Abstract 13598: Mutation of MLX Gene Plays an Important Role in the Pathogenesis of Takayasu Arteritis by Promoting Inflammasome Formation
Introduction: Our recent genome-wide association study revealed that single nucleotide polymorphisms (SNPs) of both IL12B genes which encodes IL12p40, a subunit of both IL-12 and IL-23 cytokines, 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 of unknown etiology. Although mutation of IL12B is expected to play an important role in mediating the development of TA through modulating the level of cytokines, it remains unknown how MLX mutation is associated with the pathogenesis of TA.
Hypothesis: SNP of the MLX (rs665268), a missense mutation of MLX that alters the 139th glutamine to arginine (Gln139Arg), upregulates the factor(s) associated with the development of TA.
Methods and Results: Pull-down assays demonstrated that mutation of Gln139Arg on MLX recombinant protein enhanced the heterodimer formation of MLX with MondoA, a binding partner of MLX that promotes thioredoxin-interacting protein (TXNIP) expression. When a plasmid expressing mutant of Gln139Arg on MLX (MLX-Q139R) was co-transfected with a plasmid expressing MondoA and a TXNIP promoter-containing reporter plasmid into human aortic smooth muscle cells (hASMCs), the TXNIP promoter activity was significantly increased compared to the wild type MLX (MLX-WT) (MLX-Q139R: 63138.3 ± 2557.9 RLU* vs. MLX-WT: 31262.6 ± 3433.2 RLU, *p < 0.05). These results suggest that alteration from Gln139, a neutral amino acid (AA) locating on the DNA binding site of MLX, to Arg, a basic AA with a positive electric charge, enhances formation of the MLX-MondoA-DNA complex. The protein level of both TXNIP and NLRP3, a major component of inflammasome upregulated by TXNIP, was significantly accumulated (TXNIP: 4.5 fold, NLRP3: 3.8 fold) in hASMCs transfected with MLX-Q139R than compared to those in transfected with MLX-WT. Consistently, immunostaining demonstrated that NLRP3 in the cytosol of SMCs accumulated more prominently in the aortas of TA than in normal aortas.
Conclusion: Mutation of Gln139Arg on MLX plays a crucial role in the pathogenesis of TA through facilitating NLRP3 accumulation, which in turn promoting inflammasome formation in hASMCs.
Author Disclosures: Y. Maejima: None. N. Tamura: None. M. Isobe: None.
- © 2014 by American Heart Association, Inc.