Abstract O.21: Inositol 1,4,5 triphosphate 3- kinase C regulates NLRP3 Inflammasome activation in Kawasaki disease

Abstract

Background: ITPKC controls calcium homeostasis and was identified in genome-wide studies to be associated with susceptibility and severity of KD. NLRP3 is activated by danger signals, leading to inflammasome activation and release of IL-1beta and IL-18. Ca 2+ mobilization mediates NLRP3 activation. We studied the contribution of ITPKC and NLRP3 inflammasome activation in KD. Methods: Cytokine levels were measured using ELISA. Gene expression was assayed using Illumina HumanHT-12v4. EBV-transformed B-cell lines from KD patients with different ITPKC genotypes were used to study the gene and protein expression and Ca 2+ flux using qRT-PCR, Western blot analysis, and FACS respectively. In vivo and in vitro analyses from ITPKC-deficient and wildtype mice were performed using ELISA, spinning disc confocal and Westerns, to determine cytokine release, Ca 2+ flux and protein expression responses respectively. Results: Children with KD show increased circulating IL-1beta, IL-18, IL-1RA and IL18BP protein during acute phase of KD (KD n=48, febrile controls n=41 p<0.001). NLRP3 and its associated inflammasome complex, and the IL-1[[Unsupported Character - Symbol Font ]] and IL18 receptor genes were up-regulated nearly two fold during the acute KD compared to matched convalescent controls (n=171, p<0.001). Pathway analysis showed specific up-regulation of NLRP3 related genes. The KD-associated genetic polymorphism in ITPKC (rs28493229) is functional, directly modulating [Ca 2+ ] i mobilization resulting in NLRP3 activation and increased production of IL-1beta and IL-18, as demonstrated by gene expression, circulating protein levels and functional assays of PBMCs and immortalized cell lines from affected children. These biologic data are partnered with evidence showing resistance to IVIG therapy in those with the ITPKC polymorphism associated with the highest basal and stimulated [Ca 2+ ] i levels. Studies using ITPKC-deficient mice in an animal model of KD support the molecular, cellular and clinical findings in affected children. Significance: ITPKC regulates NLRP3 activation via control of [Ca 2+ ] i mobilization, directing production of IL-1beta and IL-18, pointing to the key role of calcium mobilization in the immunopathogenesis of KD.