Improvement of in vitro-produced bovine embryo treated with coagulansin-A under heat-stressed condition

Heat stress has large effects on reproduction including conception rate in cattle. In this study, we examined the effects of coagulansin-A (coa-A), a steroidal lactone, on acquired thermo tolerance during in vitro production of bovine embryos. Oocytes were incubated in in vitro maturation (IVM) media with or without coa-A at two different temperatures, 40.5˚C and 42˚C, for 20 h. The treatment of coa-A significantly improved blastocyst development only at 40.5˚C (P < 0.05). Interestingly, immunofluorescence analysis demonstrated that coa-A induced heat shock protein 70 (HSP70) and phosphatidylinositol-3-kinase (PI3K), but significantly attenuated nuclear factor kappa B (NF-κB) and cyclooxygenase-2 (COX2). To determine the expression patterns of related genes at the transcription level, qRT-PCR was performed. Expression of HSP70 and PI3K was elevated, whereas expression of NF-κB, COX2 and inducible nitric oxide synthase (iNOS) was significantly (P < 0.05) downregulated in the coa-A-treated group compared with the control group. Moreover, pro-apoptotic genes were downregulated, and antiapoptic genes were upregulated in the coa-A group. We also counted the total cell number and apoptotic nuclei at the blastocyst and found that more cell numbers (143.1 ± 1.5) and less apoptotic damages (6.4 ± 0.5) in the coa-A treatment group comparing to control group (131.4 ± 2.0 and 10.8 ± 0.5), indicating the enhanced embryo quality. In conclusion, our results demonstrate that the coa-A not only improved the blastocyst development in vitro but also increased their resistance to heat stress condition through induction of HSP70/PI3K.