Parathyroid hormone (PTH) inhibits terminal chondrocyte differentiation and type X collagen production in cultured whole chick sterna.
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In cartilage, hypertrophy is the terminal stage of chondrocyte differentiation. Type X collagen expression is a marker for this stage of development. PTH has been shown to repress articular cartilage differentiation. PTH is also required for normal chondrocyte development through the prehypertrophic stage. We used a serum-free whole chick sterna model to determine PTH effects on chondrocyte terminal differentiation using type X collagen expression as a marker. We addressed the following questions. 1) Does PTH inhibit terminal differentiation of hyaline cartilage chondrocytes? 2) Are PTH effects dose dependent? 3) Is there a temporal window when PTH is more effective? 14 day sterna were cultured for 8 days in PTH concentrations ranging from 10-5 to 10-7M and examined for type X collagen expression. Type X collagen was detected using immuno-histochemistry and visualized with confocal microscopy. Increasing PTH concentration led to decreased type X collagen expression. To determine stage dependent effects, 14 day sterna were given one dose of 10-7 M PTH on one day of the first 7 days of culturing. Sternal lengths after 24 hr. exposure to PTH were determined. PTH increased sternal length only until day 6 of culture. In conclusion, our results suggest that PTH may inhibit hyaline cartilage development in the prehypertrophic stages and has minimal effect on cells that have entered terminal differentiation.