Researchers from the Morinaga Milk Industry Co, Japan reported previously that microRNA (miRNA) are present in whey fractions of human breast milk, bovine milk, and rat milk. Moreover, they confirmed that many mRNA species are present in rat milk whey. These RNA were resistant to acidic conditions and to RNase, but were degraded by detergent. Thus, these RNA are likely packaged in membrane vesicles such as exosomes. However, functional extracellular circulating RNA in bodily fluids, such as blood miRNA, are present in various forms.
In the current study, the researchers used bovine raw milk and total RNA purified from exosomes (prepared by ultracentrifugation) and ultracentrifuged supernatants, and analyzed them using miRNA and mRNA microarrays to clarify which miRNA and mRNA species are present in exosomes, and which species exist in other forms. Microarray analyses revealed that most mRNA in milk whey were present in exosomes, whereas miRNA in milk whey were present in supernatant as well as exosomes. The RNA in exosomes might exert functional effects because of their stability. Therefore, they also investigated whether bovine milk-derived exosomes could affect human cells using THP-1 cells. Flow cytometry and fluorescent microscopy studies revealed that bovine milk exosomes were incorporated into differentiated THP-1 cells. These results suggest that bovine milk exosomes might have effects in human cells by containing RNA.
Uptake of bovine raw milk whey-derived exosomes by macrophages. (A–C) Fluorescence microscopy images; 7-AAD (BD Biosciences, San Diego, CA) was used to label the nuclei of THP-1 cells (red), and PKH67 (Sigma-Aldrich, St. Louis, MO) was used to label the exosomes (green). (D) The uptake of fluorescence-labeled exosomes into THP-1 cells at various conditions was evaluated using a flow cytometer.