The impact of exposure to serum lipids during in vitro culture on the transcriptome of bovine blastocysts

In vitro culture has a detrimental impact on early embryonic development, and serum addition to IVC is recognized to compromise blastocyst quality. Particularly, serum fatty acids affect embryonic lipid composition and reduce cryopreservation survival. To understand the molecular pathways of serum-induced embryonic stress, this study examined the early development of bovine embryos produced in different protein- or lipid-supplemented culture media: BSA alone (control), BSA + serum lipid fraction (SELF), delipidated serum and total serum. These protein-lipid treatments were applied from the eight to 16 cell stages to the blastocyst stage. As planned, SELF treatment increased the fatty acid concentration in the medium compared with control medium but did not induce embryo toxicity. However, microarray comparison between blastocysts cultured in BSA without or with SELF revealed differential transcriptomic profile associated with ceramide-induced oxidative stress and inflammation. Moreover, the SELF treatment had a significant impact on genes involved in cholesterol metabolism (LDLR, HMGCS1), with the potential upstream control of the transcription factors SREBP and PPARA, two major regulators of cholesterol metabolism. In addition, the expression of pluripotence-related genes (APEX, CLDN6) was downregulated in blastocysts subjected to either SELF or total serum. Taken together, these results illustrate how the early embryonic transcriptome responds to increased lipid exposure through an inflammatory and metabolic signature.