| Abstract |
Retinoic acid (RA) plays an important role in bone metabolism in vivo through osteoclast activation and bone resorption. Retinoid X-activated receptor beta (RXRbeta) has been implicated in the genetic spinal defect of ossification of the posterior longitudinal ligament (OPLL). In this study, we examined the effects of 9-cis RA and all-trans RA (ATRA) on the proliferation, differentiation, and RXRbeta expression of the murine preosteoblastic cell line MC3T3-E1. Both 9-cis RA and ATRA dose-dependently inhibited the increase in total soluble protein content at concentrations of 10 and 100 nM after 4 and 8 d co-culture with MC3T3-E1 cells. The inhibitory effect of 9-cis RA was slightly stronger than that of ATRA. Histone H4 mRNA expression was dose-dependently suppressed by both RAs on day 1. Alkaline phosphatase activity was increased by both RAs at 10 and 100 nM concentrations on day 4, with 9-cis RA-induced activity slightly stronger than that of ATRA. Osteopontin mRNA expression was increased by both RAs on day 1, but was suppressed on day 4. Bone Gla protein mRNA expression was inhibited by 10 and 100 nM 9-cis RA and by 100 nM ATRA on day 14. RXRbeta mRNA expression was increased by 9-cis RA, an RXRbeta ligand, in a dose-dependent manner. Our results suggested that while both RAs suppressed proliferation and stimulated the maturation of preosteoblastic MC3T3-E1 cells, 9-cis RA was slightly more potent than ATRA. It also appeared that RAs may contribute to the development of heterotopic ossification, including OPLL.
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