House dust mite-driven neutrophilic airway inflammation in mice with TNFAIP3-deficient myeloid cells is IL-17-independent

Dectin-1 aggravates neutrophil inflammation through caspase-11/4-mediated macrophage pyroptosis in asthma

BACKGROUND

The pattern recognition receptor Dectin-1 was initially discovered to play a pivotal role in mediating pulmonary antifungal immunity and promoting neutrophil-driven inflammation. Recent studies have revealed that Dectin-1 is overexpressed in asthma, but the specific mechanism remains elusive. Additionally, Dectin-1 has been implicated in promoting pyroptosis, a hallmark of severe asthma airway inflammation. Nevertheless, the involvement of the non-classical pyroptosis signal caspase-11/4 and its upstream regulatory mechanisms in asthma has not been completely explored.

METHODS

House dust mite (HDM)-induced mice was treated with Dectin-1 agonist Curdlan, Dectin-1 inhibitor Laminarin, and caspase-11 inhibitor wedelolactone separately. Subsequently, inflammatory cells in bronchoalveolar lavage fluid (BALF) were analyzed. Western blotting was performed to measure the protein expression of caspase-11 and gasdermin D (GSDMD). Cell pyroptosis and the expression of chemokine were detected in vitro. The correlation between Dectin-1 expression, pyroptosis factors and neutrophils in the induced sputum of asthma patients was analyzed.

RESULTS

Curdlan appeared to exacerbate neutrophil airway inflammation in asthmatic mice, whereas wedelolactone effectively alleviated airway inflammation aggravated by Curdlan. Moreover, Curdlan enhanced the release of caspase-11 activation fragments and N-terminal fragments of gasdermin D (GSDMD-N) stimulated by HDM both in vivo or in vitro. In mouse alveolar macrophages (MH-S cells), Curdlan/HDM stimulation resulted in vacuolar degeneration and elevated lactate dehydrogenase (LDH) release. In addition, there was an upregulation of neutrophil chemokines CXCL1, CXCL3, CXCL5 and their receptor CXCR2, which was suppressed by wedelolactone. In asthma patients, a positive correlation was observed between the expression of Dectin-1 on macrophages and caspase-4 (the human homology of caspase-11), and the proportion of neutrophils in induced sputum.

CONCLUSION

Dectin-1 activation in asthma induced caspase-11/4 mediated macrophage pyroptosis, which subsequently stimulated the secretion of chemokines, leading to the exacerbation of airway neutrophil inflammation.

Physiological estrogen levels are dispensable for the sex difference in immune responses during allergen-induced airway inflammation

Women show an increased prevalence of adult-onset asthma compared to men and previous studies have shown that testosterone inhibits while estrogen worsens allergen-induced airway inflammation. However, detailed knowledge about the aggravating effects of estrogen on immune responses remain unclear. Defining the effects of physiological levels of estrogen on immune responses in asthma would aid in the development of improved treatment strategies. In this study, the importance of estrogen for the sex difference in asthma was determined using a murine model of house dust mite (HDM)-induced airway inflammation on intact female and male mice, as well as on ovariectomized (OVX) female mice treated with a physiological dose of 17β-estradiol (E2). Innate and adaptive immune responses were defined in bronchoalveolar lavage fluid, mediastinal lymph node (mLN) and lung tissue. The results reveal increased numbers of lung eosinophils, macrophages, and dendritic cells in female but not in male mice after HDM challenge. Females also exhibit higher numbers of Th17 cells in both mLN and lung in response to HDM. However, treatment of OVX mice with physiological levels of E2 does not influence any of the analyzed cell populations. Together, this study confirms the previously reported sex difference in allergen-induced airway inflammation and show that female mice mount stronger innate and adaptive immune responses to HDM challenge, but these effects are not mediated by physiological levels of E2.

Decreased ubiquitin modifying enzyme A20 associated with hyper-responsiveness to ovalbumin challenge following intrauterine growth restriction

BACKGROUND

Intrauterine growth restriction (IUGR) is strongly correlated with an increased risk of asthma later in life. Farm dust protects mice from developing house dust mite-induced asthma, and loss of ubiquitin modifying enzyme A20 in lung epithelium would abolish this protective effect. However, the mechanisms of A20 in the development of asthma following IUGR remains unknown.

METHODS

An IUGR rat model induced by maternal nutrient restriction was used for investigating the role of A20 in the response characteristics of IUGR rats to ovalbumin (OVA) challenge. The ubiquitination of proteins and N6-methyladenosine (m6A) modifications were used to further assess the potential mechanism of A20.

RESULTS

IUGR can reduce the expression of A20 protein in lung tissue of newborn rats and continue until 10 weeks after birth. OVA challenging can increase the expression of A20 protein in lung tissue of IUGR rats, but its level was still significantly lower than the control OVA group. The differentially ubiquitinated proteins in lung tissues were also observed in IUGR and normal newborn rats. Furthermore, this ubiquitination phenomenon continued from the newborn to adulthood. In the detected RNA methylations, m6A abundance of the motif GGACA was the highest. The higher abundances of m6A modification of A20 mRNA from IUGR were negatively correlated with the trend of A20 protein levels.

CONCLUSION

These findings indicate A20 as a key regulator during the development of asthma following IUGR, providing further insight into the prevention of asthma induced by environmental factors.

The role of GLS1-mediated glutaminolysis/2-HG/H3K4me3 and GSH/ROS signals in Th17 responses counteracted by PPARγ agonists

Background: Peroxisome proliferator-activated receptor gamma (PPARγ) has the ability to counter Th17 responses, but the full mechanisms remain elusive. Herein, we aimed to elucidate this process in view of cellular metabolism, especially glutaminolysis.

Methods: MTT, CCK-8, Annexin V-FITC/PI staining or trypan blue exclusion assays were used to analyze cytotoxicity. Flow cytometry and Q-PCR assays were applied to determine Th17 responses. The detection of metabolite levels using commercial kits and rate-limiting enzyme expression using western blotting assays was performed to illustrate the metabolic activity. ChIP assays were used to examine H3K4me3 modifications. Mouse models of dextran sulfate sodium (DSS)-induced colitis and house dust mite (HDM)/lipopolysaccharide (LPS)-induced asthma were established to confirm the mechanisms studied in vitro.

Results: The PPARγ agonists rosiglitazone and pioglitazone blocked glutaminolysis but not glycolysis under Th17-skewing conditions, as indicated by the detection of intracellular lactate and α-KG and the fluorescence ratios of BCECF-AM. The PPARγ agonists prevented the utilization of glutamine and thus directly limited Th17 responses even when Foxp3 was deficient. The mechanisms were ascribed to restricted conversion of glutamine to glutamate by reducing the expression of the rate-limiting enzyme GLS1, which was confirmed by GLS1 overexpression. Replenishment of α-KG and 2-HG but not succinate weakened the effects of PPARγ agonists, and α-KG-promoted Th17 responses were dampened by siIDH1/2. Inhibition of KDM5 but not KDM4/6 restrained the inhibitory effect of PPARγ agonists on IL-17A expression, and the H3K4me3 level in the promoter and CNS2 region of the il-17 gene locus down-regulated by PPARγ agonists was rescued by 2-HG and GLS1 overexpression. However, the limitation of PPARγ agonists on the mRNA expression of RORγt was unable to be stopped by 2-HG but was attributed to GSH/ROS signals subsequent to GLS1. The exact role of PPARγ was proved by GW9662 or PPARγ knockout, and the mechanisms for PPARγ-inhibited Th17 responses were further confirmed by GLS1 overexpression in vivo.

Conclusion: PPARγ agonists repressed Th17 responses by counteracting GLS1-mediated glutaminolysis/2-HG/H3K4me3 and GSH/ROS signals, which is beneficial for Th17 cell-related immune dysregulation.

Leukotriene B4 receptors play critical roles in house dust mites-induced neutrophilic airway inflammation and IL-17 production

Increased levels of neutrophils in bronchoalveolar lavage fluid (BALF) were associated with asthma severity. As leukotriene B4 (LTB₄) is a principal chemoattractant molecule for neutrophils, its receptors, BLT1 and BLT2, may contribute to neutrophil-dominant airway inflammation. In the present study, we established a mouse model of steroid-resistant, neutrophil-dominant airway inflammation by house dust mite (HDM)/lipopolysaccharide (LPS) sensitization and HDM challenge, and we investigated whether BLT1/BLT2 signaling was associated with the development of neutrophilic airway inflammation. Blockade of BLT1 or BLT2 significantly suppressed airway inflammation and IL-17 production in this mouse model. The 5-LO and 12-LO enzymes, which catalyze the synthesis of BLT1/BLT2 ligands, were also critically associated with neutrophil-dominant airway inflammation and the synthesis of IL-17. Collectively, our results suggest that the 5-/12-LO-BLT1/BLT2-linked cascade significantly contributes to neutrophil-dominant severe airway inflammation via IL-17 synthesis in HDM-induced neutrophilic asthma.

Developments in the mechanisms of allergy in 2018 through the eyes of Clinical and Experimental Allergy, Part I

In the first of two linked articles, we describe the development in the mechanisms underlying allergy as described by Clinical & Experimental Allergy and other journals in 2018. Experimental models of allergic disease, basic mechanisms and clinical mechanisms are all covered.