Prostaglandins Mediate the Stimulation of Deoxyribonucleic Acid Synthesis by Transforming Growth Factor α in Hen Granulosa Cells during Ovarian Follicular Development1

Abstract

The present study was an examination of the possible involvement of specific membrane lipid metabolites of prostaglandins (PGs), leukotrienes (LTs), lysophosphatidic acid (LPA), and lysophophatidyl choline (LPC) in transforming growth factor a- (TGFα) induced DNA synthesis by granulosa cells during follicular development. Granulosa cells from the first (F1) and the fifth and sixth (F5-6) largest preovulatory follicles were cultured for 18 h in the presence of TGFα and/or an inhibitor of either phospholipase A₂, (PLA₂), cyclooxygenase, or lipoxygenase, LTs, LPA, LPC, and/or PGs. TGFα-induced, but not basal, DNA synthesis in Fl and F5-6 granulosa cells was suppressed by inhibitors of PLA₂ and cyclooxygenase but not of lipoxygenase. The inhibition was concentration-dependent and could be attenuated by exogenous PGE₂. Likewise, PGF and PGE production was suppressed by these inhibitors. Moreover, PGE₂, and, to a lesser extent, PGF_2α, increased basal [³H]thymidine incorporation and enhanced DNA synthesis induced by a submaximal stimulatory concentration of TGFα. The mitogenic effect of PGs was more evident in granulosa cells from F5-6 follicles than in those from F1 follicles. In contrast, LTs (LTB₄, LTC₄, LTD₄), (+)5(s)-hydroxy- (6E,8Z,llZ,14Z)-eicosatetraenoic acid (5-HETE), and lysophospholipids (LPA and LPC) had no effect on granulosa cell DNA synthesis, irrespective of the stage of ovarian follicular development and the presence of TGFα and PGE₂. These studies demonstrate that 1) arachidonic metabolites of cyclooxygenase, but not lipoxygenase pathway and arachidonate lysophospholipid by-products (LPA and LPC), are involved in the regulation of granulosa cell DNA synthesis by TGFα; 2) compared to PGs of the F series, PGE₂ and PGE₁, are more effective in either mimicking the action of TGFα or potentiating the mitogenic response of the cells to the growth factor; and 3) the DNA synthetic response of the hen granulosa cell to PGs is greater in granulosa cells from F5-6 than in those from F1 follicles. These findings are consistent with our concept that an increase in PG production is a necessary element in the TGFα-regulated cascade of biochemical events leading to chicken granulosa cell mitogenesis during hen ovarian follicular development.