Transition cows: hepatic endocannabinoid system gene expression in response to prepartal plane of nutrition and the effects of genetic merit on genes of lipid metabolism in adipose tissue

摘要

Two experiments were conducted on transition cows to evaluate 1) hepatic endocannabinoid system gene expression in response to prepartal plane of nutrition. 2) effects of genetic merit on lipid metabolism in adipose tissue. For the objective of first experiment, we examined mRNA expression via qPCR of endocannabinoid receptors (CNR1, CNR2), enzymes that synthesize FAE (HRASLS5, NAPEPLD), enzymes that degrade FAE (FAAH, NAAA, MGLL), and the hormone precursor proopiomelanocortin (POMC) in liver at -14, 7, 14, and 30 d around parturition from cows fed a control (CON; NEL = 1.34 Mcal/kg) or moderate-energy (OVER; NEL = 1.62 Mcal/kg) diet during the dry period. Expression of CNR2 and POMC was greater at 7 d in cows fed OVER due to a decrease in expression between -14 and 7 d in cows fed CON. Cows fed CON had an increase in expression of FAAH, HRASLS5, NAAA, MGLL, and POMC between 7 and 14 d; for FAAH and HRASLS5 such response led to greater expression at 14 d vs. cows fed OVER. Cows fed OVER vs. CON had a ~2-fold increase in expression of MGLL between -14 and 7 d followed by a gradual decrease through 30 d at which point expression was still greater in OVER vs. CON. Fatty acid amide hydrolase, MGLL, and HRASLS5 were the most abundant genes measured. Expression of the hepatic endocannabinoid system and POMC was altered by plane of dietary energy prepartum particularly during the first 2 wk postpartum. In the second experiment, we measured weekly dry matter intake, milk production, blood glucose and NEFA with rate of lipogenesis and lipolysis in adipose tissues of dairy cows differ for genetic merit (high genetic merit, HGM; low genetic merit, LGM). Adipose tissue biopsies were taken at -21, 7, 28 and 56 d around parturition. The mRNA expression of lipogenic genes; enzymes (PCK1, FASN, DGAT2, SCD), transcription regulators (MLXIPL, PPARG, THRSP, WNT10B, SREBF1) and genes involved in lipolysis; classical lipolytic geness (LIPE, PNPLA2, MGLL, ADRB2, ADFP, ABHD5), genes controlling lipolysis (INSR, AKT1, PDE3A, PDE3B, PRKAA1, PRKAA2, FOXO1, SIRT1), and other proteins (GHR, CAV1, ADIPOQ, TNF1) was also measured. Dry matter intake, blood glucose and NEFA were not significantly different in both groups. Milk production had the tendency to produce more milk in HGM cows after 6 wks of lactation. Rate of lipogenesis and lipolysis was different in both groups. Expression of all lipogenic genes almost had similar pattern through transition period. Cows with HGM had lower expression of lipogenic genes after parturition. The expression decreased at d 7 after parturition which gradually increased to d 28 and substantially lowest at d 56. Interestingly, the expression of most of the lipolytic enzymes, receptors and proteins was also similar in both groups and subsequently decreased after parturition. The rate of lipogenesis was accompanied with gene expression after 1 wk of parturition but rate of lipolysis did not show coordinated pattern with gene expression. Results indicate that response showed by endocannabinoid system genes in liver may play a role in the physiological adaptations to the onset of lactation, including energy balance and feed intake. Results from experiment two suggest the control of adipose tissue metabolism at transcriptional level although post-translational control of lipolytic genes would be more important for lipolysis in adipose tissue.