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ObjectiveGout is characterised by severe interleukin (IL)-1-mediated joint inflammation induced by monosodium urate crystals. Since IL-37 is a pivotal anti-inflammatory cytokine suppressing the activity of IL-1, we conducted genetic and functional studies aimed at elucidating the role of IL-37 in the pathogenesis and treatment of gout.MethodsVariant identification was performed by DNA sequencing of all coding bases of IL37 using molecular inversion probe-based resequencing (discovery cohort: gout n=675, controls n=520) and TaqMan genotyping (validation cohort: gout n=2202, controls n=2295). Predictive modelling of the effects of rare variants on protein structure was followed by in vitro experiments evaluating the impact on protein function. Treatment with recombinant IL-37 was evaluated in vitro and in vivo in a mouse model of gout.ResultsWe identified four rare variants in IL37 in six of the discovery gout patients; p.(A144P), p.(G174Dfs*16), p.(C181*) and p.(N182S), whereas none emerged in healthy controls (Fisher’s exact p-value=0.043). All variants clustered in the functional domain of IL-37 in exon 5 (p-value=5.71×10−5). Predictive modelling and functional studies confirmed loss of anti-inflammatory functions and we substantiated the therapeutic potential of recombinant IL-37 in the treatment of gouty inflammation. Furthermore, the carrier status of p.(N182S)(rs752113534) was associated with increased risk (OR=1.81, p-value=0.031) of developing gout in hyperuricaemic individuals of Polynesian ancestry.ConclusionHere, we provide genetic as well as mechanistic evidence for the role of IL-37 in the pathogenesis of gout, and highlight the therapeutic potential of recombinant IL-37 for the treatment of gouty arthritis.

BackgroundInterleukin(IL)-1 signaling is of major importance in human innate cytokine responses. Common variants in related genes have been linked to various inflammation-mediated diseases and stimulation-induced cytokine responses, but the role of rare variants remains to be elucidated.MethodsIn this study, we characterize the role of rare and common genetic variation, as identified by molecular inversion probe-based sequencing, in 48 genes related to the IL-1 pathway. Using a systems biology approach, we examined the inter-individual variability of in vitro stimulation-specific human cytokine responses from 463 healthy individuals of the Human Functional Genomics Project and assessed the role of rare and common genetic variants, separately and combined, by means of the Sequence Kernel Association Test.ResultsWe identified strong associations for rare genetic variants in NCF4 (adjP=7.2E−05) and CASP1 (adjP=3.0E−05) with IL-6 production in response to PHA and LPS stimulation, respectively. In addition, common variants in IL36A and IL38 were associated to both C. albicans-induced IL-1β (IL36AadjP=0.0442; IL38adjP=0.0092) and IL-6 production (IL36AadjP=0.0037; IL38adjP=0.0082), an effect that was stronger at the subpathway level both for IL-1β (adjP=0.0017) and IL-6 (adjP=1.8E−04). The common variant signature for the IL-1β and IL-6 response to C. albicans was confirmed by an association with all anti-inflammatory genes (adjP=1.87E−03 and adjP=5.75E−04), and we validated this finding for non-coding common variants. Lastly, we identified a burden of rare variants in pro-inflammatory genes and LPS-induced IL-6 production (adjP=2.42E−04), and a new role for anti-inflammatory rare variants on S. aureus-stimulated IL-6 production (adjP=6.71E−03).ConclusionsIn conclusion, we show that both common and rare genetic variation in genes of the IL-1 pathway, separately and combined, differentially influence in vitro cytokine responses to various stimuli in healthy individuals. This study therefore accentuates potential mechanisms that are translatable into new hypothesis-driven characterization of common and rare variant involvement in a wide variety of inflammatory and immunological mechanisms and diseases.