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

Abstract 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.