Functions of transforming growth factor-beta family type I receptors and Smad proteins in the hypertrophic maturation and osteoblastic differentiation of chondrocytes.
We investigated the effects of bone morphogenetic protein (BMP)-2, a member of the transforming growth factor-beta superfamily, on the regulation of the chondrocyte phenotype, and we identified signaling molecules involved in this regulation. BMP-2 triggers three concomitant responses in mouse primary chondrocytes and chondrocytic MC615 cells. First, BMP-2 stimulates expression or synthesis of type II collagen. Second, BMP-2 induces expression of molecular markers characteristic of pre- and hypertrophic chondrocytes, such as Indian hedgehog, parathyroid hormone/parathyroid hormone-related peptide receptor, type X collagen, and alkaline phosphatase. Third, BMP-2 induces osteocalcin expression, a specific trait of osteoblasts. Constitutively active forms of transforming growth factor-beta family type I receptors and Smad proteins were overexpressed to address their role in this process. Activin receptor-like kinase (ALK)-1, ALK-2, ALK-3, and ALK-6 were able to reproduce the hypertrophic maturation of chondrocytes induced by BMP-2. In addition, ALK-2 mimicked further the osteoblastic differentiation of chondrocytes induced by BMP-2. In the presence of BMP-2, Smad1, Smad5, and Smad8 potentiated the hypertrophic maturation of chondrocytes, but failed to induce osteocalcin expression. Smad6 and Smad7 impaired chondrocytic expression and osteoblastic differentiation induced by BMP-2. Thus, our results indicate that Smad-mediated pathways are essential for the regulation of the different steps of chondrocyte and osteoblast differentiation and suggest that additional Smad-independent pathways might be activated by ALK-2.
Valcourt
Ulrich
U
Institut de Biologie et Chimie des Protéines, UMR 5086 CNRS/Université Claude Bernard Lyon 1, 7 passage du Vercors, 69367 Lyon Cedex 07, France.
Gouttenoire
Jérôme
J
Moustakas
Aristidis
A
Herbage
Daniel
D
Mallein-Gerin
Frédéric
F
D030201:Activin Receptors, Type I / Q000502:physiology*; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D002454:Cell Differentiation; D002460:Cell Line; D019902:Chondrocytes / Q000187:drug effects / Q000502:physiology*; D024043:Collagen Type II / Q000235:genetics; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D006984:Hypertrophy; D051379:Mice; D010006:Osteoblasts / Q000187:drug effects / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000502:physiology*; D051785:Smad Proteins; D051898:Smad1 Protein; D015534:Trans-Activators / Q000502:physiology*; D016212:Transforming Growth Factor beta
C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D024043:Collagen Type II; D004268:DNA-Binding Proteins; D011506:Proteins; D018125:Receptors, Transforming Growth Factor beta; C497399:SMAD1 protein, human; D051785:Smad Proteins; D051898:Smad1 Protein; C497401:Smad1 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; C425423:ACVR1 protein, human; D030201:Activin Receptors, Type I; D000077293:Receptor, Transforming Growth Factor-beta Type I