VLDL best predicts aortic root atherosclerosis in LDL receptor deficient mice

Abstract

Hyperlipidemia is a major risk factor for developing atherosclerosis in humans, and epidemiological studies have correlated specific lipoprotein levels with cardiovascular disease risk. Murine models of atherosclerosis rely on the induction of hyperlipidemia for vascular lesions to form, but the pathogenic contributions attributed to different lipoprotein populations are not well defined. To address this issue, we analyzed over 300 LDL receptor (LDLR) deficient mice that have been fed a high-fat diet and for which a full lipoprotein profile and aortic root atherosclerosis values were assessed. Overall, aortic root atherosclerosis is best predicted by plasma VLDL cholesterol levels with less predictive value derived from either LDL or HDL cholesterol. Triglyceride levels are more atherogenic in female mice, especially immune competent females, and depletion of the adaptive immune system leads to a global reduction in plasma lipid levels and aortic root lesion size yet does not appear to alter the atherogenic potential of individual lipoprotein subspecies. In contrast, HDL-cholesterol is a better predictor of aortic root atherosclerosis in apoE-deficient mice. In summary, this large scale analysis of high-fat diet fed LDLR deficient mice highlight the relationship between different plasma lipid components, especially VLDL-cholesterol, and aortic root atherosclerosis.

Fig. 1.

Box and whisker plots relating terminal plasma lipid parameters to aortic root atherosclerosis as assessed in LDLR^−/− mice after 12 weeks of high-fat diet feeding. Each plot encompasses the entire data set (n = 321 mice) divided into progressive quartiles (Q1–Q4) based on increasing plasma lipid levels for each variable (n∼80 mice per quartile). Displayed is the squared correlation coefficient (R² value) for the corresponding linear regression from the scatter plot (not shown) relating each lipid variable to resultant aortic root atherosclerosis. Statistically significant differences between adjacent quartiles as well as the Q1 to Q4 comparison are shown. ANOVA comparing means of Q1 through Q4 exhibited statistical significance (P < 0.001) for each parameter except LDL Cholesterol (P = 0.052). Error bars represent SD.

Fig. 2.

The extent of aortic root atherosclerosis is independently associated with both high levels of VLDL cholesterol and low levels of HDL cholesterol in the circulation. This chart is based on the entire data set (n = 321 mice) with each individual bar representing approximately 20 mice. Progressive quartiles for VLDL cholesterol and HDL cholesterol are based on increasing levels of cholesterol for each lipid variable.

Fig. 3.

Subgroup analysis based on gender. Each graph plots the lipid variable (mg/dl) against the resultant aortic root atherosclerosis for both males (blue squares) and females (pink diamonds). Each color coded linear regression (blue for males and pink for females) has the corresponding squared correlation coefficient (R² value) displayed. The slope of the female triglyceride regression line is significantly different than the slope of the male triglyceride regression line (P < 0.001).

Fig. 4.

Subgroup analysis based on adaptive immune status. Each graph plots the lipid variable (mg/dl) against the resultant aortic root atherosclerosis for adaptive immune competent (blue diamonds), adaptive immune-deficient (red squares), and adaptive immune partially deficient (gray triangles) mice. Each color coded linear regression (blue for adaptive immune competent, red for adaptive immune deficient, and gray for adaptive immune partially deficient mice) has the corresponding squared correlation coefficient (R² value) displayed.

Fig. 5.

Box and whisker plots relating terminal plasma lipid parameters to aortic root atherosclerosis in immune competent and fully immune incompetent LDLR^−/− mice separated by gender. Each plot encompasses the data set divided into progressive quartiles (Q1–Q4) based on increasing plasma lipid levels for each variable (n∼12–18 mice per quartile). Displayed is the squared correlation coefficient (R² value) for the corresponding linear regression from the scatter plot (not shown) relating each lipid variable to resultant aortic root atherosclerosis. Statistically significant differences between adjacent quartiles as well as the Q1 to Q4 comparison are shown. Error bars represent SD.

Fig. 6.

ApoE^−/− mice. A: Analysis of aortic root atherosclerosis. Each graph plots the plasma lipid level (mg/dl) against the resultant aortic root atherosclerosis and has the corresponding squared correlation coefficient (R² value) displayed. B: Progressive quartiles for VLDL cholesterol and HDL cholesterol and the corresponding aortic root atherosclerotic lesion size are plotted.