Journal of Bone and Mineral Research最新文献

Disuse-induced bone loss is a common consequence of spaceflight and prolonged bed rest. Intraosseous blood vessel volume and number are decreased in rodents after sciatic nerve resection, and femoral and tibial perfusion and blood flow to the femoral shaft and marrow are reduced after hindlimb unloading. However, it is unclear if alterations in the flow of blood contribute to botulinum toxin (BTX)-induced bone loss. The objective of this study was to assess patterns of tibial bone loss and alterations in blood flow in murine hindlimbs following BTX injection. We hypothesize that flow of blood to the affected hindlimb will diminish along with bone mass and structure. Skeletally mature C57Bl/6J female were injected with BTX (n = 15) or vehicle (n = 14). Paralysis was confirmed using digit abduction, wire hang tests, and activity analysis. In vivo microCT and ex vivo synchrotron tomography were used to assess bone mass, microstructure, (re)modeling, as well as vascular and lacunar porosity. Blood flow in the hindlimbs and cardiac structure/function was monitored by echocardiography. After 3 wk, BTX-injected tibiae had 16% lower cortical thickness and 66% lower trabecular bone volume fraction compared to baseline. MicroCT-based timelapse morphometry showed bone loss was predominantly at endocortical surfaces. Bone loss in the contralateral limb was coincident with reduced rearing capability of BTX-injected mice compared to vehicle controls. Bony vascular canal thickness and surface area were reduced, but there was no change in lacunar properties due to BTX. In vivo ultrasound demonstrated increased velocity time integral for blood flow due to BTX injection in femoral and popliteal but not in saphenous arteries. Thus, BTX led to significant bone loss in hindlimbs, while increasing blood velocity in the femoral popliteal arteries and decreasing vascular porosity. The vascular response to BTX differs from what has been observed in other hindlimb unloading models.

Pregnancy and lactation require large amounts of calcium, potentially depleting the young-adult bone. This study investigated BMD and fluctuations of BMD resulting from parity and lactation in the PEAK-25 cohort, a prospective observational study of women all aged 25 at inclusion and 35 at follow-up. The analyses used women who were nulliparous at baseline and parous (n = 573) or nulliparous (n = 177) 10 yr later. Parity, regardless of number of pregnancies, had no negative impact; indeed, spine BMD at age 35 was higher (2.1%; p = .043). Likewise, BMD did not differ in women who breastfed, were nonlactating or nulliparous. Even the cumulative duration of breastfeeding did not make a difference. Overall, regardless of parity, in the cohort, by age 35 BMD was already decreasing, with overall losses at the FN (∆, -3.4%) and TH (∆, -2.7%), although not the spine (∆, 0.9%). Yet, BMD fluctuations associated with pregnancy, lactation, and weaning were seen in the short term. Comparing those pregnant >24 mo with those <24 mo prior to DXA, BMD was lowest in women more recently pregnant (FN, -2.2%, TH -2.7%). Women pregnant within 12 mo had 4% lower TH BMD compared with more than 36 mo (p = .054, padjusted = .032). Cumulative duration of breastfeeding was associated with bone loss, particularly beyond 15 mo (FN: ∆, -4.3%; TH: ∆, -3.7%) and lower spine BMD accretion. Despite such periods of loss, BMD recovers, evidenced by time-from-weaning to DXA. Women weaning within 6 mo of measurement had lower FN BMD than those where the interval was >24 mo (6.6% vs 1.7%; p < .001). In conclusion and despite repeated fluctuations in BMD resulting from the physiological demands of multiple pregnancies and periods of breastfeeding, BMD recovers and ultimately does not differ from that of identically aged women without children.

Chronic kidney disease (CKD) may be complicated by mineral and bone disorders (CKD-MBD). Data on the association between estimated glomerular filtration rate (eGFR) and bone microarchitecture are limited. We studied the link between eGFR and bone microarchitecture (baseline, changes) assessed by high resolution peripheral quantitative computed tomography (HR-pQCT) in older men followed for 8 years. In 826 men aged ≥60, eGFR was calculated using three equations based on creatinin and cystatin C: CKDEPI-2012, EKFC without race and sex, CKDEPI-2021 without race. Bone microarchitecture was assessed at the distal radius and distal tibia by HR-pQCT at baseline, then after 4 and 8 years. Reaction force and failure load were estimated by microfinite element analysis. Changes in bone measures across the eGFR classes were explored using linear mixed effect models. At baseline, distal radius bone microarchitecture did not differ across the eGFR groups (CKDEPI-2012), whereas distal tibia trabecular measures and failure load were higher in men with decreased eGFR. During the follow-up, lower eGFR was associated with more rapid decrease in total bone mineral density (Tt.BMD), cortical area (Ct.Ar) and BMD (Ct.BMD), trabecular BMD (Tb.BMD), and failure load at the distal radius. Low eGFR was also associated with faster increase in trabecular area (Tb.Ar) and trabecular distribution heterogeneity (Tb.1/N.SD). At the distal tibia, low eGFR was associated with more rapid decrease in Tt.BMD, Ct.Ar, Ct.BMD, Tb.1/N.SD, and failure load as well as with faster increase in Tb.Ar. The patterns were similar for changes expressed as percentages. The patterns were similar for two other equations. Lower eGFR is associated with faster decline in cortical bone microarchitecture and bone strength at the distal radius and tibia in older men. This phenomenon may contribute to the higher fracture risk in older adults with CKD.

More than 770 genetic skeletal disorders have been described, most with disease-causing variants reported in one of over 550 different genes. The ClinGen Skeletal Disorders Gene Curation Expert Panel was established to determine the strength of evidence that supports specific gene-disease relationships. Such information can assist clinical testing laboratories in choosing genes that should be included on diagnostic panels. Nine genes accounting for the most frequently encountered skeletal dysplasias (COL1A1, COL1A2, COL2A1, FGFR3, SLC26A2, TRPV4, COMP, ALPL, and SOX9) associated in the medical literature with 26 different skeletal disorders were reviewed using a semi-quantitative scoring framework. This framework is utilized by ClinGen to assess the clinical validity of gene-disease relationships. All nine genes were "Definitively" associated with at least one skeletal disorder and several were associated with multiple clinically or radiographically distinct skeletal conditions. Among these 26 gene-disease relationships, the ClinGen Skeletal Disorders Gene Curation Expert Panel determined that 22 (84.6%) had Definitive relationships, 2 (7.7%) had Moderate relationships, and 2 (7.7%) had Limited relationships. None of the 26 gene-disease relationships were Disputed or Refuted. For Moderate and Limited gene-disease relationships, clinical and genetic reports from additional probands and their families are needed to upgrade these gene-disease relationships to Definitive. Up-to-date assessments about the strength of the relationship between genes and phenotypes should improve the sensitivity and specificity of genetic testing in individuals with skeletal disease. The expert curations for the nine aforementioned genes are published on the ClinGen website.

The regulation of bone physiology and pathophysiology is intricately controlled by a complex interplay of cellular and molecular mechanisms. In these processes, the precise spatiotemporal coordination of biological activities in bone-resident cells plays a central role. Recently, liquid-liquid phase separation (LLPS), a mechanism underlying membraneless biomolecular condensate formation, has emerged as a transformative area of research. LLPS refers to the phase transition of biomolecules under specific conditions, leading to the formation of biomolecular condensates, which orchestrate diverse cellular functions. In this review, we provide a comprehensive synthesis of how LLPS influences bone turnover, focusing on its role in regulating bone homeostasis and its dysregulation in bone disease pathogenesis. Furthermore, aside from addressing the current challenges and limitations in this nascent field, we explore the implications of LLPS in bone regeneration, preventive strategies, and precision medicine. Despite LLPS research being in its early stages, its rapid advancement underscores its crucial role in bone biology and highlights the urgent need to integrate LLPS insights with translational approaches to advance therapeutic interventions for bone disorders.

G protein α-subunit (Gαs), encoded by GNAS, mediates GPCR signaling through cAMP second messenger pathways, and plays a pivotal role in craniofacial morphogenesis and osteoblast differentiation. Craniosynostosis, one of the most prevalent craniofacial developmental anomalies, is characterized by the premature fusion of cranial sutures. Here, we identify germline heterozygous variants in GNAS as a novel genetic cause of craniosynostosis. Affected individuals presented with multiple-suture synostosis, recognizable dysmorphic features, brachydactyly, short stature, with or without hormone resistance. We identified three de novo missense variants (c.286A>G;p.K96E, c.758A>G;p.Y253C, and c.691C>T;p.R231C) and one maternally inherited splicing variant (c.1039-2A>G). Functional analyses using bioluminescence resonance energy transfer (BRET) assays compared these variants to well-characterized activating variants p.R201H and p.Q227L. All tested variants impaired trimeric G protein assembly to varying degrees and exhibited reduced coupling with PTHR1. While the p.R201H and p.Q227L variants induced excessive cAMP production, the craniosynostosis-associated variants either displayed decreased basal cAMP levels or reduced agonist-induced cAMP production compared to wild-type, suggesting an inactivating nature. In zebrafish models, heterozygous gnas inactivation recapitulated human phenotypes, including multiple-suture synostosis, craniofacial abnormalities, and short stature. Mechanistically, GNAS haploinsufficiency in human mesenchymal stem cells promoted osteogenic differentiation through disrupted cAMP-CREB signaling, which relieved SMAD6-mediated repression of RUNX2 transcription. This study establishes inactivating GNAS variants as a genetic cause of craniosynostosis, uncovers a disease mechanism linking G protein inactivation to craniosynostosis through defective GPCR signal transduction.

Objectives: The Wnt/β-catenin signaling pathway is a classical pathway that regulates bone metabolism. The G protein inhibitory α subunits 1 and 3 (Gαi1/3) can couple with multiple growth factor/cytokine receptors and act as universal adaptor proteins to mediate the activation of key downstream signaling pathways. However, it remains unclear whether and how Gαi1/3 proteins mediate Wnt/β-catenin signal transduction.

Methods: In this study, we utilized single-cell sequencing analysis and employed viral transfection and gene editing techniques to alter the expression of Gαi1/3 in mouse embryonic osteoblast precursor cells (MC3T3-E1). We examined the relationship between Gαi1/3 expression and the Wnt/β-catenin signaling pathway. Immunoprecipitation and confocal experiments were conducted to further explore the mechanisms by which Gαi1/3 exerts its functions. Osteogenic-related protein levels were detected by Western blotting, and the effects of Gαi1/3 proteins on osteogenic function were examined through ALP and Alizarin Red staining. Additionally, micro-CT was used to compare bone mass in mice with different levels of Gαi1/3 expression, showing the relationship between Gαi1/3 and bone formation.

Results: Our findings indicate that Gαi1/3 proteins are significantly inversely correlated with age. Gαi1/3, rather than Gαi2, mediates the Wnt/β-catenin signaling pathway and promotes osteogenesis. Mechanistically, Gαi1/3 interacts with Axin1 and recruits it to the cell membrane, leading to inactivation of the β-catenin degradation complex. This results in β-catenin accumulation and nuclear translocation, where it activates transcription of osteogenic genes. In vivo experiments further confirm that knockdown of Gαi1/3 significantly inhibits bone formation in mice.

Conclusions: Our study identified Gαi1/3 as key regulatory proteins in Wnt/β-catenin signaling-mediated osteogenesis, and further elucidated its molecular mechanism in bone formation, which may provide a new therapeutic target for osteoporosis.