Heat Shock Protein 70 Improves In Vitro Embryo Yield and Quality from Heat Stressed Bovine Oocytes.

Simple Summary: The Holstein cows are among the most thermosensitive farm animals. In this breed, during the heat stress periods, fertility is seriously compromised due to induced alterations of the endocrine status, reduced fertilizing capacity of the oocyte and increased embryo deaths. To combat the deleterious effects of stress, cells synthesize a series of specific molecules that are mainly involved in cellular protection against the heat insult, called heat shock proteins (HSPs). Here, we examined the effects of supplementing HSP70 in in vitro matured bovine oocytes under thermoneutral or heat stress conditions, and we assessed its efficacy on in vitro embryo yield and quality; the latter was determined on the basis of the expression of various genes related to important cellular functions. It was manifested that HSP70 addition into the in vitro maturation medium restores the developmental competence of heat stressed oocytes and improves the quality of the in vitro produced embryos. Heat shock protein 70 (HSP70) is a chaperon that stabilizes unfolded or partially folded proteins, preventing inappropriate inter- and intramolecular interactions. Here, we examined the developmental competence of in vitro matured oocytes exposed to heat stress with or without HSP70. Bovine oocytes were matured for 24 h at 39 °C without (group C39) or with HSP70 (group H39) and at 41 °C for the first 6 h, followed by 16 h at 39 °C with (group H41) or without HSP70 (group C41). After insemination, zygotes were cultured for 9 days at 39 °C. Cleavage and embryo yield were assessed 48 h post insemination and on days 7, 8, 9, respectively. Gene expression was assessed by RT-PCR in oocytes, cumulus cells and blastocysts. In C41, blastocysts formation rate was lower than in C39 and on day 9 it was lower than in H41. In oocytes, HSP70 enhanced the expression of three HSP genes regardless of incubation temperature. HSP70 at 39 °C led to tight coordination of gene expression in oocytes and blastocysts, but not in cumulus cells. Our results imply that HSP70, by preventing apoptosis, supporting signal transduction, and increasing antioxidant protection of the embryo, protects heat stressed maturing bovine oocyte and restores its developmental competence. [ABSTRACT FROM AUTHOR]