Anti-apoptotic action of insulin-like growth factor-I during human preimplantation embryo development

Insulin-like growth factor 1 (ICF-I) has been shown to increase the proport ion of embryos forming blastocysts and the number of inner cell mass cells in human and other mammalian preimplantation embryos. Here we examined whet her the increased cell number resulted from increased cell division or decr eased cell death. Normally fertilized, Day 2 human embryos of good morphology were cultured t o Day 6 in glucose-free Earle's balanced salt solution supplemented with 1 mM glutamine, with (n = 42) and without (n = 45) 1.7 nM ICF-I. Apoptotic ce lls in Day 6 blastocysts were identified using terminal deoxynucleotidyl dU TP terminal transferase (TUNEL) labeling to detect DNA fragmentation and 4' -6-diamidino-2-phenylindole (DAPI) counterstain to evaluate nuclear morphol ogy. The number of nuclei and extent of DNA and nuclear fragmentation was a ssessed using laser scanning confocal microscopy. IGF-I significantly increased the proportion of embryos developing to the b lastocyst stage from 49% (control) to 74% (+IGF-I) (P < 0.05). ICF-I also s ignificantly decreased the mean proportion of apoptotic nuclei from 16.3 +/ - 2.9% (-IGF-I) to 8.7 +/- 1.4% (+IGF-I) (P ( 0.05). The total number of ce lls remained similar between both groups (61.7 +/- 4.6 with ICF-I; 54.5 +/- 5.1 without IGF-I). The increased number of blastocysts combined with redu ced cell death suggests that ICF-I is rescuing embryos in vitro which would otherwise arrest and acting as a survival factor during preimplantation hu man development.