Characterization of Sheep Milk Extracellular Vesicle-miRNA by Sequencing and Comparison with Cow Milk

SIMPLE SUMMARY: Milk provides significant health benefits for mammals, especially as the primary nutrient sources of neonates. Milk was recognized as the epigenetic “doping system” during mammalian development in recent research due to the bioactive component extracellular vesicles, which can act as mediators of intercellular communication, and even as signal carriers between different individuals, especially mothers and babies, by the containing regulatory miRNAs. It is widely accepted that although cow milk is generally more consumed by humans, sheep milk is more suitable for infants. However, compared with cow milk, few studies have focused on the sheep milk extracellular vesicles, which select specific types of miRNA to encapsulate. This study clarified the sheep milk extracellular vesicle-miRNA profiling by sequencing and made a comparison with that of cow milk. The results of this study provide more documents for the milk bioactive components in different species. ABSTRACT: Milk can mediate maternal-neonatal signal transmission by the bioactive component extracellular vesicles (EVs), which select specific types of miRNA to encapsulate. The miRNA profiling of sheep milk EVs was characterized by sequencing and compared with that of cow milk. Nanoparticle tracking analysis revealed that the concentration of sheep milk EVs was 1.3 ± 0.09 × 10(12) particles/mL and the diameter was peaked at 131.2 ± 0.84 nm. Sheep milk EVs contained various small RNAs, including tRNA, Cis-regulatory element, rRNA, snRNA, other Rfam RNA, and miRNA, which held about 36% of all the small RNAs. In total, 84 types of miRNA were annotated with Ovis aries by miRBase (version 22.0) in sheep milk EVs, with 75 shared types of miRNAs in all samples. The miR-26a, miR-191, let-7f, let-7b and miR-10b were highly expressed both in cow and sheep milk EVs, and 14 sheep milk EV-miRNAs in the top 20, occupying 98% of the total expression, were immune-related. Although pathway analysis showed different potential functions of cow and sheep milk EV-miRNAs, there were still some shared points: lipid metabolism (phospholipase D, glycerophospholipid and glycosylphosphatidylinositol), calcium metabolism, and nerve conduction (axon guidance and synapse). This study provides reference for the bioactive components in the milk of different species.