EFFECT OF 1,25-DIHYDROXYVITAMIN-D3 ON INDUCTION OF CHONDROCYTE MATURATION IN CULTURE - EXTRACELLULAR-MATRIX GENE-EXPRESSION AND MORPHOLOGY

Chondrocytes, derived from a tissue that remains as permanent hyaline cartilage in vivo (embryonic chicken caudal sterna) were treated with 10-8to 10‑8M 1, 25-dihydroxyvitamin D3 [1, 25(OH)2D3]. These nonadherent rounded chondrocytes acquired an adherent, polygonal morphology in a dosedependent fashion with 1, 25(OH)2D3treatment. During the first 4 days of 1, 25(OH)2D3treatment cell flattening was associated with a 10-fold increase in β-actin and fibronectin and their corresponding messenger RNAs (mRNAs). After adherence over the 12 days of continuous hormone treatment, a 2- to 4-fold increase in DNA synthesis and DNA accumulation were observed for the highest hormone dose (10-8 M). Over the same time course total collagen synthesis decreased 35-50% primarily due to decreased type II collagen synthesis, which accompanied comparable decreases in its mRNA. In contrast, both cvl(I) and α2(I) showed a continuous 5- to 10-fold increase; however, type I collagen protein synthesis remained undetectable, indicating translational control of the type I collagen synthesis. α1(X) mRNAs showed a 2- 3-fold increase after 12 days of hormone treatment, and its polypeptide was clearly detected by sodium dodecyl sulfate polyacrylamide gel analysis. Type IX collagen synthesis showed a 2-fold increase in synthesis and its mRNA levels during the first 4 days of 1, 25(OH)2D3treatment but thereafter had levels comparable to control cultures. Analysis of proteoglycan synthesis and core protein mRNA levels showed there was a 2-fold increase in core protein mRNAs while proteoglycan synthesis, as assessed by 35S incorporation, showed only a 10-20% increase. Direct hormone effects vs. those secondary to altered cellular morphology were determined by blocking cell adherence by growth of the l, 25(OH)2D3-treated cultures on bacteriological petri dishes. All of the observed effects on cytoskeletal and collagen mRNAs were blocked except the elevations observed in proteoglycan core protein and al(IX) mRNAs. DNA contents in hormone-treated cultures also remained elevated. These results suggest that 1, 25(OH)2D3both activates and suppresses specific genes, promoting chondrocyte maturation toward a more hypertrophic phenotype. However, prevention of the initial morphological alterations that are induced by 1, 25(OH)2D3blocks many of the subsequent changes in connective tissue expression. © 1990 by The Endocrine Society.