BAP1 promotes osteoclast function by metabolic reprogramming

Proteins extracted from placenta regulate osteogenic differentiation of human mesenchymal stem cells

Placenta is a medical waste, but the human placenta-derived proteins (hPDPs) have highly significant application value. The precise mechanism of injectable hPDPs gel on bone regeneration has been scarcely studied. In this study, a succinct methodology was employed to extract all proteins in the placenta. Proteomic analysis revealed that key gene ontology (GO) terms, signaling pathways, and osteogenic stimulators in PDPs, such as THY1, GDF15, SPARC, GPNMB, PARK7, EFEMP1, and LRP. In order to provide evidence supporting the ability of injectable hPDPs to promote osteogenesis and osteogenic differentiation (OD), the in vitro experiments utilizing human mesenchymal stem cells (hMSCs) and in vivo heterotopic osteogenesis animal models were conducted to assess the bone-forming ability of hPDPs. Results demonstrated that hPDPs accelerated OD of hMSCs and enhanced osteogenesis. Proteomic data, qPCR, immunofluorescence (IF) staining, RNA-sequencing data, KEGG, and GO enrichment analysis were utilized to elucidate the mechanisms underlying hPDP-induced OD. The findings indicated that the PDPs could promote OD through the activation of osteogenic stimulators and multiple signaling pathways, especially the BMP2/TGF-β signaling pathway and the iron metabolism pathway. This research elucidated the function and mechanism of PDPs in OD, providing valuable insights into their potential clinical applications. The findings suggest a novel strategy for utilizing medical waste or their stimulators as biocompatible materials for bone tissue engineering applications.

UnitedMet harnesses RNA-metabolite covariation to impute metabolite levels in clinical samples

Comprehensively studying metabolism requires metabolite measurements. Such measurements, however, are often unavailable in large cohorts of tissue samples. To address this basic barrier, we propose a Bayesian framework ('UnitedMet') that leverages RNA-metabolite covariation to impute otherwise unmeasured metabolite levels from widely available transcriptomic data. UnitedMet is equally capable of imputing whole pool sizes and outcomes of isotope tracing experiments. We apply UnitedMet to investigate the metabolic impact of driver mutations in kidney cancer, identifying an association between BAP1 and a highly oxidative tumor phenotype. We similarly apply UnitedMet to determine that advanced kidney cancers upregulate oxidative phosphorylation relative to early-stage disease, that oxidative metabolism in kidney cancer is associated with inferior outcomes to anti-angiogenic therapy and that kidney cancer metastases demonstrate elevated oxidative phosphorylation. UnitedMet provides a scalable tool for assessing metabolic phenotypes when direct measurements are infeasible, facilitating unexplored avenues for metabolite-focused hypothesis generation.

Posttranslational Modification in Bone Homeostasis and Osteoporosis

Bone is responsible for providing mechanical protection, attachment sites for muscles, hematopoiesis micssroenvironment, and maintaining balance between calcium and phosphorate. As a highly active and dynamically regulated organ, the balance between formation and resorption of bone is crucial in bone development, damaged bone repair, and mineral homeostasis, while dysregulation in bone remodeling impairs bone structure and strength, leading to deficiency in bone function and skeletal disorder, such as osteoporosis. Osteoporosis refers to compromised bone mass and higher susceptibility of fracture, resulting from several risk factors deteriorating the balanced system between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. This balanced system is strictly regulated by translational modification, such as phosphorylation, methylation, acetylation, ubiquitination, sumoylation, glycosylation, ADP-ribosylation, S-palmitoylation, citrullination, and so on. This review specifically describes the updating researches concerning bone formation and bone resorption mediated by posttranslational modification. We highlight dysregulated posttranslational modification in osteoblast and osteoclast differentiation. We also emphasize involvement of posttranslational modification in osteoporosis development, so as to elucidate the underlying molecular basis of osteoporosis. Then, we point out translational potential of PTMs as therapeutic targets. This review will deepen our understanding between posttranslational modification and osteoporosis, and identify novel targets for clinical treatment and identify future directions.

FSH exacerbates bone loss by promoting osteoclast energy metabolism through the CREB-MDH2-NAD+ axis

AIMS

Osteoclast energy metabolism is a promising target for treating diseases characterized by high osteoclast activity, such as osteoporosis. However, the regulatory factors involved in osteoclast bioenergetic processes are still in the early stages of being fully understood. This study reveals the effects of follicle-stimulating hormone (FSH) on osteoclast energy metabolism.

METHODS

The Lyz2-Cre-Flox model selectively deletes FSH receptor (FSHR) from osteoclast precursor cells to generate Fshrf/f; Lyz2-Cre (Fshrf/f; Cre) mice. Bone quality was assessed using micro-computed tomography, histomorphometric analysis, and dual-fluorescence labeling. The in vitro assays measured oxygen consumption rate, extracellular acidification rate, pyruvate content, and mitochondrial membrane potential to determine metabolic flux. RNA-seq, LC-MS, dual-luciferase reporter assays, and chromatin immunoprecipitation (ChIP) assays were used to elucidate the underlying mechanisms.

RESULTS

FSHR deficiency in osteoclasts protected bone from resorption under normal and ovariectomized conditions. FSHR-deficient osteoclasts have reduced nicotinamide adenine dinucleotide (NAD+) levels, impairing osteoclast activity and energy metabolism. Mechanistically, FSH influenced NAD+ levels via the CREB/MDH2 axis. Treatment with FSH monoclonal antibodies rescued bone loss in OVX mice and reduced bone marrow NAD+ levels.

CONCLUSIONS

Targeting FSH may be a promising metabolic modulation strategy for treating osteoporosis and other diseases associated with high osteoclast activity.

Metabolism-epigenetic interaction-based bone and dental regeneration: From impacts and mechanisms to treatment potential

Metabolic pathways exhibit fluctuating activities during bone and dental loss and defects, suggesting a regulated metabolic plasticity. Skeletal remodeling is an energy-demanding process related to altered metabolic activities. These metabolic changes are frequently associated with epigenetic modifications, including variations in the expression or activity of enzymes modified through epigenetic mechanisms, which directly or indirectly impact cellular metabolism. Metabolic reprogramming driven by bone and dental conditions alters the epigenetic landscape by modulating the activities of DNA and histone modification enzymes at the metabolite level. Epigenetic mechanisms modulate the expression of metabolic genes, consequently influencing the metabolome. The interplay between epigenetics and metabolomics is crucial in maintaining bone and dental homeostasis by preserving cell proliferation and pluripotency. This review, therefore, aims to examine the effects of metabolic reprogramming in bone and dental-related cells on the regulation of epigenetic modifications, particularly acetylation, methylation, and lactylation. We also discuss the effects of chromatin-modifying enzymes on metabolism and the potential therapeutic benefits of dietary compounds as epigenetic modulators. In this review, we highlight the inconsistencies in current research findings and suggest potential approaches to translate fundamental insights into clinical treatments for bone and tooth diseases.

MTHFD2 promotes osteoclastogenesis and bone loss in rheumatoid arthritis by enhancing CKMT1-mediated oxidative phosphorylation

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by disrupted bone homeostasis. This study investigated the effect and underlying mechanisms of one-carbon metabolism enzyme methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) on osteoclast differentiation and bone loss in RA.

METHODS

The expression of MTHFD2 was examined in CD14 + monocytes and murine bone marrow-derived macrophages (BMMs). RNA-sequencing was performed to evaluate the regulatory mechanisms of MTHFD2 on osteoclastogenesis. Extracellular flux assay, JC-1 staining, and transmission electron microscopy were used to detect mitochondrial function and energy metabolism changes during osteoclast formation. Collagen-induced arthritis (CIA) mice were used to evaluate the therapeutic effect of MTHFD2 knockdown on bone loss. Bone volume and osteoclast counts were quantified by μCT and histomorphometry.

RESULTS

Elevated MTHFD2 was observed in RA patients and CIA mice with a positive correlation to bone resorption parameters. During osteoclast formation, MTHFD2 was significantly upregulated in both human CD14 + monocytes and murine BMMs. The application of MTHFD2 inhibitor and MTHFD2 knockdown suppressed osteoclastogenesis, while MTHFD2 overexpression promoted osteoclast differentiation in vitro. RNA-sequencing revealed that MTHFD2 inhibition blocked oxidative phosphorylation (OXPHOS) in osteoclasts, leading to decreased adenosine triphosphate (ATP) production and mitochondrial membrane potential without affecting mitochondrial biogenesis. Mechanistically, inhibition of MTHFD2 downregulated the expression of mitochondrial creatine kinase 1 (CKMT1), which in turn affected phosphocreatine energy shuttle and OXPHOS during osteoclastogenesis. Further, a therapeutic strategy to knock down MTHFD2 in knee joint in vivo ameliorated bone loss in CIA mice.

CONCLUSIONS

Our findings demonstrate that MTHFD2 is upregulated in RA with relation to joint destruction. MTHFD2 promotes osteoclast differentiation and arthritic bone erosion by enhancing mitochondrial energy metabolism through CKMT1. Thus, targeting MTHFD2 may provide a potential new therapeutic strategy for tackling osteoclastogenesis and bone loss in RA.

Targeting novel regulated cell death: disulfidptosis in cancer immunotherapy with immune checkpoint inhibitors

The battle against cancer has evolved over centuries, from the early stages of surgical resection to contemporary treatments including chemotherapy, radiation, targeted therapies, and immunotherapies. Despite significant advances in cancer treatment over recent decades, these therapies remain limited by various challenges. Immune checkpoint inhibitors (ICIs), a cornerstone of tumor immunotherapy, have emerged as one of the most promising advancements in cancer treatment. Although ICIs, such as CTLA-4 and PD-1/PD-L1 inhibitors, have demonstrated clinical efficacy, their therapeutic impact remains suboptimal due to patient-specific variability and tumor immune resistance. Cell death is a fundamental process for maintaining tissue homeostasis and function. Recent research highlights that the combination of induced regulatory cell death (RCD) and ICIs can substantially enhance anti-tumor responses across multiple cancer types. In cells exhibiting high levels of recombinant solute carrier family 7 member 11 (SLC7A11) protein, glucose deprivation triggers a programmed cell death (PCD) pathway characterized by disulfide bond formation and REDOX (reduction-oxidation) reactions, termed "disulfidptosis." Studies suggest that disulfidptosis plays a critical role in the therapeutic efficacy of SLC7A11high cancers. Therefore, to investigate the potential synergy between disulfidptosis and ICIs, this study will explore the mechanisms of both processes in tumor progression, with the goal of enhancing the anti-tumor immune response of ICIs by targeting the intracellular disulfidptosis pathway.

Divergent Requirements for Glutathione Biosynthesis During Osteoclast Differentiation In Vitro and In Vivo

Glutathione (GSH) is the most abundant antioxidant in the cell, and it is responsible for neutralizing reactive oxygen species (ROS). ROS can promote osteoclast differentiation and stimulate bone resorption and are some of the primary drivers of bone loss with aging and loss of sex steroids. Despite this, the role of GSH biosynthesis during osteoclastogenesis remains controversial. Here, we show that the requirements for GSH biosynthesis during osteoclastogenesis in vitro and in vivo are unique. Using a metabolomics approach, we discovered that both oxidative stress and GSH biosynthesis increase during osteoclastogenesis. Inhibiting GSH biosynthesis in vitro via the pharmacological or genetic inhibition of glutamate cysteine ligase (GCLC) prevented osteoclast differentiation. Conversely, the genetic ablation of GCLC in myeloid cells using LysMCre resulted in a decrease in bone mass in both male and female mice. The decreased bone mass of the LysMCre;Gclcfl/fl mice was attributed to increased osteoclast numbers and elevated bone resorption. Collectively, our data provide strong genetic evidence that GSH biosynthesis is essential for the regulation of osteoclast differentiation and bone resorption in mice. Moreover, these findings highlight the necessity of complementing in vitro studies with in vivo genetic studies.

Research progress of cysteine transporter SLC7A11 in endocrine and metabolic diseases

SLC7A11, often called xCT, belongs to the SLC family of transporters, which mediates the cellular influx of cystine and the efflux of glutamate. These transport processes are crucial for synthesizing GSH, enhancing the cell's ability to mitigate oxidative stress (OS). Emerging studies highlight the pivotal role of OS in triggering and exacerbating various metabolic and endocrine disorders, underlining the critical importance of regulating SLC7A11 expression levels. This study reviews the diverse roles of SLC7A11 in endocrine and metabolic diseases, examining its relationship with the metabolism of three key nutrients: proteins and amino acids, carbohydrates, and lipids. Additionally, the involvement of SLC7A11 in the onset and development of various common endocrine and metabolic disorders is analyzed. Additionally, it provides an overview of the current clinical and experimental use of SLC7A11 inhibitors and agonists. This review aims to offer insightful perspectives into the involvement of SLC7A11 in endocrine and metabolic pathologies and to foster the development of innovative therapeutic strategies that target SLC7A11.

GRAMMAR-Lambda Delivers Efficient Understanding of the Genetic Basis for Head Size in Catfish

The shape of the skull plays a crucial role in the evolution and adaptation of species to their environments. In the case of aquaculture fish, the size of the head is also an important economic trait, as it is linked to fillet yield and ornamental value. This study applies our GRAMMAR-Lambda method to perform a genome-wide association study analysis on loci related to head size in catfish. Compared with traditional GWAS methods, the GRAMMAR-Lambda method offers higher computational efficiency, statistical power, and stability, especially in complex population structures. This research identifies many candidate genes closely related to cranial morphology in terms of head length, width, and depth in catfish, including bmpr1bb, fgfrl1b, nipbl, foxp2, and pax5, etc. Based on the results of gene-gene interaction analysis, we speculate that there may be frequent genetic interactions between chromosome 19 and chromosome 29 in bone development. Additionally, many candidate genes, gene families, and mechanisms (such as SOCE mechanisms) affecting skeletal development and morphology have been identified. These findings contribute to our understanding of the genetic architecture of head size and will support marker-assisted breeding in aquaculture, also reflecting the potential application of the GRAMMAR-Lambda method in genetic studies of complex traits.

Unlocking the potential of histone modification in regulating bone metabolism

Bone metabolism plays a crucial role in maintaining normal bone tissue homeostasis and function. Imbalances between bone formation and resorption can lead to osteoporosis, osteoarthritis, and other bone diseases. The dynamic and complex process of bone remodeling is driven by various factors, including epigenetics. Histone modification, one of the most important and well-studied components of epigenetic regulation, has emerged as a promising area of research in bone metabolism. Different histone proteins and modification sites exert diverse effects on osteogenesis and osteoclastogenesis. In this review, we summarize recent progress in understanding histone modifications in bone metabolism, including specific modification sites and potential regulatory enzymes. Comprehensive knowledge of histone modifications in bone metabolism could reveal new therapeutic targets and treatment strategies for bone diseases.

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.

Nanographene Oxide Promotes Angiogenesis by Regulating Osteoclast Differentiation and Platelet-Derived Growth Factor Secretion

An imbalanced system of angiogenesis-osteoblasts-osteoclasts is regarded as the main factor in bone remodeling dysfunction diseases or osseointegration loss. Osteoclast precursors are the key cells that accelerate bone-specific angiogenesis and maintain normal osteoblast and osteoclast function. Graphene oxide is an effective scaffold surface modification agent with broad application prospects in bone tissue engineering. However, the effect of graphene oxide on the interaction between osteoclasts and angiogenesis has not yet been elucidated. In this study, a rat calvarial defect model was established and treated with an electrochemically derived nanographene oxide (ENGO) hydrogel. Higher angiogenesis and platelet-derived growth factor (PDGF) B in preosteoclasts were observed in the ENGO group compared with that in the control group. Moreover, in vitro experiments demonstrate the efficacy of ENGO in substantially reducing the expression of the receptor activator of nuclear factor-kappaB ligand (RANKL)-induced osteoclast-associated markers and inhibiting bone resorption activity. Additionally, ENGO enhances the secretion of the osteoclast-derived coupling factor PDGF-BB and promotes angiogenesis. Our investigation revealed the crucial role of isocitrate dehydrogenase 1 (IDH1) in the ENGO-mediated regulation of osteoclast differentiation and PDGF-BB secretion. The decreased expression of IDH1 reduces the level of histone lysine demethylase 7A (KDM7A) and subsequently increases the H3K9me2 level in the cathepsin K promoter region. In summary, we found that ENGO promotes angiogenesis by inhibiting the maturity of RANKL-induced osteoclasts and enhancing PDGF-BB secretion. These results indicate that ENGO holds promise for the application in fostering osteoclast-endothelial cell crosstalk, providing an effective strategy for treating bone resorption and osteoclast-related bone loss diseases.

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.

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.