Akt Serine/Threonine Kinase 1 Regulates de Novo Fatty Acid Synthesis through the Mammalian Target of Rapamycin/Sterol Regulatory Element Binding Protein 1 Axis in Dairy Goat Mammary Epithelial Cells

Abstract

Akt serine/threonine kinase acts as a central mediator in the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, regulating a series of biological processes. In lipid metabolism, Akt activation regulates a series of gene expressions, including genes related to intracellular fatty acid synthesis. However, the regulatory mechanisms of Akt in dairy goat mammary lipid metabolism have not been elaborated. In this study, the coding sequences of goat Akt1 gene were cloned and analyzed. Gene expression of Akt1 in different lactation stages was also investigated. For in vitro studies, a eukaryotic expression vector of Akt1 was constructed and transfected to goat mammary epithelial cells (GMECs), and specific inhibitors of Akt/mammalian target of rapamycin (mTOR) signaling were applied to GMECs. Results showed that Akt1 protein was highly conserved, and its mRNA was highly expressed in midlactation. In vitro studies indicated that Akt1 phosphorylation activated mTOR and subsequently enhanced sterol regulatory element binding protein 1 (SREBP1), thus increasing intracellular triacylglycerol content. Inhibition of Akt/mTOR signaling down-regulated the gene expression of lipogenic genes. Overall, Akt1 plays an important role in regulating de novo fatty acid synthesis in goat mammary epithelial cells, and this process probably is through the mTOR/SREBP1 axis.

Phosphorylation of AKT serine/threonine kinase and abundance of milk protein synthesis gene networks in mammary tissue in response to supply of methionine in periparturient Holstein cows

“…Recent in vitro and in vivo studies with ruminant mammary cells provided evidence that AKT regulates de novo fatty acid synthesis via the mTORC1/ sterol regulatory element binding transcription factor 1 (SREBF1) axis (Li et al, 2016(Li et al, , 2018Zhang et al, 2018). Thus, nutritional activation of mTORC1 or AKT could not only alter milk protein, but also mammary lipid synthesis, in part through upregulation of gene networks controlling those processes (Pauloin and Chanat, 2012;Caron et al, 2015;Zhang et al, 2018). Whether such relationships exist in bovine mammary tissue during early lactation when the cow experiences systemic insulin resistance is unknown.…”

Effect of different exogenous fatty acids on the cytosolic triacylglycerol content in bovine mammary cells

“…The lactating mammary gland, thus, uses LCFA derived from both dietary fats and TAG released from adipose tissue. Lactating mammary epithelial cells are highly active in synthesis of FA de novo ( Zhang et al., 2018 ). Bovine mammary epithelial cells have the ability to produce a remarkable amount of lipid ( Johnson et al., 2010 ); this lipogenic capacity probably affected results from the current study and influenced transfer of some FA from cytosol to media by decreasing TAG accumulation in cytosol.…”

Proteomic analysis revealed T cell hyporesponsiveness induced by Haemonchus contortus excretory and secretory proteins

“…Total RNA samples were extracted, and the resulting cDNA was synthesized by reverse transcription PCR in accordance with the manufacturer's specifications. Transcriptional analysis of candidate genes was conducted by real-time PCR with a standard procedure on a QuantStudio 3 Real Time PCR System (Applied Biosystems, Carlsbad, CA, USA) using published specific primers for endogenous reference genes and target genes (Additional file 1) [21,[23][24][25][26][27][28][29][30]. The amplification efficiencies and correlation coefficients were verified to be stable and similar, and the relative mRNA expression levels of candidate genes were calculated by the 2 −ΔΔCt method.…”