Molecular hydrogen alleviates asthma through inhibiting IL-33/ILC2 axis

Asthma is one of the most common noninfectious chronic diseases characterized by type II inflammation. This study aimed to investigate the effects of molecular hydrogen on the pathogenesis of asthma. OVA sensitized asthma mouse model and house dust mite treated 16HBE cellular model were established and hydrogen/oxygen mixture was used to treat asthmatic mice and 16HBE cells. Serum and BALF cytokines were measured with specific ELISA assays. E-cadherin and ZO-1 were detected by immunohistochemical staining and expression of caspase 3 and 9, NF-κB, IL-33 and ST2 was assessed by quantitative real-time PCR, western blot and/or immunofluorescence. IL-33 promoter activity was analyzed by dual-luciferase assay. ILC2 population was assayed by flow cytometry and differentially expressed miRNAs were detected using miRNA array. Serum and BALF levels of IL-33 and other alarmin and type II cytokines were greatly increased by OVA and inhibited by H2 in asthmatic mice. The expression of NF-κB (p65) and ST2 was upregulated by OVA and suppressed by H2. ILC2 population was markedly increased in OVA-induced asthmatic mice, and such increase was inhibited by H2. E-cadherin and ZO-1 levels in airway tissues of asthmatic mice were significantly lower than that of control mice, and the reduction was recovered by H2 treatment. H2 alleviated HDM induced apoptosis of 16HBE cells, upregulation of IL-33 and ST2, and elevation of IL-33 promoter activity. A group of miRNAs differentially expressed in HDM and HDM + H2 treated 16HBE cells were identified. These data demonstrated that H2 is efficient in suppressing allergen-induced asthma and could be developed as a therapeutics for asthma and other conditions of type II inflammation.