Activation of peroxisome proliferator-activated receptor alpha increases the expression and activity of microsomal triglyceride transfer protein in the liver

• Microsomal triglyceride transfer protein (MTP) is rate-limiting in the assembly and secretion of lipoproteins containing apolipoprotein (apo) B. Previously we demonstrated that Wy 14,643 (Wy), a peroxisome proliferator-activated receptor (PPAR) alpha agonist, increases apoB-100 secretion despite decreased triglyceride synthesis. In this study, we sought to determine whether PPARalpha activation increases MTP expression and activity. Treatment with Wy increased hepatic MTP expression and activity in rats and mice and increased MTP expression in primary cultures of rat and mouse hepatocytes. Addition of actinomycin D blocked this increase and the MTP promoter (-136 to +67) containing a conserved DR1 element was activated by Wy, showing that PPARalpha activates transcription of the gene. Wy did not affect MTP expression in the intestine or in cultured hepatocytes from PPARalpha-null mice. A retinoid X receptor agonist (9-cis-retinoic acid), but not a PPARgamma agonist (rosiglitazone), increased MTP mRNA expression in cultured hepatocytes from both wild type and PPARalpha-null mice. In rat hepatocytes incubated with Wy, MTP mRNA levels increased between 6 and 24 h, and MTP protein expression and apoB-100 secretion increased between 24 and 72 h. In conclusion, PPARalpha activation stimulates hepatic MTP expression via increased transcription of the Mtp gene. This effect is paralleled by a change in apoB-100 secretion, indicating that the effect of Wy on apoB-100 secretion is mediated by increased expression of MTP.

Nyckelord

Animals

Apolipoproteins B/metabolism/secretion

Carrier Proteins/*genetics/*metabolism

Cell Line

Cells

Cultured

Dactinomycin/pharmacology

*Gene Expression Regulation/drug effects

Hepatocytes/drug effects/metabolism

Liver/cytology/drug effects/*metabolism

Male

Mice

Mice

Inbred C57BL

PPAR alpha/*metabolism

Promoter Regions (Genetics)/genetics

Pyrimidines/pharmacology

RNA

Messenger/genetics/metabolism

Rats

Rats

Sprague-Dawley

Thiazolidinediones/pharmacology

Transcription

Genetic/drug effects

Tretinoin/pharmacology

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)