MiR-143 Regulates Milk Fat Synthesis by Targeting Smad3 in Bovine Mammary Epithelial Cells

Milk fat is the main nutritional component of milk and is also an important indicator for evaluating milk quality. Substantial evidence has implicated miRNAs in the synthesis of milk fat. miR-143 is one of the miRNAs closely related to lipid metabolism. Herein, miR-143 upregulation remarkably promoted the production of lipid droplets and increased the level of intracellular triglyceride (TAG). Meanwhile, miR-143 suppression overtly repressed TAG synthesis and lipid droplet accumulation in bovine mammary epithelial cells (BMECs). At the same time, miR-143 significantly upregulated the genes associated with lipid synthesis, including PPARγ, SCD1, CEBPβ, and SREBP1. To examine the regulatory mechanism of miR-143 in milk fat synthesis, Smad3 was predicted as a new potential miR-143 target gene by TargetScan. Further studies found that miR-143 expression was inversely related to the levels of Smad3 mRNA and protein. Furthermore, luciferase reporter assays confirmed Smad3 to be a miR-143 direct target. Moreover, Smad3 gene silencing significantly increased intracellular TAG level in BMECs. These findings revealed that miR-143 promotes the TAG synthesis in BMECs via increasing the lipid synthesis related gens expression by targeting Smad3. The results of this study can be exploited in devising novel approaches for improving the nutritional value of milk in dairy cows.