Expression of free fatty acid receptors in the liver of periparturient dairy cows supplemented with essential fatty acids and conjugated linoleic acid

Free fatty acid receptors (FFAR) are molecular sensors involved in the regulation of energy metabolism. Free fatty acid receptors are expressed in the bovine liver, although their biological functions are not fully understood. Our objectives were to study the expression of hepatic FFAR in periparturient dairy cows supplemented or not with a mixture of essential fatty acids (EFA) and CLA, and to investigate potential associations between FFAR and metabolic adaptation during the transition period. Multiparous Holstein cows received abomasal infusions of either coconut oil (control; n = 8) or a mixture of EFA and CLA (EFACLA; n = 8) from −9 to 9 wk relative to parturition. Liver samples were collected at −3, 0, 4, and 9 wk relative to parturition. We quantified the liver expression of FFAR (FFAR1–4 and GPR84) and peroxisome proliferator-activated receptor delta (PPARD) by real-time quantitative PCR. Repeated-measurement correlations and multilevel multiple factor analysis (MFA) were used to investigate the links between FFAR and other metabolic parameters (i.e., energy balance, blood metabolic indicators, liver proteomics, and liver gene expression). All targeted FFAR were expressed in the liver, except for FFAR4. We found no effects of EFACLA or interactions with time for the expressed FFAR. FFAR1, FFAR2, and GPR84 expression decreased from −3 to 9 wk relative to parturition, whereas FFAR3 remained constant from −3 to 4 wk, then decreased at 9 wk postpartum. We observed strong correlations between FFAR, and moderate correlations between FFAR and PPARD. Multivariate (MFA) and univariate (correlation) analyses revealed weak links between FFAR liver expression and other metabolic parameters (e.g., IGFBP3 liver expression and plasma IGFBP-2). Downregulation of FFAR in the liver from pre- to postpartum may prevent receptors hyperactivation during periods of high free fatty acid concentrations. Physiological relevance and individual contributions of FFAR to the hepatic metabolism require further investigation.