Sphingosine-1-phosphate/S1PR2-mediated signaling triggers Smad1/5/8 phosphorylation and thereby induces Runx2 expression in osteoblasts

• Published in: Bone (New York, N.Y.) N.Y.), 2016-12, Vol.93, p.1-11
• Main Authors: Higashi, Katsumasa, Matsuzaki, Etsuko, Hashimoto, Yoko, Takahashi-Yanaga, Fumi, Takano, Aiko, Anan, Hisashi, Hirata, Masato, Nishimura, Fusanori
• Format: Article
• Language: English
• Subjects: Alkaline Phosphatase - metabolism; Animals; Biomarkers - metabolism; Cell Differentiation; Cell Line; Cell Nucleus - metabolism; Core Binding Factor Alpha 1 Subunit - genetics; Core Binding Factor Alpha 1 Subunit - metabolism; Lysophospholipids - metabolism; Mice, Inbred C57BL; Models, Biological; Orthopedics; Osteoblast; Osteoblasts - cytology; Osteoblasts - metabolism; Phosphorylation; Protein Transport; Receptors, Lysosphingolipid - metabolism; rho-Associated Kinases - metabolism; rhoA GTP-Binding Protein - metabolism; RhoA/ROCK; RNA, Messenger - genetics; RNA, Messenger - metabolism; Runx2; Signal Transduction; Smad Proteins - metabolism; Smads; Sphingosine - analogs & derivatives; Sphingosine - metabolism; Sphingosine-1-phosphate
• ISSN: 8756-3282; 1873-2763
• DOI: 10.1016/j.bone.2016.09.003

Abstract Sphingosine-1-phosphate (S1P) is a signaling sphingolipid that also plays crucial roles in bone regeneration. Recently, we reported that the S1P receptors S1PR1 and S1PR2 were mainly expressed in osteoblast-like cells, and that the S1P/S1PR1 signaling pathway up-regulated osteoprotegerin and osteoblast differentiation. However, the involvement of S1P/S1PR2 signaling in osteoblast differentiation is not well understood. Here we investigate the role of S1P/S1PR2-mediated signaling in osteoblast differentiation and clarify the underlying signaling mechanisms. We found that an S1P/S1PR2/Gi-independent signaling pathway activated RhoA activity, leading to phosphorylation of Smad1/5/8 in mouse osteoblast-like MC3T3-E1 cells and primary osteoblasts. Furthermore, this signaling pathway promoted nuclear translocation of Smad4, and increased the amount of Smad6/7 protein in the nucleus. S1P also up-regulated runt-related transcription factor 2 (Runx2) expression through S1PR2/RhoA/ROCK/Smad1/5/8 signaling. Moreover, we found that S1P partially triggered S1PR2/RhoA/ROCK pathway leading to bone formation in vivo . These findings suggest that S1P induces RhoA activity, leading to the phosphorylation of Smad1/5/8, thereby promoting Runx2 expression and differentiation in osteoblasts. Our findings describe novel molecular mechanisms in S1P/S1PR2-mediated osteoblast differentiation that could aid future studies of bone regeneration.