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. Der f 2 stimulates the phospholipase C gamma/protein kinase C alpha/p38 mitogen-activated protein kinase pathway in BEAS-2B cells by activating phospho- lipase D1 (PLD1). According to initial studies in animal disease models, IL-13 can induce all features of allergic asthma independent of other Th2 cytokines. Airway epithelial cells act as initiators, mediators, and supervisors in innate and adaptive immune responses and effectively bridge innate and adaptive immunity.
Following Der f 2 treatment to BEAS-2B cells, IL-13 mRNA expression was increased at 15 min and sustained up to 60 min, and in a dose-dependent manner. Der f 2 increased phosphorylation of Akt were sustained for up to 30 min, and in a dose-dependent manner.
Akt activity was inhibited by LY294002, a chemical inhibitor of PI3K, pretreatment. In the context of Der f 2 exposure, Akt functions downstream of PI3K. In BEAS-2B cells, LY294002 attenuated Der f 2-induced IL- 13 mRNA expression. The expression of DN-Akt decreased the Der f 2-induced phosphorylation of Akt. Overexpression of WT-Akt increased IL-13 mRNA expression induced by treatment with Der f 2, but the expression was decreased by overexpression of DN-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-jB reporter activity following Der f 2 exposure was abolished by LY29400.
The IKK inhibitor, BAY 11-7085, effectively inhibited the phosphorylation of IkBa by Der f 2 as well as reduced Der f 2-induced NF-kB transactivation to the basal level in BEAS-2B cells, 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. 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. Der f 2 administration increased the phosphorylation of Akt and IjBa especially in the bronchial epithelial cells in the lung tissue sections, and these increases were inhibited by pre-administration of LY294002.
In human bronchial epithelial cells, Der f 2 induces IL-13 expression via the PLD1-regulated signaling pathways; however, extensive studies have demonstrated the involvement of the PI3K/Akt pathway in allergic asthma both in vitro and in vivo, suggesting the PI3K/Akt pathway as a potential target for asthma therapy. In allergic asthma models, NF-kB has been shown to be required for allergen-induced expression of pro-inflamma- tory molecules, such as IL-4, IL-5, IL-13, IL-6, and IL-8.