Furthermore, inhibition of the Akt and Erk pathways in vivo had a negative effect on follicular fluid oestradiol production and follicle growth in sheep. Taken together, these results suggest an important role for Akt and Erk signalling pathways in mediating the effects of the gonadotropins and IGF on follicle cell function and on follicular development. The stimulation of inhibin A, activin A, follistatin, oestra diol, progesterone and cell number by FSH and IGF in granulosa cells in vitro agrees with earlier findings. However, the regulation of the Akt and Erk pathways in relation to these hormonal and proliferative changes has not been studied previously in the bovine model.
Increases in Akt and Erk signalling proteins in response to FSH and IGF stimulation suggest a role for Akt and Erk sig nal transduction pathways in FSH and IGF mediated gran ulosa cell development as reflected by cell proliferation survival and production of inhibin A, activin A, follista tin, oestradiol, and progesterone. The signifi cant reductions in hormonal output as a result of inhibition selleck chemical FR 180204 of the Akt and Erk pathways further support a role for Akt and Erk in FSH and IGF mediated action in granulosa cells. However, there appear to be differences in the relative importance of each pathway with respect to the endpoints measured. Our findings suggest that Akt is important in mediating the effects of FSH on inhibin A, activin A, oestradiol and progesterone secretion and also important in mediating IGF I stimulated inhibin A, activin A, follistatin, oestradiol and progesterone secre tion by granulosa cells.
In addition, the results also sug gest that the Erk pathway is involved in mediating FSH induced activin A and oestradiol production, and proges terone secretion selleck induced by both FSH and IGF I stimula tion of granulosa cells in vitro. The regulation of activin A secretion by FSH and IGF dis played a similar pattern to that of oestradiol with the Erk pathway only involved in FSH stimulated production and the Akt pathway involved in both FSH and IGF stimu lated production. Inhibition of the Erk pathway had no effect on inhibin A concentrations. Only the Akt pathway was indicated in regulating the production of inhibin A. However, this might be a simplistic view of what is hap pening. Activin is known to upregulate FSH receptors and aromatase gene expression, thus promoting production of oestradiol. Additionally, expression of the inhibin subunit is increased in response to activin A. Previ ous work suggests that activin A may mediate the effects of FSH stimulation on oestradiol and inhibin A produc tion but this explanation remains to be proved.