Cytokine regulation of facilitated glucose transport in human articular chondrocytes

The role of HIF-1α in hypoxic metabolic reprogramming in osteoarthritis

The joint dysfunction caused by osteoarthritis (OA) is increasingly becoming a major challenge in global healthcare, and there is currently no effective strategy to prevent the progression of OA. Therefore, better elucidating the relevant mechanisms of OA occurrence and development will provide theoretical basis for formulating new prevention and control strategies. Due to long-term exposure of cartilage tissue to the hypoxic microenvironment of joints, metabolic reprogramming changes occur. Hypoxia-inducible factor-1alpha (HIF-1α), as a core gene regulating hypoxia response in vivo, plays an important regulatory role in the hypoxic metabolism of chondrocytes. HIF-1α adapts to the hypoxic microenvironment by regulating metabolic reprogramming changes such as glycolysis, oxidative phosphorylation (OXPHOS), amino acid metabolism, and lipid metabolism in OA chondrocytes. In addition, HIF-1α also regulates macrophage polarization and synovial inflammation, chondrocytes degeneration and extracellular matrix (ECM) degradation, subchondral bone remodeling and angiogenesis in the hypoxic microenvironment of OA, and affects the pathophysiological progression of OA. Consequently, the regulation of chondrocytes metabolic reprogramming by HIF-1α has become an important therapeutic target for OA. Therefore, this article reviews the mechanism of hypoxia affecting chondrocyte metabolic reprogramming, focusing on the regulatory mechanism of HIF-1α on chondrocyte metabolic reprogramming, and summarizes potential effective ingredients or targets targeting chondrocyte metabolic reprogramming, in order to provide more beneficial basis for the prevention and treatment of clinical OA and the development of effective drugs.

LDHA-induced histone lactylation mediates the development of osteoarthritis through regulating the transcription activity of TPI1 gene

Osteoarthritis (OA) is a worldwide joint disease, leading to the physical pain, stiffness, and even disability. Lactate dehydrogenase A (LDHA) is known as a lactylation mediator that can regulate histone lactylation of its target genes. However, the role of LDHA-mediated histone H3 lysine 18 lactylation (H3K18la) in OA progression is yet to be clarified. Our study aims at revealing the role and mechanism of LDHA-mediated histone lactylation in the glycolysis of chondrocytes. In this study, we determined at first that the H3K18la level was enhanced in OA. Energy metabolism such as glycolysis is often altered in OA progress. Therefore, we further explored the mechanism mediating glycolysis and thus promoting OA progress. Moreover, glycolysis was enhanced in LPS-induced OA cell model, as evidenced by the increased glucose consumption and lactate production. Furthermore, we silenced LDHA for loss-of-function assays. The results showed that knockdown of LDHA suppressed glycolysis of LPS-induced chondrocytes. In vivo animal study demonstrated that knockout of LDHA recovered cartilage injury of OA mice. Mechanistically, we uncovered that LDHA-mediated H3K18la in TPI1 promoter enhanced the transcription activity of TPI1. Mutation of K69 site was found to ameliorate LPS-induced glycolysis in OA cell model. In conclusion, our study reveals the role of LDHA-mediated H3K18la of TPI1 promoter in OA progress.

Metabolic reprogramming in skeletal cell differentiation

The human skeleton is a multifunctional organ made up of multiple cell types working in concert to maintain bone and mineral homeostasis and to perform critical mechanical and endocrine functions. From the beginning steps of chondrogenesis that prefigures most of the skeleton, to the rapid bone accrual during skeletal growth, followed by bone remodeling of the mature skeleton, cell differentiation is integral to skeletal health. While growth factors and nuclear proteins that influence skeletal cell differentiation have been extensively studied, the role of cellular metabolism is just beginning to be uncovered. Besides energy production, metabolic pathways have been shown to exert epigenetic regulation via key metabolites to influence cell fate in both cancerous and normal tissues. In this review, we will assess the role of growth factors and transcription factors in reprogramming cellular metabolism to meet the energetic and biosynthetic needs of chondrocytes, osteoblasts, or osteoclasts. We will also summarize the emerging evidence linking metabolic changes to epigenetic modifications during skeletal cell differentiation.

Rosiglitazone retards the progression of iron overload-induced osteoarthritis by impeding chondrocyte ferroptosis

Ferroptosis is implicated in several diseases, including iron overload-induced osteoarthritis (IOOA), which is marked by oxidative stress, iron imbalance, and lipid peroxidation. Given rosiglitazone's (RSG) ability to inhibit lipid peroxidation and ferroptosis, this study aims to assess its therapeutic potential for treating IOOA. Our in vitro results show that RSG targets acyl-CoA synthetase long-chain family member 4 to mitigate impairments induced by interleukin-1 beta and ferric ammonium citrate, including cell apoptosis, senescence, inflammatory responses, extracellular matrix degradation, and ferroptosis. RSG reduced intracellular iron content, alleviated oxidative stress and lipid peroxidation, mitigated damage to membrane-bound organelles, and enhanced glucose transport. Additionally, pre-treatment with RSG imparted anti-ferroptotic properties to chondrocytes. In vivo, RSG alleviated cartilage degradation, inflammatory responses, and ferroptosis in mice with IOOA. In conclusion, RSG exhibits chondroprotective and anti-ferroptotic effects by suppressing lipid peroxidation and restoring iron homeostasis, highlighting its potential for treating IOOA.

Activation of cellular antioxidative stress and migration activities by purified components from immortalized stem cells from human exfoliated deciduous teeth

Although stem cell-based regenerative medicine has been extensively studied, it remains difficult to reconstruct three dimensional tissues and organs in combination with vascular systems in vitro. One clinically successful therapy is transplantation of mesenchymal stem cells (MSC) into patients with graft versus host disease. However, transplanted cells are immediately damaged and destroyed because of innate immune reactions provoked by thrombogenic inflammation, and patients need to take immunosuppressive drugs for the immunological regulation of allogeneic cells. This reduces the benefits of stem cell transplantation. Therefore, alternative therapies are more realistic options for clinical use. In this study, we aimed to take advantage of the therapeutic efficacy of MSC and use multiple cytokines released from MSC, that is, stem cells from human exfoliated deciduous teeth (SHEDs). Here, we purified components from conditioned media of immortalized SHED (IM-SHED-CM) and evaluated the activities of intracellular dehydrogenase, cell migration, and antioxidative stress by studying the cells. The immortalization of SHED could make the stable supply of CM possible. We found that the fractionated component of 50-100 kD from IM-SHED-CM had higher efficacy than the original IM-SHED-CM in terms of intracellular dehydrogenase and cell migration in which intracellular signal transduction was activated via receptor tyrosine kinases, and the glutathione peroxidase and reductase system was highly active. Although antioxidative stress activities in the fractionated component of 50-100 kD had slightly lower than that of original IM-SHE-CM, the fraction still had the activity. Thus, the use of fractionated components of 50-100 kD from IM-SHED-CM could be an alternative choice for MSC transplantation because the purified components from CM could maintain the effect of cytokines from SHED.

The metabolic characteristics and changes of chondrocytes in vivo and in vitro in osteoarthritis

Osteoarthritis (OA) is an intricate pathological condition that primarily affects the entire synovial joint, especially the hip, hand, and knee joints. This results in inflammation in the synovium and osteochondral injuries, ultimately causing functional limitations and joint dysfunction. The key mechanism responsible for maintaining articular cartilage function is chondrocyte metabolism, which involves energy generation through glycolysis, oxidative phosphorylation, and other metabolic pathways. Some studies have shown that chondrocytes in OA exhibit increased glycolytic activity, leading to elevated lactate production and decreased cartilage matrix synthesis. In OA cartilage, chondrocytes display alterations in mitochondrial activity, such as decreased ATP generation and increased oxidative stress, which can contribute to cartilage deterioration. Chondrocyte metabolism also involves anabolic processes for extracellular matrix substrate production and energy generation. During OA, chondrocytes undergo considerable metabolic changes in different aspects, leading to articular cartilage homeostasis deterioration. Numerous studies have been carried out to provide tangible therapies for OA by using various models in vivo and in vitro targeting chondrocyte metabolism, although there are still certain limitations. With growing evidence indicating the essential role of chondrocyte metabolism in disease etiology, this literature review explores the metabolic characteristics and changes of chondrocytes in the presence of OA, both in vivo and in vitro. To provide insight into the complex metabolic reprogramming crucial in chondrocytes during OA progression, we investigate the dynamic interaction between metabolic pathways, such as glycolysis, lipid metabolism, and mitochondrial function. In addition, this review highlights prospective future research directions for novel approaches to diagnosis and treatment. Adopting a multifaceted strategy, our review aims to offer a comprehensive understanding of the metabolic intricacies within chondrocytes in OA, with the ultimate goal of identifying therapeutic targets capable of modulating chondrocyte metabolism for the treatment of OA.

The association between diabetes mellitus and musculoskeletal disorders: a systematic review and meta-analysis

Background

Despite the fact that DM patients are living longer, research on the prevalence of MSDs and other related illnesses is still lacking compared to that of other comorbidities. This study systematically reviewed and meta-analyzed cohort studies to determine the association between diabetes mellitus (DM) and musculoskeletal disorders (MSDs).

Methods

A comprehensive search of international databases, including Medline (PubMed), Web of Science, Scopus, and Embase, was conducted up to June 2023 to identify relevant studies investigating the association between MSDs and DM.

Results

The meta-analysis included ten cohort studies with a total of 308,445 participants. The pooled risk ratio (RR) estimate for the association between MSDs and DM was 1.03 (95% CI 1.00-1.06). Based on subgroup analysis, the association between longer duration (more than 7), European, below the age of 70, and female patients was higher than the others.

Conclusion

In conclusion, the results of this meta-analysis suggest that there may be an association between MSDs and diabetes in people with diabetes. These findings add to the existing knowledge on this topic and highlight the importance of recognition and management of MSDs in people with DM. There is a need for further research to investigate the underlying mechanisms and to develop targeted interventions for the prevention and management of MSDs in this population.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=381787, identifier CRD42022381787.

Sirtuin 1 in osteoarthritis: Perspectives on regulating glucose metabolism

Osteoarthritis (OA) is a degenerative disease characterised by articular cartilage destruction, and its complex aetiology contributes to suboptimal clinical treatment outcomes. A close association exists between glucose metabolism dysregulation and OA pathogenesis. Owing to the unique environment of low oxygen and glucose concentrations, chondrocytes rely heavily on their glycolytic capacity, exhibiting distinct spatiotemporal differences. However, under pathological stimulation, chondrocytes undergo excessive glycolytic activity while mitochondrial respiration and other branches of glucose metabolism are compromised. This metabolic change induces cartilage degeneration by reprogramming the inflammatory responses. Sirtuins, a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent deacetylases, regulate glucose metabolism in response to energy fluctuations in different cellular compartments，alleviating metabolic stress. SIRT1, the most extensively studied sirtuin, participates in maintaining glucose homeostasis in almost all key metabolic tissues. While actively contributing to the OA progression and displaying diverse biological effects in cartilage protection, SIRT1's role in regulating glucose metabolism in chondrocytes has not received sufficient attention. This review focuses on discussing the beneficial role of SIRT1 in OA progression from a metabolic regulation perspective based on elucidating the primary characteristics of chondrocyte glucose metabolism. We also summarise the potential mechanisms and therapeutic strategies targeting SIRT1 in chondrocytes to guide clinical practice and explore novel therapeutic directions.

Cross-talk of inflammation and chondrocyte intracellular metabolism in osteoarthritis

Osteoarthritis is a disease that impacts millions around the world, leading to significant financial and medical burden for patients and the healthcare system. However, no effective biomarkers or disease modifying therapeutics exist for the early identification and management of the disease. Inflammation drives chondrocytes to express extracellular matrix (ECM) degrading enzymes and interruption of this pathway is a viable target to prevent degradation of cartilage. It has been demonstrated that inflammation can alter the intracellular metabolism of chondrocytes, a process known as metabolic reprogramming. This metabolic reprogramming is critical for cartilage breakdown by shifting chondrocytes to an ECM-catabolic state and likely as a potential therapeutic target for osteoarthritis. Metabolic modulators hold the potential to reduce chondrocyte inflammatory responses and protect cartilage. In this narrative review, we explore some of the existing examples of interactions between metabolism and inflammatory pathways in chondrocytes. We summarize the impact of inflammatory stimulation on various metabolic pathways and describe several examples by which targeting of metabolism is able to modulate ECM-degrading activity of chondrocytes to protect against cartilage damage.

Ultrasound-Guided Interventions for Carpal Tunnel Syndrome: A Systematic Review and Meta-Analyses

Carpal tunnel syndrome (CTS) is the most common peripheral entrapment, and recently, ultrasound-guided perineural injection (UPIT) and percutaneous flexor retinaculum release (UPCTR) have been utilized to treat CTS. However, no systematic review or meta-analysis has included both intervention types of ultrasound-guided interventions for CTS. Therefore, we performed this review using four databases (i.e., PubMed, EMBASE, Scopus, and Cochrane) to evaluate the quality of evidence, effectiveness, and safety of the published studies on ultrasound-guided interventions in CTS. Among sixty studies selected for systemic review, 20 randomized treatment comparison or controlled studies were included in six meta-analyses. Steroid UPIT with ultrasound guidance outperformed that with landmark guidance. UPIT with higher-dose steroids outperformed that with lower-dose steroids. UPIT with 5% dextrose in water (D5W) outperformed control injection and hydrodissection with high-volume D5W was superior to that with low-volume D5W. UPIT with platelet-rich plasma outperformed various control treatments. UPCTR outperformed open surgery in terms of symptom improvement but not functional improvement. No serious adverse events were reported in the studies reviewed. The findings suggest that both UPIT and UPCTR may provide clinically important benefits and appear safe. Further treatment comparison studies are required to determine comparative therapeutic efficacy.

Acute cytokine treatment stimulates glucose uptake and glycolysis in human keratinocytes

During inflammation, cellular glucose uptake and glycolysis are upregulated to meet an increased energy demand. For example, keratinocyte glycolysis is essential for progression of psoriasis. Therefore, understanding the regulation of glucose metabolism in keratinocytes is of importance. Here, we show that the pro-inflammatory cytokines IFNγ and TNF together rapidly induce glucose uptake, glycolysis, and glycolytic capacity in cultured keratinocytes. Furthermore, we found that acute IFNγ and TNF stimulation induces glucose transporter 4 (GLUT4) translocation to the plasma membrane and engages AMPK-dependent intracellular signaling. Together, these findings suggest acute cytokine-induced glucose metabolism in keratinocytes could contribute to inflammation in psoriatic disease, and that GLUT4 is involved in these processes.

Glucose metabolism in skeletal cells

The mammalian skeleton is integral to whole body physiology with a multitude of functions beyond mechanical support and locomotion, including support of hematopoiesis, mineral homeostasis and potentially other endocrine roles. Formation of the skeleton begins in the embryo and mostly from a cartilage template that is ultimately replaced by bone through endochondrial ossification. Skeletal development and maturation continue after birth in most species and last into the second decade of postnatal life in humans. In the mature skeleton, articular cartilage lining the synovial joint surfaces is vital for bodily movement and damages to the cartilage are a hallmark of osteoarthritis. The mature bone tissue undergoes continuous remodeling initiated with bone resorption by osteoclasts and completed with bone formation from osteoblasts. In a healthy state, the exquisite balance between bone resorption and formation is responsible for maintaining a stable bone mass and structural integrity, while meeting the physiological needs for minerals via controlled release from bone. Disruption of the balance in favor of bone resorption is the root cause for osteoporosis. Whereas osteoclasts pump molar quantities of hydrochloric acid to dissolve the bone minerals in a process requiring ATP hydrolysis, osteoblasts build bone mass by synthesizing and secreting copious amounts of bone matrix proteins. Thus, both osteoclasts and osteoblasts engage in energy-intensive activities to fulfill their physiological functions, but the bioenergetics of those and other skeletal cell types are not well understood. Nonetheless, the past ten years have witnessed a resurgence of interest in studies of skeletal cell metabolism, resulting in an unprecedented understanding of energy substrate utilization and its role in cell fate and activity regulation. The present review attempts to synthesize the current findings of glucose metabolism in chondrocytes, osteoblasts and osteoclasts. Advances with the other relevant cell types including skeletal stem cells and marrow adipocytes will not be discussed here as they have been extensively reviewed recently by others (van Gastel and Carmeliet, 2021). Elucidation of the bioenergetic mechanisms in the skeletal cells is likely to open new avenues for developing additional safe and effective bone therapies.

An appraisal of the current status of inhibition of glucose transporters as an emerging antineoplastic approach: Promising potential of new pan-GLUT inhibitors

Neoplastic cells displayed altered metabolism with accelerated glycolysis. Therefore, these cells need a mammoth supply of glucose for which they display an upregulated expression of various glucose transporters (GLUT). Thus, novel antineoplastic strategies focus on inhibiting GLUT to intersect the glycolytic lifeline of cancer cells. This review focuses on the current status of various GLUT inhibition scenarios. The GLUT inhibitors belong to both natural and synthetic small inhibitory molecules category. As neoplastic cells express multiple GLUT isoforms, it is necessary to use pan-GLUT inhibitors. Nevertheless, it is also necessary that such pan-GLUT inhibitors exert their action at a low concentration so that normal healthy cells are left unharmed and minimal injury is caused to the other vital organs and systems of the body. Moreover, approaches are also emerging from combining GLUT inhibitors with other chemotherapeutic agents to potentiate the antineoplastic action. A new pan-GLUT inhibitor named glutor, a piperazine-one derivative, has shown a potent antineoplastic action owing to its inhibitory action exerted at nanomolar concentrations. The review discusses the merits and limitations of the existing GLUT inhibitory approach with possible future outcomes.

The Metabolic Landscape in Osteoarthritis

Articular cartilage function depends on the temporal and zonal distribution of coordinated metabolic regulation in chondrocytes. Emerging evidence shows the importance of cellular metabolism in the molecular control of the cartilage and its dysregulation in degenerative diseases like osteoarthritis (OA). Compared to most other tissues, chondrocytes are sparsely located in the extracellular matrix, lacking the typical proximity of neural, vascular, and lymphatic tissue. Making up under 5% of the total tissue weight of cartilage, chondrocytes have a relative deficiency of access to nutrients and oxygen, as well as limited pathways for metabolite removal. This makes cartilage a unique tissue with hypocellularity, prolonged metabolic rate, and tissue turnover. Studies in the past decade have shown that several pathways of central carbon metabolism are essential for cartilage homeostasis. Here, we summarised the literature findings on the role of cellular metabolism in determining the chondrocyte function and how this metabolic dysregulation led to cartilage aging in OA and provided an outlook on how the field may evolve in the coming years. Although the various energy metabolism pathways are inextricably linked with one another, for the purpose of this review, we initially endeavoured to examine them individually and in relative isolation. Subsequently, we comment on what is known regarding the integration and linked signalling pathways between these systems and the therapeutic opportunities for targeting OA metabolism.

Mechanism of Glucose Water as a Neural Injection: A Perspective on Neuroinflammation

The entrapment of peripheral nerves is associated with chronic neuroinflammation and neuropathic pain, and perineural injection therapy with glucose is emerging as an effective treatment for peripheral entrapment neuropathy. However, the mechanism underlying the pharmacological effect of glucose on nerves remains unclear. One of the hypothesized mechanisms is that glucose reduces neurogenic inflammation. Therefore, we investigated the effects of high glucose concentrations on cytokine-induced neuroinflammation in vitro. Human SH-SY5Y neuronal cells were challenged with 10 ng/mL TNF-α for 16 h and subsequently treated with different glucose concentrations (0–25 mM) for 24 h. Cell viability was evaluated using the diphenyltetrazolium bromide assay, and proinflammatory cytokine levels were assessed using ELISA and quantitative PCR. In addition, mRNA levels of NF-κB and cyclooxygenase-2 were analyzed using quantitative PCR. Exposure to 10 ng/mL TNF-α resulted in decreased viability of SH-SY5Y cells and significant upregulation of IL-6, IL-1β, NF-κB, and cyclooxygenase-2. Subsequent exposure to high glucose levels (25 mM) markedly reduced the upregulation of IL-6, IL-1β, cyclooxygenase-2, and NF-κB, and restored the functional metabolism of SH-SY5Y cells, compared with that of the normal glucose control. Our findings suggest that high glucose concentrations can mitigate TNF-α-induced NF-κB activation, upregulation of proinflammatory cytokines, and metabolic dysfunction.

Impaired glucose metabolism underlies articular cartilage degeneration in osteoarthritis

Osteoarthritis (OA) is the leading joint disease characterized by cartilage destruction and loss of mobility. Accumulating evidence indicates that the incidence and severity of OA increases with diabetes, implicating systemic glucose metabolism in joint health. However, a definitive link between cellular metabolism in articular cartilage and OA pathogenesis is not yet established. Here, we report that in mice surgically induced to develop knee OA through destabilization of medial meniscus (DMM), expression of the main glucose transporter Glut1 is notably reduced in joint cartilage. Inducible deletion of Glut1 specifically in the Prg4-expressing articular cartilage accelerates cartilage loss in DMM-induced OA. Conversely, forced expression of Glut1 protects against cartilage destruction following DMM. Moreover, in mice with type I diabetes, both Glut1 expression and the rate of glycolysis are diminished in the articular cartilage, and the diabetic mice exhibit more severe cartilage destruction than their nondiabetic counterparts following DMM. The results provide proof of concept that boosting glucose metabolism in articular chondrocytes may ameliorate cartilage degeneration in OA.

Interleukin -1β Promotes Lung Adenocarcinoma Growth and Invasion Through Promoting Glycolysis via p38 Pathway

Background

There is a close relationship among inflammation, glycolysis, and tumors. The IL-1 family includes important inflammatory cytokines, among which IL-1β has been widely studied. In this study, we focused on the effect of IL-1β on glycolysis of lung adenocarcinoma (LUAD) cells in vivo and in vitro and explored its possible mechanisms.

Methods

A bioinformatic database and quantitative real-time PCR were used to analyze the expression of glycolysis-related enzyme genes and their correlations with IL1β in human LUAD samples. The human LUAD cell line A549 and Lewis lung carcinoma LLC cell line were stimulated with IL-1β. In vitro treatment effects, including glycolysis level, migration, and invasion were evaluated with a glucose assay kit, lactate assay kit, Western blotting, wound healing, and the transwell method. We established a mouse model of subcutaneous tumors using LLC cells pretreated with IL-1β and analyzed in vivo treatment effects through positron-emission tomography-computed tomography and staining. Virtual screening and molecular dynamic simulation were used to screen potential inhibitors of IL-1β.

Results

Our results showed that IL1β was positively correlated with the expression of glycolysis-related enzyme genes in LUAD. Glycolysis, migration, and invasion significantly increased in A549 and LLC stimulated with IL-1β. In vivo, IL-1β increased growth, mean standard uptake value, and pulmonary tumor metastasis, which were inhibited by the glycolysis inhibitor 2-deoxy-D-glucose and p38-pathway inhibitors. Small molecular compound ZINC14610053 was suggested being a potential inhibitor of IL-1β.

Conclusion

IL-1β promotes glycolysis of LUAD cells through p38 signaling, further enhancing tumor-cell migration and invasion. These results show that IL-1β links inflammation to glycolysis in LUAD, and targeting IL-1β and the glycolysis pathway may be a potential therapeutic strategy for lung cancer.

Deletion of Glut1 in early postnatal cartilage reprograms chondrocytes toward enhanced glutamine oxidation

Glucose metabolism is fundamental for the functions of all tissues, including cartilage. Despite the emerging evidence related to glucose metabolism in the regulation of prenatal cartilage development, little is known about the role of glucose metabolism and its biochemical basis in postnatal cartilage growth and homeostasis. We show here that genetic deletion of the glucose transporter Glut1 in postnatal cartilage impairs cell proliferation and matrix production in growth plate (GPs) but paradoxically increases cartilage remnants in the metaphysis, resulting in shortening of long bones. On the other hand, articular cartilage (AC) with Glut1 deficiency presents diminished cellularity and loss of proteoglycans, which ultimately progress to cartilage fibrosis. Moreover, predisposition to Glut1 deficiency severely exacerbates injury-induced osteoarthritis. Regardless of the disparities in glucose metabolism between GP and AC chondrocytes under normal conditions, both types of chondrocytes demonstrate metabolic plasticity to enhance glutamine utilization and oxidation in the absence of glucose availability. However, uncontrolled glutamine flux causes collagen overmodification, thus affecting extracellular matrix remodeling in both cartilage compartments. These results uncover the pivotal and distinct roles of Glut1-mediated glucose metabolism in two of the postnatal cartilage compartments and link some cartilage abnormalities to altered glucose/glutamine metabolism.

Ex Vivo Equine Cartilage Explant Osteoarthritis Model: A Metabolomics and Proteomics Study

Osteoarthritis is an age-related degenerative musculoskeletal disease characterized by loss of articular cartilage, synovitis, and subchondral bone sclerosis. Osteoarthritis pathogenesis is yet to be fully elucidated with no osteoarthritis-specific biomarkers in clinical use. Ex vivo equine cartilage explants (n = 5) were incubated in tumor necrosis factor-α (TNF-α)/interleukin-1β (IL-1β)-supplemented culture media for 8 days, with the media removed and replaced at 2, 5, and 8 days. Acetonitrile metabolite extractions of 8 day cartilage explants and media samples at all time points underwent one-dimensional (1D) ¹H nuclear magnetic resonance metabolomic analysis, with media samples also undergoing mass spectrometry proteomic analysis. Within the cartilage, glucose and lysine were elevated following TNF-α/IL-1β treatment, while adenosine, alanine, betaine, creatine, myo-inositol, and uridine decreased. Within the culture media, 4, 4, and 6 differentially abundant metabolites and 154, 138, and 72 differentially abundant proteins were identified at 1–2, 3–5, and 6–8 days, respectively, including reduced alanine and increased isoleucine, enolase 1, vimentin, and lamin A/C following treatment. Nine potential novel osteoarthritis neopeptides were elevated in the treated media. Implicated pathways were dominated by those involved in cellular movement. Our innovative study has provided insightful information on early osteoarthritis pathogenesis, enabling potential translation for clinical markers and possible new therapeutic targets.

Polyvalent therapeutic vaccine for type 2 diabetes mellitus: Immunoinformatics approach to study co-stimulation of cytokines and GLUT1 receptors

Background

Type 2 diabetes mellitus (T2DM) is a worldwide disease that have an impact on individuals of all ages causing micro and macro vascular impairments due to hyperglycemic internal environment. For ultimate treatment to cure T2DM, association of diabetes with immune components provides a strong basis for immunotherapies and vaccines developments that could stimulate the immune cells to minimize the insulin resistance and initiate gluconeogenesis through an insulin independent route.

Methodology

Immunoinformatics based approach was used to design a polyvalent vaccine for T2DM that involved data accession, antigenicity analysis, T-cell epitopes prediction, conservation and proteasomal evaluation, functional annotation, interactomic and in silico binding affinity analysis.

Results

We found the binding affinity of antigenic peptides with major histocompatibility complex (MHC) Class-I molecules for immune activation to control T2DM. We found 13-epitopes of 9 amino acid residues for multiple alleles of MHC class-I bears significant binding affinity. The downstream signaling resulted by T-cell activation is directly regulated by the molecular weight, amino acid properties and affinity of these epitopes. Each epitope has important percentile rank with significant ANN IC₅₀ values. These high score potential epitopes were linked using AAY, EAAAK linkers and HBHA adjuvant to generate T-cell polyvalent vaccine with a molecular weight of 35.6 kDa containing 322 amino acids residues. In silico analysis of polyvalent construct showed the significant binding affinity (− 15.34 Kcal/mol) with MHC Class-I. This interaction would help to understand our hypothesis, potential activation of T-cells and stimulatory factor of cytokines and GLUT1 receptors.

Conclusion

Our system-level immunoinformatics approach is suitable for designing potential polyvalent therapeutic vaccine candidates for T2DM by reducing hyperglycemia and enhancing metabolic activities through the immune system.

LDHA-mediated ROS generation in chondrocytes is a potential therapeutic target for osteoarthritis

The contribution of inflammation to the chronic joint disease osteoarthritis (OA) is unclear, and this lack of clarity is detrimental to efforts to identify therapeutic targets. Here we show that chondrocytes under inflammatory conditions undergo a metabolic shift that is regulated by NF-κB activation, leading to reprogramming of cell metabolism towards glycolysis and lactate dehydrogenase A (LDHA). Inflammation and metabolism can reciprocally modulate each other to regulate cartilage degradation. LDHA binds to NADH and promotes reactive oxygen species (ROS) to induce catabolic changes through stabilization of IκB-ζ, a critical pro-inflammatory mediator in chondrocytes. IκB-ζ is regulated bi-modally at the stages of transcription and protein degradation. Overall, this work highlights the function of NF-κB activity in the OA joint as well as a ROS promoting function for LDHA and identifies LDHA as a potential therapeutic target for OA treatment.

Elevated Glucose Levels Preserve Glucose Uptake, Hyaluronan Production, and Low Glutamate Release Following Interleukin-1β Stimulation of Differentiated Chondrocytes

OBJECTIVE

Chondrocytes are responsible for remodeling and maintaining the structural and functional integrity of the cartilage extracellular matrix. Because of the absence of a vascular supply, chondrocytes survive in a relatively hypoxic environment and thus have limited regenerative capacity during conditions of cellular stress associated with inflammation and matrix degradation, such as osteoarthritis (OA). Glucose is essential to sustain chondrocyte metabolism and is a precursor for key matrix components. In this study, we investigated the importance of glucose as a fuel source for matrix repair during inflammation as well as the effect of glucose on inflammatory mediators associated with osteoarthritis.

DESIGN

To create an OA model, we used equine chondrocytes from 4 individual horses that were differentiated into cartilage pellets in vitro followed by interleukin-1β (IL-1β) stimulation for 72 hours. The cells were kept at either normoglycemic conditions (5 mM glucose) or supraphysiological glucose concentrations (25 mM glucose) during the stimulation with IL-1β.

RESULTS

We found that elevated glucose levels preserve glucose uptake, hyaluronan synthesis, and matrix integrity, as well as induce anti-inflammatory actions by maintaining low expression of Toll-like receptor-4 and low secretion of glutamate.

CONCLUSIONS

Adequate supply of glucose to chondrocytes during conditions of inflammation and matrix degradation interrupts the detrimental inflammatory cycle and induces synthesis of hyaluronan, thereby promoting cartilage repair.

Diabetic hip arthropathy is associated with a higher prevalence of femoral head chondromalacia: a case-controlled study

INTRODUCTION

No previous studies have characterised hip joint disease in diabetic patients undergoing hip arthroscopy. The purpose of our study was to evaluate intra-articular hip pathology and surgical variables in patients with diabetes compared to matched, non-diabetic controls. We hypothesised that diabetic patients would demonstrate a higher prevalence and severity of hip chondral pathology.

METHODS

We retrospectively reviewed 795 consecutive hip arthroscopies performed by a single surgeon between 2010 and 2015. Patients ⩾18 years of age without a history of diabetes served as controls and were matched based on age, sex, body mass index, duration of symptoms, and operative side. Clinical symptoms, preoperative physical examination, and radiologic and intraoperative findings were assessed. The primary outcomes were the acetabular and femoral head chondromalacia index (CMI), calculated as the product of the Outerbridge chondromalacia grade and surface area (mm²*severity).

RESULTS

15 diabetic patients were matched to 137 non-diabetic controls. Diabetic patients demonstrated a higher prevalence of femoral head chondromalacia compared to controls both on magnetic resonance imaging (45.5% vs. 7.5%, p = 0.002) and during arthroscopy (100% vs. 75.9%, p = 0.042). Femoral head chondromalacia in diabetic patients had higher Outerbridge grade (2.4 vs. 2.0, p = 0.030) but similar CMI (513.0 vs. 416.4, p = 0.298) compared to controls.

DISCUSSION

Femoral head chondral pathology was more prevalent and of higher severity grade in diabetic patients. The prevalence, size, and severity of acetabular chondral disease were similar between diabetic and non-diabetic patients. Multivariate analysis demonstrated that diabetic status was independently associated with the presence of femoral head chondromalacia.

Urate transport capacity of glucose transporter 9 and urate transporter 1 in cartilage chondrocytes

Chronic gouty arthritis, caused by a persistent increase in, and the deposition of, soluble uric acid (sUA), can induce pathological chondrocyte destruction; however, the effects of urate transport and intracellular sUA on chondrocyte functionality and viability are yet to be fully determined. Thus, the aim of the present study was to investigate the presence and functionality of a urate transport system in chondrocytes. The expression profiles of two primary urate reabsorptive transporters, glucose transporter 9 (GLUT9) and urate transporter 1 (URAT1), in human articular cartilage and chondrocyte cell lines were examined via western blotting, reverse transcription-quantitative PCR, immunohistochemistry and immunofluorescence. Then, chondrocytes were incubated with exogenous sUA at increasing concentrations. Negative control assays were conducted via the specific knockdown of GLUT9 and URAT1 with lentiviral short hairpin (sh)RNAs, and by pretreatment with benzbromarone, a known inhibitor of the two transporters. Intracellular UA concentrations were measured using colorimetric assays. The expression levels of GLUT9 and URAT1 were determined in cartilage tissues and chondrocyte cell lines. Incubation of chondrocytes with sUA led to a concentration-dependent increase in intracellular urate concentrations, which was inhibited by GLUT9 or URAT1 knockdown, or by benzbromarone pretreatment (27.13±2.70, 44.22±2.34 and 58.46±2.32% reduction, respectively). In particular, benzbromarone further decreased the already-reduced intracellular UA concentrations in HC-shGLUT9 and HC-shURAT1 cells by 46.79±2.46 and 39.79±2.22%, respectively. Cells overexpressing GLUT9 and URAT1 were used as the positive cell control, which showed increased intracellular UA concentrations that could be reversed by treatment with benzbromarone. In conclusion, chondrocytes may possess an active UA transport system. GLUT9 and URAT1 functioned synergistically to transport UA into the chondrocyte cytoplasm, which was inhibited by specific gene knockdowns and drug-induced inhibition. These results may be fundamental in the further investigation of the pathological changes to chondrocytes induced by sUA during gouty arthritis, and identified UA transport processes as potential targets for the early control of chronic gouty arthritis.

The Emerging Role of Glucose Metabolism in Cartilage Development

PURPOSE OF REVIEW

Proper cartilage development is critical to bone formation during endochondral ossification. This review highlights the current understanding of various aspects of glucose metabolism in chondrocytes during cartilage development.

RECENT FINDINGS

Recent studies indicate that chondrocytes transdifferentiate into osteoblasts and bone marrow stromal cells during endochondral ossification. In cartilage development, signaling molecules, including IGF2 and BMP2, tightly control glucose uptake and utilization in a stage-specific manner. Perturbation of glucose metabolism alters the course of chondrocyte maturation, suggesting a key role for glucose metabolism during endochondral ossification. During prenatal and postnatal growth, chondrocytes experience bursts of nutrient availability and energy expenditure, which demand sophisticated control of the glucose-dependent processes of cartilage matrix production, cell proliferation, and hypertrophy. Investigating the regulation of glucose metabolism may therefore lead to a unifying mechanism for signaling events in cartilage development and provide insight into causes of skeletal growth abnormalities.

Glucose metabolism induced by Bmp signaling is essential for murine skeletal development

Much of the mammalian skeleton originates from a cartilage template eventually replaced by bone via endochondral ossification. Despite much knowledge about growth factors and nuclear proteins in skeletal development, little is understood about the role of metabolic regulation. Here we report that genetic deletion of the glucose transporter Glut1 (Slc2a1), either before or after the onset of chondrogenesis in the limb, severely impairs chondrocyte proliferation and hypertrophy, resulting in dramatic shortening of the limbs. The cartilage defects are reminiscent to those caused by deficiency in Bmp signaling. Importantly, deletion of Bmpr1a in chondrocytes markedly reduces Glut1 levels in vivo, whereas recombinant BMP2 increases Glut1 mRNA and protein levels, boosting glucose metabolism in primary chondrocytes. Biochemical studies identify a Bmp-mTORC1-Hif1a signaling cascade resulting in upregulation of Glut1 in chondrocytes. The results therefore uncover a hitherto unknown connection between Bmp signaling and glucose metabolism in the regulation of cartilage development.

It is unclear how metabolic regulation affects development of the skeleton. Here, the authors show that deletion of the glucose transporter Glut1 (Slc2a1) both prior to and following chondrogenesis in the mouse limb impairs chondrocyte proliferation and shortening of the limbs, modulated by BMP signaling.

Distinct metabolic programs induced by TGF-β1 and BMP2 in human articular chondrocytes with osteoarthritis

Objectives

Cellular energy metabolism is important for the function of all tissues, including cartilage. Recent studies indicate that superficial and deep subpopulations of articular chondrocytes (ACs) have distinct metabolic profiles. At the cellular and molecular level, osteoarthritis (OA) is characterised by alteration from a healthy homoeostatic state towards a catabolic state. Several molecular pathways, including transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) signalling, have been identified as critical players in the pathogenesis and progression of OA. However, the manner in which these factors influence cellular energy metabolism in ACs is not well understood. This study investigates the effect of TGF-β or BMP signalling on energy metabolism in human articular chondrocytes (hACs).

Methods

ACs were isolated from residual macroscopically full thickness and intact cartilage from the femoral condyle of human samples obtained from patients with OA. ACs were treated with Vehicle (control), TGF-β1 or BMP2 for 48–72 hours. Metabolic assays were performed to determine glucose consumption, lactate production and adenosine triphosphate (ATP) production, whereas the mitochondrial stress test was performed to determine oxygen consumption rate. Protein was isolated to assess translational activity and was evaluated using Western blot.

Results

We showed that TGF-β1, known to maintain chondrocyte homoeostasis, stimulated glycolysis by upregulating key glycolytic factors, such as glucose transporter 1 (Glut1) and hexokinase II, while reducing oxidative phosphorylation in hACs. In contrast, BMP2 enhanced mitochondrial metabolism and oxidative phosphorylation and had a minimal effect on key glycolytic regulators.

Conclusions

Our data revealed distinct metabolic programs induced by TGF-β1 and BMP2 in hACs, suggesting that the regulation of cellular metabolism may represent a new mechanism underlying the pathogenesis of OA.

The translational potential of this article

The findings define the regulation of energy metabolism as a potential novel therapeutic approach for the treatment of OA.

Metabolic Adaptation of Human CD4+ and CD8+ T-Cells to T-Cell Receptor-Mediated Stimulation

Linking immunometabolic adaptation to T-cell function provides insight for the development of new therapeutic approaches in multiple disease settings. T-cell activation and downstream effector functions of CD4⁺ and CD8⁺ T-cells are controlled by the strength of interaction between the T-cell receptor (TCR) and peptides presented by human leukocyte antigens (pHLA). The role of TCR–pHLA interactions in modulating T-cell metabolism is unknown. Here, for the first time, we explore the relative contributions of the main metabolic pathways to functional responses in human CD4⁺ and CD8⁺ T-cells. Increased expression of hexokinase II accompanied by higher basal glycolysis is demonstrated in CD4⁺ T-cells; cytokine production in CD8⁺ T-cells is more reliant on oxidative phosphorylation. Using antigen-specific CD4⁺ and CD8⁺ T-cell clones and altered peptide ligands, we demonstrate that binding affinity tunes the underlying metabolic shift. Overall, this study provides important new insight into how metabolic pathways are controlled during antigen-specific activation of human T-cells.

Effects of single or combined induction of diabetes mellitus and knee osteoarthritis on some biochemical and haematological parameters in rats

Clinical evidences on the coexistence of diabetes mellitus (DM) and osteoarthritis (OA) dated back to the 1960s. Therefore, the study investigated the effects of induced DM and/or knee osteoarthritis (KOA) on some biochemical and haematological parameters in adult male Wistar rats. Twenty rats were used for this study. They were randomly divided into 4 groups (N=5 rats) which included: Normal control; Osteoarthritic (OA) control; Diabetic control; and, Diabetic+Osteoarthritic (D+OA) control. DM was induced in overnight fasted rats by the administration of streptozotocin (65mg/kg b.w., i.p.) 15min after the administration of nicotinamide (110mg/kg, b.w., i.p.). However, KOA was induced by the intra-articular injection of 4mg of sodium monoiodoacetate in 40μl of normal saline. In the D+OA group, KOA was induced about 12h after the induction of DM. The rats were left untreated for four weeks. Afterwards, the experiment was terminated. The results showed that both DM and OA featured hypercortisolism and dyslipidaemia. The additive effects of both conditions were observed on the lipid profile and some haematological indices in the D+OA group. Unlike DM, OA had mild adverse effects on the haematological profile. Nevertheless, it significantly contributed to hyperglycaemia in the D+OA group, even though it had no significant effect on the insulin resistance. However, the hypocalcaemic and glycogenolytic effects of DM were negated by OA. In conclusion, the coexistence of DM and OA presents a greater challenge on the biochemical and haematological profiles than the individual disease. But, this prediction could sometimes be annulled by the intervention of endogenous homeostatic mechanisms.

Effects of sesamin on chondroitin sulfate proteoglycan synthesis induced by interleukin-1beta in human chondrocytes

Background

Numerous studies have reported on the health benefits of sesamin, a major lignin found in sesame (S. indicum) seeds. Recently, sesamin was shown to have the ability to promote chondroitin sulfate proteoglycan synthesis in normal human chondrocytes. This study assesses the anti-inflammatory effect of sesamin on proteoglycans production in 3D chondrocyte cultures.

Methods

To evaluate the effects of sesamin on IL-1β-treated human articular chondrocytes (HAC) pellets, the pellets were pre-treated with IL-1β then cultured in the presence of various concentrations of sesamin for 21 days. During that period, the expression of IL-1β, glycosaminoglycans (GAGs) content and Chondroitin sulfate proteoglycans (CSPGs) synthesis genes (ACAN, XT-1, XT-2, CHSY1 and ChPF) was measured. The GAGs accumulation in the extracellular matrix was determined on day 21 by histological analysis.

Results

There was clear evidence that sesamin upregulated expression of all the CSPGs synthesis genes, in contrast to the down-regulation of IL-1β expression both in genes and in protein levels. The level of release and matrix accumulation of GAGs in IL-1β pre-treated HAC pellets in the presence of sesamin was recovered. These results correlate with the histological examination which showed that sesamin enhanced matrix CSPGs accumulation.

Conclusions

Sesamin enhances CSPGs synthesis, suppresses IL-1β expression and ameliorates IL-1β induced inflammation in human chondrocytes. Sesamin could have therapeutic benefits for treating inflammation in osteoarthritis.

The role of metabolism in the pathogenesis of osteoarthritis

Metabolism is important for cartilage and synovial joint function. Under adverse microenvironmental conditions, mammalian cells undergo a switch in cell metabolism from a resting regulatory state to a highly metabolically activate state to maintain energy homeostasis. This phenomenon also leads to an increase in metabolic intermediates for the biosynthesis of inflammatory and degradative proteins, which in turn activate key transcription factors and inflammatory signalling pathways involved in catabolic processes, and the persistent perpetuation of drivers of pathogenesis. In the past few years, several studies have demonstrated that metabolism has a key role in inflammatory joint diseases. In particular, metabolism is drastically altered in osteoarthritis (OA) and aberrant immunometabolism may be a key feature of many phenotypes of OA. This Review focuses on aberrant metabolism in the pathogenesis of OA, summarizing the current state of knowledge on the role of impaired metabolism in the cells of the osteoarthritic joint. We also highlight areas for future research, such as the potential to target metabolic pathways and mediators therapeutically.

Osteoarthritis and type 2 diabetes mellitus: What are the links?

Osteoarthritis (OA) is the most frequent joint disorder and one of the leading cause of disability. During a long time, it was considered as the consequence of aging and mechanical stress on cartilage. Recent advances in the knowledge of OA have highlighted that it is a whole joint disease with early modifications of synovium and subchondral bone but also that it is associated with obesity and metabolic syndrome through systemic mechanisms. In the past year, type 2 diabetes has been described in two meta-analyzes as an independent risk factor for OA. In vivo models of diabetes corroborated epidemiological studies. Indeed, diabetic rodents display a spontaneous and a more severe experimental OA than their non-diabetic counterparts, which can be partially prevented by diabetes treatment (insulin, pioglitazone). The negative impact of diabetes on joints could be explain by the induction of oxidative stress and pro-inflammatory cytokines but also by advanced age products accumulation in joint tissues exposed to chronic high glucose concentration. Insulin resistance might also impair joint tissue because of a local insulin resistance of diabetic synovial membrane but also by the systemic low grade inflammation state related to obesity and insulin resistant state.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

OBJECTIVE

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation.

DESIGN

SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes.

RESULTS

SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage.

CONCLUSIONS

SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

NK cell count and glucotransporter 4 (GLUT4) expression in subjects with type 2 diabetes and colon cancer

BACKGROUND

Type 2 diabetes (T2D) and colon cancer (CC) are numbered among the most common diseases in the world. The decreased activity of natural killer (NK) cells previously revealed in both mentioned pathological states may be correlated with impaired expression of GLUT4 as the major insulin-dependent glucose transporter in these cells.

METHODS

The aim of this study was to evaluate GLUT4 expression and NK cells number in subjects with T2D and/or CC in comparison with control group. We evaluated 78 individuals divided into four groups: (1) patients with CC and T2DM, (2) patients with CC, (3) patients with T2DM (4) healthy control. GLUT4 expression on the surface of NK cells was measured using flow cytometry and phenotyping of NK cell was performed by immunofluorescent method.

RESULTS

Subjects with diabetes had the highest GLUT4 expression (21.35 ± 7.2 %) in comparison with other groups (P < 0.01). The mean values of GLUT4 expression in group with CC and in patients with both T2D and CC were similar (1.4 ± 0.4 % vs 1.5 ± 1.0 %; respectively). These values were significantly lower than in control group (12.6 ± 2.9 %; P < 0.01). In patients with T2D and CC the number of NK cells (20.15 ± 6.6 %) was significantly higher than in other groups, i.e. in group with T2D (14.08 ± 5.7 %), in group with CC (9.21 ± 3.6 %) and in control group (9.48 ± 4.7 %), respectively (P < 0.01).

CONCLUSIONS

It seems that there is a need to pay more attention to the high incidence of colon cancer among patients with type 2 diabetes. Decreased GLUT4 expression observed on NK cells in patients with colon cancer may be responsible for dysfunction of these cells and the higher carcinogenic risk in type 2 diabetic subjects.

MicroRNA-155 suppresses autophagy in chondrocytes by modulating expression of autophagy proteins

OBJECTIVE

Autophagy dysfunction has been reported in osteoarthritis (OA) cartilage. The objective of this study was to investigate the role of microRNA-155 (miR-155), which is overexpressed in OA, in the regulation of autophagy in human chondrocytes.

DESIGN

Rapamycin (50 nM) and 2-deoxyglucose (2-DG) (5 mM) were used to stimulate autophagy in primary human articular chondrocytes and in the T/C28a2 human chondrocyte cell line. Cells were transfected with LNA GapmeR or mimic specific for miR-155 and autophagy flux was assessed by LC3 western blotting and by Cyto-ID(®) dye quantification in autophagic vacuoles. Expression of predicted miR-155 targets in the autophagy pathway were analyzed by real-time PCR and western blotting.

RESULTS

Autophagy flux induced by rapamycin and 2-DG was significantly increased by miR-155 LNA, and significantly decreased after miR-155 mimic transfection in T/C28a2 cells and in human primary chondrocytes. These effects of miR-155 on autophagy were related to suppression of gene and protein expression of key autophagy regulators including Ulk1, FoxO3, Atg14, Atg5, Atg3, Gabarapl1, and Map1lc3.

CONCLUSION

MiR-155 is an inhibitor of autophagy in chondrocytes and contributes to the autophagy defects in OA.

O-GlcNAcylation: a bridge between glucose and cell differentiation

Glucose is the major energy supply and a critical metabolite for most cells and is especially important when cell is differentiating. High or low concentrations of glucose enhances or inhibits the osteogenic, chondrogenic and adipogenic differentiation of cell via the insulin, transforming growth factor‐β and peroxisome proliferator‐activated receptor γ pathways, among others. New evidence implicates the hexosamine biosynthetic pathway as a mediator of crosstalk between glucose flux, cellular signalling and epigenetic regulation of cell differentiation. Extracellular glucose flux alters intracellular O‐GlcNAcylation levels through the hexosamine biosynthetic pathway. Signalling molecules that are important for cell differentiation, including protein kinase C, extracellular signal‐regulated kinase, Runx2, CCAAT/enhancer‐binding proteins, are modified by O‐GlcNAcylation. Thus, O‐GlcNAcylation markedly alters cell fate during differentiation via the post‐transcriptional modification of proteins. Furthermore, O‐GlcNAcylation and phosphorylation show complex interactions during cell differentiation: they can either non‐competitively occupy different sites on a substrate or competitively occupy a single site or proximal sites. Therefore, the influence of glucose on cell differentiation via O‐GlcNAcylation offers a potential target for controlling tissue homoeostasis and regeneration in ageing and disease. Here, we review recent progress establishing an emerging relationship among glucose concentration, O‐GlcNAcylation levels and cell differentiation.

Metabolic stress-induced joint inflammation and osteoarthritis

Osteoarthritis (OA) is a heterogeneous disorder with several risk factors. Among them, obesity has a major impact on both loading and non-loading joints. Mechanical overload and activity of systemic inflammatory mediators derived from adipose tissue (adipokines, free fatty acids (FFA), reactive oxygen species (ROS)) provide clues to the increased incidence and prevalence of OA in obesity. Recently, research found greater OA prevalence and incidence in obese patients with cardiometabolic disturbances than "healthy" obese patients, which led to the description of a new OA phenotype - metabolic syndrome (MetS)-associated OA. Indeed, individual metabolic factors (diabetes, dyslipidemia, and hypertension) may increase the risk of obesity-induced OA. This review discusses hypotheses based on pathways specific to a metabolic factor in MetS-associated OA, such as the role of advanced glycation end products (AGEs) and glucose toxicity. A better understanding of these phenotypes based on risk factors will be critical for designing trials of this specific subset of OA.

Meniscus is more susceptible than cartilage to catabolic and anti-anabolic effects of adipokines

OBJECTIVE

This study compared the effects on cartilage and meniscus matrix catabolism and biosynthesis of several adipokines implicated in osteoarthritis (OA).

DESIGN

Bovine cartilage and meniscus explants were cultured for 1 or 9 days in serum-free medium alone or with 0.02, 0.2, or 2 μg/ml of leptin, visfatin, adiponectin, or resistin. Media were supplemented with (3)H-proline or (35)S-sodium sulfate to evaluate protein and sulfated glycosaminoglycan (sGAG) accumulation on the last day of culture. Explants were assayed for radiolabel, sGAG, and DNA contents. Cultured media were assayed for sGAG, nitrite and lactate dehydrogenase.

RESULTS

Cartilage tissue was minimally affected by adipokines, with only the highest resistin dose increasing sGAG release and nitrite production compared to controls. In sharp contrast, meniscus tissue was responsive to several adipokines, with elevated sGAG and nitrite release following treatment with resistin, leptin, or visfatin. Cartilage sGAG content was unaltered by adipokine treatment whereas meniscal sGAG content significantly decreased with resistin dosage. Protein ((3)H) incorporation was unaffected by adipokine treatment in both tissues. sGAG ((35)S) incorporation did not significantly vary with adipokine treatment in cartilage but was inhibited by treatment with leptin, visfatin, and resistin in meniscus.

CONCLUSION

Our results indicate that meniscal tissue is more susceptible to adipokine-stimulated catabolism than is cartilage. Resistin had the strongest effect of the adipokines tested, inducing sGAG release in both tissues and depleting sGAG content in meniscus. These results suggest that increased adipokine levels due to obesity or joint injury may alter the mechanical integrity of the knee joint through biological pathways.

Characterization of diabetic osteoarthritic cartilage and role of high glucose environment on chondrocyte activation: toward pathophysiological delineation of diabetes mellitus-related osteoarthritis

OBJECTIVE

To examine the relationship between osteoarthritis (OA) and type 2 diabetes mellitus (DM).

METHODS

OA cartilage from DM and non-DM patients undergoing knee replacement were stimulated by IL-1β for 24 h and release of interleukin-6 (IL-6) and prostaglandin E2 (PGE2) was measured. Primary cultured murine chondrocytes were stimulated for 24 and 72 h with or without IL-1β (5 ng/mL) under normal-glucose (5.5 mM) or high-glucose (25 mM) conditions. The expression and release of pro-inflammatory mediators (IL-6, cyclooxygenase 2 [COX2]/PGE2) were analyzed by quantitative RT-PCR and ELISA/EIA. Glucose uptake was assessed with ((14)C)-2-deoxyglucose. Reactive oxygen species (ROS) and nitric oxide (NO) production were measured. To analyze the mechanism of IL-1β-induced inflammation, cells were pretreated or treated with inhibitors of glucose transport (cytochalasin B), the polyol pathway (epalrestat), mitochondrial oxidative stress (MitoTEMPO) or nitric oxide synthase (l-NAME).

RESULTS

With IL-1β stimulation, IL-6 and PGE2 release was greater in human DM than non-DM OA cartilage (2.7- and 3-fold, respectively) (P < 0.05). In vitro, with IL-1β stimulation, IL-6 and COX2 mRNA expression, IL-6 and PGE2 release, and ROS and NO production were greater under high-than normal-glucose conditions in cultured chondrocytes. IL-1β-increased IL-6 release was reduced with cytochalasin B, epalrestat, L-NAME or MitoTEMPO treatment (-45%, -62%, -38% and -40%, respectively).

CONCLUSION

OA cartilages from DM patients showed increased responsiveness to IL-1β-induced inflammation. Accordingly, high glucose enhanced IL-1β-induced inflammation in cultured chondrocytes via oxidative stress and the polyol pathway. High glucose and diabetes may thus participate in the increased inflammation in OA.

Insulin Response Genes in Different Stages of Periodontal Disease

Bacterial infections are known to alter glucose metabolism within tissues via mechanisms of inflammation. We conducted this study to examine whether insulin response genes are differentially expressed in gingival tissues, comparing samples from experimental gingivitis and periodontitis subjects to those from healthy individuals. Total RNA was extracted from gingival biopsies from 26 participants: 8 periodontally healthy, 9 experimental gingivitis, and 9 periodontitis subjects. Gene expression patterns were evaluated with a polymerase chain reaction array panel to examine 84 candidate genes involved with glucose metabolism, insulin resistance, and obesity. Array data were evaluated with a t test adjusted by the false discover rate (P < 0.05), and ingenuity pathway analysis was performed for statistical testing of pathways. Although tissue samples were not sufficient to enable protein quantification, we confirmed the upregulation of the key gene using lipopolysaccharide-stimulated primary gingival epithelial cells by Western blot. The mRNA expression patterns of genes that are associated with insulin response and glucose metabolism are markedly different in experimental gingivitis subjects compared with healthy controls. Thirty-two genes are upregulated significantly by at least 2-fold, adjusted for false discover rate (P < 0.05). Periodontitis subjects show similar but attenuated changes in gene expression patterns, and no genes meet the significance criteria. Ingenuity pathway analysis demonstrates significant activation of the carbohydrate metabolism network in experimental gingivitis but not in periodontitis. G6PD protein increases in response to lipopolysaccharide stimulation in primary gingival epithelial cells, which is in the same direction as upregulated mRNA in tissues. Acute gingival inflammation may be associated with tissue metabolism changes, but these changes are not evident in chronic periodontitis. This study suggests that acute gingival inflammation may induce localized changes that modify tissue insulin/glucose metabolism.

Mitochondrial respiration and redox coupling in articular chondrocytes

Introduction

Chondrocytes rely primarily on glycolysis to meet cellular energy needs, but recent studies implicate impaired mitochondrial function in osteoarthritis (OA) pathogenesis. Our objectives were to investigate the ability of chondrocytes to upregulate mitochondrial respiration when challenged with a nutrient stress and determine the effect on mediators of chondrocyte oxidative homeostasis.

Methods

Primary bovine chondrocytes were isolated and cultured in alginate beads. Mitochondrial respiration was stimulated by culturing cells with galactose-supplemented media for a period of 1 or 5 days. Metabolic flexibility was assessed by measuring metabolite and enzymatic biomarkers of glycolytic and mitochondrial metabolism. Oxidative homeostasis was assessed by measuring (1) cellular glutathione content and redox homeostasis, (2) rates of nitric oxide and superoxide production, and (3) the abundance and activity of cellular anti-oxidant proteins, especially the mitochondrial isoform of superoxide dismutase (SOD2). The regulatory role of hypoxia-inducible factor 2α (HIF-2α) in mediating the metabolic and redox responses was evaluated by chemical stabilization with cobalt chloride (CoCl₂).

Results

After 5 days of galactose culture, lactate production and lactate dehydrogenase activity were reduced by 92% (P <0.0001) and 28% (P = 0.051), respectively. Conversely, basal oxygen consumption increased 35% (P = 0.042) without increasing mitochondrial content. Glutathione redox homeostasis was unaffected by galactose culture. However, the production of nitric oxide and superoxide and the expression and activity of SOD2 were significantly reduced after 5 days in galactose culture. Nuclear protein expression and gene expression of HIF-2α, a transcription factor for SOD2, were significantly downregulated (more than twofold; P <0.05) with galactose culture. CoCl₂-mediated stabilization of HIF-2α during the initial galactose response phase attenuated the reduction in SOD2 (P = 0.028) and increased cell death (P = 0.003).

Conclusions

Chondrocyte metabolic flexibility promotes cell survival during a nutrient stress by upregulating mitochondrial respiration and reducing the rate of reactive nitrogen and oxygen species production. These changes are coupled to a substantial reduction in the expression and activity of the mitochondrial anti-oxidant SOD2 and its pro-catabolic transcription factor HIF-2α, suggesting that an improved understanding of physiologic triggers of chondrocyte metabolic flexibility may provide new insight into the etiology of OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0566-9) contains supplementary material, which is available to authorized users.

Is osteoarthritis a metabolic disease?

Obesity, together with aging and injury, is among the main risk factors for osteoarthritis. Obesity-related osteoarthritis can affect not only the weight-bearing joints, but also the hands, suggesting a role for circulating mediators released by the adipose tissue and known as adipokines. Thus, osteoarthritis may have a systemic metabolic component. Evidence from both epidemiological and biological studies support the concept of metabolic osteoarthritis, defined as a broad clinical phenotype that includes obesity-related osteoarthritis. Thus, osteoarthritis can be related to metabolic syndrome or to an accumulation of metabolic abnormalities. In addition, studies have demonstrated associations linking osteoarthritis to several components of the metabolic syndrome, such as hypertension and type 2 diabetes, independently from obesity or any of the other known risk factors for osteoarthritis. Both in vitro and in vitro findings indicate a deleterious effect of lipid and glucose abnormalities on cartilage homeostasis. Chronic low-grade inflammation is a feature shared by osteoarthritis and metabolic disorders and may contribute to the genesis of both. Thus, osteoarthritis is emerging as a disease that has a variety of phenotypes including a metabolic phenotype, in addition to the age-related and injury-related phenotypes.

Diabetes is an independent predictor for severe osteoarthritis: results from a longitudinal cohort study

OBJECTIVE

To evaluate if type 2 diabetes is an independent risk predictor for severe osteoarthritis (OA).

RESEARCH DESIGN AND METHODS

Population-based cohort study with an age- and sex-stratified random sample of 927 men and women aged 40-80 years and followed over 20 years (1990-2010).

RESULTS

Rates of arthroplasty (95% CI) were 17.7 (9.4-30.2) per 1,000 person-years in patients with type 2 diabetes and 5.3 (4.1-6.6) per 1,000 person-years in those without (P < 0.001). Type 2 diabetes emerged as an independent risk predictor for arthroplasty: hazard ratios (95% CI), 3.8 (2.1-6.8) (P < 0.001) in an unadjusted analysis and 2.1 (1.1-3.8) (P = 0.023) after adjustment for age, BMI, and other risk factors for OA. The probability of arthroplasty increased with disease duration of type 2 diabetes and applied to men and women, as well as subgroups according to age and BMI. Our findings were corroborated in cross-sectional evaluation by more severe clinical symptoms of OA and structural joint changes in subjects with type 2 diabetes compared with those without type 2 diabetes.

CONCLUSIONS

Type 2 diabetes predicts the development of severe OA independent of age and BMI. Our findings strengthen the concept of a strong metabolic component in the pathogenesis of OA.

Renal transport of uric acid: evolving concepts and uncertainties

In addition to its role as a metabolic waste product, uric acid has been proposed to be an important molecule with multiple functions in human physiologic and pathophysiologic processes and may be linked to human diseases beyond nephrolithiasis and gout. Uric acid homeostasis is determined by the balance between production, intestinal secretion, and renal excretion. The kidney is an important regulator of circulating uric acid levels by reabsorbing about 90% of filtered urate and being responsible for 60% to 70% of total body uric acid excretion. Defective renal handling of urate is a frequent pathophysiologic factor underpinning hyperuricemia and gout. Despite tremendous advances over the past decade, the molecular mechanisms of renal urate transport are still incompletely understood. Many transport proteins are candidate participants in urate handling, with URAT1 and GLUT9 being the best characterized to date. Understanding these transporters is increasingly important for the practicing clinician as new research unveils their physiologic characteristics, importance in drug action, and genetic association with uric acid levels in human populations. The future may see the introduction of new drugs that act specifically on individual renal urate transporters for the treatment of hyperuricemia and gout.

Novel molecular mechanisms of antitumor action of dichloroacetate against T cell lymphoma: Implication of altered glucose metabolism, pH homeostasis and cell survival regulation

Pyruvate dehydrogenase kinase (PDK) inhibits pyruvate dehydrogenase (PDH) activity and thus promotes energetic switch from mitochondrial glucose oxidation to cytoplasmic glycolysis in cancerous cells (a phenomenon known as the 'Warburg effect') for their energy need, which facilitates the cancer progression by resisting induction of apoptosis and promoting tumor metastasis. Thus, in the present investigation, we explored the molecular mechanisms of the tumoricidal action of dichloroacetate (DCA), a pyruvate dehydrogenase kinase inhibitor, on cells of a murine T cell lymphoma, designated as Dalton's lymphoma (DL). In vitro treatment of tumor cells with DCA inhibited their survival accompanied by a modulation of the biophysical composition of tumor-conditioned medium with respect to pH, glucose and lactate. DCA treatment also altered expression of HIF1-α and pH regulators: VATPase and MCT1 and production of cytokines: IL-10, IL-6 and IFN-γ. Moreover, we also observed an alteration in the expression of other apoptosis and cell survival regulatory molecules: PUMA, GLUT1, Bcl2, p53, CAD, caspase-3 and HSP70. The study discusses the role of novel molecular mechanisms underlying DCA-dependent inhibition of tumor cell survival. This study shows for the first time that DCA-dependent alteration of tumor cell survival involves altered pH homeostasis and glucose metabolism. Thus, these findings will provide a new insight for therapeutic applications of DCA as a novel antineoplastic agent against T cell lymphoma.

Involvement of SIK3 in glucose and lipid homeostasis in mice

Salt-inducible kinase 3 (SIK3), an AMP-activated protein kinase-related kinase, is induced in the murine liver after the consumption of a diet rich in fat, sucrose, and cholesterol. To examine whether SIK3 can modulate glucose and lipid metabolism in the liver, we analyzed phenotypes of SIK3-deficent mice. Sik3(-/-) mice have a malnourished the phenotype (i.e., lipodystrophy, hypolipidemia, hypoglycemia, and hyper-insulin sensitivity) accompanied by cholestasis and cholelithiasis. The hypoglycemic and hyper-insulin-sensitive phenotypes may be due to reduced energy storage, which is represented by the low expression levels of mRNA for components of the fatty acid synthesis pathways in the liver. The biliary disorders in Sik3(-/-) mice are associated with the dysregulation of gene expression programs that respond to nutritional stresses and are probably regulated by nuclear receptors. Retinoic acid plays a role in cholesterol and bile acid homeostasis, wheras ALDH1a which produces retinoic acid, is expressed at low levels in Sik3(-/-) mice. Lipid metabolism disorders in Sik3(-/-) mice are ameliorated by the treatment with 9-cis-retinoic acid. In conclusion, SIK3 is a novel energy regulator that modulates cholesterol and bile acid metabolism by coupling with retinoid metabolism, and may alter the size of energy storage in mice.