# Functional analysis and identification of miRNAs associated with lipid metabolism from milk-derived exosomes

## TL;DR

This study identifies miRNAs in milk exosomes that regulate lipid metabolism in cow mammary cells, offering new insights into milk fat synthesis.

## Contribution

The study reveals novel miRNA pathways (miR-423-5p/APOA5 and miR-125b/SLC27A1) that regulate lipid metabolism in bovine mammary epithelial cells via exosomes.

## Key findings

- Milk-derived exosomes contain miR-423-5p and miR-125b, which modulate lipid synthesis and oxidation in bovine mammary cells.
- miR-423-5p promotes lipid accumulation by targeting APOA5, while miR-125b inhibits lipolysis by repressing SLC27A1.
- Exosomal miRNAs represent a novel mechanism for regulating milk fat synthesis in lactating mammary glands.

## Abstract

Exosomes are crucial mediators of intercellular communication. As a key component of milk, milk-derived exosomes are abundant in genetic cargo, particularly microRNAs (miRNAs), indicating their potential role in regulating mammary gland physiology. Therefore, this study aimed to investigate the specificity of miRNAs in milk-derived exosomes and their regulatory roles in lipid synthesis in bovine mammary epithelial cells (BMECs).

Based on 17,838 DHI records showing a significantly higher milk fat percentage (MFP) in late lactation (4.24% ± 1.07%), 10 high- (5.96% ± 0.26%, HMF) and 10 low-MFP (1.68% ± 0.23%, LMF) cows were selected during this stage for milk-derived exosome isolation and miRNA profiling. Exosomes isolated via differential ultracentrifugation were verified as 50–150 nm vesicles expressing CD9, CD81, and TSG101. miRNA sequencing identified 1,320 differentially expressed miRNAs (496 upregulated and 824 downregulated) between the HMF_EXO and LMF_EXO groups. Uptake assays confirmed that BMECs internalized these exosomes, and qRT-PCR validation showed that miR-423-5p and miR-125b were significantly upregulated and downregulated in HMF_EXO- and LMF_EXO-treated BMECs, respectively. Functionally, exosomal miR-423-5p promoted intracellular lipid accumulation and TG synthesis in BMECs by targeting APOA5, whereas miR-125b inhibited lipolysis and fatty acid oxidation by repressing SLC27A1.

This study demonstrates that milk-derived exosomal miRNAs represent a novel mechanism for regulating milk fat synthesis. Specifically, miR-423-5p and miR-125b directly modulated lipid metabolism in BMECs via the miR-423-5p/APOA5 and miR-125b/SLC27A1 pathways. These findings provide new insights into the molecular regulation of milk fat synthesis and highlight the importance of exosome-mediated intercellular communication in the lactating mammary gland.

The online version contains supplementary material available at 10.1186/s40104-025-01331-5.