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

• Published in: Journal of bone and mineral research Vol. 29; no. 7; pp. 1586 - 1596
• Main Authors: Moon, Jung‐Sun, Kim, Sun‐Hun, Oh, Sin‐Hye, Jeong, Yong‐Wook, Kang, Jee‐Hae, Park, Jong‐Chun, Son, Hye‐Ju, Bae, Suk, Park, Byung‐Il, Kim, Min‐Seok, Koh, Jeong‐Tae, Ko, Hyun‐Mi
• Format: Journal Article
• Language: English
• Published: United States Wiley Subscription Services, Inc 01.07.2014
• Subjects: Animals; BMP; BONE; Bone Morphogenetic Protein 2 - pharmacology; Calcification, Physiologic - drug effects; Cell Differentiation - drug effects; Cell Line; Core Binding Factor Alpha 1 Subunit - metabolism; Humans; MAP Kinase Kinase Kinases - metabolism; Mice, Inbred C57BL; Osteoblasts - cytology; Osteoblasts - drug effects; Osteoblasts - enzymology; Osteogenesis - drug effects; p38 Mitogen-Activated Protein Kinases - metabolism; Phosphorylation - drug effects; Protein Binding - drug effects; Receptors, G-Protein-Coupled - metabolism; RELAXIN; Relaxin - pharmacology; RXFP; Smad Proteins - metabolism; BONE; BMP; RXFP; RELAXIN
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1002/jbmr.2197

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.