Abstract 10031: Smooth Muscle-Specific OGT Deletion Inhibits Vascular Calcification in Diabetic Mice
Objective: Vascular calcification progresses rapidly in patients with diabetes mellitus and increases risk of cardiovascular events and death. We and others have demonstrated vascular calcification in experimental diabetic models. We found that increased vascular calcification was associated with elevated protein O-linked GlcNAc modification (O-GlcNAcylation) in human diabetic arteries, and in low-dose streptozotocin (STZ)-induced and Akita mutant diabetic mice. The present study determined the effects of inhibition of O-GlcNAc transferase (OGT), the enzyme that catalyzes O-GlcNAcylation, on vascular calcification in diabetic mice.
Methods and Results: We generated smooth muscle cell (SMC)-specific OGT deletion mice (ΔOGTSMC) by crossing OGT floxed C57BL/6 mice with SMC-specific Cre transgenic mice (SMMHCCre). Cre-mediated OGT deletion was induced by tamoxifen injection in mice at 8 weeks of age. SMC-specific OGT deletion did not affect blood glucose, but significantly inhibited protein O-GlcNAcylation exclusively in SMC. STZ-induced vascular calcification was markedly inhibited in the ΔOGTSMC mice. Furthermore, the ΔOGTSMC mice were bred into the Akita mutant background. Similar to the STZ-induced diabetic model, vascular calcification was significantly inhibited in the ΔOGTSMC Akita mutant mice. At the molecular level, OGT deletion decreased expression of Runx2, a key regulator of VSMC osteogenic differentiation, in the diabetic vasculature. Activation of AKT, an important upstream signal for Runx2 upregulation, was significantly inhibited by OGT deletion. Mechanistic studies demonstrated that glucose-induced activation of AKT at S473 was blunted by OGT deletion. In addition, we identified two new O-GlcNAcylation sites on AKT, at T430 and T479, were critical for AKT activation, Runx2 upregulation and VSMC calcification.
Conclusion: We have demonstrated a crucial role for vascular O-GlcNAcylation and OGT in regulating diabetic vascular calcification, and identified a new mechanism of OGT-regulated AKT O-GlcNAcylation in promoting SMC calcification. Our studies have uncovered novel mechanisms linking glucose metabolism to vascular dysfunction and revealed therapeutic targets for diabetic vascular calcification.
- © 2013 by American Heart Association, Inc.