The orphan receptor tyrosine kinase Ror2 promotes osteoblast differentiation and enhances ex vivo bone formation.
Ror2 is a receptor tyrosine kinase, the expression of which increases during differentiation of pluripotent stem cells to osteoblasts and then declines as cells progress to osteocytes. To test whether Ror2 plays a role in osteoblastogenesis, we investigated the effects of Ror2 overexpression and down-regulation on osteoblastic lineage commitment and differentiation. Expression of Ror2 in pluripotent human mesenchymal stem cells (hMSCs) by adenoviral infection caused formation of mineralized extracellular matrix, which is the ultimate phenotype of an osteogenic tissue. Concomitantly, Ror2 over-expression inhibited adipogenic differentiation of hMSCs as monitored by lipid formation. Ror2 shifted hMSC fate toward osteoblastogenesis by inducing osteogenic transcription factor osterix and suppressing adipogenic transcription factors CCAAT/enhancer-binding protein alpha and peroxisome proliferator activated receptor gamma. Infection with Ror2 virus also strongly promoted matrix mineralization in committed osteoblast-like MC3T3-E1 cells. Expression of Ror2 in a human preosteocytic cell line by stable transfection also promoted further differentiation, as judged by inhibited alkaline phosphatase activity, potentiated osteocalcin secretion, and increased cellular apoptosis. In contrast, down-regulation of Ror2 expression by short hairpin RNA essentially abrogated dexamethasone-induced mineralization of hMSCs. Furthermore, down-regulation of Ror2 expression in fully differentiated SaOS-2 osteosarcoma cells inhibited alkaline phosphatase activity. We conclude that Ror2 initiates commitment of MSCs to osteoblastic lineage and promotes differentiation at early and late stages of osteoblastogenesis. Finally, using a mouse calvariae ex vivo organ culture model, we demonstrate that these effects of Ror2 result in increased bone formation, suggesting that it may also activate mature osteoblasts.
Liu
Yan
Y
Women's Health and Musculoskeletal Biology, Wyeth Research, 500 Arcola Road, Collegeville, Pennsylvania 19426, USA.
Bhat
Ramesh A
RA
Seestaller-Wehr
Laura M
LM
Fukayama
Shoichi
S
Mangine
Annamarie
A
Moran
Robert A
RA
Komm
Barry S
BS
Bodine
Peter V N
PV
Billiard
Julia
J
D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000378:metabolism; D002113:Calcification, Physiologic / Q000502:physiology; D002454:Cell Differentiation; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D015536:Down-Regulation; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D009924:Organ Culture Techniques; D010006:Osteoblasts / Q000166:cytology* / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis; D047495:PPAR gamma / Q000378:metabolism; D039904:Pluripotent Stem Cells / Q000166:cytology* / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D057050:Receptor Tyrosine Kinase-like Orphan Receptors; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012886:Skull / Q000166:cytology; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000378:metabolism
D022763:CCAAT-Enhancer-Binding Protein-alpha; D005938:Glucocorticoids; D047495:PPAR gamma; D011956:Receptors, Cell Surface; D000076182:Sp7 Transcription Factor; C478163:SP7 protein, human; D014157:Transcription Factors; D015675:Osteocalcin; D003907:Dexamethasone; C078716:ROR1 protein, human; C078717:ROR2 protein, human; D020794:Receptor Protein-Tyrosine Kinases; D057050:Receptor Tyrosine Kinase-like Orphan Receptors