TGFbeta/BMP type I receptors ALK1 and ALK2 are essential for BMP9-induced osteogenic signaling in mesenchymal stem cells

J Biol Chem. 2010 Sep 17;285(38):29588-98. doi: 10.1074/jbc.M110.130518. Epub 2010 Jul 13.

Abstract

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Activin Receptors, Type I / genetics
  • Activin Receptors, Type I / metabolism*
  • Activin Receptors, Type II
  • Alkaline Phosphatase / metabolism
  • Animals
  • Cell Line
  • Cells, Cultured
  • Culture Media, Conditioned / pharmacology
  • Enzyme Activation / drug effects
  • Growth Differentiation Factor 2 / genetics
  • Growth Differentiation Factor 2 / metabolism*
  • Humans
  • Mesenchymal Stem Cells / drug effects
  • Mesenchymal Stem Cells / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Osteogenesis / drug effects*
  • Osteogenesis / genetics
  • Protein Binding
  • RNA, Small Interfering
  • Reverse Transcriptase Polymerase Chain Reaction
  • X-Ray Microtomography

Substances

  • Culture Media, Conditioned
  • Growth Differentiation Factor 2
  • RNA, Small Interfering
  • Activin Receptors, Type I
  • Activin Receptors, Type II
  • Acvr1 protein, mouse
  • Acvrl1 protein, mouse
  • Alkaline Phosphatase