Journal of Bone and Mineral Research最新文献

Achondroplasia (ACH), the most common skeletal dysplasia in humans, is caused by gain-of-function mutations in fibroblast growth factor receptor 3 (FGFR3). Activation of FGFR3 and its downstream signaling pathways lead to disturbed chondrogenesis in ACH. Nevertheless, the pathogenic mechanism of ACH has yet not been fully elucidated. Previous studies have indicated that FGF and BMP signaling may have opposing actions on the growth plate development. To clarify the crosstalk between FGFR3 and activin receptor-like kinase 3 (ALK3) signaling in ACH, we generated caALK3col2-ACH mice expressing a constitutively active mutant of ALK3 in the chondrocytes of mice with ACH resulting from a Gly369Cys mutation in FGFR3. Unexpectedly, these mice exhibited a more severe chondrodysplasia phenotype than ACH mice, as evidenced by a greater decrease in chondrocyte proliferation and impaired hypertrophy of chondrocytes in the growth plates. These changes were correlated with an increased expression of p21 and activation of ERK/MAPK pathway. This study provides an in vivo genetic demonstration of the imbalanced interaction between the FGFR3 and ALK3 signaling pathways in the growth plate of caALK3col2-ACH mice, suggesting that the ERK/MAPK pathway play an essential role in growth plate chondrogenesis.

The polygenic risk score genetic quantitative ultrasound speed of sound (gSOS) was developed using machine learning algorithms in adults of European ancestry and associates with reduced odds of fracture in adults. We aimed to determine if gSOS was associated with bone health in children. Two observational studies of children were evaluated: (1) children enrolled in the Bone Mineral Density in Childhood Study (BMDCS) with genetic data (N = 1727) and (2) children with genetic data for research at the Children's Hospital of Philadelphia (CHOP; N = 10 301). Genetic variants were used to calculate gSOS and genetic ancestry. For the BMDCS, puberty stage, dietary calcium, physical activity, and fracture accumulation (none or ≥1 fracture) were self-reported, height and weight were measured and BMI calculated. Areal BMD (aBMD) of the lumbar spine, hip, radius, and whole body were assessed by DXA and expressed as Z-scores. The CHOP study paired genetic data with documentation of fracture in the electronic health record (EHR). Genetic quantitative ultrasound speed of sound associated with higher aBMD Z-scores across 7 skeletal sites [eg, a 1 SD increase in gSOS associated with 0.17 (95% CI: 0.10-0.24) higher LS aBMD Z-score]. These associations were consistent for males and females, age, puberty stage, and lifestyle factors, and most consistent among children of European genetic ancestry. A 1 SD increase in gSOS associated with 24% reduced likelihood of self-reported fracture in the BMDCS (OR = 0.76, 95% CI: 0.66, 0.88) and a 12% reduced likelihood of a recorded fracture in the CHOP EHR (OR = 0.88; 95% CI: 0.82, 0.95). No sex or genetic ancestry differences were found. A higher gSOS score associated with higher aBMD at multiple skeletal sites and reduced odds of fracture in two independent pediatric samples. This genetic tool may have clinical utility to help enhance bone health in early life and protect against fracture across the lifespan.

Dentin, the primary hard tissue of teeth, is formed through the differentiation of dental mesenchymal progenitor cells into odontoblasts. Primary cilia, essential organelles on the surface of mesenchymal cell populations, are dynamically regulated in length and play a crucial role in dentinogenesis. However, the specific role of primary cilia length stability, in the regulation of cell function and dentin formation and repair, remains to be fully elucidated. Through spatial transcriptome analysis combined with mouse molar development studies, we found that ciliary membrane gene Arl13b specifically maintains cilia length homeostasis by suppressing cilia decapitation. ARL13B deficiency, which results in cilia shortening, would interfere with the differentiation fate of dental mesenchymal progenitor cells. Mechanistically, the abnormally shortened cilia disrupt intraflagellar transport-mediated SHH signaling within cilia, thereby inhibiting the odontoblastic differentiation, and ultimately affecting tertiary dentin formation during injury repair. These findings indicate that the maintenance of primary cilia length homeostasis is crucial for the repair and regeneration of dentin.

Current guidelines are split on the role that imaging has in the clinical assessment of osteoarthritis, yet clinical computed tomography (CT) imaging has now revealed how a 3D approach can improve prediction of total hip replacement (THR) over 2D measures alone. We applied 2D grading and measurement along with 3D cortical bone mapping to ordinary clinical CT imaging of the pelvis in a cohort of healthy older people, aiming to discover which of these features had clinical utility in predicting total hip replacement (THR) within 8 years and which were related to baseline hip pain. Using a nested case-control design in the AGES-Reykjavik study, 74 future THR cases were age and sex-matched with 184 controls from the cohort (age 74±5yrs). Baseline assessment involved a validated hip pain questionnaire and pelvic CT. The following were performance-tested using ROC analysis and Clinical Utility Index: (i) hip pain; (ii) Kellgren and Lawrence grade (K&L grade), (iii) minimum joint space width (mJSW); and (iv) 3D cortical bone thickness (CTh). The clinical utility index for prediction of future THR from baseline pain was poor at 0.28, with the inclusion of imaging improving this to 0.79 (K&L grade) and 0.82 (3D CTh). Self-reported hip pain at baseline was also a poor-to-marginal predictor of THR (AUC=0.63), but 3D cortical thickening at the femoral head was predictive of future THR (0.81). Having radiographic osteoarthritis strongly predicted THR irrespective of hip pain (0.85). Combining hip pain, K&L grade and 3D cortical thickness gave optimal prediction (0.88). Ascertainment bias may have occurred if primary care physicians requested their own radiographs of their patients' hips. Imaging features from standard clinical CT identifies patients at high risk of progression to surgery for osteoarthritis, regardless of baseline pain.

Runt-related transcription factor 2 (RUNX2) is essential for skeletogenesis, and mutations in its gene cause cleidocranial dysplasia (CCD), an autosomal dominant skeletal disorder. The evolutionarily conserved 128-amino acid Runt homology domain (RHD) of human RUNX2 is essential for DNA binding and heterodimerization, and serves as a mutation hotspot associated with severe CCD phenotypes. To elucidate the functional impact of pathogenic RHD mutations in vivo, we generated two novel mouse lines: one carrying a missense mutation, c.695G>A, p.Arg232Gln (p.R232Q), corresponding to the human RUNX2 c.674G>A, p.Arg225Gln (p.R225Q), and the other harboring a frameshift mutation, c.697_698delGA, p.Glu233Thrfs*9 (p.E233Tfs*9), causing a premature stop codon. Homozygous Runx2R232Q/R232Q and Runx2E233Tfs*9/E233Tfs*9 mice lacked membranous ossification, whereas heterozygous Runx2R232Q/+ and Runx2E233Tfs*9/+ mice displayed typical CCD-like skeletal features, including an open anterior fontanelle and clavicle hypoplasia. Unexpectedly, heterozygotes carrying pathogenic RHD mutations developed small root-like protrusions, mostly one but rarely two, at the pulp chamber floor of three-rooted maxillary first molars during furcation, revealing a previously unrecognized dental phenotype. Dual luciferase assays showed that p.R232Q almost completely lost transactivation of the osteocalcin enhancer/promoter. Immunostaining showed that wild-type Runx2 was robustly expressed in osteoblasts and hypertrophic chondrocytes during bone formation, while the p.R232Q mutant Runx2 in Runx2R232Q/R232Q mice exhibited reduced expression in hypertrophic chondrocytes and partially impaired nuclear localization. These abnormalities led to defective osteoblast differentiation and chondrocyte maturation. Thus, our mutant mouse model provides a valuable in vivo platform to study CCD pathogenesis, mechanisms of tooth root furcation, and therapeutic interventions targeting dysfunctional RHD.

SOX9 and RUNX2 are lineage defining transcription factors that drive differentiation of chondrocyte and osteoblast lineages respectively from osteochondral progenitors. In limb development, these progenitors are specified first by SOX9 expression required for mesenchymal condensation prior to RUNX2 activation and osteochondral differentiation to chondrocyte and osteoblast lineages. Unlike limb development, the anterior craniofacial skeleton arises from multipotent cranial neural crest cells (cNCCs). To examine the temporal activation of SOX9 and RUNX2 within cNCCs, we utilized a combination of immunofluorescence to detect endogenous proteins and mouse genetic reporters to label SOX9 and RUNX2 expressing cells. We find that RUNX2 is expressed broadly throughout cNCCs of the first branchial arch that will give rise to developing mandibular tissue at a timepoint prior to osteochondral lineage determination. Substantial SOX9 expression is activated subsequently within differentiating chondrocytes. These findings were validated by fluorescent reporters inserted in the 3' untranslated regions (3'UTRs) of Sox9 and Runx2. Although the GFP based Runx2 reporter did not delete any 3'UTR sequences, homozygous Runx2GFP/GFP pups develop postnatal deficiencies in intramembranous and endochondral ossification that correlate with enhanced expression of RUNX2 protein in osteoblasts and hypertrophic chondrocytes. We find that this RUNX2 upregulation leads to compaction of growth plates, facilitates the transition of columnar chondrocytes to hypertrophy, and restricts terminal hypertrophic differentiation. Runx2GFP/GFP phenotypes model the human disorder, Metaphyseal Dysplasia with Maxillary Hypoplasia and Brachydactyly (MDMHB), resulting from RUNX2 enhanced activity due to intragenic duplications. Altogether, this reporter model provides a valuable tool for studying RUNX2 function in early cNCC-derived lineages and highlights the high sensitivity of ossification pathways to RUNX2 dosage.

Evidence indicating that inflammation is commonly associated with ectopic osteogenesis in certain autoimmune and infectious conditions challenges the dogma that inflammatory responses always suppress bone formation. In this study, we find that systemic administration of lipopolysaccharide (LPS) to mice causes not only inflammation in bone marrow, as expected, but also stimulates periosteal bone formation. This response can be reproduced in vitro as bone marrow supernatants from LPS-treated mice induce robust osteogenesis of osteoprogenitors compared to supernatants from PBS-treated counterparts. Periosteal bone accrual is partly dependent on periosteal leptin receptor-positive (LepR)+ osteoprogenitors but not bone marrow LepR+ or adiponectin (Adq)+ osteoprogenitors and correlates with pyroptosis within bone marrow. Consistent with the dependence of periosteal osteogenesis on pyroptosis, this response is slightly attenuated in Nlrp3-/- or caspase-1-/- mice but significantly inhibited in caspase-11-/-, caspase-1-/-;caspase-11-/-, or Gsdmd-/- mice. Our study reveals a novel role for pyroptosis in which lysed cells release intracellular contents that stimulate osteoprogenitors and promote osteogenic differentiation within the periosteal compartment.