Bovine preimplantation embryos are reliant on nutrients secreted by the uterine epithelium for survival. The uterine epithelium releases lipid-bound extracellular vesicles (EVs) that carry RNAs and proteins; however, the metabolic content of these EVs has not been investigated. Our objectives were to characterize EVs released from immortalized bovine uterine epithelial (BUTE) cells, characterize the metabolic contents of BUTE cell EVs, and determine how estradiol and progesterone affect their secretion and metabolic content. We successfully isolated EVs from BUTE cells, as determined by nanoparticle tracking, transmission electron microscopy, and western blot. EVs isolated from BUTE cells were similar in size and morphology to those observed in vivo. These EVs contain numerous metabolites, mainly related to amino acid metabolism. Estradiol increased EV secretion and altered the EV content of 8 metabolites related to lipid production. Progesterone also increased EV section and altered 4 lipid-related metabolites in the EVs. In conclusion, BUTE cells are a valid model to study EV secretion from the uterine epithelium. Estradiol and progesterone increased EV secretion and altered metabolites related to lipid metabolism. EVs may carry lipids or other nutrients to the embryo, supporting embryo elongation.
Sandoval et al. (Mon,) studied this question.