Cholinergic sensing of allergen exposure by airway epithelium promotes type 2 immunity in the lungs

BACKGROUND

Nonneuronal cells, including epithelial cells, can produce acetylcholine (ACh). Muscarinic ACh receptor antagonists are used clinically to treat asthma and other medical conditions; however, knowledge regarding the roles of ACh in type 2 immunity is limited.

OBJECTIVE

Our aim was to investigate the roles of epithelial ACh in allergic immune responses.

METHODS

Human bronchial epithelial (HBE) cells were cultured with allergen extracts, and their ACh production and IL-33 secretion were studied in vitro. To investigate immune responses in vivo, naive BALB/c mice were treated intranasally with different muscarinic ACh receptor antagonists and then exposed intranasally to allergens.

RESULTS

At steady state, HBE cells expressed cellular components necessary for ACh production, including choline acetyltransferase and organic cation transporters. Exposure to allergens caused HBE cells to rapidly release ACh into the extracellular medium. Pharmacologic or small-interfering RNA-based blocking of ACh production or autocrine action through the M3 muscarinic ACh receptors in HBE cells suppressed allergen-induced ATP release, calcium mobilization, and extracellular secretion of IL-33. When naive mice were exposed to allergens, ACh was quickly released into the airway lumen. A series of clinical M3 muscarinic ACh receptor antagonists inhibited allergen-induced IL-33 secretion and innate type 2 immune response in the mouse airways. In a preclinical murine model of asthma, an ACh receptor antagonist suppressed allergen-induced airway inflammation and airway hyperreactivity.

CONCLUSIONS

ACh is released quickly by airway epithelial cells on allergen exposure, and it plays an important role in type 2 immunity. The epithelial ACh system can be considered a therapeutic target in allergic airway diseases.

Allergen-induced DNA release by the airway epithelium amplifies type 2 immunity

BACKGROUND

Alternaria alternata and house dust mite exposure evokes IL-33 secretion from the airway epithelium, which functions as an alarmin to stimulate type 2 immunity. Extracellular DNA (eDNA) is also an alarmin that intensifies inflammation in cystic fibrosis, chronic obstructive pulmonary disease, and asthma.

OBJECTIVE

We investigated the mechanisms underlying allergen-evoked DNA mobilization and release from the airway epithelium and determined the role of eDNA in type 2 immunity.

METHODS

Human bronchial epithelial (hBE) cells were used to characterize allergen-induced DNA mobilization and extracellular release using comet assays to measure DNA fragmentation, Qubit double-stranded DNA assays to measure DNA release, and DNA sequencing to determine eDNA composition. Mice were used to investigate the role of eDNA in type 2 immunity.

RESULTS

Alternaria extract rapidly induces mitochondrial and nuclear DNA release from human bronchial epithelial cells, whereas house dust mite extract induces mitochondrial DNA release. Caspase-3 is responsible for nuclear DNA fragmentation and becomes activated after cleavage by furin. Analysis of secreted nuclear DNA showed disproportionally higher amounts of promotor and exon sequences and lower intron and intergenic regions compared to predictions of random DNA fragmentation. In mice, Alternaria-induced type 2 immune responses were blocked by pretreatment with a DNA scavenger. In caspase-3-deficient mice, Alternaria-induced DNA release was suppressed. Furthermore, intranasal administration of mouse genomic DNA with Alternaria amplified secretion of IL-5 and IL-13 into bronchoalveolar lavage fluid while DNA alone had no effect.

CONCLUSION

These findings highlight a novel, allergen-induced mechanism of rapid DNA release that amplifies type 2 immunity in airways.

Abstract P082: Exposure To Excess Albumin Causes Inflammatory Activation Of The Proximal Tubule

In previous studies, we used chronic servo control experiments to show that renal inflammation is a secondary event in salt-sensitive hypertension, with pressure amplifying renal immune cell infiltration in Dahl salt-sensitive (SS) rats. In contrast, albuminuria occurs early in the development of hypertension and facilitates its progression. In this study, we tested the hypothesis that albuminuria causes release of pro-inflammatory cytokines in the proximal tubule, which in turn may initiate renal inflammation.We exposed the apical membrane of human proximal tubule cell monolayers (RPTEC-TERT1) to human serum albumin (HSA, 10 mg/ml, n=8) for 24 and 48hrs. Control cells were kept in standard media without HSA (n=8). The concentrations of 47 cytokines were measured in the basolateral (BM) and apical (AM) media using Luminex assays. After 24hrs we found that 18 cytokines were significantly higher in the BM and 14 in the AM relative to controls. At 48hrs, 17 cytokines were significantly higher in the BM and 15 in the AM. Notably, we found significant increases in basolateral release of several chemokines, including CCL2 (24hrs: 6.1±0.9 vs. 40.6±8.9, 48hrs: 20.1±4.5 vs. 85.8±15.6 pg/mg), CXCL1 (24hrs: 1.3±0.3 vs. 39.5±12.2, 48hrs: 3.4±1.1 vs. 94.2±41.4 pg/mg), and IL-8 (24hrs: 1.3±0.4 vs. 11.6±3.7, 48hrs: 2.1±0.5 vs. 10.1±3 pg/mg). We propose that HSA-induced chemokine secretion facilitates immune cell recruitment and the initiation of renal inflammation. To track the progression of albuminuria and proximal tubule injury in SS rats we performed daily urine collections in rats fed either a high-salt (HS, 4.0% NaCl, n=6) or a control-salt (CS, 0.4% NaCl, n=5) diet for 7-days. In SS rats fed HS, albuminuria preceded proximal tubule injury. Urinary albumin was elevated after 2-days of HS (22.6±6.5 vs. 61.1±18.7 mg/day) whereas Kidney Injury Molecule-1 (KIM-1) was increased after 5-days of HS (15.5±1.5 vs. 31.3±5.6 ng/day).To conclude, in vitro exposure to excess albumin causes significant increases in the levels of multiple cytokines involved in the initiation of inflammation. In SS rats fed HS, albuminuria precedes proximal tubule injury. Together these data suggest that albuminuria may facilitate hypertension through the initiation of renal inflammation.

Fungal allergen-induced IL-33 secretion involves cholesterol-dependent, VDAC-1-mediated ATP release from the airway epithelium

KEY POINTS

Alternaria aeroallergens induce the release of ATP from human bronchial epithelial (HBE) cells by activating a conductive pathway involving voltage-dependent anion channel-1 (VDAC-1) and by exocytosis of ATP localized within membrane vesicles. Inhibition of VDAC-1 blocked Alternaria-evoked Ca²⁺ uptake across the plasma membrane of HBE cells and interleukin (IL)-33 release into the extracellular media. Reducing cholesterol content with a cholesterol scavenger (β-methylcyclodextrin) or statin compound (simvastatin) blocked ATP and IL-33 release by lowering the expression of VDAC-1 in the plasma membrane. Pretreatment with simvastatin for 24 h also inhibited the increase in tight junction macromolecule permeability that occurs following Alternaria exposure. These results establish a novel role for VDAC-1 as a mechanism underlying ATP release induced by fungal allergens and suggests a possible therapeutic use for cholesterol lowering compounds in reducing Alternaria-stimulated allergic inflammation.

ABSTRACT

Human bronchial epithelial (HBE) cells exposed to allergens derived from the common saprophytic fungus, Alternaria alternata release ATP, which in turn stimulates P2X₇ receptor-mediated Ca²⁺ uptake across the plasma membrane. The subsequent increase in intracellular calcium concentration induces proteolytic processing and secretion of interleukin (IL)-33, a critical cytokine involved in the initiation of allergic airway inflammation. A major objective of the present study was to identify the mechanism responsible for conductive ATP release. The results show that pretreatment of HBE cells with inhibitors of the voltage-dependent anion channel-1 (VDAC-1) or treatment with a VDAC-1 selective blocking antibody or silencing mRNA expression of the channel by RNA interference, inhibit Alternaria-evoked ATP release. Moreover, inhibition of VDAC-1 channel activity or reducing protein expression blocked the secretion of IL-33. Similarly, reducing the cholesterol content of HBE cells with simvastatin or the cholesterol scavenger β-methylcyclodextrin also blocked ATP release and IL-33 secretion by decreasing the level of VDAC-1 expression in the plasma membrane. In addition, simvastatin inhibited the increase in tight junction macromolecule permeability that was previously observed after Alternaria exposure. These results demonstrate a novel function for VDAC-1 as the conductive mechanism responsible for Alternaria-induced ATP release, an essential early step in the processing, mobilization and secretion of IL-33 by the airway epithelium. Furthermore, the simvastatin-evoked reduction of VDAC-1 expression in the plasma membrane, suggests the possibility that cholesterol lowering compounds may be beneficial in alleviating allergic airway inflammation induced by fungal allergens.

P2Y receptor regulation of K2P channels that facilitate K+ secretion by human mammary epithelial cells

The objective of this study was to determine the molecular identity of ion channels involved in K⁺ secretion by the mammary epithelium and to examine their regulation by purinoceptor agonists. Apical membrane voltage-clamp experiments were performed on human mammary epithelial cells where the basolateral membrane was exposed to the pore-forming antibiotic amphotericin B dissolved in a solution with intracellular-like ionic composition. Addition of the Na⁺ channel inhibitor benzamil reduced the basal current, consistent with inhibition of Na⁺ uptake across the apical membrane, whereas the K_Ca3.1 channel blocker TRAM-34 produced an increase in current resulting from inhibition of basal K⁺ efflux. Treatment with two-pore potassium (K2P) channel blockers quinidine, bupivacaine and a selective TASK1/TASK3 inhibitor (PK-THPP) all produced concentration-dependent inhibition of apical K⁺ efflux. qRT-PCR experiments detected mRNA expression for nine K2P channel subtypes. Western blot analysis of biotinylated apical membranes and confocal immunocytochemistry revealed that at least five K2P subtypes (TWIK1, TREK1, TREK2, TASK1, and TASK3) are expressed in the apical membrane. Apical UTP also increased the current, but pretreatment with the PKC inhibitor GF109203X blocked the response. Similarly, direct activation of PKC with phorbol 12-myristate 13-acetate produced a similar increase in current as observed with UTP. These results support the conclusion that the basal level of K⁺ secretion involves constitutive activity of apical K_Ca3.1 channels and multiple K2P channel subtypes. Apical UTP evoked a transient increase in K_Ca3.1 channel activity, but over time caused persistent inhibition of K2P channel function leading to an overall decrease in K⁺ secretion.

Soy isoflavones enhance β-defensin synthesis and secretion in endometrial epithelial cells with exposure to TLR3 agonist polyinosinic-polycytidylic acid

PROBLEM

β-defensins are important innate chemical barriers that protect the endometrium from pathogen invasion. The effects of soy isoflavones, genistein and daidzein, on the expression and secretion of porcine β-defensins (PBD) in endometrial epithelial cells were investigated under normal or poly I:C-stimulated conditions.

METHOD OF STUDY

Primary cultured porcine endometrial epithelial (PE) cells were pretreated with genistein or daidzein followed by poly I:C inoculation. During treatment, the culture media were analyzed for PBD 1-4 secretion by ELISA and the total RNA for PBD gene expression by quantitative RT-PCR.

RESULTS

Porcine endometrial epithelial cells constitutively expressed PBD 1-4 and secreted PBD-1, PBD-2, and PBD-4. Genistein and daidzein enhanced PBD-2 expression and PBD-2 and PBD-3 secretion. These compounds also potentiated PBD-2 and PBD-3 expression and secretion which were upregulated by poly I:C.

CONCLUSION

Soy isoflavones, genistein and daidzein, could be potentially used for promoting the innate host defense of endometrium against infection.

Enhanced Secretion of Beta-Defensins in Endometrial Tissues and Epithelial Cells by Soy Isoflavones

Objective

This study aimed to investigate whether endometrial tissues and endometrial epithelial cells were capable of secreting beta-defensin (BD)-1 and -2, and soy isoflavones genistein or daidzein could promote these BD secretions. The effect of genistein on Cl- secretion in correlation with the BD secretion was also examined.

Material and Method

Endometrial tissues or glandular epithelial cell monolayer were mounted in Ussing chamber for measurement of electrical parameters. The sample solutions from apical and basolateral compartments were collected before and after genistein or daidzein addition for the measurement of BD-1 and-2 levels by using ELISA technique.

Results

Endometrial tissues and epithelial cells constitutively secreted both BD-1 and -2 mostly at the apical compartment. Both genistein and daidzein induced BDs secretion which reached a peak at 5-15 min. The apical secretion of BDs was coincidence with increased Cl- secretion induced by genistein.

Conclusion

Endometrial tissues and epithelial cells contributes to basal host defense against infection by secretion of BD-1 and -2, which could be enhanced by genistein or daidzein. This finding implies that these potent constituents of soy isoflavones may be useful to promote the innate immune function of human endometrium.