Citrullination of NF‐κB p65 by PAD2 as a Novel Therapeutic Target for Modulating Macrophage Polarization in Acute Lung Injury

Mediating protein citrullination, peptidyl arginine deiminase 2 (PAD2) has recently been reported to influence macrophage phenotypes. However, the mechanisms of PAD2 on macrophage function in Pseudomonas aeruginosa (PA)-induced acute lung injury syndrome (ALI) remains unclear. Utilizing single-cell RNA sequencing and mass spectrometry-based proteomics, a new citrullination site at arginine 171 (R171) is discovered within nuclear factor- κB (NF-κB) p65 catalyzed by PAD2, which modulates PAD2-NF-κB p65-importin α3 pathway and its downstream M1/M2 macrophage polarization. Building on these findings, a cell-specific targeted therapeutic strategy using gold nanoparticles (AuNPs) conjugated with a novel PAD2 inhibitor, AFM41a, and an intercellular adhesion molecule-1 (ICAM-1) antibody is developed. This approach enables the selective delivery of the inhibitor to M1-polarized macrophages in the PA-infected alveolar niche. In vivo, this nanomedicine reduces excessive inflammation and promotes M1-to-M2 polarization to inhibit ALI. This study highlights the role of PAD2-mediated citrullination in macrophage polarization and introduces a promising nanoparticle-based therapy for PA-induced ALI.