Ablation of Adenosine Monophosphate-Activated Protein Kinase α1 in Vascular Smooth Muscle Cells Promotes Diet-Induced Atherosclerotic Calcification In Vivo
Rationale: Atherosclerotic calcification is highly linked with plaque rapture. How calcification is regulated is poorly characterized.
Objective: We sought to determine the contributions of AMPK in atherosclerotic calcification.
Methods and Results: Aortic calcification was evaluated in aortic roots and brachiocephalic arteries of atherosclerotic prone ApoE-/- mice or in mice with dual deficiencies of ApoE and AMPKα isoforms in whole body (ApoE-/-/AMPKα1-/- and ApoE--/-/AMPKα2-/-) or vascular smooth muscle cell (VSMC)-specific or macrophage- specific knockout of AMPKα1 fed with western diet for 24 weeks. Genetic deficiency of AMPKα1 but not AMPKα2 promoted atherosclerotic calcification and the expression of Runt-related transcription factor (Runx2). Conversely, chronic administration of metformin, which activated AMPK, markedly reduced atherosclerotic calcification and Runx2 expression in ApoE-/- mice but had less effects in ApoE-/-/AMPKα1-/-mice. Furthermore, VSMC- but not macrophage-specific ablation of AMPKα1 promoted aortic calcification in vivo. Ablation of AMPKα1 in VSMC prevented Runx2 from proteasome degradation in parallel with aberrant osteoblastic differentiation of VSMC while AMPK activation promoted Runx2 post-translational modification by small ubiquitin-like modifier (SUMO, SUMOylation) which is associated with its instability. Mechanically, we found AMPKα1 directly phosphorylated protein inhibitor of activated STAT-1 (PIAS1), the SUMO E3-ligase of Runx2, at serine 510, to promote its SUMO E3-ligase activity. Finally, mutation of PIAS1 at serine 510 suppressed metformin-induced Runx2 SUMOylation, and subsequently prevented metformin's effect on reducing oxLDL-triggered Runx2 expression in VSMC.
Conclusions: AMPKα1 phosphorylated PIAS1 to promote Runx2 SUMOyalation and subsequently lead to its instability. AMPKα1 deficiency in VSMC increased Runx2 expression and promoted atherosclerotic calcification in vivo.
- atherosclerotic calcification
- osteoblastic differentiation
- AMP-activated protein kinase signal transduction
- SUMO ligase
- vascular smooth muscle
- Received January 5, 2016.
- Revision received May 21, 2016.
- Accepted June 2, 2016.