Glutamine Metabolism Controls Chondrocyte Identity and Function

Jawbone periosteum-derived cells with high osteogenic potential controlled by R-spondin 3

The jawbone periosteum, the easily accessible tissue responding to bone repair, has been overlooked in the recent development of cell therapy for jawbone defect reconstruction. Therefore, this study aimed to elucidate the in vitro and in vivo biological characteristics of jawbone periosteum-derived cells (jb-PDCs). For this purpose, we harvested the jb-PDCs from 8-week-old C57BL/6 mice. The in vitro cultured jb-PDCs (passages 1 and 3) contained skeletal stem/progenitor cells and exhibited clonogenicity and tri-lineage differentiation capacity. When implanted in vivo, the jb-PDCs (passage 3) showed evident ectopic bone formation after 4-week subcutaneous implantation, and active contribution to repair the critical-size jawbone defects in mice. Molecular profiling suggested that R-spondin 3 was strongly associated with the superior in vitro and in vivo osteogenic potentials of jb-PDCs. Overall, our study highlights the significance of comprehending the biological characteristics of the jawbone periosteum, which could pave the way for innovative cell-based therapies for the reconstruction of jawbone defects.

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.

Functional Amino Acids in the Regulation of Bone and Its Diseases

Bone as a vigorous tissue is constantly undergoing bone remodeling. The homeostasis of bone remodeling requires combined efforts of multifarious bone cells. Amino acids (AA), known as essential components of life support, are closely related to the regulation of bone homeostasis. In recent years, the concept of functional amino acids (FAAs) has been proposed, which is defined as AA that regulate key metabolic pathways to improve health, survival, growth, development, lactation, and reproduction of organisms, to highlight their outstanding contributions in the body. In the hope of exploring new therapeutic strategies, this review focus on summarizing recent progress in the vital role of FAAs in bone homeostasis maintaining and potential implications of FAAs in bone-related diseases, and discussing related mechanisms. The results showed that FAAs are closely related to bone metabolism and therapeutic strategy targeting FAAs metabolism is one of the future trends for bone disorders, while the explorations about possible impact of FAAs-based diets are still limited.

Glutaminolysis provides nucleotides and amino acids to regulate osteoclast differentiation in mice

Osteoclasts are bone resorbing cells that are essential to maintain skeletal integrity and function. While many of the growth factors and molecular signals that govern osteoclastogenesis are well studied, how the metabolome changes during osteoclastogenesis is unknown. Using a multifaceted approach, we identified a metabolomic signature of osteoclast differentiation consisting of increased amino acid and nucleotide metabolism. Maintenance of the osteoclast metabolic signature is governed by elevated glutaminolysis. Mechanistically, glutaminolysis provides amino acids and nucleotides which are essential for osteoclast differentiation and bone resorption in vitro. Genetic experiments in mice found that glutaminolysis is essential for osteoclastogenesis and bone resorption in vivo. Highlighting the therapeutic implications of these findings, inhibiting glutaminolysis using CB-839 prevented ovariectomy induced bone loss in mice. Collectively, our data provide strong genetic and pharmacological evidence that glutaminolysis is essential to regulate osteoclast metabolism, promote osteoclastogenesis and modulate bone resorption in mice.

Identification of genomic regions associated with fatty acid metabolism across blood, liver, backfat and muscle in pigs

BACKGROUND

The composition and distribution of fatty acids (FA) are important factors determining the quality, flavor, and nutrient value of meat. In addition, FAs synthesized in the body participate in energy metabolism and are involved in different regulatory pathways in the form of signaling molecules or by acting as agonist or antagonist ligands of different nuclear receptors. Finally, synthesis and catabolism of FAs affect adaptive immunity by regulating lymphocyte metabolism. The present study performed genome-wide association studies using FA profiles of blood, liver, backfat and muscle from 432 commercial Duroc pigs.

RESULTS

Twenty-five genomic regions located on 15 Sus scrofa chromosomes (SSC) were detected. Annotation of the quantitative trait locus (QTL) regions identified 49 lipid metabolism-related candidate genes. Among these QTLs, four were identified in more than one tissue. The ratio of C20:4n-6/C20:3n-6 was associated with the region on SSC2 at 7.56-14.26 Mb for backfat, liver, and muscle. Members of the fatty acid desaturase gene cluster (FADS1, FADS2, and FADS3) are the most promising candidate genes in this region. Two QTL regions on SSC14 (103.81-115.64 Mb and 100.91-128.14 Mb) were identified for FA desaturation in backfat and muscle. In addition, two separate regions on SSC9 at 0 - 14.55 Mb and on SSC12 at 0-1.91 Mb were both associated with the same multiple FA traits for backfat, with candidate genes involved in de novo FA synthesis and triacylglycerol (TAG) metabolism, such as DGAT2 and FASN. The ratio C20:0/C18:0 was associated with the region on SSC5 at 64.84-78.32 Mb for backfat. Furthermore, the association of the C16:0 content with the region at 118.92-123.95 Mb on SSC4 was blood specific. Finally, candidate genes involved in de novo lipogenesis regulate T cell differentiation and promote the generation of palmitoleate, an adipokine that alleviates inflammation.

CONCLUSIONS

Several SNPs and candidate genes were associated with lipid metabolism in blood, liver, backfat, and muscle. These results contribute to elucidating the molecular mechanisms implicated in the determination of the FA profile in different pig tissues and can be useful in selection programs that aim to improve health and energy metabolism in pigs.

Role of extracellular vesicles associated with microRNAs and their interplay with cuproptosis in osteoporosis

Osteoporosis (OP)-associated fractures can result in severe morbidity and disability, reduced quality of life, and death. Previous studies have suggested that small noncoding RNAs, for example, small regulatory microRNAs (miRNAs), play a key role in OP by inhibiting target gene expression. Cuproptosis, a recently proposed copper-induced cell death pathway, is linked with OP. Here, we describe the contribution of exosomal miRNAs and cuproptosis to OP. First, we highlight the characteristics of exosomes and roles of exosome-related miRNAs. Next, we discuss the relationship between cuproptosis and OP. Subsequently, we analyze the crosstalk of exosomal miRNAs with cuproptosis in the development of OP. This review aims to investigate a new clinical treatment method for OP.

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.

Activation of the PGC-1α-mediated mitochondrial glutamine metabolism pathway attenuates female offspring osteoarthritis induced by prenatal excessive prednisone

Osteoarthritis is a chronic, age-related joint disease. Previous studies have shown that osteoarthritis develops during intrauterine development. Prednisone is frequently used to treat pregnancies complicated by autoimmune diseases. However, limited research has been conducted on the enduring effects of prednisone use during pregnancy on the offspring. In this study, we investigated the effect of excessive prednisone exposure on cartilage development and susceptibility to osteoarthritis in the offspring. We found that prenatal prednisone exposure (PPE) impaired cartilage extracellular matrix (ECM) synthesis, resulting in poor cartilage pathology in female offspring during the adult period, which was further exacerbated after long-distance running stimulation. Additionally, PPE suppressed cartilage development during the intrauterine period. Tracing back to the intrauterine period, we found that Pred, rather than prednisone, decreased glutamine metabolic flux, which resulted in increased oxidative stress, and decreased histone acetylation, and expression of cartilage phenotypic genes. Further, PGC-1α-mediated mitochondrial biogenesis, while PPE caused hypermethylation in the promoter region of PGC-1α and decreased its expression in fetal cartilage by activating the glucocorticoid receptor, resulting in a reduction of glutamine flux controlled by mitochondrial biogenesis. Additionally, overexpression of PGC-1α (either pharmacological or through lentiviral transfection) reversed PPE- and Pred-induced cartilage ECM synthesis impairment. In summary, this study demonstrated that PPE causes chondrodysplasia in female offspring and increases their susceptibility to postnatal osteoarthritis. Hence, targeting PGC-1α early on could be a potential intervention strategy for PPE-induced osteoarthritis susceptibility.

Mitochondria: a breakthrough in combating rheumatoid arthritis

As a chronic autoimmune disease with complex aetiology, rheumatoid arthritis (RA) has been demonstrated to be associated with mitochondrial dysfunction since mitochondrial dysfunction can affect the survival, activation, and differentiation of immune and non-immune cells involved in the pathogenesis of RA. Nevertheless, the mechanism behind mitochondrial dysfunction in RA remains uncertain. Accordingly, this review addresses the possible role and mechanisms of mitochondrial dysfunction in RA and discusses the potential and challenges of mitochondria as a potential therapeutic strategy for RA, thereby providing a breakthrough point in the prevention and treatment of RA.

Glutamine Mitigates Oxidative Stress-Induced Matrix Degradation, Ferroptosis, and Pyroptosis in Nucleus Pulposus Cells via Deubiquitinating and Stabilizing Nrf2

Aims: Intervertebral disc degeneration (IDD) is closely related to low back pain, which is a prevalent age-related problem worldwide; however, the mechanism underlying IDD is unknown. Glutamine, a free amino acid prevalent in plasma, is recognized for its anti-inflammatory and antioxidant properties in various diseases, and the current study aims to clarify the effect and mechanism of glutamine in IDD. Results: A synergistic interplay was observed between pyroptosis and ferroptosis within degenerated human disc specimens. Glutamine significantly mitigated IDD in both ex vivo and in vivo experimental models. Moreover, glutamine protected nucleus pulposus (NP) cells after tert-butyl hydroperoxide (TBHP)-induced pyroptosis, ferroptosis, and extracellular matrix (ECM) degradation in vitro. Glutamine protected NP cells from TBHP-induced ferroptosis by promoting the nuclear factor erythroid 2-related factor 2 (Nrf2) accumulation by inhibiting its ubiquitin-proteasome degradation and inhibiting lipid oxidation. Innovation and Conclusions: A direct correlation is evident in the progression of IDD between the processes of pyroptosis and ferroptosis. Glutamine suppressed oxidative stress-induced cellular processes, including pyroptosis, ferroptosis, and ECM degradation through deubiquitinating Nrf2 and inhibiting lipid oxidation in NP cells. Glutamine is a promising novel therapeutic target for the management of IDD.

Relationships between matrix mineralization, oxidative metabolism, and mitochondrial structure during ATDC5 murine chondroprogenitor cell line differentiation

The mechanistic relationships between the progression of growth chondrocyte differentiation, matrix mineralization, oxidative metabolism, and mitochondria content and structure were examined in the ATDC5 murine chondroprogenitor cell line. The progression of chondrocyte differentiation was associated with a statistically significant (p ≤ 0.05) ~2-fold increase in oxidative phosphorylation. However, as matrix mineralization progressed, oxidative metabolism decreased. In the absence of mineralization, cartilage extracellular matrix mRNA expression for Col2a1, Aggrecan, and Col10a1 were statistically (p ≤ 0.05) ~2-3-fold greater than observed in mineralizing cultures. In contrast, BSP and Phex that are associated with promoting matrix mineralization showed statistically (p ≤ 0.05) higher ~2-4 expression, while FGF23 phosphate regulatory factor was significantly lower (~50%) in mineralizing cultures. Cultures induced to differentiate under both nonmineralizing and mineralizing media conditions showed statistically greater basal oxidative metabolism and ATP production. Maximal respiration and spare oxidative capacity were significantly elevated (p ≤ 0.05) in differentiated nonmineralizing cultures compared to those that mineralized. Increased oxidative metabolism was associated with both an increase in mitochondria volume per cell and mitochondria fusion, while mineralization diminished mitochondrial volume and appeared to be associated with fission. Undifferentiated and mineralized cells showed increased mitochondrial co-localization with the actin cytoskeletal. Examination of proteins associated with mitochondria fission and apoptosis and mitophagy, respectively, showed levels of immunological expression consistent with the increasing fission and apoptosis in mineralizing cultures. These results suggest that chondrocyte differentiation is associated with intracellular structural reorganization, promoting increased mitochondria content and fusion that enables increased oxidative metabolism. Mineralization, however, does not need energy derived from oxidative metabolism; rather, during mineralization, mitochondria appear to undergo fission and mitophagy. In summary, these studies show that as chondrocytes underwent hypertrophic differentiation, they increased oxidative metabolism, but as mineralization proceeds, metabolism decreased. Mitochondria structure also underwent a structural reorganization that was further supportive of their oxidative capacity as the chondrocytes progressed through their differentiation. Thus, the mitochondria first underwent fusion to support increased oxidative metabolism, then underwent fission during mineralization, facilitating their programed death.

Glutamine-derived peptides: Current progress and future directions

Glutamine, the most abundant amino acid in the body, plays a critical role in preserving immune function, nitrogen balance, intestinal integrity, and resistance to infection. However, its limited solubility and instability present challenges for its use a functional nutrient. Consequently, there is a preference for utilizing glutamine-derived peptides as an alternative to achieve enhanced functionality. This article aims to review the applications of glutamine monomers in clinical, sports, and enteral nutrition. It compares the functional effectiveness of monomers and glutamine-derived peptides and provides a comprehensive assessment of glutamine-derived peptides in terms of their classification, preparation, mechanism of absorption, and biological activity. Furthermore, this study explores the potential integration of artificial intelligence (AI)-based peptidomics and synthetic biology in the de novo design and large-scale production of these peptides. The findings reveal that glutamine-derived peptides possess significant structure-related bioactivities, with the smaller molecular weight fraction serving as the primary active ingredient. These peptides possess the ability to promote intestinal homeostasis, exert hypotensive and hypoglycemic effects, and display antioxidant properties. However, our understanding of the structure-function relationships of glutamine-derived peptides remains largely exploratory at current stage. The combination of AI based peptidomics and synthetic biology presents an opportunity to explore the untapped resources of glutamine-derived peptides as functional food ingredients. Additionally, the utilization and bioavailability of these peptides can be enhanced through the use of delivery systems in vivo. This review serves as a valuable reference for future investigations of and developments in the discovery, functional validation, and biomanufacturing of glutamine-derived peptides in food science.

Metabolic regulation of skeletal cell fate and function

Bone development and bone remodelling during adult life are highly anabolic processes requiring an adequate supply of oxygen and nutrients. Bone-forming osteoblasts and bone-resorbing osteoclasts interact closely to preserve bone mass and architecture and are often located close to blood vessels. Chondrocytes within the developing growth plate ensure that bone lengthening occurs before puberty, but these cells function in an avascular environment. With ageing, numerous bone marrow adipocytes appear, often with negative effects on bone properties. Many studies have now indicated that skeletal cells have specific metabolic profiles that correspond to the nutritional microenvironment and their stage-specific functions. These metabolic networks provide not only skeletal cells with sufficient energy, but also biosynthetic intermediates that are necessary for proliferation and extracellular matrix synthesis. Moreover, these metabolic pathways control redox homeostasis to avoid oxidative stress and safeguard cell survival. Finally, several intracellular metabolites regulate the activity of epigenetic enzymes and thus control the fate and function of skeletal cells. The metabolic profile of skeletal cells therefore not only reflects their cellular state, but can also drive cellular activity. Insight into skeletal cell metabolism will thus not only advance our understanding of skeletal development and homeostasis, but also of skeletal disorders, such as osteoarthritis, diabetic bone disease and bone malignancies.

Elevated nutrient availability enhances chondrocyte metabolism and biosynthesis in tissue-engineered cartilage

OBJECTIVE

Chondrocytes, which typically rely on anaerobic metabolism, exhibit upregulated biosynthetic activity when subjected to conditions that elicit mixed aerobic-anaerobic metabolism. Previously, we observed that increasing media volume resulted in the transition from anaerobic to mixed aerobic-anaerobic metabolism. Maximal extracellular matrix (ECM) accumulation occurred at this transition as a result of changes in hypoxia-inducible factor 1α signaling and associated hypoxic gene expression. This study aimed to explore the effect of further increases in media availability on ECM synthesis and chondrocyte metabolism.

METHODS

Primary bovine chondrocytes were grown in 3D high-density tissue culture under varying levels of media availability (4-16 mL/106 cells). Changes in ECM accumulation and metabolism were determined through biochemical assays and 13C-metabolic flux analysis (13C-MFA).

RESULTS

Increasing media volumes resulted in higher accumulation of cartilaginous ECM (collagen and proteoglycans) and cellularity. Extracellular metabolite measurements revealed that elevated media availability led to increased glucose and glutamine metabolism, along with increased anaerobic activity. 13C-MFA utilizing [U-13C] glucose demonstrated that increased media availability significantly impacted central carbon metabolism, upregulating all glucose-related metabolic pathways (glycolysis, lactate fermentation, the tricarboxylic acid (TCA) cycle, hexosamine biosynthetic pathway, and the malate-aspartate shuttle). Furthermore, 13C-MFA indicated that glutamine was donating carbons to the TCA cycle, and additional studies involving [U-13C] glutamine tracing supported this notion.

CONCLUSIONS

Elevated media availability upregulates ECM synthesis and leads to significant changes in metabolic phenotype. Glutamine plays an important role in chondrocyte metabolism and increases in glutamine metabolism correlate with increases in ECM accumulation.

Tricarboxylic Acid Cycle Regulation of Metabolic Program, Redox System, and Epigenetic Remodeling for Bone Health and Disease

Imbalanced osteogenic cell-mediated bone gain and osteoclastic remodeling accelerates the development of osteoporosis, which is the leading risk factor of disability in the elderly. Harmonizing the metabolic actions of bone-making cells and bone resorbing cells to the mineralized matrix network is required to maintain bone mass homeostasis. The tricarboxylic acid (TCA) cycle in mitochondria is a crucial process for cellular energy production and redox homeostasis. The canonical actions of TCA cycle enzymes and intermediates are indispensable in oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis for osteogenic differentiation and osteoclast formation. Knockout mouse models identify these enzymes' roles in bone mass and microarchitecture. In the noncanonical processes, the metabolites as a co-factor or a substrate involve epigenetic modification, including histone acetyltransferases, DNA demethylases, RNA m6A demethylases, and histone demethylases, which affect genomic stability or chromatin accessibility for cell metabolism and bone formation and resorption. The genetic manipulation of these epigenetic regulators or TCA cycle intermediate supplementation compromises age, estrogen deficiency, or inflammation-induced bone mass loss and microstructure deterioration. This review sheds light on the metabolic functions of the TCA cycle in terms of bone integrity and highlights the crosstalk of the TCA cycle and redox and epigenetic pathways in skeletal tissue metabolism and the intermediates as treatment options for delaying osteoporosis.

Metabolic Characteristics and Discriminative Diagnosis of Growth Hormone Deficiency and Idiopathic Short Stature in Preadolescents and Adolescents

Growth hormone deficiency (GHD) and idiopathic short stature (ISS) are the most common types of short stature (SS), but little is known about their pathogenesis, and even less is known about the study of adolescent SS. In this study, nuclear magnetic resonance (NMR)-based metabolomic analysis combined with least absolute shrinkage and selection operator (LASSO) were performed to identify the biomarkers of different types of SS (including 94 preadolescent GHD (PAG), 61 preadolescent ISS (PAI), 43 adolescent GHD (ADG), and 19 adolescent ISS (ADI)), and the receiver operating characteristic curve (ROC) was further used to evaluate the predictive power of potential biomarkers. The results showed that fourteen, eleven, nine, and fifteen metabolites were identified as the potential biomarkers of PAG, PAI, ADG, and ADI compared with their corresponding controls, respectively. The disturbed metabolic pathways in preadolescent SS were mainly carbohydrate metabolism and lipid metabolism, while disorders of amino acid metabolism played an important role in adolescent SS. The combination of aspartate, ethanolamine, phosphocholine, and trimethylamine was screened out to identify PAI from PAG, and alanine, histidine, isobutyrate, methanol, and phosphocholine gave a high classification accuracy for ADI and ADC. The differences in metabolic characteristics between GHD and ISS in preadolescents and adolescents will contribute to the development of individualized clinical treatments in short stature.

TSPAN8+ myofibroblastic cancer-associated fibroblasts promote chemoresistance in patients with breast cancer

Cancer-associated fibroblasts (CAFs) are abundant stromal cells in the tumor microenvironment that promote cancer progression and relapse. However, the heterogeneity and regulatory roles of CAFs underlying chemoresistance remain largely unclear. Here, we performed a single-cell analysis using high-dimensional flow cytometry analysis and identified a distinct senescence-like tetraspanin-8 (TSPAN8)+ myofibroblastic CAF (myCAF) subset, which is correlated with therapeutic resistance and poor survival in multiple cohorts of patients with breast cancer (BC). TSPAN8+ myCAFs potentiate the stemness of the surrounding BC cells through secretion of senescence-associated secretory phenotype (SASP)-related factors IL-6 and IL-8 to counteract chemotherapy. NAD-dependent protein deacetylase sirtuin 6 (SIRT6) reduction was responsible for the senescence-like phenotype and tumor-promoting role of TSPAN8+ myCAFs. Mechanistically, TSPAN8 promoted the phosphorylation of ubiquitin E3 ligase retinoblastoma binding protein 6 (RBBP6) at Ser772 by recruiting MAPK11, thereby inducing SIRT6 protein destruction. In turn, SIRT6 down-regulation up-regulated GLS1 and PYCR1, which caused TSPAN8+ myCAFs to secrete aspartate and proline, and therefore proved a nutritional niche to support BC outgrowth. By demonstrating that TSPAN8+SIRT6low myCAFs were tightly associated with unfavorable disease outcomes, we proposed that the combined regimen of anti-TSPAN8 antibody and SIRT6 activator MDL-800 is a promising approach to overcome chemoresistance. These findings highlight that senescence contributes to CAF heterogeneity and chemoresistance and suggest that targeting TSPAN8+ myCAFs is a promising approach to circumvent chemoresistance.

Structure-activity relationships for alkyl-phenanthrenes support two independent but interacting synergistic models for PAC mixture potency

Multiple lines of evidence at whole animal, cellular and molecular levels implicate polycyclic aromatic compounds (PACs) with three rings as drivers of crude oil toxicity to developing fish. Phenanthrene (P0) and its alkylated homologs (C1- through C4-phenanthrenes) comprise the most prominent subfraction of tricyclic PACs in crude oils. Among this family, P0 has been studied intensively, with more limited detail available for the C4-phenanthrene 1-methyl-7-isopropyl-phenanthrene (1-M,7-IP, or retene). While both compounds are cardiotoxic, P0 impacts embryonic cardiac function and development through direct blockade of K+ and Ca2+ currents that regulate cardiomyocyte contractions. In contrast, 1-M,7-IP dysregulates aryl hydrocarbon receptor (AHR) activation in developing ventricular cardiomyocytes. Although no other compounds have been assessed in detail across the larger family of alkylated phenanthrenes, increasing alkylation might be expected to shift phenanthrene family member activity from K+/Ca2+ ion current blockade to AHR activation. Using embryos of two distantly related fish species, zebrafish and Atlantic haddock, we tested 14 alkyl-phenanthrenes in both acute and latent developmental cardiotoxicity assays. All compounds were cardiotoxic, and effects were resolved into impacts on multiple, highly specific aspects of heart development or function. Craniofacial defects were clearly linked to developmental cardiotoxicity. Based on these findings, we suggest a novel framework to delineate the developmental toxicity of petrogenic PAC mixtures in fish, which incorporates multi-mechanistic pathways that produce interactive synergism at the organ level. In addition, relationships among measured embryo tissue concentrations, cytochrome P4501A mRNA induction, and cardiotoxic responses suggest a two-compartment toxicokinetic model that independently predicts high potency of PAC mixtures through classical metabolic synergism. These two modes of synergism, specific to the sub-fraction of phenanthrenes, are sufficient to explain the high embryotoxic potency of crude oils, independent of as-yet unmeasured compounds in these complex environmental mixtures.

Hypoxia rewires glucose and glutamine metabolism in different sources of skeletal stem and progenitor cells similarly, except for pyruvate

Skeletal stem and progenitor cells (SSPCs) are crucial for bone development, homeostasis, and repair. SSPCs are considered to reside in a rather hypoxic niche in the bone, but distinct SSPC niches have been described in different skeletal regions, and they likely differ in oxygen and nutrient availability. Currently it remains unknown whether the different SSPC sources have a comparable metabolic profile and respond in a similar manner to hypoxia. In this study, we show that cell proliferation of all SSPCs was increased in hypoxia, suggesting that SSPCs can indeed function in a hypoxic niche in vivo. In addition, low oxygen tension increased glucose consumption and lactate production, but affected pyruvate metabolism cell-specifically. Hypoxia decreased tricarboxylic acid (TCA) cycle anaplerosis and altered glucose entry into the TCA cycle from pyruvate dehydrogenase to pyruvate carboxylase and/or malic enzyme. Finally, a switch from glutamine oxidation to reductive carboxylation was observed in hypoxia, as well as cell-specific adaptations in the metabolism of other amino acids. Collectively, our findings show that SSPCs from different skeletal locations proliferate adequately in hypoxia by rewiring glucose and amino acid metabolism in a cell-specific manner.

Glutamine suppresses senescence and promotes autophagy through glycolysis inhibition-mediated AMPKα lactylation in intervertebral disc degeneration

Regulating metabolic disorders has become a promising focus in treating intervertebral disc degeneration (IDD). A few drugs regulating metabolism, such as atorvastatin, metformin, and melatonin, show positive effects in treating IDD. Glutamine participates in multiple metabolic processes, including glutaminolysis and glycolysis; however, its impact on IDD is unclear. The current study reveals that glutamine levels are decreased in severely degenerated human nucleus pulposus (NP) tissues and aging Sprague-Dawley (SD) rat nucleus pulposus tissues, while lactate accumulation and lactylation are increased. Supplementary glutamine suppresses glycolysis and reduces lactate production, which downregulates adenosine-5'-monophosphate-activated protein kinase α (AMPKα) lactylation and upregulates AMPKα phosphorylation. Moreover, glutamine treatment reduces NP cell senescence and enhances autophagy and matrix synthesis via inhibition of glycolysis and AMPK lactylation, and glycolysis inhibition suppresses lactylation. Our results indicate that glutamine could prevent IDD by glycolysis inhibition-decreased AMPKα lactylation, which promotes autophagy and suppresses NP cell senescence.

Supersulfides support bone growth by promoting chondrocyte proliferation in the growth plates

OBJECTIVES

While chondrocytes have mitochondria, they receive little O2 from the bloodstream. Sulfur respiration, an essential energy production system in mitochondria, uses supersulfides instead of O2. Supersulfides are inorganic and organic sulfides with catenated sulfur atoms and are primarily produced by cysteinyl tRNA synthetase-2 (CARS2). Here, we investigated the role of supersulfides in chondrocyte proliferation and bone growth driven by growth plate chondrocyte proliferation.

METHODS

We examined the effects of NaHS, an HS-/H2S donor, and cystine, the cellular source of cysteine, on the proliferation of mouse primary chondrocytes and growth of embryonic mouse tibia in vitro. We also examined the effect of RNA interference acting on the Cars2 gene on chondrocyte proliferation in the presence of cystine.

RESULTS

NaHS (30 μmol/L) enhanced tibia longitudinal growth in vitro with expansion of the proliferating zone of their growth plates. While NaHS (30 μmol/L) also promoted chondrocyte proliferation only under normoxic conditions (20 % O2), cystine (0.5 mmol/L) promoted it under both normoxic and hypoxic (2 % O2) conditions. Cars2 gene knockdown abrogated the ability of cystine (0.5 mmol/L) to promote chondrocyte proliferation under normoxic conditions, indicating that supersulfides produced by CARS2 were responsible for the cystine-dependent promotion of bone growth.

CONCLUSIONS

The presented results indicate that supersulfides play a vital role in bone growth achieved by chondrocyte proliferation in the growth plates driven by sulfur respiration.

Chondrocyte membrane-coated nanoparticles promote drug retention and halt cartilage damage in rat and canine osteoarthritis

Osteoarthritis (OA) is a chronic joint disease characterized by progressive degeneration of articular cartilage. A challenge in the development of disease-modifying drugs is effective delivery to chondrocytes. The unique structure of the joint promotes rapid clearance of drugs through synovial fluid, and the dense and avascular cartilage extracellular matrix (ECM) limits drug penetration. Here, we show that poly(lactide-co-glycolic acid) nanoparticles coated in chondrocyte membranes (CM-NPs) were preferentially taken up by rat chondrocytes ex vivo compared with uncoated nanoparticles. Internalization of the CM-NPs was mediated primarily by E-cadherin, clathrin-mediated endocytosis, and micropinocytosis. These CM-NPs adhered to the cartilage ECM in rat knee joints in vivo and penetrated deeply into the cartilage matrix with a residence time of more than 34 days. Simulated synovial fluid clearance studies showed that CM-NPs loaded with a Wnt pathway inhibitor, adavivint (CM-NPs-Ada), delayed the catabolic metabolism of rat and human chondrocytes and cartilage explants under inflammatory conditions. In a surgical model of rat OA, drug-loaded CM-NPs effectively restored gait, attenuated periarticular bone remodeling, and provided chondroprotection against cartilage degeneration. OA progression was also mitigated by CM-NPs-Ada in a canine model of anterior cruciate ligament transection. These results demonstrate the feasibility of using chondrocyte membrane-coated nanoparticles to improve the pharmacokinetics and efficacy of anti-OA drugs.

Phytochemical studies of white mulberry fruits (Morus alba L.)

Medicinal preparations made from plant materials have been widely used for many years due to their high pharmacological efficacy and safety of use. Therefore, a study of white mulberry fruits (Morus alba L.) for the content of substances is very important for the pharmaceutical industry such as flavonoids, alkaloids, polysaccharides, minerals, vitamins, and amino acids. White mulberry has a wide distribution area around the world, including in Kazakhstan, especially in the southern regions of the country (Almaty, Zhambyl, and Turkestan regions). The composition of the fruits of this plant is significantly influenced by the area where the trees grow, and therefore, the establishment of a specific composition of biologically active substances is very important. In the course of this study, such methods as gas chromatography were used-mass spectrometry of an extract obtained using carbon dioxide under subcritical conditions, atomic absorption, gravimetric, and spectrophotometric methods. As a result, for the first time in Kazakhstan, the composition of white mulberry fruits (Morus alba L.), namely, biologically active substances, has been identified, such as alkaloids, flavonoids, vitamins, macro- and microelements, and amino acids and fatty acids; in addition, the percentage composition of the above compounds has been determined. The results of the study show a comparative analysis of the component composition of white mulberry fruits (Morus alba L.) in various areas of tree growth, including outside of Kazakhstan. The obtained data testify to the great possibilities of using this raw material in medicine, pharmacology, and the food industry.

Combined Transcriptomics and Metabolomics Identify Regulatory Mechanisms of Porcine Vertebral Chondrocyte Development In Vitro

Porcine body length is closely related to meat production, growth, and reproductive performance, thus playing a key role in the profitability of the pork industry. Cartilage development is critical to longitudinal elongation of individual vertebrae. This study isolated primary porcine vertebral chondrocytes (PVCs) to clarify the complex mechanisms of elongation. We used transcriptome and target energy metabolome technologies to confirm crucial genes and metabolites in primary PVCs at different differentiation stages (0, 4, 8, and 12 days). Pairwise comparisons of the four stages identified 4566 differentially expressed genes (DEGs). Time-series gene cluster and functional analyses of these DEGs revealed four clusters related to metabolic processes, cartilage development, vascular development, and cell cycle regulation. We constructed a transcriptional regulatory network determining chondrocyte maturation. The network indicated that significantly enriched transcription factor (TF) families, including zf-C2H2, homeobox, TF_bZIP, and RHD, are important in cell cycle and differentiation processes. Further, dynamic network biomarker (DNB) analysis revealed that day 4 was the tipping point for chondrocyte development, consistent with morphological and metabolic changes. We found 24 DNB DEGs, including the TFs NFATC2 and SP7. Targeted energy metabolome analysis showed that most metabolites were elevated throughout chondrocyte development; notably, 16 differentially regulated metabolites (DRMs) were increased at three time points after cell differentiation. In conclusion, integrated metabolome and transcriptome analyses highlighted the importance of amino acid biosynthesis in chondrocyte development, with coordinated regulation of DEGs and DRMs promoting PVC differentiation via glucose oxidation. These findings reveal the regulatory mechanisms underlying PVC development and provide an important theoretical reference for improving pork production.

The serine synthesis pathway drives osteoclast differentiation through epigenetic regulation of NFATc1 expression

Bone-resorbing osteoclasts are vital for postnatal bone health, as increased differentiation or activity results in skeletal pathologies such as osteoporosis. The metabolism of mature osteoclasts differs from their progenitor cells, but whether the observed metabolic changes are secondary to the altered cell state or actively drive the process of cell differentiation is unknown. Here, we show that transient activation of the serine synthesis pathway (SSP) is essential for osteoclastogenesis, as deletion of the rate-limiting enzyme phosphoglycerate dehydrogenase in osteoclast progenitors impairs their differentiation and results in increased bone mass. In addition, pharmacological phosphoglycerate dehydrogenase inhibition abrogated bone loss in a mouse model of postmenopausal osteoporosis by blocking bone resorption. Mechanistically, SSP-derived α-ketoglutarate is necessary for histone demethylases that remove repressive histone methylation marks at the nuclear factor of activated T cells, cytoplasmic 1 (Nfatc1) gene locus, thereby inducing NFATc1 expression and consequent osteoclast maturation. Taken together, this study reveals a metabolic-epigenetic coupling mechanism that directs osteoclast differentiation and suggests that the SSP can be therapeutically targeted to prevent osteoporotic bone loss.

2P-FLIM unveils time-dependent metabolic shifts during osteogenic differentiation with a key role of lactate to fuel osteogenesis via glutaminolysis identified

BACKGROUND

Human mesenchymal stem cells (hMSCs) utilize discrete biosynthetic pathways to self-renew and differentiate into specific cell lineages, with undifferentiated hMSCs harbouring reliance on glycolysis and hMSCs differentiating towards an osteogenic phenotype relying on oxidative phosphorylation as an energy source.

METHODS

In this study, the osteogenic differentiation of hMSCs was assessed and classified over 14 days using a non-invasive live-cell imaging modality-two-photon fluorescence lifetime imaging microscopy (2P-FLIM). This technique images and measures NADH fluorescence from which cellular metabolism is inferred.

RESULTS

During osteogenesis, we observe a higher dependence on oxidative phosphorylation (OxPhos) for cellular energy, concomitant with an increased reliance on anabolic pathways. Guided by these non-invasive observations, we validated this metabolic profile using qPCR and extracellular metabolite analysis and observed a higher reliance on glutaminolysis in the earlier time points of osteogenic differentiation. Based on the results obtained, we sought to promote glutaminolysis further by using lactate, to improve the osteogenic potential of hMSCs. Higher levels of mineral deposition and osteogenic gene expression were achieved when treating hMSCs with lactate, in addition to an upregulation of lactate metabolism and transmembrane cellular lactate transporters. To further clarify the interplay between glutaminolysis and lactate metabolism in osteogenic differentiation, we blocked these pathways using BPTES and α-CHC respectively. A reduction in mineralization was found after treatment with BPTES and α-CHC, demonstrating the reliance of hMSC osteogenesis on glutaminolysis and lactate metabolism.

CONCLUSION

In summary, we demonstrate that the osteogenic differentiation of hMSCs has a temporal metabolic profile and shift that is observed as early as day 3 of cell culture using 2P-FLIM. Furthermore, extracellular lactate is shown as an essential metabolite and metabolic fuel to ensure efficient osteogenic differentiation and as a signalling molecule to promote glutaminolysis. These findings have significant impact in the use of 2P-FLIM to discover potent approaches towards bone tissue engineering in vitro and in vivo by engaging directly with metabolite-driven osteogenesis.

Glutamine deficiency drives transforming growth factor-β signaling activation that gives rise to myofibroblastic carcinoma-associated fibroblasts

Tumor-promoting carcinoma-associated fibroblasts (CAFs), abundant in the mammary tumor microenvironment (TME), maintain transforming growth factor-β (TGF-β)-Smad2/3 signaling activation and the myofibroblastic state, the hallmark of activated fibroblasts. How myofibroblastic CAFs (myCAFs) arise in the TME and which epigenetic and metabolic alterations underlie activated fibroblastic phenotypes remain, however, poorly understood. We herein show global histone deacetylation in myCAFs present in tumors to be significantly associated with poorer outcomes in breast cancer patients. As the TME is subject to glutamine (Gln) deficiency, human mammary fibroblasts (HMFs) were cultured in Gln-starved medium. Global histone deacetylation and TGF-β-Smad2/3 signaling activation are induced in these cells, largely mediated by class I histone deacetylase (HDAC) activity. Additionally, mechanistic/mammalian target of rapamycin complex 1 (mTORC1) signaling is attenuated in Gln-starved HMFs, and mTORC1 inhibition in Gln-supplemented HMFs with rapamycin treatment boosts TGF-β-Smad2/3 signaling activation. These data indicate that mTORC1 suppression mediates TGF-β-Smad2/3 signaling activation in Gln-starved HMFs. Global histone deacetylation, class I HDAC activation, and mTORC1 suppression are also observed in cultured human breast CAFs. Class I HDAC inhibition or mTORC1 activation by high-dose Gln supplementation significantly attenuates TGF-β-Smad2/3 signaling and the myofibroblastic state in these cells. These data indicate class I HDAC activation and mTORC1 suppression to be required for maintenance of myCAF traits. Taken together, these findings indicate that Gln starvation triggers TGF-β signaling activation in HMFs through class I HDAC activity and mTORC1 suppression, presumably inducing myCAF conversion.

Moderate mechanical strain and exercise reduce inflammation and excessive autophagy in osteoarthritis by downregulating mitofusin 2

AIMS

The major pathological mechanisms of osteoarthritis (OA) progression include inflammation, autophagy, and apoptosis, etc. Moderate mechanical strain and exercise effectively improve chondrocyte degeneration by reducing these adverse factors. Mitofusin 2 (MFN2) is a crucial regulatory factor associated with inflammation, autophagy and apoptosis, and its expression is regulated by exercise. This study aims to elucidate the effects of moderate mechanical strain and exercise on MFN2 expression and its influence on OA progression.

MAIN METHODS

Destabilization of the medial meniscus (DMM) surgery was performed on rats to induce an OA rat model. Subsequently, adeno-associated virus (overexpression/knockdown) intra-articular injection or moderate treadmill exercise was administered to evaluate the effects of these treatments on MFN2 expression and OA progression. Overexpressed plasmids and siRNA vectors were used to regulate MFN2 expression in chondrocytes. An inflammatory degeneration cell model was generated by IL-1β stimulation. Moderate mechanical strain was applied to MFN2-overexpressing cells to explore their interactions.

KEY FINDINGS

MFN2 overexpression aggravated inflammation by activating the NF-κB and P38 pathways and induced excessive autophagy by inhibiting the PI3K/AKT/mTOR pathway, thereby causing chondrocyte apoptosis and metabolic disorder. Moderate mechanical strain partially reversed these adverse effects. In the DMM rat model, MFN2 overexpression in articular cartilage exacerbated OA progression, whereas MFN2 knockdown and treadmill exercise alleviated cartilage degeneration, inflammation, and mechanical pain.

SIGNIFICANCE

MFN2 is a critical factor mediating the association between inflammation and excessive autophagy in OA progression. Moderate mechanical strain and treadmill exercise may improve OA through downregulating MFN2 expression. This study may provide a theoretical basis for exercise therapy in OA treatment.

Optimization of piggyBac Transposon System Electrotransfection in Sheep Fibroblasts

Electroporation is a non-viral mediated transfection technique, which has the advantages of being harmless, easy to operate, and less expensive. This transfection method can be used for almost all cell types and has gradually become the preferred transfection method for mammalian gene editing. However, further improvements are needed in electroporation efficiency. There is no universal standard electrotransfection step for different types of cells, and the inappropriate electroporation parameters will result in a low transfection efficiency and high cell mortality. Here, we systematically optimized the electrotransfection parameters of piggyBac transposon system into sheep fetal fibroblasts for the first time. We found that the cell transfection efficiency and cell viability could be improved by using traditional cell culture medium DMEM/F12 as an electroporation buffer, and simultaneously using the square-wave pulsing program of 200 V, 2 pulses, 20 ms length, and 20 μg DNA (3 μg/μL) in 4 mm cuvette, and the transfection efficiency and cell viability could eventually reach 78.0% and 40.9%, respectively. The purpose of this study is to provide a method reference and theoretical basis for the plasmid electrotransfection in mammal cells.

Glutathione limits RUNX2 oxidation and degradation to regulate bone formation

Reactive oxygen species (ROS) are natural products of mitochondrial oxidative metabolism and oxidative protein folding. ROS levels must be well controlled, since elevated ROS has been shown to have deleterious effects on osteoblasts. Moreover, excessive ROS is thought to underlie many of the skeletal phenotypes associated with aging and sex steroid deficiency in mice and humans. The mechanisms by which osteoblasts regulate ROS and how ROS inhibits osteoblasts are not well understood. Here, we demonstrate that de novo glutathione (GSH) biosynthesis is essential in neutralizing ROS and establish a proosteogenic reduction and oxidation reaction (REDOX) environment. Using a multifaceted approach, we demonstrate that reducing GSH biosynthesis led to acute degradation of RUNX2, impaired osteoblast differentiation, and reduced bone formation. Conversely, reducing ROS using catalase enhanced RUNX2 stability and promoted osteoblast differentiation and bone formation when GSH biosynthesis was limited. Highlighting the therapeutic implications of these findings, in utero antioxidant therapy stabilized RUNX2 and improved bone development in the Runx2+/- haplo-insufficient mouse model of human cleidocranial dysplasia. Thus, our data establish RUNX2 as a molecular sensor of the osteoblast REDOX environment and mechanistically clarify how ROS negatively impacts osteoblast differentiation and bone formation.

Spotlight on GOT2 in Cancer Metabolism

GOT2 is at the nexus of several critical metabolic pathways in homeostatic cellular and dysregulated cancer metabolism. Despite this, recent work has emphasized the remarkable plasticity of cancer cells to employ compensatory pathways when GOT2 is inhibited. Here, we review the metabolic roles of GOT2, highlighting findings in both normal and cancer cells. We emphasize how cancer cells repurpose cell intrinsic metabolism and their flexibility when GOT2 is inhibited. We close by using this framework to discuss key considerations for future investigations into cancer metabolism.

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.

Characterization of Chromatin Accessibility in Fetal Bovine Chondrocytes

Despite significant advances of the bovine epigenome investigation, new evidence for the epigenetic basis of fetal cartilage development remains lacking. In this study, the chondrocytes were isolated from long bone tissues of bovine fetuses at 90 days. The Assay for Transposase-Accessible Chromatin with high throughput sequencing (ATAC-seq) and transcriptome sequencing (RNA-seq) were used to characterize gene expression and chromatin accessibility profile in bovine chondrocytes. A total of 9686 open chromatin regions in bovine fetal chondrocytes were identified and 45% of the peaks were enriched in the promoter regions. Then, all peaks were annotated to the nearest gene for Gene Ontology (GO) and Kyoto Encylopaedia of Genes and Genomes (KEGG) analysis. Growth and development-related processes such as amide biosynthesis process (GO: 0043604) and translation regulation (GO: 006417) were enriched in the GO analysis. The KEGG analysis enriched endoplasmic reticulum protein processing signal pathway, TGF-β signaling pathway and cell cycle pathway, which are closely related to protein synthesis and processing during cell proliferation. Active transcription factors (TFs) were enriched by ATAC-seq, and were fully verified with gene expression levels obtained by RNA-seq. Among the top50 TFs from footprint analysis, known or potential cartilage development-related transcription factors FOS, FOSL2 and NFY were found. Overall, our data provide a theoretical basis for further determining the regulatory mechanism of cartilage development in bovine.

Activation of Piezo1 promotes osteogenic differentiation of aortic valve interstitial cell through YAP-dependent glutaminolysis

Hemodynamic overload and dysregulation of cellular metabolism are involved in development of calcific aortic valve disease (CAVD). However, how mechanical stress relates to metabolic changes in CAVD remains unclear. Here, we show that Piezo1, a mechanosensitive ion channel, regulated glutaminase 1 (GLS1)-mediated glutaminolysis to promote osteogenic differentiation of valve interstitial cells (VICs). In vivo, two models of aortic valve stenosis were constructed by ascending aortic constriction (AAC) and direct wire injury (DWI). Inhibition of Piezo1 and GLS1 in these models respectively mitigated aortic valve lesion. In vitro, Piezo1 activation induced by Yoda1 and oscillatory stress triggered osteogenic responses in VICs, which were prevented by Piezo1 inhibition or knockdown. Mechanistically, Piezo1 activation promoted calcium-dependent Yes-associated protein (YAP) activation. YAP modulated GLS1-mediated glutaminolysis, which enhanced osteogenic differentiation through histone acetylation of runt-related transcription factor 2 (RUNX2) promoters. Together, our work provided a cross-talk between mechanotransduction and metabolism in the context of CAVD.

Cardamonin alleviates chondrocytes inflammation and cartilage degradation of osteoarthritis by inhibiting ferroptosis via p53 pathway

Osteoarthritis (OA) is a common degenerative joint disease, mainly presented by the deterioration of articular cartilage. Amounts of data demonstrated this deterioration is composed of oxidative stress, pro-inflammation and chondrocyte death events. Ferroptosis is a novel form of cell death that differs from apoptosis and autophagy, recent studies have shown that chondrocyte ferroptosis contributes to the development of osteoarthritis. Cardamonin (CAD) has been demonstrated to possess antioxidant and anti-inflammatory properties in several diseases, whether CAD may influence the OA progression is still obscure. Therefore, we aimed to determine whether CAD alleviates chondrocyte ferroptosis and its effect on OA with potential mechanism. In this study, we found that inflammation, cartilage degradation and ferroptosis induced by interleukin-1β (IL-1β) were significantly alleviated by CAD. Moreover, the administration of the ferroptosis inhibitor, Deferoxamine (DFO) reversed the inflammatory and cartilage degradation effects of IL-1β as well. Chondrocyte mitochondrial morphology and function were alleviated by both CAD and DFO. We found that CAD increased collagen II, p53, SLC7A11 GPX4 expression and decreased MMP13, iNOS, COX2 expression in chondrocytes, further investigation showed that the P53 signaling pathway was involved. In vivo, intra-articular injection of CAD significantly ameliorated cartilage damage in a rat OA model, induced collagen II and SLC7A11 expression by immunohistochemistry. Our study proves that CAD ameliorated OA cartilage degradation by regulating ferroptosis via P53 signaling pathway, suggesting a potential role of CAD in OA treatment.

Nutrient metabolism of the nucleus pulposus: A literature review

Cells take in, consume, and synthesize nutrients for numerous physiological functions. This includes not only energy production but also macromolecule biosynthesis, which will further influence cellular signaling, redox homeostasis, and cell fate commitment. Therefore, alteration in cellular nutrient metabolism is associated with pathological conditions. Intervertebral discs, particularly the nucleus pulposus (NP), are avascular and exhibit unique metabolic preferences. Clinical and preclinical studies have indicated a correlation between intervertebral degeneration (IDD) and systemic metabolic diseases such as diabetes, obesity, and dyslipidemia. However, a lack of understanding of the nutrient metabolism of NP cells is masking the underlying mechanism. Indeed, although previous studies indicated that glucose metabolism is essential for NP cells, the downstream metabolic pathways remain unknown, and the potential role of other nutrients, like amino acids and lipids, is understudied. In this literature review, we summarize the current understanding of nutrient metabolism in NP cells and discuss other potential metabolic pathways by referring to a human NP transcriptomic dataset deposited to the Gene Expression Omnibus, which can provide us hints for future studies of nutrient metabolism in NP cells and novel therapies for IDD.

Amino acid metabolism in skeletal cells

Amino acid metabolism regulates essential cellular functions, not only by fueling protein synthesis, but also by supporting the biogenesis of nucleotides, redox factors and lipids. Amino acids are also involved in tricarboxylic acid cycle anaplerosis, epigenetic modifications, next to synthesis of neurotransmitters and hormones. As such, amino acids contribute to a broad range of cellular processes such as proliferation, matrix synthesis and intercellular communication, which are all critical for skeletal cell functioning. Here we summarize recent work elucidating how amino acid metabolism supports and regulates skeletal cell function during bone growth and homeostasis, as well as during skeletal disease. The most extensively studied amino acid is glutamine, and osteoblasts and chondrocytes rely heavily on this non-essential amino acid during for their functioning and differentiation. Regulated by lineage-specific transcription factors such as SOX9 and osteoanabolic agents such as parathyroid hormone or WNT, glutamine metabolism has a wide range of metabolic roles, as it fuels anabolic processes by producing nucleotides and non-essential amino acids, maintains redox balance by generating the antioxidant glutathione and regulates cell-specific gene expression via epigenetic mechanisms. We also describe how other amino acids affect skeletal cell functions, although further work is needed to fully understand their effect. The increasing number of studies using stable isotope labelling in several skeletal cell types at various stages of differentiation, together with conditional inactivation of amino acid transporters or enzymes in mouse models, will allow us to obtain a more complete picture of amino acid metabolism in skeletal cells.

Glucose transporters GLUT1, GLUT3, and GLUT4 have different effects on osteoblast proliferation and metabolism

Bone is an active tissue that undergoes constant remodeling. Bone formation requires energy and one of the energy sources of bone-forming osteoblasts is glucose, which is transported inside the cells via glucose transporters. However, the role of class I glucose transporters in the differentiation and metabolism of osteoblasts and their precursors, bone marrow mesenchymal stromal cells (BMSCs) remains inconclusive. Our aim was to characterize the expression and contribution of main class I glucose transporters, GLUT1, GLUT3, and GLUT4, during osteoblast proliferation and differentiation. To investigate the role of each GLUT, we downregulated GLUTs with siRNA technology in primary rat BMSCs. Live-cell imaging and RNA-seq analysis was used to evaluate downstream pathways in silenced osteoblasts. Glucose transporters GLUT1, GLUT3, and GLUT4 had distinct expression patterns in osteoblasts. GLUT1 was abundant in BMSCs, but rapidly and significantly downregulated during osteoblast differentiation by up to 80% (p < 0.001). Similar downregulation was observed for GLUT4 (p < 0.001). In contrast, expression levels of GLUT3 remained stable during differentiation. Osteoblasts lacked GLUT2. Silencing of GLUT4 resulted in a significant decrease in proliferation and differentiation of preosteoblasts (p < 0.001) and several pathways related to carbohydrate metabolism and cell signaling were suppressed. However, silencing of GLUT3 resulted in increased proliferation (p < 0.001), despite suppression of several pathways involved in cellular metabolism, biosynthesis and actin organization. Silencing of GLUT1 had no effect on proliferation and less changes in the transcriptome. RNA-seq dataset further revealed that osteoblasts express also class II and III glucose transporters, except for GLUT7. In conclusion, GLUT1, -3 and -4 may all contribute to glucose uptake in differentiating osteoblasts. GLUT4 expression was clearly required for osteoblast proliferation and differentiation. GLUT1 appears to be abundant in early precursors, but stable expression of GLUT3 suggest also a role for GLUT3 in osteoblasts. Presence of other GLUT members may further contribute to fine-tuning of glucose uptake. Together, glucose uptake in osteoblast lineage appears to rely on several glucose transporters to ensure sufficient energy for new bone formation.

Direct Reprogramming of Mouse Subchondral Bone Osteoblasts into Chondrocyte-like Cells

Treatment of full-thickness articular cartilage defects with exposure of subchondral bone often seen in osteoarthritic conditions has long been a great challenge, especially with a focus on the feasibility of in situ cartilage regeneration through minimally invasive procedures. Osteoblasts that situate in the subchondral bone plate may be considered a potentially vital endogenous source of cells for cartilage resurfacing through direct reprogramming into chondrocytes. Microarray-based gene expression profiles were generated to compare tissue-specific transcripts between subchondral bone and cartilage of mice and to assess age-dependent differences of chondrocytes as well. On osteoblast cell lines established from mouse proximal tibial subchondral bone, sequential screening by co-transduction of transcription factor (TF) genes that distinguish chondrocytes from osteoblasts reveals a shortlist of potential reprogramming factors exhibiting combined effects in inducing chondrogenesis of subchondral bone osteoblasts. A further combinatorial approach unexpectedly identified two 3-TF combinations containing Sox9 and Sox5 that exhibit differences in reprogramming propensity with the third TF c-Myc or Plagl1, which appeared to direct the converted chondrocytes toward either a superficial or a deeper zone phenotype. Thus, our approach demonstrates the possibility of converting osteoblasts into two major chondrocyte subpopulations with two combinations of three genes (Sox9, Sox5, and c-Myc or Plagl1). The findings may have important implications for developing novel in situ regeneration strategies for the reconstruction of full-thickness cartilage defects.

Functional gelatin hydrogel scaffold with degraded-release of glutamine to enhance cellular energy metabolism for cartilage repair

Cartilage defect is one of the most common pathogenesis of osteoarthritis (OA), a degenerative joint disease that affects millions of people globally. Due to lack of nutrition and local metabolic inertia, the repair of cartilage has always been a difficult problem to be urgently solved. Herein, a functional gelatin hydrogel scaffold (GelMA-AG) chemically modified with alanyl-glutamine (AG) is proposed and prepared. The GelMA-AG can release glutamine through in vivo degradation that can activate the energy metabolism process of chondrocytes, thus effectively promoting damaged cartilage repair. The results demonstrate that compared with the AG-free gelatin hydrogel (GelMA), GelMA-AG exhibits an increase in both the mitochondrial membrane potential level and the production of intracellular adenosine triphosphate (ATP), while the intracellular reactive oxygen species (ROS) of chondrocytes is decreased, thus contributing to the higher level of cellular metabolism and the lower inflammation in cartilage tissue. In contrast to GelMA (Reduced Modulus (Er): 24.33 MPa), the Er value of the remodeled rabbit knee articular cartilage is up to 70.14 MPa, which is more comparable to natural cartilage. In particular, this strategy does not involve exogenous cells and growth factors, and the therapeutic strategy of actively regulating the metabolic microenvironment through a functional gelatin hydrogel scaffold represents a new and prospective idea for the design of tissue engineering biomaterials in cartilage repair with simplification and effectiveness.

A Cryoprotectant-Gel Composite Designed to Preserve Articular Cartilage during Frozen Osteoarticular Autograft Reconstruction for Malignant Bone Tumors: An Animal-Based Study

OBJECTIVE

We designed a highly adhesive cryoprotectant-gel composite (CGC), based on regular liquid-form cryoprotectant base (CB), aiming to protect cartilage tissue during frozen osteoarticular autograft reconstruction for high-grade sarcoma around the joint. This study aimed to evaluate its effectiveness in rat and porcine distal femur models.

DESIGN

Fresh articular cartilage samples harvested from distal rat and porcine femurs were divided into 4 test groups: untreated control group, liquid nitrogen (LN) freezing group, LN freezing group pretreated with CB (CB group), and LN freezing group pretreated with CGC (CGC group). Microscopic and macroscopic evaluation of cartilage condition, TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay, and apoptotic protein analysis of chondrocytes were performed to confirm our results.

RESULTS

In the rat model, CGC could prevent articular cartilage from roughness and preserve more proteoglycans when compared with the LN freezing and CB groups. Western blot analysis showed CGC could prevent cartilage from LN-induced apoptosis supported by caspase-3/8 apoptotic signaling cascade. Macroscopically, we observed CGC could reduce both articular clefting and loss of articular luminance after freezing in the porcine model. In both models, CGC could reduce articular chondrocytes from degeneration. Fewer TUNEL-positive apoptotic and more viable chondrocytes in cartilage tissue were observed in the CGC group in our animal models.

CONCLUSION

Our study proved that CGC could effectively prevent cartilage surface and chondrocytes from cryoinjury after LN freezing. Freezing articular cartilage surrounded with high concentration of CGC can be a better alternative to preserve articular cartilage during limb salvage surgery for malignant bone tumor.

1H NMR Metabolite Monitoring during the Differentiation of Human Induced Pluripotent Stem Cells Provides New Insights into the Molecular Events That Regulate Embryonic Chondrogenesis

The integration of cell metabolism with signalling pathways, transcription factor networks and epigenetic mediators is critical in coordinating molecular and cellular events during embryogenesis. Induced pluripotent stem cells (IPSCs) are an established model for embryogenesis, germ layer specification and cell lineage differentiation, advancing the study of human embryonic development and the translation of innovations in drug discovery, disease modelling and cell-based therapies. The metabolic regulation of IPSC pluripotency is mediated by balancing glycolysis and oxidative phosphorylation, but there is a paucity of data regarding the influence of individual metabolite changes during cell lineage differentiation. We used ¹H NMR metabolite fingerprinting and footprinting to monitor metabolite levels as IPSCs are directed in a three-stage protocol through primitive streak/mesendoderm, mesoderm and chondrogenic populations. Metabolite changes were associated with central metabolism, with aerobic glycolysis predominant in IPSC, elevated oxidative phosphorylation during differentiation and fatty acid oxidation and ketone body use in chondrogenic cells. Metabolites were also implicated in the epigenetic regulation of pluripotency, cell signalling and biosynthetic pathways. Our results show that ¹H NMR metabolomics is an effective tool for monitoring metabolite changes during the differentiation of pluripotent cells with implications on optimising media and environmental parameters for the study of embryogenesis and translational applications.

Glutamine metabolism modulates chondrocyte inflammatory response

Osteoarthritis is the most common joint disease in the world with significant societal consequences but lacks effective disease-modifying interventions. The pathophysiology consists of a prominent inflammatory component that can be targeted to prevent cartilage degradation and structural defects. Intracellular metabolism has emerged as a culprit of the inflammatory response in chondrocytes, with both processes co-regulating each other. The role of glutamine metabolism in chondrocytes, especially in the context of inflammation, lacks a thorough understanding and is the focus of this work. We display that mouse chondrocytes utilize glutamine for energy production and anabolic processes. Furthermore, we show that glutamine deprivation itself causes metabolic reprogramming and decreases the inflammatory response of chondrocytes through inhibition of NF-κB activity. Finally, we display that glutamine deprivation promotes autophagy and that ammonia is an inhibitor of autophagy. Overall, we identify a relationship between glutamine metabolism and inflammatory signaling and display the need for increased study of chondrocyte metabolic systems.

Amino acid metabolism: challenges and opportunities for the therapeutic treatment of leukemia and lymphoma

Leukemia and lymphoma-the most common hematological malignant diseases-are often accompanied by complications such as drug resistance, refractory diseases and relapse. Amino acids (AAs) are important energy sources for malignant cells. Tumor-mediated AA metabolism is associated with the immunosuppressive properties of the tumor microenvironment, thereby assisting malignant cells to evade immune surveillance. Targeting abnormal AA metabolism in the tumor microenvironment may be an effective therapeutic approach to address the therapeutic challenges of leukemia and lymphoma. Here, we review the effects of glutamine, arginine and tryptophan metabolism on tumorigenesis and immunomodulation, and define the differences between tumor cells and immune effector cells. We also comment on treatments targeting these AA metabolism pathways in lymphoma and leukemia and discuss how these treatments have profound adverse effects on tumor cells, but leave the immune cells unaffected or mildly affected.

Novel peptides from sea cucumber intestinal hydrolysates promote longitudinal bone growth in adolescent mice through accelerating cell cycle progress by regulating glutamine metabolism

Sea cucumber intestines are recognized as a major by-product in the sea cucumber processing industry and have been shown to exhibit bioactive properties. However, whether the sea cucumber intestine is beneficial for osteogenesis remains unknown. In this study, low molecular weight peptides rich in glutamate/glutamine were obtained from sea cucumber intestines (SCIP) by enzymatic hydrolysis, and orally administered to adolescent mice to investigate the effects on longitudinal bone growth. The results showed that the SCIP supplement significantly increased the femur length and new bone formation rate by 9.6% and 56.3%, and elevated the levels of serum osteogenic markers alkaline phosphatase (ALP), Collagen I and osteocalcin (OCN). Notably, H&E staining showed that SCIP significantly increased the height of the growth plate, in which the height of the proliferation zone was elevated by 95.6%. Glutamine is a major determinant of bone growth. SCIP supplement significantly increased glutamine levels in the growth plate by 44.2% and upregulated the expression of glutamine metabolism-related enzymes glutaminase 1 (Gls1) and glutamate dehydrogenase 1 (GLUD1) in the growth plate. Furthermore, SCIP supplement upregulated growth plate acetyl coenzyme A levels to promote histone acetylation and accelerated cell cycle progression by upregulating Sox9 expression, thereby contributing to rapid chondrocyte proliferation. To the best of our knowledge, this is the first report where SCIP could enhance longitudinal bone growth via promoting growth plate chondrocyte proliferation. The present study will provide new ideas and a theoretical basis for the high-value utilization of sea cucumber intestines.

Alanyl-Glutamine Protects against Lipopolysaccharide-Induced Liver Injury in Mice via Alleviating Oxidative Stress, Inhibiting Inflammation, and Regulating Autophagy

Acute liver injury is a worldwide problem with a high rate of morbidity and mortality, and effective pharmacological therapies are still urgently needed. Alanyl-glutamine (Ala-Gln), a dipeptide formed from L-alanine and L-glutamine, is known as a protective compound that is involved in various tissue injuries, but there are limited reports regarding the effects of Ala-Gln in acute liver injury. This present study aimed to investigate the protective effects of Ala-Gln in lipopolysaccharide (LPS)-induced acute liver injury in mice, with a focus on inflammatory responses and oxidative stress. The acute liver injury induced using LPS (50 μg/kg) and D-galactosamine (D-Gal) (400 mg/kg) stimulation in mice was significantly attenuated after Ala-Gln treatment (500 and 1500 mg/kg), as evidenced by reduced plasma alanine transaminase (ALT) (p < 0.01, p < 0.001), aspartate transaminase (AST) (p < 0.05, p < 0.001), and lactate dehydrogenase (LDH) (p < 0.01, p < 0.001) levels, and accompanied by improved histopathological changes. In addition, LPS/D-Gal-induced hepatic apoptosis was also alleviated by Ala-Gln administration, as shown by a greatly decreased ratio of TUNEL-positive hepatocytes, from approximately 10% to 2%, and markedly reduced protein levels of cleaved caspase-3 (p < 0.05, p < 0.001) in liver. Moreover, we found that LPS/D-Gal-triggered oxidative stress was suppressed after Ala-Gln treatment, the effect of which might be dependent on the elevation of SOD and GPX activities, and on GSH levels in liver. Interestingly, we observed that Ala-Gln clearly inhibited LPS/D-Gal exposure-induced macrophage accumulation and the production of proinflammatory factors in the liver. Furthermore, Ala-Gln greatly regulated autophagy in the liver in LPS/D-Gal-treated mice. Using RAW264.7 cells, we confirmed the anti-inflammatory role of Ala-Gln-targeting macrophages.

Distinct Roles of Glutamine Metabolism in Benign and Malignant Cartilage Tumors With IDH Mutations

Enchondromas and chondrosarcomas are common cartilage neoplasms that are either benign or malignant, respectively. The majority of these tumors harbor mutations in either IDH1 or IDH2. Glutamine metabolism has been implicated as a critical regulator of tumors with IDH mutations. Using genetic and pharmacological approaches, we demonstrated that glutaminase-mediated glutamine metabolism played distinct roles in enchondromas and chondrosarcomas with IDH1 or IDH2 mutations. Glutamine affected cell differentiation and viability in these tumors differently through different downstream metabolites. During murine enchondroma-like lesion development, glutamine-derived α-ketoglutarate promoted hypertrophic chondrocyte differentiation and regulated chondrocyte proliferation. Deletion of glutaminase in chondrocytes with Idh1 mutation increased the number and size of enchondroma-like lesions. In contrast, pharmacological inhibition of glutaminase in chondrosarcoma xenografts reduced overall tumor burden partially because glutamine-derived non-essential amino acids played an important role in preventing cell apoptosis. This study demonstrates that glutamine metabolism plays different roles in tumor initiation and cancer maintenance. Supplementation of α-ketoglutarate and inhibiting GLS may provide a therapeutic approach to suppress enchondroma and chondrosarcoma tumor growth, respectively. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Exosomes derived from hypoxia preconditioned mesenchymal stem cells laden in a silk hydrogel promote cartilage regeneration via the miR-205-5p/PTEN/AKT pathway

Tissue engineering has promising prospects for cartilage regeneration. However, there remains an urgent need to harvest high quality seed cells. Bone marrow mesenchymal cells (BMSCs), and in particular their exosomes, might promote the function of articular chondrocytes (ACs) via paracrine mechanisms. Furthermore, preconditioned BMSCs could provide an enhanced therapeutic effect. BMSCs naturally exist in a relatively hypoxic environment (1%-5% O₂); however, they are usually cultured under higher oxygen concentrations (21% O₂). Herein, we hypothesized that hypoxia preconditioned exosomes (H-Exos) could improve the quality of ACs and be more conducive to cartilage repair. In our study, we compared the effects of exosomes derived from BMSCs preconditioned with hypoxia and normoxia (N-Exos) on ACs, demonstrating that H-Exos significantly promoted the proliferation, migration, anabolism and anti-inflammation effects of ACs. Furthermore, we confirmed that hypoxia preconditioning upregulated the expression of miR-205-5p in H-Exos, suggesting that ACs were promoted via the miR-205-5p/PTEN/AKT pathway. Finally, an injectable silk fibroin (SF) hydrogel containing ACs and H-Exos (SF/ACs/H-Exos) was utilized to repair cartilage defects and effectively promote cartilage regeneration in vivo. The application of SF/ACs/H-Exos hydrogel in cartilage regeneration therefore has promising prospects. STATEMENT OF SIGNIFICANCE: Cartilage tissue engineering (CTE) has presented a promising prospect. However, the quality of seed cells is an important factor affecting the repair efficiency. Our study demonstrates for the first time that the exosomes derived from hypoxia preconditioned BMSCs (H-Exos) effectively promote the proliferation, migration and anabolism of chondrocytes and inhibit inflammation through miR-205-5p/PTEN/AKT pathway. Furthermore, we fabricated an injectable silk fibrion (SF) hydrogel to preserve and sustained release H-Exos. A complex composed of SF hydrogel, H-Exos and chondrocytes can effectively promote the regeneration of cartilage defects. Therefore, this study demonstrates that hypoxia pretreatment could optimize the therapeutic effects of BMSCs-derived exosomes, and the combination of exosomes and SF hydrogel could be a promising therapeutic method for cartilage regeneration.

Fundamentals of OA. An initiative of Osteoarthritis and Cartilage. Obesity and metabolic factors in OA

OBJECTIVE

Obesity was once considered a risk factor for knee osteoarthritis (OA) primarily for biomechanical reasons. Here we provide an additional perspective by discussing how obesity also increases OA risk by altering metabolism and inflammation.

DESIGN

This narrative review is presented in four sections: 1) metabolic syndrome and OA, 2) metabolic biomarkers of OA, 3) evidence for dysregulated chondrocyte metabolism in OA, and 4) metabolic inflammation: joint tissue mediators and mechanisms.

RESULTS

Metabolic syndrome and its components are strongly associated with OA. However, evidence for a causal relationship is context dependent, varying by joint, gender, diagnostic criteria, and demographics, with additional environmental and genetic interactions yet to be fully defined. Importantly, some aspects of the etiology of obesity-induced OA appear to be distinct between men and women, especially regarding the role of adipose tissue. Metabolomic analyses of serum and synovial fluid have identified potential diagnostic biomarkers of knee OA and prognostic biomarkers of disease progression. Connecting these biomarkers to cellular pathophysiology will require future in vivo studies of joint tissue metabolism. Such studies will help reveal when a metabolic process or a metabolite itself is a causal factor in disease progression. Current evidence points towards impaired chondrocyte metabolic homeostasis and metabolic-immune dysregulation as likely factors connecting obesity to the increased risk of OA.

CONCLUSIONS

A deeper understanding of how obesity alters metabolic and inflammatory pathways in synovial joint tissues is expected to provide new therapeutic targets and an improved definition of "metabolic" and "obesity" OA phenotypes.

De novo serine synthesis regulates chondrocyte proliferation during bone development and repair

The majority of the mammalian skeleton is formed through endochondral ossification starting from a cartilaginous template. Cartilage cells, or chondrocytes, survive, proliferate and synthesize extracellular matrix in an avascular environment, but the metabolic requirements for these anabolic processes are not fully understood. Here, using metabolomics analysis and genetic in vivo models, we show that maintaining intracellular serine homeostasis is essential for chondrocyte function. De novo serine synthesis through phosphoglycerate dehydrogenase (PHGDH)-mediated glucose metabolism generates nucleotides that are necessary for chondrocyte proliferation and long bone growth. On the other hand, dietary serine is less crucial during endochondral bone formation, as serine-starved chondrocytes compensate by inducing PHGDH-mediated serine synthesis. Mechanistically, this metabolic flexibility requires ATF4, a transcriptional regulator of amino acid metabolism and stress responses. We demonstrate that both serine deprivation and PHGDH inactivation enhance ATF4 signaling to stimulate de novo serine synthesis and serine uptake, respectively, and thereby prevent intracellular serine depletion and chondrocyte dysfunction. A similar metabolic adaptability between serine uptake and de novo synthesis is observed in the cartilage callus during fracture repair. Together, the results of this study reveal a critical role for PHGDH-dependent serine synthesis in maintaining intracellular serine levels under physiological and serine-limited conditions, as adequate serine levels are necessary to support chondrocyte proliferation during endochondral ossification.