Relaxin Augments BMP-2–Induced Osteoblast Differentiation and Bone Formation

Authors

  • Jung-Sun Moon,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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    • *These authors contributed equally to this work.
  • Sun-Hun Kim,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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    • *These authors contributed equally to this work.
  • Sin-Hye Oh,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Yong-Wook Jeong,

    1. Department of Microbiology, College of Medicine, Seonam University, Namwon, Korea
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  • Jee-Hae Kang,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Jong-Chun Park,

    1. Department of Microbiology, College of Medicine, Seonam University, Namwon, Korea
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  • Hye-Ju Son,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Suk Bae,

    1. Department of Biological Science, Natural Sciences, Chonnam National University, Gwangju, Korea
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  • Byung-Il Park,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Min-Seok Kim,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Jeong-Tae Koh,

    1. Dental Science Research Institute, Medical Research Center for Biomineralization Disorders, School of Dentistry, Chonnam National University, Gwangju, Korea
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  • Hyun-Mi Ko

    Corresponding author
    1. Department of Microbiology, College of Medicine, Seonam University, Namwon, Korea
    • Address correspondence to: Hyun-Mi Ko, PhD, Department of Microbiology, College of Medicine, Seonam University, Namwon, Chonbuk 590-711, Republic of Korea. E-mail: gusalrh@hanmail.net

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ABSTRACT

Relaxin (Rln), a polypeptide hormone of the insulin superfamily, is an ovarian peptide hormone that is involved in a diverse range of physiological and pathological reactions. In this study, we investigated the effect of Rln on bone morphogenetic protein 2 (BMP-2)-induced osteoblast differentiation and bone formation. Expression of Rln receptors was examined in the primary mouse bone marrow stem cells (BMSCs) and mouse embryonic fibroblast cell line C3H/10T1/2 cells by RT-PCR and Western blot during BMP-2–induced osteoblast differentiation. The effect of Rln on osteoblast differentiation and mineralization was evaluated by measuring the alkaline phosphatase activity, osteocalcin production, and Alizarin red S staining. For the in vivo evaluation, BMP-2 and/or Rln were administered with type I collagen into the back of mice, and after 3 weeks, bone formation was analyzed by micro–computed tomography (µCT). Western blot was performed to determine the effect of Rln on osteoblast differentiation-related signaling pathway. Expression of Rxfp 1 in BMSCs and C3H/10T1/2 cells was significantly increased by BMP-2. In vitro, Rln augmented BMP-2–induced alkaline phosphatase expression, osteocalcin production, and matrix mineralization in BMSCs and C3H/10T1/2 cells. In addition, in vivo administration of Rln enhanced BMP-2–induced bone formation in a dose-dependent manner. Interestingly, Rln synergistically increased and sustained BMP-2–induced Smad, p38, and transforming growth factor-β activated kinase (TAK) 1 phosphorylation. BMP-2–induced Runx 2 expression and activity were also significantly augmented by Rln. These results show that Rln enhanced synergistically BMP-2–induced osteoblast differentiation and bone formation through its receptor, Rxfp 1, by augmenting and sustaining BMP-2–induced Smad and p38 phosphorylation, which upregulate Runx 2 expression and activity. These results suggest that Rln might be useful for therapeutic application in destructive bone diseases. © 2014 American Society for Bone and Mineral Research.

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