Circadian rhythm does not affect the miRNA cargo of bovine raw milk extracellular vesicles
Extracellular vesicles (EVs) and their microRNA (miRNA) cargo have been suggested as potential biomarkers for mammary gland health in cattle. However, milk is a dynamic fluid, and its biologically active components, including miRNAs, could be subject to changes throughout the day. The current study aimed to evaluate the circadian fluctuation of milk EVs miRNA cargo to assess the feasibility of milk EVs as future biomarkers for mammary gland health management. Milk from four healthy dairy cows was collected manually from one quarter during four consecutive days in the two daily milking sessions in the morning and the afternoon. The SCC was determined, and the milk EVs were isolated from skimmed milk. The presence of EVs was confirmed by transmission electron microscopy (TEM), tunable resistive pulse sensing (TRPS), and western blot (WB). Small RNA libraries were produced from 10 ng of extracted RNA and sequenced in two lanes of a HiSeq2500. The heterogeneity and integrity of EVs and the protein EV markers CD9, CD81, and TSG101 were confirmed by TEM and WB. The sequencing revealed that despite daily fluctuation in other milk components, like the somatic cells during milking sessions, the miRNA cargo abundance in milk EVs stayed constant. Our results show that the miRNA cargo of milk EVs is very stable regardless of the hour of the day, supporting their potential use as diagnostic markers for mammary gland health. Overall design: 28 samples: 14 Morning, 14 Evening