Heterozygous inactivation of Gnas in adipose-derived mesenchymal progenitor cells enhances osteoblast differentiation and promotes heterotopic ossification

Authors

  • Robert J Pignolo,

    Corresponding author
    1. Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    3. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    • Departments of Medicine and Orthopaedic Surgery, University of Pennsylvania School of Medicine, 424B Stemmler Hall, 36th Street and Hamilton Walk, Philadelphia, PA 19104-6081, USA.
    Search for more papers by this author
  • Meiqi Xu,

    1. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Elizabeth Russell,

    1. Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Alec Richardson,

    1. Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Josef Kaplan,

    1. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Paul C Billings,

    1. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Frederick S Kaplan,

    1. Department of Medicine, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    3. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author
  • Eileen M Shore

    1. Department of Orthopaedic Surgery, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    2. Department of Genetics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    3. Center for Research in FOP and Related Disorders, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
    Search for more papers by this author

Abstract

Human genetic disorders sharing the common feature of subcutaneous heterotopic ossification (HO) are caused by heterozygous inactivating mutations in GNAS, a gene encoding multiple transcripts including two stimulatory G proteins, the α subunit of the stimulatory G protein (Gsα) of adenylyl cyclase, and the extralong form of Gsα, XLαs. In one such disorder, progressive osseous heteroplasia (POH), bone formation initiates within subcutaneous fat before progressing to deeper tissues, suggesting that osteogenesis may involve abnormal differentiation of mesenchymal precursors that are present in adipose tissues. We determined by immunohistochemical analysis that GNAS protein expression is limited to Gsα in bone-lining cells and to Gsα and XLαs in osteocytes. By contrast, the GNAS proteins Gsα, XLαs, and NESP55 are detected in adipocytes and in adipose stroma. Although Gnas transcripts, as assessed by quantitative RT-PCR, show no significant changes on osteoblast differentiation of bone-derived precursor cells, the abundance of these transcripts is enhanced by osteoblast differentiation of adipose-derived mesenchymal progenitors. Using a mouse knockout model, we determined that heterozygous inactivation of Gnas (by disruption of the Gsα-specific exon 1) abrogates upregulation of multiple Gnas transcripts that normally occurs with osteoblast differentiation in wild-type adipose stromal cells. These transcriptional changes in Gnas+/− mice are accompanied by accelerated osteoblast differentiation of adipose stromal cells in vitro. In vivo, altered osteoblast differentiation in Gnas+/− mice manifests as subcutaneous HO by an intramembranous process. Taken together, these data suggest that Gnas is a key regulator of fate decisions in adipose-derived mesenchymal progenitor cells, specifically those which are involved in bone formation. © 2011 American Society for Bone and Mineral Research

Ancillary