Abstract 340: Single Nucleotide Polymorphism of MLX Gene Plays a Crucial Role in the Pathogenesis of Takayasu Arteritis Through Facilitating Inflammasome Formation of the Aorta
We have identified that single nucleotide polymorphisms (SNPs) of both IL12B gene which encodes IL-12p40 and MLX gene, which encodes a basic helix-loop-helix leucine zipper transcription factor, were significantly associated with clinical manifestations of Takayasu arteritis (TA), an autoimmune systemic arteritis, by genome-wide association study (GWAS). Recently, we reported that SNP of IL12B plays an important role in mediating the development of TA through modulating the level of IL-12p40-related cytokines, including IL-12 and IL-23. However, it remains unknown whether MLX mutation is associated with the pathogenesis of TA. Here, we elucidate that whether SNP of the MLX (rs665268), a missense mutation of MLX that alters the 139th glutamine to arginine (Q139R), upregulates the factor(s) associated with the development of TA. Pull-down assays with recombinant proteins demonstrated that mutation of Q139R on MLX protein enhanced the heterodimer formation of MLX with MondoA, a binding partner of MLX that promotes thioredoxin-interacting protein (TXNIP) expression. As Gln is a neutral amino acid, we speculated that alteration from Gln139 to Arg139, which confers a positive charge to the DNA binding site of MLX, should enhance formation of the MLX-MondoA-DNA complex. Consistent with our hypothesis, luciferase reporter gene assays showed that the TXNIP promoter activity of human aortic smooth muscle cells (hASMCs) co-transfected with TXNIP promoter-containing reporter, MondoA and MLX-Q139R plasmids was significantly higher than those with the wild type MLX (MLX-WT) (MLX-Q139R: 63138 ± 2557 RLU* vs. MLX-WT: 31263 ± 3433 RLU, *p < 0.05). The protein levels of both NLRP3 and procaspase-1, major components of inflammasome upregulated by TXNIP, was significantly increased in hASMCs transfected with MLX-Q139R than compared to those in transfected with MLX-WT. Immunohistochemical analyses of the human aortas revealed that NLRP3 in the SMCs accumulated more prominently in the aortas of TA than those in normal ones.
In conclusion, Q139R mutation on MLX plays a crucial role in the pathogenesis of TA through facilitating NLRP3 accumulation, which in turn facilitating inflammasome formation in the aorta.
Author Disclosures: Y. Maejima: None. N. Tamura: None. Y. Ito: None. M. Isobe: None.
This research has received full or partial funding support from the American Heart Association, National Center.
- © 2015 by American Heart Association, Inc.