Thrombospondin-1 restricts interleukin-36g-mediated neutrophilic inflammation during pseudomonas aeruginosa pulmonary infection

Abstract

Interleukin-36g (IL-36g), a member of the IL-1 cytokine superfamily, amplifies lung inflammation and impairs host defense during acute pulmonary Pseudomonas aeruginosa infection. To be fully active, IL-36g is cleaved at its N-terminal region by pro-teases such as neutrophil elastase (NE) and cathepsin S (CatS). However, it remains unclear whether limiting extracellular proteolysis restrains the inflammatory cascade trig-gered by IL-36g during P. aeruginosa infection. Thrombospondin-1 (TSP-1) is a matricellu-lar protein with inhibitory activity against NE and the pathogen-secreted Pseudomonas elastase LasB—both proteases implicated in amplifying inflammation. We hypothesized that TSP-1 tempers the inflammatory response during lung P. aeruginosa infection by in-hibiting the proteolytic environment required for IL-36g activation. Compared to wild-type (WT) mice, TSP-1-deficient (Thbs12/2) mice exhibited a hyperinflammatory response in the lungs during P. aeruginosa infection, with increased cytokine production and an unrestrained extracellular proteolytic environment characterized by higher free NE and LasB, but not CatS activity. LasB cleaved IL-36g proximally to M19 at a cleavage site distinct from those generated by NE and CatS, which cleave IL-36g proximally to Y16 and S18, respectively. N-terminal truncation experiments in silico predicted that the M19 and the S18 isoforms bind the IL-36R complex almost identically. IL-36g neutralization amelio-rated the hyperinflammatory response and improved lung immunity in Thbs12/2 mice during P. aeruginosa infection. Moreover, administration of cleaved IL-36g induced cyto-kine production and neutrophil recruitment and activation that was accentuated in Thbs12/2 mice lungs. Collectively, our data show that TSP-1 regulates lung neutrophilic inflammation and facilitates host defense by restraining the extracellular proteolytic environment required for IL-36g activation. IMPORTANCE Pseudomonas aeruginosa pulmonary infection can lead to exaggerated neutrophilic inflammation and tissue destruction, yet host factors that regulate the neutrophilic response are not fully known. IL-36g is a proinflammatory cytokine that dramatically increases in bioactivity following N-terminal processing by proteases. Here, we demonstrate that thrombospondin-1, a host matricellular protein, limits N-terminal processing of IL-36g by neutrophil elastase and the Pseudomonas aerugi-nosa-secreted protease LasB. Thrombospondin-1-deficient mice (Thbs12/2) exhibit a hyperinflammatory response following infection. Whereas IL-36g neutralization reduces inflammatory cytokine production, limits neutrophil activation, and improves host defense in Thbs12/2 mice, cleaved IL-36g administration amplifies neutrophilic inflammation in Thbs12/2 mice. Our findings indicate that thrombospondin-1 guards against feed-forward neutrophilic inflammation mediated by IL-36g in the lung by restraining the extracellular proteolytic environment.