The effect of prostaglandins on in vitro limb cartilage differentiation

A variety of studies indicate that a key event in limb chondrogenic differentiation is a cellular condensation process during which an intimate cell-cell interaction occurs that triggers cartilage differentiation by elevating cAMP levels. It has recently been demonstrated that when limb mesenchymal cells are subjected to high density monolayer culture under conditions conducive to chondrogenesis, they synthesize several prostaglandins, including PGE2 and prostacyclin, which are important local modulators of cAMP formation in a number of cells and tissues. In the present study, we demonstrate that exogenous PGE2 stimulates the in vitro chondrogenic differentiation of the subridge mesoderm of the embryonic chick limb bud. The stimulatory effect of PGE2 is greatly potentiated by the phosphodiesterase inhibitor, theophylline, suggesting its influence on chondrogenesis is mediated by its ability to increase cAMP levels. The stimulatory effect of PGE2 is dose-dependent and can be detected at a concentration as low as 10(-8)M. PGE1 is just as effective as PGE2 in stimulating in vitro chondrogenesis, whereas PGA1 and PGF1 alpha are less than half as effective. Thromboxane B2 has no effect on chondrogenesis. On the basis of our results, the possibility that endogenous prostaglandins might regulate limb cartilage differentiation by acting as local regulators of cAMP content is discussed.