Signaling and Signal Transduction in Endocrine Tissues
(W750) INHIBITION OF PHOSPHORYLATION OF AKT AND ERK INHIBITS OVARIAN FOLLICLE GROWTH AND DECREASES ESTRADIOL PRODUCTION IN SHEEP IN VIVO.
Ryan, Kate1, Martin, Finian1, Evans, Alex1, 1 University College Dublin, Dublin, Ireland
ABSTRACT- The intracellular signalling mechanisms regulating dominant follicle development are unclear. Ovarian follicles develop in cohorts that are initially similar in size and functional ability; however, despite developing in the same endocrine environment, the dominant follicle(s) undergoes continued proliferation and survival while remaining subordinate follicles regress. Previously we have shown that dominant follicle development is associated with high levels of the signalling molecules Akt and Erk and their phosphorylated forms (p–Akt, p–Erk) and that inhibition of p–Akt and p–Erk inhibited FSH– and IGF– induced estradiol production in bovine granulosa cells in vitro. The aim of this study was to investigate the effect of inhibiting Akt and Erk phosphorylation on dominant follicle development and oestradiol production in vivo. Eighteen ewes were synchronised and on day three of cycle the largest (dominant) follicle was identified, measured, follicular fluid sampled (32G needle) and all other follicles ablated via laparotomy. Ewes were assigned to four groups: Control (n = 4; follicle injected with DMSO), Akt inhibitor (n = 5; LY294002), Erk inhibitor (n = 5; PD98059) or Akt + Erk inhibitor (n = 4; all intrafollicular injections to give a final follicular fluid concentration 50 M). Ewes recovered from surgery and were then slaughtered 48 h later when the ovaries were recovered, follicles measured and follicular fluid collected. In the control animals follicles grew from 5.3±0.4mm to 6.8±0.8 mm (P=0.029) whereas there was no change in diameters in the treated groups (combined mean 5.18±0.17 to 5.18±0.26 mm; P>0.10). In the control animals, follicular fluid estradiol concentrations were not different between the time of treatment and follicle collection (39±9 to 26±5 ng/ml; P=0.163) but decreased in all other groups (PD 69±20 to 21±9, P=0.011; LY 46±13 to 7±3, P=0.009; PD+LY 52±18 to 10±5 ng/ml, P=0.043). These results show that in vivo inhibition of the signal transduction pathways involving Akt or Erk inhibit follicle growth and decrease estradiol production, indicating their importance in dominant follicle development. (Supported by Enterprise Ireland and Science Foundation Ireland)
KEY WORDS: Follicle, Sheep, Akt, Erk