Role of prostaglandins in the suppression of apoptosis in hen granulosa cells by transforming growth factor alpha

Although transforming growth factor alpha (TGF-alpha) is known to be an imp ortant survival factor for granulosa cells, the cellular and molecular mech anisms involved are uncertain. The purpose of the present study was to inve stigate the possible involvement of prostaglandins in the anti-apoptotic ac tion of TGF-alpha. Hen granulosa cells from healthy prehierarchical follicl es (2-6 mm) cultured in serum-free medium underwent spontaneous apoptosis a s demonstrated by DNA fragmentation and nuclear chromatin condensation. TGF -alpha (20 ng ml(-1)) stimulated maximum synthesis of prostaglandins (PGE a nd PGF) in granulosa cells and completely inhibited serum deprivation-induc ed apoptosis. The addition of an inhibitor of cyclooxygenase (COX; N-(2-cyc lohexyloxy-4-nitrophenyl)methanesulfonamide (NS398) or ibuprofen) or phosph olipase A(2) (PLA(2); aristolochic acid, 2-p-amylcinnamoyl amino-4-chlorobe nzoic acid (ONO-RS-82) or arachidonyl triflouro methyl ketone (TFMK)), to t he culture medium markedly suppressed the TGF-alpha -induced prostaglandin synthesis and significantly increased granulosa cell apoptosis. The apoptot ic effect of NS398 and aristolochic acid was completely inhibited by exogen ous prostaglandins (PGF(2 alpha), PGE(1), PGE(2)) and arachidonic acid, res pectively. However, exogenous prostaglandins failed to inhibit the PLA(2) i nhibitor-induced apoptotic DNA fragmentation, implying that in addition to prostaglandins, arachidonic acid or leukotrienes may be important in transd ucing the anti-apoptotic action of TGF-alpha. In the absence of exogenous T GF-alpha, prostaglandins had no significant influence on granulosa cell apo ptosis induced by serum withdrawal. These findings indicate that prostaglan din synthesis is a necessary, but not sufficient, event in the suppression of granulosa cell apoptosis by TGF-alpha. Whether arachidonic acid or leuko trienes ave important in the anti-apoptotic action of TGF-alpha in hen gran ulosa cells remains to be determined.