Congenic mice demonstrate the presence of QTLs conferring obesity and hypercholesterolemia on chromosome 1 in the TALLYHO mouse

Abstract

The TALLYHO (TH) mouse presents a metabolic syndrome of obesity, type 2 diabetes, and hyperlipidemia. Highly significant quantitative trait loci (QTLs) linked to adiposity and hypercholesterolemia were previously identified on chromosome (Chr) 1 in a genome-wide scan of F2 mice from C57BL/6J (B6) x TH. In this study, we generated congenic mouse strains that carry the Chr 1 QTLs derived from TH on a B6 background; B6.TH-Chr1-128Mb (128Mb in size) and B6.TH-Chr1-92Mb (92Mb in size, proximally overlapping). We characterized these congenic mice on chow and high fat (HF) diets. On chow, B6.TH-Chr1-128Mb congenic mice exhibited a slightly larger body fat mass compared with B6.TH-Chr1-92Mb congenic and B6 mice, while body fat mass between B6.TH-Chr1-92Mb congenic and B6 mice was comparable. Plasma total cholesterol levels were significantly higher in B6.TH-Chr1-128Mb congenics compared to B6.TH-Chr1-92Mb congenic and B6 mice. Again, there was no difference in plasma total cholesterol levels between B6.TH-Chr1-92Mb congenic and B6 mice. All animals gained more body fat and exhibited higher plasma total cholesterol levels when fed HF diets than fed chow, but these increases were greater in B6.TH-Chr1-128Mb congenics than in B6.TH-Chr1-92Mb congenic and B6 mice. These results confirmed the effect of the 128Mb TH segment from Chr 1 on body fat and plasma cholesterol values and showed that the distal segment of Chr 1 from TH is necessary to cause both phenotypes. Through bioinformatic approaches, we generated a list of potential candidate genes within the distal region of Chr 1 and tested Ifi202b and Apoa2. We conclude that Chr 1 QTLs largely confer obesity and hypercholesterolemia in TH mice and can be promising targets for identifying susceptibility genes. Congenic mouse strains will be a valuable resource for gene identification.

Figure 1

B6.TH-Chr1 congenic intervals on chromosome 1. Genetic markers shown at the top were used to allelotype the congenic interval. The open and filled boxes represent a C57BL/6 (B6) and TALLYHO (TH) allele, respectively. Mb: Megabase

Figure 2

(A) Body fat mass (14 wk), (B) plasma insulin levels (14–25 wk), (C) intraperitoneal glucose tolerance test (14–18 wk), and plasma (D) total cholesterol and (E) triglyceride levels (20–27 wk) in B6, B6.TH-Chr1-128Mb congenic, and B6.TH-Chr1-92Mb congenic mice fed chow and high fat (HF) diets (males). Data were reported as means ± SEM (N is indicated in each bar). Group means labeled with different letters are significantly different (P <0.05). wk: weeks of age

Figure 3

Expression of Ifi202b in B6 and B6.TH-Chr1 congenic mice. (A) PCR amplification of exon 1 and part of exon 2 from cDNA (epididymal adipose tissue) of B6, B6.TH-Chr1-92Mb, B6.TH-Chr1-128Mb, and TH mice using a primer set of F and R as indicated in the scheme, (B) sequence comparison of the PCR product of TH to the sequence of NZO derived from GenBank accession number JX945582, and the mRNA levels of Ifi202b in epididymal adipose tissue from (C) B6, B6.TH-Chr1-128Mb, B6.TH-Chr1-92Mb mice on chow and (D) from B6.TH-Chr1-128Mb congenic mice on chow and HF diets. Data were reported as means ± SEM (N=3–4 each group, 17–27 weeks of age). * P <0.05.

Figure 4

The mRNA levels of Apoa2 in liver from B6 and B6.TH-Chr1-128Mb congenic mice on chow and HF diets (males, 15–24 weeks of age). Changes in gene expression were expressed as fold change relative to mean values for B6 mice. Data were reported as means ± SEM (N=5–7 each group). * P <0.05.