The Effects of Heat Shock Protein 70 Addition in the Culture Medium on the Development and Quality of In Vitro Produced Heat Shocked Bovine Embryos

SIMPLE SUMMARY: European dairy cows are extremely sensitive to heat stress. During hot summers milk yield is suppressed, welfare status of the cows is aggravated, and their fertility is seriously compromised. The observed subfertility is attributed to endocrinological alterations and mainly to inability of the early embryo to develop uneventfully until the implantation stages. To protect the integrity and the functionality of their cells, all mammals have inherent defense mechanisms against external insults. A major representative of these molecules are the heat shock proteins (HSPs) that are secreted by almost all cells. In this study, we examined the effects of exogenous HSP70 on the developmental competence and quality of early embryos produced in vitro, after 24-h exposure to slightly elevated temperature. Our findings imply that the temperature rise is detrimental for the developmental potential of the early embryos, and that the HSP70 can partly mitigate the harmful effects of heat stress, by improving the embryo yield and by reducing the adverse effects of heat stress on some embryo quality characteristics. ABSTRACT: The aims of the present study were to examine the effects of HSP70 addition in the in vitro culture medium of day 3 embryos on their developmental competence and quality. Bovine oocytes (n = 1442) were in vitro matured, inseminated and cultured for the first two days according to standardized methods. The presumptive zygotes were randomly allocated in three experimental groups: Control, C (embryos cultured at 39 °C throughout the culture period), group C41 (temperature was raised to 41 °C from the 48th to 72nd h post insemination (p.i.) and then it returned at 39 °C for the remaining culture period), and group H41 (the temperature modification was the same as in C41 and during heat exposure, HSP70 was added in the culture medium). Cleavage and embryo yield were assessed 48 h p.i. and on days 7, 8, 9, respectively and gene expression in day 7 blastocysts was assessed by RT-PCR. Blastocyst yield was the highest in group C39; and higher in group H41 compared to group C41. From the gene expression analyses, altered expression of 11 genes was detected among groups. The analysis of the orchestrated patterns of gene expression differed between groups. The results of this study confirm the devastating effects of heat stress on embryo development and provide evidence that HSP70 addition at the critical stages can partly counterbalance, without neutralizing, the negative effects of the heat insult on embryos, acting mainly through mechanisms related to energy deployment.