scholarly journals Recombinant sclerostin antagonizes effects of ex vivo mechanical loading in trabecular bone and increases osteocyte lacunar size

2018 ◽  
Vol 314 (1) ◽  
pp. C53-C61 ◽  
Author(s):  
M. Kogawa ◽  
K. A. Khalid ◽  
A. R. Wijenayaka ◽  
R. T. Ormsby ◽  
A. Evdokiou ◽  
...  
Keyword(s):  
Trabecular Bone ◽  
Calcium Concentration ◽  
Ex Vivo ◽  
Bone Mineralization ◽  
Apparent Stiffness ◽  
Important Regulator ◽  
Osteocytic Osteolysis ◽  
Control Bone ◽  
Osteocyte Lacunar ◽  
Calcein Uptake

Sclerostin has emerged as an important regulator of bone mass. We have shown that sclerostin can act by targeting late osteoblasts/osteocytes to inhibit bone mineralization and to upregulate osteocyte expression of catabolic factors, resulting in osteocytic osteolysis. Here we sought to examine the effect of exogenous sclerostin on osteocytes in trabecular bone mechanically loaded ex vivo. Bovine trabecular bone cores, with bone marrow removed, were inserted into individual chambers and subjected to daily episodes of dynamic loading. Cores were perfused with either osteogenic media alone or media containing human recombinant sclerostin (rhSCL) (50 ng/ml). Loaded control bone increased in apparent stiffness over time compared with unloaded bone, and this was abrogated in the presence of rhSCL. Loaded bone showed an increase in calcein uptake as a surrogate of mineral accretion, compared with unloaded bone, in which this was substantially inhibited by rhSCL treatment. Sclerostin treatment induced a significant increase in the ionized calcium concentration in the perfusate and the release of β-CTX at several time points, an increased mean osteocyte lacunar size, indicative of osteocytic osteolysis, and the expression of catabolism-related genes. Human primary osteocyte-like cultures treated with rhSCL also released β-CTX from their matrix. These results suggest that osteocytes contribute directly to bone mineral accretion, and to the mechanical properties of bone. Moreover, it appears that sclerostin, acting on osteocytes, can negate this effect by modulating the dimensions of the lacunocanalicular porosity and the composition of the periosteocyte matrix.

scholarly journals Hdac3 regulates bone modeling by suppressing osteoclast responsiveness to RANKL

2020 ◽  
Vol 295 (51) ◽  
pp. 17713-17723
Author(s):  
David H. H. Molstad ◽  
Anna M. Mattson ◽  
Dana L. Begun ◽  
Jennifer J. Westendorf ◽  
Elizabeth W. Bradley
Keyword(s):  
Bone Resorption ◽  
Bone Formation ◽  
Trabecular Bone ◽  
Transcriptional Activity ◽  
Ex Vivo ◽  
Bone Mineralization ◽  
Osteoclast Differentiation ◽  
Bone Modeling ◽  
Osteoclast Number ◽  
Sphingosine 1 Phosphate

Hdac3 is a lysine deacetylase that removes acetyl groups from histones and additional proteins. Although Hdac3 functions within mesenchymal lineage skeletal cells are defined, little is known about Hdac3 activities in bone-resorbing osteoclasts. In this study we conditionally deleted Hdac3 within Ctsk-expressing cells and examined the effects on bone modeling and osteoclast differentiation in mice. Hdac3 deficiency reduced femur and tibia periosteal circumference and increased cortical periosteal osteoclast number. Trabecular bone was likewise reduced and was accompanied by increased osteoclast number per trabecular bone surface. We previously showed that Hdac3 deacetylates the p65 subunit of the NF-κB transcriptional complex to decrease DNA-binding and transcriptional activity. Hdac3-deficient osteoclasts demonstrate increased K310 NF-κB acetylation and NF-κB transcriptional activity. Hdac3-deficient osteoclast lineage cells were hyper-responsive to RANKL and showed elevated ex vivo osteoclast number and size and enhanced bone resorption in pit formation assays. Osteoclast-directed Hdac3 deficiency decreased cortical and trabecular bone mass parameters, suggesting that Hdac3 regulates coupling of bone resorption and bone formation. We surveyed a panel of osteoclast-derived coupling factors and found that Hdac3 suppression diminished sphingosine-1-phosphate production. Osteoclast-derived sphingosine-1-phosphate acts in paracrine to promote bone mineralization. Mineralization of WT bone marrow stromal cells cultured with conditioned medium from Hdac3-deficient osteoclasts was markedly reduced. Expression of alkaline phosphatase, type 1a1 collagen, and osteocalcin was also suppressed, but no change in Runx2 expression was observed. Our results demonstrate that Hdac3 controls bone modeling by suppressing osteoclast lineage cell responsiveness to RANKL and coupling to bone formation.

Ex Vivo Human Trabecular Bone Model for Biocompatibility Evaluation of Calcium Phosphate Composites Modified with Spray Dried Biodegradable Microspheres

2013 ◽  
Vol 2 (10) ◽  
pp. 1361-1369 ◽  
Author(s):  
Julia Schnieders ◽  
Uwe Gbureck ◽  
Oliver Germershaus ◽  
Marita Kratz ◽  
David B. Jones ◽  
...  
Keyword(s):  
Calcium Phosphate ◽  
Trabecular Bone ◽  
Ex Vivo ◽  
Biodegradable Microspheres ◽  
Bone Model ◽  
Human Trabecular Bone ◽  
Spray Dried

scholarly journals LOSS OF PROTEINPOLYSACCHARIDES AT SITES WHERE BONE MINERALIZATION IS INITIATED

1972 ◽  
Vol 20 (4) ◽  
pp. 279-292 ◽  
Author(s):  
D. BAYLINK ◽  
J. WERGEDAL ◽  
E. THOMPSON
Keyword(s):  
Calcium Concentration ◽  
Bone Mineralization ◽  
Bone Matrix ◽  
Indirect Evidence ◽  
Experimental Conditions ◽  
Acid Polysaccharide ◽  
Major Acid ◽  
Tibial Cortex

In both ground sections and demineralized frozen sections of the rat tibial cortex, osteoid but not mature bone matrix stained for proteinpolysaccharides with the Alcian Blue and toluidine blue techniques. The loss of proteinpolysaccharide staining occurred precisely at the mineralizing front, which was identified by in vivo lead or procion markers, not only in normal animals but also in animals in which osteoid width was either increasing or decreasing. In vitro, both proteases and saccharidases abolished proteinpolysaccharide staining of osteoid. Critical electrolyte concentration and other procedures indicated that the major acid polysaccharide component in osteoid is chondroitin sulfate. Consistent with these findings, electron microprobe analyses revealed that sulfur concentration was high in osteoid but dropped abruptly as calcium concentration increased at the mineralizing front. The precise synchronization between loss of proteinpolysaccharides and onset of mineralization under various experimental conditions provides strong indirect evidence that the loss of these macromolecules is somehow involved in initiation of mineralization in bone.

The ex-vivo effects of thyroid status and extracellular calcium concentration on rat atrial and ventricular electrophysiology

1988 ◽  
Vol 66 (1) ◽  
pp. 90-94 ◽  
Author(s):  
R. W. Gristwood ◽  
A. L. Rothaul
Keyword(s):  
Action Potential ◽  
Action Potential Duration ◽  
Calcium Concentration ◽  
Ex Vivo ◽  
Additional Treatment ◽  
Extracellular Calcium ◽  
Krebs Solution ◽  
Thyroid Status ◽  
Extracellular Calcium Concentration ◽  
Atrial Electrophysiology

The purpose of this study was to explore the relationship between the thyroid status and both ventricular and atrial electrophysiology in the rat. The study was extended to consider the effects of altering the extracellular calcium concentration. The work was performed in two sections. First, hypothyroid animals were compared with euthyroid (untreated animals); second, hypothyroid animals were compared with hyperthyroid animals. Rats were rendered hypothyroid by pretreatment with the goitrogen methimazole and hyperthyroid by additional treatment with triiodothyronine. Action potential recordings were obtained using standard microelectrode techniques. Action potential measurements were made initially in a Krebs solution to which had been added 2.55 mM calcium (higher Ca Krebs solution) and at the end of each experiment after stabilization with Krebs solution to which had been added 1.28 mM calcium (lower Ca Krebs solution). Assessment of the change in action potential duration on transition from higher to lower Ca Krebs solution revealed that the euthyroid preparations demonstrated less prolongation of action potential duration than the hypothyroid group, and the hyperthyroid group showed hardly any response to reduction in calcium concentration.

scholarly journals A Role for the Calcitonin Receptor to Limit Bone Loss During Lactation in Female Mice by Inhibiting Osteocytic Osteolysis

Endocrinology ◽  
2015 ◽  
Vol 156 (9) ◽  
pp. 3203-3214 ◽  
Author(s):  
Michele V. Clarke ◽  
Patricia K. Russell ◽  
David M. Findlay ◽  
Stephen Sastra ◽  
Paul H. Anderson ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Direct Action ◽  
Bone Matrix ◽  
Physiological Role ◽  
Mrna Levels ◽  
Calcitonin Receptor ◽  
Micro Computed Tomography ◽  
Littermate Control ◽  
Osteocytic Osteolysis ◽  
Osteocyte Lacunar

During lactation, the large transfer of calcium from the mother to the milk is primarily sourced from the maternal skeleton. To determine whether the calcitonin receptor (CTR) plays a physiological role to protect the skeleton from excessive resorption during lactation, we assessed the maternal skeleton of global CTR knockout (CTRKO) and littermate control mice at the end of lactation (postnatal day 21). Micro-computed tomography analyses showed no effect on trabecular or cortical bone in the distal femur and L1 vertebra of maternal global CTR deletion at the end of lactation in global CTRKO mice compared with that in control mice. Bone resorption, as assessed by osteoclast number and activity at the end of lactation, was unaffected by maternal CTR deletion. Cathepsin K, carbonic anhydrase 2, matrix metalloproteinase 13, and receptor activator of nuclear factor-κB ligand mRNA levels, however, were markedly elevated by 3- to 6.5-fold in whole bone of lactating global CTRKO females. Because these genes have been shown to be up-regulated in osteocytes during lactation when osteocytes resorb their surrounding bone matrix, together with their reported expression of the CTR, we determined the osteocyte lacunar area in cortical bone. After lactation, the top 20% of osteocyte lacunar area in global CTRKO mice was 10% larger than the top 20% in control mice. These data are consistent with an increased osteocytic osteolysis in global CTRKO mice during lactation, which is further supported by the increased serum calcium observed in global CTRKO mice after lactation. These results provide evidence for a physiological role for the CTR to protect the maternal skeleton during lactation by a direct action on osteocytes to inhibit osteolysis.

scholarly journals Erf affects commitment and differentiation of osteoprogenitor cells in cranial sutures via the retinoic acid pathway

2021 ◽  
Author(s):  
Angeliki Vogiatzi ◽  
Ismini Baltsavia ◽  
Emmanuel Dialynas ◽  
Vasiliki Theodorou ◽  
Yan Zhou ◽  
...  
Keyword(s):  
Retinoic Acid ◽  
Osteogenic Differentiation ◽  
Late Onset ◽  
Ex Vivo ◽  
Bone Mineralization ◽  
Cell Types ◽  
Underlying Mechanism ◽  
Cranial Bone ◽  
Exogenous Addition ◽  
Stem And Progenitor Cells

ETS2 repressor factor (ERF) haploinsufficiency causes late onset craniosynostosis (OMIM 600775; CRS4) in humans while in mice Erf-insufficiency also leads to a similar multi-suture synostosis phenotype preceded by mildly reduced calvarium ossification. However, neither the cell types affected nor the effects per se have been identified so far. Here we establish an ex vivo system for the expansion of suture-derived mesenchymal stem and progenitor cells (sdMSCs) and analyze the role of Erf levels in their differentiation. Cellular data suggest that Erf-insufficiency specifically decreases osteogenic differentiation of sdMSCs resulting in the initially delayed mineralization of the calvarium. Transcriptome analysis indicates that Erf is required for efficient osteogenic lineage commitment of sdMSCs. Elevated retinoic acid catabolism due to increased levels of the cytochrome P450 superfamily member Cyp26b1 as a result of decreased Erf levels appears to be the underlying mechanism leading to defective differentiation. Exogenous addition of retinoic acid can rescue the osteogenic differentiation defect suggesting that Erf affects cranial bone mineralization during skull development through retinoic acid gradient regulation

scholarly journals Trib1 regulates eosinophil lineage commitment and identity by restraining the neutrophil program

Blood ◽  
2019 ◽  
Vol 133 (22) ◽  
pp. 2413-2426 ◽  
Author(s):  
Ethan A. Mack ◽  
Sarah J. Stein ◽  
Kelly S. Rome ◽  
Lanwei Xu ◽  
Gerald B. Wertheim ◽  
...  
Keyword(s):  
Ex Vivo ◽  
Receptor Expression ◽  
Lineage Commitment ◽  
Hematopoietic Stem ◽  
Interleukin 5 ◽  
Eosinophil Migration ◽  
Enhancer Binding Protein ◽  
Important Regulator ◽  
And Function

Abstract Eosinophils and neutrophils are critical for host defense, yet gaps in understanding how granulocytes differentiate from hematopoietic stem cells (HSCs) into mature effectors remain. The pseudokinase tribbles homolog 1 (Trib1) is an important regulator of granulocytes; knockout mice lack eosinophils and have increased neutrophils. However, how Trib1 regulates cellular identity and function during eosinophilopoiesis is not understood. Trib1 expression markedly increases with eosinophil-lineage commitment in eosinophil progenitors (EoPs), downstream of the granulocyte/macrophage progenitor (GMP). Using hematopoietic- and eosinophil-lineage–specific Trib1 deletion, we found that Trib1 regulates both granulocyte precursor lineage commitment and mature eosinophil identity. Conditional Trib1 deletion in HSCs reduced the size of the EoP pool and increased neutrophils, whereas deletion following eosinophil lineage commitment blunted the decrease in EoPs without increasing neutrophils. In both modes of deletion, Trib1-deficient mice expanded a stable population of Ly6G+ eosinophils with neutrophilic characteristics and functions, and had increased CCAAT/enhancer binding protein α (C/EBPα) p42. Using an ex vivo differentiation assay, we found that interleukin 5 (IL-5) supports the generation of Ly6G+ eosinophils from Trib1-deficient cells, but is not sufficient to restore normal eosinophil differentiation and development. Furthermore, we demonstrated that Trib1 loss blunted eosinophil migration and altered chemokine receptor expression, both in vivo and ex vivo. Finally, we showed that Trib1 controls eosinophil identity by modulating C/EBPα. Together, our findings provide new insights into early events in myelopoiesis, whereby Trib1 functions at 2 distinct stages to guide eosinophil lineage commitment from the GMP and suppress the neutrophil program, promoting eosinophil terminal identity and maintaining lineage fidelity.

scholarly journals Sugars may control bone mineralization

2007 ◽  
Vol 10 (12) ◽  
pp. 15
Author(s):  
Jonathan Wood
Keyword(s):  
Bone Mineralization ◽  
Control Bone
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