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      Molecular Pathophysiology of Ossification of the Posterior Longitudinal Ligament (OPLL)

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          Abstract

          Ossification of the posterior longitudinal ligament (OPLL) can be defined as an ectopic ossification in the tissues of spinal ligament showing a hyperostotic condition. OPLL is developed mostly in the cervical spine and clinical presentations of OPLL are majorly myelopathy and/or radiculopathy, with serious neurological pathology resulting in paralysis of extremities and disturbances of motility lowering the quality of life. OPLL is known to be an idiopathic and multifactorial disease, which genetic factors and non-genetic factors including diet, obesity, physical strain on the posterior longitudinal ligament, age, and diabetes mellitus, are involved into the pathogenesis. Up to now, surgical management by decompressing the spinal cord is regarded as standard treatment for OPLL, although there might be the risk of development of reprogression of ossification. The molecular pathogenesis and efficient therapeutic strategy, especially pharmacotherapy and/or preventive intervention, of OPLL has not been clearly elucidated and suggested. Therefore, in this review, we tried to give an overview to the present research results on OPLL, in order to shed light on the potential pharmacotherapy based on molecular pathophysiologic aspect of OPLL, especially on the genetic/genomic factors involved into the etiology of OPLL.

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          Most cited references85

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          TGF-β and BMP Signaling in Osteoblast Differentiation and Bone Formation

          Transforming growth factor-beta (TGF-β)/bone morphogenic protein (BMP) signaling is involved in a vast majority of cellular processes and is fundamentally important throughout life. TGF-β/BMPs have widely recognized roles in bone formation during mammalian development and exhibit versatile regulatory functions in the body. Signaling transduction by TGF-β/BMPs is specifically through both canonical Smad-dependent pathways (TGF-β/BMP ligands, receptors and Smads) and non-canonical Smad-independent signaling pathway (e.g. p38 mitogen-activated protein kinase pathway, MAPK). Following TGF-β/BMP induction, both the Smad and p38 MAPK pathways converge at the Runx2 gene to control mesenchymal precursor cell differentiation. The coordinated activity of Runx2 and TGF-β/BMP-activated Smads is critical for formation of the skeleton. Recent advances in molecular and genetic studies using gene targeting in mice enable a better understanding of TGF-β/BMP signaling in bone and in the signaling networks underlying osteoblast differentiation and bone formation. This review summarizes the recent advances in our understanding of TGF-β/BMP signaling in bone from studies of genetic mouse models and human diseases caused by the disruption of TGF-β/BMP signaling. This review also highlights the different modes of cross-talk between TGF-β/BMP signaling and the signaling pathways of MAPK, Wnt, Hedgehog, Notch, and FGF in osteoblast differentiation and bone formation.
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            Deletion of a single allele of the Dkk1 gene leads to an increase in bone formation and bone mass.

            Wnt/beta-catenin signaling has been proven to play a central role in bone biology. Unexpectedly, the Wnt antagonist Dkk2 is required for terminal osteoblast differentiation and mineralized matrix formation. We show that Dkk1, unlike Dkk2, negatively regulates osteoblast differentiation and bone formation. The Wnt co-receptor LRP5 is a critical regulator of bone mass. Dickkopf (Dkk) proteins act as natural Wnt antagonists by bridging LRP5/6 and Kremen, inducing the internalization of the complex. Wnt antagonists are thus expected to negatively regulation bone formation. However, Dkk2 deficiency results in increased bone, questioning the precise role of Dkks in bone metabolism. In this study, we investigated specifically the role of Dkk1 in bone in vitro and in vivo. Using rat primary calvaria cells, we studied the effect of retroviral expression of Dkk1 on osteoblast differentiation. In addition, the effect of Dkk1 osteoblast was studied in MC3T3-E1 cells by means of recombinant protein. Finally, to address the role of Dkk1 in vivo, we analyzed the bone phenotype of Dkk1(+/-) animals. Retroviral expression of Dkk1 in rat primary calvaria cells resulted in a complete inhibition of osteoblast differentiation and formation of mineralized nodules, with a marked decrease in the expression of alkaline phosphatase. Dkk1 expression also increased adipocyte differentiation in these cell cultures. Recombinant murine Dkk1 (rmDkk1) inhibited spontaneous and induced osteoblast differentiation of MC3T3-E1 cells. To determine the role of Dkk1 in vivo and overcome the embryonic lethality of homozygous deletion, we studied the bone phenotype in heterozygous Dkk1-deficient mice. Structural, dynamic, and cellular analysis of bone remodeling in Dkk1(+/-) mice showed an increase in all bone formation parameters, with no change in bone resorption, leading to a marked increase in bone mass. Importantly, the number of osteoblasts, mineral apposition, and bone formation rate were all increased several fold. We conclude that Dkk1 protein is a potent negative regulator of osteoblasts in vitro and in vivo. Given that a heterozygous decrease in Dkk1 expression is sufficient to induce a significant increase in bone mass, antagonizing Dkk1 should result in a potent anabolic effect.
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              Ossification of the posterior longitudinal ligament of the cervical spine: etiology and natural history.

              Review article.
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                Author and article information

                Journal
                Biomol Ther (Seoul)
                Biomol Ther (Seoul)
                Biomol Ther (Seoul)
                ksp
                Biomolecules & Therapeutics
                The Korean Society of Applied Pharmacology
                1976-9148
                2005-4483
                July 2019
                02 May 2019
                : 27
                : 4
                : 342-348
                Affiliations
                [1 ]Department of Orthopaedic Surgery and Institute of Health Sciences, Gyeongsang National University School of Medicine and Gyeongsang National University Hospital, Jinju 52727, Republic of Korea
                [2 ]Smith Liberal Arts College and Department of Addiction Science, Graduate School, Sahmyook University, Seoul 01795, Republic of Korea
                [3 ]Department of Pharmacology, School of Medicine, Chungnam National University, Daejeon 35015, Republic of Korea
                Author notes
                [†]

                The first two authors contributed equally to this work.

                [* ]Corresponding Authors: E-mail: hscspine@ 123456hanmail.net (Hwang SC), LCJ123@ 123456cnu.ac.kr (Lee CJ), Tel: +82-55-750-8102 (Hwang SC), +82-42-580-8255 (Lee CJ), Fax: +82-55-750-8104 (Hwang SC), +82-42-585-6627 (Lee CJ)
                Article
                bt-27-342
                10.4062/biomolther.2019.043
                6609106
                31042677
                3a2bccf9-915e-470f-978a-6b23c47eb360
                Copyright ©2019, The Korean Society of Applied Pharmacology

                This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 08 March 2019
                : 31 March 2019
                : 09 April 2019
                Categories
                Review

                opll,pathophysiology,novel therapeutic approach
                opll, pathophysiology, novel therapeutic approach

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