Feed restriction, but not L-carnitine infusion, alters the liver transcriptome by inhibiting sterol synthesis and mitochondrial oxidative phosphorylation and increasing gluconeogenesis in mid-lactation dairy cows

Abomasal carnitine infusion during acute feed restriction increases hepatic fatty acid oxidation and decreases liver lipid in dairy cows. Eight mid-lactation Holstein cows were used in a replicated 4 x 4 Latin square design with 14-d periods. A 2 x 2 factorial arrangement was used to determine the effects of water infusion + ad libitum dry matter intake (DMI), water infusion + restricted DMI (50% of previous 5-d average), L-carnitine infusion (20 g/d) + ad libitum DMI, or L-carnitine infusion + restricted DMI. Liver RNA from 7 healthy cows was used for transcriptome profiling using a bovine microarray. An ANOVA with a false discovery rate was used to identify treatment and interaction effects. A substantial transcriptome change was observed only with DMI restriction, resulting in 312 (155 downregulated, 157 upregulated) differentially expressed genes. Quantitative PCR was performed to verify microarray data and measure expression of additional genes not present on the microarray. The quantitative PCR data confirmed the effect of feed restriction but not of L-carnitine treatment. Feed restriction increased expression of GPX3 and of genes associated with gluconeogenesis (PC, PDK4), inflammation (SAA3), and signaling (ADIPOR2). In contrast, feed restriction downregulated BBOX, a key for L-carnitine biosynthesis, and the transcription factor HNF4A. The bioinformatics functional analysis of genes affected by DMI restriction uncovered biosynthesis of cholesterol and energy generation by mitochondrial respiration as the most relevant and inhibited functions. The data also indicated an increase of flux toward gluconeogenesis. We interpreted those results as a likely response of the liver to spare energy and provide glucose for the lactating mammary gland during feed deprivation.