Neutrophils activate alveolar macrophages by producing caspase-6-mediated cleavage of IL-1 receptor-associated kinase-M

Mutations in the Vicinity of the IRAK3 Guanylate Cyclase Center Impact Its Subcellular Localization and Ability to Modulate Inflammatory Signaling in Immortalized Cell Lines

Interleukin-1 receptor-associated kinase 3 (IRAK3) modulates the magnitude of cellular responses to ligands perceived by interleukin-1 receptors (IL-1Rs) and Toll-like receptors (TLRs), leading to decreases in pro-inflammatory cytokines and suppressed inflammation. The molecular mechanism of IRAK3's action remains unknown. IRAK3 functions as a guanylate cyclase, and its cGMP product suppresses lipopolysaccharide (LPS)-induced nuclear factor kappa-light-chain-enhancer of activated B cell (NFκB) activity. To understand the implications of this phenomenon, we expanded the structure-function analyses of IRAK3 through site-directed mutagenesis of amino acids known or predicted to impact different activities of IRAK3. We verified the capacity of the mutated IRAK3 variants to generate cGMP in vitro and revealed residues in and in the vicinity of its GC catalytic center that impact the LPS-induced NFκB activity in immortalized cell lines in the absence or presence of an exogenous membrane-permeable cGMP analog. Mutant IRAK3 variants with reduced cGMP generating capacity and differential regulation of NFκB activity influence subcellular localization of IRAK3 in HEK293T cells and fail to rescue IRAK3 function in IRAK3 knock-out THP-1 monocytes stimulated with LPS unless the cGMP analog is present. Together, our results shed new light on the mechanism by which IRAK3 and its enzymatic product control the downstream signaling, affecting inflammatory responses in immortalized cell lines.

Neutrophils, functions beyond host defense

Neutrophils are the most abundant, ephemeral cell type in human blood. As the first line of defense in the host immune system, neutrophils mature in the bone marrow after undergoing multiple stages of development and then are released into the peripheral blood and conduct a surveillance function. Recent advances in cutting-edge techniques such as single-cell sequencing have uncovered the complexity and plasticity of neutrophils under homeostatic and inflammatory conditions. The exploration of neutrophil heterogeneity and function under disease and homeostasis settings has revealed many unexpected roles of neutrophils beyond a phagocyte. Furthermore, neutrophils are known to actively communicate with innate and adaptive immunocytes via direct or indirect interactions, allowing the modulation of various immune cells. In this review, we will discuss the versatile identities of neutrophils that have been discovered in recent decades, as well as the interplay between neutrophils and other cells.

Entamoeba histolytica exploits the autophagy pathway in macrophages to trigger inflammation in disease pathogenesis

The mechanism whereby Entamoeba histolytica (Eh) binding with macrophages at the intercellular junction triggers aggressive pro-inflammatory responses in disease pathogenesis is not well understood. The host intracellular protein degradation process autophagy and its regulatory proteins are involved in maintenance of cellular homeostasis and excessive inflammatory responses. In this study we unraveled how Eh hijacks the autophagy process in macrophages to dysregulate pro-inflammatory responses. Direct contact of live Eh with macrophages activated caspase-6 that induced rapid proteolytic degradation of the autophagy ATG16L1 protein complex independent of NLRP3 inflammasome and caspase-3/8 activation. Crohn's disease susceptible ATG16L1 T300A variant was highly susceptible to Eh-mediated degradation that augmented pro-inflammatory cytokines in mice. Quantitative proteomics revealed downregulation of autophagy and vesicle-mediated transport and upregulation of cysteine-type endopeptidase pathways in response to Eh. We conclude during Eh-macrophage outside-in signaling, ATG16L1 protein complex plays an overlooked regulatory role in shaping the pro-inflammatory landscape in amebiasis.

Caspase-Dependent Cleavage of DDX21 Suppresses Host Innate Immunity

DEAD (Glu-Asp-Ala-Glu) box RNA helicases have been proven to contribute to antiviral innate immunity. The DDX21 RNA helicase was identified as a nuclear protein involved in rRNA processing and RNA unwinding. DDX21 was also proven to be the scaffold protein in the complex of DDX1-DDX21-DHX36, which senses double-strand RNA and initiates downstream innate immunity. Here, we identified that DDX21 undergoes caspase-dependent cleavage after virus infection and treatment with RNA/DNA ligands, especially for RNA virus and ligands. Caspase-3/6 cleaves DDX21 at D126 and promotes its translocation from the nucleus to the cytoplasm in response to virus infection. The cytoplasmic cleaved DDX21 negatively regulates the interferon beta (IFN-β) signaling pathway by suppressing the formation of the DDX1-DDX21-DHX36 complex. Thus, our data identify DDX21 as a regulator of immune balance and most importantly uncover a potential role of DDX21 cleavage in the innate immune response to virus.

Dietary phenotype and advanced glycation end-products predict WTC-obstructive airways disease: a longitudinal observational study

Background

Diet is a modifier of metabolic syndrome which in turn is associated with World Trade Center obstructive airways disease (WTC-OAD). We have designed this study to (1) assess the dietary phenotype (food types, physical activity, and dietary habits) of the Fire Department of New York (FDNY) WTC-Health Program (WTC-HP) cohort and (2) quantify the association of dietary quality and its advanced glycation end product (AGE) content with the development of WTC-OAD.

Methods

WTC-OAD, defined as developing WTC-Lung Injury (WTC-LI; FEV₁ < LLN) and/or airway hyperreactivity (AHR; positive methacholine and/or positive bronchodilator response). Rapid Eating and Activity Assessment for Participants-Short Version (REAP-S) deployed on 3/1/2018 in the WTC-HP annual monitoring assessment. Clinical and REAP-S data of consented subjects was extracted (7/17/2019). Diet quality [low-(15–19), moderate-(20–29), and high-(30–39)] and AGE content per REAP-S questionnaire were assessed for association with WTC-OAD. Regression models adjusted for smoking, hyperglycemia, hypertension, age on 9/11, WTC-exposure, BMI, and job description.

Results

N = 9508 completed the annual questionnaire, while N = 4015 completed REAP-S and had spirometry. WTC-OAD developed in N = 921, while N = 3094 never developed WTC-OAD. Low- and moderate-dietary quality, eating more (processed meats, fried foods, sugary drinks), fewer (vegetables, whole-grains),and having a diet abundant in AGEs were significantly associated with WTC-OAD. Smoking was not a significant risk factor of WTC-OAD.

Conclusions

REAP-S was successfully implemented in the FDNY WTC-HP monitoring questionnaire and produced valuable dietary phenotyping. Our observational study has identified low dietary quality and AGE abundant dietary habits as risk factors for pulmonary disease in the context of WTC-exposure. Dietary phenotyping, not only focuses our metabolomic/biomarker profiling but also further informs future dietary interventions that may positively impact particulate matter associated lung disease.

Synergistic Effect of WTC-Particulate Matter and Lysophosphatidic Acid Exposure and the Role of RAGE: In-Vitro and Translational Assessment

World Trade Center particulate matter (WTC-PM)-exposed firefighters with metabolic syndrome (MetSyn) have a higher risk of WTC lung injury (WTC-LI). Since macrophages are crucial innate pulmonary mediators, we investigated WTC-PM/lysophosphatidic acid (LPA) co-exposure in macrophages. LPA, a low-density lipoprotein metabolite, is a ligand of the advanced glycation end-products receptor (AGER or RAGE). LPA and RAGE are biomarkers of WTC-LI. Human and murine macrophages were exposed to WTC-PM, and/or LPA, and compared to controls. Supernatants were assessed for cytokines/chemokines; cell lysate immunoblots were assessed for signaling intermediates after 24 h. To explore the translatability of our in-vitro findings, we assessed serum cytokines/chemokines and metabolites of symptomatic, never-smoking WTC-exposed firefighters. Agglomerative hierarchical clustering identified phenotypes of WTC-PM-induced inflammation. WTC-PM induced GM-CSF, IL-8, IL-10, and MCP-1 in THP-1-derived macrophages and induced IL-1α, IL-10, TNF-α, and NF-κB in RAW264.7 murine macrophage-like cells. Co-exposure induced synergistic elaboration of IL-10 and MCP-1 in THP-1-derived macrophages. Similarly, co-exposure synergistically induced IL-10 in murine macrophages. Synergistic effects were seen in the context of a downregulation of NF-κB, p-Akt, -STAT3, and -STAT5b. RAGE expression after co-exposure increased in murine macrophages compared to controls. In our integrated analysis, the human cytokine/chemokine biomarker profile of WTC-LI was associated with discriminatory metabolites (fatty acids, sphingolipids, and amino acids). LPA synergistically elaborated WTC-PM’s inflammatory effects in vitro and was partly RAGE-mediated. Further research will focus on the intersection of MetSyn/PM exposure.

Newly Identified Function of Caspase-6 in ZBP1-mediated Innate Immune Responses, NLRP3 Inflammasome Activation, PANoptosis, and Host Defense

Caspase-6 was discovered decades ago, but its roles in biological processes remain largely unknown. Recently, we have demonstrated that caspase-6 plays a critical role in influenza A virus (IAV)-induced cell death and innate immune responses. During IAV infection, Z-DNA binding protein 1 (ZBP1) initiates ZBP1-PANoptosome assembly to drive inflammasome activation and cell death, and we showed that caspase-6 interacts with RIPK3 to enhance the interaction between RIPK3 and ZBP1, thus promoting PANoptosome assembly. Moreover, the caspase activity of caspase-6 is not required for tins process, suggesting a caspase-independent function of caspase-6 during IAV infection. Additionally, we found that caspase-6 is required for the alternative activation of alveolar macrophages in response to IAV infection. Our findings provide an opportunity to reconsider the physiological role of caspase-6.

Constitutive ablation of caspase-6 reduces the inflammatory response and behavioural changes caused by peripheral pro-inflammatory stimuli

Traditionally, the family of caspases has been subcategorised according to their respective main roles in mediating apoptosis or inflammation. However, recent studies have revealed that caspases participate in diverse cellular functions beyond their canonical roles. Caspase-6 (C6) is one such protease known for its role as a pro-apoptotic executioner caspase and its aberrant activity in several neurodegenerative diseases. In addition to apoptosis, C6 has been shown to regulate B-cell activation and differentiation in plasma cells as well as macrophage activation. Furthermore, C6 has recently been postulated to play a role in mediating the inflammatory response through the production of TNF-α. In this study we further examine the role of C6 in mediating the inflammatory response and its contribution to the manifestation of behavioural abnormalities in mice. We find that C6 is a positive regulator of TNF-α transcription in macrophages and that ablation of C6 reduces lipopolysaccharide (LPS)-induced TNF-α levels in plasma. Furthermore, loss of C6 attenuates LPS-induced behavioural changes in mice and protects neurons from cytokine-mediated toxicity. These data further support the involvement of C6 in the inflammatory response and point to a previously unknown role for C6 in the pathophysiology of depression.

An updated view on the functions of caspases in inflammation and immunity

The binary classification of mammalian caspases as either apoptotic or inflammatory is now obsolete. Emerging data indicate that all mammalian caspases are intricately involved in the regulation of inflammation and immunity. They participate in embryonic and adult tissue homeostasis, control leukocyte differentiation, activation and effector functions, and mediate innate and adaptive immunity signaling. Caspases also promote host resistance by regulating anti-oxidant defense and pathogen clearance through regulation of phagosomal maturation, actin dynamics and phagosome-lysosome fusion. Beyond apoptosis, they regulate inflammatory cell death, eliciting rapid pyroptosis of infected cells, while inhibiting necroptosis-mediated tissue destruction and chronic inflammation. In this review, we describe the cellular and molecular mechanisms underlying non-apoptotic functions of caspases in inflammation and immunity and provide an updated view of their functions as central regulators of tissue homeostasis and host defense.

Caspase-6 mediates resistance against Burkholderia pseudomallei infection and influences the expression of detrimental cytokines

Caspase-6 is a member of the executioner caspases and known to play a role in innate and adaptive immune processes. However, its role in infectious diseases has rarely been addressed yet. We here examined the impact of caspase-6 in an in vivo infection model using the Gram-negative rod Burkholderia pseudomallei, causing the infectious disease melioidosis that is endemic in tropical and subtropical areas around the world. Caspase-6-/- and C57BL/6 wild type mice were challenged with B. pseudomallei for comparing mortality, bacterial burden and inflammatory cytokine expression. Bone-marrow derived macrophages were used to analyse the bactericidal activity in absence of caspase-6. Caspase-6 deficiency was associated with higher mortality and bacterial burden in vivo after B. pseudomallei infection. The bactericidal activity of caspase-6-/- macrophages was impaired compared to wild type cells. Caspase-6-/- mice showed higher expression of the IL-1β gene, known to be detrimental in murine melioidosis. Expression of the IL-10 gene was also increased in caspase-6-/- mice as early as 6 hours after infection. Treatment with exogenous IL-10 rendered mice more susceptible against B. pseudomallei challenge. Thus, caspase-6 seems to play a crucial role for determining resistance against the causative agent of melioidosis. To our knowledge this is the first report showing that caspase-6 is crucial for mediating resistance in an in vivo infection model. Caspase-6 influences the expression of detrimental cytokines and therefore seems to be important for achieving a well-balanced immune response that contributes for an efficient elimination of the pathogen.

Identification of Caspase-6 as a New Regulator of Alternatively Activated Macrophages

Alternatively activated macrophages (AAMs) play essential roles in the promotion of tissue remodeling, vasculogenesis, and tumor progression; however, the detailed mechanisms underlying the activation of AAMs remain largely unknown. Here, by using quantitative proteomic analysis, we identified 62 proteins that were up-regulated in IL-4-induced macrophages. Among these, Caspase-6 was increased significantly. Caspase-6 is important in the apoptotic signaling pathway; however, its role in non-apoptosis is also reported. Here, we first examined the non-apoptotic role of Caspase-6 in the alternative activation of macrophages after administration of IL-4, 4T1 tumor conditional medium, or co-culture with 4T1 cells. Both treatments promoted alternative activation of RAW264.7 cells and primary macrophages, whereas disruption of caspase-6 expression and activity could markedly suppress the biomarker levels of AAMs. Overexpression of Caspase-6 could significantly promote the activation of AAMs. Importantly, we further present evidence that caspase-6 could regulate breast cancer cell invasion by modulating MMP-2 and MMP-9 expression in 4T1 tumor-associated macrophages, as ablation of protein levels or activity of caspase-6 suppressed tumor cell invasion in vitro In conclusion, the observed results markedly expanded our views of the dynamic changes in protein composition during alternative activation of macrophages, and they revealed a critical new role of caspase-6 in regulating this cellular biological process, which suggested that caspase-6 might be a key nod molecule to regulate immunological steady-state and be a therapeutic candidate for tumor immunotherapy.

Caspase 6 has a protective role in SOD1(G93A) transgenic mice

In amyotrophic lateral sclerosis (ALS), it has been suggested that the process of neurodegeneration starts at the neuromuscular junction and is propagated back along axons towards motor neurons. Caspase-dependent pathways are well established as a cause of motor neuron death, and recent work in other disease models indicated a role for caspase 6 in axonal degeneration. Therefore we hypothesised that caspase 6 may be involved in motor neuron death in ALS. To investigate the role of caspase 6 in ALS we profiled protein levels of caspase-6 throughout disease progression in the ALS mouse model SOD1(G93A); this did not reveal differences in caspase 6 levels during disease. To investigate the role of caspase 6 further we generated a colony with SOD1(G93A) transgenic mice lacking caspase 6. Analysis of the transgenic SOD1(G93A); Casp6(-/-) revealed an exacerbated phenotype with motor dysfunction occurring earlier and a significantly shortened lifespan when compared to transgenic SOD1(G93A); Casp6(+/+) mice. Immunofluorescence analysis of the neuromuscular junction revealed no obvious difference between caspase 6(+/+) and caspase 6(-/-) in non-transgenic mice, while the SOD1(G93A) transgenic mice showed severe degeneration compared to non-transgenic mice in both genotypes. Our data indicate that caspase-6 does not exacerbate ALS pathogenesis, but may have a protective role.

IRAK-M regulates the inhibition of TLR-mediated macrophage immune response during late in vitro Leishmania donovani infection

Intramacrophage protozoan parasite Leishmania donovani, causative agent of visceral leishmaniasis, escapes Toll-like receptor (TLR) dependent early host immune response by inducing the deubiquitinating enzyme A20, which is sustained up to 6 h postinfection only. Therefore, Leishmania must apply other means to deactivate late host responses. Here, we elucidated the role of IL-1 receptor-associated kinase M (IRAK-M), a negative regulator of TLR signaling, in downregulating macrophage proinflammatory response during late hours of in vitro infection. Our data reveal a sharp decline in IRAK1 and IRAK4 phosphorylation at 24 h postinfection along with markedly reduced association of IRAK1-TNF receptor associated factor 6, which is mandatory for TLR activation. In contrast, IRAK-M was induced after A20 levels decreased and reached a maximum at 24 h postinfection. IRAK-M induction coincided with increased stimulation of TGF-β, a hallmark cytokine of visceral infection. TGF-β-dependent signaling-mediated induction of SMAD family of proteins, 2, 3, and 4 plays important roles in transcriptional upregulation of IRAK-M. In infected macrophages, siRNA-mediated silencing of IRAK-M displayed enhanced IRAK1 and IRAK4 phosphorylation with a concomitant increase in downstream NF-κB activity and reduced parasite survival. Taken together, the results suggest that IRAK-M may be targeted by L. donovani to inhibit TLR-mediated proinflammatory response late during in vitro infection.

Does Caspase-6 Have a Role in Perinatal Brain Injury?

Apoptotic mechanisms are centre stage for the development of injury in the immature brain, and caspases have been shown to play a pivotal role during brain development and in response to injury. The inhibition of caspases using broad-spectrum agents such as Q-VD-OPh is neuroprotective in the immature brain. Caspase-6, an effector caspase, has been widely researched in neurodevelopmental disorders and found to be important following adult stroke, but its function in the neonatal brain has yet to be detailed. Furthermore, caspases may be important in microglial activation; microglia are required for optimal brain development and following injury, and their close involvement during neuronal cell death suggests that apoptotic cues such as caspase activation may be important in microglial activation. Therefore, in this study we aimed to investigate the possible apoptotic and non-apoptotic functions caspase-6 may have in the immature brain in response to hypoxia-ischaemia. We examined whether caspases are involved in microglial activation. We assessed cleaved caspase-6 expression following hypoxia-ischaemia and conducted primary microglial cultures to assess whether the broad-spectrum inhibitor Q-VD-OPh or caspase-6 gene deletion affected lipopolysaccharide (LPS)-mediated microglial activation and phenotype. We observed cleaved caspase-6 expression to be low but present in the cell body and cell processes in both a human case of white matter injury and 72 h following hypoxia-ischaemia in the rat. Gene deletion of caspase-6 did not affect the outcome of brain injury following mild (50 min) or severe (60 min) hypoxia-ischaemia. Interestingly, we did note that cleaved caspase-6 was co-localised with microglia that were not of apoptotic morphology. We observed that mRNA of a number of caspases was modulated by low-dose LPS stimulation of primary microglia. Q-VD-OPh treatment and caspase-6 gene deletion did not affect microglial activation but modified slightly the M2b phenotype response by changing the time course of SOCS3 expression after LPS administration. Our results suggest that the impact of active caspase-6 in the developing brain is subtle, and we believe there are predominantly other caspases (caspase-2, −3, −8, −9) that are essential for the cell death processes in the immature brain.

The structure function of the death domain of human IRAK-M

BACKGROUND

IRAK-M is an inhibitor of Toll-like receptor signaling that acts by re-directing IRAK-4 activity to TAK1 independent NF-κB activation and by inhibition of IRAK-1/IRAK-2 activity. IRAK-M is expressed in monocytes/macrophages and lung epithelial cells. Lack of IRAK-M in mice greatly improves the resistance to nosocomial pneumonia and lung tumors, which entices IRAK-M as a potential therapeutic target. IRAK-M consists of an N-terminal death domain (DD), a dysfunctional kinase domain and unstructured C-terminal domain. Little is known however on IRAK-M's structure-function relationships.

RESULTS

Since death domains provide the important interactions of IRAK-1, IRAK-2 and IRAK-4 molecules, we generated a 3D structure model of the human IRAK-M-DD (residues C5-G119) to guide mutagenesis studies and predict protein-protein interaction points. First we identified the DD residues involved in the endogenous capacity of IRAK-M to activate NF-κB that is displayed upon overexpression in 293T cells. W74 and R97, at distinct interfaces of the IRAK-M-DD, were crucial for this endogenous NF-κB activating capacity, as well as the C-terminal domain (S445-E596) of IRAK-M. Resulting anti-inflammatory A20 and pro-inflammatory IL-8 transcription in 293T cells was W74 dependent, while IL-8 protein expression was dependent on R97 and the TRAF6 binding motif at P478. The IRAK-M-DD W74 and R97 binding interfaces are predicted to interact with opposite sides of IRAK-4-DD's. Secondly we identified DD residues important for the inhibitory action of IRAK-M by stable overexpression of mutants in THP-1 macrophages and H292 lung epithelial cells. IRAK-M inhibited TLR2/4-mediated cytokine production in macrophages in a manner that is largely dependent on W74. R97 was not involved in inhibition of TNF production but was engaged in IL-6 down-regulation by IRAK-M. Protein-interactive residues D19-A23, located in between W74 and R97, were also observed to be crucial for inhibition of TLR2/4 mediated cytokine induction in macrophages. Remarkably, IRAK-M inhibited TLR5 mediated IL-8 production by lung epithelial cells independent of W74 and R97, but dependent on D19-A23 and R70, two surface-exposed regions that harbor predicted IRAK-2-DD interaction points of IRAK-M.

CONCLUSION

IRAK-M employs alternate residues of its DD to inhibit the different inflammatory mediators induced by varying TLRs and cells.

Lung cell-specific modulation of LPS-induced TLR4 receptor and adaptor localization

Lung infection by Gram-negative bacteria is a major cause of morbidity and mortality in humans. Lipopolysaccharide (LPS), located in the outer membrane of the Gram-negative bacterial cell wall, is a highly potent stimulus of immune and structural cells via the TLR4/MD2 complex whose function is sequentially regulated by defined subsets of adaptor proteins. Regulatory mechanisms of lung-specific defense pathways point at the crucial role of resident alveolar macrophages, alveolar epithelial cells, the TLR4 receptor pathway, and lung surfactant in shaping the innate immune response to Gram-negative bacteria and LPS. During the past decade intracellular spatiotemporal localization of TLR4 emerged as a key feature of TLR4 function. Here, we briefly review lung cell type- and compartment-specific mechanisms of LPS-induced TLR4 regulation with a focus on primary resident hematopoietic and structural cells as well as modifying microenvironmental factors involved.

Extracellular caspase-6 drives murine inflammatory pain via microglial TNF-α secretion

Increasing evidence indicates that the pathogenesis of neuropathic pain is mediated through spinal cord microglia activation. The intracellular protease caspase-6 (CASP6) is known to regulate neuronal apoptosis and axonal degeneration; however, the contribution of microglia and CASP6 in modulating synaptic transmission and pain is unclear. Here, we found that CASP6 is expressed specifically in C-fiber axonal terminals in the superficial spinal cord dorsal horn. Animals exposed to intraplantar formalin or bradykinin injection exhibited CASP6 activation in the dorsal horn. Casp6-null mice had normal baseline pain, but impaired inflammatory pain responses. Furthermore, formalin-induced second-phase pain was suppressed by spinal injection of CASP6 inhibitor or CASP6-neutralizing antibody, as well as perisciatic nerve injection of CASP6 siRNA. Recombinant CASP6 (rCASP6) induced marked TNF-α release in microglial cultures, and most microglia within the spinal cord expressed Tnfa. Spinal injection of rCASP6 elicited TNF-α production and microglia-dependent pain hypersensitivity. Evaluation of excitatory postsynaptic currents (EPSCs) revealed that rCASP6 rapidly increased synaptic transmission in spinal cord slices via TNF-α release. Interestingly, the microglial inhibitor minocycline suppressed rCASP6 but not TNF-α-induced synaptic potentiation. Finally, rCASP6-activated microglial culture medium increased EPSCs in spinal cord slices via TNF-α. Together, these data suggest that CASP6 released from axonal terminals regulates microglial TNF-α secretion, synaptic plasticity, and inflammatory pain.

One airway: Biomarkers of protection from upper and lower airway injury after World Trade Center exposure

BACKGROUND

Firefighters exposed to World Trade Center (WTC) dust have developed chronic rhinosinusitis (CRS) and abnormal forced expiratory volume in 1 s (FEV1). Overlapping but distinct immune responses may be responsible for the clinical manifestations of upper and lower airway injury. We investigated whether a panel of inflammatory cytokines, either associated or not associated with WTC-LI, can predict future chronic rhinosinusitis disease and its severity.

METHODS

Serum obtained within six months of 9/11/2001 from 179 WTC exposed firefighters presenting for subspecialty evaluation prior to 3/2008 was assayed for 39 cytokines. The main outcomes were medically managed CRS (N = 62) and more severe CRS cases requiring sinus surgery (N = 14). We tested biomarker-CRS severity association using ordinal logistic regression analysis.

RESULTS

Increasing serum IL-6, IL-8, GRO and neutrophil concentration reduced the risk of CRS progression. Conversely, increasing TNF-α increased the risk of progression. In a multivariable model adjusted for exposure intensity, increasing IL-6, TNF-α and neutrophil concentration remained significant predictors of progression. Elevated IL-6 levels and neutrophil counts also reduced the risk of abnormal FEV1 but in contrast to CRS, increased TNF-α did not increase the risk of abnormal FEV1.

CONCLUSIONS

Our study demonstrates both independent and overlapping biomarker associations with upper and lower respiratory injury, and suggests that the innate immune response may play a protective role against CRS and abnormal lung function in those with WTC exposure.

Maternal allergen exposure reprograms the developmental lung transcriptome in atopic and normoresponsive rat pups

The "fetal origins hypothesis" argued that physiological changes consequent to in utero exposures ultimately contribute to disease susceptibility in later life. The dramatic increase in asthma prevalence is attributed to early exposures acting on preexisting asthma-susceptible genotypes. We showed previously that distinct transcriptome signatures distinguish the developmental respiratory phenotype of atopic (Brown Norway, BN) and normoresponsive (Lewis) rats. We aimed to determine whether maternal allergen exposure would influence asthma pathogenesis by reprogramming primary patterns of developmental lung gene expression. Postnatal offspring of dams sensitized to ovalbumin before mating and challenged during pregnancy were assessed for lung function, inflammatory biomarkers, and respiratory gene expression. Although maternal ovalbumin exposure resulted in characteristic features of an allergic response (bronchoalveolar lavage neutrophils, IgE, methacholine-induced lung resistance) in offspring of both strains, substantial strain-specific differences were observed in respiratory gene expression. Of 799 probes representing the top 5% of transcriptomic variation, only 112 (14%) were affected in both strains. Strain-specific gene signatures also exhibited marked differences in enrichment for gene ontologies, with immune regulation and cell proliferation being prominent in the BN strain, cell cycle and microtubule assembly gene sets in the Lewis strain. Multiple ovalbumin-specific probes in both strains were also differentially expressed in lymphoblastoid cell lines from human asthmatic vs. nonasthmatic sibling pairs. Our data point to the existence of distinct, genetically programmed responses to maternal exposures in developing lung. These different response patterns, if recapitulated in human fetal development, can contribute to long-term pulmonary health including interindividual susceptibility to asthma.

Pulmonary surfactant protein A and surfactant lipids upregulate IRAK-M, a negative regulator of TLR-mediated inflammation in human macrophages

Alveolar macrophages (AMs) are exposed to frequent challenges from inhaled particulates and microbes and function as a first line of defense with a highly regulated immune response because of their unique biology as prototypic alternatively activated macrophages. Lung collectins, particularly surfactant protein A (SP-A), contribute to this activation state by fine-tuning the macrophage inflammatory response. During short-term (10 min-2 h) exposure, SP-A's regulation of human macrophage responses occurs through decreased activity of kinases required for proinflammatory cytokine production. However, AMs are continuously exposed to surfactant, and the biochemical pathways underlying long-term reduction of proinflammatory cytokine activity are not known. We investigated the molecular mechanism(s) underlying SP-A- and surfactant lipid-mediated suppression of proinflammatory cytokine production in response to Toll-like receptor (TLR) 4 (TLR4) activation over longer time periods. We found that exposure of human macrophages to SP-A for 6-24 h upregulates expression of IL-1 receptor-associated kinase M (IRAK-M), a negative regulator of TLR-mediated NF-κB activation. Exposure to Survanta, a natural bovine lung extract lacking SP-A, also enhances IRAK-M expression, but at lower magnitude and for a shorter duration than SP-A. Surfactant-mediated upregulation of IRAK-M in macrophages suppresses TLR4-mediated TNF-α and IL-6 production in response to LPS, and IRAK-M knockdown by small interfering RNA reverses this suppression. In contrast to TNF-α and IL-6, the surfactant components upregulate LPS-mediated immunoregulatory IL-10 production, an effect reversed by IRAK-M knockdown. In conclusion, these data identify an important signaling regulator in human macrophages that is used by surfactant to control the long-term alveolar inflammatory response, i.e., enhanced IRAK-M activity.

Comparison of WTC dust size on macrophage inflammatory cytokine release in vivo and in vitro

Background

The WTC collapse exposed over 300,000 people to high concentrations of WTC-PM; particulates up to ∼50 mm were recovered from rescue workers’ lungs. Elevated MDC and GM-CSF independently predicted subsequent lung injury in WTC-PM-exposed workers. Our hypotheses are that components of WTC dust strongly induce GM-CSF and MDC in AM; and that these two risk factors are in separate inflammatory pathways.

Methodology/Principal Findings

Normal adherent AM from 15 subjects without WTC-exposure were incubated in media alone, LPS 40 ng/mL, or suspensions of WTC-PM_10–53 or WTC-PM_2.5 at concentrations of 10, 50 or 100 µg/mL for 24 hours; supernatants assayed for 39 chemokines/cytokines. In addition, sera from WTC-exposed subjects who developed lung injury were assayed for the same cytokines. In the in vitro studies, cytokines formed two clusters with GM-CSF and MDC as a result of PM_10–53 and PM_2.5. GM-CSF clustered with IL-6 and IL-12(p70) at baseline, after exposure to WTC-PM_10–53 and in sera of WTC dust-exposed subjects (n = 70) with WTC lung injury. Similarly, MDC clustered with GRO and MCP-1. WTC-PM_10–53 consistently induced more cytokine release than WTC-PM_2.5 at 100 µg/mL. Individual baseline expression correlated with WTC-PM-induced GM-CSF and MDC.

Conclusions

WTC-PM_10–53 induced a stronger inflammatory response by human AM than WTC-PM_2.5. This large particle exposure may have contributed to the high incidence of lung injury in those exposed to particles at the WTC site. GM-CSF and MDC consistently cluster separately, suggesting a role for differential cytokine release in WTC-PM injury. Subject-specific response to WTC-PM may underlie individual susceptibility to lung injury after irritant dust exposure.

Interleukin-1 receptor-associated kinase-3 is a key inhibitor of inflammation in obesity and metabolic syndrome

Background

Visceral obesity is associated with the rising incidence of type 2 diabetes and metabolic syndrome. Low-grade chronic inflammation and oxidative stress synergize in obesity and obesity-induced disorders.

Objective

We searched a cluster of molecules that support interactions between these stress conditions in monocytes.

Methods

RNA expressions in blood monocytes of two independent cohorts comprising 21 and 102 obese persons and 46 age-matched controls were determined by microarray and independently validated by quantitative RT-PCR analysis. The effect of three-month weight loss after bariatric surgery was determined. The effect of RNA silencing on inflammation and oxidative stress was studied in human monocytic THP-1 cells.

Results

Interleukin-1 receptor-associated kinase-3 (IRAK3), key inhibitor of IRAK/NFκB-mediated chronic inflammation, is downregulated in monocytes of obese persons. Low IRAK3 was associated with high superoxide dismutase-2 (SOD2), a marker of mitochondrial oxidative stress. A comparable expression profile was also detected in visceral adipose tissue of the same obese subjects. Low IRAK3 and high SOD2 was associated with a high prevalence of metabolic syndrome (odds ratio: 9.3; sensitivity: 91%; specificity: 77%). By comparison, the odds ratio of high-sensitivity C-reactive protein, a widely used marker of systemic inflammation, was 4.3 (sensitivity: 69%; specificity: 66%). Weight loss was associated with an increase in IRAK3 and a decrease in SOD2, in association with a lowering of systemic inflammation and a decreasing number of metabolic syndrome components. We identified the increase in reactive oxygen species in combination with obesity-associated low adiponectin and high glucose and interleukin-6 as cause of the decrease in IRAK3 in THP-1 cells in vitro.

Conclusion

IRAK3 is a key inhibitor of inflammation in association with obesity and metabolic syndrome. Our data warrant further evaluation of IRAK3 as a diagnostic and prognostic marker, and as a target for intervention.