c-Jun N-terminal kinase mediates constitutive human eosinophil apoptosis

Nerve Growth Factor and Autoimmune Diseases

NGF plays a crucial immunomodulatory role and increased levels are found in numerous tissues during autoimmune states. NGF directly modulates innate and adaptive immune responses of B and T cells and causes the release of neuropeptides and neurotransmitters controlling the immune system activation in inflamed tissues. Evidence suggests that NGF is involved in the pathogenesis of numerous immune diseases including autoimmune thyroiditis, chronic arthritis, multiple sclerosis, systemic lupus erythematosus, mastocytosis, and chronic granulomatous disease. Furthermore, as NGF levels have been linked to disease severity, it could be considered an optimal early biomarker to identify therapeutic approach efficacy. In conclusion, by gaining insights into how these molecules function and which cells they interact with, future studies can devise targeted therapies to address various neurological, immunological, and other disorders more effectively. This knowledge may pave the way for innovative treatments based on NGF manipulation aimed at improving the quality of life for individuals affected by diseases involving neurotrophins.

GOAT: Gene-level biomarker discovery from multi-Omics data using graph ATtention neural network for eosinophilic asthma subtype

MOTIVATION

Asthma is a heterogeneous disease where various subtypes are established and molecular biomarkers of the subtypes are yet to be discovered. Recent availability of multi-omics data paved a way to discover molecular biomarkers for the subtypes. However, multi-omics biomarker discovery is challenging because of the complex interplay between different omics layers.

RESULTS

We propose a deep attention model named Gene-level biomarker discovery from multi-Omics data using graph ATtention neural network (GOAT) for identifying molecular biomarkers for eosinophilic asthma subtypes with multi-omics data. GOAT identifies genes that discriminate subtypes using a graph neural network by modeling complex interactions among genes as the attention mechanism in the deep learning model. In experiments with multi-omics profiles of the COREA (Cohort for Reality and Evolution of Adult Asthma in Korea) asthma cohort of 300 patients, GOAT outperforms existing models and suggests interpretable biological mechanisms underlying asthma subtypes. Importantly, GOAT identified genes that are distinct only in terms of relationship with other genes through attention. To better understand the role of biomarkers, we further investigated two transcription factors, CTNNB1 and JUN, captured by GOAT. We were successful in showing the role of the transcription factors in eosinophilic asthma pathophysiology in a network propagation and transcriptional network analysis, which were not distinct in terms of gene expression level differences.

AVAILABILITY AND IMPLEMENTATION

Source code is available https://github.com/DabinJeong/Multi-omics_biomarker. The preprocessed data underlying this article is accessible in data folder of the github repository. Raw data are available in Multi-Omics Platform at http://203.252.206.90:5566/, and it can be accessible when requested.

Sialic acid-binding immunoglobulin-like lectin 8 (Siglec-8) is an activating receptor mediating β2-integrin-dependent function in human eosinophils

BACKGROUND

Siglec-8 is a CD33 subfamily cell-surface receptor selectively expressed on human eosinophils. After cytokine priming, Siglec-8 mAb or glycan ligand binding causes eosinophil apoptosis associated with reactive oxygen species (ROS) production. Most CD33-related Siglecs function as inhibitory receptors, but the ability of Siglec-8 to stimulate eosinophil ROS production and apoptosis suggests that Siglec-8 might instead function as an activating receptor.

OBJECTIVE

We sought to determine the role of IL-5 priming and identify the signaling molecules involved in Siglec-8 function for human eosinophils.

METHODS

We used an mAb and/or a multimeric synthetic sulfated sialoglycan ligand recognizing Siglec-8 in combination with integrin blocking antibodies, pharmacologic inhibitors, phosphoproteomics, and Western blot analysis to define the necessity of various proteins involved in Siglec-8 function for human eosinophils.

RESULTS

Cytokine priming was required to elicit the unanticipated finding that Siglec-8 engagement promotes rapid β2-integrin-dependent eosinophil adhesion. Also novel was the finding that this adhesion was necessary for subsequent ROS production and apoptosis. Siglec-8-mediated ROS was generated through reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation because pretreatment of eosinophils with catalase (an extracellular superoxide scavenger) or NSC 23766 (a Rac GTPase inhibitor) completely inhibited Siglec-8-mediated eosinophil apoptosis. Finally, engagement of Siglec-8 on IL-5-primed eosinophils resulted in increased phosphorylation of Akt, p38, and c-Jun N-terminal kinase 1 that was also β2-integrin dependent; pharmacologic inhibition of these kinases completely prevented Siglec-8-mediated eosinophil apoptosis.

CONCLUSIONS

These data demonstrate that Siglec-8 functions uniquely as an activating receptor on IL-5-primed eosinophils through a novel pathway involving regulation of β2-integrin-dependent adhesion, NADPH oxidase, and a subset of protein kinases.

JNK-TLR9 signal pathway mediates allergic airway inflammation through suppressing melatonin biosynthesis

Toll-like receptors (TLRs) play pivotal role in the pathogenesis of allergic airway diseases such as asthma. TLR9 is one of the most extensively studied TLRs as an approach to treat asthma. In this study, we investigated the role of TLR9 in the allergic airway inflammation and the underlying mechanism. Wild-type (WT) mice and TLR9(-/-) mice were sensitized and challenged with OVA to establish allergic airway disease model. We found that the expression of TLR9 was elevated concomitantly with airway inflammation post-OVA challenge, and TLR9 deficiency effectively inhibited airway inflammation, including serum OVA-specific immunoglobulin E (IgE), pulmonary inflammatory cell recruitment, mucus secretion, and bronchoalveolar lavage fluid (BALF) inflammatory cytokine production. Meanwhile, the protein expression of hydroxyindole-o-methyltransferase (HIOMT) in lung tissues, the level of melatonin in serum, and BALF were reduced in OVA-challenged WT mice, while these reductions were significantly restored by TLR9 deficiency. Additionally, we showed that although TLR9 deficiency had no effect on OVA-induced phosphorylation of JNK, inhibition of JNK by specific inhibitor SP600125 significantly decreased OVA-induced expression of TLR9, suggesting that JNK is the upstream signal molecular of TLR9. Furthermore, SP600125 treatment promoted resolution of allergic airway inflammation in OVA-challenged WT mice, but not further ameliorated allergic airway inflammation in OVA-challenged TLR9(-/-) mice. Similarly, SP600125 significantly restored the protein expression of HIOMT and the level of melatonin in OVA-challenged WT mice, while such effect was not further enhanced by TLR9 deficiency. Collectively, our results indicated that JNK-TLR9 signal pathway mediates allergic airway inflammation through suppressing melatonin biosynthesis.

Mitochondria in the center of human eosinophil apoptosis and survival

Eosinophils are abundantly present in most phenotypes of asthma and they contribute to the maintenance and exacerbations of the disease. Regulators of eosinophil longevity play critical roles in determining whether eosinophils accumulate into the airways of asthmatics. Several cytokines enhance eosinophil survival promoting eosinophilic airway inflammation while for example glucocorticoids, the most important anti-inflammatory drugs used to treat asthma, promote the intrinsic pathway of eosinophil apoptosis and by this mechanism contribute to the resolution of eosinophilic airway inflammation. Mitochondria seem to play central roles in both intrinsic mitochondrion-centered and extrinsic receptor-mediated pathways of apoptosis in eosinophils. Mitochondria may also be important for survival signalling. In addition to glucocorticoids, another important agent that regulates human eosinophil longevity via mitochondrial route is nitric oxide, which is present in increased amounts in the airways of asthmatics. Nitric oxide seems to be able to trigger both survival and apoptosis in eosinophils. This review discusses the current evidence of the mechanisms of induced eosinophil apoptosis and survival focusing on the role of mitochondria and clinically relevant stimulants, such as glucocorticoids and nitric oxide.

Regulation of spontaneous eosinophil apoptosis-a neglected area of importance

Asthma is characterized by the accumulation of eosinophils in the airways in most phenotypes. Eosinophils are inflammatory cells that require an external survival-prolonging stimulus such as granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin (IL)-5, or IL-3 for survival. In their absence, eosinophils are programmed to die by spontaneous apoptosis in a few days. Eosinophil apoptosis can be accelerated by Fas ligation or by pharmacological agents such as glucocorticoids. Evidence exists for the relevance of these survival-prolonging and pro-apoptotic agents in the regulation of eosinophilic inflammation in inflamed airways. Much less is known about the physiological significance and mechanisms of spontaneous eosinophil apoptosis even though it forms the basis of regulation of eosinophil longevity by pathophysiological factors and pharmacological agents. This review concentrates on discussing the mechanisms of spontaneous eosinophil apoptosis compared to those of glucocorticoid- and Fas-induced apoptosis. We aim to answer the question whether the external apoptotic stimuli only augment the ongoing pathway of spontaneous apoptosis or truly activate a specific pathway.

Nitric oxide induces apoptosis in GM-CSF-treated eosinophils via caspase-6-dependent lamin and DNA fragmentation

Asthma is characterized by accumulation of eosinophils in the lungs and delayed apoptosis may be one mechanism leading to eosinophilia. Nitric oxide (NO), present in inflamed lungs, has been shown to possess both anti- and proeosinophilic properties. We previously showed that NO induces apoptosis in the presence of survival prolonging cytokine IL-5 in human eosinophils. In the present study, we examined the intracellular mechanisms of NO-induced apoptosis in granulocyte macrophage-colony stimulating factor (GM-CSF)-treated eosinophils concentrating on the role of caspases and calpains. Eosinophils were isolated from human blood and apoptosis was determined by relative DNA fragmentation assay, morphological analysis and/or Annexin-V FITC assay. We showed that NO-donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) induced apoptosis in GM-CSF-treated eosinophils. SNAP-induced DNA fragmentation was totally prevented by an inhibitor of caspase-6 (Z-VEID-FMK). Decreased levels of caspase-6 proenzyme and increased amounts of cleaved lamin A/C in SNAP-treated cells indicated activation of caspase-6. Furthermore, SNAP-induced lamin A/C and B fragmentation was totally abolished by an inhibitor of caspase-6. According to our results, caspase-6 mediates lamin and DNA fragmentation also in spontaneously dying eosinophils. Inhibitor of calpains prevented most of DNA fragmentation related to spontaneous apoptosis but had no effect in eosinophils undergoing NO-induced apoptosis. In the present study we showed that caspase-6 is essential for the executive phase involving lamin and DNA fragmentation in both NO-induced and spontaneous eosinophil apoptosis. However, differences in the involvement of calpains suggest that the intracellular signalling in NO-induced apoptosis has specific features at the level of proteases. This study demonstrates new mechanisms for NO-induced and spontaneous apoptosis in human eosinophils.

Histone deacetylase inhibitors induce apoptosis in human eosinophils and neutrophils

Background

Granulocytes are important in the pathogenesis of several inflammatory diseases. Apoptosis is pivotal in the resolution of inflammation. Apoptosis in malignant cells is induced by histone deacetylase (HDAC) inhibitors, whereas HDAC inhibitors do not usually induce apoptosis in non-malignant cells. The aim of the present study was to explore the effects of HDAC inhibitors on apoptosis in human eosinophils and neutrophils.

Methods

Apoptosis was assessed by relative DNA fragmentation assay, annexin-V binding, and morphologic analysis. HDAC activity in nuclear extracts was measured with a nonisotopic assay. HDAC expression was measured by real-time PCR.

Results

A HDAC inhibitor Trichostatin A (TSA) induced apoptosis in the presence of survival-prolonging cytokines interleukin-5 and granulocyte-macrophage colony stimulating factor (GM-CSF) in eosinophils and neutrophils. TSA enhanced constitutive eosinophil and neutrophil apoptosis. Similar effects were seen with a structurally dissimilar HDAC inhibitor apicidin. TSA showed additive effect on the glucocorticoid-induced eosinophil apoptosis, but antagonized glucocorticoid-induced neutrophil survival. Eosinophils and neutrophils expressed all HDACs at the mRNA level except that HDAC5 and HDAC11 mRNA expression was very low in both cell types, HDAC8 mRNA was very low in neutrophils and HDAC9 mRNA low in eosinophils. TSA reduced eosinophil and neutrophil nuclear HDAC activities by ~50-60%, suggesting a non-histone target. However, TSA did not increase the acetylation of a non-histone target NF-κB p65. c-jun-N-terminal kinase and caspases 3 and 6 may be involved in the mechanism of TSA-induced apoptosis, whereas PI3-kinase and caspase 8 are not.

Conclusions

HDAC inhibitors enhance apoptosis in human eosinophils and neutrophils in the absence and presence of survival-prolonging cytokines and glucocorticoids.

Metabolomic biomarkers in a model of asthma exacerbation: urine nuclear magnetic resonance

RATIONALE

Airway obstruction in patients with asthma is associated with airway dysfunction and inflammation. Objective measurements including sputum analysis can guide therapy, but this is often not possible in typical clinical settings. Metabolomics is the study of molecules generated by metabolic pathways. We hypothesize that airway dysfunction and inflammation in an animal model of asthma would produce unique patterns of urine metabolites measured by multivariate statistical analysis of high-resolution proton nuclear magnetic resonance ((1)H NMR) spectroscopy data.

OBJECTIVES

To develop a noninvasive means of monitoring asthma status by metabolomics and urine sampling.

METHODS

Five groups of guinea pigs were studied: control, control treated with dexamethasone, sensitized (ovalbumin, administered intraperitoneally), sensitized and challenged (ovalbumin, administered intraperitoneally, plus ovalbumin aerosol), and sensitized-challenged with dexamethasone. Airway hyperreactivity (AHR) to histamine (administered intravenously) and inflammation were measured. Multivariate statistical analysis of NMR spectra based on a library of known urine metabolites was performed by partial least-squares discriminant analysis. In addition, the raw NMR spectra exported as xy-trace data underwent linear discriminant analysis.

MEASUREMENTS AND MAIN RESULTS

Challenged guinea pigs developed AHR and increased inflammation compared with sensitized or control animals. Dexamethasone significantly improved AHR. Using concentration differences in metabolites, partial least-squares discriminant analysis could discriminate challenged animals with 90% accuracy. Using only three or four regions of the NMR spectra, linear discriminant analysis-based classification demonstrated 80-90% separation of the animal groups.

CONCLUSIONS

Urine metabolites correlate with airway dysfunction in an asthma model. Urine NMR analysis is a promising, noninvasive technique for monitoring asthma in humans.

Antieosinophilic activity of simendans

Simendans are novel agents used in the treatment of decompensated heart failure. They sensitize troponin C to calcium and open ATP-sensitive potassium channels and have been shown to reduce cardiac myocyte apoptosis. The aim of the present study was to evaluate whether simendans reduce pulmonary eosinophilia and regulate eosinophil apoptosis. Bronchoalveolar lavage (BAL) eosinophilia was evaluated in ovalbumin-sensitized mice. Effects of simendans on apoptosis in isolated human eosinophils were assessed by relative DNA fragmentation assay, annexin V-binding, and morphological analysis. Dextrosimendan [(+)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl)hydrazono]propanedinitrile] reduced ovalbumin-induced BAL-eosinophilia in sensitized mice. Levosimendan [(-)-[[4-(1,4,5,6-tetrahydro-4-methyl-6-oxo-3-pyridazinyl)phenyl]hydrazono]propanedinitrile] and dextrosimendan reversed interleukin (IL)-5-afforded survival of human eosinophils by inducing apoptosis in vitro. Even high concentrations of IL-5 were not able to overcome the effect of dextrosimendan. Dextrosimendan further enhanced spontaneous apoptosis as well as that induced by CD95 ligation, without inducing primary necrosis. Dextrosimendan-induced DNA fragmentation was shown to be dependent on caspase and c-Jun NH2-terminal kinase activation, whereas extracellular signal-regulated kinase, p38 mitogen-activated kinase, and ATP-sensitive potassium channels seemed to play no role in its actions. Taken together, our results show that simendans possess antieosinophilic activity and may be useful for the treatment of eosinophilic inflammation.