Background/Purpose: TNF Receptor-Associated Periodic Syndrome (TRAPS) is one of the autoinflammatory diseases. TRAPS is caused by heterozygous mutations in the TNFRSF1A gene. Although more than 100 TNFRSF1A mutations have been reported, only a few mutations such as T79M have been shown as TRAPS mutations. Previous studies suggested that mutant TNFR1 accumulates in the endoplasmic reticulum (ER), resulting in inflammatory responses owing to excessive ER stress. Reflecting the mechanism, the cell surface expression of T79M TNFR1 has been previously shown to be decreased. Recently, we have identified two TRAPS patients with a novel G87V mutation. In this study, we examined the effects of the novel G87V mutation using a cell model by comparing with the T79M mutation and low-penetrant mutations (R121Q, T90I).

Methods: Wild-type (WT) or mutant TNFRSF1A (G87V, T79M, R121Q, T90I) constructs were transfected into HEK-293 cells. The cell surface and intracellular expression levels were determined by flow cytometry. To examine the effect of G87V mutation in the patients, we measured the mitochondrial reactive oxygen species (ROS) in the peripheral blood mononuclear cells (PBMCs) of the patients and healthy donors. To evaluate the susceptibility to various inflammatory stimuli, PBMCs from TRAPS patients and healthy donors were treated with Toll-like receptor (TLR) ligands. Cytokine and chemokine profiles in the supernatant were determined by the Milliplex Human Cytokine/chemokine magnetic bead premixed 29-plex kit.

Results: The cell surface expression of TNFR1 was decreased in the G87V and T79M mutant cells compared to WT TNFR1-transfected cells. In contrast, the R92Q and T90I mutations did not suppress the cell surface expression of TNFR1. Mitochondrial ROS levels were increased in both monocytes and lymphocytes from TRAPS patients compared to those in cells from healthy individuals. In cytokine assay, PBMCs from the TRAPS patients tended to produce a larger amount of IL-6 in response to a low concentration (0.1 ng/ml) of LPS (TRAPS patient 1973.0 ± 923.4 pg/ml vs. healthy individual 46.9 ± 25.2 pg/ml). FSL-1 (TLR2/6 ligand) stimulation enhanced IL-8 production in the TRAPS PBMCs compared to that in control PBMCs (TRAPS patient 6604.8 ± 1325.0 pg/ml vs. healthy individual 3777.2 ± 2104.2 pg/ml, p< 0.05). Additionally, we found increased production of GM-CSF in response to LPS in the TRAPS PBMCs (TRAPS patient 45.6 ± 21.4 pg/ml vs. healthy individual 17.4 ± 10.9 pg/ml, p< 0.05). However, the secretion of IL-1α, IL-1β, and TNF in the TRAPS PBMCs was not increased. Conclusion: The G87V TNFR1 was not expressed on the cell surface, similar to the pathogenic T79M mutation. The TLR2/6 ligand and cytokines (IL-8 and GM-CSF) are suggested to be involved in the pathophysiological mechanism underlying TRAPS. Our findings obtained from patients harboring unique mutations provide novel insight for better understanding of the inflammatory responses of TRAPS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-study-of-the-novel-g87v-mutation-in-the-tnfrsf1a-gene-identified-in-a-family-with-tnf-receptor-associated-periodic-syndrome-traps/