Gut microbiome in mice gets stressed within 24 hours on a high-fat diet

In a recent study published in the journal Cell Reports, researchers in Cincinnati, USA, assessed the impact of dietary alteration to a high-fat diet (HFD) on the intestine.

A significant change in diet over time can affect metabolism and physiology. In the United States, a caloric imbalance may be one factor contributing to obesity. From 1999 to 2018, the number of people who suffered from obesity rose from 30.5% to 42.4%, while metabolic diseases like dyslipidemia and diabetes rose from 25.3% to 34.2%. Long-term variations in diet are known to cause obesity and metabolic diseases, but it is not clear how quickly a change in diet can cause changes in the body.

Study: A dietary change to a high-fat diet initiates a rapid adaptation of the intestine. Image Credit: Alexei Logvinovich / Shutterstock

About the study

In the present study, researchers assessed the response of intestinal epithelial cells to an HFD using physiological measurements and single-cell transcriptomics.

The team used indirect calorimetry to survey adult wild-type mice fed normal chow or switched to an HFD for seven days and assess the impact. First, the amount of oxygen consumed (V_O2) along with carbon dioxide expiration (V_CO2) was estimated to calculate the respiratory exchange ratio (RER), which showed the primary fuel source that the body metabolizes. Also, the team measured the total energy needed for homeostasis, called energy expenditure (EE).

The team also assessed whether an adaptive response in the proximal intestine toward acute HFD caused these metabolic changes in the whole body. Intestinal proliferation was examined along with the crypts’ depth and the villus’s height after one, three, or seven days on an HFD. Single-cell ribonucleic acid sequencing (scRNA-seq) was also performed on adult mice’s duodenum and jejunum epithelial cells at all time points. After checking the quality of the cells and filtering them, the team combined the datasets of cells obtained from mice that consumed normal chow and mice that were fed an HFD for one, three, or seven days. The normal chow cells were used as the reference dataset.

The team further analyzed how each cluster of cells responded to HFD using differential gene expression analysis. The transcriptional signature associated with glutamate/glutamine metabolism was also evaluated using genes from the Molecular Signatures Database (MSigDB).

Results

Within the first day of HFD feeding, RER levels decreased from around 0.9 to 0.8, and these differences were maintained over time. On the first day, EE rose from approximately 0.2 to 0.5 kcal/min to almost 0.4 to 0.6 kcal/min. Over the course of seven days, there were no significant differences in the amount of water consumed or ambulatory movements. Mice fed an HFD gained weight while exhibiting higher energy intake from the first day. After one day of consuming an HFD, these results showed that the mice’s metabolism changed over the whole body, and there may have also been changes in their intestines.

There was an increase in EdU (5-ethynyl-2’-deoxyuridine) incorporation after one day of HFD consumption. However, the depth of intestinal crypts or the height of the villus did not change. The team also assessed any alterations in the death of intestinal cells using cleaved caspase-3 staining along with terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) staining and found no differences at any of the assessed time points. These results showed that the HFD caused a proliferative response within one day, but this did not change the size of the intestinal surface area over the course of one week. Additionally,  all the expected cell types, like EEC, enterocytes, enterocyte progenitors (EPs), goblet, Paneth cells, secretory progenitors (SPs), tuft, and stem/early-transit amplifying (TA) zone cells, were identified.

Analysis of the transcriptional alterations induced by HFD was performed with Biological Process Gene Ontology Terms (GO-Terms), which showed that genes for fatty acid metabolic pathways had higher expression levels in several cell types after just one day of HFD. This suggested that the intestinal epithelium shifted away from the usually utilized glutamine/glutamate metabolism. There was also an immediate downregulation observed after one day of HFD. Gene set enrichment analysis (GSEA) showed that most epithelial cells had upregulated genes that facilitated fatty acid metabolism, as evidenced by normalized enrichment scores (NESs). In particular, NESs associated with fatty acid metabolism increased at one and three days of HFD. This suggested that the body’s metabolism reacted quickly to the increase in luminal fat. By seven days, the fatty acid metabolism NESs had declined to indicate that enterocytes had adapted to the change to HFD.

After one day on an HFD, there was an upregulation of stress-related genes for all epithelial cell populations. Based on the scRNA-seq data, stem/early-TA, along with Paneth cells, tended to exhibit dramatic changes in gene expression in response to cellular stress. The stem/early-TA subset was found to upregulate heat-shock protein genes, and GSEA upregulated unfolded protein response (UPR) genes. This showed that stem/early-TA cells react to HFD immediately with a stress response.

This study demonstrated a multi-pronged approach to assessing how animals respond to diet changes by evaluating whole-body metabolism, tissue function, morphology, and single-cell transcriptomics. Functional and transcriptional analyses showed that all types of intestinal epithelial cells were altered within 24 hours. Furthermore, within a week, the intestinal epithelium had been modified to maximize fat absorption. Plasticity of the intestinal wall may have evolved during times of nutrient scarcity but could now be linked to obesity, metabolic disease, and inflammation during times of nutrient excess.