Abstract 217: Metabolic Survival Signal Rescues Cardiac Myocytes from ER Stress-Induced Death
The hexosamine biosynthetic pathway supplies the monosaccharide donor for a unique, metabolic post-translational modification involving the beta-O-linkage of N-acetylglucosamine (O-GlcNAc) to Ser/Thr sites on proteins. We recently showed augmentation of such signaling can rescue cardiomyocytes from lethal injury. Because both O-GlcNAc signaling and ER stress are implicated in diabetes and heart failure, we hypothesized that they can interact and that O-GlcNAc signaling could serve as an acute survival mechanism in the context of ER stress. We initially performed dose (up to 1 ug/mL) and time course (up to 24 h) studies with two different inducers of ER stress (brefeldin A - BfA; tunicamycin) in neonatal rat cardiac myocytes (n = 4/group). There was time- and dose-dependent augmentation of O-GlcNAc signaling following induction of ER stress. To evaluate whether such augmentation in O-GlcNAc signaling was beneficial, we used an inhibitor (PUGNAc) of the enzyme that removes O-GlcNAc from proteins (i.e. O-GlcNAcase) and observed additional elevation in O-GlcNAc levels and significant (p < 0.05) attenuation of ER stress-induced cell death (14 +/− 7% in BfA + PUGNAc vs 32 +/− 9% in BfA alone), according to PI positivity (n = 6/group). Next, we adenovirally (Ad) overexpressed the enzyme that adds O-GlcNAc to proteins (OGT), resulting in augmentation of O-GlcNAc levels. AdOGT significantly (p<0.05) attenuated ER stress-induced cell death (38 +/− 3% in BfA + AdOGT vs 47 +/− 3% in BfA + AdGFP), according to PI positivity (n = 6/group). Immunoblot analyses (n = 4/group) revealed augmentation of O-GlcNAc signaling repressed activation of several ER stress-induced death proteins (e.g. caspase 12, PARP, and CHOP). Augmented O-GlcNAc signaling promotes cell survival during lethal ER stress. Although alterations in O-GlcNAc signaling and ER stress both occur in heart failure and diabetes, we provide direct evidence that O-GlcNAc signaling and ER stress significantly interact in the absence of the complex pathologies of heart failure and diabetes. Thus, these results provide a novel framework for potential interaction between O-GlcNAc signaling and ER stress in diabetes and heart failure.
This research has received full or partial funding support from the American Heart Association, AHA National Center.