Volumetric bone density, microarchitecture, and strength measures using HR-pQCT are valuable measures of bone health in pediatrics. Our cross-sectional study evaluated bone measure reproducibility in pediatric participants using repeat HR-pQCT (XtremeCT II, Scanco Medical) scans of non-dominant distal tibia and radius of 30 healthy children and adolescents (7-17 yr, 47% female) by 2 technicians. Additionally, we examined HR-pQCT and micro-CT of 26 cadaveric distal tibia specimens to evaluate agreement between the modalities. All HR-pQCT scans were analyzed using manufacturer-provided software (Image Processing Language, Scanco Medical) and a fully automated, previously validated, in-house algorithm, offering measures of bone microstructure (eg, trabecular plate-rod distribution, transverse trabeculae, trabecular bone strength) currently unavailable in the manufacturer-provided software. Root-mean-squared percent coefficient of variation (RMS-%CV) assessed precision and least significant change. Intraclass correlation coefficients (ICCs) using absolute-agreement, 2-way random-effects models assessed reliability. Pearson’s correlation coefficients and ICC assessed linear relationships and agreements between HR-pQCT and micro-CT, respectively. In children and adolescents, RMS-%CV of HR-pQCT-derived trabecular bone measures at distal tibia and radius ranged from 0.8-4.4 to 0.8-6.0, respectively. Most cortical bone results were in a similar range. Both computational algorithms showed ICC > 0.90. RMS-%CV and least significant change values were lower for tibia than radius. ICCs were lower for cortical than trabecular outcomes. Most cadaveric results showed ICC > 0.83, other than trabecular bone thickness and modulus (ICC = 0.7). Pearson’s r (>0.86) suggested strong correlations for almost all parameters. HR-pQCT and micro-CT results using in-house algorithm did not differ significantly, while manufacturer-provided algorithm results showed lower yet still moderate reliability (ICC > 0.55). Reliability of the second-generation HR-pQCT in pediatric participants is excellent—better in tibia vs radius. Our results support the high reproducibility of XtremeCT II scans and thus the use of this clinical imaging modality in studies of pediatric bone health.

This study aimed to evaluate and compare the efficacy and safety of romosozumab vs denosumab in hemodialysis (HD) patients with osteoporosis. A 12-mo observational study was conducted involving HD patients with osteoporosis at a single dialysis center. The study compared outcomes between 2 treatment groups: romosozumab (210 mg monthly, n = 21) and denosumab (60 mg every 6 mo, n = 24). Treatment allocation was based on cardiovascular history. Changes in bone mineral density (BMD), bone turnover markers (P1NP, TRACP-5b, and intact PTH), complications, and fractures were assessed. Serum calcium levels were monitored weekly. After 12 mo, patients receiving romosozumab showed significantly greater improvements in lumbar spine (LS) BMD compared to denosumab (14.6% vs 6.3%, p < .05). Both treatments demonstrated comparable increases in femoral neck (FN) BMD (4.3% vs 6.0%, p = .41). Bone turnover markers showed distinct patterns between groups, with romosozumab producing more pronounced early effects. P1NP levels increased significantly in the romosozumab group at 6 mo (+41.2%) before declining toward baseline, while showing sustained suppression in the denosumab group. The incidence of osteoporotic fractures was one case per group (vertebral fracture in romosozumab group, hip fracture in denosumab group). One case of injection site reactions was observed in the romosozumab group. Mean serum calcium levels remained stable in both groups throughout the study period. The treatment of romosozumab appears to be more effective than denosumab for improving BMD in HD patients with osteoporosis, particularly at the LS. Both treatment approaches demonstrated acceptable safety profiles, though careful monitoring of calcium levels and cardiovascular status is recommended.

Experimental studies suggest an association between sleep disturbances and osteoporosis risk, but epidemiological data remain inconclusive. This study investigated associations and possible causality between 4 sleep traits and osteoporosis risk, as well as BMD, in a large population-based cohort. We analyzed 402 533 UK Biobank participants with no history of osteoporosis at baseline (44.8% men, mean age 56.6 yr [SD 8.1], median follow-up 13.1 [IQR 12.8-14.4] yr). Multivariable-adjusted regression analyses assessed the associations between self-reported sleep traits at baseline and osteoporosis incidence, and BMD T-scores at the femoral neck, lumbar spine and radius. Two-sample Mendelian randomization (MR) was employed to provide evidence of potential causality. Self-reported short (<7 h) and long (>8 h) sleep durations, insomnia symptoms, daytime dozing, and evening chronotype were all associated with increased osteoporosis incidence. Conversely, no associations were observed between sleep traits and T-scores, except that an evening chronotype was associated with lower femoral neck T-score. Having a greater number of poor sleep behaviors was associated with increased osteoporosis risk and lower T-scores. MR did not support a causal relationship between sleep traits and osteoporosis risk or BMD. Since all sleep behaviors are associated with osteoporosis risk, assessing sleep patterns could be valuable to identify individuals-at-risk. However, the absence of causal evidence and limited associations with BMD suggest that sleep disturbances do not influence bone remodeling directly. Instead, the interaction between sleep and osteoporosis may involve unidentified mechanisms requiring further investigation.

A 16-yr-old male with a genetically undiagnosed neurodevelopmental disorder (NDD) was admitted to our outpatient clinic for skeletal assessment. DXA and HR-pQCT showed a severely reduced BMD and a pronounced reduction of trabecular and cortical bone mass. Lateral vertebral assessment identified multiple previously unrecognized vertebral fractures of the thoracic and lumbar spine. Laboratory tests indicated an activated bone turnover, which was confirmed by an increased number of osteoclasts and osteoblasts in an undecalcified tibia biopsy of the patient. Treatment of the severe osteoporosis was initiated with neridronate. Trio exome sequencing in the patient and healthy parents did not uncover a genetic cause of the disease. Importantly, however, targeted sequencing of the RNU4-2 gene, which encodes the U4 small nuclear RNA (a major component of the splicing machinery), identified a heterozygous causative variant in the patient. This led to the molecular diagnosis of ReNU syndrome. RNU4-2 pathogenic variants underlie a NDD with multisystemic involvement, including skeletal abnormalities. Therefore, this case not only underlines the relevance of osteologic assessment and therapy in individuals with NDDs, but also highlights the necessity of future research efforts to elucidate the bone pathologies in ReNU syndrome.

Stromal cells are critical regulators of hematopoietic stem/progenitor cells and skeletal homeostasis. Although precise systems for functional analysis are critical to investigate mechanistically bone and bone marrow (BM)-derived stromal cells, the establishment of reproducible, highly enriched ex vivo methods for stromal cell isolation, culture and evaluation have been challenging, leading to inconsistent data on stromal cell function. In this work, we carefully tested ex vivo culture of murine stromal cells from BM and bone and discovered abundant and persistent contamination of monocytes and macrophages. We succeeded in establishing highly enriched ex vivo culture system for stromal cells by eliminating persistent monocytes and macrophages using selection against the immunological markers F4/80, Ly6C, and CD45. Transcriptional and functional assays of enriched stromal cell culture revealed differential characteristics of stromal cells from different origins, a dormant signature for bone-derived cells and a highly proliferative progenitor-like signature for BM-derived cells. Monocyte and macrophage contamination reduced signatures of immature stromal cells such as expression levels of SOX9 and CD140a as well as the cells' ability to support hematopoietic stem and progenitor cells based on our growth factor-free co-culture system of hematopoietic cells and stromal cells followed by in vivo functional assays. The inhibitory effects of macrophages on stromal cells may be explained by their potent production of inflammatory cytokines such as CXCL2, CCL3, and complement factor (C1q) confirmed by protein immunoassay of culture supernatant, as well as the differential contribution of pre-osteoblasts to the stromal cell population. This study highlights the functional diversity of stromal cells depending on the microenvironment of origin while addressing a critical limitation of murine ex vivo systems. Our robust culture system enables the study of isolated stromal cells function as well as the impact of stromal cells-macrophage crosstalk.

Fibrodysplasia ossificans progressiva (FOP) is a genetic disease characterized by extraskeletal heterotopic ossification (HO). The underlying mechanism is the aberrant activation of bone morphogenetic protein (BMP) signaling caused by a point mutation in the ACVR1 gene. Although FOP is an ultra-rare disease, its symptoms severely impair patients' daily activities and quality of life. Furthermore, the HO is also observed in broader clinical contexts, including major surgeries and trauma, highlighting the significance of its study. We have previously reported that rapamycin suppressed Activin-A-triggered progression of cartilage formation in FOP mice. We recently found that the ACVR2B-Fc fusion protein produced by mesenchymal stem/stromal cells derived from induced pluripotent stem cells (iMSCs) attenuates BMP signaling activated by Activin-A and BMP-9 in FOP patient-derived iMSCs. Transplantation of ACVR2B-Fc-producing iMSCs (iMSC2B-Fc/Luci) reduces primary HO in FOP mice. In this study, we found that intraperitoneal administration of rapamycin reduced primary HO in a dose-dependent manner in FOP-ACVR1R206H transgenic mice. A low concentration of rapamycin (0.3mg/kg, 5 times/wk) efficiently suppressed chondrogenesis. The combination of iMSC2B-Fc/Luci transplantation with low concentration of rapamycin significantly reduced primary and recurrent HO. Rapamycin improved cell survival in transplanted iMSC2B-Fc/Luci cells by attenuating chemokine secretion, likely resulting in improved ACVR2B-Fc fusion protein production. Our results suggest that combining stem cell therapy and rapamycin can reduce primary HO and surgery-induced HO.

Hypercementosis has been previously reported in mice lacking progressive ankylosis protein (Ank KO mice, or Ank, KO - knockout, WT - wildtype) due to decreased levels of the mineralization inhibitor inorganic pyrophosphate. However, the impact of hypercementosis on alveolar bone remodeling and periodontal ligament (PDL) maintenance from orthodontic forces during orthodontic tooth movement (OTM) remains unclear. To investigate the roles of ANK protein on tooth movement, PDL maintenance, alveolar bone remodeling, and tooth root resorption, we performed a split-mouth model of OTM induced by a closed-coil spring stretched between the maxillary first molar and maxillary incisors in Ank KO and WT mice (including both males and females). Micro-computed tomographic analysis revealed a 36.6% reduction in OTM in Ank KO mice compared with WT mice, although OTM-induced thickening of PDL was found to be similar in both groups. While reduced tissue mineral density (TMD) of the alveolar bone was observed in WT mice, TMD in Ank KO mice was maintained. Loss of Ank leads to wider roots with thicker cementum on the untreated, contralateral side, whereas a significant increase in OTM-induced root resorption was observed on the lateral tension side. Histologic analysis of root resorption confirmed these data and showed increased resorption lacunae located prevalently in the OTM tooth root cementum of Ank KO mice. Using a quantitative PCR array of bone-associated markers to interrogate total RNA harvested from PDL tissues along the root surface, we found alterations in gene expression from OTM in both WT and Ank KO mice, which included genes involved in bone remodeling, calciotropic hormones and receptors, cytokines, growth factors, and receptors. Our findings advance the understanding of the role of Ank in regulating mineralization in the periodontium as well as factors involved in root resorption.

Tumor-induced osteomalacia (TIO) is a rare disorder characterized by impaired bone mineralization due to phosphate wasting. Long-term changes in BMD and microarchitecture after surgical cure or medical therapy in TIO are not well understood. This study describes changes in BMD, microarchitecture, and bone strength in patients with TIO following surgical cure or medical therapy. A prospective cohort study included adults diagnosed with TIO from May 2018 to 2024, categorized into those with surgical cure and those on medical therapy. Follow-up assessments were classified as early (median 8 mo), intermediate (median 17 mo), and long-term (median 26 mo). Fifteen patients were included: seven achieved surgical cure, and eight remained on medical therapy. Lumbar spine BMD increased by +19% at early, +27% at intermediate, and +15% at long-term follow-up. Total hip BMD increased by +31%, +36%, and +31% at early, intermediate, and long-term assessments, respectively. All patients achieved a normal lumbar spine BMD, while 91% attained a normal total hip BMD. At the distal tibia, substantial increases in bone microarchitecture parameters—cortical area (Ct.Ar), cortical volumetric density (Ct.vBMD), and cortical thickness (Ct.Th)—were observed. Notably, Ct.Th improved to levels comparable to healthy controls. Bone strength improved by 13% but was not statistically significant, probably due to the small sample size. At the distal radius, most parameters remained stable. Patients with surgical cure showed more rapid and substantial improvements in BMD and cortical microarchitecture than non-cured patients, but these differences did not reach statistical significance. Overall, bone recovery in TIO is gradual, with gains in spine and hip BMD and significant improvements in tibial cortical parameters. However, some aspects of bone microarchitecture remained below control levels, underscoring the need for ongoing monitoring and individualized management strategies.

Dysregulation of Kirsten rat sarcoma virus (KRAS) plays crucial roles in many tumors. It is reported that KRAS could promote proliferation of osteosarcoma (OS) cells. Nonetheless, the contribution of KRAS to the invasion and spread of OS is still not well understood. This study aimed to investigate KRAS-driven metastasis and the mechanisms behind it in human OS. Tissue microarrays were utilized to assess KRAS expression and its relationship with clinicopathological characteristics. The migratory and invasive abilities of OS cells were evaluated through wound-healing assays and transwell analysis. Furthermore, the regulatory mechanisms of KRAS in human OS were analyzed using RNA sequencing, tandem mass tags assays, multiple immunofluorescence assays, micro-CT, and bioluminescence imaging. In vivo experiments were conducted using established lung metastatic models. Our data showed that downregulation of KRAS in human OS cells could inhibit cell migration and invasion in vitro and in vivo (tumor metastasis model by tail vein injection in BALB/c nude mice). We identify IL-17A, a crucial marker of IL-17 signal pathway, as a downstream target of KRAS. The reduction of KRAS may suppress matrix metalloproteinase (MMP1), MMP3, and MMP9, which are recognized as proteins associated with tumor metastasis, through a mechanism dependent on IL-17 signaling. In summary, these findings indicate that KRAS could serve as a potential biomarker for therapeutic strategies in human OS. Mechanistically, our data revealed that KRAS knockdown affects tumor metastasis by inactivating IL-17 signal pathway via IL-17A-dependent manner.