Glucose sensor O-GlcNAcylation coordinates with phosphorylation to regulate circadian clock

Quantitative and site-specific chemoproteomic profiling of O-GlcNAcylation in Drosophila

Protein O-GlcNAcylation plays a crucial role in Drosophila melanogaster development. Dysregulation of O-GlcNAc transferase (sxc/Ogt) and O-GlcNAcase (Oga) disrupts early embryogenesis and locomotor behavior. It is therefore of great interest to identify and quantitatively analyze O-GlcNAcylation sites in Drosophila. Here, we perform quantitative and site-specific profiling of O-GlcNAcylation in Drosophila by employing a chemoenzymatic labeling strategy. A total of 2196 unambiguous O-GlcNAcylation sites and 1308 O-GlcNAcylated proteins are identified. Quantitative analysis of O-GlcNAcylation in the head of Drosophila with sxc/Ogt knockdown in GABAergic neurons reveals a reduction in O-GlcNAcylation of several proteins involved in muscle development, consistent with the phenotypic defects observed in sxc/Ogt RNAi Drosophila. Furthermore, quantitative analysis of O-GlcNAcylation under a high-sugar diet reveals altered O-GlcNAcylation of several proteins associated with obesity and neurological diseases, such as Hex-A and Ankyrin 2. Our study not only establishes an effective method for large-scale identification of O-GlcNAcylation sites, but also provides a valuable resource for studying O-GlcNAc biology in Drosophila.

Periodic dietary restriction of animal products induces metabolic reprogramming in humans with effects on cardiometabolic health

Dietary interventions constitute powerful approaches for disease prevention and treatment. However, the molecular mechanisms through which diet affects health remain underexplored in humans. Here, we compare plasma metabolomic and proteomic profiles between dietary states for a unique group of individuals who alternate between omnivory and restriction of animal products for religious reasons. We find that short-term restriction drives reductions in levels of lipid classes and of branched-chain amino acids, not detected in a control group of individuals, and results in metabolic profiles associated with decreased risk for all-cause mortality. We show that 23% of proteins whose levels are affected by dietary restriction are druggable targets and reveal that pro-longevity hormone FGF21 and seven additional proteins (FOLR2, SUMF2, HAVCR1, PLA2G1B, OXT, SPP1, HPGDS) display the greatest magnitude of change. Through Mendelian randomization we demonstrate potentially causal effects of FGF21 and HAVCR1 on risk for type 2 diabetes, of HPGDS on BMI, and of OXT on risk for lacunar stroke. Collectively, we find that restriction-associated reprogramming improves metabolic health and emphasise high-value targets for pharmacological intervention.

Metabolites-mediated posttranslational modifications in cardiac metabolic remodeling: Implications for disease pathology and therapeutic potential

The nonenergy - producing functions of metabolism are attracting increasing attention, as metabolic changes are involved in discrete pathways modulating enzyme activity and gene expression. Substantial evidence suggests that myocardial metabolic remodeling occurring during diabetic cardiomyopathy, heart failure, and cardiac pathological stress (e.g., myocardial ischemia, pressure overload) contributes to the progression of pathology. Within the rewired metabolic network, metabolic intermediates and end-products can directly alter protein function and/or regulate epigenetic modifications by providing acyl groups for posttranslational modifications, thereby affecting the overall cardiac stress response and providing a direct link between cellular metabolism and cardiac pathology. This review provides a comprehensive overview of the functional diversity and mechanistic roles of several types of metabolite-mediated histone and nonhistone acylation, namely O-GlcNAcylation, lactylation, crotonylation, β-hydroxybutyrylation, and succinylation, as well as fatty acid-mediated modifications, in regulating physiological processes and contributing to the progression of heart disease. Furthermore, it explores the potential of these modifications as therapeutic targets for disease intervention.

Brain O-GlcNAcylation: Bridging physiological functions, disease mechanisms, and therapeutic applications

O-GlcNAcylation, a dynamic post-translational modification occurring on serine or threonine residues of numerous proteins, plays a pivotal role in various cellular processes, including gene regulation, metabolism, and stress response. Abundant in the brain, O-GlcNAcylation intricately governs neurodevelopment, synaptic assembly, and neuronal functions. Recent investigations have established a correlation between the dysregulation of brain O-GlcNAcylation and a broad spectrum of neurological disorders and injuries, spanning neurodevelopmental, neurodegenerative, and psychiatric conditions, as well as injuries to the central nervous system (CNS). Manipulating O-GlcNAcylation has demonstrated neuroprotective properties against these afflictions. This review delineates the roles and mechanisms of O-GlcNAcylation in the CNS under both physiological and pathological circumstances, with a focus on its neuroprotective effects in neurological disorders and injuries. We discuss the involvement of O-GlcNAcylation in key processes such as neurogenesis, synaptic plasticity, and energy metabolism, as well as its implications in conditions like Alzheimer's disease, Parkinson's disease, and ischemic stroke. Additionally, we explore prospective therapeutic approaches for CNS disorders and injuries by targeting O-GlcNAcylation, highlighting recent clinical developments and future research directions. This comprehensive overview aims to provide insights into the potential of O-GlcNAcylation as a therapeutic target and guide future investigations in this promising field.

Uncovering the intricacies of O-GlcNAc modification in cognitive impairment: New insights from regulation to therapeutic targeting

O-linked β-N-acetylglucosamine (O-GlcNAc) represents a post-translational modification that occurs on serine or threonine residues on various proteins. This conserved modification interacts with vital cellular pathways. Although O-GlcNAc is widely distributed throughout the body, it is particularly enriched in the brain, where most proteins are O-GlcNAcylated. Recent studies have established a causal link between O-GlcNAc regulation in the brain and alterations in neurophysiological function. Alterations in O-GlcNAc levels in the brain are associated with the pathogenesis of several neurogenic diseases that can lead to cognitive impairment. Remarkably, manipulation of O-GlcNAc levels demonstrated a protective effect on cognitive function. Although the precise molecular mechanism of O-GlcNAc modification in the nervous system remains elusive, its regulation is fundamental to multiple neural and cognitive functions, fluctuating levels during normal and pathological cognitive processes. In this review, we highlight the significant functional importance of O-GlcNAc modification in pathological cognitive impairments and the potential application of O-GlcNAc as a promising target for the intervention or amelioration of cognitive impairments.

Regulation of Sleep Amount by CRTC1 via Transcription of Crh in Mice

The cAMP response element binding protein (CREB) is required for regulation of daily sleep amount, whereas gain of function of CREB-regulated transcription coactivator 1 (CRTC1) causes severe insomnia in mice. However, the physiological functions of CRTCs and their downstream target genes in the regulation of sleep amount remain unclear. Here, we use an adult brain chimeric (ABC)-expression/knock-out platform for somatic genetic analysis of sleep in adult male mice. ABC expression of constitutively active mutant CRTC1/2CA in the mouse brain neurons significantly reduces the amount of non-rapid eye movement sleep (NREMS) and/or rapid eye movement sleep (REMS). Consistent with the fact that SIK3 phosphorylates and inhibits CRTCs, ABC expression of CRTC1/2/3CA rescues the hypersomnia phenotype of Sleepy (Sik3Slp ) mice. While ABC-Crtc2KO or Crtc3KO causes no sleep phenotype, ABC-Crtc1KO or ABC expression of dominant-negative CRTC (dnCRTC) results in a modest reduction of NREMS amount accompanied with elevated NREMS delta power. Moreover, ABC expression of CRTC1CA or dnCRTC in the excitatory neurons causes bidirectional changes of NREMS/REMS amount and/or NREMS delta power. The ability of CRTC1CA to regulate sleep requires its transactivation domain and CREB-binding domain and is dependent on CREB. Furthermore, we showed that inducible ABC expression of corticotropin-releasing hormone (Crh) and brain-derived neurotrophic factor (Bdnf)-two target genes of CRTCs-significantly reduces daily sleep amount. Notably, ABC-CrhKO , but not BdnfKO , rescues the insomnia phenotype of ABC-CRTC1CA mice. Taken together, these results indicate that the CREB-CRTC1 complex regulates daily sleep amount by modulating the transcription of Crh in the mouse brain neurons.

PERspectives on circadian cell biology

Daily rhythms in the activities of PERIOD proteins are critical to the temporal regulation of mammalian physiology. While the molecular partners and genetic circuits that allow PERIOD to effect auto-repression and regulate transcriptional programmes are increasingly well understood, comprehension of the time-resolved mechanisms that allow PERIOD to conduct this daily dance is incomplete. Here, we consider the character and controversies of this central mammalian clock protein with a focus on its intrinsically disordered nature.This article is part of the Theo Murphy meeting issue 'Circadian rhythms in infection and immunity'.

Epigenetic Mechanisms in the Transcriptional Regulation of Circadian Rhythm in Mammals

Almost all organisms, from the simplest bacteria to advanced mammals, havea near 24 h circadian rhythm. Circadian rhythms are highly conserved across different life forms and are regulated by circadian genes as well as by related transcription factors. Transcription factors are fundamental to circadian rhythms, influencing gene expression, behavior in plants and animals, and human diseases. This review examines the foundational research on transcriptional regulation of circadian rhythms, emphasizing histone modifications, chromatin remodeling, and Pol II pausing control. These studies have enhanced our understanding of transcriptional regulation within biological circadian rhythms and the importance of circadian biology in human health. Finally, we summarize the progress and challenges in these three areas of regulation to move the field forward.

Opportunities for Therapeutic Modulation of O-GlcNAc

O-Linked β-N-acetylglucosamine (O-GlcNAc) is an essential, dynamic monosaccharide post-translational modification (PTM) found on serine and threonine residues of thousands of nucleocytoplasmic proteins. The installation and removal of O-GlcNAc is controlled by a single pair of enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Since its discovery four decades ago, O-GlcNAc has been found on diverse classes of proteins, playing important functional roles in many cellular processes. Dysregulation of O-GlcNAc homeostasis has been implicated in the pathogenesis of disease, including neurodegeneration, X-linked intellectual disability (XLID), cancer, diabetes, and immunological disorders. These foundational studies of O-GlcNAc in disease biology have motivated efforts to target O-GlcNAc therapeutically, with multiple clinical candidates under evaluation. In this review, we describe the characterization and biochemistry of OGT and OGA, cellular O-GlcNAc regulation, development of OGT and OGA inhibitors, O-GlcNAc in pathophysiology, clinical progress of O-GlcNAc modulators, and emerging opportunities for targeting O-GlcNAc. This comprehensive resource should motivate further study into O-GlcNAc function and inspire strategies for therapeutic modulation of O-GlcNAc.

O-GlcNAcylation of circadian clock protein Bmal1 impairs cognitive function in diabetic mice

Neuronal damage in the hippocampus induced by high glucose has been shown to promote the onset and development of cognitive impairment in diabetes, but the underlying molecular mechanism remains unclear. Guided by single-cell RNA sequencing, we here report that high glucose increases O-GlcNAcylation of Bmal1 in hippocampal neurons. This glycosylation promotes the binding of Clock to Bmal1, resulting in the expression of transcription factor Bhlhe41 and its target Dnajb4. Upregulated Dnajb4 in turn leads to ubiquitination and degradation of the mitochondrial Na + /Ca2+ exchanger NCLX, thereby inducing mitochondrial calcium overload that causes neuronal damage and cognitive impairment in mice. Notably, Bhlhe41 downregulation or treatment with a short peptide that specifically blocks O-GlcNAcylation of Bmal1 on Ser424 mitigated these adverse effects in diabetic mouse models. These data highlight the crucial role of O-GlcNAcylation in circadian clock gene expression and may facilitate the design of targeted therapies for diabetes-associated cognitive impairment.

14-3-3ε augments OGT stability by binding with S20-phosphorylated OGT

The relationship between O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) and mitosis is intertwined. Besides the numerous mitotic OGT substrates that have been identified, OGT itself is also a target of the mitotic machinery. Previously, our investigations have shown that Checkpoint kinase 1 (Chk1) phosphorylates OGT at Ser-20 to increase OGT levels during cytokinesis, suggesting that OGT levels oscillate as mitosis progresses. Herein we studied its underlying mechanism. We set out from an R17C mutation of OGT, which is a uterine carcinoma mutation in The Cancer Genome Atlas. We found that R17C abolishes the S20 phosphorylation of OGT, as it lies in the Chk1 phosphorylating consensus motif. Consistent with our previous report that pSer-20 is essential for OGT level increases during cytokinesis, we further demonstrate that the R17C mutation renders OGT less stable, decreases vimentin phosphorylation levels and results in cytokinesis defects. Based on bioinformatic predictions, pSer-20 renders OGT more likely to interact with 14-3-3 proteins, the phospho-binding signal adaptor/scaffold protein family. By screening the seven isoforms of 14-3-3 family, we show that 14-3-3ε specifically associates with Ser-20-phosphorylated OGT. Moreover, we studied the R17C and S20A mutations in xenograft models and demonstrated that they both inhibit uterine carcinoma compared to wild-type OGT, probably due to less cellular reproduction. Our work is a sequel of our previous report on pS20 of OGT and is in line with the notion that OGT is intricately regulated by the mitotic network.

Light-Dependent Circadian Rhythm Governs O-GlcNAc Cycling to Influence Cognitive Function in Adult Zebrafish

This study explores the 24-h rhythmic cycle of protein O-GlcNAcylation within the brain and highlights its crucial role in regulating the circadian cycle and neuronal function based on zebrafish as an animal model. In our experiments, disruption of the circadian rhythm, achieved through inversion of the light-dark cycle or daytime melatonin treatment, not only impaired the rhythmic changes of O-GlcNAcylation along with altering expression patterns of O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) in zebrafish brain but also significantly impeded learning and memory function. In particular, circadian disruption affected rhythmic expression of protein O-GlcNAcylation and OGT in the nuclear fraction. Notably, the circadian cycle induces rhythmic alterations in O-GlcNAcylation of H2B histone protein that correspond to changes in H3 trimethylation. Disruption of the cycle interfered with these periodic histone code alterations. Pharmacological inhibition of OGT with OSMI-1 disrupted the wake-sleep patterns of zebrafish without affecting expression of circadian rhythm-regulating genes. OSMI-1 inhibited the expression of c-fos, bdnf, and calm1, key genes associated with brain function and synaptic plasticity, and decreased the binding of O-GlcNAcylated H2B and OGT to promoter regions of these genes. The collective findings support the potential involvement of circadian cycling of the O-GlcNAc histone code in regulating synaptic plasticity and brain function. Overall, data from this study provide evidence that protein O-GlcNAcylation serves as a pivotal posttranslational mechanism integrating circadian signals and neuronal function to regulate rhythmic physiology.

A metabolic perspective to sleep genetics

The metabolic signals that regulate sleep and the metabolic functions that occur during sleep are active areas of research. Prior studies have focused on sugars and nucleotides but new genetic evidence suggests novel functions of lipid and amino acid metabolites in sleep. Additional genetic studies of energetic signaling pathways and the circadian clock transcription factor network have increased our understanding of how sleep responds to changes in the metabolic state. This review focuses on key recent insights from genetic experiments in humans and model organisms to improve our understanding of the interrelationship between metabolism and sleep.

The multifaceted role of intracellular glycosylation in cytoprotection and heart disease

The modification of nuclear, cytoplasmic, and mitochondrial proteins by O-linked β-N-actylglucosamine (O-GlcNAc) is an essential posttranslational modification that is common in metozoans. O-GlcNAc is cycled on and off proteins in response to environmental and physiological stimuli impacting protein function, which, in turn, tunes pathways that include transcription, translation, proteostasis, signal transduction, and metabolism. One class of stimulus that induces rapid and dynamic changes to O-GlcNAc is cellular injury, resulting from environmental stress (for instance, heat shock), hypoxia/reoxygenation injury, ischemia reperfusion injury (heart attack, stroke, trauma hemorrhage), and sepsis. Acute elevation of O-GlcNAc before or after injury reduces apoptosis and necrosis, suggesting that injury-induced changes in O-GlcNAcylation regulate cell fate decisions. However, prolonged elevation or reduction in O-GlcNAc leads to a maladaptive response and is associated with pathologies such as hypertrophy and heart failure. In this review, we discuss the impact of O-GlcNAc in both acute and prolonged models of injury with a focus on the heart and biological mechanisms that underpin cell survival.

Interorgan rhythmicity as a feature of healthful metabolism

The finding that animals with circadian gene mutations exhibit diet-induced obesity and metabolic syndrome with hypoinsulinemia revealed a distinct role for the clock in the brain and peripheral tissues. Obesogenic diets disrupt rhythmic sleep/wake patterns, feeding behavior, and transcriptional networks, showing that metabolic signals reciprocally control the clock. Providing access to high-fat diet only during the sleep phase (light period) in mice accelerates weight gain, whereas isocaloric time-restricted feeding during the active period enhances energy expenditure due to circadian induction of adipose thermogenesis. This perspective focuses on advances and unanswered questions in understanding the interorgan circadian control of healthful metabolism.

Review: Protein O-GlcNAcylation regulates DNA damage response: A novel target for cancer therapy

The DNA damage response (DDR) safeguards the stable genetic information inheritance by orchestrating a complex protein network in response to DNA damage. However, this mechanism can often hamper the effectiveness of radiotherapy and DNA-damaging chemotherapy in destroying tumor cells, causing cancer resistance. Inhibiting DDR can significantly improve tumor cell sensitivity to radiotherapy and DNA-damaging chemotherapy. Thus, DDR can be a potential target for cancer treatment. Post-translational modifications (PTMs) of DDR-associated proteins profoundly affect their activity and function by covalently attaching new functional groups. O-GlcNAcylation (O-linked-N-acetylglucosaminylation) is an emerging PTM associated with adding and removing O-linked N-acetylglucosamine to serine and threonine residues of proteins. It acts as a dual sensor for nutrients and stress in the cell and is sensitive to DNA damage. However, the explanation behind the specific role of O-GlcNAcylation in the DDR remains remains to be elucidated. To illustrate the complex relationship between O-GlcNAcylation and DDR, this review systematically describes the role of O-GlcNAcylation in DNA repair, cell cycle, and chromatin. We also discuss the defects of current strategies for targeting O-GlcNAcylation-regulated DDR in cancer therapy and suggest potential directions to address them.

The Function, Regulation, and Mechanism of Protein Turnover in Circadian Systems in Neurospora and Other Species

Circadian clocks drive a large array of physiological and behavioral activities. At the molecular level, circadian clocks are composed of positive and negative elements that form core oscillators generating the basic circadian rhythms. Over the course of the circadian period, circadian negative proteins undergo progressive hyperphosphorylation and eventually degrade, and their stability is finely controlled by complex post-translational pathways, including protein modifications, genetic codon preference, protein-protein interactions, chaperon-dependent conformation maintenance, degradation, etc. The effects of phosphorylation on the stability of circadian clock proteins are crucial for precisely determining protein function and turnover, and it has been proposed that the phosphorylation of core circadian clock proteins is tightly correlated with the circadian period. Nonetheless, recent studies have challenged this view. In this review, we summarize the research progress regarding the function, regulation, and mechanism of protein stability in the circadian clock systems of multiple model organisms, with an emphasis on Neurospora crassa, in which circadian mechanisms have been extensively investigated. Elucidation of the highly complex and dynamic regulation of protein stability in circadian clock networks would greatly benefit the integrated understanding of the function, regulation, and mechanism of protein stability in a wide spectrum of other biological processes.

Regulation of protein O-GlcNAcylation by circadian, metabolic, and cellular signals

O-linked β-N-acetylglucosamine (O-GlcNAcylation) is a dynamic post-translational modification that regulates thousands of proteins and almost all cellular processes. Aberrant O-GlcNAcylation has been associated with numerous diseases, including cancer, neurodegenerative diseases, cardiovascular diseases, and type 2 diabetes. O-GlcNAcylation is highly nutrient-sensitive since it is dependent on UDP-GlcNAc, the end product of the hexosamine biosynthetic pathway (HBP). We previously observed daily rhythmicity of protein O-GlcNAcylation in a Drosophila model that is sensitive to the timing of food consumption. We showed that the circadian clock is pivotal in regulating daily O-GlcNAcylation rhythms given its control of the feeding-fasting cycle and hence nutrient availability. Interestingly, we reported that the circadian clock also modulates daily O-GlcNAcylation rhythm by regulating molecular mechanisms beyond the regulation of food consumption time. A large body of work now indicates that O-GlcNAcylation is likely a generalized cellular status effector as it responds to various cellular signals and conditions, such as ER stress, apoptosis, and infection. In this review, we summarize the metabolic regulation of protein O-GlcNAcylation through nutrient availability, HBP enzymes, and O-GlcNAc processing enzymes. We discuss the emerging roles of circadian clocks in regulating daily O-GlcNAcylation rhythm. Finally, we provide an overview of other cellular signals or conditions that impact O-GlcNAcylation. Many of these cellular pathways are themselves regulated by the clock and/or metabolism. Our review highlights the importance of maintaining optimal O-GlcNAc rhythm by restricting eating activity to the active period under physiological conditions and provides insights into potential therapeutic targets of O-GlcNAc homeostasis under pathological conditions.

Protein O-GlcNAcylation: The sweet hub in liver metabolic flexibility from a (patho)physiological perspective

O-GlcNAcylation is a dynamic, reversible and atypical O-glycosylation that regulates various cellular physiological processes via conformation, stabilisation, localisation, chaperone interaction or activity of target proteins. The O-GlcNAcylation cycle is precisely controlled by collaboration between O-GlcNAc transferase and O-GlcNAcase. Uridine-diphosphate-N-acetylglucosamine, the sole donor of O-GlcNAcylation produced by the hexosamine biosynthesis pathway, is controlled by the input of glucose, glutamine, acetyl coenzyme A and uridine triphosphate, making it a sensor of the fluctuation of molecules, making O-GlcNAcylation a pivotal nutrient sensor for the metabolism of carbohydrates, amino acids, lipids and nucleotides. O-GlcNAcylation, particularly prevalent in liver, is the core hub for controlling systemic glucose homeostasis due to its nutritional sensitivity and precise spatiotemporal regulation of insulin signal transduction. The pathology of various liver diseases has highlighted hepatic metabolic disorder and dysfunction, and abnormal O-GlcNAcylation also plays a specific pathological role in these processes. Therefore, this review describes the unique features of O-GlcNAcylation and its dynamic homeostasis maintenance. Additionally, it explains the underlying nutritional sensitivity of O-GlcNAcylation and discusses its mechanism of spatiotemporal modulation of insulin signal transduction and liver metabolic homeostasis during the fasting and feeding cycle. This review emphasises the pathophysiological implications of O-GlcNAcylation in nonalcoholic fatty liver disease, nonalcoholic steatohepatitis and hepatic fibrosis, and focuses on the adverse effects of hyper O-GlcNAcylation on liver cancer progression and metabolic reprogramming.

Cullin5 drives experimental asthma exacerbations by modulating alveolar macrophage antiviral immunity

Asthma exacerbations caused by respiratory viral infections are a serious global health problem. Impaired antiviral immunity is thought to contribute to the pathogenesis, but the underlying mechanisms remain understudied. Here using mouse models we find that Cullin5 (CUL5), a key component of Cullin-RING E3 ubiquitin ligase 5, is upregulated and associated with increased neutrophil count and influenza-induced exacerbations of house dust mite-induced asthma. By contrast, CUL5 deficiency mitigates neutrophilic lung inflammation and asthma exacerbations by augmenting IFN-β production. Mechanistically, following thymic stromal lymphopoietin stimulation, CUL5 interacts with O-GlcNAc transferase (OGT) and induces Lys48-linked polyubiquitination of OGT, blocking the effect of OGT on mitochondrial antiviral-signaling protein O-GlcNAcylation and RIG-I signaling activation. Our results thus suggest that, in mouse models, pre-existing allergic injury induces CUL5 expression, impairing antiviral immunity and promoting neutrophilic inflammation for asthma exacerbations. Targeting of the CUL5/IFN-β signaling axis may thereby serve as a possible therapy for treating asthma exacerbations.

Circadian rhythm disturbances involved in ozone-induced glucose metabolism disorder in mouse liver

Ozone (O3) is a key environmental factor for developing diabetes. Nevertheless, the underlying mechanisms remain unclear. This study aimed to investigate alterations of glycometabolism in mice after O3 exposure and the role of circadian rhythms in this process. C57BL/6 male mice were randomly assigned to O3 (0.5 ppm) or filtered air for four weeks (4 h/day). Then, hepatic tissues of mice were collected at 4 h intervals within 24 h after O3 exposure to test. The results showed that hepatic circadian rhythm genes oscillated abnormally, mainly at zeitgeber time (ZT)8 and ZT20 after O3 exposure. Furthermore, detection of glycometabolism (metabolites, enzymes, and genes) revealed that O3 caused change in the daily oscillations of glycometabolism. The serum glucose content decreased at ZT4 and ZT20, while hepatic glucose enhanced at ZT16 and ZT24(0). Both G6pc and Pck1, which are associated with hepatic gluconeogenesis, significantly increased at ZT20. O3 exposure disrupted glycometabolism by increasing gluconeogenesis and decreasing glycolysis in mice liver. Finally, correlation analysis showed that the association between Bmal1 and O3-induced disruption of glycometabolism was the strongest. The findings emphasized the interaction between adverse outcomes of circadian rhythms and glycometabolism following O3 exposure.

Cardioprotective O-GlcNAc signaling is elevated in murine female hearts via enhanced O-GlcNAc transferase activity

The post-translational modification of intracellular proteins by O-linked β-GlcNAc (O-GlcNAc) has emerged as a critical regulator of cardiac function. Enhanced O-GlcNAcylation activates cytoprotective pathways in cardiac models of ischemia-reperfusion (I/R) injury; however, the mechanisms underpinning O-GlcNAc cycling in response to I/R injury have not been comprehensively assessed. The cycling of O-GlcNAc is regulated by the collective efforts of two enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), which catalyze the addition and hydrolysis of O-GlcNAc, respectively. It has previously been shown that baseline heart physiology and pathophysiology are impacted by sex. Here, we hypothesized that sex differences in molecular signaling may target protein O-GlcNAcylation both basally and in ischemic hearts. To address this question, we subjected male and female WT murine hearts to ex vivo ischemia or I/R injury. We assessed hearts for protein O-GlcNAcylation, abundance of OGT, OGA, and glutamine:fructose-6-phosphate aminotransferase (GFAT2), activity of OGT and OGA, and UDP-GlcNAc levels. Our data demonstrate elevated O-GlcNAcylation in female hearts both basally and during ischemia. We show that OGT activity was enhanced in female hearts in all treatments, suggesting a mechanism for these observations. Furthermore, we found that ischemia led to reduced O-GlcNAcylation and OGT-specific activity. Our findings provide a foundation for understanding molecular mechanisms that regulate O-GlcNAcylation in the heart and highlight the importance of sex as a significant factor when assessing key regulatory events that control O-GlcNAc cycling. These data suggest the intriguing possibility that elevated O-GlcNAcylation in females contributes to reduced ischemic susceptibility.

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.

Multi-omics profiling reveals rhythmic liver function shaped by meal timing

Post-translational modifications (PTMs) couple feed-fast cycles to diurnal rhythms. However, it remains largely uncharacterized whether and how meal timing organizes diurnal rhythms beyond the transcriptome. Here, we systematically profile the daily rhythms of the proteome, four PTMs (phosphorylation, ubiquitylation, succinylation and N-glycosylation) and the lipidome in the liver from young female mice subjected to either day/sleep time-restricted feeding (DRF) or night/wake time-restricted feeding (NRF). We detect robust daily rhythms among different layers of omics with phosphorylation the most nutrient-responsive and succinylation the least. Integrative analyses reveal that clock regulation of fatty acid metabolism represents a key diurnal feature that is reset by meal timing, as indicated by the rhythmic phosphorylation of the circadian repressor PERIOD2 at Ser971 (PER2-pSer971). We confirm that PER2-pSer971 is activated by nutrient availability in vivo. Together, this dataset represents a comprehensive resource detailing the proteomic and lipidomic responses by the liver to alterations in meal timing.

Metabolic and chemical architecture of the mammalian circadian clock

Circadian rhythms are endogenous periodic biological processes that occur on a daily timescale. These rhythms are generated by a transcriptional/translational feedback loop that consists of the CLOCK-BMAL1 heterodimeric transcriptional activator complex and the PER1/2-CRY1/2-CK1δ/ε repressive complex. The output pathways of this molecular feedback loop generate circadian rhythmicity in various biological processes. Among these, metabolism is a primary regulatory target of the circadian clock which can also feedback to modulate clock function. This intertwined relationship between circadian rhythms and metabolism makes circadian clock components promising therapeutic targets. Despite this, pharmacological therapeutics that target the circadian clock are relatively rare. In this review, we hope to stimulate interest in chemical chronobiology by providing a comprehensive background on the molecular mechanism of mammalian circadian rhythms and their connection to metabolism, highlighting important studies in the chemical approach to circadian research, and offering our perspectives on future developments in the field.

PERIOD phosphorylation leads to feedback inhibition of CK1 activity to control circadian period

PERIOD (PER) and Casein Kinase 1δ regulate circadian rhythms through a phosphoswitch that controls PER stability and repressive activity in the molecular clock. CK1δ phosphorylation of the familial advanced sleep phase (FASP) serine cluster embedded within the Casein Kinase 1 binding domain (CK1BD) of mammalian PER1/2 inhibits its activity on phosphodegrons to stabilize PER and extend circadian period. Here, we show that the phosphorylated FASP region (pFASP) of PER2 directly interacts with and inhibits CK1δ. Co-crystal structures in conjunction with molecular dynamics simulations reveal how pFASP phosphoserines dock into conserved anion binding sites near the active site of CK1δ. Limiting phosphorylation of the FASP serine cluster reduces product inhibition, decreasing PER2 stability and shortening circadian period in human cells. We found that Drosophila PER also regulates CK1δ via feedback inhibition through the phosphorylated PER-Short domain, revealing a conserved mechanism by which PER phosphorylation near the CK1BD regulates CK1 kinase activity.

d-Glucosamine induces circadian phase delay by promoting BMAL1 degradation through AMPK/mTOR pathway

Circadian rhythms are closely linked to the metabolic network through circadian feedback regulation. The hexosamine biosynthetic pathway (HBP) is a branch of glucose metabolism that affects circadian rhythms through the O-linked N-acetylglucosamine modification (O-GlcNAcylation) of clock proteins. Here, we found out that, among the downstream metabolites regulated by d-glucosamine (GlcN) in HBP salvage pathway, only GlcN is able to induce circadian phase delay both in vitro and in vivo. Mechanistic studies indicated that the phase-shift induced by GlcN is independent of O-GlcNAcylation. Instead, GlcN selectively up-regulates p-AMPK activity, leading to the inhibition of mTOR signaling pathway, and thus down-regulation of p-BMAL1 both in human cell line and mouse tissues. Moreover, GlcN promoted BMAL1 degradation via proteasome pathway. These findings reveal a novel molecular mechanism of GlcN in regulating clock phase and suggest the therapeutic potential of GlcN as new use for an old drug in the future treatment of shift work and circadian misalignment.

Single nucleotide polymorphisms (SNPs) in circadian genes: Impact on gene function and phenotype

Circadian rhythm is an endogenous timing system that allows an organism to anticipate and adapt to daily changes and regulate various physiological variables such as the sleep-wake cycle. This rhythm is governed by a molecular circadian clock mechanism, generated by a transcriptional and translational feedback loop (TTFL) mechanism. In mammals, TTFL is determined by the interaction of four main clock proteins: BMAL1, CLOCK, Cryptochromes (CRY), and Periods (PER). BMAL1 and CLOCK form dimers and initiate the transcription of clock-controlled genes (CCG) by binding an E-box element with the promotor genes. Among CCGs, PERs and CRYs accumulate in the cytosol and translocate into the nucleus, where they interact with the BMAL1/CLOCK dimer and inhibit its activity. Several epidemiological and genetic studies have revealed that circadian rhythm disruption causes various types of disease. In this chapter, we summarize the effect of core clock gene SNPs on circadian rhythm and diseases in humans.

Mapping the signaling network of BIN2 kinase using TurboID-mediated biotin labeling and phosphoproteomics

Elucidating enzyme-substrate relationships in posttranslational modification (PTM) networks is crucial for understanding signal transduction pathways but is technically difficult because enzyme-substrate interactions tend to be transient. Here, we demonstrate that TurboID-based proximity labeling (TbPL) effectively and specifically captures the substrates of kinases and phosphatases. TbPL-mass spectrometry (TbPL-MS) identified over 400 proximal proteins of Arabidopsis thaliana BRASSINOSTEROID-INSENSITIVE2 (BIN2), a member of the GLYCOGEN SYNTHASE KINASE 3 (GSK3) family that integrates signaling pathways controlling diverse developmental and acclimation processes. A large portion of the BIN2-proximal proteins showed BIN2-dependent phosphorylation in vivo or in vitro, suggesting that these are BIN2 substrates. Protein-protein interaction network analysis showed that the BIN2-proximal proteins include interactors of BIN2 substrates, revealing a high level of interactions among the BIN2-proximal proteins. Our proteomic analysis establishes the BIN2 signaling network and uncovers BIN2 functions in regulating key cellular processes such as transcription, RNA processing, translation initiation, vesicle trafficking, and cytoskeleton organization. We further discovered significant overlap between the GSK3 phosphorylome and the O-GlcNAcylome, suggesting an evolutionarily ancient relationship between GSK3 and the nutrient-sensing O-glycosylation pathway. Our work presents a powerful method for mapping PTM networks, a large dataset of GSK3 kinase substrates, and important insights into the signaling network that controls key cellular functions underlying plant growth and acclimation.

Emerging Role of Protein O-GlcNAcylation in Liver Metabolism: Implications for Diabetes and NAFLD

O-linked b-N-acetyl-glucosaminylation (O-GlcNAcylation) is one of the most common post-translational modifications of proteins, and is established by modifying the serine or threonine residues of nuclear, cytoplasmic, and mitochondrial proteins. O-GlcNAc signaling is considered a critical nutrient sensor, and affects numerous proteins involved in cellular metabolic processes. O-GlcNAcylation modulates protein functions in different patterns, including protein stabilization, enzymatic activity, transcriptional activity, and protein interactions. Disrupted O-GlcNAcylation is associated with an abnormal metabolic state, and may result in metabolic disorders. As the liver is the center of nutrient metabolism, this review provides a brief description of the features of the O-GlcNAc signaling pathway, and summarizes the regulatory functions and underlying molecular mechanisms of O-GlcNAcylation in liver metabolism. Finally, this review highlights the role of O-GlcNAcylation in liver-associated diseases, such as diabetes and nonalcoholic fatty liver disease (NAFLD). We hope this review not only benefits the understanding of O-GlcNAc biology, but also provides new insights for treatments against liver-associated metabolic disorders.

Adaptation to glucose starvation is associated with molecular reorganization of the circadian clock in Neurospora crassa

The circadian clock governs rhythmic cellular functions by driving the expression of a substantial fraction of the genome and thereby significantly contributes to the adaptation to changing environmental conditions. Using the circadian model organism Neurospora crassa, we show that molecular timekeeping is robust even under severe limitation of carbon sources, however, stoichiometry, phosphorylation and subcellular distribution of the key clock components display drastic alterations. Protein kinase A, protein phosphatase 2 A and glycogen synthase kinase are involved in the molecular reorganization of the clock. RNA-seq analysis reveals that the transcriptomic response of metabolism to starvation is highly dependent on the positive clock component WC-1. Moreover, our molecular and phenotypic data indicate that a functional clock facilitates recovery from starvation. We suggest that the molecular clock is a flexible network that allows the organism to maintain rhythmic physiology and preserve fitness even under long-term nutritional stress.

Evolution of casein kinase 1 and functional analysis of new doubletime mutants in Drosophila

Circadian clocks are timing devices that rhythmically adjust organism's behavior, physiology, and metabolism to the 24-h day-night cycle. Eukaryotic circadian clocks rely on several interlocked transcription-translation feedback loops, where protein stability is the key part of the delay between transcription and the appearance of the mature proteins within the feedback loops. In bilaterian animals, including mammals and insects, the circadian clock depends on a homologous set of proteins. Despite mostly conserved clock components among the fruit fly Drosophila and mammals, several lineage-specific differences exist. Here we have systematically explored the evolution and sequence variability of insect DBT proteins and their vertebrate homologs casein kinase 1 delta (CKIδ) and epsilon (CKIε), dated the origin and separation of CKIδ from CKIε, and identified at least three additional independent duplications of the CKIδ/ε gene in Petromyzon, Danio, and Xenopus. We determined conserved regions in DBT specific to Diptera, and functionally tested a subset of those in D. melanogaster. Replacement of Lysine K224 with acidic residues strongly impacts the free-running period even in heterozygous flies, whereas homozygous mutants are not viable. K224D mutants have a temperature compensation defect with longer free-running periods at higher temperatures, which is exactly the opposite trend of what was reported for corresponding mammalian mutants. All DBTs of dipteran insects contain the NKRQK motif at positions 220-224. The occurrence of this motif perfectly correlates with the presence of BRIDE OF DOUBLETIME, BDBT, in Diptera. BDBT is a non-canonical FK506-binding protein that physically interacts with Drosophila DBT. The phylogeny of FK506-binding proteins suggests that BDBT is either absent or highly modified in non-dipteran insects. In addition to in silico analysis of DBT/CKIδ/ε evolution and diversity, we have identified four novel casein kinase 1 genes specific to the Drosophila genus.

Divergent remodeling of the skeletal muscle metabolome over 24 h between young, healthy men and older, metabolically compromised men

24 h whole-body substrate metabolism and the circadian clock within skeletal muscle are both compromised upon metabolic disease in humans. Here, we assessed the 24 h muscle metabolome by serial muscle sampling performed under 24 h real-life conditions in young, healthy (YH) men versus older, metabolically compromised (OMC) men. We find that metabolites associated with the initial steps of glycolysis and hexosamine biosynthesis are higher in OMC men around the clock, whereas metabolites associated with glutamine-alpha-ketoglutarate, ketone, and redox metabolism are lower in OMC men. The night period shows the largest number of differently expressed metabolites. Both groups demonstrate 24 h rhythmicity in half of the metabolome, but rhythmic metabolites only partially overlap. Specific metabolites are only rhythmic in YH men (adenosine), phase shifted in OMC men (cis-aconitate, flavin adenine dinucleotide [FAD], and uridine diphosphate [UDP]), or have a reduced 24 h amplitude in OMC men (hydroxybutyrate and hippuric acid). Our data highlight the plasticity of the skeletal muscle metabolome over 24 h and large divergence across the metabolic health spectrum.

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.

O-GlycNacylation Remission Retards the Progression of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is a metabolic disease spectrum associated with insulin resistance (IR), from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatocellular carcinoma (HCC). O-GlcNAcylation is a posttranslational modification, regulated by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Abnormal O-GlcNAcylation plays a key role in IR, fat deposition, inflammatory injury, fibrosis, and tumorigenesis. However, the specific mechanisms and clinical treatments of O-GlcNAcylation and NAFLD are yet to be elucidated. The modification contributes to understanding the pathogenesis and development of NAFLD, thus clarifying the protective effect of O-GlcNAcylation inhibition on liver injury. In this review, the crucial role of O-GlcNAcylation in NAFLD (from NAFL to HCC) is discussed, and the effect of therapeutics on O-GlcNAcylation and its potential mechanisms on NAFLD have been highlighted. These inferences present novel insights into the pathogenesis and treatments of NAFLD.

Integration of O-GlcNAc into Stress Response Pathways

The modification of nuclear, mitochondrial, and cytosolic proteins by O-linked βN-acetylglucosamine (O-GlcNAc) has emerged as a dynamic and essential post-translational modification of mammalian proteins. O-GlcNAc is cycled on and off over 5000 proteins in response to diverse stimuli impacting protein function and, in turn, epigenetics and transcription, translation and proteostasis, metabolism, cell structure, and signal transduction. Environmental and physiological injury lead to complex changes in O-GlcNAcylation that impact cell and tissue survival in models of heat shock, osmotic stress, oxidative stress, and hypoxia/reoxygenation injury, as well as ischemic reperfusion injury. Numerous mechanisms that appear to underpin O-GlcNAc-mediated survival include changes in chaperone levels, impacts on the unfolded protein response and integrated stress response, improvements in mitochondrial function, and reduced protein aggregation. Here, we discuss the points at which O-GlcNAc is integrated into the cellular stress response, focusing on the roles it plays in the cardiovascular system and in neurodegeneration.

Complex physiology and clinical implications of time-restricted eating

Time-restricted eating (TRE) is a dietary intervention that limits food consumption to a specific time window each day. The effect of TRE on body weight and physiological functions has been extensively studied in rodent models, which have shown considerable therapeutic effects of TRE and important interactions among time of eating, circadian biology, and metabolic homeostasis. In contrast, it is difficult to make firm conclusions regarding the effect of TRE in people because of the heterogeneity in results, TRE regimens, and study populations. In this review, we 1) provide a background of the history of meal consumption in people and the normal physiology of eating and fasting; 2) discuss the interaction between circadian molecular metabolism and TRE; 3) integrate the results of preclinical and clinical studies that evaluated the effects of TRE on body weight and physiological functions; 4) summarize other time-related dietary interventions that have been studied in people; and 4) identify current gaps in knowledge and provide a framework for future research directions.

Nutrient-sensitive protein O-GlcNAcylation shapes daily biological rhythms

O-linked-N-acetylglucosaminylation (O-GlcNAcylation) is a nutrient-sensitive protein modification that alters the structure and function of a wide range of proteins involved in diverse cellular processes. Similar to phosphorylation, another protein modification that targets serine and threonine residues, O-GlcNAcylation occupancy on cellular proteins exhibits daily rhythmicity and has been shown to play critical roles in regulating daily rhythms in biology by modifying circadian clock proteins and downstream effectors. We recently reported that daily rhythm in global O-GlcNAcylation observed in Drosophila tissues is regulated via the integration of circadian and metabolic signals. Significantly, mistimed feeding, which disrupts coordination of these signals, is sufficient to dampen daily O-GlcNAcylation rhythm and is predicted to negatively impact animal biological rhythms and health span. In this review, we provide an overview of published and potential mechanisms by which metabolic and circadian signals regulate hexosamine biosynthetic pathway metabolites and enzymes, as well as O-GlcNAc processing enzymes to shape daily O-GlcNAcylation rhythms. We also discuss the significance of functional interactions between O-GlcNAcylation and other post-translational modifications in regulating biological rhythms. Finally, we highlight organ/tissue-specific cellular processes and molecular pathways that could be modulated by rhythmic O-GlcNAcylation to regulate time-of-day-specific biology.

O-GlcNAcylation: An Emerging Protein Modification Regulating the Hippo Pathway

Simple Summary

The contact point between the Hippo pathway, which serves as a central hub for various external environments, and O-GlcNAcylation, which is a non-canonical glycosylation process acting as a dynamic regulator in various signal transduction pathways, has recently been identified. This review aims to summarize the function of O-GlcNAcylation as an intrinsic and extrinsic regulator of the Hippo pathway.

Abstract

The balance between cellular proliferation and apoptosis and the regulation of cell differentiation must be established to maintain tissue homeostasis. These cellular responses involve the kinase cascade-mediated Hippo pathway as a crucial regulator. Hence, Hippo pathway dysregulation is implicated in diverse diseases, including cancer. O-GlcNAcylation is a non-canonical glycosylation that affects multiple signaling pathways through its interplay with phosphorylation in the nucleus and cytoplasm. An abnormal increase in the O-GlcNAcylation levels in various cancer cells is a potent factor in Hippo pathway dysregulation. Intriguingly, Hippo pathway dysregulation also disrupts O-GlcNAc homeostasis, leading to a persistent elevation of O-GlcNAcylation levels, which is potentially pathogenic in several diseases. Therefore, O-GlcNAcylation is gaining attention as a protein modification that regulates the Hippo pathway. This review presents a framework on how O-GlcNAcylation regulates the Hippo pathway and forms a self-perpetuating cycle with it. The pathological significance of this self-perpetuating cycle and clinical strategies for targeting O-GlcNAcylation that causes Hippo pathway dysregulation are also discussed.

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.

A New Strategy for High-Efficient Tandem Enrichment and Simultaneous Profiling of N-Glycopeptides and Phosphopeptides in Lung Cancer Tissue

N-glycosylation and phosphorylation, two common posttranslational modifications, play important roles in various biological processes and are extensively studied for biomarker and drug target screening. Because of their low abundance, enrichment of N-glycopeptides and phosphopeptides prior to LC–MS/MS analysis is essential. However, simultaneous characterization of these two types of posttranslational modifications in complex biological samples is still challenging, especially for tiny amount of samples obtained in tissue biopsy. Here, we introduced a new strategy for the highly efficient tandem enrichment of N-glycopeptides and phosphopeptides using HILIC and TiO₂ microparticles. The N-glycopeptides and phosphosites obtained by tandem enrichment were 21%–377% and 22%–263% higher than those obtained by enriching the two PTM peptides separately, respectively, using 160–20 μg tryptic digested peptides as the starting material. Under the optimized conditions, 2798 N-glycopeptides from 434 N-glycoproteins and 5130 phosphosites from 1986 phosphoproteins were confidently identified from three technical replicates of HeLa cells by mass spectrometry analysis. Application of this tandem enrichment strategy in a lung cancer study led to simultaneous characterization of the two PTM peptides and discovery of hundreds of differentially expressed N-glycosylated and phosphorylated proteins between cancer and normal tissues, demonstrating the high sensitivity of this strategy for investigation of dysregulated PTMs using very limited clinical samples.

Nutrition, metabolism, and epigenetics: pathways of circadian reprogramming

Food intake profoundly affects systemic physiology. A large body of evidence has indicated a link between food intake and circadian rhythms, and ~24-h cycles are deemed essential for adapting internal homeostasis to the external environment. Circadian rhythms are controlled by the biological clock, a molecular system remarkably conserved throughout evolution. The circadian clock controls the cyclic expression of numerous genes, a regulatory program common to all mammalian cells, which may lead to various metabolic and physiological disturbances if hindered. Although the circadian clock regulates multiple metabolic pathways, metabolic states also provide feedback on the molecular clock. Therefore, a remarkable feature is reprogramming by nutritional challenges, such as a high-fat diet, fasting, ketogenic diet, and caloric restriction. In addition, various factors such as energy balance, histone modifications, and nuclear receptor activity are involved in the remodeling of the clock. Herein, we review the interaction of dietary components with the circadian system and illustrate the relationships linking the molecular clock to metabolism and critical roles in the remodeling process.

Demystifying the O-GlcNAc Code: A Systems View

Post-translational modification with O-linked β-N-acetylglucosamine (O-GlcNAc), a process referred to as O-GlcNAcylation, occurs on a vast variety of proteins. Mounting evidence in the past several decades has clearly demonstrated that O-GlcNAcylation is a unique and ubiquitous modification. Reminiscent of a code, protein O-GlcNAcylation functions as a crucial regulator of nearly all cellular processes studied. The primary aim of this review is to summarize the developments in our understanding of myriad protein substrates modified by O-GlcNAcylation from a systems perspective. Specifically, we provide a comprehensive survey of O-GlcNAcylation in multiple species studied, including eukaryotes (e.g., protists, fungi, plants, Caenorhabditis elegans, Drosophila melanogaster, murine, and human), prokaryotes, and some viruses. We evaluate features (e.g., structural properties and sequence motifs) of O-GlcNAc modification on proteins across species. Given that O-GlcNAcylation functions in a species-, tissue-/cell-, protein-, and site-specific manner, we discuss the functional roles of O-GlcNAcylation on human proteins. We focus particularly on several classes of relatively well-characterized human proteins (including transcription factors, protein kinases, protein phosphatases, and E3 ubiquitin-ligases), with representative O-GlcNAc site-specific functions presented. We hope the systems view of the great endeavor in the past 35 years will help demystify the O-GlcNAc code and lead to more fascinating studies in the years to come.

The Beginner’s Guide to O-GlcNAc: From Nutrient Sensitive Pathway Regulation to Its Impact on the Immune System

The addition of N-acetyl glucosamine (GlcNAc) on the hydroxy group of serine/threonine residues is known as O-GlcNAcylation (OGN). The dynamic cycling of this monosaccharide on and off substrates occurs via O-linked β-N-acetylglucosamine transferase (OGT) and O-linked β-N-acetylglucosaminase (OGA) respectively. These enzymes are found ubiquitously in eukaryotes and genetic knock outs of the ogt gene has been found to be lethal in embryonic mice. The substrate scope of these enzymes is vast, over 15,000 proteins across 43 species have been identified with O-GlcNAc. OGN has been known to play a key role in several cellular processes such as: transcription, translation, cell signaling, nutrient sensing, immune cell development and various steps of the cell cycle. However, its dysregulation is present in various diseases: cancer, neurodegenerative diseases, diabetes. O-GlcNAc is heavily involved in cross talk with other post-translational modifications (PTM), such as phosphorylation, acetylation, and ubiquitination, by regulating each other’s cycling enzymes or directly competing addition on the same substrate. This crosstalk between PTMs can affect gene expression, protein localization, and protein stability; therefore, regulating a multitude of cell signaling pathways. In this review the roles of OGN will be discussed. The effect O-GlcNAc exerts over protein-protein interactions, the various forms of crosstalk with other PTMs, and its role as a nutrient sensor will be highlighted. A summary of how these O-GlcNAc driven processes effect the immune system will also be included.

Cryptochrome proteins regulate the circadian intracellular behavior and localization of PER2 in mouse suprachiasmatic nucleus neurons

The suprachiasmatic nucleus (SCN), the master circadian clock of the mammalian brain, coordinates cellular clocks across the organism to regulate daily rhythms of physiology and behavior. SCN timekeeping pivots around transcriptional/translational feedback loops whereby PERIOD (PER) and CRYPTOCHROME (CRY) proteins associate and enter the nucleus to inhibit their own expression. The individual and interactive behaviors of PER and CRY and the mechanisms that regulate them are poorly understood. We combined fluorescence imaging of endogenous PER2 and viral vector–expressed CRY in SCN slices and show how CRYs, acting via their C terminus, control nuclear localization and mobility of PER2 to dose-dependently initiate SCN timekeeping and control its period. Our results reveal PER and CRY interactions central to the SCN clockwork.

The ∼20,000 cells of the suprachiasmatic nucleus (SCN), the master circadian clock of the mammalian brain, coordinate subordinate cellular clocks across the organism, driving adaptive daily rhythms of physiology and behavior. The canonical model for SCN timekeeping pivots around transcriptional/translational feedback loops (TTFL) whereby PERIOD (PER) and CRYPTOCHROME (CRY) clock proteins associate and translocate to the nucleus to inhibit their own expression. The fundamental individual and interactive behaviors of PER and CRY in the SCN cellular environment and the mechanisms that regulate them are poorly understood. We therefore used confocal imaging to explore the behavior of endogenous PER2 in the SCN of PER2::Venus reporter mice, transduced with viral vectors expressing various forms of CRY1 and CRY2. In contrast to nuclear localization in wild-type SCN, in the absence of CRY proteins, PER2 was predominantly cytoplasmic and more mobile, as measured by fluorescence recovery after photobleaching. Virally expressed CRY1 or CRY2 relocalized PER2 to the nucleus, initiated SCN circadian rhythms, and determined their period. We used translational switching to control CRY1 cellular abundance and found that low levels of CRY1 resulted in minimal relocalization of PER2, but yet, remarkably, were sufficient to initiate and maintain circadian rhythmicity. Importantly, the C-terminal tail was necessary for CRY1 to localize PER2 to the nucleus and to initiate SCN rhythms. In CRY1-null SCN, CRY1Δtail opposed PER2 nuclear localization and correspondingly shortened SCN period. Through manipulation of CRY proteins, we have obtained insights into the spatiotemporal behaviors of PER and CRY sitting at the heart of the TTFL molecular mechanism.

Tailoring multifunctional magnetic cationic metal-organic framework composite for synchronous enrichment of phosphopeptides/glycopeptides

Herein, for the first time, a multifunctional magnetic cationic MOF composite (Fe3O4@ILI-01@Ti4+) was successfully prepared for the synchronous enrichment of phosphopeptides/glycopeptides. The as-prepared Fe3O4@ILI-01@Ti4+ bears attractive properties like abundant surface...

The Circadian Clock and Obesity

The modern way of life has dramatically affected our biological rhythms. Circadian rhythms, which are generated by an endogenous circadian clock, are observed in a large number of physiological functions including metabolism. Proper peripheral clock synchronization by different signals including appropriate feeding/fasting cycles is essential to coordinate and temporally gate metabolic processes. In this chapter, we emphasize the importance of nutrient sensing by peripheral clocks and highlight the major role of peripheral and central clock communication to locally regulate metabolic processes and ensure optimal energy storage and expenditure. As a consequence, changes in eating behavior and/or bedtime, as occurs upon shift work and jet lag, have direct consequences on metabolism and participate in the increasing prevalence of obesity and associated metabolic diseases such as type 2 diabetes and non-alcoholic fatty liver disease. In this setting, time-restricted feeding has been suggested as an efficient approach to ameliorate metabolic parameters and control body weight.

A multidisciplinary perspective on the complex interactions between sleep, circadian, and metabolic disruption in cancer patients

Sleep is a basic need that is frequently set aside in modern societies. This leads to profound but complex physiological maladaptations in the body commonly referred to as circadian disruption, which recently has been characterized as a carcinogenic factor and reason for poor treatment outcomes, shortened survival, and reduced quality of life in cancer patients. As sleep and circadian physiology in cancer patients spans several disciplines including nursing science, neurology, oncology, molecular biology and medical technology, there is a lack of comprehensive and integrated approaches to deal with this serious and growing issue and at best a fractionated understanding of only part of the problem among researchers within each of these segments. Here, we take a multidisciplinary approach to comprehensively review the diagnosis and impact of sleep and circadian disruption in cancer patients. We discuss recent discoveries on molecular regulation of the circadian clock in healthy and malignant cells, the neurological and endocrine pathways controlling sleep and circadian rhythmicity, and their inputs to and outputs from the organism. The benefits and drawbacks of the various technologies, devices, and instruments used to assess sleep and circadian function, as well as the known consequences of sleep disruption and how sleep can be corrected in cancer patients, will be analyzed. We will throughout the review highlight the extensive crosstalk between sleep, circadian rhythms, and metabolic pathways involved in malignancy and identify current knowledge gaps and barriers for addressing the issue of sleep and circadian disruption in cancer patients. By addressing these issues, we hope to provide a foundation for further research as well as better and more effective care for the patients in the future.

O-GlcNAcylation links oncogenic signals and cancer epigenetics

Prevalent dysregulation of epigenetic modifications plays a pivotal role in cancer. Targeting epigenetic abnormality is a new strategy for cancer therapy. Understanding how conventional oncogenic factors cause epigenetic abnormality is of great basic and translational value. O-GlcNAcylation is a protein modification which affects physiology and pathophysiology. In mammals, O-GlcNAcylation is catalyzed by one single enzyme OGT and removed by one single enzyme OGA. O-GlcNAcylation is affected by the availability of the donor, UDP-GlcNAc, generated by the serial enzymatic reactions in the hexoamine biogenesis pathway (HBP). O-GlcNAcylation regulates a wide spectrum of substrates including many proteins involved in epigenetic modification. Like epigenetic modifications, abnormality of O-GlcNAcylation is also common in cancer. Studies have revealed substantial impact on HBP enzymes and OGT/OGA by oncogenic signals. In this review, we will first summarize how oncogenic signals regulate HBP enzymes, OGT and OGA in cancer. We will then integrate this knowledge with the up to date understanding how O-GlcNAcylation regulates epigenetic machinery. With this, we propose a signal axis from oncogenic signals through O-GlcNAcylation dysregulation to epigenetic abnormality in cancer. Further elucidation of this axis will not only advance our understanding of cancer biology but also provide new revenues towards cancer therapy.

Clock-modulated checkpoints in time-restricted eating

Time-restricted eating (TRE), which limits the daily meal timing to a window of 6-12 h, has been shown to reduce the risks of cardiometabolic diseases through consolidating circadian rhythms of metabolism and physiology. Recent advances indicate that canonical circadian clocks are dispensable for the actions of TRE in the liver, and that meal timing entrains circadian rhythms in peripheral tissues in a tissue-specific manner (e.g., the liver and fat are readily entrainable, whereas the heart and kidneys are resistant). Here, we propose that TRE engages clock-modulated checkpoints (CCPs) to reset circadian rhythms of tissue functions. Elucidation of CCPs would reveal the mechanistic basis of tissue responsiveness to TRE, and facilitate the use of TRE in precision medicine for cardiometabolic diseases.