Pyk2 regulates megakaryocyte-induced increases in osteoblast number and bone formation

Authors

  • Ying-Hua Cheng,

    1. Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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    • The first two authors contributed equally to this work.
  • R Adam Hooker,

    1. Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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    • The first two authors contributed equally to this work.
  • Khanh Nguyen,

    1. Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Rita Gerard-O'Riley,

    1. Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
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  • David L Waning,

    1. Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Brahmananda R Chitteti,

    1. Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Tomas E Meijome,

    1. Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Hui Lin Chua,

    1. Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Artur P Plett,

    1. Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Christie M Orschell,

    1. Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Edward F Srour,

    1. Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
    2. Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, USA
    3. Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Lindsey D Mayo,

    1. Herman B. Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN, USA
    2. Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Fredrick M Pavalko,

    1. Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Angela Bruzzaniti,

    Corresponding author
    1. Department of Oral Biology, Indiana University School of Dentistry, Indianapolis, IN, USA
    • Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
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  • Melissa A Kacena

    Corresponding author
    1. Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA
    • Department of Orthopaedic Surgery, Indiana University School of Medicine, Indianapolis, IN, USA
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Address correspondence to: Melissa Kacena, PhD, Department of Orthopaedic Surgery, Indiana University School of Medicine, 1120 South Drive, FH 115, Indianapolis, IN 46202, USA. E-mail: mkacena@iupui.edu. Angela Bruzzaniti, PhD, Department of Oral Biology, Indiana University School of Dentistry, 1121 West Michigan Street, DS 241, Indianapolis, IN 46202, USA. E-mail: abruzzan@iupui.edu

ABSTRACT

Preclinical and clinical evidence from megakaryocyte (MK)-related diseases suggests that MKs play a significant role in maintaining bone homeostasis. Findings from our laboratories reveal that MKs significantly increase osteoblast (OB) number through direct MK-OB contact and the activation of integrins. We, therefore, examined the role of Pyk2, a tyrosine kinase known to be regulated downstream of integrins, in the MK-mediated enhancement of OBs. When OBs were co-cultured with MKs, total Pyk2 levels in OBs were significantly enhanced primarily because of increased Pyk2 gene transcription. Additionally, p53 and Mdm2 were both decreased in OBs upon MK stimulation, which would be permissive of cell cycle entry. We then demonstrated that OB number was markedly reduced when Pyk2−/− OBs, as opposed to wild-type (WT) OBs, were co-cultured with MKs. We also determined that MKs inhibit OB differentiation in the presence and absence of Pyk2 expression. Finally, given that MK-replete spleen cells from GATA-1–deficient mice can robustly stimulate OB proliferation and bone formation in WT mice, we adoptively transferred spleen cells from these mice into Pyk2−/− recipient mice. Importantly, GATA-1–deficient spleen cells failed to stimulate an increase in bone formation in Pyk2−/− mice, suggesting in vivo the important role of Pyk2 in the MK-induced increase in bone volume. Further understanding of the signaling pathways involved in the MK-mediated enhancement of OB number and bone formation will facilitate the development of novel anabolic therapies to treat bone loss diseases.

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