BCAT1 promotes osteoclast maturation by regulating branched-chain amino acid metabolism

RUNX1::ETO and CBFβ::MYH11 converge on aberrant activation of BCAT1 to confer a therapeutic vulnerability in core-binding factor-acute myeloid leukaemia

Effectively targeting transcription factors in therapeutic interventions remains challenging, especially in core-binding factor-acute myeloid leukaemia (CBF-AML) characterized by RUNX1::ETO and CBFβ::MYH11 fusions. However, recent studies have drawn attention towards aberrant amino acid metabolisms as actionable therapeutic targets. Here, by integrating the expression profile and genetic makeup in AML cohort, we found higher BCAT1 expression in CBF-AML patients compared with other subtypes. Metabolic profiling revealed that high BCAT1 expression led to reprogrammed branch amino acid metabolism in CBF-AML and was associated with sphingolipid pathway relating to the fitness of leukaemia cells, supported by transcriptomic profiling. Mechanistically, we demonstrated in cell lines and primary patient samples that BCAT1 was directly activated by RUNX1::ETO and CBFβ::MYH11 fusion proteins similarly in a RUNX1-dependent manner through rewiring chromatin conformation at the BCAT1 gene locus. Furthermore, BCAT1 inhibition resulted in blunted cell cycle, enhanced apoptosis and myeloid differentiation of CBF-AML cells in vitro, and alleviated leukaemia burden and prolonged survival in vivo. Importantly, pharmacological inhibition of BCAT1 using the specific inhibitor Gabapentin demonstrated therapeutic effects, as evidenced by delayed leukaemia progression and improved survival in vivo. In conclusion, our study uncovers BCAT1 as a genetic vulnerability and a promising targeted therapeutic opportunity for CBF-AML.

The Role of Branched Chain Ketoacid Dehydrogenase Kinase (BCKDK) in Skeletal Muscle Biology and Pathogenesis

Muscle wasting can be caused by nutrition deficiency and inefficient metabolism of amino acids, including Branched Chain Amino Acids (BCAAs). Branched Chain Amino Acids are a major contributor to the metabolic needs of healthy muscle and account for over a tenth of lean muscle mass. Branched chain alpha-ketoacid dehydrogenase (BCKD) is the rate limiting enzyme of BCAA metabolism. Inhibition of BCKD is achieved through a reversible phosphorylation event by Branched Chain a-ketoacid dehydrogenase kinase (BCKDK). Our study set out to determine the importance of BCKDK in the maintenance of skeletal muscle. We used the Gene Expression Omnibus Database to understand the role of BCKDK in skeletal muscle pathogenesis, including aging, muscular disease, and interrupted muscle metabolism. We found BCKDK expression levels were consistently decreased in pathologic conditions. These results were most consistent when exploring muscular disease followed by aging. Based on our findings, we hypothesize that decreased BCKDK expression alters BCAA catabolism and impacts loss of normal muscle integrity and function. Further research could offer valuable insights into potential therapeutic strategies for addressing muscle-related disorders.

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.

Energy homeostasis in the bone

The bone serves as an energy reservoir and actively engages in whole-body energy metabolism. Numerous studies have determined fuel requirements and bioenergetic properties of bone under physiological conditions as well as the dysregulation of energy metabolism associated with bone metabolic diseases. Here, we review the main sources of energy in bone cells and their regulation, as well as the endocrine role of the bone in systemic energy homeostasis. Moreover, we discuss metabolic changes that occur as a result of osteoporosis. Exploration in this area will contribute to an enhanced comprehension of bone energy metabolism, presenting novel possibilities to address metabolic diseases.

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.

Absorption and transport properties of a codfish-derived peptide and its protective effect on bone loss in ovariectomized mice

A potential osteogenic tetradecapeptide with the amino acid sequence GETNPADSKPGSIR (P-GM-2) was identified from Gadus morhua. The present study aimed to elucidate its absorption and transport properties using Caco-2/HT29-MTX co-culture monolayers and to evaluate its osteogenic activity using an ovariectomized mouse model. The results showed that P-GM-2 could cross Caco-2/HT29-MTX co-culture barriers intactly with an apparent permeability coefficient of 4.02 × 10-6 cm s-1via the TJ-mediated passive paracellular pathway. Pharmacokinetic results revealed that P-GM-2 was detectable in the blood of mice within 5 min of oral administration and reached its maximum concentration at 30 min. Furthermore, the oral administration of P-GM-2 for a duration of three months has been found to effectively regulate the secretion of key markers of bone turnover, thereby protecting against bone microstructure degeneration and bone loss in ovariectomized mice. Importantly, no toxicity related to the treatment was observed. Taken together, these findings offer valuable insights into the absorption and transport mechanisms of P-GM-2, highlighting its potential as a safe and effective active ingredient for preventing osteoporosis.

Gut Clostridium sporogenes-derived indole propionic acid suppresses osteoclast formation by activating pregnane X receptor

Bone homeostasis is maintained by osteoclast-mediated bone resorption and osteoblast-mediated bone formation. A dramatic decrease in estrogen levels in postmenopausal women leads to osteoclast overactivation, impaired bone homeostasis, and subsequent bone loss. Changes in the gut microbiome affect bone mineral density. However, the role of the gut microbiome in estrogen deficiency-induced bone loss and its underlying mechanism remain unknown. In this study, we found that the abundance of Clostridium sporogenes (C. spor.) and its derived metabolite, indole propionic acid (IPA), were decreased in ovariectomized (OVX) mice. In vitro assays suggested that IPA suppressed osteoclast differentiation and function. At the molecular level, IPA suppressed receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced pregnane X receptor (PXR) ubiquitination and degradation, leading to increased binding of remaining PXR with P65. In vivo daily IPA administration or repeated C. spor. colonization protected against OVX-induced bone loss. To protect live bacteria from the harsh gastric environment and delay the emptying of orally administered C. spor. from the intestine, a C. spor.-encapsulated silk fibroin (SF) hydrogel system was developed, which achieved bone protection in OVX mice comparable to that achieved with repeated germ transplantation or daily IPA administration. Overall, we found that gut C. spor.-derived IPA was involved in estrogen deficiency-induced osteoclast overactivation by regulating the PXR/P65 complex. The C. spor.-encapsulated SF hydrogel system is a promising tool for combating postmenopausal osteoporosis without the disadvantages of repeated germ transplantation.

Anti‑osteoclastogenic effect of fermented mealworm extract by inhibiting RANKL‑induced NFATc1 action

Augmented osteoclast activity and differentiation can lead to destructive bone diseases, such as arthritis and osteoporosis. Therefore, modulating osteoclastogenesis and differentiation may serve to be a possible strategy for treating such diseases. Tenebrio molitor larvae, also known as mealworms, are considered a good source of protein with nutritional value, digestibility, flavor and functional properties, such as antioxidant, anti-diabetic and anti-obesity effects. However, the role of mealworms in osteoclastogenesis remains poorly understood. The present study therefore investigated the effects of fermented mealworm extract (FME) on receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis in bone marrow-derived macrophages (BMMs) whilst also attempting to understand the underlying mechanism, if any. The cells treated with RANKL were used as the negative control. To prepare FME, defatted mealworm powder was fermented with a Saccharomyces cerevisiae strain, and then extracted with fermented alcohol. Cell viability of BMMs isolated from 5-week-old Institute of Cancer Research mice was measured using Cell Counting Kit-8 assay. Subsequently, the effects of FME on osteoclast differentiation were measured using tartrate-resistant acid phosphatase (TRAP) staining. In addition, expression of markers associated with osteoclast differentiation was assessed by reverse transcription-quantitative PCR. Expression of nuclear factor of activated T-cells cytoplasmic 1 (NFATc1) was assessed by western blotting. TRAP staining revealed that FME inhibited osteoclast differentiation in a dose-dependent manner (10-100 µg/ml) without causing cytotoxicity. Specifically, the formation of osteoclasts appear to have been suppressed by FME as indicated by the reduction in the number of TRAP-positive multinucleated cells observed. Furthermore, FME treatment significantly decreased the mRNA expression of c-Fos, whilst also significantly decreasing the expression of NFATc1 on both protein and mRNA levels. c-Fos and NFATc1 are transcription factors that can regulate osteoclast differentiation. FME treatment also reduced the expression of genes associated with osteoclast differentiation and function, including dendritic cell-specific transmembrane protein, osteoclast associated Ig-like receptor, Cathepsin K and TRAP, compared with that in the control group. Subsequently, FME was found to effectively suppress RANKL-induced osteoclast differentiation compared with that by the non-fermented mealworm extract. These findings suggest that FME may confer anti-osteoclastogenic effects, providing insights into its potential application in treatment of osteoporosis.

Osteoclast Cancer Cell Metabolic Cross-talk Confers PARP Inhibitor Resistance in Bone Metastatic Breast Cancer

The majority of patients with late-stage breast cancer develop distal bone metastases. The bone microenvironment can affect response to therapy, and uncovering the underlying mechanisms could help identify improved strategies for treating bone metastatic breast cancer. Here, we observed that osteoclasts reduced the sensitivity of breast cancer cells to DNA damaging agents, including cisplatin and the PARP inhibitor (PARPi) olaparib. Metabolic profiling identified elevated glutamine production by osteoclasts. Glutamine supplementation enhanced the survival of breast cancer cells treated with DNA damaging agents, while blocking glutamine uptake increased sensitivity and suppressed bone metastasis. GPX4, the critical enzyme responsible for glutathione oxidation, was upregulated in cancer cells following PARPi treatment through stress-induced ATF4-dependent transcriptional programming. Increased glutamine uptake and GPX4 upregulation concertedly enhanced glutathione metabolism in cancer cells to help neutralize oxidative stress and generate PARPi resistance. Analysis of paired patient samples of primary breast tumors and bone metastases revealed significant induction of GPX4 in bone metastases. Combination therapy utilizing PARPi and zoledronate, which blocks osteoclast activity and thereby reduces the microenvironmental glutamine supply, generated a synergistic effect in reducing bone metastasis. These results identify a role for glutamine production by bone-resident cells in supporting metastatic cancer cells to overcome oxidative stress and develop resistance to DNA-damaging therapies.

SIGNIFICANCE

Metabolic interaction between osteoclasts and tumor cells contributes to resistance to DNA-damaging agents, which can be blocked by combination treatment with PARP and osteoclast inhibitors to reduce bone metastatic burden.

Unraveling the intricacies of osteoclast differentiation and maturation: insight into novel therapeutic strategies for bone-destructive diseases

Osteoclasts are the principal cells that efficiently resorb bone. Numerous studies have attempted to reveal the molecular pathways leading to the differentiation and activation of osteoclasts to improve the treatment and prevention of osteoporosis and other bone-destructive diseases. While the cumulative knowledge of osteoclast regulatory molecules, such as receptor activator of nuclear factor-kB ligand (RANKL) and nuclear factor of activated T cells 1 (NFATc1), contributes to the understanding of the developmental progression of osteoclasts, little is known about how the discrete steps of osteoclastogenesis modify osteoclast status but not the absolute number of osteoclasts. The regulatory mechanisms involved in osteoclast maturation but not those involved in differentiation deserve special attention due to their potential use in establishing a more effective treatment strategy: targeting late-phase differentiation while preserving coupled bone formation. Recent studies have shed light on the molecules that govern late-phase osteoclast differentiation and maturation, as well as the metabolic changes needed to adapt to shifting metabolic demands. This review outlines the current understanding of the regulation of osteoclast differentiation, as well as osteoclast metabolic adaptation as a differentiation control mechanism. Additionally, this review introduces molecules that regulate the late-phase osteoclast differentiation and thus minimally impact coupled bone formation.

Proteomic profiling of human menisci from mild joint degeneration and end-stage osteoarthritis versus healthy controls

Objective

To gain new insight into the molecular changes of the meniscus by comparing the proteome profiles of healthy controls with mild degeneration and end-stage osteoarthritis (OA).

Method

We obtained tissue plugs from lateral and medial menisci of 37 individuals (central part of the posterior horn) classified as healthy (n ​= ​12), mild signs of joint damage (n ​= ​13) and end-stage OA (n ​= ​12). The protein profile was analysed by nano-liquid chromatography-mass spectrometry using data-independent acquisition and quantified by Spectronaut. Linear-mixed effects modelling was applied to extract the between-group comparisons.

Results

A similar protein profile was observed for the mild group as compared to healthy controls while the most different group was end-stage OA mainly for the medial compartment. When a pattern of gradual change in protein levels from healthy to end-stage OA was required, a 42-proteins panel was identified, suggesting a potential role in OA development. The levels of QSOX1 were lower and G6PD higher in the mild group following the proposed protein abundance pattern. Qualitative protein changes suggest lower levels of CYTL1 as a potential biomarker of early joint degradation.

Conclusion

For future targeted proteomic approaches, we propose a candidate panel of 42 proteins based on gradually altered meniscal posterior horn protein abundance patterns associated with joint degradation.

Novel Insights into Osteoclast Energy Metabolism

PURPOSE OF REVIEW

Osteoclasts are crucial for the dynamic remodeling of bone as they resorb old and damaged bone, making space for new bone. Metabolic reprogramming in these cells not only supports phenotypic changes, but also provides the necessary energy for their highly energy-consuming activity, bone resorption. In this review, we highlight recent developments in our understanding of the metabolic adaptations that influence osteoclast behavior and the overall remodeling of bone tissue.

RECENT FINDINGS

Osteoclasts undergo metabolic reprogramming to meet the energy demands during their transition from precursor cells to fully mature bone-resorbing osteoclasts. Recent research has made considerable progress in pinpointing crucial metabolic adaptations and checkpoint proteins in this process. Notably, glucose metabolism, mitochondrial biogenesis, and oxidative respiration were identified as essential pathways involved in osteoclast differentiation, cytoskeletal organization, and resorptive activity. Furthermore, the interaction between these pathways and amino acid and lipid metabolism adds to the complexity of the process. These interconnected processes can function as diverse fuel sources or have independent regulatory effects, significantly influencing osteoclast function. Energy metabolism in osteoclasts involves various substrates and pathways to meet the energetic requirements of osteoclasts throughout their maturation stages. This understanding of osteoclast biology may provide valuable insights for modulating osteoclast activity during the pathogenesis of bone-related disorders and may pave the way for the development of innovative therapeutic strategies.

Metabolic control of cancer metastasis: role of amino acids at secondary organ sites

Most cancer-related deaths are caused by the metastases, which commonly develop at multiple organ sites including the brain, bone, and lungs. Despite longstanding observations that the spread of cancer is not random, our understanding of the mechanisms that underlie metastatic spread to specific organs remains limited. However, metabolism has recently emerged as an important contributor to metastasis. Amino acids are a significant nutrient source to cancer cells and their metabolism which can serve to fuel biosynthetic pathways capable of facilitating cell survival and tumor expansion while also defending against oxidative stress. Compared to the primary tumor, each of the common metastatic sites exhibit vastly different nutrient compositions and environmental stressors, necessitating the need of cancer cells to metabolically thrive in their new environment during colonization and outgrowth. This review seeks to summarize the current literature on amino acid metabolism pathways that support metastasis to common secondary sites, including impacts on immune responses. Understanding the role of amino acids in secondary organ sites may offer opportunities for therapeutic inhibition of cancer metastasis.

Plasma Levels of Branched Chain Amino Acids, Incident Hip Fractures, and Bone Mineral Density of the Hip and Spine

OBJECTIVE

Branched chain amino acids (BCAA) are building blocks for protein, an essential component of bone. However, the association of plasma levels of BCAA with fractures in populations outside of Hong Kong or with hip fractures in particular is not known. The purpose of these analyses was to determine the relationship of BCAA including valine, leucine, and isoleucine and total BCAA (SD of the sum of Z-scores for each BCAA) with incident hip fractures and bone mineral density (BMD) of the hip and lumbar spine in older African American and Caucasian men and women in the Cardiovascular Health Study.

DESIGN

Longitudinal analyses of association of plasma levels of BCAA with incident hip fractures and cross-sectional BMD of the hip and lumbar spine from the Cardiovascular Health Study.

SETTING

Community.

PARTICIPANTS

A total of 1850 men (38% of cohort) and women; mean age 73 years.

MAIN OUTCOME MEASURES

Incident hip fractures and cross-sectional BMD of the total hip, femoral neck, and lumbar spine.

RESULTS

In fully adjusted models, over 12 years of follow-up, we observed no significant association between incident hip fracture and plasma values of valine, leucine, isoleucine, or total BCAA per 1 SD higher of each BCAA. Plasma values of leucine but not valine, isoleucine, or total BCAA, were positively and significantly associated with BMD of the total hip (P = .03) and femoral neck (P = .02), but not the lumbar spine (P = .07).

CONCLUSIONS

Plasma levels of the BCAA leucine may be associated with higher BMD in older men and women. However, given the lack of significant association with hip fracture risk, further information is needed to determine whether BCAAs would be novel targets for osteoporosis therapies.

The biological functions and metabolic pathways of valine in swine

Valine is an essential amino acid and a type of branched-chain amino acid. Due to the involvement of branched-chain amino acids in various metabolic pathways, there has been a surge of interests in valine nutrition and its role in animal physiology. In pigs, the interactions between valine and other branched-chain amino acids or aromatic amino acids are complex. In this review, we delve into the interaction mechanism, metabolic pathways, and biological functions of valine. Appropriate valine supplementation not only enhances growth and reproductive performances, but also modulates gut microbiota and immune functions. Based on past observations and interpretations, we provide recommended feed levels of valine for weaned piglets, growing pigs, gilts, lactating sows, barrows and entire males. The summarized valine nutrient requirements for pigs at different stages offer valuable insights for future research and practical applications in animal husbandry.

BAP1 promotes osteoclast function by metabolic reprogramming

Treatment of osteoporosis commonly diminishes osteoclast number which suppresses bone formation thus compromising fracture prevention. Bone formation is not suppressed, however, when bone degradation is reduced by retarding osteoclast functional resorptive capacity, rather than differentiation. We find deletion of deubiquitinase, BRCA1-associated protein 1 (Bap1), in myeloid cells (Bap1∆LysM), arrests osteoclast function but not formation. Bap1∆LysM osteoclasts fail to organize their cytoskeleton which is essential for bone degradation consequently increasing bone mass in both male and female mice. The deubiquitinase activity of BAP1 modifies osteoclast function by metabolic reprogramming. Bap1 deficient osteoclast upregulate the cystine transporter, Slc7a11, by enhanced H2Aub occupancy of its promoter. SLC7A11 controls cellular reactive oxygen species levels and redirects the mitochondrial metabolites away from the tricarboxylic acid cycle, both being necessary for osteoclast function. Thus, in osteoclasts BAP1 appears to regulate the epigenetic-metabolic axis and is a potential target to reduce bone degradation while maintaining osteogenesis in osteoporotic patients.

Amino Acid Metabolism in Bone Metastatic Disease

PURPOSE OF REVIEW

Breast and prostate tumors frequently metastasize to the bone, but the underlying mechanisms for osteotropism remain elusive. An emerging feature of metastatic progression is metabolic adaptation of cancer cells to new environments. This review will summarize the recent advances on how cancer cells utilize amino acid metabolism during metastasis, from early dissemination to interactions with the bone microenvironment.

RECENT FINDINGS

Recent studies have suggested that certain metabolic preferences for amino acids may be associated with bone metastasis. Once in the bone microenvironment, cancer cells encounter a favorable microenvironment, where a changing nutrient composition of the tumor-bone microenvironment may alter metabolic interactions with bone-resident cells to further drive metastatic outgrowth. Enhanced amino acid metabolic programs are associated with bone metastatic disease and may be further augmented by the bone microenvironment. Additional studies are necessary to fully elucidate the role of amino acid metabolism on bone metastasis.

Complex Extract of Polygonatum sibiricum and Nelumbinis semen Improves Menopause Symptoms via Regulation of Estrogen Receptor Beta in an Ovariectomized Rat Model

Menopause is a hormone-deficiency state that causes facial flushing, vaginal dryness, depression, anxiety, insomnia, obesity, osteoporosis, and cardiovascular disease as ovarian function decreases. Hormone-replacement therapy is mainly used to treat menopause; however, its long-term use is accompanied by side effects such as breast cancer and endometriosis. To identify the effect of a complex extract of Polygonatum sibiricum (PS) and Nelumbinis semen (NS) on improving menopause without side effects, an ovariectomized rat model was established to analyze several menopause symptoms. Compared to single extracts, the complex extract restored vaginal epithelial cell thickness and decreased serotonin concentration by increasing the estrogen receptors ERα (ESR1) and ERβ (ESR2), depending on the ratio. Although the complex extract exerted a lower weight-loss effect than the single extracts, improved blood-lipid metabolism was observed after increasing high-density lipoprotein cholesterol levels and decreasing low-density lipoprotein cholesterol and triglyceride levels, and ovariectomy-induced osteoporosis was alleviated by suppressing osteoclast production. Thus, by increasing only ERβ expression without regulating ERα expression in the uterus, the complex extract of PS and NS may be a natural treatment for improving menopause symptoms without side effects, such as endometriosis.

BCAT1, as a prognostic factor for HCC, can promote the development of liver cancer through activation of the AKT signaling pathway and EMT

More and more studies have shown that Branched chain amino acid transaminase 1 (BCAT1) is involved in the occurrence and development of a variety of tumors. However, the mechanism of its occurrence and development in hepatocellular carcinoma (HCC) remains unclear. Here, we demonstrated the relationship between BCAT1 and AKT signaling pathway, as well as EMT, and the clinical significance of BCAT1 by using BCAT1 expression in 5 cell lines and 113 liver cancer and non-liver cancer tissue samples. The results showed that the expression of AKT was positively correlated with BCAT1 in HCC tissues, and BCAT1 could promote the progression of HCC cells through the AKT signaling pathway. Clinical analysis and Bioinformatics technology analysis revealed that BCAT1 was correlated with poor prognosis, and BCAT1 expression in the HCC tissues was evidently correlated with tumor number, vascular invasion, Edmondson grade and TNM stage (P < 0.05). In vitro studies showed that BCAT1 increased the invasion and migration of in MHCC-97H cells a d Huh7 cells. By inhibiting the expression of the BCAT1 gene, we detected the corresponding changes in the expression levels of Twist, E-cadherin and Vimentin, confirming that BCAT1 may promote the invasion and migration of HCC cells through epithelial-mesenchymal transformation (EMT). Overall, BCAT1 can activate AKT signaling pathway and EMT to promote the development and metastasis of HCC cells. this study may provide new ideas and directions for cancer diagnosis and treatment.

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.

Amino acid metabolism in primary bone sarcomas

Primary bone sarcomas, including osteosarcoma (OS) and Ewing sarcoma (ES), are aggressive tumors with peak incidence in childhood and adolescence. The intense standard treatment for these patients consists of combined surgery and/or radiation and maximal doses of chemotherapy; a regimen that has not seen improvement in decades. Like other tumor types, ES and OS are characterized by dysregulated cellular metabolism and a rewiring of metabolic pathways to support the biosynthetic demands of malignant growth. Not only are cancer cells characterized by Warburg metabolism, or aerobic glycolysis, but emerging work has revealed a dependence on amino acid metabolism. Aside from incorporation into proteins, amino acids serve critical functions in redox balance, energy homeostasis, and epigenetic maintenance. In this review, we summarize current studies describing the amino acid metabolic requirements of primary bone sarcomas, focusing on OS and ES, and compare these dependencies in the normal bone and malignant tumor contexts. We also examine insights that can be gleaned from other cancers to better understand differential metabolic susceptibilities between primary and metastatic tumor microenvironments. Lastly, we discuss potential metabolic vulnerabilities that may be exploited therapeutically and provide better-targeted treatments to improve the current standard of care.