Protein Kinase Inhibitor γ Reciprocally Regulates Osteoblast and Adipocyte Differentiation by Downregulating Leukemia Inhibitory Factor

Authors

  • Xin Chen,

    1. Department of Orthopaedics, University of North Carolina, North Carolina, USA
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  • Bryan S. Hausman,

    1. Department of Orthopaedics, University of North Carolina, North Carolina, USA
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  • Guangbin Luo,

    1. Department of Genetics and Genome Sciences, University of North Carolina, North Carolina, USA
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  • Guang Zhou,

    1. Department of Orthopaedics, University of North Carolina, North Carolina, USA
    2. Department of Genetics and Genome Sciences, University of North Carolina, North Carolina, USA
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  • Shunichi Murakami,

    1. Department of Orthopaedics, University of North Carolina, North Carolina, USA
    2. Department of Genetics and Genome Sciences, University of North Carolina, North Carolina, USA
    3. Center for Regenerative Medicine, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
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  • Janet Rubin,

    1. Department of Medicine, University of North Carolina, North Carolina, USA
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  • Edward M. Greenfield

    Corresponding author
    1. Department of Orthopaedics, University of North Carolina, North Carolina, USA
    2. Center for Regenerative Medicine, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
    3. Department of Pathology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
    • Correspondence: Edward M. Greenfield, Ph.D., Harry E. Figgie III M.D. Professor of Orthopaedics, Director of Orthopaedic Research, Department of Orthopaedics, Case Medical Center, Case Western Reserve University, Biomedical Research Building, Room 331, 2109 Adelbert Road, Cleveland, Ohio 44106, USA. Telephone: 216-368-1331; Fax: 216-368-1332; e-mail: emg3@cwru.edu

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  • Author contributions: X.C.: conception and design, collection and/or assembly of data, data analysis and interpretation, manuscript writing, and final approval of manuscript; B.S.H.: conception and design, provision of study material or patients, collection and/or assembly of data, data analysis and interpretation, manuscript writing, and final approval of manuscript; G.L., G.Z., E.M.G., and S.M.: conception and design, data analysis and interpretation, manuscript writing, and final approval of manuscript; J.R.: provision of study material or patients, data analysis and interpretation, manuscript writing, and final approval of manuscript.

Abstract

The protein kinase inhibitor (Pki) gene family inactivates nuclear protein kinase A (PKA) and terminates PKA-induced gene expression. We previously showed that Pkig is the primary family member expressed in osteoblasts and that Pkig knockdown increases the effects of parathyroid hormone and isoproterenol on PKA activation, gene expression, and inhibition of apoptosis. Here, we determined whether endogenous levels of Pkig regulate osteoblast differentiation. Pkig is the primary family member in murine embryonic fibroblasts (MEFs), murine marrow-derived mesenchymal stem cells, and human mesenchymal stem cells. Pkig deletion increased forskolin-dependent nuclear PKA activation and gene expression and Pkig deletion or knockdown increased osteoblast differentiation. PKA signaling is known to stimulate adipogenesis; however, adipogenesis and osteogenesis are often reciprocally regulated. We found that the reciprocal regulation predominates over the direct effects of PKA since adipogenesis was decreased by Pkig deletion or knockdown. Pkig deletion or knockdown also simultaneously increased osteogenesis and decreased adipogenesis in mixed osteogenic/adipogenic medium. Pkig deletion increased PKA-induced expression of leukemia inhibitory factor (Lif) mRNA and LIF protein. LIF neutralizing antibodies inhibited the effects on osteogenesis and adipogenesis of either Pkig deletion in MEFs or PKIγ knockdown in both murine and human mesenchymal stem cells. Collectively, our results show that endogenous levels of Pkig reciprocally regulate osteoblast and adipocyte differentiation and that this reciprocal regulation is mediated in part by LIF. Stem Cells 2013;31:2789–2799

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