Journal
JOURNAL OF ORTHOPAEDIC RESEARCH
Volume 24, Issue 11, Pages 2095-2105Publisher
WILEY
DOI: 10.1002/jor.20233
Keywords
apoptosis; hypertrophy; collagen type X
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Funding
- Intramural NIH HHS Funding Source: Medline
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Endochondral ossification is initiated by differentiation of mesenchymal cells into chondrocytes, which produce a cartilaginous matrix, proliferate, mature, and undergo hypertrophy, followed by matrix calcification, and substitution of cartilage by bone. A number of hormones and growth factors have been implicated in this process. Using in vitro, long-term, high-density, micromass cultures of chick embryonic mesenchyme, that recapitulate the process of chondrogenesis, chondrocyte maturation, and hypertrophy, we have investigated the importance of a balance between proliferation and apoptosis in cartilage maturation, focusing specifically on the effects of transforming growth factor-beta 1 (TGF-P1) and the thyroid hormone, triiodothyronine (T3). Our results showed that TGF-P1 stimulates proliferation, by week 2 of culture, and T3 inhibits proliferation by week 3. Cell size increases in cultures treated with T3. Collagen type X is expressed in all culture, and delay in matrix deposition is seen only in the cultures treated with TGF-beta 1. T3 stimulates alkaline phosphatase activity, but not calcification. T3 enhances apoptosis, as seen by TUNEL staining, and internucleosomal DNA fragmentation. The results support the roles of T3 and TGF-beta in cartilage maturation, i.e., TGF-beta 1 stimulates proliferation and suppresses hypertrophy, while T3 stimulates hypertrophy and apoptosis. (c) 2006 Orthopaedic Research Society.
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