Peroxisome proliferator-activated receptor gamma as a novel therapeutic target in asthma

PD-1 expression affects cytokine production by ILC2 and is influenced by peroxisome proliferator-activated receptor-γ

Introduction

Innate lymphoid cells (ILCs) can provide early cytokine help against a variety of pathogens in the lungs and gastrointestinal tract. Type 2 ILC (ILC2) are comparable to T helper 2 cells found in the adaptive immune system, which secrete cytokines such as interleukin 5 (IL‐5) and IL‐13 and have been found to play roles in host defense against helminth infections and in allergic responses. Recent studies have identified that programmed cell death protein 1 (PD‐1) and peroxisome proliferator activated receptor‐γ (PPAR‐γ) are highly expressed by ILC2. We examined whether PD‐1 plays a role in ILC2 function and whether there was any connection between PD‐1 and PPAR‐γ

Methods

To ensure that only innate immune cells were present, ILC2 cells were examined from RAG1^−/− and PD‐1^−/−xRAG1^−/− mice under steady‐state or following inoculation with IL‐33. We also tested ILC2 generated from bone marrow of RAG1^−/− and PD‐1^−/−xRAG1^−/− mice for their production of cytokines. These in vitro‐derived ILC2 were also exposed to agonist and antagonist of PPAR‐γ.

Results

We found that ILC2 from PD‐1^−/−xRAG1^−/− mice had reduced frequencies of IL‐5 and IL‐13 producing cells both in vitro upon IL‐33 stimulation and in vivo following intraperitoneal administration of IL‐33 when compared with ILC2 from RAG1^−/− mice. However, by adding IL‐2, IL‐25, and thymic stromal lymphopoietin to the in vitro cultures, the frequency of IL‐5 and IL‐13 expressing ILC2 from PD‐1^−/−xRAG1^−/− mice became similar to the frequency observed for ILC2 from RAG1^−/− mice. In addition, PPAR‐γ agonists and antagonists were found to increase and decrease PD‐1 expression on ILC2 respectively.

Conclusions

These findings illustrate that chronic loss of PD‐1 plays a role in ILC2 function and PD‐1 expression can be modulated by PPAR‐γ.

Associations of Genetic Polymorphisms Relevant to Metabolic Pathway of Vitamin D3 with Development and Prognosis of Childhood Bronchial Asthma

This study was aimed at investigating the correlation between genetic polymorphisms relevant to metabolic pathway of vitamin D3 (VD₃) and susceptibility to childhood bronchial asthma. Altogether 143 childhood patients with bronchial asthma and 143 healthy children of Chinese Han ethnicity were enrolled in this study. The key single-nucleotide polymorphisms (SNPs) were identified by HaploView 4.2 software and selected from previous investigations. Genomic DNAs were isolated from peripheral blood samples by using TaqMan Blood DNA kits. The genotyping of SNPs was performed by TaqMan SNPs genotyping assay. Odds ratios and corresponding 95% confidence intervals were calculated to evaluate the association between SNPs and susceptibility to bronchial asthma. Statistical analyses were conducted by using SPSS 13.0 software. Rs10766197 of CYP2R1, rs7041 and rs4588 of CG, rs4646536 of CYP27B1, rs2228570, rs7975232, and rs1544410 of VDR, as well as rs1805192 and rs10865710 of PPAR were shown to be significantly associated with increased risk of bronchial asthma. Besides, prognosis of childhood bronchial asthma, which was represented as Saint George Respiratory Questionnaire (SGRQ) scoring, was closely linked with CYP2R1 rs10766197, CYP27B1 rs4646536, VDR rs7975232, VDR rs1544410, PPAR rs1805192, and PPAR rs10865710. The haplotype analysis suggested that TA and CG of CG rs7041/rs4588, CA and AG of VDR rs7975232/rs1544410, and CC of PPAR rs1805192/rs10865710 were, respectively, correlated with levels of VD, IL-4, and IL-5. And only haplotypes of VDR showed associations with risk of bronchial asthma during childhood, whereas hardly any significance could be observed between the haplotypes and behavior of quality-of-life (SGRQ) scoring. Significant associations were found between rs10766197 of CYP2R1, rs7041 and rs4588 of CG, rs4646536 of CYP27B1, rs2228570, rs7975232, and rs1544410 of VDR, as well as rs1805192 and rs10865710 of PPAR and susceptibility to and prognosis of childhood bronchial asthma, providing novel targets for treating the disorder.

Enhanced expression of Organic Cation Transporters in bronchial epithelial cell layers following insults associated with asthma - Impact on salbutamol transport

Increasing evidence suggests Organic Cation Transporters (OCT) might facilitate the absorption of inhaled bronchodilators, including salbutamol, across the lung epithelium. This is essentially scarred and inflamed in asthma. Accordingly, the impact of epithelial insults relevant to asthma on OCT expression and salbutamol transport was evaluated in air-liquid interfaced layers of the human broncho-epithelial cell line Calu-3. These were physically injured and allowed to recover for 48h or exposed to the pro-inflammatory stimulant lipopolysaccharide (LPS) for 48h and the aeroallergen house dust mite (HDM) for 8h twice over 48h. Increases in transporter expression were measured following each treatment, with the protein levels of the OCTN2 subtype consistently raised by at least 50%. Interestingly, OCT upregulation upon LPS and HDM challenges were dependent on an inflammatory event occurring in the cell layers. Salbutamol permeability was higher in LPS exposed layers than in their untreated counterparts and in both cases, was sensitive to the OCT inhibitor tetraethylammonium. This study is the first to show epithelial injury, inflammation and allergen abuse upregulate OCT in bronchial epithelial cells, which might have an impact on the absorption of their substrates in diseased lungs.

Low molecular weight components of pollen alter bronchial epithelial barrier functions

The bronchial epithelium plays a key role in providing a protective barrier against many environmental substances of anthropogenic or natural origin which enter the lungs during breathing. Appropriate responses to these agents are critical for regulation of tissue homeostasis, while inappropriate responses may contribute to disease pathogenesis. Here, we compared epithelial barrier responses to different pollen species, characterized the active pollen components and the signaling pathways leading to epithelial activation. Polarized bronchial cells were exposed to extracts of timothy grass (Phleum pratense), ragweed (Ambrosia artemisifolia), mugwort (Artemisia vulgaris), birch (Betula alba) and pine (Pinus sylvestris) pollens. All pollen species caused a decrease in ionic permeability as monitored trans-epithelial electrical resistance (TER) and induced polarized release of mediators analyzed by ELISA, with grass pollen showing the highest activity. Ultrafiltration showed that the responses were due to components <3kDa. However, lipid mediators, including phytoprostane E1, had no effect on TER, and caused only modest induction of mediator release. Reverse-phase chromatography separated 2 active fractions: the most hydrophilic maximally affected cytokine release whereas the other only affected TER. Inhibitor studies revealed that JNK played a more dominant role in regulation of barrier permeability in response to grass pollen exposure, whereas ERK and p38 controlled cytokine release. Adenosine and the flavonoid isorhamnetin present in grass pollen contributed to the overall effect on airway epithelial barrier responses. In conclusion, bronchial epithelial barrier functions are differentially affected by several low molecular weight components released by pollen. Furthermore, ionic permeability and innate cytokine production are differentially regulated.

Small RNA profiling reveals deregulated phosphatase and tensin homolog (PTEN)/phosphoinositide 3-kinase (PI3K)/Akt pathway in bronchial smooth muscle cells from asthmatic patients

BACKGROUND

Aberrant expression of small noncoding RNAs (sncRNAs), microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs) in particular, define several pathologic processes. Asthma is characterized by airway hyperreactivity, chronic inflammation, and airway wall remodeling. Asthma-specific miRNA profiles were reported for bronchial epithelial cells, whereas sncRNA expression in asthmatic bronchial smooth muscle (BSM) cells is almost completely unexplored.

OBJECTIVE

We sought to determine whether the primary BSM sncRNA expression profile is altered in asthmatic patients and identify targets of differentially expressed sncRNAs.

METHODS

Small RNA sequencing was used for sncRNA profiling in BSM cells (from 8 asthmatic and 6 nonasthmatic subjects). sncRNA identification and differential expression analysis was performed with iMir software. Experimentally validated miRNA targets were identified by using Ingenuity Pathway Analysis, and putative piRNA targets were identified by using miRanda software.

RESULTS

BSM cells from asthmatic patients showed abnormal expression of 32 sncRNAs (26 miRNAs, 5 piRNAs, and 1 small nucleolar RNA). Target prediction for deregulated miRNAs and piRNAs revealed experimentally validated and predicted mRNA targets expressed in the BSM cells. Thirty-eight of these mRNAs represent major targets for deregulated miRNAs and might play important roles in the pathophysiology of asthma. Interestingly, 6 of these mRNAs were previously associated with asthma, considered as novel therapeutic targets for treatment of this disease, or both. Signaling pathway analysis revealed involvement of 38 miRNA-targeted mRNAs in increased cell proliferation through phosphatase and tensin homolog and phosphoinositide 3-kinase/Akt signaling pathways.

CONCLUSIONS

BSM cells of asthmatic patients are characterized by aberrant sncRNA expression that recapitulates multiple pathologic phenotypes of these cells.

Chenodeoxycholic acid attenuates ovalbumin-induced airway inflammation in murine model of asthma by inhibiting the T(H)2 cytokines

Asthma is a complex highly prevalent airway disease that is a major public health problem for which current treatment options are inadequate. Recently, farnesoid X receptor (FXR) has been shown to exert anti-inflammatory actions in various disease conditions, but there have been no reported investigations of Chenodeoxycholic acid (CDCA), a natural FXR agonist, in allergic airway inflammation. To test the CDCA effectiveness in airway inflammation, ovalbumin (OVA)-induced acute murine asthma model was established. We found that lung tissue express FXR and CDCA administration reduced the severity of the murine allergic airway disease as assessed by pathological and molecular markers associated with the disease. CDCA treatment resulted in fewer infiltrations of cells into the airspace and peribronchial areas, and decreased goblet cell hyperplasia, mucus secretion and serum IgE levels which was increased in mice with OVA-induced allergic asthma. The CDCA treatment further blocked the secretion of TH2 cytokines (IL-4, IL-5 and IL-13) and proinflammatory cytokine TNF-α indicate that the FXR and its agonists may have potential for treating allergic asthma.

Antiallergic Function of KR62980, a Peroxisome Proliferator-Activated Receptor-γ Agonist, in a Mouse Allergic Rhinitis Model

PURPOSE

Peroxisome proliferator-activated receptor γ (PPAR-γ) has been shown to play an important role in the control of inflammatory responses acting on macrophages, mast cells, T cells and eosinophils. A novel PPAR-γ ligand, KR62980 have been recently focused on due to the lower undesirable effects than other PPAR-γ ligands such as rosiglitazone and pioglitazone. The present study was aimed to investigate the effects of KR62980 on nasal symptoms and immunopathological profiles in allergic nasal mucosa in murine allergic rhinitis model.

METHODS

BALB/c mice were sensitized and challenged intranasally with ovalbumin (OVA). KR62980 was administered intraperitoneally or orally 3 hours before each intranasal OVA challenge.

RESULTS

Administration of KR62980 significantly decreased the number of nasal rubbing, nasal sneezing, ova-specific IgE and total IgE in serum, secretion of Interleukin (IL)-4, IL-5, and IL-17 from the spleen and eosinophilic infiltration in the nasal mucosa. KR62980 decreased the expression of IL-4, IL-5 and IL-10 mRNAs in the nasal mucosal tissue, while, it elevated the level of IL-10 and IFN-γ in splenocyte culture. KR62980 seemed to decrease IL-17 level in local and systemic level even though it did not reach to statistical significance. The anti-inflammatory effect was more definite when the KR62980 was administered intraorally than intraperitoneally.

CONCLUSIONS

A novel PPAR-γ ligand, KR62980 can attenuate OVA-induced allergic inflammation in mice mainly through modulation of Th2 cytokines. This finding suggests that PPAR-γ might have a role in the treatment of allergic rhinitis.

Novel genes in Human Asthma Based on a Mouse Model of Allergic Airway Inflammation and Human Investigations

Purpose

Based on a previous gene expression study in a mouse model of asthma, we selected 60 candidate genes and investigated their possible roles in human asthma.

Methods

In these candidate genes, 90 SNPs were genotyped using MassARRAY technology from 311 asthmatic children and 360 healthy controls of the Hungarian (Caucasian) population. Moreover, gene expression levels were measured by RT PCR in the induced sputum of 13 asthmatics and 10 control individuals. t-tests, chi-square tests, and logistic regression were carried out in order to assess associations of SNP frequency and expression level with asthma. Permutation tests were performed to account for multiple hypothesis testing.

Results

The frequency of 4 SNPs in 2 genes differed significantly between asthmatic and control subjects: SNPs rs2240572, rs2240571, rs3735222 in gene SCIN, and rs32588 in gene PPARGC1B. Carriers of the minor alleles had reduced risk of asthma with an odds ratio of 0.64 (0.51-0.80; P=7×10^-5) in SCIN and 0.56 (0.42-0.76; P=1.2×10^-4) in PPARGC1B. The expression levels of SCIN, PPARGC1B and ITLN1 genes were significantly lower in the sputum of asthmatics.

Conclusions

Three potentially novel asthma-associated genes were identified based on mouse experiments and human studies.

Rosiglitazone, a peroxisome proliferator-activated receptor-γ agonist, attenuates airway inflammation by inhibiting the proliferation of effector T cells in a murine model of neutrophilic asthma

An imbalanced Th17-mediated immune response contributes substantially to neutrophilic asthma. Studies have also demonstrated that peroxisome proliferator-activated receptor-γ (PPARγ) plays a critical role in inflammatory disease. However, the effect of PPARγ on airway inflammation in neutrophilic asthma remains unclear. In the current study, we evaluated the potential therapeutic role of rosiglitazone (RSG) in a new mouse model of asthma characterised by increased neutrophils rather than eosinophils. A co-culture system of DCs with CD4+ naïve T cells was established to evaluate the effects of RSG on T cell differentiation. After challenge with OVA, mice developed the typical pathophysiological features of asthma, including an increased number of neutrophils in the BALF and the up-regulation of IL-17. The numbers of Th17 cells and Th2 cells were also greatly elevated in the lungs. The administration of rosiglitazone reduced the pathophysiological features of asthma and decreased the up-regulated inflammatory mediators and cytokines. Furthermore, the cell viability in the co-culture system was markedly reduced by RSG. T-bet, Gata-3 and RORγt mRNA were down-regulated by RSG. These findings suggest that PPARγ is critical for airway inflammation during neutrophilic asthma, possibly due to its effect on Th cell proliferation and differentiation. These findings suggest that the therapeutic effect of rosiglitazone in neutrophilic asthma is partially due to the role of the PPARγ pathway in regulating T cell proliferation and differentiation.

Interleukin-17 regulation: an attractive therapeutic approach for asthma

Interleukin (IL)-17 is recognized to play a critical role in numerous immune and inflammatory responses by regulating the expression of various inflammatory mediators, which include cytokines, chemokines, and adhesion molecules. There is growing evidence that IL-17 is involved in the pathogenesis of asthma. IL-17 orchestrates the neutrophilic influx into the airways and also enhances T-helper 2 (Th2) cell-mediated eosinophilic airway inflammation in asthma. Recent studies have demonstrated that not only inhibitor of IL-17 per se but also diverse regulators of IL-17 expression reduce antigen-induced airway inflammation, bronchial hyperresponsiveness, and Th2 cytokine levels in animal models of asthma. This review will summarize the role of IL-17 in the context of allergic airway inflammation and discuss the therapeutic potential of various strategies targeting IL-17 for asthma.

Anti-allergic function and regulatory mechanisms of KR62980 in allergen-induced airway inflammation

The ligand-activated transcription factor, peroxisome proliferator-activated receptor (PPAR)gamma, and its ligands inhibit pro-inflammatory cytokine production by immune cells, thus exerting anti-inflammatory activity. As a non-thiazolidinedione PPARgamma ligand, KR62980 has anti-diabetic and anti-adipogenic activities, but its anti-inflammatory function has yet to be characterized. In this study, we investigated the functions and mechanisms of KR62980 in the activation and differentiation of CD4+ T helper (Th) cells by comparing its effects with those of a thiazolidinedione PPARgamma ligand, rosiglitazone. KR62980 dose-dependently and significantly suppressed TCR-triggered Th cell proliferation by suppressing IL-2/IL-2Ralpha-mediated signaling. Both KR62980 and rosiglitazone suppressed IFNgamma production in a dose-dependent manner, whereas IL-4 gene expression was specifically suppressed by only KR62980. In addition, sustained KR62980 treatment diminished Th2 cytokine production by inhibiting c-Maf expression. In vivo administration of KR62980 in a model of allergic asthma significantly attenuated eotaxin-induced eosinophil infiltration, allergic cytokine production and collagen deposition in the lung. KR62980 also decreased goblet cell hyperplasia in the airway and mucous cell metaplasia in nasal epithelium, concurrent with decreases of allergic Th2 cytokines and IL-17 in the draining lymph node. In conclusion, a novel PPARgamma ligand, KR62980, suppresses in vitro Th2 cell differentiation and attenuates in vivo OVA-induced airway inflammation, suggesting a beneficial role for KR62980 in the treatment of allergic asthma and allergic rhinitis.