Bone

PurposeOsteoporosis and associated hip fractures are a major public health concern. Dualenergy X-ray Absorptiometry (DXA) remains the diagnostic gold standard, but its areal (a) bone mineral density (BMD) measurements have limited sensitivity, as many fractures occur at T-scores above -2.5. Three-dimensional (3D) DXA provides compartment-specific volumetric parameters of the hip, potentially improving osteoporosis management. This study aimed to establish reference data for 3D-DXA parameters to improve osteoporosis management and investigate potential compartmental imbalances at the hip. MethodThis multicenter, cross-sectional, population-based observational study (SEIOMM-3D-DXA project), supported by the Spanish Society for Bone and Mineral Metabolism (SEIOMM), analyzed hip DXA scans from 1366 Spanish men and women across six centers. 3D-DXA analyses were conducted using the 3D-Shaper software (3D-Shaper Medical, Barcelona, Spain), producing estimates of trabecular volumetric (v) BMD and cortical surface (s) BMD. Age- and sex-specific reference curves were generated using the LMS method, and thresholds were established based on regression with T-score values. Moreover, trabecular vBMD and cortical sBMD Z-scores were calculated to evaluate potential compartmental imbalances. ResultsThe derived aBMD curves closely aligned with the NHANES III Caucasian reference. Sex-specific thresholds for trabecular vBMD and cortical sBMD were established for patient stratification. Z-score comparisons revealed significant discrepancies between trabecular and cortical compartments in 52.0% of females and 48.7% of males, underlining the importance of compartment-specific bone assessment. ConclusionsThis study establishes reference curves for clinical interpretation of 3D-DXA parameters and demonstrates the potential of 3D-DXA to capture compartmental imbalances at the hip. Mini AbstractIn this study, hip scans from over a thousand men and women in Spain were analyzed to create normative reference values for 3D-DXA parameters. These results can help doctors better stratify people based on the status of each part of the bone and improve the management of osteoporosis.

IntroductionTrabecular bone exhibits brittle behaviour governed by microscale deformation and damage processes, yet quantitative characterisation of crack progression remains challenging because classical fracture mechanics approaches do not apply to architecturally discontinuous porous tissues. This study evaluates whether synchrotron X-ray computed tomography (XCT) combined with digital volume correlation (DVC) can provide a practical experimental approach for quantifying crack opening behaviour in human trabecular bone. MethodSemicylindrical specimens harvested from femoral heads of hip-fracture donors (n = 5) and non-fracture controls (n = 5) underwent stepwise three-point-bending during XCT imaging. Full-field displacement maps enabled direct measurement of crack mouth opening displacement (CMOD), crack length (a), and their ratio, CMOD/a, used here as a geometry-normalised comparative descriptor of brittle response. Automated crack segmentation using phase-congruency crack detection (PCCD) was compared against manual measurements. ResultsXCT-DVC successfully resolved three-dimensional displacement discontinuities during crack initiation and propagation in all specimens. Hip-fracture donors exhibited significantly lower critical crack-opening ratios (CMOD/a)* than Controls (0.31 vs 0.47; p = 0.008) and reached mechanical instability at lower applied loads, consistent with a more brittle structural response under this test configuration. Despite these differences, total crack extension ({Delta}a*) was similar between groups. Automated crack tracking using phase-congruency-based segmentation showed excellent agreement with manual measurements (r{superscript 2} = 0.98), confirming reliable extraction of crack geometry from DVC displacement fields. DiscussionThese results indicate that XCT-DVC can provide a practical approach for quantifying crack-opening behaviour in trabecular bone when classical fracture-mechanics parameters are not applicable in anatomically constrained specimens. The reduced critical crack-opening ratios and earlier instability observed in Hip-fracture donors are consistent with a more brittle comparative mechanical response that is not captured by crack extension alone. The strong agreement between automated and manual crack measurements further supports displacement-based descriptors as reliable comparative indicators of brittle behaviour in porous, architecturally discontinuous tissues. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/714043v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@31c5d7org.highwire.dtl.DTLVardef@1b3d9a4org.highwire.dtl.DTLVardef@95df7borg.highwire.dtl.DTLVardef@1834216_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical abstractC_FLOATNO C_FIG

3D-DXA reconstructs DXA hip scans to 3-dimensional images allowing measurement of trabecular and cortical bone parameters. Given the higher image quality of GE Healthcare iDXA than GE Healthcare Prodigy, it could be hypothesized that the reconstruction might differ, thereby affecting 3D-DXA results. The aim of the study was to assess agreement and precision of 3D-DXA cortical and trabecular femur parameters between Prodigy and iDXA densitometers in adult subjects. The study cohort was composed of 391 men and women recruited from 3 clinical centers (USA and Brazil). All subjects were scanned on either Prodigy or iDXA scanners. Short-term precision was assessed on two Prodigy and two iDXA densitometers. 3D-DXA analyses were performed using 3D-Shaper software version 2.14. Agreement between densitometers was assessed by regression and Bland-Altman analyses. Short-term precision was determined following International Society for Clinical Densitometry recommendations. Strong agreements for 3D-DXA parameters were obtained between devices regardless of the center or the DXA device model (all R2 > 0.96). Bland-Altman analyses demonstrated statistically (p < 0.05), but not clinically, significant difference between both aBMD and 3D-DXA measurements obtained using Prodigy and iDXA scanners. Short-term precision of areal BMD and 3D-DXA parameters was similar between densitometers. This study demonstrated excellent 3D-DXA measurement agreement and similar precision between iDXA and Prodigy densitometers. These data provide evidence that no adjustments are required when using 3D-Shaper software on iDXA or Prodigy instruments. Mini AbstractWe assessed agreement and precision of 3D-DXA parameters between GE Healthcare Prodigy and iDXA densitometers in adults. Strong agreement was observed between devices, and short-term precision was comparable. Findings indicate that no adjustment is needed when using 3D-DXA with GE Healthcare densitometers.

Background: A previous meta-analysis by Singh-Ospina et al. (2017) suggested that Gender affirming hormone treatment (GAHT) does not change transgender mens bone mineral density (BMD) at any clinically relevant site; emerging studies and advances in synthesis methods necessitate an updated evaluation. The primary aim was to update the bone measures of Singh-Ospina et al. (2017), with the secondary aim to expand measures to how GAHT affects musculoskeletal health. Methods: A systematic review with meta-analysis was conducted using studies published in English up to 31 July 2024, identified through three electronic databases (PubMed, Embase, SportDiscus), and final cross-referencing in summer 2025. Primary outcomes were longitudinal changes in femoral neck (FN), lumbar spine (LS), and total hip (TH) bone mineral density (BMD). Secondary outcomes included body composition and muscle strength. Standardised effect sizes (Hedges g) were pooled using the inverse heterogeneity (IVhet) model. Results: GAHT (4 years) was not associated with significant longitudinal changes in FN, LS, or TH BMD. In contrast, substantial anabolic effects were observed, including increases in BMI (g = 0.13), body mass (g = 0.18), fat-free mass (g = 0.59), and muscle strength (g = 0.86). Heterogeneity was high for muscle strength, FN and TH BMD, limiting confidence in pooled estimates. Conversely, changes in LS BMD, BMI, body mass and fat-free mass demonstrated low heterogeneity and greater consistency across studies. Conclusion: Masculinising GAHT does not negatively affect clinically relevant BMD sites while reliably increasing lean mass and muscle strength; however, the evidence base remains methodologically weak and highly variable, particularly for FN and TH. The need for continued clinical monitoring of bone health and muscle function, alongside high-quality longitudinal research incorporating advanced imaging modalities such as HR pQCT is emphasised. Strengthening the evidence base will be essential for clarifying long-term skeletal trajectories as transgender men age. PROSPERO registration: CRD42024573102

BackgroundDexamethasone (DEX) is used in vitro to promote osteogenic differentiation of human bone marrow mesenchymal stromal cells (hBMSCs). In clinical use, however, glucocorticoids induce osteoblast and osteocyte apoptosis while increasing osteoclast survival, leading overall to osteoporosis and high fracture risk. The overall impact of DEX on the differentiation of human progenitor cells remains contradictory and not fully understood, highlighting the need for further investigation using sequencing approaches as in vitro results will naturally influence further translational research. MethodshBMSCs were induced to osteogenic differentiation for 7 days using different concentrations of either DEX or the nonsteroidal glucocorticoid receptor agonist (+)-ZK216348. cDNA library preparation and RNA sequencing (RNAseq) were performed using Oxford Nanopore Technologies. Differentially expressed genes and pathways associated to the transactivation or transrepression activity of DEX were identified. Sequencing results were validated by qPCR, protein analysis, and with a functional assay on peripheral blood mononuclear cells to determine the overall effect of the BMSC supernatant. ResultsHierarchical clustering of RNAseq data identified eight subclusters with shared regulatory patterns. Enrichment analysis revealed that both upregulated and downregulated genes are involved in ossification and extracellular matrix organization pathways. Several pro- and anti-inflammatory genes were differentially regulated. qPCR analysis validated the upregulation of CXCL1, CXCL8, IL18, and COL8A1, while MMP1 and CXCL12 expression decreased in response to DEX. Comparing DEX results with those obtained using (+)-ZK216348 helped distinguish the potential mechanisms regulating the expression of specific genes. Notably, CXCL8 upregulation occurred through transactivation, whereas COL8A1 upregulation is downstream of a transrepressed gene. Further in vitro experiments confirmed that DEX significantly increased CXCL8 expression and IL-8 secretion. However, hPBMC responses indicated no significant pro- or anti-inflammatory effects from hBMSC conditioned medium. ConclusionsIn conclusion, the effects of DEX on the transcriptome of hBMSCs in a pro-osteogenic environment do not fully replicate the acquisition of an osteogenic phenotype. Several genes associated with ossification, extracellular matrix organization, and inflammation were dysregulated. The unique expression patterns of pro-inflammatory cytokines and collagen types warrant further investigation to elucidate their roles in osteogenic differentiation and bone homeostasis.

Individuals with chronic kidney disease (CKD) have higher rates of hip fracture and post-fracture mortality. Although they may develop age-related osteoporosis similar to those without CKD, they may also exhibit CKD-related metabolic bone disease (MBD), characterized by low, high, or mixed turnover at similar levels of bone mineral density (BMD). Because BMD does not provide information about turnover status, clinical decision-making is challenging. This study evaluated the associations between circulating bone-turnover biomarkers and static histomorphometry in patients undergoing hip-fracture surgery. In this cross-sectional study, we enrolled adults with and without CKD, defined as estimated glomerular filtration rate (eGFR) [&le;]60 ml/min/1.73m{superscript 2} (CKD-EPI 2021), undergoing hip-fracture surgery. Blood samples, bone specimens from the femoral head or greater trochanter, and demographic and clinical data were collected at the time of surgery. Plasma biomarkers included -Klotho, bone alkaline phosphatase (BAP), dickkopf-related protein 1 (DKK-1), fibroblast growth factor 23 (FGF23), tartrate-resistant acid phosphatase 5b (TRAP5b), parathyroid hormone (PTH), and sclerostin. Logistic regression models, adjusted for age, gender, eGFR, and osteoporosis, assessed associations with CKD status. Tertiles of osteoblast surface (Ob.S/BS) and eroded surface (ES/BS) were defined in participants without CKD and applied to the full cohort. Multinomial and multivariable linear regression evaluated associations of biomarkers with these histomorphometry parameters. Among 97 enrolled participants (mean age 80 {+/-} 11 years; 67% female), 68% had CKD. Of 75 with complete biomarker and histomorphometry data, 96% demonstrated low bone turnover. CKD was associated with lower trabecular thickness (Tb.Th) and higher osteoid thickness (O.Th), osteoid volume (OV/BV), and osteoid surface (OS/BS), suggesting thinner, largely unmineralized trabeculae. Higher BAP (222.2% difference per doubling; 95% CI 77.2-485.8) and TRAP5b (319.3%; 95% CI 128.3-669.5) were directly associated with Ob.S/BS and ES/BS, whereas sclerostin was inversely associated with ES/BS (-28.9%; 95% CI -44.8 to -7.1). PTH was not associated with bone-turnover measures. These findings suggest that BAP, TRAP5b, and sclerostin may provide useful adjunct information alongside PTH for assessing bone turnover and guiding therapy in patients with and without CKD.

Bone is a dynamic tissue that continuously adapts its structure in response to mechanical loading, an essential process for maintaining skeletal health. However, this adaptive capacity declines with aging, contributing to increased fragility and fracture risk. Developing therapeutic strategies that preserve or restore bone mechanoadaptation in patients with increased bone fragility requires identifying key molecular regulators of this process. We applied spatial transcriptomics (GeoMx, NanoString) to characterize gene expression changes induced by mechanical loading in the murine tibia, focusing on periosteal and bone compartments in regions under tension and compression. Spatial data were validated and cross-compared with previously published bulk RNA-seq and laser-capture microdissection datasets, identifying a set of 12 genes consistently regulated by loading across independent platforms and laboratories. As part of a functional analysis, we selected Slc13a5, a citrate transporter implicated in bone mineralization and metabolism. Conditional deletion of Slc13a5 in osteolineage cells using Osteocalcin-Cre significantly increased the loading-induced mineralizing surface in tensile regions compared with Cre- Slc13a5fl/fl littermates. In addition, Slc13a5 cKO mice exhibited lower resorption around the neutral axis after loading compared to controls. Together, these findings identify Slc13a5 as a regulator of bone adaptation in regions experiencing low mechanical stimulation and suggest it as a potential therapeutic target for conditions characterized by impaired mechanoadaptive responses. This study highlights spatial transcriptomics as a powerful gene discovery framework for bone, enabling identification of novel targets to understand mechanisms and develop therapies. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=181 SRC="FIGDIR/small/711126v1_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@5bf180org.highwire.dtl.DTLVardef@4c33b7org.highwire.dtl.DTLVardef@d75668org.highwire.dtl.DTLVardef@169fa97_HPS_FORMAT_FIGEXP M_FIG C_FIG

Pathologic vertebral fractures are a major complication in metastatic spine disease. However, current clinical scores, such as Spinal Instability Neoplastic Score (SINS), show limited predictive capability, particularly within the indeterminate range where most clinical uncertainty lies. This study aimed to develop and evaluate quantitative computed tomography (qCT)-based subject-specific finite element (SSFE) models to predict vertebral strength in presence of different metastatic lesion types. Twelve ex vivo human spine segments, each containing one metastatic (n=12) and one adjacent control vertebra (n=12), were scanned using qCT and calibrated using a calibration phantom. Homogenised nonlinear finite element models were developed with spatially heterogeneous, isotropic, density-dependent material properties and loaded under uniaxial compression corresponding to 1.9% apparent strain. Ultimate failure load, stiffness, and strain distributions were compared between metastatic and control vertebrae. Predicted failure load ranged from 0.2 kN to 6.2 kN (mean. {+/-} standard deviation: 1.8 {+/-} 1.6 kN metastatic; 1.7 {+/-} 1.5 kN control), with no statistically significant difference between groups (p > 0.05). Normalised failure load varied widely, reflecting lesion-specific mechanical heterogeneity. Lytic lesions generally weakened vertebrae, whereas mixed and blastic lesions occasionally enhanced strength, likely due to localised sclerosis or reactive bone formation. High compressive axial strains (greater than 0.019) were frequently concentrated near the endplates, particularly in lytic vertebrae. qCT-derived bone mineral density strongly correlated with failure load (R{superscript 2} = 0.74-0.77). These findings highlight the complexity of metastatic vertebral mechanics and demonstrate that qCT-based SSFE modelling provides a quantitative framework for assessing fracture risk, complementing conventional imaging-based tools.

Aging is associated with decreased bone formation and bone mass and increased fracture risk. Wnt pathway activation by mechanical loading is a potent strategy to improve bone mass, however, load-induced bone formation is diminished with aging. Neutralizing antibody (Ab) therapies targeting Wnt pathway inhibitors Sclerostin (Scl) and Dickkopf-related protein 1 (Dkk1) have proven successful in preclinical and clinical osteoporotic conditions. We asked whether treatment combining Scl-Ab and Dkk1-Ab can increase load-induced bone formation in a preclinical model of osteoporosis. Aged (22-month) C57BL/6N female mice underwent combination Scl-Ab plus Dkk1-Ab therapy (15 mg/kg each; subcutaneously; 2x/wk; saline control) for 2 weeks, concomitant with a mechanical loading regimen previously shown to induce modest bone formation in tibias of aged mice (-2200 {varepsilon}, 1200 cycles/day, 5 day/wk). Changes in bone morphology and formation were assessed by longitudinal microCT and dynamic histomorphometry, respectively. Molecular indices of bone formation and Wnt pathway activation were assessed by qPCR of cortical bone. Treatment with Scl-Ab plus Dkk1-Ab induced significant improvements in cancellous (BV/TV +50%) and cortical morphology (Ct.Th +25%) in non-loaded limbs of antibody-treated mice vs. vehicle control mice. Importantly, periosteal bone formation rate was 10-fold higher in loaded limbs of antibody versus vehicle treated mice, indicating a synergistic effect. Gene expression analysis showed that antibody treatment and loading synergistically upregulated Wnt1 expression, which may have contributed to the observed synergistic effect on bone formation. These results confirm the potent anabolic effect of combination Scl plus Dkk1 antibody treatment. Moreover, they show that antibody treatment and skeletal loading are more effective at increasing periosteal bone formation in aged mice than either treatment alone. These findings support the concept that combinatorial therapy using dual Scl and Dkk1 antibodies plus weight-bearing exercise may be an effective treatment for age-related osteoporosis.

BackgroundThe effects of dexamethasone during in vitro human osteogenesis present a complex picture. On one side, dexamethasone promotes the osteogenic differentiation of human bone marrow mesenchymal stromal cells (BMSCs) by downregulating SOX9. On the other side, it simultaneously promotes adipogenesis through the upregulation of PPARG. The regulation of SOX9 and PPARG levels appears to be mediated by the transactivation function of the glucocorticoid receptor (GR), suggesting an indirect effect of dexamethasone on SOX9 downregulation. This study aims to determine whether PPAR-{gamma} affects the expression levels of SOX9, as suggested by several studies. MethodsHuman BMSCs were isolated from bone marrow and cultured in different osteogenic induction media containing 10 or 100 nM dexamethasone. Undifferentiated cells were used as control. Cells were treated either with a pharmacological PPAR-{gamma} inhibitor (T0070907) or with a PPARG-targeting siRNA. Differentiation markers or PPAR-{gamma} target genes were analysed by RT-qPCR. Mineral deposition was assessed by Alizarin Red staining. Two-way ANOVA followed by a Sidak multiple comparison test was used to compare the effects of treatments. ResultsPharmacological inhibition of PPAR-{gamma} had a mild effect on the expression of PPAR-{gamma} target genes but hindered adipocyte formation. Neither RUNX2 nor SOX9 expression were affected by T0070907. siRNA treatment successfully downregulated PPARG expression, as well as that of PPAR-{gamma} target genes LPL, LPAR1, and ADIPOQ. Contrary to expectations, RUNX2 was significantly downregulated by the PPARG-siRNA treatment during osteogenic differentiation both in the absence and presence of dexamethasone, while SOX9 levels were downregulated in undifferentiated cells. Overall, Alizarin Red staining analysis showed no change in mineralization levels when PPARG expression or activity was inhibited. ConclusionsUnderstanding how dexamethasone regulates human BMSC differentiation is crucial to refine current in vitro models. These results suggest that PPAR-{gamma} is not involved in SOX9 or RUNX2 repression during in vitro osteogenic differentiation of human cells.

Osteosarcoma is the most common pediatric bone tumor yet has limited treatment options, especially for metastatic cases with a 20% adjusted 5-year survival rate. Current therapies are non-specific, involving primary tumor resection with DNA-damaging chemotherapies like methotrexate, doxorubicin, and cisplatin. Few effective treatment options exist for metastases. Targeting metabolism involving cancers reduced mitochondrial functionality remains underexplored in osteosarcoma. We investigated the therapeutic potential in human osteosarcoma primary and metastatic cell lines of metabolic modulating drugs including metformin, cycloheximide, mitochondrial ETC inhibitors (antimycin A, metformin), dichloroacetate, and imipridones (ONC201, ONC206) on mitochondrial function and cell viability, individually and combined under various nutrient conditions across our lines. Results confirmed osteosarcoma cells are more dependent on glucose than osteoblasts but also require mitochondrial function for survival, highlighting the therapeutic potential of metabolic pathways. Osteosarcoma cell viability was reduced when any metabolic drug treatment was combined with conditions forcing reliance on mitochondrial OXPHOS capacity. Combination metabolic therapies, particularly ONC201/ONC206/metformin in 143B cells, and to a lesser extent DCA and ONC201 with either ONC206 or antimycin A, showed enhanced cytotoxicity compared to single agents, with a good therapeutic index based on minimal toxicity to normal osteoblast cells. The degree of effectiveness varied across cell lines, underscoring the importance of personalized treatment strategies. RNA-Seq transcriptome analysis revealed that effective nutrient and metabolic drug treatments triggered widespread regulatory changes in osteosarcoma cells involving increased translation/splicing with decreased mitochondrial processes such as cholesterol biosynthesis. These results demonstrate the utility of developing combined metabolic and chemotherapeutic treatments for osteosarcoma.

The cartilaginous growth plate (GP) is responsible for all bone elongation during post-natal growth yet must simultaneously contribute to mechanical epiphyseal stability for articulation. How the GP balances these dual functions across the bone-cartilage-bone epiphyseal interface during complex load-growth transitions is not defined. Herein, we examine regulation and mechanobiology of GP bridges - mineralised trans-physeal GP structures - to explore whether they serve these dual GP functions. We have determined the effects of age and sex, short- and long-term joint loading and several established and new osteotropic pharmacological agents on mouse tibial GP bridge number and areal density using micro-computed tomography. We also explored temporal formation and progression of GP bridges by serial in vivo scanning and we imaged epiphyseal load-transfer in young and mature mice in situ via synchrotron X-ray computed tomography (sCT) of intact joints under physiologically oriented load. Our utilisation of digital volume correlation revealed regional 3D load-induced strain inhomogeneities in the GP that are synchronised to bridge location and this was substantiated using finite element modelling. Furthermore, direct micro- and sCT examinations showed that bridges consistently contain a singular epiphyseal/metaphyseal discontinuity which appear to serve a novel mechanical base isolation role to minimise shear stress across the GP. Our data indicate that bridges are regulatable, dynamic structures that synchronise GP strains and exhibit sensitivity to local joint mechanics. We highlight that trans-physeal bridges may contribute to longitudinal bone growth cessation whilst simultaneously stabilising the epiphysis by absorbing compression and shear strains.

To optimize osteoporosis therapy with the parathyroid hormone fragment teriparatide (PTH1-34), we sought to determine whether strontium (Sr) could potentiate the bone anabolic action of intermittent PTH1-34 in ovariectomized rats. Female rats were either Sham-operated or ovariectomized (Ovx) at 6 months of age. Eight weeks after surgery, Ovx rats received either vehicle solutions, 625 mg/kg/day Sr (5 days per week), 8 {micro}g/kg/day PTH1-34 (5 days per week), or the combined treatments for 8 weeks. PTH1-34 reversed Ovx-induced deterioration of trabecular microarchitecture, apparent volumetric bone mineral density (vBMD), and strength, whereas Sr alone increased tissue-level vBMD without significantly affecting trabecular bone mass. Co-treatment with Sr and PTH1-34 further increased trabecular thickness, apparent and tissue-level vBMD, bone material properties (force and working energy), and trabecular bone strength compared with PTH1-34 alone. In cortical bone, PTH1-34 increased bone volume, cortical thickness, and apparent vBMD, while co-treatment further enhanced cortical thickness and apparent vBMD, maintained the Sr-induced increase in tissue-level vBMD, and significantly improved bone strength. In primary osteoblast cultures, Sr and PTH1-34, administered either alone or in combination, increased Rankl and decreased Opg expression, consistent with the elevated urinary levels of the bone resorption marker deoxypyridinoline in vivo. Sr or PTH1-34 alone stimulated Igf1 and Alpl expression, whereas co-stimulation further enhanced these osteogenic markers. In conclusion, combining Sr with PTH1-34 integrates the osteoanabolic effects of PTH1-34 on bone mass with the mineral-level effects of Sr on bone material properties, leading to synergistic stimulation of bone formation and superior improvements in bone quality and strength.

BackgroundLongitudinal bone growth occurs via the process of endochondral ossification, involving a complex interplay of chondrocyte proliferation, differentiation, and matrix remodelling. As with all mammalian cells, chondrocytes require dynamin for mitochondrial fission, to shuttle vesicles from the Golgi apparatus, and for both clathrin- and caveolin-mediated endocytosis. Here, we aimed to test the functions of dynamin on bone growth. To do so, we applied dynasore - a small molecule that is a reversible dynamin inhibitor - to mouse metatarsal bones cultured ex vivo. We assessed gross changes using bone length measurements and histomorphometry, and combined this with EdU detection, immunostaining, super-resolution microscopy and transmission electron microscopy. ResultsDynasore induced a dose-dependent hormetic effect on bone elongation: while high concentrations (220 {micro}M) impaired growth and abolished chondrocyte proliferation, low-dose treatment (40 {micro}M) significantly increased longitudinal bone growth. Histological analysis demonstrated that low dose dynasore augmented epiphyseal cartilage expansion and matrix accumulation, particularly within the resting and proliferative zones, while reducing chondrocyte proliferation. Immunostaining indicated that 40 {micro}M dynasore preserved collagen type X synthesis, activated mTORC1 signalling, and blocked autophagy, based on SQSTM1 accumulation. Low dose dynasore treatment expanded the thickness of the filamentous actin layer at the plasma membrane and deepened collagen fiber-containing endocytic pits, indicating that impaired cartilage remodelling was associated with growth-associated matrix accumulation. ConclusionsThis study reveals that dynasore exerts hormetic effects on growth plate chondrocytes, wherein low doses stimulate bone elongation, and high doses impair chondrocyte function.

BackgroundComputational modeling is a tool being deployed for orthopaedic solutions but its use in the hand and wrist remains limited. This work used a model to simulate a clinically relevant provocative scaphoid shift maneuver (SSM) with different levels of scapholunate interosseous ligament (SLIL) injuries to observe the effect on different metrics. MethodsA personalized model simulated the full SSM motion cycle from ulnar deviation with extension to radial deviation with flexion informed by the participants motion obtained from dynamic computed tomography. Models repeated the SSM under different levels of SLIL injury and reported changes in joint kinematics, contact mechanics, and ligament forces. ResultsThe fully injured model increased scaphoid dorsal translation, flexion, and radial deviation compared to the intact condition and caused a subluxation of the scaphoid. Radioscaphoid contact areas were approximately 200% greater in the fully injured model compared with all others and the fully injured model was the only condition where contact force decreased across the motion cycle. Ligament forces in the intact condition were on average 33.0 N and 54.2 N for the volar and dorsal SLIL, respectively. Lastly, the long radiolunate, an extrinsic stabilizer, had forces that increased following SLIL injury. ConclusionsComputational models can successfully recreate clinically observed behaviors of an SSM, including scaphoid subluxation, while providing new insights via quantification of contact mechanics and ligament forces. Contact mechanics metrics may be important for understanding the long-term progression of untreated SLIL injuries to osteoarthritis. Additionally, ligament force metrics may explain the progression of SLIL injuries from volar SLIL to dorsal SLIL and highlight the importance of repairing extrinsic stabilizers of the joint, due to increased force sharing following SLIL injury. This work provides a pathway to future studies investigating the effects of SLIL injury and repair, both acutely and chronically.

BackgroundBone formation during development and repair is divergently modulated by osteoblast (OB)-derived vascular endothelial growth factor (VEGF) which drives the skeletal sexual dimorphism of the bone vasculature. While the extracellular matrix (ECM) provides both structural and instructive cues to developing vasculature, the contributions of the bone matrix to this skeletal vascular dimorphism in bone remains undefined at the cellular level. MethodsPrimary OBs were isolated from neonatal female and male C57BL/6 long bones and cultured under basal or osteogenic conditions. ECM composition was quantified by Raman spectroscopy. Primary murine bone marrow endothelial cells (BMECs) were seeded directly onto established OB layers and maintained in heterotypic cocultures to assess contact-mediated effects of OB ECM on BMEC survival and expansion. OB-conditioned media (CM) was used to evaluate soluble-factor contributions, with VEGF-A concentration quantified by ELISA. ResultsRaman spectroscopy, on individual OBs from monotypic cultures, revealed sexually dimorphic ECM signatures that were independent of cellular growth profiles. Female OB matrices were enriched with type I collagen-specific proline and hydroxyproline and octacalcium phosphate with enhanced collagen intra-strand stability consistent with a matrix-dominant signature. Male OB matrices exhibited relatively lower type I collagen content and higher carbonated apatite resulting in an elevated mineral-to-matrix ratio indicative of advanced mineral maturation. After 24-hours of heterotypic culture of BMECs with OBs, BMEC numbers were 1.39-fold higher when in contact with male OBs. CM treatment of BMECs did not recapitulate these effects despite higher VEGF-A release from male OBs. ConclusionsSex differences in OB ECM are linked to divergent, contact-dependent regulation of BMEC behaviour. These findings suggest that differences in matrix maturation stat contribute to the sex-specific regulation of the skeletal vascular niche. Elucidating the mechanisms that regulate sex-specific OB-ECM production may reveal new therapeutic targets for selectively modulating pathological skeletal angiogenesis in men and women. SummaryBone is a sexually dimorphic organ, with men and women differing in bone size, strength and risk of fracture. The skeletal vasculature is essential for bone growth and repair, with bone forming osteoblast (OB) cells influencing blood vessel development through the skeletal extracellular matrix (ECM). Although the interactions between OB and vascular cells are crucial for lifelong skeletal health, it is not yet known whether sex differences in bone structure between men and women arise from differences in OB activity, or whether this divergence is driven by sex differences in blood vessel growth. Here, we show that male and female mouse OBs deposit distinct ECMs that differentially influence vascular endothelial cell behaviour. Female OBs produce a collagen-rich matrix with low mineral content. In contrast, male OB matrices contain less collagen and more mineral while releasing elevated levels of blood vessel promoting VEGF-A than females. When placed directly onto these OBs, vascular cell growth was greater when in contact with male than female OBs. Notably, this sex-dependent effect requires direct contact between both cell types and was not reproduced by exposure to OB-derived substances alone. These findings identify a cellular mechanism by which sex differences in OB matrix composition influences vascular cell behaviour in bone. Understanding how OB-vascular interactions differ by sex may help explain variation in bone health, healing capacity and disease risk between men and women. Further, our approach may support the discovery of new therapeutic targets that support bone growth and repair while targeting abnormal blood vessel growth in a sex-specific manner. HighlightsO_LIPrimary OBs from male and female C57BL/6 mouse long bones synthesise compositionally distinct ECMs. C_LIO_LIFemale OB matrices are type I collagen-rich and enriched with octacalcium phosphate, whereas male OB matrices contain less type I collagen and higher levels of carbonated apatite. C_LIO_LIBone marrow-derived endothelial cell (BMEC) growth is enhanced in heterotypic cocultures with male, but not female, OBs after 24 hours. C_LIO_LIMale OBs release higher levels of the pro-angiogenic factor VEGF-A than female OBs. C_LIO_LIThe sex-specific effects of the OB ECM on BMECs is contact-dependent and are not reproduced by treatment with OB-derived conditioned media. C_LI

RNF43 and ZNRF3 are transmembrane E3 ubiquitin ligases that negatively regulate Wnt signaling by promoting ubiquitination and degradation of Frizzled receptors. Loss of either gene enhances Wnt/{beta}-catenin signaling and has been linked to tumorigenesis. Wnt signaling is a key regulator of skeletal development and bone homeostasis, and pharmacologic activation of this pathway is an established therapy for osteoporosis. In Xenopus laevis, simultaneous disruption of rnf43 and znrf3 results in supernumerary limb formation; however, their roles in mammalian limb development and skeletal maintenance remain unclear. We demonstrate that mice homozygous for null alleles of both Rnf43 and Znrf3 do not develop supernumerary limbs. Because activation of Wnt/{beta}-catenin signaling in osteoblasts increases bone mass, we hypothesized that osteoblast-specific deletion of Rnf43 and/or Znrf3 would produce a high-bone-mass phenotype. Instead, osteoblast-specific loss of Znrf3 resulted in age-and sex-dependent reductions in trabecular bone mass, characterized by decreased bone mineral density and bone volume fraction, reduced trabecular number, and increased trabecular separation. Cortical bone exhibited increased cross-sectional size with reduced cortical area fraction and altered structural properties, while tissue mineral density was unchanged. In contrast, deletion of Rnf43 had minimal skeletal effects, and combined deletion of both genes did not exacerbate the phenotype observed with loss of Znrf3 alone. These findings identify Znrf3 as the dominant functional paralog regulating bone architecture in mature osteoblasts and underscore the importance of evaluating skeletal geometry when modulating upstream Wnt regulators.

Osteoblasts generate bone by secreting collagen and mineralizing it in response to various signaling cues. We have previously shown that the majority of ATP generated by differentiated osteoblasts in response to glucose is through glycolysis in contrast to undifferentiated cells that are more dependent on oxidative phosphorylation. To confirm our previous findings, metabolomics was performed for unlabeled polar metabolites, revealing elevated glycolytic metabolites at the later stages of differentiation. Krebs cycle (TCA cycle) metabolites were also changed confirming metabolic rerouting with differentiation. We hypothesized that an increase in mitophagy shifts ATP generation towards glycolysis resulting in the observed bioenergetic and metabolic changes. Utilizing calvarial osteoblasts isolated from a mitophagy reporter mouse model (MitoQC), an increase in mitophagy and the mitophagy receptor, Bnip3, was observed with osteoblast differentiation. KD of Bnip3 in osteoblasts inhibited differentiation and mineralization arising from impaired mitochondrial function. In vivo, male Bnip3 null mice exhibited a significant decrease in osteoblast numbers resulting in lower bone mass. Mechanistically we identified decreased fusion and increased fission factors, impaired stress signaling and increased proapoptotic factors in the absence of Bnip3. These data demonstrate for the first time that BNIP3 expression and mitophagy during osteoblast differentiation are necessary for relieving mitochondrial stress to maintain optimal bone mass.

Purpose To determine whether clinically significant weight loss (>5% of body weight) is associated with slower 2-year knee cartilage degeneration in individuals with and without radiographic osteoarthritis. This study used a cartilage structural assessment score derived from the spatial distribution of cartilage thickness, referred to as the Cartilage Thickness Score (CTh-Score). It is based on cartilage thickness patterns and scores the cartilage between 0 and 100, with higher scores indicating greater severity. Methods We conducted a retrospective matched cohort study within the Osteoarthritis Initiative. High-resolution cartilage thickness maps (CTh-Maps), along with their corresponding CTh-Score, were extracted from a public repository. Participants with complete radiographic and MRI data at baseline and 24 months were stratified by baseline Kellgren-Lawrence (KL) grade into non-radiographic OA (non-ROA; KL<2) and radiographic OA (ROA; KL>=2). Within strata, cases (>5% 2-year weight loss) were propensity score-matched 1:2 to weight-stable controls on age, sex, height, weight, KL grade, joint space width (JSW), KOOS Pain, baseline CTh-Score, and mean cartilage thickness in the medial and lateral femoral and tibial compartments. The primary outcome was 2-year change (delta) in CTh-Score, where higher values indicate worsening. Secondary outcomes were delta JSW, delta regional mean cartilage thickness, and delta KOOS Pain. Non-parametric tests were used. Results We included 164 cases and 328 controls in non-ROA, and 266 cases and 532 controls in ROA. Median (interquartile range) weight loss was -6.10 kg (-8.90, -4.70) versus +0.30 kg (-1.30, 2.20) in non-ROA and -6.80 kg (-9.10, -5.02) versus +0.40 kg (-1.40, 2.82) in ROA (both p<0.001). Weight loss was associated with significantly smaller 2-year increases in CTh-Score: in non-ROA, median 1.58 (0.61, 6.53) vs 3.14 (0.44, 7.12) (p=0.005); in ROA, median 1.69 (0.97, 6.71) vs 2.90 (0.19, 7.38) (p=0.004). No between-group differences were detected for delta JSW or delta regional mean cartilage thickness in any of the 4 ROIs. A trend toward greater KOOS Pain improvement with weight loss was observed in ROA: 2.75 (-3.35, 13.40) vs 0.00 (-5.60, 8.40) (p=0.06). Conclusions Achieving >5% weight loss over 2 years is associated with approximately 50% lower progression in median cartilage degeneration, as assessed by CTh-Score, in both non-ROA and ROA. No change was observed with conventional structural metrics. These findings support weight management as a structural disease-modifying strategy and highlight CTh-Score as a sensitive endpoint.

BackgroundWe previously reported that extracellular vesicles derived from osteoblastic, osteoclastic, and mixed prostate cancer (PCa) cells promote osteoclast differentiation and inhibit osteoblast differentiation via the transfer of miR-92a-1-5p. However, at the same time, osteoblastic miRNAs also exist in PCa extracellular vesicles. In the present study, we focused on discovering (1) the roles of miR-375 and miR-148a-3p delivered by PCa extracellular vesicles in bone homeostasis and bone metastasis, and (2) an explanation for the co-existence of osteoblastic miRNAs and osteoclastic miRNAs in prostate cancer extracellular vesicles. MethodsConditional medium, miRNA mimics, and miRNAs overexpressed lentiviruses were employed to discover the roles of miR-375 and miR-148a-3p delivered by PCa extracellular vesicles in bone homeostasis and tumor growth. Target gene prediction and siRNAs were employed to discover the target gene(s) for miR-375 and miR-148a-3p. Droplet digital PCR (ddPCR) of the PCa extracellular vesicle miRNAs were utilized to evaluate miRNA expression at different metastatic phases. ResultsConditional medium from prostate cancer cell culture promoted osteoblast differentiation, as confirmed by ALP staining and Alizarin red staining. miR-375 and miR-148a-3p promoted osteoblast differentiation in vitro by reducing KLF4 expression, associated with increased osteoblast function as shown by ALP staining, Alizarin red staining, and Alp mRNA expression. In vivo, miR-375 and miR-148a-3p overexpressing MDA PCa 2b cells promoted osteoblastogenesis and tumor growth, which were confirmed by micro computed tomography and in vivo imaging. siRNA targeting KLF4 similarly enhanced osteoblast function and tumor cell proliferation. Based on the miRNA ddPCR data for PCa extracellular vesicles, osteoclastic and osteoblastic miRNAs existed in different bone metastatic phases. ConclusionsThese findings suggest that miR-375 and miR-148a-3p delivered by PCa extracellular vesicles regulate osteoblast function and tumor growth via targeting KLF4. Osteoclastic miR-92a-1-5p is active during the early phases of bone metastasis, while osteoblastic miR-375 and miR-148a-3p function during the late phases.