Cellular senescence in bone

Dynamic transcriptome analysis of osteal macrophages identifies a distinct subset with senescence features in experimental osteoporosis

Given the potential fundamental function of osteal macrophages in bone pathophysiology, we study here their precise function in experimental osteoporosis. Gene profiling of osteal macrophages from ovariectomized mice demonstrated the upregulation of genes that were involved in oxidative stress, cell senescence, and apoptotic process. A single-cell RNA-Seq analysis revealed that osteal macrophages were heterogeneously clustered into 6 subsets that expressed proliferative, inflammatory, antiinflammatory, and efferocytosis gene signatures. Importantly, postmenopausal mice exhibited an increase in subset 3 that showed a typical gene signature of cell senescence and inflammation. These findings suggest that the decreased production of estrogen due to postmenopausal condition altered the osteal macrophage subsets, resulting in a shift toward cell senescence and inflammatory conditions in the bone microenvironment. Furthermore, adoptive macrophage transfer onto calvarial bone was performed, and mice that received oxidatively stressed macrophages exhibited greater osteolytic lesions than control macrophages, suggesting the role of these cells in the development of inflammaging in the bone microenvironment. Consistently, depletion of senescent cells and the oxidatively stressed macrophage subset alleviated the excessive bone loss in postmenopausal mice. Our data provided insight into the pathogenesis of osteoporosis and shed light on a therapeutic approach for the treatment or prevention of postmenopausal osteoporosis.

DNA Tetrahedron Delivering miR-21-5p Promotes Senescent Bone Defects Repair through Synergistic Regulation of Osteogenesis and Angiogenesis

Compromised osteogenesis and angiogenesis is the character of stem cell senescence, which brought difficulties for bone defects repairing in senescent microenvironment. As the most abundant bone-related miRNA, miRNA-21-5p plays a crucial role in inducing osteogenic and angiogenic differentiation. However, highly efficient miR-21-5p delivery still confronts challenges including poor cellular uptake and easy degradation. Herein, TDN-miR-21-5p nanocomplex is constructed based on DNA tetrahedral (TDN) and has great potential in promoting osteogenesis and alleviating senescence of senescent bone marrow stem cells (O-BMSCs), simultaneously enhancing angiogenic capacity of senescent endothelial progenitor cells (O-EPCs). Of note, the activation of AKT and Erk signaling pathway may direct regulatory mechanism of TDN-miR-21-5p mediated osteogenesis and senescence of O-BMSCs. Also, TDN-miR-21-5p can indirectly mediate osteogenesis and senescence of O-BMSCs through pro-angiogenic growth factors secreted from O-EPCs. In addition, gelatin methacryloyl (GelMA) hydrogels are mixed with TDN and TDN-miR-21-5p to fabricate delivery scaffolds. TDN-miR-21-5p@GelMA scaffold exhibits greater bone repair with increased expression of osteogenic- and angiogenic-related markers in senescent critical-size cranial defects in vivo. Collectively, TDN-miR-21-5p can alleviate senescence and induce osteogenesis and angiogenesis in senescent microenvironment, which provides a novel candidate strategy for senescent bone repair and widen clinical application of TDNs-based gene therapy.

Stiffening symphony of aging: Biophysical changes in senescent osteocytes

Senescent osteocytes are key contributors to age-related bone loss and fragility; however, the impact of mechanobiological changes in these cells remains poorly understood. This study provides a novel analysis of these changes in primary osteocytes following irradiation-induced senescence. By integrating subcellular mechanical measurements with gene expression analyses, we identified significant, time-dependent alterations in the mechanical properties of senescent bone cells. Increases in classical markers such as SA-β-Gal activity and p16Ink4a expression levels confirmed the senescence status post-irradiation. Our key findings include a time-dependent increase in cytoskeletal Young's modulus and altered viscoelastic properties of the plasma membrane, affecting the contractility of primary osteocytes. Additionally, we observed a significant increase in Sclerostin (Sost) expression 21 days post-irradiation. These biophysical changes may impair osteocyte mechanosensation and mechanotransduction, contributing to bone fragility. This is the first study to time-map senescence-associated mechanical changes in the osteocyte cytoskeleton. Our findings highlight the potential of biophysical markers as indicators of cellular senescence, providing more specificity than traditional, variable biomolecular markers. We believe these results may support biomechanical stimulation as a potential therapeutic strategy to rejuvenate aging osteocytes and enhance bone health.

When do the pathological signs become evident? Study of human mesenchymal stem cells in MDPL syndrome

Aging syndromes are rare genetic disorders sharing the features of accelerated senescence. Among these, Mandibular hypoplasia, Deafness and Progeroid features with concomitant Lipodystrophy (MDPL; OMIM #615381) is a rare autosomal dominant disease due to a de novo in-frame deletion in POLD1 gene, encoding the catalytic subunit of DNA polymerase delta. Here, we investigated how MSCs may contribute to the phenotypes and progression of premature aging syndromes such as MDPL. In human induced pluripotent stem cells (hiPSCs)-derived MSCs of three MDPL patients we detected several hallmarks of senescence, including (i) abnormal nuclear morphology, (ii) micronuclei presence, (iii) slow cell proliferation and cell cycle progression, (iv) reduced telomere length, and (v) increased levels of mitochondrial reactive oxygen species (ROS). We newly demonstrated that the pathological hallmarks of senescence manifest at an early stage of human development and represent a warning sign for the progression of the disease. Dissecting the mechanisms underlying stem cell dysfunction during aging can thereby contribute to the development of timely pharmacological therapies for ameliorating the pathological phenotype.

Targeting MCH Neuroendocrine Circuit in Lateral Hypothalamus to Protect Against Skeletal Senescence

Neuroendocrine regulation is essential for maintaining metabolic homeostasis. However, whether neuroendocrine pathway influence bone metabolism and skeletal senescence is unelucidated. Here, a central neuroendocrine circuit is identified that directly controls osteogenesis. Using virus based tracing, this study is identified that melanin concentrating hormone (MCH) expressing neurons in the lateral hypothalamus (LH) are connected to the bone. Chemogenetic activation of MCH neurons in the LH induces osteogenesis, whereas inhibiting these neurons reduces osteogenesis. Meanwhile, MCH is released into the circulation upon chemogenetic activation of these neurons. Single cell sequencing reveals that blocking MCH neurons in the LH diminishes osteogenic differentiation of bone marrow stromal cells (BMSCs) and induces senescence. Mechanistically, MCH promotes BMSC differentiation by activating MCHR1 via PKA signaling, and activating MCHR1 by MCH agonists attenuate skeletal senescence in mice. By elucidating a brain-bone connection that autonomously enhances osteogenesis, these findings uncover the neuroendocrinological mechanisms governing bone mass regulation and protect against skeletal senescence.

The senolytic agent ABT263 ameliorates osteoporosis caused by active vitamin D insufficiency through selective clearance of senescent skeletal cells

Background/Objective

Active vitamin D insufficiency accelerates the development of osteoporosis, with senescent bone cells and the senescence-associated secretory phenotype (SASP) playing crucial roles. This study aimed to investigate whether the senolytic agent ABT263 could correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent cells.

Methods

Bone marrow mesenchymal stem cells (BM-MSCs) from young and aged mice were treated with ABT263 in vitro, and 1,25(OH)2D-insufficient (Cyp27b1+/-) mice were administered ABT263 in vivo. Cellular, molecular, imaging, and histopathological analyses were performed to compare treated cells and mice with control groups.

Results

ABT263 induced apoptosis in senescent BM-MSCs by downregulating Bcl2 and upregulating Bax expression. It also induced apoptosis in senescent BM-MSCs from 1,25(OH)2D-insufficient mice. ABT263 administration corrected bone loss caused by 1,25(OH)2D insufficiency by increasing bone density, bone volume, trabecular number, trabecular thickness, and collagen synthesis. It also enhanced osteoblastic bone formation and reduced osteoclastic bone resorption in vivo. ABT263 treatment corrected the impaired osteogenic action of BM-MSCs by promoting their proliferation and osteogenic differentiation. Furthermore, it corrected oxidative stress and DNA damage caused by 1,25(OH)2D insufficiency by increasing SOD-2 and decreasing γ-H2A.X expression. Finally, ABT263 corrected bone cell senescence and SASP caused by 1,25(OH)2D insufficiency by reducing the expression of senescence and SASP-related genes and proteins.

Conclusion

ABT263 can correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent skeletal cells, reducing oxidative stress, DNA damage, and SASP, and promoting bone formation while inhibiting bone resorption. These findings provide new insights into the potential therapeutic application of senolytic agents in the treatment of osteoporosis associated with active vitamin D insufficiency.

The translational potential of this article

This study highlights the therapeutic potential of ABT263, a senolytic compound, in treating osteoporosis caused by active vitamin D insufficiency. By selectively eliminating senescent bone cells and their associated SASP, ABT263 intervention demonstrates the ability to restore bone homeostasis, prevent further bone loss, and promote bone formation. These findings contribute to the growing body of research supporting the use of senolytic therapies for the prevention and treatment of age-related bone disorders. The translational potential of this study lies in the development of novel therapeutic strategies targeting cellular senescence to combat osteoporosis, particularly in cases where vitamin D insufficiency is a contributing factor. Further clinical studies are warranted to validate the efficacy and safety of ABT263 and other senolytic agents in the treatment of osteoporosis in humans.

Zhuangyao Jianshen Wan ameliorates senile osteoporosis in SAMP6 mice through Modulation of the GCN5L1-mediated PI3K/Akt/wnt signaling pathway

Background

Senile osteoporosis (SOP) is a systemic bone disease characterized by increased susceptibility to fractures. However, there is currently no effective treatment for SOP. The Zhuangyao Jianshen Wan (ZYJSW) pill is traditionally believed to possess kidney-nourishing and bone-strengthening effects, demonstrating efficacy in treating fractures. Despite this, its effectiveness and mechanism in SOP remain unclear. This study aims to investigate the therapeutic potential of ZYJSW in treating SOP in senescence accelerated mouse prone 6 (SAMP6, P6) mice, and elucidate the underlying mechanisms.

Methods

Four-month-old SAMP6 mice were categorized into six groups: the model group (SAMP6), low, medium, and high-dose ZYJSW treatment groups, calcitriol treatment (positive control 1) group, and metformin treatment (positive control 2) group. Gastric administration was carried out for 15 weeks, and a normal control group comprising four-month-old Senescence-Accelerated Mouse Resistant 1 (SAMR1) mice. Changes in body weight, liver and kidney function, bone protective effects, and muscle quality were evaluated using various assays, including H&E staining, Goldner staining, bone tissue morphology analysis, Micro-CT imaging, and biomechanical testing. Qualitative analysis and quality control of ZYJSW were performed via LC-MS/MS analysis. To explore mechanisms, network pharmacology and proteomics were employed, and the identified proteins were validated by Western blotting.

Results

Oral administration of ZYJSW to P6 mice exerted preventive efficacy against osteopenia, impaired bone microstructure, and poor bone and muscle quality. ZYJSW attenuated the imbalance in bone metabolism by promoting bone formation, as evidenced by the upregulation of key factors such as Runt-related transcription factor 2 (RUNX2), Bone Morphogenetic Protein (BMP2), Osteoprotegerin (OPG) and Osteocalcin (OCN), while simultaneously inhibiting bone resorption through the downregulation of TNF receptor associated factor 6 (TRAF6), Tartrate resistant acid phosphatase (TRAP), Receptor activator for nuclear factor-κB ligand (RANKL) and Cathepsin K (CTSK). Additionally, ZYJSW enhanced muscle structure and function by counteracting the elevation of Ubiquitin (Ub), Muscle RING-finger protein-1 (Murf-1), F-Box Protein 32 (FBOX32), and Myogenin (Myog). Network pharmacology predictions, proteomics analysis corroborated by published literature demonstrated the role of ZYJSW involving in safeguarding mitochondrial biogenesis. This was achieved by suppressing GCN5L1 expression, contributing to the heightened expression of TFAM, PGC-1α, and nuclear respiratory factor-1 (NRF-1) proteins. ZYJSW also positively modulated Wnt signaling pathways responsible for bone formation, due to regulating expressions of key components like β-catenin, GSK-3β, and LRP5. In addition, ZYJSW causes the downregulation of the PI3K/Akt pathway by inhibiting the phosphorylation of both PI3K and Akt.

Conclusions

The study highlights the significance of ZYJSW in preserving the health of both bone and muscle in P6 mice, potentially through the regulation of the GCN5L1-mediated PI3K/Akt/Wnt signaling pathway.

The translational potential of this article

Our research provides evidence and a mechanistic rationale for ZYJSW as a candidate for SOP treatment, offering insights for further exploration and strategy development.

Deciphering Osteosarcopenia through the hallmarks of aging

Osteosarcopenia is a major driver of functional loss and a risk factor for falls, fractures, disability and mortality in older adults, urgently requiring the development of effective interventions to address it. The hallmarks of aging provide a theoretical and practical framework that allows for the structured organization of current knowledge and the planning of new development lines. This article comprehensively reviews the currently available literature on the role of the hallmarks of aging in the development of osteosarcopenia, thereby offering a panoramic view of the state of the art and knowledge gaps in this field.

Skeletal stem and progenitor cells in bone physiology, ageing and disease

Skeletal stem cells (SSCs) and related progenitors with osteogenic potential, collectively termed skeletal stem and/or progenitor cells (SSPCs), are crucial for providing osteoblasts for bone formation during homeostatic tissue turnover and fracture repair. Besides mediating normal bone physiology, they also have important roles in various metabolic bone diseases, including osteoporosis. SSPCs are of tremendous interest because they represent prime future targets for osteoanabolic therapies and bone regenerative medicine. Remarkable progress has been made in characterizing various SSC and SSPC populations in postnatal bone. SSPCs exist in the periosteum and within the bone marrow stroma, including subsets localizing around arteriolar and sinusoidal blood vessels; they can display osteogenic, chondrogenic, adipogenic and/or fibroblastic potential, and exert critical haematopoiesis-supportive functions. However, much remains to be clarified. By the current markers, bona fide SSCs are commonly contained within broader SSPC populations characterized by considerable heterogeneity and overlap, whose common versus specific functions in health and disease have not been fully unravelled. Here, we review the present knowledge of the identity, fates and relationships of SSPC populations in the postnatal bone environment, their contributions to bone maintenance, the changes observed upon ageing, and the effect of metabolic diseases such as osteoporosis and diabetes mellitus.

Melatonin-loaded bioactive microspheres accelerate aged bone regeneration by formation of tunneling nanotubes to enhance mitochondrial transfer

The repair of bone defects in the elderly individuals is significantly delayed due to cellular senescence and dysfunction, which presents a challenge in clinical settings. Furthermore, there are limited effective methods available to promote bone repair in older individuals. Herein, melatonin-loaded mesoporous bioactive glasses microspheres (MTBG) were successfully prepared based on their mesoporous properties. The repair of bone defects in aged rats was significantly accelerated by enhancing mitochondrial function through the sustained release of melatonin and bioactive ions. MTBG effectively rejuvenated senescent bone marrow mesenchymal stem cells (BMSCs) by scavenging excessive reactive oxygen species (ROS), stabilizing the mitochondrial membrane potential (ΔΨm), and increasing ATP synthesis. Analysis of the underlying mechanism revealed that the formation of tunneling nanotubes (TNTs) facilitated the intercellular transfer of mitochondria, thereby resulting in the recovery of mitochondrial function. This study provides critical insights into the design of new biomaterials for the elderly individuals and the biological mechanism involved in aged bone regeneration.

Advances in targeted therapies for age-related osteoarthritis: A comprehensive review of current research

Osteoarthritis (OA) is a common degenerative joint disease that disproportionately impacts the elderly population on a global scale. As aging is a significant risk factor for OA, there is a growing urgency to develop specific therapies that target the underlying mechanisms of aging associated with this condition. This summary seeks to offer a thorough introduction of ongoing research efforts aimed at developing therapies to combat senescence in the context of OA. Cellular senescence plays a pivotal role in both the deterioration of cartilage integrity and the perpetuation of chronic inflammation and tissue remodeling. Consequently, targeting SnCs has emerged as a promising therapeutic approach to alleviate symptoms and hinder the progression of OA. This review examines a range of approaches, including senolytic drugs targeting SnCs, senomorphics that modulate the senescence-associated secretory phenotype (SASP), and interventions that enhance immune system clearance of SnCs. Novel methodologies, such as utilizing novel materials for exosome delivery and administering anti-aging medications with precision, offer promising avenues for the precise treatment of OA. Accumulating evidence underscores the potential of targeting senescence in OA management, potentially facilitating the development of more effective and personalized therapeutic interventions.

Cellular senescence by loss of Men1 in osteoblasts is critical for age-related osteoporosis

Recent evidence suggests an association between age-related osteoporosis and cellular senescence in the bone; however, the specific bone cells that play a critical role in age-related osteoporosis and the mechanism remain unknown. Results revealed that age-related osteoporosis is characterized by the loss of osteoblast Men1. Osteoblast-specific inducible knockout of Men1 caused structural changes in the mice bones, matching the phenotypes in patients with age-related osteoporosis. Histomorphometrically, Men1-knockout mice femurs decreased osteoblastic activity and increased osteoclastic activity, hallmarks of age-related osteoporosis. Loss of Men1 induces cellular senescence via mTORC1 activation and AMPK suppression, rescued by metformin treatment. In bone morphogenetic protein-indued bone model, loss of Men1 leads to accumulation of senescent cells and osteoporotic bone formation, which are ameliorated by metformin. Our results indicate that cellular senescence in osteoblasts plays a critical role in age-related osteoporosis and that osteoblast-specific inducible Men1-knockout mice offer a promising model for developing therapeutics for age-related osteoporosis.

Senescence of skeletal stem cells and their contribution to age-related bone loss

Human aging is linked to bone loss, resulting in bone fragility and an increased risk of fractures. This is primarily due to an age-related decline in the function of bone-forming osteoblastic cells and accelerated cellular senescence within the bone microenvironment. Here, we provide a detailed discussion of the hypothesis that age-related defective bone formation is caused by senescence of skeletal stem cells, as they are the main source of bone forming osteoblastic cells and influence the composition of bone microenvironment. Furthermore, this review discusses potential strategies to target cellular senescence as an emerging approach to treat age-related bone loss.

Exploring the action mechanism of Oxalis corniculata L. decoction in treating osteoarthritis utilizing liquid chromatography-mass spectrometry technology combined with network pharmacology

This study aimed to identify the chemical constituents of Oxalis corniculata L. decoction. Furthermore, the mechanism of action of O corniculata L. decoction in treating osteoarthritis (OA) was investigated utilizing network pharmacology. The chemical composition of the O corniculata L. decoction was analyzed by employing UHPLC-Q-Exactive-MS/MS. Subsequently, a "compound-target-pathway" network was established through network pharmacology, offering a novel approach to identify the molecular mechanism underlying the treatment of OA with O corniculata L. decoction. Ultimately, the molecular docking technique was employed to validate the binding ability of the active ingredients with therapeutic targets. A total of 539 compounds were identified in O corniculata L. decoction. Topological analysis of the protein-protein interaction network indicated that compounds, including guanosine, naringenin-7-O-beta-D-glucuronide, noroxyhydrastinine, and chrysophanol 8-O-glucoside, have therapeutic potential for OA. In addition, GAPDH, TNF, TP53, epidermal growth factor receptor, and ESR1 may be key targets for the treatment of OA, primarily involving lipid and atherosclerosis, cellular senescence, IL-17 signaling pathway, and epidermal growth factor receptor tyrosine kinase inhibitor resistance signaling pathways. This method preliminarily identified the chemical composition of O corniculata L. decoction and predicted the active ingredients, potential targets, and signaling pathways of O corniculata L. decoction in treating OA. The findings of this research revealed the potential function of O corniculata L. decoction in anti-inflammation, alongside its ability to promote osteoblast proliferation and differentiation, providing new ideas for the processing of O corniculata L. herbs and related drug development.

Targeting miR-29 mitigates skeletal senescence and bolsters therapeutic potential of mesenchymal stromal cells

Mesenchymal stromal cell (MSC) senescence is a key factor in skeletal aging, affecting the potential of MSC applications. Identifying targets to prevent MSC and skeletal senescence is crucial. Here, we report increased miR-29 expression in bone tissues of aged mice, osteoporotic patients, and senescent MSCs. Genetic overexpression of miR-29 in Prx1-positive MSCs significantly accelerates skeletal senescence, reducing cortical bone thickness and trabecular bone mass, while increasing femur cross-sectional area, bone marrow adiposity, p53, and senescence-associated secretory phenotype (SASP) levels. Mechanistically, miR-29 promotes senescence by upregulating p53 via targeting Kindlin-2 mRNA. miR-29 knockdown in BMSCs impedes skeletal senescence, enhances bone mass, and accelerates calvarial defect regeneration, also reducing lipopolysaccharide (LPS)-induced organ injuries and mortality. Thus, our findings underscore miR-29 as a promising therapeutic target for senescence-related skeletal diseases and acute inflammation-induced organ damage.

Serum Amyloid P Secreted by Bone Marrow Adipocytes Drives Skeletal Amyloidosis

The accumulation of amyloid fibrils has been identified in tissues outside the brain, yet little is understood about the formation of extracerebral amyloidosis and its impact on the aging process of these organs. Here, we demonstrate that both transgenic mice modeling Alzheimer's disease (AD) and naturally aging mice exhibit accumulated senescent bone marrow adipocytes (BMAds), accompanied by amyloid deposits surrounding the BMAds. Senescent BMAds acquire a secretory phenotype, resulting in a marked increase in the secretion of serum amyloid P component (SAP), also known as pentraxin 2 (PTX2). SAP/PTX2 colocalizes with amyloid deposits around senescent BMAds in vivo and is sufficient to promote the formation of insoluble amyloid deposits from soluble Aβ peptides in in vitro and ex vivo 3D BMAd-based culture experiments. Additionally, Combined treatment with SAP/PTX2 and Aβ peptides promotes osteoclastogenesis but inhibits osteoblastogenesis of the precursor cells. Transplantation of senescent BMAds into the bone marrow cavity of healthy young mice is sufficient to induce bone loss. Finally, pharmacological depletion of SAP/PTX2 from aged mice abolishes bone marrow amyloid deposition and effectively rescues the low bone mass phenotype. Thus, senescent BMAds, through the secretion of SAP/PTX2, contribute to the age-associated development of skeletal amyloidosis and resultant bone deficits.

Interplay Between Skeletal and Hematopoietic Cells in the Bone Marrow Microenvironment in Homeostasis and Aging

PURPOSE OF THE REVIEW

In this review, we discuss the most recent scientific advances on the reciprocal regulatory interactions between the skeletal and hematopoietic stem cell niche, focusing on immunomodulation and its interplay with the cell's mitochondrial function, and how this impacts osteoimmune health during aging and disease.

RECENT FINDINGS

Osteoimmunology investigates interactions between cells that make up the skeletal stem cell niche and immune system. Much work has investigated the complexity of the bone marrow microenvironment with respect to the skeletal and hematopoietic stem cells that regulate skeletal formation and immune health respectively. It has now become clear that these cellular components cooperate to maintain homeostasis and that dysfunction in their interaction can lead to aging and disease. Having a deeper, mechanistic appreciation for osteoimmune regulation will lead to better research perspective and therapeutics with the potential to improve the aging process, skeletal and hematologic regeneration, and disease targeting.

Unraveling the molecular and immunological landscape: Exploring signaling pathways in osteoporosis

Osteoporosis, characterized by compromised bone density and microarchitecture, represents a significant global health challenge, particularly in aging populations. This comprehensive review delves into the intricate signaling pathways implicated in the pathogenesis of osteoporosis, providing valuable insights into the pivotal role of signal transduction in maintaining bone homeostasis. The exploration encompasses cellular signaling pathways such as Wnt, Notch, JAK/STAT, NF-κB, and TGF-β, all of which play crucial roles in bone remodeling. The dysregulation of these pathways is a contributing factor to osteoporosis, necessitating a profound understanding of their complexities to unveil the molecular mechanisms underlying bone loss. The review highlights the pathological significance of disrupted signaling in osteoporosis, emphasizing how these deviations impact the functionality of osteoblasts and osteoclasts, ultimately resulting in heightened bone resorption and compromised bone formation. A nuanced analysis of the intricate crosstalk between these pathways is provided to underscore their relevance in the pathophysiology of osteoporosis. Furthermore, the study addresses some of the most crucial long non-coding RNAs (lncRNAs) associated with osteoporosis, adding an additional layer of academic depth to the exploration of immune system involvement in various types of osteoporosis. Finally, we propose that SKP1 can serve as a potential biomarker in osteoporosis.

Marrow Adipocyte Senescence in the Pathogenesis of Bone Loss

PURPOSE OF REVIEW

Beyond aging, senescent cells accumulate during multiple pathological conditions, including chemotherapy, radiation, glucocorticoids, obesity, and diabetes, even earlier in life. Therefore, cellular senescence represents a unifying pathogenic mechanism driving skeletal and metabolic disorders. However, whether senescent bone marrow adipocytes (BMAds) are causal in mediating skeletal dysfunction has only recently been evaluated.

RECENT FINDINGS

Despite evidence of BMAd senescence following glucocorticoid therapy, additional evidence for BMAd senescence in other conditions has thus far been limited. Because the study of BMAds presents unique challenges making these cells difficult to isolate and image, here we review issues and approaches to overcome such challenges, and present advancements in isolation and histological techniques that may help with the future study of senescent BMAds. Further insights into the roles of BMAd senescence in the pathogenesis of skeletal dysfunction may have important basic science and clinical implications for human physiology and disease.

Epigenetic regulations of cellular senescence in osteoporosis

Osteoporosis (OP) is a prevalent age-related disease that is characterized by a decrease in bone mineral density (BMD) and systemic bone microarchitectural disorders. With age, senescent cells accumulate and exhibit the senescence-associated secretory phenotype (SASP) in bone tissue, leading to the imbalance of bone homeostasis, osteopenia, changes in trabecular bone structure, and increased bone fragility. Cellular senescence in the bone microenvironment involves osteoblasts, osteoclasts, and bone marrow mesenchymal stem cells (BMSCs), whose effects on bone homeostasis are regulated by epigenetics. Therefore, the epigenetic regulatory mechanisms of cellular senescence have received considerable attention as potential targets for preventing and treating osteoporosis. In this paper, we systematically review the mechanisms of aging-associated epigenetic regulation in osteoporosis, emphasizing the impact of epigenetics on cellular senescence, and summarize three current methods of targeting cellular senescence, which is helpful better to understand the pathogenic mechanisms of cellular senescence in osteoporosis and provides strategies for the development of epigenetic drugs for the treatment of osteoporosis.

Reactive oxygen-scavenging polydopamine nanoparticle coated 3D nanofibrous scaffolds for improved osteogenesis: Toward an aging in vivo bone regeneration model

Tissue engineered scaffolds aimed at the repair of critical-sized bone defects lack adequate consideration for our aging society. Establishing an effective aged in vitro model that translates to animals is a significant unmet challenge. The in vivo aged environment is complex and highly nuanced, making it difficult to model in the context of bone repair. In this work, 3D nanofibrous scaffolds generated by the thermally-induced self-agglomeration (TISA) technique were functionalized with polydopamine nanoparticles (PD NPs) as a tool to improve drug binding capacity and scavenge reactive oxygen species (ROS), an excessive build-up that dampens the healing process in aged tissues. PD NPs were reduced by ascorbic acid (rPD) to further improve hydrogen peroxide (H2O2) scavenging capabilities, where we hypothesized that these functionalized scaffolds could rescue ROS-affected osteoblastic differentiation in vitro and improve new bone formation in an aged mouse model. rPDs demonstrated improved H2O2 scavenging activity compared to neat PD NPs, although both NP groups rescued the alkaline phosphatase activity (ALP) of MC3T3-E1 cells in presence of H2O2. Additionally, BMP2-induced osteogenic differentiation, both ALP and mineralization, was significantly improved in the presence of PD or rPD NPs on TISA scaffolds. While in vitro data showed favorable results aimed at improving osteogenic differentiation by PD or rPD NPs, in vivo studies did not note similar improvements in ectopic bone formation an aged model, suggesting that further nuance in material design is required to effectively translate to improved in vivo results in aged animal models.

Cellular Senescence and Inflammaging in the Bone: Pathways, Genetics, Anti-Aging Strategies and Interventions

Advancing age is associated with several age-related diseases (ARDs), with musculoskeletal conditions impacting millions of elderly people worldwide. With orthopedic conditions contributing towards considerable number of patients, a deeper understanding of bone aging is the need of the hour. One of the underlying factors of bone aging is cellular senescence and its associated senescence associated secretory phenotype (SASP). SASP comprises of pro-inflammatory markers, cytokines and chemokines that arrest cell growth and development. The accumulation of SASP over several years leads to chronic low-grade inflammation with advancing age, also known as inflammaging. The pathways and molecular mechanisms focused on bone senescence and inflammaging are currently limited but are increasingly being explored. Most of the genes, pathways and mechanisms involved in senescence and inflammaging coincide with those associated with cancer and other ARDs like osteoarthritis (OA). Thus, exploring these pathways using techniques like sequencing, identifying these factors and combatting them with the most suitable approach are crucial for healthy aging and the early detection of ARDs. Several approaches can be used to aid regeneration and reduce senescence in the bone. These may be pharmacological, non-pharmacological and lifestyle interventions. With increasing evidence towards the intricate relationship between aging, senescence, inflammation and ARDs, these approaches may also be used as anti-aging strategies for the aging bone marrow (BM).

Emerging perfluoroalkyl substances retard skeletal growth by accelerating osteoblasts senescence via ferroptosis

Due to the persistent nature and significant negative impacts of perfluorooctanoic acid (PFOA) on human health and other organisms, the emergence of new PFOA alternatives, such as perfluoro (2-methyl-3-oxhexanoic) acid (GenX) and perfluoro-3,6,9-trioxyundecanoic acid (PFO3TDA), have drawn significant attention. However, the toxic effects of PFOA and its substitutes on bones remain limited. In this study, we administered different concentrations of PFOA, GenX, and PFO3TDA via gavage to 3-week-old male BALB/C mice for four weeks. X-ray and micro-CT scans revealed shortening of the femur and tibia and significant reduction in bone density. Additionally, PFOA, GenX, and PFO3TDA promoted osteoblast senescence and impaired osteogenic capabilities. This was characterized by a decrease in the expression of osteogenesis-related genes (OCN, ALP, Runx2, etc.) and an increase in the expression of aging and inflammation-related factors (p16INK4a, P21, MMP3, etc). Furthermore, RNA sequencing revealed activation of the ferroptosis pathway in PFOA-treated osteoblasts, characterized by notable lipid peroxidation and excessive iron accumulation. Finally, by inhibiting the ferroptosis pathway with ferrostatin-1 (Fer-1), we effectively alleviated the senescence of MC3T3-E1 cells treated with PFOA, GenX, and PFO3TDA, and improved their osteogenic capabilities. Therefore, our study provides a new therapeutic insight into the impact of PFOA and its substitutes on bone growth and development.

Skeleton-derived extracellular vesicles in bone and whole-body aging: From mechanisms to potential applications

The skeleton serves as a supportive and protective organ for the body. As individuals age, their bone tissue undergoes structural, cellular, and molecular changes, including the accumulation of senescent cells. Extracellular vesicles (EVs) play a crucial role in aging through the cellular secretome and have been found to induce or accelerate age-related dysfunction in bones and to contribute further via the circulatory system to the aging of phenotypes of other bodily systems. However, the extent of these effects and their underlying mechanisms remain unclear. Therefore, this paper attempts to give an overview of the current understanding of age-related alteration in EVs derived from bones. The role of EVs in mediating communications among bone-related cells and other body parts is discussed, and the significance of bones in the whole-body aging process is highlighted. Ultimately, it is hoped that gaining a clearer understanding of the relationship between EVs and aging mechanisms may serve as a basis for new treatment strategies for age-related degenerative diseases in the skeleton and other systems.

Clinical validation of C12FDG as a marker associated with senescence and osteoarthritic phenotypes

Chronic conditions associated with aging have proven difficult to prevent or treat. Senescence is a cell fate defined by loss of proliferative capacity and the development of a pro-inflammatory senescence-associated secretory phenotype comprised of cytokines/chemokines, proteases, and other factors that promotes age-related diseases. Specifically, an increase in senescent peripheral blood mononuclear cells (PBMCs), including T cells, is associated with conditions like frailty, rheumatoid arthritis, and bone loss. However, it is unknown if the percentage of senescent PBMCs associated with age-associated orthopedic decline could be used for potential diagnostic or prognostic use in orthopedics. Here, we report senescent cell detection using the fluorescent compound C12FDG to quantify PBMCs senescence across a large cohort of healthy and osteoarthritic patients. There is an increase in the percent of circulating C12FDG+ PBMCs that is commensurate with increases in age and senescence-related serum biomarkers. Interestingly, C12FDG+ PBMCs and T cells also were found to be elevated in patients with mild to moderate osteoarthritis, a progressive joint disease that is strongly associated with inflammation. The percent of C12FDG+ PBMCs and age-related serum biomarkers were decreased in a small subgroup of study participants taking the senolytic drug fisetin. These results demonstrate quantifiable measurements in a large group of participants that could create a composite score of healthy aging sensitive enough to detect changes following senolytic therapy and may predict age-related orthopedic decline. Detection of peripheral senescence in PBMCs and subsets using C12FDG may be clinically useful for quantifying cellular senescence and determining how and if it plays a pathological role in osteoarthritic progression.

Apigenin and Rutaecarpine reduce the burden of cellular senescence in bone marrow stromal stem cells

Introduction

Osteoporosis is a systemic age-related disease characterized by reduced bone mass and microstructure deterioration, leading to increased risk of bone fragility fractures. Osteoporosis is a worldwide major health care problem and there is a need for preventive approaches.

Methods and results

Apigenin and Rutaecarpine are plant-derived antioxidants identified through functional screen of a natural product library (143 compounds) as enhancers of osteoblastic differentiation of human bone marrow stromal stem cells (hBMSCs). Global gene expression profiling and Western blot analysis revealed activation of several intra-cellular signaling pathways including focal adhesion kinase (FAK) and TGFβ. Pharmacological inhibition of FAK using PF-573228 (5 μM) and TGFβ using SB505124 (1μM), diminished Apigenin- and Rutaecarpine-induced osteoblast differentiation. In vitro treatment with Apigenin and Rutaecarpine, of primary hBMSCs obtained from elderly female patients enhanced osteoblast differentiation compared with primary hBMSCs obtained from young female donors. Ex-vivo treatment with Apigenin and Rutaecarpine of organotypic embryonic chick-femur culture significantly increased bone volume and cortical thickness compared to control as estimated by μCT-scanning.

Discussion

Our data revealed that Apigenin and Rutaecarpine enhance osteoblastic differentiation, bone formation, and reduce the age-related effects of hBMSCs. Therefore, Apigenin and Rutaecarpine cellular treatment represent a potential strategy for maintaining hBMSCs health during aging and osteoporosis.

Mesoporous bioactive glass scaffolds for the delivery of bone marrow stem cell-derived osteoinductive extracellular vesicles lncRNA promote senescent bone defect repair by targeting the miR-1843a-5p/Mob3a/YAP axis

Bone repair in elderly patients poses a huge challenge due to the age-related progressive decline in regenerative abilities attributed to the senescence of bone marrow stem cells (BMSCs). Bioactive scaffolds have been applied in bone regeneration due to their various biological functions. In this study, we aimed to fabricate functionalized bioactive scaffolds through loading osteoinductive extracellular vesicles (OI-EVs) based on mesoporous bioactive glass (MBG) scaffolds (1010 particles/scaffold) and to investigate its effects on osteogenesis and senescence of BMSCs. The results suggested that OI-EVs upregulate the proliferative and osteogenic capacities of senescent BMSCs. More importantly, The results showed that loading OI-EVs into MBG scaffolds achieved better bone regeneration. Furthermore, OI-EVs and BMSCs RNAs bioinformatics analysis indicated that OI-EVs play roles through transporting pivotal lncRNA acting as a "sponge" to compete with Mob3a for miR-1843a-5p to promote YAP dephosphorylation and nuclear translocation, ultimately resulting in elevated proliferation and osteogenic differentiation and reduced senescence-related phenotypes. Collectively, these results suggested that the OI-EVs lncRNA ceRNA regulatory networks might be the key point for senescent osteogenesis. More importantly, the study indicated the feasibility of loading OI-EVs into scaffolds and provided novel insights into biomaterial design for facilitating bone regeneration in the treatment of senescent bone defects. STATEMENT OF SIGNIFICANCE: Constructing OI-EVs/MBG delivering system and verification of its bone regeneration enhancement in senescent defect repair. Aging bone repair poses a huge challenge due to the age-related progressive degenerative decline in regenerative abilities attributed to the senescence of BMSCs. OI-EVs/MBG delivering system were expected as promising treatment for senescent bone repair, which could provide an effective strategy for bone regeneration in elderly patients. Clarification of potential OI-EVs lncRNA ceRNA regulatory mechanism in senescent bone regeneration OI-EVs play important roles through transferring lncRNA-ENSRNOG00000056625 sponging miR-1843a-5p that targeted Mob3a to activate YAP translocation into nucleus, ultimately alleviate senescence, promote proliferation and osteogenic differentiation in O-BMSCs, which provides theoretical basis for EVs-mediated therapy in future clinical works.

YAP/TAZ as Molecular Targets in Skeletal Muscle Atrophy and Osteoporosis

Skeletal muscles and bones are closely connected anatomically and functionally. Age-related degeneration in these tissues is associated with physical disability in the elderly and significantly impacts their quality of life. Understanding the mechanisms of age-related musculoskeletal tissue degeneration is crucial for identifying molecular targets for therapeutic interventions for skeletal muscle atrophy and osteoporosis. The Hippo pathway is a recently identified signaling pathway that plays critical roles in development, tissue homeostasis, and regeneration. The Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key downstream effectors of the mammalian Hippo signaling pathway. This review highlights the fundamental roles of YAP and TAZ in the homeostatic maintenance and regeneration of skeletal muscles and bones. YAP/TAZ play a significant role in stem cell function by relaying various environmental signals to stem cells. Skeletal muscle atrophy and osteoporosis are related to stem cell dysfunction or senescence triggered by YAP/TAZ dysregulation resulting from reduced mechanosensing and mitochondrial function in stem cells. In contrast, the maintenance of YAP/TAZ activation can suppress stem cell senescence and tissue dysfunction and may be used as a basis for the development of potential therapeutic strategies. Thus, targeting YAP/TAZ holds significant therapeutic potential for alleviating age-related muscle and bone dysfunction and improving the quality of life in the elderly.

Magnesium-containing bioceramics stimulate exosomal miR-196a-5p secretion to promote senescent osteogenesis through targeting Hoxa7/MAPK signaling axis

Stem cell senescence is characterized by progressive functional dysfunction and secretory phenotypic changes including decreased proliferation, dysfunction of osteogenic and angiogenic differentiation, increased secretion of the senescence-associated secretory phenotype (SASP), which bring difficulties for bone repair. Rescuing or delaying senescence of aged bone marrow mesenchymal stem cells (O-BMSCs) was considered as effective strategy for bone regeneration in aging microenvironment. Magnesium (Mg) ion released from bioceramics was reported to facilitate bone regeneration via enhancing osteogenesis and alleviating senescence. In this study, Akermanite biocreamics (Akt) containing Mg ion as a model was demonstrated to promote osteogenesis and angiogenesis effects of O-BMSCs by activating the MAPK signaling pathway in vitro. Moreover, the enhanced osteogenesis effects might be attributed to enhanced Mg-containing Akt-mediated exosomal miR-196a-5p cargo targeting Hoxa7 and activation of MAPK signaling pathway. Furthermore, the in vivo study confirmed that 3D-printed porous Mg-containing Akt scaffolds effectively increased bone regeneration in cranial defects of aged rats. The current results indicated that the exosomal-miR-196a-5p/Hoxa7/MAPK signaling axis might be the potential mechanism underlying Akt-mediated osteogenesis. The exosome-meditaed therapy stimulated by the released Mg ion contained in Akt biocreamics or other biomaterials might serve as a candidate strategy for bone repair in aged individuals.

Elimination of Senescent Osteocytes by Bone-Targeting Delivery of β-Galactose-Modified Maytansinoid Prevents Age-Related Bone Loss

The accumulation of senescent cells in bone during aging contributes to senile osteoporosis, and clearance of senescent cells by senolytics could effectively alleviate bone loss. However, the applications of senolytics are limited due to their potential toxicities. Herein, small extracellular vesicles (sEVs) have been modified by incorporating bone-targeting peptide, specifically (AspSerSer)6, to encapsulate galactose-modified Maytansinoids (DM1). These modified vesicles are referred to as (AspSerSer)6-sEVs/DM1-Gal, and they have been designed to specifically clear the senescent osteocytes in bone tissue. In addition, the elevated activity of lysosomal β-galactosidase in senescent osteocytes, but not normal cells in bone tissue, could break down DM1-Gal to release free DM1 for selective elimination of senescent osteocytes. Mechanically, DM1 could disrupt tubulin polymerization, subsequently inducing senescent osteocytes apoptosis. Further, administration of bone-targeting senolytics to aged mice could alleviate aged-related bone loss without non-obvious toxicity. Overall, this bone-targeting senolytics could act as a novel candidate for specific clearance of senescent osteocytes, ameliorating age-related bone loss, with a promising therapeutic potential for senile osteoporosis.

Rejuvenating Aged Bone Repair through Multihierarchy Reactive Oxygen Species-Regulated Hydrogel

Aging exacerbates the dysfunction of tissue regeneration at multiple levels and gradually diminishes individual's capacity to withstand stress, damage, and disease. The excessive accumulation of reactive oxygen species (ROS) is considered a hallmark feature of senescent stem cells, which causes oxidative stress, deteriorates the host microenvironment, and eventually becomes a critical obstacle for aged bone defect repair. Till now, the strategies cannot synchronously and thoroughly regulate intracellular and extracellular ROS in senescent cells. Herein, a multihierarchy ROS scavenging system for aged bone regeneration is developed by fabricating an injectable PEGylated poly(glycerol sebacate) (PEGS-NH2 )/poly(γ-glutamic acid) (γ-PGA) hydrogel containing rapamycin-loaded poly(diselenide-carbonate) nanomicelles (PSeR). This PSeR hydrogel exhibits highly sensitive ROS responsiveness to the local aged microenvironment and dynamically releases drug-loaded nanomicelles to scavenge the intracellular ROS accumulated in senescent bone mesenchymal stem cells. The PSeR hydrogel effectively tunes the antioxidant function and delays senescence of bone mesenchymal stem cells by safeguarding DNA replication in an oxidative environment, thereby promoting the self-renewal ability and enhancing the osteogenic capacity for aged bone repair in vitro and in vivo. Thus, this multihierarchy ROS-regulated hydrogel provides a new strategy for treating degenerative diseases.

Association between bone mineral density and coronary plaque burden in patients with coronary artery disease: a cross-sectional study using quantitative computed tomography

PURPOSE

To evaluate the association between osteoporosis and coronary calcification and coronary plaque burden in patients with atherosclerosis and coronary artery disease (CAD).

METHODS

This study included 290 men and 177 postmenopausal women with angiography-confirmed atherosclerosis or CAD who underwent chest multidetector row computed tomography covering L1-L2 between September 2020 and October 2021. Quantitative computed tomography was used to measure the lumbar vertebra's bone mineral density (BMD). The coronary artery calcium score (CACS) and total coronary plaque burden were quantified using the Agatston and modified Gensini scores, respectively. Associations between BMD and CACS and modified Gensini scores were assessed using multivariate regression analysis. Lasso regression was used in model selection.

RESULTS

In men, BMD was inversely associated with CACS [ β  = -0.24; 95% confidence interval (CI), -0.35 to -0.13; P  < 0.001) and coronary artery calcification (CAC) presence [odds ratio (OR) = 0.71; 95% CI, 0.52-0.96; P  = 0.03) in the unadjusted model. After adjusting for age, modified Gensini score, prior percutaneous coronary intervention and hypertension, BMD was inversely associated with CACS ( β  = -0.11; 95% CI, -0.22 to -0.01; P  = 0.04). In postmenopausal women, BMD was inversely associated with CACS ( β  = -0.24; 95% CI, -0.39 to 0.10; P  < 0.001) and CAC presence (OR = 0.66; 95% CI, 0.47-0.92; P  = 0.01) in the unadjusted model but no other models ( P  > 0.05). In both sexes, BMD did not correlate with the modified Gensini score or CAD prevalence (all P  > 0.05).

CONCLUSION

In patients with coronary atherosclerosis and CAD, BMD of the lumbar vertebra correlated inversely with CACS in men but not postmenopausal women. Additionally, BMD did not correlate with the modified Gensini score in both sexes.

Cellular senescence of renal tubular epithelial cells in acute kidney injury

Cellular senescence represents an irreversible state of cell-cycle arrest during which cells secrete senescence-associated secretory phenotypes, including inflammatory factors and chemokines. Additionally, these cells exhibit an apoptotic resistance phenotype. Cellular senescence serves a pivotal role not only in embryonic development, tissue regeneration, and tumor suppression but also in the pathogenesis of age-related degenerative diseases, malignancies, metabolic diseases, and kidney diseases. The senescence of renal tubular epithelial cells (RTEC) constitutes a critical cellular event in the progression of acute kidney injury (AKI). RTEC senescence inhibits renal regeneration and repair processes and, concurrently, promotes the transition of AKI to chronic kidney disease via the senescence-associated secretory phenotype. The mechanisms underlying cellular senescence are multifaceted and include telomere shortening or damage, DNA damage, mitochondrial autophagy deficiency, cellular metabolic disorders, endoplasmic reticulum stress, and epigenetic regulation. Strategies aimed at inhibiting RTEC senescence, targeting the clearance of senescent RTEC, or promoting the apoptosis of senescent RTEC hold promise for enhancing the renal prognosis of AKI. This review primarily focuses on the characteristics and mechanisms of RTEC senescence, and the impact of intervening RTEC senescence on the prognosis of AKI, aiming to provide a foundation for understanding the pathogenesis and providing potentially effective approaches for AKI treatment.

Monocyte alteration in elderly hip fracture healing: monocyte promising role in bone regeneration

Individual aged with various change in cell and cellular microenvironments and the skeletal system undergoes physiological changes that affect the process of bone fracture healing. These changes are accompanied by alterations in regulating critical genes involved in this healing process. Unfortunately, the elderly are particularly susceptible to hip bone fractures, which pose a significant burden associated with higher morbidity and mortality rates. A notable change in older adults is the increased expression of activation, adhesion, and migration markers in circulating monocytes. However, there is a decrease in the expression of co-inhibitory molecules. Recently, research evidence has shown that the migration of specific monocyte subsets to the site of hip fracture plays a crucial role in bone resorption and remodeling, especially concerning age-related factors. In this review, we summarize the current knowledge about uniqueness characteristics of monocytes, and their potential regulation and moderation to enhance the healing process of hip fractures. This breakthrough could significantly contribute to the comprehension of aging process at a fundamental aging mechanism through this initiative would represent a crucial stride for diagnosing and treating age related hip fracture.

Biomimetic Therapeutics for Bone Regeneration: A Perspective on Antiaging Strategies

Advances in modern medicine and the significant reduction in infant mortality have steadily increased the population's lifespan. As more and more people in the world grow older, incidence of chronic, noncommunicable disease is anticipated to drastically increase. Recent studies have shown that improving the health of the aging population is anticipated to provide the most cost-effective and impactful improvement in quality of life during aging-driven disease. In bone, aging is tightly linked to increased risk of fracture, and markedly decreased regenerative potential, deeming it critical to develop therapeutics to improve aging-driven bone regeneration. Biomimetics offer a cost-effective method in regenerative therapeutics for bone, where there are numerous innovations improving outcomes in young models, but adapting biomimetics to aged models is still a challenge. Chronic inflammation, accumulation of reactive oxygen species, and cellular senescence are among three of the more unique challenges facing aging-induced defect repair. This review dissects many of the innovative biomimetic approaches research groups have taken to tackle these challenges, and discusses the further uncertainties that need to be addressed to push the field further. Through these research innovations, it can be noted that biomimetic therapeutics hold great potential for the future of aging-complicated defect repair.

In Vitro Osteogenesis Study of Shell Nacre Cement with Older and Young Donor Bone Marrow Mesenchymal Stem/Stromal Cells

Bone void-filling cements are one of the preferred materials for managing irregular bone voids, particularly in the geriatric population who undergo many orthopedic surgeries. However, bone marrow mesenchymal stem/stromal cells (BM-MSCs) of older-age donors often exhibit reduced osteogenic capacity. Hence, it is crucial to evaluate candidate bone substitute materials with BM-MSCs from the geriatric population to determine the true osteogenic potential, thus simulating the clinical situation. With this concept, we investigated the osteogenic potential of shell nacre cement (SNC), a bone void-filling cement based on shell nacre powder and ladder-structured siloxane methacrylate, using older donor BM-MSCs (age > 55 years) and young donor BM-MSCs (age < 30 years). Direct and indirect cytotoxicity studies conducted with human BM-MSCs confirmed the non-cytotoxic nature of SNC. The standard colony-forming unit-fibroblast (CFU-F) assay and population doubling (PD) time assays revealed a significant reduction in the proliferation potential (p < 0.0001, p < 0.05) in older donor BM-MSCs compared to young donor BM-MSCs. Correspondingly, older donor BM-MSCs contained higher proportions of senescent, β-galactosidase (SA-β gal)-positive cells (nearly 2-fold, p < 0.001). In contrast, the proliferation capacity of older donor BM-MSCs, measured as the area density of CellTrackerTM green positive cells, was similar to that of young donor BM-MSCs following a 7-day culture on SNC. Furthermore, after 14 days of osteoinduction on SNC, scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) showed that the amount of calcium and phosphorus deposited by young and older donor BM-MSCs on SNC was comparable. A similar trend was observed in the expression of the osteogenesis-related genes BMP2, RUNX2, ALP, COL1A1, OMD and SPARC. Overall, the results of this study indicated that SNC would be a promising candidate for managing bone voids in all age groups.

Relationship of the bone phenotype of the Klotho mutant mouse model of accelerated aging to changes in skeletal architecture that occur with chronological aging

Introduction

Due to the relatively long life span of rodent models, in order to expediate the identification of novel therapeutics of age related diseases, mouse models of accelerated aging have been developed. In this study we examined skeletal changes in the male and female Klotho mutant (kl/kl) mice and in male and female chronically aged mice to determine whether the accelerated aging bone phenotype of the kl/kl mouse reflects changes in skeletal architecture that occur with chronological aging.

Methods

2, 6 and 20-23 month old C57BL/6 mice were obtained from the National Institute of Aging aged rodent colony and wildtype and kl/kl mice were generated as previously described by M. Kuro-o. Microcomputed tomography analysis was performed ex vivo to examine trabecular and cortical parameters from the proximal metaphyseal and mid-diaphyseal areas, respectively. Serum calcium and phosphate were analyzed using a colorimetric assay. The expression of duodenal Trpv6, which codes for TRPV6, a vitamin D regulated epithelial calcium channel whose expression reflects intestinal calcium absorptive efficiency, was analyzed by quantitative real-time PCR.

Results and discussion

Trabecular bone volume (BV/TV) and trabecular number decreased continuously with age in males and females. In contrast to aging mice, an increase in trabecular bone volume and trabecular number was observed in both male and female kl/kl mice. Cortical thickness decreased with advancing age and also decreased in male and female kl/kl mice. Serum calcium and phosphate levels were significantly increased in kl/kl mice but did not change with age. Aging resulted in a decline in Trpv6 expression. In the kl/kl mice duodenal Trpv6 was significantly increased. Our findings reflect differences in bone architecture as well as differences in calcium and phosphate homeostasis and expression of Trpv6 between the kl/kl mutant mouse model of accelerated aging and chronological aging. Although the Klotho deficient mouse has provided a new understanding of the regulation of mineral homeostasis and bone metabolism, our findings suggest that changes in bone architecture in the kl/kl mouse reflect in part systemic disturbances that differ from pathophysiological changes that occur with age including dysregulation of calcium homeostasis that contributes to age related bone loss.

A Missense Variant in TP53 Could Be a Genetic Biomarker Associated with Bone Tissue Alterations

Metabolic bone diseases cover a broad spectrum of disorders that share alterations in bone metabolism that lead to a defective skeleton, which is associated with increasing morbidity, disability, and mortality. There is a close connection between the etiology of metabolic bone diseases and genetic factors, with TP53 being one of the genes associated therewith. The single nucleotide polymorphism (SNP) Arg72Pro of TP53 is a genetic factor associated with several pathologies, including cancer, stroke, and osteoporosis. Here, we aim to analyze the influence of the TP53 Arg72Pro SNP on bone mass in humanized Tp53 Arg72Pro knock-in mice. This work reports on the influence of the TP53 Arg72Pro polymorphism in bone microarchitecture, OPG expression, and apoptosis bone status. The results show that the proline variant of the TP53 Arg72Pro polymorphism (Pro72-p53) is associated with deteriorated bone tissue, lower OPG/RANK ratio, and lower apoptosis in bone tissue. In conclusion, the TP53 Arg72Pro polymorphism modulates bone microarchitecture and may be a genetic biomarker that can be used to identify individuals with an increased risk of suffering metabolic bone alterations.

Organoid extracellular vesicle-based therapeutic strategies for bone therapy

With the rapid development of population ageing, bone-related diseases seriously affecting the life of the elderly. Over the past few years, organoids, cell clusters with specific functions and structures that are self-induced from stem cells after three-dimensional culture in vitro, have been widely used for bone therapy. Moreover, organoid extracellular vesicles (OEVs) have emerging as promising cell-free nanocarriers due to their vigoroso physiological effects, significant biological functions, stable loading capacity, and great biocompatibility. In this review, we first provide a comprehensive overview of biogenesis, internalisation, isolation, and characterisation of OEVs. We then comprehensively highlight the differences between OEVs and traditional EVs. Subsequently, we present the applications of natural OEVs in disease treatment. We also summarise the engineering modifications of OEVs, including engineering parental cells and engineering OEVs after isolation. Moreover, we provide an outlook on the potential of natural and engineered OEVs in bone-related diseases. Finally, we critically discuss the advantages and challenges of OEVs in the treatment of bone diseases. We believe that a comprehensive discussion of OEVs will provide more innovative and efficient solutions for complex bone diseases.

Lycopene Improves Bone Quality in SAMP6 Mice by Inhibiting Oxidative Stress, Cellular Senescence, and the SASP

SCOPE

Cellular senescence (CS) is closely related to tissue ageing including bone ageing. CS and the senescence-associated secretory phenotype (SASP) have emerged as critical pathogenesis elements of senile osteoporosis. This study aims to investigate the effect of lycopene on senile osteoporosis.

METHODS AND RESULTS

The senescence-accelerated mouse prone 6 (SAMP6) strain of mice is used as the senile osteoporosis model. Daily ingestion of lycopene for 8 weeks preserves the bone mass, density, strength, and microarchitecture in the SAMP6 mice. Moreover, these alterations are associated with a decrease in oxidative stress in the senile osteoporosis model. In addition, there is a reduction in osteoblast and osteocyte senescence and the SASP in the bone tissues of the SAMP6 mice. Lycopene improves bone health likely due to its antioxidant properties that may be linked with the regulation of CS and SASP in the SAMP6 mice.

CONCLUSION

These results suggest that lycopene may be beneficial for the management of senile osteoporosis by inhibiting oxidative stress, CS, and the SASP.

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.

Telomere length as a predictive biomarker in osteoporosis (Review)

Telomeres are the ends of chromosomes that protect them from DNA damage. There is evidence to suggest that telomere shortening appears with advanced age. Since aging is a significant risk factor for developing age-related complications, it is plausible that telomere shortening may be involved in the development of osteoporosis. The present review summarizes the potential of telomere shortening as a biomarker for detecting the onset of osteoporosis. For the purposes of the present review, the following scientific databases were searched for relevant articles: PubMed/NCBI, Cochrane Library of Systematic Reviews, Scopus, Embase and Google Scholar. The present review includes randomized and non-randomized controlled studies and case series involving humans, irrespective of the time of their publication. In six out of the 11 included studies providing data on humans, there was at least a weak association between telomere length and osteoporosis, with the remaining studies exhibiting no such association. As a result, telomere shortening may be used as a biomarker or as part of a panel of biomarkers for tracking the onset and progression of osteoporosis.

Hyperbaric oxygen therapy exerts anti-osteoporotic effects in obese and lean D-galactose-induced aged rats

Obesity accelerates the aging processes, resulting in an aggravation of aging-induced osteoporosis. We investigated the anti-osteoporotic effect of hyperbaric oxygen therapy (HBOT) in obese- and lean-aged rats through measurement of cellular senescence, hypoxia, inflammation, antioxidants, and bone microarchitecture. Obese and lean male Wistar rats were injected with 150 mg/kg/day of D-galactose for 8 weeks to induce aging. Then, all rats were randomly given either sham or HBOT for 14 days. Metabolic parameters were determined. Expression by bone mRNA for cellular senescence, hypoxia, inflammation, antioxidative capacity, and bone remodeling were examined. Micro-computed tomography and atomic absorption spectroscopy were performed to evaluate bone microarchitecture and bone mineral profiles, respectively. We found that HBOT restored the alterations in the mRNA expression level of p16, p21, HIF-1α, TNF-α, IL-6, RANKL, RANK, NFATc1, DC-STAMP, Osx, ALP, and Col1a1 in the bone in obese-and lean- aging rats. In obese-aging rats, HBOT increased the level of expression of Sirt1 and CuZnSOD mRNA and diminished the expression level of HIF-2α and ctsk mRNA to the same levels as the control group. However, HBOT failed to alter catalase and OCN mRNA expression in obese-aged rats. HBOT partially improved the bone microarchitecture in obese-aged rats, but completely restored it in lean-aged rats. Interestingly, HBOT protected against obesity-induced demineralization in obese-aged rats. In summary, HBOT exerts an anti-osteoporotic effect in lean-aged rats and prevents some, but not all the negative effects of obese-aged conditions on bone health. Therefore, HBOT is considered as a potential therapy for aging-induced osteoporosis, regardless of obese status.

Molecular and Cellular Mechanisms of Osteoporosis

Osteoporosis is a widespread systemic disease characterized by a decrease in bone mass and an imbalance of the microarchitecture of bone tissue. Experimental and clinical studies devoted to investigating the main pathogenetic mechanisms of osteoporosis revealed the important role of estrogen deficiency, inflammation, oxidative stress, cellular senescence, and epigenetic factors in the development of bone resorption due to osteoclastogenesis, and decreased mineralization of bone tissue and bone formation due to reduced function of osteoblasts caused by apoptosis and age-depended differentiation of osteoblast precursors into adipocytes. The current review was conducted to describe the basic mechanisms of the development of osteoporosis at molecular and cellular levels and to elucidate the most promising therapeutic strategies of pathogenetic therapy of osteoporosis based on articles cited in PubMed up to September 2023.

Tissue-specific expression of senescence biomarkers in spontaneously hypertensive rats: evidence of premature aging in hypertension

Background

Cellular senescence is an age-related physiological process that contributes to tissue dysfunction and accelerated onset of chronic metabolic diseases including hypertension. Indeed, elevation of blood pressure in hypertension coincides with premature vascular aging and dysfunction. In addition, onsets of metabolic disturbance and osteopenia in patients with hypertension have also been reported. It is possible that hypertension enhances premature aging and causes progressive loss of function in multiple organs. However, the landscape of cellular senescence in critical tissues affected by hypertension remains elusive.

Materials and Methods

Heart, liver, bone, hypothalamus, and kidney were collected from spontaneously hypertensive rats (SHR) and age- and sex-matched normotensive Wistar rats (WT) at 6, 12, 24 and 36 weeks of age (n = 10 animals/group). Changes in mRNA levels of senescence biomarkers namely cyclin-dependent kinase (CDK) inhibitors (CDKIs), i.e., Cdkn2a (encoding p16Ink4a) and Cdkn1a (encoding p21cip1) as well as senescence-associated secretory phenotypes (SASPs), i.e., Timp1, Mmp12, Il6 and Cxcl1, were determined. Additionally, bone collagen alignment and hydroxy apatite crystal dimensions were determined by synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS) techniques.

Results

Real-time PCR revealed that transcript levels of genes encoding CDKIs and SASPs in the heart and liver were upregulated in SHR from 6 to 36 weeks of age. Expression of Timp1 and Cxcl1 was increased in bone tissues isolated from 36-week-old SHR. In contrast, we found that expression levels of Timp1 and Il6 mRNA were decreased in hypothalamus and kidney of SHR in all age groups. Simultaneous SAXS/WAXS analysis also revealed misalignment of bone collagen fibers in SHR as compared to WT.

Conclusion

Premature aging was identified in an organ directly affected by high blood pressure (i.e., heart) and those with known functional defects in SHR (i.e., liver and bone). Cellular senescence was not evident in organs with autoregulation of blood pressure (i.e., brain and kidney). Our study suggested that cellular senescence is induced by persistently elevated blood pressure and in part, leading to organ dysfunction. Therefore, interventions that can both lower blood pressure and prevent cellular senescence should provide therapeutic benefits for treatment of cardiovascular and metabolic consequences.

Understanding the Consequences of Fatty Bone and Fatty Muscle: How the Osteosarcopenic Adiposity Phenotype Uncovers the Deterioration of Body Composition

Adiposity is central to aging and several chronic diseases. Adiposity encompasses not just the excess adipose tissue but also body fat redistribution, fat infiltration, hypertrophy of adipocytes, and the shifting of mesenchymal stem cell commitment to adipogenesis. Bone marrow adipose tissue expansion, inflammatory adipokines, and adipocyte-derived extracellular vesicles are central to the development of osteopenic adiposity. Adipose tissue infiltration and local adipogenesis within the muscle are critical in developing sarcopenic adiposity and subsequent poorer functional outcomes. Ultimately, osteosarcopenic adiposity syndrome is the result of all the processes noted above: fat infiltration and adipocyte expansion and redistribution within the bone, muscle, and adipose tissues, resulting in bone loss, muscle mass/strength loss, deteriorated adipose tissue, and subsequent functional decline. Increased fat tissue, typically referred to as obesity and expressed by body mass index (the latter often used inadequately), is now occurring in younger age groups, suggesting people will live longer with the negative effects of adiposity. This review discusses the role of adiposity in the deterioration of bone and muscle, as well as adipose tissue itself. It reveals how considering and including adiposity in the definition and diagnosis of osteopenic adiposity, sarcopenic adiposity, and osteosarcopenic adiposity will help in better understanding the pathophysiology of each and accelerate possible therapies and prevention approaches for both relatively healthy individuals or those with chronic disease.

Integrative profiling of metabolome and transcriptome of skeletal muscle after acute exercise intervention in mice

This study aims to explore the molecular regulatory mechanisms of acute exercise in the skeletal muscle of mice. Male C57BL/6 mice were randomly assigned to the control group, and the exercise group, which were sacrificed immediately after an acute bout of exercise. The study was conducted to investigate the metabolic and transcriptional profiling in the quadriceps muscles of mice. The results demonstrated the identification of 34 differentially expressed metabolites (DEMs), with 28 upregulated and 6 downregulated, between the two groups. Metabolic pathway analysis revealed that these DEMs were primarily enriched in several, including the citrate cycle, propanoate metabolism, and lysine degradation pathways. In addition, the results showed a total of 245 differentially expressed genes (DEGs), with 155 genes upregulated and 90 genes downregulated. KEGG analysis indicated that these DEGs were mainly enriched in various pathways such as ubiquitin mediated proteolysis and FoxO signaling pathway. Furthermore, the analysis revealed significant enrichment of DEMs and DEGs in signaling pathways such as protein digestion and absorption, ferroptosis signaling pathway. In summary, the identified multiple metabolic pathways and signaling pathways were involved in the exercise-induced physiological regulation of skeletal muscle, such as the TCA cycle, oxidative phosphorylation, protein digestion and absorption, the FoxO signaling pathway, ubiquitin mediated proteolysis, ferroptosis signaling pathway, and the upregulation of KLF-15, FoxO1, MAFbx, and MuRF1 expression could play a critical role in enhancing skeletal muscle proteolysis.

The role of cellular senescence in metabolic diseases and the potential for senotherapeutic interventions

Cellular senescence represents an irreversible state of cell cycle arrest induced by various stimuli strongly associated with aging and several chronic ailments. In recent years, studies have increasingly suggested that the accumulation of senescent cells is an important contributor to the decline of organ metabolism, ultimately resulting in metabolic diseases. Conversely, the elimination of senescent cells can alleviate or postpone the onset and progression of metabolic diseases. Thus, a close relationship between senescent cells and metabolic diseases is found, and targeting senescent cells has emerged as an alternative therapy for the treatment of metabolic diseases. In this review, we summarize the role of cellular senescence in metabolic diseases, explore relevant therapeutic strategies for metabolic diseases by removing senescent cells, and provide new insights into the treatment of metabolic diseases.

Senescent Stem Cell Dysfunction and Age-Related Diseases

As the body ages, it experiences a gradual decline in the functioning of cells, tissues, and systems, which eventually leads to dysfunction and increased susceptibility to disease. At the cellular level, a reduction in the activity or number of stem cells is an important feature of cell senescence, and such changes may also directly drive the aging of the organism. Thus, finding ways to prevent or even reverse stem cell senescence holds promise for the development of aging therapies in tissues and organisms. This review discusses the relationship between changes in stem cell senescence, tissues aging, and related diseases, focusing on four categories of tissue stem cells: hematopoietic stem cells, mesenchymal stromal/stem cells (MSCs), intestinal stem cells, and muscle stem cells.

Oxidative stress in intervertebral disc degeneration: Molecular mechanisms, pathogenesis and treatment

Low back pain (LBP) is a leading cause of labour loss and disability worldwide, and it also imposes a severe economic burden on patients and society. Among symptomatic LBP, approximately 40% is caused by intervertebral disc degeneration (IDD). IDD is the pathological basis of many spinal degenerative diseases such as disc herniation and spinal stenosis. Currently, the therapeutic approaches for IDD mainly include conservative treatment and surgical treatment, neither of which can solve the problem from the root by terminating the degenerative process of the intervertebral disc (IVD). Therefore, further exploring the pathogenic mechanisms of IDD and adopting targeted therapeutic strategies is one of the current research hotspots. Among the complex pathophysiological processes and pathogenic mechanisms of IDD, oxidative stress is considered as the main pathogenic factor. The delicate balance between reactive oxygen species (ROS) and antioxidants is essential for maintaining the normal function and survival of IVD cells. Excessive ROS levels can cause damage to macromolecules such as nucleic acids, lipids, and proteins of cells, affect normal cellular activities and functions, and ultimately lead to cell senescence or death. This review discusses the potential role of oxidative stress in IDD to further understand the pathophysiological processes and pathogenic mechanisms of IDD and provides potential therapeutic strategies for the treatment of IDD.