Fn14 Exacerbates Acute Lung Injury by Activating the NLRP3 Inflammasome in Mice
Abstract Background: Uncontrolled inflammation is an important factor in the occurrence and development of acute lung injury (ALI). Fibroblast growth factor-inducible 14 (Fn14) takes part in the pathological process of a variety of inflammatory diseases. However, the role of Fn14 in ALI has not yet been elucidated. Methods: C57BL/6J mice were used in this study. ALI model was induced by intratracheal injection of lipopolysaccharide (LPS, 5 mg/kg). The effects of Fn14 receptor blocker ATA (20 mg/kg) on lung injury, inflammatory cell infiltration, inflammatory factor secretion, and oxidative stress in mice were observed. The activation of NLRP3 inflammasome was detected by qPCR, Western blot, and ELISA. Prophylactic or therapeutic ATA was administered to observe its effect on the survival rate of ALI mice. In vitro, primary mouse peritoneal macrophages were used to activate the NLRP3 inflammasome by LPS or LPS+ATP. Fn14 was activated by recombinant TWEAK, or knockdown by lentivirus, and the effects on NLRP3 inflammasome activation was detected.Results: We found that ATA significantly downregulated the expression of Fn14 in the lungs and improved the survival rate of mice receiving a lethal dose of LPS. ATA also attenuated lung tissue damage by decreasing the infiltration of macrophages and neutrophils, reducing inflammation, and suppressing oxidative stress. Interestingly, we found that ATA strongly inhibited the activation of NLRP3 inflammasome in the lungs of ALI mice. Furthermore, in vitro, exogenous TWEAK, a natural ligand of Fn14, enhanced the levels of NLRP3 and Caspase-1 p10 and the maturation and secretion of IL-1β in the primary murine macrophages, eventually leading to the activation of NLRP3 inflammasome. In addition, the expression of Fn14, NLRP3, and Caspase-1 p10 and the production of IL-1β were effectively blocked by Fn14 shRNA in macrophages. In mechanism, the activation of Fn14 promoted the production of reactive oxygen species in activated macrophages. Conclusion:Our study first reports that the activation of Fn14 aggravates ALI by amplifying the activation of NLRP3 inflammasome. Therefore, blocking Fn14 may be a potential way to treat ALI.