Coordination of lipid droplet-associated proteins during the transition period of Holstein dairy cows.

Dairy cows often experience negative energy balance with the onset of lactation, and severe or prolonged negative energy balance can contribute to declines in overall fitness. Energy stores, in the form of adipose tissue triacylglycerides, are mobilized during times of energy deficit, and recent research has implicated several proteins associated with the lipid droplet as lipolytic regulators. The objective of this study was to determine if these novel proteins associated with lipolytic regulation are altered with the changing metabolic demands of lactation. Weekly blood samples were collected from 26 Holstein cows from 21 d before expected parturition through 28 d postpartum, and again at 150 d postpartum. Serum nonesterified fatty acids, glycerol, and β-hydroxybutyrate were measured. Energy balance was calculated from daily feed intake and milk yield, weekly body weight, and monthly milk component measurements. Adipose tissue biopsies were taken 21 d before expected parturition (-21 d) and at 5, 21, and 150 d postpartum. Semiquantitative Western blotting was used to measure abundance of hormone-sensitive lipase (HSL), phosphorylated HSL, perilipin, phosphorylated perilipin (PPLIN), adipose triglyceride lipase (ATGL), and comparative gene identity-58 (CGI-58). Abundance of ATGL was less at 5 and 21 d in milk (DIM) compared with -21 and 150 DIM, even though cows were in negative energy balance and experiencing increased rates of lipolysis in early lactation. In contrast, phosphorylated HSL and PPLIN increased with increasing lipolysis immediately after parturition. Additionally, PPLIN was negatively correlated with milk yield at 5, 21, and 150 d postpartum, and negatively correlated with feed intake and energy balance at 21 d postpartum. This result is consistent with the hypothesis that phosphorylation of perilipin is responsive to signals for increased triaclyglyceride mobilization. Finally, a consistent negative correlation between abundance of perilipin and CGI-58 proteins was observed throughout the transition period. These results confirm that novel lipolytic proteins in adipose tissue are regulated at the level of protein abundance and phosphorylation during the periparturient period and into mid lactation.