MOUSE MECKEL CARTILAGE CHONDROCYTES EVOKE BONE-LIKE MATRIX AND FURTHER TRANSFORM INTO OSTEOCYTE-LIKE CELLS IN CULTURE

Background: we reported that when Meckel's cartilage was transplanted ectopically, chondrocytes transformed into osteocyte-like cells accomp anying the extracellular calcified matrix. However, we could not deter mine whether the osteocyte-like cells were derived from host tissues o r from Meckel's cartilage itself. Therefore, we examined whether the M eckel's cartilage chondrocytes, which have a retrogressive ultimate fa te, are capable of inducing the observed calcification and further tra nsform into osteocyte-like cells in culture. Methods: Meckelian chondr ocytes isolated enzymatically were plated at a low density and grown i n alpha-MEM containing 10% FBS at 37 degrees C under 5% CO2 in air for up to 4 weeks. Results: Chondrocytes were fibroblast-like cells early in culture, but gradually transformed from polygonal cells into typic al chondrocytes showing metachromasia with toluidine blue staining. Af ter an additional week of culture, the chondrocytes transformed from l arge to small round cells accompanying nodule formations. Small round cells multiple-layered actively, and showed more intense alkaline phos phatase (ALPase) activity. Immunostaining identified type II collagen in the extracellular matrix at 2 weeks of culture, and type I collagen and osteocalcin were later synthesized by round cells. von Kossa's re action showed extensive precipitation of calcification throughout the flocculent materials. Ultrastructural analysis showed that the cells s urrounded by calcified matrix strongly resembled osteocytes. Conclusio ns: The present study suggested that the Meckel's cartilage chondrocyt es can express the osteocyte-like phenotype in vitro during synthesis of bone-type marker proteins such as osteocalcin or type I collagen. ( C) 1996 Wiley-Liss, Inc.