Salidroside improves bovine embryo quality by mitigating oxidative stress and regulating mitochondrial lipid metabolism

In vitro production techniques for bovine embryos can improve reproductive efficiency and expand quality breeding stock, but lipid metabolism disturbances during in vitro embryo culture can decrease embryo quality. Salidroside (SAL) is a glycoside extracted from the rhizome of the medicinal plant Rhodiola rosea that has antioxidant, antiaging, anti-inflammatory, and lipid metabolism-regulating effects. This study demonstrated that the addition of SAL to the culture medium of bovine embryos during in vitro culture increased the blastocyst rate and number of blastocyst cells and improved bovine blastocyst totipotency and proliferation. SAL reduced the lipid droplet content in bovine blastocysts and increased the levels of lipolysis-related genes (PNPLA2, LIPE, and MGLL). Fatty acids serve as ligands to activate PPARα and promote the transcription and expression of downstream fatty acid β-oxidation-related genes (CPT1A, CPT2, ACOX1, and ACOX2). SAL reduced the ROS level, increased the GSH level, increased the expression of antioxidant-related proteins (Nrf2 and downstream HO-1), and increased the levels of antioxidant enzyme-related genes (GPx1, SOD1, SOD2, and CAT) in bovine embryos. SAL increased the mitochondrial membrane potential and mitochondrial function, number, and distribution; facilitated mitochondria‒lipid droplet interactions; increased fatty acid availability to mitochondria; and further enhanced fatty acid β-oxidation. In conclusion, SAL not only acts as an antioxidant to reduce oxidative stress generated during in vitro bovine embryo culture but also promotes lipolysis to produce free fatty acids (FFA) to activate PPARα, enhances fatty acid β-oxidation, regulates lipid metabolism, and reduces the lipid content in blastocysts, thereby improving embryo developmental competence.