Externalized histones fuel pulmonary fibrosis via a platelet-macrophage circuit of TGFβ1 and IL-27

Externalized histones erupt from the nucleus as extracellular traps, are associated with several acute and chronic lung disorders, but their implications in the molecular pathogenesis of interstitial lung disease are incompletely defined. To investigate the role and molecular mechanisms of externalized histones within the immunologic networks of pulmonary fibrosis, we studied externalized histones in human and animal bronchoalveolar lavage (BAL) samples of lung fibrosis. Neutralizing anti-histone antibodies were administered in bleomycin-induced fibrosis of C57BL/6 J mice, and subsequent studies used conditional/constitutive knockout mouse strains for TGFβ and IL-27 signaling along with isolated platelets and cultured macrophages. We found that externalized histones (citH3) were significantly (P < 0.01) increased in cell-free BAL fluids of patients with idiopathic pulmonary fibrosis (IPF; n = 29) as compared to healthy controls (n = 10). The pulmonary sources of externalized histones were Ly6G+CD11b+ neutrophils and nonhematopoietic cells after bleomycin in mice. Neutralizing monoclonal anti-histone H2A/H4 antibodies reduced the pulmonary collagen accumulation and hydroxyproline concentration. Histones activated platelets to release TGFβ1, which signaled through the TGFbRI/TGFbRII receptor complex on LysM+ cells to antagonize macrophage-derived IL-27 production. TGFβ1 evoked multiple downstream mechanisms in macrophages, including p38 MAPK, tristetraprolin, IL-10, and binding of SMAD3 to the IL-27 promotor regions. IL-27RA-deficient mice displayed more severe collagen depositions suggesting that intact IL-27 signaling limits fibrosis. In conclusion, externalized histones inactivate a safety switch of antifibrotic, macrophage-derived IL-27 by boosting platelet-derived TGFβ1. Externalized histones are accessible to neutralizing antibodies for improving the severity of experimental pulmonary fibrosis.

THE IMMUNOPATHOGENESIS OF POLYMICROBIAL SEPSIS

ABSTRACT

This report deals with the advances made in the areas of complement and its role in sepsis, both in mice and in humans. The study relates to work over the past 25 years (late 1990s to October 2022). During this period, there has been very rapid progress in understanding the activation pathways of complement and the activation products of complement, especially the anaphylatoxin C5a and its receptors, C5aR1 and C5aR2. Much has also been learned about these pathways of activation that trigger activation of the innate immune system and the array of strong proinflammatory cytokines that can cause cell and organ dysfunction, as well as complement products that cause immunosuppression. The work in septic humans and mice, along with patients who develop lung dysfunction caused by COVID-19, has taught us that there are many strategies for treatment of humans who are septic or develop COVID-19-related lung dysfunction. To date, treatments in humans with these disorders suggest that we are in the midst of a new and exciting area related to the complement system.

Differential inflammatory responses of the native left and right ventricle associated with donor heart preservation

BACKGROUND

Dysfunction and inflammation of hearts subjected to cold ischemic preservation may differ between left and right ventricles, suggesting distinct strategies for amelioration.

METHODS AND RESULTS

Explanted murine hearts subjected to cold ischemia for 0, 4, or 8 h in preservation solution were assessed for function during 60 min of warm perfusion and then analyzed for cell death and inflammation by immunohistochemistry and western blotting and total RNA sequencing. Increased cold ischemic times led to greater left ventricle (LV) dysfunction compared to right ventricle (RV). The LV experienced greater cell death assessed by TUNEL+ cells and cleaved caspase-3 expression (n = 4). While IL-6 protein levels were upregulated in both LV and RV, IL-1β, TNFα, IL-10, and MyD88 were disproportionately increased in the LV. Inflammasome components (NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3), adaptor molecule apoptosis-associated speck-like protein containing a CARD (ASC), cleaved caspase-1) and products (cleaved IL-1β and gasdermin D) were also more upregulated in the LV. Pathway analysis of RNA sequencing showed increased signaling related to tumor necrosis factor, interferon, and innate immunity with ex-vivo ischemia, but no significant differences were found between the LV and RV. Human donor hearts showed comparable inflammatory responses to cold ischemia with greater LV increases of TNFα, IL-10, and inflammasomes (n = 3).

CONCLUSIONS

Mouse hearts subjected to cold ischemia showed time-dependent contractile dysfunction and increased cell death, inflammatory cytokine expression and inflammasome expression that are greater in the LV than RV. However, IL-6 protein elevations and altered transcriptional profiles were similar in both ventricles. Similar changes are observed in human hearts.

Role of Complement and Histones in Sepsis

The wide use of the mouse model of polymicrobial sepsis has provided important evidence for events occurring in infectious sepsis involving septic mice and septic humans. Nearly 100 clinical trials in humans with sepsis have been completed, yet there is no FDA-approved drug. Our studies of polymicrobial sepsis have highlighted the role of complement activation products (especially C5a anaphylatoxin and its receptors C5aR1 and C5aR2) in adverse effects of sepsis. During sepsis, the appearance of these complement products is followed by appearance of extracellular histones in plasma, which have powerful proinflammatory and prothrombotic activities that cause cell injury and multiorgan dysfunction in septic mice. Similar responses occur in septic humans. Histone appearance in plasma is related to complement activation and appearance of C5a and its interaction with its receptors. Development of the cardiomyopathy of sepsis also depends on C5a, C5a receptors and histones. Neutralization of C5a with antibody or absence of C5aR1 blocks appearance of extracellular histones and cell and organ failure in sepsis. Survival rates in septic mice are greatly improved after blockade of C5a with antibody. We also review the various strategies in sepsis that greatly reduce the development of life-threatening events of sepsis.

Requirement of Complement C6 for Intact Innate Immune Responses in Mice

Over the first days of polymicrobial sepsis, there is robust activation of the innate immune system, causing the appearance of proinflammatory cytokines and chemokines, along with the appearance of extracellular histones, which are highly proinflammatory and prothrombotic. In the current study, we studied different innate immune responses in mice with knockout (KO) of complement protein 6 (C6). Polymorphonuclear neutrophils (PMNs) from these KO mice had defective innate immune responses, including defective expression of surface adhesion molecules, generation of superoxide anion, and appearance of reactive oxygen species and histone release after activation of PMNs, along with defective phagocytosis. In addition, in C6-/- mice, the NLRP3 inflammasome was defective both in PMNs and in macrophages. When these KO mice were subjected to polymicrobial sepsis, their survival was improved, associated with reduced levels in the plasma of proinflammatory cytokines and chemokines and lower levels of histones in plasma. In addition, sepsis-induced cardiac dysfunction was attenuated in these KO mice. In a model of acute lung injury induced by LPS, C6-/- mice showed reduced PMN buildup and less lung epithelial/endothelial cell dysfunction (edema and hemorrhage). These data indicate that C6-/- mice have reduced innate immune responses that result in less organ injury and improved survival after polymicrobial sepsis.

Disruption of Neutrophil Extracellular Traps (NETs) Links Mechanical Strain to Post-traumatic Inflammation

Inflammation after trauma is both critical to normal wound healing and may be highly detrimental when prolonged or unchecked with the potential to impair physiologic healing and promote de novo pathology. Mechanical strain after trauma is associated with impaired wound healing and increased inflammation. The exact mechanisms behind this are not fully elucidated. Neutrophil extracellular traps (NETs), a component of the neutrophil response to trauma, are implicated in a range of pro-inflammatory conditions. In the current study, we evaluated their role in linking movement and inflammation. We found that a link exists between the disruption and amplification of NETs which harbors the potential to regulate the wound's response to mechanical strain, while leaving the initial inflammatory signal necessary for physiologic wound healing intact.

New strategies for treatment of infectious sepsis

In this mini review, we describe the molecular mechanisms in polymicrobial sepsis that lead to a series of adverse events including activation of inflammatory and prothrombotic pathways, a faulty innate immune system, and multiorgan dysfunction. Complement activation is a well-established feature of sepsis, especially involving generation of C5a and C5b-9, along with engagement of relevant receptors for C5a. Activation of neutrophils by C5a leads to extrusion of DNA, forming neutrophil extracellular traps that contain myeloperoxidase and oxidases, along with extracellular histones. Generation of the distal complement activation product, C5b-9 (known as the membrane attack complex, MAC), also occurs in sepsis. C5b-9 activates the NLRP3 inflammasome, which damages mitochondria, together with appearance in plasma of IL-1β and IL-18. Histones are strongly proinflammatory as well as being prothrombotic, leading to activation of platelets and development of venous thrombosis. Multiorgan dysfunction is also a feature of sepsis. It is well known that septic cardiomyopathy, which if severe, can lead to death. This complication in sepsis is linked to reduced levels in cardiomyocytes of three critical proteins (SERCA2, NCX, Na⁺ /K⁺ -ATPase). The reductions in these three key proteins are complement- and histone-dependent. Dysfunction of these ATPases is linked to the cardiomyopathy of sepsis. These data suggest novel targets in the setting of sepsis in humans.

GM-CSF Administration Improves Defects in Innate Immunity and Sepsis Survival in Obese Diabetic Mice

Sepsis is the leading cause of death in the intensive care unit with an overall mortality rate of 20%. Individuals who are obese and have type 2 diabetes have increased recurrent, chronic, nosocomial infections that worsen the long-term morbidity and mortality from sepsis. Additionally, animal models of sepsis have shown that obese, diabetic mice have lower survival rates compared with nondiabetic mice. Neutrophils are essential for eradication of bacteria, prevention of infectious complications, and sepsis survival. In diabetic states, there is a reduction in neutrophil chemotaxis, phagocytosis, and reactive oxygen species (ROS) generation; however, few studies have investigated the extent to which these deficits compromise infection eradication and mortality. Using a cecal ligation and puncture model of sepsis in lean and in diet-induced obese mice, we demonstrate that obese diabetic mice have decreased "emergency hematopoiesis" after an acute infection. Additionally, both neutrophils and monocytes in obese, diabetic mice have functional defects, with decreased phagocytic ability and a decreased capacity to generate ROS. Neutrophils isolated from obese diabetic mice have decreased transcripts of Axl and Mertk, which partially explains the phagocytic dysfunction. Furthermore, we found that exogenous GM-CSF administration improves sepsis survival through enhanced neutrophil and monocytes phagocytosis and ROS generation abilities in obese, diabetic mice with sepsis.

Obesity and type 2 diabetes mellitus drive immune dysfunction, infection development, and sepsis mortality

Obesity and type 2 diabetes mellitus (T2D) are global pandemics. Worldwide, the prevalence of obesity has nearly tripled since 1975 and the prevalence of T2D has almost doubled since 1980. Both obesity and T2D are indolent and chronic diseases that develop gradually, with cellular physiologic changes occurring before the clinical signs and symptoms of the diseases become apparent. Individuals with obesity and T2D are physiologically frail and have an increased risk of infections and mortality from sepsis. Improvement in the morbidity and mortality of these at-risk populations would provide a great societal benefit. We believe that the worsened outcomes observed in these patient populations is due to immune system dysfunction that is triggered by the chronic low-grade inflammation present in both diseases. As immune modulatory therapies have been utilized in other chronic inflammatory diseases, there is an emerging role for immune modulatory therapies that target the chronically affected immune pathways in obese and T2D patients. Additionally, bariatric surgery is currently the most successful treatment for obesity and is the only weight loss method that also causes a sustained, substantial improvement of T2D. Consequently, bariatric surgery may also have a role in improving immunity in these patient populations.

Role of complement C5a and histones in septic cardiomyopathy

Polymicrobial sepsis (after cecal ligation and puncture, CLP) causes robust complement activation with release of C5a. Many adverse events develop thereafter and will be discussed in this review article. Activation of complement system results in generation of C5a which interacts with its receptors (C5aR1, C5aR2). This leads to a series of harmful events, some of which are connected to the cardiomyopathy of sepsis, resulting in defective action potentials in cardiomyocytes (CMs), activation of the NLRP3 inflammasome in CMs and the appearance of extracellular histones, likely arising from activated neutrophils which form neutrophil extracellular traps (NETs). These events are associated with activation of mitogen-activated protein kinases (MAPKs) in CMs. The ensuing release of histones results in defective action potentials in CMs and reduced levels of [Ca²⁺]i-regulatory enzymes including sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2) and Na⁺/Ca²⁺ exchanger (NCX) as well as Na⁺/K⁺-ATPase in CMs. There is also evidence that CLP causes release of IL-1β via activation of the NLRP3 inflammasome in CMs of septic hearts or in CMs incubated in vitro with C5a. Many of these events occur after in vivo or in vitro contact of CMs with histones. Together, these data emphasize the role of complement (C5a) and C5a receptors (C5aR1, C5aR2), as well as extracellular histones in events that lead to cardiac dysfunction of sepsis (septic cardiomyopathy).

Understanding Immunosuppression after Sepsis

Following a severe primary infection or trauma, the risk of developing pneumonia increases due to acquired immune defects collectively known as sepsis-induced immunosuppression. In this issue of Immunity, Roquilly et al. (2017) show that dendritic cells and macrophages developing in the lung after the resolution of a severe infection acquire tolerogenic properties that contribute to persistent immunosuppression and susceptibility to secondary infections.

The immune system's role in sepsis progression, resolution, and long-term outcome

Sepsis occurs when an infection exceeds local tissue containment and induces a series of dysregulated physiologic responses that result in organ dysfunction. A subset of patients with sepsis progress to septic shock, defined by profound circulatory, cellular, and metabolic abnormalities, and associated with a greater mortality. Historically, sepsis-induced organ dysfunction and lethality were attributed to the complex interplay between the initial inflammatory and later anti-inflammatory responses. With advances in intensive care medicine and goal-directed interventions, early 30-day sepsis mortality has diminished, only to steadily escalate long after "recovery" from acute events. As so many sepsis survivors succumb later to persistent, recurrent, nosocomial, and secondary infections, many investigators have turned their attention to the long-term sepsis-induced alterations in cellular immune function. Sepsis clearly alters the innate and adaptive immune responses for sustained periods of time after clinical recovery, with immune suppression, chronic inflammation, and persistence of bacterial representing such alterations. Understanding that sepsis-associated immune cell defects correlate with long-term mortality, more investigations have centered on the potential for immune modulatory therapy to improve long-term patient outcomes. These efforts are focused on more clearly defining and effectively reversing the persistent immune cell dysfunction associated with long-term sepsis mortality.

Complement-induced activation of MAPKs and Akt during sepsis: role in cardiac dysfunction

Polymicrobial sepsis in mice causes myocardial dysfunction after generation of the complement anaphylatoxin, complement component 5a (C5a). C5a interacts with its receptors on cardiomyocytes (CMs), resulting in redox imbalance and cardiac dysfunction that can be functionally measured and quantitated using Doppler echocardiography. In this report we have evaluated activation of MAPKs and Akt in CMs exposed to C5a in vitro and after cecal ligation and puncture (CLP) in vivo In both cases, C5a in vitro caused activation (phosphorylation) of MAPKs and Akt in CMs, which required availability of both C5a receptors. Using immunofluorescence technology, activation of MAPKs and Akt occurred in left ventricular (LV) CMs, requiring both C5a receptors, C5aR1 and -2. Use of a water-soluble p38 inhibitor curtailed activation in vivo of MAPKs and Akt in LV CMs as well as the appearance of cytokines and histones in plasma from CLP mice. When mouse macrophages were exposed in vitro to LPS, activation of MAPKs and Akt also occurred. The copresence of the p38 inhibitor blocked these activation responses. Finally, the presence of the p38 inhibitor in CLP mice reduced the development of cardiac dysfunction. These data suggest that polymicrobial sepsis causes cardiac dysfunction that appears to be linked to activation of MAPKs and Akt in heart.-Fattahi, F., Kalbitz, M., Malan, E. A., Abe, E., Jajou, L., Huber-Lang, M. S., Bosmann, M., Russell, M. W., Zetoune, F. S., Ward, P. A. Complement-induced activation of MAPKs and Akt during sepsis: role in cardiac dysfunction.

Selective Biological Responses of Phagocytes and Lungs to Purified Histones

Histones invoke strong proinflammatory responses in many different organs and cells. We assessed biological responses to purified or recombinant histones, using human and murine phagocytes and mouse lungs. H1 had the strongest ability in vitro to induce cell swelling independent of requirements for toll-like receptors (TLRs) 2 or 4. These responses were also associated with lactate dehydrogenase release. H3 and H2B were the strongest inducers of [Ca2+]i elevations in phagocytes. Cytokine and chemokine release from mouse and human phagocytes was predominately a function of H2A and H2B. Double TLR2 and TLR4 knockout (KO) mice had dramatically reduced cytokine release induced in macrophages exposed to individual histones. In contrast, macrophages from single TLR-KO mice showed few inhibitory effects on cytokine production. Using the NLRP3 inflammasome protocol, release of mature IL-1β was predominantly a feature of H1. Acute lung injury following the airway delivery of histones suggested that H1, H2A, and H2B were linked to alveolar leak of albumin and the buildup of polymorphonuclear neutrophils as well as the release of chemokines and cytokines into bronchoalveolar fluids. These results demonstrate distinct biological roles for individual histones in the context of inflammation biology and the requirement of both TLR2 and TLR4.

Diabetes and Sepsis: Risk, Recurrence, and Ruination

Sepsis develops when an infection surpasses local tissue containment. A series of dysregulated physiological responses are generated, leading to organ dysfunction and a 10% mortality risk. When patients with sepsis demonstrate elevated serum lactates and require vasopressor therapy to maintain adequate blood pressure in the absence of hypovolemia, they are in septic shock with an in-hospital mortality rate >40%. With improvements in intensive care treatment strategies, overall sepsis mortality has diminished to ~20% at 30 days; however, mortality continues to steadily climb after recovery from the acute event. Traditionally, it was thought that the complex interplay between inflammatory and anti-inflammatory responses led to sepsis-induced organ dysfunction and mortality. However, a closer examination of those who die long after sepsis subsides reveals that many initial survivors succumb to recurrent, nosocomial, and secondary infections. The comorbidly challenged, physiologically frail diabetic individuals suffer the highest infection rates. Recent reports suggest that even after clinical "recovery" from sepsis, persistent alterations in innate and adaptive immune responses exists resulting in chronic inflammation, immune suppression, and bacterial persistence. As sepsis-associated immune defects are associated with increased mortality long-term, a potential exists for immune modulatory therapy to improve patient outcomes. We propose that diabetes causes a functional immune deficiency that directly reduces immune cell function. As a result, patients display diminished bactericidal clearance, increased infectious complications, and protracted sepsis mortality. Considering the substantial expansion of the elderly and obese population, global adoption of a Western diet and lifestyle, and multidrug resistant bacterial emergence and persistence, diabetic mortality from sepsis is predicted to rise dramatically over the next two decades. A better understanding of the underlying diabetic-induced immune cell defects that persist following sepsis are crucial to identify potential therapeutic targets to bolster innate and adaptive immune function, prevent infectious complications, and provide more durable diabetic survival.

Complement and sepsis-induced heart dysfunction

It is well known that cardiac dysfunction develops during sepsis in both humans and in rodents (rats, mice). These defects appear to be reversible, since after "recovery" from sepsis, cardiac dysfunction disappears and the heart returns to its function that was present before the onset of sepsis. Our studies, using in vivo and in vitro models, have demonstrated that C5a and its receptors (C5aR1 and C5aR2) play key roles in cardiac dysfunction developing during sepsis. Use of a neutralizing antibody to C5a largely attenuates cardiac dysfunction and other adverse events developing during sepsis. The molecular basis for cardiac dysfunctions is linked to generation of C5a and its interaction with C5a receptors present on surfaces of cardiomyocytes (CMs). It is established that C5a interactions with C5a receptors leads to significant reductions involving faulty contractility and relaxation in CMs. In addition, C5a interactions with C5a receptors on CMs results in reductions in Na⁺/K⁺-ATPase in CMs. This ATPase is essential for intact action potentials in CMs. The enzymatic activity and protein for this ATPase were strikingly reduced in CMs during sepsis by unknown mechanisms. In addition, C5a interactions with C5aRs also caused reductions in CM homeostatic proteins that regulate cytosolic [Ca²⁺]i in CMs: sarco/endoplasmic reticulum Ca²⁺-ATPase2 (SERCA2) and Na⁺/Ca²⁺ exchanger (NCX). In the absence of C5a receptors, defects in SERCA2 and NCX in CMs after sepsis are strikingly attenuated. These observations suggest new strategies to protect the heart from dysfunction developing during sepsis.

Investigation of hydrogen induced fluorescence in C60 and its potential use in luminescence down shifting applications

Herein the photophysical properties of hydrogenated fullerenes (fulleranes) synthesized by direct hydrogenation utilizing hydrogen pressure (100 bar) and elevated temperatures (350 °C) are compared to the fulleranes C₆₀H₁₈ and C₆₀H₃₆ synthesized by amine reduction and the Birch reduction, respectively. Through spectroscopic measurements and density functional theory (DFT) calculations of the HOMO-LUMO gaps of C₆₀H_x (0 ≤ x ≤ 60), we show that hydrogenation significantly affects the electronic structure of C₆₀ by decreasing conjugation and increasing sp³ hybridization. This results in a blue shift of the emission maximum as the number of hydrogen atoms attached to C₆₀ increases. Correlations in the emission spectra of C₆₀H_x produced by direct hydrogenation and by chemical methods also support the hypothesis of the formation of C₆₀H₁₈ and C₆₀H₃₆ during direct hydrogenation with emission maxima of 435 and 550 nm respectively. We also demonstrate that photophysical tunability, stability, and solubility of C₆₀H_x in a variety of organic solvents make them easily adaptable for application as luminescent down-shifters in heads-up displays, light-emitting diodes, and luminescent solar concentrators. The utilizization of carbon based materials in these applications can potentially offer advantages over commonly utilized transition metal based quantum dot chromophores. We therefore propose that the controlled modification of C₆₀ provides an excellent platform for evaluating how individual chemical and structural changes affect the photophysical properties of a well-defined carbon nanostructure.

Complement-induced activation of the cardiac NLRP3 inflammasome in sepsis

Cardiac dysfunction develops during sepsis in humans and rodents. In the model of polymicrobial sepsis induced by cecal ligation and puncture (CLP), we investigated the role of the NLRP3 inflammasome in the heart. Mouse heart homogenates from sham-procedure mice contained high mRNA levels of NLRP3 and IL-1β. Using the inflammasome protocol, exposure of cardiomyocytes (CMs) to LPS followed by ATP or nigericin caused release of mature IL-1β. Immunostaining of left ventricular frozen sections before and 8 h after CLP revealed the presence of NLRP3 and IL-1β proteins in CMs. CLP caused substantial increases in mRNAs for IL-1β and NLRP3 in CMs which are reduced in the absence of either C5aR1 or C5aR2. After CLP, NLRP3^-/- mice showed reduced plasma levels of IL-1β and IL-6. In vitro exposure of wild-type CMs to recombinant C5a (rC5a) caused elevations in both cytosolic and nuclear/mitochondrial reactive oxygen species (ROS), which were C5a-receptor dependent. Use of a selective NOX2 inhibitor prevented increased cytosolic and nuclear/mitochondrial ROS levels and release of IL-1β. Finally, NLRP3^-/- mice had reduced defects in echo/Doppler parameters in heart after CLP. These studies establish that the NLRP3 inflammasome contributes to the cardiomyopathy of polymicrobial sepsis.-Kalbitz, M., Fattahi, F., Grailer, J. J., Jajou, L., Malan, E. A., Zetoune, F. S., Huber-Lang, M., Russell, M. W., Ward, P. A. Complement-induced activation of the cardiac NLRP3 inflammasome in sepsis.

Complement Destabilizes Cardiomyocyte Function In Vivo after Polymicrobial Sepsis and In Vitro

There is accumulating evidence during sepsis that cardiomyocyte (CM) homeostasis is compromised, resulting in cardiac dysfunction. An important role for complement in these outcomes is now demonstrated. Addition of C5a to electrically paced CMs caused prolonged elevations of intracellular Ca(2+) concentrations during diastole, together with the appearance of spontaneous Ca(2+) transients. In polymicrobial sepsis in mice, we found that three key homeostasis-regulating proteins in CMs were reduced: Na(+)/K(+)-ATPase, which is vital for effective action potentials in CMs, and two intracellular Ca(2+) concentration regulatory proteins, that is, sarcoplasmic/endoplasmic reticulum calcium ATPase 2 and the Na(+)/Ca(2+) exchanger. Sepsis caused reduced mRNA levels and reductions in protein concentrations in CMs for all three proteins. The absence of either C5a receptor mitigated sepsis-induced reductions in the three regulatory proteins. Absence of either C5a receptor (C5aR1 or C5aR2) diminished development of defective systolic and diastolic echocardiographic/Doppler parameters developing in the heart (cardiac output, left ventricular stroke volume, isovolumic relaxation, E' septal annulus, E/E' septal annulus, left ventricular diastolic volume). We also found in CMs from septic mice the presence of defective current densities for Ik1, l-type calcium channel, and Na(+)/Ca(2+) exchanger. These defects were accentuated in the copresence of C5a. These data suggest complement-related mechanisms responsible for development of cardiac dysfunction during sepsis.

Melatonin alleviates acute lung injury through inhibiting the NLRP3 inflammasome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are clinically severe respiratory disorders, and there are currently no Food and Drug Administration-approved drug therapies. Melatonin is a well-known anti-inflammatory molecule, which has proven to be effective in ALI induced by many conditions. Emerging studies suggest that the NLRP3 inflammasome plays a critical role during ALI. How melatonin directly blocks activation of the NLRP3 inflammasome in ALI remains unclear. In this study, using an LPS-induced ALI mouse model, we found intratracheal (i.t.) administration of melatonin markedly reduced the pulmonary injury and decreased the infiltration of macrophages and neutrophils into lung. During ALI, the NLRP3 inflammasome is significantly activated with a large amount of IL-1β and the activated caspase-1 occurring in the lung. Melatonin inhibits the activation of the NLRP3 inflammasome by both suppressing the release of extracellular histones and directly blocking histone-induced NLRP3 inflammasome activation. Notably, i.t. route of melatonin administration opens a more efficient therapeutic approach for treating ALI.

New Insights into Molecular Mechanisms of Immune Complex-Induced Injury in Lung

While the phlogistic activities of IgM or IgG immune complexes (ICs) have been well established as complement-activating agents and seem likely to play important roles in humans with vasculitis, certain types of glomerulonephritis as well as in a variety of autoimmune diseases, the predominant clinical strategies have involved the use of immunosuppressive or anti-inflammatory drugs. Over the past decade, new insights into molecular events developing during IC models in rodents have identified new phlogistic products that may be candidates for therapeutic blockade. Extracellular histones, located in the web-like structures of neutrophil extracellular traps, are released from complement-activated polymorphonuclear neutrophils (PMNs) downstream of IC deposition. Extracellular histones appear to be a new class of highly tissue-damaging products derived from complement-activated PMNs. Histones have also been discovered in cell-free broncho-alveolar lavage fluids from humans with acute respiratory distress syndrome (ARDS). Recent studies emphasize that in the setting of ARDS-like reactions in rodents, extracellular histones are released and are exceedingly proinflammatory, tissue damaging, and prothrombotic. Such studies suggest that in humans with ARDS, extracellular histones may represent therapeutic targets for blockade.

Sepsis-induced immune dysfunction: can immune therapies reduce mortality?

Sepsis is a systemic inflammatory response induced by an infection, leading to organ dysfunction and mortality. Historically, sepsis-induced organ dysfunction and lethality were attributed to the interplay between inflammatory and antiinflammatory responses. With advances in intensive care management and goal-directed interventions, early sepsis mortality has diminished, only to surge later after "recovery" from acute events, prompting a search for sepsis-induced alterations in immune function. Sepsis is well known to alter innate and adaptive immune responses for sustained periods after clinical "recovery," with immunosuppression being a prominent example of such alterations. Recent studies have centered on immune-modulatory therapy. These efforts are focused on defining and reversing the persistent immune cell dysfunction that is associated with mortality long after the acute events of sepsis have resolved.

Anti-inflammatory interventions-what has worked, not worked, and what may work in the future

Our Introductory Commentary relates to many topics that are linked to inflammatory responses and how these responses are regulated in order to promote healing of damaged tissues and bring about effective clearance of infectious agents. In non-infectious situations, cells and tissues release products (danger associated molecular patterns) that can trigger damaging inflammatory responses. These products must be effectively dealt with in order to avoid serious tissue injury. We provide a perspective about many decades of research into the inflammatory response and describe strategies that have achieved success in restraining inflammatory responses, as well as many approaches that have not been clinically effective. With development of new technologies such as advanced genomic analysis, highly sensitive and sophisticated mass spectrometry and related approaches, as well as the ability to employ mutagenesis induction, we are beginning to define highly sophisticated molecular pathways that previously were opaque. This progress may well have clinical relevance, and we may be on the edge of a scientific revolution in the broad area of inflammation.

Therapeutic targeting of acute lung injury and acute respiratory distress syndrome

There is no Food and Drug Administration-approved treatment for acute respiratory distress syndrome (ARDS), in spite of the relatively large number of patients with the diagnosis. In this report, we provide an overview of preclinical studies and a description of completed and future clinical trials in humans with ARDS. Preclinical studies dealing with acute lung injury have suggested roles for complement and complement receptors, as well as the evolving role of histones, but details of these pathways are inadequately understood. Anti-inflammatory interventions have not been convincingly effective. Various cell growth factors are being considered for clinical study. Interventions to block complement activation or its products are under consideration. Stem cell therapies have shown efficacy in preclinical studies, which have motivated phase I/II trials in humans with ARDS.

Organ distribution of histones after intravenous infusion of FITC histones or after sepsis

Histones appear in plasma during infectious or non-infectious sepsis and are associated with multiorgan injury. In the current studies, intravenous infusion of histones resulted in their localization in major organs. In vitro exposure of mouse macrophages to histones caused a buildup of histones on cell membranes followed by localization into cytosol and into the nucleus. After polymicrobial sepsis (cecal ligation and puncture), histones appeared in plasma as well as in a multiorgan pattern, peaking at 8 h followed by decline. In lungs, histones and neutrophils appeared together, with evidence for formation of neutrophil extracellular traps (NETs), which represent an innate immune response to trap and kill bacteria and other infectious agents. In liver, there was intense NET formation, featuring linear patterns containing histones and strands of DNA. When neutrophils were activated in vitro with C5a or phorbol myristate acetate, NET formation ensued. While formation of NETs represents entrapment and killing of infectious agents, the simultaneous release from neutrophils of histones often results in tissue/organ damage.

The molecular fingerprint of lung inflammation after blunt chest trauma

Background

After severe blunt chest trauma, the development of an acute lung injury (ALI) is often associated with severe or even lethal complications. Especially in multiple injured patients after blunt chest trauma ALI/ARDS [acute respiratory distress syndrome (ARDS)] is frequent. However, in the initial posttraumatic phase, inflammatory clinical signs are often not apparent and underlying changes in gene-expression profile are unknown.

Methods

Therefore, inflammation in lung tissue following blunt chest trauma was characterized in a well-defined bilateral lung injury model. Using DNA microarrays representing 9240 genes, the temporal sequence of blunt chest trauma-induced gene-expression patterns in lung tissue was examined.

Results

The results suggest an activation of a highly complex transcriptional program in response to chest trauma. Chest trauma led to elevated expression levels of inflammatory and coagulatory proteins (such as TNFα receptor, IL-1α, IL-1β, C3, NF-κB and plasminogen activator). However, upregulation of proteins was found, usually incoherent of exerting effects in blunt thoracic trauma (pendrin, resistin, metallothionein and glucocorticoid-induced leucine zipper). Furthermore, significant downregulation was observed as early as 10 min after trauma for cytokines and complement factors (LCR-1, C4) as well as for intracellular signaling molecules (inhibitory protein phosphatase) and ion-channels (voltage-dependent Ca²⁺ channel).

Conclusions

Taken together, the provided global perspective of the inflammatory response following blunt chest trauma could provide a molecular framework for future research in trauma pathophysiology.

Experimental design of complement component 5a-induced acute lung injury (C5a-ALI): a role of CC-chemokine receptor type 5 during immune activation by anaphylatoxin

Excessive activation of the complement system is detrimental in acute inflammatory disorders. In this study, we analyzed the role of complement-derived anaphylatoxins in the pathogenesis of experimental acute lung injury/acute respiratory distress syndrome (ALI/ARDS) in C57BL/6J mice. Intratracheal administration of recombinant mouse complement component (C5a) caused alveolar inflammation with abundant recruitment of Ly6-G(+)CD11b(+) leukocytes to the alveolar spaces and severe alveolar-capillary barrier dysfunction (C5a-ALI; EC(50[C5a]) = 20 ng/g body weight). Equimolar concentrations of C3a or desarginated C5a (C5a(desArg)) did not induce alveolar inflammation. The severity of C5a-ALI was aggravated in C5-deficient mice. Depletion of Ly6-G(+) cells and use of C5aR1(-/-) bone marrow chimeras suggested an essential role of C5aR1(+) hematopoietic cells in C5a-ALI. Blockade of PI3K/Akt and MEK1/2 kinase pathways completely abrogated lung injury. The mechanistic description is that C5a altered the alveolar cytokine milieu and caused significant release of CC-chemokines. Mice with genetic deficiency of CC-chemokine receptor (CCR) type 5, the common receptor of chemokine (C-C motif) ligand (CCL) 3, CCL4, and CCL5, displayed reduced lung damage. Moreover, treatment with a CCR5 antagonist, maraviroc, was protective against C5a-ALI. In summary, our results suggest that the detrimental effects of C5a in this model are partly mediated through CCR5 activation downstream of C5aR1, which may be evaluated for potential therapeutic exploitation in ALI/ARDS.

Role of extracellular histones in the cardiomyopathy of sepsis

The purpose of this study was to define the relationship in polymicrobial sepsis (in adult male C57BL/6 mice) between heart dysfunction and the appearance in plasma of extracellular histones. Procedures included induction of sepsis by cecal ligation and puncture and measurement of heart function using echocardiogram/Doppler parameters. We assessed the ability of histones to cause disequilibrium in the redox status and intracellular [Ca(2+)]i levels in cardiomyocytes (CMs) (from mice and rats). We also studied the ability of histones to disturb both functional and electrical responses of hearts perfused with histones. Main findings revealed that extracellular histones appearing in septic plasma required C5a receptors, polymorphonuclear leukocytes (PMNs), and the Nacht-, LRR-, and PYD-domains-containing protein 3 (NLRP3) inflammasome. In vitro exposure of CMs to histones caused loss of homeostasis of the redox system and in [Ca(2+)]i, as well as defects in mitochondrial function. Perfusion of hearts with histones caused electrical and functional dysfunction. Finally, in vivo neutralization of histones in septic mice markedly reduced the parameters of heart dysfunction. Histones caused dysfunction in hearts during polymicrobial sepsis. These events could be attenuated by histone neutralization, suggesting that histones may be targets in the setting of sepsis to reduce cardiac dysfunction.

Cutting edge: critical role for C5aRs in the development of septic lymphopenia in mice

In the early stages of sepsis, lymphocytes undergo apoptosis, resulting in lymphopenia and immunosuppression. The trigger for septic lymphopenia is unknown. Using the polymicrobial model of murine sepsis, we investigated the role of C5a receptors in septic lymphopenia. In wild-type mice, cecal ligation and puncture resulted in splenocyte apoptosis and significant lymphopenia after 3 d, which was not observed in C5aR1(-/-) or C5aR2(-/-) mice. Our data show that mouse neutrophils exposed to recombinant mouse C5a cause release of histones in a dose-dependent and time-dependent manner. Histone levels in spleen were significantly elevated following cecal ligation and puncture but were reduced by the absence of C5aR1. Histones induced significant lymphocyte apoptosis in vitro. Ab-mediated neutralization of histones prevented the development of lymphopenia in sepsis. Together, these results describe a new pathway of septic lymphopenia involving complement and extracellular histones. Targeting of this pathway may have therapeutic benefit for patients with sepsis or other serious illness.

Interruption of macrophage-derived IL-27(p28) production by IL-10 during sepsis requires STAT3 but not SOCS3

Severe sepsis and septic shock are leading causes of morbidity and mortality worldwide. Infection-associated inflammation promotes the development and progression of adverse outcomes in sepsis. The effects of heterodimeric IL-27 (p28/EBI3) have been implicated in the natural course of sepsis, whereas the molecular mechanisms underlying the regulation of gene expression and release of IL-27 in sepsis are poorly understood. We studied the events regulating the p28 subunit of IL-27 in endotoxic shock and polymicrobial sepsis following cecal ligation and puncture. Neutralizing Abs to IL-27(p28) improved survival rates, restricted cytokine release, and reduced bacterial burden in C57BL/6 mice during sepsis. Genetic disruption of IL-27 signaling enhanced the respiratory burst of macrophages. Experiments using splenectomized mice or treatment with clodronate liposomes suggested that macrophages in the spleen may be a significant source of IL-27(p28) during sepsis. In cultures of TLR4-activated macrophages, the frequency of F4/80(+)CD11b(+)IL-27(p28)(+) cells was reduced by the addition of IL-10. IL-10 antagonized both MyD88-dependent and TRIF-dependent release of IL-27(p28). Genetic deletion of STAT3 in Tie2-Cre/STAT3flox macrophages completely interrupted the inhibition of IL-27(p28) by IL-10 after TLR4 activation. In contrast, IL-10 remained fully active to suppress IL-27(p28) with deletion of SOCS3 in Tie2-Cre/SOCS3flox macrophages. Blockade of IL-10R by Ab or genetic deficiency of IL-10 resulted in 3-5-fold higher concentrations of IL-27(p28) in endotoxic shock and polymicrobial sepsis. Our studies identify IL-10 as a critical suppressing factor for IL-27(p28) production during infection-associated inflammation. These findings may be helpful for a beneficial manipulation of adverse IL-27(p28) release during sepsis.

Lung inflammation and damage induced by extracellular histones

Despite decades of research, acute respiratory distress syndrome (ARDS) remains an important clinical challenge due to an incomplete understanding of the pathophysiological mechanisms. No FDA-approved drug therapy currently exists for treatment of humans with ARDS. There is accumulating evidence in rodents and humans suggesting that extracellular histones are strong drivers of inflammation and tissue damage. We recently described an important role for extracellular histones during acute lung injury (ALI) in mice (Bosmann et al., FASEB J. 27:5010-5021 (2013)). Extracellular histones were detected in bronchoalveolar lavage fluids (BALF) from patients with ARDS but not in BALF from non-ARDS patients in intensive care units. Extracellular histones were also detected in BALF from mice during experimental ALI. The presence of extracellular histones was dependent on the two C5a receptors (C5aR and C5L2) and availability of neutrophils. Extracellular histones were highly pro-inflammatory, and caused severe damage to respiratory function. Intratracheal instillation of histones resulted in pro-inflammatory mediator production, epithelial cell damage, disturbances in alveolar-capillary gas exchange, lung consolidation, activation of the coagulation cascade, and in some cases, death. Antibody-mediated neutralization of extracellular histones attenuated C5a-induced ALI. Together, these data suggested a prominent role for extracellular histones in the pathophysiology of ALI. The predominant source of histones in ALI may be neutrophils that have been activated by C5a to form neutrophil extracellular traps (NETs). Therapeutic targeting of extracellular histones may provide a novel approach to combat ARDS in humans.

Persistent neutrophil dysfunction and suppression of acute lung injury in mice following cecal ligation and puncture sepsis

Sepsis, both in humans and in rodents, is associated with persistent immunosuppression accompanied by defects in innate immunity during the acute phase of sepsis. Mice were rendered septic by cecal ligation and puncture (CLP) followed by the induction of acute lung injury, employing distal airway deposition of IgG immune complexes, in order to quantitatively evaluate innate immune responses following the induction of sepsis. Suppression of innate immune responses in the lung occurred as early as 12 h after CLP and up to 21 days thereafter. The mechanism of innate immune defects included a reduced leak of albumin into the lungs together with reduced levels of tumor necrosis factor in bronchoalveolar lavage fluids and increased levels of interleukin-10 that were persistent. Bone marrow-derived neutrophils (polymorphonuclear neutrophils; PMNs) from CLP mice also had reduced levels of the activation marker CD11b and a depressed respiratory burst following stimulation in vitro. These results were not observed in mice with endotoxemia, where the innate inflammatory response was preserved. However, sustained lymphopenia was present in both models, suggesting differential regulation of innate and adaptive immunity in the two sepsis models. These data indicate that CLP induced a prolonged suppression of inflammatory responses both in the lung and systemically, as defined by bone marrow-derived PMN dysfunction.