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Hendrickx G, Boudin E, Mateiu L, Yorgan TA, Steenackers E, Kneissel M, Kramer I, Mortier G, Schinke T, Van Hul W. An Additional Lrp4 High Bone Mass Mutation Mitigates the Sost-Knockout Phenotype in Mice by Increasing Bone Remodeling. Calcif Tissue Int 2024; 114:171-181. [PMID: 38051321 DOI: 10.1007/s00223-023-01158-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 10/31/2023] [Indexed: 12/07/2023]
Abstract
Pathogenic variants disrupting the binding between sclerostin (encoded by SOST) and its receptor LRP4 have previously been described to cause sclerosteosis, a rare high bone mass disorder. The sclerostin-LRP4 complex inhibits canonical WNT signaling, a key pathway regulating osteoblastic bone formation and a promising therapeutic target for common bone disorders, such as osteoporosis. In the current study, we crossed mice deficient for Sost (Sost-/-) with our p.Arg1170Gln Lrp4 knock-in (Lrp4KI/KI) mouse model to create double mutant Sost-/-;Lrp4KI/KI mice. We compared the phenotype of Sost-/- mice with that of Sost-/-;Lrp4KI/KI mice, to investigate a possible synergistic effect of the disease-causing p.Arg1170Trp variant in Lrp4 on Sost deficiency. Interestingly, presence of Lrp4KI alleles partially mitigated the Sost-/- phenotype. Cellular and dynamic histomorphometry did not reveal mechanistic insights into the observed phenotypic differences. We therefore determined the molecular effect of the Lrp4KI allele by performing bulk RNA sequencing on Lrp4KI/KI primary osteoblasts. Unexpectedly, mostly genes related to bone resorption or remodeling (Acp5, Rankl, Mmp9) were upregulated in Lrp4KI/KI primary osteoblasts. Verification of these markers in Lrp4KI/KI, Sost-/- and Sost-/-;Lrp4KI/KI mice revealed that sclerostin deficiency counteracts this Lrp4KI/KI effect in Sost-/-;Lrp4KI/KI mice. We therefore hypothesize that models with two inactivating Lrp4KI alleles rather activate bone remodeling, with a net gain in bone mass, whereas sclerostin deficiency has more robust anabolic effects on bone formation. Moreover, these effects of sclerostin and Lrp4 are stronger in female mice, contributing to a more severe phenotype than in males and more detectable phenotypic differences among different genotypes.
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Affiliation(s)
- Gretl Hendrickx
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium
- Department of Human Genetics, KU Leuven, Louvain, Belgium
| | - Eveline Boudin
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium
| | - Ligia Mateiu
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium
| | - Timur A Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Ellen Steenackers
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium
| | - Michaela Kneissel
- Diseases of Aging and Regenerative Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Ina Kramer
- Diseases of Aging and Regenerative Medicine, Novartis Institutes for BioMedical Research, Basel, Switzerland
| | - Geert Mortier
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium
- Department of Human Genetics, KU Leuven, Louvain, Belgium
| | - Thorsten Schinke
- Department of Osteology and Biomechanics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Wim Van Hul
- Centre for Medical Genetics, University and University Hospital of Antwerp, Antwerp, Belgium.
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Morfin C, Sebastian A, Wilson SP, Amiri B, Murugesh DK, Hum NR, Christiansen BA, Loots GG. Mef2c regulates bone mass through Sost-dependent and -independent mechanisms. Bone 2024; 179:116976. [PMID: 38042445 DOI: 10.1016/j.bone.2023.116976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 11/16/2023] [Accepted: 11/17/2023] [Indexed: 12/04/2023]
Abstract
Mef2c is a transcription factor that mediates key cellular behaviors that promote endochondral ossification and bone formation. Previously, Mef2c has been shown to regulate Sost transcription via its osteocyte-specific enhancer, ECR5, and conditional deletions of Mef2cfl/fl with either Col1-Cre or Dmp1-Cre produced generalized high bone mass (HBM) consistent with Van Buchem Disease phenotypes. However, Sost-/-; Mef2cfl/fl; Dmp1-Cre mice produced a significantly higher bone mass phenotype that Sost-/- alone suggesting that Mef2c modulates bone mass through additional mechanisms, independent of Sost. To identify new Mef2c transcriptional targets important in bone metabolism, we profiled gene expression by single-cell RNA sequencing in subpopulations of cells isolated from Mef2cfl/fl; Dmp1-Cre and Mef2cfl/fl; Bglap-Cre femurs, both strains exhibiting similar high bone mass phenotypes. However, we found Mef2cfl/fl; Bglap-Cre to also display a growth plate defect characterized by an expansion of several osteoprogenitor subpopulations. Differential gene expression analysis identified a total of 96 up- and 2434 down- regulated genes in Mef2cfl/fl; Bglap-Cre and 176 up- and 1041 down- regulated genes in Mef2cfl/fl; Dmp1-Cre bone cell subpopulations compared to wildtype mice. Mef2c deletion affected the transcriptomes across several cell types including mesenchymal progenitors (MP), osteoprogenitors (OSP), osteoblast (OB), and osteocyte (OCY) subpopulations. Several energy metabolism genes such as Uqcrb, Ndufv2, Ndufs3, Ndufa13, Ndufb9, Ndufb5, Cox6a1, Cox5a, Atp5o, Atp5g2, Atp5b, Atp5 were significantly down regulated in Mef2c-deficient OBs and OCYs, in both strains. Binding motif analysis of promoter regions of differentially expressed genes identified Mef2c binding in Bone Sialoprotein (BSP/Ibsp), a gene known to cause increased trabecular BV/TV in the femurs of Ibsp-/- mice. Immunohistochemical analysis confirmed the absence of Ibsp protein in OBs and OCYs. These findings suggests that the HBM in Sost-/-; Mef2cfl/fl; Dmp1-Cre is caused by a multitude of transcriptional changes in genes that regulate bone formation, two of which are Sost and Ibsp.
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Affiliation(s)
- Cesar Morfin
- School of Natural Sciences, University of California, Merced, CA, United States; Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States; Department of Orthopaedic Surgery, University of California Davis Health, Sacramento, CA, United States
| | - Aimy Sebastian
- Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States
| | - Stephen P Wilson
- Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States
| | - Beheshta Amiri
- Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States
| | - Deepa K Murugesh
- Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States
| | - Nicholas R Hum
- Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States
| | - Blaine A Christiansen
- Department of Orthopaedic Surgery, University of California Davis Health, Sacramento, CA, United States
| | - Gabriela G Loots
- School of Natural Sciences, University of California, Merced, CA, United States; Physical and Life Sciences Directorate, Lawrence Livermore, National Laboratories, Livermore, CA, United States; Department of Orthopaedic Surgery, University of California Davis Health, Sacramento, CA, United States.
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Moriishi T, Komori T. Osteocytes: Their Lacunocanalicular Structure and Mechanoresponses. Int J Mol Sci 2022; 23:ijms23084373. [PMID: 35457191 PMCID: PMC9032292 DOI: 10.3390/ijms23084373] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 04/13/2022] [Accepted: 04/13/2022] [Indexed: 11/29/2022] Open
Abstract
Osteocytes connect with neighboring osteocytes and osteoblasts through their processes and form an osteocyte network. Shear stress on osteocytes, which is induced by fluid flow in the lacunae and canaliculi, has been proposed as an important mechanism for mechanoresponses. The lacunocanalicular structure is differentially developed in the compression and tension sides of femoral cortical bone and the compression side is more organized and has denser and thinner canaliculi. Mice with an impaired lacunocanalicular structure may be useful for evaluation of the relationship between lacunocanalicular structure and mechanoresponses, although their bone component cells are not normal. We show three examples of mice with an impaired lacunocanalicular structure. Ablation of osteocytes by diphtheria toxin caused massive osteocyte apoptosis, necrosis or secondary necrosis that occurred after apoptosis. Osteoblast-specific Bcl2 transgenic mice were found to have a reduced number of osteocyte processes and canaliculi, which caused massive osteocyte apoptosis and a completely interrupted lacunocanalicular network. Osteoblast-specific Sp7 transgenic mice were also revealed to have a reduced number of osteocyte processes and canaliculi, as well as an impaired, but functionally connected, lacunocanalicular network. Here, we show the phenotypes of these mice in physiological and unloaded conditions and deduce the relationship between lacunocanalicular structure and mechanoresponses.
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Affiliation(s)
- Takeshi Moriishi
- Department of Cell Biology, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8588, Japan;
| | - Toshihisa Komori
- Department of Molecular Bone Biology, Nagasaki University Graduate School of Biomedical Sciences, Nagasaki 852-8588, Japan
- Correspondence: ; Tel.: +81-95-819-7637; Fax: +81-95-819-7638
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Moriishi T, Ito T, Fukuyama R, Qin X, Komori H, Kaneko H, Matsuo Y, Yoshida N, Komori T. Sp7 Transgenic Mice with a Markedly Impaired Lacunocanalicular Network Induced Sost and Reduced Bone Mass by Unloading. Int J Mol Sci 2022; 23:3173. [PMID: 35328592 DOI: 10.3390/ijms23063173] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Revised: 02/24/2022] [Accepted: 03/14/2022] [Indexed: 12/13/2022] Open
Abstract
The relationship of lacunocanalicular network structure and mechanoresponse has not been well studied. The lacunocanalicular structures differed in the compression and tension sides, in the regions, and in genders in wild-type femoral cortical bone. The overexpression of Sp7 in osteoblasts resulted in thin and porous cortical bone with increased osteoclasts and apoptotic osteocytes, and the number of canaliculi was half of that in the wild-type mice, leading to a markedly impaired lacunocanalicular network. To investigate the response to unloading, we performed tail suspension. Unloading reduced trabecular and cortical bone in the Sp7 transgenic mice due to reduced bone formation. Sost-positive osteocytes increased by unloading on the compression side, but not on the tension side of cortical bone in the wild-type femurs. However, these differential responses were lost in the Sp7 transgenic femurs. Serum Sost increased in the Sp7 transgenic mice, but not in the wild-type mice. Unloading reduced the Col1a1 and Bglap/Bglap2 expression in the Sp7 transgenic mice but not the wild-type mice. Thus, Sp7 transgenic mice with the impaired lacunocanalicular network induced Sost expression by unloading but lost the differential regulation in the compression and tension sides, and the mice failed to restore bone formation during unloading, implicating the relationship of lacunocanalicular network structure and the regulation of bone formation in mechanoresponse.
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Yadav PS, Feng S, Cong Q, Kim H, Liu Y, Yang Y. Stat3 loss in mesenchymal progenitors causes Job syndrome-like skeletal defects by reducing Wnt/β-catenin signaling. Proc Natl Acad Sci U S A 2021; 118:e2020100118. [PMID: 34172578 PMCID: PMC8256036 DOI: 10.1073/pnas.2020100118] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Job syndrome is a rare genetic disorder caused by STAT3 mutations and primarily characterized by immune dysfunction along with comorbid skeleton developmental abnormalities including osteopenia, recurrent fracture of long bones, and scoliosis. So far, there is no definitive cure for the skeletal defects in Job syndrome, and treatments are limited to management of clinical symptoms only. Here, we have investigated the molecular mechanism whereby Stat3 regulates skeletal development and osteoblast differentiation. We showed that removing Stat3 function in the developing limb mesenchyme or osteoprogenitor cells in mice resulted in shortened and bow limbs with multiple fractures in long bones that resembled the skeleton symptoms in the Job Syndrome. However, Stat3 loss did not alter chondrocyte differentiation and hypertrophy in embryonic development, while osteoblast differentiation was severely reduced. Genome-wide transcriptome analyses as well as biochemical and histological studies showed that Stat3 loss resulted in down-regulation of Wnt/β-catenin signaling. Restoration of Wnt/β-catenin signaling by injecting BIO, a small molecule inhibitor of GSK3, or crossing with a Lrp5 gain of function (GOF) allele, rescued the bone reduction phenotypes due to Stat3 loss to a great extent. These studies uncover the essential functions of Stat3 in maintaining Wnt/β-catenin signaling in early mesenchymal or osteoprogenitor cells and provide evidence that bone defects in the Job Syndrome are likely caused by Wnt/β-catenin signaling reduction due to reduced STAT3 activities in bone development. Enhancing Wnt/β-catenin signaling could be a therapeutic approach to reduce bone symptoms of Job syndrome patients.
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Affiliation(s)
- Prem Swaroop Yadav
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115
| | - Shuhao Feng
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115
| | - Qian Cong
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115
| | - Hanjun Kim
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115
| | - Yuchen Liu
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115
| | - Yingzi Yang
- Department of Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115;
- Harvard Stem Cell Institute, Cambridge, MA 02138
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Costa S, Fairfield H, Farrell M, Murphy CS, Soucy A, Vary C, Holdsworth G, Reagan MR. Sclerostin antibody increases trabecular bone and bone mechanical properties by increasing osteoblast activity damaged by whole-body irradiation in mice. Bone 2021; 147:115918. [PMID: 33737193 PMCID: PMC8076093 DOI: 10.1016/j.bone.2021.115918] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/22/2021] [Accepted: 03/11/2021] [Indexed: 12/16/2022]
Abstract
Irradiation therapy causes bone deterioration and increased risk for skeletal-related events. Irradiation interferes with trabecular architecture through increased osteoclastic activity, decreased osteoblastic activity, and increased adipocyte expansion in the bone marrow (BM), which further compounds bone-related disease. Neutralizing antibodies to sclerostin (Scl-Ab) increase bone mass and strength by increasing bone formation and reducing bone resorption. We hypothesized that treatment with Scl-Ab would attenuate the adverse effects of irradiation by increasing bone volume and decreasing BM adipose tissue (BMAT), resulting in better quality bone. In this study, 12-week-old female C57BL/6J mice were exposed to 6 Gy whole-body irradiation or were non-irradiated, then administered Scl-Ab (25 mg/kg) or vehicle weekly for 5 weeks. Femoral μCT analysis confirmed that the overall effect of IR significantly decreased trabecular bone volume/total volume (Tb.BV/TV) (2-way ANOVA, p < 0.0001) with a -43.8% loss in Tb.BV/TV in the IR control group. Scl-Ab independently increased Tb.BV/TV by 3.07-fold in non-irradiated and 3.6-fold in irradiated mice (2-way ANOVA, p < 0.0001). Irradiation did not affect cortical parameters, although Scl-Ab increased cortical thickness and area significantly in both irradiated and non-irradiated mice (2-way ANOVA, p < 0.0001). Femoral mechanical testing confirmed Scl-Ab significantly increased bending rigidity and ultimate moment independently of irradiation (2-way ANOVA, p < 0.0001). Static and dynamic histomorphometry of the femoral metaphysis revealed osteoblast vigor, not number, was significantly increased in the irradiated mice treated with Scl-Ab. Systemic alterations were assessed through serum lipidomic analysis, which showed that Scl-Ab normalized lipid profiles in the irradiated group. This data supports the theory of sclerostin as a novel contributor to the regulation of osteoblast activity after irradiation. Overall, our data support the hypothesis that Scl-Ab ameliorates the deleterious effects of whole-body irradiation on bone and adipose tissue in a mouse model. Our findings suggest that future research into localized and systemic therapies after irradiation exposure is warranted.
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Affiliation(s)
- Samantha Costa
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA
| | - Heather Fairfield
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA
| | - Mariah Farrell
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA
| | - Connor S Murphy
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA
| | - Ashley Soucy
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA
| | - Calvin Vary
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA
| | | | - Michaela R Reagan
- Maine Medical Center Research Institute, Scarborough, ME, USA; University of Maine Graduate School of Biomedical Science and Engineering, Orono, ME, USA; Tufts University School of Medicine, Boston, MA, USA.
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Lim KE, Bullock WA, Horan DJ, Williams BO, Warman ML, Robling AG. Co-deletion of Lrp5 and Lrp6 in the skeleton severely diminishes bone gain from sclerostin antibody administration. Bone 2021; 143:115708. [PMID: 33164872 PMCID: PMC7770084 DOI: 10.1016/j.bone.2020.115708] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2020] [Revised: 10/01/2020] [Accepted: 10/20/2020] [Indexed: 01/14/2023]
Abstract
The cysteine knot protein sclerostin is an osteocyte-derived secreted inhibitor of the Wnt co-receptors LRP5 and LRP6. LRP5 plays a dominant role in bone homeostasis, but we previously reported that Sost/sclerostin suppression significantly increased osteogenesis regardless of Lrp5 presence or absence. Those observations suggested that the bone forming effects of sclerostin inhibition can occur through Lrp6 (when Lrp5 is suppressed), or through other yet undiscovered mechanisms independent of Lrp5/6. To distinguish between these two possibilities, we generated mice with compound deletion of Lrp5 and Lrp6 selectively in bone, and treated them with sclerostin monoclonal antibody (Scl-mAb). All mice were homozygous flox for both Lrp5 and Lrp6 (Lrp5f/f; Lrp6f/f), and varied only in whether or not they carried the Dmp1-Cre transgene. Positive (Cre+) and negative (Cre-) mice were injected with Scl-mAb or vehicle from 4.5 to 14 weeks of age. Vehicle-treated Cre+ mice exhibited significantly reduced skeletal properties compared to vehicle-treated Cre- mice, as assessed by DXA, μCT, pQCT, and histology, indicating that Lrp5/6 deletions were effective and efficient. Scl-mAb treatment improved nearly every bone-related parameter among Cre- mice, but the same treatment in Cre+ mice resulted in little to no improvement in skeletal properties. For the few endpoints where Cre+ mice responded to Scl-mAb, it is likely that antibody-induced promotion of Wnt signaling occurred in cell types earlier in the mesenchymal/osteoblast differentiation pathway than the Dmp1-expressing stage. This latter conclusion was supported by changes in some histomorphometric parameters. In conclusion, unlike with the deletion of Lrp5 alone, the bone-selective late-stage co-deletion of Lrp5 and Lrp6 significantly impairs or completely nullifies the osteogenic action of Scl-mAb, and highlights a major role for both Lrp5 and Lrp6 in the mechanism of action for the bone-building effects of sclerostin antibody.
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Affiliation(s)
- Kyung-Eun Lim
- Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Whitney A Bullock
- Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Daniel J Horan
- Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Bart O Williams
- Program for Skeletal Disease and Tumor Microenvironment, Center for Cancer and Cell Biology, Van Andel Research Institute, Grand Rapids, MI, USA
| | - Matthew L Warman
- Department of Orthopaedic Surgery, Boston Children's Hospital, Boston, MA, USA
| | - Alexander G Robling
- Department of Anatomy, Cell Biology & Physiology, Indiana University School of Medicine, Indianapolis, IN, USA; Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, Indianapolis, IN, USA; Richard L. Roudebush VA Medical Center, Indianapolis, IN, USA; Indiana Center for Musculoskeletal Health, Indianapolis, IN, USA.
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Abstract
Bone-related studies have been widely carried out by culturing cells on two-dimensional (2D) culture system because of its easiness of handling, but these 2D in vitro achievements may imply a distinct outcome compared with the in vivo situation. On the contrary, three-dimensional (3D) culture system has been suggested as a better biomimetic in vitro model by providing an appropriate cell-cell or cell-matrix interaction. In this study, we successfully reconstructed a 3D disk type of scaffold-free tissue (SFT) using mouse osteoblast-like cells, which evoked an osteocyte differentiation within 2 days. Particularly, the SFT was also utilized as an in vitro osteocytic model to elucidate the effect of hypoxia on cellular differentiation capability. As a result, the hypoxia upregulated a matured osteocyte marker, Sost, in the SFT, whereas both osteoblast and osteocyte markers were significantly downregulated by hypoxia in the 2D conventional monolayer model. The results imply that the hypoxia may enhance the initiation of osteocyte differentiation and retain the osteocyte differentiation in the 3D culture system. Of note, we reported the significance of 3D culture system that might represent the in vivo situation regarding cellular response to stimuli. Hence, our study suggests wide applications of SFT using osteoblast cells as a novel in vitro osteocyte model for the osteocyte-related studies. Impact statement In this study, we fabricated a three-dimensional (3D) disk type of scaffold-free osteocytic tissue, termed scaffold-free tissue (SFT), reconstructed by mouse osteoblast-like cells. It induced an osteocyte differentiation of osteoblast-like cells in the SFT within 2 days. Moreover, we first showed that a matured osteocyte marker, Sost, was modulated by hypoxia in the SFT in a different manner compared with the two-dimensional (2D) monolayer. These results highlighted the significance of 3D culture system that might represent the in vivo situation regarding cellular response to stimuli. Of note, our model can be utilized as a new in vitro osteocyte model for the osteocyte-related studies.
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Affiliation(s)
- Jeonghyun Kim
- Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan
| | - Taiji Adachi
- Institute for Frontier Life and Medical Sciences, Kyoto University, Kyoto, Japan
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Albiol L, Büttner A, Pflanz D, Mikolajewicz N, Birkhold AI, Kramer I, Kneissel M, Duda GN, Checa S, Willie BM. Effects of Long-Term Sclerostin Deficiency on Trabecular Bone Mass and Adaption to Limb Loading Differ in Male and Female Mice. Calcif Tissue Int 2020; 106:415-430. [PMID: 31873756 DOI: 10.1007/s00223-019-00648-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2019] [Accepted: 12/09/2019] [Indexed: 01/08/2023]
Abstract
A new therapeutic option to treat osteoporosis is focused on Wnt signaling and its inhibitor sclerostin, a product of the Sost gene. In this work, we study the effect of sclerostin deficiency on trabecular bone formation and resorption in male and female mice and whether it affects mechano-responsiveness. Male and female 10- and 26-week-old Sost knockout (KO) and littermate controls (LCs) were subjected to in vivo mechanical loading of the left tibia for 2 weeks. The right tibia served as internal control. The mice were imaged using in vivo micro-computed tomography at days 0, 5, 10, and 15 and tibiae were collected for histomorphometric analyses after euthanasia. Histomorphometry and micro-CT-based 3D time-lapse morphometry revealed an anabolic and anti-catabolic effect of Sost deficiency although increased trabecular bone resorption accompanied by diminished trabecular bone formation occurred with age. Loading led to diminished resorption in adult female but not in male mice. A net gain in bone volume could be achieved with mechanical loading in Sost KO adult female mice, which occurred through a further reduction in resorbed bone volume. Our data show that sclerostin deficiency has a particularly positive effect in adult female mice. Sclerostin antibodies are approved to treat postmenopausal women with high risk of osteoporotic fractures. Further studies are required to clarify whether both sexes benefit equally from sclerostin inhibition.
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Affiliation(s)
- Laia Albiol
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
- Berlin-Brandenburg School for Regenerative Therapies, Berlin, Germany
| | - Alexander Büttner
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - David Pflanz
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Nicholas Mikolajewicz
- Department of Dentistry, McGill University, Montreal, Canada
- Research Centre, Shriners Hospital for Children-Canada, 1003 Decarie Blvd, Montreal, QC, H4A 0A9, Canada
| | - Annette I Birkhold
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
- Continuum Biomechanics and Mechanobiology Research Group, Institute of Applied Mechanics, University of Stuttgart, Stuttgart, Germany
| | | | | | - Georg N Duda
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Sara Checa
- Julius Wolff Institute, Charité - Universitätsmedizin Berlin, Berlin, Germany
| | - Bettina M Willie
- Department of Pediatric Surgery, McGill University, Montreal, Canada.
- Research Centre, Shriners Hospital for Children-Canada, 1003 Decarie Blvd, Montreal, QC, H4A 0A9, Canada.
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10
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Albiol L, Cilla M, Pflanz D, Kramer I, Kneissel M, Duda GN, Willie BM, Checa S. Sost deficiency leads to reduced mechanical strains at the tibia midshaft in strain-matched in vivo loading experiments in mice. J R Soc Interface 2019; 15:rsif.2018.0012. [PMID: 29669893 DOI: 10.1098/rsif.2018.0012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2018] [Accepted: 03/22/2018] [Indexed: 12/18/2022] Open
Abstract
Sclerostin, a product of the Sost gene, is a Wnt-inhibitor and thus negatively regulates bone accrual. Canonical Wnt/β-catenin signalling is also known to be activated in mechanotransduction. Sclerostin neutralizing antibodies are being tested in ongoing clinical trials to target osteoporosis and osteogenesis imperfecta but their interaction with mechanical stimuli on bone formation remains unclear. Sost knockout (KO) mice were examined to gain insight into how long-term Sost deficiency alters the local mechanical environment within the bone. This knowledge is crucial as the strain environment regulates bone adaptation. We characterized the bone geometry at the tibial midshaft of young and adult Sost KO and age-matched littermate control (LC) mice using microcomputed tomography imaging. The cortical area and the minimal and maximal moment of inertia were higher in Sost KO than in LC mice, whereas no difference was detected in either the anterior-posterior or medio-lateral bone curvature. Differences observed between age-matched genotypes were greater in adult mice. We analysed the local mechanical environment in the bone using finite-element models (FEMs), which showed that strains in the tibiae of Sost KO mice are lower than in age-matched LC mice at the diaphyseal midshaft, a region commonly used to assess cortical bone formation and resorption. Our FEMs also suggested that tissue mineral density is only a minor contributor to the strain distribution in tibial cortical bone from Sost KO mice compared to bone geometry. Furthermore, they indicated that although strain gauging experiments matched strains at the gauge site, strains along the tibial length were not comparable between age-matched Sost KO and LC mice or between young and adult animals within the same genotype.
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Affiliation(s)
- Laia Albiol
- Julius Wolff Institute, Charité-Universitätsmedizin Berlin, Berlin, Germany.,Brandenburg School for Regenerative Therapies, Berlin, Germany
| | - Myriam Cilla
- Centro Universitario de la Defensa, Academia General Militar, Zaragoza, Spain.,Aragon Institute of Engineering Research (I3A), University of Zaragoza, Zaragoza, Spain
| | - David Pflanz
- Julius Wolff Institute, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Ina Kramer
- Novartis Institutes for BioMedical Research, Basel, Switzerland
| | | | - Georg N Duda
- Julius Wolff Institute, Charité-Universitätsmedizin Berlin, Berlin, Germany.,Brandenburg School for Regenerative Therapies, Berlin, Germany
| | - Bettina M Willie
- Julius Wolff Institute, Charité-Universitätsmedizin Berlin, Berlin, Germany.,Research Centre, Shriners Hospital for Children-Canada, Department of Pediatric Surgery, McGill University, Montreal, Canada
| | - Sara Checa
- Julius Wolff Institute, Charité-Universitätsmedizin Berlin, Berlin, Germany
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11
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Morse A, Cheng TL, Schindeler A, McDonald MM, Mohanty ST, Kneissel M, Kramer I, Little DG. Dkk1 KO Mice Treated with Sclerostin Antibody Have Additional Increases in Bone Volume. Calcif Tissue Int 2018; 103:298-310. [PMID: 29845410 DOI: 10.1007/s00223-018-0420-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/24/2018] [Accepted: 04/05/2018] [Indexed: 12/17/2022]
Abstract
Dickkopf-1 (DKK1) and sclerostin are antagonists of the Wnt/β-catenin pathway and decreased expression of either results in increased bone formation and mass. As both affect the same signaling pathway, we aimed to elucidate the redundancy and/or compensation of sclerostin and DKK1. Weekly sclerostin antibody (Scl-Ab) was used to treat 9-week-old female Dkk1 KO (Dkk1-/-:Wnt3+/-) mice and compared to Scl-Ab-treated wild-type mice as well as vehicle-treated Dkk1 KO and wild-type animals. While Wnt3 heterozygote (Wnt3+/-) mice show no bone phenotype, Scl-Ab and vehicle-treated control groups of this genotype were included. Specimens were harvested after 3 weeks for microCT, bone histomorphometry, anti-sclerostin immunohistochemistry, and biomechanical testing. Scl-Ab enhanced bone anabolism in all treatment groups, but with synergistic enhancement seen in the cancellous compartment of Dkk1 KO mice (bone volume + 55% Dkk1 KO p < 0.01; + 22% wild type p < 0.05). Scl-Ab treatment produced less marked increases in cortical bone of the tibiae, with anabolic effects similar across genotypes. Mechanical testing confirmed that Scl-Ab improved strength across all genotypes; however, no enhancement was seen within Dkk1 KO mice. Dynamic bone labeling showed that Scl-Ab treatment was associated with increased bone formation, regardless of genotype. Immunohistochemical staining for sclerostin protein indicated no differences in the Dkk1 KO mice, indicating that the increased Wnt signaling associated with DKK1 deficiency was not compensated by upregulation of sclerostin protein. These data suggest complex interactions between Wnt signaling factors in bone, but critically illustrate synergy between DKK1 deficiency and Scl-Ab treatment. These data support the application of dual-targeted therapeutics in the modulation of bone anabolism.
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Affiliation(s)
- Alyson Morse
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, NSW, 2145, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Tegan L Cheng
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, NSW, 2145, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Aaron Schindeler
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, NSW, 2145, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Michelle M McDonald
- Bone Biology Program, The Garvan Institute of Medical Research, Sydney, Australia
| | - Sindhu T Mohanty
- Bone Biology Program, The Garvan Institute of Medical Research, Sydney, Australia
| | | | | | - David G Little
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, NSW, 2145, Australia.
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia.
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12
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Abstract
Sclerosteosis and van Buchem disease (VBD) are two rare autosomal recessive disorders that results from osteoblast hyperactivity, in which progressive bone overgrowth leads to very dense bones, distortion of the face, and entrapment of cranial nerves. Sclerosteosis is caused by loss-of-function mutations in the SOST gene which encodes a secreted glycoprotein, sclerostin. VBD is caused by a noncoding deletion that removes a SOST-specific regulatory element in bone. In bone, SOST is expressed predominantly by osteocytes and sclerostin suppresses bone formation by inhibiting the canonical Wnt signaling pathway. Here we describe how human genetics studies in sclerosteosis and VBD patients, in combination with the generation of transgenic and knockout mice, has led to a better understanding of the role of sclerostin in bone metabolism.
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Affiliation(s)
- Aimy Sebastian
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA
| | - Gabriela G Loots
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA; School of Natural Sciences, University of California, Merced, CA 95343, USA.
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13
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Mosey H, Núñez JA, Goring A, Clarkin CE, Staines KA, Lee PD, Pitsillides AA, Javaheri B. Sost Deficiency does not Alter Bone's Lacunar or Vascular Porosity in Mice. Front Mater 2017; 4:27. [PMID: 29349060 PMCID: PMC5769812 DOI: 10.3389/fmats.2017.00027] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
SCLEROSTIN (Sost) is expressed predominantly in osteocytes acting as a negative regulator of bone formation. In humans, mutations in the SOST gene lead to skeletal overgrowth and increased bone mineral density, suggesting that SCLEROSTIN is a key regulator of bone mass. The function of SCLEROSTIN as an inhibitor of bone formation is further supported by Sost knockout (KO) mice which display a high bone mass with elevated bone formation. Previous studies have indicated that Sost exerts its effect on bone formation through Wnt-mediated regulation of osteoblast differentiation, proliferation, and activity. Recent in vitro studies have also suggested that SCLEROSTIN regulates angiogenesis and osteoblast-to-osteocyte transition. Despite this wealth of knowledge of the mechanisms responsible for SCLEROSTIN action, no previous studies have examined whether SCLEROSTIN regulates osteocyte and vascular configuration in cortices of mouse tibia. Herein, we image tibiae from Sost KO mice and their wild-type (WT) counterparts with high-resolution CT to examine whether lack of SCLEROSTIN influences the morphometric properties of lacunae and vascular canal porosity relating to osteocytes and vessels within cortical bone. Male Sost KO and WT mice (n = 6/group) were sacrificed at 12 weeks of age. Fixed tibiae were analyzed using microCT to examine cortical bone mass and architecture. Then, samples were imaged by using benchtop and synchrotron nano-computed tomography at the tibiofibular junction. Our data, consistent with previous studies show that, Sost deficiency leads to significant enhancement of bone mass by cortical thickening and bigger cross-sectional area and we find that this occurs without modifications of tibial ellipticity, a measure of bone shape. In addition, our data show that there are no significant differences in any lacunar or vascular morphometric or geometric parameters between Sost KO mouse tibia and WT counterparts. We, therefore, conclude that the significant increases in bone mass induced by Sost deficiency are not accompanied by any significant modification in the density, organization, or shape of osteocyte lacunae or vascular content within the cortical bone. These data may imply that SCLEROSTIN does not modify the frequency of osteocytogenic recruitment of osteoblasts to initiate terminal osteocytic differentiation in mice.
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Affiliation(s)
- Henry Mosey
- Skeletal Biology Group, Comparative Biomedical Sciences, The Royal Veterinary College, London, United Kingdom
| | - Juan A. Núñez
- Faculty of Natural and Environmental Sciences, Biological Sciences, University of Southampton, Southampton, United Kingdom
| | - Alice Goring
- Faculty of Natural and Environmental Sciences, Biological Sciences, University of Southampton, Southampton, United Kingdom
| | - Claire E. Clarkin
- Faculty of Natural and Environmental Sciences, Biological Sciences, University of Southampton, Southampton, United Kingdom
| | - Katherine A. Staines
- School of Applied Sciences, Edinburgh Napier University, Edinburgh, United Kingdom
| | - Peter D. Lee
- Manchester X-Ray Imaging Facility, University of Manchester, Manchester, United Kingdom
| | - Andrew A. Pitsillides
- Skeletal Biology Group, Comparative Biomedical Sciences, The Royal Veterinary College, London, United Kingdom
| | - Behzad Javaheri
- Skeletal Biology Group, Comparative Biomedical Sciences, The Royal Veterinary College, London, United Kingdom
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14
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Morse A, McDonald MM, Schindeler A, Peacock L, Mikulec K, Cheng TL, Liu M, Ke HZ, Little DG. Sclerostin Antibody Increases Callus Size and Strength but does not Improve Fracture Union in a Challenged Open Rat Fracture Model. Calcif Tissue Int 2017; 101:217-228. [PMID: 28391431 DOI: 10.1007/s00223-017-0275-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Accepted: 03/28/2017] [Indexed: 10/19/2022]
Abstract
Open fractures remain a challenge in orthopedics. Current strategies to intervene are often inadequate, particularly in severe fractures or when treatment is delayed. Sclerostin is a negative regulator of bone growth and sclerostin-neutralizing antibodies (Scl-Ab) can increase bone mass and strength. The application of these antibodies to improve orthopedic repair has shown varied results, and may be dependent on the location and severity of the bony injury. We examined Scl-Ab treatment within an established rat osteotomy model with periosteal stripping analogous to open fracture repair. In one study, Scl-Ab was given 25 mg/kg bi-weekly, either from the time of fracture or from 3 weeks post-fracture up to an end-point of 12 weeks. A second study treated only delayed union open fractures that did not show radiographic union by week 6 post-fracture. Outcome measures included radiographic union, microCT analysis of bone volume and architecture, and histology. In the first study, Scl-Ab given from either 0 or 3 weeks significantly improved callus bone volume (+52%, p < 0.05 and +58%, p < 0.01) at 12 weeks, as well as strength (+48%, p < 0.05 and +70%, p < 0.05). Despite these improvements, union rate was not changed. In the second study treating only established delayed fractures, bony callus volume was similarly increased by Scl-Ab treatment; however, this did not translate to increased biomechanical strength or union improvement. Sclerostin antibody treatment has limited effects on the healing of challenging open fractures with periosteal stripping, but shows the greatest benefits on callus size and strength with earlier intervention.
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Affiliation(s)
- Alyson Morse
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Michelle M McDonald
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
- Bone Biology Program, The Garvan Institute of Medical Research, Sydney, Australia
| | - Aaron Schindeler
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Lauren Peacock
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
| | - Kathy Mikulec
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
| | - Tegan L Cheng
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia
| | - Min Liu
- Amgen Inc, Thousand Oaks, USA
| | | | - David G Little
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Westmead, Australia.
- Discipline of Paediatrics and Child Health, Faculty of Medicine, University of Sydney, Sydney, Australia.
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15
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Abstract
Hyperhomocysteinemia (HHCY) is a risk factor for osteoporosis but whether HHCY affects bone mineralization or not is still ambiguous. Herein we evaluated whether homocysteine affects tissue mineral density (TMD) of cortical bone and if so the role of osteocytes. CD1 mice administered with homocysteine (5 mg/100 g body weight, i.p.) for 7, 15 and 30 days showed temporal changes in TMD and osteocyte lacunar density in femoral cortices. Short-term administration of homocysteine (day 7) increased osteocyte lacunar density and reduced TMD evidenced by microCT50 while prolonged administration of homocysteine (day 30) reinstated TMD and lacunar density to baseline values. Major differences were decreased number of nucleated osteocyte lacunae, increased number of empty lacunae and cleaved caspase 3-positive osteocyte lacunae in day 30 HHCY bone evidenced by H&E staining and immunohistochemistry. Other differences were induction in mineralization genes like Dmp1, Phex and Sost in cortical bone by real-time PCR and increased number of Dmp1- and Sost-positive osteocyte lacunae in day 30 HHCY bone evidenced by immunohistochemistry. Both HHCY day 7 and day 30 samples showed reduced Young's modulus demonstrating that biomechanical property of bone was lost during early HHCY itself, which did not improve with recovery of TMD. Our results thus demonstrate occurrence of two phases in cortical bone upon HHCY: the early phase that involved loss of TMD and increase in osteocyte numbers and a late phase that involved osteocyte reprogramming, apoptosis and mineralization, which reinstated TMD but compromised biomechanical property. To conclude, osteocytes have a potential role in arbitrating bone pathogenesis during HHCY.
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Affiliation(s)
- Viji Vijayan
- Molecular Sciences LaboratoryNational Institute of Immunology, New Delhi, India
| | - Sarika Gupta
- Molecular Sciences LaboratoryNational Institute of Immunology, New Delhi, India
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16
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Robling AG, Kang KS, Bullock WA, Foster WH, Murugesh D, Loots GG, Genetos DC. Sost, independent of the non-coding enhancer ECR5, is required for bone mechanoadaptation. Bone 2016; 92:180-188. [PMID: 27601226 PMCID: PMC6673653 DOI: 10.1016/j.bone.2016.09.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/07/2016] [Revised: 08/29/2016] [Accepted: 09/02/2016] [Indexed: 11/17/2022]
Abstract
Sclerostin (Sost) is a negative regulator of bone formation that acts upon the Wnt signaling pathway. Sost is mechanically regulated at both mRNA and protein level such that loading represses and unloading enhances Sost expression, in osteocytes and in circulation. The non-coding evolutionarily conserved enhancer ECR5 has been previously reported as a transcriptional regulatory element required for modulating Sost expression in osteocytes. Here we explored the mechanisms by which ECR5, or several other putative transcriptional enhancers regulate Sost expression, in response to mechanical stimulation. We found that in vivo ulna loading is equally osteoanabolic in wildtype and Sost-/- mice, although Sost is required for proper distribution of load-induced bone formation to regions of high strain. Using Luciferase reporters carrying the ECR5 non-coding enhancer and heterologous or homologous hSOST promoters, we found that ECR5 is mechanosensitive in vitro and that ECR5-driven Luciferase activity decreases in osteoblasts exposed to oscillatory fluid flow. Yet, ECR5-/- mice showed similar magnitude of load-induced bone formation and similar periosteal distribution of bone formation to high-strain regions compared to wildtype mice. Further, we found that in contrast to Sost-/- mice, which are resistant to disuse-induced bone loss, ECR5-/- mice lose bone upon unloading to a degree similar to wildtype control mice. ECR5 deletion did not abrogate positive effects of unloading on Sost, suggesting that additional transcriptional regulators and regulatory elements contribute to load-induced regulation of Sost.
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Affiliation(s)
- Alexander G Robling
- Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA; Department of Biomedical Engineering, Indiana University/Purdue University at Indianapolis, Indianapolis, IN 46202, USA
| | - Kyung Shin Kang
- Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Whitney A Bullock
- Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - William H Foster
- Department of Anatomy, Physiology and Cell Biology, University of California Davis, Davis, CA, USA
| | - Deepa Murugesh
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
| | - Gabriela G Loots
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA; Molecular and Cell Biology Unit, School of Natural Sciences, University of California at Merced, Merced, CA, USA
| | - Damian C Genetos
- Department of Anatomy, Physiology and Cell Biology, University of California Davis, Davis, CA, USA.
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17
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Collette NM, Yee CS, Hum NR, Murugesh DK, Christiansen BA, Xie L, Economides AN, Manilay JO, Robling AG, Loots GG. Sostdc1 deficiency accelerates fracture healing by promoting the expansion of periosteal mesenchymal stem cells. Bone 2016; 88:20-30. [PMID: 27102547 PMCID: PMC6277141 DOI: 10.1016/j.bone.2016.04.005] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 03/16/2016] [Accepted: 04/05/2016] [Indexed: 02/07/2023]
Abstract
Loss of Sostdc1, a growth factor paralogous to Sost, causes the formation of ectopic incisors, fused molars, abnormal hair follicles, and resistance to kidney disease. Sostdc1 is expressed in the periosteum, a source of osteoblasts, fibroblasts and mesenchymal progenitor cells, which are critically important for fracture repair. Here, we investigated the role of Sostdc1 in bone metabolism and fracture repair. Mice lacking Sostdc1 (Sostdc1(-/-)) had a low bone mass phenotype associated with loss of trabecular bone in both lumbar vertebrae and in the appendicular skeleton. In contrast, Sostdc1(-/-) cortical bone measurements revealed larger bones with higher BMD, suggesting that Sostdc1 exerts differential effects on cortical and trabecular bone. Mid-diaphyseal femoral fractures induced in Sostdc1(-/-) mice showed that the periosteal population normally positive for Sostdc1 rapidly expands during periosteal thickening and these cells migrate into the fracture callus at 3days post fracture. Quantitative analysis of mesenchymal stem cell (MSC) and osteoblast populations determined that MSCs express Sostdc1, and that Sostdc1(-/-) 5day calluses harbor >2-fold more MSCs than fractured wildtype controls. Histologically a fraction of Sostdc1-positive cells also expressed nestin and α-smooth muscle actin, suggesting that Sostdc1 marks a population of osteochondral progenitor cells that actively participate in callus formation and bone repair. Elevated numbers of MSCs in D5 calluses resulted in a larger, more vascularized cartilage callus at day 7, and a more rapid turnover of cartilage with significantly more remodeled bone and a thicker cortical shell at 21days post fracture. These data support accelerated or enhanced bone formation/remodeling of the callus in Sostdc1(-/-) mice, suggesting that Sostdc1 may promote and maintain mesenchymal stem cell quiescence in the periosteum.
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Affiliation(s)
- Nicole M Collette
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA
| | - Cristal S Yee
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA; Molecular and Cell Biology Unit, School of Natural Sciences, University of California at Merced, Merced, CA, USA
| | - Nicholas R Hum
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA
| | - Deepa K Murugesh
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA
| | | | - LiQin Xie
- Regeneron Pharmaceuticals, Tarrytown, NY, USA
| | | | - Jennifer O Manilay
- Molecular and Cell Biology Unit, School of Natural Sciences, University of California at Merced, Merced, CA, USA
| | | | - Gabriela G Loots
- Biology and Biotechnology Division, Lawrence Livermore National Laboratory, 7000 East Avenue, L-452, Livermore, CA 94550, USA; Molecular and Cell Biology Unit, School of Natural Sciences, University of California at Merced, Merced, CA, USA.
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18
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Sun W, Shi Y, Lee WC, Lee SY, Long F. Rictor is required for optimal bone accrual in response to anti-sclerostin therapy in the mouse. Bone 2016; 85:1-8. [PMID: 26780446 PMCID: PMC4896354 DOI: 10.1016/j.bone.2016.01.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 12/23/2015] [Accepted: 01/13/2016] [Indexed: 01/08/2023]
Abstract
Wnt signaling has emerged as a major target pathway for the development of novel bone anabolic therapies. Neutralizing antibodies against the secreted Wnt antagonist sclerostin (Scl-Ab) increase bone mass in both animal models and humans. Because we have previously shown that Rictor-dependent mTORC2 activity contributes to Wnt signaling, we test here whether Rictor is required for Scl-Ab to promote bone anabolism. Mice with Rictor deleted in the early embryonic limb mesenchyme (Prx1-Cre;Rictor(f/f), hereafter RiCKO) were subjected to Scl-Ab treatment for 5weeks starting at 4months of age. In vivo micro-computed tomography (μCT) analyses before the treatment showed that the RiCKO mice displayed normal trabecular, but less cortical bone mass than the littermate controls. After 5weeks of treatment, Scl-Ab dose-dependently increased trabecular and cortical bone mass in both control and RiCKO mice, but the increase was significantly blunted in the latter. Dynamic histomorphometry revealed that the RiCKO mice formed less bone than the control in response to Scl-Ab. In addition, the RiCKO mice possessed fewer osteoclasts than normal under the basal condition and exhibited lesser suppression in osteoclast number by Scl-Ab. Consistent with the fewer osteoclasts in vivo, bone marrow stromal cells (BMSC) from the RiCKO mice expressed less Rankl but normal levels of Opg or M-CSF, and were less effective than the control cells in supporting osteoclastogenesis in vitro. The reliance of Rankl on Rictor appeared to be independent of Wnt-β-catenin or Wnt-mTORC2 signaling as Wnt3a had no effect on Rankl expression by BMSC from either control or RICKO mice. Overall, Rictor in the limb mesenchymal lineage is required for the normal response to the anti-sclerostin therapy in both bone formation and resorption.
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Affiliation(s)
- Weiwei Sun
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Anatomy, Histology and Embryology, Nanjing Medical University, Nanjing, China
| | - Yu Shi
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Wen-Chih Lee
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Seung-Yon Lee
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA
| | - Fanxin Long
- Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Medicine, Washington University School of Medicine, St. Louis, MO 63110, USA; Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO 63110, USA.
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19
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Falk B, Haddad F, Klentrou P, Ward W, Kish K, Mezil Y, Radom-Aizik S. Differential sclerostin and parathyroid hormone response to exercise in boys and men. Osteoporos Int 2016; 27:1245-1249. [PMID: 26361948 PMCID: PMC4767572 DOI: 10.1007/s00198-015-3310-z] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Accepted: 08/31/2015] [Indexed: 01/28/2023]
Abstract
SUMMARY Physical exercise benefits bone structure and mineralization, especially in children. Immediately following high-impact exercise, PTH increased and returned to resting values within 24 h in both groups, while sclerostin increased in men but not in boys. The underlying mechanisms and implication of this age-related differential response are unclear. INTRODUCTION Circulating sclerostin, a negative regulator of bone, decreases during puberty and increases in adulthood. Parathyroid hormone (PTH) is inversely related to sclerostin. In mice, sclerostin decreases following 24 h of mechanical stimulation. Its response to exercise in humans and, especially in children, in whom high-impact physical exercise benefits bone structure and mineralization is unclear. The aim of this study was to investigate the acute response of sclerostin to a single exercise session of high mechanical loading and the corresponding changes in PTH in boys and men. METHODS Twelve boys (10.2 ± 0.4 years old) and 17 young men (22.7 ± 0.8 years old) underwent a protocol of plyometric exercises (total 144 jumps). Blood samples were collected pre-, 5 min, 1 h, and 24 h post-exercise. RESULTS Boys had significantly higher resting values of sclerostin compared with men (150 ± 37 vs. 111 ± 34 pg/ml, respectively, p = 0.006). Following exercise, sclerostin markedly increased in men but this response was attenuated in boys (at 5 min: 51 ± 38 vs. 14 ± 21%, respectively, p = 0.005). PTH levels were similar in boys and men at rest and throughout the 24-h study period, increasing significantly (p < 0.001) 5 min after exercise, decreasing after 60 min post-exercise and returning to resting values within 24 h. CONCLUSION Although the PTH response was similar in boys and men, the sclerostin response was greater in men. The combined increases in PTH and sclerostin immediately post-exercise appear contrary to the accepted osteogenic effect of exercise. The underlying mechanisms and full implication of the differential response between children and adults need to be further examined.
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Affiliation(s)
- B Falk
- Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada.
| | - F Haddad
- Pediatric Exercise and Genomics Research Center, University of California, Irvine, CA, USA
| | - P Klentrou
- Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada
| | - W Ward
- Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada
| | - K Kish
- Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada
| | - Y Mezil
- Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada
| | - S Radom-Aizik
- Pediatric Exercise and Genomics Research Center, University of California, Irvine, CA, USA
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20
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Zhang D, Park BM, Kang M, Nam H, Kim EJ, Bae C, Lim SK. The systemic effects of sclerostin overexpression using ΦC31 integrase in mice. Biochem Biophys Res Commun 2016; 472:471-6. [PMID: 26845353 DOI: 10.1016/j.bbrc.2016.01.178] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 01/29/2016] [Indexed: 11/29/2022]
Abstract
Sclerostin, encoded by the Sost gene, is mainly produced by osteocytes in bone and antagonizes the Wnt/β-catenin signaling pathway, which is a requisite for bone formation. Currently, human anti-sclerostin antibodies are being tested in phase III clinical trials. In addition, serum sclerostin levels are reported to be associated with bone mineral density and fracture risk in normal individuals; however, the correlation between serum sclerostin and bone mass remains controversial. To study the effects of the continuous exposure of exogenous sclerostin on bone, a ΦC31 integrase system, which has the characteristics of site-specificity and efficiency, was applied for the delivery of the Sost gene in this study. We injected Sost-attB plasmid with or without ΦC31 integrase plasmid into the mouse tail vein using a hydrodynamic-based method. The site-specific integration of the Sost gene into the mouse genome was confirmed by examining a pseudo-attP site on the hepatic genomic DNA. Sclerostin was expressed in the hepatocytes, secreted into the blood flow, and maintained at high concentrations in the mice with both Sost-attB plasmid and ΦC31 integrase plasmid injections, which was observed by serial measurement. Moreover, the mice with long-term high levels of serum sclerostin showed trabecular bone loss on micro-CT analysis. Peripheral B cell populations were not affected. Our results suggested that sclerostin could be expressed in the liver and sustained successfully at high levels in the blood by using the ΦC31 integrase system, leading to trabecular bone loss. These findings may help to further ascertain the effects of sclerostin introduced exogenously on the skeleton.
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Affiliation(s)
- Dongdong Zhang
- Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, Republic of Korea; Division of Endocrinology & Metabolism, Department of Internal Medicine, Affiliated Yantai Hospital of Binzhou Medical University, Yantai, PR China
| | - Bo Mi Park
- Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, Republic of Korea
| | - Myengmo Kang
- Division of Endocrinology and Endocrine Research Institute, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - HeeJin Nam
- Division of Endocrinology and Endocrine Research Institute, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Eun Jin Kim
- Division of Endocrinology and Endocrine Research Institute, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - ChuHyun Bae
- Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, Republic of Korea
| | - Sung Kil Lim
- Brain Korea 21 PLUS Project for Medical Science, Yonsei University, Seoul, Republic of Korea; Division of Endocrinology and Endocrine Research Institute, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Republic of Korea.
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21
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Canalis E, Bridgewater D, Schilling L, Zanotti S. Canonical Notch activation in osteocytes causes osteopetrosis. Am J Physiol Endocrinol Metab 2016; 310:E171-82. [PMID: 26578715 PMCID: PMC4719030 DOI: 10.1152/ajpendo.00395.2015] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 11/12/2015] [Indexed: 01/01/2023]
Abstract
Activation of Notch1 in cells of the osteoblastic lineage inhibits osteoblast differentiation/function and causes osteopenia, whereas its activation in osteocytes causes a distinct osteopetrotic phenotype. To explore mechanisms responsible, we established the contributions of canonical Notch signaling (Rbpjκ dependent) to osteocyte function. Transgenics expressing Cre recombinase under the control of the dentin matrix protein-1 (Dmp1) promoter were crossed with Rbpjκ conditional mice to generate Dmp1-Cre(+/-);Rbpjκ(Δ/Δ) mice. These mice did not have a skeletal phenotype, indicating that Rbpjκ is dispensable for osteocyte function. To study the Rbpjκ contribution to Notch activation, Rosa(Notch) mice, where a loxP-flanked STOP cassette is placed between the Rosa26 promoter and the NICD coding sequence, were crossed with Dmp1-Cre transgenic mice and studied in the context (Dmp1-Cre(+/-);Rosa(Notch);Rbpjκ(Δ/Δ)) or not (Dmp1-Cre(+/-);Rosa(Notch)) of Rbpjκ inactivation. Dmp1-Cre(+/-);Rosa(Notch) mice exhibited increased femoral trabecular bone volume and decreased osteoclasts and bone resorption. The phenotype was reversed in the context of the Rbpjκ inactivation, demonstrating that Notch canonical signaling was accountable for the phenotype. Notch activation downregulated Sost and Dkk1 and upregulated Axin2, Tnfrsf11b, and Tnfsf11 mRNA expression, and these effects were not observed in the context of the Rbpjκ inactivation. In conclusion, Notch activation in osteocytes suppresses bone resorption and increases bone volume by utilization of canonical signals that also result in the inhibition of Sost and Dkk1 and upregulation of Wnt signaling.
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Affiliation(s)
- Ernesto Canalis
- Department of Orthopedic Surgery and the University of Connecticut Musculoskeletal Institute, Farmington, Connecticut; and Department of Medicine, University of Connecticut Health, Farmington, Connecticut
| | - David Bridgewater
- Department of Orthopedic Surgery and the University of Connecticut Musculoskeletal Institute, Farmington, Connecticut; and
| | - Lauren Schilling
- Department of Orthopedic Surgery and the University of Connecticut Musculoskeletal Institute, Farmington, Connecticut; and
| | - Stefano Zanotti
- Department of Orthopedic Surgery and the University of Connecticut Musculoskeletal Institute, Farmington, Connecticut; and Department of Medicine, University of Connecticut Health, Farmington, Connecticut
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22
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Sebastian A, Hum NR, Hudson BD, Loots GG. Cancer-Osteoblast Interaction Reduces Sost Expression in Osteoblasts and Up-Regulates lncRNA MALAT1 in Prostate Cancer. Microarrays (Basel) 2015; 4:503-19. [PMID: 27600237 DOI: 10.3390/microarrays4040503] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 10/17/2015] [Accepted: 10/22/2015] [Indexed: 12/29/2022]
Abstract
Dynamic interaction between prostate cancer and the bone microenvironment is a major contributor to metastasis of prostate cancer to bone. In this study, we utilized an in vitro co-culture model of PC3 prostate cancer cells and osteoblasts followed by microarray based gene expression profiling to identify previously unrecognized prostate cancer–bone microenvironment interactions. Factors secreted by PC3 cells resulted in the up-regulation of many genes in osteoblasts associated with bone metabolism and cancer metastasis, including Mmp13, Il-6 and Tgfb2, and down-regulation of Wnt inhibitor Sost. To determine whether altered Sost expression in the bone microenvironment has an effect on prostate cancer metastasis, we co-cultured PC3 cells with Sost knockout (SostKO) osteoblasts and wildtype (WT) osteoblasts and identified several genes differentially regulated between PC3-SostKO osteoblast co-cultures and PC3-WT osteoblast co-cultures. Co-culturing PC3 cells with WT osteoblasts up-regulated cancer-associated long noncoding RNA (lncRNA) MALAT1 in PC3 cells. MALAT1 expression was further enhanced when PC3 cells were co-cultured with SostKO osteoblasts and treatment with recombinant Sost down-regulated MALAT1 expression in these cells. Our results suggest that reduced Sost expression in the tumor microenvironment may promote bone metastasis by up-regulating MALAT1 in prostate cancer.
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23
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Li C, Wang W, Xie L, Luo X, Cao X, Wan M. Lipoprotein receptor-related protein 6 is required for parathyroid hormone-induced Sost suppression. Ann N Y Acad Sci 2015; 1364:62-73. [PMID: 25847683 DOI: 10.1111/nyas.12750] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Revised: 02/02/2015] [Accepted: 02/19/2015] [Indexed: 02/05/2023]
Abstract
Parathyroid hormone (PTH) suppresses the expression of the bone formation inhibitor sclerostin (Sost) in osteocytes by inducing nuclear accumulation of histone deacetylases (HDACs) to inhibit the myocyte enhancer factor 2 (MEF2)-dependent Sost bone enhancer. Previous studies revealed that lipoprotein receptor-related protein 6 (LRP6) mediates the intracellular signaling activation and the anabolic bone effect of PTH. Here, we investigated whether LRP6 mediates the inhibitory effect of PTH on Sost using an osteoblast-specific Lrp6-knockout (LRP6-KO) mouse model. An increased level of Sost mRNA expression was detected in femur tissue from LRP6-KO mice, compared to wild-type littermates. The number of osteocytes expressing sclerostin protein was also increased in bone tissue of LRP6-KO littermates, indicating a negative regulatory role of LRP6 on Sost/sclerostin. In wild-type littermates, intermittent PTH treatment significantly suppressed Sost mRNA expression in bone and the number of sclerostin(+) osteocytes, while the effect of PTH was much less significant in LRP6-KO mice. Additionally, PTH-induced downregulation of MEF2C and 2D, as well as HDAC changes in osteocytes, were abrogated in LRP6-KO mice. These data indicate that LRP6 is required for PTH suppression of Sost expression.
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Affiliation(s)
- Changjun Li
- Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland.,Institute of Endocrinology and Metabolism, Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Weishan Wang
- Department of Orthopaedics, Medical College of Shihezi University, Shihezi, Xinjiang, China
| | - Liang Xie
- Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland.,State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China
| | - Xianghang Luo
- Institute of Endocrinology and Metabolism, Second Xiangya Hospital, Central South University, Changsha, Hunan, China
| | - Xu Cao
- Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | - Mei Wan
- Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland
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24
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Morse A, Yu NYC, Peacock L, Mikulec K, Kramer I, Kneissel M, McDonald MM, Little DG. Endochondral fracture healing with external fixation in the Sost knockout mouse results in earlier fibrocartilage callus removal and increased bone volume fraction and strength. Bone 2015; 71:155-63. [PMID: 25445453 DOI: 10.1016/j.bone.2014.10.018] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2014] [Revised: 09/24/2014] [Accepted: 10/24/2014] [Indexed: 12/11/2022]
Abstract
Sclerostin deficiency, via genetic knockout or anti-Sclerostin antibody treatment, has been shown to cause increased bone volume, density and strength of calluses following endochondral bone healing. However, there is limited data on the effect of Sclerostin deficiency on the formative early stage of fibrocartilage (non-bony tissue) formation and removal. In this study we extensively investigate the early fibrocartilage callus. Closed tibial fractures were performed on Sost(-/-) mice and age-matched wild type (C57Bl/6J) controls and assessed at multiple early time points (7, 10 and 14days), as well as at 28days post-fracture after bony union. External fixation was utilized, avoiding internal pinning and minimizing differences in stability stiffness, a variable that has confounded previous research in this area. Normal endochondral ossification progressed in wild type and Sost(-/-) mice with equivalent volumes of fibrocartilage formed at early day 7 and day 10 time points, and bony union in both genotypes by day 28. There were no significant differences in rate of bony union; however there were significant increases in fibrocartilage removal from the Sost(-/-) fracture calluses at day 14 suggesting earlier progression of endochondral healing. Earlier bone formation was seen in Sost(-/-) calluses over wild type with greater bone volume at day 10 (221%, p<0.01). The resultant Sost(-/-) united bony calluses at day 28 had increased bone volume fraction compared to wild type calluses (24%, p<0.05), and the strength of the fractured Sost(-/-) tibiae was greater than that that of wild type fractured tibiae. In summary, bony union was not altered by Sclerostin deficiency in externally-fixed closed tibial fractures, but fibrocartilage removal was enhanced and the resultant united bony calluses had increased bone fraction and increased strength.
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Affiliation(s)
- A Morse
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia; Discipline of Paediatrics and Child Health, Sydney Medical School, University of Sydney, Sydney, Australia.
| | - N Y C Yu
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia; Discipline of Paediatrics and Child Health, Sydney Medical School, University of Sydney, Sydney, Australia.
| | - L Peacock
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia.
| | - K Mikulec
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia.
| | - I Kramer
- Novartis Pharma, Basel, Switzerland.
| | | | - M M McDonald
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia.
| | - D G Little
- Orthopaedic Research & Biotechnology Unit, The Children's Hospital at Westmead, Sydney, Australia; Discipline of Paediatrics and Child Health, Sydney Medical School, University of Sydney, Sydney, Australia.
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25
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You L, Chen L, Pan L, Gu WS, Chen JY. Zinc finger protein 467 regulates Wnt signaling by modulating the expression of sclerostin in adipose derived stem cells. Biochem Biophys Res Commun 2014; 456:598-604. [PMID: 25490389 DOI: 10.1016/j.bbrc.2014.11.120] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Accepted: 11/23/2014] [Indexed: 01/30/2023]
Abstract
Osteoporosis is a metabolic disease in which a disruption of the balance between bone formation by osteoblasts and bone resorption by osteoclasts leads to the progressive deterioration of bone density and quality. Tissue engineering approaches to the treatment of osteoporosis depend on the identification of factors that promote the differentiation of progenitor cells towards an osteoblastic phenotype. In the present study, we expanded on prior findings on the role of zinc finger protein 467 (Zfp467) in the osteoblastic differentiation of adipose-derived stem cells (ADSCs) and explored the underlying mechanisms. We showed that Zfp467 binds to and regulates the expression of the SOST gene, which encodes a secreted glycoprotein named sclerostin (Sost) that is expressed exclusively by osteocytes and functions as a negative regulator of bone formation through the modulation of Wnt signaling. Overexpression of Zfp467 in ADSCs inhibited Wnt signaling by promoting binding of Sost to the Wnt coreceptors LRP5/6 and disrupting Wnt induced Frizzled-LRP6 complex formation, and siRNA mediated Sost silencing reversed the inhibition of Wnt signaling by Zfp467 in ADSCs. Our results indicate that Zfp467 regulates the differentiation of ADSCs via a mechanism involving Sost-mediated inhibition of Wnt signaling, suggesting potential therapeutic targets for the treatment of osteoporosis.
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Affiliation(s)
- Li You
- Department of Endocrinology and Metabolism, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China.
| | - Lin Chen
- Department of Endocrinology and Metabolism, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China
| | - Ling Pan
- Department of Endocrinology and Metabolism, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China
| | - Wen-Sha Gu
- Department of Endocrinology and Metabolism, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China
| | - Jin-Yu Chen
- Department of Endocrinology and Metabolism, Shanghai First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200080, China
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26
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Yorgan TA, Schinke T. Relevance of Wnt signaling for osteoanabolic therapy. Mol Cell Ther 2014; 2:22. [PMID: 26056589 PMCID: PMC4452071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Figures] [Subscribe] [Scholar Register] [Received: 05/22/2014] [Accepted: 07/08/2014] [Indexed: 11/21/2023]
Abstract
The Wnt signaling pathway is long known to play fundamental roles in various aspects of embryonic development, but also in several homeostatic processes controlling tissue functions in adults. The complexity of this system is best underscored by the fact that the mammalian genome encodes for 19 different Wnt ligands, most but not all of them acting through an intracellular stabilization of β-catenin, representing the key molecule within the so-called canonical Wnt signaling pathway. Wnt ligands primarily bind to 10 different serpentine receptors of the Fzd family, and this binding can be positively or negatively regulated by additional molecules present at the surface of the respective target cells. One of these molecules is the transmembrane protein Lrp5, which has been shown to act as a Wnt co-receptor. In 2001, Lrp5, and thereby Wnt signaling, entered center stage in the research area of bone remodeling, a homeostatic process controlling bone mass, whose disturbance causes osteoporosis, one of the most prevalent disorders worldwide. More specifically, it was found that inactivating mutations of the human LRP5 gene cause osteoporosis-pseudoglioma syndrome, a rare genetic disorder characterized by impaired bone formation and persistence of hyaloid vessels in the eyeballs. In addition, activating LRP5 mutations were identified in individuals with osteosclerosis, a high bone mass condition characterized by excessive bone formation. Especially explained by the lack of cost-effective osteoanabolic treatment options, these findings had an immediate impact on the research regarding the bone-forming cell type, i.e. the osteoblast, whose differentiation and function is apparently controlled by Wnt signaling. This review summarizes the most important results obtained in a large number of studies, involving tissue culture experiments, mouse models and human patients. While there are still many open questions regarding the precise molecular interactions controlling Wnt signaling in osteoblasts, it is obvious that understanding this pathway is a key to optimize the therapeutic strategies for treating various skeletal disorders, including osteoporosis.
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Affiliation(s)
- Timur A Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, 20246 Germany
| | - Thorsten Schinke
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, 20246 Germany
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27
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Abstract
The Wnt signaling pathway is long known to play fundamental roles in various aspects of embryonic development, but also in several homeostatic processes controlling tissue functions in adults. The complexity of this system is best underscored by the fact that the mammalian genome encodes for 19 different Wnt ligands, most but not all of them acting through an intracellular stabilization of β-catenin, representing the key molecule within the so-called canonical Wnt signaling pathway. Wnt ligands primarily bind to 10 different serpentine receptors of the Fzd family, and this binding can be positively or negatively regulated by additional molecules present at the surface of the respective target cells. One of these molecules is the transmembrane protein Lrp5, which has been shown to act as a Wnt co-receptor. In 2001, Lrp5, and thereby Wnt signaling, entered center stage in the research area of bone remodeling, a homeostatic process controlling bone mass, whose disturbance causes osteoporosis, one of the most prevalent disorders worldwide. More specifically, it was found that inactivating mutations of the human LRP5 gene cause osteoporosis-pseudoglioma syndrome, a rare genetic disorder characterized by impaired bone formation and persistence of hyaloid vessels in the eyeballs. In addition, activating LRP5 mutations were identified in individuals with osteosclerosis, a high bone mass condition characterized by excessive bone formation. Especially explained by the lack of cost-effective osteoanabolic treatment options, these findings had an immediate impact on the research regarding the bone-forming cell type, i.e. the osteoblast, whose differentiation and function is apparently controlled by Wnt signaling. This review summarizes the most important results obtained in a large number of studies, involving tissue culture experiments, mouse models and human patients. While there are still many open questions regarding the precise molecular interactions controlling Wnt signaling in osteoblasts, it is obvious that understanding this pathway is a key to optimize the therapeutic strategies for treating various skeletal disorders, including osteoporosis.
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Affiliation(s)
- Timur A Yorgan
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, 20246 Germany
| | - Thorsten Schinke
- Department of Osteology and Biomechanics, University Medical Center Hamburg Eppendorf, Hamburg, 20246 Germany
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28
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Abstract
Mechanical loading is essential to maintain normal bone metabolism and the balance between bone formation and resorption. The cellular mechanisms that control mechanotransduction are not fully defined, but several key pathways have been identified. We discuss the roles of several components of the Wnt signaling cascade, namely Lrp5, Lrp6, and β-catenin in mechanical loading-induced bone formation. Lrp5 is an important Wnt co-receptor for regulating bone mass and mechanotransduction, and appears to function principally by augmenting bone formation. Lrp6 also regulates bone mass but its action might involve resorption as well as formation. The role of Lrp6 in mechanotransduction is unclear. Studies addressing the role of β-catenin in bone metabolism and mechanotransduction highlight the uncertainties in downstream modulators of Lrp5 and Lrp6. Taken together, these data indicate that mechanical loading might affect bone regulation triggering the canonical Wnt signaling (and perhaps other pathways) not only via Lrp5 but also via Lrp6. Further work is needed to clarify the role of the Wnt signaling pathway in Lrp5 and/or Lrp6-mediated mechanotransduction, which could eventually lead to powerful therapeutic agents that might mimic the anabolic effects of mechanical stimulation.
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Affiliation(s)
- Kyung Shin Kang
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
| | - Alexander G. Robling
- Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
- Department of Biomedical Engineering, Indiana University–Purdue University at Indianapolis, Indianapolis, IN, USA
- Richard L. Roudebush VA Medical Center, Indianapolis, IN, USA
- *Correspondence: Alexander G. Robling, Department of Anatomy and Cell Biology, Indiana University School of Medicine, 635 Barnhill Drive, MS 5035, Indianapolis, IN 46202, USA e-mail:
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29
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Collette NM, Yee CS, Murugesh D, Sebastian A, Taher L, Gale NW, Economides AN, Harland RM, Loots GG. Sost and its paralog Sostdc1 coordinate digit number in a Gli3-dependent manner. Dev Biol 2013; 383:90-105. [PMID: 23994639 DOI: 10.1016/j.ydbio.2013.08.015] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Revised: 08/15/2013] [Accepted: 08/16/2013] [Indexed: 01/08/2023]
Abstract
WNT signaling is critical in most aspects of skeletal development and
homeostasis, and antagonists of WNT signaling are emerging as key regulatory
proteins with great promise as therapeutic agents for bone disorders. Here we
show that Sost and its paralog Sostdc1 emerged
through ancestral genome duplication and their expression patterns have diverged
to delineate non-overlapping domains in most organ systems including
musculoskeletal, cardiovascular, nervous, digestive, reproductive and
respiratory. In the developing limb, Sost and
Sostdc1 display dynamic expression patterns with
Sost being restricted to the distal ectoderm and
Sostdc1 to the proximal ectoderm and the mesenchyme. While
Sostdc1–/– mice lack any obvious
limb or skeletal defects, Sost–/–
mice recapitulate the hand defects described for Sclerosteosis patients.
However, elevated WNT signaling in
Sost–/–;
Sostdc1–/– mice causes
misregulation of SHH signaling, ectopic activation of Sox9 in
the digit 1 field and preaxial polydactyly in a Gli1- and Gli3-dependent manner.
In addition, we show that the syndactyly documented in Sclerosteosis is present
in both Sost–/– and
Sost–/–;
Sostdc1–/– mice, and is driven
by misregulation of Fgf8 in the AER, a region lacking
Sost and Sostdc1 expression. This study
highlights the complexity of WNT signaling in skeletal biology and disease and
emphasizes how redundant mechanism and non-cell autonomous effects can synergize
to unveil new intricate phenotypes caused by elevated WNT signaling.
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