801
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Cobb J, Dierich A, Huss-Garcia Y, Duboule D. A mouse model for human short-stature syndromes identifies Shox2 as an upstream regulator of Runx2 during long-bone development. Proc Natl Acad Sci U S A 2006; 103:4511-5. [PMID: 16537395 PMCID: PMC1450202 DOI: 10.1073/pnas.0510544103] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Deficiencies or mutations in the human pseudoautosomal SHOX gene are associated with a series of short-stature conditions, including Turner syndrome, Leri-Weill dyschondrosteosis, and Langer mesomelic dysplasia. Although this gene is absent from the mouse genome, the closely related paralogous gene Shox2 displays a similar expression pattern in developing limbs. Here, we report that the conditional inactivation of Shox2 in developing appendages leads to a strong phenotype, similar to the human conditions, although it affects a different proximodistal limb segment. Furthermore, using this mouse model, we establish the cellular etiology of these defects and show that Shox2 acts upstream the Runx2 gene, a key regulator of chondrogenesis.
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Affiliation(s)
- John Cobb
- *Department of Zoology and Animal Biology and National Research Center “Frontiers in Genetics,” Sciences III, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland; and
| | - Andrée Dierich
- Institut de Génétique et de Biologie Moléculaire et Cellulaire/Institut Clinique de la Souris, Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médicale/Université Louis Pasteur/Collège de France, BP 10142, 67404 Strasbourg, France
| | - Yolande Huss-Garcia
- Institut de Génétique et de Biologie Moléculaire et Cellulaire/Institut Clinique de la Souris, Centre National de la Recherche Scientifique/Institut National de la Santé et de la Recherche Médicale/Université Louis Pasteur/Collège de France, BP 10142, 67404 Strasbourg, France
| | - Denis Duboule
- *Department of Zoology and Animal Biology and National Research Center “Frontiers in Genetics,” Sciences III, University of Geneva, Quai Ernest Ansermet 30, 1211 Geneva 4, Switzerland; and
- To whom correspondence should be addressed. E-mail:
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802
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803
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Nie X, Luukko K, Fjeld K, Kvinnsland IH, Kettunen P. Developmental expression of Dkk1-3 and Mmp9 and apoptosis in cranial base of mice. J Mol Histol 2006; 36:419-26. [PMID: 16521043 DOI: 10.1007/s10735-005-9014-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2005] [Accepted: 12/22/2005] [Indexed: 11/24/2022]
Abstract
The Dickkopf (Dkk) family and Mmp9 are important for apoptosis and a number of other developmental processes. However, little is known about their roles in the development of cranial base, which is an important structure for coordinated development and growth of the craniofacial skeletons. In order to establish whether and in what way these genes are involved in cranial base development, we examined their expression patterns and cell apoptosis. Dkk1 was first seen in the perichondral mesenchyme in restricted domains from E14, and later in the migrating mesenchymal cells within the cartilage. Thereafter, it was widespread throughout the bones of the cranial base. The expression was downregulated in postnatal stages. Dkk2 was localized in the perichondral mesenchyme outlining the anterior cranial base in embryogenesis. Dkk3 was mainly detected in the occipital-vertebral joint at E13 and E14. Mmp9 transcripts were clustered in the inner layer of perichondral mesenchyme, juxtaposed with the terminally differentiated hypertrophic chondrocytes from E14. Later Mmp9-expressing cells were found at the sites of chondrocyte apoptosis. This was particularly clear at the distal ends of the synchondroses. These data indicate that Mmp9 regulates skeletogenesis in cranial base in a manner that is largely similar to that of the appendicular skeletons. Expression of Dkks suggests other roles that remain to be defined.
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Affiliation(s)
- Xuguang Nie
- Section of Anatomy and Cell Biology, Department of Biomedicine, University of Bergen, Bergen, Norway.
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804
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Hill TP, Taketo MM, Birchmeier W, Hartmann C. Multiple roles of mesenchymal beta-catenin during murine limb patterning. Development 2006; 133:1219-29. [PMID: 16495310 DOI: 10.1242/dev.02298] [Citation(s) in RCA: 109] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Recently canonical Wnt signaling in the ectoderm has been shown to be required for maintenance of the apical ectodermal ridge (AER) and for dorsoventral signaling. Using conditional gain- and loss-of-function beta-catenin alleles, we have studied the role of mesenchymal beta-catenin activity during limb development. Here, we show that loss of beta-catenin results in limb truncations due to a defect in AER maintenance. Stabilization of beta-catenin also results in truncated limbs, caused by a premature regression of the AER. Concomitantly, in these limbs, the expression of Bmp2, Bmp4 and Bmp7, and of the Bmp target genes Msx1, Msx2 and gremlin, is expanded in the mesenchyme. Furthermore, we found that the expression of Lmx1b, a gene exclusively expressed in the dorsal limb mesenchyme and involved in dorsoventral patterning, is reduced upon loss of beta-catenin activity and is expanded ventrally in gain-of-function limbs. However, the known ectodermal regulators Wnt7a and engrailed 1 are expressed normally. This suggests that Lmx1b is also regulated, in part, by a beta-catenin-mediated Wnt signal, independent of the non-canoncial Wnt7a signaling pathway. In addition, loss of beta-catenin results in a severe agenesis of the scapula. Concurrently, the expression of two genes, Pax1 and Emx2, which have been implicated in scapula development, is lost in beta-catenin loss-of-function limbs; however, only Emx2 is upregulated in gain-of-function limbs. Mesenchymal beta-catenin activity is therefore required for AER maintenance, and for normal expression of Lmx1b and Emx2.
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Affiliation(s)
- Theo P Hill
- Research Institute of Molecular Pathology, IMP, Dr Bohr-Gasse 7, A-1030 Vienna, Austria
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805
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Hartmann C. A Wnt canon orchestrating osteoblastogenesis. Trends Cell Biol 2006; 16:151-8. [PMID: 16466918 DOI: 10.1016/j.tcb.2006.01.001] [Citation(s) in RCA: 241] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Revised: 11/09/2005] [Accepted: 01/19/2006] [Indexed: 12/22/2022]
Abstract
Several transcription factors have been identified that control the differentiation of osteoblasts; however, relatively little is known about the signaling pathways involved in regulating the differentiation process. Recently, the canonical Wnt-beta-catenin pathway has been implicated in osteoblastogenesis. This review focuses on the role of the canonical Wnt-beta-catenin pathway during embryonic development, where it is required for the differentiation of osteoblasts from a precursor that is shared with the chondrocyte lineage and the requirement of this pathway during postnatal life in bone homeostasis. The recent findings covered in this review are major advances in our understanding of skeletal development and promise new therapeutic avenues for tissue engineering and treatment of osteoporosis.
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Affiliation(s)
- Christine Hartmann
- Institute of Molecular Pathology, Dr. Bohr-Gasse 7, 1030 Vienna, Austria.
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806
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Glass DA, Karsenty G. Molecular bases of the regulation of bone remodeling by the canonical Wnt signaling pathway. Curr Top Dev Biol 2006; 73:43-84. [PMID: 16782455 DOI: 10.1016/s0070-2153(05)73002-7] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Osteoporosis is a common, prevalent, and debilitating condition, particularly in postmenopausal women. Genetics play a major role in determining peak bone mass and fracture risk, but few genes have been demonstrated conclusively to be involved, much less the signaling pathways with which they are affiliated. The identification of mutations in the gene Lrp5, a Wnt coreceptor, as the cause for both osteoporotic and high-bone mass disorders implicated the canonical Wnt signaling pathway in bone mass regulation. Since Lrp5, other Wnt components have been identified as being regulators of bone mass, and Wnt target genes affecting bone homeostasis have begun to be elucidated. This chapter looks at the various components of the canonical Wnt signaling pathway and the data indicating that this pathway plays a major role in the control of both bone formation and bone resorption, the two key aspects of bone remodeling.
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Affiliation(s)
- Donald A Glass
- Department of Molecular and Human Genetics, Bone Disease Program of Texas, Baylor College of Medicine, Houston, 77030, USA
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807
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Abstract
Transforming growth factor-beta (TGF-beta) superfamily members play diverse roles in all aspects of cartilage development and maintenance. It is well established that TGF-betas and bone morphogenetic proteins (BMPs) play distinct roles in the growth plate. This chapter discusses key experiments and experimental approaches that have revealed these roles, and progress toward the identification of previously unsuspected roles. Current understanding of the mechanisms by which different TGF-beta and BMP pathways exert their functions is discussed. Finally attempts to utilize this information to promote cartilage regeneration, and important issues for future research, are outlined.
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Affiliation(s)
- Robert Pogue
- Department of Orthopaedic Surgery, University of California Los Angeles, California 90095, USA
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808
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Abstract
The identification of a link between bone mass in humans and gain- [high bone mass (HBM) trait] or loss-of-function [osteoporosis pseudoglioma (OPPG) syndrome] mutations in the Wnt coreceptor lipoprotein receptor-related protein (LRP)5 or in the Wnt antagonist sclerostin (sclerosteosis, Van Buchem syndrome) has called the attention of academic and industry scientists and clinicians to the importance of this signaling pathway in skeletal biology and disease. Multiple genetic and pharmacological manipulations of Wnt signaling in mice have since then confirmed the central role of this pathway in both the establishment of peak bone mass and its maintenance throughout life. Wnt signaling appears to be located downstream of bone morphogenetic proteins (BMPs), itself induced by Hedgehog (Hh) signaling, suggesting that it is the successive recruitment of these three intracellular signaling cascades that allow the full expression of the genetic patterns that characterize the osteoblast, the cell responsible for the formation of bone.
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Affiliation(s)
- Roland Baron
- Yale University School of Medicine New Haven, Connecticut 06520, USA
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809
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Kahler RA, Galindo M, Lian J, Stein GS, van Wijnen AJ, Westendorf JJ. Lymphocyte enhancer-binding factor 1 (Lef1) inhibits terminal differentiation of osteoblasts. J Cell Biochem 2006; 97:969-83. [PMID: 16267835 DOI: 10.1002/jcb.20702] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Lef1 is a transcriptional regulator of the Wnt/beta-catenin signaling cascade. Wnts directly augment bone formation and osteoblast differentiation from mesenchymal stem cells by receptor-mediated pathways involving Lrp5 and Frizzled. We previously reported that Lef1 represses Runx2-dependent activation of the late osteoblast differentiation gene, osteocalcin. Lef1 is expressed in preosteoblasts but is undetectable in fully differentiated osteoblasts. To determine if downregulation of Lef1 is necessary for osteoblast maturation, we constitutively overexpressed Lef1 in MC3T3-E1 preosteoblasts. Lef1-overexpressing cells produced alkaline phosphatase (ALP) and osteocalcin later, and at lower levels than control cells. Moreover, the extracellular matrices of Lef1-overexpressing cell cultures never mineralized. To further examine the role of Lef1 in osteoblasts, we suppressed Lef1 expression in MC3T3-E1 cells by RNA interference. Transient expression of a Lef1 shRNA efficiently reduced murine Lef1 levels and transcriptional activity. Stable suppression of Lef1 in MC3T3 preosteoblasts did not affect proliferation or Runx2 levels; however, ALP production and matrix mineralization were accelerated by 3-4 days. Gene chip analyses identified 14 genes that are differentially regulated in Lef1-suppressed cells. These data outline a role for Lef1 in delaying osteoblast maturation and suggest that Lef1 controls the expression of multiple genes in osteoblasts.
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Affiliation(s)
- Rachel A Kahler
- Graduate Program in Microbiology, Immunology and Cancer Biology, University of Minnesota, Minneapolis, Minnesota 55455, USA
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810
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Abstract
Bone and cartilage and their disorders are addressed under the following headings: functions of bone; normal and abnormal bone remodeling; osteopetrosis and osteoporosis; epithelial-mesenchymal interaction, condensation and differentiation; osteoblasts, markers of bone formation, osteoclasts, components of bone, and pathology of bone; chondroblasts, markers of cartilage formation, secondary cartilage, components of cartilage, and pathology of cartilage; intramembranous and endochondral bone formation; RUNX genes and cleidocranial dysplasia (CCD); osterix; histone deacetylase 4 and Runx2; Ligand to receptor activator of NFkappaB (RANKL), RANK, osteoprotegerin, and osteoimmunology; WNT signaling, LRP5 mutations, and beta-catenin; the role of leptin in bone remodeling; collagens, collagenopathies, and osteogenesis imperfecta; FGFs/FGFRs, FGFR3 skeletal dysplasias, craniosynostosis, and other disorders; short limb chondrodysplasias; molecular control of the growth plate in endochondral bone formation and genetic disorders of IHH and PTHR1; ANKH, craniometaphyseal dysplasia, and chondrocalcinosis; transforming growth factor beta, Camurati-Engelmann disease (CED), and Marfan syndrome, types I and II; an ACVR1 mutation and fibrodysplasia ossificans progressiva; MSX1 and MSX2: biology, mutations, and associated disorders; G protein, activation of adenylyl cyclase, GNAS1 mutations, McCune-Albright syndrome, fibrous dysplasia, and Albright hereditary osteodystrophy; FLNA and associated disorders; and morphological development of teeth and their genetic mutations.
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Affiliation(s)
- M Michael Cohen
- Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada.
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811
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Matsuo N, Tanaka S, Gordon MK, Koch M, Yoshioka H, Ramirez F. CREB-AP1 protein complexes regulate transcription of the collagen XXIV gene (Col24a1) in osteoblasts. J Biol Chem 2005; 281:5445-52. [PMID: 16373341 DOI: 10.1074/jbc.m509923200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Collagen XXIV is a newly discovered and poorly characterized member of the fibril-forming family of collagen molecules, which displays unique structural features of invertebrate fibrillar collagens and is expressed predominantly in bone tissue. Here we report the characterization of the proximal promoter of the mouse gene (Col24a1) and its regulation in osteoblastic cells. Using well characterized murine models of osteoblast differentiation, we found that the Col24a1 gene is activated sometime before onset of the late differentiation marker osteocalcin. Additional analyses revealed that Col24a1 produces equal amounts of two alternatively spliced products with different 5'-untranslated sequences that originate from distinct transcriptional start sites. Cell transfection experiments in combination with DNA binding assays demonstrated that Col24a1 promoter activity in ROS17/2.8 osteosarcoma cells is under the control of an upstream cis-acting element, which is shared by both transcripts and is recognized by specific combinations of c-Jun, CREB1, ATF1, and ATF2 dimers. Consistent with these results, overexpression of c-Jun, ATF1, ATF2, or CREB1 in transiently transfected osteoblastic cells stimulated transcription from reporter gene constructs driven by the Col24a1 promoter to different degrees. Moreover, chromatin immunoprecipitation experiments showed that these nuclear factors bind the same upstream sequence of the endogenous Col24a1 gene. Collectively these data provide new information about transcriptional control of collagen fibrillogenesis, in addition to implicating for the first time CREB-AP1 protein complexes in the regulation of collagen gene expression in osteoblasts.
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Affiliation(s)
- Noritaka Matsuo
- Laboratory of Genetics and Organogenesis, Research Division of the Hospital for Special Surgery, and Department of Physiology and Biophysics, Weill Medical College, Cornell University, New York, NY 10021, USA
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812
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Kieslinger M, Folberth S, Dobreva G, Dorn T, Croci L, Erben R, Consalez GG, Grosschedl R. EBF2 Regulates Osteoblast-Dependent Differentiation of Osteoclasts. Dev Cell 2005; 9:757-67. [PMID: 16326388 DOI: 10.1016/j.devcel.2005.10.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Revised: 09/20/2005] [Accepted: 10/17/2005] [Indexed: 11/22/2022]
Abstract
Communication between bone-depositing osteoblasts and bone-resorbing osteoclasts is required for bone development and homeostasis. Here, we identify EBF2, a member of the early B cell factor (EBF) family of transcription factors that is expressed in osteoblast progenitors, as a regulator of osteoclast differentiation. We find that mice homozygous for a targeted inactivation of Ebf2 show reduced bone mass and an increase in the number of osteoclasts. These defects are accompanied by a marked downregulation of the osteoprotegerin (Opg) gene, encoding a RANK decoy receptor. EBF2 binds to sequences in the Opg promoter and transactivates the Opg promoter in synergy with the Wnt-responsive LEF1/TCF:beta-catenin pathway. Taken together, these data identify EBF2 as a regulator of RANK-RANKL signaling and osteoblast-dependent differentiation of osteoclasts.
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Affiliation(s)
- Matthias Kieslinger
- Gene center and Institute for Biochemistry, University of Munich, 81377 Munich, Germany
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813
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Abstract
Osteoblasts influence bone mass by the amount of bone they synthesize and by regulating osteoclasts, the cells that degrade bone. In the December issue of Developmental Cell, Kieslinger et al. (2005) show that immature osteoblasts regulate expression of the osteoclast inhibitor, osteoprotegerin, through an early B cell factor and β-catenin signaling.
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Affiliation(s)
- Brendan F Boyce
- Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA
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814
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Clément-Lacroix P, Ai M, Morvan F, Roman-Roman S, Vayssière B, Belleville C, Estrera K, Warman ML, Baron R, Rawadi G. Lrp5-independent activation of Wnt signaling by lithium chloride increases bone formation and bone mass in mice. Proc Natl Acad Sci U S A 2005; 102:17406-11. [PMID: 16293698 PMCID: PMC1297659 DOI: 10.1073/pnas.0505259102] [Citation(s) in RCA: 376] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2005] [Indexed: 01/15/2023] Open
Abstract
One of the well characterized cell biologic actions of lithium is the inhibition of glycogen synthase kinase-3beta and the consequent activation of canonical Wnt signaling. Because deficient Wnt signaling has been implicated in disorders of reduced bone mass, we tested whether lithium could improve bone mass in mice. We gavage-fed lithium chloride to 8-week-old mice from three different strains (Lrp5(-/-), SAMP6, and C57BL/6) and assessed the effect on bone metabolism after 4 weeks of therapy. Lrp5(-/-) mice lack the Wnt coreceptor low-density lipoprotein receptor-related protein 5 and have markedly reduced bone mass. Lithium, which is predicted to act downstream of this receptor, restored bone metabolism and bone mass to near wild-type levels in these mice. SAMP6 mice have accelerated osteoporosis due to inadequate osteoblast renewal. Lithium significantly improved bone mass in these mice and in wild-type C57BL/6 mice. We found that lithium activated canonical Wnt signaling in cultured calvarial osteoblasts from Lrp5(-/-) mice ex vivo and that lithium-treated mice had increased expression of Wnt-responsive genes in their bone marrow cells in vivo. These data lead us to conclude that lithium enhances bone formation and improves bone mass in mice and that it may do so via activation of the canonical Wnt pathway. Lithium has been used safely and effectively for over half a century in the treatment of bipolar illness. Prospective studies in patients receiving lithium should determine whether it also improves bone mass in humans.
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815
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Reinhold MI, Kapadia RM, Liao Z, Naski MC. The Wnt-inducible transcription factor Twist1 inhibits chondrogenesis. J Biol Chem 2005; 281:1381-8. [PMID: 16293629 DOI: 10.1074/jbc.m504875200] [Citation(s) in RCA: 127] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Wnt signaling is essential for many developmental processes, including skeletogenesis. To investigate the effects of Wnt signaling during skeletogenesis we studied the effects of Wnt on cultured chondrocytic cells and differentiating limb-bud mesenchyme. We showed that Wnt3a strongly repressed chondrogenesis and chondrocyte gene expression. Canonical Wnt signaling was responsible for the repression of differentiation, as evidenced by results showing that inhibition of glycogen synthase kinase 3 or expression of beta-catenin caused similar repression of differentiation. Significantly, we showed that the transcription repressor Twist1 is induced by canonical Wnt signaling. Expression of Twist1 strongly inhibited chondrocyte gene expression and short hairpin RNA knockdown of Twist1 transcript levels caused increased expression of the chondrocyte-specific genes aggrecan and type II collagen. Interestingly, Twist1 interfered with BMP2-induced expression of aggrecan and type II collagen expression and knockdown of Twist1 augmented BMP2-induced aggrecan and type II collagen expression. These data support the conclusions that Twist1 contributes to the repression of chondrogenesis and chondrocyte gene expression resulting from canonical Wnt signaling and that Twist1 interferes with BMP-dependent signaling.
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Affiliation(s)
- Martina I Reinhold
- Department of Pathology, University of Texas Health Science Center, San Antonio, Texas 78229, USA
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816
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Magne D, Vinatier C, Julien M, Weiss P, Guicheux J. Mesenchymal stem cell therapy to rebuild cartilage. Trends Mol Med 2005; 11:519-26. [PMID: 16213191 DOI: 10.1016/j.molmed.2005.09.002] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Revised: 09/09/2005] [Accepted: 09/22/2005] [Indexed: 12/13/2022]
Abstract
Disorders affecting cartilage touch almost the whole population and are one of the leading causes of invalidity in adults. To repair cartilage, therapeutic approaches initially focused on the implantation of autologous chondrocytes, but this technique proved unsatisfactory because of the limited number of chondrocytes obtained at harvest. The discovery that several adult human tissues contain mesenchymal stem cells (MSCs) capable of differentiating into chondrocytes raised the possibility of injecting MSCs to repair cartilages. The important data published recently on the factors controlling chondrocyte commitment must be thoroughly considered to make further progress towards this therapeutic approach. The potential application of MSC therapy provides new hope for the development of innovative treatments for the repair of cartilage disorders.
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Affiliation(s)
- David Magne
- INSERM EM 99-03, 1 place A. Ricordeau, 44042 Nantes Cedex 1, France
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817
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Rawadi G, Roman-Roman S. Wnt signalling pathway: a new target for the treatment of osteoporosis. Expert Opin Ther Targets 2005; 9:1063-77. [PMID: 16185158 DOI: 10.1517/14728222.9.5.1063] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The prevention and treatment of osteoporosis traditionally involves the use of antiresorptive agents that target osteoclast function. Antiresorptive therapy is not associated with a significant increase in bone mass and, thus, only partially reduces the risk of fractures. For that reason, the search for anabolic agents, which target osteoblast function, represents an urgent medical need. The first approved bone anabolic drug for the treatment of osteoporosis was teriparatide (human parathyroid hormone 1-34). Recently, both human genetics and animal studies have pointed out the role of the Wnt/LRP5 pathway as a major regulator of bone mass accrual. Wnts are secreted glycoproteins that bind to receptor complexes including low-density lipoprotein receptor-related protein (LRP)-5/6 and Frizzled proteins. A subsequent intracellular cascade of events stabilises beta-catenin, leading to its translocation into the nucleus where, associated with Tcf/Lef transcription factors, it triggers gene expression. The existence of many potential pharmacological targets in this pathway makes it attractive for bone anabolic drug discovery.
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Affiliation(s)
- Georges Rawadi
- Prostrakan Pharmaceuticals, 102 route de noisy, 93230 Romainville, France.
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818
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Gaur T, Lengner CJ, Hovhannisyan H, Bhat RA, Bodine PVN, Komm BS, Javed A, van Wijnen AJ, Stein JL, Stein GS, Lian JB. Canonical WNT signaling promotes osteogenesis by directly stimulating Runx2 gene expression. J Biol Chem 2005; 280:33132-40. [PMID: 16043491 DOI: 10.1074/jbc.m500608200] [Citation(s) in RCA: 852] [Impact Index Per Article: 44.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Both activating and null mutations of proteins required for canonical WNT signaling have revealed the importance of this pathway for normal skeletal development. However, tissue-specific transcriptional mechanisms through which WNT signaling promotes the differentiation of bone-forming cells have yet to be identified. Here, we address the hypothesis that canonical WNT signaling and the bone-related transcription factor RUNX2/CBFA1/AML3 are functionally linked components of a pathway required for the onset of osteoblast differentiation. Our findings show that, in bone of the SFRP1 (secreted frizzled-related protein-1)-null mouse, which exhibits activated WNT signaling and a high bone mass phenotype, there is a significant increase in expression of T-cell factor (TCF)-1, Runx2, and the RUNX2 target gene osteocalcin. We demonstrate by mutational analysis that a functional TCF regulatory element responsive to canonical WNT signaling resides in the promoter of the Runx2 gene (-97 to -93). By chromatin immunoprecipitation, recruitment of beta-catenin and TCF1 to the endogenous Runx2 gene is shown. Coexpression of TCF1 with canonical WNT proteins resulted in a 2-5-fold activation of Runx2 promoter activity and a 7-8-fold induction of endogenous mRNA in mouse pluripotent mesenchymal and osteoprogenitor cells. This enhancement was abrogated by SFRP1. Taken together, our results provide evidence for direct regulation of Runx2 by canonical WNT signaling and suggest that Runx2 is a target of beta-catenin/TCF1 for the stimulation of bone formation. We propose that WNT/TCF1 signaling, like bone morphogenetic protein/transforming growth factor-beta signaling, activates Runx2 gene expression in mesenchymal cells for the control of osteoblast differentiation and skeletal development.
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Affiliation(s)
- Tripti Gaur
- Department of Cell Biology and the Cancer Center, University of Massachusetts Medical School, Worcester, Massachusetts 01655-0106, USA
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819
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Glass DA, Bialek P, Ahn JD, Starbuck M, Patel MS, Clevers H, Taketo MM, Long F, McMahon AP, Lang RA, Karsenty G. Canonical Wnt signaling in differentiated osteoblasts controls osteoclast differentiation. Dev Cell 2005; 8:751-64. [PMID: 15866165 DOI: 10.1016/j.devcel.2005.02.017] [Citation(s) in RCA: 1157] [Impact Index Per Article: 60.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2004] [Revised: 01/31/2005] [Accepted: 02/16/2005] [Indexed: 12/31/2022]
Abstract
Inactivation of beta-catenin in mesenchymal progenitors prevents osteoblast differentiation; inactivation of Lrp5, a gene encoding a likely Wnt coreceptor, results in low bone mass (osteopenia) by decreasing bone formation. These observations indicate that Wnt signaling controls osteoblast differentiation and suggest that it may regulate bone formation in differentiated osteoblasts. Here, we study later events and find that stabilization of beta-catenin in differentiated osteoblasts results in high bone mass, while its deletion from differentiated osteoblasts leads to osteopenia. Surprisingly, histological analysis showed that these mutations primarily affect bone resorption rather than bone formation. Cellular and molecular studies showed that beta-catenin together with TCF proteins regulates osteoblast expression of Osteoprotegerin, a major inhibitor of osteoclast differentiation. These findings demonstrate that beta-catenin, and presumably Wnt signaling, promote the ability of differentiated osteoblasts to inhibit osteoclast differentiation; thus, they broaden our knowledge of the functions Wnt proteins have at various stages of skeletogenesis.
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MESH Headings
- Animals
- Bone Development
- Cell Differentiation
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Gene Expression Regulation, Developmental
- Glycoproteins/genetics
- Glycoproteins/metabolism
- In Situ Hybridization
- Intercellular Signaling Peptides and Proteins/genetics
- Intercellular Signaling Peptides and Proteins/physiology
- LDL-Receptor Related Proteins
- Lac Operon
- Low Density Lipoprotein Receptor-Related Protein-5
- Mice
- Mice, Knockout
- Mice, Mutant Strains
- Mice, Transgenic
- Osteoblasts/cytology
- Osteoblasts/metabolism
- Osteoclasts/cytology
- Osteoclasts/metabolism
- Osteogenesis
- Osteopetrosis/etiology
- Osteoprotegerin
- Receptors, Cytoplasmic and Nuclear/genetics
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, LDL/deficiency
- Receptors, LDL/genetics
- Receptors, Tumor Necrosis Factor/genetics
- Receptors, Tumor Necrosis Factor/metabolism
- Signal Transduction
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Wnt Proteins
- beta Catenin
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Affiliation(s)
- Donald A Glass
- Department of Molecular and Human Genetics, Bone Disease Program of Texas, Houston, 77030, USA
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820
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Research Highlights. Nat Med 2005. [DOI: 10.1038/nm0605-604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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821
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Abstract
Three exciting papers in this issue of Developmental Cell provide new insights into the regulation of chondrocytic, osteoblastic, and osteoclastic differentiation during skeletal development and postnatal growth. The studies demonstrate that Wnt/beta-catenin signaling represents both a mechanism in mesenchymal precursor cells for selecting between chondrocytic and osteoblastic fates as well as a mechanism in osteoblasts for stimulating the production of an inhibitor of osteoclast formation.
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Affiliation(s)
- Elona Kolpakova
- Department of Oral and Developmental Biology, Harvard School of Dental Medicine, Boston, MA 02115, USA
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822
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Abstract
Chondrogenesis is the earliest phase of skeletal development, involving mesenchymal cell recruitment and migration, condensation of progenitors, and chondrocyte differentiation, and maturation and resulting in the formation of cartilage and bone during endochondral ossification. This process is controlled exquisitely by cellular interactions with the surrounding matrix, growth and differentiation factors, and other environmental factors that initiate or suppress cellular signaling pathways and transcription of specific genes in a temporal-spatial manner. Vertebrate limb development is controlled by interacting patterning systems involving prominently the fibroblast growth factor (FGF), bone morphogenetic protein (BMP), and hedgehog pathways. Both positive and negative signaling kinases and transcription factors, such as Sox9 and Runx2, and interactions among them determine whether the differentiated chondrocytes remain within cartilage elements in articular joints or undergo hypertrophic maturation prior to ossification. The latter process requires extracellular matrix remodeling and vascularization controlled by mechanisms that are not understood completely. Recent work has revealed novel roles for mediators such as GADD45beta, transcription factors of the Dlx, bHLH, leucine zipper, and AP-1 families, and the Wnt/beta-catenin pathway that interact at different stages during chondrogenesis.
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Affiliation(s)
- Mary B Goldring
- Department of Medicine, Division of Rheumatology, Beth Israel Deaconess Medical Center, New England Baptist Bone and Joint Institute and Harvard Medical School, Boston, MA 02115, USA.
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