130 INSULIN-LIKE GROWTH FACTOR-1 AND INTERLEUKIN-11 AS POSSIBLE SURVIVAL FACTORS FOR THE BOVINE PREIMPLANTATION EMBRYO EXPOSED TO STRESS

Abstract

Both IGF-1 and interleukin-11 (IL-11) are survival factors that modify response to cell injury. Moreover, IGF-1 promotes preimplantation development (Mol. Reprod. Dev. 62, 489) and IL-11 has been reported to reduce effects of heat shock on bovine embryos (Theriogenology 59, 343). For this study, it was hypothesized that IGF-1 and IL-11 improve survival of bovine embryos exposed to lethal stimuli. Embryos were produced in vitro and cultured in KSOM medium. Treatment effects were analyzed using least squares ANOVA with the GLM procedure of SAS (SAS Inst., Inc., Cary, NC, USA). In Exp. 1, 100 ng mL⁻¹ IGF-1 increased (P < 0.01) the percent of oocytes that became blastocyst at 8 days post-insemination (dpi) (19.0% for control v. 24.5% for IGF-1; SEM = 1.3%; 7 replicates; 105 embryos/treatment). For Exp. 2, embryos were cultured ± 100 ng mL⁻¹ IGF-1. At 5 dpi, embryos ≥16 cells were cultured at either 38.5°C for 24 h or 41°C for 9 h and then 38.5°C for 15 h followed by TUNEL analysis (7 replicates; 86–100 embryos/treatment). At 38.5°C, IGF-1 did not affect total cell number (60.5 v. 64.4 for control and IGF-1, respectively; SEM = 2.3) or percent of blastomeres undergoing apoptosis as determined by TUNEL (5.9% v. 5.7%; SEM = 0.6%). Heat shock reduced total cell number (P < 0.05) and increased the percent of cells that were TUNEL-positive (P < 0.001). For heat-shocked embryos, total cell number was 46.0 for control v. 59.8 for IGF-1 (SEM = 2.3) and percent of TUNEL-positive blastomeres was 11.6% for control v. 5.9% for IGF-1 (SEM = 0.6%). Effects of heat shock were less for IGF-1-treated embryos (temperature × IGF-1, P = 0.07 for cell number and P < 0.01 for TUNEL). For Exp. 3 (4 replicates; 111–136 embryos/treatment), embryos were cultured ± 100 ng mL⁻¹ IGF-1 beginning at the 1-cell stage in control medium (KSOM), ethanol (1.0%; v/v) or gossypol (10 μg mL⁻¹ in 1% ethanol). Percent of blastocysts at 8 dpi was affected by treatment (P < 0.01) and IGF-1 (P < 0.04). Without IGF-1, least-squares means were 24.6%, 13.6% and 0.9% for control, ethanol, and gossypol, respectively (SEM = 1.7%). With IGF-1, least-squares means were 29.3 ± 3.4%, 26.5 ± 1.6%, and 8.7% ± 1.7% for control, ethanol, and gossypol (control v. ethanol, NS; control v. gossypol, P < 0.01). Thus, IGF-1 blocked the effect of ethanol on development. For Exp. 4, putative zygotes were cultured ± 10 ng mL⁻¹ human IL-11 (4 replicates; 201–214 zygotes/treatment). At 3 dpi, embryos remained at 38.5°C or were cultured at 41°C for 9 h and then returned to 38.5°C. Heat shock reduced (P < 0.01) the percent of putative zygotes and cleaved embryos that became blastocysts at 8 dpi but IL-11 had no effect at either temperature (percent zygotes to blastocysts = 25.3% and 25.6% for control and IL-11 at 38.5°C and 14.0% and 11.8% for control and IL-11 at 41°C; SEM = 3.4%). In conclusion, IGF-1 blocked induction of apoptosis caused by heat shock and the reduction in development caused by ethanol. Thus, IGF-1 may play an important role in early development by acting as a survival factor. There was no evidence that IL-11 conferred thermoprotection to bovine embryos. (Support: USDA NRICGP 2002-35203-12664, USDA IFAFS #2001-52101-11318, and USDA TSTAR 2001-34135-11150.)