Changes in the expression of hepatic genes involved in cholesterol homeostasis in dairy cows in the transition period and at different stages of lactation

Abstract

This study was performed to investigate changes in expression level of genes involved in hepatic cholesterol metabolism in the transition from pregnancy to lactation and during different stages of lactation in dairy cows. Therefore, relative mRNA abundances of several genes involved in various pathways of cholesterol homeostasis in liver biopsy samples of 20 dairy cows, taken in late pregnancy (3wk prepartum) and early lactation (1, 5, and 14wk postpartum), were determined. At 1wk postpartum, hepatic mRNA abundances of genes involved in cholesterol synthesis (3-hydroxy-3-methylglutaryl-coenzyme A reductase, mevalonate kinase, and farnesyl diphosphate synthase), cholesterol uptake from blood (low-density lipoprotein receptor), bile acid synthesis (cholesterol-7α-hydroxylase), cholesterol efflux [ATP-binding cassette (ABC) transporter A1 and ABCG1], esterification of cholesterol (acyl-coenzyme A:cholesterol acyltransferase), and proteins involved in assembly and secretion of very low-density lipoproteins (microsomal triglyceride transfer protein, ApoB100) were increased compared with 3wk prepartum. The mRNA abundances of most of these genes decreased after 1wk of lactation and reached levels in 5 and 14wk of lactation similar to those at 3wk prepartum. Only mRNA abundances of cholesterol-7α-hydroxylase, ABC transporters, and ApoB100 remained at 5 and 14wk postpartum at levels higher than those at 3wk prepartum. Hepatic cholesterol abundance was highest at 1wk postpartum and was, thereafter, decreasing to values similar to that at 3wk prepartum. Overall, this study shows that the onset of lactation is associated with an increased expression of various genes involved in cholesterol metabolism in the liver of dairy cows, suggesting that pronounced changes in hepatic cholesterol metabolism take place in the periparturient phase.