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

Abstract

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.

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

“…Thermotolerance in the developing embryo seems to be associated with the embryonic genome activation (8cell stage) [46], while the previous stages are exhibiting increased thermosensitivity [6,7,45,47]. In a previous study we have shown that the supplementation of in vitro maturation medium with HSP70 results in elevated thermotolerance capacity of oocytes under conditions of artificial heat stress and the effects are maintained at until the blastocysts stage [36]. Similarly, in the present study, the protective role of HSP70 was confirmed for…”

“…Thermotolerance in the developing embryo seems to be associated with the embryonic genome activation (8-cell stage) [ 46 ], while the previous stages are exhibiting increased thermosensitivity [ 6 , 7 , 45 , 47 ]. In a previous study we have shown that the supplementation of in vitro maturation medium with HSP70 results in elevated thermotolerance capacity of oocytes under conditions of artificial heat stress and the effects are maintained at until the blastocysts stage [ 36 ]. Similarly, in the present study, the protective role of HSP70 was confirmed for the very early embryonic stages, as the supplementation of HSP70 in the heat stressed group showed significantly increased blastocysts yield compared to the heat stressed embryos without supplementation; however, the blastocysts yield was not restored at the levels of the C39 group.…”

“…All stages of the in vitro embryo production (IVP) were carried out according to the standardized laboratory protocols that have been previously described [ 36 , 37 ]. All chemicals were purchased from Sigma Chemical Company (Poole, UK), unless otherwise stated.…”

“…This dramatic drop in embryo production and quality can be partly reversed with the addition of HSP70 in the maturation medium. Similarly, the addition of HSP70 altered the expression of genes related to metabolism, oxidation, apoptosis and thermotolerance in the cumulus cells and the early embryos [ 36 ]. The overarching goal of the present study was to examine whether the negative effects of exposing early bovine embryos to elevated temperature (41 °C) for 24 h could be mitigated by the addition of HSP70 into the culture medium.…”

Fertilization with follicular fluid reduces HSP70 and BAX expression on bovine in vitro embryos

“…The protein encoded by HSP70 functions as a heat shock‐associated chaperone. The expression of HSP70 is considered a response mechanism that protects the embryo from the harmful effects of various sources of stress, helping to maintain cell stability and prevent apoptosis under conditions of thermal and oxidative stress (Stamperna et al., 2021). HSP70 is known to be an important inhibitor of apoptotic pathways (Lanneau et al., 2007), with its expression being upregulated to prevent apoptosis when cells encounter lethal stimuli (Stankiewicz et al., 2005).…”