Factor XI Deficiency Protects Against Atherogenesis in Apolipoprotein E/Factor XI Double Knockout Mice

Abstract

Objective: Atherosclerosis and atherothrombosis are still major causes of mortality in the Western world, even after the widespread use of cholesterol-lowering medications. Recently, an association between local thrombin generation and atherosclerotic burden has been reported. Here, we studied the role of factor XI (FXI) deficiency in the process of atherosclerosis in mice.

Approach and results: Apolipoprotein E/FXI double knockout mice, created for the first time in our laboratory. There was no difference in cholesterol levels or lipoprotein profiles between apolipoprotein E knockout and double knockout mice. Nevertheless, in 24-week-old double knockout mice, the atherosclerotic lesion area in the aortic sinus was reduced by 32% (P=0.004) in comparison with apolipoprotein E knockout mice. In 42-week-old double knockout mice, FXI deficiency inhibited atherosclerosis progression significantly in the aortic sinus (25% reduction, P=0.024) and in the aortic arch (49% reduction, P=0.028), with a prominent reduction of macrophage infiltration in the atherosclerotic lesions.

Conclusions: FXI deprivation was shown to slow down atherogenesis in mice. The results suggest that the development of atherosclerosis can be prevented by targeting FXI.

Keywords: atherosclerosis; factor XI.

Figure 1

Phenotype characterization of mice. A, Factor XI (FXI) detected by Western blot in plasma of C57BL/6, FXI knockout (KO), apolipoprotein E (apoE) KO, and apoE/FXI double KO (DKO) mice using biotinylated 14E11 antibody. B, FXI activity in plasma of C57BL/6 (n=7), FXI KO (n=10), apoE KO (n=14), apoE/FXI DKO (n=12), and apoE/FXI^+/− (n=5) mice according to activated partial thromboplastin time–based assay.

Figure 2

Plasma lipid levels. A, Plasma cholesterol levels of C57BL/6 (n=6), factor XI knockout (FXI KO; n=12), apolipoprotein E knockout (apoE KO; n=20), apoE/FXI double KO (DKO; n=20), and apoE/FXI^+/− (n=8) 42-week-old mice. B, Plasma triglyceride levels of C57BL/6 (n=6), FXI KO (n=14), apoE KO (n=20) apoE/FXI DKO (n=19), and apoE/FXI^+/− (n=8) 42-week-old mice. C, Cholesterol distribution in the very low–density lipoprotein (VLDL), LDL, and high-density lipoprotein (HDL) of C57BL/6, FXI KO, apoE KO, and apoE/FXI DKO 42-week-old mice as measured by fast performance liquid chromatography. Pooled plasma from each experimental group was assessed. Each point represents the mean of 2 separation measurements. Bars are mean±SE; means without a common letter differ; P<0.05.

Figure 3

Aortic sinus atherosclerotic lesion area of 24- and 42-week-old mice. A, Lesion area of 24-week-old C57BL/6 (n=8), factor XI knockout (FXI KO; n=12), apolipoprotein E knockout (apoE KO; n=14), and apoE/FXI double KO (DKO; n=8) mice and (B) 42-week-old C57BL/6 (n=6), FXI KO (n=14), apoE KO (n=20), apoE/FXI DKO (n=21), and apoE/FXI^+/− (n=8) mice. Atherosclerotic lesion area was quantified after staining with Oil Red O. Empty circles represent mean of 3 sections per mouse. Black circles represent group mean±SE. Representative aortic sinus lesions of each group of (C) 24-week-old mice: C57BL/6, FXI KO, apoE KO, and apoE/FXI DKO and (D) 42-week-old mice: C57BL/6, FXI KO, apoE KO, apoE/FXI DKO, and apoE/FXI^+/− (magnification ×40). N.S. indicates not significant.

Figure 4

Atherosclerosis assessment of the aortic arch in 42-week-old mice. A, Atherosclerotic lesion area of apolipoprotein E knockout (apoE KO) mice (n=7) compared with apoE/factor XI double KO (FXI DKO) mice (n=7) at 42 weeks of age. The atherosclerotic lesion area was quantified by Sudan IV staining. Empty circles represent mean area of 3 sections per mouse. Black circles represent group mean±SE. B, Representative photographs of aortic arch of 24- and 42-week-old mice.

Figure 5

Collagen content in the apolipoprotein E (apoE)/factor XI double knockout (FXI DKO) mice. Atherosclerotic lesion area was quantified after staining with Oil Red O and collagen content by Masson-trichrome staining in apoE KO (n=8) and apoE/FXIDKO (n=8).

Figure 6

Macrophage infiltration in aortic sinus atherosclerotic lesions in apolipoprotein E (apoE) and apoE/factor XI double knockout (FXI DKO) 42-week-old mice. Macrophage infiltration was assessed by anti-CD68 antibody.