Abstract
Chondrocyte differentiation is a fundamental
process during endochondral ossification.
Retinoic acid (RA) has been shown to regulate this
process, however, the mechanisms underlying RA
regulation of chondrogenesis are not clearly
understood. Chondroprogenitor cells, ATDC5
have been shown to be a useful in vitro model for
examining the multiple step differentiation of
chondrocytes. The present study investigated the
mechanisms underlying RA regulation of chondrogenesis
using ATDC5 cell culture.
In this study, we show that RA suppresses the
cell growth, cartilage nodule formation, accumulation
of proteoglycan, alkaline phosphatase
(ALPase) activity and mineralization and that RA
dose dependently upregulates the levels of type X
collagen and matrix metalloproteinase-13 (MMP-13)
mRNA which are marker proteins of hypertrophic
chondrocytes, in ATDC5 cells. The addition of protein
synthesis inhibitor, cycloheximide (CHX), partially
inhibits the induction of type X collagen and
MMP-13 mRNA by RA. In this system, RA upregulates
the mRNA level of Runx2/Cbfa1 (type II), a
positive regulator for mineralization, and downregulates
the mRNA of Indian hedgehog (Ihh),
parathyroid hormone related protein (PTHrP),
negative regulators for terminal differentiation.
However, RA downregulates ALPase, bone gla
protein (BGP) mRNAs and mineralization. These
data indicate that RA stimulates cartilage differentiation,
however, cell condensation and cartilage
nodule formation may be candidates of primary
importance in the terminal differentiation of chondrocytes.
