TGFbeta/BMP type I receptors ALK1 and ALK2 are essential for BMP9-induced osteogenic signaling in mesenchymal stem cells.
Mesenchymal stem cells (MSCs) are bone marrow stromal cells that can differentiate into multiple lineages. We previously demonstrated that BMP9 is one of the most potent BMPs to induce osteogenic differentiation of MSCs. BMP9 is one of the least studied BMPs. Whereas ALK1, ALK5, and/or endoglin have recently been reported as potential BMP9 type I receptors in endothelial cells, little is known about type I receptor involvement in BMP9-induced osteogenic differentiation in MSCs. Here, we conduct a comprehensive analysis of the functional role of seven type I receptors in BMP9-induced osteogenic signaling in MSCs. We have found that most of the seven type I receptors are expressed in MSCs. However, using dominant-negative mutants for the seven type I receptors, we demonstrate that only ALK1 and ALK2 mutants effectively inhibit BMP9-induced osteogenic differentiation in vitro and ectopic ossification in MSC implantation assays. Protein fragment complementation assays demonstrate that ALK1 and ALK2 directly interact with BMP9. Likewise, RNAi silencing of ALK1 and ALK2 expression inhibits BMP9-induced BMPR-Smad activity and osteogenic differentiation in MSCs both in vitro and in vivo. Therefore, our results strongly suggest that ALK1 and ALK2 may play an important role in mediating BMP9-induced osteogenic differentiation. These findings should further aid us in understanding the molecular mechanism through which BMP9 regulates osteogenic differentiation of MSCs.
Luo
Jinyong
J
Key Laboratory of Diagnostic Medicine designated by Chinese Ministry of Education, The Affiliated Hospitals of Chongqing Medical University, Chongqing 400016, China.
Tang
Min
M
Huang
Jiayi
J
He
Bai-Cheng
BC
Gao
Jian-Li
JL
Chen
Liang
L
Zuo
Guo-Wei
GW
Zhang
Wenli
W
Luo
Qing
Q
Shi
Qiong
Q
Zhang
Bing-Qiang
BQ
Bi
Yang
Y
Luo
Xiaoji
X
Jiang
Wei
W
Su
Yuxi
Y
Shen
Jikun
J
Kim
Stephanie H
SH
Huang
Enyi
E
Gao
Yanhong
Y
Zhou
Jian-Zhong
JZ
Yang
Ke
K
Luu
Hue H
HH
Pan
Xiaochuan
X
Haydon
Rex C
RC
Deng
Zhong-Liang
ZL
He
Tong-Chuan
TC
D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism*; D030301:Activin Receptors, Type II; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D017077:Culture Media, Conditioned / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D055427:Growth Differentiation Factor 2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010012:Osteogenesis / Q000187:drug effects* / Q000235:genetics; D011485:Protein Binding; D034741:RNA, Small Interfering; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055114:X-Ray Microtomography
D017077:Culture Media, Conditioned; D055427:Growth Differentiation Factor 2; D034741:RNA, Small Interfering; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; C498943:Acvr1 protein, mouse; C498931:Acvrl1 protein, mouse; D000469:Alkaline Phosphatase