Pluripotent stem cell models of Blau syndrome reveal an IFN-<gamma>-dependent inflammatory response in macrophages

Background: Blau syndrome, or early-onset sarcoidosis, is a juvenile-onset systemic granulomatosis associated with a mutation in Nucleotide-binding oligomerization domain 2 (NOD2). The underlying mechanisms of Blau syndrome leading to autoinflammation are still unclear, and there is currently no effective specific treatment for Blau syndrome. Objectives: To elucidate the mechanisms of autoinflammation in Blau syndrome, we sought to clarify the relation between disease associated-mutant NOD2 and the inflammatory response in human samples. Methods: Blau syndrome-specific induced pluripotent stem cells (iPSCs) lines were established. To precisely evaluate the in vitro phenotype of iPSC-derived cells, the disease-associated NOD2 mutation of iPSCs was corrected using a CRISPR/Cas9 system. We also introduced the same NOD2 mutation into a control iPSC line. These isogenic iPSCs were then differentiated into monocytic cell lineages, and the status of NF-?B pathway and proinflammatory cytokine secretion were investigated. Results: We focused on the signals that upregulate the expression of NOD2, especially IFN-? signaling. IFN-? treatment of NOD2-mutant macrophages induced ligand-independent NF-?B activation and proinflammatory cytokine production. IFN-? treatment acted as a priming signal through the up-regulation of NOD2 protein and recruitment of NOD2 on the basement membrane. Conversely, the production of proinflammatory cytokines by MDP, a ligand of NOD2, was decreased in mutant macrophages. Conclusions: Our data support the significance of ligand-independent autoinflammation in the pathophysiology of Blau syndrome. Our comprehensive isogenic disease-specific iPSC panel provides a useful platform for probing therapeutic and diagnostic clues for the treatment of Blau syndrome patients. Overall design: RNA-sequencing was conducted to identify the genes expressed in reponse to stimulation in different manners between WT and MT cells

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Takada S, Kambe N, Kawasaki Y, Niwa A, Honda-Ozaki F, Kobayashi K, Osawa M, Nagahashi A, Semi K, Hotta A, Asaka I, Yamada Y, Nishikomori R, Heike T, Matsue H, Nakahata T, Saito MK