Date on Master's Thesis/Doctoral Dissertation


Document Type

Doctoral Dissertation

Degree Name

Ph. D.


Physiology and Biophysics

Committee Chair

Jones, Steven Paul

Author's Keywords

Myocardial ischemia; O-GlcNAc; Oxidative stress; Endoplasmic reticulum stress


Coronary heart disease


O -linked ß-N-acetylglucosamine ( O -GlcNAc) is an inducible, dynamically cycling, and reversible post-translational modification of serine/threonine amino acid residues of nucleocytoplasmic and mitochondrial proteins. O -GlcNAc transferase (OGT) adds, while O -GlcNAcase (GCA) removes O -GlcNAc from proteins. Albeit being a recruitable stress-induced signal in other tissues, the role of O -GlcNAc in the heart is unknown. Therefore, we hypothesized that O -GlcNAc is recruited in the heart during acute stress, and enhanced O-GlcNAc is cardioprotective. Subjecting neonatal rat cardiac myocytes (NRCMs) to hypoxia, or mice to myocardial ischemia reduced O-GlcNAc signaling. Augmented O-GlcNAc signaling attenuated, while diminished O-GlcNAc signaling exacerbated post-hypoxic cardiomyocyte death. To determine how O-GlcNAc protects, we identified numerous proteins including voltage dependent anionic channel (VDAC) to be O-GlcNAc-modified via mass spectrometry and immunoprecipitation. Since VDAC is a putative member of the mitochondrial permeability transition pore (mPTP), we hypothesized that one mechanism of O-GlcNAc-mediated cardioprotection is by blocking mPTP formation. We ascertained if O-GlcNAc signaling affects key players in ischemic/hypoxic injury, Ca 2+ overload and oxidative stress, both inducers of mPTP. Enhanced O-GlcNAc significantly mitigated, while, reduced O-GlcNAc aggravated post-hypoxic Ca 2+ overload and ROS generation. Furthermore, augmented O-GlcNAc reduced, while, diminished O-GlcNAc sensitized mitochondria to mPTP formation according to Ca 2+ -induced swelling. Since mPTP formation induces loss of mitochondrial membrane potential (?? m ), we evaluated whether O-GlcNAc signaling affects post-hypoxic ?? m recovery. Enhanced O-GlcNAc significantly improved, while reduced O-GlcNAc minimized post-hypoxic ?? m recovery. Because ER stress contributes to ischemia-reperfusion injury, we evaluated whether inhibiting maladaptive ER stress reponse maybe another mechanism through which O-GlcNAc signaling cardioprotects. Indeed, augmented O-GlcNAc reduced maladaptive ER stress response according to diminished CHOP levels and PI positivity. To determine if such in vitro protection could be translated in vivo , we augmented O-GlcNAc levels (with PUGNAc) in adult, wild-type C57BL6 mice, subjected them to 40 minutes of left anterior descending coronary artery ligation, then reperfused for 24 hours, and assessed infarct size. Augmented O-GlcNAc levels significantly decreased infarct size. We conclude that O-GlcNAc mediates cardioprotection in vitro and in vivo via attenuating maladaptive ER stress response and recruitment of early events in the mitochondria! death pathway leading to mPTP formation.