Oviductal epithelial cells transcriptome and extracellular vesicles characterization during thermoneutral and heat stress conditions in dairy cows.

In this study, the transcriptome of oviductal epithelial cells and certain characteristics of their extracellular vesicles of dairy cows were described under thermoneutral and heat stress conditions. Twenty cows were compared in springtime at THI = 65.6 ± 0.90 and in summertime at THI = 78.36 ± 2.73. During each season, the estrous cycles of the cows were synchronized, and on day 3 of the ensuing cycle, a blood sample was collected for progesterone determination, while their oviducts were collected after slaughter. Epithelial cells and oviductal fluid were collected from the oviduct ipsilateral and contralateral to the corpus, respectively. For the gene expression study, a comparative transcriptomic approach, using RNASeq, was performed on cells collected from the ipsilateral and the contralateral oviducts. The size and the concentration of extracellular vesicles (EVs) at both seasons were analyzed using Transmission Electron Microscopy and Nanoparticle tracking analysis and specific proteins were detected by Western blotting. Progesterone concentration was higher during the thermoneutral period. Between seasons, divergent expression of genes related to immune system, contractility, gamete protection and lncRNAs was found. The size and the concentration of the EVs did not differ between seasons, however, the concentration in the ipsilateral oviduct tended to be lower (p = 0.09) from the contralateral one in the summer, but not in the spring. Our results show for the first time that HS could be involved with alterations in the oviductal cells' gene expression and in the changes in concentration of EVs in the oviductal lumen. Our results imply that the altered oviductal environment during HS could be associated with the suppressed summer fertility in dairy cows.