Abstract 12458: Protein L-isoaspartyl O-methyltransferase Attenuates Endothelial Activation Through Inhibitory Interaction With TRAF6 and ICAM1

Abstract

Introduction: Endothelial activation provokes expression of cell surface adhesion molecules to facilitate circulating leukocyte diapedesis, which demands rigorous surveillance to prevent excessive inflammation response and host damage. As a repair enzyme, protein L-isoaspartyl O-methyltransferase (PIMT) methylates and converts isoaspartyl (isoAsp) residuals back to conventional form to avoid protein damage and aging. However, the role of PIMT in vascular homeostasis remains to be delineated. Methods and Results: Murine acute lung injury (ALI) model was deployed to investigate the significance of PIMT in endothelial activation and vascular inflammation. Results showed that mice harboring heterozygous deletion of PIMT displayed exacerbated pulmonary vascular inflammation. Ectopic overexpression of PIMT protected endothelial cells against endotoxin stimulated endothelial activation, as characterized by attenuated expression of inflammatory cytokines, chemokines, cell adhesion molecules and monocytic adherence to activated endothelial cells. Mechanistically, we found that PIMT inhibits lipopolysaccharide (LPS)-induced endothelial NF-κB transactivation. Tumor necrosis factor receptor-associated factor 6 (TRAF6) was identified as a dynamic binding partner and substrate of PIMT in regulating NF-κB signaling. PIMT catalyzed methylation at an asparagine derived isoAsp residual of TRAF6 directly prevented its oligomerization and auto-ubiquitination. Strikingly, we also found that PIMT specifically impeded N-glycosylation at multiple sites of endothelial intercellular adhesion molecule 1 (ICAM1). The hypo-glycosylated ICAM1 elicited impaired interaction with cell skeletal and reduced stability, which further diminished endothelial activation. Conclusions: PIMT negatively modulates endothelial activation through restricting activation of TRAF6 and inhibiting N-glycosylation of adhesion molecules. Our study provides a novel insight into the role of protein O-methylation in regulating endothelial inflammation and suggest that targeting PIMT may have potential therapeutic applications in treating inflammatory vascular disorders.