Osteoblastic Bone Formation Research Articles

Mitochondrial maintenance as a novel target for treating steroid-induced osteonecrosis of femoral head: a narrative review.

The pathogenesis of steroid-induced osteonecrosis of the femoral head (SONFH) remains unclear; however, emerging evidence suggests that mitochondrial injury plays a significant role. This review aims to elucidate the involvement of mitochondrial dysfunction in SONFH and explore potential therapeutic targets. A comprehensive literature search was conducted in PubMed, Web of Science, and Elsevier ScienceDirect, focusing on mitochondrial homeostasis, including mitophagy, mitochondrial biogenesis, mitochondrial dynamics, and oxidative stress in SONFH. Ultimately, we included and analyzed a total of 16 studies. Glucocorticoids initially promote but later inhibit mitochondrial biogenesis in osteoblasts, leading to excessive ROS production and mitochondrial dysfunction. This dysfunction impairs osteoblast survival and bone formation, contributing to SONFH progression. Key proteins such as mitochondrial transcription factor A (TFAM) and peroxisome proliferator-activated receptor γ coactivator 1-α (PGC1α) are potential therapeutic targets for promoting mitochondrial biogenesis and reducing ROS-induced damage. Enhancing mitochondrial function and reducing oxidative stress in osteoblasts may prevent or slow the progression of SONFH. Future research should focus on developing these strategies.

Mapping RANKL- and OPG-expressing cells in bone tissue: the bone surface cells as activators of osteoclastogenesis and promoters of the denosumab rebound effect.

Denosumab is a monoclonal anti-RANKL antibody that inhibits bone resorption, increases bone mass, and reduces fracture risk. Denosumab discontinuation causes an extensive wave of rebound resorption, but the cellular mechanisms remain poorly characterized. We utilized in situ hybridization (ISH) as a direct approach to identify the cells that activate osteoclastogenesis through the RANKL/OPG pathway. ISH was performed across species, skeletal sites, and following recombinant OPG (OPG:Fc) and parathyroid hormone 1-34 (PTH) treatment of mice. OPG:Fc treatment in mice induced an increased expression of RANKL mRNA mainly in trabecular, but not endocortical bone surface cells. Additionally, a decreased expression of OPG mRNA was detected in bone surface cells and osteocytes of both compartments. A similar but more pronounced effect on RANKL and OPG expression was seen one hour after PTH treatment. These findings suggest that bone surface cells and osteocytes conjointly regulate the activation of osteoclastogenesis, and that OPG:Fc treatment induces a local accumulation of osteoclastogenic activation sites, ready to recruit and activate osteoclasts upon treatment discontinuation. Analysis of publicly available single-cell RNA sequencing (scRNAseq) data from murine bone marrow stromal cells revealed that Tnfsf11+ cells expressed high levels of Mmp13, Limch1, and Wif1, confirming their osteoprogenitor status. ISH confirmed co-expression of Mmp13 and Tnfsf11 in bone surface cells of both vehicle- and OPG:Fc-treated mice. Under physiological conditions of human/mouse bone, RANKL is expressed mainly by osteoprogenitors proximate to the osteoclasts, while OPG is expressed mainly by osteocytes and bone-forming osteoblasts.

Delivery of a Jagged1-PEG-MAL hydrogel with pediatric human bone cells regenerates critically sized craniofacial bone defects

Current treatments for congenital and acquired craniofacial (CF) bone abnormalities are limited and costly. Conventional methods involve surgical correction, short-term stabilization, and long-term bone grafting, which may include problematic allografts and limited autografts. While bone morphogenetic protein 2 (BMP2) has been used for bone regeneration, it can cause bone overgrowth and life-threatening inflammation. Bone marrow-derived mesenchymal stem cell therapies, though promising, are not Food and Drug Administration approved and are resource intensive. Thus, there is a need for effective, affordable, and less side-effect-prone bone regenerative therapies. Previous research demonstrated that JAGGED1 induces osteoblast commitment in murine cranial neural crest cells through a NOTCH-dependent non-canonical pathway involving JAK2–STAT5. We hypothesize that delivery of JAGGED1 and induction of its downstream NOTCH non-canonical signaling in pediatric human osteoblasts constitutes an effective bone regenerative treatment. Delivering pediatric human bone-derived osteoblast-like cells to an in vivo murine bone loss model of a critically sized cranial defect, we identified that JAGGED1 promotes human pediatric osteoblast commitment and bone formation through p70 S6K phosphorylation. This approach highlights the potential of JAGGED1 and its downstream activators as innovative treatments for pediatric CF bone loss.

Delivery of a Jagged1-PEG-MAL hydrogel with pediatric human bone cells regenerates critically sized craniofacial bone defects.

Current treatments for congenital and acquired craniofacial (CF) bone abnormalities are limited and costly. Conventional methods involve surgical correction, short-term stabilization, and long-term bone grafting, which may include problematic allografts and limited autografts. While bone morphogenetic protein 2 (BMP2) has been used for bone regeneration, it can cause bone overgrowth and life-threatening inflammation. Bone marrow-derived mesenchymal stem cell therapies, though promising, are not Food and Drug Administration approved and are resource intensive. Thus, there is a need for effective, affordable, and less side-effect-prone bone regenerative therapies. Previous research demonstrated that JAGGED1 induces osteoblast commitment in murine cranial neural crest cells through a NOTCH-dependent non-canonical pathway involving JAK2-STAT5. We hypothesize that delivery of JAGGED1 and induction of its downstream NOTCH non-canonical signaling in pediatric human osteoblasts constitutes an effective bone regenerative treatment. Delivering pediatric human bone-derived osteoblast-like cells to an in vivo murine bone loss model of a critically sized cranial defect, we identified that JAGGED1 promotes human pediatric osteoblast commitment and bone formation through p70 S6K phosphorylation. This approach highlights the potential of JAGGED1 and its downstream activators as innovative treatments for pediatric CF bone loss.

Measuring Calcium Levels in Bone-Resorbing Osteoclasts and Bone-Forming Osteoblasts.

Bone remodeling is a crucial, dynamic process that renews bone and maintains mineral homeostasis. It consists of several steps, including osteoclastic bone resorption and osteoblastic bone formation and mineralization. Intracellular calcium signaling is essential for osteoclast and osteoblast differentiation and activity. Here, we describe the differentiation of human osteoclasts and osteoblasts in vitro and provide common methods to determine cell differentiation and activity. We then describe protocols for measuringintracellular calcium in these cells using Fura2-AM.

Role of in-situ electrical stimulation on early-stage mineralization and in-vitro osteogenesis of electroactive bioactive glass composites

Bioactive glass (BAG) has emerged as an effective bone graft substitute due to its diverse qualities of biocompatibility, bioactivity, osteoblast adhesion and enhanced revascularization. However, inferior osteogenic capacity of BAG compared to autologous bone grafts continues to limiting it's wide-spread clinical applications towards repairing of bone fractures and healing. In this study, we have fabricated BAG composites with 0.5 to 2 wt% bismuth ferrite (BF, a multiferroic material) with an aim to generate in-situ electrical charges pertinent to early-stage bone regeneration thus mimicking nature bone, which is a piezoelectric material. The fabricated BAG composites were characterised in terms of microstructures, phase analysis, remanent polarization, wettability and subsequently evaluated for in vitro cell proliferation and osteogenesis with and without magnetic field exposure (200 mT, 30 min./day). Pre-osteoblast cells from mice (MC3T3-E1) seeded on these composites exhibited excellent cell growth without any cytotoxicity, which is further supported by FITC/DAPI staining and a live/dead assay. The results of Alizarin Red S assay and increased levels of Alkaline Phosphatase (ALP) activity, at 21 days of culture, suggest that the BAG-BF composites promote in vitro osteogenic differentiation of pre-osteoblast cells. The enhanced osteogenesis of BAG-BF composites was also confirmed through qRT-PCR analysis, which showed rapid upregulation of osteoblastogenic specific genes namely RunX-2, Collagen-1, Bone Sialo Protein, and ALP after 21 days. Additionally, the osteogenic differentiation was assessed by the Western Blot technique, which revealed significantly higher band intensity of osteogenic markers in BAG-1.5 BF and BAG-2 BF composites than pure BAG. These findings clearly demonstrate that in-situ electrical stimulation and osteoconductive capacity of BF reinforced BAG composites have positive impact on osteoblast cell development, bone formation, and healing.

AOP Report: Development of an adverse outcome pathway for deposition of energy leading to bone loss.

Bone loss, commonly seen in osteoporosis, is a condition that entails a progressive decline of bone mineral density and microarchitecture, often seen in post-menopausal women. Bone loss has also been widely reported in astronauts exposed to a plethora of stressors and in patients with osteoporosis following radiotherapy for cancer. Studies on mechanisms are well documented but the causal connectivity of events to bone loss development remains incompletely understood. Herein, the adverse outcome pathway (AOP) framework was used to organize data and develop a qualitative AOP beginning from deposition of energy (the molecular initiating event) to bone loss (the adverse outcome). This qualitative AOP was developed in collaboration with bone loss research experts to aggregate relevant findings, supporting ongoing efforts to understand and mitigate human system risks associated with radiation exposures. A literature review was conducted to compile and evaluate the state of knowledge based on the modified Bradford Hill criteria. Following review of 2029 studies, an empirically supported AOP was developed, showing the progression to bone loss through many factors affecting the activities of bone-forming osteoblasts and bone-resorbing osteoclasts. The structural, functional, and quantitative basis of each proposed relationship was defined, for inference of causal changes between key events. Current knowledge and its gaps relating to dose-, time- and incidence-concordance across the key events were identified, as well as modulating factors that influence linkages. The new priorities for research informed by the AOP highlight areas for improvement to enable development of a quantitative AOP used to support risk assessment strategies for space travel or cancer radiotherapy.

Extracorporeal Magnetotransduction Therapy as a New Form of Electromagnetic Wave Therapy: From Gene Upregulation to Accelerated Matrix Mineralization in Bone Healing.

Electromagnetic field therapy is gaining attention for its potential in treating bone disorders, with Extracorporeal Magnetotransduction Therapy (EMTT) emerging as an innovative approach. EMTT offers a higher oscillation frequency and magnetic field strength compared to traditional Pulsed Electromagnetic Field (PEMF) therapy, showing promise in enhancing fracture healing and non-union recovery. However, the mechanisms underlying these effects remain unclear. This study demonstrates that EMTT significantly enhances osteoblast bone formation at multiple levels, from gene expression to extracellular matrix mineralization. Key osteoblastogenesis regulators, including SP7 and RUNX2, and bone-related genes such as COL1A1, ALPL, and BGLAP, were upregulated, with expression levels surpassing those of the control group by over sevenfold (p < 0.001). Enhanced collagen synthesis and mineralization were confirmed by von Kossa and Alizarin Red staining, indicating increased calcium and phosphate deposition. Additionally, calcium imaging revealed heightened calcium influx, suggesting a cellular mechanism for EMTT's osteogenic effects. Importantly, EMTT did not compromise cell viability, as confirmed by live/dead staining and WST-1 assays. This study is the first to show that EMTT can enhance all phases of osteoblastogenesis and improve the production of critical mineralization components, offering potential clinical applications in accelerating fracture healing, treating osteonecrosis, and enhancing implant osseointegration.

7858 Increasing Severity of Growth Hormone Deficiency is Associated with Lower Vertebral Strength

Abstract Disclosure: R. Boutin: None. M. Haines: None. R. Shahid: None. C. Mark: None. C. Gill: None. M. Bredella: None. K.K. Miller: Other; Self; Pfizer, Inc. L.E. Dichtel: Consulting Fee; Self; Lumos Pharma. Grant Recipient; Self; Lumos Pharma, Perspectum Ltd. Research Investigator; Self; Recordati, Novo Nordisk. Stock Owner; Self; Marea Therapeutics. Other; Self; Third Rock Ventures. Objective: Growth hormone (GH) stimulates osteoblast differentiation, while insulin-like growth factor-1 (IGF-1) stimulates osteoblast proliferation and bone formation. Retrospective studies have demonstrated a 2-to-3-fold increased fracture risk in adults with GH deficiency (GHD) due to organic hypothalamic or pituitary disease, particularly at vertebral sites. Adults with overweight/obesity produce relatively less GH than lean individuals, and serum IGF-1 levels are associated positively with BMD in adults with obesity. Yet, no published studies have examined the relationship between degree of GHD across these groups and vertebral strength, an understudied measure of bone quality in part because HR-pQCT cannot image this skeletal site. We hypothesized that there would be an inverse association between degree of GHD and vertebral strength, independent of age and BMI. Methods: Cross-sectional study of 134 estrogen-replete (with regular menses or taking estrogen) women: 16 with GHD secondary to hypopituitarism (HP, severe GHD), 91 with obesity (OB) without a hypothalamic/pituitary disorder (relative GHD), and 37 lean controls (LC) without a hypothalamic/pituitary disorder (normal GH production). Peak-stimulated GH was assessed by GHRH-arginine testing. CT imaging at the L4 vertebra was performed to determine vertebral cross-sectional area and total integrated volumetric bone mineral density (Int.vBMD), from which estimates of vertebral strength were calculated. Results: Mean age [44±9 (mean±SD) (HP) vs. 35±7 (OB) vs. 30±7 (LC) y, p&amp;lt;0.005] and BMI [30±6 (HP) vs. 34±6 (OB) vs. 22±2 (LC) kg/m2, p&amp;lt;0.004] differed between all groups. As expected, peak-stimulated GH was highest in LC (28.3 ± 9.5 ng/mL) followed by OB (12.4 ± 8.9 ng/mL) and HP (2.4 ± 1.7 ng/mL), p&amp;lt;0.0001. IGF-1 Z-scores were higher in LC (0.0 ± 0.6) and OB (0.0 ± 0.7) vs. HP (-1.4 ± 0.7), p&amp;lt;0.0001. Int.vBMD and vertebral strength were higher in LC and OB vs. HP [Int.vBMD (g/cm3) LC 0.21±0.04 and OB 0.21±0.04 vs. HP 0.16±0.03, and vertebral strength (N) LC 4540±850 and 4743±91 vs. HP 3542±651, both p&amp;lt;0.0001], which remained significant when adjusted for age and BMI (p≤0.01). Peak-stimulated GH and IGF-1 Z-scores were positively associated with vertebral strength (GH R=0.33, p=0.003 and IGF-1 Z-score R=0.41, p&amp;lt;0.0001) and Int.vBMD (GH R=0.46, p&amp;lt;0.0001 and IGF-1 Z-score R=0.40, p&amp;lt;0.0001), which remained significant when adjusted for age and BMI. Among the subset of patients without organic pituitary disease (LC and OB only), IGF-1 Z-scores remained positively associated with vertebral strength (R=0.24, p&amp;lt;0.03) and Int.vBMD (R=0.22, p&amp;lt;0.05). Conclusions: These findings suggest that severe GHD is associated with impaired vertebral volumetric bone density and strength. Moreover, the relative GHD of obesity may contribute to lower vertebral bone density and strength in otherwise healthy adults with overweight/obesity. Presentation: 6/3/2024

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

Background/ObjectiveActive vitamin D insufficiency accelerates the development of osteoporosis, with senescent bone cells and the senescence-associated secretory phenotype (SASP) playing crucial roles. This study aimed to investigate whether the senolytic agent ABT263 could correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent cells. MethodsBone marrow mesenchymal stem cells (BM-MSCs) from young and aged mice were treated with ABT263 in vitro, and 1,25(OH)2D-insufficient (Cyp27b1+/−) mice were administered ABT263 in vivo. Cellular, molecular, imaging, and histopathological analyses were performed to compare treated cells and mice with control groups. ResultsABT263 induced apoptosis in senescent BM-MSCs by downregulating Bcl2 and upregulating Bax expression. It also induced apoptosis in senescent BM-MSCs from 1,25(OH)2D-insufficient mice. ABT263 administration corrected bone loss caused by 1,25(OH)2D insufficiency by increasing bone density, bone volume, trabecular number, trabecular thickness, and collagen synthesis. It also enhanced osteoblastic bone formation and reduced osteoclastic bone resorption in vivo. ABT263 treatment corrected the impaired osteogenic action of BM-MSCs by promoting their proliferation and osteogenic differentiation. Furthermore, it corrected oxidative stress and DNA damage caused by 1,25(OH)2D insufficiency by increasing SOD-2 and decreasing γ-H2A.X expression. Finally, ABT263 corrected bone cell senescence and SASP caused by 1,25(OH)2D insufficiency by reducing the expression of senescence and SASP-related genes and proteins. ConclusionABT263 can correct osteoporosis caused by active vitamin D insufficiency by selectively clearing senescent skeletal cells, reducing oxidative stress, DNA damage, and SASP, and promoting bone formation while inhibiting bone resorption. These findings provide new insights into the potential therapeutic application of senolytic agents in the treatment of osteoporosis associated with active vitamin D insufficiency. The translational potential of this articleThis study highlights the therapeutic potential of ABT263, a senolytic compound, in treating osteoporosis caused by active vitamin D insufficiency. By selectively eliminating senescent bone cells and their associated SASP, ABT263 intervention demonstrates the ability to restore bone homeostasis, prevent further bone loss, and promote bone formation. These findings contribute to the growing body of research supporting the use of senolytic therapies for the prevention and treatment of age-related bone disorders. The translational potential of this study lies in the development of novel therapeutic strategies targeting cellular senescence to combat osteoporosis, particularly in cases where vitamin D insufficiency is a contributing factor. Further clinical studies are warranted to validate the efficacy and safety of ABT263 and other senolytic agents in the treatment of osteoporosis in humans.

8693 Dexamethasone Increases Bone Mass In Mice

Abstract Disclosure: F. Sultana: None. M.L. Temple: None. S. Kim: None. V. Ryu: None. F. Korkmaz: None. A. Gumerova: None. P. Georgii: None. U. Cheliadinova: None. D. Vasilyeva: None. V. Laurencin: None. R. Witztum: None. O. Barak: None. L. Cullen: None. A.R. Pallapati: None. S. Rojekar: None. J. Gimenez Roig: None. D. Lizneva: None. W. Zhou: None. T. Yuen: None. M. Zaidi: None. Severe osteoporosis and bone fractures are strongly associated with long-term or recurring glucocorticoid use in people. Steroids have traditionally been used as an anti-inflammatory and immunosuppressive agent, and while their use has been widely implicated in causing bone loss by suppressing osteoblastic bone formation, recent data have consistently shown mixed results in mice. It is also important to stress that dexamethasone (DEX) in particular has been used for over three decades in cell cultures to stimulate osteoblast formation. We therefore posit that mechanisms other than direct steroid effects on osteoblasts contribute to bone loss, and that, at least physiologically, steroids stimulate (rather than inhibit) bone formation. Here, we have aimed to clarify the effects of DEX on bone metabolism. We first studied the effects of low and high doses of DEX (1 mg/kg and 10 mg/kg), given daily as intraperitoneal injections to 8-week-old C57BL/6 mice. Micro-CT showed that DEX markedly increased bone microarchitecture, including the bone volume fraction, connectivity density, and trabecular number, while decreasing trabecular spacing in femoral epiphyses compared with vehicle-injected controls. Serum levels of adrenocorticotropic hormone (ACTH) and corticosterone did not change following DEX. These findings suggest that both low and high DEX doses are anabolic to the skeleton. Reaffirming these data, we found that adrenalectomy (with salt replacement) caused a significant decline in bone mineral density. Likewise, Tpit-/- mice, in which ACTH and corticosterone are both reduced, display reduced bone microarchitectural parameters, together with low mineralizing surface and bone formation rates on dynamic histomorphometry, impaired osteoblast formation in Cfu-f cultures, and lowered expression of the osteoblastogenesis genes Bmp2, Ibsp, Runx2 and Sp7. Finally, deleting the glucocorticoid receptor (Gr) specifically in osteoclasts in Acp5-Cre;Grfl/fl mice had no effect on microarchitectural parameters at the spine or proximal tibial metaphysis. However, and importantly, absent GR in the osteoclast, DEX increased bone mass significantly, suggesting that its notable anabolic action was mediated by the osteoblast. Our findings challenge the longstanding premise that steroids directly impact the osteoblast to cause bone loss, and that other mechanisms, such as reduced ACTH levels and/or central effects of DEX, may play a key role. Presentation: 6/1/2024

Interactions between kisspeptin and bone: Cellular mechanisms, clinical evidence, and future potential.

The neuropeptide kisspeptin and its cognate receptor have been extensively studied in reproductive physiology, with diverse and well-established functions, including as an upstream regulator of pubertal onset, reproductive hormone secretion, and sexual behavior. Besides classical reproduction, both kisspeptin and its receptor are extensively expressed in bone-resorbing osteoclasts and bone-forming osteoblasts, which putatively permits direct bone effects. Accordingly, this sets the scene for recent compelling findings derived from in vitro experiments through to in vivo and clinical studies revealing prominent regulatory interactions for kisspeptin signaling in bone metabolism, as well as certain oncological aspects of bone metabolism. Herein, we comprehensively examine the experimental evidence obtained to date supporting the interaction between kisspeptin and bone. A comprehensive understanding of this emerging facet of kisspeptin biology is fundamental to exploiting the future therapeutic potential of kisspeptin-based medicines as a novel strategy for treating bone-related disorders.

Osteoporosis and inflammation: Cause to effect or comorbidity?

Osteoporosis (OP) was long viewed as an inevitable process of aging, due to an imbalance between osteoclast bone resorbing and osteoblast bone formation function, leading to a negative balance in bone remodeling. This leads to low bone mass and increased bone fragility putting the patient at risk for fracture. While this view still holds, a better understanding disclosed that OP can occur at any age, as a comorbidity or a complication of many diseases and treatments. Differentiation, maturation, and function of osteoclasts and osteoblasts are affected by many factors from different morbidities: endocrine, metabolic, mechanical and inflammatory. Inflammatory diseases are often complicated by a generalized bone loss that subsequently leads to OP. Factors such as glucocorticoid treatment, immobilization, malnutrition, and insufficient intake of vitamin D play a role. However, the inflammatory process itself is involved and the resulting bone loss is termed immune-mediated bone loss. Experiments on animals and on humans, in addition to clinical studies, shed light on the role of inflammation in OP.

Osteoking prevents bone loss and enhances osteoblastic bone formation by modulating the AGEs/IGF-1/β-catenin/OPG pathway in type 2 diabetic db/db mice.

Type 2 diabetic osteoporosis (T2DOP) is a skeletal metabolic syndrome characterized by impaired bone remodeling due to type 2 diabetes mellitus, and there are drawbacks in the present treatment. Osteoking (OK) is widely used for treating fractures and femoral head necrosis. However, OK is seldom reported in the field of T2DOP, and its role and mechanism of action need to be elucidated. Consequently, this study investigated whether OK improves bone remodeling and the mechanisms of diabetes-induced injury. We used db/db mice as a T2DOP model and stimulated MC3T3-E1 cells (osteoblast cell line) with high glucose (HG, 50 mM) and advanced glycation end products (AGEs, 100 µg/mL), respectively. The effect of OK on T2DOP was assessed using a combined 3-point mechanical bending test, hematoxylin and eosin staining, and enzyme-linked immunosorbent assay. The effect of OK on enhancing MC3T3-E1 cell differentiation and mineralization under HG and AGEs conditions was assessed by an alkaline phosphatase activity assay and alizarin red S staining. The AGEs/insulin-like growth factor-1(IGF-1)/β-catenin/osteoprotegerin (OPG) pathway-associated protein levels were assayed by western blot analysis and immunohistochemical staining. We found that OK reduced hyperglycemia, attenuated bone damage, repaired bone remodeling, increased tibial and femoral IGF-1, β-catenin, and OPG expression, and decreased receptor activator of nuclear kappa B ligand and receptor activator of nuclear kappa B expression in db/db mice. Moreover, OK promoted the differentiation and mineralization of MC3T3-E1 cells under HG and AGEs conditions, respectively, and regulated the levels of AGEs/IGF-1/β-catenin/OPG pathway-associated proteins. In conclusion, our results suggest that OK may lower blood glucose, alleviate bone damage, and attenuate T2DOP, in part through activation of the AGEs/IGF-1/β-catenin/OPG pathway.

Ferroptosis: Regulatory mechanisms and potential targets for bone metabolism: A review.

Bone homeostasis is a homeostasis process constructed by osteoblast bone formation and osteoclast bone resorption. Bone homeostasis imbalance and dysfunction are the basis for the development of various orthopedic diseases such as osteoporosis, osteoarthritis, and steroid-induced avascular necrosis of femoral head. Previous studies have demonstrated that ferroptosis can induce lipid peroxidation through the generation of reactive oxygen species, activate a number of signaling pathways, and participate in the regulation of osteoblast bone formation and osteoclast bone resorption, resulting in bone homeostasis imbalance, which is an important factor in the pathogenesis of many orthopedic diseases, but the mechanism of ferroptosis is still unknown. In recent years, it has been found that, in addition to iron metabolism and intracellular antioxidant system imbalance, organelle dysfunction is also a key factor affecting ferroptosis. This paper takes this as the starting point, reviews the latest literature reports at home and abroad, elaborates the pathogenesis and regulatory pathways of ferroptosis and the relationship between ferroptosis and various organelles, and summarizes the mechanism by which ferroptosis mediates bone homeostasis imbalance, with the aim of providing new directions for the research related to ferroptosis and new ideas for the prevention and treatment of bone and joint diseases.

Bmi-1 Epigenetically Orchestrates Osteogenic and Adipogenic Differentiation of Bone Marrow Mesenchymal Stem Cells to Delay Bone Aging.

With the increase in the aging population, senile osteoporosis (SOP) has become a major global public health concern. Here, it is found that Prx1 and Bmi-1 co-localized in trabecular bone, bone marrow cavity, endosteum, and periosteum. Prx1-driven Bmi-1 knockout in bone-marrow mesenchymal stem cells (BMSCs) reduced bone mass and increased bone marrow adiposity by inhibiting osteoblastic bone formation, promoting osteoclastic bone resorption, downregulating the proliferation and osteogenic differentiation of BMSCs, and upregulating the adipogenic differentiation of BMSCs. However, Prx1-driven Bmi-1 overexpression showed a contrasting phenotype to Prx1-driven Bmi-1 knockout in BMSCs. Regarding mechanism, Bmi-1-RING1B bound to DNMT3A and promoted its ubiquitination and inhibited DNA methylation of Runx2 at the region from 45047012 to 45047313bp, thus promoting the osteogenic differentiation of BMSCs. Moreover, Bmi-1-EZH2 repressed the transcription of Cebpa by promoting H3K27 trimethylation at the promoter region -1605 to -1596 bp, thus inhibiting the adipogenic differentiation of BMSCs. It is also found that Prx1-driven Bmi-1 overexpression rescued the SOP induced by Prx1-driven Bmi-1 knockout in BMSCs. Thus, Bmi-1 functioned as a hub protein in the epigenetic regulation of BMSCs differentiation to delay bone aging. The Prx1-driven Bmi-1 overexpression in BMSCs can be used as an approach for the translational therapy of SOP.

Osteogenic differentiation capabilities of multiarm PEG hydrogels: involvement of gel–gel-phase separation in cell differentiation

AbstractThe development of bioactive scaffolds is essential for tissue engineering because of the influence of material physicochemical properties on cellular activities. Recently, we discovered that percolation-induced 4-arm polyethylene glycol (PEG) hydrogels achieved gel–gel phase separation (GGPS), which has tissue affinity in vivo. However, whether the 4-arm structure is the optimal configuration for the use of PEG hydrogels as scaffolds remains unclear. In this study, we investigated the effect of an increased branching factor on GGPS. Compared with the 4-arm PEG hydrogel, the 8-arm PEG hydrogel presented a greater degree of GGPS and increased hydrophobicity. We introduced the RGD sequence into PEG hydrogels to directly assess the biological activity of GGPS, with a particular focus on its effects on the activity of bone-forming osteoblasts. Although the 8-arm PEG hydrogel did not enhance cell adhesion, it enhanced osteoblast differentiation compared with the 4-arm PEG hydrogel. Therefore, the 8-arm PEG hydrogel mediated by GGPS shows promise as a scaffold for osteoblast differentiation and holds potential as a foundation for future advancements in bone tissue engineering.

The people behind the papers - Yukiko Kuroda and Koichi Matsuo.

Developing bones can adapt their shape in response to mechanical stresses from neighbouring growing organs. In a new study, Koichi Matsuo and colleagues examine how bone-forming osteoblasts and bone-resorbing osteoclasts coordinate growth in the mouse fibula. They describe the process called 'endo-forming trans-pairing', where bone resorption by osteoclasts in the outer periosteum is paired with bone formation by osteoblasts in the inner endosteum to shape the growing bone. To learn more about the story behind the paper, we caught up with first author Yukiko Kuroda and the corresponding author Koichi Matsuo, Professor at the School of Medicine, Keio University, Japan.

Stanniocalcin 1 and 1,25-dihydroxyvitamin D3 cooperatively regulate bone mineralization by osteoblasts

Stanniocalcin 1 (STC1) is a calcium- and phosphate-regulating hormone that is expressed in all tissues, including bone tissues, and is involved in calcium and phosphate homeostasis. Previously, STC1 expression was found to be increased by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] administration in renal proximal tubular cells. In this study, we investigated whether STC1 directly regulates osteoblast differentiation or reciprocally controls the effects of 1,25(OH)2D3 on osteoblasts to contribute to bone homeostasis. We found that STC1 inhibited osteoblast differentiation in vitro and bone morphogenetic protein 2 (BMP2)-induced ectopic bone formation in vivo. Moreover, 1,25(OH)2D3 increased STC1 expression through direct binding to the Stc1 promoter of the vitamin D receptor (VDR). STC1 activated the 1,25(OH)2D3–VDR signaling pathway through the upregulation of VDR expression mediated by the inhibition of Akt phosphorylation in osteoblasts. STC1 further increased the effects of 1,25(OH)2D3 on receptor activator of nuclear factor-κB ligand (RANKL) secretion and inhibited osteoblast differentiation by exhibiting a positive correlation with 1,25(OH)2D3. The long-bone phenotype of transgenic mice overexpressing STC1 specifically in osteoblasts was not significantly different from that of wild-type mice. However, compared with that in the wild-type mice, 1,25(OH)2D3 administration significantly decreased bone mass in the STC1 transgenic mice. Collectively, these results suggest that STC1 negatively regulates osteoblast differentiation and bone formation; however, the inhibitory effect of STC1 on osteoblasts is transient and can be reversed under normal conditions. Nevertheless, the synergistic effect of STC1 and 1,25(OH)2D3 through 1,25(OH)2D3 administration may reduce bone mass by inhibiting osteoblast differentiation.

Therapeutic Insights into Low-intensity Vibration for Generating Induced Tumor-Suppressive Cells and Modulating the Bone Microenvironment

Bone frequently serves as a metastatic site for breast and prostate cancers. Given the potential of low-intensity vibration (LIV) to increase bone health and reduce cancer risk, this study investigated the impact of LIV on cancer cells, as well as noncancer cells such as lymphocytes and peripheral blood mononuclear cells (PBMCs). The results revealed that LIV exposure not only suppressed cancer cell migration but also triggered the generation of induced tumor-suppressing (iTS) cells. Conditioned medium (CM) derived from LIV-treated PBMCs shrank freshly isolated breast and prostate cancer tissues, and when CM was combined with a chemotherapeutic agent, additional antitumor effects were observed. Notably, iTS cell-derived CM hindered the maturation of the receptor activator of nuclear factor-kappa B ligand (RANKL)-stimulated bone-resorbing osteoclasts while promoting the differentiation of bone-forming osteoblasts. Intriguingly, the anticancer effects induced by LIV were replicated by simply shaking a cell-containing tube with a regular tube shaker. Using mass spectrometry-based proteomics, this study revealed enrichment of tumor-suppressing proteins, including enolase 1, moesin (MSN), and aldolase A (ALDOA), which are commonly found in oncogene-activated iTS cells, in LIV-induced CM. Sad1 and UNC-84 domain containing 1 (SUN1), a core component of the linker of the nucleoskeleton and cytoskeleton (LINC) complex, exhibited heightened expression, notably enhancing the response of lymphocytes to LIV. An ex vivo bone cancer model further demonstrated the potent anticancer effects of lymphocyte-derived CM. In conclusion, this study underscores the pivotal role of LIV in preventing bone loss in the tumor microenvironment.