Experiment
The current study is a proof-of concept study. The goal was to fine map previously identified quantitative trait loci (QTL) affecting atherosclerosis in mice using a novel association analysis on a sensitized genetic background.
In this proof of concept paper, strong evidence has been presented that the strategy works, with the potential of greatly narrowing the regions of the mouse genome that contribute to differences in atherosclerosis susceptibility. The authors had previously reported on the successful application of the EMMA algorithm for correction of the significant population structure existing among inbred strains of mice, allowing association analysis using common inbred strains of mice [J:158389].
Compared to linkage analysis, association analysis has much improved mapping resolution because it utilizes the many historical recombinations that have occurred during the generation of inbred strains rather than the much smaller number of recombinations that occur in a genetic cross.
In order to induce significant atherosclerotic lesions, a sensitized genetic background utilizing the (the human apolipoprotein B transgene) was generated. The lesions were about 10-fold larger than those obtained using a high fat, cholic acid diet alone. It was noteworthy that the results among the BXH subset of RI strains surveyed with the human apoB transgene were highly concordant with previous studies from the Paigen laboratory, suggesting that the genetic factors contributing to fatty streaks and more advanced lesions showed considerable overlap. [Table].
Hemizygous B6.Cg-Tg(APOB)1102Sgy/Tac mice were bred to 22 different inbed strains [Sup Table 1] to generate 288 F1 heterozygous mice carrying the transgene. Beginning at 9 weeks of age the mice were fed an atherogenic diet with cholic acid. After 16 weeks of the diet plasma lipoproteins and atherosclerosis were quantified.
The original study in BXH Apoe -/- mice (B6.129P2-Apoetm1Unc/J x C3.129P2(B6)-Apoetm1Unc) identified the Ath30 locus on Chr 1 with a 95% confidence interval of 8 Mb, from 72 to 80 Mb, containing over 300 genes, [J:140288].
Using association analysis three SNPs were observed (rs31896983, rs32179781 and rs30136637) in the Ath30 region that were strongly associated with atherosclerosis in both males and females, reducing the Ath30 interval in the current analysis to a 2 Mb region between 74.8 to 76.8 Mb on Chr 1, containing only 31 genes. This allowed for the elimination several positional candidates from the initial cross, such as 2310007B03Rik. Analysis of SNPs with coding changes identified 13 of the 31 genes in the interval, with missense variants.
Next, eQTL analysis of the aorta was performed. Two genes had highly significant local eQTL, Des and Glb1l. To further examine the possible role of these candidates in atherogenesis the expression in cells derived from aortas from wild-type and Apoe -/- mice were compared, the results indicated that Des mRNA levels are induced prior to initiation of extensive atherosclerosis at 4 weeks of age and elevated expression continues into more advanced lesion development at 24 weeks of age. There were no effects on Glb1l.
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