Dynamics of IGF signalling during the ovulatory peak in women undergoing ovarian stimulation.

CONTEXT: IGF signalling is known to affect human ovarian follicular function during growth and development. However, the role of the IGF system is unknown during the ovulatory peak, which is characterized by profound changes in granulosa cell (GCs) mitosis and function.

OBJECTIVE: How is the IGF system expressed and regulated during the midcycle surge in women?

DESIGN: Follicular fluid (FF) and granulosa cells (GCs) were collected during the ovulatory peak from two specific time-points. One sample was obtained before oocyte pick up (OPU): before ovulation trigger (OT) (T = 0 h) or at 12, 17, or 32 h after OT, and one sample was obtained at OPU 36 h after OT.

SETTING: University hospital.

PATIENTS/PARTICIPANTS: Fifty women undergoing ovarian stimulation were included.

MAIN OUTCOME MEASURE: Gene expression profiles were assessed by microarray analysis of GCs. IGF-related proteins in the FF were assessed by using immunoassays or by determination of activity with a proteinase assay.

RESULTS: Expression of proteins promoting IGF activity (i.e., IGF2, PAPPA, and IRS1) together with proliferation markers were downregulated on a transcriptional level in GCs after OT, whereas proteins inhibiting the IGF signal (i.e., IGFBPs, IGF2R, and STC1) were upregulated. STC1 gene expression and protein levels were greatly upregulated after OT with a parallel steep downregulation of PAPP-A proteolytic activity.

CONCLUSIONS: These data suggest that downregulation of IGF signalling mediated by increased STC1 expression is instrumental for the sudden cessation in GC proliferation and onset of differentiation during the ovulatory peak.