USP4 controls neutrophil spreading through stabilising IQGAP1 during lung inflammation

Background Protein availability critically influences innate immune reactivity and the extent of immune-mediated tissue injury. A key unresolved question is how specific protein homeostasis networks within immune cells such as neutrophils can be modulated to mitigate the detrimental outcomes of acute inflammation. Methods We established an acute lung injury (ALI) model in immune-specific ubiquitin-specific peptidase 4 (USP4) knockout chimeric (BM-Usp4 −/− ) and control (BM-WT) mice. Using cytometry by time-of-flight (CyTOF) mass cytometry, quantitative proteomics, immunoprecipitation-mass spectrometry and neutrophil functional assays, we elucidated the molecular mechanism of USP4 in a specific neutrophil migratory behaviour—spreading—as well as the therapeutic potential of USP4 inhibitors in acute respiratory distress syndrome (ARDS). Results USP4 expression was upregulated in blood and pulmonary leucocytes from patients with ARDS and ALI mice (p=0.049, p=0.0086), but downregulated in mouse lung parenchyma (lipopolysaccharide vs control, p=0.0019). BM-Usp4 −/− mice exhibited attenuated lung injury and neutrophil infiltration (in lung tissue and bronchoalveolar lavage fluid, p