Metabolomic study of the LDL receptor null mouse fed a high-fat diet reveals profound perturbations in choline metabolism that are shared with ApoE null mice

Failure to express or expression of dysfunctional low-density lipoprotein receptors (LDLR) causes familial hypercholesterolemia in humans, a disease characterized by elevated blood cholesterol concentrations, xanthomas, and coronary heart disease, providing compelling evidence that high blood cholesterol concentrations cause atherosclerosis. In this study, we used 1H nuclear magnetic resonance spectroscopy to examine the metabolic profiles of plasma and urine from the LDLR knockout mice. Consistent with previous studies, these mice developed hypercholesterolemia and atherosclerosis when fed a high-fat/cholesterol/cholate-containing diet. In addition, multivariate statistical analysis of the metabolomic data highlighted significant differences in tricarboxylic acid cycle and fatty acid metabolism, as a result of high-fat/cholesterol diet feeding. Our metabolomic study also demonstrates that the effect of high-fat/cholesterol/cholate diet, LDLR gene deficiency, and the diet-genotype interaction caused a significant perturbation in choline metabolism, notably the choline oxidation pathway. Specifically, the loss in the LDLR caused a marked reduction in the urinary excretion of betaine and dimethylglycine, especially when the mice are fed a high-fat/cholesterol/cholate diet. Furthermore, as we demonstrate that these metabolic changes are comparable with those detected in ApoE knockout mice fed the same high-fat/cholesterol/cholate diet they may be useful for monitoring the onset of atherosclerosis across animal models

Complement C1q Reduces Early Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient Mice

We explored the role of the classic complement pathway in atherogenesis by intercrossing C1q-deficient mice (C1qa(−/−)) with low-density lipoprotein receptor knockout mice (Ldlr(−/−)). Mice were fed a normal rodent diet until 22 weeks of age. Aortic root lesions were threefold larger in C1qa(−/−)/Ldlr(−/−) mice compared with Ldlr(−/−) mice (3.72 ± 1.0% aortic root versus 1.1 ± 0.4%; mean ± SEM, P < 0.001). Furthermore, the cellular composition of lesions in C1qa(−/−)/Ldlr(−/−) was more complex, with an increase in vascular smooth muscle cells. The greater aortic root lesion size in C1qa(−/−)/Ldlr(−/−) mice occurred despite a significant reduction in C5b-9 deposition per lesion unit area, suggesting the critical importance of proximal pathway activity. Apoptotic cells were readily detectable by cleaved caspase-3 staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling assay, and electron microscopy in C1qa(−/−)/Ldlr(−/−), whereas apoptotic cells were not detected in Ldlr(−/−) mice. This is the first direct demonstration of a role for the classic complement pathway in atherogenesis. The greater lesion size in C1qa(−/−)/Ldlr(−/−) mice is consistent with the emerging homeostatic role for C1q in the disposal of dying cells. This study suggests the importance of effective apoptotic cell removal for containing the size and complexity of early lesions in atherosclerosis