Citrullination of VDAC3 by PAD2 restricts mitochondrial metabolism and suppresses macrophage reprogramming in sepsis

Sepsis is a life-threatening inflammatory disorder characterized by immune dysregulation and organ failure, and while peptidylarginine deiminase-2 (PAD2) regulates immune responses via citrullination, its role in immunometabolism remains unclear. Here we identify a PAD2-dependent mechanism that impairs mitochondrial glutamine metabolism and macrophage polarization during sepsis. Through single-cell RNA sequencing of bronchoalveolar lavage fluid from septic mice, we found that Pad2 ^-/- promotes M2 macrophage polarization, reduces lung injury, and improves survival. Using mass spectrometry-based citrullinomics, we identified voltage-dependent anion channel-3 (VDAC3) as a PAD2 substrate, and further demonstrated that PAD2-mediated citrullination at residue R252 suppresses glutamine transport and α-ketoglutarate (α-KG) production, thereby impairing oxidative phosphorylation (OXPHOS) and M2 reprogramming. Notably, substitution of R252 with alanine recapitulated Pad2 ^-/-phenotypes, and consistent with this, Pad2 ^-/- mice exhibited enhanced OXPHOS, attenuated inflammation, and improved outcomes in a Pseudomonas aeruginosa-induced model of sepsis and lung injury. Collectively, these findings establish the PAD2-VDAC3-glutamine axis as a key immunometabolic checkpoint that links post-translational modification to mitochondrial metabolism and macrophage function, suggesting that targeting this pathway may offer a promising strategy to restore immune balance in sepsis.