Identification and characterization of differentially expressed exosomal microRNAs in bovine milk infected with Staphylococcus aureus

Shaoyang Ma,Eveline M Ibeagha-Awemu,Xin Zhao,Chao Tong

doi:10.1186/s12864-019-6338-1

Abstract

BackgroundMicroRNAs (miRNAs) in milk-derived exosomes may reflect pathophysiological changes caused by mastitis. This study profiled miRNAs in exosomes from both normal milk and mastitic milk infected by Staphylococcus aureus (S. aureus). The potential targets for differentially expressed (DE) miRNAs were predicted and the target genes for bta-miR-378 and bta-miR-185 were also validated.ResultsTotal RNA from milk exosomes was collected from healthy cows (n = 3, the control group) and S. aureus infected cows (n = 6, the SA group). Two hundred ninety miRNAs (221 known and 69 novel ones) were identified. Among them, 22 known and 15 novel miRNAs were differentially expressed. Target genes of DE miRNAs were significantly enriched in intracellular protein transport, endoplasmic reticulum and identical protein binding. The expression of two miRNAs (bta-miR-378 and bta-miR-185) with high read counts and log2 fold changes (> 3.5) was significantly higher in mastitic milk infected with S. aureus. One target gene (VAT1L) of bta-miR-378 and five target genes (DYRK1B, MLLT3, HP1BP3, NPR2 and PGM1) of bta-miR-185 were validated.ConclusionDE miRNAs in exosomes from normal and S. aureus infected milk were identified. The predicted targets for two DE miRNAs (bta-miR-378 and bta-miR-185) were further validated. The linkage between the validated target genes and diseases suggested that we should pay particular attention to exosome miRNAs from mastitic milk in terms of milk safety.

Highlights

MicroRNAs in milk-derived exosomes may reflect pathophysiological changes caused by mastitis
Identification of S. aureus in bovine milk Based on colony counting and polymerase chain reaction (PCR) results for nuc and bacterial 16S rRNA genes, 13.95% (42/301) milk samples were infected with S. aureus
Isolation and detection of exosome from bovine milk Bovine milk exosomes with approximately 100 nm in diameter were observed (Additional file 1: Figure S1a)

Summary

Introduction

MicroRNAs (miRNAs) in milk-derived exosomes may reflect pathophysiological changes caused by mastitis. The potential targets for differentially expressed (DE) miRNAs were predicted and the target genes for bta-miR-378 and bta-miR-185 were validated. MicroRNAs (miRNAs) are short noncoding (~ 22 nucleotide in length), regulatory RNAs that modulate gene expression at the post-transcriptional level, mostly via binding to perfectly/partially complementary sites at the 3′-UTR of target mRNAs [1]. The majority of milk’s miRNAs are transported and protected by the lipid bilayer of extracellular vesicles, predominantly exosomes of about 100 nm in diameter secreted by mammary epithelial cells [4]. Exosomes are cell-derived vesicles that are present in all biological fluids including blood, saliva, urine, amniotic fluid, bronchoalveolar lavage fluid and milk [5, 6].

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