Browsing by Subject "Osteocyte"
Now showing 1 - 10 of 17
Results Per Page
Sort Options
Item Bone Mass and Strength are Significantly Improved in Mice Overexpressing Human WNT16 in Osteocytes(Springer, 2017-04) Alam, Imranul; Reilly, Austin M.; Alkhouli, Mohammed; Gerard-O’Riley, Rita L.; Kasipathi, Charishma; Oakes, Dana K.; Wright, Weston B.; Acton, Dena; McQueen, Amie K.; Patel, Bhavmik; Lim, Kyung-Eun; Robling, Alexander G.; Econs, Michael J.; Medicine, School of MedicineRecently, we demonstrated that osteoblast-specific overexpression of human WNT16 increased both cortical and trabecular bone mass and structure in mice. To further identify the cell-specific role of Wnt16 in bone homeostasis, we created transgenic (TG) mice overexpressing human WNT16 in osteocytes using Dmp1 promoter (Dmp1-hWNT16 TG) on C57BL/6 (B6) background. We analyzed bone phenotypes and serum bone biomarkers, performed gene expression analysis and measured dynamic bone histomorphometry in Dmp1-hWNT16 TG and wild-type (WT) mice. Compared to WT mice, Dmp1-hWNT16 TG mice exhibited significantly higher whole-body, spine and femoral aBMD, BMC and trabecular (BV/TV, Tb.N, and Tb.Th) and cortical (bone area and thickness) parameters in both male and female at 12 weeks of age. Femur stiffness and ultimate force were also significantly improved in the Dmp1-hWNT16 TG female mice, compared to sex-matched WT littermates. In addition, female Dmp1-hWNT16 TG mice displayed significantly higher MS/BS, MAR and BFR/BS compared to the WT mice. Gene expression analysis demonstrated significantly higher mRNA level of Alp in both male and female Dmp1-hWNT16 TG mice and significantly higher levels of Osteocalcin, Opg and Rankl in the male Dmp1-hWNT16 TG mice in bone tissue compared to sex-matched WT mice. These results indicate that WNT16 plays a critical role for acquisition of both cortical and trabecular bone mass and strength. Strategies designed to use WNT16 as a target for therapeutic interventions will be valuable to treat osteoporosis and other low bone mass conditions.Item Conditional Deletion of Murine Fgf23: Interruption of the Normal Skeletal Responses to Phosphate Challenge and Rescue of Genetic Hypophosphatemia(Wiley, 2016-06) Clinkenbeard, Erica L.; Cass, Taryn A.; Ni, Pu; Hum, Julia M.; Bellido, Teresita; Allen, Matthew R.; White, Kenneth E.; Department of Medical and Molecular Genetics, School of MedicineThe transgenic and knockout (KO) animals involving Fgf23 have been highly informative in defining novel aspects of mineral metabolism, but are limited by shortened lifespan, inability of spatial/temporal FGF23 control, and infertility of the global KO. To more finely test the role of systemic and genetic influences in FGF23 production, a mouse was developed that carried a floxed ("f")-Fgf23 allele (exon 2 floxed) which demonstrated in vivo recombination when bred to global-Cre transgenic mice (eIIa-cre). Mice homozygous for the recombined allele ("Δ") had undetectable serum intact FGF23, elevated serum phosphate (p < 0.05), and increased kidney Cyp27b1 mRNA (p < 0.05), similar to global Fgf23-KO mice. To isolate cellular FGF23 responses during phosphate challenge, Fgf23(Δ/f) mice were mated with early osteoblast type Iα1 collagen 2.3-kb promoter-cre mice (Col2.3-cre) and the late osteoblast/early osteocyte Dentin matrix protein-1-cre (Dmp1-cre). Fgf23(Δ/f) /Col2.3-cre(+) and Fgf23(Δ/f) /Dmp1-cre(+) exhibited reduced baseline serum intact FGF23 versus controls. After challenge with high-phosphate diet Cre(-) mice had 2.1-fold to 2.5-fold increased serum FGF23 (p < 0.01), but Col2.3-cre(+) mice had no significant increase, and Dmp1-cre(+) mice had only a 37% increase (p < 0.01) despite prevailing hyperphosphatemia in both models. The Fgf23(Δ/f) /Col2.3-cre was bred onto the Hyp (murine X-linked hypophosphatemia [XLH] model) genetic background to test the contribution of osteoblasts and osteocytes to elevated FGF23 and Hyp disease phenotypes. Whereas Hyp mice maintained inappropriately elevated FGF23 considering their marked hypophosphatemia, Hyp/Fgf23(Δ/f) /Col2.3-cre(+) mice had serum FGF23 <4% of Hyp (p < 0.01), and this targeted restriction normalized serum phosphorus and ricketic bone disease. In summary, deleting FGF23 within early osteoblasts and osteocytes demonstrated that both cell types contribute to baseline circulating FGF23 concentrations, and that targeting osteoblasts/osteocytes for FGF23 production can modify systemic responses to changes in serum phosphate concentrations and rescue the Hyp genetic syndrome.Item Defective cancellous bone structure and abnormal response to PTH in cortical bone of mice lacking Cx43 cytoplasmic C-terminus domain(Elsevier, 2015-12) Pacheco-Costa, Rafael; Davis, Hannah M.; Sorenson, Chad; Hon, Mary C.; Hassan, Iraj; Reginato, Rejane D.; Allen, Matthew R.; Bellido, Teresita; Plotkin, Lilian I.; Department of Anatomy & Cell Biology, IU School of MedicineConnexin 43 (Cx43) forms gap junction channels and hemichannels that allow the communication among osteocytes, osteoblasts, and osteoclasts. Cx43 carboxy-terminal (CT) domain regulates channel opening and intracellular signaling by acting as a scaffold for structural and signaling proteins. To determine the role of Cx43 CT domain in bone, mice in which one allele of full length Cx43 was replaced by a mutant lacking the CT domain (Cx43(ΔCT/fl)) were studied. Cx43(ΔCT/fl) mice exhibit lower cancellous bone volume but higher cortical thickness than Cx43(fl/fl) controls, indicating that the CT domain is involved in normal cancellous bone gain but opposes cortical bone acquisition. Further, Cx43(ΔCT) is able to exert the functions of full length osteocytic Cx43 on cortical bone geometry and mechanical properties, demonstrating that domains other than the CT are responsible for Cx43 function in cortical bone. In addition, parathyroid hormone (PTH) failed to increase endocortical bone formation or energy to failure, a mechanical property that indicates resistance to fracture, in cortical bone in Cx43(ΔCT) mice with or without osteocytic full length Cx43. On the other hand, bone mass and bone formation markers were increased by the hormone in all mouse models, regardless of whether full length or Cx43(ΔCT) were or not expressed. We conclude that Cx43 CT domain is involved in proper bone acquisition; and that Cx43 expression in osteocytes is dispensable for some but not all PTH anabolic actions.Item The essential role of Stat3 in bone homeostasis and mechanotransduction(2014) Zhou, Hongkang; Li, Jiliang; Marrs, James; Stocum, David L.; Atkinson, Simon; Aguilar, R. Claudio; Yokota, Hiroki, 1955-Signal Transducer and Activator of Transcription 3 (Stat3) is a transcription factor expressed in bone and joint cells that include osteoblasts, osteocytes, osteoclasts, and chondrocytes. Stat3 is activated by a variety of cytokines and growth factors, including IL-6/gp130 family cytokines. These cytokines not only regulate the differentiation of osteoblasts and osteoclasts, but also regulate proliferation of chondrocytes through Stat3 activation. In 2007, mutations of Stat3 have been confirmed to cause a rare human immunodeficiency disease – Job syndrome which presents skeletal abnormalities like: reduced bone density (osteopenia), scoliosis, hyperextensibility of joints, and recurrent pathological bone fractures. Changes in the Stat3 gene alter the structure and function of the Stat3 proteins, impairing its ability to control the activity of other genes. However, little is known about the effects of Stat3 mutations on bone cells and tissues. To investigate the in vivo physiological role of Stat3 in bone homeostasis, osteoblast/osteocyte-specific Stat3 knockout (KO) mice were generated via the Cre-LoxP recombination system. The osteoblast/osteocyte-specific Stat3 KO mice showed bone abnormalities and an osteoporotic phenotype because of a reduced bone formation rate. Furthermore, inactivation of Stat3 decreased load-driven bone formation, and the disruption of Stat3 in osteoblasts suppressed load-driven mitochondrial activity, which led to an elevated level of reactive oxygen species (ROS) in cultured primary osteoblasts. Stat3 has been found to be responsive to mechanical stimulation, and might play an important role in mechanical signal transduction in osteocytes. To investigate the role Stat3 plays in mechanical signaling transduction, osteocyte-specific Stat3 knockout (KO) mice were created. Inactivation of Stat3 in osteocytes presented a significantly reduced load-driven bone formation. Decreased osteoblast activity indicated by reduced osteoid surface was also found in osteocyte-specific Stat3 KO mice. Moreover, sclerostin (SOST) protein which is a critical osteocyte-specific inhibitor of bone formation, its encoded gene SOST expression has been found to be enhanced in osteocyte-specific Stat3 KO mice. Thus, these results clearly demonstrated that Stat3 plays an important role in bone homeostasis and mechanotransduction, and Stat3 is not only involved in bone-formation-important genes regulation in the nucleus but also in mediation of ROS and oxidative stress in mitochondria.Item Glucocorticoid Excess in Bone and Muscle(Springer, 2018-03) Sato, Amy Y.; Peacock, Munro; Bellido, Teresita; Anatomy and Cell Biology, School of MedicineGlucocorticoids (GC), produced and released by the adrenal glands, regulate numerous physiological processes in a wide range of tissues. Because of their profound immunosuppressive and anti-inflammatory actions, GC are extensively used for the treatment of immune and inflammatory conditions, the management of organ transplantation, and as a component of chemotherapy regimens for cancers. However, both pathologic endogenous elevation and long-term use of exogenous GC are associated with severe adverse effects. In particular, excess GC has devastating effects on the musculoskeletal system. GC increase bone resorption and decrease formation leading to bone loss, microarchitectural deterioration and fracture. GC also induce loss of muscle mass and strength leading to an increased incidence of falls. The combined effects on bone and muscle account for the increased fracture risk with GC. This review summarizes the advance in knowledge in the last two decades about the mechanisms of action of GC in bone and muscle and the attempts to interfere with the damaging actions of GC in these tissues with the goal of developing more effective therapeutic strategies.Item Irisin Mediates Effects on Bone and Fat via αV Integrin Receptors(Elsevier, 2018-12-13) Kim, Hyeonwoo; Wrann, Christiane D.; Jedrychowski, Mark; Vidoni, Sara; Kitase, Yukiko; Nagano, Kenichi; Zhou, Chenhe; Chou, Joshua; Parkman, Virginia-Jeni A.; Novick, Scott J.; Strutzenberg, Timothy S.; Pascal, Bruce D.; Le, Phuong T.; Brooks, Daniel J.; Roche, Alexander M.; Gerber, Kaitlyn K.; Mattheis, Laura; Chen, Wenjing; Tu, Hua; Bouxsein, Mary L.; Griffin, Patrick R.; Baron, Roland; Rosen, Clifford J.; Bonewald, Lynda F.; Spiegelman, Bruce M.; Orthopaedic Surgery, School of MedicineIrisin is secreted by muscle, increases with exercise, and mediates certain favorable effects of physical activity. In particular, irisin has been shown to have beneficial effects in adipose tissues, brain, and bone. However, the skeletal response to exercise is less clear, and the receptor for irisin has not been identified. Here we show that irisin binds to proteins of the αV class of integrins, and biophysical studies identify interacting surfaces between irisin and αV/β5 integrin. Chemical inhibition of the αV integrins blocks signaling and function by irisin in osteocytes and fat cells. Irisin increases both osteocytic survival and production of sclerostin, a local modulator of bone remodeling. Genetic ablation of FNDC5 (or irisin) completely blocks osteocytic osteolysis induced by ovariectomy, preventing bone loss and supporting an important role of irisin in skeletal remodeling. Identification of the irisin receptor should greatly facilitate our understanding of irisin's function in exercise and human health.Item Mechanical Loading-Driven Tumor Suppression Is Mediated by Lrp5-Dependent and Independent Mechanisms(MDPI, 2021-01-13) Feng, Yan; Liu, Shengzhi; Zha, Rongrong; Sun, Xun; Li, Kexin; Robling, Alexander; Li, Baiyan; Yokota, Hiroki; Biomedical Engineering, School of Engineering and TechnologyBone is mechanosensitive and lipoprotein receptor-related protein 5 (Lrp5)-mediated Wnt signaling promotes loading-driven bone formation. While mechanical loading can suppress tumor growth, the question is whether Lrp5 mediates loading-driven tumor suppression. Herein, we examined the effect of Lrp5 using osteocyte-specific Lrp5 conditional knockout mice. All mice presented noticeable loading-driven tumor suppression in the loaded tibia and non-loaded mammary pad. The degree of suppression was more significant in wild-type than knockout mice. In all male and female mice, knee loading reduced cholesterol and elevated dopamine. It reduced tumor-promoting nexin, which was elevated by cholesterol and reduced by dopamine. By contrast, it elevated p53, TNF-related apoptosis-inducing ligand (TRAIL), and chemerin, and they were regulated reversely by dopamine and cholesterol. Notably, Lrp5 overexpression in osteocytes enhanced tumor suppression, and osteoclast development was inhibited by chemerin. Collectively, this study identified Lrp5-dependent and independent mechanisms for tumor suppression. Lrp5 in osteocytes contributed to the loaded bone, while the Lrp5-independent regulation of dopamine- and cholesterol-induced systemic suppression.Item Myostatin inhibits osteoblastic differentiation by suppressing osteocyte-derived exosomal microRNA-218: A novel mechanism in muscle-bone communication(American Society for Biochemistry and Molecular Biology, 2017-06-30) Qin, Yiwen; Peng, Yuanzhen; Zhao, Wei; Pan, Jianping; Ksiezak-Reding, Hanna; Cardozo, Christopher; Wu, Yingjie; Divieti Pajevic, Paola; Bonewald, Lynda F.; Bauman, William A.; Qin, Weiping; Medicine, School of MedicineMuscle and bone are closely associated in both anatomy and function, but the mechanisms that coordinate their synergistic action remain poorly defined. Myostatin, a myokine secreted by muscles, has been shown to inhibit muscle growth, and the disruption of the myostatin gene has been reported to cause muscle hypertrophy and increase bone mass. Extracellular vesicle-exosomes that carry microRNA (miRNA), mRNA, and proteins are known to perform an important role in cell-cell communication. We hypothesized that myostatin may play a crucial role in muscle-bone interactions and may promote direct effects on osteocytes and on osteocyte-derived exosomal miRNAs, thereby indirectly influencing the function of other bone cells. We report herein that myostatin promotes expression of several bone regulators such as sclerostin (SOST), DKK1, and RANKL in cultured osteocytic (Ocy454) cells, concomitant with the suppression of miR-218 in both parent Ocy454 cells and derived exosomes. Exosomes produced by Ocy454 cells that had been pretreated with myostatin could be taken up by osteoblastic MC3T3 cells, resulting in a marked reduction of Runx2, a key regulator of osteoblastic differentiation, and in decreased osteoblastic differentiation via the down-regulation of the Wnt signaling pathway. Importantly, the inhibitory effect of myostatin-modified osteocytic exosomes on osteoblast differentiation is completely reversed by expression of exogenous miR-218, through a mechanism involving miR-218-mediated inhibition of SOST. Together, our findings indicate that myostatin directly influences osteocyte function and thereby inhibits osteoblastic differentiation, at least in part, through the suppression of osteocyte-derived exosomal miR-218, suggesting a novel mechanism in muscle-bone communication.Item Neonatal iron deficiency causes abnormal phosphate metabolism by elevating FGF23 in normal and ADHR mice.(Wiley, 2014-02) Clinkenbeard, Erica L.; Farrow, Emily G.; Summers, Lelia J.; Cass, Taryn A.; Roberts, Jessica L.; Bayt, Christine; Lahm, Tim; Albrecht, Marjorie; Allen, Matthew R.; Peacock, Munro; White, Kenneth E.; Department of Medical and Molecular Genetics, IU School of MedicineFibroblast growth factor 23 (FGF23) gain of function mutations can lead to autosomal dominant hypophosphatemic rickets (ADHR) disease onset at birth, or delayed onset following puberty or pregnancy. We previously demonstrated that the combination of iron deficiency and a knock-in R176Q FGF23 mutation in mature mice induced FGF23 expression and hypophosphatemia that paralleled the late-onset ADHR phenotype. Because anemia in pregnancy and in premature infants is common, the goal of this study was to test whether iron deficiency alters phosphate handling in neonatal life. Wild-type (WT) and ADHR female breeder mice were provided control or iron-deficient diets during pregnancy and nursing. Iron-deficient breeders were also made iron replete. Iron-deficient WT and ADHR pups were hypophosphatemic, with ADHR pups having significantly lower serum phosphate (p < 0.01) and widened growth plates. Both genotypes increased bone FGF23 mRNA (>50 fold; p < 0.01). WT and ADHR pups receiving low iron had elevated intact serum FGF23; ADHR mice were affected to a greater degree (p < 0.01). Iron-deficient mice also showed increased Cyp24a1 and reduced Cyp27b1, and low serum 1,25-dihydroxyvitamin D (1,25D). Iron repletion normalized most abnormalities. Because iron deficiency can induce tissue hypoxia, oxygen deprivation was tested as a regulator of FGF23, and was shown to stimulate FGF23 mRNA in vitro and serum C-terminal FGF23 in normal rats in vivo. These studies demonstrate that FGF23 is modulated by iron status in young WT and ADHR mice and that hypoxia independently controls FGF23 expression in situations of normal iron. Therefore, disturbed iron and oxygen metabolism in neonatal life may have important effects on skeletal function and structure through FGF23 activity on phosphate regulation.Item Osteocyte-Driven Bone Remodeling(Springer, 2014-01) Bellido, Teresita; Department of Medicine, IU School of MedicineOsteocytes, the most abundant cells in bone, have been long postulated to detect and respond to mechanical and hormonal stimuli and to coordinate the function of osteoblasts and osteoclasts. The discovery that the inhibitor of bone formation sclerostin is primarily expressed in osteocytes in bone and downregulated by anabolic stimuli provided a mechanism by which osteocytes influence the activity of osteoblasts. Advances of the last few years provided experimental evidence demonstrating that osteocytes also participate in the recruitment of osteoclasts and the initiation of bone remodeling. Apoptotic osteocytes trigger yet-to-be-identified signals that attract osteoclast precursors to specific areas of bone, which in turn differentiate to mature, bone-resorbing osteoclasts. Osteocytes are also the source of molecules that regulate the generation and activity of osteoclasts, such as OPG and RANKL; and genetic manipulations of the mouse genome leading to loss or gain of function or to altered expression of either molecule in osteocytes markedly affect bone resorption. This review highlights these investigations and discusses how the novel concept of osteocyte-driven bone resorption and formation impacts our understanding of the mechanisms by which current therapies control bone remodeling.