1,25(OH)2D3 and dihydrotestosterone interact to regulate proliferation and differentiation of epiphyseal chondrocytes

Growth plate chondrocytes are affected by 1,25(OH)₂D₃ and androgens, which may critically interact to regulate proliferation and differentiation during the male pubertal growth spurt. We investigated possible interactions of 1,25(OH)₂D₃ and the non-aromatizable androgen dihydrotestosterone (DHT) in primary chondrocyte cultures from young male rats. DHT and 1,25(OH)₂D₃ independently stimulated DNA synthesis and cell proliferation in a dose-dependent manner with maximally effective doses of 10^-8 M] and 10^-12 M], respectively. Both DHT and 1,25(OH)₂D₃ stimulated the expression and release of IGF-I, and the proliferative effects of each hormone were prevented by an IGF-I antibody. DHT and 1,25(OH)₂D₃ increased messenger RNAs (mRNAs) of their cognate receptors and of IGF-I receptor mRNA (IGF-I-R). 1,25(OH)₂D₃ also stimulated mRNA of the androgen receptor (AR), whereas DHT did not affect mRNA of the vitamin-D receptor (VDR). Coincubation with both steroid hormones did not stimulate receptor mRNAs more than either hormone alone. The proliferative effects of DHT and 1,25(OH)₂D₃ were completely inhibited by simultaneous incubation with both hormones, despite potentiation of IGF-I synthesis. In contrast, both hormones synergistically stimulated cell differentiation as judged by alkaline phosphatase activity, collagen X mRNA, and matrix calcification in long-term experiments. We conclude that DHT and 1,25(OH)₂D₃ interact with respect to chondrocyte proliferation and cell differentiation. The proliferative effects of both hormones are mediated by local IGF-I synthesis. Simultaneous coincubation with both hormones blunts the proliferative effect exerted by either hormone alone, in favor of a more marked stimulation of cell differentiation.