Bone histomorphometry: standardization of nomenclature, symbols, and units. Report of the ASBMR Histomorphometry Nomenclature Committee

Global Trends in Research of Programmed Cell Death in Osteoporosis: A Bibliometric and Visualized Analysis (2000-2023)

Osteoporosis (OP) is a systemic metabolic bone disease that is characterized by decreased bone mineral density and microstructural damage to bone tissue. Recent studies have demonstrated significant advances in the research of programmed cell death (PCD) in OP. However, there is no bibliometric analysis in this research field. This study searched the Web of Science Core Collection (WoSCC) database for literature related to OP and PCD from 2000 to 2023. This study used VOSviewers 1.6.20, the "bibliometrix" R package, and CiteSpace (6.2.R3) for bibliometric and visualization analysis. A total of 2905 articles from 80 countries were included, with China and the United States leading the way. The number of publications related to PCD in OP is increasing year by year. The main research institutions are Shanghai Jiao Tong University, Chinese Medical University, Southern Medical University, Zhejiang University, and Soochow University. Bone is the most popular journal in the field of PCD in OP, and the Journal of Bone and Mineral Research is the most co-cited journal. These publications come from 14,801 authors, with Liu Zong-Ping, Yang Lei, Manolagas Stavros C, Zhang Wei, and Zhao Hong-Yan having published the most papers. Ronald S. Weinstein was co-cited most often. Oxidative stress and autophagy are the current research hot spots for PCD in OP. This bibliometric study provides the first comprehensive summary of trends and developments in PCD research in OP. This information identifies the most recent research frontiers and hot directions, which will provide a definitive reference for scholars studying PCD in OP.

Transmembrane protein 53 craniotubular dysplasia (OMIM # 619727): The skeletal disease and consequent blindness of this new disorder

Craniotubular dysplasia, Ikegawa type (OMIM #619727) denotes the autosomal recessive skeletal disease identified in 2021 featuring blindness acquired in childhood. Five young members of four Indian families harbored a homozygous indel within TMEM53 (OMIM *619722), the gene that encodes transmembrane protein 53 (TMEM53). When intact, TMEM53 spans the nuclear envelope of osteoprogenitor cells, dampens BMP-SMAD signaling, and thereby slows bone formation. Consequently, defective TMEM53 accelerates osteogenesis. Herein, an American boy is compound heterozygous for a novel deletion and a novel missense mutation within TMEM53. His vision and sensorineural hearing became impaired. Radiographic survey revealed diploic thickening of his skull, broad calvarial and facial bones, skeletal modeling errors, vertebral body flattening, wide ribs, and osteopenia of expanded bones. DXA areal bone density (gm/cm2) Z-scores were low. His optic, auditory, and spinal canals were narrow. Mineral metabolism was intact. Serum alkaline phosphatase and osteocalcin levels were normal yet CTX was high. Iliac crest histomorphometry documented accelerated bone formation. His acute vision loss briefly improved following prednisone administration, optic canal decompression, and optic nerve sheath fenestration, but then progressed despite further surgeries and zoledronate treatment aimed to suppress bone turnover. Next generation sequencing of genes associated with elevated skeletal mass, including from high bone turnover, did not suggest an etiology. Whole genome sequencing then revealed within TMEM53: i) a paternally transmitted 54-base deletion, which included the mRNA splice acceptor site for exon 2 as well as 31 bases of exonic sequence (c. 62-23_92del), and ii) a maternally transmitted missense variant (c.650C > T, p.Ser217Leu: NM_024587.4/NP_078863.2) which is extremely rare in gnomAD (frequency = 0.000036), replaces Ser217 highly conserved across species, and is scored as damaging by SIFT and Mutation Taster. We call this new osteopathy TMEM53 craniotubular dysplasia.

Computationally efficient dominant load-based local bone microstructure reconstruction method using topology optimization

The bone microstructure of the human proximal femur is clinically crucial for diagnosing skeletal pathologies, such as osteoporosis and bone metastases. The topology optimization-based bone microstructure method obtains these bone microstructures by converting low-resolution (LR) images into high-resolution images. However, this method is inherently computationally inefficient as it requires numerous finite elements, iterative analyses, and parallel computations. Therefore, this study proposes a novel topology optimization-based localised bone microstructure reconstruction method using the dominant load, which highly affects the selected region of interest (ROI), for efficient resolution enhancement. The load dependency of selected ROIs is quantified with a load dependency score. Then, the localised finite element model is constructed based on the local load estimation. Finally, the selected dominant load is applied as an input for the topology optimization-based bone microstructure reconstruction method. The reconstructed bone microstructure was similar to that of the conventional method. The localised finite element model applied by the dominant load effectively and accurately reconstructed the bone morphology and exhibited high computational efficiency. In conclusion, the dominant load-based approach can be used to construct a reasonable trabecular bone structure for ROI with high computational efficiency. The predictive performance of the proposed method was validated and showed promise for accurate trabecular bone structure prediction without additional radiation exposure.

Deletion of the transcription factor EBF1 in perivascular stroma disrupts skeletal homeostasis and precipitates premature aging of the marrow microenvironment

Early B cell factor 1 (EBF1) is a transcription factor expressed by multiple lineages of stromal cells within the bone marrow. While cultures of Ebf1-deficient cells have been demonstrated to have impaired differentiation into either the osteoblast or adipogenic lineage in vitro by several groups, in vivo there has been a nominal consequence of the loss of EBF1 on skeletal development. In this study we used Prx-cre driven deletion of Ebf1 to eliminate EBF1 from the entire mesenchymal lineage of the skeleton and resolve this discrepancy. We report here that EBF1 is expressed primarily in the Mesenchymal Stem and Progenitor Cell (MSPC)-Adipo, MSPC-Osteo, and the Early Mesenchymal Progenitors, and that loss of EBF1 has a plethora of consequences to maintenance of the skeleton throughout adulthood. Stroma from the Prx-cre;Ebf1fl/fl bones had impaired osteogenic differentiation, an age-dependent loss of CFU-F, and elevated senescence accompanying Ebf1-deletion. New bone formation was reduced after 3 months, and resulted in a quiescent bone environment with fewer osteoblasts and an accompanied reduction in osteoclast-mediated remodeling. Consequently, bones were less ductile at a younger age, and deletion of EBF1 dramatically impaired fracture repair. Disruption of EBF1 in perivascular populations also rearranged the vascular network within these bones and disrupted cytokine signaling from key hematopoietic niches resulting in anemia, reductions in B cells, and myeloid skewing of marrow hematopoietic lineages. Mechanistically we observed disrupted BMP signaling within Ebf1-deficient progenitors with reduced SMAD1-phosphorylation, and elevated secretion of the soluble BMP-inhibitor Gremlin from the MSPC-Adipo cells. Ebf1-deficient progenitors also exhibited posttranslational suppression of glucocorticoid receptor expression. Together, these results suggest that EBF1 signaling is required for mesenchymal progenitor mobilization to maintain the adult skeleton, and that the primary action of EBF1 in the early mesenchymal lineage is to promote proliferation, and differentiation of these perivascular cells to sustain a healthy tissue.

Sclerostin and Wnt Signaling in Idiopathic Juvenile Osteoporosis Using High-Resolution Confocal Microscopy for Three-Dimensional Analyses

BACKGROUND

Idiopathic juvenile osteoporosis (IJO) is a rare condition characterized by low bone mass that can increase the risk of fractures in children. Treatment options for these patients are limited as the molecular mechanisms of disease initiation and progression are incompletely understood. Sclerostin inhibits canonical Wnt signaling, which is important for the bone formation activity of osteoblasts, and elevated sclerostin has been implicated in adult osteoporosis.

OBJECTIVE

To evaluate the role of sclerostin in IJO, high-resolution confocal microscopy analyses were performed on bone biopsies collected from 13 pediatric patients.

METHODS

Bone biopsies were stained with sclerostin, and β-catenin antibodies showed elevated expression across osteocytes and increased sclerostin-positive osteocytes in 8 of the 13 total IJO patients (62%).

RESULTS

Skeletal sclerostin was associated with static and dynamic histomorphometric parameters. Further, colocalization analyses showed that bone sclerostin colocalized with phosphorylated β-catenin, a hallmark of Wnt signaling that indicates Wnt inhibition. In contrast, sclerostin-positive osteocytes were not colocalized with an "active" unphosphorylated form of β-catenin.

CONCLUSIONS

These results support a model that altered levels of sclerostin and Wnt signaling activity occur in IJO patients.

Sex-Specific Effects of THRβ Signaling on Metabolic Responses to High Fat Diet in Mice

Thyroid hormone (TH) plays a crucial role in regulating the functions of both bone and adipose tissue. Given that TH exerts its cholesterol-lowering effects in hepatic tissue through the TH receptor-β (TRβ), we hypothesized that TRβ agonist therapy using MGL3196 (MGL) would be effective in treating increased adiposity and bone loss in response to a 12-week high-fat diet (HFD) in adult C57BL/6J mice. Transcriptional and serum profiling revealed that HFD-induced leptin promoted weight gain in both males and females, but MGL only suppressed leptin induction and weight gain in males. In vitro studies suggest that estrogen suppresses MGL activity in adipocytes, indicating that estrogen might interfere with MGL-TRβ function. Compared to systemic adiposity, HFD reduced bone mass in male but not female mice. Paradoxically, MGL treatment reversed macroscopic bone mineral density loss in appendicular bones, but micro-CT revealed that MGL exacerbated HFD-induced trabecular bone loss, and reduced bone strength. In studies on the mechanisms for HFD effects on bone, we found that HFD induced Rankl expression in male femurs that was blocked by MGL. By ex vivo assays, we found that RANKL indirectly represses osteoblast lineage allocation of osteoprogenitors by induction of inflammatory cytokines TNFα, IL-1β, and CCL2. Finally, we found that MGL functions in both systemic adiposity and bone by nongenomic TRβ signaling, as HFD-mediated phenotypes were not rescued in TRβ147F knockout mice with normal genomic but defective nongenomic TRβ signaling. Our findings demonstrate that the negative effects of HFD on body fat and bone phenotypes are impacted by MGL in a gender-specific manner.

Celebrating 50-years: the history and future of the International Society of Bone Morphometry

The International Society of Bone Morphometry (ISBM) is dedicated to advancing research, education, and clinical practice for osteoporosis and other bone disorders by developing and improving tools for the quantitative imaging and analysis of bone. Its initial core mission was to promote the proper use of morphometric techniques in bone research and to educate and train clinicians and basic scientists in bone morphometry. This article chronicles the evolution of the ISBM and the history and development of bone morphometric techniques for the past 50-years, starting with workshops on bone morphometry in 1973, to the formal incorporation of the ISBM in 1996, to today. We also provide a framework and vision for the coming decades. This effort was led by ISBM presidents Dr Erica L. Scheller (2022-2024) and Dr Thomas J. Wronski (2009-2012) in collaboration with all other living ISBM presidents. Though the underlying techniques and questions have changed over time, the need for standardization of established tools and discovery of novel approaches for bone morphometry remains a constant. The ISBM fulfills this need by providing a forum for the exchange of ideas, with a philosophy that encourages the open discussion of pitfalls and challenges among clinicians, scientists, and industry partners. This facilitates the rapid development and adaptation of tools to meet emerging demands within the field of bone health at a high level.

Bone marrow lesions in knee osteoarthritis assessed by dynamic contrast-enhanced MRI with histopathological correlations

BACKGROUND

Bone marrow lesions (BMLs) in knee osteoarthritis (OA) have been assessed histopathologically and by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI); however, a direct comparison of the results has not been reported.

PURPOSE

To evaluate and compare the findings by DCE-MRI and histopathology of subchondral BMLs in knee OA.

MATERIAL AND METHODS

In total, 19 patients with medial tibiofemoral knee OA undergoing total knee arthroplasty were analyzed. Preoperative MRI, including a DCE sequence, was performed, and bone biopsies were obtained from the resected specimens corresponding to BML areas. The contrast enhancement by DCE-MRI was analyzed using semi-quantitative (area under the curve [AUC]), peak enhancement [PE]), and quantitative (Ktrans, Kep) methods. Enhancement in the medial OA compartment was compared with similar areas in a normal lateral compartment, and the DCE characteristics of BMLs were correlated with semi-quantitatively graded histopathological features.

RESULTS

AUC and PE were significantly higher in medial tibial and femoral BMLs compared with the values in the lateral condyles; Ktrans and Kep were only significantly higher in the tibial plateau. In the tibia, AUC and PE were significantly correlated with the grade of vascular proliferation, and PE also with the degree of marrow fibrosis. There was no significant correlation between AUC/PE and histopathological findings in the femur and no correlation between quantitative DCE parameters and histopathological findings.

CONCLUSION

BML characteristics by semi-quantitative DCE in the form of AUC and PE may be used as parameters for the degree of histopathological vascularization in the bone marrow whereas quantitative DCE data were less conclusive.

Regional difference in the distribution of alkaline phosphatase, PHOSPHO1, and calcein labeling in the femoral metaphyseal trabeculae in parathyroid hormone-administered mice

OBJECTIVES

This study aimed to elucidate whether the administration of parathyroid hormone (PTH) results in remodeling- or modeling-based bone formation in different regions of the murine femora, and whether the PTH-driven bone formation would facilitate osteoblastic differentiation into osteocytes.

METHODS

Six-week-old male C57BL/6J mice were employed to examine the distribution of alkaline phosphatase (ALP), PHOSPHO1, podoplanin, and calcein labeling in two distinct long bone regions: the metaphyseal trabeculae close to the chondro-osseous junction (COJ) and those distant from the COJ in three mouse groups, a control group receiving a vehicle (Sham group) and groups receiving hPTH (1-34) twice a day (PTH BID group) or four times a day (PTH QID group) for two weeks.

RESULTS

The Sham group showed PHOSPHO1-reactive mature osteoblasts localized primarily at the COJ, whereas the PTH BID/QID groups exhibited extended lines of PHOSPHO1-reactive osteoblasts even in regions distant from the COJ. The PTH QID group displayed fragmented calcein labeling in trabeculae close to the COJ, whereas continuous labeling was observed in trabeculae distant from the COJ. Osteoblasts tended to express podoplanin and PHOSPHO1 independently in the close and distant regions of the Sham group, while osteoblasts in the PTH-administered groups showed immunoreactivity of podoplanin and PHOSPHO1 together in the close and distant regions.

CONCLUSIONS

Administration of PTH may accelerate remodeling-based bone formation in regions close to the COJ while predominantly inducing modeling-based bone formation in distant regions. PTH appeared to simultaneously facilitate osteoblastic bone mineralization and differentiation into osteocytes in both remodeling- and modeling-based bone formation.

Engineering a targeted and safe bone anabolic gene therapy to treat osteoporosis in alveolar bone loss

Alveolar bone loss in elderly populations is highly prevalent and increases the risk of tooth loss, gum disease susceptibility, and facial deformity. Unfortunately, there are very limited treatment options available. Here, we developed a bone-targeted gene therapy that reverses alveolar bone loss in patients with osteoporosis by targeting the adaptor protein Schnurri-3 (SHN3). SHN3 is a promising therapeutic target for alveolar bone regeneration, because SHN3 expression is elevated in the mandible tissues of humans and mice with osteoporosis while deletion of SHN3 in mice greatly increases alveolar bone and tooth dentin mass. We used a bone-targeted recombinant adeno-associated virus (rAAV) carrying an artificial microRNA (miRNA) that silences SHN3 expression to restore alveolar bone loss in mouse models of both postmenopausal and senile osteoporosis by enhancing WNT signaling and osteoblast function. In addition, rAAV-mediated silencing of SHN3 enhanced bone formation and collagen production of human skeletal organoids in xenograft mice. Finally, rAAV expression in the mandible was tightly controlled via liver- and heart-specific miRNA-mediated repression or via a vibration-inducible mechanism. Collectively, our results demonstrate that AAV-based bone anabolic gene therapy is a promising strategy to treat alveolar bone loss in osteoporosis.

Bone microstructural characteristics or positional changes of condyle head affect short-term condyle head resorption after orthognathic surgery

Condylar resorption occurs in some cases after orthognathic surgery, and the risk factors associated with postoperative condylar head resorption have been extensively described. Nevertheless, even in cases with a combination of risk factors, postoperative condylar resorption may not appear. This study analyzed the microstructure and three-dimensional positional change of the condylar bone via imaging in patients who have undergone bimaxillary orthognathic surgery to determine whether the microstructure or condylar position differs between patients with and without postoperative condylar resorption. Among asymptomatic patients who underwent bimaxillary surgery between April 2021 and March 2022 at our department, 17 patients were analyzed, limited to "female," "skeletal Class II," and "high-angle cases," which are known risk factors for mandibular head resorption. Multidetector computed tomography was performed on these patients before and 6 months after surgery, and the bone microstructure of the condylar head and the three-dimensional positional changes of the condylar bone and the proximal bony fragments were compared with the presence of postoperative condyle resorption using the bone morphology software TRI/3D-BON. Patients with condylar bone abnormalities before surgery and those with high trabecular bone density can develop postoperative resorption if the condyle is misaligned by surgery.

Age-related changes in densitometry and histomorphometry of long bone during the pubertal growth spurt in male rats

Because experimental studies to determine the developmental toxicity of exposure to various substances in children are impossible, many studies use immature male rats. This study aimed to provide normative data for longitudinal bone growth with age during the puberty in male rats. In order to evaluate long bone growth and mineralization we examined bone size and bone density by dual-energy X-ray absorptiometry, analyzed histomorphometry of the growth plate, and serum hormone levels relevant to bone growth from postnatal day (PD)20 to PD60. The length and weight of long bones increased strongly by PD40, and no further increase was observed after PD50. On the other hand, tibial growth plate height decreased sharply after PD50 along with a reduction in the number of cells and columns, which was probably responsible for the absence of further lengthening of long bones. Parameters related to bone formation such as bone area ratio, and the thickness and number of trabeculae, also increased significantly between PD40 and PD50. Furthermore, serum levels of IGF-1 peaked at PD30 and testosterone increased rapidly on and after PD40, when IGF-1 levels were going down. These changes may participate in the parallel increase in mineral acquisition, as well as lengthening of long bones. Our findings provide comprehensive data for changes in bone density, histomorphometry of long bones, and hormone levels relevant to bone growth during the growth spurt. This will be useful for planning animal toxicological studies, particularly for deciding on the appropriate age of animals to use in given experiments.

Vasorin as an actor of bone turnover?

Bone diseases are increasing with aging populations and it is important to identify clues to develop innovative treatments. Vasn, which encodes vasorin (Vasn), a transmembrane protein involved in the pathophysiology of several organs, is expressed during the development in intramembranous and endochondral ossification zones. Here, we studied the impact of Vasn deletion on the osteoblast and osteoclast dialog through a cell Coculture model. In addition, we explored the bone phenotype of Vasn KO mice, either constitutive or tamoxifen-inducible, or with an osteoclast-specific deletion. First, we show that both osteoblasts and osteoclasts express Vasn. Second, we report that, in both KO mouse models but not in osteoclast-targeted KO mice, Vasn deficiency was associated with an osteopenic bone phenotype, due to an imbalance in favor of osteoclastic resorption. Finally, through the Coculture experiments, we identify a dysregulation of the Wnt/β-catenin pathway together with an increase in RANKL release by osteoblasts, which led to an enhanced osteoclast activity. This study unravels a direct role of Vasn in bone turnover, introducing a new biomarker or potential therapeutic target for bone pathologies.

Dickkopf-1 (DKK1) blockade mitigates osteogenesis imperfecta (OI) related bone disease

BACKGROUND

The current treatment of osteogenesis imperfecta (OI) is imperfect. Our study thus delves into the potential of using Dickkopf-1 antisense (DKK1-AS) to treat OI.

METHODS

We analysed serum DKK1 levels and their correlation with lumbar spine and hip T-scores in OI patients. Comparative analyses were conducted involving bone marrow stromal cells (BMSCs) and bone tissues from wild-type mice, untreated OI mice, and OI mice treated with DKK1-ASor DKK1-sense (DKK1-S).

RESULTS

Significant inverse correlations were noted between serum DKK1 levels and lumbar spine (correlation coefficient = - 0.679, p = 0.043) as well as hip T-scores (correlation coefficient = - 0.689, p = 0.042) in OI patients. DKK1-AS improved bone mineral density (p = 0.002), trabecular bone volume/total volume fraction (p < 0.001), trabecular separation (p = 0.010), trabecular thickness (p = 0.001), trabecular number (p < 0.001), and cortical thickness (p < 0.001) in OI mice. DKK1-AS enhanced the transcription of collagen 1α1, osteocalcin, runx2, and osterix in BMSC from OI mice (all p < 0.001), resulting in a higher von Kossa-stained matrix area (p < 0.001) in ex vivo osteogenesis assays. DKK1-AS also reduced osteoclast numbers (p < 0.001), increased β-catenin and T-cell factor 4 immunostaining reactivity (both p < 0.001), enhanced mineral apposition rate and bone formation rate per bone surface (both p < 0.001), and decreased osteoclast area (p < 0.001) in OI mice. DKK1-AS upregulated osteoprotegerin and downregulated nuclear factor-kappa B ligand transcription (both p < 0.001). Bone tissues from OI mice treated with DKK1-AS exhibited significantly higher breaking force compared to untreated OI mice (p < 0.001).

CONCLUSIONS

Our study elucidates that DKK1-AS has the capability to enhance bone mechanical properties, restore the transcription of osteogenic genes, promote osteogenesis, and inhibit osteoclastogenesis in OI mice.

Crosstalk between ALK3(BMPR1A) deficiency and autophagy signaling mitigates pathological bone loss in osteoporosis

Postmenopausal osteoporosis is recognized to be one of the major skeleton diseases strongly associated with impaired bone formation. Previous reports have indicated that the importance of bone morphogenetic protein (BMP) signaling of osteoblast lineage in bone development via classical Smad signaling, however, its critical role in osteoporosis is still not well understood. In the current study, we aim to investigate the pathological role of BMPR1A, a key receptor of BMPs, in osteoporosis and its underlying mechanism. We first found that knockdown of BMPR1A by using Col1a1-creER in osteoblasts mitigated early bone loss of osteoporosis in mice, yet along with late bone maturation defects by reducing mineral adherence rate and bone formation rate in vivo. At the cellular level, we then observed that BMPR1A deficiency promoted the proliferation of pre-osteoblasts under osteoporotic conditions but hindered their late-stage mineralization. We finally elucidated that BMPR1A deficiency compensatorily triggered mTOR-autophagy perturbation by a higher level in early osteoporotic pre-osteoblasts thus resulting in the enhancement of transient cell proliferation but impairment of final mineralization. Taken together, this study indicated the significance of BMPR1A-mTOR/autophagy axis, as a double-edged sword, in osteoporotic bone formation and provided new cues for therapeutic strategies in osteoporosis.

In chronic kidney disease altered cardiac metabolism precedes cardiac hypertrophy

Conduit arterial disease in chronic kidney disease (CKD) is an important cause of cardiac complications. Cardiac function in CKD has not been studied in the absence of arterial disease. In an Alport syndrome model bred not to have conduit arterial disease, mice at 225 days of life (dol) had CKD equivalent to humans with CKD stage 4-5. Parathyroid hormone (PTH) and FGF23 levels were one log order elevated, circulating sclerostin was elevated, and renal activin A was strongly induced. Aortic Ca levels were not increased, and vascular smooth muscle cell (VSMC) transdifferentiation was absent. The CKD mice were not hypertensive, and cardiac hypertrophy was absent. Freshly excised cardiac tissue respirometry (Oroboros) showed that ADP-stimulated O2 flux was diminished from 52 to 22 pmol/mg (P = 0.022). RNA-Seq of cardiac tissue from CKD mice revealed significantly decreased levels of cardiac mitochondrial oxidative phosphorylation genes. To examine the effect of activin A signaling, some Alport mice were treated with a monoclonal Ab to activin A or an isotype-matched IgG beginning at 75 days of life until euthanasia. Treatment with the activin A antibody (Ab) did not affect cardiac oxidative phosphorylation. However, the activin A antibody was active in the skeleton, disrupting the effect of CKD to stimulate osteoclast number, eroded surfaces, and the stimulation of osteoclast-driven remodeling. The data reported here show that cardiac mitochondrial respiration is impaired in CKD in the absence of conduit arterial disease. This is the first report of the direct effect of CKD on cardiac respiration.NEW & NOTEWORTHY Heart disease is an important morbidity of chronic kidney disease (CKD). Hypertension, vascular stiffness, and vascular calcification all contribute to cardiac pathophysiology. However, cardiac function in CKD devoid of vascular disease has not been studied. Here, in an animal model of human CKD without conduit arterial disease, we analyze cardiac respiration and discover that CKD directly impairs cardiac mitochondrial function by decreasing oxidative phosphorylation. Protection of cardiac oxidative phosphorylation may be a therapeutic target in CKD.

Eldecalcitol Induces Minimodeling-Based Bone Formation and Inhibits Sclerostin Synthesis Preferentially in the Epiphyses Rather than the Metaphyses of the Long Bones in Rats

This study aimed to examine minimodeling-based bone formation between the epiphyses and metaphyses of the long bones of eldecalcitol (ELD)-administered ovariectomized rats. Sixteen-week-old female rats were divided into four groups: sham-operated rats receiving vehicle (Sham group), ovariectomized (OVX) rats receiving vehicle (Vehicle group), or ELDs (30 or 90 ng/kg BW, respectively; ELD30 and ELD90 groups). ELD administration increased bone volume and trabecular thickness, reducing the number of osteoclasts in both the epiphyses and metaphyses of OVX rats. The Sham and Vehicle groups exhibited mainly remodeling-based bone formation in both regions. The epiphyses of the ELD groups showed a significantly higher frequency of minimodeling-based bone formation than remodeling-based bone formation. In contrast, the metaphyses exhibited significantly more minimodeling-based bone formation in the ELD90 group compared with the ELD30 group. However, there was no significant difference between minimodeling-based bone formation and remodeling-based bone formation in the ELD90 group. While the minimodeling-induced new bone contained few sclerostin-immunoreactive osteocytes, the underlying pre-existing bone harbored many. The percentage of sclerostin-positive osteocytes was significantly reduced in the minimodeling-induced bone in the epiphyses but not in the metaphyses of the ELD groups. Thus, it seems likely that ELD could induce minimodeling-based bone formation in the epiphyses rather than in the metaphyses, and that ELD-driven minimodeling may be associated with the inhibition of sclerostin synthesis.

In vivo validation of highly customized cranial Ti-6AL-4V ELI prostheses fabricated through incremental forming and superplastic forming: an ovine model study

Cranial reconstructions are essential for restoring both function and aesthetics in patients with craniofacial deformities or traumatic injuries. Titanium prostheses have gained popularity due to their biocompatibility, strength, and corrosion resistance. The use of Superplastic Forming (SPF) and Single Point Incremental Forming (SPIF) techniques to create titanium prostheses, specifically designed for cranial reconstructions was investigated in an ovine model through microtomographic and histomorphometric analyses. The results obtained from the explanted specimens revealed significant variations in bone volume, trabecular thickness, spacing, and number across different regions of interest (VOIs or ROIs). Those regions next to the center of the cranial defect exhibited the most immature bone, characterized by higher porosity, decreased trabecular thickness, and wider trabecular spacing. Dynamic histomorphometry demonstrated differences in the mineralizing surface to bone surface ratio (MS/BS) and mineral apposition rate (MAR) depending on the timing of fluorochrome administration. A layer of connective tissue separated the prosthesis and the bone tissue. Overall, the study provided validation for the use of cranial prostheses made using SPF and SPIF techniques, offering insights into the processes of bone formation and remodeling in the implanted ovine model.

Moringa oleifera leaf extract promotes the healing of critical sized bone defects in the mandibles of rabbits

OBJECTIVE

The search for an osteopromotive material that enhances the efficacy of alloplasts in reconstructive surgeries has been going on for years. This study aimed to histologically and histomorphometrically evaluate the efficiency of Moringa oleifera leaf extract as an osteopromotive biomaterial.

DESIGN

The study is a prospective randomized controlled animal study. 24 adult male New Zealand rabbits were equally allocated into test and control groups. Critical-sized bone defects were created in the edentulous areas of the mandibles of rabbits. The defects of the control group were filled with Beta-tricalcium Phosphate, while the defects of the test group were filled with Beta-tricalcium Phosphate combined with Moringa oleifera leaf extract. The results were evaluated histologically and histomorphometrically.

RESULTS

Histological and histomorphometric analysis showed a significant increase in the surface area of bone and the number of osteoblasts in test groups compared to those in the control groups.

CONCLUSION

Moringa oleifera leaf extract has a positive effect on bone regeneration in critical-sized bone defects.

Modelling the Effects of Growth and Remodelling on the Density and Structure of Cancellous Bone

A two-stage model is proposed for investigating remodelling characteristics in bone over time and distance to the growth plate. The first stage comprises a partial differential equation (PDE) for bone density as a function of time and distance from the growth plate. This stage clarifies the contributions to changes in bone density due to remodelling and growth processes and tracks the rate at which new bone emanates from the growth plate. The second stage consists of simulating the remodelling process to determine remodelling characteristics. Implementing the second stage requires the rate at which bone moves away from the growth plate computed during the first stage. The second stage is also needed to confirm that remodelling characteristics predicted by the first stage may be explained by a realistic model for remodelling and to compute activation frequency. The model is demonstrated on microCT scans of tibia of juvenile female rats in three experimental groups: sham-operated control, oestrogen deprived, and oestrogen deprived followed by treatment. Model predictions for changes in bone density and remodelling characteristics agree with the literature. In addition, the model provides new insight into the role of treatment on the density of new bone emanating from the growth plate and provides quantitative descriptions of changes in remodelling characteristics beyond what has been possible to ascertain by experimentation alone.

Chronic di(2-ethylhexyl) phthalate exposure at environmental-relevant doses induces osteoporosis by disturbing the differentiation of bone marrow mesenchymal stem cells

Di(2-ethylhexyl) phthalate (DEHP) is a widely used plastic additive with persistent characteristics in the environment. This study was designed to investigate the detrimental effects of chronic DEHP exposure at environmental-relevant doses on bone metabolism and the underlying mechanisms. It was found that exposure to 25 μg/kg bw and 50 μg/kg bw DEHP for 29 weeks led to a reduction of whole-body bone mineral density (BMD), femur microstructure damage, decreased femur new bone formation, and increased femur bone marrow adipogenesis in C57BL/6 female mice, which was not observed in mice exposed to 5000 μg/kg bw DEHP. Further in vitro study showed that DEHP treatment robustly promoted adipogenic differentiation and suppressed osteogenic differentiation of the bone marrow mesenchymal stem cells (BMSCs). Mechanistically, DEHP exposure resulted in elevated expressions of DYRK1B, CDK5, PPARγ, and p-PPARγSer273 in both bone tissue and BMSCs. Interestingly, co-IP analysis showed potential interactions among DYRK1B, PPARγ, and CDK5. Lastly, antagonists of DYRK1B and CDK5 effectively alleviated the BMSCs differentiation disturbance induced by DEHP. These results suggest that DEHP may disturb the BMSCs differentiation by upregulating the PPARγ signaling which may be associated with the activation of DYRK1B and CDK5.

Evaluation of the Mechanical and Adhesion Characteristics of Indirect Restorations Manufactured with Three-Dimensional Printing

The aim of this study was to investigate the marginal fit and bond strength characteristics of onlay restorations manufactured by three-dimensional printing (Varseo XS, Bego GmbH, Bremen, Germany) and CAD/CAM (CAMcube, Montreal, QC, Canada) systems. Class II onlay cavities on sixty mandibular molars were prepared in cavities and restored in three separate groups using different fabrication methods. Digital and conventional impressions were taken to design the restorations in the CAD system (DWOS, Straumann GmbH, Freiburg, Germany). To evaluate the marginal fit and void volumes, all specimens were scanned with microcomputed tomography. A microshear test was performed to compare the bond strength of the restorations to the tooth surface. The marginal fit values measured for the 3D-printed and CAD/CAM onlay restorations were found to be at clinically acceptable levels (<120 µm), and no significant difference could be observed between the three different fabrication methods (p > 0.05). According to the microshear test results, the CAD/CAM group had the highest bond strength values before (34.82 MPa) and after (26.87 MPa) thermal cycling (p < 0.05), while the 3D-printed and conventionally produced onlays had similar results (p < 0.05). 3D printing technology is a promising option for indirect restorations; however, the post-production phase is as crucial as the printing and cementation phases.

Transcriptomic landscape of human induced pluripotent stem cell-derived osteogenic differentiation identifies a regulatory role of KLF16

Osteogenic differentiation is essential for bone development and metabolism, but the underlying gene regulatory networks have not been well investigated. We differentiated mesenchymal stem cells, derived from 20 human induced pluripotent stem cell lines, into preosteoblasts and osteoblasts, and performed systematic RNA-seq analyses of 60 samples for differential gene expression. We noted a highly significant correlation in expression patterns and genomic proximity among transcription factor (TF) and long noncoding RNA (lncRNA) genes. We identified TF-TF regulatory networks, regulatory roles of lncRNAs on their neighboring coding genes for TFs and splicing factors, and differential splicing of TF, lncRNA, and splicing factor genes. TF-TF regulatory and gene co-expression network analyses suggested an inhibitory role of TF KLF16 in osteogenic differentiation. We demonstrate that in vitro overexpression of human KLF16 inhibits osteogenic differentiation and mineralization, and in vivo Klf16+/- mice exhibit increased bone mineral density, trabecular number, and cortical bone area. Thus, our model system highlights the regulatory complexity of osteogenic differentiation and identifies novel osteogenic genes.

The combined treatment of insulin and naringin improves bone properties in rats with type 1 diabetes mellitus

We have studied the effects of individual and combined treatment of insulin (I) and naringin (NAR) on the bone structure and biomechanical properties of femurs from streptozotocin (STZ)-induced diabetic rats. Male Wistar rats were divided into five groups: (1) controls, (2) STZ-induced diabetic rats, (3) STZ-induced diabetic rats treated with I, (4) STZ-induced diabetic rats treated with NAR, and (5) STZ-induced diabetic rats treated with I + NAR. Bone mineral density (BMD), bone histomorphometry, biomechanical testing, and bone biomarker expressions were accomplished in femur of all animals, as well as serum biochemical analyses. The combined treatment of I + NAR increased the body weight and the femur BMD from STZ-induced diabetic rats. The bone biomechanical properties and the bone morphology of the femurs from STZ-induced diabetic rats were also improved by the combined treatment. The increased number of osteoclasts in STZ-induced diabetic rats was partially prevented by I, NAR, or I + NAR. NAR or I + NAR completely blocked the decrease in the number of osteocalcin (+) cells in the femur from STZ-induced diabetic rats. RUNX family transcription factor 2 immunostaining was much lower in STZ-induced diabetic rats than in control animals; the combination of I + NAR totally blocked this effect. The combined treatment not only ameliorated bone quality and function, but also normalized the variables related to glucose metabolism. Therefore, the combination of I + NAR might be a better therapeutic strategy than the individual I or NAR administration to reduce bone complications in diabetic patients.

An Additional Lrp4 High Bone Mass Mutation Mitigates the Sost-Knockout Phenotype in Mice by Increasing Bone Remodeling

Pathogenic variants disrupting the binding between sclerostin (encoded by SOST) and its receptor LRP4 have previously been described to cause sclerosteosis, a rare high bone mass disorder. The sclerostin-LRP4 complex inhibits canonical WNT signaling, a key pathway regulating osteoblastic bone formation and a promising therapeutic target for common bone disorders, such as osteoporosis. In the current study, we crossed mice deficient for Sost (Sost-/-) with our p.Arg1170Gln Lrp4 knock-in (Lrp4KI/KI) mouse model to create double mutant Sost-/-;Lrp4KI/KI mice. We compared the phenotype of Sost-/- mice with that of Sost-/-;Lrp4KI/KI mice, to investigate a possible synergistic effect of the disease-causing p.Arg1170Trp variant in Lrp4 on Sost deficiency. Interestingly, presence of Lrp4KI alleles partially mitigated the Sost-/- phenotype. Cellular and dynamic histomorphometry did not reveal mechanistic insights into the observed phenotypic differences. We therefore determined the molecular effect of the Lrp4KI allele by performing bulk RNA sequencing on Lrp4KI/KI primary osteoblasts. Unexpectedly, mostly genes related to bone resorption or remodeling (Acp5, Rankl, Mmp9) were upregulated in Lrp4KI/KI primary osteoblasts. Verification of these markers in Lrp4KI/KI, Sost-/- and Sost-/-;Lrp4KI/KI mice revealed that sclerostin deficiency counteracts this Lrp4KI/KI effect in Sost-/-;Lrp4KI/KI mice. We therefore hypothesize that models with two inactivating Lrp4KI alleles rather activate bone remodeling, with a net gain in bone mass, whereas sclerostin deficiency has more robust anabolic effects on bone formation. Moreover, these effects of sclerostin and Lrp4 are stronger in female mice, contributing to a more severe phenotype than in males and more detectable phenotypic differences among different genotypes.

Lateral bone ridge expansion and internal tissue replacement for vertebral body growth in Pacific bluefin tuna Thunnus orientalis

Vertebral growth is an essential developmental process to support the expansion of the vertebrate body. In teleosts, the lateral side of the vertebral bodies develops to form different structures among species in the late stages of vertebral growth, although lateral structures are not apparent in the early stages. Lateral structures are one of the structural features that determine the diversity of teleost vertebrae. However, explanations for the formation of lateral structures are conflicting because few reports have investigated the growth of teleost vertebral bodies. To clarify the growth process, we analyzed the morphological changes in the vertebral body of Pacific bluefin tuna Thunnus orientalis at different developmental stages using micro-computed tomography (CT) scans. The micro-CT scans showed that the vertebral centrum formed a plate-like ridge on the lateral side along the cranial-caudal direction and extended laterally with increasing thickness. Simultaneously, the proximal region of the lateral ridges became porous as the vertebrae grew to form bone marrow cavities. Furthermore, we used histological observations to describe the relationship between these morphological changes and osteoblast and osteoclast activities. Osteoblasts accumulated on the distal edges of the lateral ridges, whereas osteoclasts were distributed in the bone marrow cavities. These observations suggest that bone resorption occurs proximally to form bone marrow cavities in addition to bone synthesis at the edges of the lateral ridges. The bone marrow cavities were occupied by blood vessels, extracellular matrix, and adipocytes, and the internal tissue composition changed to increase the area of adipose tissue. Because the ratio of bone volume decreases in large vertebrae, bone formation and resorption are regulated to separate the external cortical and internal trabecular bones to support the vertebrae. This study is the first to report the formation of lateral structures and can be applied to similar lateral structures in the vertebrae of other teleost species.

3'-Sialyllactose alleviates bone loss by regulating bone homeostasis

Osteoporosis is a common skeletal disease that results in an increased risk of fractures. However, there is no definitive cure, warranting the development of potential therapeutic agents. 3'-Sialyllactose (3'-SL) in human milk regulates many biological functions. However, its effect on bone metabolism remains unknown. This study aimed to investigate the molecular mechanisms underlying the effect of 3'-SL on bone homeostasis. Treatment of human bone marrow stromal cells (hBMSCs) with 3'-SL enhanced osteogenic differentiation and inhibited adipogenic differentiation of hBMSCs. RNA sequencing showed that 3'-SL enhanced laminin subunit gamma-2 expression and promoted osteogenic differentiation via the phosphatidylinositol 3‑kinase/protein kinase B signaling pathway. Furthermore, 3'-SL inhibited the receptor activator of nuclear factor κB ligand-induced osteoclast differentiation of bone marrow-derived macrophages through the nuclear factor κB and mitogen‑activated protein kinase signaling pathway, ameliorated osteoporosis in ovariectomized mice, and positively regulated bone remodeling. Our findings suggest 3'-SL as a potential drug for osteoporosis.

Acidosis induces significant changes to the murine supraspinatus enthesis organic matrix

Rotator cuff pathology is a common musculoskeletal condition that disproportionately affects older adults, as well as patients with diabetes mellitus and chronic kidney disease. It is known that increased age and kidney dysfunction have been correlated to acidotic states, which may be related to the increased incidence of rotator cuff injury. In order to investigate the potential relationship between acidosis and rotator cuff composition and mechanics, this study utilizes a 14-day murine model of metabolic acidosis and examines the effects on the supraspinatus tendon-humeral head attachment complex. The elastic matrix in the enthesis exhibited significant changes beginning at day 3 of acidosis exposure. At day 3 and day 7 timepoints, there was a decrease in collagen content seen in both mineralized and unmineralized tissue as well as a decrease in mineral:matrix ratio. There is also evidence of both mineral dissolution and reprecipitation as buffering ions continually promote pH homeostasis. Mechanical properties of the tendon-to-bone attachment were studied; however, no significant changes were elicited in this 14-day model of acidosis. These findings suggest that acidosis can result in significant changes in enthesis composition over the course of 14 days; however, enthesis mechanics may be more structurally mediated rather than affected by compositional changes.

Biomechanical and histomorphological analysis of the mandible in rats with chronic kidney disease

The present study aimed to investigate the biomechanical and histomorphological features of mandibles in an adenine-induced chronic kidney disease-mineral and bone disorder (CKD-MBD) rat model of CKD. A total of 14 Sprague-Dawley rats were randomized into the following two groups: control group and CKD group. At the end of the sixth week, all rats were euthanized, and serum was collected for biochemical marker tests. Macroscopic bone growth and biomechanical parameters were measured in the right hemimandible, while the left hemimandible was used for bone histomorphometric analysis. Compared to the control group, the CKD group showed a significant increase in serum creatinine, blood urea nitrogen, and serum parathyroid hormone at the end of the sixth week. The biomechanical structural properties significantly decreased in the CKD group compared to the control group. Bone histomorphometric analysis indicated that the trabecular bone volume of rats in the CKD group was significantly lower than that of the control group. In the CKD groups, the bone formation parameters of the trabecular bone were significantly increased, while the bone mineralization apposition rates of both the trabecular bone and periosteal cortical bone were significantly increased. The rat CKD model showed deteriorated structural mechanics, low trabecular bone volume, high trabecular bone formation, increased trabecular bone mineralization apposition rate, and increased cortical bone mineralization apposition rate, which met the characteristics of osteitis fibrosa, indicating that this model is a useful tool for the study of mandible diseases in CKD patients.

Differential osteoblastic activity in primary metaphyseal trabecular and secondary trabeculae of c-fos deficient mice

OBJECTIVES

It has been highlighted that osteoblastic activities in remodeling-based bone formation are coupled with osteoclastic bone resorption while those in modeling-based bone formation are independent of osteoclasts. This study aimed to verify whether modeling-based bone formation can occur in the absence of osteoclasts.

METHODS

We performed histochemical analyses on the bone of eight-week-old male wild-type and c-fos-/- mice. Histochemical analyses were conducted on primary trabeculae near the chondro-osseous junction (COJ), sites of modeling-based bone formation, and secondary trabeculae, sites of remodeling-based bone formation, in the femora and tibiae of mice.

RESULTS

Alkaline phosphatase (ALP) immunoreactivity, a marker of osteoblastic lineages, was observed in the metaphyseal trabeculae of wild-type mice, while ALP was scattered throughout the femora of c-fos-/- mice. PHOSPHO1, an enzyme involved in matrix vesicle-mediated mineralization, was predominantly detected in primary trabeculae and also within short lines of osteoblasts in secondary trabeculae of wild-type mice. In contrast, femora of c-fos-/- mice showed several patches of PHOSPHO1 positivity in the primary trabeculae, but there were hardly any patches of PHOSPHO1 in secondary trabeculae. Calcein labeling was consistently observed in primary trabeculae close to the COJ in both wild-type and c-fos-/- mice; however, calcein labeling in the secondary trabeculae was only detected in wild-type mice. Transmission electron microscopic examination demonstrated abundant rough endoplasmic reticulum in the osteoblasts in secondary trabeculae of wild-type mice, but not in those of c-fos-/- mice.

CONCLUSIONS

Osteoblastic activities at the sites of modeling-based bone formation may be maintained in the absence of osteoclasts.

Utility and Limitations of TALLYHO/JngJ as a Model for Type 2 Diabetes-Induced Bone Disease

Type 2 diabetes mellitus (T2DM) increases risk of fractures due to bone microstructural and material deficits, though the mechanisms remain unclear. Preclinical models mimicking diabetic bone disease are required to further understand its pathogenesis. The TALLYHO/JngJ (TH) mouse is a polygenic model recapitulating adolescent-onset T2DM in humans. Due to incomplete penetrance of the phenotype ~25% of male TH mice never develop hyperglycemia, providing a strain-matched nondiabetic control. We performed a comprehensive characterization of the metabolic and skeletal phenotype of diabetic TH mice and compared them to either their nondiabetic TH controls or the recommended SWR/J controls to evaluate their suitability to study diabetic bone disease in humans. Compared to both controls, male TH mice with T2DM exhibited higher blood glucose levels, weight along with impaired glucose tolerance and insulin sensitivity. TH mice with/without T2DM displayed higher cortical bone parameters and lower trabecular bone parameters in the femurs and vertebrae compared to SWR/J. The mechanical properties remained unchanged for all three groups except for a low-energy failure in TH mice with T2DM only compared to SWR/J. Histomorphometry analyses only revealed higher number of osteoclasts and osteocytes for SWR/J compared to both groups of TH. Bone turnover markers procollagen type 1 N-terminal propeptide (P1NP) and tartrate-resistant acid phosphatase (TRAP) were low for both groups of TH mice compared to SWR/J. Silver nitrate staining of the femurs revealed low number of osteocyte lacunar and dendrites in TH mice with T2DM. Three-dimensional assessment showed reduced lacunar parameters in trabecular and cortical bone. Notably, osteocyte morphology changed in TH mice with T2DM compared to SWR/J. In summary, our study highlights the utility of the TH mouse to study T2DM, but not necessarily T2DM-induced bone disease, as there were no differences in bone strength and bone cell parameters between diabetic and non-diabetic TH mice. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Radiation-induced bone loss in mice is ameliorated by inhibition of HIF-2α in skeletal progenitor cells

Radiotherapy remains a common treatment modality for cancer despite skeletal complications. However, there are currently no effective treatments for radiation-induced bone loss, and the consequences of radiotherapy on skeletal progenitor cell (SPC) survival and function remain unclear. After radiation, leptin receptor-expressing cells, which include a population of SPCs, become localized to hypoxic regions of the bone and stabilize the transcription factor hypoxia-inducible factor-2α (HIF-2α), thus suggesting a role for HIF-2α in the skeletal response to radiation. Here, we conditionally knocked out HIF-2α in leptin receptor-expressing cells and their descendants in mice. Radiation therapy in littermate control mice reduced bone mass; however, HIF-2α conditional knockout mice maintained bone mass comparable to nonirradiated control animals. HIF-2α negatively regulated the number of SPCs, bone formation, and bone mineralization. To test whether blocking HIF-2α pharmacologically could reduce bone loss during radiation, we administered a selective HIF-2α inhibitor called PT2399 (a structural analog of which was recently FDA-approved) to wild-type mice before radiation exposure. Pharmacological inhibition of HIF-2α was sufficient to prevent radiation-induced bone loss in a single-limb irradiation mouse model. Given that ~90% of patients who receive a HIF-2α inhibitor develop anemia because of off-target effects, we developed a bone-targeting nanocarrier formulation to deliver the HIF-2α inhibitor to mouse bone, to increase on-target efficacy and reduce off-target toxicities. Nanocarrier-loaded PT2399 prevented radiation-induced bone loss in mice while reducing drug accumulation in the kidney. Targeted inhibition of HIF-2α may represent a therapeutic approach for protecting bone during radiation therapy.

Centrosome clustering control in osteoclasts through CCR5-mediated signaling

Osteoclasts uniquely resorb calcified bone matrices. To exert their function, mature osteoclasts maintain the cellular polarity and directional vesicle trafficking to and from the resorbing bone surface. However, the regulatory mechanisms and pathophysiological relevance of these processes remain largely unexplored. Bone histomorphometric analyses in Ccr5-deficient mice showed abnormalities in the morphology and functional phenotype of their osteoclasts, compared to wild type mice. We observed disorganized clustering of nuclei, as well as centrosomes that organize the microtubule network, which was concomitant with impaired cathepsin K secretion in cultured Ccr5-deficient osteoclasts. Intriguingly, forced expression of constitutively active Rho or Rac restored these cytoskeletal phenotypes with recovery of cathepsin K secretion. Furthermore, a gene-disease enrichment analysis identified that PLEKHM1, a responsible gene for osteopetrosis, which regulates lysosomal trafficking in osteoclasts, was regulated by CCR5. These experimental results highlighted that CCR5-mediated signaling served as an intracellular organizer for centrosome clustering in osteoclasts, which was involved in the pathophysiology of bone metabolism.

Lipolysis supports bone formation by providing osteoblasts with endogenous fatty acid substrates to maintain bioenergetic status

Bone formation is a highly energy-demanding process that can be impacted by metabolic disorders. Glucose has been considered the principal substrate for osteoblasts, although fatty acids are also important for osteoblast function. Here, we report that osteoblasts can derive energy from endogenous fatty acids stored in lipid droplets via lipolysis and that this process is critical for bone formation. As such, we demonstrate that osteoblasts accumulate lipid droplets that are highly dynamic and provide the molecular mechanism by which they serve as a fuel source for energy generation during osteoblast maturation. Inhibiting cytoplasmic lipolysis leads to both an increase in lipid droplet size in osteoblasts and an impairment in osteoblast function. The fatty acids released by lipolysis from these lipid droplets become critical for cellular energy production as cellular energetics shifts towards oxidative phosphorylation during nutrient-depleted conditions. In vivo, conditional deletion of the ATGL-encoding gene Pnpla2 in osteoblast progenitor cells reduces cortical and trabecular bone parameters and alters skeletal lipid metabolism. Collectively, our data demonstrate that osteoblasts store fatty acids in the form of lipid droplets, which are released via lipolysis to support cellular bioenergetic status when nutrients are limited. Perturbations in this process result in impairment of bone formation, specifically reducing ATP production and overall osteoblast function.

The selective norepinephrine reuptake inhibitor reboxetine promotes late-stage fracture healing in mice

Impaired fracture healing is of high clinical relevance, as up to 15% of patients with long-bone fractures display non-unions. Fracture patients also include individuals treated with selective norepinephrine reuptake inhibitors (SNRI). As SNRI were previously shown to negatively affect bone homeostasis, it remained unclear whether patients with SNRI are at risk of impaired bone healing. Here, we show that daily treatment with the SNRI reboxetine reduces trabecular bone mass in the spine but increases cortical thickness and osteoblast numbers in the femoral midshaft. Most importantly, reboxetine does not impair bone regeneration in a standardized murine fracture model, and even improves callus bridging and biomechanical stability at late healing stages. In sum, reboxetine affects bone remodeling in a site-specific manner. Treatment does not interfere with the early and intermediate stages of bone regeneration and improves healing outcomes of the late-stage fracture callus in mice.

Dissociation of clinical, laboratory, and bone biopsy findings in adult X-linked hypophosphatemia: a case report

X‑linked hypophosphatemia (XLH) is a phosphate wasting disorder. Typical serum constellations include low serum phosphate as well as high alkaline phosphatase (ALP) and fibroblast growth factor 23 (FGF-23 ) levels. Adult XLH patients usually suffer from (pseudo)fractures, enthesopathies, impaired mobility, and osteoarthritis. We report the case of a middle-aged woman with clinically mild disease, relatively balanced laboratory values, but bone non-healing of the femur post-surgery. Transiliac bone biopsy revealed pronounced osteomalacia and severe deterioration of bone microstructure. Due to the lack of XLH-typical symptoms, the patient was not substituted with calcitriol and phosphate in adulthood. Thus, laboratory findings and radiological examinations do not necessarily reflect bone metabolism in XLH. Bone biopsies should be considered in unclear cases or prior to surgery in adults with XLH.

Apolipoprotein E deficiency attenuated osteogenesis via down-regulating osterix

Apolipoprotein E (ApoE), a ligand for low-density lipoprotein receptors, is strongly induced during osteogenesis and has a physiologic role in regulating osteoblast function, but the mechanisms of its action are still unclear. The study aims to elucidate the influence and molecular mechanisms of ApoE on bone formation. An ovariectomy-induced osteoporotic model were conducted in ApoE knockout (ApoE-/-) mice to study the effect of ApoE on the bone system. Bone quality were assessed through bone mineral density and histomorphometric analysis. To investigate the underlying role and mechanisms of ApoE during osteogenesis, primary osteoblasts from the calvariums of newborn ApoE-/- or wild-type (WT) mice were cultured in the osteoblastic differentiation medium in vitro for further research. Our animal experiment data showed that ApoE-/- mice exhibited bone loss, exacerbated by estrogen deprivation after ovariectomy. ApoE deficiency attenuated osteoblast activity and inhibited osteoblast osteogenesis, accompanied by decreased osterix expression. ApoE deficiency did not affect primary osteoblast viability and collagen-1 expression. Moreover, osteoprotegerin expression in ApoE-/- osteoblasts was reduced compared to WT controls. Our study demonstrated that ApoE gene deficiency contributed to bone loss and attenuated osteogenesis by down-regulating osterix expression.

Selective Androgen Receptor Modulators Combined with Treadmill Exercise Have No Bone Benefit in Healthy Adult Rats

The effects of combination treatments using the selective androgen receptor modulators (SARMs) ostarine (OST) or ligandrol (LIG) with treadmill exercise (TE) were studied in healthy adult rats. Fifteen-week-old male Wistar rats were divided into groups (n = 10/group). Experiment 1 consisted of (1) Control group: sedentary rats receiving vehicle; (2) OST: sedentary rats receiving OST; (3) TE: training rats receiving vehicle; (4) OST + TE: training rats receiving OST. Experiment 2 consisted of (1) LIG: sedentary group receiving LIG; (2) LIG + TE: training group receiving LIG. The TE regime was as follows: 25 m/min, 5° elevation, 40 min, five times/week, and the sedentary regime was 5 min, three times/week. OST and LIG were administered subcutaneously (0.4 mg/kg body weight/day, five times/week). After eight weeks, bone samples underwent microcomputed tomographical, biomechanical, histological, and ashing analyses. All the treatments had weak effects on the bone structure without affecting bone biomechanics. The OST + TE improved bone structure, while the LIG + TE had unfavorable effects. In serum, OST, OST + TE, and LIG + TE altered cholesterol and lipoprotein levels; TE did not change the serum parameters. The SARM treatments had no clear bone benefit, and the serum effects can be considered as side effects. TE represents a safe treatment. Because SARMs are increasingly applied in gyms along with physical activities, attention should be paid to possible side effects.

Simultaneous bilateral basicervical femoral neck fractures in a patient with osteomalacia: A case report and literature review

A thin patient with a history of eating disorders developed basicervical femoral neck fracture bilaterally and simultaneously due to vitamin D deficiency osteomalacia. A careful evaluation in thin patients with thigh pain, including bone biopsy, is required to avoid overlooking osteomalacia.

Neuropilin 2 in osteoblasts regulates trabecular bone mass in male mice

Introduction

Neuropilin 2 (NRP2) mediates the effects of class 3 semaphorins and vascular endothelial growth factor and is implicated in axonal guidance and angiogenesis. Moreover, NRP2 expression is suggested to be involved in the regulation of bone homeostasis. Indeed, osteoblasts and osteoclasts express NRP2 and male and female global Nrp2 knockout mice have a reduced bone mass accompanied by reduced osteoblast and increased osteoclast counts.

Methods

We first examined the in vitro effect of the calciotropic hormone 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on Nrp2 transcription in osteoblasts. We next generated mice with a conditional deletion of Nrp2 in the osteoblast cell lineage under control of the paired related homeobox 1 promoter and mice with a conditional Nrp2 knockdown in osteoclasts under control of the Lysozyme promoter. Mice were examined under basal conditions or after treatment with either the bone anabolic vitamin D3 analog WY 1048 or with 1,25(OH)2D3.

Results and discussion

We show that Nrp2 expression is induced by 1,25(OH)2D3 in osteoblasts and is associated with enrichment of the vitamin D receptor in an intronic region of the Nrp2 gene. In male mice, conditional deletion of Nrp2 in osteoblast precursors and mature osteoblasts recapitulated the bone phenotype of global Nrp2 knockout mice, with a reduced cortical cross-sectional tissue area and lower trabecular bone content. However, female mice with reduced osteoblastic Nrp2 expression display a reduced cross-sectional tissue area but have a normal trabecular bone mass. Treatment with the vitamin D3 analog WY 1048 (0.4 μg/kg/d, 14 days, ip) resulted in a similar increase in bone mass in both genotypes and genders. Deleting Nrp2 from the osteoclast lineage did not result in a bone phenotype, even though in vitro osteoclastogenesis of hematopoietic cells derived from mutant mice was significantly increased. Moreover, treatment with a high dose of 1,25(OH)2D3 (0.5 μg/kg/d, 6 days, ip), to induce osteoclast-mediated bone resorption, resulted in a similar reduction in trabecular and cortical bone mass. In conclusion, osteoblastic Nrp2 expression is suggested to regulate bone homeostasis in a sex-specific manner.

Experimental Model for the Study of Reparative Bone Regeneration in the Reconstruction of the Lower Jaw

An experimental in vivo model has been developed on the rabbit mandible to study reparative regeneration of alveolar bone after intercortical split osteotomy and the role of the periosteum in the process of reparative osteogenesis. The peculiarity of this model is fixation of the periosteum over the reconstruction zone, which allows preserving the bone block displaced during surgery and leads to the formation of an organotypic structure of the regenerate with cortical and spongy bone.

BMP-2 (and partially GDF-5) coating significantly accelerates and augments bone formation close to hydroxyapatite/tricalcium-phosphate/brushite implant cylinders for tibial bone defects in senile, osteopenic sheep

Bilateral defects (diameter 8 mm) in the medial tibial head of senile, osteopenic female sheep (n = 48; 9.63 ± 0.10 years; mean ± SEM) were treated with hydroxyapatite (HA)/beta-tricalcium phosphate (β-TCP)/dicalcium phosphate dihydrate (DCPD; brushite) cylinders coated with BMP-2 (25 or 250 micrograms) or growth differentiation factor (GDF)-5 (125 or 1250 micrograms; left side); cylinders without BMP served as controls (right side). Three, 6, and 9 months post-operation (n = 6 each group), bone structure and formation were analyzed in vivo by X-ray and ex vivo by osteodensitometry, histomorphometry, and micro-computed tomography (micro-CT) at 3 and 9 months. Semi-quantitative X-ray evaluation showed significantly increasing bone densities around all implant cylinders over time. High-dose BMP-2-coated cylinders (3 and 9 months) and low-dose GDF-5-coated cylinders (3 and 6 months) demonstrated significantly higher densities than controls (dose-dependent for BMP-2 at 3 months). This was confirmed by osteodensitometry at 9 months for high-dose BMP-2-coated cylinders (and selected GDF-5 groups), and was again dose-dependent for BMP-2. Osteoinduction by BMP-2 was most pronounced in the adjacent bone marrow (dynamic histomorphometry/micro-CT). BMP-2 (and partially GDF-5) significantly increased the bone formation in the vicinity of HA/TCP/DCPD cylinders used to fill tibial bone defects in senile osteopenic sheep and may be suitable for surgical therapy of critical size, non-load-bearing bone defects in cases of failed tibial head fracture or defect healing.

Immunolocalization of Enzymes/Membrane Transporters Related to Bone Mineralization in the Metaphyses of the Long Bones of Parathyroid-Hormone-Administered Mice

The present study aimed to demonstrate the immunolocalization and/or gene expressions of the enzymes and membrane transporters involved in bone mineralization after the intermittent administration of parathyroid hormone (PTH). The study especially focused on TNALP, ENPP1, and PHOSPHO1, which are involved in matrix vesicle-mediated mineralization, as well as PHEX and the SIBLING family, which regulate mineralization deep inside bone. Six-week-old male mice were subcutaneously injected with 20 μg/kg/day of human PTH (1-34) two times per day (n = 6) or four times per day (n = 6) for two weeks. Additionally, control mice (n = 6) received a vehicle. Consistently with an increase in the volume of the femoral trabeculae, the mineral appositional rate increased after PTH administration. The areas positive for PHOSPHO1, TNALP, and ENPP1 in the femoral metaphyses expanded, and the gene expressions assessed by real-time PCR were elevated in PTH-administered specimens when compared with the findings in control specimens. The immunoreactivity and/or gene expressions of PHEX and the SIBLING family (MEPE, osteopontin, and DMP1) significantly increased after PTH administration. For example, MEPE immunoreactivity was evident in some osteocytes in PTH-administered specimens but was hardly observed in control specimens. In contrast, mRNA encoding cathepsin B was significantly reduced. Therefore, the bone matrix deep inside might be further mineralized by PHEX/SIBLING family after PTH administration. In summary, it is likely that PTH accelerates mineralization to maintain a balance with elevated matrix synthesis, presumably by mediating TNALP/ENPP1 cooperation and stimulating PHEX/SIBLING family expression.

Taurine deficiency as a driver of aging

Aging is associated with changes in circulating levels of various molecules, some of which remain undefined. We find that concentrations of circulating taurine decline with aging in mice, monkeys, and humans. A reversal of this decline through taurine supplementation increased the health span (the period of healthy living) and life span in mice and health span in monkeys. Mechanistically, taurine reduced cellular senescence, protected against telomerase deficiency, suppressed mitochondrial dysfunction, decreased DNA damage, and attenuated inflammaging. In humans, lower taurine concentrations correlated with several age-related diseases and taurine concentrations increased after acute endurance exercise. Thus, taurine deficiency may be a driver of aging because its reversal increases health span in worms, rodents, and primates and life span in worms and rodents. Clinical trials in humans seem warranted to test whether taurine deficiency might drive aging in humans.

Pathophysiology of bone disease in chronic kidney disease: from basics to renal osteodystrophy and osteoporosis

Chronic kidney disease (CKD) is a highly prevalent disease that has become a public health problem. Progression of CKD is associated with serious complications, including the systemic CKD-mineral and bone disorder (CKD-MBD). Laboratory, bone and vascular abnormalities define this condition, and all have been independently related to cardiovascular disease and high mortality rates. The "old" cross-talk between kidney and bone (classically known as "renal osteodystrophies") has been recently expanded to the cardiovascular system, emphasizing the importance of the bone component of CKD-MBD. Moreover, a recently recognized higher susceptibility of patients with CKD to falls and bone fractures led to important paradigm changes in the new CKD-MBD guidelines. Evaluation of bone mineral density and the diagnosis of "osteoporosis" emerges in nephrology as a new possibility "if results will impact clinical decisions". Obviously, it is still reasonable to perform a bone biopsy if knowledge of the type of renal osteodystrophy will be clinically useful (low versus high turnover-bone disease). However, it is now considered that the inability to perform a bone biopsy may not justify withholding antiresorptive therapies to patients with high risk of fracture. This view adds to the effects of parathyroid hormone in CKD patients and the classical treatment of secondary hyperparathyroidism. The availability of new antiosteoporotic treatments bring the opportunity to come back to the basics, and the knowledge of new pathophysiological pathways [OPG/RANKL (LGR4); Wnt-ß-catenin pathway], also affected in CKD, offers great opportunities to further unravel the complex physiopathology of CKD-MBD and to improve outcomes.

SIRT6-PAI-1 axis is a promising therapeutic target in aging-related bone metabolic disruption

The mechanistic regulation of bone mass in aged animals is poorly understood. In this study, we examined the role of SIRT6, a longevity-associated factor, in osteocytes, using mice lacking Sirt6 in Dmp-1-expressing cells (cKO mice) and the MLO-Y4 osteocyte-like cell line. cKO mice exhibited increased osteocytic expression of Sost, Fgf23 and senescence inducing gene Pai-1 and the senescence markers p16 and Il-6, decreased serum phosphate levels, and low-turnover osteopenia. The cKO phenotype was reversed in mice that were a cross of PAI-1-null mice with cKO mice. Furthermore, senescence induction in MLO-Y4 cells increased the Fgf23 and Sost mRNA expression. Sirt6 knockout and senescence induction increased HIF-1α binding to the Fgf23 enhancer sequence. Bone mass and serum phosphate levels were higher in PAI-1-null aged mice than in wild-type mice. Therefore, SIRT6 agonists or PAI-1 inhibitors may be promising therapeutic options for aging-related bone metabolism disruptions.

Trabecular bone microcrack accumulation in patients treated with bisphosphonates for durations up to 16 years

This study quantified the length, number, and density of microcracks in bone from patients treated with bisphosphonates as a function of duration. Anterior iliac crest bone samples from 51 osteoporotic Caucasian females continuously treated with oral bisphosphonates for 1-16 years were obtained by bone biopsy. Samples were histologically processed and analyzed for bone area, microcrack number, and microcrack length. The analyses used statistical modeling and considered patient age, bone mineral density, bone volume/total volume, trabecular thickness, and bone turnover as potential covariates. Microcrack density (number of microcracks/total examined bone area) was linearly related (p = 0.018) to bisphosphonate treatment duration. None of the analyzed covariates contributed significantly to the observed relationship between microcrack density and bisphosphonate treatment duration. Observed increases in microcrack density with increasing bisphosphonate treatment duration is important because increasing levels of microcracks may not only affect bone remodeling but also reduce elastic modulus and are suspected to adversely affect other mechanical properties that may influence fracture risk. The present findings add to our prior results showing changes in bone material properties and modulus with bisphosphonate treatment duration and thereby provide a more comprehensive assessment of the relationship between bisphosphonate treatment duration and bone quality. Statement of Clinical Significance: The present findings provide information guiding clinical use of oral bisphosphonates for post-menopausal osteoporosis therapy.

Mouse Models of Mineral Bone Disorders Associated with Chronic Kidney Disease

Patients with chronic kidney disease (CKD) inevitably develop mineral and bone disorders (CKD–MBD), which negatively impact their survival and quality of life. For a better understanding of underlying pathophysiology and identification of novel therapeutic approaches, mouse models are essential. CKD can be induced by surgical reduction of a functional kidney mass, by nephrotoxic compounds and by genetic engineering specifically interfering with kidney development. These models develop a large range of bone diseases, recapitulating different types of human CKD–MBD and associated sequelae, including vascular calcifications. Bones are usually studied by quantitative histomorphometry, immunohistochemistry and micro-CT, but alternative strategies have emerged, such as longitudinal in vivo osteoblast activity quantification by tracer scintigraphy. The results gained from the CKD–MBD mouse models are consistent with clinical observations and have provided significant knowledge on specific pathomechanisms, bone properties and potential novel therapeutic strategies. This review discusses available mouse models to study bone disease in CKD.

Facts to Consider in Developing Materials That Emulate the Upper Jawbone: A Microarchitecture Study Showing Unique Characteristics at Four Different Sites

The maxilla is generally acknowledged as being more trabecular than the mandible. Allograft currently available for use in the maxillofacial region is harvested from the hip and long bones, irrespective of their local characteristics, and grafted onto the jawbones. Other alternative are autograft or commercially available bone substitutes. Due to their inherent differences, an in-depth understanding of the bone microarchitecture is important to develop the most compatible graft for use at the maxilla. This cross-sectional study aimed to determine the microstructures of bone harvested from different sites of the maxilla, to be used for standard setting. Forty-nine specimens from seven human cadavers were harvested from the zygomatic buttress, anterior maxillary sinus wall, anterior nasal spine and anterior palate. Each bone block, measuring of 10 mm × 5 mm, was harvested using rotary instruments. Bone analysis was performed following micro-computed tomography to obtain trabecular number (Tb.N), trabecular separation (Tb.Sp), trabecular thickness (Tb.Th), and bone volume fraction (BV/TV). There were site-related differences, with BV/TV that ranged between 37.38% and 85.83%. The Tb.N was the lowest at the palate (1.12 (mm−1)) and highest at the anterior maxillary sinus wall (1.41 (mm−1)) region. The palate, however, had the highest trabecular separation value (Tb.Sp) at 0.47 mm. The TB.Th was the lowest at the anterior nasal spine (0.34 mm) but both the zygoma and anterior maxillary sinus regions shared the highest Tb.Th (0.44 mm). Except for having the lowest Th.Sp (0.35 mm), the anterior maxillary sinus wall consistently showed higher values together with the zygomatic buttress in all other parameters. Concurring with current clinical practice of harvesting autograft from the zygomatic buttress and anterior maxillary sinus wall, their bony characteristic serve as the microarchitecture standard to adopt when developing new bone graft materials for use in the maxilla.

Juvenile Bone Toxicity: Study Considerations, Regulations, and Techniques for Assessment

Recommendations on study designs that adequately evaluate the in-life effects leading to juvenile bone toxicity, the various imaging modalities that can aid interpretation of the bone effects, biomarkers that may be useful, and regulatory issues were presented in this 2020 ACT symposium. The pathologies encountered in past studies were briefly mentioned. The first speaker covered study design and the numbers of juveniles that may be necessary to power the evaluation. Changes in the International Council for Harmonisation (IHC) guidelines were reviewed. The second speaker launched the rest of the symposium by describing the tools that may help assess juvenile bone toxicity, specifically those used to monitor bone toxicity, healing, and remodeling as they relate or drive the study design including model, species selection, and age. The third speaker addressed in more depth the micro-Computed Tomography (CT) applications in juvenile toxicology for evaluation of skeletal elements and bone growth in both embryo-fetal development (EFD) and pre and postnatal development (PPND) studies. Lastly, a regulatory perspective on strategies to assess juvenile bone toxicity and the concerns of the regulatory agency with respect to these potential changes in the juvenile population was addressed.