A diet defined by its content of bovine milk exosomes and their RNA cargos has moderate effects on gene expression, amino acid profiles and grip strength in skeletal muscle in C57BL/6 mice

Abstract

Exosomes are nanoparticles that transfer cargos from donor cells to recipient cells where they elicit changes in gene expression and metabolism. Evidence suggests that exosomes and their cargos are also absorbed from dietary sources such as bovine milk, and bovine exosomes promote the growth of myofibers in murine C2C12 myotube cell cultures. The aim of the current study was to determine whether the dietary intake of bovine milk exosomes alters strength, gene expression and amino acid profiles in murine skeletal muscles. Male and female C57BL/6 mice, age three weeks, were fed an AIN93G-based, exosome and RNA-depleted (ERD) diet for six weeks; controls were fed an exosome and RNA-sufficient (ERS) diet. Variables of feeding behavior, metabolism, grip strength, liver and kidney function, amino acid profiles, and gene expression patterns were analyzed by using metabolic cages, grip strength analyzers, clinical chemistry analyzers, targeted LC/MS-MS, and RNA sequencing analysis. The diets had no effect on food and water intake, respiratory exchange rate, physical activity, grip strength, markers of liver and kidney dysfunction, and amino acid profiles in muscle. Only twelve and nine mRNAs were differentially expressed in skeletal muscle from female and male mice, respectively, fed ERD and ERS diets. The modest effect of the ERD diet on gene expression and levels of free amino acids in skeletal muscle is consistent with observations that bovine milk exosomes and their cargos accumulate in tissues other than skeletal muscle.

Keywords: Amino Acids; Exosomes; Gene Expression; Milk; Skeletal Muscle.

Figure 1.

Effect of exosome and RNA-defined diets on front forearm grip strength in C57BL/6 mice fed ERD and ERS diets. Values are means ± standard errors (n=5).

Figure 2.

Principal component analysis (A) and hierarchical clustering (B) of amino acid levels in mice fed ERD and ERS diets (n=5 ERS and n=4 ERD males and females).

Figure 3.

Heat map of differentially expressed genes (≥2-fold change) in ERD vs. ERS females (A) and males (B) (n=3).

Figure 4.

Relative mRNA expression of Tmem100, Rhobtbb1, Socs2, and I16rα (negative control) and protein expression of Socs2 and β-actin (control) in skeletal muscle in female C57BL/6 mice fed ERS and ERD diets. Values are means ± standard errors of RT-qPCR analysis. *P<0.05, **P<0.01 vs. ERS-fed mice (n=4).