Targeting cellular senescence prevents age-related bone loss in mice. Nat Med. 2017;23:1072-1079. [PMID: 28825716 PMCID: PMC5657592 DOI: 10.1038/nm.4385]

Cardioprotective effect of senotherapy in chronically obese middle-aged female rats may be mediated by a MERCSs/Nrf2 interaction

Hypercaloric intake promotes the development of obesity, a risk factor for cardiovascular disease (CVD). In recent years, it has been suggested that senescent cells have negative implications for the outcome of these chronic pathologies, and senotherapy has emerged as a novel intervention to reduce damage to the organism. However, it is unclear whether the accumulation of senescent cells induces alterations at the cardiac level in rats fed a hypercaloric diet (HD) and if the use of senotherapeutics can reverse it. To address this question, we used middle-aged female rats fed HD from 21 days to 15 months of age. Under our experimental conditions, rats exhibited cardiac hypertrophy and fibrosis, accumulation of senescent cells, changes in mitochondrial morphology, and oxidative stress. Rats were treated for 2 months with senolytic (dasatinib + quercetin, DQ) or senomorphic (sulforaphane, SFN) agents. Interestingly, the HD rats showed cardiac improvement after the treatment. Our data suggest a possible link mechanism between Nrf2 activation and mitochondria-endoplasmic reticulum contact sites (MERCSs) preservation, activated by SFN rather than by the DQ combination, which allowed cardiac structure maintenance in HD rats decreasing the harmful effects of senescent cells.

Exercise alleviates osteoporosis by regulating the secretion of the Senescent Associated Secretory Phenotype

As the elderly population grows, the number of patients with metabolic bone diseases such as osteoporosis has increased sharply, posing a significant threat to public health and social economics. Although pharmacological therapies for osteoporosis demonstrate therapeutic benefits, their prolonged use is associated with varying degrees of adverse effects. As a non-pharmacological intervention, exercise is widely recognized for its cost-effectiveness, safety, and lack of toxic side effects, making it a recommended treatment for osteoporosis prevention and management. Previous studies have demonstrated that exercise can improve metabolic bone diseases by modulating the Senescent Associated Secretory Phenotype (SASP). However, the mechanisms through which exercise influences SASP remain unclear. Therefore, this review aims to summarize the effects of exercise on SASP and elucidate the specific mechanisms by which exercise regulates SASP to alleviate osteoporosis, providing a theoretical basis for osteoporosis through exercise and developing targeted therapies.

Changing landscape of hematopoietic and mesenchymal cells and their interactions during aging and in age-related skeletal pathologies

Aging profoundly impacts mesenchymal and hematopoietic lineage cells, including their progenitors-the skeletal stem cells (SSCs) and hematopoietic stem cells (HSCs), respectively. SSCs are crucial for skeletal development, homeostasis, and regeneration, maintaining bone integrity by differentiating into osteoblasts, adipocytes, and other lineages that contribute to the bone marrow (BM) microenvironment. Meanwhile, HSCs sustain hematopoiesis and immune function. With aging, SSCs and HSCs undergo significant functional decline, partly driven by cellular senescence-a hallmark of aging characterized by irreversible growth arrest, secretion of pro-inflammatory factors (senescence associated secretory phenotype, SASP), and impaired regenerative potential. In SSCs, senescence skews lineage commitment toward adipogenesis at the expense of osteogenesis, contributing to increased bone marrow adiposity , reduced bone quality, and osteoporosis. Similarly, aged HSCs exhibit diminished self-renewal, biased differentiation, and heightened inflammation, compromising hematopoietic output and immune function. In this review, we examine the age-related cellular and molecular changes in SSCs and HSCs, their lineage decisions in the aging microenvironment, and the interplay between skeletal and hematopoietic compartments. We also discuss the role of senescence-driven alterations in BM homeostasis and how targeting cellular aging mechanisms may offer therapeutic strategies for mitigating age-related skeletal and hematopoietic decline.

Unraveling the functional and molecular interplay between cellular senescence and the unfolded protein response

Senescence is a complex cellular state that can be considered as a stress response phenotype. A decade ago, we suggested the intricate connections between unfolded protein response (UPR) signaling and the development of the senescent phenotype. Over the past ten years, significant advances have been made in understanding the multifaceted role of the UPR in regulating cellular senescence, highlighting its contribution to biological processes such as oxidative stress and autophagy. In this updated review, we expand these interconnections with the benefit of new insights, and we suggest that targeting specific components of the UPR could provide novel therapeutic strategies to mitigate the deleterious effects of senescence, with significant implications for age-related pathologies and geroscience.

Identification of senescence-related biomarkers for osteoporosis based on microarray analysis, Mendelian randomization, and experimental validation

Osteoporosis, characterized by decreased bone mineral density, is a common skeletal disorder in the aging population. Cellular senescence is a key factor in the pathophysiology of osteoporosis. This study aimed to identify senescence-related biomarkers and evaluate the functional role in osteoporosis by integrating microarray analysis, Mendelian randomization (MR), and experimental validation. Osteoporosis-related microarray dataset was downloaded from the Gene Expression Omnibus database for differential expression analysis. We integrated summary-level data from genome-wide association studies on osteoporosis with protein quantitative trait loci data to identify genes with causal relationships to osteoporosis. The senescence-related biomarker gene was identified using the SenMayo gene set and evaluated for the predictive performance through receiver operating characteristic (ROC) curve analysis. Functional enrichment analysis was conducted to explore the underlying mechanisms. Validation of gene expression was performed using quantitative real-time PCR in 50 clinical samples from patients with osteoporosis and controls. A total of 33 differentially expressed genes were identified between osteoporosis and control samples. MR analysis revealed 90 genes with causal effects on osteoporosis. Subsequently, CXCL1 was identified as the key senescence-related biomarker gene. ROC curve analysis demonstrated good predictive performance with an area under the curve value of 0.708. Functional enrichment analysis showed a significant association between CXCL1 and immune-related pathways in osteoporosis. The expression of the gene was successfully validated in clinical samples. This study identified and validated CXCL1 as a senescence-related biomarker with causal effects on osteoporosis through a combination of microarray analysis, MR, and experimental validation. These findings offer insights into the molecular mechanisms of osteoporosis and could inform the development of treatment strategies.

Combined Effects of Mechanical Loading and Piezo1 Chemical Activation on 22-Months-Old Female Mouse Bone Adaptation

With age, bones mechanosensitivity is reduced, which limits their ability to adapt to loading. The exact mechanism leading to this loss of mechanosensitvity is still unclear, making developing effective treatment challenging. Current treatments mostly focus on preventing bone mass loss (such as bisphosphonates) or promoting bone formation (such as Sclerostin inhibitors) to limit the decline of bones mass. However, treatments do not target the cause of bone mass loss which may be, in part, due to the bone's inability to initiate a normal bone mechanoadaptation response. In this work, we investigated the effects of 2 weeks of tibia loading, and Piezo1 agonist injection in vivo on 22-month-old mouse bone adaptation response. We used an optimized loading profile, which induced high fluid flow velocity and low strain magnitude in adult mouse tibia. We found that tibia loading and Yoda2 injection have an additive effect on increasing cortical bone parameters in 22-month-old mice. In vivo osteocytes calcium signaling imaging suggests that Yoda2 is able to reach osteocytes and activate Piezo1. This combination of mechanical and chemical stimulation could be a promising treatment strategy to help promote bone formation in patients who have low bone mass due to aging.

Advancing T-cell immunotherapy for cellular senescence and disease: Mechanisms, challenges, and clinical prospects

Cellular senescence is a complex biological process with a dual role in tissue homeostasis and aging-related pathologies. Accumulation of senescent cells promotes chronic inflammation, tissue dysfunction, age-related diseases, and tumor suppression. Recent advancements in immunotherapy have positioned T cell-based approaches as precision tools for the targeted clearance of senescent cells, offering a novel avenue for anti-aging interventions. This review explores the molecular mechanisms underlying cellular senescence, focusing on its immunogenic features and interactions with T cells, including T-cell activation, antigen recognition, modulation of tumor microenvironment (TME), and immune evasion strategies. Innovations such as chimeric antigen receptor (CAR)-T cells, immune checkpoint therapies, and SASP-neutralizing approaches are highlighted as breakthrough strategies for enhancing senescent cell eradication. The integration of multi-omics and artificial intelligence is further catalyzing the development of personalized therapies to amplify immune surveillance and tissue rejuvenation. Clinically, T cell-based interventions hold promise for mitigating age-related pathologies and extending healthspan, yet challenges remain in optimizing target specificity, countering immunosuppressive niches, and overcoming immune senescence in aging populations. This review synthesizes current advances and challenges, highlighting the potential of T cell immunotherapy as a cornerstone of anti-aging medicine and emphasizing the need for interdisciplinary innovation to translate preclinical findings into transformative therapies for aging and age-related diseases.

The adverse effects of chemotherapy on bone mass are not prevented by senolytics

Cancer survivors experience many short- and long-term side effects caused by chemotherapy, including low bone mineral density and deterioration of bone microarchitecture. Administration of chemotherapy drugs to disease free mice causes rapid bone loss. However, whether the bone effects persist throughout life and the mechanisms responsible remain unclear. One plausible cause of chemotherapy-induced bone loss is cellular senescence. Here, female mice were administered doxorubicin, cyclophosphamide and docetaxel, a chemotherapy regimen commonly used in breast cancer patients, in combination with two types of drugs that kill senescent cells (senolytics), namely dasatinib + quercetin or piperlongumine. Mice receiving chemotherapy experienced a rapid decrease in trabecular bone mass, which was detectable two weeks after initiation of treatment and was associated with increased expression of senescence markers. None of the senolytics prevented the effects of chemotherapy on bone mass. In separate experiments, we examined the skeletal effects of chemotherapy six and twelve months after the cessation of treatment. The deleterious effects of chemotherapy on bone mass remained up to 12 months after cessation of treatment, while no markers of senescence could be detected in bone. Together, these results suggest that the deleterious effects of this chemotherapy regimen on bone health are not due to the accumulation of senescent cells.

In vitro senescence and senolytic functional assays

A detailed understanding of aging biology and the development of anti-aging therapeutic strategies remain imperative yet inherently challenging due to the protracted nature of aging. Cellular senescence arises naturally through replicative exhaustion and is accelerated by clinical treatments or environmental stressors. The accumulation of senescent cells-defined by a loss of mitogenic potential, resistance to apoptosis, and acquisition of a pro-inflammatory secretory phenotype-has been implicated as a key driver of chronic disease, tissue degeneration, and organismal aging. Recent studies have highlighted the therapeutic promise of senolytic drugs, which selectively eliminate senescent cells. Compelling results from preclinical animal studies and ongoing clinical trials underscore this potential. However, the clinical translation of senolytics requires further pharmacological validation to refine selectivity, minimize toxicity, and determine optimal dosing. Equally important is the evaluation of senolytics' potential to restore tissue structure and function by reducing the senescent cell burden. In vitro tissue culture models offer a powerful platform to advance these efforts. This review summarizes the current landscape of in vitro systems used for inducing cellular senescence-referred to as "senescence assays"-and for screening senolytic drugs-referred to as "senolytic assays". We conclude by discussing key challenges to improving mechanistic insight, predictive accuracy, and clinical relevance in senolytic drug development, as well as emerging applications of senolytic therapies.

Cellular senescence in age-related musculoskeletal diseases

Aging is typically associated with decreased musculoskeletal function, leading to reduced mobility and increased frailty. As a hallmark of aging, cellular senescence plays a crucial role in various age-related musculoskeletal diseases, including osteoporosis, osteoarthritis, intervertebral disc degeneration, and sarcopenia. The detrimental effects of senescence are primarily due to impaired regenerative capacity of stem cells and the pro-inflammatory environment created by accumulated senescent cells. The secreted senescence-associated secretory phenotype (SASP) can induce senescence in neighboring cells, further amplifying senescent signals. Although the removal of senescent cells and the suppression of SASP factors have shown promise in alleviating disease progression and restoring musculoskeletal health in mouse models, clinical trials have yet to demonstrate significant efficacy. This review summarizes the mechanisms of cellular senescence in age-related musculoskeletal diseases and discusses potential therapeutic strategies targeting cellular senescence.

Characterization of Human Senescent Cell Biomarkers for Clinical Trials

There is an increasing need for biomarkers of senescent cell burden to facilitate the selection of participants for clinical trials. p16Ink4a is encoded by the CDKN2A locus, which produces five variant transcripts in humans, two of which encode homologous p16 proteins: p16Inka4a, encoded by p16_variant 1, and p16ɣ, encoded by p16_variant 5. While distinct quantitative polymerase chain reaction primers can be designed for p16_variant 5, primers for p16_variant 1 also measure p16_variant 5 (p16_variant 1 + 5). In a recent clinical trial evaluating the effects of the senolytic combination, dasatinib + quercetin (D + Q), on bone metabolism in postmenopausal women, we found that women in the highest tertile for T-cell expression of p16_variant 5 had the most robust skeletal responses to D + Q. Importantly, the assessment of p16_variant 5 was more predictive of these responses than p16_variant 1 + 5. Here, we demonstrate that in vitro, p16_variant 1 + 5 increased rapidly (Week 1) following the induction of DNA damage, whereas p16_variant 5 increased later (Week 4), suggesting that p16_variant 5 becomes detectable only when the abundance of senescent cells reaches some threshold. Further analysis identified a SASP panel in plasma that performed as well in identifying postmenopausal women with a positive skeletal response to D + Q. Collectively, our findings provide further support for the T-cell p16_variant 5 assay as a biomarker for selecting participants in clinical trials of senolytic interventions. In addition, our data indicate that correlated plasma SASP markers could be used in lieu of the more technically challenging T-cell p16 assay. Trial Registration: ClinicalTrials.gov identifier: NCT04313634.

The context-dependent effect of cellular senescence: From embryogenesis and wound healing to aging

Aging is characterized by a steady loss of physiological integrity, leading to impaired function and increased vulnerability to death. Cell senescence is a biological process that progresses with aging and is believed to be a key driver of age-related diseases. Senescence, a hallmark of aging, also demonstrates its beneficial physiological aspects as an anti-cancer, pro-regenerative, homeostatic, and developmental mechanism. A transitory response in which the senescent cells are quickly formed and cleared may promote tissue regeneration and organismal fitness. At the same time, senescence-related secretory phenotypes associated with extended senescence can have devastating effects. The fact that the interaction between senescent cells and their surroundings is very context-dependent may also help to explain this seemingly opposing pleiotropic function. Further, mitochondrial dysfunction is an often-unappreciated hallmark of cellular senescence and figures prominently in multiple feedback loops that induce and maintain the senescent phenotype. This review summarizes the mechanism of cellular senescence and the significance of acute senescence. We concisely introduced the context-dependent role of senescent cells and SASP, aspects of mitochondrial biology altered in the senescent cells, and their impact on the senescent phenotype. Finally, we conclude with recent therapeutic advancements targeting cellular senescence, focusing on acute injuries and age-associated diseases. Collectively, these insights provide a future roadmap for the role of senescence in organismal fitness and life span extension.

Genetics- and age-driven neuroimmune and disc changes underscore herniation susceptibility and pain-associated behaviors in SM/J mice

There are no appropriate mouse models to study the pathophysiology of spontaneous disc herniations in a wild-type setting. SM/J mice, a poor healer inbred strain, presented a high incidence of age-associated lumbar disc herniations with neurovascular innervations. Transcriptomic comparisons of the SM/J annulus fibrosus with human tissues showed shared pathways related to immune cell activation and inflammation. Notably, aged SM/J mice showed increased pain sensitization and neuroinflammation with altered extracellular matrix regulation in the dorsal root ganglia and spinal cord. There were increased T cells in the vertebral marrow, and cytometry by time-of-flight analysis showed increased splenic CD8+ T cells, nonspecific activation of CD8+ memory T cells, and enhanced interferon-γ production in the myeloid compartment. Single-cell RNA sequencing of peripheral blood mononuclear cells showed more B cells, with lower proportions of T cells, monocytes, and granulocytes. This study highlights the contribution of genetic background and aging to increased susceptibility of spontaneous intervertebral disc herniations in a clinically relevant murine model.

Attenuation of Cellular Senescence and Improvement of Osteogenic Differentiation Capacity of Human Liver Stem Cells Using Specific Senomorphic and Senolytic Agents

Expansion of adult stem cells in culture increases the percent of senescent cells, reduces their differentiation capacity and limits their clinical use. Here, we investigated whether treatment with certain senotherapeutic drugs would reduce the accumulation of senescent cells during expansion of human liver stem cells (HLSCs) while maintaining their differentiation capacity. Our results demonstrate that chronic treatment with the senomorphic XJB-5-131 or the senolytics cocktail D + Q reduced the number of senescent cells and significantly reduced the expression of senescence-associated genes and several inflammatory SASP factors in later passage HLSCs. Additionally, treatment with XJB-5-131 and D + Q improved the capacity of HLSCs to undergo osteogenic differentiation following extensive in vitro expansion. Overall, our data demonstrate that treatment with XJB-5-13 or D + Q results in a reduction in the percentage of replication-induced senescent HLSCs and likely other types of adult stem cells and improve the potential therapeutic use of later passage human stem cells.

Insights into age-related osteoporosis from senescence-based preclinical models and human accelerated aging paradigms

Preclinical models of age-related osteoporosis have been developed based on the accumulation and clearance of senescent cells. The former include animal models based on telomere dysfunction and focal radiation; the latter based on genetic and pharmacological targeting (i.e., removal) of senescent cells. The weight of evidence using these models suggests that cellular senescence plays a key role in the pathophysiology of aging-onset bone loss with the senescence-associated secretory phenotype (SASP) mediating local and systemic deleterious effects on the skeleton. Mitochondrial dysfunction has also been implicated in senescence and age-related comorbidities, including osteoporosis, and knock-in mutations in the mtDNA polymerase gamma (Polg) gene in mice may recapitulate similar respiratory chain complex defects in aged individual with osteoporosis. This and other contributions to senile osteoporosis may also be identified by the careful evaluation of non-genetic paradigms of human accelerated aging. Premature aging syndromes, especially those with a prominent bone loss phenotype, include clinical scenarios of skeletal unloading, premature ovarian failure and survival from childhood cancers. These non-hereditary progeroid syndromes implicate the involvement of lineage switching to an adipogenic fate, inhibition of Wnt signaling, increased osteoclastogenesis and activation frequency of osteoclasts, as well as the substantial burden of senescent cell accumulation.

Tracing Cellular Senescence in Bone: Time-Dependent Changes in Osteocyte Cytoskeleton Mechanics and Morphology

Aging-related bone loss significantly impacts the growing elderly population globally, leading to debilitating conditions such as osteoporosis. Senescent osteocytes play a crucial role in the aging process of bone. This longitudinal study examines the impact of continuous local and paracrine exposure to senescence-associated secretory phenotype (SASP) factors on biophysical and biomolecular markers in osteocytes. Significant cytoskeletal stiffening in irradiated (IR) osteocytes are found, accompanied by expansion of F-actin areas and a decline in dendritic integrity. These changes, correlating with alterations in pro-inflammatory cytokine levels and osteocyte-specific gene expression, support the reliability of biophysical markers for identifying senescent osteocytes. Notably, local accumulation of SASP factors have a more pronounced impact on osteocyte biophysical properties than paracrine effects, suggesting that the interplay between local and paracrine exposure can substantially influence cellular aging. This study underscores the importance of osteocyte mechanical and morphological properties as biophysical markers of senescence, highlighting their time dependence and differential effects of local and paracrine SASP exposure. Collectively, the investigation into biophysical senescence markers offers unique and reliable functional hallmarks for the non-invasive identification of senescent osteocytes, providing insights that can inform therapeutic strategies to mitigate aging-related bone loss.

Enhancing immunity during ageing by targeting interactions within the tissue environment

Immunity declines with age. This results in a higher risk of age-related diseases, diminished ability to respond to new infections and reduced response to vaccines. The causes of this immune dysfunction are cellular senescence, which occurs in both lymphoid and non-lymphoid tissue, and chronic, low-grade inflammation known as 'inflammageing'. In this Review article, we highlight how the processes of inflammation and senescence drive each other, leading to loss of immune function. To break this cycle, therapies are needed that target the interactions between the altered tissue environment and the immune system instead of targeting each component alone. We discuss the relative merits and drawbacks of therapies that are directed at eliminating senescent cells (senolytics) and those that inhibit inflammation (senomorphics) in the context of tissue niches. Furthermore, we discuss therapeutic strategies designed to directly boost immune cell function and improve immune surveillance in tissues.

Mechanisms of mitochondrial reactive oxygen species action in bone mesenchymal cells

Mitochondrial (mt)ROS, insufficient NAD+, and cellular senescence all contribute to the decrease in bone formation with aging. ROS can cause senescence and decrease NAD+, but it remains unknown whether these mechanisms mediate the effects of ROS in vivo. Here, we generated mice lacking the mitochondrial antioxidant enzyme Sod2 in osteoblast lineage cells targeted by Osx1-Cre and showed that Sod2ΔOsx1 mice had low bone mass. Osteoblastic cells from these mice had impaired mitochondrial respiration and attenuated NAD+ levels. Administration of an NAD+ precursor improved mitochondrial function in vitro but failed to rescue the low bone mass of Sod2ΔOsx1 mice. Single-cell RNA-sequencing of bone mesenchymal cells indicated that ROS had no significant effects on markers of senescence but disrupted parathyroid hormone signaling, iron metabolism, and proteostasis. Our data supports the rationale that treatment combinations aimed at decreasing mtROS and senescent cells and increasing NAD+ should confer additive effects in delaying age-associated osteoporosis.

Protocol for isolation of human bone marrow stromal cells and characterization of cellular metabolism

Bone marrow stromal cells (BMSCs) serve as a valuable reservoir of multipotent stem cells important in the regulation of bone homeostasis and energy metabolism. Here, we present a protocol for isolating human BMSCs (hBMSCs) and characterizing their cellular metabolism related to hBMSC functional properties. We describe steps for bioenergetics, cell senescence, and production of reactive oxygen species (ROS), together with description of the data analysis. These assays provide information on hBMSC metabolic status valuable to regenerative medicine and therapeutic applications. For complete details on the use and execution of this protocol, please refer to Tencerova et al.1.

Stone L, Haglund L. Senolytic treatment for low back pain

Senescent cells (SnCs) accumulate because of aging and external cellular stress throughout the body. They adopt a senescence-associated secretory phenotype (SASP) and release inflammatory and degenerative factors that actively contribute to age-related diseases, such as low back pain (LBP). The senolytics, o-vanillin and RG-7112, remove SnCs in human intervertebral discs (IVDs) and reduce SASP release, but it is unknown whether they can treat LBP. sparc-/- mice, with LBP, were treated orally with o-vanillin and RG-7112 as single or combination treatments. Treatment reduced LBP and SASP factor release and removed SnCs from the IVD and spinal cord. Treatment also lowered degeneration scores in the IVDs, improved vertebral bone quality, and reduced the expression of pain markers in the spinal cord. Together, our data suggest RG-7112 and o-vanillin as potential disease-modifying drugs for LBP and other painful disorders linked to cell senescence.

Genetic ablation of p16 mitigates premature osteoporosis induced by PTHrP nuclear localization sequence and C-terminal deletion through inhibition of cellular senescence

BACKGROUND

Premature osteoporosis caused by parathyroid hormone-related peptide (PTHrP) dysfunction presents significant bone health challenges. The role of p16-mediated cellular senescence in this condition remains unclear.

METHODS

Using a Pthrp knock-in (KI) mouse model lacking the nuclear localization sequence and C-terminus of PTHrP, we generated p16⁻⁄⁻KI mice and compared them with wild-type, p16⁻⁄⁻, and KI mice. We analyzed survival, skeletal phenotypes, bone marrow mesenchymal stem cell (BM-MSC) function, and molecular markers of senescence.

RESULTS

Genetic ablation of p16 in KI mice extended their lifespan, increased body size and weight, and improved skeletal growth. Micro-CT analysis revealed significantly increased bone volume, while histological studies showed enhanced chondrocyte proliferation and osteoblast function in p16⁻⁄⁻KI mice compared to KI mice. In vitro experiments demonstrated enhanced differentiation capacity and reduced senescence of BM-MSCs from p16⁻⁄⁻KI mice, as evidenced by increased colony formation and osteogenic marker expression. Molecular analyses indicated that p16 knockout partially reversed oxidative stress, DNA damage, and cellular senescence observed in KI mice, shown by upregulated antioxidant enzymes, reduced DNA damage markers, and decreased senescence markers.

CONCLUSIONS

p16-mediated cellular senescence plays a crucial role in premature osteoporosis caused by PTHrP dysfunction. Targeting cellular senescence pathways may offer a promising therapeutic strategy for treating premature osteoporosis and age-related bone loss.

Dasatinib and Quercetin Mitigate Age-Related Alveolar Bone Inflammaging and Neutrophil Infiltration

OBJECTIVE

Age-related alveolar bone resorption poses a major dental health challenge, yet its mechanisms and treatments are poorly understood. This study investigates the impact of dasatinib and quercetin (D + Q) treatment on senescent cells (SnCs), senescence-associated secretory phenotype (SASP), and neutrophil infiltration in aged alveolar bone, aiming to develop new strategies for combating age-related bone resorption.

METHODS

C57BL/6 mice (2 and 18 months) were used to examine alveolar bone resorption, inflammaging, and neutrophil infiltration. Aged mice received D + Q treatment to assess therapeutic effects. Key measurements included cementoenamel junction to the alveolar bone crest (CEJ-ABC) distance, periodontal ligament (PDL) thickness, osteometabolism markers, SnCs accumulation, SASP expression, and neutrophil infiltration.

RESULTS

Aged alveolar bone showed increased CEJ-ABC distance, atrophied periodontal ligament, and unbalanced osteometabolism, along with elevated SnCs, SASP, and neutrophils compared to young controls. D + Q treatment improved these conditions by reducing CEJ-ABC distance, enhancing periodontal ligament health, and boosting bone metabolism. It also lowered the expression of SnCs, SASP, and neutrophil markers.

CONCLUSION

D + Q treatment effectively mitigates alveolar bone aging by clearing SnCs, lowering SASP levels, and reducing neutrophil aggregation, presenting a novel approach for age-related bone resorption.

Specnuezhenide Alleviates Senile Osteoporosis by Activating TGR5/FXR Signaling in Bone Marrow Mesenchymal Stem Cells and RANKL-Induced Osteoclasts

Background

Specnuezhenide (SPN) is an iridoid glycoside isolated from Fructus Ligustri Lucidi, an herb prescribed for the treatment of senile osteoporosis. However, the direct role of SPN on bone metabolism remains unclear. In this study, the effects of SPN on d-galactose (d-gal)-induced mice, bone marrow mesenchymal stem cells (BMSCs), and nuclear factor-κB ligand-induced osteoclasts were examined.

Methods

Micro-computed tomography was used to observe the bone microstructure. Osteogenesis was examined using Western blotting and alkaline phosphatase staining. Osteoclastogenesis was examined using Western blotting and F-actin ring staining. Senescence-associated β-galactosidase was used to detect cell senescence. In addition, the expression of Takeda G protein-coupled receptor 5 (TGR5)/farnesoid X receptor (FXR) signaling pathway-related genes and proteins was determined through quantitative real-time polymerase chain reaction and immunofluorescence.

Results

Oral administration of SPN improved the bone microstructure in d-gal-induced mice and increased bone mineral density, bone volume, trabecular thickness, and trabecular number. SPN also upregulated the expression of the osteogenesis markers osteocalcin, bone morphogenetic protein 2, and runt-related transcription factor 2 and downregulated the expression of the osteoclasis markers tartrate-resistant acid phosphatase, nuclear factor-κB, and nuclear factor of activated T-cells in the d-gal-induced bone. Furthermore, SPN increased alkaline phosphatase staining, inhibited F-actin ring formation, and reduced the activity of senescence-associated β-galactosidase in vitro. Mechanistically, SPN activated the TGR5/FXR pathway in d-gal-induced BMSCs and osteoclasts. The protective effects of SPN were abolished after addition of the TGR5 inhibitor SBI-115 or FXR inhibitor DY268. Moreover, SPN could elevate the protein and mRNA levels of TGR5, FXR, and the downstream small heterodimer partner in d-gal-induced bone.

Conclusion

SPN alleviated senile osteoporosis and cell senescence by activating the TGR5/FXR pathway.

Targeting senescent cells for the treatment of age-associated diseases

Cellular senescence, which entails cellular dysfunction and inflammatory factor release-the senescence-associated secretory phenotype (SASP)-is a key contributor to multiple disorders, diseases and the geriatric syndromes. Targeting senescent cells using senolytics has emerged as a promising therapeutic strategy for these conditions. Among senolytics, the combination of dasatinib and quercetin (D + Q) was the earliest and one of the most successful so far. D + Q delays, prevents, alleviates or treats multiple senescence-associated diseases and disorders with improvements in healthspan across various pre-clinical models. While early senolytic therapies have demonstrated promise, ongoing research is crucial to refine them and address such challenges as off-target effects. Recent advances in senolytics include new drugs and therapies that target senescent cells more effectively. The identification of senescence-associated antigens-cell surface molecules on senescent cells-pointed to another promising means for developing novel therapies and identifying biomarkers of senescent cell abundance.

Deficiency of ATF2 retards senescence induced by replication stress and pamidronate in mouse jaw bone marrow stem cells

The aging process is associated with a loss of bone mass and an accumulation of senescent cells, which is under epigenetic control. Morphological and molecular analysis revealed a notable reduction in bone mass and alveolar crest height in aged mice, accompanied by increased levels of senescent mouse jaw bone marrow stem cells (mJBMSCs). To investigate whether specific transcription factors are involved, assay for transposase-accessible chromatin with sequencing (ATAC-seq) was performed on mJBMSCs isolated from 2-, 4-, 8-, and 20-month-old mice. In 20-month-old mJBMSCs, increased chromatin accessibility was observed alongside elevated expression of activating transcription factor 2 (ATF2) in both cells and alveolar bone. Silencing Atf2 in mJBMSCs failed to reverse physiological aging, but delayed replication stress and pamidronate (PAM) induced senescence. The analysis of ATAC-seq and RNA sequencing indicated that the differentially expressed genes upregulated by PAM but downregulated by ATF2 deficiency were related to some key biological processes, including negative regulation of cell proliferation, inflammatory response, adipogenesis, and cellular senescence. The dual-luciferase assay was conducted to demonstrate that ATF2 enhances Cdkn2a transcription by binding to its promoter region. Our findings suggest significant chromatin alterations in aged mJBMSCs, positioning ATF2 as a potential target for combating externally induced senescence.

A pilot study of senolytics to improve cognition and mobility in older adults at risk for Alzheimer's disease

BACKGROUND

This single-arm study evaluates the feasibility, safety, and preliminary effects of two senolytic agents, Dasatinib and Quercetin (DQ), in older adults at risk of Alzheimer's disease.

METHODS

Participants took 100 mg of Dasatinib and 1250 mg of Quercetin for two days every two weeks over 12 weeks. Recruitment rate, adverse events, absolute changes in functional outcomes, and percent changes in biomarkers were calculated. Spearman correlations between functional and biomarker outcomes were performed.

FINDINGS

Approximately 10% of telephone-screened individuals completed the intervention (n = 12). There were no serious adverse events related to the intervention. Mean Montreal Cognitive Assessment (MoCA) scores non-significantly increased following DQ by 1.0 point (95% CI: -0.7, 2.7), but increased significantly by 2.0 points (95% CI: 0.1, 4.0) in those with lowest baseline MoCA scores. Mean percent change in tumour necrosis factor-alpha (TNF-α), a key product of the senescence-associated secretory phenotype (SASP), non-significantly decreased following DQ by -3.0% (95% CI: -13.0, 7.1). Changes in TNF-α were significantly and inversely correlated with changes in MoCA scores (r = -0.65, p = 0.02), such that reductions in TNF- α were correlated with increases in MoCA scores.

INTERPRETATION

This study suggests that intermittent DQ treatment is feasible and safe; data hint at potential functional benefits in older adults at risk of Alzheimer's disease. The observed reduction in TNF-α and its correlation with increases in MoCA scores suggests that DQ may improve cognition by modulating the SASP. However, there was not an appropriate control group. Data are preliminary and must be interpreted cautiously.

FUNDING

National Institute on Ageing grants R21AG073886 and R33AG061456 funded this research.

A Functionalized 3D-Printed Ti6Al4V "Cell Climbing Frame" Inspired by Marine Sponges to Recruit and Rejuvenate Autologous BMSCs in Osteoporotic Bone Repair

Osteoporosis, characterized by low bone mass and high fracture risk, challenges orthopedic implant design. Conventional 3D-printed Ti6Al4V scaffolds are mechanically robust but suffer from poor bone regeneration in osteoporotic patients due to stress shielding and cellular senescence. In this study, a functionalized 3D-printed Ti6Al4V "Cell Climbing Frame" is developed, aiming to adapt to the mechanical microenvironment of osteoporosis, effectively recruit and support the adhesion and growth of autologous bone marrow mesenchymal stem cells (BMSCs), while rejuvenating senescent cells for improved bone regeneration. Inspired by marine sponges, the processing accuracy limitations of selective laser melting (SLM) technology is broke through innovatively constructing a hierarchical porous structure with macropores and micropores nested within each other. Results demonstrate that the unique hierarchical porous scaffold reduces the elastic modulus, facilitates blood penetration, and enhances cell adhesion and growth. Further surface functionalization with E7 peptides and exosomes promotes the attraction and rejuvenation of BMSCs and boosts migration, proliferation, and osteogenic differentiation in vitro. In vivo, the functionalized "Cell Climbing Frame" accelerates bone repair in osteoporotic rats, while delaying surrounding bone loss, enabling robust multi-stage osseointegration. This innovation advances 3D-printed regenerative implants for osteoporotic bone repair.

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.

Rejuvenation of Bone Marrow Mesenchymal Stem Cells: Mechanisms and Their Application in Senile Osteoporosis Treatment

Bone marrow mesenchymal stromal cells (BM-MSCs) are multipotent cells present in bone marrow; they play a crucial role in the process of bone formation. Cellular senescence is defined as a stable state of cell cycle arrest that impairs the functioning of cells. Research has shown that aging triggers a state of senescence in BM-MSCs, leading to a reduced capacity for osteogenic differentiation and the accumulation of senescent cells, which can accelerate the onset of various diseases. Therefore, it is essential to explore mechanisms and strategies for the rejuvenation of senescent BM-MSCs. Senile osteoporosis (SOP) is a metabolic bone disease characterized by reduced bone formation. The senescence of BM-MSCs is considered one of the most important factors in the occurrence and development of SOP. Therefore, the rejuvenation of BM-MSCs for the treatment of SOP represents a promising strategy. This work provides a summary of the functional alterations observed in senescent BM-MSCs and a systematic review of the mechanisms that facilitate the rejuvenation of senescent BM-MSCs. Additionally, we analyze the progress in and the limitations associated with the application of rejuvenated senescent BM-MSCs to treat SOP, with the aim of providing new insights for the prevention and treatment of SOP.

Engineered extracellular vesicles with sequential cell recruitment and osteogenic functions to effectively promote senescent bone repair

Senescent mandibular bone repair poses a formidable challenge without a completely satisfactory strategy. Endogenous cell recruitment and osteogenic differentiation are two sequential stages in bone regeneration, and disruptions in these two processes present significant obstacles to senescent bone repair. To address these issues, engineered extracellular vesicles (EV) with sequential stem cell recruitment and osteogenic functions were developed. This study demonstrated that Apt19s-engineered extracellular vesicles (Apt19s-EV) recognize and recruit bone marrow mesenchymal stem cells derived from old rats (O-BMSCs) specifically and effectively. MiR-376b-5p, identified by RNA sequencing and transfection, was significantly decreased in O-BMSCs, and it was selected to construct miR-376b-5p-engineered extracellular vesicles (376b-EV). 376b-EV could promote osteogenesis and alleviate senescence of O-BMSCs by targeting Camsap1. To combine the advantages of Apt19s and miR-376b-5p, dual engineered extracellular vesicles (Apt-376b-EV) comprising both Apt19s and miR-376b-5p modifications were constructed. To further validate its function, Gelatin methacryloyl (GelMA) hydrogel was used as a carrier to construct the Apt-376b-EV@GelMA delivery system. The in vitro results have demonstrated that Apt-376b-EV@GelMA could recruit O-BMSCs, alleviate senescence and promote osteogenic differentiation sequentially. Notably, the in vivo study also showed that Apt-376b-EV@GelMA could sequentially recruit endogenous stem cells and enhance new bone formation in senescent bone fracture and critical-sized defect models. In summary, the dual engineered extracellular vesicles, Apt-376b-EV, offer an appealing solution for recruiting endogenous stem cells and promoting bone repair sequentially in the senescent microenvironment, which may broaden the clinical applications of engineered EV and provide valuable strategies for treating senescent bone-related diseases in the future clinical work.

Oversecretion of CCL3 by Irradiation-Induced Senescent Osteocytes Mediates Bone Homeostasis Imbalance

Various stressors such as ionizing radiation (IR), chemotherapeutic agents, oxidative stress, and inflammatory responses can trigger the stress-induced premature senescence (SIPS) of cells in the bone microenvironment, including osteocytes. However, little is known about the mechanisms underlying the senescent cellular regulation of the differentiation potential and bone homeostasis. Here, we report a secretory change in senescent osteocytes activated by IR, its subsequent impact on osteogenic and osteoclastic differentiation, and the inflammatory cascade response. It was observed that osteocytes exhibited altered biological function, persistent and incomplete DNA damage repair, and characteristic senescence phenotypes after exposure to IR in vitro. Meanwhile, a concomitant increase in the CC chemokine ligand 3 (CCL3), a key component of the senescence-associated secretory phenotype (SASP), was observed in the IR-induced senescent osteocytes, which could further downregulate the osteogenic differentiation and enhance the osteoclastic differentiation in cell supernatant co-culture experiments. Notably, the enhancement of the PI3K/Akt/NF-κB signaling pathway in IR-induced senescent osteocytes appears to be an essential driver of the imbalance between the osteogenic and osteoclastic differentiation potentials. Taken together, these data suggest a novel role of CCL3 in IR-induced bone homeostatic imbalance through SASP cascade secretion, mediated by the PI3K/Akt/NF-κB signaling pathway.

Golgi-restored vesicular replenishment retards bone aging and empowers aging bone regeneration

Healthy aging is a common goal for humanity and society, and one key to achieving it is the rejuvenation of senescent resident stem cells and empowerment of aging organ regeneration. However, the mechanistic understandings of stem cell senescence and the potential strategies to counteract it remain elusive. Here, we reveal that the aging bone microenvironment impairs the Golgi apparatus thus diminishing mesenchymal stem cell (MSC) function and regeneration. Interestingly, replenishment of cell aggregates-derived extracellular vesicles (CA-EVs) rescues Golgi dysfunction and empowers senescent MSCs through the Golgi regulatory protein Syntaxin 5. Importantly, in vivo administration of CA-EVs significantly enhanced the bone defect repair rate and improved bone mass in aging mice, suggesting their therapeutic value for treating age-related osteoporosis and promoting bone regeneration. Collectively, our findings provide insights into Golgi regulation in stem cell senescence and bone aging, which further highlight CA-EVs as a potential rejuvenative approach for aging bone regeneration.

Anti-aging chitosan/gelatin film crosslinked byα-arbutin for bone regeneration by free radical scavenging to prevent osteoblast senescence

Osteoblasts play a critical role in maintaining bone homeostasis. Senescence causes by free radical-mediated oxidative stress may affect the viability and osteogenic differentiation potential of osteoblast during bone formation. To eliminate the impacts of senescent cells by free radical scavenging is an optimal option for bone regeneration in age-related bone disease, such as osteoporosis (OP) and periodontitis. In this study, we fabricated an antioxidant film (CG-ARB) by crosslinking chitosan (C) and gelatin (G) usingα-Arbutin (ARB) as a crosslinker. The morphological, physicochemical, and radical scavenging characteristics of the films were investigated. Its antioxidative ability to prevent osteoblast senescence for restoration of osteogenic differentiation was analyzedin vitro. A Sprague-Dawley rat model with critical size calvarial defect was used to evaluate the bone regeneration and biosafetyin vivo. The results demonstrated that CG-ARB formed a dense fiber membrane, allowing for the gradual and sustained release of ARB for at least 10 d. ARB exerted antioxidant effect that prevented osteoblast senescencein vitroand promote bone healingin vivo. Furthermore, CG-ARB did not cause hemolysis or organ toxicity, and was therefore, considered biosafe. These results indicated that CG-ARB film could be an ideal drug delivery system for sustained released of ARB in bone defect repair.

Senescent myoblasts exhibit an altered exometabolome that is linked to senescence-associated secretory phenotype signaling

Cellular senescence has been implicated in the aging-related dysfunction of satellite cells, the resident muscle stem cell population primarily responsible for the repair of muscle fibers. Despite being in a state of permanent cell cycle arrest, these cells remain metabolically active and release an abundance of factors that can have detrimental effects on the cellular microenvironment. This phenomenon is known as the senescence-associated secretory phenotype (SASP), and its metabolic profile is poorly characterized in senescent muscle. In the present investigation, we examined the intracellular and extracellular metabolome of C2C12 myoblasts using a bleomycin (BLEO)-mediated model of DNA damage-induced senescence. We also evaluated the relationship between the senescent metabolic phenotype and SASP signaling through molecular and network-based analyses. Senescent myoblasts exhibited a significantly altered extracellular metabolome (i.e., exometabolome), including increased secretion of several aging-associated metabolites. Four of these metabolites-trimethylamine-N-oxide (TMAO), xanthine, choline, and oleic acid-were selected for individual dose-response experiments to determine whether they could drive the senescence phenotype. Although most of the tested metabolites did not independently alter senescence markers, oleic acid treatment of healthy myoblasts significantly upregulated the SASP genes Ccl2, Cxcl12, and Il33 (p < 0.05). A gene-metabolite interaction network further revealed that oleic acid was one of the most interconnected metabolites to key senescence-associated genes. Notably, oleic acid interacted with several prominent SASP genes, suggesting a potential epigenetic effect between this monounsaturated fatty acid and SASP regulation. In summary, the exometabolome, particularly oleic acid, is implicated in SASP signaling within senescent myoblasts.NEW & NOTEWORTHY Cellular senescence and its accompanying secretory phenotype [i.e., the senescence-associated secretory phenotype (SASP)] have been linked to the aging-associated dysfunction of skeletal muscle, yet little is known about this phenomenon in satellite cells. We report that senescent myoblasts experience a significantly altered extracellular metabolome primarily characterized by the substantial release of nonesterified fatty acids. Targeted evaluation of several extracellular senescence-associated metabolites reveals a potential epigenetic role for long-chain fatty acids, particularly oleic acid, in regulating SASP-related gene expression.

Osteoking inhibits apoptosis of BMSCs in osteoporotic rats via PI3K/AKT signaling pathway

In China, Osteoking is a commonly used treatment and preventive measure for osteoporosis. The pathophysiology of osteoporosis is closely associated with apoptosis; however, it remains unclear whether the role of Osteoking in promoting bone formation is linked to apoptosis.

AIM OF STUDY

This study aims to investigate whether Osteoking inhibits apoptosis of BMSCs in osteoporotic rats via the PI3K/AKT signaling pathway and to conduct a detailed exploration of this mechanism. The goal is to provide a theoretical basis for the clinical application of Osteoking in osteoporosis treatment.

METHODS

A rat model of osteoporosis was established through bilateral ovariectomy (OVX), followed by treatment with Osteoking. After ten weeks of therapy, BMD was evaluated. The biomechanics of the left tibia were measured, the left femur was sequenced, and the right tibia was stained using histomorphometric and Masson's staining methods. Peripheral serum was collected to measure bone-related markers, including E2, PINP, and CTX. RNA-Seq results were verified using the remaining bone samples. Comparative analysis demonstrated the efficacy of Osteoking in treating osteoporosis and provided preliminary insights into the underlying mechanisms. Primary BMSCs were cultured using bone marrow apposition. CCK8 assays were conducted to screen the intervention conditions of Osteoking and LY294002. Various concentrations of Osteoking-containing serum and LY294002 were tested separately to determine the optimal intervention concentration for drug delivery. The impact of Osteoking on lipid formation was also evaluated. Following treatment of BMSCs from OVX rats with Sham serum, OVX serum, OVX + LY294002 serum, and Osteoking + LY294002 serum, the expression of PI3K/AKT/mTOR, osteogenesis-related regulatory factors, and apoptosis-related regulatory factors was assessed. Flow cytometry was employed to evaluate apoptosis in BMSCs.

RESULTS

Osteoking significantly improved whole-body BMD and bone biomechanical indices in OVX rats. It also significantly elevated the serum levels of E2 and PINP while reducing the level of CTX, which significantly improved bone microstructure and promoted new bone formation. RNA-seq analysis indicated that the therapeutic mechanism involved the PI3K/AKT signaling pathway. Osteoking increased the expression of RUNX2 and decreased the expression of PPAR-γ, a marker of lipogenesis, in OVX rats. Extraction of BMSCs for subsequent studies revealed a significant reduction in proliferation and osteogenic differentiation, along with an increase in lipogenic differentiation, in the OVX group. Osteoking treatment inhibited the expression of PPAR-γ and increased the expression of RUNX2 in BMSCs. Additionally, Osteoking reversed the LY294002-mediated inhibition of PI3K/AKT/mTOR signaling pathway activation, increased the expression of the apoptosis-protecting protein Bcl2, and decreased the expression of apoptosis-associated proteins Caspase3 and Bax.

CONCLUSION

Osteoking markedly improved bone microstructure, biomechanics, and bone density in OVX rats. Osteoking-containing serum reversed the imbalance in lineage differentiation in OVX rats, characterized by reduced osteogenic differentiation and increased lipid differentiation of BMSCs. Furthermore, Osteoking-containing serum significantly increased BMSC proliferation and prevented apoptosis in OVX rats through the PI3K/AKT signaling pathway.

Tracing Cellular Senescence in Bone: Time-Dependent Changes in Osteocyte Cytoskeleton Mechanics and Morphology

Aging-related bone loss significantly impacts the growing elderly population globally, leading to debilitating conditions such as osteoporosis. Senescent osteocytes play a crucial role in the aging process of bone. This longitudinal study examines the impact of continuous local and paracrine exposure to senescence-associated secretory phenotype (SASP) factors on senescence-associated biophysical and biomolecular markers in osteocytes. We found significant cytoskeletal stiffening in irradiated osteocytes, accompanied by expansion of F-actin areas and a decline in dendritic integrity. These changes, correlating with alterations in pro-inflammatory cytokine levels and osteocyte-specific gene expression, support the reliability of biophysical markers for identifying senescent osteocytes. Notably, local accumulation of SASP factors had a more pronounced impact on osteocyte properties than paracrine effects, suggesting that the interplay between local and paracrine exposure could substantially influence cellular aging. This study underscores the importance of osteocyte mechanical and morphological properties as biophysical markers of senescence, highlighting their time-dependence and differential effects of local and paracrine SASP exposure. Collectively, our investigation into biophysical senescence markers offer unique and reliable functional hallmarks for non-invasive identification of senescent osteocytes, providing insights that could inform therapeutic strategies to mitigate aging-related bone loss.

The senolytic cocktail, dasatinib and quercetin, impacts the chromatin structure of both young and senescent vascular smooth muscle cells

One promising strategy to alleviate aging symptoms is the treatment with senolytics that is compounds which selectively eliminate senescent cells. Some therapies aim to reduce symptoms of cellular senescence without senescent cell eradication (senomorphic activity). However, senotherapies raise many questions concerning the selectivity, safety and efficiency of senolitic drugs. A vital question is how the senolytic compounds affect young proliferating cells. In our study, we checked the impact of quercetin and dasatinib (D + Q), one of the promising drug mixtures of drugs, on chromatin structure in young and senescent cells. We analyzed the effect of a single and triple drug treatment on vascular smooth muscle cells. We have shown that D + Q impacts the chromatin in both young and senescent cells. In senescent cells, D + Q caused some symptoms of chromatin "rejuvenation" but in young cells some changes characteristic of senescent cells were observed. The alterations in young cells appeared only transiently and chromatin returned to the initial state after 24 h of recovery. The complexity of chromatin staining and nucleus morphology evaluation indicated that a triple treatment makes senescent cells more similar to the young ones than a single treatment. However, the analysis of senescence markers suggested that a single treatment with D + Q caused slightly less pronounced senescence characteristics and was more efficient in alleviating the features of senescence than a triple treatment. It is still an open question whether the alterations caused by D + Q are beneficial or harmful in the long term; however, so far, it can be concluded that the effects depend on cell type and the physiological context.

Irisin reshapes bone metabolic homeostasis to delay age-related osteoporosis by regulating the multipotent differentiation of BMSCs via Wnt pathway

Introduction

Bone aging is linked to changes in the lineage differentiation of bone marrow stem cells (BMSCs), which show a heightened tendency to differentiate into adipocytes instead of osteoblasts. The therapeutic potential of irisin in addressing age-related diseases has garnered significant attention. More significantly, irisin has the capacity to enhance bone mass recovery and sustain overall bone health. Its mechanism of action in preventing osteoporosis has generated considerable interest within the research community. Nonetheless, the targeting effect of irisin on age-related osteoporosis and its underlying molecular biological mechanisms remain unclear.

Methods

The specific role of irisin in osteogenic-adipogenic differentiation in young or aging BMSCs was evaluated by multiple cells staining and quantitative real-time PCR (RT-qPCR) analysis. RNA-seq and protein Western blotting excavated and validated the key pathway by which irisin influences the fate determination of aging BMSCs. The macroscopic and microscopic changes of bone tissue in aging mice were examined using Micro-computed tomography (Micro-CT) and morphological staining.

Results

It was noted that irisin affected the multilineage differentiation of BMSCs in a manner dependent on the dosage. Simultaneously, the Wnt signaling pathway might be a crucial mechanism through which irisin sustains the bone-fat balance in aging BMSCs and mitigates the decline in pluripotency. In vivo, irisin reduced bone marrow fat deposition in aging mice and effectively alleviating the occurrence of bone loss.

Conclusion

Irisin mediates the Wnt signaling pathway, thereby influencing the fate determination of BMSCs. In addition, it is essential for preserving metabolic equilibrium in the bone marrow microenvironment and significantly contributes to overall bone health. The findings provide new evidence for the use of iris extract in the treatment of age-related osteoporosis.

Senolytic therapy combining Dasatinib and Quercetin restores the chondrogenic phenotype of human osteoarthritic chondrocytes by the release of pro-anabolic mediators

Cellular senescence is associated with various age-related disorders and is assumed to play a major role in the pathogenesis of osteoarthritis (OA). Based on this, we tested a senolytic combination therapy using Dasatinib (D) and Quercetin (Q) on aged isolated human articular chondrocytes (hACs), as well as in OA-affected cartilage tissue (OARSI grade 1-2). Stimulation with D + Q selectively eliminated senescent cells in both, cartilage explants and isolated hAC. Furthermore, the therapy significantly promoted chondroanabolism, as demonstrated by increased gene expression levels of COL2A1, ACAN, and SOX9, as well as elevated collagen type II and glycosaminoglycan biosynthesis. Additionally, D + Q treatment significantly reduced the release of SASP factors (IL6, CXCL1). RNA sequencing analysis revealed an upregulation of the anabolic factors, inter alia, FGF18, IGF1, and TGFB2, as well as inhibitory effects on cytokines and the YAP-1 signaling pathway, explaining the underlying mechanism of the chondroanabolic promotion upon senolytic treatment. Accordingly, stimulation of untreated hAC with conditioned medium of D + Q-treated cells similarly induced the expression of chondrogenic markers. Detailed analyses demonstrated that chondroanabolic effects could be mainly attributed to Dasatinib, while monotherapeutical application of Quercetin or Navitoclax did not promote the chondroanabolism. Overall, D + Q therapy restored the chondrogenic phenotype in OA hAC most likely by creating a pro-chondroanabolic environment through the reduction of SASP factors and upregulation of growth factors. This senolytic approach could therefore be a promising candidate for further testing as a disease-modifying osteoarthritis drug.

Cellular senescence as a source of chronic microinflammation that promotes the aging process

Why and how do we age? This physiological phenomenon that we all experience remains a great mystery, largely unexplained even in this age of scientific and technological progress. Aging is a significant risk factor for numerous diseases, including cancer. However, underlying mechanisms responsible for this association remain to be elucidated. Recent findings have elucidated the significance of the accumulation of senescent cells and other inflammatory cells in organs and tissues with age, and their deleterious effects, such as the induction of inflammation in the microenvironment, as underlying factors contributing to organ dysfunction and disease development. Cellular senescence is a cellular phenomenon characterized by a permanent cessation of cell proliferation and secretion of several proinflammatory cytokines (senescence associated secretory phenotypes). Notably, the elimination of senescent cells from aging individuals has been demonstrated to alleviate age-related organ and tissue dysfunction, as well as various geriatric diseases. This review summarizes the molecular mechanisms by which senescent cells are induced and contribute to age-related diseases, as well as the technologies that ameliorate them.

Cordycepin-Loaded Dental Pulp Stem Cell-Derived Exosomes Promote Aged Bone Repair by Rejuvenating Senescent Mesenchymal Stem Cells and Endothelial Cells

Aging impairs bone marrow mesenchymal stem cell (BMSC) functions as well as associated angiogenesis which is critical for bone regeneration and repair. Hence, repairing bone defects in elderly patients poses a formidable challenge in regenerative medicine. Here, the engineered dental pulp stem cell-derived exosomes loaded with the natural derivative of adenosine Cordycepin (CY@D-exos) are fabricated by means of the intermittent ultrasonic shock, which dually rejuvenates both senescent BMSCs and endothelial cells and significantly improve bone regeneration and repair in aged animals. CY@D-exos can efficiently overcome the senescence of aged BMSCs and enhance their osteogenic differentiation by activating NRF2 signaling and maintaining heterochromatin stability. Importantly, CY@D-exos also potently overcomes the senescence of vascular endothelial cells and promotes angiogenesis. In vivo injectable gelatin methacryloyl (GelMA) hydrogels with sustained release of CY@D-exos can accelerate bone injury repair and promote new blood vessel formation in aged animals. Taken together, these results thus demonstrate that cordycepin-loaded dental pulp stem cell-derived exosomes display considerable potential to be developed as a next-generation therapeutic agent for promoting aged bone regeneration and repair.

USP7 Inhibition Promotes Early Osseointegration in Senile Osteoporotic Mice

Although elderly osteoporotic patients have similar implant survival rates compared with those of normal individuals, they require longer healing periods to achieve proper osseointegration. This may be related to chronic inflammatory responses and impaired stem cell repair functions in the osteoporotic bone microenvironment. Recently, the deubiquitinating enzyme, ubiquitin-specific peptidase 7 (USP7), was found to regulate the macrophage immune response and modulate stem cell osteogenic differentiation. The selective inhibitor of USP7, P5091, has also been found to promote bone repair and homeostasis in osteoporotic conditions. However, the roles of USP7 and P5091 in osteoimmunology and dental implant osseointegration under senile osteoporotic conditions remain unclear. In this study, USP7 depletion and P5091 were shown to inhibit inflammation in senescent bone marrow-derived macrophages (BMDMs) and promote osteogenic differentiation in aged bone marrow mesenchymal stromal cells (BMSCs). Furthermore, mRNA-Seq revealed that USP7 depletion could enhance efferocytosis in senescent BMDMs through the EPSIN1/low-density lipoprotein receptor-related protein 1 (LRP1) pathway and selectively induce apoptosis (senolysis) in aged BMSCs. In senile osteoporotic mice, we found that the osseointegration period was prolonged compared with young mice, and P5091 promoted the early stage of osseointegration, which may be related to macrophage efferocytosis around the implant. Collectively, this study suggests that USP7 inhibition may accelerate the osseointegration process in senile osteoporotic conditions by promoting macrophage efferocytosis and aged BMSCs apoptosis. This has implications for understanding the cellular interactions and signaling mechanisms in the peri-implant bone microenvironment under osteoporotic conditions. It may also provide clinical significance in developing new therapies to enhance osseointegration quality and shorten the edentulous period in elderly osteoporotic patients.

Senolytics cocktail dasatinib and quercetin alleviate chondrocyte senescence and facet joint osteoarthritis in mice

BACKGROUND CONTEXT

Low back pain (LBP) is a pervasive issue, causing substantial economic burden and physical distress worldwide. Facet joint osteoarthritis (FJ OA) is believed to be a significant contributor to this problem. However, the precise role of chondrocyte senescence in FJ OA remains unclear, as does whether the clearance of chondrocyte senescence can alleviate the progression of FJ OA.

PURPOSE

The goal of this study was to understand the potential of Dasatinib (D) and Quercetin (Q) as a treatment to clear chondrocyte senescence during the progression of FJ OA.

STUDY DESIGN

We used a preclinical bipedal standing mice model with the administration of Dasatinib (D) (5 mg/kg) and Quercetin (Q) (50 mg/kg) after 10 weeks of bipedal standing.

MATERIALS AND METHODS

Human degenerative lumbar facet joint (LFJ) samples were obtained to investigate the relationship between chondrocyte cellular senescence and LFJ osteoarthritis (OA). Subsequently, we established an in vitro model of excessive mechanical stress on chondrocytes and an in vivo bipedal standing mice model to induce LFJ OA. IHC (immunohistochemistry) staining in vivo and SA-β-gal staining, qRT-PCR and Western blot analysis were applied to test the senolytic effect of the combination of Dasatinib (D) and Quercetin (Q). IHC staining and X-ray microscope were also performed to examine the contribution of D+Q to the anabolism in cartilage and subchondral bone recoupling. Immunofluorescence and Western blot analysis in vitro and IHC staining in vivo were conducted to assess the impact of D+Q on the regulation of the NF-κB pathway activation during chondrocyte senescence.

RESULTS

We observed that facet joint cartilage degeneration is associated with chondrocyte cellular senescence in both human and mouse degenerative samples. Following treatment with D+Q in vitro, cellular senescence was significantly reduced. Upon oral gavage administration of D+Q in the bipedal standing mice model, decreased cellular senescence and reversed chondrocyte anabolism were observed. Furthermore, administration of D+Q maintained subchondral bone remodeling homeostasis and potentially reversed the activation of the NF-κB pathway in chondrocytes of the lumbar facet joint.

CONCLUSIONS

In summary, our investigation unveiled a significant correlation between chondrocyte senescence and LFJOA. Treatment with the senolytic combination of D+Q in FJ OA yielded a notable reduction in chondrocyte senescence, along with a decrease in the release of SASP factors. Additionally, it facilitated the promotion of cartilage anabolism, maintenance of subchondral bone coupling, and amelioration of NF-κB pathway activation.

CLINICAL SIGNIFICANCE

Our outcomes revealed that D+Q, the renowned combination used for senolytic treatment, alleviate the progression of LFJ OA. The utilization of D+Q as a senolytic demonstrates a novel and promising alternative for LFJ OA treatment.

Senescence landscape in the liver following sepsis and senolytics as potential therapeutics

Senescence, caused by cell-cycle arrest, is a hallmark of aging. Senescence has also been described in embryogenesis, wound healing, and acute injuries. Sepsis is characterized by a dysregulated host response to infection, leading to organ dysfunction and mortality. Most of the pathophysiology of human sepsis is recapitulated in the mouse model of polymicrobial sepsis, developed by cecal ligation and puncture (CLP). In this report, we demonstrate a rapid onset of cellular senescence in the liver of mice subjected to CLP-induced sepsis, characterized by the upregulation of p21, p53, and other senescence markers, including SA-βgal. Using RNAscope, confocal microscopy, and flow cytometry, we further confirm the emergence of p21-expressing senescence phenotype in the liver 24 h after sepsis induction. Senescence was observed in several cell types in the liver, including hepatocytes, endothelial cells, and macrophages. We determined the landscape of senescence phenotype in murine sepsis by single-cell sequencing, which further ascertained that this cell fate is not confined to any particular cell type but displays a heterogeneous distribution. Furthermore, we observed a significant reduction in mortality following sepsis when mice were treated with senolytics, a combination of dasatinib and quercetin, before the CLP surgery. Our experiments unequivocally demonstrated a rapid development of cellular senescence with sepsis and, for the first time, described the senescence landscape in the sepsis liver and the possible role of senescent cells in the worsening outcome following sepsis.

Global Highly Cited Publication Trends and Research Hotspots in Osteoporosis and Bone Metabolic Cells: A Bibliometric and Visualization Analysis from 2013 to 2023

BACKGROUND

Bone metabolic diseases such as osteoporosis are caused by disruption of the metabolic balance between osteoblasts and osteoclasts. Thousands of papers have been published on osteoporosis and bone metabolizing cells. The purpose of this study is to draw the publication trend of highly cited literature in this field through bibliometrics and to explore the research hotspot analysis.

OBJECTIVE

This paper provides a comprehensive analysis of the impact of countries/regions, research institutions, authors, keywords, relevant journals, and references in the field of osteoporosis and bone metabolic cells research, with a specific focus on the theme of "Osteoporosis and bone metabolic cells". Furthermore, utilizing bibliometric methods, the study aims to offer valuable insights and references for future research endeavors, as well as clinical prevention and treatment strategies in this domain.

METHODS

The Web of Science (WOS) Core Collection database was examined in order to identify articles with high citation counts from 2013 to 31 October 2023. The citation counts, authors, year of publication, source, journal, geographical origin, subject, article type, and level of evidence were further analyzed using the R bibliometric package. The VOSviewer software was utilized to visualize word co-occurrence in a total of 251 articles.

RESULTS

Our search strategy included 251 highly cited articles published between 2013 and 2023 in the field of osteoporosis and bone metabolic cells. The number of publications in this field remains consistently high, indicating ongoing research interest. Notably, the United States has made significant achievements and contributions in this area. Xie Hui, Cao Xu, and Goodman, Stewart are among the main contributors to these advancements. Nature medicine has the highest journal impact factor of 82.9, highlighting its prominence. The journal of bone and mineral research ranks first with 1,322 citations. Keyword research topics in this field include osteoclast differentiation, osteoblast differentiation, and mesenchymal stem cells. Through citation analysis, we found that 195 articles have been cited more than 100 times, demonstrating their significance and impact.

CONCLUSION

This study analyzed the relationship between osteoporosis and bone metabolic cells using a bibliometric method. The results of these analyses can help researchers gain a more direct and scientific understanding of trends in the field. Additionally, it can provide guidance in identifying hot research directions and offer new ideas for the prevention and treatment of osteoporosis.

Regulating Mitochondrial Aging via Targeting the Gut-Bone Axis in BMSCs With Oral Hydrogel Microspheres to Inhibit Bone Loss

The gut-bone axis is a promising target for osteoporosis treatment, yet existing delivery systems lack precise targeting. Herein, an oral hydrogel microsphere system (E7-Lipo@Alg/Cs) is developed using gas microfluidic and ionic crosslinking technologies to deliver drugs to bone marrow mesenchymal stem cells (BMSCs) via the gut-bone axis, regulating mitochondrial aging. A BMSC-affine peptide is conjugated onto liposomes encapsulating Fisetin, followed by incorporation into alginate-calcium hydrogel microspheres. Chitosan is electrostatically adsorbed onto the microsphere surface, creating a core-shell structure that adheres to intestinal epithelial cells, withstands gastric acid, and facilitates targeted delivery to BMSCs through the intestinal-bone axis. In vitro, the system effectively enhances mitochondrial function and reverses BMSC aging, while in vivo studies demonstrate prolonged drug activity, restored osteogenic differentiation, and bone regeneration. RNA-seq indicates activation of the AMPK-SIRT1 pathway, reversing mitochondrial aging in BMSCs and promoting aged bone tissue regeneration. This oral hydrogel microsphere system provides a targeted and efficient strategy for regulating mitochondrial function and preventing bone loss, offering significant clinical potential for osteoporosis treatment.

The Hippo Signaling Pathway Manipulates Cellular Senescence

The Hippo pathway, a kinase cascade, coordinates with many intracellular signals and mediates the regulation of the activities of various downstream transcription factors and their coactivators to maintain homeostasis. Therefore, the aberrant activation of the Hippo pathway and its associated molecules imposes significant stress on tissues and cells, leading to cancer, immune disorders, and a number of diseases. Cellular senescence, the mechanism by which cells counteract stress, prevents cells from unnecessary damage and leads to sustained cell cycle arrest. It acts as a powerful defense mechanism against normal organ development and aging-related diseases. On the other hand, the accumulation of senescent cells without their proper removal contributes to the development or worsening of cancer and age-related diseases. A correlation was recently reported between the Hippo pathway and cellular senescence, which preserves tissue homeostasis. This review is the first to describe the close relationship between aging and the Hippo pathway, and provides insights into the mechanisms of aging and the development of age-related diseases. In addition, it describes advanced findings that may lead to the development of tissue regeneration therapies and drugs targeting rejuvenation.

A prospective study of associations between accelerated biological aging and twenty musculoskeletal disorders

BACKGROUND

Musculoskeletal disorders pose major public health challenges, and accelerated biological aging may increase their risk. This study investigates the association between biological aging and musculoskeletal disorders, with a focus on sex-related differences.

METHODS

We analyzed data from 172,332 UK Biobank participants (mean age of 56.03 ± 8.10 years). Biological age was calculated using the KDM-BA and PhenoAge algorithms based on blood biomarkers. Musculoskeletal disorders were diagnosed using the ICD-10 criteria, with sample sizes ranging from 1,182 to 23,668. Logistic regression assessed cross-sectional associations between age acceleration (AA) metrics and musculoskeletal disorders. Accelerated Failure Time (AFT) model was used for survival analysis to evaluate the relationships between AAs and musculoskeletal disorders onset. Models were adjusted for demographic, lifestyle, and socio-economic covariates. The threshold of P-values were set by the Holm-Bonferroni correction.

RESULTS

Cross-sectional analyses reveal significant associations between AAs and fourteen musculoskeletal disorders. Survival analyses indicate that AAs significantly accelerate the onset of nine musculoskeletal disorders, including inflammatory polyarthropathies (RTKDM-BA = 0.993; RTPhenoAge = 0.983), systemic connective tissue disorders (RTKDM-BA = 0.987; RTPhenoAge = 0.980), spondylopathies (RTPhenoAge= 0.994), disorders of bone density and structure (RTPhenoAge= 0.991), gout (RTPhenoAge= 0.968), arthritis (RTPhenoAge= 0.991), pain in joint (RTPhenoAge= 0.989), low back pain (RTPhenoAge= 0.986), and osteoporosis (RTPhenoAge= 0.994). Sensitivity analyses are consistent with the primary findings. Sex-specific variations are observed, with AAs accelerating spondylopathies, arthritis, and low back pain in females, while osteoporosis is accelerated in males.

CONCLUSION

Accelerated biological aging is significantly associated with the incidence of several musculoskeletal disorders. These insights highlight the importance of biological age assessments in gauging musculoskeletal disorder risk, aiding early detection, prevention, and management.

LEP O-GlcNAcylation inactivates NF-κB pathway by suppressing LEP protein level and thus mediates cellular senescence and osteogenic differentiation in mouse mesenchymal stem cells

BACKGROUND

Cellular senescence is a key driver of decreased bone formation and osteoporosis. Leptin (LEP) has been implicated in cellular senescence and osteogenic differentiation. The aim of this study was to investigate the mechanisms by which LEP mediates cellular senescence and osteogenic differentiation.

METHODS

C3H10T1/2 cells were treated with etoposide to induce cellular senescence, which was assessed by β-galactosidase staining. Quantitative real-time PCR and western blotting were used to measure the levels of senescence markers p21 and p16, as well as osteogenic differentiation-related genes ALP, COL1A1, and RUNX2. Alkaline phosphatase (ALP) staining and alizarin red S staining were performed to evaluate osteogenic differentiation. The NF-κB pathway and O-GlcNAcylation were assessed by western blotting.

RESULTS

Etoposide treatment increased the number of senescent cells and the levels of p21 and p16, along with elevated LEP expression. These effects were reversed by LEP knockdown. Additionally, LEP knockdown increased ALP staining density and osteoblast mineralization nodules, as well as the mRNA and protein levels of ALP, COL1A1, and RUNX2, indicating that LEP knockdown promoted osteogenic differentiation in C3H10T1/2 cells. Mechanistically, LEP knockdown inactivated the NF-κB pathway by inhibiting the nuclear translocation of p65. Furthermore, OGT was found to promote O-GlcNAcylation of LEP at the S50 site.

CONCLUSION

Our findings demonstrated that O-GlcNAcylation of LEP inactivated the NF-κB pathway by reducing LEP protein levels, thereby inhibiting cellular senescence and promoting osteogenic differentiation in C3H10T1/2 cells. This study may provide a novel therapeutic target for the treatment of osteoporosis.