Fibrinogen deficiency reduces vascular accumulation of apolipoprotein(a) and development of atherosclerosis in apolipoprotein(a) transgenic mice

Abstract

To test directly whether fibrin(ogen) is a key binding site for apolipoprotein(a) [apo(a)] in vessel walls, apo(a) transgenic mice and fibrinogen knockout mice were crossed to generate fibrin(ogen)-deficient apo(a) transgenic mice and control mice. In the vessel wall of apo(a) transgenic mice, fibrin(ogen) deposition was found to be essentially colocalized with focal apo(a) deposition and fatty-streak type atherosclerotic lesions. Fibrinogen deficiency in apo(a) transgenic mice decreased the average accumulation of apo(a) in vessel walls by 78% and the average lesion (fatty streak type) development by 81%. Fibrinogen deficiency in wild-type mice did not significantly reduce lesion development. Our results suggest that fibrin(ogen) provides one of the major sites to which apo(a) binds to the vessel wall and participates in the generation of atherosclerosis.

Figure 1

Immunofluorescent and histochemical staining of fibrin(ogen) and apo(a) accumulation and lipid deposition in proximal sections of mouse aorta after 2 months of an atherogenic diet. Representative adjacent sections are shown for the three different types of staining. (A–D) Immunohistochemical staining of fibrin(ogen) in apo(a), apo(a)/Fib^−/−, wild-type, and Fib^−/− mice, respectively. (E–H) Immunofluorescent staining of apo(a) accumulation. (I–L) Oil-red O staining for fatty streak lesions. Note more lipid is in the apo(a) mice, including the edge of the valve and the vessel walls. Fibrin(ogen) staining is essentially colocalized with apo(a) accumulation and fatty streak lesions. (Scale bar equals 50 μm.)

Figure 2

Quantitative analyses of immunofluorescent-stained apo(a) accumulation and oil-red O-stained lipid lesions in the proximal aorta of apo(a) and apo(a)/Fib^−/− mice all maintained on high-fat diet. (A) Group mean of average vessel wall intensity [arbitrary units (1–250)/area (number of pixels)] in apo(a) (n = 11) and apo(a)/Fib^−/− mice (n = 8). The mean of average intensity for apo(a) mice is 53.7 ± 3.3; for apo(a)/Fib^−/− mice it is 11.8 ± 2.2 (P = 1.17 × 10 ⁻⁸). The staining was performed as one batch. (B) Average lipid lesion area per section per mouse (females, ○; males, □). The mean of the average lesion area per section per mouse is 11,584 ± 3,465 μm² for the apo(a) mice and 2,161 ± 889 μm² for the apo(a)/Fib^−/− mice. The median is 7,865 μm² (range: 0–53,560) for the apo(a) mice and 1,560 μm² (range: 0–6,760) for the apo(a)/Fib^−/− mice (P = 0.02).