Biology Of Exosomes And Their MicroRNA Cargos In Human And Bovine Milk

Exosomes are small, cargo-containing vesicles secreted by cells to facilitate intercellular communication. Of exosome cargos, microRNAs are especially interesting because of their involvement in gene regulation. Recently, our lab has shown that exosomes and their microRNA cargo are absorbed through the diet and elicit effects exogenously. Human and animal milk contain exosomes, which may have implications in infant and adult nutrition. There is evidence that bovine milk exosomes enhance growth of murine C2C12 myotube cell cultures, but whether this translates to muscle in vivo is unknown. The USDA National Nutrient Database for Standard Reference is lacking up-to-date information about human milk constituents, including their exosome and microRNA content. This thesis focuses on two specific aims: 1) the effect of dietary bovine milk exosomes on strength, gene expression and amino acid profiles in murine skeletal muscles and 2) the feasibility and methodological groundwork for studying microRNA in exosomes from small volumes of human milk. Aim 1: Mice were fed exosome-defined diets and variables of feeding behavior, metabolism, grip strength, liver and kidney function, amino acid profiles, and gene expression patterns were assessed. No effects were observed for food and water intake, respiratory exchange rate, physical activity, grip strength, markers of liver and kidney dysfunction, and amino acid profiles in muscle. Only a modest effect on gene expression in skeletal muscle was observed, consistent with recent observations that bovine milk exosomes and their cargos accumulate in tissues other than skeletal muscle. Aim 2: The content of extracellular vesicles (EVs) in human milk was assessed under different storage conditions at timed intervals. Exosomes were purified from 1 mL of fresh human milk and their microRNA content was assessed by microRNA-sequencing analysis and compared to that in three brands of infant formula. Storage conditions were determined a confounder when analyzing microRNAs in human milk exosomes. MicroRNA-sequencing analysis is feasible in exosomes from small volumes of milk and the content of microRNAs in infant formulas was negligible compared to human milk. Advisor: Janos Zemplen