Aging exacerbates spontaneous atherosclerosis in apolipoprotein E deficient mice

Abstract

Atherosclerosis is an age‐related chronic inflammatory disease of the large arteries that is associated with endothelial dysfunction and hyperlipidemia, the severity and clinical outcomes of which are not only determined by plaque size, but also plaque quality and vulnerability. Thus, we aimed to determine the impact of advancing age on both the size and severity of spontaneously developed plaques in the descending aorta and aortic root of young (Y: 5–6 mo, N=29), middle‐aged (MA: 8–10 mo, N=15) and old (O: 16–17 mo, N=34) apolipoprotein E‐deficient (ApoE−/−) mice fed an atherogenic diet (AD) for 3–8 wks. Total aortic plaque area was determined after 3, 5 and 8 wk on AD. Compared to young, aortic percent plaque area was higher in old after 3, 5 and 8 wk of AD and in middle‐aged after 5 and 8 wk of AD (all p<0.05). Plaque area was also higher in old compared to middle‐aged after 5 wk of AD (p<0.05) (Fig 1). Aortic root plaque size and quality were assessed by a board certified veterinary pathologist on H&E sections from the mice used above combined over weeks on diet. Plaque grade was determined according to modified AHA classifications and plaque quality was determined by histological scoring for characteristics such as mineralization and intraplaque hemorrhage. Pathologist was blinded to group and data were analyzed using mean values when duplicate samples were available. Differences in morphometric measures were determined by ANOVA with LSD post hoc and in plaque quality measures by Mann‐Whitney nonparametric tests. Aortic root mean plaque area was higher in old mice (0.31±0.03 mm2), compared with middle‐aged (0.12±0.02 mm2, p<0.05) and young (0.19±0.04 mm2, p<0.05). When present, the necrotic core area was not different with age, but the percent of plaques that demonstrated a necrotic core increased with advancing age (Y: 11%, MA: 25% and O: 32%). Compared to young (2.8±0.2), plaque grade was higher in old (3.3±0.1, p<0.05) but not middle‐aged (2.9±0.3, p>0.05) mice. Histological scoring for plaque mineralization was higher in old compared to middle‐aged (p<0.05) and young (p<0.05) mice, and was present in 47% of aortic plaques from old mice compared to 13% and 10% of plaques from middle‐aged and young. Scoring for intraplaque hemorrhage was also increased in old mice (p<0.05) compared to middle‐aged and young, and was present in 21% of plaques from old mice but absent in plaques from middle‐aged and young. This increase in plaque burden and severity was associated with increased plasma lipids with aging such that plasma total cholesterol, LDL, and TG were higher in old (2393±26, 692±50, 252±20 mg/dl) compared to middle‐aged (1834±248, 544.0±74, 174.0±42, all p<0.05) and young (1792±139, 532.6±28, 173.2±13, all p<0.05) mice. Taken together, these findings suggest that there is an age‐associated exacerbation of the size and severity of atherosclerotic plaques that is associated with an increase in plasma lipids in response to the same dietary insult and may contribute to higher prevalence of stroke and MI with advancing age due to unstable plaques.Support or Funding InformationNational Institute on Aging (R01 AG048366, R01 AG050238 K02 AG045339 and R01 AG060395) and US Department of Veterans Affairs (I01 BX002151, I01 BX004492).Aging exacerbates the spontaneous atherosclerotic plaque burden in the aorta of ApoE−/− mice in response to atherogenic diet (AD).Whole aortic plaque area was determined after 3, 5 and 8 wk on AD. Compared to young (Y) percent of plaque area in the aorta was higher in old (O) after 3, 5 and 8 wk of AD and in middle‐age (MA) after 5 and 8 wk of AD. *p<0.05 Vs. Young, # p<0.05 Vs. Middle‐aged.Figure 1