Novel Pycard gene polymorphism impairs Nlpr3 inflammasome-induced IL-1β production in mice selected for low inflammatory response

ABSTRACT

A SNP based linkage study in mouse lines phenotypically selected for maximal (AIRmax) or minimal (AIRmin) acute inflammatory response (AIR), mapped a major locus, Inflammatory response modulator 1 (Irm1) at 128Mb (3.5Mb interval) in chr 7 controlling AIR, measured by leukocyte and IL-6 levels in exudates and IL-1β production by circulating leukocytes after Nlpr3 inflammasome activation. Sequencing of this region in mice with extreme high or low IL-1β levels revealed 14 SNPs between the two groups, narrowing the locus interval to 420Kb. Candidate genes at Irm1 include Pycard with an undescribed exon 3 (C/T) mutation leading to E19K substitution at the pyrin domain, and Itgam, Rgs10 and BC017158 with intronic SNPs. In Pycard, the C allele was fixed in high responder AIRmax mice whereas the C and T alleles frequencies were 39% and 61%, respectively in AIRmin. We then investigated the effect of this novel Pycard SNP in inflammation phenotypes.Methods AIRmin mice bearing the 3 genotypes at Pycard CC, CT, TT were produced by genotype-assisted mating. Inflammatory response was measured in AIRmax and in the 3 AIRmin sublines by the number of infiltrating cells and IL-6 concentration in the 24h exudate induced by sc Biogel P-100 bead injection and ex vivo IL-1β production by circulating leukocytes after E coli LPS (1 ug) and ATP (5mM) activation.Results IL-1β levels were similar in AIRmaxCC (4.5-±0.4 ng/ml) and AIRminCC (3.4±2.4 ng/ml) whereas AIRminCT produced 0.3±0.5 and AIRminTT <0.05 ng/ml IL-1β. Leukocyte influx and IL-6 levels in inflammatory exudates were not affected.Conclusion The E19K substitution in Pycard causes a negative effect in inflammasome activation for IL-1β production, without interfering in other inflammation phenotypes.