Dietary Bioactive Components
Objectives : Exosomes are natural nanoparticles that can be found in most body fluids including milk. Bovine milk exosomes (BME) are bioavailable and transfer cargos such as RNAs, lipids and proteins across species boundaries. Previous competitor studies implicated galactose-modifications in exosome surface proteins in exosome transport. The objective of our study was to assess the importance of glycan modifications in BME surface glycoproteins for BME uptake and distribution in human intestinal cells (FHs cells) and mice.
Methods : BME were isolated from milk by differential centrifugation ( Fig. 1 ). Putative glycan binding sites on the surfaces of BME were identified by LC/MS-MS and bioinformatics protocols and confirmed by eastern blotting. Surface glycans were altered using proteases, glycosidases and blocking of glycans with lectins for subsequent transport and distribution studies ( Table 1 ). The uptake of BME by FHs cells was assessed using membrane and RNA cargo-labeled BME. The distribution of BME in mice was assessed using BME transfected with fluorophore (IRDye)-labeled synthetic miR-320a in C57BL/6 mice and MGAT-1 tamoxifen inducible conditional knockout (CKO) mice ages 5-8 weeks. One-way ANOVA and Bonferroni’s multiple comparison were used for statistical analyses; P < 0.05 was considered significant.
Results : We identified 49 (N), 13 (O) and 13 (C) putative glycan binding sites on the BME surface, and confirmed the presence of mannose, galactose, N-acetylgalactose, fucose and neuraminate (Fig. 2). Galactose and N-acetylgalactosamine residues on the surface of BME were of particular importance for their uptake by FHs cells, whereas N-acetylglucosamine on the surface of FHs cells was more important than other glycans for BME uptake (Fig. 3). Enzymatic and genetic removal of glycans in BME and MGAT-1 CKO, respectively, caused a loss of BME accumulation in murine livers and pancreas (Fig. 4).
Conclusions : Distinct glycan features are essential for the uptake of BME in mice. The study laid a foundation to assess the importance of glycan modifications in infant formulas and the homing of drug-loaded exosomes to sites of disease.
Funding Sources :
NIFA, NIH, Bill & Melinda Gates Foundation, PureTech Health, and USDA Hatch & Multistate. J.Z. is a consultant for PureTech.