The role of protein O-GlcNAcylation in diabetic cardiomyopathy.

It is well established that diabetes markedly increases the risk of multiple types of heart disease including heart failure. However, despite substantial improvements in the treatment of heart failure in recent decades the relative increased risk associated with diabetes remains unchanged. There is increasing appreciation of the importance of the post translational modification by O-linked-N-acetylglucosamine (O-GlcNAc) of serine and threonine residues on proteins in regulating cardiomyocyte function and mediating stress responses.

Acute increase of protein O-GlcNAcylation in mice leads to transcriptome changes in the brain opposite to what is observed in Alzheimer's Disease.

Enhancing protein O-GlcNAcylation by pharmacological inhibition of the enzyme O-GlcNAcase (OGA) is explored as a strategy to decrease tau and amyloid-beta phosphorylation, aggregation, and pathology in Alzheimer's disease (AD). There is still more to be learned about the impact of enhancing global protein O-GlcNAcylation, which is important for understanding the mechanistic path of using OGA inhibition to treat AD. In this study, we investigated the acute effect of pharmacologically increasing O-GlcNAc levels, using OGA inhibitor Thiamet G (TG), on normal mouse brains.

Impact of -GlcNAcylation elevation on mitophagy and glia in the dentate gyrus.

-GlcNAcylation is a dynamic and reversible protein post-translational modification of serine or threonine residues which modulates the activity of transcriptional and signaling pathways and controls cellular responses to metabolic and inflammatory stressors. We and others have shown that -GlcNAcylation has the potential to regulate autophagy and mitophagy to play a critical role in mitochondrial quality control, but this has not been assessed in the brain. This is important since mitochondrial dysfunction contributes to the development of neurodegenerative disease.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABARs.

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAR inhibitory postsynaptic currents (eIPSCs) onto hippocampal principal cells.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly at a neurosteroid site on GABAARs.

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAR inhibitory post synaptic currents (eIPSCs) onto hippocampal principal cells.

Protein glycosylation in cardiovascular health and disease.

Protein glycosylation, which involves the attachment of carbohydrates to proteins, is one of the most abundant protein co-translational and post-translational modifications. Advances in technology have substantially increased our knowledge of the biosynthetic pathways involved in protein glycosylation, as well as how changes in glycosylation can affect cell function. In addition, our understanding of the role of protein glycosylation in disease processes is growing, particularly in the context of immune system function, infectious diseases, neurodegeneration and cancer.

Forskolin reverses the O-GlcNAcylation dependent decrease in GABAAR current amplitude at hippocampal synapses possibly through a neurosteroid site on GABAARs.

GABAergic transmission is influenced by post-translational modifications, like phosphorylation, impacting channel conductance, allosteric modulator sensitivity, and membrane trafficking. O-GlcNAcylation is a post-translational modification involving the O-linked attachment of β-N-acetylglucosamine on serine/threonine residues. Previously we reported an acute increase in O-GlcNAcylation elicits a long-term depression of evoked GABAAR inhibitory post synaptic currents (eIPSCs) onto hippocampal principal cells.

The interplay between sex, time of day, fasting status, and their impact on cardiac mitochondrial structure, function, and dynamics.

Mitochondria morphology and function, and their quality control by mitophagy, are essential for heart function. We investigated whether these are influenced by time of the day (TOD), sex, and fed or fasting status, using transmission electron microscopy (EM), mitochondrial electron transport chain (ETC) activity, and mito-QC reporter mice. We observed peak mitochondrial number at ZT8 in the fed state, which was dependent on the intrinsic cardiac circadian clock, as hearts from cardiomyocyte-specific BMAL1 knockout (CBK) mice exhibit different TOD responses.

Sustained Increases in Cardiomyocyte Protein -Linked β-N-Acetylglucosamine Levels Lead to Cardiac Hypertrophy and Reduced Mitochondrial Function Without Systolic Contractile Impairment.

Background Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease through numerous mechanisms, including regulation via posttranslational modifications. A specific posttranslational modification, the addition of -linked β- acetylglucosamine (-GlcNAcylation), has been implicated in molecular mechanisms of both physiological and pathologic adaptations. The current study aimed to test the hypothesis that in cardiomyocytes, sustained protein -GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology.

Best practices in assessing cardiac protein -GlcNAcylation by immunoblot.

The modification of serine and threonine amino acids of proteins by -linked -acetylglucosamine (-GlcNAc) regulates the activity, stability, function, and subcellular localization of proteins. Dysregulation of -GlcNAc homeostasis is well established as a hallmark of various cardiac diseases, including cardiac hypertrophy, heart failure, complications associated with diabetes, and responses to acute injuries such as oxidative stress and ischemia-reperfusion. Given the limited availability of site-specific -GlcNAc antibodies, studies of changes in -GlcNAcylation in the heart frequently use pan--GlcNAc antibodies for semiquantitative evaluation of overall -GlcNAc levels.

Enzyme-based assay for quantification of UDP-GlcNAc in cells and tissues.

In this issue of , Sunden et al. develop an enzymatic assay to measure UDP-GlcNAc levels from cells and tissue. By reporting on the level of the substrate itself, this approach can potentially enhance the fields' understanding of UDP-GlcNAc concentration under a variety of conditions.

Cardiomyocyte ZKSCAN3 regulates remodeling following pressure-overload.

Autophagy is important for protein and organelle quality control. Growing evidence demonstrates that autophagy is tightly controlled by transcriptional mechanisms, including repression by zinc finger containing KRAB and SCAN domains 3 (ZKSCAN3). We hypothesize that cardiomyocyte-specific ZKSCAN3 knockout (Z3K) disrupts autophagy activation and repression balance and exacerbates cardiac pressure-overload-induced remodeling following transverse aortic constriction (TAC).

Relationships between gene expression and behavior in mice in response to systemic modulation of the O-GlcNAcylation pathway.

Enhancing protein O-GlcNAcylation by pharmacological inhibition of the enzyme O-GlcNAcase (OGA), which removes the O-GlcNAc modification from proteins, has been explored in mouse models of amyloid-beta and tau pathology. However, the O-GlcNAcylation-dependent link between gene expression and neurological behavior remains to be explored. Using chronic administration of Thiamet G (TG, an OGA inhibitor) in vivo, we used a protocol designed to relate behavior with the transcriptome and selected biochemical parameters from the cortex of individual animals.

Defining the Dynamic Regulation of O-GlcNAc Proteome in the Mouse Cortex---the O-GlcNAcylation of Synaptic and Trafficking Proteins Related to Neurodegenerative Diseases.

O-linked conjugation of ß-N-acetyl-glucosamine (O-GlcNAc) to serine and threonine residues is a post-translational modification process that senses nutrient availability and cellular stress and regulates diverse biological processes that are involved in neurodegenerative diseases and provide potential targets for therapeutics development. However, very little is known of the networks involved in the brain that are responsive to changes in the O-GlcNAc proteome. Pharmacological increase of protein O-GlcNAcylation by Thiamet G (TG) has been shown to decrease tau phosphorylation and neurotoxicity, and proposed as a therapy in Alzheimer's disease (AD).

STIM and Orai Mediated Regulation of Calcium Signaling in Age-Related Diseases.

Tight spatiotemporal regulation of intracellular Ca plays a critical role in regulating diverse cellular functions including cell survival, metabolism, and transcription. As a result, eukaryotic cells have developed a wide variety of mechanisms for controlling Ca influx and efflux across the plasma membrane as well as Ca release and uptake from intracellular stores. The STIM and Orai protein families comprising of STIM1, STIM2, Orai1, Orai2, and Orai3, are evolutionarily highly conserved proteins that are core components of all mammalian Ca signaling systems.

Cardiomyocyte stromal interaction molecule 1 is a key regulator of Ca -dependent kinase and phosphatase activity in the mouse heart.

Stromal interaction molecule 1 (STIM1) is a major regulator of store-operated calcium entry in non-excitable cells. Recent studies have suggested that STIM1 plays a role in pathological hypertrophy; however, the physiological role of STIM1 in the heart is not well understood. We have shown that mice with a cardiomyocyte deletion of STIM1 ( STIM1 ) develop ER stress, mitochondrial, and metabolic abnormalities, and dilated cardiomyopathy.

The Identification of a Novel Calcium-Dependent Link Between NAD and Glucose Deprivation-Induced Increases in Protein O-GlcNAcylation and ER Stress.

The modification of proteins by O-linked β--acetylglucosamine (O-GlcNAc) is associated with the regulation of numerous cellular processes. Despite the importance of O-GlcNAc in mediating cellular function our understanding of the mechanisms that regulate O-GlcNAc levels is limited. One factor known to regulate protein O-GlcNAc levels is nutrient availability; however, the fact that nutrient deficient states such as ischemia increase O-GlcNAc levels suggests that other factors also contribute to regulating O-GlcNAc levels.

Mitochondrial Morphology and Mitophagy in Heart Diseases: Qualitative and Quantitative Analyses Using Transmission Electron Microscopy.

Transmission electron microscopy (TEM) has long been an important technique, capable of high degree resolution and visualization of subcellular structures and organization. Over the last 20 years, TEM has gained popularity in the cardiovascular field to visualize changes at the nanometer scale in cardiac ultrastructure during cardiovascular development, aging, and a broad range of pathologies. Recently, the cardiovascular TEM enabled the studying of several signaling processes impacting mitochondrial function, such as mitochondrial fission/fusion, autophagy, mitophagy, lysosomal degradation, and lipophagy.

Branched chain amino acids selectively promote cardiac growth at the end of the awake period.

Essentially all biological processes fluctuate over the course of the day, manifesting as time-of-day-dependent variations with regards to the way in which organ systems respond to normal behaviors. For example, basic, translational, and epidemiologic studies indicate that temporal partitioning of metabolic processes governs the fate of dietary nutrients, in a manner in which concentrating caloric intake towards the end of the day is detrimental to both cardiometabolic and cardiovascular parameters. Despite appreciation that branched chain amino acids impact risk for obesity, diabetes mellitus, and heart failure, it is currently unknown whether the time-of-day at which dietary BCAAs are consumed influence cardiometabolic/cardiovascular outcomes.

New Insights Into the Biology of Protein O-GlcNAcylation: Approaches and Observations.

O-GlcNAcylation is a protein posttranslational modification that results in the addition of O-GlcNAc to Ser/Thr residues. Since its discovery in the 1980s, it has been shown to play an important role in a broad range of cellular functions by modifying nuclear, cytosolic, and mitochondrial proteins. The addition of O-GlcNAc is catalyzed by O-GlcNAc transferase (OGT), and its removal is catalyzed by O-GlcNAcase (OGA).

Fine-tuning the cardiac O-GlcNAcylation regulatory enzymes governs the functional and structural phenotype of the diabetic heart.

Aims: The glucose-driven enzymatic modification of myocardial proteins by the sugar moiety, β-N-acetylglucosamine (O-GlcNAc), is increased in pre-clinical models of diabetes, implicating protein O-GlcNAc modification in diabetes-induced heart failure. Our aim was to specifically examine cardiac manipulation of the two regulatory enzymes of this process on the cardiac phenotype, in the presence and absence of diabetes, utilising cardiac-targeted recombinant-adeno-associated viral-vector-6 (rAAV6)-mediated gene delivery.

Methods And Results: In human myocardium, total protein O-GlcNAc modification was elevated in diabetic relative to non-diabetic patients, and correlated with left ventricular (LV) dysfunction.

Reprint of: Role of O-linked N-acetylglucosamine (O-GlcNAc) modification of proteins in diabetic cardiovascular complications.

The post-translational modification of serine and threonine residues of proteins by O-linked N-acetylglucosamine (O-GlcNAc) regulates diverse cellular processes in the cardiovascular system. UDP-GlcNAc is a substrate for O-GlcNAc transferase, which catalyzes the attachment of O-GlcNAc to proteins. O-GlcNAcase catalyzes the removal of O-GlcNAc from proteins.

Role of O-linked N-acetylglucosamine (O-GlcNAc) modification of proteins in diabetic cardiovascular complications.

The post-translational modification of serine and threonine residues of proteins by O-linked N-acetylglucosamine (O-GlcNAc) regulates diverse cellular processes in the cardiovascular system. UDP-GlcNAc is a substrate for O-GlcNAc transferase, which catalyzes the attachment of O-GlcNAc to proteins. O-GlcNAcase catalyzes the removal of O-GlcNAc from proteins.

Increased Glucose Availability Attenuates Myocardial Ketone Body Utilization.

Background Perturbations in myocardial substrate utilization have been proposed to contribute to the pathogenesis of cardiac dysfunction in diabetic subjects. The failing heart in nondiabetics tends to decrease reliance on fatty acid and glucose oxidation, and increases reliance on ketone body oxidation. In contrast, little is known regarding the mechanisms mediating this shift among all 3 substrates in diabetes mellitus.

Role of -Linked -Acetylglucosamine Protein Modification in Cellular (Patho)Physiology.

In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a -acetylglucosamine moiety (-GlcNAc) via an -linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the -GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by -GlcNAc transferase (OGT) and -GlcNAcase (OGA), respectively. Since its discovery, -GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival.