Organ-specific function of PPARa

The peroxisome proliferator-activated receptor alpha (PPARα) is a fatty acid-activated transcription factor that governs a variety of biological processes. Little is known about the role of PPARα in the small intestine. Since this organ is frequently exposed to high levels of PPARα ligands via the diet, we set out to characterize the function of PPARα in small intestine using functional genomics experiments and bioinformatics tools. PPARα was expressed at high levels in both human and murine small intestine. Detailed analyses showed that PPARα was expressed highest in villus cells of proximal jejunum. Microarray analyses of total tissue samples revealed, that in addition to genes involved in fatty acid and triacylglycerol metabolism, transcription factors and enzymes connected to sterol and bile acid metabolism, including FXR and SREBP1, were specifically induced. In contrast, genes involved in cell cycle and differentiation, apoptosis, and host defense were repressed by PPARα activation. Additional analyses showed that intestinal PPARα dependent gene regulation occurred in villus cells. Functional implications of array results were corroborated by morphometric data. The repression of genes involved in proliferation and apoptosis was accompanied by a 22% increase in villus height, and a 34% increase in villus area of wild-type animals treated with WY14643. This is the first report providing a comprehensive overview of processes under control of PPARα in the small intestine. We show that PPARα is an important transcriptional regulator in small intestine, which may be of importance for the development of novel foods and therapies for obesity and inflammatory bowel diseases. Keywords: Identification of organ specifc target genes Pure bred wild-type (129S1/SvImJ) and PPARα-null (129S4/SvJae) mice were treated with the synthetic PPARα ligand WY14,643 (0.1% w/w) for 5 days. Small intestine and liver were removed and total RNA was isolated. In total 4 experimental groups were present: wild type mice fed the control diet (AIN93M), wild type mice fed the control diet supplemented with 0.1% w/w WY14,643 for 5 days, PPARα knockout mice fed the control diet, PPARα knockout mice fed the control diet supplemented with 0.1% w/wWY14,643 for 5 days. RNA of 4 biological replicates was hybridized to Affymetrix 430 2.0 arrays. Five microgram total RNA was labelled according to the ENZO-protocol, fragmented and hybridized according to Affymetrix's protocols.