All ETDs from UAB

Advisory Committee Chair

Yabing Chen

Advisory Committee Members

Victor Darley-Usmar

John Chatham

Jeonga Kim

Jianbo Wang

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Vascular calcification is prevalent in patients of diabetes mellitus, which represents an independent risk factor that positively correlated with morbidity and mortality in these patients. Vascular calcification is now recognized as a cell-regulated process of osteogenic differentiation of vascular smooth muscle cells (VSMC) in response to stress, such as hyperglycemia and oxidative stress. Both hyperglycemia and oxidative stress have been shown to induce protein modification by O-linked ß-N-acetylglucosamine modification (O-GlcNAcylation), which is also elevated in diabetes. The present studies aimed to determine the effects of protein O-GlcNAcylation on vascular calcification in diabetes, and uncover the underlying molecular mechanisms. With the use of an array of comprehensive pharmacologic and genetic approaches, including a novel SMC-specific OGT deletion mouse model, that specifically targeting OGT or OGA, we have demonstrated a causative effect of increased O-GlcNAcylation on VSMC calcification in vitro and diabetic vascular calcification in vivo. Mechanistically, increased O-GlcNAcylation promotes VSMC calcification via AKT activation that leads to upregulation of Runx2, the osteogenic transcript factor that we have previously determined to be an essential and sufficient regulator for VSMC calcification. At the molecular level, we have demonstrated direct modifications of AKT and Runx2 by O-GlcNAcylation leading to upregulation of Runx2 and VSMC calcification. The novel and unique O-GlcNAc modifications on AKT at two sites, T430 and T479, are critical for AKT phosphorylation at S473 leading to Runx2 upregualtion and VSMC calcification. Site-directed mutagenesis studies suggested that AKT O-GlcNAcylation at T430 and T479 may facilitate its interaction with mTOR complex 2 and subsequent phosphorylation by the kinase at S473. Similarly, direct O-GlcNAc modification on Runx2 at T412/S413 promoted its phosphorylation and binding to the BMP-regulated Smads that are known to be important for the osteogenic function of Runx2. Our studies have determined a new causative link between chronic increases in vascular O-GlcNAcylation and vascular calcification in diabetes and uncovered a novel mechanism underlying the regulation of AKT activation and Runx2 transactivity by their O-GlcNAcylation. These results have provided molecular insights into targeting O-GlcNAcylation and specifically O-GlcNAcylation of AKT/Runx2 signaling as potential therapy for vascular calcification in diabetes.

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