Brd4 inhibition ameliorates Pyocyanin-mediated macrophage dysfunction via transcriptional repression of reactive oxygen and nitrogen free radical pathways.

Macrophages play critical roles in the first-line immune defense against airway infections caused by Pseudomonas aeruginosa (PA). The redox-active phenazine-pyocyanin (PCN), as one of the most essential virulence factors, facilities PA-related infection via a wide spectrum of cellular oxidative damages. However, little is known for PCN cytotoxicity in macrophages. In this study, besides showing PCN-mediated reactive oxygen species (ROS) indeed involved in macrophage viability and function impairment, we at the first time demonstrated a novel role of reactive nitrogen species (RNS) pathway causing cellular damage in PCN-challenged macrophages. Using small molecule inhibitor JQ1 targeting Bromodomain and extra-terminal family proteins, we showed restrained iNOS-dependent nitric oxide (NO) production correlated with abolished Brd4 recruitment to the NOS2 (encoding inducible nitric oxide synthase-iNOS) promoter. Application of JQ1 diminished PCN-mediated peroxynitrite (ONOO) that followed ROS and NO induction, restored macrophage survival and bacteria clearance as well as repressed local inflammation in PA/PCN-challenged mice lungs. Our results uncover a novel link between PCN-mediated macrophage dysfunction and reactive free radicals that rely on Brd4-dependent transcription modulation of multiple stress-response genes, suggesting Brd4 could be a promising therapeutic target in treating PA-related lung infection.