Lactobacillus johnsonii N5 Supernatant Protects RPMI-2650 Cells from HDM-Induced Injury in Association with Suppression of the NR4A1-IRE1-XBP1-Mediated Unfolded Protein Response.

Background/Objectives: House dust mites (HDMs) are significant allergens that cause damage to nasal epithelial cells and have a role in the pathophysiology of allergic rhinitis. Lactobacillus johnsonii N5 supernatant (N5sup), a probiotic strain, exhibits possible protective properties; nevertheless, the molecular processes involved remain unclear. Methods: RPMI-2650 human nasal epithelial carcinoma cells were subjected to treatment with HDM, N5sup, or a combination of both. Results: The HDM stimulation induced a certain degree of transcriptional alterations. Compared with the control group, a total of 221 differentially expressed genes were identified in HDM-treated cells, which were mainly enriched in the IRE1-XBP1 branch of the unfolded protein response (UPR) pathway. Comprehensive investigation demonstrated that HDM increased the NR4A1-IRE1-XBP1 signaling pathway, characterized by elevated expression levels of NR4A1, ERN1 (IRE1), and XBP1. Both qRT-PCR and Western blotting verified that N5sup strongly inhibited the HDM-induced increase in NR4A1, IRE1, and XBP1. Analysis of the protein-protein interaction network further confirmed a central hub comprising NR4A1, IRE1, and XBP1. Conclusions: N5sup supernatant protects RPMI-2650 cells from HDM-induced injury, and this protective effect is associated with the NR4A1-IRE1-XBP1 pathway. These findings suggest that this signaling axis may serve as a potential therapeutic target for probiotic intervention in allergic airway diseases.