TLR9 mediates the activation of NLRP3 inflammasome and oxidative stress in murine allergic airway inflammation

Toll-like receptor 9 (TLR9) has been reported to mediate airway inflammation, however, the underlying mechanism is poorly understood. In the present study, our objective was to reveal whether TLR9 regulates NLRP3 inflammasome and oxidative stress in murine allergic airway inflammation and Raw264.7 cells. Female wild type(WT)and TLR9(-/-)mice on C57BL/6 background were used to induce allergic airway inflammation by challenge of OVA, and Raw264.7 cells with or without TLR9 knockdown by small interfering RNA (siRNA) were stimulated by S.aureus. The results demonstrated that deletion of TLR9 effectively attenuated OVA-induced allergic airway inflammation including inflammatory cells infiltration and goblet cell hyperplasia. Meanwhile, OVA-induced protein expression of NLRP3, caspase-1(p20) and mature IL-1 beta, as well as secretion of IL-1 beta and IL-18 in wild type mice (WT) was obviously suppressed by TLR9 deficiency. Concomitantly, the expression of oxidative markers 8-OhDG and nitrotyrosine was increased in OVA-challenged WT mice, while TLR9 deficiency significantly inhibited such increase. Similarly, in the in vitro study, we found that knockdown of TLR9 markedly suppressed S.aureus-induced activation of NLRP3 inflammasome and oxidative stress in Raw264.7 cells. Collectively, our findings indicated that TLR9 may mediate allergic airway inflammation via activating NLRP3 inflammasome and oxidative stress.