Endoglin is involved in BMP-2-induced osteogenic differentiation of periodontal ligament cells through a pathway independent of Smad-1/5/8 phosphorylation

J Cell Physiol. 2010 Feb;222(2):465-73. doi: 10.1002/jcp.21968.

Abstract

The periodontal ligament (PDL), a connective tissue located between the cementum of teeth and the alveolar bone of mandibula, plays a crucial role in the maintenance and regeneration of periodontal tissues. The PDL contains fibroblastic cells of a heterogeneous cell population, from which we have established several cell lines previously. To analyze characteristics unique for PDL at a molecular level, we performed cDNA microarray analysis of the PDL cells versus MC3T3-E1 osteoblastic cells. The analysis followed by validation by reverse transcription-polymerase chain reaction and immunochemical staining revealed that endoglin, which had been shown to associate with transforming growth factor (TGF)-beta and bone morphogenetic proteins (BMPs) as signaling modulators, was abundantly expressed in PDL cells but absent in osteoblastic cells. The knockdown of endoglin greatly suppressed the BMP-2-induced osteoblastic differentiation of PDL cells and subsequent mineralization. Interestingly, the endoglin knockdown did not alter the level of Smad-1/5/8 phosphorylation induced by BMP-2, while it suppressed the BMP-2-induced expression of Id1, a representative BMP-responsive gene. Therefore, it is conceivable that endoglin regulates the expression of BMP-2-responsive genes in PDL cells at some site downstream of Smad-1/5/8 phosphorylation. Alternatively, we found that Smad-2 as well as Smad-1/5/8 was phosphorylated by BMP-2 in the PDL cells, and that the BMP-2-induced Smad-2 phosphorylation was suppressed by the endoglin knockdown. These results, taken together, raise a possibility that PDL cells respond to BMP-2 via a unique signaling pathway dependent on endoglin, which is involved in the osteoblastic differentiation and mineralization of the cells.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bone Morphogenetic Protein 2 / metabolism*
  • Bone Morphogenetic Protein Receptors, Type I / metabolism
  • Calcification, Physiologic
  • Cell Differentiation
  • Cell Line
  • Endoglin
  • Gene Expression Profiling / methods
  • Growth Differentiation Factor 5 / metabolism
  • Humans
  • Immunohistochemistry
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Mice
  • Oligonucleotide Array Sequence Analysis
  • Osteoblasts / metabolism*
  • Osteogenesis* / genetics
  • Periodontal Ligament / cytology
  • Periodontal Ligament / metabolism*
  • Phosphorylation
  • Protein Serine-Threonine Kinases / metabolism
  • RNA Interference
  • RNA, Messenger / metabolism
  • Receptor, Transforming Growth Factor-beta Type I
  • Receptors, Transforming Growth Factor beta / metabolism
  • Recombinant Proteins / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Smad1 Protein / metabolism*
  • Smad5 Protein / metabolism*
  • Smad8 Protein / metabolism*
  • Time Factors
  • Transforming Growth Factor beta1 / metabolism

Substances

  • BMP2 protein, human
  • Bone Morphogenetic Protein 2
  • Endoglin
  • Eng protein, mouse
  • GDF5 protein, human
  • Growth Differentiation Factor 5
  • Intracellular Signaling Peptides and Proteins
  • RNA, Messenger
  • Receptors, Transforming Growth Factor beta
  • Recombinant Proteins
  • Smad1 Protein
  • Smad1 protein, mouse
  • Smad5 Protein
  • Smad5 protein, mouse
  • Smad8 Protein
  • Smad9 protein, mouse
  • Transforming Growth Factor beta1
  • Protein Serine-Threonine Kinases
  • Bone Morphogenetic Protein Receptors, Type I
  • Receptor, Transforming Growth Factor-beta Type I