[Show abstract][Hide abstract] ABSTRACT: C3H/HeJ (C3H) mice are extremely resistant to atherosclerosis, especially males. To understand the underlying genetic basis, we performed quantitative trait locus (QTL) analysis on a male F2 (the second generation from an intercross between 2 inbred strains) cohort derived from an intercross between C3H and C57BL/6 (B6) apolipoprotein E-deficient (Apoe(-/-)) mice.
Two hundred forty-six male F2 mice were started on a Western diet at 8 weeks of age and kept on the diet for 5 weeks. Atherosclerotic lesions in the aortic root and fasting plasma lipid levels were measured. One hundred thirty-four microsatellite markers across the entire genome were genotyped. Four significant QTLs on chromosomes (Chr) 2, 4, 9, and 15 and 4 suggestive loci on Chr1, Chr4, and Chr7 were identified for atherosclerotic lesions. Unexpectedly, the C3H allele was associated with increased lesion formation for 2 of the 4 significant QTLs. Six loci for high-density lipoprotein (HDL), 6 for non-HDL cholesterol, and 3 for triglycerides were also identified. The QTL for atherosclerosis on Chr9 replicated Ath29, originally mapped in a female F2 cohort derived from B6 and C3H Apoe(-/-) mice. This locus coincided with a QTL for HDL, and there was a moderate, but statistically significant, correlation between atherosclerotic lesion sizes and plasma HDL cholesterol levels in F2 mice.
These data indicate that most atherosclerosis susceptibility loci are distinct from those for plasma lipids except for the Chr9 locus, which exerts effect through interactions with HDL.
Journal of the American Heart Association 07/2013; 2(4):e000260. DOI:10.1161/JAHA.113.000260 · 2.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carotid atherosclerosis is the primary cause of ischemic stroke. To identify genetic factors contributing to carotid atherosclerosis, we performed quantitative trait locus (QTL) analysis using female mice derived from an intercross between C57BL/6J (B6) and BALB/cJ (BALB) apolipoprotein E (Apoe-/-) mice. 266 F2 mice were started on a Western diet at 6 weeks of age and fed the diet for 12 weeks. Atherosclerotic lesions in the left carotid bifurcation and plasma lipid levels were measured. 130 microsatellite markers across the entire genome were genotyped. Three significant QTLs, Cath1 on chromosome (Chr) 12, Cath2 on Chr5, and Cath3 on Chr13, and four suggestive QTLs on Chr6, Chr9, Chr17, and Chr18 were identified for carotid lesions. The Chr6 locus replicated a suggestive QTL and was named Cath4. Six QTLs for HDL, three QTLs for non-HDL cholesterol, and three QTLs for triglyceride were found. Of these, a significant QTL for non-HDL on Chr1 at 60.3 cM, named Nhdl13, and a suggestive QTL for HDL on ChrX were new. A significant locus for HDL (Hdlq5) was overlapping with a suggestive locus for carotid lesions on Chr9. A significant correlation between carotid lesion sizes and HDL cholesterol levels was observed in the F2 population (R=-0.153, P=0.0133). We have identified several new QTLs for carotid atherosclerosis and the locus on Chr9 may exert effect through interactions with HDL.
[Show abstract][Hide abstract] ABSTRACT: Diabetic patients have an increased risk of developing atherosclerosis and related complications compared with nondiabetic individuals. The increased cardiovascular risk associated with diabetes is due in part to genetic variations that influence both glucose homeostasis and atherosclerotic lesion growth. Mouse strains C57BL/6J (B6) and BALB/cJ (BALB) exhibit distinct differences in fasting plasma glucose and atherosclerotic lesion size when deficient in apolipoprotein E (Apoe(-/-)). Quantitative trait locus (QTL) analysis was performed to determine genetic factors influencing the 2 phenotypes.
Female F(2) mice (n=266) were generated from an intercross between B6.Apoe(-/-) and BALB.Apoe(-/-) mice and fed a Western diet for 12 weeks. Atherosclerotic lesions in the aortic root, fasting plasma glucose, and body weight were measured. 130 microsatellite markers across the entire genome were genotyped. Four significant QTLs, Ath1 on chromosome (Chr) 1, Ath41 on Chr2, Ath42 on Chr5, and Ath29 on Chr9, and 1 suggestive QTL on Chr4, were identified for atherosclerotic lesion size. Four significant QTLs, Bglu3 and Bglu12 on Chr1, Bglu13 on Chr5, Bglu15 on Chr12, and 2 suggestive QTLs on Chr9 and Chr15 were identified for fasting glucose levels on the chow diet. Two significant QTLs, Bglu3 and Bglu13, and 1 suggestive locus on Chr8 were identified for fasting glucose on the Western diet. One significant locus on Chr1 and 2 suggestive loci on Chr9 and Chr19 were identified for body weight. Ath1 and Ath42 coincided with Bglu3 and Bglu13, respectively, in the confidence interval.
We have identified novel QTLs that have major influences on atherosclerotic lesion size and glucose homeostasis. The colocalization of QTLs for atherosclerosis and diabetes suggests possible genetic connections between the 2 diseases.
[Show abstract][Hide abstract] ABSTRACT: Bglu3 is a quantitative trait locus for fasting glucose on distal chromosome 1 identified in an intercross between C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE(-/-)) mice. This locus was subsequently replicated in two separate mouse intercrosses. The objective of this study was to characterize Bglu3 through construction and analysis of a congenic strain and identify underlying candidate genes. Congenic mice were constructed by introgressing a genomic region harboring Bglu3 from C3H.apoE(-/-) into B6.apoE(-/-) mice. Mice were started with a Western diet at 6 wk of age and maintained on the diet for 12 wk. Gene expression in the liver was analyzed by microarrays. Congenic mice had significantly higher fasting glucose levels and developed more significant glucose intolerance compared with B6.apoE(-/-) mice on the Western diet. Microarray analysis revealed 336 genes to be differentially expressed in the liver of congenic mice. Further pathway analysis suggested a role for acute phase response signaling in regulating glucose intolerance. Apcs, encoding an acute phase response protein serum amyloid P (SAP), is located underneath the linkage peak of Bglu3. Multiple single nucleotide polymorphisms between B6 and C3H mice were detected within and surrounding Apcs. Apcs expression in the liver was significantly higher in congenic and C3H mice compared with B6 mice. The Western diet consumption led to a gradual rise in plasma SAP levels, which was accompanied by rising fasting glucose in both B6 and C3H apoE(-/-) mice. Expression of C3H Apcs in B6.apoE(-/-) mice aggravated glucose intolerance. Bglu3 is confirmed to be a locus affecting diabetes susceptibility, and Apcs is a probable candidate gene.
[Show abstract][Hide abstract] ABSTRACT: Type 2 diabetes mellitus (T2DM) is associated with an increased risk of atherosclerotic vascular disease, but it is unknown whether the other way around is true too. C57BL/6 (B6) and BALB/cJ (BALB) are two mouse strains that differ markedly in their susceptibility to atherosclerosis. In this study we investigated the development of diet-induced T2DM in these two strains.
When deficient in apolipoprotein E (apoE(-/-)) and fed a Western diet for 12 weeks, atherosclerosis-susceptible B6 mice developed significant hyperglycemia. In contrast, atherosclerosis-resistant BALB apoE(-/-) mice had much lower plasma glucose levels than B6.apoE(-/-) mice on either chow or Western diet and during an intraperitoneal glucose tolerance test. In response to glucose BALB.apoE(-/-) mice displayed both the first and second phases of insulin secretion but the second phase of insulin secretion was absent in B6.apoE(-/-) mice. In response to insulin B6.apoE(-/-) mice showed a deeper and longer-lasting fall in blood glucose levels while BALB.apoE(-/-) mice showed little reduction in glucose levels. Pancreatic islet area of BALB.apoE(-/-) mice on light microscopy nearly doubled the area of B6.apoE(-/-) mice. Most circulating proinflammatory cytokines were lower in BALB.apoE(-/-) than in B6.apoE(-/-) mice on the Western diet, as determined by protein arrays. Increased macrophage infiltration in islets was observed in B6.apoE(-/-) mice by immunostaining for Mac2 and also by flow cytometry.
This study demonstrates that defects in insulin secretion rather than defects in insulin resistance explain the marketed difference in susceptibility to T2DM in the B6.apoE(-/-) and BALB.apoE(-/-) mouse model. A smaller islet mass and more prominent islet inflammation may explain the vulnerability of B6.apoE(-/-) mice to diet-induced diabetes.
[Show abstract][Hide abstract] ABSTRACT: We previously identified two closely linked quantitative trait loci (QTL) on distal chromosome 1 contributing to major variations in plasma cholesterol and triglyceride levels in an intercross derived from C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE(-/-)) mice. Soat1, encoding sterol o-acyltransferase 1, is a functional candidate gene located underneath the proximal linkage peak. We sequenced the coding region of Soat1 and identified four single nucleotide polymorphisms (SNPs) between B6 and C3H mice. Two of the SNPs resulted in amino-acid substitutions (Ile147Val and His205Tyr). Functional assay revealed an increased enzyme activity of Soat1 in peritoneal macrophages of C3H mice relative to those of B6 mice despite comparable protein expression levels. Allelic variants of Soat1 were associated with variations in plasma cholesterol and triglyceride levels in an intercross between B6.apoE(-/-) and C3H.apoE(-/-) mice. Inheritance of the C3H allele resulted in significantly higher plasma lipid levels than inheritance of the B6 allele. Soat1 variants were also significantly linked to major variations in plasma esterified cholesterol levels but not with free cholesterol levels. Trangenic expression of C3H Soat1 in B6.apoE(-/-) mice resulted in elevations of plasma cholesterol and triglyceride levels. These results indicate that Soat1 is a QTL gene contributing to hyperlipidemia.
PLoS ONE 10/2011; 6(10):e25344. DOI:10.1371/journal.pone.0025344 · 3.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ath29 is an atherosclerosis susceptibility locus on chromosome 9 identified in an intercross between C57BL/6 (B6) and C3H/HeJ (C3H) apolipoprotein E-deficient (apoE(-/-)) mice. This locus was subsequently replicated in two separate intercrosses that developed early or advanced atherosclerotic lesions. The objective of this study was to characterize Ath29 through construction and analysis of a congenic strain and identify underlying candidate genes. A congenic line was constructed by introgressing the chromosomal segment harboring Ath29 from C3H.apoE(-/-) into B6.apoE(-/-) mice. Congenic mice developed significantly smaller early and advance atherosclerotic lesions than B6.apoE(-/-) mice. Microarray analysis revealed 317 genes to be differentially expressed in the aorta of congenic mice compared with B6.apoE(-/-) mice. Pathway analysis of these genes suggested the Ca(2+) signaling pathway to be implicated in regulating atherosclerosis susceptibility. Rcn2 is located underneath the linkage peak of Ath29 and involved in Ca(2+) signaling. Multiple single-nucleotide polymorphisms between B6 and C3H mice were detected within and surrounding Rcn2 with one single-nucleotide polymorphism falling within an upstream cAMP response element. Immunostaining demonstrated its expression in atherosclerotic lesions. Knockdown of Rcn2 with small interfering RNAs resulted in significant reductions in both baseline and oxidized phospholipid-induced VCAM-1 and monocyte chemoattractant protein-1 expression by endothelial cells. Ath29 is confirmed to be a major atherosclerosis susceptibility locus affecting both early and advanced lesion formation in mice, and Rcn2 is identified as a novel regulator of cytokine expression.