Docosahexaenoic acid prevents heat stress-triggered ferroptosis in early bovine embryos through lipid metabolism homeostasis

Heat waves are occurring more frequently around the world as global warming increases. Heat stress (HS) from hot and humid environments poses a significant threat to oocytes, including elevated levels of reactive oxygen species, mitochondrial dysfunction, spindle abilities, chromosomal mis-segregation, meiotic arrest, increased aneuploidy, and ultimately reduced developmental competence. Therefore, there is an urgent need to identify solutions to mitigate the negative effects of HS. In this study, HS markedly reduced the blastocyst formation rate in bovine embryos and arrested their development at the 8-cell stage. Consequently, transcriptome sequencing analysis of embryos at the 8-cell stage revealed a reduction in the expression of elongation of long-chain fatty acids very long-chain family member 2 (ELOVL2). This downregulation of ELOVL2 consequently led to a decrease in its major product, docosahexaenoic acid (DHA). Therefore, we supplemented DHA to examine whether it could mitigate HS-induced embryo development arrest. Supplementation with DHA during in vitro culture effectively counteracted the detrimental effects of HS on embryo development, including blastocyst formation rate, inner cell mass proportion, and apoptosis. Furthermore, compared with HS, DHA supplementation significantly re-established lipid metabolic homeostasis and prevented lipid peroxidation. In addition, our findings indicate that DHA prevents ferroptosis by activating the Nrf2 signaling pathway. The activation of Nrf2, in turn, restored the activity of the key antioxidant enzyme GPX4 and replenished cellular glutathione levels, thereby preventing lipid peroxidation and ferroptosis. In conclusion, HS induced bovine embryo arrest because of the deficiencies of DHA, which is regulated by ELOVL2. We found that DHA alleviates HS-induced ferroptosis by modulating the Keap1/Nrf2/GPX4 pathway, thereby improving the developmental competence of bovine embryos in vitro under HS conditions.