CaMKII Serine 280 O-GlcNAcylation Links Diabetic Hyperglycemia to Proarrhythmia.

Rationale: Diabetic hyperglycemia is associated with cardiac dysfunction and increased arrhythmia risk, and calcium/calmodulin-dependent protein kinase II (CaMKII) function has been implicated. CaMKII activity is promoted by both oxidation and O linked β-N-acetylglucosamine (O GlcNAc) of known CaMKII sites. Objective: To investigate which post-translational modifications occur in human diabetic hearts and how they alter electrophysiological and Ca2+ handling properties in hyperglycemia. Methods and Results: We assessed echocardiography, electrophysiology, Ca2+-handling, and protein expression in site-specific CaMKII mutant mice (O GlcNAc-resistant S280A and oxidation-resistant MM281/2VV knock-ins, and global and cardiac-specific knockouts), in myocytes subjected to acute hyperglycemia and angiotensin II (Ang-II) and mice after streptozotocin injections (to induce diabetes). Human patients with diabetes exhibit elevated CaMKII O GlcNAcylation but not oxidation. In mice, acute hyperglycemia increased spontaneous diastolic Ca2+ sparks and waves and arrhythmogenic action potential changes (prolongation, alternans and delayed afterdepolarizations), all of which required CaMKII-S280 O GlcNAcylation. Ang-II effects were dependent on NADPH oxidase 2 (NOX2)-mediated CaMKII MM281/2 oxidation. Diabetes led to much greater Ca2+ leak, RyR2 S2814 phosphorylation, electrophysiological remodeling, and increased susceptibility to in vivo arrhythmias, requiring CaMKII activation, predominantly via S280 O GlcNAcylation and less via MM281/2 oxidation. These effects were present in myocytes at normal glucose, but were exacerbated with the in-vivo high circulating glucose. Phospholamban (PLB) O-GlcNAcylation was increased and coincided with reduced PLB S16 phosphorylation in diabetes. Dantrolene, that reverses CaMKII-dependent proarrhythmic RyR-mediated Ca2+ leak, also prevented hyperglycemia-induced APD prolongation and delayed afterdepolarizations. Conclusions: We found that CaMKII-S280 O GlcNAcylation is required for increased arrhythmia susceptibility in diabetic hyperglycemia, which can be worsened by an additional angiotensin II-NOX2-CaMKII MM281/2 oxidation pathway. CaMKII-dependent RyR2 S2814 phosphorylation markedly increases proarrhythmic Ca2+ leak and PLB O-GlcNAcylation may limit SR Ca2+ reuptake, leading to impaired excitation-contraction coupling and arrhythmogenesis in diabetic hyperglycemia.