Abstract
Mammalian milk is not only a source of nutrition for the newborn, but also contains various components that regulate further development. For instance, milk is an abundant source of microRNAs (miRNAs), which are evolutionary conserved small non-coding RNAs that are involved in post-transcriptional regulation of target mRNA. MiRNAs present in milk can occur in extracellular vesicles (EVs), which are nanosized membrane vesicles released by many cell types as a means of intercellular communication. The membrane of EVs protects enclosed miRNAs from degradation and harbors molecules that allow specific targeting to recipient cells. Although several studies have investigated the miRNA content in milk EVs from individual species, little is known about the evolutionary conserved nature of EV-associated miRNAs among different species. In this study, we profiled the miRNA content of purified EVs from human and porcine milk. These data were compared to published studies on EVs from human, cow, porcine, and panda milk to assess the overlap in the top 20 most abundant miRNAs. Interestingly, several abundant miRNAs were shared between species (e.g., let-7 family members let-7a, let-7b, let-7f, and miR-148a). Moreover, these miRNAs have been implicated in immune-related functions and regulation of cell growth and signal transduction. The conservation of these miRNA among species, not only in their sequence homology, but also in their incorporation in milk EVs of several species, suggests that they are evolutionarily selected to regulate cell function in the newborn.
Highlights
Mother’s milk provides the newborn with more than only nutrition: it contains various complex macromolecular structures that carry signaling molecules that are delivered to the newborn
We show for the first time the miRNA profile of purified milk extracellular vesicles (EVs) isolated after differential centrifugation followed by density gradient separation
We identified 309 mature miRNAs in human milk EVs and 218 mature miRNAs in porcine milk EVs (Supplementary File 1), These numbers are in range with the miRNAs that were previously identified in milk EV enriched samples of human [n = 602 [8], n = 125 [20] and n = 610 [19]; average of 446 ± 278 miRNAs] and porcine [n = 234 [13] and n = 491 [22]; average of 363 ± 182 miRNAs]
Summary
Mother’s milk provides the newborn with more than only nutrition: it contains various complex macromolecular structures that carry signaling molecules that are delivered to the newborn. One of these signaling moieties are extracellular vesicles (EVs). Conservation of Milk EV miRNAs. EVs are generally classified into exosomes and microvesicles, which have distinct biogenesis pathways and may differ in size and cargo [1, 2]. Available methodologies do not allow discrimination between exosomes and microvesicles as the size, surface markers, and buoyant densities of these vesicle subtypes overlap [2]. We will use the generic term EVs in this study even though previously published studies attribute their findings to certain subtypes, mostly exosomes
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