Anatomical differences and atherosclerosis in apolipoprotein E-deficient mice with 129/SvEv and C57BL/6 genetic backgrounds

Abstract

There are well-known genetic background effects on atherosclerosis susceptibility in mice. To study the basis of these effects, we have generated the apolipoprotein E-null mutation in mouse embryonic stem cells of 129/SvEv origin, maintained it in the inbred strain (129-apoE), and compared these mice with those previously made in strain 129/Ola and backcrossed to a C57BL/6 genetic background (B6-apoE). Plasma cholesterol and triglyceride levels in the apoE-129 mice are twice the levels in apoE-B6, and both VLDL/chylomicron remnants and HDL particles are increased. Regression analysis of plaque size relative to the age of mice suggests that the initiation of atherosclerotic plaque development at the aortic root is slower in 129-apoE mice (intercept at 3.9 months in females and 4.1 months in males) than in B6-apoE mice (1.3 months in females and 2.8 months in males). In contrast, 129-apoE mice develop extensive plaques in the aortic arches earlier than B6-apoE mice. Distinct differences in the geometry of the aortic arch between the two strains suggest that anatomical differences may contribute to the effects of genetic background on atherosclerosis. The 129-apoE/B6-apoE pair thus provides a tool to study factors governing the relation between arterial geometry and the location of plaque development.

Figure 1

Plasma lipoprotein and apolipoprotein distributions. Plasma pooled from six mice (1ml) was separated by serial ultracentrifugation into density fractions: 1, d<1.006; 2, 1.006

Figure 2

Relationships between age and size of plaques at the aortic roots of apoE-/- mice having 129/SvEv and C57BL/6 genetic backgrounds. The slopes of the lines (40,000 - 47,000) fitted by linear least-squares regression represent the growth of plaques (in μm² per month), and the X-axis intercepts (1.3 – 4.1 mo) represent the time when plaques were initiated. n, number of animals.

Figure 3

Aortic arch and atherosclerosis. Atherosclerotic lesions in the aortic arches of three 129-apoE (left panels) and three B6-apoE (right panels) mice stained red with Sudan IVB. Note that the brachiocephalic trunks (blue arrowheads) are longer in B6-apoE than in 129-apoE mice. The attachment site of the ductus arteriosus to each aorta is indicated by a small black arrow. The black bar is 0.2 mm. lc, left common carotid artery; ls, left subclavian artery, rc, right common carotid artery; rs, right subclavian artery.

Figure 4

Plaques within the ductus arteriosus of 129-apoE mice. (A), aortic arch and ductus arteriosus in a 6 mo old 129-apoE female. Plaques are visible through the aortic wall as shiny white areas. H, heart; bt, brachiocephalic trunk; lc, left common carotid artery; ls, left subclavian artery. The ductus arteriosus (da) has a funnel-like opening at its pulmonary end (yellow arrowhead). The whiteness towards the aortic side of the ductus arteriosus indicates plaques filling the ductus. (B), longitudinal section showing the opening to the pulmonary artery side of the ductus arteriosus of a 6 mo old male 129-apoE mouse. Plaque materials within the lumen are covered with foam cells (arrowheads). Calcified materials are filling the lumen of the aortic side (arrows). Plastic section, stained with Toluidine blue. 20X. (C), cross section of the ductus arteriosus of the same animal as (B) at the aortic attachment end. The lumen contains smooth muscle cells and calcified materials (arrow). 40X. (D), cross section of the ductus arteiosus from another 6 mo old 129-apoE male showing degenerative changes of smooth muscle cells. The arrow indicates red blood cells in the lumen. 40X. (E), a cross section of the ductus arteriosus of a 5 mo old B6-apoE male showing complete obliteration of the vascular structure and fibrotic alterations.