Antibody to Hsp70 alters response of rabbit preimplantation embryos to hyperthermia in vitro.

The aim of the study was to determine a role of Hsp70 in the response of rabbit preimplantation embryos to hyperthermia (HT) in vitro. The embryos were cultured at standard (ST, 37.5 degrees C, control) or elevated (HT, 41.5 degrees C) temperature for 6h. In half of the embryos from both groups, Hsp70 was blocked by the addition of an antibody against Hsp70 into the medium at stages either prior to (<or= 8 cell) or after (morula) developmental block (DB). After 6h, the HT embryos were post-cultured at 37.5 degrees C for 16-20 h and then evaluated for developmental stages, apoptosis (TUNEL, T), cell number and quality of actin cytoskeleton. The exposure of embryos to 41.5 degrees C either before or after DB did not affect blastocysts (Bl) rate, T-index and embryo cell number. Blockage of Hsp70 before DB resulted in no embryos at the Bl stage. From the Hsp70-blocked embryos after DB, only 27.6% (ST + anti-Hsp70) and 22.6% (HT + anti-Hsp70) of blastocysts were formed, versus 71.4% (ST) and 69.7% (HT) in the non-Hsp70-blocked group. T-index of Hsp70-blocked embryos prior to DB increased from 6.8% (ST) to 28.6% (ST + anti-Hsp70) and from 6.1% (HT) to 29.6% (HT + anti-Hsp70), whilst the cell number dropped from 111 +/- 8.1 (ST) to 20.5 +/- 2.42 (ST + anti-Hsp70) and from 106.8 +/- 8.4 (HT) to 15.4 +/- 1.34 (HT + anti-Hsp70). In contrast, in the Hsp70-blocked embryos after DB, neither T-index nor cell number was changed comparing to the non-blocked. Damages to the actin cytoskeleton, like intracytoplasmic clumps or loss of actin filaments, were only minimally caused by hyperthermia but mostly were a result of Hsp70 blockage. In conclusion, the embryos at stages before the genome activation (GA) appear to be more sensitive to HT. The resistance of pre-GA embryos to HT is related to Hsp70, whilst after GA, Hsp70 is probably not the only factor of thermotolerance and the existence of an additional protective mechanism(s) is hypothesized.