Browsing by Subject "Bone Resorption"
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Item Bone Resorption by Osteoclasts: Molecular Mechanism of Pyk2 dephosphorylation by Dynamin(Office of the Vice Chancellor for Research, 2010-04-09) Eleniste, Pierre P.; Bruzzaniti, AngelaOsteoporosis is a bone disease that affects hundreds of millions of people worldwide and is characterized by low bone mass and structural deterioration of bone tissue which increases the risk of bone fracture, frailty, morbidity and mortality. Excessive bone loss is caused by osteoclasts which degrade the organic and inorganic components of bone. The specific aim of this study is to identify and characterize the signaling proteins in osteoclasts that are responsible for the bone resorbing activity of these cells. The non-receptor tyrosine kinase, Pyk2, is highly expressed in osteoclasts. Mice lacking Pyk2 have an increase in bone mass due to impairment in osteoclast function. It has been demonstrated that phosphorylation of Pyk2 at Y402 is very important for osteoclast spreading and bone resorption. Our group also reported that the GTPase dynamin controls osteoclast bone resorption in part by leading to the dephosphorylation of Pyk2, thus decreasing Pyk2’s kinase activity. In the current study we examined the intracellular mechanism by which dynamin regulates Pyk2 dephosphorylation. Our findings demonstrated that Pyk2 dephosphorylation is predominately due to GTPase activity of dynamin since expression of dynamin mutants that have reduced affinity for GTP or exhibit defective GTPase activity resulted in an increase in Pyk2 Y402 phosphorylation. We also found that that Pyk2 phosphorylation was rescued in the presence of phenyl arsine oxide (PAO), a chemical inhibitor of tyrosine phosphatases and our preliminary results indicate that the tyrosine phosphatase PTP-PEST is involved in the dynamin-mediated dephosphorylation of Pyk2. Understanding the intracellular mechanism that regulates osteoclast function may lead to the identification of novel proteins that can be targeted by anti-resorptive therapies to treat bone related diseases. Over the past few decades, bisphosphonates have played a significant role in the treatment of osteoporosis. Unfortunately, osteonecrosis of the jaw has been recently described as a harmful side effect of bisphosphonate therapy, emphasizing the need to develop alternative approaches to treat osteoporosis. Novel therapeutic approaches may one day involve inhibitors to tyrosine kinases such as Pyk2 or involve combination therapies where inhibitors are paired with bisphosphonates as a way to boost the efficacy of anti-resorptive therapies with fewer side-effects.Item The Emerging Role of Osteocytes in Cancer in Bone(Wiley, 2019-02-27) Atkinson, Emily G.; Delgado‐Calle, Jesús; Anatomy and Cell Biology, School of MedicineAdvances in the last decade have established the osteocyte, the most abundant cell in bone, as a dynamic and multifunctional cell capable of controlling bone homeostasis by regulating the function of both osteoblasts and osteoclasts. In addition, accumulating evidence demonstrates that osteocyte function is altered in several skeletal disorders, and targeting osteocytes and their derived factors improves skeletal health. Despite the remarkable progress in our understanding of osteocyte biology, there has been a paucity of information regarding the role of osteocytes in the progression of cancer in bone. Exciting, recent discoveries suggest that tumor cells communicate with osteocytes to generate a microenvironment that supports the growth and survival of cancer cells and stimulates bone destruction. This review features these novel findings and discussions regarding the impact of chemotherapy on osteocyte function and the potential of targeting osteocytes for the treatment of cancer in bone. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.Item Fluoride and Cortical Bone: A Histomorphometric Study in Rabbits(1997) Acon-Ng, Patricia; Garetto, Lawrence P.; Dunipace, Ann J.; Katona, Thomas R.; Shanks, James C.; Turner, Charles H.Fluoride has been used in the treatment of osteoporosis because of its apparent ability to directly initiate bone formation. However, fluoride's therapeutic efficacy is controversial. Clinical trials in the range of 50 to 75 mg/day demonstrated severe side effects and a lack of consistent therapeutic benefits. Animal studies have not fully proven a positive effect of fluoride on bone strength. The objective of this study was to determine the histomorphometric changes in the cortical bone of rabbits caused by high doses of fluoride. The hypothesis was that high-dose fluoride intake enhances bone modeling and inhibits bone remodeling. Twenty-four young adult (four months old) female, Dutch Belted rabbits were randomly divided in two groups. The control group received no fluoride in their drinking water, while the experimental group received 100-ppm fluoride. Both groups received approximately 12-ppm fluoride in their food. A pair of tetracycline labels was given two weeks apart before initiation of the experiment. Fluoride treatment was given for six months. A terminal pair of calcein green labels was given before the animals were euthanized. Histomorphometric measurements were made using stereological point-hit and linear-intercept methods. The histomorphometric findings were correlated with fluoride serum and bone levels and also with strength tests. The study demonstrated that fluoride increases bone modeling by increasing periosteal bone apposition and endosteal bone resorption. The net effect of fluoride was an enlargement of the cortical bone and bone marrow and, therefore, the total tissue cross-section. However, the observed increase in bone mass produced by fluoride did not have a positive effect on the mechanical properties of bone. Fluoride did not produce a change in the primary histomorphometric parameters of osteoid surface (OS/BS%) or mineralizing surface (MS/BS%). Fluoride treatment produced an increase in the cortical periosteal modified mineral apposition rate (CPMAR). The remaining dynamic indices (i.e. endosteal MAR, remodeling MAR, cortical endosteal BFR and total BFR, activation frequency and formation period) were not affected by fluoride. The study failed to show an inhibitory effect of fluoride on bone remodeling.Item Inhibition of osteocyte apoptosis prevents the increase in osteocytic receptor activator of nuclear factor κB ligand (RANKL) but does not stop bone resorption or the loss of bone induced by unloading(American Society for Biochemistry and Molecular Biology, 2015-07-31) Plotkin, Lilian I.; Gortazar, Arancha R.; Davis, Hannah M.; Condon, Keith W.; Gabilondo, Hugo; Maycas, Marta; Allen, Matthew R.; Bellido, Teresita; Department of Anatomy & Cell Biology, IU School of MedicineApoptosis of osteocytes and osteoblasts precedes bone resorption and bone loss with reduced mechanical stimulation, and receptor activator of NF-κB ligand (RANKL) expression is increased with unloading in mice. Because osteocytes are major RANKL producers, we hypothesized that apoptotic osteocytes signal to neighboring osteocytes to increase RANKL expression, which, in turn, increases osteoclastogenesis and bone resorption. The traditional bisphosphonate (BP) alendronate (Aln) or IG9402, a BP analog that does not inhibit resorption, prevented the increase in osteocyte apoptosis and osteocytic RANKL expression. The BPs also inhibited osteoblast apoptosis but did not prevent the increase in osteoblastic RANKL. Unloaded mice exhibited high serum levels of the bone resorption marker C-telopeptide fragments of type I collagen (CTX), elevated osteoclastogenesis, and increased osteoclasts in bone. Aln, but not IG9402, prevented all of these effects. In addition, Aln prevented the reduction in spinal and femoral bone mineral density, spinal bone volume/tissue volume, trabecular thickness, mechanical strength, and material strength induced by unloading. Although IG9402 did not prevent the loss of bone mass, it partially prevented the loss of strength, suggesting a contribution of osteocyte viability to strength independent of bone mass. These results demonstrate that osteocyte apoptosis leads to increased osteocytic RANKL. However, blockade of these events is not sufficient to restrain osteoclast formation, inhibit resorption, or stop bone loss induced by skeletal unloading.Item The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure(Public Library of Science, 2020-07-30) Davidson, Rebecca K.; Himes, Evan R.; Takigawa, Shinya; Chen, Andy; Horn, M. Ryne; Meijome, Tomas; Wallace, Joseph M.; Kacena, Melissa A.; Yokota, Hiroki; Nguyen, Andrew V.; Li, Jiliang; Biology, School of ScienceSignal 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.Item Parathyroid hormone receptor signaling induces bone resorption in the adult skeleton by directly regulating the RANKL gene in osteocytes(The Endocrine Society, 2014-08) Ben-awadh, Abdullah N.; Delgado-Calle, Jesus; Tu, Xiaolin; Kuhlenschmidt, Kali; Allen, Matthew R.; Plotkin, Lilian I.; Bellido, Teresita; Department of Anatomy and Cell Biology, IU School of MedicinePTH upregulates the expression of the receptor activator of nuclear factor κB ligand (Rankl) in cells of the osteoblastic lineage, but the precise differentiation stage of the PTH target cell responsible for RANKL-mediated stimulation of bone resorption remains undefined. We report that constitutive activation of PTH receptor signaling only in osteocytes in transgenic mice (DMP1-caPTHR1) was sufficient to increase Rankl expression and bone resorption. Resorption in DMP1-caPTHR1 mice crossed with mice lacking the distal control region regulated by PTH in the Rankl gene (DCR−/−) was similar to DMP1-caPTHR1 mice at 1 month of age, but progressively declined to reach values undistinguishable from wild-type (WT) mice at 5 months of age. Moreover, DMP1-caPTHR1 mice exhibited low tissue material density and increased serum alkaline phosphatase activity at 5 month of age, and these indices of high remodeling were partially and totally corrected in compound DMP1-caPTHR1;DCR−/− male mice, and less affected in female mice. Rankl expression in bones from DMP1-caPTHR1 mice was elevated at both 1 and 5 months of age, whereas it was high, similar to DMP1-caPTHR1 mice at 1 month, but low, similar to WT levels at 5 months in compound mice. Moreover, PTH increased Rankl and decreased Sost and Opg expression in ex vivo bone organ cultures established from WT mice, but only regulated Sost and Opg expression in cultures from DCR−/− mice. PTH also increased RANKL expression in osteocyte-containing primary cultures of calvarial cells, in isolated murine osteocytes, and in WT but not in DCR−/− osteocyte-enriched bones. Thus, PTH upregulates Rankl expression in osteocytes in vitro, ex vivo and in vivo, and resorption induced by PTH receptor signaling in the adult skeleton requires direct regulation of the Rankl gene in osteocytes.Item Single-Limb Irradiation Induces Local and Systemic Bone Loss in a Murine Model(Wiley Blackwell (John Wiley & Sons), 2015-07) Wright, Laura E.; Buijs, Jeroen T.; Kim, Hun-Soo; Coats, Laura E.; Scheidler, Anne M.; John, Sutha K.; She, Yun; Murthy, Sreemala; Ma, Ning; Chin-Sinex, Helen J.; Bellido, Teresita M.; Bateman, Ted A.; Mendonca, Marc S.; Mohammad, Khalid S.; Guise, Theresa A.; Department of Medicine, IU School of MedicineIncreased fracture risk is commonly reported in cancer patients receiving radiotherapy, particularly at sites within the field of treatment. The direct and systemic effects of ionizing radiation on bone at a therapeutic dose are not well-characterized in clinically relevant animal models. Using 20-week-old male C57Bl/6 mice, effects of irradiation (right hindlimb; 2 Gy) on bone volume and microarchitecture were evaluated prospectively by microcomputed tomography and histomorphometry and compared to contralateral-shielded bone (left hindlimb) and non-irradiated control bone. One week postirradiation, trabecular bone volume declined in irradiated tibias (-22%; p < 0.0001) and femurs (-14%; p = 0.0586) and microarchitectural parameters were compromised. Trabecular bone volume declined in contralateral tibias (-17%; p = 0.003), and no loss was detected at the femur. Osteoclast number, apoptotic osteocyte number, and marrow adiposity were increased in irradiated bone relative to contralateral and non-irradiated bone, whereas osteoblast number was unchanged. Despite no change in osteoblast number 1 week postirradiation, dynamic bone formation indices revealed a reduction in mineralized bone surface and a concomitant increase in unmineralized osteoid surface area in irradiated bone relative to contralateral and non-irradiated control bone. Further, dose-dependent and time-dependent calvarial culture and in vitro assays confirmed that calvarial osteoblasts and osteoblast-like MC3T3 cells were relatively radioresistant, whereas calvarial osteocyte and osteocyte-like MLO-Y4 cell apoptosis was induced as early as 48 hours postirradiation (4 Gy). In osteoclastogenesis assays, radiation exposure (8 Gy) stimulated murine macrophage RAW264.7 cell differentiation, and coculture of irradiated RAW264.7 cells with MLO-Y4 or murine bone marrow cells enhanced this effect. These studies highlight the multifaceted nature of radiation-induced bone loss by demonstrating direct and systemic effects on bone and its many cell types using clinically relevant doses; they have important implications for bone health in patients treated with radiation therapy.Item Translation of Premolars in the Dog by Controlling the Moment to Force Ration on the Crown(1968) Fortin, Jean Marc; Norman, R.; Cunningham, D.; Shafer, W.The main purpose of this investigation was to produce bodily tooth movement. A force system based on the moment to force ratio (m/p ratio) was developed and applied to the teeth by means of springs similar to those used in segmented arch technique. An histologic investigation followed the experimentation. The sample consisted of five adult dogs and a relatively young one, all males. On these dogs, light forces of 165 and 147 gms were used for a period of 17, 30 and 35 days. and heavy forces of 490, 450 and 455 gms were used for a period of 120, 107 and 106 days. An intraperitoneal injection of a vital dye, procion red H8BS, was made before placing the appliance in the mouth and used as a marker between old and new bone. Bodily tooth movement was assessed by measuring new bone apposition on the tension side. Most of the teeth did show pure bodily movement, however, slight tipping was noticed in some instances. Direct bone resorption was recorded in all the teeth moved with light and heavy forces with the exception of very few small areas of hyalinization. The only difference between light and heavy forces was in the severity of root resorption. It was found that the heavier the force, the greater was the anchorage loss. The rate of tooth movement was continuous but not constant.