Inhibition of macrophage inflammasome assembly and pyroptosis with GC-1 ameliorates acute lung injury

Rationale: Acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) is a critical syndrome with a mortality rate of up to 40%, and it is characterized by a prominent inflammatory cascade. The inflammasome and pyroptosis play crucial regulatory roles in regulating various inflammatory-related diseases by serving as pivotal signaling platforms for inflammatory responses and mediating the release of substantial quantities of inflammatory factors. Our previous studies confirmed that GC-1, a clinical-stage thyroid hormone analog, effectively mitigated pulmonary fibrosis by restoring mitochondrial function in epithelial cells. However, the potential effects of GC-1 on macrophage inflammasome assembly and pyroptosis in lung injury as well as the underlying mechanisms, remain unclear. Methods: The effects of GC-1 on lung injury, oxidative damage and inflammation were evaluated in two murine models of ALI (LPS- or HCl-induced models) by assessing lung pathology, the concentrations of IL-1β and IL-18 in BAL fluid, inflammasome and the levels of inflammasome- and pyroptosis-related proteins. Additionally, the impact of GC-1 on ROS-mediated inflammasome assembly and pyroptosis was investigated by examining ROS levels, Nrf2 signaling, and inflammasome adaptor protein ASC levels in mouse alveolar macrophages and human THP-1 macrophages treated with LPS and ATP. The Nrf2 inhibitor ML385 and the mitochondrial-ROS inhibitor Mito-TEMPO were used to further elucidate the effect of GC-1 on the Nrf2-p53-ASC pathway. Results: GC-1 significantly alleviated inflammation and lung injury in ALI model mice, as indicated by pulmonary pathology, inflammatory cytokine levels, ROS production and pyroptosis rates. Consistently, GC-1 inhibited ASC recruitment and oligomerization in macrophages, which suppressed the gasdermin D-mediated release of IL-1β and IL-18. These findings indicated a reduction in inflammasome assembly and pyroptosis initiation. Further research revealed that GC-1 may mitigate oxidative stress induced by mitochondrial damage through Nrf2 signaling, thereby inhibiting the expression of ROS-activated p53 and the target gene ASC. This protective effect of GC-1 could be reversed by ML385 and mimicked by Mito-TEMPO. Conclusions: This study presents a novel mechanism for treating ALI in which GC-1 inhibits macrophage ROS-mediated inflammasome assembly and pyroptosis through Nrf2-p53-ASC pathway. These findings highlight the promising potential of the use of GC-1 as an anti-inflammatory and antioxidant drug in the treatment of ALI/ARDS.