A new link to airway obstruction in asthma

Aspirin exacerbated respiratory disease (AERD): molecular and cellular diagnostic & prognostic approaches

Aspirin-exacerbated respiratory disease (AERD) is characterized by immune cells dysfunction. This study aimed to investigate the molecular mechanisms involved in AERD pathogenesis. Relevant literatures were identified by a PubMed search (2005-2019) of english language papers using the terms "Aspirin-exacerbated respiratory disease", "Allergic inflammation", "molecular mechanism" and "mutation". According to the significant role of inflammation in AERD development, ILC-2 is known as the most important cell in disease progression. ILC-2 produces cytokines that induce allergic reactions and also cause lipid mediators production, which activates mast cells and basophils, ultimately. Finally, Monoclonal antibody and Aspirin desensitization in patients can be a useful treatment strategy for prevention and treatment.

Glucagon Like Peptide-1 (GLP-1) Modulates OVA-Induced Airway Inflammation and Mucus Secretion Involving a Protein Kinase A (PKA)-Dependent Nuclear Factor-κB (NF-κB) Signaling Pathway in Mice

Asthma is a common chronic pulmonary inflammatory disease, featured with mucus hyper-secretion in the airway. Recent studies found that glucagon like peptide-1 (GLP-1) analogs, including liraglutide and exenatide, possessed a potent anti-inflammatory property through a protein kinase A (PKA)-dependent signaling pathway. Therefore, the aim of current study was to investigate the value of GLP-1 analog therapy liraglutide in airway inflammation and mucus secretion in a murine model of ovalbumin (OVA)-induced asthma, and its underlying molecular mechanism. In our study, BALB/c mice were sensitized and challenged by OVA to induce chronic asthma. Pathological alterations, the number of cells and the content of inflammatory mediators in bronchoalveolar lavage fluid (BALF), and mucus secretion were observed and measured. In addition, the mRNA and protein expression of E-selectin and MUC5AC were analyzed by qPCR and Western blotting. Then, the phosphorylation of PKA and nuclear factor-κB (NF-κB) p65 were also measured by Western blotting. Further, NF-κB p65 DNA binding activity was detected by ELISA. OVA-induced airway inflammation, airway mucus hyper-secretion, the up-regulation of E-selectin and MUC5AC were remarkably inhibited by GLP-1 in mice (all p < 0.01). Then, we also found that OVA-reduced phosphorylation of PKA, and OVA-enhanced NF-κB p65 activation and NF-κB p65 DNA binding activity were markedly improved by GLP-1 (all p < 0.01). Furthermore, our data also figured out that these effects of GLP-1 were largely abrogated by the PKA inhibitor H-89 (all p < 0.01). Taken together, our results suggest that OVA-induced asthma were potently ameliorated by GLP-1 possibly through a PKA-dependent inactivation of NF-κB in mice, indicating that GLP-1 analogs may be considered an effective and safe drug for the potential treatment of asthma in the future.

Smoking-mediated up-regulation of GAD67 expression in the human airway epithelium

Background

The production of gamma-amino butyric acid (GABA) is dependent on glutamate decarboxylases (GAD65 and GAD67), the enzymes that catalyze the decarboxylation of glutamate to GABA. Based on studies suggesting a role of the airway epithelial GABAergic system in asthma-related mucus overproduction, we hypothesized that cigarette smoking, another disorder associated with increased mucus production, may modulate GABAergic system-related gene expression levels in the airway epithelium.

Methods

We assessed expression of the GABAergic system in human airway epithelium obtained using bronchoscopy to sample the epithelium and microarrays to evaluate gene expression. RT-PCR was used to confirm gene expression of GABAergic system gene in large and small airway epithelium from heathy nonsmokers and healthy smokers. The differences in the GABAergic system gene was further confirmed by TaqMan, immunohistochemistry and Western analysis.

Results

The data demonstrate there is a complete GABAergic system expressed in the large and small human airway epithelium, including glutamate decarboxylase, GABA receptors, transporters and catabolism enzymes. Interestingly, of the entire GABAergic system, smoking modified only the expression of GAD67, with marked up-regulation of GAD67 gene expression in both large (4.1-fold increase, p < 0.01) and small airway epithelium of healthy smokers (6.3-fold increase, p < 0.01). At the protein level, Western analysis confirmed the increased expression of GAD67 in airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05). There was a significant positive correlation between GAD67 and MUC5AC gene expression in both large and small airway epithelium (p < 0.01), implying a link between GAD67 and mucin overproduction in association with smoking.

Conclusions

In the context that GAD67 is the rate limiting enzyme in GABA synthesis, the correlation of GAD67 gene expression with MUC5AC expressions suggests that the up-regulation of airway epithelium expression of GAD67 may contribute to the increase in mucus production observed in association with cigarette smoking.

Trial registration

NCT00224198; NCT00224185

Association of SLC6A12 variants with aspirin-intolerant asthma in a Korean population

Aspirin-intolerant asthma (AIA) occurs from asthma exacerbation after exposure to aspirin. However, the underlying mechanisms of AIA occurrence are still unclear. The critical role of the solute carrier family 6 (neurotransmitter transporter, betaine/GABA) member 12 (SLC6A12) gene in GABAergic transmission, which is associated with mucus production in asthma, makes it a candidate gene for AIA association study. Eight single nucleotide polymorphisms (SNPs) in SLC6A12 were genotyped in 163 aspirin-intolerant asthma (AIA) and 429 aspirin-tolerant asthma (ATA) patients of Korean ethnicity. Associations between polymorphisms of SLC6A12 and AIA were analysed using multivariate logistic analysis. Results showed that two polymorphisms and a haplotype in SLC6A12, rs499368 (P= 0.005; P(corr)= 0.03), rs557881 (non-synonymous C10R, P= 0.007; P(corr)= 0.04), and SLC6A12_BL1_ht1 (P= 0.009; P(corr)= 0.05) respectively, were significantly associated with AIA after multiple testing corrections. In addition, SNPs of SLC6A12 were significantly associated with the fall rate of FEV(1) by aspirin provocation suggesting that SLC6A12 could affect reversibility of lung function abnormalities in AIA patients. Although these results are preliminary and future replications are needed to confirm these findings, this study showed evidence of association between variants in SLC6A12 and AIA occurrence among asthmatics in a Korean population.

Gamma-aminobutyric acid nurtures allergic asthma

Asthma often occurs as a result of immune-based inflammatory responses, which consequently cause pathological changes in airway structural cells. However, the underlying mechanisms of airway pathology in asthma are still not fully understood. Our recent studies revealed a critical role of gamma-aminobutyric acid (GABA) signalling pathway in the airway epithelium of allergic asthma through its ability to stimulate mucus production. This review briefly describes the GABAergic signalling system and its role in the regulation of mucus protein production in bronchial airway epithelial cells.