Change in subcutaneous adipose tissue metabolism and gene network expression during the transition period in dairy cows, including differences due to sire genetic merit1

Adipose metabolism is an essential contributor to the efficiency of milk production, and metabolism is controlled by several mechanisms, including gene expression of critical proteins; therefore, the objective of this study was to determine how lactational state and the genetic merit of dairy cattle affects adipose tissue (AT) metabolism and mRNA expression of genes known to control metabolism. Animals of high (HGM) and low genetic merit (LGM) were fed to requirements, and weekly dry matter intake, milk production, blood glucose, and nonesterified fatty acids were measured. Subcutaneous AT biopsies were collected at -21, 7, 28 and 56 d in milk (DIM). The mRNA expression of genes coding for lipogenic enzymes [phosphoenolpyruvate carboxykinase 1 (soluble) (PCK1), fatty acid synthase (FASN), diacylglycerol O-acyltransferase 2 (DGAT2), and stearoyl-coenzyme A desaturase (SCD)], transcription regulators [peroxisome proliferator-activated receptor γ (PPARG), thyroid hormone responsive (THRSP), wingless-type MMTV integration site family, member 10B (WNT10B), sterol regulatory element binding transcription factor 1 (SREBF1), and adiponectin (ADIPOQ)], lipolytic enzymes [hormone-sensitive lipase (LIPE), patatin-like phospholipase domain containing 2 (PNPLA2), monoglyceride lipase (MGLL), adrenoceptor β-2 (ADRB2), adipose differentiation-related protein (ADFP), and α-β-hydrolase domain containing 5 (ABHD5)], and genes controlling the sensing of intracellular energy [phosphodiesterase 3A (PDE3A); PDE3B; protein kinase, AMP-activated, α-1 catalytic subunit (PRKAA1); PRKAA2; and growth hormone receptor (GHR)] was measured. Dry matter intake, blood glucose, and nonesterified fatty acid concentrations did not differ between genetic merit groups. Milk production was greater for HGM cows from 6 to 8 wk postpartum. As expected, the rates of lipogenesis decreased in early lactation, whereas stimulated lipolysis increased. At 7 DIM, lipogenesis in HGM cows increased as a function of substrate availability (0.5, 1, 2, 3, 4, or 8mM acetic acid), whereas the response in LGM cows was much less pronounced. However, the lipogenic response at 28 DIM reversed and rates were greater in tissue from LGM than HGM cows. Peak lipolytic response, regardless of DIM, was observed at the lowest dose of isoproterenol (10(-8)M), and -21 d tissue had a greater lipolysis rate than tissue at 7, 28, and 56 d. In HGM compared with LGM cows, stimulated lipolysis at 7 and 28 DIM was greater but peaked at 10(-7)M isoproterenol, suggesting differences in tissue responsiveness due to genetic merit. Regardless of genetic merit, the expression of lipogenic genes decreased markedly in early lactation, whereas those controlling lipolysis stayed similar or decreased slightly. Cows of HGM had lower expression of lipogenic genes after parturition and through 56 DIM. In contrast, the expression of most of the lipolytic enzymes, receptors and proteins was similar in all cows pre- and postpartum. These results confirm that gene transcription is a major control mechanism for AT lipogenesis during early lactation, but that control of lipolysis is likely primarily by posttranslational mechanisms.