Abstract
BackgroundThe biosynthesis of milk fat affects both the technological properties and organoleptic quality of milk and dairy products. MicroRNAs (miRNAs) are endogenous small non-coding RNAs that inhibit the expression of their mRNA targets and are involved in downstream signaling pathways that control several biological processes, including milk fat synthesis. miR-34b is a member of the miR-34 miRNA cluster, which is differentially expressed in the mammary gland tissue of dairy cows during lactation and dry periods. Previous studies have indicated miR-34b is a potential candidate gene that plays a decisive role in regulating milk fat synthesis; therefore, it is important to focus on miR-34b and investigate its regulatory effect on the biosynthesis of milk fat in bovine mammary epithelial cells (BMECs).ResultsIn this study, elevated miR-34b levels reduced milk fat synthesis, upregulated 1,999 genes, and downregulated 2,009 genes in BMECs. Moreover, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of differentially expressed genes suggested that miR-34b may play an inhibitory role in milk fat synthesis via the protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway by reducing phosphorylation levels. Notably, the mTOR activator MHY1485 rescued the inhibitory effect of miR-34b. Furthermore, we demonstrated that retinoic acid-induced protein 14 (RAI14) is a target of miR-34b via TargetScan and immunofluorescence assays. RAI14 mRNA and protein levels were significantly decreased by the miR-34b mimic and increased by the miR-34b inhibitor. Moreover, the reduction in RAI14 levels led to the inhibition of the Akt/mTOR signaling pathway.ConclusionsOverall, our results identified a miR-34b-RAI14-Akt/mTOR regulatory network, while also providing a theoretical basis for the molecular breeding of dairy cows.
Highlights
Milk fat biosynthesis has received considerable attention because of its influence on the technological properties and organoleptic quality of milk and dairy products [1]
We mainly focused on exploring the gene network that regulates synthesis of milk fat, and clarified a miRNA–mRNA signaling pathway network which plays an important role in milk fat synthesis
Our results showed that the miR-34b mimic decreased TAG content and droplet numbers in bovine mammary epithelial cells (BMECs), while treatment with the miR-34b inhibitor markedly increased TAG content and droplet numbers in BMECs when compared to their corresponding NCs (Fig. 1c-e)
Summary
Milk fat biosynthesis has received considerable attention because of its influence on the technological properties and organoleptic quality of milk and dairy products [1]. MiRNAs thereby have an important role in various cellular processes such as cell proliferation, differentiation, programmed apoptosis and cell death [7, 8] These small RNAs may be a crucial factor in mammogenesis through their regulation of downstream genes. MicroRNAs (miRNAs) are endogenous small non-coding RNAs that inhibit the expression of their mRNA targets and are involved in downstream signaling pathways that control several biological processes, including milk fat synthesis. Previous studies have indicated miR-34b is a potential candidate gene that plays a decisive role in regulating milk fat synthesis; it is important to focus on miR-34b and investigate its regulatory effect on the biosynthesis of milk fat in bovine mammary epithelial cells (BMECs)
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