Oxidative stress generated by hemorrhagic shock recruits Toll-like receptor 4 to the plasma membrane in macrophages

Distinct TLR-mediated pathways regulate house dust mite-induced allergic disease in the upper and lower airways

BACKGROUND

Allergic rhinitis (AR) and asthma are 2 entities of allergic airway diseases that frequently occur together, which is referred to as united airways. In contrast to this general concept, we hypothesized that innate immunity of the upper and lower airways is respectively distinctive, because the immunologic conditions of the nasal and lung mucosa as well as the functions of the immune cells within their epithelia are different.

OBJECTIVE

We wanted to identify distinctive mechanisms of innate immunity in the nose and lung mucosa, which are responsible for house dust mite (HDM)-induced AR and allergic asthma (AA), respectively.

METHODS

We constructed a mouse model of AR or AA induced by sensitization and consequent provocation with HDM extracts.

RESULTS

HDM-derived β-glucans, rather than LPS, were proven to be essential to activating innate immunity in the nasal mucosa and triggering AR, which depended on Toll-like receptor 2 (TLR2), but not on TLR4; however, the LPS/TLR4 signaling axis, rather than β-glucans/TLR2, was critical to HDM-induced AA. These differences were attributed to the specific role of β-glucans and LPS in inducing the surface expression of TLR2 and TLR4 and their translocation to lipid rafts in nasal and bronchial epithelial cells, respectively. We also showed that dual oxidase 2-generated reactive oxygen species mediate both β-glucan-induced TLR2 activation and LPS-induced TLR4 activation.

CONCLUSIONS

We describe a novel finding of distinctive innate immunity of the nose and lungs, respectively, which trigger AR and AA, by showing the critical role of HDM-induced TLR activation via dual oxidase 2-mediated reactive oxygen species.

Expression of toll-like receptor 4 contributes to corneal inflammation in experimental dry eye disease

Purpose. To investigate the corneal expression of toll-like receptor (TLR) 4 and determine its contribution to the immunopathogenesis of dry eye disease (DED). Methods. Seven to 8-week-old female C57BL/6 mice were housed in a controlled environment chamber and administered scopolamine to induce experimental DED. Mice received intravenous TLR4 inhibitor (Eritoran) to block systemic TLR4-mediated activity. The expression of TLR4 by the corneal epithelium and stroma was evaluated using real-time polymerase chain reaction and flow cytometry. Corneal fluorescein staining (CFS) was performed to evaluate clinical disease severity. The corneal expression of proinflammatory cytokines (IL-1β, IL-6, TNF, and CCL2), corneal infiltration of CD11b(+) antigen-presenting cells, and lymph node frequency of mature MHC-II(hi) CD11b(+) cells were assessed. Results. The epithelial cells of normal corneas expressed TLR4 intracellularly; however, DED significantly increased the cell surface expression of TLR4. Similarly, flow cytometric analysis of stromal cells revealed a significant increase in the expression of TLR4 proteins by DED-induced corneas as compared with normal corneas. DED increased the mRNA expression of TLR4 in corneal stromal cells, but not epithelial cells. TLR4 inhibition decreased the severity of CFS and significantly reduced the mRNA expression of IL-1β, IL-6, and TNF. Furthermore, TLR4 inhibition significantly reduced the corneal infiltration of CD11b(+) cells and the lymph node frequency of MHC-II(hi) CD11b(+) cells. Conclusions. These results suggest that DED increases the corneal expression of TLR4 and that TLR4 participates in the inflammatory response to ocular surface desiccating stress.

HDL and ApoA-I inhibit antigen presentation-mediated T cell activation by disrupting lipid rafts in antigen presenting cells

OBJECTIVE

Depletion of cholesterol by methyl-β-cyclodextrin (MCD) on peptide-loaded antigen presenting cells (APCs) inhibits antigen presentation and T cell activation. However, whether membrane cholesterol efflux induced by high-density lipoprotein (HDL) and apolipoprotein A-I (apoA-I) also results in inhibition of antigen presentation and T cell activation is still unknown.

METHODS AND RESULTS

Various types of APCs, including B cells, macrophages and dendritic cells (DCs), were first loaded with antigen, then incubated with HDL and apoA-I to decrease cellular membrane cholesterol content. After being treated with HDL and apoA-I, APCs demonstrated decreased potential to activate T cells, and this decrease correlated with an increase in cholesterol efflux from APCs. Cholesterol repletion reversed the inhibitory effects of HDL and apoA-I, demonstrating that the observed reduction in T cell proliferation is mediated through cholesterol. Furthermore, lipid raft analysis showed that HDL and apoA-I reduced cholesterol and major histocompatibility (MHC) class II protein content in lipid rafts, suggesting that cholesterol efflux from APCs to HDL and apoA-I inhibits antigen presentation and T cell activation by reducing lipid rafts assembly in APCs.

CONCLUSION

HDL and apoA-I inhibit the capacity of APCs to stimulate T cell activation, and this inhibition can be attributed to cholesterol efflux and the ensuing disruption of plasma membrane lipid rafts in APCs. Overall, these findings suggest that cholesterol efflux mediated by HDL and apoA-I may serve to link immunity and cardioprotection.

Saturated fatty acids activate TLR-mediated proinflammatory signaling pathways

Toll-like receptor 4 (TLR4) and TLR2 were shown to be activated by saturated fatty acids (SFAs) but inhibited by docosahexaenoic acid (DHA). However, one report suggested that SFA-induced TLR activation in cell culture systems is due to contaminants in BSA used for solubilizing fatty acids. This report raised doubt about proinflammatory effects of SFAs. Our studies herein demonstrate that sodium palmitate (C16:0) or laurate (C12:0) without BSA solubilization induced phosphorylation of inhibitor of nuclear factor-κB α, c-Jun N-terminal kinase (JNK), p44/42 mitogen-activated-kinase (ERK), and nuclear factor-κB subunit p65, and TLR target gene expression in THP1 monocytes or RAW264.7 macrophages, respectively, when cultured in low FBS (0.25%) medium. C12:0 induced NFκB activation through TLR2 dimerized with TLR1 or TLR6, and through TLR4. Because BSA was not used in these experiments, contaminants in BSA have no relevance. Unlike in suspension cells (THP-1), BSA-solubilized C16:0 instead of sodium C16:0 is required to induce TLR target gene expression in adherent cells (RAW264.7). C16:0-BSA transactivated TLR2 dimerized with TLR1 or TLR6 and through TLR4 as seen with C12:0. These results and additional studies with the LPS sequester polymixin B and in MyD88(-/-) macrophages indicated that SFA-induced activation of TLR2 or TLR4 is a fatty acid-specific effect, but not due to contaminants in BSA or fatty acid preparations.

The sterile immune response during hepatic ischemia/reperfusion

Hepatic ischemia and reperfusion elicits an immune response that lacks a microbial constituent yet poses a potentially lethal threat to the host. In this sterile setting, the immune system is alarmed by endogenous danger signals that are release by stressed and dying liver cells. The detection of these immunogenic messengers by sentinel leukocyte populations constitutes the proximal trigger for a self-perpetuating cycle of inflammation, in which consecutive waves of cytokines and chemokines orchestrate the influx of various leukocyte subsets that ultimately confer tissue destruction. This review focuses on the temporal organization of sterile hepatic inflammation, using surgery-induced trauma as a template disease state.

Macrophage SR-BI regulates LPS-induced pro-inflammatory signaling in mice and isolated macrophages

Scavenger receptor BI (SR-BI), an HDL receptor, plays a key role in reverse cholesterol transport. In mice, disruption of SR-BI results in hypersensitivity to lipopolysaccharide (LPS) and bacteria-induced septic shock due to adrenal insufficiency and abnormal hepatic pathogen clearance. In this study, we identify an anti-inflammatory role of macrophage SR-BI. Using bone marrow transplantation, we report an enhanced pro-inflammatory response to LPS in wild-type (WT) mice receiving SR-BI-null compared with WT bone marrow cells and a reduced response in SR-BI-null mice receiving WT compared with SR-BI-null cells. Although significant, SR-BI deficiency limited to bone marrow-derived cells promoted a relatively modest enhancement of the inflammatory response to LPS in mice compared with the effect of whole-body SR-BI deletion. Consistent with earlier findings, SR-BI-null primary macrophages exhibited a greater inflammatory cytokine response to LPS than control macro phages. In addition, we showed that overexpression of SR-BI in J774 macrophages attenuated the inflammatory response to LPS. The LPS-induced cytokine expression in both WT and SR-BI-null macrophages was dependent not only on NFκB as previously reported but also on JNK and P38 cell signaling pathways. The increased inflammatory signaling in SR-BI-null cells was not related to alterations in cellular cholesterol content. We conclude that SR-BI plays an important function in regulating the macrophage inflammatory response to LPS.

NADPH phagocyte oxidase knockout mice control Trypanosoma cruzi proliferation, but develop circulatory collapse and succumb to infection

(•)NO is considered to be a key macrophage-derived cytotoxic effector during Trypanosoma cruzi infection. On the other hand, the microbicidal properties of reactive oxygen species (ROS) are well recognized, but little importance has been attributed to them during in vivo infection with T. cruzi. In order to investigate the role of ROS in T. cruzi infection, mice deficient in NADPH phagocyte oxidase (gp91(phox) (-/-) or phox KO) were infected with Y strain of T. cruzi and the course of infection was followed. phox KO mice had similar parasitemia, similar tissue parasitism and similar levels of IFN-γ and TNF in serum and spleen cell culture supernatants, when compared to wild-type controls. However, all phox KO mice succumbed to infection between day 15 and 21 after inoculation with the parasite, while 60% of wild-type mice were alive 50 days after infection. Further investigation demonstrated increased serum levels of nitrite and nitrate (NOx) at day 15 of infection in phox KO animals, associated with a drop in blood pressure. Treatment with a NOS2 inhibitor corrected the blood pressure, implicating NOS2 in this phenomenon. We postulate that superoxide reacts with (•)NO in vivo, preventing blood pressure drops in wild type mice. Hence, whilst superoxide from phagocytes did not play a critical role in parasite control in the phox KO animals, its production would have an important protective effect against blood pressure decline during infection with T. cruzi.

Macrophage migration inhibitory factor in protozoan infections

Macrophage migration inhibitory factor (MIF) is a cytokine that plays a central role in immune and inflammatory responses. In the present paper, we discussed the participation of MIF in the immune response to protozoan parasite infections. As a general trend, MIF participates in the control of parasite burden at the expense of promoting tissue damage due to increased inflammation.

The role of toll-like receptor-4 in the development of multi-organ failure following traumatic haemorrhagic shock and resuscitation

Haemorrhagic shock and resuscitation (HS/R) following major trauma results in a global ischaemia and reperfusion injury that may lead to multiple organ dysfunction syndrome (MODS). Systemic activation of the immune system is fundamental to the development of MODS in this context, and shares many features in common with the systemic inflammatory response syndrome (SIRS) that complicates sepsis. An important advancement in the understanding of the innate response to infection involved the identification of mammalian toll-like receptors (TLRs) expressed on cells of the immune system. Ten TLR homologues have been identified in humans and toll-like receptor-4 (TLR4) has been studied most intensively. Initially found to recognise bacterial lipopolysaccharide (LPS), it has also recently been discovered that TLR4 is capable of activation by endogenous 'danger signal' molecules released following cellular injury; this has since implicated TLR4 in several non-infectious pathophysiologic processes, including HS/R. The exact events leading to multi-organ dysfunction following HS/R have not yet been clearly defined, although TLR4 is believed to play a central role as has been shown to be expressed at sites including the liver, lungs and myocardium following HS/R. Multi-organ dysfunction syndrome remains an important cause of morbidity and mortality in trauma patients, and current therapy is based on supportive care. Understanding the pathophysiology of HS/R will allow for the development of targeted therapeutic strategies aimed at minimising organ dysfunction and improving patient outcomes following traumatic haemorrhage. A review of the pathogenesis of haemorrhagic shock is presented, and the complex, yet critical role of TLR4 as both a key mediator and therapeutic target is discussed.

Ischemia and reperfusion--from mechanism to translation

Ischemia and reperfusion-elicited tissue injury contributes to morbidity and mortality in a wide range of pathologies, including myocardial infarction, ischemic stroke, acute kidney injury, trauma, circulatory arrest, sickle cell disease and sleep apnea. Ischemia-reperfusion injury is also a major challenge during organ transplantation and cardiothoracic, vascular and general surgery. An imbalance in metabolic supply and demand within the ischemic organ results in profound tissue hypoxia and microvascular dysfunction. Subsequent reperfusion further enhances the activation of innate and adaptive immune responses and cell death programs. Recent advances in understanding the molecular and immunological consequences of ischemia and reperfusion may lead to innovative therapeutic strategies for treating patients with ischemia and reperfusion-associated tissue inflammation and organ dysfunction.

Report of the 'mechanisms of lung injury and immunomodulator interventions in influenza' workshop, 21 March 2010, Ventura, California, USA

Please cite this paper as: Howard et al. (2011) Report of the ‘Mechanisms of lung injury and immunomodulator interventions in influenza’ workshop, 21 March 2010, Ventura, California, USA*. Influenza and Other Respiratory Viruses 5(6), 453–e475.

The clinical course of influenza and the extent of lung injury are determined by both viral and host factors, as well as sometimes secondary bacterial infections and exacerbations of underlying conditions. The balance between viral replication and the host immune responses is central to disease pathogenesis, and the extent of lung injury in severe influenza infections may be due in part to overly exuberant or dysregulated innate inflammatory responses or sometimes deficient responses. Acute respiratory distress syndrome (ARDS) is the principal cause of respiratory failure associated with severe influenza. ARDS can be triggered by both direct lung insults (e.g. respiratory pathogens) and systemic insults (e.g. sepsis), and the lung damage is exacerbated by the inflammatory response associated with either infectious or non‐infectious insults. This workshop aimed to review the current understanding of lung injury in acute influenza and describe cellular and molecular mechanisms of lung injury that are common to influenza and infections by other respiratory pathogens. In addition, therapeutic agents that target host response proteins and pathways were identified and investigational agents in development reviewed. A logical strategy would be to combine antiviral treatment with drugs that modify excessive host responses or supplement deficient ones. However, a better understanding of common cell signalling pathways associated with acute lung injury caused by influenza and other pathogens is necessary to understand immunopathologic causes of lung injury. This will help determine which immunomodulatory interventions might be useful, and to predict the appropriate timing and consequences of their use.

Trauma hemorrhagic shock-induced lung injury involves a gut-lymph-induced TLR4 pathway in mice

Background

Injurious non-microbial factors released from the stressed gut during shocked states contribute to the development of acute lung injury (ALI) and multiple organ dysfunction syndrome (MODS). Since Toll-like receptors (TLR) act as sensors of tissue injury as well as microbial invasion and TLR4 signaling occurs in both sepsis and noninfectious models of ischemia/reperfusion (I/R) injury, we hypothesized that factors in the intestinal mesenteric lymph after trauma hemorrhagic shock (T/HS) mediate gut-induced lung injury via TLR4 activation.

Methods/Principal Findings

The concept that factors in T/HS lymph exiting the gut recreates ALI is evidenced by our findings that the infusion of porcine lymph, collected from animals subjected to global T/HS injury, into naïve wildtype (WT) mice induced lung injury. Using C3H/HeJ mice that harbor a TLR4 mutation, we found that TLR4 activation was necessary for the development of T/HS porcine lymph-induced lung injury as determined by Evan's blue dye (EBD) lung permeability and myeloperoxidase (MPO) levels as well as the induction of the injurious pulmonary iNOS response. TRIF and Myd88 deficiency fully and partially attenuated T/HS lymph-induced increases in lung permeability respectively. Additional studies in TLR2 deficient mice showed that TLR2 activation was not involved in the pathology of T/HS lymph-induced lung injury. Lastly, the lymph samples were devoid of bacteria, endotoxin and bacterial DNA and passage of lymph through an endotoxin removal column did not abrogate the ability of T/HS lymph to cause lung injury in naïve mice.

Conclusions/Significance

Our findings suggest that non-microbial factors in the intestinal mesenteric lymph after T/HS are capable of recreating T/HS-induced lung injury via TLR4 activation.

Enhancing Nrf2 pathway by disruption of Keap1 in myeloid leukocytes protects against sepsis

RATIONALE

Sepsis syndrome is characterized by inappropriate amplified systemic inflammatory response and bacteremia that promote multiorgan failure and mortality. Nuclear factor-erythroid 2 p45-related factor 2 (Nrf2) regulates a pleiotropic cytoprotective defense program including antioxidants and protects against several inflammatory disorders by inhibiting oxidative tissue injuries. However, the role of enhanced Nrf2 activity in modulating innate immune responses to microbial infection and pathogenesis of sepsis is unclear.

OBJECTIVES

To determine whether Nrf2 in myeloid leukocytes alters inflammatory response and protects against sepsis.

METHODS

Mice with deletion of Nrf2 or kelch-like ECH-associated protein (Keap1) in myeloid leukocyte cells and respective floxed controls were subjected to cecal ligation and puncture-induced sepsis and were assessed for survival, organ injury, systemic inflammation, and bacteremia. Using LPS-stimulated peritoneal macrophages, Toll-like receptor (TLR) 4 surface trafficking and downstream signaling events were analyzed.

MEASUREMENTS AND MAIN RESULTS

Mortality, organ injury, circulating levels of inflammatory mediators, and bacteremia were markedly reduced in LysM-Keap1(-/-) compared with respective floxed controls (Keap1(f/f) or Nrf2(f/f)) and significantly elevated in LysM-Nrf2(-/-) mice after cecal ligation and puncture. Peritoneal macrophages from septic LysM-Keap1(-/-) mice showed a greater bacterial phagocytic activity compared with LysM-Nrf2(-/-) and floxed controls. LPS stimulation resulted in greater reactive oxygen species-induced cell surface transport of TLR4 from trans-Golgi network and subsequent TLR4 downstream signaling (recruitment of MYD88 and TRIF, phosphorylation of IkB and IRF3, and cytokine expression) in macrophages of LysM-Nrf2(-/-) compared with LysM-Keap1(-/-) mice and floxed controls.

CONCLUSIONS

Our study shows that Nrf2 acts as a critical immunomodulator in leukocytes, controls host inflammatory response to bacterial infection, and protects against sepsis.

Application of laser postionization secondary neutral mass spectrometry/time-of-flight secondary ion mass spectrometry in nanotoxicology: visualization of nanosilver in human macrophages and cellular responses

Silver nanoparticles (SNP) are the subject of worldwide commercialization because of their antimicrobial effects. Yet only little data on their mode of action exist. Further, only few techniques allow for visualization and quantification of unlabeled nanoparticles inside cells. To study SNP of different sizes and coatings within human macrophages, we introduce a novel laser postionization secondary neutral mass spectrometry (Laser-SNMS) approach and prove this method superior to the widely applied confocal Raman and transmission electron microscopy. With time-of-flight secondary ion mass spectrometry (TOF-SIMS) we further demonstrate characteristic fingerprints in the lipid pattern of the cellular membrane indicative of oxidative stress and membrane fluidity changes. Increases of protein carbonyl and heme oxygenase-1 levels in treated cells confirm the presence of oxidative stress biochemically. Intriguingly, affected phagocytosis reveals as highly sensitive end point of SNP-mediated adversity in macrophages. The cellular responses monitored are hierarchically linked, but follow individual kinetics and are partially reversible.

Magnesium sulfate mitigates lung injury induced by bilateral lower limb ischemia-reperfusion in rats

BACKGROUND

Lower limb ischemia-reperfusion (I/R) elicits oxidative stress and causes inflammation in lung tissues that may lead to lung injury. Magnesium sulfate (MgSO(4)) possesses potent anti-oxidation and anti-inflammation capacity. We sought to elucidate whether MgSO(4) could mitigate I/R-induced lung injury. As MgSO(4) is an L-type calcium channel inhibitor, the role of the L-type calcium channels was elucidated.

MATERIALS AND METHODS

Adult male rats were allocated to receive I/R, I/R plus MgSO(4) (10, 50, or 100 mg/kg), or I/R plus MgSO(4) (100 mg/kg) plus the L-type calcium channels activator BAY-K8644 (20 μg/kg) (n = 12 in each group). Control groups were run simultaneously. I/R was induced by applying rubber band tourniquets high around each thigh for 3 h followed by reperfusion for 3 h. After euthanization, degrees of lung injury, oxidative stress, and inflammation were determined.

RESULTS

Arterial blood gas and histologic assays, including histopathology, leukocyte infiltration (polymorphonuclear leukocytes/alveoli ratio and myeloperoxidase activity), and lung water content, confirmed that I/R caused significant lung injury. Significant increases in inflammatory molecules (chemokine, cytokine, and prostaglandin E(2) concentrations) and lipid peroxidation (malondialdehyde concentration) confirmed that I/R caused significant inflammation and oxidative stress in rat lungs. MgSO(4), at the dosages of 50 and 100 mg/kg but not 10 mg/kg, attenuated the oxidative stress, inflammation, and lung injury induced by I/R. Moreover, BAY-K8644 reversed the protective effects of MgSO(4).

CONCLUSIONS

MgSO(4) mitigates lung injury induced by bilateral lower limb I/R in rats. The mechanisms may involve inhibiting the L-type calcium channels.

Role of connexins in microvascular dysfunction during inflammation

In arterioles, a locally initiated diameter change can propagate rapidly along the vessel length (arteriolar conducted response), thus contributing to arteriolar hemodynamic resistance. The response is underpinned by electrical coupling along the arteriolar endothelial layer. Connexins (Cx; constituents of gap junctions) are required for this coupling. This review addresses the effect of acute systemic inflammation (sepsis) on arteriolar conduction and interendothelial electrical coupling. Lipopolysaccharide (LPS; an initiating factor in sepsis) and polymicrobial sepsis (24 h model) attenuate conducted vasoconstriction in mice. In cultured microvascular endothelial cells harvested from rat and mouse skeletal muscle, LPS reduces both conducted hyperpolarization–depolarization along capillary-like structures and electrical coupling along confluent cell monolayers. LPS also tyrosine-phosphorylates Cx43 and serine-dephosphorylates Cx40. Since LPS-reduced coupling is Cx40- but not Cx43-dependent, only Cx40 dephosphorylation may be consequential. Nitric oxide (NO) overproduction is critical in advanced sepsis, since the removal of this overproduction prevents the attenuated conduction. Consistently, (i) exogenous NO in cultured cells reduces coupling in a Cx37-dependent manner, and (ii) the septic microvasculature in vivo shows no Cx40 phenotype. A complex role emerges for endothelial connexins in sepsis. Initially, LPS may reduce interendothelial coupling and arteriolar conduction by targeting Cx40, whereas NO overproduction in advanced sepsis reduces coupling and conduction by targeting Cx37 instead.

Rons formation under restrictive reperfusion does not affect organ dysfunction early after hemorrhage and trauma

Reactive oxygen species have been implicated in the pathophysiology of early reperfusion. We aimed to determine 1) reactive oxygen and nitrogen species (RONS) formation in organs of rats and 2) its pathophysiological relevance during a phase of restrictive reperfusion after hemorrhagic/traumatic shock (HTS). Fifty-seven male Sprague-Dawley rats were subjected to a clinically relevant HTS model, featuring laparotomy, bleeding, and a phase of restrictive reperfusion. The RONS scavenger 1-hydroxy-3-carboxy-2,2,5,5-tetramethyl-pyrrolidine hydrochloride (continuous i.v. infusion) and electron paramagnetic resonance spectroscopy were applied for RONS (primarily superoxide and peroxynitrite) detection. Compared with sham-operated animals, the organ-specific distribution of RONS changed during restrictive reperfusion after HTS. Reactive oxygen and nitrogen species formation increased during restrictive reperfusion in red blood cells and ileum only but decreased in the kidney and remained unchanged in other organs. Hemorrhagic traumatic shock followed by restrictive reperfusion resulted in metabolic acidosis, dysfunction of liver and kidney, and increased oxidative burst capacity in circulating cells. Plasma RONS correlated with shock severity and organ dysfunction. However, RONS scavenging neither affected organ dysfunction nor oxidative burst capacity nor myeloperoxidase activity in lung when compared with the shock controls. In summary, a phase of restrictive reperfusion does not increase RONS formation in most organs except in intestine and red blood cells. Moreover, scavenging of RONS does not affect the early organ dysfunction manifested at the end of a phase of restrictive reperfusion.

Hyaluronan fragments contribute to the ozone-primed immune response to lipopolysaccharide

Hyaluronan is a high-molecular mass component of pulmonary extracelluar matrix, and lung injury can generate a low-molecular mass hyaluronan (HA) fragment that functions as endogenous ligand to cell surface receptors CD44 and TLR4. This leads to activation of intracellular NF-κB signaling and proinflammatory cytokine production. Based on previous information that ozone exposure causes increased HA in bronchial alveolar lavage fluid and ozone pre-exposure primes immune response to inhaled LPS, we hypothesized that HA production during ozone exposure augments the inflammatory response to LPS. We demonstrate that acute ozone exposure at 1 part per million for 3 h primes the immune response to low-dose aerosolized LPS in C57BL/6J mice, resulting in increased neutrophil recruitment into the airspaces, increased levels of protein and proinflammatory cytokines in the bronchoalveolar lavage fluid, and increased airway hyperresponsiveness. Intratracheal instillation of endotoxin-free HA (25 μg) enhances the biological response to inhaled LPS in a manner similar to ozone pre-exposure. In vitro studies using bone marrow-derived macrophages indicate that HA enhances LPS responses measured by TNF-α production, while immunofluorescence staining of murine alveolar macrophages demonstrates that HA induces TLR4 peripheralization and lipid raft colocalization. Collectively, our observations support that ozone primes macrophage responsiveness to low-dose LPS, in part, due to HA-induced TLR4 peripheralization in lung macrophages.

Heme amplifies the innate immune response to microbial molecules through spleen tyrosine kinase (Syk)-dependent reactive oxygen species generation

Infectious diseases that cause hemolysis are among the most threatening human diseases, because of severity and/or global distribution. In these conditions, hemeproteins and heme are released, but whether heme affects the inflammatory response to microorganism molecules remains to be characterized. Here, we show that heme increased the lethality and cytokine secretion induced by LPS in vivo and enhanced the secretion of cytokines by macrophages stimulated with various agonists of innate immune receptors. Activation of nuclear factor κB (NF-κB) and MAPKs and the generation of reactive oxygen species were essential to the increase in cytokine production induced by heme plus LPS. This synergistic effect of heme and LPS was blocked by a selective inhibitor of spleen tyrosine kinase (Syk) and was abrogated in dendritic cells deficient in Syk. Moreover, inhibition of Syk and the downstream molecules PKC and PI3K reduced the reactive oxygen species generation by heme. Our results highlight a mechanism by which heme amplifies the secretion of cytokines triggered by microbial molecule activation and indicates possible pathways for therapeutic intervention during hemolytic infectious diseases.

Toll-like receptors 2 and 4: initiators of non-septic inflammation in critical care medicine?

PURPOSE

Although the role of Toll-like receptors (TLRs) in bacterial infection and sepsis is well characterized, recent studies have also shown that TLR4 and TLR2 can play an important role in contributing to acute inflammatory processes and organ dysfunction in settings in which LPS or other bacterial products are not present. This review presents not only insights into pathophysiologic mechanisms that contribute to organ dysfunction and outcome in critical illness, but also direct therapeutic approaches to ameliorating such TLR-mediated responses that may potentially be of clinical benefit in critically ill patients.

METHOD

Literature review of the role of TLR4 and TLR2 in sterile inflammation relevant to critical care medicine using PubMed search, including original papers in English from 1990 to 2010.

CONCLUSION

There is increasing evidence that TLR4 and TLR2 are not only receptors for bacterial products, but also can be activated through other mechanisms relevant to the pathophysiology of critical illnesses. There is evidence that TLR4 and TLR2 are involved in ischemia-reperfusion injury and trauma where Gram-negative or Gram-positive bacteria are not detectible in the circulation or local organ sites, such as the lungs. In these settings TLRs can transduce other proinflammatory signals and thereby contribute to cellular activation leading to acute lung injury and other organ system dysfunction. The consequences of TLR4 and TLR2 activation through reactive oxygen species (ROS), heat shock proteins, and other non-LPS dependent mechanisms may be different from those associated with binding of the membrane component of bacteria to TLR4 or TLR2 and may produce different signatures of gene activation and release of proinflammatory mediators.

Macrophage ABCA1 reduces MyD88-dependent Toll-like receptor trafficking to lipid rafts by reduction of lipid raft cholesterol

We previously showed that macrophages from macrophage-specific ATP-binding cassette transporter A1 (ABCA1) knockout (Abca1(-M/-M)) mice had an enhanced proinflammatory response to the Toll-like receptor (TLR) 4 agonist, lipopolysaccharide (LPS), compared with wild-type (WT) mice. In the present study, we demonstrate a direct association between free cholesterol (FC), lipid raft content, and hyper-responsiveness of macrophages to LPS in WT mice. Abca1(-M/-M) macrophages were also hyper-responsive to specific agonists to TLR2, TLR7, and TLR9, but not TLR3, compared with WT macrophages. We hypothesized that ABCA1 regulates macrophage responsiveness to TLR agonists by modulation of lipid raft cholesterol and TLR mobilization to lipid rafts. We demonstrated that Abca1(-M/-M) vs. WT macrophages contained 23% more FC in isolated lipid rafts. Further, mass spectrometric analysis suggested raft phospholipid composition was unchanged. Although cell surface expression of TLR4 was similar between Abca1(-M/-M) and WT macrophages, significantly more TLR4 was distributed in membrane lipid rafts in Abca1(-M/-M) macrophages. Abca1(-M/-M) macrophages also exhibited increased trafficking of the predominantly intracellular TLR9 into lipid rafts in response to TLR9-specific agonist (CpG). Collectively, our data suggest that macrophage ABCA1 dampens inflammation by reducing MyD88-dependent TLRs trafficking to lipid rafts by selective reduction of FC content in lipid rafts.

Glaucomatous tissue stress and the regulation of immune response through glial Toll-like receptor signaling

PURPOSE

To determine the regulation of immune system activity associated with Toll-like receptor (TLR) signaling in glaucoma.

METHODS

Retinal protein samples obtained from human donor eyes with (n = 10) or without (n = 10) glaucoma were analyzed by a quantitative proteomic approach involving mass spectrometry. Cellular localization of TLR2, -3, and -4 was also determined by immunohistochemical analysis of an additional group of human donor eyes with glaucoma (n = 34) and control eyes (n = 20). In addition, in vitro experiments were performed in rat retinal microglia and astrocytes to determine glial TLR expression and immunoregulatory function after exposure to exogenous heat shock proteins (HSPs) and H(2)O(2)-induced oxidative stress.

RESULTS

Proteomic analyses of the human retina detected expression and differential regulation of different TLRs in glaucomatous samples. Parallel to the upregulation of TLR signaling, proteomic findings were also consistent with a prominent increase in the expression of HSPs in glaucoma. Immunohistochemical analysis supported upregulated expression of TLRs on both microglia and astrocytes in the glaucomatous retina. In vitro experiments provided additional evidence that HSPs and oxidative stress upregulate glial TLR and MHC class II expression and cytokine production through TLR signaling and stimulate proliferation and cytokine secretion of co-cultured T cells during antigen presentation.

CONCLUSIONS

The findings of this study support the upregulation of TLR signaling in human glaucoma, which may be associated with innate and adaptive immune responses. In vitro findings showed that components of glaucomatous tissue stress, including upregulated HSPs and oxidative stress, may initiate the immunostimulatory signaling through glial TLRs.

NADPH oxidase-dependent reactive oxygen species mediate amplified TLR4 signaling and sepsis-induced mortality in Nrf2-deficient mice

Sepsis syndrome is characterized by a dysregulated inflammatory response to infection. NADPH oxidase-dependent reactive oxygen species (ROS) play significant roles in the pathophysiology of sepsis. We previously showed that disruption of Nrf2, a master regulator of antioxidant defenses, caused a dysregulation of innate immune response that resulted in greater mortality in a polymicrobial sepsis and LPS shock model; however, the underlying mechanisms are unclear. In the current study, compared with wild-type (Nrf2(+/+)) macrophages, we observed greater protein kinase C-induced NADPH oxidase-dependent ROS generation in Nrf2-disrupted (Nrf2(-/-)) macrophages that was modulated by glutathione levels. To address the NADPH oxidase-mediated hyperinflammatory response and sepsis-induced lung injury and mortality in Nrf2(-/-) mice, we used double knockout mice lacking Nrf2 and NADPH oxidase subunit, gp91(phox) (Nrf2(-/-)//gp91(phox-/-)). Compared with Nrf2(+/+) macrophages, LPS induced greater activation of TLR4 as evident by TLR4 surface trafficking and downstream recruitment of MyD88 and Toll/IL-1R domain-containing adaptor in Nrf2(-/-) macrophages that was diminished by ablation of gp91(phox). Similarly, phosphorylation of IkappaB and IFN regulatory factor 3 as well as cytokine expression was markedly higher in Nrf2(-/-) macrophages; whereas, it was similar in Nrf2(+/+) and Nrf2(-/-)//gp91(phox-/-). In vivo studies showed greater LPS-induced pulmonary inflammation in Nrf2(-/-) mice that was significantly reduced by ablation of gp91(phox). Furthermore, LPS shock and polymicrobial sepsis induced early and greater mortality in Nrf2(-/-) mice; whereas, Nrf2(-/-)//gp91(phox-/-) showed prolonged survival. Together, these results demonstrate that Nrf2 is essential for the regulation of NADPH oxidase-dependent ROS-mediated TLR4 activation and lethal innate immune response in sepsis.

Structured regulation of inflammation during respiratory viral infection

Innate immune cells including macrophages, dendritic cells, and granulocytes are resident within or patrol very different microenvironments in the host. Their activity or responsiveness to antigen is dictated by site-specific factors. Because of the constant exposure to environmental antigens and commensal microorganisms, mucosal immunity needs to be more constrained than peripheral counterparts to prevent unnecessary inflammation. The epithelial surfaces that dominate all mucosal tissues provide an ideal regulator since innate immune cells are often in intimate contact with, or lie immediately beneath, them and a breach in epithelial integrity would signal a damaging event and release innate immunity from their influence. We discuss the role of the respiratory epithelium in raising the threshold of innate immune cell activation at homoeostasis, how its absence triggers innate immunity, and how inflammatory resolution often produces an altered homoeostatic environment that can affect the next inflammatory event at this site.

Linking oxidative stress to inflammation: Toll-like receptors

Injury caused by oxidative stress occurs in many clinical scenarios involving ischemia and reperfusion such as organ transplantation, hemorrhagic shock (HS), myocardial infarction, and cerebral vascular accidents. Activation of the immune system as a result of disturbances in the redox state of cells seems to contribute to tissue and organ damage in these conditions. The link between oxidative stress and inflammatory pathways is poorly understood. Recently, Toll-like receptors (TLRs) have been shown to mediate the inflammatory response seen in experimental ischemia and reperfusion (I/R). The TLR family of receptors involved in alerting the innate immune system of danger seems to be activated by damage-associated molecular pattern molecules (DAMPs) that are released during conditions of oxidative stress. In this review, we examine the role of TLRs in various experimental models of oxidative stress such as HS and I/R. We also report on potential DAMPs that may interact with TLRs in mediating injury. Finally, potential mechanisms by which reactive oxygen species from NADPH oxidase can signal the commencement of inflammatory pathways through TLRs are explored.

Characterization of transglutaminase type II role in dendritic cell differentiation and function

DCs play an essential role in the endotoxic shock, and their profound depletion occurs in septic patients and septic mice. TG2(-/-) mice are more resistant to the endotoxic shock induced by LPS. Here, we studied the cellular and molecular basis of this effect, analyzing the role of the enzyme in DC maturation and function. We show that TG2 is up-regulated drastically during the final, functional maturation of DCs consequent to LPS treatment. In keeping with this finding, the inhibition of the enzyme cross-linking activity determines the impairment of DC function highlighted by wide phenotypic changes associated with a reduced production of cytokines (IL-10, IL-12) after LPS treatment and a lower ability to induce IFN-gamma production by naïve T cells. The in vivo analysis of DCs obtained from TG2(-/-) mice confirmed that the enzyme ablation leads to an impairment of DC maturation and their reduced responsiveness to LPS treatment. In fact, a marked decrease in DC death, TLR4 down-regulation, and impaired up-regulation of MHCII and CD86 were observed in TG2(-/-) mice. Taken together, these data suggest that TG2 plays an important role in regulating the response of DCs to LPS and could be a candidate target for treating endotoxin-induced sepsis.

Oxidant alterations in CD16 expression are cytoskeletal induced

Oxidative stress during reperfusion of ischemia is associated with a phenotypic change in circulating monocytes from CD14++CD16- to a proinflammatory CD14+CD16+ subpopulation resulting in altered immunity and development of organ failure. However, the mechanism responsible remains unknown. We hypothesize that this phenotypic change, modeled by hydrogen peroxide exposure in vitro, is due to oxidative-induced intracellular calcium flux and distinct cytoskeletal and lipid raft changes. Peripheral blood monocytes obtained from healthy volunteers underwent 100 mM H2O2 exposure for 0 to 24 h. Selected cells were pretreated with 2 microM cytochalasin D, 1 microM lactrunculin A, or 30 microM 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid for 30 min. Cells underwent fluorescence-activated cell sorter for CD14, CD16, and cytokine expression. Cellular and lipid raft CD16 expression was determined by immunoblot and confocal microscopy. H2O2 exposed monocytes underwent a rapid time-dependent increase in the surface expression of CD16 from 12.81% +/- 3.53% to 37.12% +/- 7.61% at 24 h (P = 0.001). Total cellular CD16 was not changed by H2O2, but an increase in lipid raft and decrease in intracellular CD16 expression were seen after H2O2 exposure. This increase in CD16 expression was associated with a 27% increase in intracellular TNF-alpha, an alteration in actin polymerization, and the formation of raft macrodomains. These changes induced by H2O2 were inhibited by inhibition of actin polymerization (cytochalasin D and lactrunculin A) and intracellular calcium flux [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid]. This study provides the first evidence that phenotypic alterations induced by oxidative stress during reperfusion may occur as a result of changes in cytoskeletal architecture due to calcium flux that result in lipid raft alterations rather than solely from demargination and/or production of bone marrow-derived CD16+ monocytes.

Fatty acids modulate Toll-like receptor 4 activation through regulation of receptor dimerization and recruitment into lipid rafts in a reactive oxygen species-dependent manner

The saturated fatty acids acylated on Lipid A of lipopolysaccharide (LPS) or bacterial lipoproteins play critical roles in ligand recognition and receptor activation for Toll-like Receptor 4 (TLR4) and TLR2. The results from our previous studies demonstrated that saturated and polyunsaturated fatty acids reciprocally modulate the activation of TLR4. However, the underlying mechanism has not been understood. Here, we report for the first time that the saturated fatty acid lauric acid induced dimerization and recruitment of TLR4 into lipid rafts, however, dimerization was not observed in non-lipid raft fractions. Similarly, LPS and lauric acid enhanced the association of TLR4 with MD-2 and downstream adaptor molecules, TRIF and MyD88, into lipid rafts leading to the activation of downstream signaling pathways and target gene expression. However, docosahexaenoic acid (DHA), an n-3 polyunsaturated fatty acid, inhibited LPS- or lauric acid-induced dimerization and recruitment of TLR4 into lipid raft fractions. Together, these results demonstrate that lauric acid and DHA reciprocally modulate TLR4 activation by regulation of the dimerization and recruitment of TLR4 into lipid rafts. In addition, we showed that TLR4 recruitment to lipid rafts and dimerization were coupled events mediated at least in part by NADPH oxidase-dependent reactive oxygen species generation. These results provide a new insight in understanding the mechanism by which fatty acids differentially modulate TLR4-mediated signaling pathway and consequent inflammatory responses which are implicated in the development and progression of many chronic diseases.

Nrf2 protects against airway disorders

Nuclear factor-erythroid 2 related factor 2 (Nrf2) is a ubiquitous master transcription factor that regulates antioxidant response elements (AREs)-mediated expression of antioxidant enzyme and cytoprotective proteins. In the unstressed condition, Kelch-like ECH-associated protein 1 (Keap1) suppresses cellular Nrf2 in cytoplasm and drives its proteasomal degradation. Nrf2 can be activated by diverse stimuli including oxidants, pro-oxidants, antioxidants, and chemopreventive agents. Nrf2 induces cellular rescue pathways against oxidative injury, abnormal inflammatory and immune responses, apoptosis, and carcinogenesis. Application of Nrf2 germ-line mutant mice has identified an extensive range of protective roles for Nrf2 in experimental models of human disorders in the liver, gastrointestinal tract, airway, kidney, brain, circulation, and immune or nerve system. In the lung, lack of Nrf2 exacerbated toxicity caused by multiple oxidative insults including supplemental respiratory therapy (e.g., hyperoxia, mechanical ventilation), cigarette smoke, allergen, virus, bacterial endotoxin and other inflammatory agents (e.g., carrageenin), environmental pollution (e.g., particles), and a fibrotic agent bleomycin. Microarray analyses and bioinformatic studies elucidated functional AREs and Nrf2-directed genes that are critical components of signaling mechanisms in pulmonary protection by Nrf2. Association of loss of function with promoter polymorphisms in NRF2 or somatic and epigenetic mutations in KEAP1 and NRF2 has been found in cohorts of patients with acute lung injury/acute respiratory distress syndrome or lung cancer, which further supports the role for NRF2 in these lung diseases. In the current review, we address the role of Nrf2 in airways based on emerging evidence from experimental oxidative disease models and human studies.

Oxidative stress induces lipid-raft-mediated activation of Src homology 2 domain-containing protein-tyrosine phosphatase 2 in astrocytes

Several protein phosphatases are involved in neuroprotection in response to ischemic brain injury. Here, we report that reactive oxygen species (ROS)-mediated oxidative stress promotes phosphorylation of endogenous SHP-2 through lipid rafts in rat primary astrocytes. SHP-2 was transiently phosphorylated during hypoxia/reoxygenation, an effect abrogated by a ROS scavenger and an NADPH oxidase inhibitor. Additionally, exogenous treatment with hydrogen peroxide (H(2)O(2)) triggered SHP-2 phosphorylation in a time- and dose-dependent manner and led to its translocation into lipid rafts. H(2)O(2)-mediated SHP-2 phosphorylation and translocation were inhibited by filipin III and methyl-beta-cyclodextrin (MCD), lipid-raft-disrupting agents. In the presence of H(2)O(2), SHP-2 formed a complex with STAT-3 and reduced the steady-state STAT-3 phosphorylation level. Interestingly, the effect of H(2)O(2) on SHP-2 phosphorylation was cell-type specific. Remarkably, SHP-2 phosphorylation was induced strongly by H(2)O(2) in astrocytes, but barely detectable in microglia. Our results collectively indicate that SHP-2 is activated by ROS-mediated oxidative stress in astrocytes and functions as a component of the raft-mediated signaling pathway that acts through dephosphorylation and inactivation of other phosphotyrosine proteins, such as STAT-3.

Oxidative stress augments toll-like receptor 8 mediated neutrophilic responses in healthy subjects

Background

Excessive oxidative stress has been reported to be generated in inflamed tissues and contribute to the pathogenesis of inflammatory lung diseases, exacerbations of which induced by viral infections are associated with toll-like receptor (TLR) activation. Among these receptors, TLR8 has been reported as a key receptor that recognizes single-strand RNA virus. However, it remains unknown whether TLR8 signaling is potentiated by oxidative stress. The aim of this study is to examine whether oxidative stress modulates TLR8 signaling in vitro.

Methods

Human peripheral blood neutrophils were obtained from healthy non-smokers and stimulated with TLR 7/8 agonist imidazoquinoline resiquimod (R848) in the presence or absence of hydrogen peroxide (H₂O₂). Neutrophilic responses including cytokine release, superoxide production and chemotaxis were examined, and the signal transduction was also analyzed.

Results

Activation of TLR8, but not TLR7, augmented IL-8 release. The R848-augmented IL-8 release was significantly potentiated by pretreatment with H₂O₂ (p < 0.01), and N-acetyl-L-cysteine reversed this potentiation. The combination of H₂O₂ and R848 significantly potentiated NF-kB phosphorylation and IkBα degradation. The H₂O₂-potentiated IL-8 release was suppressed by MG-132, a proteosome inhibitor, and by dexamethasone. The expressions of TLR8, myeloid differentiation primary response gene 88 (MyD88), and tumor necrosis factor receptor-associated factor 6 (TRAF6) were not affected by H₂O₂.

Conclusion

TLR8-mediated neutrophilic responses were markedly potentiated by oxidative stress, and the potentiation was mediated by enhanced NF-kB activation. These results suggest that oxidative stress might potentiate the neutrophilic inflammation during viral infection.

Cigarette smoke regulates the expression of TLR4 and IL-8 production by human macrophages

BACKGROUND

Toll-like receptors (TLRs) are present on monocytes and alveolar macrophages that form the first line of defense against inhaled particles. The importance of those cells in the pathophysiology of chronic obstructive pulmonary disease (COPD) has well been documented. Cigarette smoke contains high concentration of oxidants which can stimulate immune cells to produce reactive oxygen species, cytokines and chemokines.

METHODS

In this study, we evaluated the effects of cigarette smoke medium (CSM) on TLR4 expression and interleukin (IL)-8 production by human macrophages investigating the involvement of ROS.

RESULTS AND DISCUSSION

TLR4 surface expression was downregulated on short term exposure (1 h) of CSM. The downregulation could be explained by internalization of the TLR4 and the upregulation by an increase in TLR4 mRNA. IL-8 mRNA and protein were also increased by CSM. CSM stimulation increased intracellular ROS-production and decreased glutathione (GSH) levels. The modulation of TLR4 mRNA and surface receptors expression, IRAK activation, IkappaB-alpha degradation, IL-8 mRNA and protein, GSH depletion and ROS production were all prevented by antioxidants such as N-acetyl-L-cysteine (NAC).

CONCLUSION

TLR4 may be involved in the pathogenesis of lung emphysema and oxidative stress and seems to be a crucial contributor in lung inflammation.

Immune homeostasis in the respiratory tract and its impact on heterologous infection

Innate immunity at mucosal surfaces requires additional restraint to prevent inflammation to innocuous antigens or commensal microorganisms. The threshold above which airway macrophages become activated is raised by site-specific factors including the receptors for transforming growth factor beta, interleukin 10 and CD200; the ligands for which are produced by, or expressed on, respiratory epithelium. We discuss such site-specific regulation and how this is continually altered by prior infections. Resetting of innate reactivity represents a strategy for limiting excessive inflammation, but in some may pre-dispose to secondary bacterial pneumonia.

Toll-like receptor 2 is essential for the sensing of oxidants during inflammation

RATIONALE

The mechanisms by which oxidants are sensed by cells and cause inflammation are not well understood.

OBJECTIVES

This study aimed to determine how cells "sense" soluble oxidants and how this is translated into an inflammatory reaction.

METHODS

Monocytes, macrophages, or HEK293 cells (stably transfected with human Toll-like receptor [TLR]2, TLR2/1, TLR2/6, or TLR4/MD2-CD14) were used. CXC ligand-8 (CXCL8) levels were measured using ELISA. Phosphorylated IL-1 receptor-associated kinase 1 levels were measured using Western blot. TLR2(-/-) and TLR4(-/-) mice were challenged with oxidants, and inflammation was measured by monitoring cell infiltration and KC levels.

MEASUREMENTS AND MAIN RESULTS

Oxidants evoked the release of CXCL8 from monocytes/macrophages; this was abrogated by pretreatment with N-acetylcysteine or binding antibodies to TLR2 and was associated with the rapid phosphorylation of IL-1 receptor-associated kinase 1. Oxidants added to HEK293 cells transfected with TLR2, TLR1/2, or TLR2/6 but not TLR4/MD2-CD14 or control HEK nulls resulted in the release of CXCL8. Oxidant challenge delivered intraperitoneally (2-24 hours) or by inhalation to the lungs (3 days) resulted in a robust inflammation in wild-type mice. TLR2(-/-) mice did not respond to oxidant challenge in either model. TLR4(-/-) mice responded as wild-type mice to oxidants at 2 hours but as TLR2(-/-) mice at later time points.

CONCLUSIONS

Oxidant-TLR2 interactions provide a signal that initiates the inflammatory response.

Lipopolysaccharide plus hypoxia and reoxygenation synergistically reduce electrical coupling between microvascular endothelial cells by dephosphorylating connexin40

We showed that lipopolysaccharide (LPS) or hypoxia and reoxygenation (H/R) decreases electrical coupling between microvascular endothelial cells by targeting the gap junction protein connexin40 (Cx40), tyrosine kinase-, ERK1/2-, and PKA-dependently. Since LPS can compromise microvascular blood flow, resulting in micro-regional H/R, the concurrent LPS + H/R could reduce coupling to a much greater extent than LPS or H/R alone. We examined this possibility in a model of cultured microvascular endothelial cells (mouse skeletal muscle origin) in terms of electrical coupling and the phosphorylation status of Cx40. To assess coupling, we measured the spread of electrical current injected into the cell monolayer and computed the intercellular resistance as an inversed measure of coupling. In wild type cells, but not in Cx40 null cells, concurrent LPS + H/R synergistically increased resistance by approximately 270%, well above the level observed for LPS or H/R alone. Cx37 and Cx43 protein expression did not differ between Cx40 null and wild type cells. LPS + H/R increased resistance PKA- and PKC-dependently. By immunoprecipitating Cx40, we found that LPS + H/R reduced serine phosphorylation to a much greater degree than that observed for LPS or H/R alone. Further, PKA-specific, but not PKC-specific serine phosphorylation of Cx40 was also significantly reduced following LPS + H/R. This reduction was prevented by tyrosine kinase and MEK1/2 inhibition, by PKA activation, and mimicked in control cells by PKA inhibition. We conclude that LPS + H/R initiates tyrosine kinase- and ERK1/2-sensitive signaling that synergistically reduces inter-endothelial electrical coupling by dephosphorylating PKA-specific serine residues of Cx40.

Increased cellular free cholesterol in macrophage-specific Abca1 knock-out mice enhances pro-inflammatory response of macrophages

Macrophage-specific Abca1 knock-out (Abca1(-)(M)(/-)(M)) mice were generated to determine the role of macrophage ABCA1 expression in plasma lipoprotein concentrations and the innate immune response of macrophages. Plasma lipid and lipoprotein concentrations in chow-fed Abca1(-)(M)(/-)(M) and wild-type (WT) mice were indistinguishable. Compared with WT macrophages, Abca1(-)(M)(/-)(M) macrophages had a >95% reduction in ABCA1 protein, failed to efflux lipid to apoA-I, and had a significant increase in free cholesterol (FC) and membrane lipid rafts without induction of endoplasmic reticulum stress. Lipopolysaccharide (LPS)-treated Abca1(-)(M)(/-)(M) macrophages exhibited enhanced expression of pro-inflammatory cytokines and increased activation of the NF-kappaB and MAPK pathways, which could be diminished by silencing MyD88 or by chemical inhibition of NF-kappaB or MAPK. In vivo LPS injection also resulted in a higher pro-inflammatory response in Abca1(-)(M)(/-)(M) mice compared with WT mice. Furthermore, cholesterol depletion of macrophages with methyl-beta-cyclodextrin normalized FC content between the two genotypes and their response to LPS; cholesterol repletion of macrophages resulted in increased cellular FC accumulation and enhanced cellular response to LPS. Our results suggest that macrophage ABCA1 expression may protect against atherosclerosis by facilitating the net removal of excess lipid from macrophages and dampening pro-inflammatory MyD88-dependent signaling pathways by reduction of cell membrane FC and lipid raft content.

Acute neurodegeneration and the inflammasome: central processor for danger signals and the inflammatory response?

Activation of the inflammatory response is a crucial event in the adverse outcome of cerebral ischemia, which is promoted by proinflammatory cytokines such as interleukin (IL)-1beta. Although caspase-1 is necessary for IL-1beta processing, the 'upstream' signaling pathways were, until recently, essentially unknown. Fortunately, the inflammasome, a multiprotein complex responsible for activating caspase-1 and caspase-5, has recently been characterized. The activation of the inflammasome can result in one of several consequences such as cytokine secretion, cell death, or the development of a stress-resistant state. The significance of the inflammasome for the initiation of the inflammatory response during systemic diseases has already been shown and members of the inflammasome complex were recently found to be induced in acute brain injury. However, the specific pathophysiologic role of the inflammasome in neurodegenerative disorders still remains to be clarified. The underlying theories (e.g., danger signal theory) along with the signaling pathways that link the inflammasome to acute neurodegeneration will be discussed here. Furthermore, the stimuli that potentially activate the inflammasome in cerebral ischemia will be specified, as well as their relation to well-known pathways activating the innate immune response (e.g., Toll-like receptor signaling) and the consequences that result from their activation (beneficial versus deleterious).

Genetic ablation of NADPH oxidase enhances susceptibility to cigarette smoke-induced lung inflammation and emphysema in mice

Cigarette smoke (CS) induces recruitment of inflammatory cells in the lungs leading to the generation of reactive oxygen species (ROS), which are involved in lung inflammation and injury. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a multimeric system that is responsible for ROS production in mammalian cells. We hypothesized that NADPH oxidase-derived ROS play an important role in lung inflammation and injury and that targeted ablation of components of NADPH oxidase (p47(phox) and gp91(phox)) would protect lungs against the detrimental effects of CS. To test this hypothesis, we exposed p47(phox-/-) and gp91(phox-/-) mice to CS and examined inflammatory response and injury in the lung. Surprisingly, although CS-induced ROS production was decreased in the lungs of p47(phox-/-) and gp91(phox-/-) mice compared with wild-type mice, the inflammatory response was significantly increased and was accompanied by development of distal airspace enlargement and alveolar destruction. This pathological abnormality was associated with enhanced activation of the TLR4-nuclear factor-kappaB pathway in response to CS exposure in p47(phox-/-) and gp91(phox-/-) mice. This phenomenon was confirmed by in vitro studies in which treatment of peritoneal macrophages with a nuclear factor-kappaB inhibitor reversed the CS-induced release of proinflammatory mediators. Thus, these data suggest that genetic ablation of components of NADPH oxidase enhances susceptibility to the proinflammatory effects of CS leading to airspace enlargement and alveolar damage.

Identification of oxidative stress and Toll-like receptor 4 signaling as a key pathway of acute lung injury

Multiple lung pathogens such as chemical agents, H5N1 avian flu, or SARS cause high lethality due to acute respiratory distress syndrome. Here we report that Toll-like receptor 4 (TLR4) mutant mice display natural resistance to acid-induced acute lung injury (ALI). We show that TLR4-TRIF-TRAF6 signaling is a key disease pathway that controls the severity of ALI. The oxidized phospholipid (OxPL) OxPAPC was identified to induce lung injury and cytokine production by lung macrophages via TLR4-TRIF. We observed OxPL production in the lungs of humans and animals infected with SARS, Anthrax, or H5N1. Pulmonary challenge with an inactivated H5N1 avian influenza virus rapidly induces ALI and OxPL formation in mice. Loss of TLR4 or TRIF expression protects mice from H5N1-induced ALI. Moreover, deletion of ncf1, which controls ROS production, improves the severity of H5N1-mediated ALI. Our data identify oxidative stress and innate immunity as key lung injury pathways that control the severity of ALI.

Early events in the recognition of danger signals after tissue injury

The systemic inflammatory response observed in the setting of overwhelming infection bears striking similarities to that observed in the setting of severe traumatic injury from a clinical and physiologic standpoint. Recent observations have demonstrated that these disparate clinical entities share common mediators on a molecular level. TLRs, specifically TLR4, and the endogenous molecule high-mobility group box 1 are among the mediators that are known to play a role in inflammation in the setting of sepsis. Evidence is accumulating that demonstrates that these mediators also play a role in the host response to tissue injury. Here, we highlight findings from the 7th World Conference on Trauma, Shock, Inflammation and Sepsis in Munich, Germany, in the context of this growing body of literature.