Physiological role of vitamin a in growth cartilage cells: Low concentrations of retinoic acid strongly promote the proliferation of rabbit costal growth cartilage cells in culture

We have demonstrated that high concentrations of retinoic acid (RA) inhibit expression of the differentiated phenotypes of rabbit costal chondrocytes in culture [M. Takigawa et al (1980) Proc. Natl. Acad. Sci. U. S. 77, 1481- 1485]. In this study we examined the effects of low concentrations of RA on rabbit costal chondrocytes cultured in medium containing vitamin A- deficient serum. In vitamin A- deficient medium, chondrocytes isolated from growth cartilage (GC) proliferated only very slowly, and RA strongly stimulated their proliferation. This stimulatory effect was observable at a concentration of 10^{- 10} M RA and maximal at a concentration of 10^{- 8} M. RA at 10^{- 8} M did not change GC cells from a typical polygonal shape to fibroblast-like cells or inhibit their synthesis of type II collagen. Moreover, RA-treated cells did not synthesize type I collagen. RA inhibited glycosamino-glycan (GAG) synthesis by the cells dose-dependently, but did not change the distribution profile of proteoglycan monomers as determined by glycerol gradient centrifugation. The inhibitory action of RA on GAG synthesis was reversible: after removal of RA from the culture, the rate of GAG synthesis increased within 2 days. In contrast, resting cartilage (RC) cells proliferated well in vitamin A- deficient medium without addition of RA, and RA (10^{- 8} M) stimulated their proliferation only slightly. Furthermore, the inhibitory effect of RA on GAG synthesis in RC cells was much weaker than that in GC cells. These observations suggest a physiological role of RA in cartilage in stimulating the proliferation of GC cells without causing drastic change in their differentiated phenotypes.