Inhibition of IL-4/STAT6/IRF4 signaling reduces the epithelial-mesenchymal transition in eosinophilic chronic rhinosinusitis with nasal polyps

Abstract

Background: Previous studies have shown that epithelial-to-mesenchymal transition (EMT) in nasal epithelial cells is critical for tissue remodeling of chronic rhinosinusitis with nasal polyps (CRSwNP). However, the precise mechanism underlying the EMT remains poorly understood. This study aimed to investigate the role of interleukin-4 (IL-4)/signal transducer and activator of transcription 6 (STAT6)/interferon regulatory factor 4 (IRF4) signaling pathway on EMT in eosinophilic CRSwNP.

Methods: We performed quantitative real-time polymerase chain reaction, immunohistochemistry, immunofluorescent staining, and Western blotting to evaluate the expression of STAT6, IRF4, and EMT markers in sinonasal mucosal samples. Effects of IL-4-induced EMT were determined using primary human nasal epithelial cells (hNECs) from patients with eosinophilic CRSwNP. Wound scratch assay, cell morphology, Western blotting, and immunofluorescence cytochemistry were performed to evaluate EMT, and EMT-related markers. Next, human THP-1 monocytic cells were stimulated by phorbolate-12-myristate-13-acetate to differentiate into M0 and were subsequently polarized into M1 with lipopolysaccharide and interferon-γ, M2 with IL-4. The markers of the macrophage phenotype were assessed by Western blotting. The co-culture system was built to explore the interaction between macrophages (THP-1 cells) and hNECs. After co-culture with M2 macrophages, EMT-related markers of primary hNECs were evaluated by immunofluorescence cytochemistry and Western blotting. Enzymelinked immunosorbent assays were used to detect transforming growth factor beta 1 (TGF-β1) in THP-1-derived supernatants.

Results: STAT6 and IRF4 mRNA and protein expression were significantly upregulated in both eosinophilic and noneosinophilic nasal polyps compared with control tissues. The expression of STAT6 and IRF4 in eosinophilic nasal polyps was higher than those in noneosinophilic nasal polyps. STAT6 and IRF4 were not only expressed in epithelial cells but also in macrophages. The number of STAT6⁺CD68⁺ cells and IRF4⁺CD68⁺ cells in eosinophilic nasal polyps was higher than those in noneosinophilic nasal polyps and control tissues. EMT was enhanced in eosinophilic CRSwNP compared to the healthy controls and noneosinophilic CRSwNP. IL-4-stimulated human nasal epithelial cells exhibited EMT characteristics. The hNECs co-cultured with M2 macrophages demonstrated high levels of EMT-related markers. The TGF-β1 level was significantly induced by IL-4 and elevated (M2) rather than control macrophages. The inhibition of STAT6 by AS1517499 reduced the expression of IRF4 in epithelial cells and macrophages and counteracted IL-4-induced EMT in epithelial cells.

Conclusion: In eosinophilic nasal polyps, IL-4 induces STAT6 signaling to upregulate IRF4 expression in epithelial cells and macrophages. IL-4 promotes EMT of hNECs through the STAT6/IRF4 signaling pathway. IL-4-induced M2 macrophages enhanced EMT of hNECs. Inhibition of STAT6 can downregulate the expression of IRF4 and suppress the EMT process, thus providing a new strategy for the treatment of nasal polyps.

Keywords: Chronic rhinosinusitis; Epithelial-to-mesenchymal transition; Interferon regulatory factor 4; Interleukin-4; Nasal polyps; Signal transducer and activator of transcription 6.