House dust mite allergen Der f 2 induces interleukin-13 expression by activating the PI3K/Akt pathway (1)
Asthma is an inflammatory disease of the airways in which T helper type 2 (Th2) cells and related cytokines interleukin-4 (IL-4), IL-5, and IL-13 are critical to asthma pathobiology. The mite group 2 allergen Der f 2 is one of the most important HDM allergens, as Der f 2 immunoglobulin E (IgE) levels are elevated in 70–80 % of allergic patients. IL-13 can induce all features of allergic asthma independent of other Th2 cytokines. In addition, the importance of IL-13 in allergic diseases in humans is supported by a strong association between tissue IL-13 levels and genetic variants in the IL-13 gene with asthma and related traits.
Following Der f 2 treatment to BEAS-2B cells, IL-13 mRNA expression was increased at 15 min and sustained up to 60 min. In addition, Der f 2 induced IL-13 mRNA expression in a dose-dependent manner. Within 15 min, Der f 2 increased phosphorylation of Akt as well as that of p38, which is known to be activated by Der f 2, and the phosphorylation levels were sustained for up to 30 min. Furthermore, the activation of Akt was increased by Der f 2 in a dose-dependent manner.
LY294002, a chemical inhibitor of PI3K, treatment inhibited Akt activity. In BEAS-2B cells, LY294002 attenuated Der f 2-induced IL-13 mRNA expression. Overexpression of wild-type Akt (WT-Akt) increased the levels of phosphorylated Akt in both Der f 2-treated and non-treated cells; however, the expression of DN-Akt decreased the Der f 2-induced phosphorylation of Akt.
Der f 2 increased IkBa phosphorylation concomitant with the phosphorylation of Akt. The increased phosphorylation of Akt and IkBa as well as the increased NF-kB reporter activity following Der f 2 exposure was abolished by LY294002.
In BEAS-2B cells, the IKK inhibitor, BAY 11-7085, effectively inhibited the phosphorylation of IkBa by Der f2. Treatment with BAY 11-7085 not only inhibited the basal level of NF-kB transactivation but also reduced Der f 2-induced NF-jB transactivation to the basal level in BEAS-2B cells. The inhibition of Der f 2-induced NF-jB pathway activation by BAY 11-7085 resulted in decreased Der f 2-induced IL-13 mRNA expression.
H&E-stained tissues obtained from Der f 2-challenged mice did not exhibit any overt pathological changes, such as eosinophil infiltration and the IL-13 mRNA levels in the lung tissue lysates were increased by Der f 2, and this increase was inhibited by the administration of LY294002. Pre-administration of LY294002 inhibited this Der f 2-induced phosphorylation of Akt and IkBa.
In human bronchial epithelial cells, Der f 2 induces IL-13 expression via the PLD1-regulated signaling pathways. Inhibition of PI3K effectively reduced ovalbumin-induced asthma-related phenotypes, such as pulmonary eosinophilia, mucus hypersecretion, and airway hyperreactivity in a mouse asthma model.