Glutathione depletion and acute exercise increase O-GlcNAc protein modification in rat skeletal muscle

Impact of MG132 induced-proteotoxic stress on αB-crystallin and desmin phosphorylation and O-GlcNAcylation and their partition towards cytoskeleton

Small Heat Shock Proteins are considered as the first line of defense when proteostasis fails. Among them, αB-crystallin is expressed in striated muscles in which it interacts with desmin intermediate filaments to stabilize them, maintaining cytoskeleton's integrity and muscular functionalities. Desmin is a key actor for muscle health; its targeting by αB-crystallin is thus crucial, especially in stress conditions. αB-crystallin is phosphorylated and O-GlcNAcylated. Its phosphorylation increases consecutively to various stresses, correlated with its recruitment for cytoskeleton's safeguarding. However, phosphorylation as unique signal for cytoskeleton translocation remains controversial; indeed, O-GlcNAcylation was also proposed to be involved. Thus, there are still some gaps for a deeper comprehension of how αB-crystallin functions are finely regulated by post-translational modifications. Furthermore, desmin also bears both post-translational modifications; while desmin phosphorylation is closely linked to desmin intermediates filaments turnover, it is unclear whereas its O-GlcNAcylation could impact its proper function. In the herein paper, we aim at identifying whether phosphorylation and/or O-GlcNAcylation are involved in αB-crystallin targeting towards cytoskeleton in proteotoxic stress induced by proteasome inhibition in C2C12 myotubes. We demonstrated that proteotoxicity led to αB-crystallin's phosphorylation and O-GlcNAcylation patterns changes, both presenting a dynamic interplay depending on protein subfraction. Importantly, both post-translational modifications showed a spatio-temporal variation correlated with αB-crystallin translocation towards cytoskeleton. In contrast, we did not detect any change of desmin phosphorylation and O-GlcNAcylation. All together, these data strongly support that αB-crystallin phosphorylation/O-GlcNAcylation interplay rather than changes on desmin is a key regulator for its cytoskeleton translocation, preserving it towards stress.

Hormonal, immune, and oxidative stress responses to blood flow-restricted exercise

INTRODUCTION

Heavy-load free-flow resistance exercise (HL-FFRE) is a widely used training modality. Recently, low-load blood-flow restricted resistance exercise (LL-BFRRE) has gained attention in both athletic and clinical settings as an alternative when conventional HL-FFRE is contraindicated or not tolerated. LL-BFRRE has been shown to result in physiological adaptations in muscle and connective tissue that are comparable to those induced by HL-FFRE. The underlying mechanisms remain unclear; however, evidence suggests that LL-BFRRE involves elevated metabolic stress compared to conventional free-flow resistance exercise (FFRE).

AIM

The aim was to evaluate the initial (<10 min post-exercise), intermediate (10-20 min), and late (>30 min) hormonal, immune, and oxidative stress responses observed following acute sessions of LL-BFRRE compared to FFRE in healthy adults.

METHODS

A systematic literature search of randomized and non-randomized studies was conducted in PubMed, Embase, Cochrane Central, CINAHL, and SPORTDiscus. The Cochrane Risk of Bias (RoB2, ROBINS-1) and TESTEX were used to evaluate risk of bias and study quality. Data extractions were based on mean change within groups.

RESULTS

A total of 12525 hits were identified, of which 29 articles were included. LL-BFRRE demonstrated greater acute increases in growth hormone responses when compared to overall FFRE at intermediate (SMD 2.04; 95% CI 0.87, 3.22) and late (SMD 2.64; 95% CI 1.13, 4.16) post-exercise phases. LL-BFRRE also demonstrated greater increase in testosterone responses compared to late LL-FFRE.

CONCLUSION

These results indicate that LL-BFRRE can induce increased or similar hormone and immune responses compared to LL-FFRE and HL-FFRE along with attenuated oxidative stress responses compared to HL-FFRE.

High-Intensity Interval Training Induces Protein Lactylation in Different Tissues of Mice with Specificity and Time Dependence

Protein lysine lactylation (Kla) is a novel protein acylation reported in recent years, which plays an important role in the development of several diseases with pathologically elevated lactate levels, such as tumors. The concentration of lactate as a donor is directly related to the Kla level. High-intensity interval training (HIIT) is a workout pattern that has positive effects in many metabolic diseases, but the mechanisms by which HIIT promotes health are not yet clear. Lactate is the main metabolite of HIIT, and it is unknown as to whether high lactate during HIIT can induce changes in Kla levels, as well as whether Kla levels differ in different tissues and how time-dependent Kla levels are. In this study, we observed the specificity and time-dependent effects of a single HIIT on the regulation of Kla in mouse tissues. In addition, we aimed to select tissues with high Kla specificity and obvious time dependence for lactylation quantitative omics and analyze the possible biological targets of HIIT-induced Kla regulation. A single HIIT induces Kla in tissues with high lactate uptake and metabolism, such as iWAT, BAT, soleus muscle and liver proteins, and Kla levels peak at 24 h after HIIT and return to steady state at 72 h. Kla proteins in iWAT may affect pathways related to glycolipid metabolism and are highly associated with de novo synthesis. It is speculated that the changes in energy expenditure, lipolytic effects and metabolic characteristics during the recovery period after HIIT may be related to the regulation of Kla in iWAT.

Liuwei Dihuang formula ameliorates chronic stress-induced emotional and cognitive impairments in mice by elevating hippocampal O-GlcNAc modification

A substantial body of evidence has indicated that intracerebral O-linked N-acetyl-β-D-glucosamine (O-GlcNAc), a generalized post-translational modification, was emerging as an effective regulator of stress-induced emotional and cognitive impairments. Our previous studies showed that the Liuwei Dihuang formula (LW) significantly improved the emotional and cognitive dysfunctions in various types of stress mouse models. In the current study, we sought to determine the effects of LW on intracerebral O-GlcNAc levels in chronic unpredictable mild stress (CUMS) mice. The dynamic behavioral tests showed that anxiety- and depression-like behaviors and object recognition memory of CUMS mice were improved in a dose-dependent manner after LW treatment. Moreover, linear discriminate analysis (LEfSe) of genera abundance revealed a significant difference in microbiome among the study groups. LW showed a great impact on the relative abundance of these gut microbiota in CUMS mice and reinstated them to control mouse levels. We found that LW potentially altered the Uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) biosynthesis process, and the abundance of O-GlcNAcase (OGA) and O-GlcNAc transferase (OGT) in CUMS mice, which was inferred using PICRUSt analysis. We further verified advantageous changes in hippocampal O-GlcNAc modification of CUMS mice following LW administration, as well as changes in the levels of OGA and OGT. In summary, LW intervention increased the levels of hippocampal O-GlcNAc modification and ameliorated the emotional and cognitive impairments induced by chronic stress in CUMS mice. LW therefore could be considered a potential prophylactic and therapeutic agent for chronic stress.

O-GlcNAcylation is a gatekeeper of porcine myogenesis

Although it has long been known that growth media withdrawal is a prerequisite for myoblast differentiation and fusion, the underpinning molecular mechanism remains somewhat elusive. Using isolated porcine muscle satellite cells (SCs) as the model, we show elevated O-GlcNAcylation by O-GlcNAcase (OGA) inhibition impaired SC differentiation (D5 P < 0.0001) but had unnoticeable impacts on SC proliferation. To explore the mechanism of this phenotype, we examined the expression of the transcription factor myogenin, a master switch of myogenesis, and found its expression was downregulated by elevated O-GlcNAcylation. Because insulin/IGF-1/Akt axis is a strong promoter of myoblast fusion, we measured the phosphorylated Akt and found that hyper O-GlcNAcylation inhibited Akt phosphorylation, implying OGA inhibition may also work through interfering with this critical differentiation-promoting pathway. In contrast, inhibition of O-GlcNAc transferase (OGT) by its specific inhibitor had little impact on either myoblast proliferation or differentiation (P > 0.05). To confirm these in vitro findings, we used chemical-induced muscle injury in the pig as a model to study muscle regenerative myogenesis and showed how O-GlcNAcylation functions in this process. We show a significant decrease in muscle fiber cross sectional area (CSA) when OGA is inhibited (P < 0.05), compared to nondamaged muscle, and a significant decrease compared to control and OGT inhibited muscle (P < 0.05), indicating a significant impairment in porcine muscle regeneration in vivo. Together, the in vitro and in vivo data suggest that O-GlcNAcylation may serve as a nutrient sensor during SC differentiation by gauging cellular nutrient availability and translating these signals into cellular responses. Given the importance of nutrition availability in lean muscle growth, our findings may have significant implications on how muscle growth is regulated in agriculturally important animals.

Protein O-GlcNAcylation in Metabolic Modulation of Skeletal Muscle: A Bright but Long Way to Go

O-GlcNAcylation is an atypical, dynamic and reversible O-glycosylation that is critical and abundant in metazoan. O-GlcNAcylation coordinates and receives various signaling inputs such as nutrients and stresses, thus spatiotemporally regulating the activity, stability, localization and interaction of target proteins to participate in cellular physiological functions. Our review discusses in depth the involvement of O-GlcNAcylation in the precise regulation of skeletal muscle metabolism, such as glucose homeostasis, insulin sensitivity, tricarboxylic acid cycle and mitochondrial biogenesis. The complex interaction and precise modulation of O-GlcNAcylation in these nutritional pathways of skeletal muscle also provide emerging mechanical information on how nutrients affect health, exercise and disease. Meanwhile, we explored the potential role of O-GlcNAcylation in skeletal muscle pathology and focused on its benefits in maintaining proteostasis under atrophy. In general, these understandings of O-GlcNAcylation are conducive to providing new insights into skeletal muscle (patho) physiology.

Regulation of the urea cycle by CPS1 O-GlcNAcylation in response to dietary restriction and aging

O-linked N-acetyl-glucosamine glycosylation (O-GlcNAcylation) of intracellular proteins is a dynamic process broadly implicated in age-related disease, yet it remains uncharacterized whether and how O-GlcNAcylation contributes to the natural aging process. O-GlcNAc transferase (OGT) and the opposing enzyme O-GlcNAcase (OGA) control this nutrient-sensing protein modification in cells. Here, we show that global O-GlcNAc levels are increased in multiple tissues of aged mice. In aged liver, carbamoyl phosphate synthetase 1 (CPS1) is among the most heavily O-GlcNAcylated proteins. CPS1 O-GlcNAcylation is reversed by calorie restriction and is sensitive to genetic and pharmacological manipulations of the O-GlcNAc pathway. High glucose stimulates CPS1 O-GlcNAcylation and inhibits CPS1 activity. Liver-specific deletion of OGT potentiates CPS1 activity and renders CPS1 irresponsive to further stimulation by a prolonged fasting. Our results identify CPS1 O-GlcNAcylation as a key nutrient-sensing regulatory step in the urea cycle during aging and dietary restriction, implying a role for mitochondrial O-GlcNAcylation in nutritional regulation of longevity.

O-GlcNAcylation: The Underestimated Emerging Regulators of Skeletal Muscle Physiology

O-GlcNAcylation is a highly dynamic, reversible and atypical glycosylation that regulates the activity, biological function, stability, sublocation and interaction of target proteins. O-GlcNAcylation receives and coordinates different signal inputs as an intracellular integrator similar to the nutrient sensor and stress receptor, which target multiple substrates with spatio-temporal analysis specifically to maintain cellular homeostasis and normal physiological functions. Our review gives a brief description of O-GlcNAcylation and its only two processing enzymes and HBP flux, which will help to better understand its physiological characteristics of sensing nutrition and environmental cues. This nutritional and stress-sensitive properties of O-GlcNAcylation allow it to participate in the precise regulation of skeletal muscle metabolism. This review discusses the mechanism of O-GlcNAcylation to alleviate metabolic disorders and the controversy about the insulin resistance of skeletal muscle. The level of global O-GlcNAcylation is precisely controlled and maintained in the "optimal zone", and its abnormal changes is a potential factor in the pathogenesis of cancer, neurodegeneration, diabetes and diabetic complications. Although the essential role of O-GlcNAcylation in skeletal muscle physiology has been widely studied and recognized, it still is underestimated and overlooked. This review highlights the latest progress and potential mechanisms of O-GlcNAcylation in the regulation of skeletal muscle contraction and structural properties.

FOXA2 inhibits doxorubicin-induced apoptosis via transcriptionally activating HBP rate-limiting enzyme GFPT1 in HCC cells

Apoptosis plays an important role in both carcinogenesis and cancer treatment. Understanding the mechanisms through which resistance to apoptosis occurs in cancer cells has huge implications for cancer treatment. Although pieces of evidence have shown that elevated levels of global O-GlcNAcylation play an anti-apoptotic role in myriad cancers, the underlying mechanism is still ambiguous. In this study, we demonstrated that FOXA2, an essential transcription factor for liver homeostasis and hepatocellular carcinoma (HCC) development, inhibits doxorubicin (DOX)-induced apoptosis through elevating cellular O-GlcNAcylation in HCC cells. In response to DOX treatment, elevated FOXA2 and global O-GlcNAcylation level was observed in HCC cells, and higher FOXA2 levels indicated lower levels of DOX-induced apoptosis. Subsequently, we demonstrated that FOXA2 is a direct transcriptional activator of the hexosamine biosynthetic pathway (HBP) rate-limiting enzyme GFPT1. The upregulation of FOXA2 expression induced the synthesis of intracellular UDP-GlcNAc, which is the sugar substrate of O-GlcNAcylation produced by the HBP. The flux through the HBP elevated the global O-GlcNAcylation level and led to the activation of survival signaling pathways in HCC cells. Furthermore, GFPT1 was proved to be an important downstream regulator of FOXA2-mediated apoptotic suppression. These results provide insights into the molecular mechanism by which FOXA2 inhibits DOX-induced HCC cell apoptosis and suggest that targeting FOXA2 might offer a new strategy for HCC treatment.

The glyco-redox interplay: Principles and consequences on the role of reactive oxygen species during protein glycosylation

Reactive oxygen species (ROS) carry out prime physiological roles as intracellular signaling agents, yet pathologically high concentrations of ROS cause irreversible damage to biomolecules, alter cellular programs and contribute to various diseases. While decades of intensive research have identified redox-related patterns and signaling pathways, very few addressed how the glycosylation machinery senses and responds to oxidative stress. A common trait among ROS and glycans residing on glycoconjugates is that they are both highly dynamic, as they are quickly fine-tuned in response to stressors such as inflammation, cancer and infectious diseases. On this account, the delicate balance of the redox potential, which is tightly regulated by dozens of enzymes including NOXs, and the mitochondrial electron transport chain as well as the fluidity of glycan biosynthesis resulting from the cooperation of glycosyltransferases, glycosidases, and nucleotide sugar transporters, is paramount to cell survival. Here, we review the broad spectrum of the interplay between redox changes and glycosylation with respect to their principle consequences on human physiology.

Role of O-linked N-acetylglucosamine in the homeostasis of metabolic organs, and its potential links with diabetes and its complications

Recent studies using genetically manipulated mouse models have shown the pivotal role of O-linked N-acetylglucosamine modification (O-GlcNAcylation) in the metabolism of multiple organs. The molecular mechanism involves the sensing of glucose flux by the hexosamine biosynthesis pathway, which leads to the adjustment of cellular metabolism to protect against changes in the environment of each organ through O-GlcNAcylation. More recently, not only glucose, but also fluxes of amino acids and fatty acids have been reported to induce O-GlcNAcylation, affecting multiple cellular processes. In this review, we discuss how O-GlcNAcylation maintains homeostasis in organs that are affected by diabetes mellitus: skeletal muscle, adipose tissue, liver and pancreatic β-cells. Furthermore, we discuss the importance of O-GlcNAcylation in the pathogenesis of diabetic complications. By elucidating the molecular mechanisms whereby cellular homeostasis is maintained, despite changes in metabolic flux, these studies might provide new targets for the treatment and prevention of diabetes and its complications.

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

In the mid-1980s, the identification of serine and threonine residues on nuclear and cytoplasmic proteins modified by a N-acetylglucosamine moiety (O-GlcNAc) via an O-linkage overturned the widely held assumption that glycosylation only occurred in the endoplasmic reticulum, Golgi apparatus, and secretory pathways. In contrast to traditional glycosylation, the O-GlcNAc modification does not lead to complex, branched glycan structures and is rapidly cycled on and off proteins by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery, O-GlcNAcylation has been shown to contribute to numerous cellular functions, including signaling, protein localization and stability, transcription, chromatin remodeling, mitochondrial function, and cell survival. Dysregulation in O-GlcNAc cycling has been implicated in the progression of a wide range of diseases, such as diabetes, diabetic complications, cancer, cardiovascular, and neurodegenerative diseases. This review will outline our current understanding of the processes involved in regulating O-GlcNAc turnover, the role of O-GlcNAcylation in regulating cellular physiology, and how dysregulation in O-GlcNAc cycling contributes to pathophysiological processes.

O-GlcNAcylation as a regulator of the functional and structural properties of the sarcomere in skeletal muscle: An update review

Although the O-GlcNAcylation process was discovered in 1984, its potential role in the physiology and physiopathology of skeletal muscle only emerged 20 years later. An increasing number of publications strongly support a key role of O-GlcNAcylation in the modulation of important cellular processes which are essential for skeletal muscle functions. Indeed, over a thousand of O-GlcNAcylated proteins have been identified within skeletal muscle since 2004, which belong to various classes of proteins, including sarcomeric proteins. In this review, we focused on these myofibrillar proteins, including contractile and structural proteins. Because of the modification of motor and regulatory proteins, the regulatory myosin light chain (MLC2) is related to several reports that support a key role of O-GlcNAcylation in the fine modulation of calcium activation parameters of skeletal muscle fibres, depending on muscle phenotype and muscle work. In addition, another key function of O-GlcNAcylation has recently emerged in the regulation of organization and reorganization of the sarcomere. Altogether, this data support a key role of O-GlcNAcylation in the homeostasis of sarcomeric cytoskeleton, known to be disturbed in many related muscle disorders.

Mobilization of iron from ferritin: new steps and details

Much evidence indicates that iron stored in ferritin is mobilized through protein degradation in lysosomes, but concerns about this process have lingered, and the mechanistic details of its aspects are lacking. In the studies presented here, ⁵⁹Fe-labeled ferritin was induced by preloading hepatic (HepG2) cells with radiolabeled Fe. Placing these cells in a medium containing desferrioxamine resulted in the loss of ferritin-⁵⁹Fe, but adding high concentrations of reducing agents or modulating the internal GSH concentration failed to alter the rates of ferritin-⁵⁹Fe release. Confocal microscopy showed that Fe deprivation increased the movement of ferritin into lysosomes and hyperaccumulation was observed when lysosomal proteolysis was inhibited. It also resulted in the rapid movement of DMT1 to lysosomes, which was inhibited by bafilomycin. Ferrihydrite crystals isolated from purified rat liver/spleen ferritin were solubilized at pH 5 and 7 by GSH, ascorbate, citrate and lysosomal fluids obtained from livers and J774a.1 macrophages. The inhibition of DMT1/Nramp2 and siRNA knockdown of Nramp1 each reduced the transfer of ⁵⁹Fe from lysosomes to the cytosol; and hepatocyte-specific knockout of DMT1 in mice prevented the release of Fe from the liver responding to EPO treatment, but did not inhibit lysosomal ferritin degradation. We conclude that ferritin-Fe mobilization does not occur through changes in cellular concentrations of reducing/chelating agents but by the coordinated movement of ferritin and DMT1 to lysosomes, where the ferrihydrite crystals exposed by ferritin degradation dissolve in the lysosomal fluid, and the reduced iron is transported back to the cytosol via DMT1 in hepatocytes, and by both DMT1 and Nramp1 in macrophages, prior to release into the blood or storage in ferritin.

Functional crosstalk among oxidative stress and O-GlcNAc signaling pathways

In metazoans, thousands of intracellular proteins are modified with O-linked β-N-acetylglucosamine (O-GlcNAc) in response to a wide range of stimuli and stresses. In particular, a complex and evolutionarily conserved interplay between O-GlcNAcylation and oxidative stress has emerged in recent years. Here, we review the current literature on the connections between O-GlcNAc and oxidative stress, with a particular emphasis on major signaling pathways, such as KEAP1/NRF2, FOXO, NFκB, p53 and cell metabolism. Taken together, this work sheds important light on the signaling functions of protein glycosylation and the mechanisms of stress responses alike and illuminates how the two are integrated in animal cell physiology.

Early and Persistent O-GlcNAc Protein Modification in the Streptozotocin Model of Alzheimer's Disease

 O-GlcNAc transferase (OGT), an enzyme highly expressed in brain tissue, catalyzes the addition of N-acetyl-glucosamine (GlcNAc) to hydroxyl residues of serine and threonine of proteins. Brain protein O-GlcNAcylation is diminished in Alzheimer's disease (AD), and OGT targets include proteins of the insulin-signaling pathway (e.g., insulin receptor susbtrate-1, IRS-1). We hypothesized that ICV streptozotocin (STZ) also affects O-GlcNAc protein modification. We investigated hippocampal metabolic changes in Wistar rats, particularly OGT levels and insulin resistance, as well as related astroglial activities, immediately after ICV STZ administration (first week) and later on (fourth week). We found an early (at one week) and persistent (at fourth week) decrease in OGT in the ICV STZ model of AD, characterized by a spatial cognitive deficit. Consistent with this observation, we observed a decrease in protein O-GlnNAc modification at both times. Increased phosphorylation at serine-307 of IRS-1, which is related to insulin resistance, was observed on the fourth week. The decrease in OGT and consequent protein O-GlnNAc modifications appear to precede the decrease in glucose uptake and increment of the glyoxalase system observed in the hippocampus. Changes in glial fibrillary acidic protein and S100B in the hippocampus, as well as the alterations in cerebrospinal fluid S100B, confirm the astrogliosis. Moreover, decreases in glutamine synthetase and glutathione content suggest astroglial dysfunction, which are likely implicated in the neurodegenerative cascade triggered in this model. Together, these data contribute to the understanding of neurochemical changes in the ICV STZ model of sporadic AD, and may explain the decreases in protein O-GlcNAc levels and insulin resistance observed in AD.

Protein O-GlcNAc Modification Increases in White Blood Cells After a Single Bout of Physical Exercise

Background

Protein O-linked N-acetylglucosamine (O-GlcNAc) is a dynamic posttranslational modification influencing the function of many intracellular proteins. Recently it was revealed that O-GlcNAc regulation is modified under various stress states, including ischemia and oxidative stress. Aside from a few contradictory studies based on animal models, the effect of exercise on O-GlcNAc is unexplored.

Purpose

To evaluate O-GlcNAc levels in white blood cells (WBC) of human volunteers following physical exercise.

Methods

Young (age 30 ± 5.2), healthy male volunteers (n = 6) were enlisted for the study. Blood parameters including metabolites, ions, “necro”-enzymes, and cell counts were measured before and after a single bout of exercise (2-mile run). From WBC samples, we performed western blots to detect O-GlcNAc modified proteins. The distribution of O-GlcNAc in WBC subpopulations was assessed by flow cytometry.

Results

Elevation of serum lactic acid (increased from 1.3 ± 0.4 to 6.9 ± 1.7 mM), creatinine (from 77.5 ± 6.3 U/L to 102.2 ± 7.0 μM), and lactate dehydrogenase (from 318.5 ± 26.2 to 380.5 ± 33.2 U/L) confirmed the effect of exercise. WBC count also significantly increased (from 6.6 ± 1.0 to 8.4 ± 1.4 G/L). The level of O-GlcNAc modified proteins in WBCs showed significant elevation after exercise (85 ± 51%, p < 0.05). Flow cytometry revealed that most of this change could be attributed to lymphocytes and monocytes.

Conclusion

Our results indicate that short-term exercise impacts the O-GlcNAc status of WBCs. O-GlcNAc modification could be a natural process by which physical activity modulates the immune system. Further research could elucidate the role of O-GlcNAc during exercise and validate O-GlcNAc as a biomarker for fitness assessment.

OGT-related mitochondrial motility is associated with sex differences and exercise effects in depression induced by prenatal exposure to glucocorticoids

BACKGROUND

Prenatal exposure to glucocorticoids (GCs) has been found to trigger abnormal behaviors and deleterious neurological effects on offspring both in animals and in humans. The sex differences in depression have been replicated in numerous studies across cultures, persisting throughout the reproductive years. As an X-linked gene in rodents and in humans, O-GlcNAc transferase (OGT) may provide a novel perspective for the sex differences in depression.

METHODS

In the last third of pregnancy (gestational day 14-21), rats were subcutaneously administered either 0.13mg/kg dexamethasone-21-phosphate disodium salt (0.1mg/kg DEX) or vehicle (0.9% saline) once a day for 7 days. Adolescent (4 weeks) offspring were then trained in a swimming program or not.

RESULTS

Here we found that adult offspring rats exposed to DEX prenatally exhibited sex-specific depression-like behaviors, males being more vulnerable than females. Swimming exercise ameliorated the above-mentioned depressive syndromes, which may be a compensatory effect for male disadvantage suffering from prenatal stress. Furthermore, the effects of prenatal DEX exposure and swimming exercise on depression were associated with OGT-related mitochondrial motility, including PINK1/Parkin pathway and AKT/GSK3β pathway.

LIMITATIONS

Representative kymographs of mitochondrial motility were not detected and no causal effects were obtained by OGT gene overexpression or gene knockout in this study.

CONCLUSIONS

Our results provide a new perspective for better understanding sex differences and exercise effects in depression and may offer new mechanism-based therapeutic targets for depression.

Involvement of O-GlcNAcylation in the Skeletal Muscle Physiology and Physiopathology: Focus on Muscle Metabolism

Skeletal muscle represents around 40% of whole body mass. The principal function of skeletal muscle is the conversion of chemical energy toward mechanic energy to ensure the development of force, provide movement and locomotion, and maintain posture. This crucial energy dependence is maintained by the faculty of the skeletal muscle for being a central place as a "reservoir" of amino acids and carbohydrates in the whole body. A fundamental post-translational modification, named O-GlcNAcylation, depends, inter alia, on these nutrients; it consists to the transfer or the removal of a unique monosaccharide (N-acetyl-D-glucosamine) to a serine or threonine hydroxyl group of nucleocytoplasmic and mitochondrial proteins in a dynamic process by the O-GlcNAc Transferase (OGT) and the O-GlcNAcase (OGA), respectively. O-GlcNAcylation has been shown to be strongly involved in crucial intracellular mechanisms through the modulation of signaling pathways, gene expression, or cytoskeletal functions in various organs and tissues, such as the brain, liver, kidney or pancreas, and linked to the etiology of associated diseases. In recent years, several studies were also focused on the role of O-GlcNAcylation in the physiology and the physiopathology of skeletal muscle. These studies were mostly interested in O-GlcNAcylation during muscle exercise or muscle-wasting conditions. Major findings pointed out a different "O-GlcNAc signature" depending on muscle type metabolism at resting, wasting and exercise conditions, as well as depending on acute or long-term exhausting exercise protocol. First insights showed some differential OGT/OGA expression and/or activity associated with some differential stress cellular responses through Reactive Oxygen Species and/or Heat-Shock Proteins. Robust data displayed that these O-GlcNAc changes could lead to (i) a differential modulation of the carbohydrates metabolism, since the majority of enzymes are known to be O-GlcNAcylated, and to (ii) a differential modulation of the protein synthesis/degradation balance since O-GlcNAcylation regulates some key signaling pathways such as Akt/GSK3β, Akt/mTOR, Myogenin/Atrogin-1, Myogenin/Mef2D, Mrf4 and PGC-1α in the skeletal muscle. Finally, such involvement of O-GlcNAcylation in some metabolic processes of the skeletal muscle might be linked to some associated diseases such as type 2 diabetes or neuromuscular diseases showing a critical increase of the global O-GlcNAcylation level.

Nuclear factor-erythroid-2 related transcription factor-1 (Nrf1) is regulated by O-GlcNAc transferase

The Nrf1 (Nuclear factor E2-related factor 1) transcription factor performs a critical role in regulating cellular homeostasis. Using a proteomic approach, we identified Host Cell Factor-1 (HCF1), a co-regulator of transcription, and O-GlcNAc transferase (OGT), the enzyme that mediates protein O-GlcNAcylation, as cellular partners of Nrf1a, an isoform of Nrf1. Nrf1a directly interacts with HCF1 through the HCF1 binding motif (HBM), while interaction with OGT is mediated through HCF1. Overexpression of HCF1 and OGT leads to increased Nrf1a protein stability. Addition of O-GlcNAc decreases ubiquitination and degradation of Nrf1a. Transcriptional activation by Nrf1a is increased by OGT overexpression and treatment with PUGNAc. Together, these data suggest that OGT can act as a regulator of Nrf1a.

Exercise training increases protein O-GlcNAcylation in rat skeletal muscle

Protein O-GlcNAcylation has emerged as an important intracellular signaling system with both physiological and pathophysiological functions, but the role of protein O-GlcNAcylation in skeletal muscle remains elusive. In this study, we tested the hypothesis that protein O-GlcNAcylation is a dynamic signaling system in skeletal muscle in exercise and disease. Immunoblotting showed different protein O-GlcNAcylation pattern in the prototypical slow twitch soleus muscle compared to fast twitch EDL from rats, with greater O-GlcNAcylation level in soleus associated with higher expression of the modulating enzymes O-GlcNAc transferase (OGT), O-GlcNAcase (OGA), and glutamine fructose-6-phosphate amidotransferase isoforms 1 and 2 (GFAT1, GFAT2). Six weeks of exercise training by treadmill running, but not an acute exercise bout, increased protein O-GlcNAcylation in rat soleus and EDL There was a striking increase in O-GlcNAcylation of cytoplasmic proteins ~50 kDa in size that judged from mass spectrometry analysis could represent O-GlcNAcylation of one or more key metabolic enzymes. This suggests that cytoplasmic O-GlcNAc signaling is part of the training response. In contrast to exercise training, postinfarction heart failure (HF) in rats and humans did not affect skeletal muscle O-GlcNAcylation level, indicating that aberrant O-GlcNAcylation cannot explain the skeletal muscle dysfunction in HF Human skeletal muscle displayed extensive protein O-GlcNAcylation that by large mirrored the fiber-type-related O-GlcNAcylation pattern in rats, suggesting O-GlcNAcylation as an important signaling system also in human skeletal muscle.

Changes in O-Linked N-Acetylglucosamine (O-GlcNAc) Homeostasis Activate the p53 Pathway in Ovarian Cancer Cells

O-GlcNAcylation is a dynamic post-translational modification consisting of the addition of a single N-acetylglucosamine sugar to serine and threonine residues in proteins by the enzyme O-linked β-N-acetylglucosamine transferase (OGT), whereas the enzyme O-GlcNAcase (OGA) removes the modification. In cancer, tumor samples present with altered O-GlcNAcylation; however, changes in O-GlcNAcylation are not consistent between tumor types. Interestingly, the tumor suppressor p53 is modified by O-GlcNAc, and most solid tumors contain mutations in p53 leading to the loss of p53 function. Because ovarian cancer has a high frequency of p53 mutation rates, we decided to investigate the relationship between O-GlcNAcylation and p53 function in ovarian cancer. We measured a significant decrease in O-GlcNAcylation of tumor tissue in an ovarian tumor microarray. Furthermore, O-GlcNAcylation was increased, and OGA protein and mRNA levels were decreased in ovarian tumor cell lines not expressing the protein p53. Treatment with the OGA inhibitor Thiamet-G (TMG), silencing of OGA, or overexpression of OGA and OGT led to p53 stabilization, increased nuclear localization, and increased protein and mRNA levels of p53 target genes. These data suggest that changes in O-GlcNAc homeostasis activate the p53 pathway. Combination treatment of the chemotherapeutic cisplatin with TMG decreased tumor cell growth and enhanced cell cycle arrest without impairing cytotoxicity. The effects of TMG on tumor cell growth were partially dependent on wild type p53 activation. In conclusion, changes in O-GlcNAc homeostasis activate the wild type p53 pathway in ovarian cancer cells, and OGA inhibition has the potential as an adjuvant treatment for ovarian carcinoma.

Modulation of angiotensin II signaling following exercise training in heart failure

Sympathetic activation is a consistent finding in the chronic heart failure (CHF) state. Current therapy for CHF targets the renin-angiotensin II (ANG II) and adrenergic systems. Angiotensin converting enzyme (ACE) inhibitors and ANG II receptor blockers are standard treatments along with β-adrenergic blockade. However, the mortality and morbidity of this disease is still extremely high, even with good medical management. Exercise training (ExT) is currently being used in many centers as an adjunctive therapy for CHF. Clinical studies have shown that ExT is a safe, effective, and inexpensive way to improve quality of life, work capacity, and longevity in patients with CHF. This review discusses the potential neural interactions between ANG II and sympatho-excitation in CHF and the modulation of this interaction by ExT. We briefly review the current understanding of the modulation of the angiotensin type 1 receptor in sympatho-excitatory areas of the brain and in the periphery (i.e., in the carotid body and skeletal muscle). We discuss possible cellular mechanisms by which ExT may impact the sympatho-excitatory process by reducing oxidative stress, increasing nitric oxide. and reducing ANG II. We also discuss the potential role of ACE2 and Ang 1-7 in the sympathetic response to ExT. Fruitful areas of further investigation are the role and mechanisms by which pre-sympathetic neuronal metabolic activity in response to individual bouts of exercise regulate redox mechanisms and discharge at rest in CHF and other sympatho-excitatory states.