Quantitative trait locus mapping of genetic modifiers of metabolic syndrome and atherosclerosis in low-density lipoprotein receptor-deficient mice: identification of a locus for metabolic syndrome and increased atherosclerosis on chromosome 4

Abstract

Objective: The purpose of this study was to examine genetic factors responsible for metabolic syndrome and atherosclerosis in a setting of low-density lipoprotein (LDL) receptor deficiency in a cross between C57BL/6J (B6) and PERA/Ei (PERA) inbred mouse strains.

Methods and results: Comparison of metabolic phenotypes in B6 and PERA strains revealed the PERA genetic background to be dramatically more susceptible to hyperleptinemia, hyperglycemia, hypertriglyceridemia, elevated insulin levels, and body fat increase than the B6 background. To facilitate genetic analysis, metabolic syndrome-related traits and atherosclerotic lesion area were measured in 167 [(PERAxB6.129S7-Ldlr(tm1Her))xB6.129S7-Ldlr(tm1Her)]N2 male and female backcross mice that were homozygous for the Ldlr null allele. Quantitative trait locus analysis was performed using 153 polymorphic microsatellite markers spanning the genome. On chromosome 4, we identified a locus influencing plasma triglyceride, insulin, and leptin concentrations, body weight, and atherosclerosis. Several other genetic loci were identified with separate effects on plasma insulin, body weight, high-density lipoprotein cholesterol, and atherosclerosis.

Conclusions: The PERA strain is highly susceptible to the development of metabolic syndrome after feeding a Western-type diet. This susceptibility is due, in part, to a locus on murine chromosome 4 in which PERA alleles predispose to adiposity, increased insulin, and accelerated atherogenesis in the absence of marked hyperlipidemia.

Figure 1

Likelihood plots for metabolic syndrome and atherosclerosis quantitative trait loci (QTLs) in [(PERAxB6-Ldlr^−/−)F1 × B6-Ldlr^−/−]N2 mice. Plots were created using the interval mapping function of Map Manager QTXb19, including a bootstrap test shown as a histogram estimating the confidence interval for the major QTL on each chromosome. Three straight vertical lines on each plot represent significance thresholds for the likelihood ratio statistic (LRS) indicating “suggestive”, “significant” or “highly significant” peaks as calculated by permutation analysis (the genome-wide significance thresholds of P = 0.63, P = 0.05, and P = 0.001, respectively are shown from left to right). Black plots reflect the LRS calculated at 1-cM intervals. Red plots represent the additive regression coefficient indicating the effect of the B6 allele: if B6 represents the high allele then the red plot will be to the right of the graph; if it represents the low allele then the red plot will be to the left.

Figure 2

Distribution of plasma total cholesterol in fractions separated by fast protein liquid chromatography (FPLC) in [(PERAxB6-Ldlr^−/−)F1 × B6-Ldlr^−/−]N2 male mice fed a Western-type diet (two weeks) grouped by genotype at D4Mit143. Plasma was pooled from 10 mice per group. BB, homozygous for B6 alleles; BP, heterozygous for B6 and PERA/Ei alleles.

Figure 3

Characterization of plasma leptin levels, food intake, body composition, and the major signal-transducing B isoform of the leptin receptor (Lepr-B) mRNA levels in C57BL/6J (B6) and PERA/Ei (PERA) male mice fed a Western-type diet (two weeks). Values are expressed as mean ± SD of 9–10 B6 and 4–6 PERA mice.