Phosphorylation of CHOP (C/EBP Homologous Protein) by the AMP-Activated Protein Kinase Alpha 1 in Macrophages Promotes CHOP Degradation and Reduces Injury-Induced Neointimal Disruption In Vivo

Rationale: Elevated levels of CHOP (C/EBP homologous protein), a member of the C/EBP transcription factor family, in advanced atherosclerotic plaques is reported to be associated with atherosclerotic plaque rupture in humans. However, the molecular mechanism by which CHOP accumulation occurs is poorly defined. Objective: The aim of this study was to investigate if (1) macrophage AMPK (AMP-activated protein kinase) regulates cellular CHOP accumulation and (2) whole-body Ampk deletion leads to neointimal disruption. Methods and Results: In isolated or cultured macrophages, Ampk1 deletion markedly increased apoptosis and CHOP, whereas pharmacological activation of AMPK dramatically reduced CHOP protein level via promoting CHOP degradation by proteasome. In addition, cotransfection of Chop-specific siRNA, but not control siRNA, markedly reduced apoptosis in macrophages transfected with Ampk1-specific siRNA. Mechanistically, AMPK1 was found to coimmunoprecipitate with CHOP and phosphorylate CHOP at serine 30. Furthermore, serine 30 phosphorylation of CHOP triggered its ubiquitination and proteasomal degradation. In a mouse model of plaque stability, deletion of Ampk1 but not Ampk2 promoted injury-induced neointimal disruption. This was paralleled by increased CHOP expression and apoptosis in vivo. Finally, transfection of Chop-specific siRNA but not control siRNA reduced both CHOP level and injury-induced neointimal disruption in vivo. Conclusions: Our results indicate that AMPK1 mediates CHOP ubiquitination and proteasomal degradation in macrophages by promoting the phosphorylation of CHOP at serine 30. We conclude that AMPK1 might be a valid therapeutic target in preventing atherosclerotic vulnerable plaque formation.