Steroidogenesis, proliferation and apoptosis in bovine granulosa cells: role of tumour necrosis factor-α and its possible signalling mechanisms

Abstract

This study was designed to investigate the presence of bioactive tumour necrosis factor-α (TNF-α) in bovine fluid collected from small (<5 mm) and large (>8 mm) follicles, as well as the production of the cytokine by the granulosa cells collected from the same type of follicles. Moreover, the effectiveness of 10, 1 and 0.1 ng mL^-1 of human TNF-α (hTNF-α) in affecting the main parameters of granulosa cell function, progesterone (P₄) and oestradiol-17β (E₂) production, cell proliferation and apoptosis, was tested. In addition, the study aimed to determine whether the signalling mechanisms of TNF-α in these cells involve cAMP, nitric oxide or prostaglandin E₂ (PGE₂) and F_2α (PGF_2α). It emerged that bioactive TNF-α is present in follicular fluid from both types of follicles and can be measured in media conditioned by granulosa cells from large follicles. As for the effects of hTNF-α , it inhibits P₄ production in cells from both types of follicles and stimulates E₂ output in those from small follicles; it does not affect proliferation, but it stimulates granulosa cell apoptosis. Finally, the effects of hTNF-α on bovine granulosa cells are not mediated by nitric oxide or cAMP, as neither of these substances were affected by treatment with the cytokine; however, in some way, they could be mediated through PGE₂ and PGF_2α, the production of which was inhibited by TNF-α in cells from small follicles.