Expression of putative fatty acid transporter genes are regulated by peroxisome proliferator-activated receptor α and γ activators in a tissue- and inducer-specific manner

Abstract

Regulation of gene expression of three putative long-chain fatty acid transport proteins, fatty acid translocase (FAT), mitochondrial aspartate aminotransferase (mAspAT), and fatty acid transport protein (FATP), by drugs that activate peroxisome proliferator-activated receptor (PPAR) α and γ were studied using normal and obese mice and rat hepatoma cells. FAT mRNA was induced in liver and intestine of normal mice and in hepatoma cells to various extents only by PPARα-activating drugs. FATP mRNA was similarly induced in liver, but to a lesser extent in intestine. The induction time course in the liver was slower for FAT and FATP mRNA than that of an mRNA encoding a peroxisomal enzyme. An obligatory role of PPARα in hepatic FAT and FATP induction was demonstrated, since an increase in these mRNAs was not observed in PPARα-null mice. Levels of mAspAT mRNA were higher in liver and intestine of mice treated with peroxisome proliferators, while levels in hepatoma cells were similar regardless of treatment. In white adipose tissue of KKAy obese mice, thiazolidinedione PPARγ activators (pioglitazone and troglitazone) induced FAT and FATP more efficiently than the PPARα activator, clofibrate. This effect was absent in brown adipose tissue. Under the same conditions, levels of mAspAT mRNA did not change significantly in these tissues. In conclusion, tissue-specific expression of FAT and FATP genes involves both PPARα and -γ. Our data suggest that among the three putative long-chain fatty acid transporters, FAT and FATP appear to have physiological roles. Thus, peroxisome proliferators not only influence the metabolism of intracellular fatty acids but also cellular uptake, which is likely to be an important regulatory step in lipid homeostasis.