HMGB1 impairs nasal epithelial barrier via regulating autophagy in the pathogenesis of allergic rhinitis

Background Numerous studies indicate that the epithelial barrier was disrupted in allergic rhinitis (AR). High-mobility group box 1(HMGB1) plays a significant role in activating inflammation. We aimed to explore whether HMGB1 could impair the epithelial barrier in AR and investigate its underlying mechanism. Methods Nasal secretions and nasal specimens were collected. Expression of HMGB1 and tight junction (TJ) proteins were measured by RT-qPCR, western blotting and immunofluorescence in control subjects and AR patients. Hematoxylin and eosin staining was used for histological examination. Cell proliferation and migration were assessed by CCK-8 and wound healing assays. Primary human nasal epithelial cells (pHNECs) were processed by air-liquid interface (ALI) technique and treated with recombinant HMGB1 protein. Lentivirus mRFP-sGFP-LC3 was transfected to detect autophagy flux. An OVA-induced mouse model was used to investigate the role of HMGB1 in vivo . Results The level of HMGB1 was significantly elevated in the nasal secretions of AR patients (P < 0.001) and positively correlated with symptom severity (VAS scores) (r = 0.4863, P=0.0064). Both ex vivo nasal tissues and in vitro air-liquid interface (ALI) cultures from AR patients showed reduced expression of tight junction proteins (Occludin, Claudin-1) (P < 0.05). In pHNECs, HMGB1 treatment further decreased the expression of ZO-1, Occludin, and Claudin-1, while promoting cell proliferation and migration (P < 0.01). Mechanistically, HMGB1 blocked the autophagosome degradation, as evidenced via increased LC3-II and P62 expression by HMGB1; restoration of autophagy with rapamycin reversed these effects and rescued barrier function. In an OVA-induced mouse model of AR, pharmacological inhibition of HMGB1 with glycyrrhizin (GLY) or ethyl pyruvate (EP) alleviated sneezing and nasal rubbing symptoms (P < 0.05) and improved epithelial barrier integrity. Conclusion HMGB1 was highly expressed in AR patients and correlated with disease severity. It impaired the integrity of the epithelial barrier by inhibiting the degradation of autophagosomes. Both GLY and EP treatments restored impaired epithelial barrier by inhibiting HMGB1.