cAMP Response Element Binding Protein 1 (CREB1) Promotes Monounsaturated Fatty Acid Synthesis and Triacylglycerol Accumulation in Goat Mammary Epithelial Cells

Abstract

cAMP response element binding protein 1 (CREB1) is a member of the leucine zipper transcription factor family of DNA binding proteins. Although studies in non-ruminants have demonstrated a crucial role of CREB1 in lipid synthesis in liver and adipose tissue, it is unknown if this transcription regulator exerts control of fatty acid synthesis in ruminant mammary cells. To address this question, we first defined the expression dynamics of CREB1 in mammary tissue during lactation. Analysis of CREB1 in mammary tissue revealed higher mRNA abundance in mammary tissue harvested at peak lactation. Overexpression of CREB1 markedly upregulated sterol regulatory element binding transcription factor 1 (SREBP1), fatty acid synthase (FASN), acetyl-coenzyme A carboxylase α (ACACA), elongase of very long chain fatty acids 6 (ELOVL6), lipoprotein lipase (LPL), fatty acid binding protein 3 (FABP3), lipin 1 (LPIN1) and diacylglycerol acyltransferase 1 (DGAT1), but had no effect on glycerol-3-phosphate acyltransferase, mitochondrial (GPAM) or 1-acylglycerol-3-phosphate O-acyltransferase 6 (AGPAT6). In addition, overexpressing CREB1 led to a significant increase in the concentration and desaturation index of C16:1 (palmitoleic acid) and C18:1 (oleic acid), along with increased concentration of triacylglycerol. Taken together, these results highlight an important role of CREB1 in regulating lipid synthesis in goat mammary epithelial cells. Thus, manipulation of CREB1 in vivo might be one approach to improve the quality of goat milk.

Keywords: dairy nutrition; fatty acid composition; goat milk; monounsaturated fatty acids.

Figure 1

Comparison of amino acid sequences between dairy goat, human, cattle and mouse CREB gene. The gray portion indicates the aligned amino acids, the blue portion indicates a conservative substitution in the aligned amino acids, the pink portion indicates a nonconservative substitution in the aligned amino acids and the conservative representative bZIP regions are in the red line.

Figure 2

mRNA expression of cAMP response element binding protein 1 (CREB1) in mammary tissue from the dry period and peak lactation. Values are means ± SEM for 6 individuals. * Significantly higher (p < 0.05) compared with the dry period.

Figure 3

cAMP response element binding protein 1 (CREB1) influences the expression of genes related to fatty acid (FA) metabolism in goat mammary epithelial cells (GMEC). GMEC were transfected with Ad-CREB1 or Ad-GFP for 48 h and then collected for mRNA extraction. Panel (A). mRNA expression of CREB1. Panel (B). mRNA expression of genes related to de novo fatty acid synthesis and desaturation (ACACA, FASN, SREBF1, SCD1, ELOVL6). Panel (C). mRNA expression of genes related to FA uptake and transport (LPL and FABP3). Panel (D). mRNA expression of genes related to TAG synthesis and lipid droplet formation (DGAT1, GPAM, LPIN1, AGPAT6). Data are means ± SEM for three independent experiments. * p < 0.05 vs. control (Ad-GFP). ** p < 0.01 vs. control (Ad-GFP).

Figure 4

Overexpression of cAMP response element binding protein 1 (CREB1) changes intracellular fatty acid content. Data are means ± SEM for 3 individual experiments. * p < 0.05 vs. control (Ad-GFP).

Figure 5

Overexpression of cAMP response element binding protein 1 (CREB1) changes the intracellular fatty acid (FA) desaturation index and triacylglycerol (TAG) content in goat mammary epithelial cells (GMEC). GMEC were transfected with Ad-CREB1 or Ad-GFP for 48 h and then collected for fatty acid analysis. Panel (A–C) depicted the C16:1 desaturation index, C18:1 desaturation index and total TAG, respectively, in GMEC infected with Ad-CREB1 compared with the control (Ad-GFP). Data are means ± SEM for 3 individual experiments. * p < 0.05 vs. control (Ad-GFP). Significance was declared at p < 0.05.