Erschienen in:
01.01.2012 | Original Article
FGF and ERK signaling coordinately regulate mineralization-related genes and play essential roles in osteocyte differentiation
verfasst von:
Ai Kyono, Nanthawan Avishai, Zhufeng Ouyang, Gary E. Landreth, Shunichi Murakami
Erschienen in:
Journal of Bone and Mineral Metabolism
|
Ausgabe 1/2012
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Abstract
To examine the roles of FGF and ERK MAPK signaling in osteocyte differentiation and function, we performed microarray analyses using the osteocyte cell line MLO-Y4. This experiment identified a number of mineralization-related genes that were regulated by FGF2 in an ERK MAPK-dependent manner. Real-time PCR analysis indicated that FGF2 upregulates Ank, Enpp1, Mgp, Slc20a1, and Dmp1 in MLO-Y4 cells. Consistent with this observation, the selective FGF receptor inhibitor PD173074 decreased Ank, Enpp1, Slc20a1, and Dmp1 mRNA expression in mouse calvaria in organ culture. Since Dmp1 plays a central role in osteocyte differentiation and mineral homeostasis, we further analyzed FGF regulation of Dmp1. Similar to FGF2, FGF23 upregulated Dmp1 expression in MLO-Y4 cells in the presence of Klotho. Furthermore, increased extracellular phosphate levels partially inhibited FGF2-induced upregulation of Dmp1 mRNA expression, suggesting a coordinated regulation of Dmp1 expression by FGF signaling and extracellular phosphate. In MLO-Y4 osteocytes and in MC3T3E1 and primary calvaria osteoblasts, U0126 strongly inhibited both basal expression of Dmp1 mRNA and FGF2-induced upregulation. Consistent with the in vitro observations, real-time PCR and immunohistochemical analysis showed a strong decrease in Dmp1 expression in the skeletal elements of ERK1
−/−
; ERK2
flox/flox
; Prx1-Cre mice. Furthermore, scanning electron microscopic analysis revealed that no osteocytes with characteristic dendritic processes develop in the limbs of ERK1
−/−
; ERK2
flox/flox
; Prx1-Cre mice. Collectively, our observations indicate that FGF signaling coordinately regulates mineralization-related genes in the osteoblast lineage and that ERK signaling is essential for Dmp1 expression and osteocyte differentiation.