Endocrinology, Vol 126, 1599-1609, Copyright © 1990 by Endocrine Society

ARTICLES

Effect of 1,25-dihydroxyvitamin D3 on induction of chondrocyte maturation in culture: extracellular matrix gene expression and morphology

LC Gerstenfeld, CM Kelly, M Von Deck and JB Lian
Department of Orthopedic Surgery, Harvard Medical School, Boston, Massachusetts 02115.

Chondrocytes, derived from a tissue that remains as permanent hyaline cartilage in vivo (embryonic chicken caudal sterna) were treated with 10(-8) to 10(-8) M 1,25-dihydroxyvitamin D3 [1,25(OH)2D3]. These nonadherent rounded chondrocytes acquired an adherent, polygonal morphology in a dose-dependent fashion with 1,25(OH)2D3 treatment. During the first 4 days of 1,25(OH)2D3 treatment cell flattening was associated with a 10-fold increase in beta-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 alpha 1(I) and alpha 2(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. alpha 1(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)2D3 treatment 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 1,25(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 alpha 1(IX) mRNAs. DNA contents in hormone-treated cultures also remained elevated. These results suggest that 1,25(OH)2D3 both 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)2D3 blocks many of the subsequent changes in connective tissue expression.

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