GATA-1 deficiency rescues trabecular but not cortical bone in OPG deficient mice

GATA-1(low/low) mice have an increase in megakaryocytes (MKs) and trabecular bone. The latter is thought to result from MKs directly stimulating osteoblastic bone formation while simultaneously inhibiting osteoclastogenesis. Osteoprotegerin (OPG) is known to inhibit osteoclastogenesis and OPG(-/-) mice have reduced trabecular and cortical bone due to increased osteoclastogenesis. Interestingly, GATA-1(low/low) mice have increased OPG levels. Here, we sought to determine whether GATA-1 knockdown in OPG(-/-) mice could rescue the observed osteoporotic bone phenotype. GATA-1(low/low) mice were bred with OPG(-/-) mice and bone phenotype assessed. GATA-1(low/low) × OPG(-/-) mice have increased cortical bone porosity, similar to OPG(-/-) mice. Both OPG(-/-) and GATA-1(low/low) × OPG(-/-) mice, were found to have increased osteoclasts localized to cortical bone, possibly producing the observed elevated porosity. Biomechanical assessment indicates that OPG(-/-) and GATA-1(low/low) × OPG(-/-) femurs are weaker and less stiff than C57BL/6 or GATA-1(low/low) femurs. Notably, GATA-1(low/low) × OPG(-/-) mice had trabecular bone parameters that were not different from C57BL/6 values, suggesting that GATA-1 deficiency can partially rescue the trabecular bone loss observed with OPG deficiency. The fact that GATA-1 deficiency appears to be able to partially rescue the trabecular, but not the cortical bone phenotype suggests that MKs can locally enhance trabecular bone volume, but that MK secreted factors cannot access cortical bone sufficiently to inhibit osteoclastogenesis or that OPG itself is required to inhibit osteoclastogenesis in cortical bone

Nmp4/CIZ suppresses the response of bone to anabolic parathyroid hormone by regulating both osteoblasts and osteoclasts

How parathyroid hormone (PTH) increases bone mass is unclear, but understanding this phenomenon is significant to the improvement of osteoporosis therapy. Nmp4/CIZ is a nucleocytoplasmic shuttling transcriptional repressor that suppresses PTH-induced osteoblast gene expression and hormone-stimulated gains in murine femoral trabecular bone. To further characterize Nmp4/CIZ suppression of hormone-mediated bone growth, we treated 10-week-old Nmp4-knockout (KO) and wild-type (WT) mice with intermittent human PTH(1–34) at 30 μg/kg daily or vehicle, 7 days/week, for 2, 3, or 7 weeks. Null mice treated with hormone (7 weeks) gained more vertebral and tibial cancellous bone than WT animals, paralleling the exaggerated response in the femur. Interestingly, Nmp4/CIZ suppression of this hormone-stimulated bone formation was not apparent during the first 2 weeks of treatment. Consistent with the null mice enhanced PTH-stimulated addition of trabecular bone, these animals exhibited an augmented hormone-induced increase in serum osteocalcin 3 weeks into treatment. Unexpectedly, the Nmp4-KO mice displayed an osteoclast phenotype. Serum C-terminal telopeptide, a marker for bone resorption, was elevated in the null mice, irrespective of treatment. Nmp4-KO bone marrow cultures produced more osteoclasts, which exhibited elevated resorbing activity, compared to WT cultures. The expression of several genes critical to the development of both osteoblasts and osteoclasts was elevated in Nmp4-KO mice at 2 weeks, but not 3 weeks, of hormone exposure. We propose that Nmp4/CIZ dampens PTH-induced improvement of trabecular bone throughout the skeleton by transiently suppressing hormone-stimulated increases in the expression of proteins key to the required enhanced activity and number of both osteoblasts and osteoclasts

Machine-learning, MRI bone shape and important clinical outcomes in osteoarthritis: data from the Osteoarthritis Initiative

Objectives: Osteoarthritis (OA) structural status is imperfectly classified using radiographic assessment. Statistical shape modelling (SSM), a form of machine-learning, provides precise quantification of a characteristic 3D OA bone shape. We aimed to determine the benefits of this novel measure of OA status for assessing risks of clinically important outcomes. Methods: The study used 4796 individuals from the Osteoarthritis Initiative cohort. SSM-derived femur bone shape (B-score) was measured from all 9433 baseline knee MRIs. We examined the relationship between B-score, radiographic Kellgren-Lawrence grade (KLG) and current and future pain and function as well as total knee replacement (TKR) up to 8 years. Results: B-score repeatability supported 40 discrete grades. KLG and B-score were both associated with risk of current and future pain, functional limitation and TKR; logistic regression curves were similar. However, each KLG included a wide range of B-scores. For example, for KLG3, risk of pain was 34.4 (95% CI 31.7 to 37.0)%, but B-scores within KLG3 knees ranged from 0 to 6; for B-score 0, risk was 17.0 (16.1 to 17.9)% while for B-score 6, it was 52.1 (48.8 to 55.4)%. For TKR, KLG3 risk was 15.3 (13.3 to 17.3)%; while B-score 0 had negligible risk, B-score 6 risk was 35.6 (31.8 to 39.6)%. Age, sex and body mass index had negligible effects on association between B-score and symptoms. Conclusions: B-score provides reader-independent quantification using a single time-point, providing unambiguous OA status with defined clinical risks across the whole range of disease including pre-radiographic OA. B-score heralds a step-change in OA stratification for interventions and improved personalised assessment, analogous to the T-score in osteoporosis

The proto‐oncogene function of Mdm2 in bone

Mouse double minute 2 (Mdm2) is a multifaceted oncoprotein that is highly regulated with distinct domains capable of cellular transformation. Loss of Mdm2 is embryonically lethal, making it difficult to study in a mouse model without additional genetic alterations. Global overexpression through increased Mdm2 gene copy number (Mdm2Tg) results in the development of hematopoietic neoplasms and sarcomas in adult animals. In these mice, we found an increase in osteoblastogenesis, differentiation, and a high bone mass phenotype. Since it was difficult to discern the cell lineage that generated this phenotype, we generated osteoblast‐specific Mdm2 overexpressing (Mdm2TgOb) mice in 2 different strains, C57BL/6 and DBA. These mice did not develop malignancies; however, these animals and the MG63 human osteosarcoma cell line with high levels of Mdm2 showed an increase in bone mineralization. Importantly, overexpression of Mdm2 corrected age‐related bone loss in mice, providing a role for the proto‐oncogenic activity of Mdm2 in bone health of adult animals

C-Mpl Is Expressed on Osteoblasts and Osteoclasts and Is Important in Regulating Skeletal Homeostasis

C-Mpl is the receptor for thrombopoietin (TPO), the main megakaryocyte (MK) growth factor, and c-Mpl is believed to be expressed on cells of the hematopoietic lineage. As MKs have been shown to enhance bone formation, it may be expected that mice in which c-Mpl was globally knocked out (c-Mpl(-/-) mice) would have decreased bone mass because they have fewer MKs. Instead, c-Mpl(-/-) mice have a higher bone mass than WT controls. Using c-Mpl(-/-) mice we investigated the basis for this discrepancy and discovered that c-Mpl is expressed on both osteoblasts (OBs) and osteoclasts (OCs), an unexpected finding that prompted us to examine further how c-Mpl regulates bone. Static and dynamic bone histomorphometry parameters suggest that c-Mpl deficiency results in a net gain in bone volume with increases in OBs and OCs. In vitro, a higher percentage of c-Mpl(-/-) OBs were in active phases of the cell cycle, leading to an increased number of OBs. No difference in OB differentiation was observed in vitro as examined by real-time PCR and functional assays. In co-culture systems, which allow for the interaction between OBs and OC progenitors, c-Mpl(-/-) OBs enhanced osteoclastogenesis. Two of the major signaling pathways by which OBs regulate osteoclastogenesis, MCSF/OPG/RANKL and EphrinB2-EphB2/B4, were unaffected in c-Mpl(-/-) OBs. These data provide new findings for the role of MKs and c-Mpl expression in bone and may provide insight into the homeostatic regulation of bone mass as well as bone loss diseases such as osteoporosis

Lnk Deficiency Leads to TPO-Mediated Osteoclastogenesis and Increased Bone Mass Phenotype

The Lnk adapter protein negatively regulates the signaling of thrombopoietin (TPO), the main megakaryocyte (MK) growth factor. Lnk-deficient (-/-) mice have increased TPO signaling and increased MK number. Interestingly, several mouse models exist in which increased MK number leads to a high bone mass phenotype. Here we report the bone phenotype of these mice. MicroCT and static histomorphometric analyses at 20 weeks showed the distal femur of Lnk-/- mice to have significantly higher bone volume fraction and trabecular number compared to wild-type (WT) mice. Notably, despite a significant increase in the number of osteoclasts (OC), and decreased bone formation rate in Lnk-/- mice compared to WT mice, Lnk-/- mice demonstrated a 2.5-fold greater BV/TV suggesting impaired OC function in vivo. Additionally, Lnk-/- mouse femurs exhibited non-significant increases in mid-shaft cross-sectional area, yet increased periosteal BFR compared to WT femurs was observed. Lnk-/- femurs also had non-significant increases in polar moment of inertia and decreased cortical bone area and thickness, resulting in reduced bone stiffness, modulus, and strength compared to WT femurs. Of note, Lnk is expressed by OC lineage cells and when Lnk-/- OC progenitors are cultured in the presence of TPO, significantly more OC are observed than in WT cultures. Lnk is also expressed in osteoblast (OB) cells and in vitro reduced alkaline phosphatase activity was observed in Lnk-/- cultures. These data suggest that both direct effects on OB and OC as well as indirect effects of MK in regulating OB contributes to the observed high bone mass. J. Cell. Biochem. 118: 2231-2240, 2017

Comparative analysis of authorship trends in the Journal of Hand Surgery European and American volumes: A bibliometric analysis

Background The purpose of this study was to better understand the authorship publishing trends in the field of hand surgery. To accomplish this, a comparative analysis was completed between the European and American volumes of the Journal of Hand Surgery (JHSE and JHSA) over the past three decades. Well-established bibliometric methods were used to examine one representative year from each of the past three decades. The focus of the study was to examine changes in author gender over time as well as to compare authorship trends across the two volumes. Materials and methods All JHSA and JHSE publications from 1985, 1995, 2005, and 2015 were placed into a Microsoft Excel spreadsheet. Data was collected for each publication including the gender of first and corresponding authors, corresponding author position, corresponding author country of origin, number of credited institutions, authors, printed pages, and references. Countries were grouped by regions. Results A total of 450 and 763 manuscripts from JHSE and JHSA, respectively, met inclusion criteria. JHSE and JHSA both showed increases in most variables analyzed over time. Both journals showed an increase in female first and corresponding authors. JHSE and JHSA displayed a rise in collaboration between institutions and countries. Conclusions Both JHSE and JHSA display increasing female inclusion in the hand surgery literature, which has traditionally been a male dominated field. The observed increase in collaboration between institutions and countries is likely linked to advances in technology that allow sharing of information more conveniently and reliably than was previously possible. As further advances are made socially and technologically, hopefully these trends will continue, leading to faster and higher quality research being generated in the field of hand surgery

Skeletal adaptations in young male mice after 4 weeks aboard the International Space Station

Gravity has an important role in both the development and maintenance of bone mass. This is most evident in the rapid and intense bone loss observed in both humans and animals exposed to extended periods of microgravity in spaceflight. Here, cohabitating 9-week-old male C57BL/6 mice resided in spaceflight for ~4 weeks. A skeletal survey of these mice was compared to both habitat matched ground controls to determine the effects of microgravity and baseline samples in order to determine the effects of skeletal maturation on the resulting phenotype. We hypothesized that weight-bearing bones would experience an accelerated loss of bone mass compared to non-weight-bearing bones, and that spaceflight would also inhibit skeletal maturation in male mice. As expected, spaceflight had major negative effects on trabecular bone mass of the following weight-bearing bones: femur, tibia, and vertebrae. Interestingly, as opposed to the bone loss traditionally characterized for most weight-bearing skeletal compartments, the effects of spaceflight on the ribs and sternum resembled a failure to accumulate bone mass. Our study further adds to the insight that gravity has site-specific influences on the skeleton

The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure

Signal Transducer and Activator of Transcription 3 (STAT3) has recently been shown to be involved in bone development and has been implicated in bone diseases, such as Job’s Syndrome. Bone growth and changes have been known for many years to differ between sexes with male bones tending to have higher bone mass than female bones and older females tending to lose bone mass at faster rates than older males. Previous studies using conditional knock mice with Stat3 specifically deleted from the osteoblasts showed both sexes exhibited decreased bone mineral density (BMD) and strength. Using the Cre-Lox system with Cathepsin K promotor driving Cre to target the deletion of the Stat3 gene in mature osteoclasts (STAT3-cKO mice), we observed that 8-week old STAT3-cKO female femurs exhibited significantly lower BMD and bone mineral content (BMC) compared to littermate control (CN) females. There were no differences in BMD and BMC observed between male knock-out and male CN femurs. However, micro-computed tomography (μCT) analysis showed that both male and female STAT3-cKO mice had significant decreases in bone volume/tissue volume (BV/TV). Bone histomorphometry analysis of the distal femur, further revealed a decrease in bone formation rate and mineralizing surface/bone surface (MS/BS) with a significant decrease in osteoclast surface in female, but not male, STAT3-cKO mice. Profiling gene expression in an osteoclastic cell line with a knockdown of STAT3 showed an upregulation of a number of genes that are directly regulated by estrogen receptors. These data collectively suggest that regulation of STAT3 differs in male and female osteoclasts and that inactivation of STAT3 in osteoclasts affects bone turnover more in females than males, demonstrating the complicated nature of STAT3 signaling pathways in osteoclastogenesis. Drugs targeting the STAT3 pathway may be used for treatment of diseases such as Job’s Syndrome and osteoporosis

The Effects of High Fat Diet, Bone Healing, and BMP-2 Treatment on Endothelial Cell Growth and Function

Angiogenesis is a vital process during the regeneration of bone tissue. The aim of this study was to investigate angiogenesis at the fracture site as well as at distal locations from obesity-induced type 2 diabetic mice that were treated with bone morphogenetic protein-2 (BMP-2, local administration at the time of surgery) to heal a femoral critical sized defect (CSD) or saline as a control. Mice were fed a high fat diet (HFD) to induce a type 2 diabetic-like phenotype while low fat diet (LFD) animals served as controls. Endothelial cells (ECs) were isolated from the lungs (LECs) and bone marrow (BMECs) 3 weeks post-surgery, and the fractured femurs were also examined. Our studies demonstrate that local administration of BMP-2 at the fracture site in a CSD model results in complete bone healing within 3 weeks for all HFD mice and 66.7% of LFD mice, whereas those treated with saline remain unhealed. At the fracture site, vessel parameters and adipocyte numbers were significantly increased in BMP-2 treated femurs, irrespective of diet. At distal sites, LEC and BMEC proliferation was not altered by diet or BMP-2 treatment. HFD increased the tube formation ability of both LECs and BMECs. Interestingly, BMP-2 treatment at the time of surgery reduced tube formation in LECs and humeri BMECs. However, migration of BMECs from HFD mice treated with BMP-2 was increased compared to BMECs from HFD mice treated with saline. BMP-2 treatment significantly increased the expression of CD31, FLT-1, and ANGPT2 in LECs and BMECs in LFD mice, but reduced the expression of these same genes in HFD mice. To date, this is the first study that depicts the systemic influence of fracture surgery and local BMP-2 treatment on the proliferation and angiogenic potential of ECs derived from the bone marrow and lungs