Purpose: CpG-ODN has been found to attenuate allergic airway inflammation in our previous study. Here, we aimed to further investigate whether CpG-ODN exerts such effect via regulating endoplasmic reticulum (ER) stress and revealed the underlying mechanism.
Methods: Five-week-old C57BL/6 mice were randomly grouped and treated with or without CpG-ODN or/and SP600125. Meantime, RAW264.7 cells were used to investigate the effect of CpG-ODN on OVA-induced ER stress in vitro. The cellularity of bronchoalveolar lavage fluid (BALF) was classified and counted after Wright–Giemsa staining. HE and PAS staining methods were applied to analyze airway inflammation. The protein levels of IL-4, IL-5, IL-13, p-JNK, JNK, CHOP, XBP1, ATF6α and GRP78 in lung tissues were detected by Western blotting. Correspondingly, the ER stress markers were detected by Western blotting and immunofluorescence in RAW264.7 cells.
Results: In OVA-induced allergic airway inflammation, CpG-ODN significantly suppressed inflammatory cells infiltration, goblet cell hyperplasia and the protein expression of Th2 cytokines. Moreover, OVA exposure strongly increased the activation of ER stress with higher protein expressions of CHOP, XBP1, ATF6α and GRP78. However, these OVA-induced increase of ER stress markers were markedly suppressed by CpG-ODN treatment. In addition, exposure to OVA significantly increased the phosphorylation of JNK, which was significantly reduced by CpG-ODN treatment. Remarkably, single treatment of SP600125, an antagonist of JNK, functioned similarly as CpG-ODN in mitigating allergic airway inflammation and suppressing OVA-induced activation of ER stress; however, no significant synergistic effect was evidenced by combined treatment of SP600125 and CpG-ODN. Furthermore, in OVA-stimulated RAW264.7 cells, we also found that OVA stimulation increased the expressions of ER stress markers, and CpG-ODN significantly reduced their expression levels via suppressing the phosphorylation of JNK.
Conclusion: These results indicated that CpG-ODN mitigates allergic airway inflammation via suppressing the activation of JNK-medicated ER stress.
Keywords: asthma, CpG-ODN, SP600125, endoplasmic reticulum homeostasis