Inflammasome-Independent and Atypical Processing of IL-1β Contributes to Acid Aspiration-Induced Acute Lung Injury

• Published in: The Journal of immunology (1950) 2019-07, Vol.203 (1), p.236-246
• Main Authors: Mizushina, Yoshiko, Karasawa, Tadayoshi, Aizawa, Kenichi, Kimura, Hiroaki, Watanabe, Sachiko, Kamata, Ryo, Komada, Takanori, Mato, Naoko, Kasahara, Tadashi, Koyama, Shinichiro, Bando, Masashi, Hagiwara, Koichi, Takahashi, Masafumi
• Format: Article
• Language: English
• Subjects: Acute Lung Injury - immunology; Animals; Disease Models, Animal; Female; Humans; Inflammasomes - metabolism; Interleukin-1beta - genetics; Interleukin-1beta - metabolism; Mice; Mice, Inbred C57BL; Mice, Knockout; NLR Family, Pyrin Domain-Containing 3 Protein - genetics; NLR Family, Pyrin Domain-Containing 3 Protein - metabolism; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Pneumonia, Aspiration - immunology; Protein Processing, Post-Translational; Signal Transduction; THP-1 Cells
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.1900168

Inflammation plays a pivotal role in the pathophysiology of gastric aspiration-induced acute lung injury (ALI). However, its mechanism remains unclear. In this study, we investigated the role of NLRP3 inflammasome-driven IL-1β production in a mouse model of acid aspiration-induced inflammation and ALI. Acid aspiration-induced inflammatory responses and ALI in wild-type mice were significantly attenuated in IL-1β mice, but not NLRP3 mice. In vitro experiments revealed that severe acidic stress (pH 1.75) induced the processing of pro-IL-1β into its 18-kDa mature form (p18-IL-1β), which was different from the caspase-1-processed 17-kDa form (p17-IL-1β), in human THP-1 macrophages and primary murine macrophages. Deficiency of NLRP3 and caspase-1 had no effect on acidic stress-produced IL-1β. The production of IL-1β by severe acidic stress was prevented by inhibitors of serine proteases [4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride], but not of cysteine proteases (E-64), cathepsin G, or inflammasome. The cathepsin D inhibitor pepstatin A inhibited IL-1β production induced by mild acidic stress (pH 6.2) or lactic acid, but not severe acidic stress. Using mass spectrometry and processing-site mutants of pro-IL-1β, we identified D109 as a novel cleavage site of pro-IL-1β in response to severe acidic stress and calculated the theoretical molecular mass of the mature form to be 18.2 kDa. The bioactivity of acidic stress-produced IL-1β was confirmed by its ability to promote p38 phosphorylation and chemokine upregulation in alveolar epithelial cells. These findings demonstrate a novel mechanism of acid-induced IL-1β production and inflammation independent of NLRP3 inflammasome and provide new insights into the therapeutic strategies for aspiration pneumonitis and ALI.