Identification of Senescent Cells in the Bone Microenvironment

Multifunctional scaffolds for bone repair following age-related biological decline: Promising prospects for smart biomaterial-driven technologies

The repair of large bone defects due to trauma, disease, and infection can be exceptionally challenging in the elderly. Despite best clinical practice, bone regeneration within contemporary, surgically implanted synthetic scaffolds is often problematic, inconsistent, and insufficient where additional osteobiological support is required to restore bone. Emergent smart multifunctional biomaterials may drive important and dynamic cellular crosstalk that directly targets, signals, stimulates, and promotes an innate bone repair response following age-related biological decline and when in the presence of disease or infection. However, their role remains largely undetermined. By highlighting their mechanism/s and mode/s of action, this review spotlights smart technologies that favorably align in their conceivable ability to directly target and enhance bone repair and thus are highly promising for future discovery for use in the elderly. The four degrees of interactive scaffold smartness are presented, with a focus on bioactive, bioresponsive, and the yet-to-be-developed autonomous scaffold activity. Further, cell- and biomolecular-assisted approaches were excluded, allowing for contemporary examination of the capabilities, demands, vision, and future requisites of next-generation biomaterial-induced technologies only. Data strongly supports that smart scaffolds hold significant promise in the promotion of bone repair in patients with a reduced osteobiological response. Importantly, many techniques have yet to be tested in preclinical models of aging. Thus, greater clarity on their proficiency to counteract the many unresolved challenges within the scope of aging bone is highly warranted and is arguably the next frontier in the field. This review demonstrates that the use of multifunctional smart synthetic scaffolds with an engineered strategy to circumvent the biological insufficiencies associated with aging bone is a viable route for achieving next-generation therapeutic success in the elderly population.

Analysis of the relationship between age-related erythrocyte dysfunction and fatigue

With the declining birth rates and aging societies in developed countries, the average age of the working population is increasing. Older people tend to get tired more easily, so prevention of fatigue is important to improve the quality of life for older workers. This study aimed to assess the mechanism of fatigue in older people, especially focused on relation between dysfunction of erythrocyte and fatigue. Total power (TP), which is the value of autonomic nerve activity, was measured as a value of fatigue and significantly decreased in workers with aging. As properties of senescent erythrocytes, the erythrocyte sedimentation rate and damaged erythrocytes population increased with aging and correlated with TP. These results suggested that the accumulation of damaged erythrocytes contributes to fatigue. Recent studies revealed that senescence-associated secretory phenotype (SASP), a phenomenon in which senescent cells secrete a variety of cytokines, affected hematopoiesis in bone marrow. We analyzed the effects of SASP factors on erythropoiesis and found that Interleukin -1α (IL-1α) suppressed erythrocyte differentiation of hematopoietic stem cells in vitro. We also showed that IL-1α levels in human blood and saliva increase with aging, suggesting the possibility that IL-1α level in saliva can be used to predict the decline in hematopoietic function.

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.

Single-cell multi-omics identify novel regulators required for osteoclastogenesis during aging

Age-related osteoporosis manifests as a complex pathology that disrupts bone homeostasis and elevates fracture risk, yet the mechanisms facilitating age-related shifts in bone marrow macrophages/osteoclasts (BMMs/OCs) lineage are not fully understood. To decipher these mechanisms, we conducted an investigation into the determinants controlling BMMs/OCs differentiation. We performed single-cell multi-omics profiling on bone marrow samples from mice of different ages (1, 6, and 20 months) to gain a holistic understanding of cellular changes across time. Our analysis revealed that aging significantly instigates OC differentiation. Importantly, we identified Cebpd as a vital gene for osteoclastogenesis and bone resorption during the aging process. Counterbalancing the effects of Cebpd, we found Irf8, Sox4, and Klf4 to play crucial roles. By thoroughly examining the cellular dynamics underpinning bone aging, our study unveils novel insights into the mechanisms of age-related osteoporosis and presents potential therapeutic targets for future exploration.

Evaluating the role of biological age in osteoporosis risk among middle-aged and older adults: A nationwide perspective

OBJECTIVES

This study aimed to investigate the association between biological age acceleration and osteoporosis (OP) risk in middle-aged and older adults using data from the National Health and Nutrition Examination Survey (NHANES). The research focused on analyzing the relationship between two biological aging metrics, Klemera-Doubal Method Age (KDMAge) and Phenotypic Age (PhenoAge), and OP risk.

METHODS

The study analyzed data from NHANES, which included 6550 participants aged 50 and above from survey cycles 2005-2010 and 2017-2018. Linear and logistic regression were used to investigate the relationship between biological age acceleration (KDMAgeAccel and PhenoAgeAccel) and OP. Subgroup analysis was performed by age, gender and other factors. Multivariable Cox regression analysis yielded Hazard Ratios (HRs) relating biological age acceleration to mortality were evaluated. The study also considered the mediating roles of body mass index (BMI).

RESULTS

KDMAgeAccel (odds ratio [OR] = 2.34, 95 % CI, 1.72-3.18) and PhenoAgeAccel (OR = 2.03, 95 % CI, 1.48-2.78) were significantly associated with increased OP risk and reduced bone mineral density (BMD). Specifically, higher KDMAgeAccel and PhenoAgeAccel were linked to higher OP prevalence and lower BMD at multiple sites. Subgroup analyses indicated that the association between accelerated biological age acceleration and OP risk was consistent across different demographics. Mediation analysis revealed that BMI partially mediated the relationship between accelerated biological age and OP, although other mechanisms are likely involved. Statistical analysis indicated that individuals with higher biological age metrics had increased mortality risk related to OP.

CONCLUSION

The findings suggest that accelerated biological age is a robust predictor of OP risk and related mortality. KDMAgeAccel and PhenoAgeAccel could serve as valuable biomarkers for identifying individuals at high risk for OP, guiding preventive strategies.

Aged bone marrow macrophages drive systemic aging and age-related dysfunction via extracellular vesicle-mediated induction of paracrine senescence

The accumulation and systemic propagation of senescent cells contributes to physiological aging and age-related pathology. However, which cell types are most susceptible to the aged milieu and could be responsible for the propagation of senescence has remained unclear. Here we found that physiologically aged bone marrow monocytes/macrophages (BMMs) propagate senescence to multiple tissues, through extracellular vesicles (EVs), and drive age-associated dysfunction in mice. We identified peroxisome proliferator-activated receptor α (PPARα) as a target of microRNAs within aged BMM-EVs that regulates downstream effects on senescence and age-related dysfunction. Demonstrating therapeutic potential, we report that treatment with the PPARα agonist fenofibrate effectively restores tissue homeostasis in aged mice. Suggesting conservation to humans, in a cohort study of 7,986 participants, we found that fenofibrate use is associated with a reduced risk of age-related chronic disease and higher life expectancy. Together, our findings establish that BMMs can propagate senescence to distant tissues and cause age-related dysfunction, and they provide supportive evidence for fenofibrate to extend healthy lifespan.

Targeting Cell Senescence and Senolytics: Novel Interventions for Age-Related Endocrine Dysfunction

Multiple changes occur in hormonal regulation with aging and across various endocrine organs. These changes are associated with multiple age-related disorders and diseases. A better understanding of responsible underling biological mechanisms could help in the management of multiple endocrine disorders over and above hormone replacement therapy (HRT). Cellular senescence is involved in multiple biological aging processes and pathologies common in elderly individuals. Cellular senescence, which occurs in many older individuals but also across the lifespan in association with tissue damage, acute and chronic diseases, certain drugs, and genetic syndromes, may contribute to such endocrine disorders as osteoporosis, metabolic syndrome, and type 2 diabetes mellitus. Drugs that selectively induce senescent cell removal, "senolytics,", and drugs that attenuate the tissue-destructive secretory state of certain senescent cells, "senomorphics," appear to delay the onset of or alleviate multiple diseases, including but not limited to endocrine disorders such as diabetes, complications of obesity, age-related osteoporosis, and cancers as well as atherosclerosis, chronic kidney disease, neurodegenerative disorders, and many others. More than 30 clinical trials of senolytic and senomorphic agents have already been completed, are underway, or are planned for a variety of indications. Targeting senescent cells is a novel strategy that is distinct from conventional therapies such as HRT, and thus might address unmet medical needs and can potentially amplify effects of established endocrine drug regimens, perhaps allowing for dose decreases and reducing side effects.

Targeting TGF-β signaling, oxidative stress, and cellular senescence rescues osteoporosis in gerodermia osteodysplastica

GORAB is a key regulator of Golgi vesicle transport and protein glycanation. Loss of GORAB function in gerodermia osteodysplastica (GO) causes shortening of glycosaminoglycan chains, leading to extracellular matrix disorganization that results in wrinkled skin, osteoporosis and elevated TGF-β signaling. In this study, we investigated the role of TGF-β-signaling, oxidative stress, and resulting cellular senescence in the osteoporosis phenotype of GO. Treatment of GorabPrx1 conditional knockouts with the TGF-β neutralizing antibody 1D11 rescued the trabecular bone loss, indicating that TGF-β overactivation causes osteoporosis in GO. Using an inducible knockout system, we demonstrated that TGF-β dysregulation was not a cell-intrinsic effect of GORAB inactivation, but a consequence of a disorganized extracellular matrix. Enhanced TGF-β signaling caused elevated Nox4 expression in GorabPrx1 mutants and in GO patients' fibroblasts, resulting in overproduction of mitochondrial superoxide. The resulting oxidative stress was detected in GORAB null cells and also in wildtype bystander cells. The same effect was observed in zebrafish after TALEN-mediated gorab inactivation, indicating that the pathway is evolutionarily conserved. Treating GorabPrx1 mutants with the antioxidant N-acetylcysteine ameliorated the osteoporosis phenotype. TGF-β induced oxidative stress coincided with accumulation of DNA damage and elevated expression of senescence markers. Inactivation of Cdkn2a in the GorabPrx1 rescued the osteoporosis phenotype. Reduced colony formation and altered subpopulations of bone marrow stromal cells were normalized upon inactivation of Cdkn2a, thus further demonstrating the relevance of cellular senescence in the pathogenesis. Our results shed light on the causative role of a TGF-β-Nox4-senescence axis and therapeutic strategies for GO.

Effects of intermittent senolytic therapy on bone metabolism in postmenopausal women: a phase 2 randomized controlled trial

Preclinical evidence demonstrates that senescent cells accumulate with aging and that senolytics delay multiple age-related morbidities, including bone loss. Thus, we conducted a phase 2 randomized controlled trial of intermittent administration of the senolytic combination dasatinib plus quercetin (D + Q) in postmenopausal women (n = 60 participants). The primary endpoint, percentage changes at 20 weeks in the bone resorption marker C-terminal telopeptide of type 1 collagen (CTx), did not differ between groups (median (interquartile range), D + Q -4.1% (-13.2, 2.6), control -7.7% (-20.1, 14.3); P = 0.611). The secondary endpoint, percentage changes in the bone formation marker procollagen type 1 N-terminal propeptide (P1NP), increased significantly (relative to control) in the D + Q group at both 2 weeks (+16%, P = 0.020) and 4 weeks (+16%, P = 0.024), but was not different from control at 20 weeks (-9%, P = 0.149). No serious adverse events were observed. In exploratory analyses, the skeletal response to D + Q was driven principally by women with a high senescent cell burden (highest tertile for T cell p16 (also known as CDKN2A) mRNA levels) in which D + Q concomitantly increased P1NP (+34%, P = 0.035) and reduced CTx (-11%, P = 0.049) at 2 weeks, and increased radius bone mineral density (+2.7%, P = 0.004) at 20 weeks. Thus, intermittent D + Q treatment did not reduce bone resorption in the overall group of postmenopausal women. However, our exploratory analyses indicate that further studies are needed testing the hypothesis that the underlying senescent cell burden may dictate the clinical response to senolytics. ClinicalTrials.gov identifier: NCT04313634 .

Musculoskeletal imaging of senescence

Senescent cells play a vital role in the pathogenesis of musculoskeletal (MSK) diseases, such as chronic inflammatory joint disorders, rheumatoid arthritis (RA), and osteoarthritis (OA). Cellular senescence in articular joints represents a response of local cells to persistent stress that leads to cell-cycle arrest and enhanced production of inflammatory cytokines, which in turn perpetuates joint damage and leads to significant morbidities in afflicted patients. It has been recently discovered that clearance of senescent cells by novel "senolytic" therapies can attenuate the chronic inflammatory microenvironment of RA and OA, preventing further disease progression and supporting healing processes. To identify patients who might benefit from these new senolytic therapies and monitor therapy response, there is an unmet need to identify and map senescent cells in articular joints and related musculoskeletal tissues. To fill this gap, new imaging biomarkers are being developed to detect and characterize senescent cells in human joints and musculoskeletal tissues. This review article will provide an overview of these efforts. New imaging biomarkers for senescence cells are expected to significantly improve the specificity of state-of-the-art imaging technologies for diagnosing musculoskeletal disorders.

Mitochondrial RNA cytosolic leakage drives the SASP

Senescent cells secrete proinflammatory factors known as the senescence-associated secretory phenotype (SASP), contributing to tissue dysfunction and aging. Mitochondrial dysfunction is a key feature of senescence, influencing SASP via mitochondrial DNA (mtDNA) release and cGAS/STING pathway activation. Here, we demonstrate that mitochondrial RNA (mtRNA) also accumulates in the cytosol of senescent cells, activating RNA sensors RIG-I and MDA5, leading to MAVS aggregation and SASP induction. Inhibition of these RNA sensors significantly reduces SASP factors. Furthermore, BAX and BAK plays a key role in mtRNA leakage during senescence, and their deletion diminishes SASP expression in vitro and in a mouse model of Metabolic Dysfunction Associated Steatohepatitis (MASH). These findings highlight mtRNA's role in SASP regulation and its potential as a therapeutic target for mitigating age-related inflammation.

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.

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.

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.

Aging human abdominal subcutaneous white adipose tissue at single cell resolution

White adipose tissue (WAT) is a robust energy storage and endocrine organ critical for maintaining metabolic health as we age. Our aim was to identify cell-specific transcriptional aberrations that occur in WAT with aging. We leveraged full-length snRNA-Seq and histology to characterize the cellular landscape of human abdominal subcutaneous WAT in a prospective cohort of 10 younger (≤30 years) and 10 older individuals (≥65 years) balanced for sex and body mass index (BMI). The older group had greater cholesterol, very-low-density lipoprotein, triglycerides, thyroid stimulating hormone, and aspartate transaminase compared to the younger group (p < 0.05). We highlight that aging WAT is associated with adipocyte hypertrophy, increased proportions of lipid-associated macrophages and mast cells, an upregulation of immune responses linked to fibrosis in pre-adipocyte, adipocyte, and vascular populations, and highlight CXCL14 as a biomarker of these processes. We show that older WAT has elevated levels of senescence marker p16 in adipocytes and identify the adipocyte subpopulation driving this senescence profile. We confirm that these transcriptional and phenotypical changes occur without overt fibrosis and in older individuals that have comparable WAT insulin sensitivity to the younger individuals.

Guidelines for minimal information on cellular senescence experimentation in vivo

Cellular senescence is a cell fate triggered in response to stress and is characterized by stable cell-cycle arrest and a hypersecretory state. It has diverse biological roles, ranging from tissue repair to chronic disease. The development of new tools to study senescence in vivo has paved the way for uncovering its physiological and pathological roles and testing senescent cells as a therapeutic target. However, the lack of specific and broadly applicable markers makes it difficult to identify and characterize senescent cells in tissues and living organisms. To address this, we provide practical guidelines called "minimum information for cellular senescence experimentation in vivo" (MICSE). It presents an overview of senescence markers in rodent tissues, transgenic models, non-mammalian systems, human tissues, and tumors and their use in the identification and specification of senescent cells. These guidelines provide a uniform, state-of-the-art, and accessible toolset to improve our understanding of cellular senescence in vivo.

The role of calcium channels in osteoporosis and their therapeutic potential

Osteoporosis, a systemic skeletal disorder marked by diminished bone mass and compromised bone microarchitecture, is becoming increasingly prevalent due to an aging population. The underlying pathophysiology of osteoporosis is attributed to an imbalance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. Osteoclasts play a crucial role in the development of osteoporosis through various molecular pathways, including the RANK/RANKL/OPG signaling axis, cytokines, and integrins. Notably, the calcium signaling pathway is pivotal in regulating osteoclast activation and function, influencing bone resorption activity. Disruption in calcium signaling can lead to increased osteoclast-mediated bone resorption, contributing to the progression of osteoporosis. Emerging research indicates that calcium-permeable channels on the cellular membrane play a critical role in bone metabolism by modulating these intracellular calcium pathways. Here, we provide an overview of current literature on the regulation of plasma membrane calcium channels in relation to bone metabolism with particular emphasis on their dysregulation during the progression of osteoporosis. Targeting these calcium channels may represent a potential therapeutic strategy for treating osteoporosis.

Ageing-related bone and immunity changes: insights into the complex interplay between the skeleton and the immune system

Ageing as a natural irreversible process inherently results in the functional deterioration of numerous organ systems and tissues, including the skeletal and immune systems. Recent studies have elucidated the intricate bidirectional interactions between these two systems. In this review, we provide a comprehensive synthesis of molecular mechanisms of cell ageing. We further discuss how age-related skeletal changes influence the immune system and the consequent impact of immune system alterations on the skeletal system. Finally, we highlight the clinical implications of these findings and propose potential strategies to promote healthy ageing and reduce pathologic deterioration of both the skeletal and immune systems.

Hdac3-deficiency increases senescence-associated distention of satellite DNA and telomere-associated foci in osteoprogenitor cells

Histone deacetylase 3 (Hdac3) is an epigenetic regulator of gene expression and interacts with skeletal transcription factors such as Runx2. We previously reported that conditional deletion of Hdac3 in Osterix-Cre recombinase-expressing osteoprogenitor cells (Hdac3 CKOOsx) caused osteopenia and increased marrow adiposity, both hallmarks of skeletal aging. We also showed that Runx2+ cells within osteogenic cultures of Hdac3-depleted bone marrow stromal cells (BMSCs) contain lipid droplets (LDs). Cellular senescence, a nonproliferative metabolically active state, is associated with increased marrow adiposity, bone loss, and aging. In this study, we sought to determine if Hdac3 depleted Runx2+ pre-osteoblasts from young mice exhibit chromatin changes associated with early cellular senescence and how these events correlate with the appearance of LDs. We first confirmed that BMSCs from Hdac3 CKOOsx mice have more Runx2 + LD+ cells compared with controls under osteogenic conditions. We then measured senescence-associated distention of satellite (SADS) DNA and telomere-associated foci (TAFs) in Hdac3 CKOOsx and control BMSCs. In situ, Runx2+ cells contained more SADS per nuclei in Hdac3 CKOOsx femora than in controls. Runx2+ BMSCs from Hdac3 CKOOsx mice also contained more SADS and TAFs per nuclei than Runx2+ cells from age-matched control mice in vitro. SADs and TAFs were present at similar levels in Runx2 + LD+ cells and Runx2 + LD- cells from Hdac3 CKOOsx mice. Hdac inhibitors also increased the number of SADS in Runx2 + LD+ and Runx2 + LD- WT BMSCs. Senolytics reduced viable cell numbers in Hdac3 CKOOsx BMSC cultures. These data demonstrate that the depletion of Hdac3 in osteochondral progenitor cells triggers LD formation and early events in cellular senescence in Runx2+ BMSCs through mutually exclusive mechanisms.

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.

Senescence in the bone marrow microenvironment: A driver in development of therapy-related myeloid neoplasms

Therapy-related myeloid neoplasms (t-MN) are a growing concern due to the continued use of cytotoxic therapies to treat malignancies. Cytotoxic therapies have been shown to drive therapy-induced senescence in normal tissues, including in the bone marrow microenvironment (BMME), which plays a crucial role in supporting normal hematopoiesis. This review examines recent work that focuses on the contribution of BMME senescence to t-MN pathogenesis, as well as offers a perspective on potential opportunities for therapeutic intervention.

Skeletal stem and progenitor cells in bone development and repair

Bone development, growth, and repair are complex processes involving various cell types and interactions, with central roles played by skeletal stem and progenitor cells. Recent research brought new insights into the skeletal precursor populations that mediate intramembranous and endochondral bone development. Later in life, many of the cellular and molecular mechanisms determining development are reactivated upon fracture, with powerful trauma-induced signaling cues triggering a variety of postnatal skeletal stem/progenitor cells (SSPCs) residing near the bone defect. Interestingly, in this injury context, the current evidence suggests that the fates of both SSPCs and differentiated skeletal cells can be considerably flexible and dynamic, and that multiple cell sources can be activated to operate as functional progenitors generating chondrocytes and/or osteoblasts. The combined implementation of in vivo lineage tracing, cell surface marker-based cell selection, single-cell molecular analyses, and high-resolution in situ imaging has strongly improved our insights into the diversity and roles of developmental and reparative stem/progenitor subsets, while also unveiling the complexity of their dynamics, hierarchies, and relationships. Albeit incompletely understood at present, findings supporting lineage flexibility and possibly plasticity among sources of osteogenic cells challenge the classical dogma of a single primitive, self-renewing, multipotent stem cell driving bone tissue formation and regeneration from the apex of a hierarchical and strictly unidirectional differentiation tree. We here review the state of the field and the newest discoveries in the origin, identity, and fates of skeletal progenitor cells during bone development and growth, discuss the contributions of adult SSPC populations to fracture repair, and reflect on the dynamism and relationships among skeletal precursors and differentiated cell lineages. Further research directed at unraveling the heterogeneity and capacities of SSPCs, as well as the regulatory cues determining their fate and functioning, will offer vital new options for clinical translation toward compromised fracture healing and bone regenerative medicine.

Skeletal phenotypes and molecular mechanisms in aging mice

Aging is an inevitable physiological process, often accompanied by age-related bone loss and subsequent bone-related diseases that pose serious health risks. Research on skeletal diseases caused by aging in humans is challenging due to lengthy study durations, difficulties in sampling, regional variability, and substantial investment. Consequently, mice are preferred for such studies due to their similar motor system structure and function to humans, ease of handling and care, low cost, and short generation time. In this review, we present a comprehensive overview of the characteristics, limitations, applicability, bone phenotypes, and treatment methods in naturally aging mice and prematurely aging mouse models (including SAMP6, POLG mutant, LMNA, SIRT6, ZMPSTE24, TFAM, ERCC1, WERNER, and KL/KL-deficient mice). We also summarize the molecular mechanisms of these aging mouse models, including cellular DNA damage response, senescence-related secretory phenotype, telomere shortening, oxidative stress, bone marrow mesenchymal stem cell (BMSC) abnormalities, and mitochondrial dysfunction. Overall, this review aims to enhance our understanding of the pathogenesis of aging-related bone diseases.

Relationship between admission blood urea nitrogen levels and postoperative length of stay in patients with hip fracture: A retrospective study

To investigate the relationship between admission blood urea nitrogen (BUN) levels and postoperative length of stay (LOS) in hip fracture (HF) patients. This retrospective study retrieved related data from the MIMIC-IV database, of which the laboratory variables were taken preoperatively. The patients were divided into 4 groups according to the BUN quartile levels. After exploring the nonlinear relationship between BUN and LOS by generalized additive model, their connection was further analyzed using the generalized linear models, quantile regression models, and interaction analysis. Receiver operating characteristic curve analysis and decision curve analysis were performed to evaluate its value in predicting first intensive care unit admission and in-hospital mortality. Totally 1274 patients with HF were enrolled in the study. There was a nonlinear relationship between BUN and LOS (P < .05). Besides, BUN was an independent predictor for LOS after adjusting different covariates in 3 models (P < .05). Age served as a significant interactor in this relationship (P < .05). Moreover, receiver operating characteristic curve and decision curve analysis revealed the predictive value of BUN for intensive care unit admission and in-hospital mortality in HF. Admission BUN level as a cost-effective and easy-to-collect biomarker is significantly related to LOS in patients with HF. It helps clinicians to identify potential high-risk populations and take effective preventions before surgery to reduce postoperative LOS.

Efferocytosis and Bone Dynamics

PURPOSE OF REVIEW

This review summarizes the recently published scientific evidence regarding the role of efferocytosis in bone dynamics and skeletal health.

RECENT FINDINGS

Several types of efferocytes have been identified within the skeleton, with macrophages being the most extensively studied. Efferocytosis is not merely a 'clean-up' process vital for maintaining skeletal homeostasis; it also plays a crucial role in promoting resolution pathways and orchestrating bone dynamics, such as osteoblast-osteoclast coupling during bone remodeling. Impaired efferocytosis has been associated with aging-related bone loss and various skeletal pathologies, including osteoporosis, osteoarthritis, rheumatoid arthritis, and metastatic bone diseases. Accordingly, emerging evidence suggests that targeting efferocytic mechanisms has the potential to alleviate these conditions. While efferocytosis remains underexplored in the skeleton, recent discoveries have shed light on its pivotal role in bone dynamics, with important implications for skeletal health and pathology. However, there are several knowledge gaps and persisting technical limitations that must be addressed to fully unveil the contributions of efferocytosis in bone.

SenNet recommendations for detecting senescent cells in different tissues

Once considered a tissue culture-specific phenomenon, cellular senescence has now been linked to various biological processes with both beneficial and detrimental roles in humans, rodents and other species. Much of our understanding of senescent cell biology still originates from tissue culture studies, where each cell in the culture is driven to an irreversible cell cycle arrest. By contrast, in tissues, these cells are relatively rare and difficult to characterize, and it is now established that fully differentiated, postmitotic cells can also acquire a senescence phenotype. The SenNet Biomarkers Working Group was formed to provide recommendations for the use of cellular senescence markers to identify and characterize senescent cells in tissues. Here, we provide recommendations for detecting senescent cells in different tissues based on a comprehensive analysis of existing literature reporting senescence markers in 14 tissues in mice and humans. We discuss some of the recent advances in detecting and characterizing cellular senescence, including molecular senescence signatures and morphological features, and the use of circulating markers. We aim for this work to be a valuable resource for both seasoned investigators in senescence-related studies and newcomers to the field.

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.

AMH protects the ovary from doxorubicin by regulating cell fate and the response to DNA damage

Anti-Müllerian hormone (AMH) protects the ovarian reserve from chemotherapy, and this effect is most pronounced with Doxorubicin (DOX). However, the mechanisms of DOX toxicity and AMH rescue in the ovary remain unclear. Herein, we characterize these mechanisms in various ovarian cell types using scRNAseq. In the mesenchyme, DOX activates the intrinsic apoptotic signaling pathway through p53 class mediators, particularly affecting theca progenitors, while co-treament with AMH halts theca differentiation and reduces apoptotic gene expression. In preantral granulosa cells, DOX upregulates the cell cycle inhibitor Cdkn1a and dysregulates Wnt signaling, which are ameliorated by AMH co-treatment. Finally, in follicles, AMH induces Id3 , a protein involved in DNA repair, which is necessary to prevent the accumulation of DNA lesions marked by γ-H2AX in granulosa cells. Altogether this study characterizes cell, and follicle stage-specific mechanisms of AMH protection of the ovary, offering promising new avenues for fertility preservation in cancer patients undergoing chemotherapy.

Highlights

Doxorubicin treatment induces DNA damage that activates the p53 pathway in stromal and follicular cells of the ovary.AMH inhibits the proliferation and differentiation of theca and granulosa cells and promotes follicle survival following Doxorubicin insult.AMH treatment mitigates Doxorubicin-induced DNA damage in the ovary by preventing the accumulation of γ-H2AX-positive unresolved foci, through increased expression of ID3, a protein involved in DNA repair.

The impact of ageing mechanisms on musculoskeletal system diseases in the elderly

Ageing is an inevitable process that affects various tissues and organs of the human body, leading to a series of physiological and pathological changes. Mechanisms such as telomere depletion, stem cell depletion, macrophage dysfunction, and cellular senescence gradually manifest in the body, significantly increasing the incidence of diseases in elderly individuals. These mechanisms interact with each other, profoundly impacting the quality of life of older adults. As the ageing population continues to grow, the burden on the public health system is expected to intensify. Globally, the prevalence of musculoskeletal system diseases in elderly individuals is increasing, resulting in reduced limb mobility and prolonged suffering. This review aims to elucidate the mechanisms of ageing and their interplay while exploring their impact on diseases such as osteoarthritis, osteoporosis, and sarcopenia. By delving into the mechanisms of ageing, further research can be conducted to prevent and mitigate its effects, with the ultimate goal of alleviating the suffering of elderly patients in the future.

Compliant substrates mitigate the senescence associated phenotype of stress induced mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are a promising cell population for musculoskeletal cell-based therapies due to their multipotent differentiation capacity and complex secretome. Cells from younger donors are mechanosensitive, evidenced by changes in cell morphology, adhesivity, and differentiation as a function of substrate stiffness in both two- and three-dimensional culture. However, MSCs from older individuals exhibit reduced differentiation potential and increased senescence, limiting their potential for autologous use. While substrate stiffness is known to modulate cell phenotype, the influence of the mechanical environment on senescent MSCs is poorly described. To address this question, we cultured irradiation induced premature senescent MSCs on polyacrylamide hydrogels and assessed expression of senescent markers, cell morphology, and secretion of inflammatory cytokines. Compared to cells on tissue culture plastic, senescent MSCs exhibited decreased markers of the senescence associated secretory phenotype (SASP) when cultured on 50 kPa gels, yet common markers of senescence (e.g., p21, CDKN2A, CDKN1A) were unaffected. These effects were muted in a physiologically relevant heterotypic mix of healthy and senescent MSCs. Conditioned media from senescent MSCs on compliant substrates increased osteoblast mineralization compared to conditioned media from cells on TCP. Mixed populations of senescent and healthy cells induced similar levels of osteoblast mineralization compared to healthy MSCs, further indicating an attenuation of the senescent phenotype in heterotypic populations. These data indicate that senescent MSCs exhibit a decrease in senescent phenotype when cultured on compliant substrates, which may be leveraged to improve autologous cell therapies for older donors.

Focus on senescence: Clinical significance and practical applications

The older population is increasing worldwide, and life expectancy is continuously rising, predominantly thanks to medical and technological progress. Healthspan refers to the number of years an individual can live in good health. From a gerontological viewpoint, the mission is to extend the life spent in good health, promoting well-being and minimizing the impact of aging-related diseases to slow the aging process. Biologically, aging is a malleable process characterized by an intra- and inter-individual heterogeneous and dynamic balance between accumulating damage and repair mechanisms. Cellular senescence is a key component of this process, with senescent cells accumulating in different tissues and organs, leading to aging and age-related disease susceptibility over time. Removing senescent cells from the body or slowing down the burden rate has been proposed as an efficient way to reduce age-dependent deterioration. In animal models, senotherapeutic molecules can extend life expectancy and lifespan by either senolytic or senomorphic activity. Much research shows that dietary and physical activity-driven lifestyle interventions protect against senescence. This narrative review aims to summarize the current knowledge on targeting senescent cells to reduce the risk of age-related disease in animal models and their translational potential for humans. We focused on studies that have examined the potential role of senotherapeutics in slowing the aging process and modifying age-related disease burdens. The review concludes with a general discussion of the mechanisms underlying this unique trajectory and its implications for future research.

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.

Eldecalcitol protected osteocytes against ferroptosis of D-gal-induced senescent MLO-Y4 cells and ovariectomized mice

BACKGROUND

Active vitamin D analog eldecalcitol is clinically applied in treatment of postmenopausal osteoporosis. This study aims to determine the role of eldecalcitol in the protection of osteocytes from senescence and the associated ferroptosis.

METHODS

The MLO-Y4 osteocytes were exposed to D-gal inducing senescence. The ovariectomized (OVX) mice treated with D-gal using as an aging inducer were intraperitoneally injected with eldecalcitol. The multiplexed confocal imaging, fluorescence in situ hybridization and transmission electron microscopy were applied in assessing osteocytic properties. Immunochemical staining and immunoblotting were carried out to detect abundance and expression of molecules.

RESULTS

The ablation of vitamin D receptor led to a reduction in amounts of osteocytes, a loss of dendrites, an increase in mRNA expression of SASP factors and in protein expression of senescent factors, as well as changes in mRNA expression of ferroptosis-related genes (PTGS2 & RGS4). Eldecalcitol reversed senescent phenotypes of MLO-Y4 cells shown by improving cell morphology and density, decreasing β-gal-positive cell accumulation, and down-regulating protein expression (P16, P21 & P53). Eldecalcitol reduced intracellular ROS and MDA productions, elevated JC-1 aggregates, and up-regulated expression of Nrf2 and GPX4. Eldecalcitol exhibited osteopreserve effects in D-gal-induced aging OVX mice. The confocal imaging displayed its improvement on osteocytic network organization. Eldecalcitol decreased the numbers of senescent osteocytes at tibial diaphysis by SADS assay and attenuated mRNA expression of SASP factors as well as down-regulated protein expression of senescence-related factors and restored levels of ferroptotic biomarkers in osteocytes-enriched bone fraction. It reduced 4-HNE staining area, stimulated Nrf2-positive staining, and promoted nuclear translocation of Nrf2 in osteocytes of mice as well as inhibited and promoted protein expression of 4-HNE and Nrf2, respectively, in osteocytes-enriched bone fraction.

CONCLUSIONS

The present study revealed the ameliorative effects of eldecalcitol on senescence and the associated ferroptosis of osteocytes, contributing to its preservation against osteoporosis of D-gal-induced senescent ovariectomized mice.

Osteoarthritis: Insights into Diagnosis, Pathophysiology, Therapeutic Avenues, and the Potential of Natural Extracts

Osteoarthritis (OA) stands as a prevalent and progressively debilitating clinical condition globally, impacting joint structures and leading to their gradual deterioration through inflammatory mechanisms. While both non-modifiable and modifiable factors contribute to its onset, numerous aspects of OA pathophysiology remain elusive despite considerable research strides. Presently, diagnosis heavily relies on clinician expertise and meticulous differential diagnosis to exclude other joint-affecting conditions. Therapeutic approaches for OA predominantly focus on patient education for self-management alongside tailored exercise regimens, often complemented by various pharmacological interventions primarily targeting pain alleviation. However, pharmacological treatments typically exhibit short-term efficacy and local and/or systemic side effects, with prosthetic surgery being the ultimate resolution in severe cases. Thus, exploring the potential integration or substitution of conventional drug therapies with natural compounds and extracts emerges as a promising frontier in enhancing OA management. These alternatives offer improved safety profiles and possess the potential to target specific dysregulated pathways implicated in OA pathogenesis, thereby presenting a holistic approach to address the condition's complexities.

Bibliometric study and visualization of cellular senescence associated with osteoarthritis from 2009 to 2023

BACKGROUND

Osteoarthritis is a common degenerative joint disease that is highly prevalent in the elderly population. Along with the occurrence of sports injuries, osteoarthritis is gradually showing a younger trend. Osteoarthritis has many causative factors, and its pathogenesis is currently unknown. Cellular senescence is a stable form of cell cycle arrest exhibited by cells in response to external stimuli and plays a role in a variety of diseases. And it is only in the last decade or so that cellular senescence has gradually become cross-linked with osteoarthritis. However, there is no comprehensive bibliometric analysis in this field. The aim of this study is to present the current status and research hotspots of cellular senescence in the field of osteoarthritis, and to predict the future trends of cellular senescence in osteoarthritis research from a bibliometric perspective.

METHODS

This study included 298 records of cellular senescence associated with osteoarthritis from 2009 to 2023, with data from the Web of Science Core Collection database. CiteSpace, Scimago Graphica software, VOSviewer, and the R package "bibliometrix" software were used to analyze regions, institutions, journals, authors, and keywords to predict recent trends in cellular senescence related to osteoarthritis research.

RESULTS

The number of publications related to cellular senescence associated with osteoarthritis is increasing year by year. China and the United States contribute more than 70% of the publications and are the mainstay of research in this field. Central South University is the most active institution with the largest number of publications. International Journal of Molecular Sciences is the most popular journal in the field with the largest number of publications, while Osteoarthritis and Cartilage is the most cited journal. Loeser, Richard F. is not only the most prolific author, but also the most frequently cited author, contributing greatly to the field.

CONCLUSION

In the last decade or so, this is the first bibliometric study that systematically describes the current status and development trend of research on cellular senescence associated with osteoarthritis. The study comprehensively and systematically summarizes and concludes the research hotspots and development trends, providing valuable references for researchers in this field.

Osteoclasts and osteoarthritis: Novel intervention targets and therapeutic potentials during aging

Osteoarthritis (OA), a chronic degenerative joint disease, is highly prevalent among the aging population, and often leads to joint pain, disability, and a diminished quality of life. Although considerable research has been conducted, the precise molecular mechanisms propelling OA pathogenesis continue to be elusive, thereby impeding the development of effective therapeutics. Notably, recent studies have revealed subchondral bone lesions precede cartilage degeneration in the early stage of OA. This development is marked by escalated osteoclast-mediated bone resorption, subsequent imbalances in bone metabolism, accelerated bone turnover, and a decrease in bone volume, thereby contributing significantly to the pathological changes. While the role of aging hallmarks in OA has been extensively elucidated from the perspective of chondrocytes, their connection with osteoclasts is not yet fully understood. There is compelling evidence to suggest that age-related abnormalities such as epigenetic alterations, proteostasis network disruption, cellular senescence, and mitochondrial dysfunction, can stimulate osteoclast activity. This review intends to systematically discuss how aging hallmarks contribute to OA pathogenesis, placing particular emphasis on the age-induced shifts in osteoclast activity. It also aims to stimulate future studies probing into the pathological mechanisms and therapeutic approaches targeting osteoclasts in OA during aging.

Osteocytes and Paget's Disease of Bone

PURPOSE OF REVIEW

To describe the contributions of osteocytes to the lesions in Paget's disease, which are characterized by locally overactive bone resorption and formation.

RECENT FINDINGS

Osteocytes, the most abundant cells in bone, are altered in Paget's disease lesions, displaying increased size, decreased canalicular length, incomplete differentiation, and less sclerostin expression compared to controls in both patients and mouse models. Pagetic lesions show increased senescent osteocytes that express RANK ligand, which drives osteoclastic bone resorption. Abnormal osteoclasts in Paget's disease secrete abundant IGF1, which enhances osteocyte senescence, contributing to lesion formation. Recent data suggest that osteocytes contribute to lesion formation in Paget's disease by responding to high local IGF1 released from abnormal osteoclasts. Here we describe the characteristics of osteocytes in Paget's disease and their role in bone lesion formation based on recent results with mouse models and supported by patient data.

Aging and the emerging role of cellular senescence in osteoarthritis

OBJECTIVE

The correlation between age and incidence of osteoarthritis (OA) is well known but the causal mechanisms involved are not completely understood. This narrative review summarizes selected key findings from the past 30 years that have elucidated key aspects of the relationship between aging and OA.

METHODS

The peer-reviewed English language literature was searched on PubMed using keywords including senescence, aging, cartilage, and osteoarthritis, for original studies and reviews published from 1993 to 2023 with a major focus on more recent studies. Manuscripts most relevant to aging and OA that examined one or more of the hallmarks of aging were selected for further review.

RESULTS

All proposed hallmarks of aging have been observed in articular cartilage and some have also been described in other joint tissues. Hallmarks include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, disabled macroautophagy, chronic inflammation, and dysbiosis. There is evidence that these age-related changes contribute to the development of OA in part by promoting cellular senescence. Senescence may therefore serve as a downstream mediator that connects numerous aging hallmarks to OA, likely through the senescence-associated secretory phenotype that is characterized by increased production of proinflammatory cytokines and matrix metalloproteinases.

CONCLUSIONS

Progress over the past 30 years has provided the foundation for emerging therapies, such as senolytics and senomorphics, that hold promise for OA disease modification. Mechanistic studies utilizing physiologically-aged animals and cadaveric human joint tissues will be important for continued progress.

Kaempferol: Paving the path for advanced treatments in aging-related diseases

Aging-related diseases (ARDs) are a major global health concern, and the development of effective therapies is urgently needed. Kaempferol, a flavonoid found in several plants, has emerged as a promising candidate for ameliorating ARDs. This comprehensive review examines Kaempferol's chemical properties, safety profile, and pharmacokinetics, and highlights its potential therapeutic utility against ARDs. Kaempferol's therapeutic potential is underpinned by its distinctive chemical structure, which confers antioxidative and anti-inflammatory properties. Kaempferol counteracts reactive oxygen species (ROS) and modulates crucial cellular pathways, thereby combating oxidative stress and inflammation, hallmarks of ARDs. Kaempferol's low toxicity and wide safety margins, as demonstrated by preclinical and clinical studies, further substantiate its therapeutic potential. Compelling evidence supports Kaempferol's substantial potential in addressing ARDs through several mechanisms, notably anti-inflammatory, antioxidant, and anti-apoptotic actions. Kaempferol exhibits a versatile neuroprotective effect by modulating various proinflammatory signaling pathways, including NF-kB, p38MAPK, AKT, and the β-catenin cascade. Additionally, it hinders the formation and aggregation of beta-amyloid protein and regulates brain-derived neurotrophic factors. In terms of its anticancer potential, kaempferol acts through diverse pathways, inducing apoptosis, arresting the cell cycle at the G2/M phase, suppressing epithelial-mesenchymal transition (EMT)-related markers, and affecting the phosphoinositide 3-kinase/protein kinase B signaling pathways. Subsequent studies should focus on refining dosage regimens, exploring innovative delivery systems, and conducting comprehensive clinical trials to translate these findings into effective therapeutic applications.

Telomeres, cellular senescence, and aging: past and future

Over half a century has passed since Alexey Olovnikov's groundbreaking proposal of the end-replication problem in 1971, laying the foundation for our understanding of telomeres and their pivotal role in cellular senescence. This review paper delves into the intricate and multifaceted relationship between cellular senescence, the influence of telomeres in this process, and the far-reaching consequences of telomeres in the context of aging and age-related diseases. Additionally, the paper investigates the various factors that can influence telomere shortening beyond the confines of the end-replication problem and how telomeres can exert their impact on aging, even in the absence of significant shortening. Ultimately, this paper stands as a tribute to the pioneering work of Olovnikov, whose seminal contributions established the solid foundation upon which our ongoing explorations of telomeres and the aging process are based.

Single-cell Transcriptome Analysis Identifies Senescent Osteocytes as Contributors to Bone Destruction in Breast Cancer Metastasis

Breast cancer bone metastases increase fracture risk and are a major cause of morbidity and mortality among women. Upon colonization by tumor cells, the bone microenvironment undergoes profound reprogramming to support cancer progression that disrupts the balance between osteoclasts and osteoblasts, leading to bone lesions. Whether such reprogramming affects matrix-embedded osteocytes remains poorly understood. Here, we demonstrate that osteocytes in breast cancer bone metastasis develop premature senescence and a distinctive senescence-associated secretory phenotype (SASP) that favors bone destruction. Single-cell RNA sequencing identified osteocytes from mice with breast cancer bone metastasis enriched in senescence and SASP markers and pro-osteoclastogenic genes. Using multiplex in situ hybridization and AI-assisted analysis, we detected osteocytes with senescence-associated distension of satellites, telomere dysfunction, and p16Ink4a expression in mice and patients with breast cancer bone metastasis. In vitro and ex vivo organ cultures showed that breast cancer cells promote osteocyte senescence and enhance their osteoclastogenic potential. Clearance of senescent cells with senolytics suppressed bone resorption and preserved bone mass in mice with breast cancer bone metastasis. These results demonstrate that osteocytes undergo pathological reprogramming by breast cancer cells and identify osteocyte senescence as an initiating event triggering bone destruction in breast cancer metastases.

Astragaloside IV alleviates macrophage senescence and d-galactose-induced bone loss in mice through STING/NF-κB pathway

BACKGROUND

Senile osteoporosis (SOP) is an age-related metabolic bone disease that currently lacks specific therapeutic interventions. Thus, this study aimed to investigate the effect of Astragaloside IV (AS-IV) on macrophage senescence, bone marrow mesenchymal stem cell (BMSC) osteogenesis, and SOP progression.

METHODS

A senescent macrophage model was established and treated with varying concentrations of AS-IV. Cell activity was measured using the CCK8 assay. The senescence levels of macrophages were evaluated through β-galactosidase staining, PCR, and immunofluorescence. Macrophage mitochondrial function was assessed using ROS and JC-1 staining. Macrophage polarization was evaluated through PCR, Western blot, and immunofluorescence. The inhibitory effects of AS-IV on macrophage senescence were investigated using Western blot analysis. Furthermore, the effects of macrophage conditioned medium (CM) on BMSCs osteogenic were detected using ALP, alizarin red, and PCR.

RESULTS

AS-IV inhibited macrophage senescence and M1 polarization, alleviated mitochondrial dysfunction, and promoted M2 polarization. Mechanistically, it suppressed the STING/NF-κB pathway in H2O2-activated macrophages. Conversely, the STING agonist c-di-GMP reversed the effects of AS-IV on macrophage senescence. Additionally, AS-IV-induced macrophage CM promoted BMSC osteogenic differentiation. In vivo, AS-IV treatment ameliorated aberrant bone microstructure and bone mass loss in the SOP mouse model, inhibited macrophage senescence, and promoted M2 polarization.

CONCLUSIONS

By modulating the STING/NF-κB signaling pathway, AS-IV potentially inhibited macrophage senescence and stimulated osteogenic differentiation of BMSCs, thus exerting an anti-osteoporotic effect. Consequently, AS-IV may serve as an effective therapeutic candidate for the treatment of osteoporosis.

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.

Recent advances in senescence-associated secretory phenotype and osteoporosis

The worldwide elderly population is on the rise, and aging is a major osteoporosis risk factor. Senescent cells accumulation can have a detrimental effect the body as we age. The senescence-associated secretory phenotype (SASP), an essential cellular senescence hallmark, is an important mechanism connecting cellular senescence to osteoporosis. This review describes in detail the characteristics of SASPs and their regulatory agencies, and shed fresh light on how SASPs from different senescent cells contribute to osteoporosis development. Furthermore, we summarized various innovative therapy techniques that target SASPs to lower the burden of osteoporosis in the elderly and discussed the potential challenges of SASPs-based therapy for osteoporosis as a new clinical trial.

Aging impairs the osteocytic regulation of collagen integrity and bone quality

Poor bone quality is a major factor in skeletal fragility in elderly individuals. The molecular mechanisms that establish and maintain bone quality, independent of bone mass, are unknown but are thought to be primarily determined by osteocytes. We hypothesize that the age-related decline in bone quality results from the suppression of osteocyte perilacunar/canalicular remodeling (PLR), which maintains bone material properties. We examined bones from young and aged mice with osteocyte-intrinsic repression of TGFβ signaling (TβRIIocy-/-) that suppresses PLR. The control aged bone displayed decreased TGFβ signaling and PLR, but aging did not worsen the existing PLR suppression in male TβRIIocy-/- bone. This relationship impacted the behavior of collagen material at the nanoscale and tissue scale in macromechanical tests. The effects of age on bone mass, density, and mineral material behavior were independent of osteocytic TGFβ. We determined that the decline in bone quality with age arises from the loss of osteocyte function and the loss of TGFβ-dependent maintenance of collagen integrity.

Cellular senescence is associated with osteonecrosis of the femoral head while mesenchymal stem cell conditioned medium inhibits bone collapse

Osteonecrosis of the femoral head (ONFH) is a type of ischemic osteonecrosis that causes pain, loss of function, and femoral head collapse. Here, we analyzed samples of femoral heads excised from patients with ONFH to clarify the relationship between ischemic osteonecrosis and cellular senescence. X-gal staining was strong and p16INK4a-positive cells were abundant in the transitional region of ONFH. The β-galactosidase-positive cells in the transitional region were also positive for nestin, periostin, or DMP-1. In contrast, no β-galactosidase-positive cells were detected in the healthy region. The senescence-associated p16INK4a, p21, and p53 were upregulated in ONFH tissue. We also examined and analyzed a mouse ischemic femoral osteonecrosis model in vivo to verify the association between ONFH and cellular senescence. Human mesenchymal stem cell-conditioned medium (MSC-CM) was administered to determine its therapeutic efficacy against cellular senescence and bone collapse. MSC-CM reduced the number of senescent cells and downregulated the aforementioned senescence-related genes. It also decreased the number of empty lacunae 4 weeks after ischemia induction and promoted bone formation. At 6 weeks post-surgery, MSC-CM increased the trabecular bone volume, thereby suppressing bone collapse. We conclude that cellular senescence is associated with ONFH and that MSC-CM suppresses bone collapse in this disorder.

The role of NLRP3 inflammasome in aging and age-related diseases

The gradual aging of the global population has led to a surge in age-related diseases, which seriously threaten human health. Researchers are dedicated to understanding and coping with the complexities of aging, constantly uncovering the substances and mechanism related to aging like chronic low-grade inflammation. The NOD-like receptor protein 3 (NLRP3), a key regulator of the innate immune response, recognizes molecular patterns associated with pathogens and injury, initiating an intrinsic inflammatory immune response. Dysfunctional NLRP3 is linked to the onset of related diseases, particularly in the context of aging. Therefore, a profound comprehension of the regulatory mechanisms of the NLRP3 inflammasome in aging-related diseases holds the potential to enhance treatment strategies for these conditions. In this article, we review the significance of the NLRP3 inflammasome in the initiation and progression of diverse aging-related diseases. Furthermore, we explore preventive and therapeutic strategies for aging and related diseases by manipulating the NLRP3 inflammasome, along with its upstream and downstream mechanisms.

A comparison of bone microarchitectural and transcriptomic changes in murine long bones in response to hindlimb unloading and aging

Age- and disuse-related bone loss both result in decreases in bone mineral density, cortical thickness, and trabecular thickness and connectivity. Disuse induces changes in the balance of bone formation and bone resorption like those seen with aging. There is a need to experimentally compare these two mechanisms at a structural and transcriptomic level to better understand how they may be similar or different. Bone microarchitecture and biomechanical properties were compared between 6- and 22-month-old C57BL/6 J male control mice and 6-month-old mice that were hindlimb unloaded (HLU) for 3 weeks. Epiphyseal trabecular bone was the compartment most affected by HLU and demonstrated an intermediate bone phenotype between age-matched controls and aged controls. RNA extracted from whole-bone marrow-flushed tibiae was sequenced and analyzed. Differential gene expression analysis additionally included 4-month-old male mice unloaded for 3 weeks compared to age-matched controls. Gene ontology analysis demonstrated that there were age-dependent differences in differentially expressed genes in young adult mice. Genes related to downregulation of cellular processes were most affected in 4-month-old mice after disuse whereas those related to mitochondrial function were most affected in 6-month-old mice. Cell-cycle transition was downregulated with aging. A publicly available dataset (GSE169292) from 3-month female C57BL/6 N mice unloaded for 7 days was included in ingenuity pathway analysis (IPA) with the other datasets. IPA was used to identify the leading canonical pathways and upstream regulators in each HLU age group. IPA identified "Senescence Pathway" as the second leading canonical pathway enriched in mice exposed to HLU. HLU induced activation of the senescence pathway in 3-month and 4-month-old mice but inhibited it in 6-month-old mice. In conclusion, we demonstrate that hindlimb unloading and aging initiate similar changes in bone microarchitecture and gene expression. However, aging is responsible for more significant transcriptome and tissue-level changes compared to hindlimb unloading.