Nutrition modulates Fto and Irx3 gene transcript levels, but does not alter their DNA methylation profiles in rat white adipose tissues

The fat mass and obesity associated (Fto) and iroquois homeobox 3 (Irx3) genes have been recognised as important obesity-related genes. Studies on the expression of these genes in the fat tissue of human and mouse have produced inconsistent results, while similar data on rat are limited. Environmental factors such as diet, should be considered as potential modulators of gene transcript levels through epigenetic mechanisms including DNA methylation. The aim of this study was to evaluate transcription levels and DNA methylation profiles of rat Fto and Irx3 genes in two white adipose tissue depots in response to high-fat and high-protein diets. The relative transcript levels of Fto and Irx3 were shown to be tissue-specific with higher levels detected in subcutaneous fat tissue than in abdominal fat tissue. Moreover, negative correlations between the transcripts of both genes were observed for subcutaneous fat tissue. The identified interactions (e.g. diet×duration of diet regimen) indicated that the diet had an impact on the transcript level; however, this effect was dependent on the duration of the diet regimen. The high-fat diet led to upregulation of Fto and Irx3 linearly with time across the two tissues. DNA methylation of the regulatory regions of the studied genes was very low and not related with the tissue, diet, or duration of diet regimen. Our study revealed that diet was an important factor modulating transcription of Fto and Irx3, but its effect is time-dependent. In contrast, the DNA methylation profiles of Fto and Irx3 were not altered by nutrition, which may indicate that the feeding type, when applied postnatally, did not affect DNA methylation of these genes.