Sphingosine-1-phosphate/S1PR2-mediated signaling triggers Smad1/5/8 phosphorylation and thereby induces Runx2 expression in osteoblasts.
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.
Periodontal Section, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
Katsumasa
K
Higashi
Periodontal Section, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan; Section of Operative Dentistry and Endodontology, Department of Odontology, Fukuoka Dental College, Fukuoka, Japan. Electronic address: matsuzaki@college.fdcnet.ac.jp.
Etsuko
E
Matsuzaki
Periodontal Section, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
Yoko
Y
Hashimoto
Department of Clinical Pharmacology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Fumi
F
Takahashi-Yanaga
Periodontal Section, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
Aiko
A
Takano
Section of Operative Dentistry and Endodontology, Department of Odontology, Fukuoka Dental College, Fukuoka, Japan.
Hisashi
H
Anan
Laboratory of Molecular and Cellular Biochemistry, Faculty of Dental Science, Kyushu University, Fukuoka, Japan. Electronic address: hirata1@dent.kyushu-u.ac.jp.
Masato
M
Hirata
Periodontal Section, Division of Oral Rehabilitation, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
Fusanori
F
Nishimura
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics* / Q000378:metabolism; D008246:Lysophospholipids / Q000378:metabolism*; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D049349:Receptors, Lysosphingolipid / Q000378:metabolism*; D015398:Signal Transduction; D051785:Smad Proteins / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000378:metabolism; D054460:rho-Associated Kinases / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
D015415:Biomarkers; D050659:Core Binding Factor Alpha 1 Subunit; D008246:Lysophospholipids; D012333:RNA, Messenger; D049349:Receptors, Lysosphingolipid; D051785:Smad Proteins; C060506:sphingosine 1-phosphate; D054460:rho-Associated Kinases; D000469:Alkaline Phosphatase; D020742:rhoA GTP-Binding Protein; D013110:Sphingosine
Osteoblast; RhoA/ROCK; Runx2; Smads; Sphingosine-1-phosphate