Muscle-derived extracellular vesicles improve disuse-induced osteoporosis by rebalancing bone formation and bone resorption

Bone and muscle crosstalk in ageing and disease

Interorgan communication between bone and skeletal muscle is central to human health. A dysregulation of bone-muscle crosstalk is implicated in several age-related diseases. Ageing-associated changes in endocrine, inflammatory, nutritional and biomechanical stimuli can influence the differentiation capacity, function and survival of mesenchymal stem cells and bone-forming and muscle-forming cells. Consequently, the secretome phenotype of bone and muscle cells is altered, leading to impaired crosstalk and, ultimately, catabolism of both tissues. Adipose tissue acts as a third player in the bone-muscle interaction by secreting factors that affect bone and muscle cells. Physical exercise remains the key biological stimulus for bone-muscle crosstalk, either directly via the release of cytokines from bone, muscle or adipocytes, or indirectly through extracellular vesicles. Overall, bone-muscle crosstalk is considered an inherent process necessary to maintain the structure and function of both tissues across the life cycle. This Review summarizes the latest biomedical advances in bone-muscle crosstalk as it pertains to human ageing and disease. We also outline future research priorities to accommodate the understanding of this rapidly emerging field.

The existing evidence for the use of extracellular vesicles in the treatment of osteoporosis: a review

Osteoporosis is a systemic metabolic bone disease characterized by decreased bone mass, microstructural deterioration, and increased fracture risk. The crucial role of extracellular vesicles (EVs) in the occurrence and development of osteoporosis has garnered attention, with vesicle-based treatments showing significant promise. Compared to conventional osteoporosis medications, EVs possess characteristics of naturalness, selectivity, and adaptability, and more importantly, they have negligible side effects. Hence, this review discusses the applications of natural and engineered EVs in osteoporosis are comprehensively outlined. Unfortunately, the absence of consensus on the extraction, purification, characterization, and storage of EVs has resulted in a lack of clinical evidence supporting their application in patients with osteoporosis. Although significant progress is still needed before the clinical use of EVs can be achieved, their substantial potential remains undeniable. Moreover, considering the complexity of bone metabolism in osteoporosis and the heterogeneity of EVs, further investigation into the functional subpopulations of different exosomes will facilitate their application.

Exercise for Postmenopausal Bone Health - Can We Raise the Bar?

PURPOSE OF REVIEW

This review summarises the latest evidence on effects of exercise on falls prevention, bone mineral density (BMD) and fragility fracture risk in postmenopausal women, explores hypotheses underpinning exercise-mediated effects on BMD and sheds light on innovative concepts to better understand and harness the skeletal benefits of exercise.

RECENT FINDINGS

Multimodal exercise programs incorporating challenging balance exercises can prevent falls. Emerging clinical trial evidence indicates supervised progressive high-intensity resistance and impact training (HiRIT) is efficacious in increasing lumbar spine BMD and is safe and well-tolerated in postmenopausal women with osteoporosis/osteopenia. There remains uncertainty regarding durability of this load-induced osteogenic response and safety in patients with recent fractures. Muscle-derived myokines and small circulating extracellular vesicles have emerged as potential sources of exercise-induced muscle-bone crosstalk but require validation in postmenopausal women. Exercise has the potential for multi-modal skeletal benefits with i) HiRIT to build bone, and ii) challenging balance exercises to prevent falls, and ultimately fractures. The therapeutic effect of such exercise in combination with osteoporosis pharmacotherapy should be considered in future trials.

In Vivo Reprogramming of Tissue-Derived Extracellular Vesicles for Treating Chronic Tissue Injury Through Metabolic Engineering

Extracellular vesicles (EVs) have emerged as promising therapeutics for regenerative medicine, but the efficacy of current exogenous EV-based therapies for treating chronic tissue injury is still unsatisfactory. Exercise can affect skeletal muscle EV secretion and that this process regulates the systemic health-promoting role of exercise, suggesting that fine-tuning of endogenous tissue EV secretion may provide a new therapeutic avenue. Here, this work reports that in vivo reprogramming of EV secretion via metabolic engineering is a promising strategy for treating chronic diseases. Briefly, exercise enhanced mitochondrial metabolism and EV production in healthy skeletal muscles, and EVs from healthy skeletal muscles subjected to exercise or metabolic engineering (boosting mitochondrial biogenesis via AAV-mediated muscle-specific TFAM overexpression) exerted cellular protective effects in vitro. In injured skeletal muscles, in vivo metabolic engineering therapy could reprogram EV secretion patterns (reducing pathological EV compositions while increasing beneficial EV compositions) by regulating multiple EV biogenesis and cargo sorting pathways. Reprogrammed muscle-derived EVs could reach major organs and tissues via the circulation and then simultaneously attenuated multiple-tissue (e.g., muscle and kidney) injury in chronic kidney disease. This study highlights that in vivo reprogramming of tissue-derived EVs via a metabolic engineering approach is a potential strategy for treating diverse chronic diseases.

Muscle-Derived Bioactive Factors: MyoEVs and Myokines

Overview of the functions and applications of myokines and MyoEVs.

Molecular mechanism of mitochondrial autophagy mediating impaired energy metabolism leading to osteoporosis

Osteoporosis (OP) is a bone metabolic disease caused by decreased bone mass leading to destruction of bone microstructure. Treatment of OP is characterized by a lifelong nature, causing extreme financial and psychological burdens to patients. Hormonal abnormalities, cellular autophagy, Ferroptosis, and oxidative stress are all part of the intricate and varied pathophysiology of OP. Recent research has revealed that mitochondrial dysfunction is a significant factor in the onset and progression of OP. By regulating bone marrow mesenchymal stem cell differentiation through various signaling pathways and cytokines, abnormal mitochondrial energy metabolism brought on by oxidative stress processes impacts osteoblast and osteoclast proliferation and differentiation, causing an imbalance in bone metabolism that ultimately results in OP. Therefore, one possible method to prevent and manage OP may be to use mitochondria as a carrier to trigger osteogenic differentiation of bone marrow mesenchymal stem cells from mitochondrial energy consumption, oxidative stress, autophagy, and osteoclast death. In order to offer some theoretical references and therapeutic approaches for the clinical prevention and treatment of OP, we will examine the pathophysiology of OP from mitochondrial dysfunction in this work.

Muscle-derived extracellular vesicles mediate crosstalk between skeletal muscle and other organs

Skeletal muscle (SKM) has crucial roles in locomotor activity and posture within the body and also functions have been recognized as an actively secretory organ. Numerous bioactive molecules are secreted by SKM and transported by extracellular vesicles (EVs), a novel class of mediators of communication between cells and organs that contain various types of cargo molecules including lipids, proteins and nucleic acids. SKM-derived EVs (SKM-EVs) are intercellular communicators with significant roles in the crosstalk between SKM and other organs. In this review, we briefly describe the biological characteristics, composition, and uptake mechanisms of EVs, particularly exosomes, comprehensively summarize the regulatory effects of SKM-EVs on the function of, which include myogenesis, muscle repair and regeneration, as well as metabolic regulation. Furthermore, we explore the impact of SKM- EVs on various organs including bone, the cardiovascular system, adipose tissue, and nervous system. As emerging evidence suggests that SKM-EVs are involved in the development and regulation of type 2 diabetes (T2D), systemic inflammation, and other chronic diseases, we also highlight the potential of SKM-EVs as therapeutic targets and diagnostic biomarkers, emphasizing the need for further research to elucidate the complex mechanisms underlying intercellular communication in physiological and pathological contexts.

Selection of the Anti-Osteoporosis Active Ingredients of Fructus Psoraleae-Eucommia-Drynariae Rhizoma Based on Solid-Phase Bio-Cell Chromatography and HPLC-MS Analysis

Osteoporosis (OP) is a prevalent metabolic bone disease globally. Currently, the development of Traditional Chinese Medicine (TCM) resources to unblock joints, strengthen bones, and enhance muscle function to regulate anti-osteogenic and anabolic metabolism and thus reshape intraosseous homeostasis was an effective way to alleviate OP. The F-E-D formula, comprising Fructus Psoraleae, Eucommia, and Drynariae Rhizoma, has shown efficacy in treating OP. However, its complex natural components necessitate the screening and simplification of bioactive compounds to further elucidate their therapeutic mechanisms and enhance therapeutic efficacy. In this study, we first used drug-target binding to produce different effects, which in turn exhibited different retention characteristics on the stationary phase. Using osteoblasts and osteoclasts as stationary phases, a chromatographic system (Solid-phase Bio-cell Chromatography, SBC) had been constructed to mimic the drug-target interaction, and the separation, analysis, and bioactivity screening of the chemical components of F-E-D had been performed. Then, the above collected eluates were analyzed by fine metabolomics, and 95 effective metabolites were initially screened and combined with database screening to finally select betaine, L-fucose, and itaconic acid as potentially active candidate compound monomers for the interaction with osteoblast-osteoclast in F-E-D. In terms of cell validation experiments, we found that the screened active monomers significantly inhibited the formation of osteoclasts, and the itaconic acid-treated group played a significant inhibitory effect on the expression of inflammatory factors TNF-α and IL-6. The above experimental data showed that the monomeric active ingredients in TCM could be effectively screened by solid-phase bio-chromatography and HPLC-MS, and the in vitro cellular experiments verified that the active monomers of TCM slowed down the progression of OP by inhibiting osteoclast production and alleviating the expression of inflammation.

Novel osteogenic peptide from bovine bone collagen hydrolysate: Targeted screening, molecular mechanism, and stability analysis

This study aimed to screen for a novel osteogenic peptide based on the calcium-sensing receptor (CaSR) and explore its molecular mechanism and gastrointestinal stability. In this study, a novel osteogenic peptide (Phe-Ser-Gly-Leu, FSGL) derived from bovine bone collagen hydrolysate was successfully screened by molecular docking and synthesised by solid phase peptide synthesis for further analysis. Cell experiments showed that FSGL significantly enhanced the osteogenic activity of MC3T3-E1 cells by acting on CaSR, including proliferation (152.53%), differentiation, and mineralization. Molecular docking and molecular dynamics further demonstrated that FSGL was a potential allosteric activator of CaSR, that turned on the activation switch of CaSR by closing the Venus flytrap (VFT) domain and driving the two protein chains in the VFT domain to easily form dimers. In addition, 96.03% of the novel osteogenic peptide FSGL was stable during gastrointestinal digestion. Therefore, FSGL showed substantial potential for enhancing the osteogenic activity of osteoblasts. This study provided new insights for the application of CaSR in the targeted screening of osteogenic peptides to improve bone health.

The impact of exosomes on bone health: A focus on osteoporosis

Osteoporosis is a widespread chronic condition. Although standard treatments are generally effective, they are frequently constrained by side effects and the risk of developing drug resistance. A promising area of research is the investigation of extracellular vesicles (EVs), including exosomes, microvesicles, and apoptotic bodies, which play a crucial role in bone metabolism. Exosomes, in particular, have shown significant potential in both the diagnosis and treatment of osteoporosis. EVs derived from osteoclasts, osteoblasts, mesenchymal stem cells, and other sources can influence bone metabolism, while exosomes from inflammatory and tumor cells may exacerbate bone loss, highlighting their dual role in osteoporosis pathology. This review offers a comprehensive overview of EV biogenesis, composition, and function in osteoporosis, focusing on their diagnostic and therapeutic potential. We examine the roles of various types of EVs and their cargo-proteins, RNAs, and lipids-in bone metabolism. Additionally, we explore the emerging applications of EVs as biomarkers and therapeutic agents, emphasizing the need for further research to address current challenges and enhance EV-based strategies for managing osteoporosis.

Sarcopenic obesity and osteoporosis: Research progress and hot spots

Sarcopenic obesity (SO) and osteoporosis (OP) are associated with aging and obesity. The pathogenesis of SO is complex, including glucolipid and skeletal muscle metabolic disorders caused by inflammation, insulin resistance, and other factors. Growing evidence links muscle damage to bone loss. Muscle-lipid metabolism disorders of SO disrupt the balance between bone formation and bone resorption, increasing the risk of OP. Conversely, bones also play a role in fat and muscle metabolism. In the context of aging and obesity, the comprehensive review focuses on the effects of mechanical stimulation, mesenchymal stem cells (MSCs), chronic inflammation, myokines, and adipokines on musculoskeletal, at the same time, the impact of osteokines on muscle-lipid metabolism were also analyzed. So far, exercise combined with diet therapy is the most effective strategy for increasing musculoskeletal mass. A holistic treatment of musculoskeletal diseases is still in the preliminary exploration stage. Therefore, this article aims to improve the understanding of musculoskeletal -fat interactions in SO and OP, explores targets that can provide holistic treatment for SO combined with OP, and discusses current limitations and challenges. We hope to provide relevant ideas for developing specific therapies and improving disease prognosis in the future.

Integrating transcriptomic and proteomic data for a comprehensive molecular perspective on the association between sarcopenia and osteoporosis

BACKGROUND

Osteoporosis and sarcopenia are common age-related conditions characterized by the progressive loss of bone density and muscle mass, respectively. Their co-occurrence, often referred to as osteosarcopenia, presents significant challenges in elderly care due to increased fragility and functional impairment. Existing studies have identified shared pathological mechanisms between these conditions, including inflammation, hormonal imbalances, and metabolic dysregulation, but a comprehensive understanding of their molecular interplay remains incomplete.

OBJECTIVE

This study aims to deepen our understanding of the molecular interactions between sarcopenia and osteoporosis through an integrated omics approach, revealing potential therapeutic targets and biomarkers.

METHODS

Employing a combination of proteomics and transcriptomics analyses, this study analyzed bone and muscle tissue samples from patients diagnosed with osteoporosis and osteosarcopenia. Techniques included high-throughput sequencing and label-free proteomics, supported by advanced bioinformatics tools for data analysis and functional annotation of genes and proteins.

RESULTS

The study found marked differences in gene and protein expressions between osteoporosis and osteosarcopenia tissues. Specifically, genes like PDIA5, TUBB1, and CYFIP2 in bone, along with MYH7 and NCAM1 in muscle, exhibited differential expression at both mRNA and protein levels. Pathway analyses revealed the significance of oxidative-reduction balance, cellular metabolism, and immune response in the progression of these conditions. Importantly, the study pinpointed osteoclast differentiation and NF-kappa B signaling pathways as critical in the molecular dynamics of osteosarcopenia, suggesting potential targets for therapy.

CONCLUSIONS

This study utilized transcriptomics and proteomics to identify key genes and proteins impacting sarcopenia and osteoporosis, employing advanced network tools to delineate interaction networks and crucial signaling pathways. It highlighted genes like PDIA5 and TUBB1, consistently expressed in both analyses, involved in pathways such as osteoclast differentiation and cytokine interactions. These insights enhance understanding of the molecular interplay in bone and muscle degeneration with aging, suggesting directions for future research into therapeutic interventions and prevention strategies for age-related degenerative diseases.

Histone deacetylase inhibition enhances extracellular vesicles from muscle to promote osteogenesis via miR-873-3p

Regular physical activity is widely recognized for reducing the risk of various disorders, with skeletal muscles playing a key role by releasing biomolecules that benefit multiple organs and tissues. However, many individuals, particularly the elderly and those with clinical conditions, are unable to engage in physical exercise, necessitating alternative strategies to stimulate muscle cells to secrete beneficial biomolecules. Histone acetylation and deacetylation significantly influence exercise-induced gene expression, suggesting that targeting histone deacetylases (HDACs) could mimic some exercise responses. In this study, we explored the effects of the HDAC inhibitor Trichostatin A (TSA) on human skeletal muscle myoblasts (HSMMs). Our findings showed that TSA-induced hyperacetylation enhanced myotube fusion and increased the secretion of extracellular vesicles (EVs) enriched with miR-873-3p. These TSA-EVs promoted osteogenic differentiation in human bone marrow mesenchymal stem cells (hBMSCs) by targeting H2 calponin (CNN2). In vivo, systemic administration of TSA-EVs to osteoporosis mice resulted in significant improvements in bone mass. Moreover, TSA-EVs mimicked the osteogenic benefits of exercise-induced EVs, suggesting that HDAC inhibition can replicate exercise-induced bone health benefits. These results demonstrate the potential of TSA-induced muscle-derived EVs as a therapeutic strategy to enhance bone formation and prevent osteoporosis, particularly for individuals unable to exercise. Given the FDA-approved status of various HDAC inhibitors, this approach holds significant promise for rapid clinical translation in osteoporosis treatment.

Prospects and challenges of tissue-derived extracellular vesicles

Extracellular vesicles (EVs) are considered a vital component of cell-to-cell communication and represent a new frontier in diagnostics and a means to identify pathways for therapeutic intervention. Recently, studies have revealed the importance of tissue-derived EVs (Ti-EVs), which are EVs present in the interstitial spaces between cells, as they better represent the underlying physiology of complex, multicellular tissue microenvironments in biology and disease. EVs are native, lipid bilayer membraned nano-sized particles produced by all cells that are packaged with varied functional biomolecules including proteins, lipids, and nucleic acids. They are implicated in short- and long-range cellular communication and may elicit functional responses in recipient cells. To date, studies have often utilized cultured cells or biological fluids as a source for EVs that do not capture local molecular signatures of the tissue microenvironment. Recent work utilizing Ti-EVs has elucidated novel biomarkers for disease and provided insights into disease mechanisms that may lead to the development of novel therapeutic agents. Still, there are considerable challenges facing current studies. This review explores the vast potential and unique challenges for Ti-EV research and provides considerations for future studies that seek to advance this exciting field.

Extracellular vesicles may provide an alternative detoxification pathway during skeletal muscle myoblast ageing

Skeletal muscle (SM) acts as a secretory organ, capable of releasing myokines and extracellular vesicles (SM-EVs) that impact myogenesis and homeostasis. While age-related changes have been previously reported in murine SM-EVs, no study has comprehensively profiled SM-EV in human models. To this end, we provide the first comprehensive comparison of SM-EVs from young and old human primary skeletal muscle cells (HPMCs) to map changes associated with SM ageing. HPMCs, isolated from young (24 ± 1.7 years old) and older (69 ± 2.6 years old) participants, were immunomagnetically sorted based on the presence of the myogenic marker CD56 (N-CAM) and cultured as pure (100% CD56+) or mixed populations (MP: 90% CD56+). SM-EVs were isolated using an optimised protocol combining ultrafiltration and size exclusion chromatography (UF + SEC) and their biological content was extensively characterised using Raman spectroscopy (RS) and liquid chromatography mass spectrometry (LC-MS). Minimal variations in basic EV parameters (particle number, size, protein markers) were observed between young and old populations. However, biochemical fingerprinting by RS highlighted increased protein (amide I), lipid (phospholipids and phosphatidylcholine) and hypoxanthine signatures for older SM-EVs. Through LC-MS, we identified 84 shared proteins with functions principally related to cell homeostasis, muscle maintenance and transcriptional regulation. Significantly, SM-EVs from older participants were comparatively enriched in proteins involved in oxidative stress and DNA/RNA mutagenesis, such as E3 ubiquitin-protein ligase TTC3 (TTC3), little elongation complex subunit 1 (ICE1) and Acetyl-CoA carboxylase 1 (ACACA). These data suggest SM-EVs could provide an alternative pathway for homeostasis and detoxification during SM ageing.

Crosstalk between muscle and bone

Clinical studies revealed a relationship between osteoporosis and sarcopenia. Based on this background, crosstalk between muscle and bone has emerged as a novel research field in the past decade. Among the interactions that occur between muscle and bone, humoral factors, such as osteokines and myokines, affect distant muscles and bones, respectively. Recent studies proposed several important myokines that have an impact on bone, such as myostatin and irisin. Signaling by these myokines has potential as a target for drug development and biomarkers for exercise. Mechanical stress, endocrine disorders, and chronic kidney disease partly affect bone through various myokines in crosstalk between muscle and bone. Moreover, the involvement of extracellular vesicles from bone or muscle as communication tools in the interactions between muscle and bone was recently proposed. Further clinical studies are needed to clarify the significance of myokine regulation under physiological and pathophysiological states in humans.

RNA sequencing-based approaches to identifying disulfidptosis-related diagnostic clusters and immune landscapes in osteoporosis

Disulfidptosis, a newly recognized cell death triggered by disulfide stress, has garnered attention for its potential role in osteoporosis (OP) pathogenesis. Although sulfide-related proteins are reported to regulate the balance of bone metabolism in OP, the precise involvement of disulfidptosis regulators remains elusive. Herein, leveraging the GSE56815 dataset, we conducted an analysis to delineate disulfidptosis-associated diagnostic clusters and immune landscapes in OP. Subsequently, vertebral bone tissues obtained from OP patients and controls were subjected to RNA sequencing (RNA-seq) for the validation of key disulfidptosis gene expression. Our analysis unveiled seven significant disulfidptosis regulators, including FLNA, ACTB, PRDX1, SLC7A11, NUBPL, OXSM, and RAC1, distinguishing OP samples from controls. Furthermore, employing a random forest model, we identified four diagnostic disulfidptosis regulators including FLNA, SLC7A11, NUBPL, and RAC1 potentially predictive of OP risk. A nomogram model integrating these four regulators was constructed and validated using the GSE35956 dataset, demonstrating promising utility in clinical decision-making, as affirmed by decision curve analysis. Subsequent consensus clustering analysis stratified OP samples into two different disulfidptosis subgroups (clusters A and B) using significant disulfidptosis regulators, with cluster B exhibiting higher disulfidptosis scores and implicating monocyte immunity, closely linked to osteoclastogenesis. Notably, RNA-seq analysis corroborated the expression patterns of two disulfidptosis modulators, PRDX1 and OXSM, consistent with bioinformatics predictions. Collectively, our study sheds light on disulfidptosis patterns, offering potential markers and immunotherapeutic avenues for future OP management.

Roles of Myokines and Muscle-Derived Extracellular Vesicles in Musculoskeletal Deterioration under Disuse Conditions

Prolonged inactivity and disuse conditions, such as those experienced during spaceflight and prolonged bedrest, are frequently accompanied by detrimental effects on the motor system, including skeletal muscle atrophy and bone loss, which greatly increase the risk of osteoporosis and fractures. Moreover, the decrease in glucose and lipid utilization in skeletal muscles, a consequence of muscle atrophy, also contributes to the development of metabolic syndrome. Clarifying the mechanisms involved in disuse-induced musculoskeletal deterioration is important, providing therapeutic targets and a scientific foundation for the treatment of musculoskeletal disorders under disuse conditions. Skeletal muscle, as a powerful endocrine organ, participates in the regulation of physiological and biochemical functions of local or distal tissues and organs, including itself, in endocrine, autocrine, or paracrine manners. As a motor organ adjacent to muscle, bone tissue exhibits a relative lag in degenerative changes compared to skeletal muscle under disuse conditions. Based on this phenomenon, roles and mechanisms involved in the communication between skeletal muscle and bone, especially from muscle to bone, under disuse conditions have attracted widespread attention. In this review, we summarize the roles and regulatory mechanisms of muscle-derived myokines and extracellular vesicles (EVs) in the occurrence of muscle atrophy and bone loss under disuse conditions, as well as discuss future perspectives based on existing research.

The role and applications of extracellular vesicles in osteoporosis

Osteoporosis is a widely observed condition characterized by the systemic deterioration of bone mass and microarchitecture, which increases patient susceptibility to fragile fractures. The intricate mechanisms governing bone homeostasis are substantially impacted by extracellular vesicles (EVs), which play crucial roles in both pathological and physiological contexts. EVs derived from various sources exert distinct effects on osteoporosis. Specifically, EVs released by osteoblasts, endothelial cells, myocytes, and mesenchymal stem cells contribute to bone formation due to their unique cargo of proteins, miRNAs, and cytokines. Conversely, EVs secreted by osteoclasts and immune cells promote bone resorption and inhibit bone formation. Furthermore, the use of EVs as therapeutic modalities or biomaterials for diagnosing and managing osteoporosis is promising. Here, we review the current understanding of the impact of EVs on bone homeostasis, including the classification and biogenesis of EVs and the intricate regulatory mechanisms of EVs in osteoporosis. Furthermore, we present an overview of the latest research progress on diagnosing and treating osteoporosis by using EVs. Finally, we discuss the challenges and prospects of translational research on the use of EVs in osteoporosis.

Exosomal non-coding RNAs: Emerging insights into therapeutic potential and mechanisms in bone healing

Exosomes are nano-sized extracellular vesicles (EVs) released by diverse types of cells, which affect the functions of targeted cells by transporting bioactive substances. As the main component of exosomes, non-coding RNA (ncRNA) is demonstrated to impact multiple pathways participating in bone healing. Herein, this review first introduces the biogenesis and secretion of exosomes, and elucidates the role of the main cargo in exosomes, ncRNAs, in mediating intercellular communication. Subsequently, the potential molecular mechanism of exosomes accelerating bone healing is elucidated from the following four aspects: macrophage polarization, vascularization, osteogenesis and osteoclastogenesis. Then, we systematically introduce construction strategies based on modified exosomes in bone regeneration field. Finally, the clinical trials of exosomes for bone healing and the challenges of exosome-based therapies in the biomedical field are briefly introduced, providing solid theoretical frameworks and optimization methods for the clinical application of exosomes in orthopedics.

Mechanical loading intensities affect the release of extracellular vesicles from mouse bone marrow-derived hematopoietic progenitor cells and change their osteoclast-modulating effect

Low-intensity loading maintains or increases bone mass, whereas lack of mechanical loading and high-intensity loading decreases bone mass, possibly via the release of extracellular vesicles by mechanosensitive bone cells. How different loading intensities alter the biological effect of these vesicles is not fully understood. Dynamic fluid shear stress at low intensity (0.7 ± 0.3 Pa, 5 Hz) or high intensity (2.9 ± 0.2 Pa, 1 Hz) was used on mouse hematopoietic progenitor cells for 2 min in the presence or absence of chemical compounds that inhibit release or biogenesis of extracellular vesicles. We used a Receptor activator of nuclear factor kappa-Β ligand-induced osteoclastogenesis assay to evaluate the biological effect of different fractions of extracellular vesicles obtained through centrifugation of medium from hematopoietic stem cells. Osteoclast formation was reduced by microvesicles (10 000× g) obtained after low-intensity loading and induced by exosomes (100 000× g) obtained after high-intensity loading. These osteoclast-modulating effects could be diminished or eliminated by depletion of extracellular vesicles from the conditioned medium, inhibition of general extracellular vesicle release, inhibition of microvesicle biogenesis (low intensity), inhibition of ESCRT-independent exosome biogenesis (high intensity), as well as by inhibition of dynamin-dependent vesicle uptake in osteoclast progenitor cells. Taken together, the intensity of mechanical loading affects the release of extracellular vesicles and change their osteoclast-modulating effect.

Exploring the mechanism of Astragali radix for promoting osteogenic differentiation based on network pharmacology, molecular docking, and experimental validation

The present study used network pharmacology and molecular docking to predict the active ingredients and mechanisms of action of Astragalus radix (AR) to promote osteogenic differentiation of bone marrow mesenchymal stem cells (BM-MSCs), and cell experiments were conducted for verification. First, network pharmacology was used to predict the effective components, targets, and mechanisms of action of AR to promote osteogenic differentiation. The effective components and corresponding target proteins of AR, and the target proteins of osteogenic differentiation were collected through the database. The intersection targets of the two were used for the construction and analysis of a protein-protein interaction (PPI) network. Gene Oncology (GO) and Kyoto Encyclopedia of Genes, and Genomes (KEGG) enrichment analyses were conducted. Next, molecular docking technology was carried out to verify the interaction between the active ingredient and the target protein, and to select the appropriate effective active ingredient. Finally, the results of network pharmacology analysis were verified by in vitro experiments. A total of 95 potential targets were retrieved by searching the intersection of AR and osteogenic differentiation targets. PPI network analysis indicated that RAC-α-serine-threonine-protein kinase (Akt1) was considered to be the most reliable target for AR to regulate osteogenic differentiation. GO enrichment analysis included 21 biological processes, 21 cellular components and 100 molecular functions. KEGG enrichment analysis indicated that the class I phosphatidylinositol-3 kinase (PI3K)-serine-threonine kinase (Akt) signaling pathway may play an important role in promoting osteogenic differentiation. The results of molecular docking showed that quercetin's performance was improved compared with that of kaempferol. In vitro experiments showed that quercetin promoted the expression of osteogenic marker proteins (including collagen I, Runt-related transcription factor 2 and osteopontin) in BMSCs and activated the PI3K/Akt signaling pathway. AR acted on Akt1 targets through its main active component quercetin, and promoted the osteogenic differentiation of BM-MSCs by activating the PI3K/Akt signaling pathway.

Can extracellular vesicles be considered as a potential frontier in the treatment of intervertebral disc disease?

As a global public health problem, low back pain (LBP) caused by intervertebral disc degeneration (IDD) seriously affects patients' quality of life. In addition, the prevalence of IDD tends to be younger, which brings a huge burden to individuals and society economically. Current treatments do not delay or reverse the progression of IDD. The emergence of biologic therapies has brought new hope for the treatment of IDD. Among them, extracellular vesicles (EVs), as nanoscale bioactive substances that mediate cellular communication, have now produced many surprising results in the research of the treatment of IDD. This article reviews the mechanisms and roles of EVs in delaying IDD and describes the prospects and challenges of EVs.

Consequences of Aging on Bone

With the aging of the global population, the incidence of musculoskeletal diseases has been increasing, seriously affecting people's health. As people age, the microenvironment within skeleton favors bone resorption and inhibits bone formation, accompanied by bone marrow fat accumulation and multiple cellular senescence. Specifically, skeletal stem/stromal cells (SSCs) during aging tend to undergo adipogenesis rather than osteogenesis. Meanwhile, osteoblasts, as well as osteocytes, showed increased apoptosis, decreased quantity, and multiple functional limitations including impaired mechanical sensing, intercellular modulation, and exosome secretion. Also, the bone resorption function of macrophage-lineage cells (including osteoclasts and preosteoclasts) was significantly enhanced, as well as impaired vascularization and innervation. In this study, we systematically reviewed the effect of aging on bone and the within microenvironment (including skeletal cells as well as their intracellular structure variations, vascular structures, innervation, marrow fat distribution, and lymphatic system) caused by aging, and mechanisms of osteoimmune regulation of the bone environment in the aging state, and the causal relationship with multiple musculoskeletal diseases in addition with their potential therapeutic strategy.

Skeletal muscle-derived extracellular vesicles transport glycolytic enzymes to mediate muscle-to-bone crosstalk

Identification of cues originating from skeletal muscle that govern bone formation is essential for understanding the crosstalk between muscle and bone and for developing therapies for degenerative bone diseases. Here, we identified that skeletal muscle secreted multiple extracellular vesicles (Mu-EVs). These Mu-EVs traveled through the bloodstream to reach bone, where they were phagocytized by bone marrow mesenchymal stem/stromal cells (BMSCs). Mu-EVs promoted osteogenic differentiation of BMSCs and protected against disuse osteoporosis in mice. The quantity and bioactivity of Mu-EVs were tightly correlated with the function of skeletal muscle. Proteomic analysis revealed numerous proteins in Mu-EVs, some potentially regulating bone metabolism, especially glycolysis. Subsequent investigations indicated that Mu-EVs promoted the glycolysis of BMSCs by delivering lactate dehydrogenase A into these cells. In summary, these findings reveal that Mu-EVs play a vital role in BMSC metabolism regulation and bone formation stimulation, offering a promising approach for treating disuse osteoporosis.

A Recombinant Parathyroid Hormone-Related Peptide Locally Applied in Osteoporotic Bone Defect

The local application of drug-loaded bioactive scaffold materials is one of the important directions to solve the clinical problem of osteoporotic (OP) bone defects. This study retains the advantages of drug loading and mechanical properties of natural 3D bioactive scaffolds. The scaffolds are functionally modified through chemical and self-assembly approaches with application of polydopamine (PDA) nanoparticles and parathyroid hormone-related peptide-1 (PTHrP-1) for efficient local drug loading. This study investigates the effects of the novel bioactive scaffolds on ossification, osteoclastogenesis, and macrophage polarization. This work elucidates the effects of the scaffolds in regulating osteoclastic activity and new bone formation in vitro. Further studies on the establishment and repair of OP bone defects in small animals are conducted, and the potential of natural bioactive porous scaffold materials to promote the repair of OP bone defects is initially verified. The preparation of safe and economical anti-OP bone repair material provides a theoretical basis for clinical translational applications.