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      Increased sclerostin associated with stress fracture of the third metacarpal bone in the Thoroughbred racehorse

      , 1 , 2 , 3

      Bone & Joint Research

      Sclerostin, Microdamage, Bone fracture, Apoptosis, Osteocyte

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          Abstract

          Objectives

          The exact aetiology and pathogenesis of microdamage-induced long bone fractures remain unknown. These fractures are likely to be the result of inadequate bone remodelling in response to damage. This study aims to identify an association of osteocyte apoptosis, the presence of osteocytic osteolysis, and any alterations in sclerostin expression with a fracture of the third metacarpal (Mc-III) bone of Thoroughbred racehorses.

          Methods

          A total of 30 Mc-III bones were obtained; ten bones were fractured during racing, ten were from the contralateral limb, and ten were from control horses. Each Mc-III bone was divided into a fracture site, condyle, condylar groove, and sagittal ridge. Microcracks and diffuse microdamage were quantified. Apoptotic osteocytes were measured using TUNEL staining. Cathepsin K, matrix metalloproteinase-13 (MMP-13), HtrA1, and sclerostin expression were analyzed.

          Results

          In the fracture group, microdamage was elevated 38.9% ( sd 2.6) compared with controls. There was no difference in the osteocyte number and the percentage of apoptotic cells between contralateral limb and unraced control; however, there were significantly fewer apoptotic cells in fractured samples (p < 0.02). Immunohistochemistry showed that in deep zones of the fractured samples, sclerostin expression was significantly higher (p < 0.03) than the total number of osteocytes. No increase in cathepsin K, MMP-13, or HtrA1 was present.

          Conclusion

          There is increased microdamage in Mc-III bones that have fractured during racing. In this study, this is not associated with osteocyte apoptosis or osteocytic osteolysis. The finding of increased sclerostin in the region of the fracture suggests that this protein may be playing a key role in the regulation of bone microdamage during stress adaptation.

          Cite this article: N. Hopper, E. Singer, F. Henson. Increased sclerostin associated with stress fracture of the third metacarpal bone in the Thoroughbred racehorse. Bone Joint Res 2018;7:94–102. DOI: 10.1302/2046-3758.71.BJR-2016-0202.R4.

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          Most cited references 45

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          NIH Image to ImageJ: 25 years of image analysis.

          For the past 25 years NIH Image and ImageJ software have been pioneers as open tools for the analysis of scientific images. We discuss the origins, challenges and solutions of these two programs, and how their history can serve to advise and inform other software projects.
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            Is Open Access

            The Amazing Osteocyte

            The last decade has provided a virtual explosion of data on the molecular biology and function of osteocytes. Far from being the “passive placeholder in bone,” this cell has been found to have numerous functions, such as acting as an orchestrator of bone remodeling through regulation of both osteoclast and osteoblast activity and also functioning as an endocrine cell. The osteocyte is a source of soluble factors not only to target cells on the bone surface but also to target distant organs, such as kidney, muscle, and other tissues. This cell plays a role in both phosphate metabolism and calcium availability and can remodel its perilacunar matrix. Osteocytes compose 90% to 95% of all bone cells in adult bone and are the longest lived bone cell, up to decades within their mineralized environment. As we age, these cells die, leaving behind empty lacunae that frequently micropetrose. In aged bone such as osteonecrotic bone, empty lacunae are associated with reduced remodeling. Inflammatory factors such as tumor necrosis factor and glucocorticoids used to treat inflammatory disease induce osteocyte cell death, but by different mechanisms with potentially different outcomes. Therefore, healthy, viable osteocytes are necessary for proper functionality of bone and other organs. © 2011 American Society for Bone and Mineral Research.
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              Sclerostin mediates bone response to mechanical unloading through antagonizing Wnt/beta-catenin signaling.

              Reduced mechanical stress leads to bone loss, as evidenced by disuse osteoporosis in bedridden patients and astronauts. Osteocytes have been identified as major cells responsible for mechanotransduction; however, the mechanism underlying the response of bone to mechanical unloading remains poorly understood. In this study, we found that mechanical unloading of wildtype mice caused decrease of Wnt/beta-catenin signaling activity accompanied by upregulation of Sost. To further analyze the causal relationship among these events, Sost gene targeting mice were generated. We showed that sclerostin selectively inhibited Wnt/beta-catenin in vivo, and sclerostin suppressed the activity of osteoblast and viability of osteoblasts and osteocytes. Interestingly, Sost(-/-) mice were resistant to mechanical unloading-induced bone loss. Reduction in bone formation in response to unloading was also abrogated in the mutant mice. Moreover, in contrast to wildtype mice, Wnt/beta-catenin signaling was not altered by unloading in Sost(-/-) mice. Those data implied that sclerostin played an essential role in mediating bone response to mechanical unloading, likely through Wnt/beta-catenin signaling. Our findings also indicated sclerostin is a promising target for preventing disuse osteoporosis.
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                Author and article information

                Contributors
                Role: Research Associate
                Role: Senior Lecturer in Equine Orthopaedics
                Role: Senior Lecturer in Equine Surgery
                Journal
                Bone Joint Res
                Bone & Joint Research
                2046-3758
                January 2018
                8 February 2018
                : 7
                : 1
                : 94-102
                Affiliations
                [1 ]Department of Surgery, University of Cambridge
                [2 ]Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, School of Veterinary Medicine, Leahurst, Chester High Road, Neston CH64 6SW, UK
                [3 ]Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge CB3 0ES, UK and Division of Trauma and Orthopaedic Surgery, University of Cambridge, Hills Road, Cambridge BC2 0QQ, UK
                Author notes
                Article
                10.1302_2046-3758.71.BJR-2016-0202.R4
                10.1302/2046-3758.71.BJR-2016-0202.R4
                5805827
                29363519
                © 2018 Hopper et al.

                This is an open-access article distributed under the terms of the Creative Commons Attributions licence (CC-BY-NC), which permits unrestricted use, distribution, and reproduction in any medium, but not for commercial gain, provided the original author and source are credited.

                Categories
                Bone Biology
                10
                Sclerostin
                Microdamage
                Bone Fracture
                Apoptosis
                Osteocyte

                osteocyte, sclerostin, microdamage, bone fracture, apoptosis

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