"Exosomics"-A Review of Biophysics, Biology and Biochemistry of Exosomes With a Focus on Human Breast Milk

Abstract

Exosomes are biomolecular nanostructures released from cells. They carry specific biomolecular information and are mainly researched for their exquisite properties as a biomarker source and delivery system. We introduce exosomes in the context of other extracellular vesicles, describe their biophysical isolation and characterisation and discuss their biochemical profiling. Motivated by our interest in early-life nutrition and health, and corresponding studies enrolling lactating mothers and their infants, we zoom into exosomes derived from human breast milk. We argue that these should be more extensively studied at proteomic and micronutrient profiling level, because breast milk exosomes provide a more specific window into breast milk quality from an immunological (proteomics) and nutritional (micronutrient) perspective. Such enhanced breast milk exosome profiling would thereby complement and enrich the more classical whole breast milk analysis and is expected to deliver more functional insights than the rather descriptive analysis of human milk, or larger fractions thereof, such as milk fat globule membrane. We substantiate our arguments by a bioinformatic analysis of two published proteomic data sets of human breast milk exosomes.

Keywords: breast milk; exosome; maternal health; micronutrient; proteomics.

Figure 1

(a) Schematic representation of exosome biogenesis: first, multivesicular endosomes are formed (MVEs), which encompass the exosomes. The MVEs can either fuse with the plasma membrane, releasing the exosomes into the extracellular matrix (see zoomed schematic), or fuse with the lysosome for degradation. Microvesicles are formed via direct blebbing from the plasma membrane. Exosomes contain protein, DNA, RNA and surface membrane proteins, which are specific to the cell of origin and are not limited to cell surface proteins (Colombo et al., 2014).

Figure 2

Protein Network generated with the 188 proteins identified in the combined human breast milk exosome proteomics dataset (Admyre et al.,; Larssen et al.). The red square shows a cluster of chemokines.