Regulation of prostaglandin E₂ production by vitamin D metabolites in growth zone and resting zone chondrocyte cultures is dependent on cell maturation

The production of PGE₂ by chondrocytes and its regulation by vitamin D metabolites was examined in this study as a function of cell maturation. Costochondral chondrocytes, derived from the resting zone and growth zone cartilage, were grown in culture to fourth passage. At confluence, they were exposed to 10^-8-10^-11M 1,25-(OH)₂D₃₆ or to 10^-7-10^-10M 24,25-(OH)₂D₃ for either five minutes or 3,6,12, or 24 hours. Indomethacin (10^-7M) was added to one-half of the cultures to block the production of PGE₂. The amount of PGE₂ released into the media was determined by radioimmunoassay. Both growth zone and resting zone cells produced PGE₂ in a time-dependent manner; PGE₂ concentration was greater in the resting zone cell cultures. 1,25-(OH)₂D₃ stimulated PGE₂ production by growth zone cells in a dose-dependent manner, significant at 10^-8-10^-10M. This effect was observed at 3 hours and remained elevated during the 24 hours of culture. 1,25-(OH)₂D₃ had no effect on PGE₂ production by resting zone cells. However, 24,25-(OH)₂D₃ (10^-7-10^-8M) inhibited PGE₂ production from 3-24 hours. No effect was noted when 24,25-(OH)₂D₃ was added to growth zone cells. Indomethacin reduced PGE₂ production to baseline values in all groups examined. The results indicate that chondrocytes in culture produce PGE₂. Production is regulated by vitamin D₃ metabolites and is cell maturation-dependent. The correlation between hormone-dependent PGE₂ production and phospholipase A₂ activity suggests that the effects of 1,25-(OH)₂D₃ and 24,25-(OH)₂D₃ on chondrocytes may be mediated, in part, by changes in phospholipase A₂ activity, arachidonic acid release, and PGE₂ production. PGE₂ may then act as a second messenger in a paracrine or autocrine manner.