The hyper-expression of NLRP4 characterizes the occurrence of macrophage activation syndrome assessing STING pathway in adult-onset Still's disease.

To assess stimulator of interferon genes (STING) pathway in patients with adult-onset Still's disease (AOSD) who were complicated or not by macrophage activation syndrome (MAS), evaluating peripheral blood mononuclear cells (PBMCs), and synovial tissues. The relative mRNA expression of key molecules of the STING pathway (i.e. CGAS, NLRP4, PKDC, STING1, XRCC5, and XRCC6) and interferon (IFN)-γ was assessed in PBMCs obtained from patients with AOSD, who were complicated or not by MAS, and healthy controls (HCs). A bulky RNA sequencing was performed in synovial tissues from two patients with AOSD. Finally, the ability of heavy ferritin subunit (FeH) to induce the expression of NLRP4 was evaluated in cultured macrophages. Twenty patients with AOSD were analysed. Out of them, seven patients were complicated by MAS. Assessing mRNA relative expression in PBMCs, STING1, NLRP4, XRCC6, and IFN-γ were significantly expressed in AOSD than HCs. The mRNA relative expression of CGAS, PKDC, and XRCC5 did not differ between patients and HCs. Furthermore, NLRP4 and IFN-γ resulted to be significantly increased in patients with AOSD complicated by MAS than others. By RNA-sequencing analysis, we observed that Nlrp4 gene was significantly up-regulated in patients with AOSD. Following the stimulation with FeH, an increased expression of NLRP4 was observed in cultured macrophages. In conclusion, an increased expression of some key molecules of STING pathway characterized patients with AOSD. In addition, our results suggested that a hyper-activity of NLRP4 may be observed in patients with MAS. Furthermore, FeH increased the expression of NLRP4 in cultured macrophages.