Effect of an inflammatory stimulus on mitochondrial functionality in liver cells of dairy cows

Abstract

Mitochondria are essential organelles with key roles in metabolism and health; their function is influenced by various exogenous and endogenous factors. Dairy cows undergo a negative energy balance (EB) and a systemic inflammation around parturition that is interrelated with the metabolism of nutrients like fatty acids (FA) and can ultimately affect the productive efficiency of the animals. The oxidation of FA is localized in the mitochondria and L-Carnitine (CAR) is required for their transport into the mitochondria for generating energy. The objective of this study was to evaluate the effects of a controlled inflammation induced by lipopolysaccharide (LPS) in mid lactation when the EB has turned positive on pathways related to mitochondrial FA metabolism in the liver of dairy cows receiving a dietary CAR supplement or not (CON, control). Holstein cows (n = 43, parity: 2-5) were randomly assigned to either CON (n = 21) or CAR (n = 22; 25 g CAR/cow/day) from day - 42 until day +112 relative to calving. At day +111, all cows were intravenously infused with LPS (0.5 μg/kg body weight). To identify potential changes of hepatic FA metabolism, mRNA abundance of genes involved in FA metabolism were determined in liver biopsy samples taken at day -42, +100, +112, and +126. The Microfluidic qPCR technology was used to quantify the mRNA abundance of 41 genes involved in FA metabolism and 8 endogenous reference genes. Besides, the hepatic abundance of 3 target proteins related to the FA metabolism was assessed on d +100 and +112 (equal to -11 and +1 days relative to the LPS challenge) from 22 cows (n =11 per group) by a capillary Western blotting method. The effectiveness of the CAR supplementation was confirmed by elevated CAR concentrations in the CAR but not the CON groups. The mRNA and protein data were statistically evaluated by mixed models, using time and treatment as well as their interaction as fixed effects. The CAR supplementation at the used dosage did not affect the mRNA of genes related to hepatic FA metabolism, with the exception of solute carrier family 27 member 2 (SLC27A2) and carnitine palmitoyltransferase 1 (CPT1) that are related to the activation of FA to FA-acyl-CoA esters and to mitochondrial FA oxidation, respectively. In contrast, LPS affected the mRNA abundance of more genes, among which were enoyl-CoA hydratase 1 (ECH1) and acyl-CoA oxidase 2 (ACOX2) that are involved in peroxisomal β-oxidation. This may point to a shift in hepatic FA metabolism from mitochondrial towards peroxisomal β-oxidation. In addition, changes in protein abundance were solely observed with LPS, independent of treatment: acetyl-CoA carboxylase alpha (ACACA, mitochondrial FA oxidation pathway) was downregulated during inflammation. The results show the effects of inflammation during a balanced energy status on hepatic FA metabolism at the level of pathway-selected mRNA and protein. They thus contribute to understanding the interplay of energy metabolism and immune reaction in dairy cows.