Urate-induced epigenetic modifications in myeloid cells

M Badii,C A Dinarello,M M Helsen,D Macartney-Coxson,O I Gaal,B Novakovic,L K Stamp,L A B Joosten,V Klück,T O Crişan,R Davar,E Habibi,H G Stunnenberg,S T Keating,A J Phipps-Green,M G Netea,N Dalbeth,T R Merriman,M C Cleophas

doi:10.1186/s13075-021-02580-1

Abstract

ObjectivesHyperuricemia is a metabolic condition central to gout pathogenesis. Urate exposure primes human monocytes towards a higher capacity to produce and release IL-1β. In this study, we assessed the epigenetic processes associated to urate-mediated hyper-responsiveness.MethodsFreshly isolated human peripheral blood mononuclear cells or enriched monocytes were pre-treated with solubilized urate and stimulated with LPS with or without monosodium urate (MSU) crystals. Cytokine production was determined by ELISA. Histone epigenetic marks were assessed by sequencing immunoprecipitated chromatin. Mice were injected intraarticularly with MSU crystals and palmitate after inhibition of uricase and urate administration in the presence or absence of methylthioadenosine. DNA methylation was assessed by methylation array in whole blood of 76 participants with normouricemia or hyperuricemia.ResultsHigh concentrations of urate enhanced the inflammatory response in vitro in human cells and in vivo in mice, and broad-spectrum methylation inhibitors reversed this effect. Assessment of histone 3 lysine 4 trimethylation (H3K4me3) and histone 3 lysine 27 acetylation (H3K27ac) revealed differences in urate-primed monocytes compared to controls. Differentially methylated regions (e.g. HLA-G, IFITM3, PRKAB2) were found in people with hyperuricemia compared to normouricemia in genes relevant for inflammatory cytokine signaling.ConclusionUrate alters the epigenetic landscape in selected human monocytes or whole blood of people with hyperuricemia compared to normouricemia. Both histone modifications and DNA methylation show differences depending on urate exposure. Subject to replication and validation, epigenetic changes in myeloid cells may be a therapeutic target in gout.

Highlights

Urate is the end-point metabolite in purine catabolism in humans and is regarded as an alarmin released from disintegrating cells at times of stress or cell death [1, 2]
While IL-1β production capacity was strongly diminished after 48 h of culture (Fig.2A, B; 24 h resting periods and onwards), persistent effects were observed for reduction of IL-1 receptor antagonist (IL-1Ra) (Fig.2C, D) and for induction of IL-6 (Fig. 2E, F)
IL-1β (A-B), IL-1Ra (C-D), and IL-6 (E-F) were measured in the supernatants of cells, data are representative for 3 independent experiments and 6 different volunteers, graphs depict individual values with paired samples shown in identical symbols, bars and error bars represent means+/−SEM

Summary

Introduction

Urate is the end-point metabolite in purine catabolism in humans and is regarded as an alarmin released from disintegrating cells at times of stress or cell death [1, 2]. MSU crystals have been shown to induce IL-1β release through activation of the NLRP3 inflammasome [4]. They recruit ASC (Inflammasome Adaptor Protein Apoptosis-Associated Speck-Like Protein Containing CARD) at the inflammasome formation site through the polymerization of tubulin [5]. MSU crystals alone are insufficient for a gout flare and second signals are required to act in synergy with MSU crystals Such second signals can be pathogen-related ligands such as lipopolysaccharide (LPS) [6], Pam3Cys [7], or sterile stimuli such as fatty acids (e.g., stearate) [8], or the C5a component of the complement [9]

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