The role of osteoblasts in energy homeostasis

Update on the correlation between mitochondrial function and osteonecrosis of the femoral head osteocytes

Mitochondrial health is maintained in a steady state through mitochondrial dynamics and autophagy processes. Recent studies have identified healthy mitochondria as crucial regulators of cellular function and survival. This process involves adenosine triphosphate (ATP) synthesis by mitochondrial oxidative phosphorylation (OXPHOS), regulation of calcium metabolism and inflammatory responses, and intracellular oxidative stress management. In the skeletal system, they participate in the regulation of cellular behaviors and the responses of osteoblasts, osteoclasts, chondrocytes, and osteocytes to external stimuli. Indeed, mitochondrial damage or dysfunction occurs in the development of a few bone diseases. For example, mitochondrial damage may lead to an imbalance in osteoblasts and osteoclasts, resulting in osteoporosis, osteomalacia, or poor bone production, and chondrocyte death and inflammatory infiltration in osteoarthritis are the main causes of cartilage degeneration due to mitochondrial damage. However, the opposite exists for osteosarcoma, where overactive mitochondrial metabolism is able to accelerate the proliferation and migration of osteosarcoma cells, which is a major disease feature. Bone is a dynamic organ and osteocytes play a fundamental role in all regions of bone tissue and are involved in regulating bone integrity. This review examines the impact of mitochondrial physiological function on osteocyte health and summarizes the microscopic molecular mechanisms underlying its effects. It highlights that targeted therapies focusing on osteocyte mitochondria may be beneficial for osteocyte survival, providing a new insight for the diagnosis, prevention, and treatment of diseases associated with osteocyte death.

Targeted disruption of PRC1.1 complex enhances bone remodeling

Polycomb repressive complexes (PRCs) are pivotal epigenetic regulators that preserve cell identity by restricting transcription responses to sub-threshold extracellular signals. Their roles in osteoblast function and bone formation remain unclear. Here in aging osteoblasts, we found marked activation of PRC1.1 complex, with KDM2B acting as a chromatin-binding factor and BCOR and PCGF1 enabling histone H2A monoubiquitylation (H2AK119ub1). Osteoblast-specific Kdm2b inactivation significantly enhances bone remodeling under steady-state conditions and in scenarios of bone loss. This enhancement is attributed to H2AK119ub1 downregulation and subsequent Wnt signaling derepression. Furthermore, we developed a small molecule termed iBP, that specifically inhibits the interaction between BCOR and PCGF1, thereby suppressing PRC1.1 activity. Notably, iBP administration promotes bone formation in mouse models of bone loss. Therefore, our findings identify PRC1.1 as a critical epigenetic brake on bone formation and demonstrate that therapeutic targeting of this complex enhances Wnt pathway activation, offering a promising strategy against skeletal deterioration.

Endogenous dysregulated energy and amino acid metabolism delay scaffold-guided large volume bone regeneration in a diabetic rat model with Leptin receptor deficiency

Scaffold-guided bone regeneration (SGBR) offers a promising solution for treating large-volume bone defects. However, its efficacy in compromised healing environments, such as those associated with metabolic conditions like Type 2 Diabetes (T2D), remains poorly understood. This study evaluates the potential of 3D-printed polycaprolactone (PCL) scaffolds for large-volume bone regeneration in preclinical models simulating T2D-induced metabolic challenges. Our results reveal that scaffolds alone are insufficient to overcome the metabolic barriers to effective bone regeneration. Metabolomic analysis of regenerating tissue identified significant disruptions in key metabolic pathways involved in energy production and amino acid synthesis in T2D rats compared to controls. Notably, aconitic acid, ornithine, and glycine levels were elevated in non-diabetic conditions, whereas phosphoenolpyruvate was markedly increased under T2D conditions. Secondary harmonic generation (SHG) imaging further demonstrated impaired collagen organization within T2D regenerating tissue, correlating with disrupted collagen synthesis critical for bone matrix formation. In vitro, the exogenous supplementation of alpha-ketoglutarate (α-KG)-a crucial citric acid cycle intermediate-enhanced mineralized tissue formation in human adipose-derived mesenchymal stem cells (hAdMSCs) from T2D donors, achieving levels superior to non-T2D cells. These findings underscore the metabolic underpinnings of impaired bone regeneration in T2D. Optimized 3D printed scaffolds alone do not counterbalance the impaired regeneration in T2D. Here we highlight a therapeutic potential of metabolic supplementation to optimize SGBR outcomes. This study provides a critical foundation for advancing translational research and developing regenerative therapies tailored to high-risk metabolic disease populations. STATEMENT OF SIGNIFICANCE: Scaffold-guided bone regeneration (SGBR) holds great promise for addressing large bone defects, but its efficacy in metabolically challenged conditions like Type 2 Diabetes (T2D) remains limited. This study uses a metabolomics-driven approach to reveal how metabolic dysregulation in T2D, including disruptions in energy and amino acid pathways, impairs collagen organization and extracellular matrix (ECM) formation-critical for successful bone healing. By identifying α-ketoglutarate (α-KG) as a potential supplement to restore metabolic balance, this work offers novel insights into enhancing scaffold performance under compromised conditions. These findings provide a foundation for integrating bioactive compounds into scaffold designs, advancing personalized strategies in regenerative medicine, and addressing a critical gap in bone defect treatment for diabetic patients.

Clinical Progress in Mesenchymal Stem Cell Therapy: A Focus on Rheumatic Diseases

BACKGROUND

Rheumatic diseases are chronic immune-mediated disorders affecting multiple organ systems and significantly impairing patients' quality of life. Current treatments primarily provide symptomatic relief without offering a cure. Mesenchymal stem cells (MSCs) have emerged as a promising therapeutic option due to their ability to differentiate into various cell types and their immunomodulatory, anti-inflammatory, and regenerative properties. This review aims to summarize the clinical progress of MSC therapy in rheumatic diseases, highlight key findings from preclinical and clinical studies, and discuss challenges and future directions.

METHODOLOGY

A comprehensive review of preclinical and clinical studies on MSC therapy in rheumatic diseases, including systemic lupus erythematosus, rheumatoid arthritis, ankylosing spondylitis, osteoarthritis, osteoporosis, Sjögren's syndrome, Crohn's disease, fibromyalgia, systemic sclerosis, dermatomyositis, and polymyositis, was conducted. Emerging strategies to enhance MSC efficacy and overcome current limitations were also analyzed.

RESULTS AND DISCUSSION

Evidence from preclinical and clinical studies suggests that MSC therapy can reduce inflammation, modulate immune responses, and promote tissue repair in various rheumatic diseases. Clinical trials have demonstrated potential benefits, including symptom relief and disease progression delay. However, challenges such as variability in treatment response, optimal cell source and dosing, long-term safety concerns, and regulatory hurdles remain significant barriers to clinical translation. Standardized protocols and further research are required to optimize MSC application.

CONCLUSION

MSC therapy holds promise for managing rheumatic diseases, offering potential disease-modifying effects beyond conventional treatments. However, large-scale, well-controlled clinical trials are essential to establish efficacy, safety, and long-term therapeutic potential. Addressing current limitations through optimized treatment protocols and regulatory frameworks will be key to its successful integration into clinical practice.

Bone-derived factors mediate crosstalk between skeletal and extra-skeletal organs

Bone has long been acknowledged as a fundamental structural entity that provides support and protection to the body's organs. However, emerging research indicates that bone plays a crucial role in the regulation of systemic metabolism. This is achieved through the secretion of a variety of hormones, cytokines, metal ions, extracellular vesicles, and other proteins/peptides, collectively referred to as bone-derived factors (BDFs). BDFs act as a medium through which bones can exert targeted regulatory functions upon various organs, thereby underscoring the profound and concrete implications of bone in human physiology. Nevertheless, there remains a pressing need for further investigations to elucidate the underlying mechanisms that inform the effects of bone on other body systems. This review aims to summarize the current findings related to the roles of these significant modulators across different organs and metabolic contexts by regulating critical genes and signaling pathways in vivo. It also addresses their involvement in the pathogenesis of various diseases affecting the musculoskeletal system, circulatory system, glucose and lipid metabolism, central nervous system, urinary system, and reproductive system. The insights gained from this review may contribute to the development of innovative therapeutic strategies through a focused approach to bone secretomes. Continued research into BDFs is expected to enhance our understanding of bone as a multifunctional organ with diverse regulatory roles in human health.

Gouqi-derived Nanovesicles (GqDNVs) promoted MC3T3-E1 cells proliferation and improve fracture healing

BACKGROUND

Lycium barbarum L., also known as Gouqi, a traditional Chinese herbal medicine, is widely utilized in health care products and clinical therapies. Its muscle and bone strengthening efficacy has been recorded in medical classics for a long time. In addition, plant exosome-like nanovesicles (PELNVs) have attracted more and more attention owing to their biological traits. Therefore, we intended to explore the functions, regulatory role, and underlying mechanism of Gouqi-derived Nanovesicles (GqDNVs) on fracture healing.

METHODS

In this study, we employed the sucrose density gradient differential ultracentrifugation to isolate GqDNVs. The effects of GqDNVs on the proliferation and differentiation of MC3T3-E1 cells were evaluated using the CCK-8 assay, ALP activity measurement, and cell scratch assay. Additionally, leveraging a fracture mouse model, we utilized Micro-CT, immunological staining, and histologic analyses to comprehensively assess the impact of GqDNVs on fracture healing in mice.

RESULTS

GqDNVs stimulated cell viability, increased ALP activity, and promoted cellular osteogenic protein expression (OPN, ALP, and RUNX2). Subsequently, in the mouse fracture model, trabecular thickness, and bone marrow density were increased in the GqDNVs treatment group after 28 days of injection. Meanwhile, the expressions of OPN and BGP were significantly elevated after both 14 and 28 days. Additionally, the expressions of p-PI3K/PI3K, p-Akt/Akt, p-mTOR/mTOR, p-4EBP1/4EBP1 and p-p70S6K/ p70S6K were also increased after14 days of treatment.

CONCLUSIONS

GqDNVs effectively promoted the proliferation and differentiation of MC3T3-E1 cells. Furthermore, GqDNVs could improve fracture healing, which is associated with PI3K/Akt/mTOR/p70S6K/4EBP1 signaling pathway.

Natural collagen scaffold with intrinsic piezoelectricity for enhanced bone regeneration

Materials-mediated piezoelectric signals have been widely applied in bone regeneration. Collagen is the most abundant protein in the human body, and native collagen with complete tertiary structure shows efficient piezoelectricity. However, the traditional collagen scaffolds are lack of piezoelectricity due to the destruction of the complete tertiary structure. Here, natural collagen scaffolds with the complete tertiary structure were prepared. Alkali treatment made the collagen scaffold lose piezoelectricity. The collagen with/without piezoelectricity (PiezoCol/NCol) scaffolds both possessed good cytocompatibility and promoted cell adhesion. After being implanted subcutaneously, the NCol scaffold almost did not affect bone regeneration with/without ultrasound treatment. However, under ultrasound treatment, the PiezoCol scaffold promoted the new bone formation with enhanced osteogenic differentiation, angiogenesis, and neural differentiation, meaning that piezoelectricity endows collagen with satisfactory promotion for bone regeneration. Meanwhile, the PiezoCol scaffold can also accelerate bone formation without ultrasound treatment, which should be attributed to the daily exercise-caused weak piezoelectric stimulation. Further, the proteomic analysis revealed the mechanism by which the PiezoCol scaffold promoted bone tissue formation via mainly upregulating the PI3K-Akt signaling pathway. This study provides a new strategy to enhance the osteoinduction of collagen scaffold for bone regeneration by maintaining intrinsic piezoelectricity.

Extracellular osmolarity regulates osteoblast migration through the TRPV4-Rho/ROCK signaling

For precise bone formation, osteoblasts need to accurately migrate to specific sites guided by various biochemical and mechanical cues. During this migration, fluctuations in extracellular osmolarity may arise from shifts in the surrounding fluid environment. However, as a main regulator of cell morphology and function, whether the extracellular osmolarity change may affect osteoblast migration remains unclear. Here, we provide evidence showing that changes in extracellular osmolarity significantly impact osteoblast migration, with a hypotonic environment enhancing it while a hypertonic environment inhibiting it. Further, our findings reveal that a hypotonic treatment increases intracellular pressure, activating the Transient Receptor Potential Vanilloid 4 (TRPV4) channel. This activation of TRPV4 modulates stress fibers, focal adhesions (FAs), and cell polarity through the Rho/ROCK signaling pathway, ultimately impacting osteoblast migration. Our findings provide valuable insights into the significant influence of extracellular osmolarity on osteoblast migration, which has potential implications for enhancing our understanding of bone remodeling.

Mesenchymal stromal cells in bone marrow niche of patients with multiple myeloma: a double-edged sword

Multiple myeloma (MM) is a hematological malignancy defined by the abnormal proliferation and accumulation of plasma cells (PC) within the bone marrow (BM). While multiple myeloma impacts the bone, it is not classified as a primary bone cancer. The bone marrow microenvironment significantly influences the progression of myeloma and its treatment response. Mesenchymal stromal cells (MSCs) in this environment engage with myeloma cells and other bone marrow components via direct contact and the secretion of soluble factors. This review examines the established roles of MSCs in multiple facets of MM pathology, encompassing their pro-inflammatory functions, contributions to tumor epigenetics, effects on immune checkpoint inhibitors (ICIs), influence on reprogramming, chemotherapy resistance, and senescence. This review investigates the role of MSCs in the development and progression of MM.

Effect of artificial gravity on calcaneal bone marrow adipose tissue and mineral content in female and male participants in 60 days of bed rest

Modulation of bone marrow adipose tissue (BMAT) with prolonged inactivity was reported in haemopoietic but not in non-haemopoietic bones. This prospective randomized controlled trial submitted 16 men and 8 women to 60 days of 6° head-down-tilt bed rest. They were assigned to control, continuous or intermittent artificial gravity (AG) interventions. The AG consisted of daily centrifugation at 2g for 30 min. The serial foot pain questionnaire, MRI and dual-energy X-ray absorptiometry of the calcaneus were performed at baseline, during bed rest and at reambulation. At baseline, all groups had comparable calcaneal BMAT (P = 0.581) and bone mineral density (BMD) (P = 0.574). After bed rest, 83% of participants reported foot pain. Calcaneal BMAT was not significantly modulated after 60 days of bed rest (control, +0.2% ± 0.8%; continuous AG, +0.5% ± 1.1%; and intermittent AG, +0.1% ± 1.5%; P = 0.368). Calcaneal BMD was reduced at reambulation days 3 and 11 after 60 days of bed rest (-0.05 ± 0.06 and -0.06 ± 0.12 g/cm2, respectively; P = 0.008 and P = 0.020). The AG interventions did not significantly alter calcaneal BMAT or BMD. Sex-based analyses demonstrated calcaneal BMD loss in men but not in women. Calcaneal BMAT and BMD were inversely correlated in women and in men (Spearman's ρ, -0.40 and -0.28, respectively; both P = 0.020). Sixty days of bed rest caused foot pain and calcaneal demineralization not rescued by AG interventions. Although inversely correlated with BMD, calcaneal BMAT was not statistically increased by 60 days of head-down-tilt bed rest, possibly owing to a ceiling effect, and no bone marrow reconversion was measured at reambulation. These results have clinical relevance when returning to activities after prolonged bed rest or returning from space.

Plasma levels of amino acids and osteoporosis: a cross-sectional study

The role of amino acids (AAs) with bone health is still controversial. We examined the association between AAs and osteoporosis in a cross-sectional study of 135 participants aged 45 years or older from the Second Hospital of Jilin University. Plasma AAs were measured with targeted quantitative methodology. We measured bone mineral density (BMD) with dual energy x-ray absorptiometry, and osteoporosis was defined as a T-score ≤ -2.5. We estimated odds ratios (OR) and corresponding 95% confidence intervals (CIs) for the associations between AAs (per 1 standard deviation increase) with osteoporosis. Approximately 18.5% of participants (n = 25) had osteoporosis. Total (adjusted β = 0.052; P = 0.002) and non-essential AA (adjusted β = 0.064; P = 0.002) levels were associated with femoral neck BMD T-scores. Greater levels of total (adjusted OR: 0.734; 95% CI: 0.655-0.821), essential (adjusted OR: 0.763; 95% CI: 0.623-0.934) and non-essential AAs (adjusted OR: 0.721; 95% CI: 0.629-0.826) were associated with lower odds of osteoporosis. Higher tryptophan (adjusted OR: 0.498; 95% CI: 0.281-0.882), cysteine (adjusted OR: 0.561; 95% CI: 0.321-0.983), glycine (adjusted OR: 0.513; 95% CI: 0.285-0.922), and ornithine levels (adjusted OR: 0.581; 95% CI: 0.345-0.978) were associated with reduced osteoporosis risk. Higher AA levels were associated with higher femoral neck BMD, and lower odds of osteoporosis.

Recapitulation of endochondral ossification by hPSC-derived SOX9+ sclerotomal progenitors

Endochondral ossification generates most of the load-bearing bones, recapitulating it in human cells remains a challenge. Here, we report generation of SOX9+ sclerotomal progenitors (scl-progenitors), a mesenchymal precursor at the pre-condensation stage, from human pluripotent stem cells and development of osteochondral induction methods for these cells. Upon lineage-specific induction, SOX9+ scl-progenitors have not only generated articular cartilage but have also undergone spontaneous condensation, cartilaginous anlagen formation, chondrocyte hypertrophy, vascular invasion, and finally bone formation with stroma, thereby recapitulating key stages during endochondral ossification. Moreover, self-organized growth plate-like structures have also been induced using SOX9+ scl-progenitor-derived fusion constructs with chondro- and osteo-spheroids, exhibiting molecular and cellular similarities to the primary growth plates. Furthermore, we have identified ITGA9 as a specific surface marker for reporter-independent isolation of SOX9+ scl-progenitors and established a culture system to support their expansion. Our work highlights SOX9+ scl-progenitors as a promising tool for modeling human skeletal development and bone/cartilage bioengineering.

Knockdown of lncRNA XR_877193.1 suppresses ferroptosis and promotes osteogenic differentiation via the PI3K/AKT signaling pathway in SONFH

Ferroptosis is a novel form of regulated cell death characterized by the iron-dependent accumulation of lipid peroxides. Recent research has suggested that ferroptosis in osteoblasts contributes to steroid-induced osteonecrosis of the femoral head (SONFH). However, the relationship between ferroptosis and SONFH remains unclear. In this study, in vitro experiments show that dexamethasone (Dex) treatment reduces the expressions of key ferroptosis regulators, SLC7A11 and GPX4, in MC3T3-E1 cells. This reduction leads to a decrease in intracellular glutathione (GSH) levels, accompanied by elevated levels of total iron, malondialdehyde (MDA), and reactive oxygen species (ROS). Importantly, the ferroptosis inhibitor ferrostatin-1 (Fer-1) effectively reverses Dex-induced ferroptosis in MC3T3-E1 cells. Furthermore, RNA-seq analysis reveals that the long noncoding RNA (lncRNA) XR_877193.1is significantly upregulated in Dex-treated MC3T3-E1 cells. Functional studies demonstrate that the knockdown of lncRNA XR_877193.1 promotes osteogenic differentiation by inhibiting Dex-induced ferroptosis in MC3T3-E1 cells, whereas its overexpression exacerbates cell death via ferroptosis. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis reveals that the differentially expressed lncRNA XR_877193.1 is enriched in ferroptosis-related pathways, including the PI3K/AKT signaling pathway. Moreover, PI3K/AKT inhibitors reverse ferroptosis in MC3T3-E1 cells inhibited by lncRNA XR_877193.1 knockdown. Collectively, our findings indicate that lncRNA XR_877193.1 knockdown exerts anti-ferroptosis effects by stimulating the PI3K/AKT signaling pathway, suggesting a promising therapeutic strategy for attenuating SONFH.

Rhythms in Remodeling: Posttranslational Regulation of Bone by the Circadian Clock

The circadian clock is a fundamental timekeeping system that regulates rhythmic biological processes in response to environmental light-dark cycles. In mammals, core clock genes (CLOCK, BMAL1, PER, and CRY) orchestrate these rhythms through transcriptional-translational feedback loops, influencing various physiological functions, including bone remodeling. Bone homeostasis relies on the coordinated activities of osteoblasts, osteoclasts, and osteocytes, with increasing evidence highlighting the role of circadian regulation in maintaining skeletal integrity. Disruptions in circadian rhythms are linked to bone disorders such as osteoporosis. Posttranslational modifications (PTMs), including phosphorylation, acetylation, and ubiquitination, serve as crucial regulators of both circadian mechanisms and bone metabolism. However, the specific role of PTMs in integrating circadian timing with bone remodeling remains underexplored. This review examines the intersection of circadian regulation and PTMs in bone biology, elucidating their impact on bone cell function and homeostasis. Understanding these interactions may uncover novel therapeutic targets for skeletal diseases associated with circadian disruptions.

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

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

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.

LRP5 promotes adipose progenitor cell fitness and adipocyte insulin sensitivity

BACKGROUND

WNT signaling plays a key role in postnatal bone formation. Individuals with gain-of-function mutations in the WNT co-receptor LRP5 exhibit increased lower-body fat mass and potentially enhanced glucose metabolism, alongside high bone mass. However, the mechanisms by which LRP5 regulates fat distribution and its effects on systemic metabolism remain unclear. This study aims to explore the role of LRP5 in adipose tissue biology and its impact on metabolism.

METHODS

Metabolic assessments and imaging were conducted on individuals with gain- and loss-of-function LRP5 mutations, along with age- and BMI-matched controls. Mendelian randomization analyses were used to investigate the relationship between bone, fat distribution, and systemic metabolism. Functional studies and RNA sequencing were performed on abdominal and gluteal adipose cells with LRP5 knockdown.

RESULTS

Here we show that LRP5 promotes lower-body fat distribution and enhances systemic and adipocyte insulin sensitivity through cell-autonomous mechanisms, independent of its bone-related functions. LRP5 supports adipose progenitor cell function by activating WNT/β-catenin signaling and preserving valosin-containing protein (VCP)-mediated proteostasis. LRP5 expression in adipose progenitors declines with age, but gain-of-function LRP5 variants protect against age-related fat loss in the lower body.

CONCLUSIONS

Our findings underscore the critical role of LRP5 in regulating lower-body fat distribution and insulin sensitivity, independent of its effects on bone. Pharmacological activation of LRP5 in adipose tissue may offer a promising strategy to prevent age-related fat redistribution and metabolic disorders.

Reducing PDK4 level constitutes a pivotal mechanism for glucocorticoids to impede osteoblastic differentiation through the enhancement of ferroptosis in mesenchymal stem cells

BACKGROUND

This study mainly explores the possible role and mechanism of pyruvate dehydrogenase kinase 4 (PDK4) in the onset and development of Glucocorticoid-induced osteoporosis (GIOP), and seeks potential targets for the treatment of GIOP.

METHODS

Mesenchymal stem cells (MSCs) were treated with osteogenic induction medium. An in vitro osteogenic damage model was established by exposing MSCs to a high concentration (10- 6 M) of dexamethasone (DEX). Osteogenic markers were measured with real-time quantitative polymerase chain reaction, western blot, alkaline phosphatase staining, and Alizarin Red S staining. Ferroptosis markers were assessed through reactive oxygen species (ROS) fluorescent probe, transmission electron microscopy, and measurement of malondialdehyde (MDA). The potential mechanism was investigated using RT-qPCR, western blot, lysosomal probes, molecular docking, and other analytical approaches. The role of PDK4 was validated by using a GIOP rat model, micro-computed tomography and Masson's trichrome staining.

RESULTS

High concentrations (10- 6 M) of DEX inhibited osteogenic differentiation in C3H10T1/2 cells, and PDK4 exhibited the opposite effect. PDK4 partially reversed the osteogenic inhibitory effect of DEX both in vivo and in vitro. DEX caused mitochondrial shrinkage and disappearance of cristae in C3H10T1/2 cells, as well as an increase in total iron, ROS, MDA contents, and the level of ferroptosis key factors. These changes were partially weakened by PDK4. The ferroptosis inhibitor ferrostatin-1 partially blocked the inhibitory effect of DEX, while ferroptosis inducer RSL3 inhibited osteogenic differentiation and weakened the reversal effect of PDK4. DEX reduced the protein level of PDK4, which was partially weakened by Bafilomycin A1. The molecular docking results showed that DEX can directly bind with PDK4.

CONCLUSION

PDK4 can enhance the osteogenic differentiation ability of MSCs and bone mass of GIOP rats. DEX may promote the degradation of PDK4 via lysosome pathway, through which to weaken the osteogenic ability of MSCs by increasing ferroptosis. PDK4 may become a potential target for improving GIOP.

Repair mechanisms of bone system tissues based on comprehensive perspective of multi-omics

Bone disorders affect more than half of the adult population worldwide who may have a poor quality of life and physical independence worldwide. Multi-omic techniques are increasingly adopted and applied to determine the molecular mechanisms of bone tissue repair, providing perspective towards personalized medical intervention. Data from genomics, epigenomics, transcriptomics, proteomics, glycomics, and lipidomics were combined to elucidate dynamic processes in bone repair. In this narrative review, the key role of genetic and epigenetic factors in regulating injured cellular responses is highlighted, and changes in RNA and protein expression during the healing phase, as well as glucolipid metabolism adaptation, are described in detail how the repair process is affected. In a word, the integration of multi-omic techniques in this review not only benefits the comprehensive identification of new biomarkers, but also facilitates the development of personalized treatment strategies of bone disorders to revolutionize regenerative medicine.

Elevated Circulating Sclerostin Levels in Frail Older Adults: Implications beyond Bone Health

BACKGRUOUND

Sclerostin, initially recognized for its pivotal role in bone metabolism, has gained attention for its multifaceted impact on overall human health. However, its influence on frailty-a condition that best reflects biological age-has not been thoroughly investigated.

METHODS

We collected blood samples from 244 older adults who underwent comprehensive geriatric assessments. Sclerostin levels were quantified using an enzyme-linked immunosorbent assay. Frailty was assessed using two validated approaches: the phenotypic model by Fried and the deficit accumulation frailty index (FI) by Rockwood.

RESULTS

After controlling for sex, age, and body mass index, we found that serum sclerostin levels were significantly elevated in frail individuals compared to their robust counterparts (P<0.001). There was a positive correlation between serum sclerostin concentrations and the FI (P<0.001). Each standard deviation increase in serum sclerostin was associated with an odds ratio of 1.87 for frailty (P=0.003). Moreover, participants in the highest quartile of sclerostin levels had a significantly higher FI and a 9.91-fold increased odds of frailty compared to those in the lowest quartile (P=0.003 and P=0.039, respectively).

CONCLUSION

These findings, which for the first time explore the association between circulating sclerostin levels and frailty, have significant clinical implications, positioning sclerostin as one of potential blood-based biomarkers for frailty that captures the comprehensive physical, mental, and social aspects of the elderly, extending beyond its traditional role in bone metabolism.

The mechanism of action of indole-3-propionic acid on bone metabolism

Indole-3-propionic acid (IPA), a metabolite produced by gut microbiota through tryptophan metabolism, has recently been identified as playing a pivotal role in bone metabolism. IPA promotes osteoblast differentiation by upregulating mitochondrial transcription factor A (Tfam), contributing to increased bone density and supporting bone repair. Simultaneously, it inhibits the formation and activity of osteoclasts, reducing bone resorption, possibly through modulation of the nuclear factor-κB (NF-κB) pathway and downregulation of osteoclast-associated factors, thereby maintaining bone structural integrity. Additionally, IPA provides indirect protection to bone health by regulating host immune responses and inflammation via activation of receptors such as the Aryl hydrocarbon Receptor (AhR) and the Pregnane X Receptor (PXR). This review summarizes the roles and signaling pathways of IPA in bone metabolism and its impact on various bone metabolic disorders. Furthermore, we discuss the therapeutic potential and limitations of IPA in treating bone metabolic diseases, aiming to offer novel strategies for clinical management.

Citrate: a key signalling molecule and therapeutic target for bone remodeling disorder

Bone remodeling is a continuous cyclic process that maintains and regulates bone structure and strength. The disturbance of bone remodeling leads to a series of bone metabolic diseases. Recent studies have shown that citrate, an intermediate metabolite of the tricarboxylic acid (TCA) cycle, plays an important role in bone remodeling. But the exact mechanism is still unclear. In this study, we focused on the systemic regulatory mechanism of citrate on bone remodeling, and found that citrate is involved in bone remodeling in multiple ways. The participation of citrate in oxidative phosphorylation (OXPHOS) facilitates the generation of ATP, thereby providing substantial energy for bone formation and resorption. Osteoclast-mediated bone resorption releases citrate from bone mineral salts, which is subsequently released as an energy source to activate the osteogenic differentiation of stem cells. Finally, the differentiated osteoblasts secrete into the bone matrix and participate in bone mineral salts formation. As a substrate of histone acetylation, citrate regulates the expression of genes related to bone formation and bone reabsorption. Citrate is also a key intermediate in the metabolism and synthesis of glucose, fatty acids and amino acids, which are three major nutrients in the organism. Citrate can also be used as a biomarker to monitor bone mass transformation and plays an important role in the diagnosis and therapeutic evaluation of bone remodeling disorders. Citrate imbalance due to citrate transporter could result in the supression of osteoblast/OC function through histone acetylation, thereby contributing to disorders in bone remodeling. Therefore, designing drugs targeting citrate-related proteins to regulate bone citrate content provides a new direction for the drug treatment of diseases related to bone remodeling disorders.

A trend of osteocalcin in diabetes mellitus research: bibliometric and visualization analysis

Background

Osteocalcin has attracted attention for its potential role in diabetes management. However, there has been no bibliometric assessment of scientific progress in this field.

Methods

We analysed 1680 articles retrieved from the Web of Science Core Collection (WoSCC) between 1 January 1986 and 10 May 2024 using various online tools.

Result

These papers accumulated 42,714 citations,with an average of 25.43 citations per paper. Publication output increased sharply from 1991 onwards. The United States and China are at the forefront of this research area.

Discussion

The keywords were grouped into four clusters: 'Differential and functional osteocalcin genes', 'Differential expression of osteocalcin genes in relation to diabetes mellitus', 'Role of osteocalcin in the assessment of osteoporosis and diabetes mellitus', and 'Indirect involvement of osteocalcin in metabolic processes'. Analysis using the VoS viewer suggests a shift in research focus towards the correlation between osteocalcin levels and diabetic complications, the clinical efficacy of therapeutic agents or vitamins in the treatment of osteoporosis in diabetic patients, and the mechanisms by which osteocalcin modulates insulin action. The proposed focus areas are "osteocalcin genes", "insulin regulation and osteoporosis ", "different populations", "diabetes-related complications" and "type 2 diabetes mellitus","effect of osteocalcin expression on insulin sensitivity as well as secretion","osteocalcin expression in different populations of diabetic patients and treatment-related studies".

Matrix Gla protein suppresses osteoblast senescence and promotes osteogenic differentiation by the PI3K-AKT signaling pathway

Age-related bone loss in mice is associated with senescent cell accumulation and reduced bone formation by osteoblasts. Matrix Gla protein (MGP), secreted by osteoblasts, is pivotal in regulating the bone extracellular matrix mineralization. Previous research has demonstrated that Mgp null mice exhibit osteopenia and fractures, and ultimately die prematurely. To elucidate the mechanisms underlying MGP's role of MGP in bone metabolism, we generated osteoblast-specific Mgp knockout (Mgp cKO) mice by crossing Mgpfl/fl mice with Bglap-Cre mice. The study revealed that in 3-month-old Mgp cKO male mice, trabecular bone volume decreased, and the senescence marker protein p21 increased. Primary osteoblasts from Mgp cKO mice exhibited markers of DNA damage and senescence, such as increased γH2AX foci, p21, and senescence-associated β-galactosidase staining, as well as attenuated cellular proliferation and osteogenic differentiation abilities. In addition, bone marrow stromal cells' colony formation and spontaneous osteogenic ability were impaired in Mgp cKO mice, whereas osteoclastogenesis was enhanced. In vitro treatment with recombinant human MGP promotes osteogenesis in osteoblasts derived from Mgp cKO mice via the PI3K-AKT signaling pathway. Thus, our results suggest that MGP is protective by suppressing osteoblast senescence, offering new insights into potential therapeutic strategies for age-related osteoporosis.

Humanized In Vivo Bone Tissue Engineering: In Vitro Preculture Conditions Control the Structural, Cellular, and Matrix Composition of Humanized Bone Organs

Bone tissue engineering (BTE) has long sought to elucidate the key factors controlling human/humanized bone formation for regenerative medicine and disease modeling applications, yet with no definitive answers due to the high number and co-dependency of parameters. This study aims to clarify the relative impacts of in vitro biomimetic 'preculture composition' and 'preculture duration' before in vivo implantation as key criteria for the optimization of BTE design. These parameters are directly related to in vitro osteogenic differentiation (OD) and mineralization and are being investigated across different osteoprogenitor-loaded biomaterials, specifically fibrous calcium phosphate-polycaprolactone (CaP-mPCL) scaffolds and gelatin methacryloyl (GelMA) hydrogels. The results show that OD and mineralization levels prior to implantation, enhanced by a mineralization medium supplement to the osteogenic medium (OM), significantly improve ectopic BTE outcomes, regardless of the biomaterial type. Specifically, preculture conditions are pivotal in achieving more faithful mimicry of human bone structure, cellular and extracellular matrix composition and organization, and provide control over bone marrow composition. This work emphasizes the potential of using biomimetic culture compositions, specifically the addition of a mineralization medium as a cost-effective and straightforward approach to enhance BTE outcomes, facilitating rapid development of bone models with superior quality and resemblance to native bone.

Exploring the Biological Impact of β-TCP Surface Polarization on Osteoblast and Osteoclast Activity

β-tricalcium phosphate (β-TCP) is a widely utilized resorbable bone graft material, whose surface charge can be modified by electrical polarization. However, the specific effects of such a charge modification on osteoblast and osteoclast functions remain insufficiently studied. In this work, electrically polarized β-TCP with a high surface charge density was synthesized and evaluated in vitro in terms of its physicochemical properties and biological activity. Polarization was performed to achieve a high surface charge density, which was quantified using a thermally stimulated depolarization current. The proliferation and differentiation of MC3T3-E1 osteoblast-like cells were assessed via WST-8 and alkaline phosphatase assays. Tartrate-resistant acid phosphatase (TRAP) activity and a resorption pit assay were used to evaluate the impact of surface charge on RAW264.7 osteoclast-like cell activity. Polarized β-TCP exhibited a surface charge of 1.3 mC cm-2. Electrically polarized surfaces significantly enhanced osteoblast proliferation and differentiation. TRAP activity assays demonstrated effective osteoclast differentiation of RAW264.7 cells, with enhanced activity observed on charged surfaces. Resorption pit assays further revealed improved osteoclast resorption capacity on β-TCP surfaces with a polarized charge. These findings indicate that β-TCP with a highly dense surface charge promotes osteoblast proliferation and differentiation, as well as osteoclast activity and resorption capacity.

Hydroxyurea blunts mitochondrial energy metabolism and osteoblast and osteoclast differentiation exacerbating trabecular bone loss in sickle cell mice

Sickle cell disease (SCD) is a severe hematological disorder characterized by erythrocyte sickling that causes significant morbidity and mortality. Skeletal complications of SCD include a high incidence of bone loss, especially in vertebrae, leading to fragility fractures that contribute to disease burden. Whether hydroxyurea (HU), a front-line therapy for SCD ameliorates bone disease has not been established. To investigate HU action on SCD-related vertebral defects, we used HU-treated "Townes" mice, an SCD animal model and performed high-resolution micro-computed tomography (µCT) imaging to resolve bone volume and micro-architectural structure of cortical and trabecular bone, the two major compartments contributing to bone mass and strength. Our data revealed that cortical bone was significantly diminished in the vertebrae of skeletally mature (representing adults) and immature (representing children) SCD mice, while only mature mice lost trabecular bone mass. Administration of HU ameliorated cortical bone loss in mature SCD mice, but paradoxically promoted trabecular bone decline in both groups. We further investigated the mechanisms of HU action in wild-type C57BL6/J mice. HU caused dose-dependent trabecular bone loss due to diminished osteoclast and osteoblast function, indicative of a low bone turnover state. Mechanistic investigations in vitro revealed that HU impeded osteoblast-progenitor proliferation and early differentiation, and diminished osteoclastogenic cytokine production, blunting osteoclast formation as well as the activity of mature osteoclasts. HU further, suppressed mitochondrial, but not glycolytic energy metabolism in both differentiating osteoblasts and differentiated osteoclasts. Collectively, these findings reveal that despite ameliorating cortical bone loss, HU inhibits trabecular bone formation and resorption, by suppressing mitochondrial energy metabolism and blunting the differentiation and/or activity of osteoblasts and osteoclasts. Together HU drives a low bone turnover state culminating in trabecular bone loss. Further investigation into HU's impact on bone in SCD patients is warranted for understanding and managing skeletal complications in this population.

Understanding the Causes of Keel Bone Damage and Its Effects on the Welfare of Laying Hens

Keel bone damage (KBD) is a prominent concern within the realm of the egg-laying industry, exerting substantial impacts on the welfare and productivity of laying hens. This comprehensive review undertakes a detailed exploration of the diverse factors contributing to KBD, such as inadequate calcium sources in the medullary bone, genetic factors, nutritional deficiencies, and physical stressors. The consequences of KBD on production performance, stress and inflammation levels, and the physical and chemical properties of the keel are meticulously examined. Additionally, the review evaluates the existing methods for assessing KBD, including keel curvature scoring, imaging techniques, palpation, biomechanical testing, behavioral observations, and biochemical markers. Finally, management strategies, including nutritional adjustments, genetic selection, and environmental modifications, are proposed to potentially mitigate the prevalence and severity of KBD, thereby aiming to enhance the welfare and productivity of laying hens.

Impact of hypoxia on alveolar bone dynamics and remodeling

Oxygen is a fundamental requirement for cellular metabolism. Hypoxia is a state of oxygen deprivation of the tissues. Cells develop numerous adaptive mechanisms to survive hypoxic insult. Alveolar bone is a unique structure that encases and protects the tooth. Literature reports that hypoxia, in all forms, impacts alveolar bone health. The hypoxia-inducible pathway appears to play a key role in mediating changes in alveolar bone metabolism. Embryonic hypoxia plays a vital role in craniofacial skeletal development. Further, hypoxia has been anticipated in the repair of extraction sockets. Alveolar bone cells respond distinctly to hypoxic conditions with both beneficial and detrimental effects. Studies have demonstrated enhanced alveolar bone resorption upon hypoxic stimuli. However, hypoxia has also been shown to have potential therapeutic effects on alveolar bone by triggering an angiogenic response. Additionally, the type, duration, and mode of hypoxia are critical in triggering varied responses in alveolar bone metabolism. The main objective of this review is to recapitulate the effects of different types of hypoxia on the tooth supporting apparatus and to analyze some of the presumptive mechanisms underlying hypoxia-induced changes in alveolar bone remodeling.

Cardamonin attenuates iron overload-induced osteoblast oxidative stress through the HIF-1α/ROS pathway

BACKGROUND

Osteoporosis(OP) is a bone disease under research. Iron overload is a significant risk factor. Iron balance is crucial for bone metabolism and biochemical processes. When there is an excess of iron in the body, it tends to produce reactive oxygen species (ROS) which can cause oxidative damage to cells. The flavonoid compound, Cardamonin (CAR), possesses potent anti-inflammatory and anti-iron overload properties that can be beneficial in mitigating the risk of OP.

PURPOSE

This study investigates the potential therapeutic interventions and underlying mechanisms of CAR for treating OP in individuals with iron overload.

METHODS

The model of iron-overloaded mice was established by intraperitoneally injecting iron dextran(ID) into the mice. OP severity was evaluated with micro-CT and Hematoxylin-Eosin (HE) staining in vivo. In vitro, the iron-overloaded osteoblast model was induced by ferric ammonium citrate. Cell counting kit 8 assay to evaluate cell viability, Annexin V-FITC/PI assay to detect cell apoptosis. A range of cellular markers were detected, including the variation in mitochondrial membrane potential (MMP), levels of malondialdehyde (MDA), ROS, and lipid hydroperoxide (LPO).

RESULTS

CAR can reverse bone loss in iron overload-induced OP mouse models in vivo. CAR attenuates the impairment of iron overload on the activity and apoptosis of MC3T3-E1 cells as well as the accumulation of ROS and LPO activation via HIF-1α/ROS pathways.

CONCLUSION

CAR downregulating HIF-1α pathways prevents inhibition of iron overload-induced osteoblasts dysfunctional by attenuating ROS accumulation, reducing oxidative stress, promotes bone formation, and alleviates OP.

Total osteocalcin levels are independently associated with worse testicular function and a higher degree of hypothalamic-pituitary-gonadal axis activation in Klinefelter syndrome

PURPOSE

The role of osteocalcin (OCN) in pubertal development, male hypogonadism, and the effect of testosterone (Te) replacement therapy (TRT) remains unclear. We aimed to investigate the total OCN (tOCN) concentrations in male patients with Klinefelter syndrome (KS), a model of adult hypergonadotropic hypogonadism.

METHODS

This retrospective longitudinal study investigated 254 male patients with KS (47,XXY) between 2007 and 2021 at an academic referral center, categorized as (1) prepubertal, (2) pubertal, and (3) adults. All prepubertal patients were Te-naïve. Adult patients were subcategorized as (1) eugonadal, (2) hypogonadal, and (3) receiving TRT. We also analyzed 18 adult patients with available tOCN levels before and 3 months after TRT commencement.

RESULTS

The tOCN levels varied throughout the lifespan according to pubertal status, were highest in eugonadal and significantly lower in TRT subjects, correlated with both LH (p = 0.017) and FSH levels (p = 0.004) in adults, and significantly declined after 3 months of TRT (p = 0.006) in the adult KS cohort. HPG-axis hormones levels demonstrated no correlation in prepubertal boys. Adjustment for age and body mass index confirmed previous results and revealed significant inverse correlations with total Te (p = 0.004), calculated free Te (p = 0.016), the Te/LH (p = 0.010), and calculated free Te/LH ratios (p = 0.031).

CONCLUSION

In KS, a model of male hypergonadotropic hypogonadism, tOCN levels were not associated with gonadal function during normal prepuberty and pubertal development but were associated with worse testicular function and a higher degree of HPG stimulation in adults. TRT acutely reduced tOCN levels in adults.

Association between physical activity and mortality in patients with osteoporosis: a cohort study of NHANES

We utilized data from the NHANES to investigate the impact of physical activity on mortality in osteoporotic patients. Our study suggests that osteoporotic patients may require higher volumes of physical activity to reduce mortality risk compared to the general population. In osteoporotic patients, the dose-response relationships between physical activity volumes and both all-cause and cardiovascular mortality were linear. In contrast, these relationships were non-linear in participants without osteoporosis.

PURPOSE

To determine the impact of physical activity on mortality in osteoporotic patients.

METHODS

A total of 5606 participants were included in this study, including 716 osteoporosis patients. Physical activity was assessed using standardized questionnaire. Participants were categorized into four groups: inactive (no physical activity), low active (physical activity volumes < 150 min/week), moderate active (≥ 150 min/week but < 300 min/week), and high active (≥ 300 min/week). Multivariable Cox regression models, using the inactive group as the reference and adjusted for potential confounders, were performed to estimate the hazard ratio (HR) and 95% confidence interval (CI).

RESULTS

Osteoporotic patients demonstrated higher mortality rates attributed to various causes compared to non-osteoporosis participants. Physical activity was associated with lower mortality regardless of osteoporosis status. However, Multivariable Cox regression analysis indicated that among osteoporosis patients, only those engaging in ≥ 300 min/week physical activity experienced a significant decrease in mortality (all-cause mortality, HR (95% CI) 0.453 (0.268, 0.767) and cardiovascular mortality, HR (95% CI) 0.521 (0.259, 1.049)), surpassing the threshold of 150 min observed in non-osteoporosis patients. In sensitivity analysis, or when the proportion of vigorous physical activity was included as a confounder in the multivariate Cox regression analysis, only the high active group still showed a significant reduction in mortality. No significant interactions were observed when the analysis was stratified according to age, sex, and body mass index (P for interaction > 0.05). Restricted cubic spline analysis revealed a linear relationship between physical activity volume and all-cause mortality (P < 0.01 [overall] and P = 0.470 [non-linearity]) and cardiovascular-specific mortality (P = 0.003 [overall] and P = 0.610 [non-linearity]) in patients with osteoporosis. In contrast, these relationships were non-linear in participants without osteoporosis.

CONCLUSION

Patients with osteoporosis need to engage in ≥ 300 min/week physical activity to significantly reduce their mortality risk. And the higher the volume of physical activity, the lower the risk of death.

Insulin resistance, bone health, and fracture risk

Insulin resistance, defined as an impaired biological response to insulin stimulation in target tissues, arises most frequently in the presence of central obesity. Although obesity is generally associated with increased bone mass, recent data challenge this view and, if complicated by T2DM, obese patients are at high risk for fragility fractures. IR may play a key role in this increased fracture risk through effects on bone quality rather than bone quantity. Further understanding of the mechanisms and approaches to prevent osteoporotic fractures in IR-related diseases is needed.

CLINICAL RELEVANCE

The dramatic increase in obesity and metabolic syndrome (MetS) over the last half-century has led to a worldwide epidemic of type 2 diabetes mellitus (T2DM) as well as in the incidence of insulin resistance (IR). IR is defined as an impaired biological response to insulin stimulation in target tissues and is primarily related to the liver, muscle, and adipose tissue. The most frequent underlying cause is central obesity, and it is known that excess abdominal adipose tissue secretes increased amounts of free fatty acids, which directly affects insulin signalling, reduces glucose uptake in muscle, and triggers excessive triglyceride synthesis and gluconeogenesis in the liver. When pancreatic β cells are unable to secrete the higher levels of insulin needed, T2DM, the main complication of IR, occurs.

OBSERVATIONS

Although obesity is generally associated with increased bone mass, recent data challenge this view and highlight the multifaceted nature of the obesity-bone relationship. Patients with T2DM are at significant risk for well-known complications of diabetes, including retinopathy, nephropathy, macrovascular disease, and neuropathy, but it is clear that they are also at high risk for fragility fractures. Moreover, recent data provide strong evidence that IR may key role in the increased fracture risk observed in both obesity and T2DM.

CONCLUSIONS

In this concise review article, the role of IR in increased risk of osteoporotic fractures in MetS, obesity, and T2DM is discussed and summarised, including consideration of the need for fracture risk assessment as a 'preventive measure', especially in patients with T2DM and chronic MetS with abdominal obesity. Personalised and targeted diagnostic and therapeutic approaches to prevent osteoporotic fractures in IR-related diseases are needed and could make significant contributions to health outcomes.

Bone complications of cancer treatment

With the advancements in conventional treatment modalities such as radiation, chemotherapy, and surgery, as well as the emergence of immunotherapy, the overall cure rate for solid tumor malignancies has experienced a significant increase. However, it is unfortunate that exposure to cancer treatments can have detrimental effects on the function of osteoblasts and osteoclasts, disturbing bone metabolic homeostasis in patients, as well as causing damage to bone marrow cells and other bone tissues. Consequently, certain tumor treatment options may pose a risk for subsequent bone diseases. Common bone disorders associated with cancer treatment include osteonecrosis, bone loss, and secondary bone tumors. (1)Cancer treatment-related osteonecrosis is primarily linked to the use of radiation therapy and certain chemicals, such as bisphosphonates, denosumab, antiangiogenic agents, and immunomodulators. It has been observed that high-dose radiation therapy is more likely to result in osteonecrosis. (2)Chemicals and hormones, particularly sex hormones, glucocorticoids, and thyroid hormones or thyrotropic hormones, are among the factors that can contribute to cancer treatment-related bone loss. (3)Secondary bone tumors differ from metastases originating from primary tumors, and radiotherapy plays a significant role in their development, while chemotherapy may also exert some influence. Radiogenic secondary bone tumors are predominantly malignant, with osteosarcoma being the most common type. Chemotherapy may be a risk factor for the relatively rare occurrence of secondary Ewing sarcoma of the bone. These treatment-related bone disorders have a considerable adverse impact on the prognosis of cancer patients. Hence, it is imperative to prioritize the bone health of patients undergoing cancer treatment and give it further attention.

A monoallelic variant in CCN2 causes an autosomal dominant spondyloepimetaphyseal dysplasia with low bone mass

Cellular communication network factor 2 (CCN2) is a secreted extracellular matrix-associated protein, and its aberrantly increased expression has been implicated in a diversity of diseases involving pathological processes of fibrosis, chronic inflammation, or tissue injury, which has promoted the evaluation of CCN2 as therapeutic targets for multiple disorders. However, human phenotypes associated with CCN2 deficiency have remained enigmatic; variants in CCN2 have not yet been associated with a human phenotype. Here, we collected families diagnosed with spondyloepimetaphyseal dysplasia (SEMD), and screened candidate pathogenic genes for families without known genetic causes using next-generation sequencing. We identified a monoallelic variant in signal peptide of CCN2 (NM_001901.2: c.65 G > C [p.Arg22Pro]) as the cause of SEMD in 14 subjects presenting with different degree of short stature, premature osteoarthritis, and osteoporosis. Affected subjects showed decreased serum CCN2 levels. Cell lines harboring the variant displayed decreased amount of CCN2 proteins in culture medium and an increased intracellular retention, indicating impaired protein secretion. And the variant weakened the stimulation effect of CCN2 on osteogenesis of bone marrow mesenchymal stem cells. Zebrafish ccn2a knockout model and osteoblast lineage-specific Ccn2-deficient mice (Ccn2fl/fl;Prx1Cre) partially recapitulated the phenotypes including low bone mass observed in affected subjects. Pathological mechanism implicated in the skeletal abnormality in Ccn2fl/fl;Prx1Cre mice involved decreased bone formation, increased bone resorption, and abnormal growth plate formation. Collectively, our study indicate that monoallelic variants in CCN2 lead to a human inherited skeletal dysplasia, and highlight the critical role of CCN2 in osteogenesis in human.

Enhancing bone regeneration and immunomodulation via gelatin methacryloyl hydrogel-encapsulated exosomes from osteogenic pre-differentiated mesenchymal stem cells

Mesenchymal stem cell-derived exosomes (MSC-Exos) have emerged as promising candidates for cell-free therapy in tissue regeneration. However, the native osteogenic and angiogenic capacities of MSC-Exos are often insufficient to repair critical-sized bone defects, and the underlying immune mechanisms remain elusive. Furthermore, achieving sustained delivery and stable activity of MSC-Exos at the defect site is essential for optimal therapeutic outcomes. Here, we extracted exosomes from osteogenically pre-differentiated human bone marrow mesenchymal stem cells (hBMSCs) by ultracentrifugation and encapsulated them in gelatin methacryloyl (GelMA) hydrogel to construct a composite scaffold. The resulting exosome-encapsulated hydrogel exhibited excellent mechanical properties and biocompatibility, facilitating sustained delivery of MSC-Exos. Osteogenic pre-differentiation significantly enhanced the osteogenic and angiogenic properties of MSC-Exos, promoting osteogenic differentiation of hBMSCs and angiogenesis of human umbilical vein endothelial cells (HUVECs). Furthermore, MSC-Exos induced polarization of Raw264.7 cells from a pro-inflammatory phenotype to an anti-inflammatory phenotype under simulated inflammatory conditions, thereby creating an immune microenvironment conducive to osteogenesis. RNA sequencing and bioinformatics analysis revealed that MSC-Exos activate the p53 pathway through targeted delivery of internal microRNAs and regulate macrophage polarization by reducing DNA oxidative damage. Our study highlights the potential of osteogenic exosome-encapsulated composite hydrogels for the development of cell-free scaffolds in bone tissue engineering.

Metabolic reprogramming in skeletal cell differentiation

The human skeleton is a multifunctional organ made up of multiple cell types working in concert to maintain bone and mineral homeostasis and to perform critical mechanical and endocrine functions. From the beginning steps of chondrogenesis that prefigures most of the skeleton, to the rapid bone accrual during skeletal growth, followed by bone remodeling of the mature skeleton, cell differentiation is integral to skeletal health. While growth factors and nuclear proteins that influence skeletal cell differentiation have been extensively studied, the role of cellular metabolism is just beginning to be uncovered. Besides energy production, metabolic pathways have been shown to exert epigenetic regulation via key metabolites to influence cell fate in both cancerous and normal tissues. In this review, we will assess the role of growth factors and transcription factors in reprogramming cellular metabolism to meet the energetic and biosynthetic needs of chondrocytes, osteoblasts, or osteoclasts. We will also summarize the emerging evidence linking metabolic changes to epigenetic modifications during skeletal cell differentiation.

Synthesis and Antiosteoporotic Characterization of Diselenyl Maleimides: Discovery of a Potent Agent for the Treatment of Osteoporosis by Targeting RANKL

To discover new osteoclast-targeting antiosteoporosis agents, we identified forty-six diselenyl maleimides, which were efficiently prepared using a novel, simple, and metal-free method at room temperature in a short reaction time. Among them, 3k showed the most marked inhibition of osteoclast differentiation with an IC50 value of 0.36 ± 0.03 μM. Moreover, 3k significantly suppressed RANKL-induced osteoclast formation, bone resorption, and osteoclast-specific genes expression in vitro. Mechanistic studies revealed that 3k remarkably blocked the RANKL-induced mitogen-activated protein kinase (MAPK) and NF-κB signaling pathways. In ovariectomized mice, intragastric administration of 3k significantly alleviated bone loss, exhibiting an effect similar to that of alendronate. Surface plasmon resonance assay and microscale thermophoresis assay results suggested that RANKL might be a potential molecular target for 3k. Collectively, the findings presented above provided a novel candidate for further development of bone antiresorptive drugs that target RANKL.

Microenvironment-Responsive Targeted Nanomedicine for a Collaborative Integration of Tumor Theranostics and Bone Defect Repair

Despite advancements in breast cancer treatment, bone metastases remain a significant concern for advanced breast cancer patients. Current theranostics strategies face challenges in integrating tumor theranostics and bone formation. Herein, this work develops an activatable targeted nanomedicine AuMnCO@BSA-N3 (AMCBN) to enable a novel collaborative integration of second near-infrared (NIR-II) fluorescence imaging guided precise theranostics for breast cancer bone metastases and osteogenic microenvironment remolding. This strategy employs a chemical coordination between noble metal complex and metal carbonyl (MnCO), with surface modification of azide groups to enhance tumor affinity through passive and active targeting. The initiated respondent behavior of AMCBN by tumor microenvironment accelerate the degradation of coordinated MnCO, resulting in a rapid release of multifunctional agents for efficient chemodynamic therapy (CDT)/gas synergistic therapy. Meanwhile, the exceptional bone-binding properties enable the efficient and controlled release of Mn2+ ions and carbon monoxide (CO) in the bone microenvironment, thereby facilitating the expression of osteogenesis-related proteins and establishing a novel synchronous theranostics process for tumor-bone repair.

Osteocalcin: A potential marker to identify and monitor girls with rapidly progressive central precocious puberty

AIM

To evaluate the suitability of serum osteocalcin (OC) as a marker to distinguish between rapidly and non-rapidly progressive central precocious puberty (RP-CPP and NRP-CPP), as well as its potential to assess growth rates following treatment with gonadotropin-releasing hormone agonist (GnRHa).

METHODS

Serum levels of OC were measured using enzyme-linked immunosorbent assays in girls diagnosed with either RP-CPP or NRP-CPP as well as in normal control subjects. Receiver operating characteristic (ROC) curve analysis was performed to determine the cut-off value for OC. Multivariate linear regression analysis was used to analyse the main influencing factors associated with OC.

RESULTS

Serum OC levels were higher in the CPP girls when compared to normal controls (110.76 ± 43.69 vs 55.97 ± 20.96 ng/mL, P < 0.001). The level in the RP-CPP group was higher than the NRP-CPP group (153.28 ± 33.89 vs 88.33 ± 29.26 ng/mL, P < 0.001). The cut-off value of OC levels for distinguishing between RP-CPP and NRP-CPP was 107.05 ng/mL, the sensitivity was 94.7% and the specificity was 77.8%, which was superior to using the basal luteinising hormone (B-LH) levels, and the area under ROC curve (AUC) were 0.933 versus 0.695, respectively. Following 1-2 years of treatment with GnRHa for girls with CPP, both OC levels and the growth rates decreased to pre-pubertal values. B-LH levels, bone age and body weight were also significant factors, which affected OC levels.

CONCLUSIONS

Serum OC levels may be a useful marker for distinguishing RP-CPP from NRP-CPP. In addition, it was also found to be a useful predictor for growth rate during GnRHa treatment.

Trajectory-centric framework TrajAtlas reveals multi-scale differentiation heterogeneity among cells, genes, and gene modules in osteogenesis

Osteoblasts, the key cells responsible for bone formation and the maintenance of skeletal integrity, originate from a diverse array of progenitor cells. However, the mechanisms underlying osteoblast differentiation from these multiple osteoprogenitors remain poorly understood. To address this knowledge gap, we developed a comprehensive framework to investigate osteoblast differentiation at multiple scales, encompassing cells, genes, and gene modules. We constructed a reference atlas focused on differentiation, which incorporates various osteoprogenitors and provides a seven-level cellular taxonomy. To reconstruct the differentiation process, we developed a model that identifies the transcription factors and pathways involved in differentiation from different osteoprogenitors. Acknowledging that covariates such as age and tissue type can influence differentiation, we created an algorithm to detect differentially expressed genes throughout the differentiation process. Additionally, we implemented methods to identify conserved pseudotemporal gene modules across multiple samples. Overall, our framework systematically addresses the heterogeneity observed during osteoblast differentiation from diverse sources, offering novel insights into the complexities of bone formation and serving as a valuable resource for understanding osteogenesis.

The short-chain fatty acid receptors Gpr41/43 regulate bone mass by promoting adipogenic differentiation of mesenchymal stem cells

Bone is a dynamic tissue that is constantly remodeled throughout adult life. Recently, it has been shown that bone turnover decreases shortly after food consumption. This process has been linked to the fermentation of non-digestible food ingredients such as inulin by gut microbes, which results in the production of the short-chain fatty acids (SCFAs) acetate, propionate and butyrate. SCFAs exert various metabolic functions, which in part can be explained by activation of G protein-coupled receptors (Gpr) 41 and 43. However, the potential relevance of a SCFA-Gpr41/43 signaling axis for bone metabolism has not been established. The aim of our study is to investigate the role of Gpr41/43 in bone metabolism and osteogenic differentiation of mesenchymal stem cells. For this purpose, we analyzed the skeletal phenotype of wild type controls (WT) and Gpr41/43 double knockout (Gpr41/43 dKO) mice fed either a chow or an inulin-enriched diet. In addition, we isolated bone marrow derived mesenchymal stem cells from WT and Gpr41/43 dKO mice and differentiated them into osteoblasts in the absence or presence of acetate. MicroCT scanning of femoral bones of Gpr41/43 dKO mice revealed a significant increase of trabecular bone volume and trabecular compared to WT controls. Treatment of WT bone marrow-derived osteoblasts with acetate resulted in decreased mineralization and substantial downregulation of bone formation markers such as Phex, Ptgs2 and Col1a1. Notably, this effect was strongly attenuated in differentiated osteoblasts lacking Gpr41/43. Inversely, acetate supplementation resulted in higher levels of adipocyte marker genes including Pparg, Lpl and Adipoq in bone marrow-derived cells from WT mice, an effect blunted in differentiated cells isolated from Gpr41/43 dKO mice. Overall, these data indicate that acetate regulates bone architecture via SCFA-Gpr41/43 signaling by modulating the osteogenic versus adipogenic differentiation of mesenchymal stem cells.

Research on Bone Cells in Health and Disease

Bone-forming osteoblasts, osteocytes, and bone-resorbing osteoclasts are responsible for life-long skeletal remodeling [...].

The Emerging Role of the Mitochondrial Respiratory Chain in Skeletal Aging

Maintenance of mitochondrial homeostasis is crucial for ensuring healthy mitochondria and normal cellular function. This process is primarily responsible for regulating processes that include mitochondrial OXPHOS, which generates ATP, as well as mitochondrial oxidative stress, apoptosis, calcium homeostasis, and mitophagy. Bone mesenchymal stem cells express factors that aid in bone formation and vascular growth. Positive regulation of hematopoietic stem cells in the bone marrow affects the differentiation of osteoclasts. Furthermore, the metabolic regulation of cells that play fundamental roles in various regions of the bone, as well as interactions within the bone microenvironment, actively participates in regulating bone integrity and aging. The maintenance of cellular homeostasis is dependent on the regulation of intracellular organelles, thus understanding the impact of mitochondrial functional changes on overall bone metabolism is crucially important. Recent studies have revealed that mitochondrial homeostasis can lead to morphological and functional abnormalities in senescent cells, particularly in the context of bone diseases. Mitochondrial dysfunction in skeletal diseases results in abnormal metabolism of bone-associated cells and a secondary dysregulated microenvironment within bone tissue. This imbalance in the oxidative system and immune disruption in the bone microenvironment ultimately leads to bone dysplasia. In this review, we examine the latest developments in mitochondrial respiratory chain regulation and its impacts on maintenance of bone health. Specifically, we explored whether enhancing mitochondrial function can reduce the occurrence of bone cell deterioration and improve bone metabolism. These findings offer prospects for developing bone remodeling biology strategies to treat age-related degenerative diseases.

Sensory nerve regulation of bone homeostasis: Emerging therapeutic opportunities for bone-related diseases

Understanding the intricate interplay between sensory nerves and bone tissue cells is of paramount significance in the field of bone biology and clinical medicine. The regulatory role of sensory nerves in bone homeostasis offers a novel perspective for the development of targeted therapeutic interventions for a spectrum of bone-related diseases, including osteoarthritis, osteoporosis, and intervertebral disc degeneration. By elucidating the mechanisms through which sensory nerves and their neuropeptides influence the differentiation and function of bone tissue cells, this review aims to shed light on emerging therapeutic targets that harness the neuro-skeletal axis for the treatment and management of debilitating bone disorders. Moreover, a comprehensive understanding of sensory nerve-mediated bone regulation may pave the way for the development of innovative strategies to promote bone health and mitigate the burden of skeletal pathologies in clinical practice.

Effects of low dietary calcium and lipopolysaccharide challenges on production performance, eggshell quality, and bone metabolism of laying hens

Dietary calcium supply is essential for bone development and egg production in laying hens. This study investigated the effects of low dietary calcium and lipopolysaccharide (LPS) induced immune challenge in aged laying hens. A total of thirty-two Hy-Line Brown laying hens at 80 weeks old with an average laying rate of 62% were randomly divided into two groups and fed a normal calcium diet (3.57% Ca, NCA) or low calcium diet (2.08% Ca, LCA). At 88 weeks, the experiment was designed using a 2 × 2 factorial arrangement, and hens were intraperitoneally injected with saline (SAL) or LPS (0.5 mg/kg, 0.5 mg/kg, or 1.5 mg/kg body weight) once every 48 h intervals over 5 days. Production performance, egg quality, and bone physiology were evaluated. Results showed that LPS challenge decreased the hen-day egg production, egg mass, and eggshell traits (p < 0.05), but increased (p < 0.05) the calcium content of the tibia compared to SAL-injected hens. LCA diet decreased (p < 0.05) the hen-day egg production, and eggshell traits such as weight, percentage, strength, and thickness compared to the NCA diet. LCA diet increased the serum alkaline phosphatase (ALP) activity (p < 0.01) and tibial expression of ALP (p < 0.05) compared to NCA diet. LPS injection suppressed both the serum ALP activity (p < 0.05) and tibial expression of ALP (p < 0.001) compared to SAL injection. Furthermore, LPS injection increased (p < 0.05) the expression of both pro and anti-inflammatory cytokines in the spleen and tibia. The expression of cathepsin K ( Cts K ) and matrix metalloproteinase 9 ( MMP-9 ) were downregulated by LPS injection (p < 0.001). Broken and shell-less egg production and calcium content of eggshell, as well as tibial mRNA expression of osteocalcin ( Ocn ), tumor necrosis factor-alpha ( TNF-α ) and tartrate-resistant acid phosphatase ( TRAP ) were affected by the interaction (p < 0.05) of diet and injection. Therefore, this study demonstrated that to certain extents, low dietary calcium and LPS challenge dysregulated bone homeostasis and metabolism, with detrimental effects on the performance and eggshell quality of aged laying hens.

Effect of Cells Derived from Periodontal Ligament Tissue on Bone Formation

BACKGROUND/AIM

Recent reports indicate that sclerostin is secreted by periodontal ligament tissue-derived (PDL) cells during orthodontic force loading and that the secreted sclerostin contributes to bone metabolism. However, the detailed mechanism is poorly understood. The aim of this study was to determine how PDL cells affect bone formation.

MATERIALS AND METHODS

Rat periodontal ligament tissue was immunohistochemically stained for sclerostin. Cultured primary PDL cells, osteoblasts, and skin fibroblasts (Sfbs) isolated from rat periodontal ligament tissue, calvaria, and skin, respectively, were examined. Osteoblasts were cultured with control conditioned medium (Cont-CDM) and PDL cell culture conditioned medium (PDL-CDM) for up to 21 days. Cultured osteoblasts were then stained with alkaline phosphatase and von Kossa stain. Osteoblasts cultured in each conditioned medium were analyzed by real-time quantitative PCR for bone Gla protein (Bgp), Axin2, and Ki67 expression. PDL cells used to obtain conditioned medium were analyzed for Sost, Ectodin and Wnt1 expression and compared with expression in Sfbs.

RESULTS

Expression of sclerostin was observed in periodontal ligament tissue by immunohistochemical staining. The formation of mineralization nodules was inhibited in PDL-CDM compared with Cont-CDM in osteoblast culture. In PDL-CDM, the expression levels of Bgp and Axin2 in osteoblasts were decreased compared with Cont-CDM. In PDL cells, expression levels of Sost and Ectodin were much higher than in Sfbs; however, expression of Wnt1 was lower in PDL cells compared with Sfbs.

CONCLUSION

PDL cells secrete various proteins, including sclerostin and suppress osteogenesis in osteoblasts through the canonical Wnt pathway.

ETV2 regulating PHD2-HIF-1α axis controls metabolism reprogramming promotes vascularized bone regeneration

The synchronized development of mineralized bone and blood vessels is a fundamental requirement for successful bone tissue regeneration. Adequate energy production forms the cornerstone supporting new bone formation. ETS variant 2 (ETV2) has been identified as a transcription factor that promotes energy metabolism reprogramming and facilitates the coordination between osteogenesis and angiogenesis. In vitro molecular experiments have demonstrated that ETV2 enhances osteogenic differentiation of dental pulp stem cells (DPSCs) by regulating the ETV2- prolyl hydroxylase 2 (PHD2)- hypoxia-inducible factor-1α (HIF-1α)- vascular endothelial growth factor A (VEGFA) axis. Notably, ETV2 achieves the rapid reprogramming of energy metabolism by simultaneously accelerating mitochondrial aerobic respiration and glycolysis, thus fulfilling the energy requirements essential to expedite osteogenic differentiation. Furthermore, decreased α-ketoglutarate release from ETV2-modified DPSCs contributes to microcirculation reconstruction. Additionally, we engineered hydroxyapatite/chitosan microspheres (HA/CS MS) with biomimetic nanostructures to facilitate multiple ETV2-DPSC functions and further enhanced the osteogenic differentiation. Animal experiments have validated the synergistic effect of ETV2-modified DPSCs and HA/CS MS in promoting the critical-size bone defect regeneration. In summary, this study offers a novel treatment approach for vascularized bone tissue regeneration that relies on energy metabolism activation and the maintenance of a stable local hypoxia signaling state.

Osteocalcin: Beyond Bones

Apart from basic roles such as supporting the body, protecting internal organs, and storing calcium, the skeletal system also performs hormonal functions. In recent years, several reports have been published on proteins secreted by bones and their impact on the homeostasis of the entire body. These proteins include fibroblast growth factor 23, sclerostin, lipocalin 2, and osteocalcin. Osteocalcin, the most abundant non-collagenous protein in bone tissue, is routinely measured as a clinical marker for diagnosing bone metabolism disorders. Its molecule undergoes numerous transformations, with decarboxylation being the critical process. Decarboxylation occurs in the acidic environment typical of bone resorption, facilitating the release of the molecule into the bloodstream and enabling its hormonal action. Decarboxylated osteocalcin promotes insulin secretion and stimulates the proliferation of pancreatic islet β-cells. It also plays a role in reducing the accumulation of visceral fat and decreasing fat storage in the liver. Furthermore, decarboxylated osteocalcin levels are inversely correlated with fasting serum glucose levels, total body fat, visceral fat area, and body mass index. Apart from its role in energy metabolism, osteocalcin affects testosterone production and the synthesis of glucagon-like peptide-1. It is also actively involved in muscle-bone crosstalk and influences cognitive function.

Osteogenic mechanism of chlorogenic acid and its application in clinical practice

Natural polyphenols may have a role in counteracting oxidative stress, which is associated with aging and several bone-related diseases. Chlorogenic acid (CGA) is a naturally occurring polyphenolic compound formed by the esterification of caffeic and quininic acids with osteogenic, antioxidant, and anti-inflammatory properties. This review discusses the potential of CGA to enhance osteogenesis by increasing the osteogenic capacity of mesenchymal stem cells (MSCs), osteoblast survival, proliferation, differentiation, and mineralization, as well as its ability to attenuate osteoclastogenesis by enhancing osteoclast apoptosis and impeding osteoclast regeneration. CGA can be involved in bone remodeling by acting directly on pro-osteoclasts/osteoblasts or indirectly on osteoclasts by activating the nuclear factor kB (RANK)/RANK ligand (RANKL)/acting osteoprotegerin (OPG) system. Finally, we provide perspectives for using CGA to treat bone diseases.