High-fat feeding rapidly induces obesity and lipid derangements in C57BL/6N mice

Abstract

C57BL/6N (B6N) is becoming the standard background for genetic manipulation of the mouse genome. The B6N, whose genome is very closely related to the reference C57BL/6J genome, is versatile in a wide range of phenotyping and experimental settings and large repositories of B6N ES cells have been developed. Here, we present a series of studies showing the baseline characteristics of B6N fed a high-fat diet (HFD) for up to 12 weeks. We show that HFD-fed B6N mice show increased weight gain, fat mass, and hypercholesterolemia compared to control diet-fed mice. In addition, HFD-fed B6N mice display a rapid onset of lipid accumulation in the liver with both macro- and microvacuolation, which became more severe with increasing duration of HFD. Our results suggest that the B6N mouse strain is a versatile background for studying diet-induced metabolic syndrome and may also represent a model for early nonalcoholic fatty liver disease.

Fig. 1

Experimental design. Mice were placed on either an ad libitum control diet (dotted boxes) or on varying lengths of HFD (striped boxes) until the age of 16 weeks, at which point the mice were analysed for body composition and culled for organ harvest and blood collection

Fig. 2

Comparison of body weight of C57BL/6NTac male mice following varying durations of exposure to HFD. a Percentage body weight gain from 4 to 16 weeks of age relative to the starting body weight at 4 weeks of age which ranged from 12.2 to 20.3 g (mean = 16.9 g). Data are presented as mean percentage weight gain ± SEM. b Boxplot of terminal body weights at week 16. Median, 25th percentile, and 75th percentile (box) and the lowest and highest data points still within 1.5× interquartile range (IQR) (whiskers) for each of the HFD durations are shown. Data points falling outside the 1.5× IQR are considered outliers and represented with a filled circle. c Boxplot of terminal fat mass at 16 weeks of age as measured by DEXA

Fig. 3

Boxplots of metabolic variables of C57BL/6NTac male mice (16 weeks of age) following varying duration of exposure to HFD showing a post-anaesthesia plasma glucose concentration and b postanaesthesia plasma insulin concentration

Fig. 4

Plasma lipid variables of C57BL/6NTac male mice (16 weeks of age) following varying duration of exposure to HFD. Boxplots of a total cholesterol, b high-density lipoprotein cholesterol (HDL), c triglycerides, and d nonesterified free fatty acids (NEFAC)

Fig. 5

Analysis of liver from C57BL/6NTac male mice following varying duration of exposure to HFD. a Effect of varying exposure to HFD on liver weight (wet weight) of C57BL/6NTac male mice at 16 weeks of age. b–e Representative photomicrographs of the livers (100× magnification) from 16-week-old mice. b H&E-stained section from control liver showing no vacuolation. c H&E-stained section showing hepatocytes enlarged by microvesicular vacuoles (as shown by arrow). d H&E-stained section demonstrating hepatocytes in portal area containing macrovesicular vacuoles (as shown by arrow). e Oil-red-O-stained section demonstrating positive staining for lipid in macro and microvesicular vacuoles

Fig. 6

Effect of varying exposure to HFD on platelet counts of male mice at 16 weeks of age