Metabolic activities of partially degenerated hypertrophic chondrocytes: gene expression of hyaluronan synthases.

Ultrastructural aspects of hypertrophic chondrocytes in hamster and mouse epiphysial cartilage were examined in relation to their metabolic activities. With the hypertrophic change, cytoplasmic vacuolization proceeded leaving the partially intact endoplasmic reticulum (ER). In the hypertrophic cells, cytoplasmic hyaluronan was stained with the biotinylated hyaluronan-binding region (b-HABR) of aggrecan, and mRNAs of hyaluronan synthase (Has 1, Has 2 and Has 3) were detected by in situ hybridization. When the epiphysial cartilage was cultured in the presence of 35S, 3H-GlcNAc, 3H-proline or 14C-palmitic acid, vacuolated late hypertrophic chondrocytes were labeled with these radioactive precursors. The evidence indicates that late hypertrophic chondrocytes are metabolically active, which appears to be essential for the enlargement of chondrocytes.