No abstract

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.

Abstract-Complement-mediated vascular injury is important in the pathophysiology of atherosclerosis and myocardial infarction. Because recent evidence shows that statins have beneficial effects on endothelial cell (EC) function independent of lipid lowering, we explored the hypothesis that statins modulate vascular EC resistance to complement through the upregulation of complement-inhibitory proteins. Human umbilical vein and aortic ECs were treated with atorvastatin or simvastatin, and decay-accelerating factor (DAF), membrane cofactor protein, and CD59 expression was measured by flow cytometry. A dose-dependent increase in DAF expression of up to 4-fold was seen 24 to 48 hours after treatment. Statin-induced upregulation of DAF required increased steady-state mRNA and de novo protein synthesis. L-Mevalonate and geranylgeranyl pyrophosphate reversed the effect, confirming the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibition and suggesting that constitutive DAF expression is negatively regulated by geranylgeranylation. Neither farnesyl pyrophosphate nor squalene inhibited statin-induced DAF expression, suggesting that the effect is independent of cholesterol lowering. Statin-induced DAF upregulation was mediated by the activation of protein kinase C␣ and inhibition of RhoA and was independent of phosphatidylinositol-3 kinase and NO activity. The increased DAF expression was functionally effective, resulting in significant reduction of C3 deposition and complement-mediated lysis of antibody-coated ECs. These observations provide evidence for a novel cytoprotective action of statins on vascular endothelium that is independent of the effect on lipids and results in enhanced protection against complement-mediated injury. Modulation of complement regulatory protein expression may contribute to the early beneficial effects of statins in reducing the morbidity and mortality associated with atherosclerosis.