Myocardial hypertrophy occurs in response to multiple stressors such as hypertension or aortic stenosis. This phenomenon is initially adaptive, but frequently evolves into heart failure. Prevention of heart failure and promotion of functional compensation represent important clinical goals. However, the molecular mechanisms affecting cardiac compensation during hypertrophy remain elusive. Recent studies have found that the post- translational modification of serine/threonine residues by O-linked -N-acetylglucosamine (O-GlcNAc) increases during hypertrophy and heart failure; a process termed O-GlcNAcylation. However, several obstacles have hindered our understanding of O-GlcNAc signaling during cardiac hypertrophy. Generation of the O-GlcNAc moiety depends on shuttling glucose into an accessary pathway from glycolysis, which raises the possibility that the metabolic shifts during hypertrophy regulate O-GlcNAc signaling. However, the metabolic pathway that generates the O-GlcNAc moiety is very poorly understood and there is little data about synthesis of the O-GlcNAc moiety in the intact heart, let alone during the metabolic shifts present during hypertrophy. We also have an incomplete understanding of the basic functional effects of O-GlcNAc modifications of proteins during cardiac hypertrophy. Experimental models of heart disease demonstrate both adaptive and detrimental outcomes by elevating global O-GlcNAc levels. Technical limitations in identifying and quantifying specific O-GlcNAc protein modification sites, termed here the O-GlcNAcome, have limited our understanding of the mechanisms regulating O-GlcNAc's functional effects in the heart. However, the O- GlcNAcome has been described by our collaborators in other organs. Using GCMS, LCMS and HPLC, we will test our central working hypothesis that changes in substrate metabolism during hypertrophy affect functional compensation through O-GlcNAc signaling. Thus, the aims of this proposal are to: a) test the hypothesis that metabolic perturbations during hypertrophy regulate cardiac function by modifying global O-GlcNAcylation; b) test the hypothesis that global O-GlcNAcylation promotes successful adaptation to early pressure overload, but that prolonged global O-GlcNAcylation contributes to late cardiac dysfunction; and c) test the hypothesis that the observed and sometimes paradoxical differences in functional outcomes from global O-GlcNAcylation are due to specificity within the O-GlcNAcome. This project specifically addresses key deficits in our current knowledge of O-GlcNAc's regulation, functional effects and specifically modified proteins during cardiac hypertrophy. The resulting information will allow us to rationally develop strategies for therapeutically modulating O-GlcNAcylation.