CircMIRLET7BHG facilitates mast cell degranulation to accelerate AR progression by enhancing IL-33 mRNA stability via interacting with PTBP1

Abstract Mast cell (MC) degranulation is associated with allergic rhinitis (AR) progression. Although circMIRLET7BHG has been identified as a promoter of AR development, its potential regulatory role in MC degranulation during AR progression has not been clarified. To address this, MCs (LAD2) were co-cultured with ovalbumin (OVA)-induced human nasal mucosa epithelial cells (HNEpC), and an AR mouse model was generated through OVA stimulation. The expression levels of circMIRLET7BHG and interleukin-33 (IL-33) were assessed by qRT-PCR, while cytokine production in MCs was quantified using ELISA. MC degranulation was evaluated by toluidine blue staining, and western blotting was employed to detect the expression of polypyrimidine tract-binding protein 1 (PTBP1) and proteins related to mitochondrial fusion and fission. The interactions of PTBP1 with circMIRLET7BHG and IL-33 were verified by RNA immunoprecipitation and RNA pull-down assays, and IL-33 mRNA stability was determined using the actinomycin D assay. Co-culture of LAD2 cells with OVA-induced HNEpC demonstrated that circMIRLET7BHG knockdown inhibited MC degranulation by suppressing mitochondrial fission. Mechanistically, circMIRLET7BHG enhanced IL-33 mRNA stability through its interaction with PTBP1. IL-33 overexpression promoted mitochondrial fission and accelerated MC degranulation, whereas this effect was reversed upon circMIRLET7BHG knockdown. In OVA-induced AR mouse models, circMIRLET7BHG overexpression increased epithelial thickness, eosinophil infiltration, and apoptosis, thereby aggravating allergic symptoms by enhancing mitochondrial fission and MC degranulation via upregulation of IL-33 expression. In conclusion, these findings demonstrate that circMIRLET7BHG promotes AR progression by enhancing mitochondrial fission and MC degranulation through regulation of the PTBP1/IL-33 axis, suggesting a potential novel therapeutic target for AR treatment.