Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 2, Pages 365-370Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0507979103
Keywords
ossification; p38; Sox9
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Funding
- NCI NIH HHS [P30 CA016672, CA16672] Funding Source: Medline
- NIAMS NIH HHS [P01 AR042919, P01 AR42919] Funding Source: Medline
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Accumulating in vitro evidence suggests that the p38 mitogenactivated 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.
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