Dose-dependent effects of dietary fat on development of obesity in relation to intestinal differential gene expression in C57BL/6J mice

Abstract

Excessive intake of dietary fat is known to be a contributing factor in the development of obesity. In this study, we determined the dose-dependent effects of dietary fat on the development of this metabolic condition with a focus on changes in gene expression in the small intestine. C57BL/6J mice were fed diets with either 10, 20, 30 or 45 energy% (E%) derived from fat for four weeks (n = 10 mice/diet). We found a significant higher weight gain in mice fed the 30E% and 45E% fat diet compared to mice on the control diet. These data indicate that the main shift towards an obese phenotype lies between a 20E% and 30E% dietary fat intake. Analysis of differential gene expression in the small intestine showed a fat-dose dependent gradient in differentially expressed genes, with the highest numbers in mice fed the 45E% fat diet. The main shift in fat-induced differential gene expression was found between the 30E% and 45E% fat diet. Furthermore, approximately 70% of the differentially expressed genes were changed in a fat-dose dependent manner. Many of these genes were involved in lipid metabolism-related processes and were already differentially expressed on a 30E% fat diet. Taken together, we conclude that up to 20E% of dietary fat, the small intestine has an effective 'buffer capacity' for fat handling. From 30E% of dietary fat, a switch towards an obese phenotype is triggered. We further speculate that especially fat-dose dependently changed lipid metabolism-related genes are involved in development of obesity.

Figure 1. Body weight gain and blood glucose levels.

Body weight gain of C57BL/6J mice fed a 10E%, 20E%, 30E% or 45E% fat diet for four weeks. The data are given as means ± SE. a, b, c: bars with superscripts without a common letter differ, p<0.05.

Figure 2. Differential gene expression along the longitudinal axis of the small intestine.

For the proximal, middle and distal part of the small intestine, the numbers of genes that are differentially expressed on a 20E%, 30E% and 45E% fat diet compared to the control 10E% fat diet are plotted (A). Venn diagrams display the overlap of differentially expressed genes between the 20E%, 30E% and 45E% fat diets for each part of the small intestine (B).

Figure 3. Fat-dose dependent regulation of gene expression in the small intestine.

By applying specific inclusion criteria (A), fat-dose dependent regulation of gene expression was determined for the proximal, middle and distal part of the small intestine (B). In brackets, the percentages of fat-dose dependently changed genes are shown as part of total differentially expressed genes on the 20E%, 30E% and 45E% fat diets compared to the control 10E% fat diet. FC: fold changes, DD: dose-dependent, non-DD: non-dose-dependent.

Figure 4. Heat map diagrams of fat-dose dependently changed genes, categorized according to their biological function.

Fat-dose dependently changed genes were clustered in a heat map diagram for the proximal and middle part of the small intestine, based on their GO Biological Processes annotation. Genes involved in lipid metabolism, cell cycle/apoptosis, immune response and carbohydrate metabolism were highly overrepresented. The heat maps display fold changes of differential gene expression induced by the 20E%, 30E% and 45E% fat diets compared to the control 10E% fat diet (only genes with fold changes >1.3 or <−1.3 are shown). Red and green indicate (gradual) up- and down-regulation, respectively, whereas black means no change in gene expression.

Figure 5. Cellular localization and specific lipid metabolism-related function of fat-dose dependently changed genes.

Fat-dose dependently changed genes involved in lipid metabolism (GO Biological Processes) in the proximal part of the small intestine were categorized and visualized based on their cellular localization (GO Cellular Localization) and the specific lipid-metabolism related processes that occur in these cellular compartments. The heat maps next to the genes indicate their fat-dose dependent regulation. Red and green indicate (gradual) up- and down-regulation, respectively, whereas black means no change in gene expression. Pparα target genes are indicated in italics.