PIMT suppresses endothelial activation and vascular inflammation through methylation of TRAF6

As a repair enzyme, protein L-isoaspartyl O-methyltransferase (PIMT) methylates and converts isoaspartyl residues (isoAsp) back to conventional forms to avoid protein damage during aging and stress responses. This study aims to investigate the pathological significance of PIMT in vascular inflammation. Herein, we show that PIMT is highly expressed in lung endothelial cells (ECs), and its reduction significantly exacerbates pulmonary inflammation in a murine model of acute lung injury (ALI). Mechanistically, we identify tumor necrosis factor receptor-associated factor 6 (TRAF6) as a substrate of PIMT. PIMT-mediated methylation of TRAF6 inhibits TRAF6 oligomerization, autoubiquitination, and LPS-induced NF-κB transactivation in ECs. Importantly, in addition to transcriptionally attenuating expression of adhesion molecules, PIMT post-translationally impedes site specific N-glycosylation of intercellular adhesion molecule-1 (ICAM-1), which leads to an increased protein degradation of ICAM-1 and a subsequent inhibition of EC interaction with immune cells during inflammatory process. Our results for the first time identify PIMT-mediated protein O-methylation as a key post-translational mechanism in controlling vascular inflammation, and suggest that PIMT may represent a novel therapeutic target in inflammatory vascular diseases.