Transforming growth factor-alpha and -beta differentially regulate growth and steroidogenesis of bovine thecal cells during antral follicle development

Abstract

The actions and interactions of transforming growth factor-alpha (TGF alpha) and TGF beta on growth and differentiation of bovine thecal cells were investigated. Bovine thecal interna cells were isolated from small (less than 5 mm), medium (5-10 mm), and large (greater than 10 mm) antral follicles and cultured in the presence or absence of TGF alpha and/or TGF beta. Both [3H]thymidine incorporation and changes in cell number (i.e. DNA levels) were evaluated to determine effects on thecal cell growth. Short term treatment of cells with TGF alpha (18-24 h) stimulated thymidine incorporation, and longer term treatments (4 days) increased cell number. TGF beta suppressed thymidine incorporation below that observed in untreated cultures, but had no effect on cell number. When combined with TGF alpha, TGF beta suppressed the ability of TGF alpha to stimulate thymidine incorporation and increase cell number. The response to these growth factors was similar for cells isolated from the different stages of antral follicle development. The effects of TGF alpha and TGF beta on thecal cell differentiation were evaluated by quantitating changes in androstenedione and progesterone accumulation in cultures treated with TGFs in the absence (basal) or presence of hCG, estradiol (E2), or a combination of hCG and E2. E2 and hCG were included in this study because previous research has demonstrated that these hormones alter thecal cell steroidogenesis. Treatment with TGF alpha resulted in a suppression of basal and hormonally stimulated accumulation of androstenedione during days 0-3 of culture, whereas TGF beta did not significantly alter androstenedione accumulation. TGF alpha also suppressed progesterone accumulation during days 0-3 of culture in the absence or presence of hormones. In contrast, TGF beta stimulated accumulation of progesterone in cultures that did not contain E2, which suppressed progesterone during this period. Therefore, during days 0-3 of culture, TGF alpha appears to have suppressive effects on androstenedione and progesterone production, whereas TGF beta can stimulate progesterone production in the absence of E2. During days 3-6 of culture, thecal cell differentiation changes, and the capacity to produce androstenedione dramatically declines, while the capacity to produce progesterone increases. During this period, either TGF alpha or TGF beta slightly increased basal progesterone accumulation and partially suppressed the ability of hCG to stimulate progesterone. The effects of TGFs on thecal cell steroidogenesis were similar with cells isolated from the different stages of antral follicle development. Results from these studies provide evidence that THF alpha and TGF beta can modulate thecal cell growth and differentiation (i.e. steroidogenesis).(ABSTRACT TRUNCATED AT 400 WORDS)