Diabetic hyperglycaemia activates CaMKII and arrhythmias by O-linked glycosylation.

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is an enzyme with important regulatory functions in the heart and brain, and its chronic activation can be pathological. CaMKII activation is seen in heart failure, and can directly induce pathological changes in ion channels, Ca(2+) handling and gene transcription. Here, in human, rat and mouse, we identify a novel mechanism linking CaMKII and hyperglycaemic signalling in diabetes mellitus, which is a key risk factor for heart and neurodegenerative diseases. Acute hyperglycaemia causes covalent modification of CaMKII by O-linked N-acetylglucosamine (O-GlcNAc). O-GlcNAc modification of CaMKII at Ser 279 activates CaMKII autonomously, creating molecular memory even after Ca(2+) concentration declines. O-GlcNAc-modified CaMKII is increased in the heart and brain of diabetic humans and rats. In cardiomyocytes, increased glucose concentration significantly enhances CaMKII-dependent activation of spontaneous sarcoplasmic reticulum Ca(2+) release events that can contribute to cardiac mechanical dysfunction and arrhythmias. These effects were prevented by pharmacological inhibition of O-GlcNAc signalling or genetic ablation of CaMKIIδ. In intact perfused hearts, arrhythmias were aggravated by increased glucose concentration through O-GlcNAc- and CaMKII-dependent pathways. In diabetic animals, acute blockade of O-GlcNAc inhibited arrhythmogenesis. Thus, O-GlcNAc modification of CaMKII is a novel signalling event in pathways that may contribute critically to cardiac and neuronal pathophysiology in diabetes and other diseases.

Acute ß-adrenergic activation triggers nuclear import of histone deacetylase 5 and delays G(q)-induced transcriptional activation.

During hemodynamic stress, catecholamines and neurohumoral stimuli may induce co-activation of G(q)-coupled receptors and ß-adrenergic receptors (ß-AR), leading to cardiac remodeling. Dynamic regulation of histone deacetylase 5 (HDAC5), a transcriptional repressor, is crucial during stress signaling due to its role in epigenetic control of fetal gene markers. Little is known about its regulation during acute and chronic ß-AR stimulation and its cross-interaction with G(q) signaling in adult cardiac myocytes. Here, we evaluate the potential cross-talk between G(q)-driven and ß-AR mediated signaling at the level of nucleocytoplasmic shuttling of HDAC5. We show the translocation of GFP-tagged wild type HDAC5 or mutants (S279A and S279D) in response to ß-AR or G(q) agonists. Isoproterenol (ISO) or PKA activation results in strong nuclear accumulation of HDAC5 in contrast to nuclear export driven by Ca(2+)-calmodulin protein kinase II and protein kinase D. Moreover, nuclear accumulation of HDAC5 under acute ISO/PKA signaling is dependent on phosphorylation of Ser-279 and can block subsequent G(q)-mediated nuclear HDAC5 export. Intriguingly, the attenuation of G(q)-induced export is abolished after chronic PKA activation, yet nuclear HDAC5 remains elevated. Last, the effect of chronic ß-AR signaling on HDAC5 translocation was examined in adult myocytes from a rabbit model of heart failure, where ISO-induced nuclear import is ablated, but G(q)-agonist mediated export is preserved. Acute ß-AR/PKA activation protects against hypertrophic signaling by delaying G(q)-mediated transcriptional activation. This serves as a key physiological control switch before allowing genetic reprogramming via HDAC5 nuclear export during more severe stress, such as heart failure.