Phosphorylation of C/EBP Homologous Protein (CHOP) 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 C/EBP homologous protein (CHOP), 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 AMP-activated kinase (AMPK) regulates cellular CHOP accumulation and (2) whole-body Ampk deletion leads to neointimal disruption.
Methods and Results: In isolated or cultured macrophages, Ampkα1 deletion markedly increased apoptosis and CHOP, whereas pharmacological activation of AMPK dramatically reduced CHOP protein level via promoting CHOP degradation by proteasome. In addition, co-transfection of Chop-specific siRNA, but not control siRNA, markedly reduced apoptosis in macrophages transfected with Ampkα1-specific siRNA. Mechanistically, AMPKα1 was found to co-immunoprecipitate 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 Ampkα1 but not Ampkα 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 AMPKα1 mediates CHOP ubiquitination and proteasomal degradation in macrophages by promoting the phosphorylation of CHOP at serine 30. We conclude that AMPKα1 might be a valid therapeutic target in preventing atherosclerotic vulnerable plaque formation.
- Received July 4, 2016.
- Revision received August 31, 2016.
- Accepted September 19, 2016.