Toll-like receptor 4-myeloid differentiation factor 88 signaling contributes to ventilator-induced lung injury in mice

Inhibition of importin-7 attenuates ventilator-induced lung injury by targeting nuclear translocation of p38

BACKGROUND

The ability of p38 to phosphorylate substrates in the nucleus and the role of nuclear p38 in the regulation of inflammation have focused attention on the subcellular localization of the kinase. Although it is clear that p38 shuttles to the nucleus upon stimulation, the mechanisms that regulate p38 nuclear input in response to mechanical stretch remain to be determined.

METHODS

Cyclic stretch (CS)-induced nuclear translocation of p38 was determined by Western blotting and immunofluorescence. The p38 interacting protein was identified using endogenous pull-down and protein binding assays. The potential role of importin-7 (Imp7) in CS-induced nuclear translocation of p38 and p38-dependent gene expression was confirmed using a series of in vitro and in vivo experiments. Furthermore, we tested the therapeutic potential of intratracheal administration of Imp7 siRNA-loaded nanoparticles in the ventilator-induced lung injury (VILI) mouse model.

RESULTS

We show that CS induced phosphorylation-dependent nuclear translocation of p38, which required the involvement of microtubules and dynein. Endogenous pull-down assay revealed Imp7 to be a potential p38-interacting protein, and the direct interaction between p38 and Imp7 was confirmed by in vitro and in vivo binding assays. Furthermore, silencing Imp7 inhibited CS-induced nuclear translocation of p38 and subsequent cytokine production. Notably, intratracheal administration of Imp7 siRNA nanoparticles attenuated lung inflammation and histological damage in the VILI mouse model.

CONCLUSIONS

Our findings uncover a key role for Imp7 in the process of p38 nuclear import after CS stimulation and highlight the potential of preventing p38 nuclear translocation in treatment of VILI.

Xuebijing injection inhibited neutrophil extracellular traps to reverse lung injury in sepsis mice via reducing Gasdermin D

The mortality of sepsis and septic shock remains high worldwide. Neutrophil extracellular traps (NETs) release is a major cause of organ failure and mortality in sepsis. Targeting Gasdermin D (GSDMD) can restrain NETs formation, which is promising for sepsis management. However, no medicine is identified without severe safety concerns for this purpose. Xuebijing injection (XBJ) has been demonstrated to alleviate the clinical symptoms of COVID-19 and sepsis patients, but there are not enough animal studies to reveal its mechanisms in depth. Therefore, we wondered whether XBJ relieved pulmonary damage in sepsis by suppressing NETs formation and adopted a clinically relevant polymicrobial infection model to test this hypothesis. Firstly, XBJ effectively reversed lung injury caused by sepsis and restrained neutrophils recruitment to lung by down-regulating proinflammatory chemokines, such as CSF-3, CXCL-2, and CXCR-2. Strikingly, we found that XBJ significantly reduced the expressions of NETs component proteins, including citrullinated histone H3 (CitH3), myeloperoxidase (MPO), and neutrophil elastase (NE). GSDMD contributes to the production of NETs in sepsis. Notably, XBJ exhibited a reduced effect on the expressions of GSDMD and its upstream regulators. Besides, we also revealed that XBJ reversed NETs formation by inhibiting the expressions of GSDMD-related genes. Collectively, we demonstrated XBJ protected against sepsis-induced lung injury by reversing GSDMD-related pathway to inhibit NETs formation.

Ventilator-induced lung-injury in mouse models: Is there a trap?

Ventilator-induced lung injury (VILI) is a serious acute injury to the lung tissue that can develop during mechanical ventilation of patients. Due to the mechanical strain of ventilation, damage can occur in the bronchiolar and alveolar epithelium resulting in a cascade of events that may be fatal to the patients. Patients requiring mechanical ventilation are often critically ill, which limits the possibility of obtaining patient samples, making VILI research challenging. In vitro models are very important for VILI research, but the complexity of the cellular interactions in multi-organ animals, necessitates in vivo studies where the mouse model is a common choice. However, the settings and duration of ventilation used to create VILI in mice vary greatly, causing uncertainty in interpretation and comparison of results. This review examines approaches to induce VILI in mouse models for the last 10 years, to our best knowledge, summarizing methods and key parameters presented across the studies. The results imply that a more standardized approach is warranted.

TLR4 is required for macrophage efferocytosis during resolution of ventilator-induced lung injury

Mechanical ventilation is a life-sustaining therapy for patients with respiratory failure but can cause further lung damage known as ventilator-induced lung injury (VILI). However, the intrinsic molecular mechanisms underlying recovery of VILI remain unknown. Phagocytosis of apoptotic cells (also known as efferocytosis) is a key mechanism orchestrating successful resolution of inflammation. Here we show the positive regulation of macrophage Toll-like receptor (TLR) 4 in efferocytosis and resolution of VILI. Mice were depleted of alveolar macrophages and then subjected to injurious ventilation (tidal volume, 20 mL/kg) for 4 h. On day 1 after mechanical ventilation, Tlr4^+/+ or Tlr4^-/- bone marrow-derived macrophages (BMDMs) were intratracheally administered to alveolar macrophage-depleted mice. We observed that mice depleted of alveolar macrophages exhibited defective resolution of neutrophilic inflammation, exuded protein, lung edema, and lung tissue injury after ventilation, whereas these delayed responses were reversed by administration of Tlr4^+/+ BMDMs. Importantly, these proresolving effects by Tlr4^+/+ BMDMs were abolished in mice receiving Tlr4^-/- BMDMs. The number of macrophages containing apoptotic cells or bodies in bronchoalveolar lavage fluid was much less in mice receiving Tlr4^-/- BMDMs than that in those receiving Tlr4^+/+ BMDMs. Macrophage TLR4 deletion facilitated a disintegrin and metalloprotease 17 maturation and enhanced Mer cleavage in response to mechanical ventilation. Heat shock protein 70 dramatically increased Mer tyrosine kinase surface expression, phagocytosis of apoptotic neutrophils, and rescued the inflammatory phenotype in alveolar macrophage-depleted mice receiving Tlr4^+/+ BMDMs, but not Tlr4^-/- BMDMs. Our results suggest that macrophage TLR4 promotes resolution of VILI via modulation of Mer-mediated efferocytosis.

TLR4/TRAF6/NOX2 signaling pathway is involved in ventilation-induced lung injury via endoplasmic reticulum stress in murine model

In ventilation-induced lung injury (VILI), prolonged nonpathogen-mediated inflammation is triggered as a result of alveolar hyperinflation. In our previous study, we suggested that endoplasmic reticulum (ER) stress-mediated inflammation was involved in VILI, but how ER stress is triggered remains unknown. Toll-like receptor 4 (TLR4) activation plays an important role in mechanical ventilation (MV)-induced lung inflammation, however, it is unknown whether ER stress is activated by TLR4 to participate in VILI. In this study, C57BL/6 mice were exposed to MV with high tidal volumes (HTV 20 ml/kg). Mice were pretreated with TAK-242 the TLR4 inhibitor, C25-140, the TRAF6 inhibitor, or GSK2795039, the NOX2 inhibitor. Lung tissue and bronchoalveolar lavage fluid (BALF) were collected to measure lung injury, inflammatory responses and mRNA/protein expression associated with ER stress and the TLR4/TRAF6/NOX2 signaling pathway. Our results indicate that MV with HTV caused the TLR4/TRAF6/NOX2 signaling pathway activation and production of large amounts of ROS, which led to ER stress and NF-κB mediated inflammation in VILI. Furthermore, TLR4/TRAF6/NOX2 signaling pathway inhibition attenuated ER stress response and alleviate lung injury in mice.

Roles of phosphatidyl inositol 3 kinase gamma (PI3Kγ) in respiratory diseases

Phosphatidyl inositol 3 kinase gamma (PI3Kγ) is expressed in all the cell types that are involved in airway inflammation and disease, including not only leukocytes, but also structural cells, where it is expressed at very low levels under physiological conditions, while is significantly upregulated after stress. In the airways, PI3Kγ behaves as a trigger or a controller, depending on the pathological context. In this review, the contribution of PI3Kγ in a plethora of respiratory diseases, spanning from acute lung injury, pulmonary fibrosis, asthma, cystic fibrosis and response to both bacterial and viral pathogens, will be commented.

WISP1 and TLR4 on Macrophages Contribute to Ventilator-Induced Lung Injury

Injurious mechanical ventilation has been shown to directly affect pulmonary and systemic immune responses. How these responses propagate or attenuate remains unknown. The goal of this study was to further determine whether toll-like receptor (TLR) 4 and WNT1-inducible signaling pathway protein 1 (WISP1) could contribute to injurious mechanical ventilation, especially focusing on the role of macrophages during experimental ventilator-induced lung injury. A prospective, randomized, and controlled animal study was designed, and male, wild-type (WT) C57BL/6 mice, TLR4 knockout (TLR4^-/-), and lyzTLR4 knockout (lyzTLR4^-/-) mice aging 8~12 weeks were used. Animals were anesthetized and randomized to spontaneous breathing (SB) group or to high tidal volume (VT, 20 ml/kg) mechanical ventilation (HTV) group. Histological evaluation, alveolar-capillary permeability of Evan's blue albumin (EBA), WISP1 protein levels, macrophage inflammatory protein-2 (MIP-2), and interleukin-6 (IL-6) in plasma and bronchoalveolar lavage fluid (BALF) concentrations were analyzed. HTV group was associated with a significant increase of WISP1 and EBA ratio in C57BL/6 mice, a significant decrease of WISP1 protein levels, and a significant decrease of IL-6, MIP-2 in plasma, and BALF concentrations of pro-inflammatory cytokines in TLR4^-/- and lyzTLR4^-/- knockout mice. In TLR4^-/- mice and lyzTLR4^-/- mice, there were also significant differences between SB group and HTV group in terms of H&E score and EBA ratio and level of pro-inflammation cytokines. The entire TLR4-targeted mice could further improve various inflammatory changes and damages when compared with lyzTLR4-targeted mice. What is more, TLR4^-/- mice and lyzTLR4^-/- mice reacted differently to rWISP1 and/or BMMC treated. TLR4^-/- mice had no response to rWISP1, while lyzTLR4^-/- mice still showed drastic response to both treatments. TLR4 and WISP1, especially the former one, on macrophages could contribute to releasing of pro-inflammatory cytokines during ventilator-induced lung injury. Injurious mechanical ventilation may result in an immune response which is similar to that of infection.

Protective function of DJ-1/PARK7 in lipopolysaccharide and ventilator-induced acute lung injury

Oxidative stress is considered one of the early underlying contributors of acute lung injury (ALI) and ventilator-induced lung injury (VILI). DJ-1, also known as PARK7, has a well-established role as an antioxidant. We have previously shown maintaining oxidative balance via the ATF3-Nrf2 axis was important in protection from ALI. Here, we exclusively characterize the role of DJ-1 in sterile LPS-induced ALI and VILI. DJ-1 protein expression was increased after LPS treatment in human epithelial and endothelial cell lines and lungs of wild-type mice. DJ-1 deficient mice exhibited greater susceptibility to LPS-induced acute lung injury as demonstrated by increased cellular infiltration, augmented levels of pulmonary cytokines, enhanced ROS levels and oxidized by-products, increased pulmonary edema and cell death. In a two-hit model of LPS and mechanical ventilation (MV), DJ-1 deficient mice displayed enhanced susceptibility to inflammation and lung injury. Collectively, these results identify DJ-1 as a negative regulator of ROS and inflammation, and suggest its expression protects from sterile lung injury driven by high oxidative stress.

Mechanical Ventilation with Moderate Tidal Volume Exacerbates Extrapulmonary Sepsis-Induced Lung Injury via IL33-WISP1 Signaling Pathway

ABSTRACT

IL-33 and WNT1-inducible secreted protein (WISP1) play central roles in acute lung injury (ALI) induced by mechanical ventilation with moderate tidal volume (MTV) in the setting of sepsis. Here, we sought to determine the inter-relationship between IL-33 and WISP1 and the associated signaling pathways in this process.We used a two-hit model of cecal ligation puncture (CLP) followed by MTV ventilation (4 h 10 mL/kg) in wild-type, IL-33-/- or ST2-/- mice or wild-type mice treated with intratracheal antibodies to WISP1. Macrophages (Raw 264.7 and alveolar macrophages from wild-type or ST2-/- mice) were used to identify specific signaling components.CLP + MTV resulted in ALI that was partially sensitive to genetic ablation of IL-33 or ST2 or antibody neutralization of WISP1. Genetic ablation of IL-33 or ST2 significantly prevented ALI after CLP + MTV and reduced levels of WISP1 in the circulation and bronchoalveolar lung fluid. rIL-33 increased WISP1 in alveolar macrophages in an ST2, PI3K/AKT, and ERK dependent manner. This WISP1 upregulation and WNT β-catenin activation were sensitive to inhibition of the β-catenin/TCF/CBP/P300 nuclear pathway.We show that IL-33 drives WISP1 upregulation and ALI during MTV in CLP sepsis. The identification of this relationship and the associated signaling pathways reveals a number of possible therapeutic targets to prevent ALI in ventilated sepsis patients.

Toll-Like Receptor-4-Mediated Inflammation is Involved in Intermittent Hypoxia-Induced Lung Injury

PURPOSE

Intermittent hypoxia (IH) is a recognized risk factor for multiple organs damage, resulting in lung injury. Its pathophysiology is still poorly understood. Toll-like receptor 4 (TLR4) signaling plays a critical role in host immune response to invading pathogen and non-infectious tissue injury. The role of TLR4-mediated inflammation in IH-induced lung injury was investigated in this study.

METHODS

Lean adult male TLR4-deficient (TLR4^-/-) mice and their controls (C57BL/6 mice) were exposed to either IH (FiO₂ 6-8% for 25 s, 150 s/cycle, 8 h/day) or air (normoxic mice) for 6 weeks. Animals were sacrificed after 6-week exposure, and the lung tissues were harvested for morphological and inflammatory analyses. The expression of TLR4 and nuclear factor kappa-B (NF-κB) P65 were examined by real-time quantitative polymerase chain reaction and immunohistochemical method. Serum cytokine levels of interleukin (IL)-6 and tumor necrosis factor-alpha (TNF-α) were analyzed by enzyme-linked immunosorbent assay.

RESULTS

IH induced morphological and inflammation changes in the lung. IH for 6 weeks induced higher expression of TLR4 (C57BL/6-N vs C57BL/6-IH, P < 0.05) and resulted in higher release of TNF-α, IL-6 (P < 0.05), and NF-κB P65 (P < 0.05). These alterations were remitted by TLR4 deletion.

CONCLUSIONS

TLR4-mediated inflammation plays an important role in the development of IH-induced lung injury in mice, possibly through mechanisms involving nuclear factor-κB. Targeting TLR4/NF-κB pathway could represent a further therapeutic option for sleep apnea patients.

The Role of Voltage-Gated Sodium Channel 1.8 in the Effect of Atropine on Heart Rate: Evidence From a Retrospective Clinical Study and Mouse Model

Atropine is commonly used to counter the effects of the parasympathetic neurotransmitter acetylcholine on heart rate in clinical practice, such as in the perioperative period; however, individual differences in the response to atropine are huge. The association between SCN10A/voltage-gated sodium channel 1.8 (Na_V1.8) and cardiac conduction has been demonstrated; however, the exact role of SCN10A/Na_V1.8 in the heart rate response to atropine remains unclear. To identify the role of SCN10A variants that influence the heart rate responses to atropine, we carried out a retrospective study in 1,005 Han Chinese subjects. Our results showed that rs6795970 was associated with the heart rate response to atropine. The heart rate responses to atropine and methoctramine in Na_V1.8 knockout mice were lower, whereas the heart rate response to isoproterenol was like those in wild type mice. Furthermore, we observed that the Na_V1.8 blocker A-803467 alleviated the heart rate response to atropine in wild type mice. The retrospective study revealed a previously unknown role of Na_V1.8 in controlling the heart rate response to atropine, as shown by the animal study, a speculative mechanism that may involve the cardiac muscarinic acetylcholine receptor M2.

M1 Macrophage Activated by Notch Signal Pathway Contributed to Ventilator-Induced Lung Injury in Chronic Obstructive Pulmonary Disease Model

BACKGROUND

Ventilator-induced lung injury (VILI) in chronic obstructive pulmonary disease (COPD) is still a problem. We intended to explore the role of macrophage polarity in VILI and the underlying mechanism.

MATERIALS AND METHODS

COPD model was created by cigarette smoke and ventilated. Macrophages were isolated, and the wet/dry (W/D) ratio was determined after modeling, and proteins in bronchoalveolar lavage fluid (BALF) were assessed by bicinchoninic acid assay. Histopathology was observed by Hematoxylin-Eosin staining. Tumor necrosis factor (TNF)-α and interleukin (IL)-6 levels were measured by enzyme-linked immunosorbent assay. Macrophage polarity was assessed by flow cytometry. Protein levels were measured by Western blot and mRNA by quantitative real-time polymerase chain reaction.

RESULTS

Pathology statement was worsened, and the W/D ratio, protein level in BALF, TNF-α level, and IL-6 levels were elevated in cigarette smoke-induced COPD model. Notch-1 intracellular domain, hairy and enhancer of split (Hes) 1, Hes5, hairy/enhancer-of-split related with YRPW motif protein 1, CD86, TNF-α, and inducible nitric oxide synthases expressions were raised, whereas CD206, IL-4, and IL-10 expressions were decreased in macrophages after ventilation, shifting macrophage polarity to M1 phenotype. After the inhibition of Notch signaling, pathology statement was improved, and the W/D ratio, protein level in BALF, TNF-α, IL-6, Notch-1 intracellular domain, Hes1, Hes5, hairy/enhancer-of-split related with YRPW motif protein 1, CD86, TNF-α, and inducible nitric oxide synthases expressions were decreased while CD206, IL-4, and IL-10 expressions were elevated after ventilation, shifting macrophage polarity to M2 phenotype partially.

CONCLUSIONS

Mechanical ventilation in cigarette-induced COPD could activate the Notch signal pathway and further shift the polarity of macrophage toward M1 phenotype, leading to VILI in cigarette-induced COPD.

Expression profiling analysis of long noncoding RNAs in a mouse model of ventilator-induced lung injury indicating potential roles in inflammation

The key regulators of inflammation underlying ventilator-induced lung injury (VILI) remain poorly defined. Long noncoding RNAs (lncRNAs) have been implicated in the inflammatory response of many diseases; however, their roles in VILI remain unclear. We, therefore, performed transcriptome profiling of lncRNA and messenger RNA (mRNA) using RNA sequencing in lungs collected from mice model of VILI and control groups. Gene expression was analyzed through RNA sequencing and quantitative reverse transctiption polymerase chain reaction. A comprehensive bioinformatics analysis was used to characterize the expression profiles and relevant biological functions and for multiple comparisons among the controls and the injury models at different time points. Finally, lncRNA-mRNA coexpression networks were constructed and dysregulated lncRNAs were analyzed functionally. The mRNA transcript profiling, coexpression network analysis, and functional analysis of altered lncRNAs indicated enrichment in the regulation of immune system/inflammation processes, response to stress, and inflammatory pathways. We identified the lncRNA Gm43181 might be related to lung damage and neutrophil activation via chemokine receptor chemokine (C-X-C) receptor 2. In summary, our study provides an identification of aberrant lncRNA alterations involved in inflammation upon VILI, and lncRNA-mediated regulatory patterns may contribute to VILI inflammation.

The effect of aerosolized indomethacin on lung inflammation and injury in a rat model of blunt chest trauma

Background

Acute lung contusion from blunt chest trauma (BCT) is characterized by an intense inflammatory response in the pulmonary parenchyma, which is associated with acute lung injury (ALI), acute respiratory distress syndrome and ventilator-associated pneumonia. We hypothesized that aerosolized indomethacin may reduce pulmonary inflammation and ALI in a rat model of BCT.

Methods

Sprague-Dawley rats were anesthetized and received a tracheotomy for administration of aerosolized medication through a catheter. The BCT procedure involved free-dropping a hollow metal weight (200 g) from a height of 25.5, 38.3 or 51.2 cm onto the right thorax. We administered 1 mg/kg of indomethacin or 1 mL/kg of saline intratracheally 15 minutes after BCT. The sham group had a similar procedure without the exposure to BCT and treatment. Three hours postimpact, we obtained arterial blood gas and analyzed bronchoalveolar lavage for protein concentration, polymorphonuclear leukocytes (PMN) and cytokine levels, and lung tissue samples were taken for histopathological analysis.

Results

The rats’ mean arterial pressure and heart rate dropped immediately postimpact but recovered close to that of the sham group after 30 minutes in both control and treatment groups. Compared to BCT alone, indomethacin significantly reduced the total protein level in the lungs (1.06 ± 0.39 mg/mL v. 3.75 ± 1.95 mg/mL, p = 0.006) and alveolar FD-70 leak (0.23 ± 0.19 μg/mL v. 0.53 ± 0.19 μg/mL, p = 0.02). Indomethacin also significantly attenuated the acute inflammatory response in percent PMN (13.33 ±7.5% v. 28.0 ± 12.96%, p = 0.04). Tumour necrosis factor-α and interleukin-6 decreased in the indomethacin group, but the decreases were not significant compared with other groups.

Conclusion

Aerosolized indomethacin has a protective effect against alveloar tissue permeability and inflammatory response induced by BCT.

Non‑canonical Wnt signaling contributes to ventilator‑induced lung injury through upregulation of WISP1 expression

Mechanical ventilation may cause ventilator-induced lung injury (VILI). Canonical Wnt signaling has been reported to serve an important role in the pathogenesis of VILI. Bioinformatics analysis revealed that canonical and non-canonical Wnt signaling pathways were activated in VILI. However, the role of non-canonical Wnt signaling in the pathogenesis of VILI remains unclear. The present study aimed to analyze the potential role of non-canonical Wnt signaling in VILI pathogenesis. Lung injury was assessed via Evans blue albumin permeability and histological scoring, as well as by inflammatory cytokine expression and total protein concentration in bronchoalveolar lavage fluid. The relative protein expression of canonical and non-canonical Wnt signaling pathway components were examined via western blotting and immunohistochemistry. The results demonstrated that 6 h of mechanical ventilation at low tidal volume (LTV; 6 ml/kg) or moderate tidal volume (MTV; 12 ml/kg) induced lung injury in sensitive A/J mice. Ventilation with MTV increased the protein levels of Wnt-induced secreted protein 1 (WISP1), Rho-associated protein kinase 1 (ROCK1), phosphorylated (p)-Ras homolog gene family, member A and p-C-Jun N-terminal kinase (JNK). Inhibition of ROCK1 by Y27632 and JNK by SP600125 attenuated MTV-induced lung injury and decreased the expression of proteins involved in non-canonical Wnt signaling, including WISP1. In conclusion, non-canonical Wnt signaling participates in VILI by modulating WISP1 expression, which has been previously noted as critical for VILI development. Therefore, the non-canonical Wnt signaling pathway may provide a preventive and therapeutic target in VILI.

WISP1 mediates lung injury following hepatic ischemia reperfusion dependent on TLR4 in mice

BACKGROUND

Hepatic ischemia-reperfusion injury (IRI) is a common pathological phenomenon, which causes hepatic injury as well as remote organ injuries such as the lung. Several mediators, such as oxidative stress, Ca²⁺ overload and neutrophil infiltration, have been implied in the pathogenesis of liver and remote organ injuries following reperfusion. WNT1 inducible signaling pathway protein 1 (WISP1) is an extracellular matrix protein that has been associated with the onset of several malignant diseases. Previous work in our group has demonstrated WISP1 is upregulated and contributes to proinflammatory cascades in hepatic IRI. However, the role of WISP1 in the pathogenesis of lung injury after hepatic IRI still remains unknown.

METHODS

Male C57BL/6 mice were used to examine the expression and role of WISP1 in the pathogenesis of lung injuries after hepatic IRI and explore its potential mechanisms in mediating lung injuries.

RESULTS

We found WISP1 was upregulated in lung tissues following hepatic IRI. Treatment with anti-WISP1 antibody ameliorated lung injuries with alteration of cytokine profiles. Administration with rWISP1 aggravated lung injuries following hepatic IRI through excessive production of proinflammatory cytokines and inhibition of anti-inflammatory cytokines.

CONCLUSIONS

In this study, we concluded that WISP1 contributed to lung injuries following hepatic IRI through TLR4 pathway.

Mechanical ventilation enhances extrapulmonary sepsis-induced lung injury: role of WISP1-αvβ5 integrin pathway in TLR4-mediated inflammation and injury

Background

High tidal volume ventilation of healthy lungs or exacerbation of existing acute lung injury (ALI) by more moderate mechanical ventilation (MTV) produces ventilator-induced lung injury. It is less clear whether extrapulmonary sepsis sensitizes the lung to MTV.

Methods

We used a two-hit model of cecal ligation and puncture (CLP) followed 12 h later by MTV (10 ml/kg; 6 h) to determine whether otherwise noninjurious MTV enhances CLP-induced ALI by contrasting wildtype and TLR4^−/− mice with respect to: alveolar-capillary permeability, histopathology and intrapulmonary levels of WNT-inducible secreted protein 1 (WISP1) and integrin β5; plasma levels of cytokines and chemokines (TNF-α, IL-6, MIP-2, MCP-1) and intrapulmonary neutrophil infiltration; and other inflammatory signaling via intrapulmonary activation of JNK, p38 and ERK. A separate cohort of mice was pretreated with intratracheal neutralizing antibodies to WISP1, integrin β5 or IgG as control and the presented phenotyping repeated in a two-hit model; there were 10 mice per group in these first three experiments. Also, isolated peritoneal macrophages (PM) from wildtype and TLR4^−/−, MyD88^−/− and TRIF^−/− mice were used to identify a WISP1–TLR4–integrin β5 pathway; and the requisite role of integrin β5 in WISP1-induced cytokine and chemokine production in LPS-primed PM was examined by siRNA treatment.

Results

MTV, that in itself did not cause ALI, exacerbated increases in alveolar-capillary permeability, histopathologic scoring and indices of pulmonary inflammation in mice that previously underwent CLP; the effects of this two-hit model were abrogated in TLR4^−/− mice. Attendant with these findings was a significant increase in intrapulmonary WISP1 and integrin β5 in the two-hit model. Anti-WISP1 or anti-integrin β5 antibodies partially inhibited the two-hit phenotype. In PM, activation of TLR4 led to an increase in integrin β5 expression that was MyD88 and NF-κB dependent. Recombinant WISP1 increased LPS-induced cytokine release in PM that was inhibited by silencing either TLR4 or integrin β5.

Conclusions

These data show for the first time that otherwise noninjurious mechanical ventilation can exacerbate ALI due to extrapulmonary sepsis underscoring a potential interactive contribution of common events (sepsis and mechanical ventilation) in critical care, and that a WISP1–TLR4–integrin β5 pathway contributes to this phenomenon.

Electronic supplementary material

The online version of this article (10.1186/s13054-018-2237-0) contains supplementary material, which is available to authorized users.

Toll-like receptor-4 deficiency alleviates chronic intermittent hypoxia-induced renal injury, inflammation, and fibrosis

BACKGROUND

Obstructive sleep apnea (OSA)-associated chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH) triggered renal damage. This study aims to investigate the role of toll-like receptor-4 (TLR4) in underlying mechanism involved chronic intermittent hypoxia (CIH)-induced renal damage.

METHODS

C57BL/6J mice with normal TLR4 (TLR4 WT) or deficient TLR4 (TLR4 KO) were divided into four groups and exposed to normal air (NA) and CIH: TLR4 WT + NA, TLR4 KO + NA, TLR4 WT + CIH, and TLR4 KO + CIH. CIH lasted for 8 h/day and 7 days/week for 6 weeks. Renal injury and inflammation were evaluated by histology and ELISA. Renal tubular apoptosis, macrophages, and fibroblasts recruitment were determined by TUNEL assay, immunofluorescence, and western blot.

RESULTS

In response to CIH, TLR4 deficiency alleviated renal histological injury, renal dysfunction, and fibrosis. TLR4 deficiency ameliorated renal dysfunction (serum BUN and creatinine) and tubular endothelial apoptosis determined by immunofluorescence staining of CD31 and TUNEL, and western blot of apoptotic protein (caspase-3, c-caspase-3, and Bax/Bcl-2 ratio). Furthermore, we also found TLR4 deficiency abrogated CIH-induced macrophages (CD68) and fibroblasts (α-SMA) recruitment, further reducing expression of extra-cellular matrix protein (collagen I and collagen IV) and inflammatory cytokines release (IL-6, TNF-α, and MCP-1). Finally, we used immunohistochemistry to demonstrate that TLR4 deficiency attenuated increased expression of MyD88 and NF-kB p65 after CIH treatment.

CONCLUSIONS

Our data suggest that TLR4 plays a vital role in CIH-induced renal injury, inflammation and fibrosis, and inhibition of TLR4 probably provides a therapeutic potential for CIH-induced kidney damage.

The triggering receptor expressed by myeloid cells-1 activates TLR4-MyD88-NF-κB-dependent signaling to aggravate ventilation-induced lung inflammation and injury in mice

The triggering receptor expressed by myeloid cells-1 (TREM-1) plays an important role in infectious and autoimmune diseases but how it contributes to ventilation-induced lung injury (VILI) and inflammation is unclear. Here, we examine the possibility that TREM-1 activates signaling dependent on Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (Myd88) and nuclear factor (NF)-κB, which leads in turn to VILI. In a mouse model of VILI, which we validated based on lung edema and histopathology as well as cytokine levels, we examine mRNA and protein levels of TREM-1, TLR4, MyD88, NF-κB and its inhibitory protein I-κB in animals subjected to ventilation at normal or high tidal volume. The extent of lung edema, injury and inflammation were higher in the high tidal volume animals, as were the expression levels of all proteins examined. Treatment with TREM-1 agonist aggravated these effects, whereas treatment with TREM-1 antagonist attenuated them. Our results suggest that aggravation of VILI by TREM-1 in mice may be associated with TLR4-MyD88-NF-κB-dependent signaling.

Dexmedetomidine reduces ventilator-induced lung injury (VILI) by inhibiting Toll-like receptor 4 (TLR4)/nuclear factor (NF)-κB signaling pathway

Mechanical ventilation (MV) may lead to ventilator-induced lung injury (VILI). Previous research has shown that dexmedetomidine attenuates pulmonary inflammation caused by MV, but the underlying mechanisms remain unclear. Our study aims to test whether dexmedetomidine has a protective effect against VILI and to explore the possible molecular mechanisms using the rat model. Thirty adult male Wistar rats weighing 200-250 g were randomly assigned to 5 groups (n = 6): control, low tidal volume MV (LMV), high tidal volume (HVT) MV (HMV), HVT MV + dexmedetomidine (DEX), HVT MV + dexmedetomidine + yohimbine (DEX+Y). Rats were euthanized after being ventilated for 4 hours. Pathological changes, lung wet/dry (W/D) weight ratio, lung myeloperoxidase (MPO) activity, levels of inflammatory cytokines (i.e., interleukin [IL]-1β, tumor necrosis factor alpha [TNF-α], and IL-6) in the bronchoalveolar lavage fluid (BALF) and lung tissues, expression of Toll-like receptor 4 (TLR4) and nuclear factor (NF)-κB, and activation of NF-κB in lung tissues were measured. Compared with HMV, DEX group showed fewer pathological changes, lower W/D ratios and decreased MPO activity of the lung tissues and lower concentrations of the inflammatory cytokines in the BALF and lung tissues. Dexmedetomidine significantly inhibited the expression of TLR4 and NF-κB and activation of NF-κB. Yohimbine partly alleviated the effects of dexmedetomidine. Dexmedetomidine reduced the inflammatory response to HVT-MV and had a protective effect against VILI, with the inhibition of the TLR4/NF-κB signaling pathway, at least partly via α2-adrenoceptors.

RNA‑sequencing analysis of aberrantly expressed long non‑coding RNAs and mRNAs in a mouse model of ventilator‑induced lung injury

Long non-coding RNAs (lncRNAs) are closely associated with the regulation of various biological processes and are involved in the pathogenesis of numerous diseases. However, to the best of our knowledge, the role of lncRNAs in ventilator‑induced lung injury (VILI) has yet to be evaluated. In the present study, high‑throughput sequencing was applied to investigate differentially expressed lncRNAs and mRNAs (fold change >2; false discovery rate <0.05). Bioinformatics analysis was employed to predict the functions of differentially expressed lncRNAs. A total of 104 lncRNAs (74 upregulated and 30 downregulated) and 809 mRNAs (521 upregulated and 288 downregulated) were differentially expressed in lung tissues from the VILI group. Gene ontology analysis demonstrated that the differentially expressed lncRNAs and mRNAs were mainly associated with biological functions, including apoptosis, angiogenesis, neutrophil chemotaxis and skeletal muscle cell differentiation. The top four enriched pathways were the tumor necrosis factor (TNF) signaling pathway, P53 signaling pathway, neuroactive ligand‑receptor interaction and the forkhead box O signaling pathway. Several lncRNAs were predicted to serve a vital role in VILI. Subsequently, three lncRNAs [mitogen‑activated protein kinase kinase 3, opposite strand (Map2k3os), dynamin 3, opposite strand and abhydrolase domain containing 11, opposite strand] and three mRNAs (growth arrest and DNA damage‑inducible α, claudin 4 and thromboxane A2 receptor) were measured by reverse transcription‑quantitative polymerase chain reaction, in order to confirm the veracity of RNA‑sequencing analysis. In addition, Map2k3os small interfering RNA transfection inhibited the expression of stretch‑induced cytokines [TNF‑α, interleukin (IL)‑1β and IL‑6] in MLE12 cells. In conclusion, the results of the present study provided a profile of differentially expressed lncRNAs in VILI. Several important lncRNAs may be involved in the pathological process of VILI, which may be useful to guide further investigation into the pathogenesis for this disease.

Transduced PEP-1-Heme Oxygenase-1 Fusion Protein Attenuates Lung Injury in Septic Shock Rats

Oxidative stress and inflammation have been identified to play a vital role in the pathogenesis of lung injury induced by septic shock. Heme oxygenase-1 (HO-1), an effective antioxidant and anti-inflammatory and antiapoptotic substance, has been used for the treatment of heart, lung, and liver diseases. Thus, we postulated that administration of exogenous HO-1 protein transduced by cell-penetrating peptide PEP-1 has a protective role against septic shock-induced lung injury. Septic shock produced by cecal ligation and puncture caused severe lung damage, manifested in the increase in the lung wet/dry ratio, oxidative stress, inflammation, and apoptosis. However, these changes were reversed by treatment with the PEP-1-HO-1 fusion protein, whereas lung injury in septic shock rats was alleviated. Furthermore, the septic shock upregulated the expression of Toll-like receptor 4 (TLR4) and transcription factor NF-κB, accompanied by the increase of lung injury. Administration of PEP-1-HO-1 fusion protein reversed septic shock-induced lung injury by downregulating the expression of TLR4 and NF-κB. Our study indicates that treatment with HO-1 protein transduced by PEP-1 confers protection against septic shock-induced lung injury by its antioxidant, anti-inflammatory, and antiapoptotic effects.

Mitochondrial damage pathways in ventilator induced lung injury (VILI): an update

Although reduced tidal volumes have improved patient survival during ventilation for acute lung injury, further improvements will require pharmacologic interventions of the cellular pathways for inflammation and injury. We previously reported that pretreatment with mitochondrial targeted mtDNA repair enzymes largely prevented lung injury and inflammation during a protocol for moderately severe ventilation induced lung injury. GSH/GSSG ratios indicated that free radical production had been reduced to baseline levels by treatment. The central role of the alveolar macrophages and cellular mechanisms of injury are discussed. This includes a rapid calcium entry and mitochondrial production of excessive reactive oxygen species. Excessive ROS can then result in activation of the NLRP3 inflammasome and secretion of IL-1 and IL-18 by caspase-1. A simultaneous activation of NFkB to transcribe pro forms of the cytokines is stimulated by damage associated molecular pattern (DAMP) recognition receptors. These are primarily TLR4 responding to various cellular damage products and TLR9 responding to mtDNA fragments that appear to be primarily involved. Intervention in these pathways could result in useful future clinical treatments.

Saquinavir Ameliorates Liver Warm Ischemia-Reperfusion-Induced Lung Injury via HMGB-1- and P38/JNK-Mediated TLR-4-Dependent Signaling Pathways

Liver ischemia and reperfusion (I/R) induce local and distant tissue injuries, contributing to morbidity and mortality in a wider range of pathologies. This is especially seen under uncontrolled aseptic inflammatory conditions, leading to injury of remote organs, such as lung injury, and even failure. Saquinavir (SQV) is a kind of HIV protease inhibitor that possesses an anti-inflammatory property. In this study, we investigated whether SQV suppresses Toll-like receptor 4- (TLR4-) dependent signaling pathways of high-mobility group box 1 (HMGB1) and P38/JNK, conferring protection against murine liver I/R-induced lung injury. To investigate our hypothesis, C57BL/6 mice and TLR4 knockout mice (TLR4^−/−) were used to perform the study. SQV administration markedly attenuated remote lung tissue injury after 1-hour ischemia and 6-hour reperfusion of the liver. To our expectation, SQV attenuated I/R-induced lung edema, hyperpermeability, and pathological injury. The beneficial effects of SQV were associated with decreased levels of circulating and lung tissue inflammatory cytokines, such as IL-6, IL-1β, TNF-α, and iNOS. The protective effect of SQV was also associated with decreased lung tissue expression of HMGB1, TLR-4, and p-P38/JNK, but not p-ERK in wild-type liver I/R mice. Overall, this study demonstrated a new role of SQV, facilitating negative regulation of HMGB1- and P38/JNK-mediated TLR-4-dependent signaling pathways, conferring protection against liver I/R-induced lung injury.

Neutrophil Extracellular Traps Are Pathogenic in Ventilator-Induced Lung Injury and Partially Dependent on TLR4

The pathogenesis of ventilator-induced lung injury (VILI) is associated with neutrophils. Neutrophils release neutrophil extracellular traps (NETs), which are composed of DNA and granular proteins. However, the role of NETs in VILI remains incompletely understood. Normal saline and deoxyribonuclease (DNase) were used to study the role of NETs in VILI. To further determine the role of Toll-like receptor 4 (TLR4) in NETosis, we evaluated the lung injury and NET formation in TLR4 knockout mice and wild-type mice that were mechanically ventilated. Some measures of lung injury and the NETs markers were significantly increased in the VILI group. DNase treatment markedly reduced NETs markers and lung injury. After high-tidal mechanical ventilation, the NETs markers in the TLR4 KO mice were significantly lower than in the WT mice. These data suggest that NETs are generated in VILI and pathogenic in a mouse model of VILI, and their formation is partially dependent on TLR4.

High-mobility group box 1 protein is involved in the protective effect of Saquinavir on ventilation-induced lung injury in mice

Saquinavir (SQV) is the first FDA approved HIV protease inhibitor. Previous studies showed that SQV can limit Toll-like receptor-4 (TLR4)-mediated inflammatory pathway and nuclear factor-κB (NF-κB) activation, thereby playing a protective role in many kinds of diseases. High-mobility group box 1 (HMGB1) has been identified as an inflammatory mediator and it might express its toxicity in a short period of time in ventilator-induced lung injury (VILI). In this study, C57BL/6 mice were randomly divided into four groups (n = 10): control group and control with SQV group (Con + SQV) were spontaneous breath. HTV group (HTV) received high tidal volume ventilation (HTV) for 4 h. HTV with SQV group (HTV + SQV) were pretreated with 5 mg/kg of SQV for 7 days before HTV. Mice were sacrificed after 4 h of HTV. Lung wet/dry weight (W/D) ratio, alveolar-capillary permeability to Evans blue albumin (EBA), cell counts, total proteins in bronchoalveolar lavage fluid (BALF), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) level in BALF and lung tissue, and lung histopathology were examined. Our results showed that HTV caused significant lung injury and NF-κB activation, which was correlated with the increase of TNF-α and IL-6 levels in BALF and plasma. SQV pretreatment significantly attenuated pulmonary inflammatory injury, as well as NF-κB activation. These findings indicate that the protective effect of SQV may be associated with the inhibition of NF-κB activation and HMGB1 expression in mice.

Cyclic stretch induced IL-33 production through HMGB1/TLR-4 signaling pathway in murine respiratory epithelial cells

Interleukin 33 (IL-33), an inflammatory and mechanically responsive cytokine, is an important component of a TLR4-dependent innate immune process in mucosal epithelium. Although TLR4 also plays a role in sensing biomechanical stretch, a pathway of stretch-induced TLR4-dependent IL-33 biosynthesis has not been revealed. In the current study, we show that short term (6 h) cyclic stretch (CS) of cultured murine respiratory epithelial cells (MLE-12) increased intracellular IL-33 expression in a TLR4 dependent fashion. There was no detectable IL-33 in conditioned media in this interval. CS, however, increased release of the notable alarmin, HMGB1, and a neutralizing antibody (2G7) to HMGB1 completely abolished the CS mediated increase in IL-33. rHMGB1 increased IL-33 synthesis and this was partially abrogated by silencing TLR4 suggesting additional receptors for HMGB1 are involved in its regulation of IL-33. Collectively, these data reveal a HMGB1/TLR4/IL-33 pathway in the response of respiratory epithelium to mechanical stretch.

Intravenous superoxide dismutase as a protective agent to prevent impairment of lung function induced by high tidal volume ventilation

Background

Positive-pressure mechanical ventilation is essential in assisting patients with respiratory failure in the intensive care unit and facilitating oxygenation in the operating room. However, it was also recognized as a primary factor leading to hospital-acquired pulmonary dysfunction, in which pulmonary oxidative stress and lung inflammation had been known to play important roles. Cu/Zn superoxide dismutase (SOD) is an important antioxidant, and possesses anti-inflammatory capacity. In this study, we aimed to study the efficacy of Cu/Zn SOD, administered intravenously during high tidal volume (HTV) ventilation, to prevent impairment of lung function.

Methods

Thirty-eight male Sprague-Dawley rats were divided into 3 groups: 5 h ventilation with (A) low tidal volume (LTV; 8 mL/kg; n = 10), (B) high tidal volume (HTV; 18 mL/kg; n = 14), or (C) HTV and intravenous treatment of Cu/Zn SOD at a dose of 1000 U/kg/h (HTV + SOD; n = 14). Lung function was evaluated both at baseline and after 5-h ventilation. Lung injury was assessed by histological examination, lung water and protein contents in the bronchoalveolar lavage fluid (BALF). Pulmonary oxidative stress was examined by concentrations of methylguanidine (MG) and malondialdehyde (MDA) in BALF, and antioxidative activity by protein expression of glutathione peroxidase-1 (GPx-1) in the lung. Severity of lung inflammation was evaluated by white blood cell and differential count in BALF, and protein expression of inducible nitric oxide synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), tumor necrosis factor-α (TNF-α), matrix metalloproteinase-9 (MMP-9), and mRNA expression of nuclear factor-κB (NF-κB) in the lung. We also examined protein expression of surfactant protein (SP)-A and D and we measured hourly changes in serum nitric oxide (NO) level.

Results

Five hours of LTV ventilation did not induce a major change in lung function, whereas 5 h of HTV ventilation induced apparent combined restrictive and obstructive lung disorder, together with increased pulmonary oxidative stress, decreased anti-oxidative activity and increased lung inflammation (P < 0.05). HTV ventilation also decreased SP-A and SP-D expression and suppressed serum NO level during the time course of ventilation. Cu/Zn SOD administered intravenously during HTV ventilation effectively reversed associated pulmonary oxidative stress and lung inflammation (P < 0.05); moreover, it preserved SP-A and SP-D expressions in the lung and increased serum nitric oxide (NO) level, enhancing vascular NO bioavailability.

Conclusions

HTV ventilation can induce combined restrictive and obstructive lung disorders. Intravenous administration of Cu/Zn SOD during HTV ventilation can prevent lung function impairment and lung injury via reducing pulmonary oxidative stress and lung inflammation, preserving pulmonary surfactant expression, and enhancing vascular NO bioavailability.

Regulation of NADPH oxidases in skeletal muscle

The only known function of NAD(P)H oxidases is to produce reactive oxygen species (ROS). Skeletal muscles express three isoforms of NAD(P)H oxidases (Nox1, Nox2, and Nox4) that have been identified as critical modulators of redox homeostasis. Nox2 acts as the main source of skeletal muscle ROS during contractions, participates in insulin signaling and glucose transport, and mediates the myocyte response to osmotic stress. Nox2 and Nox4 contribute to skeletal muscle abnormalities elicited by angiotensin II, muscular dystrophy, heart failure, and high fat diet. Our review addresses the expression and regulation of NAD(P)H oxidases with emphasis on aspects that are relevant to skeletal muscle. We also summarize: i) the most widely used NAD(P)H oxidases activity assays and inhibitors, and ii) studies that have defined Nox enzymes as protagonists of skeletal muscle redox homeostasis in a variety of health and disease conditions.

Toll-like receptor 4 knockout ameliorates neuroinflammation due to lung-brain interaction in mechanically ventilated mice

Toll-like receptor 4 (TLR4) is a crucial receptor in the innate immune system, and increasing evidence supports its role in inflammation, stress, and tissue injury, including injury to the lung and brain. We aimed to investigate the effects of TLR4 on neuroinflammation due to the lung-brain interaction in mechanically ventilated mice. Male wild-type (WT) C57BL/6 and TLR4 knockout (TLR4 KO) mice were divided into three groups: (1) control group (C): spontaneous breathing; (2) anesthesia group (A): spontaneous breathing under anesthesia; and (3) mechanical ventilation group (MV): 6h of MV under anesthesia. The behavioral responses of mice were tested with fear conditioning tests. The histological changes in the lung and brain were assessed using hematoxylin-eosin (HE) staining. The level of TLR4 mRNA in tissue was measured using reverse transcription-polymerase chain reaction (RT-PCR). The levels of inflammatory cytokines were measured with an enzyme-linked immunosorbent assay (ELISA). Microgliosis, astrocytosis, and the TLR4 immunoreactivity in the hippocampus were measured by double immunofluorescence. MV mice exhibited impaired cognition, and this impairment was less severe in TLR4 KO mice than in WT mice. In WT mice, MV increased TLR4 mRNA expression in the lung and brain. MV induced mild lung injury, which was prevented in TLR4 KO mice. MV mice exhibited increased levels of inflammatory cytokines, increased microglia and astrocyte activation. Microgliosis was alleviated in TLR4 KO mice. MV mice exhibited increased TLR4 immunoreactivity, which was expressed in microglia and astrocytes. These results demonstrate that TLR4 is involved in neuroinflammation due to the lung-brain interaction and that TLR4 KO ameliorates neuroinflammation due to lung-brain interaction after prolonged MV. In addition, Administration of a TLR4 antagonist (100μg/mice) to WT mice also significantly attenuated neuroinflammation of lung-brain interaction due to prolonged MV. TLR4 antagonism may be a new and novel approach for the treatment and management of neuroinflammation in long-term mechanically ventilated patients.

RGD peptides protects against acute lung injury in septic mice through Wisp1-integrin β6 pathway inhibition

Acute lung injury is a common consequence of sepsis, a life-threatening inflammatory response caused by severe infection. In this study, we elucidate the attenuating effects of synthetic Arg-Gly-Asp-Ser peptides (RGDs) on acute lung injury in a sepsis mouse model. We further reveal that the beneficial effects of RGDs stem from their negative regulation of the Wisp1 (WNT1-inducible signaling pathway)-integrin β6 pathway. After inducing sepsis using cecal ligation and puncture (CLP), mice were randomized into experimental and control groups, and survival rates were recorded over 7 days, whereas only 20% of mice subjected to CLP survived when compared with untreated controls; the addition of RGDs to this treatment regimen dramatically increased the survival rate to 80%. Histological analysis revealed acute lung injury in CLP-treated mice, whereas those subjected to the combined treatment of CLP and RGDs showed a considerable decrease in lung injury severity. The addition of RGDs also dramatically attenuated other common sepsis-associated effects, such as increased white blood cell number in bronchoalveolar lavage fluid and decreased pulmonary capillary barrier function. Furthermore, treatment with RGDs decreased the serum and bronchoalveolar lavage fluid levels of inflammatory cytokines such as tumor necrosis factor α and interleukin 6, contrary to the CLP treatment alone that increased the levels of these proteins. Interestingly, however, RGDs had no detectable effect on bacterial invasion following sepsis induction. In addition, mice treated with RGDs showed decreased levels of wisp1 and integrin β6 when compared with CLP-treated mice. In the present study, a linkage between Wisp1 and integrin β6 was evaluated in vivo. Most strikingly, RGDs resulted in a decreased association of Wisp1 with integrin β6 based on coimmunoprecipitation analyses. These data suggest that RGDs ameliorate acute lung injury in a sepsis mouse model by inhibiting the Wisp1-integrin β6 pathway.

Lung endothelial barrier protection by resveratrol involves inhibition of HMGB1 release and HMGB1-induced mitochondrial oxidative damage via an Nrf2-dependent mechanism

High-mobility group box 1 (HMGB1) contributes to lung vascular hyperpermeability during ventilator-induced lung injury. We aimed to determine whether the natural antioxidant resveratrol protected against HMGB1-induced endothelial hyperpermeability both in vitro and in vivo. We found that HMGB1 decreased vascular endothelial (VE)-cadherin expression and increased endothelial permeability, leading to mitochondrial oxidative damage in primary cultured mouse lung vascular endothelial cells (MLVECs). Both the mitochondrial superoxide dismutase 2 mimetic MnTBAP and resveratrol blocked HMGB1-induced mitochondrial oxidative damage, VE-cadherin downregulation, and endothelial hyperpermeability. In in vivo studies, anesthetized male ICR mice were ventilated for 4h using low tidal volume (6 ml/kg) or high tidal volume (HVT; 30 ml/kg) ventilation. The mice were injected intraperitoneally with resveratrol immediately before the onset of ventilation. We found that resveratrol attenuated HVT-associated lung vascular hyperpermeability and HMGB1 production. HVT caused a significant increase in nuclear factor-erythroid 2-related factor 2 (Nrf2) nuclear translocation and Nrf2 target gene expression in lung tissues, which was further enhanced by resveratrol treatment. HMGB1 had no effect on Nrf2 activation, whereas resveratrol treatment activated the Nrf2 signaling pathway in HMGB1-treated MLVECs. Moreover, Nrf2 knockdown reversed the inhibitory effects of resveratrol on HMGB1-induced mitochondrial oxidative damage and endothelial hyperpermeability. The inhibitory effect of resveratrol on cyclic stretch-induced HMGB1 mRNA expression in primary cultured MLVECs was also abolished by Nrf2 knockdown. In summary, this study demonstrates that resveratrol protects against lung endothelial barrier dysfunction initiated by HVT. Lung endothelial barrier protection by resveratrol involves inhibition of mechanical stretch-induced HMGB1 release and HMGB1-induced mitochondrial oxidative damage. These protective effects of resveratrol might be mediated through an Nrf2-dependent mechanism.

Mechanical ventilation modulates Toll-like receptors 2, 4, and 9 on alveolar macrophages in a ventilator-induced lung injury model

OBJECTIVE

To investigate the role of Toll-like receptor 2 (TLR2), TLR4, TLR9 and myeloid differentiation factor 88 (MyD88) on alveolar macrophages in ventilator-induced lung injury (VILI).

METHODS

Male, adult pathogen-free Sprague-Dawley rats weighing 300-350 g were used in this study. Animals were tracheotomized and allowed to breathe spontaneously for 4 h or mechanically ventilated for 4 h with low or high tidal volume (7 or 40 mL/kg). TLR2, TLR4, and TLR9, MyD-88 and NF-κΒ of alveolar macrophages' expression under the different ventilation conditions were detected. Pulmonary permeability, lung inflammatory, IL-6 and IL-1β were assessed as well.

RESULTS

Rats subjected to high tidal volume showed significantly greater pulmonary permeability and lung inflammatory than the control rats. Alveolar macrophages from rats subjected to high tidal volume also showed significantly higher protein expression of TLR2 (0.59±0.049 vs. 0.35±0.036 and 0.36±0.031, both P<0.001), TLR4 (0.845±0.0395 vs. 0.401±0.026 and 0.403±0.020, both P<0.001), TLR9 (0.727±0.074 vs. 0.383±0.039 and 0.367±0.043, both P<0.001), MyD-88 (1.01±0.060 vs. 0.485±0.045 and 0.507±0.046, both P<0.001) and NF-κΒ (0.776±0.067 vs. 0.448±0.043 and 0.481±0.047, both P<0.001), as well as significantly higher concentrations of IL-6 (7.32±0.24 vs. 2.42±0.13 and 2.44±0.32, both P<0.001) and IL-1β (139.95±9.37 vs. 53.63±5.26 and 53.55±6.63, both P<0.001) than the control and low tidal volume group.

CONCLUSIONS

The overexpression of TLR2, TLR4, and TLR9 on alveolar macrophages and release of pro-inflammatory cytokines play a role in VILI.

Kinetic profiling of in vivo lung cellular inflammatory responses to mechanical ventilation

Mechanical ventilation, through overdistension of the lung, induces substantial inflammation that is thought to increase mortality among critically ill patients. The mechanotransduction processes involved in converting lung distension into inflammation during this ventilator-induced lung injury (VILI) remain unclear, although many cell types have been shown to be involved in its pathogenesis. This study aimed to identify the profile of in vivo lung cellular activation that occurs during the initiation of VILI. This was achieved using a flow cytometry-based method to quantify the phosphorylation of several markers (p38, ERK1/2, MAPK-activated protein kinase 2, and NF-κB) of inflammatory pathway activation within individual cell types. Anesthetized C57BL/6 mice were ventilated with low (7 ml/kg), intermediate (30 ml/kg), or high (40 ml/kg) tidal volumes for 1, 5, or 15 min followed by immediate fixing and processing of the lungs. Surprisingly, the pulmonary endothelium was the cell type most responsive to in vivo high-tidal-volume ventilation, demonstrating activation within just 1 min, followed by the alveolar epithelium. Alveolar macrophages were the slowest to respond, although they still demonstrated activation within 5 min. This order of activation was specific to VILI, since intratracheal lipopolysaccharide induced a very different pattern. These results suggest that alveolar macrophages may become activated via a secondary mechanism that occurs subsequent to activation of the parenchyma and that the lung cellular activation mechanism may be different between VILI and lipopolysaccharide. Our data also demonstrate that even very short periods of high stretch can promote inflammatory activation, and, importantly, this injury may be immediately manifested within the pulmonary vasculature.

BML-111, a lipoxin receptor agonist, attenuates ventilator-induced lung injury in rats

Mechanical ventilation can cause structural and functional disturbances in the lung termed ventilator-induced lung injury (VILI). The aim of this study was to evaluate whether BML-111, a lipoxin receptor agonist, could attenuate VILI. Following induction of anesthesia and tracheostomy, Sprague-Dawley rats were ventilated with low tidal volume (6 mL/kg) or high tidal volume (20 mL/kg, HVT) for 4 h. Some rats subjected to HVT ventilation received BML-111 or vehicle (saline) by intraperitoneal injection. Some rats subjected to HVT and BML-111(1 mg/kg) received BOC-2 (a FPR2/ALX antagonist) intraperitoneally 30 min before BML-111. Sham rats were tracheotomized without ventilation. Treatment with BML-111 attenuated VILI, as evidenced by improved oxygenation and reduced histological injury compared with HVT-induced lung injury. BML-111 decreased indices of inflammation such as interleukin 1β, interleukin 6, tumor necrosis factor α, and bronchoalveolar lavage neutrophil infiltration. Administration with BML-111 suppressed the decrement of the nuclear factor κB (NF-κB) inhibitor IκB-α, diminished NF-κB activation, and reduced activation of mitogen-activated protein kinase in VILI. This study indicates that BML-111 attenuated VILI via a NF-κB and mitogen-activated protein kinase dependent mechanism. BML-111 may be a promising strategy for alleviation of VILI in patients subjected to mechanical ventilation.

The receptor for advanced glycation end products in ventilator-induced lung injury

Background

Mechanical ventilation (MV) can cause ventilator-induced lung injury (VILI). The innate immune response mediates this iatrogenic inflammatory condition. The receptor for advanced glycation end products (RAGE) is a multiligand receptor that can amplify immune and inflammatory responses. We hypothesized that RAGE signaling contributes to the pro-inflammatory state induced by MV.

Methods

RAGE expression was analyzed in lung brush and lavage cells obtained from ventilated patients and lung tissue of ventilated mice. Healthy wild-type (WT) and RAGE knockout (KO) mice were ventilated with relatively low (approximately 7.5 ml/kg) or high (approximately 15 ml/kg) tidal volume. Positive end-expiratory pressure was set at 2 cm H₂O during both MV strategies. Also, WT and RAGE KO mice with lipopolysaccharide (LPS)-induced lung injury were ventilated with the above described ventilation strategies. In separate experiments, the contribution of soluble RAGE, a RAGE isoform that may function as a decoy receptor, in ventilated RAGE KO mice was investigated. Lung wet-to-dry ratio, cell and neutrophil influx, cytokine and chemokine concentrations, total protein levels, soluble RAGE, and high-mobility group box 1 (HMGB1) presence in lung lavage fluid were analyzed.

Results

MV was associated with increased RAGE mRNA levels in both human lung brush samples and lung tissue of healthy mice. In healthy high tidal volume-ventilated mice, RAGE deficiency limited inflammatory cell influx. Other VILI parameters were not affected. In our second set of experiments where we compared RAGE KO and WT mice in a 2-hit model, we observed higher pulmonary cytokine and chemokine levels in RAGE KO mice undergoing LPS/high tidal volume MV as compared to WT mice. Third, in WT mice undergoing the LPS/high tidal volume MV, we observed HMGB1 presence in lung lavage fluid. Moreover, MV increased levels of soluble RAGE in lung lavage fluid, with the highest levels found in LPS/high tidal volume-ventilated mice. Administration of soluble RAGE to LPS/high tidal volume-ventilated RAGE KO mice attenuated the production of inflammatory mediators.

Conclusions

RAGE was not a crucial contributor to the pro-inflammatory state induced by MV. However, the presence of sRAGE limited the production of pro-inflammatory mediators in our 2-hit model of LPS and high tidal volume MV.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-014-0022-1) contains supplementary material, which is available to authorized users.

Neutrophil elastase inhibitor reduces ventilation-induced lung injury via nuclear factor-κB and NF-κB repressing factor in mice

Mechanical ventilation used in patients with acute lung injury can damage pulmonary epithelial cells through production of inflammatory cytokines, oxygen radicals, and neutrophil infiltration, termed ventilator-induced lung injury. Neutrophil elastase, nuclear factor-κB (NF-κB), and NF-κB repressing factor (NRF) have previously been shown to participate in the regulation of macrophage inflammatory protein-2 (MIP-2) during airway inflammation. However, the mechanisms regulating interactions among mechanical ventilation, neutrophil influx, and NF-κB/NRF remain unclear. Thus, we hypothesized that neutrophil elastase inhibitor attenuated ventilation-induced neutrophil recruitment and MIP-2 production through inhibition of the NF-κB/NRF pathway. Male C57BL/6 mice were exposed to low-tidal-volume (6 mL/kg) or high-tidal-volume (30 mL/kg) mechanical ventilation using room air with or without 2 µg/g NF-κB inhibitor SN50 or 6 µg/g NRF short interfering RNA or 100 µg/g neutrophil elastase inhibitor administration. Nonventilated mice served as a control group. Evan blue dye, lung wet-to-dry weight ratio, free radicals, myeloperoxidase, histopathologic grading of lung tissue, inflammatory cytokines, Western blot of NF-κB and NRF, and gene expression of NRF were measured to establish the extent of lung injury. Neutrophil elastase inhibitor ameliorated high-tidal-volume ventilation-induced lung injury, neutrophil influx, production of MIP-2 and malondialdehyde, activation of NF-κB and NRF, apoptotic epithelial cell death, and disruption of bronchial microstructure in mice. Mechanical stretch-augmented acute lung injury was also attenuated through pharmacological inhibition of NF-κB activity by SN50 and NRF expression by NRF short interfering RNA. Our data suggest that neutrophil elastase inhibitor attenuates high-tidal-volume mechanical ventilation-induced neutrophil influx, oxidative stress, and production of MIP-2, at least partly, through inhibition of NF-κB/NRF pathway. Understanding the protective effects of neutrophil elastase inhibitor associated with the reduction of MIP-2 allow clarification of the pathophysiological mechanisms regulating severe lung inflammation and development of possible therapeutic strategies involved in acute lung injury.

Sessile alveolar macrophages communicate with alveolar epithelium to modulate immunity

Tissue-resident macrophages of barrier organs constitute the first line of defense against pathogens at the systemic interface with the ambient environment. In lung, resident alveolar macrophages (AMs) provide sentinel function against inhaled pathogens¹. Bacterial constituents ligate toll-like receptors (TLRs) on AMs², causing AMs to secrete proinflammatory cytokines³ that activate alveolar epithelial receptors⁴, leading to recruitment of neutrophils that engulf pathogens^5,6. However, since the AM-induced immune response could itself cause tissue injury, it is unclear how AMs modulate the response to prevent injury. Here, through real-time alveolar imaging in situ, we show that a subset of AMs attached to the alveolar wall, formed connexin 43 (Cx43)-containing gap junctional channels (GJCs) with the epithelium. During lipopolysaccharide (LPS)-induced inflammation, the AMs remained alveolus-attached and sessile, and they established intercommunication through synchronized Ca²⁺ waves, using the epithelium as the conducting pathway. The intercommunication was immunosuppressive, involving Ca²⁺ dependent activation of Akt, since AM-specific knockout of Cx43 enhanced alveolar neutrophil recruitment and secretion of proinflammatory cytokines in the bronchoalveolar lavage (BAL). The picture emerges of a novel immunomodulatory process in which a subset of alveolus-attached AMs intercommunicates immunosuppressive signals to reduce endotoxin-induced lung inflammation.

High levels of S100A8/A9 proteins aggravate ventilator-induced lung injury via TLR4 signaling

Background

Bacterial products add to mechanical ventilation in enhancing lung injury. The role of endogenous triggers of innate immunity herein is less well understood. S100A8/A9 proteins are released by phagocytes during inflammation. The present study investigates the role of S100A8/A9 proteins in ventilator-induced lung injury.

Methods

Pulmonary S100A8/A9 levels were measured in samples obtained from patients with and without lung injury. Furthermore, wild-type and S100A9 knock-out mice, naive and with lipopolysaccharide-induced injured lungs, were randomized to 5 hours of spontaneously breathing or mechanical ventilation with low or high tidal volume (V_T). In addition, healthy spontaneously breathing and high V_T ventilated mice received S100A8/A9, S100A8 or vehicle intratracheal. Furthermore, the role of Toll-like receptor 4 herein was investigated.

Results

S100A8/A9 protein levels were elevated in patients and mice with lung injury. S100A8/A9 levels synergistically increased upon the lipopolysaccharide/high V_T MV double hit. Markers of alveolar barrier dysfunction, cytokine and chemokine levels, and histology scores were attenuated in S100A9 knockout mice undergoing the double-hit. Exogenous S100A8/A9 and S100A8 induced neutrophil influx in spontaneously breathing mice. In ventilated mice, these proteins clearly amplified inflammation: neutrophil influx, cytokine, and chemokine levels were increased compared to ventilated vehicle-treated mice. In contrast, administration of S100A8/A9 to ventilated Toll-like receptor 4 mutant mice did not augment inflammation.

Conclusion

S100A8/A9 proteins increase during lung injury and contribute to inflammation induced by HV_T MV combined with lipopolysaccharide. In the absence of lipopolysaccharide, high levels of extracellular S100A8/A9 still amplify ventilator-induced lung injury via Toll-like receptor 4.

A TLR4-interacting SPA4 peptide inhibits LPS-induced lung inflammation

The interaction between surfactant protein-A (SP-A) and TLR4 is important for host defense. We have recently identified an SPA4 peptide region from the interface of SP-A-TLR4 complex. Here, we studied the involvement of the SPA4 peptide region in SP-A-TLR4 interaction using a two-hybrid system, and biological effects of SPA4 peptide in cell systems and a mouse model. HEK293 cells were transfected with plasmid DNAs encoding SP-A or a SP-A-mutant lacking SPA4 peptide region and TLR4. Luciferase activity was measured as the end-point of SP-A-TLR4 interaction. NF-κB activity was also assessed simultaneously. Next, the dendritic cells or mice were challenged with Escherichia coli-derived LPS and treated with SPA4 peptide. Endotoxic shock-like symptoms and inflammatory parameters (TNF-α, NF-κB, leukocyte influx) were assessed. Our results reveal that the SPA4 peptide region contributes to the SP-A-TLR4 interaction and inhibits the LPS-induced NF-κB activity and TNF-α. We also observed that the SPA4 peptide inhibits LPS-induced expression of TNF-α, nuclear localization of NF-κB-p65 and cell influx, and alleviates the endotoxic shock-like symptoms in a mouse model. Our results suggest that the anti-inflammatory activity of the SPA4 peptide through its binding to TLR4 can be of therapeutic benefit.

Pre-treatment with allopurinol or uricase attenuates barrier dysfunction but not inflammation during murine ventilator-induced lung injury

Introduction

Uric acid released from injured tissue is considered a major endogenous danger signal and local instillation of uric acid crystals induces acute lung inflammation via activation of the NLRP3 inflammasome. Ventilator-induced lung injury (VILI) is mediated by the NLRP3 inflammasome and increased uric acid levels in lung lavage fluid are reported. We studied levels in human lung injury and the contribution of uric acid in experimental VILI.

Methods

Uric acid levels in lung lavage fluid of patients with acute lung injury (ALI) were determined. In a different cohort of cardiac surgery patients, uric acid levels were correlated with pulmonary leakage index. In a mouse model of VILI the effect of allopurinol (inhibits uric acid synthesis) and uricase (degrades uric acid) pre-treatment on neutrophil influx, up-regulation of adhesion molecules, pulmonary and systemic cytokine levels, lung pathology, and regulation of receptors involved in the recognition of uric acid was studied. In addition, total protein and immunoglobulin M in lung lavage fluid and pulmonary wet/dry ratios were measured as markers of alveolar barrier dysfunction.

Results

Uric acid levels increased in ALI patients. In cardiac surgery patients, elevated levels correlated significantly with the pulmonary leakage index. Allopurinol or uricase treatment did not reduce ventilator-induced inflammation, IκB-α degradation, or up-regulation of NLRP3, Toll-like receptor 2, and Toll-like receptor 4 gene expression in mice. Alveolar barrier dysfunction was attenuated which was most pronounced in mice pre-treated with allopurinol: both treatment strategies reduced wet/dry ratio, allopurinol also lowered total protein and immunoglobulin M levels.

Conclusions

Local uric acid levels increase in patients with ALI. In mice, allopurinol and uricase attenuate ventilator-induced alveolar barrier dysfunction.

Ventilation with "clinically relevant" high tidal volumes does not promote stretch-induced injury in the lungs of healthy mice

OBJECTIVE

Ventilator-induced lung injury is a crucial determinant of the outcome of mechanically ventilated patients. Increasing numbers of mouse studies have identified numerous pathways and mediators that are modulated by ventilation, but it is conceptually difficult to reconcile these into a single paradigm. There is substantial variability in tidal volumes used in these studies and no certainty about the pathophysiology that such varied models actually represent. This study was designed to investigate whether ventilation strategies ranging from "very high" to more "clinically relevant" tidal volumes induce similar pathophysiologies in healthy mice or represent distinct entities.

DESIGN

In vivo study.

SETTING

University research laboratory.

SUBJECTS

C57/Bl6 mice.

INTERVENTIONS

Anesthetized mice were ventilated with various tidal volumes up to 40 mL/kg.

MEASUREMENTS AND MAIN RESULTS

Respiratory system compliance and arterial blood gases were used to evaluate physiological variables of injury. Lung wet:dry weight ratio, lavage fluid protein, and cytokines were used to assess pulmonary edema and inflammation. All ventilation strategies induced changes in respiratory system compliance, although the pattern of change was unique for each strategy. Ventilation with 10 mL/kg and 40 mL/kg also induced decreases in arterial PO2 and blood pressure. Any physiological changes induced during the 10, 20, and 30 mL/kg strategies were largely reversed by recruitment maneuvers at the end of the protocol. Markers of pulmonary edema and inflammation indicated that only 40 mL/kg induced substantial increases in both, consistent with development of lung injury.

CONCLUSIONS

Tidal volumes up to 20 mL/kg are unlikely to induce substantial lung overstretch in models using healthy, young mice. Signs of injury/inflammation using such models are likely to result from other factors, particularly alveolar derecruitment and atelectasis. The results of such studies may need to be reevaluated before clinical relevance can be accurately determined.

WNT1-inducible signaling pathway protein 1 contributes to ventilator-induced lung injury

Although strides have been made to reduce ventilator-induced lung injury (VILI), critically ill patients can vary in sensitivity to VILI, suggesting gene-environment interactions could contribute to individual susceptibility. This study sought to uncover candidate genes associated with VILI using a genome-wide approach followed by functional analysis of the leading candidate in mice. Alveolar-capillary permeability after high tidal volume (HTV) ventilation was measured in 23 mouse strains, and haplotype association mapping was performed. A locus was identified on chromosome 15 that contained ArfGAP with SH3 domain, ankyrin repeat and PH domain 1 (Asap1), adenylate cyclase 8 (Adcy8), WNT1-inducible signaling pathway protein 1 (Wisp1), and N-myc downstream regulated 1 (Ndrg1). Information from published studies guided initial assessment to Wisp1. After HTV, lung WISP1 protein increased in sensitive A/J mice, but was unchanged in resistant CBA/J mice. Anti-WISP1 antibody decreased HTV-induced alveolar-capillary permeability in sensitive A/J mice, and recombinant WISP1 protein increased HTV-induced alveolar-capillary permeability in resistant CBA/J mice. HTV-induced WISP1 coimmunoprecipitated with glycosylated Toll-like receptor (TLR) 4 in A/J lung homogenates. After HTV, WISP1 increased in strain-matched control lungs, but was unchanged in TLR4 gene-targeted lungs. In peritoneal macrophages from strain-matched mice, WISP1 augmented LPS-induced TNF release that was inhibited in macrophages from TLR4 or CD14 antigen gene-targeted mice, and was attenuated in macrophages from myeloid differentiation primary response gene 88 gene-targeted or TLR adaptor molecule 1 mutant mice. These findings support a role for WISP1 as an endogenous signal that acts through TLR4 signaling to increase alveolar-capillary permeability in VILI.

miR-146a regulates mechanotransduction and pressure-induced inflammation in small airway epithelium

Mechanical ventilation generates biophysical forces, including high transmural pressures, which exacerbate lung inflammation. This study sought to determine whether microRNAs (miRNAs) respond to this mechanical force and play a role in regulating mechanically induced inflammation. Primary human small airway epithelial cells (HSAEpCs) were exposed to 12 h of oscillatory pressure and/or the proinflammatory cytokine TNF-α. Experiments were also conducted after manipulating miRNA expression and silencing the transcription factor NF-κB or toll-like receptor proteins IRAK1 and TRAF6. NF-κB activation, IL-6/IL-8/IL-1β cytokine secretion, miRNA expression, and IRAK1/TRAF6 protein levels were monitored. A total of 12 h of oscillatory pressure and TNF-α resulted in a 5- to 7-fold increase in IL-6/IL-8 cytokine secretion, and oscillatory pressure also resulted in a time-dependent increase in IL-6/IL-8/IL-1β cytokine secretion. Pressure and TNF-α also resulted in distinct patterns of miRNA expression, with miR-146a being the most deregulated miRNA. Manipulating miR-146a expression altered pressure-induced cytokine secretion. Silencing of IRAK1 or TRAF6, confirmed targets of miR-146a, resulted in a 3-fold decrease in pressure-induced cytokine secretion. Cotransfection experiments demonstrate that miR-146a's regulation of pressure-induced cytokine secretion depends on its targeting of both IRAK1 and TRAF6. MiR-146a is a mechanosensitive miRNA that is rapidly up-regulated by oscillatory pressure and plays an important role in regulating mechanically induced inflammation in lung epithelia.

Effects of penehyclidine hydrochloride on pulmonary contusion from blunt chest trauma in rats

BACKGROUND AND OBJECTIVE

Toll-like receptor 4 (TLR4) is widely recognised as a pattern recognition receptor (PRR) in the triggering of innate immunity. Lung inflammation and systemic innate immune responses are dependent on TLR4 activation undergoing pulmonary contusion. Therefore, the author investigated the effects of penehyclidine hydrochloride (PHC) on the expression of TLR4 and inflammatory responses of blunt chest trauma-induced pulmonary contusion.

MATERIALS AND METHODS

Male Sprague-Dawley (SD) rats were randomly assigned into three groups: normal control (NC) group, pulmonary contusion (PC) group and penehyclidine hydrochloride treatment (PHC) group. Pulmonary contusion was induced in anesthetised rats at fixed chest impact energy of 2.45J. Lung injury was assessed by the histopathology changes, arterial blood gas and myeloperoxidase (MPO) activity of lung. The serum tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels were measured using enzyme-linked immunosorbent assays (ELISA). The expression of TLR4 was determined by immunohistochemistry.

RESULTS

Blunt chest trauma produced leucocytosis in the interstitial capillaries, hypoxemia, and increased MPO activity. The expressions of TNF-α, IL-6 and TLR4 in the lung were significantly enhanced during pulmonary contusion. PHC treatments effectively attenuated pulmonary inflammation responses, as shown by improved pulmonary oxygenation, histopathology damage, decreased the MPO activity, the expressions of TNF-α, IL-6, and TLR4 after lung injury.

CONCLUSION

It might be concluded that PHC exhibit anti-inflammatory and protective effects in traumatic lung injury via the inhibition of the TLR4 pathway.

Revised Starling equation and the glycocalyx model of transvascular fluid exchange: an improved paradigm for prescribing intravenous fluid therapy

I.V. fluid therapy does not result in the extracellular volume distribution expected from Starling's original model of semi-permeable capillaries subject to hydrostatic and oncotic pressure gradients within the extracellular fluid. Fluid therapy to support the circulation relies on applying a physiological paradigm that better explains clinical and research observations. The revised Starling equation based on recent research considers the contributions of the endothelial glycocalyx layer (EGL), the endothelial basement membrane, and the extracellular matrix. The characteristics of capillaries in various tissues are reviewed and some clinical corollaries considered. The oncotic pressure difference across the EGL opposes, but does not reverse, the filtration rate (the 'no absorption' rule) and is an important feature of the revised paradigm and highlights the limitations of attempting to prevent or treat oedema by transfusing colloids. Filtered fluid returns to the circulation as lymph. The EGL excludes larger molecules and occupies a substantial volume of the intravascular space and therefore requires a new interpretation of dilution studies of blood volume and the speculation that protection or restoration of the EGL might be an important therapeutic goal. An explanation for the phenomenon of context sensitivity of fluid volume kinetics is offered, and the proposal that crystalloid resuscitation from low capillary pressures is rational. Any potential advantage of plasma or plasma substitutes over crystalloids for volume expansion only manifests itself at higher capillary pressures.

Myocardial ischemia activates an injurious innate immune signaling via cardiac heat shock protein 60 and Toll-like receptor 4

Innate immune response after transient ischemia is the most common cause of myocardial inflammation and may contribute to injury, yet the detailed signaling mechanisms leading to such a response are not well understood. Herein we tested the hypothesis that myocardial ischemia activates interleukin receptor-associated kinase-1 (IRAK-1), a kinase critical for the innate immune signaling such as that of Toll-like receptors (TLRs), via a mechanism that involves heat shock proteins (HSPs) and TLRs. Coronary artery occlusion induced a rapid myocardial IRAK-1 activation within 30 min in wild-type (WT), TLR2(-/-), or Trif(-/-) mice, but not in TLR4(def) or MyD88(-/-) mice. HSP60 protein was markedly increased in serum or in perfusate of isolated heart following ischemia/reperfusion (I/R). In vitro, recombinant HSP60 induced IRAK-1 activation in cells derived from WT, TLR2(-/-), or Trif(-/-) mice, but not from TLR4(def) or MyD88(-/-) mice. Both myocardial ischemia- and HSP60-induced IRAK-1 activation was abolished by anti-HSP60 antibody. Moreover, HSP60 treatment of cardiomyocytes (CMs) led to marked activation of caspase-8 and -3, but not -9. Expression of dominant-negative mutant of Fas-associated death domain protein or a caspase-8 inhibitor completely blocked HSP60-induced caspase-8 activation, suggesting that HSP60 likely activates an apoptotic program via the death-receptor pathway. In vivo, I/R-induced myocardial apoptosis and cytokine expression were significantly attenuated in TLR4(def) mice or in WT mice treated with anti-HSP60 antibody compared with WT controls. Taken together, the current study demonstrates that myocardial ischemia activates an innate immune signaling via HSP60 and TLR4, which plays an important role in mediating apoptosis and inflammation during I/R.

The essential roles of Toll-like receptor signaling pathways in sterile inflammatory diseases

Toll-like receptors (TLRs) form a family of pattern recognition receptors with at least 11 members in human and 13 in mouse. TLRs recognize a wide variety of putative host-derived agonists that have emerged as key mediators of innate immunity. TLR signaling also plays an important role in the activation of the adaptive immune system by inducing pro-inflammatory cytokines and upregulating costimulatory molecules of antigen presenting cells. Inappropriate activation of TLRs by self-components generated by damaged tissues may result in sterile inflammation. This review discusses the contribution of TLR signaling to the initiation and progression of non-infectious inflammatory processes, such as ischemia and reperfusion (I/R) injury, tissue repair and regeneration and autoimmune diseases. The involvement of TLR signaling in the pathogenesis of sterile inflammation-related diseases may provide novel targets for the development of therapeutics.