Metabolic Transition of Milk Lactose Synthesis and Up-regulation by AKT1 in Sows from Late Pregnancy to Lactation

Lactose plays a crucial role in controlling milk volume by inducing water toward into the mammary secretory vesicles from the mammary epithelial cell cytoplasm, thereby maintaining osmolality. In current study, we determined the expression of several lactose synthesis related genes, including glucose transporters (glucose transporter 1, glucose transporter 8, sodium-glucose cotransporter 1, sodium-glucose cotransporter 3, and sodium-glucose cotransporter 5), lactose synthases (a-lactalbumin and beta 1,4-galactosyltransferase), and hexokinases (hexokinase-1 and hexokinase-2) in sow mammary gland tissue at day 17 before delivery, on the 1st day of lactation and at peak lactation. The data showed that glucose transporter 1 was the dominant glucose transporter within sow mammary gland and that expression of each glucose transporter 1, sodium-glucose cotransporter 1, hexokinase-1, hexokinase-2, alpha-lactalbumin, and beta 1,4-galactosyl-transferase were increased (p < 0.05) when the sows transited from late pregnancy to peak lactation. AKT1 overexpressed mammary epithelial cells were then constructed, and the results indicated that AKT1 increases (p < 0.01) the expression of hexokinase-1 and glucose transporter 1. In summary, lactose synthesis was significantly elevated with the increase of milk production and AKT1 could positively regulate lactose synthesis.