MicroRNA-mediated gene regulation is important for the regulation of fatty acid metabolism and synthesis. Our previous study uncovered that the miR-145 expression is higher in the lactating mammary gland of dairy cows than in the dry-period, but the underlying molecular mechanism is incompletely understood. In this study, we have investigated the potential role of miR-145 in bovine mammary epithelial cells (BMECs). We found that the expression of miR-145 gradually increased during lactation. CRISPR/Cas9-mediated knockout (KO) of miR-145 in BMECs results in the downregulated expression of fatty acid metabolism-associated genes. Further results revealed that miR-145 KO reduced total triacylglycerol (TAG) and cholesterol (TC) accumulation and altered the composition of intracellular fatty acids (C16:0, C18:0, and C18:1). Conversely, miR-145 overexpression had the opposite effect. Bioinformatics online program predicted that miR-145 targets the 3'-UTR of the Forkhead Box O1 (FOXO1) gene. Subsequently, FOXO1 was identified as a direct target of miR-145 by qRT-PCR, Western blot analysis, and luciferase reporter assay. Furthermore, siRNA-mediated silencing of FOXO1 promoted fatty acid metabolism and TAG synthesis in BMECs. Additionally, we observed the involvement of FOXO1 in the transcriptional activity of the sterol regulatory element-binding protein 1 (SREBP1) gene promoter. Overall, our findings indicated that miR-145 relieves the inhibitory effect of FOXO1 on SREBP1 expression by targeting FOXO1 and subsequently regulating fatty acid metabolism. Thus, our results provide valuable information on the molecular mechanisms for improving milk yield and quality from the perspective of miRNA-mRNA networks.
Keywords: BMECs; FOXO1; SREBP1; fatty acid metabolism; miR-145.