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Context: Fragility fractures increase risks for future fractures, morbidity, and mortality. Available pharmacotherapy for underlying osteoporosis is safe and effective but underused. Objective: To improve pharmacotherapy rate representing secondary prevention of osteoporotic fractures. Methods: This single-center, observational, follow-up study included patients with fragility fractures admitted to the Massachusetts General Hospital between February 2016 and December 2019. For patients admitted to the orthopedics service with fragility fracture, the Massachusetts General Hospital Fracture Liaison Service (FLS) was systematically consulted. Initial outpatient follow-up with FLS was established in conjunction with the orthopedic postoperative follow-up visit. Patients at risk for failing timely outpatient follow-up were administered zoledronic acid (ZA) during the index fracture hospitalization. The main outcome measures were percentage of patients with fragility fracture(s) started on pharmacotherapy for osteoporosis and average length of stay and 30-day readmission rate of patients treated with ZA. Results: Compared with baseline (8-11%) and reference (5-20%) rates, integration of FLS to the orthopedics service, along with appropriate inpatient administration of ZA, increased the pharmacotherapy rate to 70% (412/589) among eligible patients with verified treatment status. Inpatient ZA administration neither affected the average length of stay nor 30-day readmission rate. Treatment status of 37.9% (471/1240) of the study patients remained unknown due to lack of or unknown follow-up. Conclusion: Integration of a FLS and orthopedics services along with inpatient ZA administration improved the osteoporosis pharmacotherapy rate among patients with fragility fracture(s) who often had obstacles for outpatient follow-up. [ABSTRACT FROM AUTHOR]

Rodent models are commonly used to evaluate parathyroid hormone (PTH) and PTH-related protein (PTHrP) ligands and analogues for their pharmacologic activities and potential therapeutic utility toward diseases of bone and mineral ion metabolism. Divergence, however, in the amino acid sequences of rodent and human PTH receptors (rat and mouse PTH1Rs are 91% identical to the human PTH1R) can lead to differences in receptor-binding and signaling potencies for such ligands when assessed on rodent vs human PTH1Rs, as shown by cell-based assays in vitro. This introduces an element of uncertainty in the accuracy of rodent models for performing such preclinical evaluations. To overcome this potential uncertainty, we used a homologous recombination-based knockin (KI) approach to generate a mouse (in-host strain C57Bl/6N) in which complementary DNA encoding the human PTH1R replaces a segment (exon 4) of the murine PTH1R gene so that the human and not the mouse PTH1R protein is expressed. Expression is directed by the endogenous mouse promoter and hence occurs in all biologically relevant cells and tissues and at appropriate levels. The resulting homozygous hPTH1R-KI (humanized) mice were healthy over at least 10 generations and showed functional responses to injected PTH analog peptides that are consistent with a fully functional human PTH1R in target bone and kidney cells. The initial evaluation of these mice and their potential utility for predicting behavior of PTH analogues in humans is reported here. [ABSTRACT FROM AUTHOR]

Human adult height reflects the outcome of childhood skeletal growth. Growth plate (epiphyseal) chondrocytes are key determinants of height. As epiphyseal chondrocytes mature and proliferate, they pass through three developmental stages, which are organized into three distinct layers in the growth plate: (i) resting (round), (ii) proliferative (flat), and (iii) hypertrophic. Recent genomewide association studies (GWASs) of human height identified numerous associated loci, which are enriched for genes expressed in growth plate chondrocytes. However, it remains unclear which specific genes expressed in which layers of the growth plate regulate skeletal growth and human height. To connect the genetics of height and growth plate biology, we analyzed GWAS data through the lens of gene expression in the three dissected layers of murine newborn tibial growth plate. For each gene, we derived a specificity score for each growth plate layer and regressed these scores against gene‐level p values from recent height GWAS data. We found that specificity for expression in the round cell layer, which contains chondrocytes early in maturation, is significantly associated with height GWAS p values (p = 8.5 × 10−9); this association remains after conditioning on specificity for the other cell layers. The association also remains after conditioning on membership in an "Online Mendelian Inheritance in Man (OMIM) gene set" (genes known to cause monogenic skeletal growth disorders, p < 9.7 × 10−6). We replicated the association in RNA‐sequencing (RNA‐seq) data from maturing chondrocytes sampled at early and late time points during differentiation in vitro: we found that expression early in differentiation is significantly associated with p values from height GWASs (p = 6.1 × 10−10) and that this association remains after conditioning on expression at 10 days in culture and on the OMIM gene set (p < 0.006). These findings newly implicate genes highlighted by GWASs of height and specifically expressed in the round cell layer as being potentially important regulators of skeletal biology. © 2021 American Society for Bone and Mineral Research (ASBMR). [ABSTRACT FROM AUTHOR]

Blocking the Wnt inhibitor, sclerostin, increases the rate of bone formation in rodents and in humans. On a cellular level, the antibody against sclerostin acts by increasing osteoblast numbers partly by activating the quiescent bone‐lining cells in vivo. No evidence currently exists, to determine whether blocking sclerostin affects early cells of the osteoblast lineage. Here we use a lineage‐tracing strategy that uses a tamoxifen‐dependent cre recombinase, driven by the Sox9 promoter to mark early cells of the osteoblast lineage. We show that, when adult mice are treated with the rat‐13C7, an antibody that blocks sclerostin action in rodents, it increases the numbers of osteoblast precursors and their differentiation into mature osteoblasts in vivo. We also show that rat‐13C7 administration suppresses adipogenesis by suppressing the differentiation of Sox9creER+ skeletal precursors into bone marrow adipocytes in vivo. Using floxed alleles of the CTNNB1 gene encoding β‐catenin, we show that these precursor cells express the canonical Wnt signaling mediator, β‐catenin, and that the actions of the rat‐13C7 antibody to increase the number of early precursors is dependent on direct stimulation of Wnt signaling. The increase in osteoblast precursors and their progeny after the administration of the antibody leads to a robust suppression of apoptosis without affecting the rate of their proliferation. Thus, neutralizing the Wnt‐inhibitor sclerostin increases the numbers of early cells of the osteoblast lineage osteoblasts and suppresses their differentiation into adipocytes in vivo. © 2021 American Society for Bone and Mineral Research (ASBMR). [ABSTRACT FROM AUTHOR]

ABSTRACT Sclerostin antibody (Scl-Ab) increases osteoblast activity, in part through increasing modeling-based bone formation on previously quiescent surfaces. Histomorphometric studies have suggested that this might occur through conversion of bone lining cells into active osteoblasts. However, direct data demonstrating Scl-Ab-induced conversion of lining cells into active osteoblasts are lacking. Here, we used in vivo lineage tracing to determine if Scl-Ab promotes the conversion of lining cells into osteoblasts on periosteal and endocortical bone surfaces in mice. Two independent, tamoxifen-inducible lineage-tracing strategies were used to label mature osteoblasts and their progeny using the DMP1 and osteocalcin promoters. After a prolonged 'chase' period, the majority of labeled cells on bone surfaces assumed a thin, quiescent morphology. Then, mice were treated with either vehicle or Scl-Ab (25 mg/kg) twice over the course of the subsequent week. After euthanization, marked cells were enumerated, their thickness quantified, and proliferation and apoptosis examined. Scl-Ab led to a significant increase in the average thickness of labeled cells on periosteal and endocortical bone surfaces, consistent with osteoblast activation. Scl-Ab did not induce proliferation of labeled cells, and Scl-Ab did not regulate apoptosis of labeled cells. Therefore, direct reactivation of quiescent bone lining cells contributes to the acute increase in osteoblast numbers after Scl-Ab treatment in mice. © 2016 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

ABSTRACT Sclerostin is a potent inhibitor of osteoblastogenesis. Interestingly, newly diagnosed multiple myeloma (MM) patients have high levels of circulating sclerostin that correlate with disease stage and fractures. However, the source and impact of sclerostin in MM remains to be defined. Our goal was to determine the role of sclerostin in the biology of MM and its bone microenvironment as well as investigate the effect of targeting sclerostin with a neutralizing antibody (scl-Ab) in MM bone disease. Here we confirm increased sclerostin levels in MM compared with precursor disease states like monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM. Furthermore, we found that a humanized MM xenograft mouse model bearing human MM cells (NOD-SCID.CB17 male mice injected intravenously with 2.5 million of MM1.S-Luc-GFP cells) demonstrated significantly higher concentrations of mouse-derived sclerostin, suggesting a microenvironmental source of sclerostin. Associated with the increased sclerostin levels, activated β-catenin expression levels were lower than normal in MM mouse bone marrow. Importantly, a high-affinity grade scl-Ab reversed osteolytic bone disease in this animal model. Because scl-Ab did not demonstrate significant in vitro anti-MM activity, we combined it with the proteasome inhibitor carfilzomib. Our data demonstrated that this combination therapy significantly inhibited tumor burden and improved bone disease in our in vivo MM mouse model. In agreement with our in vivo data, sclerostin expression was noted in marrow stromal cells and osteoblasts of MM patient bone marrow samples. Moreover, MM cells stimulated sclerostin expression in immature osteoblasts while inhibiting osteoblast differentiation in vitro. This was in part regulated by Dkk-1 secreted by MM cells and is a potential mechanism contributing to the osteoblast dysfunction noted in MM. Our data confirm the role of sclerostin as a potential therapeutic target in MM bone disease and provides the rationale for studying scl-Ab combined with proteasome inhibitors in MM. © 2016 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

ABSTRACT In humans, aging and glucocorticoid treatment are associated with reduced bone mass and increased marrow adiposity, suggesting that the differentiation of osteoblasts and adipocytes may be coordinately regulated. Within the bone marrow, both osteoblasts and adipocytes are derived from mesenchymal progenitor cells, but the mechanisms guiding the commitment of mesenchymal progenitors into osteoblast versus adipocyte lineages are not fully defined. The heterotrimeric G protein subunit Gsα activates protein kinase A signaling downstream of several G protein-coupled receptors including the parathyroid hormone receptor, and plays a crucial role in regulating bone mass. Here, we show that targeted ablation of Gsα in early osteoblast precursors, but not in differentiated osteocytes, results in a dramatic increase in bone marrow adipocytes. Mutant mice have reduced numbers of mesenchymal progenitors overall, with an increase in the proportion of progenitors committed to the adipocyte lineage. Furthermore, cells committed to the osteoblast lineage retain adipogenic potential both in vitro and in vivo. These findings have clinical implications for developing therapeutic approaches to direct the commitment of mesenchymal progenitors into the osteoblast lineage. © 2014 American Society for Bone and Mineral Research [ABSTRACT FROM AUTHOR]

ABSTRACT The biomedical research enterprise-and the public support for it-is predicated on the belief that discoveries and the conclusions drawn from them can be trusted to build a body of knowledge which will be used to improve human health. As in all other areas of scientific inquiry, knowledge and understanding grow by layering new discoveries upon earlier ones. The process self-corrects and distills knowledge by discarding false ideas and unsubstantiated claims. Although self-correction is inexorable in the long-term, in recent years biomedical scientists and the public alike have become alarmed and deeply troubled by the fact that many published results cannot be reproduced. The chorus of concern reached a high pitch with a recent commentary from the NIH Director, Francis S. Collins, and Principal Deputy Director, Lawrence A. Tabak, and their announcement of specific plans to enhance reproducibility of preclinical research that relies on animal models. In this invited perspective, we highlight the magnitude of the problem across biomedical fields and address the relevance of these concerns to the field of bone and mineral metabolism. We also suggest how our specialty journals, our scientific organizations, and our community of bone and mineral researchers can help to overcome this troubling trend. © 2014 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Wnt signaling is essential for osteogenesis and also functions as an adipogenic switch, but it is not known if interrupting wnt signaling via knockout of β-catenin from osteoblasts would cause bone marrow adiposity. Here, we determined whether postnatal deletion of β-catenin in preosteoblasts, through conditional cre expression driven by the osterix promoter, causes bone marrow adiposity. Postnatal disruption of β-catenin in the preosteoblasts led to extensive bone marrow adiposity and low bone mass in adult mice. In cultured bone marrow-derived cells isolated from the knockout mice, adipogenic differentiation was dramatically increased, whereas osteogenic differentiation was significantly decreased. As myoblasts, in the absence of wnt/β-catenin signaling, can be reprogrammed into the adipocyte lineage, we sought to determine whether the increased adipogenesis we observed partly resulted from a cell-fate shift of preosteoblasts that had to express osterix (lineage-committed early osteoblasts), from the osteoblastic to the adipocyte lineage. Using lineage tracing both in vivo and in vitro we showed that the loss of β-catenin from preosteoblasts caused a cell-fate shift of these cells from osteoblasts to adipocytes, a shift that may at least partly contribute to the bone marrow adiposity and low bone mass in the knockout mice. These novel findings indicate that wnt/β-catenin signaling exerts control over the fate of lineage-committed early osteoblasts, with respect to their differentiation into osteoblastic versus adipocytic populations in bone, and thus offers potential insight into the origin of bone marrow adiposity. © 2012 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

Intermittent administration of parathyroid hormone (PTH) increases bone mass, at least in part, by increasing the number of osteoblasts. One possible source of osteoblasts might be conversion of inactive lining cells to osteoblasts, and indirect evidence is consistent with this hypothesis. To better understand the possible effect of PTH on lining cell activation, a lineage tracing study was conducted using an inducible gene system. Dmp1-CreERt2 mice were crossed with ROSA26R reporter mice to render targeted mature osteoblasts and their descendents, lining cells and osteocytes, detectable by 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside (X-gal) staining. Dmp1-CreERt2(+):ROSA26R mice were injected with 0.25 mg 4-OH-tamoxifen (4-OHTam) on postnatal days 3, 5, 7, 14, and 21. The animals were euthanized on postnatal day 23, 33, or 43 (2, 12, or 22 days after the last 4-OHTam injection). On day 43, mice were challenged with a subcutaneous injection of human PTH (1-34, 80 µg/kg) or vehicle once daily for 3 days. By 22 days after the last 4-OHTam injection, most X-gal (+) cells on the periosteal surfaces of the calvaria and the tibia were flat. Moreover, bone formation rate and collagen I(α1) mRNA expression were decreased at day 43 compared to day 23. After 3 days of PTH injections, the thickness of X-gal (+) cells increased, as did their expression of osteocalcin and collagen I(α1) mRNA. Electron microscopy revealed X-gal-associated chromogen particles in thin cells prior to PTH administration and in cuboidal cells following PTH administration. These data support the hypothesis that intermittent PTH treatment can increase osteoblast number by converting lining cells to mature osteoblasts in vivo. © 2012 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

The article highlights a study that focuses on the signals sent out by bone morphogenetic protein (BMP) and Wnt signaling pathways, which can be useful in the treatment of bone mass density modification. BMP signals are initiated by the activation of type I and type II serine-threonine kinase receptors and its osteogenic function has been proven to play a critical role in osteoblastogenesis. The study was able to conclude that there is an negative regulation in BMP receptor type IA of the endogenous bone mass, which can be mediated by SOST and DKK1.

The article presents a discussion of the role of cells of the osteoblast lineage in the bone marrow microenvironment that is supportive of hematopoiesis. The function of osteoblasts in supporting hematopoietic stem cells (HSCs) is also described, noting the ways that osteoblast precursors at various stages support developing B lymphocytes.

The article focuses on the effect of disrupted signaling by bone morphogenetic proteins (BMP) in osteoblasts via receptor type IA (RIA) on endogenous bone metabolism. The conclusion is that BMPRIA signals affect bone formation and resorption in osteoblasts and reduces bone mass in mutant mice who were given tamoxifen.