Abstract: 408

INSULIN-LIKE GROWTH FACTOR (IGF)-INDUCED APOPTOSIS IN THE MOUSE BLASTOCYST IS REPRODUCED BY BLOCKING THE IGF-1 RECEPTOR AND IS REVERSED BY EXPOSURE TO TRANSFORMING GROWTH FACTOR-.

Kelle Moley^{1 *}, Maggie Chi¹ , Ying Cui¹
Department of Obstetrics and Gynecology, Washington University School of Medicine, St. Louis, MO 63110 ¹

Polycystic ovary syndrome can cause increased pregnancy loss and elevated levels of bioactive IGF-1. We have shown that exposure of two-cell mouse embryos to 130 nM IGF-1 for 72 h leads to significant apoptosis in the blastocyst as compared to 1.3 nM IGF-1. Also, high IGF-1 leads to decreased protein levels and activity of the IGF-1 receptor (IGF-1R). In this study, we hypothesized that decreasing IGF-1R expression with antisense oligonucleotides or blocking IGF-1R activity with neutralizing antibodies would recreate the apoptotic event. First, two-cell mouse embryos were cultured for 72 h in KSOM containing 1.3 nM or 130 nM IGF-1 or a blocking antibody, IR3 (1 g/ml). Decreased receptor autophosphorylation was confirmed by immunoprecipitation and Western analysis. Using terminal dUTP nick end-labeling (TUNEL) technique and confocal microscopy, we found 46±8.7% TUNEL-positive nuclei in the IR3 exposed embryos, similar to 130 nM IGF-1 and significantly higher than 1.3 nM. Next, 4-cell embryos were cultured for 48 h in KSOM containing 0.5 M antisense (AS) or sense (S) oligonucleotides to mouse IGF-1R. Decreased expression was confirmed by confocal microscopy and Western. We found significantly higher TUNEL-positive nuclei among embryos exposed to AS vs S. Also, IR3 blockade interfered with insulin-stimulated glucose uptake, a IGF-1R regulated event in the blastocyst. Finally, co-culturing in high IGF-1 plus TGF- reversed the effects of excess IGF-1 on apoptosis and glucose uptake. This event was specific for TGF-. In summary, blocking the IGF-1R by AS or antibody induces apoptosis in the blastocyst suggesting that down-regulation of IGF-1R may be responsible for high IGF-1 induced apoptosis. TGF- prevents this event and may be acting via a paracrine signaling pathway involving glucose transport.

    This abstract is being presented on Monday, August 2 at 2:45 PM at Todd 125.