Bta-miR-125a Regulates Milk-Fat Synthesis by Targeting SAA1 mRNA in Bovine Mammary Epithelial Cells

Xiaogang Cui,Jiao Feng,Changxin Wu,Tianqi Yuan,Zhengyu Fang

doi:10.3390/agriculture12030344

Abstract

The nutritional value of cow milk mainly depends on its fatty acid content and protein composition. The identification of genes controlling milk production traits and their regulatory mechanisms is particularly important for accelerating genetic progress in the breeding of dairy cows. On the basis of mammary gland transcriptome analyses, in this study we identified an miRNA, bta-miR-125a, that could control bovine milk-fat production by targeting the 3′ untranslated region (UTR) of the serum amyloid A-1 (SAA1) mRNA. The presence of synthetic bta-miR-125a (i.e., an miR-125a mimic) significantly down-regulated the expression of luciferase from mRNAs containing the binding sequence for bta-miR-125a in the 3′-UTR in a dual-luciferase reporter assay. Furthermore, the presence of the miR-125a mimic decreased the steady-state level of the SAA1 protein, but increased the accumulation of triglycerides and cholesterol content in bovine mammary epithelial cells (MAC-Ts). Blocking the function of bta-miR-125a using a specific inhibitor decreased the level of triglycerides and cholesterol content in the cells. These results indicate that bta-miR-125a can serve as a positive regulator of lipid synthesis in mammary epithelial cells, which acts by targeting SAA1 gene expression.

Highlights

Cow milk is regarded as a basic food in many diets worldwide [1], and contains most of the essential elements required for healthy human nutrition
MiRanda, predicting that the 30 -untranslated region (UTR) of the serum amyloid A-1 (SAA1) mRNA was a target of bta-miR-125a
These results suggest that bta-miR-125a may inhibit the expression of SAA1 by targeting its 30 -UTR in Mammary alveolar cell-T (MAC-T) cells

Summary

Introduction

Cow milk is regarded as a basic food in many diets worldwide [1], and contains most of the essential elements required for healthy human nutrition. Milk fat is a milk quality indicator, and a determining element of the nutritional value of milk. It is composed of lipid droplets, which mainly consist of triacylglycerides (TAGs), which are synthesized and released from the bovine mammary epithelial cells. The milk-fat levels and composition are affected by various factors, including heredity, nutrition, physiological conditions and the environment. The SAA protein is synthesized in the liver, and has been shown to be involved in the metabolism of lipids [7]. The SAA1 and SAA2 isoforms are mainly synthesized in hepatocytes, and are primarily associated with high-density lipoprotein (HDL) [9]. The SAA4 isoform is an HDLassociated apolipoprotein, and constitutively expressed at relatively low levels in both human and mouse liver [13]. The SAA4 isoform function is largely unknown [14]

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