Abstract
Normal intervertebral disc contains high levels of group II phospholipase A2 (PLA2) . To examine its functional roles in disc, we studied the synthesis and secretion of phospholipase A2 in cultured rabbit annulus fibrosus and articular chondrocytes. Basal PLA2 activity of annulus fibrosus chondrocytes was very low (0.3 nmol/min/microplate well), whereas the cells spontaneously secreted significant amounts of prostaglandin E2 (PGE2) . Addition of interleukin-1β (IL-1β) (200 U/ml) to culture media caused a 10-fold increase in cell-associated PLA2 activity within 5 h and further rapid increase to the maximal level with time (41 nmol/min/well at 40 h) . IL-1β also activated secretion of both PGE2 and PLA2 from the annulus fibrosus chondrocytes; the extracellular PLA2 activity increased with a lag time of about 10 h and continued to increase linearly with further incubation (13 nmol/min/well at 40 h) . Cultured articular chondrocytes exhibited similar responses to the cytokine stimulation. Immunohistochemical analysis using a polyclonal anti-rat-group II PLA2 showed that the IL-1β stimulated annulus fibrosus and articular chondrocytes contained immunoreactivity both in the cytoplasm and nucleus, whereas chondrocytes in normal disc and articular cartilage contained immunoreactivity only in the cytoplasm. These results suggest that group II PLA2 plays a role in secretion and subcellular traffic of substances involved in the production and degradation of extracellular matrix in chondrocytes, and that the subcellular localization of PLA2 is linked to the regulation of the enzyme function.
