Background: Heart failure is a leading cause of death worldwide and is associated with the rising prevalence of obesity, hypertension and diabetes. O -GlcNAcylation is a post-translational modification of intracellular proteins and serves as a metabolic rheostat for cellular stress. The total levels of O -GlcNAcylation are determined by nutrient and metabolic flux, in addition to the net activity of two enzymes, O -GlcNAc transferase (OGT) and O -GlcNAcase (OGA). Failing myocardium is marked by increased O -GlcNAcylation, but it is unknown if excessive O -GlcNAcylation contributes to cardiomyopathy and heart failure. Methods: We developed two new transgenic mouse models with myocardial overexpression of OGT and OGA to control O -GlcNAcylation independent of pathological stress. Results: We found that OGT transgenic hearts showed increased O -GlcNAcylation, and developed severe dilated cardiomyopathy, ventricular arrhythmias and premature death. In contrast, OGA transgenic hearts had lower O -GlcNAcylation but identical cardiac function to wild type littermate controls. Additionally, OGA transgenic hearts were resistant to pathological stress induced by pressure overload with attenuated myocardial O -GlcNAcylation levels after stress and decreased pathological hypertrophy compared to wild type controls. Interbreeding OGT with OGA transgenic mice rescued cardiomyopathy and premature death, despite persistent elevation of myocardial OGT. Transcriptomic and functional studies revealed disrupted mitochondrial energetics with impairment of complex I activity in hearts from OGT transgenic mice. Complex I activity was rescued by OGA transgenic interbreeding, suggesting an important role for mitochondrial complex I in O -GlcNAc mediated cardiac pathology. Conclusions: Our data provide evidence that excessive O -GlcNAcylation causes cardiomyopathy, at least in part, due to defective energetics. Enhanced OGA activity is well tolerated and attenuation of O -GlcNAcylation is beneficial against pressure overload induced pathologic remodeling and heart failure. These findings suggest attenuation of excessive O -GlcNAcylation may represent a novel therapeutic approach for cardiomyopathy.

Despite the clear association between myocardial injury, heart failure and depressed myocardial energetics, little is known about upstream signals responsible for remodeling myocardial metabolism after pathological stress. Here, we report increased mitochondrial calmodulin kinase II (CaMKII) activation and left ventricular dilation in mice one week after myocardial infarction (MI) surgery. By contrast, mice with genetic mitochondrial CaMKII inhibition are protected from left ventricular dilation and dysfunction after MI. Mice with myocardial and mitochondrial CaMKII overexpression (mtCaMKII) have severe dilated cardiomyopathy and decreased ATP that causes elevated cytoplasmic resting (diastolic) Ca 2+ concentration and reduced mechanical performance. We map a metabolic pathway that rescues disease phenotypes in mtCaMKII mice, providing insights into physiological and pathological metabolic consequences of CaMKII signaling in mitochondria. Our findings suggest myocardial dilation, a disease phenotype lacking specific therapies, can be prevented by targeted replacement of mitochondrial creatine kinase or mitochondrial-targeted CaMKII inhibition.

CaMKII (the multifunctional Ca2+ and calmodulin-dependent protein kinase II) is a highly validated signal for promoting a variety of common diseases, particularly in the cardiovascular system. Despite substantial amounts of convincing preclinical data, CaMKII inhibitors have yet to emerge in clinical practice. Therapeutic inhibition is challenged by the diversity of CaMKII isoforms and splice variants and by physiological CaMKII activity that contributes to learning and memory. Thus, uncoupling the harmful and beneficial aspects of CaMKII will be paramount to developing effective therapies. In the last decade, several targeting strategies have emerged, including small molecules, peptides, and nucleotides, which hold promise in discriminating pathological from physiological CaMKII activity. Here we review the cellular and molecular biology of CaMKII, discuss its role in physiological and pathological signaling, and consider new findings and approaches for developing CaMKII therapeutics. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 63 is January 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.