Protein O-GlcNAcylation: a new signaling paradigm for the cardiovascular system

New insights into phytochemicals via protein glycosylation focused on aging and diabetes

BACKGROUND

Protein glycosylation as a common post-translational modification that has significant impacts on protein folding, enzymatic activity, and interfering with receptor functioning. In recent years, with the rapid development of glycopeptide enrichment and analysis technology and the deepening of glycosylation research, glycosylation has gradually become a sign of disease occurrence and development. Multiple investigations suggest that protein glycosylation affect the advances of diabetes and aging.

PURPOSE AND METHODS

This review was focused on the action mechanisms of glycosylated proteins production, permanent abnormalities in extracellular matrix component function, inflammatory and reactive oxygen species production, as well as the glycosylated characterizations of diabetes and aging. Further, advances in glycosylation analysis and detection methods are presented for the first time, highlighting for needed future developments. All literatures were gathered from PubMed and Google Scholar.

RESULTS

Herein, we review how protein glycosylation impacts the progression of diabetes and aging. Specifically, we focus on various types of glycosylation, including N-linked glycosylation, O-linked glycosylation, C-glycosylation, S-glycosylation, and glycophosphatidylinositol (GPI) anchors. N-linked glycosylation and O-linked glycosylation are commonly observed glycosylation forms, wherein O-GlcNAcylation plays a significant role in diabetes, while N-glycan could serve as biomarkers for identifying inflammation and aging.

CONCLUSIONS

Protein glycosylation produces a vastly larger number of core glycan structures through utilizing at least 173 glycosyltransferases and repeated common scaffolds. Single protein may contain multiple glycosylation sites, and the structure and occupancy of glycan at each site may be different, resulting in the macro heterogeneity of protein glycosylation. This review will contribute to how protein glycosylation impacts the life progress of cells and its association with diseases.

O-GlcNAcylation and Phosphorylation Crosstalk in Vascular Smooth Muscle Cells: Cellular and Therapeutic Significance in Cardiac and Vascular Pathologies

More than 400 different types of post-translational modifications (PTMs), including O-GlcNAcylation and phosphorylation, combine to co-ordinate almost all aspects of protein function. Often, these PTMs overlap and the specific relationship between O-GlcNAcylation and phosphorylation has drawn much attention. In the last decade, the significance of this dynamic crosstalk has been linked to several chronic pathologies of cardiovascular origin. However, very little is known about the pathophysiological significance of this crosstalk for vascular smooth muscle cell dysfunction in cardiovascular disease. O-GlcNAcylation occurs on serine and threonine residues which are also targets for phosphorylation. A growing body of research has now emerged linking altered vascular integrity and homeostasis with highly regulated crosstalk between these PTMs. Additionally, a significant body of evidence indicates that O-GlcNAcylation is an important contributor to the pathogenesis of neointimal hyperplasia and vascular restenosis responsible for long-term vein graft failure. In this review, we evaluate the significance of this dynamic crosstalk and its role in cardiovascular pathologies, and the prospects of identifying possible targets for more effective therapeutic interventions.

Glucosamine-Mediated Hexosamine Biosynthesis Pathway Activation Uses ATF4 to Promote "Exercise-Like" Angiogenesis and Perfusion Recovery in PAD

BACKGROUND

Endothelial cells (ECs) use glycolysis to produce energy. In preclinical models of peripheral arterial disease, further activation of EC glycolysis was ineffective or deleterious in promoting hypoxia-dependent angiogenesis, whereas pentose phosphate pathway activation was effective. Hexosamine biosynthesis pathway, pentose phosphate pathway, and glycolysis are closely linked. Glucosamine directly activates hexosamine biosynthesis pathway.

METHODS

Hind-limb ischemia in endothelial nitric oxide synthase knockout (eNOS-/-) and BALB/c mice was used. Glucosamine (600 μg/g per day) was injected intraperitoneally. Blood flow recovery was assessed using laser Doppler perfusion imaging and angiogenesis was studied by CD31 immunostaining. In vitro, human umbilical vein ECs and mouse microvascular ECs with glucosamine, L-glucose, or vascular endothelial growth factor (VEGF165a) were tested under hypoxia and serum starvation. Cell Counting Kit-8, tube formation, intracellular reactive oxygen species, electric cell-substrate impedance sensing, and fluorescein isothiocyanate dextran permeability were assessed. Glycolysis and oxidative phosphorylation were assessed by seahorse assay. Gene expression was assessed using RNA sequencing, real-time quantitative polymerase chain reaction, and Western blot. Human muscle biopsies from patients with peripheral arterial disease were assessed for EC O-GlcNAcylation before and after supervised exercise versus standard medical care.

RESULTS

On day 3 after hind-limb ischemia, glucosamine-treated versus control eNOS-/- mice had less necrosis (n=4 or 5 per group). Beginning on day 7 after hind-limb ischemia, glucosamine-treated versus control BALB/c mice had higher blood flow, which persisted to day 21, when ischemic muscles showed greater CD31 staining per muscle fiber (n=8 per group). In vitro, glucosamine versus L-glucose ECs showed improved survival (n=6 per group) and tube formation (n=6 per group). RNA sequencing of glucosamine versus L-glucose ECs showed increased amino acid metabolism (n=3 per group). That resulted in increased oxidative phosphorylation (n=8-12 per group) and serine biosynthesis pathway without an increase in glycolysis or pentose phosphate pathway genes (n=6 per group). This was associated with better barrier function (n=6-8 per group) and less reactive oxygen species (n=7 or 8 per group) compared with activating glycolysis by VEGF165a. These effects were mediated by activating transcription factor 4, a driver of exercise-induced angiogenesis. In muscle biopsies from humans with peripheral arterial disease, EC/O-GlcNAcylation was increased by 12 weeks of supervised exercise versus standard medical care (n=6 per group).

CONCLUSIONS

In cells, mice, and humans, activation of hexosamine biosynthesis pathway by glucosamine in peripheral arterial disease induces an "exercise-like" angiogenesis and offers a promising novel therapeutic pathway to treat this challenging disorder.

O-GlcNAcylation: Crosstalk between Hemostasis, Inflammation, and Cancer

O-linked β-N-acetylglucosamine (O-GlcNAc, O-GlcNAcylation) is a post-translational modification of serine/threonine residues of proteins. Alterations in O-GlcNAcylation have been implicated in several types of cancer, regulation of tumor progression, inflammation, and thrombosis through its interaction with signaling pathways. We aim to explore the relationship between O-GlcNAcylation and hemostasis, inflammation, and cancer, which could serve as potential prognostic tools or clinical predictions for cancer patients' healthcare and as an approach to combat cancer. We found that cancer is characterized by high glucose demand and consumption, a chronic inflammatory state, a state of hypercoagulability, and platelet hyperaggregability that favors thrombosis; the latter is a major cause of death in these patients. Furthermore, we review transcription factors and pathways associated with O-GlcNAcylation, thrombosis, inflammation, and cancer, such as the PI3K/Akt/c-Myc pathway, the nuclear factor kappa B pathway, and the PI3K/AKT/mTOR pathway. We also review infectious agents associated with cancer and chronic inflammation and potential inhibitors of cancer cell development. We conclude that it is necessary to approach both the diagnosis and treatment of cancer as a network in which multiple signaling pathways are integrated, and to search for a combination of potential drugs that regulate this signaling network.

Changes in transcriptomic landscape with macronutrients intake switch are independent from O-GlcNAcylation levels in heart throughout postnatal development in rats

Background

Dietary intake and metabolism variations are associated with molecular changes and more particularly in the transcriptome. O-GlcNAcylation is a post-translational modification added and removed respectively by OGT and OGA. The UDP-GlcNAc, the substrate of OGT, is produced by UAP1 and UAP1L1. O-GlcNAcylation is qualified as a metabolic sensor and is involved in the modulation of gene expression. We wanted to unveil if O-GlcNAcylation is linking metabolic transition to transcriptomic changes and to highlight modifications of O-GlcNAcylation during the postnatal cardiac development.

Methods

Hearts were harvested from rats at birth (D0), before (D12) and after suckling to weaning transition with normal (D28) or delayed weaning diet from D12 to D28 (D28F). O-GlcNAcylation levels and proteins expression were evaluated by Western blot. Cardiac transcriptomes were evaluated via 3'SRP analysis.

Results

Cardiac O-GlcNAcylation levels and nucleocytoplasmic OGT (ncOGT) were decreased at D28 while full length OGA (OGA) was increased. O-GlcNAcylation levels did not changed with delayed weaning diet while ncOGT and OGA were respectively increased and decreased. Uapl1 was the only O-GlcNAcylation-related gene identified as differentially expressed throughout postnatal development.

Conclusion

Macronutrients switch promotes changes in the transcriptome landscape that are independent from O-GlcNAcylation levels. UAP1 and UAP1L1 are not the main regulator element of O-GlcNAcylation throughout postnatal development.

Forskolin rescues hypoxia-induced cognitive dysfunction in zebrafish with potential involvement of O-GlcNAc cycling regulation

Repeated sublethal hypoxia exposure induces brain inflammation and affects the initiation and progression of cognitive dysfunction. Experiments from the current study showed that hypoxic exposure downregulates PKA/CREB signaling, which is restored by forskolin (FSK), an adenylate cyclase activator, in both Neuro2a (N2a) cells and zebrafish brain. FSK significantly protected N2a cells from hypoxia-induced cell death and neurite shrinkage. Intraperitoneal administration of FSK for 5 days on zebrafish additionally led to significant recovery from hypoxia-induced social interaction impairment and learning and memory (L/M) deficit. FSK suppressed hypoxia-induced neuroinflammation, as indicated by the observed decrease in NF-κB activation and GFAP expression. We further investigated the potential effect of FSK on O-GlcNAcylation changes induced by hypoxia. Intriguingly FSK induced marked upregulation of the protein level of O-GlcNAc transferase catalyzing addition of the GlcNAc group to target proteins, accompanied by elevated O-GlcNAcylation of nucleocytoplasmic proteins. The hypoxia-induced O-GlcNAcylation decrease in the brain of zebrafish was considerably restored following FSK treatment. Based on the collective results, we propose that FSK rescues hypoxia-induced cognitive dysfunction, potentially through regulation of HBP/O-GlcNAc cycling.

Revealing the conformational dynamics of UDP-GlcNAc recognition by O-GlcNAc transferase via Markov state model

The O-linked N-acetylglucosamine (O-GlcNAc) glycosylation is a critical post-translational modification and closely linked to various physiological and pathological conditions. The O-GlcNAc transferase (OGT) functions as the only glycosyltransferase of O-GlcNAc glycosylation by transferring GlcNAc from UDP-GlcNAc to serine or threonine residues on protein substrates. The interaction mode of UDP-GlcNAc against OGT has been preliminarily revealed by the crystal structures, yet an atomic-level comprehension for the conformational dynamics of the recognition process remains elusive. Here, we construct the Markov state model based on extensive all-atom molecular dynamics (MD) simulations with an aggregated simulation time of ∼9 μs, and reveal that the UDP-GlcNAc recognition process by OGT encompasses four key metastable states, occurring within an estimated timescale of ∼10 μs. During UDP-GlcNAc recognition process, we find the pyrophosphate moiety (P2O52-) initially anchors to the active pocket via salt bridge and hydrogen bonds, facilitating subsequent binding of the uridine and GlcNAc moieties. Furthermore, the functional roles of K842 involved in the salt bridge with P2O52- were evaluated through extra mutant MD simulations. Overall, our study provides valuable insights into the UDP-GlcNAc recognition mechanism by OGT, which could further aid in mechanistic studies of O-GlcNAc glycosylation and drug development targeting on OGT.

Augmented O-GlcNAcylation exacerbates right ventricular dysfunction and remodeling via enhancement of hypertrophy, mitophagy, and fibrosis in mice exposed to long-term intermittent hypoxia

Previously, we showed that augmented O-linked N-acetylglucosaminylation (O-GlcNAcylation) mitigates cardiac remodeling in O-GlcNAc transferase-transgenic (Ogt-Tg) mice exposed to acute (2-week) intermittent hypoxia (IH) by suppressing nuclear factor of activated T cells (NFAT) and nuclear factor kappa B (NF-κB) via the O-GlcNAcylation of glycogen synthase kinase 3 beta (GSK-3β) and NF-κB p65. Because this effect is time dependent, we exposed Ogt-Tg mice to IH for 4 weeks (IH4W) in the present study. O-GlcNAcylation was significantly enhanced in Ogt-Tg mice vs. wild-type (WT) mice exposed to normoxia and IH4W. Total O-GlcNAcylation levels were significantly increased in WT and Ogt-Tg mice after IH4W vs. normoxia. After IH4W, Ogt-Tg mice displayed significantly exacerbated signs of cardiac hypertrophy and fibrosis in the right ventricles (RVs) but not the left ventricles (LVs). Echocardiography revealed IH4W-induced right ventricular dysfunction. Phosphorylated GSK-3β levels were increased in Ogt-Tg mice vs. WT mice after IH4W, whereas phosphorylated NF-κB p65 levels were unaffected. Mitophagy, which is associated with cardiac dysfunction, was increased in the RVs of Ogt-Tg mice after IH4W. Furthermore, the levels of phosphorylated dynamin-related protein 1 (p-Drp1) were significantly increased, and the expression of mitofusin-2 (MFN2) was significantly decreased. In human embryonic kidney cells, mitochondrial uncoupler-induced mitochondrial dysfunction was accelerated in Ogt-overexpressing cells. In addition to increasing the levels of phosphorylated Smad2, IH4W promoted cardiac fibrosis in the RVs of Ogt-Tg mice. Thus, augmented O-GlcNAcylation may aggravate IH4W-induced right ventricular dysfunction and remodeling by promoting hypertrophy, mitophagy, and fibrosis via GSK-3β inactivation, an increased p-Drp-1/MFN2 ratio, and Smad2 activation, respectively.

O-GlcNAcylation: an important post-translational modification and a potential therapeutic target for cancer therapy

O-linked β-d-N-acetylglucosamine (O-GlcNAc) is an important post-translational modification of serine or threonine residues on thousands of proteins in the nucleus and cytoplasm of all animals and plants. In eukaryotes, only two conserved enzymes are involved in this process. O-GlcNAc transferase is responsible for adding O-GlcNAc to proteins, while O-GlcNAcase is responsible for removing it. Aberrant O-GlcNAcylation is associated with a variety of human diseases, such as diabetes, cancer, neurodegenerative diseases, and cardiovascular diseases. Numerous studies have confirmed that O-GlcNAcylation is involved in the occurrence and progression of cancers in multiple systems throughout the body. It is also involved in regulating multiple cancer hallmarks, such as metabolic reprogramming, proliferation, invasion, metastasis, and angiogenesis. In this review, we first describe the process of O-GlcNAcylation and the structure and function of O-GlcNAc cycling enzymes. In addition, we detail the occurrence of O-GlcNAc in various cancers and the role it plays. Finally, we discuss the potential of O-GlcNAc as a promising biomarker and novel therapeutic target for cancer diagnosis, treatment, and prognosis.

Sex Differences in Pulmonary Hypertension

Pulmonary hypertension (PH) includes multiple diseases that share as common characteristic an elevated pulmonary artery pressure and right ventricular involvement. Sex differences are observed in practically all causes of PH. The most studied type is pulmonary arterial hypertension (PAH) which presents a gender bias regarding its prevalence, prognosis, and response to treatment. Although this disease is more frequent in women, once affected they present a better prognosis compared to men. Even if estrogens seem to be the key to understand these differences, animal models have shown contradictory results leading to the birth of the estrogen paradox. In this review we will summarize the evidence regarding sex differences in experimental animal models and, very specially, in patients suffering from PAH or PH from other etiologies.

Dexmedetomidine Inhibits NF-κB-Transcriptional Activity in Neurons Undergoing Ischemia-Reperfusion by Regulating O-GlcNAcylation of SNW1

Dexmedetomidine (Dex) is neuroprotective in ischemia-reperfusion (I/R) by suppressing inflammation but the underlying molecular mechanisms are not known. SNW domain-containing protein 1 (SNW1) is a coactivator of the pro-inflammatory transcription factor NF-κB p65. Because SNW1 is regulated by O-GlcNAcylation, we aimed to determine whether this modification influences NF-κB transcriptional activity in neurons undergoing I/R and how Dex may affect the O-GlcNAcylation of SNW1. SH-SY5Y and PC12 cells under hypoxia/reoxygenation (H/R) conditions were treated with Dex and with inhibitors of O-GlcNAc transferase (OGT). O-GlcNAc levels in SNW1 and effects of SNW1 on NF-κB p65 were determined by immunoprecipitation. H/R increased SNW1 protein levels but inhibited O-GlcNAcylation of SNW1. A Luciferase reporter assay demonstrated that increased SNW1 levels led to increased NF-κB p65 activity and increased secretion of neuron-derived inflammatory factors demonstrated by ELISA. Dex reversed the H/R-induced increase of SNW1 protein by upregulating OGT and enhancing O-GlcNAcylation of SNW1. Dex suppression of the SNW1/NF-κB complex resulted in neuroprotection in vitro and in a middle cerebral artery occlusion model in vivo. PKA and ERK1/2 inhibitors abolished the effect of Dex on OGT protein. Taken together, these data indicate that Dex inhibits NF-κB-transcriptional activity in neurons undergoing I/R by regulating O-GlcNAcylation of SNW1.

The Case for, and Challenges of, Human Cardiac Tissue in Advancing Phosphoprotein Research

Cardiovascular disease (CVD) and stroke affect over 92 million Americans and account for nearly 1 out of 3 deaths in the US. The use of animal models in cardiovascular research has led to considerable advances in treatment and in our understanding of the pathophysiology of many CVDs. Still, animals may not fully recapitulate human disease states; species differences have long been postulated to be one of the main reasons for a failure of translation between animals and humans in drug discovery and development. Indeed, it has become increasingly clear over the past few decades that to answer certain biomedical questions, like the physiological mechanisms that go awry in many human CVDs, animal tissues may not always be the best option to use. While human cardiac tissue has long been used for laboratory research, published findings often contradict each other, leading to difficulties in interpretation. Current difficulties in utilizing human cardiac tissue include differences in acquisition time, varying tissue procurement protocols, and the struggle to define a human “control” sample. With the tremendous emphasis on translational research that continues to grow, research studies using human tissues are becoming more common. This mini review will discuss advantages, disadvantages, and considerations of using human cardiac tissue in the study of CVDs, paying specific attention to the study of phosphoproteins.

Circadian regulation of cardiac metabolism

Circadian rhythm evolved to allow organisms to coordinate intrinsic physiological functions in anticipation of recurring environmental changes. The importance of this coordination is exemplified by the tight temporal control of cardiac metabolism. Levels of metabolites, metabolic flux, and response to nutrients all oscillate in a time-of-day-dependent fashion. While these rhythms are affected by oscillatory behavior (feeding/fasting, wake/sleep) and neurohormonal changes, recent data have unequivocally demonstrated an intrinsic circadian regulation at the tissue and cellular level. The circadian clock - through a network of a core clock, slave clock, and effectors - exerts intricate temporal control of cardiac metabolism, which is also integrated with environmental cues. The combined anticipation and adaptability that the circadian clock enables provide maximum advantage to cardiac function. Disruption of the circadian rhythm, or dyssynchrony, leads to cardiometabolic disorders seen not only in shift workers but in most individuals in modern society. In this Review, we describe current findings on rhythmic cardiac metabolism and discuss the intricate regulation of circadian rhythm and the consequences of rhythm disruption. An in-depth understanding of the circadian biology in cardiac metabolism is critical in translating preclinical findings from nocturnal-animal models as well as in developing novel chronotherapeutic strategies.

Hypertonic stress modulates eNOS function through O-GlcNAc modification at Thr-866

O-GlcNAcylation, an energy-sensitive posttranslational modification, can regulate the activity of endothelial nitric oxide synthase (eNOS). Previous studies found that Thr866 is the key site for low-glucose-mediated regulation of eNOS O-GlcNAc. However, it is not known whether this activity functions through the Thr866 site concomitant with other physical and chemical factors. Therefore, we first explored the effects of physical and chemical factors on eNOS O-GlcNAc and its Thr866 site. In this study, hypertonic stress, hyperthermia and hydrogen peroxide all increased the expression levels of eNOS O-GlcNAc, whereas hypoxia and high levels of alcohol had no effect. on the expression levels of eNOS O-GlcNAc; by contrast, low pH led to a decrease in eNOS O-GlcNAc levels. Notably, eNOS O-GlcNAc protein levels were unchanged after Thr866 site mutation only under hypertonic conditions, suggesting that hypertonic stress may act through the Thr866 site. Upon exploring the mechanism of hypertonic stress on eNOS O-GlcNAc activity and function, we found that hypertonic stress can upregulate the expression of O-linked N-acetylglucosamine (GlcNAc) transferase (OGT), which is dependent on AMPK. When AMPK was knocked out, the upregulation of OGT expression and increased O-GlcNAc modifications induced by hypertonic stress were reversed.

Hyper-O-GlcNAcylation impairs insulin response against reperfusion-induced myocardial injury and arrhythmias in obesity

Myocardial ischemia/reperfusion (I/R) injury is a major determinant of morbidity and mortality in patients undergoing treatment for cardiac disease. A variety of treatments are reported to have benefits against reperfusion injury, yet their cardioprotective effects seem to be diminished in obesity, and the underlying mechanism remains elusive. In this study, we found that db/db mice exhibit cardiac hyper-O-GlcNAcylation. In parallel, palmitate treatment (200 mM; 12 h) in H9c2 cells showed an increase in global protein O-GlcNAcylation, along with an impaired insulin response against reperfusion injury. To investigate whether O-GlcNAcylation underlies this phenomenon, glucosamine was used to increase global protein O-GlcNAc levels. Interestingly, histological staining, electrophysiological studies, serum cardiac markers and oxidative stress biomarker assays showed that preischemic treatment with glucosamine attenuated insulin cardioprotection against myocardial infarction, arrhythmia and oxidative stress. Mechanistically, glucosamine treatment decreased insulin-stimulated Akt phosphorylation, a key modulator of cell survival. Furthermore, inhibition of O-GlcNAcylation via 6-diazo-5-oxo-l-norleucine (DON) apparently increased insulin-induced Akt phosphorylation and restored its cardioprotective response against reperfusion injury in palmitate-induced insulin-resistant H9c2 cells. Our findings demonstrated that obesity-induced hyper-O-GlcNAcylation might contribute to the attenuation of insulin cardioprotection against I/R injury.

Combination of multiple computational methods revealing specific sub-sectional recognition and hydrogen-bond dependent transportation of CKII peptide fragment in O-GlcNAc transferase

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Mechanism of CKII peptide recognition, transportation and binding in OGT is obtained.

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Peptide delivery is strong exothermic, highly dependent on hydrogen bond network.

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Typical ‘spread’ & ‘V’ conformation change noticed for peptide accompanies stable OGT.

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Specific subsection of peptide has diverse performance in its recognition and delivery.

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Multiple methods combination may be used in other bio-system with flexible substrate.

O-linked β-N-acetyl-D-glucosamine (O-GlcNAc) transferase (OGT) is an essential enzyme in many cellular physiological catalytic reactions that regulates protein O-GlcNAcylation. Aberrant O-GlcNAcylation is related to insulin resistance, diabetic complications, cancer and neurodegenerative diseases. Understanding the peptide delivery in OGT is significant in comprehending enzymatic catalytic process, target-protein recognition and pathogenic mechanism. Herein extensive molecular dynamics (MD) simulations combined with various techniques are utilized to study the recognizing and binding mechanism of peptide fragment extracted from casein kinase II by OGT from atomic level. The residues of His496, His558, Thr633, Lys634, and Pro897 are demonstrated to play a dominant role in the peptide stabilization via hydrogen bonds and σ-π interaction, whose van der Waals and non-polar solvent effects provide the main driving force. In addition, two channels are identified. The delivery mode, mechanism together with thermodynamic and dynamic characterizations for the most favorable channel are determined. The peptide is more inclined to be recognized by OGT through the cavity comprised of residues 799–812, 893–899, and 865–871, and Tyr13-terminal is prior recognized to Met26-terminal. The transportation process is accompanied with conformation changes between the “spread” and “V” shapes. The whole process is strong exothermic that is highly dependent on the variation of hydrogen bond interactions between peptide and OGT as well as the performance of different subsections of peptide. Besides that, multiple computational methods combinations may contribute meaningfully to calculation of similar bio-systems with long and flexible substrate.

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. The impact of rAAV6-delivered O-GlcNAc transferase (rAAV6-OGT, facilitating protein O-GlcNAcylation), O-GlcNAcase (rAAV6-OGA, facilitating de-O-GlcNAcylation) and empty vector (null) were determined in non-diabetic and diabetic mice. In non-diabetic mice, rAAV6-OGT was sufficient to impair LV diastolic function and induce maladaptive cardiac remodelling, including cardiac fibrosis and increased Myh-7 and Nppa pro-hypertrophic gene expression, recapitulating characteristics of diabetic cardiomyopathy. In contrast, rAAV6-OGA (but not rAAV6-OGT) rescued LV diastolic function and adverse cardiac remodelling in diabetic mice. Molecular insights implicated impaired cardiac PI3K(p110α)-Akt signalling as a potential contributing mechanism to the detrimental consequences of rAAV6-OGT in vivo. In contrast, rAAV6-OGA preserved PI3K(p110α)-Akt signalling in diabetic mouse myocardium in vivo and prevented high glucose-induced impairments in mitochondrial respiration in human cardiomyocytes in vitro.

CONCLUSION

Maladaptive protein O-GlcNAc modification is evident in human diabetic myocardium, and is a critical regulator of the diabetic heart phenotype. Selective targeting of cardiac protein O-GlcNAcylation to restore physiological O-GlcNAc balance may represent a novel therapeutic approach for diabetes-induced heart failure.

TRANSLATIONAL PERSPECTIVE

There remains a lack of effective clinical management of diabetes-induced cardiac dysfunction, even via conventional intensive glucose-lowering approaches. Here we reveal that the modification of myocardial proteins by O-GlcNAc, a glucose-driven process, is not only increased in human diabetic myocardium, but correlates with reduced cardiac function in affected patients. Moreover, manipulation of the two regulatory enzymes of this process exert opposing influences on the heart, whereby increasing O-GlcNAc transferase (OGT) is sufficient to replicate the cardiac phenotype of diabetes (in the absence of this disease), while increasing O-GlcNAc-ase (OGA) rescues diabetes-induced impairments in both cardiac dysfunction and remodelling. Cardiac O-GlcNAcylation thus represents a novel therapeutic target for diabetes-induced heart failure.

Subchronic toxicity evaluation of glucosamine and glucosamine in combination with chondroitin sulfate in obese Zucker rats

D-glucosamine is a widely consumed dietary supplement used to promote joint health and treat osteoarthritis. It also stimulates intracellular hexosamine flux and increases transforming growth factor β1 (TGFβ1) mRNA expression and insulin resistance in animal studies. The effects of D-glucosamine exposure were investigated in obese Zucker rats. Male (leprfa/leprfa) Zucker rats were exposed to 30, 120, 300 and 600 mg D-glucosamine HCl per kg/day either alone or with chondroitin sulfate (24, 96, 240 and 480 mg/kg/day respectively) for 90 days. After 4 weeks exposure, these doses produced CmaxD-glucosamine concentrations of up to 24 μM in tail vein serum concurrent with a transient 30% increase in blood glucose concentration in the 600 mg/kg/day dose group. D-Glucosamine did not significantly alter body weight, blood glucose or serum insulin levels at any dose tested after 13 weeks exposure, but did increase urinary TGFβ1 concentrations. The Zucker rats developed nephropathy and scrotal sores that were related to their hyperglycemia and obesity, and D-glucosamine exposure exacerbated these conditions to a small extent. The incidence of pulmonary osseous metaplasia was increased in rats exposed to D-glucosamine and a single incidence of adrenal osseous metaplasia was noted in one animal exposed to 600/480 mg D-glucosamine HCl/chondroitin sulfate. These lesions may have been treatment related. These studies suggest that the risk of adverse effects of oral D-glucosamine is small compared to that of hyperglycemia in these animals, but the potential for TGFβ1-mediated pathologies, such as osseous metaplasia and renal nephropathy may be increased.

Proteome-wide profiling and mapping of post translational modifications in human hearts

Post translational modifications (PTMs) are covalent modifications of proteins that can range from small chemical modifications to addition of entire proteins. PTMs contribute to regulation of protein function and thereby greatly increase the functional diversity of the proteome. In the heart, a few well-studied PTMs, such as phosphorylation and glycosylation, are known to play essential roles for cardiac function. Yet, only a fraction of the ~ 300 known PTMs have been studied in a cardiac context. Here we investigated the proteome-wide map of PTMs present in human hearts by utilizing high-resolution mass spectrometry measurements and a suite of PTM identification algorithms. Our approach led to identification of more than 150 different PTMs across three of the chambers in human hearts. This finding underscores that decoration of cardiac proteins by PTMs is much more diverse than hitherto appreciated and provides insights in cardiac protein PTMs not yet studied. The results presented serve as a catalogue of which PTMs are present in human hearts and outlines the particular protein and the specific amino acid modified, and thereby provides a detail-rich resource for exploring protein modifications in human hearts beyond the most studied PTMs.

Possible Susceptibility Genes for Intervention against Chemotherapy-Induced Cardiotoxicity

Recent therapeutic advances have significantly improved the short- and long-term survival rates in patients with heart disease and cancer. Survival in cancer patients may, however, be accompanied by disadvantages, namely, increased rates of cardiovascular events. Chemotherapy-related cardiac dysfunction is an important side effect of anticancer therapy. While advances in cancer treatment have increased patient survival, treatments are associated with cardiovascular complications, including heart failure (HF), arrhythmias, cardiac ischemia, valve disease, pericarditis, and fibrosis of the pericardium and myocardium. The molecular mechanisms of cardiotoxicity caused by cancer treatment have not yet been elucidated, and they may be both varied and complex. By identifying the functional genetic variations responsible for this toxicity, we may be able to improve our understanding of the potential mechanisms and pathways of treatment, paving the way for the development of new therapies to target these toxicities. Data from studies on genetic defects and pharmacological interventions have suggested that many molecules, primarily those regulating oxidative stress, inflammation, autophagy, apoptosis, and metabolism, contribute to the pathogenesis of cardiotoxicity induced by cancer treatment. Here, we review the progress of genetic research in illuminating the molecular mechanisms of cancer treatment-mediated cardiotoxicity and provide insights for the research and development of new therapies to treat or even prevent cardiotoxicity in patients undergoing cancer treatment. The current evidence is not clear about the role of pharmacogenomic screening of susceptible genes. Further studies need to done in chemotherapy-induced cardiotoxicity.

Cytoplasmic Citrate Flux Modulates the Immune Stimulatory NKG2D Ligand MICA in Cancer Cells

Immune surveillance of cancer cells is facilitated by the Natural Killer Group 2D (NKG2D) receptor expressed by different lymphocyte subsets. It recognizes NKG2D ligands that are rarely expressed on healthy cells, but upregulated by tumorigenesis, presenting a target for immunological clearance. The molecular mechanisms responsible for NKG2D ligand regulation remain complex. Here we report that cancer cell metabolism supports constitutive surface expression of the NKG2D ligand MHC class I chain-related proteins A (MICA). Knockout of the N-glycosylation gene N-acetylglucosaminyltransferase V (MGAT5) in HEK293 cells induced altered metabolism and continuous high MICA surface expression. MGAT5 knockout cells were used to examine the association of cell metabolism and MICA expression through genetic, pharmacological and metabolic assays. Findings were verified in cancer cell lines. Cells with constitutive high MICA expression showed enhanced spare respiratory capacity and elevated mitochondrial efflux of citrate, determined by extracellular flux analysis and metabolomics. MICA expression was reduced by inhibitors of mitochondrial function, FCCP and etomoxir e.g., and depended on conversion of citrate to acetyl-CoA and oxaloacetate by ATP citrate lyase, which was also observed in several cancer cell types. Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) analysis revealed that upregulated MICA transcription was associated with an open chromatin structure at the MICA transcription start site. We identify mitochondria and cytoplasmic citrate as key regulators of constitutive MICA expression and we propose that metabolic reprogramming of certain cancer cells facilitates MICA expression and NKG2D-mediated immune recognition.

O-GlcNAc impairs endothelial function in uterine arteries from virgin but not pregnant rats: The role of GSK3β

Increased O-Linked β-N-acetylglucosamine (O-GlcNAc) is observed in several pathologies, and unbalanced O-GlcNAcylation levels favor endothelial dysfunction. Whether augmented O-GlcNAc impacts the uterine artery (UA) function and how it affects the UA during pregnancy remains to be elucidated. We hypothesized that glucosamine treatment increases O-GlcNAc, leading to uterine artery dysfunction and this effect is prevented by pregnancy. Pregnant (P) and non-pregnant (NP) Wistar rats were treated with glucosamine (300 mg/kg; i.p.) for 21 days. Concentration response-curves (CRC) to acetylcholine (in the presence or absence of L-NAME) and sodium nitroprusside were performed in UAs. In NP rats, glucosamine treatment increased O-GlcNAc expression in UAs accompanied by decreased endothelium-dependent relaxation, which was abolished by L-NAME. Endothelial nitric oxide synthase (eNOS) activity and total Akt expression were decreased by glucosamine-treatment in NP rats. Further, NP rats treated with glucosamine displayed increased glycogen synthase kinase 3 beta (GSK3β) activation and O-GlcNAc-transferase (OGT) expression in the UA. P rats treated with glucosamine displayed decreased O-GlcNAc in UAs and it was accompanied by improved relaxation to acetylcholine, whereas eNOS and GSK3β activity and total Akt and OGT expression were unchanged. Sodium nitroprusside-induced relaxation was not changed in all groups, indicating that glucosamine treatment led to endothelial dysfunction in NP rats. The underlying mechanism is, at least in part, dependent on Akt/GSK3β/OGT modulation. We speculate that during pregnancy, hormonal alterations play a protective role in preventing O-GlcNAcylation-induced endothelial dysfunction in the UAs.

Metabolic Coordination of Physiological and Pathological Cardiac Remodeling

Metabolic pathways integrate to support tissue homeostasis and to prompt changes in cell phenotype. In particular, the heart consumes relatively large amounts of substrate not only to regenerate ATP for contraction but also to sustain biosynthetic reactions for replacement of cellular building blocks. Metabolic pathways also control intracellular redox state, and metabolic intermediates and end products provide signals that prompt changes in enzymatic activity and gene expression. Mounting evidence suggests that the changes in cardiac metabolism that occur during development, exercise, and pregnancy as well as with pathological stress (eg, myocardial infarction, pressure overload) are causative in cardiac remodeling. Metabolism-mediated changes in gene expression, metabolite signaling, and the channeling of glucose-derived carbon toward anabolic pathways seem critical for physiological growth of the heart, and metabolic inefficiency and loss of coordinated anabolic activity are emerging as proximal causes of pathological remodeling. This review integrates knowledge of different forms of cardiac remodeling to develop general models of how relationships between catabolic and anabolic glucose metabolism may fortify cardiac health or promote (mal)adaptive myocardial remodeling. Adoption of conceptual frameworks based in relational biology may enable further understanding of how metabolism regulates cardiac structure and function.

Cholinergic drugs ameliorate endothelial dysfunction by decreasing O-GlcNAcylation via M3 AChR-AMPK-ER stress signaling

AIMS

Obesity is associated with increased cardiovascular morbidity and mortality. It is accompanied by augmented O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins via increasing hexosamine biosynthetic pathway (HBP) flux. However, the changes and regulation of the O-GlcNAc levels induced by obesity are unclear.

MAIN METHODS

High fat diet (HFD) model was induced obesity in mice with or without the cholinergic drug pyridostigmine (PYR, 3 mg/kg/d) for 22 weeks and in vitro human umbilical vein endothelial cells (HUVECs) was treated with high glucose (HG, 30 mM) with or without acetylcholine (ACh).

KEY FINDINGS

PYR significantly reduced body weight, blood glucose, and O-GlcNAcylation levels and attenuated vascular endothelial cells detachment in HFD-fed mice. HG addition induced endoplasmic reticulum (ER) stress and increased O-GlcNAcylation levels and apoptosis in HUVECs in a time-dependent manner. Additionally, HG decreased levels of phosphorylated AMP-activated protein kinase (AMPK). Interestingly, ACh significantly blocked damage to HUVECs induced by HG. Furthermore, the effects of ACh on HG-induced ER stress, O-GlcNAcylation, and apoptosis were prevented by treating HUVECs with 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP, a selective M3 AChR antagonist) or compound C (Comp C, an AMPK inhibitor). Treatment with 5-aminoimidazole-4-carboxamide ribose (AICAR, an AMPK activator), 4-phenyl butyric acid (4-PBA, an ER stress inhibitor), and 6-diazo-5-oxonorleucine (DON, a GFAT antagonist) reproduced a similar effect with ACh.

SIGNIFICANCE

Activation of cholinergic signaling ameliorated endothelium damage, reduced levels of ER stress, O-GlcNAcylation, and apoptosis in mice and HUVECs under obese conditions, which may function through M3 AChR-AMPK signaling.

Leukoencephalopathy due to variants in GFPT1-associated congenital myasthenic syndrome

OBJECTIVE

To determine the molecular etiology of disease in 4 individuals from 2 unrelated families who presented with proximal muscle weakness and features suggestive of mitochondrial disease.

METHODS

Clinical information and neuroimaging were reviewed. Genome sequencing was performed on affected individuals and biological parents.

RESULTS

All affected individuals presented with muscle weakness and difficulty walking. In one family, both children had neonatal respiratory distress while the other family had 2 children with episodic deteriorations. In each family, muscle biopsy demonstrated ragged red fibers. MRI was suggestive of a mitochondrial leukoencephalopathy, with extensive deep cerebral white matter T2 hyperintense signal and selective involvement of the middle blade of the corpus callosum. Through genome sequencing, homozygous GFPT1 missense variants were identified in the affected individuals of each family. The variants detected (p.Arg14Leu and p.Thr151Lys) are absent from population databases and predicted to be damaging by in silico prediction tools. Following the genetic diagnosis, nerve conduction studies were performed and demonstrated a decremental response to repetitive nerve stimulation, confirming the diagnosis of myasthenia. Treatment with pyridostigmine was started in one family with favorable response.

CONCLUSIONS

GFPT1 encodes a widely expressed protein that controls the flux of glucose into the hexosamine-biosynthesis pathway that produces precursors for glycosylation of proteins. GFPT1 variants and defects in other enzymes of this pathway have previously been associated with congenital myasthenia. These findings identify leukoencephalopathy as a previously unrecognized phenotype in GFPT1-related disease and suggest that mitochondrial dysfunction could contribute to this disorder.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

O-GlcNAc Modification During Pregnancy: Focus on Placental Environment

Successful placentation is a key event for fetal development, which commences following embryo implantation into the uterine wall, eliciting decidualization, placentation, and remodeling of blood vessels to provide physiological exchange between embryo-fetus and mother. Several signaling pathways are recruited to modulate such important processes and specific proteins that regulate placental function are a target for the glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc), or O-GlcNAcylation. This is a reversible post-translational modification on nuclear and cytoplasmic proteins, mainly controlled by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). O-GlcNAcylation has been implicated as a modulator of proteins, both in physiological and pathological conditions and, more recently, O-GlcNAc has also been shown to be an important modulator in placental tissue. In this mini-review, the interplay between O-GlcNAcylation of proteins and placental function will be addressed, discussing the possible implications of this post-translational modification through placental development and pregnancy.

Metabolic Mechanisms of Exercise-Induced Cardiac Remodeling

Exercise has a myriad of physiological benefits that derive in part from its ability to improve cardiometabolic health. The periodic metabolic stress imposed by regular exercise appears fundamental in driving cardiovascular tissue adaptation. However, different types, intensities, or durations of exercise elicit different levels of metabolic stress and may promote distinct types of tissue remodeling. In this review, we discuss how exercise affects cardiac structure and function and how exercise-induced changes in metabolism regulate cardiac adaptation. Current evidence suggests that exercise typically elicits an adaptive, beneficial form of cardiac remodeling that involves cardiomyocyte growth and proliferation; however, chronic levels of extreme exercise may increase the risk for pathological cardiac remodeling or sudden cardiac death. An emerging theme underpinning acute as well as chronic cardiac adaptations to exercise is metabolic periodicity, which appears important for regulating mitochondrial quality and function, for stimulating metabolism-mediated exercise gene programs and hypertrophic kinase activity, and for coordinating biosynthetic pathway activity. In addition, circulating metabolites liberated during exercise trigger physiological cardiac growth. Further understanding of how exercise-mediated changes in metabolism orchestrate cell signaling and gene expression could facilitate therapeutic strategies to maximize the benefits of exercise and improve cardiac health.

Increased O-Linked N-Acetylglucosamine Modification of NF-ΚB and Augmented Cytokine Production in the Placentas from Hyperglycemic Rats

Inflammation as a result of NF-κB activation may result from the classical (canonical) pathway, with disconnection of the IκB inhibitor and subsequent nuclear translocation or, alternatively, by post-translational modifications of modulatory proteins or NF-κB subunits (non-canonical pathway). We hypothesized that hyperglycemia-induced increased glycosylation with O-linked N-acetylglucosamine (O-GlcNAc) of NF-κB in placental tissue leads to augmented production of pro-inflammatory cytokines, culminating in placental dysfunction and fetal restriction growth. Single injections of streptozotocin (40 mg/kg) or vehicle were used to induce hyperglycemia or normoglycemia, respectively, in female Wistar rats. After 3 days, rats were mated and pregnancy confirmed. Placental tissue was collected at 21 days of pregnancy. Placental expression of p65 subunit was similar between groups. However, nuclear translocation of p65 subunit, showing greater activation of NF-κB, was increased in the hyperglycemic group. Reduced expression of IκB and increased expression of phosphorylated IκB^Ser32 were observed in the placenta from hyperglycemic rats, demonstrating increased classical NF-κB activation. Augmented modification of O-GlcNAc-modified proteins was found in the placenta from hyperglycemic rats and p65 subunit was a key O-GlcNAc target, as demonstrated by immunoprecipitation. Tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) expressions were increased in the placenta from hyperglycemic rats. Furthermore, placental weight was increased, whereas fetal weight was decreased under hyperglycemic conditions. TNF-α and IL-6 demonstrated positive correlations with placental weight and negative correlations with fetal weight and placental efficiency. Therefore, under hyperglycemic conditions, a modulatory role of O-GlcNAc in NF-κB activity was demonstrated in the placenta, contributing to fetal and placental dysfunction due to inflammatory cytokine exacerbation.

Endothelial Cell Metabolism in Atherosclerosis

Atherosclerosis and its sequelae, such as myocardial infarction and stroke, are the leading cause of death worldwide. Vascular endothelial cells (EC) play a critical role in vascular homeostasis and disease. Atherosclerosis as well as its independent risk factors including diabetes, obesity, and aging, are hallmarked by endothelial activation and dysfunction. Metabolic pathways have emerged as key regulators of many EC functions, including angiogenesis, inflammation, and barrier function, processes which are deregulated during atherogenesis. In this review, we highlight the role of glucose, fatty acid, and amino acid metabolism in EC functions during physiological and pathological states, specifically atherosclerosis, diabetes, obesity and aging.

O-Glycosylation with O-linked β-N-acetylglucosamine increases vascular contraction: Possible modulatory role on Interleukin-10 signaling pathway

AIMS

The interleukin-10 (IL-10) is an immuno-regulatory cytokine that plays a protective effect in the vasculature. IL-10 binding to its receptor, activating the IL-10/JAK1/STAT3 cascade to exert its effects. Therefore, STAT3 phosphorylation is essential for IL-10 actions. O-Glycosylation with linked β-N-acetylglucosamine (O-GlcNAc) is a post-translational modification able to regulate many proteins by interfering with protein on a phosphorylation level. Our aim was to determine whether O-GlcNAc promotes the inhibition of IL-10-pathway (JAK1/STAT3/IL-10), inactivationg its action in the vasculature.

MAIN METHODS

Mice (C57BL/6) aortic segments were incubated with vehicle or Thiamet G (0.1 mM, for 24 h) to increase global O-GlcNAc levels. Aortas from knockout mice for IL-10 were also used. Vascular reactivity and western blot tests were performed to evaluate protein expression.

KEY FINDINGS

High levels of O-GlcNAc, induced by Thiamet G incubation, increased vascular expression of JAK1, but decreased expression and activity of STAT3. In addition, IL-10 levels were diminished in arteries treated with Thiamet G. Absence of IL-10, as well as augmented O-GlcNAcylation, increased vascular reactivity to constrictor stimuli, an effect that was abolished by ERK 1/2 inhibitor. High levels of O-GlcNAc and the absence of IL-10 also leads to increased vascular expression of ERK1/2.

SIGNIFICANCE

Our data suggest that O-GlcNAc modification seems to (dys)regulate IL-10 signaling pathway and consequently, compromise the protective effect of this cytokine in vasculature. It is possible that there is a promising relationship in pathophysiological conditions where changes in O-GlcNAcylation and IL-10 levels are observed, such as hypertension and diabetes.

Metabolic Regulation of Angiogenesis in Diabetes and Aging

Impaired angiogenesis and endothelial dysfunction are hallmarks of diabetes and aging. Clinical efforts at promoting angiogenesis have largely focused on growth factor pathways, with mixed results. Recently, a new repertoire of endothelial intracellular molecules critical to endothelial metabolism has emerged as playing an important role in regulating angiogenesis. This review thus focuses on the emerging importance and therapeutic potential of these proteins and of endothelial bioenergetics in diabetes and aging.

O-linked N-acetyl-glucosamine deposition in placental proteins varies according to maternal glycemic levels

AIMS

Hyperglycemia increases glycosylation with O-linked N-acetyl-glucosamine (O-GlcNAc) contributing to placental dysfunction and fetal growth impairment. Our aim was to determine how O-GlcNAc levels are affected by hyperglycemia and the O-GlcNAc distribution in different placental regions.

MAIN METHODS

Female Wistar rats were divided into the following groups: severe hyperglycemia (>300 mg/dL; n = 5); mild hyperglycemia (>140 mg/dL, at least than two time points during oral glucose tolerance test; n = 7) or normoglycemia (<120 mg/dL; n = 6). At 21 days of pregnancy, placental tissue was collected and processed for morphometry and immunohistochemistry analyses, or properly stored at -80 °C for protein quantification by western blot.

KEY FINDINGS

Placental index was increased only in severe hyperglycemic rats. Morphometric analysis showed increased junctional zone and decreased labyrinth region in placentas exclusively from the severe hyperglycemic group. Proteins targeted by O-GlcNAc were detected in all regions, with increased O-GlcNAc levels in the hyperglycemic group compared to control and mild hyperglycemic rats. Proteins in endothelial and trophoblast cells were the main target for O-GlcNAc. Whereas no changes in O-GlcNAc transferase (OGT) expression were detected, O-GlcNAcase (OGA) expression was reduced in placentas from the severe hyperglycemic group and augmented in placentas from the mild hyperglycemic group, compared with their respective control groups.

SIGNIFICANCE

Placental O-GlcNAc overexpression may contribute to placental dysfunction, as indicated by the placental index. Additionally, morphometric alterations, occurring simultaneously with increased O-GlcNAc accumulation in the placental tissue may contribute to placental dysfunction during hyperglycemia.

How glycosylation aids tumor angiogenesis: An updated review

Glycosylation is an enzymatic process in which a carbohydrate is attached to a functional group from another molecule. Glycosylation is a crucial post translational process in protein modification. The tumor microenvironment produces altered glycans that contribute to cancer progression and aggressiveness. Abnormal glycosylation is widely observed in tumor angiogenesis. Despite many attempts to decipher the role of glycosylation in different aspects of cancer, little is known regarding the roles of glycans in angiogenesis. The blood vessels in tumors are often used to transport oxygen and nutrients for tumor progression and metastasis. The crosstalk within the tumor microenvironment can induce angiogenesis by manipulating these glycans to hijack the normal angiogenesis process, thus promoting tumor growth. Abnormal glycosylation has been shown to promote tumor angiogenesis by degrading the extracellular matrix to activate the angiogenic signaling pathways. This review highlights the latest update on how glycosylation can contribute to tumor angiogenesis that may affect treatment outcomes.

Metabolomic analysis of longissimus from underperforming piglets relative to piglets with normal preweaning growth

Background

Recent increases in intra-litter variability in weaning weight have raised swine production costs. A contributor to this variability is the normal birth weight pig that grows at a slower rate than littermates of similar birth weight. The goal of this study was to interrogate biochemical profiles manifested in skeletal muscle originating from slow growing (SG) and faster growing littermates (control), with the aim of identifying differences in metabolic pathway utilization between skeletal muscle of the SG pig relative to its littermates. Samples of longissimus muscle from littermate pairs of pigs were collected at 21 d of age for metabolomic analysis (Metabolon, Inc., Durham, NC).

Results

Birth weights did not differ between littermate pairs of SG and Control pigs (P > 0.05). Weaning weights differed by 1.51 ± 0.19 kg (P < 0.001). Random forest (RF) analysis was effective at segregating the metabolome of muscle samples by growth rate, resulting in a predictive accuracy of 81% versus random segregation (50%). Decreases in sugars in the pentose phosphate pathway (PPP) in the longissimus of SG pigs were detected (P < 0.05). Decreases were also apparent in glycolytic intermediates (glycerol-3-phosphate and lactate) and key glycolysis-derived intermediates (glucose-6-phosphate and fructose-6-phosphate; P < 0.05). SG pigs had increased levels of phospholipids, lysolipids, diacylglycerols, and sphingolipids (P < 0.05). Pathway analysis identified a cluster of molecules associated with muscle and collagen/extracellular matrix breakdown that are increased in the SG pig (glutamate, 3-methylhistidine and hydroxylated proline moieties; P < 0.05). Nicotinate metabolism was altered in SG pigs, resulting in a 78% decrease in the nicotinamide adenine dinucleotide pool (P < 0.05).

Conclusions

These metabolomic data provide the first evidence for biochemical mechanisms that should be investigated to determine if they have a potential role in the slow growth in some normal birth weight piglets that contribute to increased intra-litter variability in weaning weights and provides essential information and potential targets for the development of nutritional intervention strategies.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0251-3) contains supplementary material, which is available to authorized users.

Glucosamine for the Treatment of Osteoarthritis: The Time Has Come for Higher-Dose Trials

Although clinical trials with glucosamine in osteoarthritis have yielded mixed results, leading to doubts about its efficacy, the utility of glucosamine for preventing joint destruction and inflammation is well documented in rodent models of arthritis, including models of spontaneous osteoarthritis. The benefit of oral glucosamine in adjuvant arthritis is markedly dose dependent, likely reflecting a modulation of tissue levels of UDP-N-acetylglucosamine that in turn influences mucopolysaccharide synthesis and the extent of protein O-GlcNAcylation. Importantly, the minimal oral dose of glucosamine that exerts a detectible benefit in adjuvant arthritis achieves plasma glucosamine levels similar to those achieved when the standard clinical dose of glucosamine, 1.5 g daily, is administered as a bolus. The response of plasma glucosamine levels to an increase in glucosamine intake is nearly linear. Remarkably, every published clinical trial with glucosamine has employed the same 1.5 g dose that Rottapharm recommended for its proprietary glucosamine sulfate product decades ago, yet there has never been any published evidence that this dose is optimal with respect to efficacy and side effects. If this dose is on the edge of demonstrable clinical efficacy when experimental design is ideal, then variations in the patient populations targeted, the assessment vehicles employed, and the potency of glucosamine preparations tested could be expected to yield some null results. Failure to employ bolus dosing may also be a factor in the null results observed in the GAIT study and other trials. Clinical studies evaluating the dose dependency of glucosamine's influence on osteoarthritis are long overdue.

Increased O-GlcNAcylation of Endothelial Nitric Oxide Synthase Compromises the Anti-contractile Properties of Perivascular Adipose Tissue in Metabolic Syndrome

Under physiological conditions, the perivascular adipose tissue (PVAT) negatively modulates vascular contractility. This property is lost in experimental and human obesity and in the metabolic syndrome, indicating that changes in PVAT function may contribute to vascular dysfunction associated with increased body weight and hyperglycemia. The O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins (O-GlcNAcylation) is a unique posttranslational process that integrates glucose metabolism with intracellular protein activity. Increased flux of glucose through the hexosamine biosynthetic pathway and the consequent increase in tissue-specific O-GlcNAc modification of proteins have been linked to multiple facets of vascular dysfunction in diabetes and other pathological conditions. We hypothesized that chronic consumption of glucose, a condition that progresses to metabolic syndrome, leads to increased O-GlcNAc modification of proteins in the PVAT, decreasing its anti-contractile effects. Therefore, the current study was devised to determine whether a high-sugar diet increases O-GlcNAcylation in the PVAT and how increased O-GlcNAc interferes with PVAT vasorelaxant function. To assess molecular mechanisms by which O-GlcNAc contributes to PVAT dysfunction, thoracic aortas surrounded by PVAT were isolated from Wistar rats fed either a control or high sugar diet, for 10 and 12 weeks. Rats chronically fed a high sugar diet exhibited metabolic syndrome features, increased O-GlcNAcylated-proteins in the PVAT and loss of PVAT anti-contractile effect. PVAT from high sugar diet-fed rats for 12 weeks exhibited decreased NO formation, reduced expression of endothelial nitric oxide synthase (eNOS) and increased O-GlcNAcylation of eNOS. High sugar diet also decreased OGA activity and increased superoxide anion generation in the PVAT. Visceral adipose tissue samples from hyperglycemic patients showed increased levels of O-GlcNAc-modified proteins, increased ROS generation and decreased OGA activity. These data indicate that O-GlcNAcylation contributes to metabolic syndrome-induced PVAT dysfunction and that O-GlcNAcylation of eNOS may be targeted in the development of novel therapies for vascular dysfunction in conditions associated with hyperglycemia.

O-Linked β-N-Acetylglucosamine Modification of A20 Enhances the Inhibition of NF-κB (Nuclear Factor-κB) Activation and Elicits Vascular Protection After Acute Endoluminal Arterial Injury

OBJECTIVE

Recently, we have demonstrated that acute glucosamine-induced augmentation of protein O-linked β-N-acetylglucosamine (O-GlcNAc) levels inhibits inflammation in isolated vascular smooth muscle cells and neointimal formation in a rat model of carotid injury by interfering with NF-κB (nuclear factor-κB) signaling. However, the specific molecular target for O-GlcNAcylation that is responsible for glucosamine-induced vascular protection remains unclear. In this study, we test the hypothesis that increased A20 (also known as TNFAIP3 [tumor necrosis factor α-induced protein 3]) O-GlcNAcylation is required for glucosamine-mediated inhibition of inflammation and vascular protection.

APPROACH AND RESULTS

In cultured rat vascular smooth muscle cells, both glucosamine and the selective O-linked N-acetylglucosaminidase inhibitor thiamet G significantly increased A20 O-GlcNAcylation. Thiamet G treatment did not increase A20 protein expression but did significantly enhance binding to TAX1BP1 (Tax1-binding protein 1), a key regulatory protein for A20 activity. Adenovirus-mediated A20 overexpression further enhanced the effects of thiamet G on prevention of TNF-α (tumor necrosis factor-α)-induced IκB (inhibitor of κB) degradation, p65 phosphorylation, and increases in DNA-binding activity. A20 overexpression enhanced the inhibitory effects of thiamet G on TNF-α-induced proinflammatory cytokine expression and vascular smooth muscle cell migration and proliferation, whereas silencing endogenous A20 by transfection of specific A20 shRNA significantly attenuated these inhibitory effects. In balloon-injured rat carotid arteries, glucosamine treatment markedly inhibited neointimal formation and p65 activation compared with vehicle treatment. Adenoviral delivery of A20 shRNA to the injured arteries dramatically reduced balloon injury-induced A20 expression and inflammatory response compared with scramble shRNA and completely abolished the vascular protection of glucosamine.

CONCLUSIONS

These results suggest that O-GlcNAcylation of A20 plays a key role in the negative regulation of NF-κB signaling cascades in TNF-α-treated vascular smooth muscle cells in culture and in acutely injured arteries, thus protecting against inflammation-induced vascular injury.

Associations of Endogenous Estradiol and Testosterone Levels With Plaque Composition and Risk of Stroke in Subjects With Carotid Atherosclerosis

RATIONALE

Sex steroids may play a role in plaque composition and in stroke incidence.

OBJECTIVES

To study the associations of endogenous estradiol and testosterone with carotid plaque composition in elderly men and postmenopausal women with carotid atherosclerosis, as well as with risk of stroke in this population.

METHODS AND RESULTS

Data of 1023 postmenopausal women and 1124 men (≥45 years) with carotid atherosclerosis, from prospective population-based RS (Rotterdam Study), were available. At baseline, total estradiol (TE) and total testosterone (TT) were measured. Carotid atherosclerosis was assessed by ultrasound, whereas plaque composition (presence of calcification, lipid core, and intraplaque hemorrhage) was assessed by magnetic resonance imaging. TE and TT were not associated with calcified carotid plaques in either sex. TE was associated with presence of lipid core in both sexes (in women odds ratio, 1.48 [95% confidence interval [CI], 1.02-2.15]; in men odds ratio, 1.23 [95% CI, 1.03-1.46]), whereas no association was found between TT and lipid core in either sex. Higher TE (odds ratio, 1.58 [95% CI, 1.03-2.40]) and lower TT (odds ratio, 0.82 [95% CI, 0.68-0.98]) were associated with intraplaque hemorrhage in women but not in men. In women, TE was associated with increased risk of stroke (hazard ratio, 1.98 [95% CI, 1.01-3.88]), whereas no association was found in men. TT was not associated with risk of stroke in either sex.

CONCLUSIONS

TE was associated with presence of vulnerable carotid plaque as well as increased risk of stroke in women, whereas no consistent associations were found for TT in either sex.

Electrophilic probes for deciphering substrate recognition by O-GlcNAc transferase

O-linked β-N-acetylglucosamine (O-GlcNAc) transferase (OGT) is an essential human glycosyltransferase that adds O-GlcNAc modifications to numerous proteins. However, little is known about the mechanism with which OGT recognizes various protein substrates. Here we report on GlcNAc electrophilic probes (GEPs) to expedite the characterization of OGT-substrate recognition. Data from mass spectrometry, X-ray crystallization, and biochemical and radiolabeled kinetic assays support the application of GEPs to rapidly report the impacts of OGT mutations on protein substrate or sugar binding and to discover OGT residues crucial for protein recognition. Interestingly, we found that the same residues on the inner surface of the N-terminal domain contribute to OGT interactions with different protein substrates. By tuning reaction conditions, a GEP enables crosslinking of OGT with acceptor substrates in situ, affording a unique method to discover genuine substrates that weakly or transiently interact with OGT. Hence, GEPs provide new strategies to dissect OGT-substrate binding and recognition.

Glycosylation with O-linked β-N-acetylglucosamine induces vascular dysfunction via production of superoxide anion/reactive oxygen species

Overproduction of superoxide anion (•O₂^-) and O-linked β-N-acetylglucosamine (O-GlcNAc) modification in the vascular system are contributors to endothelial dysfunction. This study tested the hypothesis that increased levels of O-GlcNAc-modified proteins contribute to •O₂^- production via activation of NADPH oxidase, resulting in impaired vasodilation. Rat aortic segments and vascular smooth muscle cells (VSMCs) were incubated with vehicle (methanol) or O-(2-acetamido-2-deoxy-d-glucopyranosylidenamino) N-phenylcarbamate (PUGNAc) (100 μM). PUGNAc produced a time-dependent increase in O-GlcNAc levels in VSMC and decreased endothelium-dependent relaxation, which was prevented by apocynin and tiron, suggesting that •O₂^- contributes to endothelial dysfunction under augmented O-GlcNAc levels. Aortic segments incubated with PUGNAc also exhibited increased levels of reactive oxygen species, assessed by dihydroethidium fluorescence, and augmented •O₂^- production, determined by lucigenin-enhanced chemiluminescence. Additionally, PUGNAc treatment increased Nox-1 and Nox-4 protein expression in aortas and VSMCs. Translocation of the p47^phox subunit from the cytosol to the membrane was greater in aortas incubated with PUGNAc. VSMCs displayed increased p22^phox protein expression after PUGNAc incubation, suggesting that NADPH oxidase is activated in conditions where O-GlcNAc protein levels are increased. In conclusion, O-GlcNAc levels reduce endothelium-dependent relaxation by overproduction of •O₂^- via activation of NADPH oxidase. This may represent an additional mechanism by which augmented O-GlcNAc levels impair vascular function.

Integration of flux measurements to resolve changes in anabolic and catabolic metabolism in cardiac myocytes

Although ancillary pathways of glucose metabolism are critical for synthesizing cellular building blocks and modulating stress responses, how they are regulated remains unclear. In the present study, we used radiometric glycolysis assays, [¹³C₆]-glucose isotope tracing, and extracellular flux analysis to understand how phosphofructokinase (PFK)-mediated changes in glycolysis regulate glucose carbon partitioning into catabolic and anabolic pathways. Expression of kinase-deficient or phosphatase-deficient 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase in rat neonatal cardiomyocytes co-ordinately regulated glycolytic rate and lactate production. Nevertheless, in all groups, >40% of glucose consumed by the cells was unaccounted for via catabolism to pyruvate, which suggests entry of glucose carbons into ancillary pathways branching from metabolites formed in the preparatory phase of glycolysis. Analysis of ¹³C fractional enrichment patterns suggests that PFK activity regulates glucose carbon incorporation directly into the ribose and the glycerol moieties of purines and phospholipids, respectively. Pyrimidines, UDP-N-acetylhexosamine, and the fatty acyl chains of phosphatidylinositol and triglycerides showed lower ¹³C incorporation under conditions of high PFK activity; the isotopologue ¹³C enrichment pattern of each metabolite indicated limitations in mitochondria-engendered aspartate, acetyl CoA and fatty acids. Consistent with this notion, high glycolytic rate diminished mitochondrial activity and the coupling of glycolysis to glucose oxidation. These findings suggest that a major portion of intracellular glucose in cardiac myocytes is apportioned for ancillary biosynthetic reactions and that PFK co-ordinates the activities of the pentose phosphate, hexosamine biosynthetic, and glycerolipid synthesis pathways by directly modulating glycolytic intermediate entry into auxiliary glucose metabolism pathways and by indirectly regulating mitochondrial cataplerosis.

GFAT1 phosphorylation by AMPK promotes VEGF-induced angiogenesis

Activation of AMP-activated protein kinase (AMPK) in endothelial cells regulates energy homeostasis, stress protection and angiogenesis, but the underlying mechanisms are incompletely understood. Using a label-free phosphoproteomic analysis, we identified glutamine:fructose-6-phosphate amidotransferase 1 (GFAT1) as an AMPK substrate. GFAT1 is the rate-limiting enzyme in the hexosamine biosynthesis pathway (HBP) and as such controls the modification of proteins by O-linked β-N-acetylglucosamine (O-GlcNAc). In the present study, we tested the hypothesis that AMPK controls O-GlcNAc levels and function of endothelial cells via GFAT1 phosphorylation using biochemical, pharmacological, genetic and in vitro angiogenesis approaches. Activation of AMPK in primary human endothelial cells by 5-aminoimidazole-4-carboxamide riboside (AICAR) or by vascular endothelial growth factor (VEGF) led to GFAT1 phosphorylation at serine 243. This effect was not seen when AMPK was down-regulated by siRNA. Upon AMPK activation, diminished GFAT activity and reduced O-GlcNAc levels were observed in endothelial cells containing wild-type (WT)-GFAT1 but not in cells expressing non-phosphorylatable S243A-GFAT1. Pharmacological inhibition or siRNA-mediated down-regulation of GFAT1 potentiated VEGF-induced sprouting, indicating that GFAT1 acts as a negative regulator of angiogenesis. In cells expressing S243A-GFAT1, VEGF-induced sprouting was reduced, suggesting that VEGF relieves the inhibitory action of GFAT1/HBP on angiogenesis via AMPK-mediated GFAT1 phosphorylation. Activation of GFAT1/HBP by high glucose led to impairment of vascular sprouting, whereas GFAT1 inhibition improved sprouting even if glucose level was high. Our findings provide novel mechanistic insights into the role of HBP in angiogenesis. They suggest that targeting AMPK in endothelium might help to ameliorate hyperglycaemia-induced vascular dysfunction associated with metabolic disorders.

Insights into the role of maladaptive hexosamine biosynthesis and O-GlcNAcylation in development of diabetic cardiac complications

Diabetes mellitus significantly increases the risk of heart failure, independent of coronary artery disease. The mechanisms implicated in the development of diabetic heart disease, commonly termed diabetic cardiomyopathy, are complex, but much of the impact of diabetes on the heart can be attributed to impaired glucose handling. It has been shown that the maladaptive nutrient-sensing hexosamine biosynthesis pathway (HBP) contributes to diabetic complications in many non-cardiac tissues. Glucose metabolism by the HBP leads to enzymatically-regulated, O-linked attachment of a sugar moiety molecule, β-N-acetylglucosamine (O-GlcNAc), to proteins, affecting their biological activity (similar to phosphorylation). In normal physiology, transient activation of HBP/O-GlcNAc mechanisms is an adaptive, protective means to enhance cell survival; interventions that acutely suppress this pathway decrease tolerance to stress. Conversely, chronic dysregulation of HBP/O-GlcNAc mechanisms has been shown to be detrimental in certain pathological settings, including diabetes and cancer. Most of our understanding of the impact of sustained maladaptive HBP and O-GlcNAc protein modifications has been derived from adipose tissue, skeletal muscle and other non-cardiac tissues, as a contributing mechanism to insulin resistance and progression of diabetic complications. However, the long-term consequences of persistent activation of cardiac HBP and O-GlcNAc are not well-understood; therefore, the goal of this timely review is to highlight current understanding of the role of the HBP pathway in development of diabetic cardiomyopathy.

Dietary Calanus oil antagonizes angiotensin II-induced hypertension and tissue wasting in diet-induced obese mice

BACKGROUND

We have recently shown that Calanus oil, which is extracted from the marine copepod Calanus finmarchicus, reduces fat deposition, suppresses adipose tissue inflammation and improves insulin sensitivity in high fat-fed rodents. This study expands upon our previous observations by examining whether dietary supplementation with Calanus oil could antagonize angiotensin II (Ang II)-induced hypertension and ventricular remodeling in mice given a high fat diet (HFD).

METHODS

C57BL/6J mice were initially subjected to 8 weeks of HFD with or without 2% (w/w) Calanus oil. Thereafter, animals within each group were randomized for the administration of either Ang II (1µg/kg/min) or saline for another two weeks, while still on the same dietary regimen.

RESULTS

Ang II caused a marked decline in body and organ weights in mice receiving non-supplemented HFD, a response which was clearly attenuated in mice receiving Calanus oil supplementation. Furthermore, Ang II-induced elevation in blood pressure was also attenuated in the Calanus oil-supplemented group. As expected, infusion of Ang II produced hypertrophy and up-regulation of marker genes (mRNA level) of both hypertrophy and fibrosis in cardiac muscle, but this response was unaffected by dietary Calanus oil. Fibrosis and inflammation were up-regulated also in the aorta following Ang II infusion. However, the inflammatory response was blocked by Calanus oil supplementation. A final, and unexpected, finding was that dietary intake of Calanus oil caused a robust increase in the level of O-GlcNAcylation in cardiac tissue.

CONCLUSION

These results suggest that dietary intake of oil from the marine copepod Calanus finmarchicus could be a beneficial addition to conventional hypertension treatment. The compound attenuates inflammation and the severe metabolic stress caused by Ang II infusion. Although the present study suggests that the anti-hypertensive effect of the oil (or its n-3 PUFAs constituents) is related to its anti-inflammatory action in the vessel wall, other mechanisms such as interaction with intracellular calcium mechanisms or a direct antagonistic effect on Ang II receptors should be examined.

O-GlcNAc-ylation in the Nuclear Pore Complex

O-GlcNAc-ylation is the post-translational addition of an O-linked β-N-acetylglucosamine to the serine and threonine residues of thousands of proteins in eukaryotic cells. Specifically, half of the thirty different types of protein components in the nuclear pore complex (NPC) are modified by O-GlcNAc, of which the majority are intrinsically disordered nucleoporins (Nups) containing multiple phenylalanine-glycine (FG) repeats. Moreover, these FG-Nups form a strict selectivity barrier with a high density of O-GlcNAc in the NPC to mediate bidirectional trafficking between the cytoplasm and nucleus. However, the roles that O-GlcNAc plays in the structure and function of the NPC remain obscure. In this review paper, we will discuss the current knowledge of O-GlcNAc-ylated Nups, highlight some new techniques used to probe O-GlcNAc's roles in the nuclear pore, and finally propose a new model for the effect of O-GlcNAc on the NPC's permeability.