Molecular aspects of tibial dyschondroplasia in the chicken: II. Effects of 1,25(OH) 2D 3 on the expression of type X collagen and alkaline phosphatase activity in growth plate chondrocytes

Abstract

The present study investigated the regulation of type X collagen expression in normal and dyschondroplastic (TD) growth plate chondrocytes by vitamin D metabolites. Type X collagen mRNA transcription was 20% lower in vitamin D deficient growth plate cartilage as compared to normal chondrocytes obtained from chicks fed a diet supplemented with 5 μg vitamin D 3/kg diet. Administration of 1,25(OH) 2D 3 to rachitic chicks increased type X collagen mRNA levels. Higher concentrations of 1,25(OH) 2D 3 (10 −10 versus 10 −12 M) and lower levels of extracellular calcium (5 mM versus 20 mM) were required to stimulate type X collagen gene expression in cultured chondrocytes from TD chicks compared to normal chicks. The growth of chondrocytes from normal chicks was reduced by high concentrations (≥ 10 −8M) of 1,25(OH) 2D 3, whereas the inhibitory effect was not observed in chondrocytes from TD chicks. While low concentrations (10 −13 – 10 −11M) of 1,25(OH) 2D 3 had no effect on the alkaline phosphatase (AP) activity of chondrocytes from normal chicks, the activity was increased in TD chicks. Although high concentrations (≥ 10 −10M) of 1,25(OH) 2D 3 inhibited AP activity in normal chondrocytes, even higher levels (≥ 10 −8M) were required to produce an inhibitory effect in TD chondrocytes. These results indicate that TD chondrocytes are more resistant to vitamin D 3 action than normal chondrocytes.