The Role of Osteoactivin in Osteoblast Development and Function

Summary

Principal Investigator: Fayez F Safadi
Abstract: From a study in which we discovered osteoactivin (OA) in bone, we demonstrated that OA mRNA and protein are expressed in osteoblasts and its expression exhibited a temporal pattern being at highest levels during the later stages of matrix maturation and mineralization. Furthermore, the protein is synthesized, processed, glycosylated and secreted by osteoblasts. Using gain-of-function and loss-of-function approaches in osteoblasts, we found that down-regulation of OA decreased osteoblast differentiation and function and over- expression increased osteoblast differentiation and function in vitro. We also demonstrated that the secreted form of OA regulates osteoblast differentiation and function. Treatment with recombinant OA promotes bone formation in vivo. The importance of OA in osteogenesis was confirmed in mice with the null allele for OA and in mice with a natural mutation in the OA gene caused a premature stop codon that results in the generation of a truncated OA protein. Both of these mice exhibit a skeletal phenotype associated with decreased bone mass. During the previous funding period and since the last submission, we established colonies of OA KO and OA mut. mice, and also generated transgenic (Tg) mice that over-express OA in bone. Preliminary data from OA KO, OA mut. and Tg mice support the hypothesis that OA is a novel bone anabolic factor which is synthesized and secreted by osteoblasts, and acts either as an ECM-associated signaling molecule or downstream of BMP2 to regulate osteoblast differentiation and function. In addition to its effects on osteoblasts, we present data showing that OA affects osteoclast differentiation, and we hypothesize that these abnormalities are secondary to altered production of osteoclastogenic factors (e.g. RANKL) by stromal cells/osteoblasts in the bone microenvironment. Studies proposed in aim 1 will evaluate the effects of OA deficiency (OA KO), truncated OA (OA mut.) or OA over-expression (Tg) on bone in vivo, and assess the differentiation and function of bone cells (osteoblasts and osteoclasts) derived from these mice in primary cultures. The presence of various domains in OA might reflect different functions, and evaluation the structure/function relationship and role of the various domains of OA on normal osteoblast differentiation will be investigated in aim 2 of this application. During the previous funding period, we also showed that the secreted isoform of OA can function as an ECM-associated (matricellular) protein and demonstrated that osteoblasts attach to OA via the [unreadable]v[unreadable]1 integrin, resulting in the formation of focal adhesions, cytoskeletal reorganization and the activation of FAK. Studies proposed in aim 3 will test the hypothesis that OA acts as a matricellular protein that binds to specific cell surface integrins on osteoblasts to initiate integrin-activated signaling, cytoskeletal reorganization, and regulate cell function. We recently demonstrated that BMP2 regulates OA expression and that OA is a downstream mediator of BMP2-induced osteoblast function, a response that is mediated by the Smad signaling pathway. We present preliminary data that BMP2 stimulates the recruitment of Smad1, Dlx5 and CBP to the OA promoter and this effect is dependent on the stage of osteoblast differentiation. Studies proposed in aim 4 will investigate the mechanism whereby OA acts as a downstream mediator of BMP2- induced osteoblast differentiation and function, and will evaluate the effects of BMP2 in stimulating the recruitment of Smad1, homeodomain proteins, and CBP co-activators to the OA promoter for transcriptional regulation during osteoblast differentiation. Proposed experiments are expected to generate novel information regarding the effects of OA deficiency or over-expression on bone formation/remodeling in vivo, its mechanisms of action in osteoblasts, and the molecular requirements for OA induction by BMP2 in osteoblasts.
Funding Period: 2002-08-01 - 2015-05-31
more information: NIH RePORT

Top Publications

  1. ncbi A peptide from thrombospondin 1 modulates experimental erosive arthritis by regulating connective tissue growth factor
    Joanne M Manns
    Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    Arthritis Rheum 54:2415-22. 2006
  2. ncbi Osteoactivin acts as downstream mediator of BMP-2 effects on osteoblast function
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140, USA
    J Cell Physiol 210:26-37. 2007
  3. ncbi Amelioration of inflammation, angiogenesis and CTGF expression in an arthritis model by a TSP1-derived peptide treatment
    Mario C Rico
    Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania, USA
    J Cell Physiol 211:504-12. 2007
  4. ncbi Osteoactivin, an anabolic factor that regulates osteoblast differentiation and function
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, Temple University, School of Medicine, 3400 North Broad Street, Philadelphia, PA 19140, USA
    Exp Cell Res 314:2334-51. 2008
  5. ncbi Temporal and spatial expression of osteoactivin during fracture repair
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    J Cell Biochem 111:295-309. 2010
  6. ncbi Homeodomain transcription factors regulate BMP-2-induced osteoactivin transcription in osteoblasts
    Maneet Singh
    Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    J Cell Physiol 227:390-9. 2012
  7. ncbi Osteoactivin induces transdifferentiation of C2C12 myoblasts into osteoblasts
    Gregory R Sondag
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio School of Biomedical Sciences, Kent State University, Kent, Ohio
    J Cell Physiol 229:955-66. 2014
  8. ncbi Osteoactivin promotes osteoblast adhesion through HSPG and αvβ1 integrin
    Fouad M Moussa
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio School of Biomedical Sciences, Kent State University, Kent, Ohio
    J Cell Biochem 115:1243-53. 2014
  9. pmc Mutation in osteoactivin decreases bone formation in vivo and osteoblast differentiation in vitro
    Samir M Abdelmagid
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio
    Am J Pathol 184:697-713. 2014

Detail Information

Publications9

  1. ncbi A peptide from thrombospondin 1 modulates experimental erosive arthritis by regulating connective tissue growth factor
    Joanne M Manns
    Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    Arthritis Rheum 54:2415-22. 2006
    ....
  2. ncbi Osteoactivin acts as downstream mediator of BMP-2 effects on osteoblast function
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, School of Medicine, Temple University, Philadelphia, Pennsylvania 19140, USA
    J Cell Physiol 210:26-37. 2007
    ..Our findings suggest that BMP-2 regulates OA expression through the Smad1 signaling pathway. Our data also emphasize that OA protein acts as a downstream mediator of BMP-2 effects on osteoblast differentiation and function...
  3. ncbi Amelioration of inflammation, angiogenesis and CTGF expression in an arthritis model by a TSP1-derived peptide treatment
    Mario C Rico
    Department of Physiology, Temple University School of Medicine, Philadelphia, Pennsylvania, USA
    J Cell Physiol 211:504-12. 2007
    ....
  4. ncbi Osteoactivin, an anabolic factor that regulates osteoblast differentiation and function
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, Temple University, School of Medicine, 3400 North Broad Street, Philadelphia, PA 19140, USA
    Exp Cell Res 314:2334-51. 2008
    ..Collectively, our data suggest that OA acts as a positive regulator of osteoblastogenesis...
  5. ncbi Temporal and spatial expression of osteoactivin during fracture repair
    Samir M Abdelmagid
    Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    J Cell Biochem 111:295-309. 2010
    ..Taken together, these results suggest the possibility that OA plays an important role in bone formation and serves as a positive regulator of fracture healing...
  6. ncbi Homeodomain transcription factors regulate BMP-2-induced osteoactivin transcription in osteoblasts
    Maneet Singh
    Department of Anatomy and Cell Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140, USA
    J Cell Physiol 227:390-9. 2012
    ..Collectively, our results show that the BMP-2-induced OA transcription is differentially regulated by Dlx3, Dlx5, and Msx2 during osteoblast differentiation...
  7. ncbi Osteoactivin induces transdifferentiation of C2C12 myoblasts into osteoblasts
    Gregory R Sondag
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio School of Biomedical Sciences, Kent State University, Kent, Ohio
    J Cell Physiol 229:955-66. 2014
    ..Taken together, our results suggest that OA is able to induce transdifferentiation of myoblasts into osteoblasts through increasing levels of phosphorylated FAK...
  8. ncbi Osteoactivin promotes osteoblast adhesion through HSPG and αvβ1 integrin
    Fouad M Moussa
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio School of Biomedical Sciences, Kent State University, Kent, Ohio
    J Cell Biochem 115:1243-53. 2014
    ....
  9. pmc Mutation in osteoactivin decreases bone formation in vivo and osteoblast differentiation in vitro
    Samir M Abdelmagid
    Department of Anatomy and Neurobiology, Northeast Ohio Medical University NEOMED, Rootstown, Ohio
    Am J Pathol 184:697-713. 2014
    ..Interestingly, TGF-β receptors and Smad-2/3 phosphorylation were up-regulated in D2J osteoblasts, suggesting that OA contributes to TGF-β signaling. These data confirm the anabolic role of OA in postnatal bone formation. ..

Research Grants30

  1. HORMONAL CONTROL OF CALCIUM METABOLISM
    John T Potts; Fiscal Year: 2013
    ....
  2. Osteoclastic Protein-Tyrosine Phosphatase and Resorption
    Kin Hing William Lau; Fiscal Year: 2013
    ..This project may allow disclose novel targets for development of more effective anti-resorptive therapies for osteoporosis and related disease. Thus, this project is highly relevant to the VA patient care mission. ..
  3. Glucocorticoids, Bone Strength and Angiogenesis
    ROBERT STEWART WEINSTEIN; Fiscal Year: 2013
    ..The proposed studies aimed at the mechanisms of the loss of bone strength in GIO should provide new insights that are sorely needed and immediately vital to veterans health care. ..
  4. Biomechanical Stimulation &Skeletal Health in Adolescents with Anorexia Nervosa
    Amy D DiVasta; Fiscal Year: 2013
    ..Given the health care burden associated with the current epidemic of osteoporosis in the elderly, establishing effective measures to prevent bone loss during childhood and adolescence is paramount. ..
  5. Pharmacology of Risperidone Effects on Bone Remodeling and Energy Metabolism
    Karen L Houseknecht; Fiscal Year: 2013
    ....
  6. Signaling in Inflammation, Stress, and Tumorigenesis
    GEORGE ROBERT STARK; Fiscal Year: 2013
    ..abstract_text> ..
  7. Interventions and Mechanisms of Disuse Osteopenia
    Daniel S Perrien; Fiscal Year: 2013
    ..These studies will determine whether Sirt1 and its substrates in osteoblasts and/or osteocytes are potential therapeutic targets for novel interventions for disuse osteopenia and, potentially, bone loss from a variety of other causes. ..
  8. Control of Bone Formation in Craniometaphyseal Dysplasia
    ERNST J REICHENBERGER; Fiscal Year: 2013
    ..We also expect a broad impact on the field of bone remodeling as the mutation in this animal model affects some key mechanisms for bone mineralization and regulation of bone cells. ..
  9. Connection of Mineral and Energy Metabolism by the Nuclear Receptor PPAR-gamma
    Yihong Wan; Fiscal Year: 2013
    ..Therefore, this investigation will significantly impact the broader scientific, clinical, and patient community. ..
  10. Osteocyte Regulation of Bone/Muscle with Age
    Lynda F Bonewald; Fiscal Year: 2013
    ..The results of these experiments should lead to novel therapeutics for the prevention and treatment of both osteoporosis and sarcopenia. ..
  11. Mitochondrial Dysfunction in Neurodegeneration of Aging
    Gary E Gibson; Fiscal Year: 2013
    ..Successful completion of the goals of these projects can be expected to provide new insights into neurodegenerative processes and contribute to novel approaches to ameliorating age-related neurodegenerations. ..
  12. Conditional Knockout of Calcium Receptors in Bone Cells
    Dolores M Shoback; Fiscal Year: 2013
    ....
  13. MOLECULAR AND CELLULAR MECHANISMS OF OSTEOPOROSIS
    Stavros C Manolagas; Fiscal Year: 2013
    ....
  14. Cellular Senescence and Aging
    James L Kirkland; Fiscal Year: 2013
    ..Our approach will provide timely, innovative, and clinically relevant interventional results based on addressing the fundamental question of the role of cellular senescence that has remained unanswered for many years. ..