Retinoic acid-induced Smad3 expression is required for the induction of osteoblastogenesis of mesenchymal stem cells

Differentiation. 2011 Sep;82(2):57-65. doi: 10.1016/j.diff.2011.05.003. Epub 2011 May 25.

Abstract

Mesenchymal stem cells are pluripotent precursor cells that can differentiate into osteoblasts, adipocytes, chondrocytes and myocytes. Despite their important therapeutic potential little is known about the transcriptional cascades that govern lineage decisions in these cells. Treatment of C3H10T1/2 mouse mesenchymal stem cells with retinoic acid (RA) inhibits adipogenesis and enhances osteoblastogenesis. In particular, RA treatment stimulates the expression of the osteoblast master regulator, runt-related transcription factor 2 (Runx2), whose expression is necessary for the formation of bone. We have shown previously in mesenchymal stem cells that RA acts to stimulate osteoblastogenesis by interfering with the actions of the bzip transcription factor CCAAT/Enhancer Binding Protein beta (C/EBPβ), where it binds to a negative regulatory element within the Runx2 promoter and inhibits its expression. Herein we show that Smad3, whose expression is stimulated by RA, relays the effects of RA on differentiation by initiating the displacement of C/EBPβ from the Runx2 promoter. In addition to stimulating Smad3 expression, RA also stimulated the nuclear localization of this factor, such that in the absence of RA, ectopic Smad3 was unable to drive osteoblastogenesis. While not sufficient to promote osteoblastogenesis, knockdown of Smad3 using a specific shRNA prevented the RA-mediated stimulation of differentiation and displacement of C/EBPβ from the Runx2 P1 promoter. Taken together, these data indicate that Smad3 is an important mediator of RA activity during mesenchymal stem cell differentiation and is necessary for the stimulation of osteoblastogenesis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipogenesis / drug effects
  • Adipogenesis / genetics
  • Animals
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism
  • Cell Differentiation / drug effects*
  • Cell Line
  • Core Binding Factor Alpha 1 Subunit / genetics
  • Core Binding Factor Alpha 1 Subunit / metabolism
  • Gene Expression Regulation
  • Intracellular Signaling Peptides and Proteins
  • Mesenchymal Stem Cells / cytology*
  • Mesenchymal Stem Cells / metabolism
  • Mice
  • Mice, Inbred C3H
  • Osteoblasts / cytology*
  • Osteoblasts / metabolism
  • Promoter Regions, Genetic
  • RNA-Binding Proteins
  • Smad3 Protein / antagonists & inhibitors
  • Smad3 Protein / genetics
  • Smad3 Protein / metabolism*
  • Tretinoin / pharmacology*

Substances

  • Carrier Proteins
  • Core Binding Factor Alpha 1 Subunit
  • Ebna1bp2 protein, mouse
  • Intracellular Signaling Peptides and Proteins
  • RNA-Binding Proteins
  • Runx2 protein, mouse
  • Smad3 Protein
  • Tretinoin