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Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation.

ABSTRACT: Accumulating in vitro evidence suggests that the p38 mitogen-activated protein kinase (MAPK) pathway is involved in endochondral ossification. To investigate the role of this pathway in endochondral ossification, we generated transgenic mice with expression in chondrocytes of a constitutively active mutant of MKK6, a MAPK kinase that specifically activates p38. These mice had a dwarf phenotype characterized by reduced chondrocyte proliferation, inhibition of hypertrophic chondrocyte differentiation, and a delay in the formation of primary and secondary ossification centers. Histological analysis with in situ hybridization showed reduced expression of Indian hedgehog, PTH/PTH-related peptide receptor (PTH, parathyroid hormone), cyclin D1, and increased expression of p21 in chondrocytes. In addition, both in vivo and in transfected cells, p38 signaling increased the transcriptional activity of Sox9, a transcription factor essential for chondrocyte differentiation. In agreement with this observation, transgenic mice that express a constitutively active mutant of MKK6 in chondrocytes showed phenotypes similar to those of mice that overexpress SOX9 in chondrocytes. These observations are consistent with the notion that increased activity of Sox9 accounts at least in part for the phenotype caused by constitutive activation of MKK6 in chondrocytes. Therefore, our study provides in vivo evidence for the role of p38 in endochondral ossification and suggests that Sox9 is a likely downstream target of the p38 MAPK pathway.

SUBMITTER: Zhang R

PROVIDER: S-EPMC1326166 | biostudies-literature | 2006 Jan

REPOSITORIES: biostudies-literature

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Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation.

Zhang Ren R Murakami Shunichi S Coustry Françoise F Wang Ying Y de Crombrugghe Benoit B

Proceedings of the National Academy of Sciences of the United States of America 20051230 2

Accumulating in vitro evidence suggests that the p38 mitogen-activated protein kinase (MAPK) pathway is involved in endochondral ossification. To investigate the role of this pathway in endochondral ossification, we generated transgenic mice with expression in chondrocytes of a constitutively active mutant of MKK6, a MAPK kinase that specifically activates p38. These mice had a dwarf phenotype characterized by reduced chondrocyte proliferation, inhibition of hypertrophic chondrocyte differentiat ...[more]

PMID: 16387856

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Project description:Aberrant fibroblast growth factor receptor 3 (FGFR3) signaling disrupts chondrocyte proliferation and growth plate size and architecture, leading to various chondrodysplasias or bone overgrowth. These observations suggest that the duration, intensity and cellular context of FGFR signaling during growth plate chondrocyte maturation require tight, regulated control for proper bone elongation. However, the machinery fine-tuning FGFR signaling in chondrocytes is incompletely defined. We report here that neurofibromin, a Ras-GAP encoded by Nf1, has an overlapping expression pattern with FGFR1 and FGFR3 in prehypertrophic chondrocytes, and with FGFR1 in hypertrophic chondrocytes during endochondral ossification. Based on previous evidence that neurofibromin inhibits Ras-ERK signaling in chondrocytes and phenotypic analogies between mice with constitutive FGFR1 activation and Nf1 deficiency in Col2a1-positive chondrocytes, we asked whether neurofibromin is required to control FGFR1-Ras-ERK signaling in maturing chondrocytes in vivo. Genetic Nf1 ablation in Fgfr1-deficient chondrocytes reactivated Ras-ERK1/2 signaling in hypertrophic chondrocytes and reversed the expansion of the hypertrophic zone observed in mice lacking Fgfr1 in Col2a1-positive chondrocytes. Histomorphometric and gene expression analyses suggested that neurofibromin, by inhibiting Rankl expression, attenuates pro-osteoclastogenic FGFR1 signaling in hypertrophic chondrocytes. We also provide evidence suggesting that neurofibromin in prehypertrophic chondrocytes, downstream of FGFRs and via an indirect mechanism, is required for normal extension and organization of proliferative columns. Collectively, this study indicates that FGFR signaling provides an important input into the Ras-Raf-MEK-ERK1/2 signaling axis in chondrocytes, and that this input is differentially regulated during chondrocyte maturation by a complex intracellular machinery, of which neurofibromin is a critical component.

Dataset Information

Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation.

Publications

Constitutive activation of MKK6 in chondrocytes of transgenic mice inhibits proliferation and delays endochondral bone formation.

Similar Datasets

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