an inflammatory response via Toll/IL-1 signaling in the heart, which contributes to cardiac injury and contractile dysfunction.

Nitric oxide synthase-2 induction optimizes cardiac mitochondrial biogenesis after endotoxemia

Mitochondrial biogenesis protects metabolism from mitochondrial dysfunction produced by activation of innate immunity by lipopolysaccharide (LPS) or other bacterial products. Here we tested the hypothesis in mouse heart that activation of toll-like receptor-4 (TLR4), which induces early-phase genes that damage mitochondria, also activates mitochondrial biogenesis through induction of nitric oxide synthase (NOS2). We compared three strains of mice: wild type (Wt) C57BL/6J, TLR4(-/-), and NOS2(-/-)for cardiac mitochondrial damage and mitochondrial biogenesis by real-time RT-PCR, Western analysis, immunochemistry, and isoform analysis of myosin heavy chain (MHC) after sublethal heat-killed Escherichia coli (HkEC). After HkEC, Wt mice displayed significant myocardial mtDNA depletion along with enhanced TLR4 and NOS2 gene and protein expression that normalized in 72 h. HkEC generated less cytokine stress in TLR4(-/-)and NOS2(-/-)than Wt mice, NOS2(-/-)mice had mtDNA damage comparable to Wt, and both knockout strains failed to restore mtDNA copy number because of mitochondrial transcriptosome dysfunction. Wt mice also showed the largest beta-MHC isoform switch, but MHC recovery lagged in the NOS2(-/-)and TLR4(-/-)strains. The NOS2(-/-)mice also unexpectedly revealed the codependency of TLR4 expression on NOS2. These findings demonstrate the decisive participation of NOS2 induction by TLR4 in optimization of mitochondrial biogenesis and MHC expression after gram-negative challenge.

Proestrus female rats are more resistant to right ventricular pressure overload

Multiple studies of left ventricular dysfunction suggest that females may be more resistant to ischemia or endotoxemia. However, sex differences in right ventricular (RV) responses to pressure overload and/or endotoxemia have not been elucidated. We hypothesized that females would maintain better RV function during acute pressure overload (APO), endotoxemia, or a simultaneous insult from both processes. Age-matched male and proestrus female Sprague-Dawley rats were given an intraperitoneal injection of either phosphate buffered saline or LPS. Six hours after injection, hearts were removed by median sternotomy and isolated via Langendorff. End-diastolic pressures were sequentially elevated past physiologic levels by increasing the volume of a latex balloon that was inserted into the RV. Male RV function was depressed to a greater degree after APO injury compared with that in females (developed pressure: male, 44.97 mmHg vs. female, 58.23 mmHg). Interestingly though, at a physiologic end-diastolic pressure of 5 mmHg, endotoxic males and females maintained equivalent RV function. However, with concurrent endotoxic insult and APO, RV function was better maintained in males as compared with that in females (developed pressure: male, 59% of control versus female, 41% of control). Furthermore, tissue levels of IL-1 and IL-6, but not IL-10, were increased after endotoxin exposure but did not differ based on sex. Through this study, we have shown that sex differences exist in RV dysfunction, and that different cardiac insults diversely affect myocardial function. Understanding these differences may allow for the implementation of novel therapeutic treatment options that are designed to attenuate RV cardiovascular collapse.

Oral insulin up-regulates Toll-like receptor 4 expression and enhances intestinal recovery following lipopolysaccharide-induced gut injury in a rat

In the present study, we evaluated the protective effect of oral insulin (OI) on intestinal mucosa following lipopolysaccharide-induced intestinal damage in a rat. Male Sprague-Dawley rats were divided into three experimental groups: Sham rats, LPS-rats that were treated with lipopolysaccharide (LPS), and LPS-INS rats that were treated with OI given in drinking water 72 h before and following injection of LPS. Intestinal structural changes, enterocyte proliferation, enterocyte apoptosis, and mucosal expression of Toll-like receptor 4 (TLR4) were determined 24 h after the last LPS injection. LPS-INS animals showed a significantly greater bowel and mucosal weight in jejunum and ileum, mucosal DNA and protein in jejunum and ileum, villus height in ileum, crypt depth in jejunum and ileum, cell proliferation rates in jejunum, and significantly lower apoptotic index in ileum compared to LPS- animals. LPS rats demonstrated 50% increase in TLR4 expression in jejunum compared to sham animals. Treatment with OI resulted in a three-fold increase in TLR4 expression in jejunum, compared to LPS animals. In conclusion, OI improves intestinal recovery after LPS endotoxemia in a rat.

Biomarker evidence of myocardial cell injury is associated with mortality in acute respiratory distress syndrome

OBJECTIVE

Although a number of studies have reported elevated levels of markers of myocardial necrosis among critically ill patients, the association between these markers and outcome remains poorly studied in patients with lung injury. We investigated the association of elevated troponin and creatine phosphokinase isoenzyme levels with mortality and organ failure in subjects with acute respiratory distress syndrome.

DESIGN

Retrospective study.

SETTING

Tertiary academic medical center.

PATIENTS

A total of 305 subjects with acute respiratory distress syndrome enrolled in a prospective intensive care unit cohort.

INTERVENTION

None.

MEASUREMENTS AND MAIN RESULTS

Cardiac biomarker data were available on 248 of 305 patients with acute respiratory distress syndrome (81%), of which 89 patients had at least one elevated cardiac marker level (35%). The presence of an elevated cardiac marker was associated with significantly higher mortality (p = .01) and was an independent predictor of mortality (p = .02) among patients with lower severity of illness (Acute Physiology and Chronic Health Evaluation III, <79). Patients with at least one elevated cardiac marker also had significantly more organ system derangement, including noncardiovascular organ system failures (p = .02).

CONCLUSIONS

Patients with acute respiratory distress syndrome have a high prevalence of elevated cardiac markers. The presence of elevated cardiac markers is independently associated with increased 60-day mortality and increased organ failure. This association is most pronounced among patients with lower severity of illness. These results indicate that occult myocardial injury may be an important factor in acute respiratory distress syndrome morbidity and mortality. Further study of the relevant causal relationships and mechanisms is warranted.

Effects of IL-10 and age on IL-6, IL-1beta, and TNF-alpha responses in mouse skeletal and cardiac muscle to an acute inflammatory insult

Exaggerated proinflammatory cytokine responses can be observed with aging, and reduced levels of the anti-inflammatory cytokine IL-10 may contribute to these responses. IL-10 can reduce IL-6, IL-1beta, and TNF-alpha expression in nonmuscle tissues; however, no studies have examined the combined effects of IL-10 and age on cytokine responses in skeletal and cardiac muscle. These experiments tested the hypothesis that the absence of IL-10, in vivo, is associated with greater IL-6, TNF-alpha, and IL-1beta responses to an inflammatory challenge in skeletal and cardiac muscle and that aging exaggerates these responses. We compared IL-6, IL-1beta, and TNF-alpha mRNA and protein levels in skeletal and cardiac muscle of young (4 mo) and mature (10-11 mo) wild-type (IL-10(+/+)) and IL-10 deficient (IL-10(-/-)) mice following LPS. Skeletal and cardiac IL-6 mRNA and protein were elevated by LPS for IL-10(+/+) and IL-10(-/-) mice with greater responses in the IL-10(-/-) mice (P < 0.01). In skeletal muscle these effects were greater in mature than young mice (P < 0.01). IL-1beta mRNA and protein responses to LPS were greater in cardiac muscle of young but not mature IL-10(-/-) mice compared with IL-10(+/+) (P < 0.01). However, IL-1beta responses were greater in mature than young mice, but only in IL-10(+/+) groups (P < 0.05). The absence of IL-10 was associated with higher TNF-alpha protein levels in cardiac muscle (P < 0.05). The results provide the first in vivo evidence that the absence of IL-10 is associated with a greater IL-6 response to LPS in skeletal and cardiac muscles, and in skeletal muscle aging further exaggerates these responses.

Identification and characterization of a dysfunctional cardiac myocyte phenotype: role of bacteria, Toll-like receptors, and endothelin

Cardiac myocyte dysfunction is clearly identified as underlying the acute heart failure associated with bacterial infection, as well as the chronic syndrome following cardiac damage, but the mechanisms leading to dysfunction in each case are not fully established. It is thought that local hormones such as endothelin 1 (ET-1) can increase the risk of heart failure in acute or chronic conditions. In the current study, we characterize myocytes as populations and identify a novel phenotype of the ventricular cardiac myocyte that does not contract appropriately on electrical stimulation. The noncontractile cardiac myocytes were viable and had normal calcium transients. The proportion of noncontractile cardiac myocytes was increased by bacteria (gram-positive Staphylococcus aureus or gram-negative Escherichia coli). Using selective ligands or myocytes from genetically modified mice, we established that the effects of S. aureus were mediated by Toll-like receptor 2/6 and of E. coli by Toll-like receptor 4. The transition to the noncontractile phenotype was strongly inhibited by ETA antagonism but unaffected by inhibition of NOS, suggesting that ET-1 and not NO mediates this phenomenon. These results are the first to describe the characteristics of this noncontractile phenotype and the mechanisms of its induction by bacteria. Description of the myocyte population, instead of effects only on individual cells, will be more relevant to the prediction of the depression of cardiac function.

Bacterial DNA induces myocardial inflammation and reduces cardiomyocyte contractility: role of toll-like receptor 9

AIMS

Myocardial function is severely compromised during sepsis. Several underlying mechanisms have been proposed. The innate immune system, i.e. toll-like receptor (TLR) 2 and 4, significantly contributes to cardiac dysfunction. Little is known regarding TLR9 and its pathogenic ligand bacterial DNA in the myocardium. We therefore studied the role of TLR9 in myocardial inflammation and cardiac contractility.

METHODS AND RESULTS

Wild-type (WT, C57BL/6) and TLR9-deficient (TLR9-D) mice and isolated cardiomyocytes were challenged with synthetic bacterial DNA (CpG-ODN). Myocardial contractility as well as markers of inflammation/signalling were determined. Isolated cardiomyocytes incorporated fluorescence-marked CpG-ODN. In WT mice, CpG-ODN caused a robust response in hearts demonstrated by increased levels of tumour necrosis factor (TNF-alpha), interleukin (IL)-1beta, IL-6, inducible nitric oxide synthase (iNOS), and nuclear factor kappaB activity. This inflammatory response was absent in TLR9-D mice. Under similar conditions, contractility measurements of isolated ventricular cardiomyocytes demonstrated a TLR9-dependent loss of sarcomeric shortening after CpG-ODN exposure. This observation was iNOS dependent as the application of a specific iNOS inhibitor reversed sarcomeric shortening to normal levels.

CONCLUSION

Our data suggest that bacterial DNA contributes to myocardial cytokine production and loss of cardiomyocyte contractility via TLR9.

Toll-like receptor 4 mediates the early inflammatory response after cold ischemia/reperfusion

BACKGROUND

Ischemia/reperfusion (I/R) injury leads to graft dysfunction and may contribute to alloimmune responses posttransplantation. The molecular mechanisms of cold I/R injury are only partially characterized but may involve toll-like receptor (TLR)-4 activation by endogenous ligands. We tested the hypothesis that TLR4 mediates the early inflammatory response in the setting of cold I/R in a murine cardiac transplant model.

METHODS

Syngeneic heart transplants were performed in mutant mice deficient in TLR4 signaling (C3H/HeJ) and wild-type mice (C3H/HeOuJ). Transplants were also performed between the strains (mutant hearts into wild-type recipients and the converse). Donor hearts were subjected to 2 hr of cold ischemia. The grafts were retrieved at 3 and 24 hr after reperfusion. Serum samples were collected for cytokine analysis. Reverse-transcription polymerase chain reaction and histologic analysis were used to assess intra-graft inflammation.

RESULTS

After transplant, serum tumor necrosis factor (TNF), interleukin (IL)-6, JE/monocyte chemotractant protein (MCP)-1, IL-1beta, and troponin I levels, as well as intragraft TNF, IL-1beta, IL-6, early growth response (EGR)-1, intercellular adhesion molecule (ICAM)-1, and inducible nitric oxide synthase (iNOS) mRNA levels, were significantly lower in the mutant-->mutant group compared to the wild-type-->wild-type group (P< or =0.05). Intermediate levels of serum IL-6, JE/MCP-1, as well as intragraft TNF, IL-1beta, IL-6, and ICAM-1 mRNA were observed after transplants in the mutant-->wild-type and wild-type-->mutant groups. Immunohistochemistry revealed less myocardial nuclear factor-kappaB nuclear translocation at and less neutrophil infiltration in the mutant-->mutant group compared to the wild-type-->wild-type group.

CONCLUSIONS

These findings demonstrate that TLR4 signaling is central to both the systemic and intragraft inflammatory responses that occur after cold I/R in the setting of organ transplantation and that TLR4 signaling on both donor and recipient cells contributes to this response.

Protection against lipopolysaccharide-induced myocardial dysfunction in mice by cardiac-specific expression of soluble Fas

The mechanisms responsible for myocardial dysfunction in the setting of sepsis remain undefined. Fas ligation with its cognate ligand (FasL) induces apoptosis and activates cellular inflammatory responses associated with tissue injury. We determined whether interruption of Fas/FasL interaction by cardiac-specific expression of soluble Fas (sFas), a competitive inhibitor of FasL, would improve myocardial dysfunction and inflammation in a lipopolysaccharide (LPS)-induced mouse model of sepsis. Wild-type (WT) and sFas transgenic mice were injected intraperitoneally with 10 mg/kg LPS or with an equivalent volume of saline. At 18 h after LPS administration, echocardiographic evaluation revealed a significant decrease in left ventricular fractional shortening in the WT mice, whereas the fractional shortening was preserved in the sFas mice. Activation of nuclear factor-kappa B (NF-kappaB) and the increase in the transcript levels of proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 resulting from LPS treatment were attenuated in the myocardium of sFas mice. sFas expression also inhibited LPS-induced upregulation of Toll-like receptor 4 (TLR-4) and inducible nitric oxide synthase (iNOS), and formation of peroxynitrite in the myocardium. LPS-induced increase in caspase-3/7 activity and apoptotic cell death were suppressed in sFas mice compared with WT mice. LPS-induced lung injury and increase in lung water content were also significantly reduced in sFas mice. These data indicate that neutralization of FasL by expression of sFas significantly preserves cardiac function and reduces inflammatory responses in the heart, suggesting that Fas/FasL signaling pathway is important in mediating the deleterious effects of LPS on myocardial function.

Functional significance of the TLR4/11367 polymorphism identified in Chinese Han population

Toll-like receptor 4 (TLR4) is the central signaling receptor for lipopolysaccharide (LPS) in mammals. This study was designed to investigate the functional significance of the G11367C polymorphism, which is a novel variant we identified in the 3' untranslated region of TLR4 gene in Chinese Han population. Three hundred seventy healthy volunteers were selected. The TLR4/11367 polymorphism was genotyped using single-tube bidirectional allele-specific amplification method. The TLR4 protein expression on peripheral leukocytes and plasma tumor necrosis factor alpha levels were determined by means of flow cytometry and enzyme-linked immunosorbent assay. The post-transcriptional effect of the 11367 polymorphism was evaluated by means of reporter gene assay and real-time quantitative polymerase chain reaction. The G11367C polymorphism is a common allele in Chinese Han population, with minor allele frequency of 14.7%. In response to ex vivo LPS stimulation, the TLR4 expression on the surface of peripheral leukocytes and the plasma tumor necrosis factor alpha levels were significantly lower in carriers of 11367C variant allele than in carriers of 11367G allele. This association was allele dose dependent. We also found that the activity and the mRNA expression of luciferase was significantly smaller in human embryonic kidney 293 cells transfected with construct containing 11367C allele than in those transfected with construct containing 11367G allele. Together, these results suggest that the TLR4/11367 polymorphism may be a functional single nucleotide polymorphism, which could attenuate the LPS-induced transmembrane signaling through the alteration of post-transcriptional regulation of 3' untranslated region and target gene expression.

Selective impairment of nuclear factor-kappaB-dependent gene transcription in adult cardiomyocytes: relevance for the regulation of the inflammatory response in the heart

The ability of neonatal and adult cardiomyocytes to activate the nuclear factor (NF)-kappaB pathway in response to lipopolysaccharide and interleukin-1beta challenge has been investigated and compared with that of peritoneal macrophages. The activation of the IkappaB kinase and the phosphorylation and degradation of IkappaBalpha and IkappaBbeta was much lower in adult cardiomyocytes than in the neonatal counterparts and macrophages. This restricted activation of the NF-kappaB pathway resulted in a significant reduction in the time of nuclear activation of NF-kappaB, as deduced by electrophoretic mobility shift assays and in the transcription of target genes, such as IkappaBalpha, cyclooxygenase-2 (COX-2) and nitric-oxide synthase-2 (NOS-2). Studies on chromatin immunoprecipitation showed binding of NF-kappaB proteins to the regulatory kappaB sites identified in the promoters of the IkappaBalpha, COX-2, and NOS-2 genes in macrophages and, to a lower extent, in neonatal cardiomyocytes. The binding to these kappaB sites in adult cardiomyocytes was observed only in the IkappaBalpha promoter and was minimal or absent in the COX-2 and NOS-2 promoters, respectively, suggesting a restricted activation of NF-kappaB-regulated genes in these cells. These data indicate that the function of the NF-kappaB pathway in adult cardiomyocytes is limited in time, which results in the expression of a reduced number of genes and provides a functional explanation for the absence of NOS-2 inducibility in these cells under proinflammatory conditions.

The interaction between myocardial depressant factors in endotoxemic cardiac dysfunction: role of TNF-alpha in TLR4-mediated ICAM-1 expression

Multiple pro-inflammatory mediators contribute to cardiac dysfunction caused by bacterial lipopolysaccharide (LPS). The rapid TNF-alpha response is likely involved in the induction of down-stream myocardial depressant factors. Studies by our laboratory and others indicate an important role for ICAM-1 in endotoxemic cardiac dysfunction through leukocyte-independent mechanisms. The purpose of this study was to determine: whether ICAM-1 knockout improves cardiac function during endotoxemia and whether TLR4 and TNF-alpha regulate LPS-induced myocardial ICAM-1 expression.

METHODS AND RESULTS

Mice were treated with Escherichia coli LPS (0.5mg/kg iv). Myocardial ICAM-1 levels were analyzed by immunoblotting and left ventricular developed pressure (LVDP) was assessed by the Langendorff technique. In wild-type mice, peak ICAM-1 levels were observed at 4h when myocardial contractility was depressed. Myocardial contractility was improved following LPS in mice lacking functional TLR4, TNF-alpha or ICAM-1. TLR4 mutation abolished ICAM-1 expression with abrogation of precedent TNF-alpha response. Similarly, TNF-alpha knockout reduced myocardial ICAM-1 level following LPS treatment.

CONCLUSIONS

ICAM-1 contributes to the mechanism of endotoxemic cardiac dysfunction. TNF-alpha is involved in the regulation of myocardial ICAM-1 expression by TLR4.

Antagonism of lipopolysaccharide-induced blood pressure attenuation and vascular contractility

OBJECTIVE

Aim was to assess whether lipopolysaccharide (LPS)-induced decrease of total peripheral resistance depends on Toll-like receptor (TLR)4 signaling and whether it is sensitive to NO-synthase or TLR4 antagonists.

METHODS AND RESULTS

C3H/HeN mice (control), expressing a functional, and C3H/HeJ mice, expressing a nonfunctional TLR4, were compared. LPS (20 mg/kg) was injected i.p. 6 hours before hemodynamic measurements. L-NAME and SMT, inhibitors of NO production, and Eritoran, a TLR4 antagonist, were tested for their impact on vascular contractility. Aortic rings were incubated for 6 hours with or without LPS (1 microg/mL), or with LPS+Eritoran (2 microg/mL) and their phenylephrine-induced contractility was measured using a myograph. The expression of cytokines in aortic tissue was examined by real-time polymerase chain reaction. In control mice LPS induced a significant decrease of blood pressure and an increase of heart rate, whereas C3H/HeJ remained unaffected. LPS induced an increase of cytokine expression and a depression of vascular contractility only in control mice but not in C3H/HeJ. L-NAME and SMT increased contractility in all rings and restored LPS-dependent depression of contractility. Eritoran prevented LPS-induced loss of contractility.

CONCLUSIONS

LPS upregulates cytokine expression via TLR4 and induces attenuation of smooth muscle contractility which can be effectively antagonized.

Mechanisms of sepsis-induced cardiac dysfunction

OBJECTIVES

To review mechanisms underlying sepsis-induced cardiac dysfunction in general and intrinsic myocardial depression in particular.

DATA SOURCE

MEDLINE database.

DATA SYNTHESIS

Myocardial depression is a well-recognized manifestation of organ dysfunction in sepsis. Due to the lack of a generally accepted definition and the absence of large epidemiologic studies, its frequency is uncertain. Echocardiographic studies suggest that 40% to 50% of patients with prolonged septic shock develop myocardial depression, as defined by a reduced ejection fraction. Sepsis-related changes in circulating volume and vessel tone inevitably affect cardiac performance. Although the coronary circulation during sepsis is maintained or even increased, alterations in the microcirculation are likely. Mitochondrial dysfunction, another feature of sepsis-induced organ dysfunction, will also place the cardiomyocytes at risk of adenosine triphosphate depletion. However, clinical studies have demonstrated that myocardial cell death is rare and that cardiac function is fully reversible in survivors. Hence, functional rather than structural changes seem to be responsible for intrinsic myocardial depression during sepsis. The underlying mechanisms include down-regulation of beta-adrenergic receptors, depressed postreceptor signaling pathways, impaired calcium liberation from the sarcoplasmic reticulum, and impaired electromechanical coupling at the myofibrillar level. Most, if not all, of these changes are regulated by cytokines and nitric oxide.

CONCLUSIONS

Integrative studies are needed to distinguish the hierarchy of the various mechanisms underlying septic cardiac dysfunction. As many of these changes are related to severe inflammation and not to infection per se, a better understanding of septic myocardial dysfunction may be usefully extended to other systemic inflammatory conditions encountered in the critically ill. Myocardial depression may be arguably viewed as an adaptive event by reducing energy expenditure in a situation when energy generation is limited, thereby preventing activation of cell death pathways and allowing the potential for full functional recovery.

Toll-like receptor 4 deficiency: smaller infarcts, but no gain in function

Backgound

It has been reported that Toll-like receptor 4 (TLR4) deficiency reduces infarct size after myocardial ischemia/reperfusion (MI/R). However, measurement of MI/R injury was limited and did not include cardiac function. In a chronic closed-chest model we assessed whether cardiac function is preserved in TLR4-deficient mice (C3H/HeJ) following MI/R, and whether myocardial and systemic cytokine expression differed compared to wild type (WT).

Results

Infarct size (IS) in C3H/HeJ assessed by TTC staining after 60 min ischemia and 24h reperfusion was significantly smaller than in WT. Despite a smaller infarct size, echocardiography showed no functional difference between C3H/HeJ and WT. Left-ventricular developed pressure measured with a left-ventricular catheter was lower in C3H/HeJ (63.0 ± 4.2 mmHg vs. 77.9 ± 1.7 mmHg in WT, p < 0.05). Serum cytokine levels and myocardial IL-6 were higher in WT than in C3H/HeJ (p < 0.05). C3H/HeJ MI/R showed increased myocardial IL-1β and IL-6 expression compared to their respective shams (p < 0.05), indicating TLR4-independent cytokine activation due to MI/R.

Conclusion

These results demonstrate that, although a mutant TLR4 signaling cascade reduces myocardial IS and serum cytokine levels, it does not preserve myocardial function. The change in inflammatory response, secondary to a non-functional TLR-4 receptor, may contribute to the observed dichotomy between infarct size and function in the TLR-4 mutant mouse.

Aldose reductase mediates endotoxin-induced production of nitric oxide and cytotoxicity in murine macrophages

Aldose reductase (AR) is a ubiquitously expressed protein with pleiotrophic roles as an efficient catalyst for the reduction of toxic lipid aldehydes and mediator of hyperglycemia, cytokine, and growth factor-induced redox-sensitive signals that cause secondary diabetic complications. Although AR inhibition has been shown to be protective against oxidative stress signals, the role of AR in regulating nitric oxide (NO) synthesis and NO-mediated apoptosis has not been elucidated to date. We therefore investigated the role of AR in regulating lipopolysaccharide (LPS)-induced NO synthesis and apoptosis in RAW 264.7 macrophages. Inhibition or RNA interference ablation of AR suppressed LPS-stimulated production of NO and overexpression of iNOS mRNA. Inhibition or ablation of AR also prevented the LPS-induced apoptosis, cell cycle arrest, activation of caspase-3, p38-MAPK, JNK, NF-kappaB, and AP1. In addition, AR inhibition prevented the LPS-induced down-regulation of Bcl-xl and up-regulation of Bax and Bak in macrophages. L-Arginine increased and L-NAME decreased the severity of cell death caused by LPS and AR inhibitors prevented it. Furthermore, inhibition of AR prevents cell death caused by HNE and GS-HNE, but not GS-DHN. Our findings for the first time suggest that AR-catalyzed lipid aldehyde-glutathione conjugates regulate the LPS-induced production of inflammatory marker NO and cytotoxicity in RAW 264.7 cells. Inhibition or ablation of AR activity may be a potential therapeutic target in endotoximia and other inflammatory diseases.

ELUCIDATION OF TOLL-LIKE RECEPTOR AND ADAPTER PROTEIN SIGNALING IN VASCULAR DYSFUNCTION INDUCED BY GRAM-POSITIVE STAPHYLOCOCCUS AUREUS OR GRAM-NEGATIVE ESCHERICHIA COLI

Pathogens contain specific pathogen-associated molecular patterns, which activate pattern recognition receptors of the innate immune system such as Toll-like receptors (TLRs). Although there is a clear evidence of how macrophages sense pathogens, we know less about such processes in vessels. This is critical to understand because activation of vascular cells and the subsequent induction of inflammatory genes by bacteria are crucial events in the development of septic shock. In the current study we have used genetically modified mice to investigate the role of TLRs, adapter proteins, tumor necrosis factor alpha (TNFalpha), and nitric oxide synthase II (NOSII) in vascular dysfunction induced by Gram-positive (Staphylococcus aureus) or Gram-negative (Escherichia coli) bacteria. Our data show that Gram-positive S. aureus or Gram-negative E. coli causes vascular dysfunction via the induction of NOSII. For S. aureus, this process requires TLR2, TLR6, myeloid differentiation factor 88 (MyD88) adapter-like, MyD88, and TNF, but not TLR4 or TLR1. Vascular dysfunction induced by E. coli requires TLR4 but has no requirement for TLR2, TLR1, TLR6, or TNF, and a partial but incomplete requirement of MyD88 and TIR domain-containing adapter inducing interferon-beta. Staphylococcus aureus induced NOSII protein expression in vascular smooth muscle cells but not in macrophages, whereas E. coli induced NOSII in both cell types. Our data are the first to establish the definitive roles of specific TLRs in the sensing of Gram-positive and Gram-negative bacteria by vessels and demonstrate that macrophages and blood vessels may differ in their response to pathogens.

Role of Toll-like receptor 4 for the pathogenesis of acute lung injury in Gram-negative sepsis

BACKGROUND AND OBJECTIVE

Proinflammatory cytokines as well as nitric oxide (NO) play a major role in mediating the response to lipopolysaccharide (LPS). The present study tested the hypothesis that LPS induces proinflammatory cytokines in the lung via the Toll-like receptor 4 (TLR4)/CD14 signalling cascade.

METHODS

Control mice and TLR4-deficient (TLR4-D) mice were used to test TLR4-mediated effects of LPS. Both strains received either Escherichia coli LPS (20 mg kg-1 intraperitoneal) or saline and their lungs were collected at different time points. Pulmonary nuclear factor kappaB (NFkappaB) activation was investigated with electromobility shift assay. mRNA expression of inflammatory mediators and their corresponding receptors were detected with Ribonuclease Protection Assay. Protein expression was detected by ELISA and western blotting. Inducible NO synthase (iNOS) expression was monitored by RT-PCR and iNOS activity by conversion of l-arginine to citrulline. Immune cells were sampled by bronchoalveolar lavage (BAL) and classified.

RESULTS

LPS application induced CD14-, but not TLR4 protein expression in control mice. Activation of pulmonary NFkappaB was observed within 60 min in control, but not in TLR4-D mice. Six hours of LPS administration induced a significant increase in pulmonary tumour necrosis factor alpha-, interleukin-1beta- and interleukin-6 mRNA and protein expression in control mice compared to TLR4-D mice. Furthermore, LPS induced a significantly higher increase of the iNOS expression and catalytic activity in control mice than in TLR4-D mice. BAL revealed an increase in total cell count in all LPS treated mice.

CONCLUSION

Our findings suggest that TLR4 plays a key role for regulating the expression of relevant cytokines within the lung during endotoxic shock.

Myocardial injury modulates the innate immune system and changes myocardial sensitivity

OBJECTIVE

Transverse aortic constriction (TAC) results in a transient increase of proinflammatory cytokines, which return to baseline levels within 3 d. In contrast to cytokine baseline levels, the myocardium remains capable to respond even stronger to a new stimulus. As the molecular mechanisms for this phenomenon are unknown, we tested whether TAC modulates the innate immune system in mice and changes the inflammatory reaction to a new stimulus.

METHODS

Following 3 d of TAC or sham-operation procedure (SOP), LPS (20 mg/kg) or PBS (control) were administered intraperitoneal for 10 min as well as for 6 h. Hemodynamic parameters were recorded to measure the effects of TAC and LPS. After TAC/SOP alone CD14 expression was monitored and after additional 6 h of LPS/PBS the expression of CD14, TLR4 and proinflammatory cytokines were determined by western-blot, ELISA and RNase protection assay, respectively. Following TAC/SOP and 10 min of LPS/PBS, NFkappaB activation was investigated by EMSA.

RESULTS

TAC induced cardiac hypertrophy and elevated blood pressure. LPS application led to hypotension and other symptoms of sepsis. CD14 expression increased after TAC alone and even further after additional LPS challenge. However, we did not detect changes of TLR4 expression. Also NFkappaB activation increased after LPS challenge higher in the TAC than in the SOP group. LPS-stimulation induced also higher cytokine expression in the TAC than in the SOP group.

CONCLUSION

TAC modulates innate immunity by regulating the expression of CD14 and changes the myocardial tissue to respond more powerful to LPS.