Angiotensin II infusion promotes ascending aortic aneurysms: attenuation by CCR2 deficiency in apoE-/- mice

Abstract

AngII (angiotensin II) induces atherosclerosis and AAAs (abdominal aortic aneurysms) through multiple proposed mechanisms, including chemotaxis. Therefore, we determined the effects of whole-body deficiency of the chemokine receptor CCR2 (CC chemokine receptor 2) on these diseases. To meet this objective, apoE (apolipoprotein E)-/- mice that were either CCR2+/+ or CCR2-/-, were infused with either saline or AngII (1000 ng.kg-1 of body weight.min-1) for 28 days via mini-osmotic pumps. Deficiency of CCR2 markedly attenuated both atherosclerosis and AAAs, unrelated to systolic blood pressure or plasma cholesterol concentrations. During the course of the present study, we also observed that AngII infusion led to large dilatations that were restricted to the ascending aortic region of apoE-/- mice. The aortic media in most of the dilated area was thickened. In regions of medial thickening, distinct elastin layers were discernable. There was an expansion of the distance between elastin layers in a gradient from the intimal to the adventitial aspect of the media. This pathology differed in a circumscribed area of the anterior region of ascending aortas in which elastin breaks were focal and almost transmural. All regions of the ascending aorta of AngII-infused mice had diffuse medial macrophage accumulation. Deficiency of CCR2 greatly attenuated the AngII-induced lumen dilatation in the ascending aorta. This new model of ascending aortic aneurysms has pathology that differs markedly from AngII-induced atherosclerosis or AAAs, but all vascular pathologies were attenuated by CCR2 deficiency.

Figure 1. Deletion of CCR2 attenuates the development of AngII-induced atherosclerosis and AAAs

Each symbol represents individual animals, diamonds represent means, and bars are S.E.M. (A) Area of aortic intima covered with atherosclerotic lesions as measured by en face analysis. *P<0.001 and #P<0.005 for comparisons of saline and AngII infusions within genotypes; †P<0.001 for comparisons of CCR2^+/+ and CCR2^−/− within AngII-infused groups. (B) Mean lesion area per section in the aortic root. *P=0.003 for comparison of saline and AngII infusion within CCR2^+/+ groups; †P<0.001 for comparisons of CCR2^+/+ and CCR2^−/− within AngII-infused groups. P<0.005 for comparisons of saline and AngII infusions within genotypes. (C) Aneurysm size was measured as width of abdominal aorta. *P<0.001 for comparisons of saline and AngII infusions; #P<0.001 for comparisons of CCR2^+/+ and CCR2^−/− within AngII-infused groups.

Figure 2. AngII infusion induces ascending aortic aneurysms

Examples of aortic arches from apoE^−/− mice infused with either saline (A) or AngII (B). The blue lines designated as 1 and 2 represent the areas sectioned and represented in Figure 3.

Figure 3. Histological and cellular characteristics of AngII-induced ascending aortic aneurysms

(A), (D) and (G) are harvested from a saline-infused CCR2^+/+ mouse. Sections derived from the area defined by line 1 in Figure 2 are shown in (B), (E) and (H), and the anterior portion of the region in line 2 is represented in (C), (F) and (I). Sections were stained with haematoxylin and eosin (A–C), Gomori trichrome (D–F) and immunostained for macrophages (positive cells are red; G–I). The orientation of aortas is described in (A), (B) and (C) by L, lumen; M, media; A, adventitia. Magnification, × 400.

Figure 4. Deletion of CCR2 attenuates AngII-induced ascending aorta medial expansion

Ascending aortic thickness was measured from images (n=3–6 mice/group) using image analysis software. Histobars represent groups, and error bars represent S.E.M. *P=0.002 for comparison of saline and AngII. #P=0.007 for comparison of CCR2^+/+ and CCR2^−/− within AngII infusion.

Figure 5. Deletion of CCR2 attenuates AngII-induced ascending aortic aneurysms

Ascending aortic diameters (A) and intimal areas (B) of arch regions were measured from images of pinned aortas using image analysis software. Circles and triangles represent individual mice, diamonds are means and bars represent S.E.M. (A) *P<0.001 for comparison of AngII and saline infusion in both genotypes. #P<0.001 for comparison of genotype within AngII infusion groups. (B) *P<0.001 for comparison of AngII and saline infusion in CCR2^+/+ mice. #P<0.001 for comparison of CCR2^+/+ and CCR2^−/− mice infused with AngII. †P<0.001 for comparison of saline and AngII infusion in CCR2^−/− mice.