RESUMO
BACKGROUND: Palindromic rheumatism (PR) is an infrequent form of periodic arthritis. Based on the similarity of the pathogenesis of PR to autoinflammatory syndromes, we previously found that the dominant-active splice variant of the inflammasome adaptor protein, apoptosis-associated speck-like protein containing a CARD (ASC), which lacks exon 2 (Δexon2), is expressed in Japanese patients with PR. OBJECTIVE: Elucidation of the mechanism of Δexon2 ASC production and the effect of IL-1ß on splicing. METHODS: The genomic DNA of Japanese patients with PR was sequenced. The effect of the observed single nucleotide polymorphisms (SNPs) on ASC splicing was determined via exon trapping using THP-1 cells stimulated with interleukin-1 beta (IL-1ß) or ceramide. To investigate the genes that affect alternative splicing via IL-1ß, we analyzed the transcriptome of IL-1ß-treated THP-1 cells using RNA sequencing. RESULTS: We found the rs8056505 A->G SNP located in the 5'-untranslated region of the genomic ASC gene in patients and that Δexon2 expression was induced by this SNP, whereas it was suppressed by IL-1ß or ceramide. We detected 131,426 transcripts and identified 52 differentially expressed genes (DEGs) consisting of 41 downregulated genes and 11 upregulated genes in IL-1ß-stimulated THP-1 cells. The splicing-related gene MASCRNA was the most significantly induced gene by IL-1ß. CONCLUSIONS: We propose a cyclic expression model in which ASC alternates between wild-type and Δexon2 expression regulated by the rs8056505 G allele and splicing factors induced by IL-1ß. This cycle may be correlated with the formation of periodic PR pathologies.
RESUMO
BACKGROUND: Palindromic rheumatism (PR) is a rare periodic arthritis characterized by relapsing short episodes of arthritis. Although the pathogenesis of PR is still unclear, the clinical condition is similar to that of autoinflammatory diseases caused by dysregulation of inflammasome-related genes. OBJECTIVE: We analyzed the inflammasome adapter PYD and CARD domain-containing protein/apoptosis-associated speck-like protein containing a CARD (PYCARD/ASC) in Japanese patients with PR. METHODS: Serum interleukin (IL)-1ß concentrations in three Japanese patients with PR were measured. We also cloned PYCARD/ASC cDNA variants and expressed them in THP-1 cells to determine their effects on inflammasome activity following stimulation with phorbol 12-myristate 13-acetate and monosodium urate. Lysates of recombinant THP-1 cells were subjected to co-immunoprecipitation assays. RESULTS: Serum IL-1ß concentrations were significantly elevated in patients with PR, and a splice variant of PYCARD/ ASC mRNA lacking exon 2 (Δexon2) was dominantly expressed compared with that in controls. Moreover, IL-1ß secretion was significantly increased in THP-1 cells expressing Δexon2PYCARD/ASC compared with that in cells expressing the wild-type protein. The amount of NLRP3 bound to Δexon2PYCARD/ASC was increased after stimulation, whereas that bound to the wild-type protein was decreased. There were no differences in caspase-1 binding. CONCLUSIONS: Δexon2 PYCARD/ASC was associated with the pathogenesis of PR.