Paradoxical effects of tumour necrosis factor-α on rat granulosa cell DNA synthesis

Abstract

Tumour necrosis factor- α (TNF-α ) has been proposed as an intraovarian modulator of granulosa cell function. The effect of TNF-α on DNA synthesis in cultured rat granulosa cells was examined. Tumour necrosis factor-α stimulated thymidine incorporation when added in the presence of transforming growth factor-β (TGF-β). In contrast, the co-mitogenic effect of follicle-stimulating hormone (FSH) and TGF-β was inhibited in a dose-dependent manner by TNF-α . Inhibition of FSH-dependent DNA synthesis by TNF-α was also found when cultures were co-stimulated with activin A. The inhibitory action of TNF-α on FSH-treated cultures was not associated with changes in cell viability. The inhibitory effects of TNF-α could not be solely explained by a decrease in cAMP levels, since TNF-α was also able to inhibit the stimulation by dibutyryl-cAMP and TGF-β on granulosa cell DNA synthesis. These results suggest that TNF-α regulation of granulosa cell growth is elicited either independently or downstream from gonadotrophin-induced cAMP production. The actions of TNF-α could be only partially mimicked by a cell-permeable analogue of ceramide, thus indicating that actions of this cytokine can not be fully ascribed to an activation of sphingomyelinase. Data presented here indicate that, in addition to its previously demonstrated inhibitory effects on gonadotrophin-induced cell differentiation, TNF-α may also exert a marked inhibition on hormonally stimulated immature granulosa cell proliferation. In contrast to this inhibitory action, this cytokine could amplify the mitogenic action of putative intraovarian growth regulators such as TGF-β. These observations add further support to the notion that TNF-α plays a physiological role as a paracrine modulator of follicle development and may be also relevant to the alteration of ovarian function during physiopathological processes.