title: Effects of TGF-beta1 and triiodothyronine on cartilage maturation: in vitro analysis using long-term high-density micromass cultures of chick embryonic limb mesenchymal cells.
abstract: 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-beta1 (TGF-beta1) and the thyroid hormone, triiodothyronine (T3). Our results showed that TGF-beta1 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-beta1. 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 stimulates proliferation and suppresses hypertrophy, while T3 stimulates hypertrophy and apoptosis.
authors.affiliation: Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis, and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Building 50, Room 1523, MSC 8022, Bethesda, Maryland 20892-8022, USA.
authors.forename: Maria A
authors.initials: MA
authors.lastname: Mello
authors.forename: Rocky S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015415:Biomarkers / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects; D002356:Cartilage / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D049108:Cell Enlargement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D002642:Chick Embryo; D024121:Collagen Type X / Q000235:genetics / Q000378:metabolism; D053938:DNA Fragmentation; D004338:Drug Combinations; D005121:Extremities / Q000196:embryology; D008648:Mesoderm / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D015415:Biomarkers; D024121:Collagen Type X; D004338:Drug Combinations; D012333:RNA, Messenger; D053773:Transforming Growth Factor beta1; D014284:Triiodothyronine; D000469:Alkaline Phosphatase