Abundance of mRNA of apolipoprotein B100, apolipoprotein E, and microsomal triglyceride transfer protein in liver from periparturient dairy cows

Abstract

Limited secretion of very low density lipoproteins (VLDL) in dairy cows is strongly related to fatty liver and other metabolic disorders in the early postpartum. Currently, there is limited information on which roles apolipoprotein B100 (ApoB100), apolipoprotein E (ApoE), and microsomal triglyceride transfer protein (MTP)play in that VLDL limitation. To our knowledge, no studies have simultaneously measured ApoB100, ApoE, and MTP mRNA in periparturient dairy cows. Therefore, a trial was conducted to assess liver gene expression of these proteins in transition dairy cows and to evaluate the relationships between their expression and metabolic status. Eight multiparous Holstein cows were monitored during the transition period. To evaluate metabolic and nutritional status, body condition score was registered, and plasma indexes of energy metabolism and VLDL were determined from 35 d before to 35 d after calving. Liver biopsies were performed on d −35, 3, and 35 relative to day of calving, and gene expression of ApoB100, ApoE, andMTPwere determined on liver tissue. Body condition, plasma glucose and VLDL decreased, and plasma NEFA and BHBA increased after calving. Compared with values of d −35, on d 3 after calving the ApoB100 mRNA synthesis was lower, whereas MTP and ApoE mRNA abundance were higher. Negative correlation (r = −0.57) between plasma NEFA concentration and ApoB100 mRNA abundance, and positive correlation between ApoB100 mRNA abundance and plasma cholesterol (r = 0.65) and plasma albumins (r = 0.52) were detected at 3 d postpartum. Data on changes of gene expression of the 3 main proteins involved in the regulation of synthesis and secretion of VLDL in the liver suggest that decreased mRNA for ApoB100 may be consistent with decreased synthesis and/or secretion ofVLDL from liver during the periparturient period.