O-GlcNAcylation: a bridge between glucose and cell differentiation

Low-intensity pulsed ultrasound (LIPUS) promotes skeletal muscle regeneration by regulating PGC-1α/AMPK/GLUT4 pathways in satellite cells/myoblasts

Low-Intensity Pulsed Ultrasound (LIPUS) holds therapeutic potential in promoting skeletal muscle regeneration, a biological process mediated by satellite cells and myoblasts. Despite their central roles in regeneration, the detailed mechanistic of LIPUS influence on satellite cells and myoblasts are not fully underexplored. In the current investigation, we administrated LIPUS treatment to injured skeletal muscles and C2C12 myoblasts over five consecutive days. Muscle samples were collected on days 6 and 30 post-injury for an in-depth histological and molecular assessment, both in vivo and in vitro with immunofluorescence analysis. During the acute injury phase, LIPUS treatment significantly augmented the satellite cell population, concurrently enhancing the number and size of newly formed myofibers whilst reducing fibrosis levels. At 30 days post-injury, the LIPUS-treated group demonstrated a more robust satellite cell pool and a higher myofiber count, suggesting that early LIPUS intervention facilitates satellite cell proliferation and differentiation, thereby promoting long-term recovery. Additionally, LIPUS markedly accelerated C2C12 myoblast differentiation, with observed increases in AMPK phosphorylation in myoblasts, leading to elevated expression of Glut4 and PGC-1α, and subsequent glucose uptake and mitochondrial biogenesis. These findings imply that LIPUS-induced modulation of myoblasts may culminate in enhanced cellular energy availability, laying a theoretical groundwork for employing LIPUS in ameliorating skeletal muscle regeneration post-injury. NEW & NOTEWORTHY: Utilizing the cardiotoxin (CTX) muscle injury model, we investigated the influence of LIPUS on satellite cell homeostasis and skeletal muscle regeneration. Our findings indicate that LIPUS promotes satellite cell proliferation and differentiation, thereby facilitating skeletal muscle repair. Additionally, in vitro investigations lend credence to the hypothesis that the regulatory effect of LIPUS on satellite cells may be attributed to its capability to enhance cellular energy metabolism.

13C Metabolic Flux Analysis in Chondrocytes Reveals a Novel Switch in Metabolic Phenotype

Chondrocytes are typically known for their anaerobic metabolism both in vivo and under culture conditions in vitro. However, chondrocytes have been shown to display greater biosynthetic activity when subjected to conditions that elicit aerobic metabolism. We have previously shown that tissue formation by chondrocytes can be upregulated by controlling nutrient availability and that this response arises from changes in glucose metabolism. The aim of the present study was to further characterize these changes through 13C-metabolic flux analysis (13C-MFA), as well as to determine the most optimal response. Primary bovine chondrocytes were grown in scaffold-free high-density tissue culture. [U-13C] glucose labeling experiments were combined with a tissue-specific metabolic network model to carry out 13C-MFA under varying levels of nutrient availability. 13C-MFA results demonstrated that when subjected to increasing nutrient availability, chondrocytes switch from a predominately anaerobic to a mixed aerobic-anaerobic phenotype. This metabolic switch was attributed to the saturation of the lactate fermentation pathway and metabolite overflow toward the tricarboxylic acid cycle. This effect appears to be similar to, but the inverse of, the Crabtree effect ("inverse Crabtree effect"). The relationships between metabolic flux and nutrient availability were then utilized to identify culture conditions that promote enhanced tissue formation. This novel metabolic effect presents a simple but effective approach for enhancing the biosynthetic response of chondrocytes-a key requirement to develop functional engineered cartilaginous tissue for joint resurfacing.

O-GlcNAcylation of TLR4 inhibits osteogenic differentiation of periodontal ligament stem cells

BACKGROUND

Toll-like receptor 4 (TLR4)-mediated inflammatory responses are associated with diabetes and periodontitis, which are dysregulated by O-GlcNAcylation.

OBJECTIVE

This study aimed to investigate the effects of O-GlcNAc transferase (OGT)-mediated TLR4 O-GlcNAcylation on the osteogenesis of periodontal ligament stem cells (PDLCs).

METHODS

PDLCs were treated with high glucose (HG) to establish a cell model. Osteogenic differentiation was evaluated using western blotting, an alkaline phosphatase activity assay, and an alizarin red S staining assay. The regulation of OGT on the O-GlcNAcylation of TLR4 was analyzed using co-immunoprecipitation, immunoprecipitation, western blotting, and immunofluorescence staining.

RESULTS

The results showed that HG inhibited osteogenic differentiation and promoted inflammatory response. Knockdown of OGT promoted osteogenic differentiation of HG-treated PDLCs. OGT interacted with TLR4 and increased the O-GlcNAcylation and protein levels of TLR4 in the cytomembrane of PDLCs. Moreover, silenced TLR4 reversed the effects on osteogenic differentiation induced by OGT in HG-treated PDLCs.

CONCLUSION

O-GlcNAcylation of TLR4 induced by OGT suppresses osteogenic differentiation of PDLCs after HG stimulation. The findings suggest a promising strategy for treating DP.

The molecular mechanisms of glycosaminoglycan biosynthesis regulating chondrogenesis and endochondral ossification

Disorders of chondrocyte differentiation and endochondral osteogenesis are major underlying factors in skeletal developmental disorders, including tibial dysplasia (TD), osteoarthritis (OA), chondrodysplasia (ACH), and multiple epiphyseal dysplasia (MED). Understanding the cellular and molecular pathogenesis of these disorders is crucial for addressing orthopedic diseases resulting from impaired glycosaminoglycan synthesis. Glycosaminoglycan is a broad term that refers to the glycan component of proteoglycan macromolecules. It is an essential component of the cartilage extracellular matrix and plays a vital role in various biological processes, including gene transcription, signal transduction, and chondrocyte differentiation. Recent studies have demonstrated that glycosaminoglycan biosynthesis plays a regulatory role in chondrocyte differentiation and endochondral osteogenesis by modulating various growth factors and signaling molecules. For instance, glycosaminoglycan is involved in mediating pathways such as Wnt, TGF-β, FGF, Ihh-PTHrP, and O-GlcNAc glycosylation, interacting with transcription factors SOX9, BMPs, TGF-β, and Runx2 to regulate chondrocyte differentiation and endochondral osteogenesis. To propose innovative approaches for addressing orthopedic diseases caused by impaired glycosaminoglycan biosynthesis, we conducted a comprehensive review of the molecular mechanisms underlying chondrocyte glycosaminoglycan biosynthesis, which regulates chondrocyte differentiation and endochondral osteogenesis. Our analysis considers the role of genes, glycoproteins, and associated signaling pathways during chondrogenesis and endochondral ossification.

O-GlcNAcylation: the sweet side of epigenetics

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

Glutamine metabolism and optimal immune and CNS function

Nutrients can impact and regulate cellular metabolism and cell function which is particularly important for the activation and function of diverse immune subsets. Among the critical nutrients for immune cell function and fate, glutamine is possibly the most widely recognised immunonutrient, playing key roles in TCA cycle, heat shock protein responses and antioxidant systems. In addition, glutamine is also involved with inter-organ ammonia transport, and this is particularly important for not only immune cells, but also to the brain, especially in catabolic situations such as critical care and extenuating exercise. The well characterised fall in blood glutamine availability has been the main reason for studies to investigate the possible effects of glutamine replacement via supplementation but many of the results are in poor agreement. At the same time, a range of complex pathways involved in glutamine metabolism have been revealed via supplementation studies. This article will briefly review the function of glutamine in the immune system, with emphasis on metabolic mechanisms, and the emerging role of glutamine in the brain glutamate/gamma-amino butyric acid cycle. In addition, relevant aspects of glutamine supplementation are discussed.

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.

Role of Diet in Stem and Cancer Stem Cells

Diet and lifestyle factors greatly affect health and susceptibility to diseases, including cancer. Stem cells’ functions, including their ability to divide asymmetrically, set the rules for tissue homeostasis, contribute to health maintenance, and represent the entry point of cancer occurrence. Stem cell properties result from the complex integration of intrinsic, extrinsic, and systemic factors. In this context, diet-induced metabolic changes can have a profound impact on stem cell fate determination, lineage specification and differentiation. The purpose of this review is to provide a comprehensive description of the multiple “non-metabolic” effects of diet on stem cell functions, including little-known effects such as those on liquid-liquid phase separation and on non-random chromosome segregation (asymmetric division). A deep understanding of the specific dietetic requirements of normal and cancer stem cells may pave the way for the development of nutrition-based targeted therapeutic approaches to improve regenerative and anticancer therapies.

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.

The Interaction Between Intracellular Energy Metabolism and Signaling Pathways During Osteogenesis

Osteoblasts primarily mediate bone formation, maintain bone structure, and regulate bone mineralization, which plays an important role in bone remodeling. In the past decades, the roles of cytokines, signaling proteins, and transcription factors in osteoblasts have been widely studied. However, whether the energy metabolism of cells can be regulated by these factors to affect the differentiation and functioning of osteoblasts has not been explored in depth. In addition, the signaling and energy metabolism pathways are not independent but closely connected. Although energy metabolism is mediated by signaling pathways, some intermediates of energy metabolism can participate in protein post-translational modification. The content of intermediates, such as acetyl coenzyme A (acetyl CoA) and uridine diphosphate N-acetylglucosamine (UDP-N-acetylglucosamine), determines the degree of acetylation and glycosylation in terms of the availability of energy-producing substrates. The utilization of intracellular metabolic resources and cell survival, proliferation, and differentiation are all related to the integration of metabolic and signaling pathways. In this paper, the interaction between the energy metabolism pathway and osteogenic signaling pathway in osteoblasts and bone marrow mesenchymal stem cells (BMSCs) will be discussed.

Type 2 Diabetic Mellitus Inhibits Skin Renewal through Inhibiting WNT-Dependent Lgr5+ Hair Follicle Stem Cell Activation in C57BL/6 Mice

BACKGROUND

Hair follicles are important accessory organs of the skin, and it is important for skin renewal and performs variety of important functions. Diabetes can cause several dermatoses; however, its effect on hair follicles is unclear. The purpose of this study was to investigate the effect of type II diabetes (T2DM) on the hair follicles of mice.

METHODS

Seven-week-old male C57BL/6 littermate mice were divided into two groups. The treatment group was injected with streptozotocin (STZ) to induce T2DM, and the control group was parallelly injected with the same dose of buffer. Seven days after injection, the back is depilated to observe the hair follicle regeneration. Hair follicle regeneration was observed by naked eyes and HE staining. The proliferation of the skin cells was observed by PCNA and K14 staining. The altered genes were screened by RNA sequencing and verified by qRT-PCR. In addition, Lgr5 + GFP/mTmG transgenic mice were used to observe the effect of T2DM on Lgr5 hair follicle stem cells (HFSC). And the expression of WNT4 and WNT8A were measured by Western Blot.

RESULTS

T2DM inhibited hair follicle regeneration. Compared to control mice, T2DM mice had smaller hair follicles, reduced skin thickness, and less expression of PCNA and K14. RNA sequencing showed that the two groups had significant differences in cell cycle and proliferation-related pathways. Compared with the control mice, the mRNA expression of Lgr4, Lgr5, Wnt4, and Wnt8a was decreased in the T2DM group. Moreover, T2DM inhibited the activation of Lgr5 HFSC and the expression of WNT4 and WNT8A.

CONCLUSIONS

T2DM inhibited hair follicle regeneration and skin cells proliferation by inhibiting WNT-dependent Lgr5 HFSC activation. This may be an important reason for the reduction of skin renewal ability and the formation of chronic wounds caused by diabetes. It is important for the treatment of chronic diabetic wounds and the development of tissue engineering.

The Hexosamine Biosynthetic Pathway as a Therapeutic Target after Cartilage Trauma: Modification of Chondrocyte Survival and Metabolism by Glucosamine Derivatives and PUGNAc in an Ex Vivo Model

The hexosamine biosynthetic pathway (HBP) is essential for the production of uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), the building block of glycosaminoglycans, thus playing a crucial role in cartilage anabolism. Although O-GlcNAcylation represents a protective regulatory mechanism in cellular processes, it has been associated with degenerative diseases, including osteoarthritis (OA). The present study focuses on HBP-related processes as potential therapeutic targets after cartilage trauma. Human cartilage explants were traumatized and treated with GlcNAc or glucosamine sulfate (GS); PUGNAc, an inhibitor of O-GlcNAcase; or azaserine (AZA), an inhibitor of GFAT-1. After 7 days, cell viability and gene expression analysis of anabolic and catabolic markers, as well as HBP-related enzymes, were performed. Moreover, expression of catabolic enzymes and type II collagen (COL2) biosynthesis were determined. Proteoglycan content was assessed after 14 days. Cartilage trauma led to a dysbalanced expression of different HBP-related enzymes, comparable to the situation in highly degenerated tissue. While GlcNAc and PUGNAc resulted in significant cell protection after trauma, only PUGNAc increased COL2 biosynthesis. Moreover, PUGNAc and both glucosamine derivatives had anti-catabolic effects. In contrast, AZA increased catabolic processes. Overall, “fueling” the HBP by means of glucosamine derivatives or inhibition of deglycosylation turned out as cells and chondroprotectives after cartilage trauma.

DHODH and cancer: promising prospects to be explored

Human dihydroorotate dehydrogenase (DHODH) is a flavin-dependent mitochondrial enzyme catalyzing the fourth step in the de novo pyrimidine synthesis pathway. It is originally a target for the treatment of the non-neoplastic diseases involving in rheumatoid arthritis and multiple sclerosis, and is re-emerging as a validated therapeutic target for cancer therapy. In this review, we mainly unravel the biological function of DHODH in tumor progression, including its crucial role in de novo pyrimidine synthesis and mitochondrial respiratory chain in cancer cells. Moreover, various DHODH inhibitors developing in the past decades are also been displayed, and the specific mechanism between DHODH and its additional effects are illustrated. Collectively, we detailly discuss the association between DHODH and tumors in recent years here, and believe it will provide significant evidences and potential strategies for utilizing DHODH as a potential target in preclinical and clinical cancer therapies.

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

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

Stem cell fate determination through protein O-GlcNAcylation

Embryonic and adult stem cells possess the capability of self-renewal and lineage-specific differentiation. The intricate balance between self-renewal and differentiation is governed by developmental signals and cell-type-specific gene regulatory mechanisms. A perturbed intra/extracellular environment during lineage specification could affect stem cell fate decisions resulting in pathology. Growing evidence demonstrates that metabolic pathways govern epigenetic regulation of gene expression during stem cell fate commitment through the utilization of metabolic intermediates or end products of metabolic pathways as substrates for enzymatic histone/DNA modifications. UDP-GlcNAc is one such metabolite that acts as a substrate for enzymatic mono-glycosylation of various nuclear, cytosolic, and mitochondrial proteins on serine/threonine amino acid residues, a process termed protein O-GlcNAcylation. The levels of GlcNAc inside the cells depend on the nutrient availability, especially glucose. Thus, this metabolic sensor could modulate gene expression through O-GlcNAc modification of histones or other proteins in response to metabolic fluctuations. Herein, we review evidence demonstrating how stem cells couple metabolic inputs to gene regulatory pathways through O-GlcNAc-mediated epigenetic/transcriptional regulatory mechanisms to govern self-renewal and lineage-specific differentiation programs. This review will serve as a primer for researchers seeking to better understand how O-GlcNAc influences stemness and may catalyze the discovery of new stem-cell-based therapeutic approaches.

Current molecular aspects in the development and treatment of diabetes

Diabetes mellitus (DM) leads to microvascular, macrovascular, and neurological complications. Less is understood about the mechanisms of this disease that give rise to weak bones. The many molecular mechanisms proposed to explain the damage caused by chronic hyperglycemia are organ and tissue dependent. Since all the different treatments for DM involve therapeutic activity combined with side effects and each patient represents a unique condition, there is no generalized therapy. The alterations stemming from hyperglycemia affect metabolism, osmotic pressure, oxidative stress, and inflammation. In part, hemodynamic modifications are linked to the osmotic potential of the excess of carbohydrates implicated in the disease. The change in osmotic balance increases as the disease progresses because hyperglycemia becomes chronic. The aim of the current contribution is to provide an updated overview of the molecular mechanisms that participate in the development and treatment of diabetes.

Metabolic rearrangements in primary liver cancers: cause and consequences

Primary liver cancer (PLC) is the fourth most frequent cause of cancer-related death. The high mortality rates arise from late diagnosis and the limited accuracy of diagnostic and prognostic biomarkers. The liver is a major regulator, orchestrating the clearance of toxins, balancing glucose, lipid and amino acid uptake, managing whole-body metabolism and maintaining metabolic homeostasis. Tumour onset and progression is frequently accompanied by rearrangements of metabolic pathways, leading to dysregulation of metabolism. The limitation of current therapies targeting PLCs, such as hepatocellular carcinoma and cholangiocarcinoma, points towards the importance of deciphering this metabolic complexity. In this Review, we discuss the role of metabolic liver disruptions and the implications of these processes in PLCs, emphasizing their clinical relevance and value in early diagnosis and prognosis and as putative therapeutic targets. We also describe system biology approaches able to reconstruct the metabolic complexity of liver diseases. We also discuss whether metabolic rearrangements are a cause or consequence of PLCs, emphasizing the opportunity to clinically exploit the rewired metabolism. In line with this idea, we discuss circulating metabolites as promising biomarkers for PLCs.

Glucose regulates tissue-specific chondro-osteogenic differentiation of human cartilage endplate stem cells via O-GlcNAcylation of Sox9 and Runx2

BACKGROUND

The degenerative disc disease (DDD) is a major cause of low back pain. The physiological low-glucose microenvironment of the cartilage endplate (CEP) is disrupted in DDD. Glucose influences protein O-GlcNAcylation via the hexosamine biosynthetic pathway (HBP), which is the key to stem cell fate. Thiamet-G is an inhibitor of O-GlcNAcase for accumulating O-GlcNAcylated proteins while 6-diazo-5-oxo-L-norleucine (DON) inhibits HBP. Mechanisms of DDD are incompletely understood but include CEP degeneration and calcification. We aimed to identify the molecular mechanisms of glucose in CEP calcification in DDD.

METHODS

We assessed normal and degenerated CEP tissues from patients, and the effects of chondrogenesis and osteogenesis of the CEP were determined by western blot and immunohistochemical staining. Cartilage endplate stem cells (CESCs) were induced with low-, normal-, and high-glucose medium for 21 days, and chondrogenic and osteogenic differentiations were measured by Q-PCR, western blot, and immunohistochemical staining. CESCs were induced with low-glucose and high-glucose medium with or without Thiamet-G or DON for 21 days, and chondrogenic and osteogenic differentiations were measured by Q-PCR, western blot, and immunohistochemical staining. Sox9 and Runx2 O-GlcNAcylation were measured by immunofluorescence. The effects of O-GlcNAcylation on the downstream genes of Sox9 and Runx2 were determined by Q-PCR and western blot.

RESULTS

Degenerated CEPs from DDD patients lost chondrogenesis, acquired osteogenesis, and had higher protein O-GlcNAcylation level compared to normal CEPs from LVF patients. CESC chondrogenic differentiation gradually decreased while osteogenic differentiation gradually increased from low- to high-glucose differentiation medium. Furthermore, Thiamet-G promoted CESC osteogenic differentiation and inhibited chondrogenic differentiation in low-glucose differentiation medium; however, DON acted opposite role in high-glucose differentiation medium. Interestingly, we found that Sox9 and Runx2 were O-GlcNAcylated in differentiated CESCs. Finally, O-GlcNAcylation of Sox9 and Runx2 decreased chondrogenesis and increased osteogenesis in CESCs.

CONCLUSIONS

Our findings demonstrate the effect of glucose concentration on regulating the chondrogenic and osteogenic differentiation potential of CESCs and provide insight into the mechanism of how glucose concentration regulates Sox9 and Runx2 O-GlcNAcylation to affect the differentiation of CESCs, which may represent a target for CEP degeneration therapy.

De Novo Lipogenesis as a Source of Second Messengers in Adipocytes

PURPOSE OF REVIEW

Obesity is a major risk factor for type 2 diabetes. Although adipose tissue allows storage of excess calories in periods of overnutrition, in obesity, adipose tissue metabolism becomes dysregulated and can promote metabolic diseases. This review discusses recent advances in understandings how adipocyte metabolism impacts metabolic homeostasis.

RECENT FINDINGS

The ability of adipocytes to synthesize lipids from glucose is a marker of metabolic fitness, e.g., low de novo lipogenesis (DNL) in adipocytes correlates with insulin resistance in obesity. Adipocyte DNL may promote synthesis of special "insulin sensitizing" signaling lipids that act hormonally. However, each metabolic intermediate in the DNL pathway (i.e., citrate, acetyl-CoA, malonyl-CoA, and palmitate) also has second messenger functions. Mounting evidence suggests these signaling functions may also be important for maintaining healthy adipocytes. While adipocyte DNL contributes to lipid storage, lipid precursors may have additional second messenger functions critical for maintaining adipocyte health, and thus systemic metabolic homeostasis.

Glucosamine Hydrochloride and N-Acetylglucosamine Influence the Response of Bovine Chondrocytes to TGF-β3 and IGF in Monolayer and Three-Dimensional Tissue Culture

Background

Glucosamine hydrochloride (GlcN·HCl) has been shown to inhibit cell growth and matrix synthesis, but not with N-acetyl-glucosamine (GlcNAc) supplementation. This effect might be related to an inhibition of critical growth factors (GF), or to a different metabolization of the two glucosamine derivatives. The aim of the present study was to evaluate the synergy between GlcN·HCl, GlcNAc, and GF on proliferation and cartilage matrix synthesis.

Method

Bovine chondrocytes were cultivated in monolayers for 48 h and in three-dimensional (3D) chitosan scaffolds for 30 days in perfusion bioreactors. Serum-free (SF) medium was supplemented with either growth factors (GF) TGF-β (5 ng mL^-1) and IGF-I (10 ng mL^-1), GlcN·HCl or GlcNAc at 1mM each or both. Six groups were compared according to medium supplementation: (a) SF control; (b) SF + GlcN·HCl; (c) SF + GlcNAc; (d) SF + GF; (e) SF + GF + GlcN·HCl; and (f) SF + GF + GlcNAc. Cell proliferation, proteoglycan, collagen I (COL1), and collagen II (COL2) synthesis were evaluated.

Results

The two glucosamines showed opposite effects in monolayer culture: GlcN·HCl significantly reduced proliferation and GlcNAc significantly augmented cellular metabolism. In the 30 days 3D culture, the GlcN·HCl added to GF stimulated cell proliferation more than when compared to GF only, but the proteoglycan synthesis was smaller than GF. However, GlcNAc added to GF improved the cell proliferation and proteoglycan synthesis more than when compared to GF and GF/GlcN·HCl. The synthesis of COL1 and COL2 was observed in all groups containing GF.

Conclusion

GlcN·HCl and GlcNAc increased cell growth and stimulated COL2 synthesis in long-time 3D culture. However, only GlcNAc added to GF improved proteoglycan synthesis.

Pathways from epigenomics and glycobiology towards novel biomarkers of addiction and its radical cure

The recent demonstration that addiction-relevant neuronal ensembles defined by known master transcription factors and their connectome is networked throughout mesocorticolimbic reward circuits and resonates harmonically at known frequencies implies that single-cell pan-omics techniques can improve our understanding of Substance Use Disorders (SUD's). Application of machine learning algorithms to such data could find diagnostic utility as biomarkers both to define the presence of the disorder and to quantitate its severity and find myriad applications in a developmental pipeline towards therapeutics and cure. Recent epigenomic studies have uncovered a wealth of clinically important data relating to synapse-nucleus signalling, memory storage, lineage-fate determination and cellular control and are contributing greatly to our understanding of all SUD's. Epigenetics interacts extensively with glycobiology. Glycans decorate DNA, RNA and many circulating critical proteins particularly immunoglobulins. Glycosylation is emerging as a major information-laden post-translational protein modification with documented application for biomarker development. The integration of these two emerging cutting-edge technologies provides a powerful and fertile algorithmic-bioinformatic space for the development both of SUD biomarkers and novel cutting edge therapeutics.

HYPOTHESES

These lines of evidence provide fertile ground for hypotheses relating to both diagnosis and treatment. They suggest that biomarkers derived from epigenomics complemented by glycobiology may potentially provide a bedside diagnostic tool which could be developed into a clinically useful biomarker to gauge both the presence and the severity of SUD's. Moreover they suggest that modern information-based therapeutics acting on the epigenome, via RNA interference or by DNA antisense oligonucleotides may provide a novel 21st century therapeutic development pipeline towards the radical cure of addictive disorders. Such techniques could be focussed and potentiated by neurotrophic vectors or the application of interfering electric or magnetic fields deep in the medial temporal lobes of the brain.

Hyperglycaemia-induced miR-301a promotes cell proliferation by repressing p21 and Smad4 in prostate cancer

Hyperglycaemia promotes the development of Prostate cancer (PCa). However, the roles of miRNAs in this disease process and the underlying mechanisms are largely unknown. In this study, we recruited 391 PCa patients in China and found that PCa patients with high level blood glucose (≥100 mg/dL) trended to have high Gleason score (GS ≥ 7). miRNA-301a levels were significantly higher in prostate cancer than that in normal prostate tissues. Hyperglycaemia or high glucose treatment induced miR-301a expression in prostate tissues or PCa cell lines. miR-301a suppressed the expression of p21 and Smad4, and subsequently promoted G1/S cell cycle transition and cell proliferation in vitro and xenograft growth in nude mice in vivo. Furthermore, knockdown of p21 and Smad4 mimicked the effects of miR-301a overexpression. Restoration of p21 and smad4 could interrupt the effects of miR-301a overexpression. Importantly, inhibition of miR-301a severely blocked high glucose-induced PCa cell growth both in vitro and in vivo. These results revealed a novel molecular link between hyperglycaemia and PCa. The miR-301a plays an important role in the hyperglycaemia-associated cancer growth, and represents a novel therapeutic target for PCa.

Conditions Inducing Excessive O-GlcNAcylation Inhibit BMP2-Induced Osteogenic Differentiation of C2C12 Cells

Hyperglycemic conditions in diabetic patients can affect various cellular functions, including the modulation of osteogenic differentiation. However, the molecular mechanisms by which hyperglycemia affects osteogenic differentiation are yet to be clarified. This study aimed to investigate whether the aberrant increase in protein O-linked-β-N-acetylglucosamine glycosylation (O-GlcNAcylation) contributes to the suppression of osteogenic differentiation due to hyperglycemia. To induce osteogenic differentiation, C2C12 cells were cultured in the presence of recombinant human bone morphogenetic protein 2 (BMP2). Excessive protein O-GlcNAcylation was induced by treating C2C12 cells with high glucose, glucosamine, or N-acetylglucosamine concentrations or by O-GlcNAc transferase (OGT) overexpression. The effect of O-GlcNAcylation on osteoblast differentiation was then confirmed by examining the expression levels of osteogenic marker gene mRNAs, activity of alkaline phosphatase, and transcriptional activity of Runx2, a critical transcription factor for osteoblast differentiation and bone formation. Cell treatment with high glucose, glucosamine or N-acetylglucosamine increased O-GlcNAcylation of Runx2 and the total levels of O-GlcNAcylated proteins, which led to a decrease in the transcriptional activity of Runx2, expression levels of osteogenic marker genes (Runx2, osterix, alkaline phosphatase, and type I collagen), and activity of alkaline phosphatase. These inhibitory effects were rescued by lowering protein O-GlcNAcylation levels by adding STO45849, an OGT inhibitor, or by overexpressing β-N-acetylglucosaminidase. Our findings suggest that excessive protein O-GlcNAcylation contributes to high glucose-suppressed osteogenic differentiation.

FGF23 Induction of O-Linked N-Acetylglucosamine Regulates IL-6 Secretion in Human Bronchial Epithelial Cells

The hexosamine biosynthetic pathway (HBP) generates the substrate for the O-linked β-N-acetylglucosamine (O-GlcNAc) modification of proteins. The HBP also serves as a stress sensor and has been reported to be involved with nuclear factor of activated T-cells (NFAT) activation, which can contribute to multiple cellular processes including cell metabolism, proliferation, and inflammation. In our previously published report, Fibroblast Growth Factor (FGF) 23, an important endocrine pro-inflammatory mediator, was shown to activate the FGFR4/phospholipase Cγ (PLCγ)/nuclear factor of activated T-cells (NFAT) signaling in chronic inflammatory airway diseases such as cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD). Here, we demonstrate that FGF23 increased the O-GlcNAc modification of proteins in HBECs. Furthermore, the increase in O-GlcNAc levels by FGF23 stimulation resulted in the downstream activation of NFAT and secretion of interleukin-6 (IL-6). Conversely, inhibition of FGF23 signaling and/or O-GlcNAc transferase (OGT)/O-GlcNAc reversed these effects. Collectively, these data suggest that FGF23 induced IL-6 upregulation and secretion is, at least, partially mediated via the activation of the HBP and O-GlcNAc levels in HBECs. These findings identify a novel link whereby FGF23 and the augmentation of O-GlcNAc levels regulate airway inflammation through NFAT activation and IL-6 upregulation in HBECs. The crosstalk between these signaling pathways may contribute to the pathogenesis of chronic inflammatory airway diseases such as COPD and CF as well as metabolic syndromes, including diabetes.

Elevated O-GlcNAcylation stabilizes FOXM1 by its reduced degradation through GSK-3β inactivation in a human gastric carcinoma cell line, MKN45 cells

O-GlcNAcylation is a dynamic post-translational modification of cytonuclear proteins for intracellular signaling. Elevated O-GlcNAcylation is a general feature of cancer and contributes to cancer progression, and recent studies indicate the contribution to increasing incidence of various types of cancer in diabetic patients. However, the role of O-GlcNAcylation in tumor progression is not fully elucidated. Forkhead box M1 (FOXM1), a master mitotic transcription factor, has been implicated in all major hallmarks of cancer, and is wildly expressed in solid tumors. Given that FOXM1 expression was reported to be elevated in gastric cancer, we examined the effect of high glucose or an inhibitor of O-GlcNAc hydrolase, Thiamet G (TMG), on FOXM1 protein expression in a human gastric cancer cell line, MKN45 cells, and confirmed that FOXM1 protein level and the cell proliferation were upregulated. To investigate the molecular mechanisms by which FOXM1 protein expression is regulated by O-GlcNAcylation, the effect of high glucose and TMG on FOXM1 ubiquitination was examined in MKN45 cells. As a result, the ubiquitination and degradation of FOXM1 protein were both suppressed by high glucose and TMG treatment. However, the O-GlcNAcylation was not detected on FOXM1 but not on GSK-3β. High glucose and TMG treatment increased phospho-serine 9 GSK-3β, an inactive form, and the degradation of FOXM1 protein was suppressed by treatment of GSK-3β inhibitors in MKN45 cells. Taken together, we suggest that high glucose and elevated O-GlcNAcylation stabilize FOXM1 protein by its reduced degradation via GSK-3β inactivation in MKN45 cells, suggesting that the higher risk of gastric cancer in diabetic patients could be partially due to O-GlcNAcylation-mediated FOXM1 stabilization.

O-GlcNAc transferase promotes fatty liver-associated liver cancer through inducing palmitic acid and activating endoplasmic reticulum stress

BACKGROUND & AIMS

O-GlcNAc transferase (OGT) is a unique glycosyltransferase involved in metabolic reprogramming. We investigated the functional role of OGT in non-alcoholic fatty liver disease-associated hepatocellular carcinoma (NAFLD-HCC).

METHODS

The biological function of OGT in NAFLD-HCC was determined by gain- or loss- of OGT functional assays in vitro and in nude mice. OGT target factors and pathways were identified by liquid chromatography-tandem mass spectrometry (LC-MS), promoter luciferase assay, DNA binding activity assay and Western blot.

RESULTS

OGT was upregulated in 12 out of 18 (66.7%) NAFLD-HCC tumor tissues by transcriptome sequencing, which was confirmed in additional NAFLD-HCC tumor tissues and cell lines. Biofunctional investigation demonstrated that OGT significantly increased cell growth (p<0.001), clonogenicity (p<0.01), migration and invasion (p<0.05) ability in vitro, and promoted xenograft tumor growth as well as lung metastasis in nude mice. The oncogenic effect of OGT was investigated, we found that OGT significantly induced palmitic acid production identified by LC-MS, which enhanced the protein expression of endoplasmic reticulum (ER) stress masters of glucose-regulated protein 78 and inositol-requiring enzyme 1α. Consequently, OGT significantly activated JNK/c-jun/AP-1 cascade by increasing protein expression of p-JNK, p-c-Jun and activation of AP-1; and induced NF-κB pathway through enhancing the protein levels of p-IKKα/ p-IKKβ, p-p65, p-p50 and the NF-κB DNA binding activity. Notably, OGT inhibition by its antagonist (ST045849) suppressed cell proliferation in vitro (p<0.001) and in xenograft mice models (p<0.05).

CONCLUSIONS

OGT plays an oncogenic role in NAFLD-associated HCC through regulating palmitic acid and inducing ER stress, consequently activating oncogenic JNK/c-jun/AP-1 and NF-κB cascades.

LAY SUMMARY

OGT, a unique glycosyltransferase enzyme, was identified to be upregulated in non-alcoholic fatty liver disease-associated hepatocellular carcinoma tissues by transcriptome sequencing. Here, we found that OGT plays a role in cancer by promoting tumor growth and metastasis in both cell models and animal models. This effect is mediated by the induction of palmitic acid.