AUTHOR=Wang Jiqing , Hao Zhiyun , Hu Liyan , Qiao Lirong , Luo Yuzhu , Hu Jiang , Liu Xiu , Li Shaobin , Zhao Fangfang , Shen Jiyuan , Li Mingna , Zhao Zhidong 

TITLE=MicroRNA-199a-3p regulates proliferation and milk fat synthesis of ovine mammary epithelial cells by targeting VLDLR

JOURNAL=Frontiers in Veterinary Science

VOLUME=9

YEAR=2022

URL=https://www.frontiersin.org/journals/veterinary-science/articles/10.3389/fvets.2022.948873

DOI=10.3389/fvets.2022.948873

ISSN=2297-1769

ABSTRACT=<p>In our previous study, microRNA (miR)-199a-3p was found to be the most upregulated miRNA in mammary gland tissue during the non-lactation period compared with the peak-lactation period. However, there have been no reports describing the function of miR-199a-3p in ovine mammary epithelial cells (OMECs) and the biological mechanisms by which the miRNA affects cell proliferation and milk fat synthesis in sheep. In this study, the effect of miR-199a-3p on viability, proliferation, and milk fat synthesis of OMECs was investigated, and the target relationship of the miRNA with very low-density lipoprotein receptor (<italic>VLDLR</italic>) was also verified. Transfection with a miR-199a-3p mimic increased the viability of OMECs and the number of Edu-labeled positive OMECs. In contrast, a miR-199-3p inhibitor had the opposite effect with the miR-199a-3p mimic. The expression levels of three marker genes were also regulated by both the miR-199a-3p mimic and miR-199-3p inhibitor in OMECs. Together, these results suggest that miR-199a-3p promotes the viability and proliferation of OMECs. A dual luciferase assay confirmed that miR-199a-3p can target <italic>VLDLR</italic> by binding to the 3′-untranslated regions (3'UTR) of the gene. Further studies found a negative correlation in the expression of miR-199a-3p with <italic>VLDLR</italic>. The miR-199a-3p mimic decreased the content of triglycerides, as well as the expression levels of six milk fat synthesis marker genes in OMECs, namely, lipoprotein lipase gene (<italic>LPL</italic>), acetyl-CoA carboxylase alpha gene (<italic>ACACA</italic>), fatty acid binding protein 3 gene (<italic>FABP3</italic>), <italic>CD36</italic>, stearoyl-CoA desaturase gene (<italic>SCD</italic>), and fatty acid synthase gene (<italic>FASN</italic>). The inhibition of miR-199a-3p increased the level of triglycerides and the expression of <italic>LPL, ACACA, FABP3, SCD</italic>, and <italic>FASN</italic> in OMECs. These findings suggest that miR-199a-3p inhibited milk fat synthesis of OMECs. This is the first study to reveal the molecular mechanisms by which miR-199a-3p regulates the proliferation and milk fat synthesis of OMECs in sheep.</p>