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Abstract Objectives Gout is caused by the response of the innate immune system to monosodium urate (MSU) crystals. A recent gout GWAS identified a signal of genetic association at a locus encompassing IL1RN-IL1F10. Colocalisation analysis using Genotype Tissue Expression Database (GTEx) eQTL data showed that the signal overlaps with genetic control of IL1RN/IL1F10 gene expression. We assess the functional implications of IL1RN rs9973741, the lead gout-associated variant. Methods We conducted functional validation of IL1RN rs9973741 in patients with gout and controls. The transcription level of IL1RN/IL1F10 was investigated in unstimulated or MSU-crystal co-stimulated PBMCs. Ex vivo functional assays were performed in PBMCs stimulated with C16 + MSU crystals or LPS for 24 h. Cytokine levels were assessed by ELISA. Results In unstimulated PBMCs, no association of IL1RN rs9973741 (gout risk allele G) to IL1RN expression was observed while IL-1F10 was hindered by low expression at both transcriptional and protein levels. However, G allele carriers showed lower IL1RN expression in PBMCs stimulated with C16/MSU crystal and lower concentrations of circulating IL-1Ra in both controls and gout patients. PBMCs depicted less spontaneous IL-1Ra release in GG homozygous controls and lower IL-1Ra production in response to C16 + MSU crystal costimulation in patients with gout. The G allele was associated with elevated IL-1β cytokine production in response to C16 + MSU crystal stimulation in controls. Conclusions The gout risk allele G associates with lower circulating IL-1Ra, lower IL-1Ra production in PBMC assays and elevated IL-1β production in PBMCs challenged with C16 + MSU crystals but not in unchallenged cells. Our data indicate that the genetic signal that associates with gout at IL1RN-IL1F10 region functions to alter expression of IL-1Ra when stimulated by MSU crystals.

Abstract Gout is a common autoinflammatory joint diseases characterized by deposition of monosodium urate (MSU) crystals which trigger an innate immune response mediated by inflammatory cytokines. IGF1R is one of the loci associated with both urate levels and gout susceptibility in GWAS to date, and IGF-1-IGF-1R signaling is implicated in urate control. We investigate the role of IGF-1/IGF1R signaling in the context of gouty inflammation. Also, we test the gout and urate-associated IGF1R rs6598541 polymorphism for association with the inflammatory capacity of mononuclear cells. For this, freshly isolated human peripheral blood mononuclear cells (PBMCs) were exposed to recombinant IGF-1 or anti-IGF1R neutralizing antibody in the presence or absence of solubilized urate, stimulated with LPS/MSU crystals. Also, the association of rs6598541 with IGF1R and protein expression and with ex vivo cytokine production levels after stimulation with gout specific stimuli was tested. Urate exposure was not associated with IGF1R expression in vitro or in vivo. Modulation of IGF1R did not alter urate-induced inflammation. Developing urate-induced trained immunity in vitro was not influenced in cells challenged with IGF-1 recombinant protein. Moreover, the IGF1R rs6598541 SNP was not associated with cytokine production. Our results indicate that urate-induced inflammatory priming is not regulated by IGF-1/IGF1R signaling in vitro. IGF1R rs6598541 status was not asociated with IGF1R expression or cytokine production in primary human PBMCs. This study suggests that the role of IGF1R in gout is tissue-specific and may be more relevant in the control of urate levels rather than in inflammatory signaling in gout.

Summary: Gout is an autoinflammatory disease triggered by a complex innate immune response to MSU crystals and inflammatory triggers. While hyperuricemia is an obligatory risk factor for the development of gout, the majority of individuals with hyperuricemia never develop gout but have an increased risk of developing cardiometabolic disorders. Current management of gout aims at MSU crystal dissolution by lowering serum urate. We apply a targeted proteomic analysis, using Olink inflammation panel, to a large group of individuals with gout, asymptomatic hyperuricemia, and normouricemic controls, and we show a urate-driven inflammatory signature. We add in vivo evidence of persistent immune activation linked to urate exposure and describe immune pathways involved in the pathogenesis of gout. Our results support a pro-inflammatory effect of asymptomatic hyperuricemia and pave the way for new research into targetable mechanisms in gout and cardiometabolic complications of asymptomatic hyperuricemia.