Endoglin is involved in BMP-2-induced osteogenic differentiation of periodontal ligament cells through a pathway independent of Smad-1/5/8 phosphorylation.
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.
Ishibashi
Osamu
O
Department of Molecular Anatomy and Medicine, Nippon Medical School, Tokyo, Japan. ishibashi@nms.ac.jp
Ikegame
Mika
M
Takizawa
Fumio
F
Yoshizawa
Tatsuya
T
Moksed
Md Ali
MA
Iizawa
Futabako
F
Mera
Hisashi
H
Matsuda
Akio
A
Kawashima
Hiroyuki
H
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D052005:Bone Morphogenetic Protein Receptors, Type I / Q000378:metabolism; D002113:Calcification, Physiologic; D002454:Cell Differentiation; D002460:Cell Line; D000071063:Endoglin; D020869:Gene Expression Profiling / Q000379:methods; D055428:Growth Differentiation Factor 5 / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D010006:Osteoblasts / Q000378:metabolism*; D010012:Osteogenesis / Q000235:genetics; D010513:Periodontal Ligament / Q000166:cytology / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D051898:Smad1 Protein / Q000378:metabolism*; D051902:Smad5 Protein / Q000378:metabolism*; D051904:Smad8 Protein / Q000378:metabolism*; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D000071063:Endoglin; C502004:Eng protein, mouse; C525893:GDF5 protein, human; D055428:Growth Differentiation Factor 5; D047908:Intracellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D018125:Receptors, Transforming Growth Factor beta; D011994:Recombinant Proteins; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D051902:Smad5 Protein; C497798:Smad5 protein, mouse; D051904:Smad8 Protein; C491621:Smad9 protein, mouse; D053773:Transforming Growth Factor beta1; D017346:Protein Serine-Threonine Kinases; D052005:Bone Morphogenetic Protein Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I