Protein O-GlcNAcylation levels are regulated independently of dietary intake in a tissue and time-specific manner during rat postnatal development

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.

O-GlcNAcylation in ischemic diseases

Protein glycosylation is an extensively studied field, with the most studied forms being oxygen or nitrogen-linked N-acetylglucosamine (O-GlcNAc or N-GlcNAc) glycosylation. Particular residues on proteins are targeted by O-GlcNAcylation, which is among the most intricate post-translational modifications. Significantly contributing to an organism's proteome, it influences numerous factors affecting protein stability, function, and subcellular localization. It also modifies the cellular function of target proteins that have crucial responsibilities in controlling pathways related to the central nervous system, cardiovascular homeostasis, and other organ functions. Under conditions of acute stress, changes in the levels of O-GlcNAcylation of these proteins may have a defensive function. Nevertheless, deviant O-GlcNAcylation nullifies this safeguard and stimulates the advancement of several ailments, the prognosis of which relies on the cellular milieu. Hence, this review provides a concise overview of the function and comprehension of O-GlcNAcylation in ischemia diseases, aiming to facilitate the discovery of new therapeutic targets for efficient treatment, particularly in patients with diabetes.

O-GlcNAcylation levels remain stable regardless of the anaesthesia in healthy rats

Anaesthetics are used daily in human and veterinary medicine as well as in scientific research. Anaesthetics have an impact on cell homeostasis especially through modulation of protein post-translational modifications. O-GlcNAcylation, a ubiquitous post-translational modification, plays a role in many biological processes. The aims of this study were to evaluate whether (1) anaesthesia influences O-GlcNAcylation and (2) its stimulation affects physiological parameters. Male Wistar rats (n = 38) were anaesthetized with ketamine-xylazine or isoflurane. They randomly received either an intravenous injection of Ringer's lactate or NButGT (10mg/kg) in order to increase O-GlcNAcylation levels. One hour after induction of anaesthesia, haemodynamic parameters and plasmatic markers were evaluated. Heart, brain and lungs were harvested and O-GlcNAcylation levels and O-GlcNAc-related enzymes were evaluated by western blot. Cardiac and pulmonary O-GlcNAcylation levels and cardiac, cerebral and pulmonary O-GlcNAc associated enzyme expression were not impacted with anaesthesia. Compared with ketamine-xylazine, isoflurane had a lower impact on blood pressure, heart rate and glycaemia. Pharmacological stimulation of O-GlcNAcylation by NButGT did not affect the physiological parameters. This study offers unprecedented insights into the regulation of O-GlcNAcylation and O-GlcNAc related enzymes during anaesthesia. Pharmacological stimulation of O-GlcNAcylation over a 1-h period did not disrupt the physiological balance in healthy anaesthetized rats.

O-GlcNAcylation: the sweet side of epigenetics

Histones display a wide variety of post-translational modifications, including acetylation, methylation, and phosphorylation. These epigenetic modifications can influence chromatin structure and function without altering the DNA sequence. Histones can also undergo post-translational O-GlcNAcylation, a rather understudied modification that plays critical roles in almost all biological processes and is added and removed by O-linked N-acetylglucosamine transferase and O-GlcNAcase, respectively. This review provides a current overview of our knowledge of how O-GlcNAcylation impacts the histone code both directly and by regulating other chromatin modifying enzymes. This highlights the pivotal emerging role of O-GlcNAcylation as an essential epigenetic marker.

O-GlcNAcylation: cellular physiology and therapeutic target for human diseases

O-linked-β-N-acetylglucosamine (O-GlcNAcylation) is a distinctive posttranslational protein modification involving the coordinated action of O-GlcNAc transferase and O-GlcNAcase, primarily targeting serine or threonine residues in various proteins. This modification impacts protein functionality, influencing stability, protein-protein interactions, and localization. Its interaction with other modifications such as phosphorylation and ubiquitination is becoming increasingly evident. Dysregulation of O-GlcNAcylation is associated with numerous human diseases, including diabetes, nervous system degeneration, and cancers. This review extensively explores the regulatory mechanisms of O-GlcNAcylation, its effects on cellular physiology, and its role in the pathogenesis of diseases. It examines the implications of aberrant O-GlcNAcylation in diabetes and tumorigenesis, highlighting novel insights into its potential role in cardiovascular diseases. The review also discusses the interplay of O-GlcNAcylation with other protein modifications and its impact on cell growth and metabolism. By synthesizing current research, this review elucidates the multifaceted roles of O-GlcNAcylation, providing a comprehensive reference for future studies. It underscores the potential of targeting the O-GlcNAcylation cycle in developing novel therapeutic strategies for various pathologies.

Foetal recapitulation of nutrient surplus signalling by O-GlcNAcylation and the failing heart

The development of the foetal heart is driven by increased glucose uptake and activation of mammalian target of rapamycin (mTOR) and hypoxia-inducible factor-1α (HIF-1α), which drives glycolysis. In contrast, the healthy adult heart is governed by sirtuin-1 (SIRT1) and adenosine monophosphate-activated protein kinase (AMPK), which promote fatty-acid oxidation and the substantial mitochondrial ATP production required for survival in a high-workload normoxic environment. During cardiac injury, the heart recapitulates the foetal signalling programme, which (although adaptive in the short term) is highly deleterious if sustained for long periods of time. Prolonged increases in glucose uptake in cardiomyocytes under stress leads to increased flux through the hexosamine biosynthesis pathway; its endproduct - uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) - functions as a critical nutrient surplus sensor. UDP-GlcNAc drives the post-translational protein modification known as O-GlcNAcylation, which rapidly and reversibly modifies thousands of intracellular proteins. Both O-GlcNAcylation and phosphorylation act at serine/threonine residues, but whereas phosphorylation is regulated by hundreds of specific kinases and phosphatases, O-GlcNAcylation is regulated by only two enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which adds or removes GlcNAc (N-acetylglucosamine), respectively, from target proteins. Recapitulation of foetal programming in heart failure (regardless of diabetes) is accompanied by marked increases in O-GlcNAcylation, both experimentally and clinically. Heightened O-GlcNAcylation in the heart leads to impaired calcium kinetics and contractile derangements, arrhythmias related to activation of voltage-gated sodium channels and Ca2+ /calmodulin-dependent protein kinase II, mitochondrial dysfunction, and maladaptive hypertrophy, microvascular dysfunction, fibrosis and cardiomyopathy. These deleterious effects can be prevented by suppression of O-GlcNAcylation, which can be achieved experimentally by upregulation of AMPK and SIRT1 or by pharmacological inhibition of OGT or stimulation of OGA. The effects of sodium-glucose cotransporter 2 (SGLT2) inhibitors on the heart are accompanied by reduced O-GlcNAcylation, and their cytoprotective effects are reportedly abrogated if their action to suppress O-GlcNAcylation is blocked. Such an action may represent one of the many mechanisms by which enhanced AMPK and SIRT1 signalling following SGLT2 inhibition leads to cardiovascular benefits. These observations, taken collectively, suggest that UDP-GlcNAc functions as a critical nutrient surplus sensor (which acting in concert with mTOR and HIF-1α) can promote the development of cardiomyopathy.

First comprehensive identification of cardiac proteins with putative increased O-GlcNAc levels during pressure overload hypertrophy

Protein posttranslational modifications (PTMs) by O-GlcNAc globally rise during pressure-overload hypertrophy (POH). However, a major knowledge gap exists on the specific proteins undergoing changes in O-GlcNAc levels during POH primarily because this PTM is low abundance and easily lost during standard mass spectrometry (MS) conditions used for protein identification. Methodologies have emerged to enrich samples for O-GlcNAcylated proteins prior to MS analysis. Accordingly, our goal was to identify the specific proteins undergoing changes in O-GlcNAc levels during POH. We used C57/Bl6 mice subjected to Sham or transverse aortic constriction (TAC) to create POH. From the hearts, we labelled the O-GlcNAc moiety with tetramethylrhodamine azide (TAMRA) before sample enrichment by TAMRA immunoprecipitation (IP). We used LC-MS/MS to identify and quantify the captured putative O-GlcNAcylated proteins. We identified a total of 700 putative O-GlcNAcylated proteins in Sham and POH. Two hundred thirty-three of these proteins had significantly increased enrichment in POH over Sham suggesting higher O-GlcNAc levels whereas no proteins were significantly decreased by POH. We examined two MS identified metabolic enzymes, CPT1B and the PDH complex, to validate by immunoprecipitation. We corroborated increased O-GlcNAc levels during POH for CPT1B and the PDH complex. Enzyme activity assays suggests higher O-GlcNAcylation increases CPT1 activity and decreases PDH activity during POH. In summary, we generated the first comprehensive list of proteins with putative changes in O-GlcNAc levels during POH. Our results demonstrate the large number of potential proteins and cellular processes affected by O-GlcNAc and serve as a guide for testing specific O-GlcNAc-regulated mechanisms during POH.

Beneficial Effects of O-GlcNAc Stimulation in a Young Rat Model of Sepsis: Beyond Modulation of Gene Expression

The young population, which is particularly at risk of sepsis, is, paradoxically, rarely studied. Acute stimulation of O-GlcNAcylation, a post-translational modification involved in metabolic regulation, cell survival and stress response, is beneficial in young rats with sepsis. Considering that sepsis impacts the gene expression profile and that O-GlcNAcylation is a regulator of transcription, the aims of this study are to (i) unveil beneficial mechanisms of O-GlcNAcylation and (ii) decipher the relationship between O-GlcNAcylation and transcription during sepsis. Endotoxemic challenge was induced in 28-day-old male rats using a lipopolysaccharide injection (E. coli O111:B4, 20 mg·kg−1) and compared to control rats (NaCl 0.9%). One hour after, rats were assigned to no therapy or fluidotherapy (NaCl 0.9%, 10 mL.kg−1) ± NButGT (10 mg·kg−1) to stimulate O-GlcNAc levels. Cardiac O-GlcNAcylation levels were evaluated via Western blot and gene transcription using 3′ SRP analysis. Lipopolysaccharide injection favorizes inflammatory state with the overexpression of genes involved in the NF-κB, JAK/STAT and MAPK pathways. NButGT treatment increased cardiac O-GlcNAcylation levels (p < 0.05). Yet, the mRNA expression was not impacted two hours after fluidotherapy or NButGT treatment. In conclusion, O-GlcNAc stimulation-induced beneficial effects are not dependent on the gene expression profile at the early phase of sepsis.

The Endothelial Dysfunction Could Be a Cause of Heart Failure with Preserved Ejection Fraction Development in a Rat Model

50% of patients with heart failure have a preserved ejection fraction (HFpEF). Numerous studies have investigated the pathophysiological mechanisms of HFpEF and have shown that endothelial dysfunction plays an important role in HFpEF. Yet no studies answered whether endothelial dysfunction could be the cause or is the consequence of HFpEF. Recently, we have shown that the endothelial overexpression of human β3-adrenoreceptor (Tgβ3) in rats leads to the slow development of diastolic dysfunction over ageing. The aim of the study is to decipher the involvement of endothelial dysfunction in the HFpEF development. For that, we investigated endothelial and cardiac function in 15-, 30-, and 45-week-old wild-type (WT) and Tgβ3 rats. The aortic expression of •NO synthase (NOS) isoforms was evaluated by Western blot. Finally, electron paramagnetic resonance measurements were performed on aortas to evaluate •NO and O2•- production. Vascular reactivity was altered as early as 15 weeks of age in response to isoproterenol in Tgβ3 aortas and mesenteric arteries. NOS1 (neuronal NOS) expression was higher in the Tgβ3 aorta at 30 and 45 weeks of age (30 weeks: WT: $1.00\pm 0.21$ ; Tgβ3: $6.08\pm 2.30$ ; 45 weeks: WT: $1.00\pm 0.12$ ; Tgβ3: $1.55\pm 0.17$ ; $p<0.05$ ). Interestingly, the endothelial NOS (NOS3) monomer form is increased in Tgβ3 rats at 45 weeks of age (ratio NOS3 dimer/NOS3 monomer; WT: $1.00\pm 0.37$ ; Tgβ3: $0.13\pm 0.05$ ; $p<0.05$ ). Aortic •NO production was increased by NOS2 (inducible NOS) at 15 weeks of age in Tgβ3 rats (+52% vs. WT). Aortic O2•- production was increased in Tgβ3 rats at 30 and 45 weeks of age (+75% and+76%, respectively, vs. WT, $p<0.05$ ). We have shown that endothelial dysfunction and oxidative stress are present as early as 15 weeks of age and therefore conclude that endothelial dysfunction could be a cause of HFpEF development.

A roadmap for the characterization of energy metabolism in human cardiomyocytes derived from induced pluripotent stem cells

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) are an increasingly employed model in cardiac research and drug discovery. As cellular metabolism plays an integral role in determining phenotype, the characterization of the metabolic profile of hiPSC-CM during maturation is crucial for their translational application. In this study we employ a combination of methods including extracellular flux, 13C-glucose enrichment and targeted metabolomics to characterize the metabolic profile of hiPSC-CM during their maturation in culture from 6 weeks, up to 12 weeks. Results show a progressive remodeling of pathways involved in energy metabolism and substrate utilization along with an increase in sarcomere regularity. The oxidative capacity of hiPSC-CM and particularly their ability to utilize fatty acids increased with time. In parallel, relative glucose oxidation was reduced while glutamine oxidation was maintained at similar levels. There was also evidence of increased coupling of glycolysis to mitochondrial respiration, and away from glycolytic branch pathways at later stages of maturation. The rate of glycolysis as assessed by lactate production was maintained at both stages but with significant alterations in proximal glycolytic enzymes such as hexokinase and phosphofructokinase. We observed a progressive maturation of mitochondrial oxidative capacity at comparable levels of mitochondrial content between these time-points with enhancement of mitochondrial network structure. These results show that the metabolic profile of hiPSC-CM is progressively restructured, recapitulating aspects of early post-natal heart development. This would be particularly important to consider when employing these cell model in studies where metabolism plays an important role.

The dual role of the hexosamine biosynthetic pathway in cardiac physiology and pathophysiology

The heart is a highly metabolic organ with extensive energy demands and hence relies on numerous fuel substrates including fatty acids and glucose. However, oxidative stress is a natural by-product of metabolism that, in excess, can contribute towards DNA damage and poly-ADP-ribose polymerase activation. This activation inhibits key glycolytic enzymes, subsequently shunting glycolytic intermediates into non-oxidative glucose pathways such as the hexosamine biosynthetic pathway (HBP). In this review we provide evidence supporting the dual role of the HBP, i.e. playing a unique role in cardiac physiology and pathophysiology where acute upregulation confers cardioprotection while chronic activation contributes to the onset and progression of cardio-metabolic diseases such as diabetes, hypertrophy, ischemic heart disease, and heart failure. Thus although the HBP has emerged as a novel therapeutic target for such conditions, proposed interventions need to be applied in a context- and pathology-specific manner to avoid any potential drawbacks of relatively low cardiac HBP activity.

An O-GlcNAcylomic Approach Reveals ACLY as a Potential Target in Sepsis in the Young Rat

Sepsis in the young population, which is particularly at risk, is rarely studied. O-GlcNAcylation is a post-translational modification involved in cell survival, stress response and metabolic regulation. O-GlcNAc stimulation is beneficial in adult septic rats. This modification is physiologically higher in the young rat, potentially limiting the therapeutic potential of O-GlcNAc stimulation in young septic rats. The aim is to evaluate whether O-GlcNAc stimulation can improve sepsis outcome in young rats. Endotoxemic challenge was induced in 28-day-old rats by lipopolysaccharide injection (E. Coli O111:B4, 20 mg·kg-1) and compared to control rats (NaCl 0.9%). One hour after lipopolysaccharide injection, rats were randomly assigned to no therapy, fluidotherapy (NaCl 0.9%, 10 mL·kg-1) ± NButGT (10 mg·kg-1) to increase O-GlcNAcylation levels. Physiological parameters and plasmatic markers were evaluated 2h later. Finally, untargeted mass spectrometry was performed to map cardiac O-GlcNAcylated proteins. Lipopolysaccharide injection induced shock with a decrease in mean arterial pressure and alteration of biological parameters (p < 0.05). NButGT, contrary to fluidotherapy, was associated with an improvement of arterial pressure (p < 0.05). ATP citrate lyase was identified among the O-GlcNAcylated proteins. In conclusion, O-GlcNAc stimulation improves outcomes in young septic rats. Interestingly, identified O-GlcNAcylated proteins are mainly involved in cellular metabolism.

Protein O-GlcNAcylation levels are regulated independently of dietary intake in a tissue and time-specific manner during rat postnatal development

Aim

Metabolic sources switch from carbohydrates in utero, to fatty acids after birth and then a mix once adults. O‐GlcNAcylation (O‐GlcNAc) is a post‐translational modification considered as a nutrient sensor. The purpose of this work was to assess changes in protein O‐GlcNAc levels, regulatory enzymes and metabolites during the first periods of life and decipher the impact of O‐GlcNAcylation on cardiac proteins.

Methods

Heart, brain and liver were harvested from rats before and after birth (D‐1 and D0), in suckling animals (D12), after weaning with a standard (D28) or a low‐carbohydrate diet (D28F), and adults (D84). O‐GlcNAc levels and regulatory enzymes were evaluated by western blots. Mass spectrometry (MS) approaches were performed to quantify levels of metabolites regulating O‐GlcNAc and identify putative cardiac O‐GlcNAcylated proteins.

Results

Protein O‐GlcNAc levels decrease drastically and progressively from D‐1 to D84 (13‐fold, P < .05) in the heart, whereas the changes were opposite in liver and brain. O‐GlcNAc levels were unaffected by weaning diet in any tissues. Changes in expression of enzymes and levels of metabolites regulating O‐GlcNAc were tissue‐dependent. MS analyses identified changes in putative cardiac O‐GlcNAcylated proteins, namely those involved in the stress response and energy metabolism, such as ACAT1, which is only O‐GlcNAcylated at D0.

Conclusion

Our results demonstrate that protein O‐GlcNAc levels are not linked to dietary intake and regulated in a time and tissue‐specific manner during postnatal development. We have identified by untargeted MS putative proteins with a particular O‐GlcNAc signature across the development process suggesting specific role of these proteins.