Dietary fatty acids have myriads of effects on human health and disease. Many of these effects are likely achieved by altering expression of genes. Several transcription factors have been shown to be responsive to fatty acids, including SREBP-1c, NF-kB, RXRs, LXRs, FXR, HNF4α, and PPARs. However, the relative importance of these transcription factors in regulation of gene expression by dietary fatty acids remains unclear. Here, we take advantage of a unique experimental design using synthetic triglycerides composed of one single fatty acid in combination with gene expression profiling to examine the acute effects of individual dietary fatty acids on hepatic gene expression in mice. The dietary interventions were performed in parallel in wild-type and PPARα-/- mice, enabling the determination of the specific contribution of PPARα. Depending on chain length and degree of saturation, dietary fatty acids caused a statistically significant change in expression of over 400 genes. Surprisingly, the far majority of genes regulated by dietary fatty acids in wild-type mice were unaltered in mice lacking PPARα, indicating PPARα-dependent regulation. We conclude that the effects of dietary fatty acids on hepatic gene expression are almost entirely mediated by PPARα, indicating that PPARα dominates fatty acid-dependent gene regulation in liver. Keywords: identification of target genes
2-6 months old male pure bred wild-type (129S1/SvImJ) and PPARα -/- (129S4/SvJae) mice were used.
Wild-type and PPARα -/- mice fasted for 4 hours received a single dose of 400 µl synthetic triglyceride (tridecanoin – C10:0, triolein – C18:1, trilinolein – C18:2, trilinolenin – C18:3, trieicosapentaenoin – C20:5 or tridocosahexaenoin – C22:6), the synthetic PPARα agonists WY14643 or fenofibrate (400 μl of 10 mg/ml in 0.5% carboxymethyl cellulose, CMC) or control (400 μl of 0.5% CMC). 6 hours after gavage, mice were killed and livers extracted.
(Please note: Experiments with C10:0, C18:2 and C18:3 were carried out a few months later than the rest of the treatments. Therefore there is a second set of control arrays – named control2 – which belong to these three treatment groups.)
Liver total RNA from biological replicates was hybridized onto Affymetrix mouse genome 430 2.0 GeneChip arrays. Five microgram total RNA was labelled according to the ENZO-protocol, fragmented and hybridized according to Affymetrix's protocols.