Inhibition of macrophage pyroptosis protects against sepsis-induced injury to the alveolar epithelial barrier.

BACKGROUND: Acute lung injury (ALI) is characterized by alveolar epithelial barrier dysfunction, largely driven by excessive inflammation. This study aimed to elucidate the specific role and mechanism of macrophage pyroptosis in sepsis-induced epithelial injury. METHODS: We established an in vitro sepsis model using lipopolysaccharide (LPS)-stimulated macrophages, employing the NLRP3 inhibitor MCC950. Activation of the NLRP3 pathway and pyroptosis markers was assessed. The functional impact on the alveolar epithelial barrier was then evaluated by treating epithelial cells with conditioned medium (CM) from these macrophages. The protective effect of MCC950 was further verified in a murine model of LPS-induced septic ALI. RESULTS: LPS stimulation potently activated the NLRP3 inflammasome in macrophages, leading to robust pyroptosis, as indicated by a significant increase in caspase-1 activity, lactate dehydrogenase (LDH) release, and the secretion of interleukin-1 β (IL-1β) and IL-18. Pre-treatment with MCC950 completely abolished this activation. CM from LPS-activated macrophages (LPS-CM) induced severe epithelial barrier injury, manifesting as a significant increase in epithelial cell death and monolayer permeability, and a marked downregulation of tight junction proteins zonula occludens-1 (ZO-1) and occludin. Crucially, all these aforementioned effects were significantly attenuated when epithelial cells were incubated with CM from macrophages pre-treated with MCC950, demonstrating that inhibiting macrophage pyroptosis preserves epithelial barrier integrity. In vivo, MCC950 administration markedly alleviated LPS-induced lung injury, reducing pulmonary edema and alveolar-capillary barrier leakage. CONCLUSIONS: Macrophage pyroptosis, activated via the LPS/NLRP3 pathway, is a pivotal mechanism in sepsis-induced alveolar epithelial barrier dysfunction. Pharmacological inhibition of this pathway represents a promising therapeutic strategy for ALI.