MRGPRX2 Gain-of-Function Mutation Drives Enhanced Mast Cell Reactivity in Chronic Spontaneous Urticaria.

Abstract

Background: Mast cell activation plays a central role in the pathogenesis of Chronic spontaneous urticaria (CSU). Mutations in mast cell receptors have been suggested as a potential mechanism underlying CSU. MRGPRX2 has been proposed to contribute to the pathogenesis of CSU. However, the relationship between mutations in MRGPRX2 and their impact on disease severity and receptor function remains poorly understood.

Methods: 80 CSU patients were included in the study. Peripheral blood was collected for DNA sequencing in the coding exon of MRGPRX2. UAS7 scores and laboratory tests were recorded, serum MRGPRX2 levels were measured by ELISA. RBL-2H3 cells were transfected with wild-type (WT) MRGPRX2 and mutant variants. Flow cytometry and immunofluorescence staining were used to assess MRGPRX2 cell surface expression. Functional assays were performed to measure degranulation by β-hexosaminidase release, calcium mobilization, and cytokine synthesis by RT-qPCR. Additionally, phosphorylation of signaling kinases was detected by western blotting.

Results: Missense variants of MRGPRX2 185A>G (n=8, 10%) and 185A>G+46A>C co-mutations (n=23, 28.75%) were identified in CSU patients. Patients carrying 185A>G mutation had significantly higher UAS7 scores, lower circulating basophil and lymphocyte counts than those with WT MRGPRX2. The 185A>G mutation but not 185A>G+46A>C was associated with increased MRGPRX2 expression in both CSU patients and RBL-2H3 cells expressing the 185A>G mutation. Cells transfected with the 185A>G mutation demonstrated increased mast cell degranulation, calcium mobilization, cytokine synthesis, and ERK phosphorylation upon MRGPRX2 activation, whereas the 46A>C+185A>G co-mutation did not show these changes.

Conclusions: The 185A>G mutation in MRGPRX2 contributes to a gain-of-function phenotype that is associated with enhanced disease activity in CSU patients.