IRE1α/XBP-1 promotes β-catenin signaling activation of airway epithelium in lipopolysaccharide-induced acute lung injury

Inhibition of IRE1α/XBP1 axis alleviates LPS-induced acute lung injury by suppressing TXNIP/NLRP3 inflammasome activation and ERK/p65 signaling pathway

BACKGROUND

Acute lung injury or acute respiratory distress syndrome (ALI/ARDS) is a devastating clinical syndrome with high incidence and mortality rates. IRE1α-XBP1 pathway is one of the three major signaling axes of endoplasmic reticulum stress that is involved in inflammation, metabolism, and immunity. The role and potential mechanisms of IRE1α-XBP1 axis in ALI/ARDS has not well understood.

METHODS

The ALI murine model was established by intratracheal administration of lipopolysaccharide (LPS). Hematoxylin and eosin (H&E) staining and analysis of bronchoalveolar lavage fluid (BALF) were used to evaluate degree of lung injury. Inflammatory responses were assessed by ELISA and RT-PCR. Apoptosis was evaluated using TUNEL staining and western blot. Moreover, western blot, immunohistochemistry, and immunofluorescence were applied to test expression of IRE1α, XBP1, NLRP3, TXNIP, IL-1β, ERK1/2 and NF-κB p65.

RESULTS

The expression of IRE1α significantly increased after 24 h of LPS treatment. Inhibition of the IRE1α-XBP1 axis with 4µ8C notably improved LPS-induced lung injury and inflammatory infiltration, reduced the levels of IL-6, IL-1β, and TNF-α, and decreased cell apoptosis as well as the activation of the NLRP3 inflammasome. Besides, in LPS-stimulated Beas-2B cells, both 4µ8C and knockdown of XBP1 diminished the mRNA levels of IL-6 and IL-1B, inhibited cell apoptosis and reduced the protein levels of TXNIP, NLRP3 and secreted IL-1β. Mechanically, the phosphorylation and nuclear translocation of ERK1/2 and p65 were significantly suppressed by 4µ8C and XBP1 knockdown.

CONCLUSIONS

In summary, our findings suggest that IRE1α-XBP1 axis is crucial in the pathogenesis of ALI/ARDS, whose suppression could mitigate the pulmonary inflammatory response and cell apoptosis in ALI through the TXNIP/NLRP3 inflammasome and ERK/p65 signaling pathway. Our study may provide new evidence that IRE1α-XBP1 may be a promising therapeutic target for ALI/ARDS.

Quercetin Alleviates the Progression of Chronic Rhinosinusitis Without Nasal Polyps by Inhibiting Nasal Mucosal Inflammation and Epithelial Apoptosis

Chronic rhinosinusitis (CRS) is a common chronic inflammatory upper respiratory tract, has a major subtype of CRS without nasal polyps (CRSsNP), constituting a great global health problem. Quercetin exerts the important roles in several inflammatory diseases. However, its function in CRSsNP remains unclear. In this study, quercetin dose-dependently alleviated allergic nasal symptoms of increased frequencies of sneezing and nasal scratching in Staphylococcus aureus-constructed CRSsNP mice. Importantly, quercetin attenuated the histopathological changes of nasal mucosa tissue in model mice, including mucosal thickening, glandular hyperplasia, noticeable mast cells, and inflammatory cell infiltration. Concomitantly, quercetin alleviated the increased mucosal inflammation in CRSsNP mice by suppressing the transcripts and releases of pro-inflammatory IL-1β, IL-6, and IL-4. Notably, quercetin restrained X-box binding protein 1 (XBP1)-mediated activation of the HIF-1α/wnt-β-catenin axis in nasal mucosal tissues in CRSsNP model. Intriguingly, intranasal instillation of Lv-XBP1 offset the protective efficacy of quercetin against the progression of CRSsNP by suppressing the production of inflammatory cytokine IL-1β, IL-6, and IL-4, frequency of sneezing and nasal scratching, and histopathological changes of nasal mucosa tissues. In vitro, higher expression of XBP1 was observed in human nasal epithelial cells (HNECs) of CRSsNP relative to the normal HNECs. Moreover, elevation of XBP1 by Lv-XBP1 treatment suppressed cell proliferation and increased apoptosis of CRSsNP HNECs. Mechanistically, XBP1 overexpression increased the expression of HIF-1α and β-catenin, indicating the activation of the HIF-1α/wnt-β-catenin axis. Nevertheless, treatment with quercetin inhibited XBP1-induced cell apoptosis and reversed XBP1-mediated inhibition in cell proliferation in HNECs, as well as the activation of the HIF-1α/wnt-β-catenin axis. Thus, these findings reveal that quercetin may attenuate the progression of CRSsNP by inhibiting nasal mucosal inflammation and epithelial barrier dysfunction via blocking the XBP1/HIF-1α/wnt-β-catenin pathway, supporting a promising agent against CRSsNP.

GLUT1 Promotes NLRP3 Inflammasome Activation of Airway Epithelium in Lipopolysaccharide-Induced Acute Lung Injury

Acute lung injury (ALI) is a devastating clinical syndrome caused by different factors, with high morbidity and mortality. Lung injury and inflammation caused by lipopolysaccharide (LPS) can be modulated by NLRP3 inflammasome activation, yet its exact function within the airway epithelium is still unknown. Meanwhile, glucose transporter protein 1 (GLUT1) contributes to a number of inflammatory illnesses, including ALI. The present study aimed to assess GLUT1's function in NLRP3 inflammasome activation of airway epithelium in LPS-induced acute lung injury. BALB/c mice and BEAS-2B cells were exposed to LPS (5 mg/kg and 200 μg/mL, respectively), with or without GLUT1 antagonists (WZB117 or BAY876). LPS up-regulated pulmonary expression of NLRP3 and GLUT1 in mice, which could be blocked by WZB117 or BAY876. Pharmacological inhibition of GLUT1 in vivo significantly attenuated lung tissue damage, neutrophil accumulation, and proinflammatory factors release (TNF-α, IL-6, and IL-1β) in LPS-exposed mice. Meanwhile, the activation markers of NLRP3 inflammasome (ASC, caspase-1, IL-1β, and IL-18) induced by LPS were also suppressed. In cultured BEAS-2B cells, LPS induced an increase in GLUT1 expression and triggered activation of the NLRP3 inflammasome, both of which were inhibited by GLUT1 antagonists. These results illustrate that GLUT1 participates in LPS-induced ALI and promotes the activation of the NLRP3 inflammasome in airway epithelial cells.